JPH10294533A - Nitride compound semiconductor laser and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable carriers to be effectively injected into an active layer and to enable a nitride semiconductor laser to be restrained from operating in a high-order mode, to operate on a low operating voltage, and to be enhanced in low-noise characteristics by a method wherein a mesa-type current injection layer is provided above the active layer, and a current block is provided to the side of the mesa-type current injection layer to form a current constriction structure. SOLUTION: Two parallel grooves cut in the surface of a multilayer structure SL are filled up with insulator (polymide) or semiconductor material for the formation of a current block layer 111. A polyimide layer not only functions as a layer to stop and constrict a current but also is suitable for a light trapping region used for restraining a high-order mode. N-type Gax Iny Alz N (x+y+z=1, 0<=x, y, z<=1) can be used as the above semiconductor material, wherein a PN junction is formed to constrict a current. The current blocking layer 111 is formed on N-type In0.1 Ga0.9 , provided so as to reach near an active layer 105 in a P-type clad layer 106, and effectively restrains an injected current from diffusing in a lateral direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor device using a nitride compound semiconductor material, and more particularly to a gallium nitride-based blue-violet semiconductor laser and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, GaN, InGaN, GaAl
Gallium nitride-based compound semiconductors such as N and InGaAlN have attracted attention as materials for short-wavelength semiconductor lasers intended for application to high-density optical disk systems and the like. This is because laser light having a short oscillation wavelength can reduce the condensed light size, which is effective for increasing the recording density.

In order to oscillate a semiconductor laser with a threshold current, it is necessary to efficiently inject carriers into the active layer, and it is important to form a pn junction having a heterojunction and a current confinement structure. In addition, a semiconductor laser used as a pickup light source for an optical disk needs to control the oscillation mode, and appropriately absorbs laser light protruding from the active layer to increase the refractive index difference and reduce the gain of higher-order modes by absorption. It is important to form a structure that causes stable fundamental transverse mode oscillation.

However, as a nitride compound semiconductor laser, only a so-called gain waveguide structure laser in which only an electrode stripe structure or a p-type semiconductor layer is formed in a ridge structure has been reported. On the other hand, the fact that the multiple quantum well structure active layer can reduce the threshold current density with respect to the bulk active layer
It is known in conventional material systems such as GaAlP system and the like, and a nitride compound semiconductor laser uses a multiple quantum well structure active layer from the beginning. On the contrary, the threshold current is still high,
Since the operating voltage is high, the power consumption is large and the life is short, and the oscillated laser light has a large noise and cannot be applied to an optical disk system. Further, since the conventional gain waveguide type semiconductor laser can realize only an optical output of about several mW, the 30 m required for erasing / recording of the optical disk system is required.
It is not suitable for a high-power semiconductor laser of W or more.

[0005] This is because it is difficult to inject high-density and high-efficiency carriers into the quantum well active layer, it is difficult to form a structure capable of controlling the fundamental transverse mode for low noise characteristics, and it is difficult to form a plurality of semiconductors. This is because lasers cannot be easily integrated. That is, carriers are injected into the active layer at a high current density required for the basic transverse mode gain while forming a suitable absorption region where only the basic transverse mode gain can be obtained, and without confining the current from the electrodes to the active layer. Was difficult.
In addition, since it is difficult to alternately form the current confinement region and the absorption region, it has been difficult to integrate a plurality of nitride compound semiconductor lasers.

As described above, in order to realize a highly reliable gallium nitride-based blue-violet semiconductor laser which operates at a low threshold current and a low voltage and is continuously oscillated in a fundamental transverse mode, which is practically used for an optical disk or the like, It is important to efficiently inject carriers into the layer and to form a structure that absorbs higher-order modes. However, at present, a structure that satisfies these conditions has not yet been obtained.

[0007]

As described above, conventionally, in a semiconductor laser using a nitride compound semiconductor, it is difficult to form a current confinement structure capable of controlling a fundamental transverse mode, and not only is the noise characteristic poor. High-density carriers cannot be injected into the active layer, and it has been difficult to realize an element having a low threshold current, a low operating voltage, low noise characteristics, and a high optical output.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. It is an object of the present invention not only to easily form a basic transverse mode control structure but also to perform high-density carrier injection into an active layer. It is an object of the present invention to provide a highly reliable nitride compound semiconductor laser having a low threshold current, a low operating voltage, a low noise characteristic and a high current confinement structure.

[0009]

In order to achieve the above object, the present invention employs the following configuration. That is, the present invention provides a gallium nitride-based compound semiconductor (Ga _x In _y Al
_zN : x + y + z = 1, 0 ≦ x, y, z ≦ 1). In a semiconductor laser in which an active layer is sandwiched between semiconductor layers of different conductivity types, carriers are formed on the active layer and carriers are formed in the active layer. A current confinement structure for injection is formed in a mesa shape, and a side surface of the mesa current confinement structure is covered with a current block layer.

Here, preferred embodiments of the present invention include the following. (1) The current block layer is an organic insulating film, an oxide film, or a gallium nitride-based compound semiconductor having a different conductivity from the mesa-type current confinement structure. (2) The active layer has a multiple quantum well structure. (3) The relationship between the width W1 of the current constriction structure and the film thickness W2 of the semiconductor layer in contact with the electrode metal having a different conductivity type under the active layer is W1 ≦ 4 · W2. (4) There are a plurality of mesa-type current confinement structures.

The present invention also provides a method of manufacturing a gallium nitride compound semiconductor laser in which an active layer is sandwiched between semiconductor layers of different conductivity types.
Forming an electrode, forming an etching-resistant mask metal on the p-electrode, forming a window with a photoresist on a part of the semiconductor layer surface on the active layer for forming a current blocking layer, Forming a groove using the etching-resistant mask metal and photoresist; and filling the groove to form the current blocking layer.

According to the present invention, in the nitride compound semiconductor laser, the mesa-type current confinement structure is provided on the active layer, and the current blocking layer is provided on the side surface of the mesa-type current confinement structure. Highly reliable continuous oscillation with current, low operating voltage and low noise characteristics becomes possible.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a sectional view showing a schematic configuration of a gallium nitride based blue semiconductor laser device according to a first embodiment of the present invention. In the figure, 101 is a sapphire substrate, and LS is a laminated structure made of a gallium nitride-based compound semiconductor formed on the substrate 101. That is, in the multilayer structure LS, 102 is a GaN buffer layer, 103 is an n-type GaN contact layer (Si-doped, impurity concentration 5 × 1018 cm ⁻³ , layer thickness 4 μm), 104 is an n-type Al _0.15 Ga _0.85 N cladding layer ( Si dope, 1 ×
1018 ^-3 , 0.3 μm) and 105 are SCHs in which a GaN waveguide region (undoped, 0.1 μm), an active region having a quantum well structure, and a p-type GaN waveguide region (Mg doped, 0.1 μm) are stacked. -MQW (Separate Confinement He
tero-structure multi-Quantum Well) The active layer (where the active region is 10 pairs of an In _0.2 Ga _0.8 N quantum well layer (undoped, 2 nm) and an In _0.05 Ga _0.95 N barrier layer (undoped, 4 nm)). 106 has a p-type Al _0.15 Ga
_0.85 N cladding layer (Mg doped, 1 × 1018 cm ⁻³ ,
0.3 μm), 107 is a p-type GaN contact layer (Mg
Dope, 1 × 10 18 cm ⁻³ , 1 μm).

Reference numeral 108 denotes an SiO ₂ insulating film, and 109 denotes Pt (10 nm) / Ti (50 nm) / Pt (30n).
m) / Au (100 nm) p-side electrode, 100 is C
Reference numeral 112 denotes an n-side electrode having a Ti / Au structure, and reference numeral 113 denotes a mounting film having a Cr / Au structure. Although not particularly shown, a high reflection coating in which TiO ₂ / SiO ₂ is laminated in multiple layers is applied to the laser light emitting end face.

According to the present invention, two substantially parallel grooves are formed on the surface of the laminated structure LS, and the current blocking layer 1 is formed by embedding an insulator or a semiconductor material in the grooves.
11 are provided. As an insulator material for forming the current block layer 111, for example, polyimide can be used as the insulator. The current blocking layer 1
As a semiconductor material for forming 11, for example, n-type Ga
_{x In y Al x N (x} + y + z = 1,0 ≦ x, y, z ≦
1) and the like. That is, by using an n-type semiconductor, a pn junction can be formed to effectively confine the current.

The current block layer 111 buried with polyimide functions as a layer that blocks current and blocks current, and also functions as a light confinement region. Polyimide is extremely suitable as a light confinement region for suppressing higher-order modes because its light absorption is as high as 90 to 60% in a wavelength band of 400 to 450 nm.

When, for example, an n-type In _0.1 Ga _0.9 N layer is used as the material of the current blocking layer 111, this material is transparent with respect to the oscillation wavelength, so that high-order transverse mode light can be effectively removed. By absorbing, fundamental transverse mode oscillation can be obtained.

Here, as shown in FIG. 1, it is desirable that the current blocking layer 111 be formed deep in the p-type cladding layer 106 so as to reach the vicinity of the active layer 105. The reason is that, when the current blocking layer 111 is formed deeper in the p-type cladding layer 106, diffusion of the injected current in the lateral direction is more effectively suppressed, and higher-order mode light is also more effective. This is because it can be absorbed.

That is, the active layer 1 of the p-type cladding layer 106
By forming the current blocking layer 111 to the position near 05, the current path in the lateral direction can be cut off, the current can be effectively confined, and the fundamental transverse mode oscillation can be further promoted.

Next, a method for manufacturing the above-mentioned nitride compound semiconductor laser will be described with reference to the process sectional views of FIGS. 2A to 2F. Here, a case where polyimide is used as a material of the current blocking layer 111 will be described as an example.

First, as shown in FIG. 2A, a layer from the GaN buffer layer 102 to the p-type CaN contact layer 107 is grown on a sapphire substrate by metal organic chemical vapor deposition (hereinafter abbreviated as MOCVD). . Next, a partial region of the semiconductor layer crystal-grown for forming an n-electrode is etched to the n-type GaN contact layer 103 to form a mesa. Although not particularly shown, the GaN buffer layer 102 is 550
By forming a two-layer structure in which 30 nm is deposited at 1 ° C. and then 1 μm is grown at 1100 ° C., a flat nitride compound semiconductor layer with few crystal defects can be grown thereon.

Next, as shown in FIG. 2B, a 900 nm thick SiO ₂ insulating film 108 is deposited on the entire surface of the wafer,
A Ti / Au structure n-side electrode 112 is formed on a part of the aN contact layer 103. It is desirable that the n-side electrode 112 is formed at a position parallel to a stripe-shaped current confinement structure to be formed later and at a distance of 10 μm or less. Further, when the thickness of the n-type GaN contact layer 103 is 2 μm or more,
If the carrier concentration is 2 × 1018 cm ⁻³ or more, it is possible to suppress the total element resistance component between the light emitting region and the n-side electrode and the contact resistance component of the n-electrode to 1 Ω or less. Thus, the semiconductor laser can be driven at a low voltage.

Next, as shown in FIG. 2C, Pt (10 nm) / Ti (50 nm) / Pt (30
nm) / Au (100 nm) laminated p-side electrode 109
And a Ni dry etching mask 910 made of nickel (Ni) having a layer thickness of 1 μm is formed in a stripe shape having a width of 3 μm. The width of the p-side electrode 109 and the Ni dry etching mask 910 is preferably in the range of 2 μm to 8 μm.

Next, as shown in FIG. 2D, openings having a width of 10 μm are provided on both sides of the p-side electrode 109 and the Ni dry etching mask 910 by using a photoresist 912. Further, a groove G is formed for the current confinement structure up to the p-Al _0.15 Ga _0.85 N cladding layer 106 by a dry etching method containing a chlorine gas, and the photoresist 912 and the Ni dry etching mask 910 are removed. Here, the angle θ of the side surface in forming the groove G by the dry etching method is preferably 90 °. However, if θ is in the range of 90 ° to 135 °, the width of current injection into active layer 105 is from 0 μm to +2.
Since it is within the error range of 6 μm, the upper limit of the threshold current can be suppressed to about twice at the maximum.

In addition, as a result of examining the relationship between the interval W1 of the current blocking layer and the transverse mode, it was found that when the interval W1 was 8 μm or less, the basic mode tended to occur. Therefore, it is desirable to determine the interval between the grooves G so that W1 is 8 μm or less.

On the other hand, when the gallium nitride-based crystal layer is grown on the sapphire substrate 101, the crystal strain is reduced by setting the thickness to 2 μm or more, and a flat crystal layer tends to be obtained.

Further, from the viewpoint of electric resistance, the n-type layer has a sheet resistance higher by one digit or more than the p-type layer. The distance between the current blocking layers is equal to the n-type GaN contact layer 1.
It has been found that if the relationship of not more than four times the layer thickness W2 of No. 03 is satisfied, the element resistance on the n-side does not substantially affect characteristics such as operating voltage and power consumption during laser oscillation. Specifically, if W1 is set to four times or less of W2, the ratio of the resistance component contributing to the operating voltage of the semiconductor laser is about p: n = 10: 1, and the resistance component on the n side of the element is , P-side resistance component is negligibly small, and the element resistance is uniquely determined by the resistance component of the p-type layer.

From the above examination results, when the relationship between the current block layer interval W1 and the n-type GaN contact layer thickness W2 satisfies the condition of W1 ≦ 4 · W2, a good-quality nitride on a sapphire substrate is obtained. Gallium crystal layer can be grown,
It has been found that the fundamental transverse mode can be suppressed and the element resistance can be sufficiently reduced.

Further, according to the present invention, the width of the current injection is determined by the width of the p-electrode 109 in the self-alignment process, so that it is suitable for forming a narrow current confinement structure. That is, even in the current confinement structure where the width of current injection is narrow, p
There is an advantage that the contact area of the electrode 109 can be maximized, and as a result, an increase in resistance of the electrode contact portion can be prevented.

Next, as shown in FIG. 2E, polyimide is coated on the entire surface of the wafer except for the upper portion of the n-side electrode 112, and is etched by oxygen ashing until the p-side electrode 109 is exposed. Thus, the current blocking layer 111 can be formed by embedding the polyimide in the groove G. In this case, it is easy to use photosensitive polyimide. However, the entire surface of the wafer is coated with polyimide, and the n-side electrode 112 is formed using a normal lithography process.
Only the upper part may be exposed.

When n-type In _0.1 Ga _0.9 N is used as the material of the current blocking layer 111, an n-type In _0.1 Ga _0.9 N layer is deposited on the entire surface of the wafer instead of polyimide, and the p-side electrode 109 is exposed. Etching may be performed until the etching is completed. Thus, the n-type In _0.1 Ga _{0.9 is formed in the} groove G.
The current blocking layer 111 in which the N layer is embedded can be formed.

Here, even if a material such as polyimide remains on the side surface or the upper surface of the SiO ₂ insulating film 108 or on a part of the n-side electrode 112, the characteristics of the device are not adversely affected unless a problem occurs in the wiring. Needless to say. In addition, instead of polyimide or n-type In _0.1 Ga _0.9 N, another layer of an insulator or n-type Ga _x In _y Al _x N (x + y + z = 1, 0) is used instead of polyimide or n-type In _0.1 Ga _0.9 N.
≦ x, y, z ≦ 1).

Next, as shown in FIG. 2 (f), p
An electrode pad 110 is formed. Next, the back surface of the sapphire substrate 101 is mirror-polished to reduce the thickness of the substrate 101 to 50 μm.
I do. Furthermore, the mounting film 11 having a Cr / Au laminated structure
Form 3 Then, it is cleaved along a plane perpendicular to the substrate. Although not particularly shown, TiO ₂ /
A high reflection coat in which SiO ₂ is laminated in multiple layers is applied. Further, as shown in FIG. 1, a heat sink 1 having high thermal conductivity, such as copper (Cu), cubic boron nitride, or diamond.
A layer 121 metallized with Ti / Pt / Au or the like on 20
Is mounted using gold-tin (AuSu) eutectic solder 122. Note that wirings 123a for current injection,
123b uses a gold (Au) wire or an aluminum (Al) wire.

The semiconductor laser according to this embodiment has a threshold current of 60 mA and an oscillation wavelength of 42 when the cavity length is 0.5 mm.
At 0 nm, the operating voltage was 5.2 V and continuous oscillation occurred at room temperature. Furthermore, the device life at 50 ° C. and 30 mW drive is 5000.
The relative intensity noise from 20 ° C to 70 ° C for more than
It was 140 dB / Hz or less. In the case of this laser, p-AI _0.15 Ga is self-aligned with respect to the p-side electrode 109.
By forming a current confinement structure having a depth of up to _0.85 N cladding layer 106, it is possible not only to suppress the lateral diffusion of current in the p-type layer but also to increase the efficiency of carrier injection into the SCH-MQW active layer 105. By forming the current block layer 111 with polyimide, a good light confinement region can be formed, and higher modes can be suppressed. SCH-
The MQW active layer 105 is composed of a SiO ₂ insulating film 108 and TiO ₂
The surface leakage current can be suppressed by making the structure completely covered by the / SiO ₂ multilayer structure high reflection coat. Therefore, continuous oscillation at room temperature was achieved with low current injection, and further low noise characteristics were obtained.

Next, a second embodiment of the present invention will be described. FIG. 3 is a sectional view illustrating a schematic configuration of a gallium nitride based blue semiconductor laser device according to a second embodiment of the present invention. In the figure, 201 is a sapphire substrate, LS
Is a laminated structure made of a gallium nitride-based compound semiconductor formed thereon. That is, in the multilayer structure LS, 202 is a GaN buffer layer, and 203 is an n-type Ga
N contact layer (Si-doped, 5 × 1018 cm ⁻³ , 4
μm), 204 is an n-type A1 _0.15 Ga _0.85 N cladding layer (Si-doped, 1 × 10 18 cm ⁻³ , 0.3 μm), 2
Reference numeral 05 denotes a quantum well composed of 10 In _0.2 Ga _0.8 N quantum wells (undoped, 2 nm) on a GaN waveguide region (undoped, 0.1 μm) and an In _0.05 Ga _0.95 N barrier layer (undoped, 4 nm) sandwiching the quantum well. An SCH-MQW (Separate Confinement Hete) formed by stacking a structure active region and a p-type GaN waveguide region (Mg doped, 0.1 μm)
ro-structure Multi-Quantum Well) The active layer 206 is a p-A1 _0.15 Ga _0.85 N cladding layer (Mg doped, 1 ×)
1018 cm ⁻³ , 0.3 μm) and 207 are p-GaN contact layers (Mg doped, 1 × 10 18 cm ⁻³ , 1 μm)
m).

Reference numeral 208 denotes an SiO ₂ insulating film, and 209 denotes Pt (10 nm) / Ti (50 nm) / Pt (30n).
m) / Au (100 nm) structure p-side electrode, 210 is Cr
/ Au structure p electrode pad, 211 is a current block layer, 2
Reference numeral 12 denotes a Ti / Au structure n-side electrode, and reference numeral 213 denotes a Cr / Au structure mounting film. Although not particularly described, a high-reflection coating in which TiO ₂ / SiO ₂ is laminated in multiple layers is applied to the laser light emitting end face.

This embodiment is different from the first embodiment of the present invention shown in FIG. 1 in that the layer 211 for current block and light confinement is n-type A1 _0.15 Ga in FIG.
Up to _0.85 N cladding layer 204, n-type G in the case of FIG.
That is, each of them reaches the aN contact layer 203. By adjusting the dry etching time in the manufacturing process, the depth of the layer 211 can be adjusted. The outline of the manufacturing process will be described first.
From the GaN buffer layer 202 on the sapphire substrate
The illustrated semiconductor laser can be manufactured by growing up to the type GaN contact layer 207, then forming a groove, and further embedding an insulator such as polyimide.
The specific manufacturing process is almost the same as that of the first embodiment, and thus the description is omitted.

Here, as shown in FIG. 3A, the current blocking layer 211 is formed of an n-type A1 _0.15 Ga _0.85 N cladding layer 2.
In the case where it is formed to reach 04, current constriction can be more effectively achieved than the element shown in FIG. Further, since the active layer 205 can be separated by the block layer 211, fundamental transverse mode oscillation can be easily generated. However, in this case, the n-type layer 20
4 and the block layer 211 are in contact with each other.
It is desirable to use an insulator such as polyimide as the material 11.

On the other hand, as shown in FIG. 3B, when the current blocking layer 211 is formed up to the n-type GaN contact layer 203, the current injected through the electrode is more effectively constricted. . Conductive SiC as substrate material
In the case where n-side electrodes are used, the n-side electrode is not provided above the substrate 213 as illustrated. It can be provided below the substrate. In such a case, in particular, FIG.
With the configuration of (b), the injection electrode can be effectively constricted.

As a result of trial calculation of the semiconductor laser having the structure shown in FIG. 3A, when the cavity length is 0.5 mm, the threshold current 55
mA, the oscillation wavelength was 420 nm, and the operating voltage was 5.1 V. Further, the device life at 50 ° C. and 30 mW drive was 5000 hours or more, and the relative intensity noise from 20 ° C. to 70 ° C. was −145 dB / Hz or less. In the case of this laser, n-type Al _0.15 G
By forming a current confinement structure up to the a _0.85 N cladding layer 204, the lateral diffusion of the current is suppressed and the SCH
-The efficiency of carrier injection into the MQW active layer 205 can be improved. In addition, by using polyimide having a high light absorption of 90 to 60% in a wavelength band of 400 to 450 nm, a light confinement region can be effectively formed and a higher mode can be effectively suppressed. Further, the SCH-MQW active layer 205 is composed of the SiO ₂ insulating film 208 and the TiO ₂ / SiO
_The surface leakage current can be suppressed by adopting a structure that is completely covered by the _two- layer structure high reflection coat. Therefore, continuous oscillation at room temperature was achieved with low current injection, and further low noise characteristics were obtained.

Further, when the p-side electrode 209 is formed, the p-side electrode becomes n-type In _0.1 Ga due to a pattern shift or the like.
Even if it is formed in contact with the _0.9 N current block layer 211,
Since an insulator such as polyimide was used, a large increase in threshold current did not occur.

Next, a third embodiment of the present invention will be described. FIG. 4 is a cross-sectional view illustrating a schematic configuration of a gallium nitride based blue semiconductor laser device according to a third embodiment of the present invention. In the figure, reference numeral 301 denotes a sapphire substrate;
Is a laminated structure made of a gallium nitride-based compound semiconductor formed thereon.

In the laminated structure LS, 302 is GaN
Buffer layer, 300 is an n-type GaN contact layer (Si-doped, 5 × 1018 cm ⁻³ , 4 μm), 304 is an n-type A
l _0.15 Ga _0.85 N cladding layer (Si-doped, 1 × 101
8 cm ⁻³ , 0.3 μm) and 305 are ln _0.2 Ga _0.8 N quantum wells (undoped, 2 nm) on a GaN waveguide region (Andor, 0.1 μm) and In sandwiching them.
_A quantum well structure active region composed of a _0.05 Ga _0.95 N barrier layer (undoped, 4 nm), and a p-type GaN waveguide region (M
g-doped, 0.1 μm)
W (Separate Confinement Hetero-structure Multi-Qu
antum Well) active layer 306 is p-type Al _0.15 Ga _0.85 N
Cladding layer (Mg doped, 1 × 1018 cm ⁻³ , 0.3
μm) and 307 are p-type GaN contact layers (Mg doped, 1 × 1018 cm ^{−3 11} μm).

Reference numeral 308 denotes an SiO ₂ insulating film, and reference numeral 309 denotes Pt (10 nm) / Ti (50 nm) / Pt (30n).
m) / Au (100 nm) structure p-side electrode, 310 is Cr
/ Au structure p electrode pad, 311 is current block layer, 3
Reference numeral 12 denotes an n-side electrode having a Ti / Au structure, and 313 denotes a mounting film having a Cr / Au structure. Although not particularly shown, a high reflection coating in which TiO ₂ / SiO ₂ is laminated in multiple layers is applied to the laser light emitting end face.

This embodiment differs from the first embodiment of the present invention shown in FIG. 1 in that four current blocks 311 are provided. As a result, the current injection region and the laser emission port are formed at three places, so that a so-called “multi-beam type” laser element can be formed. The manufacturing process of this semiconductor laser is substantially the same as that of the first embodiment of the present invention, and therefore will not be described. Here, the layer 311 is first insulator such as the embodiment similarly to the polyimide or _{n-Ga x In y Al z} N (x + y of the present invention for confining current blocking and light
+ Z = 1, 0 ≦ x, y, z ≦ 1) can be used.

According to the third embodiment of the present invention, the resonator length is set to 0.1.
In the case of 5 mm, the threshold current is 180 mA and the oscillation wavelength is 420
nm, the operating voltage was 5.6 V, and continuous oscillation was performed at room temperature. Further, the maximum light output was 100 mW. In the case of the present laser, compared to the first embodiment of the present invention, by using a plurality of layers for the current block and light confinement, the number of current injection regions and the number of laser emission ports were increased, and further higher light output characteristics were obtained. . As described above, since a high light output can be easily obtained, according to this embodiment, a high-output laser pointer or the like can be easily realized.

Next, a fourth embodiment of the present invention will be described. FIG. 5 is a sectional view illustrating a schematic configuration of a gallium nitride based blue semiconductor laser device according to a fourth embodiment of the present invention. In the figure, 501 is a sapphire substrate, LS
Is a laminated structure made of a gallium nitride-based compound semiconductor formed thereon. In the laminated structure LS,
502 is a GaN buffer layer, 503 is an n-type GaN contact layer (Si-doped, 5 × 1018 cm ⁻³ , 4 μm),
504 denotes an n-type Al _0.15 Ga _0.85 N cladding layer (Si-doped, 1 × 10 18 cm ⁻³ , 0.3 μm), 505 denotes Ga
1n0.2 on N waveguide region (Andor, 0.1 μm)
An active region of a quantum well structure composed of 10 layers of Ga0.8N quantum wells (undoped, 2 nm) and an In0.05Ga0.95N barrier layer (undoped, 4 nm) sandwiching them, and a p-type GaN waveguide region (Mg-doped, 0.1 nm). SCH-MQW (Separate Confinement H)
etero-structure Multi-Quantum Well) Active layer, 506
_{Denotes a} p-type Al _0.15 Ga _0.85 N cladding layer (Mg-doped, 1
× 1018 cm ^-3 , 0.3 μm), 507 is p-type GaN
Contact layer (Mg doped, 1 × 1018 cm ⁻³ 1μ)
m).

Reference numeral 508 denotes an SiO ₂ insulating film;
A, 509B are Pt (10 nm) / Ti (50 nm) /
Pt (30 nm) / Au (100 nm) structure p-side electrode,
510A and 510B are Cr / Au structure p electrode pads, 5
11A and 511B are current blocking layers and 512 is Ti / A
The u-structure n-side electrode 513 is a mounting film having a Cr / Au structure. Although not particularly shown, a high reflection coating in which TiO ₂ / SiO ₂ is laminated in multiple layers is applied to the end face of the laser beam.

This embodiment also has three or more current blocking layers 511A and 511B as in the third embodiment shown in FIG. This embodiment differs from the third embodiment in that the distance between the current blocking layers 511A and 511B is not constant. That is, in the present embodiment, the p-side electrode 509A
Of the current blocking layers 511A and 511A on both sides of the p-side electrode 509B are large.
B and 511B are narrow. In the present embodiment, the p-side electrodes 509A and 509B having different intervals are used.
Are formed separately, each having a separate electrode pad 510.
A, 510B.

According to the present embodiment, the current blocking layers 511A, 511A,
By making the intervals of 11B different, each laser can be used for different applications.

For example, if the distance between the current blocking layers 511A and 511A on both sides of the p-side electrode 509A is about 8 μm, an optical output of about 20 to 30 mW can be obtained and used as a light source for writing data in an optical disk system. be able to. On the other hand, if the distance between the current blocking layers 511B and 511B on both sides of the p-side electrode 509B is set to, for example, about 2 μm, low-power fundamental transverse mode oscillation laser light suitable for data reading of an optical disk system is driven at a low current. Condition can be obtained. That is, reading and writing of the optical disk can be realized by one semiconductor laser chip, and the optical system of the system can be made compact. In this case, if the thickness of the active layer in the laser portion having a large gap between the current blocking layers is larger than the thickness of the active layer in the laser portion having a small gap between the current blocking layers, the light output of the high-power laser is reduced. It can be further increased.

According to the present embodiment, a plurality of laser portions can be arranged in an array in one semiconductor laser element, and a high-output laser pointer and a display device using a laser can be realized. Become. In this case, the RG is adjusted by adjusting the composition of the active layer for each laser unit.
Lasers of three colors B can be integrated, and a raster scan type image display using one optical lens can be easily realized. In particular, large-screen display outdoors can be performed with low power consumption.

Note that the current block 51 in this embodiment is
1A and 511B are also made of an insulator such as polyimide or n-type Ga _x In _y Al _z N, similarly to the above-described embodiments.
(X + y + = 1, 0 ≦ x, y, z ≦ 1) and the like can be appropriately selected.

Next, a fifth embodiment of the present invention will be described. FIG. 6 is a sectional view illustrating a schematic configuration of a gallium nitride based blue semiconductor laser device according to a fifth embodiment of the present invention. In the figure, reference numeral 601 denotes a sapphire substrate;
Is a laminated structure made of a gallium nitride-based compound semiconductor. In the laminated structure LS, 602 is a GaN buffer layer, 603 is an n-type GaN contact layer (Si-doped, 5
× 1018 cm ^-3 , 4 μm), 604 is n-type AI _0.15 G
a _0.85 N Glad layer (Si doped, 1 × 1018c
m ⁻³ , 0.3 μm), 605 is a GaN waveguide region (undoped, 0.1 μm) with 10 layers of In _0.2 Ga _0.8 N quantum wells (undoped, 2 nm) and ln _0.05 sandwiching it.
SCH-MQW in which a quantum well structure active region composed of a Ga _0.95 N barrier layer (undoped, 4 nm) and a p-type GaN waveguide region (Mg doped, 0.1 μm) are further laminated.
(Separate Confinement Hetero-structure Multi -Qua
ntum Well) Active layer 606 is p-type A10.15Ga
0.85N cladding layer (Mg doped, 1 × 1018cm
^{-3, 0.3μm),} 607 a p-type GaN contact layer (Mg ^{doped, 2 × 1017cm -3, 1μm)} , 614
Is a p ⁺ -type GaN contact layer (Mg-doped, 2 × 101
8 cm ^-3 , 0.1 μm).

Reference numeral 608 denotes an SiO ₂ insulating film, and 609 denotes Pt (10 nm) / Ti (50 nm) / Pt (30n).
m) / Au (100 nm) structure p-side electrode, 610 is Cr
/ Au structure p electrode pad, 611 is a current blocking layer,
612 is a Ti / Au structure n-side electrode, and 613 is Cr / Au
It is a mounting membrane with a structure. Although not particularly shown, a high reflection coating in which TiO ₂ / SiO ₂ is laminated in multiple layers is applied to the laser light emitting end face.

This embodiment is different from the first embodiment of the present invention shown in FIG.
7 and the p ⁺ -type GaN contact layer 614 are formed such that the carrier concentration becomes higher near the electrode.
It has a step structure. This can be realized by appropriately adjusting the impurity concentration when forming the contact layers 607 and 614. The other main parts of the manufacturing process are substantially the same as those of the above-described embodiment, and thus will not be described. Here, the current block and the layer 611 for optical confinement are n-type Ga _x, as in the first embodiment of the present invention.
In _y Al _z N (x + y + z = 1, 0 ≦ x, y, z ≦
Any composition that satisfies 1) may be used.

According to the present example, when the resonator length was 0.5 mm, the threshold current was 180 mA, the oscillation wavelength was 420 nm, the operating voltage was 5.3 V, and continuous oscillation was performed at room temperature. Further, the maximum light output was 100 mW. The life at an optical output of 5 mW was 7000 hours or more. In the case of this laser, as compared with the characteristics of the first embodiment of the present invention, the operating voltage was reduced because the contact resistance with the p-electrode was reduced, and the heat generation was suppressed, so that the element life could be extended. Also, p ⁺ type GaN
Small p-type Ga energy gap than the p-type GaN contact layer 614 comprises _{In x In y Al z N (} x +
y + z = 1,0 ≦ x, With z ≦ 1,0 <y ≦ 1) , it is possible to higher carrier concentration than the p-type GaN contact layer 607, p ⁺ -type GaN contact layer 6
As in the case of No. 14, the operating voltage could be reduced.

Next, a sixth embodiment of the present invention will be described. FIG. 7 is a schematic sectional view of a semiconductor laser in which the semiconductor laser of the present invention is flip-chip mounted on a patterned heat sink. FIG. 1 shows the gallium nitride-based blue semiconductor laser of the first embodiment described above as an example of the semiconductor laser.

In the semiconductor laser device shown in FIG. 7, the back surface of the sapphire substrate 101 is mirror-polished to a thickness of 50 μm, and the mounting film 1 having a Cr / Au structure is used.
13 was vapor-deposited and cleaved along a plane perpendicular to the current confinement structure, and the cleaved face was subjected to a high reflection coating in which TiO ₂ / SiO ₂ was laminated in multiple layers. The heat sink 520 is
u, cubic boron nitride or diamond, etc., and a groove CG for electrode separation is formed on the surface thereof, and an electrode pattern 521 such as Ti / Pt / Au is selectively formed. Metallized. The semiconductor laser element is mounted using a solder material 122 such as AuSn eutectic, AuGe eutectic or AuSi eutectic so that its electrodes 110 and 112 are respectively connected on the electrode pattern 521 of the heat sink 520. .

According to the present embodiment, when the resonator length was 0.5 mm, the threshold current was 60 mA, the oscillation wavelength was 420 nm, and the operating voltage was 5.2 V. 50 ° C, 3
The device life at 0 mW drive is 10,000 hours or more, 2
The relative intensity noise from 0 ° C. to 70 ° C. is −140 dB /
Hz or less. In the case of this laser, the heat generated in the active layer 105 can be released from the heat sink 520 immediately below, so that the heat radiation is excellent and the element life is improved. As the semiconductor laser device used in the present embodiment, the semiconductor laser of any of the embodiments of the present invention can be used in the same manner, and it goes without saying that the same effect can be obtained.

The embodiment of the invention has been described with reference to specific examples. However, the invention is not limited to these specific examples. For example, in each of the above-described embodiments, the groove G after the etching is made of polyimide or n.
Ga _x In _y Al _z N (x + y + z = 1, 0 ≦ x,
y, z ≦ 1) and the like,
Although 311 411 511 are formed, the present invention is not limited to this. In addition, a similar effect can be obtained by using an insulator capable of blocking a current or a semiconductor material.

Further, the p-side electrode and the n-side electrode are not limited to the embodiments. In addition, for example, Au-Be / Au, Au-Zn / Au, Pt / Ni
/ Au, Au-Zn / Ti / Au, etc., and Al / Ti / Au, Al / Ni / Au, Al
/ Au, Ni / Al / Ti / Au, Au-Sn / Au,
Various selections such as Au-Ge / Ni / Au can be made. Further, in order to improve the ohmic properties of the respective electrodes, a contrivance may be made to increase the impurity concentration on the surface of the p-GaN contact layer or the n-GaN contact layer by using ion implantation or the like.

Further, the composition and thickness of each semiconductor layer constituting the semiconductor laser can be adjusted as appropriate. Also,
Its conductivity type can also be reversed. Further, the present invention can be applied to an optical device such as a light receiving element such as a photodiode and a light modulation element in addition to a light emitting element such as a semiconductor laser and a light emitting diode.

[0064]

As described above in detail, according to the present invention, in the nitride compound semiconductor laser, a mesa-type current injection layer is provided on the active layer, and a current block is formed on a side surface of the mesa-type current injection layer. By providing the layer, not only can a current confinement structure be formed, but also a basic transverse mode control structure can be formed. This makes it possible to efficiently inject carriers into the active layer and suppress higher-order modes,
Low threshold current, low operating voltage, low noise characteristics and high reliability,
A nitride compound semiconductor laser can be realized, and the laser performance required as a light source of an optical disk system or the like can be satisfied.

According to the present invention, the current confinement structure can be easily and accurately formed by the self-alignment process. Furthermore, since the array can be easily formed by the same process, a high-output laser required for erasing and recording in the optical disk system can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram related to a first embodiment of the present invention.

FIG. 2 is a diagram related to a manufacturing process of the first embodiment of the present invention.

FIG. 3 is a diagram related to a second embodiment of the present invention.

FIG. 4 is a diagram related to a third embodiment of the present invention.

FIG. 5 is a diagram related to a fourth embodiment of the present invention.

FIG. 6 is a diagram related to a fifth embodiment of the present invention.

FIG. 7 is a diagram related to a sixth embodiment of the present invention,
FIG. 4 is a diagram illustrating an example in which the laser according to the first embodiment is mounted on a heat sink.

[Explanation of symbols]

101, 201, 301, 401 sapphire substrate 102, 202, 302, 402 GaN buffer layer 103, 203, 303, 403 n-GaN contact layer 104, 204, 304, 404 n-Al _0.15 Ga
_0.85 N cladding layers 105, 205, 305, 405 ... SCH-MQW active layers 106, 206, 306, 406 ... p-Al _0.15 Ga
_0.85 N cladding layer 107,207,307,407 ... p-GaN contact layer 108, 208, 308, 408 ... SiO ₂ insulating film 109,209,309,409 ... Pt / Ti / Pt /
Au structure p-side electrode 110, 210, 310, 410 ... p electrode pad 111, 311, 411 ... polyimide 112, 212, 312, 412 ... Ti / Au structure n-side electrode 113, 213, 313, 413 ... Cr / Au structure Assembly membrane 120, 520 ... heat sink

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masayuki Ishikawa 1 Tokoba, Komukai Toshiba-cho, Saisaki-ku, Kawasaki-shi, Kanagawa

Claims (12)

[Claims] A gallium nitride-based compound semiconductor (Ga _x In)
_y Al _z N: x + y + Z = 1, 0 ≦ x, y, z ≦ 1), wherein the active layer is sandwiched between semiconductor layers of different conductivity types. A nitride compound semiconductor laser, wherein a current confinement structure for injecting carriers is formed in a mesa shape, and a side surface of the mesa current confinement structure is covered with a current blocking layer made of an insulator. 2. A gallium nitride-based compound semiconductor (Ga _x In)
_y Al _z N: x + y + Z = 1, 0 ≦ x, y, z ≦ 1), wherein the active layer is sandwiched between semiconductor layers of different conductivity types. A nitride compound, wherein a current constriction structure for injecting carriers is formed in a mesa shape, and a side surface of the mesa type current confinement structure is covered with a gallium nitride-based compound semiconductor current block layer having different conductivity. Semiconductor laser. 3. The nitride compound semiconductor laser according to claim 1, wherein the active layer has a multiple quantum well structure. 4. The nitride compound semiconductor laser according to claim 1, wherein the relationship between the width W1 of the current confinement structure and the thickness W2 of the semiconductor layer in contact with the electrode metal having a different conductivity type under the active layer is expressed as W1. .Ltoreq.4.W2. A nitride compound semiconductor laser. 5. The nitride compound semiconductor laser according to claim 1, wherein a plurality of mesa-type current confinement structures are provided. 6. A gallium nitride-based compound semiconductor (Ga _x ) comprising a laminated structure including at least a first conductive type clad layer, an active layer, and a second conductive layer clad layer provided on a substrate.
In _y Al _z N: x + y + z = 1, 0 ≦ x, y, z ≦
1) In the laser, at least two grooves are provided on a main surface of the laminated structure on the side of the cladding layer of the second conductivity type;
A gallium nitride-based compound semiconductor laser, wherein a current block layer made of an insulator is provided in each of the grooves. 7. The nitride compound semiconductor laser according to claim 6, wherein said current blocking layer has a depth reaching said second conductivity type cladding layer. 8. The nitride compound semiconductor laser according to claim 6, wherein said current blocking layer has a depth reaching said cladding layer of said first conductivity type. 9. The multilayer structure further includes a first conductivity type contact layer formed below the first conductivity type cladding layer, and the current blocking layer includes the first conductivity type contact layer. 7. The nitride compound semiconductor laser according to claim 6, having a depth reaching the layer. 10. The nitride compound semiconductor laser according to claim 6, wherein said insulator forming said current blocking layer is polyimide. 11. A gallium nitride-based compound semiconductor (Ga _x ) comprising a laminated structure including at least a first conductivity type clad layer, an active layer, and a second conductivity type clad layer provided on a substrate.
In _y Al _z N: x + y + z = 1, 0 ≦ x, y, z ≦
1) In the laser, at least two grooves are provided on a main surface of the laminated structure on the side of the cladding layer of the second conductivity type;
A gallium nitride-based compound semiconductor laser, wherein a current blocking layer made of a first conductivity type gallium nitride-based compound semiconductor is provided in each of the grooves. 12. A method of manufacturing a gallium nitride-based compound semiconductor laser in which an active layer is sandwiched between semiconductor layers of different conductivity types, wherein a step of forming a p-electrode on the surface of the semiconductor layer on the land of the active layer; An etching-resistant mask metal is formed thereon, and a window is formed with a photoresist on a part of the surface of the semiconductor layer on the land of the active layer for forming a current blocking layer, and the etching-resistant mask metal and the photoresist are used. Forming a current blocking layer by filling the groove and forming the current blocking layer.