We present the fabrication of GaAs/AlGaAs Multiple (from three to five) concentric nanoring structures by an innovative growth method based on droplet epitaxy and characterized by short time As supply to the Ga droplets at different substrate temperatures. The formation mechanism has been interpreted on the basis of a detailed ex situ and in situ characterization of nanostructure morphology and surface reconstruction. We introduce design criteria which will allow to obtain concentric quantum ring structures of the desired complexity.

The fabrication, by droplet epitaxy, of a class of quantum nanostructures characterized by a regular, nanometres high, flat disks with a diameter of hundreds of nanometres and a hole at the centre encircled by a ring a few nanometres high, is presented here. A detailed analysis of the growth kinetics performed via in situ and ex situ probes allows us to propose a working model for the formation of these structures.

We present a unified model of compound semiconductor growth based on kinetic Monte Carlo simulations in tandem with experimental results that can describe and predict the mechanisms for the formation of various types of nanostructures observed during droplet epitaxy. The crucial features of the model include the explicit and independent representation of atoms with different species and the ability to treat solid and liquid phases independently. Using this model, we examine nanostructural evolution in droplet epitaxy. The model faithfully captures several of the experimentally observed structures, including compact islands and nanorings. Moreover, simulations show the presence of Ga/GaAs core-shell structures that we validate experimentally. A fully analytical model of droplet epitaxy that explains the relationship between growth conditions and the resulting nanostructures is presented, yielding key insight into the mechanisms of droplet epitaxy.

The fabrication, by pure self-assembly, of GaAs/AlGaAs dot-ring quantum nanostructures is presented. The growth is performed via droplet epitaxy, which allows for the fine control, through As flux and substrate temperature, of the crystallization kinetics of nanometer scale metallic Ga reservoirs deposited on the surface. Such a procedure permits the combination of quantum dots and quantum rings into a single, multi-functional, complex quantum nanostructure.

Low temperature photoluminescence spectroscopy is used to analyze the effects of the postgrowth thermal annealing on the electronic structure ad carrier dynamics of GaAs∕AlGaAs quantum dot and quantum ring structures grown by droplet epitaxy. All the samples show a large increase in the photoluminescence efficiencies after the thermal treatment due to sizeable reduction in the material defectivity. Modifications of the photoluminescence band, which depend on thermal annealing temperature, are found and quantitatively interpreted by means of a simple model based on the Al–Ga interdiffusion.