This work investigates the impact of incorporating an AlGaN back barrier (BB) in buffer-free AlGaN/GaN high electron mobility transistors (HEMTs) on SiC. Both devices use an AlN nucleation layer (NL) for vertical isolation, while the modified structure introduces an Al0.2Ga0.8N BB beneath the GaN channel. The reference device without the BB exhibits strong electrostatic confinement but suffers from pronounced current collapse linked to traps in the AlN nucleation region. In contrast, the device with the AlGaN BB maintains short-channel control while reducing vertical electric-field crowding and mitigating dynamic trapping. Drain current transient spectroscopy confirms the suppression of a slow trap component associated with the AlN NL. At 40 GHz, these improvements result in enhanced power-added efficiency and output power density, reaching 43% and 2.9 W/mm, respectively, compared with 40% and 2.2 W/mm for the reference device. The results demonstrate that the AlGaN BB effectively improves the dynamic and millimeter-wave performance of buffer-free GaN HEMTs and supports further device scaling for high-power RF applications.
Grandpierron et al. (Sun,) studied this question.