Ellipsometric characterization and density-functional theory analysis of anisotropic optical properties of single-crystal α-SnS

We report on the anisotropic optical properties of single-crystal tin monosulfide (SnS). The components epsilon(a), epsilon(b), and epsilon(c) of the pseudodielectric-function tensor - + i spectra are taken from 0.73 to 6.45 eV by spectroscopic ellipsometry. The measured spectra are in a good agreement with the results of the calculated dielectric response from hybrid density functional theory. The spectra show the direct band-gap onset and a total of eight above-band-gap optical structures that are associated with the interband-transition critical points (CPs). We obtain accurate CP energies by fitting analytic CP expressions to second-energy-derivatives of the data. Their probable electronic origins and implications for photovoltaic applications are discussed. (C) 2014 AIP Publishing LLC.