Non-destructive assessment of the polarity of GaN nanowire ensembles using low-energy electron diffraction and x-ray photoelectron diffraction

Romanyuk, O.; Fernández-Garrido, Sergio; Jiřı́ček, P.; Bartoš, I.; Geelhaar, Lutz; Brandt, O.; Paskova, T.

doi:10.1063/1.4905651

Cited by 25 publications

(20 citation statements)

References 35 publications

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“…32 The polarity of the GaN NWs was investigated on a macroscopic scale by KOH etching. 33,34 For this purpose, several pieces of the sample were etched in a 5M KOH aqueous solution at 40 • C for different times. The subsequent analysis of the samples by scanning electron microscopy (not shown here) revealed that, upon KOH exposure, all the investigated NWs become shorter.…”

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confidence: 99%

Molecular beam epitaxy of single crystalline GaN nanowires on a flexible Ti foil

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Gao

et al. 2016

Applied Physics Letters

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We demonstrate the self-assembled growth of vertically aligned GaN nanowire ensembles on a flexible Ti foil by plasma-assisted molecular beam epitaxy. The analysis of single nanowires by transmission electron microscopy reveals that they are single crystalline. Low-temperature photoluminescence spectroscopy demonstrates that, in comparison to standard GaN nanowires grown on Si, the nanowires prepared on the Ti foil exhibit a equivalent crystalline perfection, a higher density of basal-plane stacking faults, but a reduced density of inversion domain boundaries. The room-temperature photoluminescence spectrum of the nanowire ensemble is not influenced or degraded by the bending of the substrate. The present results pave the way for the fabrication of flexible optoelectronic devices based on GaN nanowires on metal foils.The integration of electronic and optoelectronic devices on flexible substrates is motivated by the vision of novel and/or economically relevant applications. 1,2 In this context, inorganic semiconductor nanowires (NWs) have recently emerged as promising candidates for flexible electronics and optoelectronics. 2,3 Their large aspect ratio facilitates the expulsion of threading dislocation at the NW sidewalls, leading to their complete absence in the upper sections of well-developed NWs. This effect alleviates the requirement of lattice matching with the substrate and thus lifts the stringent constraints concerning the choice of the substrate material. 4,5 Indeed, the direct growth of semiconductor NW ensembles on flexible substrates has already been demonstrated for different material systems: ZnO NWs on polymer-based indium-tin-oxide coated substrates 6 and on paper, 7 Ge NWs on plastic films 8 as well as on Au coated Al foils 9 and Si NWs on stainless steel. 10 However, the direct growth of inorganic semiconductors on flexible substrates is frequently hampered by either the low melting point of the organic materials used as substrate 11 or the occurrence of interfacial reactions when semiconductors are directly grown on metallic surfaces. 12,13 To overcome these issues and extend the possible range of material combinations, the wet etching of the substrate followed by NW embedding in a plastic film, 14 and different lift-off techniques such as dry transfer 15,16 and transfer printinting 17,18 have been developed. Using these methods, arrays of vertically oriented CdS 14 and Si 11,19 NWs have been fabricated on flexible substrates. Regarding group-III nitrides, the material of choice for solid-state lighting and high-power electronics, the integration of GaN NWs on flexible substrates has been achieved either by transferring NW arrays grown on Si to polymer films 20,21 or by a lift-off process of NW ensembles grown on graphene coated Cu substrates. 22 Metal foils are a particularly interesting type of substrate because they are not only flexible but also exhibit excellent electrical and thermal conductivities as well as a high optical reflectance. However, as pointed out above, the direct growth of...

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confidence: 99%

Molecular beam epitaxy of single crystalline GaN nanowires on a flexible Ti foil

Calabrese

Corfdir

Gao

et al. 2016

Applied Physics Letters

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“…29, 07745 Jena, Germany increasing magnitude of strain in the (In,Ga)N layer, axial (In,Ga)N/GaN(0001) nanowire heterostructures are considered as a promising alternative to planar structures for long-wavelength emission [13]. In molecular beam epitaxy (MBE), N-polar GaN nanowires spontaneously form on various technologically attractive substrates such as Si [14] or metal foils [15,16] while retaining their single-crystal nature. Using MBE, (In,Ga)N quantum disks (QDs) can be subsequently synthesized on the GaN nanowires.…”

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confidence: 99%

Ga-Polar (In,Ga)N/GaN Quantum Wells Versus N-Polar (In,Ga)N Quantum Disks in GaN Nanowires: A Comparative Analysis of Carrier Recombination, Diffusion, and Radiative Efficiency

et al. 2017

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We investigate the radiative and nonradiative recombination processes in planar (In,Ga)N/GaN(0001) quantum wells and (In,Ga)N quantum disks embedded in GaN(0001) nanowires using photoluminescence spectroscopy under both continuous-wave and pulsed excitation. The photoluminescence intensities of these two samples quench only slightly between 10 and 300 K, which is commonly taken as evidence for high internal quantum efficiencies. However, a side-by-side comparison shows that the absolute intensity of the Ga-polar quantum wells is two orders of magnitude higher than that of the N-polar quantum disks. A similar difference is observed for the initial decay time of photoluminescence transients obtained by time-resolved measurements, indicating the presence of a highly efficient nonradiative decay channel for the quantum disks. In apparent contradiction to this conjecture, the decay of both samples is observed to slow down dramatically after the initial rapid decay. Independent of temperature, the transients approach a power law for longer decay times, reflecting that recombination occurs between individual electrons and holes with varying spatial separation. Employing a coupled system of stochastic integro-differential equations taking into account both radiative and nonradiative Shockley-Read-Hall recombination of spatially separate electrons and holes as well as their diffusion, we obtain simulated transients matching the experimentally obtained ones. The results reveal that even dominant nonradiative recombination conserves the power law decay for (In,Ga)N/GaN{0001} quantum wells and disks.

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“…The polarity of GaN NWs formed directly on such a nitridated Si(111) surface has been debated for a long time. In earlier work, the GaN NWs were mostly reported to be Ga polar [17,29,[31][32][33][34], while recent studies (which also include ensemble investigations with far better statitics) indicate that GaN NWs grow predominantly or even exclusively N polar [35][36][37][38][39][40]. In any case, whether IDB * s form for GaN NWs on nitridated Si(111), and if so, at which density, are open questions.…”

Section: Introductionmentioning

confidence: 99%

Nature of excitons bound to inversion domain boundaries: Origin of the 3.45-eV luminescence lines in spontaneously formed GaN nanowires on Si(111)

et al. 2016

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We investigate the 3.45-eV luminescence band of spontaneously formed GaN nanowires on Si(111) by photoluminescence and cathodoluminescence spectroscopy. This band is found to be particularly prominent for samples synthesized at comparatively low temperatures. At the same time, these samples exhibit a peculiar morphology, namely, isolated long nanowires are interspersed within a dense matrix of short ones. Cathodoluminescence intensity maps reveal the 3.45-eV band to originate primarily from the long nanowires. Transmission electron microscopy shows that these long nanowires are either Ga polar and are joined by an inversion domain boundary with their short N-polar neighbors, or exhibit a Ga-polar core surrounded by a N-polar shell with a tubular inversion domain boundary at the core/shell interface. For samples grown at high temperatures, which exhibit a uniform nanowire morphology, the 3.45-eV band is also found to originate from particular nanowires in the ensemble and thus presumably from inversion domain boundaries stemming from the coexistence of Nand Ga-polar nanowires. For several of the investigated samples, the 3.45-eV band splits into a doublet. We demonstrate that the higher-energy component of this doublet arises from the recombination of two-dimensional excitons free to move in the plane of the inversion domain boundary. In contrast, the lower-energy component of the doublet originates from excitons localized in the plane of the inversion domain boundary. We propose that this in-plane localization is due to shallow donors in the vicinity of the inversion domain boundaries.

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Non-destructive assessment of the polarity of GaN nanowire ensembles using low-energy electron diffraction and x-ray photoelectron diffraction

Cited by 25 publications

References 35 publications

Molecular beam epitaxy of single crystalline GaN nanowires on a flexible Ti foil

Molecular beam epitaxy of single crystalline GaN nanowires on a flexible Ti foil

Ga-Polar (In,Ga)N/GaN Quantum Wells Versus N-Polar (In,Ga)N Quantum Disks in GaN Nanowires: A Comparative Analysis of Carrier Recombination, Diffusion, and Radiative Efficiency

Nature of excitons bound to inversion domain boundaries: Origin of the 3.45-eV luminescence lines in spontaneously formed GaN nanowires on Si(111)

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