Ultrafast carriers' separation imaging in WS2-WSe2 in plane heterojunction by transient reflectivity microscopy

TL;DR

This study uses transient reflectivity microscopy to directly visualize and measure ultrafast charge separation and carrier dynamics at the atomic interface of WS2-WSe2 in-plane heterojunctions, revealing key parameters for device applications.

Contribution

It demonstrates the application of transient reflectivity microscopy for real-time imaging of carrier behavior at nanometer scales in 2D heterojunctions, providing new insights into their electrical properties.

Findings

Electron drift velocity: 30 nm/ps

Hole drift velocity: 10.6 nm/ps

Depletion layer width: 300 nm

Abstract

Carrier transport in nanodevices plays a crucial role in determining their functionality. In the post-Moore era, the behavior of carriers near surface or interface domains the function of the whole devices. However, the femtosecond dynamics and nanometer-scale movement of carriers pose challenges for imaging their behavior. Techniques with high spatial-temporal resolution become imperative for tracking their intricate dynamics. In this study, we employed transient reflectivity microscopy to directly visualize the charge separation in the atomic interface of WS2-WSe2 in-plane heterojunctions. The carriers' drifting behavior was carefully tracked, enabling the extraction of drift velocities of 30 nm/ps and 10.6 nm/ps for electrons and holes. Additionally, the width of the depletion layer was determined to be 300 nm based on the carriers' moving trajectory. This work provides essential parameters for the potential effective utilization of these covalent in-plane heterojunctions,and demonstrates the success of transient optical imaging in unraveling the electrical behavior of nano devices, paving the way for a new avenue of electro-optical analysis.