XRD, XPS, OPTICAL AND ELECTRICAL STUDIES ON THE CONVERSION OF SNS THIN-FILMS TO SNO2

Results on the thermal decomposition of chemically deposited SnS thin films to sub-stoichiometric and near-stoichiometric SnO2 thin films on glass substrates are presented. The SnS-to-SnO2 conversion is illustrated using X-ray diffraction spectra, X-ray photoelectron spectroscopy (XPS), optical transmittance spectra and electrical characteristics. SnS thin films of approximately 0.7 mu m thickness and appearing deep red in transmission could be converted to transparent SnO2-x films at temperatures above 325 degrees C. It requires about 20 h at 350 degrees C, 2 h 45 min at 400 degrees C, 30 min at 450 degrees C or 10 min at 500 degrees C for the near-complete conversion, but a relatively thinner film (of 0.25 mu m) requires only about 30 min for the conversion at 400 degrees C. At the threshold of the transformation, the films show sheet resistance of about 10(4) Omega/square, which increases upon prolonged annealing to about 10(9) Omega/square for 18 h annealing at 500 degrees C. The ratio of dark sheet resistance to photo sheet resistance is about ten for SnS films under 600 W m(-2) tungsten-halogen light and is about 10(3) for SnO2 films.