Si overlayers have been grown under ultrahigh vacuum conditions on GaAs (100) single crystals by means of molecular beam epitaxy. For growth temperatures above 400thinsp;deg;C (2times;1) lowhyphen;energy electron diffraction patterns of the Si overlayers were observed at all film thicknesses produced (1ndash;5000 Aring;). By means of Auger electron spectroscopy it was found that the surface of the grown Si was enriched with As and Ga. Two different mechanisms contribute to the enrichment and lead to a high (sim;1018/cm3) background doping level. With Rutherford backscattering using ion channeling it was found that there is considerable lattice disorder at the Sihyphen;GaAs interface, although the crystal quality of the Si improves markedly towards the Si surface for thicker layers where the minimum channeling yield drops to 9percnt;. With medium energy ion scattering it was established that no island formation occurs during initial stages of the growth.
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