Phonon-Assisted Photoluminescence and Ultrafast Exciton Dynamics in Two-Dimensional Silicon Carbide

TL;DR

This study uses ab initio methods to analyze phonon-assisted photoluminescence and ultrafast exciton dynamics in 2D silicon carbide, revealing dominant phonon interactions and rapid exciton relaxation.

Contribution

It provides the first detailed ab initio analysis of phonon-assisted emission and ultrafast exciton relaxation in 2D silicon carbide, benchmarking against hBN.

Findings

High energy optical phonons dominate sideband formation.

Exciton lifetime is approximately 300 fs at 10 K.

Monolayer SiC is an efficient platform for phonon-assisted emission.

Abstract

Phonon assisted photoluminescence provides a direct window into exciton phonon interactions in low dimensional semiconductors. Using fully ab initio many body perturbation theory, including finite momentum Bethe Salpeter calculations, we investigate phonon assisted emission and exciton dynamics in 2D hexagonal silicon carbide (hSiC) and benchmark its response against 2D h boron nitride (hBN). By explicitly resolving exciton phonon matrix elements, we identify high energy optical TO LO phonons as the dominant contributors to sideband formation and quantify their spectral weights. hSiC exhibits pronounced phonon-assisted sidebands comparable to h BN, despite a smaller exciton phonon energy separation and fewer resolved replicas. The bright KK exciton governs near UV zero phonon emission, while intervalley excitons acquire radiative character through symmetry allowed optical-phonon coupling. Temperature dependent scattering rates reveal an ultrashort bright exciton lifetime of approximately 300 fs at 10 K, highlighting rapid exciton relaxation driven by intrinsic phonon channels. These results establish monolayer SiC as a symmetry activated platform for efficient, strain-free phonon assisted emission and provide a quantitative framework for ultrafast exciton dynamics in wide bandgap 2D semiconductors.