Orbital hybridization as the driving mechanism for enhanced dielectric permittivity in ScAlN

Materials with high permittivity play an important role in solid-state device design and subsequent performance via improved electric field and charge control. In this study, we investigate dielectric properties of ScxAl1−xN as a function of ScN fraction, x, to understand the variation of dielectric properties in terms of structural and electronic properties in this system. Employing first-principles calculations based on density functional theory, we show that the permittivity in ScxAl1−xN reaches its maximum value at an ScN fraction of about 43%. Increasing ScN beyond this alloy concentration results in unstable phonon modes with negative frequencies, indicating that ScxAl1−xN with x > ∼43% is not stable in the wurtzite phase and a phase transition is warranted. The dielectric permittivity was found to decrease dramatically with x > ∼43% if it is constrained to remain in the wurtzite phase. We further investigate the interplay between the phonons and electrons for their roles in deciding the overall permittivity and understanding the origin of the noted variation in the dielectric properties of ScxAl1−xN as a function of ScN fraction. We find that the degrees of hybridization between the Sc-d and N-p orbitals play a critical role in explaining the noted dielectric behavior. This finding establishes that orbital hybridization is a key design parameter for tuning the dielectric response in nitrides, drawing a direct conceptual parallel to the well-known mechanism driving ferroelectricity in perovskite oxides such as PbTiO3.