Affiliations: [a] CNR-INFM-S3-CNISM and Dipartimento di Fisica, Università di Modena e Reggi Emilia, Via Campi 213/A, I-41100 Modena, Italy | [b] CNR-INFM-S3 and Dipartimento di Scienze e Metodi dell'Ingegneria, Università di Modena e Reggio Emilia, via G. Amendola 2, I-42100 Reggio Emilia, Italy | [c] European Theoretical Spectroscopy Facility (ETSF) and Dipartimento di Fisica – Università di Roma “Tor Vergata” Via della Ricerca Scientifica 1, I-00133 Roma, Italy | [d] CNR-INFM-Coherentia and Dipartimento di Fisica, Università di Napoli “Federico II”, Complesso Universitario Monte S. Angelo, Via Cintia, I-80126 Napoli, Italy | [x] Department of Chemistry, University of Patras, Greece | [y] Department of Physics, University of Patras, Greece
Abstract: The absorption and the emission spectra of undoped and doped silicon nanocrystals of different size and surface terminations have been calculated within a first-principles framework. The effects induced by the creation of an electron-hole pair on the atomic structure and on the optical spectra of hydrogenated silicon nanoclusters as a function of dimension are discussed showing the strong interplay between the structural and optical properties of the system. Starting from the hydrogenated clusters, (i) different Si/O bonding at the cluster surface and (ii) different doping configurations have been considered. We have found that the presence of a Si-O-Si bridge bond at the nanocrystal surface gives rise to significant excitonic luminescence features in the near-visible range that are in fair agreement with photoluminescence (PL) measurements on oxidized and SiO2 embedded nanocrystals. The study of the structural, electronic and optical properties of simultaneously n- and p-type doped hydrogenated silicon nanocrystals with boron and phosphorous impurities have shown that B-P co-doping is energetically favorable with respect to single B- or P-doping and that the two impurities tend to occupy nearest neighbors sites. The co-doped nanocrystals present band edge states localized on the impurities that are responsible of a red-shifted absorption threshold with respect to that of pure un-doped nanocrystals in agreement with the experiment.
