Dielectric functions of as-grown and annealed Ga$_{1-x}$Mn$_{x}$As thin films

We have investigated the dielectric functions of a series of as-grown as well as annealed Ga$_{1-x}$Mn$_{x}$As thin films using spectroscopic ellipsometry. After determining the alloy compositions using x-ray diffraction experiments, a rotating analyzer spectroscopic ellipsometer was used to measure the complex reflection ratio for each of the films in the energy range between 0.9-6.5~eV. By modelling the ellipsometric data, the dielectric functions for each of the Ga$_{1-x}$Mn$_{x}$As samples were determined. All of the dielectric functions displayed the critical point structures related to the higher order electronic transitions, and showed differences between the as-grown and the annealed sample spectra.