The gettering of impurities, and the H passivation of defects in edge-defined film-fed grown multi-crystalline material, were studied after emitter diffusion by a spun-on P dopant-source, back-surface field-formation by screen-printed Al, and post-deposition annealing of plasma-enhanced chemical vapour deposited silicon nitride coatings. The nitride-induced hydrogenation of defects was studied, in conjunction with Al back-surface field-formation, in order to investigate the synergistic effect of Al gettering and the nitride hydrogenation of bulk defects. It was found that post-deposition annealing of the nitride at temperatures ranging from 450 to 850C, without the co-formation of Al on the back, did not provide any appreciable passivation or hydrogenation of the bulk defects. However, simultaneous annealing of the nitride and the formation of Al back surfaces at 850C significantly enhanced the hydrogenation ability of the nitride film. Nitride deposition and subsequent annealing, following Al back-surface formation, was found to be less effective in passivating bulk defects. It was proposed that the Al-enhanced hydrogenation arising from a nitride film was the result of vacancy generation at the Al/Si interface; due to alloying. The tendency of H to react with vacancies provided a chemical potential gradient that increased the flux of atomic H from the nitride film and into the bulk Si. Moreover, the vacancies could dissociate H molecules; thus increasing the atomic-H content of the bulk Si. This enhanced defect passivation, and improved the minority carrier lifetime.

Hydrogenation of Defects in Edge-Defined Film-Fed Grown Aluminum-Enhanced Plasma Enhanced Chemical Vapor Deposited Silicon Nitride Multicrystalline Silicon J.W.Jeong, M.D.Rosenblum, J.P.Kalejs, A.Rohatgi: Journal of Applied Physics, 2000, 87[10], 7551-7