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

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 $(6.8\pm 0.2)$ eV. Using optical spectroscopy to obtain the h-BN optical band gap, the exciton binding energy is determined as being of $(0.7\pm 0.2)$ 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.

arXiv comment50 Pages, 8 Figures, 100+ references

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• Band gap measurements of monolayer h-BN and insights into carbon-related point defects
• Polarons in two-dimensional atomic crystals
• Vacancy-Induced Boron Nitride Monolayers as Multifunctional Materials for Metal Ion Batteries and Hydrogen Storage Applications
• Theoretical methods for excitonic physics in two-dimensional materials
• Rhombohedral and Turbostratic Boron Nitride Polytypes Investigated by X-ray Absorption Spectroscopy
• Ultrafast phonon-mediated dephasing of color centers in hexagonal boron nitride probed by electron beams
• Impacts of dielectric screening on the luminescence of monolayer WSe${}_2$
• Color Centers in Hexagonal Boron Nitride
• Large shift current via in-gap and charge-neutral exciton excitations in BN nanotubes and single BN layer
• Cathodoluminescence spectroscopy of monolayer hexagonal boron nitride
• Design and implementation of a device based on an off-axis parabolic mirror to perform luminescence experiments in a scanning tunneling microscope
• Spintronics in 2D graphene-based van der Waals heterostructures
• Carbon-based single photon emitters in hexagonal boron nitride with triplet ground state
• Current-induced brightening of vacancy-related emitters in hexagonal boron nitride
• Tunable exciton polaritons in band-gap engineered hexagonal boron nitride
• An atlas of photonic and plasmonic materials for cathodoluminescence microscopy