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