Semiconductor laser device

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;

a second clad layer formed on the active layer; and

a window region formed near end facets of the semiconductor laser device, the window region including a laser light path, the window region having a window region active layer of a wider band gap than a band gap of the active layer, wherein:

the active layer and the window region active layer contain AlGaInP, and the active layer includes at least one blocking layer and at least one well layer,

compression strain is applied to the well layer and tensile strain is applied to the blocking layer, and

a sum of products of strain amounts and film thickness in the active layer is set to a negative value, and

the second clad layer contains zinc in the window region, and

the band gap of the active layer is increased by diffused zinc from the second clad layer in the window region.

2. The semiconductor laser device as claimed in claim 1 , wherein

a strain amount ε wi of the well layer of an ith (i=1, . . . , n) order is defined as ε wi =(a wi −a)/a, and a strain amount ε bj of the barrier layer of a jth (j=1, . . . , m) order is defined as ε bj =(a bj −a)/a provided that a lattice constant of the semiconductor substrate is a, the lattice constant of the ith well layer is a wi , and the film thickness thereof is t wi , and the lattice constant of the jth barrier layer is a bj and the film thickness thereof is t bj , and

the sum of the products of the strain amounts and the film thickness, ξ act , in the active layer is represented by ξ act =Σ(ε wi ×t wi )+Σ(ε bj ×t bj ) provided that a total number of the well layers is n and a total number of the barrier layers is m.

3. 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.

4. The semiconductor laser device as claimed in claim 1 , 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.

5. The semiconductor laser device as claimed in claim 1 , wherein

the strain amount ε wi , the film thickness t wi , the strain amount ε bj , the film thickness t bj , and the sum of the products of the strain amounts and the film thickness ξ act are set as follows:

0%<ε wi ≦1.0%

−1.4%≦ε bj <0%

3 nm<t wi <8 nm

3 nm<t bj <8 nm

−1.97×10 −10 <ξ act <0.

6. 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.

7. The semiconductor laser device as claimed in claim 1 , wherein

the semiconductor substrate consists of GaAs, the first clad layer consists of AlGaInP, and the second clad layer consists of AlGaInP.

8. The semiconductor laser device as claimed in claim 1 , wherein

the semiconductor substrate consists of GaAs, the first clad layer consists of AlGaInP, and the second clad layer consists of AlGaInP, the well layer consists of GaInP, and the barrier layer consists of AlGaInP.

9. The semiconductor laser device as claimed in claim 8 , wherein

the blocking layer and the light guide layer consist of AlGaInP, and

a 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.