Impact of band non-parabolicity on the onset voltage in a nanowire tunnel field-effect transistor

The phonon-assisted band-to-band tunneling (BTBT) current has been computed for a cylindrical nanowire tunneling field-effect transistor (TFET) with an all-round gate covering the source region. Although we have considered relatively thick wires, i.e. diameters ranging between 5 and 8 nm, we found that BTBT is considerably affected by the carrier confinement in the radial direction. Therefore, a self-consistent solution of the Schrödinger and Poisson equations must be carried out. For the latter, we have implemented a non-linear variational principle based on the modified local density approximation taking into account non-parabolic corrections for both conduction and valence bands. Our findings show not only that the confinement effects in nanowire TFETs have a stronger impact on the onset voltage of the tunneling current in comparison with their planar counterparts but also that the value of the onset voltage is overestimated when the valence band nonparabolicity is ignored.