2D, Physical-Vapor Growth of Low-Coercivity, Epitaxial Ferroelectric Sc_0.3Al_0.7N on Scalable Substrates

Ferroelectric nitrides attract immense attention due to their excellent electrical, mechanical, and thermal properties as well as for their compatibility with scalable semiconductor technology. The availability of high-quality nitride films possessing tailorable coercive voltage and field, however, remains challenging, and is a key for deeper exploration of switching dynamics and practical applications in low-power devices. 2D growth of epitaxial thin (≲20 nm) c-axis-oriented Sc_0.3Al_0.7N films is reported on Al₂O₃ (0001) and on electrically conductive 4H-SiC (0001), obtained by reflection high-energy electron diffraction-monitored layer-by-layer physical vapor deposition growth. Films exhibit high quality, as evidenced by rocking curve full-width at half-maximum (FWHM) as narrow as ≈0.02°, and an atomically abrupt film-substrate interface with low dislocation density. The coercive field of Sc_0.3Al_0.7N/4H-SiC (0001) heterostructures is as low as 2.75 MV cm^-1. Moreover, a high endurance of >10⁹ cycles at saturation polarization is achieved. Density functional theory calculations of a model system reveal that an improved crystal quality, including atomically abrupt ferroelectric nitride-metal interface, facilitates the reduction in the switching barriers, and leads to reduced coercivity. These findings demonstrate the feasibility of obtaining high-quality epitaxial ferroelectric nitride films on highly scalable and radiation-resistant substrates, and their potential for energy-efficient electronic devices.