JPH02178987A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To reduce an astigmatic difference and to prevent the astigmatic difference from varying due to variation in output power by forming a first waveguide mechanism of a light absorption layer outside a groove and a layer thickness region of a first clad layer protruding into the groove, and increasing the thickness of a second clad layer of a stripelike region larger than that of a region except the region to form a second waveguide mechanism. CONSTITUTION:A first waveguide mechanism consists of a light absorption layer 1 outside a stripelike groove 10 of a width W1 and a region having a thickness larger than that of a first clad layer 3 protruding into a groove 10. The thickness of a second clad layer 5 in a stripelike region of a width W2 is larger than that of a second clad layer 5 in a region except the region in the stripelike region of the width W2 to form a second waveguide mechanism, and the groove width W1 is larger than the region width W2. A light generated in an active layer 4 is guided by the second waveguide mechanism on the basis of a refractive index difference of narrow width. Thus, an astigmatic difference can be reduced, and variation in the astigmatic difference due to output fluctuation is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device that stably oscillates up to high output and a semiconductor laser device that has low noise characteristics.

(Prior Art) Semiconductor lasers are being put into practical use as light sources for various optical information processing devices such as compact disc players and optical disc memories. In order to maximize its properties in these fields, it is important that semiconductor lasers oscillate in a stable fundamental transverse mode. Therefore, the semiconductor laser elements used in these devices usually have some type of refractive index waveguide mechanism.

As a semiconductor laser device having a refractive index waveguide mechanism, the sixth
V-channeled
5ubstrateInner 5tripe) lasers are well known. An nGaAs current blocking layer 102 is formed on a pGaAs substrate 101 by a liquid phase growth method,
A V-shaped groove 103 reaching the substrate 101 from the surface thereof is formed. Again, pAIG was continuously grown using the liquid phase growth method.
aAs cladding layer 104. A I GaAs active layer 10
5. n-AlGaAs cladding layer 106 and n-GaA
An s cap layer 107 is formed. Due to the characteristics of the liquid phase growth method, the cladding layer 104 grows filling the V-shaped groove 103, and the surface of the cladding layer 1.04 after growth becomes a flat surface. Furthermore, an n-side electrode 108 and a p-side electrode 109 are formed.

In this vsrs semiconductor laser, the current blocking layers 102 on both sides of the V-shaped groove 103 selectively absorb high-order transverse modes of the laser beam, so that extremely stable fundamental transverse mode oscillation
This occurs in the active layer 105 above the groove 103.

(Problem to be solved by the invention) The second semiconductor laser device oscillates in an extremely stable fundamental transverse mode from low output to high output, but since the refractive index waveguide is formed by optical absorption, the optical waveguide region is The wavefront of the guided laser light is curved. Therefore, the beam waist deviates from the end face of the laser element, resulting in an astigmatism difference. Moreover, this astigmatism difference changes depending on the optical output, so it becomes an even bigger problem when the optical output is changed. In a rewritable optical disk system, it is desirable that one semiconductor laser element perform both high-power writing operations and low-output reading operations. In such a case, since only one type of optical system is provided between the semiconductor laser element and the disk, it is necessary that the astigmatism difference does not change depending on the output of the laser beam.

The semiconductor laser device shown in FIG. 6 normally oscillates in a single mode. It is known that when a semiconductor laser device that oscillates in a single longitudinal mode is used in a video disk system, very large noise called return light noise is generated by reflected light from two disks. In order to reduce return noise, semiconductor laser devices that utilize automatic oscillation are often used.

The automatic oscillation laser device is obtained by setting the structural parameters to appropriate values in the sixth VSIS laser device. That is, it can be obtained by setting the difference in equipolar refractive index between the optical waveguide region of the V-shaped groove 103 and the regions on both sides of the V-shaped groove 103 to be appropriately small.

If the settings are shifted in this manner, the two oscillation spectrum I-waveforms become multi-longitudinal modes, the spectrum width of each longitudinal mode becomes wider, and low noise characteristics can be obtained.

However, to cause this automatic oscillation.

It is necessary to create an unstable state in which the distribution of carriers and light in the oscillation region varies temporally and spatially. This VS
In the IS self-oscillation laser, the carrier injection width and the light distribution are determined by the V-groove 103, so these cannot be changed independently. Therefore, it is not always possible to obtain carrier injection width and light distribution size suitable for self-sustained oscillation, and the yield of devices that produce self-sustained oscillation is extremely low.

The present invention has been made to solve the above-mentioned problems.9 The purpose of the present invention is to oscillate in the fundamental transverse mode, have a small astigmatism difference, and do not change the astigmatism difference depending on the output of the laser beam. An object of the present invention is to provide a semiconductor laser device. Another object of the present invention is to provide an automatic oscillation semiconductor laser device having a structure capable of producing self-oscillation devices at a high yield.

(Means for Solving the Problems) The semiconductor laser device of the present invention has a laminated structure including a light absorption layer, a first cladding layer, an active layer, and a second cladding layer, and has a stripe shape with a width of 1 W. A first waveguide mechanism is formed by the light absorption layer outside the groove and a thicker region of the first cladding layer where the first cladding layer protrudes into the groove. A second waveguide mechanism is formed by making the thickness of the second cladding layer in the striped area larger than the thickness of the second cladding layer in areas other than the striped area, and the width W1 is larger than the width W2, thereby achieving the above object.

In addition, the semiconductor laser device of the present invention has a laminated structure having a light absorption layer, a first cladding layer, an active layer, and a second cladding layer, and the light absorption on the outside of a striped groove having a width of 2W. a first cladding layer protruding into the groove;
A waveguide mechanism is formed by a thicker region of the cladding layer, and a carrier injection path with a width W3 is formed in the second cladding layer, and the width W1 is larger than the width W3. ” Objective 2 is achieved.

(Function) The semiconductor laser device of the present invention has two waveguide mechanisms. The light generated in the active layer is guided by a second waveguide mechanism having a narrow width (W2). The basic transverse mode is mostly W2
However, since the second higher-order transverse mode seeps out to a large extent in the direction of the junction surface, it is absorbed by the light absorption layer outside the groove forming the first waveguide mechanism. Only the fundamental transverse mode is selectively guided by absorption of the higher-order transverse mode.

Since the fundamental transverse mode is guided by the second waveguide mechanism based on the refractive index difference, the astigmatism difference can be reduced. Furthermore, the astigmatism difference does not change even if the output changes.

Further, in the semiconductor laser device of the present invention, since the gear injection path and the waveguide mechanism are separated, the light distribution and the width of the carrier injection path can be changed independently. Therefore, it is possible to set the size of the light distribution and the width of the carrier injection path suitable for automatic oscillation.

(Example) Examples of the present invention will be described below.

The first part is a cross-sectional view showing an embodiment of the semiconductor laser device of the present invention. The manufacturing process will be explained below. p-G
An n-GaAs current blocking layer 2 (about 1 μm thick) is grown on the aAs substrate 1 by liquid phase growth. This current blocking layer 2 acts as a light absorption layer. Next, this current blocking layer 2
A striped groove 10 with a width W of 711 m was formed from the surface of the substrate 1 to the substrate 1. p=A again by liquid phase growth method
IGaAs first cladding layer 3 (thickness 1.2 μm),
AlGaAs active layer 4 (thickness 4 μm), n-AIC
; an aAs second cladding layer 5 (thickness: 1..2 μm) and an n-GaAs cap layer 6 (thickness: 0.5 μm) were continuously formed. Next, using a photolithography method and a dry etching method, two wooden side grooves 11 and 1 with a diameter of 10 μm are formed from the surface of the cap layer 6 to the second cladding layer 5.
2 was formed. By forming these two side grooves 11 and 12, a ridge portion 13 having a width W2-4 μM was formed. Gutter 1
1 and 12, the residual thickness dc of the second cladding layer 5 is from 0.2 to
0°3μ''. Next, plasma CV
The SiNx insulating film 7 was formed by method D, and the SiNx insulating film on the upper flat surface of the ridge portion 13 was removed again using photolithography or the like. Next, polish substrate 1 to approximately 1
The n-side electrode 8 and the p-side electrode 9 were formed to have a thickness of 0.00 μm.

In this embodiment, a first waveguide based on optical absorption is formed by the second cladding layer 5 inside the groove 10 having a width W1-7 μm and the current blocking layer 2 outside the groove 10.

Furthermore, the ridge portion 13 having a width W2-4 μm and the two side grooves 11 and 12 on the outside of the ridge portion 13 form two regions of the second cladding layer 5 having different thicknesses. A second waveguide is formed based on the equipolarized refractive index difference that occurs between these two regions.

The light generated in the active layer 4 is first guided by a second waveguide having a smaller width. The fundamental transverse mode is guided to the region where the ridge portion 13 having the width W2 exists.

The higher-order transverse mode oozes out more toward the junction surface of the semiconductor laser element than the fundamental transverse mode, so the ridge portion 13
The current leaks outward from the region where the current exists and is absorbed by the current blocking layer 2 constituting the first waveguide. and the second
Since a refractive index waveguide mechanism operates in the waveguide, the astigmatism difference of the emitted laser light is reduced and does not change even with output fluctuations.

In this example, the astigmatism difference was 5 μm or less. Furthermore, the astigmatism difference hardly varied from low to high output.

FIG. 2 is a sectional view showing a second embodiment of the invention.

A strip-like groove 30 (width W, = 7 μm) is formed on the n-GaAs substrate 21, and the n-GaAs first cladding layer 22. AlGaAs active layer 23. p-
A, ]GaAs second cladding layer 24. and p −G a
The AS cap layer 25 was continuously laminated. Next, the width W
In order to form a 2-4 μm ridge portion 33, two side grooves 31 and 32 reaching the second cladding layer 24 were formed.

In these side ditches, the residual thickness of the first and second cladding layers is 0.2 to 0.
It is formed to have a thickness of 3 μm. Furthermore, a SiNx insulating film 26 was formed in a portion excluding the ridge portion 33. Ridge part 3
An n-side electrode 27 and an n-side electrode 28 were formed on the substrate 21 and on the substrate 21, respectively.

In this embodiment, the light absorption layers on both sides of the groove 30 are formed of the substrate 21. The substrate 21 is an n-type semiconductor, which is the opposite of the embodiment shown in FIG. Since the diffusion rate of electrons in the semiconductor is greater than that of electrons, the width of the region where the gain of the active layer can be obtained is limited by the ridge portion 27 in this embodiment.

In this example as well, the astigmatism difference was as small as about 5 μm. Changes in astigmatism were also small due to output fluctuations.

A third embodiment of the present invention is not shown in FIG. Striped grooves 50 (width W-7 μm) are formed in the n-GaAs substrate 41, and n-AIGaA, s first
Cladding layer 42. AI, Ga1. , yAS active layer 43.
p-AIX Ga1-, lAs second cladding layer 44. n
A lz Ga+-z As current blocking layer 45 (z
>x), and an n-GaAs surface protective layer 46 was grown.

Next, width W2=
A 4gm striped two-part groove 54 was formed. In this embodiment, by changing the Al mixed crystal ratio in the second cladding layer 44 and the current blocking layer 45, the current blocking layer 45 can be selectively formed.
5 can be etched. Next, p-
Alu Ga+-u As cladding layer 47 (IJ<z)
, a p-GaAs scan layer 48 was grown.

Next, the substrate 42 side of the wafer is polished to about 100 μm,
An n-side electrode 51 and an n-side electrode 52 were formed.

In this embodiment as well, the light absorption layer outside the groove 50 is formed by the substrate 41.

In the semiconductor laser device of this embodiment, since the oscillation region is completely buried in the crystal layer, the heat dissipation characteristics are improved.

The astigmatism difference of the semiconductor laser device of this example was about 5 μm. Changes in astigmatism due to output fluctuations were also small.

No. 1111 shows a fourth embodiment of the present invention. n-GaA
A striped groove 50 (width W-7 μm) is formed on the s-substrate 41, and then n-A, ]GaAs is formed by liquid phase growth.
First class layer 42. AlGaAs active layer 43. p-
AlGaAs second cladding layer 44. After forming a p-GaAs regrowth auxiliary layer 60, a mesa portion 55 having a width W2-4 μm was formed by photolithography and etching. Next, an n-CaAs buried layer 61 and a p-GaAs scan 1 layer 62 were formed by MOCVD. Furthermore, n
A side electrode 51 and an n-side electrode 52 were formed.

The astigmatism difference of the semiconductor laser device of this example was about 5 μm. Changes in astigmatism due to output fluctuations were also small.

The fifth embodiment of the present invention is shown in the fifth leap. The semiconductor laser device of this example has a laminated structure similar to that shown in FIG. Unlike the embodiment shown in FIG. 2, the width W2 of the ridge portion 33 formed by the side grooves 31 and 32 is
is 2 to 3 μm, which is small. and gutter 31
The depth of grooves 31 and 32 is also small, and the second groove under side grooves 31 and 32 is
The thickness dc of the cladding layer 24 is 0.4 to 0.5. ! /I
It is I+ and thick.

In this embodiment, the thickness of the second cladding layer 24 in the ridge portion 33 and the side grooves 31 and 32 is large, so the refractive index waveguide mechanism in these portions is weak. Therefore, the light is guided by a waveguide formed by the first cladding layer 22 in the groove 30 and the substrates 21 on both sides of the groove 30. Width W of groove 30
, is larger than the width W2 of the ridge portion 33 serving as a carrier injection path, the light distribution becomes larger than the carrier injection path, resulting in an automatic oscillation state. As described above, according to the configuration of this embodiment, the width of the carrier injection path and the size of the light distribution can be set independently.

Noise level (S/N ratio) of the semiconductor laser device of this example
is approximately 956.0 for a light output of 3 to 5 mW. It was B. The yield of devices that produce self-assisted oscillation was about 80%.

(Effects of the Invention) The semiconductor laser device of the present invention has such a small astigmatism difference and small fluctuations in the astigmatism difference over a wide output range, so it can also be used in a rewritable optical disk system.

Furthermore, the semiconductor laser device of the present invention has low noise characteristics due to automatic oscillation, and devices that generate automatic oscillation can be manufactured at a high yield.

~1-1-0 before the old 11 page FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the invention, FIG. 3 is a sectional view showing a third embodiment of the invention, and FIG. 4 is a sectional view showing a fourth embodiment of the invention. , FIG. 5 is a sectional view of an automatic oscillation semiconductor laser device showing a fifth embodiment of the present invention, and FIG. 6 is a sectional view showing an example of a semiconductor laser device having a conventional waveguide mechanism based on light absorption. .

1-p-G a As substrate, 2- n-G a
A s current blocking layer, 3...P-△l CaAs first
Cladding layer 4 ・AIGaAs active layer,
5-n-AIGaAS second cladding layer, 10,30.5
0...Groove, ■112.31. ．． 32...Gutter, 13
...Ridge portion, 2141-n-GaAs substrate, 22.
42-n-AGaAs first cladding layer, 23.43-A
IGaAs active layer, 24.44.=p-AIGaAs second cladding layer, 45...n-A]GaAs current blocking layer 54...upper groove, 55... mesa portion.

2.

Claims (1)

[Claims] 1. A multilayer structure including a light absorption layer, a first cladding layer, an active layer, and a second cladding layer, and the light absorption layer outside a striped groove having a width W_1; A first waveguide mechanism is formed by the first cladding layer and a thicker region of the first cladding layer protruding into the groove, and a first waveguide mechanism is formed by the first cladding layer and a thicker region of the first cladding layer protruding into the groove, and A semiconductor laser device in which the thickness of the cladding layer is made larger than the thickness of the second cladding layer in a region other than the region to form a second waveguide mechanism, and the width W_1 is larger than the width W_2. 2. A laminated structure having a light absorption layer, a first cladding layer, an active layer, and a second cladding layer, the light absorption layer outside the striped groove having a width W_1 and the first cladding layer. A waveguide mechanism is formed by a thick region of the first cladding layer protruding into the groove, a carrier injection path having a width W_3 is formed in the second cladding layer, and the width W_1 is A semiconductor laser element with a width larger than W_3.