The authors have investigated the role of the Si excess on the photoluminescence properties of Er doped substoichiometric SiOx layers. They demonstrate that the Si excess has two competing roles: when agglomerated to form Si nanoclusters Si-nc’s it enhances the Er excitation efficiency but it also introduces new nonradiative decay channels. When Er is excited through an energy transfer from Si-nc’s, the beneficial effect on the enhanced excitation efficiency prevails and the Er emission increases with increasing Si content. However, when pumped resonantly, the Er luminescence intensity always decreases with increasing Si content. These data are presented and their implications are discussed.
What is the difference between the skin of the Statue of Liberty in New York, and an electric wire? Both are made of the same material (copper), but they have different properties because of the shape. Now, get your shrinking machine and make your electric wire smaller than one of your hair. Do you expect the wire to keep the same properties? Nope, of course!
You can do really amazing thing just changing the shape and the size of any material. This is what I did to enable new light sources made of silicon. All our electronics devices are made of silicon. Unfortunately, it cannot emit light by itself. But, if you fabricate a silicon wire smaller than a virus, things will change.
I investigated the growth of silicon and germanium nanowires by a self-assembled method, using electron beam evaporation. This is a relatively unexploited technique that offers a pathway towards high throughput production. By properly varying the experimental parameters of the evaporation it is possible to define the length, density and crystallographic orientation of the wires. The structural properties have been correlated to the atomistic growth mechanism. Moreover, we explored the possibility to bend and restore the wires. Ion beam irradiation amorphizes the nanowires, causing their bending in the direction opposite to the beam. A full recovery is possible after thermal annealing.
I explored a top-down approach as well. Metal-Assisted Chemical Etching is a full VLSI compatible process to grow very thin nanowires of arbitrary length and controlled doping. Room-temperature photoluminescence and electroluminescence has been demonstrated from silicon nanowires. Moreover, I introduced an innovative approach, based on the combination of standard Electron Beam Lithography and reactive ion etching, for nanopatterning nanowires in any arbitrary geometry. We demonstrate broadband photoluminescence enhancement up to approximately one order of magnitude after a reliable engineering of periodic and aperiodic array patterns.