Determination of the thickness and spectral dependence of the refractive index of Al$_x$In$_{1-x}$Sb epitaxial layers from reflectance spectra

A nondestructive method for measuring the thicknesses of epitaxial layers of Al$_x$In$_{1-x}$Sb alloys based on interference effects in reflectance spectra measured in a wide wavelength range (1–28 $\mu$m) is implemented. The studied 0.9–3.3 $\mu$m thick Al$_x$In$_{1-x}$Sb layers are grown on highly lattice-mismatched GaAs substrates by molecular beam epitaxy. The found thicknesses are in good agreement with the independent data of scanning electron microscopy. The spectral dependence of the refractive index $n(E)$ of Al$_x$In$_{1-x}$Sb layers is measured both for the regions of transparency and fundamental absorption. The refractive index for the case of $E<E_0$ was calculated by a double-oscillator model using a refined experimental dependence of the band gap on the composition $E_0(x)$. The experimental data on the $n(E)$ of Al$_x$In$_{1-x}$Sb for energies $E >E_0$ are found based on the interference pattern.