Bonding nature of conduction states in electron-deficient semiconductors: Mg2Si

Abstract

The electronic properties of Mg2Si are calculated with the self-consistent pseudopotential method. The resulting energy bands agree with those of previous empirical pseudopotential calculations, are consistent with interband optical data, but are at variance with photoemission measurements since they predict the existence of a 3.5 eV inter-valence energy gap. Analysis of the electronic charge distribution shows that the material is ionic with weak Mg-Si bonds. The first four conduction bands are formed from bonding molecular orbitals which extend throughout the unit cell. This surprising feature, probably common to other electron deficient semiconductors, is correlated to the low value of the energy gap in Mg2Si, Mg2Ge, and Mg2Sn.