JP3976294B2 - Method for manufacturing nitride-based compound semiconductor light-emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a nitride compound semiconductor crystal on a substrate and a nitride compound semiconductor light emitting device produced by using the method.
[0002]
[Prior art]
Conventionally, nitride-based compound semiconductors have been used or studied as light-emitting elements and high-power devices. For example, in the case of light-emitting elements, technically from blue to orange by adjusting the composition of the light-emitting elements. It can be used as a wide light-emitting element. In recent years, blue light emitting diodes and green light emitting diodes have been put to practical use by utilizing the characteristics, and blue-violet semiconductor lasers are being developed as semiconductor laser elements.
[0003]
When a nitride-based compound semiconductor is manufactured as the light emitting element, a current injection layer having n-type characteristics is usually formed on a substrate on which a nitride-based compound semiconductor is epitaxially grown, such as a mirror-polished sapphire (0001) substrate, A light emitting layer and a current injection layer exhibiting p-type characteristics are formed thereon. It is known that the emission intensity increases when a quantum well having a thickness of 10 nm or less is used for the light emitting layer, and the emission wavelength can be varied by adjusting the In composition ratio of the light emitting layer made of InGaN, for example. As an epitaxial growth method, vapor phase growth techniques such as MOCVD and MBE are used. For example, in the MOCVD method, a sapphire (0001) surface substrate is treated in a reducing atmosphere of about 1000 ° C., ammonia is supplied to perform initial nitriding of the substrate surface, and a GaN or AlN buffer layer is formed at a low temperature of about 500 ° C. The temperature is raised to about 1000 ° C. to produce a nitride compound semiconductor crystal.
[0004]
In general, the quantum well may be formed of only one layer, but it is known that the light emission efficiency can be increased by using a multiple quantum well structure (MQW) having a well layer and a barrier layer. However, when a light-emitting device is manufactured using a quantum well structure made of a nitride-based compound semiconductor (eg, InGaN) containing In, the lattice mismatch with the sapphire substrate is as large as 13%, and the quantum well is formed from the substrate interface. There are high density of threading dislocations that reach the surface. For this reason, the current flowing through the dislocation is a component that does not contribute to light emission, which causes an increase in drive current density and heat generation. In addition, since the chemical thermal equilibrium state during crystal growth of nitride-based compound semiconductors containing In is very unstable, In aggregates or disperses around dislocations, resulting in a desired quantum well structure with a uniform In composition. It is difficult to form. Even if a desired quantum well structure having an In composition can be formed, it is difficult to form a quantum well layer with good crystallinity, and it is difficult to realize high light emission efficiency. In addition, for the reasons described above, the In composition of the nitride-based compound semiconductor film having In forming the quantum well structure and the uniformity of the film thickness are impaired in the substrate, and the target emission wavelength is uniformly distributed over the entire surface of the substrate. It is difficult to manufacture a light-emitting element having light emission intensity.
[0005]
In order to solve the above-mentioned problems, Japanese Patent Laid-Open No. 9-23026 discloses that the emission characteristic is improved by two-stage growth through a buffer layer with the angle formed by the sapphire substrate surface and the C-plane ((0001) plane) within 5 °. Techniques for improving are disclosed. In the above publication, only the technology related to the brightness improvement in the light emitting device (LED) is shown, and the technology related to the improvement of the flatness of the outermost surface of the crystal and the reduction of the crystal dislocation density which affect the element formation process and the characteristics of the light emitting device Is not disclosed.
[0006]
[Problems to be solved by the invention]
In the MOCVD method, crystal growth is performed through initial nitriding and a low-temperature buffer layer. However, this method has a high dislocation density and insufficient crystal quality, which is particularly problematic in a laser device driven at a high current density. Further, even when the substrate surface tilt angle is simply within 5 °, the step density on the substrate surface is not sufficiently defined, in other words, the surface flatness is not sufficient. The crystal quality and surface state of semiconductors vary sensitively.
[0007]
In the case of an inclination angle of about 0.2 ° to 5 ° disclosed in the conventional example, a nitride compound semiconductor grown on a (0001) plane sapphire substrate, for example, GaN has dislocations generated from the interface with the substrate. It exists in high density. This is because the sapphire substrate and GaN have a lattice constant difference that facilitates three-dimensional growth and the use of a sapphire substrate with an inclination angle from the <0001> direction in the range of 0.2 ° to 5 ° is not uniform. This is thought to be because the steps on the substrate surface distributed in the hinder the orderly step flow growth.
[0008]
In heteroepitaxial growth, the buffer layer formed at low temperature is amorphous or polycrystalline, but is crystallized under the conditions close to homoepitaxial growth at high temperature, while receiving information from the substrate by the rearrangement of atoms. Has the effect of allowing growth. However, in a system having a large lattice mismatch such as sapphire and GaN, the effect of the buffer layer is insufficient, and the buffer layer forming conditions for absorbing the step difference on the substrate surface due to the inclination angle from the <0001> direction are Limited to a narrow range.
[0009]
Similar to the buffer layer, the initial nitridation of the substrate surface also works closer to homoepitaxial growth, but the nitriding process is governed by oxygen atom desorption near the sapphire surface and diffusion of nitrogen atoms from the gas phase, so the initial substrate surface shape is Proceed while keeping. Therefore, a step on the surface of the sapphire substrate having an inappropriate inclination angle remains less affected by nitriding. A microscopic surface of such a substrate is schematically shown in FIG. Steps 102 in the atomic layer order are unevenly distributed on the substrate 101. The source species that have reached the substrate surface reach stable sites on the substrate surface, that is, step 102 of the atomic layer while repeating migration and re-detachment, and form growth nuclei 103, but growth nucleation is not reflected reflecting the step distribution. It becomes uniform. Accordingly, two-dimensional growth (a mode in which layers are layered one by one) is hindered in growth on a substrate that does not define an inclination angle, and a three-dimensional nuclear growth mode in which crystal growth locally proceeds mainly. Threading dislocations are generated from the places where the two adjacently connect.
[0010]
In addition, if the composition uniformity and crystallinity of the layer containing In are insufficient and a higher efficiency light-emitting diode or a low-threshold semiconductor laser is to be manufactured, the conventional low-current driving current can be achieved only with conventional technology. Therefore, a light emitting element with high luminous efficiency cannot be obtained. Therefore, there has been a demand for manufacturing a light-emitting element having better electrical characteristics and light-emitting characteristics.
[0011]
[Means for Solving the Problems]
[0012]
[0013]
[0014]
[0015]
[0016]
The method of manufacturing a nitride-based compound semiconductor light-emitting device described in the present application is a manufacturing method of a nitride-based compound semiconductor light-emitting device in which a stacked body having an active layer sandwiched between layers having different conductivity types is vapor-phase grown on a sapphire substrate. In the method, the crystal orientation of the surface of the sapphire substrate is inclined in the range of 0.05 ° or more and 0.2 ° or less in the <11-20> direction or <1-100> direction from the <0001> direction. And
[0017]
[0018]
In the method of manufacturing a nitride-based compound semiconductor light-emitting device described in the present application, the active layer is formed of one or a plurality of well layers and a barrier layer, and after formation of one or both of the well layer and the barrier layer, It has the process of providing the growth interruption for a fixed time.
[0019]
The method for producing a nitride-based compound semiconductor light-emitting device described in this application is characterized in that the growth interruption time after the growth of the barrier layer is not less than 1 second and not more than 60 minutes.
[0020]
The method for producing a nitride-based compound semiconductor light-emitting device described in this application is characterized in that the growth interruption time after the growth of the well layer is not less than 1 second and not more than 60 minutes.
[0021]
The method for manufacturing a nitride-based compound semiconductor light-emitting device described in the present application is characterized in that a carrier gas mainly containing nitrogen is allowed to flow when the growth is interrupted.
[0022]
The method for manufacturing a nitride-based compound semiconductor light-emitting device described in the present application is characterized in that a carrier gas mainly containing nitrogen and a group V source gas are allowed to flow when the growth is interrupted.
[0023]
In the present invention, as a means for solving the above-described problems, when manufacturing a light-emitting element using a nitride-based compound semiconductor composed of a plurality of In-containing layers as a light-emitting layer, first, the crystal orientation is changed from the <0001> direction to the extreme. Using a slightly inclined substrate such as sapphire or GaN, threading dislocations are reduced, current paths that do not contribute to light emission are reduced, and surface flatness of the active layer base layer is improved. Further, after that, a light emitting layer composed of a plurality of well layers and a barrier layer is grown, and after the formation of the nitride-based compound semiconductor layer that becomes the well layer, a growth interruption for a certain period is provided, and the well layer is in contact with the well layer. After the formation of a nitride compound semiconductor that becomes a barrier layer with a larger band gap energy than the layer, a process of providing a growth interruption for a certain period is followed by further improving the surface state and making the composition of the active layer uniform. And
[0024]
As shown above, the surface seen in the conventional example is as shown in FIG. 1, but in the present invention, it is as shown in FIG. By stepping the substrate 201 from the <0001> direction to the <11-20> direction or the <1-100> direction with an angle, the steps 202 are uniformly distributed, and the step density is optimally controlled. As a result, the growth nuclei 203 are uniformly formed on the entire surface of the substrate, resulting in orderly step flow growth. In this state, stable two-dimensional growth is realized.
[0025]
In the case of an inclination angle of about 0.2 ° to 5 ° disclosed in the conventional example, a nitride compound semiconductor grown on a (0001) plane sapphire substrate, for example, GaN has dislocations generated from the interface with the substrate. It exists at a high density (1 × 10 11 cm −2 or more). This is because the three-dimensional growth is easy due to the difference in the lattice constant between the sapphire substrate and GaN, and the step flow growth with orderly steps on the substrate surface that is unevenly distributed because the tilt angle from the <0001> direction is not specified. It is thought that this is because of the inhibition.
[0026]
In heteroepitaxial growth, the buffer layer formed at low temperature is amorphous or polycrystalline, but is crystallized under the conditions close to homoepitaxial growth at high temperature, while receiving information from the substrate by the rearrangement of atoms. Has the effect of allowing growth. However, in a system having a large lattice mismatch such as sapphire and GaN, the effect of the buffer layer is insufficient, and the buffer layer forming conditions for absorbing the step difference on the substrate surface due to the inclination angle from the <0001> direction are Limited to a narrow range. Even in the case of homoepitaxial growth on a GaN substrate, it is desirable to form a buffer layer with a certain thickness in order to reduce the surface energy and achieve uniform growth in the plane. It is important to set the steps to the optimum state.
[0027]
Similar to the buffer layer, the initial nitridation of the substrate surface also works closer to homoepitaxial growth, but the nitriding process is governed by oxygen atom desorption near the sapphire surface and diffusion of nitrogen atoms from the gas phase, so the initial substrate surface shape is Proceed while keeping. Therefore, the step on the substrate surface where the tilt angle is not defined remains without being affected by nitriding so much that it inhibits step flow growth and generates dislocations.
[0028]
In the present invention, the step density on the outermost surface is regulated to an optimum state by tilting the sapphire substrate from the <0001> direction to the <11-20> direction or the <1-100> direction, and stable two-dimensional growth is achieved. Promote. A laser or a light-emitting diode manufactured using a substrate inclined from 0.05 ° to 0.2 ° in the <11-20> direction or the <1-100> direction from the <0001> direction is a nitride compound to be laminated. Increasing the quality of semiconductors improves the light emission efficiency, and in particular, extends the life of lasers.
[0029]
Furthermore, by providing a growth interruption after the formation of the nitride-based compound semiconductor serving as a barrier layer, the composition of the raw material species incorporated into the solid phase can be prevented from agglomerating and the composition non-uniformity can be eliminated. As a result, the surface flatness is further improved. At that time, a remarkable effect can be obtained by setting the growth interruption time to 1 second or more and 60 minutes or less. Similarly, when the growth interruption time provided after the formation of the nitride compound semiconductor to be the well layer is set to 1 second or more and 60 minutes or less, a further effect appears. Further, when the growth is interrupted, a more remarkable effect appears by flowing a carrier gas mainly containing nitrogen or a carrier gas mainly containing nitrogen and a group V source gas.
[0030]
When a light-emitting element is manufactured, a higher effect can be obtained by using a slightly inclined substrate and growth interruption together. That is, when threading dislocations exist in a crystal grown using a normal substrate, In aggregated around the dislocations does not diffuse in the layer. Therefore, it is effective to reduce the threading dislocation density using a slightly tilted substrate and eliminate In aggregation around the dislocations by interrupting the growth.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
First, the present invention will be described in detail. Generally, when a nitride compound semiconductor is crystal-grown, sapphire, SiC, GaN, GaAs, spinel (MgAl2O4), or the like is used as a substrate. As a method for crystal growth, metal organic vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE), and hydride vapor phase epitaxy (HVPE) are usually used.
[0032]
Among these, considering the crystallinity and productivity of the nitride compound semiconductor to be produced, the most common method is to use sapphire or GaN as the substrate and the MOCVD method as the growth method.
[0033]
FIG. 3 shows a schematic diagram of the MOCVD apparatus used for manufacturing the embodiment of the present application. In the figure, 301 is a (0001) plane sapphire substrate inclined from 0.05 ° to 0.2 ° in the <11-20> or <1-100> direction from the <0001> direction on the carbon susceptor (302). Has been placed. A carbon resistance heater is also disposed in the susceptor, and the substrate temperature can be monitored and controlled by a thermocouple. 303 is a water-cooled reaction tube made of double quartz. As the group V source, ammonia (306) is used, and as the group III source, trimethylgallium (hereinafter referred to as TMG), trimethylaluminum (hereinafter referred to as TMA), trimethylindium (hereinafter referred to as TMI) ( 307a to 307c) were used by bubbling with nitrogen gas or hydrogen gas. Further, SiH4 (309) was used as an n-type doping material, and biscyclopentadienylmagnesium (hereinafter referred to as Cp2Mg) (307d) was used as a p-type doping material. Each raw material is accurately controlled by the mass flow controller (308), introduced into the reaction tube from the raw material inlet (304), and discharged from the exhaust gas outlet (305).
[0034]
Next, a typical example of a crystal growth procedure for forming a nitride compound semiconductor laser / light emitting diode will be described with reference to FIG. First, the substrate (401) is cleaned and placed in a crystal growth apparatus. The substrate is heat-treated at a temperature of about 1100 ° C. for about 10 minutes in a hydrogen atmosphere, and then the temperature is lowered to about 500 ° C. to 600 ° C. When the temperature becomes constant, the carrier gas is changed to nitrogen, the total flow rate of nitrogen gas is 10 l / min, ammonia is flowed at about 3 l / min, and after a few seconds, TMG is flowed at about 20 μmol / min, and the buffer is kept at a low temperature for about 1 minute. A GaN film (402) as a layer was grown. The thickness of the grown film is about 20 nm.
[0035]
Thereafter, the supply of TMG is stopped, the temperature is raised to 1050 ° C., and about 50 μmol / min of TMG and about 10 nmol / min of SiH 4 gas are supplied again to grow an n-type GaN film (403) by about 4 μm. Next, 10 μmol / min of TMA is supplied to grow an n-type Al 0.15 Ga 0.85 N film (404) having a thickness of 0.5 μm. This layer is an optical confinement layer and is not necessary when manufacturing a light emitting diode.
[0036]
Next, the supply of TMA is stopped, and a GaN film (405) having a thickness of about 0.1 μm is grown. This layer is a light guide layer and is not necessary when manufacturing a light emitting diode. Thereafter, the supply of SiH4 and TMG is stopped, and the temperature of the substrate is lowered to about 850 ° C. to 700 ° C. This temperature is one parameter that determines the emission wavelength of the light emitting element, and the emission wavelength tends to be longer as the temperature is lower. The substrate temperature described above is a temperature for producing a purple-green light emitting element, and if the necessary wavelength band is not in the purple-green wavelength band, there is no problem even if the substrate temperature is changed. When the temperature is stabilized, TMG is supplied at 10 μmol / min and TMI is supplied at 10 μmol / min, and a barrier layer for forming an active layer (406) made of In0.05Ga0.95N is grown to a thickness of about 5 nm. During the growth of the active layer, SiH4 may be flowed at about 10 nmol / min.
[0037]
After the growth of the barrier layer, the supply of TMG and TMI is once stopped, and the growth is interrupted for 1 second to 60 minutes while the carrier gas and the NH3 gas are supplied. Thereafter, TMG is supplied again at 10 μmol / min and TMI is supplied at 50 μmol / min, and the well layer of the active layer made of In0.2Ga0.8N is grown to a thickness of about 3 nm. After the well layer growth, the supply of TMG and TMI is stopped again, and the growth is interrupted for 1 second to 60 minutes while supplying the carrier gas and NH3 gas. The growth of the well layer and the barrier layer as the active layer is repeated to grow the multiple quantum wells with the required number of layers, and finally the barrier layer is grown to finish the growth of the active layer (406). In a normal case, it has been found that an element having the highest luminous efficiency can be obtained by changing the number of well layers from two to five.
[0038]
After the active layer growth, for the purpose of preventing sublimation of the InGaN film, 10 μmol / min of TMG, 5 μmol / min of TMA, and Cp 2 Mg are supplied, and an AlGaN layer (407) having a thickness of about 30 nm is grown. Thereafter, the supply of TMG, TMA, and Cp2Mg is stopped, and the substrate temperature is raised to 1050 ° C. again. After raising the temperature, 50 μmol / min of TMG and Cp 2 Mg are supplied, and a light guide layer (408) made of p-type GaN is grown to 0.1 μm. This layer is not necessary when manufacturing a light emitting diode. Next, 10 μmol / min of TMA is supplied to grow a p-type Al 0.15 Ga 0.85 N film (409) having a thickness of 0.5 μm. This layer is an optical confinement layer and is not necessary when manufacturing a light emitting diode. After the growth is completed, the supply of TMA is stopped, and a contact layer (410) made of p-type GaN is grown by about 0.5 μm. After the completion, the supply of TMG and Cp2Mg is stopped and the substrate heating is ended.
[0039]
FIG. 5 shows the growth temperature in the vicinity of the active layer and the supply amount of each raw material. In the figure, reference numerals 501, 502, 503, 504, 505, and 506 denote growth interruption, barrier layer growth, well layer growth, n-type GaN film growth, p-type GaN growth, and AlGaN sublimation prevention layer growth, respectively. Indicates the period during which
[0040]
When the temperature reaches room temperature, the substrate is taken out from the crystal growth apparatus, and a part of the n-type GaN is exposed by reactive ion etching, and the necessary shape of the insulating film (411) and the p-type electrode (412a) An n-type electrode (412b) is formed by a vapor deposition method. The end face from which light is extracted is formed by cleaving the substrate.
[0041]
When a light emitting diode is manufactured, an end face by cleavage is not necessary, and light is transmitted from the p-type electrode side or the n-type electrode side.
[0042]
In the above example, the growth is interrupted after using the slightly tilted substrate. However, the crystallinity is sufficiently improved as compared with the prior art even without interrupting the growth.
[0043]
Furthermore, although the details of the cause of the increase in the light emission intensity of the light-emitting element by producing the light-emitting element on the slightly tilted substrate and performing the growth interruption during the growth of the active layer, the nitride-based compound semiconductor containing In is not known. It grows in a chemically unstable state at high temperatures, and dislocations penetrating through the film have the effect of aggregating In, and crystals exist in good condition immediately after the growth of the nitride-based compound semiconductor layer containing In. Not done. Therefore, first, by reducing the threading dislocation density using a vicinal substrate, and further being exposed to heat in a nitrogen atmosphere, the In aggregation in the nitride-based compound semiconductor containing In is eliminated and a stable phase state is obtained. It seems that it will naturally settle down and shift to a good crystalline state. In particular, it is speculated that the crystal state of the barrier layer adjacent to the well layer that contributes to light emission has a great influence on the improvement of the crystal quality of the well layer.
[0044]
In this example, the case where a GaN film is grown as the low-temperature buffer layer has been described. However, even if AlxGa1-xN (0.ltoreq.x.ltoreq.1) is used as the low-temperature buffer layer, there is no problem in manufacturing a light emitting device. There is no.
[0045]
In addition, when GaN is used as a substrate, it is not necessary to perform heat treatment in a hydrogen atmosphere and growth of a buffer layer at a low temperature, and raise the temperature in a carrier gas mainly composed of an inert gas and an NH3 atmosphere. , TMG and / or SiH4 can be introduced simultaneously with the growth of the underlying GaN film.
[0046]
Example 1
A sapphire (0001) substrate that is mirror-polished by tilting 0.05 ° from the <0001> direction to the <1-100> direction is set in a normal horizontal MOCVD reactor and heated to 1100 ° C. while supplying hydrogen. And perform thermal cleaning for 10 minutes. Thereafter, the temperature was lowered to 600 ° C., a 50 nm GaN buffer layer was deposited, the temperature was raised to 1000 ° C. while supplying ammonia, and an undoped GaN layer was grown to a thickness of 5 μm. This GaN film has an average surface roughness of 1.0 nm, a half-width of a double crystal X-ray diffraction peak of 2.5 arcmin, an electron concentration of 4 × 10 15 cm −3, and a mobility of 500 cm 2 / V · sec as measured by a step gauge. Good crystal properties were obtained.
[0047]
Even when an AlN buffer layer deposited with a thickness of 50 nm at a substrate temperature of 600 ° C. is used instead of the GaN buffer layer used in the above embodiment using the same substrate as described above, a GaN layer grown on the buffer layer Then, good crystal characteristics equivalent to those described above were obtained. Further, after the thermal cleaning in the above process, the GaN layer formed even if the buffer layer and the GaN layer are grown by the same method as described above after initial nitriding of the surface of the sapphire substrate at 1100 ° C. for 10 minutes in an ammonia atmosphere. The crystal characteristics were as good as those described above.
[0048]
(Comparative Example 1)
For comparison, when an undoped GaN layer was grown in the same process as in Example 1 using a sapphire substrate tilted 2.1 ° from <0001> to the <1-100> direction, two-dimensional growth was inhibited. As a result, unevenness was generated, and the average surface roughness was 2.0 nm, the half width of the double crystal X-ray diffraction peak was 4 arcmin, the electron concentration was 10 16 cm −3, and the mobility was 90 cm 2 / V · sec.
[0049]
Therefore, in the above process, even if the deposition temperature of the buffer layer is changed to 550 ° C. and the thickness is changed to 40 nm, the average surface roughness does not change to 2.0 nm, and the crystal characteristics are 3.5 armin and 8 × 10 15 cm. −3, 200 cm 2 / V · sec, which does not reach the characteristics of the crystal when the GaN layer is formed using the sapphire substrate having the inclination angle of 0.05 ° shown in the first embodiment.
[0050]
Here, the surface orientation of the sapphire substrate is changed from 0.02 ° to 0.5 ° from the <0001> direction to the <1-100> direction, and the same process as in Example 1 and Conventional Example 1 is performed. The results of investigating the surface roughness (flatness) and threading dislocation density of the formed GaN layer are shown by ● in FIG. In the range of 0.02 ° to 0.045 ° and 0.21 ° to 0.5 °, irregularities were generated on the surface due to poor crystal growth caused by the inclination angle of the sapphire substrate surface.
[0051]
Further, the surface roughness and threading dislocation density correspond to each other almost one-on-one, and in the case of a GaN layer having a surface roughness of 1.5 nm or less, the threading dislocation density can be suppressed to 10 9 cm −2, but the surface roughness is 1.5 nm. It was also found that the thickness exceeding 5 × 10 10 cm −2 is larger in the layer exceeding 1. That is, when the inclination of the surface orientation of the surface of the sapphire substrate is in the range of 0.05 ° to 0.2 °, the surface roughness is small and the threading dislocation can be suppressed to a relatively small value.
[0052]
This is because, within this tilt angle range, good two-dimensional growth is realized during the growth of the GaN layer (a situation where a GaN layer is stacked by one atomic layer is realized), which is locally observed during three-dimensional nucleus growth. It is considered that the effect is that there is no progressing growth, and the generation of threading dislocations in the region where the GaN crystals in the local growth region peculiar to the three-dimensional nucleus growth are adjacently in contact with each other can be suppressed.
[0053]
(Example 2)
Next, an embodiment of the present invention in the case where a sapphire substrate inclined in a direction different from that of Example 1 by 90 ° will be described. In this example, a mirror-polished sapphire (0001) substrate tilted by 0.15 ° in the <11-20> direction from the <0001> direction was set in a normal horizontal MOCVD apparatus reactor, and the same as in Example 1. An undoped GaN layer was grown by this process. The crystal characteristics of the GaN layer produced in this example are as good as an average surface roughness of 1.1 nm, a double crystal X-ray diffraction half width of 2.6 arcmin, an electron concentration of 4 × 10 15 cm −3, and a mobility of 500 cm 2 / V · sec. Met.
[0054]
Further, using the same substrate as described above in the present example, even when the deposition temperature of the GaN or AlN or AlGaN buffer layer is changed in the range of 500 ° C. to 650 ° C. and the thickness is changed in the range of 40 nm to 70 nm, the formed GaN layer As a result, almost no change was observed in the characteristics, and a good GaN layer could be obtained. Further, even if a step of initial nitriding the surface of the sapphire substrate in an ammonia atmosphere before the buffer layer was formed, the crystal characteristics of the GaN layer were the same.
[0055]
(Comparative Example 2)
For comparison with Example 2, a GaN layer was grown in the same process as Example 2 using a sapphire (0001) substrate tilted by 1.8 ° in the <11-20> direction. The crystal characteristics of the film were significantly deteriorated as compared with the case of Example 2, and irregularities having an average roughness of 2.0 nm or more were generated on the surface. Further, as in Example 2, the deposition temperature of the GaN, AlN, or AlGaN buffer layer was changed in the range of 500 ° C. to 650 ° C. and the thickness was changed in the range of 40 nm to 70 nm. However, the crystal characteristics of the GaN layer were greatly improved. There wasn't.
[0056]
Here, GaN was formed by the same process as in Example 2 using a sapphire substrate whose surface orientation was changed from 0.02 ° to 0.5 ° in the <0001> to <11-20> direction. The results of measurement of the surface roughness and threading dislocation density of the GaN layer when the layer is grown are shown in FIG. Similarly to the case of tilting in the <1-100> direction, even when tilted in the <11-20> direction, when the tilt angle is 0.045 ° or less and 0.21 ° or more, the average surface roughness Increased to 1.5 nm or more.
[0057]
It was also found that the threading dislocation density in this case increased to 5 × 10 10 cm −2 or more. On the other hand, when the surface orientation of the sapphire substrate is tilted from the (0001) plane in the <11-20> direction within a range of 0.05 ° to 0.2 °, the average surface roughness of the GaN layer is significantly reduced. Planarization was achieved up to about 0.8 nm. In addition, the threading dislocation density of the GaN layer having a small average surface roughness can be suppressed to a relatively small value of 3 × 10 9 cm −2.
[0058]
As described above, it has been found that the surface orientation of the sapphire substrate has a great influence on the average surface roughness and threading dislocation density of the GaN crystal layer formed thereon. This improvement in crystallinity is achieved by changing the growth conditions (substrate temperature and thickness) of the buffer layer, and also the growth temperature of the GaN layer itself from 1100 ° C. to 950 ° C., 1000 ° C., 1150 ° C., and 1200 ° C. It was confirmed that it was most important to set the inclination angle of the surface orientation of the sapphire substrate within the range of 0.05 ° to 0.2 °.
[0059]
(Example 3)
FIG. 7 shows an example of an LED manufactured using the nitride compound semiconductor of the present application. In the figure, 701 is a sapphire (0001) substrate, 702 is a GaN buffer layer, 703 is an n-type GaN contact layer, 704 is an InGaN active layer made of an In0.2Ga0.8N single quantum well layer, and 705 is a p-type AlGaN protective layer. 706 are p-type GaN contact layers, 707 is a p-type electrode, and 708 is an n-type electrode. Using a sapphire (0001) substrate 701 mirror-polished by tilting 0.05 ° from the <0001> direction to the <1-100> direction, a GaN buffer layer 702 is deposited to a thickness of 50 nm at a substrate temperature of 600 ° C. The temperature was raised to 1000 ° C., and an n-type GaN contact layer 703 was grown to a thickness of 5 μm using ammonia, TMG and SiH 4. At this time, the n-type GaN contact layer 703 contains n-type impurities at a density of 1 × 10 18 cm −3.
[0060]
Subsequently, the substrate temperature is decreased to 750 ° C., and the InGaN active layer 704 of the In 0.2 Ga 0.8 N single quantum well layer is made 3.5 nm thick using Mg, TMG, TMI, and Mg-doped p-type Al 0.1 Ga 0. After the .9N protective layer 705 was grown to a thickness of 30 nm, the substrate temperature was raised again to 1000 ° C., and a p-type GaN contact layer 706 having a thickness of 0.5 μm was grown using ammonia, TMG, and Cp 2 Mg. After completion of the growth, the wafer substrate was taken out and subjected to a heat treatment at 800 ° C. for 20 minutes in a nitrogen atmosphere, and an LED was produced using etching and electrode formation steps according to a conventional method. The n-type electrode 708 is Al, and the p-type electrode 707 is Au / Ni.
[0061]
When a forward current of 20 mA was passed through the completed LED, the emission peak wavelength was 450 nm, the half width of the emission spectrum was 13 nm, and the luminance was 2 cd. Further, when the light emission pattern of the LED element of this example was observed, light was emitted uniformly over almost the entire surface of the InGaN active layer 704, and a fine light emission intensity distribution was not observed. In this case, the variation in emission intensity was suppressed to ± 20% or less.
[0062]
Also in this example, the crystallinity of the surface of the n-type GaN contact layer 703 in the state immediately before the growth of the InGaN active layer 704 was evaluated. Unlike Examples 1 and 2, Si is added as an impurity to the n-type GaN contact layer 703 that is the base of the InGaN active layer 704. When the average surface roughness and threading dislocation density were evaluated, Example 1 The same good characteristics were confirmed. However, in this case, although the surface roughness was somewhat deteriorated as compared with the state of Example 1 in which no Si was added, the range was 1.1 nm to 1.3 nm at most, and the thickness of the InGaN active layer 704 was 3 It was confirmed that control was possible to be smaller than 5 nm. The threading dislocation density at this time was also suppressed to a relatively low level of 5 × 10 9 cm −2.
[0063]
In addition, as a result of evaluating an LED element in which only the inclination angle of the substrate was changed using the same method as in this example, in an element in the inclination angle range of 0.05 ° to 0.2 °, Similar narrowing of the half-value width of the emission spectrum, uniform emission intensity distribution, and improvement in emission efficiency were observed. In this case, the same effect could be confirmed in any case of <1-100><11-20> as the direction of the inclination angle. As shown in FIG. 6, this effect is considered to be a result of reducing the surface roughness of the grown nitride semiconductor layer and forming an active layer on a very flat film.
[0064]
(Comparative Example 3)
For comparison, when a forward current of 20 mA was passed through an LED produced by the same method as in Example 3 using a sapphire substrate inclined by 0.25 ° from the <0001> direction to the <1-100> direction, The emission wavelength was 450 nm, which was the same as that in Example 3. However, it was found that the half-value width of the emission spectrum was 35 nm, which was wider than that in Example 3, and the luminance was 900 mcd, indicating that the emission efficiency was lowered. Further, in the evaluation of the light emission pattern, it was found that the distribution of the light emission intensity within the element surface was as large as ± 70%. Therefore, according to the present invention, the full width at half maximum of the emission spectrum is narrowed, and the color purity and the emission intensity are significantly improved. In addition, the distribution of the emission intensity within the element surface can be made uniform.
[0065]
This is because the surface of the n-type GaN contact layer 703, which is the base of the InGaN active layer 704, is planarized so as to have an average roughness sufficiently smaller than the thickness of the quantum well 704, so that the thickness of the InGaN active layer 704 is reduced. This is a result of uniformization in the plane. Such an effect of narrowing the half width of the emission spectrum can be confirmed when the average surface roughness of the n-type GaN contact layer 703 is smaller than the thickness of the InGaN active layer 704, and in particular, half the thickness of the InGaN active layer 704. This was prominent when:
[0066]
In Example 3 above, the average roughness of the n-type GaN contact layer surface is 1.1 nm to 1.2 nm, which is about 30 to 40% of the thickness of the InGaN active layer 704 (3.5 nm). I understand that. Further, regarding the uniformity of the light emission pattern, similarly, by making the surface roughness of the n-type GaN contact layer 703 smaller than the thickness of the InGaN active layer 704, the distribution of the light emission intensity in the element plane is more than ± 50%. It was possible to reduce the intensity, and desirably, the emission intensity distribution could be made uniform to ± 25% or less by making this roughness half or less of the thickness of the InGaN active layer 704.
[0067]
In the nitride-based compound semiconductor light-emitting device having the quantum well active layer as described above, it is desirable that the thickness of the active layer is set to 3.5 nm or more because the luminous efficiency is high. Therefore, when the surface roughness of the underlying n-type GaN contact layer 703 is 1.8 nm or less, which is approximately half the thickness of the active layer, the effect of uniform light emission becomes significant. That is, as shown in FIG. 6, if the inclination angle of the sapphire substrate surface from the <0001> direction is 0.05 ° or more and 0.2 ° or less, this condition is satisfied, the uniformity is high, and the light emission efficiency is high. It turns out that it can be realized.
[0068]
Example 4
FIG. 8 shows an example of a semiconductor laser manufactured using a nitride compound semiconductor to which the present invention is applied. In the figure, 801 is a sapphire substrate, 802 is a GaN buffer layer, 803 is an n-type contact layer, 804 is an n-type cladding layer, 805 is an active layer, 806 is a p-type evaporation prevention layer, 807 is a p-type cladding layer, and 808 is A p-type contact layer, 809 is a current confinement layer, 810 is a p-type electrode, and 811 is an n-type electrode.
[0069]
A sapphire (0001) substrate that is mirror-polished by tilting 0.05 ° from the <0001> direction to the <1-100> direction is set in a reactor of a MOCVD apparatus, and is 50 nm thick using ammonia and TMG at a substrate temperature of 500 ° C. The GaN buffer layer 802 was grown.
[0070]
Next, the substrate temperature is raised to 1000 ° C., and an n-type contact layer 803 made of GaN having a thickness of 0.4 μm is grown using ammonia, TMG, and SiH 4, and then 0.2 μm using ammonia, TMG, TMA, and SiH 4. An n-type cladding layer 804 made of thick n-type Al0.15Ga0.85N was grown. The electron concentration of this layer is 2 × 10 18 cm −3. Stop TMG, TMA, SiH4, lower the substrate temperature to 700 ° C, ammonia, TMG, TMI, 1.5nm thick In0.25Ga0.75N well layer and 3.0nm thick In0.05Ga0.95N barrier layer An active layer 805 consisting of three layers was grown.
[0071]
Subsequently, a p-type evaporation prevention layer 806 made of p-type Al0.1Ga0.9N having a thickness of 6 nm is grown using ammonia, TMG, TMA, and Cp2Mg. After growing the p-type evaporation prevention layer 806, the substrate temperature is raised to 1050 ° C., and a p-type cladding layer 807 made of 0.2 μm p-type Al0.15Ga0.85N is grown using ammonia, TMG, TMA and Cp2Mg. The supply of TMA is stopped, and a p-type contact layer 808 made of 0.5 μm p-type GaN is grown.
[0072]
After completion of the above steps, the substrate is taken out from the reactor of the MOCVD apparatus, and the p-type cladding layer 807 and the p-type contact layer 808 made of p-type Al0.15Ga0.85N are subjected to heat treatment at 800 ° C. for 20 minutes in a nitrogen atmosphere. Perform p-type. Subsequently, etching and electrode formation were performed according to a conventional method, and the laser element was fabricated by dividing by scribing or dicing. The n-type electrode 811 is Ti / Al, and the p-type electrode 810 is Au / Ni.
[0073]
When a current was passed through the completed device at room temperature, laser oscillation at a wavelength of 432 nm was observed with a threshold current of 40 mA, and the rising voltage at this time was 4V. Further, the drive current at the time of 5 mW output was 47 mA, and the drive voltage was 4.6V. Further, it was confirmed that the device lifetime at room temperature was 10,000 hours or more.
[0074]
As described above, the low oscillation threshold current can be realized and the reliability is improved because the average roughness of the surface of the n-type cladding layer 804 serving as the base of the active layer 805 of the multiple quantum well can be reduced. It is. In this case, the layer immediately below the active layer 805 contains 15% Al0.15Ga0.85N and Al, and the GaN buffer layer 802 is included between the sapphire substrate 801 and the active layer 805 as compared with the case of the third embodiment. The difference is that three layers are inserted. However, as a result of evaluating the surface of the n-type cladding layer 804 in the state immediately before the growth of the active layer 805 of the device of this example, a result almost similar to the case of the undoped GaN layer indicated by ● in FIG. Obtained.
[0075]
That is, the average roughness of the surface of the n-type cladding 804 in Example 4 was as small as 1.1 to 1.3 nm, and the threading dislocation density was as small as 5 × 10 9 cm −2. At this time, the average surface roughness of the n-type cladding layer 804 is made smaller than the thickness (1.5 nm) of each quantum well layer constituting the active layer 805 of the multiple quantum well. This makes the emission pattern uniform (that is, uniform gain in the optical waveguide direction and reduction of absorption loss in the semiconductor laser) and narrows the half-value width of the emission spectrum (that is, the half-value width of the gain in the semiconductor laser). Is realized.
[0076]
Therefore, it has become possible to efficiently realize laser oscillation with a semiconductor laser. Thus, it was confirmed that the present invention has the same effect not only in improving the quality of the GaN layer but also in the case of AlGaN.
[0077]
Further, in this example, when only the inclination angle of the sapphire substrate was changed from the above 0.05 ° to 0.15 °, 0.20 °, and the same device was produced and evaluated, The oscillation threshold currents of 45 mA and 50 mA and the device lifetime at room temperature were 12000 hours and 7000 hours, respectively, and a semiconductor laser with good characteristics could be realized.
[0078]
(Comparative Example 4)
For comparison, when a current was passed through the laser element manufactured by the above method using a sapphire substrate inclined by 0.25 ° from the <0001> direction to the <1-100> direction, a laser oscillation of 432 nm was obtained at a threshold current of 250 mA. Was observed. The rising voltage was 4V. The driving current at the time of 5 mW output was 280 mA, and the driving voltage was 4.9V. The device lifetime at room temperature was 100 hours or less.
[0079]
Similarly, when a sapphire substrate having an inclination angle of 0.03 ° is applied and a semiconductor laser similar to that of Example 4 is manufactured, the oscillation threshold current is 100 mA or more, and the device lifetime at room temperature is less than 300 hours. As compared with Example 4, the device characteristics were remarkably deteriorated.
[0080]
(Example 5)
In this example, regarding a light-emitting diode manufactured using a slightly inclined substrate, the relationship between the substrate slight inclination angle, the threading dislocation density present in the element, the surface roughness, and the emission intensity at the time of current injection is shown.
[0081]
As a substrate, a (0001) plane sapphire substrate is used which is mirror-polished with an inclination angle of 0.02 ° to 0.5 ° in the <11-20> and <1-100> directions from the <0001> direction. A nitride-based compound semiconductor layer is sequentially grown by the above-described method.
[0082]
The growth conditions of the active layer are first adjusted after the n-type GaN layer is grown so that the substrate temperature becomes a constant temperature while flowing NH3. When the substrate temperature was stabilized, TMG, TMI, and SiH4 were introduced at 10 μmol / min, 10 μmol / min, and 5 nmol / min, respectively, and In0.05Ga0.95N serving as a barrier layer of the active layer was grown to a thickness of about 5 nm. . Subsequently, TMG, TMI, and SiH4 were introduced at 10 μmol / min, 50 μmol / min, and 5 nmol / min, respectively, and In0.2Ga0.8N serving as a well layer of the active layer was grown to a thickness of about 3 nm. After the well layer growth, the supply amount of TMG was reduced to 10 μmol / min, and the barrier layer of the active layer was grown again. After the growth of the barrier layer, the process of growing the well layer was repeated. Finally, the barrier layer was grown and an AlGaN film for the purpose of preventing sublimation of InGaN was grown to about 30 nm by the method described in the embodiment. In this example, the element was fabricated with three well layers forming the active layer. After the growth of AlGaN, a sample in which a p-type layer was grown by the method described in the embodiment and a sample as a light emitting diode were produced through processes such as electrode formation.
[0083]
A sample prepared by this method and having no electrode formed was observed by a cross-sectional TEM to evaluate the threading dislocation density, and the surface roughness was measured with a step gauge. The same result as in FIG. 6 was obtained. In any case, when the substrate tilt angle is in the range of 0.02 ° to 0.045 ° and 0.21 ° to 0.5 °, high-density threading dislocations and surface roughness are caused by crystal growth failure caused by the tilt of the substrate surface. Has occurred. In addition, a large number of dot-like regions having a diameter of several nm due to In aggregation were observed in the active layer. When the inclination is 0.05 ° to 0.2 °, threading dislocations are remarkably reduced, and the surface roughness is improved to 1.8 nm or less, which is sufficiently smaller than the thickness of each quantum well layer. From cross-sectional TEM observation, it was found that the surface flatness was improved from the growth stage of the n-type GaN of the underlayer. As a result of elimination of In aggregation in the active layer due to the reduction of threading dislocations, almost no dot-like region was observed, and the layer thickness fluctuation of the quantum well active layer was improved by improving the flatness of the underlayer.
[0084]
The result of investigating the luminescence intensity when a current of 20 mA was passed through a sample formed into an element by forming an electrode with respect to the substrate tilt angle from the <0001> direction to the <11-20> and <1-100> directions was shown. As shown in FIG. ● represents an inclination from <0001> to <1-100>, and ◯ represents an inclination angle from <0001> to <11-20>. As can be seen from FIG. 9, the emission intensity increases in the range of the inclination angle from 0.05 ° to 0.2 °.
[0085]
FIG. 10 shows the results of investigating the influence of the growth temperature of the multiple quantum well active layer in the inclination from <0001> to <1-100>. ● is when the growth temperature is 700 ° C., ○ is when the temperature is 750 ° C., and Δ is when the temperature is 800 ° C. As shown in FIG. 10, the influence of the fine substrate tilt angle on the light emission intensity varies slightly depending on the growth temperature, but in any case, the light emission intensity increases with the substrate tilt of 0.05 ° to 0.2 °. From the comparison between FIG. 6, FIG. 9, and FIG. 10, the correlation between threading dislocation and light emission intensity is clear, and the present invention can provide light emission intensity equal to or higher than that produced by the prior art with a lower driving current. I understand that. This means that the current path that does not contribute to light emission is reduced by the present invention.
[0086]
In this example, an example in which the number of well layers in the active layer is three was described. However, the effects of the multiple quantum wells of two layers and four to ten layers were the same as in this example.
[0087]
Further, when a laser is manufactured by the same method, the laser manufactured on a slightly inclined substrate of 0.05 ° to 0.2 ° has high emission intensity for the same current value, and starts oscillation according to the emission intensity. The threshold current density tended to decrease.
[0088]
(Example 6)
In this example, the relationship between the light emission intensity at the time of current injection and the growth interruption time after growth of the active layer and the barrier layer was determined for a light emitting diode having a barrier layer and an active layer produced on a vicinal substrate using growth interruption. Show.
[0089]
Using a (0001) plane sapphire substrate that is mirror-polished with an inclination angle of 0.15 ° from the <0001> direction to the <1-100> direction as the substrate, the nitride-based compound semiconductor layers are sequentially formed by the method described in the embodiment. Grew up.
[0090]
First, after growing the n-type GaN layer, the active layer is adjusted so that the substrate temperature becomes a constant temperature while flowing NH3, and when the substrate temperature is stabilized, TMG, TMI and SiH4 are each 10 μmol / min. 10 μmol / min and 5 nmol / min were introduced, and In0.05Ga0.95N, which is a barrier layer forming an active layer, was grown to a thickness of about 5 nm. Thereafter, the supply of TMG, TMI, and SiH4 is temporarily stopped, and a certain growth interruption is performed while the carrier gas and the NH3 gas are supplied. Thereafter, TMG, TMI, and SiH4 were introduced again at 10 μmol / min, 50 μmol / min, and 5 nmol / min, respectively, and In0.2Ga0.8N serving as a well layer of the active layer was grown to a thickness of about 3 nm. After the well layer growth, the supply amount of TMG was reduced to 10 μmol / min, and the barrier layer of the active layer was grown again. After the growth of the barrier layer, the process of growing the well layer through interruption of growth for a certain period is repeated. Finally, the barrier layer is grown and an AlGaN film for the purpose of preventing sublimation of InGaN by the method described in the embodiment is formed to 30 nm. Growing up. A growth interruption may or may not be provided between the AlGaN film and the InGaN barrier layer where the active layer is terminated. However, it has been found that when the number of well layers is two or less, the emission intensity due to current injection of the light emitting element is higher when the growth interruption is provided even after the terminating barrier layer is grown. In this example, the element was fabricated with three well layers forming the active layer.
[0091]
After the growth of AlGaN, a p-type layer was grown by the method shown in the embodiment, and a light emitting diode was manufactured through processes such as electrode formation.
[0092]
FIG. 11 shows the results of investigating the light emission intensity when a current of 20 mA was passed through the light emitting diode manufactured by this method, using the growth interruption time after growth of the barrier layer as a parameter. In the figure, ● indicates when the growth temperature of the multi-quantum well active layer is 700 ° C., ○ indicates when the temperature is 750 ° C., Δ indicates when the temperature is 800 ° C. The light emission intensity is when the growth interruption time at the growth temperature is 0 seconds, and the intensity indicated by a circle or a triangle is the average value of the light emission intensity.
[0093]
As is clear from comparison with FIGS. 9 and 11, it is understood that the emission intensity is further increased by using the growth interruption in addition to the slightly inclined substrate.
[0094]
As shown in FIG. 10, the influence on the light emission intensity due to the growth interruption slightly changes depending on the growth temperature, but in any case, the light emission intensity increases due to the growth interruption for 1 second or more. When the growth temperature of the active layer is high, the growth interruption period is short. Conversely, when the growth temperature is low, a longer growth interruption period is more effective. As shown in the figure, when the growth temperature is 700 ° C., the growth interruption time is effective from about 1 second to about 60 minutes, and the period during which the effect is particularly effective is from 1 second to 10 minutes. . When the growth temperature was 750 ° C., the growth interruption time was effective from about 1 second to about 15 minutes, and the period during which the effect was particularly effective was from 1 second to 5 minutes.
[0095]
When the growth temperature was 800 ° C., the growth interruption time was effective from about 1 second to about 5 minutes, and the period during which the effect was particularly effective was from 1 second to 2 minutes.
[0096]
In the present embodiment, an example using a (0001) plane sapphire substrate that is mirror-polished with an inclination angle of 0.15 ° from the <0001> direction to the <1-100> direction has been described. It was confirmed that the same effect was exhibited even when tilted in the other direction within the range of 0 ° to 0.2 °.
[0097]
In the present embodiment, an example in which the number of well layers in the active layer is 3 has been described. However, the effect of the multi-quantum well from 2 layers and from 4 layers to 10 layers has the same tendency as in this embodiment. Yes, when a laser is manufactured by the same method, a laser in which an active layer is formed by interrupting the growth of the barrier layer has a high emission intensity for the same current value, and a threshold current that starts oscillation according to the emission intensity. The density tended to be low.
[0098]
(Example 7)
In this example, a constant growth interruption was performed after the growth of the barrier layer of the active layer using a (0001) plane sapphire substrate that was mirror-polished with an inclination angle of 0.15 ° from the <0001> direction to the <1-100> direction. Similarly, after the growth of the well layer of the active layer, the light emission intensity in the current injection of the light emitting diode and the growth interruption after the well layer growth are also observed after the well layer growth of the active layer. We report an example of investigating the relationship with time. The growth method of each layer forming the light emitting diode is the same as the method shown in the second embodiment. Hereinafter, conditions for growing the active layer will be described.
[0099]
First, after growing n-type GaN, the substrate temperature is adjusted to a constant temperature while NH3 is allowed to flow. When the substrate temperature was stabilized, TMG, TMI, and SiH4 were introduced at 10 μmol / min, 10 μmol / min, and 5 nmol / min, respectively, and In0.05Ga0.95N serving as a barrier layer of the active layer was grown to a thickness of about 5 μm. . Thereafter, the supply of TMG, TMI, and SiH4 is temporarily stopped, and a certain growth interruption is performed while the carrier gas and the NH3 gas are supplied. Thereafter, TMG, TMI, and SiH4 gas were again introduced at 10 μmol / min, 15 μmol / min, and 5 nmol / min, respectively, and In0.2Ga0.8N serving as a well layer of the active layer was grown to a thickness of about 5 μm. Thereafter, the supply of TMG, TMI, and SiH4 is temporarily stopped, and a certain growth interruption is performed while the carrier gas and the NH3 gas are supplied. After the barrier layer growth and the well layer growth, the process of growing the respective layers adjacent to each other through the growth interruption for a certain period is repeated, and finally the barrier layer is grown by the method described in the embodiment. An AlGaN film for the purpose of preventing the sublimation of InGaN was grown to about 30 nm. A growth interruption may or may not be provided between the present AlGaN film and the InGaN barrier layer where the active layer terminates. However, it has been found that when the number of well layers is two or less, the emission intensity due to current injection into the light emitting element is stronger when the growth interruption is provided even after the terminating barrier layer is grown. In this example, the element was fabricated with three well layers forming the active layer. The growth interruption time after the barrier layer growth was 60 seconds.
[0100]
FIG. 12 shows the result of investigating the light emission intensity when a current of 20 mA is passed through the light emitting diode manufactured by this method, using the growth interruption time after the well layer growth as a parameter. In the figure, ● indicates when the growth temperature of the multi-quantum well active layer is 700 ° C., ○ indicates when the temperature is 750 ° C., Δ indicates when the temperature is 800 ° C., and the broken line drawn at the intensity 10 indicates the growth temperature at each growth temperature. The light emission intensity is when the growth interruption time is 0 second, and the intensity indicated by a circle or triangle is the average value of the light emission intensity.
[0101]
As is clear from a comparison between FIG. 9 and FIG. 12, it is understood that the emission intensity is further increased by using the growth interruption in addition to the slightly inclined substrate.
[0102]
As shown in FIG. 12, the influence on the emission intensity due to the growth interruption after the well layer growth slightly changes depending on the growth temperature, but in any case, the emission intensity increases due to the growth interruption for 1 second or more. When the growth temperature of the active layer is high, the growth interruption time is short. Conversely, when the growth temperature is low, it is effective that the growth interruption time is long.
[0103]
As shown in FIG. 12, when the growth temperature is 700 ° C., the growth interruption time is effective from about 1 second to about 60 minutes, and the period in which the effect is particularly effective is from 1 second to 10 minutes. . When the growth temperature was 750 ° C., the growth interruption time was effective from about 1 second to about 15 minutes, and the period during which the effect was particularly effective was 1 second to 5 minutes.
[0104]
In the case where the growth temperature is 800 ° C., the growth interruption time is effective from about 1 second to about 5 minutes, and the period in which the effect particularly appears is from 1 second to 2 minutes.
[0105]
Further, when the growth is interrupted only after growing the well layer without growing the barrier layer after growing the barrier layer, the effect is as great as shown in FIG. Was not confirmed, and the increase in the emission intensity was only about 3 times at the maximum.
[0106]
(Example 8)
In this example, a light-emitting diode was manufactured by the method shown in Example 5 using (0001) plane sapphire mirror-polished with an inclination angle of 0.15 ° from the <0001> direction to the <1-100> direction as the substrate. Describes the results of investigating the light-emitting characteristics of light-emitting diodes when the mixing ratio of the carrier gas hydrogen gas and nitrogen gas is changed during the growth interruption period after growth of the barrier layer that forms the active layer. To do.
[0107]
In FIG. 13, the growth temperature of the active layer is fixed at 750 ° C., the growth interruption time after the growth of the barrier layer is 60 seconds, and the ratio of nitrogen gas to hydrogen gas is changed without changing the total amount of carrier gas flowing during the growth interruption. The relationship between the light emission wavelength and the intensity of the light-emitting diode manufactured by supplying differently is shown. ● indicates the emission intensity, and ○ indicates the emission wavelength. As shown in FIG. 13, as the N2 ratio of the carrier gas decreases, the emission wavelength tends to be shorter and the emission intensity also tends to decrease. This tendency shows the same tendency even when the growth temperature of the active layer is as high as about 800 ° C. or as low as about 700 ° C. Further, in the case where not only the growth interruption after the barrier layer growth but also the growth interruption is provided after the growth of the well layer, the use of N2 as the carrier gas during the growth interruption has a stronger emission intensity and longer wavelength. It showed a trend toward wavelength.
[0108]
Example 9
In this example, a light-emitting diode was manufactured by the method shown in Example 1 using (0001) plane sapphire that was mirror-polished with an inclination angle of 0.15 ° from the <0001> direction to the <1-100> direction as the substrate. The results of investigating the relationship between the growth interruption time and the emission intensity when the amount of NH 3 gas introduced during the period of interruption of growth after growth of the barrier layer forming the active layer is changed will be described.
[0109]
FIG. 14 shows the result of measuring the light emission intensity of the light emitting diode when the growth temperature of the active layer is fixed at 750 ° C. and the NH 3 introduction amount and the growth interruption time are changed. ● is when NH3 = 5 l / min, ○ is when NH3 = 3 l / min, and Δ is when NH3 = 0 l / min.
[0110]
As shown in FIG. 14, it was confirmed that the emission intensity increased even when the amount of NH3 introduced was zero. However, the effect of increasing the emission intensity was more noticeable by the introduction of NH3. Since the interruption time can be set long, the manufacturing becomes easy. This tendency shows the same tendency even when the growth temperature of the active layer is as high as about 800 ° C. or as low as about 700 ° C. In addition to the growth interruption after the barrier layer growth, the same tendency was shown when the growth interruption was provided after the well layer growth.
[0111]
(Example 10)
In this example, regarding a light-emitting diode manufactured using a GaN finely inclined substrate, the relationship between the finely inclined angle of the GaN substrate, the threading dislocation density present in the element, the surface roughness, and the emission intensity at the time of current injection is shown.
[0112]
As a substrate, a (0001) plane GaN substrate that is mirror-polished with an inclination angle of 0.02 ° to 0.5 ° in the <11-20> and <1-100> directions from the <0001> direction is shown in the embodiment. The nitride-based compound semiconductor layers were sequentially grown by the above-described method, and the active layer was grown by the procedure described in Example 5 without interrupting the growth between the respective layers. The number of well layers forming the active layer is three. After the device structure growth, a sample in which a p-type layer was grown by the method shown in the embodiment and a sample as a light emitting diode were manufactured through processes such as electrode formation.
[0113]
A sample prepared by the above method and having no electrode formed was observed by a cross-sectional TEM to evaluate the threading dislocation density, and the surface roughness was measured with a step gauge. The results are shown in FIG. In the figure, ● represents inclination in the <1-100> direction, and ○ represents inclination in the <11-20> direction. In any case, when the substrate tilt angle is in the range of 0.02 ° to 0.045 ° and 0.21 ° to 0.5 °, high-density threading dislocations and surface roughness are caused by crystal growth failure caused by the tilt of the substrate surface. Has occurred. On the other hand, when the inclination is 0.05 ° to 0.2 °, threading dislocations are remarkably reduced, and the surface roughness is sufficiently smaller than the thickness of each quantum well layer, which is further improved over the element on the slightly inclined sapphire substrate, and is less than 4 nm. there were. From cross-sectional TEM observation, it was found that the surface flatness was improved from the growth stage of the n-type GaN of the underlayer. By reducing threading dislocations, In aggregation in the active layer was eliminated, and by improving the flatness of the underlying layer, fluctuations in the thickness of the quantum well active layer were improved.
[0114]
Next, the emission intensity when a current of 20 mA is passed through the sample formed into an element by forming an electrode on the sample is the substrate tilt angle from the <0001> direction to the <11-20> and <1-100> directions. The results of the investigation are shown in FIG. ● is an inclination from <0001> to <1-100>, and ◯ is an inclination from <11-20>. It can be seen that the emission intensity increases at an inclination of 0.05 ° to 0.2 °.
[0115]
FIG. 17 shows the influence of the growth temperature of the multiple quantum well active layer in the tilted substrate from <0001> to <1-100>. As shown in the figure, the influence of the fine substrate tilt angle on the light emission intensity varies slightly depending on the growth temperature, but in any case, the light emission intensity increases with a substrate tilt of 0.05 ° to 0.2 °. Although this tendency is the same as that of the slightly inclined sapphire substrate, it can be seen that the improvement effect is larger. From the comparison between FIG. 6 and FIG. 9, FIG. 10, FIG. 15, FIG. 16, and FIG. 17, the correlation between threading dislocations and emission intensity is clear even in the device fabricated on the slightly tilted GaN substrate. It can be seen that the same or higher emission intensity can be obtained with a lower driving current as compared with the case of the above. This means that the current path that does not contribute to light emission is reduced by the present invention.
[0116]
In this example, an example in which the number of well layers in the active layer is three was described. However, the effects of the multiple quantum wells of two layers and four to ten layers were the same as in this example.
[0117]
Further, when a laser is manufactured by the same method, the laser manufactured on a slightly inclined substrate of 0.05 ° to 0.2 ° has high emission intensity for the same current value, and starts oscillation according to the emission intensity. The threshold current density tended to be lower, and the degree of decrease was more remarkable than when fabricated on a slightly inclined sapphire substrate.
[0118]
(Example 11)
In this example, the relationship between the emission intensity at the time of current injection and the growth interruption time after growth of the active layer and the barrier layer for a light-emitting diode having a barrier layer and an active layer produced on a vicinal GaN substrate using growth interruption. Indicates.
[0119]
Using a (0001) plane GaN substrate mirror-polished with an inclination angle of 0.15 ° from the <0001> direction to the <1-100> direction as the substrate, the nitride-based compound semiconductor layers are sequentially formed by the method described in the embodiment. Grew up.
[0120]
First, after growing the n-type GaN layer, the active layer is adjusted so that the substrate temperature becomes a constant temperature while flowing NH3, and when the substrate temperature is stabilized, TMG, TMI and SiH4 are each 10 μmol / min. 10 μmol / min and 5 nmol / min were introduced, and In0.05Ga0.95N, which is a barrier layer forming an active layer, was grown to a thickness of about 5 nm. Thereafter, the supply of TMG, TMI, and SiH4 is temporarily stopped, and a certain growth interruption is performed while the carrier gas and the NH3 gas are supplied. Thereafter, TMG, TMI, and SiH4 were introduced again at 10 μmol / min, 50 μmol / min, and 5 nmol / min, respectively, and In0.2Ga0.8N serving as a well layer of the active layer was grown to a thickness of about 3 nm. After the well layer growth, the supply amount of TMG was reduced to 10 μmol / min, and the barrier layer of the active layer was grown again. After the growth of the barrier layer, the process of growing the well layer through interruption of growth for a certain period is repeated. Finally, the barrier layer is grown and an AlGaN film for the purpose of preventing sublimation of InGaN by the method described in the embodiment is formed to 30 nm. Growing up. A growth interruption may or may not be provided between the AlGaN film and the InGaN barrier layer where the active layer is terminated. However, it has been found that when the number of well layers is two or less, the emission intensity due to current injection of the light emitting element is higher when the growth interruption is provided even after the terminating barrier layer is grown. In this example, the element was fabricated with three well layers forming the active layer.
[0121]
After the growth of AlGaN, a p-type layer was grown by the method shown in the embodiment, and a light emitting diode was manufactured through processes such as electrode formation.
[0122]
FIG. 18 shows the results of investigating the light emission intensity when a current of 20 mA was passed through a light emitting diode manufactured by this method, using the growth interruption time after growth of the barrier layer as a parameter. ● is when the growth temperature of the multi-quantum well active layer is 700 ° C., ◯ is when it is 750 ° C., and Δ is when it is 800 ° C. In the figure, the broken line drawn at the position of intensity 400 is the emission intensity when the growth interruption time at each growth temperature is 0 seconds, and the intensity indicated by a circle or triangle is the average value of the emission intensity.
[0123]
As is clear from comparison between FIG. 16 and FIG. 18, it is understood that the emission intensity is further increased by using the growth interruption in addition to the slightly inclined GaN substrate.
[0124]
As shown in FIG. 18, the influence on the light emission intensity due to the growth interruption slightly changes depending on the growth temperature, but in any case, the light emission intensity increases due to the growth interruption for 1 second or more. When the growth temperature of the active layer is high, the growth interruption period is short. Conversely, when the growth temperature is low, the longer the growth interruption period, the greater the effect. As shown in the figure, when the growth temperature is 700 ° C., the growth interruption time is effective from about 1 second to about 60 minutes, and the period during which the effect is particularly effective is from 1 second to 10 minutes. . When the growth temperature was 750 ° C., the growth interruption time was effective from about 1 second to about 15 minutes, and the period during which the effect was particularly effective was from 1 second to 5 minutes. When the growth temperature was 800 ° C., the growth interruption time was effective from about 1 second to about 5 minutes, and the period during which the effect was particularly effective was from 1 second to 2 minutes.
[0125]
In the present embodiment, an example using a (0001) plane GaN substrate that is mirror-polished with an inclination angle of 0.15 ° from the <0001> direction to the <1-100> direction has been described. It was confirmed that the same effect was exhibited even when tilted in the other direction within the range of 0 ° to 0.2 °.
[0126]
In the present embodiment, an example in which the number of well layers in the active layer is 3 has been described. However, the effect of the multi-quantum well from 2 layers and from 4 layers to 10 layers has the same tendency as in this embodiment. Yes, when a laser is manufactured by the same method, a laser in which an active layer is manufactured by interrupting the growth of the barrier layer has a high emission intensity for the same current value, and a threshold current at which oscillation starts according to the emission intensity The density tended to be low.
[0127]
(Example 12)
In this example, a constant growth interruption was performed after the growth of the barrier layer of the active layer using a (0001) plane GaN substrate mirror-polished with an inclination angle of 0.15 ° from the <0001> direction to the <1-100> direction. Similarly, after the growth of the well layer of the active layer, the light emission intensity in the current injection of the light emitting diode and the growth interruption after the well layer growth are also observed after the well layer growth of the active layer. We report an example of investigating the relationship with time. The growth method of each layer forming the light emitting diode is the same as the method shown in the sixth embodiment. Hereinafter, conditions for growing the active layer will be described.
[0128]
First, after growing n-type GaN, the substrate temperature is adjusted to a constant temperature while NH3 is allowed to flow. When the substrate temperature was stabilized, TMG, TMI, and SiH4 were introduced at 10 μmol / min, 10 μmol / min, and 5 nmol / min, respectively, and In0.05Ga0.95N serving as a barrier layer of the active layer was grown to a thickness of about 5 μm. . Thereafter, the supply of TMG, TMI, and SiH4 is temporarily stopped, and a certain growth interruption is performed while the carrier gas and the NH3 gas are supplied. Thereafter, TMG, TMI, and SiH4 gas were again introduced at 10 μmol / min, 15 μmol / min, and 5 nmol / min, respectively, and In0.2Ga0.8N serving as a well layer of the active layer was grown to a thickness of about 5 μm. Thereafter, the supply of TMG, TMI, and SiH4 is temporarily stopped, and a certain growth interruption is performed while the carrier gas and the NH3 gas are supplied. After the barrier layer growth and the well layer growth, the process of growing the respective layers adjacent to each other through the growth interruption for a certain period is repeated, and finally the barrier layer is grown by the method described in the embodiment. An AlGaN film for the purpose of preventing the sublimation of InGaN was grown to about 30 nm. A growth interruption may or may not be provided between the present AlGaN film and the InGaN barrier layer where the active layer terminates. However, it has been found that when the number of well layers is two or less, the emission intensity due to current injection of the light emitting element is higher when the growth interruption is provided even after the terminating barrier layer is grown. In this example, the element was fabricated with three well layers forming the active layer. The growth interruption time after the barrier layer growth was 60 seconds.
[0129]
FIG. 19 shows the result of investigating the light emission intensity when a current of 20 mA was passed through the light emitting diode manufactured by this method, using the growth interruption time after the well layer growth as a parameter. ● is when the growth temperature of the multi-quantum well active layer is 700 ° C., ◯ is when it is 750 ° C., and Δ is when it is 800 ° C. In the figure, the broken line drawn at the position of intensity 400 is the emission intensity when the growth interruption time at each growth temperature is 0 seconds, and the intensity indicated by a circle or triangle is the average value of the emission intensity.
[0130]
As is clear from comparison between FIG. 16 and FIG. 19, it can be seen that the emission intensity is further increased by using the growth interruption in addition to the slightly inclined GaN substrate.
[0131]
As shown in FIG. 19, the influence on the emission intensity due to the growth interruption after the well layer growth slightly changes depending on the growth temperature, but in any case, the emission intensity increases due to the growth interruption for 1 second or more. When the growth temperature of the active layer is high, the growth interruption time is short. Conversely, when the growth temperature is low, it is effective that the growth interruption time is long. In the case where the growth temperature is 700 ° C., the growth interruption time is effective from about 1 second to about 60 minutes. Particularly, the period in which the effect appears is from 1 second to 10 minutes, and the growth temperature is 750 ° C. In this case, the growth interruption time is effective from about 1 second to about 15 minutes, and the period in which the effect is particularly effective is from 1 second to 5 minutes.
[0132]
In the case where the growth temperature is 800 ° C., the growth interruption time is effective from about 1 second to about 5 minutes, and the period in which the effect particularly appears is from 1 second to 2 minutes. On the other hand, when the growth is interrupted only after growing the well layer without growing the barrier layer after growing the barrier layer, the effect is as great as shown in FIG. Was not confirmed, and the increase in the emission intensity was only about 3 times at the maximum.
[0133]
As described above, the embodiment has been described. The present invention is not limited to the combination of the material and the layer structure shown in the above embodiment, but includes a double heterostructure composed of a combination of a GaN active layer / AlGaN cladding layer, and the like. The same effect can be obtained in a semiconductor laser device having a single quantum well and multiple quantum wells made of a nitride compound semiconductor as active layers. In particular, the effect in the case of using the quantum well active layer is remarkable, and the improvement of the characteristics of the light emitting device by the application of the base layer having an average surface roughness smaller than the thickness of the quantum well active layer is remarkable.
[0134]
【The invention's effect】
According to the present invention, a nitride-based compound semiconductor crystal having an improved average surface roughness and crystal quality as compared with the prior art can be epitaxially grown. That is, by using a (0001) plane sapphire substrate that is mirror-polished with an inclination angle of 0.05 ° to 0.2 ° from the <0001> direction to the <1-100> direction or the <11-20> direction, Promotes two-dimensional growth and reduces dislocations in the crystal. Further, in a nitride compound semiconductor light emitting device having a multilayer film made of a nitride compound semiconductor containing In as an active layer, a nitride system having high emission intensity by providing a growth interruption for a certain period after the active layer is grown. A compound semiconductor light emitting device is provided. Thus, the light-emitting element and the electronic element manufactured using the method of the present invention can have improved characteristics and lifetime.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the surface of a substrate whose tilt angle is not defined and three-dimensional growth.
FIG. 2 is a schematic cross-sectional view showing a substrate surface and a two-dimensional growth in which a tilt angle from a <0001> direction is defined according to the present invention.
FIG. 3 is a schematic view of a crystal growth apparatus used in this example.
FIG. 4 is a schematic view of a light-emitting element manufactured using a nitride-based compound semiconductor.
FIG. 5 is a diagram showing a growth temperature in the vicinity of an active layer and a supply amount of each raw material.
FIG. 6 is a graph showing the relationship between the tilt angle of the substrate surface, the threading dislocation density, and the average surface roughness.
7 is a cross-sectional view of an LED shown in Example 3. FIG.
8 is a sectional view of a laser shown in Example 4. FIG.
FIG. 9 is a graph showing the relationship between the tilt angle of the sapphire substrate surface and the light emission intensity of the light emitting element.
FIG. 10 is a graph showing the relationship between the substrate tilt angle and the light emission intensity of the light emitting element when the growth temperature of the light emitting layer is changed.
FIG. 11 is a graph showing the relationship between the growth interruption time after growth of the barrier layer and the light emission intensity of the light emitting device.
FIG. 12 is a graph showing the relationship between the growth interruption time after the well layer growth and the light emission intensity of the light emitting element.
FIG. 13 is a graph showing the relationship between the nitrogen partial pressure of the carrier gas, the emission intensity of the light emitting element, and the emission wavelength.
FIG. 14 is a graph showing the relationship between the amount of NH 3 during growth interruption and the light emission intensity of the light emitting element.
FIG. 15 is a graph showing the relationship between the inclination angle of the GaN substrate surface, the threading dislocation density, and the average surface roughness.
FIG. 16 is a graph showing the relationship between the tilt angle of the GaN substrate surface and the light emission intensity of the light emitting element.
FIG. 17 is a graph showing the relationship between the GaN substrate tilt angle and the light emission intensity of the device when the growth temperature of the light emitting layer is changed.
FIG. 18 is a graph showing the relationship between the growth interruption time after growth of the barrier layer and the light emission intensity of the device.
FIG. 19 is a diagram showing the relationship between the growth interruption time after the well layer growth and the light emission intensity of the device.
[Explanation of symbols]
101 ... Board
102 ... Step
103 ... Growth nucleus
201 ... substrate
202 ... step
203 ... Growth nucleus
401 ... Board
402: GaN film as a buffer layer
403 ... n-type GaN
404: n-type Al0.15Ga0.85N film
405 ... GaN film
406 ... active layer
407 ... AlGaN film
408 ... p-type GaN film
409 ... p-type Al0.15Ga0.85N film
410 ... p-type GaN contact layer
411 ... Insulating film
412a ... p-type electrode
412b ... n-type electrode
501: Growth interruption period
502 ... Growth period of the barrier layer
503 ... well layer growth period
504 ... Growth period of n-type GaN
505 ... Growth period of p-type GaN
506: Growth period of the sublimation preventing layer
701: Sapphire (0001) substrate
702 ... GaN buffer layer
703 ... n-type GaN contact layer
704 ... InGaN active layer
705 ... p-type AlGaN protective layer
706... P-type GaN contact layer
707 ... p-type electrode
708 ... n-type electrode
801: Sapphire substrate
802 ... GaN buffer layer
803 ... n-type contact layer
804 ... n-type cladding layer
805 ... Active layer
806 ... p-type evaporation prevention layer
807 ... p-type cladding layer
808 ... p-type contact layer
809 ... Current confinement layer
810 ... p-type electrode
811 ... n-type electrode

Claims (6)

In a method for manufacturing a nitride-based compound semiconductor light-emitting element, in which a nitride-based compound semiconductor laminate having an active layer sandwiched between layers having different conductivity types is vapor-phase grown on a sapphire substrate,
Nitriding characterized in that the crystal orientation of the sapphire substrate surface is inclined in the range of 0.05 ° or more and 0.2 ° or less in the <11-20> direction or <1-100> direction from the <0001> direction. Manufacturing method of physical compound semiconductor light emitting device. The active layer is formed of one or more well layers and barrier layers,
2. The method of manufacturing a nitride-based compound semiconductor light-emitting element according to claim 1, further comprising a step of providing a growth interruption for a predetermined time after formation of one or both of the well layer and the barrier layer. The method for producing a nitride-based compound semiconductor light-emitting device according to claim 2, wherein the growth interruption time after the growth of the barrier layer is 1 second or more and 60 minutes or less. The method for producing a nitride-based compound semiconductor light-emitting device according to claim 2, wherein the growth interruption time after the well layer growth is 1 second or more and 60 minutes or less. 5. The method for producing a nitride-based compound semiconductor light-emitting element according to claim 2, wherein a carrier gas mainly containing nitrogen is allowed to flow when the growth is interrupted. 5. The method for producing a nitride-based compound semiconductor light-emitting element according to claim 2, wherein a carrier gas mainly containing nitrogen and a group V source gas are allowed to flow when the growth is interrupted.

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