Electronic Structure of Sr2Cu2ZnO2S2 Layered Oxysulfide with CuS Layers

The electronic structure of p-type semiconducting Sr2Cu2ZnO2S2 (SCZOS) was examined experimentally and theoretically. The band gap of SCZOS estimated by the optical absorption of its thin film was 2.7 eV, which is relatively large in chalcogenide semiconductors. Normal and inverse photoemission spectra were measured to observe the valence band or conduction band structure of this material. The observed band structure revealed that the Fermi level of SCZOS was located at the top of the valence band, and the bottom of the conduction band was approximately 2.5 eV above the Fermi level. These results demonstrate the wide-gap and p-type semiconducting nature of SCZOS. Comparison of the photoemission spectra with the density of states calculated by the tight-binding method led to the conclusion that the top of the valence band is mainly composed of a hybridized (Cu 3d)−(S 3p) band, and the bottom of the conduction band primarily consists of a dispersed Zn 4s band.