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The effects of GaAs overgrowth on the structural properties of large low-growth-rate InAs quantum dots (LGR-QDs) grown on GaAs(001) are examined using in situ scanning tunneling microscopy. Strongly anisotropic surface diffusion produces a characteristic valley-ridge structure above the LGR-QDs and the surface is not planarized even after a cap thickness >400 Å. The evolution of surface morphology proceeds very differently to the case of smaller conventional growth rate QDs capped under the same conditions, due to the different initial strain states of the QDs.

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Scanning tunneling microscopy has been used to investigate the effects of annealing and quenching on InAs/GaAs(001) quantum dots (QD) grown at a low growth rate by molecular beam epitaxy (MBE). Significant changes in QD number density, average volume (of more than one order of magnitude), wetting layer morphology, and QD volume density have been observed after in situ annealing for up to 90 s at a growth temperature of 485 °C providing direct evidence for a QD ripening process resembling that observed in other heteroepitaxial growth systems. Inefficient sample removal from the growth chamber and cooling (quenching) leads to unintentional annealing and ripening of the QDs and/or the appearance of clusters on the sample surface. The appearance of these clusters can have a significant impact on any statistical analysis of QD samples. Our results show that MBE-grown InAs/GaAs(001) QDs are kinetically controlled structures even at low growth rates, and underline the importance of the quench method in minimizing postgrowth changes in the characteristics of the uncapped QD array and preserving the in situ surface morphology for ex situ surface studies.

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