Cooling Dynamics of Photoexcited Carriers in Si Studied by Using Optical Pump and Terahertz Probe Spectroscopy

TL;DR

This study investigates how photoexcited carriers in silicon cool down and form excitons, using optical pump and terahertz probe spectroscopy, revealing detailed thermalization and cooling mechanisms.

Contribution

It provides a microscopic analysis of carrier cooling and exciton formation dynamics in silicon, combining experimental spectroscopy with theoretical modeling.

Findings

Observed exciton formation via 1s-2p transition at 12 meV

Quantified electron and hole cooling rates matching experiments

Identified phonon scattering as key to thermalization process

Abstract

We investigated the photoexcited carrier dynamics in Si by using optical pump and terahertz probe spectroscopy in an energy range between 2 meV and 25 meV. The formation dynamics of excitons from unbound e-h pairs was studied through the emergence of the 1s-2p transition of excitons at 12 meV (3 THz). We revealed the thermalization mechanism of the photo-injected hot carriers (electrons and holes) in the low temperature lattice system by taking account of the interband and intraband scattering of carriers with acoustic and optical phonons. The overall cooling rate of electrons and holes was numerically calculated on the basis of a microscopic analysis of the phonon scattering processes, and the results well account for the experimentally observed carrier cooling dynamics. The long formation time of excitons in Si after the above-gap photoexcitation is reasonably accounted for by the thermalization process of photoexcited carriers.