Bias-controlled multifunctional transport properties of BP/InSe van der Waals heterostructures

Abstract

Van der Waals (vdW) heterostructures consisting of a variety of two-dimensional (2D) materials with different physical properties possess a wide freedom to design diverse electronic devices. In particular, the strong electrostatic tunability of 2D materials provides the rich potential for multifunctional devices operating differently depending on the gate or drain bias. Here, we investigate black phosphorus (BP)/indium selenide (InSe) heterostructures encapsulated by hexagonal boron nitride (h-BN). At a positive drain bias (VD), which is applied on the BP while the InSe is grounded, our heterostructures shows a weak negative differential transconductance (NDT) property or a nearly constant mid-state depending on the magnitude of VD. This can be employed for a ternary-logic transistor, and we also demonstrate the operation of a ternary logic inverter with a differentiation between each state of ~ 1V. By contrast, at a negative VD, our device shows much stronger NDT properties; the peak current increases up to ~ 3 μA and the peak to valley ratio reaches higher than 103 at VD = -2V, which is distinctively superior compared to other NDT devices. We will systematically discuss those electrical properties as a function of the drain bias, the carrier density, thickness of the BP layer and the channel length of BP or InSe. The impact of the contact resistances will be also addressed in detail, accompanied with the four-probe channel resistivities and band alignment analysis. Furthermore, we fabricate the BP-InSe metal junction device and overlap-only device to fully explore the impact of the BP-only, InSe-only and BP/InSe overlap region on the NDT characteristics.