Effect of Sc spatial distribution on the electronic and ferroelectric properties of AlScN

While aluminum scandium nitride based ferroelectric materials have shown significant promise for non-volatile memory applications, difficulties relating challenges in device performance, such as electrical leakage, to structural characteristics motivate improved understanding of the fundamental structure-property relationship. Spinodal decomposition has been reported in this material system, consistent with our observation of compositional segregation in AlScN films grown by reactive sputter epitaxy. To better understand the effects of spatially non-uniform Sc concentrations, the electronic and ferroelectric (FE) properties of AlScN as a function of Sc distribution are studied using density functional theory (DFT). We explore the impact of Sc-rich atomic planes in wurtzite AlScN with Sc concentration ranging from 0 to 44 at% through a supercell approach. We find that while spontaneous polarization decreases with Sc concentration (∼133 to 102 μC cm^-2), periodic Sc-rich planar clusters slow this effect, suggesting that phase segregation counters the effects of increasing Sc composition. Furthermore, the FE switching barrier per formula unit (f.u.) as a function of composition exhibits a local maximum of 0.60 eV f.u.^-1 at 25% Sc concentration in the presence of Sc-rich planes but decreases monotonically (0.51 to 0.28 eV f.u.^-1) if Sc is uniformly distributed, suggesting that the spatial distribution of Sc plays an important role in the optoelectronic properties of the material by changing the energy landscape. Sc clustering also decreases the bandgap of the material. This study shows that the structural complexity arising from spatial composition modulation provides tunability of ferroelectric properties in AlScN ferroelectrics.