Epitaxial Graphene Technology for Quantum Metrology

Doctoral thesis, 2015

Graphene grown on silicon carbide by high-temperature annealing (SiC/G) is a strong contender in the race towards large-scale graphene electronics applications. The unique electronic properties of this system lead to a remarkably robust and accurate Hall resistance quantisation of 0.1 parts per billion, making SiC/G devices highly desirable for the endeavour of quantum resistance metrology. However, major challenges for this technology remain, such as control of the charge carrier density and reproducibility of material growth and device properties. The main aims of the work presented in this Thesis are to understand and improve the performance and reproducibility of SiC/G devices for quantum Hall resistance metrology. Moreover, in this work we developed further understanding of material issues such as the homogeneity of SiC/G for applications in quantum metrology, and ultimately wafer scale electronics. By correlating the nanoscopic growth features of SiC/G with electron transport measurements, we were able to reveal the wafer scale electronic homogeneity of monolayer graphene grown on SiC. We developed disparate gating methods to enable quantum Hall effect at lower magnetic fields (B = 2-5 T) and to study electron transport close to charge neutrality, useful for metrology. We investigated the role of the reconstructed SiC morphology and bilayer graphene inclusions on the reproducibility of nominally monolayer graphene quantum Hall devices, and reveal the important consequences for quantum resistance metrology. The above-mentioned studies were assisted by the development of optical microscopy methods to accurately identify single and multilayer domains of epitaxial graphene in addition to the nanoscopic details of the reconstructed SiC surface. This was found to be an important step of rapid and non-invasive quality control leading to improved device performance and reproducibility for quantum metrology applications. While the focus has been placed on quantum metrology devices, the findings and technologies developed in this Thesis work are readily applicable to investigate other two-dimensional materials and graphene systems, in both research and industrial environments.