Electronic structures of alkali metal (Li, Na, K, Rb, and Cs) monosilicides

The electronic structures of LiSi, NaSi, RbSi, and CsSi have been calculated using a first-principle pseudopotential method to clarify the possibility of band-gap broadening of BaSi2 by alloying with alkali metals. All of them are found to be semiconductors with the calculated indirect band gaps of 1.17 eV (LiSi) and 1.24 eV (NaSi) or the calculated direct band gaps of 1.32 eV (KSi), 1.38 eV (RbSi), and 1.66 eV (CsSi). The general tendency that the gap values of these ionic semiconductors are increased as their ionicities are increased and alkali metal incorporation into BaSi2 will be hopeful to broaden its band-gap.