Formation Of Stacking Fault Tetrahedra During Epitaxial Growth of Silicon and Germanium-Silicon Layers on {111} Silicon Substrates

Abstract

ABSTRACTTransmission electron microscopy was used to characterize defects formed in silicon (Si) and germanium-silicon (Ge-Si) alloy layers grown sequentially by molecular-beam epitaxy (MBE) on {111} Si substrates. Stacking fault tetrahedra (SFT) were found to form in these epitaxial layers. In addition, the apex of the SFT are seen to be pointing down toward the Si substrate, with most of the SFT tips converging exactly at the Si/Si and the Ge-Si/Si interfaces. Diffraction contrast experiments using various two-beam conditions have shown that the stacking faults bounding the SFT are of intrinsic (vacancy) type. In the case of a Si layer on the Si substrate, it is reasoned that the SFT are caused by impurities on the surface of the Si substrate prior to deposition. However, in the Ge-Si layer, it is believed that the formation of the S FT is due to local stresses caused by the structural ordering/phase separation of the Ge atoms.