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Abstract: Nanocrystalline CaSi films with thicknesses from 80 to 130 nm were grown on high-resistance silicon substrates with orientations (111) and (100) by the methods of low-temperature (190–330°C) molecular-beam epitaxy and low-temperature (330°C) solid-phase epitaxy, for which the microstructure, phase composition, and crystal structures were studied. It is found that the polycrystalline, nanocrystalline (NC), and amorphous CaSi and CaSi2films are characterized by preferential contribution of holes in the range 1.4–300 K. In magnetic fields 1–4 T and at temperatures 40–100 K, a giant linear magnetoresistive effect (MRE) (to 500%) was observed for the first time in CaSi films with the contribution of another CaSi2phase. In CaSi2film containing another phase (CaSi), peaks are detected on the temperature dependences of the resistivity and the Hall coefficient that correspond to a phase transition. In addition, in this film, the transition from the positive MRE to negative MRE is observed at Т= 120–200 K. This effect is not observed in the single-phase CaSi2film, which corresponds to a certain reconstruction of carrier flows in a magnetic field only in the two-phase system. The study of the thermoelectric properties of CaSi and CaSi2films shows that the semimetallic type of the conduction in them leads to the independence of the positive Seebeck coefficient Т= 330–450 K. It is found that the maximum contribution to the Seebeck coefficient and the power factor are observed in the amorphous CaSi film in the case of the presence of some fraction of NC Ca2Si phase. In the single-phase CaSi2films, the Seebeck coefficient and the power factor are halved due to an increase in the hole concentration as compared to the CaSi films.

Abstract: Growth and the optical properties of epitaxial heterostructures Si(111)/(CrSi2 nanocrystallites)/Si(111) based on nanosized islands of chromium disilicide (CrSi2) 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°C followed by the epitaxial growth of silicon at 750°C. The specific features of changes in the density and sizes of CrSi2 islands on the silicon surface were determined at T = 750°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 Cr2Si2 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.