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21 May 2001

Volume 78, Issue 21, pp. 3163-3363

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Percolation transition of thermoelectric properties in PbTe thin films

E. I. Rogacheva, I. M. Krivulkin, O. N. Nashchekina, A. Yu. Sipatov, V. A. Volobuev, and M. S. Dresselhaus

Appl. Phys. Lett. 78, 3238 (2001); http://dx.doi.org/10.1063/1.1357809 (3 pages) | Cited 10 times

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Extrema were observed in the film thickness d dependence of various thermoelectric parameters (Seebeck coefficient S, electrical conductivity σ, Hall coefficient RH, charge carrier mobility μ, and power factor P) of epitaxial PbTe/(001) KCl thin films prepared by thermal evaporation in vacuum and protected from oxidation by an EuS layer. We attribute the observed extrema in properties and the high values of μ and P at d ≈ 50 nm to the percolation transition from an island-like to a continuous film and to the self-organization of the islands, which can occur not only in quantum dot superlattices but also in an individual layer. © 2001 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.50.Lw Thermoelectric effects

Photo-enhanced negative differential resistance and photo-accelerated time-dependent dielectric breakdown in thin nitride-oxide dielectric film

Fen Chen, Baozhen Li, Rajarao Jammy, Roger A. Dufresne, and Alvin W. Strong

Appl. Phys. Lett. 78, 3241 (2001); http://dx.doi.org/10.1063/1.1373409 (3 pages) | Cited 2 times

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Photo-enhanced negative differential resistance (NDR) and photo-accelerated time-dependent dielectric breakdown (TDDB) were observed in thin nitride–oxide (N–O) dielectric film biased with gate negative under tungsten lamp illumination. The photo-induced leakage current and photo-accelerated TDDB show dramatic asymmetry under negative and positive gate bias with constant photo-illumination. Our experiments suggest a unique current conduction mechanism in this nitride thin film. A two-carrier conduction induced positive feedback transport process under negative gate bias, and a two-carrier conduction induced self-limiting transport process under positive gate bias are proposed to qualitatively explain the experimental data. The nitride thin film device possessing a light-enhanced NDR can be employed to develop Si-based optoelectronic devices such as switching and logic control. © 2001 American Institute of Physics.
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73.50.Pz Photoconduction and photovoltaic effects
73.61.Ng Insulators
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Fq High-field and nonlinear effects
77.22.Jp Dielectric breakdown and space-charge effects

Characteristics of n+–p junction leakage induced by tantalum pentoxide gate insulator and gate reoxidation

Chang-Yong Kang, Young-Gwan Kim, and Dae-Gwan Kang

Appl. Phys. Lett. 78, 3244 (2001); http://dx.doi.org/10.1063/1.1370983 (3 pages) | Cited 1 time

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This letter will present the n+–p junction characteristics in tantalum pentoxide gate dielectric (Ta2O5) and gate reoxidation ambient. The n+–p junctions in n-type metal–oxide–silicon field effect transistor fabricated with different gate dielectrics and post-thermal conditions were characterized by current–voltage measurements. The current–voltage measurements of junction leakage of Ta2O5 gate dielectric without gate reoxidation (MT1) show the hump characteristics due to the precipitates of oxide near the junction depletion regime. And their leakage mechanism is phonon-assisted tunneling, which facilitates the hopping of electrons from the valence band into the shallow attractive Coulomb center via the interface states in the precipitate, leaving holes in the valence band. However, the junction leakage currents of Ta2O5 dielectric with gate reoxidation in hydrogen rich ambient (MT2) are higher than those of thermal oxide samples and their leakage mechanism is Schottky barrier lowering due to the enhanced diffusion of oxygen into the junction depletion region. © 2001 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Cy Elemental semiconductors
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
71.20.Mq Elemental semiconductors
85.30.Tv Field effect devices
73.40.Gk Tunneling
73.20.At Surface states, band structure, electron density of states
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
81.65.Mq Oxidation
72.20.Ee Mobility edges; hopping transport
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Energy level control for self-assembled InAs quantum dots utilizing a thin AlAs layer

J. S. Kim, P. W. Yu, J. Y. Leem, J. I. Lee, S. K. Noh, Jong Su Kim, S. M. Kim, J. S. Son, U. H. Lee, J. S. Yim, and D. Lee

Appl. Phys. Lett. 78, 3247 (2001); http://dx.doi.org/10.1063/1.1373410 (3 pages) | Cited 8 times

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Ground-state energy of InAs quantum dots (QDs) in the GaAs matrix can be changed significantly by introducing a thin AlAs layer (1 nm). The photoluminescence (PL) peak position of the QDs grown directly on the thin AlAs layer is blueshifted by 171 meV from that of the QDs grown without the AlAs layer. QDs grown on an additional GaAs thin layer on top of the AlAs layer have PL peaks systematically redshifted to lower energy as the GaAs layer becomes thicker. Time-resolved PL shows that the QDs have similar lifetimes, attesting to the fact that all the QDs grown in this way are of high quality, although the energy level change is large and a thin AlAs layer is introduced. © 2001 American Institute of Physics.
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73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
81.16.Dn Self-assembly
81.07.Ta Quantum dots

Photoreflectance line shape symmetry and quantum-well ground-state exciton energy in vertical-cavity surface-emitting laser structures

Sandip Ghosh, Thomas J. C. Hosea, and Stephanie B. Constant

Appl. Phys. Lett. 78, 3250 (2001); http://dx.doi.org/10.1063/1.1374233 (3 pages) | Cited 16 times

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We report photoreflectance studies on the coupling between the Fabry–Perot cavity mode (CM) and the quantum well (QW) ground-state excitonic feature in vertical-cavity surface-emitting laser structures. Changes in the symmetry of the CM-QW spectral feature occur when the angle of incidence of the probe beam is altered. Using detailed simulations, we explain how this is related to an unusual reversal of the roles of the Seraphin coefficients and QW dielectric function, in determining the line shape. Our study suggests a way to find the exciton energy, in situations where a distinct QW feature is not seen because of large broadening of the QW dielectric function combined with high reflectivity of Bragg mirrors and relatively narrow CM width. © 2001 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
73.21.Fg Quantum wells
78.67.De Quantum wells
78.30.Fs III-V and II-VI semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Fabrication of wirelike InAs quantum dots on 2°-off GaAs (100) substrates by changing the thickness of the InAs layer

Hyo Jin Kim, Young Ju Park, Young Min Park, Eun Kyu Kim, and Tae Whan Kim

Appl. Phys. Lett. 78, 3253 (2001); http://dx.doi.org/10.1063/1.1362337 (3 pages) | Cited 19 times

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Wirelike InAs quatum dots (QDs) grown on 2°-off (100) GaAs substrates by changing the thickness of the InAs layer were successfully fabricated. The sizes of the InAs QDs along the step lines increased with increasing the thickness of the InAs layer, and their increases were attributed to transform of the InAs QDs into the wirelike InAs QDs. The optimal thicknesses of the InAs layers for the wirelike QDs and the interval of the wirelike QDs were significantly affected by the terrace width resulting from the bunching effect due to the thickness variations of the GaAs buffer layers grown on 2°-off (100) GaAs substrates. These results indicate that these wirelike InAs QDs are useful for applications in nanoelectronic devices, such as wrap gate single electron transistors. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots

Comparative study of current–voltage characteristics of Ni and Ni(Pt)-alloy silicided p+/n diodes

D. Z. Chi, D. Mangelinck, S. K. Lahiri, P. S. Lee, and K. L. Pey

Appl. Phys. Lett. 78, 3256 (2001); http://dx.doi.org/10.1063/1.1374496 (3 pages) | Cited 14 times

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A comparative study of the I–V characteristics of p+/n diodes silicided with a pure Ni and Ni(Pt) alloy has been performed. Higher saturation currents as well as abnormal reverse I–V characteristics were observed for some of the diodes which were silicided with pure Ni at 700 °C while good I–V characteristics were observed for other diodes. Our results show that the forward current in the diodes with good I–V characteristics is dominated by electron diffusion in the p+ region. For diodes with higher saturation currents, it has been concluded that both forward and reverse currents in these diodes are dominated by the current following through Schottky contacts that are formed due to inadvertent penetration of NiSi spikes through the p+ region into n region. The formation of Schottky contact was not observed in diodes silicided with a Ni(Pt) alloy, providing a clear evidence of enhanced thermal stability of Pt containing NiSi. © 2001 American Institute of Physics.
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85.30.Kk Junction diodes
85.40.Ls Metallization, contacts, interconnects; device isolation
85.30.De Semiconductor-device characterization, design, and modeling
73.30.+y Surface double layers, Schottky barriers, and work functions

Photon-induced current of polycrystalline-silicon thin-film transistors

H. Ikeda

Appl. Phys. Lett. 78, 3259 (2001); http://dx.doi.org/10.1063/1.1374224 (3 pages) | Cited 5 times

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Photon-induced current (Iph) in polycrystalline-silicon thin-film transistors (poly-Si TFTs) has been investigated using a line-shaped light beam scanning method. In the off-state region, photon-excited carriers in the channel region diffuse to the drain with the diffusion length independent of the poly-Si grain size. The diffusion length is also independent whether poly-Si is hydrogenated or not. This phenomenon is observed in both n-channel and p-channel TFTs. In the subthreshold region, Iph follows the general transport equation in poly-Si. In the inversion region, Iph is proportional only to the total amount of excited carriers in the channel. © 2001 American Institute of Physics.
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85.30.Tv Field effect devices
73.50.Pz Photoconduction and photovoltaic effects

Tracking of conduction phenomena and degradation in organic light emitting diodes by current noise measurements

M. Sampietro, G. Ferrari, D. Natali, U. Scherf, K. O. Annan, F. P. Wenzl, and G. Leising

Appl. Phys. Lett. 78, 3262 (2001); http://dx.doi.org/10.1063/1.1374516 (3 pages) | Cited 12 times

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Noise current analysis, both in time and frequency, is proposed as a means to sense variations of the microscopic conduction in organic light emitting diodes and to track their time evolution. The sensitivity of the technique would allow to correlate the carriers conduction properties with the corresponding changes in the microscopic morphology of the organic layers as obtained with structural or spectroscopic investigations. The method is shown to be very effective also in sensing the initial state and the growth of organic diodes catastrophic degradation in large advance to current monitoring or other techniques. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.60.Bt Optoelectronic device characterization, design, and modeling
73.61.Ph Polymers; organic compounds
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
73.50.Td Noise processes and phenomena

Lateral current spreading in GaN-based light-emitting diodes utilizing tunnel contact junctions

Seong-Ran Jeon, Young-Ho Song, Ho-Jin Jang, Gye Mo Yang, Soon Won Hwang, and Sung Jin Son

Appl. Phys. Lett. 78, 3265 (2001); http://dx.doi.org/10.1063/1.1374483 (3 pages) | Cited 45 times

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InGaN/GaN multiple-quantum-well light-emitting-diode structures utilizing tunnel contact junctions grown by metalorganic chemical vapor deposition have been demonstrated. The p+/n+ GaN tunnel junctions are located in the upper cladding layers of conventional devices, allowing n-type GaN instead of p-type GaN as a top contact layer. Thus, metal ohmic contacts are done at the same time on the top and the lower contact layers. The reverse-biased tunnel contact junction provides lateral current spreading without semitransparent electrode and spatially uniform luminescence exhibiting an improved radiative efficiency. The tunnel contact junction is shown to be an effective method to make possible hole injection via a lateral electron current, with only a small penalty in voltage drop compared to conventional devices. © 2001 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.40.Ns Metal-nonmetal contacts
73.40.Gk Tunneling
73.63.Hs Quantum wells
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Vortex circulation control in mesoscopic ring magnets

M. Kläui, J. Rothman, L. Lopez-Diaz, C. A. F. Vaz, J. A. C. Bland, and Z. Cui

Appl. Phys. Lett. 78, 3268 (2001); http://dx.doi.org/10.1063/1.1361282 (3 pages) | Cited 72 times

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We present a simple method to control the direction of the circulation of the magnetization in mesoscopic ring magnets, using a uniform magnetic field only. The method is based on the nucleation free switching which occurs when the rings switch from the near-saturated state, referred to as the “onion state,” to the flux-closed vortex state. Two possible onion states, forward or reverse magnetized, are possible for a given direction of the magnetic field. Going from the forward or the backward onion state, both local scanning Kerr microscopy measurements and micromagnetic simulations show that the clockwise or the counterclockwise vortex state, respectively, can be selected due to asymmetric pinning of the two domain walls that are present in the onion state. © 2001 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
75.50.Cc Other ferromagnetic metals and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Structural and magnetic properties of GaMnAs layers with high Mn-content grown by migration-enhanced epitaxy on GaAs(100) substrates

J. Sadowski, R. Mathieu, P. Svedlindh, J. Z. Domagała, J. Bak-Misiuk, K. Światek, M. Karlsteen, J. Kanski, L. Ilver, H. Åsklund, and U. Södervall

Appl. Phys. Lett. 78, 3271 (2001); http://dx.doi.org/10.1063/1.1370535 (3 pages) | Cited 32 times

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Ferromagnetic GaMnAs containing up to 10% Mn has been grown by migration-enhanced epitaxy at a substrate temperature of 150 °C. The lattice constant of hypothetical zinc-blende structure MnAs is determined to be 5.90 Å, which deviates somewhat from previously reported values. This deviation is ascribed to growth-condition-dependent density of point defects. Magnetization measurements showed an onset of ferromagnetic ordering around 75 K for the GaMnAs layer with 10% Mn. This means that the trend of falling Curie temperatures with increasing Mn concentrations above 5.3% is broken. © 2001 American Institute of Physics.
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68.55.A- Nucleation and growth
81.05.Ea III-V semiconductors
75.50.Pp Magnetic semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.66.Fn Inorganic compounds

Tantalum oxide as an alternative low height tunnel barrier in magnetic junctions

P. Rottländer, M. Hehn, O. Lenoble, and A. Schuhl

Appl. Phys. Lett. 78, 3274 (2001); http://dx.doi.org/10.1063/1.1374223 (3 pages) | Cited 31 times

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Magnetic tunnel junctions with a barrier of tantalum oxide were prepared by plasma oxidation of sputter-deposited tantalum. They show magnetoresistance ratios of 2.5% at room temperature and 4% at low temperatures. The material exhibits low barrier heights of ∼0.4 eV. This makes it possible to substantially increase the barrier thickness, compared to a barrier of aluminum oxide. The resulting decrease of coupling between the ferromagnetic layers is easily seen. Tantalum oxide appears to be a candidate for use as a tunnel barrier of spin-dependent tunneling devices. © 2001 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.75.Dd Magnetic memory using magnetic tunnel junctions
72.25.Mk Spin transport through interfaces
75.47.De Giant magnetoresistance
81.65.Mq Oxidation
52.77.-j Plasma applications

Negative thermal expansion and magnetic properties of Y2Al3Fe14−xMnx compounds

Yanming Hao, Yan Gao, Bowen Wang, Jingping Qu, Yangxian Li, Jifan Hu, and Jiachun Deng

Appl. Phys. Lett. 78, 3277 (2001); http://dx.doi.org/10.1063/1.1371968 (3 pages) | Cited 19 times

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The structure and magnetic properties of Y2Al3Fe14−xMnx (x = 0–12) compounds have been investigated by means of x-ray diffraction and magnetization measurements. The Y2Al3Fe14−xMnx compounds have a hexagonal Th2Ni17-type structure. Their unit-cell volumes increase slowly with increasing x first, then increases rapidly with the further increase of x. This implies that there exists a positive spontaneous volume magnetostriction in the magnetic state of Y2Al3Fe14−xMnx compounds. X-ray diffraction of the Y2Al3Fe11Mn3 compound from 150 to 300 K shows that there appears a negative coefficient of thermal expansion, math ≈ −7.5×10−5/K, from 185 to 200 K. The Curie temperature and the saturation magnetization of these compounds show a rapid drop with increasing x. © 2001 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
65.40.De Thermal expansion; thermomechanical effects
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.-s Critical-point effects, specific heats, short-range order
75.50.Bb Fe and its alloys

Separation of reversible domain-wall motion and magnetization rotation components in susceptibility spectra of amorphous magnetic materials

S. S. Yoon and C. G. Kim

Appl. Phys. Lett. 78, 3280 (2001); http://dx.doi.org/10.1063/1.1374519 (3 pages) | Cited 6 times

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The reversible susceptibility spectra are measured for rectangular Co66Fe4NiB14Si15 samples with various easy-axis angles, α, relative to the sample axis. A phenomenological method is proposed for the reversible spectra to separate the relaxation processes of domain-wall motion and magnetization rotation. The separation provides a method for measuring the static susceptibilities and the relaxation frequencies for the two reversible magnetization processes. The α and the longitudinal stress dependence show that the separated spectra with relaxation frequencies near 360 kHz and 1.6 MHz correspond to relaxations of domain-wall motion and to magnetization rotation, respectively. © 2001 American Institute of Physics.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.50.Bb Fe and its alloys
75.30.Gw Magnetic anisotropy
75.60.Ch Domain walls and domain structure
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Optimization of electronic-band alignments at ferroelectric (ZnxCd1−x)S/Si(100) interfaces

Y. Hotta, E. Rokuta, H. Tabata, H. Kobayashi, and T. Kawai

Appl. Phys. Lett. 78, 3283 (2001); http://dx.doi.org/10.1063/1.1356724 (3 pages) | Cited 15 times

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We have obtained ferroelectric characteristics from nonoxide (ZnxCd1−x)S (x = 0.1–0.3) thin films. On the basis of x-ray photoelectron and visible–ultraviolet light absorption spectroscopy measurements, the conduction-band discontinuity at the (ZnxCd1−x)S/Si(100) interfaces is found to vary between 0.4 and 1.3 eV with a change in composition x between 0.1 and 0.9. The leakage current density, which strongly depends on the conduction-band discontinuity, is reduced to less than 10−6 A/cm2 at a gate voltage of 4 V. © 2001 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.40.Fy Semiconductors
78.66.Hf II-VI semiconductors
78.66.Db Elemental semiconductors and insulators
77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films

Improved electrical properties of (Pb, La)TiO3 thin films using compositionally and structurally compatible LaNiO3 thin films as bottom electrodes

Dinghua Bao, Naoki Wakiya, Kazuo Shinozaki, Nobuyasu Mizutani, and Xi Yao

Appl. Phys. Lett. 78, 3286 (2001); http://dx.doi.org/10.1063/1.1375831 (3 pages) | Cited 22 times

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Homogeneous LaNiO3 thin films were grown on thermally oxidized silicon (SiO2/Si) substrates by a sol-gel technique, for the subsequent sol-gel deposition of (Pb, La)TiO3 thin films, under the assumption that the structural and compositional compatibility between ferroelectric films and bottom electrodes could lead to enhanced electrical properties of ferroelectric thin films. In this work, the LaNiO3 films served three functions: the first was used as bottom electrodes for the fabrication of integrated ferroelectric devices on Si due to their low resistivity; the second was used as a seeding layer, promoting perovskite phase formation due to their structural compatibility with ferroelectric films; and the third was to suppress the composition diffusion between ferroelectric films and bottom electrodes due to their composition compatibility. The experimental results demonstrated that (Pb, La)TiO3 films prepared on the LaNiO3/SiO2/Si substrates had excellent electrical properties. The dielectric constant and dielectric loss were 1468 and 0.033, respectively. The dielectric constant is rather high among the values reported for (Pb, La)TiO3 thin films. The remanent polarization and coercive field were 4.24 μC/cm2 and 23.2 kV/cm, respectively. © 2001 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
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.22.Ej Polarization and depolarization

Stress-induced leakage current in ultrathin SiO2 layers and the hydrogen dispersive transport model

M. Houssa, A. Stesmans, R. J. Carter, and M. M. Heyns

Appl. Phys. Lett. 78, 3289 (2001); http://dx.doi.org/10.1063/1.1375003 (3 pages) | Cited 24 times

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The time dependence of the current density variation ΔJ(t) observed during constant gate voltage stress of metal–oxide–semiconductor capacitors with ultrathin gate oxide and oxynitride layers is investigated. The generation of bulk neutral defects in the SiO2 layer is calculated within a dispersive transport model, assuming that these defects are induced by the random hopping of H+ ions in the gate oxide layer. It is shown that the stress–voltage and gate-oxide-thickness dependence of ΔJ(t) can be quite well explained by this dispersive hydrogen transport model. © 2001 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
85.30.Tv Field effect devices
66.30.H- Self-diffusion and ionic conduction in nonmetals

Epitaxial growth of the first five members of the Srn+1TinO3n+1 Ruddlesden–Popper homologous series

J. H. Haeni, C. D. Theis, D. G. Schlom, W. Tian, X. Q. Pan, H. Chang, I. Takeuchi, and X.-D. Xiang

Appl. Phys. Lett. 78, 3292 (2001); http://dx.doi.org/10.1063/1.1371788 (3 pages) | Cited 53 times

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The first five members of the Srn+1TinO3n+1 Ruddlesden–Popper homologous series, i.e., Sr2TiO4, Sr3Ti2O7, Sr4Ti3O10, Sr5Ti4O13, and Sr6Ti5O16, have been grown by reactive molecular beam epitaxy. A combination of atomic absorption spectroscopy and reflection high-energy electron diffraction intensity oscillations were used for the strict composition control necessary for the synthesis of these phases. X-ray diffraction and high-resolution transmission electron microscope images confirm that these films are epitaxially oriented and nearly free of intergrowths. Dielectric measurements indicate that the dielectric constant tensor coefficient ϵ33 increases from a minimum of 44±4 in the n = 1(Sr2TiO4) film to a maximum of 263±2 in the n = ∞(SrTiO3) film. © 2001 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
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Multiwalled carbon nanotubes as ultrasensitive electrometers

L. Roschier, R. Tarkiainen, M. Ahlskog, M. Paalanen, and P. Hakonen

Appl. Phys. Lett. 78, 3295 (2001); http://dx.doi.org/10.1063/1.1362281 (3 pages) | Cited 15 times

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We show that it is possible to construct low-noise single-electron transistors (SETs) using free-standing multiwalled carbon nanotubes. The 1/fα-noise of our devices, 6×10−6e/math at 45 Hz, is close in the performance to the best metallic SETs of today. © 2001 American Institute of Physics.
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85.35.Kt Nanotube devices
85.65.+h Molecular electronic devices
81.07.De Nanotubes
85.35.Gv Single electron devices
81.05.ub Fullerenes and related materials
07.68.+m Photography, photographic instruments; xerography
73.63.Fg Nanotubes

Wavelength dependence of laser-induced phase transformations in semiconductor quantum dots

M. Gajdardziska-Josifovska, V. Lazarov, J. Reynolds, and V. V. Yakovlev

Appl. Phys. Lett. 78, 3298 (2001); http://dx.doi.org/10.1063/1.1347226 (3 pages) | Cited 5 times

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We study the effect of wavelength on the laser-induced phase transformation in semiconductor quantum dots. In our earlier report [Yakovlev et al., Appl. Phys. Lett. 76, 2050 (2000)], we discovered that a nanosecond pulse of 532 nm radiation results in a phase transformation of CdS nanocrystals from an orthorhombic to cubic phase. In this study, we find that irradiation with the pulse of a different wavelength (355 nm) results in a completely different transformation to a hexagonal wurtzite phase and a significant broadening of nanocrystal size distribution. The nanocrystal stoichiometry remained unchanged by the laser irradiation, as verified by energy dispersive x-ray spectroscopy. © 2001 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.82.Fk Semiconductors
64.70.K- Solid-solid transitions
61.66.Bi Elemental solids
61.66.Dk Alloys
61.46.-w Structure of nanoscale materials
61.82.Rx Nanocrystalline materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Displacement currents and the real part of high-frequency conductance of the resonant-tunneling diode

Michael N. Feiginov

Appl. Phys. Lett. 78, 3301 (2001); http://dx.doi.org/10.1063/1.1372357 (3 pages) | Cited 9 times

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I have shown that weak variation of the tunnel transparency of the collector barrier with bias has substantial (and frequently crucial) effect on the high-frequency properties of the resonant-tunneling diodes (RTDs). Also it has been shown that the real part of the RTD conductance can be negative and large at the frequencies much higher than the reciprocal quasibound-state lifetime in the quantum well between the barriers of RTD, if (as opposed to common practice) the RTD collector is heavily doped and does not have thick spacer layers. The displacement currents are responsible for the effects. A simple equivalent circuit of RTD is proposed, and it fairly well describes the published experimental data. © 2001 American Institute of Physics.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.De Semiconductor-device characterization, design, and modeling
73.50.Mx High-frequency effects; plasma effects

Oxide-assisted growth and optical characterization of gallium-arsenide nanowires

W. S. Shi, Y. F. Zheng, N. Wang, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 78, 3304 (2001); http://dx.doi.org/10.1063/1.1371966 (3 pages) | Cited 29 times

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This letter reports the synthesis and optical characterization of GaAs nanowires obtained by oxide-assisted laser ablation of a mixture of GaAs and Ga2O3. The GaAs nanowires have lengths up to tens of micrometers and diameters in the range of 10–120 nm, with an average of 60 nm. The nanowires have a thin oxide layer covering a crystalline GaAs core with a [111] growth direction. Raman scattering and photoluminescence (PL) characterizations of GaAs nanowires reveal that the spectral peaks significantly shifted and broadened from those of bulk GaAs material. The changes in these spectra are mainly attributed to impurities, defects, and residual stress in the GaAs nanowires. © 2001 American Institute of Physics.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.67.Lt Quantum wires
81.07.Vb Quantum wires
78.55.Cr III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
68.65.La Quantum wires (patterned in quantum wells)
81.65.Mq Oxidation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Condensed phase growth of single-wall carbon nanotubes from laser annealed nanoparticulates

D. B. Geohegan, H. Schittenhelm, X. Fan, S. J. Pennycook, A. A. Puretzky, M. A. Guillorn, D. A. Blom, and D. C. Joy

Appl. Phys. Lett. 78, 3307 (2001); http://dx.doi.org/10.1063/1.1371796 (3 pages) | Cited 17 times

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Single-wall carbon nanotubes (SWNT) were grown to micron lengths by laser-annealing nanoparticulate soot containing short (∼50 nm long) nanotube “seeds.” The “seeded” nanoparticulate soot was produced by restricting the time spent by an ablation plume inside an 800 °C oven following laser vaporization of a C–Ni–Co target. The soot collected from the laser vaporization apparatus was placed inside graphite crucibles under argon, and heated by a CO2 laser. In situ pyrometry was used to estimate the sample temperature. Length distributions of SWNT bundles in the unannealed and annealed samples were measured by transmission electron microscopy and field emission scanning electron microscopy. Annealing treatments exceeding 1600 °C produced no increase in nanotube length, while lower temperatures in the 1000–1300 °C range were optimal for growth. These experiments indicate that SWNT grow by the conversion of condensed phase nanomaterial during annealing, a similar mechanism to that proposed for growth during normal laser–vaporization production. © 2001 American Institute of Physics.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
81.16.Mk Laser-assisted deposition

Free-standing SiGe-based nanopipelines on Si (001) substrates

O. G. Schmidt and N. Y. Jin-Phillipp

Appl. Phys. Lett. 78, 3310 (2001); http://dx.doi.org/10.1063/1.1373408 (3 pages) | Cited 35 times

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Thin solid films form nanopipelines if the films are released from a substrate and put back onto their own surface. We give a detailed description of free-standing SiGe-based nanopipelines created on Si (001) substrates. The initial layer sequence is grown by molecular beam epitaxy and comprises SiGe-based epitaxial layers grown on a Ge sacrificial layer. After selectively etching away the Ge sacrificial layer, SiGe nanopipelines have formed on the surface. Nanopipelines as long as 20 μm with diameters ranging from 50 to 530 nm are fabricated. We show that SiGe nanopipelines perform multiple revolutions if selective etching is carried out long enough. Adding carbon to Si epitaxial layers is proposed to extend the design freedom of Si-based nanopipelines and nanotubes. © 2001 American Institute of Physics.
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81.07.De Nanotubes
81.16.Rf Micro- and nanoscale pattern formation
61.46.-w Structure of nanoscale materials
81.65.Cf Surface cleaning, etching, patterning
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Hd Other semiconductors
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