Photocurrent studies on encapsulated two-dimensional transition metal dichacogenides

Abstract

Atomically thin group VI transition metal dichalcogenides (TMDCs), as a representative family of two-dimensional semiconductors, are believed to be competitive materials for future optoelectronic devices due to their favorably direct bandgap in the monolayer limit. The reduced dimensionality of TMDC monolayers also makes them ideal platforms to study the physics in low-dimensional systems such as enhanced excitonic effects. On the other hand, the strong spin-orbital coupling combined with the inversion symmetry breaking structure results in a significant connection between the spin and valley degrees of freedom, which unlock a new opportunity to manipulate the behavior of the electrons. Recently, the monolayer TMDC-based 2D heterostructures have rapidly attracted researchers’ attention for their significantly enhanced optical and electrical properties. The study in this thesis mainly focused on the exciton-related dynamics in monolayer tungsten diselenide (WSe2). The valley relaxation process in monolayer tungsten diselenide is measured by time-resolved Kerr rotation technique. The valley relaxation processes of different excitations are discussed. A long valley relaxation time of free carriers is discovered. The photocurrent is studied in an h-BN encapsulated monolayer WSe2 device. The generation of photocurrent is observed, and the photocurrent spectroscopy measurement is performed. Moreover, a systematic fabrication method of the h-BN encapsulated monolayer WSe2 device is presented.