Beryllium-incorporated ScAlN/GaN HEMTs with low off-current and high current stress stability

Abstract

We present GaN high-electron-mobility transistors (HEMTs) with Be-incorporated Sc0.15Al0.85N barrier layers, nearly lattice-matched to GaN and grown by molecular beam epitaxy. Compared to previous ScAlN/GaN HEMTs, our devices exhibit an ultra-low off-state current (Ioff) <10−6 mA/mm, a high on/off current ratio (Ion/Ioff) > 108, and a low subthreshold swing ∼120 mV/dec. They also achieve an on-current (Ion) of 415 mA/mm with a 1 μm gate length and demonstrate excellent stability under current stress and elevated temperatures, with minimal threshold voltage (VT) shift and slightly increased Ion, unlike the current collapse typically seen in AlGaN/GaN HEMTs. The improvement is attributed to Be-induced deep acceptor traps, which compensate for donor-like traps likely associated with scandium and nitrogen-related defects, as confirmed by x-ray photoelectron spectroscopy. These Be-related acceptor traps can capture electrons during the off-state, thereby suppressing gate leakage, and release the trapped electrons under thermal stress, effectively mitigating current collapse induced by donor traps in the on-state. These findings highlight the potential of Be-doped ScAlN/GaN HEMTs for high-power, high-frequency applications.