Atomistic modeling of anharmonic phonon-phonon scattering in nanowires

Abstract

Phonon transport is simulated in ultra-scaled nanowires in the presence of anharmonic phononphonon scattering. A modified valence-force-field model containing four types of bond deformation is employed to describe the phonon bandstructure. The inclusion of five additional bond deformation potentials allows to account for anharmonic effects. Phonon-phonon interactions are introduced through inelastic scattering self-energies solved in the self-consistent Born approximation in the Nonequilibrium Green's Function formalism. After calibrating the model with experimental data, the thermal current, resistance, and conductivity of <100>-, <110>-, and <111>-oriented Si nanowires with different lengths and temperatures are investigated in the presence of anharmonic phononphonon scattering and compared to their ballistic limit. It is found that all the simulated thermal currents exhibit a peak at temperatures around 200 K if phonon scattering is turned-on while they monotonically increase when this effect is neglected. Finally, phonon transport through Si-Ge-Si nanowires is considered.

Atomistic modeling of coupled electron-phonon transport in nanowire transistors

“…[22,27] the electron-phonon ( ) and the phonon-electron ( ) self-energies in Eqs. (10) and (11) are exact, but difficult to implement from a numerical point of view.…”

“…Once convergence is achieved, the charge and current densities as well as the distribution of the phonon population are calculated as in Refs. [22,27]. Furthermore, the electron and phonon energy currents flowing between the s th and s th + 1 slab (unit cell) of the simulated structures can be computed as…”

Nonequilibrium Green’s function method for quantum thermal transport

“…Our experience seems to indicate that, with just the perturbative terms, it is not possible to produce correct diffusive transport for large sizes [57,65]. The next step is to use self-consistent Born approximation [65,100,101], keeping only the lowest order self-energy diagrams (see Fig. 5 in Ref.…”

Phonon-limited low-field mobility in silicon: Quantum transport vs. linearized Boltzmann Transport Equation

“…Here, we use this formalism to simulate bulk Si and Si nanowires in the presence of electron-phonon scattering in the self-consistent Born approximation. [21][22][23] The electron-phonon interactions take the form of scattering self-energies defined as follows:…”

“…[21][22][23] Full-band and atomistic simulations are computationally very intensive, especially those including electron-phonon scattering. It is therefore necessary to introduce physical and numerical approximations to keep the computational burden manageable.…”