Growth Characteristics and Electronic Properties ofEpitaxial NdNiO₃ Thin Films by Atomic Layer Deposition

The transition to next-generation electronics is inevitable and will require innovative architectures and materials functionalities. The multifunctional and often strongly coupled behaviors of transition metal oxides can offer alternative pathways to more energy-efficient devices, such as transistors. Here, we study thin films of NdNiO₃ for its potential as a transistor channel switching material owing to the metal–insulator transition it exhibits at ∼200 K in bulk. The thin films exhibit high structural integrity and relevant functional properties when deposited by atomic layer deposition (ALD) under industrial processing conditions, thus providing a viable pathway for device integration. By varying the ratio of binary oxide subcycles, we can precisely obtain the stoichiometric NdNiO₃ composition for which the thin films become epitaxial as deposited at 225 °C on SrTiO₃(001). Prior to annealing, the specific resistivities at room temperature show a dependence on the out-of-plane lattice parameter, <i>c</i>, with a nonlinear increase from 10^–4 to 10^–1 Ωcm as <i>c</i> increases. After annealing at 650 °C in air, both the out-of-plane lattice parameters and resistivities converge toward a narrow range (<i>c</i> = 3.789–3.794 Å and 10^–4 Ωcm, respectively). X-ray diffraction and reciprocal space mapping reveal that annealing also has the effect of increasing the strain in the thin films; however, they remain partially relaxed from the substrate. A metal–insulator transition takes place at 140 K under cooling and 175 K upon heating back to room temperature.