Highly crystalline In₂S₃ thin films epitaxially grown on sapphire substrates

Indium sulfide (In₂S₃) thin films were deposited on glass and sapphire substrates by physical co-evaporation of the elements. The deposition parameters were varied to optimize the structural properties of the thin films. The sample epitaxially grown on a-sapphire substrate shows the smoothest surface and the highest crystallinity. The optical absorption properties were found to be independent on the deposition parameters and substrate material. We found for In₂S₃ a weakly pronounced absorption onset at 1.7 eV and a strong one at 2.5 eV, which can be attributed to direct band–band transitions located at 2.1 and 2.7 eV, respectively. Electrical characterization reveals photovoltaic activity with p-ZnCo₂O₄/ n-In₂S₃ heterodiodes but low performance due to non-ideal heterojunction properties. We further find a strong, persistent photoconductivity, which manifests itself in a strong time-dependence of the dark resistivity after the samples were exposed to light.