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 (X-0), 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 (X-0), 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.