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18 Feb 2002

Volume 80, Issue 7, pp. 1111-1310

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Thermodynamic stability and diffusivity of near-equiatomic Ni–Mn alloys

Ling Ding, Peter F. Ladwig, Xinyan Yan, and Y. Austin Chang

Appl. Phys. Lett. 80, 1186 (2002); http://dx.doi.org/10.1063/1.1450042 (3 pages) | Cited 8 times

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The equilibrium phase diagram of the nickel-manganese system is determined between 500 and 850 °C, in the composition range between 25 and 70 at. % Ni. A combination of electron probe microanalysis, x-ray diffraction, and optical microscopy was employed to analyze 47 samples that were annealed anywhere from three to seven months. The equiatomic, antiferromagnetic, L10-NiMn phase that is of considerable technological interest was found to exist continuously between 500 and 700 °C. No other intermediate phases were found in this study at low temperatures. These results are in contrast to the currently accepted phase diagram published in most handbooks. A hot-isobaric-pressing method was used to initially bond samples that were subsequently used to determine interdiffusion coefficients in the Ni–Mn system at 650 °C. The Boltzmann–Matano method [T. Heumann, Z. Phys. Chem. 201, 168 (1952)] allowed the calculation of these interdiffusion coefficients across the α-Mn, β-Mn, γ-Mn, L10-NiMn, and γ-Ni phases. © 2002 American Institute of Physics.
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81.30.Bx Phase diagrams of metals, alloys, and oxides
66.30.Fq Self-diffusion in metals, semimetals, and alloys
75.50.Ee Antiferromagnetics
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Normal-incidence Ge quantum-dot photodetectors at 1.5 μm based on Si substrate

S. Tong, J. L. Liu, J. Wan, and Kang L. Wang

Appl. Phys. Lett. 80, 1189 (2002); http://dx.doi.org/10.1063/1.1449525 (3 pages) | Cited 30 times

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Coherent Ge quantum dots embedded in Si spacing layers were grown on Si substrate by molecular-beam epitaxy in the Stranski–Krastanov mode. Photoluminescence measurement showed a Ge-dot-related peak at 1.46 μm. p-i-n photodiodes with the intrinsic layer containing Ge dots were fabricated, and current–voltage (I–V) measurement showed a low dark current density of 3×10−5 A/cm2 at −1 V. A strong photoresponse at 1.3–1.52 μm originating from Ge dots was observed, and at normal incidence, an external quantum efficiency of 8% was achieved at −2.5 V. © 2002 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.40.+w Photoconduction and photovoltaic effects
78.67.Hc Quantum dots
73.63.Kv Quantum dots
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Improved extraction of carrier concentration and depletion width from capacitance–voltage characteristics of silicon n+–p-well junction diodes

A. Poyai, C. Claeys, and E. Simôen

Appl. Phys. Lett. 80, 1192 (2002); http://dx.doi.org/10.1063/1.1435809 (3 pages) | Cited 6 times

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An accurate method is proposed for the extraction of the carrier concentration profile (pp well) and the depletion width (Wp well) in a p-well region from high-frequency capacitance measurements by accounting for the series resistance and the capacitance of the n+ region. Wp well was calculated from the capacitance in the p-well region (Cp well), while pp well was derived from the slope of the plot 1/Cp well2 versus reverse bias. The pp well extracted was compared with profiles obtained from spreading resistance probe results. The differences between the two techniques are within 15% in the accessible depletion width, which will be discussed in view of the depth resolution anticipated. © 2002 American Institute of Physics.
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85.30.Kk Junction diodes
73.61.Cw Elemental semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Control of p- and n-type conductivity in sputter deposition of undoped ZnO

Gang Xiong, John Wilkinson, Brian Mischuck, S. Tüzemen, K. B. Ucer, and R. T. Williams

Appl. Phys. Lett. 80, 1195 (2002); http://dx.doi.org/10.1063/1.1449528 (3 pages) | Cited 96 times

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Recent theoretical studies have concluded that the low formation enthalpies of intrinsic donor defects should preclude achievement of p-type conductivity in undoped ZnO grown in thermal equilibrium with a molecular oxygen reservoir. This letter demonstrates that reactive sputtering can produce intrinsic p-type ZnO, controlled by adjusting the oxygen partial pressure in the sputtering plasma. We report the properties of p–n homojunctions fabricated in this way, and characterize transport in the films by Hall measurements. Our finding of p-type conductivity in undoped ZnO grown with dissociated oxygen is qualitatively consistent with the effect of higher chemical potential of atomic oxygen reactant on defect formation enthalpies. This parallels to some degree the recent attention to nitrogen acceptor incorporation by means of dissociating nitrogen source gases. © 2002 American Institute of Physics.
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73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
81.15.Cd Deposition by sputtering
71.55.Gs II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
68.55.-a Thin film structure and morphology
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Observation of the Mott–Gurney law in tris (8-hydroxyquinoline) aluminum films

M. Kiy, P. Losio, I. Biaggio, M. Koehler, A. Tapponnier, and P. Günter

Appl. Phys. Lett. 80, 1198 (2002); http://dx.doi.org/10.1063/1.1449527 (3 pages) | Cited 23 times

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We show that tris (8-hydroxyquinoline) aluminum (Alq3) thin films produced and characterized under ultrahigh vacuum conditions present a well-defined squared-law dependence of the injected current on the applied voltage at applied electric fields of the order of 0.25–1 MV/cm. From this, one derives an electric-field-independent electron mobility of the order of 10−7 cm2/(V s), with a variation between different samples of about one order of magnitude. Observations of current–voltage characteristics with clear indications of trap-filling and space-charge-limited conduction at high fields in Alq3 excludes the existence of traps with an exponential distribution of trap energies, as is commonly assumed in amorphous materials. © 2002 American Institute of Physics.
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73.61.Ng Insulators
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
73.50.Fq High-field and nonlinear effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

A nanofabrication scheme for InAs/AlSb heterostructures

M. J. Yang, K. A. Cheng, C. H. Yang, and J. C. Culbertson

Appl. Phys. Lett. 80, 1201 (2002); http://dx.doi.org/10.1063/1.1449526 (3 pages) | Cited 12 times

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We report a technique for nanofabrication in the InAs/GaSb/AlSb 6.1 Å material system that utilizes the large difference in the surface Fermi level pinning position for InAs [Efs(InAs)] compared with that for AlSb. An InAs/AlSb single quantum well is capped with a 3 nm, intentionally p-doped InAs layer. As a result of its construction and a relatively low Efs(InAs) there are no free carriers in the InAs/AlSb single quantum well making the quantum well insulating as-grown. Simply by selectively removing the thin p-doped InAs cap layer with a wet etch, the surface Fermi level becomes pinned on AlSb and shifted upward by half an electron volt. This results in a drastic change in band bending and creates a conducting electron channel in the buried InAs quantum well. We demonstrate with experiment and the support of a self-consistent band bending calculation that this scheme is highly effective for nanofabrication. © 2002 American Institute of Physics.
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81.16.-c Methods of micro- and nanofabrication and processing
81.07.St Quantum wells
81.05.Ea III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
73.21.Fg Quantum wells
73.63.Hs Quantum wells
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Evidence for nonlinear macroscopic polarization in III–V nitride alloy heterostructures

Vincenzo Fiorentini, Fabio Bernardini, and Oliver Ambacher

Appl. Phys. Lett. 80, 1204 (2002); http://dx.doi.org/10.1063/1.1448668 (3 pages) | Cited 119 times

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We provide explicit rules to calculate the nonlinear polarization for nitride alloys of arbitrary composition, and hence, the bound sheet charge induced by polarization discontinuity at the interfaces between different alloy and binary (epi)layers. We then present experimental results and simulations of polarization-related quantities in selected nitride-alloy-based heterostructure systems. The agreement of experiment and simulation, also in comparison to previous approaches, strongly suggests that the macroscopic polarization of nitride alloys is indeed nonlinear as a function of composition. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.65.-j Piezoelectricity and electromechanical effects
77.22.Ej Polarization and depolarization
68.65.Fg Quantum wells

ZnRh2O4: A p-type semiconducting oxide with a valence band composed of a low spin state of Rh3+ in a 4d6 configuration

Hiroshi Mizoguchi, Masahiro Hirano, Satoru Fujitsu, Tomonari Takeuchi, Kazushige Ueda, and Hideo Hosono

Appl. Phys. Lett. 80, 1207 (2002); http://dx.doi.org/10.1063/1.1450252 (3 pages) | Cited 33 times

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It is demonstrated that a ZnRh2O4 normal spinel with a band gap of ∼2.1 eV is a unique material as a p type wide-gap semiconductor. The electrical conductivity of the sputtered film was 0.7 S cm−1 at 300 K with no intentional doping. The electronic structure was investigated by photoemission and inverse photoemission measurements and indicated that the band gap is composed mainly of ligand field splitting of an octahedrally coordinated Rh3+ octahedron between fully occupied t2g6 and empty eg0 sets. © 2002 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
71.20.Nr Semiconductor compounds
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.70.-g Interactions of particles and radiation with matter
72.80.Jc Other crystalline inorganic semiconductors
71.70.Ch Crystal and ligand fields

Optical and electrical properties of Mg-doped p-type AlxGa1−xN

J. Li, T. N. Oder, M. L. Nakarmi, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 80, 1210 (2002); http://dx.doi.org/10.1063/1.1450038 (3 pages) | Cited 49 times

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Mg-doped AlxGa1−xN epilayers with Al content up to 0.27 were grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD). p-type conduction in these alloys has been achieved, as confirmed by variable temperature Hall-effect measurements. Emission lines of band-to-impurity transitions of free electrons with neutral Mg acceptors as well as localized excitons have been observed in the p-type AlxGa1−xN alloys. The Mg acceptor activation energies EA were deduced from photoluminescence spectra and were found to increase with Al content and agreed very well with those obtained by Hall measurements. From the measured activation energy as a function of the Al content, EA versus x the resistivity of AlxGa1−xN alloys with high Al contents can be deduced. Our results thus indicated that alternative methods for acceptor activation in AlGaN alloys with high Al contents must be developed. Our results have also shown that PL measurements provide direct means of obtaining EA, especially where this cannot be obtained accurately by electrical methods due to high resistance of Mg-doped AlxGa1−xN alloys with high Al content. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.55.Eq III-V semiconductors

Photocurrent studies of an active polymer layer in a resonant microcavity

Th. B. Singh, U. V. Waghmare, and K. S. Narayan

Appl. Phys. Lett. 80, 1213 (2002); http://dx.doi.org/10.1063/1.1448171 (3 pages) | Cited 7 times

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A microcavity enhanced photodiode, consisting of an active semiconducting-polymer layer is studied in detail. The photodiode spectral response indicates features which specifically arise from the cavity geometry factors, as expected from the simulation of the optical-field pattern within the cavity. The results indicate the tuning of photodetection energy range far below the band gap of semiconducting polymer along with sizable gain and speed. © 2002 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.66.Qn Polymers; organic compounds

PbTe based superlattice structures with high thermoelectric efficiency

H. Beyer, J. Nurnus, H. Böttner, A. Lambrecht, T. Roch, and G. Bauer

Appl. Phys. Lett. 80, 1216 (2002); http://dx.doi.org/10.1063/1.1448388 (3 pages) | Cited 38 times

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We report on an enhanced thermoelectric figure of merit ZT = σS2T/λ (where σ is electrical conductivity, S is thermopower, T is absolute temperature, and λ is thermal conductivity) for PbTe/PbSe0.20Te0.80 superlattices (SLs) and PbTe doping SLs due to a reduction of the thermal conductivity λ parallel to the layer planes. Despite a small decrease of the power factors σS2 due to a reduction of σ in these superlattices, the figure of merit is higher as compared to the corresponding bulk materials and reaches maximum values in the temperature range between 400 and 570 K.© 2002 American Institute of Physics.
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73.61.Le Other inorganic semiconductors
73.50.Lw Thermoelectric effects
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Logarithmically perturbed two dimensional oscillator model of a quantum-dot nanostructure

Mark W. Coffey

Appl. Phys. Lett. 80, 1219 (2002); http://dx.doi.org/10.1063/1.1448663 (3 pages) | Cited 2 times

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We present a logarithmically perturbed two-dimensional isotropic oscillator model of a quantum-dot nanostructure. The logarithmic potential has an ionic line charge physical origin. We estimate the magnitude of this line charge and we obtain the matrix elements required by perturbation theory. The measured ground-state energy depression for a GaAs/AlGaAs/InGaAs heterostructure can be quantitatively accounted for by the model (although not uniquely). We include the effects of nonzero angular momentum states, which play a significant role in determining the dot current–voltage curves. We mention the immediate selection rule imposed by a perturbing potential of rotational symmetry, together with further analytic results. © 2002 American Institute of Physics.
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73.21.La Quantum dots

Hydrogen response mechanism of Pt–GaN Schottky diodes

J. Schalwig, G. Müller, U. Karrer, M. Eickhoff, O. Ambacher, M. Stutzmann, L. Görgens, and G. Dollinger

Appl. Phys. Lett. 80, 1222 (2002); http://dx.doi.org/10.1063/1.1450044 (3 pages) | Cited 79 times

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Besides silicon carbide, group-III nitrides are also suitable large-band-gap semiconductor materials for high-temperature gas sensor devices. Exposing GaN-based Schottky diodes with catalytically active platinum electrodes to hydrogen, we observed a decrease of the rectifying characteristics which we attribute to a decrease in Schottky barrier height. Current–voltage and elastic recoil detection measurements were used to investigate the H-sensing behavior of such devices. Our results indicate an interfacial effect as the origin of the sensor response to hydrogen. © 2002 American Institute of Physics.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
82.45.Jn Surface structure, reactivity and catalysis
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
73.40.Ei Rectification

Common-emitter current–voltage characteristics of a pnp GaN bipolar junction transistor

Kazuhide Kumakura, Toshiki Makimoto, and Naoki Kobayashi

Appl. Phys. Lett. 80, 1225 (2002); http://dx.doi.org/10.1063/1.1447593 (3 pages) | Cited 7 times

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We fabricated a pnp GaN bipolar junction transistor and investigated its common-emitter current–voltage characteristics. The device structures were grown by metalorganic vapor phase epitaxy on a sapphire substrate. The base thickness was 0.12 μm and its doping concentration was estimated to be lower than mid-1017 cm−3. We have obtained a maximum common-emitter current gain of 50 at room temperature for collector current ranging from −10−5 to −10−4 A. © 2002 American Institute of Physics.
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85.30.Pq Bipolar transistors

Acoustic phonon scattering of two-dimensional electrons in GaN/AlGaN heterostructures

W. Knap, E. Borovitskaya, M. S. Shur, L. Hsu, W. Walukiewicz, E. Frayssinet, P. Lorenzini, N. Grandjean, C. Skierbiszewski, P. Prystawko, M. Leszczynski, and I. Grzegory

Appl. Phys. Lett. 80, 1228 (2002); http://dx.doi.org/10.1063/1.1448401 (3 pages) | Cited 19 times

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We have measured the temperature dependence of the mobility of the two-dimensional electron gas in AlGaN/GaN heterostructures grown on bulk GaN substrates. The linear dependence of the inverse mobility on temperature at temperatures below 50 K indicates the importance of acoustic phonon scattering in these high mobility heterostructures. Using the temperature dependence of the mobility at a range of carrier densities, we determined the GaN conduction band deformation potential to be ac = 9.1±0.7 eV. This result provides a crucial parameter for accurate calculations of intrinsic mobility limits in AlGaN/GaN heterostructures. © 2002 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Negative differential resistance in scanning-tunneling spectroscopy of diamond films

D. D. D. Ma, Y. G. Wang, Li Lu, C. S. Lee, and S. T. Lee

Appl. Phys. Lett. 80, 1231 (2002); http://dx.doi.org/10.1063/1.1448168 (3 pages) | Cited 4 times

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Heavily boron-doped diamond film surfaces were investigated using ultra high-vacuum scanning tunneling microscopy. Negative differential resistance (NDR) was observed in the I–V curves measured from the diamond facets using scanning tunneling spectroscopy. NDR peaks with a peak-to-valley ratio as high as 90 were observed in about half of the I–V curves measured at room temperature. The NDR phenomenon is attributed to the existence of localized electron states on the diamond film surfaces. The I–V curves obtained at the diamond grain boundaries showed the characteristics of the graphite phase, while those acquired from the grain facets manifested obvious rectification in accordance with the wide band gap of diamond. © 2002 American Institute of Physics.
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73.61.Cw Elemental semiconductors
73.50.Fq High-field and nonlinear effects
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.20.At Surface states, band structure, electron density of states
61.72.Mm Grain and twin boundaries
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Role of boron on grain sizes and magnetic correlation lengths in recording media as determined by soft x-ray scattering

Olav Hellwig, D. T. Margulies, B. Lengsfield, Eric E. Fullerton, and J. B. Kortright

Appl. Phys. Lett. 80, 1234 (2002); http://dx.doi.org/10.1063/1.1448665 (3 pages) | Cited 14 times

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We have measured the chemical grain sizes and magnetic correlation lengths in CoCr-based magnetic recording media films using resonant soft x-ray small-angle scattering. We find that the addition of boron, while leading to slightly smaller physical grains, dramatically reduces the magnetic correlation length. These results show that B additions effectively act to suppress intergranular magnetic exchange via segregation to the grain boundaries. © 2002 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.-a Thin film structure and morphology
75.50.Ss Magnetic recording materials
75.50.Cc Other ferromagnetic metals and alloys
78.70.Ck X-ray scattering
75.30.Et Exchange and superexchange interactions
61.72.Mm Grain and twin boundaries
64.75.-g Phase equilibria

Magnetic CdSe-based quantum dots grown on Mn-passivated ZnSe

L. V. Titova, J. K. Furdyna, M. Dobrowolska, S. Lee, T. Topuria, P. Moeck, and N. D. Browning

Appl. Phys. Lett. 80, 1237 (2002); http://dx.doi.org/10.1063/1.1450254 (3 pages) | Cited 15 times

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In this letter we describe the properties of self-assembled CdSe quantum dots (QDs) grown on Mn-passivated ZnSe buffers. We show that the Mn deposited on the ZnSe surface during the passivation process acts as a nucleating seed for self-assembled QD formation. For moderate amounts of Mn deposition, the dots grown in this way show a significant improvement in size uniformity compared to CdSe dots grown on ZnSe without Mn passivation. Using photoluminescence, we also show that the dots exhibit large Zeeman splitting, indicating that this growth method is suitable for fabricating magnetic QDs that exhibit strong spin polarization effects. © 2002 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Rv Passivation
68.65.Hb Quantum dots (patterned in quantum wells)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Pp Magnetic semiconductors
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
78.20.Ls Magneto-optical effects

Efficient electrical spin injection from a magnetic metal/tunnel barrier contact into a semiconductor

A. T. Hanbicki, B. T. Jonker, G. Itskos, G. Kioseoglou, and A. Petrou

Appl. Phys. Lett. 80, 1240 (2002); http://dx.doi.org/10.1063/1.1449530 (3 pages) | Cited 372 times

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We report electrical spin injection from a ferromagnetic metal contact into a semiconductor light emitting diode structure with an injection efficiency of 30% which persists to room temperature. The Schottky barrier formed at the Fe/AlGaAs interface provides a natural tunnel barrier for injection of spin polarized electrons under reverse bias. These carriers radiatively recombine, emitting circularly polarized light, and the quantum selection rules relating the optical and carrier spin polarizations provide a quantitative, model-independent measure of injection efficiency. This demonstrates that spin injecting contacts can be formed using a widely employed contact methodology, providing a ready pathway for the integration of spin transport into semiconductor processing technology. © 2002 American Institute of Physics.
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72.25.Mk Spin transport through interfaces
73.40.Ns Metal-nonmetal contacts
85.60.Jb Light-emitting devices
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
73.61.Ey III-V semiconductors
73.61.At Metal and metallic alloys
73.40.Gk Tunneling
75.50.Bb Fe and its alloys
75.70.Ak Magnetic properties of monolayers and thin films

Fast development of high coercivity in melt-spun Sm(Co,Fe,Cu,Zr)z magnets

A. Yan, A. Bollero, K. H. Müller, and O. Gutfleisch

Appl. Phys. Lett. 80, 1243 (2002); http://dx.doi.org/10.1063/1.1450253 (3 pages) | Cited 23 times

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A simple method was developed for magnetic hardening melt-spun Sm(Co,Fe,Cu,Zr)z alloys. The as-spun ribbons reached a coercivity of 2.8 T only by slow cooling from 850 to 400 °C, without the standard solid solution and isothermal aging treatments which are required for a bulk precipitation hardened 2:17 SmCo alloy. A single 1:7 phase, identical to that found in as-solubilized ribbons, was obtained in the as-spun state. At the same time, Cu and Zr are supersaturately dissolved in the 1:7 matrix by melt spinning due to its very high cooling rate. Thus, solid solution treatment can be avoided for melt-spun materials. After aging, more lamellar phase with larger width was observed by transmission electron microscope in ribbons without treatment in solution. This leads to faster development of a uniform finer cellular microstructure with a Cu-rich 1:5 cell boundary phase, which gives rise to stronger domain-wall pinning and therefore to higher coercivity. © 2002 American Institute of Physics.
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75.50.Ww Permanent magnets
07.55.Db Generation of magnetic fields; magnets
75.50.Vv High coercivity materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure

Approach to saturation in nanomagnetic systems: Easy axis distribution and interactions

R. Iglesias and H. Rubio

Appl. Phys. Lett. 80, 1246 (2002); http://dx.doi.org/10.1063/1.1447600 (3 pages) | Cited 1 time

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Using the applied field angle dependence of the approach to saturation of the magnetization, a theory for the determination of the distribution of easy axes of anisotropy and the ratio between interaction and anisotropy in bidimensional nanomagnetic materials is proposed. The usual saturation process laws in two dimensions at high and intermediate field ranges are recovered and other dependencies between the former are found and justified in terms of scaling arguments. Finally, an approximate analytical model that provides a simpler method by which to determine the easy axis distribution and interaction strength is discussed. © 2002 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
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Spectroscopic ellipsometry characterization of high-k dielectric HfO2 thin films and the high-temperature annealing effects on their optical properties

Yong Jai Cho, N. V. Nguyen, C. A. Richter, J. R. Ehrstein, Byoung Hun Lee, and Jack C. Lee

Appl. Phys. Lett. 80, 1249 (2002); http://dx.doi.org/10.1063/1.1448384 (3 pages) | Cited 55 times

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The optical properties of a set of high-k dielectric HfO2 films annealed at various high temperatures were determined by spectroscopic ellipsometry. The results show that the characteristics of the dielectric functions of these films are strongly affected by high temperature annealing. For a sample annealed at 600 °C, the film becomes polycrystalline, and its dielectric function displays a distinctive peak at 5.9 eV. On the other hand, the film remains amorphous without the 5.9 eV feature after 500 °C annealing. To model the dielectric functions, the Tauc–Lorentz dispersion was successfully adopted for these amorphous and polycrystalline films. The absorption edge was observed to shift to a higher energy at a high temperature annealing. Defects in the films were shown to relate to the appearance of a band tail above the absorption edge, and they appear to diminish with high temperature annealing. © 2002 American Institute of Physics.
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78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.55.-g Dielectric thin films

NH3-annealed atomic-layer-deposited silicon nitride as a high-k gate dielectric with high reliability

Anri Nakajima, Quazi D. M. Khosru, Takashi Yoshimoto, Toshirou Kidera, and Shin Yokoyama

Appl. Phys. Lett. 80, 1252 (2002); http://dx.doi.org/10.1063/1.1447314 (3 pages) | Cited 15 times

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Extremely thin (equivalent oxide thickness, Teq = 1.2 nm) silicon-nitride high-k (ϵr = 7.2) gate dielectrics have been formed at low temperatures (⩽550 °C) by an atomic-layer-deposition (ALD) technique with subsequent NH3 annealing at 550 °C. A remarkable reduction in leakage current, especially in the low dielectric voltage region, which will be the operating voltage for future technologies, has made it a highly potential gate dielectric for future ultralarge-scale integrated devices. Suppressed soft breakdown events are observed in ramped voltage stressing. This suppression is thought to be due to a strengthened structure of Si–N bonds and the smoothness and uniformity at the poly-Si/ALD-silicon-nitride interface. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.55.-a Thin film structure and morphology
61.72.Cc Kinetics of defect formation and annealing
85.30.Tv Field effect devices
77.22.Jp Dielectric breakdown and space-charge effects
68.35.Ct Interface structure and roughness
68.35.B- Structure of clean surfaces (and surface reconstruction)

Barium–strontium–titanate thin films for application in radio-frequency-microelectromechanical capacitive switches

S. W. Kirchoefer, E. J. Cukauskas, N. S. Barker, H. S. Newman, and W. Chang

Appl. Phys. Lett. 80, 1255 (2002); http://dx.doi.org/10.1063/1.1450263 (3 pages) | Cited 13 times

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In this letter we report the application of barium–strontium–titanate (BST) thin film oxides as the dielectric layer in radio-frequency-microelectromechanical system (rf-MEMS) capacitive switches. BST thin films deposited at ambient temperature by off-axis sputtering have been employed for application in rf-MEMS switches. Their dielectric properties have been characterized in the frequency range from 1 to 20 GHz both on magnesium oxide and on gold metal films. Switches have been fabricated which demonstrate promising on-state capacitance and good dielectric breakdown properties. Dielectric breakdown in excess of 400 kV/cm has been measured on switches cycled in excess of 2000 times during testing. © 2002 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
84.32.Dd Connectors, relays, and switches
84.32.Tt Capacitors
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.22.Jp Dielectric breakdown and space-charge effects
81.15.Cd Deposition by sputtering

Thickness-dependent phase evolution of polycrystalline Pb(Zr0.35Ti0.65)O3 thin films

Maxim B. Kelman, Lawrence F. Schloss, Paul C. McIntyre, Bryan C. Hendrix, Steven M. Bilodeau, and Jeffrey F. Roeder

Appl. Phys. Lett. 80, 1258 (2002); http://dx.doi.org/10.1063/1.1449532 (3 pages) | Cited 24 times

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The structural and electrical properties of metalorganic chemical vapor deposition-grown Pb(Zr0.35Ti0.65)O3 thin films ranging in thickness from 700 to 4000 Å have been investigated. Cross-sectional scanning electron microscopy showed that these films are columnar, with grains extending through the thickness of the film. High-resolution x-ray diffraction showed that while the thickest films are tetragonal, with reflections corresponding to a-type and c-type domains, films thinner than 1500 Å are not. Electron backscatter diffraction and hysteresis loop measurements showed that the thinnest films are ferroelectric and have a rhombohedral crystal structure. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.B- Phase transitions and Curie point
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.20.Kz Other electron-impact emission phenomena
77.80.Dj Domain structure; hysteresis
61.66.Fn Inorganic compounds
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