The electronic structures of Be, Mg and Si in zincblende BN were studied by using the tight-binding linearized muffin-tin orbitals technique. Calculations were performed by using 64-atom super-cells which were centered on either a B or a N lattice site. While Be and Mg impurities were substituted only for B, substitution for both B and N was considered in the case of Si. In each case, total-energy minimization was used to study lattice relaxation near to the impurity site, and the nature of the chemical bonding between the impurity and neighboring atoms of the host crystal was studied in detail. It was found that Be and Mg, when substituted for B, created delocalized levels which merged with states at the valence-band edge. These partially occupied levels could result in p-type conductivity, as observed experimentally. In contrast to the behavior of isolated Be and Mg impurities in crystalline BN, it was found that Si which was substituted at a B site introduced delocalized impurity states that overlapped with the conduction-band edge of the host. These levels could contribute to the n-type conductivity of Si-doped crystalline BN. When Si was substituted into the anion sub-lattice it introduced sharp, partially occupied, and highly localized levels within the forbidden gap. Experimentally observed mixtures of n-type and p-type material could therefore be accounted for by the presence of impurities of each type. The relaxation of the host lattice near to the Be and Mg impurities was outward, as was the relaxation near to Si which was substituted at a N site. Inward relaxation was predicted to occur in the case of Si which was substituted for B. Total, orbital, and shell-projected densities of states for the impurity, and up to 6 of the coordination shells nearest to the impurity, were analyzed in detail.

V.A.Gubanov, E.A.Pentaleri, C.Y.Fong, B.M.Klein: Physical Review B, 1997, 56[20], 13077-86