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Surface passivation of n- and p-type crystalline silicon wafers by amorphous silicon films



In this work we study the use of amorphous silicon (a-Si:H) layers as an alternative to silicon nitride for passivating the surface of crystalline silicon (c-Si) wafers. Intrinsic and doped amorphous silicon layers were deposited by Plasma-Enhanced Chemical Vapour Deposition onto n and p-type crystalline float-zone silicon wafers. Quasi-Steady-State Photoconductance measurements of the c-Si/a-Si:H samples were used to measure the effective carrier lifetime and surface recombination velocity before and after thermal annealing at temperatures from 250oC to 350oC. The effective lifetime is shown to increase dramatically after annealing for n- and p-type float-zone wafers when intrinsic a-Si:H is used to passivate the surfaces. However, the surface passivation for samples using doped a-Si:H layers is shown to be poor. Also, passivating hydrogen bonds from the heterojunction and the a-Si:H is shown to decrease with increasing temperatures, without detrimental effects from blistering which generally cause the effective carrier lifetime to decrease. This is attributed to the 500nm and 900nm a-Si:H layer thickness used.

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