We develop graphene-based multiple heterojunctions to realize sensors with a very high sensitivity (< 10 ppm), ultra-fast sensing time (< 10 ms), and stable repeatability. The sensing mechanism solely depends on the large change in the Fermi energy ( E-F) of graphene resulting from the absorbed molecules, which produces a large change in the output current across the heterojunction. The charge induced by the absorbed molecules remains in the graphene layer without transferring into the underlying layer owing to the well-designed band alignment among the constituent materials, which results in ultra-fast and highly sensitive performance. Furthermore, we demonstrate that with different polarities of external bias, the graphene multiple-junction sensors can be used to selectively detect different gases. In addition to the suitable band alignment, the high performance of our device arises from the sandwich structure of top and bottom electrodes, which enables to exponentially enhance the current across the Schottky junction. Moreover, the large shift of the Fermi level of graphene induced by its inherent nature of low density of states also plays an important role. Compared with all published reports, our device possesses a much better performance. Particularly, the response time is three orders of magnitude faster than those of reported values, which can provide a critical step to advance graphene based gas sensors toward real world applications. Published by AIP Publishing.
