Performance enhancement of AlGaN/GaN-based high electron mobility transistors with sputtered AlScN gate dielectric

This study explores the effects of a sputtered Al0.7Sc0.3N layer deposited onto metalorganic chemical vapor deposition-grown Al0.3Ga0.7N/GaN heterostructures, with a focus on structural and electrical properties, including DC characteristics of high-electron-mobility transistors (HEMTs). Structural analysis reveals that a 25 nm AlScN layer preserves surface roughness and barrier/channel interface quality, although relaxation occurs due to non-ideal growth conditions. Capacitance–voltage profiling indicates a sharp and uniform depletion, with reduced hysteresis post-deposition, suggesting effective passivation. Incorporation of AlScN increases the sheet carrier density from 1.4 to 1.89 × 1013 cm−2, although this is accompanied by lower mobility and a modest rise in sheet resistance from 406 to 441 Ω/sq. Devices with a 0.7 μm gate length demonstrate a saturation current of 0.98 A/mm, approximately 30% higher than reference AlGaN/GaN HEMTs. The composite barrier configuration further exhibits reduced leakage and improved insulation, but results in decreased transconductance and a pronounced threshold voltage shift from −0.8 to −7.8 V, attributed to increased barrier thickness. On-resistance also rises from 2 to 2.5 Ω mm likely due to sputter-induced contact damage. Optimization with a thinner 15 nm AlScN layer achieves a favorable balance, enhancing saturation current and soft-breakdown voltage while minimizing drawbacks in transconductance and on-resistance. Overall, sputtered AlScN serves as both a high-quality barrier and passivation layer, yielding enhanced device performance and robustness, and highlighting the future potential of sputter epitaxy to further advance GaN technology.