Gettering of transition metals in high-performance multicrystalline silicon by silicon nitride films and phosphorus diffusion

High-performance multicrystalline silicon (HP mc-Si) from directional solidification has become the mainstream industrial material for fabricating mc-Si based solar cells for photovoltaic applications. Transition metal impurities are inherently contained in HP mc-Si during ingot growth, and they are...

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Bibliographic Details
Published in:Journal of applied physics 2019-01, Vol.125 (4)
Main Authors: Liu, AnYao, Sun, Chang, Sio, Hang Cheong, Zhang, Xinyu, Jin, Hao, Macdonald, Daniel
Format: Article
Language:English
Subjects:
Applied physics
Chromium
Copper
Directional solidification
Gettering
Ingots
Iron
Metals
Minority carriers
Nickel
Organic chemistry
Phosphorus
Photoluminescence
Photovoltaic cells
Plasma enhanced chemical vapor deposition
Secondary ion mass spectrometry
Silicon nitride
Silicon wafers
Solar cells
Transition metals
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Summary:High-performance multicrystalline silicon (HP mc-Si) from directional solidification has become the mainstream industrial material for fabricating mc-Si based solar cells for photovoltaic applications. Transition metal impurities are inherently contained in HP mc-Si during ingot growth, and they are one of the major efficiency-limiting drawbacks. In this work, we investigate the gettering of transition metals (Cu, Ni, Fe, and Cr) in HP mc-Si wafers along an industrial-standard p-type HP mc-Si ingot, via examining the metal concentration and distribution in the near-surface gettering layers using secondary ion mass spectrometry. We applied both conventional phosphorus diffusion gettering and the recently developed silicon nitride (from plasma-enhanced chemical vapour deposition) gettering techniques. Both techniques are shown to remove significant quantities of metals from the silicon wafer bulk to the surface gettering layers. Improvements in the bulk minority carrier lifetimes throughout the ingot height are also observed by lifetime measurements and spatially-resolved photoluminescence imaging. The gettered Cu and Ni concentrations, as well as the as-grown dissolved Fe concentrations in the silicon wafer bulk, along the HP mc-Si ingot height are shown to follow a similar concentration profile as the metals in conventional mc-Si ingots.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.5050566