Microwave and Millimeter-Wave GaN HEMTs: Impact of Epitaxial Structure on Short-Channel Effects, Electron Trapping, and Reliability

• Published in: IEEE transactions on electron devices 2024-03, Vol.71 (3), p.1-12
• Main Authors: Zanoni, Enrico, Santi, Carlo De, Gao, Zhan, Buffolo, Matteo, Fornasier, Mirko, Saro, Marco, Pieri, Francesco De, Rampazzo, Fabiana, Meneghesso, Gaudenzio, Meneghini, Matteo, Zagni, Nicolo, Chini, Alessandro, Verzellesi, Giovanni
• Format: Article
• Language: English
• Subjects: Aluminum gallium nitride; Aluminum gallium nitrides; Barrier layers; Carrier density; Deep levels; Electric fields; electron device failure physics; Electron gas; Gallium nitride; gallium nitride high-electron-mobility transistors (GaN HEMT); Gallium nitrides; HEMT scaling; HEMTs; High electron mobility transistors; Hot electrons; Leakage current; Logic gates; Microwave transistors; millimeter wave; Millimeter waves; Nitrogen; Power amplifiers; Reliability; Semiconductor devices; short-channel effects; Silicon; Wave power; Wide band gap semiconductors
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2023.3318564

Application of gallium nitride high-electron-mobility transistors (GaN HEMTs) to millimeter-wave power amplifiers requires gate length scaling below 150 nm: in order to control short-channel effects, the gate-to-channel distance must be decreased, and the device epitaxial structure has to be completely redesigned. A high 2-D electron gas (2DEG) carrier density can be preserved even with a very thin top barrier layer by substituting AlGaN with AlN, InAl(Ga)N, or ScAlN. Moreover, to prevent interaction of hot electrons with compensating impurities and defects in the doped GaN buffer, the latter has to be separated from the channel by a back barrier. Other device designs consist in adopting a graded channel (which controls the electric field) or to adopt nitrogen-polar (N-polar) GaN growth (which decreases the distance between gate and channel, thus attenuating short-channel effects). The aim of this article is to review the various options for controlling short-channel effects, improve off-state characteristics, and reduce drain-source leakage current. Advantages and potential drawbacks of each proposed solution are analyzed in terms of current collapse (CC), dispersion effects, and reliability.