  In this work, device performances of tunneling field effect transistors
(TFETs) based on phosphorene are explored via self-consistent atomistic quantum
transport simulations. Phosphorene is an ultra-thin two-dimensional (2-D)
material with a direct band gap suitable for TFETs applications. Our simulation
shows that phosphorene TFETs exhibit subthreshold slope (SS) below 60 mV/dec
and a wide range of on-current depending on the transport direction due to
highly anisotropic band structures of phosphorene. By benchmarking with
monolayer MoTe2 TFETs, we predict that phosphorene TFETs oriented in the small
effective mass direction can yield much larger on-current at the same
on-current/off-current ratio than monolayer MoTe2 TFETs. It is also observed
that a gate underlap structure is required for scaling down phosphorene TFETs
in the small effective mass direction to suppress the source-to-drain direct
tunneling leakage current.
