Publications by authors named "Biermanns A"

In III-V nanowires the energetic barriers for nucleation in the zinc blende or wurtzite arrangement are typically of a similar order of magnitude. As a result, both arrangements can occur in a single wire. Here, we investigate the evolution of this polytypism in self-catalyzed GaAs nanowires on Si(111) grown by molecular beam epitaxy with time-resolved in situ x-ray diffraction.

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We present the results of the study of the correlation between the electrical and structural properties of individual GaAs nanowires measured in their as-grown geometry. The resistance and the effective charge carrier mobility were extracted for several nanowires, and subsequently, the same nano-objects were investigated using X-ray nanodiffraction. This revealed a number of perfectly stacked zincblende and twinned zincblende units separated by axial interfaces.

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Article Synopsis
  • InAs nanowires grown without catalysts along the [111] direction face difficulties controlling their crystal phase due to polytypism between wurtzite and zincblende structures.
  • The study uses time-resolved X-ray scattering to examine how growth conditions affect the nanowires' structure, noting that the presence of liquid indium supports the formation of predominantly wurtzite-phase nanowires.
  • High arsenic-rich conditions limit liquid indium formation, leading to structural defects in the wurtzite phase, indicating that consistent indium presence during growth is necessary for achieving high phase purity in these nanowires.
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InAs segments were grown on top of GaAs islands, initially created by droplet epitaxy on silicon substrate. We systematically explored the growth-parameter space for the deposition of InAs, identifying the conditions for the selective growth on GaAs and for purely axial growth. The axial InAs segments were formed with their sidewalls rotated by 30° compared to the GaAs base islands underneath.

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We report the impact of deposition parameters on the structure of HfO(2) covering InAs nanowires (NWs) being potential candidates for future field-effect transistors (FETs). Molecular beam epitaxial-grown Au-free InAs NWs were covered with HfO(2) deposited by atomic-layer deposition. The impact of the film thickness as well as the deposition temperature on the occurrence and amount of crystalline HfO(2) regions was investigated by high-resolution transmission electron microscopy (TEM) and x-ray diffraction.

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Vertically aligned InAs nanowires (NWs) doped with Si were grown self-assisted by molecular beam epitaxy on GaAs[111]B substrates covered with a thin SiO layer. Using out-of-plane X-ray diffraction, the influence of Si supply on the growth process and nanostructure formation was studied. It was found that the number of parasitic crystallites grown between the NWs increases with increasing Si flux.

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Grazing-incidence X-ray diffraction measurements on single GaAs nanowires (NWs) grown on a (111)-oriented GaAs substrate by molecular beam epitaxy are reported. The positions of the NWs are intentionally determined by a direct implantation of Au with focused ion beams. This controlled arrangement in combination with a nanofocused X-ray beam allows the in-plane lattice parameter of single NWs to be probed, which is not possible for randomly grown NWs.

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We study the mechanism of lattice parameter accommodation and the structure of GaAs nanowires (NWs) grown on Si(111) substrates using the Ga-assisted growth mode in molecular beam epitaxy. These nanowires grow preferentially in the zincblende structure, but contain inclusions of wurtzite at the base. By means of grazing incidence x-ray diffraction and high-resolution transmission electron microscopy of the NW-substrate interface, we show that the lattice mismatch between the NW and the substrate is released immediately after the beginning of NW growth through the inclusion of misfit dislocations, and no pseudomorphic growth is obtained for NW diameters down to 10 nm.

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Using out-of-plane and in-plane X-ray diffraction techniques, we have investigated the structure at the interface between GaAs nanowires [NWs] grown by Au-assisted molecular beam epitaxy and the underlying Si(111) substrate. Comparing the diffraction pattern measured at samples grown for 5, 60, and 1,800 s, we find a plastic strain release of about 75% close to the NW-to-substrate interface even at the initial state of growth, probably caused by the formation of a dislocation network at the Si-to-GaAs interface. In detail, we deduce that during the initial stage, zinc-blende structure GaAs islands grow with a gradually increasing lattice parameter over a transition region of several 10 nm in the growth direction.

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Article Synopsis
  • Researchers used scanning X-ray diffraction microscopy to study GaAs nanorods, which were grown without seeds through circular openings in a SiN(x) mask.
  • The X-ray technique helped determine the strain state of individual nanorods and revealed detailed morphological characteristics.
  • There were notable differences in shape, size, and strain state between rods located at the center and those at the edge of the periodic array.
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In this review we cover and describe the application of grazing incidence x-ray scattering techniques to study and characterize nanopattern formation on semiconductor surfaces by ion beam erosion under various conditions. It is demonstrated that x-rays under grazing incidence are especially well suited to characterize (sub)surface structures on the nanoscale with high spatial and statistical accuracy. The corresponding theory and data evaluation is described in the distorted wave Born approximation.

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