Semiconductor laser device and fabrication method therefor

Abstract

A semiconductor laser device has a multilayer structure including a first clad layer, an active layer, and a second clad layer stacked successively on a semiconductor substrate in order of increasing distance from the semiconductor substrate. At least one of the first clad layer and the second clad layer has a compressive distortion with respect to the semiconductor substrate. At least one of the first clad layer and the second clad layer includes a semiconductor layer having a tensile distortion with respect to the semiconductor substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a structure of a semiconductor laser device according to a first embodiment of the present invention;

FIGS. 2A to 2C are cross-sectional views illustrating a method for fabricating the semiconductor laser device according to the first embodiment in the order in which the process steps thereof are performed;

FIG. 3 is a graph showing the relationship between an aging time and a current degradation rate when an aging test is performed on the semiconductor laser device according to the first embodiment;

FIG. 4 is a graph showing the relationship between the lattice mismatch of clad layers and reliability in the semiconductor laser device according to the first embodiment;

FIG. 5 is a list of the results of an experiment performed under combined conditions for the reliability evaluation of semiconductor laser devices having different structures in the first embodiment; and

FIG. 6 is a cross-sectional view showing a structure of a semiconductor laser device according to a second embodiment of the present invention.

Claims

1. A semiconductor laser device having a multilayer structure comprising a first clad layer, an active layer, and a second clad layer stacked successively on a semiconductor substrate in order of increasing distance from the semiconductor substrate, wherein at least one of the first clad layer and the second clad layer has a compressive distortion with respect to the semiconductor substrate andat least one of the first clad layer and the second clad layer includes a semiconductor layer having a tensile distortion with respect to the semiconductor substrate.

2. The semiconductor laser device of claim 1, wherein at least one of the first clad layer and the second clad layer having the compressive distortion has a lattice mismatch of not less than 2.0×10−4 and not more than 3.0×10−3 with respect to the semiconductor substrate andthe semiconductor layer having the tensile distortion has a lattice mismatch of not less than −2.0×10−3 and not more than −2.0×10−4 with respect to the semiconductor substrate.

3. The semiconductor laser device of claim 1, wherein the second clad layer has the semiconductor layer having the tensile distortion andthe semiconductor layer having the tensile distortion functions as an etching stop layer when a ridge portion is formed in the second clad layer by etching.

4. A semiconductor laser device having a multilayer structure comprising a first clad layer, an active layer, and a second clad layer stacked successively on a semiconductor substrate in order of increasing distance from the semiconductor substrate, wherein at least one of the first clad layer and the second clad layer has a compressive distortion with respect to the semiconductor substrate andat least one of the first clad layer and the second clad layer has a heavily doped impurity region containing an impurity at a relatively high concentration and a lightly doped impurity region containing an impurity at a relatively low concentration.

5. The semiconductor laser device of claim 4, wherein the heavily doped impurity region is formed at a position further away from the active layer than a position at which the lightly doped impurity region is formed andthe lightly doped impurity region is formed at a position closer to the active layer than at the position at which the heavily doped impurity region is formed.

6. The semiconductor laser device of claim 4, wherein at least one of the first clad layer and the second clad layer having the compressive distortion has a lattice mismatch of not less than 2.0×10−4 and not more than 3.0×10−3 with respect to the semiconductor substrate.

7. The semiconductor laser device of claim 4, wherein at least one of the first clad layer and the second clad layer includes a semiconductor layer having a tensile distortion with respect to the semiconductor substrate.

8. The semiconductor laser device of claim 7, wherein the semiconductor layer having the tensile distortion has a lattice mismatch of not less than −2.0×10−3 and not more than −2.0×10−4 with respect to the semiconductor substrate.

9. The semiconductor laser device of claim 1, wherein a well layer composing the active layer has the compressive distortion with respect to the semiconductor substrate and a film thickness of not less than 20 nm.

10. The semiconductor laser device of claim 1, which has a self-sustained pulsation characteristic.

11. A method for fabricating a semiconductor laser device, the method comprising the steps of: forming, on a semiconductor substrate, a first clad layer having a lattice mismatch of not less than 2.0×10−4 and not more than 3.0×10−3 with respect to the semiconductor substrate;forming an active layer on the first clad layer;forming, on the active layer, a second clad layer having a lattice mismatch of not less than 2.0×10−4 and not more than 3.0×10−3 with respect to the semiconductor substrate and including therein a semiconductor layer having a lattice mismatch of not less than −2.0×10−3 and not more than −2.0×10−4 with respect to the semiconductor substrate; andetching the second clad layer using the semiconductor layer as an etching stop layer to form a ridge portion therein.