Strain-Dependent Optical Properties of Monolayer WSe₂

Monolayer WSe₂ exhibits a fascinating optical dark exciton ground state, which holds significant promise for advancing single-photon source and quantum information processing. In this study, we systematically explored the temperature- and strain-dependent optical properties of monolayer WSe₂ using a three-dimensional silicon-based nanowrinkle structure as a template. We observed emission from a variety of excitonic states, including bright exciton (X⁰), bright trion (X^T), dark exciton (X^D), and dark trion (X^DT), all originating from the same sample. Notably, we can selectively control and enhance their emissions. At a temperature of 153 K, the dominant emission source was the bright exciton, but as the mechanical compressive strain decreased to less than −0.015% at 105 K, dark excitons began to dominate the emission. Furthermore, when the mechanical strain was tensile and exceeded 0.03%, the intensities and energies of bright exciton (X⁰), bright trion (X^T), dark exciton (X^D), and dark trion (X^DT) remained stable, indicating that all the excitons are drawn toward regions with the highest local strain due to a funneling effect. Additionally, we found that the expansion coefficient and Debye temperature of monolayer WSe₂ were critically influenced by the strain distribution. Specifically, the expansion coefficient tripled as the strain increased from a compressive −0.05% to a tensile 0.05% strain, and the Debye temperature increased from 20 to 600 K. Considering the compatibility of silicon-based substrates and monolayer transition metal dichalcogenides with semiconductor and photonic circuits, our approach holds promise for achieving site-controlled quantum emission of specific excitons and creating high-density quantum emitters through strain engineering.