Structure Optimization of Field-Plate AlGaN/GaN HEMTs

AlGaN/GaN high electron mobility transistors (HEMTs) on 6H-SiC with varying field-plate length and gate-drain spacing were fabricated and analyzed. The classical small signal FET model and the well-known ColdFET method were used to extract the small signal parameters of the devices. Though the devices with field-plates exhibited lower better f _T characteristic, they did demonstrate better f_max, MSG and power density performances than the conventional devices without field-plate. Besides, no independence of DC characteristic on field-plate length was observed. With the increase of the field-plate length and the gate-drain spacing, the characteristic of f_T and f_max degraded due to the large parasitic effects. Loadpull method was used to measure the microwave power performance of the devices. Under the condition of continuous wave at 5.4GHz, an output power density of 4.69W/mm was obtained for device with field-plate length of 0.5mum and gate-drain length of 2mum