Unpassivated AlGaN/GaN HEMTs with CW power density of 3.2 W/mm at 25 GHz grown by plasma-assisted MBE

The Ka-band power performance of unpassivated AlGaN/GaN HEMTs grown by plasma-assisted molecular beam epitaxy on 6H-SiC substrates is reported. Transistors with a gate length of 0.2 μm, source-drain spacing of 2 μm, and 100 μm periphery displayed maximum drain currents greater than 1.6 A/mm. Small signal S-parameter measurements yielded an f_T of 53 GHz and f_MAX of 109 GHz. Passive load pull measurements at 25 GHz of 0.2×100 μm transistors yielded a power density of 3.2 W/mm with 30% PAE and 44% drain efficiency at 1.8 dB gain compression. To the knowledge of the authors, this is the first report of RF output power above 20 GHz from MBE-grown AlGaN/GaN HEMTs.