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12 Jan 2004

Volume 84, Issue 2, pp. 161-308

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 161 (2004); http://dx.doi.org/10.1063/1.1639505 (3 pages)

Hatice Altug and Jelena Vučković
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Room-temperature continuous-wave operation of InAsSb quantum-dot lasers near 2 μm based on (001) InP substrate

Yueming Qiu, David Uhl, and Sam Keo

Appl. Phys. Lett. 84, 263 (2004); http://dx.doi.org/10.1063/1.1640467 (3 pages) | Cited 20 times

Online Publication Date: 7 January 2004

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Single-stack InAsSb self-assembled quantum-dot lasers based on (001) InP substrate have been grown by metalorganic vapor-phase epitaxy. The narrow ridge waveguide lasers lased at wavelengths near 2 μm up to 25 °C in continuous-wave operation. At room temperature, a differential quantum efficiency of 13% is obtained and the maximum output optical power reaches 3 mW per facet with a threshold current density of 730 A/cm2. With increasing temperature the emission wavelength is extremely temperature stable, and a very low wavelength temperature sensitivity of 0.05 nm/°C is measured, which is even lower than that caused by the refractive index change. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Pk Continuous operation

Decay of spin-polarized hot carrier current in a quasi-one-dimensional spin-valve structure

S. Pramanik, S. Bandyopadhyay, and M. Cahay

Appl. Phys. Lett. 84, 266 (2004); http://dx.doi.org/10.1063/1.1639127 (3 pages) | Cited 11 times

Online Publication Date: 7 January 2004

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We study the spatial decay of spin-polarized hot carrier current in a spin-valve structure consisting of a semiconductor quantum wire flanked by half-metallic ferromagnetic contacts. The current decays because of D’yakonov-Perel’ spin relaxation in the semiconductor caused by Rashba and Dresselhaus spin–orbit interactions in multi-channeled transport. The associated relaxation length is found to decrease with increasing lattice temperature (in the range from 30 to 77 K) and exhibit a nonmonotonic dependence on the electric field driving the current. The relaxation lengths are several tens of microns which are at least an order of magnitude larger than what has been theoretically calculated for two-dimensional structures at comparable temperatures, spin-orbit interaction strengths, and electric fields. This improvement is a consequence of one-dimensional carrier confinement that does not necessarily suppress carrier scattering, but nevertheless suppresses D’yakonov-Perel’ spin relaxation. © 2004 American Institute of Physics.
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72.25.Rb Spin relaxation and scattering
85.75.Hh Spin polarized field effect transistors

Growth of high-quality single-wall carbon nanotubes without amorphous carbon formation

R. G. Lacerda, A. S. Teh, M. H. Yang, K. B. K. Teo, N. L. Rupesinghe, S. H. Dalal, K. K. K. Koziol, D. Roy, G. A. J. Amaratunga, W. I. Milne, M. Chhowalla, D. G. Hasko, F. Wyczisk, and P. Legagneux

Appl. Phys. Lett. 84, 269 (2004); http://dx.doi.org/10.1063/1.1639509 (3 pages) | Cited 38 times

Online Publication Date: 7 January 2004

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We report an alternative way of preparing high-quality single-wall carbon nanotubes (SWCNTs). Using a triple-layer thin film of Al/Fe/Mo (with Fe as a catalyst) on an oxidized Si substrate, the sample is exposed to a single short burst (5 s) of acetylene at 1000 °C. This produced a high yield of very well graphitized SWCNTs, as confirmed by transmission electron microscopy and Raman spectroscopy. We believe that the high temperature is responsible for the high crystallinity/straightness of the nanotubes, and the rapid growth process allows us to achieve a clean amorphous carbon (a-C) free deposition which is important for SWCNT device fabrication. The absence of a-C is confirmed by Auger electron spectroscopy, Raman spectroscopy, and electrical measurements. © 2004 American Institute of Physics.
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85.35.Kt Nanotube devices
81.16.Be Chemical synthesis methods

Carrier-induced refractive index in quantum dot structures due to transitions from discrete quantum dot levels to continuum states

A. V. Uskov, E. P. O’Reilly, D. McPeake, N. N. Ledentsov, D. Bimberg, and G. Huyet

Appl. Phys. Lett. 84, 272 (2004); http://dx.doi.org/10.1063/1.1639933 (3 pages) | Cited 23 times

Online Publication Date: 7 January 2004

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The carrier-induced refractive index in quantum dot (QD) structures due to optical transitions from QD levels to continuum states is considered. It is shown that, for large photon energies, the refractive index change is given asymptotically by the Drude formula. Calculations of the linewidth enhancement factor, α, show that α ∼ 1 due to this contribution to the total refractive index. Furthermore, for highly localized QD states, the absorption coefficient at the photon energies ∼0.8–1.0 eV due to these transitions can be on the order of 103 m−1. © 2004 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Hc Quantum dots
73.21.La Quantum dots

Wavelength tuning of InAs quantum dots grown on InP (100) by chemical-beam epitaxy

Q. Gong, R. Nötzel, P. J. van Veldhoven, T. J. Eijkemans, and J. H. Wolter

Appl. Phys. Lett. 84, 275 (2004); http://dx.doi.org/10.1063/1.1640474 (3 pages) | Cited 44 times

Online Publication Date: 7 January 2004

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We report on an effective way to continuously tune the emission wavelength of InAs quantum dots (QDs) grown on InP (100) by chemical-beam epitaxy. The InAs QD layer is embedded in a GaInAsP layer lattice matched to InP. With an ultrathin GaAs layer inserted between the InAs QD layer and the GaInAsP buffer, the peak wavelength from the InAs QDs can be continuously tuned from above 1.6 μm down to 1.5 μm at room temperature. The major role of the thin GaAs layer is to greatly suppress the As/P exchange during the deposition of InAs and subsequent growth interruption under arsenic flux, as well as to consume the segregated surface In layer floating on the GaInAsP buffer layer. © 2004 American Institute of Physics.
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81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
78.66.Fd III-V semiconductors

Structural perturbations within Ge nanocrystals in silica

A. Cheung, G. de M. Azevedo, C. J. Glover, D. J. Llewellyn, R. G. Elliman, G. J. Foran, and M. C. Ridgway

Appl. Phys. Lett. 84, 278 (2004); http://dx.doi.org/10.1063/1.1639136 (3 pages) | Cited 18 times

Online Publication Date: 7 January 2004

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Extended x-ray absorption fine structure (EXAFS) spectroscopy was used to identify structural perturbations in Ge nanocrystals produced in silica by ion implantation and annealing. Although the nanocrystals retained tetrahedral coordination, both the short- and medium-range orders were perturbed relative to bulk crystalline material. Equivalently, the nanocrystal interatomic distance distribution deviated from that of bulk crystalline Ge, exhibiting enhanced structural disorder of both Gaussian and non-Gaussian forms in the first, second, and third nearest-neighbor shells. The relative influences of nanocrystal size, bonding distortions, multiple phases, and a matrix-induced compression were considered. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.

Growth of monodispersed cobalt nanoparticles on 6H–SiC(0001) honeycomb template

Wei Chen, Kian Ping Loh, Hai Xu, and A. T. S. Wee

Appl. Phys. Lett. 84, 281 (2004); http://dx.doi.org/10.1063/1.1639508 (3 pages) | Cited 21 times

Online Publication Date: 7 January 2004

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We demonstrated an effective way of controlling the size dispersion of surface adsorbed nanoclusters by utilizing a reconstructed template with regular periodic porosity in the nanoscale range. Monodispersed cobalt (Co) nanoclusters of 3 nm sizes have been grown on the reconstructed 6H–SiC(0001) surface by electron-beam evaporation on the C-terminated 6√×6√R30° template at room temperature. In situ scanning tunneling microscopy was used to study the nucleation process of the Co nanoclusters on this template. We found that the average cluster size remains constant for different Co coverage, and the cluster density is linearly dependent on the coverage. The monodispersion of the cluster size is suggested to be due to the physical confinement of the Co clusters by the porous honeycomb structure of the SiC reconstructed surface. X-ray photoelectron spectroscopy reveals that the carbon-rich hexagon template prevents cobalt silicide formation up to an annealing temperature of 1150 °C. © 2004 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Multicolor electroluminescent devices using doped ZnS nanocrystals

K. Manzoor, S. R. Vadera, N. Kumar, and T. R. N. Kutty

Appl. Phys. Lett. 84, 284 (2004); http://dx.doi.org/10.1063/1.1639935 (3 pages) | Cited 44 times

Online Publication Date: 7 January 2004

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Alternate-current electroluminescent (ac EL) devices based on doped ZnS nanocrystals emitting blue, green, and orange-red colors are reported. ZnS nanocrystals doped with Cu+–Al3+ and Cu+–Al3+–Mn2+ combinations were synthesized by wet chemical method at room temperature. The ZnS:Cu+, Al3+ nanocrystals show blue (462 nm) and green (530 nm) EL emissions depending upon the presence and absence of sulphur vacancies, respectively. The orange EL emission (590 nm) is realized from ZnS:Cu+, Al3+, Mn2+ nanoparticles by way of nonradiative energy transfer from AlZn–CuZn pairs to MnZn. The EL devices show low turn-on voltage of ∼10 V ac @100 Hz. The mechanism of ac EL in ZnS nanocrystals has been explained wherein the excitation is attributed to the electric-field-assisted injection of electron-hole pairs from the surface regions into the interiors and their subsequent recombination therein causes emission. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Hydrothermal route to ZnO nanocoral reefs and nanofibers

Jin-Ho Choy, Eue-Soon Jang, Jung-Hee Won, Jae-Hun Chung, Du-Jeon Jang, and Young-Woon Kim

Appl. Phys. Lett. 84, 287 (2004); http://dx.doi.org/10.1063/1.1639514 (3 pages) | Cited 44 times

Online Publication Date: 7 January 2004

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ZnO nanocoral reefs and nanofibers are synthesized on the glass substrate dip coated with ZnO seed with nanoparticles with an average size of 5 nm under a hydrothermal reaction. The ratios of length to diameter for the former and the latter are determined to be 100 and 1000, respectively. In addition, we found that a threshold power density for UV lasing action could be remarkably reduced from 40 kW/cm2 for the nanocoral reefs to 8 kW/cm2 for the nanofibers by increasing the cavity length of ZnO nanowires. © 2004 American Institute of Physics.
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81.16.Be Chemical synthesis methods
81.07.-b Nanoscale materials and structures: fabrication and characterization
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