Epitaxy of high aspect ratio and wetting-layer-free InAs quantum dots on (Al)GaAs

Here we demonstrate the possibility of the fabrication of high/aspect ratio self-assembled dots that nucleate directly on (Al)GaAs spacers away from their wetting layers. We have carefully monitored the strain anisotropies, their evolution and onsets of 2D-3D transitions by in-situ RHEED and have found that should the growth of InAs be interrupted prior to the 2D-3D transition and a carefully engineered spacer layer of (Al)GaAs be introduced, the subsequent growth of InAs results into the spontaneous formation of high aspect ratio dots without the formation of cumbersome wetting layer. Post growth TEM and AFM observations confirm these finding and reveal that these dots, unlike their conventional counterparts, are highly symmetrical along the <;110>; directions and exhibit high aspect ratio with low index facets. TEM analyses also confirm that these properties are preserved after the subsequent capping of dots by GaAs or AlGaAs..