MOCVD-grown HEMTs on Al2O3 substrates

Al0.2Ga0.8N/GaN HEMTs have been fabricated from MOCVD-grown epilayers on (0001) sapphire substrates. DC current densities from 0.5 to ∼1 A/mm were achieved for gate lengths ranging from 0.75 to 0.1μm. A maximum transconductance of 207 mS/mm was measured for short gate length devices. From s-parameter measurements, ft of 59 GHz and fmax of 90 GHz were extracted. Load pull results from 0.25×150μm2 gate dimension devices indicated an output power density of 2.75 W/mm at 3 GHz and 1.7 W/mm at 10 GHz. Small signal modeling of the measured s-parameters is also presented.