Bipolarity in electrical conduction of transparent oxide semiconductor CuInO2 with delafossite structure

A transparent oxide semiconductor with delafossite structure, ${\mathrm{CuInO}}_{\mathrm{2}},$ was found to exhibit both p-type and n-type conduction by doping of an appropriate impurity and tuning of proper film-deposition conditions. Thin films of Ca-doped or Sn-doped ${\mathrm{CuInO}}_{\mathrm{2}}$ (optical band $\mathrm{gap}\text{=∼3.9\hspace{0.05em}}\mathrm{eV})$ were prepared on $\mathrm{\alpha -}{\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{3}}\mathrm{(001)}$ single crystal substrates by pulsed laser deposition method. The films were deposited at 723 K in ${\mathrm{O}}_{\mathrm{2}}$ 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 p-type conduction in the Ca-doped films, while the Seebeck coefficient of the Sn-doped films was negative indicating n-type conductivity. The electrical conductivities of Ca-doped and Sn-doped ${\mathrm{CuInO}}_{\mathrm{2}}$ thin films were ${\text{2.8×10}}^{\text{−3}} {\mathrm{S cm}}^{\mathrm{-1}}$ and ${\text{3.8×10}}^{\text{−3}} {\mathrm{S cm}}^{\mathrm{-1}},$ respectively, at 300 K.