JPH0563289A - Wide stripe type semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain a wide strip type semiconductor laser having excellent light condensing properties in a simple structure. CONSTITUTION:A central protrusion 61a is so formed in a stripe 61 that the length of a resonator of a central part becomes longer than those of both ends in a wide stripe type semiconductor laser, thereby increasing an oscillation gain at the center of the stripe 61 over that at the other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide stripe type semiconductor laser having a high output and an excellent light converging property.

[0002]

2. Description of the Related Art A higher output is desired for expanding the field of application of semiconductor lasers, but in order to increase the output, it is necessary to reduce the light density at the laser end face. Because there are many non-radiative recombination levels on the crystal surface of the laser facet, part of the laser light is absorbed there and heat is generated, so if the optical density exceeds a certain limit, the crystal melts locally. This is because it causes irreparable damage. Therefore, in order to deal with such a problem, various wide stripe type semiconductor lasers and wide stripe array type semiconductor lasers having a large light emitting area and a low light density have been developed. 6 and 7 show the basic structure of a wide stripe semiconductor laser 100 having a double hetero structure with a window, in which two upper and lower clad layers 102, 10 are formed on a substrate 104.
The active layer 101 of n-type semiconductor is grown so as to be sandwiched by 3 and then the p-type dopant is diffused into a portion corresponding to the shape of the rectangular stripe 106a by the insulating film 105 such as SiO 2 to form the light emitting region. The semiconductor substrate 100
This is a laminated structure in which electrodes 106 and 107 are formed on both upper and lower surfaces of a, and window portions with little light absorption are formed at both ends of the active layer 101.

[0003]

However, in the wide-stripe type semiconductor laser having such a structure, the far-field pattern perpendicular to the active layer has a unimodal characteristic as shown in FIG. However, since the pattern of the far-field pattern parallel to the active layer that affects the converging property of the laser light exhibits the bimodal characteristics as shown in FIG. 8B, the laser light is condensed and used. It was not suitable for such uses. It is considered that this is due to the distribution of the current (heat) inside the semiconductor in addition to the oscillation of the higher mode. Note that, in FIG. 8, θH / 2 and θV / 2 indicate half-widths of outputs in the horizontal and vertical directions on the active layer.

Therefore, as a conventional solution to such a problem, as shown in FIG.
0, the front and rear end faces 200a and 200b have partial reflection films 202 and 203 having different reflectances.
3 is increased), and the light emitting region 20 is formed.
There has been proposed a method of lowering the threshold current of the fundamental mode in No. 1 below that of the other higher-order modes to facilitate oscillation of the fundamental mode. The far-field pattern parallel to the active layer has a single-peaked characteristic in which the center is sharpened in a beam shape, but a complicated process of forming a partially reflective film is required at the time of manufacturing. It was The present invention has been made in view of the above circumstances, and even in a wide-stripe semiconductor laser, the far-field pattern parallel to the active layer exhibits a single-peak characteristic with a simple method and is excellent in light converging property. It is intended to provide a high-power semiconductor laser.

[0005]

The above object is achieved by the present invention in which the stripe shape in a wide stripe type semiconductor laser is such that the resonator length in the central portion of the light emitting region is longer than the resonator lengths at both ends. To be done.

[0006]

According to the wide stripe type semiconductor laser proposed in the present invention, since the oscillation gain in the central portion of the stripe becomes large, the fundamental mode easily oscillates. For this reason, the far-field pattern in the direction horizontal to the active layer exhibits a single-peaked characteristic and is excellent in the light-condensing characteristic.

The wide-stripe semiconductor laser of the present invention as described above is inferred from the following laser oscillation starting conditions. That is, generally, a window structure laser as shown in FIG. 4 in which the cavity length L and the gain region (light emitting region) length L1 are different is considered, and its threshold gain coefficient is defined as gth (gain coefficient when laser emission starts). Then (to simplify the explanation, the loss coefficient α is the same over the entire length of the resonator length), gth is given by gth = (L / L1) α + ln (1 / R1 · R2) / 2L1. Here, ln is a natural logarithm, and R1,
R2 is the light reflectance at the front and rear ends of the resonator, and α is the loss coefficient. From this equation, the larger L1 is, the threshold gain coefficient g
It can be seen that th becomes smaller. Since the threshold gain coefficient gth increases with the injection current, the smaller the threshold gain coefficient gth, the smaller the current value that the laser oscillation occurs.
Therefore, when applying such an oscillation condition to the semiconductor laser of the present invention, since the central protruding portion of the stripe has L1 larger than both ends thereof, the threshold gain coefficient gth also becomes small, and the threshold current value of laser oscillation is reduced. Becomes smaller.
As a result, the fundamental mode oscillation (oscillation at the central protrusion) is more easily obtained than other higher order mode oscillations, and the far-field pattern parallel to the active layer exhibits a single-peak characteristic.

[0008]

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an embodiment of the present invention, in which 1 is an active layer made of an n-type semiconductor, 2 and 3 are clad layers sandwiching the active layer 1 from above and below, 4 is a semiconductor substrate, and 5 is a laser. Current constriction required for oscillation and stripe 61
In order to define the shape of the insulating layer formed on the upper surface of the clad layer 2, the electrodes 6, 6 are formed on the upper and lower surfaces of the semiconductor substrate 1a.
It is a structure A in which 7 is deposited. The light emitting region 11 of the active layer 1 is formed in a shape matching the stripe. In the present invention, the stripe 61 is formed so that the central protruding portion 61a is formed as shown in FIGS. It is characterized in that it is made longer than both ends, and the resonator length L1 at that portion is made longer than both ends L2.

FIG. 2 more specifically shows such a semiconductor laser of the present invention. On the n-GaAs substrate 4, n-Al0.3Ga0.7As, n-Al0.3Ga0.7A
An active layer 1 made of n-Al0.06Ga0.94As is formed so as to be sandwiched between upper and lower clad layers 2 and 3 made of s, and the upper surface of the upper clad layer 2 is formed as shown in FIGS.
After forming the insulating film 5 which defines the stripe 61 having the central protruding portion 61a as shown in FIG. 2 by SiO2, a p-type dopant such as Zn is introduced from the upper surface of the upper cladding layer 2 to the inside of the active layer 1. The light emitting region 11 is formed by diffusion, and finally, the p-type and n-type electrodes 6, 6 are formed on both upper and lower surfaces of the semiconductor substrate.
7 is vapor-deposited to form an AlGaAs semiconductor laser A. In such a structure, a stripe 6 is formed by diffusing a p-type dopant such as Zn into the active layer 1 of the n-type semiconductor.
Since the light emitting region 11 is formed such that the protruding portion 61a is formed in the center of the light emitting region 1, the light emitting region 11 is formed at both end portions of the active layer 1 which are not diffused by the p-type dopant.
Since the window portion 11a having a larger effective band gap and less light absorption is formed, the end surface of the active layer 1 is resistant to damage even at high output.

The semiconductor laser of the present invention is not limited to the above structure, and as shown in FIG. 5, a plurality of stripes 61 having a central protruding portion 61a are arranged in parallel on a common semiconductor substrate 1a. The array structure B may be arranged, and in such a structure, higher output can be achieved.

[0011]

According to the wide-stripe type semiconductor laser of the present invention, the beam characteristic that the pattern of the far-field pattern parallel to the active layer becomes a unimodal shape only by changing the shape of the stripe that defines the shape of the light emitting region. Therefore, it is possible to realize a high-power semiconductor laser having excellent light-collecting properties.

[Brief description of drawings]

FIG. 1 is a perspective view in which a part of a wide stripe type semiconductor laser of the present invention is cut away.

FIG. 2 is a more detailed vertical cross-sectional structural diagram of the wide-stripe semiconductor laser of the present invention.

3 (a) and 3 (b) are views showing the shape of a wide stripe adopted in the present invention.

FIG. 4 is a diagram illustrating a basic structure of a windowed semiconductor laser.

FIG. 5 is a perspective view showing another example of the wide stripe type semiconductor laser of the present invention.

FIG. 6 is a perspective view in which a part of a conventional wide stripe type semiconductor laser is cut away.

FIG. 7 is a vertical sectional structural view of the semiconductor laser shown in FIG.

FIG. 8 is a diagram showing a far-field pattern of a conventional wide-stripe semiconductor laser.

FIG. 9 is an explanatory view of a conventional semiconductor laser having a partially reflecting surface.

10 is a pattern explanatory view of a far-field image parallel to the active layer in the semiconductor laser shown in FIG.

[Explanation of symbols]

 A, B ... Wide-stripe semiconductor laser of the present invention 1 ... Active layer 2, 3 ... Cladding layer 61 ... Stripe 61a ... Central protrusion 11 ... Light emitting region (p-type) Diffusion layer by dopant) 11a ... Window

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[Procedure amendment]

[Submission date] September 17, 1992

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Brief explanation of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a perspective view in which a part of a wide stripe type semiconductor laser of the present invention is cut away.

FIG. 2 is a more detailed vertical cross-sectional structural diagram of the wide-stripe semiconductor laser of the present invention.

3 (a) to 3 (d) are views showing the shape of a wide stripe adopted in the present invention.

FIG. 4 is a diagram illustrating a basic structure of a windowed semiconductor laser.

FIG. 5 is a perspective view showing another example of the wide stripe type semiconductor laser of the present invention.

FIG. 6 is a perspective view in which a part of a conventional wide stripe type semiconductor laser is cut away.

FIG. 7 is a vertical sectional structural view of the semiconductor laser shown in FIG.

FIG. 8 is a diagram showing a far-field pattern of a conventional wide-stripe semiconductor laser.

FIG. 9 is an explanatory view of a conventional semiconductor laser having a partially reflecting surface.

10 is a pattern explanatory view of a far-field image parallel to the active layer in the semiconductor laser shown in FIG.

[Description of Reference Signs] A, B ... Wide-stripe semiconductor laser of the present invention 1 ... Active layer 2, 3 ... Cladding layer 61 ... Stripe 61a ... Central protrusion 11 ... Light emitting region (diffusion layer by p-type dopant) 11a ... Window

Claims (1)

[Claims] 1. In a wide-stripe semiconductor laser, a central protruding portion is formed in a stripe so that the cavity length of the central portion is longer than that of both ends, and the oscillation gain in the central portion of the stripe is made larger than that of other portions. Wide-stripe semiconductor laser characterized by: