2D-2D tunneling field-effect transistors using WSe2/SnSe2 heterostructures

Abstract

Two-dimensional materials present a versatile platform for developing steep transistors due to their uniform thickness and sharp band edges. We demonstrate 2D-2D tunneling in a WSe2/SnSe2 van der Waals vertical heterojunction device, where WSe2 is used as the gate controlled p-layer and SnSe2 is the degenerately n-type layer. The van der Waals gap facilitates the regulation of band alignment at the heterojunction, without the necessity of a tunneling barrier. ZrO2 is used as the gate dielectric, allowing the scaling of gate oxide to improve device subthreshold swing. Efficient gate control and clean interfaces yield a subthreshold swing of ∼100 mV/dec for >2 decades of drain current at room temperature, hitherto unobserved in 2D-2D tunneling devices. The subthreshold swing is independent of temperature, which is a clear signature of band-to-band tunneling at the heterojunction. A maximum switching ratio ION/IOFF of 107 is obtained. Negative differential resistance in the forward bias characteristics is observed at 77 K. This work bodes well for the possibilities of two-dimensional materials for the realization of energy-efficient future-generation electronics.

Vertical Transistors Based on 2D Materials: Status and Prospects

“…A band-to-band tunneling vertical transistor has been demonstrated also using the vdW heterojunction between differently-doped layered semiconductors as WSe 2 and SnSe 2 , where WSe 2 worked as the back-gate-controlled p-layer and SnSe 2 was the degenerately n-type-doped layer [83].…”

Gate-Tunable WSe2/SnSe2 Backward Diode with Ultrahigh-Reverse Rectification Ratio

“…and WSe2 forces a highly staggered type II band alignment [30][31][32] . In this work, we exploit this property of the WSe2/SnSe2 heterojunction to demonstrate a backward diode with a large curvature coefficient of ~37 V -1 , coupled with an extremely high reverse rectification ratio of ~2.1 × 10 4 , outperforming previously reported numbers 19,20,[33][34][35][36][37][38][39][40][41][42][43] .…”

Field-effect transistors of high-mobility few-layer SnSe2

“…flakes have been made into high drive current FETs. 4 Thinner SnSe 2 flakes in combination with other 2D materials, such as black phosphorus (BP) 5 and WSe 2 , 6 have been adopted in tunneling devices, which showed pronounced negative differential resistance (with BP and WSe 2 ) or good subthreshold swing (with WSe 2 ). SnSe 2 flakes have also been used as high performance photodetectors.…”

“…Due to its heavy n doping, FETs based on SnSe 2 have been found to be very difficult (if not impossible) to turn off. [4][5][6][7]10 We solve this problem with a vertical charge distribution model and identify a critical flake thickness, below which the FET can be turned off with a simple Si back gate. With this type of device, we are able to achieve a current on-off ratio of ~10 5 at 78 K.…”