JPH02187089A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To reduce an oscillation threshold current and to enable self-excited oscillation in a wide output range by forming an active layer of multi quantum well structure and by setting an equivalent refraction factor difference between a region near a current injection path and a region of the outside thereof to a specified value. CONSTITUTION:A first clad layer 3, a first optical guide layer 4, an active layer 5 of multi quantum well structure, a second optical guide layer 4', and a second clad layer 6 are laminated on a semiconductor substrate 1. A thickness of the clad layer 6 at an outside of a ridge section 31 is made 0.2 to 0.6mum and an equivalent refraction factor difference between an outside and an inside of a region near the ridge section 31 is made 3X10<-4> to 5X10<-3>. A light confinement section is formed in a region near an emission edge face by breaking the active layer 5 of multi quantum well structure. According to this constitution, an oscillation threshold current can be reduced and self-excited oscillation can be realized in a wide output range since the active layer 5 is provided with a quantum well structure. Moreover, astigmatic difference can be reduced by forming a light confinement section to the region near the emission edge face and thereby strengthening a refraction factor waveguide mechanism.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device having low noise characteristics and a small astigmatism difference.

(Prior Art) Semiconductor laser elements have been put into practical use as light sources for audiovisual equipment and optical information processing.

One of the characteristics required of the semiconductor laser elements used in these devices is that the intensity of return light noise induced by reflected light from an optical disk or the like is small. In order to reduce optical feedback noise, there are semiconductor laser devices that utilize a phenomenon called automatic oscillation.

FIG. 6 shows an example of a conventional self-oscillation semiconductor laser device. This semiconductor laser device has VSIS for current confinement.
(V-channeled 5ubstrate In
ner Stripe) structure. This semiconductor laser device is manufactured as follows. p-GaAs
After forming the n-GaAs current blocking layer 16 on the substrate 11,
A V-shaped groove 23 reaching the substrate 11 is formed. Further p −
G ao, ssA lo, asA S cladding layer 12. p-Gao, ssA lo, +sA S active layer 13. n Gao, 5sA1o, 45AS cladding layer 14. n-GaAs key? After sequentially stacking the seven plates 7115, the P-side electrode 21 and the n-side electrode 22 are formed.

In this semiconductor laser device, the V-shaped groove 23 of the cladding layer 12
The outside thickness d and the thickness d2 of the active layer 13 are set to 0.3 μm and 0.12 μm, respectively. By setting the thicknesses d and d2 in this way, the difference Δn in equivalent refractive index between the upper part of the V-shaped groove 23 and the other parts can be set to about 3×10 −3 . If the equipolarized refractive index difference Δn is made small in this way, it becomes possible to cause self-assisted oscillation. Due to automatic oscillation, the oscillation spectrum becomes multi-longitudinal mode, and the width of each longitudinal mode becomes wider, thereby reducing the return optical noise.

(Problem B to be Solved by the Invention) In the automatic oscillation laser shown in FIG. 6, the equipolarized refractive index difference Δn is small, so the refractive index waveguide mechanism is weak.

Therefore, the distribution of light in the waveguide is large.

Since the distribution of light is large, light is absorbed by the current blocking layer 16 and the substrate 11 in regions other than the region where gain can be obtained. Such light absorption causes a disadvantage that the oscillation threshold current increases. The oscillation dark value current of the semiconductor laser device shown in FIG. 6 has a large value of 45 mA or more when the resonator length is 250 μm.

Furthermore, since the refractive index waveguide mechanism is weakened in this semiconductor laser element, the characteristics of the emitted light become close to those of a gain waveguide type semiconductor laser element. Therefore, there is a drawback that the astigmatism difference becomes large. In the semiconductor laser device shown in FIG. 6, the astigmatism difference is a large value of 15 μm or more.

Furthermore, since this semiconductor laser device has a double heterostructure, the refractive index of the two active layers tends to change depending on the amount of injected carriers. Therefore, as the optical output changes, the equipolarized refractive index difference Δn also changes, and there is a drawback that automatic oscillation cannot be maintained up to high output.

The present invention has been made in order to solve the above-mentioned problems. 2. The purpose of the present invention is to provide a self-oscillating laser with a small oscillation dark value current, which is capable of maintaining automatic oscillation over a wide output range. It is an object of the present invention to provide a semiconductor laser element which can be used as a laser diode and has a small astigmatism difference.

(Means for Solving the Problems) A semiconductor laser device of the present invention was formed on a semiconductor substrate. A laminated structure including a first cladding layer, a first optical guide layer, an active layer having a multi-quantum well structure, a second optical guide layer, and a second cladding layer, and a stripe formed above the laminated structure. the second cladding layer has a thickness of 0.2μ in an area outside the current injection path;
1 m to 0.6 μm, and the equipolarized refractive index difference between the inner and outer regions of the current injection path is 3×10 −4 to 5×1
0-' in the vicinity of at least one end face.

The above object is achieved because the portion of the active layer below the outside of the current injection path is an optical confinement portion having a lower refractive index than the active layer below the current injection path. Further, the confinement portion may be formed by destroying the multi-quantum well structure of the active layer, and further, the confinement portion may be formed by destroying the multi-quantum well structure of the active layer, and further, the confinement portion may be The refractive index difference between the cladding layer and the oscillation wavelength can also be set to 0.065 to 0.2.

(Function) In the semiconductor laser device of the present invention, since the active layer has a quantum well structure, the oscillation dark value current can be reduced. Furthermore, a current injection path for current confinement is formed above the active layer.

It can be made into a current confinement structure that does not absorb light.

This also makes it possible to reduce the oscillation dark value current. Further, automatic oscillation can be caused by setting the difference in equivalent refractive index between the region near the current injection path and the other region to 3×10 −′ to 5×10 −3 .

An optical confinement portion with a low refractive index is formed in a region near the output end face. This optical confinement layer strengthens the refractive index waveguide mechanism and reduces the astigmatism difference.

The optical confinement section can be formed by destroying the active layer having a multiple quantum well structure. Since the multi-quantum well active layer consists of very thin well layers and barrier layers, it can be destroyed by ion implantation or impurity diffusion that reaches the active layer. The destroyed portion has an average composition of the well layer and barrier layer, and has a lower refractive index than the active layer. Furthermore, since the active layer has a quantum well structure, changes in the refractive index of the active layer due to fluctuations in optical output are small, so automatic oscillation is possible over a wide output range. Furthermore, by setting the difference in refractive index between the part of the optical guide layer in contact with the active layer and the cladding layer with respect to the oscillation wavelength in the range of 0.06 to 0.2, an optical confinement effect more suitable for automatic oscillation can be obtained. be able to. And M with excellent layer thickness controllability
B E (Molecular Beam Epitax
y) Method and MOCV D (Metalorganic
Chemical Vapor Depositio
Since it becomes possible to use the n) method, it is possible to increase the appearance rate of elements in which self-assisted oscillation occurs.

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

FIG. 1(a) is a plan view showing an embodiment of the semiconductor laser device of the present invention. FIGS. 1(b) and 1(C) are cross-sectional views taken along line B-B and line C-C in FIG. 1(a), respectively. The manufacturing process will be explained below.

MB on an n-GaAs substrate 1 having a (100) plane orientation.
By the E method, an n-GaAs buffer layer 2 (thickness 0.5μ
s+), followed by Si-doped n-Gao, sA
lo, s As cladding layer 3 (thickness 1 μm.

Carrier concentration I X l OII! lc+++-') were laminated. next.

Non-doped Gal-X Al
x=0.5->0°35), then the multi-quantum well active layer 5 was formed. The multi-quantum well active layer 5 is composed of three layers of non-doped Ga 6. ssA 16.1zA s quantum well layer (70 layers thick) and two layers of non-doped Ga
o, s+, A 1 o, ssA Consisting of a S barrier layer (40 layers thick). Furthermore, non-doped G a +-*
An A l x As gradient refractive index type light guide layer 4' (thickness 0.15 μm, x-0,35 → 0.5) is formed and primary Be-doped p-Ga,,sAla,,As Cladding layer 6 (thickness l u” + carrier concentration lXl0”c
m-3) and Be-doped p-GaAs trench layer 7 (
Thickness 1 u m t Carrier concentration 3 x 10”e
Figure 1(d) is a diagram showing the Al mixed crystal ratio in the cladding layers 3 and 6, the light guides N4 and 4°, and the active layer 5. ), in the gradient refractive index type light guide layers 4 and 4', the Al mixed crystal ratio gradually increases from the side closer to the active layer to the side farther from the active layer. The difference in A1 mix crystal ratio between the part in contact with the cladding layers 3 and 6 is 0.15. This corresponds to a refractive index difference of 0°10. Next, wet etching or RIBE (Reactive
A striped ridge portion 31 was formed by dry etching using Ion Beaa+ Etching. This ridge portion 31 acts as a current injection path. The width W of the ridge portion 31 was set to 4 μm. Etching is
As shown in Figure 1).

The thickness dc of the cladding layer 6 left after etching is 0.
The process was continued until the amount was reduced to 3 μm. By setting the thickness dc to 0°3 μm, the difference in equipolar refractive index between the region where the ridge portion 31 is formed and the other regions becomes I×10−′.

Next, from one end surface from which the laser beam is emitted, the depth D-
S in the area near the end face of 50 μm excluding the ridge portion 31
i ion implantation was performed to form an ion implantation region 41 (
Figures 1(a) and (C)). The St ions were implanted to a depth that reached the cladding layer 3 below the active layer 5. Next, the SiNx insulating film 8 is formed on the part other than the upper flat surface of the ridge part 31, and the p-side electrode 21 (AuZn/Au
) and an n-side electrode 22 (AuGe/Ni) were formed.

This was made into a chip with a resonator length of 250 .mu.m by means of folds to obtain a semiconductor laser device.

In the semiconductor laser device of this embodiment, automatic oscillation can occur because the equal refractive index difference between the region near the ridge portion 31 and the outside thereof is lXl0-3 in the region excluding the vicinity of the end facet. Furthermore, by implanting Si ions, the quantum well structure in the region near the output end surface where the ridge 31 does not exist is destroyed, resulting in a low refractive index region (optical confinement region) having an average composition of the binary well layer and the barrier layer. is formed. This region has a light confinement effect due to its low refractive index, and has a larger band gap energy Eg than the multi-well active layer 5.

By thus strengthening the refractive index waveguide mechanism at the output end face, the astigmatism difference is reduced.

Further, a portion of the light guide layers 4 and 4' that is in contact with the active layer,
The difference in Al mixed crystal ratio between cladding layers 3 and 6 is 0.15.
(corresponding to a refractive index difference of 0.10), an optical confinement effect suitable for automatic oscillation appears.

The semiconductor laser device thus obtained was mounted on a heat sink with the substrate side facing down, and its characteristics were examined. The oscillation value current was 15 mA, which was a small value. The oscillation wavelength was 780 nm.

Figure 2 shows the oscillation spectrum at 3 mW output.

As is clear from FIG. 2, the emitted light has multiple longitudinal modes. And the spectral width of each longitudinal mode is wide. The spectral width of one longitudinal mode was 1.3. The automatic oscillation frequency was 1.0 GHz, and one self-oscillation was observed over a wide output range of 2 mW to 15 mW. The appearance rate of such semiconductor laser devices is 70% per wafer.
It was about.

FIG. 3 is a diagram showing changes in relative noise intensity (RIN) when the amount of returned light is changed in this embodiment. The measurement conditions were a measurement frequency of 720kHz.

The bandwidth is 10 kHz and the optical path length is 30 nm. As is clear from FIG. 3, when the amount of returned light is 3% or less, the relative noise intensity is small and is suppressed to -1358/Hz or less. The astigmatism difference was 5 μm or less.

In this embodiment, the cladding layer 6 outside the ridge portion 31
The thickness of the ridge portion 31 is O02 to 0.6 μm, and the equipolar refractive index difference between the region near the ridge portion 31 and the region outside thereof is 3×
It was confirmed that automatic oscillation occurs when the value is set to 10-4 to 5×10-'. Further, the difference in the At mixed crystal ratio between the light guide layer 4 and the 4° portion in contact with the active layer and the cladding layer 3 and 6 is 0.1 to 0.3 (refractive index difference 0.065 to 0.0. 2), it was confirmed that an optical confinement effect reaching self-sustained oscillation appears.The width W of the ridge portion is 3 to 5 μm.
.

The depth D from the end surface of the ion implantation region 41 is 20 to 10
0μI was suitable.

FIG. 4(a) is a plan view showing another embodiment of the semiconductor laser device of the present invention. FIGS. 4(b) and 4(C) are cross-sectional views taken along lines B'-B' and c'-c' in FIG. 4(a), respectively. The manufacturing process will be explained below. 1st
Similar to the example shown in the figure, n-GaA
An n-GaAs buffer layer 2 is formed on the s-substrate 1. St-doped n
Gao, msA 1o, ssA s cladding layer 3. and non-doped Ga, XA1. After sequentially stacking As gradient refractive index type light guide layers 4 (x-0, 55→0°35), a multiple quantum well active layer 5 was formed. The multi-quantum well active layer 5 has four layers of Gao, seA 1 e, r
tA S ll child well layer (70 layers thick), and 3 layers of G
a o, bsA 1 o, ssA s barrier layer (
Consists of 40 people). Furthermore, non-doped Ga1-, A
One As gradient refractive index type light guide layer 4' (x-0,35→
0.55), Be-doped T) Ga olsA l
+1°, SAs cladding layer 6. And a p-GaAs cap layer 7 was formed. FIG. 4(d) shows the A
FIG. 3 is a diagram showing l mixed crystal ratio. As shown in FIG. 4(d), in the gradient refractive index type light guides Jti4 and 4'', the A1 mix crystal ratio gradually increases from the side closer to the active layer to the side farther from the active layer.Light guide layers 4 and 4 The difference in Al mixed crystal ratio between the part in contact with the active layer and the cladding layers 3 and 6 is 0.2. This corresponds to a refractive index difference of 0°13. Next, by etching, the cladding layer 6 Two grooves 32 were formed that reached the ridge.By forming the grooves 32, a ridge portion 31 was formed.As shown in FIG. 4(a), the grooves 32 are formed.

A ridge portion 31 having a width W=3.5 μm is formed. The groove 32 is etched when the remaining thickness dc of the cladding layer 6 is 0.
．． The process was continued until the amount was 4 μm. By setting the thickness dc to 0.4 μm, the difference in equipolar refractive index between the region where the ridge portion 31 is formed and the other regions is 7×10−
' becomes. Next, Si ions were implanted into the groove 32 having a depth D of 80 μm from one end surface from which the laser beam was emitted, to form an ion implantation region 41 (FIGS. 4(a) and 4(a)).
C)). The St ions were implanted to a depth that reached the cladding layer 3 below the active layer 5. This ion implantation region 41
By forming this, an optical confinement section is formed in the same manner as in the previous embodiment. Next, a SiNx insulating film 8 was formed on a portion of the ridge portion 31 other than the upper flat surface, and further a p-side electrode 21 and an n-side electrode 22 were formed.

Since the growth side surface of a semiconductor laser device having such a shape is flat, it can be mounted on a heat sink with the growth side facing down. By doing so, the heat dissipation effect can be enhanced. The oscillation dark value current of the semiconductor laser device of this example was 18 mA. The oscillation wavelength is 786n
It was m. Automatic oscillation was observed in the power range of 2 to 18 mW.

The astigmatism difference was 5 μm or less.

FIG. 5 is a plan view showing an embodiment in which ion implantation regions 41 are formed in the vicinity of both end faces in the embodiment of FIG. 1. Like the example shown in FIG. 1, the semiconductor laser device of this example also oscillated with a low threshold current, had a small astigmatism difference (and was confirmed to oscillate automatically over a wide output range).

In the above embodiments, an example was shown in which the multiple quantum well structure in the active layer was destroyed by ion implantation as a means for forming the optical confinement region, but the method is not limited to this.
For example, this can also be done by diffusion of Zn ions.

(Effects of the Invention) As described above, the semiconductor laser device of the present invention has a low two-oscillation darkness value and produces automatic oscillation over a wide output range.

The return light noise level is small (and the astigmatism difference is reduced, so it is optimal as a light source for optical disk systems. Also, the semiconductor laser device of the present invention has an M
Since it can be manufactured by BE method or MOCVD method, it is possible to manufacture an element that causes automatic oscillation at a high yield.

4. ``Normal tongue''■ Figure 1(a) is a plan view showing one embodiment of the semiconductor laser device of the present invention, and Figures 1(b) and (C) are B of Figure 1(a), respectively. 1(d) is a cross-sectional view taken along line B and line C-C, and FIG. The figures are diagrams showing the relative noise intensity when changing the oscillation spectrum and the amount of returned light of the semiconductor laser device shown in Figure 1, respectively.
FIG. 4(a) is a plan view showing another embodiment of the present invention;
Figures (b) and (C) are cross-sectional views along lines B'-B' and c'-c' in Figure 4(a), and Figure 4(d) is a cross-sectional view along lines B'-B' and c'-c' in Figure 4(a).
FIG. 5 is a diagram showing the Al mixed crystal ratio in the active layer, optical guide layer, and cladding layer of Example a), and FIG.

FIG. 6 is a sectional view showing a conventional automatic oscillation semiconductor laser device.

1...n-GaAs substrate, 2...n-G
aAs buffer layer, 3-n-GaAlAs cladding layer,
4゜4''...GaAlAs gradient refractive index type light guide layer,
5...GaAlAs multiple quantum well active layer, 6...p
-GaAlAs cladding layer, '1-p-GaAs1-ru GaAs cladding iNx insulating film, 21... p-side electrode, 22... n-side electrode, 31.・・・Ridge part, 32・
...Groove, 41...Ion implantation region.

Figure 2 Figure 3 Return amount ('10)

Claims (1)

[Claims] 1. A first cladding layer, a first optical guide layer, an active layer having a multi-quantum well structure, a second optical guide layer, and a second cladding layer, which are formed on a semiconductor substrate. and a striped current injection path formed above the layered structure, and the second cladding layer has a thickness of 0.2 μm to 0.0 μm in a region outside the current injection path. .6 μm, and the equivalent refractive index difference between the inside and outside of the region near the current injection path is 3×10^-^4 to 5×10^-^3, and the region near at least one end face is In a semiconductor laser device, a portion of the active layer below the outside of the current injection path is used as an optical confinement portion having a lower refractive index than the active layer below the current injection path. 2. The semiconductor laser device according to claim 1, wherein the optical confinement section is formed by destroying a multiple quantum well structure of the active layer. 3. The refractive index difference between the portions of the first and second light guide layers in contact with the active layer and the first and second cladding layers is 0.065 to 0.2. The semiconductor laser device described in .