Simultaneous achievement of superior response and full recovery of titanium dioxide/graphene hybrid FET sensors for NH3 through p- to n-mode switch

Abstract

The switch in the sensing mode for better identification of donor/acceptor gases with simultaneous enhancement of the sensing performance at a fixed working temperature particularly room temperature (RT) is quite challenging for gas sensors. Herein, TiO₂/graphene hybrid field effect transistor (FET) sensors (TiO₂/GFET) with varied hybrid areas are presented. Superior sensing and recovery performances for NH₃ are achieved through sensing mode switch via gate biasing. 16.40% response and full recovery for 25 ppm NH₃ are achieved for TiO₂/GFET sensors with 100% titanium dioxide coverage (D₁₀₀) at RT (27 °C) with 15–20% humidity upon switching sensing mode from p- to n via gate biasing. Full recovery is attributed to the Coulomb interaction between charged polar donor molecules and positively polarized surface which is enhanced by the switch from p- to n-mode. The humidity can enhance response up to −35.48% for 25 ppm NH₃ with full recovery in n-mode for D₁₀₀. D₁₀₀ shows superior selectivity towards NH₃ against both electron-acceptor NO₂ and several other electron-donor analytes. The sensing behaviors for NH₃ are well elucidated using energy band diagrams based on the experimental results. This study proposes a novel idea for performance improvement of FET based sensors with p- and n-type hybrid sensing materials through p (n)- to n (p)-mode switch assisted by gate biasing by incorporating suitable electron (hole) rich materials to compensate holes (electrons) in p (n)-type materials for electron donor (acceptor) gas detection.