First-principles study of luminescence in hexagonal boron nitride single layer: Exciton-phonon coupling and the role of substrate

• Published in: Physical review materials 2023-02, Vol.7 (2), Article 024006
• Main Authors: Lechifflart, Pierre, Paleari, Fulvio, Sangalli, Davide, Attaccalite, Claudio
• Format: Article
• Language: English
• Subjects: Condensed Matter; Materials Science; Physics
• ISSN: 2475-9953; 2475-9953
• DOI: 10.1103/PhysRevMaterials.7.024006

Hexagonal boron nitride (hBN) is a wide band gap material with both strong excitonic light emission in the ultraviolet and strong exciton-phonon coupling. Luminescence experiments performed on the recently synthesized monolayer form (m-hBN) present emission spectra that differ from one another, with some suggesting a coexistence between phonon-assisted and direct emission channels. Motivated by these results, we investigated the optical response of (m-hBN) using an ab initio approach that takes into account the effects of atomic vibrations on the luminescence spectra. We construct the dynamical exciton-phonon self-energy, then use it to perturbatively correct the optical response functions and test this approach on bulk hBN as a benchmark. Within our approach we are able to estimate the renormalization of the direct peak induced by phonon-assisted transitions, and this allows us to accurately describe spectra where both processes are present. We found that the emission signal of m-hBN is strongly dependent on its interaction with the substrate, which changes its nature from direct to indirect material and modifies the screening felt by the electrons. We attribute the m-hBN emission signal to the bright direct excitons and consider the likelihood of phonon replicas appearing.