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 sol-gel films, deposited on different substrates, were implanted and annealed 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+-implanted SiO2/c-Si layers contain Si nanocrystals and their photoluminescence (PL) properties were found very similar to porous silicon (PL in the red/NIR spectral regions, PL decay time of the order of 10 mu s, PL temperature dependence well described by the exciton singlet-tripler splitting model). On the other hand, the Si+-implanted sol-gel SiO2 films exhibit room temperature PL spectra peaked in the blue-green region, PL decay is considerably faster (of the order of 1 ns) and also PL temperature dependence differs substantially from the samples of the first type. Possible influence of different substrates (silica, c-Si) is also investigated and it is shown that the observed 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 recombination of excitons in Si nanocrystals, while the fast blue PL characteristic of ion-implanted sol-gel derived SiO2 films is obviously of defect origin. (C) 2000 Elsevier Science S.A. All rights reserved.