Dielectric function and energy of the E 0 critical point of hexagonal GaN at 26 K studied by using spectroscopic ellipsometry

Abstract

We report the dielectric function from 0.74 to 6.42 eV of hexagonal GaN at 26 K, along with the energies of its E0 exciton and critical point. The GaN sample is a 1.9 µm thick film deposited on a c-plane (0001) sapphire substrate by using molecular beam epitaxy. Data were obtained with a rotating-compensator spectroscopic ellipsometer. B-splines in a multilayer-structure calculation were used to extract the optical properties of the film. The 26 K E0 excitonic and critical-point structures were significantly blue-shifted and were sharpened relative to their room-temperature equivalents.