Ultra-fast relaxation of electrons in wide-gap dielectrics

TL;DR

This paper models the ultrafast relaxation of low-energy electrons in wide-gap dielectrics like SiO2, showing rapid initial cooling via impact ionization followed by slower phonon-mediated attenuation within 200 fs.

Contribution

It introduces a phonon-based collective scattering model to simulate electron relaxation dynamics in wide-gap dielectrics, highlighting ultrafast cooling mechanisms.

Findings

Electron relaxation in SiO2 occurs within 200 fs.

Initial impact ionization cooling happens in the first 10 fs.

Slower attenuation is due to phonon interactions.

Abstract

Low-energy electrons scattered in the conduction band of a dielectric solid should behave like Bloch electrons and will interact with perturbations of the atomic lattice, i.e. with phonons. Thus the phonon-based description of low-energy scattering within an energy band structure of a solid bears certain advantages against common free-electron scattering mechanisms. Moreover, the inelastic scattering is described by the dielectric energy loss function. With these collective scattering models we have performed the simulation of excited electron relaxation and attenuation in the insulator SiO2. After excitation to a mean initial energy of several eV their energy relaxation occurs within a short time interval of 200 fs to full thermalization. There is a very rapid impact ionization cooling connected with cascading of electrons at the beginning during the first 10 fs, followed by much slower attenuation due to phonon losses in wide-gap dielectrics and insulators.