1. Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University
2. Centre for Advanced Nitride Technology, Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University
3. Faculty of Engineering, Ibaragi University
4. Optoelectronics Laboratory, Mitsubishi Chemical Corporation
5. Optoelectronics Department, Mitsubishi Chemical Corporation