Tunable Polarity in WSe2/TiS2 Van Der Waals Heterostructure

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDs) formed layered van der Waals (vdW) crystals have emerged as promising candidates for varieties of potential applications, such as gas sensors, photodetectors, light-emitting diodes, Schottky diodes and memories, due to their unique physical features. However, since the existence of the metal-induced gap states (MIGS) at metal-semiconductor interfaces, it is severely difficult to adjust their electrical properties. It was demonstrated in previous researches that various metal contacts on TMDs semiconductor exhibit regular Schottky barrier height by Fermi-level pinning effect.In this study, we suggest the van der Waals material contact between TiS2 semimetal and WSe2 semiconductor for leading van der Waals gap at their interface. Through this approach, the TiS2/WSe2 2D heterojunction can efficiently address the MIGS. Interestingly, the TiS2/WSe2 heterojunction exhibits a novel electrical transport characteristics such as distinct ambipolar and rectifying behaviors by tuning drain voltage polarity. Firstly, under reverse bias (V ds < 0), TiS2/WSe2 heterojunction operates efficiently and allows transport of the carriers at both polarities of the gate voltage (V bg < 0 and V bg > 0), namely ambipolar behavior. Secondly, under the forward bias (V ds > 0), TiS2/WSe2 heterojunction does not allow transport of the electrons at positive gate voltage (V bg > 0), but allow transport of the holes at negative gate voltage (V bg < 0), namely p-type behavior. To understand the carrier transport mechanism of these results, ultra-violet photoelectron spectroscopy (UPS) measurements were also carried out on the WSe2 and TiS2 flakes. It is noted that the TiS2/WSe2 junction plays a crucial role in determining a novel electronic property of this device. Figure 1