Electronic structures of semiconducting FeGa3, RuGa3, OsGa3, and RuIn3 with the CoGa3- or the FeGa3-type structure

Electronic structure of FeGa3, RuGa3, OsGa3 and RuIn3 with the crystal structures belonging to the space group of P4n2 (No. 118), which is usually referred to as the CoGa3-type structure, and P42/mnm (No. 136), which is usually referred to as the FeGa3-type structure, have been calculated using a first-principle pseudopotential method based on the density-functional theory within the local density approximation (LDA) with the generalized gradient correction. All of them have the similar band structure in that the valence band maximum occurs at or near A and the conduction band minimum occurs at a point between Z and Γ. From the total energies calculated, compounds with the FeGa3-type structures are more stable than those with the CoGa3-type structures. The band gaps of FeGa3, RuGa3, OsGa3 and RuIn3 with the FeGa3-type structure are about 0.50, 0.26, 0.68, and 0.30 eV, respectively, which are wider than those with the CoGa3-type structure. Calculated band gaps are wider than the observed gaps, which is unusual in the LDA calculation.