JP2011119374A - Nitride semiconductor element and method of manufacturing the same, and semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor element that improves the efficiency of light emission. <P>SOLUTION: A nitride semiconductor laser element 100 (nitride semiconductor element) includes a GaN substrate 10 in which a plane having an off angle in an a-axis direction with regard to an m plane is made a major growth plane 10a, and nitride semiconductor layers 11-18 formed on the major growth plane 10a of the GaN substrate 10. A semiconductor layer contacting with the major growth plane 10a is an InGaN layer 11 (nitride semiconductor layer containing In). Moreover, on the InGaN layer 11, a lower clad layer 12 (nitride semiconductor layer containing Al) composed of AlGaN is formed so as to contact with the upper plane of the InGaN layer 11. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor element, a manufacturing method thereof, and a semiconductor device, and more particularly, to a nitride semiconductor element including a nitride semiconductor substrate, a manufacturing method thereof, and a semiconductor device including the nitride semiconductor element. .

  Nitride semiconductors typified by GaN, AlN, InN, and mixed crystals thereof have characteristics that they have a large band gap Eg and are direct transition type semiconductor materials compared to AlGaInAs semiconductors and AlGaInP semiconductors. Yes. For this reason, these nitride semiconductors constitute semiconductor light emitting devices such as a semiconductor laser device capable of emitting light in a wavelength range from ultraviolet to green and a light emitting diode device capable of covering a wide light emission wavelength range from ultraviolet to red. It is attracting attention as a material, and is widely considered for applications such as projectors, full-color displays, and environmental and medical fields.

  In recent years, research institutions have attempted to realize semiconductor light emitting devices (green semiconductor lasers) that emit light in the green region by increasing the emission wavelength of semiconductor light emitting devices using nitride semiconductors. It is done vigorously.

  In a semiconductor light emitting device using a nitride semiconductor, a hexagonal GaN substrate (nitride semiconductor substrate) is generally used as a substrate, and its c-plane ((0001) plane) is the growth main surface. Has been. A nitride semiconductor light emitting device is formed by laminating a nitride semiconductor layer including an active layer on the c-plane. In addition, when forming a nitride semiconductor light emitting device using a nitride semiconductor substrate, an active layer containing In is generally used, and by increasing the In composition ratio, the emission wavelength is increased. Is planned.

  However, since the c-plane of the GaN substrate is a polar plane having a polarity in the c-axis direction, when a nitride semiconductor layer including an active layer is stacked on the c-plane, there is a disadvantage that spontaneous polarization occurs in the active layer. is there. In addition, when a nitride semiconductor layer including an active layer is stacked on the c-plane, the lattice strain of the active layer increases as the In composition ratio increases, and a strong internal electric field is induced in the active layer due to piezoelectric polarization. There is also an inconvenience. This internal electric field reduces the overlap of wave functions of electrons and holes, reducing the rate of recombination and light emission. For this reason, when the In composition ratio is increased in order to realize light emission in the green region, there has been a problem that the light emission efficiency is remarkably lowered as the light emission wavelength becomes longer.

  Therefore, in recent years, in order to avoid the influence of spontaneous polarization and piezoelectric polarization, a nitride semiconductor layer is laminated on the non-polar m-plane ({1-100} plane) instead of the general c-plane. Nitride semiconductor light emitting devices have been proposed. Such a nitride semiconductor light emitting device is described in, for example, Patent Document 1.

JP 2008-187044 A

  However, even when a nitride semiconductor light-emitting element is formed using a nitride semiconductor substrate having an m-plane as a main growth surface, the light emission efficiency is not sufficiently high, and there is still room for improvement of the light emission efficiency. It was.

  In addition, when the light emission efficiency (light emission by current injection: EL (Electro-Luminescence)) of a nitride semiconductor light emitting device using a nitride semiconductor substrate having an m-plane as a main growth surface was measured, the In composition of the active layer As the ratio increased, a phenomenon was observed in which the light emission efficiency rapidly decreased. Therefore, as a result of intensive research conducted by the inventors of the present invention to elucidate the cause, the cause of the decrease in luminous efficiency is the bright spot of the EL light emission pattern (in-plane light distribution when light is emitted by current injection). I found out that it was in the state. That is, it has been found that as the In composition ratio of the active layer increases, the EL light emission pattern changes to a bright spot shape as shown in FIG. Further, the bright spot-like EL light emission pattern becomes more prominent as the In composition ratio of the active layer increases. In particular, the vicinity of the green region (the In composition ratio of the active layer (well layer) is 0.15 or more). ) Showed a tendency for a bright spot-like EL emission pattern to appear remarkably. In addition, wavelength unevenness that is considered to be caused by the difference in current injection density within the surface was also observed. When the In composition ratio is further increased, the number of luminescent spots that emit light (light emission area) decreases. Thus, a strong correlation is observed between the bright spot-like EL emission pattern and the In composition ratio, and the phenomenon that the EL emission pattern becomes bright spot-like is caused when the In composition ratio of the active layer is increased. It has been found that this is a cause of a decrease in luminous efficiency. Note that the bright spot-like EL light emission pattern described above is a phenomenon that appears prominently in a nitride semiconductor light emitting device using a nitride semiconductor substrate having a nonpolar plane, particularly an m plane as a main growth surface.

  Thus, unlike a nitride semiconductor light emitting device using a c-plane, a nitride semiconductor light emitting device using a nitride semiconductor substrate having an m-plane as a growth main surface differs from the luminous efficiency due to spontaneous polarization or piezoelectric polarization. However, it has been found that there is a problem that the light emission efficiency is lowered due to the brightening of the EL light emission pattern. Such brightening of the EL light emission pattern is a serious problem because it prevents the light emission wavelength from being increased in the nitride semiconductor light emitting device using the m-plane. In particular, in a semiconductor laser element, a decrease in light emission efficiency causes a decrease in gain, which is a serious problem.

  Further, when the nitride semiconductor layer is grown on the m-plane of the nitride semiconductor substrate, the growth of the nitride semiconductor layer is likely to be unstable compared to the case where the nitride semiconductor layer is grown on the c-plane. For this reason, in the nitride semiconductor light emitting device (nitride semiconductor device) using the nitride semiconductor substrate having the m-plane as the main growth surface, there is a problem that the surface morphology of the nitride semiconductor layer is likely to deteriorate.

  The present invention has been made to solve the above-described problems, and one object of the present invention is to provide a nitride semiconductor device capable of improving the light emission efficiency, a method for manufacturing the same, and a method for nitriding the nitride semiconductor device. A semiconductor device including a physical semiconductor element is provided.

  Another object of the present invention is to provide a nitride semiconductor device in which a semiconductor layer having a good surface morphology is formed, a method for manufacturing the nitride semiconductor device, and a semiconductor device including the nitride semiconductor device.

  Still another object of the present invention is to provide a nitride semiconductor element capable of improving element characteristics, reliability, and yield, a method for manufacturing the same, and a semiconductor device including the nitride semiconductor element. is there.

  The inventors of the present application conducted various experiments paying attention to the above-mentioned problem, and as a result of intensive studies, by setting a surface having an off angle with respect to the m-plane as a growth main surface of the nitride semiconductor substrate, It has been found that it is possible to suppress the formation of bright spots in the EL emission pattern.

  That is, the nitride semiconductor device according to the first aspect of the present invention includes a nitride semiconductor substrate having a growth main surface, and a first nitride semiconductor layer formed on the growth main surface of the nitride semiconductor substrate. Yes. The main growth surface is a surface having an off-angle in the a-axis direction with respect to the m-plane, and the first nitride semiconductor layer contains In and is in contact with the main growth surface.

  In the nitride semiconductor device according to the first aspect, as described above, a surface having an off-angle in the a-axis direction with respect to the m-plane is used as a growth main surface of the nitride semiconductor substrate, so that Bright spot formation can be suppressed. That is, with this configuration, the EL light emission pattern of the nitride semiconductor element can be improved (bright spot light emission, in-plane wavelength unevenness, etc. can be suppressed). Thereby, the luminous efficiency of the nitride semiconductor device can be improved. In addition, a nitride semiconductor element with high luminance can be obtained by improving luminous efficiency. One of the reasons why the bright spot-like light emission suppression effect as described above can be obtained is that the growth main surface of the nitride semiconductor substrate has an off-angle in the a-axis direction with respect to the m-plane. This is presumably because the direction of atomic migration changes when a nitride semiconductor layer including an active layer is grown on the main surface.

  In the first aspect, the EL light emission pattern can be made uniform by suppressing the brightening of the EL light emission pattern, so that the drive voltage can also be reduced. In addition, by suppressing the bright spot light emission, an EL light emission pattern with uniform light emission can be obtained, so that the gain can be increased when the nitride semiconductor laser element is formed.

  In the first aspect, a nitride semiconductor substrate having a growth main surface that has an off-angle in the a-axis direction with respect to the m plane is used, and the growth main surface is in contact with the growth main surface. By forming the first nitride semiconductor layer containing In, the in-plane layer thickness distribution of the first nitride semiconductor layer can be made uniform, and in the semiconductor layer stacked on the first nitride semiconductor layer, Also, the in-plane layer thickness distribution can be made uniform. Thereby, a favorable surface morphology can be obtained. Note that, by improving the surface morphology, variation in element characteristics can be reduced, so that the manufacturing yield can be improved. Thereby, an element having characteristics within the standard range can be easily obtained. In addition, by improving the surface morphology, device characteristics and reliability can be improved.

  In the first aspect, by forming a first nitride semiconductor layer containing In on the nitride semiconductor substrate so as to be in contact with the main growth surface, the first nitride semiconductor layer is dislocated from the substrate. It functions as a buffer layer that reduces adverse effects such as. For this reason, it is possible to improve the light emission efficiency and improve the element characteristics and reliability.

  Furthermore, in the first aspect, by forming the first nitride semiconductor layer containing In on the nitride semiconductor substrate so as to be in contact with the growth main surface, an effect of suppressing the occurrence of cracks can also be obtained. .

  The nitride semiconductor device according to the first aspect preferably further includes a second nitride semiconductor layer containing Al formed on and in contact with the first nitride semiconductor layer. If comprised in this way, the interface of the 1st nitride semiconductor layer containing In and the 2nd nitride semiconductor layer containing Al can be made very favorable. That is, the steepness of the interface can be improved. Therefore, by configuring in this way, the surface morphology can be easily improved. In addition, the luminous efficiency can be further improved.

  In the nitride semiconductor device according to the first aspect, it is more preferable that the first nitride semiconductor layer is made of a nitride semiconductor containing In and Ga. If comprised in this way, while being able to obtain a favorable surface morphology easily, luminous efficiency can be improved easily. Moreover, if comprised in this way, an element characteristic and reliability can be improved easily. Furthermore, if comprised in this way, generation | occurrence | production of a crack can be suppressed easily.

  In the nitride semiconductor device according to the first aspect, the nitride semiconductor substrate can be made of GaN. In this case, the first nitride semiconductor layer is preferably composed of InGaN.

  In the nitride semiconductor device according to the first aspect, the nitride semiconductor substrate can be made of GaN, and the first nitride semiconductor layer can be made of AlInGaN.

  The nitride semiconductor device according to the first aspect preferably includes a second nitride semiconductor layer formed on and in contact with the first nitride semiconductor layer. In this case, the second nitride semiconductor layer is preferably composed of a nitride semiconductor containing Al and Ga. If constituted in this way, an even better surface morphology can be obtained. In addition, the luminous efficiency can be further improved.

  The nitride semiconductor device according to the first aspect includes a second nitride semiconductor layer formed on and in contact with the first nitride semiconductor layer, the nitride semiconductor substrate is made of GaN, The dinitride semiconductor layer is preferably made of AlGaN. If comprised in this way, while being able to improve luminous efficiency more easily, surface morphology can be made easier more easily.

  The nitride semiconductor device according to the first aspect preferably includes a second nitride semiconductor layer formed on and in contact with the first nitride semiconductor layer, and the nitride semiconductor substrate is made of GaN. The second nitride semiconductor layer may be made of AlInGaN. Even when configured in this manner, the light emission efficiency can be improved more easily, and the surface morphology can be improved more easily.

  In the nitride semiconductor device according to the first aspect, the absolute value of the off angle in the a-axis direction is preferably greater than 0.1 degree. With this configuration, it is possible to easily suppress the brightening of the EL emission pattern and the in-plane wavelength unevenness.

  In the nitride semiconductor device according to the first aspect, preferably, an active layer having a quantum well structure is formed on the main growth surface of the nitride semiconductor substrate, and the active layer includes two well layers. including. If comprised in this way, the inhibitory effect of luminescent spot light emission can be acquired, and a drive voltage can be reduced easily. For this reason, the light emission efficiency and device characteristics can be improved also by this.

  In the nitride semiconductor device according to the first aspect, an active layer having a quantum well structure is preferably formed on the main growth surface of the nitride semiconductor substrate, and the active layer is a single well layer. including. Even in such a configuration, the effect of suppressing bright spot light emission can be easily obtained, and the drive voltage can be easily reduced.

  In the nitride semiconductor device according to the first aspect, preferably, an active layer having a quantum well structure is formed on a main growth surface of the nitride semiconductor substrate, and the active layer includes a nitride semiconductor containing In. The In composition ratio of the well layer is 0.15 or more and 0.45 or less. In the nitride semiconductor device according to the first aspect, even when the In composition ratio of the well layer is 0.15 or more, which is a condition in which a bright spot-like EL light emission pattern appears remarkably, the bright spot of the EL light emission pattern. Therefore, the effect of suppressing bright spot light emission can be remarkably obtained. Further, when the In composition ratio of the well layer is set to 0.45 or less, the In composition ratio of the well layer becomes larger than 0.45, so that many dislocations are generated in the active layer due to strain such as lattice mismatch. It is also possible to suppress the inconvenience of entering.

  In the nitride semiconductor device according to the first aspect, an active layer having a quantum well structure is preferably formed on the main growth surface of the nitride semiconductor substrate, and the active layer includes a nitride containing Al. It has a barrier layer made of a semiconductor. If comprised in this way, it can suppress almost completely that a dark line generate | occur | produces in a light emission pattern. Thereby, since the fall of the luminous efficiency resulting from generation | occurrence | production of a dark line can be suppressed, luminous efficiency can be improved further. In the case where the barrier layer is made of a nitride semiconductor containing Al, the well layer is preferably made of InGaN.

  In the configuration including the barrier layer made of a nitride semiconductor containing Al, the barrier layer is preferably made of AlInGaN. If comprised in this way, luminous efficiency can be improved more easily.

  In the configuration including the barrier layer made of a nitride semiconductor containing Al, the barrier layer may be made of AlGaN. Thus, even when the barrier layer is made of AlGaN, the same effect as when the barrier layer is made of AlInGaN can be obtained.

  In the nitride semiconductor device according to the first aspect, an active layer having a quantum well structure is formed on the main growth surface of the nitride semiconductor substrate, and the active layer includes a plurality of barrier layers. It is preferable. In this case, at least a part of the plurality of barrier layers is preferably made of AlInGaN.

  In the nitride semiconductor device according to the first aspect, the growth main surface of the nitride semiconductor substrate may have an off-angle in the c-axis direction in addition to the a-axis direction. In this case, it is preferable that the off angle in the a-axis direction is larger than the off angle in the c-axis direction. With this configuration, it is possible to effectively suppress the formation of bright spots in the EL light emission pattern, in-plane wavelength unevenness, and the like.

  According to a second aspect of the present invention, there is provided a method for manufacturing a nitride semiconductor device comprising: preparing a nitride semiconductor substrate including a growth main surface comprising a surface having an off angle in the a-axis direction with respect to an m plane; Forming a nitride semiconductor layer on the main growth surface of the semiconductor substrate using an epitaxial growth method. The step of forming the nitride semiconductor layer includes a step of forming the first nitride semiconductor layer containing In so as to be in contact with the growth main surface.

  In the nitride semiconductor device manufacturing method according to the second aspect, as described above, by using a nitride semiconductor substrate whose growth main surface is a surface having an off-angle in the a-axis direction with respect to the m-plane, the EL It is possible to obtain a nitride semiconductor device in which the luminous pattern of the light emission pattern is suppressed. That is, with this configuration, it is possible to obtain a nitride semiconductor element in which the EL light emission pattern is improved (bright spot light emission and in-plane wavelength unevenness are suppressed). Thereby, a nitride semiconductor device with high luminance and improved luminous efficiency can be obtained.

  Further, in the second aspect, since the EL light emission pattern can be made uniform by suppressing the brightening of the EL light emission pattern, the driving voltage of the nitride semiconductor element can also be reduced. In addition, by suppressing the bright spot light emission, an EL light emission pattern with uniform light emission can be obtained, so that the gain can be increased when the nitride semiconductor laser element is formed. Further, with the above-described configuration, it is possible to suppress the formation of bright spots in the EL light emission pattern and to form nitride semiconductor layers with high flatness, so that the light emission efficiency can be improved. Thus, device characteristics and reliability can be improved. That is, a highly reliable nitride semiconductor device having excellent device characteristics can be obtained with a high yield.

  Further, in the second aspect, as described above, on the nitride semiconductor substrate whose growth main surface is a surface having an off angle in the a-axis direction with respect to the m-plane, In is in contact with the growth main surface. The surface morphology can be improved by forming the first nitride semiconductor layer including the first nitride semiconductor layer. For this reason, the device characteristics and reliability can be improved also by this. Further, by improving the surface morphology, variation in element characteristics can be reduced, so that the number of elements having characteristics within a standard range can be increased. Thereby, a yield can be improved easily.

  In the second aspect, by forming a first nitride semiconductor layer containing In on the nitride semiconductor substrate so as to be in contact with the main growth surface, the first nitride semiconductor layer is separated from the substrate. It functions as a buffer layer that reduces adverse effects such as dislocations. Thereby, the luminous efficiency can be easily improved, and the element characteristics and reliability can be easily improved.

  Furthermore, in the second aspect, an effect of suppressing generation of cracks can be obtained by forming the first nitride semiconductor layer containing In on the nitride semiconductor substrate so as to be in contact with the main growth surface.

  In the method for manufacturing a nitride semiconductor device according to the second aspect, preferably, in the step of forming the nitride semiconductor layer, the second nitride semiconductor layer containing Al is first nitrided on the first nitride semiconductor layer. Forming a contact with the physical semiconductor layer. If comprised in this way, the interface of the 1st nitride semiconductor layer containing In and the 2nd nitride semiconductor layer containing Al can be made very favorable. That is, the steepness of the interface can be improved. Therefore, by configuring in this way, the surface morphology can be improved.

  The method for manufacturing a nitride semiconductor device according to the second aspect includes a step of sequentially stacking an n-type semiconductor layer, an active layer, and a p-type semiconductor layer on a growth main surface of the nitride semiconductor substrate. preferable. In this case, the p-type semiconductor layer is preferably formed at a growth temperature of 700 ° C. or higher and lower than 1100 ° C. As described above, even when the p-type semiconductor layer is formed at a high temperature of 1000 ° C. or higher, blackening of the active layer (well layer) occurs by forming the barrier layer of the active layer from a nitride semiconductor containing Al. Can be suppressed. For this reason, since the p-type semiconductor layer can be formed at a high temperature of 1000 ° C. or more, the effect of reducing the driving voltage can be effectively obtained by forming the p-type semiconductor layer at a high temperature. Further, when the p-type semiconductor layer is formed at a growth temperature of 700 ° C. or higher, the p-type semiconductor layer is disadvantageously increased in resistance due to being formed at a growth temperature lower than 700 ° C. Can be suppressed. For this reason, the device characteristics and reliability can be improved also by this. Note that by using a nitride semiconductor substrate having a growth main surface provided with an off-angle with respect to the m-plane, p-type conduction can be obtained even when a p-type semiconductor layer is formed at a growth temperature lower than 900 ° C. Can do.

  In this case, the n-type semiconductor layer is preferably formed at a growth temperature of 900 ° C. or higher and lower than 1300 ° C. Thus, the layer surface of the n-type semiconductor layer can be planarized by forming the n-type semiconductor layer at a high temperature of 900 ° C. or higher. For this reason, by forming the active layer and the p-type semiconductor layer over the planarized n-type semiconductor layer, it is possible to suppress a decrease in crystallinity in the active layer and the p-type semiconductor layer. Thereby, a high quality crystal can be formed. Further, by forming the n-type semiconductor layer at a growth temperature lower than 1300 ° C., the surface of the nitride semiconductor substrate is re-evaporated at the time of temperature rise due to being formed at a growth temperature of 1300 ° C. or higher. It is possible to suppress the inconvenience of causing surface roughness. Therefore, with this configuration, it is possible to easily obtain a highly reliable nitride semiconductor element having excellent element characteristics and high yield.

  Furthermore, in this case, the active layer is preferably formed at a growth temperature of 600 ° C. or higher and 800 ° C. or lower. As described above, when the active layer is formed at a growth temperature of 800 ° C. or lower, the active layer is formed at a growth temperature higher than 800 ° C. (for example, 830 ° C. or higher). It is possible to suppress the disadvantage that the layer is blackened. In addition, when the active layer is formed at a growth temperature of 600 ° C. or higher, the atomic diffusion length is shortened and the crystallinity is deteriorated due to the formation at a growth temperature lower than 600 ° C. Can be suppressed. Therefore, with this configuration, a highly reliable nitride semiconductor device with excellent device characteristics can be obtained more easily and with a high yield.

  A semiconductor device according to a third aspect of the present invention is a semiconductor device provided with the nitride object element according to the first aspect.

  As described above, according to the present invention, it is possible to easily obtain a nitride semiconductor element capable of improving the light emission efficiency, a manufacturing method thereof, and a semiconductor device including the nitride semiconductor element.

  Furthermore, according to the present invention, a nitride semiconductor element having a semiconductor layer having a good surface morphology, a method for manufacturing the nitride semiconductor element, and a semiconductor device including the nitride semiconductor element can be easily obtained.

  Furthermore, according to the present invention, a nitride semiconductor element capable of improving element characteristics and reliability, a method for manufacturing the nitride semiconductor element, and a semiconductor device including the nitride semiconductor element can be easily obtained.

It is a schematic diagram (a figure showing a unit cell) for explaining a crystal structure of a nitride semiconductor. FIG. 7 is a cross-sectional view showing the structure of the nitride semiconductor laser device according to the first embodiment of the present invention (a view corresponding to a cross section taken along the line AA in FIG. 6). 1 is an overall perspective view of a nitride semiconductor laser device according to a first embodiment of the present invention. It is a schematic diagram for demonstrating the off angle of a board | substrate. FIG. 3 is a cross-sectional view showing the structure of the active layer of the nitride semiconductor laser device according to the first embodiment of the present invention. 1 is a plan view of a nitride semiconductor laser device according to a first embodiment of the present invention (a view of a nitride semiconductor laser device viewed from above). FIG. 1 is a perspective view for explaining a method of manufacturing a nitride semiconductor laser device according to a first embodiment of the present invention (a diagram for explaining a method of manufacturing a substrate). 1 is a perspective view for explaining a method of manufacturing a nitride semiconductor laser device according to a first embodiment of the present invention (a diagram for explaining a method of manufacturing a substrate). 1 is a perspective view for explaining a method of manufacturing a nitride semiconductor laser device according to a first embodiment of the present invention (a diagram for explaining a method of manufacturing a substrate). FIG. 6 is a plan view for explaining the method for producing the nitride semiconductor laser device according to the first embodiment of the present invention (the drawing for explaining the method for producing the substrate). It is sectional drawing for demonstrating the manufacturing method of the nitride semiconductor laser element by 1st Embodiment of this invention (figure for demonstrating the manufacturing method of a board | substrate). It is sectional drawing for demonstrating the manufacturing method of the nitride semiconductor laser element by 1st Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride semiconductor laser element by 1st Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride semiconductor laser element by 1st Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride semiconductor laser element by 1st Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride semiconductor laser element by 1st Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride semiconductor laser element by 1st Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride semiconductor laser element by 1st Embodiment of this invention. It is sectional drawing for demonstrating the manufacturing method of the nitride semiconductor laser element by 1st Embodiment of this invention. 1 is a perspective view of a semiconductor laser device including a nitride semiconductor laser element according to a first embodiment of the present invention. It is a perspective view of the light emitting diode element produced in order to confirm the effect of the nitride semiconductor laser element by 1st Embodiment of this invention. It is a top view for demonstrating the nitride semiconductor laser element by 2nd Embodiment of this invention. It is sectional drawing for demonstrating the nitride semiconductor laser element by 2nd Embodiment of this invention. It is sectional drawing for demonstrating the nitride semiconductor laser element by 2nd Embodiment of this invention. It is sectional drawing of the light emitting diode element by 3rd Embodiment of this invention. It is sectional drawing for demonstrating the example of the other structure of the active layer in 1st-3rd embodiment (sectional drawing which showed an example of the active layer of a SQW structure). The surface morphology when a GaN layer is formed on the growth main surface with a thickness of about 1 μm using a GaN substrate whose main surface is an off-angle in the a-axis direction with respect to the m-plane is an optical microscope. It is the microscope picture observed using. The surface when a GaN substrate having a growth principal surface with a surface having an off angle of +0.5 degrees in the c-axis direction with respect to the m-plane is used, and a GaN layer is formed on the growth principal surface with a thickness of about 1 μm. It is the microscope picture which observed the morphology using the optical microscope. It is a microscope picture which shows a bright spot-like EL light emission pattern.

  Prior to describing specific embodiments of the present invention, knowledge obtained by various studies by the inventors will be described.

  As described above, the inventors suppress the formation of bright spots in the EL light emission pattern by setting the surface having an off-angle in the a-axis direction with respect to the m-plane as the growth main surface of the nitride semiconductor substrate. Found that it is possible to do.

  On the other hand, the inventors of the present application use a nitride semiconductor substrate (GaN substrate) whose main growth surface is a surface having an off-angle in the a-axis direction with respect to the m-plane, and a GaN layer ( It was found that when a non-doped GaN layer not intentionally doped or an n-type GaN layer intentionally doped with an n-type impurity is formed with a thickness of about 1 μm, the in-plane layer thickness distribution is greatly deteriorated. The layer thickness distribution at this time is very poor compared to the layer thickness distribution when a GaN layer is formed with a thickness of about 1 μm on an m-plane GaN substrate having no off-angle in the a-axis direction. It was. As described above, when a GaN layer having the same composition as the substrate is formed on the substrate by using an epitaxial growth method such as MOCVD (Metal Organic Chemical Deposition), the phenomenon of causing a large layer thickness distribution in the plane is It is considered to be a very unique phenomenon.

  FIG. 27 shows a surface morphology when a GaN substrate having a growth principal surface with a surface having an off-angle in the a-axis direction with respect to the m-plane is used and a GaN layer is formed on the growth principal surface with a thickness of about 1 μm. It is the microscope picture observed using the optical microscope. FIG. 27 shows the surface morphology in a state where each nitride semiconductor layer is stacked on the main growth surface starting from the GaN layer. As shown in FIG. 27, very strong wavy irregularities are seen on the surface of the semiconductor layer in the direction parallel to the a-axis direction. Further, the nitride semiconductor layer of FIG. 27 has a layer thickness distribution of about 200 nm to 400 nm, and it is very difficult to form an element in the semiconductor layer in which the uniformity of the layer thickness distribution is impaired. It becomes.

  Until now, in general, a semiconductor layer having the same composition as the substrate is formed so as to be in contact with the substrate surface (main growth surface), thereby improving the flatness of the layer surface and the crystallinity of the semiconductor layer. An element is formed on the substrate. For example, if the substrate is a GaN substrate, first, a GaN layer is formed on the substrate. As a result, the composition of the substrate and the composition of the semiconductor layer (GaN layer) formed on the substrate surface (growth main surface) are the same, so there is no difference in lattice constant or thermal expansion coefficient, and distortion occurs. Is suppressed. By doing so, it is known that the GaN layer functions as a buffer layer, and a semiconductor layer having high flatness and good crystallinity can be formed. In fact, when a nitride semiconductor substrate (for example, a c-plane GaN substrate) having a c-plane as a growth main surface is used and crystal growth is performed on the growth main surface, the above-mentioned is usually performed. It has been broken. In this case (when a GaN layer is formed on a c-plane GaN substrate), a very clean surface morphology is obtained. This is considered to be a normal phenomenon.

  For reference, a GaN substrate having a growth main surface that has a +0.5 degree off-angle in the c-axis direction with respect to the m-plane is used, and a GaN layer is formed on the growth main surface with a thickness of about 1 μm. FIG. 28 shows a micrograph obtained by observing the surface morphology when formed using an optical microscope. FIG. 28 shows the surface morphology in a state where each nitride semiconductor layer is stacked on the main growth surface starting from the GaN layer.

  As shown in FIG. 28, when a GaN layer is formed on a nitride semiconductor substrate whose main growth surface is a surface having an off-angle in the c-axis direction with respect to the m-plane, the surface is in contact with the main growth surface. Morphology is slightly worse, but not significantly worse.

  However, as described above, the surface morphology of the nitride semiconductor substrate whose main growth surface is a surface having an off-angle in the a-axis direction with respect to the m-plane is significantly deteriorated. For this reason, it has been found that a nitride semiconductor substrate whose main growth surface is a surface having an off-angle in the a-axis direction with respect to the m-plane exhibits such a unique phenomenon as described above.

  Therefore, as a result of intensive studies by the inventors of the present application, in the case of a nitride semiconductor substrate whose growth main surface is a surface having an off angle in the a-axis direction with respect to the m-plane, a nitride semiconductor layer containing In It has been found that the flatness of the layer surface can be improved by forming the layer so as to be in contact with the main growth surface of the substrate. That is, with respect to a nitride semiconductor substrate having a growth principal surface that has an off-angle in the a-axis direction with respect to the m-plane, the semiconductor layer in contact with the growth principal surface of the nitride semiconductor substrate is not a GaN layer, but In. It has been found that a good surface morphology can be obtained by using a nitride semiconductor layer containing the semiconductor layer. The nitride semiconductor layer containing In is an InGaN layer, an AlInGaN layer, an AlInN layer, an InN layer, or the like.

  Further, the inventors of the present application have reduced the adverse effects such as dislocation from the substrate on the light emitting layer by reducing the nitride semiconductor layer containing In formed on the nitride semiconductor substrate in contact with the main growth surface. It was found that it can function as a buffer layer. Then, it was found that by making the nitride semiconductor layer containing In function as a buffer layer, light emission efficiency is further improved, and device characteristics and reliability are further improved.

  In particular, when the In composition ratio of the well layer of the active layer is set to 0.15 or more and 0.45 or less (when configured to emit light in a long wavelength region), the light emitting layer is formed on the substrate. In addition, since it is easily affected by the nitride semiconductor layer laminated between the active layer and the substrate, the buffer effect for reducing the adverse effect from the substrate is also more important. Similarly, the nitride semiconductor layer stacked between the active layer and the substrate is also important.

  In the above examination by the inventors of the present application, in a nitride semiconductor substrate having a growth main surface that has an off-angle in the a-axis direction with respect to the m-plane, the nitride semiconductor layer containing In is in contact with the growth main surface. Then, a nitride semiconductor layer containing Al (for example, an AlGaN layer, an AlInGaN layer, an AlN layer, etc.) is formed on the nitride semiconductor layer containing In so as to be in contact with the upper surface of the nitride semiconductor layer. Thus, it was found that the steepness of the interface between the nitride semiconductor layer containing In and the nitride semiconductor layer containing Al was improved, and a very good interface was obtained. Thereby, the deterioration of the surface morphology is suppressed and the flatness of the layer surface is improved. That is, it becomes possible to laminate a very flat Al-containing nitride semiconductor layer on a flatly laminated In-containing nitride semiconductor layer, and as an underlying layer interposed between the active layer and the substrate, A very flat and good semiconductor layer can be realized.

  In the case of a nitride semiconductor substrate having a growth main surface that has an off-angle in the a-axis direction, the effect of preventing cracks can be obtained by forming a nitride semiconductor layer containing In so as to be in contact with the growth main surface. Can also be obtained.

  As described above, the semiconductor layer in contact with the substrate surface (growth main surface) is replaced with a nitride semiconductor layer containing In (for example, an InGaN layer, an AlInGaN layer, an AlInN layer, an InN layer, etc.) instead of the GaN layer. Thus, the surface morphology is remarkably improved. Such a phenomenon is a characteristic phenomenon in the case of using a nitride semiconductor substrate whose growth main surface is a surface having an off-angle in the a-axis direction with respect to the m-plane. This is the first knowledge obtained from the examination of

  The inventors of the present application have also found that the deterioration of the surface morphology can be suppressed by preventing the GaN layer from being included in the layer structure laminated on the substrate as much as possible. It has also been found that even when a GaN layer is included in the layer structure, it is possible to suppress the deterioration of the surface morphology by reducing the total thickness of the GaN layer. The total thickness of the GaN layer is preferably between the surface of the substrate and the well layer that is a nitride semiconductor layer containing In (when multiple well layers are formed, preferably the well layer on the most substrate side). The total layer thickness of the formed GaN layer is preferably 0.7 μm or less, more preferably 0.5 μm or less. Further, it is more preferable that the total thickness of the GaN layer formed between the substrate surface and the well layer which is a nitride semiconductor layer containing In is 0.3 μm or less. The total layer thickness means the thickness of the GaN layer when there is one GaN layer, and when there are a plurality of GaN layers, the total thickness of the GaN layers is accumulated (total Means the layer thickness.

  Also in this case, it is preferable that the nitride semiconductor layer containing In is formed so as to be in contact with the growth main surface of the substrate. Furthermore, it is more preferable that a nitride semiconductor layer containing Al is formed on the nitride semiconductor layer containing In in contact with the nitride semiconductor layer. This is because if the surface morphology is deteriorated at the time of forming the active layer, the composition distribution becomes larger in the plane due to the influence of the surface morphology deteriorated by In contained in the well layer.

  In the case of using a nitride semiconductor substrate whose main growth surface is a plane having an off-angle in the a-axis direction with respect to the m plane, as described above, the layer structure (element of the light emitting element) stacked on the substrate is used. The structure is preferably configured so as not to include a GaN layer as much as possible. However, a GaN layer can be used as a light guide layer in order to perform optical confinement. In addition, a very thin GaN layer is formed into a superlattice with AlGaN, AlInGaN, or InGaN (AlGaN / GaN / AlGaN / GaN..., AlInGaN / GaN / AlInGaN / GaN..., InGaN / GaN / InGaN / GaN, etc.), the total layer thickness of GaN can be increased while suppressing deterioration of the surface morphology. The superlattice structure can be used as a light guide layer and a light cladding layer. By using the above structure, a relatively good layer can be formed using a thin GaN layer. In this case, the thickness of the thin GaN layer used in the superlattice structure is particularly preferably 1 nm or more and 50 nm or less.

  Further, in order to obtain a light emitting element or an electronic device having excellent characteristics, as described above, the layer structure laminated on the substrate does not include a GaN layer, and these layer structures are converted into InGaN, AlGaN, InAlGaN, InAlN. It is preferable to use a semiconductor layer having a composition different from that of GaN.

  In addition, as a result of further studies by the inventors of the present application, a nitride semiconductor substrate having an off angle in the a-axis direction with respect to the m-plane can be formed with a relatively good end face when cleaved. I found that there is a feature. For this reason, by using a nitride semiconductor substrate having an off-angle in the a-axis direction with respect to the m-plane, it is easy to form an end face when forming a semiconductor laser element. In addition, a nitride semiconductor layer containing In is formed on a nitride semiconductor substrate having an off-angle in the a-axis direction with respect to the m-plane so as to be in contact with the main growth surface. It has been found that when the layer becomes a buffer layer, for example, when the c-plane is cleaved, better end face formation is possible.

  Furthermore, in the above examination, the inventors of the present application have found that when a GaN layer or an InGaN layer is used for the barrier layer of the active layer, a dark line may be generated in the light emission pattern. And in order to suppress generation | occurrence | production of such a dark line, it discovered that it was very effective to comprise a barrier layer from the nitride semiconductor (For example, AlGaN, AlInGaN, AlN, etc.) containing Al. .

  When a nitride semiconductor substrate having a non-polar surface is used, when the nitride semiconductor layer containing Al or the nitride semiconductor layer containing Al and In is used for the barrier layer of the active layer, the strain of the active layer is reduced. For the purpose of suppressing the generation of dark lines, a nitride semiconductor layer containing Al and In, such as an AlInGaN layer or an AlInN layer, is preferably used as the optical cladding layer. Further, as the light guide layer, a nitride semiconductor layer containing In, such as an InGaN layer, an AlInGaN layer, or an AlInN layer, or a nitride semiconductor layer containing Al and In is preferably used. Of course, the same can be said for the case where a nitride semiconductor substrate whose growth main surface is a surface having an off-angle in the a-axis direction with respect to the m-plane is used.

  A nitride semiconductor substrate having an off angle in the a-axis direction with respect to the m-plane is a nitride semiconductor layer containing Al that has good flatness and crystallinity (for example, an AlGaN layer, an AlInGaN layer, an AlInN layer, etc.) The inventors of the present application have revealed that this is a nonpolar substrate that is very suitable for film formation. Then, using the substrate having such characteristics, the barrier layer of the active layer is formed of a nitride semiconductor layer containing Al (for example, AlGaN, AlInGaN, AlInN, etc.), thereby generating the above-described dark line. In addition to the suppression effect, it has also been found that the effect of improving the flatness and crystallinity of the barrier layer can be obtained, and the luminous efficiency can be greatly improved. In particular, when the In composition ratio of the well layer of the active layer is set to 0.15 or more and 0.45 or less (when configured to emit light in a long wavelength region), the effect of improving the light emission efficiency Is remarkably obtained.

  Further, when a nitride semiconductor substrate having an off angle in the a-axis direction with respect to the m-plane is used, the nitride semiconductor layer to be stacked is configured to include many nitride semiconductor layers containing Al, It becomes possible to form the base layer of the active layer more flatly.

  In addition, when a nitride semiconductor layer containing Al is formed on a substrate, there is a disadvantage that distortion is likely to occur due to a difference in lattice constant from the substrate or the like, while a nitride semiconductor layer containing In Is formed so as to be in contact with the main growth surface of the substrate, strain of the nitride semiconductor layer containing Al is alleviated. Thereby, even when the nitride semiconductor layer containing Al is formed on the substrate, generation of cracks is suppressed. That is, by forming a nitride semiconductor layer containing In on a nitride semiconductor substrate whose main surface is an off-angle in the a-axis direction so as to be in contact with the main growth surface, When using a nitride semiconductor substrate having a surface having an off-angle as a growth main surface, a particularly advantageous effect can be expected from the viewpoint of crack suppression. In addition, a crack suppressing effect can be obtained more effectively by combining with a technique for performing groove processing on the substrate.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments embodying the present invention will be described in detail with reference to the drawings. In the following first and second embodiments, an example in which the present invention is applied to a nitride semiconductor laser element which is an example of a nitride semiconductor element will be described. In the following third embodiment, an example in which the present invention is applied to a light-emitting diode element which is an example of a nitride semiconductor element will be described. In the following embodiments, “nitride semiconductor” refers to a semiconductor composed of Al _x Ga _y In _z N (0 ≦ x ≦ 1; 0 ≦ y ≦ 1; 0 ≦ z ≦ 1; x + y + z = 1). means.

(First embodiment)
FIG. 1 is a schematic diagram for explaining a crystal structure of a nitride semiconductor. FIG. 2 is a cross-sectional view showing the structure of the nitride semiconductor laser device according to the first embodiment of the present invention. FIG. 3 is an overall perspective view of the nitride semiconductor laser device according to the first embodiment of the present invention. 4 to 6 are views for explaining the structure of the nitride semiconductor laser device according to the first embodiment of the present invention. First, the structure of the nitride semiconductor laser element 100 according to the first embodiment of the present invention will be described with reference to FIGS.

  The nitride semiconductor constituting the nitride semiconductor laser device 100 according to the first embodiment has a hexagonal crystal structure as shown in FIG. In this crystal structure, a plane (upper surface of the hexagonal column) whose normal is the c-axis [0001] of the hexagonal crystal that can be regarded as a hexagonal column is called a c-plane (0001), and each side wall surface of the hexagonal column is an m-plane {1 -100}. In the nitride semiconductor, since there is no symmetry plane in the c-axis direction, the polarization direction is along the c-axis direction. For this reason, the c-plane exhibits different properties on the + c axis side and the −c axis side. That is, the + c plane ((0001) plane) and the −c plane ((000-1) plane) are not equivalent planes, and have different chemical properties. On the other hand, since the m-plane is a crystal plane perpendicular to the c-plane, the normal of the m-plane is orthogonal to the polarization direction. For this reason, the m-plane is a nonpolar plane with no polarity. As described above, since each of the side wall surfaces of the hexagonal column is an m-plane, the m-plane has six types of plane orientations ((1-100), (10-10), (01-10), ( −1100), (−1010), and (0−110)), these plane orientations are plane orientations equivalent to crystal geometry, and hence are collectively referred to as {1-100}. Show.

  In addition, the nitride semiconductor laser device 100 according to the first embodiment includes a GaN substrate 10 as a nitride semiconductor substrate, as shown in FIGS. The main growth surface 10a of the GaN substrate 10 is a surface having an off angle with respect to the m-plane. Specifically, the GaN substrate 10 of the nitride semiconductor laser element 100 has an off-angle in the a-axis direction ([11-20] direction) with respect to the m plane. In addition to the off-angle in the a-axis direction, the GaN substrate 10 may have an off-angle in the c-axis direction ([0001] direction).

  Here, the off angle of the GaN substrate 10 will be described in more detail with reference to FIG. First, two crystal axis directions of an a-axis [11-20] direction and a c-axis [0001] direction are defined with respect to the m-plane. These a-axis and c-axis are perpendicular to each other, and are also perpendicular to the m-axis. Further, when the crystal axis vector of the GaN substrate 10 matches the normal vector of the substrate surface (growth principal surface) (when the off-angle becomes 0 with respect to all directions), the a-axis direction and the c-axis direction The directions parallel to the m-axis direction are defined as an X direction, a Y direction, and a Z direction, respectively. Next, consider a first surface having a normal in the Y direction and a second surface having a normal in the X direction. The crystal axis vectors that appear when the crystal axis vector is projected onto the first surface and the second surface are defined as a first projection vector and a second projection vector, respectively. At this time, an angle θa formed by the first projection vector and the normal vector is an off angle in the a-axis direction, and an angle θc formed by the second projection vector and the normal vector is an off-angle in the c-axis direction. The off-angle in the a-axis direction has the same characteristics in the + direction and the − direction because the + direction and the − direction have the same surface state in terms of crystal. For this reason, it can describe with an absolute value. On the other hand, the c-axis direction is a + direction and a − direction, and there are cases where the Ga polar surface becomes stronger and the N polarity surface becomes stronger, and the characteristics differ depending on the direction. Separately described.

  Thus, the growth main surface 10a of the GaN substrate 10 according to the first embodiment is a surface inclined in the a-axis direction with respect to the m-plane {1-100}.

  In the GaN substrate 10, the absolute value of the off angle in the a-axis direction with respect to the m-plane is adjusted to an angle larger than 0.1 degree. However, since the amount of In taken into the active layer (InGaN layer such as a well layer) tends to decrease as the off-angle in the a-axis direction increases, the off-angle in the a-axis direction from the viewpoint of raw material efficiency. The absolute value of is preferably 10 degrees or less. Note that film formation is possible even when the off angle in the a-axis direction is an angle of 10 degrees or more. When the c-axis direction also has an off-angle, the off-angle in the c-axis direction is preferably adjusted to an angle greater than ± 0.1 degrees. The off angle in the c-axis direction is preferably adjusted to be smaller than the off angle in the a-axis direction.

  In the above case, it is preferable that the off angle in the a-axis direction is adjusted to an angle greater than 1 degree and 10 degrees or less. It is more preferable that the off-angle in the a-axis direction is adjusted to be in such a range because the effect of reducing the driving voltage is increased and the effect of improving the surface morphology is obtained.

  The nitride semiconductor laser device 100 according to the first embodiment is formed by laminating a plurality of nitride semiconductor layers on the growth main surface 10a of the GaN substrate 10 described above.

  Here, in the first embodiment, the semiconductor layer in contact with the growth main surface 10a of the GaN substrate 10 is composed of a nitride semiconductor layer (first nitride semiconductor layer) containing In. The semiconductor layer in contact with the upper surface of the nitride semiconductor layer containing In is composed of a nitride semiconductor layer containing Al (second nitride semiconductor layer).

Specifically, as shown in FIGS. 2 and 3, the nitride semiconductor laser device 100 according to the first embodiment is approximately on the growth main surface 10a of the GaN substrate 10 so as to be in contact with the growth main surface 10a. An InGaN layer 11 having a thickness of 0.1 μm is formed. The InGaN layer 11 is composed of n-type In _y Ga _1-y N (0 <y <1), and the In composition ratio y is set to 0.02, for example. On the InGaN layer 11, a lower cladding layer 12 made of n-type Al _0.06 Ga _0.94 N having a thickness of about 2.2 μm is formed. A lower guide layer 13 made of n-type GaN having a thickness of about 0.1 μm is formed on the lower cladding layer 12. An active layer 14 is formed on the lower guide layer 13. The InGaN layer 11 is an example of the “first nitride semiconductor layer containing In” of the present invention, and the lower cladding layer 12 is an example of the “second nitride semiconductor layer containing Al” of the present invention. . The GaN substrate 10 is configured as an n-type. Further, the InGaN layer 11 and the lower guide layer 13 may be non-doped.

  In the first embodiment, the semiconductor layer in contact with the growth main surface 10a of the GaN substrate 10 is the InGaN layer 11, so that the surface morphology of the layer surface is improved and the surface morphology is very good. Yes.

In addition to the InGaN layer 11, the semiconductor layer in contact with the growth main surface 10a of the GaN substrate 10 may be an InN layer. That is, the semiconductor layer in contact with the growth main surface 10a of the GaN substrate 10 only needs to be composed of a nitride semiconductor layer made of In _y Ga _1-y N (0 <y ≦ 1). In this case, the In composition ratio y is more preferably 0 <y ≦ 0.1, and the thickness of the nitride semiconductor layer at that time is more preferably 0.7 μm or less. When the In composition ratio y is 0 <y ≦ 0.5, the thickness of the semiconductor layer (the nitride semiconductor layer containing In) in contact with the growth main surface 10a of the GaN substrate 10 is greater than 0.1 μm, And it is preferable that it is 0.7 micrometer or less. Further, when the In composition ratio y is 0.5 <y ≦ 1.0, the thickness of the semiconductor layer (nitride semiconductor layer containing In) in contact with the growth main surface 10a of the GaN substrate 10 is from 0.05 μm. It is preferably large and 0.5 μm or less.

Further, instead of the nitride semiconductor layer made of In _y Ga _1-y N (0 <y ≦ 1), Al _a In _b Ga _c N (a + b + c) is used as the semiconductor layer in contact with the growth main surface 10a of the GaN substrate 10. = 1, 0 <a ≦ 1, 0 <b ≦ 1, 0 ≦ c <1) may be used. Also in this case, the thickness of the semiconductor layer in contact with the growth principal surface 10a is more preferably 0.7 μm or less, and further preferably more than 0.1 μm and 0.5 μm or less. Further, if the Al composition ratio a is 0 <a ≦ 0.1 and the In composition ratio b is 0 <b ≦ 0.1, it is more preferable from the viewpoint of surface morphology. Thus, by forming the nitride semiconductor layer containing Al and In in contact with the growth main surface 10a, it becomes easy to form a layer with high flatness at low temperature growth.

Further, the lower cladding layer 12 can be made of AlInGaN other than AlGaN, for example. That is, the lower cladding layer 12 can be made of a nitride semiconductor made of Al _p In _q Gar _r N (p + q + r = 1, 0 <p ≦ 1, 0 <q ≦ 1, 0 ≦ r <1). .

  As shown in FIG. 5, the active layer 14 has a quantum well structure in which well layers 14a and barrier layers 14b are alternately stacked.

In the first embodiment, the active layer 14 is made of AlGaN whose barrier layer 14b is a nitride semiconductor containing Al. Specifically, the active layer 14 includes a quantum well in which two well layers 14a made of In _x1 Ga _1-x1 N and three barrier layers 14b made of Al _x2 Ga _1-x2 N are alternately stacked. (DQW; Double Quantum Well) structure. More specifically, in the active layer 14, the first barrier layer 141b, the first well layer 141a, the second barrier layer 142b, the second well layer 142a, and the third barrier layer 143b are sequentially stacked from the lower guide layer 13 side. It is formed by being. Each of the two well layers 14a (the first well layer 141a and the second well layer 142a) is formed to a thickness of about 1.5 nm to about 4 nm. The first barrier layer 141b is formed to a thickness of about 30 nm, the second barrier layer 142b is formed to a thickness of about 16 nm, and the third barrier layer 143b is formed to a thickness of about 60 nm. ing. That is, the three barrier layers 14b are formed to have different thicknesses. With this configuration, it is possible to effectively suppress the occurrence of dark lines.

  The first barrier layer 141b is preferably formed with a thickness of 8 nm or more and 50 nm or less, and more preferably formed with a thickness of 10 nm or more and 40 nm or less. As described above, if the first barrier layer 141b is formed to a thickness of at least 8 nm, the flatness of the first barrier layer 141b formed after the growth of the lower guide layer 13 can be easily improved. Is possible. Further, if the first barrier layer 141b is formed to a thickness of 50 nm or less, carriers can be efficiently injected. The second barrier layer 142b is preferably formed with a thickness of 8 nm or more and 30 nm or less, and more preferably formed with a thickness of 10 nm or more and 20 nm or less. As described above, when the second barrier layer 142b is formed to a thickness of at least 8 nm or more, the flatness of the second barrier layer 142b formed after the growth of the first well layer 141a having a high In composition ratio can be easily achieved. Furthermore, it becomes possible to make it better. In addition, if the second barrier layer 142b is formed to a thickness of 30 nm or less, carriers can be efficiently injected. Furthermore, the third barrier layer 143b is preferably formed to a thickness of 8 nm to 100 nm, and more preferably 10 nm to 80 nm. In this way, if the third barrier layer 143b is formed to a thickness of at least 8 nm or more, it is formed after the growth of the second well layer 142a having a high In composition ratio and before the growth of the carrier block layer 15 described later. The flatness of the third barrier layer 143b to be formed can be easily improved. Further, if the third barrier layer 143b is formed to a thickness of 100 nm or less, carriers can be efficiently injected.

  In the first embodiment, the number of well layers is two. However, when the number of well layers is greater than two (for example, three or four layers), the first barrier is provided. The layer can be defined as an initial barrier layer formed on the lower layer side (substrate side) of the well layer closest to the substrate. The second barrier layer can be defined as a barrier layer sandwiched between well layers. Furthermore, the third barrier layer can be defined as a barrier layer formed on a well layer (final well layer) farthest from the substrate. By defining the first barrier layer, the second barrier layer, and the third barrier layer in this way, even when two or more well layers are formed, the preferable layer thickness conditions of the barrier layer described above are applied. Is possible. And if such conditions are satisfied, the above effects are obtained, which is preferable.

  The barrier layer may be made of AlInGaN in addition to AlGaN. In the case of a barrier layer containing Al and In, there is an advantage that a film having high flatness can be easily formed at a low temperature. Further, when the number of well layers is two or more, if the GaN layer is not used for the barrier layer sandwiched between the well layers (the second barrier layer in the first embodiment), the barrier layer may be AlGaN / AlInGaN, A two-layer structure such as AlInGaN / AlGaN, or a multilayer structure such as AlInGaN / AlGaN / AlInGaN, AlInGaN / InGaN / AlInGaN, and AlGaN / InGaN / AlGaN may be used. Furthermore, when the number of well layers is one, it is preferable that the upper layer in contact with the well layers (the side opposite to the substrate, the second barrier layer) is an AlInGaN layer. By forming the barrier layer in this way, it is possible to effectively suppress the generation of dark lines.

Moreover, in 1st Embodiment, In composition ratio x1 of the well layer 14a which comprises the active layer 14 is comprised 0.15 or more and 0.45 or less (for example, 0.2-0.25). The barrier layer 14b of the active layer 14 is made of AlGaN (Al _x2 Ga _1-x2 N), and the Al composition ratio x2 is, for example, 0 <x2 ≦ 0.08. Thus, by making the Al composition ratio x2 of the barrier layer 14b made of AlGaN (Al _x2 Ga _{1 -x2} N) 0.08 or less, light confinement can be performed efficiently. In addition, by forming the barrier layer 14b from AlGaN, it is possible to improve the light emission efficiency as compared with the conventional case where the barrier layer is formed from GaN or InGaN. In particular, when the In composition ratio x1 of the well layer 14a is not less than 0.15 and not more than 0.45, the tendency to improve the light emission efficiency is high.

  This is because, when the In composition ratio of the well layer is high, a nitride semiconductor layer containing Al as a barrier layer (for example, an AlGaN layer, an AlInGaN layer, etc.) is used to form a nitride semiconductor substrate having an m-plane as a growth main surface. It is possible to suppress dark lines that are specifically observed with a light-emitting element using the light-emitting element, which is considered to improve luminous efficiency.

  Here, in general, the well layer is often set to a thickness of about 3 nm in a region where the In composition ratio is large (x1 ≧ 0.15). However, when a barrier layer made of a nitride semiconductor containing Al (for example, AlGaN) is formed on the GaN substrate 10 having an off angle in the a-axis direction with respect to the m-plane, the thickness of the well layer is 4.0 nm. It is also possible to set as described above. The reason is considered to be that the effect of suppressing the generation of dark lines and the effect of protecting the active layer are obtained. Furthermore, the use of the GaN substrate 10 improves the flatness of the layer surface and makes the In composition very uniform in the plane. For this reason, even when the thickness of the well layer is large, it is difficult to form a local region having a high In composition. For this reason, it is considered that the well layer can be made thicker.

  Moreover, when the thickness of the well layer is larger than 8 nm, many misfit dislocations may occur. For this reason, the thickness of the well layer is preferably 8 nm or less. Further, it is preferably set in the range of about 2.5 nm to about 4.0 nm.

  For the same reason, when the thickness of the well layer is set in the range of about 1.5 nm to about 4.0 nm, the well layer is formed by forming the barrier layer from a nitride semiconductor containing Al (for example, AlGaN). The number of layers can be increased. For example, when a conventional active layer structure is employed in a nitride semiconductor laser element, the light emission efficiency is significantly deteriorated by forming three or more well layers. On the other hand, by forming the barrier layer from a nitride semiconductor containing Al, even when five well layers are formed, deterioration of light emission efficiency is suppressed. Further, in the light emitting diode element (LED), by forming the barrier layer from a nitride semiconductor containing Al, deterioration of the light emission efficiency is suppressed even when eight well layers are formed. The light-emitting diode element has a thickness smaller than that of the semiconductor laser element, and the thermal damage given to the active layer during the formation of the p-type semiconductor layer is smaller than that of the semiconductor laser element. However, the active layer (well layer) can be easily multi-layered.

  Note that the well layer of the active layer is intended to be a quantum well, and as a result, the layer thickness may fluctuate within a range of several nm or less, or may be locally doted. Including.

  The reason why the light emission efficiency is improved when the barrier layer 14b is made of a nitride semiconductor containing Al, such as AlGaN or AlInGaN, is considered as follows. That is, in a nitride semiconductor substrate whose main growth surface is a plane having an off-angle in the a-axis direction with respect to the m plane, a nitride semiconductor layer containing Al (for example, an AlGaN layer, an AlInGaN layer, an AlInN layer, etc.) is formed. Then, the surface morphology is improved. For this reason, a nitride semiconductor substrate having an off-angle in the a-axis direction with respect to the m-plane is a nitride semiconductor layer containing Al having good flatness and crystallinity (for example, an AlGaN layer, an AlInGaN layer, an AlInN layer, etc. It can be said that this is a non-polar substrate that is very suitable for film formation. Therefore, the barrier layer of the active layer is made of a nitride semiconductor containing Al (for example, an AlGaN layer, an AlInGaN layer, an AlInN layer, etc.), thereby improving the flatness of the barrier layer and having a high flatness. It is considered that the crystallinity of the well layer is improved by forming the well layer thereon. In addition, by forming the barrier layer in this way, it is possible to effectively suppress the generation of dark lines.

  When the barrier layer of the active layer is composed of a nitride semiconductor containing Al (for example, an AlGaN layer, an AlInGaN layer, an AlInN layer, etc.), the well layer is preferably composed of InGaN as described above.

As shown in FIGS. 2 and 3, a carrier block made of p-type Al _y Ga _1-y N (0 <y <1) having a thickness of 40 nm or less (for example, about 12 nm) is formed on the active layer 14. Layer 15 is formed. The carrier block layer 15 is configured such that the Al composition ratio y is 0.08 or more and 0.35 or less (for example, about 0.15). An upper guide layer 16 made of p-type Al _0.01 Ga _0.99 N having a convex portion and a flat portion other than the convex portion is formed on the carrier block layer 15. The upper guide layer 16 is configured so that the Al composition ratio is smaller than that of the cladding layer. An upper cladding layer 17 made of p-type Al _0.06 Ga _0.94 N having a thickness of about 0.5 μm is formed on the convex portion of the upper guide layer 16. A contact layer 18 made of p-type Al _0.01 Ga _0.99 N having a thickness of about 0.1 μm is formed on the upper cladding layer 17. The contact layer 18, the upper cladding layer 17, and the convex portions of the upper guide layer 16 form a striped (elongated) ridge portion 19 having a width of about 1 μm to about 10 μm (for example, about 1.5 μm). ing. As shown in FIG. 6, the ridge portion 19 is formed to extend in the Y direction (substantially c-axis [0001] direction). The p-type semiconductor layer (carrier block layer 15, upper guide layer 16, upper clad layer 17 and contact layer 18) is doped with Mg as a p-type impurity.

  Here, the contact layer 18 can be sufficiently composed of GaN, but by being composed of a nitride semiconductor layer containing Al (for example, AlGaN, AlInGaN, AlInN), the surface morphology is improved, and the layer The in-plane distribution of thickness is improved. Therefore, as described above, the contact layer 18 is preferably composed of a nitride semiconductor layer containing Al.

  In addition, as shown in FIG. 5, the distance h between the carrier block layer 15 and the well layer 14a (the well layer 14a (142a) closest to the carrier block layer 15) is the efficiency of carrier injection into the well layer 14a. In order to improve, it is set to about 60 nm. In the first embodiment, the distance h is the same as the thickness of the third barrier layer 143b.

  Note that if the distance h between the carrier block layer 15 and the well layer 14a is 200 nm or more, the current spreads when carriers diffuse from the carrier block layer 15 to the active layer 14, so that bright spot light emission occurs. Slightly suppressed. On the other hand, if the GaN substrate 10 having the growth main surface 10a having an off-angle in the a-axis direction with respect to the m-plane is used, the distance h between the carrier block layer 15 and the well layer 14a is 200 nm or more. Even if not, bright spot light emission can be effectively suppressed. For example, even when the distance h between the carrier block layer 15 and the well layer 14a is shorter than 120 nm, bright spot light emission can be effectively suppressed. A shorter distance h between the carrier block layer 15 and the well layer 14a is preferable because the injection efficiency of carriers into the well layer 14a is improved. Therefore, the efficiency of carrier injection into the well layer 14a can be improved by making the distance h between the carrier block layer 15 and the well layer 14a shorter than 120 nm.

In the nitride semiconductor laser device 100 according to the first embodiment, as shown in FIGS. 2 and 3, insulating layers 20 for current confinement are formed on both sides of the ridge portion 19. Specifically, from SiO ₂ having a thickness of about 0.1 μm to about 0.3 μm (for example, about 0.15 μm) on the upper guide layer 16, the side surface of the upper cladding layer 17, and the side surface of the contact layer 18. An insulating layer 20 is formed.

  A p-side electrode 21 is formed on the upper surfaces of the insulating layer 20 and the contact layer 18 so as to cover a part of the contact layer 18. The p-side electrode 21 is in direct contact with the contact layer 18 in a portion covering the contact layer 18. The p-side electrode 21 includes a Pd layer (not shown) having a thickness of about 15 nm, a Pt layer (not shown) having a thickness of about 15 nm, and a thickness of about 200 nm from the insulating layer 20 (contact layer 18) side. It has a multi-layer structure in which Au layers (not shown) having layers are sequentially stacked.

  On the back surface of the GaN substrate 10, an Hf layer (not shown) having a thickness of about 5 nm and an Al layer (not shown) having a thickness of about 150 nm are sequentially stacked from the back side of the GaN substrate 10. An n-side electrode 22 having a multilayered structure is formed. On the n-side electrode 22, a Mo layer (not shown) having a thickness of about 36 nm, a Pt layer (not shown) having a thickness of about 18 nm, and a thickness of about 200 nm are sequentially formed from the n-side electrode 22 side. There is formed a metallized layer 23 having a multilayer structure in which Au layers (not shown) having layers are sequentially stacked.

Furthermore, as shown in FIGS. 3 and 6, the nitride semiconductor laser device 100 according to the first embodiment includes a light emitting surface 30a from which laser light is emitted and a light reflecting surface 30b facing the light emitting surface 30a. A pair of resonator surfaces 30 is included. On the light exit surface 30a, for example, an exit side coating film (not shown) having a reflectance of 5% to 80% is formed. On the other hand, for example, a reflection side coating film (not shown) having a reflectance of 95% is formed on the light reflecting surface 30b. The reflectance of the exit side coating film is adjusted to a desired value by the oscillation output. In addition, the emission side coating film is, for example, aluminum oxynitride film or nitride film of AlO _x N _1-x (0 ≦ x ≦ 1): film thickness 30 nm / Al ₂ O ₃ (in order from the semiconductor emission surface. The reflection side coating film is composed of a multilayer film such as SiO ₂ or TiO ₂ . For example, a dielectric film such as SiN, ZrO ₂ , Ta ₂ O ₅ , or MgF ₂ may be used as a material other than the above. As the film configuration on the light emitting surface side, AlO _x N _1-x (0 ≦ x ≦ 1): film thickness 12 nm / SiN which is a silicon nitride film (film thickness: 100 nm) may be used.

As described above, the cleaved end face (c face in the first embodiment) of the m-plane nitride semiconductor substrate, or the etched end face etched by vapor phase etching or liquid phase etching is made of an aluminum oxynitride film or nitride film. By forming a certain AlO _x N _1-x (0 ≦ x ≦ 1), the ratio of non-radiative recombination at the interface between the semiconductor and the emission side coating film can be greatly reduced, and the level of COD (catalytic optical damage) is increased. It can be improved significantly. Further, AlO _x N _1-x (0 ≦ x ≦ 1) which is an aluminum oxynitride film or nitride film is more preferably the same hexagonal crystal as the nitride semiconductor. Furthermore, it is more preferable to crystallize with the nitride semiconductor aligned with the crystal axis because the ratio of non-radiative recombination is further reduced and the COD level is further improved. In order to increase the reflectance on the light emitting surface side, a silicon oxide film, an aluminum oxide film, a titanium oxide film, a tantalum oxide film, a zirconium oxide film, a silicon nitride film, A laminated film in which these are laminated may be formed.

  In addition, as shown in FIG. 6, the nitride semiconductor laser device 100 according to the first embodiment is about 300 μm to about 1800 μm in a direction orthogonal to the resonator plane 30 (Y direction (substantially c-axis [0001] direction)). (For example, about 600 μm) and a length L (chip length L (resonator length L)) in a direction along the resonator surface 30 (X direction (approximately a-axis [11-20] direction)), It has a width W (chip width W) of about 150 μm to about 600 μm (for example, about 400 μm).

  In the first embodiment, a relatively good end face can be formed by using the GaN substrate 10 in which the growth main surface 10a is a surface having an off angle in the a-axis direction with respect to the m-plane. For this reason, the pair of resonator surfaces 30 are formed on relatively good end surfaces.

  In the first embodiment, as described above, the surface having an off-angle in the a-axis direction with respect to the m-plane is the growth main surface 10a of the GaN substrate 10, thereby making the EL light emission pattern a bright spot-like surface. The wavelength unevenness inside can be suppressed. That is, with this configuration, the EL light emission pattern can be improved. Thereby, the light emission efficiency of the nitride semiconductor laser element can be improved. In addition, the luminance of the nitride semiconductor laser device 100 can be increased by improving the light emission efficiency. The reason why the bright spot-like light emission suppression effect is obtained is that the growth main surface 10a of the GaN substrate 10 has an off-angle in the a-axis direction with respect to the m-plane, so that the growth main surface 10a is on the growth main surface 10a. It is considered that when the active layer 14 (well layer 14a) is grown, the direction of migration of In atoms changes, and aggregation of In is suppressed even under conditions where the In composition ratio is high (In supply amount is large). . In addition, since the growth mode of the p-type semiconductor layer formed on the active layer 14 also changes, the activation rate of Mg, which is a p-type impurity, is improved, and the resistance of the p-type semiconductor layer is reduced. It is thought that. In addition, since the p-type semiconductor layer has a low resistance, it becomes easy to inject a current uniformly, thereby making the EL light emission pattern uniform.

  In the first embodiment, since the EL light emission pattern can be made uniform by suppressing the brightening of the EL light emission pattern, the driving voltage can also be reduced. It should be noted that by suppressing the bright spot light emission, an EL light emission pattern with uniform light emission can be obtained, so that the gain can be increased in the formation of the nitride semiconductor laser element.

  In the first embodiment, the GaN substrate 10 having the growth main surface 10a as a surface having an off angle in the a-axis direction with respect to the m-plane is used, and the growth main surface 10a is in contact with the growth main surface 10a. By forming the InGaN layer 11 as described above, the in-plane layer thickness distribution of the InGaN layer 11 can be made uniform. In addition, even in the nitride semiconductor layer stacked on the InGaN layer 11, the in-plane layer thickness distribution can be made uniform. Thereby, a favorable surface morphology can be obtained. Note that, by improving the surface morphology, variation in element characteristics can be reduced, so that the manufacturing yield can be improved. Thereby, an element having characteristics within the standard range can be easily obtained. In addition, by improving the surface morphology, device characteristics and reliability can be improved.

  In the first embodiment, the InGaN layer 11 is formed on the GaN substrate 10 so as to be in contact with the main growth surface 10a, so that the InGaN layer 11 can reduce the adverse effects such as dislocation from the GaN substrate 10. Acts as a layer. For this reason, it is possible to improve the light emission efficiency and improve the element characteristics and reliability.

  Furthermore, in the first embodiment, the InGaN layer 11 is formed on the GaN substrate 10 so as to be in contact with the growth main surface 10 a, so that the strain of the nitride semiconductor layer stacked on the InGaN layer 11 is formed by the InGaN layer 11. Can be relaxed. Thereby, even when the nitride semiconductor layer laminated | stacked on the InGaN layer 11 has the nitride semiconductor layer containing Al, it can suppress that a crack generate | occur | produces.

  In the first embodiment, the lower cladding layer 12 made of AlGaN is formed on the InGaN layer 11 so as to be in contact with the upper surface of the InGaN layer 11, so that the interface between the InGaN layer 11 and the lower cladding layer 12 is formed. Can be very good. That is, the steepness of the interface can be improved. As a result, a very flat lower cladding layer 12 can be stacked on the flatly stacked InGaN layer 11, so that the underlying layer interposed between the active layer 14 and the GaN substrate 10 is very flat. A good semiconductor layer can be formed.

In the first embodiment, the semiconductor layer in contact with the growth main surface 10a of the GaN substrate 10 is a nitride semiconductor layer made of In _y Ga _1-y N (0 <y ≦ 1) or Al _a In _b. Even when the nitride semiconductor layer is made of Ga _c N (a + b + c = 1, 0 <a ≦ 1, 0 <b ≦ 1, 0 ≦ c <1), the same effect as that obtained when the InGaN layer 11 is formed is obtained. be able to.

Even when the semiconductor layer in contact with the growth main surface 10a of the GaN substrate 10 is a nitride semiconductor layer made of In _y Ga _1-y N (0 <y ≦ 1), the nitride semiconductor layer is separated from the substrate. It can function as a buffer layer that reduces adverse effects. Considering only the effect as the buffer layer, the above effect can be obtained until the thickness of the nitride semiconductor layer made of In _y Ga _1-y N (0 <y ≦ 1) is about 1.0 μm. In view of this, the thickness of the nitride semiconductor layer made of In _y Ga _1-y N (0 <y ≦ 1) is preferably set to 0.7 μm or less.

Further, when a nitride semiconductor layer made of In _y Ga _1-y N (0 <y ≦ 1) is used as the semiconductor layer in contact with the growth main surface 10a of the GaN substrate 10, the well layer 14a constituting the active layer 14 Even if the In composition ratio x1 is in the range of 0.10 or more and 0.45 or less, the effect of improving the luminous efficiency can be obtained. In addition, when the In composition ratio x1 of the well layer 14a is in the range of 0.15 to 0.45, the effect of improving the light emission efficiency can be effectively obtained. This is because when the In composition ratio x1 of the active layer 14 is high, the influence from the GaN substrate 10 is suppressed, or the influence of the nitride semiconductor layer formed between the active layer 14 and the GaN substrate 10 is suppressed. This is because it becomes important to form a higher quality active layer 14.

In the first embodiment, a semiconductor layer (a nitride semiconductor layer containing In) in contact with the growth main surface 10a of the GaN substrate 10 is formed of Al _a In _b Ga _c N (a + b + c = 1, 0 <a ≦ 1, 0 <with a b ≦ 1,0 ≦ c <1) made of a nitride semiconductor layer, a semiconductor layer formed in contact with the layer on the (nitride semiconductor layer containing _{Al), Al p in q Ga} r When the nitride semiconductor layer is made of N (p + q + r = 1, 0 <p ≦ 1, 0 <q ≦ 1, 0 ≦ r <1), the semiconductor layer (Al _a The In composition ratio b of the (In _b Ga _c N layer) is preferably configured to satisfy the relationship of 0 <b ≦ 0.1 and b> q. In addition, the Al composition ratio a of the semiconductor layer (Al _a In _b Ga _c N layer) in contact with the growth main surface 10a of the GaN substrate 10 satisfies the relationship of 0 <a ≦ 0.1 and a <p. If it is comprised, it is more preferable.

  Thus, in 1st Embodiment, luminous efficiency can be improved significantly by comprising as mentioned above. Moreover, since the device characteristics and reliability can be improved by improving the light emission efficiency, the highly reliable nitride semiconductor laser device 100 having excellent device characteristics can be obtained.

  Further, in the first embodiment, by making the absolute value of the off angle in the a-axis direction larger than 0.1 degree, it is possible to easily suppress the brightening of the EL light emission pattern.

  When the growth main surface 10a of the GaN substrate 10 also has an off-angle in the c-axis direction with respect to the m-plane, the off-angle in the a-axis direction is set larger than the off-angle in the c-axis direction, so that the EL It is possible to effectively suppress the formation of bright spots in the light emission pattern. That is, by configuring in this way, it is possible to suppress the inconvenience that the effect of suppressing bright spot light emission is reduced due to an excessively large off angle in the c-axis direction. Thereby, luminous efficiency can be improved easily.

  In the first embodiment, the drive voltage can be easily reduced by configuring the active layer 14 of the nitride semiconductor laser device 100 in the DQW structure. For this reason, the device characteristics and reliability can be improved also by this. Even when the active layer 14 has a DQW structure, it is possible to suppress bright spot light emission of the EL light emission pattern.

In the first embodiment, the Al composition ratio y of the carrier block layer 15 made of p-type Al _y Ga _1-y N is configured to be 0.08 or more and 0.35 or less, so that the carrier (electrons) is reduced. Since a sufficiently high energy barrier can be formed, it is possible to more effectively prevent carriers injected into the active layer 14 from flowing into the p-type semiconductor layer. Thereby, it is possible to effectively suppress the formation of bright spots in the EL light emission pattern. Further, by setting the Al composition ratio y of the carrier block layer 15 to 0.35 or less, it is possible to suppress the increase in resistance of the carrier block layer 15 caused by the Al composition ratio y becoming too large. In the region where the In composition ratio x1 of the well layer 14a is large (x1 ≧ 0.15), when the Al composition ratio y of the carrier block layer 15 formed on the active layer 14 is 0.08 or more, the carrier block layer It becomes very difficult to grow 15 well. This is because as the In concentration of the well layer 14a increases, the surface flatness of the active layer 14 deteriorates, and it becomes difficult to form a layer having a high Al composition ratio y with good crystallinity. However, when the GaN substrate 10 having the growth main surface 10a as a surface having an off-angle in the a-axis direction with respect to the m-plane is used, the In composition ratio x1 of the active layer 14 (well layer 14a) is 0.15 or more and 0.00. Even in the case of 45 or less, the carrier block layer 15 having an Al composition ratio y of 0.08 or more and 0.35 or less can be formed on the active layer 14 with good crystallinity. Thereby, it is possible to effectively suppress brightening of the EL light emission pattern and make the EL light emission pattern uniform.

  In the first embodiment, the use of a nitride semiconductor layer containing Al for the barrier layer 14b of the active layer 14 can almost completely suppress the occurrence of dark lines in the light emission pattern. Thereby, since the fall of the luminous efficiency resulting from generation | occurrence | production of a dark line can be suppressed, luminous efficiency can be improved further.

  In the first embodiment, the barrier layer 14b is made of a nitride semiconductor containing Al, so that the flatness of the barrier layer 14b can be improved. For this reason, by forming the well layer 14a on the highly flat barrier layer 14b, the in-plane distribution of the In composition in the well layer 14a can be suppressed from becoming non-uniform. In addition, the crystallinity of the active layer 14 can be improved. Thereby, luminous efficiency can be improved more.

  It is more preferable that the barrier layer (for example, the third barrier layer in the first embodiment) between the carrier block layer 15 and the well layer 14a is a nitride semiconductor layer containing Al and In. Since the carrier block layer is formed with an Al composition ratio larger than that of the barrier layer, the stress from the carrier block layer is applied to the well layer. For this reason, stress can be relieved by configuring the barrier layer between the carrier block layer 15 and the well layer 14a to contain In. Further, the barrier layer between the carrier block layer 15 and the well layer 14a may be configured to include AlInGaN in part. Further, the barrier layer between the carrier block layer 15 and the well layer 14a has a two-layer structure of AlGaN / AlInGaN, AlInGaN / AlGaN, AlInGaN / InGaN, AlInGaN / AlGaN / AlInGaN, AlInGaN / InGaN / AlInGaN, AlGaN / InGaN / A multilayer structure such as AlGaN may be used. Further, the barrier layer between the carrier block layer 15 and the well layer 14a may be InGaN from the viewpoint of stress relaxation. By forming the barrier layer in this way, the generation of dark lines can be effectively suppressed.

  Further, by using the GaN substrate 10 having the growth main surface 10a provided with an off-angle in the a-axis direction with respect to the m-plane, the well layer 14a is a condition under which a bright spot-like EL light emission pattern appears remarkably. Even when the In composition ratio x1 is 0.15 or more, the formation of bright spots in the EL emission pattern can be effectively suppressed. For this reason, when the In composition ratio x1 of the well layer 14a of the active layer 14 is set to 0.15 or more, the effect of suppressing bright spot light emission can be remarkably obtained. Further, when the In composition ratio x1 of the well layer 14a is set to 0.45 or less, the In composition ratio x1 of the well layer 14a becomes larger than 0.45, so that the active layer is caused by strain such as lattice mismatch. It is possible to suppress the inconvenience that a large number of dislocations enter 14.

  Further, when AlInGaN is used for the barrier layer 14b, the light emission efficiency can be improved as in the case where AlGaN is used for the barrier layer 14b. In addition, from the viewpoint of the semiconductor laser element, there is an advantage that light confinement is improved. Also, by forming the well layer 14a on the barrier layer 14b made of AlInGaN, the efficiency of In taken into the well layer 14a can be made very good. For this reason, even when the gas flow rate of In is reduced, a high In composition ratio can be maintained. As a result, the In incorporation efficiency can be improved. As a result, it is possible to increase the wavelength more effectively. Further, since the consumption of the source gas (for example, TMI) can be reduced, there is an advantage in terms of cost.

When AlInGaN (AlsIntGauN (s + t + u = 1)) is used for the barrier layer 14b, the Al composition ratio s is preferably set in the range of 0 <s ≦ 0.08. In this case, the In composition ratio t is preferably set in a range of 0 <t ≦ 0.10, and more preferably set in a range of 0 <t ≦ 0.03. By setting in such a range, the AlInGaN barrier layer can be formed more flatly. Even when the well layer 14a made of In _x1 Ga _{1 -x1} N having a high In composition ratio x1 (for example, x1 is 0.15 or more and 0.45 or less) is formed on the flat barrier layer, it is more effective. In addition, the occurrence of dark lines can be suppressed. The preferred thickness when the barrier layer 14b is made of AlInGaN is the same as the preferred thickness when the barrier layer 14b is made of AlGaN.

  Here, the growth main surface is a dark line generation suppressing effect obtained by forming the barrier layer 14b from a nitride semiconductor layer containing Al, and a surface having an off-angle in the a-axis direction with respect to the m-plane. This effect is completely different from the bright spot-like light emission suppression effect obtained by using the nitride semiconductor substrate. That is, when a nitride semiconductor layer containing Al is used for the barrier layer 14b, a nonpolar surface such as an m-plane is effective. On the other hand, even when a barrier layer made of InGaN is used, it is possible to suppress the formation of luminescent spots in the light emission pattern by providing the off angle in the a-axis direction.

  However, when a nitride semiconductor layer containing Al is formed on a nitride semiconductor substrate having an off-angle in the a-axis direction, an effect of improving crystallinity and the like can be obtained. Therefore, a nitride having an off-angle in the a-axis direction When a semiconductor substrate is used and a nitride semiconductor layer containing Al is used for the barrier layer 14b, the crystallinity of the barrier layer 14b is improved. Thus, it is more preferable to combine both because a synergistic effect is obtained. Of course, if a nitride semiconductor substrate having an off angle in the a-axis direction is used and a nitride semiconductor layer containing Al is used for the barrier layer, the generation of dark lines can be suppressed, in addition to the generation of bright spot-like light emission. Suppression is also possible.

  7 to 19 are views for explaining a method of manufacturing the nitride semiconductor laser element according to the first embodiment of the present invention. A method for manufacturing the nitride semiconductor laser device 100 according to the first embodiment of the present invention is now described with reference to FIGS.

First, a GaN substrate 10 having a growth main surface 10a as a surface having an off angle with respect to the m-plane is prepared. The GaN substrate 10 is produced, for example, by growing a GaN crystal on a seed substrate that is a substrate cut from a GaN bulk crystal having a c-plane (0001) as a main surface. Specifically, as shown in FIG. 7, after a protective film (not shown) made of SiO ₂ is partially formed on the base substrate 300, the base substrate 300 is formed using an epitaxial growth method such as MOCVD. A GaN bulk crystal is grown on the protective film. As a result, growth starts from a portion where the protective film is not formed, and lateral growth of the GaN crystal occurs on the protective film. Then, the GaN crystals grown in the lateral direction are joined together on the protective film and continue to grow, and the GaN crystal layer 400 a is formed on the base substrate 300. The GaN crystal layer 400a is formed to be sufficiently thick so that it can be handled independently even after the base substrate 300 is removed. Next, the base substrate 300 is removed from the formed GaN crystal layer 400a by, for example, etching. Thereby, as shown in FIG. 8, a GaN bulk crystal 400 having a c-plane (0001) as a main surface is obtained. As the base substrate 300, for example, a GaAs substrate, sapphire substrate, ZnO substrate, SiC substrate, GaN substrate, or the like can be used. The thickness S of the GaN bulk crystal 400 can be set to about 3 mm, for example.

  Next, by grinding and polishing the (0001) plane and the (000-1) plane, which are both main surfaces of the obtained GaN bulk crystal 400, the average roughness Ra of both main surfaces is set to 5 nm. This average roughness Ra is an arithmetic average roughness Ra specified in JIS B 0601, and can be measured by an AFM (atomic force microscope).

  Next, by slicing the GaN bulk crystal 400 with a plurality of planes perpendicular to the [1-100] direction, a plurality of GaN crystal substrates 410 having the m-plane {1-100} as the main surface are formed with a thickness T (for example, 1 mm) (width S: 3 mm). Then, by grinding and polishing the four surfaces of the cut GaN crystal substrate 410 that have not been ground and polished, the average roughness Ra of these four surfaces is set to 5 nm. Thereafter, as shown in FIGS. 9 and 10, in the plurality of GaN crystal substrates 410, the principal surfaces are made parallel to each other, and the [0001] directions of the GaN crystal substrates 410 are made the same. , Arranged adjacent to each other.

  Subsequently, as shown in FIG. 11, a plurality of GaN crystal substrates 410 arranged adjacent to each other are used as seed substrates, and an epitaxial growth method such as an HVPE method is performed on the m-plane {1-100} of these GaN crystal substrates 410. Use to grow GaN crystals. Thereby, the GaN substrate 1 having the m-plane as the growth main surface is obtained. Next, by polishing the main surface of the obtained GaN substrate 1 by a chemical mechanical polishing process, the off-angle in the a-axis direction and the off-angle in the c-axis direction are independently controlled, and the a-axis with respect to the m-plane The off angle in the direction and the off angle in the c-axis direction are set as desired off angles. This off angle can be measured by an X-ray diffraction method. Thereby, the GaN substrate 10 is obtained in which the growth main surface is a surface having an off angle in each of the a-axis direction and the c-axis direction with respect to the m-plane.

  In the production of the GaN substrate 10, when producing a substrate with a large off-angle, when the plurality of GaN crystal substrates 410 are cut out from the GaN bulk crystal 400, the main surface of the GaN crystal substrate 410 is m-plane {1 You may cut out with a predetermined cut-off angle with respect to the [1-100] direction so that it may have a desired off angle with respect to the −100} plane. By doing so, the main surface of the GaN crystal substrate 410 becomes a surface having a desired off angle with respect to the m-plane {1-100} plane, and thus the GaN substrate 1 (10) formed on the main surface. The main surface (growth main surface) is also a surface having a desired off angle with respect to the m-plane {1-100} plane.

  Further, the GaN crystal substrate 410 can be used as the GaN substrate 10 by polishing the main surface of the GaN crystal substrate 410 cut out from the GaN bulk crystal 400 (see FIG. 8) by chemical mechanical polishing. In this case, the width S of the GaN crystal substrate 410 may be 3 mm or more.

  Here, in the first embodiment, the off angle in the a-axis direction of the GaN substrate 10 is adjusted to be an angle larger than 0.1 degree. In addition, when providing an off angle also in the c-axis direction, it is preferable to adjust the off-angle in the c-axis direction to an angle larger than ± 0.1 degrees. Further, the off angle in the c-axis direction is preferably adjusted to be smaller than the off-angle in the a-axis direction.

  Subsequently, as illustrated in FIG. 12, nitride semiconductor layers 11 to 18 are grown on the main growth surface 10 a of the obtained GaN substrate 10 by using the MOCVD method.

Specifically, on the growth main surface 10a of the GaN substrate 10, an n-type InGaN layer 11 having a thickness of about 0.1 μm and a lower cladding layer made of n-type Al _0.06 Ga _0.94 N having a thickness of about 2.2 μm. 12. A lower guide layer 13 made of n-type GaN having a thickness of about 0.1 μm and an active layer 14 are sequentially grown.

In place of the InGaN layer 11, In _y Ga _1-y N (0 <y ≦ 1) or Al _a In _b Ga _c N (a + b + c = 1, 0 <a ≦ 1, 0 <b ≦ 1, 0 A nitride semiconductor layer composed of ≦ c <1) may be formed. Further, the lower clad layer 12 may be made of, for example, AlInGaN, AlInN, AlN, etc. in addition to AlGaN.

When the active layer 14 is grown, as shown in FIG. 5, two well layers 14a made of In _x1 Ga _1-x1 N and three barrier layers 14b made of Al _x2 Ga _1-x2 N are used. And grow alternately. Specifically, for example, on the lower guide layer 13, from the lower layer to the upper layer, a first barrier layer 141b having a thickness of about 30 nm, a first well layer 141a having a thickness of about 1.5 nm to about 4 nm, A second barrier layer 142b having a thickness of about 16 nm, a second well layer 142a having a thickness of about 1.5 nm to about 4 nm, and a third barrier layer 143b having a thickness of about 60 nm are sequentially grown. As a result, an active layer 14 having a DQW structure composed of two well layers 14 a and three barrier layers 14 b is formed on the lower guide layer 13. At this time, the well layer 14a is formed so that the In composition ratio x1 is 0.15 or more and 0.45 or less (for example, 0.2 to 0.25). On the other hand, the barrier layer 14b is formed such that the Al composition ratio x2 is, for example, 0 <x2 ≦ 0.08.

Next, as shown in FIG. 12, a carrier block layer 15 made of p-type Al _y Ga _1-y N and an upper part made of p-type Al _0.01 Ga _0.99 N having a thickness of about 0.05 μm are formed on the active layer 14. A guide layer 16, an upper cladding layer 17 made of p-type Al _0.06 Ga _0.94 N having a thickness of about 0.5 μm, and a contact layer 18 made of p-type Al _0.01 Ga _0.99 N having a thickness of about 0.1 μm are sequentially grown. . At this time, the carrier block layer 15 is preferably formed so as to have a thickness of 40 nm or less (for example, about 12 nm). The carrier block layer 15 is formed so that the Al composition ratio y is 0.08 or more and 0.35 or less (for example, about 0.15). The n-type semiconductor layer (n-type GaN layer 11, lower cladding layer 12 and lower guide layer 13) is doped with, for example, Si as an n-type impurity, and a p-type semiconductor layer (carrier block layer 15, upper guide layer). Layer 16, upper cladding layer 17 and contact layer 18) are doped with Mg as a p-type impurity.

  In the first embodiment, the InGaN layer 11 that is a semiconductor layer in contact with the growth main surface 10 a of the GaN substrate 10 is preferably formed at a low temperature of 700 ° C. to 1100 ° C. More preferably, the film is formed at a temperature of 700 ° C. or higher and 900 ° C. or lower. In the case of using a nitride semiconductor substrate whose main growth surface is a surface having an off-angle in the a-axis direction with respect to the m-plane, the substrate temperature before film formation is increased to a temperature exceeding about 1100 ° C. When it is raised, N (nitrogen) or Ga (gallium) may evaporate from the substrate surface before growth due to the atmosphere in the furnace (conditions such as gas flow rate and pressure), which may cause surface roughness of the substrate. It has been found that this surface roughness is reduced at 1100 ° C. or lower and does not occur at a substrate temperature of 900 ° C. or lower. Therefore, as described above, the InGaN layer 11 is preferably formed at a growth temperature of 700 ° C. or higher and 1100 ° C. or lower. More preferably, the InGaN layer 11 is formed at a temperature of 700 ° C. or higher and 900 ° C. or lower. Note that since InGaN can be formed at a low temperature (low temperature of about 700 ° C. to 900 ° C.), surface roughness of the substrate surface can be effectively suppressed. Further, instead of the InGaN layer 11, a nitride semiconductor layer containing In other than the InGaN layer (for example, an AlInGaN layer, an AlInN layer, an InN layer, etc.) is formed on the GaN substrate 10 so as to be in contact with the growth main surface 10a. In this case, the nitride semiconductor layer is preferably formed at a growth temperature similar to the growth temperature of the InGaN layer 11 described above.

  The n-type semiconductor layer stacked on the InGaN layer 11 is formed at a growth temperature (for example, 1075 ° C.) that is 900 ° C. or higher and lower than 1300 ° C., for example. The well layer 14a of the active layer 14 is formed at a growth temperature (for example, 700 ° C.) of 600 ° C. or more and 800 ° C. or less, for example. The barrier layer 14b in contact with the well layer 14a is formed, for example, at the same growth temperature (for example, 700 ° C.) as the well layer 14a. Furthermore, the p-type semiconductor layer is formed at a growth temperature (for example, 880 ° C.) that is 700 ° C. or higher and lower than 900 ° C., for example. The growth temperature of the n-type semiconductor layer is preferably 900 ° C. or higher and lower than 1300 ° C., more preferably 1000 ° C. or higher and lower than 1300 ° C. The growth temperature of the well layer 14a of the active layer 14 is preferably 600 ° C. or higher and 830 ° C. or lower. When the In composition ratio x1 of the well layer 14a is 0.15 or higher, 600 ° C. or higher and 770 ° C. or lower is preferable. It is more preferable if it is 630 ° C. or higher and 740 ° C. or lower. The growth temperature of the barrier layer 14b of the active layer 14 is preferably the same temperature as the well layer 14a or higher than the well layer 14a. Furthermore, the growth temperature of the p-type semiconductor layer is preferably 700 ° C. or higher and lower than 900 ° C., more preferably 700 ° C. or higher and 880 ° C. or lower. Of course, even if the p-type semiconductor layer is formed at a temperature of 900 ° C. or higher, p-type conduction can be obtained. Therefore, the p-type semiconductor layer may be formed at a temperature of 900 ° C. or higher.

  In addition, when the In composition ratio of the well layer is high, if the semiconductor layer is formed at a temperature higher than the growth temperature of the well layer after the well layer is grown, thermal damage to the well layer is observed and black light is not emitted. Spots appear. This black spot is considered to be generated by aggregation of In atoms. For this reason, suppressing aggregation of In atoms leads to protection of the active layer from thermal damage. In a light emitting device (for example, a semiconductor laser device) in which a p-type semiconductor layer needs to be stacked at a growth temperature higher than the well layer growth temperature after the well layer is grown, the heat resistance of the active layer is required. According to previous studies by the present inventors, when an m-plane substrate is used, a p-type nitride semiconductor layer exhibiting p-type conduction at a lower temperature (for example, compared to a conventional c-plane substrate) (for example, , P-type AlGaN layer, p-type GaN layer, etc.) can be formed. Using this knowledge, although it is possible to use GaN or InGaN for the barrier layer, the effect of heat is reduced by using a nitride semiconductor layer containing Al (for example, an AlGaN layer, an AlInGaN layer, etc.) for the barrier layer. In addition to being able to suppress more, the occurrence of dark lines can also be suppressed. Therefore, as described above, the light emission efficiency can be further improved by forming the barrier layer from a nitride semiconductor layer containing Al. Further, a nitride semiconductor substrate having an off angle in the a-axis direction with respect to the m-plane also has an effect of improving flatness unique to the a-axis off-substrate. For this reason, by using such a nitride semiconductor substrate (m-plane a-axis off-substrate) and forming a barrier layer made of a nitride semiconductor containing Al on the main growth surface, the luminous efficiency is further improved. Is done.

In addition, as a growth raw material of these nitride semiconductors, as a group III source gas, for example, trimethylgallium ((CH ₃ ) ₃ Ga; TMG), trimethylaluminum ((CH ₃ ) ₃ Al; TMA), and Trimethylindium ((CH ₃ ) ₃ In; TMI) can be used. Further, for example, ammonia gas (NH ₃ ) can be used as the group V source gas. As for the dopant, for example, monosilane (SiH ₄ ) can be used as the n-type dopant (n-type impurity), and for example, cyclopentadienyl magnesium (CP ₂ Mg) is used as the p-type dopant (p-type impurity). Can be used.

  When the well layer is grown at a low growth temperature of 600 ° C. or higher and 770 ° C. or lower (particularly when grown at a low growth temperature of 650 ° C. or higher and 740 ° C. or lower), the growth rate of the well layer is It is preferably at least 0.7 second / second and more preferably at least 0.05 second / second and not more than 0.2 second / second.

  As described above, when the growth rate of the well layer is set low, the migration of atoms is suppressed, while the slowing of the growth rate as described above alleviates the suppression of migration, and the proper movement of atoms. Secured. Thereby, crystallinity improves and luminous efficiency improves. When the growth rate of the well layer is slower than 0.05 Å / sec, the number of atoms leaving from the crystal surface is larger than the number of atoms supplied to the crystal surface. For this reason, since the crystal surface is likely to be roughened by the etching effect, the flatness is likely to deteriorate. Therefore, the growth rate of the well layer is preferably 0.05 kg / sec or more as described above. Of course, the growth method (growth conditions) of the well layer is not limited to the above, but the light emission efficiency is further improved by forming the well layer as described above.

Furthermore, when the growth temperature of the well layer is 600 ° C. or higher and 720 ° C. or lower, hydrogen (H ₂ ) may be introduced as a carrier gas during the growth of the well layer.

  When hydrogen is introduced as a carrier gas, the gas flow rate is preferably 0.005 L / min or more and 0.100 L / min or less, more preferably 0.010 L / min or more and 0.050 L / min or less. When the gas flow rate is less than 0.005 L / min, it is difficult to obtain the effect of introducing hydrogen during the growth of the well layer. In addition, when hydrogen as a carrier gas is introduced at a gas flow rate higher than 0.100 L / min, the incorporation of In atoms can be easily reduced even when the well layer growth temperature is 600 ° C. or higher and 720 ° C. or lower. This makes it difficult to increase the wavelength.

  As described above, when hydrogen is introduced during the growth of the well layer, the satellite peak of the X-ray diffraction image becomes clear. In addition, an improvement effect such as improvement of the light emission pattern at the time of current injection can be obtained, leading to an improvement in light emission efficiency. Si or Mg can also be added to any or all of the well layers. The well layer is not limited to InGaN, and may be composed of AlInGaN. The formation method at that time is the same as that of the InGaN well layer.

  Further, the well layer and the barrier layer may be continuously grown without being interrupted, or may be interrupted.

  Further, when forming the barrier layer, the carrier gas may be only nitrogen, but a state containing hydrogen is more preferable. When hydrogen is used as the carrier gas, the hydrogen flow rate is preferably less than 1.0 L / min, more preferably 0.500 L / min or less. When the flow rate of hydrogen is 0 L / min, it is agreed that the carrier gas is only nitrogen, but by introducing hydrogen at the above flow rate, the steepness of the interface is improved. Thereby, the satellite peak of the X-ray diffraction image becomes clear. When the flow rate of hydrogen is 1.0 L / min or more, the crystal surface is likely to be rough due to the etching effect, and the flatness is likely to deteriorate. Further, when the barrier layer is made of a nitride semiconductor containing In, In atoms are difficult to be taken in.

  Further, the growth rate when the barrier layer is formed is preferably 0.05 to 1.2 liters / second, more preferably 0.05 to 0.8 liters / second. When the growth rate of the barrier layer is slower than 0.05 Å / sec, the number of atoms leaving the crystal surface is larger than the number of atoms supplied to the crystal surface. For this reason, the crystal surface is likely to be roughened by the etching effect, and the flatness may be deteriorated. Further, when the growth rate is higher than 1.2 Å / sec, the crystallinity and flatness may be deteriorated. For this reason, the growth rate of the barrier layer is preferably in the above range. Of course, the growth method (growth conditions) of the barrier layer is not limited to the above, but the light emission efficiency is further improved by forming the barrier layer as described above.

  Such a tendency is applicable to the case where the barrier layer is any one of GaN, InGaN, and AlGaN, but is more effective when the barrier layer is made of a nitride semiconductor containing Al. Most preferably, the barrier layer is composed of an AlGaN layer or an AlInGaN layer.

  When the barrier layer is made of AlInGaN, there is a method in which, for example, TMG, TMI and TMA are simultaneously supplied as group III source gases and ammonia gas is simultaneously supplied as group V source gases.

  As another method, when forming the barrier layer, TMG and TMA are simultaneously supplied as the group III source gas without supplying TMI (that is, the AlGaN layer is first formed as the barrier layer). There is a method in which an AlInGaN barrier layer is formed by automatically taking in In utilizing the residual TMI gas at the time of well layer growth, In diffusion and segregation effects. Specifically, the growth temperature of the well layer is set to 700 ° C., and TMG, TMI and ammonia gas for realizing a gas phase ratio for obtaining a desired wavelength are supplied. Thereafter, the supply of TMG and TMI is stopped, and after the growth is interrupted for several seconds, TMG, TMA and ammonia gas are supplied with the growth temperature maintained at 700 ° C. to form a barrier layer. Using this method, the composition ratio of the barrier layer was analyzed by AES (Auger analysis) measurement. As a result, an Al composition ratio of 1.0% and an In composition ratio of 2.0% were detected in the barrier layer. That is, In is automatically taken in by the above method. A barrier layer made of AlInGaN may be formed using such a method. It should be noted that the same effect can be obtained only by changing the raw material without interrupting the growth. When this method is used, as a method for controlling the incorporation of In atoms, the growth temperature of the barrier layer is 30 ° C. higher than the growth temperature of the well layer (for example, the growth temperature of the well layer is 700 ° C. In this case, since the In is evaporated by forming the film at a growth temperature of the barrier layer of 730 ° C., the AlGaN film can be formed. In addition, by increasing the flow rate of the hydrogen carrier gas when forming the barrier layer, it is possible to suppress In incorporation and AlGaN film formation is possible. In any case, In atoms were not detected from the barrier layer by AES measurement.

Subsequently, as shown in FIG. 13, the contact layer 18 has a width of about 1 μm to about 10 μm (for example, about 1.5 μm), and is formed in the Y direction (substantially c-axis [0001]). A striped (elongated) resist 450 extending in parallel with the direction is formed. Then, as shown in FIG. 14, using the RIE (reactive ion etching) method using a chlorine-based gas such as SiCl ₄ or Cl ₂ or Ar gas, the depth in the middle of the upper guide layer 16 using the resist 450 as a mask. Etching is performed. Thus, a striped (elongated) ridge is formed by the convex portion of the upper guide layer 16, the upper cladding layer 17, and the contact layer 18, and extends in parallel to each other in the Y direction (substantially c-axis [0001] direction). A portion 19 (see FIGS. 3 and 6) is formed.

Next, as shown in FIG. 15, SiO ₂ having a thickness of about 0.1 μm to about 0.3 μm (for example, about 0.15 μm) by sputtering or the like with the resist 450 left on the ridge portion 19. An insulating layer 20 made of is formed, and the ridge portion 19 is embedded. Then, by removing the resist 450 by lift-off, the contact layer 18 above the ridge portion 19 is exposed. As a result, insulating layers 20 as shown in FIG. 16 are formed on both sides of the ridge portion 19.

  Next, as shown in FIG. 17, a Pd layer (not shown) having a thickness of about 15 μm and an Au layer having a thickness of about 200 nm are formed from the substrate side (insulating layer 20 side) using a vacuum deposition method or the like. By sequentially forming (not shown), a p-side electrode 21 having a multilayer structure is formed on the insulating layer 20 (contact layer 18).

  Then, in order to make it easy to divide the substrate, the back surface of the GaN substrate 10 is ground or polished to reduce the thickness of the GaN substrate 10 to about 100 μm. Thereafter, as shown in FIG. 2, an Hf layer (not shown) having a thickness of about 5 nm from the back side of the GaN substrate 10 and a thickness of about 150 nm are formed on the back side of the GaN substrate 10 using a vacuum deposition method or the like. An n-side electrode 22 having a multilayer structure is formed by sequentially forming an Al layer (not shown) having a thickness. An Mo layer (not shown) having a thickness of about 36 nm, a Pt layer (not shown) having a thickness of about 18 nm, and an Au having a thickness of about 200 nm are formed on the n-side electrode 22 from the n-side electrode 22 side. By sequentially forming layers (not shown), a metallized layer 23 having a multilayer structure is formed. Note that before the n-side electrode 22 is formed, dry etching or wet etching may be performed for the purpose of adjusting the electrical characteristics of the n-side.

Subsequently, as shown in FIG. 18, the substrate is divided into bars by using a scribing / breaking method or a laser scribing method. As a result, a bar-shaped element whose end face is the resonator face 30 is obtained. Next, a coating is applied to the end face (resonator face 30) of the bar-like element using a technique such as vapor deposition or sputtering. Specifically, an emission side coating film (not shown) made of, for example, an aluminum oxynitride film or the like is formed on one end face serving as a light emission surface. In addition, a reflection-side coating film (not shown) made of a multilayer film such as SiO ₂ or TiO ₂ is formed on the opposite end face serving as the light reflection surface.

  Finally, by dividing the bar-shaped element along the planned dividing line P along the Y direction (substantially c-axis [0001] direction), the individual nitride semiconductor laser elements are separated as shown in FIG. Tidy up. Thus, the nitride semiconductor laser device 100 according to the first embodiment of the present invention is manufactured.

  The nitride semiconductor laser device 100 according to the first embodiment manufactured as described above is mounted on a stem 120 via a submount 110 and electrically connected to a lead pin by a wire 130 as shown in FIG. The Then, the cap 135 is welded onto the stem 120 to assemble the can package type semiconductor laser device (semiconductor device) 150.

  In the method of manufacturing the nitride semiconductor laser device 100 according to the first embodiment, as described above, the growth is performed on the GaN substrate 10 having the growth main surface 10a as a surface having an off angle in the a-axis direction with respect to the m-plane. By forming the InGaN layer 11 in contact with the main surface 10a, the surface morphology of the nitride semiconductor layer stacked on the GaN substrate 10 can be improved. Thereby, since a favorable surface morphology can be obtained, element characteristics and reliability can be improved. Further, by improving the surface morphology, the number of elements having characteristics within the standard range can be increased, so that the yield can be easily improved.

  In the first embodiment, the InGaN layer 11 is formed on the GaN substrate 10 so as to be in contact with the main growth surface 10a, so that the InGaN layer 11 can reduce the adverse effects such as dislocation from the GaN substrate 10. Acts as a layer. For this reason, it is possible to improve the light emission efficiency and improve the element characteristics and reliability.

  Furthermore, in the first embodiment, the InGaN layer 11 is formed on the GaN substrate 10 so as to be in contact with the growth main surface 10 a, so that the strain of the nitride semiconductor layer stacked on the InGaN layer 11 is formed by the InGaN layer 11. Can be relaxed. Thereby, even when the nitride semiconductor layer laminated | stacked on the InGaN layer 11 has the nitride semiconductor layer containing Al, it can suppress that a crack generate | occur | produces.

  In the first embodiment, the cleaving property is improved as compared with the m-plane GaN substrate by using the GaN substrate 10 in which the growth main surface 10a is a plane having an off angle in the a-axis direction with respect to the m-plane. be able to. For this reason, when performing end face formation (formation of the resonator surface 30) by cleavage, relatively good end face formation can be performed. Further, by forming a nitride semiconductor layer containing In (for example, InGaN layer 11) on the GaN substrate 10 so as to be in contact with the growth main surface 10a, this layer becomes a buffer layer, and a better end face is formed. be able to. Thereby, since the favorable resonator surface 30 can be obtained, element characteristics can be improved. In addition, variation in element characteristics can be reduced, and cleavage defects can be reduced, so that the yield can also be improved.

  In the first embodiment, the lower cladding layer 12 made of AlGaN is formed on the InGaN layer 11 so as to be in contact with the upper surface of the InGaN layer 11, so that the interface between the InGaN layer 11 and the lower cladding layer 12 is formed. Can be very good. That is, the steepness of the interface can be improved. As a result, a very flat lower cladding layer 12 can be stacked on the flatly stacked InGaN layer 11, so that the underlying layer interposed between the active layer 14 and the GaN substrate 10 is very flat. A good semiconductor layer can be formed. Therefore, by forming the active layer 14 on a very flat and good semiconductor layer (underlayer), the active layer 14 with good crystallinity can be formed. As a result, luminous efficiency can be improved.

In the method of manufacturing the nitride semiconductor laser device 100 according to the first embodiment, the semiconductor layer in contact with the growth main surface 10a of the GaN substrate 10 is made of In _y Ga _1-y N (0 <y ≦ 1), or Even when the nitride semiconductor layer is made of Al _a In _b Ga _c N (a + b + c = 1, 0 <a ≦ 1, 0 <b ≦ 1, 0 ≦ c <1), it is the same as when the InGaN layer 11 is formed. The effect of can be obtained. Further, the lower clad layer 12, even when the _{Al p In q Ga r N (} p + q + r = 1,0 <p ≦ 1,0 <q ≦ 1,0 ≦ r <1) made of a nitride semiconductor layer, the The same effect can be obtained.

  Next, an experiment conducted for confirming the effect of the nitride semiconductor laser element 100 according to the first embodiment will be described. In this experiment, first, a light emitting diode element 200 as shown in FIG. 21 was manufactured as the confirmation element 1, and an EL light emission pattern was observed. The reason why the light emitting diode element is used for the observation of the EL light emission pattern is that it is difficult to observe the EL light emission pattern in the nitride semiconductor laser element because the region where current is injected is narrowed by the formation of the ridge portion. Because.

  This confirmation element 1 (light-emitting diode element 200) was produced by forming a similar nitride semiconductor layer on the same GaN substrate 10 as in the first embodiment. The nitride semiconductor layer was formed using the same method as in the first embodiment. Specifically, as shown in FIG. 21, using a GaN substrate 10 having a growth main surface 10a as a surface having an off-angle with respect to the m-plane, an InGaN layer 11 and a lower cladding are formed on the growth main surface 10a. Layer 12, lower guide layer 13, active layer 14, carrier block layer 15, upper guide layer 16, upper cladding layer 17 and contact layer 18 were sequentially formed. That is, in the confirmation element 1, the semiconductor layer in contact with the growth main surface 10 a of the GaN substrate 10 is the InGaN layer 11. Next, the p-side electrode 221 was formed on the contact layer 18. The p-side electrode 221 was a transparent electrode in order to confirm the EL emission pattern. An n-side electrode 22 and a metallized layer 23 were formed on the back surface of the GaN substrate 10. Regarding the off-angle of the GaN substrate 10 in the confirmation element 1, the off-angle in the a-axis direction was 1.7 degrees, and the off-angle in the c-axis direction was +0.1 degrees. In the confirmation element 1, the In composition ratio of the well layer was 0.25, and the Al composition ratio of the barrier layer was 2%. Note that the barrier layer of the confirmation element 1 is AlGaN. By injecting current into the confirmation element 1 (light-emitting diode element 200) thus produced, the confirmation element 1 (light-emitting diode element 200) was caused to emit light, and the light emission characteristics were examined.

  Further, as the comparative element 1, a light emitting diode element in which the semiconductor layer in contact with the growth main surface was a GaN layer was produced. This comparison element 1 differs from the above-described confirmation element 1 only in that the semiconductor layer in contact with the growth main surface is a GaN layer. The GaN layer of the comparative element 1 was formed to have the same thickness as the InGaN layer 11 of the confirmation element 1. Then, the emission characteristics were examined in the same manner as in the confirmation element 1.

  When the luminous efficiency of each of the confirmation element 1 and the comparative element 1 was measured, it was confirmed that the luminous efficiency of the confirmation element 1 was improved about twice as much as the luminous efficiency of the comparative element 1. . This is because, in the confirmation element 1, the semiconductor layer in contact with the growth main surface 10 a of the GaN substrate 10 is the InGaN layer 11 so that the flatness is improved, and the crystal quality of the nitride semiconductor layer stacked on the InGaN layer 11 is improved. This is thought to be due to the improvement. In addition, the fact that the InGaN layer 11 functions as a buffer layer to obtain a buffer effect that suppresses the influence from the substrate is considered to be one of the reasons why the light emission efficiency is improved.

  Note that since both the confirmation element 1 and the comparison element 1 use a nitride semiconductor substrate whose main growth surface is a surface having an off-angle in the a-axis direction with respect to the m-plane, in any element Also, the brightening of the EL light emission pattern was suppressed, and the EL light emission pattern of uniform light emission was obtained.

  Next, as the comparative element 2 and the comparative element 3, a GaN substrate having an m-plane as a growth main surface (almost m-plane just substrate: the off angle in the a-axis direction is 0 degree, and the off angle in the c-axis direction is +0. The light emitting diode element using (05 degrees) was produced by the same method as that for the confirmation element 1 described above. In the comparative element 2, the semiconductor layer in contact with the growth main surface of the GaN substrate was an InGaN layer similar to the confirmation element 1. On the other hand, in the comparative element 3, the semiconductor layer in contact with the main growth surface of the GaN substrate was a GaN layer similar to the comparative element 2. Other configurations of the comparison elements 2 and 3 are the same as those of the confirmation element 1.

  When the luminous efficiency of each of the comparative element 2 and the comparative element 3 was measured, the luminous efficiency of the comparative element 2 in which the semiconductor layer in contact with the growth main surface of the GaN substrate was an InGaN layer was the same as that of the growth main surface of the GaN substrate. The luminous efficiency of the comparative element 3 in which the semiconductor layer in contact was a GaN layer was almost the same. That is, when a GaN substrate having an m-plane as a growth principal surface is used, the GaN substrate is different from a GaN substrate having a growth principal surface that has an off-angle in the a-axis direction with respect to the m-plane. Even when the semiconductor layer in contact with the main growth surface was an InGaN layer, the effect of improving the light emission efficiency was not clearly seen.

  Moreover, since the comparative element 2 and the comparative element 3 both use a GaN substrate having an m-plane as the growth main surface, the EL emission pattern is observed to have a bright spot shape in any of the elements. .

  Next, a plurality of confirmation elements 2 and comparison elements 4 in which the In composition ratio of the well layer was changed so that the emission wavelength was 480 nm to 530 nm were produced. The confirmation element 2 is the same as the confirmation element 1 except that the In composition ratio of the well layer is variously changed. The comparative element 4 is the same as the comparative element 1 except that the In composition ratio of the well layer is variously changed. In the same manner as described above, the luminous efficiency of these elements was measured.

  As a result, when the emission wavelength is in the range of 480 nm to 500 nm, the emission efficiency of the confirmation element 2 is improved by about 1.5 times compared to the emission efficiency of the comparison element 4, whereas the emission wavelength is in the range of 510 nm or more. Then, the luminous efficiency of the confirmation element 2 was improved about twice as much as the luminous efficiency of the comparative element 4. That is, it was recognized that the higher the In composition ratio of the active layer (well layer) and the longer the emission wavelength, the greater the effect of improving the light emission efficiency. From this, it was confirmed that the effect of improving the light emission efficiency by using the InGaN layer as the semiconductor layer in contact with the main growth surface of the GaN substrate becomes larger as the device can emit light at a long wavelength.

  Subsequently, using a plurality of GaN substrates having different off angles in the a-axis direction and off-angles in the c-axis direction, a plurality of elements similar to the light-emitting diode element 200 shown in FIG. The experiment was conducted.

  As a result, it has been clarified that by providing an off-angle in the a-axis direction with respect to the m-plane, the effect of suppressing the brightening of the EL emission pattern can be obtained. Further, when the off angle in the a-axis direction is 0.1 degrees or less, the effect of suppressing bright spot light emission is small, and when the off angle in the a-axis direction is 0.1 degrees or more, the bright spot shape of the EL light emission pattern. It became clear that the inhibitory effect of crystallization appeared. From this, it was confirmed that the formation of a bright spot in the EL light emission pattern can be suppressed by using a surface having an off-angle in the a-axis direction with respect to the m-plane as the growth main surface of the GaN substrate. It was also confirmed that the bright spot shape of the EL light emission pattern was more effectively suppressed by making the off angle in the a-axis direction larger than the off angle in the c-axis direction.

  As a nitride semiconductor laser device according to Example 1, a GaN substrate having an a-axis direction off angle of 1.9 degrees and a c-axis direction off angle of +0.4 degrees with respect to the m-plane {1-100} is used. A nitride semiconductor laser element similar to the nitride semiconductor laser element according to the first embodiment was manufactured.

Further, the In composition ratio y of the nitride semiconductor layer containing In in contact with the growth main surface of the GaN substrate (In _y Ga _1-y N (0 <y ≦ 1)) is set to 0.05, and the layer thickness is set to 0. The thickness was 12 μm. That is, in Example 1, an n-type In _0.05 Ga _0.95 N layer having a thickness of 0.12 μm was formed on the growth main surface of the GaN substrate so as to be in contact with the growth main surface. The In composition ratio of the well layer was 0.25, and the Al composition ratio of the barrier layer was 2%. Other configurations of Example 1 are the same as those of the first embodiment.

A nitride semiconductor laser element in which an n-type GaN layer having a thickness of 0.12 μm was formed instead of the n-type In _0.05 Ga _0.95 N layer was used as a comparative example. Other configurations of the nitride semiconductor laser device according to the comparative example are the same as those in the first embodiment.

  When the threshold current was measured for Example 1 and the comparative example, the threshold current value was about 90 mA in the nitride semiconductor laser element according to the comparative example, whereas the threshold current was measured in the nitride semiconductor laser element according to Example 1. Was 75 mA, and it was confirmed that the threshold current of the nitride semiconductor laser device of Example 1 was smaller than that of the comparative example. This is probably because the buffer effect and the effect of improving the flatness were obtained in Example 1, and the gain of the active layer was thereby increased.

Further, with respect to the driving voltage, it was confirmed that in the nitride semiconductor laser element according to Example 1, the driving voltage at the time of 50 mA current injection was reduced by about 0.5 V compared to the comparative example. The reason why such a result is obtained is that an n-type In _0.05 Ga _0.95 N layer is formed in contact with the main growth surface of the substrate, and the nitride containing Al is in contact with the n-type In _0.05 Ga _0.95 N layer. This is presumably because the steepness of the interface between the n-type In _0.05 Ga _0.95 N layer and the AlGaN layer (lower clad layer) was improved by forming the AlGaN layer (lower clad layer) which is a semiconductor layer. Further, by forming the n-type In _0.05 Ga _0.95 N layer, the flatness of the layer surface is improved, so that the flatness of each layer of the nitride semiconductor (the entire device structure) is also improved, and the current due to the suppression of the layer thickness fluctuations It is also considered that this is because a uniform injection effect was obtained. The emission wavelength of the nitride semiconductor laser element according to Example 1 was 505 nm.

Here, when the barrier layer is made of a nitride semiconductor containing Al, a tensile strain with respect to GaN increases, and thus cracks may occur. Moreover, since the strain applied to the active layer tends to increase by forming the barrier layer from a nitride semiconductor containing Al, it is preferable to reduce the strain (stress) as much as possible. Furthermore, in order to improve optical confinement, the Al composition ratio of the cladding layer may be increased, and in this case as well, cracks are likely to occur. However, the generation of cracks can be suppressed by making the semiconductor layer in contact with the main growth surface of the substrate a nitride semiconductor layer containing In (In _y Ga _1-y N (0 <y ≦ 1)). It was. For this reason, when the barrier layer is made of a nitride semiconductor containing Al, it can be said that it is a particularly useful technique to make the semiconductor layer in contact with the growth main surface of the substrate a nitride semiconductor layer containing In. .

In Example 2, a nitride semiconductor laser device having substantially the same structure as that of Example 1 was manufactured using the same substrate as that of Example 1. However, in Example 2, a nitride semiconductor layer made of n-type AlIn _y Ga _1-y N (0 <y ≦ 1) is used for the semiconductor layer in contact with the main growth surface of the substrate. Specifically, in Example 2, an n-type Al _0.08 In _0.04 Ga _0.88 N layer is used as the semiconductor layer in contact with the main growth surface of the substrate. In this case, the same effect as described above was obtained.

As a nitride semiconductor laser element according to Example 3, a GaN substrate having an off angle in the a-axis direction of 4 degrees and an off angle in the c-axis direction of +1 degree with respect to the m-plane {1-100} is used. Almost the same nitride semiconductor laser device was fabricated. However, in Example 3, the semiconductor layer in contact with the growth main surface of the substrate is an n-type In _0.02 Ga _0.98 N layer having a thickness of about 0.1 μm. That is, in Example 3, a nitride semiconductor layer made of n-type In _0.02 Ga _0.98 N having a thickness of about 0.1 μm is stacked on the growth main surface of the substrate so as to be in contact with the growth main surface. . On top of that, a lower clad composed of a superlattice structure of 250 periods having a structure of 1 period of n-type Al _0.12 Ga _0.88 N (layer thickness: 4 nm) / GaN (layer thickness: 2 nm) having a thickness of about 1.5 μm A layer is formed. In this case, the same effect was obtained.

(Second Embodiment)
22 to 24 are views for explaining the nitride semiconductor laser device according to the second embodiment of the present invention. FIG. 22 is a plan view of a nitride semiconductor substrate (semiconductor wafer) used for manufacturing the nitride semiconductor laser device according to the second embodiment. FIG. 23 is a plan view of the nitride semiconductor substrate (semiconductor wafer). A cross-sectional view showing a part thereof in an enlarged manner is shown. FIG. 24 is a cross-sectional view of a nitride semiconductor substrate (semiconductor wafer) on which a nitride semiconductor layer is formed. Next, a nitride semiconductor laser device according to a second embodiment of the present invention will be described with reference to FIGS.

  In the nitride semiconductor laser device according to the second embodiment, a digging region is formed in the main growth surface 10a of the GaN substrate 10 in the configuration of the first embodiment. Specifically, as shown in FIG. 22, the GaN substrate 10 (semiconductor wafer) has a plurality of recesses 2 formed by being dug in the thickness direction from the growth main surface 10a. These recesses 2 are formed so as to extend in a direction parallel to the c-axis [0001] direction, respectively, in plan view. The recesses 2 are arranged at regular intervals with a period R of about 150 μm to about 600 μm (for example, about 400 μm) in the a-axis [11-20] direction orthogonal to the c-axis [0001] direction. That is, the plurality of recesses 2 are formed in a stripe shape on the main growth surface 10 a of the GaN substrate 10. Further, in the GaN substrate 10, a region where the concave portion 2 is formed (a region where the recess is formed) is a recess region 3. On the other hand, a region where the recess 2 is not formed in the growth main surface 10a (a region not dug) is a non-digging region 4.

  As shown in FIG. 23, each of the plurality of recesses 2 includes a bottom surface portion 2a and a pair of side surface portions 2b. The pair of side surface portions 2b is set so that the inclination angle γ is a predetermined angle larger than 90 degrees. For this reason, the side part 2b of the recessed part 2 is an inclined surface. Thereby, the recessed part 2 is formed so that opening width may become large gradually toward upper direction. Further, the recess 2 has an opening width g (opening end width) of about 5 μm in the [11-20] direction and a depth f of about 5 μm in the thickness direction of the GaN substrate 10. Yes.

  Moreover, in 2nd Embodiment, as shown in FIG. 24, since the recessed part 2 (digging area | region 3) is formed in the growth main surface 10a of the GaN substrate 10, it is on the recessed part 2 (digging area | region 3). A recess 35 is formed on the surface of the nitride semiconductor layer 50 (the nitride semiconductor layers 11 to 18). The recesses 35 alleviate distortion of the nitride semiconductor layer 50 (11 to 18) caused by lattice mismatch with the GaN substrate 10 and the like. In the second embodiment, since the main growth surface 10a of the GaN substrate 10 is formed of a surface having an off-angle in the a-axis direction with respect to the m-plane, the inside of the recess 2 is in the nitride semiconductor layer 50 (11 To 18), it is difficult to be embedded.

  Further, in the second embodiment, by using the GaN substrate 10 having an off-angle in the a-axis direction, the recess 2 (digging region 3) is formed in the nitride semiconductor layer 50 (11-18) on the non-digging region 4. The layer thickness gradient region 5 is formed in which the layer thickness is gradually (gradually) decreased as the value approaches (). The layer thickness inclined region 5 is formed in a substantially strip shape extending in a direction parallel to the concave portion 2 (digging region 3) in a region near one side (for example, the right side) of the concave portion 2 (digging region 3). The layer thickness gradient region 5 also relieves distortion of the nitride semiconductor layer 50 (11 to 18) caused by lattice mismatch with the GaN substrate 10 and the like.

  The reason why the layer thickness gradient region 5 is formed in one region of the recess 2 (digging region 3) is that the growth main surface 10a of the GaN substrate 10 has an off-angle in the a-axis direction with respect to the m-plane. As a result, the flow direction of the raw material atoms changes in the direction along the a-axis, and the flow of the raw material atoms is divided by the concave portion 2 (digging region 3), whereby the concave portion 2 in the non-digging region 4 is obtained. It is also considered that this is because the supply of source atoms is reduced in the vicinity region on one side of (digging region 3). Further, the layer thickness inclined region 5 can be formed on one side (for example, the right side) of the recess 2 (digging region 3) depending on whether the off angle in the a-axis direction is positive (+) or negative (−), or the recess 2 It is determined whether it can be made on the other side (for example, the left side) of (digging area 3). This is considered to be because the flow direction of the source atoms changes depending on whether the off angle in the a-axis direction is positive (+) or negative (−). The off angle in the a-axis direction is the same regardless of whether it is positive (+) or negative (−) in crystallographic terms, and may be discussed in terms of absolute values.

  Further, in the nitride semiconductor layer 50 (11 to 18) on the non-dig region 4, the light emitting portion forming region 6 suitable for forming the ridge portion has a very small layer thickness variation compared to the layer thickness inclined region 5. Is formed. A ridge portion is formed in the light emitting portion forming region 6.

  The configuration other than the GaN substrate 10 of the second embodiment is the same as that of the first embodiment. Further, the nitride semiconductor laser device according to the second embodiment may be divided into individual elements so as to include at least a part of the concave portion 2, or individual elements so as not to include the concave portion 2. It may be divided into.

  Moreover, the said recessed part 2 can be formed using a photolithographic technique and an etching technique.

  In the second embodiment, as described above, the recess 2 (digging region 3) is formed on the growth main surface 10a side of the GaN substrate 10 to thereby form the nitride semiconductor layer (on the depression 2 (digging region 3)) ( A recess 35 can be formed on the surface of the nitride semiconductor layer 50 on the recess 2. For this reason, the lattice constant difference or the thermal expansion coefficient difference between the GaN substrate 10 and the nitride semiconductor layer formed on the growth principal surface 10a is increased, and even when the nitride semiconductor layer is distorted, The distortion of the nitride semiconductor layer formed on the non-dig region 4 can be alleviated by the above-described depression portion formed on the surface of the nitride semiconductor layer on the recess 2 (dig region 3). Thereby, it is possible to effectively suppress the occurrence of cracks in the nitride semiconductor layer.

  As described above, in the second embodiment, by forming the recess 2 in the GaN substrate 10, a very high strain relaxation effect and crack suppression effect can be obtained. Therefore, the barrier layer is made of a nitride semiconductor containing Al. Even when configured, the strain of the barrier layer can be relaxed and the generation of cracks can be suppressed. Moreover, even when the Al composition ratio of the cladding layer is increased in order to improve the light confinement, the generation of cracks can be suppressed.

  Further, by using the GaN substrate 10 in which the recess 2 (digging region 3) is formed, a nitride semiconductor layer containing In (for example, an InGaN layer) is formed so as to be in contact with the main growth surface 10a. Furthermore, the generation of cracks can be effectively suppressed. That is, by forming the nitride semiconductor layer containing In so as to be in contact with the growth main surface 10a of the GaN substrate 10, a crack suppressing effect can be obtained. As described above, the GaN substrate 10 in which the recess 2 is formed is obtained. By using it, the crack suppression effect can be obtained more effectively.

  Other effects of the second embodiment are the same as those of the first embodiment.

(Third embodiment)
FIG. 25 is a cross-sectional view of a light emitting diode device according to a third embodiment of the present invention. Next, with reference to FIG. 2 and FIG. 25, the light emitting diode element (LED; Light Emitting Diode) by 3rd Embodiment of this invention is demonstrated.

  The light emitting diode device according to the third embodiment is configured by forming the same nitride semiconductor layers on the GaN substrate 10 similar to that of the first embodiment. However, in the third embodiment, unlike the first embodiment, the lower guide layer 13 (see FIG. 2) and the upper guide layer 16 (see FIG. 2) are not formed.

Specifically, as shown in FIG. 25, an InGaN layer 11 made of n-type In _y Ga _1-y N (0 <y <1), a lower cladding layer 12, and a growth main surface 10a of the GaN substrate 10; An active layer 14, a carrier block layer 15, an upper clad layer 17 and a contact layer 18 are formed in this order. A p-side electrode 221 made of an oxide-based transparent conductive film such as ITO (Indium Tin Oxide) is formed on the contact layer 18. An n-side electrode 22 and a metallized layer 23 are formed on the back surface of the GaN substrate 10.

  In the third embodiment, the barrier layer of the active layer 14 is made of a nitride semiconductor containing Al (for example, AlGaN, AlInGaN, AlInN, etc.), as in the first and second embodiments.

In place of the InGaN layer 11, In _y Ga _1-y N (0 <y ≦ 1) or Al _a In _b Ga _c N (a + b + c = 1, 0 <a ≦ 1, 0 <b ≦ 1, 0 A nitride semiconductor layer composed of ≦ c <1) may be used.

  In the third embodiment, as described above, a nitride semiconductor layer containing In (for example, an InGaN layer 11) is inserted between the GaN substrate 10 and the lower cladding layer 12 (growth main surface of the GaN substrate 10). By making the semiconductor layer in contact with 10a a nitride semiconductor layer containing In), the light emission efficiency can be improved.

  Moreover, in 3rd Embodiment, the flatness and crystallinity of a layer surface can be improved by comprising as mentioned above. For this reason, the luminous efficiency can be improved also by this.

In Example 4, an LED was manufactured using a GaN substrate having an off angle in the a-axis direction of 3 degrees and an off angle in the c-axis direction of +0.5 degrees with respect to the m-plane {1-100}. In Example 4, a nitride semiconductor layer containing n-type In _0.02 Ga _0.98 N and having a layer thickness of about 0.5 μm is formed on the main growth surface of the substrate, and then Al _0.01 Ga _0.99 N A 4QW active layer (layer thickness: about 15 nm) / In _0.25 Ga _0.75 N (layer thickness: about 3 nm) was formed. Next, a p-type Al _0.2 Ga _0.8 N carrier blocking layer was formed on the 4QW active layer with a layer thickness of about 20 nm. Then, a p-type GaN contact layer having a thickness of about 0.2 μm was formed on the p-type Al _0.2 Ga _0.8 N carrier block layer. Thereafter, ITO, which is an oxide-based transparent conductive film, was formed on the p-type GaN contact layer with an EB (Electron Beam) vapor deposition apparatus with a layer thickness of about 50 nm, thereby forming a p-side electrode made of ITO. Also in Example 4 configured as described above, an effect of improving the light emission efficiency and an effect of suppressing the bright spot light emission were obtained.

As the oxide-based transparent conductive film, in addition to the indium oxide-based ITO transparent conductive film, In ₂ O ₃ —ZnO-based transparent conductive film, zinc oxide-based ZnO-based transparent conductive film, tin oxide-based SnO are used. _{A 2-} type transparent conductive film or the like may be used. By using these transparent conductive films, light extraction efficiency can be significantly improved. In addition, by using a nitride semiconductor substrate having an off-angle in the a-axis direction with respect to the m-plane, a p-side electrode can be formed on a p-type layer with improved surface morphology, thereby obtaining a low contact resistance. be able to. Furthermore, the luminous efficiency can be improved by suppressing luminous spot-like light emission and uniform light emission and uniform injection, and the use of the transparent conductive film for the contact electrode of the nitride semiconductor layer formed on the substrate It is very preferable because of its great merit. An ITO electrode, which can be annealed at a low temperature, is particularly preferable from the viewpoint that the active layer is hardly damaged by heat. In Example 4, the annealing process is performed at 600 ° C.

  The oxide-based transparent conductive film is formed on the contact layer in an amorphous state by an EB vapor deposition apparatus or a sputtering apparatus, and then crystallized by thermal annealing at about 400 ° C. to 700 ° C. It is more preferable to further reduce the voltage by reducing the resistance of the film. At this time, a contact layer having a very high flatness can be formed by using a nitride semiconductor substrate having an off-angle in the a-axis direction, so that the contact resistance between the oxide-based transparent conductive film and the contact layer is lowered. be able to.

In Example 5, an LED having substantially the same structure as that of Example 4 was manufactured using the same substrate as that of Example 4. However, in Example 5, a nitride semiconductor layer made of n-type AlIn _y Ga _1-y N (0 <y ≦ 1) is used for the semiconductor layer in contact with the main growth surface of the substrate. Specifically, in Example 5, an n-type Al _0.02 In _0.02 Ga _0.96 N layer is used as the semiconductor layer in contact with the main growth surface of the substrate. In this case, the same effect as described above was obtained.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the first to third embodiments, examples in which the present invention is applied to light-emitting elements such as nitride semiconductor laser elements and light-emitting diode elements, which are examples of nitride semiconductor elements, have been described. The present invention can be applied not only to devices using nitride semiconductors such as electronic devices (for example, power transistors, ICs (Integrated Circuits), LSIs (Large Scale Integrations), etc.) in general.

In the first to third embodiments, the semiconductor layer in contact with the growth main surface of the GaN substrate is an InGaN layer. However, the present invention is not limited to this, and the semiconductor in contact with the growth main surface of the GaN substrate is used. nitride containing in non InGaN layer a layer semiconductor layer _{(in y Ga 1-y N} (0 <y ≦ 1) or _{Al a in b Ga c N (} a + b + c = 1,0 <a ≦ 1,0 <b ≦ 1, 0 ≦ c <1)). For example, the semiconductor layer in contact with the main growth surface of the GaN substrate may be an AlInGaN layer, an AlInN layer, or an InN layer.

In the first to third embodiments, the nitride semiconductor layer containing In is formed so as to be in contact with the main growth surface of the substrate, and the upper surface of this layer is in contact with the nitride semiconductor layer containing In. As described above, the lower clad layer made of AlGaN is formed. However, the semiconductor layer formed in contact with the nitride semiconductor layer containing In may be made of a nitride semiconductor material other than AlGaN. Note that the semiconductor layer formed in contact with the nitride semiconductor layer containing In is a nitride semiconductor containing Al (Al _a In _b Ga _c N (a + b + c = 1, 0 <a ≦ 1, 0 <B ≦ 1, 0 ≦ c <1)).

  In the first to third embodiments, the example in which the off angle in the a-axis direction is configured to be larger than 0.1 degrees has been described. However, the present invention is not limited thereto, and the off angle in the a-axis direction is The angle may be 0.1 degrees or less. However, considering the effect of suppressing bright spot light emission, surface morphology, and the like, the off angle in the a-axis direction is preferably an angle larger than ± 0.1 degrees.

In the first to third embodiments, the example in which the quantum well structure of the active layer is configured as the DQW structure has been described. However, the present invention is not limited thereto, and the active layer is provided in the quantum well structure other than the DQW structure. It may be configured. For example, the quantum well structure of the active layer may be configured as an SQW (Single Quantum Well) structure. Specifically, for example, as shown in FIG. 26, one well layer 54a made of InGaN and 2 made of Al _0.005 Ga _0.995 N are formed on the lower guide layer 13 (lower cladding layer in the third embodiment). An active layer 54 having an SQW structure in which two barrier layers 54b are alternately stacked can be formed. The well layer 54a can be configured to have a thickness of about 3 nm to about 4 nm, and the barrier layer 54b can be configured to have a thickness of about 70 nm. In the configurations of the first to third embodiments, the drive voltage can be reduced by configuring the active layer in the SQW structure as compared to the case where the active layer is configured in the DQW structure. Specifically, in the active layer of the SQW structure, the driving voltage at the time of 50 mA current injection is reduced by about 0.1 V to 0.25 V compared to the active layer of the DQW structure. In the case of the DQW structure, this is considered to be caused by the fact that carriers in the barrier layer sandwiched between two well layers are depleted and a large electric field is applied to the barrier layer. In addition to the SQW structure, the active layer may have an MQW (Multiple Quantum Well) structure. Even when the active layer has the SQW structure or the MQW structure, the effect of suppressing bright spot light emission and the effect of improving the light emission efficiency can be obtained. Note that in the case of a multiple quantum well structure having three or more well layers, optical confinement can be effectively performed, so that the gain can be increased. Furthermore, in the MQW structure with a relatively large number of well layers used in LEDs and the like, the barrier layer is made of a nitride semiconductor containing not only Al but also In, thereby reducing lattice distortion with the well layer. Since it can do, it is more preferable.

  In addition, when the active layer is configured in a multiple quantum well structure, the first quantum well, the second quantum well,... Need not have the same layer thickness and composition, and are different from each other. Also good. In that case, the emission wavelengths from the respective quantum wells are different, but in the relationship between the first quantum well and the second quantum well, the emission wavelength of the first quantum well closest to the substrate is the shortest, and the emission of the second quantum well. The wavelength is preferably configured to be longer than the emission wavelength of the first quantum well.

  In the first to third embodiments, the example in which the GaN substrate is used as the nitride semiconductor substrate has been described. However, the present invention is not limited to this, and a nitride semiconductor substrate other than the GaN substrate may be used. For example, a nitride semiconductor substrate made of InGaN, AlGaN, AlGaInN, or the like may be used. In addition, the thickness, composition, and the like of each nitride semiconductor layer that is crystal-grown on the substrate can be appropriately combined or changed so as to meet the desired characteristics. For example, the semiconductor layers may be added or deleted, or the order of the semiconductor layers may be partially changed. Further, the conductivity type may be changed for some semiconductor layers. That is, it can be freely changed as long as basic characteristics as a nitride semiconductor element (including a nitride semiconductor laser element and a light emitting diode element) are obtained.

  In the first to third embodiments, the example in which the In composition ratio of the well layer is configured to be 0.2 to 0.25 is shown. However, the present invention is not limited to this, and the In composition ratio of the well layer is used. Can be appropriately changed within the range of 0.15 to 0.45. Further, the In composition ratio of the well layer may be a value smaller than 0.15. Further, the well layer may contain Al as long as it is within 5%. The carrier block layer may contain In as long as it is within 7%. It is preferable to include In because it is easy to form a film having good crystallinity at a low temperature, and further includes a barrier layer that includes Al or a nitride semiconductor layer that includes Al and In. This is preferable because distortion to the active layer can be reduced.

  In the first to third embodiments, the Al composition ratio x2 of the barrier layer can be appropriately changed within the range of 0 <x2 ≦ 0.08. When the barrier layer is made of AlGaN, dislocations that occur in the active layer when the In composition ratio of the well layer is increased and enter the direction parallel to the c-axis direction (when the EL emission pattern is seen, the dark line Can be suppressed). In the first and second embodiments, when the barrier layer is made of AlGaN, the In composition ratio of the nitride semiconductor layer such as the guide layer is increased in order to make the optical confinement more effective. That's fine.

  In the first to third embodiments, an example in which the barrier layer of the active layer is made of AlGaN is shown. However, the present invention is not limited to this, and barriers other than AlGaN, such as an AlInGaN layer, an AlInN layer, etc. Layers can also be constructed. And also by comprising in this way, luminous efficiency and reliability can be improved.

  In the first to third embodiments, the distance between the carrier block layer and the well layer is the same as the thickness of the third barrier layer. However, the carrier block layer and the well layer (the well on the most carrier block layer side) A plurality of nitride semiconductor layers having different compositions may be formed between the two layers. Further, it is also preferable that a part between the carrier block layer and the well layer (most well layer on the carrier block layer side) is doped with a p-type impurity such as Mg to make it p-type. In the first to third embodiments, non-doping is performed.

  Moreover, although the said 1st-3rd embodiment demonstrated the structure which formed the carrier block layer on the active layer, this invention is not restricted to this, You may make it the structure by which the carrier block layer is not formed. However, since the carrier block layer is formed, the barrier layer composed of a nitride semiconductor layer containing Al (for example, an AlGaN layer or an AlInGaN layer) has a protective function for the active layer, An effect of suppressing deterioration of the active layer after the growth of the active layer is obtained. For this reason, it is preferable that a carrier block layer is formed in a region where the In composition ratio of the well layer is large (for example, In composition ratio x1 ≧ 0.15). Here, as described above, in the nitride semiconductor light emitting device using the nitride semiconductor substrate (m-plane just substrate) having the m-plane having no off-angle as the growth main surface, the EL emission pattern has a bright spot shape. Light is emitted. This is because the carrier block layer having a relatively high Al composition ratio may have an adverse effect. On the other hand, when a nitride semiconductor substrate having a growth main surface that has an off-angle in the a-axis direction with respect to the m-plane is used, the light emission pattern can be made uniform as described above. As a result, a nitride semiconductor substrate whose main growth surface is a plane having an off-angle in the a-axis direction with respect to the m plane is a nitride semiconductor layer containing Al (for example, an AlGaN layer or an AlInGaN layer) with good crystallinity. It can be said that this is a nonpolar substrate that is very suitable for film formation. For this reason, the carrier block layer can be made to function in a better state by using a nitride semiconductor substrate having a growth main surface that has an off-angle in the a-axis direction with respect to the m-plane.

  In the first to third embodiments, the barrier layer is composed of a single layer of nitride semiconductor layer containing Al. However, the present invention is not limited to this, and the barrier layer is nitrided containing Al. A multilayer structure including at least one physical semiconductor layer (for example, a superlattice structure of InGaN and AlGaN) may be used. In that case, the layer adjacent to the well layer is preferably made of a nitride semiconductor containing Al. In the case of a multilayer structure, the layer composed of a nitride semiconductor containing Al adjacent to the well layer is preferably formed to a thickness of 1.0 nm or more, and is formed to a thickness of 3.0 nm or more. It is more preferable. Such a configuration is effective for further functioning the effect of suppressing the occurrence of dark lines, the effect of improving the heat resistance of the active layer, and the effect of improving the flatness. In nitride semiconductor laser elements, even if AlGaN, which is a nitride semiconductor layer containing Al, is used for the barrier layer, a method using InGaN for the guide layer, a method for increasing the Al composition ratio of the cladding layer, etc. By using it, it is possible to sufficiently confine light. When the Al composition ratio is increased, the occurrence of cracks due to tensile strain is feared. However, as shown in the first embodiment, the semiconductor layer in contact with the growth main surface of the substrate is a nitride semiconductor layer containing In. By doing so, it is possible to suppress the occurrence of cracks. Furthermore, as shown in the second embodiment, the generation of cracks is more effectively suppressed by performing groove processing (forming recesses) on the GaN substrate.

  In the first to third embodiments, an example in which all of the three barrier layers are AlGaN layers is shown. However, the present invention is not limited to this, and a part of the three barrier layers may be It may be an AlGaN layer. If at least one layer in contact with the well layer among the plurality of barrier layers is composed of a nitride semiconductor layer containing Al (for example, an AlGaN layer, an AlInGaN layer, an AlInN layer, etc.), the effect of improving the light emission efficiency can be obtained. . Note that the number of barrier layers differs when the number of well layers in the active layer is different, but even in this case, the above effect can be obtained by forming at least one barrier layer from a nitride semiconductor layer containing Al. can get. Taking the first embodiment as an example, for example, in order to improve the flatness of the base before forming the well layer, the first barrier layer and the second barrier layer which are the base layers before forming the well layer Are preferably nitride semiconductor layers containing Al. Further, since the AlGaN layer also serves as an evaporation preventing layer for the InGaN layer (a role for protecting the active layer), the second barrier formed on the well layer from the viewpoint of preventing evaporation (from the viewpoint of protecting the active layer). The layer and the third barrier layer may be a nitride semiconductor layer containing Al. Further, the second barrier layer has a two-layer structure of a side in contact with the first well layer and a side in contact with the second well layer, and the side of the second barrier layer in contact with the first well layer is a lower second barrier layer, The side of the second barrier layer in contact with the second well layer may be the upper second barrier layer. In order to improve the flatness of the base, the upper second barrier layer is preferably a nitride semiconductor layer containing Al. On the other hand, from the viewpoint of preventing evaporation, the lower second barrier layer is preferably a nitride semiconductor layer containing Al. All the barrier layers may be nitride semiconductor layers containing Al.

  In the first to third embodiments, the semiconductor layer formed in contact with the nitride semiconductor substrate (GaN substrate) may be an n-type conductivity type or a p-type conductivity type. Also good. Further, it may be undoped. In the case of the p-type conductivity type, a part of the p-type layer formed on the active layer and the active layer are removed by etching or the like, and an n-electrode is formed on the exposed n-type layer to supply current. You may go.

  Moreover, in the said 1st-3rd embodiment, although the example which formed the several barrier layer in different thickness was shown, this invention is not restricted to this, You may form a several barrier layer in the same thickness.

  Moreover, although the example which formed the carrier block layer in the thickness of 40 nm or less was shown in the said 1st-3rd embodiment, this invention is not limited to this, The thickness of a carrier block layer may be larger than 40 nm. The effect of the present invention can be obtained even if the carrier block layer contains about 3% In. Further, the Al composition ratio of the carrier block layer is preferably higher than the Al composition ratio of the upper cladding layer for the purpose of reducing the driving voltage.

  Moreover, in the said 1st-3rd embodiment, although the example which used Si as an n-type impurity of an n-type semiconductor layer was shown, this invention is not restricted to this, In addition to Si, for example, O, S, C, etc. may be used. As the n-type impurity, Si and O are particularly preferable.

In the above-mentioned first to third embodiments show an example in which the insulating layer from SiO _2, the present invention is not limited thereto, may be formed of an insulating material other than SiO _2. For example, the insulating layer may be made of SiN, Al ₂ O ₃ , ZrO ₂ or the like.

  In the first to third embodiments, the crystal axis directions ([1-100] direction, [11-20] direction, and [0001] direction) may be crystallographically equivalent directions.

  In the first to third embodiments, the example in which each nitride semiconductor layer is crystal-grown using the MOCVD method has been shown. However, the present invention is not limited to this, and an epitaxial growth method other than the MOCVD method is used. Alternatively, each nitride semiconductor layer may be crystal-grown. Examples of methods other than the MOCVD method include the HVPE method (Hydride Vapor Phase Epitaxy) and the MBE method (Molecular Beam Epitaxy).

  In the first and second embodiments, the lower guide layer is made of n-type GaN. However, the present invention is not limited to this, and the lower guide layer may be AlGaN, AlInGaN, It may be composed of InGaN or the like, or a superlattice structure in which these are appropriately combined. The lower guide layer is more preferably made of a nitride semiconductor containing In from the viewpoint of optical confinement. Furthermore, when InGaN, AlGaN, and AlInGaN are used for the lower guide layer, they may be intentionally non-doped without doping impurities, or may be doped with, for example, Si as an n-type impurity.

  When InGaN is used for the lower guide layer, the In composition ratio is set in a range smaller than the In composition ratio of the well layer. Preferably, the In composition ratio is larger than 0 and 0.05 or less. If the In composition ratio is 0 and the GaN layer is formed, the flatness may be deteriorated. On the other hand, when the In composition ratio is larger than 0.05, high strain is generated, and there is a concern about deterioration of crystal quality. The lower guide layer made of InGaN is preferably formed to a thickness of 0.05 μm to 0.5 μm, and more preferably 0.08 μm to 0.3 μm. If the thickness of the lower guide layer is smaller than 0.05 μm, the light confinement effect tends to be insufficient. On the other hand, when the thickness of the lower guide layer is larger than 0.4 μm, the light field confinement coefficient is reduced because the electric field intensity distribution of light spreads in the layer direction.

  When AlInGaN is used for the lower guide layer, the In composition ratio is preferably set to be larger than 0 and equal to or less than 0.10. The Al composition ratio is preferably set to be larger than 0 and 0.08 or less. Furthermore, the lower guide layer made of AlInGaN is preferably formed to a thickness of 0.05 μm to 0.5 μm, and more preferably 0.07 μm to 0.3 μm. When the lower guide layer is made of AlInGaN and exceeds the above range (upper limit value of at least one of composition and thickness), the crystal quality may be deteriorated. On the other hand, in the case of at least one of the case where the composition ratio is not more than the above range and the case where the thickness is smaller than the lower limit value of the above thickness range, the light confinement effect and the flatness improvement effect are insufficient.

In the first and second embodiments, the upper guide layer is made of p-type Al _0.01 Ga _0.99 N. However, the present invention is not limited to this, and the upper guide layer is made of GaN, AlGaN or You may comprise from AlInGaN and may comprise the superlattice structure which combined these. If there is no problem from the viewpoint of optical confinement and far-field images, a p-type cladding layer may be directly stacked on the carrier block layer without forming the p-side guide layer (upper guide layer). Is possible.

When the upper guide layer is formed, when the upper guide layer is a non-doped GaN layer that is not doped with impurities, and a p-type GaN layer that is doped with p-type impurities is further formed, Among the layer thicknesses, the p-type GaN layer thickness (total layer thickness) L _pgan and the p-type impurity-doped GaN layer (the n-type GaN layer intentionally n-type impurity doped, the deliberate impurity It is preferable that the relationship with the layer thickness (total layer thickness) L _gan of the non-doped GaN layer not doped) satisfies L _gan <L _pgan . Furthermore, the layer thickness of the p-type GaN layer is preferably 0.3 μm or less. If it is larger than 0.3 μm, the light distribution is widened and the light confinement efficiency may be reduced. In addition, the flatness may be deteriorated.

  On the other hand, when the upper guide layer is a p-type GaN layer to which p-type impurity doping is applied, the flatness does not deteriorate. Therefore, the upper guide layer may be designed from the viewpoint of optical confinement. Good.

  When InGaN, AlGaN or AlInGaN is used for the upper guide layer, it may be intentionally non-doped without doping impurities, or may be doped with Mg as a p-type impurity, for example. When the upper guide layer is made of AlGaN, in the case of a non-doped AlGaN layer, the Al composition ratio is preferably set in the range of 0.0 to 0.03. In the case of a p-type AlGaN layer subjected to p-type impurity doping, the Al composition ratio is preferably set in the range of 0.0 to 0.03. When the upper guide layer is made of AlGaN, the effect of improving the flatness can be obtained. In the case of a non-doped AlGaN layer, a GaN layer having an Al composition ratio of 0 makes it difficult to obtain a sufficient flatness improvement effect. On the other hand, when the Al composition ratio is greater than 0.03, light confinement becomes insufficient. The upper guide layer made of AlGaN is preferably formed to a thickness of 0.05 μm to 0.4 μm, and more preferably 0.08 μm to 0.25 μm. If the thickness of the upper guide layer made of AlGaN is smaller than 0.05 μm, the effect of improving flatness tends to be insufficient. On the other hand, when the thickness is larger than 0.4 μm, the electric field strength distribution of light spreads in the layer direction, so that the optical confinement factor is reduced. When the upper guide layer is made of AlGaN, the optical confinement can be improved by increasing the Al composition ratio of the cladding layer. The upper guide layer is more preferably made of a nitride semiconductor containing In from the viewpoint of light confinement.

  When the upper guide layer is made of InGaN, the In composition ratio is set in a range smaller than the In composition ratio of the well layer. When the upper guide layer is a non-doped InGaN layer, the In composition ratio is preferably set to be larger than 0 and 0.05 or less. In the case where the upper guide layer is a p-type layer doped with p-type impurities, doping with Mg ensures flatness even with GaN, so that the In composition ratio of the InGaN layer is 0.0 or more and 0.05 or less. It is possible to set the range. When the upper guide layer is a non-doped InGaN layer, when the GaN layer has an In composition ratio of 0, it is difficult to obtain a sufficient flatness improvement effect. On the other hand, when the In composition ratio is larger than 0.05, the crystal quality is likely to be deteriorated due to high strain. The upper guide layer made of InGaN is preferably formed with a thickness of 0.05 μm or more and 0.5 μm or less, and more preferably formed with a thickness of 0.08 μm or more and 0.3 μm or less. When the thickness of the upper guide layer made of InGaN is smaller than 0.05 μm, the light confinement effect becomes insufficient. On the other hand, if the thickness is larger than 0.5 μm, the electric field strength distribution of light spreads in the layer direction, so that the optical confinement factor is reduced.

  When the upper guide layer is made of AlInGaN, in the case of a non-doped AlInGaN layer, the In composition ratio is preferably set in the range of 0.002 or more and 0.05 or less. Further, the Al composition ratio is preferably set in a range of greater than 0.005 and 0.05 or less. In the case of a p-type AlInGaN layer subjected to p-type impurity doping, the In composition ratio is preferably set in the range of 0.0 to 0.05. Further, the Al composition ratio is preferably set in a range of greater than 0.0 and less than or equal to 0.05. The upper guide layer made of AlInGaN is preferably formed to a thickness of 0.05 μm to 0.5 μm, and more preferably 0.07 μm to 0.3 μm. If the above range (the upper limit of at least one of the composition and thickness) is exceeded, the crystal quality may be deteriorated. On the other hand, in the case of at least one of the case where the composition ratio is not more than the above range and the case where the thickness is smaller than the lower limit value of the above thickness range, the light confinement effect and the flatness improvement effect are insufficient.

In the first embodiment, each nitride semiconductor layer formed on the GaN substrate has an example in which the nitride semiconductor layer formed on the active layer is configured not to include the GaN layer. The present invention is not limited to this, and the nitride semiconductor layer formed on the active layer may be configured to include a GaN layer. For example, the contact layer may be composed of a GaN layer. When a p-type GaN layer with p-type impurity doping is formed, the p-type GaN layer thickness (total layer thickness) L _pgan and a GaN layer without p-type impurity doping (intentionally n-type) It is preferable that the relationship between the layer thickness (total layer thickness) L _gan of the n-type GaN layer doped with impurities and the non-doped GaN layer not intentionally doped with impurities satisfies L _gan <L _pgan .

  Moreover, in the said 2nd Embodiment, the opening width of the recessed part formed in a board | substrate and the depth of a recessed part can be changed suitably. In addition, it is preferable that the opening width of a recessed part is 1 micrometer or more and 50 micrometers or less. Moreover, the cross-sectional shape of a recessed part can be changed suitably. The cross-sectional shape of the concave portion may be a Δ shape or a trapezoidal shape as long as it causes uneven steps. In addition, about the relationship between the opening width of a recessed part and the depth of a recessed part, it is preferable that the opening width is formed larger than the depth. In addition, in order to suppress the occurrence of cracks, when forming a recess (digging region) on the growth main surface of the nitride semiconductor substrate, a surface having an off angle in the a-axis direction with respect to the m plane is defined as the growth main surface. By using the nitride semiconductor substrate to be formed and forming the nitride semiconductor layer containing In so as to be in contact with the main growth surface, generation of cracks can be suppressed more effectively.

  Moreover, although the example which formed the digging area | region so that it might extend in a c-axis direction was shown in the said 2nd Embodiment, this invention is not limited to this, and a digging area | region extends in the direction which cross | intersects a c-axis direction. May be formed. In addition to the stripe shape, for example, the digging region may be formed in a lattice shape.

  In the second embodiment, the example in which the period of the recesses is set to about 400 μm is shown. However, the period of the recesses can be determined by the chip width (element width) of the nitride semiconductor laser element, and the chip width ( For example, when the element width is about 200 μm, the period of the recesses can be about 200 μm. The period (interval) of the recesses (digging area) is preferably 1 mm or less, and more preferably 400 μm or less. With this configuration, even if there is an abnormal portion on a part of the wafer (substrate) and the layer thickness fluctuates due to this, the lateral growth is divided by the depression on the surface of the semiconductor element layer on the recess. Thus, the diffusion of the layer thickness fluctuation caused by the abnormal part is suppressed. Further, when the period (interval) of the recesses (digging regions) is 5 μm or less, it becomes difficult to form the ridge portion. Therefore, the period (interval) of the recesses (digging regions) is preferably larger than 5 μm.

  Moreover, in the said 2nd Embodiment, although the example which formed the dug area | region in the board | substrate was shown by forming the recessed part which has a fixed opening width | variety linearly, this invention is not limited to this, Other than the above You may form a dug area | region in a board | substrate by forming a recessed part in a shape. For example, a digging region may be formed in the substrate by forming a zigzag-shaped concave portion or a wavy concave portion, or a digging region may be formed in the substrate by forming a concave portion having a variable opening width. It may be formed. In addition, digging regions having different shapes and digging regions having different depths and widths may exist on one substrate. Even when such a dug region is formed, the effect of the present invention can be obtained.

  In the third embodiment, a digging region (concave portion) similar to that in the second embodiment may be formed on the substrate.

2 recessed portion 3 digging region 4 non-digging region 5 layer thickness inclined region 6 light emitting portion forming region 10 GaN substrate (nitride semiconductor substrate)
10a Main growth surface 11 InGaN layer (first nitride semiconductor layer containing In)
12 Lower cladding layer (second nitride semiconductor layer containing Al)
DESCRIPTION OF SYMBOLS 13 Lower guide layer 14 Active layer 14a Well layer 14b Barrier layer 15 Carrier block layer 16 Upper guide layer 17 Upper clad layer 18 Contact layer 19 Ridge part 20 Insulating layer 21 P side electrode 22 N side electrode 23 Metallized layer 30 Resonator surface 30a Light exit surface 30b Light reflection surface 35 Depression 100 Nitride semiconductor laser element (nitride semiconductor element)
110 Submount 120 Stem 130 Wire 135 Cap 150 Semiconductor Laser Device (Semiconductor Device)

Claims (20)

A nitride semiconductor substrate having a main growth surface;
A first nitride semiconductor layer formed on a main growth surface of the nitride semiconductor substrate,
The growth main surface is a surface having an off angle in the a-axis direction with respect to the m-plane,
The first nitride semiconductor layer includes In and is formed in contact with the main growth surface.   2. The nitride semiconductor device according to claim 1, further comprising: a second nitride semiconductor layer containing Al formed on and in contact with the first nitride semiconductor layer.   3. The nitride semiconductor device according to claim 1, wherein the first nitride semiconductor layer is made of a nitride semiconductor containing In and Ga. 4. The nitride semiconductor substrate is made of GaN,
The nitride semiconductor device according to claim 1, wherein the first nitride semiconductor layer is made of InGaN. The nitride semiconductor substrate is made of GaN,
The nitride semiconductor device according to claim 1, wherein the first nitride semiconductor layer is made of AlInGaN. A second nitride semiconductor layer formed on and in contact with the first nitride semiconductor layer;
The nitride semiconductor element according to claim 1, wherein the second nitride semiconductor layer is made of a nitride semiconductor containing Al and Ga. A second nitride semiconductor layer formed on and in contact with the first nitride semiconductor layer;
The nitride semiconductor substrate is made of GaN,
The nitride semiconductor device according to claim 1, wherein the second nitride semiconductor layer is made of AlGaN. A second nitride semiconductor layer formed on and in contact with the first nitride semiconductor layer;
The nitride semiconductor substrate is made of GaN,
The nitride semiconductor device according to claim 1, wherein the second nitride semiconductor layer is made of AlInGaN.   The nitride semiconductor device according to claim 1, wherein an absolute value of an off angle in the a-axis direction is greater than 0.1 degree. On the growth main surface of the nitride semiconductor substrate, an active layer having a quantum well structure is formed,
The nitride semiconductor device according to claim 1, wherein the active layer includes two well layers. On the growth main surface of the nitride semiconductor substrate, an active layer having a quantum well structure is formed,
The nitride semiconductor device according to claim 1, wherein the active layer includes one well layer. On the growth main surface of the nitride semiconductor substrate, an active layer having a quantum well structure is formed,
The active layer includes a well layer made of a nitride semiconductor containing In,
12. The nitride semiconductor device according to claim 1, wherein an In composition ratio of the well layer is 0.15 or more and 0.45 or less. On the growth main surface of the nitride semiconductor substrate, an active layer having a quantum well structure is formed,
The nitride semiconductor device according to claim 1, wherein the active layer has a barrier layer made of a nitride semiconductor containing Al.   The nitride semiconductor device according to claim 13, wherein the barrier layer is made of AlInGaN.   The nitride semiconductor device according to claim 13, wherein the barrier layer is made of AlGaN. On the growth main surface of the nitride semiconductor substrate, an active layer having a quantum well structure is formed,
The active layer includes a plurality of barrier layers;
The nitride semiconductor device according to claim 1, wherein at least a part of the plurality of barrier layers is made of AlInGaN. The growth main surface of the nitride semiconductor substrate has an off-angle in the c-axis direction in addition to the a-axis direction,
The nitride semiconductor device according to any one of claims 1 to 16, wherein an off angle in the a-axis direction is larger than an off angle in the c-axis direction. preparing a nitride semiconductor substrate including a growth main surface composed of a surface having an off-angle in the a-axis direction with respect to the m-plane;
Forming a nitride semiconductor layer on the growth main surface of the nitride semiconductor substrate using an epitaxial growth method,
The method of forming a nitride semiconductor layer includes a step of forming a first nitride semiconductor layer containing In so as to be in contact with the main growth surface. The step of forming the nitride semiconductor layer includes
19. The nitride according to claim 18, comprising: forming a second nitride semiconductor layer containing Al on the first nitride semiconductor layer so as to be in contact with the first nitride semiconductor layer. A method for manufacturing a semiconductor device.   A semiconductor device comprising the nitride semiconductor element according to claim 1.