Structures, optical properties, and electrical transport processes of SnO2 films with oxygen deficiencies.

The structures, optical and electrical transport properties of SnO2 films, fabricated by rf sputtering method at different oxygen partial pressures, were systematically investigated. It has been found that preferred growth orientation of SnO2 film is strongly related to the oxygen partial pressure during deposition, which provides an effective way to tune the surface texture of SnO2 film. All films reveal relatively high transparency in the visible range, and both the transmittance and optical band gap increase with increasing oxygen partial pressure. The temperature dependence of resisitivities was measured from 380 K down to liquid helium temperatures. At temperature above K, besides the nearest-neighbor-hopping process, thermal activation processes related to two donor levels ( and 100 meV below the conduction band minimum) of oxygen vacancies are responsible for the charge transport properties. Below K, Mott variable-range hopping conduction process governs the charge transport properties at higher temperatures, while Efros-Shklovskii (ES) variable-range-hopping conduction process dominates the transport properties at lower temperatures. Distinct crossover from Mott type to ES type variable-range-hopping conduction process at several to a few tens kelvin are observed for all SnO2 films. [ABSTRACT FROM AUTHOR]