JPH02174287A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To acquire a semiconductor laser of a low threshold current of stable characteristics by forming a current block layer inside a mesa groove which forms a mesa protrusion in contact with a side of an active layer which is formed on the mesa protrusion through epitaxial growth extending over an entire thickness of the active layer, and by interposing it between first and second clad layers of second conductivity type. CONSTITUTION:An active layer 44 which becomes an operation region formed on a mesa protrusion 42 of a substrate 41 is interposed between a clad layer 43 of a first conductivity type and a first clad layer 45 of a second conductivity type, and a transverse direction thereof is made a BH structure which is enclosed with a current block layer 46. Both sides of the active layer 44 are controlled on an extensions of a slope 49 made by a crystal face 111B generated on a clad layer 2 of the first conductivity type, and also controlled by a current block layer 46 of the first conductivity type. That is, to make a protrusion 42 nearly a forward mesa, the current block layer 46 is formed as a surely flat surface 311 at both sides of an active layer 44 as a light emitting section which is interposed therebetween extending over the entire thickness thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to semiconductor lasers, particularly AI Ga
It relates to a buried heterojunction type (hereinafter referred to as BH type) semiconductor laser made of an As-based compound semiconductor.

[Summary of the invention]

The present invention relates to a semiconductor laser, and includes: a cladding layer of a first conductivity type; an active layer; a first second conductivity type cladding layer;
A current blocking layer of a conductive type and a second cladding layer of a second conductive type are sequentially grown as epitaxial layers, and a cladding layer of a first conductive type and a first cladding layer of a second conductive type are formed on the mesa protrusion. A current blocking layer is formed above and below the active layer of the second conductivity type so as to contact the side surface of the active layer on the mesa protrusion over the entire thickness of the active layer. A low-threshold current blocking layer is reliably formed on both sides of the active layer on the mesa protrusion by one continuous epitaxial growth. A BH type semiconductor laser can be manufactured easily and reliably.

[Conventional technology]

To produce a semiconductor laser with a low dark value current 1th, it is necessary to create a refractive index difference in the lateral direction of the active layer, that is, in a direction perpendicular to the surface direction of the active layer, and to use current blocking means to narrow the current. shall be.

In order to satisfy these two conditions, a conventional BH type semiconductor laser needs to be manufactured by performing epitaxial growth at least twice.

That is, a method is used in which a double heterojunction structure in which the active layer is sandwiched between rad layers with a large band gap is formed in the first epitaxial growth, and then the area around the ridge structure is filled in in the second epitaxial growth. When an 811 type semiconductor laser is obtained by such a method, during the etching process, the surface of the crystal comes into contact with the atmosphere, which oxidizes the surface and affects the interface of the epitaxial layer, which may reduce the characteristics of the semiconductor laser or change its characteristics. This results in heterogeneity, instability, and decreased credibility.

On the other hand, the present applicant proposed a semiconductor laser in Japanese Patent Application Laid-Open No. 183987/1983 (Japanese Patent Application No. 22989/1982) which improved the above-mentioned problems by one epitaxial growth as shown in FIG.

This semiconductor laser is, for example, as shown in FIG.
00) Sequentially continuous MOCVD on a compound semiconductor substrate (21) having a so-called inverted mesa-like protrusion (30) with an inverted trapezoidal cross section, for example in a stripe shape perpendicular to the plane of the paper, on the main surface of the crystal plane.
(Metal Organic Chemical V
n-type AfGa
A first conductivity type cladding layer (22) of As, an optical waveguide layer (23) provided as necessary, an active layer (24) of AJGaAs, and a second conductivity type cladding layer (25) of p-type AlGaAs. and a p-type GaAs cap layer (26)
And to n-type! Current blocking layer of GaAs (27
) is formed, the central part of the current blocking layer (27) is partially removed by etching, and a first electrode (28) is formed on the current blocking layer (27) including the inside of the removed part (27a). Further, second electrodes (29) are ohmically attached to the back surface of the base (21).

In this semiconductor laser, the first n-type cladding layer (22
), sidewall slopes (22a) due to the (111) B crystal plane are generated on both sides of the inverted mesa-like protrusion (30) so as to sandwich it. The epitaxial growth rate on this (111) B plane is several tenths lower than that of other crystal planes such as the (100) crystal plane. Once this occurs, this (11
1) Crystal growth on the B crystal plane apparently stops. Therefore, the leading wave layer (23) formed on this
The active layer (24) is formed separately on the inverted mesa-like protrusion (30) and on the other main surface by the slope (22a), and the active layer (24) on the inverted mesa-like protrusion (30) is formed separately.
4) Both sides of the p-type rad layer with a large bandgap (
25), and the light is confined.

[Problem to be solved by the invention]

Incidentally, the BH type semiconductor laser shown in FIG. 3 described above has the advantage of being able to improve the uniform stability and reliability of the semiconductor laser characteristics because it is formed by one epitaxial growth. After forming the current blocking layer (27), a cutout (27a) is formed here.
Requires an etching process to form. In addition, although the presence of the current blocking layer (27) has the effect of current narrowing, since this current blocking layer (27) is located on the top layer, there is a possibility that the current will spread before reaching the active layer. However, there is a problem in achieving a sufficiently low threshold current.

On the other hand, in view of this, the present application is intended to form all layers by one epitaxial growth, eliminate the need for a subsequent etching process, and ensure current narrowing or current blocking to achieve a low threshold current. There is a proposal for patent application No. 63-217829 titled "Semiconductor Laser" filed by a person. This semiconductor laser has a first
For example, a GaAs compound semiconductor substrate (1) having an n-type conductivity and a (100) crystal plane has an inverted mesa with a striped trapezoidal cross section extending in a direction perpendicular to the paper plane of FIG. MODCV is sequentially formed on the main surface of the base (1) having the projections (12).
cladding N of the first conductivity type, for example, n-type, by D.
(2) and low impurity or undoped active layer (3)
, a first cladding layer (4) of a second conductivity type, e.g., p-type, a current block N (5) of a first conductivity type, e.g., n-type, and a second cladding layer (4) of a second conductivity type, e.g., p-type. 6) and a second conductivity type cap layer (7) are epitaxially grown.

Here, the cladding layer (2) of the first conductivity type, the first and second cladding layers (4) (6) of the second conductivity type, and the current blocking layer (5) of the first conductivity type are active layers. It is made of a material with a larger band gap, that is, a smaller refractive index than layer (3).

In this case, by selecting the shape of the protrusion (12) of the base (1), its relationship with the crystal orientation, etc., the presence of the protrusion (12) causes the formation of the cladding layer (2) of the first conductivity type.
The side wall slope due to the (111)B crystal plane as described above (
2a) are formed on both sides of the striped projection (12) so as to sandwich the projection (12) and extend along the extension direction of the striped projection (12). Therefore, the active layer (3) formed on this surface hardly grows on this (111)8 surface due to the presence of this slope (2a), and the active layer (3) formed on this surface hardly grows on this (111)
) and both sides thereof, that is, inside the mesa groove, and the current blocking layer (5) is formed on both side wall slopes (2a) of the epitaxial layer including the active layer (3) formed on the protrusion (12). is formed in contact with. In other words, the current blocking layer (5) is
It is formed at a position that separates the conductive type cladding layer (4) from the similar first and second conductive type cladding layers (4) on the mesa groove other than the protrusion (12).

Regarding the second second conductivity type cladding layer (6), the first cladding layer (6) on the protrusion (12) mainly grows from other crystal planes.
The thickness of the growth is selected so as to fill the top of the second conductivity type cladding layer (4). Then, the gap layer (the first for sumo wrestlers)
A second electrode (9) is deposited on the back surface of the base (1).

According to this configuration, the active layer (3) formed on the protrusion (12) of the base (1) is connected to the first conductivity type cladding layer (2) on the protrusion (12) and the first second conductivity type cladding layer (2) on the protrusion (12). Conductive cladding layer (
4) and a current blocking layer (5) in the mesa groove. Both sides of this active layer (4) are regulated by extensions of sidewall slopes (2a) formed by the (111) B crystal planes formed in the first conductivity type cladding layer (2), and current blocking layers of the first conductivity type ( 5).

That is, in this case, current blocking layers (5) are formed on both sides of the active layer (3) itself, which is the actual operating region on the striped protrusion (12), so that ρ-
Since the npn structure is formed, current narrowing is effectively performed, and current can be effectively concentrated in the active region of the active layer (3).

In addition, the current blocking layer (5) is formed between the first and second second conductivity type cladding layers (4) and (6), and the active N ( 3), the selective etching process shown in FIG. 3 is not required after the completion of continuous crystal growth, simplifying the manufacturing process.

However, in the case of such a semiconductor laser, the main plane of the current blocking layer (5) is formed as a (311) crystal plane, but the protrusion (12) has an inverted mesa shape, that is, a steep side surface with a reverse slope. If the protrusion shape has
In fact, in the semiconductor laser described above, the (311) plane does not necessarily occur stably, and as shown in FIG. 5, the current blocking layer (5) is This causes the disadvantage that this current blocking layer (5) may or may not traverse over its entire thickness the sides of the active layer (3) which constitute the active area on the protrusion (12). , the characteristics may become non-uniform or unstable, leading to a decrease in reliability.

In the present invention, to solve this problem, the current blocking layer is formed so as to cover all sides of the active layer, which is the active region on the protrusion, by ensuring the generation of (311) planes in the current blocking layer. Provided is a semiconductor laser in which formation of a semiconductor laser is performed.

[Means to solve the problem]

As shown in FIG. 1, the present invention has a striped shape (as shown in the paper) in which the main surface (41a) is formed by a (100) crystal plane, and the side surface (42a) is a gently concave curved surface that is convex toward the base side. This compound semiconductor substrate (41) has a mesa protrusion (42) (extending in a perpendicular direction).
1) on the main surface (41a) side having the mesa protrusion (42),
The entire surface includes a cladding layer (43) of the first conductivity type and an active layer (
44), the first second conductivity type cladding layer (45), the first conductivity type current blocking layer (46), and the second second conductivity type cladding layer (47) are sequentially formed. It is formed by laminating. The current blocking layer (46) in the mesa groove (48) forming the mesa protrusion (42) is
This active layer (44) is sandwiched between the first and second conductivity type cladding layers (43) and (45) epitaxially grown on the mesa protrusion (42).
The second conductivity type cladding layer (45) and the second conductivity type cladding layer (47) are sandwiched between the first and second second conductivity type cladding layers (45) and (47) so as to be in contact with each other over the entire thickness thereof.

[Effect]

According to the configuration of the present invention, the mesa protrusion (42) of the base (41)
An active layer (44) forming an active region is formed on the first
The BH tank structure is sandwiched between a conductive type cladding layer (43) and a first and second conductive type cladding layer (45), and laterally surrounded by a current blocking layer (46).

Both sides of the active layer (44), which constitutes a substantial operating region on this mesa protrusion (42), are covered with a first conductivity type cladding layer (2).
) is regulated by the extension of the slopes (4) due to the (111)B crystal plane, and is regulated by the current blocking layer (46) of the first conductivity type.

The side surface (42a) of the mesa protrusion (42) according to the present invention is
) is a gently concave surface, that is, when the protrusion (42) is close to a normal mesa, the current blocking layer (46) is reliably formed as a flat (311) surface. therefore,
This makes it possible to reliably form the current blocking layer (46) across the entire thickness of the striped active region on the mesa protrusion (42), sandwiching the active layer (44) as a light emitting part. As a result, the current can be sufficiently narrowed and the current can be reliably concentrated in the active layer (44) on the mesa protrusion (42) where the current spreads, making it possible to construct a semiconductor laser with a low threshold current. .

Also, in the semiconductor laser according to the present invention, the current blocking layer (46) is formed between the first and second second conductivity type cladding layers (45) and (47) and automatically covers the operating region, that is, the current blocking layer (46). Since it is formed so as to restrict both sides of the active layer (44) which becomes the light emitting part, the selective etching process explained in FIG. 3 after the completion of continuous crystal growth becomes unnecessary, which simplifies the manufacturing process and This will improve trustworthiness.

〔Example〕

An example of the semiconductor laser according to the present invention is shown in FIG.
This will be explained along with an example of its manufacturing method. jVGaAs system ■-
When obtaining a group (2) compound semiconductor laser, first, as shown in FIG.
1) will be provided. This base (41) has its main surface (41a
) has a (100) crystal plane. This base (41)
An etching mask (51) on a stripe is selectively formed with a required width W on the main surface (41a) of the substrate. The mask (51) can be formed, for example, by coating a photoresist film, pattern exposure, and development. In this case, the plane along the plane of the paper is selected as the (011) plane, and the extension direction of the stripes of the mask (51) is selected to be perpendicular to this plane.

Next, from the surface (41a) side of the substrate (41), for example, a sulfuric acid-based etching solution is applied such as 1lzsO4 and H, 0□ and H.
Crystallographic etching is performed using an etching solution containing 2O mixed in a ratio of 3:1:1. In this way, etching progresses from the part not covered by the mask (51), and as shown in FIG. 2B, mesa grooves (48) are formed, and both side surfaces (42a) are made into gently curved concave surfaces. A striped mesa protrusion (42) close to a normal mesa is generated. Next, as shown in FIG. 2C, the etching mask (51) is removed, and an n-type buffer layer (not shown) is formed as necessary on the uneven surface of the base (41) by MOCVD. A first conductivity type cladding layer (43) of type A7 XGa I -XAS is epitaxially grown.

In this case, as the epitaxial growth progresses, the upper surface of the mesa protrusion (42) forms a slope (49) consisting of a (111)B crystal plane with an angle θ of approximately 55 degrees with respect to the (100) plane.
occurs spontaneously on both sides. Then, the epitaxial growth of the n-type cladding layer (43) is stopped in a state where the slope (49) due to the (111)B plane exists. Subsequently, mesa protrusions (42
) includes an n-type cladding layer (43) with a trapezoidal cross section on the active layer (
44) is epitaxially grown.

In this case, the (111)B crystal plane of the slope (49) has MO
Since epitaxial growth layers by CVD are difficult to form,
The active layer (44) does not substantially grow on this slope (49), but grows on the mesa protrusion (42) and the mesa grooves (42) on both sides thereof.
48) can be selectively separated from each other and formed only on the bottom surface.

Next, a first p-type/uxGaI-Js layer is placed on the substrate (41).
A first cladding layer (45) of the second conductivity type is epitaxially grown by MOCVD. In this case, as shown in the second diagram, the growth of the n-type cladding layer (45) progresses until the n-type cladding layer (45) reaches a position where the slopes (49) on both sides intersect on the mesa protrusion (42). 45), while mesa protrusions (12) are grown on the mesa grooves (48).
299971 layer (45) is grown to the middle position of the slope (49) of the n-type cladding layer (43) on ).

Next, as shown in FIG. 2E, for example, an n-type cladding layer (4
A current blocking layer (46) made of n-type AZxGa+-xAs having the same composition as in 3) is grown epitaxially with controlled film thickness by MOCVD. In addition, the current blocking layer (4
6) is formed to separate the n-type cladding layer (45) on the mesa protrusion (42) and the first second conductivity type (P-type) cladding layer (45) on the mesa groove (48). .

Next, as shown in FIG. 2F, the first second conductivity type (p type)
A second conductivity type (p) having the same composition as the cladding layer (45).
A tdxGa+-xAs cladding layer (47) and a highly doped cap layer (50) made of second conductivity type (p-type) GaAs are sequentially epitaxially grown by MOCVD. In this case, the second n-type cladding layer (4
7) does not grow on the slope (49) in the initial stage, but as the growth progresses, it grows (111) at the part where it meets the slope (49).
) When crystal planes other than the B-plane are generated, they are grown on the front surface including the slope (49). Therefore, the cap layer (50) on this second n-type cladding layer (47) is also grown entirely.

Next, as shown in FIG.
A semiconductor laser according to the present invention is obtained by ohmically depositing the electrode (51) and the second electrode (52) on the back surface of the base (41).

Here, each layer (43), (44), (45)
, (46), (47), (50) are a series of M
By changing the raw material gas supplied by OCVD, it can be formed in one operation, that is, in one crystal growth.

Also, an n-type cladding layer (43), a first n-type cladding layer (
45), the composition AJxGa+-*As of the n-type current blocking layer (46) and the second P cladding layer (47) and the composition A7yGa+-As of the active layer (44) are selected such that X>Y.

Note that, if necessary, an optical waveguide layer can be formed in contact with the active layer (44) by continuous MOCVD.

Further, the conductivity type of each layer may be the opposite conductivity type from that illustrated.

(Effects of the Invention) According to the above-described present invention, the active layer (44) on the mesa protrusion (42), which becomes the operating region, that is, the light emitting part, has the first conductivity type cladding layer (43) and the first second conductivity type cladding layer (43). Conductive cladding layer (4
5) and an 811-type refractive index guide structure surrounded by current block li (46), in particular, the current block layer (46) covers both sides of the active layer (44), which is the active region of the mesa protrusion (42). Since the current blocking layer (46) is formed in contact with the mesa protrusion, the current confinement acts more strongly. (42) Since it can be reliably arranged over the entire thickness of both sides of the active layer (44), which is the active region above, it is possible to reliably perform current blocking, that is, current narrowing, resulting in stable characteristics. A value current semiconductor laser can be obtained reliably.

In addition, in the present invention, it is possible to manufacture the semiconductor laser by one continuous epitaxial growth, and furthermore, the etching process after the epitaxial cell growth can be omitted. Therefore, it is possible to produce a uniform, stable, and highly reliable low threshold current semiconductor laser. It can be easily manufactured with good reproducibility.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a semiconductor laser according to the present invention, FIG. 2 is a manufacturing process diagram thereof, FIG. 3 is a sectional view showing an example of a conventional semiconductor laser, and FIG. 4 is a sectional view of a semiconductor laser as a comparative example. The sectional view and FIG. 5 are perspective views of main parts of a comparative example. (41) is a compound semiconductor substrate, (43) is a cladding layer of the first conductivity type, (44) is an active layer, and (45) is a first conductivity type cladding layer.
Conductive cladding layer, (46) is current blocking layer, (47
) is a second second conductivity type cladding layer, (50) is a cap layer, and (51) and (52) are first and second electrodes. 41 ・Base 41α Support 1 42... Mesa narrows 42a... I1 1 shi 43... 纂1傳1 [! Kura ni 1 44... Tsu sex 1 Δ5... 1 Umachi guide t! Layer 46 on ri5g... flow, ri1 AT-v-2c v! 2 '419 〒77・+To 4
48. No? ; Nose 49...Slope 50...'mgw' 91 51...1 to 1! Child and 52... Tei 2's T-el

Claims (1)

[Scope of Claims] (100) On a compound semiconductor substrate having a mesa protrusion whose principal surface is a crystal plane and whose side surfaces are gently concavely curved surfaces convex toward the base side, the mesa of the compound semiconductor substrate is provided. A cladding layer of a first conductivity type, an active layer, a first cladding layer of a second conductivity type, a current blocking layer of a first conductivity type, and a second cladding layer of a second conductivity type on a main surface having a protrusion. The current blocking layer in the mesa groove forming the mesa protrusion is formed on the side surface of the active layer epitaxially grown on the mesa protrusion over the entire thickness of the active layer. A semiconductor laser characterized by being sandwiched between first and second cladding layers of a second conductivity type so as to be in contact with each other.