High temperature dependence of the cubic phase content and optical properties of BN thin films

The temperature dependence of the cubic phase content and optical properties of Boron nitrogen (BN) thin films was studied in this paper. The BN thin films were deposited on fused silica and Si substrates by radio frequency bias magnetron sputtering. The BN film properties before and after annealing were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and UV-visible transmittance and reflection spectra. The results indicate that annealing temperature has a significant effect on the optical absorption edge, optical absorption coefficient α, refractive index n, and optical conductivity σ of BN films. The optical absorption edge shift to the high energy with annealing temperature increase indicates that the film optical band gap Eg becomes large. The change in the optical absorption properties results from the stress relaxation and phase transformation owing to the high temperature annealings. The dependence of α on the photon energy is fitted by the Urbach tail model in order to determine the Urbach energy E0. In addition, it is found that refractive index n exists clearly different dependences on temperature in visible and ultraviolet regions, and the optical conductivity σ threshold moves to high energy with increasing annealing temperatures in the threshold region.