Semiconductor laser device

Abstract

In a constitution where a first clad layer is formed on a semiconductor substrate, an active layer having the strained multiple quantum well structure is formed on the first clad layer, and a second clad layer is formed on the active layer, the sum of products of strain amounts and film thickness in the active layer is set to a negative value

Description

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects as well as advantages of the invention will become clear by the following description of preferred embodiments of the invention. A number of benefits not recited in this specification will come to the attention of those skilled in the art upon the implementation of the present invention.

FIG. 1 is an enlarged perspective view illustrating a semiconductor laser device according to a preferred embodiment 1 of the present invention.

FIG. 2 is a sectional view illustrating a manufacturing process of the semiconductor laser device according to the preferred embodiment 1.

FIG. 3 is an enlarged sectional view of clad layers and an active layer that are main part of the semiconductor laser device according to the preferred embodiment 1.

FIG. 4 is a diagram showing a relationship between a strain amount and a band gap in the preferred embodiment 1.

FIG. 5 is a diagram showing a life characteristic in relation to the sum of products of strain amounts and film thicknesses in the semiconductor laser device according to the preferred embodiment 1.

FIG. 6 is an enlarged perspective view illustrating a monolithic two-wavelength semiconductor laser device according to a preferred embodiment 2 of the present invention.

FIG. 7 is a sectional view illustrating a manufacturing process of the semiconductor laser device according to the preferred embodiment 2.

FIG. 8 shows a sectional structure of a light emitting end facet in a semiconductor laser device according to a conventional technology.

FIG. 9 is a stress evaluation chart by means of the Raman spectroscopy according to the conventional technology.

Claims

1. A semiconductor laser device comprising: a first clad layer formed on a semiconductor substrate;an active layer formed on the first clad layer and having a strained multiple quantum well structure; anda second clad layer formed on the active layer, whereina sum of products of strain amounts and film thickness in the active layer is set to a negative value.

2. The semiconductor laser device as claimed in claim 1, wherein well layers and barrier layers having reverse strains respectively are alternately laminated in the active layer, andthe sum of the products of the strain amounts and the film thickness is a sum of products of strain amounts and film thickness determined by strain amounts, film thickness and number of layers corresponding to respective lattice constants of the well and barrier layers.

3. The semiconductor laser device as claimed in claim 2, wherein a strain amount εwi of the well layer of an ith (i=1, . . . , n) order is defined as εwi=(awi−a)/a, and a strain amount εbj of the barrier layer of a jth (j=1, . . . , m) order is defined as εbj=(abj−a)/a provided that a lattice constant of the semiconductor substrate is a, the lattice constant of the ith well layer is awi and the film thickness thereof is twi, and the lattice constant of the jth barrier layer is abj and the film thickness thereof is tbj, andthe sum of the products of the strain amounts and the film thickness, ξact, in the active layer is represented by ξact=Σ(εwi×twi)+Σ(εbj×tbj) provided that a total number of the well layers is n and a total number of the barrier layers is m.

4. The semiconductor laser device as claimed in claim 1, wherein the first clad layer is an n-type clad layer, and the second clad layer is a p-type clad layer.

5. The semiconductor laser device as claimed in claim 2, wherein the barrier layer comprises a combination of a blocking layer interposed between the adjacent well layers, and a light guide layer interposed between the well layer and the clad layer.

6. The semiconductor laser device as claimed in claim 2, wherein the strain amount εwi, the film thickness twi, the strain amount εbj, the film thickness tbj, and the sum of the products of the strain amounts and the film thickness ξact are set as follows: 0%<εwi≦1.0%−1.4%≦εbj<0%3 nm<twi<8 nm3 nm<tbj<8 nm−1.97×10−10<ξact<0

7. A multi-wavelength semiconductor laser device comprising a plurality of semiconductor laser devices having different oscillation wavelengths respectively as claimed in claim 1, wherein these semiconductor laser devices are monolithically provided on the semiconductor substrate.

8. The semiconductor laser device as claimed in claim 1, wherein the semiconductor substrate consists of GaAs, the first clad layer consists of AlGaInP, the active layer consists of GaInP or AlGaInP, and the second clad layer consists of AlGaInP.

9. The semiconductor laser device as claimed in claim 2, wherein the semiconductor substrate consists of GaAs, the first clad layer consists of AlGaInP, the active layer consists of GaInP or AlGaInP, and the second clad layer consists of AlGaInP, the well layer consists of GaInP, and the barrier layer consists of AlGaInP.

10. The semiconductor laser device as claimed in claim 9, wherein the blocking layer and the light guide layer consist of AlGaInP, anda composition ratio of In to AlGa included in the blocking layer is larger than a composition ratio of In to AlGa included in the guide layer.