[13a-A401-1~11] 17.2 Graphene

▲ [13a-A401-11] Graphene PN junction formation by asymmetric work function of metal contacts

〇(PC)Ahmed HAMMAM^1,2, Manoharan Muruganathan¹, Hiroshi Mizuta^1,3 (1.JAIST, 2.Minia Univ, 3.Hitachi Cambridge Laboratory)

Keywords:Graphene, PN junction, Metal Work function

Graphene is a zero band gap two dimensional (2D) material with superior electronic properties. Since conventional chemical doping techniques of carbon-based nanostructures are challenging due to the strong C-C bonds in GNRs. Electrostatic doping is the main technique to realize graphene PN junction. However, electrostatic doping enhance carrier scattering in the area underneath the controlling gate. Furthermore, electrostatic gating increases the number of required electrodes to control the device characteristics, which leads to more fabrication complications. Here we propose a PN junction engineering by utilizing work function difference between graphene (~ 4.5 eV ) and metal contacts. Both simulation and experimental work showed that work function difference introduce doping to graphene sheet underneath the metal [1,2]. Additionally, the charge doping effect can extend to the channel as well. Therefore, Graphene PN junction can be realized by introducing asymmetric work function metal-contacts.
In this work, we used Nickel ( work function of 5.01 eV) and Aluminum (work function of 3.9 eV) as a metal contacts for source and drain electrodes. Due to its high work function, Nickel (Ni) known to introducec P-type doping and form chemical bond with Graphene [2], However, Aluminum (Al) with lower work function, expected to introduce N-type doping. Three groups of devices are fabricated ( Al-Al, Ni-Ni, and Al-Ni) using Electron beam lithography (EBL) - Lift-off technique.