WO2022270054A1

WO2022270054A1 - Nitride semiconductor light emitting element

Info

Publication number: WO2022270054A1
Application number: PCT/JP2022/012132
Authority: WO
Inventors: 幸男保科; 誠太田; 崇水野; 秀和川西
Original assignee: ソニーセミコンダクタソリューションズ株式会社
Priority date: 2021-06-23
Filing date: 2022-03-17
Publication date: 2022-12-29

Abstract

The present invention provides a nitride semiconductor light emitting element which is prevented from the occurrence of a fault without causing deterioration in the laser characteristics, thereby having an improved production yield.　This nitride semiconductor light emitting element comprises: a GaN substrate (11); a first cladding layer (12) which is superposed on the GaN substrate (11); a first light guide layer (13) which is superposed on the first cladding layer (12); an active layer (14) which is superposed on the first light guide layer (13); a second light guide layer (15) which is superposed on the active layer (14); an electron barrier layer (16) which is superposed on the second light guide layer (15); a fault suppression layer (17) which is superposed on the electron barrier layer (16); a second cladding layer (18) which is superposed on the fault suppression layer (17); and a contact layer (19) which is superposed on the second cladding layer (18). This nitride semiconductor light emitting element is configured such that the fault suppression layer (17) relaxes a stress due to a strain generated between an InGaN layer and an AlGaN layer.

Description

Nitride semiconductor light emitting device

The present disclosure relates to a nitride semiconductor light emitting device such as a nitride semiconductor laser device having a ridge.

Blue to green light emitting diodes (LED: light emitting diodes) for general lighting applications, pure blue semiconductor lasers (LD: Laser Diodes) using nitride compound semiconductors for applications such as laser displays and automotive headlight light sources ) are being developed. The active layer of a semiconductor light-emitting device using a nitride-based compound generally uses an aluminum indium gallium nitride (AlInGaN)-based quantum well layer, and the composition ratio of indium (In) in the active layer is increased. This makes it possible to obtain light emission in the blue band.

A semiconductor laser device, which is a nitride semiconductor light-emitting device, is provided with a current constriction layer to narrow the passage of current in the active layer, thereby increasing the threshold current density and thereby reducing the threshold current itself. Stripe lasers are the mainstream. A stripe laser has a ridge formed on the upper surface of the p-side semiconductor layer above the active layer. An anode electrode is formed on the ridge for electrical connection.

In addition, some semiconductor laser devices, which are nitride semiconductor light emitting devices, have an electron barrier layer made of p-type aluminum gallium nitride (AlGaN) in order to suppress electron overflow from the active layer.

Electron overflow is a phenomenon in which electrons supplied from the n-side do not emit light due to recombination with holes in the quantum well layer of the active layer and are conducted to the p-side layer. Such electron overflow causes a decrease in luminous efficiency and a deterioration in temperature characteristics as characteristics of the laser.

Therefore, in order to suppress electron overflow, a technique of providing an electron barrier layer made of AlGaN having a sufficiently large bandgap energy with respect to the well layer on the side of the p-type layer closest to the well layer is disclosed, for example, in Patent Documents. 1.

However, the aforementioned electron barrier layer requires high-concentration p-type doping in order not to deteriorate the voltage. However, forming the electron barrier layer with a high-concentration dopant worsens the threshold current due to optical loss. In particular, in a pure blue semiconductor laser device, the deterioration of the threshold current with respect to the amount of optical loss becomes remarkable, which poses a serious problem.

Further, if the doping concentration is reduced in an attempt to reduce the optical loss, there is a problem that the voltage deteriorates and a sufficient barrier effect cannot be obtained. If the electron barrier layer is eliminated, the electron overflow occurs as described above, and the luminous efficiency and temperature characteristics deteriorate.
Therefore, due to the trade-off as described above, at present, it is common to provide an electron barrier layer.

On the other hand, since the electron barrier layer has a high aluminum (Al) composition ratio, stress is generated due to strain due to the difference in lattice constant between the electron barrier layer and the optical guide layer containing In. In addition, when cleaving the wafer, a mechanical force is applied to the laser light exit facet of the nitride semiconductor light emitting device. Due to the force applied during such cleavage, an unintended minute step (also called a "fault") occurs on the laser light exit facet in the vicinity of the active layer. It is a factor of yield deterioration in

Japanese Unexamined Patent Application Publication No. 2002-200003 discloses a prior art for suppressing the strain due to the difference in lattice constant and the step due to the mechanical force applied during cleavage.
Specifically, a semiconductor substrate, a lower clad layer formed on the semiconductor substrate and having a first conductivity type, an active layer formed on the lower clad layer, an active layer formed on the active layer and the first A cap layer having a second conductivity type opposite to the conductivity type, a current confinement structure formed on the cap layer, an upper electrode layer formed on the current confinement structure, and electrically connected to the lower clad layer. A semiconductor light emitting device having a lower electrode layer is disclosed. This semiconductor light emitting device includes a stepped confinement layer interposed between the active layer and the current confinement structure. That is, by interposing the step confinement layer between the active layer and the current confinement structure, the effect of the step is confined. Here, the "step" is said to mean unevenness or undulation that occurs in different angular directions on a plane with respect to the cleaved end face (see paragraph [0008]).

JP 2006-165519 A JP 2010-093128 A

However, the technology disclosed in Patent Document 1 reduces the number of electrons that overflow beyond the electron barrier in order to confine electrons in the active layer, and has a small threshold current and a high differential efficiency. A light emitting device is provided. Therefore, it does not prevent the generation of the step.
Further, the technique disclosed in Patent Document 2 confines the influence of the step, and does not prevent the step (hereinafter referred to as "fault") itself from occurring.

The present disclosure has been made in view of these problems, and by forming a fault suppression structure on the upper part of the electron barrier layer, suppresses electron overflow, prevents deterioration of laser characteristics, and suppresses stress caused by strain. It is an object of the present invention to provide a nitride semiconductor light-emitting device capable of alleviating stress, preventing the occurrence of faults, and improving the yield during manufacturing.

The present disclosure has been made to solve the above problems, and a first aspect thereof includes a gallium nitride (GaN) substrate, a first clad layer laminated on the GaN substrate, and the first A first optical guide layer laminated on one clad layer, an active layer laminated on the first optical guide layer, a second optical guide layer laminated on the active layer, and the second optical guide An electron barrier layer laminated on a layer, a fault suppression layer laminated on the electron barrier layer, a second clad layer laminated on the fault suppression layer, and a layer laminated on the second clad layer , a nitride semiconductor light emitting device having a contact layer.

In the first aspect, the fault suppression layer is formed of aluminum gallium nitride made of Al _z Ga _(1-z) N (0≦z<1), or In _a Ga _(1-a) N ( It may be made of indium gallium nitride satisfying 0≦a≦1.

In the first aspect, the fault suppression layer may be formed of Al _z Ga _(1−z) N (0≦z<y<1) with a composition ratio of z=0.

In the first aspect, the fault suppression layer may be formed of In _a Ga _(1−a) N (0≦a≦1) with a composition ratio of a=0.

Further, in the first aspect, the fault suppression layer may be formed with a thickness of 10 nm or more.

Further, in the first aspect, the first optical guide layer and the second optical guide layer are formed of indium gallium nitride made of In _b Ga _(1−b) N (0<b<1), and the composition ratio is b and the total film thickness t of both may be 7 nm or more.

In the first aspect, the electron barrier layer is formed of aluminum gallium nitride having a thickness of 5 nm or more and made of Al _x Ga _(1-x) N (0<x<1) doped with p-type impurities. good too.

In the first aspect, the second clad layer may be made of aluminum gallium nitride made of Al _y Ga _(1-y) N (0≦z<y<1).

By taking the above aspect, a nitride semiconductor light-emitting device that suppresses electron overflow, prevents deterioration of laser characteristics, relieves stress due to distortion, prevents faults, and improves manufacturing yield. can be provided.

1 is a cross-sectional view showing a schematic structure of a nitride semiconductor light emitting device according to the present disclosure; FIG. 1 is a plan view showing a schematic structure of a nitride semiconductor light emitting device according to the present disclosure; FIG. FIG. 4 is an explanatory diagram showing the relationship between the average composition ratio of In in the optical guide layer of the nitride semiconductor light-emitting device according to the present disclosure and the occurrence rate of faults; FIG. 4 is an explanatory diagram showing the relationship between the amount of strain in the optical guide layer and the occurrence rate of faults in the nitride semiconductor light emitting device according to the present disclosure; 1 is an explanatory diagram of a method for manufacturing a nitride semiconductor light emitting device according to the present disclosure (part 1); FIG. FIG. 2 is an explanatory diagram of a method for manufacturing a nitride semiconductor light emitting device according to the present disclosure (Part 2); FIG. 3 is an explanatory diagram of a method for manufacturing a nitride semiconductor light emitting device according to the present disclosure (part 3); FIG. 4 is an explanatory diagram of a method for manufacturing a nitride semiconductor light emitting device according to the present disclosure (No. 4); FIG. 3 is a schematic diagram showing a fault generated in a nitride semiconductor light emitting device; It is a figure which shows the relationship between a lattice constant and bandgap energy.

Next, with reference to the drawings, modes for carrying out the present disclosure (hereinafter referred to as "embodiments") will be described in the following order. In the following drawings, the same or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic, and the dimensional ratios and the like of each part do not necessarily match the actual ones. In addition, it goes without saying that there are portions with different dimensional relationships and ratios between the drawings.
1. Embodiment of nitride semiconductor light emitting device according to the present disclosure2. Fault prevention of the nitride semiconductor light emitting device according to the present disclosure3. Manufacturing Method of Embodiment of Nitride Semiconductor Light Emitting Device According to Present Disclosure

<1. Embodiment of Nitride Semiconductor Light Emitting Device According to Present Disclosure>
An embodiment of a nitride semiconductor light emitting device 100 according to the present disclosure will be described below with reference to FIGS. 1 and 2. FIG. FIG. 1 is a cross-sectional view of a nitride semiconductor light emitting device 100 according to the present disclosure, viewed from a front facet 31 that is a light emitting facet. As shown in FIGS. 1 and 2, the nitride semiconductor light emitting device 100 according to the present disclosure has a ridge portion 30 protruding from the top and is formed in a substantially convex shape.

The ridge portion 30 is formed by removing both side surfaces of the contact layer 19 and the second clad layer 18 by etching such as RIE. The width of the ridge portion 30 (direction orthogonal to the resonator direction) is, for example, 500 nm to 100 μm. A region sandwiched between the front end face 31 and the rear end face 32 of the ridge portion 30 forms a reflector. In other words, a resonator that amplifies the light is formed by reciprocating the laser light between the front facet 31 and the rear facet 32 . The distance (resonator length) between the front facet 31 and the rear facet 32 is, for example, 50 μm to 3000 μm.

Both

side surfaces

30a, 30a of the ridge portion 30 are covered with an insulating layer 21. As shown in FIG. The insulating layer 21 is made of, for example, silicon oxide (SiO ₂ ) and silicon nitride (Si ₃ N ₄ ), and has a film thickness of, for example, 10 nm to 500 nm.

The nitride semiconductor light-emitting device 100 comprises a GaN substrate 11, a first clad layer 12, a first optical guide layer 13, an active layer 14, a second optical guide layer 15, an electron barrier layer 16, a fault suppressing layer 17, and the above-described A second cladding layer 18 and a contact layer 19 are sequentially laminated. A first electrode 10 that is a cathode is formed on the lower surface of the GaN substrate 11 , and a second electrode 20 that is an anode is formed on the upper surface of the contact layer 19 .

The GaN substrate 11 forms a base for laminating each layer constituting the nitride semiconductor light emitting device 100 .

The first clad layer 12 is formed to have a low refractive index in order to confine light emitted from the active layer 14, which will be described later. The first clad layer 12 is made of, for example, n-type AlGaN. The film thickness is, for example, 1000 nm or more.

The first optical guide layer 13 is a layer for confining light having a refractive index intermediate between the n-type first clad layer 12 and the active layer 14 and formed between them. The first optical guide layer 13 is made of, for example, indium gallium nitride (InGaN) made of In _b Ga _(1-b) N (0<b<1). Moreover, the film thickness is, for example, 150 nm or more.

The active layer 14 is a light-emitting region made of InGaN or the like that emits light with a wavelength corresponding to the bandgap by recombination of electrons and holes. The active layer 14 may have a multi-quantum well (MQW) structure as well as a quantum well structure. By forming the active layer 14 in a multi-quantum well structure, the number of light-emitting layers increases, so that the light emission intensity of the laser can be improved.

The second optical guide layer 15 is an optical guide layer formed on the upper surface of the first optical guide layer 13 that confines light due to the difference in refractive index so as to sandwich the active layer 14 . Like the first optical guide layer 13, the second optical guide layer 15 is made of, for example, indium gallium nitride (InGaN) made of InbGa(1- _b ₎ N (0<b<1). Moreover, the film thickness is, for example, 150 nm or more. The product of the average composition ratio b of the second optical guide layer 15 and the first optical guide layer 13 and the total film thickness t of the first optical guide layer 13 and the second optical guide layer 15 is 7 nm or more. may

The electron barrier layer 16 is an energy barrier for suppressing electron overflow from the active layer 14 and promoting recombination of electrons and holes in the active layer 14 . The electron barrier layer 16 is made of, for example, aluminum gallium nitride (AlGaN) made of Al _x Ga _(1-x) N (0<x<1). The thickness of the electron barrier layer 16 is desirably a very thin layer of, for example, 5 nm to 10 nm. Also, magnesium (Mg) is doped at 10 ¹⁹ /cm ³ or more in order to increase the energy barrier of the conduction band.

The fault suppression layer 17 is a layer for preventing occurrence of faults 35 laminated on the upper surface of the electron barrier layer 16 . The fault suppression layer 17 is, for example, aluminum gallium nitride (AlGaN) made of Al _z Ga _(1-z) N (0≦z<y<1) or In _a Ga _(1-a) N (0≦a≦1). ) is made of indium gallium nitride (InGaN). Also, the film thickness is, for example, 10 nm or more, and the p-type is configured by doping Mg at 10 ¹⁸ /cm ³ or more.

The second clad layer 18 sandwiches the active layer 14 with the second optical guide layer 15, the electron barrier layer 16 and the fault suppressing layer 17 in correspondence with the first optical guide layer 13 that confines light due to the difference in refractive index. 2 is a layer formed on the upper surface of the fault suppression layer 17 .
The second clad layer 18 is made of, for example, aluminum gallium nitride (AlGaN) made of Al _y Ga _(1-y) N (0<y<1). Also, the film thickness is, for example, 100 nm or more, and the p-type is configured by doping Mg at 5×10 ¹⁸ /cm ³ or more.

The contact layer 19 is a layer laminated on the upper surface of the second clad layer 18 and electrically connected to the second electrode 20 . Moreover, the film thickness is 10 nm or more, and for example, a p-type GaN layer doped with Mg at 10 ²¹ /cm ³ or more is configured and ohmic-connected to the second electrode 20 .

The second electrode 20 is laminated on the upper surface of the contact layer 19 . The second electrode 20 is an anode electrode to be wire-bonded with, for example, at least one gold wire (Au) or the like in the subsequent mounting process.
The second electrode 20 is formed on the upper surface of the ridge portion 30 from which both side surfaces of the contact layer 19 and the second clad layer 18 are removed by etching such as RIE.

The insulating layer 21 exposes the upper surface 20a of the second electrode 20, covers the

other side surfaces

30a, 30a of the ridge portion 30, and provides electrical insulation. The upper surface 20a of the second electrode 20 not covered with the insulating layer 21 is wire-bonded as described above. The configuration of the nitride semiconductor light emitting device 100 according to the present disclosure is as described above.

<2. Fault Prevention of Nitride Semiconductor Light Emitting Device According to Present Disclosure>
[About faults]
Fault prevention of the nitride semiconductor light emitting device 100 according to the present disclosure configured as described above will be described below.

FIG. 9 is a schematic diagram of a fault 35 generated in the front facet 31, which is the cleavage plane of the nitride semiconductor light emitting device 100. FIG. As indicated by the dashed line in this drawing, the fault 35 often occurs in a crosswise direction from the upper surface of the second cladding layer 18 slightly away from the side surface 30a of the ridge 30, diagonally to the lower left, in a horizontal direction. The occurrence of such a fault 35 affects the characteristics of the laser and becomes a factor of deteriorating the yield in manufacturing.

[Cause of fault]
Such a fault 35 is considered to occur for the following reasons.
The active layer 14 has a structure sandwiched between the first optical guide layer 13 and the second optical guide layer 15 above and below. The first optical guide layer 13 and the second optical guide layer 15 are composed of InGaN obtained by adding In to GaN (more precisely, "InGaN" of the second optical guide layer 15 is, for example, "In _b Ga _(1-b) N etc., but when it is complicated, it is simply written as "InGaN." When an InGaN layer is formed by adding In to GaN, its lattice constant becomes larger than that of the GaN layer. Therefore, compressive strain is generated in the InGaN layer.

On the other hand, the electron barrier layer 16 and the second clad layer 18 laminated on the upper surface of the second optical guide layer 15 are composed of AlGaN layers in which Al is added to GaN. When an AlGaN layer is formed by adding Al to GaN, its lattice constant becomes smaller than that of GaN. Therefore, tensile strain is generated in the AlGaN layer.

Therefore, the strain at the boundary between the second optical guide layer 15 in which In is added to GaN and the electron barrier layer 16 in which Al is added to GaN is the sum of the compressive strain and the tensile strain, so the stress becomes maximum. .
Further, force is applied to the front end surface 31 and the rear end surface 32 when cleaving the wafer (not shown). In addition to the stress due to the strain resulting from the difference in lattice constant, it is considered that the fault 35 is caused by the mechanical force applied during cleavage.

I will explain the above in more detail. FIG. 10 shows the relationship between the lattice constants and bandgap energies of InGaN, GaN, and AlGaN. That is, as shown in this figure, InN (52) has a smaller bandgap energy and a larger lattice constant than GaN (51). On the other hand, AlN(53) has a large bandgap energy and a small lattice constant. Therefore, the wavelength of InN (52) is in the infrared region, and the wavelength of AlN (53) is in the ultraviolet region. Also, the wavelength of GaN (51) is in the ultraviolet region close to the visible light region. The numerals such as "(51)" in parentheses after the chemical symbols indicating semiconductor materials such as "GaN" indicate the reference numerals in the figure. The same shall apply hereinafter. For FIG. 10, refer to "Optical Vol. 24, No. 11, p. 674, FIG. 1".

From this figure, it can be seen that light with a wavelength in the visible light region can be obtained by increasing the composition ratio of In in InGaN (62). Therefore, the active layer 14 can adjust the wavelength of the emitted light, that is, the emission color, by adjusting the composition ratio of In. However, as the composition ratio of In increases, the lattice constant becomes larger than that of GaN (51), so the compressive strain increases.

AlGaN is used on the anode side of the nitride semiconductor light-emitting device 100 because it must have an energy gap larger than the bandgap of GaN in order to inject a large current for laser oscillation. is. That is, in FIG. 10, it can be seen that the energy gap can be increased by increasing the composition ratio of Al in AlGaN (63). On the other hand, however, as the composition ratio of Al increases, the lattice constant becomes smaller than that of GaN (51), resulting in an increase in tensile strain.

Therefore, in this figure, the difference in lattice constant between InGaN (62) and AlGaN (63) is the difference 72 in lattice constant between InGaN (62) and GaN (51) and the difference 72 in lattice constant between GaN (51) and AlGaN (63). is the total value of the lattice constant difference 73 of , which is a very large value. This is the main reason why faults 35 are generated in the second clad layer 18 . In addition, it is considered that the force applied when cleaving the wafer, which will be described later, triggers the generation of the fault 35 .

[Countermeasures to prevent the occurrence of faults]
Therefore, in the nitride semiconductor light emitting device 100 according to the present disclosure, the fault suppressing layer 17 is provided between the first optical guide layer 13 and the second optical guide layer 15, which are InGaN layers, and the second clad layer 18, which is an AlGaN layer. is inserted. That is, the difference in lattice constant between InGaN (62) and AlGaN (63) (difference 72+difference 73) is the difference in lattice constant between the InGaN layer and the fault suppression layer 17, and the lattice constant between the fault suppression layer 17 and the AlGaN layer. , the effect of the stress caused by the strain generated at the boundary between the InGaN layer and the AlGaN layer is suppressed, and the generation of the fault 35 is prevented.

The lattice

constant difference

72, 73 is the value of the average composition ratio b in In _b Ga _(1−b) N (0<b<1) of the first optical guide layer 13 and the second optical guide layer 15, the electron The value of the composition ratio x in Al _x Ga _(1-x) N (0<x<1) of the barrier layer 16, the Al _y Ga _(1-y) N (0<y<1) of the second cladding layer 18 It can be adjusted by changing the value of the composition ratio y.
Further, the fault suppression layer 17 is made of Al _z Ga _(1-z) N (0≦z<y<1) (corresponding to AlGaN (63) in FIG. 10) or In _a Ga _(1-a) N (0≦a). If ≦1) (corresponding to InGaN (62) in FIG. 10), it can be adjusted by changing the value of the composition ratio z or a in this case.

In the nitride semiconductor light emitting device 100 according to the present disclosure, changing all of the above composition ratios b, x, and y will affect the laser characteristics themselves. For this reason, the value of the composition ratio z or the value of the composition ratio a of the fault suppression layer 17 that is likely to be effective, and the average composition ratio of In in the first optical guide layer 13 and the second optical guide layer 15, which are InGaN layers, It was decided to adjust by changing the value of b. That is, in FIG. 10, first, with GaN (51) as the center, the value of the Al composition ratio z of the fault suppressing layer 17 is used as a parameter, and the amount of In in the InGaN of the first optical guide layer 13 and the second optical guide layer 15 is calculated. By changing the value of the average composition ratio b, that is, by changing the InGaN (62) in this figure, the value of the composition ratio b that can prevent the generation of the fault 35 was obtained.

[Construction for Relieving Stress Due to Distortion]
As described above, the nitride semiconductor light emitting device 100 according to _the present disclosure _{includes Al x} _Ga ₍ _1-x) N (0<x<1) and the second clad layer 18 of Al _y Ga _(1-y) N (0<y<1), for example , Al _z Ga _(1-z) N (0≦z<y<1) or In _a Ga _(1-a) N layer (0≦a≦1).

That is, between the second optical guide layer 15 made of InGaN having a large compressive strain and the second cladding layer 18 made of AlGaN having a large tensile strain, an electron barrier layer 16 made of AlGaN is interposed between the fault suppression layer. By providing a strain buffer zone 17, the generation of the fault 35 itself is prevented.

Here, originally, the fault suppression layer 17 should be inserted between the second optical guide layer 15 and the electron barrier layer 16, which is the boundary between the InGaN layer and the AlGaN layer. However, such arrangement causes a problem that the gap between the active layer 14 and the electron barrier layer 16 becomes too wide, and the effect of suppressing electron overflow from the active layer 14 is reduced.

On the other hand, the electron barrier layer 16 stops electrons passing over the active layer 14, and its film thickness should be 5 nm. Therefore, if the film thickness is extremely thin, for example, 5 nm to 10 nm, the stress due to strain generated in the electron barrier layer 16 is not so large as compared with others. Also, the thinner the film is, the less the stress can be. Therefore, by forming the electron barrier layer 16 with an extremely thin film thickness, the gap between the electron barrier layer 16 laminated on the upper surface of the second optical guide layer 15 made of InGaN and the second clad layer 18 made of AlGaN is reduced. It was decided to dispose the fault suppression layer 17 on the .

[Fault prevention effect]
3 and 4, the result of taking measures to reduce the strain generated between the InGaN layer and the AlGaN layer will be described. The horizontal axis of FIG. 3 represents the average composition ratio (%) of In in the first optical guide layer 13 and the second optical guide layer 15 . The vertical axis is the fault occurrence rate. In this graph, the composition ratio (%) of Al in the AlGaN layer of the fault suppression layer 17 is used as a parameter. In this figure, the white circles are 7% Al, the black triangles are 5% Al, and the black circles are 0% Al.

In this figure, the white circle indicating that the Al composition ratio of the fault suppression layer 17 is 7% indicates that the fault occurs when the average In composition ratio of the first optical guide layer 13 and the second optical guide layer 15 exceeds 2.3%. It can be seen that the incidence increases rapidly to about 62%.
The black triangles where the Al composition ratio of the fault suppressing layer 17 is 5% indicate that the fault 35 is formed when the average In composition ratio of the first optical guide layer 13 and the second optical guide layer 15 is about 2.1%. Occur. However, even if the composition ratio of In is increased, the fault occurrence rate is about 20%, and does not increase rapidly as indicated by the white circles.

In addition, the black circles at which the Al composition ratio of the fault suppression layer 17 is 0% correspond to when the average In composition ratio of the first optical guide layer 13 and the second optical guide layer 15 is 2.5% to 2.6%. It can be seen that the fault occurrence rate is close to 0%.
That is, when the average composition ratio of In in the first optical guide layer 13 and the second optical guide layer 15 is set to approximately 2.5% to 2.6%, and the composition ratio of Al in the fault suppression layer 17 is set to 0%, the fault 35 was found not to occur.
Setting the Al composition ratio of the fault suppression layer 17 to 0% means that the fault suppression layer 17 is formed of GaN, which is the same composition as the GaN substrate 11 .

The horizontal axis of FIG. 4 is the product of the total film thickness t (nm) of the first optical guide layer 13 and the second optical guide layer 15 and the average composition ratio b of In. This becomes the amount of distortion. The vertical axis is the fault occurrence rate. In this graph, the Al composition ratio (%) of the fault suppression layer 17 is used as a parameter. In this figure, the white circles are 7% Al, the black triangles are 5% Al, and the black circles are 0% Al.

In this figure, it can be seen that for the white circles in which the Al composition ratio of the fault suppression layer 17 is 7%, the fault occurrence rate rapidly increases to about 62% when the strain amount exceeds about 8 nm.
Further, in the black triangle where the Al composition ratio of the fault suppression layer 17 is 5%, faults 35 are generated when the amount of strain exceeds about 7 nm. However, even if the amount of strain increases, the fault occurrence rate is about 20% and does not increase rapidly like the white circles.
Further, it can be seen that the black circles in which the Al composition ratio of the fault suppression layer 17 is 0% have a fault generation rate close to 0% even when the strain amount is approximately 10.5 nm.

From the above, it has been found that the fault 35 occurs when the Al composition ratio of the fault suppression layer 17 is 7% and 5%. On the other hand, it was found that faults 35 are less likely to occur when the Al composition ratio is 0%. That is, it is desirable that z=0.0 in Al _z Ga _(1−z) N (0≦z<y<1) of the fault suppression layer 17 . The fault suppression layer 17 in this case is Al _0.0 Ga _(1-0.0) N, that is, GaN. This leads to the conclusion that a=0.0 also in the In _a Ga _(1-a) N layer (0≦a≦1).
In other words, it was found that the fault suppression layer 17 should be formed of GaN having the same composition as the GaN substrate 11 .
Further, from the results shown in FIG. 4, it is considered that the occurrence of the fault 35 can be prevented by defining the amount of strain to 7 nm or less.

Here, the “total film thickness t” in “the total film thickness t (nm) of the first optical guide layer 13 and the second optical guide layer 15 × the average composition ratio b of In” and the total thickness of the second optical guide layer 15 . For example, if the film thickness of the first optical guide layer 13 is 175 nm and the film thickness of the second optical guide layer 15 is 175 nm, the total film thickness t of both is 175+175=350 nm. The “average composition ratio b” is the average value of the In composition ratios of both.

Next, based on the above test results, the total film thickness t of In _b Ga _(1−b) N (0<b<1) of the first optical guide layer 13 and the second optical guide layer 15 is 350 nm. Find the value of the average composition ratio b in each case. Since the strain amount obtained from FIG. 4 is 7 nm, substituting t=350 nm into the above equation,
t(350 nm)×b=7 nm.
When the value of the average composition ratio b is obtained from this formula, b=7 nm/350 nm=0.02.
Therefore, when 0.02 is substituted for the average composition ratio b of In _b Ga _(1−b) N, the first optical guide layer 13 and the second optical guide layer 15 are composed of In _0.02 Ga _0.98 N and Become.

That is, the first optical guide layer 13 and the second optical guide layer 15 are made of In _0.02 Ga _0.98 N, and the fault suppressing layer 17 is made of Al _0.0 Ga _(1−0.0) N=GaN. Thus, the nitride semiconductor light emitting device 100 that prevents the generation of the fault layer 35 can be obtained.
This composition ratio is a value when the total film thickness t is 350 nm. Therefore, when the total film thickness t is set to another value, the average composition ratio b can be obtained by the above calculation.
As described above, the effect of the fault suppression layer 17 and the usefulness of the configuration of the nitride semiconductor light emitting device 100 having the configuration shown in FIG. 1 were substantiated by the test results shown in FIGS.
Since the fault suppression layer 17 is for dividing the distortion of the lattice constant and relaxing the stress, the film thickness thereof should be 10 nm or more.

<3. Manufacturing Method of Embodiment of Nitride Semiconductor Light Emitting Device According to Present Disclosure>
An example of a manufacturing method of an embodiment of the nitride semiconductor light emitting device 100 according to the present disclosure will be described with reference to FIGS. 5 to 8. FIG. 5 to 8 are cross-sectional views of the laminated structure 101 viewed from the front end surface 31 side, which is the light emitting end surface. In this specification, the laminated structure 101 refers to the nitride semiconductor light emitting device 100 in the process of being formed by sequentially laminating GaN layers and the like.

[Step of forming laminated structure]
First, on the (0001) C plane of the GaN substrate 11, as shown in FIG. 12. First optical guide layer 13 on first cladding layer 12, active layer 14 on first optical guide layer 13, second optical guide layer 15 on active layer 14, p-type on second optical guide layer 15 The electron barrier layer 16, the fault suppression layer 17 on the electron barrier layer 16, the p-type second cladding layer 18 on the fault suppression layer 17, and the p-type contact layer 19 on the second cladding layer 18 with a predetermined film Thick layers are sequentially laminated.

Here, the first optical guide layer 13 and the second optical guide layer 15 are composed of In _b Ga _(1−b) N (0<b<1) so that the average value of the composition ratio b is a predetermined value. Control. Similarly, the electron barrier layer 16 controls the value of the composition ratio x of Al _x Ga _(1-x) N (0<x<1). The second clad layer 18 controls the value of the composition ratio y consisting of Al _y Ga _(1−y) N (0<y<1). The fault suppression layer 17 has a composition ratio z of Al _z Ga _(1−z) N (0≦z<y<1) or In _a Ga _(1−a) N (0≦a≦1). The value of the composition ratio a is controlled. However, according to the above test results, z=0 or a=0.
Further, the injection amount of a dopant such as Mg is controlled in order to form the electron barrier layer 16, the fault suppressing layer 17, the second cladding layer 18 and the contact layer 19 into p-type.

[Process of forming ridge]
Next, the second cladding layer 18 and the contact layer 19 are etched in the thickness direction by dry etching to form the ridge portion 30 .

Specifically, as shown in FIG. 6, first, a pad layer 20A for forming the second electrode 20 is formed on the contact layer 19. Then, as shown in FIG. After the pad layer 20A is formed on the entire surface by vacuum deposition, a strip-shaped etching resist layer is formed on the pad layer 20A by photolithography. After removing the pad layer 20A not covered with the etching resist layer using aqua regia, the etching resist layer is removed. Through such steps, the laminated structure 101 shown in FIG. 7 can be obtained. A strip-shaped second electrode 20 may be formed on the contact layer 19 by a lift-off method.

When patterning the second electrode 20, when the etching rate of the second electrode 20 is ER0 and the etching rate of the laminated structure 101 is ER1, ER0/ER1≧1×10, preferably ER0/ER1. It is desirable to satisfy ≧1×10 ² . When ER0/ER1 satisfies such a relationship, the second electrode 20 can be reliably patterned without etching the laminated structure 101 (or with slight etching).

Next, using the second electrode 20 as an etching mask, the second cladding layer 18 and the contact layer 19 are etched in the thickness direction by a dry etching method to form the ridge portion 30 . Specifically, by reactive ion etching (RIE: Reactive Ion Etching), using the second electrode 20 as an etching mask, both side surfaces of the second clad layer 18 and the contact layer 19 are etched to form a side surface portion 30a. , 30a.

Through the steps described above, the laminated structure 101 shown in FIG. 8 can be obtained. Since the ridge portion 30 is formed by the self-alignment method using the second electrode 20 patterned in a band shape as an etching mask in this manner, misalignment may occur between the second electrode 20 and the ridge portion 30. No.

[Step of forming insulating layer and first electrode]
Next, an insulating film is laminated on the entire upper surface of the ridge portion 30, and the insulating film laminated on the second electrode 20 is removed. As a result, the upper surface 20 a of the second electrode 20 is exposed, and the insulating layer 21 is formed on both side surfaces 30 a of the ridge portion 30 .
A metal layer (not shown) may be formed on the insulating layer 21 in order to improve the heat dissipation and wire bondability of the nitride semiconductor light emitting device 100 and the wettability of the mounting solder joint material.

In forming the first electrode 10, the back surface of the laminated structure 101 is polished so as to have a thickness suitable for cleaving and mounting. After the polishing is completed, an n-metal film is formed on the back surface by vapor deposition or sputtering, and a pattern is formed by lift-off, for example, to form a first electrode 10 that will serve as a cathode, as shown in FIG. Thus, a laminated structure 101 is formed.
Through the steps described above, a wafer on which the nitride semiconductor light emitting devices 100 shown in FIG. 1 are arranged can be obtained.

[Wafer Cleavage, Mounting and Inspection Process]
Next, the wafer is cleaved in a cleaving process, inspected in an inspection process, and sorted into non-defective products and defective products. The nitride semiconductor light-emitting device 100 selected as a good product by the inspection is sent to the mounting process, which is the next process. The nitride semiconductor light emitting device 100 is packaged in a mounting process and subjected to a final inspection. Thus, the nitride semiconductor light emitting device 100 according to this embodiment can be manufactured.

Since the manufacturing method of the embodiment of the nitride semiconductor light emitting device 100 according to the present disclosure has the steps as described above, it is possible to provide the high quality nitride semiconductor light emitting device 100 according to the present embodiment. .

It should be noted that the above manufacturing process is merely an example, and the order of the processes may be changed. Also, they may be replaced with new working methods, processing methods, or new equipment.

By adopting the manufacturing process as described above, the electron overflow is suppressed, the deterioration of the laser characteristics is prevented, the stress due to the strain is relieved, the occurrence of the fault 35 is prevented, and the yield at the time of manufacturing is improved. The material semiconductor light emitting device 100 can be manufactured.

Finally, the description of each embodiment described above is an example of the present disclosure, and the present disclosure is not limited to the above-described embodiments. Therefore, it goes without saying that various modifications other than the above-described embodiments can be made in accordance with the design and the like within the scope of the technical concept of the present disclosure. Also, the effects described in this specification are merely examples, and the present invention is not limited to these, and there may be other effects.

Note that the present technology can also take the following configuration.
(1)
a GaN substrate;
a first clad layer laminated on the GaN substrate;
a first optical guide layer laminated on the first cladding layer;
an active layer stacked on the first optical guide layer;
a second optical guide layer laminated on the active layer;
an electron barrier layer laminated on the second optical guide layer;
a fault suppression layer laminated on the electron barrier layer;
a second clad layer laminated on the fault suppression layer;
a contact layer laminated on the second cladding layer;
A nitride semiconductor light emitting device having
(2)
The fault suppression layer is formed of aluminum gallium nitride made of Al _z Ga _(1-z) N (0≦z<1), or made of In _a Ga _(1-a) N (0≦a≦1) The nitride semiconductor light-emitting device according to (1) above, which is made of indium gallium nitride.
(3)
The nitride according to (1) or (2) above, wherein the fault suppression layer is Al _z Ga _(1−z) N (0≦z<y<1) with a composition ratio of z=0. Semiconductor light emitting device.
(4)
The nitride semiconductor light emitting device according to (1) or (2), wherein the fault suppression layer is formed of In _a Ga _(1−a) N (0≦a≦1) with a composition ratio of a=0. element.
(5)
The nitride semiconductor light-emitting device according to any one of (1) to (4), wherein the fault suppressing layer has a thickness of 10 nm or more.
(6)
The first optical guide layer and the second optical guide layer are formed of indium gallium nitride made of In _b Ga _(1-b) N (0<b<1), and the average value of the composition ratio b and the total film of both The nitride semiconductor light-emitting device according to any one of (2) to (4), wherein the product with the thickness t is 7 nm or more.
(7)
The electron barrier layer is formed of aluminum gallium nitride having a thickness of 5 nm or more and made of Al _x Ga _(1-x) N (0<x<1) doped with p-type impurities (1) to (6). ).
(8)
The nitride semiconductor according to any one of (1) to (7), wherein the second clad layer is formed of aluminum gallium nitride composed of Al _y Ga _(1-y) N (0<y<1). light-emitting element.

REFERENCE SIGNS LIST 10 first electrode 11 GaN substrate 12 first clad layer 13 first optical guide layer 14 active layer 15 second optical guide layer 16 electron barrier layer 17 fault suppression layer 18 second clad layer 19 contact layer 20 second electrode 21 insulating layer 30 Ridge Part 30a Side Part 31 Front End Face 32 Rear End Face 35 Fault 51 Bandgap Energy and Lattice Constant of GaN 52 Bandgap Energy and Lattice Constant of InN 53 Bandgap Energy and Lattice Constant of AlN 62 Bandgap Energy and Lattice Constant of InGaN 63 Band gap energy and lattice constant of AlGaN 72 Difference in lattice constant between GaN and InGaN 73 Difference in lattice constant between GaN and AlGaN 100 Nitride semiconductor light emitting device 101 Laminated structure t Total film thickness a, b, x, y, z Composition ratio

Claims

a GaN substrate;
a first clad layer laminated on the GaN substrate;
a first optical guide layer laminated on the first cladding layer;
an active layer stacked on the first optical guide layer;
a second optical guide layer laminated on the active layer;
an electron barrier layer laminated on the second optical guide layer;
a fault suppression layer laminated on the electron barrier layer;
a second clad layer laminated on the fault suppression layer;
a contact layer laminated on the second cladding layer;
A nitride semiconductor light emitting device having
The fault suppression layer is formed of aluminum gallium nitride made of AlzGa(1- z ) N (0≤z<1), or from an InaGa (1-a) N layer (0≤a≤1) 2. The nitride semiconductor light-emitting device according to claim 1, which is made of indium gallium nitride.
2. The nitride semiconductor light-emitting device according to claim 1, wherein said fault suppressing layer is formed in Al z Ga (1-z) N (0≦z<y<1) with a composition ratio of z=0.
2. The nitride semiconductor light-emitting device according to claim 1, wherein said fault suppressing layer is formed of In a Ga (1-a) N (0≤a≤1) with a composition ratio of a=0.
The nitride semiconductor light-emitting device according to claim 1, wherein the fault suppression layer is formed to have a thickness of 10 nm or more.
The first optical guide layer and the second optical guide layer are formed of indium gallium nitride made of In b Ga (1-b) N (0<b<1), and the average value of the composition ratio b and the total film of both 3. The nitride semiconductor light emitting device according to claim 2, wherein the product with the thickness t is 7 nm or more.
2. The nitride according to claim 1, wherein the electron barrier layer is formed of aluminum gallium nitride having a thickness of 5 nm or more and made of Al x Ga (1-x) N (0<x<1) doped with p-type impurities. Semiconductor light emitting device.
2. The nitride semiconductor light emitting device according to claim 1, wherein said second clad layer is made of aluminum gallium nitride made of Al y Ga (1-y) N (0<y<1).