Influence of light-soaking and annealing on electron and hole mobility-lifetime products in a-Si:H

Light-soaking and annealing effects on majority and minority carrier properties in undoped a-Si:H and simultaneous changes in subgap optical absorption are investigated. Subgap absorption was obtained by constant photocurrent method (CPM). Electron mobility lifetime product was deduced from photoconductivity. Hole mobility-lifetime product was estimated from measurements of ambipolar diffusion length by steady state photocarrier grating technique (SSPG). Hysteresis-like behaviour is found in the relationship between mobility-lifetime products of electrons and holes during photodegradation and isothermal annealing which is a signature of distinct evolutions of the gap-states density along the different sections of the metastability cycle. Analysis of changes of the sub-gap absorption coefficient at different photon energies and numerical simulations with a recombination model suggest the consideration of two species of metastable states with different sensitivities to light-exposure and annealing. (C) 2004 Elsevier B.V. All rights reserved.