Cu content dependence of morphological, structural and optical properties for Cu₂ZnGeS₄ thin films synthesized by sulfurization of sputtered precursors

Cu₂ZnGeS₄ thin films with different Cu contents were synthesized by sulfurization of radio-frequency magnetron sputtered precursors. Microstructural characterizations using scanning electron microscopy and X-ray diffraction reveal that all of the as-prepared Cu₂ZnGeS₄ thin films are well crystallized and present a visible increase of grain size with increasing Cu content. In this case, the corresponding square resistance of these films is found to decrease from 14.2 to 1.3 kΩ/□. Furthermore, ZnS phase can be observed in the Cu-poor sample determined by Raman spectroscopy. Band gaps of the films decrease from 1.97 eV to 1.80 eV with increasing of Cu/(Zn+Ge) ratio from 0.93 to 1.13. These results are helpful to further study on Cu₂ZnGeS₄ thin films that are applicable for manufacturing solar cell.