Effect of Buffer Layer on Improvement of SnO2 Thin Film on Sapphire Substrate Formed by Mist Chemical Vapor Deposition

Tin oxide (SnO ₂ ) is an n-type wide band-gap semiconductor with excellent properties such as optical, electrical and chemical properties. In this research, SnO ₂ thin films were grown on m-plane sapphire substrates by mist chemical vapor deposition. However, it was difficult to deposit high quality SnO ₂ films because of the large lattice mismatch and the large difference in the thermal expansion coefficient between the SnO ₂ film and the sapphire substrate. To improve the quality of SnO ₂ films, we inserted a SnO ₂ buffer layer to solve the lattice mismatch problem between the substrate and the film. We found that the surface morphologies of SnO ₂ films with the buffer layers were smoother than the films without the buffer layers. Furthermore, the full width at half maximum (FWHM) of an X-ray ω-rocking curve for the SnO ₂ thin film was reduced obviously. Thus, the crystal quality of SnO ₂ films was much improved by introducing the buffer layers between the substrate and the thin films.