Optical Properties of a Magnetic Semiconductor: Chalcopyrite CuFeS. II. Calculated Electronic Structures of CuGaS₂:Fe and CuFeS₂

Abstract

In order to study the electronic structures of CuGaS 2 : Fe and CuFeS 2 , the problem is simulated by large clusters of these crystals. The system is treated as a "large molecule" and the energies and wavefunctions for the molecule are obtained using a semiempirical molecular orbital method. The unoccupied molecular orbitals originating from iron 3d orbitals in CuGaS 2 : Fe are well localized on the iron ion, while the corresponding orbitals in CuFeS 2 have a considerable admixture of sulfur 3p orbitals. The molecular orbitals corresponding to uppermost states of the valence band are composed of sulfur 3p and copper 3d orbitals. It is derived from the comparison between the observed and calculated absorption spectra that the A and B absorption bands in CuGaS 2 :Fe arise from the charge transfer transitions from the valence band to the unoccupied states originating from the iron 3d orbitals and the absorption band edge in CuFeS 2 arises from the corresponding transitions.