Spatial Mapping of Efficiency of GaN/InGaN Nanowire Array Solar Cells Using Scanning Photocurrent Microscopy

Howell, Sarah L.; Padalkar, Sonal; Yoon, KunHo; Li, Qiming; Koleske, Daniel; Wierer, Jonathan J.; Wang, George T.; Lauhon, Lincoln J.

doi:10.1021/nl402331u

Cited by 75 publications

(52 citation statements)

References 30 publications

(64 reference statements)

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“…11,31,32 In the future, focus-ion beam (FIB) milling or mechanical polishing over selected area of wires should also be considered. Promisingly, damage induced by FIB cleaving has been demonstrated to be compatible with appearance of voltage contrast.…”

Section: −3mentioning

confidence: 99%

Direct Imaging of p–n Junction in Core–Shell GaN Wires

et al. 2014

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While core−shell wire-based devices offer a promising path toward improved optoelectronic applications, their development is hampered by the present uncertainty about essential semiconductor properties along the threedimensional (3D) buried p−n junction. Thanks to a crosssectional approach, scanning electron beam probing techniques were employed here to obtain a nanoscale spatially resolved analysis of GaN core−shell wire p−n junctions grown by catalyst-free metal−organic vapor phase epitaxy on GaN and Si substrates. Both electron beam induced current (EBIC) and secondary electron voltage constrast (VC) were demonstrated to delineate the radial and axial junction existing in the 3D structure. The Mg dopant activation process in p-GaN shell was dynamically controlled by the ebeam exposure conditions and visualized thanks to EBIC mapping. EBIC measurements were shown to yield local minority carrier/exciton diffusion lengths on the p-side (∼57 nm) and the n-side (∼15 nm) as well as depletion width in the range 40−50 nm. Under reverse bias conditions, VC imaging provided electrostatic potential maps in the vicinity of the 3D junction from which acceptor N a and donor N d doping levels were locally determined to be N a = 3 × 10 18 cm −3 and N d = 3.5 × 10 18 cm −3 in both the axial and the radial junction. Results from EBIC and VC are in good agreement. This nanoscale approach provides essential guidance to the further development of core−shell wire devices.

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Section: −3mentioning

confidence: 99%

Direct Imaging of p–n Junction in Core–Shell GaN Wires

et al. 2014

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“…5,6 Consequently, these nanowire ensembles are attracting much interest for applications requiring single crystals of high structural perfection, such as demanded for light emitting or light harvesting devices. 7,8 The nanowire ensembles, however, are of such high density (10 9 . .…”

Section: Introductionmentioning

confidence: 99%

Statistical Analysis of the Shape of One-Dimensional Nanostructures: Determining the Coalescence Degree of Spontaneously Formed GaN Nanowires

Brandt

Fernández-Garrido

Zettler

et al. 2014

Crystal Growth & Design

109

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Single GaN nanowires formed spontaneously on a given substrate represent nanoscopic single crystals free of any extended defects. However, due to the high area density of thus formed GaN nanowire ensembles, individual nanowires coalesce with others in their immediate vicinity. This coalescence process may introduce strain and structural defects, foiling the idea of defect-free material due to the nanowire geometry. To investigate the consequences of this process, a quantitative measure of the coalescence of nanowire ensembles is required. We derive objective criteria to determine the coalescence degree of GaN nanowire ensembles. These criteria are based on the area-perimeter relationship of the cross-sectional shapes observed, and in particular on their circularity. Employing these criteria, we distinguish single nanowires from coalesced aggregates in an ensemble, determine the diameter distribution of both, and finally analyze the coalescence degree of nanowire ensembles with increasing fill factor.

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“…The high nanowire density is advantageous for light emitting and energy harvesting devices as well as for sensing applications [13][14][15][16]. On the other hand, GaN nanowires coalesce during growth because of their proximity [17].…”

Section: Introductionmentioning

confidence: 99%

Elastic versus Plastic Strain Relaxation in Coalesced GaN Nanowires: An X-Ray Diffraction Study

2016

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The coalescence in dense arrays of spontaneously formed GaN nanowires proceeds by bundling: adjacent nanowires bend and merge at their top, thus reducing their surface energy at the expense of the elastic energy of bending. We give a theoretical description of the energetics of this bundling process. The bending energy is shown to be substantially reduced by the creation of dislocations at the coalescence joints. A comparison of experimental and calculated x-ray diffraction profiles from ensembles of bundled nanowires demonstrates that a large part of the bending energy is indeed relaxed by plastic deformation. The residual bending manifests itself by extended tails of the diffraction profiles.

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Spatial Mapping of Efficiency of GaN/InGaN Nanowire Array Solar Cells Using Scanning Photocurrent Microscopy

Cited by 75 publications

References 30 publications

Direct Imaging of p–n Junction in Core–Shell GaN Wires

Direct Imaging of p–n Junction in Core–Shell GaN Wires

Statistical Analysis of the Shape of One-Dimensional Nanostructures: Determining the Coalescence Degree of Spontaneously Formed GaN Nanowires

Elastic versus Plastic Strain Relaxation in Coalesced GaN Nanowires: An X-Ray Diffraction Study

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