Ultra--fast carriers relaxation in bulk silicon following photo--excitation with a short and polarized laser pulse

TL;DR

This paper introduces a new ab-initio approach combining Green's functions and Density Functional Theory to accurately describe ultra-fast carrier relaxation in silicon, revealing that the observed dynamics are due to degenerate state scattering rather than inter-valley processes.

Contribution

It presents a novel theoretical framework for out-of-equilibrium carrier relaxation in silicon, challenging previous interpretations and providing a new understanding of ultra-fast dynamics.

Findings

Carrier relaxation is due to degenerate L state scattering, not inter-valley scattering.

The ultra-fast dynamics depend on the specific experimental setup.

A new definition of quasi-particle lifetimes in out-of-equilibrium conditions is proposed.

Abstract

A novel approach based on the merging of the out--of--equilibrium Green's function method with the ab-initio, Density--Functional--Theory is used to describe the ultra--fast carriers relaxation in Silicon. The results are compared with recent two photon photo--emission measurements. We show that the interpretation of the carrier relaxation in terms of L -> X inter--valley scattering is not correct. The ultra--fast dynamics measured experimentally is, instead, due to the scattering between degenerate $L$ states that is activated by the non symmetric population of the conduction bands induced by the laser field. This ultra--fast relaxation is, then, entirely due to the specific experimental setup and it can be interpreted by introducing a novel definition of the quasi--particle lifetimes in an out--of--equilibrium context.