AlGaN/GaN microwave power HEMT's

High average microwave power output density has been observed with AlGaN/GaN HEMT's grown on sapphire substrates, reaching 4.0 W/mm with 49% power-added efficiency for single gates, and 1.8 W/mm with 78% power-added efficiency for multiple gates. Using SiC substrates, an order of magnitude more heat can be removed. The breakdown electric field in the GaN channel is /spl sim/3 MV/cm, 7.5 times that of GaAs. The average transit velocity is 1-1.2/spl times/10/sup 7/ cm/s, allowing an intrinsic f/sub t/ as high as 94 GHz for 0.15 /spl mu/m gate length.