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Hydrogenated Amorphous Silicon Grown by Hot-Wire CVD at Deposition Rates up to 1 µm/minute

Published online by Cambridge University Press:  17 March 2011

Brent P. Nelson
Affiliation:
Department of Physics, Colorado School of Mines, Golden, CO 80401, U.S.A
Yueqin Xu
Affiliation:
Department of Physics, Colorado School of Mines, Golden, CO 80401, U.S.A
A. Harv Mahan
Affiliation:
Department of Physics, Colorado School of Mines, Golden, CO 80401, U.S.A
D.L. Williamson
Affiliation:
Department of Physics, Colorado School of Mines, Golden, CO 80401, U.S.A
R.S. Crandal
Affiliation:
National Renewable Energy Laboratory (NREL), Golden, CO 80401, USA
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Abstract

We grow hydrogenated amorphous-silicon (a-Si:H) by the hot-wire chemical vapor deposition (HWCVD) technique. In our standard tube-reactor we use a single filament, centered 5 cm below the substrate and obtain deposition rates up to 20 Å/s. However, by adding a second filament, and decreasing the filament-to-substrate distance, we are able to grow a-Si:H at deposition rates exceeding 167 Å/s (1 µm/min). We find the deposition rate increases with increasing deposition pressure, silane flow rate, and filament current and decreasing filament-tosubstrate distance. There are significant interactions among these parameters that require optimization to grow films of optimal quality for a desired deposition rate. Using our best conditions, we are able to maintain an AM1.5 photoconductivity-to-dark-conductivity ratio of 105 at deposition rates up to 130 Å/s, beyond which the conductivity ratio decreases. Other electronic properties decrease more rapidly with increasing deposition rate, including the ambipolar diffusion length, Urbach energy, and the as-grown defect density. Measurements of void density by small-angle X-ray scattering (SAXS) reveal an increase by well over an order of magnitude when going from one to two filaments. However, both Raman and X-ray diffraction (XRD) measurements show no change in film structure with increasing deposition rates up to 144 Å/s, and atomic force microscopy (AFM) reveals little change in topology.

Type
Research Article
Copyright
Copyright © Materials Research Society 2000

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References

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