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 spect ra measured from GaAs(001) surfaces under ultrahigh vacuum conditions which were simultaneously controlled by reflection high-energy electro n diffraction or low-energy electron diffraction certain surface recon structions can be assigned to specific RAS spectra. Arsenic-rich disor dered (4 X 4), centered (4 X 4), and (2 X 4) like surfaces are identif ied during deoxidation of the substrate at pregrowth heating. After st arting growth the RAS signal shows oscillations the period of which co rresponds to the growth of 1 ML of GaAs. This is verified by postgrowt h 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.