Dielectric Environment Sensitivity of Carbon Centers in Hexagonal Boron Nitride

Abstract

A key advantage of utilizing van‐der‐Waals (vdW) materials as defect‐hosting platforms for quantum applications is the controllable proximity of the defect to the surface or the substrate allowing for improved light extraction, enhanced coupling with photonic elements, or more sensitive metrology. However, this aspect results in a significant challenge for defect identification and characterization, as the defect's properties depend on the the atomic environment. This study explores how the environment can influence the properties of carbon impurity centers in hexagonal boron nitride (hBN). It compares the optical and electronic properties of such defects between bulk‐like and few‐layer films, showing alteration of the zero‐phonon line energies and their phonon sidebands, and enhancements of inhomogeneous broadenings. To disentangle the mechanisms responsible for these changes, including the atomic structure, electronic wavefunctions, and dielectric screening, it combines ab initio calculations with a quantum‐embedding approach. By studying various carbon‐based defects embedded in monolayer and bulk hBN, it demonstrates that the dominant effect of the change in the environment is the screening of density–density Coulomb interactions between the defect orbitals. The comparative analysis of experimental and theoretical findings paves the way for improved identification of defects in low‐dimensional materials and the development of atomic scale sensors for dielectric environments.

Color Centers in Hexagonal Boron Nitride Nanosheet-Based Heterojunctions: Implications for Quantum Emitters and Ultrathin Sensors

“…52 Furthermore, carbon-related defects have different ZPL energies and phonon sidebands in 50 nm and 10-layer hBN films, and DFT calculations with a quantumembedding approach demonstrate that the screening of density−density Coulomb interactions between the defect orbitals is the dominant dielectric effect of the surrounding hBN layers. 53 The other DFT calculations with the PBE functional show that the SiO 2 substrate can increase the ZPL of the V N N B color center by 0.22 eV, due to the interaction between the V N N B defect and hydrogen atom of the passivated SiO 2 , which is represented by a seven-layer β-cristobalite (111) slab, 54 but the real SiO 2 substrate is amorphous (Figure 1). Therefore, the screening effects of the SiO 2 substrate on vacancy-related and carbon-related color centers in hBN are still elusive, and the more reasonable atomic structure of the SiO 2 substrate and advanced computational method with many-body effects should be developed in the future.…”

“…Second, it is possible that the PL spectrum of V B –1 in hBN can be tuned by environmental screening, including the surrounding hBN layers, adsorbates, substrates, and substrate-induced strain. − Figure c shows the strain effect on the ZPL of V B –1 in hBN obtained by the HSE06 functional, and the relationship between the ZPL energy with strain ε (%) can expressed by 1.7923–0.0830ε, which means that the compressive strain can increase the ZPL energy. The compressive strain effect is equivalent to the pressure dependence of the ZPL energy.…”

“…The most recent experimental and theoretical investigations related to the substrate effects also find that the substrate plays a key role in tuning the PL spectra. − According to a few experimental investigations, compared with dielectric substrates or alumina, a gold substrate reduces the energy range of the color center with a ZPL at ∼2.1 eV in few-layer hBN nanostructures with a lateral size of 50–200 nm, and ozone treatments can reduce the ZPL line width and inhibit background emission . Furthermore, carbon-related defects have different ZPL energies and phonon sidebands in 50 nm and 10-layer hBN films, and DFT calculations with a quantum-embedding approach demonstrate that the screening of density–density Coulomb interactions between the defect orbitals is the dominant dielectric effect of the surrounding hBN layers . The other DFT calculations with the PBE functional show that the SiO 2 substrate can increase the ZPL of the V N N B color center by 0.22 eV, due to the interaction between the V N N B defect and hydrogen atom of the passivated SiO 2 , which is represented by a seven-layer β-cristobalite (111) slab, but the real SiO 2 substrate is amorphous (Figure ).…”

Electroluminescence from pure resonant states in hBN-based vertical tunneling junctions

“…The carbon doping procedure activated multiple resonances in the PL spectra in the ultraviolet, visible, and near-infrared spectral regions 33 , 37 , 38 . The translation from optical to electrical excitation requires understanding and controlling the dynamics of charge carriers participating in the tunneling and radiative recombination processes.…”

“…Their origin was related to intradefect transitions characterized by varied degrees of electron–phonon coupling quantified by Huang–Rhys factors, as thoroughly discussed in ref. 38 . A comparable emission intensity of all three resonances was observed for optical excitation at 2.56 eV with the power of 1 mW and for the electrical excitation with the current of 2 μA.…”