Advances in Zinc Oxide Materials for Quantum Applications

Advanced characterizations of zinc oxide-based materials for spintronic and quantum applications are investigated. Zinc oxide (ZnO) based materials have been explored for various applications in electronics, nanotechnology, biomedicine, power devices, and so on. Zinc oxide doped with transition metals (ZnTMO) has a potential for spintronic and quantum applications. However, its properties in this area are not well understood. In this work, characterizations of transition metal-doped zinc oxide are systematically performed and investigated to gain insights into their spin-related properties. Sets of Mn-doped ZnO and Ni-doped ZnO were epitaxially grown on sapphire substrates using metal-organic chemical vapor deposition (MOCVD). X-ray diffraction showed a nearly monocrystalline structure in the (002) direction, along with appearances of low intensity secondary phases related to the transition metal materials and host ZnO. A systematic reducing trend in the bandgap was observed in both Ni-doped and Mn-doped ZnO with increased transition metal dopant concentration. This could be due to the energy states that are introduced with the transition metals, and this shows a potential controllability in spin-inducing energy states by transition metal-doping. As per photoluminescence measurement, transition-metal doping attenuated the ultraviolet narrow band and increased emissions in the yellow-green regions. This could be due to secondary phases of TM-oxides that were formed during the MOCVD growth. Advanced Hall Effect characterizations were done to understand the inherent spin-related properties of ZnTMO. ZnTMO exhibited Anomalous Hall Effect (AHE). The transverse Hall resistivity overlapped with the longitudinal resistivity, and both these resistivity were not linear. This indicates spin-polarization in ZnTMO that is not induced by intrinsic carriers. The spin polarization in ZnTMO could be the result of TM-TM clusters, secondary phases, defects, and extrinsic carrier scattering. Annealing reversed the AHE response and indicated the influence of annealing on spin-polarizations of the AHE-causing components of ZnTMO. The mechanism for spin in ZnTMO is based on extrinsic scattering by TM centers/clusters or secondary phases. Understanding of spin mechanism in ZnTMO can help in the investigation of ZnO for quantum and other spintronic applications.