Si surface passivation by using triode-type plasma-enhanced chemical vapor deposition with thermally energized film-precursors

We fabricated hydrogenated amorphous Si (a-Si:H) passivation layers on the surfaces of Si wafers by using triode-type plasma-enhanced chemical vapor deposition with gas-heating, and discussed high-quality surface passivation for Si heterojunction solar cells. The sample with the a-Si:H layers corresponding to the highest proportion of SiH_x(x=2,3) content in SiH_x(x=1-3) content exhibited the minimum surface recombination velocity (S) after annealing. This suggests that using SiH_x(x=2,3)-rich a-Si:H grown at low-temperature as a passivation layer is advantageous to inhibit an epitaxial growth at the a-Si:H/crystalline Si interface, and that a structural relaxation of the a-Si:H takes place during post-deposition annealing, drastically improving passivation quality. Also, the importance to use a low T_sub and to optimize gas-heating and the triode technique, for obtaining simultaneously higher film quality and abrupt interface, is suggested. Low S obtained for our unoptimized samples implies the potency of this deposition technique. Nevertheless, further studies are needed to elucidate the impact of gas-heating and the triode technique on Si surface passivation. Temperature-dependent effective carrier lifetime for our samples might suggest relatively large electron affinity for an a-Si:H, which might be one possible reason for high-quality surface passivation.