Field-plated 0.25-μm gate-length AlGaN/GaN HEMTs with varying field-plate length

Metal-organic chemical vapor deposition-grown field-plated 0.25-μm gate-length AlGaN/GaN high-electron mobility transistors (HEMTs) with field-plate lengths of 0.5, 0.8, and 1.1 μm have been fabricated on 6H-SiC substrates. These 0.25-μm gate-length devices exhibited maximum drain current density of more than 1.4 A/mm and peak extrinsic transconductance of 437 mS/mm. No dependence of dc I-V as well as transfer characteristics on field-plate length was observed. With increase of field-plate length, degradation in the value of unity current gain frequency f_T and maximum frequency of oscillation f_max was observed, but there is significant improvement in breakdown voltage and power densities. Also, at 18 GHz, a continuous-wave output power density of 9.1 W/mm with power added efficiency of 23.7% was obtained for device with field-plate length of 1.1 μm, yielding the highest reported power performance of AlGaN/GaN HEMTs at 18 GHz.