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First-Principles Study of Silicon Nanocrystals: Structural and Electronic Properties, Absorption, Emission, and Doping

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Abstract:

Total energy calculations within the Density Functional Theory have been carried out in order to investigate the structural, electronic, and optical properties of un-doped and doped silicon nano-structures of different size and different surface terminations. In particular the effects induced by the creation of an electron-hole pair on the properties of hydrogenated silicon nanoclusters as a function of dimension are discussed in detail showing the strong interplay between the structural and optical properties of the system. The distortion induced on the structure by an electronic excitation of the cluster is analyzed and considered in the evaluation of the Stokes shift between absorption and emission energies. Besides we show how many-body effects crucially modify the absorption and emission spectra of the silicon nanocrystals. Starting from the hydrogenated clusters, different Si/O bonding at the cluster surface have been considered. We found that the presence of a Si—O—Si bridge bond originates significative excitonic luminescence features in the near-visible range. Concerning the doping, we consider B and P single- and co-doped Si nanoclusters. The neutral impurities formation energies are calculated and their dependence on the impurity position within the nanocrystal is discussed. In the case of co-doping the formation energy is strongly reduced, favoring this process with respect to the single doping. Moreover the band gap and the optical threshold are clearly red-shifted with respect to that of the pure crystals showing the possibility of an impurity based engineering of the absorption and luminescence properties of Si nanocrystals.

Keywords: BAND STRUCTURE; CALCULATIONS; DOPING; EMISSION MECHANISM; OPTICAL PROPERTIES; SILICON NANOCRYSTALS

Document Type: Research Article

DOI: https://doi.org/10.1166/jnn.2008.A009

Publication date: 2008-02-01

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  • Journal for Nanoscience and Nanotechnology (JNN) is an international and multidisciplinary peer-reviewed journal with a wide-ranging coverage, consolidating research activities in all areas of nanoscience and nanotechnology into a single and unique reference source. JNN is the first cross-disciplinary journal to publish original full research articles, rapid communications of important new scientific and technological findings, timely state-of-the-art reviews with author's photo and short biography, and current research news encompassing the fundamental and applied research in all disciplines of science, engineering and medicine.
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