Study of ZnO based heterostructures towards realizing high-luminous efficiency ultraviolet to blue light-emitting diodes

自2005年首次实现同外延LED以来，氧化锌（ZnO）由于其优越的性能而受到越来越多的关注。它们的性能有望从高发光效率到低成本和清洁生产力，利用丰富的来源和商业上可用的单晶衬底。本研究旨在提高导电ZnO基板上制造的LED的电致发光效率，其中垂直接触几何结构可以更好地用于实际应用。利用分子束外延技术，我们制备了由p型和n型MgZnO势垒层夹在ZnO阱层之间的双异质结构。从而实现了高效的带边电致发光。因此，我们的研究为商业化产品的开发铺平了道路。寻找一种透明的金属材料来形成更良好的欧姆接触p型层也是一个重要的方案。我们发现一种功函数大的导电聚合物具有良好的性能，并且适用于简单的自旋涂层。此外，该聚合物对于n型ZnO的肖特基接触非常有用。然而，如何正确分析空穴浓度和提高氮掺杂效率等技术问题仍有待解决。在与本研究相关的其他观点中，可以获得一些显著的成果；(1) MgZnO/ZnO异质结构中量子霍尔效应的观察（发表于高影响力期刊之一的Science） (2) MgZnO薄膜的外延生长具有创纪录的长光致发光寿命，这都表明了先进的技术水平。总的来说，成绩可以认为是显著的和令人满意的建议的内容。此外，本研究还为下一步研究课题（氧化物半导体低维结构输运性质研究）的开展提供了基本思路、知识和技术。少

Zinc oxide (ZnO) has been attracting increasing attentions due to their superior properties for making ultraviolet to blue light-emitting diodes (LED) since the first homoepitaxial LED was realized in 2005. Impacts of their performance are expected to span from high-luminous efficiency to low-cost and clean productivity, taking advantages of abundant source and commercially available single-crystalline substrates. This study aims at improvement of electro-luminescence (EL) efficiency of LED fabricated on conducing ZnO substrates, where vertical contact geometry can be utilized being preferable to practical application. Using molecular beam epitaxy technique, we have fabricated double-heterostructures consisting of ZnO well layers sandwiched by p-and n-type MgZnO barrier layers. As a result, highly efficient band-edge EL is realized. Thus, our study paves a way for development of commercial products. It is also an important protocol to search a transparent and metallic material to form … More good Ohmic contact to p-type layer. We find that a conducting polymer having a large work function has good properties as well as applicability for the use of simple spin-coating. Moreover, this polymer is found to be very useful for making Schottky contact to n-type ZnO. Nevertheless, a few technical issues such as proper analysis of hole concentration and improvement of doping efficiency of nitrogen remain to be solved in future. In other viewpoints associated with the present study, some notable achievements can be obtained; (1) observation of quantum Hall effect in MgZnO/ZnO heterostructures (published in Science, one of high-impact journals) (2) epitaxial growth of MgZnO films having record-long photoluminescence lifetime, both of which indicate state of art technology. Over all achievements can be considered remarkable and satisfactory to contents of proposal. Furthermore, basic idea, knowledge and techniques for pursuing next research subject (study of transport properties in oxide semiconductor low-dimensional structures) have been acquired through this study. Less