Epitaxial graphene on SiC: Modification of structural and electron transport properties by substrate pretreatment

TL;DR

This study demonstrates that substrate pretreatment of SiC significantly influences the structural and electronic properties of epitaxial graphene, with argon conditioning yielding superior quality suitable for quantum resistance standards.

Contribution

It introduces a novel high-temperature argon conditioning method for SiC substrates that improves graphene quality and electronic properties compared to hydrogen etching.

Findings

Argon conditioning reduces macro steps and enhances graphene uniformity.

Graphene exhibits excellent quantum Hall resistance matching theoretical values.

The method produces graphene suitable for quantum electrical standards.

Abstract

The electrical transport properties of epitaxial graphene layers are correlated with the SiC surface morphology. In this study we show by atomic force microscopy and Raman measurements that the surface morphology and the structure of the epitaxial graphene layers change significantly when different pretreatment procedures are applied to nearly on-axis 6H-SiC(0001) substrates. It turns out that the often used hydrogen etching of the substrate is responsible for undesirable high macro steps evolving during graphene growth. A more advantageous type of sub-nanometer stepped graphene layers is obtained with a new method: a high-temperature conditioning of the SiC surface in argon atmosphere. The results can be explained by the observed graphene buffer layer domains after the conditioning process which suppress giant step bunching and graphene step flow growth. The superior electronic quality is demonstrated by a less extrinsic resistance anisotropy obtained in nano-probe transport experiments and by the excellent quantization of the Hall resistance in low-temperature magneto-transport measurements. The quantum Hall resistance agrees with the nominal value (half of the von Klitzing constant) within a standard deviation of 4.5*10(-9) which qualifies this method for the fabrication of electrical quantum standards.