Comparative study between sensing properties of single layer (NiO) and heterojunction (NiO/p-Si) gas sensors based on nanostructured NiO films by spray pyrolysis

Abstract

Nickel oxide (NiO) thin films have been prepared by spray pyrolysis on quartz substrate and p-type silicon wafer, used to fabricate single layer device (Au/NiO/Au) and heterojunction device (Au/NiO/Si/Au) as a gas sensors. The structural, morphological, and optical properties of these films were investigated. The prepared films had mesoporous NiO phase with the average pore size in the range 100–500 nm. The nanostructure NiO films exhibited sensitivity with H2 and O2 target gases at room temperature. Current–voltage (I–V) characteristics of the fabricated single layer devices were studied at room temperatures in vacuum and Ohmic-like behavior was observed, while in the case of Au/p-NiO/p-Si/Au heterojunction Schottky behavior was observed. The p-NiO/p-Si heterojunction sample exhibited an excellent gas sensing response to O2 gas at room temperature and the light illumination improved the responsivity of both devices. The responsivity for the p-NiO/p-Si heterojunction at room temperature measured at an applied bias voltage of 5 V was found to be 108% for O2 gas and 82% for H2 gas compared with single layer device Au/NiO/Au 86% for O2 and 96% for H2 respectively. These results suggest that the nanostructure NiO films are promising for gas sensor applications.