AVS 47th International Symposium
    Semiconductors Wednesday Sessions
       Session SC+EL+SS-WeA

Paper SC+EL+SS-WeA4
Growth of Coherent Three-dimensional Si Islands on Ge(111)

Wednesday, October 4, 2000, 3:00 pm, Room 306

Session: Semiconductor Alloys
Presenter: A. Raviswaran, University of Illinois, Urbana-Champaign
Authors: A. Raviswaran, University of Illinois, Urbana-Champaign
C.P. Liu, University of Illinois, Urbana-Champaign
J.M. Gibson, Argonne National Laboratory
D.G. Cahill, University of Illinois, Urbana-Champaign
Correspondent: Click to Email
We study the evolution of three-dimensional islands during Si/Ge(111) epitaxy. The strain due to lattice mismatch (4.2% tensile) and the difference in the surface energies (@gamma@@sub Si@>@gamma@@sub Ge@) contribute to the formation of the three-dimensional Si islands. We grow Si islands on pseudomorphic Si@sub 0.15@Ge@sub 0.85@ buffer layers (deposited on Ge(111) substrates) in the temperature range 500°C - 650°C using MBE; the (111) orientation is used because the critical thickness of Si layers on Ge(111) is larger than that on Ge(001). We characterize the morphology and relaxation of the Si islands using ex situ AFM, TEM and SEM. Islanding occurs at 1 BL Si coverage, i.e., without the formation of a wetting layer. We observe high densities (~ 10@super 12@ cm@super -2@) of coherent, circular base islands for growth temperatures 500°C - 600°C and low Si coverage (< 2 BL Si). The density and shape of the islands is insensitive to the growth temperature. Beyond a critical width the islands relax plastically, by the nucleation and glide of misfit dislocations; this critical width is ~ 16 nm at 550°C and ~ 25 nm at 600°C. We observe large, incoherent, irregularly shaped islands at higher temperatures (> 600°C) and coverages (> 4 BL Si). As the islands transform from coherent to incoherent, coarsening occurs which results in an increase in the island width and a reduction in the island density. The high temperature (> 600°C) growths show a secondary maximum in the island density near 4 BL Si coverage.