Microwave performance of AlGaN/GaN metal insulator semiconductor field effect transistors on sapphire substrates

Metal-insulator-semiconductor field effect transistors (MISFETs) from surface-passivated undoped AlGaN/GaN heterostructures on sapphire were fabricated. Measured static output characteristics includes full channel currents (I_dss) of roughly 750 mA/mm with gate-source pinchoff voltages of -10 V and peak extrinsic transconductancies (g_m) of 100-110 mS/mm. Increased surface roughness resulting from a gate recess process to reduce the pinchoff voltage introduces gate leakage currents in the micro-amps regime. With evidence for reduced dc-to-rf dispersion from pulsed gate transfer characteristics, these devices at 4 GHz with 28.0 V bias generated maximum output power densities of 4.2 W/mm with 14.5 dB of gain and 36% power added efficiency