First-Principles Studies for Electronic Structure and Optical Properties of p-Type Calcium Doped α-Ga₂O₃

Gallium oxide (Ga₂O₃) is a promising wide-band-gap semiconductor material for UV optical detectors and high-power transistor applications. The fabrication of p-type Ga₂O₃ is a key problem that hinders its potential for realistic power applications. In this paper, pure α-Ga₂O₃ and Ca-doped α-Ga₂O₃ band structure, the density of states, charge density distribution, and optical properties were determined by a first-principles generalized gradient approximation plane-wave pseudopotential method based on density functional theory. It was found that calcium (Ca) doping decreases the bandgap by introducing deep acceptor energy levels as the intermediate band above the valence band maximum. This intermediate valence band mainly consists of Ca 3p and O 2p orbitals and is adequately high in energy to provide an opportunity for p-type conductivity. Moreover, Ca doping enhances the absorptivity and reflectivity become low in the visible region. Aside, transparency decreases compared to the pure material. The optical properties were studied and clarified by electrons-photons interband transitions along with the complex dielectric function's imaginary function.