Droplet Epitaxy Growth of Nanostructures on Patterned and (111) Substrates

Droplet epitaxy (DE) is a flexible growth technique based on molecular beam epitaxy which allows for the fabrication of density, size and shape controlled nanostructures. Being based on control of crystallization kinetic of nanoscale reservoirs of group III metal by group V irradiation, it allows for the growth 3D nanostructures on a large variety of substrates, including Si(111) and GaAs(111)A. On patterned Si substrates, we show that it is possible to obtain the fabrication of ordered and controlled array of embedded Ga nanoparticles (NPs) in a semiconductor matrix. We demonstrate that Ga droplets can be successfully trapped at the bottom of the pits due to the combined effects of capillarity condensation and nucleation kinetics, as also shown by kinetic Monte Carlo simulations [1]. DE allows for the fabrication of highly symmetric GaAs QDs on GaAs(111)A, which can be used as entangled photon emitters. We developed a procedure to control surface flatness of AlGaAs on a GaAs(111)A substrate and to control the shape of GaAs QDs to obtain highly symmetric QDs. In addition it is possible, by DE, to create a self-assembled nanopatterning of the Si(111) substrate for the subsequent growth of density and size controlled GaAs nanowires (NWs). In our method, GaAs islands are initially formed on Si(111) by DE and, subsequently, GaAs NWs are selectively grown on their top facet, which acts as a nucleation site on Si substrates with or without an oxide layer [2,3]. By DE, we can successfully tailor the number density and diameter of the template of initial GaAs islands and successively transfer the same degree of control to the final GaAs NWs. [1]M. Bollani, S. Bietti, C. Frigeri, D. Chrastina, K. Reyes, P. Smereka, J.M. Millunchick, G.M. Vanacore, M. Burghammer, a Tagliaferri, and S. Sanguinetti, Nanotechnology 25, 205301 (2014). [2]C. Somaschini, S. Bietti, A. Trampert, U. Jahn, C. Hauswald, H. Riechert, S. Sanguinetti, and L. Geelhaar, Nano Letters 13, 3607 (2013). [3]S Bietti , C Somaschini, C Frigeri, A Fedorov, L Esposito, L Geelhaar and S Sanguinetti, Journal of Physics D (accepted for publication)