Site-Specific Fabrication of Blue Quantum Emitters in Hexagonal Boron Nitride

Abstract

Hexagonal boron nitride (hBN) is gaining considerable attention as a solid-state host of quantum emitters from the ultraviolet to the near-infrared spectral ranges. However, the atomic structures of most of the emitters are speculative or unknown, and emitter fabrication methods typically suffer from poor reproducibility, spatial accuracy, or spectral specificity. Here, we present a robust, electron beam technique for site-specific fabrication of blue quantum emitters with a zero-phonon line at 436 nm (2.8 eV). We show that the emission intensity is proportional to electron dose and that the efficacy of the fabrication method correlates with a defect emission at 305 nm (4.1 eV). We attribute blue emitter generation to the fragmentation of carbon clusters by electron impact and show that the robustness and universality of the emitter fabrication technique are enhanced by a pre-irradiation annealing treatment. Our results provide important insights into photophysical properties and structure of defects in hBN and a framework for site-specific fabrication of quantum emitters in hBN.

Cathodoluminescence monitoring of quantum emitter activation in hexagonal boron nitride

“…Our measurements have revealed a saturation of the activation process, which could help to understand the physical origin of the color centers as well as the irradiation mechanism. The fact that the SPE number saturates at a relatively low density of 3 • 10 15 cm −3 is compatible with the current understanding that the irradiation modifies a pre-existing specie of finite density, rather than creating an intrinsic defect from pristine crystal [14][15][16] . This limit density corresponds to a mean distance of 70 nm between neighboring centers.…”

“…The bare CL spectrum of the flake is shown on figure 1b, where the free exciton can be observed at 215 nm, as well as three peaks around 305 nm often attributed to emission from carbon defects 18 . The presence of this sub-bandgap emission has recently been identified as a prerequisite for the generation of B-centers in hBN 15 . No PL emission from B-centers is observed prior to the irradiation process.…”

“…In this context, we have previously demonstrated the possibility to locally activate a recently discovered family of quantum emitters using an electron beam 14 . These blue-emitting color centers -abbreviated B-centers in the following -have a reproducible emission in the blue range, with very attractive optical properties, such as a high stability and a remarkably low inhomogeneous broadening of the SPE ensembles [14][15][16] . However, their microscopic structure, as well as the mechanisms at the origin of their generation, remains to be understood.…”

“…However, their microscopic structure, as well as the mechanisms at the origin of their generation, remains to be understood. The current understanding is that they stem from the modification of a complex that preexists in the as-grown hBN crystal 15,16 . We therefore refer to the generation process as an activation.…”

Identification of an Oxygen Defect in Hexagonal Boron Nitride

“…Spatially well-isolated fluorescent point defects, formed either spontaneously or by engineering, act as single-photon emitters with representing an ideal two-level system. , In comparison to the three-dimensional (3D) host, e.g., diamond or silicon carbide, the low dimensionality of hBN does not introduce unwanted surface spin noise , and enables high quantum efficiency (high light extraction ability). In addition, together with the diverse growth techniques, deterministic creation of defects has been achieved in atomic precision, which is an inevitable step toward solving the scalability issue required for quantum technologies. − Recent experiments also realized the integration of defects with other quantum architectures . These advantages of 2D defects endow them with desirable key features, including high brightness, narrow photoluminescence (PL) line shape, emission tuned by strain, ,, and electric fields …”