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(a) Schematic of the investigated sample showing the nominally grown layers. (b) Filled-state XSTM overview image showing the three In0.25Ga0.75As/GaAs layers as well as one GaAs layer in the GaP matrix. In addition two monoatomic surface steps are visible, one very close to the first InGaAs quantum-dot layer. The image was taken at a sample voltage and a tunneling current .
Filled-state XSTM images of (a),(b) a quantum dot and (c),(d) a quantum ring. The images were taken at and . Thecontours of the nanostructures are marked by the solid lines. The dashed line in (b) marks the indium-rich area. The bright spots on top of the GaP surface are supposed to be phosphorous adatoms pulled out of the cleavage surface during the scanning process (see Ref. 15 ).
(a) Filled-state XSTM image of the wetting layer region, taken at and . Arsenic-rich regions with brighter contrast are marked by (yellow) ovals. (b) Evaluation of the local lattice parameter along growth direction within the (green) box in (a). The local lattice parameter is related to the local arsenic concentration. The right scale bar and the dashed line in (b) indicate the calculated values for the local lattice parameter for strained GaAsP layers in a GaP matrix.
Evaluation of the local lattice parameter and the related stoichiometric composition along growth direction for a representative quantum dot. The graphs show the evaluated data (a) for the quantum-dot center in (red) dots and for the quantum-dot sides in (blue) squares and (b) averaged over the entire quantum-dot region in (green) squares and the corrected data in (green) open squares. For the latter the compression around the quantum-dot base is taken into account. The evaluated data in each case refer to the highlighted boxes in the XSTM images. The right scale bars and the dashed lines in the graphs indicate the calculated values for the local lattice parameter for strained GaAsP and InGaAs layers in a GaP matrix.
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