Microscopic nature of crystal phase quantum dots in ultrathin GaAs nanowires by nanoscale luminescence characterization

Loitsch, Bernhard; Müller, Marcus; Winnerl, Julia; Veit, Peter; Rudolph, Daniel; Abstreiter, G.; Finley, Jonathan J.; Bertram, F.; Christen, J.; Koblmüller, Gregor

doi:10.1088/1367-2630/18/6/063009

Cited by 13 publications

(6 citation statements)

References 49 publications

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“…We introduce these different possible recombination channels in figures 2(a) and (b). Our assignments are fully consistent with previous works, in particular references [54,55]. They can be identified in the measured PL spectra recorded near the center of NW1 and NW2 shown in figures 2(c) and (d), respectively.…”

Section: Structural and Optical Characterizationsupporting

confidence: 92%

Sub-nanosecond acousto-electric carrier redistribution dynamics and transport in polytypic GaAs nanowires

et al. 2021

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The authors report on a combined structural, optical and acousto-electric study of polytypic GaAs nanowires. Two types of nanowires with different zincblende and wurtzite crystal phase mixing are identified by transmission electron microscopy and photoluminescence spectroscopy. The nanowires exhibit characteristic recombination channels which are assigned to different types of spatially direct recombination (electron and hole within the same crystal phase segment) and spatially indirect recombination (electron and holes localized in different segments). Contact-free acousto-optoelectric spectroscopy is employed to resolve spatiotemporal charge carrier dynamics between different recombination channels induced by a piezoelectric surface acoustic wave. The observed suppression of the emission and its dynamic temporal modulation shows unambiguous fingerprints of the local bandedge variations induced by the crystal phase mixing. A nanowire, which exhibits a variation from a near-pristine zinc blende crystal structure to a highly mixed crystal phase, shows a clear dependence on the propagation direction of the acoustic wave. In contrast, no pronounced directionality is found for a nanowire with an extended near-pristine zincblende segment. The experimental findings are corroborated by solving the drift and diffusion equations of electrons and holes induced by the surface acoustic wave. The key characteristics observed in our experimental data are well reproduced in the numerical simulations by assuming two general bandedge modulations and realistic parameters for the bandedge discontinuities and transport mobilities of electrons and holes. This evidences that even all relevant physical processes are accounted for in the model.

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Section: Structural and Optical Characterizationsupporting

confidence: 92%

Sub-nanosecond acousto-electric carrier redistribution dynamics and transport in polytypic GaAs nanowires

et al. 2021

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“…Most studies in this direction have been carried out on the polytypic III-V compound semiconductor GaAs. Despite considerable efforts, the results from the vast body of literature on this subject are entirely inconsistent [9,[14][15][16][17][18][19][20][21][22][23][24]. For example, the reported values for the bandgap of WZ GaAs scatter from 20 meV below [14] to 100 meV above [17] the bandgap of ZB GaAs.…”

Section: Introductionmentioning

confidence: 99%

Electronic properties of wurtzite GaAs: A correlated structural, optical, and theoretical analysis of the same polytypic GaAs nanowire

et al. 2018

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III-V compound semiconductor nanowires are generally characterized by the coexistence of zincblende and wurtzite structures. So far, this polytypism has impeded the determination of the electronic properties of the metastable wurtzite phase of GaAs, which thus remain highly controversial. In an effort to obtain new insights into this topic, we cross-correlate nanoscale spectral imaging by near-field scanning optical microscopy with a transmission electron microscopy analysis of the very same polytypic GaAs nanowire dispersed onto a Si wafer. Thus, spatially resolved photoluminescence spectra could be unambiguously assigned to nanowire segments whose structure is known with lattice-resolved accuracy. An emission energy of 1.528 eV was observed from extended zincblende segments, revealing that the dispersed nanowire was under uniaxial strain presumably due to interaction with its supporting substrate. These crucial information and the emission energy obtained for extended pure wurtzite segments were used to perform envelope function calculations of zincblende quantum disks in a wurtzite matrix as well as the inverse structure. In these calculations, we varied the fundamental bandgap, the electron mass, and the band offset between zincblende and wurtzite GaAs. From this multi-parameter comparison with the experimental data, we deduced that the bandgap between the Γ 8 conduction and A valence band ranges from 1.532 to 1.539 eV in strain-free wurtzite GaAs, and estimated values of 1.507 to 1.514 eV for the Γ 7-A bandgap.

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“…So far, a plethora of different high-resolution imaging techniques have been explored to map the structural, compositional, and electronic nature of axial and radial quantum heterostructures in single NWs. These include, e.g., scanning transmission electron microscopy (STEM), − atom probe tomography (APT), , scanning tunnelling microscopy (STM), , electron holography, , STEM-based cathodoluminescence (CL), etc. While these techniques provide extremely high, i.e., subnanometer to atomic-level resolution, they are highly invasive and time-consuming with extensive sample preparation and damage during acquisition, and often require well-defined specimen surfaces.…”

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confidence: 99%

He-Ion Microscopy as a High-Resolution Probe for Complex Quantum Heterostructures in Core–Shell Nanowires

et al. 2018

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Core-shell semiconductor nanowires (NW) with internal quantum heterostructures are amongst the most complex nanostructured materials to be explored for assessing the ultimate capabilities of diverse ultrahigh-resolution imaging techniques. To probe the structure and composition of these materials in their native environment with minimal damage and sample preparation calls for high-resolution electron or ion microscopy methods, which have not yet been tested on such classes of ultrasmall quantum nanostructures. Here, we demonstrate that scanning helium ion microscopy (SHeIM) provides a powerful and straightforward method to map quantum heterostructures embedded in complex III-V semiconductor NWs with unique material contrast at ∼1 nm resolution. By probing the cross sections of GaAs-Al(Ga)As core-shell NWs with coaxial GaAs quantum wells as well as short-period GaAs/AlAs superlattice (SL) structures in the shell, the Al-rich and Ga-rich layers are accurately discriminated by their image contrast in excellent agreement with correlated, yet destructive, scanning transmission electron microscopy and atom probe tomography analysis. Most interestingly, quantitative He-ion dose-dependent SHeIM analysis of the ternary AlGaAs shell layers and of compositionally nonuniform GaAs/AlAs SLs reveals distinct alloy composition fluctuations in the form of Al-rich clusters with size distributions between ∼1-10 nm. In the GaAs/AlAs SLs the alloy clustering vanishes with increasing SL-period (>5 nm-GaAs/4 nm-AlAs), providing insights into critical size dimensions for atomic intermixing effects in short-period SLs within a NW geometry. The straightforward SHeIM technique therefore provides unique benefits in imaging the tiniest nanoscale features in topography, structure and composition of a multitude of diverse complex semiconductor nanostructures.

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Microscopic nature of crystal phase quantum dots in ultrathin GaAs nanowires by nanoscale luminescence characterization

Cited by 13 publications

References 49 publications

Sub-nanosecond acousto-electric carrier redistribution dynamics and transport in polytypic GaAs nanowires

Sub-nanosecond acousto-electric carrier redistribution dynamics and transport in polytypic GaAs nanowires

Electronic properties of wurtzite GaAs: A correlated structural, optical, and theoretical analysis of the same polytypic GaAs nanowire

He-Ion Microscopy as a High-Resolution Probe for Complex Quantum Heterostructures in Core–Shell Nanowires

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