1. Graduate Institute of Electro-Optical Engineering and
Department of Electronic Engineering, National TaiwanUniversity of Science and Technology, Taipei 106,Taiwan Republic of China
2. Department of Materials
Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan Republic of China
3. Institute for Materials Research (IMO), Hasselt University, 3590 Diepenbeek, Belgium
4. Department
of Physics, Tamkang University, Tamsui 251, Taiwan Republic of China