Tight-binding scheme for impurity states in semiconductors

A tight-binding approach is presented for the calculation of impurity states in semiconductors. The model provides a valid description of acceptors and donors for shallow as well as deep levels, but is expected to be most useful for intermediate levels in which conventional treatments break down. The impurity state is calculated for large supercells containing up to 64 000 atoms, and a finite-size analysis allows extrapolation to the bulk limit. Using this theory, we find very good agreement with experimental results for Ge, Si, and C acceptors in AlₓGa_1-xAs alloys.