Two-Dimensional Electronic Structures in Layered Oxychalcogenide Semiconductors, LaCuOCh (Ch=S, Se, Te) and La2CdO2Se2

ABSTRACTElectronic structures of layered oxychalcogenides, LaCuOCh (Ch=S, Se, Te) and La2CdO2Se2, were studied using ab-initio band calculations in relation to their optical and electronic properties. It was found that the dispersions of the top valence bands are much smaller in Γ-Z direction than in Γ-X direction, indicating that the electronic structure is highly two-dimensional, and that holes are confined in the CuCh or CdSe layers. The two-dimensional electronic structure is supported experimentally by staircase-like structure observed in optical absorption spectra at 10 K associated with two excitonic absorption peaks split by spin-orbit interaction of Ch ions. La2CdO2Se2has the largest bandgap due to the two-dimensional network structure of CdSe tetrahedra.