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3 Nov 2003

Volume 83, Issue 18, pp. 3647-3835

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 3737 (2003); http://dx.doi.org/10.1063/1.1623315 (3 pages)

Ian Appelbaum, D. J. Monsma, K. J. Russell, V. Narayanamurti, and C. M. Marcus
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Double-scaled potential profile in a group-III nitride alloy revealed by Monte Carlo simulation of exciton hopping

K. Kazlauskas, G. Tamulaitis, A. Žukauskas, M. A. Khan, J. W. Yang, J. Zhang, G. Simin, M. S. Shur, and R. Gaska

Appl. Phys. Lett. 83, 3722 (2003); http://dx.doi.org/10.1063/1.1625111 (3 pages) | Cited 29 times

Online Publication Date: 28 October 2003

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The temperature dependences of the peak position and width of the photoluminescence band in Al0.1In0.01Ga0.89N layers were explained by Monte Carlo simulation of exciton localization and hopping. The introduction of a doubled-scaled potential profile due to inhomogeneous distribution of indium allowed obtaining a good quantitative fit of the experimental data. Hopping of excitons was assumed to occur through localized states distributed on a 16 meV energy scale within the In-rich clusters with the average energy in these clusters dispersed on a larger (42 meV) scale. © 2003 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.55.Cr III-V semiconductors
02.70.Uu Applications of Monte Carlo methods

Light-induced defect states in hydrogenated amorphous silicon centered around 1.0 and 1.2 eV from the conduction band edge

J. M. Pearce, J. Deng, R. W. Collins, and C. R. Wronski

Appl. Phys. Lett. 83, 3725 (2003); http://dx.doi.org/10.1063/1.1624637 (3 pages) | Cited 8 times

Online Publication Date: 28 October 2003

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To take into account the presence of multiple light-induced defect states in hydrogenated amorphous silicon (a-Si:H) the evolution of the entire spectra of photoconductive subgap absorption, α(hν), has been analyzed. Using this approach two distinctly different light-induced defect states centered around 1.0 and 1.2 eV from the conduction band edge are clearly identified. Results are presented on their evolution and respective effects on carrier recombination that clearly point to the importance of these states in evaluating the stability of different a-Si:H solar cell materials, as well as elucidating the origin of the Staebler–Wronski effect. © 2003 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
71.55.Cn Elemental semiconductors
71.55.Jv Disordered structures; amorphous and glassy solids
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors
72.80.Ng Disordered solids

Inherent nature of localized states in highly planar monolayer InAs/GaAsN pseudo-alloys

I. L. Krestnikov, R. Heitz, N. N. Ledentsov, A. Hoffmann, A. M. Mintairov, T. H. Kosel, J. L. Merz, I. P. Soshnikov, and V. M. Ustinov

Appl. Phys. Lett. 83, 3728 (2003); http://dx.doi.org/10.1063/1.1623320 (3 pages) | Cited 3 times

Online Publication Date: 28 October 2003

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We have studied the optical properties of pseudo-alloy monolayer InAs/GaAsN superlattices with highly planar interfaces. In spite of the two-dimensional growth mode, we found that the photoluminescence (PL) reveals strong exciton localization through the whole PL band, dominating the spectrum up to high excitation densities and observation temperatures. Pump-and-probe PL experiments provide the following time constants: (a) the exciton relaxation time to the ground states of the localization regions is found to be ∼40–70 ps, depending on the photon energy, and (b) the time for depopulation of these localized states is between 2 and 4 ns. © 2003 American Institute of Physics.
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73.21.Cd Superlattices
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
68.35.Ct Interface structure and roughness
73.20.At Surface states, band structure, electron density of states
73.20.Fz Weak or Anderson localization
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.22.Lp Collective excitations
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Intrinsic limits on electron mobility in dilute nitride semiconductors

S. Fahy and E. P. O’Reilly

Appl. Phys. Lett. 83, 3731 (2003); http://dx.doi.org/10.1063/1.1622444 (3 pages) | Cited 43 times

Online Publication Date: 28 October 2003

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A fundamental connection is established between the composition-dependence of the conduction band edge energy and the n-type carrier scattering cross section in the ultradilute limit for semiconductor alloys, imposing general limits on the carrier mobility in such alloys. From the measured nitrogen composition dependence of the bandgap in GaAs1−xNx, the carrier scattering cross section of substitutional nitrogen defects in GaAs is estimated to be 0.3 nm2. Within an independent scattering approximation, the carrier mobility is then estimated to be ∼ 1000 cm2/V s for a nitrogen atomic concentration of 1%, comparable to the highest measured mobility in high-quality GaInNAs samples at these N concentrations, but substantially higher than that found in many samples. This gives an intrinsic upper bound on the carrier mobility in these materials. © 2003 American Institute of Physics.
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72.20.Ee Mobility edges; hopping transport
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors
61.66.Bi Elemental solids
61.66.Dk Alloys
71.20.Nr Semiconductor compounds

Band offsets for the epitaxial TiO2/SrTiO3/Si(001) system

A. C. Tuan, T. C. Kaspar, T. Droubay, J. W. Rogers, and S. A. Chambers

Appl. Phys. Lett. 83, 3734 (2003); http://dx.doi.org/10.1063/1.1625113 (3 pages) | Cited 31 times

Online Publication Date: 28 October 2003

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We have used x-ray photoelectron spectroscopy with high energy resolution to determine band discontinuities at the two buried interfaces of the epitaxial TiO2 (anatase)/SrTiO3/Si(001) system. The valence band offsets are −2.1±0.1 eV and +0.2±0.1 eV at the SrTiO3/Si and TiO2/SrTiO3 heterojunctions, respectively. Assuming bulk band gaps for the SrTiO3 and TiO2 epitaxial films, the associated conduction band offsets are +0.1±0.1 eV and +0.1±0.1 eV. Si at the interface is in a flatband state, indicating a very low density of electronic states. These results suggest that spin-polarized electron injection from ferromagnetic Co-doped TiO2 anatase into Si should be facile. © 2003 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Pq Other materials
79.60.Jv Interfaces; heterostructures; nanostructures
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.25.Mk Spin transport through interfaces
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Spin-valve photodiode

Ian Appelbaum, D. J. Monsma, K. J. Russell, V. Narayanamurti, and C. M. Marcus

Appl. Phys. Lett. 83, 3737 (2003); http://dx.doi.org/10.1063/1.1623315 (3 pages) | Cited 8 times

Online Publication Date: 28 October 2003

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An optical spin-valve effect is observed using sub-bandgap internal photoemission to generate and collect hot electrons in magnetic multilayers grown on n-Si. Approximately 1.5%–2.5% magnetoresistance is observed in this two-terminal device at low temperature, and this effect is reduced only to 1.1% at room temperature. A simple model is presented to explain the results. © 2003 American Institute of Physics.
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72.25.Fe Optical creation of spin polarized carriers
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.21.Ac Multilayers
85.60.Dw Photodiodes; phototransistors; photoresistors
73.50.Fq High-field and nonlinear effects
73.50.Mx High-frequency effects; plasma effects

Correlation between the superconducting and structural properties in MgB2 thin films prepared by molecular-beam epitaxy

Hiroki Yamazaki, Yasuyuki Hikita, Hiroki Hori, and Hidenori Takagi

Appl. Phys. Lett. 83, 3740 (2003); http://dx.doi.org/10.1063/1.1623323 (3 pages) | Cited 3 times

Online Publication Date: 28 October 2003

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Superconducting MgB2 films were prepared on an Al2O3(0001) substrate by codeposition of Mg and B using the molecular-beam epitaxy technique and the effects of the growth conditions on the structural and the superconducting properties were extensively investigated. The superconducting transition temperature Tc shows a peak as a function of the deposition-rate ratio of Mg to B2 and the stoichiometric composition is likely realized at the Tc peak. The optimum substrate temperature Ts was found to be 330 °C. Detailed structural characterizations indicate the strong suppression of structural coherence in the stoichiometric and Mg-rich films. This accounts for the fact that optimized Tc (26.6 K) is still lower than bulk Tc like in previous molecular-beam epitaxy studies. We argue that such structural disorder originates from epitaxial strain due to the lattice mismatch between the film and the substrate. © 2003 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
68.55.-a Thin film structure and morphology
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Magnetoresistance in boron carbide junctions

L. Bernard, J. Monson, A. Sokolov, Zong-Yuan Liu, C.-S. Yang, P. A. Dowben, B. Doudin, A. Harken, P. Welsch, and B. W. Robertson

Appl. Phys. Lett. 83, 3743 (2003); http://dx.doi.org/10.1063/1.1621072 (3 pages) | Cited 8 times

Online Publication Date: 28 October 2003

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Photoemission and electric transport properties of ferromagnet–insulator–ferromagnet junctions with boron carbide (C2B10) dielectric barrier are presented. Using a non-oxide barrier confidence avoids oxidation of the interfaces with the ferromagnetic layers. Photoemission confirms chemical abruptness of the interface. Magnetoresistance ratios reaching 50% are observed at low temperatures, and large nonlinearity in the current–voltage curves show that impurities in the junctions play a key role. © 2003 American Institute of Physics.
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73.40.Rw Metal-insulator-metal structures
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
79.60.Jv Interfaces; heterostructures; nanostructures

Ferromagnetism in Mn-doped CuO

S. G. Yang, T. Li, B. X. Gu, Y. W. Du, H. Y. Sung, S. T. Hung, C. Y. Wong, and A. B. Pakhomov

Appl. Phys. Lett. 83, 3746 (2003); http://dx.doi.org/10.1063/1.1623944 (3 pages) | Cited 33 times

Online Publication Date: 28 October 2003

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Ferromagnetic properties have been observed in CuO doped with 3.5–15 at. % of Mn. The transition from ferromagnetic to paramagnetic phase at TC = 80 K is associated with the metal–insulator transition. Magnetoresistance is weakly negative in the vicinity of the transition, but positive in a wide range of temperatures below TC. The experimental results suggest a possibility of interpretation in terms of the Zener double-exchange mechanism and strong electron–phonon interactions. © 2003 American Institute of Physics.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.47.Pq Other materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.60.+g Mixed conductivity and conductivity transitions
72.20.My Galvanomagnetic and other magnetotransport effects
72.25.Hg Electrical injection of spin polarized carriers
75.30.Et Exchange and superexchange interactions
63.20.K- Phonon interactions
72.80.Ga Transition-metal compounds

Recording potential of a single-domain particle

N. A. Usov, Ching-Ray Chang, and Zung-Hang Wei

Appl. Phys. Lett. 83, 3749 (2003); http://dx.doi.org/10.1063/1.1623921 (3 pages) | Cited 4 times

Online Publication Date: 28 October 2003

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The ratio of the coercive force Hc to the effective energy barrier Uef is introduced to characterize the recording capability of a single-domain particle. It is shown that this ratio depends on the shape of the energy barrier separating equivalent energy minima. The optimal shape of the barrier is obtained for particles with uniaxial and combined (both uniaxial and cubic) types of magnetic anisotropy. For the optimal shapes, the gain in the ratio Hc/Uef can achieve 20%–40% with respect to the case of a Stoner–Wohlfarth particle. © 2003 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure

Behavior of magnetic domains during structural transformations in Ni2MnGa ferromagnetic shape memory alloy

H. S. Park, Y. Murakami, D. Shindo, V. A. Chernenko, and T. Kanomata

Appl. Phys. Lett. 83, 3752 (2003); http://dx.doi.org/10.1063/1.1624633 (3 pages) | Cited 22 times

Online Publication Date: 28 October 2003

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Change in the magnetic domain structure of Ni2MnGa Heusler alloy with the structural transformation from the parent phase to the intermediate phase and subsequent transformation to the martensite was studied by in situ observations using Lorentz microscopy and electron holography. Both the parent phase and the intermediate phase showed peculiar stripe magnetic domains, and the observed magnetization distribution was similar to each other. In contrast, the magnetization distribution was dramatically modified by the transformation to the tetragonal martensite. The observation appears to indicate that the magnetization distribution in the parent phase can interact with the short-wave lattice distortions to generate the intermediate phase, via the magnetoelastic interaction, resulting in the inheritance of the original magnetization distribution into the intermediate phase. © 2003 American Institute of Physics.
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75.60.Ch Domain walls and domain structure
75.50.Cc Other ferromagnetic metals and alloys
62.20.F- Deformation and plasticity
64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction
81.40.Lm Deformation, plasticity, and creep

Nonrandom percolation behavior of grain boundary networks in high-Tc superconductors

M. Frary and C. A. Schuh

Appl. Phys. Lett. 83, 3755 (2003); http://dx.doi.org/10.1063/1.1624490 (3 pages) | Cited 15 times

Online Publication Date: 28 October 2003

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The grain boundary networks of tetragonal and orthorhombic superconductors are shown to be nonrandom through computer simulations of polycrystalline structures. For biaxially textured microstructures, the distribution of low-angle grain boundaries around triple junctions is measurably deviant from the expectations for a randomly constructed lattice. Percolation thresholds are calculated for the unhindered flow of superconducting current through a polycrystal, and are found to be significantly different from the standard random percolation threshold in two dimensions. These deviations are explained as a result of crystallographic constraints on the network topology. © 2003 American Institute of Physics.
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74.25.F- Transport properties
74.72.-h Cuprate superconductors
61.72.Mm Grain and twin boundaries

Field-effect experiments in NdBa2Cu3O7−δ ultrathin films using a SrTiO3 single-crystal gate insulator

D. Matthey, S. Gariglio, and J.-M. Triscone

Appl. Phys. Lett. 83, 3758 (2003); http://dx.doi.org/10.1063/1.1624635 (3 pages) | Cited 27 times

Online Publication Date: 28 October 2003

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We report on the electrostatic modulation of superconductivity in very thin films of cuprate superconductors using a field-effect device based on a SrTiO3 single-crystal gate insulator. A Tc modulation of 3.5 K and a 37% change of the normal state resistance have been observed in an epitaxial bilayer composed of an insulating PrBa2Cu3O7−δ layer deposited on top of a superconducting NdBa2Cu3O7−δ film, two unit cells thick. To achieve large electric fields, the thickness of the commercial dielectric single-crystal SrTiO3 substrate (also used as the gate insulator) was reduced to 110 μm. The dielectric properties of the gate insulator were characterized as a function of temperature and electric field and the magnitude of the field effect was quantified. A Tc enhancement of 2.8 K was obtained for an applied field of −1.8×106 V/m, corresponding to a polarization of −4 μC/cm2. © 2003 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.62.Yb Other effects

Magnetization reversal under nonuniform magnetic fields at conditions relevant to magnetic random access memory applications

K. S. Kim, C. E. Lee, and S. H. Lim

Appl. Phys. Lett. 83, 3761 (2003); http://dx.doi.org/10.1063/1.1625105 (3 pages) | Cited 1 time

Online Publication Date: 28 October 2003

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Magnetization reversal behavior is examined under various nonuniform fields, the conditions of which are relevant to magnetic random access memory applications. During the magnetization reversal, the end domains play a key role at a uniform field, but they play a negligible role at a nonuniform field. Instead, a ripple pattern is initially formed in the interior and it progresses to form a vortex, resulting in a reversed domain. The switching field is found to be greater in the case of a nonuniform field, but, under a bias field, it is reduced greatly to a level similar to that for a uniform field. This result may indicate a wide window for the bit selectivity under a nonuniform field in magnetic random access memory applications. © 2003 American Institute of Physics.
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75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)

Atomic-scale depth selectivity of soft x-ray resonant Kerr effect

Ki-Suk Lee, Sang-Koog Kim, and J. B. Kortright

Appl. Phys. Lett. 83, 3764 (2003); http://dx.doi.org/10.1063/1.1622123 (3 pages) | Cited 13 times

Online Publication Date: 28 October 2003

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By the use of resonant soft x-ray Kerr rotation measurements with its varying incident angle and energy, we observed various shifts of the exchange bias field of a 3.5-nm-thick Co layer in oppositely exchange-biased Ni81Fe19/Fe50Mn50/Co/Pd films. The results in conjunction with their model simulations clearly reveal that the measurements enable one to resolve varying magnetization with depth in the individual magnetic layers of such a multicomponent ultrathin layered structure on the atomic scales. Significant interference effects combined with penetration depth of resonant soft x rays, which are closely associated with their absorptive and refractive contributions, offer remarkably different depth sensitivities into the Kerr effects depending on grazing angle and resonance energy. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
75.50.Cc Other ferromagnetic metals and alloys
75.30.Et Exchange and superexchange interactions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
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First-order reversal curves diagrams for the characterization of ferroelectric switching

Alexandru Stancu, Dan Ricinschi, Liliana Mitoseriu, Petronel Postolache, and Masanori Okuyama

Appl. Phys. Lett. 83, 3767 (2003); http://dx.doi.org/10.1063/1.1623937 (3 pages) | Cited 21 times

Online Publication Date: 28 October 2003

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A method to describe the switching characteristics of the ferroelectrics is proposed, using the first-order reversal curve (FORC) diagrams. On these diagrams, the reversible and irreversible contributions to the ferroelectric polarization can be clearly separated. They are extremely sensitive to the changes of the hysteresis loops induced by degradation of the ferroelectric polarization, such as fatigue. Sharp in the fresh state, the FORC distribution becomes wide with its maximum shifted towards higher fields after 109 switching cycles. A strong increase of the reversible component was found in the fatigue state. With appropriate interpretation, these diagrams could be valuable as “fingerprints” of the switching characteristics of the ferroelectric systems in a particular state. © 2003 American Institute of Physics.
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77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis

Well-ordered arrays of pyramid-shaped ferroelectric BaTiO3 nanostructures

Wenhui Ma, Catalin Harnagea, Dietrich Hesse, and Ulrich Gösele

Appl. Phys. Lett. 83, 3770 (2003); http://dx.doi.org/10.1063/1.1625106 (3 pages) | Cited 35 times

Online Publication Date: 28 October 2003

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Monolayers of monodisperse latex spheres of micron size were used as deposition masks to fabricate arrays of ferroelectric nanostructures by pulsed laser deposition using a BaTiO3 target. First, arrays of well-ordered structures were prepared on SrTiO3:Nb (100) single-crystal substrates at room temperature. Investigations of these isolated as-deposited nanostructures by atomic force microscopy revealed that they have a pyramid-like shape with about 200 nm lateral size at half their height and form a regular hexagonal pattern. Then postdeposition annealing was used to crystallize the nanostructures. The ferroelectric properties of the crystalline structures were investigated by scanning force microscopy in piezoresponse mode. Piezoelectric hysteresis loops were recorded, demonstrating that the barium titanate nanopyramids have a remanent polarization and are switchable by an electric field, i.e., they are indeed ferroelectric. © 2003 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
61.46.-w Structure of nanoscale materials
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.16.Mk Laser-assisted deposition
81.15.Fg Pulsed laser ablation deposition
61.72.Cc Kinetics of defect formation and annealing
77.65.Bn Piezoelectric and electrostrictive constants
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Nanoscale pseudoelastic behavior of indented titanium–nickel films

X.-G. Ma and K. Komvopoulos

Appl. Phys. Lett. 83, 3773 (2003); http://dx.doi.org/10.1063/1.1623942 (3 pages) | Cited 45 times

Online Publication Date: 28 October 2003

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The pseudoelastic behavior of shape memory alloy (SMA) materials is a phenomenon associated with reversible thermoelastic martensitic transformation. Despite significant insight into macroscopic pseudoelasticity, relatively little is known about the mechanisms responsible for the pseudoelastic behavior at nanometer scales. Recent demands for powerful microdevices and high-density data storage have motivated SMA film studies. In this study, nanoindentation experiments were performed with sputtered austenite titanium–nickel (TiNi) films using a surface force microscope equipped with an acoustic emission sensor. Results reveal the occurrence of pseudoelasticity at the nanoscale and the significance of normal load, nanoindenter tip radius, and partial unloading on the transition from pseudoelastic to elastic-plastic deformation of the TiNi films. The mechanisms associated with the reversible phase transformation and the energy dissipated in TiNi films exhibiting pseudoelasticity are interpreted in the context of nanoindentation results. The findings of this work demonstrate the high potential of TiNi films in high-density storage and microactuator applications. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
81.30.Kf Martensitic transformations
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
64.70.K- Solid-solid transitions
62.20.F- Deformation and plasticity

Optical and electrical properties of in situ-annealed p-type Hg0.7Cd0.3Te epilayers grown on CdTe buffer layers for applications as infrared detectors

Y. S. Ryu, Y. B. Heo, B. S. Song, S. J. Yoon, Y. J. Kim, T. W. Kang, and T. W. Kim

Appl. Phys. Lett. 83, 3776 (2003); http://dx.doi.org/10.1063/1.1621732 (3 pages) | Cited 9 times

Online Publication Date: 28 October 2003

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Hall-effect, Fourier transform infrared (FTIR) transmission, and photopresponse measurements were performed to investigate the optical and electrical properties of as-grown and in situ-annealed Hg0.7Cd0.3Te epilayers grown on CdTe buffers on GaAs (211) B substrates layers by using molecular-beam epitaxy. Hall-effect measurements showed that as-grown n-Hg0.7Cd0.3Te epilayers were converted to p-Hg0.7Cd0.3Te epilayers due to in situ annealing. The carrier concentration and the mobility as functions of the annealing temperature were determined from the Hall-effect measurements. The FTIR spectra showed that the transmission intensity had increased in comparison to that of the as-grown Hg0.7Cd0.3Te epilayer. Hall-effect measurements showed that n-Hg0.7Cd0.3Te epilayers were converted to p-Hg0.7Cd0.3Te epilayers. The activation energy and the carrier lifetime of the annealed Hg0.7Cd0.3Te epilayer were 0.25 eV and 160 ns, respectively. These results indicate that p-type Hg0.7Cd0.3Te epilayers grown on CdTe buffer layers due to in situ thermal annealing hold promise for potential applications in infrared detector technologies. © 2003 American Institute of Physics.
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73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
85.60.Gz Photodetectors (including infrared and CCD detectors)
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
78.30.Fs III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Dn Low-field transport and mobility; piezoresistance
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Determination of size and composition of optically active CdZnSe/ZnBeSe quantum dots

Y. Gu, Igor L. Kuskovsky, J. Fung, R. Robinson, I. P. Herman, G. F. Neumark, X. Zhou, S. P. Guo, and M. C. Tamargo

Appl. Phys. Lett. 83, 3779 (2003); http://dx.doi.org/10.1063/1.1623941 (3 pages) | Cited 8 times

Online Publication Date: 28 October 2003

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The size and composition of optically active CdxZn1−xSe/Zn0.97Be0.03Se quantum dots (QDs) are determined using photoluminescence, photoluminescence excitation, and Raman scattering spectroscopies combined with a model of photoluminescence and LO phonon energies. The diameters of optically active QDs range from 5.1 to 8.0 nm with Cd composition in the range of 47%–54%, corresponding to the “small” QDs group. Additionally, surface phonons from QDs are observed in this system. © 2003 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
78.55.Et II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors

Planar nanocontacts with atomically controlled separation

Y. V. Kervennic, D. Vanmaekelbergh, L. P Kouwenhoven, and H. S. J Van der Zant

Appl. Phys. Lett. 83, 3782 (2003); http://dx.doi.org/10.1063/1.1623317 (3 pages) | Cited 17 times

Online Publication Date: 28 October 2003

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We have developed a technology to reproducibly make gaps with distance control on the single-atom scale. The gold contacts are flat on the nanometer scale and are fabricated on an oxidized aluminum film that serves as a gate. We show that these contacts are clean and can be stabilized via chemical functionalization. Deposition of conjugated molecules leads to an increase in the gap conductance of several orders of magnitude. Stable current–voltage characteristics at room temperature are slightly nonlinear. At low temperature, they are highly nonlinear and show a clear gate effect. © 2003 American Institute of Physics.
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73.63.Rt Nanoscale contacts
81.07.Lk Nanocontacts
85.65.+h Molecular electronic devices

Effects of a thin InGaAs layer on InAs quantum dots embedded in InAl(Ga)As

Jin Soo Kim, Jin Hong Lee, Sung Ui Hong, Won Seok Han, Ho-Sang Kwack, and Dae Kon Oh

Appl. Phys. Lett. 83, 3785 (2003); http://dx.doi.org/10.1063/1.1623947 (3 pages) | Cited 9 times

Online Publication Date: 28 October 2003

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Influences of a thin In0.32Ga0.68As layer on the structural and optical properties of self-assembled InAs quantum dots (QDs) embedded in an InAl(Ga)As matrix, which was lattice-matched to an InP substrate, were investigated by atomic force microscopy (AFM), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. AFM and TEM images showed that the size of QDs grown on a thin In0.32Ga0.68As layer was increased, with a reduction in size fluctuation compared to that of QDs on an InAl(Ga)As layer. The shape of the QD was also more isotropic, indicating that the QD would be closer to an ideal zero-dimensional system. The PL peak position of the InAs QDs grown on a 1.5 nm In0.32Ga0.68As layer was 1.55 μm, with linewidth broadening of 64 meV that was somewhat narrower than those of the QD samples without the In0.32Ga0.68As layer, which agreed well with the AFM and TEM results. © 2003 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
78.55.Cr III-V semiconductors
81.16.Dn Self-assembly

Conducting-tip atomic force microscopy for injection and probing of localized charges in silicon nanocrystals

Souri Banerjee, Mohamed Ali Salem, and Shunri Oda

Appl. Phys. Lett. 83, 3788 (2003); http://dx.doi.org/10.1063/1.1624469 (3 pages) | Cited 15 times

Online Publication Date: 28 October 2003

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A conducting-tip atomic force microscopy (AFM) is utilized to inject localized charges in an ensemble of closely packed nanocrystalline Si dots prepared by plasma decomposition of SiH4. A noncontact-mode topography imaging carried out to probe the charging effect indicates an increase in the apparent height of the Si nanocrystal. A generalized tip-sample force interaction model is also developed to quantitatively evaluate the deposited charge. The study prescribes that the presence of surface charges might result in an overestimation of the actual height of an object measured by AFM, which could be nontrivial for a nanomaterial in particular. © 2003 American Institute of Physics.
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68.37.Ps Atomic force microscopy (AFM)
68.47.Fg Semiconductor surfaces
73.22.-f Electronic structure of nanoscale materials and related systems
61.46.-w Structure of nanoscale materials

Dynamics of electric field induced particle alignment in nonpolar polymer matrix

Xiangyang Tai, Guozhang Wu, Hiroshi Yui, Shigeo Asai, and Masao Sumita

Appl. Phys. Lett. 83, 3791 (2003); http://dx.doi.org/10.1063/1.1624468 (3 pages) | Cited 12 times

Online Publication Date: 28 October 2003

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The dynamics of electric field induced particle alignment in nonpolar polymer matrix to build one-dimensional conductive materials was investigated. The influence of electric field on particle alignment was real-time traced by dynamic percolation measurement using carbon black (CB) filled polyethylene as a model system. The activation energy of the continuous CB path formation was calculated and found to be unchanged with CB alignment. The critical percolation concentration at thermodynamic equilibrium state ϕc∗ was deduced to characterize the anisotropism of network structure, by which the thermodynamic prerequisite electric field E∗ for the transition from three-dimensional isotropic network to one-dimensional chain could be easily found out. © 2003 American Institute of Physics.
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72.15.Nj Collective modes (e.g., in one-dimensional conductors)
64.60.A- Specific approaches applied to studies of phase transitions
72.80.Tm Composite materials

Scanning tunneling microscope mediated nanostructure fabrication from GeH4 on Si(111)-(7×7)

U. R. Schöffel, H. Rauscher, and R. J. Behm

Appl. Phys. Lett. 83, 3794 (2003); http://dx.doi.org/10.1063/1.1625110 (3 pages) | Cited 4 times

Online Publication Date: 28 October 2003

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The tungsten tip of a scanning tunneling microscope, covered with GeHx by exposure to GeH4, was used to locally grow nanometer-sized Ge or GeHx islands on a Si(111)-(7×7) surface. This was achieved by transfer of material from the tip to the surface, induced by voltage pulses. A model, based on the diffusion of adsorbates on the tip and desorption stimulated by an electric field, is presented to account for the results. © 2003 American Institute of Physics.
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81.16.Ta Atom manipulation
68.47.Fg Semiconductor surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
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