[19a-E201-1~7] 21.1 Joint Session K "Wide bandgap oxide semiconductor materials and devices"

[19a-E201-7] Electronic structure of Ce valence states and characteritics of carrier transport of high-mobility transparent conductive thin films of cerium-doped hydrogenated indium oxide

〇Tetsuya Yamamoto¹, Keisuke Kobayashi^1,2, Eiji Kobayashi³, Junichi Nomoto¹, Hisao Makino¹, Masaaki Kobata², Yuji Saito², Shinichi Fujimori², Tetsuo Okane², Hiroshi Yamagami² (1.Kochi Univ. Tech., 2.JAEA, 3.Choshu Ind. Co. Ltd.)

Keywords:highly transparent conductive oxide films, indium oxide, cerium

The post annealing treatment of as-deposited amorphous Ce-doped hydrogenated In₂O₃ (ICOH) films at 473K in air induces a transition from the amorphous to the crystalline phase associated with anomalously high Hall mobility of 145 cm²/Vsec. This paper presents a model electronic structure for this new class of transparent conducting oxide films. The validity of the model is verified based on experimentally derived electronic structures of Ce, an In-substituting dopant, ions and Fermi-edge state modified by the post-annealing which were investigated by the combination of hard x-ray photoelectron spectroscopy (HAXPES), x-ray absorption spectroscopy (XAS) and resonance photoelectron spectroscopy (RPES). The analysis shows that Ce ions are incorporated in In₂O₃ matrix with mostly Ce³⁺ charge state of localized 4f character for as-deposited films. The post annealing causes transition of considerable portion of the Ce³⁺ to Ce⁴⁺ charged states. The Ce⁴⁺ ions donate degenerated electrons in the conduction band bottom with extended In 5s character, contrasting to the cases of conventional degenerated widegap semiconductors in which a relatively narrow-width impurity band that merges into the intrinsic bands would be formed.