JP2940158B2 - Semiconductor laser device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, particularly, for example, a compound semiconductor laser device having a buried window structure.

[Summary of the Invention]

The present invention relates to a semiconductor laser device and a {100} substrate.
A mesa protrusion extending in the <011> direction is formed on the surface, and only the central portion of the mesa protrusion is formed with other side surfaces facing a predetermined distance on both side surfaces only in the vicinity of the center portion of the mesa protrusion. In this case, the other side surface facing away from the distance near the center is formed, or the other side surface is formed on the substrate on which the other side surface is not formed, sequentially by metal organic chemical vapor deposition.
By having a compound semiconductor layer including an active layer having a thickness of 100 ° or less, a window structure is reliably formed, and the reliability of the semiconductor laser device and the characteristics such as high output are improved.

[Conventional technology]

One of the factors that limit the performance of a semiconductor laser device is end face degradation. On the surface of the output end of the semiconductor laser device, the so-called end surface, the energy gap Eg
Is smaller than the bulk energy gap Eg.
For this reason, a vicious cycle occurs in which the absorption of light increases, the temperature rises due to the generation of heat, the crystallinity changes, and the energy gap Eg becomes narrower, and such end face deterioration leads to a decrease in reliability. There is a problem that the increase in output is suppressed.

In order to solve such a problem, a semiconductor laser device having a so-called end face coating has been manufactured, and SiO ₂ , S
A film such as i ₃ N ₄ or Al ₂ O ₃ was deposited on the end face to suppress oxidation and the like to prevent the end face deterioration as described above. In some end coats, it may not be possible to prevent end face deterioration.

As a structure that suppresses end face deterioration due to higher output, the energy gap near the output end face is made larger than that of bulk and is equivalently transparent to oscillating light to suppress light absorption at the end face. A so-called window structure that reinforces the end face by this has been proposed.

An example of a semiconductor laser device having this window structure is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-31481. In this example, as shown in a schematic perspective view of FIG.
After applying an insulating layer (32) such as Si ₃ N ₄ on the entire surface of the substrate (31) made of GaAs or the like, the groove width is narrow at the central part (33A) and the end part (33B In (), a groove (33) whose groove width gradually increases toward the side surface of the substrate (31) is formed in a tapered shape, and MOVPE (organic metal vapor phase epitaxy) is sequentially embedded in the groove (33). ), An n-type cladding layer (34) made of Al _x Ga _1-x As,
When an active layer (35) made of Al _y Ga _1-y As, a p-type cladding layer (36) made of Al _x Ga _1-x As, and a cap layer (37) made of p-type GaAs or the like are epitaxially grown, 7 As shown in the cross-sectional views of FIGS.
Than the thickness t ₁ of the active layer in A) (4), grooves (32)
The thickness t ₂ at the end (32B) of the relatively small. For this reason, the light density exudes to the cladding layers (34) and (36) at the end (32B), the deterioration of the end face is mitigated, and a semiconductor laser device that can operate stably with a large output for a long time is obtained.

On the other hand, as a semiconductor laser having a low threshold current I _th , an SDH (Separated Double Hetero Juice) which can be formed by one epitaxial growth operation is used.
nction) The semiconductor laser is disclosed in
61-183987.

On the other hand, the present applicant has previously described in JP-A-2-174287,
Furthermore, we proposed an SDH type semiconductor laser with lower threshold current. As shown in a schematic enlarged cross-sectional view of one example of this SDH type semiconductor laser in FIG.
The eighth main surface (51a) of the s-compound semiconductor substrate (51)
A stripe-shaped mesa projection (52) extending in the <011> crystal axis direction perpendicular to the plane of the drawing is formed. A first conductivity type, for example, an n-type cladding layer (5
3), low impurity concentration or undoped active layer (5
4), a second conductive type, for example, a p-type first cladding layer (5
5) a first conductivity type, for example, an n-type current block layer (56);
A second cladding layer (57) of a second conductivity type, for example, a p-type,
Each semiconductor layer of the conductive type cap layer (58) is formed by a single epitaxial growth. Thereafter, an electrode layer (61) is formed on the cap layer (58) and on the back surface of the base (51).
And (62), a semiconductor laser device can be obtained.

Here, the first conductivity type cladding layer (53), the second conductivity type first and second cladding layers (55) and (57), and the first conductivity type current blocking layer (56) are active. It is made of a material having a larger band gap, that is, a smaller refractive index than the layer (54).

In this case, the crystal orientation between the substrate (51) and the stripe-shaped mesa protrusion (52), the width and height of the protrusion (52), that is, the depth of the mesa groove (68) on both sides thereof, and the first conductivity type By selecting the thickness of the cladding layer (53), the active layer (54), the first cladding layer (55) of the second conductivity type, etc., the first conductivity type cladding layer (52) is formed on the mesa protrusion (52). 53), an active layer (54), and a first cladding layer (55) of the second conductivity type are formed with a slope (59) so as to be separated from those on the mesa groove, and are separated by these slopes (59). The striped epitaxial growth layer (60) is formed on the mesa protrusion (52).

This is based on the fact that in the case of the normal MOCVD method, that is, the MOCVD method using a methyl-based organic metal as a source gas, once a (111) B crystal plane is formed, epitaxial growth is unlikely to occur on this plane. Thus, a stripe-shaped epitaxial growth layer (60) is formed. In this case, the current block layer (56) is divided on both sides by the stripe-shaped epitaxial growth layer (60), and both end faces generated by the division are exactly different from those in the stripe-shaped epitaxial growth layer (60). The divided striped active layer (54) is brought into contact with both side end faces, that is, end faces facing the slope (59).

In this way, the active layer (54) in the stripe-shaped epitaxial growth layer (60) on the mesa protrusion (52) is formed so as to be sandwiched by the current blocking layer (56) having a smaller refractive index, and the lateral confinement is performed. And a current-carrying layer (56), and a second cladding layer (57) of the second conductivity type on both outer sides of the stripe-shaped epitaxial growth layer (60) due to the presence of the current blocking layer (56). A blocking layer (56), a second cladding layer (55) of the second conductivity type, and a cladding layer (5
As a result, a pnpn thyristor is formed, and the current in the thyristor is blocked, whereby the current flows in the active layer (54) of the stripe-shaped epitaxial growth layer (60) on the mesa projection (52). Are concentrated to reduce the threshold current.

[Problems to be solved by the invention]

The present invention introduces a window structure in an SDH semiconductor laser device with a low threshold current as described above,
Improve reliability and increase output.

[Means for solving the problem]

The semiconductor laser device according to the present invention has a size of {10} of the substrate (1) as shown in the enlarged schematic sectional views of FIGS.
A mesa protrusion (2) extending in the <011> direction is formed on the 0 ° surface, and only the central portion (2A) of the mesa protrusion (2) faces both side surfaces (2S) at a predetermined distance from the other side surface. (3S), and another side surface (3S) facing away from the central portion (2A) in the vicinity of the light emitting portion (2B) in the extension direction of the mesa protrusion (2), or other A compound semiconductor layer (10) including an active layer (5) having a thickness of 100 ° or less and sequentially formed by MOCVD is provided on a substrate (1) on which no side surface (3S) is formed.

[Action]

As described above, in the semiconductor laser device of the present invention, the mesa projection (2) extending in the <011> direction is formed on the {100} plane of the substrate (1), and the compound semiconductor layer (10) is formed thereon by MOCVD. Is grown epitaxially,
When the crystal plane and the crystal axis direction are selected in this manner, as described above, the {100} of the substrate (1) is formed on the mesa protrusion (2).
The (111) B plane spontaneously appears at about 55 ° with the plane, and epitaxial growth is unlikely to occur on this (111) B crystal plane. The compound semiconductor layer (10) grows epitaxially in a triangular cross-section such that the slopes intersect.

In the semiconductor laser device of the present invention, migration, that is, the movement of the compound semiconductor element during epitaxial growth hardly occurs near the central portion (2A) of the mesa protrusion (2). This is because, at the central portion (2A) of the mesa projection (2), the other side surface (3S) facing the side surface (2S) at a predetermined distance is formed on the both side surfaces (2S), and this side surface (3S) is formed.
A compound semiconductor layer having a (111) B crystal plane extending from an edge of the side surface (3S) is formed on the {100} plane constituting the mesa protrusion (2) as well as on the mesa protrusion (2). This is because the semiconductor layer (10) is sandwiched on both sides by the compound semiconductor layer formed on the upper surface of the side surface (3S).

On the other hand, migration is likely to occur at the light emitting end (2B) in the extension direction of the mesa protrusion (2), and the thickness of the compound semiconductor layer (10) grown here becomes small. This is because the other side surface (3S) facing the side surface (2S) of the mesa projection (2) is not provided, or is provided away from the central portion (2A).

For this reason, the thickness of the compound semiconductor layer (10) on the central portion (2A) of the mesa protrusion (2) is made larger than the thickness of the compound semiconductor layer (10) on the end portion (2B). be able to.

In particular, by appropriately selecting the distance between the side surface (2S) of the mesa protrusion (2) and the side surface (3S) opposed thereto, the thickness of the active layer (5) in the compound semiconductor layer (10) is reduced. Can be minutely changed at the center (2A) and the end (2B) of the mesa projection (2).

As described above, the band gap Eg of the active layer (5) of about 100 ° or less, that is, the active layer (5) having a quantum well structure is changed by minutely changing the thickness of the active layer (5). The band gap Eg is large near the light emitting end (2B) in the extension direction of the band gap, and the band gap is near the center (2A).
Eg becomes small. Therefore, the light oscillated in the central portion (2A) is transmitted to the active layer (5) at the end (2B) close to the output end face.
Inside, a structure in which light absorption hardly occurs, that is, a so-called window structure can be employed. Therefore, SD with low threshold current
In the H-type semiconductor laser device, end face deterioration can be reduced, and reliability can be improved and high output can be achieved.

〔Example〕

Hereinafter, an example of the semiconductor laser device of the present invention will be described in detail with reference to FIGS.

In this case, in order to obtain an AlGaAs III-V semiconductor laser device, first, as shown in a schematic enlarged top view of FIG. 2, {100} surface of a substrate (1) made of n-type GaAs or the like. For example, a mesa protrusion (2) extending in a <011> direction, for example, a [011] direction indicated by an arrow a is provided on a main surface (1A) composed of a (100) surface, and a mesa protrusion is provided only in a central portion (2A) thereof. Sides (3) that are close to and parallel to both sides (2S) of the projection (2)
A pair of side bases (3) having S) are provided.

The formation of the mesa projections (2) and the side bases (3) is performed by, for example, applying photolithography, that is, forming a mask layer (not shown) having a required pattern by applying a photoresist, pattern exposure, and development. Then, using this mask layer as a mask, sulfuric acid based H ₂ SO ₄ , H ₂ O ₂ and H ₂ O are 3: 1: 1
Is formed by performing crystallographic etching using an etching solution mixed at a ratio of.

FIG. 3A is a schematic enlarged cross-sectional view taken along the line AA in FIG. 2. In the center part (2A) of the mesa projection (2), both side surfaces (2S) and side base parts (3) are shown. side and is configured to be close to face (3S), to the distance W ₁ and W ₂ for example, each example 50μm approximately.

As shown in FIG. 3B, which is a schematic enlarged cross-sectional view taken along the line BB in FIG. 2, only the mesa protrusion (2) is provided at the end (2B), and the mesa protrusion (2) is extended. [01
1] The other side is not formed in a direction perpendicular to the direction and along the paper surface, that is, in the side.

Then, on such a substrate (1), a methyl-based
The first conductivity type, for example, n-type Al _x1 Ga _1-x1 As by MOCVD method
A cladding layer (4) made of, for example, GaAs and Al _y Ga
An active layer (5) having a quantum well structure by lamination with _1-y As,
A cladding layer (6) made of a second conductivity type, for example, p-type Al _x1 Ga _1-x1 As or the like is epitaxially grown.

FIGS. 1A and 1B are enlarged schematic cross-sectional views of the central portion (2A) and the end portion (2B) of the mesa projection (2) corresponding to the lines AA and BB in FIG. .

In this case, the main surface (1A) of the substrate (1) and the edge on the side base (3), that is, on the side surface (3S) side of the mesa protrusion (2) and the side surface (3S) side as described above are approximately 55 °. If the (111) B crystal plane formed spontaneously occurs, epitaxial growth is unlikely to occur on the (111) B crystal plane. Therefore, the compound semiconductor layer in which the layers (4), (5), and (6) are stacked (10) is divided and formed on the mesa projection (2), the side stand (3), and the groove between them. On the mesa projection (2), it extends from the edges of both sides (2S) (111)
The growth of the p-type cladding layer (6) is performed until the slopes composed of the B crystal planes intersect to form a laminated compound semiconductor layer (10) having a triangular cross section. By appropriately selecting the thickness of each of the layers (4), (5) and (6), the active layer (5) is formed at a height about the middle position of the compound semiconductor layer (10) having a triangular cross section, In the groove, the upper surface of the p-type cladding layer (6) is grown to an intermediate position of the compound semiconductor layer (10) so as not to contact the active layer (5) on the mesa projection (2).

At this time, at the center (2A), as shown in FIG.
Since the active layer (5) on the mesa protrusion (2) is sandwiched between the adjacent epitaxial growth layers on the side support (3), migration hardly occurs, and at the end (2B), FIG. As shown in (1), since there is no epitaxial growth layer in the peripheral portion of the active layer (5), the thickness of the active layer (5) becomes smaller than the central portion (2A) due to the migration effect. Therefore, the energy gap Eg of the quantum well structure in this portion becomes large only at the end (2B), and it is possible to form a window structure having a structure in which light absorption hardly occurs at this end (2B).

A current blocking layer (7) of the first conductivity type, for example, n-type Al _x2 Ga _{1 -x2} As, and a second conductivity type, for example, p-type Al, are formed on the entire surface of the P-type cladding layer (6). _A second cladding layer (8) made of zGa _1-z As or the like is epitaxially grown sequentially by a methyl MOCVD method. At this time, the thickness of the current blocking layer (7) is controlled and grown so as to cover the end face of the active layer (5) on the mesa projection (2) on the (111) B crystal face side.

Further, a cap layer (9) made of p-type GaAs or the like is coated with a photoresist by applying photolithography, pattern exposure, and development, and then patterned by anisotropic etching such as RIE (reactive ion etching). , Only on the central part (2A) of the mesa projection (2). Then, although not shown, electrodes are formed on the cap layer (9) and the back surface of the substrate (1) in ohmic contact, respectively, to obtain the semiconductor laser device of the present invention.

The layers (4), (5), (6), (7), and (8) can be formed by one operation, that is, one crystal growth, by switching a source gas supplied by a series of MOCVD methods.

Note that the conductivity type of each layer may be a conductivity type opposite to the illustrated one.

In the example described above, the other side surface (3S) is not formed on the side of the mesa projection (2) at the end (2B) of the mesa projection (2), but another example is shown in FIG. As shown in a schematic enlarged top view of the above, the central portion (2A) has a side surface (3S) opposed to and parallel to the side surface (2S) as in the above-described example, and an end portion where a window structure is to be formed. Toward (2B), a side pedestal portion (3T) having a tapered side surface (3T) in which the distance between the mesa protrusion (2) having a certain width and the side surface (2S) gradually increases. 3) may be provided. In this case, in the central portion (2A), as shown in FIG. 5A, the lateral cross-section is the distance between the side surfaces (2S) and (3S) in the same manner as in the above-described example.
To arranged with W ₁ and W _2, but in the end (2B),
As shown in FIG. 5 B, and spaced apart side base portions (3) and the mesa projection (2) is compared to the central portion (2A) arranged, the interval W ₃ and W ₄ is, W ₁ , W ₂ <W ₃ , W ₄ . Then, the semiconductor laser device of the present invention can be obtained by epitaxially growing the entire surface over the mesa protrusion (2) by the methyl MOCVD method in the same manner as in the above-described example.

In this case, the interval W ₁ and W ₂ of each side (2S) and (3S) in the central portion (2A), the active layer on the mesa projection (2) (5) during the epitaxial growth, less likely to occur migration 0 <W ₁ <100 μm, 0 <W ₂ <10
It is desirable that the thickness be about 0 μm.

Further, the configuration of the mesa protrusion (2) and the side surface (3S) disposed to face the side surface (2S) is not limited to the above examples, and various configurations may be employed without departing from the gist of the present invention. it can.

〔The invention's effect〕

As described above, in the semiconductor laser device of the present invention, the thickness of the compound semiconductor layer is spontaneously controlled by utilizing the migration effect at the time of epitaxial growth in the SDH semiconductor laser with a reduced threshold current. hand,
By appropriately selecting the distance between the side surface (2S) of the mesa protrusion (2) and the side surface (3S) opposed thereto, the thickness of the active layer (5) can be adjusted with respect to the central portion (2A) of the mesa protrusion (2). It can be slightly changed at the end (2B).

Therefore, the band gap Eg of the active layer (5) having a quantum well structure of about 100 ° or less is set large near the light emitting end (2B) in the extension direction of the mesa protrusion (2) and small near the center (2A). A so-called window structure can be formed in which light oscillated in the central portion (2A) is hardly absorbed at the end face. That is, in the SDH type semiconductor laser device with the lowered threshold, the end face degradation is reduced,
It is possible to improve reliability and increase output.

[Brief description of the drawings]

1A and 1B are schematic enlarged cross-sectional views of the semiconductor laser device of the present invention, FIG. 2 is a schematic enlarged top view of the semiconductor laser device of the present invention, and FIGS. 3A and 3B are semiconductor laser devices of the present invention. FIG. 4 is a schematic enlarged top view of another example of the semiconductor laser device of the present invention, and FIGS. 5A and 5B are schematic lines of main parts of the semiconductor laser device of the present invention. Enlarged sectional view, 6th
FIG. 7 is a perspective view of an example of a conventional semiconductor laser device, FIG.
7A and 7B are schematic enlarged cross-sectional views of main parts of the conventional semiconductor laser, and FIG. 8 is a schematic enlarged cross-sectional view of another example of the conventional semiconductor laser. (1) is a substrate, (2) is a mesa protrusion, (2A) is a central portion,
(2B) is an end, (2S) and (3S) are side surfaces, (3) is a side support, (4) is a first conductivity type cladding layer, (5) is an active layer, and (6) is a A two-conductivity-type first clad layer, (7) is a current blocking layer, (8) is a second-conductivity-type second clad layer, (9) is a cap layer, and (10) is a compound semiconductor layer.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-217988 (JP, A) JP-A-1-186693 (JP, A) JP-A-62-2496 (JP, A) JP-A-63-1988 73961 (JP, A) JP-A-2-174287 (JP, A) JP-A-2-31481 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01S 3/18

Claims (1)

(57) [Claims] 1. A mesa projection extending in a <011> direction is formed on a {100} face of a substrate, and other side faces facing a predetermined distance are formed on both side faces only near a central portion of the mesa projection. In the vicinity of the light emitting end in the direction of extension of the mesa protrusion, the other side surface facing away from the distance in the vicinity of the central portion is formed, or a metal organic vapor phase is formed on a substrate on which the other side surface is not formed. A semiconductor laser device comprising a compound semiconductor layer including an active layer having a thickness of 100 mm or less formed sequentially by a growth method.