JP2003060302A - Semiconductor laser and manufacturing method therefor method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser that can obtain a stable lateral mode in which the flow of current in a ridge is fixed and the current density in a light emitting region is made uniform, and in addition, the luminous intensity distribution little varies; can be mounted without rattling, and is reduced in element resistance. SOLUTION: In the ridge structure of this semiconductor composed of a contact layer, a current-blocking layer, and a third clad layer, the upper end face of the current-blocking layer and the upper end face of the contact layer or third clad layer adjoin each other and form a flat surface.

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 used as a light source for optical communication, consumer use and industrial equipment, and a method for manufacturing the same, and more particularly to a forbidden band wider than the band gap of an active layer material. The present invention relates to a semiconductor laser device having a buried ridge structure which is completely surrounded by a clad layer having energy and a manufacturing method thereof.

[0002]

2. Description of the Related Art A semiconductor light emitting device is used as a light source in the fields of information / image processing, measurement, communication, medical care, and the like, and various attempts have been made to obtain a high-output light beam. In order to realize a high-power light beam, by suppressing the spread of the current flowing through the laser element,
It is necessary to concentrate the current near the active layer region where the laser light propagates and confine the laser light in a certain region. Besides, in the semiconductor laser used as the light source,
Low threshold current and stable transverse mode oscillation are required.

Therefore, the conventional high-power semiconductor laser device employs various stripe structures that restrict the injection of current or carriers to the stripe-shaped regions not only in the vertical direction but also in the horizontal direction. .

For example, FIG. 4 shows an example of a conventionally known semiconductor laser device having a double hetero (DH) structure. The structure is a cross-sectional structure of the laser as viewed from the direction of the reflecting surface, that is, a cross section perpendicular to the cavity length direction. The structure is shown schematically. In the case of FIG. 4 showing a GaAs infrared laser, for example, 1 is a contact layer made of p-GaAs and 2 is n-GaAs.
Current blocking layer (blocking layer) 3 made of p-AlGa
A third cladding layer made of As, 4 is an etching stop layer, 5 is a second cladding layer made of p-AlGaAs, 6 is an active layer made of undoped AlGaAs, and 7 is a first cladding layer made of n-AlGaAs. Although not shown below the first cladding layer 7, n-Ga
A buffer layer made of As, an n-GaAs substrate, and an n-
It has a structure in which electrodes (negative electrodes) are sequentially formed. Note that "non-doped" is also called undoped and means that impurities are not doped.

The second clad layer 5 made of p-AlGaAs and the first clad layer 7 made of n-AlGaAs function to confine carriers in the active layer 6 made of AlGaAs. In the sectional structure shown in FIG. 4, since the active layer 6 made of AlGaAs is flat,
Carrier confinement does not occur in the lateral direction. But n
Current confinement is performed by the current blocking layer (block layer) 2 made of -GaAs. The thickness of the third cladding layer 3 made of p-AlGaAs is V-shaped, that is, p-A in the cross section viewed from the reflecting surface direction.
Since the third clad layer 3 made of 1GaAs has a trapezoidal cross section, the active layer 6 made of AlGaAs is formed.
An effective refractive index distribution is formed in the lateral direction for the laser light propagating in the vicinity, and optical waveguide is performed. This p-AlG
By the third cladding layer 3 made of aAs, AlGaA
In the active layer 6 made of s, carriers are excited in stripes to form the light emitting region 8.

However, in the semiconductor laser device having the stripe structure as shown in FIG. 4, n-Ga is used.
In the manufacturing process, the current blocking layer 2 made of As is p-GaAs.
Since the contact layer 1 made of is partially covered in a stepped shape, the light output is weakened in the vicinity of both ends in the lateral direction of the light emitting region 8, so that there is a problem that it is difficult to obtain a stable lateral mode. . The reason for this will be described in detail below with reference to the drawings.

In FIG. 4, n-Ga that serves as a current injection portion
The width of the opening of the contact layer 1 made of p-GaAs which is not covered by the current blocking layer (block layer) 2 made of As is W1, and the width at the upper portion of the ridge of the contact layer 1 made of p-GaAs is W2, n. When the width of the opening of the current blocking layer (block layer) 2 made of -GaAs on the side of the second cladding layer 5 made of p-AlGaAs is expressed as W3, the emission lateral spread angle is determined by the dimension of W2. Once the size of W2 is determined, the size of W3 is almost uniquely determined in the manufacturing process of the semiconductor laser device.

In order to oscillate a stable transverse mode, it is desired that there is no difference in current density throughout the light emitting region 8. In FIG. 4, the current blocking layer 2 made of n-GaAs is p
Since the ridge of the contact layer 1 made of -GaAs is partially covered in a stepped shape, no current flows in the covered portion, and only the current injection portion is W1. However, p-
Contact layer 1 made of GaAs and p-AlGaA
Since a current flows in the ridge of the third cladding layer 3 made of s, the injected current diffuses, and the current flows in the region of the width W2 in the contact layer 1 made of p-GaAs. In other words, in the contact layer 1 made of p-GaAs, the regions at both ends covered with the current blocking layer 2 made of n-GaAs and in which no current is injected, the current injection depends only on the diffusion, so that it is more than the central part. The current density becomes low. As a result, the current density becomes lean near both ends of the light emitting region 8 in the lateral direction, and in transverse mode oscillation,
The output becomes weak near both ends of the light emitting region 8. For example, in the case of a broad area laser, when the light intensity near both ends of the light emitting region 8 becomes weak, the near field pattern (NFP;
There is a problem that the waveguide waveform (profile) in the near field pattern does not become steep and becomes an unstable transverse mode. Further, if the current injection part W1 becomes narrow, the electrical characteristics will deteriorate and the element resistance will increase. Therefore, it is expected that a semiconductor laser device having a structure in which the contact layer 1 made of p-GaAs is not covered with the current blocking layer 2 made of n-GaAs.

Further, the shape in which the current blocking layer 2 is partially covered in a stepped manner as described above causes rattling of the element during mounting when mounting a laser. The rattling at the time of mounting is not limited to the shape in which the current blocking layer is partially covered in a stepped shape, and may occur when the current blocking layer is partially in the shape of a protrusion. Therefore, the current blocking layer and the contact layer or the third layer
It is desirable that the clad layer and the clad layer have a flat shape, and a semiconductor laser device having such a structure is expected to appear.

[0010]

SUMMARY OF THE INVENTION According to the present invention, the current density in the light emitting region is made uniform by making the current flow in the ridge constant, so that a stable transverse mode with little variation in the light emission intensity distribution. It is an object of the present invention to provide a semiconductor laser device and a method for manufacturing the same, in which there is no rattling at the time of mounting and the element resistance is reduced.

[0011]

As a result of intensive studies, the inventor of the present invention formed a ridge structure composed of a contact layer, a current blocking layer and a third cladding layer on the upper part of the semiconductor, and formed an upper end surface of the current blocking layer. It has been found that the above problems can be solved all at once by providing a structure in which a flat surface is formed by adjoining the upper surface of the contact layer or the upper surface of the third clad layer to each other.

That is, by adopting such a structure,
In particular, current injection at both ends of the ridge structure does not rely on current diffusion as in the above-described conventional semiconductor laser device, but is performed in the same manner as in the central part of the ridge structure. As a result, by adopting such a structure, it is possible to reduce the current diffusion in the ridge and to make the current flow constant in the ridge, which in turn makes the current density in the light emitting region uniform and It is possible to obtain a stable transverse mode with little variation in the intensity distribution. Moreover, since the upper end of the convex portion of the ridge structure is flat, rattling at the time of mounting can be reduced. The present inventor has conducted further studies and completed the present invention.

That is, the present invention comprises (1) a semiconductor substrate, a first clad layer formed on the semiconductor substrate, an active layer formed on the first clad layer, and an active layer formed on the active layer. A second clad layer, an etching stop layer formed on the second clad layer, a third clad layer having stripe-shaped protrusions formed on the etching stop layer, and a third clad layer Except for at least a part of the contact layer formed above and the contact layer convex portion,
A semiconductor laser device comprising a current blocking layer formed in contact with a contact layer, having a structure in which an upper end surface of the contact layer and an upper end surface of the current blocking layer are adjacent to each other to form a flat surface. A semiconductor laser device characterized in that
(2) a semiconductor substrate, a first cladding layer formed on the semiconductor substrate, an active layer formed on the first cladding layer, a second cladding layer formed on the active layer, 2 except the etching stop layer formed on the clad layer, the third clad layer having a stripe-shaped convex portion formed on the etching stop layer, and at least a part of the convex portion of the third clad layer. A semiconductor laser device comprising: a current blocking layer formed in contact with the third cladding layer; and a contact layer formed on the third cladding layer. A semiconductor laser device having a structure in which a flat surface is formed adjacent to the upper end surface of the current blocking layer, (3) a contact layer,
In a ridge structure of a semiconductor laser device including a current blocking layer and a third cladding layer, an upper end surface of the current blocking layer and an upper end surface of the contact layer or an upper end surface of the third cladding layer are adjacent to each other to form a flat surface. A ridge structure of a semiconductor laser device characterized by: (4) a semiconductor laser device characterized by having the ridge structure described in (3) above; (5) the above (1) or (2) A method of manufacturing a semiconductor laser device, comprising: forming a flat surface as described above by polishing; (6) a first clad layer, an active layer, a second clad layer, an etching stop layer, and a third clad layer on a semiconductor substrate. Of the clad layer and the contact layer are continuously grown in the above order, a step of forming an etching mask on the contact layer, the contact layer and the third layer using the etching mask. A step of selectively etching the lad layer to form a stripe-shaped convex portion having a ridge bottom, a step of removing the etching stop layer, and a step of forming a current blocking layer on the second cladding layer and on the side surface of the ridge structure. , A step formed when the current blocking layer is formed and a step formed by partially covering the current blocking layer on the contact layer, and / or a step formed when the current blocking layer formed on the ridge is removed by selective etching, unevenness, etc. And a step of flattening the non-flat part by polishing the semiconductor laser device.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below.

A semiconductor laser device having a ridge structure as a current confinement structure for allowing a current to flow only in a part of the active layer, and a current blocking layer formed by excluding at least a part of the convex portion of the ridge structure. Conventionally, for example, as will be described in detail later, was manufactured by the steps (a) to (g) shown in FIG. According to such a manufacturing process, at a part of the upper end of the ridge structure, particularly at both ends, a structure in which the current blocking layer covers the opening of the ridge structure in a stepped shape, or a shape in which the current blocking layer partially has a protrusion It cannot be avoided. More specifically, chemical vapor deposition (MOCV) using organic metal
When the current blocking layer is formed by the method D), the stepwise coating or protrusion may be formed by the migration in the selective growth using the SiO ₂ mask. In addition, when the current blocking layer formed on the ridge is removed by selective etching, the stepped coating or protrusion, and the uneven portion such as unevenness may be formed in some cases.

According to the present invention, a part of the upper end of the ridge structure, in particular, a structure in which a current blocking layer formed at both ends covers the opening of the ridge structure in a step shape, or a part of the current blocking layer is provided. It is characterized in that it has a shape having a projection on its surface and further flattens non-flat portions such as irregularities formed by selective etching. For example, when the present invention is applied to the conventional semiconductor laser device shown in FIG. 4, the semiconductor laser device has a sectional shape shown in FIG. As is clear by comparing FIG. 4 and FIG.
In the conventional semiconductor laser device, W1 <W2, whereas in the semiconductor laser device of the present invention, W1 = W.
It is 2. As described above, W1 is the width of the opening that serves as the current injection portion, and W2 is the width of the contact layer above the ridge. In the present invention, since the width W1 of the opening serving as the current injection portion is wider than that of the conventional semiconductor laser device, the element resistance can be reduced. Also, W1
When <W2, a current distribution was shown at both end portions of W2 that do not overlap with W1, and current injection was not performed, and current distribution was relied on. However, if W1 = W2, such inconvenience does not occur. The current flow in the ridge can be constant. As a result, the current density in the light emitting region becomes uniform, and a stable transverse mode with little variation in the light emission intensity distribution can be obtained. Furthermore, since the upper end surface of the convex portion of the ridge structure is flat, rattling at the time of mounting can be reduced.

The semiconductor laser device according to the present invention may have any known structure as long as it has the above characteristics. Among them, as a preferable aspect of the semiconductor laser device according to the present invention, a semiconductor laser device having the following structure can be mentioned. That is, in the ridge structure of the semiconductor laser device including the contact layer, the current blocking layer, and the third cladding layer, the upper end surface of the current blocking layer is adjacent to the upper end surface of the contact layer or the upper end surface of the third cladding layer. A ridge structure of a semiconductor laser device having a flat surface and a semiconductor laser device having the ridge structure.

The semiconductor laser device according to the present invention has a ridge structure as a current confinement structure for allowing a current to flow only in a part of the active layer. That is, the thickness of the third cladding layer is changed to a V shape, that is, the cross-sectional shape of the third cladding layer is trapezoidal in the cross section viewed from the reflecting surface direction, and the third cladding layer is Since the current blocking layer is formed except at least a part of the convex portion, the third cladding layer serves as a current injection portion.

Here, the current blocking layer may be made of any material as long as no current flows, and a known insulating material may be used. For example, SiO
₂ , compounds such as Si ₃ N ₄ , TiO ₂ or AlO ₂ ,
Alternatively, a combination of these may be used.

The substrate used in the semiconductor laser device of the present invention can be appropriately selected depending on the kind of semiconductor compound to be laminated thereon. For example, when using a GaAs-based semiconductor compound, it is preferable to use an n-GaAs substrate. When using a GaN-based semiconductor compound,
Examples include sapphire substrate, SiC substrate, GaN substrate, spinel or ZnO substrate. Further, in order to confine the laser light in the active layer, the cladding layer is preferably made of a material having a forbidden band energy wider than the band gap of the active layer material.

In the semiconductor laser device according to the present invention, it is preferable that a contact layer is laminated on the third cladding layer. In this case, the semiconductor laser device according to the present invention includes the following two modes. 1
In this mode, the third clad layer and the contact layer are laminated in this order from the bottom of the ridge structure, and the ridge structure is formed in contact with the contact layer except at least a part of the convex portion of the contact layer. A semiconductor laser device including a current blocking layer may be used. In another aspect, the third
There is a semiconductor laser device having a structure in which the upper end surface of the clad layer and the upper end surface of the current blocking layer are adjacent to each other to form a flat surface, and a contact layer is laminated on the flat surface.

Although the lower layer of the etching stop layer is referred to as the second cladding layer and the upper layer of the etching stop layer is referred to as the third cladding layer in the present specification, the second cladding layer and the third cladding layer are referred to. Since the layers are made of the same semiconductor compound, they may be collectively referred to as a second cladding layer.

As described above, since the etching stop layer is provided, the etching for forming the ridge structure (striped convex portion) can be performed with good controllability. That is, by appropriately selecting the etching stop layer and the etchant, it becomes possible to perform etching in a desired shape and depth.

In the semiconductor laser device according to the present invention, a first guide type first guide layer is provided between the first cladding layer and the active layer, and a second conductivity type first guide layer is provided between the active layer and the second cladding layer. Second
It may have a guide layer. In addition, a buffer layer may be provided between the substrate and the first cladding layer.

The semiconductor laser device according to the present invention is usually provided with a p-electrode and an n-electrode. The position of the p-electrode or the n-electrode and the structure / composition thereof are not particularly limited, and may be a structure / composition known per se. Specifically, for example, a structure in which the second conductivity type electrode is provided on the second cladding layer, the third cladding layer or the contact layer, and the first conductivity type electrode is provided on the back surface of the substrate is used. Can be mentioned. Further, as the p-electrode, for example, an electrode having a structure in which titanium (Ti), platinum (Pt), and gold (Au) are sequentially stacked is cited. Further, as the n-electrode, for example, gold germane (AuGe), nickel (N
i), titanium (Ti), platinum (Pt) and gold (Au)
An electrode in which is sequentially laminated is mentioned.

A known semiconductor compound may be used as a material forming the semiconductor laser device according to the present invention. Above all, it is preferable to use a III-V group semiconductor compound. III-
The group V semiconductor compound has a chemical formula of In _a Al _b Ga _c N _x A.
_sy P _z (a, b, c ≦ 1, a + b + c = 1, x, y,
In the case of z ≦ 1, x + y + z = 1), the composition ratios a, b and c and the semiconductors having all compositions in which x, y and z are changed within respective ranges are basically included. Further, a group in which a part of the group III elements In, Al, and Ga are replaced with B and a group in which part of the group V elements N, As, and P are replaced with Sb are also included. In the present invention, a GaAs-based semiconductor compound in which c and y are not 0 in the above chemical formula is preferable. More preferably,
Chemical formula Al _b Ga _c As (0 ≦ b <1,0 <c ≦ 1, b
+ C = 1), semiconductors of all compositions in which the composition ratios b and c are changed within their respective ranges are included. In the semiconductor laser device according to the present invention, the so-called double hetero (DH), in which the active layer and the first conductivity type first cladding layer and the second conductivity type second cladding layer are made of different semiconductor compounds, ) It is preferable to have a bonded laminated structure.

A specific embodiment of the semiconductor laser device according to the present invention will be described below with reference to FIG. FIG. 2 is a sectional view showing the structure of the semiconductor laser device of the present invention. In this embodiment, a semiconductor laser device having a buried ridge structure is
It is an example made of an aAs semiconductor compound. It goes without saying that the semiconductor laser device according to the present invention is not limited to, for example, the substrate, the type of semiconductor material and the composition thereof in the following embodiments.

In FIG. 2, reference numeral 21 is an n-GaAs substrate, and MOCVD (Metal Organic Chemical Vapor Deposi) is formed on the n-GaAs substrate 21 by thermal decomposition of an organic metal.
buffer layer 22 made of n-GaAs, the first cladding layer 23 made of n-AlGaAs, the active layer 24, the second cladding layer 25 made of p-AlGaAs, the etching stop layer 26, and the like. And a third clad layer 27 made of p-AlGaAs processed into a stripe-shaped mesa is formed.

A first clad layer 23 made of n-AlGaAs, an active layer 24, a second clad layer 25 made of p-AlGaAs, an etching stop layer 26 and p-.
The third cladding layer 27 made of AlGaAs is n-G
The active layer 24 having a double hetero structure formed on the aAs substrate 21 and having an energy bandgap corresponding to the emission wavelength is the first cladding layer 23 made of n-AlGaAs having an energy bandgap larger than that of the active layer 24. , P-AlGaAs, a second clad layer 25 and a third clad layer 27 sandwich the double hetero structure.

A current blocking layer (block layer) 28 made of n-GaAs is formed on the side surfaces of the double heterostructure portion, the third cladding layer 27 made of p-AlGaAs, and the contact layer 29 made of p-GaAs. . Then, the contact layer 29 made of p-GaAs and n-
A p-electrode 30 serving as a positive electrode is deposited on the upper surface of the GaAs current blocking layer 28, and an n-electrode 31 serving as a negative electrode is deposited on the lower surface of the n-GaAs substrate 21.

In this structure, the current confinement is performed by the current blocking layer 28 made of n-GaAs on the ridge of the contact layer 29 made of p-GaAs, and the optical waveguide is made of p-AlGaAs processed into a stripe mesa. The third clad layer 27 and the second clad layer 25 made of p-AlGaAs are formed in the current-confined portion.

The second clad layer 25 made of p-AlGaAs and the third clad layer 27 made of p-AlGaAs are the second and third layers for the sake of convenience in explaining the structure in which the etching stop layer 26 is sandwiched. Only the name of the third cladding layer is used, and p-AlGaA
second cladding layer 25 and third cladding layer 2 made of s
Since 7 is the same semiconductor, these may be collectively referred to as a second cladding layer.

The semiconductor laser device according to the present invention can be easily manufactured by a method known per se. Specifically, on the semiconductor substrate, the first clad layer, the active layer, the second layer
Of the clad layer, the etching stop layer, the third clad layer, and the contact layer are continuously grown in the above order, a step of forming an etching mask on the contact layer, and the contact layer and the third layer using the etching mask.
Step of selectively etching the clad layer to form a stripe-shaped convex portion having a ridge bottom, a step of removing the etching stop layer, and a step of forming a current blocking layer on the second clad layer and on the side surface of the ridge structure. And a step formed when forming the current blocking layer and a step formed by partially covering the current blocking layer on the contact layer, and / or a step formed by removing the current blocking layer formed on the ridge by selective etching, unevenness The semiconductor laser device according to the present invention can be manufactured by the step of flattening the non-flat portion such as by polishing.

In the step of laminating the semiconductor layer on the substrate, a known epitaxial growth method may be used.
Examples of such a method include halide vapor phase epitaxy, molecular beam epitaxy (MBE)
Method, physical vapor deposition (PVD) method such as sputtering or vacuum deposition; VPE (Vapor Phase Epitaxy) method; chemical vapor deposition (CVD) method such as metal organic chemical vapor deposition (MOCVD) method; or liquid phase epitaxy ( LPE) method and the like. Above all, it is preferable to use the MOCVD method or the VPE method, and it is more preferable to use the MOCVD method.

Next, a ridge structure is formed on the semiconductor laminated structure. The ridge structure can be manufactured by a known method such as a combination of photolithography and etching. The etching method is not particularly limited, and for example, a dry etching method such as a reactive ion dry etching (RIE) method or a reactive ion beam dry etching (RIBE) method, or a known method such as a wet etching method may be used. .

As described above, when the semiconductor laser device according to the present invention has the etching stop layer, the ridge structure can be formed with good controllability. In this case, the method for forming the ridge structure may be a known method. For example, Ga
When the AsInP clad layer is etched up to the GaInP etching stop layer, the clad layer is partially etched by a wet etching method using a hydrochloric acid-based etchant. Then, etching is performed using a sulfuric acid-based etchant until the GaInP etching layer is exposed. At this time, for sulfuric acid type etchant,
Since the GaInP etching stop layer has a low etching rate, the etching can be stopped at the etching stop layer, and a desired ridge stripe shape can be formed. Alternatively, for example, JP-A-3-1831
The method disclosed in 80 may be used.

Then, the upper end of the ridge structure, that is, the third
The current blocking layer is formed except the upper end of the clad layer or the upper end of the contact layer. More specifically, for example, by the epitaxial growth method as described above, for example, SiO ₂
An insulating material such as is laminated on the side and bottom of the protrusion of the ridge structure.

Next, the upper end of the ridge structure, that is, the upper end surface of the current blocking layer and the upper end surface of the contact layer or the upper end surface of the third cladding layer are adjacent to each other and planarized so as to form a flat surface. A known flattening technique may be used for flattening when manufacturing the semiconductor laser device according to the present invention. For example, chemical mechanical polishing (CMP) is used.
ishing) method, mechanical polishing (MP)
Method or etch back method. Of these, chemical mechanical polishing (hereinafter abbreviated as CMP) is particularly preferable.
Is the law.

Next, a preferable method for manufacturing the semiconductor laser device according to the present invention will be described with reference to FIG. Figure 3
[FIG. 6] is a process sectional view for illustrating the method of manufacturing the semiconductor laser device. It goes without saying that the method of manufacturing the semiconductor laser device according to the present invention is not limited to the method shown below such as the manufacturing process or the etchant. In the following embodiment, AlGaAs is
Is that of the _{Al x Ga (1-x)} As. In such compounds, x takes any value within the range of 0 to 1, preferably about 0.1 to 1.0.

First, the (100) plane of the n-GaAs substrate 21 shown in FIG. 3A is formed by the MOCVD method as shown in FIG.
As shown in (b), the buffer layer 22 made of n-GaAs, the first cladding layer 23 made of n-AlGaAs, the active layer 24, the second cladding layer 25 made of p-AlGaAs, and the etching stop layer are continuously formed. 26, p-Al
Third cladding layer 27 made of GaAs and p-Ga
The contact layer 29 made of As is sequentially grown to form a crystal,
A double heterostructure crystal was formed. The n-AlGaA
The first clad layer 23 made of s, the second clad layer 25 made of p-AlGaAs, the third clad layer 27, and the etching stop layer 26 are AlGaAs layers, and the etching stop layer 26 is each clad layer 23, 2.
Al composition is higher than 5, 27, and the thickness is, for example, 50 to 30.
It is a 0Å AlGaAs layer. For example, n-Al _0.4 G
a _0.6 As clad layer 23, p-Al _0.4 Ga
_0.6 As clad layer 25, p-Al _0.4 Ga _0.6
For the As clad layer 27, p-Al _0.7 Ga _0.3
The As etching stop layer 26 is used.

Then, as shown in FIG. 3C, p-G
A SiO ₂ mask 32 and a resist mask 33 were formed in stripes on the contact layer 29 made of aAs by thermal decomposition of silane gas and photolithography.

Next, as shown in FIG. 3D, SiO ₂
Using the mask 32 and the resist mask 33, the contact layer 29 made of p-GaAs is selectively etched using, for example, an ammonia-based etchant, and the third cladding layer 27 made of p-AlGaAs is used by using, for example, a tartaric acid-based etchant. Was selectively etched to form a stripe-shaped mesa ridge. Since the ridge is formed by wet etching, undercut progresses under the SiO ₂ mask 32. As described above, when selective etching is performed using tartaric acid as an etchant, the etching stop layer 26 having a high Al composition has a low etching rate, so that etching stops on the etching stop layer 26.

Next, as shown in FIG. 3E, when etching is performed using, for example, a hydrofluoric acid type etchant, the etching rate of the etching stop layer 26 having a high Al composition is opposite to that in the case of FIG. 3D. Since it is fast, the third cladding layer 27 made of p-AlGaAs already formed with the stripe-shaped mesa ridge and the second cladding layer 25 made of p-AlGaAs on the lower surface of the etching stop layer 26 are hardly eroded. Etching stop layer 26
Only the selective etching can be performed. Further, when the etching stop layer 26 is removed with a tartaric acid-based etchant, the etchant also erodes SiO ₂ , so that the SiO ₂ mask is side-etched at the same time and undercut proceeds under the resist mask.

As is clear from the above description, in this embodiment, when the etching stop layer is removed, the Si
Since the same etchant can be used for side etching of the O ₂ mask, the manufacturing process can be simplified. In addition,
In the method of manufacturing a semiconductor laser device described above, the current blocking layer may be formed without performing the step of narrowing the width of the etching mask by side etching.

Then, as shown in FIG. 3F, n is formed by MOCVD on the wafer from which the resist mask 33 has been removed.
A current blocking layer 28 made of -GaAs was grown. At this time, by selectively introducing a gas flow such as phosphine gas and trimethylgallium organometallic gas, S
GaAs was not grown on the iO ₂ mask 32 and p-Ga
The contact layer 29 made of As and the side surface of the third cladding layer 27 made of p-AlGaAs and p-AlGaA
n-GaAs is formed on the upper surface of the second cladding layer 25 made of s.
It is possible to grow the current blocking layer 28 consisting of.

Then, as shown in FIG.
_TwoThe mask 32 is removed by etching. Then figure
As shown in 3 (h), SiO_TwoThe mask 32 was removed
Later, SiO _TwoA current block consisting of n-GaAs with a mask
Step formed by migration in selective growth of stop layer 28
Polishing non-flat parts such as differences and irregularities by CMP method
To remove. Specifically, for example, ammonia base
Ridge a polishing agent in which abrasive grains such as silica are dispersed in an aqueous solution of
Polish it with a polishing object such as a polishing cloth while hanging it on the uneven part on the top.
And flatten.

Then, as shown in FIG. 3I, a p-electrode 30 and an n-electrode 30 are formed on the upper surfaces of the contact layer 29 made of p-GaAs and the current blocking layer 28 made of n-GaAs by a normal electrode attaching process. On the lower surface of the GaAs substrate 21, n-
By depositing the electrode 31, a laser wafer having the structure shown in FIG. 2 was obtained. This laser wafer is cleaved to produce a laser element. The (110) cleavage plane where the crystal is easily broken is used as the reflection surface of the resonator.

The semiconductor laser device according to the present invention is preferably applied to a high power semiconductor laser device. As the high-power semiconductor laser device, for example, a broad area semiconductor laser device, preferably a broad area semiconductor laser device having an optical output of about 10 W or more, or a narrow stripe semiconductor laser device having an optical output of about 200 mW or more is used. Can be mentioned. The semiconductor laser device according to the present invention is also preferably applied to a semiconductor laser device used as a light source such as an infrared laser.

[0049]

In the semiconductor laser device according to the present invention, since the current blocking layer does not cover the upper end of the ridge structure, current confinement is efficiently performed, and stable transverse mode oscillation with little variation in emission intensity distribution is achieved. can get. The stepped coating of the current blocking layer on the upper edge of the ridge structure or the protrusions formed on the current blocking layer are removed, and the upper edge of the convex portion of the ridge structure is flattened. The rattling of the element is reduced. Further, the opening not covered by the current blocking layer at the upper end of the ridge structure, which is the current injection portion, is wider than that of the conventional semiconductor laser device, so that the electrical characteristics are improved and, as a result, the element resistance is reduced. It has the advantage of being reduced. Such a semiconductor laser device is suitably used as a light source in the fields of information / image processing, measurement, communication, medical treatment, and the like, and is also useful as a high-output light beam.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing the structure of a semiconductor laser device according to the present invention.

FIG. 2 is a sectional view showing a structure of a semiconductor laser device according to an embodiment to which the invention is applied.

FIG. 3 is a process sectional view for explaining the manufacturing method of the semiconductor laser device.

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

[Explanation of symbols]

1 Contact layer made of p-GaAs 2 Current blocking layer (block layer) made of n-GaAs 3 Third clad layer 4 made of p-AlGaAs 4 Etching stop layer 5 Second clad layer 6 made of p-AlGaAs 6 AlGaAs Active layer 7 First clad layer 8 made of n-AlGaAs 8 Light emitting region 21 n-GaAs substrate 22 Buffer layer 23 made of n-GaAs First clad layer 24 made of n-AlGaAs 24 Active layer 25 p-AlGaAs Second clad layer 26 Etching stop layer 27 p-AlGaAs third clad layer 28 n-GaAs current blocking layer (block layer) 29 p-GaAs contact layer 30 p-electrode 31 n-electrode 32 SiO ₂ mask 33 resist mask

Claims (6)

[Claims] 1. A semiconductor substrate, a first cladding layer formed on the semiconductor substrate, an active layer formed on the first cladding layer, and a second cladding layer formed on the active layer. An etching stop layer formed on the second clad layer, a third clad layer having stripe-shaped protrusions formed on the etching stop layer, and a contact layer formed on the third clad layer And a current blocking layer formed in contact with the contact layer, except for at least a part of the contact layer convex portion, which comprises an upper end surface of the contact layer and an upper end surface of the current blocking layer. Is adjacent to each other to form a flat surface, which is a semiconductor laser device. 2. A semiconductor substrate, a first cladding layer formed on the semiconductor substrate, an active layer formed on the first cladding layer, and a second cladding layer formed on the active layer. An etching stop layer formed on the second cladding layer, a third cladding layer having stripe-shaped protrusions formed on the etching stop layer, and at least a part of the protrusions of the third cladding layer. A semiconductor laser device comprising: a current blocking layer formed in contact with the third cladding layer; and a contact layer formed on the third cladding layer. A semiconductor laser device having a structure in which an end face and an upper end face of a current blocking layer are adjacent to each other to form a flat surface. 3. A ridge structure of a semiconductor laser device comprising a contact layer, a current blocking layer and a third cladding layer, wherein the upper end surface of the current blocking layer and the upper end surface of the contact layer or the upper end surface of the third cladding layer. A ridge structure of a semiconductor laser device, characterized in that a flat surface is formed adjacently. 4. A semiconductor laser device having the ridge structure according to claim 3. 5. A method of manufacturing a semiconductor laser device, wherein the flat surface according to claim 1 or 2 is formed by polishing. 6. A first clad layer, an active layer, a second clad layer, an etching stop layer, and a third clad layer on a semiconductor substrate.
Of the clad layer and the contact layer are sequentially grown in the above order, a step of forming an etching mask on the contact layer, and the contact layer and the third clad layer are selectively etched using the etching mask to remove the ridge bottom. A step of forming the stripe-shaped convex portion having, a step of removing the etching stop layer, a step of forming a current blocking layer on the second cladding layer and a side surface of the ridge structure, and a step of forming the current blocking layer. Steps formed by projections and contact layers partially covered with a current blocking layer, and / or uneven surfaces formed by removing the current blocking layer formed on the ridge by selective etching are planarized by polishing. A method of manufacturing a semiconductor laser device, comprising: