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 gate HfO2/Al2O3 structure grown by atomic layer deposition. The stack gate consists of a thin HfO2 (30-angstrom) gate dielectric and a thin Al2O3 (20-angstrom) interfacial passivation layer (IPL). For the 50-angstrom 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 Al2O3 IPL on an AlGaN substrate. Good surface passivation effects of the Al2O3 IPL have also been confirmed by pulsed gate measurements. Devices with 1-mu m gate lengths exhibit a cutoff frequency (f(T)) 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.