We report electron photocarrier time-of-Sight measurements at high electric 6elds for two thick hydrogenated amorphous silicon (a-Si:H) pi nd-io-des. At 77 K an exponential increase in the electron mobility of 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. We propose a model for high-field efFects based on an electric jield de-pend-ent mo bility edge which accounts satisfactorily for the measured electric 6eld and temperature dependence of the electron drift mobility. ERective-temperature models do not account for our measurements since they predict field-dependent dispersion. The microscopic electron mobility po 3 cm /V s is remarkably independent of electric 6eld, temperature, and germanium alloying.

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