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

本研究的目的是证明新的光学性质来源于纳米尺寸的硅晶体形成的单晶氟化钙（CaF 2），这是一种宽带隙离子材料，在这种材料系统中，强量子限制可以预期由于大的导带不连续性在异质界面，这导致了体材料中电子-光子相互作用的奇妙变化。本研究得到的结果如下：采用CaF_2部分电离束和CaF_2与Si共沉积的分子束外延技术，发展了纳米硅的形成技术在室温下观察到可见光致发光和电致发光。通过生长温度、生长速率、流量比等因素对薄膜的发光强度和表面形貌进行优化。（3）采用快速热退火工艺提高薄膜的发光强度和均匀性。（4）利用光刻和湿化学腐蚀方法制备了具有电流阻挡SiO_2层的电流限制结构和透明导电ITO电极，研究了电流注入发光。样品的电流注入发光即使在室温下也稳定至少6小时以上。这一结果表明，镶嵌在单晶CaF_2中的纳米晶硅具有稳定的异质界面，这对硅基光子材料的制备具有重要的指导意义。

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.