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We demonstrate an efficient method to engineer the quantum confinement in a system of two quantum dots grown in a vertical stack. We achieve this by using materials with a different lattice constant for the growth of the outer and inner barriers. We monitor the resulting dot morphology with transmission electron microscopy studies and correlate the results with ensemble quantum dot photoluminescence. Furthermore, we embed the double quantum dots into diode structures and study photoluminescence as a function of bias voltage. We show that in properly engineered structures, it is possible to achieve a resonance of the hole states by tuning the energy levels with electric field. At the resonance, we observe signatures of a formation of a molecular state, hybridized over the two dots. [ABSTRACT FROM AUTHOR]

A finite-element programme has been developed to model strain relaxation in the case of epitaxial Si1-xGex/Si coherent quantum dots either with or without compositional inhomogeneities. The resulting elastic displacement fields are used to calculate the intensity of dynamical plan view TEM images of such quantum dots. Various types of linear or parabolic compositional inhomogeneities are studied. TEM images of quantum dots with such inhomogeneities are calculated as well as those of quantum dots with a homogeneous composition. They are then compared with experimental images. It is shown how the analysis of the main features of these experimental images (black/white lobes and moire-like fringes) enables us to determine the conditions in which it is possible to distinguish quantum dots with a homogeneous composition from those with compositional inhomogeneity. [ABSTRACT FROM AUTHOR]

We report on microphotoluminescence study of excitons localized by potential fluctuations in a wetting layer (WL), which accompanies InAs/GaAs quantum dots (QDs). Linear polarization of spectral lines due to localized excitons enable us to identify a neutral excitonic and biexcitonic emission. A charged exciton has also been identified. High resolution transmission electron microscopy measurements of the investigated structure reveal lateral fluctuations of In content in the WL, as well as its broadening. Both effects give rise to potential fluctuations, which can confine excitons observed in our measurements. The potential fluctuations can be regarded as “natural” QDs in the WL. [ABSTRACT FROM AUTHOR]

Formation of MnAs quantum dots in a regular ring-like distribution has been found on molecular beam epitaxy grown (GaMn)As(100) surfaces after low-temperature annealing under As capping. The appearance of the dots depends on the thickness and Mn concentration in the (GaMn)As layer. With 5 at. % substitutional Mn the quantum dots showed up for layers thicker than 100 nm. For thinner layers the surfaces of the annealed samples are smooth and well ordered with 1×2 surface reconstruction, just as for as-grown (GaMn)As. The annealed surfaces are Mn rich, and are well suited for continued epitaxial growth. [ABSTRACT FROM AUTHOR]