Bias enhanced sensitivity in amorphous/porous silicon heterojunction gas sensors

In this work we present an investigation of the electrical behavior of an innovative gas sensor based on a heterojunction between porous silicon and hydrogenated amorphous silicon. P-type porous silicon, usually obtained by an electrochemical etching of monocrystalline silicon substrate, can be used as active layer in sensors because of its high surface to volume ratio and high reactivity. A thin layer of n-type amorphous silicon, deposited by plasma enhanced chemical vapor deposition technique on the nanoporous phase structure, still maintains photoluminescence properties as well as gas sensitivity and effective recovery after gas exposure. We found higher sensitivity at higher reverse bias conditions. A detailed investigation of this phenomenon, for different gas concentrations, is presented.