Al 0.75 Ga 0.25 N/Al 0.6 Ga 0.4 N heterojunction field effect transistor with f T of 40 GHz

An Al0.75Ga0.25N/Al0.6Ga0.4N heterostructure field effect transistor with graded MBE-regrown contacts is designed, grown, and fabricated on AlN/sapphire substrate. Maximum drain current density (ID,max) of 460 mA mm−1 was obtained on transistors with gate length of 130 nm. The small signal measurement shows current/power gain cutoff frequency (fT/fmax) of 40 GHz/58 GHz, respectively. Parasitic resistance is found to be a significant factor limiting the frequency performance of the devices. The high frequency performance of devices with high Al concentration AlGaN channel demonstrate potential for high power and high frequency applications.