bluuebunny/crossref_metadata_2025 huggingface dataset:
High-power buried heterostructure InGaAsP/InP laser diodes produced by an improved regrowth process
Authors: Garbuzov D. Z. , Berishev I. E. , Ilyin Yu. V. , Ilyinskaya N. D. , Ovchinnikov A. V. , Pikhtin N. A. , Tarasov I. S.
Published: July 2002

The paper describes preparation and performance of single lateral mode buried heterostructure InGaAsP/InP, λ=1.3 μm, laser diodes. It is shown that an improvement in the mesa etching and regrowth techniques permits obtaining laser diodes whose threshold current densities are about 1 kA/cm2 and are practically independent of stripe width. The diodes thus prepared had threshold currents of 8–20 mA at a cavity length L=200–500 μm and a stripe width about 2–3 μm. The maximum continuous wave power in single lateral mode operation was 160 mW.
Monte Carlo analysis of real-space transfer in a three-terminal device
Authors: Patil M. B. , Ravaioli U.
Published: July 2002

Real-space transfer (RST) in three-terminal devices is analyzed in detail with a Monte Carlo model including size-quantization effects. A double heterojunction structure is considered with In0.25Ga0.75As as the narrow band gap material. Schrödinger’s and Poisson’s equations are solved self-consistently in one dimension to compute the subband energies and wave functions which are then used to calculate scattering rates for the two-dimensional electron gas. Electrons are injected at one end of the channel segment and the probability of RST, time required for RST etc. are calculated. Variation of these quantities with respect to longitudinal and transverse electric fields and electron density is studied. We point out that this approach is more relevant to a three-terminal device like the real-space transfer transistor than previous approaches which focus on steady-state velocity-field characteristics. We also compare the results with a semiclassical model that ignores size-quantization and observe that quantization favors RST due to the subband structure of the quantum well.
Comment on ‘‘Depth profiling of nonuniform optical absorption in thin films: Application to hydrogenated amorphous silicon’’ [J. Appl. Phys. 70, 5025 (1991)]
Authors: Grillo G. , De Angelis L.
Published: July 2002

Recently, Asano and Stutzmann [J. Appl. Phys. 70, 5025 (1991) and J. Non-Cryst. Solids 137&138, 623 (1991)] examined the effects of in-depth nonuniformity on optical absorption spectra of thin films, and reported that the amplitude of interference fringes is related to the depth profile of absorbing centers. They used this effect to analyze photothermal deflection spectra (PDS) of amorphous silicon (a-Si:H) films to get information on surface and interface defects. In a previous paper [Grillo and De Angelis, J. Non-Cryst. Solids 114, 750 (1989)], we introduced this technique to study surface/interface defects in a-Si:H, and gave the analytical formula for calculating explicitly the effect; here we show that application of this equation gives readily the shape of fringes for the cases of interest.
Electrical transport between delta layers in silicon
Authors: Kiunke W. , Hammerl E. , Eisele I. , Schulze D. , Gobsch G.
Published: July 2002

The electrical transport between locally grown delta-doped layers spaced 63–146 nm has been investigated. Electrical measurements on devices show symmetrical diode characteristics and for low-threshold voltage values, good agreement with simulations based on the Thomas–Fermi approximation is shown and thermionic emission theory exists.
The effect of bonded interface on electrical properties of bonded silicon-on-insulator wafers
Authors: Ling L. , Radzimski Z. J. , Abe T. , Shimura F.
Published: July 2002

The effect of bonded interface location on the electrical properties of silicon-on-insulator (SOI) wafers is investigated. It is demonstrated that a bonded Si/SiO2 interface can lead to an increase in boron concentration in a 1-μm-thick silicon layer measured from the interface. It is also proved that the increase in boron concentration is due to about monolayer surface boron contamination formed prior to bonding. The capacitance versus voltage (C-V) and capacitance versus time (C-t) characteristics of metal-oxide-silicon capacitors fabricated on SOI wafers can be affected by the interface of top Si/buried SiO2 under certain conditions. The bonded interface inside the buried SiO2 layer does not have evident influence on the electrical properties of SOI wafers.
Temperature distributions induced by multibeam laser irradiation
Authors: Lu Yong-Feng
Published: July 2002

A general model is derived for computing the temperature profile induced by multibeam laser irradiation in a semi-infinite substrate. The model is then applied to calculate a two-beam irradiation-induced temperature rise in different substrate materials such as Si, GaAs, and Mn-Zn ferrites for investigating the dependence of depth, beam radius, and substrate thermal properties.
Simultaneous time-averaged measurements of gas temperature and electron density in a copper-vapor laser using hydrogen emission spectroscopy
Authors: Blau P. , Smilanski I. , Rosenwaks S.
Published: July 2002

Measurements of the gas temperature and electron density in the plasma of a 100 W copper-vapor laser are presented. These parameters are simultaneously deduced from the Doppler and Stark broadening of the first four Balmer lines of the hydrogen atom emission. The analysis of the Doppler and Stark broadening involves evaluation of all other line-broadening mechanisms, including natural, pressure (van der Waals and resonance), instrumental, self-absorption, and fine-structure splitting. Iterative algorithm is employed to deconvolve the different line-shape components. The longitudinally integrated, time-averaged temperature and electron density are measured along the laser axis and found to be 4300 K and 1.3 × 1013 cm−3, respectively.
Residual donor and acceptor incorporation in InP grown using trimethylindium and tertiarybutylphosphine
Authors: Watkins S. P. , Nissen M. K. , Haacke G. , Handler E. M.
Published: July 2002

Residual donor and acceptor species were studied in a series of high purity n-type InP epilayers grown by metalorganic chemical vapor deposition using tertiarybutylphosphine and trimethylindium (TMIn). Over the entire range of growth conditions, the residual donors were found to be S and Si using magnetophotoluminescence spectroscopy. These designations agreed with the observed dependence of the transport data on growth conditions. Residual levels of Zn and Mg or Be acceptors were identified by photoluminescence (PL) measurements at low excitation powers. C acceptors were below the limits of detection by PL, as in other studies using phosphine and TMIn.
Dispersion of the linear electro-optic coefficients in GaAs
Authors: Adachi Sadao
Published: July 2002

A phenomenological expression is derived for the calculation of the spectral dependence of the linear electro-optic coefficients in zinc-blende-type semiconductors. Analyses are presented for GaAs, and results are in good agreement with published experimental data when a lifetime broadening effect is taken into consideration in the model. It is also found that the E0 gap (lowest-direct gap) strongly contributes to the dispersion of the linear electro-optic coefficients, but not to its absolute value.
Phosphorus diffusion gettering of gold in silicon: The reversibility of the gettering process
Authors: Sveinbjörnsson Einar Ö. , Engström Olof , Södervall Ulf
Published: July 2002

Phosphorus diffusion gettering of gold in silicon is a reversible process with strong temperature and phosphorus concentration dependence. We show explicitly that gold diffuses back and forth between the highly doped phosphorus layer and the bulk of the material when the annealing temperature is varied. This was investigated using secondary-ion mass spectroscopy to study the gold within the gettering layer and using deep level transient spectroscopy to estimate the gold content in the bulk. We observed no internal gettering or outdiffusion of gold as long as the gold concentration is below the solubility limit. The concentration profile of gold after successful gettering follows the phosphorus profile but virtually all the gold atoms are found in the region where the phosphorus concentration exceeds ∼3×1019 cm−3. This is related to a large solubility enhancement of gold when the phosphorus concentration is above 3×1019 cm−3. The simplest explanation for the observed gettering mechanism is formation of gold-phosphorus pairs within the highly doped phosphorus layer. However, quantitative agreement cannot be obtained between our results and a simple segregation model based on gold solubilities in lightly doped material and highly phosphorus doped silicon. If the gold solubility in the bulk is modified by taking into account, proposed supersaturation of silicon self-interstitials agreement between the model and the experimental data can be obtained.
Second-harmonic responses of modulated photoreflectance in semiconductors
Authors: Lu Yue-sheng , Zhang Shu-yi , Qian Zhong-ling
Published: July 2002

The experimental measurements of nonlinear modulated photoreflectance (MPR) phenomena in Si and GaAs wafers, in which the obvious second-harmonic (2 f) MPR signals are detected in addition to the fundamental frequency (f) MPR signals when the pumping laser power is sufficiently strong, are reported. Meanwhile, a linear-to-quadratic transition in the curve of the f MPR signal versus the pumping laser power is observed in Si samples but not in GaAs samples. It is also found that the 2 f MPR signals are more sensitive to the ion-implantation doses than the f MPR signals which are traditionally applied to monitor the ion implantation in semiconductors. It is found that the contribution of the photoinduced modulation of the surface electric field is the main source of the nonlinear MPR signals and the contribution is theoretically discussed in detail. A one-dimensional theoretical model is established, and the theoretical results are in good agreement with the experimental data. The dependencies of the f and the 2 f MPR signals on the third-order optical nonlinear susceptibility χ(3) and the surface-state density Ns are also discussed, and a method for measuring χ(3) and N4 of semiconductors is introduced.
Exciton recombination in Te-rich ZnSexTe1−x epilayers
Authors: Naumov A. , Stanzl H. , Wolf K. , Lankes S. , Gebhardt W.
Published: July 2002

ZnSexTe1−x epilayers were investigated by means of luminescence, reflectivity, and temperature dependence in the concentration range 0<x<0.4. The studied ZnSexTe1−x epilayers with thicknesses of about 1.5 μm were grown on GaAs substrates by metalorganic vapor phase epitaxy. It was found that the luminescence and reflectivity spectra of the mixed crystals are strongly affected by the compositional disorder. A continuous transition from the recombination through free and bound exciton states to the recombination of excitons localized by the compositional fluctuations of the mixed crystal was observed in the concentration region of about x=0.25. The position of the excitonic band edge was derived from the photoluminescence excitation spectra and from temperature dependence of the emission spectra.
Ferromagnetic resonance determination of fcc→hcp structural change in epitaxial Co/Mn superlattices
Authors: Ounadjela K. , Henry Y. , Farle M. , Vennegues P.
Published: July 2002

A series of epitaxial [Co24 ÅMntMn]12 superlattices (3.2 Å≤tMn≤32 Å) was grown on hcp(0001) Ru buffer layers by ultrahigh vacuum e-beam evaporation. Ferromagnetic resonance has shown that for samples with 3.2 Å≤tMn≤12 Å, the cobalt layers are predominantly fcc and almost perfectly fcc for the sample having the thinnest Mn thickness [Co24 Å/Mn3.2 Å]12. For samples with greater Mn thickness (tMn≳12 Å), the cobalt layers are predominantly hcp with structural defects corresponding either to large inclusions of fcc Co or stacking faults.
Higher-order sampling strategies in Monte Carlo simulations of electron energy distribution functions in plasmas
Authors: Ventzek Peter L. G. , Kitamori Kazutaka
Published: July 2002

A new method of gathering statistics for Monte Carlo methods, Legendre polynomial weighted sampling (LPWS), is presented. LPWS requires only a minimum of particles to extract higher-order derivative information about a particle’s distribution function. In this technique, when calculating a particle’s distribution function, higher-order derivative information about the Monte Carlo particles is recorded along with just counting the number of particles in a bin. The distribution function is then constructed from this information. Specifically, in this paper, second-order Legendre polynomial weighted sampling is employed. Legendre polynomial weighted sampling is demonstrated by calculating the electron energy distribution functions in an inductively coupled plasma reactor.
Blue second-harmonic generation in waveguides fabricated in undoped and scandium-doped KTiOPO4
Authors: Jongerius M. J. , Bolt R. J. , Sweep N. A.
Published: July 2002

The efficiency of second-harmonic generation at 425 nm has been measured in periodically segmented waveguides in undoped and 120 ppm Sc3+-doped c-axis-oriented KTiOPO4 (KTP) plates. Conversion efficiencies up to 200% and 325%/W cm2 are obtained for the two types of crystals. These efficiencies are found to have decreased by up to a factor of 2 after the generation of 2–4 mW of cw blue output power for more than 5 min, while the transmission of the pump beam is decreased by about 20%. These effects are semipermanent in undoped KTP, and are therefore ascribed to optical damage. A full recovery within a few minutes is, however, found in the Sc3+-doped KTP waveguides. The ionic conductivity along the polar axis of 120 ppm Sc3+-doped KTP has been measured to be about equal to that of undoped KTP, so that the difference in the optical damage characteristics of the waveguides is not caused by a difference in the conductivity of the substrate KTP. The conductivity of 230 ppm doped crystals is found to be about a factor of 30 lower than that of undoped KTP, and has a different dependence on current frequency. In these crystals domain inversion in the exchanged waveguide segments was not obtained.
Annealing behavior of Pd/a-Ge bilayer films
Authors: Wu Xeuhua , Feng Yuezhong , Li Boquan , Wu Ziqin , Zhang Shuyuan
Published: July 2002

Solid-state reaction and crystallization in Pd/a-Ge bilayer films of various ratios of thickness (or composition) after annealing have been investigated by transmission electron microscopy. Besides polycrystalline Pd and amorphous Ge, the Pd2Ge phase is formed in as-evaporated films with 54 and 67 at % of Ge. During annealing at 250 °C Pd2Ge and PdGe are formed. During annealing at 350 °C, besides the formation of Pd2Ge and PdGe, crystallization of amorphous Ge takes place, inducing fractal-like structures with a size of about 1 μm. The fractal dimension varies from 1.60 to 1.88, depending on the composition of the films. The fractal formation can be explained by a random successive nucleation model.
A deep-level spectroscopic technique for determining capture cross-section activation energy of Si-related DX centers in AlxGa1−xAs
Authors: Ghosh Subhasis , Kumar Vikram
Published: July 2002

A deep-level transient spectroscopy (DLTS) technique is reported for determining the capture cross-section activation energy directly. Conventionally, the capture activation energy is obtained from the temperature dependence of the capture cross section. Capture cross-section measurement is often very doubtful due to many intrinsic errors and is more critical for nonexponential capture kinetics. The essence of this technique is to use an emission pulse to allow the defects to emit electrons and the transient signal from capture process due to a large capture barrier was analyzed, in contrast with the emission signal in conventional DLTS. This technique has been applied for determining the capture barrier for silicon-related DX centers in AlxGa1−xAs for different AlAs mole fractions.
Thermal stability of GaN thin films grown on (0001) Al2O3, (011̄2) Al2O3 and (0001)Si 6H-SiC substrates
Authors: Sun C. J. , Kung P. , Saxler A. , Ohsato H. , Bigan E. , Razeghi M. , Gaskill D. K.
Published: July 2002

Single crystals of GaN were grown on (0001), (011̄2) Al2O3 and (0001)Si 6H-SiC substrates using an atmospheric pressure metalorganic chemical-vapor-deposition reactor. The relationship has been studied between the thermal stability of the GaN films and the substrate’s surface polarity. It appeared that the N-terminated (0001) GaN surface grown on (0001)Si 6H-SiC has the most stable surface, followed by the nonpolar (112̄0) GaN surface grown on (011̄2) Al2O3, while the Ga-terminated (0001) GaN surface grown on (0001) Al2O3 has the least stable surface. This is explained with the difference in the atomic configuration of each of these surfaces which induces a difference in their thermal decomposition.
Polarization and resonant absorption in intersecting cylinders and spheres
Authors: Radchik A. V. , Paley A. V. , Smith G. B. , Vagov A. V.
Published: July 2002

The polarization of a pair of merging spheres and merging cylinders of any complex dielectric constant immersed in an external electric field has been solved. Any degree of intersection, including touching, is covered by the result. The method for cylinders is based on the solution of Laplace’s equation with boundary conditions on the conjugate surfaces in a modified bicylindrical frame. The result is presented as an integral over a continuum of eigenstates. For merging spherical particles solving the boundary problem requires a Miller–Fok integral transformation. Imaginary parts of polarizabilities were calculated for aluminum cylinders and spheres to assess the spectral absorption response of small merging particles. The relative spacing has a significant influence on optical response.
Resistivity-peak anomaly in Y1Ba2Cu3O7−δ crystals and nonuniformly distributed critical-temperature inhomogeneities
Authors: Mosqueira J. , Pomar A. , Veira J. A. , Maza J. , Vidal Félix
Published: July 2002

We report the observation of a sharp peak (20% of the normal resistivity), just above the superconducting transition, in the curve of the ab-plane electrical resistivity versus temperature of some nonfully oxygenated Y1Ba2Cu3O7−δ crystals, with transition temperatures below 90 K. This resistivity anomaly may easily be explained by assuming the presence of critical temperature inhomogeneities associated with small stoichiometric (oxygen content) inhomogeneities, at long length scales, nonuniformly distributed in the crystals. Our findings directly apply to the resistivity, the thermopower, and the Hall effect behavior in other superconducting materials having nonuniformly distributed Tc inhomogeneities.
Low-temperature annealing of ion-implanted KNbO3 waveguides for second-harmonic generation
Authors: Pliska Tomas , Jundt Dieter H. , Fluck Daniel , Günter Peter , Rytz Daniel , Fleuster Martin , Buchal Christoph
Published: July 2002

Results on annealing experiments of He+ ion-implanted KNbO3 planar and channel waveguides are reported. Annealing at 150 °C for several hours leads to a reduction of the waveguide attenuation constant by more than 5 dB cm−1 at a wavelength of 457 nm without significant change of the profile of the mode confining barrier. A minimum waveguide attenuation constant of 1.3 dB cm−1 in planar and 2.2 dB cm−1 in channel waveguides at 515 nm was achieved. Second-harmonic generation measurements in the waveguides showed that the conversion efficiency can be improved by more than a factor of 2 by the annealing process.
Interfacial reactions in Ti/Si3N4 and TiN/Si diffusion couples
Authors: Paulasto M. , Kivilahti J. K. , van Loo F. J. J.
Published: July 2002

Stability and formation kinetics of TiN and silicides in Ti/Si3N4 and TiN/Si diffusion joints have been investigated. Reactions in the diffusion couples were studied experimentally in the temperature range between 950 and 1100 °C. Isothermal sections and activity diagrams of the Ti-Si-N system were calculated using the recent thermodynamic data. Both the thermodynamic calculations and experimental results indicate that TiN and Si react with each other and form TiSi2 and even Si3N4 if the activity of nitrogen is high enough. Similarly, results from the Ti/Si3N4 couple were in good accordance with calculated phase equilibria. The experiments carried out in vacuum ampoules and in a vacuum furnace showed that the gas phase has a strong effect on the reactions.
Modeling the effect of a buried layer in GaAs metal-semiconductor-metal photodetectors
Authors: Hurd C. M. , McKinnon W. R.
Published: July 2002

When an undoped heterostructure layer is buried in a conventional GaAs metal-semiconductor-metal photodetector, it is intended to improve the transient response to a pulse of light by preventing carriers that are photogenerated deep in the device from reaching the electrodes. The physics behind this strategy are investigated by means of a two-dimensional, finite-difference simulation of a practical structure. It is argued that previous experimental tests are equivocal because they do not investigate fully all the circumstances that determine the benefit of a buried layer over simpler structures. The simulation suggests that, judged from the fall time of the transient response, there are additional factors to be considered. These include the nature of the active layer and whether the illumination has a dc component.
Relaxor-normal ferroelectric transition in tetragonal-rich field of Pb(Ni1/3Nb2/3)O3-PbTiO3-PbZrO3 system
Authors: Yoon Man-Soon , Jang Hyun M.
Published: July 2002

The possibility of the existence of a spontaneous relaxor-normal ferroelectric transition was proposed and examined using Pb(Ni1/3Nb2/3)O3-PbTiO3-PbZrO3 (PNN-PT-PZ) pseudoternary system across the morphotropic phase boundary (MPB). On cooling, the PNN-PT-PZ system in the tetragonal-rich side of the MPB underwent a spontaneous transition from a relaxor to a normal ferroelectric state. This observation was explained in terms of a thermally driven transformation from an ensemble of polar microregions to normal long-range ferroelectric domains (micro-macrodomain switching). The relaxor-normal ferroelectric transition was further correlated with the rhombohedral-tetragonal first-order phase transition. Increasing the relative content of PbZrO3 enhanced dielectric dispersion characteristics but weakened the extent of relaxor-normal transition. This observation was explained by the enhanced 1:1 Nb-Zr short-range ordering and the breaking of the translational invariance of the ferroelectrically active BO6 octahedra with increasing content of PbZrO3.
Dependence of giant magnetoresistance on the number of valence electrons in the ferromagnetic constituent of granular alloys: Precipitates of face-centered cubic Fe–Co, Co–Ni, and Ni–Cu alloys in Ag matrices
Authors: Kubinski D. J. , Holloway H.
Published: July 2002

The dependence of giant magnetoresistance on the composition of ferromagnetic face-centered cubic precipitates in an Ag matrix grown epitaxially on MgO {100} is described. These compositions were chosen from the alloy ranges Ni0.6Cu0.4→Ni→NixCo1−x→ Co→Fe0.2Co0.8 to give a number of valence electrons per atom, n=n3d+n4s, in the ferromagnetic precipitates that ranged from 8.8 to 10.4. This corresponds to a decrease of the saturation magnetization from ∼1500 emu/cm3 to approximately zero. To reduce the influence of other variables the concentration of the precipitates was kept constant (at 23.5 vol %) and their size approximately so. Corrections are applied to adjust for some remaining variation in precipitate size. With other factors held constant, there is a steady increase in both the magnetoresistance ratio and the magnetic-field-dependent resistivity with increase in the saturation magnetization of the alloys, i.e., with increase in the spontaneous magnetization of the single-domain precipitates.
Interface states induced by the presence of trapped holes near the silicon–silicon-dioxide interface
Authors: DiMaria D. J. , Buchanan D. A. , Stathis J. H. , Stahlbush R. E.
Published: July 2002

Trapped holes are shown to induce ‘‘slow’’ interface states by their presence that are distinctly different from other types of interface states. These slow states can be alternately introduced and removed by sequential hole generation and annihilation. Various experiments and techniques are used to rule out explanations involving artifacts due to lateral nonuniformities in the hole trapping.
Simulation of the optical effects of particles residing on top antireflective coatings for KrF positive photoresist films
Authors: Kamoshida Mototaka , Inui Hirotomo , Ohta Toshiyuki , Kasama Kunihiko
Published: July 2002

The reflection effects of particles on developed cross-sectional photoresist patterns are simulated by using a two-dimensional waveguide model. The particles were assumed to reside on top antireflective coatings used for chemically amplified positive photoresist films. In order to improve the accuracy of the analysis, the exposure dose of KrF excimer laser light and focus position in the resist were optimized. The top antireflective coating film thickness was also adjusted to the optimum thickness for obtaining the critical dimension of 0.25 μm. Under these conditions, the light intensity distributions in the resist depth and in the lateral direction on the focal plane are discussed, and it is revealed that the influence of the particles is enhanced for the case of weaker light intensity. Finally, it is described that the antireflective coating gives a wider process margin on the smallest critical sizes of particles capable of causing pattern shorts. In conclusion, the light intensity obtained from three-dimensional Fresnel approximation is also taken into account.
Deep levels in nitrogen-implanted n-type GaAs
Authors: Chen K. M. , Jia Y. Q. , Chen Y. , Li A. P. , Jin S. X. , Liu H. F.
Published: July 2002

Ti/n-GaAs Schottky barrier diodes were prepared on nitrogen-implanted n GaAs. The Schottky barrier height of the diodes was found to be 0.96 eV, 0.12 eV higher than that of the samples without N implantation. Four distinctive electron traps E1(0.111), E2(0.234), E3(0.415), and E4(0.669) and one hole trap, H(0.545), have been observed with deep level transient spectroscopy. Defect models of these deep levels are proposed and the role of H(0.545) in the Schottky barrier formation is also discussed.
The origin of defects in SiO2 thermally grown on Czochralski silicon substrates
Authors: Itsumi Manabu , Tomita Masato , Yamawaki Masataka
Published: July 2002

We have observed the origin of defects in SiO2 thermally grown on Czochralski silicon substrates. Samples were prepared by copper decoration to locate oxide defects, focused ion beam etching to mark them, and subsequent silicon-substrate thinning for transmission electron microscope observation. Polyhedron structures with sizes ranging from 150 to 300 nm are found in the underlying silicon-substrate surface layer just under the oxide defects. Two polyhedron structures superimposed on each other are also observed. It is believed that these structures are related to the presence of oxygen precipitates. Oxide defects are thought to arise due to oxide thinning induced at the edge of the silicon-substrate surface adjacent to the octahedron structures.
Coupled model for neutral transport and charged species dynamics in high density plasma reactors
Authors: Meyyappan M. , Govindan T. R.
Published: July 2002

We present a model to study high density plasma reactors used in semiconductor processing. The model is based on a continuum approach with conservation equations for mass, momentum, and energy in a multicomponent, multitemperature system. The governing equations are radially averaged to obtain a one-dimensional model for the transport of neutrals and charged species in the flow direction. Processes at the radial wall are properly included as source/sink terms by weighting with surface area to volume ratio. The model is applied to an electron cyclotron resonance reactor and simulations of an argon discharge are presented for pressures in the range of 1–10 mTorr and flow rates of 5–80 sccm. The predictions of plasma density, electron and gas temperatures, pressure, and neutral density are consistent with experimental observations and compare favorably with data.
Dependence of the phototransport properties on the position of the Fermi level in polycrystalline CuInS2 films
Authors: Lubianiker Y. , Biton G. , Balberg I. , Walter T. , Schock H. W. , Resto O. , Weisz S. Z.
Published: July 2002

We report a simultaneous study of the phototransport properties of both the majority and minority carriers in polycrystalline CuInS2 layers. This is done for n-type as well as p-type layers. The dependencies of these properties and their light intensity exponents on the position of the Fermi level yield a picture of the recombination levels and the recombination kinetics in these layers. We show that the simplest model which is consistent with the data is that of a symmetric two-level system. One level is associated with donorlike recombination centers lying around 0.35 eV below the conduction band edge, and the other level is associated with acceptorlike recombination centers lying around 0.35 eV above the valence band edge. This interpretation of the results is shown to be consistent with the luminescence and transport data reported previously on single crystals of CuInS2.
Microstructural properties of (ZnSe/FeSe) and (ZnSe/MnSe) diluted magnetic semiconductor superlattices (abstract)
Authors: Park K. , Salamanca-Riba L. , Jonker B. T.
Published: July 2002

Recently, there has been increased research activity on Fe-, Mn-, and Co-based diluted magnetic semiconductors (DMS) because of their interesting magneto-optical properties. Potential applications of DMS usually require thin films with a high degree of structural perfection, and high quality single crystal epilayers of Zn1−xFexSe and Zn1−xCoxSe have been grown by molecular beam epitaxy (MBE). In this work, the microstructural properties of (ZnSe/FeSe) and (ZnSe/MnSe) DMS superlattices grown on (001) GaAs substrates by MBE have been investigated using transmission electron microscopy. High-quality (ZnSe/FeSe) superlattices were grown by introducing a ZnSe buffer layer on the GaAs substrate prior to the growth of the superlattice. In contrast, nominal (ZnSe/FeSe) superlattices grown directly without a buffer layer on the substrate showed evidence for interdiffusion between the constituent layers of the superlattice. Chemical ordering of the Zn and Fe atoms was also observed in the resultant Zn1−xFexSe alloys along the [001] and [110] directions. This ordered structure corresponds to the CuAu–I type structure. In contrast, the (ZnSe/MnSe) superlattices did not show interdiffusion, but contained many microtwins and 60°-type misfit dislocations. The MnSe layer in the (ZnSe/MnSe) superlattices existed as a zinc-blende structure.
Impact of criticality and phase separation on the spin dynamics of the one-dimensional t–J model
Authors: Zhang Shu , Müller Gerhard , Stolze Joachim
Published: July 2002

The recursion method is used to determine the T=0 spin dynamic structure factor Szz(q,ω) in the Luttinger liquid state and in the phase-separated state of the one-dimensional t–J model. As the exchange coupling increases from zero, the dispersions and line shapes of the dominant spin excitations are observed to undergo a major metamorphosis between the free-fermion limit and the onset of phase separation. The familiar two-spinon spectrum of the Heisenberg antiferromagnetic chain emerges gradually in the strongly phase-separated state.
Sputter deposited Co/CoO composite materials
Authors: Yi J. Y. , Platt C. L. , Rudee M. L. , Berkowitz A. E. , Cheeks T. L.
Published: July 2002

Magnetic composites consisting of ultrafine particles of Co and CoO were prepared by dc reactive magnetron sputtering in a Ar+O2 gas mixture. The films were composed of 60–140 Å particles of hcp Co and fcc CoO. The magnetization, coercivity, and particle size were found to be dependent on the O2 partial pressure, such that the magnetization decreased and the coercivity increased to a maximum value of 1000 Oe with increasing O2 partial pressure. A shift in the hysteresis loop was observed for several samples, indicating exchange coupling between the Co and CoO.
Approaches to 10 Gbit/in.2 recording (invited)
Authors: Kryder M. H. , Messner W. , Carley L. R.
Published: July 2002

The areal density of manufactured magnetic disk drives is currently advancing at a rate of about 60% per year. Assuming this continues, an areal density of 10 Gbit/in.2 will be reached sometime shortly after year 2000. In this paper, the characteristics of a disk drive with 10 Gbit/in.2 density and the requirements that such an areal density places upon the component technologies necessary to make such a drive possible are discussed. It is projected that smooth, high coercivity and fine grain media, high moment thin film write heads, spin-valve read heads, advanced signal processing techniques, and improved servo systems will make it possible to achieve this goal using flying heads and longitudinal recording.
Critical phenomena in the two-dimensional XY magnet Fe(100) on W(100)
Authors: Elmers H. J. , Hauschild J. , Liu G. H. , Gradmann U.
Published: July 2002

We experimentally investigated the magnetic phase transition of the in-plane magnetized double-layer Fe on W(100). This epitaxial system approximates the theoretical two-dimensional (2D) XY model to a large extent because of its pseudomorphic growth and structural stability. We measured the magnetization of W(100)/Fe in the vicinity of the Curie temperature TC using the diffraction of spin polarized electrons and the magnetization of W(100)/Fe/Ag in a wider temperature interval using conversion electron Mössbauer spectroscopy. The temperature dependence of the spontaneous magnetization follows a power law with an exponent β=0.22±0.03 in the temperature regime 0.3≤T/TC≤0.99. The susceptibility χ(T≳TC) can be fitted alternatively by a power law with an unusually large exponent γ≊5 or by an exponential law χ∝exp(b/√T−TC), as predicted for the 2D XY model, with b=1.6.
Structure, Curie temperature, and magnetostriction of Sm1−xPrxFe2 alloys
Authors: Wang B. W. , Cheng L. Z. , He K. Y.
Published: July 2002

The structure, Curie temperature, and magnetostriction of Sm1−xPrxFe2 alloys have been investigated using optical microscopy, x-ray diffraction, ac susceptibility, diffractometer step scanning and standard strain gauge techniques. It is found that the matrix of homogenized Sm1−xPrxFe2 alloys is the (Sm,Pr)Fe2 phase with MgCu2-type structure up to x=0.3, and the minor phases, both (Sm,Pr)Fe3, and rare earth-rich phase appear. The lattice parameter of the alloys increases slowly with increasing Pr content, but the Curie temperature goes the opposite way. The room temperature magnetostriction |λ∥−λ⊥| and easy direction magnetostriction |λ111| of Sm1−xPrxFe2 alloys exhibit a peak near x=0.1.
Study of leakage current in n-channel and p-channel polycrystalline silicon thin-film transistors by conduction and low frequency noise measurements
Authors: Angelis C. T. , Dimitriadis C. A. , Samaras I. , Brini J. , Kamarinos G. , Gueorguiev V. K. , Ivanov Tz. E.
Published: July 2002

The off-state current in n- and p-channel polycrystalline silicon thin-film transistors (polysilicon TFTs) is investigated systematically by conduction measurements at various temperatures and low-frequency noise measurements at room temperature. It is demonstrated that the leakage current is controlled by the reverse biased drain junction. The main conduction mechanisms are due to thermal generation at low electric fields and Poole–Frenkel accompanied by thermionic filed emission at high electric fields. The leakage current is correlated with the traps present in the polysilicon bulk and at the gate oxide/polysilicon interface which are estimated from the on-state current activation energy data. Analysis of the leakage current noise spectral density confirms that deep levels with uniform energy distribution in the silicon band gap are the main factors in determining the leakage current. The density of deep levels determined from noise analysis is in agreement with the value obtained from conductance activation energy analysis. The substantially lower leakage current observed in the n-channel polysilicon TFT is explained by the development of positive fixed charges at the interface near the drain junction which suppress the electric field.
Analysis of switching dynamics of asymmetric Fabry–Perot symmetric self-electro-optic effect devices with extremely shallow quantum wells
Authors: Choi Young-Wan
Published: July 2002

This article investigates the effects of asymmetric Fabry–Perot (AFP) cavity structures on the switching dynamics of symmetric self-electro-optic effect devices (S-SEEDs) made of AlxGa1−xAs/GaAs (x⩽0.05) extremely shallow quantum wells (ESQWs). We analyze the switching dynamics of AFP ESQW S-SEEDs (AE-SEEDs) by means of an impulse photocurrent response function and corresponding voltage transients of the two AFP p-i(ESQWs)-n diodes connected in series. The photocurrent response function is obtained by using an appropriate electron-hole pair generation rate and the Green’s function method. The response function includes the LO phonon scattering from bound to continuum states and the carrier transit in the continuum states. Large internal optical fields and thin intrinsic region thicknesses of AFP SEEDs reduce the required incident switching energy and operating voltage, respectively. Our analyses show that the switching energy of an impedance-matched AE-SEED is about 3.0 fJ/μm2, while that of a conventional antireflection coated ESQW S-SEED (E-SEED) is about 4.1 fJ/μm2. Considering practical RC time constants and device sizes, the switching time of an impedance-matched AE-SEED is found to be as low as 10 ps while that of an E-SEED is about 18 ps for the same incident energy of 4.1 fJ/μm2.
Epitaxial growth of ZnS on bare and arsenic-passivated vicinal Si(100) surfaces
Authors: Zhou Xiaochuan , Jiang Shan , Kirk Wiley P.
Published: July 2002

We report a detailed study of molecular beam epitaxial growth of ZnS films on bare and arsenic-passivated vicinal Si(100) surfaces. This study elucidates the initiation of microtwinning and stacking-fault defects on double-stepped substrate surfaces. The study also sheds light on the function of arsenic passivation in reducing crystal defects in ZnS epitaxial layers. Three substrate surfaces, Si(100) 2×1, Si(100):As 2×1, and Si(100):As 1×2, were used for the ZnS epitaxial growth studies. Adsorption experiments were performed to demonstrate the chemical passivation effect of an arsenic overlayer. Reflection high-energy electron diffraction was used to study growth modes and the epitaxial relationship of the ZnS layers to the substrates. Transmission electron microscopy was used to study the crystal-defect structures. Secondary ion mass spectroscopy was used to determine the chemical profiles of the heteroepitaxial interfaces of ZnS layers grown on arsenic-passivated surfaces. One of the main results demonstrated by this work is that thin ZnS films can be grown epitaxially with much better crystal quality on As-passivated Si surfaces than on bare Si surfaces.
Enhanced field emission of diamondlike carbon films due to cesiation
Authors: Pan L. S. , Felter T. E. , Ohlberg D. A. A. , Hsu W. L. , Fox C. A. , Cao R. , Vergara G.
Published: July 2002

A treatment that lowers the threshold field for field emission and increases the emission site density from a nominally n-type diamondlike carbon film is described. The film was deposited using an rf plasma of methane and nitrogen gases. The treatment involved deposition of cesium followed by a low temperature anneal. Field emission measurements were used to characterize the threshold field and emission site density before and after cesium treatment. Ultraviolet photoemission was used to study the effect of cesium on the work function. Dramatic improvements to field emission by cesiation cannot be generalized to all diamondlike samples, as similar treatment of a type IIb single-crystal (p-type) diamond did not produce as pronounced an improvement in turn-on field or emission site density.
Effects of thermal treatment of low-temperature GaN buffer layers on the quality of subsequent GaN layers
Authors: Sugiura L. , Itaya K. , Nishio J. , Fujimoto H. , Kokubun Y.
Published: July 2002

The surface morphology and crystalline quality of GaN layers grown by metalorganic chemical vapor deposition on sapphire (0001) substrates were investigated for various thermal treatment conditions of low-temperature (LT)-grown GaN buffer layers. The surface morphology and crystalline quality of subsequently grown high-temperature (HT) GaN layers strongly depended on thermal effects during the temperature ramping process after LT growth of the buffer layers. We have found that the defect density and structure are affected by this temperature ramping process, and that the generation of growth pits is closely related to defects in the HT-GaN layers. High-quality HT-GaN layers with specular surface morphology were obtained with optimum growth and ramping conditions for the LT-GaN buffer layers. Furthermore, the role of thermal treatment during the temperature ramping process was identified, and mechanisms of nucleus formation, HT-growth initiation on the LT-GaN buffer layers, and defect formation are proposed and discussed.
Spatially resolved near-field spectroscopy on localized GaInAsP/InP double heterostructures
Authors: Barenz J. , Anger P. , Hollricher O. , Marti O. , Wachter M. , Butendeich R. , Heinecke H.
Published: July 2002

We present investigations of band-gap variations on selective grown GaxIn1−xAsyP1−y multiple quantum wells (MQW, Q1.05) using near-field optical microscopy. The MQW is excited with the near-field probe and the luminescence is collected through the same tip. By this mode, we are able to detect variation of the band gap with a lateral resolution of about 550 nm at a luminescence wavelength of 1115 nm. We show a spatial band-gap modulation near the (0–11) facet of the selective grown structures, which we suggest, is a result of a variation of the material composition. Furthermore, together with the simultaneously recorded topography, we are able to allocate a recombination path at a center wavelength of λ=1115 nm to the intersection of the (01–1) and (11–1) vertical side facets, which are formed by interfacet diffusion during surface selective growth of the GaxIn1−xAsyP1−y MQW.
Growth mode-related generation of electron traps at the inverted AlAs/GaAs interface
Authors: Krispin P. , Hey R. , Kostial H. , Ploog K. H.
Published: July 2002

Discrete electronic states at the inverted AlAs/GaAs interface grown by molecular beam epitaxy are identified by deep-level transient spectroscopy and capacitance-voltage measurements. The formation of two deep traps at the inverted AlAs/GaAs interface is shown to be related to the AlAs growth mode. We attribute the deep levels to intrinsic defects which are accumulated at the inverted AlAs/GaAs interface. The total density of interfacial electron traps can be minimized by growing AlAs in the pseudo-two-dimensional mode at a comparatively low temperature of 550 °C.
Microstructural characterization of sol–gel lead–zirconate–titanate thin films
Authors: Impey S. A. , Huang Z. , Patel A. , Beanland R. , Shorrocks N. M. , Watton R. , Whatmore R. W.
Published: July 2002

The techniques of x-ray diffraction, x-ray photoelectron spectroscopy (XPS), Auger analysis, and transmission and scanning transmission electron microscopy (TEM) have been applied to the analysis of thin films of Pb(Zr0.30Ti0.70)O3 (PZT30/70) deposited at low temperatures (510 °C) by a sol–gel process onto Pt/Ti electrodes on SiO2/Si 100 substrates. It is found that the platinum film is highly oriented with the [111] axis perpendicular to the substrate plane. The ferroelectric film tends to crystallize epitaxially upon this as columnar crystals. There are indications from the TEM of the existence of a second metallic phase at the interface between the platinum and the PZT30/70 film, which may be associated with its nucleation. The TEM shows the boundaries between the individual sol–gel layers, although the growing crystallites of the PZT30/70 propagate through these boundaries unhindered. The XPS and Auger analyses have shown that Pb penetrates through the Pt layer to the underlying Ti layer, even at the low crystallization temperatures used. There is also clear evidence for diffusion of the Zr and Ti prior to, or during the crystallization process, so that the Zr migrates to the surface of each sol–gel layer. The effects of using different crystallization processes on this compositional separation and the reasons for its occurrence are discussed, as are the possible effects upon macroscopically measured ferroelectric properties.
The diffusion of tracer oxygen atoms in Ni ferrites
Authors: Fetisov V. B. , Kozhina G. A. , Fishman A. Ya. , Kurennykh T. E. , Vykhodets V. B.
Published: July 2002

Oxygen tracer diffusion in polycrystalline nickel ferrites Ni(1−x)Fe(2+x)O(4) (x=0.1; 0.2; 0.4) at temperatures of 450–700 °C was studied. The number of O18 atoms diffusing to the sample was determined using the O18(p,α)15N nuclear reaction at the energy of the primary beam particles equal to 762 keV. The nuclear physical experiments were performed on a 2 MV Van de Graaff accelerator. It has been established the oxygen diffusion is characterized by relatively small activation energy (0.89 eV for x=0.2) and low pre-exponential factors (∼10−13 cm2/s for x=0.2). These results suggest that oxygen diffusion in the ferrites under consideration occurs by means of structural vacancies with their concentration about 10−9–10−11.
Balance-equation approach to hot-electron transport in semiconductors irradiated by an intense terahertz field
Authors: Lei X. L.
Published: July 2002

We investigate the effect of a uniform intense terahertz radiation on hot-electron transport in semiconductors driven by a dc or slowly varying electric field of arbitrary strength. Using a vector potential for the high-frequency field and a scalar potential for the dc or slowly varying field, we are able to separate the center-of-mass motion from relative motion of electrons and to distinguish the slowly varying part from the rapidly oscillating part of the center-of-mass velocity. Considering the fact that relevant transport quantities are measured over a time interval much longer than the period of the terahertz radiation field, we obtain a set of momentum and energy balance equations, without invoking a perturbational treatment of the electron-photon interaction. These equations, which include all the multiphoton processes, are applied to the examination of hot-carrier transport in a GaAs-based quantum well subjected to a weak or a strong dc bias and irradiated by a terahertz radiation of various frequency and strength in both the parallel and vertical configurations. Up to as many as |n|=50 absorption and emission multiphoton channels are included in the numerical calculation. The present approach turns out to be a very convenient and efficient tool to study the effect of an intense high-frequency radiation on dc or slowly varying carrier transport in semiconductors. Its applicable frequency range and its connection with previously developed balance-equation treatment are discussed.