The First Fifty Billion Nanoseconds of Electron Photocarrier Evolution in Undoped a-Si:H

ABSTRACTThe drift of electrons generated by a 3 ns illumination impulse was studied in several undoped a-Si:H specimens by using transient photocharge measurements from 10 ns to 50 sec. The transients show four stages of evolution: band transport, deep-trapping and subsequent re-emission, and recombination. From the temperature dependence of the emission time we estimated the mean energy of the trap distribution and the attempt-to-escape frequency associated with this trap to be 0.6 eV below the conduction band and 5×1012 sec−1 respectively; this trap has been identified in previous work with the D-center found in electron spin resonance. In addition the data resolve the two orders of magnitute discrepancy between mobility-lifetime estimates from earlier charge-collection experiments and from steady-state photoconductivity.