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Evidence for Exchange Between Free and Deep Hydrogen (Deuterium) During Diffusion

Published online by Cambridge University Press:  15 February 2011

Howard M. Branz ,
Sally Asher ,
Yueqin Xu  and
Mathieu Kemp
Howard M. Branz
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401, USA
Sally Asher
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401, USA
Yueqin Xu
Affiliation:
National Renewable Energy Laboratory, Golden, CO 80401, USA
Mathieu Kemp
Affiliation:
Dept. of Engineering Physics, Ecole Polytechnique, Montreal, Quebec, Canada
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Abstract

We do not observe any immobile deuterium in secondary ion mass spectrometry D profiles taken after long anneals of hydrogenated amorphous silicon sandwich structures with a thin deuterated interior layer. This suggests that a single deep H level (∼1.4 eV deep) controls H diffusion. On its face, our result contradicts nuclear magnetic resonance and H effusion measurements that show about 30% of H in a-Si:H is “isolated” and deeply bound (∼ 2.1 eV deep). We reconcile our experimental results with the existence of isolated deep H by assuming there is a low-barrier (<< 1.4 eV) exchange process between free H and deep D. In tracer experiments, exchange has the effect of increasing the apparent emission rate of the deep D to nearly that of the shallowest trapped H. We solve for the D profiles and confirm that a deep-trapped D component is consistent with our D tracer profiles if and only if exchange processes are important. We also find that the mean distance D travels before retrapping (100–200Å) is determined by an exchange process of free D with trapped H.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 377: Symposium A – Amorphous Silicon Technology 1995 , 1995 , 331
Copyright
Copyright © Materials Research Society 1995

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References

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