材料期刊网

Growth and ordering of coherently strained Ge-rich islands in Ge/Si single layer and multilayer systems and the influence of island arrangements on the evolution of the surface morphology of Si cap layers during deposition by low-pressure chemical vapour deposition(LPCVD) on Si(001) substrates at 700℃ have been investigated by TEM of cross-section and plan-view specimens. At distances between the Ge layers of 35-50nm, vertical order of GeSi islands is observed for Ge-Si bilayer systems and for Ge-Si multilayer systems consisting of 5 layer pairs whereas lateral ordering parallel to <100> substrate directions is observed for the latter case only. In agreement with earlier results the vertical ordering in the multilayer system can be understood as result of the elastic interaction between island nuclei forming in the layers with close islands in a buried layer below. The lateral ordering along <100> may be attributed to the anisotropy of the elastic interaction. Characteristic for all Si surfaces are the spatial correlation between the presence of island-induced lattice strain and the appearance of arrays of larger square-shaped pyramids with distinct faceting and facet edges along <110>. The results reflect the importance of the control of growth parameters and of the island-induced strain state for the evolution of the Si top layer surface morphology during LPCVD growth.