FORMATION OF IMPURITY BANDS IN DOPED SEMICONDUCTORS

The determination of the widths and energetic positions of impurity bands in doped semiconductors has been performed in the past by band-structure calculations of hypothetical impurity superlattices or by applying multiple-scattering theories (e.g., the Klauder-V approximation) with essentially different results. The related problems of ionization energies in dense plasmas and of exciton ionization energies in highly excited semiconductors have additionally been treated using two-particle Green's-function techniques with the result of vanishing bandwidths with vanishing temperature for all densities below the Mott value. The reasons for these differences are discussed and the widths of impurity bands in doped semiconductors are calculated by the Wigner-Seitz method and a multiple-scattering approximation, which is correct to first order with respect to the impurity concentration.