Tin Oxide Thin Films Grown on the (1̄012) Sapphire Substrate

Tin oxide thin films were deposited on the R-cut sapphire substrate by the electron-beam evaporation of a ceramic SnO2 source. X-ray diffraction and transmission electron microscopy studies revealed that the films deposited at lower temperatures were amorphous while those grown at temperatures above 350◦C consisted of the α-SnO phase with the PbO type structure. Epitaxial α-SnO films on the R-cut sapphire substrate were obtained when deposited at 600◦C. Atomic force microscopy studies showed that films deposited at low temperature have a smooth surface, while epitaxial SnO films deposited at high temperatures (above 600◦C) have a relatively rough surface. The atomic mobilities in the films at the various deposition temperatures and the lattice mismatch between the films and the substrates ultimately determine the microstructure and surface mophology. X-ray photoelectron spectroscopy analysis shows that the Sn/O ratios are 52.7/47.6 for the amorphous film deposited at the ambient temperature (∼30◦C), 48.8/51.2 for the films deposited at 350◦C, and 49.2/50.8 for the epitaxial film deposited at 600◦C. Electrical properties were determined by four point probe measurements.