Near-bandgap optical properties of Al1−x In x N thin films grown on a c-plane freestanding GaN substrate

Abstract

We investigated the relationship between the optical constants and localized states near the band-edge in high-quality crystalline Al1−x In x N alloys, with an indium content x ranging from 0.12 to 0.22, grown on a c-plane freestanding GaN substrate. Optical constants were obtained by spectroscopic ellipsometry. The tanΨ and cosΔ spectra were fitted by the Adachi’s critical-point (AC) model. The effects of the near-band-edge localized states on the optical constants were characterized by the spectral broadening factor γ, which was obtained by the AC model. The γ increased with increasing x and this tendency also confirmed by the γ obtained by the photoluminescence excitation (PLE). The bandgap energies obtained by the AC model agree well with those obtained by the PLE. It is suggested that the indium-related near-band-edge localized states cause the spectral broadening of the refractive index and extinction coefficient spectra in Al1−x In x N alloys.