JP3194237B2 - Semiconductor laser device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device having a low operating current suitable as a light source for an optical disk or the like and a method for manufacturing the same.

[0002]

2. Description of the Related Art A conventional semiconductor laser device having an SBR structure will be described below.

FIG. 4 is a sectional view of a conventional semiconductor laser device. On an n-type gallium arsenide (GaAs) substrate 21, an n-type GaAs buffer layer 22 and an n-type indium gallium aluminum phosphide (In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P)
A p-type In _0.5 (Ga _0.3 A) having a cladding layer 23, an undoped In _0.5 Ga _0.5 P active layer 24, and a ridge 25a.
l _0.7 ) _0.5 P clad layer 25 and n-type Ga due to current confinement in portions other than ridge 25a serving as a current channel.
An As current blocking layer 26 is formed. Note that 27
Is a p-type GaAs contact layer.

In the structure shown in FIG. 4, a current injected from the p-type GaAs contact layer 27 is effectively confined in the ridge 25a, and laser oscillation occurs in the InGaP active layer 24 below the ridge 25a. At this time, n-type Ga
The refractive index of the As current blocking layer 26 is p-type In _0.5 (G
Although the refractive index of the a _0.3 Al _0.7 ) _0.5 P cladding layer 25 is larger than that of the In _0.5 Ga _0.5 P active layer 24, the forbidden band width of the n-type GaAs current blocking layer 26 is larger than that of the In _0.5 Ga _0.5 P active layer 24. N-type GaAs for laser light
The current block layer 26 becomes an absorber, and the laser beam
The GaAs current blocking layer 26 effectively traps the ridge. Generally, ridge 25a
By setting the width of the lower end of, that is, the stripe width to about 5 μm, a single transverse mode laser oscillation used for an optical disk or the like can be obtained.

[0005]

In the semiconductor laser device having the above-mentioned conventional structure, the n-type GaAs current blocking layer 26 is formed.
When the stripe width is reduced, the light absorption by the current blocking layer 26 is increased, so that the stripe width cannot be reduced to a certain extent or more. This has hindered the reduction in operating current.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a semiconductor laser device having a low operating current value.

[0007]

In order to achieve this object, a semiconductor laser device according to the present invention comprises a one-conductivity-type In _0.5 formed on at least one side of a main surface of an active layer and in contact with the active layer. (Ga _{1 -Y 1} Al _Y1 ) _0.5 P first optical guide layer;
In _0.5 (Ga) formed on the first light guide layer
_1-Y2 Al _Y2 ) _0.5 P _In0.5 (Ga) having a second light guide layer, a reverse conductive striped window formed on the second light guide layer, and a layer thickness of 400 nm or more. _1-Z Al
_Z ) A current block portion including a _0.5 P current block layer, and a one conductivity type In _0.5 (Ga _{1 -Y 3} Al _Y3 ) _0.5 P clad layer formed on the current block layer including the striped window. The relationship of Y2 <Y1 and Y2 <Y3 <Z is established between Y1, Y2, Y3 and Z that determine the Al mixed crystal ratio , and the refractive index of the current block portion is the refractive index of the cladding layer in the window portion. It is a configuration smaller than the rate.

[0008]

According to this structure, the current blocking layer In
_0.5 (Ga _{1 -Z} Al _Z ) _0.5 In _0.5 (Ga _{1 -X} A
l _x ) Laser oscillation occurs in the _0.5 P layer. Here, the refractive index of the In _0.5 (Ga _{1 -Z} Al _Z ) _0.5 P layer serving as a current blocking layer is In _0.5 (Ga
Since _1-Y3 Al _Y3) smaller than _0.5 P layer, the laser light is effectively confined in the stripe This refractive index difference. Further, In _0.5 (Ga _{1 -Z} A
l _Z ) _0.5 The forbidden band width of the P layer is In _0.5 (Ga
_1-X Al _X ) _{0.5 Since} the forbidden band width of the P layer is considerably larger, light absorption of the laser beam by the current blocking layer is eliminated.

[0009]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention. On an n-type GaAs substrate 1, an n-type GaAs buffer layer 2, In _0.5 (Ga _0.6
Al _{0. 4) 0.5} P cladding layer 3, In _0.5 Ga _0.5 P (generally _{In 0.5 (Ga 1-X Al} X) expressed by _{0 .5} P) active layer 4, p-type In _0.5 (Ga _0.6 Al _0.4 ) _0.5 P (generally represented by In _0.5 (Ga _1-Y1 Al _Y1 ) _0.5 P) First light guide layer 5, p-type In _0.5 Ga _0.5 P (generally In
_0.5 (Ga _{1 -Y 2} Al _Y2 ) _0.5 P A second optical guide layer 6 is formed, and a window 7 serving as a current channel for current confinement is formed.
In regions other than a, n-type In _0.5 (Ga _0.3 Al _0.7 )
_{A 0.5} P (generally represented by In _0.5 (Ga _{1 -Z} Al _Z ) _0.5 P) current blocking layer 7 is formed. 8 is In _0.5
The Ga _0.5 P protective layer 9 is a p-type In _0.5 (Ga _0.6 A
l _0.4 ) _0.5 P (generally In _0.5 (Ga _{1 -Y3} Al _Y3 ) _0.5
The cladding layer 10 (indicated by P) is a p-type GaAs contact layer. Hereinafter, “In _0.5 (Ga _1-x Al _x )
X in “ _0.5 P” is referred to as an Al mixed crystal ratio.

Here, in order to obtain a stable single transverse mode oscillation, the Al composition ratio of the current blocking layer 7 is set to p-type In _0.5.
(Ga _0.6 Al _0.4 ) _0.5 Set higher than the Al mixed crystal ratio of the P cladding layer 9. If the Al composition ratio of the current blocking layer 7 is the same as that of the cladding layer, the refractive index in the stripe is reduced due to the plasma effect, and it becomes an anti-guide waveguide, so that a single transverse mode oscillation cannot be obtained. . In other words, the Al composition ratio of the current blocking layer 7 is p-type In.
_When it is lower than _0.5 (Ga _0.6 Al _0.4 ) _0.5 P clad layer 9, the transverse mode becomes completely unstable, and it is not possible to achieve the intended low operating current. In this embodiment, as shown in FIG.
n _0.5 (Ga _0.6 Al _0.4 ) _0.5 It is set to 0.7 higher than the Al mixed crystal ratio of the P clad layer 9 by 0.7.

In this structure, the current injected from the p-type GaAs contact layer 10 is confined in the window 7a, and laser oscillation occurs in the In _0.5 Ga _0.5 P active layer 4 below the window 7a. Here, p-type In _0.5 (Ga _0.6 A
l _0.4 ) _0.5 P The Al mixed crystal ratio of the first light guide layer 5 is sufficiently higher than the Al mixed crystal ratio of the active layer, and carriers are effectively confined in the active layer to enable oscillation in the visible region. In this embodiment, the value is set to 0.4 in order to obtain laser oscillation in the 670 nm band. In _0.5 Ga _{0 .5} lower p-type of regrowth Al ratio
Since the regrowth is performed on the P second light guide layer, there is no problem of surface oxidation. The thickness of the second light guide layer is desirably 0.05 μm or less which does not significantly affect the light distribution. In this embodiment, the thickness is 0.01 μm.

Further, n-type In _0.5 (Ga _0.3 Al _0.7 )
The forbidden band width of the _0.5 P current blocking layer 7 is In _0.5 Ga _0.5
Since it is larger than the forbidden band width of the P active layer 4, there is no light absorption by the current blocking layer, and a device with a low operating current and a small loss of the waveguide can be obtained.

In this structure, since there is no light absorption by the current blocking layer, the laser beam is n-type In _0.5 (Ga _0.3 Al
_0.7 ) _0.5 P Spread also under the current blocking layer 7, the spectrum tends to be multimode, and a low-noise laser can be easily obtained.

Generally, X, Y1, Y which determine the Al mixed crystal ratio
2, it is only necessary to satisfy the relationship of Z>Y3> Y2 ≧ X ≧ 0 and Y1> Y2 between Y3 and Z.

FIG. 2 is a manufacturing process diagram of a semiconductor laser device according to one embodiment of the present invention. As shown in FIG. 2A, an n-type GaAs buffer layer 2 is formed on an n-type GaAs substrate 1 by MOCVD or MBE growth.
n-type In _0.5 (Ga _0.6 Al _0.4 ) _0.5 P clad layer 3
(Thickness: 1 μm), In _0.5 Ga _0.5 P active layer 4 (thickness,
0.04 μm), p-type In _0.5 (GaAl) _0.5 P first optical guide layer 5 (thickness, 0.15 μm), p-type In _0.5
Ga _0.5 P second light guide layer 6 (thickness, 0.01 μm),
n-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P current blocking layer 7 (thickness: 1.0 μm), In _0.5 Ga _0.5 P protective layer 8
(Thickness: 0.01 μm). This protective layer 8
It is necessary to protect the upper part of the n-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P current blocking layer 7 from surface oxidation. Protective layer 8
The mixed crystal ratio is preferably 0.3 or less, as in the second light guide layer 6, at which re-growth is easy, and is transparent to laser light.

The conductivity type of the active layer 4 is not particularly described, but may be p-type, n-type, or of course, undoped.

Next, as shown in FIG. 2B, a striped window 7a is formed by etching using a photolithography technique. As an etching method,
Using an etchant such as hot sulfuric acid, which can selectively etch a layer having a high Al mixed crystal ratio, selectively use In _0.5 (Ga
_0.3 Al _0.7 ) _0.5 P The current blocking layer 7 is etched. That is, the p-type In _0.5 Ga _0.5 P second optical guide layer 6 also functions as an etching stop layer. Therefore, variation due to etching is small, and a high yield can be obtained.

Here, the shape of the stripe is preferably a regular mesa shape rather than an inverted mesa shape. This is because crystal growth is more difficult in the case of an inverted mesa shape than in the case of a forward mesa shape, and there is a possibility that the yield may be reduced due to a reduction in characteristics. Actually, in the case of an inverted mesa shape,
InGaAs grown selectively on the side of the stripe
The crystallinity of 1P is impaired, and the threshold current of the manufactured device is higher than that of a device having a forward mesa shape. The characteristics of the element described later show a forward mesa shape.

As for the thickness of the current blocking layer 7, when the thickness of the current blocking layer 7 is small, the upper In _0.5
(Ga _0.6 Al _0.4 ) _{0.5 The} exudation of the laser beam to the cladding layer 9 becomes large and the transverse mode becomes unstable, so a minimum of 0.4 μm is required.

Next, as shown in FIG. 2C, the MOCV
P or In _0.5 (Ga
_{A 0.6} Al _0.4 ) _0.5 P clad layer 9 and a p-type GaAs contact layer 10 are formed by regrowth. At this time, the inside of the stripe through which current flows is a p-type In having a low Al mixed crystal ratio.
_0.5 Ga _0.5 P regrowth on the second guide layer 6
Regrowth can be performed easily. Finally, electrodes are formed on the n-type GaAs substrate and the p-type GaAs contact layer 10, respectively.

FIG. 3 shows a current-light output characteristic diagram of a semiconductor laser device according to a conventional example and an embodiment of the present invention. As shown in FIG. 3, the embodiment has a smaller threshold current value and higher efficiency than the conventional example. This is because there was no light absorption by the current blocking layer, and the waveguide loss was reduced. In one embodiment of the present invention, the resonator length is 200 μm
The operating current value required to emit 3 mW of laser light at room temperature is 28 mA. The spectrum also oscillates in multiple modes causing self-pulsation,
R of -130 dB / Hz within the range of return light rate of 0 to 10%
The value of IN was obtained, and low noise characteristics were obtained.

The structure of the present invention has a low operating current value, and is therefore effective for increasing the output of a semiconductor laser. In particular,
When the active layer has a quantum well structure, the threshold value can be further reduced and higher output can be obtained.

In all of the above embodiments, only the case where the substrate is an n-type and an n-type current blocking layer is used is shown, but the substrate may be a p-type and a p-type current blocking layer may be used. I do not care. That is, the Al composition ratio of the current blocking layer is high. This is because, in the case of a p-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P layer having a high Al mixed crystal ratio, diffusion of electrons is suppressed, so that a p-type block layer can be realized.

In all of the above embodiments, only the case where the current blocking layer is on the active layer, that is, on the side opposite to the substrate when viewed from the active layer, is shown. The same effect is obtained. Furthermore, if the current block layer has a double configuration structure in both directions,
Needless to say, the leakage current is further reduced, and the operating current can be reduced.

[0026]

As described above, according to the present invention, In _0.5 (Ga
_1-X Al _x ) _{0.5 One-} conductivity type I formed on at least one side of the main surface of the active layer made of a P layer in contact with the active layer.
n _0.5 (Ga _{1 -Y 1} Al _Y1 ) _0.5 P first light guide layer and one conductive type In _0.5 (G
a _1-Y2 Al _Y2 ) _0.5 P In _0.5 (Ga _{1 -Z} Al _Z ) _0.5 P having a second light guide layer and a window of opposite conductivity type and formed in a stripe shape on the second light guide layer the in _0.5 containing a layer, the stripe-shaped window portion _{(Ga 1-Z Al Z)} 0 .5 P
One conductivity type In _0.5 (Ga _{1 -Y 3} A) formed on the layer
l _Y3 ) X, Y having a _0.5 P layer and determining the Al mixed crystal ratio
1, Y2, Y3 and Z, Z>Y3> Y2 ≧ X ≧
Since 0 _N relationship a and Y1> Y2 is due to the structure so as to establish, at a low noise, moreover, the operating current value can provide a significantly lower semiconductor laser device as compared with the prior art.

That is, In _0.5 (G
a _1-Y1 Al _Y1 ) _0.5 P The first optical guide layer confines the carrier in the active layer, and regrowth is performed using In _{0.5 with} a low Al mixed crystal ratio.
(Ga _{1 -Y 2} Al _Y2 ) _0.5 P Since it grows on the second optical guide layer, a laser in the visible region can be easily produced.

Further, at the time of etching for forming a stripe, a selective etching method based on a difference in the Al mixed crystal ratio can be used, so that variations in etching are reduced and a high yield can be obtained.

Since the Al composition ratio of the current blocking layer is set higher than the Al composition ratio of the cladding layer, oscillation occurs in a single transverse mode, and there is no light absorption of the laser beam by the current blocking layer. Therefore, the loss of the waveguide can be greatly reduced,
The operating current value can be reduced.

Further, since the light spreads to the current blocking layer and the active layer below the current blocking layer, multi-mode oscillation of the spectrum can be easily obtained and low noise characteristics can be obtained as compared with the related art.
In particular, a reduction in the operating current value results in a reduction in the amount of heat generated in the laser mount portion, and a smaller and lighter heat sink can be used. As a result, the laser package, which has conventionally been made of metal, can be made of resin, and the size and cost of the pickup can be significantly reduced.

Although a lower operating current results in a reduction in the amount of heat generated in the active layer, a high output can be obtained. In particular, a higher output can be obtained if the active layer is formed into a quantum well. An uninvented 670n having such low noise and high output characteristics
If an m-band semiconductor laser is used as a light source for an optical disk, it is possible to eliminate a high-frequency superimposing circuit for reducing noise at the time of reading, and it is possible to significantly reduce the size of the pickup.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a step of the method for manufacturing the semiconductor laser device of FIG. 1;

FIG. 3 is a current-light output characteristic diagram of the semiconductor laser device of FIG. 1;

FIG. 4 is a cross-sectional view of a conventional semiconductor laser device.

[Explanation of symbols]

 1 n-type GaAs substrate 2 n-type GaAs buffer layer 3 n-type In_0.5(Ga_0.6Al_0.4)_0.5P cladding layer 4 In_0.5Ga_0.5P active layer (In_0.5(Ga_1-XA
l_X)_0.5Active layer composed of P layer) 5 p-type In_0.5(Ga_0.6Al_0.4)_0.5P first light guy
Layer (one conductivity type In) _0.5(Ga_1-Y1Al_Y1)_0.5P first
Light guide layer) 6p-type In_0.5Ga_0.5P second light guide layer (one conductivity type
In_0.5(Ga_1-Y2Al_Y2)_0.5P second light guide layer) 7 n-type In_0.5(Ga_0.3Al_0.7)_0.5P current block
Layer (Inverse with opposite conductivity type and striped windows)_0.5
(Ga_1-ZAl_Z)_0.5P layer) 7a Striped window 8 In_0.5Ga_0.5P protective layer 9 p-type In_0.5(Ga_0.6Al_0.4)_0.5P clad layer
(One conductivity type In_0.5(Ga_1-Y3Al_Y3)_0.5P layer) 10 p-type GaAs contact layer

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-136586 (JP, A) JP-A-3-53578 (JP, A) JP-A-3-250685 (JP, A) JP-A-60-1985 110188 (JP, A) JP-A-6-196801 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 JICST file (JOIS)

Claims (3)

(57) [Claims] At least one side of a main surface of an active layer is formed of one conductivity type In _0.5 (Ga) formed in contact with the active layer.
_1-Y1 Al _{Y1) 0.5} P and the first optical guide layer, a first light guide
_0.5 (Ga _1-Y2 Al _Y2 ) _0.5 P formed on the doped layer
A second light guide layer having a reverse conductive striped window formed on the second light guide layer and having a layer thickness of 40;
A current block portion including an In _0.5 (Ga ₁ -Z Al _Z ) _0.5 P current block layer of 0 nm or more, and one conductivity type In formed on the current block layer including the striped window;
_0.5 (Ga _{1 -Y 3} Al _Y3 ) _0.5 P clad layer
Y1 <Y2 between Y1, Y2, Y3 and Z that determine the mixed crystal ratio
A semiconductor laser device, wherein the relationship of Y1 and Y2 <Y3 <Z is satisfied, and the refractive index of the current block portion is smaller than the refractive index of the cladding layer in the window portion. 2. An In _Y3 (Ga _{1 -Z} Al _Z ) _{1 -Y 3} P () having a substrate, an active layer formed on the substrate, and a stripe-shaped window formed on the active layer. 0 <Y3 <1,
0 <Z <1) a current blocking layer, and In _Y4 (Ga _1-x Al _x ) _1-Y4 P (Y3 ≦ Y4 ≦ 1,
0 ≦ X ≦ 0.3, X < Z) and the protective layer, a cladding layer made of _{In Y5 (Ga 1-Z Al} Z) 1-Y5 P (0 ≦ Y5 <Z) on the protective layer is formed Semiconductor laser device. 3. An active layer is formed on a substrate, and In _Y3 (Ga _{1 -Z} Al _Z ) ₁ -Y ₃ P (0 <Y) is formed on the active layer.
3 <1, 0 <Z <1) Current blocking layer and In _Y4 (Ga
_1-X Al _X ) _1-Y4 P (Y3 ≦ Y4 ≦ 1, 0 ≦ X ≦ 0.3,
X <Z) a step of sequentially forming a protective layer, a step of selectively etching the current blocking layer and the protective layer to provide a window, and a step of forming In on the current blocking layer and the protective layer including the window. _Y5 (Ga _1-Z Al _Z ) _1-Y5 P (0 ≦
Forming a cladding layer comprising Y5 <Z).