A Correlative Study of Film Lifetime, Hydrogen Content, and Surface Passivation Quality of Amorphous Silicon Films on Silicon Wafers

Abstract

We examine correlations between the recombination lifetime and hydrogen content of hydrogenated amorphous silicon films (a-Si:H) and the surface passivation afforded by such films when deposited on crystalline silicon wafers, during annealing at 350-500°C. Our results show that, as the annealing duration increases, both the a-Si:H recombination lifetime and the surface recombination velocity evolve at a similar rate to the hydrogen concentration. This suggests that the loss of hydrogen during annealing is the direct cause of the reduction in the a-Si:H film lifetime, and that the loss of hydrogen occurs both at the a-Si:H/c-Si interface as well as in the bulk of a-Si:H film. We calculated the activation energy of the surface depassivation reaction during annealing to be 0.62 ± 0.1 eV, which suggests that the depassivation reaction is limited by the migration of hydrogen within the film, without significant hydrogen trapping. Secondary-ion mass spectrometry further demonstrates the loss of hydrogen across the film thickness during annealing.