High performance 0.25 μm gate-length AlGaN/GaN HEMTs on sapphire with power density of over 4.5 W/mm at 20 GHz

MOCVD-grown 0.25 μm gate-length AlGaN/GaN high electron mobility transistors (HEMTs) have been fabricated on sapphire substrates. These 0.25 μm gate-length devices exhibited maximum drain current density as high as 1.43 A/mm, peak extrinsic transconductance of 354 mS/mm, unity current gain cut-off frequency (f_T) of 61 GHz, and maximum frequency of oscillation (f_max) of 89 GHz. At 20 GHz, a continuous-wave output power density of 4.65 W/mm with power-added-efficiency of 29.9% was obtained, yielding the highest reported power performance of AlGaN/GaN HEMT grown on sapphire at 20 GHz.