Institution: | a Institute of Applied Physics, Academy of Sciences of Moldova, 2028 Chisinau, Moldova b INFM, Dipartimento di Fisica, Universitá di Cagliari, Cittadella Universitaria S.P. Monserrato-Sestu Km 0-700-09042 Monserrato, Cagliari, Italy c Laboratory of Low-Dimensional Semiconductor Structures, Technical University of Moldova, 2004 Chisinau, Moldova d Center of Nanoelectronics, Technical University of Moldova, 2004 Chisinau, Moldova |