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21 Oct 2002

Volume 81, Issue 17, pp. 3119-3293

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GaN homoepitaxy on freestanding (1math00) oriented GaN substrates

C. Q. Chen, M. E. Gaevski, W. H. Sun, E. Kuokstis, J. P. Zhang, R. S. Q. Fareed, H. M. Wang, J. W. Yang, G. Simin, M. A. Khan, Herbert-Paul Maruska, David W. Hill, Mitch M. C. Chou, and Bruce Chai

Appl. Phys. Lett. 81, 3194 (2002); http://dx.doi.org/10.1063/1.1516230 (3 pages) | Cited 45 times

Online Publication Date: 15 October 2002

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We report homoepitaxial GaN growth on freestanding (1math00) oriented (M-plane GaN) substrates using low-pressure metalorganic chemical vapor deposition. Scanning electron microscopy, atomic-force microscopy, and photoluminescence were used to study the influence of growth conditions such as the V/III molar ratio and temperature on the surface morphology and optical properties of the epilayers. Optimized growth conditions led to high quality (1math00) oriented GaN epilayers with a smooth surface morphology and strong band-edge emission. These layers also exhibited strong room temperature stimulated emission under high intensity pulsed optical pumping. Since for III-N materials the (1math00) crystal orientation is free from piezoelectric or spontaneous polarization electric fields, our work forms the basis for developing high performance III-N optoelectronic devices. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.66.Fd III-V semiconductors
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps Atomic force microscopy (AFM)
72.80.Ey III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
78.45.+h Stimulated emission

Encapsulation of phosphorus dopants in silicon for the fabrication of a quantum computer

L. Oberbeck, N. J. Curson, M. Y. Simmons, R. Brenner, A. R. Hamilton, S. R. Schofield, and R. G. Clark

Appl. Phys. Lett. 81, 3197 (2002); http://dx.doi.org/10.1063/1.1516859 (3 pages) | Cited 41 times

Online Publication Date: 15 October 2002

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The incorporation of phosphorus in silicon is studied by analyzing phosphorus δ-doped layers using a combination of scanning tunneling microscopy, secondary ion mass spectrometry, and Hall effect measurements. The samples are prepared by phosphine saturation dosing of a Si(100) surface at room temperature, a critical annealing step to incorporate phosphorus atoms, and subsequent epitaxial silicon overgrowth. We observe minimal dopant segregation ( ∼ 5 nm), complete electrical activation at a silicon growth temperature of 250 °C and a high two-dimensional electron mobility of ∼ 102 cm2/V s at a temperature of 4.2 K. These results, along with preliminary studies aimed at further minimizing dopant diffusion, bode well for the fabrication of atomically precise dopant arrays in silicon such as those found in recent solid-state quantum computer architectures. © 2002 American Institute of Physics.
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61.72.S- Impurities in crystals
72.20.My Galvanomagnetic and other magnetotransport effects
66.30.J- Diffusion of impurities
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.72.Cc Kinetics of defect formation and annealing

Coexistence of the Cu3Au type ordered structure and the fine modulation in CdxZn1−xTe epilayers grown on GaAs substrates

H. S. Lee, J. Y. Lee, T. W. Kim, D. C. Choo, and H. L. Park

Appl. Phys. Lett. 81, 3200 (2002); http://dx.doi.org/10.1063/1.1517177 (3 pages) | Cited 1 time

Online Publication Date: 15 October 2002

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Selected-area electron diffraction pattern (SADP) and transmission electron microscopy (TEM) measurements were carried out to investigate the spontaneously ordered structure in CdxZn1−xTe epitaxial layers grown on (001) GaAs substrates. The SADP showed superstructure reflections with symmetrical intensity, and the high-resolution TEM (HRTEM) image showed doublet periodicity in the contrast of the {100} and {110} lattice planes. The results of the SADP and HRTEM measurements showed that Cu3Au type ordered structures were formed in the CdxZn1−xTe epitaxial layers. The dark-field TEM image showed that the size of the Cu3Au type ordered domains with a rectangular-like shape was approximately 15 ∼ 30 nm thick, with widths ranging from 30 to 200 nm. Fine modulations in the ordered domains were also observed. These results provide important information on the microstructural properties for enhancing the efficiencies of CdxZn1−xTe-based optoelectronic devices operating at the blue-green region of the spectrum. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Density-dependent critical currents in quantum-well-coupled weak links

T. A. Eckhause, K. Lehnert, J. S. Correa, R. J. Jorstad, E. G. Gwinn, and Mason Thomas

Appl. Phys. Lett. 81, 3203 (2002); http://dx.doi.org/10.1063/1.1517174 (3 pages) | Cited 1 time

Online Publication Date: 15 October 2002

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We investigate a Josephson field-effect transistor in which the electron gas in an InAs quantum well serves as the weak link between superconducting Nb electrodes. We modulate the density Ns of electrons and the critical current Ic in the weak link by applying a voltage to an insulated gate. Measurements of the dependence of Ic on Ns are in good agreement with a model in which each occupied subband of the InAs quantum well makes an independent contribution to Ic. Inclusion of the nonparabolic band structure in InAs is crucial to this agreement. © 2002 American Institute of Physics.
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85.25.Cp Josephson devices
74.50.+r Tunneling phenomena; Josephson effects
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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Simulations and experiments on magneto-optical diffraction by an array of epitaxial Fe(001) microsquares

P. García-Mochales, J. L. Costa-Krämer, G. Armelles, F. Briones, D. Jaque, J. I. Martín, and J. L. Vicent

Appl. Phys. Lett. 81, 3206 (2002); http://dx.doi.org/10.1063/1.1514388 (3 pages) | Cited 10 times

Online Publication Date: 15 October 2002

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Magneto-optic (MO) experimental and computational studies are reported on arrays of epitaxial Fe(001) microsquares. Measuring the transverse Kerr signal, in both reflected and diffracted spots, when the array is exposed to a rotating magnetic field allows the quantification of the magnetization inhomogeneties within the microsquares. The MO signal at diffracted spots is extremely sensitive to magnetization inhomogeneities, while working at a large constant field amplitude eliminates uncertainties due to domain-wall movements. The presence of anomalous peaks at the diffracted MO response is unambiguously assigned to the matching of inhomogeneities of the magnetization distribution to the corresponding pattern periodicity. Interaction between microsquares appears as a second-order effect. © 2002 American Institute of Physics.
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78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Possible solution of the grain-boundary problem for applications of high-Tc superconductors

G. Hammerl, A. Herrnberger, A. Schmehl, A. Weber, K. Wiedenmann, C. W. Schneider, and J. Mannhart

Appl. Phys. Lett. 81, 3209 (2002); http://dx.doi.org/10.1063/1.1516831 (3 pages) | Cited 15 times

Online Publication Date: 15 October 2002

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It is shown that the critical current density of high-Tc wires can be greatly enhanced by using a three-fold approach, which consists of grain alignment, doping, and optimization of the grain architecture. According to model calculations, current densities of 4×106 A/cm2 can be achieved for an average grain alignment of 10° at 77 K. Based on this approach, a road to competitive high-Tc cables is proposed. © 2002 American Institute of Physics.
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74.72.-h Cuprate superconductors
84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
61.72.Mm Grain and twin boundaries
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Dielectric properties of sol–gel-derived MgO:Ba0.5Sr0.5TiO3 thin-film composites

M. Jain, S. B. Majumder, R. S. Katiyar, D. C. Agrawal, and A. S. Bhalla

Appl. Phys. Lett. 81, 3212 (2002); http://dx.doi.org/10.1063/1.1515879 (3 pages) | Cited 28 times

Online Publication Date: 15 October 2002

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Alternate layer deposition of heterostructured magnesium oxide (MgO):barium strontium titanate (BST) thin films is demonstrated to be an approach to synthesize dielectric films with a higher figure of merit for microwave dielectric applications. The dielectric constant and the dielectric tunability are modified by MgO insertion. The dramatic reduction in the dielectric loss tangent effectively increased the figure of merit of the heterostructured thin films as compared to the pure BST films. The significant reduction in the dielectric loss tangent values has been attributed to the minute solid solubility of MgO in the BST lattice and the induced microstructural modifications induced by the MgO layers in thin films. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Lf Composite materials
77.22.Gm Dielectric loss and relaxation
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Scanning force microscopy investigation of the Pb(Zr0.25Ti0.75)O3/Pt interface

X. M. Lu, F. Schlaphof, S. Grafström, C. Loppacher, L. M. Eng, G. Suchaneck, and G. Gerlach

Appl. Phys. Lett. 81, 3215 (2002); http://dx.doi.org/10.1063/1.1512961 (3 pages) | Cited 29 times

Online Publication Date: 15 October 2002

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We report on a novel approach for the investigation of the Pb(ZrxTi1−x)O3/Pt interface applying scanning force microscopy techniques. Ferroelectric samples (PZTfilm/Pt/SiO2/Si) were polished at a shallow angle (∼6.1°) thereby enlarging the film cross section from a 430 nm film thickness to a width of more than 4 μm. Piezoresponse force microscopy and Kelvin probe force microscopy were applied in order to deduce the dielectric polarization P and local potential distribution over the full cross section. We clearly observe a transition layer with a thickness of ∼240 nm which manifests itself both in a gradual decrease of the piezoresponse signal as a function of film thickness and in a corresponding variation of the surface potential. Furthermore, after polarization reversal due to a dc voltage applied to the tip, a different retention behavior was observed within the transition layer. The results are tentatively attributed to negatively charged defects accumulated at the PZT/Pt interface. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.65.-j Piezoelectricity and electromechanical effects
68.37.Ps Atomic force microscopy (AFM)
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena
68.35.Ct Interface structure and roughness

Oxygen tracer studies of ferroelectric fatigue in Pb(Zr,Ti)O3 thin films

Lawrence F. Schloss, Paul C. McIntyre, Bryan C. Hendrix, Steven M. Bilodeau, Jeffrey F. Roeder, and Stephen R. Gilbert

Appl. Phys. Lett. 81, 3218 (2002); http://dx.doi.org/10.1063/1.1516628 (3 pages) | Cited 12 times

Online Publication Date: 15 October 2002

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Long-range oxygen motion has been observed in Pt/Pb(Zr,Ti)O3/Ir thin-film structures after electrical fatigue cycling at room temperature. Through an exchange anneal, isotopic 18O was incorporated as a tracer into bare Pb(Zr,Ti)O3 (PZT) films, allowing secondary ion mass spectrometry measurements of the tracer profile evolution as a function of the number of polarization reversals. Observation of 18O tracer redistribution during voltage cycling, which is presumably mediated by oxygen vacancy motion, was found to be strongly dependent upon the thermal history of the film. However, there was no strong correlation between the extent of 18O tracer redistribution and the extent of polarization suppression induced by voltage cycling. Our results suggest that oxygen vacancy motion plays, at most, a secondary role in ferroelectric fatigue of PZT thin films. © 2002 American Institute of Physics.
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77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
66.30.H- Self-diffusion and ionic conduction in nonmetals
61.72.J- Point defects and defect clusters
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
77.22.Ej Polarization and depolarization

Ferroelectric properties of (117)- and (001)-oriented Bi3.25La0.75Ti3O12 polycrystalline thin films

Yu-Ming Sun, Yi-Chan Chen, Jon-Yiew Gan, and Jenn-Chang Hwang

Appl. Phys. Lett. 81, 3221 (2002); http://dx.doi.org/10.1063/1.1516234 (3 pages) | Cited 42 times

Online Publication Date: 15 October 2002

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Highly (117)- and (001)-oriented Bi3.25La0.75Ti3O12 (BLT) thin films were fabricated on Pt/TiO2/SiO2/Si(100) substrates by chemical solution deposition under the appropriate baking and crystallization conditions. The (117)-oriented BLT films exhibited higher remanent polarization (2Pr = 24 μC/cm2), than did (001)-oriented BLT films, which exhibited only a slight amount of polarization (2Pr = 6.6 μC/cm2). The results of fatigue and retention tests revealed that neither film was fatigued up to 1×1010 switching cycles, and the retained charge was unchanged for 1×104 s. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization

Dependence of ferroelectric performance of sol–gel-derived Pb(Zr,Ti)O3 thin films on bottom-Pt-electrode thickness

Ji-Eun Lim, Dong-Yeon Park, Jae Kyeong Jeong, Gregor Darlinski, Hyeong Joon Kim, Cheol Seong Hwang, Seung-Hyun Kim, Chang-Young Koo, Hyun-Jung Woo, Dong-Su Lee, and Jowoong Ha

Appl. Phys. Lett. 81, 3224 (2002); http://dx.doi.org/10.1063/1.1516830 (3 pages) | Cited 10 times

Online Publication Date: 15 October 2002

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Pb(Zr,Ti)O3 (PZT) thin films were deposited on Pt/Ti and Pt/IrO2 electrode stacks with various Pt thicknesses (30–200 nm) by a sol–gel process. The sputter-deposited Pt films showed a (111)-preferred texture irrespective of the thickness. However, a high-resolution x-ray diffraction study of the Pt films showed that the films were composed of three kinds of grains with slightly different lattice parameters. The grains with a bulk-like lattice parameter grew with increasing Pt thickness, which was accompanied with an improvement in the crystalline quality. Accordingly, the crystallization and ferroelectric behavior of the 100-nm-thick PZT films improved with increasing Pt film thickness. However, the PZT films on the Pt/IrO2 electrode showed a deteriorated ferroelectric performance due to the outward diffusion of the Ir (O) onto the Pt surface, which increases the depolarizing field and amount of charge injection by the formation of a conducting phase. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.22.Ej Polarization and depolarization
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Platinum-assisted phase transition in bismuth-based layer-structured ferroelectric CaBi4Ti4O15 thin films

Kazumi Kato, Kazuyuki Suzuki, Desheng Fu, Kaori Nishizawa, and Takeshi Miki

Appl. Phys. Lett. 81, 3227 (2002); http://dx.doi.org/10.1063/1.1517179 (3 pages) | Cited 20 times

Online Publication Date: 15 October 2002

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The phase transition of nonferroelectric pyrochlore to ferroelectric perovskite in CaBi4Ti4O15 thin films depends on platinum bottom electrodes. Rather than the strain and crystallinity of the bottom electrode, matching of the atomic arrangement to the Ca–Bi–Ti–O thin films is predominant. CaBi4Ti4O15 thin films crystallized on (200)-oriented platinum at 650 °C showed c-axis orientation. In contrast, thin films crystallized on highly crystalline (111)-oriented platinum at the same temperature contained pyrochlore grains which were about several tens of nanometers in diameter and located in the interface region. They showed P–V hysteresis loops. The remanent polarization and coercive electric field depended on platinum top electrode size. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
68.55.-a Thin film structure and morphology
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Role of grain boundaries on hydrogen-induced degradation in lead zirconate titanate thin films

Jang-Sik Lee and Seung-Ki Joo

Appl. Phys. Lett. 81, 3230 (2002); http://dx.doi.org/10.1063/1.1516233 (3 pages) | Cited 8 times

Online Publication Date: 15 October 2002

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It is well known that exposing lead zirconate titanate (PZT) thin films to hydrogen severely degrades the electrical properties. This phenomenon has been the subject of intensive study; however, there is no electrical evidence relating the hydrogen-induced degradation with the grain boundaries in the films. In this work, using large-grained PZT thin films (average grain size: 40 μm), we could measure the effects of grain boundary on the hydrogen-induced degradation in PZT thin films by locating the upper Pt electrode (8×8 μm2) sequentially from the center of the grain to the grain boundary in a controlled manner. It was found that the grain boundary was mainly responsible for the electrical degradation caused by exposure to the hydrogen. Little degradation with hydrogen exposure was observed when the Pt top electrode was located in the center of the grain. © 2002 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries
77.80.Dj Domain structure; hysteresis
77.22.Jp Dielectric breakdown and space-charge effects
77.22.Ej Polarization and depolarization
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Periodic array of intramolecular junctions of silicon nanowires

D. D. D. Ma, C. S. Lee, Y. Lifshitz, and S. T. Lee

Appl. Phys. Lett. 81, 3233 (2002); http://dx.doi.org/10.1063/1.1514399 (3 pages) | Cited 4 times

Online Publication Date: 15 October 2002

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The formation of periodic arrays of intramolecular junctions in silicon nanowires from a single growth process is reported. Scanning tunneling microscopic images show intramolecular junctions formed by fusing together two straight wire segments ( ∼ 3 nm in diameter) 5 and 10 nm long, respectively, at an angle of ∼ 30° with respect to each other. The junction repeats itself in a regular pattern along a nanowire, forming a striking superlattice ∼ 3 nm in diameter and at least several microns long. Scanning tunneling spectroscopic measurements reveal distinctly different current–voltage curves for the two different segments changing sharply across each junction. The segments are most probably formed by a periodic change of growth direction while the different electronic properties of the two segments forming the junction are attributed to the differences in surface structure and segment diameter. © 2002 American Institute of Physics.
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73.63.Nm Quantum wires
68.65.La Quantum wires (patterned in quantum wells)
81.07.Vb Quantum wires
68.65.Cd Superlattices
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Growth of self-assembled GaN quantum dots via the vapor–liquid–solid mechanism

C.-W. Hu, A. Bell, F. A. Ponce, D. J. Smith, and I. S. T. Tsong

Appl. Phys. Lett. 81, 3236 (2002); http://dx.doi.org/10.1063/1.1514394 (3 pages) | Cited 14 times

Online Publication Date: 15 October 2002

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Self-assembled nanometer-scale GaN quantum dots were fabricated on 6H–SiC(0001) substrates via the formation of Ga liquid droplets and their subsequent nitridation with a supersonic gas source seeded with NH3 molecules. The entire process was observed and controlled in situ and in real time in a low-energy electron microscope. The microstructure of the quantum dots was studied by high-resolution cross-sectional transmission electron microscopy illustrating the perfectly coherent wurtzite structure of GaN quantum dots with 5 nm base width. Spatially resolved cathodoluminescence spectra yield the characteristic band edge emission near 3.48 eV for larger size GaN dots. © 2002 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
81.07.Ta Quantum dots
78.60.Hk Cathodoluminescence, ionoluminescence
81.16.Dn Self-assembly

Light emission from the shadows: Surface plasmon nano-optics at near and far fields

S. C. Hohng, Y. C. Yoon, D. S. Kim, V. Malyarchuk, R. Müller, Ch. Lienau, J. W. Park, K. H. Yoo, J. Kim, H. Y. Ryu, and Q. H. Park

Appl. Phys. Lett. 81, 3239 (2002); http://dx.doi.org/10.1063/1.1515134 (3 pages) | Cited 48 times

Online Publication Date: 15 October 2002

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When light illuminates a thick metal film perforated with small holes, shadows appear. At the nanoscopic level, however, light can be emitted predominantly from the metal surfaces between the holes—shadows can be indeed brighter than the lighted holes. The symmetry of the near-field emission pattern is determined by the symmetry of the surface plasmon waves. Surprisingly, these nanoscopic emission patterns from the metal can be preserved to the far-field region, where the pattern becomes sinusoidal. This unusual behavior of light emission from the shadows is explained by efficient wave vector selection. © 2002 American Institute of Physics.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
42.82.-m Integrated optics

Electroluminescence at 1.54 μm in Er-doped Si nanocluster-based devices

F. Iacona, D. Pacifici, A. Irrera, M. Miritello, G. Franzò, F. Priolo, D. Sanfilippo, G. Di Stefano, and P. G. Fallica

Appl. Phys. Lett. 81, 3242 (2002); http://dx.doi.org/10.1063/1.1516235 (3 pages) | Cited 84 times

Online Publication Date: 15 October 2002

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The electroluminescence (EL) properties of Er-doped Si nanoclusters (NC) embedded in metal–oxide–semiconductor devices are investigated. Due to the presence of Si NC dispersed in the SiO2 matrix, an efficient carrier injection occurs and Er is excited, producing an intense 1.54 μm room temperature EL. The EL properties as a function of the current density, temperature, and time have been studied in detail. We have also estimated the excitation cross section for Er under electrical pumping, finding a value of ∼ 1×10−14 cm2. This value is two orders of magnitude higher than the effective excitation cross section of Er ions through Si NC under optical pumping. In fact, quantum efficiencies of ∼1% are obtained at room temperature in these devices. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.60.Fi Electroluminescence

Focused-electron-beam-induced deposition of freestanding three-dimensional nanostructures of pure coalesced copper crystals

I. Utke, A. Luisier, P. Hoffmann, D. Laub, and P. A. Buffat

Appl. Phys. Lett. 81, 3245 (2002); http://dx.doi.org/10.1063/1.1517180 (3 pages) | Cited 52 times

Online Publication Date: 15 October 2002

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We report on direct writing of three-dimensional freestanding nanostructures of Cu by use of a focused electron beam (FEB) and the metalorganic precursor hfac-Cu-TMVS. Freestanding horizontal rods were deposited over about 10 μm length and consist of small 2–5 nm Cu nanocrystals dispersed in an amorphous matrix containing carbon, fluorine, silicon, and oxygen. The freestanding horizontal rods were used as support for further vertical deposits resulting in tips of coalesced facetted Cu nanocrystals of up to 100 nm in size. The almost constant deposition rate of 5–6 nm/s is in contrast to vertical tips on bulk supports, which show a deposition rate decreasing from 23 to 10 nm/s. The above results suggest a thermal decomposition process induced by electron energy absorption. © 2002 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
85.40.Sz Deposition technology
81.05.Bx Metals, semimetals, and alloys
61.46.-w Structure of nanoscale materials

Stress-induced growth of bismuth nanowires

Yang-Tse Cheng, Anita M. Weiner, Curtis A. Wong, Michael P. Balogh, and Michael J. Lukitsch

Appl. Phys. Lett. 81, 3248 (2002); http://dx.doi.org/10.1063/1.1515885 (3 pages) | Cited 26 times

Online Publication Date: 15 October 2002

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We report a method of making nanowires of bismuth (Bi) with diameters ranging from 30 to 200 nm and lengths up to several millimeters. The nanowires are extruded spontaneously at the rate of a few micrometers per second at room temperature from the surfaces of freshly grown composite thin films consisting of Bi and chrome–nitride. The high compressive stress in these composite thin films is the driving force responsible for the nanowire formation. This mechanism can also be used to create nanowires of other materials. © 2002 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
81.07.Vb Quantum wires
61.46.-w Structure of nanoscale materials
68.65.La Quantum wires (patterned in quantum wells)
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation

Filamentation and linewidth enhancement factor in InGaAs quantum dot lasers

P. M. Smowton, E. J. Pearce, H. C. Schneider, W. W. Chow, and M. Hopkinson

Appl. Phys. Lett. 81, 3251 (2002); http://dx.doi.org/10.1063/1.1516236 (3 pages) | Cited 28 times

Online Publication Date: 15 October 2002

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We report measurements of the near-field of broad-area lasers with quantum dot and quantum well active regions designed to emit at 1 μm. The quantum dot devices exhibit less filamentation than comparable quantum well devices, and exhibit a reduction in filamentation as the injection level is increased. This is consistent with a theory that includes the Coulomb coupling between dot and wetting-layer states on a microscopic level. The theory predicts a linewidth enhancement factor from −3 to 1, depending on carrier density and inhomogeneous broadening. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Self-organized strain engineering on GaAs (311)B: Template formation for quantum dot nucleation control

Q. Gong, R. Nötzel, G. J. Hamhuis, T. J. Eijkemans, and J. H. Wolter

Appl. Phys. Lett. 81, 3254 (2002); http://dx.doi.org/10.1063/1.1516637 (3 pages) | Cited 7 times

Online Publication Date: 15 October 2002

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A matrix of closely packed cells develops during molecular-beam epitaxy of In0.35Ga0.65As on GaAs (311)B, due to strain-driven growth instability. The established lateral strain distribution generates a unique template that controls the nucleation and growth of InAs quantum dots (QDs). The QDs exhibit pronounced improvement of the structural and optical properties with efficient carrier transfer from the template. Thus, self-organization of a two-dimensionally connected quantum dot network is demonstrated. © 2002 American Institute of Physics.
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81.07.Ta Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.Dn Self-assembly
68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Impedance analysis of a radio-frequency single-electron transistor

H. D. Cheong, T. Fujisawa, T. Hayashi, Y. Hirayama, and Y. H. Jeong

Appl. Phys. Lett. 81, 3257 (2002); http://dx.doi.org/10.1063/1.1515883 (3 pages) | Cited 14 times

Online Publication Date: 15 October 2002

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We investigate rf transport through an AlGaAs/GaAs single-electron transistor (SET). The presented rf–SET scheme provides a transmission coefficient proportional to the admittance of the device, which is desirable for impedance analysis as well as for high-sensitivity charge detection. The impedance of a SET, including the small tunneling capacitance, is successfully analyzed at the high frequency of 643 MHz, and is compared with a simple model. The ability to measure the impedance of a SET would expand the measurable regime of single-electron tunneling behavior. © 2002 American Institute of Physics.
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85.35.Gv Single electron devices
85.30.De Semiconductor-device characterization, design, and modeling
84.40.Dc Microwave circuits
73.23.Hk Coulomb blockade; single-electron tunneling
73.40.Gk Tunneling

Carbon nanotube memory devices of high charge storage stability

J. B. Cui, R. Sordan, M. Burghard, and K. Kern

Appl. Phys. Lett. 81, 3260 (2002); http://dx.doi.org/10.1063/1.1516633 (3 pages) | Cited 78 times

Online Publication Date: 15 October 2002

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Molecular memory devices with semiconducting single-walled carbon nanotubes constituting a channel of 150 nm in length are described. Data storage is achieved by sweeping gate voltages in the range of 3 V, associated with a storage stability of more than 12 days at room temperature. By annealing in air or controlled oxygen plasma exposure, efficient switching devices could be obtained from thin nanotube bundles that originally showed only a small gate dependence of conductance. © 2002 American Institute of Physics.
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85.35.Kt Nanotube devices
73.63.Fg Nanotubes
81.07.Nb Molecular nanostructures

Nanopatterning of Si/SiGe electrical devices by atomic force microscopy oxidation

Xiang-Zheng Bo, Leonid P. Rokhinson, Haizhou Yin, D. C. Tsui, and J. C. Sturm

Appl. Phys. Lett. 81, 3263 (2002); http://dx.doi.org/10.1063/1.1515113 (3 pages) | Cited 12 times

Online Publication Date: 15 October 2002

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Two nanopatterning methods for silicon/silicon-germanium (Si/SiGe) heterostructures are demonstrated: (1) direct atomic force microscopy (AFM) oxidation on SiGe layers and (2) AFM oxidation on silicon followed by selective wet etching of SiGe. When directly oxidizing SiGe alloys, minimum linewidths of 20 nm were achieved by adjusting the bias voltage of the AFM tip. By AFM oxidation and selective wet etching, a 10-nm-thick conducting SiGe layer was patterned to form features under ∼50 nm. Fabricated SiGe quantum dots with side gates exhibited Coulomb blockade oscillation. © 2002 American Institute of Physics.
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81.16.Pr Micro- and nano-oxidation
81.16.Ta Atom manipulation
81.65.Cf Surface cleaning, etching, patterning
81.65.Mq Oxidation
73.23.Hk Coulomb blockade; single-electron tunneling
81.05.Cy Elemental semiconductors
81.05.Hd Other semiconductors
85.35.Ds Quantum interference devices
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Nondispersive hole transport in a spin-coated dendrimer film measured by the charge-generation-layer time-of-flight method

Jonathan P. J. Markham, Thomas D. Anthopoulos, Ifor D. W. Samuel, Gary J. Richards, Paul L. Burn, Chan Im, and Heinz Bässler

Appl. Phys. Lett. 81, 3266 (2002); http://dx.doi.org/10.1063/1.1514400 (3 pages) | Cited 15 times

Online Publication Date: 15 October 2002

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Measurements of the mobility of a first-generation (G1) bis-fluorene cored dendrimer have been performed on spin-coated samples of 500 nm thickness using the charge-generation-layer time-of-flight (TOF) technique. A 10 nm perylene charge generation layer was excited by the 532 nm line of a Q-switched Nd:YAG laser and the generated carriers swept through the dendrimer film under an applied field. We observe nondispersive hole transport in the dendrimer layer with a room-temperature mobility μ = 2.0×10−4 cm2/V s at a field of 0.55 MV/cm. There is a weak field dependence of the mobility and it increases from μ = 1.6×10−4 cm2/V s at 0.2 MV/cm to μ = 3.0×10−4 cm2/V s at 1.4 MV/cm. These results suggest that the measurement of mobility by TOF in spin-coated samples on thickness scales relevant to organic light-emitting diodes can yield valuable information, and that dendrimers are promising materials for device applications. © 2002 American Institute of Physics.
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73.61.Ph Polymers; organic compounds
85.60.Jb Light-emitting devices
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
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