bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel slip-free rapid thermal annealing of GaAs in vacuum with excellent uniformity and reproducibility
Authors: Kohno M. , Hida H. , Ogawa Y. , Fujii M. , Maeda T. , Ohata K. , Tsukada Y.
Published: July 2002

This paper describes novel rapid thermal annealing for GaAs wafers under vacuum conditions (VRTA) using a three-zone lamp power control method. The developed RTA technology eliminates generation of crystallographic slip lines and wafer deformation due to the convection effect caused by ambient gas. A three-zone lamp power control method produced excellent uniformity in the activated layer, presenting the best data ever attained by RTA. Also, numerical simulation demonstrates improved temperature uniformity achieved by a three-zone lamp power control method which reduces the edge radiation effect. Moreover, we have found that VRTA technology is particularly effective for annealing large-size GaAs wafers, which are more easily deformed or slip-lined than 2-in. wafers. We have applied VRTA to fabricating ion-implanted n+ contact regions for self-aligned 0.5-μm-gate doped-channel hetero-metal-insulator-semiconductor field-effect transistors with a lightly doped drain, and have obtained excellent Vt uniformity, σVt=19 mV, on a 2-in.-diam wafer. These features, together with a simple wafer-supporting method, using several quartz pins, cause the improved VRTA technology to provide high throughput and production yield for high-performance short-gate GaAs integrated circuits.
Rutherford backscattering and luminescence characteristics of neodymium implanted GaP, GaAs, and AlGaAs
Authors: Kozanecki A. , Groetzschel R.
Published: July 2002

GaP, GaAs, and Al0.25Ga0.75As samples implanted with neodymium were characterized by Rutherford backscattering spectroscopy and by photoluminescence. It is shown that recrystallization of room-temperature-implanted GaP and GaAs is retarded by the presence of Nd. However, the intra-4f shell luminescence spectra of Nd are independent of the crystalline state of GaAs. This suggests that local bonding of Nd to host lattice atoms is the basic factor determining the optical properties of Nd in GaAs. It is also shown that recrystallization of AlGaAs is only weakly affected by the presence of Nd in the layers. This shows AlGaAs:Nd to be a very promising material for optoelectronic applications.
Cascade structure and overlap effects in ion-beam mixing experiments
Authors: Rossi Francois , Nastasi Mike
Published: July 2002

General considerations about ion-beam mixing are reviewed: we show that the cascade structure, i.e., the distribution of spikes in the cascade volume, can have a strong influence on the ion-beam mixing efficiency. We first give an analytical expression of mixing rate versus the thermodynamic parameters and the spike distribution function in the case where the spikes are distributed randomly in the cascade and no overlap is taken into account. When several spikes occur in the same volume at the same time, it is shown that the temperature field is modified, and the jump frequency and diffusion rate change. This problem cannot be solved analytically, and we introduce a basic Monte Carlo calculation, where diffusion in the spikes in the case of overlap is treated. This calculation allows us to describe what happens when the substrate temperature is increased: starting from the hypothesis that the spike volume increases with temperature following an Arrhenius law, we find expressions for the activation energy in the thermally activated regime and the values of onset temperatures for thermally assisted diffusion under irradiation. The values found are in good agreement with experimental results published in the literature.
Capture barrier and the ionization entropy of the D
X center in Se-doped AlxGa1−xAs
Authors: Hanak Thomas R. , Ahrenkiel Richard K. , Timmons Michael L.
Published: July 2002

Recently there has been clear evidence that local alloy disorder splits the DX center in multiple levels. This effect is observed by deep-level transient spectroscopy (DLTS) from different thermal emission rates for the multiple levels in AlxGa1−xAs. We report for the first time the simultaneous measurement of two capture barrier and two ionization entropies for the DX center in Se-doped AlxGa1−xAs. The AlxGa1−xAs was grown by metalorganic chemical vapor deposition at two different alloy compositions (x=0.19 and 0.23). We obtained the capture rates from a DLTS experiment by simultaneously monitoring the two transient signals while changing the filling pulse width. The capture rates show exponential temperature dependence from which the thermal capture barriers are extracted. Together with the emission rate values the ionization entropy is calculated after modifying the appropriate equations for a degenerate semiconductor (ND>1×1017 for AlGaAs). The results are discussed in the context of other published values.
Ultraclean radioisotope marking by nuclear stimulated desorption
Authors: Kelson I. , Nir D. , Zidon A. , Dumont H. , Perraillon B. , Haustein P.
Published: July 2002

A method for ultraclean radioactive marking is presented, utilizing the process of nuclear stimulated desorption. It employs a sequence of two slow radioactive decays. The primary decay causes a nucleus to desorb from a substrate onto which it had been placed. The desorbing daughter nuclei, being themselves radioactive, then constitute an ultraclean marking flux. A manifestation of this mechanism for the special case of the 47Ca→47Sc→47Ti decay is described. An application to end-point detection in wet etching is presented and quantitatively simulated.
Analysis of a first-order reflection grating with second-harmonic generation
Authors: Weissman Z. , Hardy A. , Marom E. , Brueck S. R. J.
Published: July 2002

The operation of a first-order reflection grating, superposed on a dielectric waveguide with a second-order nonlinearity, is analyzed. Such a grating termination to a second-harmonic generating waveguide is shown to operate as an efficient wavelength-selective reflector(ω)/radiator(2ω) for the two respective harmonic input guided waves, in particular in a second-harmonic (SH) resonator. It is shown that radiation efficiency for the input SH wave depends on the phase difference between the two input waves and on the ratio between the input SH power and the SH power generated inside the grating. In certain cases the input SH wave experiences gain as it is radiated, with the fundamental input wave acting as a pump.
Differential thermal analysis of individual specimens by thermal EMF measurement
Authors: Riess I. , Safadi R. , Zilberstein E. , Tuller H. L.
Published: July 2002

The thermal electromotive force (EMF) generated across a specimen owing to a small nonuniformity in the sample’s temperature is used to follow phase transitions in the specimen. As the temperature is scanned, a first-order phase transition yields a sharp S-shaped peak in the EMF versus time, t, and temperature, T(t), curves. A transition to a superconducting state exhibits a sharp drop in EMF as was observed during measurements on YBa2Cu3O7. The dependence of the EMF on time and temperature is calculated for a first-order phase transition. Predictions are confirmed by experiment. This method is therefore useful for detecting phase transition temperatures. A practical feature of this measurement is the ability to precisely calibrate, in situ, the temperature measuring element, e.g., thermometer or thermocouple, when the transition temperature is already known.
The Auger recombination rate is larger in a GaSb quantum well than in bulk GaSb
Authors: Jiang Y. , Teich M. C. , Wang W. I.
Published: July 2002

The band-to-band Auger recombination rate in bulk GaSb and in a GaSb quantum well is calculated. It turns out to be larger in the quantum well because the threshold of the Auger process is located at the band edge where the density of states is larger in the quantum well than in bulk. A simple picture is developed to illustrate the physics of the Auger processes in bulk and quantum-well direct-band-gap semiconductors. With this picture, we propose that the composition-disorder-induced band mixing should be considered in order to explain the unusual behavior of the Auger process in an InGaAsP quantum-well structure.
Anelastic relaxations and molecular motions in polymeric electrolytes
Authors: Bartolotta A. , Carini G. , Di Marco G. , Romeo C. , Salvato G.
Published: July 2002

A study of the frequency (0.1–30 Hz) and temperature (120–373 K) behavior of the internal friction and of the dynamic modulus was carried out in polyethylene oxide (PEO)-Ba(SCN)2 polymeric electrolytes. The mechanical spectra reveal the presence of the following anelastic relaxations: (a) the γ process due to localized movements within the main chain, (b) a process due to relaxing particles introduced by salt, and (c) the αa process associated to the glass-rubber like transition. Both the γ- and αa -loss peaks are shifted to higher temperatures by the addition of salt. A careful analysis of the observed peculiarities permits us to gain an insight on the microscopic nature of the relaxation mechanisms and to associate the γ relaxation with localized segmental motion within the amorphous phase. In pure PEO and in the complex with the lowest salt content, the loss due to the melting transition of PEO crystals is also observed. The cited loss is lacking in the complexes with a salt molar fraction X>0.05, which show an enormous enhancement of the strength of the αa relaxation. It is argued that the addition of a salt with a divalent cation to semicrystalline PEO gives rise to completely amorphous single phase structures.
The role of surface tension in the growth of strained quantum wire arraysa)
Authors: Sherwin M. E. , Drummond T. J. , Srolovitz D. J.
Published: July 2002

The critical radius of a strained quantum wire and the potential strain stabilization of quantum wire arrays has been investigated for the InxGa1−xAs/GaAs system. The critical radius of the quantum wire was calculated using an energy balance approach. The wire was found to be more stable than the corresponding two-dimensional quantum well structure. The use of surface tension as a stabilization force during the growth of strained quantum wire arrays is expected to have beneficial effects for arrays with greater than 7% InAs.
Precipitation of arsenic diffused into silicon from a TiSi2 source
Authors: La Via F. , Privitera V. , Lombardo S. , Spinella C. , Raineri V. , Rimini E. , Baeri P. , Ferla G.
Published: July 2002

The diffusion into a p-type Si substrate of arsenic ions implanted into TiSi2 layers has been investigated for several thermal diffusion treatments in the 900–1100 °C temperature range. The drive-in was performed using either a rapid thermal annealing system or a traditional furnace. Shallow (20–80-nm depth) junctions were obtained with a high (1019–1020/cm3) dopant concentration at the silicide-silicon interface. The amount of diffused arsenic atoms measured by Rutherford backscattering spectrometry increases linearly with the square root of the annealing time. A similar relation was found for the amount of electrically active arsenic, as measured by Van der Pauw structure in combination with anodic oxidation. The two quantities differ and the inactive dopants precipitate in the diffused layer as seen by transmission electron microscopy. This behavior might be associated to the high tensile stress induced by the silicide layer on the surface silicon region and to its influence on the solid solubility and clustering of arsenic atoms. Precipitates are easily dissolved after thermal annealing in the absence of the TiSi2 layer.
Diffraction grating for the general oblique incidence
Authors: Seshadri S. R.
Published: July 2002

For the general oblique incidence for which the grating vector is inclined to the plane of incidence, the diffraction of a plane wave by a plane grating is treated by a perturbation technique. The transverse electric mode and the transverse magnetic mode incidences are investigated. The copolarized and the cross-polarized parts of the diffraction efficiencies are evaluated, and their dependencies on the direction of incidence are examined.
Heat transfer from a wire to hexane in a nonuniform electric field
Authors: Ryde Tuula , Arajs Sigurds , Nunge Richard J.
Published: July 2002

The influence of a nonuniform electric field (ac or dc) on heat transfer from an electrically heated platinum wire immersed in n-hexane was investigated. The platinum wire was concentrically mounted in a closed copper cylinder filled with the test liquid. The copper cylinder was placed horizontally in a constant temperature bath. Heat transfer coefficients for natural convection were obtained to serve as a reference for the electric field measurements. The electric field results showed an increase in the heat transfer rate from the wire over free convection for both ac and dc fields. The electric Nusselt numbers in ac fields were a factor of 4 higher than corresponding results in dc fields. This behavior differed from results reported in the literature for n-hexane, which was further demonstrated by replotting some of the raw data using the same physical and electrical properties employed to reduce the present experimental data.
Influence of thickness and conductivity of alignment layers on the bistability of ferroelectric liquid-crystal devices
Authors: Chieu T. C.
Published: July 2002

The bistability conditions on both the thickness and conductivity of the alignment layers as a function of spontaneous polarization and other cell parameters for ferroelectric liquid-crystal devices have been obtained analytically based on a uniform switching model. It is found that there exists a practical threshold conductivity of the alignment layers, above which good bistability can be obtained. Below this threshold conductivity, there exists a critical total alignment-layer thickness, below which bistability can be achieved. For the latter case, the two quantities depend linearly on each other, with a coefficient increasing monotonically with cell thickness, the difference between the ratio of the square of the spontaneous polarization to the rotational viscosity, and the conductivity of the liquid crystal.
The effects of processing sequences on the microwave surface resistance of TlCaBaCuO
Authors: Martens J. S. , Zipperian T. E. , Ginley D. S. , Hietala V. M. , Tigges C. P. , Plut T. A.
Published: July 2002

The effects of several microelectronic processing sequences on the high-frequency surface resistance of the high-temperature superconducting thin films in the TlCaBaCuO system have been examined. These processes include an acid etch, Br/alcohol etches, positive and negative photoresist sequences, and exposure to de-ionized water. The surface resistance decreases during the Br etch, remains constant during the negative photoresist process, and increases moderately during the positive photoresist sequence and on exposure to water. The surface resistance increases dramatically on exposure to the acid solution as might be expected from other work. The effects of extended exposures to de-ionized water and to Br etches on surface resistance are also presented.
Modeling of epitaxial silicon growth from the SiH2Cl2-H2-HCl system in an rf-heated pancake reactor
Authors: Oh In-Hwan , Takoudis Christos G.
Published: July 2002

A mathematical model of transport phenomena and epitaxial silicon growth in a pancake chemical vapor deposition reactor is presented for the SiH2Cl2-H2-HCl system. Two-dimensional conservation equations of mass, momentum, energy, and species mass developed in cylindrical coordinates along with appropriate boundary conditions are solved numerically with finite element methods. Streamlines show that the shearing force of the inlet gas flow yields recirculation zones inside the reactor and a separation point on the susceptor. Thermal and concentration boundary layers are seen to develop above the susceptor at pressures between 40 and 150 Torr, and susceptor temperatures between 850 and 1000 °C. When HCl is added to the SiH2Cl2-H2 system, as it is widely used in the selective epitaxial growth of silicon, the overall growth rate is reduced by silicon substrate etching. It is predicted that growth rates for bulk and selective epitaxy decrease monotonically with increasing HCl/SiH2Cl2 or (HCl)2/SiH2Cl2 feed flow ratios; also, this model predicts an optimal HCl/SiH2Cl2 feed flow ratio at which silicon growth rates on patternless and patterned wafers are equal to each other. The agreement between experimental and predicted growth rate profiles on patternless wafers at different temperatures and flow rates studied is seen to be satisfactory.
Scanning tunneling microscopy of hexagonal BN grown on graphite
Authors: Fukumoto H. , Hamada T. , Endo T. , Osaka Y.
Published: July 2002

The microscopic surface topography of thin BNx films grown on graphite by electron cyclotron resonance plasma chemical vapor deposition have been imaged with scanning tunneling microscopy in air. The scanning tunneling microscope has generated images of hexagonal BN with atomic resolution.
X-ray diffraction analysis of concentration and residual stress gradients in nitrogen-implanted niobium and molybdenum
Authors: Rao Satish I. , He Baoping , Houska C. R. , Grabowski K.
Published: July 2002

Large biaxial residual strains are developed after a 5-at.% implantation of N into Nb and Mo. The results indicate that the dominant source of internal strain arises from N located in interstitial sites. For Nb implanted at liquid-nitrogen temperature, the N atoms are located in octahedral sites. However, the data allow for some clustering as di- or tri-interstitials at the highest concentration (∼5 at. % N). Radiation damage is present as small vacancy and interstitial loops. Since vacancies and self-interstitials are present in nearly equal concentrations, the overall bulk dilatation cancels. However, because of their small size, a lesser core expansion has been included as a correction to the overall residual strain. Although one can obtain an estimate of the N distribution from trim, a more accurate description must include the distribution of knock-on energy. The latter has an important influence on the redistribution of N relative to that predicted by trim. Both host lattices (Nb and Mo) behave like ‘‘rigid containers’’ in directions parallel to the free surface and give a magnified elastic response normal to the free surface.
Screened potential of a charged dislocation in piezoelectric semiconductors
Authors: Shintani K.
Published: July 2002

A simplified model is proposed for analyzing the electric potential around a charged dislocation in piezoelectric semiconductors. In the analysis of the order of the Debye length, the solution for the piezoelectric potential screened by the carriers and ionized impurities is obtained. Consideration of the electrostatic potential field near the dislocation complete the determination of the solution. Numerical calculations of the potential are made for GaAs.
Simulation of transient boron diffusion during rapid thermal annealing in silicon
Authors: Heinrich Michael , Budil Matthias , Pötzl Hans W.
Published: July 2002

The transient diffusion behavior of boron during rapid thermal annealing is simulated by adapting a recently developed pair diffusion model. Boron is assumed to reside on interstitial sites after ion implantation, forming boron-interstitial pairs (BI). Decay into substitutional boron (B) and interstitials (I) starts, as the temperature rises, due to the reaction BI⇄B+I. Implantation damage has been taken into account. The model accounts for the temperature dependence of the transient diffusion effect. To reduce the problems in determining the parameters of the diffusion model and to account for equilibrium diffusion an equation is derived. This equation can be used to reduce the number of unknown parameters and to assure diffusion under equilibrium conditions to be consistent with literature values at the same time. The effectiveness is demonstrated for the simulation of the transient diffusion of boron during rapid thermal annealing.
Comment on ‘‘Nonlinear piezoelectricity and electrostriction of alpha quartz’’ [J. Appl. Phys. 6
0, 1465 (1986)]
Authors: Hruska Carl K.
Published: July 2002

The iterative least-squares method used to calculate the third-order piezoelectric and electrostrictive constants of quartz from the transit-time experiment represents no improvement over the standard least-squares fit and produces incorrect standard errors for these constants. Subsequent calculation shows that the proper standard errors are larger than believed hitherto.
Magnetic studies of Cu-based organometallic monomers and polymers
Authors: Zuo F. , Yu I. , Salamon M. B. , Hong X. , Stupp S. I.
Published: July 2002

We report here magnetic studies of Cu-based organometallic monomers and polymers. Magnetic susceptibility measurements at high temperature, on monomers having different side groups, show antiferromagnetic Curie–Weiss behavior consistent with a single spin-1/2 per Cu atom and an antiferromagnetic Curie–Weiss temperature θ≊1 K. The low-temperature magnetization remains linear to μBH/kBT ≥ 1, suggestive of 1D antiferromagnetic Heisenberg interactions. A sharp decrease in the effective spin per Cu atom is observed in the polymerized organometallic system, with the number of spins decreasing with the degree of polymerization.
A soft-x-ray-emission investigation of cobalt implanted silicon crystals
Authors: Jia J. J. , Callcott T. A. , O’Brien W. L. , Dong Q. Y. , Mueller D. R. , Rubensson J-E. , Ederer D. L. , Tan Z. , Namavar F. , Budnick J. I.
Published: July 2002

The Si L2,3 emission spectra of silicon crystals implanted with Co at doses of (1–8) × 1017 Co/cm2 have been examined using soft-x-ray-emission (SXE) spectroscopy. At the lowest dose, the spectra are little modified from that of crystalline Si, indicating that only a small fraction of Si is in the form of silicides within the probe depth of SXE spectroscopy. For higher doses and implant profiles with Co extending to the surface, there is clear evidence for ordered CoSi2 combined with richer Co phases, but little evidence for pure Si or for ordered regions of CoSi.
Influence of Cu on the native oxide growth of Si
Authors: Gräf D. , Grundner M. , Mühlhoff L. , Dellith M.
Published: July 2002

The influence of Cu on the native oxide growth on Si wafers was investigated by means of x-ray photoelectron spectroscopy and high-resolution electron energy loss spectroscopy (HREELS). The Cu coverage on the Si wafers was varied from 1012 cm−2 to about half a monolayer by adding Cu to aqueous HF in the ppm range. Immediately after the HF treatment no SiO2−x component (chemical shift ≳3.4 eV) can be measured by XPS. The chemical surface composition as characterized by HREELS is practically the same as for noncontaminated HF. A short additional water rinse of 2 min changes the chemical surface state of the Si wafers significantly. For Cu coverages more than about 1% of a monolayer, a pronounced initial oxide growth was noticed already after a 2-min water rinse with the oxide thickness depending on the amount of Cu coverage present on the Si surface. The oxide growth kinetics after storage of Cu-contaminated Si surfaces in air was studied for storage times up to 1 year. With almost no change in the chemical surface state visible directly after the HF treatment, however, an enhanced roughness of the Si wafer was noticed. The copper-induced enhancement of the oxidation of the silicon surface in combination with the oxide removal of the HF leads to an etching of the Si wafer.
Short-range order and microstructure in hydrogenated amorphous silicon
Authors: Danesh P. , Pantchev B. , Savatinova I. , Liarokapis E. , Raptis Y. S.
Published: July 2002

An experimental study has been made on the relationship between short-range order and microstructure in hydrogenated amorphous silicon films. The properties of the material have been varied by applying rf power of different magnitudes. The change in the short-range order has been characterized by Raman scattering measurements. Microstructure has been determined by means of field assisted ion exchange technique. The observed correlation between the two structural length scales suggests that the presence of dihydride groups in these materials is a key factor for the release of the silicon network strain.
A comparison of one, two, and three band calculations of contact resistance for a GaAs ohmic contact using the Wentzel-Kramers-Brillouin approximation and a numerical solution to the Schrodinger equation
Authors: Crofton J. , Barnes P. A.
Published: July 2002

We explore the different contact resistances obtained by using a one, two, and three band Wentzel-Kramers-Brillouin (WKB) calculation of the tunneling probability for majority carriers in an ohmic contact to n-type GaAs. The depletion approximation is used resulting in a parabolic potential. Finally, the calculations are repeated using a numerical solution to the wave equation in the depletion region of the semiconductor instead of employing WKB. It will be seen that the WKB approximation leads to contact resistances that are approximately twice as large as those numerically calculated from the wave equation.
Optical waveguides for surface spectroscopy: FePO4 thin-film/K+-doped glass composite optical waveguide systems having tapered velocity couplers
Authors: Itoh Kiminori , Madou Marc
Published: July 2002

Basic characteristics were examined for optical waveguides (OWGs) composed of a thin-film OWG deposited onto a diffused OWG in order to construct OWG systems suitable for biochemical sensors and for monitoring surface chemical reactions. Conditions were examined experimentally in detail for adiabatic and nonadiabatic transition of the guided light from the K+-doped glass OWG to the FePO4 thin film by changing the length of the tapered velocity couplers made at the ends of the films. A miniband structure of the FePO4 film, 1 mm wide and having 0.5-mm slopes at the ends, was constructed for optical sensing. It exhibited high sensitivity despite the fact that the FePO4 OWGs were found to have a large attenuation coefficient, 60–80 dB/cm.
Minimum sparkover voltage characteristics in air, sulphur-hexafluoride, and some solid dielectrics: A macroscopic approach
Authors: Kekez M. M. , Savic P.
Published: July 2002

Using a small number of plausible assumptions regarding the nature of the leader channel and the corona cloud in an electric discharge in a continuous medium, it is shown how a nonlinear first-order differential equation of the d’Alembert type can be derived which describes the history of the leader and corona cloud development in nondimensional terms. It is found that this solution can be used to derive a breakdown criterion which depends only on two material parameters, i.e., the minimum energy per unit length of the elongating leader channel and the average electric field in the corona cloud. These can be combined to form a single nondimensional parameter (Kekez number). The theory also shows how, for large gaps, the discharge must necessarily lead to the stepped-leader phenomenon. Comparison with experiments of other authors shows good agreement even for dielectrics of other than gaseous states of aggregation, where the concept of corona cloud requires some reinterpretation.
Static levitation in a high-T
c superconductor tile on magnet arrangements
Authors: Komori Mochimitsu , Kitamura Tadashi
Published: July 2002

Static characteristics of a levitational mechanism are studied. The levitational mechanism consists of a high-Tc superconductor tile (type-II superconductor) and a magnet arrangement of the same size bar magnets with alternating magnetic pole pattern. The levitation pressures have hysteresis loops because of the flux pinning effect. By using the alternating pole pattern of magnets larger static levitation pressure in proportion to the arrangement can be obtained over a wide area. Moreover the levitation pressure can be optimized with respect to the width of a bar magnet of the alternating pole pattern.
Inversion of conduction type in thin InSb films prepared on glass substrates
Authors: Isai Masaaki , Beerens J. , Cheeke J. D. N.
Published: July 2002

Thin InSb films with average thicknesses of 0.15 and 0.4 μm were prepared on glass substrates by evaporation of In and Sb to obtain homogeneous and In droplets-free films. The substrate-temperature dependence of some properties of the film was investigated between 350 and 470 °C. Highly (111)-oriented 0.15an 450 °C, respectively. It was observed that 0.4-μm-thick films show p-type conduction in the extrinsic temperature range. The cause of these phenomena was investigated using a secondary ion mass spectroscopy in-depth analysis. As a representative in the constituents of glass substrates, the diffusion of Na, K, Mg, Ca, Ba, B, Al, Si, Pb, and O atoms into the InSb films was investigated more precisely. Among these atoms, it was estimated that K, Mg, and Si atoms could act as acceptors in an InSb crystal contributing to the inversion of conduction type.
Effects of electron deep traps on generation lifetime in denuded zone of n-type Si wafer
Authors: Kim Hyeon Soo , Kim Eun Kyu , Min Suk-Ki
Published: July 2002

The effects of electron deep traps on generation lifetime in heat-treated n-type Czochralski-grown (111) Si were examined by generation lifetime and deep level transient spectroscopy measurements. An order of magnitude increase in generation lifetime was observed for the samples having denuded zone, which experienced the high/low heat treatment (20 h at 1100 °C+16 h at 750 °C). Deep electron traps at Ec − 0.47, 0.42, 0.39, and 0.30 eV occur in the oxygen precipitated region by heat treatment. Especially, the concentration of the Ec − 0.47 eV trap decreased below 5×1012 cm−3 in denuded zone. From these results, we conclude that enhancement of generation lifetime in denuded zone may be dominantly related to the decrease of concentration of the Ec − 0.47 eV trap.
Glasslike ultrasonic properties of Dominican amber above helium temperatures
Authors: Nava R. , Pereira D. , Amorer L.
Published: July 2002

Measurements of the ultrasonic attenuation and relative velocity changes of longitudinal waves of frequencies between 5 and 25 MHz are reported for clear yellow Dominican amber at low temperatures. Between 4 and 130 K the attenuation and velocity change are glasslike in their temperature and frequency dependencies. At higher temperatures both properties seemed to be affected by the α or β viscoelastic relaxations. Similar ultrasonic behavior is reported for commercial polymethylmethacrylate. Our results at low temperatures compare well quantitatively with data of other organic and inorganic glasses, except for the stronger logarithmic frequency-dependent velocity change which is observed for both materials.
Beam quality of direct nuclear pumped laser amplifiers
Authors: Neuman W. A. , Fincke J. R.
Published: July 2002

The achievable beam quality resulting from heavy charged particle pumping of transverse flow, gas laser amplifiers is presented. The charged particles are generated by nuclear reactions in either B4C or UO2 coated on plates parallel to the lasant flow. The character of the laser medium aberration resulting from the nonuniform energy deposition and fluid dynamic effects is discussed as well as the effects on the far-field beam quality of the amplifier. Pumping from plates parallel to the flow produces a medium aberration which is dominated by a cylindrical focus perpendicular to the flow, and a tilt in the flow direction. Beam qualities of better than 2 times diffraction limited (TDL) are obtained with a B4C fueled 1-m-long amplifier pumped at an average power deposition of 100 W/cm3 with an inlet 0.1-MPa helium flow at 100 m/s. Amplifiers using UO2 fuel coatings to pump argon under the same flow conditions with fission fragments have similar qualitative laser medium aberrations but with larger magnitude, resulting in beam qualities of ≳20 TDL for a 100 W/cm3 average power deposition.
Carrier lifetimes and threshold currents in HgCdTe double heterostructure and multi-quantum-well lasers
Authors: Jiang Y. , Teich M. C. , Wang W. I.
Published: July 2002

The Auger and radiative combination carrier lifetimes in HgCdTe bulk and quantum-well structures, with band gaps in the wavelength range 2–5 μm, are calculated. The Auger recombination rate in a HgCdTe quantum well (QW) is shown to be significantly smaller than that in bulk material. Threshold current densities of HgCdTe double-heterostructure (DH) and multiquantum-well (MQW) lasers are calculated. In a HgCdTe DH laser, Auger recombination dominates the carrier loss at threshold. In a HgCdTe MQW laser, on the other hand, radiative recombination dominates the carrier loss. MQW lasers shown improved temperature performance over conventional DH lasers.
Reflection of light ion from solid surfaces studied by Monte Carlo simulation and transport theory
Authors: Xia Yueyuan , Xu Xiangang , Tan Chunyu , Mei Liangmo , Yang Hong , Sun Xiufang
Published: July 2002

The reflection from amorphous Cu and Ni surfaces of light ions, such as H+, 3He+, and 4He+ in the energy region of 0.1–10 keV, has been studied by computer simulation and transport theory. The results show that the energy distribution of the reflected particles can be approximately described by a universal empirical formula for the whole energy region, all the angles of incidence, and the different ion-target combinations studied here, and the angular distributions of the reflected particles can be described by a cosine expansion with a few terms. In the transport theory calculation of the particle and energy reflection coefficients, the energy distribution spectra of the reflected particles are used to give a realistic surface correction. The present work is compared with both experimental data and other simulation codes.
Characterization of defects at grain boundaries of GaP and InP by infrared cathodoluminescence
Authors: Domíguez-Adame F. , Piqueras J.
Published: July 2002

Grain boundaries in GaP and InP have been studied by infrared cathodoluminescence (CL). In GaP the results indicate that there exists a depletion region beside grain boundaries where the concentration of PGa antisite defects is lower than in the bulk material. In InP the near-edge CL emission and a deep level luminescence at 1.07 eV have been found to cause similar grain boundary CL contrast.
GaAs multiple-quantum-well reflector modulators with 4:1 contrast ratios on Si
Authors: Salvador A. , Adomi K. , Kishino K. , Ünlü M. S. , Morkoç H.
Published: July 2002

Considerable modulation ratios are achieved for GaAs multiple-quantum-well reflector modulators grown on Si by inserting an AlAs/AlGaAs dielectric mirror into the device structure. Modulation ratios of up to 4:1 is attained as the external bias voltage is increased to 9 V and the 1C-1HH exciton absorption peak undergoes quantum-confirmed Stark shift. Measurements also indicate that cavity effects arising from the front surface reflection and that of the imbedded dielectric mirror strongly modify the reflectivity spectra.
Temperature control of silicon-germanium alloy epitaxial growth on silicon substrates by infrared transmission
Authors: Sturm J. C. , Garone P. M. , Schwartz P. V.
Published: July 2002

We report the application of the technique of infrared transmission to measure the temperature of silicon wafers during the growth of silicon-germanium alloy heteroepitaxial layers in a rapid thermal processing system. The silicon-germanium alloy layers have negligible absorption at 1.3 and 1.55 μm over wide ranges of thickness, composition, and strain condition. The substantial improvement of the uniformity of layers grown using the technique to measure the temperature for feedback control of the lamp power has also been demonstrated.
Collective ion acceleration by relativistic electron beams in plasmas
Authors: Galvez Miguel , Gisler Galen
Published: July 2002

A two-dimensional fully electromagnetic particle-in-cell code is used to simulate the interaction of a relativistic electron beam injected into a finite-size background neutral plasma. The simulations show that the background electrons are pushed away from the beam path, forming a neutralizing ion channel. Soon after the beam head leaves the plasma, a virtual cathode forms which travels away with the beam. However, at later times a second, quasi-stationary, virtual cathode forms. Its position and strength depends critically on the parameters of the system which critically determines the efficiency of the ion acceleration process. The background ions trapped in the electrostatic well of the virtual cathode are accelerated and at later times, the ions as well as the virtual cathode drift away from the plasma region. The surfing of the ions in the electrostatic well produces an ion population with energies several times the initial electron beam energy. It is found that optimum ion acceleration occurs when the beam-to-plasma density ratio is near unity. When the plasma is dense, the beam is a weak perturbation and accelerates few ions, while when the plasma is tenuous, the beam is not effectively neutralized, and a virtual cathode occurs right at the injection plane. The simulations also show that, at the virtual cathode position, the electron beam is pinched producing a self-focusing phenomena.
Electron-paramagnetic-resonance study of s-d exchange in PbSnMnTe
Authors: Story T. , Swüste C. H. W. , Swagten H. J. M. , van Kempen R. J. T. , de Jonge W. J. M.
Published: July 2002

Electron-paramagnetic-resonance (EPR) measurements were performed in the temperature range T=1.3–100 K in samples of the semimagnetic Pb1−x−ySnyMnxTe semiconductor with carrier concentrations p=1.6×1019−1.4×1021 cm−3. Magnetization and Hall effect were also measured. Compositions in the range 0.12<y<0.72 and x=0.02, 0.04, and 0.06 were studied. We found a strong influence of the carrier concentration on the temperature dependence of the width of EPR line (ΔH). A very rapid increase of ΔH with increasing temperature is observed in the samples with high carrier concentrations: p=5.5, 6.8, and 14×1020 cm−3. The magnitude of this effect is strongly reduced in the sample with the carrier concentration p=2.85×1020 cm−3. In n- and p-type samples with the lowest carrier concentrations (p≂2×1019 cm−3), no temperature dependence of ΔH is observed at high temperature. The strong effect of the carrier concentration on ΔH can be understood, in agreement with magnetic measurements, as a result of the two-carrier (light for p<pc=3×1020 cm−3 and very heavy, available only for p ≳ pc) Korringa relaxation mechanism.
Spin separation in diluted magnetic semiconductor quantum well systems (invited)
Authors: Jonker B. T. , Liu X. , Chou W. C. , Petrou A. , Warnock J. , Krebs J. J. , Prinz G. A.
Published: July 2002

Heterostructures containing diluted magnetic semiconductor (DMS) layers offer the possibility of magnetically tuning the heterojunction band alignment due to the extraordinarily large spin-splitting of the DMS bands (large effective g-factor). This field-dependent band alignment has significant consequences for spin-dependent carrier confinement as evidenced in magnetooptic or magneto-transport experiments. We have examined two wide-gap DMS quantum well systems in which the band alignment is dominated by the DMS spin-splitting rather than by the more commonly observed effects of differences in bandgap, natural band offset, and strain. Quantum well structures with (Zn,Fe)Se or (Zn,Mn)Se barriers and ZnSe wells have been grown to investigate magnetically tuned, spin-dependent quantum confinement. In these systems, the band offset appears almost entirely in the conduction band, so that the electrons are confined to the ZnSe wells. However, the hole confinement is continuously tunable by an external magnetic field applied normal to the layer plane, since the valence band spin-splitting is approximately an order of magnitude larger at modest fields (1 T) than the zero field VB offset. This produces a field-induced spin dependent type I/type II band alignment and a consequent spatial spin separation of the holes. The quantum well structure exhibits a type I ‘‘straddling’’ alignment for the mj=+3/2 level, with the spin ‘‘up’’ holes localized in the ZnSe wells, and a type II ‘‘staggered’’ alignment for the mj=−3/2 level in which the spin ‘‘down’’ holes are localized in the barriers. The observed exciton splittings, intensities and temperature dependence are consistent with this model. In the Zn0.91Mn0.09Se/ZnSe system, a second bound state is observed in the conduction band in the σ− polarization in magnetoreflectivity measurements. A quantitative fit to the data yields a value of approximately 1 meV for the zero field valence band offset. These systems represent the first DMS-based heterostructures in which such field-dependent confinement has been observed.
Fundamental aspects of practical applications of magnetotactic bacteria (abstract)
Authors: Pfützner H. , Futschik K. , Harasko G. , Aminpirooz S. , Schönhuber P.
Published: July 2002

Recently, we reported the possibility to apply magnetotactic bacteria for domain studies.1 The high field sensitivity (≊30 A/m) yields effective orientations in the stray field of domains and thus their visualization. Here, we discuss fundamental aspects of broader applications including the collection of bacteria. For it, by means of numerical analysis, a magnetic trap was developed in order to guide bacteria in concentration vessels. With respect to the low active velocity (100 μm/s), also possibilities of passive guidance by means of gradient fields were studied, which, however, yielded minimum intensities of more than 1 kA/m. Roughly, this is consistent with results of susceptibility measurements showing magnetic moments of only 10−14 Am2 for bacteria of 1 μm diameter. Still, passive guidance could enable rapid concentration and translocation procedures, e.g., using the bacterium as a drug carrier. Future applications could include the use of genetically manipulated bacteria in biotechnology. As a pilot study for cell fusion, the paper presents results of chain formation obtained by electric HF-field application. Contrary to usual cell types, chains were observed even after field switch-off, due to interactions of magnetic moments of neighboring bacteria.
A dc magnetic field distribution transducer (abstract)
Authors: Hristoforou E.
Published: July 2002

A new way of measuring magnetic field distribution is proposed, based on the change of the response of a magnetostrictive delay line (MDL) to varying dc magnetic field. The principal idea runs as follows: an array of wires Ci, transmitting pulsed current Ie, crosses at 45° an array of MDL Lj. The resulting pulsed field at the crossing points Pij excites an acoustic pulses in the lines, detected by short coils placed close to one end, in terms of voltage Voij. If a dc magnetic field Hdc is applied at the point Pij, the acoustic pulse and hence Voij change. Experimental results are given, showing the dependence of V0 on the applied dc field under various values of Ie for the case of a 1 mm wide Metglas 2605SC MDL. The function of Vom vs Hdc under various values of Ie is also given, where Vom is the maximum value of the absolute positive and negative peaks of V0. The first derivative of this function equals zero for two values of Hdc, corresponding to approximately equal positive and negative peaks of V0. So, having divided this function in 4 parts, comparison of these two peaks and experimental data are used to find the orientation and magnitude of the dc field on the MDL axis. It was also found that V0, corresponding to an Hdc applied at an angle v to the MDL equals the response of a dc field having a magnitude Hdc cos(v) and applied along the length of the line. So, by having another array of delay lines L′i identical but orthogonal to the previous MDL array Lj and crossing in 45° the conducting wires array Ci, we can keep the same number of crossing points. Hence, measurements from two delay lines Li and L′i corresponding to Pij, give a 2-d vector of the dc magnetic field applied at this point. The uniformity and the resolution of such a transducer can be improved by using the recently developed FeSiB wires after stress annealing. Future work is to be done to increase the frequency and the range of the measurable dc field.
Spin-spin correlations in the one-dimensional spin-1/2, antiferromagnetic Heisenberg chain
Authors: Lin H. Q. , Campbell D. K.
Published: July 2002

We have calculated the spin-spin correlations in the ground state of spin-1/2, one-dimensional, antiferromagnetic Heisenberg chain numerically. Using improved algorithms, we have been able to perform exact diagonalizations for lattices up to 30 sites and quantum Monte Carlo simulations for lattices up to 512 sites. This extensive range allows us to investigate the logarithmic dependence of spin-spin correlations. We present our results and discuss their implications.
Proton spin-lattice relaxation in low-dimensional ferromagnetic copper halides (abstract)
Authors: Marzke R. F. , Haines D. N. , Raffaelle D. P. , Chamberlin R. V. , Ramakrishna B. L.
Published: July 2002

1H spin-lattice relaxation times have been measured as functions of temperature and frequency in powder samples of the two-dimensional ferromagnetic compound (CH3NH3)2CuCl4 and in single crystals of the one-dimensional ferromagnets (C6H11NH3)CuB3 (CHAB), (C6H11NH3)CuCl3 (CHAC), and (C4H12N)CuCl3 (TMCuC). Sample temperatures were varied between 4.2 and 298 K, and NMR frequencies ranging from 12.6 to 54.0 MHz were used. Widths and shapes of the lines, typically several hundred Gauss broad at low temperatures, were recorded. The dependence of T1 upon magnetic field orientation was measured for the one-dimensional (1D) single crystal samples. Each compound showed basically two temperature regimes of different spin-lattice relaxation behavior, separated by a narrow transition temperature region. From 4.2 K, T1 in the compounds decreased strongly as the temperature was raised, a behavior expected for second-order Raman processes [K. M. Kopinga, A. M. C. Tinus, W. J. M. de Jonge, and G. C. de Vries, Phys. Rev. B 36, 5398 (1987)]. At the transition temperature region the decrease of T1 ceased, and T1 began to increase weakly and quasilinearly to 300 K. In the three 1D compounds, the transition regions occurred well below temperatures corresponding to 1D exchange interaction strengths in CHAC (∼70 K), CHAB (∼55 K), and TMCuC (∼30 K), and also above the compounds’ 3D ordering temperatures (∼1.5 K and below). We noted a correlation between the T1 transition temperatures and temperatures at which spin dimensionality ‘‘crossovers’’ are observed in magnetic susceptibilities, going from Heisenberg to non-Heisenberg behavior as the temperature is decreased. The latter occur at approximately 10 K in CHAC. TMCuC, which has the most isotropic J tensor of these compounds and also the lowest weak-strong T1 transition, does not show a spin dimensionality crossover in susceptibility down to 2 K, but based on our NMR results one would be expected at or below this temperature. Further theoretical work appears to be necessary in order to elucidate the role of magnons and solitons in the transition behavior of the temperature dependence of T1.