Carbon Vacancy Assisted Contact Resistance Engineering in Graphene FETs

Despite various remarkable properties, the state of the arts of graphene devices are still not up to the mark due to their high contact resistance. The contact resistance milestone has not been achieved yet, probably due to ambiguity in understanding graphene–metal contact properties. In this work, we did a systematic investigation of palladium–graphene contact properties using a density functional theory (DFT) and various process-based experimental approaches. Our study reveals significant interaction of palladium (Pd) with graphene. Their orbitals overlap leads to potential barrier lowering at the interface, which can be reduced further by bringing graphene closer to the bulk Pd using carbon vacancy engineering at the contacts. Thus, the carbon vacancy-assisted barrier modulation reduces contact resistance by increasing carrier transmission probabilities at the interface. The theoretical findings have been emulated experimentally by carbon vacancy engineering at the graphene field-effect transistors (FETs). Different contact-engineered graphene devices with Pd contacts show significant contact resistance reduction, measuring as low as
$\sim 78~\Omega ~\cdot ~\mu \text{m}$
at room temperature. The contact resistance shows a “V” shape curve as a function of defect density. Also, the optimum contact resistance achieved is significantly lower than their pristine counterpart, as predicted by the theoretical estimates. Due to contact engineering,
${I_{{ \mathrm{\scriptscriptstyle ON}}}}$
improves by
$\sim 6\times $
, transconductance by
$\sim 8\times $
, and device mobilities by
$\sim 6\times $
in the device FETs. These investigations and understanding can help to boost the performance of graphene FETs, especially for high-frequency RF applications.