This article provides a review of materials and devices of wide-bandgap oxide semiconductors based on ZnO, highlighting the nature of the chemical bond. The electronic structures of these materials are very different from those of conventional covalently bonded semiconductors, owing to the ionic nature of the chemical bonds. Therefore, one needs to design and optimize fabrication processes and structures of active devices containing such materials, taking into account the peculiar defect formation mechanisms. A variety of active devices that have clear advantages over the conventional ones have been demonstrated, for example, ultraviolet light-emitting diodes, quantum Hall devices, and transparent and flexible thin-film transistors with high electron mobility, paving the way for future applications. The reasons behind the successes identify future challenges in research on oxide semiconductors.
Toshio Kamiya can be reached by e-mail at email@example.com.
Kamiya is an associate professor in the Materials and Structures Laboratory at the Tokyo Institute of Technology. He started his research career as an assistant professor of Department of Inorganic Materials at Tokyo Institute of Technology in 1991, working on ferroelectric inorganic materials, and received his PhD degree in 1996. Kamiya moved to the Interdisciplinary Graduate School of Science and Engineering and worked with silicon thin films from 1996 to 2000. From 2000 to 2002, he spent two years as a visiting scholar at the Microelectronics Research Centre, Cavendish Laboratory, at the University of Cambridge, studying on single-electron transistors. Kamiya became an associate professor in 2002 and has since studied functional oxide materials. His field of research includes exploration, materials design, and device applications of new functional oxides. Kamiya has published approximately 200 scientific papers. In addition, he has received The Young Scientists' Prize by MEXT, The Advanced Technology Award by the Fuji-Sankei group, and The DV-Xα Research Award for young scientists by the Society for Discrete Variational Xα.
Masashi Kawasaki can be reached by e-mail at firstname.lastname@example.org.
Kawasaki is a professor in the WPI Advanced Institute for Materials Research at Tohoku University, Japan. He received his PhD degree from the Department of Chemical Energy Engineering at the University of Tokyo in 1989, working on amorphous semiconductor superlattices and high Tc superconducting films. Kawasaki spent two years at IBM Thomas J. Watson Research Center as a postdoctoral research fellow before he received a research associate position in 1991, and an associate professor position in 1997 at Tokyo Institute of Technology. He moved to Tohoku University as a full professor in 2001. Kawasaki is co-assigned as a team leader of Cross-Correlated Materials Research Group (CMRG) at RIKEN, chief innovation officer at COMET Corp., and a project leader of CREST of JST. His field of research includes optical, electronic, magnetic, and their mutual functionalities at the interfaces made of oxide semiconductors and correlated electron oxides. Kawasaki has published more than 400 scientific papers, from which more than 12,000 citations have been recorded (h-index = 52). In addition, he has received the IBM Japan Prize, the Marubun Scientific Award, the JSPS Prize, the Yamazaki-Teiichi Prize, and the CSJ Award for Creative Work.