This work initially compares GaN high electron mobility transistors (HEMTs) based on the established Ga-face technology and the emerging N-face technology. An investigation is then carried out on the short channel effects in ultra-scaled GaN and InP HEMTs. The dielectric effects of the passivation layer in millimeter-wave, high-power GaN HEMTs are also investigated by focusing on the effective gate length, the gate fringing capacitance, and the drain-to-gate feedback capacitance. Lastly, efficient... Mehr