Excitons and stacking order in h-BN

TL;DR

This study investigates how structural deformations in hexagonal boron nitride affect its excitonic emission spectrum, revealing that stacking order variations at local scales cause additional excitonic peaks.

Contribution

It combines experimental and theoretical methods to link local stacking order changes with emission spectrum variations in h-BN.

Findings

Emission spectra are highly inhomogeneous within individual flakes.

Additional excitons are associated with structural deformations like faceted plane folds.

Stacking order changes induce local variations in excitonic emissions.

Abstract

The strong excitonic emission at 5.75 eV of hexagonal boron nitride (h-BN) makes this material one of the most promising candidate for light emitting devices in the far ultraviolet (UV). However, single excitons occur only in perfect monocrystals that are extremely hard to synthesize, while regular h-BN samples present a complex emission spectrum with several additional peaks. The microscopic origin of these additional emissions has not yet been understood. In this work we address this problem using an experimental and theoretical approach that combines nanometric resolved cathodoluminescence, high resolution transmission electron microscopy and state of the art theoretical spectroscopy methods. We demonstrate that emission spectra are strongly inhomogeneus within individual flakes and that additional excitons occur at structural deformations, such as faceted plane folds, that lead to local changes of the h-BN stacking order.