Graphene Nanoelectronics - From Synthesis to Device Applications.

Abstract

Nanotechnology is the pinnacle of the scientific effort to breach the dimensional limit in matter. Every now and then, this technology offers us a rare glimpse into the true potential of a common material. Graphite, a material found in pencils, has been used by humans since the 4th millennium BC. When atomic particles in graphite are confined in the two-dimensional nanoscale limit, these quasiparticles enter an exclusive domain of relativistic electron theory of the Dirac equation. This single atomic sheet of carbon atoms that provides the confinement is called graphene. In this thesis, we present research efforts to harness the extraordinary attributes of graphene and explore new possibilities in the field of nanoelectronics. First, the importance of bilayer graphene and its tunable bandgap is discussed. For the first time, a rational route to synthesize wafer scale bilayer graphene is investigated using a low-pressure chemical vapor deposition (LPCVD) method. Subsequently, the existence of tunable bandgap devices are confirmed with cryogenic carrier transport measurements from dual-gate bilayer graphene transistors. We further explore the feasibility of a bilayer graphene-based, flexible, transparent conductor, and confirm the efficiency and the exceptional mechanical robustness of the material. Next, we report flexible and transparent all-graphene circuits for binary and quaternary digital modulations for the first time. Importantly, the entire modulator circuits are fabricated with graphene only, and this monolithic structure allows unprecedented mechanical flexibility and near-complete transparency. By exploiting the ambipolarity and the nonlinearity in graphene transistors, we achieved quadrature phase shift keying (QPSK) using just two graphene transistors, representing a drastic reduction in circuit complexity when compared with conventional silicon-based modulators. Lastly, we address the shortcomings of small gain in conventional graphene transistors by designing the very first graphene heterostructure bipolar junction transistor. The exploitation of graphene's low density of states and tunable Fermi level leads to graphene-semiconductor junctions with higher emitter injection efficiency compared to that of a conventional Schottky junction. This property is utilized for the invention of a graphene-based bipolar junction transistor with high on/off ratio(>100,000) and current gain (>33).