Effect of the Growth Modes of CaF2/(Si + CaF2)/CaF2/Si(111) Heterostructures on Their Photoluminescence Spectrum

This work is devoted to studying the effect of the conditions of the formation of CaF 2 F 2 /(Si + CaF 2 )/CaF 2 /Si(111) structures on their emissivity in the visible region of the spectrum. Multilayer CaF 2 /(Si + CaF 2 )/CaF 2 /Si(111) heterostructures are grown on Si(111) substrates by molecular-beam epitaxy in a closed technological cycle. Photoluminescence is excited by a He–Cd laser with an emission wavelength of 325 nm. The spectra are measured at room temperature. The parameters of the technological process are selected to obtain structures capable of emitting in the visible range of the spectrum. It is found experimentally that luminescence in the CaF 2 /(Si + CaF 2 )/CaF 2 /Si(111) structures is observed only at a ratio of Si and CaF 2 fluxes of 3.6–4.0. A 1.5-fold decrease in the growth rates of Si and CaF 2 layers, as well as a decrease in the thickness of the CaF 2 separation layers to 1 nm, does not affect the position of the maxima in the photoluminescence spectra. A change in the annealing mode of the CaF 2 /(Si + CaF 2 )/CaF 2 /Si(111) structures shifts the maximum in the photoluminescence spectra. Estimation of the sizes of silicon nanocrystals corresponding to the energies observed during photoluminescence correlates well with the experimental data of high-resolution transmission electron microscopy and photoluminescence.