Molecular beam epitaxy of In-assisted ScAlN/GaN HEMT structures with ultralow sheet resistance

ScAlN, featuring bipolar switchable spontaneous polarization along with enhanced piezoelectricity and electromechanical coupling coefficients, emerges as a highly promising ultrawide bandgap semiconductor for next-generation high-power and high-frequency electronic applications. In this work, we demonstrate an ultralow sheet resistance two-dimensional electron gas (2DEG) in ScAlN-based high electron mobility transistor (HEMT) structures, grown on sapphire substrates via molecular beam epitaxy. By employing indium (In) as a surfactant and introducing an ultrathin AlN interlayer to engineer a sharp interface, we achieve a sheet resistance of 137 Ω/□, with an electron mobility of 1020 cm²/V·s and a sheet electron density of 4.5 × 10¹³ cm⁻². The realization of ultralow sheet resistance in ScAlN/GaN heterostructures paves the way for advancements in microwave and radio frequency device technologies.