Silicon-based nanostructures for Silicon Photonics
The Holy Grail for silicon photonics has long been the development of light-emitting devices, i.e. efficient LEDs, and ultimately of silicon-based lasers. The development of efficient silicon-based light sources would in fact represent a technology with enormous societal impact, enabling full on-chip integration of optical functions within the existing CMOS technology of microelectronics. Integration of light emitters and compact lasers with Si microelectronics will enable diverse technological applications ranging from intra and inter chip optical interconnects, computing, bio-sensors, to optical and spectroscopic detection, and lab-on-a-chip diagnostics. The recent discovery of optical gain and stimulated emission in silicon nanocrystals has reenergized the field of photonics in nanostructured silicon (~350 citations at present), and began the race towards the demonstration of a fully-silicon-based laser
Figure 1: First demonstration of optical gain in nanocrystalline silicon by the Variable Stripe Length technique. The amplified spontaneous emission grows exponentially as a result of optical gain when the pumping volume of the sample is increased. Gain values as high as 80 cm-1 at 750 nm have been obtained under 390-nm ps optical pumping (from L.Pavesi, L. Dal Negro, C.Mazzoleni, G.Franzò, F.Priolo, Nature 408, 440, 2000).
Figure 2: (a) Plain view TEM image and electron diffraction pattern showing Si nanocrystals embedded in SiO2 produced by magnetron sputtering deposition (b) Cross section TEM image showing Si nanocrystals (the dark spots) embedded in amorphous silicon nitride by Plasma Enhanced Chemical Vapor Deposition
The purpose of this research activity is: a) to engineer novel, nanostructured-based materials solutions for CMOS-compatible light sources and lasers, b) to characterize and understand the physics of optical transitions in Si-based nanostructures via optical spectroscopy and light amplification techniques. The full spectrum of the activities involves different aspects of materials science engineering and characterization, including thin film deposition, thermal annealing and nanocrystals nucleation (see Fig. 1), infrared (FTIR) and visible absorption, Transmission Electron Microscopy (TEM), electrochemical etching; optical spectroscopy of nanostructures, light amplification and non-linear optical techniques along with optical device fabrication and modelling.
