Three-Dimensional Multiple-Order Twinning of Self-Catalyzed GaAs Nanowires on Si Substrates

Uccelli, Emanuele; Arbiol, Jordi; Magén, Cesar; Krogstrup, Peter; Russo-Averchi, Eleonora; Heiß, Martin; Mugny, Gabriel; Morier‐Genoud, F.; Nygård, Jesper; Morante, J.R.; Morral, Anna Fontcuberta i

doi:10.1021/nl201902w

Cited by 126 publications

(157 citation statements)

References 33 publications

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“…Nanowires were grown on oxidized Si(111) with 100 nm apertures using a self-catalysed method. The gallium nominal growth rate was 900 nm h 21 , the substrate temperature was 630 8C and the V/III ratio was 4 (refs 43,44). The p-doping of the core was achieved by adding a flux of beryllium during axial growth 45 .…”

Section: Methodsmentioning

confidence: 99%

Single-nanowire solar cells beyond the Shockley–Queisser limit

Jørgensen²,

et al. 2013

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Light management is of great importance in photovoltaic cells, as it determines the fraction of incident light entering the device. An optimal p-n junction combined with optimal light absorption can lead to a solar cell efficiency above the Shockley-Queisser limit. Here, we show how this is possible by studying photocurrent generation for a single core-shell p-i-n junction GaAs nanowire solar cell grown on a silicon substrate. At 1 sun illumination, a short-circuit current of 180 mA cm -2 is obtained, which is more than one order of magnitude higher than that predicted from the Lambert-Beer law. The enhanced light absorption is shown to be due to a light-concentrating property of the standing nanowire, as shown by photocurrent maps of the device. The results imply new limits for the maximum efficiency obtainable with III-V based nanowire solar cells under 1 sun illumination.N anowire-based solar cells hold great promise for third-generation photovoltaics and for powering nanoscale devices 1,2 . With the advent of third-generation photovoltaics, solar cells will become cheaper and more efficient than current devices. In particular, a cost reduction may be achieved by reducing material use through the fabrication of nanowire arrays and radial p-n junctions [3][4][5] . The geometry of nanowire crystals is expected to favour elastic strain relaxation, providing great freedom in the design of new compositional multijunction solar cells 6 grown on mismatched materials 7,8 . The efficiencies of nanostructured solar cells have increased over time and have now reached up to 13.8%, due to improvements in materials and new device concepts [9][10][11][12][13][14] .Light absorption in standing nanowires is a complex phenomenon, with a strong dependence on nanowire dimensions and the absorption coefficient of the raw materials [15][16][17][18] . In low-absorbing microwire arrays, such as those composed of silicon, light absorption is understood via ray optics or by calculation of the integrated local density of optical states of the nanowire film 19,20 . Interestingly, when these arrays stand on a Lambertian back-reflector, an asymptotic increase in light trapping for low filling factors (FFs) is predicted 19 . This is advantageous for improvement of the efficiency-to-cost ratio of solar cells and has led to the demonstration of microwire arrays exhibiting higher absorption than in the equivalent thickness of textured film 19,21,22 . The case for nanowires is quite different. Nanowire diameters are smaller than or comparable to the radiation wavelength. In this case, optical interference and guiding effects play a dominant role in relation to reflectivity and absorption spectra. For low-absorbing materials (for example, indirect bandgap materials such as silicon), waveguiding effects plays a key role 23,24 , whereas highly absorbing semiconductors (such as direct-bandgap GaAs) exhibit resonances that increase the total absorption several times. Nanowires lying on a substrate also exhibit such resonances, often described by Mi...

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Section: Methodsmentioning

confidence: 99%

Single-nanowire solar cells beyond the Shockley–Queisser limit

Jørgensen²,

et al. 2013

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“…24,[43][44][45] Therefore, investigating the structural defects near the interface between the substrate and the Gd-doped ZnO wetting layer is essential for a better understanding of the growth mechanism. 44 For this purpose, a cross-section along the c-axis of the NRs sample (Fig 1c) was analyzed by HRTEM.…”

Section: Growth Mechanismmentioning

confidence: 99%

Homogeneous vertical ZnO nanorod arrays with high conductivity on an in situ Gd nanolayer

et al. 2015

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CitationFlemban TH, Singaravelu V, Sasikala Devi AA, Roqan IS (2015 We demonstrate a novel, one-step, catalyst-free method for the production of size-controlled vertical highly conductive ZnO NR arrays with highly desirable characteristics by pulsed laser deposition using a Gd-doped ZnO target. Our study shows that an in situ transparent and conductive Gd nanolayer (with a uniform thickness of ~1 nm) at the interface between a latticematched (11-20) a-sapphire substrate and ZnO is formed during the deposition. This nanolayer significantly induces relaxation mechanism that controls the dislocation distribution along the growth direction; which consequently improves the formation of homogeneous vertically aligned ZnO NRs. We demonstrate that both the lattice orientation of the substrate and the Gd characteristics are important in enhancing the NR synthesis, and we report precise control of the NR density by changing the oxygen partial pressure. We show that these NRs possess high optical and electrical quality, with a mobility of 177 cm 2 (V.s), which is comparable to the best-reported mobility of ZnO NRs. Therefore, this new and simple method has significant potential for improving the performance of materials used in a wide range of electronic and optoelectronic applications.

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“…The GaAs NW cores were obtained by the Ga-assisted method 24 on (111) silicon wafers. 25 After the core reached around 10 lm in length, the Ga flux was interrupted and the As 4 flux increased, resulting in the stopping of the axial growth. The substrate temperature was then decreased from 640 C to 460 C to allow the growth of high quality epitaxial Al x Ga 1Àx As shells.…”

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confidence: 99%

Quantum dots in the GaAs/AlxGa1−xAs core-shell nanowires: Statistical occurrence as a function of the shell thickness

Francaviglia

Fontana

Conesa‐Boj

et al. 2015

Applied Physics Letters

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Quantum dots (QDs) embedded in nanowires represent one of the most promising technologies for applications in quantum photonics. Self-assembled bottom-up fabrication is attractive to overcome the technological challenges involved in a top-down approach, but it needs post-growth investigations in order to understand the self-organization process. We investigate the QD formation by selfsegregation in Al x Ga 1Àx As shells as a function of thickness and cross-section morphology. By analysing light emission from several hundreds of emitters, we find that there is a certain thickness threshold for the observation of the QDs. The threshold becomes smaller if a thin AlAs layer is pre-deposited between the GaAs nanowire core and the Al x Ga 1Àx As shell. Our results evidence the development of the quantum emitters during the shell growth and provide more guidance for their use in quantum photonics. V C 2015 AIP Publishing LLC. [http://dx

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Three-Dimensional Multiple-Order Twinning of Self-Catalyzed GaAs Nanowires on Si Substrates

Cited by 126 publications

References 33 publications

Single-nanowire solar cells beyond the Shockley–Queisser limit

Single-nanowire solar cells beyond the Shockley–Queisser limit

Homogeneous vertical ZnO nanorod arrays with high conductivity on an in situ Gd nanolayer

Quantum dots in the GaAs/AlxGa1−xAs core-shell nanowires: Statistical occurrence as a function of the shell thickness

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