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Hydrogenated Amorphous Silicon Germanium Alloys Grown by the Hot-Wire Chemical Vapor Deposition Technique

Published online by Cambridge University Press:  10 February 2011

Brent P. Nelson ,
Yueqin Xu ,
D.L. Williamson ,
Bolko Von Roedern ,
Alice Mason ,
Stephan Heck ,
A.H. Mahan ,
S.E. Schmitt ,
A.C. Gallagher  and
John Webb
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Brent P. Nelson
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
Yueqin Xu
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
D.L. Williamson
Affiliation:
Department of Physics, Colorado School of Mines, Golden, CO 80401
Bolko Von Roedern
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
Alice Mason
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
Stephan Heck
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
A.H. Mahan
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
S.E. Schmitt
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
A.C. Gallagher
Affiliation:
University of Colorado and National Institute of Standards and Technology, Boulder, CO 80309-0440
John Webb
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
Robert Reedy
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401
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Abstract

We successfully grow high-quality hydrogenated amorphous-silicon-germanium alloys (a-SiGe:H) by the hot-wire chemical-vapor deposition (HWCVD) technique using silane and germane gas mixtures. These alloys display electronic properties as good as those grown by the plasma-enhanced chemical-vapor deposition (PECVD) technique, when comparing materials with the same optical bandgaps. However, we grow materials with good electrical properties at high deposition rates—up to 40 Å/s, compared to 1–4 Å/s for PECVD materials. Our alloys exhibit similar trends with increasing Ge content to alloys grown by PECVD. The defect density, the dark conductivity, and the degree of nanostructural heterogeneity (as measured by small-angle X-ray scattering) all increase with increasing germanium content in the alloy. The nanostructural heterogeneity displays a sharp transition between 9 at.% and 14 at.% germanium. PECVD- grown a-SiGe:H alloys exhibit a similar transition at 20 at.% Ge. The photoconductivity and the ambipolar diffusion length of the alloys decrease with increasing germanium content. For a fixed silane-to-germane gas ratio, all material properties improve substantially when increasing substrate temperature (Tsub) from 220°C to 375°C. Increasing Tsub also narrows the optical bandgap and lowers the hydrogen content in the alloys for the same germane-to-silane gas ratio.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 507: Symposium A – Amorphous & Microcrystalline Silicon Technology 1998 , 1998 , 447
Copyright
Copyright © Materials Research Society 1998

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References

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