HIGH-FIELD ELECTRON-DRIFT MEASUREMENTS AND THE MOBILITY EDGE IN HYDROGENATED AMORPHOUS-SILICON

We report electron photocarrier time-of-flight measurements at high el ectric fields for two thick hydrogenated amorphous silicon (a-Si:H) p- i-n diodes. At 77 K an exponential increase in the electron mobility o f more than 100 is observed as the field is increased to E = 400 kV/cm . The dispersion parameter was field independent. We discuss previous reports of field-dependent dispersion in terms of interface effects. W e propose a model for high-field effects based on an electric-field-de pendent mobility edge which accounts satisfactorily for the measured e lectric field and temperature dependence of the electron drift mobilit y. Effective-temperature models do not account for our measurements si nce they predict field-dependent dispersion. The microscopic electron mobility mu(o) similar to 3 cm(2)/V s is remarkably independent of ele ctric field, temperature, and germanium alloying.