Patent ID: 7329894

Claim:
A semiconductor laser device comprising: a semiconductor substrate; and a semiconductor multilayer structure formed on the semiconductor substrate, wherein the multilayer structure has at least one set of semiconductor layers including a first semiconductor layer, a second semiconductor layer, and a third semiconductor layer positioned midway between both the first and second layers; and wherein, in said at least one set of the semiconductor layers, said third semiconductor layer is a Type II superlattice layer that includes first and second kinds of semiconductor layers stacked alternately, the first kind of semiconductor layers having a gradually decreased thickness, and the second of semiconductor layers having an identical thickness; when an energy position of a conduction band is viewed as energy barrier for electrons, an energy position of a conduction band of the first semiconductor layer (E C1 ) is higher than an energy position of a conduction band of the second semiconductor layer (E C2 ), and an energy position (QE C3 ) at which a quantum level in a conduction band of the third semiconductor layer is formed between E C1 and E C2 and takes a value equal to or greater than 70% and less than 100% of an energy difference between E C1 and E C2 , in absence of any voltage applied thereto; and when an energy position of a valence band is viewed as energy barrier for holes, an energy position of a valence band of the first semiconductor layer (E V1 ) is lower than an energy position of a valence band of the second semiconductor layer (E V2 ), energy positions (QE V3 ) at which quantum levels in a valence band of the third semiconductor layer are formed between E V1 and E V2 , such that an energy difference between E V1 and QE V3 increases stepwise in the direction from the first semiconductor layer toward the second semiconductor layer in absence of any voltage applied thereto.