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

Abstract

Application of gallium nitride high-electronmobility 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.

Perspectives for III-nitride photonic platforms

“…It can moreover exhibit low switching losses and enables high-frequency operation which is a key for miniaturization [65]. Meanwhile the development of high-linearity power amplifiers is a workhorse for 5G and beyond 5G networks [66,67]. To address these markets, numerous foundries integrating III-nitride materials have been developed.…”

Advanced defect spectroscopy in wide-bandgap semiconductors: review and recent results

“…As a consequence of the presence of spontaneous and piezoelectric polarization charges, the large bandgap, and the high critical electric field, GaN enabled the design of HEMTs based on the AlGaN/GaN heterojunction, which are now becoming excellent candidates for RF amplifiers for 5G and beyond [39][40][41], and power devices with a operating voltage of 650 V and more [42]. In addition, vertical power transistors targeting 1200 V and above are under study [43][44][45].…”