Molecular Doping of Epigraphene for Device Applications

Abstract: Epitaxial graphene grown on silicon carbide, or epigraphene, offers in principle a suitable platform for electronic applications of graphene which require scalable, reproducible, and high-quality material. However, one of the main drawbacks of epigraphene lies in the difficulty in controlling its carrier density, which hinders its usefulness in future applications. To solve this problem, this thesis introduces a novel molecular doping method which utilizes acceptor molecules mixed with a polymer. This combination results in a dopant blend that is simple to apply onto epigraphene, and capable of providing controllable, potent, and homogeneous doping over large areas. This technique opens many different avenues for potential applications, three of which are explored in this work. The doping method was successfully used to create practical graphene quantum resistance standards, based on the quantum Hall effect. It was confirmed by two independent metrology institutes that epigraphene meets the stringent criteria for use in precision measurements of resistance. Doped epigraphene was also used to develop magnetic field sensors. These Hall sensors were shown to rival and even surpass the best graphene-based Hall sensors reported in literature thus far, including record-low magnetic field detection limits at room temperature. These Hall sensors also demonstrated promising performance at high temperatures, with the potential to one day outmatch industrial sensors in the automotive and military temperature ranges. Lastly, doped epigraphene was used to create a proof-of-concept terahertz detector. The devices demonstrated highly sensitive and wide-band coherent detection of terahertz signals, with record-low power consumption requirements. It was found that an optimized device could potentially allow for the creation of detector arrays that can provide quantum limited detection across the entire terahertz range, and revolutionize sensors used in next-generation space telescopes.