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

本研究的目的是证明在宽禁带离子材料氟化钙(CaF2)中形成的纳米硅晶体具有新的光学性质。在这类材料系统中，由于异质界面处的大导带不连续，可能会产生强烈的量子限制，从而导致体相材料中电子-光子相互作用的迷人变化。本研究的结果如下：i)利用分子束外延技术，利用部分电离的CaF_2束外延技术，在室温下观察到了可见的光致发光和电致发光。利用生长温度、生长速率、流量比等参数对薄膜的发光强度和表面形貌进行了优化。3)为提高发光强度和均匀性，引入了快速热退火工艺。(4)采用电流阻挡SiO_2层的电流限制结构和采用光刻和湿法化学腐蚀制备的透明导电ITO电极，实现了电流注入发光。样品的电流注入发光即使在室温下至少超过6小时也是稳定的。由此可见，嵌入在单晶CaF_2中的纳米硅具有稳定的异质界面，这对硅衬底上的光子材料是有吸引力的。

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.