Thin Film Processing of Newly Found, Conductive Transparent Oxides

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Resurlts obatined in the present study are summarized in the following.1) Fabrication of single crystals of n-type conductive oxides with ultra wide band gap. Single crystals of ZnGa_2O_4 spinel and Ga_2O_3, both having band gap larger than 4.5eV and there by transparent in UV region, were successfuly produced by flux method.2)Control of conductivity of ZnGa_2O_4 and Ga_2O_3 single cystals. By exposing the single crystal to reducing atmosphere at a moderate temperature, concentration of oxygen vacancies was controlled arbitrarily. The oxygen vacancy is a donor of electrons. It was experimentally evidenced that the rutile chain which is a linear chain composed by edge sharing of oxygan octahedra is a high way of electrons by estimating Holl mobilities of partialar directions of Ga_2O_3 single cystal.3)Finding of amorphous tranparent and metallic conductive oxides. This type of material fascilitates fabrication of large scale optical waveguides which can transmit electricity simulataneoasly. Glassy, transparent and metallic oxides were found in the CdO rich composition region of CdO-GeO_2 and CdO-PbO_2 systems. Preocessing conditions for fabricating the thin films were optimiged.4)Proposition of working hypotesis for finding p-type conductive wide gap oxides. Most essential problem in this study is how we can modify localized nature of the top of valence band in oxides. In typical oxides the uppermost level of valence band is composed exclusively by O_2p atomic orbitak. Because of low energy of O_2p level, this is almost totally localizing on a single oxygen, and delocalization is not expected. Two different approaches were utilized in the problem : One is selecting the cations with ns^2 lone pair such as Tl^+, Pb^<2+> and Bi^<3+>. Another is selecting nd^<10> closed shell, cations within those cations in which the energy of the filled d band is expected to highest must be selected.