Terahertz In0.8 Ga0.2 As quantum-well HEMTs toward 6G applications

We present the systematic analysis of L g scaling behavior and the impact of the side-recess spacing $(L_{side})$ on DC and high-frequency characteristics of In 0.8 Ga 0.2 As QW HEMTs with L g from $10 \mu \mathrm{m}$ to 20 nm, aiming to explore the scaling limit of f max and thereby demonstrate THz devices. The fabricated $L_{g}= 20$ nm device with $L_{side} = 150$ nm exhibited ${DIBL}=60$ mV/V and $f_{T}/ f_{max} \quad =0.75 /1.1$ THz, while the device showed with $L_{side}=50$ nm ${DIBL}=110$ mV/V and $f_{T}/ f_{max}=0.72 /0.53$. Strict control of short-channel effects from the viewpoint of DIBL was central to maximize the enhancement of f max as L g scaled down aggressively. Moreover, we explained the physical mechanism of the decrease in f max for HEMTs with L g scaled down to sub-50 nm. The results in this work represent the best balance of f T and f max in any transistor technology and the highest f T in any FET technology.