Semiconductor laser device

Abstract

A semiconductor laser device, comprising a buffer layer of a first conductivity type, a clad layer of the first conductivity type, an active layer and a clad layer of a second conductivity type formed on a semiconductor substrate of the first conductivity type, wherein a band gap in the buffer layer of the first conductivity type has a value which is greater than a band gap of the semiconductor substrate and smaller than a band gap of the clad layer of the first conductivity type, and an impurity concentration in the buffer layer of the first conductivity type is higher than an impurity concentration in the clad layer of the first conductivity type.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional diagram showing a GaAlAs based compound semiconductor laser device according to the first embodiment of the present invention;

FIG. 2 is a graph showing the relationship between the impurity concentration of Si in the n type GaAlAs buffer layer and the operating voltage in each of the semiconductor lasers of Examples 1a to 1f of the present invention and Comparative Example 1;

FIG. 3 is a cross sectional diagram showing a GaAlAs based compound semiconductor laser device according to the second embodiment of the present invention;

FIG. 4 is a graph showing the relationship between the impurity concentration of Si in the n type GaAlAs buffer layer and the operating voltage in each of the semiconductor lasers of Examples 2a to 1e of the present invention and Comparative Example 2;

FIG. 5 is a cross sectional diagram showing a GaAlAs based compound semiconductor laser device according to the third embodiment of the present invention; and

FIG. 6 is a cross sectional diagram showing a semiconductor laser device according to the prior art.

Claims

1. A semiconductor laser device, comprising a buffer layer of a first conductivity type, a clad layer of the first conductivity type, an active layer and a clad layer of a second conductivity type formed on a semiconductor substrate of the first conductivity type, wherein a band gap in the buffer layer of the first conductivity type has a value which is greater than a band gap of the semiconductor substrate and smaller than a band gap of the clad layer of the first conductivity type, andan impurity concentration in the buffer layer of the first conductivity type is higher than an impurity concentration in the clad layer of the first conductivity type.

2. The semiconductor laser device according to claim 1, wherein the semiconductor substrate of the first conductivity type is made of GaAs and the buffer layer of the first conductivity type, the clad layer of the first conductivity type and the clad layer of the second conductivity type are made of Ga1-xAlxAs (0<x<1).

3. The semiconductor laser device according to claim 1, wherein the first conductivity type is n type and the second conductivity type is p type.

4. The semiconductor laser device according to claim 2, wherein the composition ratio of Al in the buffer layer of the first conductivity type gradually increases from the semiconductor substrate of the first conductivity type to the clad layer of the first conductivity type.

5. The semiconductor laser device according to claim 1, wherein the buffer layer of the first conductivity type is made up of plural layers.

6. The semiconductor laser device according to claim 2, further comprising a GaAs buffer layer of the first conductivity type between the GaAs semiconductor substrate of the first conductivity type and the Ga1-xAlxAs buffer layer of the first conductivity type.

7. The semiconductor laser device according to claim 1, wherein the impurity concentration of the buffer layer of the first conductivity type is 5×1017 cm−3 or more.

8. The semiconductor laser device according to claim 1, wherein the impurity concentration of the clad layer of the first conductivity type is 1×1018 cm−3 or less.

9. The semiconductor laser device according to claim 6, wherein the impurity concentration of the GaAs buffer layer of the first conductivity type is 1×1018 cm−3 or less.

10. The semiconductor laser device according to claim 2, wherein the impurity concentration in the AlxGa1-xAs buffer layer of the first conductivity type is higher than 5×1017 cm−3 in the vicinity of the interface where the AlxGa1-xAs buffer layer of the first conductivity type makes contact with the AlxGa1-xAs clad layer of the first conductivity type.

11. The semiconductor laser device according to claim 1, wherein a thickness of the region in the buffer layer of the first conductivity type, which is in the vicinity of the interface between the buffer layer of the first conductivity type and the clad layer of the first conductivity type, and where the impurity concentration is higher than that in the clad layer of the first conductivity type, is 70 nm or less.