JPH08250801A - Semiconductor laser device and its manufacture - Google Patents

Abstract

PURPOSE: To provide a highly reliable ridge type semiconductor laser device by relieving the level difference between a clad layer and contact layer caused by the difference of etching rate between both layers and preventing the deterioration of the characteristic of the device and a method for manufacturing the laser device. CONSTITUTION: A p-type Al0.25 Ga0.75 As etching buffer layer having an aluminum composition which is the intermediate composition between those of a p-type Al0.5 Ga0.5 As second clad layer 6 and p-type GaAs first clad layer 8 is formed between the layers 6 and 8. Since the layer 7 has an etching rate between those of the layers 8 and 6 against an organic acid/hydrogen peroxide solution due to its aluminum composition ratio dependency, the difference of etching rate between each layer is reduced from the conventional example and a ridge structure having a smooth side faces can be formed with high reproducibility.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having a ridge structure and its manufacturing method.

[0002]

2. Description of the Related Art FIG. 4 is a perspective view showing the structure of a conventional semiconductor laser. In the figure, 1 is an n-GaAs semiconductor substrate, 2 is an n-Al _0.5 Ga _0.5 As cladding layer, 3 is a quantum well active layer, 4 is a p-Al _0.5 Ga _0.5 As first cladding layer, and 5 is a p-Al _0.7 layer. Ga _0.3 As etching stopper layer, 6 is p-Al _0.5 Ga _0.5 As second cladding layer, 8
Is a p-GaAs first contact layer, 9 is a ridge type waveguide, 10 is an n-GaAs current blocking layer, and 11 is p-G.
aAs second contact layer, 12 is p-electrode, 13 is n-
The electrodes are shown respectively.

Next, the operation will be described. p-electrode 1
When a voltage is applied so that + is applied to the 2 side and − is applied to the n− electrode 13 side, holes are formed in the p-GaAs second contact layer 11,
p-GaAs first contact layer 8, p-Al _0.5 Ga _0.5
After passing through the As second cladding layer 6 and the p-Al _0.5 Ga _0.5 As first cladding layer 4 to the quantum well active layer 3, electrons are n-
It is injected into the quantum well active layer 3 through the GaAs semiconductor substrate 1 and the n-Al _0.5 Ga _0.5 As clad layer 2, recombination of electrons and holes occurs, and stimulated emission light is generated in the active layer. If the amount of injected carriers is made sufficiently high and light exceeding the loss of the waveguide is generated, laser oscillation occurs.

Next, the ridge structure will be described. In the ridge structure, n-Ga other than the striped ridge region is used.
In the region covered with the As current block layer 10, p−
A pn junction is formed between the AlGaAs first clad layer 4 and the p-GaAs second contact layer 11, and even if a voltage is applied so that the p-electrode 12 side becomes +, pnp is formed except in the ridge region. Since there is a reverse bias, no current flows. That is, the n-GaAs current blocking layer 10 has a function of blocking current. Therefore, the current flows only in the ridge region, so that the current is concentrated only in the region of the quantum well active layer 3 directly below the ridge, and reaches a current density sufficient for laser oscillation. In addition, n-GaAs
The current blocking layer 10 has a property of absorbing the laser light emitted from the quantum well active layer 3. This is because the band gap energy of GaAs is designed to be smaller than the effective band gap energy of the active layer 3. Therefore, the laser light is strongly absorbed on both sides of the ridge region, so that the laser light is also concentrated only near the ridge region. As a result, the horizontal transverse mode, which is important in the operating characteristics of the semiconductor laser, also has a stable single-peaked shape.

Next, a conventional method for manufacturing a semiconductor laser will be described with reference to the drawings. As shown in FIG. 5-a, n-GaA
n-Al _0.5 Ga _0.5 As cladding layer 2, active layer 3, p-Al _0.5 Ga _0.5 As first cladding layer 4, p-Al _0.7 Ga _0.3 As etching stopper layer 5, p-Al _0.5 on the semiconductor substrate 1. Ga _0.5 As second cladding layer 6, p-G
Each layer of the aAs first contact layer 8 is epitaxially grown. As shown in FIG. 5B, a stripe-shaped insulating film 14 is formed on this wafer. The material is Si ₃
N ₄ , SiO ₂ or the like is used. This insulating film 14 functions as a mask for ridge etching. That is, FIG.
As shown in -c, etching is performed using the insulating film 14 as a mask so as to form a ridge shape. In this etching, p-GaAs first contact layer 8, p-Al
_{The 0.5} Ga _0.5 As second cladding layer 6 can be etched, but the p-Al _0.7 Ga _0.3 As etching stopper layer 5 is formed.
The ridge structure can be formed with good reproducibility by using a selective etchant that is not etched.

Next, as shown in FIG. 5D, the portion other than the ridge portion is filled with the n-GaAs current blocking layer 10 by recrystallization growth. Since the insulating film 14 also serves as a mask during crystal growth, the ridge portion does not grow crystal on it.
Finally, after removing the insulating film 14 by wet or dry etching, as shown in FIG.
s Crystal growth of the second contact layer 11 is performed. Then n-
N-electrode 13, p-GaAs on the GaAs semiconductor substrate 1 side
By forming the p-electrode 12 on the second contact layer 11 side, the semiconductor laser as shown in FIG. 4 is completed.

The above is the conventional method for manufacturing a semiconductor laser device. An example of the etchant used in such a manufacturing process is a mixed solution of organic acid and hydrogen peroxide. In this etchant, the etching rate depends on the aluminum composition ratio as shown in FIG. 6, and the etching rate tends to decrease as the aluminum composition increases.
Therefore, during the selective etching, the etching of the p-GaAs first contact layer 8 is completed, and then the p-Al _0.5 Ga is completed.
_{When the 0.5} As second clad layer 6 is being etched, the progress of the side etching is different due to the difference in the etching rates of the both, and as a result, as shown in FIG.
As the side etching of the As first contact layer 8 proceeds, a step often occurs on the side surface of the ridge along the interface of the epi layer. In this case, in the subsequent step of buried growth with the n-GaAs current blocking layer 10, the side of the insulating film 14 not in contact with the p-GaAs first contact layer 8 becomes large due to side etching, and the portion under the insulating film 14 grows completely. However, a step as shown in FIG. 5D is formed on the surface of the n-GaAs current block layer. During the growth of the p-GaAs second contact layer 11, this step is formed in the cavity region 15 on both sides of the ridge as shown in FIG.
And may cause a large depression 16 on the wafer surface.

[0008]

Since the conventional ridge type semiconductor laser device is constructed as described above, p-G
The cavities 15 on both sides of the ridge caused by the difference in etching rate between the aAs first contact layer 8 and the p-Al _0.5 Ga _0.5 As second clad layer 6 deteriorate the laser characteristics, or due to the large depression 16 on the wafer surface. There has been a problem that local stress is generated, laser characteristics are deteriorated, or pattern accuracy is deteriorated at the time of transfer in a subsequent process.

The present invention has been made in order to solve the above problems, and alleviates the step between the p-contact layer and the p-clad layer caused by the difference in etching rate between them, thereby improving the laser characteristics. It is an object of the present invention to provide a highly reliable ridge-type semiconductor laser device and a method for manufacturing the same, which can prevent cavities on both sides of the ridge that are deteriorated and dents on the wafer surface.

[0010]

In a semiconductor laser device according to the present invention, a ridge type waveguide is formed by a clad layer, an etching buffer layer and a contact layer, and an etching buffer layer inserted between the clad layer and the contact layer. The aluminum composition ratio is set to an intermediate value between the aluminum composition ratios of the clad layer and the contact layer. Further, the etching buffer layer uses a graded layer whose aluminum composition ratio continuously changes from the aluminum composition ratio of the clad layer to the aluminum composition ratio of the contact layer.

According to the method of manufacturing a semiconductor laser device of the present invention, n-Al _0.5 G is formed on an n-GaAs semiconductor substrate.
a _0.5 As cladding layer, quantum well active layer, p-
First clad layer made of Al _0.5 Ga _0.5 As, p-Al
Etching stopper layer made of _0.7 Ga _0.3 As, p-
Second cladding layer made of Al _0.5 Ga _0.5 As, p-Al
Etching buffer layer made of _0.25 Ga _0.75 As, p-
By sequentially forming each layer of the first contact layer made of GaAs, forming an insulating film functioning as a ridge etching mask on the first contact layer, and performing wet etching with a mixed solution of organic acid and hydrogen peroxide. It includes a step of forming a ridge structure by etching the first contact layer, the etching buffer layer and the second cladding layer.

[0012]

In the semiconductor laser device according to the present invention, since the etching buffer layer inserted between the clad layer and the contact layer forming the ridge type waveguide has an aluminum composition ratio intermediate between the two, the etching rate is When etching is performed using an etchant having an aluminum composition ratio dependency, the etching buffer layer has an intermediate etching rate between the first contact layer and the second cladding layer, so that the etching rate between the layers is increased. The difference is reduced, and a ridge structure having a smooth side surface with no step can be formed. In addition, since the graded layer whose aluminum composition ratio changes continuously from the aluminum composition ratio of the clad layer to the aluminum composition ratio of the contact layer, there is no discontinuity in the etching rate between each layer, so it is more stable and smooth. Ridge structure is formed.

Further, by wet etching with a mixed solution of organic acid and hydrogen peroxide, the first contact layer, the etching buffer layer and the second cladding layer are selectively etched to form a ridge structure stably with good reproducibility. can do.

[0014]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a ridge type semiconductor laser device in this embodiment. In the figure, 7 is p-Al _0.25
Ga _0.75 As etching buffer layer. The same parts as those of the conventional example are designated by the same reference numerals, and the description thereof will be omitted.

Next, a method of manufacturing the semiconductor laser of this embodiment will be described with reference to the drawings. As shown in FIG. 2-a, n-G
On the aAs semiconductor substrate 1, n-Al _0.5 Ga _0.5 As clad layer 2, quantum well active layer 3, p-Al _0.5 Ga _0.5 As first clad layer 4, p-Al _0.7 Ga _0.3 As etching stopper layer 5, p- The Al _0.5 Ga _0.5 As second cladding layer 6, the p-Al _0.25 Ga _0.75 As etching buffer layer 7, and the p-GaAs first contact layer 8 are epitaxially grown. On this wafer, as shown in FIG. 2-b, a stripe-shaped insulating film 14 is formed. As the material, Si ₃ N ₄ , SiO ₂ or the like is used. This insulating film 14 functions as a mask for ridge etching. That is, as shown in FIG. 2C, etching is performed using the insulating film 14 as a mask to form a ridge shape. In this etching, the p-GaAs first contact layer 8, the p-Al _0.25 Ga _0.75 As etching buffer layer 7, and the p-Al _0.5 Ga _0.5 As second cladding layer 6 can be etched, but the p-Al _0.7 Ga _0.3 As etching is performed. The stopper layer 5 can form a ridge structure with good reproducibility by using a selective etchant that is not etched. An example of such an etchant is a mixed solution of an organic acid and hydrogen peroxide.

Next, as shown in FIG. 2D, the portion other than the ridge portion is filled with the n-GaAs current blocking layer 10 by recrystallization growth. Since the insulating film 14 also serves as a mask during crystal growth, the ridge portion does not grow crystal on it.
Subsequently, the insulating film 14 is removed by wet or dry etching, and then p-GaA is formed as shown in FIG.
s Crystal growth of the second contact layer 11 is performed, and finally n-Ga
N-electrode 13, p-GaAs second on the As semiconductor substrate 1 side
By forming the p-electrode 12 on the contact layer 11 side, the ridge type semiconductor laser device as shown in FIG. 1 is completed.

In the ridge type semiconductor laser device according to the present embodiment, the p-Al _0.5 Ga _0.5 As second cladding layer 6 is used.
The p-Al _0.25 Ga _0.75 As etching buffer layer 7 having an aluminum composition intermediate between the two is inserted between the p-GaAs first contact layer 8 and the p-GaAs first contact layer 8. The etching buffer layer 7 has an intermediate etching rate between the first contact layer 8 and the second cladding layer 6 due to the aluminum composition ratio dependency with respect to the organic acid / hydrogen peroxide solution. Become. As a result, the difference in etching rate between the layers is smaller than in the prior art, so that the step that occurs during ridge etching, which has conventionally occurred, is extremely unlikely to occur, and a ridge structure having a smooth side surface can be formed with good reproducibility. .

Example 2. P− introduced in Example 1
In order to further increase the effect of relaxing the etching rate difference with respect to the Al _0.25 Ga _0.75 As etching buffer layer 7, as shown in FIG. 3, the p-Al _0.5 Ga _0.5 As second cladding layer 6 and the p-GaAs first contact are formed. By providing the graded etching buffer layer 17 in which the aluminum composition ratio is continuously changed from 0 to 0.5 between the layers 8 to eliminate the discontinuous region from the viewpoint of the etching rate, the ridge waveguide is further stabilized. Can be formed.

[0019]

As described above, according to the present invention, since the etching buffer layer having an intermediate etching rate between the clad layer and the contact layer is inserted between the clad layer and the contact layer, the layers between the layers are not separated. The etching rate difference becomes smaller,
A ridge structure having smooth side surfaces without steps can be formed with high reproducibility, and a highly reliable semiconductor laser device can be obtained. In addition, the use of the graded layer eliminates the region where the etching rate is discontinuous between the layers, so that a more stable and smooth ridge structure can be formed.

Further, according to the manufacturing method of the present invention, the first contact layer, the etching buffer layer and the second contact layer are formed by wet etching using a mixed solution of an organic acid and hydrogen peroxide.
The clad layer can be selectively etched to form a ridge structure stably with good reproducibility.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a manufacturing flow of a semiconductor laser device according to an embodiment of the present invention.

3A is a cross-sectional view showing a semiconductor laser device according to a second embodiment of the present invention, and FIG. 3B is a view showing an Al composition ratio of a graded etching buffer layer.

FIG. 4 is a perspective view showing the structure of a conventional semiconductor laser device.

FIG. 5 is a diagram showing a manufacturing flow of a conventional semiconductor laser device.

FIG. 6 is a diagram showing a relationship between an etching rate in an organic acid / hydrogen peroxide solution and an aluminum composition ratio.

[Explanation of symbols]

1 n-GaAs semiconductor substrate, 2 n-Al _0.5 Ga _0.5
As cladding layer, 3 quantum well active layer, 4 p-Al
_0.5 Ga _0.5 As 1st clad layer, 5 p-Al _0.7 Ga
_0.3 As etching stopper layer, 6 p-Al _0.5 Ga
_0.5 As second clad layer, 7 p-Al _0.25 Ga _0.75 A
s etching buffer layer, 8 p-GaAs first contact layer, 9 ridge type waveguide, 10 n-GaAs current blocking layer, 11 p-GaAs second contact layer, 1
2 p-electrode, 13 n-electrode, 14 Ridge mask by insulating film, 15 Cavity in p-GaAs second contact layer, 16 Dimple on wafer surface, 17 Graded etching buffer layer.

Claims (3)

[Claims] 1. A ridge type waveguide having an etching buffer layer between a clad layer and a contact layer, wherein the aluminum composition ratio of the etching buffer layer is intermediate between the aluminum composition ratios of the clad layer and the contact layer. The semiconductor laser device is characterized by various values. 2. The semiconductor according to claim 1, wherein the etching buffer layer is a graded layer whose aluminum composition ratio continuously changes from the aluminum composition ratio of the cladding layer to the aluminum composition ratio of the contact layer. Laser device. 3. An n-Al is formed on an n-GaAs semiconductor substrate.
_A cladding layer made of _0.5 Ga _0.5 As, a quantum well active layer,
p-Al _0.5 Ga _0.5 As first cladding layer, p-
An etching stopper layer made of Al _0.7 Ga _0.3 As,
a second clad layer made of p-Al _0.5 Ga _0.5 As, p-
An etching buffer layer made of Al _0.25 Ga _0.75 As,
A step of sequentially forming each layer of the first contact layer made of p-GaAs, a step of forming an insulating film functioning as a ridge etching mask on the first contact layer, and a wet etching with a mixed solution of organic acid and hydrogen peroxide. And a step of etching the first contact layer, the etching buffer layer, and the second cladding layer to form a ridge structure.