Electrically pumped single-defect light emitters in WSe ₂

Abstract

Recent developments in fabrication of van der Waals heterostructures enable new type of devices assembled by stacking atomically thin layers of two-dimensional materials. Using this approach, we fabricate light-emitting devices based on a monolayer WSe 2 , and also comprising boron nitride tunnelling barriers and graphene electrodes, and observe sharp luminescence spectra from individual defects in WSe 2 under both optical and electrical excitation. This paves the way towards the realization of electrically-pumped quantum emitters in atomically thin semiconductors. In addition we demonstrate tuning by more than 1 meV of the emission energy of the defect luminescence by applying a vertical electric field. This provides an estimate of the permanent electric dipole created by the corresponding electron-hole pair. The light-emitting devices investigated in our work can be assembled on a variety of substrates enabling a route to integration of electrically pumped single quantum emitters with existing technologies in nanophotonics and optoelectronics.The recent observation of direct bandgaps in semiconducting molybdenum and tungsten dichalcogenide monolayers has led to a rise of interest to these two-dimensional (2D) materials and demonstrated their potential for future optoelectronic devices 1,2,3,4 . These one-monolayer-thick crystals are characterised by large exciton binding energies 5,6 and oscillator strengths 7 and can be combined with other layered materials to create heterostructures held together by van der Waals forces 8,9,10,11,12 . This concept has been used to form electrically driven light-emitting structures, where MoX 2 or WX 2 (X=S or Se) monolayers were used as the exciton recombination layers, thin hexagonal boron nitride (hBN) was used for tunnelling barriers and graphene -used for transparent electrodes 11,12 .

Fine structure of K-excitons in multilayers of transition metal dichalcogenides

“…Intense works have been devoted to studies of S-TMD monolayers which appeared to be the efficient light emitters, the two-dimensional semiconductors with a direct bandgap positioned at the K ± points of their 1-st hexagonal Brillouin zone (BZ) [5][6][7]. New and rich possibilities of tuning the band structure, the strength of Coulomb interaction, and thus the optical properties, are opened when stacking the S-TMD monolayers into a form of multilayers and/or hetero-layers [8][9][10][11][12][13][14][15][16]. The properties of the archetypes of S-TMD stacks which are the thermodynamically stable 2H-stacked multilayers are to be well understood first.…”

Single photon emitters in boron nitride: More than a supplementary material

“…Hexagonal boron nitride (hBN), a layered material known also as white graphite, is customarily used in cosmetic and metallurgic industry whereas its high purity single crystals promise the optical devices operating in the UV spectral range [1][2][3][4][5][6][7][8][9][10][11] and are extensively used in the research on atomically thin crystals [12][13][14], serving as nearly lattice matched and/or protecting layers for graphene and other two-dimensional systems [15][16][17][18][19]. The recent addition to explorations of hBN is the discovery of specific centres in this material, which rise a quantum light, the single photon emission (SPE) [20][21][22][23][24][25][26][27].…”

Light Sources and Photodetectors Enabled by 2D Semiconductors

“…With a vertically stacked architecture consisting of graphene, few‐layer hBN, and TMD layers (e.g., 1L WSe 2 ), narrow quantum emission was demonstrated under electrical pumping at 10 K, where electrons were injected from the graphene to the TMD layers by passing the tunnel barrier of the ultrathin hBN ( Figure a–d) . The defective nature and the doublet features of the quantum emission from vertical graphene/hBN/TMD layers/hBN/graphene junctions have been revealed at low operation voltages (e.g., 2 V) and low temperature (Figure e–g) . Meanwhile, quantum light from the lateral LED based on 1L WSe 2 was realized, where split back gates were employed to form the in‐plane p–i–n junctions .…”

“…g) EL spectra from single‐defect light emitters at various voltages. e–g) Reproduced with permission . Copyright 2016, IOP Publishing.…”