A tight-binding study of acceptor levels in semiconductors

Acceptor binding energies in zinc-blende semiconductors are determined within the tight-binding formalism. The importance of fitting the valence-band masses in the (100) as well as (111) directions is discussed, and parametrizations that specifically fit the valence-band anisotropy are used to calculate Ge acceptor levels in Al xGa1-x As alloys. The sensitivity of the calculated energies to the parameters that determine bulk masses is investigated, as well as the effect of varying the on-site energy of the impurity. A comparison is made between first-neighbor and second-neighbor hopping models. For shallow levels, both approaches give the same results. For deeper levels, however, important differences arise. Experimental evidence suggests that first-neighbor models are better suited for describing intermediate to deep levels.