JP2515725B2 - Semiconductor laser equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device, and more particularly to a device having no astigmatism and excellent noise characteristics, and a manufacturing method thereof.

[Background of the Invention]

In the so-called refractive index waveguide type device in which the laser light distribution (transverse mode) of the semiconductor laser is confined by using the refractive index of the central portion of the stripe and its outside, the oscillation spectrum line (longitudinal mode) becomes single. When such a device is used for an optical disc, return light noise due to the reflected light from the disc does not occur, but so-called astigmatism in which the position of the beam waist differs in the direction parallel to the vertical direction of the active layer,
There is a drawback that the laser beam cannot be narrowed down. Therefore, there is a demand for a device element in which the longitudinal mode is multimode and there is no astigmatism.

To this end, a method of changing the stripe structure in the optical axis direction of the semiconductor laser so that the difference in the refractive index inside the device is small and the difference in the refractive index at the laser light emitting end face is large is described in “Rib optical waveguide mode”.・ Characteristics of filter type GaAlAs laser “The 31st Spring Meeting of the Japan Society of Applied Physics, Showa 59.3.29-
4.2, Proceedings 30a-M-8.

[Object of the Invention]

The object of the present invention is to have good noise characteristics and no astigmatism,
In particular, it is to provide a semiconductor laser device suitable for an optical disc such as a video disc or a compact disc.

[Outline of Invention]

The inventor of the present application forms a stripe-shaped light emitting region in the active layer, and in the vicinity of the light end face portion of the light emitting region, the refractive index difference between the central portion of the stripe and its outer edge portion is large, and the light emitting region of the light emitting region is large. As a means for reducing the refractive index difference in the central portion, a method of making the width of the upper side of the stripe in the central portion of the light emitting region larger than the upper side of the stripe in the vicinity of the light end face was found. It was confirmed that ratio and transverse mode unification could be easily achieved.

In this case, in the inside of the device, the distance between the active layer and the current confinement layer (outer edge of the stripe) becomes large in the central part of the light emitting region, so that the current density in the central part of the stripe becomes small,
The difference in refractive index from the outer edge portion becomes small.

 FIG. 1 shows an example of a plan view of a device according to the present invention.

Example of Invention

 Examples of the present invention will be described below.

Example 1 will be described with reference to FIGS.

FIG. 1 is an example of a plan view of a laser device according to the present invention. 2 and 3 are sectional views taken along the lines AA 'and BB' in FIG.

On the n-type GaAs substrate 1, an n-type GaAlAs cladding layer 2, an undoped layer GaAlAs active layer 3, a p-type GaAlAs cladding layer 4, n.
After the type current constriction layer 5 was sequentially formed, first, the grooves 6 and 7 were formed in the current confinement layer 5 by using the chemical etching method. Groove 6
The upper side has a width of 3 to 6 μm, and the lower side (the side in contact with the active layer) has a width of 2 to 5 μm. The upper width of the groove 7 is 8-10 μm
The width of the lower portion is 7 to 9 μm, and the width of the groove contacting the active layer, that is, the residual GaAs layer is 2 to 5 μm. Also remains
The thickness d of the GaAs layer was 0.1 ± 0.05 μm.

Subsequently, a p-type GaAlAs cladding layer 8 and a p ⁺ -type GaAs cap layer are sequentially formed, and then a Cr-Au electrode 10 and an AuGe / Ni / Au electrode 11 are formed.
Was formed by vapor deposition.

Then, cleavage was performed to obtain a semiconductor laser. The astigmatism of this semiconductor laser was 5 μm or less, which was sufficiently small. Note that p
-Type GaAlAs cladding layer 4 has a thickness of 0.2-0.4 μm, active layer 3
The effect of the present invention was remarkable when the thickness was 0.03 to 0.1 μm. Further, the laser light was in a multimode inside the active layer, and the relative noise intensity due to the returning light was 1 × 10 ⁻¹³ Hz ⁻¹ or less.

The thickness of each of the other layers is 0 for the n-type cladding layer 2.
8 to 2 μm, the n-type current confinement layer 5 to 0.5 to 1.0 μm, the p-type cladding layer 8 to 0.6 to 1.8 μm, and the p ⁺ -type GaAs cap layer 9 to 0.
The AlAs composition ratio of each layer is 35 to 55% for the n-type cladding layer 2, p-type cladding layers 4 and 8 and 5 to 20% for the active layer 3, and good results are obtained in these ranges. Was obtained.

Example 2 will be described with reference to FIGS. FIG. 4 is a sectional view taken along the line AA ′ in FIG. 1 of the laser device according to this embodiment, and FIG. 5 is a sectional view taken along the line BB ′ similarly.

In the first embodiment, the current confinement layer 5 is multilayered so that residual GaAs is formed.
In this embodiment, the controllability of the layer thickness d is improved.

The current confinement layers 5 and 5'are formed of n-type GaAs, and the n-type GaAs (Al / As ratio: 0.4 to 0.55) layer 12 is formed between them to form GaAs.
Grooves are formed in layers 5 and 5'by dry etching and
Grooves were formed in the layer 12 by a chemical etching method. By this method, the thickness of the current constriction layer 5'can be stably formed.

On the p-type GaAlAs cladding layer, current confinement layer 5 ', GaAlAs
After sequentially forming the layer 12 and the current confinement layer 5, a part of the groove 6 is first formed by the dry etching method, and at the same time, the current confinement layer 5 in the central portion of the groove 6 is expanded by the dry etching method, and then the exposed GaAlAs layer is formed. 12 was removed by chemical etching. At this time, since the GaAs layer 5'is difficult to be etched by the chemical etching method, it is not etched in a short time. Then, using the mask material, the n-GaAs current constriction layer 5'is also etched and removed in a stripe shape by the dry etching method to form the groove 7.

The characteristics of the laser device having this structure were similar to those of the first embodiment.

Example 3 will be described with reference to FIG. 1 and FIGS.

Even if the cross-sectional shape of the end face and / or the vicinity of the end face of the semiconductor laser, that is, the cross-sectional view taken along the line AA 'in FIG. It was possible.

Further, the cross-sectional shape of the groove 7 inside the laser device, that is, the cross-sectional shape along BB 'in FIG. 1 may be an inverted trapezoid shown in FIG. Also, good results were obtained with a curved cross-sectional shape as shown in FIGS.

In the above description of the embodiments, the material is GaAlAs / GaAs system, but it may be InGaAsP / InP system or InGaP / GaAs system, and even if the conductivity type of the semiconductor is completely reversed, that is, the p-type and the n-type are completely reversed. The effect of the present invention can be obtained even if the active layer is p-type or n-type.

〔The invention's effect〕

Since the semiconductor laser of the present invention has a small return light noise and a small astigmatism, it does not require an isolator or an astigmatism correction lens, or can be simplified. Therefore, a device such as a video disk or a compact disk can be used. It has the effect of achieving higher performance, smaller size, and lower price.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a current confinement layer provided inside the laser device of the present invention, and FIGS. 2, 4 and 6 are A of FIG. 1 of the laser device.
A sectional view taken along the line A-A 'and FIGS. 3, 5 and 7 to 9 are sectional views taken along the line BB' in FIG. 1 of the laser apparatus. 1 ... Substrate, 2, 4, 8 ... Cladding layer, 3 ... Active layer, 5,
5 '... current confinement layer, 6 ... groove on the end face and / or in the vicinity of the end face provided on the current confinement layer, 7 ... groove inside the device provided on the current confinement layer, 9 ... cap layer, 10, 11 ... … Electrodes, 12
... n-type GaAlAs current confinement layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shun Kajimura 1-280 Higashi Koigakubo, Kokubunji City Central Research Laboratory, Hitachi, Ltd. (56) References JP-A-60-224291 (JP, A)

Claims (5)

(57) [Claims] 1. A semiconductor laser device comprising a semiconductor substrate having a multi-layered semiconductor layer including an active layer, the semiconductor laser device having a current confinement layer having a clad layer and a groove formed above the active layer. The difference between the width (W ₁ ) of the groove provided in the current confinement layer on the side close to the active layer and the width (W ₂ ) on the upper side of the groove, the width at the end face of the semiconductor layer or at the end face and in the vicinity thereof. The semiconductor laser device is characterized in that the difference in the width inside the semiconductor layer is made larger than the difference. 2. The semiconductor laser device according to claim 1, wherein the current confinement layer is formed of a semiconductor multilayer film. 3. The (W ₂ −W ₁ ) at the end face of the semiconductor layer
The semiconductor laser device according to claim 1, characterized in that 4. The semiconductor laser device according to claim 1, wherein the width of the groove on the side close to the active layer is substantially constant. 5. The semiconductor laser device according to claim _{1, wherein} (W ₂ −W ₁ ) is a positive value.