Electrically driven photon emission from individual atomic defects in monolayer WS ₂

Abstract

Quantum dot–like single-photon sources in transition metal dichalcogenides (TMDs) exhibit appealing quantum optical properties but lack a well-defined atomic structure and are subject to large spectral variability. Here, we demonstrate electrically stimulated photon emission from individual atomic defects in monolayer WS2 and directly correlate the emission with the local atomic and electronic structure. Radiative transitions are locally excited by sequential inelastic electron tunneling from a metallic tip into selected discrete defect states in the WS2 bandgap. Coupling to the optical far field is mediated by tip plasmons, which transduce the excess energy into a single photon. The applied tip-sample voltage determines the transition energy. Atomically resolved emission maps of individual point defects closely resemble electronic defect orbitals, the final states of the optical transitions. Inelastic charge carrier injection into localized defect states of two-dimensional materials provides a powerful platform for electrically driven, broadly tunable, atomic-scale single-photon sources.

Band gap measurements of monolayer h-BN and insights into carbon-related point defects

“…Nonetheless, it is noteworthy that a detailed study of the morphological and electric structure of individual point defects in h-BN is required, which can be achieved by performing STM/AFM imaging and STS measurements at cryogenic temperatures, such as what has been done in the case of point defects in single layers of transition metal dichalcogenides. [110][111][112][113] In order to obtain more insights on the observed defects, in situ PL and STM-CL experiments were carried out at 100 K and 300 K, using the experimental setup described in Figure 2. The raw luminescence data were presented in Figure 2(c) and (d), but for the proper interpretation, the spectra were corrected following the procedure explained in SM and the results are presented in Figure 4(d).…”

Substitutional doping in 2D transition metal dichalcogenides

“…Advanced techniques such as atomic resolution, aberration-corrected STEM imaging and electron energy loss spectroscopy may become essential for identifying individual impurity species, their bonding configuration, and the local strain environment in the host material [133][134][135]. High spatial resolution characterization techniques such as nano-angle-resolved photoemission spectroscopy [136], STS [137], and nano-optical [138][139][140][141] techniques are also crucial for investigating the local electronic structure around individual dopant impurities.…”

Excitonic Emission in Atomically Thin Electroluminescent Devices

“…In contrast to trions, these higher-order exciton complexes are completely undetectable at room temperature because they suffer terribly from thermal dissociation beyond ≈130 K. [87] Apart from scattering with other quasiparticles into bound states, excitons can interact with local defect or impurity sites to form localized excitons (Figure 1f), [113] which typically reside within the bandgap. [7][8][9][113][114][115] These defects can be created artificially (such as sulfur vacancies) [116] and excitons localized by them are more efficient in photo or electrical response at low injection rate [7] than delocalized ones, which can implement 2D quantum LED (Figure 1g) [113] for single-photon emission [12,115,117] at low temperatures.…”