Optical properties of Si +-ion implanted sol–gel derived SiO 2 films

Abstract

Optical properties of commonly investigated Si +-implanted SiO 2 layers (thin SiO 2 films prepared by thermal growth on c-Si substrate) are compared with those of non-conventional SiO 2 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 SiO 2 films on c-Si. Striking differences between these two types of samples were found. The conventional Si +-implanted SiO 2/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 μs, PL temperature dependence well described by the exciton singlet–triplet splitting model). On the other hand, the Si +-implanted sol–gel SiO 2 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 SiO 2 layers. The slow red PL, 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 SiO 2 films is obviously of defect origin.