SiC and GaN transistors - Is there one winner for microwave power applications?

Wide bandgap semiconductors show great promise for advancing the state of the art for high-power microwave electronic devices. Primarily due to low breakdown voltage, it has not been possible to design and fabricate solid-state transistors that can yield radio-frequency (RF) output power on the order of hundreds to thousands of watts necessary to compete with microwave vacuum tubes. This has, severely limited the use of microwave solid-state transistors and devices in power applications, such as transmitters for wireless communications systems, radars, etc. Recent improvements in the growth of wide bandgap semiconductor materials, such as SiC and the GaN-based alloys, provide the opportunity to now design and fabricate microwave transistors that demonstrate performance previously available only from microwave tubes. The most promising electronic devices for fabrication in wide bandgap semiconductors for these applications are metal-semiconductor field-effect transistors (MESFETs) fabricated from the 4H-SiC polytype and heterojunction field-effect transistors (HFETs) fabricated using the AlGaN/GaN heterojunction. These devices can provide RF output power on the order of 5-6 W/mm and 10-12 W/mm of gate periphery respectively. 4H-SiC MESFETs should produce useful performance at least through X band and AlGaN/GaN HFETs should produce useful performance well into the millimeter-wave region, and potentially as high as 100 GHz.