JP4822608B2 - Nitride-based semiconductor light-emitting device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nitride semiconductor light emitting device and a method for manufacturing the same, and more particularly to a nitride semiconductor light emitting device including a quantum well structure active layer made of a nitride semiconductor containing In and Ga and a method for manufacturing the same.
[0002]
[Prior art]
A nitride semiconductor (GaInAlN) is used as a semiconductor material of a semiconductor laser element (LD) or a light emitting diode (LED), which is a semiconductor light emitting element having an emission wavelength in the ultraviolet to green wavelength region. This semiconductor laser element using a nitride-based semiconductor is described in, for example, Technical Digest of International Workshop on Nitride Semiconductors (IWN2000) WA2-1. A cross-sectional view of a semiconductor laser device using a nitride-based semiconductor is shown in FIG. In FIG. 11, 101 is a sapphire substrate having a (0001) c plane, 102 is a GaN layer, 103 is an n-GaN contact layer, and 104 is n-Al. _0.08 Ga _0.92 N cladding layer, 105 n-GaN guide layer, 106 In _0.10 Ga _0.90 N quantum well layer and In _0.02 Ga _0.98 Multiple quantum well structure active layer composed of N barrier layer, 107 is p-Al _0.16 Ga _0.84 N layer, 108 is a p-GaN guide layer, 109 is p-Al _0.15 Ga _0.85 A p-type cladding layer in which N and GaN are alternately laminated, 110 is a p-GaN contact layer, 111 is a p-side electrode, 112 is an n-side electrode, and 113 is a current confinement SiO ₂ It is a membrane. Here, the GaN layer 102 is formed in a stripe shape having a width of 2 μm with a period of 12 μm. In addition, the multiple quantum well structure active layer 106 has an Innm thickness of 3.5 nm. _0.10 Ga _0.90 N quantum well layer and 7.0 nm thick In _0.02 Ga _0.98 It is composed of three pairs of N barrier layers, and quantum well layers and barrier layers are alternately formed.
[0003]
In this conventional manufacturing method, a metal organic chemical vapor deposition method (MOCVD method) is used to form a nitride-based semiconductor. First, after forming the GaN layer 102 on the sapphire substrate 101, the GaN layer 102 is processed into a stripe shape, and a semiconductor laser element structure from the n-GaN contact layer 103 to the p-GaN contact layer 110 is laminated thereon. Yes.
[0004]
Further, in this conventional example, the p-type cladding layer 109 and the p-GaN contact layer 110 are formed in a ridge stripe in order to confine the injection current. As a result, the stripe-shaped region into which current is injected becomes the active region. After that, the sapphire substrate 101 is thinned by polishing and then the cleave technique is used to form the resonator end face.
[0005]
However, the nitride-based semiconductor laser device of this conventional example has a problem that the characteristics are rapidly deteriorated by continuous current injection. To put this semiconductor laser device into practical use, the reliability of the device can be improved. It was an important issue. As a cause of this rapid deterioration, it is considered that defects existing in the nitride-based semiconductor material used in the active layer proliferate by current injection, and attempts have been made to reduce these defects.
[0006]
For example, in Japanese Patent Laid-Open No. 2000-156348, in order to obtain an active layer having a flat surface and few defects, the surface orientation of the surface of a sapphire substrate used as a substrate for forming a semiconductor laser device structure is 0.3 degrees from the c plane. There is shown a technique in which a semiconductor laser element structure is stacked on an inclined surface at an off angle in the range of 0.5 degrees or less.
[0007]
In Japanese Patent Laid-Open No. 2000-223743, for the same purpose, a gallium nitride substrate is used as a substrate for forming a semiconductor laser element structure, and the surface orientation of the surface is in the range of 0.03 to 10 degrees from the c-plane. A technique is shown in which a semiconductor laser device structure is stacked thereon by inclining at an off angle.
[0008]
On the other hand, apart from the technology for reducing these defects, mixed crystal materials having a spatially uniform composition due to the phase separation that occurs as a result of the presence of immiscible regions in mixed semiconductor materials of nitride-based semiconductors. It is known that fluctuations in the composition occur. In particular, InGaN, which is often used as an active layer of a nitride-based semiconductor light-emitting device, has a spatial variation in In composition due to phase separation. Therefore, in the InGaN quantum well structure active layer, a dot-like region having a high In composition is present. It is formed. Since the size of this dot is very small, it is considered to function as a quantum dot.
[0009]
For example, Japanese Laid-Open Patent Publication No. 10-14502 discloses a technique for forming an InGaN quantum well structure active layer after forming irregularities having a trigonometric waveform on the surface of a nitride-based semiconductor layer that forms an InGaN active layer. ing. In the InGaN quantum well structure active layer formed with the uneven shape in this way, the concave region has a higher In composition than the convex region, and quantum dots are formed. As a result, the threshold current value of laser oscillation can be reduced with a zero-dimensional quantum dot as compared with the case where a two-dimensional quantum well structure is used for the active layer.
[0010]
In addition, a light-emitting diode using a nitride-based semiconductor is also manufactured using an InGaN quantum well structure active layer, similarly to the semiconductor laser element.
[0011]
However, the conventional semiconductor light emitting device using the nitride semiconductor has the following problems. First, in a semiconductor laser device using a nitride semiconductor, the surface of the substrate for forming the semiconductor laser device structure is inclined at a slight off angle within 10 degrees or less from the c-plane as in the conventional example. Even if the semiconductor laser device structure is laminated thereon, the characteristics are deteriorated, and it is difficult to obtain a nitride semiconductor laser device having sufficiently improved reliability.
[0012]
Furthermore, in the conventional semiconductor laser device using the nitride semiconductor, since fluctuations in the In composition caused by phase separation of the InGaN active layer exist at random, the energy spread of the optical gain resulting from this In composition fluctuation Therefore, there is a problem that a sufficiently high optical gain cannot be obtained at the oscillation wavelength, and the oscillation threshold current value increases.
[0013]
On the other hand, in a semiconductor laser device having an InGaN quantum well structure active layer formed with a conventional concavo-convex shape, quantum dots are formed by this concavo-convex structure, but all the sizes of the quantum dots are made uniform. I can't. Therefore, due to the variation in the size, the energy gain of the optical gain is spread, and in this case, there is a problem that the oscillation threshold current value cannot be reduced.
[0014]
Furthermore, since the InGaN quantum well structure active layer is used in the light emitting diode using a nitride semiconductor as well as the semiconductor laser element using the nitride semiconductor, the influence of fluctuations in the In composition caused by phase separation. Appears in the characteristics. That is, in this active layer, the In composition is not uniform and spatial fluctuations occur. Therefore, electrons and holes that enter the active layer by current injection are first recombined in a region where the In composition is large, and the amount of injected current increases. It expands to a region with a small In composition and recombines. That is, there is a problem that the peak value of the emission wavelength is greatly blue-shifted as current is injected. This means that when the light emitting diode is used as a pixel of a full color display, the hue changes due to the injected current. Such fluctuation of the In composition caused by phase separation is particularly noticeable in the quantum well structure of a nitride-based semiconductor material containing In and Ga. Therefore, in a semiconductor light emitting device using this quantum well structure as an active layer, this problem Need to be resolved.
[0015]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and solves the above-described problems in nitride semiconductor laser elements, and has a low oscillation threshold current value and improved reliability. And it aims at providing the manufacturing method.
[0016]
As a result of investigating the cause of the deterioration of characteristics in a semiconductor laser device using a nitride-based semiconductor, the present inventor has found that spatial fluctuations in the In composition caused by phase separation cause local lattice distortion and increase the number of defects. I found it promoting.
[0017]
Therefore, by suppressing the fluctuation of the In composition, the oscillation threshold current value of the nitride-based semiconductor laser element can be reduced and the reliability thereof can be improved. Further, in the nitride-based semiconductor light-emitting diode, the amount of blue shift due to current injection can be reduced by reducing the fluctuation of the In composition.
[0018]
Further, as a result of the study by the present inventors, the spatial fluctuation of the In composition in the quantum well structure made of a nitride semiconductor containing In and Ga is caused by the non-uniform composition caused by phase separation and the In atom or Ga atom. It was found that two factors of competing generation of the composition due to the diffusion of the material occur in competition.
[0019]
Therefore, in order to reduce the influence of the composition non-uniformity due to the phase separation in this quantum well structure, the effect of the composition homogenization by diffusion may be increased. In order to increase this diffusion effect, it is conceivable to increase the diffusion coefficient by making the atoms move easily. For this purpose, it is necessary to increase the temperature of crystal growth. However, when the growth temperature is increased in this way, problems such as separation of In atoms from the growth surface occur, and the number of defects is greatly increased.
[0020]
Therefore, in contrast to this, the present inventor does not move In atoms and Ga atoms isotropically within the crystal growth plane, and suppresses movement in one direction and does not suppress in the opposite direction. As a result, it was obtained as a new finding that the effect of diffusion during crystal growth can be greatly increased even if the diffusion coefficient is the same. This is because by limiting the movement of atoms to only one direction, the diffusion is effectively promoted and the effect of homogenizing the composition is increased compared to the case where the atoms can move isotropically. .
[0021]
[Means for Solving the Problems]
In view of these points, the nitride-based semiconductor light-emitting device according to the present invention is constituted by the following inventions. That is, the nitride semiconductor light emitting device according to the present invention is sandwiched between at least one of a cladding layer and a guide layer made of a nitride semiconductor on a substrate, and made of a nitride semiconductor containing In and Ga. In a nitride-based semiconductor light emitting device having a quantum well structure active layer, the quantum well structure active layer suppresses surface movement of In atoms and Ga atoms during crystal growth in one direction within the quantum well plane. At the same time, it is characterized by being formed by crystal growth that is not suppressed in the opposite direction.
[0022]
The quantum well structure active layer may be formed in contact with a wurtzite nitride semiconductor layer having a surface having an inclination angle within a range of 15 degrees or more and 60 degrees or less from the (0001) c plane. It is.
[0023]
The substrate may be a wurtzite gallium nitride substrate whose main surface is a surface having an inclination angle in a range of 15 degrees to 60 degrees from the (0001) c plane.
[0024]
Further, the quantum well structure active layer is formed in contact with a nitride semiconductor layer having an uneven surface composed of a periodic structure of two types of stripe-shaped planes, and only one of the two types of stripe-shaped planes is formed. It is possible to intersect the substrate surface substantially perpendicularly at an angle in the range of 70 degrees to 110 degrees.
[0025]
In addition, the two types of stripe-like planes forming the irregularities on the surface of the nitride semiconductor layer have a plane width with respect to the direction forming the periodic structure of 10 nm or more in the plane perpendicular to the substrate surface. On one plane, it can be 200 nm or less.
[0026]
The method for manufacturing a nitride-based semiconductor light-emitting device according to the present invention suppresses surface movement of In atoms and Ga atoms during crystal growth in one direction in the quantum well plane and not in the opposite direction. And a step of forming a quantum well structure active layer made of a nitride semiconductor containing In and Ga by crystal growth.
[0027]
And forming a quantum well structure active layer in contact with a nitride semiconductor layer having a wurtzite structure having a surface having an inclination angle in the range of 15 degrees to 60 degrees from the (0001) c plane. Is possible.
[0028]
A step of forming a nitride semiconductor layer on a gallium nitride substrate having a wurtzite structure whose main surface is a surface having an inclination angle within a range of 15 degrees to 60 degrees from the (0001) c plane; A step of forming the quantum well structure active layer in contact with the physical semiconductor layer.
[0029]
Further, a step of forming a nitride semiconductor layer on the substrate, and irregularities formed of a periodic structure of two types of stripe-like planes on the surface of the nitride semiconductor layer, only one of the two types of planes And forming the quantum well structure active layer in contact with the nitride semiconductor layer, and forming the quantum well structure active layer in contact with the nitride semiconductor layer at an angle in the range of 70 degrees to 110 degrees. It is possible.
[0030]
In addition, two types of stripe-like planes that form irregularities on the surface of the nitride semiconductor layer have a plane width with respect to the direction forming the periodic structure of 10 nm or more in a plane that intersects the substrate surface substantially perpendicularly, It is possible to have a process formed to be 200 nm or less on the other plane.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 is a cross-sectional view showing a nitride-based semiconductor laser device according to the first embodiment of the present invention. In FIG. 1, 1 is an n-GaN substrate having a wurtzite structure whose principal surface is a plane having an inclination angle of 28 degrees from the (0001) c plane, 2 is an n-GaN layer, and 3 is n-In. _0.1 Ga _0.9 N crack prevention layer, 4 is n-Al _0.1 Ga _0.9 Nn-type cladding layer, 5 is an n-GaN guide layer, 6 is a two-layer In _0.15 Ga _0.85 N quantum well layer and three layers of In _0.03 Ga _0.97 Multiple quantum well structure active layer composed of N barrier layer, 7 is Al _0.2 Ga _0.8 N evaporation prevention layer, 8 is p-GaN guide layer, 9 is p-Al _0.1 Ga _0.9 Np-type first cladding layer, 10 is p-In _0.03 Ga _0.97 N etch stop layer, 11 is p-Al _0.1 Ga _0.9 Np-type second cladding layer, 12 is a p-GaN p-type contact layer, 13 is a p-side electrode, 14 is an n-side electrode, and 15 is SiO for current confinement ₂ It is an insulating film.
[0032]
Next, a method for manufacturing the nitride-based semiconductor laser device will be described with reference to FIG. In the following description, the case where the MOCVD method (metal organic vapor phase epitaxy) is used is shown, but any growth method capable of epitaxially growing a nitride-based semiconductor may be used, such as MBE (molecular beam epitaxy) or HVPE (hydride). Other vapor phase growth methods such as vapor phase growth method can also be used.
[0033]
First, trimethylgallium (TMG) and ammonia are placed on an n-GaN substrate 1 having a thickness of 28 μm from the (0001) c plane and having a main surface as a main surface, which is installed in a predetermined growth furnace. (NH _Three ) And silane gas (SiH) _Four ) Is used as a raw material, and a Si-doped n-GaN layer 2 having a thickness of 3 μm is grown at a growth temperature of 1050 ° C.
[0034]
Next, the growth temperature is lowered to 750 ° C., and TMG and NH _Three And SiH _Four , And trimethylindium (TMI) as a raw material, and a Si-doped n-In having a thickness of 0.1 μm _0.1 Ga _0.9 The N crack prevention layer 3 is grown.
[0035]
Next, the growth temperature is again increased to 1050 ° C., and TMG and NH _Three And SiH _Four And trimethylaluminum (TMA) as a raw material, and a Si-doped n-Al having a thickness of 1.0 μm _0.1 Ga _0.9 An Nn-type cladding layer 4 is grown.
[0036]
Subsequently, the TMA is removed from the raw material, and the Si-doped n-GaN guide layer 5 having a thickness of 0.1 μm is grown with the growth temperature kept at 1050 ° C.
[0037]
In this embodiment, the n-GaN guide layer 5 has a wurtzite structure as a result of using the n-GaN substrate 1 having a wurtzite structure whose principal surface is a plane having an inclination angle of 28 degrees from the (0001) c plane. The surface is a surface having an inclination angle of 28 degrees from the (0001) c plane.
[0038]
Thereafter, the growth temperature is again lowered to 750 ° C., and TMG and NH _Three And TMI as raw materials, on the n-GaN guide layer 5, In _0.03 Ga _0.97 N barrier layer (thickness 5 nm), In _0.15 Ga _0.85 N quantum well layer (thickness 3 nm), In _0.03 Ga _0.97 N barrier layer (thickness 5 nm), In _0.15 Ga _0.85 N quantum well layer (thickness 3 nm), In _0.03 Ga _0.97 By sequentially growing N barrier layers (thickness 5 nm), multiple quantum well structure active layers (total thickness 21 nm) 6 are formed. Continue with TMG, TMA and NH _Three Is used as a raw material, and the growth temperature remains at 750 ° C. and the thickness is 10 nm. _0.2 Ga _0.8 N evaporation prevention layer 7 is grown.
[0039]
Next, the growth temperature is again increased to 1050 ° C., and TMG and NH _Three , And cyclopentadienyl magnesium (Cp ₂ A Mg-doped p-GaN guide layer 8 having a thickness of 0.1 μm is grown using Mg) as a raw material.
[0040]
Subsequently, TMA was added to the raw material, and the growth temperature remained at 1050 ° C. and the Mg-doped p-Al having a thickness of 0.3 μm. _0.1 Ga _0.9 An Np-type first cladding layer 9 is grown.
[0041]
Next, the growth temperature is lowered to 750 ° C., and TMG and NH _Three And Cp ₂ Mg-doped p-In with a thickness of 20 nm using Mg and TMI as raw materials _0.03 Ga _0.97 N etch stop layer 10 is grown.
[0042]
Next, the growth temperature is again increased to 1050 ° C., and TMG and NH _Three And Cp ₂ Mg-doped p-Al with a thickness of 0.8 μm using Mg and TMA as raw materials _0.1 Ga _0.9 An Np-type second cladding layer 11 is grown.
[0043]
Subsequently, TMA is removed from the raw material, and the Mg-doped p-GaN p-type contact layer 12 having a thickness of 0.1 μm is grown with the growth temperature kept at 1050 ° C. to complete a nitride-based epitaxial wafer.
[0044]
Thereafter, the wafer is annealed in a nitrogen gas atmosphere at 800 ° C. to reduce the resistance of the Mg-doped p-type layer.
[0045]
Subsequently, the p-GaN p-type contact layer 12 and the p-Al are formed on the outermost surface of the p-GaN p-type contact layer 12 using a normal photolithography and dry etching technique so as to form a ridge structure in a stripe shape having a width of 2 μm. _0.1 Ga _0.9 The Np type second cladding layer 11 is etched. At this time, the etching depth is p-In. _0.03 Ga _0.97 When the N etch stop layer 10 is reached, In atoms appear on the etching surface. Therefore, it is preferable to control the etching depth accurately by stopping the etching when the In atoms are detected by elemental analysis. is there. The etch stop layer 10 may be an InGaN ternary mixed crystal or an InGaAlN quaternary mixed crystal having another In composition, as long as atoms other than Al atoms and Ga atoms can be detected and etching can be stopped.
[0046]
Subsequently, 200 nm thick SiO2 is formed on the side surface of the ridge and the surface of the p-type layer other than the ridge. ₂ The insulating film 15 is formed as a current blocking layer, and this SiO ₂ A p-side electrode 13 made of nickel and gold is formed on the surfaces of the insulating film 15 and the p-GaN p-type contact layer 12.
[0047]
Further, the back surface of the n-GaN substrate 1 of this wafer is polished by a normal polishing technique so that the thickness of the wafer is 30 μm, and an n-side electrode 14 made of titanium and aluminum is formed on the back surface of the n-GaN substrate 1. A nitride semiconductor laser device wafer is completed.
[0048]
Thereafter, the wafer is cleaved in a direction perpendicular to the ridge stripe to form a laser resonator end face, and a laser resonator is formed in a direction parallel to the ridge stripe. Here, the length of the resonator is 500 μm. Furthermore, SiO2 is formed on the end face of the resonator. ₂ And TiO ₂ Λ / 4 dielectric multilayer reflective films in which three layers are alternately stacked are formed, and the reflectance of the resonator end face is set to 60%.
[0049]
Subsequently, the laser element is divided into individual laser chips. Then, the n-side electrode 14 of each chip is bonded and mounted on the stem, and the p-side electrode 13 and the lead terminal are connected by wire bonding to complete the nitride-based semiconductor laser device.
[0050]
The nitride semiconductor laser device thus fabricated had an oscillation wavelength of 410 nm and an oscillation threshold current of 40 mA, and good laser characteristics were obtained. In addition, the device characteristics were not deteriorated, and the reliability was greatly improved. A nitride-based semiconductor laser device having such a low oscillation threshold current value and high reliability is obtained by suppressing surface movement during crystal growth of In atoms and Ga atoms in one direction in the quantum well plane. This is because the multi-quantum well structure active layer 6 made of InGaN is formed by crystal growth that is not suppressed in the opposite direction, and the spatial fluctuation of the In composition is suppressed.
[0051]
FIG. 2 is a schematic diagram showing a cross section during growth of the multiple quantum well structure active layer 6 made of InGaN in the present embodiment. In this embodiment, as a result of using the n-GaN substrate 1 having a wurtzite structure whose main surface is a plane having an inclination angle of 28 degrees from the (0001) c plane, the n-GaN guide layer 5 also has a wurtzite structure. The surface is a surface having an inclination angle of 28 degrees from the (0001) c plane. As shown in FIG. 2, the surface of the nitride semiconductor inclined from the (0001) c-plane has a terrace portion having the c-plane as a surface and a step portion having a step corresponding to one atomic layer in the c-axis direction. It has the surface shape of the periodic structure which consists of.
[0052]
The surface of the n-GaN guide layer 5 in this embodiment has a step-like step size of 0.52 nm for one atomic layer in the c-axis direction, and is perpendicular to the c-plane forming the terrace portion and the surface. Since the angle formed with the direction is 28 degrees, the width of the terrace portion is 0.98 nm. When an InGaN quantum well structure is grown on a surface having such a step structure, the movement of In atoms and Ga atoms attached to the surface from the gas phase is free in the direction of arrow A in FIG. However, in the direction of arrow B, the movement is suppressed because it is necessary to overcome the step of one atomic layer. This limits the movement of atoms only in the direction indicated by arrow A. Therefore, compared to the case where it can move isotropically, diffusion is effectively promoted and the effect of uniformizing the composition is increased. ing. As a result, the effect of diffusion during crystal growth could be greatly increased. As a result, the spatial In composition fluctuation in the multiple quantum well structure active layer 6 made of InGaN was significantly improved, and a nitride-based semiconductor laser device having a low oscillation threshold current value and high reliability was obtained.
[0053]
In the present embodiment, the n-GaN substrate 1 having a wurtzite structure whose main surface is a plane having an inclination angle of 28 degrees from the (0001) c plane is used as the substrate, but the inclination angle is not limited to this embodiment. If the tilt angle is 15 degrees or more and 60 degrees or less, a nitride-based semiconductor laser device having characteristics equivalent to those of the present embodiment can be obtained.
[0054]
FIG. 3 shows the tilt angle dependence of the oscillation threshold current value of a nitride-based semiconductor laser device fabricated in the same manner as this embodiment except for the tilt angle of the substrate. As can be seen from this figure, when the inclination angle is less than 15 degrees, the width of the c-plane constituting the terrace portion is widened, so the effect of suppressing the movement in the direction of arrow B in FIG. Spatial fluctuations increase. On the other hand, when the inclination angle is larger than 60 degrees, the width of the c-plane constituting the terrace portion is narrowed, so that the movement of atoms is also suppressed in the direction of arrow A. As a result, the effect of limiting the movement of atoms to only one direction is lost, and the spatial fluctuation of the In composition is also increased.
[0055]
In the present embodiment, as a result of using the n-GaN substrate 1 having a wurtzite structure whose main surface is a plane having an inclination angle of 28 degrees from the (0001) c plane as a substrate, the n-GaN guide layer 5 also has a wurtzite structure. However, the semiconductor material of the substrate is not particularly limited to GaN and the multiple quantum well structure active layer 6 made of InGaN. However, it may be formed so as to be in contact with the nitride semiconductor layer having a wurtzite structure having a surface having an inclination angle in the range of 15 degrees to 60 degrees from the (0001) c plane. Therefore, it may be a substrate made of a semiconductor material having another wurtzite structure such as a SiC substrate. However, in a sapphire substrate often used as a substrate of a nitride semiconductor light emitting device, in order to reduce the lattice constant difference with the nitride semiconductor layer, a nitride semiconductor layer is formed after forming a low-temperature buffer layer in contact with the substrate surface. However, when this low-temperature buffer layer is formed, the c-axis of the nitride semiconductor layer is formed perpendicularly to the substrate surface regardless of the plane orientation of the sapphire substrate surface. It becomes difficult to form a contact with a nitride semiconductor layer having a wurtzite structure having a surface having an inclination angle in the range of 15 degrees to 60 degrees from the c-plane.
[0056]
As in the present embodiment, the c-axis of the nitride semiconductor layer and the c-axis of the substrate are made parallel to form a stepped step and a terrace portion on the surface of the nitride-based semiconductor layer, and an InGaN quantum layer is formed thereon. In order to form a well structure active layer, a GaN substrate that can be stacked without forming a low-temperature buffer layer and has a good lattice constant is most preferable.
[0057]
In addition to the wurtzite structure, a zinc blend structure is also conceivable as the crystal structure of the substrate. However, the nitride-based semiconductor material is more thermally stable and has fewer defects. It is preferable to use a substrate.
[0058]
The energy gap between the n-GaN guide layer 5 and the p-GaN guide layer 8 is that of the quantum well layer constituting the multiple quantum well structure active layer 6, and the n-type cladding layer 4 or the p-type cladding layer 9. Other materials such as InGaN ternary mixed crystal, AlGaN ternary mixed crystal, and InGaAlN quaternary mixed crystal may be used as long as the material has a value between these energy gaps.
[0059]
Further, it is not necessary to dope the donor or acceptor over the entire guide layer, only a part of the multiple quantum well structure active layer 6 side may be undoped, and further the entire guide layer may be undoped. In this case, there is an advantage that the number of carriers present in the guide layer is reduced, light absorption by free carriers is reduced, and the oscillation threshold current can be further reduced.
[0060]
Two layers of In constituting the multiple quantum well structure active layer 6 _0.15 Ga _0.85 N quantum well layer and three layers of In _0.03 Ga _0.97 The composition of the N barrier layer may be set according to the required laser oscillation wavelength. If it is desired to increase the oscillation wavelength, the In composition of the quantum well layer should be increased, and if it is desired to be shortened, the In composition of the quantum well layer should be decreased. To do.
[0061]
Further, the quantum well layer and the barrier layer may be a quaternary or higher mixed crystal semiconductor containing a small amount of other elements in the InGaN ternary mixed crystal. Furthermore, the barrier layer may simply be GaN. Further, the number of quantum well layers and barrier layers is not limited to this embodiment, and other numbers may be used, or a single quantum well structure active layer may be used.
[0062]
Furthermore, the current blocking layer is SiO. ₂ Not only the insulating film 15 but also other dielectric insulating films such as SiN, or semiconductor materials having n-type conductivity and semi-insulating properties can be used.
[0063]
Further, the stripe structure for forming the active region is not limited to the ridge structure as in the present embodiment, but after forming a so-called buried structure or a current confinement layer in which etching is performed up to the n-type layer when forming the ridge. Other stripe structures such as a so-called internal current confinement structure in which the current confinement layer is etched only in a region where current is injected may be used.
[0064]
(Second Embodiment)
FIG. 4 is a sectional view showing a nitride-based semiconductor light-emitting diode according to the second embodiment of the present invention. In this figure, 21 is an n-GaN substrate having a wurtzite structure whose main surface is a plane having an inclination angle of 40 degrees from the (0001) c plane, 22 is an n-GaN layer, and 23 is In. _0.30 Ga _0.70 N quantum well structure active layer, 24 is Al _0.2 Ga _0.8 An N evaporation preventing layer, 25 is a p-GaN layer, 26 is a p-side transparent electrode, 27 is a p-side pad electrode, and 28 is an n-side electrode.
[0065]
Next, a method for fabricating the nitride semiconductor light emitting diode will be described with reference to FIG. In the following description, the case where the MOCVD method (metal organic vapor phase epitaxy) is used is shown, but any growth method capable of epitaxially growing a nitride-based semiconductor may be used, such as MBE (molecular beam epitaxy) or HVPE (hydride). Other vapor phase growth methods such as vapor phase growth method can also be used.
[0066]
First, TMG, NH is placed on an n-GaN substrate 21 having a thickness of 40 degrees from the (0001) c plane and having a tilt angle of 40 degrees as a main surface. _Three And SiH _Four As a raw material, a Si-doped n-GaN layer 22 having a thickness of 3 μm is grown at a growth temperature of 1050 ° C.
[0067]
In this embodiment, the n-GaN layer 22 has a wurtzite structure as a result of using the n-GaN substrate 21 having a wurtzite structure whose main surface is a plane having an inclination angle of 40 degrees from the (0001) c plane as the substrate. The surface is a surface having an inclination angle of 40 degrees from the (0001) c plane.
[0068]
Thereafter, the growth temperature is lowered to 750 ° C., and TMG and NH _Three And TMI as raw materials on the n-GaN layer 22 with a thickness of 3 nm. _0.30 Ga _0.70 An N quantum well structure active layer 23 is formed. Continue with TMG, TMA and NH _Three Is used as a raw material, and the growth temperature remains at 750 ° C. and the thickness is 10 nm. _0.2 Ga _0.8 An N evaporation prevention layer 24 is grown.
[0069]
Next, the growth temperature is again increased to 1050 ° C., and TMG and NH _Three , And Cp ₂ Using Mg as a raw material, a 0.5 μm-thick Mg-doped p-GaN layer 25 is grown to complete a nitride-based epitaxial wafer. Thereafter, the wafer is annealed in a nitrogen gas atmosphere at 800 ° C. to reduce the resistance of the Mg-doped p-type layer.
[0070]
Subsequently, a p-side transparent electrode 26 made of nickel and gold is formed on the entire surface of the p-GaN layer 25, and a p-side pad electrode 27 made of gold is formed on a part of the p-side transparent electrode. Further, the back surface of the n-GaN substrate 21 of this wafer is polished by a normal polishing technique so that the thickness of the wafer is 50 μm, and an n-side electrode 28 made of titanium and aluminum is formed on the back surface of the n-GaN substrate 21. A nitride semiconductor light emitting diode wafer is completed.
[0071]
Thereafter, the light emitting diode is divided into individual chips in a square shape. Then, the n-side electrode 28 of each chip is bonded and mounted on the stem, and the p-side pad electrode 27 and the lead terminal are connected by wire bonding to complete the nitride semiconductor light emitting diode.
[0072]
The nitride-based semiconductor light-emitting diode fabricated in this way had an emission wavelength of 470 nm and an optical output of 3 mW when a current of 20 mA was injected, and good device characteristics were obtained. In addition, the amount of blue shift due to current injection was reduced, and the amount of blue shift due to current injection up to 60 mA was 2 nm compared with 8 nm. The nitride-based semiconductor light-emitting diode with a reduced blue shift is obtained in this way by suppressing surface movement during crystal growth of In atoms and Ga atoms in one direction in the quantum well plane and vice versa. This is because the InGaN quantum well structure active layer 23 is formed by crystal growth that is not suppressed in the direction, and the spatial fluctuation of the In composition is suppressed.
[0073]
In the present embodiment, the n-GaN substrate 21 having a wurtzite structure having a main surface with a tilt angle of 40 degrees from the (0001) c plane is used as the substrate, but the tilt angle is not limited to this embodiment. If the inclination angle is 15 degrees or more and 60 degrees or less, a nitride-based semiconductor light-emitting diode having characteristics equivalent to those of the present embodiment can be obtained.
[0074]
In the present embodiment, as a result of using the n-GaN substrate 21 having a wurtzite structure whose main surface is a surface having an inclination angle of 40 degrees from the (0001) c-plane as the substrate, the n-GaN layer 22 also has a wurtzite structure. The surface of the substrate is a plane having an inclination angle of 40 degrees from the (0001) c plane, but the semiconductor material of the substrate is not particularly limited to GaN, and the InGaN quantum well structure active layer 23 is ( It may be formed in contact with a nitride semiconductor layer having a wurtzite structure having a surface having an inclination angle in the range of 15 degrees to 60 degrees from the (0001) c-plane. Therefore, it may be a substrate made of a semiconductor material having another wurtzite structure, such as a SiC substrate.
[0075]
Further, In constituting the quantum well structure active layer 23 _0.30 Ga _0.70 The composition of the N quantum well layer may be set according to the required emission wavelength. If it is desired to increase the emission wavelength, the In composition of the quantum well layer should be increased, and if it is desired to be shorter, the In composition of the quantum well layer should be decreased. To do.
[0076]
FIG. 5 shows the emission wavelength dependence of the blue shift amount of a nitride-based semiconductor light-emitting diode fabricated in the same manner as in this embodiment except for the In composition of the quantum well structure active layer 23.
[0077]
As a comparative example, the blue shift amount in a conventional nitride semiconductor light emitting diode using a wurtzite n-GaN substrate having a (0001) c plane as a main surface is also shown. As can be seen from FIG. 5, even if the In composition is changed, the effect of reducing the blue shift amount is obtained in all the wavelength regions from blue to green, and the blue shift amount in the conventional nitride semiconductor light emitting diode is reduced. It is reduced to about one third.
[0078]
(Third embodiment)
FIG. 6 is a cross-sectional view showing a nitride-based semiconductor laser device according to the third embodiment of the present invention. In FIG. 6, 31 is a sapphire substrate having a c-plane as a surface, 32 is a GaN buffer layer, 33 is an n-GaN n-type contact layer, and 34 is n-In. _0.1 Ga _0.9 N crack prevention layer, 35 is n-Al _0.1 Ga _0.9 Nn-type cladding layer, 36 is an n-GaN guide layer, and 37 is a two-layer In layer _0.15 Ga _0.85 N quantum well layer and three layers of In _0.03 Ga _0.97 Multiple quantum well structure active layer composed of N barrier layer, 38 is Al _0.2 Ga _0.8 N evaporation prevention layer, 39 is p-GaN guide layer, 40 is p-Al _0.1 Ga _0.9 Np-type first cladding layer 41 is p-In _0.03 Ga _0.97 N etch stop layer, 42 is p-Al _0.1 Ga _0.9 Np-type second cladding layer, 43 is a p-GaN p-type contact layer, 44 is a p-side electrode, 45 is an n-side electrode, 46 is SiO for current confinement ₂ It is an insulating film.
[0079]
In the present invention, the GaN buffer layer 32 may be made of another material such as AlN or AlGaN ternary mixed crystal as long as it can epitaxially grow a nitride-based semiconductor thereon.
[0080]
Next, a method for manufacturing the nitride-based semiconductor laser device will be described with reference to FIG. 6, FIG. 7, and FIG. In the following description, the case where the MOCVD method (metal organic vapor phase epitaxy) is used is shown, but any growth method capable of epitaxially growing a nitride-based semiconductor may be used, such as MBE (molecular beam epitaxy) or HVPE (hydride). Other vapor phase growth methods such as vapor phase growth method can also be used.
[0081]
First, TMG and NH are placed on a 350 μm-thick sapphire substrate 31 having a c-plane as a surface and placed in a predetermined growth furnace. _Three As a raw material, the GaN buffer layer 32 is grown to 35 nm at a growth temperature of 550 ° C.
[0082]
Next, the growth temperature is increased to 1050 ° C., and TMG and NH _Three And SiH _Four As a raw material, a Si-doped n-GaN n-type contact layer 33 having a thickness of 3 μm is grown. Next, the growth temperature is lowered to 750 ° C., and TMG and NH _Three And SiH _Four , And TMI as a raw material, and a Si-doped n-In having a thickness of 0.1 μm _0.1 Ga _0.9 The N crack prevention layer 34 is grown.
[0083]
Next, the growth temperature is again increased to 1050 ° C., and TMG and NH _Three And SiH _Four , And TMA as a raw material, and a 1.0 μm thick Si-doped n-Al _0.1 Ga _0.9 An Nn-type cladding layer 35 is grown. Subsequently, TMA is removed from the raw material, and the Si-doped n-GaN guide layer 36 having a thickness of 0.1 μm is grown while the growth temperature remains at 1050 ° C.
[0084]
After completing the above crystal growth, the epitaxial wafer is once taken out from the growth furnace, and a resist mask as shown in the sectional view of FIG. 8A is obtained by a photolithography technique using a photolithography mask as shown in FIG. 47 is formed on the surface of the n-GaN guide layer 36. At this time, the period of the photomask having a periodic structure in the direction of arrow A in FIG. 7 is 150 nm, and a finer mask pattern within one period is finer than the resolution of the photolithography technique. Therefore, the resist pattern is not formed and the transmittance of light from the mask is increased, so that a resist mask 47 having a cross section as shown in FIG. 8A is formed.
[0085]
As described above, the resist mask 47 has a surface having irregularities formed of a periodic structure of two types of stripe-like planes, and only one of the two types of planes intersects the substrate surface perpendicularly at an angle of 90. Further, when the resist mask 47 and the n-GaN guide layer 36 are collectively etched on the entire surface of the wafer by a normal dry etching technique, the shape of the resist mask 47 is reflected, as shown in FIG. A periodic structure having a simple cross section is formed on the surface of the n-GaN guide layer 36. This surface has an uneven surface composed of a periodic structure of two types of stripe-like planes, and only one of the two types of planes intersects the substrate surface perpendicularly at an angle of 90 degrees.
[0086]
In the present embodiment, the width of the plane with respect to the direction of the arrow A forming the periodic structure is 20 nm on the plane perpendicular to the substrate surface and 150 nm on the other plane. That is, steps of 20 nm are formed with a period of 150 nm.
[0087]
Thereafter, this epitaxial wafer is again set in the growth furnace, the growth temperature is set to 750 ° C., and TMG and NH _Three And TMI as raw materials, In _0.03 Ga _0.97 N barrier layer (thickness 5 nm), In _0.15 Ga _0.85 N quantum well layer (thickness 3 nm), In _0.03 Ga _0.97 N barrier layer (thickness 5 nm), In _0.15 Ga _0.85 N quantum well layer (thickness 3 nm), In _0.03 Ga _0.97 By sequentially growing N barrier layers (thickness 5 nm), multiple quantum well structure active layers (total thickness 21 nm) 37 are formed. Continue with TMG, TMA and NH _Three Is used as a raw material, and the growth temperature remains at 750 ° C. and the thickness is 10 nm. _0.2 Ga _0.8 N evaporation prevention layer 38 is grown. At this time, when forming the multiple quantum well structure active layer 37 made of InGaN, In atoms and Ga atoms moving in the direction of arrow A shown in FIG. In the direction, the movement is restrained due to the step formed perpendicular to the substrate surface. This limits the movement of atoms only in the direction indicated by the arrow A. Therefore, compared to the case where the atoms can move isotropically, the diffusion is promoted and the effect of homogenizing the composition is increased. As a result, the effect of diffusion during crystal growth can be significantly increased, and the spatial fluctuation of the In composition can be reduced.
[0088]
Next, the growth temperature is again increased to 1050 ° C., and TMG and NH _Three , And Cp ₂ An Mg-doped p-GaN guide layer 39 having a thickness of 0.1 μm is grown using Mg as a raw material. Subsequently, TMA was added to the raw material, and the growth temperature remained at 1050 ° C., and the Mg-doped p-Al having a thickness of 0.2 μm. _0.1 Ga _0.9 An Np-type first cladding layer 40 is grown.
[0089]
Next, the growth temperature is lowered to 750 ° C., and TMG and NH _Three And Cp ₂ Mg-doped p-In with a thickness of 20 nm using Mg and TMI as raw materials _0.03 Ga _0.97 N etch stop layer 41 is grown.
[0090]
Next, the growth temperature is again increased to 1050 ° C., and TMG and NH _Three And Cp ₂ Mg-doped p-Al with a thickness of 0.8 μm using Mg and TMA as raw materials _0.1 Ga _0.9 An Np-type second cladding layer 42 is grown. Subsequently, TMA is removed from the raw material, and a Mg-doped p-GaN p-type contact layer 43 having a thickness of 0.1 μm is grown with the growth temperature kept at 1050 ° C. to complete a nitride-based epitaxial wafer. Thereafter, the wafer is annealed in a nitrogen gas atmosphere at 800 ° C. to reduce the resistance of the Mg-doped p-type layer.
[0091]
Subsequently, the mesa structure is formed by performing etching until the n-GaN n-type contact layer 33 is exposed from the outermost surface of the p-GaN p-type contact layer 43 in a stripe shape having a width of 200 μm using normal photolithography and dry etching technology. Make it. Thereafter, using the same photolithography and dry etching techniques, the p-GaN p-type contact layer 43 and p-Al are formed on the outermost surface of the p-GaN p-type contact layer 43 so as to form a ridge structure in a stripe shape having a width of 2 μm. _0.1 Ga _0.9 The Np-type second cladding layer 42 is etched. At this time, the etching depth is p-In. _0.03 Ga _0.97 When the N etch stop layer 41 is reached, In atoms appear on the etching surface, and when the In atoms are detected by elemental analysis, the etching is stopped and the etching depth can be accurately controlled.
[0092]
Subsequently, 200 nm thick SiO2 is formed on the side surface of the ridge and the surface of the p-type layer other than the ridge. ₂ The insulating film 46 is formed as a current blocking layer. Furthermore, this SiO ₂ A p-side electrode 44 made of nickel and gold is formed on the surfaces of the insulating film 46 and the p-GaN p-type contact layer 43, and an n-side electrode 45 made of titanium and aluminum is formed on the surface of the n-GaN n-type contact layer 33 exposed by etching. To complete a nitride-based semiconductor laser device wafer.
[0093]
Thereafter, the back surface of the sapphire substrate 31 of this wafer is polished by a normal polishing technique so that the thickness of the wafer is 50 μm, and this wafer is cleaved in a direction perpendicular to the ridge stripe to form a laser resonator end face. A laser resonator is formed in a direction parallel to the ridge stripe. Here, the length of the resonator is 500 μm. Furthermore, SiO2 is formed on the end face of the resonator. ₂ And TiO ₂ Λ / 4 dielectric multilayer reflective films in which three layers are alternately stacked are formed, and the reflectance of the resonator end face is set to 60%.
[0094]
Subsequently, the laser element is divided into individual laser chips. Then, each chip is mounted on a stem with the sapphire substrate 31 facing down, and each electrode and a lead terminal are connected by wire bonding to complete a nitride semiconductor laser element.
[0095]
The nitride semiconductor laser device thus fabricated had an oscillation wavelength of 410 nm and an oscillation threshold current of 40 mA, and good laser characteristics were obtained. In addition, the device characteristics were not deteriorated, and the reliability was greatly improved. A nitride-based semiconductor laser device having such a low oscillation threshold current value and high reliability is obtained by suppressing surface movement during crystal growth of In atoms and Ga atoms in one direction in the quantum well plane. This is because the multiple quantum well structure active layer 37 made of InGaN is formed by crystal growth that is not suppressed in the opposite direction to suppress the spatial fluctuation of the In composition.
[0096]
In the present embodiment, the surface of the n-GaN guide layer 36 has an uneven surface composed of a periodic structure of two types of stripe-like planes, and only one of the two types of planes is 90 degrees from the substrate surface. Although it intersects perpendicularly at an angle, this angle is not limited to 90 degrees, and if it is 70 degrees or more and 110 degrees or less, the effect of facilitating movement of In atoms and Ga atoms on the surface only in one direction Is obtained.
[0097]
In the present embodiment, the width of the plane with respect to the direction of arrow A forming the periodic structure is 20 nm on the plane perpendicular to the substrate surface and 150 nm on the other plane. That is, a step of 20 nm is formed with a period of 150 nm, but the value of these widths is not limited to this embodiment, and is 10 nm or more on the plane perpendicular to the substrate surface and 200 nm or less on the other plane. If so, the same effect can be obtained.
[0098]
In FIG. 9, the oscillation threshold current value of the nitride-based semiconductor laser device manufactured in the same manner as in the present embodiment except that the widths of the two types of planes are changed with respect to the width of the plane perpendicular to the substrate surface. Indicates dependency.
[0099]
As can be seen from FIG. 9, when the width of the plane perpendicular to the substrate surface is 10 nm or more and the width of the other plane is 200 nm or less, the surface movement during crystal growth of In atoms and Ga atoms is quantum. It can be seen that a nitride-based semiconductor laser device having a low oscillation threshold current value can be obtained because an effect of suppressing in one direction in the well plane and not suppressing in the opposite direction is sufficiently obtained.
[0100]
When the width of the plane perpendicular to the substrate surface is 10 nm or less, the atoms can move over the step, and when the width of the other plane is 200 nm or more, the effect of the step is lost. Therefore, at this time, since the effect of facilitating the movement of In atoms and Ga atoms in only one direction within the quantum well plane cannot be obtained, the oscillation threshold current value increases.
[0101]
(Fourth embodiment)
FIG. 10 is a cross-sectional view showing a nitride-based semiconductor light-emitting diode according to the fourth embodiment of the present invention. In FIG. 10, 51 is a sapphire substrate having a c-plane as a surface, 52 is a GaN buffer layer, 53 is an n-GaN n-type contact layer, and 54 is In. _0.30 Ga _0.70 N quantum well structure active layer, 55 is Al _0.2 Ga _0.8 N evaporation prevention layer, 56 is a p-GaN layer, 57 is a p-side transparent electrode, 58 is a p-side pad electrode, and 59 is an n-side electrode.
[0102]
Next, a method for manufacturing the nitride semiconductor light emitting diode will be described with reference to FIG. In the following description, the case where the MOCVD method (metal organic vapor phase epitaxy) is used is shown, but any growth method capable of epitaxially growing a nitride-based semiconductor may be used, such as MBE (molecular beam epitaxy) or HVPE (hydride). Other vapor phase growth methods such as vapor phase growth method can also be used.
[0103]
First, TMG and NH are placed on a 350 μm thick sapphire substrate 51 having a c-plane as a surface, which is installed in a predetermined growth furnace. _Three As a raw material, the GaN buffer layer 52 is grown to 35 nm at a growth temperature of 550 ° C. Next, the growth temperature is increased to 1050 ° C., and TMG and NH _Three And SiH _Four Is used as a raw material to grow a Si-doped n-GaN n-type contact layer 53 having a thickness of 3 μm.
[0104]
After completing the above crystal growth, the epitaxial wafer is once taken out of the growth furnace, and the irregularities formed of two types of periodic structures of stripe-like planes are formed on the n-GaNn similarly to the nitride-based semiconductor laser device of the third embodiment. It is formed on the surface of the mold contact layer 53. Only one of these two types of planes intersects the substrate surface perpendicularly at an angle of 90 degrees. In the present embodiment, the width of the plane with respect to the direction forming the periodic structure is 20 nm on the plane perpendicular to the substrate surface and 150 nm on the other plane.
[0105]
After that, this epitaxial wafer was again set in the growth furnace, the growth temperature was set to 750 ° C., and TMG and NH _Three And TMI as raw materials, 3 nm thick In _0.30 Ga _0.70 An N quantum well structure active layer 54 is formed. Continue with TMG, TMA and NH _Three Is used as a raw material, and the growth temperature remains at 750 ° C. and the thickness is 10 nm. _0.2 Ga _0.8 An N evaporation preventing layer 55 is grown. At this time, when the InGaN quantum well structure active layer 54 is formed, as in the third embodiment, the movement of atoms is limited to only one direction. Thus, diffusion is promoted and the effect of uniforming the composition is increased. As a result, the effect of diffusion during crystal growth can be significantly increased, and the spatial fluctuation of the In composition can be reduced.
[0106]
Next, the growth temperature is again increased to 1050 ° C., and TMG and NH _Three , And Cp ₂ A Mg-doped p-GaN layer 56 having a thickness of 0.5 μm is grown using Mg as a raw material, thereby completing a nitride-based epitaxial wafer. Thereafter, the wafer is annealed in a nitrogen gas atmosphere at 800 ° C. to reduce the resistance of the Mg-doped p-type layer.
[0107]
Subsequently, etching is performed in a stripe shape having a width of 200 μm using normal photolithography and dry etching techniques until the n-GaN n-type contact layer 53 is exposed from the outermost surface of the p-GaN layer 56 to produce a mesa structure. . Thereafter, a p-side transparent electrode 57 made of nickel and gold is formed on the entire surface of the p-GaN layer 56, and a p-side pad electrode 58 made of gold is formed on a part of the p-side transparent electrode. Further, an n-side electrode 59 made of titanium and aluminum is formed on the surface of the n-GaN n-type contact layer 53 exposed by etching to complete a nitride semiconductor light emitting diode wafer.
[0108]
Thereafter, the back surface of the sapphire substrate 51 of this wafer is polished by a normal polishing technique so that the thickness of the wafer is 50 μm, and this light emitting diode is divided into individual chips in a square shape. Then, each chip is mounted on a stem with the sapphire substrate 51 facing down, and each electrode and a lead terminal are connected by wire bonding to complete a nitride semiconductor light emitting diode.
[0109]
The nitride-based semiconductor light-emitting diode fabricated in this manner had an emission wavelength of 470 nm and an optical output of 3 mW when a current of 20 mA was injected, and good device characteristics were obtained as in the second embodiment. In addition, the amount of blue shift due to current injection was reduced, and the amount of blue shift due to current injection up to 60 mA was 2 nm compared with 8 nm.
[0110]
The nitride-based semiconductor light-emitting diode with a reduced blue shift is obtained in this way by suppressing surface movement during crystal growth of In atoms and Ga atoms in one direction in the quantum well plane and vice versa. This is because the InGaN quantum well structure active layer 54 is formed by crystal growth that is not suppressed in the direction to suppress the spatial fluctuation of the In composition.
[0111]
In the present embodiment, the surface of the n-GaN n-type contact layer 53 in contact with the InGaN quantum well structure active layer 54 has an uneven surface having a periodic structure of two types of stripe-like planes. Only one of them intersects the substrate surface perpendicularly at an angle of 90 degrees, but this angle is not limited to 90 degrees, and movement of In atoms or Ga atoms on the surface is not limited to 70 degrees or more and 110 degrees or less. An effect of facilitating movement only in one direction can be obtained.
[0112]
In the present embodiment, the width of the plane with respect to the direction forming the periodic structure is 20 nm on the plane perpendicular to the substrate surface and 150 nm on the other plane. That is, a step of 20 nm is formed with a period of 150 nm, but the value of these widths is not limited to this embodiment, and is 10 nm or more on the plane perpendicular to the substrate surface and 200 nm or less on the other plane. If so, the same effect can be obtained.
[0113]
Further, the In constituting the quantum well structure active layer 54 _0.30 Ga _0.70 The composition of the N quantum well layer may be set according to the required emission wavelength. If it is desired to increase the emission wavelength, the In composition of the quantum well layer should be increased, and if it is desired to be shorter, the In composition of the quantum well layer should be decreased. To do. Thus, even when a nitride-based semiconductor light emitting device is manufactured in the blue to green wavelength region by changing the In composition, the effect of reducing the blue shift amount is obtained. This was reduced to about one third of the amount of blue shift in a physical semiconductor light emitting diode.
[0114]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0115]
【The invention's effect】
As described above, in the nitride-based semiconductor light-emitting device according to the present invention, the quantum well structure activity composed of a nitride semiconductor comprising In and Ga sandwiched between at least one of a cladding layer and a guide layer made of a nitride semiconductor. A unique configuration in which the layer is formed by crystal growth that suppresses surface movement during crystal growth of In atoms and Ga atoms in one direction in the quantum well plane and not in the opposite direction. Is adopted. As a result, it has been obtained as a new finding that the effect of diffusion during crystal growth can be greatly increased even if the diffusion coefficient is the same. This is considered to be due to the fact that by limiting the movement of atoms to only one direction, diffusion is promoted and the effect of homogenizing the composition is increased as compared with the case where it can move isotropically.
[0116]
As a result, a spatial fluctuation of the In composition in the quantum well structure active layer was reduced, and a nitride-based semiconductor laser device having a low oscillation threshold current value and high reliability was obtained. Furthermore, by reducing the spatial fluctuation of the In composition in the quantum well structure active layer, a nitride-based semiconductor light-emitting diode in which the amount of blue shift due to current injection is reduced in all the wavelength regions from blue to green was also obtained. .
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a nitride-based semiconductor laser device according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram showing a cross section during growth of a multiple quantum well structure active layer 6 made of InGaN in the nitride-based semiconductor laser device according to the first embodiment of the present invention.
FIG. 3 is a diagram showing a substrate tilt angle dependency of an oscillation threshold current value in the nitride-based semiconductor laser device according to the first embodiment of the present invention.
FIG. 4 is a cross-sectional view showing a nitride-based semiconductor light-emitting diode according to a second embodiment of the present invention.
FIG. 5 is a graph showing the emission wavelength dependence of the blue shift amount in the nitride-based semiconductor light-emitting diode according to the second embodiment of the present invention and a conventional nitride-based semiconductor light-emitting diode as a comparative example.
FIG. 6 is a cross-sectional view showing a nitride-based semiconductor laser device according to a third embodiment of the present invention.
FIG. 7 is a diagram showing a pattern of a photomask for photolithography used when producing a nitride-based semiconductor laser device according to a third embodiment of the present invention.
FIGS. 8A and 8B are diagrams illustrating a manufacturing process of a multiple quantum well structure active layer 37 made of InGaN used in a nitride-based semiconductor laser device according to a third embodiment of the present invention. Both b) and (c) are cross-sectional views of the manufacturing process.
FIG. 9 shows the dependence of the oscillation threshold current value on the width of the plane perpendicular to the substrate surface and the width of the other plane in the nitride-based semiconductor laser device according to the third embodiment of the present invention. FIG.
FIG. 10 is a cross-sectional view showing a nitride-based semiconductor light-emitting diode according to a fourth embodiment of the present invention.
FIG. 11 is a cross-sectional view of a conventional semiconductor laser device using a nitride semiconductor.
[Explanation of symbols]
1,21 n-GaN substrate, 2,22 n-GaN layer, 3,34 n-In _0.1 Ga _0.9 N crack prevention layer, 4,35 n-Al _0.1 Ga _0.9 Nn-type cladding layer, 5,36 n-GaN guide layer, 6,37 quantum well structure active layer, 7, 24, 38, 55 Al _0.2 Ga _0.8 N evaporation prevention layer, 8,39 p-GaN guide layer, 9,40 p-Al _0.1 Ga _0.9 Np-type first cladding layer, 10,41 p-In _0.03 Ga _0.97 N etch stop layer, 11,42 p-Al _0.1 Ga _0.9 Np-type second cladding layer, 12, 43 p-GaN p-type contact layer, 13, 44 p-side electrode, 14, 28, 45, 59 n-side electrode, 15, 46 SiO ₂ Insulating film, 23,54 In _0.30 Ga _0.70 N quantum well structure active layer, 25, 56 p-GaN layer, 26, 57p side transparent electrode, 27, 58 p side pad electrode, 31, 51 sapphire substrate, 32, 52 GaN buffer layer, 33, 53 n-GaNn type Contact layer, 47 resist mask.

Claims (6)

The substrate is sandwiched between at least one of a cladding layer and a guide layer made of a nitride semiconductor,
Having a quantum well structure active layer made of a nitride semiconductor containing In and Ga,
In nitride-based semiconductor light-emitting devices,
The substrate is a sapphire substrate having a (0001) c-plane as a surface;
The quantum well structure active layer is in contact with a nitride semiconductor layer having an uneven surface composed of two types of periodic structures of stripe-like planes, and the surface movement of In atoms and Ga atoms during crystal growth It is formed by crystal growth that suppresses in one direction and does not suppress in the opposite direction ,
Only one of the two types of stripe-shaped planes intersects the substrate surface substantially perpendicularly at an angle in the range of 70 degrees to 110 degrees,
The two types of stripe-like planes forming the irregularities on the surface of the nitride semiconductor layer have a plane width with respect to the direction forming the periodic structure of 10 nm or more in the plane perpendicular to the substrate surface. nitride-based semiconductor light-emitting device characterized der Rukoto below 200nm in a plan.   The quantum well structure active layer is formed in contact with a nitride semiconductor layer having a wurtzite structure having a surface having an inclination angle within a range of 15 degrees to 60 degrees from the (0001) c plane. The nitride-based semiconductor light-emitting device according to claim 1.   3. The gallium nitride substrate having a wurtzite structure whose principal surface is a surface having an inclination angle within a range of 15 degrees or more and 60 degrees or less from a (0001) c plane. Nitride-based semiconductor light emitting device. Forming a nitride semiconductor layer on a sapphire substrate having a (0001) c-plane as a surface;
The surface of the nitride semiconductor layer has irregularities formed of a periodic structure of two types of stripe-like planes, and only one of the two types of planes is approximately at an angle within the range of 70 degrees to 110 degrees with the substrate surface. Forming to intersect perpendicularly;
In crystal growth in which surface movement of In atoms and Ga atoms during crystal growth on the nitride semiconductor layer is suppressed in one direction in the quantum well plane and not suppressed in the opposite direction. and a quantum well structure active layer made of nitride semiconductor containing Ga have a step which is formed in contact with the nitride compound semiconductor layer,
The two kinds of stripe-like planes forming the irregularities on the surface of the nitride semiconductor layer have a plane width with respect to the direction forming the periodic structure of 10 nm or more in the plane that intersects the substrate surface almost perpendicularly. A method for manufacturing a nitride-based semiconductor light-emitting device, characterized in that the nitride-based semiconductor light-emitting device is formed to have a thickness of 200 nm or less in the plane of the substrate. Forming the quantum well structure active layer in contact with a nitride semiconductor layer having a wurtzite structure having a surface having an inclination angle within a range of 15 degrees to 60 degrees from the (0001) c-plane. The method for producing a nitride-based semiconductor light-emitting device according to claim 4 . Forming a nitride semiconductor layer on a gallium nitride substrate having a wurtzite structure whose main surface is a surface having an inclination angle within a range of 15 degrees to 60 degrees from the (0001) c-plane;
Forming the quantum well structure active layer in contact with the nitride semiconductor layer;
The method for producing a nitride-based semiconductor light-emitting device according to claim 4, comprising :

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