Changes of the band structure of Mg2Si induced by interstitial doping with nonmetallic elements

Abstract

The electronic structures and the densities of states of Mg8Si4X1 were calculated by using density functional theory, where semiconducting Mg2Si and a nonmetallic element, X, form interstitial alloys. When X is an inert gas element, the electronic structure is basically the same as that of Mg8Si4, but the bandgap increases (X = He or Ne) or decreases (X = Ar) depending on the degree of volume expansion caused by the interstitial alloying. In the case of X = electronegative element (O, F, or Cl), X works as an electron acceptor, which causes the transition of Mg2Si from an intrinsic semiconductor to a p-type semiconductor. This is also the case for X = H. When the electronegativity of X is intermediate (X = C, Si, N, P, or S), the bandgap at the R point of the reciprocal lattice of Mg8Si4 becomes negligible. When X = B, a transition to an n-type semiconductor is predicted as in the case of doping with electropositive metal elements such as Li and Al, but the bandgap at the R point of the reciprocal lattice of Mg8Si4 becomes negligible, as in the case of elements with intermediate electronegativities.