CHARACTERIZATION OF SELF-ASSEMBLED GE ISLANDS ON SI(100) BY ATOMIC-FORCE MICROSCOPY AND TRANSMISSION ELECTRON-MICROSCOPY

We present an alternative starting point of the fabrication of nanostr uctures for electronic devices by using self-assembling structures. On e way for the growth of self-assembling structures as quantum dot (QD) arrays is based on the formation of coherently strained Ge islands on Si and requires controlling of a defined island growth (Stranski-Kras tanov). For this reason we carried out systematic quantitative investi gations of the growth of Ge islands. Stacks of two layers of Ge island s with a Si spacer were grown on a Si buffer and characterized by atom ic force microscopy (AFM) and transmission electron microscopy (TEM). In the first series the Ge layer thickness was varied at a constant gr owth temperature and in the second series the growth temperature was v aried for a constant Ge laver thickness. Many of the results described in this paper confirm the expected growth behavior of Ge islands, i.e . the Stranski-Krastanov growth mode and the increasing island density with decreasing growth temperature. However, two new aspects of the i sland growth were round. Small Ge islands are already formed from 2.15 monolayers (ML) of Ge at high growth temperatures, At lower growth te mperatures (less than or equal to 645 degrees C, 6.2 ML coverage), few large islands with defects and a high density of small coherent islan ds are observed simultaneously. TEM studies of cross-sectional and pla n-view samples reveal that the small islands are elongated along (100) directions. Reasons for the formation of the two kinds of islands are discussed. (C) 1998 Elsevier Science S.A. All rights reserved.