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Thermodynamics and Kinetics of Hydrogen Evolution in Hydrogenated Amorphous Silicon Films

Published online by Cambridge University Press:  15 February 2011

Nagarajan Sridhar
Affiliation:
Also with Department of Mechanical and Aerospace Engineering, Center for Electronic and Electro-Optic Materials, State University of New York at Buffalo, NY 14260–4400, and J. Coleman, Plasma Physics Corp., P. O. Box 548, Locust Valley, NY 11650.
D. D. L. Chung
Affiliation:
Also with Department of Mechanical and Aerospace Engineering, Center for Electronic and Electro-Optic Materials, State University of New York at Buffalo, NY 14260–4400, and J. Coleman, Plasma Physics Corp., P. O. Box 548, Locust Valley, NY 11650.
W. A. Anderson
Affiliation:
Also with Department of Electrical and Computer Engineering, Center for Electronic and Electro-Optic Materials, State University of New York at Buffalo, NY 14260–4400, and J. Coleman, Plasma Physics Corp., P. O. Box 548, Locust Valley, NY 11650.
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Abstract

The enthalpy (endothermic) of hydrogen evolution from p-type (boron doped) amorphous silicon with 17 at. % H was 4.8, 10.3, 15.8 and 17.3 kJ/g, the evolution temperature was 585, 606, 625 and 644 °C and the entropy of evolution was 5.6, 11.7, 17.5 and 18.9 J/g.K at heating rates of 5, 10, 20 and 30 °C/min respectively. That the enthalpy and entropy increased with heating rate means that the evolution involves not only Si-H bond breaking, but also Si-Si bond breaking and other defect formation. The Si-Si bond breaking and defect formation were enhanced at high heating rates, which caused high rates of hydrogen evolution. For n-type (phosphorous-doped) and intrinsic amorphous silicon with 25 and 23 at. % H respectively, the enthalpy and entropy of hydrogen evolution were higher than the p-type case, due to severe defect formation resulting from the higher hydrogen content. The activation energy of hydrogen evolution was 1.38, 2.5 and 4 kJ/g for the p-type, intrinsic and n-type materials respectively. Crystallization which occurred at temperatures higher than hydrogen evolution, was delayed for the amorphous silicon film in a higher disordered state after hydrogen evolution, suggesting that hydrogen evolution influenced the crystallization process.

Type
Research Article
Copyright
Copyright © Materials Research Society 1995

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