Size effect in the optical second harmonic generation by silicon nanoparticles

A size effect has been revealed in the spectra of the second harmonic generated in a reflection from an amorphous silicon composite layer with inclusions of crystalline silicon (nanocrystallites) measured at room temperature: a decrease in the mean size of the nanocrystallites from 100 to 30 nm is accompanied by a shift of the spectral peak near 3.3 eV by 0.12 eV towards the short wavelengths and an increase in the peak width by a factor of 1.5. As a possible mechanism of this phenomenon, the effect of the structural defects on the parameters of the optical transitions in the nanocrystallites is discussed.