We have studied the formation mechanisms and morphological features of Ge i
slands grown on Si(001) substrates using gas source molecular beam epitaxy
(GSMBE). The size, the shape and the number density of Ge islands show dras
tic changes when altering parameters such as growth temperature, Ge coverag
e and Si spacer layer thickness within Ge/Si multilayers. The results also
show that certain conditions exist which can produce a large number of rela
tively small pyramidal islands which are thought to be energetically unstab
le. Moreover, only the hut-clusters, which are characteristic of low temper
ature growth, show ordering in vertically stacked Ge layers, with a concomi
tant shape change to well-organized very small pyramids. (C) 2000 Elsevier
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