氧化锌自组装量子点制备及发光应用研究

Quantum dots are promising structures used to overcome the "efficiency droop" of semiconductor light-emitting devices with quantum well structures. And the applications of oxide semiconductor on light-emitting devices have attracted much attention in recent years. However, there are still many problems to be settled about controllable growth of oxide quantum dots that can be used as the active region in a light-emitting diode. The plan of this project is to grow self-organized ZnO quantum dots in monolayer or multilayer, and investigate their luminescence properties. The very small size of ZnO quantum dots can induce quantum confined effect. And a barrier layer with wider band gap such as ZnMgO can introduce further confinement. Then carriers can be confined in the quantum dots and the efficiency of radioluminescence can be enhanced. When ZnO quantum dots are grown in multilayer with barriers between each layer, there could be coupling between quantum dots of different layers, and the luminescence efficiency can be improved further. Besides growing a series of ZnO quantum dots with uniform size and morphology in monolayer or multilayer, we intend to modulate the band gap of ZnO quantum dots by alloying, in order to increase the potential confinement and realize luminescence enhancement. In this project we will also investigate the stress states of the interface between quantum dots and the barrier layers which could affect the luminescence properties, by means of tunneling the component, thickness of the barrier layer and adopting post-growth annealing. The investigations of growth and luminescence properties of self-organized ZnO quantum dots can promote the applications of ZnO optoelectronic devices.

量子点结构能显著改善半导体量子阱结构发光器件的效率衰减问题，采用量子点结构设计已成为研制新型高效发光器件的有效手段。目前，氧化物半导体发光应用成为国际研究热点。但用作有源层的氧化物半导体量子点可控制备仍有许多难题需要解决。本项目以新型宽带隙光电功能材料氧化锌的量子点结构为研究对象，利用量子点结构本身的尺寸限制以及氧化锌所具有的更宽带隙隔离层的势阱限制，结合多层量子点之间的耦合，设计和制备多层氧化锌基自组装量子点结构。通过控制氧化锌量子点生长和掺杂的过程，制备一系列尺寸可控、形貌均匀、带隙可调的单层和多层量子点；通过控制隔离层的组分、厚度以及退火处理等参数，研究各种因素对隔离层与量子点界面处的应力状态和量子点发光性能的影响，从而实现对多层结构量子点界面状态的调控；对多层量子点结构的层数和厚度等参数进行优化，提升多层氧化锌基量子点结构的发光效率，推动其在新型高效发光二极管中的应用。

本项目采用MOCVD方法自组装生长ZnO量子点，并对ZnO量子点的生长机理及能带结构进行了研究；采用碳球模板法制备了多种ZnO基纳米晶（广义上的量子点），并对这些纳米晶的性能进行了研究。采用STM/STS对ZnO量子点生长机理的研究结果表明厚度低于1nm的ZnO量子点呈现类似于石墨的层状结构，并且具有更宽的禁带宽度（厚度为0.25nm的ZnO量子点带隙宽达5.2eV）；而厚度大于1.4nm的量子点则呈现六方铅锌矿结构，且在其禁带中同时存在施、受主缺陷能级。结合理论计算分析，确认该施、受主对为VO-VZn，从实验角度确证ZnO中存在较强的自补偿效应。这一结果不仅对于生长ZnO量子点有指导意义，对于探讨ZnO的p型掺杂机理及克服p型掺杂瓶颈也有很强的参考价值。采用碳球模板法制备的ZnO-NiO纳米晶异质结构是由相邻的ZnO、NiO纳米晶组成的超薄空壳球状结构，该结构由于形成了p-n异质结，其内建电场促进了电子、空穴的分离，因而具有优异的光催化性能，可用于光催化降解有机物。采用同样方法制备的ZnMgO纳米晶则可以在Mg含量高达48%时仍不分相，对于调控ZnO纳米晶的禁带宽度和发光波长具有重要意义。采用同样方法制备的ZrO2:Fe纳米晶具有由Fe掺杂量决定的可调的禁带宽度，而且可以实现可见光催化分解水产生氢气，具有重要的应用价值。