Carrier propagation in sputtereda-Si:H

Time-of-flight measurements have been made on a-Si:H thin films prepared by the sputtering process. The propagation of electrons can be either dispersive or nondispersive depending on the sample-preparation conditions. Samples which reveal nondispersive transport in a certain voltage and temperature regime undergo a transition to dispersive behavior when the temperature is lowered below 300 K. Activation energies for mobility of 0.18±{}0.01 eV are obtained when the transport of electrons is nondispersive. The temperature-dependent dispersion is consistent with transport taking place by a multiple trapping process. Room-temperature electron mobilities in the range 0.1-0.5 cm²/V s are found for films which have a low density of states at the Fermi level. Room-temperature hole mobilities {~}1 ×{} 10^-3 cm²/V s are found with an activation energy of 0.4 eV. In all samples measured the transport of holes is dispersive.