Self-assembled (SA) quantum dots (QDs) have been widely studied due to the facileness in their preparation. Unlike other types of QDs that require complicated fabrication processes, SA QDs are prepared merely by depositing materials that have different bandgaps and lattice constants to the with respect to the substrate by epitaxial crystal growth techniques. InAs QDs on GaAs(001) grown by MBE or MOCVD have been a typical example, and their optoelectronic properties have been extensively investigated. For device applications, it is essential that their size and spatial distribution are controlled. However, since SA QDs are formed through random processes, it is not easy to achieve size and distribution uniformity without prior processing the substrate prior to crystal growth. A number of studies have been performed to understand the fundamental mechanisms of SA QD formation that would provide us with information to achieve such goal.
Here, we performed real-time observation of SA InAs QD growth on GaAs(001) by MBE. In contrast to most previous reports that employed growth interruption, by following the time transient of RHEED specular beam in detail, we obtained information about nucleation and evolution of the QDs, and have been able to distinguish processes that are dependent and independent of growth rate. In addition, the results reveal that surface migration of In/As atoms and their incorporation into QDs, with the aid of the wetting layer, can be observed. We will also provide a quantitative discussion on these processes.