Raman scattering studies of Cu₂ZnSnS₄ thin films: Local distribution of the secondary phase Cu_2−xS and the effect of KCN etching on Cu_2−xS

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 Cu_2−xS both from Cu-rich and Cu-poor CZTS samples before the KCN etching. We found that the intensity of the Cu_2−xS-related vibration mode depended on the excitation wavelength, from which we could estimate the stoichiometry of the Cu_2−xS as x = 1. Interestingly, the Cu_2−xS 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.