Realization of defect-free epitaxial core-shell GaAs/AlGaAs nanowire heterostructures

Tambe, Michael; Lim, Sang-Kyu; Smith, Matthew J.; Allard, Lawrence F.; Gradečak, Silvija

doi:10.1063/1.3002299

Cited by 61 publications

(68 citation statements)

References 21 publications

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“…Previous studies have shown that the GaAs/AlGaAs core-shell NWs grow predominantly as cubic zinc-blende (ZB) single crystals, mainly along the <111> direction, perpendicular to the substrate surface [13,14]. Occasionally, NW segments of hexagonal wurtzite (WZ) structure have been observed to penetrate the ZB structure, as well.…”

Section: Introductionmentioning

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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Section: Introductionmentioning

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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“…Critical steps have been taken in these directions in the last years. Long single-crystal defect-free cores [6,7], selective radial doping [8], and lateral overgrowth with high-quality interfaces [9] have been successfully realized. Most importantly, complex radial modulation doped heterostructures are now being engineered in coremultishell NWs [10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Magnetophotoluminescence in GaAs/AlAs core-multishell nanowires: A theoretical investigation

et al. 2015

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The magnetophotoluminescence in modulation doped core-multishell nanowires is predicted as a function of photoexcitation intensity in nonperturbative transverse magnetic fields. We use a self-consistent field approach within the effective mass approximation to determine the photoexcited electron and hole populations, including the complex composition and anisotropic geometry of the nanomaterial. The evolution of the photoluminescence is analyzed as a function of (i) photoexcitation power, (ii) magnetic field intensity, (iii) type of doping, and (iv) anisotropy with respect to field orientation.

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“…4 Refinements in the epitaxial growth of these nanowires are therefore essential in order for their optoelectronic and crystallographic standards to approach those of bulk material. 2,6,7 Such efforts are complicated by the fact that electrical measurements conducted on nanowires to determine charge-carrier mobility are often obscured by properties of the electrical contacts. Most contactless spectroscopic probes of nanowires to date have relied upon low-temperature photoluminescence measurements to characterize optoelectronic quality by measuring excitonic dynamics and radiative quantum efficiency.…”

mentioning

confidence: 99%

Carrier Lifetime and Mobility Enhancement in Nearly Defect-Free Core−Shell Nanowires Measured Using Time-Resolved Terahertz Spectroscopy

et al. 2009

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We have used transient terahertz photoconductivity measurements to assess the efficacy of two-temperature growth and core-shell encapsulation techniques on the electronic properties of GaAs nanowires. We demonstrate that two-temperature growth of the GaAs core leads to an almost doubling in charge-carrier mobility and a tripling of carrier lifetime. In addition, overcoating the GaAs core with a larger-bandgap material is shown to reduce the density of surface traps by 82%, thereby enhancing the charge conductivity.Semiconductor nanowires are promising new materials for implementation in nanoscale electronic and optoelectronic devices. Of particular interest are III-V semiconductor nanowires, which can exhibit a direct bandgap and a high electron mobility.1 However, the large surface-to-volume ratio inherent to nanowires results in the presence of surface traps offering easy access to carrier and exciton recombination pathways.2,3 In addition, one-temperature growth techniques have been shown to cause a significant twin-defect (stacking-defect) density within the nanowires. 4 Refinements in the epitaxial growth of these nanowires are therefore essential in order for their optoelectronic and crystallographic standards to approach those of bulk material.2,6,7 Such efforts are complicated by the fact that electrical measurements conducted on nanowires to determine charge-carrier mobility are often obscured by properties of the electrical contacts. Most contactless spectroscopic probes of nanowires to date have relied upon low-temperature photoluminescence measurements to characterize optoelectronic quality by measuring excitonic dynamics and radiative quantum efficiency. 2,6However, for use of these materials in nanoelectronics and optoelectronics, it is essential to determine charge-carrier mobility and lifetime at room temperature.In this study, we have conducted transient photoconductivity measurements on an ensemble of nanowires in order to assess the effect of nearly defect-free (two-temperature) growth and core-shell encapsulation technologies on charge-carrier trapping and mobility. Optical-pump terahertz-probe spectroscopy was employed as a noncontact ultrafast probe of the room-temperature photoconductivity with subpicosecond resolution. We demonstrate that both two-temperature growth and encapsulation of the GaAs nanowires with a higher band gap material lead to significant increases in the lifetime of free charge carriers. Encapsulation of the nanowires is shown to be highly effective, reducing the areal density of surface traps to one-seventh of that for the untreated wires. Importantly, we find that moving from one-temperature growth to a two-temperature procedure (comprising a brief high-temperature step for nucleation and a longer lower-temperature phase for prolonged growth 4 ) increases the intrinsic carrier mobility of the wires from 1200 cm 2 /(V s) to 2250 cm 2 /(V s).All nanowire samples were initially grown onto a GaAs substrate as shown in a representative scanning electron microscopy ...

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Realization of defect-free epitaxial core-shell GaAs/AlGaAs nanowire heterostructures

Cited by 61 publications

References 21 publications

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

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

Magnetophotoluminescence in GaAs/AlAs core-multishell nanowires: A theoretical investigation

Carrier Lifetime and Mobility Enhancement in Nearly Defect-Free Core−Shell Nanowires Measured Using Time-Resolved Terahertz Spectroscopy

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