The electronic structure, lattice dynamics, and Raman spectra of the kesterite, stannite, and pre-mixed Cu-Au (PMCA) structures of Cu 2ZnSnS 4 (CZTS) and Cu 2ZnSnSe 4 (CZTSe) were calculated using density functional theory (DFT). Differences in longitudinal and transverse optical (LO-TO) splitting in kesterite, stannite, and PMCA structures can be used to differentiate them. The -point phonon frequencies, which give rise to Raman scattering, exhibit small but measurable shifts, for these three structures. Experimentally measured Raman scattering from CZTS and CZTSe thin films were examined in light of DFT calculations and deconvoluted to explain subtle shifts and asymmetric line shapes often observed in CZTS and CZTSe Raman spectra. Raman spectroscopy in conjunction with ab initio calculations can be used to differentiate between kesterite, stannite, and PMCA structures of CZTS and CZTSe.
Bibliographical noteFunding Information:
This work was supported primarily by the MRSEC Program of the National Science Foundation (NSF) under Award No. DMR-0819885. Parts of this work were completed at the Characterization Facility at UMN, which receives partial support from US-NSF through the MRSEC and NNIN program. A.K. gratefully acknowledges financial support from a doctoral dissertation fellowship from the University of Minnesota (UMN). M.C. acknowledges partial support from NSF Grant EAR-0810272. The authors acknowledge Andrea Floris, Paolo Umari, and Luigi Giacomazzi for useful discussions and advice on the computations. The authors are also grateful to the Minnesota Supercomputing Institute for providing the computational resources and technical support necessary for this study.