Nanocomposites and nanomaterials
Polarized luminescence of the silicon nanoparticles formed
in the (SiOх - SiOy)n superlattice
Michailovska K.V., Dan’ko V.А., Indutnyi I.Z., Shepeliavyi P.E., 
Sopinskyy M.V.
V. Lashkaryov Institute of Semiconductor Physics Natl. Acad. of Sci. of Ukraine. 45 Prospect Nauky, 03028 Kyiv, Ukraine.  
E-mail: danko-va@ukr.net

In our previous work [1], it was shown that in (nc-Si-SiOx-SiOy)n nanostructures created on the basis of (SiOx-SiOy)n superlattices, the spectral composition of their photoluminescence (PL) can be changed by changing the thickness of the layers, and/or using HF processing. This work is a continuation of studies of such structures and is devoted to the study of the polarization properties of their PL. Nanostructures were produced by thermal vacuum deposition of 27-37 pairs of SiOx-SiOy layers, where (x<y≤2), followed by annealing at 975° C. The solid SiOx layers are active - silicon nanocrystals (nc-Si) were formed in them upon annealing, and spacer SiOy layers had a porous columnar structure. Passivation of dangling bonds of silicon atoms at the nc-Si-SiOx interface was carried out by their oxidation during storage of samples in an air atmosphere. 
It was found that upon excitation of (nc-Si-SiOx-SiOy)n structures with linearly polarized light, the polarization memory (PM) effect in the PL of studied structures is observed. The dependence of the degree of PM PL on the energy of emitted quanta and the thickness of the active and spacer layers is investigated. The results are analyzed within the quantum-confined effect and dielectric confinement model. Assuming that nc-Si are almost spherical or elongated shape (nanorods) randomly oriented in the plane of the sample and using a dielectric model we calculated the polarization degree of PL from an anisotropy of nanorods. The coincidence of the calculated values with the experimental results shows that not only the size but also the shape of nc-Si depends on the thickness of the SiOx/SiOy layers. In samples with large spacer thicknesses (13 and 7.6 nm), the degree of PL polarization and its spectral dependence indicate the formation of an almost spherical nc-Si during annealing. But in samples with thinner SiOy layers (3,5 nm), nc-Si can be considered as prolate ellipsoids, the projections of the long axes of which lie in the plane of the sample. In our opinion, ellipsoidal-shaped nc-Si in such samples may be associated with uncontrolled growth of nc-Si through a thin barrier layer.
1.	Michailovska K., Indutnyi I., Shepeliavyi P., Sopinskyy M., Dan’ko V. The effect of fluorine–hydrogen treatment on the photoluminescent properties of multilayer (nc-Si-SiOx-SiOy)n nanostructures with porous barrier layers // Appl. Nanosci.- 2020.- (7 pages) https://doi.org/10.1007/s13204-020-01404-z.