Nanostructure and strain properties of core-shell GaAs/AlGaAs nanowires

Kehagias, Th.; Florini, Nikoletta; Kioseoglou, Joseph; Pavloudis, Theodore; Komninou, Ph.; Walther, T.; Moratis, K.; Hatzopoulos, Z.; Pelekanos, N.T.

doi:10.1088/0268-1242/30/11/114012

Cited by 9 publications

(11 citation statements)

References 44 publications

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“…Typical FE-SEM images of core-shell GaAs/InGaAs NWs are shown in Fig. 2 , where we observe that over 60 % of the NWs are grown along the [111] direction perpendicular to the substrate, while the rest grow along inclined {111} crystallographic orientations, consistent with results reported previously for similar growth conditions [ 15 , 16 ]. By closer inspection of the SEM images, most of the core-shell NWs display characteristic hexagonal morphology with {110} lateral facets (cf .…”

Section: Resultssupporting

confidence: 87%

Strained GaAs/InGaAs Core-Shell Nanowires for Photovoltaic Applications

et al. 2016

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We report on the successful growth of strained core-shell GaAs/InGaAs nanowires on Si (111) substrates by molecular beam epitaxy. The as-grown nanowires have a density in the order of 108 cm−2, length between 3 and 3.5 μm, and diameter between 60 and 160 nm, depending on the shell growth duration. By applying a range of characterization techniques, we conclude that the In incorporation in the nanowires is on average significantly smaller than what is nominally expected based on two-dimensional growth calibrations and exhibits a gradient along the nanowire axis. On the other hand, the observation of sharp dot-like emission features in the micro-photoluminescence spectra of single nanowires in the 900–1000-nm spectral range highlights the co-existence of In-rich enclosures with In content locally exceeding 30 %.

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Section: Resultssupporting

confidence: 87%

Strained GaAs/InGaAs Core-Shell Nanowires for Photovoltaic Applications

et al. 2016

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“…Another interesting finding is that relaxation at the outer shell sidewalls increases ( ϵ ρφ decreases) with increasing shell radius. This is in line with MD simulations, as relaxation spreads from the vertices toward the perimeter of thicker shell NWs . Moreover, the ϵ ρφ variation along the circumradius R (<112> directions) of the core‐shell hexagons as a function of the shell's Al% content, for S/NW ratio 0.5, is given in Figure (c).…”

Section: Resultssupporting

confidence: 84%

“…In our case, GaAs/Al x Ga (1− x ) As core‐shell NWs were grown on Si(111) by MBE. Cross‐sectional TEM micrographs showed that NWs consist of two usually concentric hexagons, over 1 μm long along the <111> growth direction and 80–100 nm thick, bounded by {110} crystal facets [Figure (a) and (b)] . Based on these observations we constructed the 3‐D shape model to be used in FE calculations, as shown in Figure (c).…”

Section: Resultsmentioning

confidence: 99%

“…Based on these observations we constructed the 3‐D shape model to be used in FE calculations, as shown in Figure (c). In previous research, we have employed scanning TEM and energy dispersive X‐ray (EDX) spectroscopy to determine the chemical composition of the Al x Ga (1− x ) As shell, which resulted in an average Al content of 35%. Moreover, cross‐sectional HRTEM observations have shown full elastic registration of the core and shell lattices.…”

Section: Resultsmentioning

confidence: 99%

“…Due to the very small lattice strain between the two structures

ϵ_{i j}^{m} = 0.0005

, which is far beyond the accuracy limit of the GPA method, comparison of FEM simulations with experimental data is restricted. In turn, we have performed MD atomistic calculations, which exhibited the same trend of the displacement field, although there is no exact identity between absolute values in the two methods. It should be noted that due to the six‐fold rotational symmetry of the hexagonal structure, in FEM calculations, we have used the cylindrical coordinate system, that is ρ (radial coordinate), φ (azimuth), and z (height), instead of the cartesian one.…”

Section: Resultsmentioning

confidence: 99%

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3‐D Strain Fields in Low‐Dimensional III–V Semiconductors: A Combined Finite Elements and HRTEM Approach

Florini

Dimitrakopulos

Kioseoglou

et al. 2017

Physica Status Solidi (a)

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A versatile route toward the study of strain fields of low-dimensional III-V semiconductor nanostructures is presented, by combining quantitative highresolution transmission electron microscopy (HRTEM) observations with the finite elements method (FEM). FEM facilitates a fast and straightforward threedimensional (3-D) analysis of elastic properties for various growth orientations and compositional profiles down to the nanoscale. FEM calculations are employed to simulate elastic stress-strain fields of III-V cubic heterostructures comprising InAs surface and buried quantum dots (QDs) grown on GaAs(211)B substrates, and (111)-oriented GaAs/Al x Ga (1Àx) As core-shell nanowires (NWs) on Si. The results are compared with experimental strain maps obtained from HRTEM images by geometric phase analysis (GPA), as well as with molecular dynamics (MD) atomistic simulations. In the former, the compositional grading along the growth axis was considered, and, in the latter, elastic fields were calculated as a function of the shell's chemical composition and shell-to-NW diameter ratios. The agreement between FEM calculations with experimental and theoretical results implies that the plane-stress state can adequately describe the encountered elastic fields. Most importantly, through the determined stress-strain state, strain fields can be translated into 3-D maps of chemical composition in the nanostructures, extracted from 2-D experimental projections.

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Efficient methodology to correlate structural with optical properties of GaAs nanowires based on scanning electron microscopy

et al. 2017

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Twin boundaries and boundaries between zincblende (ZB) and wurtzite (WZ) segments of GaAs-related nanowires (NWs) form intrinsic heterointerfaces with essential consequences for the application of such nanomaterials in optoelectronic devices. We show that for GaAs and GaAs/(Al, Ga)As core/shell NWs, crystal twinning along the NW axis can be imaged with a spatial resolution of 10 nm using secondary electrons in a scanning electron microscope (SEM). Changes of the crystal structure from the ZB to the WZ phase have been investigated by electron backscatter diffraction. In addition to these methods, we employ spectrally and spatially resolved cathodoluminescence measurements in the same SEM to study the correlation between the structural and optical properties in single NWs. Two GaAs/AlAs/GaAs core/shell/shell NWs differing significantly in the crystal structure along their axis have been investigated combining these three techniques in order to demonstrate the strength of the employed methodology. Our experiments show that based on commonly available SEM methods, an overview of the structural properties along an entire NW and their impact on the spectral and spatial luminescence distribution can be efficiently obtained providing a quick feedback for the optimization of growth conditions.

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Nanostructure and strain properties of core-shell GaAs/AlGaAs nanowires

Cited by 9 publications

References 44 publications

Strained GaAs/InGaAs Core-Shell Nanowires for Photovoltaic Applications

Strained GaAs/InGaAs Core-Shell Nanowires for Photovoltaic Applications

3‐D Strain Fields in Low‐Dimensional III–V Semiconductors: A Combined Finite Elements and HRTEM Approach

Efficient methodology to correlate structural with optical properties of GaAs nanowires based on scanning electron microscopy

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