Browsing by Author "Nicotra, G."

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    Light harvesting with Ge quantum dots embedded in SiO2 or Si3N4
    (A I P Publishing LLC, 2014) Cosentino, S.; Ozen, E. S.; Raciti, R.; Mio, A. M.; Nicotra, G.; Simone, F.; Crupi, I.; Turan, R.; Terrasi, A.; Aydınlı, Atilla; Mirabella, S.
    Germanium quantum dots (QDs) embedded in SiO2or in Si3N4have been studied for light harvesting purposes. SiGeO or SiGeN thin films, produced by plasma enhanced chemical vapor deposition, have been annealed up to 850°C to induce Ge QD precipitation in Si based matrices. By varying the Ge content, the QD diameter can be tuned in the 3-9 nm range in the SiO2matrix, or in the 1-2 nm range in the Si3N4matrix, as measured by transmission electron microscopy. Thus, Si3N4matrix hosts Ge QDs at higher density and more closely spaced than SiO2matrix. Raman spectroscopy revealed a higher threshold for amorphous-to-crystalline transition for Ge QDs embedded in Si3N4matrix in comparison with those in the SiO2host. Light absorption by Ge QDs is shown to be more effective in Si3N4matrix, due to the optical bandgap (0.9-1.6 eV) being lower than in SiO2matrix (1.2-2.2 eV). Significant photoresponse with a large measured internal quantum efficiency has been observed for Ge QDs in Si3N4matrix when they are used as a sensitive layer in a photodetector device. These data will be presented and discussed, opening new routes for application of Ge QDs in light harvesting devices. © 2014 AIP Publishing LLC.
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    The role of the interface in germanium quantum dots: when not only size matters for quantum confinement effects
    (Royal Society of Chemistry, 2015) Cosentino, S.; Mio, A. M.; Barbagiovanni, E. G.; Raciti, R.; Bahariqushchi, R.; Miritello, M.; Nicotra, G.; Aydınlı, Atilla; Spinella, C.; Terrasi, A.; Mirabella, S.
    Quantum confinement (QC) typically assumes a sharp interface between a nanostructure and its environment, leading to an abrupt change in the potential for confined electrons and holes. When the interface is not ideally sharp and clean, significant deviations from the QC rule appear and other parameters beyond the nanostructure size play a considerable role. In this work we elucidate the role of the interface on QC in Ge quantum dots (QDs) synthesized by rf-magnetron sputtering or plasma enhanced chemical vapor deposition (PECVD). Through a detailed electron energy loss spectroscopy (EELS) analysis we investigated the structural and chemical properties of QD interfaces. PECVD QDs exhibit a sharper interface compared to sputter ones, which also evidences a larger contribution of mixed Ge-oxide states. Such a difference strongly modifies the QC strength, as experimentally verified by light absorption spectroscopy. A large size-tuning of the optical bandgap and an increase in the oscillator strength occur when the interface is sharp. A spatially dependent effective mass (SPDEM) model is employed to account for the interface difference between Ge QDs, pointing out a larger reduction in the exciton effective mass in the sharper interface case. These results add new insights into the role of interfaces on confined systems, and open the route for reliable exploitation of QC effects. © The Royal Society of Chemistry.