Origin of high‐density hole doping and anisotropic hole transport in a wide gap layered semiconductor LaCuOSe studied by first‐principles calculations

Abstract

AbstractLaCuOSe is a wide gap (Eg = 2.8 eV) p‐type semiconductor. Epitaxial films may be converted to a degenerate semiconductor with hole concentrations (nh) > 1 × 1021 cm−3 by doping Mg ions to the La sites. We, however, found that the Mg concentration in the highest nh film was too low (<1%) to explain the high nh. Further, we observed large subgap absorption and no Burstein–Moss (BM) shift in the doped LaCuOSe, which contradict with a rigid‐band scheme. The doping stability was examined by density functional theory (DFT) calculations. The results showed that the substitution of the La site with an Mg ion needs a large extra energy and is not stable. Alternatively, copper vacancies are easily formed and work as shallow acceptors. On the other hand, it is also revealed that the calculation results are unable to explain the subgap absorption and the absence of a BM shift. Carrier transport calculations based on DFT and the Boltzmann transport theory were also performed, which provided information about anisotropic carrier transport in the layered crystal structure.