Patent ID: 7276735

Claim:
An optical semiconductor element comprising: a substrate of GaAs having a first surface and a second surface opposite to each other; a buffer layer of In j Ga 1-j As 1-k N k (0≦j≦1, 0.002≦k≦0.05) formed on said first surface of said substrate; a first conductive type clad layer formed on said buffer layer; an active layer formed on said first conductive type clad layer and comprising a well layer of In z Ga 1-z As (0≦z≦1), said well layer having a smaller bandgap than said first conductive type clad layer, said active layer having a larger thickness than its critical thickness for said semiconductor substrate based upon equilibrium theories; a second conductive type clad layer formed on said active layer and having a larger bandgap than said well layer; and a middle layer formed between said buffer layer and said first conductive type clad layer.