Cathodic Arc Zinc Oxide for Active Electronic Devices
Thesis DisciplineElectrical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The filtered cathodic vacuum arc (FCVA) technique is a well established deposition method for wear resistant mechanical coatings. More recently, this method has attracted attention for growing ZnO based transparent conducting films. However, the potential of FCVA deposition to prepare ZnO layers for electronic devices is largely unexplored. This thesis addresses the use of FCVA deposition for the fabrication of active ZnO based electronic devices. The structural, electrical and optical characteristics of unintentionally doped ZnO films grown on different sapphire substrates were systematically investigated. The potential of FCVA to grow both polar and non-polar ZnO films was demonstrated. The resulting films showed considerable promise for device applications with properties including high transparency(> 90%), moderate intrinsic carrier concentrations (10¹⁷ - 10¹⁹ cm⁻³), electron mobilities up to 110 cm⁻²/Vs, low surface roughness (< 5 nm) and well-structured photoluminescence. Post-growth annealing in oxygen at temperatures up to 800 C produced significant improvements in the electronic and optical properties of these films, due to the formation of larger grains with lower inter-grain potential barriers.
Silver oxide (AgOᵪ ) and iridium oxide (IrOᵪ) Schottky diodes fabricated on annealed FCVA ZnO films showed ideality factors as low as 1.20, barrier heights up to 0.85 eV and high sensitivity to ultraviolet light (up to ̴ 10⁻⁵ at -2 V). Transparent and opaque MESFETs fabricated on these films showed well defined field effect characteristics, channel mobilities up to 70 cm⁻²/Vs and insensitivity to 1 mW/cm⁻² visible light. These devices were further subjected to extensive bias and temperature stress tests. MESFET stability appeared to be strongly dependent on Schottky gate type, bias conditions and ZnO film morphology. Positive bias stress of AgOᵪ gated devices resulted in irreversible damage, that is thought to be due to Ag electromigration across the gate interface. Mapping of the surface potential of the ZnO channel material with Kelvin probe force microscopy suggested a strong relationship between the defect density at grain boundaries and both channel mobility and current stability. Interval growth techniques were found to reduce the density of defects at grain boundaries and produced MESFETs with higher current stability. IrOᵪ gated devices showed superior bias stability and temperature resilience from 25 C-195 C.