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Opposite effects of NO2 on electrical injection in porous silicon gas sensors

Zeno Gaburro, Claudio J. Oton, Lorenzo Pavesi, Lucio Pancheri

cond-mat.mtrl-sciarXiv:cond-mat/0311272

Abstract

The electrical conductance of porous silicon fabricated with heavily doped p-type silicon is very sensitive to NO2. A concentration of 10 ppb can be detected by monitoring the current injection at fixed voltage. However, we show that the sign of the injection variations depends on the porous layer thickness. If the thickness is sufficiently low -- of the order of few -- the injection decreases instead of increasing. We discuss the effect in terms of an already proposed twofold action of NO2, according to which the free carrier density increases, and simultaneously the energy bands are bent at the porous silicon surface.

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