High-performance hydrogen sensing properties and sensing mechanism in Pd-coated p-type Si nanowire arrays

Abstract

We report on the H2 sensing performance and sensing mechanism in Pd-coated n- and p-type Si nanowire (NW) arrays, which were fabricated by an aqueous electroless etching method and sputtering. We found that the resistance of the Pd-coated n-type Si NWs decreased from the base resistance, whereas that of the p-type Si NW arrays increased, upon exposure to H2. The sensitivity (S=1700% at 1% H2) of Pd-coated p-type NW arrays was much greater than that of the n-type NW arrays (S=75%). Furthermore, we found that the dependency of the change in carrier density on H2 concentration was significantly greater in p-type Si NW arrays, while it was negligible in the n-type NW arrays. A Schottky barrier was formed between the Pd and n-Si (ϕM>ϕSC) before exposure to H2, which changed to an Ohmic contact (ϕM<ϕSC) after H2 exposure. In contrast, an Ohmic contact was formed between the Pd and p-Si (ϕM>ϕSC) before exposure to H2, which, after exposure, changed to a Schottky barrier (ϕM<ϕSC). Therefore, the p-type Si NW arrays were much more sensitive to H2 than the n-type Si NW arrays.