The Role of Nonequilibrium Dynamical Screening in Carrier Thermalization

TL;DR

This paper explores how nonequilibrium dynamical screening influences carrier thermalization in semiconductors, using a field theoretic approach to accurately model collisions and dephasing phenomena.

Contribution

It introduces a nonequilibrium field theoretic formalism for carrier collisions and dynamical screening, providing new insights into dephasing times and their dependence on carrier density.

Findings

Dephasing times due to carrier-carrier scattering are in picoseconds at low densities.

Dephasing rate scales linearly with carrier density at ultralow densities.

The model's predictions agree with experimental observations.

Abstract

We investigate the role played by nonequilibrium dynamical screening in the thermalization of carriers in a simplified two-component two-band model of a semiconductor. The main feature of our approach is the theoretically sound treatment of collisions. We abandon Fermi's Golden rule in favor of a nonequilibrium field theoretic formalism as the former is applicable only in the long-time regime. We also introduce the concept of nonequilibrium dynamical screening. The dephasing of excitonic quantum beats as a result of carrier-carrier scattering is brought out. At low densities it is found that the dephasing times due to carrier-carrier scattering is in picoseconds and not femtoseconds, in agreement with experiments. The polarization dephasing rates are computed as a function of the excited carrier density and it is found that the dephasing rate for carrier-carrier scattering is proportional to the carrier density at ultralow densities. The scaling relation is sublinear at higher densities, which enables a comparison with experiment.