Optical Constants of Germanium Selenide Single Crystals in the Transparency Region

The refractive index, n, of GeSe single crystal is measured by the interference method in the transparency 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 satisfactory explanation of the pronounced rise in reflectance for E < Eg. The extinction coefficient, k, is calculated from the measured absorption coefficient. Measurements are performed at room temperature using plane polarized light with the plane of polarization parallel to the a and c crystallographic axes which lie in the plane of cleavage. The real and imaginary parts of the complex dielectric constant (ϵr, ϵi) as well as the reflectance and its phase change (R, φ) are calculated from the values of n and k. It is shown that GeSe single crystal exhibits birefringence. Assuming that GeSe binding is partly ionic and partly covalent, the results of the optical constants are satisfactorily fitted to the model of a single effective oscillator.