A comparative study of the structure and optical properties of copper sulfide thin films chemically deposited on various substrates

Copper sulfide (Cu sub(x)S) thin films were chemically deposited from solution onto glass, Si(100) and GaAs(100) substrates. The microstructure and morphology evolution were investigated using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. As-deposited films were found to be amorphous or semi-crystalline, while X-ray diffraction and selected area electron diffraction measurements indicated that the annealed films were composed of a mixture of Covellite(CuS) and Digenite(Cu sub(1.8)S) phases. The CuS/Cu sub(1.8)S ratio in the films was influenced by the substrate. Under the same deposition conditions, Cu sub(1.8)S-rich films were obtained on GaAs and glass substrates, and CuS-rich films were observed on a Si substrate. The deposition rate was also found to be significantly affected by the substrate, with sufficiently higher rates obtained on GaAs. The optical properties of the films were studied using Raman scattering, ellipsometry measurements and UV-VIS-NIR spectroscopy. Irradiation induced phase transformation from amorphous to crystalline phase was observed during Raman measurements due to the local laser irradiation. Band gap energies were found to be relatively similar on all substrates, with strong absorption in the visible range. These results suggest that Cu sub(x)S films can be integrated within both Si and GaAs based electronic and electro-optic devices.