Extremely low sheet resistance of ultra-thin AlN barrier HEMTs by plasma-assisted molecular beam epitaxy

Abstract AlN/GaN high-electron-mobility transistor (HEMT) equipped with ultra-thin AlN barrier epitaxial structures were grown on 6-inch and 8-inch Si-based GaN templates via plasma-assisted molecular beam epitaxy (PAMBE). The AlN barrier thickness was systematically optimized to improve the properties of two-dimensional electron gas (2DEG). Structural and electrical characterizations were performed by atomic force microscopy (AFM), transmission electron microscopy (TEM), contact and non-contact Hall measurements. At an optimal AlN barrier thickness, an extremely low sheet resistance of 159.9 Ω/□ by contact Hall and 143.8 Ω/□ by non-contact Hall was achieved on the 6-inch HEMT wafer, marking a significant improvement over state-of-the-art Si-based GaN HEMTs. The epitaxial surface exhibited excellent morphology with a root-mean-square (RMS) roughness of 0.45 nm. Moreover, cross-sectional TEM analysis of PAMBE-grown AlN/GaN HEMT revealed an atomically sharp and structurally coherent heterointerface, which is critical for achieving high electron mobility and reduced scattering loss. In addition, the 8-inch HEMT demonstrated a sheet resistance ( R s ) as low as 115 Ω/□ by non-contact Hall with a uniformity of 2.13%, outperforming competing technologies from other companies on the market.