Sensing of NO2, NH3, and C3H6O by graphene-Si Schottky diode at chosen voltage biases

Abstract

Abstract Our research aims to propose a selective gas sensor based on a single graphene-silicon Schottky junction. By polarizing the sensor with selected voltage, we move between different regions of its gas sensitivity dependent on the lighting conditions. Our results show that low detection limits (36 ppb for NO2, 238 ppb for NH3, and 640 ppb for C3H6O) are obtained under UV irradiation at -0.4 V; however, a light source power supply is required. Then, the Schottky barrier height is primarily sensitive to gas adsorption. When the sensor operates in the dark, the characteristic region of graphene between the ohmic contact with the Ni/Au electrode and a Schottky contact with Si is responsible for observing the gating effect in the structure. It is visible as a bending in the I-V curve near 0.7 V, which shifts with the adsorption of gases due to potential induced by molecular dipoles. Observing and analyzing these two effects on DC characteristics makes our sensor a highly sensitive and selective platform of low-power consumption and low-cost methodology. Additionally, the applied Schottky junction between the graphene layer and the n-doped Si base makes the sensor more resistant to humidity adsorption during storage in ambient air than other graphene-based gas sensors (graphene back-gated FET).