Room Temperature Detection of NO2 at ppb Level and Full Recovery by Effective Modulation of the Barrier Height for Titanium Oxide/Graphene Schottky Heterojunctions

Simultaneous achievement of high response, high sensitivity, low detection limit, and full recovery at room temperature (RT) is quite challenging for gas sensors. Herein, ultrathin titanium oxide/graphene Schottky heterojunction sensors (SHS) are fabricated with varying junction areas. Increasing junction area favors the sensing performance. A change of 11.822 meV in Schottky barrier height (SBH) is induced by 3 ppm NO2 exposure, accompanied by a change of -36.54% in current, approximate to 18 and 36 times that for bare titanium oxide and graphene sensors at RT, respectively. A high sensitivity of 10.430% ppm(-1), low detection limit of 28 ppb, and complete recovery for 100 ppb NO2 are simultaneously achieved at RT. 100 ppm NH3 can be detected with full recovery as well. The superior performance of SHS is predominantly attributed to the effective modulation of SBH (exponential change in current) by gas adsorption and the charge transfer to interfaces enhanced by the presence of ultrathin continuous oxide layers. The sensing mechanism can be understood via energy band diagrams. This study proposes an idea of designing SHS with ultrathin n-metal oxides and p-graphene to simultaneously achieve high sensitivity, low detection limit, and full recovery for NO2 and other gases at RT.