Performance degradation of superlattice MOSFETs due to scattering in the contacts

Abstract

Ideal, completely coherent quantum transport calculations had predicted that superlattice MOSFETs may offer steep subthreshold swing performance below 60mV/dec to around 39mV/dec. However, the high carrier density in the superlattice source suggest that scattering may significantly degrade the ideal device performance. Such effects of electron scattering and decoherence in the contacts of superlattice MOSFETs are examined through a multiscale quantum transport model developed in NEMO5. This model couples NEGF-based quantum ballistic transport in the channel to a quantum mechanical density of states dominated reservoir, which is thermalized through strong scattering with local quasi-Fermi levels determined by drift-diffusion transport. The simulations show that scattering increases the electron transmission in the nominally forbidden minigap therefore degrading the subthreshold swing (S.S.) and the ON/OFF DC current ratio. This degradation varies with both the scattering rate and the length of the scattering dominated regions. Different superlattice MOSFET designs are explored to mitigate the effects of such deleterious scattering. Specifically, shortening the spacer region between the superlattice and the channel from 3.5 nm to 0 nm improves the simulated S.S. from 51mV/dec. to 40mV/dec.

Effect of substrates on the electrical characteristics of a silicon nanowire feedback field-effect transistor under bending stresses

“…In the future, standby power consumption will account for the predominant portion of total power consumption in electronic devices; therefore, reducing off-current is crucial to low-power electronics research [4][5][6]. To overcome this limitation, a variety of sharp switching devices have been proposed and developed, such as ferroelectric negative capacitance FETs (NCFETs) [7,8], nano-electro-mechanical FETs (NEMFETs) [9][10][11][12], Landau-switch devices with air gap suspended gate [13][14][15], and superlattice nanowire FETs [16,17]. Among these innovative devices, feedback FETs have attracted a lot of interest due to their compatibility with CMOS processes.…”

Combination of Equilibrium and Nonequilibrium Carrier Statistics Into an Atomistic Quantum Transport Model for Tunneling Heterojunctions

“…The idea of combining thermalization and equilibrium statistics in non equilibrium Green's function (NEGF) was used to simulate resonant tunneling diodes (RTDs) and supperlattices [9,10] by partitioning the simulation domain to equilibrium (Eq) and non-equilibrium (Neq) regions. Such a coupled Eq-Neq quantum transport model was needed to explain experimental measurements of RTDs [9].…”

A Multiscale Modeling of Triple-Heterojunction Tunneling FETs

“…Practically, this strong, close to thermalizing, effect of electron-electron scattering is very difficult to model in the NEGF approach with an explicit self-energy due to its non-local nature, as explained in more detail in Ref. [16]. Therefore, we have developed an efficient empirical scattering model, using the NEMO5 tool [17].…”

“…This multiscale model, originally proposed in Ref. [18] for resonant tunneling diode simulation, has been generalized to be able to simulate other structures, such as the ultra-thin-body (UTB) superlattice transistors [16]. In this study, the model is further extended to consider both electron and hole transport, required for a band-to-band tunneling device simulation.…”