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Very High-Gap Tetrahedrally Coordinated Amorphous Silicon-Carbon Alloys

Published online by Cambridge University Press:  16 February 2011

Ionel Solomon
Affiliation:
Ecole Polytechnique, Laboratoire de Physique de la Matière Condensée, 91128 Palaiseau CEDEX, France.
Leandro R. Tessler
Affiliation:
On leave from: Instituto de Fisica “Gleb Wataghin”, UNICAMP, C.p. 6165, Campinas SP, Brazil
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Abstract

We have prepared a series of hydrogenated Amorphous silicon-carbon alloys a-Si1-xCx:H in conditions where the power delivered to the plasma is below the threshold of primary decomposition of CH4 (“low-power regime”). Carbon is therefore incorporated into the growing film in the form of methyl groups -CH3, thus preserving the sp3 hybridization in the solid. Since the carbon is deposited only by chemical reaction with the radicals produced by the decomposition of SiH4, its concentration in the alloys cannot exceed the value x=0.5.

The variations of the optical gap and of the “average gap” with x, as measured by optical transmission, indicate as expected the predominantly tetrahedral coordination of the carbon, with a record value of EQ4=3.6 eV for x=0.42 (3.95 eV if corrected for the Urbach-tail absorption). Since the Si-C network does not relax to a more stable lower sp2 coordination, the material is highly strained, with an Urbach tail larger than that of the standard Material.

Type
Research Article
Copyright
Copyright © Materials Research Society 1994

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