Preparation and characterization of CuInS2 thin films completely converted from CuInSe2 by sulfurization

Thin films of CuInSe2 can be completely converted to CuInS2 after annealing in elemental sulfur vapor. The conversion process was done in an MBE chamber and the film was exposed to a heated sulfur source. Our experiments showed that complete conversion of a 1.0 μm-thick CuInSe2 film into CuInS2 was achieved when the film was annealed in a sulfur beam flux of 4.5×1016 atoms/cm2 s at 450 °C for 5 min. This is the shortest conversion time ever reported for the same annealing temperature. The speed of conversion process depended on sulfur vapor flux, film crystallinity and original film composition. Among them, the film composition was the most important factor and confirmed by KCN etching of a Cu-rich sample. The PL spectrum of a converted Cu-rich CuInS2 film showed a broad emission peak at about 1.34 eV that was caused by the donor–acceptor transition and might be associated with the S-vacancy and the In-vacancy.