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

Abstract 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.