Growth and characterization of Cu2ZnxFe1-xSnS4 thin films deposited on n-type silicon substrates

Cu2FeSnS4 and Cu2ZnSnS4 ingots were successfully grown by direct melting of their high-purity constituent elements from stoichiometric compositions (copper, iron, zinc, tin and sulfide). Subsequently, thin films of CFTS and CZTS were deposited on unheated n-type silicon substrates through the vacuum evaporation method. These deposited films were sulfided for 30 min at a sulfidation treatment temperature Ts = 400 °C. The structural properties of the C (Z, F)TS thin films were studied by X-ray diffraction (XRD), Raman spectroscopy and electron backscatter diffraction (EBSD). The resulting studies suggest the existence of polycrystalline phases where CZTS has a kesterite structure and CFTS a stannite structure. Composition analysis also indicates that the synthesized C (Z,F)TS powders are close to the expected stoichiometry. A good crystallinity of CZTS followed by an increase in the average roughness value of this film is highlighted in the thin film micrographs of C (Z,F)TS. Furthermore, the Hall effect indicates that the prepared C (Z,F)TS films exhibit a manifest p-type semiconductor, and the conductivity, mobility and carrier charge concentration are higher for the CZTS thin film. The electrical conductivity of the CFTS and CZTS thin films were investigated using the impedance spectroscopy technique in the frequency range 5 Hz–13 MH. Values of activation energy are indicative of thermal activation of the conduction mechanism by jumping between localized states. Further, the analysis of the frequency and temperature dependence of the AC conductivity supports the correlated barrier hopping (CBH) model.