AlGaN/GaN MOS-HEMT With HfO₂ Dielectric and Al₂O₃ Interfacial Passivation Layer Grown by Atomic Layer Deposition

We have developed a novel AlGaN/GaN metal–oxide–semiconductor high-electron mobility transistor using a stack gateHfO₂/Al₂O₃structure grown by atomic layer deposition. The stack gate consists of a thinHfO₂(30-) gate dielectric and a thinAl₂O₃(20-) interfacial passivation layer (IPL). For the 50-stack gate, no measurableC–Vhysteresis and a smaller threshold voltage shift were observed, indicating that a high-quality interface can be achieved using aAl₂O₃IPL on an AlGaN substrate. Good surface passivation effects of theAl₂O₃IPL have also been confirmed by pulsed gate measurements. Devices with 1-gate lengths exhibit a cutoff frequency(fT)of 12 GHz and a maximum frequency of oscillation(fMAX)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.