Increased size uniformity through vertical quantum dot columns

Abstract

The effects of stacking strain-induced InAs quantum dot layers on the size uniformity and density of dots in the upper most layer have been investigated using single-dot layers, and stacks of 10 and 20 quantum dot layers with a 56 A space region of GaAs. In these multilayered structures dots from different layers are aligned in vertical columns. X-ray diffraction indicates diffraction from a superlattice of InAs and GaAs, where the InAs contribution to the diffraction is from the quantum well region which is an integral part of the dot formation process. Thus, these quantum well regions remain intact and planar throughout the stacking process. The quantum well thickness is estimated to be 1.9 InAs monolayers. Atomic-force microscopy indicates the dot density decreases with dot layers, while the average dot height and in-plane dot diameter increase with dot layers. The uniformity of dot height and in-plane diameter also increases with stacking of dot layers as has been predicted [J. Tersoff, C. Teichert and M.G. Lagally, Phys. Rev. Lett. 76 (1996) 1675].