Vertical InAs diffusion and surface ordering processes in InAs vertical quantum dot columns

Two structural processes are investigated in association with the vertical stacking of InAs strain-induced quantum dots. First, using cross-sectional scanning tunneling microscopy we investigate the In diffusion from InAs quantum dots and the quantum well that is intrinsic to the dot formation process. We observe that large-scale vertical diffusion of In is present in the quantum well regions; but in comparison, the In remains remarkably stable in the dot regions. Second, while we have previously observed increased in-plane spatial uniformity in the InAs dot distribution in the uppermost dot layer of vertical stacked structures, we here investigate the mechanism by which this ordering results. We observe a decrease in the column density by two mechanisms that may or may not be independent. First, is a bending and merging of vertical columns and second is the abrupt termination of a vertical column. (C) 1998 Published by Elsevier Science B.V. All rights reserved.