High quality Cd1−xMnxS epilayers were grown on GaAs (100) substrates via the hot-wall epitaxy method. The crystal structure of the grown Cd1−xMnxS epilayers was changed from cubic to hexagonal with Mn compositions higher than x = 0.05, as determined from x-ray diffraction patterns and scanning electron microscope images. In order to investigate the binding states and their chemical composition, Cd1−xMnxS epilayers have been characterized using x-ray photoelectron spectroscopy. The optical properties of the Cd1−xMnxS epilayers were investigated in a wide photon energy range between 2.0 and 8.5 eV using spectroscopic ellipsometry (SE) at room temperature. The data obtained using SE were analyzed in order to find the critical points of the pseudodielectric function spectra, <ɛ(E)> = <ɛ1(E)> + i<ɛ2(E)>. In addition, the second derivative spectra, d2ɛ(E)/dE2, of the pseudodielectric function of the Cd1−xMnxS epilayers were numerically calculated in order to determine the critical structures. Four structures, E0′ (H3vH3c), F1 (M4vM3c), and two E2(K3vK2c,K2vK2c) structures from 6.0 eV to 8.0 eV, were observed with variation of the Mn composition at 300 K via ellipsometric measurements for the Cd1−xMnxS epilayers. The phase transition process from a cubic structure to a hexagonal structure was observed and investigated, for the first time, for Cd1−xMnxS epilayers via SE.

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