Double-Recessed High-Frequency AlInGaN/InGaN/GaN Metal–Oxide Double Heterostructure Field-Effect Transistors

We demonstrate a low-threshold AlInGaN/InGaN/ GaN metal–oxide semiconductor double heterostructure field-effect transistor (MOS-DHFET) for high-frequency operation. A combination of an InGaN channel (for carrier confinement), a DRE process, and a new digital–oxide-deposition technique helped us to achieve MOS-DHFET devices with extremely low subthreshold leakage currents. This reduction in output conductance (short channel effect) resulted in a high cutoff gain frequency $f_T$ of about 65 GHz and a current gain frequency $f_{{\rm max}}$ of 94 GHz. The devices exhibited high drain–currents of 1.3 A/mm and delivered RF powers of 3.1 W/mm at 26 GHz with a 35 V drain bias.