Electrical and optical properties of transparent conducting homologous compounds in the indium-gallium-zinc oxide system

The homologous compounds In_1-xGa_1+xO₃(ZnO)_k (where k = 1, 2, or 3) were prepared at a temperature of 1400 °C. The solubility limits (as determined via X-ray diffractometry) were 0.47<[In]/([In]+[Ga])<0.67 for the k = 1 member, 0.35<[In]/([In]+[Ga])<0.77 for the k = 2 member, and 0.29<[In]/([In]+[Ga])<1.00 for the k = 3 member. Four-point-conductivity and diffuse-reflectance measurements were performed on as-fired and reduced samples. The band gap that was determined from diffuse reflectance increased as the Ga³⁺ content increased and k decreased. The conductivity increased as k decreased and the In³⁺ content increased. A maximum conductivity of 250 S/cm was obtained for k = 3 and [In]/([In]+[Ga]) = 1 after reduction. The minimum absorption edge of 325 nm was obtained for k = 2 and [In]/([In]+[Ga]) = 0.35 prior to reduction. The potential for metastable phases in the In-Ga-Zn-O system with enhanced transparent-conducting properties has been discussed.