Modulation spectroscopy characterization of Cu based chalcopyrites and kesterites

To investigate the composition effects on the band gap energy in different Cu based semiconducting material systems electroreflectance and photoreflectance measurements have been performed. The derivative nature of the modulation spectroscopy allows effectively probing the near band gap edge transitions, which are clearly resolved even at a room temperature. These distinct optical structures were analyzed by a three-dimensional critical point line shape model and their threshold transition energies were accurately determined.