AlGaN/GaN MOS-HEMT with Stack Gate HfO2/Al2O3 Structure Grown by Atomic Layer Deposition

We have developed a novel AlGaN/GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using stack gate IHD₂/Al₂O₃ structure grown by atomic layer deposition (ALD). The stack gate consists of a thin HfO₂ (30Aring) gate dielectric and a thin Al₂O₃ (20Aring) interfacial passivation layer (IPL). For the 50Aring stack gate, no measurable C-V hysteresis and smaller threshold voltage shift were observed, indicating that a high quality interface can be achieved using a AI₂O₃ IPL on AlGaN substrate. Good surface passivation effects of the AI₂O₃ IPL have also been confirmed by pulsed gate measurements. Devices with 1-mum gate lengths exhibit a cutoff frequency (f_T) of 12 GHz and a maximum frequency of oscillation (f_MAX) of 34 GHz.The gate leakage current is at least six orders of magnitude lower than that of the reference HEMTs at positive gate bias.