Properties of quantum emitters in different hBN sample types particularly suited for nanophotonic integration

TL;DR

This work tackles the origin and integration potential of visible-range single-photon emitters in hexagonal boron nitride (hBN) by comparing two inherently different sample types: liquid-phase exfoliated (LPE) hBN nanoflakes and layer-engineered CVD trilayers. The authors combine confocal spectroscopy, second-order intensity correlations, and near-field coupling to optical nanofibers with first-principles defect simulations to identify likely carbon-related defect candidates, notably C2C_B and C2C_N, and to exclude other possibilities such as VN_CB. They find that C2C_B best describes emitters in the CVD samples, while LPE emitters can be attributed to C2C_B or C2C_N, with Debye-Waller factors at room temperature reaching roughly 0.6–0.8, indicating strong ZPL emission. The study demonstrates a practical route to engineer and couple hBN emitters into nanophotonic networks and provides a framework for linking spectral features to atomic defects to guide deterministic emitter design.

Abstract

Single photon emitters in two-dimensional (2D) hexagonal boron nitride (hBN) are promising solid-state quantum emitters for photonic applications and quantum networks. Despite their favorable properties, much is still unknown about their characteristics and their atomic origin. We focus on two different kinds of hBN samples that particularly lend themselves for integration with nanophotonic devices, multilayer nanoflakes produced by liquid phase exfoliation (LPE) and a layer-engineered sample from hBN grown by chemical vapour deposition (CVD). We investigate their inherent defects and fit their emission properties to computationally simulated optical properties of likely carbon-related defects. Thereby we compare and elucidate the properties in different sample types particularly suited for photonic quantum networks and narrow down the origin of emitters found in these samples. Our work is thus an important step towards harnessing the full potential of single photon emitters in hBN.

Figures (11)

• Figure 1: (a) Sketch of the layer-engineered CVD grown hBN sample. An optically active hBN layer is sandwiched between two hBN protection layers. (b) Sketch of the confocal microscope set-up for investigating qantum emitters in hBN.
• Figure 2: Widefield image of a trilayer sample of hBN (left) and corresponding confocal image (right) of the marked area
• Figure 3: (a) Second order intensity correlation measurements and corresponding fit (red line) showing the typical antibunching dip of a single photon emitter. (b) For longer correlation times, photon bunching due to at least one metastable state can be observed.
• Figure 4: (a) AFM micrograph of LPE hBN platelets drop cast from suspension onto SiO$_2$ covered Si wafer. (b) Raman spectrum corresponding to (a). (c) BF-TEM, (d) SAED and (e) DF-TEM images of a single hBN flake deposited onto a lacey carbon TEM grid.
• Figure 5: (a) Confocal reflection microscopy image of LPE flakes on glass and (b) the corresponding fluorescence image