Pronounced scale-dependent charge carrier density in graphene quantum Hall devices

TL;DR

This paper investigates how the size of graphene quantum Hall devices affects carrier density and performance, revealing scale-dependent effects that inform the design of miniaturized resistance standards.

Contribution

It uncovers a pronounced scale-dependent carrier density in graphene Hall devices and uses machine learning to optimize device geometry for improved performance.

Findings

Carrier density decreases with width under electron doping

Carrier density increases with width under hole doping

Optimal device width identified around 360 micrometers

Abstract

The miniaturization of quantum Hall resistance standards (QHRS) using epitaxial graphene on silicon carbide necessitates understanding how device dimensions impact performance. This study reveals a pronounced scale-dependent carrier density in graphene Hall devices: under electron doping, carrier density decreases with increasing channel width (Wd), while the opposite occurs under hole doping. This phenomenon, most significant for Wd less than 400 um, directly influences the onset of magnetic field required for quantization. Fermi velocity measurements and angle-resolved photoemission spectroscopy (ARPES) analysis indicate that band structure modifications and electron-electron interactions underlie this size dependence. Utilizing machine learning with limited data, we optimized the device geometry, identifying a channel width of ~360 um as the optimal balance between resistance uncertainty and on-chip integration density. This work provides key insights for designing high-performance, miniaturized graphene-based QHRS arrays.