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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.

The hole confinement of self-organized GaSh/GaAs quantum dots embedded in n + p-diodes is investigated experimentally by admittance spectroscopy. The highest thermal activation energy obtained, 400 meV, refers to only weakly charged quantum dots. Detailed bias-dependent investigations allow to study state- filling and Coulomb charging effects. State filling lowers the activation energy down to 150 meV in quantum dots charged with the maximum number of about 15 holes. The observed thermal activation barrier for GaSb/GaAs quantum dots is about twice as high as for structurally comparable InAs/GaAs quantum dots.

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.

Many-body states in self-organized type II GaSbAs/GaAs quantum dots grown by metal organic chemical vapor phase deposition are studied. With increasing exciton occupation the photoluminescence shows a blue shift and becomes significantly broader developing a saturated plateau structure. The results reveal the properties of many-hole states in GaSbAs quantum dots determined by Coulomb charging and state filling.

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.

We present cross-sectional scanning tunneling microscopy results of GaSb quantum dots in GaAs, grown by metalorganic chemical vapor deposition. The size of the optically active quantum dots with base lengths of 4–8 nm and heights of about 2 nm is considerably smaller than previously published data obtained by other characterization methods. The local stoichiometry, obtained from atomically resolved images, shows a strong intermixing in the partly discontinuous wetting layer with an average GaSb content below 50%, while the GaSb content of the partly intermixed quantum dots is between 60% and 100%.

A system composed of a double layer of stacked quantum dots (QDs) of (In,Ga)As and Ga(Sb,As) was investigated by quantitative high-resolution transmission electron microscopy. The layers were grown by metalorganic chemical vapor deposition on a GaAs substrate. The strain field of the lower quantum dots determines the nucleation in the subsequent layer. Investigating this effect, the strain field as well as the composition could be measured at high resolution. Local changes of lattice distances could be quantified with a precision of 0.003nm. The error in determining the local composition inside the InxGa1−xAs resp., GaSbyAs1−y QDs amounts to ΔxIn=0.02 and ΔySb=0.03.

We have studied the photoluminescence from type-II GaSb/GaAs self-assembled quantum dots in magnetic fields up to 50 T. Our results show that at low laser power, electrons are more weakly bound to the dots than to the wetting layer, but that at high laser power, the situation is reversed. We attribute this effect to an enhanced Coulomb interaction between a single electron and dots that are multiply charged with holes.

The electronic properties of self-organized GaSb quantum dots (QDs) embedded in GaAs n+p diodes were investigated by capacitance–voltage and deep level transient spectroscopy. The localization energy of the hole ground state is 450 meV. State filling lowers the activation energy to 150 meV for completely charged QDs containing 15 holes. The hole retention time at room temperature for a single hole per QD is extrapolated to be in the microsecond range, about five orders of magnitude longer than in In(Ga)As/GaAs QDs. Hence, we consider GaSb/GaAs to be a suitable material system for future QD memory applications which require long storage times.

The formation of GaSb quantum dots in a GaAs matrix in the Stranski–Krastanow growth mode under metalorganic chemical vapor deposition conditions is investigated. Transmission electron microscopical images and photoluminescence measurements show the islands to nucleate during the GaSb deposition and to grow subsequently by mass transfer from the two-dimensional wetting layer. The evolving surface morphology indicates local equilibria between quantum dots and the surrounding wetting layer regions.

Many-particle effects are investigated in the photoluminescence of type II GaSb/GaAs quantum dots (QDs). With increasing excitation density, i.e., exciton occupation, the photoluminescence shows first a blueshift and then saturates developing a plateau region. The peculiar behavior is attributed to Coulomb charging and state filling of the localized holes to dominate the many-particle regime. A high temperature stability makes the GaSb/GaAs QDs suitable for room-temperature devices.

We report photoluminescence (PL) measurements on self-assembled GaSb/GaAs quantum dots. As the laser excitation is increased from very low levels, the PL shows a strong red shift, and then a blue shift, such that it presents a U-shaped curve. Raising the temperature causes a large (