ALD Al2O3 Passivated MBE-grown AlGaN∕GaN HEMTs on 6H-Sic

The effects of atomic-layer-deposited (ALD) Al2O3 passivation layer on AlGaN/GaN HEMTs on SiC were studied. Improved pulsed I-V characteristics and a relatively small decrease in the unity gain cutoff frequency (f(T)) and the maximum frequency of oscillation (f(max)) were observed in the devices passivated using a 45 nm-thick ALD Al2O3 layer. For 0.12 mu m gatelength devices, f(T) (f(max)) decreased to 92 GHz (115 GHz) from 120 GHz (140 GHz), while for 0.25 mu m devices, f(T) (f(max)) decreased to 58 GHz (120 GHz) from 65 GHz (137 GHz). At a drain bias of 15 V, an output power of 3 W/mm with an associated gain of 5.0 dB and PAE of 33% were obtained for the 0.25 mu m gatelength devices.