Thin Film Processing of Newly Found, Conductive Transparent Oxides

1)超宽带隙n型导电氧化物单晶的制备。用助熔剂法制备了禁带宽度大于4.5 eV、紫外区透明的ZNGA_2O_4和Ga_2O_3尖晶石单晶。通过将单晶置于中等温度的还原气氛中，可以任意控制氧空位的浓度。氧空位是电子的供体。通过估算Ga_2O_3单环部分方向的Holl迁移率，实验证明金红石链是由氧GaN八面体的边共享组成的线性链，是一种高电子方式。3)非晶态透明金属导电氧化物的发现。这种材料可用于制作可模拟传输电能的大规模光波导。在CDO-GeO_2和CDO-PbO_2系统的富CDO组分区发现了玻璃状、透明的金属氧化物。优化了制备薄膜的工艺条件。4)提出了寻找p型导电宽禁带氧化物的工作假设。这项研究中最重要的问题是如何改变氧化物中价带顶部的局域性。在典型的氧化物中，价带的最高能级完全由O_2p原子轨道组成。由于O_2p能级能量较低，这几乎完全定域在单个氧上，不会发生离域。该问题采用了两种不同的方法：一种是选择具有ns^2个孤对的阳离子，如Tl^+，Pb^&lt；2+&gt；和Bi^&lt；3+&gt；另一种是选择闭合壳层，必须选择填充d带能量最高的阳离子。

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.