Properties of GaN Nanowires Grown by Molecular Beam Epitaxy

Geelhaar, Lutz; Chèze, Caroline; Jenichen, B.; Brandt, O.; Pfüller, Carsten; Munch, S.; Rothemund, Ralph; Reitzenstein, Stephan; Forchel, A.; Kehagias, Th.; Komninou, Ph.; Dimitrakopulos, G. P.; Karakostas, Th.; Lari, Leonardo; Chalker, Paul R.; Gass, Mhairi; Riechert, H.

doi:10.1109/jstqe.2010.2098396

Cited by 104 publications

(111 citation statements)

References 54 publications

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“…A possible candidate is a transition between shallow donors and Ga vacancies acting as deep acceptors [36], whereas a recent study attributes this emission to the (C N -O N ) 0 deep donor complex [37]. The presence of the yellow band is in contrast to the majority of other NW samples, for which an absence of this luminescence in PL measurements was observed and interpreted as an indication for a low density of native point defects [30,38]. While the NW base was grown at temperatures optimized for GaN, the appearance of the yellow luminescence in this specific sample might depend sensitively on factors such as the detailed growth conditions, defect interactions, or the purity of the material.…”

Section: Contributions From Point Defectsmentioning

confidence: 97%

Localization and defects in axial (In,Ga)N/GaN nanowire heterostructures investigated by spatially resolved luminescence spectroscopy

Lähnemann¹,

Hauswald²,

Wölz³

et al. 2014

J. Phys. D: Appl. Phys.

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Abstract. (In,Ga)N insertions embedded in self-assembled GaN nanowires are of current interest for applications in solid-state light emitters. Such structures exhibit a notoriously broad emission band. We use cathodoluminescence spectral imaging in a scanning electron microscope and micro-photoluminescence spectroscopy on single nanowires to learn more about the mechanisms underlying this emission. We observe a shift of the emission energy along the stack of six insertions within single nanowires that may be explained by compositional pulling. Our results also corroborate reports that the localization of carriers at potential fluctuations within the insertions plays a crucial role for the luminescence of these nanowire based emitters. Furthermore, we resolve contributions from both structural and point defects in our measurements.

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Section: Contributions From Point Defectsmentioning

confidence: 97%

Localization and defects in axial (In,Ga)N/GaN nanowire heterostructures investigated by spatially resolved luminescence spectroscopy

Lähnemann¹,

Hauswald²,

Wölz³

et al. 2014

J. Phys. D: Appl. Phys.

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“…NWs [26], and massively in self-assembled III-Nitride NWs on Si(111) and was attributed to the natural tendency of one-dimensional structures to grow along the polar <111> and <0001> crystallographic directions without direct contact with the substrate [27,28,29].…”

Section: Structural Properties Of Gaasmentioning

confidence: 99%

Nanostructure and strain properties of core-shell GaAs/AlGaAs nanowires

Kehagias¹,

Florini²,

Kioseoglou³

et al. 2015

Semicond. Sci. Technol.

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GaAs/AlGaAs core-shell nanowires were grown on Si(111) by Ga-assisted molecular beam epitaxy via the vapor-liquid-solid mechanism. High-resolution and scanning transmission electron microscopy observations showed that nanowires were predominantly zinc-blende single crystals of hexagonal shape, grown along the [111] direction. GaAs core nanowires emerged from the Si surface and subsequently, the nanowire growth front advanced by a continuous sequence of (111) rotational twins, while the AlGaAs shell lattice was perfectly aligned with the core lattice. Occasionally, single or multiple stacking faults induced wurtzite structure nanowire pockets. The AlGaAs shell occupied at least half of the nanowire's projected diameter, while the average Al content of the shell, estimated by energy dispersive X-ray analysis, was x = 0.35. Furthermore, molecular dynamics simulations of hexagonal cross-section nanowire slices, under a new parametrization of the Tersoff interatomic potential for AlAs, showed increased atom relaxation at the hexagon vertices of the shell. This, in conjunction with the compressively strained Al 0.35 Ga 0.65 As shell close to the GaAs core, can trigger a kinetic surface mechanism that could drive Al adatoms to accumulate at the relaxed sites of the shell, namely along the diagonals of the shell's hexagon. Moreover, the absence of long-range stresses in the GaAs/Al 0.35 Ga 0.65 As coreshell system may account for a highly stable heterostructure. The latter was consolidated by temperaturedependent photoluminescence spectroscopy.

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“…The wide-band-gap semiconductor GaN is a key material in today's white-light-emitting diodes for general illumination, blue lasers, and high-power and high-frequency electronics [11]. GaN readily grows in the form of nanowires (NWs) in molecular beam epitaxy (MBE) [12,13] and metal-organic chemical vapor deposition (MOCVD) [14,15]. However, different shapes are observed, depending on the growth temperature, pressure, and chemical environment [16][17][18][19][20].…”

mentioning

confidence: 99%

Computing Equilibrium Shapes of Wurtzite Crystals: The Example of GaN

Geelhaar

Riechert

et al. 2015

Phys. Rev. Lett.

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Crystal morphologies are important for the design and functionality of devices based on low-dimensional nanomaterials. The equilibrium crystal shape (ECS) is a key quantity in this context. It is determined by surface energies, which are hard to access experimentally but can generally be well predicted by first-principles methods. Unfortunately, this is not necessarily so for polar and semipolar surfaces of wurtzite crystals. By extending the concept of Wulff construction, we demonstrate that ECSs can nevertheless be obtained for this class of materials. For the example of GaN, we identify different crystal shapes depending on the chemical potential, shedding light on experimentally observed GaN nanostructures. 68.35.Md,68.47.Fg,81.10.Aj Low-dimensional semiconductor nanostructures have attracted a lot of interest in the past decades, largely due to their applications in low-energy consumption and energyharvesting devices [1,2]. Owing to surface effects, the performance of such devices strongly depends on the nanocrystal morphology. To achieve comprehensive understanding and control of the preferred growth morphology, one must know the material's natural shape that results from its crystallographic anisotropy. Ab initio theory can generally provide more insight into this complicated issue through the calculation of surface energies since, according to Wulff's theorem [3], the equilibrium crystal shape (ECS) of a solid can be constructed by the mere knowledge of surface energies of various crystal planes. For a crystalline solid, the surface energy γ is defined as the excess free energy required to create one unit of surface area A [4],G represents the Gibbs free energy of the system that, neglecting temperature and pressure, is replaced by the total energy. The chemical potential µ i is the free energy per atom in the system for species i, and N i denotes the number of atoms of this species. In a bulk material, the total chemical potential is known from the corresponding total energy E bulk = ∑ i n i µ i , where n i is the number of atoms of species i in the bulk. Hence, the surface energy of a nonpolar plane can be extracted from density-functional-theory (DFT) results for a slab that contains two identical surfaces well separated from each other. For some polar and semipolar planes, however, individual surface energies are difficult to access, because different facets may appear at the two surfaces of the slab. To overcome this problem, a method has been proposed [5] involving two surface types on three side faces of a triangular wedge. This approach is, however, not applicable to all surfaces and crystal structures; polar surfaces in wurtzite crystals are one example [6,7]. Consequently, not every individual surface energy of wurtzite crystals can be computed; hence, the construction of the ECS seemed impossible. Recently, neglecting the different layer-stacking sequence, the surface energy of the polar c plane was estimated from the zincblende (111) plane [10].In this Letter, we show that such an approxim...

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Properties of GaN Nanowires Grown by Molecular Beam Epitaxy

Cited by 104 publications

References 54 publications

Localization and defects in axial (In,Ga)N/GaN nanowire heterostructures investigated by spatially resolved luminescence spectroscopy

Localization and defects in axial (In,Ga)N/GaN nanowire heterostructures investigated by spatially resolved luminescence spectroscopy

Nanostructure and strain properties of core-shell GaAs/AlGaAs nanowires

Computing Equilibrium Shapes of Wurtzite Crystals: The Example of GaN

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