Fundamental study for quantum effect devices using nanocrystalline silicon formed in single crystalline insulator

本研究的目的是证明在单晶氟化钙（CaF2）中形成的纳米尺寸硅晶体产生的新的光学性质，这是一种宽带隙离子材料，在这种材料体系中，由于异质界面处的大导带不连续，可以预期强量子约束，这导致了体材料中电子-光子相互作用的有趣变化。本研究的结果如下：i)采用分子束外延技术，利用CaF_2的部分电离束和CaF_2与Si的共沉积，开发了纳米晶硅的形成技术。ii)室温下观察可见光致发光和电致发光。通过生长温度、生长速率、通量比等因素对发光强度和表面形貌进行优化。iii)引入快速热退火工艺，提高发光强度和均匀性。阐明了退火时间、升温速率和环境气体对发光的影响。iv)采用具有阻流SiO_2层的限流结构和采用光刻和湿法化学蚀刻制备的透明导电ITO电极，证明了电流注入发光。即使在室温下至少6小时以上，样品的电流注入发光也很稳定。由此可见，纳米晶硅嵌入单晶CaF_2具有稳定的异质界面，这对硅衬底上的光子材料具有吸引力。

The purpose of this study is to demonstrate new optical properties originated from nanometer size silicon crystals formed in single crystalline calcium fluoride (CaF2), which is a wide band gap ionic material, In such kind of material systems, srong quantum confinement can be expected due to large conduction band discontinuity at the heterointerface, which leads fascinating changes of eletctron-photon interaction from the bulk material.Results obtained in this study are as follows.i) Formation technique of nanocrystalline silicon has been developed using molecular beam epitaxy based technique with partially ionized beam of CaF_2 and codeposition of CaF_2 and Si.ii) Visible photoluminescence and electroluminescence was observed at room temperature. Formation condition was optimized by luminescence intensity and surface morphology using the growth temperature, growth rate, flux ratio.iii) Rapid thermal annealing process was introduced for improving luminescence intensity and uniformity. Dependence of luminescence on annealing time, temperature increasing rate, ambient gas was also clarified.iv) Current injection luminescence was demonstrated using current restriction structure with current blocking SiO_2 layer and transparent conducting ITO electrode fabricated using photolithography and wet chemical etching. Current injection luminescene of the sample was stable even at room temperature at least more than six hours. From this result, nanocrystalline silicon embedded in single crystalline CaF_2 has stable heterointerface, which is atractive for photonic materials on silicon substrate.