JPH02191388A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To improve an optical damage to a level by making a clad layer perform an epitaxial growth and causing vertical side faces of the clad layer which are formed by burying inverted mesa type side faces to be formed into a reflecting face, and into a light outgoing face by an active layer. CONSTITUTION:A ridge part 4 is provided at a semiconductor substrate 2 having an active layer 1 in such a manner that a pair of both end side faces which intersect the active layer 1 and are facing each other are formed into inverted mesa type side faces 3A and 3B because of each specific crystal face. A clad layer 6 including the inner parts of mesa grooves 5 having the inverted mesa type side faces 3A and 3B is allowed to perform an epitaxial growth and buries the above side faces 3A and 3B. Then its layer 6 forms vertical side faces 7A and 7B so that the side faces intersect almost perpendicularly to the facial direction of the active layer 1. Further, the above faces 7A and 7B are formed into the reflecting face of a laser resonator, and into the outgoing face of the laser light by the active layer. Such an aperture structure in which the reflecting and outgoing faces are formed by the clad layer 6 thus improves an optical damage to a level.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a semiconductor laser, particularly a semiconductor laser having an end face structure in which a reflection surface of a resonator and a laser beam emission surface are formed by an open face of an active layer. The present invention relates to a method of manufacturing a semiconductor laser having a so-called window structure in which the end face of an active layer is covered with another semiconductor layer.

[Summary of the invention]

The present invention relates to a method for manufacturing a semiconductor laser, in which a ridge portion is provided in a semiconductor substrate having an active layer, and at least a pair of opposite end side surfaces across the active layer are inverted mesa-shaped side surfaces formed by specific crystal planes. and a step of epitaxially growing a cladding layer in a mesa groove having an inverted mesa-shaped side surface to form a vertical side surface that embeds the inverted mesa-shaped side surface, and the vertical side surface is used as a reflective surface of a laser resonator by an active layer. and serves as a laser beam emitting surface,
In particular, optical damage, so-called COD (Catastrop
The purpose is to improve the hicOptically Damage) level.

[Conventional technology]

In order to realize a high-power semiconductor laser, it is necessary to improve the COD level.

Ordinary semiconductor lasers, such as buried heterojunction (BH)
) type semiconductor laser, the plane perpendicular to the plane of the active layer constituting the laser resonator is formed by the open face of the crystal, and the end face thus formed is used as the reflective surface of the resonator and the laser beam. This is the light exit surface. However,
Semiconductor lasers that use such interfold surfaces as laser light emission surfaces have a problem with COD, which is a bottleneck in obtaining high-output semiconductor lasers.

In addition, in a semiconductor laser structure in which the output surface is formed by an interfold surface, so-called 0BIC (Optoelect
ror+ics Integrated C3rcui
It is unsuitable for application to t), and in order to put this 0EIC into practical use, it is desired to develop a semiconductor laser having a so-called window structure without the use of folds.

(Problems to be Solved by the Invention) However, there is a problem in constructing a resonator with good reproducibility and excellent characteristics in the conventional semiconductor laser having a window structure.

The object of the present invention is to solve this problem and obtain a semiconductor laser with a window structure that has excellent characteristics with good reproducibility, has a small COD, and can be easily integrated into an optical integrated circuit.

[Means for Solving the Problems] - The present invention provides, for example, a semiconductor substrate (2) having an active layer (1) as shown in FIG. 1A, and an active layer (1) as shown in FIG. 1B. ), and at least a pair of opposite end side surfaces are inverted mesa-shaped side surfaces (3A) and (3B) with specific crystal planes.
), and epitaxially growing a cladding layer (6) including the inside of the mesa groove (5) having the inverted mesa-shaped side surfaces (3A) and (3B) to form the inverted mesa-shaped side surface. (3A) and (3B) are embedded into the active layer (1).
) vertical side surfaces (7A) and (7B
), and its vertical side surfaces (7^) and (7B) are used as reflection surfaces of the laser resonator formed by the active layer (1) and as laser light emitting surfaces.

(Function) According to the above-described method of the present invention, the effective reflection surface of the resonator formed by the active layer (1) and the emission surface of the laser beam do not depend on the interfold surface, but instead form the window structure formed by the cladding layer (6). By doing so, it is possible to reduce optical damage, improve the COD level, and thereby achieve higher output and continuous light emission. 7A) and (7B) are inverted mesa-shaped side surfaces (3A) and (3
B) can be constructed by epitaxial growth, that is, by the appearance of a specified crystal plane due to the growth rate being different depending on the crystal plane, so that the vertical sides (7A) and (7B) can be reliably formed with high reproducibility. can be formed.

〔Example〕

An example of a method for manufacturing a semiconductor laser according to the present invention will be explained with reference to the drawings.

In this case, when obtaining an A I GaAs-based group ■-V compound semiconductor laser, first, as shown in FIG. 1A, a ■-V group compound semiconductor substrate (11 ) will be established. This substrate (11) has a main surface (Ila) having a (100) crystal plane. Then, on this main surface (lla), if necessary, a first conductivity type, for example, an n-type AI! is applied via a buffer layer (not shown). , a lower cladding layer (16) made of GaAs is epitaxially grown, followed by an active layer (1) made of a GaAs compound semiconductor having a smaller energy gap and higher refractive index, for example, and another conductive layer on top of this. A first cladding layer (6A) constituting the upper cladding layer (6), which is of type, for example, P type and has a larger energy bandgap, that is, a lower refractive index, than the active layer (1).
) are sequentially epitaxially grown to form a semiconductor substrate (2).

As shown in FIG. 1B, the upper first cladding layer (6A
) A stripe-shaped etching mask (8) is selectively formed on the film. This mask (8) is formed using well-known techniques such as coating a photoresist film or pattern exposure.

It can be formed by each development process. In this case, the plane along the plane of the paper is selected as the (011) crystal plane, and the extending direction of the stripes of the mask (8) is selected along the plane of the paper so that both edges are perpendicular to this.

Next, from above the upper cladding layer (6A), the active layer (1)
Crystallographic anisotropic etching is performed to a depth across the .

That is, for example, a sulfuric acid-based etching solution) 1. so
Etching is performed from above the cladding layer (6A) using an etching solution containing a mixture of 4, HtO*, and H2O in a ratio of 3:1:1. In this way, the parts not covered by the mask (8) are etched to form mesa grooves (5).
, thereby forming (
111) Inverted mesa-shaped side surface (3A) and (3
B) A striped mesa, that is, a ridge portion (4) is formed.

Next, as shown in FIG. 1C, the upper cladding layer (6A
) and the second one is made of GaAsAl, which is the same conductivity type and material.
The craft Ji (6B) is epitaxially grown including the inside of the mesa groove (5). In this way, when (110) crystal planes are formed on the inverted mesa side surfaces (3A) and (3B), this <110 > Due to the slow crystal growth rate in the axial direction, epitaxial growth apparently stops at this point, so if the epitaxial growth of the cladding layer (6B) is stopped at this point, the main surface of the substrate (2), that is, the active layer (1
) side surfaces (7A) and (7B) perpendicular to the plane are generated.

Thereafter, as shown in the first diagram, a cap N (made of, for example, a p-type low resistivity GaAs compound semiconductor layer) (
12) is epitaxially grown.

Next, as shown in FIG. 1, a first electrode (21) is deposited on the cap layer (12) in ohmic contact. In addition, the back surface of the board (2), that is, the substrate (
11), a second electrode (22) is ohmically attached to the back surface of the semiconductor laser (23) to obtain the desired semiconductor laser (23).

The semiconductor laser (23) obtained in this way has an active layer (
1) acts as an operating region, that is, a resonator, and cladding layers (6
) ((6B) ) vertical sides (7A) and (7B
) is formed into a semiconductor laser with a window structure. In this case, in the inverted mesa-shaped side surfaces (3A) and (3B) of the active layer (1), the refractive index n of the active layer (1) and the cladding layer (6B) is, for example, n=3.3 for the active layer. Compared to the cladding layer (
6B) has a small difference of about n=3.2, and this aspect (
3A) and (3B) are oblique to the active layer surface, and the refractive index difference between the cladding layer (6B) formed on these side surfaces (3A) and (3B) and the outside air is large; Also, since the outer surface of the cladding layer (6B) is perpendicular to the surface of the active layer (1) (7A) and (7B), this surface (
7A) and (7B) will act as reflective surfaces of the resonator, and these surfaces (7A) and (7B) will become laser emission surfaces.

In this case, regarding the side surface perpendicular to the extending direction of the striped ridge portion (mesa) (4) of the active layer (1),
As shown in FIG. 2, which is a sectional view taken in a direction perpendicular to the cross section of FIG.

It should be noted that various configurations other than the above-mentioned example may be adopted, such as each layer described above may be selected to have a conductivity type opposite to that illustrated.

〔Effect of the invention〕

According to the above-described method of the present invention, the substantial reflection surface of the resonator and the emission surface of the laser beam formed by the active layer (1) do not depend on the interfold surface due to the exposure of the end face of the active layer, but rather the cladding layer (6). By adopting a window structure formed by the vertical sides (7A) and (7B), it is possible to reduce optical damage and improve COD, which leads to high output and continuous light emission. In particular, in the present invention, these side surfaces (78) and (7B) are inverted mesa-shaped side surfaces (3A) and (3) formed by specific crystal planes.
B) is formed by epitaxial growth, that is, the growth rate differs depending on the crystal plane, and thus the formation of a specified crystal plane is ensured with high reproducibility. It is possible to produce semiconductor lasers with stable and excellent characteristics.

[Brief explanation of the drawing]

FIG. 1 is a linear cross-sectional view of each step of the method of the present invention, and FIG. 2 is a cross-sectional view of a semiconductor laser obtained by the method of the present invention. (2) is the substrate, (1) is the active layer, (6), (6A) and (6B) are the cladding layers, (12) is the cap layer, (4)
is a ridge portion (mesa), (3A) and (3B) are inverted mesa-shaped side surfaces, and (7A) and (7B) are vertical side surfaces.

Claims (1)

[Scope of Claims] A step of providing a semiconductor substrate having an active layer with a ridge portion having at least a pair of opposing side surfaces across the active layer that are inverted mesa-shaped side surfaces due to a specific crystal plane; epitaxially growing a cladding layer including the inside of the mesa groove having side surfaces and burying the inverted mesa type side surfaces to form vertical side surfaces, the vertical side surfaces being used as reflective surfaces of the laser resonator formed by the active layer; A method for manufacturing a semiconductor laser, characterized in that the laser beam is emitted from the laser beam.