JPS61171186A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To eliminate astigmatism by a method wherein a refractive waveguide is formed by thinning a P-GaAlAs clad layer. CONSTITUTION:An N-type Ga1-xAlxAs clad layer 2 (x=0.45), a Ga1-yAlyAs active layer 3 (y=0.14), a P-type Ga1-xAlxAs clad layer 4 (x=0.45), an N-type Ga1-sAlsAs oversaturated absorber layer 10, an N-type Ga1-uAluAs absorbed carrier leakage prevention layer 11, and an N-type GaAs current structure layer 5 are successively formed on an N-type GaAs substrate crystal 1, and a groove stripe exposing the surface of said clad layer 4 is formed by completely removing the above-mentioned layers 5, 11, and 10 by photo etching. Next, a P-type Ga1-xAlxAs clad layer 6 (x=0.45) and a P-type GaAs cap layer 7 are formed; then, a P-side electrode 8 and an N-side electrode 9 are formed. This construction facilitates the production of the low-noise laser element free of astigmatism and enables its mass production and cost reduction.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention is based on the MOCVD method (Metal Qrganic Carbon
Chemical Vapor 1) Eposition
) This article relates to the structure of a semiconductor laser according to K., and relates to the structure of a low-noise laser essential for commercial semiconductor lasers.

[Background of the invention]

A conventional MOCVD method semiconductor laser is shown in FIG.

This structure was proposed by J. J. Coleman et al., Ap
plied physics Letters, Vo
l, 37.

1980, page 262. The configuration of this laser has stripes on a cladding layer 2.4 sandwiching an active layer 3. The structure was such that the transverse mode was controlled by forming an n-type flow confinement layer 5 and burying the n-type cladding RII 6 and cap layer 7.

Note that 9.10 is a p-electrode and an n-electrode, respectively. In this structure, the mode control is of the refractive index waveguide type, and the longitudinal mode is a single mode, so the relative noise intensity (RIN) level is RIN = 10"Hz-' (there is also light returned from the optical system). case) level, and it was necessary to reduce the noise by using a high frequency superimposition method, etc.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of conventional methods, and relates to the structure of a low-noise laser, and in particular to provide a structure that stably generates self-sustained oscillation by optimizing the waveguide mechanism. There is a particular thing.

[Summary of the Invention] In order to realize a low-noise laser, a laser structure in which K causes self-sustained oscillation at a position where the oscillation spectrum is intermediate between multi-mode oscillation and single-mode oscillation is optimal. Therefore, a new structure is required that combines the functions of a gain-guided laser structure and a refractive index-guided laser structure. It is conceivable to provide this gain waveguide function by providing a weakly supersaturated absorber region outside the stripe region. However, in the conventional semiconductor laser device, the semiconductor 11 that causes absorption outside the groove stripe region is only the n-GaAS current confinement layer 5 as shown in FIG. Coefficient α
Since it is large, 10100O0' or more, it cannot operate as a supersaturated absorber. Therefore, as a result, both the vertical and horizontal modes were single. In the laser device of the present invention, Kn-G is used outside the groove stripe region as shown in FIG. 2(b).
aAs current confinement layer 5 and p-GaAtAs cladding layer 4
Since a Kn--GaAtAs supersaturated absorber layer 10 is formed between the two, the laser structure is such that self-sustained oscillation occurs.

It is important to set the molar ratio of At in the supersaturated absorber layer 10 to be equal to or smaller than the molar ratio of At in the active layer 3 in order to cause self-oscillation. Sara
n between the supersaturated absorber layer 10 and the current confinement layer 5.
-GaAtAs By providing the absorbing carrier 1 anti-leakage layer 11, carriers generated (by light absorption) are prevented from leaking into the current confinement layer 5. The molar ratio of At in the layer 11 for preventing leakage during absorption must be greater than the molar ratio of At in the supersaturated absorber 410. Furthermore, if the molar ratio of At is appropriately selected in the supersaturated absorber layer 10 and the absorption carrier leakage prevention layer 11, self-sustained oscillation can easily occur even if the thickness thereof is reduced. When each of these thicknesses is set to 1100 nm or less, the influence of the presence or absence of these two layers on the light distribution is very small and can be ignored. Therefore p GaAtAs cladding layer 4
If it is possible to appropriately reduce the thickness (~0.3 μm or less), form a refractive index waveguide, eliminate astigmatism, and cause self-sustained pulsation more easily than the supersaturated absorber JiilOK. It is closed.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail with reference to FIG.

n-type Gat-xA4 on top of n-type GaA S substrate crystal 1
As cladding layer 2 (x==0.45), Ga
tyAty A8 active layer 3 (y=0.14), I
) type Gal-11A As cladding layer 4 (x = 0
．． 45), n-type Gal-I A ts A 8 supersaturated absorber layer 10, nmoat-wAzm As absorption carrier leakage prevention layer 11, and n-type GaAs current confinement layer 5 as MO
They are sequentially formed by CVD method. n by photoetch process
fflGaAs layer 5, n-type Gat-wAtmAs absorption Φ
Yaria leak prevention layer 11, n-type Ga1-mAt*AS supersaturation absorption supersaturation absorber layer l line removal, p-type Ga1-z
At! Width 1 that exposes the surface of A S cladding layer 4
Form groove stripes of ~15 μm. Next, MOCVD
A pHGaAs cap layer 7 is formed using a pffiG at-zktx A 8 cladding 6 (x=0.45) method. Thereafter, after forming a p-side electrode 8 and an n-side electrode 9, a laser element with a resonator diameter of 300 μm was obtained by a cleavage method. In addition, the thickness dl of the activated stone and the thickness d2 of the p-cladding layer 4 become thicker, approaching a narrow stripe structure, resulting in a multi-mode oscillation disk, and thinner, resulting in a single-mode oscillation type, which reduces astigmatism. 0.0 as a condition for it to disappear
3μm<dt<0.12μm, 0.3μm<dx<1
．． 2 μm was obtained. Furthermore, under this condition without astigmatism, the condition for self-sustained oscillation is 0.05〈
z 0.14.0.15<u(0,6, and the thickness da of the supersaturated absorption layer 10 is Inm(da<0.2/Jm%
The thickness d4 of the absorption carrier leakage prevention layer 11 is lnm (da
<0-2 μm was obtained.

The prototype device oscillated continuously at room temperature at an oscillation wavelength of 780 nm with a threshold current of 30 to 50 mA, and the oscillation spectrum showed a self-oscillation spectrum.

Also, relative noise strength 1i1 (RI N ) J't~3X
Low noise of 10-''Hz-'' (with return light) was confirmed.Furthermore, astigmatism was below the measurement limit (1 μm).

At 70C, no significant deterioration was observed in the lifetime when operating at a constant light output of 10 mW even after 2000 hours, and it was revealed that the reliability was high.

In this example, a single GaAtAS layer was used as the active layer, but MQW (Multi-Quan
tum-Well) structure and GRIN (Gra
Similar results were obtained for the dedRefracdive index) structure. Moreover, the device of this example has I
Needless to say, it is also applicable to other material systems such as nGaAsp, InQap, and InGaAtp.

〔Effect of the invention〕

According to the present invention, a low-noise laser device without astigmatism can be easily manufactured by the MOCVD method and can be mass-produced, which is effective in reducing the cost of the device.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the device structure to explain the conventional method, FIG. 2 is a diagram showing the absorption coefficient distribution outside the groove stripe region to explain the present invention in detail, and FIG. 3 is a diagram showing the absorption coefficient distribution outside the groove stripe region to explain the present invention in detail. It is a structural sectional view showing an example.

Claims (1)

[Claims] 1. On the first semiconductor region of the first conductivity type, at least the first
a second semiconductor layer having a conductive amount; a third semiconductor layer having a larger refractive index and a smaller forbidden band width than the second semiconductor layer; a second conductive layer having a smaller refractive index and a larger forbidden band width than the third semiconductor layer; a fourth semiconductor layer of a first conductivity type having a smaller bandgap width than the third semiconductor layer, a sixth semiconductor layer of a first conductivity type having a larger bandgap width than the fifth semiconductor layer. , the third above
, the first semiconductor layer has a smaller forbidden band width than the fifth and sixth semiconductor layers.
After sequentially stacking conductive type seventh semiconductor layers, the fifth, sixth, and seventh semiconductor layers are removed in stripes by etching, and then the surface removed by the etching and the surface of the seventh semiconductor layer are removed by etching. A semiconductor laser device, further comprising an eighth semiconductor layer of a second conductivity type having a smaller refractive index and a larger forbidden band width than at least the third semiconductor layer. 2. The thickness of the fifth semiconductor layer is 1 nm to 0.2 μm, the thickness of the sixth semiconductor layer is 1 nm to 0.2 μm, and the stripe width removed by the etching is 1 to 15 μm. The semiconductor laser device according to claim 1, characterized in that: