JPH0555696A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To manufacture a semiconductor laser having a buried type stripe structure of small leak current, by thickly forming a second buried layer for blocking a current, in the vicinity of a mesa. CONSTITUTION:After a second buried layer 9 for blocking a current is thickly deposited covering a mesa 6, a mesa top 7 is exposed by melt-back. At the time of melt-back of the second buried layer the upper end of the first buried layer 8 on a mesa wall surface is etched together with the surface of the mesa 6. Since the first buried layer 8 surface is formed so as to form a small angle with respect to the mesa wall surface 14, the interval between the second buried layer 9 for blocking a current and the mesa is not so changed when the upper end of the first buried layer 8 is etched. Hence the first buried layer 8 on the mesa wall 14 which layer 8 determines the interval between the second buried layer 9 and the mesa 6 can be thinly and stably formed, so that a structure in which the second buried layer 9 and the mesa 6 are arranged via a small gap can be easily manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor laser having a buried stripe structure having a small leak current and a low threshold current.

With the development of large-scale, high-speed optical communication systems and information equipment, semiconductor lasers used as light sources thereof are required to have high emission intensity and high-speed modulation characteristics. Therefore, it is necessary to increase the conversion efficiency of the semiconductor laser by reducing the leak current and the threshold current.

[0003]

2. Description of the Related Art A conventional method for manufacturing a semiconductor laser having a buried stripe structure will be described. FIG. 3 is a process chart of a conventional example, showing a cross section perpendicular to the stripe of the semiconductor laser.

First, on a semiconductor substrate 1 made of n-type InP, a first cladding layer 2 made of n-type InP 2 and InGaA are formed.
The active layer 3 made of sP and the second cladding layer made of p-type InP are sequentially grown by a liquid phase epitaxial growth method (hereinafter referred to as LPE method).

Next, referring to FIG. 3A, the top of the mesa
7 is a striped oxide film (SiO ₂Membrane) is provided and this
First embedding using bromine-based etchant with mask
Striped by mesa etching to a depth in the middle of the layer
The mesa 6 is formed.

Then, the oxide film is removed, and a first buried layer 8 made of p-type InP is buried and deposited by the LPE method, and then a second buried layer 9 made of n-type InP is formed on the top 7 of the mesa. The mesas 6 are buried and deposited without being deposited.

Next, a third buried layer 12 made of p-type InP is buried and deposited on the side surface of the mesa 6, and then a third cladding layer 10 made of p-type InP and a contact layer 11 are formed with reference to FIG. Deposit using the LPE method.

After that, electrodes are provided to form a resonator to complete a semiconductor laser. In the manufacturing method of this embodiment, it is necessary to prevent the second buried layer 9 from being deposited on the top 7 of the mesa.

Therefore, when the second burying layer 9 is deposited by the LPE method, it is necessary to reduce the degree of supercooling of the solution. However, in this case, the second buried layer 9 cannot be grown thick, and the second buried layer 9 for blocking the current cannot be deposited sufficiently thick in a flat region other than the mesa 6.

As a result, the current gain of the pnp transistor, which is composed of the first and third buried layers 8 and 12 on the basis of the second buried layer 9, becomes large, and the flat region other than the mesa has a larger area than the mesa 6. A large leak current flows through.

In order to avoid the above-mentioned inconvenience that the second buried layer 9 cannot be deposited thickly and the leak current becomes large, the following method utilizing meltback has been devised.

FIG. 4 is a process chart of another conventional example, showing a cross section perpendicular to the stripe of the semiconductor laser. First, referring to FIG. 4A, the stripe-shaped mesa 6 including the first cladding layer 2, the active layer 3 and the second cladding layer 4 is oxidized on the semiconductor substrate 1 in the same manner as in the conventional example. It is formed by mesa etching using the film mask 5.

Next, referring to FIG. 4B, after the first burying layer 8 is deposited, the second burying layer 9 is deposited thickly over the top 7 of the mesa. Next, referring to FIG. 4C, the second burying layer 9 is melted back until the second burying layer deposited on the mesa top 7 is removed.

Next, referring to FIG. 4D, the third cladding layer 10 and the contact layer 11 are deposited to complete the buried structure of the semiconductor laser. FIG. 1 is a diagram for explaining the principle of the present invention, and FIG. 1 (a) is a sectional view showing details of a corner portion of a mesa in another conventional example.

In the other conventional embodiment described above, the mesa top 7
It is necessary to melt back the second buried layer 9 until the second buried layer deposited on it is removed. At this time,
Referring to (a), the exposed surface 13 is formed in such a shape that the surface of the mesa top 7 and a part of the first embedded layer 8 are simultaneously etched.

Therefore, the distance between the mesa 6 and the second buried layer is determined by the thickness of the first buried layer 8 deposited on the mesa wall surface 14 near the corner of the top 7 of the mesa. However, in the conventional method, it is desirable that the first burying layer 8 is not deposited on the top of the mesa, but is deposited on other portions with a sufficient thickness.

To achieve this, liquid phase epitaxial growth from a solution with a low degree of supercooling is used. As a result, the growth of the first buried layer 8 on the mesa top 7 is extremely slow, and the first buried layer 8 grows in the direction of the mesa wall surface 14 at substantially the same height as the mesa top 7.

Therefore, according to the conventional method, the first buried layer 8
Cannot be thinned only on the mesa sidewalls regardless of the thickness on flat areas other than the mesas. Therefore, the thickness of the first buried layer 8 cannot be reduced on the side wall of the mesa, and the gap between the mesa 6 and the second buried layer shown in FIG. 4A cannot be narrowed.

As a result, the leakage current flowing through this gap is increased.

[0020]

As described above, the second buried layer cannot be thickly deposited by the conventional method. Further, in the method of thickly depositing the second buried layer by using etch back, the first buried layer on the side wall of the mesa cannot be thinned, and the gap between the mesa and the second buried layer cannot be narrowed. Therefore, there is a problem that the leak current increases.

It is an object of the present invention to provide a method for manufacturing a semiconductor laser having a buried stripe structure with a small leak current by forming a thick second buried layer for blocking a current and close to a mesa. And

[0022]

FIG. 2 is a process chart of an embodiment of the present invention, showing a cross section perpendicular to the stripe of a semiconductor laser.

In order to solve the above problems, referring to FIG. 2, the structure of the present invention is a method of manufacturing a semiconductor laser having a buried stripe structure, in which a first conductivity type first clad is formed on a semiconductor substrate 1. A step of sequentially depositing the layer 2, the active layer 3 and the second conductivity type second clad layer 4, and using the striped mask 5 for the first clad layer 2, the active layer 3 and the second clad layer 4. The mask 5 by the etching
A step of removing the region other than to a depth in the middle of the first cladding layer 2 to form a stripe-shaped mesa 6, and then covering the mesa 6 with a second conductive type first buried layer 8 and the substrate. 1 and then melting the first buried layer 8 to expose the second cladding layer 4 on the top 7 of the mesa, and then the second buried layer of the first conductivity type. Depositing a layer 9 on top of the mesa 7 and the first buried layer 8 on the substrate 1, and then melt back the second buried layer 9 onto the top 7 of the mesa to the second cladding. A method of manufacturing a semiconductor laser, comprising a step of exposing the layer 4 and then a step of depositing a second cladding layer 10 of the second conductivity type on the substrate 1 so as to cover the top 7 of the mesa. ..

[0024]

In the present invention, referring to FIG. 2 (b), the first embedding layer 8 is deposited to cover the tops 7 of the mesas, and then, referring to FIG. 2 (c), the first embedding layer is melted back. Then, a part of the second clad layer 4 which is the uppermost layer of the mesa 6 is removed, and the first buried layer outside the mesa 6 is mesa-etched.

The etching rate of such meltback is
It is slow in the mesa 6, and fast in the first buried layer 8 on the side wall of the mesa and the flat region other than the mesa. Therefore, the exposed surface 13 is
The amount of etching is small on the top 7 of the mesa having a slow etching rate and becomes a plane parallel to the surface of the substrate 1, while the first buried layer which is fast-etched on the outer wall surface of the mesa 6 is formed at an angle close to vertical.

Therefore, referring to FIG. 1 (b), which is a sectional view showing the details of the corner portion of the mesa according to the present invention, the mesa wall surface 1
Since the first buried layer 8 on 4 is almost vertically etched as described above, its thickness is extremely thin.

Moreover, the shape of the etching surface is determined by the difference in the etching rate, and is not significantly affected by the etching time. Therefore, since the shape of the etching surface can be always formed stably, the thickness of the first burying layer 8 on the mesa wall surface 14 after the etching back can be thinly and precisely reproduced.

Next, in the configuration of the present invention, FIG.
Referring to (f), the second buried layer 9 for blocking the current,
Similar to the other conventional examples described above, the mesas 6 are covered and deposited thickly, and then the mesa tops 7 are exposed and formed by meltback.

Therefore, there is no limitation on the degree of supercooling, and the second buried layer can be deposited thickly. When the second buried layer 9 is melted back, referring to FIG. 1B, the upper end of the first buried layer 8 on the mesa wall surface 14 is etched together with the surface of the mesa 6.

However, in the present invention, since the surface of the first buried layer 8 is formed at a small angle with the mesa wall surface 14, the second buried layer 9 and the mesa that block the current even if the upper end thereof is etched are formed. The size of the gap is not much changed.

Therefore, as described above, according to the present invention, the first embedding layer 8 on the mesa wall surface 14 which determines the gap between the second embedding layer 9 and the mesa 6 can be formed in a thin and stable shape. The structure in which the second buried layer 9 and the mesa 6 are arranged with a small gap therebetween can be easily manufactured.

[0032]

EXAMPLES The present invention will be described with reference to examples. First,
Referring to FIG. 2A, the n-type InP having the plane orientation (100) is formed.
On the substrate 1, a first clad layer composed of an n-type InP layer having a thickness of 2 μm, an active layer composed of an InGaAsP layer having a thickness of 0.1 to 0.2 μm, and a p-type InP layer having a thickness of approximately 0.5 μm. Is deposited by the LPE method.

Next, an oxide film having a thickness of 200 to 300 nm, for example, is deposited by, for example, sputtering or CVD, and is photoetched to form a stripe-shaped mask 5.
Then, a mesa 6 having a width of, for example, 1 μm is formed by mesa etching using a mask 5 using a bromine-based etchant, and other regions are removed halfway to the first cladding layer 2 to a depth of 1.5 μm, for example.

Next, referring to FIG. 2B, after the first buried layer 8 made of a p-type InP layer is deposited on the mesa 6 by the LPE method to have a thickness of 0.5 μm, for example, and subsequently, FIG.
Referring to (c), the first buried layer 8 is melted back under the condition that the solution is not saturated to expose the mesa top 7, and at the same time, the first buried layer on the side surface of the mesa is etched to form the mesa. An exposed surface 13 is formed so as to extend substantially vertically from the top 7.

Next, referring to FIG. 2D, a second buried layer 9 made of an n-type InP layer is deposited by, for example, 0.5 μm on the mesa 6 by the LPE method, and then, FIG.
As in the case of the first embedding layer 8, the second embedding layer 8 is melted back and the mesa top 7 is exposed.

Next, referring to FIG. 2F, for example, the third cladding layer 1 made of a p-type InP layer having a thickness of 0.5 μm.
0 is deposited and, for example, p-type InG having a thickness of 0.2 μm is deposited.
A contact layer 11 made of an aAsP layer is deposited.

Next, the electrodes and the resonator are formed through a normal process to manufacture a semiconductor laser having a buried stripe structure.

[0038]

According to the present invention, the second buried layer for blocking current can be deposited thickly, and the second buried layer can be provided close to the mesa including the active layer.
It is possible to provide a method for manufacturing a semiconductor laser having a buried stripe structure with a small leakage current, and it is a great contribution to improving the performance of optical communication systems and information equipment.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention.

FIG. 2 is a process chart of an embodiment of the present invention

FIG. 3 is a process chart of a conventional example

FIG. 4 is a process chart of another conventional example

[Explanation of symbols]

 1 Substrate 2 First Cladding Layer 3 Active Layer 4 Second Cladding Layer 5 Mask 6 Mesa 7 Mesa Top 8 First Buried Layer 9 Second Buried Layer 10 Third Cladding Layer 11 Contact Layer 12 Third Buried Layer 13 Exposed Surface 14 Mesa Wall

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor laser having a buried stripe structure, comprising: a first clad layer (2) of a first conductivity type, an active layer (3) and a second clad layer of a second conductivity type on a semiconductor substrate (1). A step of sequentially depositing two clad layers (4), and etching the first clad layer (2), the active layer (3) and the second clad layer (4) using a stripe mask (5). A step of removing a region other than the mask (5) to an intermediate depth of the first cladding layer (2) to form a stripe-shaped mesa (6); and then, a second buried type first buried layer Depositing (8) on the substrate (1) to cover the mesa (6), and then melt back the first buried layer (8) to the second cladding on the top (7) of the mesa. A step of exposing the layer (4), and then a second buried layer (9) of the first conductivity type. Top of the mesa (7) and said first buried layer substrate covers (8) (1)
A step of depositing the second clad layer (4) on the top (7) of the mesa by melting back the second buried layer (9), and then a second conductivity. A third cladding layer (10) of a mold covering the top (7) of the mesa and depositing on the substrate (1).