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

Abstract

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 ( ${V}_{\text {ds}}$ ) can sustain impact ionization and limit BTBT, thereby balancing the conflicting requirements of ${J}\cdot {E}$ 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 ( $\text {10}^{\text {$-10$}}\text{A}$ ) at ${V}_{\text {ds}} = \text {0.9}$ V. Results highlight new viewpoints for the design optimization of steep-switching Ge JL MOSFETs.