1. Department of Physics, Al-Aqsa University, Gaza Strip, Palestinian Authority
2. Department of Physics, Islamic University Of Gaza, Gaza, P. O. Box 108, Gaza Strip, Palestinian Authority
3. Zentrum fur Halbleitertechnik und Optoelecteonik (ZHO), Faculty of Electrical and Electronics Engineering, Duisburg-Essen University, D-47057, Duisburg, Germany