Picosecond electron drift mobility measurements in hydrogenated amorphous silicon

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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. Applied Physics Letters is copyrighted by The American Institute of Physics.