1. Department of Physics/Centre for Materials Science and NanotechnologyUniversity of Oslo P.O. Box 1048, Blindern N-0316 Oslo Norway
2. Department of PhysicsChalmers University of Technology 41296 Göteborg Sweden
3. Ångström Solar CenterDivision of Solid State ElectronicsUppsala University Uppsala 75120 Sweden
4. Department of Materials Science and EngineeringKTH Royal Institute of Technology 10044 Stockholm Sweden