Raman scattering studies of Cu2ZnSnS4 thin films: Local distribution of the secondary phase Cu2−x S and the effect of KCN etching on Cu2−x S

We used X-ray diffraction (XRD) and Raman scattering spectroscopy to study Cu2ZnSnS4 (CZTS) thin films grown by using an electroplating method. We compared the Raman spectra of the CZTS thin films before and after potassium cyanide (KCN) etching. We observed a phonon mode of the secondary phase Cu2−x S both from Cu-rich and Cu-poor CZTS samples before the KCN etching. We found that the intensity of the Cu2−x S-related vibration mode depended on the excitation wavelength, from which we could estimate the stoichiometry of the Cu2−x S as x = 1. Interestingly, the Cu2−x S phonon is completely removed after the KCN etching. We could also get information regarding the local distribution of the secondary phase on the surfaces of the CZTS thin films by using micro-Raman scattering spectroscopy.