Search

The bottom-up fabrication of regular nanowire (NW) arrays on a masked substrate is technologically relevant, but the growth dynamic is rather complex due to the superposition of severe shadowing effects that vary with array pitch, NW diameter, NW height, and growth duration. By inserting GaAsP marker layers at a regular time interval during the growth of a self-catalyzed GaP NW array, we are able to retrieve precisely the time evolution of the diameter and height of a single NW. We then propose a simple numerical scheme which fully computes shadowing effects at play in infinite arrays of NWs. By confronting the simulated and experimental results, we infer that re-emission of Ga from the mask is necessary to sustain the NW growth while Ga migration on the mask must be negligible. When compared to random cosine or random uniform re-emission from the mask, the simple case of specular reflection on the mask gives the most accurate account of the Ga balance during the growth. [ABSTRACT FROM AUTHOR]

In this paper, we report for the first time the growth of GaAsSb/InAs core-shell nanowires (NWs) on Si (111) substrates by molecular-beam epitaxy. We first grow high-quality GaAsSb NWs as cores using self-catalyzed technique, then cover these cores by InAs shells. For the growth of InAs shells, we find that the optimum beam equivalent pressure ratio of As/In is only ∼5.2, but the growth temperature window is larger (from 460 to 540 °C). Also, the thickness of InAs shells increases almost linearly with extending the growth time. Because of the high-quality of GaAsSb cores, the InAs shells are continuous, smooth, and without stacking faults or twins adopted from the cores. Temperature dependent I - V curves measured from the field-effect transistor devices based on these GaAsSb/InAs core-shell NWs indicate that GaAsSb/InAs NWs without any intentional doping are electrically conductive. The growth of GaAsSb/InAs core-shell NWs opens up new possibilities for both fundamental studies and future device applications based on such natural p-n junctions. [ABSTRACT FROM AUTHOR]

Here we report on the Ga self-catalyzed growth of near full-composition-range energy-gap-tunable GaAs1-xSbx nanowires by molecular-beam epitaxy. GaAs1-xSbx nanowires with different Sb content are systematically grown by tuning the Sb and As fluxes, and the As background. We find that GaAs1-xSbx nanowires with low Sb content can be grown directly on Si(111) substrates (0 ≤ x ≤ 0.60) and GaAs nanowire stems (0 ≤ x ≤ 0.50) by tuning the Sb and As fluxes. To obtain GaAs1-xSbx nanowires with x ranging from 0.60 to 0.93, we grow the GaAs1-xSbx nanowires on GaAs nanowire stems by tuning the As background. Photoluminescence measurements confirm that the emission wavelength of the GaAs1-xSbx nanowires is tunable from 844 nm (GaAs) to 1760 nm (GaAs0.07Sb0.93). High-resolution transmission electron microscopy images show that the grown GaAs1-xSbx nanowires have pure zinc-blende crystal structure. Room-temperature Raman spectra reveal a redshift of the optical phonons in the GaAs1-xSbx nanowires with x increasing from 0 to 0.93. Field-effect transistors based on individual GaAs1-xSbx nanowires are fabricated, and rectifying behavior is observed in devices with low Sb content, which disappears in devices with high Sb content. The successful growth of high-quality GaAs1-xSbx nanowires with near full-range bandgap tuning may speed up the development of high-performance nanowire devices based on such ternaries. [ABSTRACT FROM AUTHOR]

We introduce droplet-confined alternate pulsed epitaxy for the self-catalyzed growth of GaAs nanowires on Si(111) substrates in the temperature range from 550 °C down to 450 °C. This unconventional growth mode is a modification of the migration-enhanced epitaxy, where alternating pulses of Ga and As4 are employed instead of a continuous supply. The enhancement of the diffusion length of Ga adatoms on the {11̅0} nanowire sidewalls allows for their targeted delivery to the Ga droplets at the top of the nanowires and, thus, for a highly directional growth along the nanowire axis even at temperatures as low as 450 °C. We demonstrate that the axial growth can be simply and abruptly interrupted at any time without the formation of any defects, whereas the growth rate can be controlled with high accuracy down to the monolayer scale, being limited only by the stochastic nature of nucleation. Taking advantage of these unique possibilities, we were able to probe and describe quantitatively the population dynamics of As inside the Ga droplets in specially designed experiments. After all, our growth method combines all necessary elements for precise growth control, in-depth investigation of the growth mechanisms and compatibility with fully processed Si-CMOS substrates. [ABSTRACT FROM AUTHOR]

The growth of III-III-V axial heterostructures in nanowires via the vapor-liquid-solid method is deemed to be unfavorable because of the high solubility of group III elements in the catalyst droplet. In this work, we study the formation by molecular beam epitaxy of self-catalyzed GaAs nanowires with AlxGa1-xAs insertions. The composition profiles are extracted and analyzed with monolayer resolution using high-angle annular dark-field scanning transmission electron microscopy. We test successfully several growth procedures to sharpen the heterointerfaces. For a given nanowire geometry, prefilling the droplet with Al atoms is shown to be the most efficient way to reduce the width of the GaAs/AlxGa1-xAs interface. Using the thermodynamic data available in the literature, we develop numerical and analytical models of the composition profiles, showing very good agreement with experiments. These models suggest that atomically sharp interfaces are attainable for catalyst droplets of small volumes. [ABSTRACT FROM AUTHOR]

The nucleation and evolution of InN nanowires in a self-catalyzed growth process have been investigated to probe the microscopic growth mechanism of the self-catalysis and a model is proposed for high pressure growth window at ~760 Torr. In the initial stage of the growth, amorphous InN x microparticles of cone shape in liquid phase form with assistance of an InN x wetting layer on the substrate. InN crystallites form inside the cone and serve as the seeds for one-dimensional growth along the favorable [0001] orientation, resulting in single-crystalline InN nanowire bundles protruding out from the cones. An amorphous InN x sheath around the faucet tip serves as the interface between growing InN nanowires and the incoming vapors of indium and nitrogen and supports continuous growth of InN nanowires in a similar way to the oxide sheath in the oxide-assisted growth of other semiconductor nanowires. Other InN 1D nanostructures, such as belts and tubes, can be obtained by varying the InN crystallites nucleation and initiation process. [ABSTRACT FROM AUTHOR]