Ultrafast photocurrents in MoSe₂ probed by terahertz spectroscopy

Abstract We use the terahertz (THz) emission spectroscopy to study femtosecond photocurrent dynamics in prototypical 2D semiconductor, transition metal dichalcogenide MoSe 2 . identify several distinct mechanisms producing THz radiation response an ultrashort (30 fs) optical excitation a bilayer (BL) and multilayer (ML) sample. In ML, is generated at picosecond timescale by out-of-plane currents due drift of photoexcited charge carriers surface electric field. The BL in-plane shift current. Finally, we observe oscillations about 23 from attribute quantum beats between two excitonic states with energetic separation ∼100 meV.