Quantum Hall effect of self-organized graphene monolayers on the C-face of 6H-SiC
Résumé
We review some of the electric properties of self-organized graphene monolayers on the carbon face of SiC. From sparse surface defects acting as nucleation centres, isolated graphene layers grow in the shape of triangles or ribbons on the step bunched SiC surface. Using e-beam lithography, standard Hall bars have been made. At low magnetic fields, conductance fluctuations, weak localization, electron-electron interactions are usually observed. At higher magnetic fields, the anomalous quantum Hall (QHE) effect typical of monolayer graphene is also observed. In this regime, the breakdown of the QHE appears at moderate currents, which we attribute to the persistence of impurities in the vicinity of the graphene layer. Moderate heating (150 degrees C) is not sufficient to overcome this issue, and moreover, the carrier concentration cannot be controlled. In order to control the carrier concentration, bottom-gated samples are also presented. In these devices, the carrier concentration can be modulated, but the breakdown current remains very small.