Optical properties of wurtzite CdS

Abstract

The complex dielectric functions ε(E)=ε1(E)+iε2(E) of wurtzite CdS have been measured by spectroscopic ellipsometry in the photon-energy range between 1.2 and 5.7 eV at room temperature. The measurements are made on the surface parallel to the optic axis c to extract ε(E) spectra for both the ordinary (E⊥c) and extraordinary (E∥c) rays. The measured data reveal distinct structures at energies of the E0 and E1 critical points. These data are analyzed on the basis of a simplified model of the interband transitions. Results are in satisfactory agreement with the experimental data over the entire range of photon energies. Dielectric-function-related optical constants of wurtzite CdS, such as the complex refractive index n*=n+ik, absorption coefficient α, and normal-incidence reflectivity R, are also presented. To facilitate design of various optoelectronic devices, the refractive-index data in the transparent region have been fitted to the first-order Sellmeier equation. As a byproduct, the high-frequency and static dielectric constants of wurtzite CdS are obtained as ε∞=5.23 and εs=8.28 for E⊥c and ε∞=5.29 and εs=8.73 for E∥c.