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

The local Zn/Se relative concentration at the interface in ZnSe-GaAs(001) heterostructures synthesized by molecular beam epitaxy was found to be controlled by the Zn/Se Aux ratio employed during the early growth stage of ZnSe on GaAs. Correspondingly, the valence band discontinuity varies from 1.20 eV (Zn-rich interface) to 0.58 eV (Se-rich interface). Comparison with the results of firstprinciples calculations suggests that the observed trend in band offsets is related to the establishment of neutral interfaces with different atomic configurations.

The electron effective mass, m e , has been determined by magnetophotoluminescence in as-grown and hydrogenated GaAs 1−x N x samples for a wide range of nitrogen concentrations ͑from x Ͻ 0.01% to x = 1.78%͒. A modified k·p model, which takes into account hybridization effects between N cluster states and the conduction band edge, reproduces quantitatively the experimental m e values up to x ഛ 0.6%. Experimental and theoretical evidence is provided for the N complexes responsible for the nonmonotonic and initially puzzling compositional dependence of the electron mass.

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GaAs nanowires have been grown on SiO2 and GaAs by molecular beam epitaxy using manganese as growth catalyst. Transmission electron microscopy shows that the wires have a wurtzite-type lattice and that alpha-Mn particles are found at the free end of the wires. X-ray absorption fine structure measurements reveal the presence of a significant fraction of Mn-As bonds, suggesting Mn diffusion and incorporation during wire growth. Transport measurements indicate that the wires are p-type, as expected from doping of GaAs with Mn.

Single-crystal ZnSe nanowires are grown on a prepatterned gold catalyst by molecular-beam epitaxy. Optimum selectivity and maximum nanowire densities are obtained for growth temperatures in the range 400-450 °C, but gold-assisted growth is demonstrated for temperatures as low as 300 °C. This suggests a diffusion process on/through the catalyst particle in the solid state, in contrast to the commonly assumed liquid phase growth models. Straight wires, as thin as 10 nm, nucleate together with thicker and saw-like structures. A gold particle is always found at the tip in both cases