Charge Transport On Low Dimensional Field Effect Transistors: Effects Of Interface Effects On Metal Gate Electrodes

Two-dimensional(2D) materials are attractive components of atomic-layer field-effect transistors(FETs), sensors, and photovoltaic and photoelectric devices.In this paper, using the density functional theory and non-equilibrium Green function is the combination of the quantum transport methods, studied the effect of interface between metal gate electrode and two-dimensional material on the FET, mainly have the following conclusions:1.Using the first-principles nonequilibrium Green's function method, we study effects of Cu and Ni@Cu used as the Cu-based gate electrode on the charge transport of graphene in the FET. We find that the transmission of graphene decreases with both Cu and Ni@Cu absorbed in the scatter region. And especially, noticeable transmission gaps are in presence around the Femi level. We find that both Cu(111)and Ni@Cu depress the transmission of graphene. In particular, transmission gaps of0.55 e V and 0.45 eV around the Femi level are induced by the Cu(111) in both armchair and zigzag directions. The Ni@Cu enlarges the gap in armchair direction to0.6 e V, but does little in zigzag direction. The transmission gaps are still effective,and considerable cut-off regions are found under the non-equilibrium environment.The Ni@Cu depresses the transmission of graphene more seriously than the Cu, and enlarges the transmission gap in armchair direction. The effects on the charge transport are attributed to the redistribution of electronic states of graphene. Both Cu and Ni@Cu induce the localization of states, so as to block the electronic transport.The Ni@Cu transforms the interaction between graphene and gate electrode from the physisorption to the chemisorption, and then induces more localized states, so that the transmission decreases further. Our results suggest that besides being used to impose gate voltage, the Cu-based gate electrode itself will have a considerable effect on the charge transport of graphene and induces noticeable transmission gap in the FET.2.Using the first-principles calculation, we study the interface effects between phosphorene and metal(Al,Au,Ag,Co,Ni) on the band structure of phosphorene. In comparation with graphene, graphite and TMOs, the interaction between phosphorene and metal is much stronger. According to the bonding level and the hybridization degree of ML phosphorene band structure, two classes are reveals:(1) weak chemical bonding is formed for ML phosphorene on Al, Ag and Au electrodes with smallerbinding energy and farther interlayer distance, the configuration of ML phosphorene is preserved, while(2)strong chemical bonding is formed for ML phosphorene on Co,Ni with larger binding energy, closer interlayer distance, and destroy of ML phosphorene configuration, so the initial configurations of ML phosphorene on Co and Ni interface have little effect on relaxed configuration. These studies provide the theoretical guidance for the future research of the phosphorene nano-devices which cover the metal of the phosphorene.