EVOLUTION OF SHORT-RANGE AND LONG-RANGE ORDER DURING SI INCORPORATIONON GAAS(001) OBSERVED BY RAS AND RHEED DURING MBE

The Si incorporation on GaAs (0 0 1) has been studied in real time by reflection high-energy electron diffraction (RHEED) and reflectance an isotropy spectroscopy (RAS) at conditions of enhanced adatom mobility. In the RAS spectra, besides resonances due to As and Ga dimers on the GaAs surface also features due to Si dimers in single and double lave rs as well as As dimers adsorbed on them are identified. The incorpora tion process is very complex due to Si-induced As desorption, combined incorporation of Si and As, and readsorption of As on (Si, Ga). At co nditions of high adatom mobility (low As-4 pressure) a single Si layer is nearly completed before Si incorporation in a second layer takes p lacet whereas for reduced adatom mobility (high As-4 pressure) islandi ng with Si incorporation in a double layer is found in early growth st ages.