GAAS SURFACE CONTROL DURING METALORGANIC VAPOR-PHASE EPITAXY BY REFLECTANCE ANISOTROPY SPECTROSCOPY

GaAs(001) surfaces are studied during metalorganic vapor phase epitaxy by reflectance anisotropy spectroscopy (RAS). In analogy to RAS spectra measured from GaAs(001) surfaces under ultrahigh vacuum conditions which were simultaneously controlled by reflection high-energy electron diffraction or low-energy electron diffraction certain surface reconstructions can be assigned to specific RAS spectra. Arsenic-rich disordered (4 X 4), centered (4 X 4), and (2 X 4) like surfaces are identified during deoxidation of the substrate at pregrowth heating. After starting growth the RAS signal shows oscillations the period of which corresponds to the growth of 1 ML of GaAs. This is verified by postgrowth layer thickness measurements. A (4 X 4) reconstructed surface before growth turns out to be the necessary condition for the appearance of these monolayer oscillations in the RAS signal.