Exploring multi-element substitution in AlN

Novel ferroelectric materials with improved properties such as stability and defect-tolerance are key to enabling more energy-efficient computing. Cation-substituted AlN-based materials with wurtzite-derived structures have a range of exceptional electronic, electromechanical, and dielectric properties; Al_1–xSc_xN was recently found to be a good ferroelectric. In addition, recent work showed that many other metals can be incorporated into AlN, opening the possibility of additional functionalities. Motivated by the desire to add magnetic or light emission functionality on top of ferroelectricity, we substituted Al_1–xSc_xN with rare earth cations. We employ a joint computational and experimental approach to explore the quaternary phase diagram of (Al,Sc,Gd)N. We use thermodynamic stability calculations across this pseudo-ternary heterogeneous alloy space as a function of effective growth temperature to map the phase diagram. Experimentally, we perform a high throughput exploration of this phase space using combinatorial RF sputtering combined with spatially-resolved characterization. This approach allows us to begin to understand the interplay between composition, structure, and properties in a complex phase space, which is crucial for designing and synthesizing novel functional materials.