1. Department of Materials Science
and Engineering, National Tsing-Hua University, Hsin-Chu, Taiwan 300, R.O.C.
2. Materials Physics Division, Indira Gandhi Centre for Atomic Research, Kalpakkam
603 102, India
3. Department
of Photonics Engineering, Yuan-Ze University, Chung-Li 32003, Taiwan, R.O.C.
4. Department of Physics, Tamkang University, New-Taipei 251, Taiwan, R.O.C.