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.

Hyo-Jin Kim

Publications