ALD Al ₂ O ₃ passivated MBE-grown AlGaN/GaN HEMTs on 6H-SiC

Abstract

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 (fT) and the maximum frequency of oscillation (fmax) were observed in the devices passivated using a 45 nm-thick ALD Al2O3 layer. For 0.12 µm gatelength devices, fT (fmax) decreased to 92 GHz (115 GHz) from 120 GHz (140 GHz), while for 0.25 µm devices, fT (fmax) 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 µm gatelength devices.