I. Introduction
Devices based on AlGaN/GaN have been intensively researched due to their application in high-power and high-frequency devices [1], [2]. GaN has a relatively large saturation velocity, peak electron velocity, wide bandgap, and better thermal stability compared to Si and GaAs, which makes it suitable for high-voltage and high-temperature applications [3]. Greater than 2-D electron gas (2DEG) charge density, combined with wide bandgap, provides for very large maximum drain current and high-power handling capability in AlGaN/GaN high-electron-mobility transistors (HEMTs).