1. Ångström Solar Center, Solid State Electronics; Uppsala University; Box 534 751 21 Uppsala Sweden
2. Environmental Remediation Materials Unit; National Institute for Materials Science; Ibaraki 305-0044 Japan
3. Department of Physics; University of Oslo; P. O. Box 1048 Blindern 0316 Oslo Norway
4. Laboratory for Photovoltaics, Physics and Materials Science Research Unit; University of Luxembourg; 41 rue du Brill 4422 Belvaux Luxembourg