Multiwavelength excitation Raman scattering study of polycrystalline kesterite Cu2ZnSnS4 thin films

This work presents a complete analysis of all Raman active modes of Cu2ZnSnS4 measuring with six different excitation wavelengths from near infrared to ultraviolet. Simultaneous fitting of spectra allowed identification of 18 peaks from device grade layers with composition close to stoichiometry that are attributed to the 27 optical modes theoretically expected for this crystalline structure, including detection of 5 peaks not observed previously, but theoretically predicted. Resonance effects are assumed to explain the observed increase in intensity of weak modes for near infrared and ultraviolet excitations. These results are particularly relevant for experimental discrimination of Raman modes related to secondary phases.