Strain-Tunable Single Photon Sources in WSe₂ Monolayers

Abstract

& These authors contributed equally to this work 2 ABSTRACT.The appearance of single photon sources in atomically thin semiconductors holds great promises for the development of a flexible and ultra-compact quantum technology, in which elastic strain engineering can be used to tailor their emission properties. Here, we show a compact and hybrid 2D-semiconductorpiezoelectric device that allows for controlling the energy of single photons emitted by quantum emitters localized in wrinkled WSe2 monolayers. We demonstrate that strain fields exerted by the piezoelectric device can be used to tune the energy of localized excitons in WSe2 up to 18 meV in a reversible manner, while leaving the single photon purity unaffected over a wide range. Interestingly, we find that the magnitude and in particular the sign of the energy shift as a function of stress is emitter dependent. With the help of finite element simulations we suggest a simple model that explains our experimental observations and, furthermore, discloses that the type of strain (tensile or compressive) experienced by the quantum emitters strongly depends on their localization across the wrinkles. Our findings are of strong relevance for the practical implementation of single photon devices based on two-dimensional materials as well as for understanding the effects of strain on their emission properties. KEYWORDS: single photon emitters, 2D materials, elastic strain engineering, photoluminescence, tungsten diselenide monolayers, piezoelectric devices MAIN TEXTThe family of two-dimensional (2D) semiconductor transition metal dichalcogenides (TMDs), including WS2, WSe2, MoS2 or MoSe2, offers several advantages for optoelectronic and photonic applications. They possess a variety of properties such as direct bandgap when thinned down to the monolayer, quantum confinement due to their reduced out-of-plane dimensionality, large oscillator strength and quantum efficiency, optically controlled injection of electrons with defined spins for quantum spintronics and spinphoton interfacing 1,2 . Moreover, functional multilayer heterostructures can be easily built up by simply

Topological structures of transition metal dichalcogenides: A review on fabrication, effects, applications, and potential

“…Inset: corresponding profiles along the dashed lines. Reproduced with permission 107 . Copyright 2019, American Chemical Society.…”

“…They are observed on bubbles or wrinkles 154 as these topological structures impose localized strain on TMD materials, break original crystal structures, generate defects, and modify intrinsic bandgaps. Take a wrinkled monolayer WSe 2 in Figure 5A as an example 107 . WSe 2 was placed on a piezoelectric stage and connected with electrical contacts on both sides.…”

“…F, Relationship between the simulated strain and electric field. The electric field was applied to an actuator located in A‐E in E. Reproduced with permission 107 . Copyright 2019, American Chemical Society…”

“…Similarly, compared with flat TMD devices, topological structures on TMDs exhibit immense advantages in photoelectronic devices with enhanced carrier mobility, photocurrent, and photoresponsivity 56,70,86,96,97 . Moreover, these topological structures are beneficial in fabricating flexible and stretchable optoelectronic devices owing to their ability to resist deformation due to their unique morphologies 74,98‐117 …”

Microheater Actuators as a Versatile Platform for Strain Engineering in 2D Materials

“…Moreover, this capability of adjusting the level of strain at will has opened the door to straintronic devices. [14][15][16][17][18][19] Here we demonstrate a platform to achieve fast modulation of biaxial strain in atomically thin MoS2. Our approach is based on the fabrication of ring-shaped metallic microheaters on top of polypropylene (PP), a polymer substrate with a very large thermal expansion coefficient.…”