We report on the possibility of interrupting and resuming at will the self-assisted growth of GaAs nanowires by molecular beam epitaxy. The Ga nanoparticles assisting nanowire growth on Si-treated GaAs(111)B wafers were consumed by exposure to an As flux. Condensation of a new Ga nanoparticle on the top (111)B facets of the existing GaAs nanowires was achieved by either resuming GaAs growth under Ga-rich conditions or exposing the nanowires to a Ga flux. The new Ga nanoparticles were found to assist the growth of new GaAs nanowires in epitaxial relation with the previous nanowires. The growth and regrowth processes of the nanowires are jointly described by an analytical model that can reproduce the observed experimental time dependence of nanowire length and diameter

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Deuterium (hydrogen) incorporation in dilute nitrides (e.g., GaAsN and GaPN) modifies dramatically the crystal's electronic and structural properties and represents a prominent example of defect engineering in semiconductors. However, the microscopic origin of D-related effects is still an experimentally unresolved issue. In this paper, we used nuclear reaction analyses and/or channeling, high resolution x-ray diffraction, photoluminescence, and x-ray absorption fine structure measurements to determine how the stoichiometric [D]/[N] ratio and the local structure of the N-D complexes parallel the evolution of the GaAsN electronic and strain properties upon irradiation and controlled removal of D. The experimental results provide the following picture: (i) Upon deuteration, nitrogen-deuterium complexes form with [D]/[N]=3, leading to a neutralization of the N electronic effects in GaAs and to a strain reversal (from tensile to compressive) of the N-containing layer. (ii) A moderate annealing at 250 degrees C gives [D]/[N]=2 and removes the compressive strain, therefore the lattice parameter approaches that of the N-free alloy, whereas the N-induced electronic properties are still passivated. (iii) Finally, annealings at higher temperature (330 degrees C) dissolve the deuterium-nitrogen complexes, and consequently the electronic properties and the tensile strain of the as-grown GaAsN lattice are recovered. Therefore, we conclude that the complex responsible for N passivation contains two deuterium atoms per nitrogen atom, while strain reversal in deuterated GaAsN is due to a complex with a third, less tightly bound deuterium atom