Unambiguous identification of the indirect band nature of atomically thin hexagonal boron nitride
Abstract
Atomically thin hexagonal boron nitride (h-BN), especially monolayer, has garnered increasing attention due to its intriguing optical and light-matter-interaction properties. However, its intrinsic optical properties and electronic band structure, have long remained elusive. In this study, near-resonance excited deep-UV photoluminescence/Raman spectroscopy and deep-UV reflectance contrast spectroscopy are utilized to experimentally investigate the optical properties of atomically thin h-BN across various layer numbers. It is revealed that the absence of luminescence in 1-3 layers h-BN is indicative of their indirect band gap nature, rectifying previously adopted identification of a direct band gap in monolayer BN. Notably, band-edge luminescence signals and indirect bandgap absorption start to appear in 4-layer, and the luminescence intensity increases with the number of layers, suggesting that interlayer interactions and periodicity along the z-axis enhance phonon-assisted indirect bandgap transition, even in the 4-layer case, and furthermore indicating the formation process of flat bands at the K and M valleys as the periodicity along the z direction increases. Additionally, the prominent resonance Raman signals in atomically thin h-BN underscore strong electron-phonon coupling in this material.
Keywords
Cite
@article{arxiv.2410.12545,
title = {Unambiguous identification of the indirect band nature of atomically thin hexagonal boron nitride},
author = {Lei Fu and Yuqing Hu and Ning Tang and Junxi Duan and Xionghui Jia and Huaiyuan Yang and Zhuoxian Li and Xiangyan Han and Guoping Li and Jianming Lu and Lun Dai and Weikun Ge and Bo Shen},
journal= {arXiv preprint arXiv:2410.12545},
year = {2024}
}