JP2002270970A - Nitride semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase yield by suppressing cracking. SOLUTION: In a nitride semiconductor light emitting element 1, a periodic land/groove structure is formed between an InGaN multiple quantum well active layer 107 and a (0001) face GaN substrate 101. An n-type AlGaN clad layer 105 is regrown on the land/groove structure through a low temperature buffer layer 104 and an element structure of the InGaN multiple quantum well active layer 107 is formed such that a ridge stripe is arranged directly above a groove part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-luminance nitride semiconductor light emitting device.

[0002]

2. Description of the Related Art Conventionally, nitride semiconductors have been researched and developed as light-emitting devices and high-power devices. For example, in the case of a light-emitting device, the composition of each layer constituting the device structure is adjusted according to the intended use. As a result, a wide range of light emission from blue to orange can be obtained, and a blue light emitting diode or a green light emitting diode has been put to practical use by utilizing its characteristics. Further, the development of a blue-violet semiconductor laser is underway.

When manufacturing such a light emitting device, G
aN or sapphire, SiC, ZnO, CaO, Mn
An element structure in which a nitride semiconductor crystal is grown by homoepitaxial growth or heteroepitaxial growth using O or the like as a substrate and a plurality of thin films are stacked has been manufactured.

However, because of heteroepitaxial growth, defects such as dislocations are generated from the interface between the substrate and the epitaxially grown layer due to lattice mismatch or difference in thermal expansion coefficient existing between the substrate and the epitaxially grown film. In the case of an element propagating in the growth direction and, for example, on a sapphire C-plane substrate, the density of dislocations that penetrates the active layer and appears on the surface reaches 10 ¹⁰ cm ⁻³ . Dislocations existing at a high density become non-emission centers when current is injected into the dislocations, causing an increase in ineffective currents that do not contribute to light emission. In addition, dislocation movement and proliferation occur due to heat generation, and the life of the element is shortened.

In order to prevent the propagation of dislocation generated from the interface between the substrate and the epitaxially grown film, for example, Japanese Patent Application Laid-Open
0-124500, “Gallium nitride based semiconductor device”
Attempts to solve dislocation propagation at least between the active layer and the sapphire substrate by forming an interface having periodic projections by regrowth and utilizing lateral growth from the sidewalls of the projections. . That is, JP-A-2000-12450
In the gallium nitride-based semiconductor device disclosed in Japanese Patent Publication No. 0, a method is known in which defects generated from the interface between the substrate and the epitaxial growth layer are propagated in the lateral direction, and the density of defects penetrating the active layer and reaching above the element is reduced. It has been disclosed.

[0006]

In the above-mentioned conventional configuration,
Deterioration of device characteristics due to defects can be prevented to some extent by regrowth with an interface having periodic protrusions. However, in the technology for controlling the direction of propagation of defects, lattice mismatch with the substrate or In addition, it is not possible to prevent cracks due to stress caused by a difference in thermal expansion coefficient.

In addition, the light confinement layer of the nitride semiconductor laser device usually contains Al, and there is a relatively large lattice mismatch between the light confinement layer and the other layers, and cracks occur similarly to the interface with the substrate. Cause. When cracks occur, there is a problem that the yield is greatly reduced in an element forming step such as photolithography or etching after the element structure is laminated.

In consideration of mass production, for example, in a laser device, the optical cavity length is 500 μm or less and the current injection region width is 2 μm.
When the thickness is not more than μm, the number of cracks existing in an area of 500 μm × 2 μm must be one or less. That is, 1
Unless the crack density is lower than 0 ⁵ cm ^-2, the yield in production decreases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a nitride semiconductor light emitting device capable of suppressing the occurrence of cracks and improving the yield.

[0010]

Apparatus of the present invention According to an aspect of generally a nitride semiconductor crystal can be epitaxially grown on the substrate type _{In x Ga y Al 1- (x} + y) N (0 ≦ x ≦ 1,0 ≦ x + y ≦
A nitride semiconductor light emitting device having a structure in which a plurality of nitride semiconductors represented by 1) are stacked, wherein a periodic land / groove is provided at least between an active layer of the device and a substrate; An element structure is provided on a land / groove via a low-temperature buffer layer, whereby the object is achieved.

Preferably, in the nitride semiconductor light emitting device of the present invention, the land / groove direction is <11-2.
0> direction.

Preferably, in the nitride semiconductor light emitting device of the present invention, the land / groove direction is <1-1.
00> direction.

Still preferably, in a nitride semiconductor light emitting device according to the present invention, a cross-sectional shape of the groove portion is any one of a rectangular shape, a forward mesa, an inverted mesa, and a triangle.

Preferably, the growth temperature of the low-temperature buffer layer in the nitride semiconductor light emitting device of the present invention is 4 degrees Celsius.
It is 50 degrees or more and 700 degrees C or less.

Still preferably, in a nitride semiconductor light emitting device according to the present invention, the low temperature buffer layer has a thickness of 30 nm.
It is not less than 1 μm.

Further, preferably, in the nitride semiconductor light emitting device of the present invention, the width of the land portion is not less than 2 μm and not more than 10 μm.
m or less.

Further, preferably, in the nitride semiconductor light emitting device of the present invention, the width of the groove portion is not less than 2 μm and not more than 20 μm.
μm or less.

Further, preferably, in the nitride semiconductor light emitting device of the present invention, the depth of the groove portion is 0.5 μm or more and 5 μm or less.

Further, preferably, in the nitride semiconductor light emitting device of the present invention, any one of the ridge stripe and the electrode stripe is present immediately above the groove portion.

Further, preferably, in the nitride semiconductor light emitting device of the present invention, an element structure including an active layer is laminated thereon without completely flattening the groove.

Here, the operation of the above configuration will be described. According to the first aspect, dislocations newly generated from the interface with the substrate or from the layer containing Al are reduced, and the stress in the layer is alleviated to prevent the occurrence of cracks, thereby reducing the yield in the manufacture of the light emitting device. It can be improved. The details will be described below.

The present invention is characterized in that an element structure is sequentially stacked on a substrate by homoepitaxial growth or heteroepitaxial growth.

Further, a substrate for homoepitaxial growth, such as GaN, is generally In _x Al _y Ga
A nitride semiconductor bulk crystal represented by _{1- (x + y)} N (x ≦ 1, x + y ≦ 1) is used as a substrate for heteroepitaxial growth for crystal growth of a normal nitride semiconductor such as sapphire or SiC. It is characterized in that a crystal obtained is used.

Further, when a nitride semiconductor bulk crystal is used, a land / groove structure is directly and periodically formed on the surface of the epitaxially grown film by general photolithography and etching, or the nitride is previously formed on the substrate. A plurality of semiconductor films are stacked, and then <11-20>
A land / groove structure is formed periodically in parallel to the <1-100> direction or the <1-100> direction, and the element structure including the active layer is regrown.

In the case of heteroepitaxial growth, a low-temperature buffer layer is deposited on a substrate such as sapphire or SiC by a normal heteroepitaxial growth technique, and then heated to a high temperature of 1000 ° C. or more in an atmosphere of hydrogen. After performing thermal cleaning and epitaxially growing a nitride semiconductor at about 1050 degrees Celsius, the nitride semiconductor is once taken out of the crystal growth apparatus, and periodically land / groove structure is parallel to the <11-20> direction or the <1-100> direction. Is formed, and the element structure including the active layer is regrown.

In all cases, the width of the land is 2 μm to 10 μm, the width of the groove is 2 μm to 20 μm, and the depth of the groove is 0.5 μm to 5 μm.

When the device structure including the active layer is regrown,
First, the general formula for absorbing stress In _x Ga _y Al
A low-temperature buffer layer represented by _{1- (x + y)} N (0 ≦ x ≦ 1, 0 ≦ x + y ≦ 1) is formed.

Here, the low temperature is 450 degrees Celsius or more and 7 degrees Celsius.
Means temperatures below 00 degrees. Above 450 degrees Celsius 7
Nitride is 00 degrees or less temperature ranges semiconductor In _x Ga _y Al
_{Since 1- (x + y)} N is amorphous or polycrystalline,
High stress absorption effect.

In order to show the effect of the present invention, for example, GaN
Using a (0001) substrate, a land / groove structure having a land / groove width of 5 μm / 10 μm and a groove depth of 3 μm is formed in a half area of the substrate area through photolithography and etching. A sample in which a GaN film was directly grown at 1050 degrees Celsius, and
The surface of a sample in which a GaN film was grown at 1050 degrees Celsius on the land / groove structure via a low-temperature buffer layer was observed with an optical microscope, and is schematically shown in FIG. GaN is used as the low-temperature buffer layer, and its thickness is 5
0 nm. FIG. 3A shows a case where GaN is directly grown without a low-temperature buffer layer, and FIG. 3B shows a case where GaN is grown via a low-temperature buffer layer. FIG.
In FIG. 3A and FIG. 3B, the left half area of each sample is grown on a flat surface without processing the substrate, and the land / groove structure is formed in the right half area. In FIG. 3, the thin line indicated by C is a copy of a crack generated in the sample. In the area on the left half of FIG. 3A, that is, when there is no low-temperature buffer layer and there is no land / groove structure, many cracks intersecting at an angle of 60 degrees occur on the entire surface of the sample. In the right half region of FIG. 3A where the groove structure is introduced, the number of cracks is reduced to about 1/3. Further, even when a low-temperature buffer layer is interposed, there is no land / groove structure in FIG.
Cracks occur in the left half area of (b). However, no crack is generated in the right half region of FIG. 3B (corresponding to claim 1 of the present invention) having a land / groove structure and further grown via a low-temperature buffer layer. In order to prevent cracks, it is necessary to reduce the stress in the growth layer, and it is ideal to completely eliminate the stress.

According to detailed investigations and studies by the present inventors,
The formation of the land / groove has two effects. That is, in the initial stage, the growth is started by inheriting the information from the land portion side wall where the stress is released, and the effect of realizing the growth in which the stress is relaxed, and the stress is reduced in the groove bottom surface by the high-speed lateral growth. The effect of this is that after being covered with the grown growth layer, a flat film grows uniformly in the thickness direction.

Further, by forming the low-temperature buffer layer on the land / groove structure, two effects are produced. That is, the presence of the low-temperature buffer layer between the substrate and the growth layer prevents the transmission of the information of the crystal lattice in which the stress at the bottom of the groove is not relaxed, and the crystal growth inherited only the information on the side of the groove. And the low-temperature buffer layer itself, which is amorphous or polycrystalline, deforms more freely than a single crystal in the growth process in the thickness direction after the bottom of the groove is covered by the lateral growth. This is a stress relaxation effect.

In the present invention, the reduction of cracks is realized by simultaneously exhibiting these four types of effects. When the low-temperature buffer layer is formed on the periodically formed land / groove structure and the element structure including the active layer is regrown, the land / groove structure may be completely buried and flattened. A recess may be left at least in part.

As a method of growing the device structure, metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MB)
E) and hydride vapor phase epitaxy (HVPE)
In general, various methods used for nitride semiconductor crystal growth can be appropriately used. However, in consideration of productivity, metal organic chemical vapor deposition (MOCVD) can be used at a lower cost and a larger substrate can be used as compared with other methods. ) Is most suitable.

The substrate is sapphire, SiC,
GaAs, spinel (MgA1 ₂ 0 _4), such as, in general it is possible to use viable materials nitride semiconductor crystal.
Even when the ridge structure provided with the p-type electrode is replaced with an electrode stripe structure, the effect of the present invention can be exhibited without any problem.

According to the present invention, the low-temperature buffer layer formed on the land / groove structure periodically formed in parallel with the <11-20> direction or the <1-100> direction can be combined with a layer below the low-temperature buffer layer. By freely deforming between the regrown layers, the stress of the regrown layer is relieved, and the occurrence of cracks is prevented. Thereby, a crack density lower than 10 ⁵ cm ^-2 can be realized, and the yield in production can be improved.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments 1 to 12 of the nitride semiconductor light emitting device of the present invention will be described with reference to the drawings. Generally, in crystal growth of a nitride semiconductor,
Sapphire, SiC, GaN, GaAs, spinel and the like are used as substrates. MOCV for crystal growth
D, MBE, HVPE, etc. In consideration of the growth rate, cost, and productivity of nitride semiconductors, sapphire or GaN is used as the substrate, and the fabrication of the device structure is performed based on the crystal quality and controllability of the thin film. In general,
It is preferable to use the MOCVD method. Hereinafter, in each of Embodiments 1 to 12, GaN or sapphire was used as the substrate, and the MOCVD method was used to fabricate the element structure. However, any other material that can grow a nitride semiconductor is generally used as the substrate. It goes without saying that there is no problem. Hereinafter, the state of regrowth when the present invention is applied will be described, and then, the manufacturing procedure and effects of a laser device including a nitride semiconductor multilayer film will be described. (Embodiment 1) Embodiment 1 is a case in which a laser element is manufactured on a GaN substrate by applying the present invention in which a low-temperature buffer layer is provided on a land / groove structure, and a ridge stripe is formed immediately above a groove portion. This is a case where the elements are arranged so as to be arranged.

FIG. 1 is a sectional view showing an example of the configuration of a laser device fabricated on a GaN substrate as a first embodiment of the nitride semiconductor light emitting device of the present invention. In FIG. 1, a nitride semiconductor light emitting device 1 has an n-type GaN film 102 having a thickness of 5 μm provided on a (0001) plane GaN substrate 101.
A low-temperature buffer layer 104 and a 5 μm regrown n-type Al _0.1 Ga _0.9 N cladding layer 105 on a land / groove structure in which a land portion 103 a and a groove portion 103 b are periodically formed on the type GaN film 102. n-type GaN optical guide layer 106, InGaN multiple quantum well active layer 107 as an active layer of the device, and AlGaN block layer 108
, P-type GaN optical guide layer 109, and p-type Al _0.1 Ga
_0.9 N cladding layer 110, p-type GaN layer 111,
Type GaN contact layer 112, insulating film 113, and p-type electrode 114 are provided in this order, and the (0001) plane Ga
An n-type electrode 115 is provided on the back side of the N substrate 101 to constitute a laser device. As described above, in the nitride semiconductor light emitting device 1, a periodic land / groove structure is formed between the InGaN multiple quantum well active layer 107 and the (0001) plane GaN substrate 101, and the land / groove structure is N-type Al through the low-temperature buffer layer 104
Regrown from the _0.1 Ga _0.9 N cladding layer 105, and the InG is grown so that the ridge stripe is disposed immediately above the groove portion.
An element structure including the aN multiple quantum well active layer 107 and the like is formed.

A method for manufacturing the nitride semiconductor light emitting device 1 will be described. Each layer constituting the element is grown by MOCVD. The element structure is such that an n-type GaN layer 102 is first formed on an n-type GaN substrate 101 by 5 μm (3 μm in FIG.
m) A film is grown, and then a land / groove structure composed of the land 103a and the groove 103b is periodically formed by photolithography and etching. On this land / groove structure, a low-temperature buffer layer 104
N-type Al _0.1 Ga _0.9 N cladding layer 105 for confining light from InGaN multiple quantum well active layer 107, n-type GaN light guide layer 106 for distributing light near the active layer, InGaN multiple quantum well active layer 107 An AlGaN block layer 10 for preventing sublimation of an active layer and preventing diffusion of impurities from a p-type layer in a device structure manufacturing process.
8, p-type GaN optical guide layer 109, p-type Al _0.1 Ga _0.9
An N clad layer 110, a p-type GaN layer 111, and a p-type GaN contact layer 112 are sequentially stacked. Further, the p-type GaN contact layer 112 on the outermost surface is processed into a ridge shape for confining light in the lateral direction, an insulating film 113 is formed in a predetermined shape by ordinary photolithography, and a p-type electrode 114 is attached thereon. . Further, the n-type electrode 115 is
1 is formed on the back surface.

Here, the state of regrowth of the n-type Al _0.1 Ga _0.9 N cladding layer 105 (FIG. 2) and the residual stress inside the grown film (FIGS. 4 and 5) will be specifically described with reference to the drawings. Will be described. Note that the principle of crack reduction, which is an effect of the present invention, is as described in FIG.

First, a specific example of a process for forming a periodic land / groove structure will be described.

FIGS. 2A and 2B show a procedure for forming a periodic land / groove structure.
(C) to FIG. 2 (e) show various groove cross-sectional shapes.
FIG. 2F is a diagram showing a cross-sectional structure after regrowth. FIG.
2A to 2F, the (0001) plane GaN substrate 1
01, a (0001) plane GaN substrate 201,
An n-type GaN cladding layer 202 as a specific example of the n-type GaN film 102, a low-temperature buffer layer 204 as a specific example of the low-temperature buffer layer 104, and the n-type Al _0.1 Ga _0.9 N cladding layer 10
As a specific example of No. 5, an n-type Al _0.1 Ga _0.9 N layer 205 is shown.

As shown in FIG. 2A, the thickness is 400 μm.
Then, the (0001) plane GaN substrate 201 having a diameter of 2 inches is cleaned by an ordinary method and set in a MOCVD apparatus. The substrate 201 is heated in an ammonia atmosphere and stabilized at 1050 degrees Celsius. After that, TMG is reduced to about 50 μmo1 / m
In and SiH ₄ gas are supplied at about 10 nmol / min to grow the n-type GaN cladding layer 202 to 5 μm. Here, the substrate 2 on which the n-type GaN clad layer 202 is formed
01 is once taken out of the MOCVD apparatus, a mask pattern 203 is formed by ordinary photolithography, a land / groove structure is formed by etching, and the mask pattern is completely removed. At this time, as an etching method, dry etching such as RIE or RIBE or wet etching such as molten KOH or an aqueous solution of KOH can be used. At this time, by setting the direction in which the land / groove is formed to be the <11-20> direction, a facet does not occur on the groove side wall at the time of etching, and sharp etching can be performed. The direction in which the land / groove is formed may be parallel to the <1-100> direction. However, when the groove is completely buried by regrowth, the <11-20> direction in which the lateral growth is easy is more preferable.

By adjusting the etching conditions, the cross-sectional shape of the groove portion is rectangular (FIG. 2B), forward mesa (FIG. 2C), reverse mesa (FIG. 2D), and triangular (FIG. 2D).
(E)). The land / groove structure has a land portion width L, a groove portion width G, and a groove portion depth d in FIG. 2B, for example.

After the formation of the land / groove structure, the substrate was set again in the MOCVD apparatus, and the temperature was raised to 500 ° C. in an ammonia atmosphere to reduce TMG to about 5 μm.
1 / min, and 0.1 mol / min of ammonia to supply the low-temperature buffer layer 204 shown in FIG.
A 0 nm film is formed.

In the first embodiment, the low-temperature buffer layer 204
As was chosen GaN, formula can be a amorphous or polycrystalline state _{In x Ga y Al 1- (x} + y) N (0 ≦
If it is a nitride semiconductor represented by x ≦ 1, 0 ≦ x + y ≦ 1), it may be used as a low-temperature buffer layer for absorbing stress.

After the formation of the low-temperature buffer layer 204, the TMG was stopped and the temperature was raised to 1050 degrees Celsius, and again TMG was supplied at about 50 μmol / min, TMA was supplied at 5.6 μmol, and SiH ₄ gas was supplied at about 10 nmol / min to 5 μm.
The n-type Al _0.1 Ga _0.9 N layer 2 shown in FIG.
Regrow 05.

Next, n-type Al _0.1 Ga _0.9 inside the groove
The state of the lateral regrowth of the N cladding layer 105 will be specifically described.

FIGS. 4A to 4D show lateral growth inside the groove during regrowth via the low-temperature buffer layer, and FIG. 4E shows the material concentration gradient inside the groove during growth. FIG.

The above n-type Al_0.1Ga_0.9Reconstruction of N layer 205
Take the sample several times during the run to check the growth
Then, as shown in FIGS. 4 (a) to 4 (d),
N-type Al from corner of bottom side_0.1Ga_0.9N clad
The regrown film 205a to be the layer 205 starts growing (FIG. 4)
(A)) and the regrown film 205a is
Film growth progresses in the lateral direction so that
4 (b)), and the regrown film 205a associates at the center of the groove.
(FIG. 4C), the growth proceeds in the vertical direction, and the land /
The groove structure is completely buried and flattened (FIG. 4)
(D)) n-type Al _0.1Ga_0.9N cladding layer 205
It turned out that.

The progress of the regrowth of the regrown film 205a as shown in FIGS. 4A to 4D was the same irrespective of the groove sectional shape. This indicates that the supply of the raw material during growth is governed by the concentration gradient on the sample surface. That is, as schematically shown in FIG. 4E, the isoconcentration lines X of the group III raw material are close to each other near the corner of the bottom surface of the groove, and the concentration gradient serving as a driving force for the diffusion of the raw material is large. , Preferentially compared to groove center and land
The group material is diffused, and the film growth proceeds from the groove corner side to the center. Isoconcentration line X depending on groove cross-sectional shape
Although the detailed shape of the film changes, the progress of film growth does not change regardless of the cross-sectional shape, because the concentration gradient at the corner of the groove bottom surface becomes large. In the case where the film growth is dominant in the lateral direction as described above, the growth layer takes over the information on the etching side surface where the stress has been alleviated and extends laterally, so that no new stress is generated. In the present invention, the reason why the land / groove structure is periodically formed is to promote the lateral growth of the regrown layer and suppress the generation of new stress during the growth.

Next, the stress distribution of various samples observed by the photoelasticity measuring device will be described.

FIGS. 5A and 5B are stress distribution diagrams with respect to cross sections of various samples. FIG. 5A shows an n-type Al _0.1 Ga _0.9 N layer 205 on a land / groove structure via a low-temperature buffer layer 204.
(B) is a sample in which the n-type Al _0.1 Ga _0.9 N layer 505A is regrown on the land / groove structure without the low-temperature buffer layer 204 for comparison, c) is a sample in which an n-type Al _0.1 Ga _0.9 N layer 505B is regrown on a planar n-type GaN layer 502 via only a low-temperature buffer layer 504 without forming a land / groove structure, and (d) is a sample. FIG. 10 is a diagram showing a sample prepared by a normal method without applying the land / groove structure and the low-temperature buffer layer 204 for comparison.

FIG. 5A shows that the density of the Al _0.1 Ga _0.9 N layer 205 at the isostress line Ya inside the regrown layer is reduced by applying the present invention, and the residual stress is relaxed. It turns out that it is. When the present invention is applied, the iso-stress line Ya from the n-type GaN layer 202 is absorbed and cut off in the GaN low-temperature buffer layer 204, and Al _0.1 Ga
It is characteristic that it does not propagate to the regrown layer of the _0.9 N layer 205. This indicates that the low-temperature buffer layer 204 formed in an amorphous state or a polycrystalline state at a low temperature has a function of absorbing a stress by freely deforming as compared with a single crystal and relaxing a regrown layer. Things. Since the residual stress was small, the crack density of the regrown layer was less than 10 ⁵ cm ⁻² .

On the other hand, as shown in FIG. 5B, the n-type Al is formed on the land / groove structure without interposing the low-temperature buffer layer 204.
_{When the 0.1} Ga _0.9 N layer 505A is directly regrown, FIG.
The n-type Al _0.1 Ga _0.9 N layer 5 is formed by applying only the low-temperature buffer layer 204 without forming the land / groove structure as shown in FIG.
5B, the land / groove structure and the low-temperature buffer layer 204 are not applied as shown in FIG. 5D, and the n-type Al _0.1 Ga _0.9 N layer 505C is directly regrown on a plane. And an n-type Al _0.1 Ga _0.9 N layer 505
In each of the regrown layers A, 504B, and 505C, a stress having a higher density (isostress lines Yb, Yc, Y
d) has occurred. In particular, it can be seen that the isostress line Yd in FIG. 5D has the highest density. This result indicates that it is important to simultaneously form the land / groove structure and apply the low-temperature buffer layer 204 for stress absorption to alleviate the stress in the regrown layer and effectively prevent the occurrence of cracks. It is shown that it is. That is, a land / groove structure having an effect of promoting lateral growth at a high speed by inheriting information on a groove side whose stress has been alleviated by etching in an early stage of regrowth, and freely deforming between the groove bottom and the regrown layer. Only when the low-temperature buffer layer 204 having the effect of absorbing stress is applied at the same time, a significant reduction in crack density can be realized.

In order to absorb the stress by the low-temperature buffer layer 204, the buffer layer 204 needs to be formed in an amorphous state or a polycrystalline state, and its forming temperature must be 450 ° C. or more and 700 ° C. or less. At a temperature lower than 450 degrees Celsius, the low-temperature buffer layer 204 does not grow because the group III raw material is not decomposed. Conversely, if the temperature is higher than 700 degrees Celsius, it becomes a single crystal, so that it becomes impossible to absorb stress. When the thickness of the low-temperature buffer layer 204 is smaller than 30 nm, it is impossible to sufficiently absorb the stress. Therefore, n-type A
cracks occur in the regrown layer of the l _0.1 Ga _0.9 N layer 205,
If the thickness is more than 1 μm, lattice information of the substrate, which is indispensable for epitaxial growth, is cut off, so that the crystal quality of the regrown layer deteriorates. Therefore, the thickness of the low-temperature buffer layer 204 must be 30 nm or more and 1 μm or less. If the conditions of the growth temperature and the layer thickness are satisfied, the low-temperature buffer layer 204
Can be arbitrarily selected.

By applying the present invention, the land width L, the groove width G and the depth d are variously changed, and the Al _0.1 Ga after regrowth is formed.
_When the crack density on the surface of the _0.9 N layer 205 was evaluated, the land width L was 2 μm or more and 10 μm or less, the groove width G was 2 μm or more and 10 μm or less, and the groove depth d was 0.5 μm or less.
The crack density was remarkably reduced when the thickness was from 5 μm to 5 μm. When the size of the land / groove structure was in the above range, the crack density was a value lower than 10 ⁵ cm ⁻² .
On the other hand, for comparison, the crack density in the case of regrowth without the land / groove structure was 5 × 10 ⁶ cm ^{−2, which} is 10 times or more, and the method of the present invention is remarkable against the decrease in crack density. It turns out that it shows an effect.

In a region where the land width L and the groove width G are smaller than 2 μm, the raw material does not easily reach the center of the land portion 103a and the center of the groove portion 103b in the early stage of regrowth, so that the tendency to generate voids becomes remarkable. Therefore, a region where threading dislocations are densely formed occurs, which is not suitable for manufacturing a light emitting element. Conversely, when the land width L and the groove width G are increased beyond 10 μm, the regrown layer 2
Since the vertical growth thickness exceeds the groove depth d before the association by the lateral growth of 05a occurs, voids are likely to occur at the center of the groove portion 103b and the land portion 103a, which is not preferable. When the groove depth d is 0.
If the depth is smaller than 5 μm, the raw material concentration gradient X at the corner of the bottom surface of the groove portion 103b decreases, and the lateral growth inside the groove becomes insufficient, so that a minute void is easily generated at the center of the groove portion 103b. Groove portion 103 deeper than 5 μm
In the case of b, the thickness of the regrown layer necessary for embedding the groove portion 103b exceeds 5 μm, and a new stress is generated in the regrown layer, so that cracks are easily generated. Therefore, the depth d of the groove portion 103b is 0.5 μm or more and 5 μm or more.
m or less. (Embodiment 2) In Embodiment 2, GaN is applied by applying the present invention in which a low-temperature buffer layer is provided on a land / groove structure.
This is a case where a laser device is manufactured on a substrate, and is a case where the device is formed such that a ridge stripe is arranged immediately above a land portion.

FIG. 6 is a sectional view showing an example of the configuration of a laser device fabricated on a GaN substrate as a second embodiment of the nitride semiconductor light emitting device of the present invention. In FIG. 6, a nitride semiconductor light emitting element 2 has a (0001) plane n-type GaN substrate 601.
An n-type GaN layer 602 is provided on the
2 and the land portion 603a and the groove portion 60
A low-temperature buffer layer 604 and an n-type Al _0.1 Ga _0.9 N cladding layer 60 are formed on the land / groove structure on which the 3b is formed.
5, an n-type GaN light guide layer 606, an InGaN multiple quantum well active layer 607 as an active layer of the device,
N block layer 608 and p-type GaN light guide layer 609
A p-type Al _0.1 Ga _0.9 N cladding layer 610;
an aN layer 611, a p-type GaN contact layer 612, an insulating film 613, and a p-type electrode 614 are provided in this order;
An n-type electrode 615 is provided on the back side of the (0001) plane n-type GaN substrate 601 to constitute a laser device. As described above, the nitride semiconductor light emitting device 2 includes the InGaN multiple quantum well active layer 607 and the (0001) plane GaN substrate 601.
And a periodic land / groove structure is formed, and the low-temperature buffer layer 60 is formed on the land / groove structure.
4, an n-type AlGaN cladding layer 605 is regrown, and an element structure including an InGaN multiple quantum well active layer 607 and the like is formed such that the ridge stripe is disposed immediately above the land. Note that each layer constituting the element is grown by MOCVD.

The first embodiment in which the ridge stripe is disposed immediately above the groove portion and the second embodiment in which the ridge stripe is disposed immediately above the land portion will be described below in comparison with the first embodiment. The manufacturing method will be described again.

The nitride semiconductor light emitting device 1 of the first embodiment
When manufacturing the element structure described above, the n-type GaN layer (102) is formed on the n-type GaN substrate 101 by 5 μm (or 3 μm).
After the film is grown, a land / groove structure including the land portion 103a and the groove portion 103b is periodically changed to <11.
It is formed by photolithography and etching so as to be parallel to the -20> direction. Specifically, the land width L is 5 μm, the groove width G is 15 μm, and the groove depth d is 3
μm. Land / groove formation direction is <11
By setting the -20> direction, a facet does not occur on the groove side wall at the time of etching, and sharp etching can be performed. The direction for forming the land / groove is <
Although it may be parallel to <1-100>, when the groove is completely buried by regrowth, it is easy to grow laterally.
20> direction is more preferable.

An amorphous or polycrystalline GaN is sequentially formed on the land / groove structure to absorb stress.
-Type AlG for confining light from the low-temperature buffer layer 104 made of InGaN and the InGaN multiple quantum well active layer 107
aN cladding layer 105, n-type GaN light guiding layer 106 for distributing light near the active layer, InGaN multiple quantum well active layer 107, sublimation prevention of the active layer during the device structure manufacturing process, and impurity diffusion from the p-type layer A to prevent
lGaN block layer 108, p-type GaN light guide layer 10
9, p-type AlGaN cladding layer 110, P-type GaN layer 1
11. P-type GaN contact layer 112 is laminated in this order.

The low-temperature buffer layer 104 must be amorphous or polycrystalline to absorb stress, and must be thick enough to transmit lattice information of the lower layer and sufficiently absorb stress. It is necessary to grow the film thickness to 30 nm or more and 1 μm at a temperature of not more than 30 degrees. In the first embodiment, the film thickness is grown to 50 nm at 500 degrees Celsius. The outermost p-type GaN layer 112 is processed into a ridge shape to confine light in the lateral direction, and the insulating film 11 is formed.
3 is formed by ordinary photolithography, and a p-type electrode 114 is attached. The ridge and the P-type electrode 114 are located immediately above the groove 103b. n-type electrode 115
Is formed on the back surface of the substrate 101. Observation of the outermost surface immediately after growing the element structure revealed that the crack density was 1
0 ⁵ cm ^-2 and drops below, it is understood that relaxation of the stress is remarkable. After the device forming process, the divided devices were mounted on a stem and laser-oscillated. The device was operated at a voltage of 4 V and an oscillation threshold current density of 500 A / cm ² .

For comparison with this, in the second embodiment, the position of the ridge in the layer structure shown in FIG.
A laser element arranged immediately above a was prepared. When manufacturing the element structure of the nitride semiconductor light emitting element 2 of Embodiment 2, first, the n-type GaN layer 6 is formed on the n-type GaN substrate 601.
02 is grown to 3 μm, and then the land portions 60 are periodically formed.
A land / groove structure composed of 3a and a groove portion 603b is formed by photolithography and etching. On the land / groove structure, a low-temperature buffer layer 6
04, an n-type AlGaN cladding layer 605 for confining light from the InGaN multiple quantum well active layer 607, an n-type GaN light guide layer 606 for distributing light near the active layer, an InGaN multiple quantum well active layer 607, element AlGaN block layer 60 for preventing sublimation of the active layer and preventing diffusion of impurities from the p-type layer in the structure manufacturing process
8, a p-type GaN optical guide layer 609, a p-type AlGaN cladding layer 610, a p-type GaN layer 611, and a p-type GaN contact layer 612 are stacked in this order. Outermost p-type GaN layer 6
12 is processed into a ridge for light confinement in the lateral direction, and an insulating film 613 is formed by ordinary photolithography.
A p-type electrode 614 is attached thereon. The ridge and the p-type electrode 614 are located immediately above the land 603a. The n-type electrode 615 is formed on the back surface of the substrate 601.

In this case, the crack density on the element surface is 10
Below ⁵ cm ^-2 , it was confirmed that the stress was sufficiently relaxed. After the device forming step, the divided devices were mounted on a stem and laser-oscillated. The device was operated at a voltage of 4 V and an oscillation threshold current density of 1.8 kA / cm ² .

Since the threshold current density was higher than that of the first embodiment where the ridge was located immediately above the groove portion, the cross section of the device was observed with a transmission electron microscope. 6), the density of dislocations existing in the current injection region under the ridge is 10 ⁴ cm ⁻² , whereas in the laser device of FIG.
The dislocation density in the current injection region was 10 ⁵ cm ^-2, which was ten times higher. This is because while the regrown layer in the groove part has a high stress relaxation effect, the land part has a large residual stress,
This is because the dislocation density has increased although the crack density has not yet reached 10 ⁵ cm ⁻² . further,
Observation of the etch pits on the element surface with the molten KOH revealed that the dislocation density was reflected in the groove 603b.
⁴ cm ^-2, clear difference between 9.5 × 10 ⁴ cm ^-2 in the land portion 603a was confirmed.

Further, even when the shape of the groove cross section is changed to a forward mesa, an inverted mesa or a triangle, the effect of relieving the stress of the regrown layer is remarkable, and the crack density on the element surface is 10 ⁵ c.
The value was below m ^-2 . Furthermore, even when the ridge structure provided with the p-type electrode is replaced with an electrode stripe structure, the effect of reducing cracks of the present invention is exhibited without any problem. (Embodiment 3) In Embodiment 3, a laser device is fabricated on a sapphire substrate by applying the present invention in which a low-temperature buffer layer is provided on a land / groove structure.

FIG. 7 is a sectional view showing the structure of a laser device fabricated on a sapphire substrate as a third embodiment of the nitride semiconductor light emitting device of the present invention. In FIG. 7, a nitride semiconductor light emitting device 3 has a (0001) plane sapphire substrate 701.
A GaN buffer layer 702 and an n-type GaN layer 70
3 is provided, and a land / groove structure composed of a land portion 704a and a groove portion 704b is periodically formed on a part of the n-type GaN layer 703.
A low-temperature buffer layer 705, an n-type Al _0.1 Ga _0.9 N cladding layer 706, an n-type GaN light guide layer 707, and an InGaN multiple quantum well active layer 708 as an active layer of the device
, An AlGaN block layer 709, a p-type GaN light guide layer 710, and a p-type Al _0.1 Ga _0.9 N cladding layer 711
, P-type GaN layer 712 and p-type GaN contact layer 7
13, an insulating film 714, and a p-type electrode 715 are provided in this order, and the n-type electrode 7 is formed on the remaining portion of the n-type GaN layer 703.
A laser element 16 is provided. As described above, the nitride semiconductor light emitting device 3 includes the InGaN multiple quantum well active layer 708 and the (0001) plane sapphire substrate 701.
And a periodic land / groove structure is formed between the low-temperature buffer layer 70 and the land / groove structure.
5, the ridge stripe is regrown from the n-type Al _0.1 Ga _0.9 N cladding layer 706, and the ridge stripe is formed in the groove portion 704b.
An element structure including an InGaN multiple quantum well active layer 708 and the like is formed just above the active layer. In the third embodiment shown in FIG. 7, an example is shown in which the ridge stripe is disposed immediately above the groove portion 704b. However, the present invention is not limited to this, and the ridge stripe is formed in the land portion 704a as shown in FIG. The element may be formed so as to be disposed directly above.

When manufacturing the nitride semiconductor light emitting device 3 having the above configuration, first, a GaN low-temperature buffer layer 702 is formed on a sapphire C-plane substrate 701 by a general growth technique (MOCVD method). n-type GaN layer 703
Is grown to a thickness of 3 μm.

Thereafter, a land / groove structure composed of a land portion 704a and a groove portion 704b is periodically formed on the n-type GaN layer 703 by photolithography and etching. The land width is 5 μm, the groove width is 15 μm,
The groove depth is 3 μm. By setting the direction of the land / groove structure to be the <11-20> direction, a facet does not occur on the groove side wall at the time of etching, and sharp etching can be performed. The direction in which the land / groove structure is formed may be parallel to the <1-100> direction. However, when the groove portion 704b is completely buried by the regrowth of the n-type Al _0.1 Ga _0.9 N cladding layer 706, the n-type The <11-20> direction in which the Al _0.1 Ga _0.9 N clad layer 706 is easy to grow in the lateral direction is more preferable.

Further, the land /
On the groove structure, a low-temperature buffer layer 70 made of amorphous or polycrystalline GaN for absorbing stress is formed.
5, an n-type AlGaN cladding layer 706 for confining light from the InGaN multiple quantum well active layer 708, an n-type GaN light guide layer 707 for distributing light near the active layer, and an InGaN multiplex Quantum well active layer 708, AlGa for preventing sublimation of the active layer during the device structure manufacturing process and for preventing impurity diffusion from the p-type layer
N block layer 709, p-type GaN optical guide layer 710, p
An AlGaN cladding layer 711, a p-type GaN layer 712, and a p-type GaN contact layer 713 are stacked in this order.

The low-temperature buffer layer 705 must be amorphous or polycrystalline in order to absorb stress, and must have a thickness in a range that transmits lattice information of the lower layer and sufficiently absorbs stress. Therefore, it is necessary to grow the film to a thickness of 30 nm or more and 1 μm at a temperature of 450 ° C. or more and 700 ° C. or less.

In the third embodiment, 50 degrees Celsius
A nm film was grown. The outermost p-type GaN layer 713 is processed into a ridge shape to confine light in the lateral direction, and an insulating film 714 is formed thereon in a predetermined shape by ordinary photolithography as shown in FIG. A p-type electrode 715 is attached. The ridge and the P-type electrode 715 are
04b.

On the other hand, the n-type electrode 716 is formed on the surface of the n-type GaN layer 703 after etching until the n-type GaN layer 703 is exposed, avoiding the ridge.

When the outermost surface was observed immediately after the device structure was grown, the crack density was less than 10 ⁵ cm ^-2 , as in Embodiment 2 using the GaN substrate 601, and lattice mismatch was observed. It can be seen that even in the case of large heteroepitaxial growth, the stress relaxation according to the present invention is remarkable.

After the device-forming step, the divided devices were mounted on a stem and laser-oscillated. The device was operated at a voltage of 4 V and an oscillation threshold current density of 2.0 kA / cm ² .

For comparison, a laser device as shown in FIG. 8 was prepared in which the ridge position was arranged immediately above the land portion 804a in the layer structure.

This element structure is a sapphire C-plane substrate 80
1 on a general growth method (MOCVD method)
First, a GaN low temperature buffer layer 802 is formed, followed by n
The type GaN layer 803 is grown to a thickness of 3 μm.

Thereafter, a land / groove structure including a land portion 804a and a groove portion 804b is periodically formed on the n-type AlGaN cladding layer 806 by photolithography and etching. The land width is 5 μm, the groove width is 15 μm, and the groove depth is 3 μm.

On this land / groove structure, the MOC
N for confining light from the low-temperature buffer layer 805 and the InGaN multiple quantum well active layer 808 by the VD method.
-Type AlGaN cladding layer 806, n-type GaN light guide layer 807 for distributing light near the active layer, InGaN
Multiple quantum well active layer 808, AlGaN block layer 809 for preventing sublimation of the active layer during the device structure manufacturing process and diffusion of impurities from the p-type layer, p-type GaN light guide layer 810, p-type AlGaN cladding layer 811 , P-type G
The aN layer 812 and the p-type GaN contact layer 813 are stacked in this order.

The outermost p-type GaN layer 813 is processed into a ridge shape to confine light in the lateral direction, and the insulating film 8
14 is formed into a predetermined shape by ordinary photolithography, and a P-type electrode 815 is further provided thereon. The ridge and the p-type electrode 815 are located immediately above the land 804a.

On the other hand, the n-type electrode 816 is formed on the surface of the n-type GaN layer 803 after etching until a part of the n-type GaN layer 803 is exposed, avoiding the ridge.

The crack density on the element surface was less than 10 ⁵ cm ⁻² , confirming that the stress was sufficiently relaxed.

After the device-forming step, the divided devices were mounted on a stem and laser-oscillated. The device was operated at a voltage of 4 V and an oscillation threshold current density of 2.1 kA / cm ² .

Since the threshold current density was higher than in the case where the ridge was located immediately above the groove portion 704b, the cross section of the element was observed with a transmission electron microscope.
In the device of FIG. 8, the dislocation density existing in the current injection region below the ridge is 6 × 10 ⁴ cm ⁻² , whereas in the laser device of FIG. 8, the dislocation density of the current injection region is 4 × 10 ⁵ cm 2.
It was about 7 times higher than ^-2 . This is because the stress relaxation effect is high in the regrown layer of the groove portion, the land portion large residual stress, crack density is 10 ⁵ cm ^- but have yet to over ^2, dislocation density is increased Because it is. Further, when the etch pits on the element surface were observed using molten KOH, the dislocation density was reflected, and the groove portions were 3 × 10 ⁴ cm ⁻² and the land portions were 3.5 × 10 ⁴ cm.
^-2 and a clear difference could be confirmed.

Further, the shape of the groove cross section is changed to a normal mesa and a reverse mesa.
Even if it is changed to either
The stress relaxation effect is remarkable, and the crack density on the element surface is
10 ^Fivecm^-2Below. Providing a p-type electrode 815
Even when the bridge structure is replaced with an electrode stripe structure,
The effect of the invention is exhibited without any problem.

The crack reducing effect shown in the third embodiment is based on the sapphire substrate (the sapphire C-plane substrate 701,
In addition to 801), other substrates, such as spinel, ZnO, and MgO, on which a nitride semiconductor can be heteroepitaxially grown are also effective. (Embodiment 4) In Embodiment 4, the low-temperature buffer layer and n
In this case, an n-type GaN layer is inserted between the AlGaN cladding layers.

FIG. 9 is a sectional view showing a configuration example of a laser device fabricated on a GaN substrate as a nitride semiconductor light emitting device according to a fourth embodiment of the present invention. In FIG. 9, a nitride semiconductor light emitting device 4 is a (0001) plane n-type GaN substrate 901.
First, an n-type GaN layer 902 is provided, and n-type Ga
After forming a land / groove structure on the N layer 902, the low-temperature buffer layer 904 and the n-type G
aN layer 905, n-type Al _0.1 Ga _0.9 N cladding layer 90
6, n-type GaN optical guide layer 907, InGaN multiple quantum well active layer 908, AlGaN block layer 909, p-type GaN optical guide layer 910, p-type Al _0.1 Ga _0.9 N cladding layer 911, p-type GaN layer 912, p-type A GaN contact layer 913, an insulating film 914, and a p-type electrode 915 are provided in this order, and an n-type electrode 916 is provided on the back surface side of the (0001) plane n-type GaN substrate 901 to constitute a laser device.

A method for manufacturing the nitride semiconductor light emitting device 4 will be described. When fabricating this laser device, the MO
First, on the n-type GaN substrate 901 by the CVD method,
An n-type GaN layer 902 is grown to a thickness of 3 μm, and thereafter, a land / groove structure including a land portion 903a and a groove portion 903b is periodically formed on the n-type GaN layer 902 by photolithography and etching. Land width 3 μm, groove width 10 μm, groove depth 2 μm
It is.

On the land / groove structure, a low-temperature buffer layer 904 made of amorphous or polycrystalline GaN, an n-type GaN layer 905, and an InGaN multiple quantum well active layer 908 are formed by MOCVD to absorb stress.
-Type AlGaN cladding layer 906 for confining light from the substrate, n-type GaN for distributing light near the active layer
Light guide layer 907, InGaN multiple quantum well active layer 90
8. AlGaN block layer 909, p-type GaN light guide layer 910, p-type AlG for preventing sublimation of the active layer and diffusion of impurities from the p-type layer in the process of fabricating the element structure.
aN cladding layer 911, p-type GaN layer 912, p-type Ga
The N contact layers 913 are stacked in this order.

The low-temperature buffer layer 904 must be amorphous or polycrystalline in order to absorb stress, and have a thickness within a range that transmits lattice information of the lower layer and sufficiently absorbs stress. Therefore, it is necessary to grow the film to a thickness of 30 nm or more and 1 μm at a temperature of 450 ° C. or more and 700 ° C. or less.

In the fourth embodiment, 50 degrees at 500 degrees Celsius
A nm film was grown. The outermost p-type GaN layer 913 is processed into a ridge shape to confine light in the lateral direction, and the insulating film 91 is formed.
4 is formed by ordinary photolithography, and a p-type electrode 915 is attached thereon. The ridge and the p-type electrode are located immediately above the groove 903b.

The n-type electrode 916 is formed on the back surface of the substrate 901.

When the outermost surface was observed immediately after the device structure was grown, the crack density was less than 10 ⁵ cm ^-2, and it was found that the stress was remarkably relaxed.

After the device-forming step, the divided devices were mounted on a stem and laser-oscillated. The device was operated at a voltage of 4 V and an oscillation threshold current density of 1.6 kA / cm ² .

The reason why the threshold current density is lower than that of the laser device shown in the second embodiment is that the n-type GaN layer 905 is inserted under the n-type AlGaN cladding layer 906 when the device structure is formed by regrowth. This is because the effective refractive index of the groove portion 903b is higher than that of the land portion 903a, and the light confinement efficiency in the lateral direction is improved.

Even when the ridge structure provided with the p-type electrode 915 is replaced with an electrode stripe structure, the effect of the present invention can be exhibited without any problem. Even when the cross-sectional shape of the groove portion 903b is changed from a rectangular shape to any one of a forward mesa, an inverted mesa, and a triangle, the stress relaxation effect of the regrown layer is remarkable, and the crack density on the element surface is 10 ⁵ cm ^−2. Was below the value. It was also confirmed that the lateral light confinement efficiency by inserting the n-type GaN layer 905 under the n-type AlGaN cladding layer 906 was improved regardless of the cross-sectional shape. (Embodiment 5) In Embodiment 5, the (0001) plane Ga
When manufacturing a laser device as a nitride semiconductor light emitting device 5 on an N substrate, first, a land /
After forming the groove structure, through the low-temperature buffer layer,
An example of an element structure including a quantum well active layer, which is regrown from an n-type GaN layer and formed into an element such that a ridge stripe is disposed immediately above a groove portion, will be described with reference to FIG. Also in this case, an n-type GaN layer is inserted between the low-temperature buffer layer and the n-type AlGaN cladding layer as in the fourth embodiment.

Each layer constituting the nitride semiconductor light emitting device 5 is grown by MOCVD. The element structure is shown in FIG.
As shown in FIG. 7, first, a land / groove structure including a land portion 1002a and a groove portion 1002b is formed on an n-type GaN substrate 1001 by photolithography and etching. Land width is 3μm, groove width is 10μ
m, the groove depth is 2 μm.

On this land / groove structure, the MOC
In order to absorb stress by the VD method, a low-temperature buffer layer 100 made of amorphous or polycrystalline GaN is used.
3. n-type GaN layer 1004, n-type AlGa for confining light from InGaN multiple quantum well active layer 1007
N-cladding layer 1005, n-type GaN light guide layer 1006 for distributing light near the active layer, InGaN multiple quantum well active layer 1007, prevention of sublimation of the active layer during the device structure manufacturing process, and impurity diffusion from the p-type layer AlGaN block layer 1008, p-type GaN light guide layer 1009, p-type AlGaN cladding layer 1010, p-type G
The aN layer 1011 and the p-type GaN contact layer 1012 are stacked in this order.

The low-temperature buffer layer 1003 must be amorphous or polycrystalline in order to absorb stress, and have a thickness within a range that transmits lattice information of the lower layer and sufficiently absorbs stress. Therefore, it is necessary to grow the film to a thickness of 30 nm or more and 1 μm at a temperature of 450 ° C. or more and 700 ° C. or less.

In the fifth embodiment, 50 degrees Celsius
A nm film was grown. The outermost p-type GaN layer 1012 is processed into a ridge shape to confine light in the lateral direction, and an insulating film 1013 is formed by ordinary photolithography.
The mold electrode 1014 is attached.

The ridge and the p-type electrode 1014 are located immediately above the groove 1002b. The n-type electrode 1015 is formed on the back surface of the substrate 1001.

Observation of the outermost surface immediately after the growth of the element structure revealed that the crack density was lower than 10 ⁵ cm ⁻² , and that the stress was remarkably relaxed. After the element formation process, the divided elements were mounted on a stem and laser-oscillated. The voltage was 4 V, and the oscillation threshold current density was 1.6.
It operated at kA / cm ² .

The reason why the threshold current density was lower than that of the device shown in the second embodiment is that the n-type GaN layer 1004 was inserted under the n-type AlGaN cladding layer 1005 when the device structure was formed by regrowth. This is because the effective refractive index of the groove portion 1002b is higher than that of the land portion 1002a, and the light confinement efficiency in the lateral direction is improved.

Even when the ridge structure provided with the p-type electrode 1014 is replaced with an electrode stripe structure, the effect of reducing cracks of the present invention can be exhibited without any problem.

Further, even when the groove cross section is changed from a rectangular shape to any one of a forward mesa, an inverted mesa and a triangle,
The stress relaxation effect of the regrown layer was remarkable, and the crack density on the element surface was less than 10 ⁵ cm ⁻² . Also,
It was also confirmed that the light confinement efficiency in the lateral direction by inserting n-type GaN under the n-type AlGaN cladding layer was improved irrespective of the difference in cross-sectional shape. (Embodiment 6) In this embodiment 6, the (0001) plane Ga
When manufacturing a laser device as a nitride semiconductor light emitting device 6 on an N substrate, first, an n-type GaN layer is grown, a land / groove structure is formed thereon, and the thickness is fixed.
The element structure including the quantum well active layer is re-grown from the n-type GaN layer via the low-temperature buffer layer formed at a predetermined film growth temperature (450 ° C. or more and 700 ° C. or less), and the ridge stripe is formed in the groove portion. An example in which elements are arranged directly above will be described with reference to FIGS. 9 and 11. FIG.

Each layer constituting the nitride semiconductor light emitting element 6 is grown by MOCVD. As the element structure,
As shown in FIG. 9, first, on an n-type GaN substrate 901,
An n-type GaN layer 902 is grown to 3 μm, and then a land / groove structure is periodically formed on the n-type GaN layer 902 by photolithography and etching. Land width 3 μm, groove width 10 μm, groove depth 2 μm
It is.

On the land / groove structure, MOCVD
Low-temperature buffer layer 904 of amorphous or polycrystalline GaN to absorb stress
-Type GaN layer 905, InGaN multiple quantum well active layer 90
N-type AlGaN cladding layer 906 for confining light from the substrate 8 and n-type Ga for distributing light near the active layer.
N light guide layer 907, InGaN multiple quantum well active layer 9
08, prevention of sublimation of the active layer in the process of fabricating the element structure, and p
AlGaN block layer 909, p-type GaN light guide layer 910, and p-type Al
GaN cladding layer 911, p-type GaN layer 912, p-type G
The aN contact layers 913 are stacked in this order.

The low-temperature buffer layer 904 must be amorphous or polycrystalline in order to absorb stress, and must have such a thickness that the lattice information of the lower layer is transmitted and the stress is sufficiently absorbed. Therefore, it is necessary to grow the film to a thickness of 30 nm or more and 1 μm at a temperature of 450 ° C. or more and 700 ° C. or less.

The outermost p-type GaN layer 913 is processed into a ridge to confine light in the lateral direction, an insulating film 914 is formed by ordinary photolithography, and a p-type electrode 915 is attached thereon. The ridge and the p-type electrode 915 are located immediately above the groove 903b. The n-type electrode 916 is formed on the back surface of the substrate 901.

Here, in order to examine the relationship between the crack density on the element surface and the threshold current density with respect to the growth temperature of the low-temperature buffer layer 904, the growth temperature of the low-temperature buffer layer 904 was changed from 400 ° C. to 800 ° C. A device was created.

The film growth time was fixed so that the thickness of the low-temperature buffer layer 904 was 50 nm regardless of the temperature.

FIG. 11 shows the result of plotting the crack density on the element surface and the threshold current density with respect to the film growth temperature of the low-temperature buffer layer 904. In FIG. 11, the symbol ● indicates the crack density, and the symbol Δ indicates the threshold current density. The allowable limit of the crack density (10 ⁵ cm ^-2 ) is indicated by a dashed line. The crack density is almost constant in the range of 500 to 700 degrees Celsius and does not change, and tends to gradually decrease with increasing temperature in the range of 450 to 500 degrees Celsius. At a temperature lower than 450 degrees Celsius and a temperature higher than 700 degrees Celsius, a sharp increase in crack density is observed.

When a cross section of a sample in which the low-temperature buffer layer 904 was grown at a temperature lower than 450 degrees Celsius was observed with a transmission electron microscope, the low-temperature buffer layer 904 hardly adhered or formed discrete islands. I found out. This is because, because the film growth temperature is low, the group III raw material is not sufficiently decomposed, and the uniform low temperature buffer layer 904 having a layered structure is formed.
Is not obtained.

Conversely, at a temperature higher than 700 degrees Celsius, although a low-temperature buffer layer 904 is formed, it was found from measurement by two-crystal X-ray diffraction that it was single-crystallized. At a temperature higher than 700 degrees Celsius, the low-temperature buffer layer 904 becomes single crystal, and it becomes impossible to relieve stress.
It is considered that the crack density increases.

The change in the threshold current density is similar to the crack density, and it can be seen from the device characteristics that the growth temperature of the low-temperature buffer layer 904 is preferably 450 ° C. or more and 700 ° C. or less. Even when the cross-sectional shape of the groove portion 903b was changed from a rectangular shape to a forward mesa, an inverted mesa, or a triangle, the tendency of the crack density with respect to the film growth temperature of the low-temperature buffer layer 904 was the same. Also, the same tendency was shown in heteroepitaxial growth using a sapphire substrate or the like. Even when the ridge structure in which the p-type electrode is provided is replaced with an electrode stripe structure, the crack reducing effect of the present invention can be exhibited without any problem. (Embodiment 7) In Embodiment 7, the (0001) plane Ga
When fabricating a laser device as a nitride semiconductor light emitting device 7 on an N substrate, first, an n-type GaN layer is grown,
After forming the groove structure, the temperature is fixed, and through a low-temperature buffer layer having a predetermined layer thickness (30 nm or more and 1 μm or less), n-type Ga of the element structure including the quantum well active layer is interposed.
An example in which the element is regrown from the N layer and the ridge stripe is arranged immediately above the groove portion will be described with reference to FIGS. 9 and 12. FIG.

Each of the layers constituting the nitride semiconductor light emitting device 7 is grown by MOCVD. As shown in FIG. 9, the device structure is an n-type GaN substrate 9 by MOCVD.
First, an n-type GaN layer 902 is grown to a thickness of 3 μm on the substrate 01, and then a land / groove structure is periodically formed on the n-type GaN layer 902 by photolithography and etching. The land width is 4 μm, the groove width is 10 μm, and the groove depth is 2 μm.

On the land / groove structure, a low-temperature buffer layer 904 made of amorphous or polycrystalline GaN, an n-type GaN layer 905,
N-type AlGaN cladding layer 906 for confining light from GaN multiple quantum well active layer 908, n-type GaN optical guide layer 907 for distributing light near the active layer, I
An nGaN multiple quantum well active layer 908, an AlGaN block layer 909 for preventing sublimation of the active layer and preventing diffusion of impurities from the p-type layer during the device structure fabrication process, and a p-type Ga
N light guide layer 910, p-type AlGaN cladding layer 91
1, p-type GaN layer 912, p-type GaN contact layer 91
The layers are stacked in the order of 3.

The low-temperature buffer layer 904 must be amorphous or polycrystalline in order to absorb stress, and have a thickness within a range that transmits lattice information of the lower layer and sufficiently absorbs stress. Therefore, it is necessary to grow the film to a thickness of 30 nm or more and 1 μm at a temperature of 450 ° C. or more and 700 ° C. or less.

The outermost p-type GaN layer 913 is processed into a ridge shape to confine light in the lateral direction, an insulating film 914 is formed by ordinary photolithography, and a p-type electrode 915 is formed.
Attached. The ridge and the p-type electrode 915 are located immediately above the groove 903b. The n-type electrode 916 is
1 is formed on the back surface.

Here, in order to investigate the relationship between the crack density on the element surface and the threshold current density with respect to the thickness of the low-temperature buffer layer 904, the thickness of the low-temperature buffer layer 904 was changed from 10 nm to 1.5 μm to change the laser element. Created. The film growth temperature of the low-temperature buffer layer 904 was fixed at 500 degrees Celsius regardless of the thickness.

FIG. 12 shows the result of plotting the crack density on the element surface and the threshold current density with respect to the thickness of the low-temperature buffer layer 904. In FIG. 12, the symbol ● indicates the crack density, and the symbol Δ indicates the threshold current density. The allowable limit of the crack density (cm ⁻² ) (10 ⁵ cm ⁻² or less) is indicated by a dashed line. The crack density is determined by the low-temperature buffer layer 904.
Is almost constant in a layer thickness range of 30 nm to 1.5 μm,
It tends to increase in a layer thickness region smaller than nm.

On the other hand, the threshold current density (kA / cm ² )
The cracks increase in the regrown device because the thickness is less than 30 nm and the thickness is greater than 1 μm. In a layer thickness region larger than 1 μm, although the stress is absorbed, it is expected that the crystal quality of the regrown layer is degraded.

By analogy with the heteroepitaxial growth on sapphire, when the low-temperature buffer layer 904 has a large thickness exceeding 1 μm, the crystal quality of the regrown layer is reduced by cutting off the lattice arrangement information of the sapphire substrate. It is thought to decrease.

From the crack density and device characteristics, the thickness of the low-temperature buffer layer 904 at the time of regrowth is 30 nm or more and 1
It is understood that the thickness is preferably not more than μm. The tendency with respect to the thickness of the low-temperature buffer layer 904 was the same even when the shape of the groove cross section was changed from a rectangular shape to a forward mesa, an inverted mesa, or a triangle. Also, the same tendency was shown in heteroepitaxial growth using a sapphire substrate or the like. Even when the ridge structure provided with the p-type electrode 915 is replaced with an electrode stripe structure, the effect of reducing cracks of the present invention is exhibited without any problem. (Embodiment 8) In Embodiment 8, the (0001) plane Ga
When manufacturing a laser device as the nitride semiconductor light emitting device 8 on an N substrate, first, an n-type GaN layer is grown, a land / groove structure is formed, the layer thickness and the temperature are fixed, and a predetermined composition ( Of the device structure including a quantum well active layer via a low-temperature buffer layer formed with an Al composition of less than 0.8), the device is regrown from an n-type GaN layer so that the ridge stripe is disposed immediately above the groove portion. One example of the conversion will be described with reference to FIGS. 9, 13 and 14. FIG.

Each layer constituting the nitride semiconductor light emitting element 8 is grown by MOCVD. First, the element structure of the nitride semiconductor light emitting element 8 is, as shown in FIG.
According to the D method, an n-type GaN
A layer 902 is grown 3 μm and then periodically land /
A groove structure is formed in the n-type GaN layer 902 by photolithography and etching. The land width is 3 μm, the groove width is 10 μm, and the groove depth is 2 μm.

On the land / groove structure, in order to absorb stress, amorphous or polycrystalline In _x Ga _y
Low-temperature buffer layer 904 composed of Al _{1- (x + y)} N (0 ≦ x ≦ 1, 0 ≦ x + y ≦ 1), n-type GaN layer 905, InG
n-type AlGaN cladding layer 906 for confining light from aN multiple quantum well active layer 908, n-type GaN optical guide layer 907 for distributing light near the active layer, In
GaN multiple quantum well active layer 908, AlGaN block layer 909 for preventing sublimation of the active layer and preventing diffusion of impurities from the p-type layer in the device structure fabrication process, p-type GaN
A light guide layer 910, a p-type AlGaN cladding layer 911,
A p-type GaN layer 912 and a p-type GaN contact layer 913 are stacked in this order.

The low-temperature buffer layer 904 must be amorphous or polycrystalline so as to absorb stress, and must have such a thickness as to transmit lattice information of the lower layer and sufficiently absorb stress. Therefore, it is necessary to grow the film to a thickness of 30 nm or more and 1 μm at a temperature of 450 ° C. or more and 700 ° C. or less.

The outermost p-type GaN layer 913 is processed into a ridge shape to confine light in the lateral direction, an insulating film 914 is formed by ordinary photolithography, and a p-type electrode 915 is provided thereon. The ridge and the p-type electrode are located immediately above the groove 903b. The n-type electrode 916 is
01 is formed on the back surface.

Here, in order to investigate the relationship between the crack density on the element surface and the threshold current density with respect to the composition of the low-temperature buffer layer 904, the low-temperature buffer layer 904 is formed of In _x Ga ₁ -xN.
(X ≦ 1) and Al _x Ga _1-x N (x ≦ 1), and In
Alternatively, a laser element was prepared by changing the composition of Al.
Regardless of the composition, the thickness of the low-temperature buffer layer 904 is 50 nm,
The film growth temperature was fixed at 550 ° C.

FIG. 13 shows the result of plotting the crack density on the element surface and the threshold current density with respect to the In composition of the low-temperature buffer layer 904.
FIG. 14 (nitride semiconductor light emitting element 8) shows the result of plotting the crack density and the threshold current density on the element surface for one composition. In FIGS. 13 and 14, the symbol ● indicates the crack density and the symbol Δ indicates the threshold current density. Further, the allowable limit of the crack density is indicated by a dashed line. FIG. 13 and FIG.
4, the low-temperature buffer layer 904 made of In _x Ga ₁ -xN
Although the crack density hardly changes below the allowable limit (10 ⁵ cm ⁻² ) regardless of its In composition, Al _x G
In the case of the a _1-x N low temperature buffer layer 904, it can be seen that the crack density has increased to more than 10 ⁵ cm ⁻² in the region where the Al composition is 0.8 or more. In addition, the Al composition is 0.1.
In the region of 8 or more, the yield of the device was poor due to the effect of the high crack density, and it was impossible to measure the threshold current density satisfactorily. When the Al composition is 0.8 or more, Al is locally aggregated in the low-temperature buffer layer 904, and the high-Al composition region distributed on the island inhibits the stress relaxation effect of the low-temperature buffer layer 904, and cracks occur in the device. It is thought to cause.

That is, when a nitride mixed crystal semiconductor containing Al as a composition is used as the low-temperature buffer layer 904, the macroscopic Al composition of the low-temperature buffer layer 904 is controlled to be less than 0.8, so that the low-temperature buffer layer 904 is formed. The effect of suppressing the formation of clusters having a high Al composition in 904 is obtained.

The result of the eighth embodiment and the results of the sixth and sixth embodiments are described.
7, the low-temperature buffer layer 904 for absorbing stress
It is important that the thickness of the low-temperature buffer layer 904 is amorphous or polycrystalline, and the thickness of the low-temperature buffer layer 904 does not include Al, so that the thickness of the low-temperature buffer layer 904 can be transmitted while sufficiently absorbing stress. It can be seen that if the formation temperature and thickness are satisfied, the effect of reducing cracks is exhibited regardless of the composition.

However, in the case of the low-temperature buffer layer 904 containing Al as a composition, it is necessary to adjust the composition so that the macroscopic Al composition is less than 0.8.

The cross-sectional shape of the groove is changed from a rectangular shape to a regular mesa,
The tendency (crack reduction effect) of the low-temperature buffer layer 904 with respect to the film growth temperature was the same even when the shape was changed to either the inverted mesa or the triangular shape. The same tendency (crack reduction effect) was exhibited even in heteroepitaxial growth using a sapphire substrate or the like. Even if the ridge structure in which the p-type electrode is provided is replaced with an electrode stripe structure, the crack reducing effect of the present invention is exhibited without any problem. (Embodiment 9) In Embodiment 9, the (0001) plane Ga
When manufacturing a laser device as the nitride semiconductor light emitting device 9 on an N substrate, first, an n-type GaN layer is grown to form a land / groove structure having a predetermined land width (2 μm or more and 10 μm or less). An example of an element structure including a quantum well active layer via a low-temperature buffer layer and regrown from an n-type GaN layer to form an element such that a ridge stripe is disposed immediately above a groove will be described with reference to FIGS. I will explain it.

Each layer constituting the nitride semiconductor light emitting element 9 is grown by MOCVD. As shown in FIG. 9, the device structure is an n-type GaN substrate 9 by MOCVD.
First, an n-type GaN layer 902 is grown to a thickness of 3.5 μm on the surface of the n-type GaN layer 902 by photolithography and etching.
Formed. The land width is changed from 1 μm to 15 μm, the groove width is 15 μm, and the groove depth is 3 μm.

On the land / groove structure, a low-temperature buffer layer 904 made of amorphous or polycrystalline GaN, an n-type GaN layer 905,
N-type AlGaN cladding layer 906 for confining light from GaN multiple quantum well active layer 908, n-type GaN optical guide layer 907 for distributing light near the active layer, I
nGaN multiple quantum well active layer 908, AlGaN block layer 909 for preventing sublimation of the active layer and diffusion of impurities from the p-type layer in the process of fabricating the device structure, p-type Ga
N light guide layer 910, p-type AlGaN cladding layer 91
1, p-type GaN layer 912, p-type GaN contact layer 91
The layers are stacked in the order of 3.

The low-temperature buffer layer 904 must be amorphous or polycrystalline so as to absorb stress, and must have such a thickness as to transmit lattice information of the lower layer and sufficiently absorb stress. Therefore, it is necessary to grow the film to a thickness of 30 nm or more and 1 μm at a temperature of 450 ° C. or more and 700 ° C. or less.

In the ninth embodiment, at 500 degrees Celsius, 50
A nm film was grown. The outermost p-type GaN layer 913 is processed into a ridge shape to confine light in the lateral direction, and the insulating film 91 is formed.
4 is formed by ordinary photolithography, and a p-type electrode 915 is attached thereon. Ridge part and P-type electrode 91
5 is located directly above the groove portion 903b.

The n-type electrode 916 is formed on the back surface of the substrate 901.

FIG. 15 shows the result of plotting the crack density on the element surface and the threshold current density with respect to the land width. In FIG. 15, the symbol ● indicates the crack density, and the symbol Δ indicates the threshold current density. The crack density is almost constant for all land widths, but the threshold current density tends to increase in the area smaller than 2 μm and the area larger than 10 μm.

A device having a land width smaller than 2 μm and 10
Observation of a cross section of the element wider than μm revealed that voids were generated near the center of the land. Observation of these devices with a transmission electron microscope revealed that a large number of dislocations were generated from the upper portion of the void generated near the center of the land, and a part of the dislocation penetrated into the groove along with the lateral growth. Although the effect of preventing cracks can be obtained irrespective of the land width, in a region where the land width is smaller than 2 μm and a region larger than 10 μm, the oscillation threshold current increases due to the intrusion of dislocations into the groove portion. Land width is 2μm or more and 10μm
It is as follows.

Further, even when the cross-sectional shape of the groove is changed from a rectangular shape to one of a forward mesa, an inverted mesa, and a triangle,
The tendency (crack reduction effect) with respect to the thickness of the low-temperature buffer layer 904 was the same. The same tendency (crack reduction effect) was exhibited even in heteroepitaxial growth using a sapphire substrate or the like. Even when the ridge structure in which the p-type electrode is provided is replaced with an electrode stripe structure, the crack reducing effect of the present invention can be exhibited without any problem. Embodiment 10 In Embodiment 10, when fabricating a laser device as the nitride semiconductor light emitting device 10 on a (0001) plane GaN substrate, first, an n-type GaN layer is grown,
After forming a land / groove structure with a predetermined groove width (2 μm or more and 20 μm or less), n-type GaN among the element structures including a quantum well active layer via a low-temperature buffer layer is used.
An example of regrowth from a layer will be described with reference to FIGS.

Each layer constituting the nitride semiconductor light emitting device 10 is grown by MOCVD. The element structure is shown in FIG.
As shown in (1), an n-type GaN layer 902 is first grown on the n-type GaN substrate 901 by 3 μm by MOCVD, and then a land / groove structure is periodically formed on the n-type GaN layer 902 by photolithography and etching. Form. Land width is fixed at 5 μm, groove width is 1 μm
m to 25 μm. The groove depth was 2 μm.

On the land / groove structure, a low-temperature buffer layer 904 made of amorphous or polycrystalline GaN, an n-type GaN layer 905,
N-type AlGaN cladding layer 906 for confining light from GaN multiple quantum well active layer 908, n-type GaN optical guide layer 907 for distributing light near the active layer, I
nGaN multiple quantum well active layer 908, AlGaN block layer 909 for preventing sublimation of the active layer and diffusion of impurities from the p-type layer in the process of fabricating the device structure, p-type Ga
N light guide layer 910, p-type AlGaN cladding layer 91
1, p-type GaN layer 912, p-type GaN contact layer 91
The layers are stacked in the order of 3.

The low-temperature buffer layer 904 must be amorphous or polycrystalline so as to absorb stress, and must have such a thickness as to transmit lattice information of the lower layer and sufficiently absorb stress. Therefore, it is necessary to grow the film to a thickness of 30 nm or more and 1 μm at a temperature of 450 ° C. or more and 700 ° C. or less.

In the tenth embodiment, 5 degrees at 500 degrees Celsius.
It grew to 0 nm. The outermost p-type GaN layer 913 is processed into a ridge shape to confine light in the lateral direction, and the insulating film 914 is formed.
Is formed by ordinary photolithography, and p
The mold electrode 915 is attached.

The ridge and the p-type electrode 915 are located immediately above the groove 903b.

The n-type electrode 916 is formed on the back surface of the substrate 901.

FIG. 16 shows the result of plotting the crack density on the element surface and the threshold current density with respect to the groove width.
In FIG. 16, the symbol ● indicates the crack density, and the symbol Δ indicates the threshold current density. The crack density is almost constant for all groove widths, but the threshold current density is 2 μm for the groove width.
It tends to increase in a region smaller than m and in a region where the groove width is larger than 20 μm. Observation of the cross sections of the element having a groove width smaller than 2 μm and the element having a groove width larger than 20 μm revealed that voids were generated near the center of the groove portion 903b. When these devices were observed with a transmission electron microscope, it was found that
A large number of dislocations are generated from the upper part of the voids generated near the center of b, and part of the dislocations grows along with the lateral growth.
b. Although a crack preventing effect can be obtained regardless of the groove width, the groove width is 2 μm.
In a narrower region and a region having a groove width larger than 20 μm, the oscillation threshold current increases due to an increase in dislocation.
In consideration of device characteristics, a preferable groove width is 2 μm or more and 20 μm or less.

Further, even when the cross-sectional shape of the groove portion 903b is changed from a rectangular shape to one of a forward mesa, an inverted mesa, and a triangle, the tendency (crack reduction effect) with respect to the layer thickness of the low-temperature buffer layer 904 is the same. Was. The same tendency (crack reduction effect) was exhibited even in heteroepitaxial growth using a sapphire substrate or the like. p-type electrode 9
Even if the ridge structure provided with 15 is replaced with an electrode stripe structure, the crack reducing effect of the present invention can be exhibited without any problem. (Embodiment 11) In Embodiment 11, when fabricating a laser device as a nitride semiconductor light emitting device 11 on a (0001) plane GaN substrate, an n-type GaN layer is first grown,
After forming a land / groove structure with a predetermined groove depth (0.5 μm or more and 5 μm or less), among the element structures including a quantum well active layer via a low-temperature buffer layer, n-type G
FIG. 9 shows an example in which the ridge stripe is regrown from the aN layer, and the ridge stripe is arranged immediately above the groove portion.
This will be described with reference to FIGS.

Each layer constituting the nitride semiconductor light emitting device 11 is grown by MOCVD. The element structure is shown in FIG.
As shown in the figure, an n-type GaN layer 902 is first grown on the n-type GaN substrate 901 by 6.5 μm by MOCVD, and then a land / groove structure is periodically formed by photolithography and etching. 902
Formed. Land width 3μm, groove width 15μ
m, and the groove depth was changed from 0.1 μm to 6 μm.

On the land / groove structure, a low-temperature buffer layer 904 made of amorphous or polycrystalline GaN, an n-type GaN layer 905,
N-type AlGaN cladding layer 906 for confining light from GaN multiple quantum well active layer 908, n-type GaN optical guide layer 907 for distributing light near the active layer, I
nGaN multiple quantum well active layer 908, AlGaN block layer 909 for preventing sublimation of the active layer and diffusion of impurities from the p-type layer in the process of fabricating the device structure, p-type Ga
N light guide layer 910, p-type AlGaN cladding layer 91
1, p-type GaN layer 912, p-type GaN contact layer 91
3 are sequentially laminated.

The low-temperature buffer layer 904 must be amorphous or polycrystalline so as to absorb stress, and must have a thickness in a range that transmits lattice information of the lower layer and sufficiently absorbs stress. Therefore, it is necessary to grow the film to a thickness of 30 nm or more and 1 μm at a temperature of 450 ° C. or more and 700 ° C. or less.

In the eleventh embodiment, 5 degrees at 500 degrees Celsius
A 0 nm film was grown. The outermost p-type GaN layer 913 is processed into a ridge shape to confine light in the lateral direction, and the insulating film 9 is formed.
14 is formed by ordinary photolithography, and a p-type electrode 915 is attached thereon. Ridge part and p-type electrode 9
Reference numeral 15 is located immediately above the groove portion 903b.

The n-type electrode 916 is formed on the surface of the substrate 901.

FIG. 17 shows the thickness of the regrown n-type GaN layer required to flatten the device surface with respect to the groove depth. For all groove depths, the thickness of the n-type GaN layer required to planarize the element surface is required to be equal to or greater than the groove depth, and when the groove depth exceeds 5 μm, the necessary n-type GaN layer It can be seen that the thickness is greater than the groove depth.

FIG. 18 shows the results of plotting the groove depth, the crack density on the element surface, and the threshold current density. In FIG. 18, the mark ● indicates the crack density, and the mark Δ indicates the threshold current density. The crack density (c
The permissible limit (10 ⁵ cm ⁻² ) of m ⁻² ) is indicated by a dashed line. The crack density is almost constant except for the groove depth exceeding 5 μm, but the threshold current density tends to increase in the area smaller than 0.5 μm and the area larger than 5 μm. Observation of a cross section of the element having a groove depth of less than 0.5 μm revealed that minute voids were generated near the center of the groove portion 903b. Observation with a transmission electron microscope revealed that a large number of dislocations were generated from the upper portion of the voids generated near the center of the groove portion 903b, and a part of the dislocation spread to the groove portion 903b with lateral growth. Groove portion 90 deeper than 5 μm
When the device fabricated on 3b was subjected to photoelastic measurement, the regrown n-type GaN layer required for planarization was thick,
It was found that the residual stress increased near the n-type AlGaN cladding layer and cracks were generated. Considering the crack density and device characteristics, a preferable groove depth is 0.5
It is not less than μm and not more than 5 μm.

Further, even when the cross-sectional shape of the groove portion 903b is changed from a rectangular shape to one of a forward mesa, an inverted mesa, and a triangle, the tendency (crack reduction effect) with respect to the thickness of the low-temperature buffer layer 904 is the same. Was. The same tendency (crack reduction effect) was exhibited even in heteroepitaxial growth using a sapphire substrate or the like. Even when the ridge structure in which the p-type electrode is provided is replaced with an electrode stripe structure, the crack reducing effect of the present invention can be exhibited without any problem. (Twelfth Embodiment) In a twelfth embodiment, when fabricating laser devices as nitride semiconductor light emitting devices 12a and 12b on a (0001) plane GaN substrate, first, an n-type GaN layer is grown and a land / groove structure is formed. Is formed, through the low-temperature buffer layer, from the n-type GaN layer in the element structure including the quantum well active layer so that at least a part of the groove portion has a concave cross section without generating a void,
Two examples in which elements are arranged so that the arrangement of the ridge stripes is different within the groove width will be described with reference to FIGS.

Each layer constituting the nitride semiconductor light emitting elements 12a and 12b is grown by MOCVD. First,
As shown in FIG. 19, the element structure of the nitride semiconductor light emitting element 12a is an n-type GaN substrate 19 formed by MOCVD.
An n-type GaN layer 1902 is grown to a thickness of 3 .mu.m on the first
A land / groove structure made of 3b is formed on the n-type GaN layer 1902 by photolithography and etching. The land width is 3 μm, the groove width is 10 μm, and the groove depth is 2 μm.

On the land / groove structure, a low-temperature buffer layer 1904 made of amorphous or polycrystalline GaN, an n-type GaN layer 1905,
N-type AlGaN cladding layer 1806 for confining light from InGaN multiple quantum well active layer 1908, n-type GaN light guide layer 1 for distributing light near the active layer
907, an InGaN multiple quantum well active layer 1908, an AlGaN block layer 19 for preventing sublimation of the active layer and preventing diffusion of impurities from the p-type layer during the device structure manufacturing process.
09, p-type GaN optical guide layer 1910, p-type AlGaN
Clad layer 1911, p-type GaN layer 1912, p-type Ga
The N contact layers 1913 are stacked in this order.

The low-temperature buffer layer 1904 must be amorphous or polycrystalline in order to absorb stress, and have a thickness within a range that transmits lattice information of the lower layer and sufficiently absorbs stress. Therefore, it is necessary to grow the film to a thickness of 30 nm or more and 1 μm at a temperature of 450 ° C. or more and 700 ° C. or less.

In the twelfth embodiment, 5 degrees at 500 degrees Celsius
A 0 nm film was grown. The outermost p-type GaN layer 1913 is processed into a ridge shape to confine light in the lateral direction, an insulating film 1914 is formed by ordinary photolithography, and 1915 is provided thereon. Ridge part and p-type electrode 19
Reference numeral 15 denotes a groove portion 1903b.
It is located at a portion close to the side wall intentionally left buried in a concave section.

The n-type electrode 1916 is formed on the back surface of the substrate 1901.

Immediately after growing the element structure, the top surface was observed.
It was found that the crack density was 10 ^Fivecm^-2Below
It was found that stress relaxation was remarkable. Device
After the process, the divided elements are mounted on the stem and
When the oscillation was performed, the voltage was 4 V, the oscillation threshold current density was 1.
5kA / cm^TwoWorked with. Element shown in Example 4 above
It is clear that the threshold current density is
You.

For comparison, a laser device as a nitride semiconductor light emitting device 12b shown in FIG. 20 was prepared and evaluated, with the ridge formation position being closer to the land portion 2003a.

As shown in FIG. 20, the device structure of this nitride semiconductor light emitting device 12b is obtained by MOCVD method.
First, an n-type GaN layer 200 is formed on the n-type GaN substrate 2001.
2 is grown to a thickness of 3 μm.
The land / groove structure composed of the groove portion 2003a and the groove portion 2003b is n-type G by photolithography and etching.
An aN layer 2002 is formed. The land width is 3 μm, the groove width is 10 μm, and the groove depth is 2 μm.

On the land / groove structure, a low-temperature buffer layer 2004 made of amorphous or polycrystalline GaN, an n-type GaN layer 2005,
An n-type AlGaN cladding layer 2006 for confining light from the InGaN multiple quantum well active layer 2008 and an n-type GaN light guiding layer 2 for distributing light near the active layer
007, an InGaN multiple quantum well active layer 2008, an AlGaN block layer 20 for preventing sublimation of the active layer and preventing diffusion of impurities from the p-type layer in the device structure manufacturing process.
09, p-type GaN optical guide layer 2010, p-type AlGaN
Clad layer 2011, p-type GaN layer 2012, p-type Ga
The N contact layers 2013 are sequentially stacked.

The low-temperature buffer layer 2004 must be amorphous or polycrystalline in order to absorb stress, and have a thickness within a range that transmits lattice information of a lower layer and sufficiently absorbs stress. Therefore, it is necessary to grow the film to a thickness of 30 nm or more and 1 μm at a temperature of 450 ° C. or more and 700 ° C. or less.

In the twelfth embodiment, 5 degrees at 500 degrees Celsius
A 0 nm film was grown. The outermost p-type GaN layer 2013 is processed into a ridge shape to confine light in the lateral direction, an insulating film 2014 is formed by ordinary photolithography, and a p-electrode 2015 is attached thereon.

An n-type electrode 2016 is formed on the back surface of the substrate 2001.

When the laser device was energized and oscillated, the device was operated at a voltage of 4 V and an oscillation threshold current density of 1.7 kA / cm ² . From a comparison of the two elements having different ridge positions within the groove width, as shown in FIG. 19, in the element in which the ridge is formed in a portion close to the side wall that is left buried in a concave cross-sectional state, stress relaxation is more remarkable in a region near the side wall side. It is considered that the threshold current has decreased.

Also, the groove portions 1903b, 2003b
Even when the cross-sectional shape is changed from a rectangular shape to a forward mesa, an inverted mesa, or a triangle, the stress relaxation effect of the regrown layer is remarkable, and the crack density on the element surface is less than 10 ⁵ cm ^−2. Value. In addition, it was confirmed that the light confinement efficiency in the lateral direction by inserting n-type GaN under the n-type AlGaN cladding layer was improved irrespective of the difference in cross-sectional shape. Even when the ridge structure in which the p-type electrode is provided is replaced with an electrode stripe structure, the effect of reducing cracks of the present invention is exhibited without any problem.

As described above, according to the first to twelfth embodiments, in a laser device manufactured on a heterogeneous substrate on which a nitride semiconductor such as a nitride semiconductor substrate or sapphire can be heteroepitaxially grown, first, the nitride semiconductor is formed on the substrate. By growing a layer, periodically forming a land / groove structure on its surface, and stacking the element structure by regrowth via a low-temperature buffer layer, lattice mismatch between the substrate and the nitride semiconductor and a difference in thermal expansion coefficient The stress remaining in the device structure by the lateral growth by the land / groove structure;
Cracking can be effectively prevented by using the stress absorbing effect of the low-temperature buffer layer thereon to effectively prevent cracks from occurring, and an improvement in the yield in the element forming process can be realized.

In the first to eleventh embodiments, the case where the regrowth is performed so that the groove portion is completely buried and flattened has been described. However, as described in the twelfth embodiment, the regrowth is performed over the entire groove portion. Even in the case where a concave portion is partially left without being buried and an element structure including an active layer is laminated thereon, the above-described crack reducing effect of the present invention is sufficiently exhibited.

[0175]

As described above, according to the present invention, the crack density is reduced by adding the stress absorption effect of the low-temperature buffer layer to the lateral growth effect by regrowth on the land / groove structure. Therefore, the yield in the element forming process can be improved. Further, in order to more effectively reduce the crack density, the size of the land / groove structure, the growth condition of the low-temperature buffer layer, and the thickness thereof can be specified.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a configuration example of a laser device manufactured on a GaN substrate as a nitride semiconductor light emitting device according to a first embodiment of the present invention.

FIGS. 2A and 2B are diagrams showing a procedure for forming a periodic land / groove structure, FIGS. 2C to 2E are diagrams showing groove cross-sectional shapes, and FIG. 2F is a diagram after regrowth; It is a figure showing a section structure.

3 (a) and 3 (b) are schematic diagrams showing cracks generated under different conditions. FIG.

FIGS. 4A to 4D are diagrams showing lateral growth inside a groove during regrowth via a low-temperature buffer layer, and FIGS.
FIG. 4 is a diagram showing a material concentration gradient inside a groove during growth.

FIG. 5 is a stress distribution diagram for a cross section of various samples,
(A) is a sample in which an Al _0.1 Ga _0.9 N layer is regrown on a land / groove structure via a low-temperature buffer layer, and (b) is n on a land / groove structure without a low-temperature buffer layer.
Type the Al _0.1 Ga _0.9 N layer, a re-grown sample, (c) it is only through the low-temperature buffer layer in a planar shape of the n-type GaN layer without forming a land / groove structure n-type Al _0.1 Ga _0.9 N
FIG. 4D is a diagram showing a sample in which a layer is regrown, and FIG. 4D shows a case of a sample prepared by an ordinary method without applying a land / groove structure and a low-temperature buffer layer.

FIG. 6 is a cross-sectional view showing a configuration of a laser device fabricated on a GaN substrate as a second embodiment of the nitride semiconductor light emitting device of the present invention.

FIG. 7 is a cross-sectional view showing one configuration example of a laser device fabricated on a sapphire substrate as a third embodiment of the nitride semiconductor light emitting device of the present invention.

FIG. 8 is a cross-sectional view showing another configuration example of a laser device formed on a sapphire substrate as a modification of the third embodiment in the nitride semiconductor light emitting device of the present invention.

FIG. 9 is a fourth embodiment of the nitride semiconductor light emitting device of the present invention.
It is sectional drawing which shows one structural example of the laser element produced on the GaN substrate as 6-11.

FIG. 10 shows a nitride semiconductor light emitting device according to a fifth embodiment of the present invention.
FIG. 3 is a cross-sectional view showing one configuration example of a laser device fabricated on a GaN substrate.

FIG. 11 is a diagram showing a relationship between a low-temperature buffer layer growth temperature, a crack density, and a threshold current density during regrowth in the nitride semiconductor light emitting device according to the sixth embodiment of the present invention.

FIG. 12 is a diagram showing a relationship between a layer thickness of a low-temperature buffer layer, a crack density, and a threshold current density during regrowth in a nitride semiconductor light emitting device according to a seventh embodiment of the present invention.

FIG. 13 is a diagram showing the relationship between the In composition of the low-temperature buffer layer, the crack density, and the threshold current density during regrowth in the nitride semiconductor light emitting device according to the eighth embodiment of the present invention.

FIG. 14 is a diagram showing the relationship between the Al composition of the low-temperature buffer layer, the crack density, and the threshold current density during regrowth in the nitride semiconductor light emitting device according to the eighth embodiment of the present invention.

FIG. 15 is a diagram showing a relationship between a land width, a crack density, and a threshold current density in a nitride semiconductor light emitting device according to a ninth embodiment of the present invention.

FIG. 16 is a diagram showing a relationship between a groove width, a crack density, and a threshold current density in the nitride semiconductor light emitting device according to the tenth embodiment of the present invention.

FIG. 17 is a diagram illustrating a relationship between a groove depth and a layer thickness of a regrown layer necessary for planarizing the groove in the nitride semiconductor light emitting device according to the eleventh embodiment of the present invention.

FIG. 18 is a diagram showing a relationship between a groove depth, a crack density, and a threshold current density in the nitride semiconductor light emitting device according to Embodiment 11 of the present invention.

FIG. 19 is a diagram illustrating a nitride semiconductor light emitting device according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a configuration example of a laser device manufactured on a GaN substrate as No. 2.

FIG. 20 is a cross-sectional view showing another configuration example of a laser device fabricated on a GaN substrate as a modification of Embodiment 12 in the nitride semiconductor light-emitting device of the present invention.

[Explanation of symbols]

1 to 11, 12a, 12b Nitride semiconductor light emitting device 101, 201, 601, 901, 1001, 190
1,2001 (0001) plane n-type GaN substrate 102,202,602,703,803,902
n-type GaN layers 103a, 603a, 704a, 804a, 903a,
1002a Land portions 103b, 603b, 704b, 804b, 903b,
1002b Groove section 104, 204, 604, 705, 805, 904, 1
003 Low-temperature buffer layer 105, 205, 605, 706, 806, 905, 1
005 n-type Al _{0. 1} Ga _0.9 N cladding layer 107,607,708,808,908,1007
InGaN multiple quantum well active layer 701,801 (0001) plane sapphire substrate C crack X, Ya Isoconcentration line

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Teruyoshi Takakura 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term (reference) 5F045 AA04 AB14 AB18 AD08 AD09 AD10 AF02 AF09 AF13 BB13 CA12 DA53 DA55 5F073 AA11 AA13 AA74 CA07 CA17 CB02 CB05 DA05 DA23 DA24 EA23 EA29

Claims (11)

[Claims] 1. A general formula nitride semiconductor crystal can be epitaxially grown on the substrate _{In x Ga y Al 1- (x} + y) N (0 ≦
a nitride semiconductor light emitting device having a structure in which a plurality of nitride semiconductors represented by x ≦ 1, 0 ≦ x + y ≦ 1) are stacked, wherein at least a periodic land / land is formed between the active layer of the device and the substrate. A nitride semiconductor light-emitting device in which a groove is provided and an element structure is provided on the land / groove via a low-temperature buffer layer. 2. The land / groove direction is <11−
20. The nitride semiconductor light emitting device according to claim 1, wherein the direction is 20>. 3. The direction of the land / groove is <1-1.
2. The nitride semiconductor light-emitting device according to claim 1, wherein the direction is the direction of the nitride semiconductor light-emitting device. 4. The nitride semiconductor light emitting device according to claim 1, wherein a cross-sectional shape of said groove portion is any one of a rectangular shape, a normal mesa, an inverted mesa, and a triangle. 5. The growth temperature of the low-temperature buffer layer is 4 degrees Celsius.
2. The nitride semiconductor light emitting device according to claim 1, wherein the temperature is not less than 50 degrees and not more than 700 degrees Celsius. 6. The nitride semiconductor light emitting device according to claim 1, wherein said low temperature buffer layer has a thickness of 30 nm or more and 1 μm or less. 7. The width of the land portion is 2 μm or more and 10 μm.
The nitride semiconductor light emitting device according to claim 1, wherein 8. The width of the groove portion is 2 μm or more and 20 μm.
2. The nitride semiconductor light emitting device according to claim 1, wherein m is equal to or less than m. 9. The nitride semiconductor light emitting device according to claim 1, wherein a depth of said groove portion is 0.5 μm or more and 5 μm or less. 10. The nitride semiconductor light emitting device according to claim 1, wherein said nitride semiconductor light emitting device has a structure in which any one of a ridge stripe and an electrode stripe exists right above said groove portion. 11. The groove portion is not completely flattened,
2. The nitride semiconductor light emitting device according to claim 1, wherein an element structure including an active layer is laminated thereon.