All 2D Heterostructure Tunnel Field Effect Transistors: Impact of Band Alignment and Heterointerface Quality

TL;DR

This study investigates 2D heterostructure TFETs, demonstrating that proper band alignment and high-quality heterointerfaces, especially using h-BN as a top gate insulator, enable low subthreshold swing at room temperature.

Contribution

It systematically analyzes the effects of band alignment and heterointerface quality, introducing h-BN as a defect-free top gate insulator for improved TFET performance.

Findings

Type III band alignment achieved with high doping p+-MoS2 source.

h-BN top gate reduces defect states compared to Al2O3.

Low subthreshold swing values obtained at room temperature.

Abstract

Van der Waals heterostructures are the ideal material platform for tunnel field effect transistors (TFETs) because a band-to-band tunneling (BTBT) dominant current is feasible at room temperature (RT) due to ideal, dangling bond free heterointerfaces. However, achieving subthreshold swing (SS) values lower than 60 mVdec-1 of the Boltzmann limit is still challenging. In this work, we systematically studied the band alignment and heterointerface quality in n-MoS2 channel heterostructure TFETs. By selecting a p+-MoS2 source with a sufficiently high doping level, stable gate modulation to a type III band alignment was achieved regardless of the number of MoS2 channel layers. For the gate stack formation, it was found that the deposition of Al2O3 as the top gate introduces defect states for the generation current under reverse bias, while the integration of an h-BN top gate provides a defect-free, clean interface, resulting in the BTBT dominant current even at RT. All 2D heterostructure TFETs produced by combining the type III n-MoS2/p+-MoS2 heterostructure with the h-BN top gate insulator resulted in low SS values at RT.