SURFACE PROCESSES RESPONSIBLE FOR REFLECTANCE-ANISOTROPY OSCILLATIONSDURING MOLECULAR-BEAM EPITAXY GROWTH OF GAAS(001)

Reflectance anisotropy spectroscopy (RAS) oscillations during molecula r beam epitaxy (MBE) growth of singular GaAs(001) were studied at subs trate temperatures between 500 degrees C and 610 degrees C. RAS spectr a were measured and related to surface reconstructions determined by r eflection high-energy electron diffraction (RHEED). The RAS signal sen sitively monitors surface changes when growth is initiated, With openi ng of the Ga shutter an immediate change in the RAS response indicates the modified As adsorption/desorption equilibrium due to the presence of Ga atoms on the surface. During growth of the first GaAs monolayer s RAS oscillations mirror the oscillation of the monolayer step densit y in island growth mode. From all experimental evidence it must be con cluded that the step density modulates the As dimer coverage because A s desorbs predominantly in regions close to the island boundaries.