Patent ID: 7113532

Claim:
A semiconductor laser device comprising a substrate and a multi-layer structure formed on the substrate, the multi-layer structure configured so as that an active layer is sandwiched by clad layers having a smaller refractive index but a larger band gap energy than those of the active layer, wherein: a lattice constant a adjacent of a semiconductor crystal layer adjacent to the active layer is set to be larger than a lattice constant a ac of the active layer (a ac <a adjacent ) such that they are not substantially lattice matched; and wherein the lattice constant a ac of the active layer is less than a lattice constant a sub of the substrate such that they are not substantially lattice matched, and the lattice constant a adjacent of a semiconductor crystal layer adjacent to the active layer is larger than the lattice constant a sub of the substrate such that they are not substantially lattice matched (a ac <a sub <a adjacent ).