PLASMA-ENHANCED CHEMICAL VAPOUR DEPOSITION OF A-SI:H TO PROVIDE SURFACE PASSIVATION OF C-SI SURFACES AT LOW TEMPERATURE

摘要

Excellent surface passivation has been obtained by post-deposition annealing of PECVD deposited a-Si:H thin film layers, which otherwise had low as-deposited passivation properties. Annealing near the depositiontemperature was sufficient to improve the surface passivation for both n- and p-type silicon substrates, asdemonstrated by effective carrier lifetimes increasing from initial values below 100μs to above 1ms on average.FTIR analysis of total hydrogen content and of mono- and dihydrides indicates that the presence of the latter bonds isa condition (but not a guarantee) for potential passivation. Neither total hydrogen content nor hydride concentrationchanges significantly with annealing. The surface passivation mechanism was studied by sequentially measuring theeffective lifetime as a function of annealing time and temperature. The activation energy obtained in this waysuggests that it is not the diffusion of hydrogen from within the a-Si:H film, but instead a re-arrangement of Halready near the interface, that causes the improved passivation.