1. Center of Materials Technology and Photonics and Electrical Engineering Department; Technological Educational Institute (TEI) of Crete; Heraklion 71004 Crete Greece
2. Department of Materials Science and Technology; University of Crete; Heraklion 710 03 Crete Greece
3. Institute of Electronic Structure and Laser; Foundation for Research and Technology - Hellas; P. O. Box 1527 Heraklion 711 10 Crete Greece