Sulfurization of Cu 2 (Sn,Ge)S 3 thin films deposited by co-evaporation

The sulfurization effect of Cu2(Sn1−x,Gex)S3 (CTGS) thin films deposited by low-temperature co-evaporation was investigated. As-deposited CTGS films with large Cu2GeS3 molar fractions show poor crystal quality and contamination with extra phases. After sulfurization using sulfur powder, the full width at half-maximum of X-ray diffraction peaks for CTGS films is smaller than that of the as-deposited CTGS films. Moreover, contamination of the extra phases are not observed in the sulfurized CTGS film. These results imply that single-phase thin-film CTGS is difficult to obtain by only low-temperature co-evaporation. Therefore, sulfurization is necessary to suppress extra phases and obtain single-phase CTGS films.