Exploration of photonic electronic magnetic and their mutual functionalities in non-equilibrium and transparent oxide thin films accelerated by parallel epitaxy

高T_c超导体被发现后，外延氧化物薄膜的研究得到了迅速发展，其研究领域已经扩展到铁电、磁性和光子等多种功能。晶体生长过程和异质结构的原子尺度控制探索了氧化物电子，其中氧化物半导体在实现常规半导体无法实现的应用方面发挥了重要作用。本研究以透明半导体材料如氧化锌和二氧化钛为研究对象，通过高效的并行合成方法，使其具有新颖的光、电、磁功能。这些原型器件已经被证明是氧化锌紫外发光二极管、高迁移率的氧化锌隐形晶体管、(TiCO)_2的磁性隧道结。以下是输出的例子。光子功能1.温度梯度法是平行外延法中的一种，用来优化生长条件以制备世界上最好的本征氧化锌。首次开发了重复调温技术，以促进氮作为受体的掺入和活化，从而首次制备出P型氧化锌。在氧化锌pn结中观察到紫外光发光。电子功能4.利用模拟器建立了多晶沟道氧化锌薄膜晶体管模型，阐明了影响器件性能的限制因素。在单晶氧化锌薄膜中获得了200cm2ns的场效应迁移率。首次在氧化物中观察到量子霍尔效应。磁性7.磁光效应和反常霍尔效应证实了二氧化钛中载流子的自旋极化性质。作为宽禁带磁性半导体自旋注入器件的第一个例子，我们展示了TiO2：Co的磁性隧道结。用第一性原理计算方法研究了二氧化钛：钴的电子结构。

After the discovery of high Tc superconductors, the research on epitaxial oxide thin films has been rapidly advanced to extend its research area to versatile functionalities such as ferroelectric, magnetic, and photonic ones. Atomic scale control of crystal growth process and heterostructures explore oxide electronics, among which oxide semiconductors play important role to realize applications that cannot be achieved by conventional semiconductors. In this research program, transparent semiconductors such as ZnO and TiO_2, are examined to donate novel photonic, electronic and magnetic functionalities through efficient parallel synthesis method. Such prototypical devices have been demonstrated as ZnO ultraviolet light emitting diodes, high mobility ZnO invisible transistors, magnetic tunnel junctions of (TiCo)_2. The followings are examples of the output. Photonic Functionality1. Temperature gradient method was developed as one of the parallel epitaxy method to optimize the growth conditions for making world-best intrinsic ZnO.2. P-type ZnO was produced for the first time by developing repeated temperature modulation technique to facilitate the incorporation and activation of nitrogen as acceptors.3. Ultraviolet LED was demonstrated in ZnO pn-junctions. Electronic Functionality4. Polycrystalline channel ZnO thin film transistors were formulated by a simulator and limiting factors of device performance were clarified.5. A field effect mobility of 200cm2Ns was achieved in single crystalline ZnO TFT.6. Quantum Hall effect was observed in oxide for the first time. Magnetic Functionality7. Spin polarized nature of charge carriers in TiO_2: Co was confirmed by magneto-optic and anomalous Hall effects.8. Magnetic tunnel junctions of TiO_2: Co was demonstrated as a first example of spin injection device of wide bandgap magnetic semiconductors.9. Electronic structure of TiO_2: Co was studied by first principle calculation.