Influence of the annealing treatments on the luminescence properties of SiO/SiO2 multilayers

The formation of silicon nanocrystals (Si-ncs) and their room temperature photoluminescence (PL) properties were investigated in samples elaborated by the evaporation method. Silicon oxide (SiO) single layer and SiO/SiO2 multilayers with different SiO layer thicknesses from 1 to 5 nm were prepared and annealed at different temperatures up to 1050 degrees C. The structure and the formation of Si-nc were studied by transmission electron microscopy (TEM) and by Fourier transform infrared (FTIR) absorption spectroscopy. It is demonstrated that the Si-ncs appear by the phase separation process from SiO due to the annealing treatments. Contrary to the SiO single layer, the multilayers are a powerful system to obtain highly luminescent Si-nc and to control the Si-nc size for SiO layer thicknesses lower than or equal to 4 nm. It is clearly shown that, in agreement with the quantum confinement theory, the PL energy is a decreasing function of the Si-nc size. However, thanks to the correlation between FTIR, TEM, and PL results, it is demonstrated that the PL energy is also strongly dependent on the quality of the matrix in which the Si-nc are embedded. A model based on the existence of a SiOx shell surrounding the Si-nc is proposed to explain the PL results. (c) 2006 American Institute of Physics.