A Multiscale Modeling of Triple-Heterojunction Tunneling FETs

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

Impact of body thickness and scattering on III-V triple heterojunction Fin-TFET modeled with atomistic mode space approximation

“…Traditionally, the reduced-size Hamiltonians at each sampled k are supposed to be generated by different transformation matrices because the modes contributing to electronic transport are different for different k . However, generating the transformation matrix for each sampled k is a timeconsuming process due to the basis optimization [17], [34]. In this work, we find out that generating the transformation matrix for each sampled k is not necessary since the matrix is transferable within a sizable range of k .…”

“…In this work, we expand the method to simulate UTB heterojunction TFETs. To describe the scattering of carriers in quantum wells, an efficient thermalization model, that showed to match experimental data, has been incorporated into the MS approximation [16], [17]. The simulation time of a device with 12 nm body thickness increases by 25% if the scattering is included, which is practically acceptable.…”

Impact of source doping on the performance of vertical InAs/InGaAsSb/GaSb nanowire tunneling field-effect transistors

“…MOSFETs can at higher drive voltages (V DS ) [34]. Thus, high currents require a thin barrier, which is achieved by proper band alignment, high precision gate alignment to avoid source depletion, and sufficiently high source doping with an abrupt profile.…”

Doping profile engineered triple heterojunction TFETs with 12 nm body thickness

“…The non-equilibrium quantum mechanics of the system includes the electron-electron scattering and electron-phonon scattering of carriers in these quantum wells, tunneling process at multiple interfaces, and quantum confinement effects [29]- [36]. To capture these mechanisms, atomistic quantum transport simulation, including effective thermalization [37], [38], is necessary to evaluate the device performance. Since a realspace atomistic simulation is computationally challenging for devices with a large dimension, the atomistic mode-space approach developed in Ref.…”