Optical properties of rocksalt and zinc blende AlN phases: First-principles calculations

We investigate the electronic structures and optical properties of the wurtzite, zinc blende, and rocksalt AlN phases at their structural phase transition pressures by the ultrasoft pseudopotential density functional method. We employ the Perdew-Burke-Eruzerhof form of the generalized gradient approximation available in the CASTEP code with the plane-wave basis sets to expand the periodic electron density. The dielectric function and optical properties such as reflectivity, absorption coefficient, refractive index, and electron energy-loss function are presented in a wide energy range between 0 and 50 eV. Our results reveal that for rocksalt AlN phase, the intensity of N 2p orbitals in the conduction bands obviously decreases when the pressure increases from 15 to 17 GPa. The calculated optical properties indicate that the zinc blende and wurtzite AlN phases have some similar features but the rocksalt AlN phase has other characteristics. (c) 2008 American Institute of Physics.