1. Semiconductor Development Division, Nichia Corporation, 1-1 Tatsumi, Anan, Tokushima 774-0001
2. Graduate School of Chemical Sciences and Engineering, Hokkaido University, Kita13, Nihi8, Kita-ku, Sapporo, Hokkaido 060-8628
3. Faculty of Engineering, Hokkaido University, Kita13, Nihi8, Kita-ku, Sapporo, Hokkaido 060-8628