RF Performance of 130 nm Al0.75Ga0.25N/Al0.6Ga0.4N HFETs with MBE-Regrown Contacts

AlGaN channel transistors are promising candidates for high power RF transistors due to their superior material properties. The larger breakdown field and similar saturation velocity compared to GaN make AlGaN channel transistors potentially capable of delivering higher power density at high frequencies. So far the highest reported fT is 28 GHz on Al
_0.85
Ga
_0.15
N/Al
_0.70
Ga
_0.30
N transistors with RF power density of 0.3 W/mm at 3 GHz [1]. The major obstacle to achieve high RF performance is the challenge to form good ohmic contacts to Al-rich AlGaN. Here, we show significantly better small and large signal RF performance than what have been reported on high Al-composition AlGaN transistors with regrown side contacts.