In this talk I review recent results of our group on self-assembled islands in the SiGe and InAlGaAs material system. The first part of my talk focuses on material intermixing during self-assembled island growth and on the fabrication of compact lateral quantum dot molecules as well as unstrained red-light emitting GaAs/AlGaAs quantum dots with inhomogeneous linewidths of 11 meV. The second part is devoted to the abiltiy to laterally align self-assembled quantum dots in single and multiple layers.
We use quantum dot (QD) growth and atomically precise in-situ etching to fabricate novel quantum dot structures. The key procedure to create such structures comprises an in-situ etching process with AsBr3 of GaAs capped InAs quantum dots. The AsBr3 preferably etches away those regions of the GaAs, which covers the buried InAs QDs,thus causing the formation of nanometer sized holes. If these holes are overgrown with InAs again, laterally closely spaced groups of two, three, four, five, and six QDs (lateral quantum dot molecules) form around the nanoholes.
In another approach, we overgrow the nanoholes with AlGaAs/GaAs/AlGaAs. The hole morphology is preserved by the first AlGaAs growth step, whereas the GaAs preferably diffuses into the AlGaAs holes, thus forming inverted unstrained GaAs/AlGaAs quantum dots that emit in the visible wavelength regime.The GaAs/AlGaAs quantum dots show excellent optcal properties including well-resolved ground and excited states with a linewidth of only 11 meV at low temperature.
Furthermore we grow In(Ga)As quantum dots on GaAs (001) substrates patterned with square arrays of nanometer sizes holes. We choose the growth conditions in such a way that a prefect lateral order of InGaAs QDs occurs. We study the effect of lateral alignment as a function of stacked layers and array periodicity. In perfectly ordered arrays we observe the formation of quantum dots on second order strain energy minima.