JPH05110191A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser element which easily enables the etching work to form a waveguide portion having a refraction index. CONSTITUTION:In a semiconductor laser element a protection layer 5 is provided between an active layer 4 and a second clad layer 6, the protection layer 5 is provided so that a band gap thereof becomes larger than that of the active layer 4 and the etching rate thereof becomes slower than that of the second clad layer 6. Simultaneously, a second striped projected part 12 is provided in the opposite surface of the active layer 4 in the second clad layer 6 in such a manner that it is projected on the opposite side of the active layer 4. Or, in the semiconductor laser element, a first striped projected part 11 is provided in the opposite surface of the active layer 4 in the first clad layer 3 symmetrically to the second striped projected part 12 for the active layer 4 in such a manner that it is projected on the opposite side of the active layer 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a first conductivity type semiconductor substrate, a first conductivity type first clad layer, an active layer, and a second conductivity type semiconductor substrate.
The present invention relates to a semiconductor laser device having a conductive second clad layer.

[0002]

2. Description of the Related Art In such a semiconductor laser device, stripe-shaped convex portions are provided on the second cladding layer so as to be convex on the side opposite to the active layer side, that is, the second cladding layer is mesa-shaped. A semiconductor laser device having a structure that is etched into is well known. In the semiconductor laser device having this structure, by further stacking a layer having a bandgap smaller than that of the active layer on the second clad layer, the refractive index of the region where the stripe-shaped protrusions are present is equal to that of the stripe-shaped protrusions. The region is effectively higher than that in the nonexistent region, and an effective refractive index distribution is generated in a direction perpendicular to the cavity direction and parallel to the active layer, so that single transverse mode oscillation and single longitudinal mode oscillation can be realized.

[0003]

However, in the above structure, when the second cladding layer is mesa-etched, it is necessary to perform etching so as to leave the region other than the mesa portion as thin as possible in order to create the above-mentioned refractive index distribution. is there. This etching operation needs to be performed with sufficient caution, which lowers the work efficiency, and even if the etching operation is performed carefully, it may cause overetching and damage the active layer, which reduces the production yield. There was an inconvenience. The present invention has been made in view of the above circumstances, and an object thereof is to provide a semiconductor laser device that can easily perform an etching operation without causing a reduction in yield.

[0004]

A semiconductor laser device of the present invention comprises a semiconductor substrate of a first conductivity type, a first clad layer of a first conductivity type, an active layer, and a second clad layer of a second conductivity type. The first characteristic configuration is that a protective layer is provided between the active layer and the second cladding layer, and the protective layer has a band gap of the band of the active layer. The second cladding is configured such that the etching rate of the protective layer is larger than the gap and is slower than the etching rate of the second cladding layer by the etching material that can etch the second cladding layer. In the layer, a second stripe-shaped convex portion that is convex on the side opposite to the active layer is provided on the surface opposite to the side where the active layer is present. The second characteristic configuration is the first characteristic configuration. Structure of semiconductor In the device, a first stripe-shaped convex portion that is convex on the side opposite to the side where the active layer is present in the side opposite to the side where the active layer is present in the first cladding layer is provided on the active layer. On the other hand, it is provided at a position symmetrical with the second stripe-shaped convex portion.

[0005]

According to the first characteristic structure, the first clad layer, the active layer and the second clad layer are sequentially laminated on the semiconductor substrate, and then the second clad layer is mesa-etched to form the stripe-shaped protrusions. At this time, for example, even if the concentration or temperature of the etching solution deviates from the set value and the etching thickness becomes thicker than a predetermined value and the portion of the second cladding layer to be etched is completely removed by the etching, Since the etching rate of the layer is slower than the etching rate of the second cladding layer, the etching apparently stops at the interface between the second cladding layer and the protective layer. That is, even if the etching conditions of the second clad layer vary to some extent, it is possible to prevent the active layer from being damaged by the etching by preventing the protective layer from being excessively etched. According to the second characteristic configuration, while the excessive etching is prevented by the protective layer as described above, each of the first stripe-shaped protrusions of the first cladding layer and the second stripe-shaped protrusions of the second cladding layer is The refractive index distribution due to the influence of is integrated into a refractive index distribution having a larger refractive index difference, and the position of the beam waist of laser light is perpendicular to the cavity direction and parallel to the active layer The so-called astigmatic difference that differs from the stacking direction can be reduced as much as possible.

[0006]

According to the first characteristic constitution, as described above, even if the etching conditions are slightly varied when the second cladding layer is etched, the protective layer prevents excessive etching and damages the active layer. Since this can be prevented, the etching operation can be easily performed without lowering the yield due to damage to the active layer. According to the second characteristic configuration, since the astigmatic difference can be reduced as much as possible, the emitted laser light can be easily focused on a minute spot.

[0007]

Embodiments of a semiconductor laser device to which the present invention is applied will be described with reference to the drawings. In the cross-sectional view perpendicular to the cavity direction shown in FIG. 1, an n-type GaAs buffer layer 2 is formed on an n-type GaAs substrate 1 serving as a first conductivity type semiconductor substrate.
N-type In _0.5 (G as first cladding layer of the first conductivity type)
a _0.3 Al _0.7 ) _0.5 P cladding layer 3, undoped In
GaP active layer 4, p-type In having a thickness of 0.05 to 0.1 μm
_0.5 (Ga _{1- X} Al _X ) _0.5 P (0 <X <0.7) protective layer 5, p-type In as second conductivity type second cladding layer
_0.5 (Ga _0.3 Al _0.7 ) _0.5 P clad layer 6, p-type G
Each layer of the aAs cap layer 7 is laminated, and n
An n-side electrode 8 is formed on the type GaAs substrate 1 side, and an insulating film 9 and a p-side electrode 10 are formed on the p-type GaAs cap layer 7 side.
Although not shown, the end surface of the laser element is a mirror surface due to cleavage.

Among these, the protective layer 5 is more
l The mixed crystal ratio is high, the Al mixed crystal ratio is lower than that of the second cladding layer 6, the bandgap is larger than that of the active layer 4, and the etching rate with a sulfuric acid-based etchant is higher than that of the second cladding layer 6. I'm also trying to be late. And n
In the In-type In _0.5 (Ga _0.3 Al _0.7 ) _0.5 P first cladding layer 3, the longitudinal direction is the laser cavity direction by photolithography after etching the n-type GaAs buffer layer 2 and etching techniques such as chemical etching or RIE. After forming a stripe-shaped concave portion corresponding to, the layers are stacked by liquid phase growth. As a result, the first clad layer 3 is formed with the first stripe-shaped convex portion 11 corresponding to the stripe-shaped concave portion of the buffer layer 2 and convex toward the side opposite to the side where the active layer 4 is present. The p-type GaAs cap layer 7 is formed of p-type In.
_0.5 (Ga _0.3 Al _0.7 ) _0.5 P After stacking the second clad layer 6, photolithography and chemical etching with a sulfuric acid-based etchant are performed so that the stripe-shaped convex portions have their longitudinal direction aligned with the laser cavity direction. In addition, the stripe-shaped concave portions formed in the n-type GaAs buffer layer 2 and the active layer 4 are formed so as to be positioned symmetrically with respect to each other, and then stacked by a liquid phase growth method or a growth method such as MBE. At this time, the etching depth of the second cladding layer 6 may be completely removed until the protective layer 5 is reached, or the second cladding layer 6 may be left slightly to control the etching depth. It has a wide allowable range and can be easily etched. Then, by this etching, the second stripe-shaped convex portion 12 which is convex on the side opposite to the side where the active layer 4 is present is formed. Furthermore, the p-side electrode 10 is formed into a striped insulating film 9 so that the longitudinal direction thereof coincides with the laser cavity direction by photolithography after forming the insulating film 9 and etching techniques such as chemical etching or RIE. Are removed by etching and then formed on the insulating film 9 by a vacuum deposition technique or the like.

In the semiconductor laser device having the above structure, p
The current injected from the side electrode 10 passes through the cap layer 7, the second cladding layer 6 and the protective layer 5 and reaches the active layer 4 for laser oscillation while the injection width is narrowed by the insulating film 9. The laser light generated in the active layer 4 leaks to both sides in the layer stacking direction by making the layer thickness of the active layer 4 sufficiently thin. The leaked laser light is not absorbed by the protective layer 5 having a bandgap larger than that of the active layer 4. Generally, when a portion that absorbs the laser light leaked outside the active layer and a portion that does not absorb the laser light are in contact with each other, a difference in refractive index occurs between them. That is, in the region where the first stripe-shaped protrusions 11 of the first cladding layer 3 and the second stripe-shaped protrusions of the second cladding layer 6 exist, the laser light leaked outside the active layer is not absorbed, and The laser light is absorbed in the regions on both the left and right sides, and a difference in refractive index occurs between the two regions.
In this way, the refractive index distribution is generated in the direction perpendicular to the cavity direction and parallel to the active layer. The factors causing this refractive index distribution act comprehensively from both sides of the active layer 4, and the laser light is confined in the regions corresponding to the first stripe-shaped convex portions 11 and the second stripe-shaped convex portions 12. As a result, the laser light is confined with a stronger refraction difference, and the positions of the beam waists in the direction perpendicular to the cavity direction and parallel to the active layer and the stacking direction of the layers are close to each other and the astigmatic difference occurs. Will be small.

[Other Example] In the above example, the first clad layer 3 was provided with the first stripe-shaped convex portion 11. However, the first clad layer 3 was left in a flat shape without providing the convex portion 11. Is also good. The etchant for etching the second clad layer 6 may be an etchant other than the sulfuric acid type. Further, the composition material may be, for example, an AlGaAs-based material other than the above InGaAlP-based material.

It should be noted that although reference numerals are given in the claims for convenience of comparison with the drawings, the present invention is not limited to the structures of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention.

[Explanation of symbols]

 1 1st conductivity type semiconductor substrate 3 1st conductivity type 1st clad layer 4 active layer 5 protection layer 6 2nd conductivity type 2nd clad layer 11 1st stripe-shaped convex part 12 2nd stripe-shaped convex part

Claims (2)

[Claims] 1. A semiconductor substrate (1) of a first conductivity type;
A semiconductor laser comprising a first clad layer (3) of conductivity type, an active layer (4), and a second clad layer (6) of second conductivity type.
In the device, a protective layer (5) is provided between the active layer (4) and the second cladding layer (6), and the protective layer (5) has a band gap of the active layer. The protective layer (5) which is larger than the bandgap of (4) and is made of an etching material which can etch the second cladding layer (6).
Of the active layer (4) in the second cladding layer (6), while the etching rate of the second cladding layer (6) is slower than the etching rate of the second cladding layer (6).
A semiconductor laser device having a second stripe-shaped convex portion (12), which is convex on the opposite side to the active layer (4), on the surface opposite to the side on which the present layer exists. 2. A first convex on the surface of the first cladding layer (3) opposite to the side where the active layer (4) is present, which is opposite to the side where the active layer (4) is present. 2. The semiconductor laser device according to claim 1, wherein a stripe-shaped convex portion (11) is provided at a position symmetrical to the second stripe-shaped convex portion (12) with respect to the active layer (4).