Sub-ps thermionic electron injection effects on exciton-formation dynamics at a van der Waals semiconductor/metal interface

TL;DR

This study investigates how sub-picosecond thermionic electron injection from gold into WS2 influences exciton formation, revealing ultrafast charge transfer effects crucial for optoelectronic device development.

Contribution

It provides the first experimental insights into ultrafast hot electron injection effects on exciton dynamics at a van der Waals semiconductor/metal interface.

Findings

Ultrafast hot electron injection significantly alters exciton formation.

Delay and fluence control the charge transfer dynamics.

Implications for ultrafast optoelectronic device design.

Abstract

Inorganic van der Waals bonded semiconductors like transition metal dichalcogenides are subject of intense research due to their electronic and optical properties which are promising for next-generation optoelectronic devices. In this context, understanding the ultrafast carrier dynamics, as well as charge and energy transfer at the interface between metals and semiconductors is crucial and yet quite unexplored. Here, we present an experimental study on how thermally induced ultrafast charge carrier injection affects the exciton formation dynamics in bulk WS2 by employing a pump-push-probe scheme, where a pump pulse induces thermionic injection of electrons from the gold substrate into the conduction band of the semiconductor, and another delayed push pulse excites direct transitions in the WS2. The transient response shows different dynamics on the sub-ps timescale by varying the delay between pump and push pulses or by changing the pump fluence, thus disclosing the important role of ultrafast hot electron injection on the exciton formation dynamics. Our findings might have potential impact on research fields that target the integration of ultrafast optics at the boundary of photonics and electronics, as well as in optically-driven CMOS and quantum technologies.