Self-Organization of High-Density III–V Quantum Dots on High-Index Substrates

Ordered In0.4Ga0.6As quantum dots (QDs), with the density of 109 cm-2–1011 cm-2, are fabricated on GaAs(311)B substrates by atomic-hydrogen assisted molecular beam epitaxy. The density and the dot size are mainly changed by the growth temperature between 460°C and 520°C. In sharp contrast to InAs, where we can hardly observe any ordering, and coalescence or merging of dots occurs beyond a thickness of 4 monolayers, the high-density In0.4Ga0.6As QDs do not coalesce even when the QDs are in contact with each other. The inhomogeneuos distribution of In and Ga in the QDs which are In rich at the surface is found to be responsible for this unusual behavior by reflection high energy electron diffraction studies. The atomic force microscope images show that a surface coverage of nearly 100% can be achieved. It implies the existence of lateral coupling between QDs, which is strongly supported by the photoluminscence measurements.