Quantum Emission from Defects in Single-Crystalline Hexagonal Boron Nitride

Toan Trong Tran, Cameron Zachreson, Amanuel Michael Berhane, Kerem Bray, Russell Guy Sandstrom, Lu Hua Li, Takashi Taniguchi, Kenji Watanabe, Igor Aharonovich, and Milos Toth

Phys. Rev. Applied 5, 034005 – Published 10 March 2016

Abstract

Bulk hexagonal boron nitride (hBN) is a highly nonlinear natural hyperbolic material that attracts major attention in modern nanophotonics applications. However, studies of its optical properties in the visible part of the spectrum and quantum emitters hosted by bulk hBN have not been reported to date. In this work, we study the emission properties of hBN crystals in the red spectral range using sub-band-gap optical excitation. Quantum emission from defects is observed at room temperature and characterized in detail. Our results advance the use of hBN in quantum nanophotonics technologies and enhance our fundamental understanding of its optical properties.

Received 31 July 2015

DOI:https://doi.org/10.1103/PhysRevApplied.5.034005

Physics Subject Headings (PhySH)

Defects Light-matter interaction Photonics

Optical microscopy Photoluminescence Raman spectroscopy X-ray absorption fine structure spectroscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Toan Trong Tran¹, Cameron Zachreson¹, Amanuel Michael Berhane¹, Kerem Bray¹, Russell Guy Sandstrom¹, Lu Hua Li², Takashi Taniguchi³, Kenji Watanabe³, Igor Aharonovich^1,*, and Milos Toth^1,†

¹School of Mathematical and Physical Sciences, University of Technology Sydney, Ultimo, New South Wales 2007, Australia
²Institute of Frontier Materials, Deakin University, Geelong Waurn Ponds Campus, Victoria 3216, Australia
³National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan

^*Corresponding author. Igor.Aharonovich@uts.edu.au
^†Corresponding author. Milos.Toth@uts.edu.au

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Vol. 5, Iss. 3 — March 2016

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Images

Figure 1
(a) Optical microscope image of bulk hBN. The scale bar indicates $100 μ m$ . (b) Raman scattering spectrum obtained with a 633-nm He-Ne laser showing a peak at $1365 {cm}^{- 1}$ with a FWHM of $8.2 {cm}^{- 1}$ .
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Figure 2
Optical characterization performed with a 532-nm cw laser and a 568-nm long-pass filter in the collection pathway. (a) A typical confocal map of bulk hBN showing a number of isolated emission centers and ensembles of these centers. The scale bar indicates $10 μ m$ . (b) A room-temperature photoluminescence spectrum of the isolated emission circled in the PL confocal map. The solid red and dotted gray traces represent the emitter and background spectra, respectively. The emitter spectrum reveals a pair of peaks at 618 and 629 nm that are potentially the zero-phonon lines of the defect transition. (c) An antibunching curve recorded from the defect center in (b) showing a dip of approximately 0.35, proving the single-photon emission nature of the defect. The bin size in (c) is 128 ps.
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Figure 3
(a) A typical confocal map showing isolated emission centers and ensembles of emitters. The scale bar indicates $10 μ m$ . (b) A room-temperature PL spectrum of the isolated emission that is circled in the PL confocal map, revealing a broad emission band at approximately 770–900 nm. The solid red and dotted gray traces represent the emitter and background spectra, respectively. (c) An antibunching curve recorded by continuous-wave excitation of the defect center in (b) showing a dip of approximately 0.37, proving the quantum nature of the defect. The inset shows a similar antibunching curve obtained by pulsed excitation. (d) Time-resolved fluorescence measurement of the defect center in (b) revealing a very short radiative lifetime of approximately 1.0 ns. All measurements are done using a 675-nm cw laser at room temperature, with a $855 \pm 110 nm$ band-pass filter. Pulsed $g^{2} (τ)$ and lifetime measurements (d) are conducted using a 675-nm laser with a pulse width of 45 ps, a power of $200 μ W$ , and repetition rate of 80 MHz. The bin size in (b) and (d) is 128 ps.
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Figure 4
(a) Long time-scale second-order autocorrelation function (recorded up to 0.1 s) reveals at least three possible metastable states of the defect center characterized in Fig. 3. The inset illustrates the possible excited electronic configuration of the defect center, including the existence of three metastable states. Temporal fluorescence intensity fluctuations at (b) 150, (d) 600, and (f) $2000 μ W$ and the corresponding histograms at (c) 150, (e) 600, and (g) $2000 μ W$ . The black traces in (c), (e), and (g) are corresponding simulated Poisson distributions, shown for comparison. The time-bin size in (b), (d), and (f) is 50 ms.
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