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

The shape of InAs quantum dots (QDs), grown by molecular-beam epitaxy on the GaAs(113)A surface, is studied by in situ scanning tunneling microscopy. At an early growth stage, the QDs adopt a shape given by {110}, (111)A, and {2 5 11}A bounding facets and an unresolved rounded {001} region. At a later growth stage, the QDs become elongated along [33 (2) over bar], with a reduction of the (111)A facet size and a flattening of the rounded region. This is explained by facet growth kinetics. The broad size distribution indicates growth limitation. The symmetry of the substrate is retained in the QDs, proving epitaxial growth

InAs quantum dots (QD’s) grown by molecular-beam epitaxy on GaAs(001) substrates were studied by atomically resolved in situ (without breaking a ultrahigh vacuum) scanning tunneling microscopy. A detailed sequence of shapes, appearing during the growth process, is evaluated: The smallest QD is terminated by {137}A bounding facets with a rhombic base. With increasing size, {1¯3¯5¯}B and {1¯1¯2¯}B facets appear in succession besides {137}A, making the QD more rounded. At a critical diameter of the base, the QD undergoes a shape transition from flat to steep by the formation of steeper {110} and {111} facets at the sides and gradually achieves a squared base. For all QD’s the {137}A facets remain on top. Almost all shapes that have been observed for InAs QD’s on GaAs(001) in earlier publications are covered.

Self-organized InAs quantum dots were grown by molecular-beam epitaxy on the GaAs (1̄1̄3̄) B surface. Atomically-resolved scanning tunneling microscopy images were acquired in situ. Each quantum dot grows with the same orientation relative to the substrate, with mirror symmetry to the (1̄10) plane perpendicular to the surface, and with its central part sitting on a flat base. The shape of the central part is given by {110} and (1̄1̄1̄) B bounding facets and a not-further-resolved round region. High-index surfaces such as (1̄3̄5̄) B, (3̄1̄5̄) B, and probably (1̄1̄2̄) B are derived for the base.

InAs quantum dots ͑QD's͒ were grown on the GaAs͑113͒B surface by molecular-beam epitaxy at temperatures between 435 and 490°C. Their shape, size, and number density were investigated by in-situ scanning tunnelling microscopy. The shape of the QD's is given for the most part by ͕110͖, ͑111͒B, and vicinal ͑001͒ bounding facets, and does not change significantly with growth temperature. The diameter at the base and the height of the QD's increase monotonously from 25 to 54 nm, and from 3.5 to 9.8 nm, respectively, whereas the number density decreases as temperature increases. This is explained by assuming a slight decrease of the number density of critical growth nuclei with increasing temperature. The size distribution is bimodal: besides the coherent QD's, some larger and probably incoherent islands are observed that are extended along ͓332͔. Post annealing increases the diameter and the height by about 30% and decreases the number density, but does not change the shape significantly.