JP2006324427A - Semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent reliability degradation caused by the stress of an insulating film. <P>SOLUTION: In a semiconductor laser having a ridge 8, insulating films 11a, 11b are formed along inner faces of recesses 7a, 7b, respectively. The insulating films 11a, 11b have such structures that film thicknesses are stepwise thinned toward ends 12a, 12b of each film on a p-type contact layer 6c. By forming such a structure, it is possible to mitigate a concentration of stress generated between the insulating films 11a, 11b and the p-type contact layer 6c. Thus, the life degradation of the semiconductor layer can be prevented, thereby obtaining the semiconductor layer of a long lifetime. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a structure of a semiconductor laser.

An example of a cross-sectional structure of a conventional semiconductor laser is shown in FIG. This semiconductor laser is formed on an n-type semiconductor substrate 1. An n-type electrode 2 is provided on the back surface of the n-type semiconductor substrate 1. On the n-type semiconductor substrate 1, an n-type cladding layer 3, an active layer 4, and a p-type cladding layer 5 are sequentially stacked. On the p-type cladding layer 5, p-type contact layers 6a, 6b and 6c are formed. A recess 7a is formed at a position between the p-type contact layers 6a and 6c, and a recess 7b is formed at a position between the p-type contact layers 6c and 6b. A ridge portion 8 is formed between the recess 7a and the recess 7b. An active region 4 a is provided below the ridge portion 8 of the active layer 4.
Insulating films 11 a and 11 b are formed along the inner surface of the recess 7. These films have end portions 12a and 12b, respectively. These end portions face each other on the p-type contact layer 6c. Furthermore, a p-type electrode 14 is formed so as to cover the upper surfaces of the insulating films 11a and 11b and the p-type contact layer 6c.

  When the semiconductor laser is energized, a positive bias is applied to the p-type electrode 14 and a negative bias is applied to the n-type electrode 2. Then, a current flows from the p-type electrode 14 toward the n-type electrode 2. At this time, holes and electrons are injected into the active layer 4, and light emission is caused by their combination. When the number of holes and electrons injected into the active layer 4 exceeds a threshold value, stimulated emission starts and laser oscillation occurs (see, for example, Patent Document 1).

JP-A-10-223966

When the conventional semiconductor laser is energized, stress A is generated between the insulating film 11a and the p-type contact layer 6c due to the difference in thermal expansion coefficient between the insulating films 11a and 11b and the p-type contact layer 6c. Stress A ′ is generated between the insulating film 11b and the p-type contact layer 6c. The stresses A and A ′ are concentrated near the ends 12a and 12b, respectively.
Then, as shown in FIG. 7, a transition loop (crystal defect) 15 grows along the (111) plane of the n-type semiconductor substrate 1. When the transition loop 15 reaches the active region 4a, a current concentrates on the transition. This has a problem that the life of the semiconductor laser is deteriorated.

  The present invention has been made in order to solve the above-described problems, and alleviates the stress between the semiconductor layer (p-type contact layer 6c) of the semiconductor laser and the insulating films 11a and 11b provided thereon, The object is to suppress the deterioration of the lifetime of the semiconductor laser.

The semiconductor laser according to the present invention is
An active layer that emits laser light by combining electrons and holes;
A clad layer for injecting electrons into the active layer, and a clad layer for injecting holes into the active layer, and a pair of clad layers provided so as to sandwich the active layer;
A first electrode electrically connected to one of the pair of cladding layers;
Of the pair of clad layers, a semiconductor layer formed with a predetermined width on the surface of the other clad layer;
Covers the surface of the other cladding layer, the side surface of the semiconductor layer, and a part of the surface of the semiconductor layer, has an end on the surface of the semiconductor layer, and has a film thickness toward the end. An insulating film provided to be thin; and
A second electrode covering the surface of the semiconductor layer and the insulating film;
It is provided with.
Other features of the present invention are described in detail below.

  According to the present invention, the stress between the semiconductor layer of the semiconductor laser and the insulating film provided thereon can be relieved. Thereby, the lifetime deterioration of the semiconductor laser can be suppressed, and a highly reliable semiconductor laser can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view of the semiconductor laser according to the present embodiment.
This semiconductor laser is formed using an n-type semiconductor substrate 1. An n-type electrode 2 is provided on the back surface of the n-type semiconductor substrate 1. On the n-type semiconductor substrate 1, an n-type cladding layer 3, an active layer 4, and a p-type cladding layer 5 are sequentially stacked. On the p-type cladding layer 5, p-type contact layers 6a, 6b and 6c are formed. These layers are epitaxially grown using a MOCVD (Metal Organic Chemical Vapor Deposition) method or the like. The growth direction is a direction perpendicular to the main surface of the n-type semiconductor substrate 1. These materials are compound semiconductor materials that require high reliability, such as GaAs, InP, and GaN.
A recess 7a is formed at a position between the p-type contact layers 6a and 6c, and a recess 7b is formed at a position between the p-type contact layers 6c and 6b. The p-type cladding layer 5 is exposed on the bottom surfaces of these recesses. A ridge portion 8 is formed between the recess 7a and the recess 7b. A p-type contact layer 6 c is exposed on the upper surface of the ridge portion 8. The p-type contact layer 6 c and the p-type cladding layer 5 are exposed on the side surface of the ridge portion 8. An active region 4 a is provided below the ridge portion 8 of the active layer 4.

A first insulating film 9a is formed with a film thickness of about 80 nm along the inner surface of the recess 7a. A first insulating film 9b is formed with a thickness of about 80 nm along the inner surface of the recess 7b. These films are formed so as to cover the side surface of the ridge portion 8 and ensure insulation of the side surface. As these films, silicon nitride films (SiN films) are used.
On the 1st insulating film 9a, the 2nd insulating film 10a is laminated | stacked by the film thickness of about 120 nm. On the 1st insulating film 9b, the 2nd insulating film 10b is laminated | stacked by the film thickness of about 120 nm. As these films, silicon nitride films (SiN films) are used. Hereinafter, the laminated film of the first insulating film 9a and the second insulating film 10a is referred to as an insulating film 11a as a whole. The laminated film of the first insulating film 9b and the second insulating film 10b is referred to as an insulating film 11b as a whole.

The first insulating film 9a has an end 12a, and the first insulating film 9b has an end 12b. These end portions face each other on the p-type contact layer 6c. The insulating film 11a has a stepped step portion 13a, and the insulating film 11b has a stepped step portion 13b. The step portion 13a is located between the left end of the ridge portion 8 and the end portion 12a. The step portion 13b is located between the right end of the ridge portion 8 and the end portion 12b.
In this way, the insulating films 11a and 11b have end portions on the surface of the p-type contact 6c, and the film thicknesses are gradually reduced toward the respective end portions. That is, an opening is formed on the surface of the p-type contact layer 6c by the insulating films 11a and 11b having a film thickness that decreases toward the end.
Thereby, the stress A between the insulating film 11a and the p-type contact layer 6c is dispersed in the vicinity of the end portion 12a and the vicinity of the step portion 13a. Further, the stress A ′ between the insulating film 11b and the p-type contact layer 6c is distributed in the vicinity of the end portion 12b and the step portion 13b. Therefore, compared with the prior art, stress concentration between the insulating films 11a and 11b and the p-type contact layer 6c can be reduced.

Furthermore, a p-type electrode 14 is formed on the entire surface on the insulating films 11a and 11b and on the p-type contact layer 6c. The p-type electrode 14 is in contact with the p-type contact layer 6c at a position between the end 12a and the end 12b.
When the semiconductor laser is energized, a positive bias is applied to the p-type electrode 14 and a negative bias is applied to the n-type electrode 2. Then, holes are injected from the p-type cladding layer 5 into the active layer 4, and electrons are injected from the n-type cladding layer 3 into the active layer 4. These holes and electrons are combined in the active region 4a, and the active layer 4a emits laser light.

  By making the semiconductor laser as described above, the stress concentration between the insulating films 11a and 11b and the p-type contact layer 6c can be reduced as compared with the prior art. Thereby, it is possible to suppress the transition loop (crystal defect) caused by the stress from reaching the active region 4a. Accordingly, it is possible to prevent the semiconductor laser lifetime from being deteriorated and to obtain a semiconductor laser having a long lifetime.

In the above embodiment, an n-type semiconductor substrate is used as the substrate on which the semiconductor laser is formed. However, the same effect can be obtained even if all the polarities of p and n are reversed using a p-type semiconductor substrate.
In the above embodiment, the p-type contact layer 6 c and the p-type cladding layer 5 are exposed on the side surface of the ridge portion 8. However, the p-type cladding layer 5 may not be exposed on the side surface of the ridge portion 8. For example, the p-type cladding layer 5 may have a flat shape without having a recess.

Next, a modification of the first embodiment will be described.
In the first embodiment, the first insulating films 9a and 9b are silicon nitride films (SiN films). On the other hand, in this modification, as shown in FIG. 2, the first insulating films 9a and 9b are silicon oxynitride films (SiON films). The silicon oxynitride film is a film having a smaller difference in thermal expansion coefficient from the p-type contact layer 6c compared to the silicon nitride film. For this reason, in the above case, the stress generated in the vicinity of the end portions 12a and 12b is smaller than that in the above embodiment. Thereby, the stress between the insulating films 11a and 11b and the p-type contact layer 6c can be made smaller than that in the first embodiment.
Other configurations are the same as those in the first embodiment, and thus the description thereof is omitted.

  According to the present modification, in addition to the effects of the first embodiment, the stress between the insulating films 11a and 11b and the p-type contact layer 6c can be reduced as compared with the first embodiment. Thereby, the lifetime deterioration of the semiconductor laser can be more effectively prevented.

Embodiment 2. FIG.
FIG. 3 is a cross-sectional view of the semiconductor laser according to the present embodiment. Here, the configuration different from that of the first embodiment will be mainly described.
In the first embodiment, the step portion 13a is located between the left end portion and the end portion 12a of the ridge portion 8, and the step portion 13b is located between the right end portion and the end portion 12b of the ridge portion 8. I made it. In contrast, in the present embodiment, the stepped portion 13a is positioned on the left side of the left end of the ridge portion 8, and the stepped portion 13b is positioned on the right side of the right end of the ridge portion 8. That is, the step portions 13 a and 13 b are positioned outside the both end portions of the ridge portion 8.
For example, as shown in FIG. 3, the step portion 13a is provided on the bottom surface of the recess 7a, and the step portion 13b is provided on the bottom surface of the recess 7b. With this structure, stress between the insulating films 11a and 11b and the p-type contact layer 6c is not concentrated in the vicinity of the step portions 13a and 13b. Thereby, the stress between the insulating films 11a and 11b and the p-type contact layer 6c can be reduced as compared with the first embodiment.

  In the first embodiment, the thickness of the first insulating films 9a and 9b is about 80 nm. In contrast, in the present embodiment, these film thicknesses are thinner than those in the first embodiment, for example, about 30 nm. Thereby, the stress between the insulating film 11a and the p-type contact layer 6c can be reduced in the vicinity of the end portion 12a as compared with the first embodiment. Similarly, in the vicinity of the end portion 12b, the stress between the insulating film 11b and the p-type contact layer 6c can be reduced as compared with the first embodiment. In addition, if the thickness of the first insulating films 9a and 9b is about 30 nm, sufficient insulation between the side surface of the ridge 8 and the p-type electrode 14 can be ensured.

  In the first embodiment, the thickness of the second insulating films 10a and 10b is about 120 nm. On the other hand, in the present embodiment, the film thickness is thicker than that of the first embodiment, for example, about 300 nm. For this reason, the film thickness of the insulating films 11a and 11b is thicker than that of the first embodiment at the place where the above film is formed. As a result, the capacitance between the p-type contact layer 6 c and the active layer 4 (hereinafter referred to as “element capacitance”) can be reduced in comparison with the first embodiment.

  According to the present embodiment, the stress between the insulating films 11a and 11b and the p-type contact layer 6c can be further reduced as compared with the first embodiment. As a result, it is possible to effectively prevent the deterioration of the lifetime of the semiconductor laser and obtain a long-life semiconductor laser.

Next, a modification of the second embodiment will be described.
In the second embodiment, the first insulating films 9a and 9b are silicon nitride films (SiN films). On the other hand, in this modification, as shown in FIG. 4, the first insulating films 9a and 9b are silicon oxynitride films (SiON films). The silicon oxynitride film is a film in which the stress generated between the p-type contact layer 6c is smaller than that of the silicon nitride film. For this reason, the stress generated in the vicinity of the end portions 12a and 12b is smaller than that in the second embodiment. Thereby, the stresses A and A ′ between the insulating films 11a and 11b and the p-type contact layer 6c can be made smaller than those in the second embodiment.
Since other configurations are the same as those in the second embodiment, description thereof is omitted.

  According to the present modification, in addition to the effects of the second embodiment, the stresses A and A ′ between the insulating films 11a and 11b and the p-type contact layer 6c are reduced as compared with the second embodiment. be able to. Thereby, it is possible to more effectively prevent the deterioration of the lifetime of the semiconductor laser.

Embodiment 3 FIG.
FIG. 5 is a cross-sectional view of the semiconductor laser according to the present embodiment. Here, the configuration different from that of the first embodiment will be mainly described.
In the first embodiment, the insulating films 11a and 11b have a structure in which the film thickness gradually decreases toward the end. On the other hand, in this embodiment, as shown in FIG. 5, the insulating films 11a and 11b have slope shapes 13a-12a and 13b-12b whose film thicknesses are continuously reduced toward the respective end portions. Have. By adopting such a structure, the stresses A and A ′ between the vicinity of the end portions 12a and 12b and the p-type contact layer 6c can be dispersed over a wider portion than in the first embodiment. Thereby, the stress concentration can be alleviated.
The insulating films 11a and 11b may be films made of any one material among insulating films such as a silicon nitride film and a silicon oxynitride film. Alternatively, a structure in which a plurality of different insulating films are stacked may be used. In this case, as in the modification of the first embodiment, the film having the smallest difference from the p-type contact layer 6c among the plurality of stacked films is set as the lowermost film. Thereby, the same effect as the modification of Embodiment 1 can be acquired.
Since other configurations are the same as those in the second embodiment, description thereof is omitted.

  According to the present embodiment, the stress between the insulating films 11a and 11b and the p-type contact layer 6c can be distributed over a wider portion as compared with the first embodiment. Thereby, the concentration of the stress can be further reduced as compared with the first embodiment. Therefore, it is possible to obtain a long-lived semiconductor laser by further effectively preventing the deterioration of the lifetime of the semiconductor laser.

Embodiment 4 FIG.
FIG. 6 is a cross-sectional view of the semiconductor laser according to the present embodiment. Here, the configuration different from that of the first embodiment will be mainly described.
In the first embodiment, the end portions 12a and 12b are opposed to each other on the p-type contact layer 6c. In contrast, in the present embodiment, as shown in FIG. 6, the end portions 12a and 12b are provided on the side surface of the p-type contact layer 6c.
FIG. 6 shows the case where the upper surfaces of the end portions 12a and 12b and the upper surface of the p-type contact layer 6c are on the same plane. However, these upper surfaces do not need to be on the same surface, and any one of the upper surfaces may have a low structure.
Other configurations are the same as those in the first embodiment, and thus the description thereof is omitted.

  As described in the first embodiment, the p-type contact layer 6 c is formed by epitaxial growth, and the growth direction is a direction perpendicular to the main surface of the n-type semiconductor substrate 1. For this reason, the direction of the stress B between the insulating film 11a and the p-type contact layer 6c is parallel to the direction of epitaxial growth of the p-type contact layer 6c. Similarly, the direction of stress B 'between the insulating film 11b and the p-type contact layer 6c is parallel to the direction of epitaxial growth of the p-type contact layer 6c. Therefore, the transition loop (crystal defect) due to the stress B, B ′ does not proceed in the direction of the active layer 4a. Thereby, it is possible to suppress the transition loop (crystal defect) caused by the stresses B and B ′ from reaching the active region 4a. Accordingly, it is possible to prevent the semiconductor laser lifetime from being deteriorated and to obtain a semiconductor laser having a long lifetime.

FIG. 3 is a cross-sectional view of the semiconductor laser according to the first embodiment. FIG. 6 is a cross-sectional view of a semiconductor laser according to a modification of the first embodiment. FIG. 4 is a cross-sectional view of a semiconductor laser according to a second embodiment. FIG. 6 is a cross-sectional view of a semiconductor laser according to a modification of the second embodiment. FIG. 6 is a cross-sectional view of a semiconductor laser according to a third embodiment. FIG. 6 is a cross-sectional view of a semiconductor laser according to a fourth embodiment. Sectional drawing of the conventional semiconductor laser.

Explanation of symbols

1 n-type semiconductor substrate, 2 n-type electrode, 3 n-type cladding layer, 4 active layer, 4a active region, 5 p-type cladding layer, 6 p-type contact layer, 8 ridge portion, 9a, 9b first insulating film, 10a 10b 2nd insulating film, 11a, 11b insulating film, 14 p-type electrode, 15 transition loop (crystal defect).

Claims (8)

An active layer that emits laser light by combining electrons and holes;
A clad layer for injecting electrons into the active layer, and a clad layer for injecting holes into the active layer, and a pair of clad layers provided so as to sandwich the active layer;
A first electrode electrically connected to one of the pair of cladding layers;
Of the pair of clad layers, a semiconductor layer formed with a predetermined width on the surface of the other clad layer;
Covers the surface of the other cladding layer, the side surface of the semiconductor layer, and a part of the surface of the semiconductor layer, has an end on the surface of the semiconductor layer, and has a film thickness toward the end. An insulating film provided to be thin; and
A second electrode covering the surface of the semiconductor layer and the insulating film;
A semiconductor laser comprising:   The semiconductor laser according to claim 1, wherein the insulating film has a stepped step portion that is gradually reduced toward an end portion.   The semiconductor laser according to claim 2, wherein the stepped step portion is formed on a surface of the semiconductor layer.   The semiconductor laser according to claim 2, wherein the stepped step portion is formed on a surface of the other cladding layer.   The stepped step portion is formed by laminating a plurality of different films as the insulating film and shifting the end portions of the films, and the film immediately above the semiconductor layer is the semiconductor of the plurality of different films. The semiconductor laser according to claim 2, wherein the semiconductor laser has a smallest difference in thermal expansion coefficient from that of the layer.   The semiconductor laser according to claim 1, wherein the insulating film has a slope-shaped portion that is continuously thinner toward an end portion.   The slope-shaped portion is formed in a laminated film in which a plurality of different films are stacked as the insulating film, and the film directly above the semiconductor layer has a difference in thermal expansion coefficient with the semiconductor layer among the plurality of different films. 7. The semiconductor laser according to claim 6, wherein the semiconductor laser is the smallest film. An active layer that emits laser light by combining electrons and holes;
A clad layer for injecting electrons into the active layer, and a clad layer for injecting holes into the active layer, and a pair of clad layers provided so as to sandwich the active layer;
A first electrode electrically connected to one of the pair of cladding layers;
Of the pair of clad layers, a semiconductor layer formed with a predetermined width on the surface of the other clad layer;
An insulating film covering the surface of the other cladding layer and all or part of the side surface of the semiconductor layer;
A second electrode covering the surface of the semiconductor layer and the insulating film;
A semiconductor laser comprising:

Images