Sub-Picosecond Carrier Dynamics Induced by Efficient Charge Transfer in MoTe2/WTe2 van der Waals Heterostructures.

Demonstration of van der Waals (vdW) semiconductor/metal heterostructures (SMHs) based on transition metal dichalcogenides has been a central approach in high-speed electronics by introducing ultrafast carrier dynamics. In this regard, a Weyl semimetal WTe2 is of great interest due to its vdW layered nature, low work function, and superior electrical properties. However, little is still known about its heterostructures, and a few picoseconds photocarrier lifetimes hinder its applications in high-speed electronics. Here, we propose a SMH: semimetallic Td phase WTe2 with its sister compound of semiconducting 2H phase MoTe2. Time-resolved terahertz (THz) spectroscopy demonstrated that WTe2 exhibited the significantly shorter carrier lifetimes of sub-picosecond when forming a junction with MoTe2. We provided explicit characteristic signatures, revealing charge transfer across the interface and the subsequent interlayer exciton decay. This work not only offers the extension of the THz detection scope of ultrafast phenomena from atomically thin materials but also provides a building block of vertical SMHs for high-speed electronic devices with sub-picosecond photocarrier lifetimes.