Nature of visible luminescence and its excitation in Si-SiO_x systems

Photoluminescence (PL) spectra and their temperature dependence, as well as PL excitation and Raman spectra of Si-SiO_x systems prepared by RF magnetron sputtering were investigated as a function of Si content. It was shown that PL spectrum of such systems consists of several bands. The correlation of shift of peak position of the lower-energy band from 1.38 to 1.54 eV with the change of size of Si nanocrystallites from 5 to 2.7 nm was observed. It was assumed that this PL band is connected with carrier recombination inside Si nanoparticles or with radiative transitions between a Si band and an interface level. It was shown that peak positions of the other observed bands (at 1.7, 2.06 and 2.32 eV) do not depend on the sizes of Si nanocrystallites. It was suggested that they are connected with silicon oxide defects based on the increase of intensities of these bands with increasing silicon oxide content. It was also shown that the excitation of PL is mainly due to light absorption in silicon nanocrystallites. Participation of hot carriers in excitation of defect-related bands was assumed.