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8 May 2000

Volume 76, Issue 19, pp. 2647-2800

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Temperature dependence of the band gap in InAsyP1−y

M. Wada, S. Araki, T. Kudou, T. Umezawa, S. Nakajima, and T. Ueda

Appl. Phys. Lett. 76, 2722 (2000); http://dx.doi.org/10.1063/1.126455 (3 pages) | Cited 10 times

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The temperature dependence of the band gap in InAsyP1−y (y=0–0.67) has been determined by photoluminescence, x-ray diffraction, and absorption spectra measurements. We found that the measured data within the temperature range of 77–300 K can be expressed by the equation proposed by O’Donnell and Chen. The band gap at 77 K is given by Eg = 1.407−1.073y+0.089y2, while the compositional dependence of the band gap observed at 300 K, agrees with the values previously reported. We confirmed that changes in temperature caused a slight change in the bowing parameters, and hence found that the band gap temperature dependence of InAsyP1−y (y=0–1) varies very little with changes in composition (2.5–3.5×10−4 eV/K). © 2000 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.40.Fy Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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Influence of epitaxial growth and substrate-induced defects on the breakdown of 4H–SiC Schottky diodes

Q. Wahab, A. Ellison, A. Henry, E. Janzén, C. Hallin, J. Di Persio, and R. Martinez

Appl. Phys. Lett. 76, 2725 (2000); http://dx.doi.org/10.1063/1.126456 (3 pages) | Cited 56 times

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Morphological defects and elementary screw dislocations in 4H–SiC were studied by high voltage Ni Schottky diodes. Micropipes were found to severely limit the performance of 4H–SiC power devices, whereas carrot-like defects did not influence the value of breakdown voltage. The screw dislocation density as determined by x-ray topography analysis under the active area of the diode was also found to directly affect the breakdown voltage. Only diodes with low density of screw dislocations and free from micropipes could block 2 kV or higher. © 2000 American Institute of Physics.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Hd Other semiconductors

Low-resistance ohmic contacts to p-type GaN

Y.-L. Li, E. F. Schubert, J. W. Graff, A. Osinsky, and W. F. Schaff

Appl. Phys. Lett. 76, 2728 (2000); http://dx.doi.org/10.1063/1.126457 (3 pages) | Cited 47 times

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The specific contact resistance of two types of ohmic contacts to p-type GaN is analyzed. First, an ohmic contact formed by a metal electrode deposited on a highly doped p-type GaN layer. Second, an ohmic contact formed by a metal electrode deposited on a thin GaN layer with an internal electric field caused by polarization effects. It is shown that contacts mediated by polarization effects can result, for typical materials parameters, in low contact resistances comparable or better than contacts mediated by dopant-induced surface fields. A type of contact is proposed and demonstrated. These contacts employ polarization charges to enhance tunneling transport as well as high doping. Experimental results on Ni contacts to p-type AlxGa1−xN/GaN doped superlattices are presented. The contacts have linear current–voltage characteristics with contact resistances of 9.3×10−4 Ω cm2, as inferred from linear transmission-line method measurements. The influence of annealing at temperatures ranging from 400 to 500 °C on the contact resistance is studied. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
84.32.Dd Connectors, relays, and switches
73.40.Cg Contact resistance, contact potential
61.72.Cc Kinetics of defect formation and annealing

Fabricating conductive microstructures by direct electron-beam writing on hydrogenated n-type Si-doped GaAs

S. Silvestre, E. Constant, D. Bernard-Loridant, and B. Sieber

Appl. Phys. Lett. 76, 2731 (2000); http://dx.doi.org/10.1063/1.126458 (3 pages) | Cited 2 times

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We study the changes in electronic properties of Si-doped GaAs epilayers exposed to a hydrogen plasma and then submitted to electron beams of 20 keV injection energy. Using Hall-effect measurements, we have observed the formation of Si–H complexes and their dissociation due to the electron-beam irradiation. As this last effect increases the conductivity of the epilayer, we have been able to fabricate, with an electron-beam lithography system, various conductive microstructures. Characterizations have been achieved by cathodoluminescence (CL) imaging. Actually, due to the CL reading method which has been used, we have only fabricated micronic-size structures. However, taking into account the high spatial resolution of electron-beam writing, such a process could, possibly, be used as a way of fabrication of mesoscopic structures. © 2000 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
73.25.+i Surface conductivity and carrier phenomena
78.60.Hk Cathodoluminescence, ionoluminescence

Temperature dependence of the iron donor level in silicon at device processing temperatures

H. Kohno, H. Hieslmair, A. A. Istratov, and E. R. Weber

Appl. Phys. Lett. 76, 2734 (2000); http://dx.doi.org/10.1063/1.126459 (3 pages) | Cited 9 times

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Iron depth profiles in a p-type silicon epitaxial layer on a p+-type silicon substrate have been examined by deep-level transient spectroscopy and computer simulations. By comparing the experimental results with the simulations, we revealed the position of the iron deep donor level to be 0.42±0.04 eV from the valence-band edge at 412–580 °C, which is in a device processing temperature range. The iron donor level was nearly temperature independent within error. Knowing the temperature dependence of the iron donor level at the device processing temperatures, we can design iron gettering in silicon more precisely. © 2000 American Institute of Physics.
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71.55.Cn Elemental semiconductors
61.72.Yx Interaction between different crystal defects; gettering effect

Magnetotransport studies of AlGaN/GaN heterostructures grown on sapphire substrates: Effective mass and scattering time

T. Wang, J. Bai, S. Sakai, Y. Ohno, and H. Ohno

Appl. Phys. Lett. 76, 2737 (2000); http://dx.doi.org/10.1063/1.126460 (3 pages) | Cited 27 times

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Temperature-dependent magnetotransport measurements have been carried out on high-quality two-dimensional electron gas (2DEG) in AlGaN/GaN heterostructures with different Al content grown on sapphire substrates. The GaN electron effective mass and the quantum scattering time are determined by well-resolved Shunbikov–de Hass oscillations. The electron effective mass is determined to be 19m0. The ratio of the classic scattering time to the quantum scattering time increases with increasing 2DEG sheet carrier density, which agrees very well with the previous calculation based on an ideal 2DEG in conventional semiconductor systems. Our result indicates that a low density of deep centers results in the much higher mobility of our structure compared with other reports, which is of critical importance in fabricating a high-quality 2DEG structure in AlGaN/GaN systems. © 2000 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
72.20.My Galvanomagnetic and other magnetotransport effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance

Highly electrically conductive indium–tin–oxide thin films epitaxially grown on yttria-stabilized zirconia (100) by pulsed-laser deposition

Hiromichi Ohta, Masahiro Orita, Masahiro Hirano, Hiroaki Tanji, Hiroshi Kawazoe, and Hideo Hosono

Appl. Phys. Lett. 76, 2740 (2000); http://dx.doi.org/10.1063/1.126461 (3 pages) | Cited 76 times

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Highly electrically conductive indium–tin–oxide thin films were epitaxially grown on an extremely flat (100) surface of yttria-stabilized zirconia single-crystal substrates at a substrate temperature of 600 °C by a pulsed-laser deposition technique. A resistivity down to 7.7×10−5 Ω cm was reproducibly obtained, maintaining optical transmission exceeding 85% at wavelengths from 340 to 780 nm. The carrier densities of the films were enhanced up to 1.9×1021 cm−3, while the Hall mobility showed a slight, almost linear, decrease from 55 to 40 cm2 V−1 s−1 with increasing SnO2 concentration. The low resistivity is most likely the result of the good crystal quality of the films. © 2000 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
72.80.Jc Other crystalline inorganic semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Electronic transport mechanisms of nonalloyed Pt Ohmic contacts to p-GaN

Ja-Soon Jang and Tae-Yeon Seong

Appl. Phys. Lett. 76, 2743 (2000); http://dx.doi.org/10.1063/1.126462 (3 pages) | Cited 43 times

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We report on the electronic transport mechanisms for nonalloyed Pt Ohmic contacts to p-GaN which were surface treated using a buffered oxide etch solution and (NH4)2Sx. Measurements show that the value of the effective Richardson constant (A∗∗) is 12 A cm−2 K−2, which is considerably smaller than the theoretical value of 103.8 A cm−2 K−2. Based on Hall-effect results, the two-step surface-treated contact is modeled to consist of a Pt/p+-/p-GaN structure, and the conventionally treated contact consists of a Pt/p-GaN structure. The theoretical results obtained using these models are compared with the experimental data. It is shown that for the conventionally treated contact thermionic emission dominates the current flow, whereas for the two-step surface-treated contact, field emission is dominant. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
81.05.Ea III-V semiconductors
73.40.Cg Contact resistance, contact potential
79.40.+z Thermionic emission
79.70.+q Field emission, ionization, evaporation, and desorption
81.65.Cf Surface cleaning, etching, patterning
72.20.My Galvanomagnetic and other magnetotransport effects
85.30.De Semiconductor-device characterization, design, and modeling

Influence of strain relaxation of the AlxGa1−xN barrier on transport properties of the two-dimensional electron gas in modulation-doped AlxGa1−xN/GaN heterostructures

B. Shen, T. Someya, and Y. Arakawa

Appl. Phys. Lett. 76, 2746 (2000); http://dx.doi.org/10.1063/1.126463 (3 pages) | Cited 37 times

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Influences of the thickness of the Si-doped n-type Al0.22Ga0.78N barrier and the thickness of the Al0.22Ga0.78N spacer on mobility and density of the two dimensional electron gas (2DEG) in modulation-doped Al0.22Ga0.78N/GaN heterostructures were investigated. 2DEG mobilities of 1274 cm2/V s at 300 K and 4495 cm2/V s at 77 K were reached. Both 2DEG mobility and density decrease dramatically when the Al0.22Ga0.78N barrier becomes partially relaxed, indicating that transport properties of the 2DEG are influenced significantly by the piezoelectric polarization of the Al0.22Ga0.78N layer. From our results, the critical thickness of an Al0.22Ga0.78N layer on GaN is estimated to be between 65 and 75 nm, which is much higher than that predicted by theoretical calculation. This may be attributed to the interaction of misfit dislocations and the presence of a high density of extended defects in the Al0.22Ga0.78N layer. © 2000 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Dn Low-field transport and mobility; piezoresistance
68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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Electric-pulse-induced reversible resistance change effect in magnetoresistive films

S. Q. Liu, N. J. Wu, and A. Ignatiev

Appl. Phys. Lett. 76, 2749 (2000); http://dx.doi.org/10.1063/1.126464 (3 pages) | Cited 362 times

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A large electric-pulse-induced reversible resistance change active at room temperature and under zero magnetic field has been discovered in colossal magnetoresistive (CMR) Pr0.7Ca0.3MnO3 thin films. Electric field-direction-dependent resistance changes of more than 1700% were observed under applied pulses of ∼ 100 ns duration and as low as ±5 V magnitude. The resistance changes were cumulative with pulse number, were reversible and nonvolatile. This electrically induced effect, observed in CMR materials at room temperature has both the benefit of a discovery in materials properties and the promise of applications for thin film manganites in the electronics arena including high-density nonvolatile memory. © 2000 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.47.De Giant magnetoresistance

Picosecond hot-electron energy relaxation in NbN superconducting photodetectors

K. S. Il’in, M. Lindgren, M. Currie, A. D. Semenov, G. N. Gol’tsman, Roman Sobolewski, S. I. Cherednichenko, and E. M. Gershenzon

Appl. Phys. Lett. 76, 2752 (2000); http://dx.doi.org/10.1063/1.126480 (3 pages) | Cited 51 times

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We report time-resolved characterization of superconducting NbN hot-electron photodetectors using an electro-optic sampling method. Our samples were patterned into micron-size microbridges from 3.5-nm-thick NbN films deposited on sapphire substrates. The devices were illuminated with 100 fs optical pulses, and the photoresponse was measured in the ambient temperature range between 2.15 and 10.6 K (superconducting temperature transition TC). The experimental data agreed very well with the nonequilibrium hot-electron, two-temperature model. The quasiparticle thermalization time was ambient temperature independent and was measured to be 6.5 ps. The inelastic electron–phonon scattering time τe–ph tended to decrease with the temperature increase, although its change remained within the experimental error, while the phonon escape time τes decreased almost by a factor of two when the sample was put in direct contact with superfluid helium. Specifically, τe–ph and τes, fitted by the two-temperature model, were equal to 11.6 and 21 ps at 2.15 K, and 10(±2) and 38 ps at 10.5 K, respectively. The obtained value of τe–ph shows that the maximum intermediate frequency bandwidth of NbN hot-electron phonon-cooled mixers operating at TC can reach 16(+4/−3) GHz if one eliminates the bolometric phonon-heating effect. © 2000 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.25.Am Superconducting device characterization, design, and modeling
85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions
74.10.+v Occurrence, potential candidates
74.25.Kc Phonons
74.25.Gz Optical properties

Gap symmetry and critical current of YBa2Cu3O7 step-edge Josephson junctions

Soon-Gul Lee and Yunseok Hwang

Appl. Phys. Lett. 76, 2755 (2000); http://dx.doi.org/10.1063/1.126465 (3 pages) | Cited 6 times

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Effects of d-wave symmetry on the critical current of high Tc step-edge Josephson junctions were studied theoretically by using the concept of grain-boundary junctions, and the theory was compared with experimental results of YBa2Cu3O7 step-edge junctions on SrTiO3 (100) substrates. A step-edge junction contains two grain boundaries, and each grain boundary has both in-plane and out-of-plane misorientation angles at the same time. The critical current of the step-edge junction as a function of the in-plane misorientation angle has a periodic modulation with maxima when the step line is parallel to one of the major axes of the SrTiO3 (100) substrate. Experimental results of c-oriented YBa2Cu3O7 step-edge junctions with various in-plane misorientation angles were qualitatively in good agreement with the theory. The out-of-plane misorientation angle is formed between two grains usually with the c axes perpendicular to each other and is normally not controllable. © 2000 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects

Suppression of magnetic-field pulse-induced magnetization precession by pulse tailoring

M. Bauer, R. Lopusnik, J. Fassbender, and B. Hillebrands

Appl. Phys. Lett. 76, 2758 (2000); http://dx.doi.org/10.1063/1.126466 (3 pages) | Cited 46 times

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Short magnetic-field pulses may be used in the near future to change the magnetization state in magnetic storage devices. In order to minimize the time required for this process, and thus to maximize the switching speed of such devices, the magnetization precession after the termination of the magnetic-field pulse needs to be suppressed to a maximum degree. It is demonstrated experimentally that the appropriate adjustment of the field pulse parameters may lead to a full suppression of the magnetization precession immediately upon termination of the field pulse. © 2000 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
78.66.Nk Insulators
78.20.Ls Magneto-optical effects
78.47.-p Spectroscopy of solid state dynamics

Large zinc cation occupancy of octahedral sites in mechanically activated zinc ferrite powders

S. A. Oliver, V. G. Harris, H. H. Hamdeh, and J. C. Ho

Appl. Phys. Lett. 76, 2761 (2000); http://dx.doi.org/10.1063/1.126467 (3 pages) | Cited 42 times

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The cation site occupancy of a mechanically activated nanocrystalline zinc ferrite powder was determined as (Zn0.552+Fe0.183+)tet[Zr0.452+Fe1.823+]octO4 through analysis of extended x-ray absorption fine structure measurements, showing a large redistribution of cations between sites compared to normal zinc ferrite samples. The overpopulation of cations in the octahedral sites was attributed to the ascendance in importance of the ionic radii over the crystal energy and bonding coordination in determining which interstitial sites are occupied in this structurally disordered powder. Slight changes are observed in the local atomic environment about the zinc cations, but not the iron cations, with respect to the spinel structure. The presence of Fe3+ on both sites is consistent with the measured room temperature magnetic properties. © 2000 American Institute of Physics.
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75.50.Gg Ferrimagnetics
61.46.-w Structure of nanoscale materials
75.50.Kj Amorphous and quasicrystalline magnetic materials
78.70.Dm X-ray absorption spectra
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Ferroelectricity in a pure BiFeO3 ceramic

M. Mahesh Kumar, V. R. Palkar, K. Srinivas, and S. V. Suryanarayana

Appl. Phys. Lett. 76, 2764 (2000); http://dx.doi.org/10.1063/1.126468 (3 pages) | Cited 223 times

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The difficulties in synthesizing phase pure BiFeO3 are well known. In this letter we are reporting the optimized synthesis conditions for obtaining phase pure BiFeO3 ceramic. The oxide mixing technique followed by leaching with dilute nitric acid has been used for the synthesis. X-ray diffraction pattern indicated that the sample is phase pure. Scanning electron microscopy along with energy dispersive x-ray fluorescence analysis confirmed the chemical homogeneity of the sample. No segregation of the impurity phase in the matrix was detected. Moreover, Bi/Fe atomic ratio is observed to be ∼1. The ferroelectric transition of the sample at 836 °C has been detected by differential thermal analysis. © 2000 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.80.B- Phase transitions and Curie point

Microscopic model of ferroelectricity in stress-free PbTiO3 ultrathin films

Ph. Ghosez and K. M. Rabe

Appl. Phys. Lett. 76, 2767 (2000); http://dx.doi.org/10.1063/1.126469 (3 pages) | Cited 111 times

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The ground-state polarization of PbTiO3 thin films is studied using a microscopic effective Hamiltonian with parameters obtained from first-principles calculations. Under short-circuit electrical boundary conditions, (001) films with thickness as low as three unit cells are found to have a perpendicularly polarized ferroelectric ground state with significant enhancement of the polarization at the surface. © 2000 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

Neutron intrinsic gettering on electrical property of gate oxynitride in metal-oxide-Si capacitor

Kuei-Shu Chang-Liao, Nan-Kuang Yi, and Jenn-Gwo Huang

Appl. Phys. Lett. 76, 2770 (2000); http://dx.doi.org/10.1063/1.126470 (3 pages) | Cited 2 times

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The electrical property of gate oxynitride in metal-oxide-Si capacitor is improved by a neutron-intrinsic-gettering (NIG) treatment. This improvement can be attributed to the reduction of nitrogen concentration in the oxynitride bulk and the decrease of interstitial oxygen defect in the silicon. For the oxynitride formed using NIG-treated Si substrate, the breakdown electric field is increased and the reliability is improved. A significant improvement of electrical property in gate oxynitride is observed by a NIG treatment including a fast neutron dose of 7.2×1016 cm−2 and an anneal at 1100 °C for 6 h. This NIG treatment would be promising for the improvement of electrical properties in gate oxynitrides. © 2000 American Institute of Physics.
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84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.80.Hg Neutron radiation effects
61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters
77.22.Jp Dielectric breakdown and space-charge effects

Glassy to inhomogeneous-ferroelectric crossover in (Pb, La)(Zr, Ti)O3 ceramics

V. Bobnar, Z. Kutnjak, and A. Levstik

Appl. Phys. Lett. 76, 2773 (2000); http://dx.doi.org/10.1063/1.126471 (3 pages) | Cited 27 times

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The temperature dependence of the dielectric nonlinearity a3 = ε3/ε14 has been determined in 9/65/35 (Pb, La)(Zr, Ti)O3 ceramics. In zero electric field a deep in the temperature behavior of the static a3 has been observed indicating a crossover from paraelectric-like to glass-like behavior on cooling towards the freezing transition. By varying a bias electric field another glass-to-ferroelectric crossover has been observed in the temperature dependence of the static a3. The observed crossovers as well as the temperature dependence of the linear static dielectric constant agree with the predictions of the spherical random-bond–random-field model of relaxor ferroelectrics. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point

Pyroelectric or piezoelectric compensated ferroelectric composites

Beatrix Ploss, Bernd Ploss, F. G. Shin, H. L. W. Chan, and C. L. Choy

Appl. Phys. Lett. 76, 2776 (2000); http://dx.doi.org/10.1063/1.126472 (3 pages) | Cited 36 times

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The matrix and inclusions of 0–3 composites of lead titanate (PT) in polyvinylidenefluoride trifluoroethylene (P(VDF–TrFE)) have been independently poled by a special poling method. The polarization states of both constituents are investigated by the measurement of the dynamic pyroelectric coefficients of the composites in the temperature range of 20–90 °C, within which the copolymer matrix undergoes a ferroelectric-paraelectric phase change. The pyroelectric coefficients of PT and P(VDF–TrFE) have the same sign, while their piezoelectric coefficients have opposite signs. This allows the preparation of composites with enhanced pyroelectric but reduced piezoelectric activity when the matrix and inclusions are polarized in the same direction, or vice versa if the constituents are oppositely polarized. For a PT volume fraction of 27% it was possible to prepare a pyroelectric composite with vanishing piezoelectric activity or a piezoelectric composite with vanishing pyroelectric activity by poling the matrix and inclusions in parallel or antiparallel directions. © 2000 American Institute of Physics.
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77.84.Lf Composite materials
77.70.+a Pyroelectric and electrocaloric effects
77.22.Ej Polarization and depolarization
77.65.Bn Piezoelectric and electrostrictive constants
77.80.-e Ferroelectricity and antiferroelectricity

Dielectric enhancement and ferroelectric anomaly of compositionally graded (Pb, Ca)TiO3 thin films derived by a modified sol–gel technique

Dinghua Bao, Xi Yao, and Liangying Zhang

Appl. Phys. Lett. 76, 2779 (2000); http://dx.doi.org/10.1063/1.126473 (3 pages) | Cited 42 times

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Compositionally graded (Pb, Ca)TiO3 thin films were prepared on platinum-coated silicon substrates by a monoethanolamine-modified sol–gel technique. The crystalline orientation and surface morphology of the graded films were related to the deposition sequence of the film layer. The dielectric constants, for up-graded and down-graded films annealed at 600 °C for 60 min were found to be 504 and 399, respectively. Both were larger than those reported for conventional (Pb, Ca)TiO3 thin films. The compositionally graded films had large polarization offsets in hysteresis loops when driven by an alternating electric field. The magnitude of polarization offsets displayed a power-law dependence on the electric field, and the direction of the offsets depended on the direction of the composition gradient with respect to the substrate. The offset, 120 μC/cm2 at 300 kV/cm driving electric field, was obtained. These results showed that compositionally graded (Pb, Ca)TiO3 thin films had enhanced dielectric properties and abnormal ferroelectric properties which can be used in various microelectronic devices. © 2000 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
68.55.Nq Composition and phase identification
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
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Trapping of quasiparticles of a nonequilibrium superconductor

J. P. Pekola, D. V. Anghel, T. I. Suppula, J. K. Suoknuuti, A. J. Manninen, and M. Manninen

Appl. Phys. Lett. 76, 2782 (2000); http://dx.doi.org/10.1063/1.126474 (3 pages) | Cited 25 times

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We have performed experiments where hot electrons are extracted from a normal metal into a superconductor through a tunnel junction. We have measured the cooling performance of such NIS junctions, especially in the cases where another normal metal electrode, a quasiparticle trap, is attached to the superconductor at different distances from the junction in direct metal–to–metal contact or through an oxide barrier. The direct contact at a submicron distance allows superior thermalization of the superconductor. We have analyzed theoretically the heat transport in this system. From both experiment and theory, it appears that NIS junctions can be used as refrigerators at low temperatures only with quasiparticle traps attached. © 2000 American Institute of Physics.
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74.45.+c Proximity effects; Andreev reflection; SN and SNS junctions
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

High visible rejection AlGaN photodetectors on Si(111) substrates

J. L. Pau, E. Monroy, F. B. Naranjo, E. Muñoz, F. Calle, M. A. Sánchez-García, and E. Calleja

Appl. Phys. Lett. 76, 2785 (2000); http://dx.doi.org/10.1063/1.126475 (3 pages) | Cited 23 times

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We report on the fabrication and characterization of Schottky barrier photodetectors based on Si-doped Al0.35Ga0.65N layers grown on Si(111) substrates, for solar UV-band monitoring (λ<320 nm). The epilayers have been obtained by plasma-assisted molecular-beam epitaxy, showing a full width at half maximum of 15 arcmin in x-ray diffraction measurements. A very high visible rejection (>104) and a responsivity of 5 mA/W at 257 nm are reached. The detector time response is limited by the resistance×capacitance product, with a minimum time constant of 20 ns in the zero-load-resistance limit. After photodiode voltage breakdown, the effect on the detector response is discussed. © 2000 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Pw Imaging detectors and sensors
85.30.Kk Junction diodes

InGaAsN/AlGaAs P-n-p heterojunction bipolar transistor

P. C. Chang, A. G. Baca, N. Y. Li, P. R. Sharps, H. Q. Hou, J. R. Laroche, and F. Ren

Appl. Phys. Lett. 76, 2788 (2000); http://dx.doi.org/10.1063/1.126476 (3 pages) | Cited 24 times

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We have demonstrated a functional P-n-p heterojunction bipolar transistor (HBT) using InGaAsN. The metalorganic-vapor-phase-epitaxy-grown Al0.3Ga0.7As/In0.03Ga0.97As0.99N0.01 HBT takes advantage of the narrower band gap energy (Eg = 1.2 eV) of In0.03Ga0.97As0.99N0.01, which is lattice matched to GaAs. Compared with the Al0.3Ga0.7As/GaAs material system, the Al0.3Ga0.7As/In0.03Ga0.97As0.99N0.01 material system has a larger conduction-band offset, while the valence-band offset remains comparable. This characteristic band alignment is very suitable for P-n-p HBT applications. The device’s peak current gain is 23, and it has a turn-on voltage of 0.77 V, which is 0.25 V lower than in a comparable P-n-p Al0.3Ga0.7As/GaAs HBT. © 2000 American Institute of Physics.
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85.30.Pq Bipolar transistors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
73.61.Ey III-V semiconductors

Refractive indices of InGaAsP lattice-matched to GaAs at wavelengths relevant to device design

S. G. Wallace, B. J. Robinson, P. Mascher, H. K. Haugen, D. A. Thompson, D. Dalacu, and L. Martinu

Appl. Phys. Lett. 76, 2791 (2000); http://dx.doi.org/10.1063/1.126477 (3 pages) | Cited 1 time

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The refractive indices of In1−xGaxAsyP1−y grown lattice-matched to GaAs by gas-source molecular-beam epitaxy, have been measured by variable angle spectroscopic ellipsometry. Indices in the transparent regime of these quaternaries, at 980 and 808 nm (relevant to the design of pump sources for erbium-doped fiber amplifiers and Nd:YAG lasers, respectively) and at 850 nm, are presented. © 2000 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Cr III-V semiconductors
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Surface electronic density of states of tetrahedral amorphous carbon investigated by scanning tunneling spectroscopy and ab initio calculations

K. Jarmo Koivusaari, Tapio T. Rantala, J. Levoska, and S. Leppävuori

Appl. Phys. Lett. 76, 2794 (2000); http://dx.doi.org/10.1063/1.126478 (3 pages) | Cited 6 times

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The surface electronic density of states of tetrahedral amorphous carbon has been measured by scanning tunneling microscopy and calculated by density functional theory. An analysis of these results and their comparison is presented here for a series of structures with different microscopic mass densities. The experimental structures were obtained by pulsed laser deposition with varying conditions resulting in diamond-like carbon thin films. The calculated carbon structures were generated by simulating a melting–cooling cycle with molecular dynamics using the density functional energetics within the local density approximation. The experimental and calculated densities of states show good agreement. Graphitic-like surface reconstruction is both observed at the sp3-rich tetrahedral amorphous carbon (ta-C) sample and found in the calculated ta-C slab structure. © 2000 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena
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