Quantifying charge-carrier dynamics in hexagonal boron nitride by optimized cathodoluminescence of buried interfaces*

We demonstrate high-resolution cathodoluminescence (CL) hyperspectral maps of the heterogeneous light emission from monolayers transition metal dichalcogenides (TMDs) encapsulated in hexagonal boron nitride (hBN). TMD CL crucially relies on the electron-hole (e-h) pair dynamics in the hBN encapsulation. However, there is no systematic study of the implication of these dynamics to advance high-resolution CL mapping.

Here, we address this issue by showing that the hBN thickness controls the CL spatial resolution and we estimate a minimum threshold of the e-h diffusion length in bulk hBN. We provide an optimal thickness range to achieve bright, sub-diffraction resolved CL and corroborate our approach with low-temperature hyperspectral maps, in which we isolate different forms of heterogeneity at the nanoscale.

Our approach enables the access to the properties of buried, optically active interfaces at the nanoscale and paves the way towards the full comprehension of the rich TMD optical properties.