Growth of Ge$_{1-x}$Sn$_x$ solid solution films and study of their structural properties and some of their photoelectric properties

From the charge state and closeness of the covalent radii of molecules of the solution-forming components, the possibility of the formation of the solutions Si$_{1-x}$Ge$_x$, Si$_{1-x}$Sn$_x$, (Si$_2$)$_{1-x}$(SnC)$_x$, Ge$_{1-x}$Sn$_x$, (Ge$_2$)$_{1-x}$(SiSn)$_x$, (SiC)$_{1-x}$(GeC)$_x$, (GeC)$_{1-x}$(SnC)$_x$, (SiGe)$_{1-x}$(SnC)$_x$ based on chemical elements of Group IV has been predicted. Single-crystal films of the substitutional solid solution Ge$_{1-x}$Sn$_x$ (0 $\le x\le$ 0.03) have been grown on Ge substrates by liquid-phase epitaxy. X-ray diffraction patterns, spectral photosensitivity, and the I–V characteristics of the obtained $n$-Ge–$p$-Ge$_{1-x}$Sn$_x$ heterostructures have been investigated. The lattice parameters of the epitaxial film and the substrate $a_f$ = 5.6812 $\mathring{\mathrm{A}}$ and $a_s$ = 5.6561 $\mathring{\mathrm{A}}$ have been determined. The spectral photosensitivity of the $n$-Ge–$p$-Ge$_{1-x}$Sn$_x$ heterostructures encompasses the photon energy range from 0.4 to 1.4 eV. It is shown that the forward portion of the I–V characteristics of the investigated structures at low voltages (up to 0.5 V) is described by the exponential dependence $I=I_0\exp(qV/ckT)$ and at high voltages ($V >$ 0.5 V), by the power dependence $I\propto V^{\alpha}$ with the values $\alpha$ = 2 at $V$ = (0.5–0.9) V, $\alpha$ = 1.3 at $V$ = (0.9–1.4) V, and $\alpha$ = 2 at $V >$ 1.4 V. The experimental data are explained within the double injection model for the $n$–$p$–$p$ structure using the drift mechanism of current transport in the ohmic relaxation mode taking into account the inertia of the electron exchange inside a recombination complex.