JPS61281571A - Semiconductor laser device and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce noises and astigmatism by making the difference between width on the inside of a semiconductor layer larger then that in the end surface of the semiconductor layer and a section in the vicinity of the end surface. CONSTITUTION:N-type CaAlAs clad layers 2, undoped GaAlAs active layers 3, P-type GaAlAs clad layers 4 and N-type current constriction layers 5 are formed onto N-type GaAs substrates 1 in succession, and grooves 6 and 7 are shaped to the current constriction layers 5 by using a chemical etching method. The upper width of the groove 6 extends over 6-6mum and the upper width of the groove 7 over 8-10mum, and the width of the grooves of residual GaAs layers extends over 2-5mum. P-type GaAlAs clad layers 8 and P<+> type GaAS cap layers 9 are shaped successively, and Cr-Au electrodes 10 and AuGe/Ni/Au electrodes 11 are evaporated and formed. The astigmatism of the semiconductor laser is reduced as 5mum or less, laser beams are changed into a multimode in the active layers, and relative noise strength by return beams extends over 1X10<-13>Hz<-1> or less. Accordingly, the performance of a device apparatus can be improved and size thereof may be miniaturized and cost thereof reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a semiconductor laser device, and particularly to a device free from astigmatism and having good noise characteristics, and a method for manufacturing the same.

[Background of the invention]

In a so-called refractive index waveguide device in which the laser light distribution (transverse mode) of a semiconductor laser is confined using the refractive index between the central part of the stripe and the outside thereof, the oscillation spectrum line (longitudinal mode) becomes single. When such a device is used for an optical disk, return optical noise due to reflected light from the disk does not occur, but so-called astigmatism occurs, where the beam waist position is different in the vertical and parallel directions of the active layer. The drawback is that the laser beam cannot be narrowed down. For this reason, a device element is desired that has a multi-mode longitudinal mode and is free from astigmatism.

To achieve this, a method is proposed by Shimada et al. in which the stripe structure is changed in the optical axis direction of the semiconductor laser, and the difference in refractive index is made small inside the device and the difference in refractive index is made large at the laser beam emitting end face.
゛°Lip optical waveguide mode filter type GaAtAs
This is known from ``Characteristics of Lasers'', 31st Spring Conference of the Japan Society of Applied Physics, 3/29/1980-4°2, Proceedings 30a-M-8.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor laser device with good noise characteristics and no astigmatism, which is particularly suitable for use in optical disks such as video disks and compact disks.

[Summary of the invention]

The inventor of the present application forms a striped light emitting region in the active layer, and in the vicinity of the optical end face of the light emitting region, the refractive index difference between the center part of the stripe and the outer edge thereof is large,
As a means for reducing the difference in refractive index in the center of the light emitting region, a method was discovered in which the width of the upper side of the stripe in the center of the light emitting region was made larger than the width of the upper side of the stripe in the vicinity of the optical end face, and this method It was confirmed that it is possible to easily achieve multiple longitudinal modes and single transverse modes.

In this case, inside the device, the distance between the active layer and the current confinement layer (outer edge of the stripe) becomes long in the center of one light emitting region, so the current density in the center of the stripe is small, and the difference in refractive index with the outer edge gives a small force.

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

[Embodiments of the invention]

The present invention will be explained in detail below.

Example 1 ゛1st to 3rd
This will be explained using figures.

FIG. 1 is an example of a plan view of a laser device according to the present invention. Figures 2 and 3 represent AA/and B in Figure 1.
- It is a sectional view at 'B'.

On an n-type GaAs substrate 1, an n-type Q'aA'tAS cladding layer 2, an undoped GaAtAs active layer 3, and a p-type Qa
After sequentially forming the AtAS cladding layer 4 and the n-type current confinement layer 5, grooves 6 are first formed in the current confinement layer 5 using chemical etching.
and 7 were formed. The width of the upper side of the groove 6 is 3 to 6 μm, and the width of the lower side (the side in contact with the active layer) is μm. The width of the upper side of the groove 7 is 8 to 10 μm.

The width of the lower portion is 7 to 9 μm, and the width of the groove in the portion in contact with the active layer, that is, the remaining Q a A 8 layer is 2 to 5 μm.

Also, the thickness of the residual GaAs layer dFiO, 1±0.
05pm.

Subsequently, a p-type GaAtAs cladding layer 8. p1 type Ga
An AS cap layer was sequentially formed, and then a Cr-Au electrode 10s AuGe/N1/A11 electrode 11 was formed by vapor deposition.

Next, the semiconductor V was obtained by folding. The astigmatism of this semiconductor laser was sufficiently small at 5 μm or less. Note that the thickness of the p-type GaAtAs cladding layer 4 is 0.2 to 0.4%.
pm, and the thickness of the active layer 3 was 0.03 to 0.1 μm, the effect of the present invention was remarkable. Further, inside the active layer, the laser light was not multi-mode, and the relative noise intensity due to the returned light was less than IXIO Hz-'.

The thickness of each other layer is 0.8 to 2 μm for the n-type cladding layer 2, and 0.5 to 1.0 μm for the n-type current confinement layer 5.
m, "p-type cladding layer 8 is 0.6 to 1.8 tt m
% p1 type QaAs cap layer 9 is 0.5 to 5 μm,
The AtAs 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 55 for the active layer 3.
20 inches, and good results were obtained within these ranges.

Example 2 This will be explained using FIGS. 1, 4 and 5. FIG. 4 is a sectional view taken along line AA' in FIG. 1 of the laser and apparatus according to this embodiment, and FIG. 5 is a sectional view taken along line BB' in the same way.

The current confinement layer 5 in Example 1 is multilayered to reduce residual Ga.
This example improves the controllability of the thickness d of the AS layer.

Current confinement layers 5 and 5' are formed of n-type Q a S, and n-type GaAtAs (A L / A S
Ratio: 0.4 to 0.55) layer 12 is formed, and grooves are formed in the G'aAS layers 5 and 5' by dry etching.
Grooves were formed in the AtAs layer 12 by chemical etching. By this method, the thickness of the flow constriction layer 5' could be stably formed.

After sequentially forming the current confinement layer 5', the GaAtAs layer 12, and the current confinement layer 5 on the p-type QaAtAs cladding layer, first, a part of the groove 6 is formed by dry etching, and at the same time, a part of the groove 6 is etched. The current confinement layer 5 at the center was expanded using a dry etching method, and then the exposed QaAtAS layer 12 was removed using a chemical conversion method. At this time, since the GaAs layer 5' is difficult to be etched by chemical etching, it is not etched in a short period of time. Next, using a J mask material, the n-GaAs current confinement layer 5' was etched and removed in stripes by Sitri etching to form a groove 7.

The characteristics of the laser device with this structure were also similar to those in Example 1.

Example 3 This will be explained using FIG. 1 and FIGS. 6 to 9.

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 line AA′ in FIG.
As shown in the figure, the present invention could be practiced even if the cross-sectional shape of the groove 6 was made into a t2 rectangle.

Furthermore, the cross-sectional shape of the groove 7 inside the laser device, that is,
Good results were obtained for the cross-sectional shape taken along line BB' in FIG. 1 with an inverted trapezoid as shown in FIG. 7 and with curved cross-sectional shapes as shown in FIGS. 8 and 9.

In the description of the above embodiments, the material is QaAtAS/GaAs.
However, it is an InGaA8P/In P system.

The InGaP/GaAs system may be used, or the conductivity type of the semiconductor may be completely reversed, that is, p-type and n-type! Even if completely inverted, there is often a p-stretch layer on the bottom.

``C%4 2)''E also had a book = effect. -, 1 The semiconductor laser of the present invention has low return beam noise and little astigmatism, so it does not require an isonometer or an astigmatism correction lens, or can be simplified, so it can be used for video discs and compact discs. , high-performance equipment such as disks! miniaturization, low price "°:l:nini:'"v-I
+J"Ht'F"1THJK*I/'j, 2)□,

[Brief explanation of the drawing]

Plan views of the flow constriction layer, Figures 2, 4 and 6 are cross-sectional views of the laser device taken along line AA' in Figure 1, Figures 3.5 and 7.
FIG. 9 is a sectional view taken along line BB' in FIG. 1 of the laser device. (a) 1...Substrate, 2,4.8...Clad layer, 3...
Active layer, 5.5'... Current confinement layer, 6... Groove at the end face and/or the vicinity of the end face provided in the current confinement layer, 7...
Groove inside the device provided in the current confinement layer, 9... Cap layer, 10° 11... Electrode, 12... N-type GaAtAs
Current confinement layer.

Claims (1)

[Scope of Claims] 1. A semiconductor laser formed of a multilayer semiconductor layer including an active layer on a semiconductor substrate, which has a cladding layer and a current confinement layer formed with a groove above the active layer. In a laser, the width of the groove provided in the current confinement layer on the side closer to the active layer (W_1) and the width on the upper side of the groove (W_2)
1. A semiconductor laser device characterized in that the difference in width inside the semiconductor layer is larger than the difference in width at an end face of the semiconductor layer or at and near the end face of the semiconductor layer. 2. The semiconductor laser device according to claim 1, wherein the current confinement layer is formed of a semiconductor multilayer film. 3. (W_2-W_1) on the end surface of the semiconductor layer
2. The semiconductor laser device according to claim 1, wherein: is set to zero. 4. The semiconductor laser device according to claim 1, wherein the width of the groove on the side closer 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. 6. A semiconductor laser that is formed of a multilayer semiconductor layer including an active layer on a semiconductor substrate, and has a current confinement layer in which a cladding layer and a groove are formed above the active layer, the current confinement layer being provided with a current confinement layer. The width of the groove on the side closer to the active layer (W_1
) and the upper width of the groove (W_2), in a semiconductor laser in which the difference in width inside the semiconductor layer is larger than the difference in width at the end face of the semiconductor layer or the end face and the vicinity thereof, 1. A method of manufacturing a semiconductor laser device, characterized in that the layer is formed by an organic metal thermal decomposition method, and the groove is formed by a dry etching method or a chemical etching method.