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Dependence of the Electronic Properties of Hot-Wire CVD Amorphous Silicon-Germanium Alloys on Oxygen Impurity Levels

Published online by Cambridge University Press:  01 February 2011

Shouvik Datta ,
J. David Cohen ,
Yueqin Xu ,
A. H. Mahan  and
Howard M. Branz
Shouvik Datta
Affiliation:
sdatta@uoregon.edu, University of Oregon, Physics, 1371 East 13th Avenue., Eugene, OR, 97403, United States, (541)-346 4774, (541) 346 3422
J. David Cohen
Affiliation:
dcohen@uoregon.edu, University of Oregon, Department of Physics, 1371 E 13th Avenue, Eugene, OR, 97403, United States
Yueqin Xu
Affiliation:
yueqin_xu@nrel.gov, National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO, 80401, United States
A. H. Mahan
Affiliation:
harv_mahan@nrel.gov, National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO, 80401, United States
Howard M. Branz
Affiliation:
howard_branz@nrel.gov, National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO, 80401, United States
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Abstract

We report the effects of intentionally introducing up to ∼ 5×1020/cm3 oxygen impurities into hydrogenated amorphous silicon-germanium alloys (of roughly 30at.% Ge) grown by the hot-wire chemical vapor deposition (HWCVD) method. Deep defect densities determined by drive-level capacitance profiling (DLCP) indicated a modest increase with increasing oxygen content (up to a factor of 3 at the highest oxygen level). Transient photocapacitance (TPC) spectra indicated a clear spectral signature for an optical transition between the valence band and an additional defect level which is attributed to oxygen impurities. The oxygen impurity related defect transition has an optical threshold around 1.4eV above the valence band and also results in a negative contribution to the TPC signal. This initially led us to believe that the bandtail for the higher oxygen samples was much narrower than it actually is. Surprisingly, this additional oxygen related defect level appears to have only a very minor effect upon the estimated minority carrier collection fraction. The effects of light-induced degradation upon some of these oxygen contaminated samples were also examined. We infer the existence of a significant thermal barrier to explain the observed spectral signatures of this oxygen impurity defect.

Keywords

amorphousSidefects
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 989: Symposium A – Amorphous and Polycrystalline Thin-Film Silicon Science and Technology-2007 , 2007 , 0989-A04-03
Copyright
Copyright © Materials Research Society 2007

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