13. November 2025

In his latest IEEE EDL publication, GTS scientist Lee-Chi Hung unveils new insights into on-current degradation mechanisms in ultra-scaled NSFETs featuring S/D underlap doping.

Using the Subband Boltzmann Transport Equation (SBTE) solver, the study demonstrates that underdoped S/D extensions degrade the on-current due to the formation of secondary barriers beyond the gate’s control. These barriers enhance non-equilibrium transport even in the linear regime, resulting in ID,lin saturation and causing additional on-current degradation in ID,sat. Notably, since conventional drift-diffusion (DD) simulations fail to capture this effect, it may have been previously misattributed to parasitic contact resistance. These insights offer guidance for optimizing S/D underlap doping profiles, highlighting the need to avoid excessive Gate-S/D overlap capacitance while preventing on-current degradation.

Open Access Paper

We have chosen to make the paper available through Open Access because we feel it’s important to support the free exchange of ideas. The paper is available through IEEE Xplore (DOI: 10.1109/LED.2025.3614369)

Read more about the underlying transport physics of underlap devices and explore our application examples. Please don’t hesitate to contact us directly for specific inquiries.

All covered in GTS Framework

All simulations in this work were done using the SBTE solver as part of our Nano Device Simulator (NDS) and our DD solver (Minimos-NT) available within the GTS Framework.

Carrier and current spectra along the channel
(a, c) Carrier and (b, d) current spectra along the channel, extracted at Vgs = 0.7 V and Vds = 0.05 V. The effective ground-state energy (white) and electron quasi-Fermi energy (red) are indicated by dashed lines in each figure. While (a, b) show that the current spectrum follows the band edge where ninversion peaks, (c, d) illustrate that ninversion no longer contributes to carrier conduction.
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