Nanometer-scale lateral p-n junctions in graphene/$\alpha$-RuCl$_3$ heterostructures

TL;DR

This study demonstrates the creation of intrinsic nanoscale lateral p-n junctions in graphene/$eta$-RuCl$_3$ heterostructures, revealing their potential for next-generation 2D electronic and plasmonic devices through advanced microscopy and theoretical modeling.

Contribution

It provides experimental evidence and theoretical understanding of sub-3 nm lateral p-n junctions in graphene heterostructures, advancing nanoelectronics and plasmonics.

Findings

Lateral p-n junctions with >0.6 eV band offset over <3 nm scale

Effective in-plane electric field exceeding 10^8 V/m

Validation of plasmonic response modeling with s-SNOM

Abstract

The ability to create high-quality lateral p-n junctions at nanometer length scales is essential for the next generation of two-dimensional (2D) electronic and plasmonic devices. Using a charge-transfer heterostructure consisting of graphene on $\alpha$-RuCl$_3$, we conduct a proof-of-concept study demonstrating the existence of intrinsic nanoscale lateral p-n junctions in the vicinity of graphene nanobubbles. Our multi-pronged experimental approach incorporates scanning tunneling microscopy (STM) and spectroscopy (STS) and scattering-type scanning near-field optical microscopy ($\textit{s}$-SNOM) in order to simultaneously probe both the electronic and optical responses of nanobubble p-n junctions. Our STM and STS results reveal that p-n junctions with a band offset of more than 0.6 eV can be achieved over lateral length scale of less than 3 nm, giving rise to a staggering effective in-plane field in excess of 10$^8$ V/m. Concurrent $\textit{s}$-SNOM measurements confirm the utility of these nano-junctions in plasmonically-active media, and validate the use of a point-scatterer formalism for modeling surface plasmon polaritons (SPPs). Model $\textit{ab initio}$ density functional theory (DFT) calculations corroborate our experimental data and reveal a combination of sub-angstrom and few-angstrom decay processes dictating the dependence of charge transfer on layer separation. Our study provides experimental and conceptual foundations for the use of charge-transfer interfaces such as graphene/$\alpha$-RuCl$_3$ to generate p-n nano-junctions.