Microwave operation of GaN/AlGaN-doped channel heterostructure field effect transistors

We report on the microwave operation of 1 μm gate AlGaN/GaN doped channel heterostructure field effect transistors (DC-HFET´s) with the cutoff frequency f_T of 18.3 GHz. These devices exhibit the cutoff frequency-gate length product in excess of 18 GHz/spl middot/μm, comparable to that of the state-of-the-art GaAs MESFET´s. We explain these improvements in the device performance by the increased sheet carrier density in the device channel and by a reduction in the parasitic series resistances, caused by doping the device channel.