A Multiscale Modeling of Triple-Heterojunction Tunneling FETs

TL;DR

This paper develops a multiscale transport model to evaluate the impact of scattering effects on triple-heterojunction TFETs, revealing that scattering reduces performance but still surpasses single heterojunction devices.

Contribution

It introduces a novel multiscale simulation approach combining ballistic and scattering models to analyze realistic device performance.

Findings

Scattering reduces ON-current from 460 to 254 μA/μm.

Scattering increases leakage and access resistance.

Triple-heterojunction TFETs outperform single HJ TFETs even with scattering.

Abstract

A high performance triple-heterojunction (3HJ) design has been previously proposed for tunneling FETs (TFETs). Compared with single heterojunction (HJ) TFETs, the 3HJ TFETs have both shorter tunneling distance and two transmission resonances that significantly improve the ON-state current ($I_{\rm{ON}}$). Coherent quantum transport simulation predicts, that $I_{\rm{ON}}=460\rm{\mu A/\mu m}$ can be achieved at gate length $Lg=15\rm{nm}$, supply voltage $V_{\rm{DD}}=0.3\rm{V}$, and OFF-state current $I_{\rm{OFF}}=1\rm{nA/\mu m}$. However, strong electron-phonon and electron-electron scattering in the heavily doped leads implies, that the 3HJ devices operate far from the ideal coherent limit. In this study, such scattering effects are assessed by a newly developed multiscale transport model, which combines the ballistic non-equilibrium Green's function method for the channel and the drift-diffusion scattering method for the leads. Simulation results show that the thermalizing scattering in the leads both degrades the 3HJ TFET's subthreshold swing through scattering induced leakage and reduces the turn-on current through the access resistance. Assuming bulk scattering rates and carrier mobilities, the $I_{\rm{ON}}$ is dropped from $460\rm{\mu A/\mu m}$ down to $254\rm{\mu A/\mu m}$, which is still much larger than the single HJ TFET case.