The Unique Electronic Structure of Mg2Si: Shaping the Conduction Bands of Semiconductors with Multicenter Bonding

The electronic structures of the antifluorite-type compound Mg2Si is described in which a sublattice of short cation-cation contacts creates a very low conduction band minimum. Since Mg2Si shows n-type conductivity without intentional carrier doping, the present result indicates that the cage defined by the cations plays critical roles in carrier transport similar to those of inorganic electrides, such as 12CaO center dot 7Al(2)O(3):e(-) and Ca2N. A distinct difference in the location of conduction band minimum between Mg2Si and the isostructural phase Na2S is explained in terms of factors such as the differing interaction strengths of the Si/S 3s orbitals with the cation levels, with the more core-like character of the S 3s leading to a relatively low conduction band energy at the G point. Based on these results and previous research on electrides, approaches can be devised to control the energy levels of cation sublattices in semiconductors.