Drain Work-Function-Engineered Electrically Doped PNPN Tunnel Field-Effect Transistor for Ambipolar Current Suppression

This paper proposes a drain work-function-engineered electrically doped PNPN tunnel field-effect transistor (ED-TFET) to suppress ambipolar conduction while reducing parasitic gate-drain coupling. The key novelty is a split drain polarity gate that electrostatically forms a graded N+ drain using two serial segments with different work functions: a channel-adjacent high-work-function segment (4.6 eV) and a drain-contact-side low-work-function segment (4.5 eV). This dual-work-function arrangement reshapes the drain-side carrier distribution and widens the channel-drain tunneling barrier under negative control-gate bias, which effectively suppresses ambipolar conduction. At VDS = 0.6 V, the proposed device reduces the ambipolar current at VCG = −0.6 V from 1.0 × 10–13 A/μm (conventional single-segment drain polarity gate) to 2.26 × 10–19 A/μm, while maintaining a high ON-current of 2.02 × 10–7 A/μm at VCG = 0.6 V and an ultra-low OFF-current of 3.38 × 10–19 A/μm at VCG = 0 V. The device achieves SSavg = 25.2 mV/dec and improves fT, max to 39.7 GHz. Parametric optimization of the channel-adjacent drain segment length and work function identifies a design window that maximizes the suppression of ambipolar conduction without sacrificing ON-state drive current.