Optical transparency, carrier mobility, and electrical conductivity of La-based copper layered oxychalcogenides: A density functional theory study

The family of layered oxychalcogenides has received extensive attention in the field of optoelectronics due to the wide band gaps and p-type conductivity. Herein, seven La-based copper oxide sulfides are considered to explore their unrevealed optical transparency, transport properties as well as the electrical conductivity using ab initio density functional calculations. The obtained results demonstrate that second gap may lead to degradation of the transparency for p-type semiconductors. Our predicted theoretical carrier effective masses of these compounds are expected to supply a gap in previous investigations. The temperature dependence of transport properties shows that the carrier mobility decreases with the increasing temperature because the phonon scattering is intensified as temperature increases. At room temperature, LaCuSTe exhibits a high hole mobility of 461.00 cm² v⁻¹ s⁻¹ and a high electrical conductivity of 1.48 × 10³ S cm⁻¹ which nearly reaches the conductive ability of typical n-type TCOs, like ZnO:Al, TiO₂:Nb, SnO₂:F, and Sn:In₂O₃ (on the order of 10²-10⁴ S cm⁻¹). The fundamental mechanism for the high conductivity of LaCuSTe may lies in the light hole effective masses obtained by the enhanced hybridization between 3p or 5p orbitals of S/Te atoms and the Cu-3d states. LaCuSTe is demonstrated as an intrinsic p-type conductor with a native hole concentration of 2.12 × 10¹⁵ n/cm⁻³ (requiring no external doping). It is probably due to the self-compensation effect of native donor defects in LaCuSTe is weaker than that in conductive oxides.