Transferred Monolayer And Ab Stacked Bilayer (0001) Sic Epitaxial Graphene
Graphene is a leading two dimensional (2D) material with good technological potential. Currently, it is being scaled up in synthesis methods in order to meet future demands in technology markets. In this dissertation, a study of transferred epitaxial graphene (TEG) as a synthesis method, for large area monolayer and AB stacked bilayer Graphene, is presented. Monolayer epitaxial graphene (EG) is grown on the (0001) face of silicon carbide (SiC) in an argon atmosphere at a temperature of 1600 o C. Bilayer graphene can thereafter be synthesized if needed by intercalating the monolayer in a 100% hydrogen flow at 1050 oC to release what is known as the "buffer layer" into another graphene layer forming a bilayer. Either form of graphene can subsequently be transferred off the SiC substrate to mitigate the negative effects of the substrate. We develop a transfer process based on a gold adhesion layer and demonstrate for the first time, the transfer of high quality monolayer transferred epitaxial graphene (MTEG) and AB stacked bilayer transferred epitaxial graphene (BTEG). We use Raman characterization methods to determine the number and quality of graphene layers as well as orientation for bilayers which was made possible by contrast enhancement upon substrate transfer. We report these characteristics for the first time. Extensive structural characterization that have never been done before and were made possible by the successful transfer procedure, are presented in the Transmission Electron Microscopy (TEM) section. We successfully show suspended MTEG and BTEG samples which was never shown in literature before. We fabricate Transmission Line Measurement (TLM) structures to study the quality of the contact resistance for MTEG and BTEG. We report values in the range of 600 [OMEGA].[MICRO SIGN]m for MTEG and 2400 [OMEGA].[MICRO SIGN]m for BTEG. We also fabricate Field Effect Transistors (FETs) to study the field effect mobility and carrier concentration of MTEG and BTEG. We report average room temperature field effect mobility values of around 1700 cm2/V.s with best value of 2800 cm2/V.s for MTEG. This is over two times gain in mobility before transfer and is competitive with current leading synthesis methods. We measured the room temperature field effect mobility of BTEG to be 250 cm2/V.s on average and with a best value of 335 cm2/V.s. To the knowledge of the author, there are no reports in literature on the measured mobility of BTEG. We carry out annealing studies at argon ambient of 300 oC for TEG and show unique properties for BTEG in which a demonstrated ten orders of magnitude, higher moisture absorption than MTEG is shown. A section in this dissertation will be dedicated to related work on chemical vapor deposition (CVD) hexagonal boron nitride (h-BN) which is a complimentary 2D material to graphene. Improvements on CVD growth by electropolishing the copper substrate will be demonstrated where root mean square (RMS) surface roughness of starting material is reduced from 177 nm to 12 nm, considerably improving subsequent h-BN CVD growth. A procedure for the transfer of CVD graphene onto CVD h-BN as well as fabrication of Van der Paw structures will be presented. We show initial results of improvements in mobility when CVD h-BN is used as a substrate for CVD graphene.
epitaxial graphene; AB stack; transferred
McEuen,Paul L.; Kan,Edwin Chihchuan
Ph. D., Electrical Engineering
Doctor of Philosophy
dissertation or thesis