Light emission properties of mechanical exfoliation induced extended defects in hexagonal boron nitride flakes

TL;DR

This study investigates how extended defects in mechanically exfoliated hexagonal boron nitride (hBN) flakes influence their light emission properties, revealing defect-related luminescence variations and novel emissions linked to dislocations.

Contribution

It provides new insights into the relationship between extended defects and luminescence in hBN, including the identification of a novel emission at 2.36 eV and the effects of crystal deformation.

Findings

Thinner regions show higher deep level emission.

Crystal deformation causes a blue-shift in near band edge emission.

Dislocation arrays produce a new emission at 2.36 eV.

Abstract

Recently hBN has become an interesting platform for quantum optics due to the peculiar defect-related luminescence properties. Concomitantly, hBN was established as the ideal insulating support for realizing 2D materials device, where, on the contrary, defects can affect the device performance. In this work, we study the light emission properties of hBN flakes obtained by mechanical exfoliation with particular focus on extended defects generated in the process. In particular, we tackle different issues as the light emission in hBN flakes of different thicknesses in the range of hundreds of nm, revealing a higher concentration of deep level emission in thinner area of the flake. We recognize the effect of crystal deformation in some areas of the flake with an important blue-shift (130 meV) of the room temperature near band edge emission of hBN and the concurrent presence of a novel emission at 2.36 eV related to the formation of array of dislocations. We studied the light emission properties by means of cathodoluminescence and sub-bandgap excitation photoluminescence of thickness steps with different crystallographic orientations, revealing the presence of different concentration of radiative centers. CL mapping allows to detect buried thickness steps, invisible to the SEM and AFM morphological analysis.