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Si nanoclusters (NCs) dispersed in SiO2, synthesized by high-temperature anneal of substoichiometric silicon oxide (SiOx) layer, are attracting increasing attention due to their application in fabricating optical and electronics devices, based on quantum confinement effects, by methods and processes fully compatible with the Si technology. 1, 2 Furthermore, the reduced dimensionality of quantum dots (QDs) should help in fabricating innovative photovoltaic devices that can harvest the full solar energy, in a variety of modes, among which the multiple exciton generation (MEG), 3–5 the intermediate band formation (allowing the absorption of lower energy photon), 6, 7 and the chance of modulating the absorption spectrum by changing the NC size, which should allow to tailor the light absorption onset for a better matching of the sun spectrum. 8, 9 In this scenario, Ge QDs recently received considerable attention over Si QDs for various reasons, among which were the larger absorption coefficient of the bulk material, the easier bandgap tuning due to the larger exciton Bohr radius (24 nm), 10 and the lower synthesis temperature. Moreover, theoretical calculations estimate that an indirect-to-direct transition in the Ge spectra occurs with decreasing size, and oscillator strengths are expected to be larger in Ge NS than in Si NS. 11 This last effect could be attributed to stronger overlaps of the electron wave functions on Ge atoms, 12 which could enhance the light absorption in Ge NS. To clearly understand these phenomena occurring in Si or Ge NCs, great care must be taken in the fabrication process in order to obtain well-isolated and sizecontrolled NCs …
CRC Press
Publication date: 
9 Dec 2014

Corrado Spinella, Salvo Mirabella

Biblio References: 
Pages: 377
Silicon, Germanium, and Their Alloys: Growth, Defects, Impurities, and Nanocrystals