Spray pyrolysis deposition of indium sulphide thin films

In2S3 thin films were grown by the chemical spray pyrolysis (CSP) method using the pneumatic spray set-up and compressed air as a carrier gas. Aqueous solutions containing InCl3 and SC(NH2)2 at a molar ratio of In/S = 1/3 and 1/6 were deposited onto preheated glass sheets at substrate temperatures Ts = 205–410 °C. The obtained films were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM,) optical transmission spectra, X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS). According to XRD, thin films deposited at Ts = 205–365 °C were composed of the (0 0 12) orientated tetragonal β-In2S3 phase independent of the In/S ratio in the spray solution. Depositions performed at Ts = 410 °C led to the formation of the In2O3 phase, preferably when the 1/3 solution was sprayed. Post-deposition annealing in air indicated that oxidation of the sulphide phase has a minor role in the formation of In2O3 at temperatures up to 450 °C. In2S3 films grown at Ts below 365 °C exhibited transparency over 70% in the visible spectral region and Eg of 2.90–2.96 eV for direct and 2.15–2.30 eV for indirect transitions, respectively. Film thickness and chlorine content decreased with increasing deposition temperatures. The XPS study revealed that the In/S ratio in the spray solution had a significant influence on the content of oxygen (Me–O, BE = 530.0 eV) in the In2S3 films deposited in the temperature range of 205–365 °C. Both XPS and EDS studies confirmed that oxygen content in the films deposited using the solution with the In/S ratio of 1/6 was substantially lower than in the films deposited with the In/S ratio of 1/3.