Growth and characterization of GaAs/Ge epilayers grown on Si substrates by molecular beam epitaxy

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Abstract
Epitaxial GaAs/Ge films are grown by molecular beam epitaxy (MBE) on Si substrates. The effect of various MBE growth conditions on the sample morphology, the defect density, and the optical properties of GaAs and Ge epilayers is examined. Scanning electron microscopy, plan-view and cross-sectional transmission electron microscopy, reflection high-energy electron diffraction, and photoluminescence are used to characterize epitaxial layers. It is found that the defect density decreases with increasing epilayer thickness. This is due to an annihilation process that affects both threading dislocations and stacking faults. The substrate temperature during Ge growth is found to affect the properties of both the Ge and GaAs films. GaAs surface morphology degrades and the stacking fault density increases at high Ge buffer-layer substrate temperatures; however, the threading dislocation density remains unchanged. Variations in growth conditions are correlated with defect densities and luminescence efficiencies to determine material quality and optimize growth conditions.