Steep-Switching Germanium Junctionless MOSFET With Reduced OFF-State Tunneling

In this paper, we report on the reduction of the off-state band-to-band tunneling (BTBT) while maintaining sub-60 mV/decade switching in Germanium (Ge) Junctionless (JL) transistor through well-calibrated simulations. Recognizing the product of current density (J) and electric field (E) to be the key generic parameter governing device optimization, it is shown that a device with thicker film operated at lower drain bias (Vds) can sustain impact ionization and limit BTBT, thereby balancing the conflicting requirements of J · E for tunneling and impact ionization. An optimal workfunction and gate-to-drain underlap of 5 nm in Ge JL MOSFET can further suppress BTBT while achieving a subthreshold swing of ~5 mV/decade with nearly four decades of steep current transition at the threshold voltage along with a low off-current (10
^-10
A) at V
_ds
= 0.9 V. Results highlight new viewpoints for the design optimization of steep-switching Ge JL MOSFETs.