基于ZnO单晶衬底的氧化物半导体发光二极管量子效率研究

Due to its wide, direct bandgap of 3.3 eV and large exciton binding energy of 60 meV, ZnO has been proposed as a potential material for the use in electro-optic conversion applications. Currently, relatively low quantum efficiency in the active region is also a key factor, as important as the well-known p-type doping, that limits the development of ZnO-based light-emitting devices. As compared with heteroepitaxy, homoepitaxy of ZnO films on bulk ZnO single crystal has great advantages both in quality control of the film and p-type doping. Therefore, this application plans to research on the quantum efficiency of ZnO-based light-emitting diodes (LEDs) on bulk ZnO. Homoepitaxy of ZnO by using metal-organic chemical vapor deposition (MOCVD) will be investigated to obtain high quality ZnMgO/ZnO low-dimensional structures with 2D layer-by-layer growth mode. Active region with high internal quantum efficiency will be designed based on device simulations. MOCVD parameters will be optimized to realize such high quality active region with low non-radiative recombination center number, homogeneous composition, accurate thickness, and abrupt interface. Substrate thinning and substrate transfer technique will be developed to minimize the self-absorption effect of the emitted photons in the material. Surface roughness method such as pyramid microstructures and nanorod arrays will be investigated to enhance the light extraction efficiency. ZnO-based LEDs with high external quantum efficiency will be eventually fabricated, and during this program, oxide semiconductor optoelectronic devices process will be set up.

ZnO由于具备宽直接带隙和大激子束缚能等优异特性，在面向新能源的光电转换材料和器件领域有着广阔的应用前景。目前，低的有源区量子效率是与p型掺杂具有同样重要性的制约ZnO基发光器件发展的关键问题。本项目将利用ZnO单晶衬底在薄膜外延和p型掺杂中的优点，同时规避其对光子自吸收的缺点，开展基于ZnO单晶衬底的氧化物半导体发光二极管量子效率研究。在ZnO单晶衬底上进行薄膜的MOCVD同质外延生长，实现以二维层状模式生长的ZnMgO/ZnO低维异质结构。在器件模拟仿真基础上设计出具有高内量子效率的有源区结构，优化MOCVD生长工艺，减少非辐射复合中心数目，获得组分均匀、厚度精确、界面陡峭的有源区，获得高的内量子效率。采用衬底减薄和衬底转移技术，降低材料对光子的自吸收效应；通过表面粗糙化等手段提高光子的提取效率，从而实现具有高外量子效率的LED器件。在此过程中建立起氧化物半导体光电子器件制备工艺。

ZnO由于具有宽直接带隙和大激子束缚能等优异特性，在面向新能源的光电转换材料和器件领域有着广阔的应用前景。本项目利用ZnO单晶衬底在外延薄膜质量和p型掺杂中的优点，开展了基于ZnO单晶衬底的氧化物半导体发光二极管发光效率改进的研究。项目研究了采用CVD法基于Ga掺杂ZnO单晶衬底上的ZnO纳米线阵列的同质生长，该结构的n型Ga掺杂ZnO导电层和纳米线之间形成了高质量的同质界面，从而有利于载流子的输运，为了验证其实用性，我们的工作首次将这样的Ga掺杂ZnO单晶基ZnO纳米线阵列制备染料敏化太阳能电池。项目采用Mg-N共掺杂的方案对p型ZnO的导电稳定性进行了改进。研究发现Mg的并入对ZnO掺N的掺杂效率具有促进作用。在热退火之后，我们发现MgxZn1-xO:N薄膜中的N相对含量相比ZnO:N薄膜更高，表明了N元素在MgxZn1-xO:N薄膜晶格中更为稳定。研究了n型Al掺杂ZnO薄膜的电学性质随生长及退火条件的变化。研究了ZnO，ZnMgO薄膜的干法和湿法刻蚀工艺。项目研究了ZnO薄膜的金属半导体接触，探索优化了欧姆接触和肖特基接触的制备工艺。在以上工作基础上，项目设计、生长了基于n-ZnO/i-ZnO/p-ZnMgO:N结构的发光二极管器件。项目对ZnO、MoO3、Bi2O3三元体系相图进行了研究，以试图寻找熔岩法生长ZnO单晶的合适助溶剂。为ZnO单晶生长及ZnO的相图的基础数据都提供了重要的实验基础。研究了新型半导体材料α-HgI2晶体的生长和光电性质。研究了一种在紫外光下具有高效杀菌抗菌性能的ZnO多层膜光催化剂涂层的结构设计与制备方法。另外项目还研制了i-MgZnO/p-GaN深紫外探测器以及研究了TiO2电子传输层对钙钛矿太阳能电池的影响。