High-Density, Localized Quantum Emitters in Strained 2D Semiconductors

Abstract

Two-dimensional chalcogenide semiconductors have recently emerged as a host material for quantum emitters of single photons. While several reports on defect-and strain-induced singlephoton emission from 2D chalcogenides exist, a bottom-up, lithography-free approach to producing a high density of emitters remains elusive. Further, the physical properties of quantum emission in the case of strained 2D semiconductors are far from being understood. Here, we demonstrate a bottom-up, scalable, and lithography-free approach for creating large areas of localized emitters with high density (∼150 emitters/um 2 ) in a WSe 2 monolayer. We induce strain inside the WSe 2 monolayer with high spatial density by conformally placing the WSe 2 monolayer over a uniform array of Pt nanoparticles with a size of 10 nm. Cryogenic, time-resolved, and gate-tunable luminescence measurements combined with near-field luminescence spectroscopy suggest the formation of localized states in strained regions that emit single photons with a high spatial density. Our approach of using a metal nanoparticle array to generate a high density of strained quantum emitters will be applied to scalable, tunable, and versatile quantum light sources.

Substrate-Induced Changes on the Optical Properties of Single-Layer WS2

“…From all the analysis presented in this study, it is fair to conclude that causes of PL quenching in the TMDCs over Si N substrate are a combination of strain, which led to an overlap of the orbitals in WS for this case, and the natural trend of electrons to flow from a direct gap semiconductor into an indirect one. Furthermore, the unstrained regions over the holes turned into confined areas where lasing conditions may be found, as seen in previous publications elsewhere [ 12 , 13 , 14 , 15 ].…”

“…According to Kim and coworkers [ 15 ], that also verified quantum emission in WSe recently using a different approach without drilled substrates, the quantum emission properties are far from a complete understanding. In this sense, we study experimentally the WS monolayer transferred onto drilled Si N substrate, in order to have insights about the influence of the substrate over the WS optical properties through Raman and photoluminescence measurements.…”

“…In addition, we carried out DFT-based calculations aiming to better understand the electronic properties of the Si N –WS semiconductor heterojunction. First, we performed molecular dynamics (MD) calculation in order to verify the feasibility of the junction face to the significant strain that the Si N substrate might impose to WS lattice, further confirming the strong in-plane bonding on tungsten-based TMDCs [ 15 ]. Furthermore, we also developed an analysis of the band alignment prior to the junction according to the semiconductor theory, which was confirmed by electronic band structure calculations via density functional theory (DFT).…”

Microwave Facilitated Covalent Organic Framework/Transition Metal Dichalcogenide Heterostructures

“…Exfoliated flakes of monolayer MoSe 2 were used in this case as the combination of vapor-phase growth of TMDCs at high temperatures and microwave processing was shown to disrupt SiO 2 dielectric properties required for back-gating. The monolayer flakes were first mechanically exfoliated (ME) onto the substrate in the device configuration depicted in Figure a and transfer techniques described in previous works . After transferring the TMDC monolayers, Ti/Au contacts for applying a gate bias were patterned by e-beam lithography and the evaporation process (Figure b).…”

“…The monolayer flakes were first mechanically exfoliated (ME) onto the substrate in the device configuration depicted in Figure 4a and transfer techniques described in previous works. 59 After transferring the TMDC monolayers, Ti/Au contacts for applying a gate bias were patterned by e-beam lithography and the evaporation process (Figure 4b). Few-layer COF-5 films were then deposited onto the MoSe 2 with an applied microwave power of 100 W, resulting in a 13 meV redshift in the PL of the A-exciton peak position (Figure 4c) consistent with heterostructures in Figure 2c.…”