Growth process of quantum dots precisely controlled by an AFM-assisted technique

The evolution of site-controlled QDs in molecular beam epitaxial growth in our atomic-force microscopy (AFM)-assisted control of InGaAs/GaAs quantum dots (QDs) is investigated here. Depending on a regularly round shape of a hole made by AFM lithography, the nucleation of QD begins at the center of a hole. With increasing coverage of InGaAs, the QD has the hole filled up mainly by expanding in lateral direction. The complete filling of a hole is followed by vertical growth of the QD with nearly unchanging lateral size. As a possible mechanism, strain is considered to explain the growth process of QDs in this technique.