Comparison of Additional Boundary Conditions Based on Thermoreflectance Spectra of the An=1‐Exciton in CdS Crystals at Oblique Incidence

Thermoreflectance spectra of the An=1‐exciton in CdS are measured at 8 K for angles of incidence of the light ranging from 5° to 85°, using three different spatial arrangements between the c‐axis, the E‐ and k‐vector of light. Additional boundary conditions of Pekar, Ting et al. and Agarwal et al. are discussed for the first time in terms of optical constants. The refractive indices for these additional boundary conditions are derived, considering special features of CdS, such as optical anisotropy, exciton symmetry, and effective exciton mass anisotropy. Fitting calculations based on the experimental data show that Pekar's additional boundary condition gives the best agreement between theory and experiment.