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Cross-sectional scanning tunneling microscopy results on GaSb quantum wells and dots in GaAs are found to exhibit a narrow, sharply defined contrast of the nanostructure at negative sample bias, but a smoothly broadened contrast at positive sample bias. This contrast is related to the specific type-II band alignment of GaSb/GaAs heterostructures in combination with tip-induced band bending. The corresponding model is quantitatively verified by numerical simulations of band bending and tunnel current profiles combined with calculations of cleavage-induced strain relaxation. [ABSTRACT FROM AUTHOR]

Using plan-view and cross-sectional scanning tunneling microscopy, the shape and composition of InAs/GaAs quantum dots are investigated before and after capping by GaAs. During capping, the original pyramidally shaped quantum dots become truncated, resulting in a flat (001) top facet and steeper side facets. The InAs quantum dots are found to be intermixed at their top with GaAs due to material rearrangement. Since the bottom interface of quantum dots and wetting layer is always sharp, this intermixing occurs during capping and not during quantum dot growth. Considering strain energies, a model for the capping is presented. [ABSTRACT FROM AUTHOR]

Abstract: GaSb nanostructures in GaAs, grown by metalorganic chemical vapor deposition, were studied with cross-sectional scanning tunneling microscopy. Three different samples were examined, containing a thin quantum well, a quantum well near the critical thickness for dot formation, and finally self-organized quantum dots with base lengths of 5–8nm and heights of about 2nm. The dots are intermixed with a GaSb content between 60% and 100%. Also small 3D and 2D islands were observed, possibly representing quantum dots in an early growth stage and quantum dot precursors. All GaSb layers exhibit gaps, which are indications of an island-like growth mode during epitaxy. [Copyright &y& Elsevier]

Self-assembled InAs/InGaAsP/InP(001) nanostructures are investigated using cross-sectional scanning tunneling microscopy. Atomically resolved images at both the (110) and the [formula] cleavage surface show InAs quantum dashes with almost binary composition and a truncated pyramidal shape. The quaternary matrix material directly above the InP substrate already shows a tendency toward decomposition, which gradually increases along the [001] growth direction, in particular above quantum dash layers. This decomposition, in turn, leads to an enhanced vertical correlation in the nucleation of further quantum dash layers. [ABSTRACT FROM AUTHOR]

Abstract: InAs/InGaAs quantum dots-in-a-well nanostructures based on GaAs are a promising candidate for optoelectronic devices with the important emission wavelength of . We present cross-sectional scanning tunneling microscopy data, showing material reorganization depending on the process of GaAs cap layer growth on top of the quantum dot (QD) nanostructures. QDs capped with 2nm GaAs prior to an extended growth interruption have a truncated pyramidal shape, typical base lengths of 20–25nm, and 5–7nm height. Those capped by a thicker GaAs layer show identical shapes, but their sizes are generally larger with about 30nm base length and 6–9nm height. Furthermore, some of these large QDs contain nanovoids, which form during the capping process and can be avoided in the case of a thin GaAs cap layer. [Copyright &y& Elsevier]

In this work we present a comparative cross-sectional scanning tunneling microscopy study of different InAs and InGaAs quantum dot structures grown by metalorganic vapor phase epitaxy. The varying growth conditions lead to completely different spatial structures, as distinctive quantum dots, intermixed layers, and intermixed dots. Especially the overgrowth procedure and the arrangement of growth interruptions are responsible for segregation of the InAs material. [Copyright &y& Elsevier]