Overcoming ineffective resistance modulation in p-type NiO gas sensor by nanoscale Schottky contacts.

We present a gas sensor having nanoscale Schottky contacts on an array of helical-shaped p-type NiO to overcome intrinsically ineffective resistance modulation in the bulk of p-type metal oxides upon gas exposure. The Schottky device shows an abnormal n-type sensing behavior despite using the p-type NiO under reducing gas, with the sensitivity of 142.9% at 200 ppm of hydrogen, much higher than the reference Ohmic device with 0.7% sensitivity. Based on our equivalent circuit model with the quantitative estimation of the modulations in both carrier concentration and Schottky barrier height upon gas exposure, such a high sensitivity and the abnormal sensing behavior are attributed to the predominant modulation in the barrier height at the nanoscale Schottky contacts which are uniquely designed to have top-and-bottom electrodes configuration for efficient gas adsorption and sensitive Schottky barrier height modulation.