Using a new time-resolved cathodoluminescence system dedicated to the UV spectral range, we present a first estimate of the radiative lifetime of free excitons in hBN at room temperature. This is carried out from a single experiment giving both the absolute luminescence intensity under continuous excitation and the decay time of free excitons in the time domain. The radiative lifetime of indirect excitons in hBN is equal to 27 ns, which is much shorter than in other indirect bandgap semiconductors. This is explained by the close proximity of the electron and the hole in the exciton complex, and also by the small energy difference between indirect and direct excitons. The unusually high luminescence efficiency of hBN for an indirect bandgap is therefore semi-quantitatively understood.
@article{arxiv.2107.00989,
title = {Radiative lifetime of free excitons in hexagonal boron nitride},
author = {Sébastien Roux and Christophe Arnold and Fulvio Paleari and Lorenzo Sponza and Eli Janzen and James H. Edgar and Bérangère Toury and Catherine Journet and Vincent Garnier and Philippe Steyer and Takashi Taniguchi and Kenji Watanabe and François Ducastelle and Annick Loiseau and Julien Barjon},
journal= {arXiv preprint arXiv:2107.00989},
year = {2021}
}