Patent ID: 7223993

Claim:
An optical semiconductor device comprising: a first semiconductor layer with a first type of conductivity, formed on an InP semiconductor wafer; a multi-quantum-well structure formed on said first semiconductor layer; and a second semiconductor layer formed on said multi-quantum-well structure, wherein said second semiconductor layer has a second type of conductivity different from the first type of conductivity; wherein: said multi-quantum-well structure includes, in an alternately stacked form, quantum well layers each formed of InGaAlAs which has a lattice constant different from that of said InP semiconductor wafer, and barrier layers each formed of InGaAlAsSb which has lattice constants different from those of said InP semiconductor wafer and the InGaAlAs layer; and each of the quantum well layers has first strain with respect to said InP semiconductor wafer, each of the barrier layers has second strain with respect to said InP semiconductor wafer, and a sign of the first strain and a sign of the second strain differ from each other.