bluuebunny/crossref_metadata_2025 huggingface dataset:
Doping studies of Ga0.5In0.5P organometallic vapor-phase epitaxy
Authors: Hsu C. C. , Yuan J. S. , Cohen R. M. , Stringfellow G. B.
Published: July 2002

Undoped Ga0.5In0.5P has been successfully grown by organometallic vapor-phase epitaxy on GaAs substrates with a free-electron concentration of 1016 cm−3 and a mobility of 1050 cm2/V s in nominally undoped material. The distribution coefficient of indium in the growth of Ga0.5In0.5P is nearly to unity. Both n- and p-type carrier concentrations of up to 1019 cm−3 have been obtained in the present study. Diethyltelluride and silane are used as n-type dopants. Dimethylzinc is used as the p-type dopant. Te is a very efficient dopant with a distribution coefficient kTe=54. The photoluminescence (PL) intensity increases with Te doping level to a maximum at n=2×1018 cm−3. The silicon distribution coefficient is temperature dependent, due to the incomplete pyrolysis of silane at the growth temperature. Si-doped Ga0.5In0.5P has a lower PL efficiency than Te-doped samples and is not strongly correlated with carrier concentration. The incorporation efficiency of Zn is low, with kZn =3.8×10−3, due to the high vapor pressure of Zn at the growth temperature. The PL intensity of Zn-doped Ga0.5In0.5P also increases with Zn doping level to a maximum at p=2×1018 cm−3 and is comparable to the optimum Te-doped n-type Ga0.5In0.5P. Only a single band-edge PL peak is observed in all cases.
Lateral coherence properties of broad-area semiconductor quantum well lasers
Authors: Larsson A. , Salzman J. , Mittelstein M. , Yariv A.
Published: July 2002

The lateral coherence of broad-area lasers fabricated from a GaAs/GaAlAs graded index waveguide separate confinement and single quantum well heterostructure grown by molecular-beam epitaxy was investigated. These lasers exhibit a high degree of coherence along the junction plane, thus producing a stable and very narrow far field intensity distribution.
Transient thermoreflectance from thin metal films
Authors: Paddock Carolyn A. , Eesley Gary L.
Published: July 2002

This report describes the first demonstration of thermal diffusivity measurements using picosecond transient thermoreflectance (TTR). Although previously reported methods of measuring thermal transport properties of thin films require precise knowledge of the thermal properties of the substrate, this technique allows measurements on films as thin as 100 nm without any evidence of substrate interaction. The TTR measurement is modeled with a one-dimensional heat flow equation using a two-parameter fitting routine to determine the thermal diffusivity. The validity of our approach is confirmed by the TTR measured thermal diffusivity of single crystal nickel. We have also measured the thermal diffusivity of sputtered and evaporated single element metal films. Preliminary results from TTR measurements on compositionally modulated structures are also presented.
Determination of the onset of plastic deformation in ZnSe layers grown on (100) GaAs by molecular-beam epitaxy
Authors: Kleiman J. , Park R. M. , Qadri S. B.
Published: July 2002

ZnSe layers were grown by molecular-beam epitaxy on (100) GaAs substrates to various layer thicknesses in the range 0.1–2.0 μm. The ZnSe lattice parameter normal to the heterointerface and the ZnSe and GaAs lattice parameters parallel to the heterointerface were measured by the single-crystal x-ray diffractometry technique using the high angle reflections obtained from the (006) and (444) planes. In addition, the heterointerfaces were examined by cross-sectional transmission electron microscopy. It was found that thin ZnSe layers (t<0.5 μm) grown on GaAs substrates are tetragonally distorted. The layers appear to be elastically strained up to a layer thickness in the range 0.15–0.2 μm whereupon a gradual strain-relief process occurs for layers in the thickness range 0.2≤t≤0.5 μm via the formation of misfit dislocations.
Number of modes governing spin-wave turbulence
Authors: Gill Tepper L. , Zachary W. W.
Published: July 2002

The Landau–Lifschitz equations describe the time evolution of magnetization in classical ferromagnets and are of basic importance for the understanding of magnetism. It is shown that, under quite general conditions, dissipative forms of these equations have attracting sets which are finite dimensional in a suitable sense. It follows from these results that, after an initial transient period, only a finite number of spin-wave modes contribute to the spin-wave instabilities responsible for the chaotic behavior recently found in ferromagnetic resonance, in both the tranverse and parallel pumping versions.
Raman scattering from extremely thin hard amorphous carbon films
Authors: Ramsteiner M. , Wagner J. , Wild Ch. , Koidl P.
Published: July 2002

Hard amorphous hydrogenated carbon (a-C:H) films with thicknesses varying from 10 to 2000 Å were plasma deposited on Si or Ge and studied by Raman spectroscopy. Using optical multichannel detection it was possible to record light scattering spectra from even the thinnest films. The main peak in the Raman spectrum, which is at ∼1520 cm−1 for thick (a-C:H) films, shows a frequency down shift for layers thinner than 100 Å. This mode softening, which amounts to 70 cm−1 for 10-Å a-C:H on Si, is substrate dependent. It reflects the free surface of the film as well as the carbon-substrate bonding at the interface. The Raman scattering intensity shows a pronounced enhancement for films with an optical thickness of about 1/4 of the exciting laser wavelength. This behavior is explained in terms of interference-enhanced Raman scattering.
Chaos in spin clusters: Correlation functions and spectral properties
Authors: Srivastava Niraj , Kaufman Charles , Müller Gerhard
Published: July 2002

We investigate dynamic correlation functions for a pair of exchange-coupled classical spins with biaxial exchange and/or single-site anisotropy. This represents a Hamiltonian system with two degrees of freedom for which we have previously established the integrability criteria. We discuss the impact of (non-)integrability on the autocorrelation functions and their spectral properties. We point out the role of long-time anomalies caused by low-flux cantori, which dominate the convergence properties of time averages and determine the long-time asymptotic behavior of autocorrelation functions in nonintegrable cases.
Single-crystal ac susceptibility measurements on [Co(NH3)6][CuCl5], a 3D, S=1/2 Heisenberg antiferromagnet
Authors: Moròn Mary C. , Palacio Fernando , Pons Josefina , Casabo Jaime , Merabet K. E. , Carlin Richard L.
Published: July 2002

Single-crystal ac magnetic susceptibilities of [Co(NH3)6][CuCl5] along the three crystallographic axes in the temperature range from 1.1 to 90 K are presented. The magnetic behavior is characteristic of a three-dimensional antiferromagnet, its ordering temperature being at Tc=3.8 K. Susceptibilty data can be fit to a Heisenberg S=1/2 simple cubic model using high-temperature series expansions extrapolated with Pade approximants. Good agreement is found for an exchange constant J/kB=−3.13 K and values of g factor ga=2.09, gb=gc =2.04, a,b, and c being the crystallographic axes. This result makes [Co(NH3)6][CuCl5] one of the few examples of a 3D antiferromagnetic Heisenberg S=1/2 model. The magnetic behavior below Tc indicates the existence of crystallographic domains due to the structural transition from cubic to tetragonal symmetry that the system has at about 280 K.
RETM5 and RE2TM17 permanent magnets development
Authors: Kumar Kaplesh
Published: July 2002

RETM5 and RE2TM17 (RE=rare earth, TM=transition metal) permanent magnets are discussed in this review. The scientific and technological considerations which have guided their development are described. Along with a discussion of the various research efforts reported in the literature, they help establish the framework within which most of the work can be integrated and understood. In regard to the RETM5 alloys, the review limits itself to the technologically significant SmCo5 materials; others are discussed minimally, and only to the extent that they contributed to overall magnet development efforts. Likewise, from among the fabrication technologies, the review is limited to those processes which have been demonstrated as capable of producing magnets in bulk useful form. Areas covered in this review include phase diagrams, crystal structures, magnetocrystalline anisotropy, coercivity mechanisms, fabrication technologies, processing-microstructure-property interrelationships, and thermal effects related to stability of magnet flux. Directions for future, additional work are discussed briefly as well.
Harmonic generation in nondegenerate semiconductors at low lattice temperature
Authors: Paul S. S. , Bhattacharya D. P.
Published: July 2002

The characteristics of second harmonic generation (SHG) in covalent semiconductors at low lattice temperatures are studied here over a wide range of the bias field, beginning from a weakly heated carrier ensemble up to the onset of impurity breakdown giving due consideration to the effect of recombination of the nonequilibrium carriers in the presence of shallow attractive traps. The calculations are carried out for a parabolic law of dispersion and a scalar effective mass. The results confirm that the recombination effects bring in both qualitative and quantitative changes in the SHG characteristics throughout the entire range of the bias field. Like the situation around room temperatures, the curves for the efficiency of SHG versus the bias field at low lattice temperatures also exhibit maximum, thus illustrating the optimum bias field for which the generation can be most efficient. Depending upon the lattice temperature and the material, the recombination effects may bring in a second maximum in the characteristics of SHG. The results are found to be useful for the determination of some capture parameters. The inadequacies of the theory are pointed out and the scope for further refinement is discussed.
Epitaxial Y-Ba-Cu-O thin films prepared by rf-magnetron sputtering
Authors: Setsune K. , Kamada T. , Adachi H. , Wasa K.
Published: July 2002

Superconducting Y-Ba-Cu-O thin films were prepared by a rf-magnetron sputtering process. The preparation conditions, film crystallinity, and resistivity were investigated. The composition of the films strongly depended on the oxygen partial pressure of the sputtering gas. It was found that the substrate temperature during sputtering and the selection of substrate materials governed the crystallinity of the Y-Ba-Cu-O thin films. The preferential c-axis orientation was obtained for the films prepared on (0112) sapphire, (100) MgO, and (100) SrTiO3 substrates at a substrate temperature of about 750 °C. These as-deposited films have shown the superconducting transitions which were improved by setting the optimum conditions for sputtering and subsequent anneal process.
Gain- and threshold-current dependence for multiple-quantum-well lasers
Authors: Wilcox J. Z. , Peterson G. L. , Ou S. , Yang J. J. , Jansen M. , Schechter D.
Published: July 2002

A semilogarithmic expression that accurately approximates gain-current curves of quantum-well lasers and is useful for optimization of device performance is derived. The derivation uses both a curve fitting of the calculated curves and approximate analytical evaluation of integrals that comprise the gain model. The derived expression is used to explain the observed increase in the threshold current of single- and multiple-quantum-well lasers.
Laser self-doubling in neodymium yttrium aluminum borate
Authors: Lu Bao-sheng , Wang Jun , Pan Heng-fu , Jiang Min-hua , Liu En-quan , Hou Xue-yuan
Published: July 2002

The nonlinear effects of neodymium yttrium aluminum borate NdxY1−xAl3(BO3)4 (NYAB) crystal powder samples with different Nd3+ mole percentage are reported in this paper. The optimum X value for the growth of NYAB crystals with high optical homogeneity has been determined. The performance of laser self-frequency doubling from 1.06–0.53 μm has been realized, for the first time, in a 5×3×3 mm3 NYAB crystal. The Nd3+ ions in crystal show weak absorption at 0.53 μm. The threshold energy is measured to be less than 2 mJ; the output energy of green light at 0.53 μm is more than 5 mJ and the conversion efficiency is over 10%. The experiments show that the performance is improved if the optical path length is increased and the cavity design is improved. The refractive indices n0 and ne of the crystal have been measured by the prism method at different wavelengths. The phase-matching angles of Types I and II have been obtained by solving equations for the phase-matching angles. The results are in good agreement with the experimental values. The nonlinear coefficient d11 of the NYAB crystal has been measured to be 4×10−9 esu.
Properties and structure of soda-lime aluminosilicate glasses
Authors: Shelby James E.
Published: July 2002

The properties of soda-lime aluminosilicate glasses have been measured for several series of glasses containing a constant silica content, with varying ratios of soda to lime and of modifier oxides to alumina. The results demonstrate that a systematic variation in the effect of modifier ions occurs as lime replaces soda. The sharp breaks observed in the properties of sodium aluminosilicate glasses disappear as soda is replaced by lime. A structural model is suggested to account for these changes in behavior.
Fully relativistic calculation of the hyperfine fields of 5d-impurity atoms in ferromagnetic Fe
Authors: Ebert H. , Zeller R. , Drittler B. , Dederichs P. H.
Published: July 2002

The spin-polarized, fully relativistic version of the Korringa–Kohn–Rostoker Green’s-function method of band-structure calculation has been used to calculate the electronic structure of 5d-impurity atoms dissolved in Fe. As a new feature of such investigations, the spin as well as the orbital contributions to the magnetic moments and hyperfine fields were accessible to an evaluation. For the hyperfine fields the orbital-dipolar contributions stemming from non-s-electrons of the core and the conduction band were found to be quite large and non-negligible. In addition, we found a drastic relativistic enhancement of the Fermi-contact field due to the s-electrons. For this reason a completely relativistic treatment of the hyperfine interaction of 5d-transition metals seems to be indispensable to achieve satisfying agreement with experimental data.
Optical absorption and emission of InP1−xSbx alloys
Authors: Reihlen E. H. , Jou M. J. , Fang Z. M. , Stringfellow G. B.
Published: July 2002

A detailed optical study of the metastable III/V semiconductor alloy InP1−xSbx is presented. InP1−xSbx layers are grown throughout the entire compositional range by atmospheric pressure organometallic vapor phase epitaxy on InP, InAs, and InSb substrates. Composition and strain are measured by combined electron microprobe analysis and x-ray diffractometry. The dependence of band gap on composition is experimentally established for the first time from absorption spectra measured at 10 and 300 K. The resultant value of the band-gap bowing parameter is 1.52±0.08 eV, independent of temperature. The absorption spectra show the InP1−xSbx layers to have long band tails, which extend further into the gap as the Sb concentration is increased. The band tails are induced by compositional clustering. Photoluminescence (PL) spectra are measured between 10 and 300 K. The PL peaks are assigned to recombination between carriers occupying band-tail states or to recombination via deep centers in the gap.
Kinetic description of the transition from a one-phase to a two-phase growth regime in Al/Pd lateral diffusion couples
Authors: Blanpain B. , Mayer J. W. , Liu Joyce C. , Tu K. N.
Published: July 2002

The kinetics of the solid-state reaction between Al and Pd is studied in the geometry of a lateral Al-Pd diffusion couple in the temperature range between 250 and 430 °C. The first reaction phase is the crystalline Al3Pd2(δ) phase. After the growth of Al3Pd2 reaches a critical length, the quasicrystalline decagonal Al3Pd(γ′) phase starts to grow in between the Al and the Al3Pd2 phases, and the Al3Pd2 and Al3Pd phase continue to grow simultaneously. We have fitted this simultaneous growth with a recently proposed model of kinetic suppression on the basis of interfacial reaction barriers. Excellent agreement between the data and the model is found. From the analysis the effective interface growth constant for the Al3Pd is extracted as a function of temperature.
A computational model of a dual-wavelength solid-state laser
Authors: Henderson George A.
Published: July 2002

A rate equation model of a Y-cavity solid-state laser with a single active medium operating simultaneously on two laser lines having a common upper level is described. Application is made to Nd3+ : YAG, where the 1.06-μm and 1.32-μm infrared lines can be sum-frequency mixed to produce 0.589-μm yellow radiation. The model is used to optimize cavity design with respect to efficiency of sum-frequency mixing.
Characteristics of x-ray radiation by a nonequilibrium energetic electron flow emerged from a formed ferrite filament
Authors: Watanabe K. , Furusho K. , Kashiwabara S. , Fujimoto R.
Published: July 2002

This article reports the observation of intense x-ray emission by a nonequilibrium energetic electron flow that can be produced when an explosive formed-ferrite filament is used as a plasma initiator in a high vacuum of 10−5–10−3 Torr. Exposure dose measurements and pinhole photographs for the x-ray emission have shown that x rays originate linearly along a 14.5-cm filament with a high exposure dose level of 50 mR(mili-roentgen)/pulse at 6.5 keV, the predominant x-ray energy. The x-ray emission characteristics are described in terms of the time-resolved and -integrated observations in order to infer the x-ray emission mechanism in which an interaction between energetic electron flow and a cloud of ions or neutral atoms thermally produced from the filament has to be taken into account in the close vicinity of the filament.
Computer analysis of the role of p-layer quality, thickness, transport mechanisms, and contact barrier height in the performance of hydrogenated amorphous silicon p-i-n solar cells
Authors: Arch J. K. , Rubinelli F. A. , Hou J.-Y. , Fonash S. J.
Published: July 2002

The transport simulations provided by the computer program AMPS have been used to give an in-depth analysis of the role of the p-layer contact barrier height, contact transport mechanism, p-layer thickness, and p-layer quality on the performance of hydrogenated amorphous silicon p-i-n solar cells. We demonstrate for the first time that, if the contact barrier height to the p-layer is below a critical value and if tunneling through the p-layer is not important, then the performance of cells with either active or dead p-layers varies with contact barrier height regardless of p-layer thickness. We show that, even for an optimistic p-layer active doping density of 1019 cm−3, this critical barrier height is high (∼1.2 eV). Our analysis implies that one of two situations must occur in an actual a-Si:H p-i-n structure: the p-layer contact plays an important role in determining cell efficiency, or the tunneling of holes through the front contact/p-layer interface must be important. Comparison of simulated results, with and without tunneling, with experimental data suggests that tunneling is occurring in actual devices and is important in efficient structures.
Precise determination of aluminum content in AlGaAs
Authors: Chang K. H. , Lee C. P. , Wu J. S. , Liu D. G. , Liou D. C. , Wang M. H. , Chen L. J. , Marais Mario A.
Published: July 2002

The Al composition of AlGaAs has been determined by four methods: high-resolution transmission electron microscopy (HRTEM), reflection high-energy electron diffraction (RHEED), photoluminescence (PL), and double-crystal x-ray diffraction (DCXRD). HRTEM is direct and the most accurate method because it does not involve any formula or extrapolation. Using the result obtained from HRTEM as a standard, we have calibrated the results from other methods. RHEED intensity oscillation is found to be accurate and reliable, if the growth conditions are correctly chosen. Comparing the PL results with those determined from HRTEM and RHEED, we suggest three formulas to determine the Al contents at different temperatures. We also proposed a polynomial to determine the Al concentration using the DCXRD measurement.
Ferromagnetic resonance linewidth of Fe ultrathin films grown on a bcc Cu substrate
Authors: Celinski Z. , Heinrich B.
Published: July 2002

The ferromagnetic resonance (FMR) linewidth ΔH is a parameter used to characterize ultrathin film quality. The frequency-independent part, ΔH(0), reflects the contribution of magnetic inhomogeneities. The linear part is caused by the intrinsic Gilbert damping mechanism. Recently we have found that the lattice reconstructions of substrate templates strongly affects the FMR linewidth. bcc Fe(001) films (∼10 ML) were grown on unreconstructed fcc Ag(001), bcc Cu(001), and on surface reconstructed bcc Cu(001) templates. Fe layers grown on unreconstructed Cu templates exhibited an isotropic FMR linewidth. Fe layers grown on reconstructed Cu templates, on the contrary, showed an anisotropic behavior in both the zero-frequency FMR linewidth and the intrinsic damping parameter. Other magnetic parameters such as uniaxial and 4-fold anisotropies are also discussed.
Increased thermal generation rate in GaAs due to electron-beam metallization
Authors: Stellwag T. B. , Melloch M. R. , Cooper J. A. , Sheppard S. T. , Nolte D. D.
Published: July 2002

Leakage currents due to thermal generation in a reverse-biased p-n junction can be accurately monitored by measuring the capacitance recovery transient of a p-n-p structure. Using this technique, it has been demonstrated that the thermal generation in the bulk depletion region of GaAs p-n junctions grown by molecular beam epitaxy can be as much as three orders of magnitude greater for samples metallized in electron-beam evaporators as compared to thermal evaporators. The increase in thermal generation rate is shown to be dependent upon the device area exposed during the evaporation, the type of metal initially evaporated onto the sample, the growth conditions during molecular beam epitaxy, and the depth of the p-n junction from the semiconductor surface.
Influence of doping on the structural and optoelectronic properties of amorphous and microcrystalline silicon carbide
Authors: Demichelis F. , Pirri C. F. , Tresso E.
Published: July 2002

Amorphous and microcrystalline silicon carbide, undoped and doped, has attracted a great attention for its optical and electrical properties. The introduction of dopant atoms in the network of amorphous films permits the control of electrical properties but it gives rise to a decreasing of the optical gap. Microcrystalline SiC:H films seem to provide films having a wide range of electrical conductivities without drastic change in the optical gap. This paper presents the results of a detailed study on the effects of boron and phosphorus doping on structural, optical, and electrical properties of a-SiC:H and μc-SiC:H films. An optical gap as high as 2.1 eV, together with a conductivity of 10−3 Ω−1 cm−1, are shown by doped μc-SiC:H.
Low-temperature conductivity of ZnO films prepared by chemical vapor deposition
Authors: Natsume Y. , Sakata H. , Hirayama T. , Yanagida H.
Published: July 2002

c-axis-oriented ZnO films were prepared in O2 atmosphere by chemical vapor deposition using zinc acetylacetonate for source material. A minimum value of resistivity, 2.44 Ω cm, was obtained at a film formation temperature of 550 °C. The resistivity of the films was measured at low temperatures (87–297 K). For temperatures between 200 and 297 K band conduction included boundary scattering due to both thermionic emission and thermal-field emission at the grain-boundary barriers in the films, and the activation energy obtained ranged from 1.45 to 6.32×10−2 eV. For temperatures lower than about 200 K, the conductivity deviated from linear Arrhenius plots suggesting variable range-hopping conduction. Discussions based on assumed electron mobility and concentration lead to variable range-hopping conduction by localization of electrons in impurity levels in the intermediate concentration region. Mott’s parameters in the variable range-hopping conduction were estimated for the films.
Defects in electron-irradiated GaAlAs alloys
Authors: Zaidi M. A. , Maaref H. , Zazoui M. , Bourgoin J. C.
Published: July 2002

Using deep-level transient spectroscopy, we have characterized the energy levels, barriers for electron capture, and introduction rates of the defects introduced by electron irradiation in liquid-phase epitaxy grown n-type (Te)Ga1−xAlxAs layers of various alloy composition (x=0.25, 0.40, 0.60, and 0.80). We observed five defects which present various type behaviors: energy levels linked to the valence band or to the L conduction bands, constant barriers, or varying in a manner consistent with the band structure. These results are in agreement with the understanding obtained previously on electron-induced defects in GaAs.
Recording of mid-infrared radiation in photochromic polymers
Authors: Weiss V. , Friesem A. A. , Krongauz V. A.
Published: July 2002

A new system for real-time recording of mid-infrared laser radiation, comprising photochromic spiropyran–methylmethacrylate copolymers, is investigated. The laser radiation, derived from a CO2 laser, bleached pre-colored merocyanine, thereby converting it back to spiropyran. The exposure energies at 50% of the initial merocyanine optical density was about 0.1 J/mm2 at 10.6 μm laser wavelength and 0.2 J/mm2 at 10.5 μm. The sensitivity difference at the two laser wavelengths points to differences in thermal energy dissipation mechanisms. A resolution equal or better than 40 lines/mm was achieved, and holographic gratings can be recorded in the mid-infrared.
Recombination centers in Czochralski-grown p-Si
Authors: Zazoui M. , Zaidi M. A. , Bourgoin J. C. , Strobl G.
Published: July 2002

A sensitive deep-level transient spectrometer operating in the range 300–600 K has been used to detect the defect responsible for the minority-carrier lifetime in p-type Czochralski-grown Si. The characteristics of this defect (energy level, barrier for hole capture, hole and electron capture rates, and concentration) have been determined. This level is, as expected, located near the middle of the forbidden gap. We verified that it is indeed responsible for the lifetime by a comparison between the calculated value and the result of direct measurements. If this defect is an impurity, it could be manganese.
Measurement of interface strength by the modified laser spallation technique. II. Applications to metal/ceramic interfaces
Authors: Gupta V. , Yuan J.
Published: July 2002

Part II of this series presents applications of the modified laser spallation technique to several interface systems. For metal/pyrolytic graphite (PG) interfaces, the tensile strength of interfaces between 3-μm-thick coatings of Sn, Sb, Cu, Nb, Al, and Cr on a PG substrate were measured in units of MPa to be 18.53, 5.99, 15.46, 41.16, 16.53, and 15.47, respectively. It was found that the interface fracture mechanisms depend on the elastic-plastic properties of the coatings, but are independent of the interface strength. Interface strength between diamond, SnO2, and Nb coatings on polycrystalline alumina substrates were measured to be ≳140, 320, and 280 MPa, respectively. It is shown that the brittle fracture takes place at the interface upon spalling even if the plastic deformation exists within the coatings.
Spectral characteristics of distributed feedback semiconductor lasers and their improvements by corrugation-pitch-modulated structure
Authors: Okai Makoto
Published: July 2002

Semiconductor lasers with stable longitudinal single-mode operation are essential for optical fiber communication systems. Distributed feedback (DFB) lasers are effective to obtain a stable longitudinal single-mode operation; however, stability is not enough mainly because of the spatial hole-burning effect. A corrugation-pitch-modulated (CPM) structure was proposed to improve the stability of longitudinal single-mode operation in distributed feedback lasers. CPM-DFB lasers have a unique corrugation structure to suppress the spatial hole-burning effect. This structure was obtained by a newly developed corrugation fabrication method, a photomask self-interference method. It is confirmed that the CPM-DFB lasers operate in a stable longitudinal single-mode by suppressing the spatial hole-burning effect. This structure is also suitable for narrowing the spectral linewidth for use in coherent optical fiber communication systems. Narrow spectral linewidth lasers with a CPM structure have achieved the narrowest spectral linewidth reported to date.
Mutual shielding of closely spaced dust particles in low pressure plasmas
Authors: Choi Seung J. , Kushner Mark J.
Published: July 2002

The transport of particles (‘‘dust’’) in low pressure electrical glow discharges is of interest as a result of their role in contaminating wafers during plasma etching and deposition of semiconductors. Particles (10s nm to many micrometers) negatively charge in glow discharges and, to first order, appear to be massively large negative ions around which sheaths develop. The electrical and fluid forces acting on dust particles in plasma processing discharges may cause the interparticle spacing to be less than the shielding distance around particles. The mutual shielding of dust particles is therefore of interest. In this article, we report on results from a pseudoparticle-in-cell simulation of the mutual shielding of two adjacent dust particles. Results will be discussed for charge, potential, and electrostatic forces on dust particles as a function of particle size and separation distance between two particles. We found that two closely spaced particles not only shield each other but can shadow their partner, thereby resulting in asymmetric charging of otherwise identical particles.
Hydrogen recombination on plasma facing materials
Authors: Shu W. M. , Hayashi Y. , Okuno K.
Published: July 2002

Recombination coefficients of hydrogen have been modeled respectively for the front side and the back side of plasma facing materials. On the front side, both the normal-surface sites and the imperfection-surface sites produced by the energetic ions are taken into account, and the dependence of the aerial density of active recombination sites upon the aerial density of imperfections and the balance between the chemisorption and desorption of impurity atoms at imperfections are discussed. On the back side, the effective recombination coefficient is obtained by analyzing the metal-oxide system. This parameter depends upon the solution energy for the metal and the chemisorption energy on the oxide-layer surface as well as surface coverage, if it is rate-limited by the recombination in the oxide layer; and it increases with increasing diffusion coefficient and decreasing thickness, if it is rate-limited by diffusion in the oxide layer.
Study of initial dust formation in an Ar-SiH4 discharge by laser induced particle explosive evaporation
Authors: Boufendi L. , Hermann J. , Bouchoule A. , Dubreuil B. , Stoffels E. , Stoffels W. W. , de Giorgi M. L.
Published: July 2002

The initial step of particulate growth in a dust forming low pressure radio-frequency discharge has been studied in situ by laser induced particle explosive evaporation (LIPEE). With respect to the conventional light scattering, this method has been found much more efficient to observe small nanometer size particles, especially in the case of UV excimer laser radiation. Experimental results interpreted by a simple model of laser-particle interaction show that the intensity of LIPEE continuum emission depends on the particle radius roughly as r4. This interaction is essentially different from Rayleigh scattering, as the latter varies as r6. A study of time evolution of powder formation by LIPEE emission reveals the initial formation of nanometer size crystallites and the coalescence process leading to larger scale particles. It could be demonstrated that the critical step of dust formation is the initial clustering process leading to nanometer scale crystallites.
Intrinsic giant magnetoresistance of mixed valence La-A-Mn oxide (A=Ca,Sr,Ba) (invited)
Authors: von Helmolt R. , Wecker J. , Samwer K. , Haupt L. , Bärner K.
Published: July 2002

A large intrinsic magnetoresistance has been found near the ferromagnetic transition of metallic manganese oxides with perovskite-type crystal structure. The magnetic and transport properties were measured on bulk and thin-film La1−xAxMnO3+δ with A=Ca,Sr,Ba. Assuming the double-exchange model proposed by Zener [Phys. Rev. 81, 440 (1951); 82, 403 (1951)], the strong dependence of the transport properties on the magnetic field and also on the chemical composition is attributed to the mixed Mn3+/Mn4+ valence.
Nature of half-metallic ferromagnets: Transport studies
Authors: Moodera J. S. , Mootoo D. M.
Published: July 2002

The half-metallic ferromagnetic compounds due to the absence of states at EF for minority spin electrons, as predicted by band theory, should exhibit unique features in their transport properties. Transport measurements conducted as a function of T and H for NiMnSb and PtMnSb thin films show interesting behavior. In H=0, the resistivity versus T shows the absence of the T2 dependence at low temperature found in ferromagnets such as Fe, Ni, etc. The Hall constant increases significantly below about 100 K for both compounds; NiMnSb shows a factor of seven increase. Transverse magnetoresistance changes sign between 295 and 4.2 K. Transport data seem to imply a drop in the carrier density and a large increase in their mobility at low temperatures, which is consistent with zero density of states for minority spins at EF, but additional measurements are needed to clarify theoretical understanding.
Photoconducting properties of a ladder polymer
Authors: Narayan K. S. , Taylor-Hamilton B. E. , Spry R. J. , Ferguson J. B.
Published: July 2002

The electronic properties of the ladder polymer BBL are investigated using steady state and transient photoconductivity techniques. The photocurrent response of the polymer film in the surface cell and sandwich cell configurations are compared along with the absorption spectra and the results correlated with the surface and bulk morphology. The steady state photocurrent shows a nonlinear response with respect to the electric field, and the photocurrent spectral response is accompanied by a significant tailing in the infrared region. The photocurrent is also studied as a function of photon intensity and chopper frequency. A long lived transient photocurrent (≳100 ms) is present on exposure to nanosecond laser pulses revealing the presence of deep traps.
Activation energy for CoSi and CoSi2 formation measured during rapid thermal annealing
Authors: Colgan E. G. , Cabral C. , Kotecki D. E.
Published: July 2002

The activation energies, Ea’s, for CoSi and CoSi2 formation were determined using in situ resistance measurements during rapid thermal annealing. Co films were evaporated on undoped polycrystalline Si (poly-Si) and single-crystal Si on sapphire (SOS) substrates. The resistance was monitored for heating rates from 1 to 60 °C/s up to 900 °C. There was significant thermal lag between the samples and thermocouple embedded in the susceptor wafer for heating rates greater than 20 °C/s. The thermal lag was quantified by melting Au-Si, Al-Si, and Ag-Si eutectics, and shown to be consistent with finite element modeling. The Ea’s determined from Kissinger plots for heating rates ≤20 °C/s were 2.09±0.11 and 2.03±0.08 eV for CoSi formation and 2.91±0.22 and 2.81±0.23 eV for CoSi2 formation, for Co/poly-Si and Co/SOS samples, respectively.
Raman spectra of CuAlSe2 heteroepitaxial layers
Authors: Chichibu Shigefusa , Kamata Atsushi
Published: July 2002

Room-temperature Raman spectra were measured for CuAlSe2 heteroepitaxial layers grown on GaAs (001) and GaP (001) substrates. A remarkable difference in the polarized Raman spectra was noted, and the results were attributed to be due to the lattice orientation of the epilayers on the basis of the polarization selection rules of Raman active modes. Two vibrational modes were assigned, namely the A1 mode at 189 cm−1 and longitudinal-optical B2 mode at 89 cm−1.
Adsorption-induced surface stress and its effects on resonance frequency of microcantilevers
Authors: Chen G. Y. , Thundat T. , Wachter E. A. , Warmack R. J.
Published: July 2002

It is well known that bimetallic microcantilevers can exhibit static deflection as a result of thermal effects, including exothermic adsorption of chemicals on their surfaces. It is shown here that the resonance frequency of a cantilever can change due to a combination of mass loading and change of spring constant resulting from adsorption of chemicals on the surface. Cantilevers also undergo static bending that is induced by differential surface stress. The magnitude of these effects depends upon the chemical properties of the surface and upon the amount of material adsorbed. Hence cantilever deflection as well as resonance frequency change can be used as the basis for development of novel chemical sensors.
Theoretical analysis of surface transverse waves propagating on a piezoelectric substrate under shallow groove or thin metal strip gratings
Authors: Gavignet E. , Ballandras S. , Bigler E.
Published: July 2002

Theoretical calculations are developed in the present study in order to predict propagation characteristics of surface transverse waves (STW) on piezoelectric substrates. A general model has been implemented for both cases of shallow groove or thin metal strip grating resonators. The analysis gives access to the principal STW characteristics (propagation and attenuation coefficients, velocity, electrical and mechanical amplitudes) and the dispersion curve relating the angular frequency to the propagation coefficient. The results obtained are in good agreement with previous results without piezoelectricity. Improvements on theoretical predictions are emphasized for the case of STW propagating under thin metal strips on AT-cut quartz.
H, He, and N implant isolation of n-type GaN
Authors: Binari S. C. , Dietrich H. B. , Kelner G. , Rowland L. B. , Doverspike K. , Wickenden D. K.
Published: July 2002

The effect of ion-implantation-induced damage on the resistivity of n-type GaN has been investigated. H, He, and N ions were studied. The resistivity as a function of temperature, implant concentration, and post-implant annealing temperature has been examined. Helium implantation produced material with an as-implanted resistivity of 1010 Ω-cm. He-implanted material remained highly resistive after an 800 °C furnace anneal. The damage associated with H implantation had a significant anneal stage at 250 °C and the details of the as-implanted resistivity were sample dependent. N implants had to be annealed at 400 °C to optimize the resulting resistivity but were then thermally stable to over 800 °C. The 300 °C resistivity of thermally stabilized He- and N- implanted layers was 104 Ω-cm, whereas for H-implanted layers the 300 °C resistivity was less than 10 Ω-cm.
Secondary electron emission at anode, cathode, and floating plasma-facing surfaces
Authors: Ordonez C. A. , Peterkin R. E.
Published: July 2002

The secondary electron emission coefficient is evaluated for electron impact on anode, cathode, and electrically floating plasma-facing surfaces. Two energy and angle distribution functions for electron impact on a plasma-facing surface are derived and different relations for the secondary electron emission coefficient which functionally depend on energy and angle are integrated over the distributions. One integration is in closed form and provides a parametric expression for the secondary electron emission coefficient of a plasma-facing surface. The other integrations are carried out numerically. Evaluation of the secondary electron emission coefficient for a variety of commonly-used plasma-facing materials shows that its value is near or above unity over a significant range of plasma temperatures.
Argon incorporation and silicon carbide formation during low energy argon-ion bombardment of Si(100)
Authors: Pan J. S. , Wee A. T. S. , Huan C. H. A. , Tan H. S. , Tan K. L.
Published: July 2002

Argon incorporation and the formation of silicon carbide in Si(100) by low energy Ar+ ion bombardment have been studied by angle-resolved x-ray photoelectron spectroscopy (XPS). The bombardment was performed at ion energies of 1, 1.5, and 2 keV and various ion fluences in an ultrahigh vacuum chamber equipped with XPS. The XPS measurements showed that the incorporated Ar concentrations achieved saturation in the near-surface region at ion bombardment fluences ≳1016 cm−2. The surface Ar concentrations decreased with increasing bombardment energy. No Ar bubbles on the surface of Ar+-bombarded samples were observed by atomic force microscopy under these experimental conditions suggesting that Ar bubble formation was not the main Ar trapping mechanism in our study. The SiC formation was confirmed by characteristic XPS peaks of Si 2p and C 1s for SiC. The carbide formed at lower ion fluence was of a metastable structure as inferred by XPS. Bombardment at higher ion fluence yielded a stable carbide phase through continuous ion beam mixing. No strong dependence of carbide depth distribution on bombardment energy was observed suggesting that the carbide phase is probably dispersed inside the bombarded layer and that carbon is bonded to silicon at localized defect sites.
Kinetics of silicide formation measured by in situ ramped resistance measurements
Authors: Colgan E. G. , d’Heurle F. M.
Published: July 2002

The use of ‘‘Kissinger’’ plots to analyze in situ resistance monitoring of thin-film reactions during heating at a constant rate is widely accepted. One obtains the activation energy for diffusion, at least in the case of diffusion-controlled reactions. The aim of this article is to extend the analysis one step further and show that, provided that the thickness of the layers formed is known, the same experimental and analytical techniques may yield the pre-exponential growth factor. The validity of the procedure is demonstrated by comparing the results thus obtained with data from the literature derived by conventional analysis of compound growth during isothermal annealing. Such comparisons have been made for Co2Si, CoSi, CoSi2, Pt2Si, PtSi, Ni2Si, and NiSi formation on undoped polycrystalline Si and single-crystal Si on sapphire substrates with ramp rates ranging from 10−2 °C/s to 102 °C/s. Measurements used both conventional furnace and rapid thermal annealing. In the past, the common practice has been to use the Kissinger method regardless of the sequence of growing phases. However, for phases other than the first one to be formed the direct Kissinger analysis needs to be modified. In the present cases the results obtained by means of an appropriately corrected procedure are not significantly different; that may not always be true.
Perpendicular magnetization and surface magnetoelastic anisotropy in epitaxial Cu/Ni/Cu (001)
Authors: Bochi Gabriel , Ballentine C. A. , Inglefield H. E. , Thompson C. V. , O’Handley R. C.
Published: July 2002

Epitaxial Ni films (2.0 nm<h<14 nm) have been grown on Cu/Si (001) and capped with 2.0 nm of Cu in a molecular beam epitaxy chamber. Their magnetic anisotropy has been measured ex situ in a vibrating sample magnetometer. Perpendicular magnetization is preferred over a broad Ni-thickness range: 25≤h≤140 Å. The quantitative anisotropy data are not well described by a model including bulk and surface magnetocrystalline anisotropy, Kb+Ksh, magnetostatic energy, and bulk magnetoelastic energy, Bbe(h). If surface magnetoelasticity Bse/h is considered, the data are well described and values for Ks and Bs consistent with Néel’s model are determined.
Atomic migration in Ni–Co ferrite
Authors: Kim Chul Sung , Lee Seung Wha , Park Seung Iel , Park Jae Yun , Oh Young Jei
Published: July 2002

Ni–Co ferrite has been studied with Mössbauer spectroscopy and x-ray diffraction. The crystal structure for this system is spinel, and the lattice constant is in accord with Vegard’s law. The Mössbauer spectra consist of two six-line patterns corresponding to Fe3+ at the tetrahedral (A) and octahedral (B) sites. The Néel temperature increases linearly with Ni concentration, suggesting the superexchange interacion for the Ni–O–Fe link is stronger than that for the Co–O–Fe link. It is found that Debye temperatures for the A and B sites of CoFe2O4 and NiFe2O4 are found to be θA=734 K, θB=248 K, and θA=378 K, θB=357 K, respectively. The intensity ratio of the A to B patterns is found to increase at low temperatures with increasing temperature due to the large difference of Debye temperatures of the two sites and to decrease at high temperatures due to migration of Fe3+ ions from A to B sites. Atomic migration of CoFe2O4 starts near 400 K and increases rapidly with increasing temperature to such a degree that 69% of the ferric ions as the A sites have moved over to the B sites by 780 K. It is noted that, as the Ni concentration in cobalt ferrite increases, the Debye temperatures tend to decrease the migration at the A and B sites is slow.
An approach based on Brownian motion for the simulation of ultrasmall semiconductor devices
Authors: Arokianathan Clinton R. , Asenov Asen , Davies John H.
Published: July 2002

We present an approach to the simulation of ultrasmall semiconductor devices based on Brownian motion of the carriers described by the Langevin equation. It follows the trajectories of individual particles in real space but does not require the computational effort of a full Monte Carlo simulation. This method is particularly useful for modeling very small devices where individual impurities and carriers must be considered, and the dynamics need to be treated atomistically, in a full-scale three-dimensional simulation.
Determination of the viscous and thermal characteristic lengths of plastic foams by ultrasonic measurements in helium and air
Authors: Leclaire Ph. , Kelders L. , Lauriks W. , Melon M. , Brown N. , Castagnède B.
Published: July 2002

The acoustic wave most commonly transmitted and detected in the high-porosity absorbent materials used in noise control is generally the air-borne slow compressional wave. In a new experiment, the air saturating the sample is replaced by helium and the transmission is studied at ultrasonic frequencies (70–600 kHz). The experiment is quite easily performed using standard ultrasonics and vacuum equipment. The main purpose of this work is to propose a method to determine simultaneously both the viscous and thermal characteristic lengths with the same precision. These two parameters characterize the viscous and the thermal interactions between the frame and the fluid at high frequencies. The characteristic lengths are deduced from the high-frequency asymptotic behavior of either the velocity or the attenuation curves obtained in the sample saturated by air and by helium. It also appears that due to the properties of helium, the discrepancy previously observed between predictions and measurements is shifted toward higher frequencies.
Activation volume of α-Fe particles in alumite films
Authors: Li Feiyue , Metzger Robert M.
Published: July 2002

The time-dependent properties of arrays of elongated and mutually aligned iron particles in alumite (anodized aluminum oxide film) have been studied. At a constant particle diameter of 11 nm, the magnetic viscosity is nearly independent of the particle length (varied from 140 to 440 nm). The activation volume (1.1 to 1.2×10−18 cm3) is almost independent of the particle length and fields: this nearly constant value is much smaller than previously reported values, but very close to the theoretical superparamagnetic limit 1.0×10−18 cm3 at room temperature.