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Electronic transport study of high deposition rate HWCVD a-Si:H by the microwavephotomixing technique

Published online by Cambridge University Press:  17 March 2011

S.R. Sheng ,
R. Braunstein ,
B.P. Nelson  and
Y. Xu
S.R. Sheng
Affiliation:
Department of Physics and Astronomy, University of California, Los Angeles, California 90024, USA
R. Braunstein
Affiliation:
Department of Physics and Astronomy, University of California, Los Angeles, California 90024, USA
B.P. Nelson
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401, USA
Y. Xu
Affiliation:
National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, Colorado 80401, USA
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Abstract

The electronic transport properties of high deposition rate a-Si:H films prepared by HWCVD have been investigated in detail by employing the microwave photomixing technique. The high deposition rates (up to 1 µm/min.) were achieved by adding a second filament, increasing deposition pressure, silane flow rate, and decreasing filament-to-substrate distance. The effect of the deposition rate on the resultant film properties with respect to the substrate temperature, deposition pressure and silane flow rate was studied. It was found that the film transport properties do not change monotonically with increasing deposition rate. The photoconductivity peaks at ∼70-90 Å/s, where both the drift mobility and lifetime peak, consistent with the deposition rate dependence of the range and depth of the potential fluctuations. High quality, such as a photoconductivity-to-dark-conductivity ratio of ∼105 and nearly constant low charged defect density, can be maintained at deposition rates up to ∼150 Å/s, beyond which the film properties deteriorate rapidly as a result of an enhanced effect of the long-range potential fluctuations due to a considerable increase in the concentration of the charged defects. Our present results indicate that medium silane flow rate, low pressure, and higher substrate temperature are generally required to maintain high quality films at high deposition rates.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 664: Symposium A – Amorphous and Heterogeneous Silicon-Based Films-2001 , 2001 , A23.4
Copyright
Copyright © Materials Research Society 2001

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References

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