Optical characterization of Cu2ZnSnSe4 grown by thermal co-evaporation

Cu2ZnSnSe4 thin films with different substrate temperature and Cu flux were grown by thermal co-evaporation. Raman scattering, photoluminescence, and contactless electroreflectance (ER) measurements were performed. The Raman spectra of Cu2ZnSnSe4 show two main peaks at 170 and 192 cm− 1. The photoluminescence spectrum shows a peak below 1.0 eV. Franz–Keldysh oscillations (FKOs) were observed in the ER spectra. From the analysis of the FKOs, the bandgap energy of Cu2ZnSnSe4 thin films is estimated to be 1.07 eV at 90 K and 0.99 eV at room temperature. We conclude that the bandgap energy of Cu2ZnSnSe4 thin films is around 1.0 eV.