Are electrical properties of an aluminum–porous silicon junction governed by dangling bonds?

Abstract

Using an aluminum–porous p+ silicon junction, we have realized a sensor which dc current increases up to two orders of magnitude in the presence of ammonia, as for a series of various gases. To interpret quantitatively this phenomenon, we assume that the conductivity is governed by the width of a channel resulting from the partial depletion of silicon located between two pores. This depleted region is due to the charges trapped on surface states associated with the Si–SiO2 interface where SiO2 is the native silicon oxide. When some gas is adsorbed, mainly on Si–H bonds, we propose there is an electrical screening of the interface states (mainly dangling bonds located in the neighborhood of the Si–H bonds), leading to a decrease of the depleted region, i.e., an increase of the width of the channel and thus an increase of the current.