Fully Epitaxial Ferroelectric III-Nitride Semiconductors: From Materials to Devices

Recent studies have shown that the incorporation of scandium (Sc) can transform conventional III -nitride semiconductors to be ferroelectric, with switchable polarization and significantly enhanced electrical, piezoelectric, and nonlinear optical properties. These unique characteristics, together with its tunable ultrawide bandgap, have made ScAlN one of the most promising semiconductors for future high-power, high-frequency, and high-temperature electronics, acoustic resonators and filters, micro/nano-electromechanical systems (MEMS), neuromorphic and edge computing/intelligence. Sputter deposition has been widely employed for the synthesis of ScAlN films, which show limited material quality. Recently, great progress has been made in the epitaxial growth of single-crystalline wurtzite phase ScAlN utilizing standard epitaxial approaches, including molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), which enable the seamless integration with the mature Si-based and GaN-based technologies. To date, however, the realization of ferroelectric ScAlN has been largely limited to sputter deposition. 1 It has remained a daunting challenge to achieve single crystalline ferroelectric Sc-III-nitrides. Moreover, the currently reported ScAlN exhibits extremely high unintentional impurities (e.g., 0 and C), which severely limit their practical device application.2 Therefore, the ability to improve the material quality, realize robust ferroelectric polarization switching, and demonstrate device concepts of fully epitaxial ScAlN -based heterostructures is essential for the emerging applications of Sc-III-nitrides.