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Electrical Conductivity in Transparent ZnGa2O4: Reduction and Surface‐Layer Structure Transformation

1998; Wiley; Volume: 81; Issue: 1 Linguagem: Inglês

10.1111/j.1151-2916.1998.tb02311.x

1551-2916

Zheng Yan, Humihiko Takei, Hiroshi Kawazoe,

Ga2O3 and related materials

An optically transparent and electrically conductive surface layer has been obtained by hydrogen annealing a bulk single crystal of ZnGa 2 O 4 , where a band gap as wide as 4.0 eV has been calculated from the results of optical transmittance. The carriers are mainly generated from oxygen vacancies. The conductivity is 10 −1 S/cm at a temperature of 290 K, and the activation energy of donors, which is derived from the conductivity‐temperature relation, is 0.02 eV. Although various reduction conditions have been used to increase the thickness of the conductive layer, it is limited to ∼50 µm. Zinc depletion at the surface layer of all the annealed samples has been detected, and a two‐layer reduction process of the hydrogen annealing has been suggested. X‐ray precession photographs show a structural transformation from the normal spinel Fd 3 m space group to the rhombohedral R3 m space group of the conductive layer, which seems to be related to the conversion of zinc atoms from a tetrahedral coordination to an octahedral coordination. The converted electronic configuration of the surface layer, which is caused by the position shift of zinc atoms, is thought to be beneficial to high conductivity.