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

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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