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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 Breakthrough Made in Detecting Carbon Impurities in Gallium Nitride Crystals via Light Research News Breakthrough Made in Detecting Carbon Impurities in Gallium Nitride Crystals via Light 2019-12-05 Carbon impurity has long hindered efficiency in nitride-based electronic and optical devices. But Researchers at Tohoku University, have discovered a method that can quickly detect carbon impurity using light. The use of blue and white light-emitting diodes (LEDs) that use nitride semiconductors- specifically indium gallium nitride (InGaN) and gallium nitride (GaN) - has led to a steep increase in energy efficiency. Naturally, researchers have tried to replicate this in optical and electronic applications by using nitride semiconductors. However, a common issue arises due to carbon impurity, which significantly degrades performance. Carbon impurity leads to deep-traps, an undesirable electronic defect by which performance is substantially reduced. However, detecting carbon impurity in semiconductor crystals is a time-consuming and costly process. Some methods necessitate creating additional electrodes onto the crystal. Thus, raising costs and inhibiting the inspection speed. Other methods result in the breakage of nitride crystals; therefore, rendering the crystals useless. Nevertheless, Associate Professor for the Institute of Multidisciplinary Research for Advanced Materials at Tohoku University, Kazunobu Kojima and his team solved this problem by creating a way to identify carbon impurity using a probing technique utilizing light that makes no physical contact with the crystals. The technique is named omnidirectional photoluminescence (ODPL) spectroscopy. The process of ODPL firstly involves illuminating a crystal, such as GaN, via external light. The external light is absorbed by the crystal, thereby stimulating it. In order to return to its initial state, therefore, the crystal creates a light to dissipate excess energy. GaN crystals under photo-excitation. Carbon concentration level from left to right: high, medium, and low. ⒸKazunobu Kojima Utilizing the ODPL allows for the quick evaluation of photoluminescence efficiency with high accuracy. Since carbon impurity reduces the photoluminescence efficiency, researchers can also determine the carbon concentration by assessing the PL efficiency. Professor Kojima explained the benefits of such a system. "Optical probing technologies are immensely beneficial due to their nondestructive nature. By using light, we can therefore, help detect carbon impurity which is ultimately such a hindrance for GaN devices, such as LEDs and power transistors." An added benefit of the ODPL spectroscopy is that is not only limited to nitride-semiconductor-based application. It can check any light-emitting materials that contain optical and electronic properties. An example would be perovskites, which is currently used in the manufacturing of high-efficiency solar cells. Publication Details: Title: Roles of carbon impurities and intrinsic nonradiative recombination centers on the carrier recombination processes of GaN crystalsAuthors: K. Kojima, F. Horikiri, Y. Narita, T. Yoshida, H. Fujikura, and S. F. ChichibuJournal: Applied Physics ExpressDOI: 10.7567/1882-0786/ab5adc Press release in Japanese Contact: Kazunobu KojimaInstitute of Multidisciplinary Research for Advanced Materials, Tohoku UniversityEmail: kkojimatohoku.ac.jpWebsite: https://researchmap.jp/7000010041/?lang=english 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