Simultaneous Achievement of Superior Response and Full Recovery of Titanium Dioxide/Graphene Hybrid FET Sensor for NH3 through p- to n- Mode Switch
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 sensor with 100% titanium dioxide coverage (D100) at RT (27℃) 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 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. 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 via incorporating proper electron (hole) rich materials to compensate holes (electrons) in p (n)- type materials for electron donor (acceptor) gases detection.