Optical, phononic and semiconductor properties of magnesium silicide films formed on silicon by layer-by-layer (Mg+Si) reactive epitaxy

Magnesium silicide films were formed on n-type Si (111) substrates with resistivities ranging from 2 to 15 Ohm·cm (samples 1 and 2) and from 0.1 to 0.5 Ohm·cm (samples 3 and 4) using reactive epitaxy with layer-by-layer deposition of magnesium and silicon layers at a temperature of 250 °C. The article presents the results of a study of the morphology, optical and phononic properties, and the band gap of samples containing magnesium silicide films with thicknesses of 496, 682, 1143, and 414 nm, according to SEM data on a cross section. Atomic force microscopy showed that the films of all samples were formed by the Volmer-Weber mechanism, with the islands coalescing into clusters and grains. The island area of the film of the first sample ranges from 0.12 to 0.48 μm², the second — from 0.02 to 0.06 μm², the third — from 0.01 to 0.04 μm², and the fourth — from 0.04 to 0.09 μm². The islands coalesce into clusters and grains. In all grown films, Raman scattering (RS) peaks were detected at 258, 348, and 693 cm^-1, which correspond to the formation of Mg₂Si. In the IR spectra, the minimum transmittance at a wavenumber of 270 cm^-1 varies from 0.04 to 0.01, which corresponds to an increase in the absorption of IR photons with an increase in the thickness of the Mg₂Si films in the grown samples. The reflection and transmission spectra of the grown films revealed both interference peaks (below 1.5 eV) and a peak with an energy of 2.2−2.3 eV, corresponding to the interband transition in Mg₂Si. Based on the infrared absorption spectra, the indirect band gap width was calculated for each film: 0.80 and 0.86 eV for samples 1 and 2; 0.77 and 0.79 eV for samples 3 and 4.