Band gap measurements of monolayer h-BN and insights into carbon-related point defects

Román, Ricardo Javier Peña; Costa, Fábio J. R.; Zobelli, Alberto; Elias, Christine; Valvin, Pierre; Cassabois, Guillaume; GIL, BERNARD; Summerfield, Alex; Cheng, Tin S; Mellor, Chris J; Beton, Peter H; Novikov, Sergei V; Zagonel, Luiz Fernando

Abstract

Being a flexible wide band gap semiconductor, hexagonal boron nitride (h-BN) has great potential for technological applications like efficient deep ultraviolet light sources, building block for two-dimensional heterostructures and room temperature single photon emitters in the ultraviolet and visible spectral range. To enable such applications, it is mandatory to reach a better understanding of the electronic and optical properties of h-BN and the impact of various structural defects. Despite the large efforts in the last years, aspects such as the electronic band gap value, the exciton binding energy and the effect of point defects remained elusive, particularly when considering a single monolayer. Here, we directly measured the density of states of a single monolayer of h-BN epitaxially grown on highly oriented pyrolytic graphite, by performing low temperature scanning tunneling microscopy (STM) and spectroscopy (STS). The observed h-BN electronic band gap on defect-free regions is (6.8 ± 0.2) eV. Using optical spectroscopy to obtain the h-BN optical band gap, the exciton binding energy is determined as being of (0.7 ± 0.2) eV. In addition, the locally excited cathodoluminescence and photoluminescence show complex spectra that are typically associated to intragap states related to carbon defects. Moreover, in some regions of the monolayer h-BN we identify, using STM, point defects which have intragap electronic levels around 2.0 eV below the Fermi level.

Citation

Román, R. J. P., Costa, F. J. R., Zobelli, A., Elias, C., Valvin, P., Cassabois, G., …Zagonel, L. F. (2021). Band gap measurements of monolayer h-BN and insights into carbon-related point defects. 2D Materials, 8(4), Article 044001. https://doi.org/10.1088/2053-1583/ac0d9c

• Journal Article Type: Article
• Acceptance Date: Jun 22, 2021
• Online Publication Date: Jul 7, 2021
• Publication Date: 2021-10
• Deposit Date: Jun 28, 2021
• Publicly Available Date: Jul 8, 2022
• Journal: 2D Materials
• Electronic ISSN: 2053-1583
• Publisher: IOP Publishing
• Peer Reviewed: Peer Reviewed
• Volume: 8
• Issue: 4
• Article Number: 044001
• DOI: https://doi.org/10.1088/2053-1583/ac0d9c
• Keywords: Mechanical Engineering; General Materials Science; Mechanics of Materials; General Chemistry; Condensed Matter Physics
• Public URL: https://nottingham-repository.worktribe.com/output/5724308
• Publisher URL: https://iopscience.iop.org/article/10.1088/2053-1583/ac0d9c
• Additional Information: This is the Accepted Manuscript version of an article accepted for publication in 2D Materials. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it. The Version of Record is available online at https://iopscience.iop.org/article/10.1088/2053-1583/ac0d9c