JPS6336591A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain an array type semiconductor laser, in which a threshold current value is decreased, a far field pattern is stabilized, manufacturing is simplified, reproducibility is improved and others are implemented, by providing a plurality of recesses and protrusions on a semiconductor substrate, making the widths of the recesses and the protrusions different, and making pitches between light emitting regions of an active layer approximately equal. CONSTITUTION:First and second clad layers 12 and 14, which have a large energy band gap, are formed on a semiconductor substrate 11. An active layer 13 having a small energy band gap is formed between the clad layers 12 and 14. Thus a double heterojunction type semiconductor laser is formed. A plurality of stripe-shaped recesses and protrudsions are formed on the semiconductor substrate 11. The relationship between a width Wa of a recess 15 and a width Wb of a protrusion 16 is made to be Wanot equal to Wb. Pitches d1, d2, d3... between the positions of step parts 17, which are to become light emitting regions, are made equal. Thus a desiragble light emitting state as the array type semiconductor laser can be obtained. The semiconductor laser characterized by small astigmatism, stabilized operation and a low threshold current value can be constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a semiconductor laser, and particularly to an array type laser in which a plurality of light emitting parts are arranged, a so-called laser array.

[Summary of the invention]

The present invention is a double heterojunction array type semiconductor laser, in which a plurality of step portions are formed in the active layer by forming uneven portions on the semiconductor substrate, and each of these step portions serves as a light emitting portion. In this case, by selecting the widths of the concave and convex parts of the semiconductor substrate, the pinch of each light emitting part is made uniform, and by using a structure that utilizes steps, it has excellent stability. To be able to configure a semiconductor laser.

[Conventional technology]

For example, as shown in FIG. 5, a conventional array type semiconductor laser in which a plurality of light emitting parts are arranged in parallel includes an n-type first cladding layer (2) on an n-type semiconductor substrate (1). ,
An active layer (31), a p-type second cladding layer (41), and a p-type cap layer (5) are sequentially formed by epitaxial growth, and boron ions or protons are selectively implanted across the camp layer (5). striped current confinement regions (6) with high resistance arranged in parallel are formed. In the electrode, a forward voltage is applied between the picture electrodes (7) and (8), thereby forming a current path in a limited manner between each current confinement region, and forming an active layer (3) under a portion facing the current confinement region. There is a structure in which a plurality of light emitting parts are arranged so that an oscillation region is formed in the area indicated by the broken line a in FIG. Letters (Applied Physics
s Letters) 1, 0ctober 1982
It is disclosed in pp614-616.

The array-type semiconductor laser having such a configuration has a problem that the dark value current Tth is relatively high because it has a gain-guided laser configuration, and the far-field pattern becomes unstable as the output increases.

In addition, as other array type semiconductor lasers, for example,
As shown in the figure, the second cladding layer (4) has a structure in which n-type striped light absorption regions (9) are arranged in parallel at a required interval, and the light absorption regions (9) and The light from the active layer (3) in the opposing portion is efficiently absorbed to create a difference in effective refractive index between the portion facing the light absorption region (9) and the portion not facing the light absorption region (9).
As shown by the broken line a in the figure, the light absorption region (9
) has been proposed in which an array-type semiconductor laser is constructed in which a large number of light emitting parts are arranged with an oscillation region limitedly formed in a portion that does not face the light emitting part.

However, when manufacturing a semiconductor laser with such a configuration, for example, a first semiconductor laser is first formed on an n-type semiconductor substrate (1).
cladding layer (2), active layer (3), a lower cladding N (4A) constituting a part of the second cladding layer, and an n-type light absorption region, that is, an active layer (3) on top of this. N(9), which has a smaller energy bandgap compared to N(9), is formed on the entire surface by a series of epitaxial growths, such as vapor phase epitaxy (MOCVD) using organometallic substances, or molecular beam epitaxy (MBE), and then this epitaxial growth. The process was temporarily stopped, and the semiconductor substrate (1) having each layer (21 (31 (4A) and (9)) was taken out from the vapor phase growth apparatus, and the light absorption region (9) was selectively etched. This is formed into a stripe shape, and then placed in the epitaxial apparatus that performs the above-mentioned MOCVD or MBE, and the next epitaxial growth operation is performed, so that the cladding layer (4B) on the upper layer of the second cladding layer (4) absorbs light. The upper p-type cladding layer N is connected to the lower cladding layer (4A) in the part where the light absorption region (9) is removed, including above the region (9).
(4B) is formed, and then a p-type cap layer (5) is epitaxially grown thereon.

However, when using such a method, as described above, the first cladding layer (2) and the active layer (3) are formed on the semiconductor substrate (11).
), the lower second cladding layer (4A), the upper second cladding layer (4B) after the first epitaxial operation for forming the light absorption region (9) and the etching operation for the light absorption region (9). Since the second epitaxial operation for epitaxially growing the cap layer (5) is performed separately, the workability is extremely low, and the separation of both epitaxial operations results in low crystallinity between the semiconductor layers, resulting in poor reproducibility of characteristics.
Problems arise with stability.

, [Problems to be Solved by the Invention] The present invention can solve the above-mentioned problems, namely, reduce the dark value current rth, stabilize the far field pattern, simplify manufacturing, and improve reproducibility. The present invention provides an array type semiconductor laser as described above.

[Means for solving problems]

In the present invention, as shown in FIG. 1, a first cladding layer (12) and a second cladding layer each having a larger energy band than an active layer (described later) are formed on a semiconductor substrate (11) of one conductivity type. These first and second
In a double heterojunction semiconductor laser in which an active Ji (13) having an energy band gap smaller than that of the cladding layer of the semiconductor substrate (11) is formed, each semiconductor layer of the semiconductor substrate (11) has a single layer on the main surface on the side where each semiconductor layer is epitaxially grown. A plurality of striped uneven portions are formed extending in the direction, that is, in the direction perpendicular to the main surface in FIG.

In this case, the concave portions (15) and convex portions (16) are formed alternately, but the width Wa of the concave portions (15) and the convex portions (16)
) and the width wb is assumed to be Wa≠wb. The first cladding layer (12), active layer (13) and second cladding layer (1) thus formed on the semiconductor substrate (11) are
4) on each interface, that is, the double heterojunction surface, the substrate (
The unevenness corresponds to the unevenness of 1).

That is, steps (17) having opposite inclinations to each other are formed so as to be alternately arranged in parallel at portions corresponding to the boundaries between the recesses (15) and the projections (16). In other words, these steps (1
Bent parts (31a) and (3) are provided on the upper and lower edges of 7).
1b).

In the present invention, as described above, by setting Wa≠wb, the arrangement pitches of the steps (17) are made uniform.

(18) is the cap layer provided on the second cladding layer (14), (19) and (20) are the camp layer (18)
These are counter electrodes provided on the top and the back surface of the substrate (11).

The semiconductor substrate (11) and the first cladding layer (12) are selected to have the same conductivity type, the second cladding layer (12) is formed to have a conductivity type opposite to that of the first cladding layer, and the cap layer (
18) is also selected to have the same conductivity type as the second cladding layer (14), for example.

[Effect]

In this configuration, when a forward voltage is applied between the electrodes (19) and (20), the first cladding layer (12) and the second cladding layer (1
4) The central portion of each stage M (17) sandwiched between the bent portions (31a) and (31b) of the upper and lower edges of the active layer (3) sandwiched between each operates as an oscillating portion and emits light. do. That is, based on the difference in the refractive index of light due to the decrease in the refractive index due to the small substantial thickness of the active N(3) in the bent portions (31a) and (31b) (light confinement, that is, the refractive index guide mechanism) occurs at the step (17).In this way, an array-type semiconductor laser is constructed in which a plurality of light emitting parts are arranged, each of which uses each step (17) as a light emitting region.

In this case, each step (1
The arrangement pitch of 7), that is, the arrangement pitch of the light emitting regions can be set at equal intervals, so that a semiconductor laser array without pitch unevenness is formed.

〔Example〕

Further, an embodiment of the semiconductor laser according to the present invention will be described in detail with reference to FIG. In this example, for example, n-type Ga
A semiconductor substrate (11) made of a semiconductor substrate cut out on the (100) plane of an As single crystal is prepared, and its −
As shown in FIG. 2, a plurality of striped mesa grooves or recesses (15) are formed on the main surface, and protrusions (16) are formed between the recesses (15). This recess (15)
can be formed by chemical etching using a photoresist as an etching mask. In this case, by selecting the pattern direction of the etching mask, the side surface (15a) of the recess (15) can be formed as a (111) plane, for example. can do. The height of the convex portion (16), that is, the depth of the concave portion (15) is, for example, 200 to 30 mm.
It can be formed by a relatively shallow groove of about 0.000 people. Then, as shown in FIG. 1, for example, n-type AQo,
A first cladding layer made of 45 Gao and 55 As is formed to have a thickness of 1.5 μm, for example, and a layer of Nlo
, 1o Gao, sAs is formed to a thickness of 500 nm, and on top of this is formed a p-type active layer (13) having the same composition as the first cladding layer, for example A! 2o, <
A second cladding layer (14) of s Gao, 55As is formed to a thickness of 1.5 μm, and a p-type GaAs cap layer (18) of the same conductivity type as the second cladding layer (14) is further formed on this. ) is formed to a thickness of 0.5 μm. The first Clara Frfi1 (12), the active layer (13), the second cladding layer (14), and the carrier/1 layer (18) can be formed by a series of epitaxial operations using the MOCVD method or the MB2 method. Also, in this case, the recess (15)
By setting Wa>Wb, the valley widths Wa and wb of the convex portions (16) are successively adjacent between each step (17) of the active layer (13) caused by the presence of the concave portions (15) and the convex portions (16). Distance di, d2 between matching steps (17). d3-.- are respectively selected as d1=d2=di-. Then, boron ions or protons, etc., are selectively implanted into both sides of the array portion of the step (17) and between the array portions, except for the portions corresponding to each step (17), to create a high resistance. A current confinement region (21) is formed. Then, one electrode (19), for example, an alloy electrode made of Ti/Pt/Au, is provided on the cap layer (18), and the substrate (11
) is provided with an alloy electrode (20) made of AuGe/Ni. In such a configuration, if a forward voltage is applied between the picture electrodes (19) and (20), the current confinement region (2
Except for 1), the current is concentrated in the part where these are formed, that is, the step (17) is concentrated, and the bent part (
Step (1) surrounded by (3La) and (31b)
In step 7), light emission is efficiently generated, and a semiconductor laser array in which these light emitting regions are arranged is formed.

In the above example, as shown in FIG. 2, the concave portion (15) opens upward, which is a so-called forward mesa type structure, but as shown in FIG. 3, a reverse mesa type structure is used. In this case, for example, the growth direction of the first cladding layer (12) formed thereon is approximately the same as that shown in FIG. 3 due to the anisotropy of its crystal growth. A groove (121) is formed in the hard layer (12) that does not follow the irregularities on the substrate (11) but becomes wider upward.

Therefore, even in this case, the required step (17) can be formed in the active layer (13) as explained in FIG.

In addition, in the example explained in FIG. 1, the current confinement region (
21) is a case where a high resistance region is selectively formed. For example, as shown in FIG. 4, a cap layer (
18) It is also possible to form an insulating layer (22) covering the parts other than the current-carrying part and depositing the electrode (19) thereon. In some cases, the high resistance region or insulating layer for current confinement is formed only on the outermost side of the array arrangement part of the light emitting part, that is, the step (17), and the arrangement of the high resistance region or insulating layer for current confinement is formed only on the outermost side of the array arrangement part of the step (17), and Even if such a current confinement means is not specially provided, it is possible to construct an array type semiconductor laser in which the light emitting regions are separated by the refractive index guide mechanism formed by each step (17).

In addition, in this configuration, the first cladding layer (12) has a uniformly relatively large thickness in other parts including the stepped part of the active layer (17), that is, the part that becomes the light emitting region. This is selected to avoid a mechanism in which a difference in effective refractive index occurs due to optical loss in which light from the active layer (13) is absorbed by the semiconductor substrate (11).

In the above-described example, the semiconductor substrate (11) is made of a GaAs single crystal substrate, but an uneven portion is formed on the substrate, and a buffer layer is then formed on the surface of the substrate. It can also be a semiconductor substrate (11).

Furthermore, although the above example describes the case where the semiconductor substrate (11) is n-type, it may be formed as p-type and have a conductivity type opposite to that of each part shown in the figure. i (11) and each semiconductor layer are also Al
It is not limited to GaAs-based compound semiconductors, but can also be composed of various compound semiconductors.

〔Effect of the invention〕

According to the semiconductor laser according to the present invention, the semiconductor substrate (11
), a plurality of unevenness (15) (16) is formed on the active layer (13) to form a step (17) sandwiched between the bent portions (31a) and (31b), respectively, thereby separating and arranging the light emitting regions. The convex part (16)
By setting the widths of the concave portions (15) to different predetermined widths, the intervals between the arranged light emitting regions can be set at equal pitches, so that it is possible to obtain a preferable light emitting state as an array type semiconductor laser. can.

In addition, in the configuration of the present invention, the active layer (13) has a step (1
7), and constitutes a light emitting mechanism based on a refractive index guide type mechanism sandwiched between bent parts (31a) and (31b), so astigmatism is small and stable operation is achieved, and the dark value current 1th This makes it possible to construct a semiconductor laser with a low energy consumption. Incidentally, although the step is formed, the thickness of the first cladding I'5 (12) is
The distance between the active layer (13) and the semiconductor substrate (11) between the part where the step is present and the part where the step is not present, that is, the thickness of the first cladding layer (12), is determined by the difference between the step and the other part. It is also conceivable to change the structure so that the semiconductor substrate (11) absorbs the light from the active layer (13) in the part where the step 17) does not exist to form an effective refractive index difference due to the optical loss difference. However, in this case, since a pure refractive index guide type configuration is not formed, problems such as increased astigmatism occur, and a difference in thickness occurs in this first cladding H (12). Therefore, it is necessary to make the height of the unevenness on the semiconductor substrate (11) sufficiently large. For this reason, the step (17) in the active layer, that is, the distance between the bent portions (31a) and (31b) in the light emitting part becomes large, and in each step (17), each of the bent portions (31a) and (31b) However, according to the present invention, light is absorbed by the semiconductor substrate (11) in each part of the first ground layer (12), although this causes the inconvenience that light is emitted in the vicinity and the operation of transverse mode oscillation becomes unstable. Since the thickness is unnecessary, the height of the recess (15) of the semiconductor substrate (11) is set to 2 as described above.
Since it is possible to select a sufficiently small interval of 200 to 3,000 people, the above-mentioned disadvantages such as the generation of unnecessary light emitting parts or the spread of the light emitting parts can be avoided. By being able to adopt a pure refractive index guide type configuration, it brings about many benefits such as the above-mentioned reduction in the dark value current rth and destabilization of the far field pattern.

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of a semiconductor laser according to the present invention, FIG. 2 is a cross-sectional view of its semiconductor substrate, FIG. 3 is a cross-sectional view of another example of a semiconductor substrate, and FIG. 4 is a semiconductor laser according to the present invention. FIGS. 5 and 6 are enlarged linear sectional views of the other side, respectively, of conventional semiconductor lasers. (11) is a semiconductor substrate, (12) and (14) are first and second cladding layers, (13) is an active layer, (18) is a cap layer, and (19) and (20) are electrodes.

Claims (1)

[Claims] A double heterojunction semiconductor comprising first and second cladding layers with a large energy bandgap formed on a semiconductor substrate and an active layer with a small energy bandgap sandwiched between these cladding layers. A semiconductor laser, wherein the semiconductor substrate has a plurality of concave and convex portions, and the concave portions and the convex portions have different widths so that the pitch intervals of the light emitting regions of the active layer are approximately equal.