Electronic structure evolution and exciton energy shifting dynamics in WSe₂: from monolayer to bulk

Abstract

Exciton related processes in two-dimensional (2D) transition metal dichalcogenides (TMDCs) play important roles in their optoelectronic applications. In this work, through broadband transient absorption spectroscopy, the electronic band structure evolution, exciton energy shifting dynamics and power-dependence spectral characteristics of WSe2 layers, including monolayer, bilayer, tri-layer and bulk WSe2 under 400 nm and 800 nm excitations are investigated. Particularly, under 400 nm excitation, due to the hot-exciton effect, the A-exciton energy shifting dynamics in WSe2 layers have been analysized in detail, where thicker WSe2 samples possess slower hot-exciton cooling lifetimes, and the exciton recombination approaches are affected by the band structure and interlayer interactions, in comparison with that under 800 nm excitation. The power-dependence spectral evolution in WSe2 layers suggests that the charged states like trions could be facilitated in tri-layer WSe2 (or thicker samples) at the same experimantal conditions. These findings in WSe2 layers could provide a deep insight into the hot-exciton related processes in 2D TMDCs from transient experiments ponit of view.

Electronic state evolution of oxygen-doped monolayer WSe2 assisted by femtosecond laser irradiation

“…A-exciton and B-exciton states are the band-edge states due to the spin–orbital splitting at the K point, A′-exciton state is related to the high-energy excited-state levels of the A-exciton state, and the C-exciton state is originated from the band-nesting region in the band structure. 35–38 For the IFsLI treatment, the IFsLI case 1 represents a moderate modification for monolayer WSe 2 . And the IFsLI case 2 represents a strongly modified result for monolayer WSe 2 .…”

Ultrafast dynamics of spin relaxation in monolayer WSe2 and the WSe2/graphene heterojunction

“…Circularly polarized femtosecond pump-probe system setup 37,38 In all TA experiments, a circularly polarized femtosecond transient absorption system was used to detect monolayer WSe 2 and WSe 2 /graphene heterojunction samples. First, the 800 nm pump pulse with a frequency of 250 Hz is divided into two beams.…”