Liquid-phase epitaxy of the (Si$_2$)$_{1-x-y}$(Ge$_2$)$_x$(GaAs)$_y$ substitutional solid solution (0 $\le x\le$ 0.91, 0 $\le y\le$ 0.94) and their electrophysical properties

(Si$_2$)$_{1-x-y}$(Ge$_2$)$_x$(GaAs)$_y$ substitutional solid solutions (0 $\le x\le$ 0.91, 0 $\le y\le$ 0.94) are grown by liquid-phase epitaxy from a Pb-based solution-melt on Si substrates with the (111) crystallographic orientation. The chemical composition of the epitaxial films is studied by X-rays probe microanalysis, and the distribution profile of solid solution components is determined. Spectral dependences of the photosensitivity and photoluminescence of the $n$-Si-$p$(Si$_2$)$_{1-x-y}$(Ge$_2$)$_x$(GaAs)$_y$ heterostructures are studied at room and liquid-nitrogen temperatures. Two maxima are found in the photoluminescence spectra of the (Si$_2$)$_{1-x-y}$(Ge$_2$)$_x$(GaAs)$_y$ films (0 $\le x\le$ 0.91, 0 $\le y\le$ 0.94) against the background of a broad emission spectrum. The fundamental maximum with an energy of 1.45 eV is caused by the band-to-band recombination of solid solution carriers, and an additional maximum with an energy of 1.33 eV is caused by the recombination of carriers with the participation of impurity levels of the Si–Si bond (Si$_2$ is covalently coupled with the tetrahedral lattice of the solid solution host).