Unrevealed electronic and optical properties of the layered oxychalcogenides (LaO)CuCh (Ch = S, Se, Te): A density-functional study

We calculate the electronic and optical properties of layered oxychalcogenide (LaO)CuCh (Ch = S, Se, Te) systems by using generalized gradient approximation method based on density-functional theory. As the results, we obtain direct bandgap for Ch = S, Se, and Te of 1.67, 1.44, and 1.20 eV, respectively. We also find that valence band for each Ch element can be divided into three states, i.e., antibonding and bonding states that come from strong hybridization of Cu 3d-t(2g) and Ch p, and nonbonding states that come from localized Cu 3d-e(g) states. The local symmetry of Cu ion is distorted tetrahedral due to JahnTeller distortion on Cu 3d states, in which d(zx) and d(zy) are at the same energy level. Using DrudeLorentz model, highest dielectric constants and optical dichroism are found in (LaO)CuTe, while p-type conductivity is stronger in (LaO)CuSe system. Energy levels of plasmonic states can also be tuned by changing Ch element. Our results comprehensively present the electronic properties of (LaO)CuCh systems and predict the dielectric functions and plasmonic features, which are essential for novel functional device applications. (C) 2017 The Japan Society of Applied Physics