Spatiotemporal Imaging of Thickness-Induced Band Bending Junctions

TL;DR

This paper introduces a new type of semiconductor junction called a 'band bending junction' in Van der Waals materials, demonstrating how thickness variations can control carrier dynamics and enable novel electronic and optoelectronic devices.

Contribution

It reports the discovery and characterization of a thickness-dependent band bending junction in MoS2, using advanced microscopy and simulations to reveal its properties.

Findings

Lateral surface potential differences depend on MoS2 thickness.

Band bending junctions enable lateral charge separation.

Potential for new devices based on thickness variation rather than doping.

Abstract

Van der Waals materials exhibit naturally passivated surfaces and can form versatile heterostructures, enabling observation of carrier transport mechanisms not seen in three-dimensional materials. Here we report observation of a "band bending junction", a new type of semiconductor homojunction whose surface potential landscape depends solely on a difference in thickness between the two semiconductor regions atop a buried heterojunction interface. Using MoS2 on Au to form a buried heterojunction interface, we find that lateral surface potential differences can arise in MoS2 from the local extent of vertical band bending in thin and thick MoS2 regions. Using scanning ultrafast electron microscopy, we examine the spatiotemporal dynamics of photogenerated charge carriers and find that lateral carrier separation is enabled by a band bending junction, which is confirmed with semiconductor transport simulations. Band bending junctions may therefore enable new electronic and optoelectronic devices in Van der Waals materials that rely on thickness variations rather than doping to separate charge carriers.