STRUCTURAL CHARACTERIZATIONS OF INITIAL NUCLEATION OF GAAS ON SI FILMS GROWN BY MODULATED MOLECULAR-BEAM EPITAXY

Structural characterizations by plan-view and high resolution cross-sectional transmission electron microscopy (TEM) on 150angstrom thick GaAs on Si films grown by a modulated molecular beam (MMBE) technique and conventional molecular beam epitaxy (MBE) at 300-degrees-C are reported. From the coverage of Moire interference fringes on plan-view electron micrographs, it is found that the nucleation of GaAs deposited by MMBE is more two-dimensional than conventional MBE. High resolution cross-sectional TEM micrographs show that the interfacial defects consist almost solely of partial dislocations for both samples. A model is constructed to explain this phenomenon by considering the magnitude of strain relieved by each type of misfit dislocation relative to its energy of formation. The effect of thermal annealing on the interfacial defect structures of these samples is also reported.