The effect of different covalent bond connections and doping on transport properties of planar graphene/MoS/graphene heterojunctions.

The electronic transport properties of in-plane graphene/MoS/graphene heterojunctions are studied using density functional theory and the nonequilibrium Green's function method. It is found that different covalent bond connections cause different electron distributions, such as accumulation or depletion, on the contact surface. The C-S structure exhibits more electron accumulation and depletion, indicating that the electrons can easily transfer from MoS to graphene. Since the three structures all form covalent or ionic bonds, the tunneling barrier for carriers is very small. The C-S structure exhibits a smaller p-type Schottky barrier, indicating that it has better transport properties than the other two structures. We found that the effective doping method can reduce the Schottky-barrier height (SBH), resulting in smaller contact resistance. Thus, the current-voltage curves of the undoped and doped C-S structures exhibit rectification and approximately linear characteristics under a given bias, which agrees with experimental reports. These results provide insight for designing high-performance devices.