  Schottky barrier field-effect transistors (SBFETs) based on few and mono
layer phosphorene are simulated by the non-equilibrium Green's function
formalism. It is shown that scaling down the gate oxide thickness results in
pronounced ambipolar I-V characteristics and significant increase of the
minimal leakage current. The problem of leakage is especially severe when the
gate insulator is thin and the number of layer is large, but can be effectively
suppressed by reducing phosphorene to mono or bilayer. Different from
two-dimensional graphene and layered dichalcogenide materials, both the
ON-current of the phosphorene SBFETs and the metal-semiconductor contact
resistance between metal and phosphorene strongly depend on the transport
crystalline direction.
