Spatial carrier separation evaluated with a relaxation time distribution in doping-modulated amorphous silicon multilayers

Abstract

The relationship between spatial carrier separation and screening depth of internal electric field in doping-modulated amorphous multilayers is discussed qualitatively based on an analysis of relaxation-time distribution. Since dominant recombination kinetics between spatially separated electrons and holes is considered to be tunneling recombination, the relaxation time is related with mutual distance between carriers. It is found that spatial carrier separation is already incomplete under a very weak excitation intensity of around 0.1 mW or very slight screening of the internal electric field. At the intermediate excitation-intensity region extending over several orders of magnitude until complete screening of the internal electric field is established, the mutual separation between carriers reduces very slowly in accordance with a very gradual increase in screening of the internal electric field. This is a characteristic feature of the doping-modulated amorphous multilayers, and may result from comparable thickness between space-charge region and unit undoped layer in the multilayer.