Abstract
Hexagonal boron nitride (hBN) is a wide-band gap van der Waals material able to host light-emitting centers behaving as single photon sources. Here, we report the generation of color defects in hBN nanosheets dispersed on different kinds of substrates by thermal treatment processes. The optical properties of these defects have been studied using microspectroscopy techniques and far-field simulations of their light emission. Using these techniques, we have found that subsequent ozone treatments of the deposited hBN nanosheets improve the optical emission properties of created defects, as revealed by their zero-phonon linewidth narrowing and reduction of background emission. Microlocalized color defects deposited on dielectric substrates show bright (≈1 MHz) and stable room-temperature light emission with zero-phonon line peak energy varying from 1.56 to 2.27 eV, being the most probable value 2.16 eV. In addition to this, we have observed a substrate dependence of the optical performance of the generated color defects. The energy range of the emitters prepared on gold substrates is strongly reduced, as compared to that observed in dielectric substrates or even alumina. We attribute this effect to the quenching of low-energy color defects (these of energies lower than 1.9 eV) when gold substrates are used, which reveals the surface nature of the defects created in hBN nanosheets. Results described here are important for future quantum light experiments and their integration in photonic chips.
Highlights
Hexagonal boron nitride is a low-dimensional van der Waals material with a honey-comb crystal lattice structure similar to graphene
Optical microscopy and scanning electron microscopy (SEM) images of dispersed Hexagonal boron nitride (hBN) nanosheets on the Si substrate are depicted in Figure S1b−e in Supporting Information
We found more than 2 times higher occurrence of color defects in hBN nanosheets deposited on the heated Si substrate than in pristine nanosheets dried at room temperature, by comparing their respective micro-PL maps
Summary
Hexagonal boron nitride (hBN) is a low-dimensional van der Waals material with a honey-comb crystal lattice structure similar to graphene (see Figure S1a in Supporting Information SI) It is an electrical insulator with a large band gap of ≈6 eV1 and an exciton binding energy of ≈130 meV.[2] The low-dimensional character, smooth surface, insulating properties, and very high chemical stability[3] make hBN a suitable ideal platform for the fabrication of enhanced electronic and optoelectronic nanodevices, where hBN can be used as a protective and dielectric layer.[4−6] Another outstanding property of hBN is related to recently discovered point color defects, which are very attractive for a variety of applications as single-photon sources.[7−11] The physical origin of these point color defects is not yet well-known, it is related to the presence of several different crystal vacancies[12−14], and atom impurities[13,15−17] in the hBN crystal lattice. Lattice imperfections might lead to electron-phonon coupling and the formation of undesired phonon side-band (SB) emission.[30,31] extrinsic surface defects might serve as charge traps
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