Sub-50 nm Terahertz In0.8Ga0.2As Quantum-Well High-Electron-Mobility Transistors for 6G Applications

We present a systematic study on the gate length (
${L}_{{g}}\text {)}$
scaling behavior and the impact of the side-recess spacing (
${L}_{\text {side}}\text {)}$
on dc and high-frequency characteristics of In0.8Ga0.2As quantum-well (QW) high-electron-mobility transistors (HEMTs) with
${L}_{{g}}$
from 10
$\mu $
m to 20 nm, for the purpose of understanding the scaling limit of maximum oscillation frequency (
${f}_{\text {max}}\text {)}$
and thereby demonstrating terahertz devices. The fabricated In0.8Ga0.2As QW HEMTs with
${L}_{{g}} =20$
nm and
${L}_{\text {side}} =150$
nm exhibited values of drain-induced-barrier-lowering (DIBL) of 60 mV/V, current-gain cutoff frequency (
${f}_{{T}}\text {)}$
of 0.75 THz, and
${f}_{\text {max}}$
of 1.1 THz, while the device with
${L}_{\text {side}} =50$
nm showed DIBL of 110 mV/V and
${f}_{{T}}$
/
${f}_{\text {max}}$
of 0.72/0.53 THz. It was central to strictly control short-channel effects (SCEs) from the perspective of DIBL to maximize the improvement of
${f}_{\text {max}}$
, as
${L}_{{g}}$
was scaled down deeply. In an effort to understand the
${L}_{{g}}$
scaling behavior of
${f}_{\text {max}}$
, we carried out the small-signal modeling for both types of devices and found that the increase of the intrinsic output conductance (
${g}_{\text {oi}}\text {)}$
played a critical role in determining
${f}_{\text {max}}$
in short-
${L}_{{g}}$
HEMTs. On the contrary, the fabricated devices with
${L}_{\text {side}} =150$
nm exhibited a tight control of SCEs at
${L}_{{g}}$
of 20 nm. As a result,
${f}_{\text {max}}$
in those devices was boosted to 1.1 THz, and more importantly this high
${f}_{\text {max}}$
was maintained even as
${L}_{{g}}$
was scaled down to 20 nm. The results in this work represent the best balance of
${f}_{{T}}$
and
${f}_{\text {max}}$
in any transistor technology on any material system, displaying both
${f}_{{T}}$
and
${f}_{\text {max}}$
in excess of 700 GHz simultaneously.