Abstract
In the present work, details of the crystal growth (Bridgeman method) and optical reflection spectroscopy for two single crystals (X = S, Te) were reported. Detailed ab-initio DFT calculations of the structural, electronic and optical properties of the crystals were performed for a deeper understanding of the experimentally obtained optical data. The special attention is paid to the electron charge density distribution, carrier mobility, optical reflectivity spectra and finally the anisotropy of the corresponding optical functions were studied. Were established a relations with carrier mobility, the optical anisotropy and electronic band structures for the titled crystals and compared with the optical reflectance spectra, covering the range of principal inter-band transitions. The origin of the calculated bands and effects of the anion substitution (Se by Te) on the crystal properties are studied. The role of screening effects is discussed by a comparison of the GGA and LDA approaches, including the electronic band dispersion and effective masses anisotropy. The possible changes of the inter-band transition are considered. The relation between the space charge density distribution and optical features is established. Finally was explained the origin of the observed discrepancies between the experimental and theoretical data. (C) 2017 Elsevier B.V. All rights reserved.