基于氧化锌微米线与银薄膜的表面等离子体Fabry-Perot微腔研究

Lower cost, higher power and shorter wavelength of ultraviolet semiconductor lasers have motivated interest in zinc oxide (ZnO) due to its wide direct bandgap (3.37eV) and a large exciton binding energy (60 meV). While possessing natural resonant cavities, such as Fabry-Perot cavity, Whispering-Gallery Mode cavity, ZnO nanowires and microwires could provide an ideal platform to realize laser diodes, efficient light emitting devices (LEDs) and so on. Micro/ nanometer ZnO single crystal can be used to design and build novel microcavities, and can be obtained single photon and multiphoton excitation mode, as well as the UV stimulated radiation with distinct mode characteristics at room temperature. The interactions in the cavity between electron, excitons and photons can also be studied, in order to obtain the polaritons stimulated radiation. In recent years, the recent advent of high performance, high output has led to the design of optical components and novel cavity devices, such as plasmonic nano/micro cavities, plasmonic nanoparticles. Therefore, a new kind of hybrid plasmonic Fabry-Perot microcavities based on ZnO microwire with quadrilateral cross section and double metal films could be designed and built. The gap region inserted silver films and microwire with low-index materials can be treated as the spaser, where the coupling interaction between microwire mode and hybrid plasmonic Fabry-Perot microcavity mode could be established to study the excitation and transport phenomena of surface plasmon wave under optical pumping. The coupling between microwire modes and hybrid plasmonic Fabry-Perot microcavity modes can be applied to achieve the enhanced UV lasing output.

氧化锌具有宽禁带（3.37eV）和强激子结合能（60 meV）在短波长光电器件领域，具有独特的竞争优势。氧化锌微纳米结构拥有天然的微纳腔体，比如法布里-珀罗谐振腔（Fabry-Perot cavity），新型回音壁模（WGM）激光谐振腔等，为研究宽禁带半导体紫外激光输出模式提供了天然的平台。目前，利用ZnO微纳米单晶构建新型微腔，能够在室温下获得了单根微米棒中光子激发的、模式结构清晰的紫外受激辐射。然而宽禁带半导体激光器的研制进展缓慢，发光以及激光激射功率依然上不去，究其原因除了材料制备外就是如何构建高质量的光学谐振腔。因此，本项目希望在四面柱体结构的ZnO微米线上设计和构建表面等离子体Fabry-Perot基微米级谐振腔。在微米线与金属薄膜之间存在亚波长区域能调控光学微腔中银表面等离子激元的激发、输运过程与氧化锌激子之间的相互作用，以实现表面等离子体Fabry-Perot模式的激光输出。

本项目研究过程中，我们针对ZnO基微纳结构的可控性生长，n-型/p-型掺杂，ZnO高品质的光学谐振腔，金属纳米结构的表面等离子体激元对ZnO基微腔Q增强、光泵浦激光输出增强等物理特性，进而基于掺杂ZnO微米线构筑新型电致发光器件等方面展开了研究。研究结果在Small, Adv. Funct. Mater., ACS Photonics, Nanoscale，ACS Appl. Mater & Interface，J. Mater. Chem. C等国际刊物发表SCI论文11篇, 包括Small, J. Mater. Chem. C，Nanoscale期刊封面或封底报道论文4篇。培养3名博士获得学位。主要的进展与创新成果列举如下： .（1）利用单层石墨烯优异的光学、电学等特性，构建了Graphene@ZnO微米线复合光学微腔，实现了石墨烯表面等离子体激元共振增强ZnO基WGM模式的光泵浦激射增强，通过对Graphene/ZnO界面处杂化表面等离子体波传输特性的理论分析与模拟，发现石墨烯的表面等离子体激元的局域特性能极大的改善ZnO微米线的波导损耗，提高光场限域性，从而实现光泵浦激射的增强。 .（2）通过调控生长条件，实现了ZnO微纳结构的可控性生长，比如横截面为四边形的ZnO微米线，微米带；以及横截面为六边形的ZnO微米线。在针对ZnO微米线光学、电学特性的改性上，通过对反应源的掺杂实现n-/p-型ZnO微米线的掺杂，极大的调控ZnO微米线单根导电能力。 .（3）通过Ga/Sb等元素的掺杂，基于单根微米线MSM结构，实现电致发光，发光区局限于微米线的中间区域，且发光的亮度以及发光区的长度随注入电流的增加而出现明显的增强；同时我们对其电致发光的物理机制进行初步的研究，这是一种新型的电致发光现象，有别于现有的物理机制，因此我们构筑一种新型的 “semiconducting emitters”..（4）随着Ga元素含量的增加会造成大量的电子，进而形成对ZnO导带的填充，使得Fermi能级进入导带中，形成ZnO近带边发光的蓝移；我们制备了单根ZnO:Ga微米线异质结发光二极管。二极管能极大的抑制ZnO:Ga/p-GaN结区界面处的发光，将结区耗尽层限域在ZnO:Ga微米线中。同时，随微米线中Ga元素含量的增加，可实现异质结二极管在紫外波段发光峰可控。