Picosecond electron drift mobility measurements in hydrogenated amorphous silicon

The electron photocarrier drift mobility in undoped, hydrogenated amorphous silicon was measured in the picosecond domain using optically detected time-of-flight techniques based on the electroabsorption effect. The electron drift mobility at room temperature was approximately 3 cm² /V s between 50 and 500 ps at electric fields of (1-3)×10⁵ V/cm, essentially the same as the mobility measured in the nanosecond domain. The picosecond measurement constrains transport models postulating larger electron mobilities shortly after photogeneration; the mobility lifetime product for a short-time process must be less than 3×10^-11 cm² /V. A slightly superlinear dependence of drift velocity upon an electric field was also found which could not be explained by dispersion effects.