Ultrafast Drift Current Terahertz Emission Amplification in the Monolayer WSe 2 /Si Heterostructure.

Two-dimensional transition metal dichalcogenides (TMDs) have great potential application for seamless on-chip integration due to their strong photon-electron-spin-valley coupling. However, the contact-free measurements of the valley-coupled photocurrent in TMDs is still challenging. Here, ultrafast terahertz emission spectroscopy is employed to investigate the photocurrent dynamics in monolayer WSe 2 , and an interface-induced drift current amplification is found in the WSe 2 /Si heterostructure. The amplification of terahertz emission comes from the photocurrent enlarged by band bending in the WSe 2 and Si junction, and the amplification ratio increase further near the valley resonant transition of WSe 2 . In addition, the valley-momentum locked photocurrent in the WSe 2 /Si heterostructure reserves the same chirality with monolayer WSe 2 at room temperature. These findings could provide a new method for manipulating valley-momentum locked photocurrent by photon helicity and open new avenues for TMD-based valley-polarized terahertz emission devices.