Spectroscopic Ellipsometry Investigation of Optical Constants and Dispersion Parameters of TlGaS ₂ Single Crystals

ABSTRACT

Spectroscopic ellipsometry measurements were performed on freshly cleaved layer‐plane (001) surfaces of TlGaS ₂ crystals, with the surface normal approximately oriented along the reciprocal‐lattice direction , in the photon‐energy range of 1.2–6.2 eV at room temperature. The measured ellipsometric parameters, acquired at a fixed incidence angle and analyzed using ambient–substrate model, were used to determine the dielectric function as well as the effective refractive index and extinction coefficient for the present oblique‐reflection configuration. From these effective optical functions, corresponding absorption coefficient, optical penetration depth, and dielectric‐related response functions were derived. The derived absorption spectrum exhibits a pronounced absorption‐edge feature near 2.43 eV, as identified from the first derivative of the absorption coefficient with respect to photon energy. The low‐energy dispersion behavior was analyzed using Wemple–DiDomenico single‐oscillator model. In addition, the surface and volume energy‐loss functions were evaluated to further characterize the effective electronic response in the measured geometry. The resulting effective optical parameters provide a configuration‐specific description of the optical response of TlGaS ₂ , relevant to optoelectronic and photonic applications. Because TlGaS ₂ is a monoclinic and optically anisotropic crystal, these quantities do not represent the complete intrinsic dielectric tensor or separately resolved polarization‐dependent optical constants of the material.