Investigation of collection efficiencies much larger than unity in a-Si : H p-i-n structures

An apparent quantum efficiency much larger than unity is observed under rev erse bias voltage conditions, in hydrogenated amorphous silicon p-i-n struc tures. High collection efficiencies are measured for low-level probe illumi nation of the device n side with red light, with simultaneous bias illumina tion from the device p side with strongly absorbed blue light. The photogat ing effect responsible varies experimentally with reverse bias voltage, and collection efficiencies for the probe excitation of up to 50 are obtained. Detailed computer simulations corroborate such high values of quantum effi ciency and the underlying mechanisms for the effect are revealed. We presen t the influence on quantum efficiency of bias light wavelength and photon f lux, probe light photon flux, applied voltage, and defect density. (C) 1999 American Institute of Physics. [S0021-8979(99)01801-0].