ZnO发光二极管研制与发光效率提升机制研究

In this project, we highlight the fabrication of ZnO-based LED and mechanism of advancing its luminescence efficiency. Na doping is developed to explore p-type ZnO single crystalline films via MOCVD and MBE technique. Specifically elements, such as Mg etc., are proposed to weaken the compensation of intrinsic donors, and reduce the energy level of Na acceptor. And assistant dopant H is introduced to play an important role in restraining interstitial dopants. P-type doping with high hole concentration and high stability is expected be achieved in this project. The studies on advancing luminescence efficiency of ZnO-LED will be concentrated on the preparation and structural designing of high quality ZnO/ZnMgO quantum wells with atomic-level controlled interfaces. The carriers will be high efficiently confined and high luminescence efficiency can be foreseen. High efficient LED fabrication packages the optimized LED structures and p-type ohmic contact using multilayer metals. We aim at obtaining high inject efficiency and high outer luminescence efficiency simultaneously. In this project, we will develop independently the preparation of ZnO-based single crystalline films, p-type doping strategies (including exploring metal-organic sodium source), bandgap engineering, even the p-type ohmic contact and LED structures. Our strategy will not only pave the way for further research and industrialization of ZnO-based devices, but be highly significant to novel materials and devices oriented to energy saving white light illumination.

本项目针对ZnO发光二极管（LED）研制和发光效率提升机制，采用MOCVD、MBE方法制备Na掺杂ZnO单晶薄膜；同时引入合适元素(Mg等)对能带结构、Na受主能级、近邻配位和局部应变进行调控，抑制本征施主补偿、降低受主能级、提高受主掺杂量和稳定性；并采用辅助掺杂剂H提高Na受主替代比，进一步提高空穴浓度和p型稳定性。通过优化工艺实现界面原子级精控，外延生长高质量ZnO/ZnMgO多量子阱；通过多量子阱组分和带阶设计，高效限制载流子，提高发光内量子效率。设计合适LED结构、多层金属p型欧姆接触，构筑注入和出光效率一致优化ZnO-LED芯片体系。本项目从ZnO基薄膜生长、p型掺杂技术（包括钠MO源）、能带调控到LED器件结构设计及制备，整个流程都具有自主知识产权，为今后深入研究和产业化奠定基础。该项目研究为面向能源半导体节能白光照明技术发展提供新材料和新器件体系，具有重要科学意义和实用价值。

宽带隙半导体ZnO具有激子束缚能高等优点，可望获得高效激子发光和低阈值激射，在短波长发光方面具有广阔的应用前景。但由于稳定p型掺杂很难获得，ZnO激子发光效率受缺陷等多种非辐射复合过程影响，ZnO-LED的发光性能还有很大的提升空间。本项目针对ZnO-LED研制及发光效率提升这两个关键科学问题，利用分子束外延方法生长出晶体质量和光学质量都很高的ZnO,ZnMgO薄膜及ZnO/ZnMgO多量子阱结构，为高效发光提供材料基础。主要选取Na为受主掺杂剂，通过Be-Mg共掺调控能带和掺杂引入的应变，提高了p型性能；并深入研究Na掺杂机理及稳定性机制，发现Na受主存在两个能级新现象，阐明其失活机理是受主向施主转变，为p型稳定性提供理论依据。系统研究了ZnO中激子复合动力学，探明了影响ZnO激子发光效率的主要因素，并探索了表面等离激元耦合以及离子注入消除锌空位两条途径以提升发光效率，将ZnO材料发光内量子效率最高提高到40%以上。在此基础上，在pn结中集成ZnO/ZnMgO多量子阱作为发光有源层，研制出性能良好的ZnO-LED器件，在室温下获得375 nm紫外带边电致发光，为高效发光器件奠定基础。本项目研究丰富了ZnO掺杂、发光和器件物理的知识体系，为ZnO基发光器件的性能提升提供了科学依据和可行途径，具有重要的科学意义和潜在应用价值。