Optical and Electronic Structural Properties of Cu₃N Thin Films: A First-Principles Study (LDA + U)

A comprehensive study on the electronic structure and optical properties of a Cu₃N film is performed by the first-principles study using density functional theory. The Hubbard (U) term is added in the local density approximation approach for improvement of the theoretical band gap energy. The band structure of the Cu₃N unit cell shows a strong hybridization of Cu 3d and N 2p orbitals in the near-valence band region (M) because of their antibonding states which are also observed by molecular orbitals (HOMO-LUMO). The conduction band is dominated by a very small amount of Cu 3p and N 2p orbitals. The density of states exhibits a negligible deformation in Cu-N bonding. The Cu₃N thin film deposited by the DC magnetron-sputtering technique shows a polycrystalline structure with a nonstoichiometric Cu₃N phase. The experimentally obtained optical band gap and refractive index of the Cu₃N film are 1.44 eV and 2.14, respectively, which are comparable with those from the theoretical approximation.