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

A series of polycrystalline 1 mum 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 2-4x10(17) cm(-3) and 25-30 cm(2)/V s, respectively. Potential barriers and trap concentrations were calculated to be 30 meV and 2.3x10(12) cm(-2), respectively. Upon N-2/vacuum annealing at 670 K for 15-20 min, the potential barrier height decreased to 8 meV and the electron mobility increased to 58 cm(2)/V s. When doped with ammonia, the mobility of as-grown samples decreased to 0.5 cm(2)/V s. The magnitude of the potential barriers varied, with ammonia doping, from 175 to 31 meV with trap densities of 4.7-1.2x10(12) cm(-3), respectively. Upon vacuum/N-2 annealing at 670 K for 20 min, the electron mobilities of ammonia doped films recovered to 50-71 cm(2)/V s, whereas the height of the potential barriers decreased to 3-4 meV with trap concentrations of 8-9x10(11) cm(-2). The observed changes in the electrical properties are well described by a double back-to-back Schottky barrier model. (C) 2004 American Institute of Physics.