Growth and characterization of silicon/germanium heterostructures of silicon(001) surface and germanium nano-dots on patterned silicon(001) surface

The epitaxial growth of Si/Ge heterostructures on the Si(001) surface has been the subject of much research because of its interesting properties and technological applications. Scientifically Ge/Si(001) is interesting because it is an ideal system to study strained heteroepitaxy. Such strained heteroepitaxial layers of Si/Ge on Si(001) can have superior device performance compared to Si based devices.; In this thesis, using x-ray synchrotron radiation, we have performed structural studies of Si/Ge heterostructures grown on Si(001) by surfactant mediated epitaxy with Bi as the surfactant. High resolution measurements were performed using the x-ray standing wave technique to characterize the structure of atomic layers in ultra-thin Ge films on Si(001) Our results indicate that the Ge atomic layers are highly commensurate with the Si substrate lattice in the in-plane direction but less so in the surface normal direction. Using grazing incidence x-ray diffraction we measured the critical thickness for pseudomorphic growth of Ge on Si(001) with Bi as surfactant to be 7 monolayers (ML). In comparison with Ge growth without Bi, segregation of Ge in the Si cap layer was suppressed and the Ge film was partially relaxed at 10 ML. Using x-ray specular reflectivity we measured the Ge-Si cap interface roughness and found it to be significantly larger for Ge film thicknesses above 7 ML.; We also investigated the morphology of Ge nano-dots grown by molecular beam epitaxy on lithographically patterned Si(001) stripe-mesas. Our atomic force microscopy (AFM) images for Ge grown on stripe-mesas show increased uniformity in Ge nano-dot size, shape, and orientation compared with Ge nano-dots grown on a planar Si(001) surface. On stripe-mesas we also observed preferential growth of Ge nano-dots along the edges of the stripe-mesas.