We investigated the effects of various field plate and buried gate structures on the DC and small signal characteristics of 4H-silicon carbide (SiC) metal-semiconductor field-effect transistors (MESFETs). In comparison with the source-connected field plate, the gate-connected field plate exhibited superior frequency response while having similar DC characteristics. In order to further enhance the output power, dual field plates were employed in conjunction with a buried gate structure.

A buried gate AlGaAs/InGaAs heterojunction FET (HJFET) with gate breakdown voltage of 30 V was examined for high drain bias (higher than 10 V) operation. High breakdown voltage was realized due to the optimization of the narrow recess depth. A 1.4 mm HJFET has exhibited an output power of 30.2 dBm (1050 mW) with 50% power added efficiency (PAE) and 12.1 dB linear gain at 12 GHz with a 13 V drain bias. An internal matching circuit for a 16.8 mm HJFET was designed using a large-signal load impedance determined from load-pull measurement. The 16.8 mm internally-matched HJFET has delivered 38.9 dBm (7.8 W) output power with 46% PAE and 11.6 dB linear gain at 12 GHz with a drain bias of 13 V. This is the first report of higher than 10 V operation of an X- and Ku-band power HJFET with the excellent power performance.