First-Principles Study of Electronic Structure and Optical Properties of La-Doped AlN

As a wide-bandgap semiconductor material with small dielectric constant and good thermal stability, aluminium nitride (AlN) can theoretically emit light in the deep ultraviolet wavelength region, so it is important in expanding the response of AlN in the visible region. In order to study the influences of La doping on the photoelectric properties of wurtzite AlN crystal, the first-principle plane-wave pseudopotential method and generalized gradient approximation were used to study the lattice constants, electronic structure and optical properties of undoped and La-doped AlN. The calculation results indicate that the intrinsic AlN is a direct-bandgap semiconductor material which both conduction band bottom and valence band top being at the G point, but La-doped AlN forms an indirect-bandgap semiconductor in which the conduction band bottom is at the G point and the valence band top is at the F point. The peak of the density of states is reduced near Fermi energy, and the electronic localization features are significantly diminished. The La doping makes the forbidden band width of AlN narrow, which reduces the photon energy needed for the electron transition, and shows a red shift phenomenon, which expands the influence on visible light. Therefore, this provides a theoretical basis for the study of the photoelectric properties of rare-earth-metal La-doped AlN.