Thermally activated double-carrier transport in epitaxial graphene on vanadium-compensated 6H-SiC as revealed by Hall effect measurements

Abstract

In this report we demonstrate the results of charge carriers transport studies in graphene using a Hall effect sensor fabricated on quasi-free-standing monolayer graphene grown on a semi-insulating on-axis vanadium-compensated 6H-SiC(0001) substrate in an epitaxial Chemical Vapor Deposition process. The sensor is passivated with aluminum oxide through atomic layer deposition and offers current-mode sensitivity of 140 V/AT with thermal stability of − 0.02%/K within the range between 80 and 573 K. The electrical properties of the graphene layer are determined as a function of temperature ranging from 300 to 770 K. High-temperature characteristics of passivated and not passivated graphene are compared and their profiles explained through a double-carrier transport involving the spontaneous-polarization-induced holes in the graphene layer and the thermally activated electrons from a shallow donor level of nitrogen in the quasi-cubic (k1) site and a deep acceptor level of vanadium in the hexagonal (h) site both present in the bulk of the vanadium-compensated SiC substrate. Finally, we conclude that this mechanism is directly responsible for the limitation of the thermal stability of the sensor's current-mode sensitivity.