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Study of Surface Passivation of CZ c-Si by PECVD a-Si:H Films; A Comparison Between Quasi-Steady-State and Transient Photoconductance Decay Measurement

Published online by Cambridge University Press:  13 May 2013

Omid Madani Ghahfarokhi
Affiliation:
NEXT ENERGY ∙ EWE Research Centre for Energy Technology at Carl von Ossietzky University Oldenburg, Carl-von-Ossietzky-Str. 15, 26129 Oldenburg, Germany
Karsten von Maydell
Affiliation:
NEXT ENERGY ∙ EWE Research Centre for Energy Technology at Carl von Ossietzky University Oldenburg, Carl-von-Ossietzky-Str. 15, 26129 Oldenburg, Germany
Carsten Agert
Affiliation:
NEXT ENERGY ∙ EWE Research Centre for Energy Technology at Carl von Ossietzky University Oldenburg, Carl-von-Ossietzky-Str. 15, 26129 Oldenburg, Germany
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Abstract

We have investigated the passivation of low lifetime non-polished Czochralski (CZ) mono-crystalline silicon (c-Si) wafers by hydrogenated amorphous silicon (a-Si:H), deposited by plasma enhanced chemical vapor deposition (PECVD) technique. The dependence of the effective lifetime (τeff) on the deposition parameters including hydrogen gas flow, power and temperature has been studied. Minority carrier lifetime was measured as deposited and also after an annealing step in both quasi-steady-state (QSS) and transient mode of photoconductance decay. By comparison between τeff measured in each of the aforementioned modes, two distinguishable behaviors could be observed. Moreover, to get further insight into the surface passivation mechanism, we have modeled the recombination at a-Si:H/c-Si interface based on the amphoteric nature of dangling bonds. The results of our modeling show that the discrepancy observed between QSS and transient mode is due to the high recombination rate that exists in the bulk of defective CZ wafer and also partly related to the different thicknesses monitored in each mode. So, by comparison between the injection level dependency of τeff measured in QSS and transient modes, we introduce a valuable technique for the evaluation of c-Si bulk lifetime.

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Articles
Copyright
Copyright © Materials Research Society 2013 

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References

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