Effect of the chromium layer thickness on the morphology and optical properties of heterostructures Si(111)/(CrSi$_2$ nanocrystallites)/Si(111)

Growth and the optical properties of epitaxial heterostructures Si(111)/(CrSi$_2$ nanocrystallites)/Si(111) based on nanosized islands of chromium disilicide (CrSi$_2$) on Si(111) were studied using low-energy electron diffraction, atomic-force microscopy, and optical reflection and transmission spectroscopy. The heterostructures with thicknesses of 0.1, 0.3, 0.6, 1.0, and 1.5 nm were formed by reactive epitaxy at a temperature of 500$^\circ$C followed by the epitaxial growth of silicon at 750$^\circ$C. The specific features of changes in the density and sizes of CrSi$_2$ islands on the silicon surface were determined at $T$ = 750$^\circ$C as the chromium layer thickness was increased. It was established that, in the heterostructures with chromium layer thicknesses exceeding 0.6 nm, a small part of faceted Cr$_2$Si$_2$ nanocrystallites (NCs) emerge into near-surface region of the silicon, which is confirmed by the data from optical reflectance spectroscopy and an analysis of the spectral dependence of the absorption coefficient. A critical size of NCs is shown to exist above which their shift to the silicon surface is hampered. The decreased density of emerging NCs at chromium layer thicknesses of 1.0–1.5 nm is associated with the formation of coarser NCs within a silicon layer, which is confirmed by the data from differential reflection spectroscopy.