Raman Scattering of Light in Thin Films of Fe, Cr, and Ca Silicides on Silicon and Sapphire

Epitaxial and polycrystalline films of iron (Fe), chromium (Cr), and calcium (Ca) silicides of various thicknesses (from 3.2 to 380 nm) were grown on silicon and sapphire substrates in ultrahigh vacuum by three methods (solid-phase epitaxy, reactive epitaxy and molecular beam epitaxy). The crystal structure and matching with the silicon lattice were determined for them using the X-ray diffraction method. A comparative analysis of Raman scattering spectra and far-IR spectroscopy spectra showed that films of semiconductor silicides have the strongest Raman peaks, and the detected shifts in their positions are caused by distortions in the silicide lattices. It has been established that in films of iron and chromium monosilicides at a fixed laser excitation wavelength ( λ=628.3 nm) and a power of 3.4 mW, the strength of the Raman peaks decreases with decreasing film thickness and they disappear completely at a thickness below 10 nm. Chromium trisilicide films were grown on single-crystal sapphire, which made it possible for the first time to detect for it active Raman phonons at λ=488 nm and a power of 0.42 mW at wave numbers 214.3 and 273.1 cm ^-1 . The studied films of transition metal monosilicides are of significant interest from the perspective of their possible use as materials for thermoelectronics and spintronics, and systematized information on active Raman phonons and IR active phonons will make it possible to quickly determine the type of phase formed immediately after film growth.