Dielectric function of hexagonal AlN films determined by spectroscopic ellipsometry in the vacuum-uv spectral range

Abstract

The optical properties of thin epitaxial AlN films have been determined in the 5--10 eV energy range using a spectroscopic ellipsometer operating with synchrotron radiation. Measurements at low temperatures (down to 120 K) were performed to enhance spectral features and to determine the temperature dependence of interband critical points. Our data are in qualitative agreement with recent reflectance experiments but show larger amplitudes and additional structures in the vicinity of the fundamental absorption edge. The possible origin of these structures is discussed on the basis of calculations of the electronic energy bands.