Abstract

AlGaN/GaN Heterostructure Field Effect Transistors (HFETs) are suitable candidates for high-power and high-frequency applications. Although GaN possesses a broad peak in its drift-velocity versus electric-field (i.e., vd-E) characteristics, with very large peak drift-velocity and a pronounced region of negative differential mobility, oftentimes a purely-saturating approximation of vd-E characteristics is considered to be adequate for the evaluation of the drain-current characteristics of AlGaN/GaN HFETs. In contradiction to this belief, it was deemed necessary to investigate the accuracy of this purely-saturating transport characteristics in evaluation of the scalability of the current-drive of AlGaN/GaN HFETs with gate-length. This evaluation is carried out by considering both the realistic steady-state drift transport characteristics and the purely-saturating approximation of the drift transport characteristics. Results show that the drain-current of AlGaN/GaN HFET is less scalable, than expected on the basis of the purely-saturating drift transport characteristics. The predictability of this scaling-trend with the improvement in the Ohmic contact technology is also investigated.
In addition, in this study two newly-developed AlGaN/GaN HFETs, known as island-, and fin-isolated, are evaluated from the point of view of gate-lag and frequency-dispersion. These studies are deemed important for further development of these novel device technologies. The studies are carried out over a wide range of temperatures. Variation of the observed gate-lag profiles with temperature provided important signatures linking the fabrication technology of these new device types with reliability concerns. In light of this study, suggestions are made to improve the aforementioned technologies.