JP2000232254A - Semiconductor laser and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser which is high in output and reliability and easily manufactured at a low cost and a manufacturing method thereof. SOLUTION: This semiconductor laser is manufactured through a manner where a GaAlAs lower clad layer 12, a GaAs bulk active layer 13, and a GaAlAs upper clad layer 14 are grown on a GaAs substrate 11, a light projection edge face and its vicinity are etched as far as the lower clad layer 12, an undoped GaAlAs lower clad layer 15, an undoped GaAlAs core layer 16, and an undoped GaAlAs upper clad layer 17 are selectively and locally regrown on the above etched part through an MOVPE method, a GaAlAs upper clad layer 18 and a GaAs contact layer 19 are grown, an optical waveguide 10 is formed in the direction of light projection through an ECR plasma etching, a front surface electrode and a rear surface electrode are formed, the substrate 11 is cleaved, and then an anti-reflection film is formed on the front edge face, and a high reflecting film is formed on the rear edge face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-power semiconductor used for optical disks, solid-state laser excitation, laser beam printers, optical fiber amplifier excitation, optical communication, laser processing, laser treatment, and the like. The present invention relates to a method for manufacturing a laser and a semiconductor laser, and particularly to GaAlAs and InGa
It is effective when applied to increase the output of an Al-containing material system such as AlP.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for higher power semiconductor lasers as light sources for optical disks and laser printers, or as optical fiber amplifiers and light sources for exciting solid lasers. Often a problem with high power operation of semiconductor lasers is catastrophic failure (COD) due to degradation of the light-emitting end face induced by high light density. The problem is Al
This is particularly noticeable in short-wavelength semiconductor lasers containing. For this reason, a region (hereinafter, referred to as a “window region”) having a wider band gap than the active layer, that is, a semiconductor layer having absorptivity to oscillating light (hereinafter, referred to as a “window region”) is defined as The above problem is solved by providing a structure (hereinafter, referred to as a “window structure”) provided around the light emitting side end face.

In a semiconductor laser having such a window structure, for example, in a manufacturing process of a pn-embedded laser, an active layer in a window region is etched and removed at the same time as stripe formation etching, and the removed portion is entirely pn-embedded. It can be manufactured by growing (hereinafter referred to as “pn buried growth method”) (for example, see “Electron. Lett.” Vol. 30; p. 1766; (1994) and the like).

Further, for example, in a manufacturing process of a quantum well semiconductor laser, by diffusing impurities into a window region or performing a heat treatment after ion implantation, the quantum well in the window region is mixed and made non-absorbing ( (Hereinafter, referred to as “quantum well alloying method”) (for example, “The 58th Annual Meeting of the Japan Society of Applied Physics”, p. 1127; 4a-ZC-12; (March 1997 ), `` Proceedings of the 45th Joint Lecture on Applied Physics, '' p. 1113; 29a-ZH-9;
(March 1998) etc.).

Further, for example, in a general semiconductor laser manufacturing process, a wafer is divided into strips by cleavage to form chip end faces constituting resonators, and a large number of laser elements are arranged in an array. (Hereinafter, referred to as “bar”), and the semiconductor layer is epitaxially grown on the chip end face (hereinafter, referred to as “epitaxial growth method on chip end face”) (for example, see Japanese Patent Application Laid-Open No. H5-251824). ).

[0006]

In a semiconductor laser having a window structure as described above, it is preferable that the window region be non-conductive because good device characteristics can be obtained. Because if the window area is conductive,
This is because an increase in the threshold value and a decrease in the differential efficiency due to the reactive current to the window region cannot be avoided. Further, in order to suppress an increase in threshold value and a decrease in differential efficiency due to divergence of oscillation light in the window region, the window region desirably has an optical waveguide structure. Furthermore, it is desirable that the optical waveguide structure in the window region can be designed independently of the optical waveguide structure in the active region. This is for minimizing the connection loss (hereinafter referred to as “radiation mode”) between the optical waveguides due to the difference in the refractive index distribution between the window region and the active region.

However, since the semiconductor laser manufactured by the pn buried growth method described above does not have an optical waveguide structure in the window region, it is possible to suppress an increase in threshold value and a decrease in differential efficiency due to divergence of oscillation light in the window region. Can not. Further, since a pn-embedded laser is premised, it cannot be applied to the production of an optical waveguide laser (ridge waveguide laser) having a high productivity and having a convex shape.

Further, in order to perform current narrowing by utilizing the reverse bias of the pn junction which has been buried and regrown, it is necessary to etch the active layer to a depth of about 1 μm and regrow the buried to a thickness of about 2 μm. There is GaAlAs
In the case of an Al-containing material-based semiconductor laser such as InGaAlP or InGaAlP, there are the following difficulties. Since the Al composition ratio increases as the distance from the active layer increases, a layer having a high Al composition ratio appears when the above-described deep etching is performed, and it is difficult to sufficiently remove an oxide layer generated on the etching surface. Yes, it is difficult to maintain reliability for a long time. It is difficult for GaAlAs or InGaAlP to regrow in a selected region. In particular, the higher the Al composition of the regrown layer and the larger the grown film thickness, the more remarkable.

In the above-described quantum well alloying method, since a window structure is manufactured by thermal diffusion or ion implantation, it is difficult to make the window region non-conductive. In many cases, the window region becomes conductive. As a result, reactive current is injected into the window region, and the threshold value increases. As one method for solving this problem, semi-insulation is performed by injecting protons into the window region. However, in the semiconductor laser having the window structure manufactured in this manner, although the initial characteristic value is significantly improved, the injected protons move during long-term operation, and thus high reliability is maintained for a long time. It was difficult. In addition, since the refractive index of the mixed crystal window region is uniquely determined by the epitaxial structure of the active region, there is no design freedom for minimizing the radiation mode between the window region and the active region. Furthermore, since the semiconductor laser having a quantum well active layer is assumed, it cannot be applied to a semiconductor laser having a bulk active layer.

On the other hand, in the above-described epitaxial growth method on the chip end face, since a window structure having a thickness of several tens to several hundreds of nm is manufactured by epitaxial growth on the chip end face, problems such as divergence of oscillation light and injection of reactive current actually occur. However, since the width of the bar was very small, being several hundreds of μm, the handleability was very poor. Further, since it is assumed that epitaxial growth is performed on the side surface of the bar, the manufacturing efficiency is very poor.

Accordingly, an object of the present invention is to provide a semiconductor laser having high output and high reliability which can be easily manufactured at low cost, and a method of manufacturing the semiconductor laser.

[0012]

According to a first aspect of the present invention, there is provided a semiconductor laser having a band gap smaller than that of an active layer including an active layer. A window region composed of a wide semiconductor layer is provided, and the window region has a structure in which an undoped high refractive index semiconductor layer is sandwiched between a lower low refractive index semiconductor layer and an upper low refractive index semiconductor layer, and has an epitaxial structure in the stacking direction. And a convex optical waveguide along the light emitting direction.

A semiconductor laser according to a second aspect of the present invention is the semiconductor laser according to the first aspect, wherein the undoped high refractive index semiconductor layer in the window region is adapted to match the eigenmodes of the active region and the window region. Is set.

A semiconductor laser according to a third aspect of the present invention is the semiconductor laser according to the second aspect of the present invention, wherein the undoped high refractive index semiconductor layer is thinner than the active layer.

A semiconductor laser according to a fourth aspect of the present invention is the semiconductor laser according to the first aspect, wherein the undoped high refractive index semiconductor layer in the window region is adapted to match an eigenmode between the active layer and the window region. Is set.

According to a fifth aspect of the present invention, in the semiconductor laser according to the fourth aspect of the present invention, a refractive index of the undoped high refractive index semiconductor layer is substantially equal to a refractive index of the active layer. .

A semiconductor laser according to a sixth aspect of the present invention is the semiconductor laser according to the first aspect, wherein the active layer and the undoped high refractive index semiconductor layer are made of an InGaAs single or multiple strained quantum well. Features.

According to a seventh aspect of the present invention, there is provided a method of manufacturing a semiconductor laser, comprising: epitaxially growing a lower low refractive index semiconductor layer in a stacking direction;
After growing the active layer on the lower low refractive index semiconductor layer,
After removing the periphery of the light emitting side end face of the active layer by etching, an undoped high refractive index semiconductor layer having a wider band gap than the active layer is epitaxially grown in the stacking direction on the removed portion, and the active layer and the undoped semiconductor layer are removed. An epitaxial growth of the upper low-refractive-index semiconductor layer on the high-refractive-index semiconductor layer, the growth of the upper layer on the upper low-refractive-index semiconductor layer, and the formation of a convex optical waveguide along the light emitting direction. Features.

According to an eighth aspect of the present invention, in the semiconductor laser manufacturing method of the seventh aspect, the active layer is made of GaAs and the lower low refractive index semiconductor layer is made of GaAlAs. Wherein the periphery of the light emitting side end face of the active layer is etched with an ammonia / hydrogen peroxide based etchant.

According to a ninth aspect of the present invention, there is provided a semiconductor laser manufacturing method according to the seventh aspect, wherein the active layer comprises an InGaAs single or multiple strained quantum well, and The low-refractive-index semiconductor layer has a GaAs layer or a GaAlAs layer, and the periphery of the light emitting side end face of the active layer is alternately etched with a carboxylic acid-based etchant and an ammonia / hydrogen peroxide-based etchant. It is characterized by.

According to a tenth aspect of the present invention, there is provided a semiconductor laser manufacturing method according to the seventh aspect, wherein the active layer is made of GaAs, GaAlAs or In.
One of GaAsP or a combination thereof, and the lower low refractive index semiconductor layer is made of InGaP.
It has a P layer or an InGaAlP layer, and the periphery of the light emitting side end face of the active layer is etched with a sulfuric acid-based etchant.

[Operation] In the semiconductor laser according to the present invention, the window region has an optical waveguide structure by an epitaxial structure in the epitaxial laminating direction, and has a convex shape (ridge stripe) along the light emitting direction in the epitaxial in-plane direction. ) Forms an optical waveguide, so that an increase in threshold and a decrease in differential efficiency due to divergence of oscillation light in the window region can be suppressed.

Further, since the high refractive index semiconductor layer in the window region is undoped, injection of a reactive current into the window region can be reduced, and semi-insulation such as proton injection is not required.

Furthermore, by epitaxially growing the window region as a selective region, an optical waveguide structure can be designed in the window region independently of the active region. Therefore, by adjusting the refractive index and the thickness of the undoped high-refractive-index semiconductor layer in the window region, the eigenmode of the window region can be matched with the eigenmode of the active region. Radiation mode can be reduced to a level at which there is no practical problem.

On the other hand, in the method of manufacturing a semiconductor laser according to the present invention, etching for forming a window region only needs to be performed on an active layer or a layer near the active layer. No exposure of tall layers. Therefore, deterioration due to oxidation of the etched surface can be avoided.

In addition, the semiconductor layer may be selectively regrown in the selected region only by the same thickness as that of the active layer. With a laser, there is no need to grow a layer with a high Al composition. Therefore, the difficulty of selective growth of a material containing Al can be greatly reduced.

Further, since the window region is formed by selectively growing the semiconductor layer before the division into the bar state, a semiconductor laser having a window structure can be manufactured without reducing the productivity. .

Further, since the optical waveguide type (ridge waveguide type) having a convex shape with good productivity is assumed, and the active layer may be a quantum well or a bulk, a conventional structure having a window structure is used. There is a great advantage as compared with the semiconductor laser manufacturing method described above.

Further, when the active layer, the lower low refractive index semiconductor layer, and the etching solution have the above-described composition, the active layer can be etched without removing the lower low refractive index semiconductor layer. The etching of the active layer can be stopped at the lower low refractive index semiconductor layer.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of a semiconductor laser and a method of manufacturing a semiconductor laser according to the present invention will be described below, but the present invention is not limited to these embodiments.

[First Embodiment] A first embodiment of a semiconductor laser and a method of manufacturing a semiconductor laser according to the present invention will be described with reference to FIGS. FIG.
FIG. 2 is a sectional view showing a schematic structure of the semiconductor laser.
FIG. 2 is a sectional view taken along the line II-II in FIG. 1 and shows a case where a GaAs bulk active layer is applied.

First, GaAlA is formed on a GaAs substrate 11.
s lower cladding layer 12, GaAs bulk active layer 13
And an upper cladding layer 14 of GaAlAs is epitaxially grown in the stacking direction.

Subsequently, the periphery of the light emitting side end face serving as the window region is etched by a sulfuric acid / hydrogen peroxide-based wet etching solution to a depth reaching the lower cladding layer 12.

Next, a lower cladding layer 15 of undoped GaAlAs, a core layer 16 of undoped GaAlAs, an undoped GaAs layer around the etched end face of the light emitting side.
The upper cladding layer 17 of lAs is selectively grown in a selected region by metal organic vapor phase epitaxy (MOVPE). Here, the interface position between the lower cladding layer 15 and the core layer 16 is matched with the interface position between the lower cladding layer 12 and the bulk active layer 13, and the interface position between the core layer 16 and the upper cladding layer 17 is set as the bulk active layer 13. The surface of the upper clad layer 17 was made flush with the surface of the upper clad layer 14 so as to coincide with the interface position between the upper clad layer 14 and the upper clad layer 14.

Subsequently, an upper cladding layer 18 of GaAlAs and a contact layer 19 of GaAs are grown over the entire upper surfaces of the upper cladding layers 14 and 17 by MOVPE.

An optical waveguide (hereinafter referred to as a "projection" hereinafter) is formed on the wafer thus manufactured by electron cyclotron resonance (ECR) plasma etching using a mixed gas of boron trichloride (BCl ₃ ) gas and argon (Ar) gas. After forming 10 along the light emitting direction, forming a front surface electrode and a back surface electrode, and dividing by cleavage, an anti-reflection film is formed on the front end face, and a high reflection film is formed on the rear end face. I do.

That is, the lower cladding layer 12 (the lower low refractive index semiconductor layer) is epitaxially grown in the laminating direction,
After the bulk active layer 13 (active layer) is grown on the lower clad layer 12, the light emitting side end face of the bulk active layer 13 is formed together with the light emitting side end face of the upper clad layer 14 grown on the bulk active layer 13. After the periphery has been removed by etching, the lower cladding layer 1 grown on the removed portion
A core layer 16 (undoped high refractive index semiconductor layer) having a wider band gap than the active layer 13 is epitaxially grown in the stacking direction on the active layer 13, and the upper cladding layers 14 and 17 are formed on the bulk active layer 13 and the core layer 16. The upper clad layer 18 (upper low-refractive index semiconductor layer) is epitaxially grown through the intermediary layer, the contact layer 19 (upper layer) is grown on the upper clad layer 18, and the ridge stripe 10 is formed along the light emitting direction. .

By manufacturing as described above, the semiconductor laser according to the present embodiment is provided around the light emitting side end face of the active region including the lower cladding layer 12, the bulk active layer 13, the upper cladding layers 14, 18, and the like. , The bulk active layer 13
The core layer 16 having a wider band gap is sandwiched between the lower cladding layer 12 and the upper cladding layer 18 via the lower cladding layer 15 and the upper cladding layer 17 to form an epitaxial structure in the stacking direction. Is provided along the light emission direction.

In the present embodiment, the bulk active layer 1
Although GaAs is applied to No. 3, GaAlAs can also be applied. Also, instead of the bulk active layer 13, G
It is also possible to apply an aAs / GaAlAs-based quantum well active layer.

[Second Embodiment] A second embodiment of the semiconductor laser and the method of manufacturing the semiconductor laser according to the present invention will be described with reference to FIGS. Note that FIG.
FIG. 4 is a sectional view showing a schematic structure of the semiconductor laser.
FIG. 4 is a cross-sectional view taken along the line IV-IV in FIG. 3 and shows a case where an InGaP bulk active layer is applied.

First, InGaAs is formed on a GaAs substrate 11.
The lower cladding layer 22 of 1P, the bulk active layer 23 of InGaP, and the upper cladding layer 24 of InGaAlP are epitaxially grown.

Subsequently, when the periphery of the light-emitting-side end face serving as a window region is etched to a depth reaching the lower cladding layer 22, undoped InGaAs is added to the etched portion.
IP lower cladding layer 25, undoped InGaAlP
Of the core layer 26 and the upper clad layer 27 of undoped InGaAlP are selectively grown by MOVPE. Here, the interface position between the lower cladding layer 25 and the core layer 26 is matched with the interface position between the lower cladding layer 22 and the bulk active layer 23, and the interface position between the core layer 26 and the upper cladding layer 27 is set as the bulk active layer 23. The surface of the upper clad layer 27 was made flush with the surface of the upper clad layer 24 so as to coincide with the interface position between the upper clad layer 24 and the upper clad layer 24.

Next, the upper cladding layer 28 of InGaAlP and the contact layer 19 of GaAs are grown over the entire upper surfaces of the upper cladding layers 24 and 27 by MOVPE.

BCl ₃ was added to the wafer thus manufactured.
After the ridge stripe 20 is formed along the light emitting direction by ECR plasma etching using a mixed gas of a gas and an Ar gas, a front electrode and a back electrode are formed and divided by cleavage. And a high reflection film is formed on the rear end face.

That is, the lower cladding layer 22 (the lower low refractive index semiconductor layer) is epitaxially grown in the laminating direction,
After the bulk active layer 23 (active layer) is grown on the lower cladding layer 22, the periphery of the light emitting side end face of the bulk active layer 23 and the vicinity of the light emitting side end face of the upper cladding layer 24 grown on the bulk active layer 23 are also obtained. Is removed by etching, a core layer 26 (undoped high-refractive index semiconductor layer) having a band gap wider than that of the bulk active layer 23 is epitaxially grown on the lower clad layer 25 grown on the removed portion in the stacking direction, An upper cladding layer 28 (upper low-refractive index semiconductor layer) is epitaxially grown on the bulk active layer 23 and the core layer 26 via the upper cladding layers 24 and 27, and the contact layer 1 is formed on the upper cladding layer 28.
9 (upper layer) and ridge stripe 2
0 was formed along the light emission direction.

By manufacturing as described above, the semiconductor laser according to the present embodiment is provided near the light emitting side end face of the active region including the lower cladding layer 22, the bulk active layer 23, the upper cladding layers 24 and 28, and the like. , The bulk active layer 23
The core layer 26 having a wider band gap is sandwiched between the lower cladding layer 22 and the upper cladding layer 28 via the lower cladding layer 25 and the upper cladding layer 27, and an epitaxial structure is formed in the laminating direction. Is provided along the light emission direction.

In the present embodiment, the bulk active layer 2
Although InGaP was applied to No. 3, InGaAlP can also be applied. Further, instead of the bulk active layer 23, an InGaP / InGaAlP-based quantum well active layer can be applied.

[Third Embodiment] A third embodiment of the semiconductor laser and the method of manufacturing the semiconductor laser according to the present invention will be described with reference to FIGS. FIG.
FIG. 6 is a sectional view showing a schematic structure of the semiconductor laser.
FIG. 6 is a cross-sectional view taken along the line VI-VI in FIG. 5 and shows a case where a bulk active layer of GaAs is applied to a structure having a light separation confinement layer.

First, the lower cladding layer 32 of Ga _0.5 Al _0.5 As, the lower light separation / confinement layer 32a of Ga _0.75 Al _0.25 As, the bulk active layer 13 of GaAs, the Ga _0.75 Al
An upper optical isolation confinement layer 34a of _0.25 As is grown on the GaAs substrate 11 by MOVPE.

Subsequently, after removing the upper light separating / confining layer 34a around the light emitting side end face serving as the window region by ECR plasma etching using a mixed gas of BCl ₃ gas and Ar gas, an ammonia / hydrogen peroxide based By immersing in the etchant, the bulk active layer 13 around the light emitting side end face is removed. Although the ammonia / hydrogen peroxide-based etchant has a high erosion property to GaAs, it has a low erosion property to GaAlAs, so that the bulk active layer 13 can be easily removed by etching without removing the lower light separation / confinement layer 32a. That is, the etching of the bulk active layer 13 can be stopped at the lower light isolation / confinement layer 32a.

Next, a sulfuric acid-based wet etching solution was used.
After finishing the surface treatment, undo
Ga_0.9Al_0.1As core layer 36 and undoped
Ga _0.75Al_0.25The upper light separation / confinement layer 37a of As
Regrowth is performed in a selective region by the MOVPE method. here
Thus, the interface between the core layer 36 and the upper light separation / confinement layer 37a
The positions are the bulk active layer 13 and the upper optical isolation confinement layer 34a.
And the upper light separation confinement layer 37a
Is flush with the surface of the upper light separation / confinement layer 34a.
It was to so.

Next, the upper light separation / confinement layers 34a, 37
Ga over the entire surface of a_0.5Al _0.5Upper class of As
The pad layer 38 and the GaAs contact layer 19 are
It was grown by the PE method.

BCl ₃ was added to the wafer thus manufactured.
After the ridge stripe 30 is formed along the light emitting direction by ECR plasma etching using a mixed gas of a gas and an Ar gas, a front electrode and a back electrode are formed and divided by cleavage. And a high reflection film is formed on the rear end face.

That is, the lower cladding layer 32 (the lower low refractive index semiconductor layer) is epitaxially grown in the laminating direction,
A lower light separation / confinement layer 32 is formed on the lower cladding layer 32.
a (lower low refractive index semiconductor layer) via bulk active layer 13
After the (active layer) is grown, the periphery of the light exit side end face of the bulk active layer 13 and the periphery of the light exit side end face of the upper light separation / confinement layer 34a grown on the bulk active layer 13 are removed by etching. The core layer 36 having a wider band gap than the bulk active layer 13 is formed in the removed portion.
(Undoped high-refractive-index semiconductor layer) is epitaxially grown in the stacking direction, and an upper cladding layer 38 (upper low-refractive-index semiconductor layer) is epitaxially grown on the bulk active layer 13 and the core layer 36 via the upper optical isolation confinement layers 34a and 37a. To form a contact layer 19 on the upper cladding layer 38.
(Upper layer) and the ridge stripe 30
Is formed along the light emitting direction.

By manufacturing in this manner, the semiconductor laser according to the present embodiment includes the lower cladding layer 32, the lower light separation / confinement layer 32a, the bulk active layer 13, the upper light separation / confinement layer 34a, the upper clad layer 38, and the like. The core layer 36 having a wider band gap than the bulk active layer 13 is provided around the light emitting side end face of the active region having the lower cladding layer 32 and the upper cladding layer 32a via the lower light separation / confinement layer 32a and the upper light separation / confinement layer 37a. Forming an epitaxial structure in the stacking direction with a structure sandwiched between layers 38,
A window region having the ridge stripe 30 along the light emission direction is provided.

The semiconductor laser thus manufactured oscillates at a threshold current of 25 mA and has a maximum optical output of 400
mW. In addition, constant light output operation (50 ° C., 200 m
W), the accelerated degradation test showed that COD (Catastro
(phic Optical Damage) Free operation was confirmed. Also,
The driving current increase rate after 10000 hours is 1
% Or less.

In a semiconductor laser having a window structure, since the refractive index distributions of the active region and the window region cannot be completely matched, the coupling loss between the active region and the window region cannot be completely eliminated. . Since the coupling mode and the emission mode between the active region and the window region cannot be focused on a single spot, the application to an optical disk or a laser printer causes a problem such as an increase in the diameter of a focused spot, and an optical fiber. In the case of application to an amplifier, a problem such as reduction in coupling efficiency of a single mode optical fiber is induced. However, in the semiconductor laser according to the present invention, by adjusting the refractive index and the thickness of the core layer in the window region, the emission mode can be reduced to a level at which there is no practical problem.

FIG. 7 shows a vertical far-field image when the thickness of the core layer 36 in the window region is the same as that of the bulk active layer 13. FIG. FIG. 9 shows a vertical far-field image when the thickness is smaller than that of the active layer 13. FIG. 9 shows the case where the thickness of the core layer 36 in the window region is the same as that in FIG. 9 is a graph showing a vertical far-field image in the case (10% in FIG. 8), that is, when the refractive index of the core layer 36 is substantially the same as the refractive index of the bulk active layer 13. FIG.
8, the shoulder portion appearing on the negative angle side is a radiation mode caused by mode mismatch.

As can be seen from FIGS. 7 and 8, when the thickness of the core layer 36 is smaller than that of the bulk active layer 13, the radiation mode can be reduced. At this time, the single mode fiber coupling efficiency was improved by about 10%. As can be seen from FIG. 9, if the Al composition is further reduced to 5%, that is, the refractive index is made substantially the same, the shoulder portion can be almost eliminated, and the single-mode fiber coupling efficiency is further improved by several percent. . The improvement in single mode fiber coupling efficiency is due to eigenmode matching between the active region and the window region.

[Fourth Embodiment] A fourth embodiment of the semiconductor laser and the method of manufacturing the semiconductor laser according to the present invention will be described with reference to FIGS. 10 is a cross-sectional view showing a schematic structure of the semiconductor laser, and FIG. 11 is a cross-sectional view taken along line XI-XI of FIG. In this case, the strained quantum well active layer is applied.

First, the lower cladding layer 42 of Ga _0.8 Al _0.2 As, the lower second light separation / confinement layer 42b of Ga _0.9 Al _0.1 As, and the lower first light separation / confinement layer 4 of GaAs
2a, InGaAs serving as a well layer and GaAs serving as a barrier layer
s and a plurality of strained quantum well active layers 43 in which a plurality of layers are stacked (single) or alternately in a plurality of layers (multiple layers), an upper first optical isolation / confinement layer 44a of GaAs, and an upper second optical isolation / confinement layer 44b of Ga _0.9 Al _0.1 As. MOVPE on GaAs substrate 11
Grow by the method.

Subsequently, after the upper second light separation / confinement layer 44b around the light emitting side end face is removed by ECR plasma etching using a mixed gas of BCl ₃ gas and Ar gas, an ammonia / hydrogen peroxide etching solution is used. The upper first light separation / confinement layer 42a in the window region is removed by etching, and then alternately immersed in a carboxylic acid-based etchant such as citric acid or tartaric acid and an ammonia / hydrogen peroxide-based etchant. Of the strained quantum well active layer 43 by etching, that is, when the strained quantum well active layer 43 is a single layer, the well layer is removed by etching with a carboxylic acid-based etching solution and then the barrier layer is etched with an ammonia / hydrogen peroxide-based etching solution. Is removed by etching, and when the strained quantum well active layer 43 has multiple layers, a carboxylic acid-based etch Grayed solution under the well layer are repeated necessary number of times alternately and that the barrier layer is removed by etching with an ammonia / hydrogen peroxide-based etching solution is removed by etching.

The ammonia / hydrogen peroxide etching solution can selectively etch GaAs with respect to InGaAs, and the carboxylic acid etching solution can be GaAs.
Since the selective etching of InGaAs with respect to s is possible, the upper first light separation / confinement layer 44a and the strained quantum well active layer can be etched without removing the lower first light separation / confinement layer 42a by etching as described above. 43 can be easily removed, that is, the etching of the strained quantum well active layer 43 can be stopped at the lower first light separation / confinement layer 42a.

Next, after the surface treatment with a sulfuric acid-based wet etching solution, the undoped GaAs core layer 46 and Ga _0.9 Al _0.1 As upper third light separation / confinement layer 47b are selected in the window region by MOVPE. Regrow. Here, the interface position between the core layer 46 and the upper third light separation / confinement layer 47b in the window region is located between the upper first light separation / confinement layer 44a and the upper third light separation / confinement layer 47 in the window region.
The surface of b was made flush with the surface of the upper second light separation / confinement layer 44b.

Next, the upper second and third light separation / confinement layers 44
b, 47b _0.8Al_0.2As
Upper cladding layer 48 and GaAs contact layer 19
Was grown by the MOVPE method.

BCl ₃ was added to the wafer thus fabricated.
After the ridge stripe 40 is formed along the light emitting direction by ECR plasma etching using a mixed gas of a gas and an Ar gas, a front electrode and a back electrode are formed and divided by cleavage. And a high reflection film is formed on the rear end face.

That is, the lower cladding layer 42 (the lower low refractive index semiconductor layer) is epitaxially grown in the stacking direction.
When a strained quantum well active layer 43 (active layer) is grown on the lower clad layer 42 via lower first and two light separation / confinement layers 42a and 42b (lower low refractive index semiconductor layers), After removing the periphery of the light exit side end face of the strained quantum well active layer 43 together with the periphery of the light exit side end face of the upper first and two light separation / confinement layers 44a and 44b grown on the layer 43 by etching, A core layer 46 (undoped high-refractive index semiconductor layer) having a band gap wider than the strained quantum well active layer 43 is epitaxially grown in the stacking direction, and upper first to three light separation confinements are formed on the strained quantum well active layer 43 and the core layer 46. Layers 44a, 44b, 47
The upper cladding layer 48 (upper low-refractive index semiconductor layer) was epitaxially grown through b, the contact layer 19 (upper layer) was grown on the upper cladding layer 48, and the ridge stripe 40 was formed along the light emitting direction. It is.

By manufacturing as described above, the semiconductor laser according to the present embodiment includes the lower cladding layer 42, the lower first and two-beam separation / confinement layers 42a and 42b, the strained quantum well active layer 43, and the upper first and second layers. Two-light separation confinement layers 44a, 4
4b, a core layer 46 having a wider band gap than the strained quantum well active layer 43 is provided around the light emitting side end face of the active region including the upper cladding layer 48 and the like. Third light separation confinement layer 47
b through the lower cladding layer 42 and the upper cladding layer 4
8, a window region having an epitaxial structure in the stacking direction and having the ridge stripe 40 along the light emitting direction is provided.

The semiconductor laser thus manufactured oscillates at a threshold current of 30 mA and has a maximum optical output of 700
mW. In addition, constant light output operation (50 ° C., 300 m
When a deterioration acceleration test was performed in W), COD-free operation was confirmed. The increase rate of the driving current after 10000 hours had passed was 1% or less.

FIG. 12 shows a vertical far-field image in the case where the thickness of the core layer 46 in the window region is the same as the combined thickness of the strained quantum well active layer 43 and the upper first light separation / confinement layer 44a. FIG. 13 shows the core layer 46 in the window area.
14 shows a vertical far-field image when the thickness of the strained quantum well active layer 43 and the upper first optical isolation / confinement layer 44a is smaller than the total thickness, and FIG. 14 shows the thickness of the core layer 46 in the window region. 13 is the same as that of FIG.
From GaAs to InGaAs-based strained quantum well (however,
The composition ratio of In is smaller than that of the strained quantum well active layer 43. )
7 is a graph showing a far-field image in the vertical direction when the refractive index of the core layer 46 is made substantially the same as the refractive index of the strained quantum well active layer 43.

As can be seen from FIGS. 12 and 13, the core layer 4
When the thickness of the layer 6 is smaller than the total thickness of the strained quantum well active layer 43 and the upper first optical isolation / confinement layer 44a, the radiation mode can be reduced. Also, as can be seen from FIG.
If the core layer 46 is changed from GaAs to an InGaAs-based strained quantum well, the radiation mode can be further reduced.

In the present embodiment, GaAs is used as the barrier layer of the strained quantum well active layer 43 and the lower first light separation / confinement layer 42a, but instead, an ammonia / hydrogen peroxide based etchant is used. And GaAs having the same aggressiveness as GaAs against carboxylic acid-based etchant
1As (however, the Al composition ratio is 15% or less) can also be used.

[Fifth Embodiment] A fifth embodiment of the semiconductor laser and the method of manufacturing the semiconductor laser according to the present invention will be described with reference to FIGS. FIG. 15 is a cross-sectional view showing a schematic structure of the semiconductor laser, and FIG. 16 is a cross-sectional view taken along line XVI-XVI in FIG. In this case, the strained quantum well active layer is applied.

First, the lower cladding layer 42 of Ga _0.8 Al _0.2 As, the lower second light separation / confinement layer 42b of Ga _0.9 Al _0.1 As, and the lower first light separation / confinement layer 4 of GaAs
2a, InGaAs serving as a well layer and GaAs serving as a barrier layer
The strained quantum well active layer 43 in which s is stacked (single) or alternately multiple (multiple) are stacked on the GaAs substrate 11 by MOVPE on the GaAs upper first optical isolation confinement layer 44a.

Subsequently, when the upper first light separation / confinement layer 44a around the light emitting side end face is removed by etching with an ammonia / hydrogen peroxide based etchant, a carboxylic acid based etchant such as citric acid or tartaric acid is removed. By alternately immersing in a hydrogen oxide-based etchant,
The strained quantum well active layer 43 in the window region is removed. That is, when the strained quantum well active layer 43 is a single layer, the well layer is removed by etching with a carboxylic acid-based etchant, and then the barrier is removed with an ammonia / hydrogen peroxide-based etchant. When the layer is etched away and the strained quantum well active layer 43 is multiple, the well layer is etched away with a carboxylic acid-based etchant and the barrier layer is etched away with an ammonia / hydrogen peroxide-based etchant alternately. Repeat as many times as necessary.

The ammonia / hydrogen peroxide etching solution can selectively etch GaAs with respect to InGaAs, and the carboxylic acid etching solution can be GaAs.
Since the selective etching of InGaAs with respect to s is possible, the upper first light separation / confinement layer 44a and the strained quantum well active layer can be etched without removing the lower first light separation / confinement layer 42a by etching as described above. 43 can be easily removed, that is, the etching of the strained quantum well active layer 43 can be stopped at the lower first light separation / confinement layer 42a.

Next, after performing a surface treatment with a sulfuric acid-based wet etching solution, the undoped GaAs core layer 46 is selectively regrown in the window region by the MOVPE method, and then the upper portion of Ga _0.9 Al _0.1 As is removed. The second light separation / confinement layer 54b is connected to the upper first light separation / confinement layer
4a and on the core layer 46. Here, the interface between the core layer 46 and the upper second light separation / confinement layer 54b is located between the upper first light separation / confinement layers 44a.

Next, the upper cladding layer 48 of Ga _0.8 Al _0.2 As and the contact layer 19 of GaAs are formed on the upper second light separation / confinement layer 54b by MOVPE.
Grown by the method.

The wafer thus produced was treated with BCl ₃
After the ridge stripe 40 is formed along the light emitting direction by ECR plasma etching using a mixed gas of a gas and an Ar gas, a front electrode and a back electrode are formed and divided by cleavage. And a high reflection film is formed on the rear end face.

That is, the lower cladding layer 42 (the lower low refractive index semiconductor layer) is epitaxially grown in the laminating direction,
When a strained quantum well active layer 43 (active layer) is grown on the lower clad layer 42 via lower first and two light separation / confinement layers 42a and 42b (lower low refractive index semiconductor layers), After removing the periphery of the light exit side end face of the strained quantum well active layer 43 together with the periphery of the light exit side end face of the upper first light separation / confinement layer 44a grown on the layer 43, the strained quantum well active layer 43 A core layer 46 (undoped high refractive index semiconductor layer) having a wider band gap than the layer 43 is epitaxially grown in the stacking direction;
On the strained quantum well active layer 43 and the core layer 46, the upper first
The upper cladding layer 48 (upper low-refractive index semiconductor layer) is epitaxially grown via the two-light separation / confinement layers 44a and 54b, the contact layer 19 (upper layer) is grown on the upper cladding layer 48, and the ridge stripe 40 is irradiated with light. It was formed along the emission direction.

By manufacturing in this manner, the semiconductor laser of the present embodiment has a lower cladding layer 42, a lower first and two-light separating and confining layers 42a and 42b, a strained quantum well active layer 43, and an upper first and second layers. Two-light separation confinement layers 44a, 5
4b, a core layer 46 having a wider band gap than the strained quantum well active layer 43 is provided around the light emitting side end face of the active region including the upper cladding layer 48 and the like. Second light separation / confinement layer 54
b through the lower cladding layer 42 and the upper cladding layer 4
8, a window region having an epitaxial structure in the stacking direction and having the ridge stripe 40 along the light emitting direction is provided.

The semiconductor laser thus manufactured oscillates at a threshold current of 30 mA and has a maximum optical output of 700
mW. In addition, constant light output operation (50 ° C., 300 m
When a deterioration acceleration test was performed in W), COD-free operation was confirmed. Further, the increase rate of the driving current after 10,000 hours was 0.2% or less.

That is, in this embodiment, the layer containing Al, including the etched end face, is manufactured without exposing it to the air at all, so that the reliability is further improved as compared with the above-described embodiment. be able to.

[Sixth Embodiment] A sixth embodiment of the semiconductor laser and the method of manufacturing the semiconductor laser according to the present invention will be described with reference to FIGS. FIG. 17 is a sectional view showing a schematic structure of the semiconductor laser, and FIG. 18 is a sectional view taken along line XVIII-XVIII in FIG.
This is a case where an InGaAsP-based bulk active layer is applied to a structure having a light separation confinement layer.

[0085] First, In _0.5 Ga _0.4 Al _0.1 lower clad layer 62 of P, In _0.5 Ga _0.5 P lower optical separate confinement layer 62a, In _0.45 Ga _0.55 As _0.1 bulk active layer 63 of P _0.9, In _0.5 Ga _0.5 P Is grown on the GaAs substrate 11 by the MOVPE method.

Subsequently, the upper light separation / confinement layer 64 around the light emission side end face is etched with a hydrochloric acid (HCl) based etchant.
After removing a, H ₂ SO ₄ based etchant
The bulk active layer 63 is etched without removing the lower optical confinement layer 62a, that is, the bulk active layer 63
Can be stopped at the lower light separation / confinement layer 62a.

Next, after processing with an H ₂ SO ₄ type etching solution, an undoped In _0.5 Ga _0.5 P core layer 66 is grown in the window region around the light-emitting side end face, and In _0.5 Ga _0.4 Al _0.1 P upper cladding layer 68
On the upper light separation / confinement layer 64a and the core layer 66.
It is grown thereon by MOVPE. Here, the core layer 6
The interface between the upper cladding layer 68 and the upper cladding layer 68 was located between the upper light confinement layers 64a.

Subsequently, a GaAs contact layer 19 was grown on the entire upper cladding layer 68 by MOVPE.

The thus prepared wafer was treated with BCl ₃
After the ridge stripe 60 is formed along the light emitting direction by ECR plasma etching using a mixed gas of a gas and an Ar gas, a front electrode and a back electrode are formed and divided by cleavage. And a high reflection film is formed on the rear end face.

That is, the lower cladding layer 62 (the lower low refractive index semiconductor layer) is epitaxially grown in the stacking direction.
A lower light separation / confinement layer 62 is formed on the lower cladding layer 62.
a (lower low-refractive-index semiconductor layer) via bulk active layer 63
After the (active layer) is grown, the periphery of the light exit side end face of the bulk active layer 63 and the periphery of the light exit side end face of the upper light separation / confinement layer 64a grown on the bulk active layer 63 are removed by etching. A core layer 66 having a wider band gap than the bulk active layer 63 is provided in the removed portion.
(Undoped high refractive index semiconductor layer) is epitaxially grown in the stacking direction, an upper cladding layer 68 (upper low refractive index semiconductor layer) is epitaxially grown on the bulk active layer 63 and the core layer 66, and a contact layer 19 is formed on the upper cladding layer 68. (The upper layer) was grown, and the ridge stripe 60 was formed along the light emission direction.

By manufacturing in this manner, the semiconductor laser according to the present embodiment includes a lower cladding layer 62, a lower light separation / confinement layer 62a, a bulk active layer 63, an upper light separation / confinement layer 64a, an upper cladding layer 68, and the like. A structure in which a core layer 66 having a wider band gap than the bulk active layer 63 is sandwiched between the lower cladding layer 62 and the upper cladding layer 68 via the lower light separation / confinement layer 62a around the light emitting side end face of the active region having Thus, a window region having an epitaxial structure in the stacking direction and having the ridge stripe 60 along the light emission direction is provided.

The semiconductor laser manufactured as described above oscillates at a threshold current of 30 mA and has a maximum light output of 300 mA.
mW. In addition, constant light output operation (50 ° C, 150m
When a deterioration acceleration test was performed in W), COD-free operation was confirmed. The increase rate of the driving current after 10000 hours had passed was 1% or less.

[0093]

According to the semiconductor laser of the present invention, the window region has an optical waveguide structure by the epitaxial structure in the epitaxial laminating direction, and the optical waveguide has a convex shape along the light emitting direction in the epitaxial plane direction. Because of this, it is possible to suppress an increase in threshold value and a decrease in differential efficiency due to divergence of oscillation light in the window region.

Further, since the high refractive index semiconductor layer of the semiconductor layer is undoped, injection of a reactive current into the window region can be reduced. Therefore, semi-insulation such as proton injection can be eliminated.

Further, by selectively epitaxially growing the window region, the optical waveguide structure can be designed in the window region independently of the active region. Therefore, by adjusting the refractive index and the thickness of the undoped high-refractive-index semiconductor layer in the window region, the eigenmode of the window region can be matched with the eigenmode of the active region. Radiation mode can be reduced to a level at which there is no practical problem.

On the other hand, in the method of manufacturing a semiconductor laser according to the present invention, etching for forming a window region only needs to be performed on an active layer or a layer near the active layer. No exposure of tall layers. For this reason, deterioration due to oxidation of the surface having a high Al composition ratio can be avoided.

Further, the semiconductor layer may be grown not only in the same thickness as the active layer but also very thinly, and it is sufficient if the semiconductor layer does not absorb the oscillating light. You don't have to. Therefore, the difficulty of selective growth of a material containing Al can be greatly reduced.

Further, since the window region is formed by selectively growing the semiconductor layer before the division into the bar state, a semiconductor laser having a window structure can be manufactured without lowering the productivity. .

Further, since the optical waveguide type (ridge waveguide type) having a convex shape with good productivity is assumed, and the active layer may be a quantum well or a bulk, a conventional structure having a window structure may be used. There is a great advantage as compared with the semiconductor laser manufacturing method described above.

Specifically, for example, a semiconductor laser manufactured by a pn embedding method has a point that a window region has an optical waveguide structure in both a lamination direction and an in-plane direction, and a ridge waveguide excellent in productivity. Have different points.

The semiconductor laser manufactured by the quantum well alloying method is characterized in that the high refractive index semiconductor layer of the semiconductor layer in the window region is undoped and that the active layer does not need to have a quantum well structure. different.

Further, the semiconductor laser is different from the semiconductor laser manufactured by the epitaxial growth method on the chip end face in that the window region has an optical waveguide structure including an undoped layer, so that it is not necessary to further shorten the window region length.

On the other hand, the pn embedding method is such that the etching depth of the window region is small, so that even a semiconductor laser of an Al-containing material does not need to expose a layer having a high Al composition at the time of etching, and that the pn burying method has a problem in that The difference lies in that the growth step only needs to be performed extremely thinly for a layer having a low Al composition.

The quantum well alloying method is characterized in that it is not necessary to perform proton injection or the like for reducing the injection of reactive current into the window region, and because the window region is formed by selective region epitaxial growth. The difference is that the optical waveguide structure of the window region can be designed independently of the active region.

Further, the difference from the epitaxial growth method on the chip end face is that a window region is formed before the wafer is divided into bar states.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a schematic structure of a first embodiment of a semiconductor laser according to the present invention.

FIG. 2 is a sectional view taken along the line II-II in FIG.

FIG. 3 is a sectional view showing a schematic structure of a second embodiment of the semiconductor laser according to the present invention.

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 2;

FIG. 5 is a sectional view showing a schematic structure of a third embodiment of the semiconductor laser according to the present invention.

6 is a sectional view taken along the line VI-VI in FIG. 5;

FIG. 7 is a graph of a vertical far-field image of the semiconductor laser of FIG. 5;

8 is a graph of a vertical far-field pattern when the thickness of the core layer in the window region of the semiconductor laser of FIG. 5 is smaller than that of the bulk active layer.

FIG. 9 shows that the thickness of the core layer in the window region of the semiconductor laser of FIG.
It is a graph of the vertical direction far-field image when 1 composition is set to 5%.

FIG. 10 is a sectional view illustrating a schematic structure of a fourth embodiment of the semiconductor laser according to the present invention;

FIG. 11 is a sectional view taken along line XI-XI of FIG. 10;

FIG. 12 is a graph of a vertical far-field image of the semiconductor laser of FIG. 10;

FIG. 13 is a graph of a vertical far-field image in the case where the thickness of the core layer in the window region of the semiconductor laser of FIG. 10 is smaller than the combined thickness of the strained quantum well active layer and the upper first optical isolation confinement layer. It is.

FIG. 14 shows that the thickness of the core layer in the window region of the semiconductor laser of FIG. 10 is made thinner than the combined thickness of the strained quantum well active layer and the upper first optical isolation confinement layer, and the core layer is made of G.
It is a graph of the far-field image of a longitudinal direction at the time of changing into a strain quantum well of InGaAs system from aAs.

FIG. 15 is a sectional view showing a schematic structure of a fifth embodiment of the semiconductor laser according to the present invention.

16 is a sectional view taken along the line XVI-XVI in FIG.

FIG. 17 is a sectional view illustrating a schematic structure of a sixth embodiment of the semiconductor laser according to the present invention;

18 is a sectional view taken along line XVII-XVII of FIG. 17;

[Explanation of symbols]

Reference Signs List 10 optical waveguide (ridge stripe) 11 substrate (GaAs) 12 lower cladding layer (GaAlAs) 13 bulk active layer (GaAs) 14 upper cladding layer (GaAlAs) 15 lower cladding layer (undoped GaAlAs) 16 core layer (undoped GaAlAs) 17 upper part Cladding layer (undoped GaAlAs) 18 Upper cladding layer (GaAlAs) 19 Contact layer (GaAs) 20 Optical waveguide (ridge stripe) 22 Lower cladding layer (InGaAlP) 23 Bulk active layer (InGaP) 24 Upper cladding layer (InGaAlP) 25 Lower cladding Layer (undoped InGaAlP) 26 core layer (undoped InGaAlP) 27 upper cladding layer (undoped InGaAlP) 28 upper cladding layer (InGaAlP) 30 light guide Waveguide (ridge stripe) 32 Lower cladding layer (Ga _0.5 Al _0.5 As) 32 a Lower light separation confinement layer (Ga _0.75 Al _0.25 A)
s) 34a Upper light separation confinement layer (Ga _0.75 Al _0.25 A
s) 36 core layer (undoped Ga _0.9 Al _0.1 As) 37a upper light separation confinement layer (undoped Ga _0.75 A)
l _0.25 As) 38 Upper cladding layer (Ga _0.5 Al _0.5 As) 40 Optical waveguide (ridge stripe) 42 Lower cladding layer (Ga _0.8 Al _0.2 As) 42 a Lower first light separation confinement layer (GaAs) 42 b Lower second light separation Confinement layer (Ga _0.9 Al _0.1
As) 43 Strained quantum well active layer (InGaAs / GaAs) 44a Upper first optical isolation confinement layer (GaAs) 44b Upper second optical isolation confinement layer (Ga _0.9 Al _0.1
As) 46 core layer (undoped GaAs) 47b upper third light separation / confinement layer (Ga _0.9 Al _0.1
As) 48 Upper cladding layer (Ga _0.8 Al _0.2 As) 54b Upper second light separation confinement layer (Ga _0.9 Al _0.1
As) 60 Optical waveguide (ridge stripe) 62 Lower cladding layer (In _0.5 Ga _0.4 Al _0.1 P) 62 a Lower optical isolation confinement layer (In _0.5 Ga _0.5 P) 63 Bulk active layer (In _0.45 Ga _0.55 As _0.1 P) 64 a Upper Light separation confinement layer (In _0.5 Ga _0.5 P) 66 Core layer (undoped In _0.5 Ga _0.5 P) 68 Upper cladding layer (In _0.5 Ga _0.4 Al _0.1 P)

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) H01S 5/343 H01S 3/18 648 677 (72) Inventor Jiro Tenmei 3-19 Nishishinjuku, Shinjuku-ku, Tokyo No. 2 Inside Nippon Telegraph and Telephone Corporation (72) Tomohiro Shibata Inventor 3--19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Mitsuru Sugo 3--19, Nishi-Shinjuku, Shinjuku-ku, Tokyo No. 2 Nippon Telegraph and Telephone Corporation F-term (reference) 5F004 AA16 BA14 DA11 DA23 DB19 EA10 EA22 EA23 EA28 5F043 AA14 BB07 BB27 DD15 FF01 FF04 FF10 GG10 5F073 AA13 AA74 AA83 AA87 AA89 CA04 DA07

Claims (10)

[Claims] 1. A window region comprising a semiconductor layer having a wider band gap than the active layer is provided around an end face of the active region having an active layer on the light emission side, and the window region is provided below an undoped high refractive index semiconductor layer. A semiconductor laser having a structure sandwiched between a low-refractive-index semiconductor layer and an upper low-refractive-index semiconductor layer, having an epitaxial structure in a stacking direction, and having a convex optical waveguide along a light emitting direction. 2. The method according to claim 1, wherein the thickness of the undoped high refractive index semiconductor layer in the window region is set so as to match the eigenmodes of the active region and the window region. Semiconductor laser. 3. The semiconductor laser according to claim 2, wherein said undoped high refractive index semiconductor layer is thinner than said active layer. 4. The semiconductor device according to claim 1, wherein the refractive index of the undoped high-refractive-index semiconductor layer in the window region is set so as to match the eigenmodes of the active region and the window region. Semiconductor laser. 5. The semiconductor laser according to claim 4, wherein a refractive index of said undoped high refractive index semiconductor layer is substantially equal to a refractive index of said active layer. 6. The semiconductor laser according to claim 1, wherein the active layer and the undoped high-refractive-index semiconductor layer are made of a single or multiple strained quantum well of InGaAs system. 7. When the lower low-refractive-index semiconductor layer is epitaxially grown in the laminating direction and an active layer is grown on the lower low-refractive-index semiconductor layer, the periphery of the light-emitting-side end face of the active layer is removed by etching. In the removed portion, an undoped high refractive index semiconductor layer having a band gap wider than the active layer is epitaxially grown in the stacking direction, and an upper low refractive index semiconductor layer is epitaxially grown on the active layer and the undoped high refractive index semiconductor layer. A method of manufacturing a semiconductor laser, comprising: growing an upper layer on the upper low refractive index semiconductor layer; and forming a convex optical waveguide along the light emitting direction. 8. The method according to claim 1, wherein the active layer is made of GaAs.
The lower low refractive index semiconductor layer has a layer of GaAlAs;
8. The method according to claim 7, wherein the periphery of the light emitting side end face of the active layer is etched with an ammonia / hydrogen peroxide based etchant. 9. The active layer is made of an InGaAs single or multiple strained quantum well, and the lower low-refractive index semiconductor layer has a GaAs layer or a GaAlAs layer, and the light emitting side of the active layer. 8. The method according to claim 7, wherein the periphery of the end face is alternately etched with a carboxylic acid-based etchant and an ammonia / hydrogen peroxide-based etchant. 10. The active layer is made of GaAs, GaAlAs.
Or any one of InGaAsP or a combination thereof, and the lower low-refractive-index semiconductor layer has an InGaP layer or an InGaAlP layer, and the periphery of the light emitting side end face of the active layer is exposed to a sulfuric acid-based etchant. 8. The method according to claim 7, wherein etching is performed.