An explicit connection between the electronic structure and the anisotropic high conductivity of delafossite-type PdCoO2 has been established by angle-resolved photoemission spectroscopy (ARPES) and core-level x-ray photoemission spectroscopy. The ARPES spectra show that a large hexagonal electronlike Fermi surface (FS) consists of very dispersive Pd 4d states. The carrier velocity and lifetime are determined from the ARPES data, and the conductivity is calculated by a solution of the Boltzmann equation, which demonstrates that the high anisotropic conductivity originates from the high carrier velocity, the large two-dimensional FS, and the long lifetime of the carriers.

Electrical properties of acceptor (Mn, Mg or Mn + Mg)-doped BaTiO 3 ceramic have been studied in terms of oxygen vacancy concentration, various doping levels and electrical degradation behaviors. The solubility limit of Mn on Ti sites was confirmed to be close to or less than 1.0 mol%. Oxygen vacancy concentration of Ba(Ti 0.995−x Mg 0.005 Mn x )O 2.995−y (x = 0, 0.005, 0.01) was estimated to be ∼50 times greater than that of the un-doped BaTiO 3 . The leakage current of 0.5 mol% Mn-doped BaTiO 3 was stable with time, which was much lower than that of the un-doped BaTiO 3 . The BaTiO 3 specimen co-doped with 0.5 mol% Mg and 1.0 mol% Mn showed the lowest leakage current below 10 −10 A. It was confirmed that leakage currents of Mg-doped and un-doped BaTiO 3 under dc field are effectively suppressed by Mn co-doping as long as the Mn doping level is greater than Mg contents.

Degradation behaviors of Mg-doped BaTiO3 have been studied in terms of oxygen vacancy concentration and microstructural development. Mg-doped BaTiO3 powders were precisely synthesized by the Pechini method. As MgO content was increased to 1.0 mol%, Curie points moved to lower temperatures and dielectric constants decreased. The specimens doped with MgO showed higher leakage currents under the continuously applied dc field at a high temperature (100°C) during the aging process, compared with the undoped BaTiO3. With low levels of MgO (<1.0 mol%), the microstructure is similar to that of undoped BaTiO3, whereas a significant reduction in grain size was observed with higher levels (>2.0 mol%).

Ga-doped ZnO ͑ZnO:Ga͒ films were grown by metalorganic chemical vapor deposition as transparent conducting layers for GaN light-emitting diodes ͑LEDs͒. The forward voltage of LEDs with ZnO:Ga was 3.3 V at 20 mA. The low forward voltage was attributed to the removal of a resistive ZnGa 2 O 4 phase, decreased resistivity of ZnO:Ga films, and increased hole concentration in p-GaN by thermal annealing process. The light output power of LEDs with ZnO:Ga was increased by 25% at 20 mA compared to that of LEDs with Sn-doped indium oxide due to the enhanced transmittance and the increased hole concentration in p-GaN.

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