  Black phosphorus (BP) tunneling transistors (TFETs) using heterojunction (He)
are investigated by atomistic quantum transport simulations. It is observed
that edge states have a great impact on transport characteristics of BP
He-TFETs, which result in the potential pinning effect and deteriorate the gate
control. While, on-state current can be effectively enhanced by using hydrogen
to saturate the edge dangling bonds in BP He-TFETs, in which edge states are
quenched. By extending layered BP with a smaller band gap to the channel region
and modulating the BP thickness, device performance of BP He-TFETs can be
further optimized and fulfill the requirements of the international technology
road-map for semiconductors (ITRS) 2013 for low power applications. In 15 nm
3L-1L and 4L-1L BP He-TFETs along armchair direction on-state current can reach
above 10$^3$ $\mu$A/$\mu$m with the fixed off-state current of 10 $pA/\mu$m. It
is also found that ambipolar effect can be effectively suppressed in BP
He-TFETs.
