Detection of secondary phases in co-evaporated Cu2ZnSnSe4 thin films by Raman spectroscopy

We prepared CZTSe thin films by the co-evaporation method. In order to investigate the presence of various kinds of secondary phases, we also prepared reference ZnSe, SnSe, CuSnSe, and CuSe thin films in the same way. The depth dependence of the secondary phases was investigated by preparing samples that are sputtered to various depths. We used Raman spectroscopy measurement with several lasers to detect secondary phases. CZTSe films were compared with the reference films, and only ZnSe and MoSe₂ phases were detected. The relative amount of ZnSe varied with the depth from the sample surface. The ZnSe Raman peak seems to originate from the top and the bottom of the sample since the signal decreased initially and then increased as deeper parts of the film were probed. Intensity of CZTSe peak did not change much until the bottom part of the sample was reached and the MoSe₂ peak appeared.