Sulfurization approach using sulfur vapor, graphite box and H2S gas atmospheres for co-sputtered Cu2ZnSnS4 thin film

In this work we have prepared Cu₂ZnSnS₄ (CZTS) precursor by magnetron co-sputtering using Cu, SnS and ZnS sputter targets. We employed three sulfurization approaches to prepare CZTS thin film and further compared their characterizations. In one approach, the precursor was sulfurized in a two zone tubular furnace directly exposed to the S vapor with N₂ gas. In second approach, similar precursor was sulfurized in the same furnace but inside a graphite box together with 500mg of sulphur powder was evaporated in N₂ gas inert atmosphere. Finally, in third approach precursor was sulfurized in the same furnace and was directly exposed to the H₂S gas (balanced with 97 vol% of N₂ gas) at flow rate of 50sccm. All sulphurization approaches were performed at temperature of 550°C for 60 min at atmospheric pressure. We have analyzed that the film sulfurized in H₂S gas leads to compact grain structure, desired elemental composition, good optical and electrical characterization than when sulfurization was carried out in S vapor and S vapor in a graphite box under same thermodynamic conditions. The elemental composition of film was also analyzed by Secondary ion mass spectrometry (SIMS). The film was further analyzed by X-ray diffractometer (XRD), Raman scattering, X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM) which showed Cu₂ZnSnS₄ is the kesterite phase. The optical and electrical properties clearly shows CZTS film with an optical band gap of 1.5 eV, absorption coefficient of 8.5×10⁴ cm^-1 and p-type semiconducting behavior with charge carrier concentration of 3.09×10¹⁷ cm^-3.