title: Light-Induced Peroxide Formation in ZnO: Origin of Persistent Photoconductivity.
abstract: The persistent photoconductivity (PPC) in ZnO has been a critical problem in opto-electrical devices employing ZnO such as ultraviolet sensors and thin film transistors for the transparent display. While the metastable state of oxygen vacancy (VO) is widely accepted as the microscopic origin of PPC, recent experiments on the influence of temperature and oxygen environments are at variance with the VOmodel. In this study, using the density-functional theory calculations, we propose a novel mechanism of PPC that involves the hydrogen-zinc vacancy defect complex (2H-VZn). We show that a substantial amount of 2H-VZncan exist during the growth process due to its low formation energy. The light absorption of 2H-VZnleads to the metastable state that is characterized by the formation of (peroxide) around the defect, leaving the free carriers in the conduction band. Furthermore, we estimate the lifetime of photo-electrons to be ~20 secs, which is similar to the experimental observation. Our model also explains the experimental results showing that PPC is enhanced (suppressed) in oxygen-rich (low-temperature) conditions. By revealing a convincing origin of PPC in ZnO, we expect that the present work will pave the way for optimizing optoelectronic properties of ZnO.
authors.affiliation: Department of Materials Science and Engineering and Research Institute of Advanced Materials, Seoul National University, 151-742, South Korea.
authors.forename: Youngho
authors.initials: Y
authors.lastname: Kang
authors.affiliation: Center for Correlated Electron Systems Institute for Basic Science (IBS) Seoul 151-747, South Korea.|Department of Physics and Astronomy, Seoul National University, Seoul 151-747, Korea.
authors.forename: Ho-Hyun
authors.initials: HH
authors.lastname: Nahm
authors.affiliation: Department of Materials Science and Engineering and Research Institute of Advanced Materials, Seoul National University, 151-742, South Korea.
authors.forename: Seungwu
authors.initials: S
authors.lastname: Han