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11 Oct 1999

Volume 75, Issue 15, pp. 2163-2335

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Fine structures of photoresponse spectra in quantum well infrared photodetector

Ning Li, Y. Fu, M. Karlsteen, M. Willander, Na Li, X. Q. Liu, X. Z. Yuan, W. Lu, and S. C. Shen

Appl. Phys. Lett. 75, 2238 (1999); http://dx.doi.org/10.1063/1.124976 (3 pages) | Cited 5 times

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We study the fine structures in the photoresponse spectra of GaAs/AlGaAs quantum well infrared photodetectors and the influences from γ irradiation (1-16 Mrad), rapid time annealing (800, 850 and 900 °C for 30 s) and ion implantation (450 keV 0.7×, 1.0× and 5.0×1015 cm−2). With the theoretical analysis a ±-monolayer change has been concluded in the well width of the as-grown GaAs quantum wells in our photodetector. The γ irradiation decreases the carrier lifetime (the relaxation energy Γ increases with the irradiation dose α in the manner of Γ∝α1.5), while the rapid thermal annealing and ion-implantation processes enhance the Al diffusion across the GaAs/AlGaAs heterointerfaces the relaxation energy increases at the same time. © 1999 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
61.80.Ed γ-ray effects
61.82.Fk Semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.72.uj III-V and II-VI semiconductors

Determination of photoluminescence mechanism in InGaN quantum wells

Philippe Riblet, Hideki Hirayama, Atsuhiro Kinoshita, Akira Hirata, Takuo Sugano, and Yoshinobu Aoyagi

Appl. Phys. Lett. 75, 2241 (1999); http://dx.doi.org/10.1063/1.124977 (3 pages) | Cited 63 times

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We report on the unambiguous experimental determination of the photoluminescence mechanism in a set of In0.25Ga0.75N quantum wells. Instead of studying the photoluminescence for different In contents, we have investigated it as a function of the quantum well width in combination with a similar study performed on GaN quantum wells. In this way, we show that the photoluminescence is not coming from quantum dots or very localized states in the quantum well, but from the quantum well itself under the influence of a piezoelectric field induced by strain. The previously reported abnormal photoluminescence shifts and temperature dependencies can thus be explained. © 1999 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

High electron mobility polycrystalline silicon thin-film transistors on steel foil substrates

Ming Wu, Kiran Pangal, J. C. Sturm, and Sigurd Wagner

Appl. Phys. Lett. 75, 2244 (1999); http://dx.doi.org/10.1063/1.124978 (3 pages) | Cited 29 times

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Thin-film transistors have been fabricated in polycrystalline silicon films on steel foil. The polycrystalline silicon films were formed by the crystallization of hydrogenated amorphous silicon, which had been deposited on 200-μm-thick foils of stainless steel coated with ∼0.5-μm-thick layers of SiO2. We employed crystallization temperatures (and duration) of 600 °C (6 h), 650 °C (1 h), and 700 °C (10 min). Top-gate transistors made from films crystallized at 650 °C have an average electron field-effect mobility of 64 cm2/V s, with equal values in the linear and saturated regimes. Thus steel substrates permit a substantial reduction in crystallization time over glass substrates, and afford polysilicon with high electron mobility. © 1999 American Institute of Physics.
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85.30.Tv Field effect devices
81.05.Cy Elemental semiconductors

Polarization dependent photocurrent spectroscopy of InAs/GaAs quantum dots

L. Chu, M. Arzberger, A. Zrenner, G. Böhm, and G. Abstreiter

Appl. Phys. Lett. 75, 2247 (1999); http://dx.doi.org/10.1063/1.124979 (3 pages) | Cited 36 times

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We have performed interband photocurrent spectroscopy on self-assembled InAs/GaAs quantum dots using a graded index separate confinement heterostructure in waveguide geometry. The photocurrent spectrum of the quantum dots is found to be shifted to higher energies in comparison to the photoluminescence spectrum. The polarization dependent measurements show that the valence band ground states of strained InAs islands have heavy hole character. In a structure with seven vertically stacked quantum dot layers separated by 10 nm GaAs spacers, we find a change in the photocurrent spectra which is evidence for vertical coupling. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.50.Pz Photoconduction and photovoltaic effects

Scanning capacitance microscopy of AlGaN/GaN heterostructure field-effect transistor epitaxial layer structures

K. V. Smith, E. T. Yu, J. M. Redwing, and K. S. Boutros

Appl. Phys. Lett. 75, 2250 (1999); http://dx.doi.org/10.1063/1.124980 (3 pages) | Cited 13 times

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Scanning capacitance microscopy is used to characterize local electronic properties in an AlxGa1−xN/GaN heterostructure field-effect transistor epitaxial layer structure. Lateral inhomogeneity in electronic properties is clearly observed, at length scales ranging from ∼0.1 to >2 μm, in images obtained at fixed bias voltages. Acquisition of a series of images over a wide range of bias voltages allows local electronic structure to be probed with nanoscale spatial resolution both laterally and in depth. Combined with theoretical analysis of charge and potential distributions in the epitaxial layer structure under applied bias, these studies suggest that the dominant factor contributing to the observed variations in electronic structure is local lateral variations in AlxGa1−xN layer thickness. © 1999 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
85.30.Tv Field effect devices

Strain relaxation of InxGa1−xAs during lateral oxidation of underlying AlAs layers

P. Chavarkar, L. Zhao, S. Keller, A. Fisher, C. Zheng, J. S. Speck, and U. K. Mishra

Appl. Phys. Lett. 75, 2253 (1999); http://dx.doi.org/10.1063/1.124981 (3 pages) | Cited 13 times

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Strain relaxation of hypercritical thickness InxGa1−xAs layers has been observed during lateral oxidation of underlying AlAs layers. Strain relaxation of InxGa1−xAs layers was studied as a function of indium composition and the AlAs oxidation temperature. It is proposed that the enhanced strain relaxation is due to two factors. The first is enhanced motion of threading dislocations due to stresses generated during the lateral oxidation process. The second is the porous nature of the InxGa1−xAs/Al2O3 interface that minimizes the interaction of threading dislocations with existing misfit dislocation segments. The extent of strain relaxation increases with increasing oxidation temperature, whereas the efficiency of strain relaxation was found to decrease with increasing indium composition. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.65.Mq Oxidation
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

Anisotropic patterns formed in Ag–As–S ion-conducting amorphous semiconductor films by polarized light

Keiji Tanaka, Tamihiro Gotoh, and Hideki Hayakawa

Appl. Phys. Lett. 75, 2256 (1999); http://dx.doi.org/10.1063/1.124982 (3 pages) | Cited 6 times

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Linearly polarized light can produce an anisotropic surface corrugation in amorphous chalcogenide films of Ag–As–S. The corrugation resembles a mouth whisker consisting of narrow fringes which are parallel to the electric field of light and streaks which radiate from the illuminated spot to directions nearly perpendicular to the electric field. Optical birefringence of about 0.01 appears with this pattern. A photo–electro–ionic interaction, which produces a form-birefringent structure, seems to be responsible for the formation process. © 1999 American Institute of Physics.
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81.65.-b Surface treatments
81.05.Gc Amorphous semiconductors
78.66.Jg Amorphous semiconductors; glasses
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.43.Fs Glasses
68.55.-a Thin film structure and morphology
78.20.Fm Birefringence
61.82.Fk Semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Energetics of segregation in β-C2BN

R. Q. Zhang, K. S. Chan, H. F. Cheung, and S. T. Lee

Appl. Phys. Lett. 75, 2259 (1999); http://dx.doi.org/10.1063/1.124983 (3 pages) | Cited 7 times

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We show that β-phase boron–carbon–nitrogen (C2BN) structures energetically favor segregation into superlattices of alternating diamond and cubic boron nitride (cBN) layers. Local-density functional calculations of total energies using pseudopotential approximations and a plane-wave basis set of the β-C2BN systems with different thicknesses of alternating diamond and cBN layers grown along the (001) direction found a decrease in the formation energy with an increase in the layer thickness. We consider this phenomenon to be a result of the charge redistribution in each layer due to interface formation. Our study indicates that the deviation of charge distributions from those in pure diamond and cBN structures due to the existence of BN–C junctions in β-C2BN may result in difficulties in its synthesis. © 1999 American Institute of Physics.
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64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
71.15.Nc Total energy and cohesive energy calculations
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
68.35.Ct Interface structure and roughness

Electrostatic mechanism for cooling semiconductor heterostructures

Luis G. C. Rego and George Kirczenow

Appl. Phys. Lett. 75, 2262 (1999); http://dx.doi.org/10.1063/1.124984 (3 pages) | Cited 3 times

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We introduce the physical concepts of an electrostatic mechanism for cooling semiconductor heterostructures. The cooling results from an adiabatic expansion that redistributes electrons among the quasi-two-dimensional subbands of a quantum well, and can be controlled by an external electric field perpendicular to the plane of the well. Under ideal conditions, the final temperature is half of the original and the dynamics of the process is completely universal and reversible. The applicability of this mechanism is verified by self-consistent calculations for AlGaAs/GaAs quantum wells at temperatures below 1 K. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment

Phonon-assisted tunneling and interface quality in nanocrystalline Si/amorphous SiO2 superlattices

L. Tsybeskov, G. F. Grom, P. M. Fauchet, J. P. McCaffrey, J.-M. Baribeau, G. I. Sproule, and D. J. Lockwood

Appl. Phys. Lett. 75, 2265 (1999); http://dx.doi.org/10.1063/1.124985 (3 pages) | Cited 20 times

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We report on the interface quality and phonon-assisted tunneling in nanocrystalline Si (nc-Si)/amorphous SiO2 (a-SiO2) superlattices (SLs) prepared by magnetron sputtering and thermal crystallization of nanometer-thick a-Si layers. Phonon-assisted tunneling is observed in a bipolar nc-Si based structure, which confirms that the nc-Si/a-SiO2 junction is not only abrupt but also nearly defect free. The conclusion is supported by capacitance–voltage measurements from which the estimated interface defect density is found to be ∼ 1011 cm−2 for an eight-period SL. Such high quality interfaces hold considerable promise for the development of nc-Si SL quantum devices. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.35.Ct Interface structure and roughness
73.40.Gk Tunneling
63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions
73.61.Cw Elemental semiconductors

High rate etching of SiC using inductively coupled plasma reactive ion etching in SF6-based gas mixtures

F. A. Khan and I. Adesida

Appl. Phys. Lett. 75, 2268 (1999); http://dx.doi.org/10.1063/1.124986 (3 pages) | Cited 61 times

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Inductively coupled plasma (ICP) reactive ion etching of SiC was investigated using SF6 plasmas. Etch rates were studied as a function of substrate bias voltage (−3 to −500 V), ICP coil power (500–900 W), and chamber pressure (1–6 mT). The highest etch rate (970 nm/min) for SiC yet reported was achieved. Anisotropic etch profiles with highly smooth surfaces free of micromasking effects were obtained. The addition of O2 to the SF6 plasma was found to slightly increase the etch rate. © 1999 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Hd Other semiconductors
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Substitutional carbon reduction in SiGeC alloys grown by rapid thermal chemical vapor deposition

C. W. Liu, Y. D. Tseng, and Y. S. Huang

Appl. Phys. Lett. 75, 2271 (1999); http://dx.doi.org/10.1063/1.124987 (3 pages) | Cited 3 times

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The substitutional carbon reduction in Si1−x−yGexCy strained layers, annealed at high temperatures, increases the compressive strain in the originally strain-compensated alloys. From the rocking curve simulation, the maximum amount of carbon reduction was below 0.9% for the various samples which were annealed below 1000 °C in the nitrogen flow. The interstitial silicon injection by thermal oxidation of the Si cap on the Si1−x−yGexCy layer enhances the reduction of substitutional carbon to a concentration of 1.3%. Oxidation of Si1−x−yGexCy alloys yields a Ge-enriched Si1−xGex layer with the Ge concentration larger than the initial content, and the formation of 3C silicon carbide precipitate is observed by the Fourier transform infrared spectroscopy. © 1999 American Institute of Physics.
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68.55.Nq Composition and phase identification
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments
81.65.Mq Oxidation
78.30.Hv Other nonmetallic inorganics
78.66.Li Other semiconductors
68.60.Bs Mechanical and acoustical properties

Synchrotron-radiation-induced anisotropic wet etching of GaAs

Qing Ma, Derrick C. Mancini, and Richard A. Rosenberg

Appl. Phys. Lett. 75, 2274 (1999); http://dx.doi.org/10.1063/1.124988 (3 pages) | Cited 7 times

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A room-temperature photoenhanced chemical wet etching process for n-type GaAs using x rays from a synchrotron radiation source is described. HNO3:H2O was used as the etching solution. This process produces smoothly etched surfaces on n-GaAs with a root-mean-square surface roughness of 0.7–2.0 nm, which compares favorably to the unetched surface roughness (0.4 nm). Dependence of the etching rate on x-ray intensity and energy, solution concentration, and semiconductor doping type are reported. © 1999 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
82.50.-m Photochemistry
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.80.Cb X-ray effects
82.20.Pm Rate constants, reaction cross sections, and activation energies

Heating of photogenerated electrons and holes in highly excited GaN epilayers

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

Appl. Phys. Lett. 75, 2277 (1999); http://dx.doi.org/10.1063/1.124989 (3 pages) | Cited 12 times

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Heating of nonequilibrium carriers under intense off-resonant photogeneration was investigated in GaN epilayers at T = 80 K. We determined that under these extreme conditions hot electrons and hot holes exhibit different patterns of energy dissipation. A good agreement between the experimental data and modeling results was achieved by assuming negligible efficiency of optical-phonon emission by holes. This implies that hot holes, contrary to hot electrons, are unable to establish a smooth distribution function above the threshold of optical phonon emission. We attribute this effect to a large hole mass, strong carrier–phonon coupling, and large optical-phonon energies in GaN. © 1999 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Fq High-field and nonlinear effects
73.50.Pz Photoconduction and photovoltaic effects
63.20.K- Phonon interactions
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations

Effect of substrate temperature and V/III flux ratio on In incorporation for InGaN/GaN heterostructures grown by plasma-assisted molecular-beam epitaxy

M. L. O’Steen, F. Fedler, and R. J. Hauenstein

Appl. Phys. Lett. 75, 2280 (1999); http://dx.doi.org/10.1063/1.124990 (3 pages) | Cited 9 times

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Reflection high-energy electron diffraction (RHEED) and laterally spatially resolved high resolution x-ray diffraction (HRXRD) have been used to identify and characterize rf plasma-assisted molecular-beam epitaxial growth factors which strongly affect the efficiency of In incorporation into InxGa1−xN epitaxial materials. HRXRD results for InxGa1−xN/GaN superlattices reveal a particularly strong dependence of average alloy composition math upon both substrate growth temperature and incident V/III flux ratio. For fixed flux ratio, results reveal a strong thermally activated behavior, with over an order-of-magnitude decrease in math with increasing growth temperature within the narrow range 590–670 °C. Within this same range, a further strong dependence upon V/III flux ratio is observed. The decreased In incorporation at elevated substrate temperatures is tentatively attributed to In surface-segregation and desorption processes. RHEED observations support this segregation/desorption interpretation to account for In loss. © 1999 American Institute of Physics.
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81.05.Ea III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.66.Bi Elemental solids
61.66.Dk Alloys
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
68.35.Fx Diffusion; interface formation

Charge-trapping properties of gate oxide grown on nitrogen-implanted silicon substrate

D. Misra

Appl. Phys. Lett. 75, 2283 (1999); http://dx.doi.org/10.1063/1.124991 (3 pages) | Cited 5 times

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Charge-trapping properties of ultrathin gate oxide grown on a nitrogen-implanted silicon substrate were investigated using high-field Fowler–Nordheim injection. By applying an empirical model and monitoring threshold voltage shift due to current stress, it was found that both hole trapping and electron trapping are suppressed in the nitrogen-implanted oxide. Smaller trap-generation rate compared to pure SiO2 film was also noticed. Our results indicate that nitrogen implantation into silicon substrate before gate oxide growth is an alternate way to incorporate nitrogen into the Si/SiO2 interface. © 1999 American Institute of Physics.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.uf Ge and Si
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
85.40.Ry Impurity doping, diffusion and ion implantation technology

Evolutionary phase diagrams for plasma-enhanced chemical vapor deposition of silicon thin films from hydrogen-diluted silane

Joohyun Koh, A. S. Ferlauto, P. I. Rovira, C. R. Wronski, and R. W. Collins

Appl. Phys. Lett. 75, 2286 (1999); http://dx.doi.org/10.1063/1.124992 (3 pages) | Cited 57 times

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Real-time optical studies have been applied to develop phase diagrams that characterize plasma-enhanced chemical vapor deposition (PECVD) of silicon thin films at low temperature (200 °C). The deposition phase diagrams describe regimes over which predominantly amorphous and microcrystalline Si phases are obtained as a function of the accumulated thickness and the hydrogen-to-silane gas flow ratio R = [H2]/[SiH4] in the PECVD process. The diagrams for different substrates provide insights into optimization of amorphous Si materials and solar cells. © 1999 American Institute of Physics.
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81.05.Cy Elemental semiconductors
64.70.-p Specific phase transitions
81.30.Dz Phase diagrams of other materials
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Gc Amorphous semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
84.60.Jt Photoelectric conversion
78.66.Jg Amorphous semiconductors; glasses
61.43.Dq Amorphous semiconductors, metals, and alloys
78.66.Db Elemental semiconductors and insulators

Light emission spectra of individual GaAs quantum wells induced by scanning tunneling microscope

T. Tsuruoka, Y. Ohizumi, R. Tanimoto, and S. Ushioda

Appl. Phys. Lett. 75, 2289 (1999); http://dx.doi.org/10.1063/1.124993 (3 pages) | Cited 16 times

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We have investigated the light emission from individual single GaAs quantum wells of cleaved (110) AlGaAs/GaAs heterostructures, using the scanning tunneling microscope tip as a local injection source of minority carriers. Single emission peaks were observed to shift to the high-energy side with decreasing well width. The emission peaks are assigned to the transition between n = 1 single-quantum-well electron and heavy-hole states of the respective wells. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
78.60.-b Other luminescence and radiative recombination

Gated negative-effective-mass ballistic terahertz generators

A. N. Korshak, Z. S. Gribnikov, N. Z. Vagidov, and V. V. Mitin

Appl. Phys. Lett. 75, 2292 (1999); http://dx.doi.org/10.1063/1.124994 (3 pages) | Cited 7 times

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We consider gate control of terahertz generation in planar ballistic diodes with a negative-effective-mass section in a dispersion relation of current carriers in a current-conducting channel. Such a generation in ballistic p+pp+ or n+nn+ diodes occurs as a result of plasma instability development and self-organization of a regular oscillation regime. Conditions of existence and oscillation frequencies are calculated. The gate can also serve as an oscillation-collecting electrode. We consider double-gate designs, side by side with conventional single-gate designs. The double-gate devices allow us to separate circuits for direct and high-frequency currents. © 1999 American Institute of Physics.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.Kk Junction diodes
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Magnetotransport and magnetic domain structure in compressively strained colossal magnetoresistance films

Yan Wu, Y. Suzuki, U. Rüdiger, J. Yu, A. D. Kent, T. K. Nath, and C. B. Eom

Appl. Phys. Lett. 75, 2295 (1999); http://dx.doi.org/10.1063/1.124995 (3 pages) | Cited 69 times

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We have studied the magnetoresistance (MR) of compressively strained La0.7Sr0.3MnO3 (LSMO) films in various magnetic states in order to understand the role of magnetic domain structure on magnetotransport. In thin films of LSMO on (100) LaAlO3, the perpendicular magnetic anisotropy results in perpendicularly magnetized domains with fine scale ∼200 nm domain subdivision, which we image directly at room temperature using magnetic force microscopy. The main MR effects can be understood in terms of bulk colossal MR and anisotropic MR. We also find evidence for a small domain wall contribution to the MR, which is an order of magnitude larger than expected from a double exchange model. © 1999 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.30.Gw Magnetic anisotropy
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Cc Other ferromagnetic metals and alloys
75.47.Gk Colossal magnetoresistance

Effect of magnetocrystalline anisotropy on the magnetic properties of Fe-rich R–Fe–B nanocomposite magnets

T. Zhao, Q. F. Xiao, Z. D. Zhang, M. Dahlgren, R. Grössinger, K. H. J. Buschow, and F. R. de Boer

Appl. Phys. Lett. 75, 2298 (1999); http://dx.doi.org/10.1063/1.124996 (3 pages) | Cited 13 times

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Nanocomposite ribbons consisting of hard-magnetic R2Fe14B (R=rare-earth) and soft-magnetic Fe3B phases were produced by melt spinning and subsequent heat treatment. Alloys of composition Nd4−xSmxFe77.5B18.5, with x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 all showing strong remanence enhancement, were selected to investigate the effect of the magnetocrystalline anisotropy of the R2Fe14B-type phase on the exchange coupling with the soft-magnetic phase in the nanocomposite magnets. An enhancement of exchange coupling due to anisotropy reduction was found, as expected on the basis of the model of Kneller and Hawig. A maximum of the energy product (BH)max was achieved for x = 0.2 after annealing at 700 °C. The thermomagnetic behavior also changes upon substitution of Sm for Nd. © 1999 American Institute of Physics.
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75.50.Kj Amorphous and quasicrystalline magnetic materials
75.30.Gw Magnetic anisotropy
75.50.Ww Permanent magnets
75.30.Et Exchange and superexchange interactions
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Rs Electrical and magnetic properties related to treatment conditions

Highly balanced long-baseline single-layer high-Tc superconducting quantum interference device gradiometer

A. Eulenburg, E. J. Romans, C. Carr, A. J. Millar, G. B. Donaldson, and C. M. Pegrum

Appl. Phys. Lett. 75, 2301 (1999); http://dx.doi.org/10.1063/1.124997 (3 pages) | Cited 18 times

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We describe a direct-current superconducting quantum interference device (SQUID) first-order gradiometer fabricated from a single layer of YBa2Cu3O7 on a 30×10 mm2 bicrystal substrate. The device has a baseline of 13 mm and an intrinsic balance of ∼ 10−3. The gradient sensitivity at 77 K and 1 kHz is 50 fT/(cmmath) in magnetic shielding and 260 fT/(cmmath) when operated unshielded in our laboratory. An antiparallel two-SQUID coupling scheme is employed to optimize the device’s balance to at least 3×10−5. © 1999 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
85.25.Dq Superconducting quantum interference devices (SQUIDs)

Tuning exchange bias

P. Miltényi, M. Gierlings, M. Bamming, U. May, G. Güntherodt, J. Nogués, M. Gruyters, C. Leighton, and Ivan K. Schuller

Appl. Phys. Lett. 75, 2304 (1999); http://dx.doi.org/10.1063/1.124998 (3 pages) | Cited 67 times

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The exchange bias shift of the hysteresis loop, HE, in antiferromagnetic/ferromagnetic layer systems can be easily controlled (within certain limits) by cooling in zero field from different magnetization states above the antiferromagnetic Néel temperature, TN. This indicates that for moderate cooling fields, HE is determined by the magnetization state of the ferromagnet at TN, and not by the strength of the cooling field. © 1999 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.50.Ee Antiferromagnetics
75.50.Cc Other ferromagnetic metals and alloys
75.30.Sg Magnetocaloric effect, magnetic cooling
75.40.-s Critical-point effects, specific heats, short-range order
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Enhanced magnetoresistance effect in layered systems

M. S. Ferreira, J. d’Albuquerque e Castro, R. B. Muniz, and Murielle Villeret

Appl. Phys. Lett. 75, 2307 (1999); http://dx.doi.org/10.1063/1.124999 (3 pages) | Cited 8 times

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Magnetoresistance ratios several orders of magnitude higher than those of conventional multilayers may be obtained with much smaller saturation fields in magnetic layers separated by a periodically modulated structure. Conditions for the occurrence of such effect, as well as the possible use of these systems as spin-filter devices and magnetic logical gates, are discussed. © 1999 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
85.70.-w Magnetic devices

Harmonic frequency mixing in Bi2Sr2CaCu2O8+X intrinsic Josephson junctions

H. B. Wang, Y. Aruga, T. Tachiki, Y. Mizugaki, J. Chen, K. Nakajima, T. Yamashita, and P. H. Wu

Appl. Phys. Lett. 75, 2310 (1999); http://dx.doi.org/10.1063/1.125000 (3 pages) | Cited 7 times

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In a c-axis junction stack (10 μm×10 μm in a-b plane) patterned on a Bi2Sr2CaCu2O8+X single crystal, we performed harmonic mixings between a 100 GHz signal and up to the 98th harmonic of a local oscillator at about 1 GHz. The dependence of PIF on V, where PIF is the mixing output at the intermediate frequency and V is the dc voltage across the junction stack, was strongly affected by the local oscillator power levels. For low values of local oscillator power, the optimum operation point where PIF became maximum was around zero bias, and typical multi-branch structure of PIF vs V curves were observed. For high values of local oscillator power, the optimum operation point moved to the high-voltage region. In both cases, interesting oscillations occurred on the PIF vs V curves. Our experimental results led us to believe that intrinsic Josephson junctions can be good candidates for high frequency applications and the harmonic mixing may be a useful probe to investigate plasma phenomena in the layered superconductors. © 1999 American Institute of Physics.
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85.25.Cp Josephson devices
84.30.Qi Modulators and demodulators; discriminators, comparators, mixers, limiters, and compressors
74.72.-h Cuprate superconductors
84.40.Dc Microwave circuits
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