Identifying carbon as the source of visible single-photon emission from hexagonal boron nitride

Abstract

Single photon emitters (SPEs) in hexagonal boron nitride (hBN) have garnered significant attention over the last few years due to their superior optical properties. However, despite the vast range of experimental results and theoretical calculations, the defect structure responsible for the observed emission has remained elusive. Here, by controlling the incorporation of impurities into hBN via various bottom-up synthesis methods and directly through ion implantation we provide direct evidence that the visible SPEs are carbon related. Room temperature optically detected magnetic resonance (ODMR) is demonstrated on ensembles of these defects. We perform ion implantation experiments and confirm that only carbon implantation creates SPEs in the visible spectral range. Computational analysis of the simplest 12 carbon-containing defect species suggest the negatively charged V B C N − defect as a viable 53 candidate and predict that out-of-plane deformations make the defect environmentally sensitive. 54Our results resolve a long-standing debate about the origin of single emitters at the visible range 55 grown epitaxially. 28, 29 The energy detuning between the ZPL of the ensemble and phonon sideband (PSB) peak is ~176 meV on average (Extended Data Fig. 1). 30, 31 X-ray photoelectron spectroscopy (XPS) was used to quantify the incorporation of carbon (Extended Data Fig. 2). Figure 1b(c) demonstrate a near linear correlation between C-B (C-N) bonding and increasing TEB flux, with C-B bonding being roughly an order of magnitude more prevalent than C-N bonding. Preferential formation of C-B bonds follows logically from noting the B species are introduced with three pre-existing bonds to C. PL intensity of the resulting ensemble emission likewise displays a linear correlation with carbon concentration (Extended Data Fig. 3). Based on these results, we advance that the SPE emission at ~580 nm in hBN is likely to originate from a carbon-related defect complex. Figure 1-Photoluminescence from MOVPE hBN Samples. a. MOVPE hBN grown with increasing flow rates of triethyl borane (TEB). As TEB flow increases, the fluorescence of SPE ensembles increases. b. Percentage of B-C bonding with increasing TEB flow evaluated by XPS. c. Percentage of N-C bonding with increasing TEB flow evaluated by XPS. d. Room temperature ODMR displayed as relative contrast, spin-dependent variation in photoluminescence (∆PL/PL), observed from the ~585 nm ensemble emission of MOPVE hBN (TEB 60) at applied fields of 19, 24, and 29 mT respectively. e.

Controlled generation of luminescent centers in hexagonal boron nitride by irradiation engineering

“…The versatile processes in our RIE reactor allow irradiation engineering by tuning both the irradiation energy and the irradiation fluence. This is novel compared to previous studies of high-energy irradiation ( 26 , 27 ) and oxygen plasma ( 24 , 25 ) processes, since highly directional ions with a narrow energy distribution were used in the present work. The density of generated luminescent centers changes with both irradiation energy and fluence, while increasing the irradiation fluence shows a substantial enhancement of the density.…”

“…Besides thermal annealing of hBN of various qualities, oxygen plasma ( 24 , 25 ) and high-energy oxygen irradiation ( 26 , 27 ) have been used to generate quantum emitters in hBN. However, applying irradiation engineering, i.e., tuning both irradiation energy and irradiation fluence (defined as the number of atoms per area), remains unexplored on hBN, while this technique can create defects controllably in other 2D materials ( 28 ).…”

Photoluminescence, photophysics, and photochemistry of the VB− defect in hexagonal boron nitride

“…approaches. Another significant aspect of the methods, applied to model ten-ring and larger compounds, is the use of mixed quantum-mechanics/molecular-mechanics (QM/MM) approaches utilizing, in the MM part, an AMBER [38] force field fitted to reproduce DFT-calculated properties of h-BN [39]. all lowest-energy states of each spin and spatial symmetry, no analytical gradients for geometry optimization available in the software used in this study a See the SM Sec.…”

“…(6) Application of the ONIOM [72,73] approach to QM/MM to extend model sizes. This uses an AMBER [38] force field for the MM part, parametrized to mimic CAM-B3LYP/D3 results [39]. Two rings are retained in the QM part only, leading to very computationally efficient calculations.…”

Luminescence properties of hexagonal boron nitride powders probed by deep UV photoluminescence spectroscopy

“…Thus, the sharp emission lines observed in the UV region could be related to carbon defects which are generated during the annealing process. Carbon-related defect is also proposed as the source of emitters in the visible spectral range [ 25 ].…”