Initial stage of heteroepitaxy of Ge on Si(111)-7 × 7 and (100)-2 × 1 surfaces studied by low-energy electron-loss spectroscopy (LEELS)

Abstract

The initial stage of heteroepitaxial growth of Ge on Si surfaces has been investigated by low-energy electron-loss spectroscopy (LEELS) combined with low-energy electron diffraction (LEED) and Auger-electron spectroscopy (AES). Ge was deposited onto Si(111)-7 × 7 and (100)-2 × 1 surfaces maintained at RT, 350°C and 500°C. At RT, the LEELS spectrum of Si(111) and (100) surfaces evolves to that of amorphous Ge (a-Ge) with increase in Ge thickness. Below one monolayer (1 ML) coverage, the surface plasmon of Si splits into two peaks due to a Ge-induced transition at localized GeSi bonds. At high temperatures, the bulk plasmon maintains about the same energy up to ∼ 30 Å deposition of Ge, consistent with a pseudomorphic growth of thin Ge layers (∼ 4 ML) followed by islands formation on the layers. With 30 Å deposition, the surface-related structures in the LEELS Spectrum of Ge on Si(111) become similar to those of a clean Ge(111) surface, while those of Ge on Si(100) are rather weak compared with those of the clean Ge(100) surface. The (7 × 7) structure of the Si(111) surface is replaced by a (5 × 5) one which may be caused by the formation of GeGe bonds with Ge deposition of 1.5–2 ML. However, in spite of the appearance of the (5 × 5) pattern in LEED, the LEELS measurements reveal that the back-bond surface states of Si remain up to some critical thickness depending on the deposition and/or annealing temperature.