Optical properties of Si+-ion implanted sol-gel derived SiO2 films

Optical properties of commonly investigated Si+-implantrd SiO2 layers (thin SiO2 films prepared by thermal growth on c-Si substrate) are compared with those of non-conventional SiO2 layers fabricated by sol-gel process. The s ol-gel films, deposited on different substrates, were implanted and anneale d in a similar way as the thermal SiO2 films on c-Si. Striking differences between these two types of samples were found. The conventional Si+-implant ed SiO2/c-Si layers contain Si nanocrystals and their photoluminescence (PL ) properties were found very similar to porous silicon (PL in the red/NIR s pectral regions, PL decay time of the order of 10 mu s, PL temperature depe ndence well described by the exciton singlet-tripler splitting model). On t he other hand, the Si+-implanted sol-gel SiO2 films exhibit room temperatur e PL spectra peaked in the blue-green region, PL decay is considerably fast er (of the order of 1 ns) and also PL temperature dependence differs substa ntially from the samples of the first type. Possible influence of different substrates (silica, c-Si) is also investigated and it is shown that the ob served PL is an inherent property of the implanted sol-gel SiO2 layers. Thr slow red FL, in agreement with other authors, is ascribed to radiative rec ombination of excitons in Si nanocrystals, while the fast blue PL character istic of ion-implanted sol-gel derived SiO2 films is obviously of defect or igin. (C) 2000 Elsevier Science S.A. All rights reserved.