Structure and light emission of Si-rich Al₂O₃ and Si-rich-SiO₂ nanocomposites

This work presents the comparative investigation of Si_x(Al ₂O₃)_1-x and Si_x(SiO ₂)_1-x films with different excess Si content, x, grown by RF magnetron sputtering. Their properties were investigated by means of Raman scattering, X-ray diffraction, Electron paramagnetic resonance and photoluminescence methods. As-deposited films with the x ≥ 0.3 were found to be two-phase systems that contained an amorphous Si phase. Contrary to Si _x(SiO₂)_1-x films, tensile stresses were observed for Si_x(Al₂O₃)_{1- x} samples due to lattice mismatch between the film and quartz substrate. The Si nanocrystals (Si-ncs) were formed upon annealing at 1150 °C for 30 min in nitrogen flow in both types of samples. Along with this, for the films with the x > 0.3, amorphous Si phase was also detected, but its contribution was smaller in the Si_x(Al₂O ₃)_1-x films. Besides, the Si-ncs embedded in Al₂O₃ host remained under tensile stresses after annealing. For the films with the same x values, the Si-ncs in Al ₂O₃ were found to be larger than those embedded in SiO₂. Photoluminescence spectra showed that the main radiative channel in Si_x(SiO₂)_1-x films is exciton recombination in Si-ncs, while in Si_x(Al₂O3) _1-x films the defect related emission prevails due to higher amount of interface defects in the Si_x(Al₂O ₃)_1-x. The nature of these defects is discussed.