Fluoride/Oxide Super Hetero-nanostructures for Advanced Photonic Devices

本研究的目的是展示宽禁带半导体纳米晶体如氧化锌（ZnO）或BeZnSe在单晶氟化钙（CaF_2）中形成的紫外（UV）光发射，所述氟化钙是一种宽禁带离子材料。利用这种异质结构，有望实现基于CaF_2量子势垒隧穿注入的紫外发光器件。此外，由于异质界面处的大的导带不连续性，可以利用强的量子限制，导致体材料中电子-光子相互作用发生有趣的变化。采用射频溅射和分子束外延技术在CaF_2/Si（111）衬底上生长纳米氧化锌（ZnO）。优化了生长温度、背景气压、射频功率和后退火条件.波长紫外光致发光 关于我们 在室温下观察到380 nm的发射波长和电致发光。透射电子显微镜（TEM）的晶格图像清楚地证实了CaF_2/ZnO/CaF_2形成了尖锐的异质界面。以发光强度和表面形貌为指标，优化了生长条件.为了提高发光强度，引入了氧气或超高真空热退火工艺。研究了退火温度、时间、压力对发光的影响.电流注入发光是利用隧道注入结构与透明导电ITO电极，通过光刻和干法刻蚀制作。在室温下清楚地观察到UV发光，并且发光稳定。由此可见，纳米ZnO嵌入单晶CaF_2中具有稳定的异质界面，这对硅衬底上的紫外光子材料具有很大的吸引力.本文首次报道了在CaF_2/Si（111）衬底上生长的BeZnSe的紫外发射。这种材料系统的优点是与硅衬底晶格匹配。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