TFETs

A tunnel field-effect transistor (TFET) is a type of transistor in which the primary conduction mechanism is band-to-band tunneling through a p–n junction under the control of a gate electrode. Unlike conventional metal–oxide–semiconductor FETs, which rely on thermionic emission over a barrier, TFETs modulate current by changing the tunneling probability via gate-induced band bending. Structures typically feature a doped source and drain separated by a channel, with a gate that controls the depletion region.

Operation: In the off state the tunneling current is suppressed by a wide depletion region; when a gate voltage shifts the bands to align the source valence band with the channel conduction band, band-to-band tunneling increases, producing current. The subthreshold slope can in principle be steeper than 60 mV/dec at room temperature, enabling lower supply voltages and reduced power, but practical devices often deviate due to traps and leakage.

Variants: Homojunction TFETs use the same material for source, channel, and drain, while heterojunction TFETs (HJT) employ abrupt material changes at the source/channel interface to enhance tunneling. Materials include III–V and Ge combinations, as well as two-dimensional material implementations. Architectures include gate-all-around nanowire or fin structures and vertical TFETs.

Advantages and challenges: TFETs promise steep subthreshold slope and low-power operation, but typically suffer from comparatively low on-current, higher contact and resistance challenges, device-to-device variability, and sensitivity to traps and defects. Material quality, interface engineering, and scalable fabrication are active research areas.

History and outlook: TFET concepts emerged in the late 20th century, with experimental demonstrations in the 2000s and renewed progress in the 2010s through heterojunction and 2D-material approaches. Ongoing work seeks to improve drive current while preserving steep-slope behavior for ultra-low-power integrated circuits.