Optical, structural, and vibrational properties of In 2 S 3 thin films by sputtering-RF for applications in optoelectronics devices

Experimental results on the crystalline orientation properties, energy band gap, and Raman vibrational modes of Indium Sulfide (In 2 S 3 ) thin films grown by Sputtering in Radio Frequency mode are presented. The In 2 S 3 thin films were grown at 25, 200, and 300 °C; thereafter the samples were thermally annealed in air for 30 min at 450 °C, in order to improve their crystalline and physical properties. Energy dispersive x-ray spectroscopy results showed that the β -In 2 S 3 crystallographic phase became predominant as the substrate temperature increased. For the optical transmittance spectra, it was observed that the deposited In 2 S 3 thin films at 300 °C and with thermal annealing showed an increase in their band gap energy of nearly 60 meV. The direct energy bandgap of In 2 S 3 films varied in the range 2.76–2.82 eV. The scanning electron microcopy image and elemental analysis shows a better morphology, and an increase in O and Sn when the In 2 S 3 samples were subjected to thermal annealed and the substrate temperature increased, respectively. Photoluminescence spectra were obtained at room temperature and showed two emission bands around 1.75 (709 nm) and 2.35 eV (527 nm), one related to interstitial indium donor sites (In i ) and oxygen acceptor vacancies (O Vs ), and the second to an emission band corresponding to the transition sulfur donor-indium acceptor. As the substrate temperature increased and thermal annealing of In 2 S 3 was performed, the 1.75 eV emission bands increased in intensity with respect to the 2.35 eV band. From the Raman measurements, it was observed that the vibrational peaks were better defined as the substrate temperature increased and In 2 S 3 underwent thermal annealing. In addition, to study the spinel-like defect structure, the peaks corresponding to the five main vibrational modes of In 2 S 3 were identified as the A lg mode, E g mode, and three modes of the F 2g species.