Optical functions from 0.02 to 6 eV of AlxGa1−xSb/GaSb epitaxial layers

The complex refractive index ñ=n+ik and the dielectric function ε̃=ε1+iε2 at room temperature of AlxGa1−xSb films with 0⩽x⩽0.5, grown by molecular beam epitaxy on a GaSb substrate, were determined from 0.02 to 6 eV by using the complementary data from fast Fourier transform far-infrared, dispersive, and ellipsometric spectrometry. The effect of the native oxide was accounted for and the self-consistency of the optical functions was checked in the framework of the Kramers–Kronig causality relations. In the restrahlen region the dielectric function was well fitted by classical Lorentz oscillators; in the transparent region below the fundamental gap E0, the refractive index was modeled by a Sellmeier dispersion relation, and in the interband region the dielectric function near the critical points was analyzed through standard line shapes. Interpolating the fitting parameters or the interband dielectric spectra, it was possible to obtain the optical functions for any concentration x between 0.0 and 0.5.