Self-aligned graphene field effect transistors with surface transfer doped source/drain access regions
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Since its discovery in 2004, graphene has been widely touted as a potential replacement for silicon in the next generation of electronic circuits owing to its exceptionally high carrier mobilities and its ultra-thin body. Graphene field effect transistors (GFETs) show promising potential for use in analog and radio frequency (RF) applications, with theoretically predicted THz frequencies only being limited by fabrication challenges. High series resistance of the source/drain access regions in a GFET is one such major factor responsible for performance degradation. In this thesis, a simple and straightforward scheme of reducing this resistance by self-aligned spin-on-doping of graphene using surface transfer dopants is presented. Back-gated GFETs were fabricated on Si/SiO2 and doped using various surface transfer dopants. A novel method of spin-on-doping graphene using poly(ethyleneimine) (PEI) was developed. Top-gated GFETs with mobilities up to 6,900 cm2/Vs were fabricated and their access regions were spin-on-doped in a self-aligned manner offering a 3X reduction in the series resistance. GFET drive currents improved by up to 4X and transconductances up to 3X after self-aligned doping. GFETs were also fabricated on insulating quartz substrates with mobilities up to 5,600 cm2/Vs and showed performance enhancements up to 2X after self-aligned doping.