Si$_{1-x}$Ge$_x$/Si heterostructures grown by molecular-beam epitaxy on silicon-on-sapphire substrates

The growth of heterostructures with Si$_{1-x}$Ge$_x$ layers on $(1\bar{1}02)$ sapphire substrates by molecular-beam epitaxy with a silicon sublimation source and a germanium gas source (GeH$_4$) is reported. The systematic study of the influence of substrate temperature and thickness of the silicon buffer layer shows that the optimal conditions for growing epitaxial Si$_{1-x}$Ge$_x$ layers are provided at a temperature of $T_S$ = 375–400$^\circ$C. There are significant differences in the orientations of Si$_{1-x}$Ge$_x$ layers, depending on the thickness $d$ of the Si buffer layer: the preferred orientations are (100) at $d\ge$ 100 nm and (110) for thinner layers. Heterostructures with thick ($\sim$1 $\mu$m) Si$_{1-x}$Ge$_x$ layers, doped with erbium atoms, exhibit intense photoluminescence at $\lambda$ = 1.54 $\mu$m.