Controlled electrical conductivity in SnO2 thin films by oxygen or hydrocarbon assisted atomic layer epitaxy

The conventional atomic layer epitaxy process for pure SnO2 thin films uses SnCl4 and H2O as precursors and Np as the carrier gas. By applying gas-phase additives (n-hexane, ozone) or using oxygen as a carrier gas, a reduced electrical conductivity of the solid was obtained. This phenomenon is associated with the modifications in the grain structure and/or in the point defect concentration. To verify this, structural studies by X-ray diffraction, atomic force microscopy, Auger electron spectroscopy, and secondary ion mass spectroscopy were performed. The results suggest that the variations in electrical resistivity (0.1-89 Omega cm) are predominantly due to variations in the electronic carrier concentration, i.e., oxygen vacancy and/or chlorine-impurity concentrations, which were induced by gas-phase additives. The most promising additive was hexane, as it resulted in SnO2 firms of the lowest conductivity as well as the highest crystallinity and stoichiometry. The strength of this effect was, however, dependent on the position of hexane pulse in the pulsing sequence. (C) 1999 The Electrochemical Society. S0013-4651(98)04-017-8. All rights reserved.