Transport properties of undoped and NH3-doped polycrystalline SnO2 with low background electron concentrations

Abstract

A series of polycrystalline 1 μm thick SnO2 films were deposited onto borosilicate glass substrates by atmospheric pressure chemical vapor deposition. Unintentionally doped as-grown SnO2 layers had electron concentrations and mobility of 2–4×1017cm−3 and 25–30cm2∕Vs, respectively. Potential barriers and trap concentrations were calculated to be 30 meV and 2.3×1012cm−2, respectively. Upon N2∕vacuum annealing at 670 K for 15–20 min, the potential barrier height decreased to 8 meV and the electron mobility increased to 58cm2∕Vs. When doped with ammonia, the mobility of as-grown samples decreased to 0.5cm2∕Vs. The magnitude of the potential barriers varied, with ammonia doping, from 175 to 31 meV with trap densities of 4.7–1.2×1012cm−3, respectively. Upon vacuum∕N2 annealing at 670 K for 20 min, the electron mobilities of ammonia doped films recovered to 50–71cm2∕Vs, whereas the height of the potential barriers decreased to 3–4 meV with trap concentrations of 8–9×1011cm−2. The observed changes in the electrical properties are well described by a double back-to-back Schottky barrier model.