The gas-source molecular-beam epitaxy (GSMBE) of β-${\mathrm{FeSi}}_2$ 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$${\mathrm{H}}_6$ as the silicon gas source, are discussed. Fe(CO${)}_5$ acts as the Fe source for the silicide growth in both processes. Concerning surface roughness, thickness uniformity, and substrate/overlayer interface sharpness, best growth temperatures are found to be from 450 to 550 °C for both the ${\mathrm{SiH}}_4$ and ${\mathrm{Si}}_2$${\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 (${\mathit{E}}_{\mathit{g}}$∼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 β-${\mathrm{FeSi}}_2$ layers are μ∼2 ${\mathrm{cm}}^2$/V s and p∼2×${10}^{18}$ ${\mathrm{cm}}^{\mathrm{-}3}$, respectively.

• Received 17 November 1994

DOI:https://doi.org/10.1103/PhysRevB.51.17780