Strain-driven modification of the Ge/Si growth mode in stacked layers: A way to produce Ge islands having equal size in all layers

The Ge/Si growth process in standard stacked layers of self-assembled Ge/Si (001) islands was studied using in situ reflection high-energy electron dif fraction, transmission electron microscopy and photoluminescence spectrosco py. It was found that the decrease of the Ge critical thickness in the uppe r layers of a stacked layer is the main parameter which leads to the increa se of the upper island size and height. Such an evolution of the Ge critica l thickness could be explained by an accumulation of elastic strain induced by the lower Ge islands and wetting layers in the Si spacer layers. This r esult opened the ways to the realization of stacked layers in which the isl ands have equal size in all layers even for stacked intervals being reduced down to about 1 nm. (C) 2000 Elsevier Science S.A. All rights reserved.