Fluoride/Oxide Super Hetero-nanostructures for Advanced Photonic Devices

本研究的目的是证明在硅衬底上外延生长的宽禁带离子材料氧化锌(ZnO)或单晶氟化钙(CaF_2)中形成的BeZnSe等宽禁带半导体纳米晶体的紫外光发射。利用这种异质结构，基于隧道注入穿过CaF_2量子垒的紫外光发射器件是有希望的。此外，由于异质界面处大的导带不连续，可以利用强的量子限制，这导致了与体相材料相比电子-光子相互作用的引人注目的变化。采用射频溅射和分子束外延技术在CaF2/Si(111)衬底上生长纳米氧化锌。优化了生长温度、本底压力、射频功率和后退火条件。WAv…的紫外光致发光在室温下观察到较长的380 nm电致发光。透射电子显微镜的点阵图像清楚地证实了CaF_2/ZnO/CaF_2形成了尖锐的异质界面。根据发光强度和表面形貌对生长条件进行了优化。为了提高发光强度，引入了氧气或超高真空的热退火工艺。阐明了发光随退火温度、时间、压力的变化规律。利用光刻和干法刻蚀制备了透明导电ITO电极的隧道注入结构，实现了电流注入发光。在室温下观察到明显的紫外光发射，且发光稳定。由此可见，镶嵌在单晶CaF_2中的纳米氧化锌具有稳定的异质界面，这对硅基紫外光光子材料具有很大的吸引力。首次研究了在CaF_2/Si(111)衬底上生长的BeZnSe的紫外光发射。这种材料体系的优点是与硅衬底的晶格匹配。较少

The purpose of this study is to demonstrate ultra violet (UV) light emission from nanometer size crystals of wide gap semiconductors such as zinc oxide (ZnO), or BeZnSe formed in single crystalline calcium fluoride (CaF_2), which is a wide band gap ionic material epitaxially grown on silicon substrate. Using the heterostructures, UV emitting devices based on tunneling injection through CaF_2 quantum barriers can be expected. And moreover, strong quantum confinement can be utilized due to large conduction band discontinuity at the heterointerface, which leads fascinating changes of electron-photon interaction from the bulk material.Results obtained in this study are as follows.1. Formation technique of nanocrystalline zinc oxide (ZnO) on CaF_2/Si(111) substrate has been developed using RF sputtering followed by regrowth of CaF_2 by molecular beam epitaxy. Growth temperature, background pressure, RF power and post annealing condition was optimized.2. Ultra-violet photoluminescence at wav … More elength of 380 nm and electroluminescence was observed at room temperature. Transmission electron microscopy (TEM) lattice image clearly confirmed that sharp heterointerface of CaF_2/ZnO/CaF_2 was formed. Growth condition was optimized by luminescence intensity and surface morphology.3. Thermal annealing process in oxygen or ultra-high vacuum was introduced for improving luminescence intensity. Dependence of luminescence on annealing temperature, time, pressure was clarified.4. Current injection luminescence was demonstrated using tunneling injection structure with transparent conducting ITO electrode fabricated using photolithography and dry etching. UV luminescence was clearly observed at room temperature and the luminescence was stable. From this result, nanocrystalline ZnO embedded in single crystalline CaF_2 has stable heterointerface, which is attractive for UV photonic materials on silicon substrate.5. UV emission from BeZnSe grown on CaF_2/Si(111) has been demonstrated for the first time. The advantage of this material system is lattice matched with silicon substrate. Less