Effects of nanowire coalescence on their structural and optical properties on a local scale

Consonni, Vincent; Knelangen, M.; Jahn, U.; Trampert, A.; Geelhaar, Lutz; Riechert, H.

doi:10.1063/1.3275793

Cited by 88 publications

(80 citation statements)

References 22 publications

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“…This type of stacking faults is characterized by an emission at 3.42 eV in the low temperature (6 K) PL spectrum. 99 A surface state located approximately 2.6 eV above the valence band was observed for GaN nanorods using deep level optical spectroscopy measurement, which is absent in AlGaN/GaN core-shell nanorods. 100 Li et al investigated the defect-related luminescence using spatially-resolved cathodoluminescence measurements.…”

Section: Structural and Surfaced Related Optical And Electrical Pmentioning

confidence: 99%

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GaN based nanorods for solid state lighting

Li¹,

Waag

2012

Journal of Applied Physics

491

394

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In recent years, GaN nanorods are emerging as a very promising novel route toward devices for nano-optoelectronics and nano-photonics. In particular, core-shell light emitting devices are thought to be a breakthrough development in solid state lighting, nanorod based LEDs have many potential advantages as compared to their 2 D thin film counterparts. In this paper, we review the recent developments of GaN nanorod growth, characterization, and related device applications based on GaN nanorods. The initial work on GaN nanorod growth focused on catalyst-assisted and catalyst-free statistical growth. The growth condition and growth mechanisms were extensively investigated and discussed. Doping of GaN nanorods, especially p-doping, was found to significantly influence the morphology of GaN nanorods. The large surface of 3 D GaN nanorods induces new optical and electrical properties, which normally can be neglected in layered structures. Recently, more controlled selective area growth of GaN nanorods was realized using patterned substrates both by metalorganic chemical vapor deposition (MOCVD) and by molecular beam epitaxy (MBE). Advanced structures, for example, photonic crystals and DBRs are meanwhile integrated in GaN nanorod structures. Based on the work of growth and characterization of GaN nanorods, GaN nanoLEDs were reported by several groups with different growth and processing methods. Core/shell nanoLED structures were also demonstrated, which could be potentially useful for future high efficient LED structures. In this paper, we will discuss recent developments in GaN nanorod technology, focusing on the potential advantages, but also discussing problems and open questions, which may impose obstacles during the future development of a GaN nanorod based LED technology.

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Section: Structural and Surfaced Related Optical And Electrical Pmentioning

confidence: 99%

“…21,99 In catalyst-assisted GaN nanorod growth, they can be observed originated from the different stacking sequence of metal catalyst. 21 The I 1 -type of basal plane stacking faults was observed to nucleate on the dislocation networks, which is induced by the coalescence of GaN nanorods.…”

Section: Structural and Surfaced Related Optical And Electrical Pmentioning

confidence: 99%

GaN based nanorods for solid state lighting

Li¹,

Waag

2012

Journal of Applied Physics

491

394

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“…Upon coalescence, a small tilt may be accommodated elastically, but a larger tilt as well as a twist will result in dislocated tilt/twist boundaries reminiscent of small-angle grain boundaries in polycrystalline thin films. 12,13 Coalescence is thus likely to introduce inhomogeneous strain 10,14 as well as nonradiative recombination, 12,15,16 phenomena one associates with heteroepitaxial thin films rather than with nanowire ensembles. The detrimental impact of coalescence on the structural perfection of dense nanowire ensembles may prevent these nanostructures to realize their full potential for applications.…”

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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“…18,23 The resulting defects at grain boundaries between newly coalesced nanorods form non-recombination centres, detrimental to the crystal perfection and future applications of arrays of nanorods. 24,25 The problem of growing ultra-high density non-coalesced arrays of III-N nanorods, although investigated in depth, has not been answered to date. In this article we present the first synthesis of wafer-scale, dislocation-free arrays of AlN nanorods via an MOCVD space filling approach.…”

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confidence: 99%