Scaled ultra-wide bandgap AlGaN polarization-graded FET with ultra-thin buffer layer

We report on the design and experimental demonstration of ultra-wide-bandgap AlGaN polarization-graded field-effect transistors (PolFETs) with ultra-thin channels aimed at enabling high current capability, RF performance, and reduced thermal resistance. Polarization-graded AlGaN layers and ultra-thin pseudomorphic AlGaN buffer layers are employed to achieve low thermal resistance while maintaining high structural quality. The demonstrated PolFETs achieve a maximum soft-saturation drain current density of 800 mA/mm at VG = 4 V and ∼500 mA/mm at VG = 0 V, along with current- and power-gain cutoff frequencies (fT/fmax) of 26/28 GHz, respectively. Small-signal modeling was performed to analyze parasitic and transit delays, and gate-resistance thermometry was implemented to characterize device thermal behavior and benchmark against state-of-the-art AlGaN HEMTs. The ultra-thin AlGaN PolFET exhibits a thermal resistance of 12 K mm/W, representing a significant reduction compared to conventional AlGaN transistor structures. These results demonstrate the feasibility of polarization-engineered ultra-wide-bandgap AlGaN transistors for RF and mm-wave applications, with the added advantage of improved thermal performance.