There is a need for high power solid state devices operating in the microwave frequency range for both radar applications and high frequency communications networks. While GaAs and InP technologies have demonstrated operation at extremely high frequencies, the power that they can generate is very limited. In order to replace traveling wave tubes, solid state devices must demonstrate higher operating power levels and higher reliability that have been shown to date. High electron mobility transistors (HEMT'S) fabricated with wide bandgap semiconductors such as the GaN/AlN material system have the potential to fulfill this need. The wide bandgap should translate into very high operating voltages and very temperature operation, which lead to high power levels and high reliability. However, the power levels attained to date using sapphire substrates has been very limited. silicon carbide (SiC) is the best substrate for high frequency, high power devices based on GaN because it can handle ten times the power density of a sapphire substrate due to its extremely high thermal conductivity. In addition, the epitaxial film qualities of both GaN and AlN are superior when grown on SiC, and this should lead to HEMT's with better frequency response, higher performance and increased reliability. The Phase I program results showed great promise for this technology. A transconductance of 60 mS/mm was achieved, and the devices could dissipate more than 5 times as much dc power than has been shown for GaN HEMT's grown on sapphire substrates. Further development of these devices is proposed for Phase II, with strong emphasis being placed on optimizing the epitaxial growth process as well as the device fabrication. The primary Army application area for GaN/SiC power microwave devices is in EW/ECM systems. GaN/AlGaN/SiC HEMT's have the potential to provide much higher power levels at a given frequency than can be obtained with Si or GaAs devices. The ability to operate at higher temperature will also give a large advantage in system design. Commercial applications would be for power amplifiers for cellular telephone base stations and for solid state UHF broadcast systems for digital and HDTV television.
Keywords: Gan Solid State Sic Hfet Hemt Algan Microwave
