Bipolar Electrical Conductive Transparent Oxide, CuInO₂

<jats:title>ABSTRACT</jats:title><jats:p>A transparent oxide semiconductor with delafossite structure, CuInO<jats:sub>2</jats:sub>, was found to exhibit both <jats:italic>p</jats:italic>-type and <jats:italic>n</jats:italic>-type conduction by doping of an appropriate impurity and tuning of proper film-deposition conditions. Thin films of Ca-doped or Sn-doped CuInO<jats:sub>2</jats:sub> were prepared on -Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> (001) single crystal substrates by pulsed laser deposition method. The films were deposited at 723 K in O<jats:sub>2</jats:sub> atmosphere of 1.0 Pa for the Ca-doped films or 1.5 Pa for the Sn-doped films. The positive sign of the Seebeck coefficient demonstrated <jats:italic>p</jats:italic>-type conduction in the Ca-doped films, while the Seebeck coefficient of the Sn-doped films was negative indicating <jats:italic>n</jats:italic>-type conductivity. The electrical conductivities of Ca-doped and Sn-doped CuInO<jats:sub>2</jats:sub> thin films were 2.8×10<jats:sup>−3</jats:sup> S·cm<jats:sup>−1</jats:sup> and 3.8×10<jats:sup>−3</jats:sup> S·cm<jats:sup>−1</jats:sup>, respectively, at 300 K. The optical band gap of each film was estimated to be ∼3.9 eV. Since CuInO<jats:sub>2</jats:sub> exhibited bipolarity in electrical conduction, transparent <jats:italic>p-n</jats:italic> homojunctions based on CuInO<jats:sub>2</jats:sub> were fabricated on (111) surface of yttria-stabilized zirconia single-crystal substrates. The structure of the diode was In<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>:Sn / <jats:italic>n</jats:italic>-CuInO<jats:sub>2</jats:sub>:Sn / <jats:italic>p</jats:italic>-CuInO<jats:sub>2</jats:sub>:Ca / In<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub>:Sn electrode on the substrate. The contact between the <jats:italic>n</jats:italic>-and <jats:italic>p</jats:italic>-type CuInO<jats:sub>2</jats:sub> semiconducting oxides was found to be rectifying. The turn-on voltage was ∼1.8 V.</jats:p>