Patent ID: 7218658

Claim:
A semiconductor laser device comprising: a first semiconductor layer of a first conductive type having a first bandgap energy and a first impurity concentration; a second semiconductor layer of the first conductive type having a second bandgap energy and a second impurity concentration, laminated on said first semiconductor layer; an active layer having a third bandgap energy lower than said first and second bandgap energies, laminated on said first semiconductor layer with said second semiconductor layer interposed between said active layer and said first semiconductor layer; a third semiconductor layer of a second conductive type having a fourth bandgap energy higher than said third bandgap energy, laminated on said first semiconductor layer with said active layer and said second semiconductor layer interposed between said third semiconductor layer and said first semiconductor layer; a fourth semiconductor layer of said first conductive type having a third impurity concentration, disposed between said first semiconductor layer and said second semiconductor layer, and having both a higher conduction band energy level than the conduction band energy levels of said first and second semiconductor layers and a higher valence band energy level than the valence band energy levels of said first and second semiconductor layers, or having both a lower conduction band energy level than the conduction band energy levels of said first and second semiconductor layers and a lower valence band energy level than the valence band energy level of said first and second semiconductor layers; and a semiconductor substrate disposing, on a surface thereof, said first semiconductor layer, said second semiconductor layer, said active layer, said third semiconductor layer, and said fourth semiconductor layer such that either said first semiconductor layer or said third semiconductor layer is adjacent to and opposes said semiconductor substrate, and having the same conductive type as that of said one of said first semiconductor layer and said third semiconductor layer being adjacent to said semiconductor substrate.