Single photon emitters in exfoliated WSe2 structures

TL;DR

This study identifies and characterizes single photon emitters at the edges of exfoliated WSe2 layers, revealing their potential for quantum optoelectronic applications due to sharp emission lines and photon antibunching.

Contribution

It demonstrates the existence of single photon emitters in WSe2 flakes at their edges, linking their optical properties to the material's two-dimensional structure.

Findings

Sharp emission lines with 0.1 meV linewidth observed at edges

Emission exhibits photon antibunching, confirming single photon emission

Optical responses are consistent with two-dimensional properties of WSe2

Abstract

Crystal structure imperfections in solids often act as efficient carrier trapping centers which, when suitably isolated, act as sources of single photon emission. The best known examples of such attractive imperfections are wellwidth or composition fluctuations in semiconductor heterostructures (resulting in a formation of quantum dots) and coloured centers in wide bandgap (e. g., diamond) materials. In the case of recently investigated thin films of layered compounds, the crystal imperfections may logically be expected to appear at the edges of commonly investigated few-layer flakes of these materials, exfoliated on alien substrates. Here, we report on comprehensive optical microspectroscopy studies of thin layers of tungsten diselenide, WSe2, a representative semiconducting dichalcogenide with a bandgap in the visible spectral range. At the edges of WSe2 flakes, transferred onto Si/SiO2 substrates, we discover centers which, at low temperatures, give rise to sharp emission lines (0.1 meV linewidth). These narrow emission lines reveal the effect of photon antibunching, the unambiguous attribute of single photon emitters. The optical response of these emitters is inherently linked to two-dimensional properties of the WSe2 monolayer, as they both give rise to luminescence in the same energy range, have nearly identical excitation spectra and very similar, characteristically large Zeeman effects. With advances in the structural control of edge imperfections, thin films of WSe2 may provide added functionalities, relevant for the domain of quantum optoelectronics.