  Using self-consistent quantum transport simulation on realistic devices, we
show that InAs band-to-band Tunneling Field Effect Transistors (TFET) with a
heavily doped pocket in the gate-source overlap region can offer larger ON
current and steeper subthreshold swing as compared to conventional tunneling
transistors. This is due to an additional tunneling contribution to current
stemming from band overlap along the body thickness. However, a critical
thickness is necessary to obtain this advantage derived from 'vertical'
tunneling. In addition, in ultra small InAs TFET devices, the subthreshold
swing could be severely affected by direct source-to-drain tunneling through
the body.
