Deterministic hBN bubbles as a versatile platform for studies on single-photon emitters

TL;DR

This work addresses reproducibility challenges in studying single-photon emitters (SPEs) in hexagonal boron nitride (hBN) by employing large-area MOVPE-grown hBN on sapphire as a scalable, activation-free platform. By inducing bubbles through electron-beam irradiation, the authors introduce a multifunctional system where wrinkle-network geometry yields mechanically stable, cryogenic-friendly domes that simultaneously enhance SPE emission via optical interference rather than strain and enable emitter relocation. They demonstrate ~$100-200\%$ emission enhancement for SPEs with a ZPL near $2.3\ \,\mathrm{eV}$ and antibunched statistics ($g^{(2)}(0)=0.02\pm0.05$), supported by Raman mappings and $E_F=|E/E_0|^4$ simulations that link enhancements to interference effects. Scalable matrix-patterned bubbles and a mask-based approach enable deterministic positioning, establishing a reproducible platform for extensive SPE studies in hBN and aiding efforts to identify the nature of SPEs in this material system.

Abstract

Single-photon emitters (SPEs) in two-dimensional materials are highly promising candidates for quantum technologies. SPEs in hexagonal boron nitride (hBN) have been widely investigated, but mostly in exfoliated or powder samples that require an activation process, making it difficult to compare studies and reproduce results. Here, we address this problem and propose a platform based on large-area metaloraganic vapour phase epitaxy (MOVPE)-grown hBN, which combines reproducibility and scalability with the ability to readily host SPEs without activation. Through the creation of bubbles via electron-beam irradiation, we achieve additional functionalities, including an interference-mediated enhancement of emission by approximately 100-200\%, dedicated structures that allow the relocation of individual emitters across different systems, and the opportunity to investigate strain-induced effects. Moreover, in contrast to other gas-filled bubbles that deflate at low temperatures, our bubbles remain stable under cryogenic conditions, allowing studies as a function of temperature. To improve the control over the shape and position of bubbles, we demonstrate a~mask-based method that enables deterministic control over bubble formation. The presented hBN bubbles constitute a versatile platform for reproducible studies of hBN-based emitters, providing a reliable insight into their nature and properties.

Figures (9)

• Figure 1: AFM images of a small bubble with the size comparable to a single cell of the wrinkle network: a) top view, b) side view. The scale bar in a) is 500 nm. The total area is 1.5 $\mathrm{\text{\textmu} m}$$\times$ 1.5 $\mathrm{\text{\textmu} m}$.
• Figure 2: (a-d) AFM images of bubbles B1-B4. Scale bars are 2 $\mathrm{\text{\textmu} m}$. The logarithmic color scale highlights the presence of wrinkles and smaller bubbles close to the main bubble. (e-h) cross-sectional profiles of bubbles B1-B4 fitted using Eq. \ref{['eq1']}. Black points - experimental data, green (blue) curves - fits with fixed $\alpha$=1 ($\alpha$=2), red curves - model described in the text.
• Figure 3: Results of PL mapping measurements conducted on bubbles B1-B4 (each column refers to one bubble). (a-d) optical microscope images of mapped bubbles. (e-h) maps of the total integrated PL intensity in the range 2.0 - 2.33 eV. White circles in (a-h) indicate the bubble positions. Bubbles are rotated compared to Figure \ref{['figure2']}. Scale bars are 3 $\mathrm{\text{\textmu} m}$. (i-j) PL spectra of defects acquired along cyan lines on e) and f) with a 0.3 $\mathrm{\text{\textmu} m}$ step. (k-l) PL spectra of defects marked by black circles in g) and h). The sharp peaks at $\sim$ 2.28 eV are sapphire Raman modes.
• Figure 4: Results of low temperature (1.7 K) PL measurements on single emitters on an hBN bubble. a) and b) time evolution of emission of unstable and stable single-photon emitters, respectively. c) angular dependence of the linearly polarized ZPL emission intensity. d) second order correlation function curve obtained for the stable single-photon emitter: red circles - experimental points, black curve - fit.
• Figure 5: Mapping results for a 25 $\mathrm{\text{\textmu} m}$$\times$ 25 $\mathrm{\text{\textmu} m}$ hBN area. The material in dashed squares was irradiated with an electron beam. a) optical image of the mapped area. b) map of the total integrated PL signal in the range 2.0 eV - 2.33 eV. Scale bars are 5 $\mathrm{\text{\textmu} m}$. c) spectra acquired in points marked by black circles in b).