Conduction Mechanisms in Epitaxial NiO/Graphene Gas Sensors

TL;DR

This study demonstrates that NiO/graphene/SiC sensors can detect NO2 at sub-ppb levels with high sensitivity and reversible p-type/n-type switching, driven by NiO-induced Fermi level shifts.

Contribution

It reveals the conduction mechanism switch in NiO/graphene sensors is caused by NiO layer effects, enabling highly sensitive gas detection.

Findings

Sensors detect NO2 below 1 ppb concentration.

NiO layer causes conduction type switch in graphene.

Sensor response is reversible and highly sensitive.

Abstract

Integrated, highly sensitive and reversible sensor devices for toxic and hazardous gases in environmental pollution monitoring can be realized with graphene-based materials. Here we show that, single layer graphene grown on SiC can be utilized to implement sensor devices being extremely sensitive towards NO2 showing an n-type response. A second type of sensor with an added NiO layer on top of the single layer graphene changed its response to p-type but did not reduce its sensitivity. We show that the conduction switch from n-type to p-type was not a consequence of an alteration of the graphene layer but is found to be an effect of the NiO layer. We find that the NiO leads to lowering of the Fermi level to a point that a crossing of the Dirac Point in the graphene switched the conduction type. These sensors were tested in the 100 ppb NO2 regime, showing good response and a detection limit extrapolated to be below 1 ppb. This new NiO/graphene/SiC configuration can be an attractive p-type sub-ppb sensor platform for NO2 and related gases.