Heteroepitaxy of β-FeSi2 on Si by gas-source MBE

The gas-source molecular-beam epitaxy (GSMBE) of β-FeSi₂ layers on Si(111) and Si(001) has been studied. Results from two different growth processes, depending on the choice of either SiH₄ or Si₂H₆ 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 SiH₄ and Si₂H₆ 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 (E_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-FeSi₂ layers are μ~2 cm²/V s and p~2×10¹⁸ cm^-3, respectively.