Optical constants of tin selenide single crystals by interference method

Abstract

The refractive index, n, of SnSe single crystals was measured by reflectance after normalization to account for the pronounced rise below the energy gap n was also measured by the interference method in the transparent region. An effective thickness smaller than the true one is introduced to account for the photon scattering by the layer structure of the material in this region. The effective thickness hypothesis gives a satisfactory explanation of the pronounced rise in reflectance for E < E g . The extinction coefficient, k, was calculated from the measured absorption coefficient. Measurements were performed at room temperature using plane polarized light with the plane of polarization parallel to the a- and b-crystallographic axes which lie in the cleavage plane. The real and imaginary parts of the complex dielectric constant (ϵ r , ϵ i ) were calculated from n and k. It is shown that the SnSe single crystal exhibits birefringence. Assuming that the SnSe binding is partly ionic and partly covalent, the results of the optical constants are satisfactorily fitted to the model of a single effective oscillator.