Near-deterministic activation of room-temperature quantum emitters in hexagonal boron nitride

Abstract

Emerging quantum technologies for cryptography, computing and metrology exploit quantum mechanical effects for enhanced information processing and nanoscale sensing. Though different platform systems are currently being explored, light-based quantum technologies using single-photon emitters as the basic building block are among the frontrunners 1 . Several strategies have been used to realize deterministic single photon sources in the solid state 2 , including quantum dots 3 , single molecules 4 , and point defects in wide bandgap materials such as diamond and silicon carbide 5-9 . Single photon emitters in novel van der Waals materials have garnered recent attention due to their potential for integration with waveguides, microcavities, and other passive components typical in photonic devices. Example 2D systems hosting quantum emitters include WSe 2 and MoS 2 as well as other transition metal dichalcogenides (TMDs) 10-14 .Here we focus on hexagonal boron nitride (hBN), a wide bandgap semiconductor where defect emission has been shown to be tunable and robust at room temperature 15-22 and above 23 . We use confocal microscopy to investigate the photoluminescence (PL) of point defects within thin hBN flakes deposited on a lithographically patterned SiO 2 substrate. Due to Van der Waals forces the flake conforms to the surface topography thus accumulating significant local strain near protruding features. Using large structured arrays of different sizes and geometries we find nearly perfect correspondence between the strained areas of the flake and defect emission. Our modeling supports the notion of defect activation via charge trapping in deformation potential wells. The physics at play has some similarities with that governing the dynamics of excitons in WSe 2 monolayers subjected to comparable geometries, as reported recently 24,25 . Unlike TMDs, however, the wide bandgap of hBN can accommodate large potential modulations, sufficient to stabilize the defect charge at room temperature. In particular, we calculate deformation potential wells as deep as 500 meV confined to regions of tensile and compressive strain in the hBN flake that correlate well with the spatial localization of the emitters.For the first set of experiments we use an array of 155-nm-high nanopillars with diameters ranging from 200 to 700 nm fabricated via electron beam lithography over a large-area silica substrate (Figure 1a); the sample is a commercial, 20-nmthick flake of hBN grown via chemical vapor deposition (CVD). We follow a wet transfer protocol 26 to drape the flake on the patterned silica substrate (see Methods). This technique takes advantage of the Van der Waals forces to make the flake conform to the surface topography. As an illustration, Figure 1b shows an atomic force microscopy (AFM) image from an hBN fragment where the 20-nm-thick flake folds on itself: We identify single-and double-layer sections near the left and right areas, respectively; bare pillars -visible on the lower, right corner of the image -provide a direct view...

Strain-tunable orbital, spin-orbit, and optical properties of monolayer transition-metal dichalcogenides

“…As a general trend observed in the experimental studies, biaxial strain induces a significantly stronger modulation when compared to uniaxial strain, a fact also supported by ab-initio calculations [53,54]. Furthermore, by strain engineering it is possible to localize excitons in specific * klaus.zollner@physik.uni-regensburg.de regions, which is a viable approach to obtain spatially and spectrally isolated quantum emitters based on 2D materials [51,[55][56][57][58].…”

Dynamically tuned non-classical light emission from atomic defects in hexagonal boron nitride

“…The obtained lifetimes (τ PL values outlined in Fig. 2c) are consistent with the characteristic decay times found in other monolayer and multilayer h-BN samples 7,8,10,13,25,26 .…”

Identifying defect-related quantum emitters in monolayer WSe2

“…Recently, it has been discovered that a single-layer TMD can be used as a host material for single quantum emitters [6][7][8][9][10][11][12] at low temperature, which provides a new platform to develop on-chip integrated single photon source and quantum information processing. In addition, the single photon emission has been realized with several approaches, such as heterostructures driven electrically [13], nanoscale strain engineering [14][15][16][17] and sub-nm focused helium ion irradiation [18], which are mostly defect related. Meanwhile, the properties of such a 2D host of quantum emitters have been intensely investigated, including 3D localized trions in heterostuctures [19], manipulation of fine structure splitting (FSS) [20] and photon-phonon interaction [21].…”