Improvement of Contact Resistance of Graphene Devices Via AuCl3 Doping

Abstract

Graphene, an atomically thin semi-metal with sp2–bonded carbon atoms arranged in a honeycomb lattice is at center stage of intense research in the field of fundamental physics as well as in low-cost flexible transparent electronics, photovoltaics or microelectronics devices. For electronic devices application, the metal - graphene contact resistance is forefront obstacles hindering further progress of any graphene-based devices. The contact resistance degrades the on-state current of charge-based field-effect-transistor. Gold chloride (AuCl3) doping has been reported for reducing the sheet resistance of graphene films for transparent electrodes. In this work, we used the gold chloride (AuCl3) solution doping only to the metal-graphene contact area to reduce the contact resistance without changing graphene film properties. First, graphene film was grown using chemical vapor deposition (CVD) method. Active pattern was formed by lithography and reactive ion etching (RIE). The metal-graphene pad area was defined by lithography. The exposed graphene surface area for metal pads was dipped in AuCl3 solution. Here we changed the AuCl3 concentration to see the concentration effect. After that, Ti/Au pad metal was evaporated using thermal evaporator. AuCl3 doping was done only to metal-graphene contact interface. KPFM was employed to measure the surface potential of graphene. The Raman spectroscopy and XPS spectra were analyzed before/after the doping of AuCl3 solution on contact area. The contact resistance of un-treated graphene devices, 1773 Ohm.um decreased to 987 Ohm.um after 5mM-treatment, and decreased to 897 Ohm.um after 10mM-AuCl3 doping. At doping above 10mM doping, the contact resistance did not decreased further. We also characterized the contact resistance change with time. The contact resistance of AuCl3-treated graphene increased by ~13% after 2 months. On the contrary, the sheet resistance of AuCl3-treated graphene film(without any photomask) increased by ~50% after 1 month. The contact resistance increase is much less than the sheet resistance change. This could be explained by the fact that the metal pad covers the AuCl3. This research was supported by the MOTIE (10052928) and KSRC (Korea Semiconductor Research Consortium) support program for the development of future semiconductor devices.