Controlling the formation of quantum dot pairs using nanohole templates

Epitaxial growth of lateral quantum dot molecules

“…After 20 nm buffer growth, the nanohole outline is much flatter and wider at the bottom, and two quantum dots nucleate at the corners of the hole, where the surface curvature changes most rapidly. The preferential nucleation is due to net migration towards the hole, which we attribute to a greater step density in the hole which reduces the adatom lifetime 18. The dots (in a QDM) inside the nanoholes are (5–10) nm high and (35–45) nm in diameter.…”

“…Modifying the shape of the nanoholes with a thin GaAs layer leads to the formation of lateral In(Ga)As QDMs during InAs overgrowth 18. The change in dimensions of the nanohole during GaAs overgrowth is shown in Fig.…”

“…The depth increases initially with GaAs buffer deposition, reaching a maximum of (15 ± 1) nm after 15 nm buffer growth and then decreases, becoming very shallow ((2.9 ± 0.6) nm) by 40 nm buffer growth. The initial increase in depth implies that the concave curvature is not the dominant driving force for adatom migration during the initial stages of growth 18.…”

“…There are several ways to modify the substrate morphology in order to guide the growth of lateral QDMs. For example, QDMs have been grown on the facet edges of mounds 15, 16, at the corners of pyramidal structures formed during selective area epitaxy 17 or on the edges and the bottom of nanoholes 11, 12, 18–22.…”

“…It is also possible to use ex situ patterning to create nanoholes which allows the QDM to be positioned at a pre‐determined location 11, 24, 25, if the pattern size and growth conditions are carefully selected 22, 24. A third method is to create nanoholes in situ by excess gallium droplet etching, where the transition from QD to QDM is achieved by a suitable choice of a thin GaAs buffer to change the nanohole profile 18 or by change in arsenic (As) species 19.…”