1. FBK-irst, via Sommarive 18, 38050 Povo-Trento, Italy, CSMFO Laboratory, CNR-IFN, via alla Cascata 56/C, 38050 Povo-Trento, Italy, Department of Materials and Devices, CNR, via dei Taurini 19, 00185 Roma, Italy, Optoelectronic Technologies Laboratory, Nello Carrara Institute of Applied Physics, IFAC-CNR, via Panciatichi 64, I-50127 Firenze, Italy, and Materials Engineering and Industrial Technologies Department, University of Trento, via Mesiano 77, 38100 Trento, Italy