Direct-current generation due to wave mixing in semiconductors

We describe an effect of the generation of direct current which may arise i n semiconductors or semiconductor microstructures due to a mixing of cohere nt electromagnetic radiations of commensurate frequencies. The effect is, i n essence, due to a nonparabolicity of the electron energy bands and is str onger in systems where this nonparabolicity is greater. We have made exact calculations in the framework of the Kane model, applicable to narrow-gap s emiconductors and the tight-binding model which we employ for a description of a semiconductor superlattice.