Nanoscale recessed T-gated ScAlN/GaN-HEMT on SiC wafer with graded back-barrier and Fe-doped buffer for future RF power amplifiers: a simulation study

Abstract

ScAlN, with its ultra-wide band gap and ferroelectric properties, offers promising enhancements for GaN-HEMTs expanding the device-application space. In this work, we report the DC/RF characteristics of lattice-matched Sc_0.18Al_0.82N/GaN-HEMT (SG-HEMT) built on SiC wafer. The SG-HEMT features a graded AlGaN back-barrier (g-AlGaN BB) that enhances the conduction-band (CB) disruption at the AlGaN/GaN interface, improving charge confinement. We examine the impact of Sc_0.18Al_0.82N barrier thickness (T_B) and gate-recess height (T_R) on device performance. As the gate-to-channel distance decreases, transconductance (G_M) increases due to enhanced gate control, and the threshold voltage (V_TH) shifts positively, exhibiting immunity to short-channel effects (SCEs) while preserving a better aspect ratio. Then the scaling behavior of SG-HEMT is explored with different gate lengths (L_G). Besides, the impact of L_SD scaling was studied through comprehensive simulations, and the device-performance metrics were thoroughly analyzed. The findings reveal that a 40 nm L_G device achieves the highest G_M of 423.8 mS/mm, an I_{D_peak} of 2.58 A/mm, and a peak f_T of 239.2 GHz, attributable to the higher polarization of ScAlN and impeded parasitic channel development as an outcome of the g-AlgaN BB, suggesting that lateral scaling is a viable method for enhancing device performance. This work manifests that high current densities can be achieved owing to a high sheet charge density at Sc_0.18Al_0.82N/GaN interface, highlighting the significant potential of SG-HEMTs for enhancing output power at the device level in millimeter-wave (mmw) frequencies and propelling HEMT functionalities.