Dynamic Control of Excitons in Single-Layer WSe₂ with Surface Acoustic Waves

Two-dimensional (2D) single-layer transition metal dichalcogenide (1L-TMD) semiconductors have great potential to enable next-generation optoelectronic technologies because they are atomically thin two-dimensional systems with excellent optical and electrical properties. For example, 1L-TMDs exhibit bright optical emission due to their direct bandgap and large exciton binding energies. Among the family of 1L-TMD semiconductors, 1L-WSe₂ exhibits narrow optical emission at low temperatures from a large suite of different types of excitons, which are the dominant electronic excited states in the 2D semiconductor. These excitons govern light-matter interactions, from simple light absorption to the emission of non-classical states of light, such as single-photon generation. It is therefore essential to control and manipulate the excitons and their dynamics to employ these states in photonic, electronic, and quantum technologies. In this work, we study how surface acoustic waves (SAWs) dynamically manipulate excitonic states in mechanically exfoliated 1L-WSe₂ that is dry-transferred onto GaAs-based SAW devices. The fabrication procedure utilizes several steps to ensure efficient coupling between the SAWs and the 1L-WSe₂. The SAWs have frequencies of ~3.2 GHz and stimulate the 1L-WSe₂ with both electric fields and strain. Corroborating previous studies, we demonstrate photoluminescence quenching of the excitonic states in 1L-WSe₂ by the SAW stimulation at room temperature. In addition, the strength of the SAW modulation of the excitons is found to depend on excitation energy, as well as the speed of the modulation, and how the SAWs alter the spatial distribution of excitonic emission. Ongoing anti-stokes Raman spectroscopy is being used to understand how the SAW stimulation changes the lattice temperature of the 1L-WSe₂ along with time-resolved spectroscopy to characterize how the SAWs affect the relaxation dynamics to develop a comprehensive model of SAW-exciton interactions in 2D TMD semiconductors. The studies aim to open new opportunities for controllable optoelectronic and photonic quantum devices based on 2D semiconductors integrated with SAW devices.