Determination of the size, shape, and composition of indium-flushed self-assembled quantum dots by transmission electron microscopy

Abstract

Single and multiple layers of self-assembled InAs quantum dots (QDs) produced by the indium-flush technique have been studied by transmission electron microscopy (TEM) in an effort to develop techniques to reproducibly grow QDs of uniform size and shape. To monitor the changes in QD dimensions, plan-view samples of capped single layers were studied as well as cross-sectional samples of QDs in multiple layers and stacks. The changes in the observed round- and square-shaped QD images under various plan-view TEM imaging conditions, as well as the contrast reversal in the center of QD images viewed in cross-section are modeled using the many-beam Bloch-wave approach, including strain. The sizes and shapes of the QDs are determined through the interpretation of the observed (primarily strain) contrast in plan-view and the observed (primarily atomic number) contrast in cross-sectional TEM.

Determination of the shape and indium distribution of low-growth-rate InAs quantum dots by cross-sectional scanning tunneling microscopy

“…[10][11][12][13] It was also reported that the shape strongly depends on the growth parameters during MBE. 13 Performing measurements on the natural ͑110͒ cleavage plane implies that the shape and size found in the cross-sectional images depend on the position of each dot with respect to the cleavage plane and the actual dot shape.…”

“…8 The dot shape and thus the electronic properties can, however, change significantly after coverage with a capping layer. High resolution transmission electron microscopy can be used to investigate covered quantum dots, 1,6,7,9,10 but this method suffers from averaging effects, which hamper the investigation of, for example, interface roughness and alloy fluctuations. In this study, cross-sectional scanning-tunneling microscopy ͑X-STM͒ is employed to obtain a conclusive and comprehensive determination of the shape, size, and composition of SQDs.…”

Magnetically driven coupling of electronic states in quantum dot molecules

“…Especially, during the last decade it has become possible to fabricate realistic semiconductor quantum dots in laboratories. Various experimental results demonstrate that InAs/GaAs quantum dots can have diverse shapes, such as disk, ellipsoid, or conical shapes with a circular top view cross section and a large area-to-height aspect ratio (see for instance [2,3]). Coupled quantum dots allow us to form an artificial molecule.…”

Influence of quantum dots shape approximation on size reconstructed from atomic force microscopy measurements

“…The dimensions of quantum dots (QDs) are usually deter− mined using transmission electron microscopy (TEM) [1,2] scanning tunnelling microscopy (STM) [3] and atomic force microscopy (AFM) [4,5]. Most popular are AFM measure− ments as this method is simple, fast and does not require so− phisticated sample preparation.…”