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 E-0, E-1 and E-2 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. (C) 2016 Elsevier B.V. All rights reserved.