JPH09148670A - Semiconductor laser and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make mesa etching process unnecessary, and prevent the decrease of uniformity of element characteristics, by arranging an active layer in a trench constitute by both side surfaces of a current blocking layer whose crystal face index is (111) B face and a semiconductor substrate surface. SOLUTION: On a P-InP substrate 1 of crystal face index (001), an SiO2 stripe(ST) 19 is formed parallel with the light output direction <100>. By using the ST 19 as a mask, an N-InP block layer 2 and a P-InP block layer 3 are grown. By adjusting film formation conditions, a (111) B face turns to a slant on account of the dependence of growth speed on the face orientation. After the ST 19 is eliminated and a clad layer 4, an active later 5 and a buried layer 6 are grown in order, growing is once interrupted. An active layer 6a is automatically formed in a trench surrounded by the (111) B slant face and the P-InP substrate 1. Growing is again started, and a buried layer 6b and a cap layer 7 are grown. Further an SiO2 film, an N electrode and a P electrode are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser which has a low threshold value, can reduce the number of steps in a manufacturing process, and has good stability, and as a result, can easily reduce the cost.

[0002]

2. Description of the Related Art Buried Heterostruc
(ture) type semiconductor laser has a structure suitable for lowering the threshold value due to the current confinement by the narrow active layer (1 to 2 μm) and the current blocking layer. As an example of the BH type laser,
Journal of Applied Physics Volume 51 4
P. 539 1980 (J. Appl. Phys., 51, 4539
(1980)). In this example, a mesa obtained by etching the active layer is formed by liquid layer epitaxy growth (LPE; Liqu).
It is embedded by the id phase epitaxy method to form a good current block layer.

In recent years, metal-organic vapor phase epitaxy (MOCV) is superior to the LPE method in that the growth layer has a large area and is highly uniform.
D; Due to the progress of Metalorganic Chemical Vapor Deposition) technology, a BH type laser in which all epitaxial growth is carried out by the MOCVD method was developed.
echnology Letters, Vol.4, No.9 1992
p. 954), the report is described.

The cross-sectional structure of this BH type laser is shown in FIG. This structure is manufactured by growth by the MOCVD method three times, and the manufacturing method is outlined below. beginning,
On the p-InP substrate 1, an InGaAsP active layer 5 and n
-InP clad layer 14 is grown. Next, wet etching is performed using SiO ₂ as a mask to form a mesa stripe, and the active layer width is controlled to 1.5 μm. After the mesa etching, the second growth is performed to form the p-InP sidewall layer 20, the n-InP block layer 2, and the p-InP.
The block layer 3 is selectively grown on both sides of the mesa stripe.
Then, after removing SiO ₂ , as the third growth,
The n-InP buried layer 6 and the n-InGaAsP cap layer 7 are grown. After that, an n electrode and ap electrode are formed.

By the above procedure, a good current confinement structure can be manufactured in a relatively large area. However, the conventional BH type laser requires a mesa etching step,
For this reason, it is a factor of lowering the uniformity of device characteristics within the wafer surface. This is because it is necessary to precisely control the mesa size such as width and depth over the entire surface of the wafer in order to obtain uniform device characteristics. This is because the shape and arrangement of the current blocking layer during the groWth growth change, and this greatly affects the device characteristics such as the threshold current.

[0006]

An object of the present invention is to simplify the manufacturing method as compared with the conventional BH type laser and to improve the controllability of the size, shape and arrangement of the active layer and the current block layer. An object of the present invention is to provide a low-cost BH type semiconductor laser or the like having improved yield and low cost.

[0007]

In order to solve the above problems, according to the present invention, a semiconductor laser having an active layer and a current blocking layer on a semiconductor substrate having a (001) plane has a plane index of A structure in which an active layer is arranged inside a groove formed by both side surfaces of a current blocking layer, which is a (111) B surface, and a semiconductor substrate surface is used as a stripe structure of a semiconductor laser.

In the (111) B plane of this structure, a stripe of a silicon oxide film or a silicon nitride film in the <110> direction is formed on a (001) plane semiconductor substrate, and this stripe is used as a selective growth mask to form 10 to 100 Torr. Decompression M
It is formed on both sides of the stripe when the current block layer is epitaxially grown at a growth temperature of 600 to 700 ° C. by the OCVD method.

The active layer is formed by removing the stripes and then again using the low pressure MOCVD method under the above conditions. At this time, epitaxial growth does not occur on the (111) B plane,
By utilizing the property of growing only on the (001) plane, it is possible to form an active layer in the groove. The above epitaxial growth utilizes the plane orientation dependence of the growth rate. The flattening of the device surface is performed by embedding the groove portion by the atmospheric pressure MOCVD method which does not depend on the plane orientation of the growth rate. The semiconductor laser having the above structure can be manufactured by using the above means.

According to the present invention, the stripe structure of the semiconductor laser can be formed only by the epitaxial growth by the MOCVD method without including the etching step. This simplifies the manufacturing method, and facilitates the dimensional control of the active layer and the current blocking layer and the optimization of the shape and arrangement. As a result, a low-threshold, high-efficiency semiconductor laser can be manufactured with good uniformity within the wafer surface, and the yield is improved.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, referring to FIG. 1 to FIG.
An embodiment of the present invention will be described. FIG. 1 shows a cross-sectional view perpendicular to the light emitting direction of a semiconductor laser device according to one embodiment of the present invention, and FIG. 3 shows its manufacturing procedure.

First, as shown in FIG. 3A, on the p-InP substrate 1 having a surface index (001), the light emitting direction <
Width 0.3 in parallel to the 110> μm of SiO ₂ stripe 1
9 is formed. This SiO ₂ patterning is performed by CVD
A resist mask pattern is formed on the SiO ₂ film formed by the photolithography method by the photolithography technique, and then the dry etching method is used.

After removing the resist, the SiO ₂ stripe 1
Using 9 as a mask, the n-InP block layer 2 (thickness 0.6 μm) and the p-InP block layer 3 (thickness 1.5 μm) are sequentially grown selectively by the low pressure MOCVD method. The growth condition at this time is that the carrier gas H ₂ pressure in the chamber is 40 T.
The orr and substrate temperature are 600 ° C. In this case, due to the plane orientation dependence of the growth rate, epitaxial growth does not occur on the (111) B plane, and (11) as shown in FIG.
1) A shape in which the B surface is a slope is obtained.

Next, the SiO ₂ stripes 19 are removed by buffer hydrofluoric acid, and then the p-InP cladding layer 4 (thickness 0.8 μm) and InGaA are formed again by the low pressure MOCVD method.
The sP active layer 5 and the n-InP buried layer 6a (having a thickness of 0.2 μm)
m) is sequentially grown, and the epitaxial growth is temporarily stopped. At this time, the growth condition is that the chamber pressure is 40 Torr,
The substrate temperature is 600 ° C. Therefore, (111) B
Since epitaxial growth does not occur on the slope, a width of 1.4 μm is formed inside the slope and the groove surrounded by the p-InP substrate 1.
The active layer is automatically formed.

Next, after introducing a carrier gas into the chamber and setting the internal pressure to 1 atm, the epitaxial growth is restarted and the n-InP burying layer 6b (thickness 2.0 μm) and n-I are formed.
An nGaAsP cap layer 7 (thickness: 0.3 μm) is sequentially grown.
In this case, the dependence of the epitaxial growth rate on the plane orientation disappears, and the growth rate in the groove increases, so that the inside of the groove can be embedded and the surface can be flattened (FIG. 3).
(C)).

Thereafter, as shown in FIG. 1, a SiO ₂ film 8 is formed on the surface of the element by the CVD method, and the portion directly above the active layer 5 is wet-etched to open a window having a width of about 10 μm. Then, the n-electrode 9 is formed on the front surface side by vacuum vapor deposition, and the substrate is polished to a thickness of 100 μm on the back surface side.
The p-electrode 10 is formed by vacuum vapor deposition and heating at 400 ° C. or higher.

In the semiconductor laser of the present invention, as described above, since the stripe structure is formed only by the epitaxial growth by the MOCVD method, which has better controllability than etching, InGaAs is used.
The spacing between the P active layer 5 and the n-InP block layer 2 is 0.2 μm.
Can be easily brought close to and can be reproduced with good reproducibility. Also,
In this manufacturing method, it is easy to introduce a multiple quantum well structure into the active layer. Therefore, it is possible to manufacture a semiconductor laser having a low threshold value and high efficiency with a high yield.
Although the p-type InP substrate is used in this embodiment, the structure using the n-type InP substrate shown in FIG. 2 can be realized by the same manufacturing method. In addition, in the present invention, InGaAsP
Although the / InP system is used, other material systems such as GaAlAs / GaAs system are also possible.

[0018]

INDUSTRIAL APPLICABILITY According to the present invention, the dimensions of the active layer and the current blocking layer can be obtained by epitaxial growth without using etching.
Since the shape and arrangement are controlled, these controllability is better and the distribution in the wafer plane is smaller than that of the conventional buried heterostructure semiconductor laser. Therefore, it is possible to stably manufacture an element structure having a uniform characteristic with a low leak current, and thus it is possible to provide a low-cost semiconductor laser with improved yield.

[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 of a semiconductor laser device according to another embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating the manufacturing process of the embodiment of the present invention.

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

[Explanation of symbols]

1 ... p-InP substrate, 2 ... n-InP block layer, 3 ...
p-InP block layer, 4 ... p-InP clad layer, 5
... InGaAsP active layer, 6, 6a, 6b ... n-InP
Buried layer, 7 ... n-InGaAsP cap layer, 8 ... Si
O ₂ film, 9 ... n electrode, 10 ... p electrode.

Claims (3)

[Claims] 1. A semiconductor laser having an active layer and a current block layer on a semiconductor substrate having a plane index of (001) and both side surfaces of the current block layer having a plane index of (111) B. A semiconductor laser, wherein the active layer is arranged inside a groove formed on the surface of the semiconductor substrate. 2. The semiconductor substrate according to claim 1, wherein
When a stripe in the 110> direction is formed, epitaxial growth is performed using the stripe as a selective growth mask, the current block layer is formed on both sides of the stripe, and then the current block layer is formed after removing the stripe. A method of manufacturing a semiconductor laser, wherein the active layer is formed by epitaxial growth in the trench having the (111) B planes on both sides as the both sides formed at the same time, and the device surface is flattened by buried growth. 3. The semiconductor laser according to claim 2, wherein epitaxial growth of the active layer and the current block layer is performed by a low pressure MOCVD method, and subsequent element flattening buried growth is performed by epitaxial growth by a normal pressure MOCVD method. Manufacturing method.