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III-V Molecular-Beam Epitaxy

The III-V MBE located in L-NESS is an EPI GEN II system previously owned by Pirelli Company. It is equipped with an As valved cell for the fine control of the As flux during the experiments and other 5 material sources: Ga, In, Al, Be and Si. Our system is constituted by 3 chambers: growth chamber, buffer chamber and introduction chamber. With this machine we are currently investigating the growth of advanced nanostructures.

Droplet Epitaxy (DE) is a method for the fabrication of self-assembled high quality nanostructures, proposed and developed by Koguchi and co-workers since 1991. As an alternative to the more conventional Stranski-Krastanow growth mode, DE has been successfully applied to the fabrication of III-V semiconductor nanostructures. It exploits the self-organization of group III elements such as Ga, In and Al which, deposited on the substrate at temperatures higher than their melting points, automatically form nanometre-sized droplets. At this point, a group V element flux is supplied for the crystallization of every droplet into a III-V nanostructure. The main advantages of this approach are: the fabrication of 3D quantum nanostructures on both lattice-mismatched (InAs/GaAs) and lattice-matched systems (GaAs/AlGaAs); the control of the presence or absence of the wetting layer at the interface between the two materials, and the fine shape engineering of the nanocrystal. Indeed, by changing the growth conditions different shapes have been obtained during the last 20 years: quantum dots, quantum rings, concentric multiple quantum rings, quantum dot molecules, and so on.