bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical activation of beryllium in preamorphized gallium arsenide
Authors: Opyd W. G. , Gibbons J. F.
Published: July 2002

Beryllium was ion implanted into GaAs that had been previously amorphized by a liquid-nitrogen-temperature arsenic implant. After rapid thermal annealing complete electrical activation of the beryllium was indicated by carrier profiles measured by van der Pauw–Hall and electrochemical capacitance-voltage techniques. Diffusion of the beryllium profile as determined by secondary-ion-mass spectroscopy was suppressed in the arsenic-preamorphized layer. The combined effects of an amorphous layer to suppress ion channeling and excess arsenic to suppress diffusion resulted in a very abrupt beryllium-implanted layer. The high electrical activation of the ion-implanted beryllium represents what we believe is the first successful attempt to activate an impurity implanted into a preamorphized gallium arsenide layer.
Theoretical study of the Pd-B complex in silicon
Authors: Wu Ji-an , Zhou Jie , Zhang Da-ren
Published: July 2002

We report the results for the electronic structure of the interstitial Pd-substitutional B complex in silicon. The self-consistent field calculations were performed within the framework of scattered-wave Xα cluster method. Compared with the electronic structures of the isolated substitutional B in silicon and of the isolated interstitial Pd in silicon, we found that the shallow acceptor B impurity state is deepened by the perturbation from the Pd atom. The ionic model, which is currently accepted to describe interstitial 3d transition metal-III A group shallow acceptor impurity pair, is not quite suitable to deal with the system of Pd-B complex in silicon.
Chemical removal of contaminants from thin film Bi4Sr3Ca3Cu4O16+x surfaces
Authors: Vasquez R. P. , Housley R. M.
Published: July 2002

A solution of Br in absolute ethanol, previously shown to be effective at removing nonsuperconducting species from Y-Ba-Cu-O thin film surfaces, is shown to also be effective in treating Bi-Sr-Ca-Cu-O thin film surfaces. X-ray photoelectron spectra obtained after etching are consistent with previously reported results obtained from samples cleaved or scraped in vacuum.
Characterization of high-purity InP by photoluminescence
Authors: Inoue T. , Kainosho K. , Hirano R. , Shimakura H. , Kanazawa T. , Oda O.
Published: July 2002

InP polycrystals grown by the HB technique and InP single crystals grown by the liquid-encapsulated Czochralski technique have been evaluated by photoluminescence. It was found that as the carrier concentration is decreased, the photoluminescence spectrum shows finer structures. When the carrier concentration is less than 9×1014 cm−3, a strong free-exciton peak could be observed.
Elimination of stacking faults in a silicon epitaxial layer of (100) orientation by heat treatment
Authors: Cai Tianhai
Published: July 2002

Elimination of stacking faults in a silicon epitaxial layer of (100) orientation by heat treatment has been investigated by observing repeated etching patterns. Similar to the (111) orientation case, two types of stacking faults are observed: one is eliminated easily by heat treatment and the other is stable and cannot be eliminated. This communication describes the results of experiments and observations on the stacking faults elimination of a (100) face epitaxial layer. From the experimental results, it was found that elimination proceeds locally not only from the surface of the growth layer to the substrate, but also from partial dislocation of the stacking fault under the surface of the growth layer. Elimination at the partial dislocation is explained.
Fast metastable argon atoms from a hot-cathode discharge
Authors: Hardy K. A. , Gillman E. , Sheldon J. W.
Published: July 2002

Metastable atoms emitted from the anode of a hot-cathode low-voltage Ar gas discharge produce two peaks in the time-of-flight distribution. The slow peak typifies atoms with a thermal velocity distribution in the discharge. The fast peak can be approximated by a Gaussian function, and its dependence on the discharge current, voltage, and pressure is presented. The origin of the fast peak is investigated experimentally and shown to represent fast Ar(3P2,0 ) from the discharge.
Magnetic behavior of the Hf(Fe1−xAlx)2 system (abstract)
Authors: Sampaio L. C. , da Cunha S. F.
Published: July 2002

Magnetic properties of pseudobinary compounds Hf(Fe1−xAlx)2 have been investigated as a function of temperature and concentration in the range 0≤x≤0.60. The present work is motivated to understand the role of Hf in the system, compared to the systems Y(Fe1−xAlx)2 and Zr(Fe1−xAlx)2, where freezing phenomena characteristic of a cluster-glass regime can be observed in the Y case in the concentration range 0.1≤x≤0.35.1 The magnetization measurements are made as a function of temperature and static magnetic applied field. The system shows a mixture of a C14 (hexagonal) and a C15 (cubic) Laves phase structures from x=0 up to x<0.15; for x≥0.15, only the C14 hexagonal phase is present. The Curie temperature TC decreases with Al concentration and tends to TC=0 about x=0.60. We have observed an irreversible behavior of the magnetization curves as a function of temperature when the samples are cooled with (FC) and without (ZFC) an external field, up to temperatures near TC. In the low-temperature range the magnetization drops with temperature for ZFC measurements. No saturation was observed even in high magnetic fields up to 80 kOe, indicating a high anisotropy energy. An S-type behavior is observed in the initial experiments for high Al concentrations (40% and 50%) and low temperatures. A great decrease of the coercive field with increase of temperature is also observed; for 50% Al, this dependence can be fitted by an exponential. All the phenomena can be explained by domain wall pinning. The difference between ZFC and FC curves is related to the rapid decrease of the magnetic hardness by thermal activation as the temperature increases. A magnetic phase diagram is presented.
Systematics of enhancement in magneto-optical thin films
Authors: Bryant J. , Parker M. R.
Published: July 2002

The results of a previous analytical study [R. Gamble, P. H. Lissberger, and M. P. Parker, IEEE Trans. Magn. MAG-21, 1651 (1985)] of shot-noise-limited signal-to-noise ratio (SNR) in thin multilayers containing a magnetic storage layer are compared with those obtained using practical numerically designed quadrilayers and bilayers. Both studies clearly demonstrate that multilayer enhancement of the Kerr magneto-optical effect is at its least favorable for currently fashionable RETM films such as GdTb/FeCo alloys. By contrast, low-absorption film media such as garnets can derive comparatively much greater benefits from appropriate multilayer design. In the present analysis the general characteristics of the resonant dispersion of Kerr rotation in bilayer systems are also examined.
Domain nucleation and wall velocity in amorphous TbFeCo thin films (abstract)
Authors: Marinero E. E. , Hirscher M. , Egami T.
Published: July 2002

Domain reversal processes in Si3N4-overcoated TbFeCo 800-Å-thick films have been investigated utilizing nanosecond laser irradiation and polarization microscopy. The sputter-deposited thin films are first magnetically saturated and then subjected to reversing fields of various magnitudes. The kinetics of the domain growth is measured in situ utilizing the polar Kerr effect and the nucleation is directly observed with the polarizing microscope. For low values of the reversing field, nucleation is observed to occur at defects in the thin film. In all cases studied so far, we have established that following the onset of nucleation, the reversal process occurs via domain growth. We have determined the temperature dependence of domain nucleation and wall velocity during laser annealing and the nanosecond results are discussed with reference to existing models for domain wall motion.
Influence of Mn moments on the properties of RMn2 compounds (R=Y and light rare earths)
Authors: Labroo Sunil , Willis Frank , Ali Naushad
Published: July 2002

The influence of Mn moments on the magnetism of RMn2 compounds, where R=Y, Pr, Nd, and Sm, has been investigated using SQUID magnetometry, thermal expansion, electrical resistivity, and magnetoresistance measurements. RMn2 compounds, with R=Y, Pr, Nd, and Sm, order antiferromagnetically at 116, 115, 105, and 94 K, respectively. According to thermal expansion data all these materials undergo a first-order phase transition from a paramagnetic to a magnetically ordered state, and this effect is believed to be caused by the collapse of the Mn moment at the transition. For the YMn2 compound, the resistivity has a T3 temperature dependence below 38 K and a positive magnetoresistance in the ordered phase, indicating that the Mn moments are localized below TN in this compound. Above TN, however, the Mn moments become itinerant which is reflected as a gradual increase in susceptibility χ with increasing temperature. In PrMn2, NdMn2, and SmMn2 the resistivity does not follow a simple temperature power law and the magnetoresistance varies from negative to positive values depending on the temperature and field. The transition temperatures in these materials differ significantly from the de Gennes factor and it is believed that the ordering is brought about by antiferromagnetic coupling between Mn moments.
Field-induced magnetization of amorphous FexRu80−xB20
Authors: Jackson E. M. , Bhagat S. M. , Manheimer M. A. , Paulose P. L. , Nagarajan V.
Published: July 2002

Using an electron-spin resonance (ESR) technique at 10 GHz we have determined the temperature dependence of the field-induced magnetization in amorphous FexRu80−xB20 with 60≤x≤65. This concentration range includes a ferromagnet, a spin glass, and several reentrants. The ferromagnet displays typical T3/2 temperature dependence, while all other concentrations display the T dependence characteristic of spin glasses.
Spin-glass behavior of Zn1−xCoxS
Authors: Shand P. M. , Lewicki A. , Crooker B. C. , Giriat W. , Furdyna J. K.
Published: July 2002

The magnetic susceptibility of the new cobalt-based dilute magnetic semiconductor Zn1−x Cox S was measured for concentrations 0.03≤x≤0.103 and temperatures 22 mK≤T≤4.2 K. A paramagnetic-to-spin-glass transition was found for all samples. In contrast to the behavior in the manganese-based compounds, the freezing temperatures in this material could not be fitted to a simple power-law dependence on concentration. This difference is discussed in terms of an additional long-range dipolar coupling.
Temperature dependence of critical neutron scattering in Cr+0.2 at. % V and chromium
Authors: Noakes D. R. , Holden T. M. , Fawcett Eric
Published: July 2002

The dynamic magnetic susceptibilities, χ(Q,ω), of Cr+0.2 at. % V and chromium were measured in the temperature range (TN−15 K)<(TN+20 K) by neutron scattering. Here, χ (Q,ω) of Cr+0.2 at. % V is clearly incommensurate, in contrast to the apparently commensurate inelastic scattering seen in pure chromium. The observed form of the scattering for each material does not qualitatively change in going from above TN (paramagnetic) to below it (antiferromagnetic). Since no discontinuity in elastic magnetic intensity was observed in the alloy crystal, analysis in terms of the critical phenomena of a second-order phase transition can now be attempted.
Thermal expansion at the metamagnetic transition in single-crystalline heavy-fermion (Ce,La)Ru2Si2
Authors: Lacerda A. , de Visser A. , Puech L. , Lejay P. , Haen P. , Flouquet J.
Published: July 2002

We present measurements of the volume expansion (αv) in magnetic fields up to 8.5 T and in the temperature range 1.3 K<T<20 K on the heavy-fermion compounds Ce1−xLaxRu2Si2 (x=0 and 0.05). In reduced scales the two compounds present the same low temperature Grüneisen coefficients. Emphasis is given on the strong field dependence of the low temperature extremum of αv. The validity of scaling law with pressure is verified. The interest to use a magnetic field to approach a magnetic instability is strongly underlined.
Magnetic and structural characteristics of the Nd2(Co,Fe)7B3 system
Authors: Huang M. Q. , Ma B. M. , Zhang L. Y. , Wallace W. E. , Sankar S. G.
Published: July 2002

Nd2Co7−xFexB3 alloys have been synthesized and studied at temperatures from 4 to 1100 K at fields up to 90 kOe. The structure and magnetic properties vary significantly with changing Fe content. The main phase is observed to be of hexagonal symmetry for x<3. For x>4 it is multiphase, the major phase having tetragonal symmetry. The Tc increases from 330 to 885 K when x varies from 0 to 3, then decreases from 885 to 577 K when x increases from 3 to 7. The saturation magnetization is 8μB/fu at 4.2 K, for Nd2Co7B3; it increases with increasing Fe content. The alloys exhibit a conical (0<x<3) and an axial (x>4) magnetocrystalline anisotropy at 295 K. They all exhibit conical magnetic anisotropy at 77 K.
Magnetostriction in (TbxDy1−x)80Gd20 single crystals
Authors: Spano M. L. , Clark A. E. , Wun-Fogle M. , Lynn H. D.
Published: July 2002

Gd has been added to binary alloys of Tb and Dy in order to raise the magnetic transition temperature and zero-anisotropy temperature of the alloys. Magnetostriction and differential-scanning-calorimetry measurements were made on four samples of the alloy system (TbxDy1−x)80Gd20 over temperatures from 50 to 300 K in applied fields of 6–20 kOe. The two lowest-order basal-plane magnetostriction constants were derived from the data, as was the basal-plane anisotropy constant. The addition of 20% Gd was found to increase the magnetic transition temperatures, but to decrease or eliminate the zero-anisotropy temperature.
The influence of quenching rate on the magnetic properties of microcrystalline alloys Co80Zr20−xBx
Authors: Stroink G. , Stadnik Z. M. , Viau G. , Dunlap R. A.
Published: July 2002

Magnetic properties of melt-spun Co80Zr20−xBx microcrystalline alloys (0≤x≤8) depend crucially on the quench rate.The optimized values of Hc =2.68 kOe and (BH)max =2.10 MG Oe were obtained for Co80Zr16B4 melt-spun with the substrate surface velocity of 48 m/s. A new crystalline phase of Co5Zr was observed.
Structural and magnetic properties of Ti/Co multilayers
Authors: Van Leeuwen Robert , England Craig D. , Dutcher John R. , Falco Charles M. , Bennett Wayne R. , Hillebrands B.
Published: July 2002

We have investigated the structural and magnetic properties of sputter-deposited Ti/Co multilayer thin films. Sample composition was determined by Rutherford backscattering spectrometry. The crystal structure and composition modulation were examined with several x-ray diffraction techniques. X-ray diffraction analysis showed that the Ti and Co layers grow in the hcp structure and that the films are strongly textured along the (002) direction and are structurally incoherent. Composition modulation was confirmed from low-angle x-ray diffraction measurements. Vibrating-sample magnetometry (VSM) and Brillouin light scattering (BLS) were used to determine the magnetic properties of the films. VSM measurements of samples with Co layer thicknesses less than ≊22 Å showed no measurable net magnetization, while those with greater Co layer thicknesses had both in-plane and perpendicular components. Using a simple model, the measured thickness dependence of the magnetization can be explained by assuming that 11.3 Å of Co at each Ti interface is nonmagnetic with bulk magnetization for the remaining Co. Perpendicular volume and interface anisotropy constants obtained from the VSM data were Ks=0.23 erg/cm2 and Kv=3.5×106 erg/cm3, respectively. Excellent agreement was obtained between the best fit magnetic parameters for the VSM and the BLS data.
Novel magnetic phenomena in lamellar copper oxide superconductors (invited) (abstract)
Authors: Birgeneau R. J.
Published: July 2002

In the lamellar copper oxide superconductors, magnetic phenomena play a fundamental role. Pure La2CuO4 is a nearly ideal realization of the two-dimensional, S= 1/2 Heisenberg model, a system of basic interest in statistical physics. Doping with holes has a dramatic effect on the Cu2+-Cu2+ spin correlations. A hole concentration of 2% is sufficient to destroy the Néel state and to produce a novel spin-glass phase. In this talk we will review the results of a series of neutron-scattering studies of the static and dynamic spin fluctuations in the antiferromagnetic, spin-glass, and superconducting regions of the La2−xSrxCuO4 phase diagram. Emphasis will be placed on recent results in the pure material La2CuO4 (Ref. 1) and in the superconductor La1.85Sr0.15CuO4.2 For a general review see Ref. 3.
Parameters that influence the magnetic properties of Fe-Nd-B and R-Co particles (abstract)
Authors: Bogatin Y.
Published: July 2002

The parameters that produce optimum magnetic properties in Fe-Nd-B and R-Co alloy powders are discussed (R denotes rare earth). It is shown that the maximum properties are obtained at an optimum powder particle size of 2 μm. In particles of this optimum size, an outer layer of chemically heterogeneous compounds is found by using a combination of x-ray-diffraction, Auger-spectroscopy, and optical-microscopy techniques on powder samples given various milling and annealing treatments. This outer layer undergoes more plastic deformation than the center of the particle during crushing and grinding operations. The magnetic properties of the powder are not simply related to the particle size, surface area, or density of dislocations. The magnetic properties depend mainly on the chemical heterogeneity of the powder particle. Optimum magnetic properties are obtained when every powder particle is a single crystal with a continuous surface layer that is chemically heterogeneous and plastically deformed. The degradation of magnetic properties with further grinding below the optimum particle size is explained by the fact that fracturing and further deformation destroys the chemically heterogeneous zone of the single-crystal particle.
Magnetizing rare-earth alloy magnets at elevated temperatures
Authors: Agarwala A. K.
Published: July 2002

It is well known that high magnetic fields are needed to fully magnetize rare-earth based magnets. Even with the conventional magnetizing process employing a large amplitude magnetic pulse (mp), this poses practical difficulties and limits the number of poles and various application specific pole designs required in a magnet. On investigating magnetizability of these magnets, it was concluded that magnetizing can be effectively performed at much lower magnetic fields than normally needed if the temperature of the magnet during the magnetizing process is raised and maintained within a predetermined range. In an experiment, an anisotropic melt-spun Nd-Fe-B magnet of dimension 1×1×0.73 cm3 (easy-axis along the shorter dimension) was fully magnetized at a temperature between 90 and 110 °C using a mp of amplitude 22.8 kOe. The same sample at room temperature required a mp of amplitude above 42 kOe to get fully magnetized. Similar data for sintered Sm-Co and sintered as well as rapidly quenched isotropic Nd-Fe-B alloys are presented. The optimum ranges of temperatures are explained as a result of thermal deterioration on the magnet’s intrinsic coercivity and remanence properties, and the limiting effect of demagnetizing field on the magnetizing process.
Domain wall pinning by magnetic inhomogeneities in Sm(CoNi)2.5
Authors: Chen X. , Gaunt P.
Published: July 2002

Domain wall (thin 180° wall) pinning by pinning sites of atomic size is studied by a new model which is based on the argument that the temperature dependence of the coercivity originates from both thermal activation of the domain wall and the temperature dependence of the height of the energy barriers. This model successfully describes the temperature dependence of the coercivity of a Sm(CoNi)2.5 ferromagnet.
Magnetic phase transitions in Nd2CuO4
Authors: Skanthakumar S. , Zhang H. , Clinton T. W. , Sumarlin I. W. , Li W-H. , Lynn J. W. , Fisk Z. , Cheong S-W.
Published: July 2002

Polarized and unpolarized neutron scattering techniques along with x-ray diffraction have been used to study the magnetic and structural properties of a single crystal of Nd2CuO4. Long-range magnetic order of the Cu moments develops at TN=245 K, with a simple antiferromagnetic configuration of spins as found in La2NiO4, while the spin directions may be either collinear or noncollinear. Additional abrupt transitions are observed at 75 and 30 K, in which spin reorientations take place. Bragg peaks associated with the crystal structure are found at the same positions as the magnetic Bragg peaks, and indicate that a small distortion of the basic tetragonal structure has occurred above 300 K. At low temperatures the Nd moments also order antiferromagnetically (TN=1.5 K), while an additional transition of a continuous nature is observed at 150 mK.
Magnetic properties of fine cobalt particles prepared by metal atom reduction
Authors: Yiping L. , Hadjipanayis G. C. , Sorensen C. M. , Klabunde K. J.
Published: July 2002

Ultrafine particles of cobalt were prepared under argon by reduction of cobalt halide solutions in diglyme ether with metallic lithium and a naphthalene catalyst. The fine particles had a particle diameter in the range 50–1200 Å. The size was dependent on the reaction temperature. X-ray diffraction showed crystalline particles of α-Co and CoO. Because the ratio of the metal core to oxidized shell decreases with particle size, the smaller particles displayed much lower magnetization and higher coercivity at low temperature. The anisotropy constant K changes slightly with particle size and has a value close to the bulk value.
Novel direct overwriting technology for magneto-optical disks by exchange-coupled RE-TM quadrilayered films
Authors: Fukami T. , Nakaki Y. , Tokunaga T. , Taguchi M. , Tsutsumi K.
Published: July 2002

A light-intensity-modulation method for direct overwrite using a magneto-optical disk with exchange-coupled RE-TM quadrilayered film has been developed. This film consists of a ‘‘memory layer,’’ a ‘‘writing layer,’’ a ‘‘switching layer,’’ and an ‘‘initializing layer.’’ The initializing layer is used to initialize the writing layer, and the switching layer is used to switch off the coupling between the writing layer and the initializing layer above the Curie temperature of the switching layer. These two layers have made direct overwrite with only a conventional bias magnet possible.
Thermally stable ohmic contacts to n-type GaAs. VI. InW contact metal
Authors: Kim H.-J. , Murakami Masanori , Price W. H. , Norcott M.
Published: July 2002

The electrical properties and thermal stability of In/W Ohmic contacts in n-type GaAs were studied by analyzing interfacial microstructure using cross-sectional transmission electron microscopy and measuring the contact resistances by transmission line method. Indium layers with various thicknesses were deposited directly on GaAs substrates, which were kept at room or liquid-nitrogen temperature. The lower contact resistances (Rc) were obtained when the contacts were prepared at liquid-nitrogen temperature. These low Rc values were due to formation of large-areal InxGa1−xAs phases on the GaAs substrate after annealing at temperatures higher than 600 °C. The In layer thicknesses of the In/W contacts prepared at liquid-nitrogen temperature strongly affected the contact resistances as well as the thermal stability after contact formation. The optimum In layer thickness which provided the best electrical properties and thermal stability was determined to be 3 nm. The In(3 nm)/W contacts yielded Rc values less than 0.2 Ω mm and the Rc values did not deteriorate after annealing at 400 °C for more than 20 h. The contacts with In layer thicknesses thinner than 3 nm resulted in higher Rc values due to insufficient InxGa1−xAs phases at the metal/GaAs interfaces. The contacts with In layer thicknesses thicker than 3 nm resulted in poor thermal stability due to formation of large amounts of In-rich In(Ga,As) phases with low melting points. The present In(3 nm)/W Ohmic contacts are believed to be the simplest metallurgy with excellent electrical properties and thermal stability among In-based Ohmic contacts.
A knock-on model to explain enhanced perimeter leakage in ion-implanted metal-oxide-semiconductor structures
Authors: Stinson M. G. , Osburn C. M.
Published: July 2002

An enhanced leakage current through thin SiO2 gate insulators following ion implantation of source/drain regions in self-aligned gate complementary-metal-oxide semiconductors has been examined. The enhanced leakage current degrades insulator properties and is localized at the perimeter of the gate feature. A model of ion mixing between the gate material, oxide layer, and underlying silicon at the gate-feature edge has been used to explain the degradation. The atomic weight of the implant species is critical, with heavier species like arsenic demonstrating a severe degree of degradation. Implantation of lighter species like boron results in minimal degradation at normal dose levels. The gate-electrode material is also important. Electrodes formed with the highest-atomic-weight and density materials demonstrate the most degradation. Gate charging during the ion-implantation process does not significantly impact the degree to which samples are degraded at the implant currents used in this work.
Electrical properties of Nd1.85Ce0.15CuO4−y at high temperatures
Authors: Munakata Fumio , Kawano Takashi , Nozaki Ayumi , Yamauchi H.
Published: July 2002

The temperature dependence of electrical resistivity of Nd1.85Ce0.15CuO4−y was measured with oxygen partial pressure fixed at 2.08×10−1, 1.8×10−2, 8.1×10−4, and 3.3×10−6 atm. The oxygen partial pressure dependence of resistivity indicated that the charge carriers in Nd1.85Ce0.15CuO4−y were electrons. The temperature dependence of resistivity exhibited a linear metallic behavior at high temperatures and a semiconductorlike behavior at low temperatures, having a minimum at an intermediate temperature. Difficulties are pointed out in obtaining a unified view for the mechanism of normal electrical conduction in Nd1.85Ce0.15CuO4−y .
Pt/Ti/n-InP nonalloyed ohmic contacts formed by rapid thermal processing
Authors: Katz A. , Weir B. E. , Chu S. N. G. , Thomas P. M. , Soler M. , Boone T. , Dautremont-Smith W. C.
Published: July 2002

Low resistance nonalloyed ohmic contacts of e-gun evaporated Pt/Ti to S doped n-InP 5×1017, 1×1018, and 5×1018 cm−3 have been fabricated by rapid thermal processing. The contacts to the lower doped substrates (5×1017 and 1×1018 cm−3) were rectifying as-deposited as well as after heat treatment at temperatures lower than 350 °C. Higher processing temperatures stimulated the Schottky to ohmic contact conversion with minimum specific contact resistance of 1.5×10−5 and 5×10−6 Ω cm2, respectively, as a result of rapid thermal processing at 450 °C for 30 s. Heating at a temperature of 550 °C again yielded a Schottky contact. The contact to the 5×1018 cm−3 InP was ohmic as deposited with a specific contact resistance value of 1.1×10−4 Ω cm2. Supplying heat treatment to the contact caused a decrease of the specific contact resistance to a minimum of 8×10−7 Ω cm2 as a result of rapid thermal processing at 450 °C for 30 s. In all cases, this heat treatment caused a limited interfacial reactions between the Ti and the InP, and resulted in an almost abrupt interface. Heating at temperatures higher than 500 °C resulted in an interfacial intermixing and a mutual migration and reaction of the Ti and the semiconductor elements. The Pt/Ti bilayer structure was highly tensile as deposited (5×109 dyn cm−2) and became stress-free as a result of the interfacial reactions which took place while heating the samples to temperature of 400 °C or higher.
Multilevel model analysis of energy extraction from a KrF laser medium by short pulses
Authors: Kannari Fumihiko
Published: July 2002

Amplification of short pulse KrF lasers is theoretically studied by using both coherent and incoherent interaction models, which consist of five vibrational levels in the upper laser state and a single repulsive lower laser state. The multilevel models predict a significant decrease in the saturation energies for short applied laser pulses. When the laser pulse width is extremely short (≤1 ps), the higher vibrational levels in the upper KrF laser state are repumped from the lower laser state instead of being extracted by the laser pulse. Since the small-signal gain also decreases as the applied pulse width decreases, due to mismatch between the laser pulse and the KrF gain spectrum, the energy extraction efficiencies for subpicosecond laser pulses deteriorate significantly. For longer pulse widths (≥10 ps), population repumping from the KrF(C) state increases the effective saturation energy of the KrF(B) state. A steady-state population of ≊28% relative to the B-state population is estimated for the C state from recent experimental results of KrF gain recovery.
Shallow levels, deep levels and electrical characteristics in Zn-doped GaInP/InP
Authors: Chen J. F. , Chen J. C. , Lee Y. S. , Choi Y. W. , Xie K. , Liu P. L. , Anderson W. A. , Wie C. R.
Published: July 2002

Zn-doped GaxIn1−xP epilayers grown by metalorganic chemical vapor deposition have been studied in a wide range of GaP mole fraction. The Zn distribution coefficient was studied as a function of alloy composition. With a constant flow rate of diethylzinc, a decreasing net hole concentration was observed with increasing GaP mole fraction. The I-V characteristics of Au on p-GaxIn1−xP Schottky diodes show a deviation from an ideal thermionic behavior as the lattice mismatch increases. This deviation was analyzed in terms of the shunt resistance which decreased exponentially with the mismatch. A dominant hole trap located at EV+0.84 eV was detected by deep-level transient spectroscopy in a Ga0.032In0.968P layer. The density of this hole trap significantly increases with increasing lattice mismatch.
Modification of zirconia film properties by low-energy ion bombardment during reactive ion-beam deposition
Authors: Kao A. S. , Gorman G. L.
Published: July 2002

The effect of low-energy ion bombardment on the structure and properties of zirconia films deposited by reactive ion-beam process is investigated. Bombardment of 100-eV Ar+ during film growth is shown to induce a substantial relaxation of the residual stress as a result of structural modification by the increased mobility of adatoms. Concurrently, the oxygen gettering capability, or film stoichiometry, is improved by the enhanced diffusion of oxygen on substrate surface. The structural change by thermal annealing, up to 600 °C, demonstrates that fine-grained (200–400 Å) cubic zirconia can be stabilized down to room temperature without alloying stabilizers. The impingement of low-energy Ar+ during film growth results in an as-deposited film microstructure which promotes the growth of the cubic-phase crystallites upon post-deposition annealing as well as the texturing of film plane into (111) orientation. The refractive index and optical transmission of the zirconia films are shown to be dependent predominantly upon the oxygen content in the film and less sensitive to the improved atomic packing due to the low-energy Ar+ bombardment.
A single hybrid interferometer for infrared and visible testing
Authors: Lewandowski Jacques
Published: July 2002

An infrared (10 μm) wave front is recorded holographically on a dynamic recording medium consisting of a thin oil film on a glass substrate. The phase hologram obtained is used to restore the information of the infrared wave front or alternatively as a diffraction grating for a visible reconstruction beam. This property is applied to implement a single hybrid interferometer (Michelson or Mach–Zehnder) for the simultaneous testing of infrared and/or visible optical components. Experimental results for both visible and infrared components (parallel plate, lens) confirm the usefulness of this interferometer.
Properties and device applications of hydrogenated amorphous silicon carbide films
Authors: Rahman M. M. , Yang C. Y. , Sugiarto D. , Byrne A. S. , Ju M. , Tran K. , Lui K. H. , Asano T. , Stickle W. F.
Published: July 2002

Hydrogenated amorphous silicon carbide (a-SiC:H) films were deposited with a radio-frequency plasma-enhanced chemical vapor deposition system which utilizes a dc electric field applied independently of the inductively coupled rf field. The source gases were SiH4 and CH4. It was found that application of an electric field directed out of the substrate surface enhances the growth rate and yields some improvements in photoconductivity. The compositions of the films were evaluated by x-ray photoelectron spectroscopy for a range of source gas mixtures. In order to assess the applicability of a-SiC:H thin films, heterojunction a-SiC:H/crystalline Si (c-Si) diodes were fabricated and their electrical characteristics evaluated. The diode capacitance-voltage results confirmed a step junction, which was consistent with the abruptness of the interface demonstrated by high-resolution transmission electron microscopy. The heterojunction diodes also showed good rectifying properties, suggesting promise for a-SiC:H in device applications.
Effect of temperature on data retention of silicon-oxide-nitride-oxide-semiconductor nonvolatile memory transistors
Authors: Miller S. L. , McWhorter P. J. , Dellin T. A. , Zimmerman G. T.
Published: July 2002

The discharge behavior of silicon-oxide-nitride-oxide-semiconductor nonvolatile memory transistors is investigated for a range of programming and storage temperatures spanning −55 °C to 200 °C. A number of empirical observations strongly limit the nature of the mechanisms that govern charge injection and decay. Both electrons and holes contribute to the charge storage properties of the transistors, and the decay properties of both are thermally activated with a continuous distribution of activation energies (trap depths). Charge decay, for both charge states, is negligibly limited by mechanisms other than those which are strongly thermally activated. The programming temperature, relative to the storage temperature, significantly impacts the retention time of the excess electron state, while not affecting the long term decay of the excess hole state. The experimental results also have significant implications regarding proper retention screening techniques and nonvolatile ROM programming techniques.
X-ray photoelectron spectroscopy and Auger electron spectroscopy analyses of the initial growth mechanism of CdTe layers on (100) GaAs by metalorganic vapor phase epitaxy
Authors: Ekawa Mitsuru , Yasuda Kazuhito , Sone Syuji , Sugiura Yoshiyuki , Saji Manabu , Tanaka Akikazu
Published: July 2002

X-ray photoelectron spectroscopy and Auger electron spectroscopy measurements were performed to investigate the initial growth mechanism and the selection of growth orientations of CdTe layers grown on (100) GaAs by metalorganic vapor phase epitaxy (MOVPE). The surface stoichiometry of the GaAs substrate was found to recover when annealed in a H2 flow atmosphere (500 °C, 5 min), although the surface was initially in an As-rich condition after chemical etching by H2SO4:H2O2:H2O=5:1:1. No oxide was observed at both the etched and H2 annealed GaAs surfaces. Preferential adsorption of Te occurred on the GaAs surface when H2 annealing was carried out in the growth reactor in the presence of residual CdTe deposits. One monolayer of Te with a thickness of about 1.8 Å was adsorbed on the GaAs surface when the H2 annealed GaAs was exposed to diethyltelluride during the cooling period from the annealing temperature to the growth temperature (420 °C). On the other hand, minimal adsorption of Cd occurred when the H2 annealed GaAs was exposed to dimethylcadmium during the above period. (100) CdTe growth was reproducibly achieved when the GaAs surface was completely covered by one monolayer of Te before growth, otherwise (111) growth occurred. Differences in the initial growth mechanism between MOVPE and molecular-beam epitaxy are also discussed.
The structure and properties of phthalocyanine films grown by the molecular beam epitaxy technique. III. Preparation and characterization of lutetium diphthalocyanine films
Authors: Hoshi Hajime , Dann Anthony J. , Maruyama Yusei
Published: July 2002

Two types of epitaxial films of lutetium diphthalocyanine, LuPc2, have been obtained on KBr, LuPc2 /KBr, and on the film of fluoro-bridged aluminum phthalocyanine polymer, (AlPcF)n, on KBr, LuPc2 /(AlPcF)n /KBr, by the molecular beam epitaxy technique. Their structures have been studied by transmission electron microscopy as well as scanning electron microscopy. The phase of LuPc2 /KBr is bidirectionally oriented tetragonal, KBr(100)((10)1/2×(10)1/2) R±27°-LuPc2. The phase of LuPc2 /(AlPcF)n /KBr is predominantly unidirectionally oriented tetragonal, KBr(100)(3×3)R45°-LuPc2 /(AlPcF)n, but some bidirectional orthorhombic phase, KBr(100)C(6×3)R45°-LuPc2 /(AlPcF)n, is also present.
Charge trapping and interface state generation in metal-oxide-semiconductor capacitors due to Fowler–Nordheim tunneling injection at low temperatures
Authors: Sakashita M. , Zaima S. , Yasuda Y.
Published: July 2002

Electrical phenomena in metal-oxide-semiconductor capacitors caused by Fowler–Nordheim tunneling injection of electrons have been studied at temperatures ranging from 77 to 300 K. It has been found that the shift of flatband voltages (ΔVFB) depends on the oxidation temperature and that low-temperature oxidation is desirable for the reduction of ΔVFB . The dependence of ΔVFB on the injection temperature shows a characteristic feature: The ΔVFB reduces with decreasing injection temperature in the range above 180 K and, on the other hand, is almost independent of the injection temperature in the range below 180 K. These results are mainly attributable to the injection temperature dependence of interface state generation. The injection temperature dependence of interface state density clearly indicates that two generation mechanisms of interface states are present. In addition, we have found a power-law dependence of the generated interface states on ΔVFB, independent of oxidation and injection conditions.
Deep level spectroscopy in p-GaSe single crystals
Authors: Micocci G. , Siciliano P. , Tepore A.
Published: July 2002

Deep levels have been examined in nonintentionally doped p-type gallium selenide single crystals using photoinduced current transient spectroscopy measurements. Two hole trapping levels at 0.20 and 0.80 eV above the valence band have been observed and the corresponding thermal capture cross section evaluated. The possible origin and nature of these centers are also discussed.
Thermal modeling of laser-addressed liquid-crystal displays
Authors: Evans K. E. , Nkansah M. A.
Published: July 2002

Optical-absorption calculations and finite-element methods are used to calculate time-dependent temperature profiles in two contrasting laser-addressed liquid-crystal displays. It is shown that the presence of conducting electrode layers has a significant effect on the temperature profiles both by affecting the optical-absorption characteristics of the cell and the resulting thermal conductivity. It is shown that efficient optical absorption does not necessarily result in the best cell-addressing performance.
Anomalous elastic behavior in superlattices of twist grain boundaries in silicon
Authors: Phillpot S. R. , Wolf D. , Lutsko J. F.
Published: July 2002

The elastic constants and moduli of superlattices of high-angle twist grain boundaries on the two densest crystallographic planes of silicon are calculated using Stillinger and Weber’s three-body potential. While in both cases the Young’s and shear moduli are found to be softened, the Poisson ratios and some elastic constants, in particular C33 (in the direction of the interface-plane normal), are found to be hardened. It is shown that the elastic behavior is determined by the structural disorder at the interfaces, and that it cannot be understood in terms of the dimensional changes of the system alone. A comparison with similar calculations for metallic superlattices elucidates the role of the covalent nature of bonding of silicon on its elastic behavior.
Some optical and electron microscope comparative studies of excimer laser-assisted and nonassisted molecular-beam epitaxically grown thin GaAs films on Si
Authors: Lao Pudong , Tang Wade C. , Rajkumar K. C. , Guha S. , Madhukar A. , Liu J. K. , Grunthaner F. J.
Published: July 2002

We present results of Raman and Rayleigh scattering, near-band-edge photoluminescence, and electron microscope examination of GaAs thin films (<0.3 μm) grown on Si(100)+4°〈011〉 substrates via molecular-beam epitaxy with part of the 2-in. wafer under KrF excimer laser irradiation. Comparative examination of laser-assisted and nonassisted growth areas on the same wafer reveals differences in the nature and degree of strain and structural defects. It is found that the Rayleigh scattering intensity is higher and the longitudinal-optical mode Raman peak is broader in the non-laser-irradiated region indicating a higher degree of disorder. The luminescence is higher from the laser-irradiated region. These differences between the non-laser- and laser-irradiated regions on the same wafer are partially caused by a difference in the film thickness of the two regions. Near-edge photoluminescence peak position reflects the presence of compressive stress in these thin GaAs films (both in the non-laser- and laser-irradiated areas), indicating incomplete strain relaxation by dislocations even though the thickness is significantly higher than the thermodynamic ground-state estimates of the critical thickness. Transmission electron microscope studies on the laser-irradiated and nonirradiated areas reveal no discernible differences in the density of dislocations in the thin films studied. However, representative samples from both areas cut perpendicular to the tilt axis about which the substrate was tilted away from a perfect (100) surface exhibit an asymmetry in the distribution of the twins among the two {111} variants which have the tilt axis as the common zone axis. This asymmetry has been observed only for the twins extending from the film-substrate interface to the film surface. A correlation between such twins and the substrate step orientation is established.
Controlled doping of GaAs films grown with tertiarybutylarsine
Authors: Lum R. M. , Klingert J. K. , Stevie F. A.
Published: July 2002

To assess the suitability of alternative arsenic compounds for device applications, development of growth procedures for controlled n and p doping are required. In this paper we report the first studies of the doping characteristics of sulfur, silicon, and carbon species in GaAs films grown with tertiarybutylarsine, t-BuAsH2. Hydrogen sulfide, H2S, and hexamethyldisilane, (CH3)6Si2, were used as dopant sources. The effects of growth temperature, dopant source concentration, V/III ratio and substrate crystallographic orientation on dopant incorporation were investigated. We demonstrate the capability of controllably doping GaAs films grown with t-BuAsH2, and report the first fabrication of active devices (n+-n metal-semiconductor field effect transistors) from t-BuAsH2-grown material. These devices exhibited dc and microwave performance comparable to that achieved with arsine-grown devices.
Extended Goodman model for series resistance masking on bulky semiconductor junction capacitance
Authors: Chan C. L. , Shih I.
Published: July 2002

The effect of series resistance on the apparent semiconductor junction capacitance C′ has been studied after Goodman [J. Appl. Phys. 34, 329 (1963)] in an attempt to explain the occurrence of minima in the apparent C′−2 vs voltage characteristics at high frequencies and for a large series resistance. A correction scheme has been formulated to convert C′−2 into the actual C−2 at any bias and frequency. The present model is consistent with the apparent capacitance behavior of a commercial Si Zener diode in series with a discrete resistor.
Pulse response characteristics of ZnO varistors
Authors: Modine F. A. , Wheeler R. B.
Published: July 2002

A study is reported of the influences of temperature, circuit resistance, and pulse repetition rate on the ZnO varistor inductive pulse response that is disclosed by voltage overshoot and current undershoot. Exponential time constants are fitted to the voltage overshoot and the current undershoot obtained by using high- and low-impedance pulse supplies, respectively. Nearly identical time constants of a few microseconds are found at room temperature, but the voltage overshoot exhibits a temperature-independent time constant whereas the current undershoot exhibits a shorter time constant at low temperature. However, it is also demonstrated that small increases in circuit resistance can change the shape of the current undershoot and cause a decrease in the calculated time constant. It is concluded that the temperature dependence of the current undershoot is a direct consequence of the temperature dependence of the grain resistivity and that it does not result from a temperature-dependent barrier response. The response to repeated pulses reveals a significant polarization current even when a varistor is in the highly conducting breakdown state. A long-term memory of preceding pulses is associated with this polarization current. The inductive response of a varistor is complicated by the influence of this memory, and a shorter-term memory attributed to the lifetime of electron holes.
Effects of etching with a mixture of HCl gas and H2 on the GaAs surface cleaning in molecular-beam epitaxy
Authors: Saito Junji , Kondo Kazuo
Published: July 2002

I n situ cleaning of GaAs substrates with a HCl gas and hydrogen mixture prior to molecular-beam epitaxy has been investigated. The chemical reaction during etching was monitored using a quadrupole mass spectrometer. After etching, reflection high-energy electron diffraction patterns revealed (2×4) arsenic-stabilized surfaces and (4×2) gallium-stabilized surfaces as reconstructed structures in the gas-etched substrate surface. These structures suggest that the gas-etched substrate surface is atomically flat, resembling an epitaxial layer surface. To study the effect of gas etching, the carrier depletion layer and the residual carbon impurity around the substrate epitaxial interface were measured by capacitance-voltage carrier profiling and secondary-ion mass spectroscopy. After gas etching, the carrier depletion was greatly reduced, from 1.2×1012 to 1×1010 cm−2. The carbon impurity around the interface also decreased by one order of magnitude. We discussed the surface-cleaning mechanism using the atomic hydrogen terminating model of the GaAs surface during etching. We then applied this etching technique to in situ cleaning of semi-insulating GaAs substrates prior to the growth of selectively doped GaAs/N-AlGaAs heterostructures with very thin GaAs buffer layers.
On-wafer correlation between total EL2 concentration, shallow acceptor concentration, and Hall properties in semi-insulating GaAs
Authors: Brierley Steven K. , Hendriks Henry T.
Published: July 2002

By combining infrared absorption measurement of EL2 concentration with conventional measurement of Hall resistivity and mobility, the correlations between the total (neutral plus ionized) EL2 concentration, the net acceptor concentration, and the Hall characteristics across a semi-insulating GaAs wafer have been determined. An increase in the total EL2 concentration is found to be accompanied by a decrease in the resistivity and increase in mobility. Furthermore, there is a positive correlation between the EL2 concentration and the net acceptor concentration.