Complementary tunneling transistors based on WSe2/SnS2 van der Waals heterostructure

Dear editor, Two-dimensional (2D) semiconductors have emerged as one of the most promising material candidates for next-generation electronic devices [1]. Owing to the broad range of bandgap diversity and the pristine interface, 2D semiconductors have triggered tremendous research interest for various device applications, especially in tunnel field-effect transistors (TFETs) [2–4]. To date, most of the experimental demonstrations of 2D-based TFETs mainly focus on either n-type or p-type device, and are realized in different material systems, which is not preferred for highly-integrated circuits. In [5], both n-type and p-type TFETs based on the reconfigured structure and black phosphorus (BP) material have been realized through electrical modulation of carrier types of the source and the drain. However, due to the inherent small band gap of BP, the leakage current and on/off current ratio of devices are unsatisfactory. Complementary TFETs based on the same 2D material system with superior performance are still in urgent need. Moreover, most of the 2D TFET reports focus on the reduction of effective tunnel barrier height for drive current enhancement, while few studies have been reported for the improvement of output characteristics. Some typical features in the output curves of TFETs, such as super-linear onset phenomenon, could degrade the dynamic property and static noise margin of digital circuits [6]. Therefore, both transfer and output characteristics should be considered for the complementary TFET design. Taking into consideration of transfer and output characteristics, both n-type and p-type TFETs are designed and experimentally demonstrated based on the WSe2/SnS2 van der Waals heterostructure. The type-II band alignment of WSe2/SnS2 heterostructure with reduced effective tunnel barrier height is beneficial for high tunnel current, and the thicknesses of WSe2 and SnS2 in n-TFET and pTFET are optimized separately to suppress the super-linear onset in output curves. The fabricated complementary TFETs show on/off current ratio of 10, which is much higher than that of the previously reported BP TFETs [5]. The tunneling mechanism of fabricated devices is also confirmed by the temperature-dependence characteristics. Device structure and design principle. Figures 1(a) and (b) show the schematic structures of the bottom-gated complementary TFETs based on van der Waals heterostructure in this study. The SiO2 and highly-doped Si are used as the gate dielectric and the bottom gate, respectively. The channel layer is designed to be under the source layer so that the channel potential could be controlled by the bottom gate with the better gate controllability. Besides, taking into consideration of both transfer and output characteristics, the 2D-based complementary TFETs are designed according to the following principles. Take the pTFET for example.