Revealing multiple classes of stable quantum emitters in hexagonal boron nitride with correlated optical and electron microscopy

Abstract

Single photon emitters (SPEs) in solids have emerged as promising candidates for quantum photonic sensing, 1-3 communications, 4, 5 and computing. 6, 7 Defects in hexagonal boron nitride (hBN) exhibit high-brightness, room-temperature quantum emission, 8-10 but their large spectral variability and unknown local structure significantly challenge their technological utility. Here, we directly correlate hBN quantum emission with the material's local strain using a combination of photoluminescence (PL), cathodoluminescence (CL) and nanobeam electron diffraction. Across 40 emitters and 15 samples, we observe zero phonon lines (ZPLs) in PL and CL ranging from 540-720 nm. CL mapping reveals that multiple defects and distinct defect species located within an optically-diffraction-limited region can each contribute to the observed PL spectra. Local strain maps indicate that strain is not required to activate the emitters and is not solely responsible for the observed ZPL spectral range. Instead, four distinct defect classes are responsible for the observed emission range. One defect class has ZPLs near 615 nm with predominantly matched CL-PL responses; it is not a straintuned version of another defect class with ZPL emission centered at 580 nm. A third defect class at 650 nm has low visible-frequency CL emission; and a fourth defect species centered at 705 nm has a small, ∼10 nm shift between its CL and PL peaks. All studied defects are stable upon both electron and optical irradiation. Our results provide an important foundation for atomic-scale optical characterization of color centers, as well as a foundation for engineering defects with precise emission properties. 1 arXiv:1901.05952v2 [cond-mat.mtrl-sci]

Dangling Bonds in Hexagonal Boron Nitride as Single-Photon Emitters

“…It has been shown that h-BN flakes are predominantly N terminated [21][22][23]. Boron DBs will therefore be relatively rare (occurring, e.g., at corners or kinks [24]), in agreement with experimental observations. In the ground state, the B DB is doubly occupied.…”

Interlayer Bound Wannier Excitons in Germanium Sulfide

“…The small peak centered at 3.02 eV is attributed to the hBN film; most likely it is due to the second-order diffraction of the band edge emission by the gating that is not filtered in the set-up. However, we cannot entirely exclude that it might be a defect-related emission [44], although rather unlikely due to the broad full width at half maximum of the peak. Additionally, it is worth mentioning that for thinner flakes (below 45 nm), the signal-to-noise ratio was too low and no obvious peak at 1.69 eV could be observed with our current setup.…”

Giant shift upon strain on the fluorescence spectrum of VNNB color centers in h-BN

“…One of the key candidates for this external perturbation is the local strain that may vary significantly in the h-BN samples, in particular, in polycrystalline h-BN samples. In another recent work, on the other hand, four different types of emitters have been found by means of combined chatodoluminescence and photoluminescence study where the applied stress did not change the brightness of emitters and the shift in ZPL was in the 10 meV region 39 . Yet another experiment also found a relatively small shift upon applied stress on a given emitter 40 .…”