Ge/GaAs Heterostructure TFET With Schottky Contact to Suppress Ambipolar and Trap-Assisted Tunneling
Jyi-Tsong Lin, Hong-Syue Ho
Abstract
In this article, we present a novel heterostructure tunnel field-effect transistor (HSC-TFET) with a Schottky contact drain, utilizing a gate over a substantial portion of the source metal overlap. This results in a complete gate-to-source metal overlap, ensuring a robust electric field that drives dominant line tunneling. Consequently, this leads to an exceptionally high tunneling probability and a significant tunneling current, resulting in an extremely steeper subthreshold swing (SS). Furthermore, we propose a hetero Ge-GaAs structure to mitigate the shortcomings of a Ge-only structure, such as high leakage current, significant ambipolar effects, and worse trap-assisted tunneling (TAT). The proposed HSC-TFET employs a drain region utilizing a wider bandgap GaAs material coupled with a Schottky contact, resulting in a smooth modulation of the drain potential and effectively extending the tunneling distance. This approach successfully suppresses ambipolar leakage current and the TAT effect. The Ge source region, due to its small bandgap, results in shorter tunneling distances and, consequently, higher tunneling probabilities. This showcases a superior switching ratio and ON-state current when compared to other material combinations. Based on the feasibility of the actual fabrication process, through rigorous 2-D simulation studies, we achieved a high ON-state current of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.65\times 10^{-4}$ </tex-math></inline-formula> A/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${V}_{\text {D}}$ </tex-math></inline-formula> = 0.4 V, a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ </tex-math></inline-formula> ratio of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.38\times 10^{{10}}$ </tex-math></inline-formula> , and an average subthreshold slope of 23.83 mV/dec, making it an ideal candidate for ultralow-power Internet of Things (IoT) applications.