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

Abstract

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.