非对称氧化锌悬空薄膜微腔回音壁模紫外激射研究

Based on the wide direct bandgap (3.4 eV) and large exciton binding energy(60 meV), zinc oxide (ZnO) has been thought of the most promising candidate material for ultraviolet(UV) laser. As a natural whispering gallery mode (WGM) microcavitiy, ZnO single crystal can predominantly emit out the WGM lasing with a low threshold and high quality (Q) factor from its hexagonal corners, but the multi-directional emission is adverse for the ZnO WGM laser’s practicability, which restricts the WGM laser’s integration with optoelectronic chips. Therefore, an asymmetrical suspending ZnO thin film microcavity supported by cantilever is designed and fabricated using the advanced micro-nano fabrication technology, which is in favor of the integration with optoelectronic chips. The light transfers by the WGM way in the microcavity, and the perpendicular directional optical mode in the microcavity is also strongly restricted, because of total internal reflection at the boundary of thin film microcavity. The WGM effect and optical confinement can greatly reduce the optical loss of the microcavitiy, and obtain unidirectional emission of ZnO WGM ultraviolet lasing. The project will study the physical phenomena and processes in the asymmetrical ZnO microcavity, including ultraviolet lasing generation, transmission, amplification and optical oscillation. And the stimulated emission properties of different asymmetrical shaped microcavities such as unidirectional emission, the threshold, Q factor and lasing mode will be investigated. Also, the methods and physical basis of improving the WGM laser’s properties will be explored. It will provide theoretical and technical support for new physical processes, the design and preparation of lasers.

ZnO宽直接带隙（3.4 eV），强激子结合能(60 meV)，是制备紫外激光器的理想材料。ZnO单晶作为天然的回音壁模（WGM）微腔可以获得低阈值高品质因子（Q）的激光，但是激光从其六个棱角的分散性发射降低了ZnO WGM激光器的实用性，限制了其与光电子器件的集成。因此，申请人利用先进的微纳加工技术设计并制备一种面向光电子器件集成的由悬臂梁支撑的非对称ZnO悬空薄膜微腔，光线在微腔边界处的全内反射以WGM形式传导，并且垂直方向的光学模也受到强烈限制。这种WGM传导作用和光学限制极大地降低了微腔的光学损耗，可以获得单方向性发射的高Q值WGM紫外激光。本项目利用非对称ZnO悬空薄膜微腔研究紫外光的产生、传播、放大和振荡的物理现象与过程，探讨不同形状的非对称微腔的激射特性如发射方向、阈值、Q值、模式结构等，探索提高激光性能的方法与物理依据，为新型激光器的设计和制备提供重要的理论和技术支持。

硅基片上光源是当前半导体技术皇冠上的明珠，它的研制成功将会引领整个硅基光电子集成技术的重大变革。而半导体WGM微腔激光器是一种理想的光源。本项目主要研究WGM激光器器件，主要包含以下内容：.1.利用ZnO单晶微棒成功构建了回音壁微腔，设计并制备了ZnO微米棒/PMMA/p-GaN 回音壁模微微激光器阵列，提高了ZnO腔体的相对折射率，调整了器件的能带结构，进而提高了电泵浦激光的性能，，通过多个微腔的并行工作，提高了电泵浦激光的功率。 .2.利用制备的ZnO单晶微米棒，构建可以发出不同波段回音壁模激光的 ZnO微米棒/R6G结构，经过光泵浦实现，实现了紫外波段和橙色波段的回音壁模激光，并且探讨了同轴模式的激光的循环共振机制。.3.设计并制备“圆+锥角”的非对称悬空薄膜微腔，获得了单方向性辐射的高增益低损耗的GaN WGM紫外激光，对微光源的集成有重要意义。.4.制备直径为4.9微米侧壁带光栅的的GaN悬空微盘，获得了高品质因子低阈值的GaN单模WGM激光，.5.设计并制备了GaN悬浮微环激光器，在室温下观察到了回音壁紫外激光。激光阈值150 kW/cm2, 品质因子1800,发现激射的7个激光峰来自于三种不同模式，研究了环形激光中的WGM微腔的共振机理。.6.通过MOCVD生长和微加工技术获得了悬空的GaN/Graphene六边形单晶，获得了高品质因子的WGM紫外GaN激光，并且利用制备的器件研究了体温范围内的温度传感器。.7.设计并制备圆加狭缝的GaN悬浮微盘激光器，微腔的横截面设计为带缺口的圆形状通过空气狭缝可以调控微腔的模式结构，提高WGM激光的品质因子，同时实现WGM激光的方向性辐射，为下一步实现锁模激光器提供了研究基础。.8.利用MOCVD在p-GaN薄膜进行选择性生长制备GaN六边形单晶阵列，形成同质结激光器阵列，为下一步的目标是制备电泵浦的微型WGM激光器提供的研究基础。