AlGaN/GaN MOS-HEMT With $\hbox{HfO}_{2}$ Dielectric and $\hbox{Al}_{2}\hbox{O}_{3}$ Interfacial Passivation Layer Grown by Atomic Layer Deposition

Abstract
We have developed a novel AlGaN/GaN metal-oxide-semiconductor high-electron mobility transistor using a stack gate HfO 2 /Al 2 O 3 structure grown by atomic layer deposition. The stack gate consists of a thin HfO 2 (30-A) gate dielectric and a thin Al 2 O 3 (20- A) interfacial passivation layer (IPL). For the 50-A stack gate, no measurable C - V hysteresis and a smaller threshold voltage shift were observed, indicating that a high-quality interface can be achieved using a Al 2 O 3 IPL on an AlGaN substrate. Good surface passivation effects of the Al 2 O 3 IPL have also been confirmed by pulsed gate measurements. Devices with 1- mum gate lengths exhibit a cutoff frequency ( fT ) of 12 GHz and a maximum frequency of oscillation ( f MAX ) of 34 GHz, as well as a maximum drain current of 800 mA/mm and a peak transconductance of 150 mS/mm, whereas the gate leakage current is at least six orders of magnitude lower than that of the reference high-electron mobility transistors at a positive gate bias.