Defect-related luminescence of Si/SiO₂ layers

Photoluminescence (PL), photoluminescence excitation (PLE), and Raman spectra of Si-SiO_x layers were measured as a function of Si content. Samples were prepared by co-sputtering of Si and SiO₂ and post-annealing. The average size of Si nanoparticles was estimated from Raman measurements. It was shown that, in general, the PL spectra consist of two bands with maxima in the 'red' and 'green' spectral ranges. The 'red' PL band is complex and contains two (IR and red (R)) components. The shift of the peak position of the IR component from 1.38 to 1.54 eV correlates with the decrease of the Si nanoparticle size from 5 to 2.7 nm. It was shown that this PL component could be ascribed to carrier recombination in silicon nanoparticles. The R component of the 'red' band as well as the 'green' band have similar dependences of the peak positions and intensities on the Si content and can be ascribed to defect-related luminescence. It was concluded that the light absorption in silicon nanocrystallites plays the main role in PLE process. Hot-carrier participation in the excitation of defect-related bands was deduced.