Ellipsometric study of the optical response of ZnS:Cr for PV applications

Optical properties of highly chromium doped (2–4 at.%) zinc sulfide made by pulsed laser deposition have been studied by spectroscopic ellipsometry in the spectral range of 0.73–5.90 eV. The characteristic optical features of the ZnS are a direct bandgap with absorption onset at 3.6 eV, with E0, E1 and E2 critical points around 3.7, 5.7 and 7 eV. Excitonic effects were observed to be strong in this material – in line with the literature. The sub-bandgap absorption accredited to the chromium doping appears as a broad sub-bandgap feature increasing monotonously with increased doping concentration at a given growth temperature. In this report, we discuss three different approaches to extract and analyze the optical properties in terms of the complex dielectric function.