Optical constants of germanium sulphide single crystal by interference method

Abstract

The refractive index, n, of a GeS single crystal was measured by the interference method in the transparency region. An effective thickness smaller than the true one was introduced to account for the scattering by the layer structure of the material in this region. The effective thickness hypothesis gave 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 plane of cleavage. The real and imaginary parts of the complex dielectric constant (ϵ r, ϵ i) as well as the reflectance and its phase change ( R, Φ) were calculated from the values of n and k. It was shown that the GeS single crystal exhibits birefringence. Assuming that GeS binding is partly ionic and partly covalent, the optical constants were satisfactorily fitted to the model of single effective oscillator.