Strain Controls Charge Carrier Lifetimes in Monolayer WSe2: Ab Initio Time Domain Analysis.

Abstract

Mono- and few-layer transition metal dichalcogenides (TMDs) are among the most appealing candidates for electronic and optoelectronic devices. During synthesis, TMDs actively interact with substrates, which induce notable strain and influence significantly charge carriers in TMDs. By performing time-domain ab initio simulations on monolayer WSe2, we demonstrate that charge carrier lifetimes vary by a factor of 3 within a typical 1% strain range, the bandgap changes by 0.2 eV, and electron-phonon interactions vary by 60%. Fortuitously, the most common tensile strain extends the lifetimes. The changes arise because of modifications in interatomic interactions. Further, compared to the optimized structure, at ambient temperature the bandgap drops by 0.1 eV and fluctuates by 0.1 eV. WSe2 obeys linear response within 1% strain; however, further strain leads to nonlinear qualitative changes in WSe2 electronic properties. The conduction band is affected more strongly than the valence band. Charges couple to phonons within a 100-400 cm-1 frequency range, with the strongest coupling to in-plane and out-of-plane modes at 250 cm-1. The reported findings agree with the available experiments and should be generic to other 2D materials. The strain effects need to be considered during TMD synthesis and provide means to control and tune TMD properties for 2D device applications.