Anisotropy of surface optical properties at BN(110): An ab initio study

We present a calculation of the linear optical properties of the nonpolar (110) surface of cubic boron nitride, performed within the first-principle density-functional theory and local-density approximation scheme. The reflectance anisotropy (RA) spectrum is analyzed in relation to the better known spectrum of the GaAs(110) surface and to the existing tight-binding results for GaN(110). Previous results for the RA spectrum of GaN(110) obtained in tight-binding scheme are here confirmed, including a negative structure at the onset. For BN(110) the present first ab initio results show the fundamental role played by surface-states transitions at the onset of the RA spectrum. The origin of the optical structures is studied in comparison with the RA spectra of GaAs(110) and GaN(110), in connection with the differences in ionicity between nitrides and GaAs, and considering the specific relaxation occurring at nitrides (110) surfaces.