Few-layered α-MoTe2 Schottky junction for a high sensitivity chemical-vapour sensor

Abstract

For the first time, we connect in series two α-MoTe₂-based Schottky diodes (SDs) to form a back-to-back diode using the micromechanical exfoliation method. The α-MoTe₂ SD exhibits an excellent ON/OFF current ratio of ∼10³ and low-voltage operation at 5 V. Although various studies of α-MoTe₂ field-effect transistors (FETs), phototransistors, and p–n diodes have been reported, there are no reported theoretical or experimental studies of α-MoTe₂ for chemical sensing. Here, we experimentally assess the SD and a FET for gas sensing with exposure to different concentrations of NO₂ and NH₃. Interestingly, the α-MoTe₂ SD showed a faster response and recovery time to NH₃ and NO₂ than the α-MoTe₂ FET owing to its Schottky junction, which is favorable for detecting the Schottky-barrier height change due to gas exposure. The SD showed a fast response of 15 s when exposed to 70-ppb NO₂ and ∼1 s when exposed to 70 ppb NH₃ with a relative resistance change of 13% and 101%, respectively, and this was attributed to its physisorption process. In addition, our results are confirmed by density functional theory. The α-MoTe₂-based SD is shown to be promising as an electrical rectifier or as a gas sensor owing to its simple and inexpensive electrical circuitry and excellent performance, including its low voltage, high ON/OFF current ratio and good sensitivity to toxic gases at room temperature. Further, it may be suitable for diverse uses, such as chemical and biosensing applications.