We present a novel approach for the growth of GaAs nanowires (NWs) with controllable number density and diameter, which consists of the combination between droplet epitaxy (DE) and self-assisted NW growth. 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 nucleation site. By DE we can successfully tailor number density and diameter of the template of initial GaAs islands and the same degree of control is transferred to the final GaAs NWs. We show how, by a suitable choice of V/III flux ratio, a single NW can be accommodated on top of each GaAs base island. By transmission electron microscopy, as well as cathodo- and photo-luminescence spectroscopy we confirmed the high structural and optical quality of GaAs NWs grown by our method. We believe that this combined approach can be more generally applied to the fabrication of different homo- or hetero-epitaxial NWs, nucleated on the top of predefined islands obtained by DE.
"Quantum dots have then been demonstrated around the nanoholes . Also, metallic droplets have been successfully utilized in the fabrications of various quantum- and nanostructures such as quantum rings [6-9], quantum dots [10-12], and nanowires (NWs)  through ‘droplet epitaxy’ following the successful fabrication of homo-epitaxial GaAs nanocrystals on a GaAs substrate . In addition, Au droplets have been adapted as catalysts for the fabrication of diverse NWs via various epitaxial approaches and have attracted extensive interest due to their unique properties such as surface plasmonic resonance, biosensing, quantum size effect, and biology [15-18]. "
[Show abstract][Hide abstract] ABSTRACT: In this paper, we report the effect of Au thickness on the self-assembled Au droplets on GaAs (111)A and (100). The evolution of Au droplets on GaAs (111)A and (100) with the increased Au thickness progress in the Volmer-Weber growth mode results in distinctive 3-D islands. Under an identical growth condition, depending on the thickness of Au deposition, the self-assembled Au droplets show different size and density distributions, while the average height is increased by approximately 420% and the diameter is increased by approximately 830%, indicating a preferential lateral expansion. Au droplets show an opposite evolution trend: the increased size along with the decreased density as a function of the Au thickness. Also, the density shifts on the orders of over two magnitude between 4.23 × 10(10) and 1.16 × 10(8) cm(-2) over the thickness range tested. At relatively thinner thicknesses below 4 nm, the self-assembled Au droplets sensitively respond to the thickness variation, evidenced by the sharper slopes of dimensions and density plots. The results are systematically analyzed and discussed in terms of atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), cross-sectional surface line profiles, and Fourier filter transform (FFT) power spectra.
Nanoscale Research Letters 08/2014; 9(1):407. DOI:10.1186/1556-276X-9-407 · 2.78 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Semiconductor nanowires composed of III-V materials have enormous potential to add new functionality to electronics and optical applications. However, integration of these promising structures into applications is severely limited by the current near-universal reliance on gold nanoparticles as seeds for nanowire fabrication. Although highly controlled fabrication is achieved, this metal is entirely incompatible with the Si-based electronics industry. In this Feature we review the progress towards developing gold-free bottom-up synthesis techniques for III-V semiconductor nanowires. Three main categories of nanowire synthesis are discussed: selective-area epitaxy, self-seeding and foreign metal seeding, with main focus on the metal-seeded techniques. For comparison, we also review the development of foreign metal seeded synthesis of silicon and germanium nanowires. Finally, directions for future development and anticipated important trends are discussed. We anticipate significant development in the use of foreign metal seeding in particular. In addition, we speculate that multiple different techniques must be developed in order to replace gold and to provide a variety of nanowire structures and properties suited to a diverse range of applications.
[Show abstract][Hide abstract] ABSTRACT: Droplet epitaxy was proposed to fabricate quantum dots in the early 1990s. Even though many research efforts have been devoted to droplet epitaxy since then, it is only until recently that droplet epitaxy has received worldwide attention. Compared with the well-known Stranski–Krastanow (S–K) growth mode, droplet epitaxy consists of the formation and crystallization of droplets, which enables fabrication of three-dimensional nanostructures in both lattice-mismatched and lattice-matched material systems. The flexibility of the droplet epitaxy growth method has brought to light the great potential of droplet epitaxy in optoelectronic applications. However, most works on droplet epitaxy focus on fabrication, optical properties and understanding the growth mechanisms of various nanostructures. In terms of device applications, droplet epitaxy has fallen behind conventional nanostructure self-assembly using the S–K mode. One of the major reasons is the relative low optical quality of the nanostructures obtained at low growth temperatures, and so careful attention has to be given to growth conditions to create device-grade materials. Through the developments in droplet epitaxy in the last decade, the issues can be overcome and more importantly a rich spectrum of nanostructures can be obtained, which enables the development of novel devices. This review focuses on recent developments in droplet epitaxy and presents the challenge and promise of its application in the optoelectronic field.
Journal of Physics D Applied Physics 04/2014; 47(17):173001. DOI:10.1088/0022-3727/47/17/173001 · 2.72 Impact Factor
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