Identifying Carbon as the Source of Visible Single Photon Emission from Hexagonal Boron Nitride (2003.00949v3)

Abstract: Single photon emitters (SPEs) in hexagonal boron nitride (hBN) have garnered significant attention over the last few years due to their superior optical properties. However, despite the vast range of experimental results and theoretical calculations, the defect structure responsible for the observed emission has remained elusive. Here, by controlling the incorporation of impurities into hBN and by comparing various synthesis methods, we provide direct evidence that the visible SPEs are carbon related. Room temperature optically detected magnetic resonance (ODMR) is demonstrated on ensembles of these defects. We also perform ion implantation experiments and confirm that only carbon implantation creates SPEs in the visible spectral range. Computational analysis of hundreds of potential carbon-based defect transitions suggest that the emission results from the negatively charged VBCN- defect, which experiences long-range out-of-plane deformations and is environmentally sensitive. Our results resolve a long-standing debate about the origin of single emitters at the visible range in hBN and will be key to deterministic engineering of these defects for quantum photonic devices.

• The paper identifies carbon defects as the primary source for visible single photon emission in hBN.
• It employs controlled synthesis, ion implantation, and room-temperature ODMR to correlate carbon presence with photoluminescence.
• TD-DFT results confirm the V_C-B_N⁻ defect model, supporting scalable quantum photonic device design.

Carbon as the Determinant for Single Photon Emission in Hexagonal Boron Nitride

In their rigorous paper, Mendelson et al. investigate the origin of visible single photon emitters (SPEs) in hexagonal boron nitride (hBN), an emergent material for quantum photonics due to its remarkable optical properties. Despite numerous experimental and theoretical efforts, the defect structure responsible for visible emission remained undetermined until this work. The authors present evidence that carbon defects are the key contributors to visible SPEs in hBN through a combination of synthetic control, optical analysis, and computational modeling.

Experimental Approach and Results

The researchers systematically explored carbon incorporation in hBN using various synthesis methods, including metal-organic vapor phase epitaxy (MOVPE), molecular beam epitaxy (MBE), and the conversion of highly oriented pyrolytic graphite (HOPG) to hBN. By tuning carbon concentrations in these processes, they established a correlation between carbon presence and photoluminescence (PL) from SPEs.

A pivotal part of their methodology involved ion implantation experiments. By exclusively implanting carbon ions into MOVPE-grown hBN films, they demonstrated that only carbon, and not silicon or oxygen, could induce SPEs in the visible range without additional annealing, firmly implicating carbon in the emission mechanism.

Another notable result is the successful operation of optically detected magnetic resonance (ODMR) at room temperature on ensembles of these carbon-related defects, a significant advancement over previous studies that required cryogenic conditions. The quantum nature of the emission from isolated defects was further confirmed by measuring the second-order auto-correlation function, highlighting the robust photophysical properties of the carbon-based defects.

Computational Insights

Theoretical investigations using time-dependent density functional theory (TD-DFT) supplemented the experimental findings by proposing the negatively charged V_C-B_N^- defect as the defect state responsible for the visible emission. This defect undergoes considerable out-of-plane distortions that are environmentally sensitive, explaining the variability in spectral properties across different samples. The calculations, aligned with observed experimental data, support the hypothesis of carbon-based defects being central to the SPEs in hBN.

Implications and Future Directions

Identifying carbon defects as the source of visible SPEs in hBN has important implications for the design and engineering of quantum photonic devices. Given the room temperature stability and addressability of these defects, they promise advancements in scalable quantum information technologies. This research advances the controlled engineering of defects in hBN, potentially enabling new quantum network components and spin-photon interfaces.

Looking forward, the paper opens pathways for exploring other potential atomic defects in 2D materials and their roles in photonic applications. Additionally, the unique environmental sensitivity of the carbon-based defects could be exploited for applications requiring precise external tunability.

Conclusion

Mendelson et al. offer compelling experimental and theoretical evidence linking carbon incorporation in hBN with the occurrence of visible SPEs, providing the first conclusive identification of the defect structure responsible for these emissions. This insight significantly contributes to the fundamental understanding of defect-induced emissions in hBN and sets the stage for future innovations in quantum photonics leveraging hBN's unique properties.