JPH02178984A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To maintain a self-excited oscillation in a wide output range and to reduce an astigmatic difference by specifying the thickness of a second clad layer in a region outside the near region of a current injection path, equivalent refractive index difference between the side and the outside of the near region of the current junction path, and the width of the current injection path. CONSTITUTION:The thickness of a second clad layer 6 in a region outside the near region of a current injection path 31 is 0.2-0.4mum, an equivalent refractive index difference between the inside and the outside of the near region of the current injection path 31 is 3X10<-4>-5X10<-3>, and the width W1 of the current injection path 31 at least in one end face near region is smaller than the width W2 of the current injection path 31 in a region except the end face near region. Thus, since the difference of equivalent refractive index between the region near the current injection path and the region except it is 3X10<-4>-5X10<-3> to generate a self-excited oscillation and the widths W1, W2 of the current injection path satisfy W1<W2, the effect of self focusing is strengthened only at the end face near region. Thus, the astigmatic difference of the emitting light can be reduced while the self-excited oscillation is maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser device that utilizes automatic oscillation and has low noise characteristics.

(Prior Art) Semiconductor laser devices are used as light sources for audiovisual equipment and optical information processing. Semiconductor laser elements used in these devices are required to have low intensity of return optical noise induced by reflected light from a disk or the like. An automatic oscillation laser is an example of a semiconductor laser device with reduced optical feedback noise.

FIG. 8 shows an example of an automatic oscillation laser. This semiconductor laser has VSIS (V channel) for current confinement.
d 5ubstrate Inner 5tripe)
It has a structure. n on the p-G a As substrate 11
- After forming the GaAs current blocking layer 16, a V-shaped groove 23 reaching the substrate 11 is formed. Further p Gao, ss
A 10.45A S cladding layer 12. p Ga
o, asA 1615AS active layer 13. n Gao,
55AIo, a5AS cladding layer 14. , n-GaAs
After sequentially laminating the cap layer 15, the p-side electrode 21. An n-side electrode 22 is formed. In this semiconductor laser device, the thickness dl of the cladding layer 12 outside the V-shaped groove 23 and the thickness dl of the active layer 1
The thickness d2 of 3 is 0.3 μm and 0.12 pm, respectively.
is set to . By setting the thicknesses dl 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 . By reducing the equivalent refractive index difference Δn in this manner, automatic oscillation can occur.

(Problems to be Solved by the Invention) In the automatic oscillation laser shown in FIG. 8, since the equivalent refractive index difference is small, 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. A problem arises in that the oscillation dark value current increases due to such light absorption.

The oscillation dark value current of the semiconductor laser device in Fig. 8 is the cavity length 2.
In the case of 50 μm, the value is as large as 45 mA or more.

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. Therefore, there is a drawback that the astigmatism difference becomes large. In the semiconductor laser device shown in Figure 8, the astigmatism difference is 15 μm.
This is a large value.

Furthermore, since this semiconductor laser device has a double heterostructure, the refractive index of the active layer tends to change depending on the amount of injected carriers. Therefore, there is a drawback that the equivalent refractive index difference changes with fluctuations in optical output, and automatic oscillation cannot be maintained up to high output.

The present invention has been made to solve the above-mentioned problems. 1. An object of the present invention is to provide an automatic oscillation laser with a small oscillation dark value current, which can maintain self-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.

[Failure to solve the problem]

The semiconductor laser device of the present invention includes a first cladding layer, a first optical guide layer, an active layer having a quantum well structure, a second optical guide layer, and a second cladding layer formed on a semiconductor substrate. A layered structure and a striped current injection path formed above the layered structure, the second cladding layer having a thickness of 0.2 in an area outside the area near the current injection path.
μm to 0.4 am, and the equivalent refractive index difference between the inner and outer regions of the current injection path is 3×10−′ to 5×
10-3, wherein a width WI of the current injection path in a region near at least one end face is smaller than a width W2 of the current injection path in a region other than the region near the end face;
This achieves the above objective.

Further, in the semiconductor laser device of the present invention, the widths W1 and W2 of the current injection path may satisfy the following relationships: 2 pm≦W1≦4 μm, and 3 μm≦W2≦5 μm, and further, the widths W1 and W2 of the current injection path may satisfy the following relationships: a portion of the layer in contact with the active layer; and 2 the first and second layers.
The refractive index difference between the cladding layer and the cladding layer can also be set to 0065 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, since the current injection path for current confinement is formed above the active layer, a current confinement structure that does not absorb light can be achieved.5 This also makes it possible to reduce the oscillation dark value current. And M B with excellent layer thickness controllability
E (Molecular Beam Bprtaxy)
Law and MOCV D (MetaIorgan:cCh
chemical vapor deposition)
Since it becomes possible to use the method, the appearance rate of automatic oscillation semiconductor laser devices can be increased. Moreover, 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 . Since the widths W1 and W2 of the current injection path are set to W<W2, the self-focusing effect is enhanced only in the region near the end face. This reduces the astigmatism difference of the emitted light while maintaining automatic oscillation. 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. Therefore, automatic oscillation is possible over a wide output range. Furthermore, by setting the difference in refractive index for the oscillation wavelength between the part of the optical guide layer in contact with the active layer and the cladding layer to a range of 0.065 to 0.2, an optical confinement effect suitable for automatic oscillation is obtained. be able to.

(Example) Examples of the present invention will be described below. Figure 1(a)
FIG. 1 is a plan view showing an embodiment of a semiconductor laser device of the present invention. Figure 1 (b) and (C) are respectively 111F
It is a sectional view taken along the line BB and the line CC in (a). The manufacturing process will be explained below.

MB on n-○aAs substrate 1 having (100) plane orientation.
By E method, n-GaAS buffer layer 2 (thickness 1 μm)
followed by Si-doped n-GaO,5A I
6. A sAs crystalline layer 3 (thickness: 1 μm, carrier concentration I x 1018 cm-') was laminated. Next, a non-doped Ga + -x Alx As graded refractive index optical guide layer 4 (thickness: 0.15 μm, x=0.5→0.35) was formed, and then a multi-quantum well active layer 5 was formed. The multi-quantum well active layer 5 has three layers of non-doped Ga o, e
eA, Io, + zA S quantum well layer (thickness 70
), and two layers of non-doped G a O, 65 A l
o.

Consists of 3 SA S barrier layers (40 layers thick). Furthermore, a non-doped Ga, □Alx As graded refractive index optical guide layer 4° (thickness 0.15 μm, x = 0.35→0.5) is formed, and then a Be-doped p Gao, sA, 1o, s
As cladding layer 6 (thickness 1 pm, gearia concentration I
x 10"cm-3) and p-GaAs cap layer 7 (thickness 1 μm, carrier concentration 3 x 10"cm-3).
") were formed. FIG. 1(d) shows the cladding layers 3 and 6.
1(d) shows the A1 mixed crystal ratio in the optical guide layers 4 and 4" and the active layer 5. As shown in FIG. The Al mixed crystal ratio gradually increases from near to far. Difference in Al mixed crystal ratio between the parts of the optical guide layers 4 and 4' that are in contact with the active layer and the cladding layers 3 and 6 is 0.15.

This corresponds to a refractive index difference of 0.10 with respect to the oscillation wavelength.

Next, wet etching or RI B E (Reac
The ridge portion 31 was formed by dry etching using tive beam etching.

As shown in Figure 1(a), the depth is D-30μ from the output end face.
In the region near the end face of m, a portion having a width W of -2 μm is left unetched and becomes a ridge portion 31a. Further, in a region other than the region near the end face, a portion having a width W2-4 μm is left unetched and becomes a ridge portion 31. Etching is continued until the thickness dc of the cladding layer 6 remaining after etching becomes 0.2 μm as shown in FIGS. 1(b) and 1(C). By setting the thickness dc to 0.2 μm, the difference in equivalent refractive index between the region where the ridge portions 31 and 31a are formed and the other region is 5×10 −3 . Next, a 5tNx insulating film 8 was formed on parts other than the upper surfaces of the ridge parts 31 and 31a, and then a 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 μm using the folds to obtain a semiconductor laser device.

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 dark value current was 1.5 mA, which was a small value. The oscillation wavelength was 783 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 1.25. The automatic oscillation frequency was 0°9 GHz, and automatic oscillation was observed over a wide range of output power from 2 mW to 18 mW. The appearance rate of such semiconductor laser devices is 70 per wafer.
It was about %.

FIG. 3 shows the change in relative noise intensity (RIN) when the amount of returned light is changed in this embodiment. Measurement conditions are measurement frequency: 720 kHz, hand width: 10 kHz.
, the optical path length is 30 mm. As is clear from Figure 3, the relative noise intensity is small when the amount of returned light is 3% or less, -13
It is kept below 5dB/Hz. The astigmatism difference was 5 μm or less.

An element having a structure similar to that of this example was fabricated, and the width WI of the ridge portion 31a in the region near the end face and the width W2 of the ridge portion 31 in the region other than the region near the end face were both 4 μm.
The astigmatism difference was 15-20 μm. Thus, it can be seen that the astigmatism difference of the semiconductor laser device of this example is extremely small.

In this example, the cladding layer thickness dc was set to 0. 2μm～0
．． 4μm (equal polarized refractive index difference 3X10-'~5x10-3
It was confirmed that an automatic oscillation laser with a small astigmatism difference can be obtained by setting W<W2.

Note that the two widths W are 2 to 4 μm, and the one width W2 is 3 to 5 μm.

It was appropriate to keep it in the range of The depth value is 1
0-100 μM was suitable.

In addition, in the three embodiments, the difference in A1 mix crystal ratio between the parts of the optical guide layers 4 and 4 in contact with the active layer and the cladding layers 3 and 6 is 0.10 to 0.30 (refractive index difference 0.065~0.
2), it was confirmed that an automatic oscillation laser can be obtained. It has been confirmed that within this range, automatic oscillation occurs even if the number of well layers and barrier layers in the multi-quantum well structure is changed or even in a single quantum well structure. Further, in this example, although the optical guide layer is of a gradient refractive index type, it was confirmed that automatic oscillation occurs even in an optical guide layer having a single mixed crystal ratio as long as the difference in the A1 mixed crystal ratio is within the above range.

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. 1
Similar to the example shown in the figure, n-GaA
n-GaAs buffer layers 2 and 5 on the s-substrate 1
iF-pun Ga 0.4SA lo, ssA
S cladding layer 3. and non-doped G a I-X A
] XAS gradient refractive index type light guide layer 4 (x=0.5
5→0.35) were sequentially laminated. Next is non-doped Gao
, +++++Alo, +□As single quantum well active layer 5"
(70 people thick). Furthermore, non-doped Ga+-
xA1xAs gradient refractive index type light guide layer 4'' (x=o,
35→0. 55), Be-doped pG ao
, a5A lo, 5sAs cladding layer 6. and p-G
An aAs cap layer 7 was formed. FIG. 4(d) is a diagram showing the A1 mixed crystal ratio in the cladding layers 3 and 6, the optical guide layers 4 and 4', and the active layer 5'. As shown in FIG. 4(d), in the gradient refractive index type light guide layers 4 and 4', the A1 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 mixed crystal ratio between the parts of the optical guide layers 4 and 4' that are in contact with the active layer and the cladding layers 3 and 6 is 0.
．． It is 2. This corresponds to a refractive index difference of 0.13. Next, two grooves 32 were formed by etching. By forming the groove 32, the ridge portions 31 and 31. a is formed. As shown in FIG. 4(a), the groove 32 is formed in a region near the end face at a depth D-40 μm from the output end face with a width W1-3 μm, leaving a solid portion 31a. A ridge portion 31 having a width W2-5 μm is formed in a region other than the region near the end face. The groove 32 was etched until the remaining thickness dc of the cladding layer 6 was 0.25 μm. By setting the thickness dc to 0.25 μm, the difference in isolateral refractive index between the region where the p ridge portions 31 and 31a are formed and the other region becomes 2×10 −3 . Next, SiN
An insulating film 8 is formed, and a p-side electrode 21 and an n-side electrode 2 are formed.
2 was 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 1.3 mA. The oscillation wavelength is 785
It was nm. Automatic oscillation was observed in the power range of 2 to 15 mW.

The astigmatism difference was 5 μm or less.

FIG. 5 shows another embodiment of the invention. The semiconductor laser device of this embodiment has a laminated structure similar to that of the semiconductor laser device of FIG. 1, but the ridge portion 31.
The width of a gradually decreases toward the output end face,
4μm in the part in contact with the ridge part 31, 211μm in the end face
It is m. Moreover, the ridge portion 31. The depth from the end surface of a is 50 μm. Residual thickness of cladding layer dc is 0.3μ
It is m.

It was confirmed that the semiconductor laser device of this example also oscillates at a low threshold current like the semiconductor laser devices shown in the first test and FIG. 4, and automatically oscillates in a wide output range with a small astigmatism difference. It was also confirmed that even when the ridge portions 31 and 31a were formed by two grooves as in the embodiment shown in FIG. 4, a semiconductor laser device having the same characteristics as described above could be obtained.

FIG. 6 shows an embodiment in which a ridge portion 31b narrower than the ridge portion 31 is formed near an end surface other than the end surface where the ridge portion 31a of the embodiment shown in FIG. 1 is present. Ridge part 31
Width W3 of b is 2μn+, depth D” of width W3 is 3
It is 0 μm. It was confirmed that this semiconductor laser device also oscillates with a low threshold current, has a small astigmatism difference, and automatically oscillates over a wide output range.

FIG. 7 shows an embodiment in which narrow ridge portions are formed near the end faces on both sides of the embodiment shown in FIG. 4, and the widths of these ridge portions gradually become smaller. The ridges 31.31a and 31b are formed by forming grooves 32.

The widths of the ridge portions 31a and 31b gradually increase from the widths W1 and W3 at their respective end faces to the width W2 of the ridge portion 31. The width W3 of the ridge portion 31b is 3 μm, and the depth D
゛ is 50 μm. It was confirmed that this semiconductor laser device also oscillates with a low threshold current, has a small astigmatism difference, and automatically oscillates over a wide output range.

(Effects of the Invention) The semiconductor laser device of the present invention has a low two-oscillation dark value, automatic oscillation over a wide output range, a low return light noise level, and a reduced astigmatism difference. Ideal as a light source for the system. In addition, the semiconductor laser device of the present invention can be produced using the MBE method or MOC method, which has excellent layer thickness controllability.
Since it can be manufactured by the VD method, elements that produce automatic oscillation can be manufactured with a high yield.

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 respectively similar to Figure 1(a). FIG. 1(d) is a cross-sectional view taken along line B-B and line C-C of this example, and FIG. FIG. 3 is a diagram showing the relative noise intensity when changing the oscillation spectrum and the amount of returned light of the semiconductor laser device shown in FIG. 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).
Figures 5 to 7 are plan views showing other examples of the present invention, and Figure 8 is a diagram showing the Al mixed crystal ratio in the active layer, optical guide layer, and cladding layer of Example a). FIG. 2 is a cross-sectional view showing an automatic oscillation semiconductor laser device.

1-=n-GaAs substrate, 2-n-G
a As buffer layer, 3-n-GaA1. As crystal/node layer, 4゜4゛...GaAlAs graded refractive index optical guide layer, 5...GaAIAs multiple quantum well active layer, 5゛...GaAs single quantum well active layer ,
6...p-GaA]As cladding layer, 7...p-
GaAs cap layer, 8.SiNx insulating film, 21
...P side electrode, 22...n side electrode, 31.31a,
31b...Ridge part, 32...Groove.

that's all

Claims (1)

[Claims] 1. A first cladding layer formed on a semiconductor substrate and a first
A laminated structure having a light guide layer, an active layer having a quantum well structure, a second light guide layer, and a second cladding layer, and a striped current injection path formed above the laminated structure. The thickness of the second cladding layer in the region outside the region near the current injection path is 0.2 μm to 0.4 μm, and the equivalent refractive index between the inside and outside of the region near the current injection path is The difference is 3×10^-^4 to 5×10^-^3,
A semiconductor laser element in which a width W_1 of the current injection path in a region near at least one end face is smaller than a width W_2 of the current injection path in a region other than the region near the end face. 2. The widths W_1 and W_2 of the current injection path are 2 μm≦W
The semiconductor laser device according to claim 1, which satisfies the following relationships: _1≦4 μm, and 3 μm≦W_2≦5 μm. 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. 2. The semiconductor laser device according to 2.