Thermalization Effect in semiconductor Si, and metallic silicide NiSi2, CoSi2 by using Non-Adiabatic Molecular Dynamics Approach

TL;DR

This paper investigates the thermalization processes of carriers in silicon and silicide materials using nonadiabatic molecular dynamics, revealing energy-dependent thermalization times and higher scattering rates in silicides, informing low-power transistor design.

Contribution

It applies a state-of-the-art nonadiabatic molecular dynamics method to study carrier thermalization in silicon and silicides, providing detailed energy-dependent scattering insights.

Findings

Thermalization time increases with energy level.

Partially thermalizes within sub-100 fs timescale.

Silicides exhibit scattering rates 100 times higher than silicon.

Abstract

Recently, cold source transistor (CSFET) with steep-slope subthreshold swing (SS) < 60 mV/decade has been proposed to overcome Boltzmann tyranny in its ballistic regime. However the scattering, especially by inelastic scattering may lead serious SS degradation through cold carrier thermalization. In this study, the electronic excitation/relaxation dynamic process is investigated theoretically by virtue of the state-of-the-art nonadiabatic molecular dynamics (NAMD) method, i.e., the mixed quantum-classical NAMD. The mixed quantum-classical NAMD considers both carrier decoherence and detailed balance to calculate the cold carrier thermalization and transfer processes in semiconductor Si, and metallic silicide (NiSi2 and CoSi2). The dependence of the thermalization factor, relaxation time, scattering time and scattering rate on energy level are obtained. The thermalization of carrier gradually increases from low energy to high energy. Partially thermalization from the ground state to reach the thermionic current window is realized with sub-100 $fs$ time scale. Fully thermalization to entail energy region depends on the barrier height sensitively, i.e., the scattering rate decreases exponentially as the energy of the out-scattering state increase. The scattering rate of NiSi2 and CoSi2 is 2 orders of magnitude higher than that of Si, arising from their higher density of states than that in Silicon This study can shed light on the material design for low power tunneling FET as well as the emerging CSFET.