Heteroepitaxy of beta -FeSi2 on Si by gas-source MBE.

Abstract

The gas-source molecular-beam epitaxy (GSMBE) of \ensuremath{\beta}-${\mathrm{FeSi}}_{2}$ layers on Si(111) and Si(001) has been studied. Results from two different growth processes, depending on the choice of either ${\mathrm{SiH}}_{4}$ or ${\mathrm{Si}}_{2}$${\mathrm{H}}_{6}$ as the silicon gas source, are discussed. Fe(CO${)}_{5}$ acts as the Fe source for the silicide growth in both processes. Concerning surface roughness, thickness uniformity, and substrate/overlayer interface sharpness, best growth temperatures are found to be from 450 to 550 \ifmmode^\circ\else\textdegree\fi{}C for both the ${\mathrm{SiH}}_{4}$ and ${\mathrm{Si}}_{2}$${\mathrm{H}}_{6}$ GSMBE processes. In situ electron spectroscopy combined with transmission-electron-microscopy structural analysis allows the identification of the grown silicide phases; furthermore, a heavily p-type doped accumulation layer is found to form at the surface, as revealed by high-resolution electron-energy-loss spectroscopy. High defect optical absorption is measured below the edge region (${\mathit{E}}_{\mathit{g}}$\ensuremath{\sim}0.87) and compared with common semiconductor materials. The RT electrical properties as measured by Hall effect are shown to be masked by a contribution from the substrate. At 77 K the mobility and carrier concentration of the grown \ensuremath{\beta}-${\mathrm{FeSi}}_{2}$ layers are \ensuremath{\mu}\ensuremath{\sim}2 ${\mathrm{cm}}^{2}$/V s and p\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$, respectively.