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International Affairs Students Current Students Alumni Faculty/Staff Careers--> TOHOKU UNIVERSITYCREATING GLOBAL EXCELLENCE Search 日本語 Contact Tohoku University --> About Facts & Figures Facilities Organization Chart History President's Message Top Global University Project Designated National University Global Network Promotional Videos Academics Undergraduate Graduate Courses in English Exchange Programs Summer Programs Double Degree Programs Academic Calendar Syllabus Admissions Undergraduate Admissions Graduate Admissions Fees and Expenses Financial Aid Research Feature Highlights Research Releases University Research News Research Institutes Visitor Research Center Research Profiles Academic Research Staff Campus Life International Support Office IT Services Facilities Dining & Shops Campus Bus Clubs & Circles News University News Research--> Arts & Culture Health & Sports Campus & Community Press Release--> International Visit Alumni Careers Events Exhibits Music Special Event Lecture Alumni--> Map & Directions Campus Maps & Bus--> Facilities Map--> TOHOKUUNIVERSITY About Academics Admissions Research Campus Life News Events International Affairs Students Current Students Alumni Faculty/Staff Promotional Videos Subscribe to our Newsletter Map & Directions Contact Jobs & Vacancies Emergency Information Site Map 日本語 Close Home Research News To Accelerate or Decelerate in the Light-emitting Process of Zinc-Oxide Crystals Research News To Accelerate or Decelerate in the Light-emitting Process of Zinc-Oxide Crystals 2020-12-04 A recent study has measured the internal quantum efficiency (IQE) of Zinc-Oxide (ZnO) crystals in both the light-emitting process and non-light-emitting process. "Obtaining a quantitative breakdown of IQE from both processes allows us to better design semiconductors to improve IQE," said professor Kazunobu Kojima, lead author of the study. Highly efficient electronic and optical devices are essential for reducing energy consumption and for the realization of an eco-friendly society. ZnO is an attractive material among direct-bandgap semiconductors. They possess light-emitting properties as well as toughness to sustain large electric field that enables them to power electronic devices because of their large bandgap energy and large exciton binding energy. This also makes them suitable in radiation-resistant thin-film-transistors and heterostructure field-effect-transistors. In high-quality ZnO crystals, nonradiative recombination centers (NRCs) are important for the near-band-edge (NBE) emission. These centers act as undesired energy dissipation channels and reduce the IQE of the NBE emission. To understand whether the light-emitting process or the non-light-emitting process was more important in determining the behavior of IQE, Kojima and his colleagues measured the IQE values of Zn0 crystal grown by the hydrothermal method. To do so, they employed a technique created by Kojima and fellow researchers known as omnidirectional photoluminescence (ODP) spectroscopy - a nondestructive method for probing semiconducting crystals with light to detect defects and impurities. The IQE curve obtained by the ODPL spectroscopy (left). The Y axis represents the IQE percentage, the lower X axis represents the excitation light power density Pcw (W cm-2) whilst the upper X axis represents the excitation rate G (sec-1 cm-2). The separated light-emitting rate (WR) and non-light-emitting rate (WNR) (right). The Y axis represents the inverse of rate (ns), the lower X axis represents the excitation light power density Ppulse (nJ/cm2) whilst the upper X axis represents the excited carrier concentration nini (cm-2). ©Tohoku University. The IQE characteristics in ZnO crystals were examined under photo pumping conditions. IQE values indicated a constant behavior for weak photo pumping conditions and a monotonic increase for strong excitation. Because a significant decrease was observed for the non-light-emitting process with photo pumping, the origin of the IQE increase was revealed to be dominated by the deceleration of the non-light-emitting process due to the saturation of NRCs. Publication Details: Title:Correlation between the internal quantum efficiency and photoluminescence lifetime of the near-band-edge emission in a ZnO single crystal grown by hydrothermal methodAuthors: Kazunobu Kojima and Shigefusa F. ChichibuJournal: Applied Physics ExpressDOI: 10.35848/1882-0786/abcd73 Press release in Japanese Contact: Kazunobu Kojima (Profile)Institute of Multidisciplinary Research for Advanced MaterialsEmail: kkojimatohoku.ac.jp Archives 2014&＃24180; 2015&＃24180; 2016&＃24180; 2017&＃24180; 2018&＃24180; 2019&＃24180; 2020&＃24180; 2021&＃24180; 2022&＃24180; 2023&＃24180; Page Top About Tohoku University Academics Admissions Research Campus Life News Events International Affairs Students Alumni Promotional Videos Subscribe to our Newsletter Map & Directions Contact Tohoku University Jobs & Vacancies Emergency Information Site Map Media Enquiries Parent & Family Support Public Facilities Contact Tohoku University