Résumé:

Graphene on silicon carbide is a promising material for applications in metrology. The best conditions are achieved for low doping but standard gating techniques usually degrade the electron mobility in these devices. As a consequence, very few transport measurements at low-doping have been reported so far. We present a technique to control the graphene doping without degrading its quality. Magnetotransport measurements near the charge neutrality point allow us to 1) quantify the disorder; 2) demonstrate an ambipolar quantum Hall effect which we explain in terms of an inhomogeneous disorder distribution; and 3) observe giant nonlocal resistances whose origin is currently under study.