Optical properties of multilayer materials based on silicon and nanosized magnesium silicide crystallites

Abstract

We have studied the optical properties of silicon with incorporated nanocrystallites of semiconducting magnesium silicide by optical spectroscopy and Raman spectroscopy. We have calculated the optical functions of samples grown with different numbers of layers of incorporated magnesium silicide nanocrystallites. We have determined the contribution of magnesium silicide to the electronic structure of multilayer samples in the photon energy range 1.5-3.0 eV. We have studied the phonon structure of the grown multilayer samples, based on analysis of two-phonon and three-phonon resonances in silicon and Mg 2 Si.Introduction. Today researchers are paying serious attention to silicon with incorporated nanocrystallites of semiconductor silicides [1-5], since such materials have novel optical and electrical properties that are important for designing new semiconductor devices based on silicon. Magnesium silicide (Mg 2 Si) may be used as a narrow-gap semiconductor (E g = 0.37-0.70 eV [6, 7]) for silicon planar technology. The technology for obtaining thin epitaxial films based on silicon is complicated by the low magnesium/silicon coefficient of adhesion and its revaporization at temperatures above 400 o C [8]. Nevertheless, formation of incorporated nanosized Mg 2 Si crystallites in silicon by the ion incorporation method [9] or by the solid-phase epitaxy method [10,11] is of interest to both basic and applied research for designing silicon-containing materials with new optical properties.We know [12] that Mg 2 Si has an antifluorite structure and belongs to the space group Fm3m, the space group for an octahedron (O h ). From phonon vibration theory (within the harmonic expansion) [13,14] for crystals with a center of symmetry, one-phonon optical transitions (resonances) are forbidden. However, a Mg 2 Si crystal has pronounced ionicity of the Mg-Si bond, leading to an induced static dipole moment, as a result of which a one-phonon reststrahl band is formed in the optical transmission spectra with strong absorption on longitudinal (ν LO ) = 327 cm -1 ) and transverse (ν TO = 267 cm -1 ) optical phonons [15]. In the reflectance spectrum (the reststrahl band) of a Mg 2 Si single crystal [15], an additional peak is also observed which is interpreted for ionic alkali metal fluoride compounds [16] as the contribution of two-phonon resonances [17]. However, its contribution to the phonon structure was not considered in [15]. The appearance of only a one-phonon resonance was used in calculations of the Raman-active (ν TO R =

INFLUENCE OF EMBEDDED LOW-DIMENSIONAL Mg2Si ON THE CONDUCTIVITY OF Si/Mg2Si/Si(111) HETEROSYSTEMS

“…Si(111) wafers with 1-45 Ω⋅cm resistivity were used as substrates for different series of growth experiments. Growth procedure, topography and optical properties of Si/Mg 2 Si/Si (111) heterosystems are described in [1][2][3]. For measurements of electrical conductivity the contacts were prepared by the ultrasonic compression of an aluminium wire to the sample after that the silver paste was applied atop aluminium contacts.…”

“…The possibility of embedding of low-dimensional magnesium silicide (Mg 2 Si) inside silicon matrix has been shown in our previous works [1][2][3]. Si/Mg 2 Si/Si(111) heterosystems are characterized by bigger thermoelectric power than the silicon substrates on which they are grown.…”

“…But 2D Mg 2 Si layer is embedded in the polycrystalline silicon matrix with sizes grains appreciably larger than 15 nm. However, it is impossible to explain the nature of increasing of the thermoelectric power coefficient for Si/Mg 2 Si/Si(111) heterosystems using only optical and sample topography data [2][3].…”

Optoelectronic Properties of Hydrogenated Amorphous Substoichiometric Silicon Carbide with Low Carbon Content Deposited on Semi‐Transparent Boron‐Doped Diamond

“…The problem of increasing the light conversion efficiency of photodiodes based on hydrogenated amorphous silicon a‐Si:H has remained for decades . Heterojunction thin‐film solar cells with embedded nanoparticles exhibit an enhanced spectral response in a wavelength range from 400 to 1200 nm, but the formation of nanoparticles requires a relatively high temperature, whereas the optimal deposition temperature used for a‐Si:H is around 250 °C . While hydrogenated amorphous substoichiometric silicon carbide a‐Si 1− x C x :H is often prepared at temperatures below 300 °C, CH 4 suppresses polycrystalline Si growth in favor of H‐rich amorphous a‐Si 1− x C x :H at elevated deposition temperatures .…”

A simple phase transformation strategy for converting silicon nanowires into metal silicide nanowires: Magnesium silicide

“…Another broad peak at 345 cm −1 corresponding to the Fröhlich-interactioninduced Raman-inactive longitudinal optical (LO) mode of Mg 2 Si was also observed in the spectra [32]. The peak at 432 cm −1 is expected to be the result of the interfacial stress arising from the boundaries between Mg 2 Si nanowires and the bulk silicon wafer [33]. Finally, Raman modes at 290 and 519 cm −1 corresponding to the second-order transverse acoustic phonon mode 2TA and F 2g of silicon [34] were also observed in Fig.…”