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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 5–8 nm and heights of about 2 nm. 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.

Pulsed magnetic fields are used to study a variety of self-assembled semiconductor nanostructures. We illustrate the power of the technique with two recent examples. In the first, we study confinement in InAs quantum dots on (1 0 0) and (3 1 1) B oriented GaAs substrates as a function of InAs coverage. We demonstrate that Stranski–Krastanow growth occurs for (1 0 0) substrates, but show that for (3 1 1) B substrates there is no such transition—rather the dots evolve from fluctuations in the wetting layer. In the second example, we investigate the Coulomb binding of ‘free’ electrons to holes confined to type-II GaSb/GaAs quantum dots. We find that at low laser power the electrons are repelled from the dots (by strain), but that by optical pumping the dots may be multiply charged, attracting the electrons, and more than doubling the binding energy.

We explore the Coulomb binding of electrons to holes confined to type-II GaSb self-assembled quantum dots. We demonstrate that at low laser power electrons are more weakly bound to holes trapped by the dots than to holes in the wetting layer. On the other hand, at high laser power the hydrogenic binding energy of dot excitons increases by more than a factor of two, and so exceeds that of wetting layer excitons. We attribute this to the strong binding of ‘core’ electrons to dots that are highly charged with holes by optical pumping.

The temporal evolution of the size and the shape of self-organized InAs/GaAs quantum dots (QDs) grown using MOCVD is investigated. During a growth interruption after the deposition of the QD material a ripening process is observed, where some QDs grow at the expense of other QDs. A multimodal distribution of the QD ground-state transition energies is observed and attributed to QDs differing in height by entire numbers of atomic monolayers. This distribution is used to track the evolution of the QD ensemble during the growth interruption more detailed. A shape transition from very flat, truncated-pyramid-like QDs to higher, more pyramidal QDs is suggested. An additional antimony flux at the end of the growth interruption leads to an accelerated ripening resulting in a significant red shift of the QD luminescence, which is explained by the surfactant properties of antimony on InAs.

Metalorganic vapor phase epitaxy of GaSb quantum dots (QDs) grown on top of a layer of InAs seed QDs shows a vertically aligned correlation if thin GaAs spacer layers deposited at low temperature are used. Introduction of an annealing step after spacer deposition strongly improves the crystalline quality of the spacer layer. Vertically anticorrelated ordering is found on annealed spacers in addition to aligned ordering. Good optical properties are achieved for stacked QD structures with an InGaAs QD layer on top of seeded GaSb QDs. The photoluminescence of these structures is red shifted by 75 meV with respect to the emission of a single InGaAs QD layer.

The formation of GaSb quantum dots on a GaAs (0 0 1) substrate under metalorganic chemical vapor deposition conditions is investigated. Transmission electron microscopy images and photoluminescence measurements show the island density to be determined in an initial kinetically controlled phase. Subsequently, mass transfer from the two-dimensional wetting layer sustains the growth of the GaSb quantum dots (QDs). Many-particle e=ects in the type II QDs are investigated by excitation- and temperature-dependent photoluminescence measurements. The peculiar optical behavior is dominated by Coulomb charging and state ?lling of the localized holes. ? 2002 Elsevier Science B.V. All rights reserved.

Self-organized formation of GaSb quantum dots during MOCVD growth has been studied. Thin GaSb layers are deposited on GaAs (0 0 1), followed by a growth interruption before the deposition of a GaAs layer. The GaSb growth is performed using low V/III ratios and growth temperatures between 510°C and 550°C. Undercritical GaSb depositions lead to inhomogenities in the composition and thickness of such layers. Photoluminescence measurements suggest these quantum islands to provide zero-dimensional confinement for holes. The dependence of the luminescence on the growth temperatures indicates the formation of the quantum islands to be kinetically controlled.