title: Opening an electrical band gap of bilayer graphene with molecular doping.
abstract: The opening of an electrical band gap in graphene is crucial for its application for logic circuits. Recent studies have shown that an energy gap in Bernal-stacked bilayer graphene can be generated by applying an electric displacement field. Molecular doping has also been proposed to open the electrical gap of bilayer graphene by breaking either in-plane symmetry or inversion symmetry; however, no direct observation of an electrical gap has been reported. Here we discover that the organic molecule triazine is able to form a uniform thin coating on the top surface of a bilayer graphene, which efficiently blocks the accessible doping sites and prevents ambient p-doping on the top layer. The charge distribution asymmetry between the top and bottom layers can then be enhanced simply by increasing the p-doping from oxygen/moisture to the bottom layer. The on/off current ratio for a bottom-gated bilayer transistor operated in ambient condition is improved by at least 1 order of magnitude. The estimated electrical band gap is up to ∼111 meV at room temperature. The observed electrical band gap dependence on the hole-carrier density increase agrees well with the recent density-functional theory calculations. This research provides a simple method to obtain a graphene bilayer transistor with a moderate on/off current ratio, which can be stably operated in air without the need to use an additional top gate.
authors.affiliation: Research Center for Applied Sciences, Academia Sinica, Taipei, 11529, Taiwan.
authors.forename: Wenjing
authors.initials: W
authors.lastname: Zhang
authors.forename: Cheng-Te
authors.initials: CT
authors.lastname: Lin
authors.forename: Keng-Ku
authors.initials: KK
authors.lastname: Liu
authors.forename: Teddy
authors.initials: T
authors.lastname: Tite
authors.forename: Ching-Yuan
authors.initials: CY
authors.lastname: Su
authors.forename: Chung-Huai
authors.initials: CH
authors.lastname: Chang
authors.forename: Yi-Hsien
authors.initials: YH
authors.lastname: Lee
authors.forename: Chih-Wei
authors.initials: CW
authors.lastname: Chu
authors.forename: Kung-Hwa
authors.initials: KH
authors.lastname: Wei
authors.forename: Jer-Lai
authors.initials: JL
authors.lastname: Kuo
authors.forename: Lain-Jong
authors.initials: LJ
authors.lastname: Li