Negative magnetoresistance in Ti-cleaned single-layer graphene

Symmetric graphene tunnelingfield-effect transistors (SymFETs) consisting of two independently gated graphene layers separated by a potential barrier have been proposed as a room-temperature resonant tunneling device. In a SymFET, the inelastic-coherent length (L_ϕ) of the electrons is considered to be one of the important characteristic scattering lengths. Weak localization (WL) is a good tool to estimate L_ϕ In this study, the surface of the chemical-vapor- deposited single-layer graphene was Ticleaned after performing the conventional fabrication processes for graphene transistors. We found that the charge-neutral point (V_CNP) shifted to a lower back-gate voltage and the mobility increased owing to Ticleaning. Ti-cleaned Hall bars were investigated at 0.3 K under magnetic fields of up to 14 T. Negative magnetoresistance(MR) appears because of the WL effect, and the MR increases as the back-gate voltage (V_G) approaches V_CNP. From a fitting analysis using the theoretical formulation of WL, we found that L_ϕ was greater than 100 nm and that L_ϕ decreased as V_G approached V_CNP because of electron-hole puddles and electron-electron interaction.