ABSTRACT
Zinc oxide (ZnO) is one of the II–VI semiconductor materials with a wide direct bandgap of 3.37 eV and a large exciton binding energy of 60 mV. In addition, ZnO is environmentally friendly and presents high thermal stability, low cost, and abundant availability. Because of these advantages, ZnO is considered as one of the most promising materials for generating high-efficiency short-wavelength excitonic luminescence and fabricating semiconductor lasers with a low threshold. In this chapter, properties of ZnO are introduced and recent progress in ZnO-based light-emitting diode (LED) research is reviewed. The ZnO thin-film LEDs and ZnO nanostructure LEDs are discussed in detail. With regard to ZnO thin-film LEDs, though ZnO-based homojunction LEDs have been continuously researched, the lack of reproducibility of high-quality p-type ZnO is still the bottleneck hindering their further development. Then, the advantages of ZnO are explored and exploited by forming ZnO-based heterojunctions, such as metal–insulator–semiconductor (MIS) heterojunction, n–n heterojunction, p–n heterojunction, and other complicated structures, including multiple heterojunction LEDs, and quantum well (QW) and multiple quantum well (MQW) LEDs. Meanwhile, various kinds of novel ZnO-based LEDs with nanoscale structures have been fabricated recently. They show exciting and satisfactory performance. With regard to ZnO-based LEDs, we have much more work to do. We believe they will emit bright short-wavelength light, even bright short-wavelength laser, in future.
