High power GaN/AlGaN/GaN HEMTs operating at 2 to 25 GHz grown by plasma-assisted molecular beam epitaxy

We report on the growth and power performance of GaN/AlGaN/GaN high electron mobility transistors (HEMTs) grown by plasma-assisted molecular beam epitaxy (MBE) on semi-insulating SiC substrates. We detail the MBE growth conditions that consistently produce high mobility two-dimensional electron gases (2DEGs) with room temperature mobility of /spl sim/1400 cm/sup 2//Vs at a sheet density of 1.2/spl times/10/sup 13/ cm/sup -2/. Transistors fabricated from these layers have demonstrated power densities in excess of 8 W/mm at 2 GHz, 6 W/mm at 7 GHz, and 3 W/mm at 25 GHz. All power data is achieved without the use of a SiN surface passivation layer. Central to the achievement of high power operation is the reduction of RF dispersion. Our growth studies have focused on the suppression of RF dispersion and maximizing RF output power. Pulsed IV and gate lag measurements are used to quantify the amount of dispersion in different heterostructure designs and to elucidate the trapping mechanisms responsible for gate lag.