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

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 H-2 and O-2 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 O-2 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 O-2 gas and 82% for H-2 gas compared with single layer device Au/NiO/Au 86% for O-2 and 96% for H-2 respectively. These results suggest that the nanostructure NiO films are promising for gas sensor applications.