JP2538258B2 - Semiconductor laser - Google Patents

Description

The present invention relates to a semiconductor laser.

[Conventional technology]

Generally, when manufacturing an inner stripe type semiconductor laser, a current block layer is formed on a semiconductor substrate by a liquid phase epitaxial growth method (hereinafter referred to as an LPE method), and the current block layer is formed on the surface layer of a lower semiconductor substrate by etching or the like. Forming a V-shaped stripe reaching up to and reaching LP in the stripe and on the current blocking layer.
A semiconductor lower clad layer is formed by the E method, and a semiconductor active layer and a semiconductor upper clad layer are sequentially formed on the lower clad layer by the LPE method, and a semiconductor cap layer is formed on the upper clad layer by the LPE method. Then, electrodes are formed respectively on the lower surface of the substrate and the upper surface of the cap layer to manufacture an inner stripe type semiconductor laser.

By the way, recently, as the application of the semiconductor laser to consumer electronic devices, other industrial devices, and the like has advanced, there has been a demand for higher output of the semiconductor laser. A method is considered, and an effective method is to reduce the thickness of the semiconductor active layer. In this case, the current threshold value of laser oscillation increases due to the thinning of the entire active layer. The inconvenience occurs.

Therefore, as another example, a semiconductor laser having a so-called window structure in which a window region is provided in the vicinity of the emission end face portion of the laser chip in order to reduce light absorption at the laser light emission end face is considered. There is an active layer flat window type semiconductor laser as described in, for example, Technical Report of the Institute of Electronics and Communication Engineers, OQE86-66, pp.37-42 (1986).

This is because a current block layer is formed on a semiconductor substrate having a convex mesa stripe in the center of the upper surface, a V stripe reaching the surface layer of the mesa stripe is formed in the center of the current block layer, and the current block layer is formed. A first layer thickness control groove is formed on both sides of the V stripe in the central excitation region in the front-back direction, and the first layer is formed on both sides of the V stripe in the window regions at the front and rear ends of the current block layer. A groove having a width and a depth larger than that of the thickness control groove is formed.

In the case of such a semiconductor laser having a flat window structure of the active layer, the thickness of the active layer in the excitation region is thicker than that in the window region, unlike a normal window structure semiconductor laser. The current threshold of laser oscillation becomes low and the non-oscillation state is maintained in the window region, so the carrier concentration increases and the absorption of laser light decreases.
Moreover, the active layer in the excitation region can be flattened to stabilize the transverse mode, and high output can be achieved.

[Problems to be solved by the invention]

However, in the case of the above-mentioned active layer flat type window structure semiconductor laser, the V stripe must be formed so as to be accurately positioned in the central portion of the lower mesa stripe, and the step of forming the V stripe is extremely difficult. However, there is a problem in that the yield is reduced.

Therefore, it is a technical object of the present invention to simplify the manufacturing process, improve the yield, and easily obtain a high-power semiconductor laser.

[Means for solving problems]

According to the present invention, in a semiconductor laser including first and second clad layers sandwiching an active layer, the first clad layer is separated into a stripe-shaped first convex portion and the first convex portion. In addition to having second and third convex portions on both sides thereof, the first
The current blocking layer is provided in contact with the first cladding layer so as to exclude the tops of the convex portions, the portions of the current blocking layer corresponding to both sides of the first convex portion are close to the active layer. It is characterized by doing.

[Action]

According to the present invention, in a semiconductor laser including first and second clad layers sandwiching an active layer, the first clad layer is separated into a stripe-shaped first convex portion and the first convex portion. In addition to having second and third convex portions on both sides thereof, the first
The current blocking layer is provided in contact with the first cladding layer so as to exclude the tops of the convex portions, the portions of the current blocking layer corresponding to both sides of the first convex portion are close to the active layer. Therefore, the 0th-order transverse mode is hardly absorbed in the block layer adjacent to the active layer in the portion corresponding to both sides of the first protrusion, and both sides of the 0th-order transverse mode (the first protrusion Higher-order transverse mode light such as the first-order transverse mode generated at both sides (above) is absorbed. As a result, the 0th-order transverse mode exists without being absorbed, and the presence of the higher-order transverse mode is suppressed, so that the transverse mode is stable and a high-power semiconductor laser can be easily realized.

〔Example〕

Next, the present invention will be described in detail with reference to the drawings showing one embodiment thereof.

First, as shown in FIG. 2 (a),
LP on a p-type GaAs substrate (1) with a size of 300 μm × 300 μm
A current blocking layer (2) made of n-type GaAs having a thickness of 1.3 μm is formed by the E method, and by etching, a V width of 2.0 μm in the upper part and 1.7 μm in the front-back direction is formed in the central portion of the block layer (2). Form a letter stripe (3).

Next, as shown in FIG. 2 (b), on both sides of the central stripe (3) over a length of 200 μm in the front-rear direction, except for the regions of 25 μm from the front and rear ends of the upper surface of the block layer (2), respectively. , A recess (4) having an upper width of 10 μm and a depth of 0.7 μm is formed by etching, provided that the depth of the recess (4) is the lower block layer (2) of the recess (4).
However, the thickness is set so that the current constriction effect is not lost.

At this time, a mask having a shape in which the distance between the stripe (3) and the both recesses (4) is separated by 5 μm is used so that a flat portion remains between the stripe (3) and both the recesses (4).

2 (a) and 2 (b) are a front view of cutting at the front end portion or the rear end portion and a front view of cutting at the center portion in a state where the stripe (3) and the recess (4) are formed.

Then, a semiconductor lower clad layer (first clad layer) (5) made of p-type GaAlAs is formed in the stripe (3), both concave portions (4) and on the block layer (2) by the LPE method, and this lower part is formed. On the clad layer (5), the semiconductor active layer (6) made of p-type GaAlAs and the n-type are formed by the LPE method.
A semiconductor upper clad layer (second clad layer) (7) made of GaAlAs is sequentially formed to form a double heterojunction layer, and a semiconductor cap layer (8) made of n-type GaAs is formed on the upper clad layer by the LPE method. Then, electrodes are respectively formed on the lower surface of the substrate (1) and the upper surface of the cap layer (8) to manufacture an inner stripe type semiconductor laser.

In such a semiconductor laser, the lower clad layer (5) has a stripe-shaped first convex portion in the stripe (3), and a second convex portion in the concave portions (4) and (4), respectively.
It has a 3rd convex part.

At this time, the lower clad layer (5), the active layer (6), the upper clad layer (7), and the cap layer (8) are formed under the conditions of a substrate temperature of 820 ° C and a cooling rate of 0.5 ° C / min. , The growth time of each layer is 50 seconds, 0.1 seconds, 6 respectively
60 seconds and 1000 seconds.

And when each layer (5)-(8) is formed by the LPE method on the above-mentioned conditions, the cutting front view in a front-end part or a rear-end part, and the cutting front view in a center part are each FIG. As shown in b).

That is, since the recesses (4) and (4) are formed on both sides of the stripe (3) at the center of the block layer (2) in the front-rear direction, the stripes are formed when the lower clad layer (5) is formed by the LPE method. The lower cladding layer (5) grows so as to fill (3) and both recesses (4), (4), and as a result, the surface of the lower cladding layer (5) is not flat and the stripes (3) and both When the active layer (6) is formed on the lower clad layer (5) by the LPE method, depressions corresponding to the recesses (4) and (4) are formed, and the stripes (3), the recesses (4) and (4) are formed. ), The active layer (6) grows so as to fill the recessed part, and the growth rate of the active layer (6) in the recessed part becomes faster than the growth rate of the active layer (6) in the other flat part, As shown in FIG. 3 (b), the active layer (6) in the recessed portion. Thickness becomes thicker,
An excitation region (9) having a low laser oscillation current threshold value is formed in the central portion.

On the other hand, at the front and rear ends where the recess (4) is not formed,
Since the phenomenon described above does not occur, as shown in FIG. 3 (a), the thickness of the active layer (6) is uniform and thin, and a window region (10) having a high laser oscillation current threshold is formed. ) Is formed, and a semiconductor laser having a window structure is obtained.

Therefore, according to the above-mentioned embodiment, since the stripes (3) are formed on the flat block layer (2) formed on the flat substrate (1), as in the case of the conventional active layer flat type semiconductor laser. In addition, the step of forming a convex mesa stripe on the semiconductor substrate is not necessary, and the difficulty in accurately forming the V stripe at the center of the mesa stripe is eliminated, and the manufacturing process can be simplified. Therefore, it is possible to improve the manufacturing yield of the semiconductor laser and easily obtain a high-output semiconductor laser.

〔The invention's effect〕

According to the present invention, in a semiconductor laser including first and second clad layers sandwiching an active layer, the first clad layer is separated into a stripe-shaped first convex portion and the first convex portion. In addition to having second and third convex portions on both sides thereof, the first
The current blocking layer is provided in contact with the first cladding layer so as to exclude the tops of the convex portions, the portions of the current blocking layer corresponding to both sides of the first convex portion are close to the active layer. Therefore, the 0th-order transverse mode is hardly absorbed in the block layer adjacent to the active layer in the portion corresponding to both sides of the first protrusion, and both sides of the 0th-order transverse mode (the first protrusion Higher-order transverse mode light such as the first-order transverse mode generated at both sides (above) is absorbed. As a result, the 0th-order transverse mode exists without being absorbed, and the presence of the higher-order transverse mode is suppressed, so that the transverse mode is stable and a high-power semiconductor laser can be easily realized.

[Brief description of drawings]

The drawings show one embodiment of a method for manufacturing a semiconductor laser according to the present invention. FIG. 1 is a partially cutaway perspective view of the manufactured semiconductor laser, and FIGS. 2 and 3 are cutting front views in different manufacturing steps. Each drawing (a) is a cutting front view at a front end portion or a rear end portion, and each drawing (b) is a cutting front view at a central portion. (1) ... Substrate, (2) ... Current blocking layer, (3) ...
... V-shaped stripes, (4) ... recesses, (5) ... lower clad layer, (6) ... active layer, (7) ... upper clad layer.

Claims (1)

(57) [Claims] 1. A semiconductor laser comprising first and second clad layers sandwiching an active layer, wherein the first clad layer is separated into stripe-shaped first convex portions and the first convex portions. The second and third convex portions on both sides of the lever, and
By providing a current blocking layer in contact with the first cladding layer so as to exclude the tops of the convex portions, the current blocking layer has portions corresponding to both sides of the first convex portion close to the active layer. A semiconductor laser characterized by: