Performance Optimization of Monolayer 1T/1T’-2H MoX2 Lateral Heterojunction Transistors

Abstract

Recently, 2-D transition metal dichalcogenides (TMDs) lateral heterojunction field-effect transistors (FETs) have been demonstrated experimentally, in which metallic TMDs were used for the source/drain. In this work, we systematically investigate the contact property and device performance of monolayer 1T/1T $^{\prime }$ -2H MoS2, MoSe2, and MoTe2 FETs. Schottky barrier (SB) heights are extracted from density functional theory calculations, and nonequilibrium Green’s function transport simulations have been performed to study device characteristics. Our simulation results show that the inherent SB strongly affects the overall performance of these devices. Here, we optimize the performance of TMD lateral heterojunction FETs by using two different approaches. First, we have improved the electrostatic control by scaling equivalent oxide thickness and gate underlap, which boosts both ON- and OFF-state characteristics, making the device suitable for high-performance applications. On the other hand, moderate doping has been used in the gate underlap region, improving ON/OFF current ratio with negligible impacts on ON-state characteristics, and this approach is more preferred for low-power applications. This study reveals that 1T $^{\prime }$ -2H MoTe2 FET shows the highest ON current ( $\sim 1$ mA/ $\mu \text{m}$ ) among the three with a reasonably small subthreshold swing (80 mV/dec) if properly scaled, while 1T-2H MoS2 FET exhibits the highest ${I} _{\scriptscriptstyle{\text{ON}}}/{I} _{\scriptscriptstyle{\text{OFF}}}$ (~107) when ohmic contact is established with moderate doping in the gate underlap region. This study not only provides physical insight into the electronic devices based on novel TMD heterostructures but also suggests engineering practice for device performance optimization in experiments.