Affiliation: | (1) Institut d'Electronique Fondamentale, URA CNRS, Université Paris-Sud, Bât. 220, F-91405 Orsay Cedex, France;(2) CECM/CNRS, 15, rue G. Urbain, F-94400 Vitry-sur-Seine, France;(3) Present address: Institute of Electronics BAS, 72 Blvd. Tzarigradsko Chaussee, 1784 Sofia, Bulgaria |