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III-nitrides and related alloys are widely used for optoelectronics and as acoustic resonators. Ferroelectric wurtzite nitrides are of particular interest because of their potential for direct integration with Si and wide bandgap semiconductors and unique polarization switching characteristics; such interest has taken off since the first report of ferroelectric Al1−xScxN alloys. However, the coercive fields needed to switch polarization are on the order of MV/cm, which are 1–2 orders of magnitude larger than oxide perovskite ferroelectrics. Atomic-scale point defects are known to impact the dielectric properties, including breakdown fields and leakage currents, as well as ferroelectric switching. However, very little is known about the native defects and impurities in Al1−xScxN and their effect on the dielectric and ferroelectric properties. In this study, we use first-principles calculations to determine the formation energetics of native defects and unintentional oxygen incorporation and their effects on the polarization switching barriers in Al1−xScxN alloys. We find that nitrogen vacancies are the dominant native defects, and unintentional oxygen incorporation on the nitrogen site is present in high concentrations. They introduce multiple mid-gap states that can lead to premature dielectric breakdown and increased temperature-activated leakage currents in ferroelectrics. We also find that nitrogen vacancy and substitutional oxygen reduce the switching barrier in Al1−xScxN at low Sc compositions. The effect is minimal or even negative (increases barrier) at higher Sc compositions. Unintentional defects are generally considered to adversely affect ferroelectric properties, but our findings reveal that controlled introduction of point defects by tuning synthesis conditions can instead benefit polarization switching in ferroelectric Al1−xScxN at certain compositions.

 

Low-energy compute-in-memory architectures promise to reduce the energy demand for computation and data storage. Wurtzite- type ferroelectrics are promising options for both performance and integration with existing semiconductor processes. The Al1-xScxN alloy is among the few tetrahedral materials that exhibit polarization switching, but the electric field required to switch the polarization is too high (few MV/cm). Going beyond binary com- pounds, we explore the search space of multinary wurtzite-type compounds. Through this large-scale search, we identify four prom- ising ternary nitrides and oxides, including Mg2PN3, MgSiN2, Li2SiO3, and Li2GeO3, for future experimental realization and engi- neering. In >90% of the considered multinary materials, we identify unique switching pathways and non-polar structures that are distinct from the commonly assumed switching mechanism in AlN-based materials. Our results disprove the existing design principle based on the reduction of the wurtzite c/a lattice parameter ratio when comparing different chemistries while sup- porting two emerging design principles—ionicity and bond strength. 

Creation, stabilization, characterization, and control of single transition metal (TM) atoms may lead to significant advancement of the next-generation catalyst. Metal organic network (MON) in which single TM atoms are coordinated and separated by organic ligands is a promising class of material that may serve as a single atom catalyst. Our density functional theory-based calculations of MONs in which dipyridyl tetrazine (DPTZ) ligands coordinate with a TM atom to form linear chains leads to two types of geometries of the chains. Those with V, Cr, Mo, Fe, Co, Pt, or Pd atoms at the coordination center are planar while those with Au, Ag, Cu, or Ni are non-planar. The formation energies of the chains are high (∼2.0–7.9 eV), suggesting that these MON can be stabilized. Moreover, the calculated adsorption energies of CO and O₂on the metal atom at center of the chains with the planar configuration lie in the range 1.0–3.0 eV for V, Cr, Mo, Fe, and Co at the coordination center, paving the way for future studies of CO oxidation on TM-DPTZ chains with the above five atoms at the coordination center.