Ultrafast Charge Transfer Mechanism in Van der Waals Heterostructures of Topological Insulators with 2D Materials

Abstract

Hybridizing topological materials (TM) with twodimensional (2D) materials has resulted in interesting structures, such as van der Waals heterostructures (vdW), having potential in optoelectronics. However, the performance of devices made out of such structures relies on the charge carrier interactions among the layers, which establishes the basic trade-off between the kinetically controlled charge carrier dynamics at the interface and the performance of vdW-based devices. In this perspective, three vdW are fabricated using a wet transfer technique, and the structures are probed to study the charge carrier and phonon dynamics among the TM (a few layered Bi 2 Te 3 ) and 2D systems. The three different vdW fabricated in this article are graphene/Bi 2 Te 3 (G/BT), fluorographene/Bi 2 Te 3 (FG/BT), and monolayer MoS 2 /Bi 2 Te 3 (MS/BT). Raman spectroscopy establishes the formation of all of these vdW and indicates the occurrence of the charge transfer (CT) phenomenon among them, which is further probed using ultrafast pump−probe spectroscopy. The charge carrier and phonon dynamics reveal the presence of the occurrence of the CT mechanism in all of the vdW. These spectra are further used to model the bands between different types of heterointerfaces, such as the Schottky junction between graphene and Bi 2 Te 3 and the type II heterojunction between FG/BT and MS/BT. With the help of band alignment and charge carrier and phonon dynamics studies presented, a unique CT mechanism and excitonic peak tunability in vdW are proven, where such information is essential in developing highly sensitive optoelectronic and spintronic devices