Enhanced gas sensing by graphene-silicon Schottky diodes under UV irradiation

The effect of ultraviolet (UV) or blue irradiation on graphene/n-doped silicon Schottky junctions toward gas sensing was investigated. Schottky diodes were subjected to oxidizing nitrogen dioxide (NO2, 1-3 ppm) and reducing tetrahydrofuran (THF, 50-200 ppm), showing significantly different responses observed on the current-voltage (I -V) characteristics, especially under UV light (275 nm). NO2 affected the resistive part of the forward region of the I -V curves, where graphene's resistance dominates, and increased the junction current. A low detection limit of 75 ppb was obtained for NO2 detection at a 4 V voltage bias. THF influenced the reverse and forward regions, shifting the exponential parts of the characteristics, indicating the impact on the Schottky barrier height, and reducing the detection limit to 31 ppm. The adsorption of organic molecules increased the Schottky barrier height by up to tens of meV due to the dominating photogating effect. The width of the junction area may be crucial for optimizing graphene-silicon Schottky-based sensors and improving their performance, together with irradiation-induced modulation, to become one of the most advanced gas mixture sensors. The ease of fabrication of large-area graphene and forming stable graphene-silicon junctions determine a simple method for developing efficient gas sensing platforms.