bluuebunny/crossref_metadata_2025 huggingface dataset:
Detailed electrical characterization of
DX
centers in Se-doped AlxGa1−xAs
Authors: Dueñas S. , Pinacho R. , Castán E. , Quintanilla L. , Peláez R. , Barbolla J.
Published: July 2002

DX centers in selenium doped AlxGa1−xAs with two values of the aluminum content, x=0.34 and 0.48, are carefully analyzed by three different techniques: deep level transient spectroscopy (DLTS), admittance spectroscopy, and the capacitance voltage transient technique (CVTT). We use conceptual differences between these techniques to extract important information about the nature of the DX centers. Good agreement is found between the capacitance transients recorded during the DLTS measurements and those obtained by CVTT at every point in the space charge region. From that, we conclude that is the very nature of the DX centers the solely responsible for the anomalies found in DLTS results. The main cause for these anomalies is the thermal dependence of the electron capture rate of these centers. CVTT curves also reveal that no electric field enhanced emission processes take place for these centers. For our analysis of the shape of the DLTS and admittance spectroscopy curves we conclude that several DX levels exist, according to the alloy broadening theory. Finally, some simulations of the DLTS spectra were made. These calculations reveal the important effect of experimental parameters such as the filling pulse duration, the velocity of the temperature scan, and the initial conditions of the occupation factor of the deep levels on the DLTS curves.
Spatial resolution of localized photoluminescence by near-field scanning optical microscopy
Authors: Safvi S. A. , Liu J. , Kuech T. F.
Published: July 2002

A numerical model describing the spatial resolution limitations on localized band edge photoluminescence (PL) and trap-based luminescence, obtained through near-field scanning optical microscopy (NSOM), is presented. Calculations were carried out for NSOM measurements performed in the tip illumination mode. Variations in surface recombination velocity, probe aperture, and the physical structure on the achievable spatial resolution were investigated. These calculations indicate that the drift of photogenerated minority carriers to the surface narrows their lateral distribution, leading to improved spatial resolution. There is a weak dependence on the spatial resolution of the photoluminescence on the tip aperture. An order of magnitude reduction of the illuminating tip aperture resulted in only a minor improvement in the lateral spatial resolution of the emitted PL. The spatial resolution of the localized trap luminescence is presented within the context of typical material structures.
Synthesis and magnetic properties of iron nitride films deposited on Ge(100) by reactive ion beam sputtering
Authors: Ding Xing-zhao , Zhang Fu-min , Yan Jian-sheng , Shen Hong-lie , Wang Xi , Liu Xiang-huai , Shen De-Fang
Published: July 2002

Iron nitride films were deposited on Ge(100) wafers by a reactive ion beam sputter deposition of iron in an ammonia atmosphere. The composition and microstructure of these films were monitored by Rutherford backscattering spectroscopy analyses and x-ray diffraction experiments. The magnetic properties of these films were determined by a vibrating sample magnetometer. It was found that Ge(100) substrate is profitable for epitaxial growth of the α′′ phase. The optimum ammonia pressure for α′/α′′ phase formation was about 5×10−4 Torr. The saturation magnetization σs of each as-deposited Fe–N film is higher than that of a pure iron film. However, the film with the highest α′/α′′ phase content did not exhibit the largest σs value. The variation of σs of the Fe–N films during annealing at a temperature of 180 °C in a flowing nitrogen atmosphere was also investigated. It was found that there is no direct relationship between the higher σs values and the α′/α′′ phase in these Fe–N films.
Localized surface nucleation of magnetization reversal
Authors: Suhl Harry , Neal Bertram H.
Published: July 2002

Standard treatments of the magnetization reversal of fine particles yield a reversal mechanism that begins with nucleation of a nonuniform or uniform energy barrier state that involves virtually the entire sample volume. Accordingly, the barrier height is essentially proportional to the sample volume. Such strong volume dependence is not observed, especially in measurements of thermally activated reversal. Numerical micromagnetic analysis also shows a variety of surface reversal modes depending on the ratio of the particle size to the exchange length. An analytic model for surface nucleation is presented here for an idealized system to illustrate this phenomenon. The corresponding barrier height does not depend on sample volume, though it may depend on surface area. Any additional size dependence will arise from the finite front velocity with which the reversal propagates. An example of thermally activated reversal is given that shows “effective” reversal volumes that correspond to these surface reversal modes, and thus, can be much smaller than the sample volume.
Photoresist etching with dielectric barrier discharges in oxygen
Authors: Falkenstein Zoran , Coogan John J.
Published: July 2002

This article presents results on the surface etching of a Novolak-type polymer (Shipley, SPR2) on Si wafers using dielectric barrier discharges in oxygen at high pressures and room temperature. The etching depth is measured by mechanical profilometry as a function of gap spacing and gas pressure. Figures of merit are generated allowing comparison with conventional plasma surface treatment, as etch rate per power density coupled onto the sample surface (nm J−1 cm2), or coupled into the gas volume (nm J−1 cm3). Energy-density specific etch rates were measured as a function of the gap spacing (d) and the total oxygen gas pressure (p), as well as a function of the product of pd in the gas pressure range of 50–1500 mbar and of the gap spacing range of 1–20 mm. At a constant gap spacing and pressure, the removal rate is a linear function of the applied power density. The highest achieved etching rate per surface energy density is 2.2 nm J−1 cm2 at 730 mbar and 1 mm (0.2 nm J−1 cm3) and the highest etching rate per volumetric energy density is 0.85 nm J−1 cm3 at 290 mbar and 7 mm (0.87 nm J−1 cm2). The surface of the etched photoresist is characterized using mechanical profilometry and scanning electron microscopy. The results obtained in this work suggest that dielectric barrier discharges can be an efficient, alternative plasma source for general surface processing, because they can provide nonthermal discharges also near atmospheric pressures and thereby eliminate the need of costly vacuum systems.
Microstructural modification in Co/Cu giant-magnetoresistance multilayers
Authors: Christides C. , Stavroyiannis S. , Boukos N. , Travlos A. , Niarchos D.
Published: July 2002

Three different classes of [Co/1.1 nm/Cu/2.1 nm]30 multilayers were grown by magnetron sputtering deposition. The effect of magnetostatic interactions on the giant-magnetoresistance (GMR) and magnetic properties are examined in relation to the induced changes in the film microstructure as it is varied by: (i) the substrate surface roughness and (ii) the effect of thermal isolation of the Si(100) substrate from the cooling plate during deposition. A remarkable variation in shape and magnitude of GMR, and in the magnetic (M-H) loops, is observed for the three classes of films. It is found that there are three characteristic features in every sample that vary systematically: (i) The (ΔR/R)max ratio. (ii) The magnetic field range where a GMR loop reaches its minimum value. (iii) The (M-H) loops that vary from the characteristic antiferromagnetic to a typical ferromagnetic loop shape. Two well-separated grain size distributions below and above 12 nm were found from transmission electron microscopy. The smaller grains are associated with the appearance of a considerable fraction of ferromagnetically coupled regions in the multilayer.
Characterization of silicon surfaces in HF solution using microwave reflectivity
Authors: Natarajan Arun , Oskam Gerko , Searson Peter C.
Published: July 2002

Determination of the band bending in a semiconductor in contact with a solution is not straightforward since the potential is partitioned between the space charge layer in the semiconductor and the Helmholtz layer on the solution side of the interface. In deep depletion, a change in the applied potential usually appears across the space charge layer, however, under conditions of weak depletion or accumulation, the applied potential is partitioned between the two double layers and the band bending is usually unknown. In this article we show how microwave reflectivity measurements can be used to determine the potential distribution at the semiconductor/solution interface.
The role of interfaces in polymeric light-emitting diodes
Authors: Östergård T. , Pal A. J. , Stubb H.
Published: July 2002

Langmuir–Blodgett films of poly(3-hexylthiophene) and poly(methyl methacrylate) have been used to prepare organic dc and ac light-emitting diodes (LEDs). The transient as well as steady state properties of the LEDs have been studied. In order to explain electroluminescence (EL), charge transport mechanisms, and the role of interfaces in organic LEDs, transient EL, luminance–voltage and luminance–current measurements have been performed both for single layer and multilayer devices. The transient measurements were performed by applying a single square-wave voltage pulse or a square-wave ac voltage. We have shown that the time delay observed in transient EL measurements of single layer LEDs is mainly due to accumulation of charge carriers and not due to carrier transit times. The interfaces were found to have a major role on the operation of organic LEDs.
Extension of the impedance field method to the noise analysis of a semiconductor junction: Analytical approach
Authors: Bulashenko O. M. , Gomila G. , Rubı́ J. M. , Kochelap V. A.
Published: July 2002

We present an analytical procedure to perform the local noise analysis of a semiconductor junction when both the drift and diffusive parts of the current are important. The method takes into account space-inhomogeneous and hot-carriers conditions in the framework of the drift-diffusion model, and it can be effectively applied to the local noise analysis of different devices: n+nn+ diodes, Schottky barrier diodes, field-effect transistors, etc., operating under strongly inhomogeneous distributions of the electric field and charge concentration.
Photothermal properties of bulk and layered materials by the picosecond acoustics technique
Authors: Bonello Bernard , Perrin Bernard , Rossignol Clément
Published: July 2002

The picosecond acoustic technique is a pump and probe method associated with a lock-in amplification scheme. It involves the excitation of the sample by an ultrashort optical pulse and the monitoring of the subsequent relaxation processes by a weaker pulse delayed with respect to the former. In particular, information about the temperature evolution a short duration after the pump pulse is absorbed can be obtained. We examine here the different time scales involved in such an experiment. We show that the photothermal signal is superimposed on a continuous background originating from the modulation of the pump beam for synchronous detection. We also derive expressions for the cooling rate of both bulk and layered specimens after an instantaneous heating and we show experimentally that this macroscopic approach is valid after a delay of several picoseconds.
X-ray characterization of buried allotaxially grown CoSi2 layers in Si(100)
Authors: Zimmermann U. , Schlomka J.-P. , Tolan M. , Stettner J. , Press W. , Hacke M. , Mantl S.
Published: July 2002

An x-ray study of the interface morphology and lattice parameters of buried expitaxial CoSi2 layers in Si(100) is presented. Specular reflectivity, diffuse and crystal truncation rod scattering, together with grazing incidence diffraction yield detailed information about the interface quality and lattice mismatch. It turns out that the CoSi2 interfaces are considerably smoothened by an annealing step at 1150 °C. Also the in-plane correlation length of the roughness increases yielding laterally smoother interfaces. While the perpendicular lattice parameter is between that of a free relaxed and a pseudomorphic structure and a linear contraction as function of the annealing temperature is obtained, grazing incidence diffraction reveals the opposite effect for the in-plane lattice mismatch.
Preconditioning of c-plane sapphire for GaN molecular beam epitaxy by electron cyclotron resonance plasma nitridation
Authors: Heinlein Christian , Grepstad Jostein K. , Einfeldt Sven , Hommel Detlef , Berge Torunn , Grande Alf P.
Published: July 2002

Nitridation of c-plane sapphire is commonly employed in molecular beam epitaxy of GaN, in order to improve the crystalline quality of the deposited layers. In this study, we use x-ray photoelectron spectroscopy, Auger sputter profiling, reflection high energy electron diffraction, low energy electron diffraction, and atomic force microscopy to examine chemical and structural properties of sapphire (0001) substrate upon exposure to nitrogen activated by an electron cyclotron resonance plasma source. Incorporation of nitrogen into the sapphire surface was verified with x-ray photoelectron spectroscopy, and a monolayer of surface nitride is formed after approximately 60 min of nitridation at a substrate temperature of 620 °C. The thickness of the surface nitride layer is on the order of 4.5–6 Å for nitridation times ranging from 60 to 180 min, as estimated from the recorded nitrogen Auger sputter profiles. Reflection high energy electron diffraction gave clear evidence for formation of surface aluminum nitride, after prolonged (60 min) nitridation.
Influences on relaxation of exchange biasing in NiO/Ni66Co18Fe16 bilayers
Authors: van der Heijden P. A. A. , Maas T. F. M. M. , Kools J. C. S. , Roozeboom F. , van der Zaag P. J. , de Jonge W. J. M.
Published: July 2002

The stability of the exchange biasing field, Heb has been studied for NiO/Ni66Co18Fe16 bilayers. A forced antiparallel alignment of the ferromagnetic magnetization to Heb results in a gradual decrease and even a reversal of Heb. The decrease of Heb increases with temperature and is independent of the external field and NiO layer thickness. This decrease can be interpreted by a thermally assisted relaxation process. A new effect of the relaxation process on Heb is demonstrated by using different cooling rates.
Magnetostrictive properties of polymer-bonded amorphous Tb–Fe–B composites
Authors: Kim S. R. , Kang S. Y. , Park J. K. , Nam J. T. , Son Derac , Lim S. H.
Published: July 2002

Amorphous ribbons of an alloy with the composition (Tb0.33Fe0.67)0.98B0.02, which exhibit good magnetostrictive properties at low magnetic fields, are bonded with a phenol-based binder to fabricate bulk composites. Efforts to determine optimum fabrication parameters are made by examining magnetic and mechanical properties of bulk compacts obtained at various fabrication conditions. From the binder content dependence of magnetostriction and compressive strength, the optimum binder content is estimated to be about 4.3 wt %, taking into account magnetostrictive and mechanical properties and the necessity of reducing nonmagnetic binder content. The two properties of magnetostriction and compressive strength vary nearly linearly with the compaction pressure; as the compaction pressure varies from 0.25 to 1.0 GPa, magnetostriction decreases but compressive strength increases, making it difficult to determine the optimum compaction pressure. A magnetostriction of 493 ppm (at 1.1 kOe) is achieved from the present bulk composites, together with a high dλ/dH (sensitivity of magnetostriction with applied magnetic field) of 1 ppm/Oe.
Anomalous behavior of temperature and bias-voltage dependence of tunnel-type giant magnetoresistance in insulating granular systems
Authors: Mitani S. , Takanashi K. , Yakushiji K. , Fujimori H.
Published: July 2002

We have investigated temperature and bias-voltage dependence of tunnel-type giant magnetoresistance (MR) in Co–Al–O insulating granular films. A remarkable enhancement of MR which is larger than the theoretical value by a simple model is observed for Co–Al–O granular films at low temperatures, and it steeply decreases with increasing temperature. On the other hand, the MR does not decrease with increasing bias voltage although the resistivity decreases by a few orders of magnitude. Furthermore, it has been found that the effect of temperature is definitely different from that of bias voltage. The anomalous behavior is in contrast to that of macroscopic tunnel junctions, suggesting the significant effect of Coulomb blockade in granular systems.
Calculation of the energy barriers in strongly interacting many-particle systems
Authors: Berkov D. V.
Published: July 2002

A numerical method which allows the evaluation of the energy barrier height between any two metastable states in a many-particle system with continuous degrees of freedom and arbitrary interparticle interaction is presented. The method uses the minimization of the Onsager–Machlup action corresponding to the given path between the two states. The path which minimizes this action is supposed to be the optimal path between the states under consideration and the height of the energy barrier separating these states is determined as the energy barrier along this optimal path. Test results for a simple two-dimensional potential (where the optimal path can easily be visualized) and for a dipolar glass are presented.
Atomistic modeling of high-concentration effects of impurity diffusion in silicon
Authors: List S. , Ryssel H.
Published: July 2002

The vacancy mechanism of dopant diffusion in silicon is investigated on a microscopic model level. The concentration dependence of the dopant diffusion constant in the high-concentration regime is simulated using the Monte-Carlo method and an atomistic model of clustering and precipitation. The simulation takes into account the microscopic forces between particles (dopant atoms and vacancies) in a quantitative manner. Since sufficiently accurate data for the binding strength and shape of the interaction potentials are not available, we analyze a variety of model approaches for these interactions to come to general conclusions for the macroscopic consequences of microscopic models. First, pure attractive forces between dopants and vacancies as usually assumed in the literature [S. M. Hu, Phys. Status Solidi B 60, 595 (1973)] are discussed. In contradiction to previous results from the literature [S. T. Dunham and C. D. Wu, J. Appl. Phys. 78, 2362 (1995)] we find that with this approach it is not possible to fit the experimental results. Also, models with repulsive dopant–dopant potentials of Coulomb shape together with attractive dopant–vacancy forces are found to give unrealistic results. On the other hand, a good fit to the experimental data is obtained with the assumption of a nonbinding dopant–vacancy interaction that only increases the mobility of the vacancy in the neighborhood of a dopant. The parameters of the atomistic potential are derived from a fit of the simulations to the experimental values. The simulation results for the different microscopic approaches are also used to give an assessment of the validity of models for high-concentration diffusion that are based on percolation theory [D. Mathiot and J. C. Pfister, J. Phys. (France) Lett. 43, L-453 (1982); D. Mathiot and J. C. Pfister, J. Appl. Phys. 66, 970 (1989)].
Pore formation on the silicon–metal interface in silicon–on–insulator structures
Authors: Akimov A. G. , Barabanenkov M. Yu. , Mordkovich V. N.
Published: July 2002

Pore formation is considered on the interface between a metal film and upper silicon layer in silicon-on-insulator (SOI) structures under high temperature conditions. It is assumed that the interface transmits silicon self–interstitials and collects vacancies, which results in the vacancy-related defect formation. The role of the buried insulator as a diffusion barrier for point defects is discussed. It is shown that vacancy pileup on the metal–silicon layer interface depends on the deformation introduced in the silicon layer by both the metal film and buried insulator. A metallization technique based on multicomponent amorphous metal films is shown to produce long-life SOI-based devices.
Effects of spacer layers on the Wigner function simulation of resonant tunneling diodes
Authors: Garcı́a-Garcı́a J. J. , Oriols X. , Martı́n F. , Suñé J.
Published: July 2002

The effects of spacer layer width and asymmetry on the simulation of quantum transport in resonant tunneling diodes are studied. The results show that these layers significantly influence the I–V characteristic, which presents important differences under direct or reverse bias polarity in devices with asymmetric spacer layers. These differences are interpreted in terms of potential profile comparisons of the simulated structures and are in qualitative agreement with experimental data.
Characterization of carrier concentration and stress in GaAs metal-semiconductor field-effect transistor by cathodoluminescence spectroscopy
Authors: Yoshikawa M. , Iwagami K. , Ishida H.
Published: July 2002

We have measured the cathodoluminescence spectra around the gate electrode in the cross section of a GaAs metal-semiconductor field-effect transistor with a detector and proposed a new technique to estimate the carrier concentration and stress in electronic devices, using cathodoluminescence spectroscopy. From a comparison between maps of the peak intensity and peak-energy shift, it is found that there is heavy carrier doping in the drain and source regions and that the carrier concentration is about 6×1017 atoms/cm3. The carrier concentration estimated from the peak-energy shift agrees well with that obtained from the capacitance–voltage method. Furthermore, it is found that there is hardly any carrier doping and that stresses are relaxed at a distance of about 2 μm from the gate electrode. Cathodoluminescence spectroscopy is a useful technique for estimating the two-dimensional distribution of the carrier concentration and stress in electronic devices within a short amount of time.
Effect of growth temperature on the properties of evaporated tantalum pentoxide thin films on silicon deposited using oxygen radicals
Authors: Grahn J. V. , Hellberg P.-E. , Olsson E.
Published: July 2002

The effect of growth temperature (170–730 °C) on the properties of as-deposited 1000 Å thick Ta2O5 films has been studied. The layers were grown by evaporation of tantalum metal on silicon exposed to a flux of oxygen radicals. X-ray diffractometry (XRD) and high-resolution cross-sectional transmission electron microscopy (XTEM) revealed that films grown at or below 400 °C were deposited in an amorphous state. The layers grown at 520 °C were observed to be in a nanocrystalline state with no discernible grain boundaries whereas films grown at 650 °C demonstrated distinct grain boundary formation in the β-phase modification of Ta2O5 as evidenced by XTEM and XRD analyses. For the highest growth temperature of 730 °C, the XRD pattern indicated the presence of an impurity phase in the β-Ta2O5 film. XTEM revealed an abrupt 20–30 Å thick layer, presumably SiO2, between the Ta2O5 layer and the silicon substrate for all films. The measured relative static dielectric constant was found to increase with increasing growth temperature accompanied by an increase in film refractive index. For the amorphous layers, the leakage currents were lower for films grown at 380 °C than for films grown at 170 °C. This is proposed to be related to the reduction of annealable short-range defects in the amorphous Ta2O5 film with increasing growth temperature. For polycrystalline layers, the leakage currents were much higher compared to amorphous films, suggesting that crystal-induced defects play an important role in determining the leakage current even for the nanocrystalline film grown at 520 °C.
Emission and emittance measurements of electron beams generated from Cu and diamond photocathodes
Authors: Nassisi V. , Beloglazov A. , Giannico E. , Perrone M. R. , Rainò A.
Published: July 2002

We report on the electron emission from Cu and diamond film cathodes irradiated with two ultraviolet excimer laser beams working at 308 nm XeCl, and 222 nm KrCl. The beam emittance measurements were performed using a new experimental setup composed of two movable slit arrays. The electron beam phase space areas were determined by splitting the beam in small beamlets and measuring the beamlet direction spread via small cups and slits. The highest emission was obtained at the lowest laser wavelength. With a 4 mm2 beam spot and 0.5 mJ laser energy the maximum currents from the Cu and diamond film cathode were 370 and 410 mA, respectively, and the corresponding emittances were 18 and 27 (π mm mrad). From these values the normalized beam brightness was estimated to be 4.6×109 A(π m rad)−2 for the Cu cathode and 2.3×109 A(π m rad)−2 for the diamond cathode. By increasing the laser energy and the spot beam the maximum extracted current was 16.4 A from the Cu cathode with the KrCl laser.
Tight-binding studies of the tendency for boron to cluster in c-Si. I. Development of an improved boron–boron model
Authors: Rasband Paul B. , Clancy Paulette , Roberts Bruce W.
Published: July 2002

A tight-binding model for B–B interactions has been developed to study the stability of small boron clusters in crystalline silicon. The model was produced by fitting to the band structure determined by local-density approximation calculations on periodic supercells. This model is able to reproduce, relatively accurately, the cohesive energy of free boron clusters as determined by self-consistent field and configuration-interaction calculations.
Photoreflectance study of growth mode in InAs–GaAs quasimonolayer single quantum wells
Authors: Geddo M. , Capizzi M. , Patanè A. , Martelli F.
Published: July 2002

Photoreflectance measurements have been performed in a number of InAs/GaAs single-quantum wells with nominal thickness L ranging from 0.6 to 2.0 ML. The InAs growth mode was investigated by analyzing the evolution, with increasing coverage, of the optical response associated with the InAs layer. For L⩽1.6 ML, the experimentally derived energies for the optical transition originating in the InAs are consistent with those evaluated in a simple square-well envelope-function scheme. The dependence of the photoreflectance line shape broadening on L is well described up to L=1.4 ML in terms of a disordered InAs/GaAs interface made by interconnected InAs and GaAs islands with a typical size of order 2 nm. For L=1.6 ML, the quantum well spectral features broaden abruptly and vanish for L=2 ML, suggesting the disappearance of the InAs 2D layer in favor of a predominant nucleation of large quantum dots.
Diffusivity of oxygen in Czochralski silicon at 400–750 °C
Authors: Takeno Hiroshi , Hayamizu Yoshinori , Miki Katsuhiko
Published: July 2002

Diffusivity of oxygen in Czochralski silicon crystal in the temperature range of 400–750 °C has been determined from macroscopic oxygen precipitation behavior. The oxygen diffusivities at several nucleation temperatures from 400 to 750 °C were deduced from precipitated oxygen concentrations after a series of precipitate growth heat treatments, 800 °C/4 h and 1000 °C/16 h, using an extended nucleation theory. The measured oxygen diffusivity at 450–650 °C is 2–4×10−14 cm2/s, independent of the temperature, and considerably larger than the generally accepted normal diffusivity of Di=0.13 exp(−2.53 eV/kT). Moreover, the diffusivity at 450 °C is found to be roughly proportional to the interstitial oxygen concentration. It is suggested that this dependence of oxygen diffusivity on interstitial oxygen concentration can be explained by a model involving fast diffusing oxygen molecules.
Evaluation of densities and mobilities for heavy and light holes in p-type Hg1−xCdxTe molecular beam epitaxy films from magnetic-field-dependent Hall data
Authors: Gui Yongsheng , Li Biao , Zheng Guozhen , Chang Yong , Wang Shanli , He Li , Chu Junhao
Published: July 2002

The densities and mobilities of heavy and light holes have been simultaneously determined at various temperatures (1.2–300 K) in two molecular beam epitaxy-grown p-type Hg1−xCdxTe (x=0.224) samples from variable magnetic-field Hall measurements. The separation of the contribution from the light hole and heavy hole was achieved by a hybrid approach consisting of mobility spectrum analysis followed by a multicarrier fitting procedure. An acceptor energy level at ∼13 meV above the valence band, as well as various mass ratios of light to heavy holes for different temperature were obtained. In addition, the minority carrier (electron) and the surface two-dimensional electron concentrations and mobilities have also been derived as a function of temperature. The explicit experimental values obtained in this work should be useful to physics and modeling of HgCdTe infrared detectors.
Exchange anisotropy in epitaxial Fe3O4/CoO and Fe3O4/CoxFe3−xO4 bilayers grown by pulsed laser deposition
Authors: Kleint C. A. , Krause M. K. , Höhne R. , Walter T. , Semmelhack H. C. , Lorenz M. , Esquinazi P.
Published: July 2002

Magnetic exchange anisotropy has been studied in epitaxial Fe3O4 based bilayers grown by pulsed laser deposition on MgO substrates. Measurements of the exchange biasing of the Fe3O4 magnetization curves were performed on (100)- and (111)-oriented Fe3O4 (20 nm)/CoO (20 nm) bilayers and (100)-oriented Co0.16Fe2.84O4 (190 nm)/Fe3O4 (40–370 nm) bilayers. The effective exchange bias field Heb and coupling energy were found to be 10–102 kA/m and 1–2 mJ/m2, respectively. The dependence of Heb on the thickness d of the soft magnetic component (magnetite) of the cobalt ferrite/magnetite bilayer Heb∼1/d is found to be in agreement with the predictions of a Stoner–Wohlfarth-type model. The order of magnitude and the temperature dependence of Heb for the Fe3O4/CoO bilayers are similar to those of bilayers prepared by molecular beam epitaxy.
Time dependent dielectric breakdown of paraelectric barium-strontium-titanate thin film capacitors for memory device applications
Authors: Huang Shu-chun , Chen Hong-ming , Wu Shich Chuan , Ya-min Lee Joseph
Published: July 2002

Barium-strontium-titanate (BST) is an important material for dynamic random access memory capacitor applications. In this work, BST thin films are prepared by the sol-gel method and metal-BST-metal capacitors are fabricated. The time dependent dielectric breakdown (TDDB) of the BST capacitors is measured and analyzed. A new extrapolation method is developed to obtain the TDDB lifetime from the time to breakdown (tBD) data. The leakage current is found to depend on the applied electric field in a power law relationship. The exponent in the power law relation is close to 1 in the low field region (lower than 16 MV/m) and is about 16.5 in the high field region (larger than 16 MV/m). A correlation between the leakage current and the TDDB lifetime is established. The extrapolated lifetime is about 1012 s at 3.3 V for 330-nm-thick films.
Low-field giant magnetoresistance in (111)-textured Co/Au multilayers prepared with magnetron sputtering
Authors: Stavroyiannis S. , Christides C. , Niarchos D. , Kehagias Th. , Komninou Ph. , Karakostas Th.
Published: July 2002

A series of magnetron-sputtered [Co(1 nm)/Au(tAu)]30 multilayers (MLs) has been deposited on Si(100) substrates covered with a 100 nm thick SiNx buffer layer. The samples were examined with x-ray diffraction (XRD), magnetotransport (MR), isothermal magnetization (M-H), and transmission electron microscopy (TEM) measurements. The quality of the interface and layer stacking in these MLs was observed with cross-section TEM and examined with superlattice refinement of the XRD patterns, where an (111) preferred orientation is evident along the growth direction. Three MR maxima, with values ΔR/Rs=3.5%, 1.3%, and 1.1% were observed for Au layer thicknesses (tAu) of 2.5, 3.9, and 5.1 nm, respectively, in a range of applied magnetic fields less than ±100 Oe, that are attributed to the giant magnetoresistance (GMR) effect. In the [Co(1 nm)/Au(2.4 nm)]30 sample, the GMR coercivity is two orders of magnitude less than that observed in epitaxial structures. This makes the sputtered Co/Au MLs possible candidates for use in GMR applications. Below tAu=2 nm a maximum anisotropic MR effect of 2% is observed for tAu=0.6 nm.
Study of the thermal aftereffect on longitudinal recording media by magnetic force microscopy
Authors: Matsunuma Satoshi , Tamai Ichiro , Kanbe Tetsuya , Tanahashi Kiwamu , Ishikawa Akira , Hosoe Yuzuru
Published: July 2002

We investigated the thermal aftereffect of 383 K annealing of longitudinal recording media through the structural analysis of all-ones patterns observed by magnetic force microscopy (MFM). The transition width increased by 31% after annealing, and the peak height of the MFM signal decreased by 36% even at a low linear recording density of 50 kFCI. The root mean square (rms) values of the MFM signal were reduced after annealing as the recording density rose to 200 kFCI, but at 250 kFCI or higher, the rms value did not change and large magnetic clusters appeared in the tracks. The growth of nonperiodic magnetic clusters after annealing was investigated through statistical analysis. The written bits were subtracted by using a two-dimensional fast Fourier transformation (FFT) method. The number of clusters with a diameter of less than 150 nm decreased after annealing, while the number of larger clusters increased. Also, the average cluster diameter increased as the linear recording density rose. After annealing, the average diameter increased, but did not change with the recording density. The accumulated area fraction as a function of the magnetic cluster size before and after annealing revealed a change in the distribution of the relatively large (>100 nm) clusters, and the change in the proportion of large clusters seems to be the main cause of the annealing after effect on the written bits.
Kerr imaging of a Co/Pt bimodal magneto-optical medium
Authors: Fry Richard A. , Bennett Lawrence H. , Della Torre Edward
Published: July 2002

Spatially resolved magneto-optical (MO) images of a (0.3 nm Co/1.2 nm Pt)15 multilayer film with perpendicular magnetic anisotropy have been obtained by Kerr microscopy. This material exhibits a major hysteresis loop with two-step magnetization reversal. The MO images display four possible “stable” magnetic states distinguished by four different intensities. This behavior is explained by the presence of two different magnetic phases each which has a stable magnetization state either parallel or antiparallel to the applied field, and which may reverse quasi-independently from one another.
Eddy current losses in anisotropic media subject to rotating magnetic fluxes
Authors: Mayergoyz Isaak , Serpico Claudio
Published: July 2002

In the article, the analysis of “rotational” eddy current losses is carried out for elliptical polarizations of magnetic flux and magnetically nonlinear anisotropic media. Elliptical polarizations of magnetic flux and constitutive relations for anisotropic media are treated as perturbations of circular polarizations of the magnetic flux and constitutive relations for isotropic media, respectively. By using the mathematical machinery of perturbation technique, simple expressions for electromagnetic fields are derived and applied to the calculation of eddy current losses.
Interaction between Fe, dopants, and secondary defects in MeV Fe ion implanted InP
Authors: Gasparotto Andrea , Carnera Alberto , Frigeri Cesare , Priolo Francesco , Fraboni Beatrice , Camporese Andrea , Rossetto Gilberto
Published: July 2002

We investigate the role of damage production and annealing in determining the Fe redistribution properties when implanting Fe at MeV energies in n-type InP. Fe ion implantation is performed at 2 MeV on (100) InP substrates, both undoped and Sn doped (1.5×1018 cm−3). Implants are performed both at room temperature (RT) and at 200 °C (HT), with doses ranging from 1×1013 to 1.2×1015 cm−2. A double implantation experiment is also performed, coimplanting Fe and P to investigate the influence of the P induced damage on the Fe redistribution/accumulation. Annealing is performed in the temperature range between 650 and 800 °C using flowing phosphine to prevent surface decomposition. To characterize the damage of our samples before and after annealing we employ Rutherford backscattering spectrometry in channeling condition and transmission electron microscopy; Fe depth profiles are measured by secondary ions mass spectrometry. A strict correlation is found between the position of Fe accumulation peaks and that of secondary defects formed in RT implanted samples during annealing; in particular it is shown that end of range dislocation loops and interfaces between damaged and undamaged crystal regions act as gettering sites for Fe atoms. The accumulation process is controlled by Fe diffusion that is greatly enhanced by the presence of mobile point defects related to the implantation damage; on the contrary it is shown that Sn doping has a strong retarding action on Fe diffusion. It is demonstrated that the strong reduction in damage production related to dynamic annealing in HT implantation can be used to reduce or avoid Fe redistribution/accumulation phenomena, leading to fairly stable implantation profiles also for high annealing temperatures and long annealing times.
Quantum size and composition effects in photoacoustic spectra of FexZr1−xO2 clusters
Authors: Liu F. X. , Zhang X. Y. , Wu Q. , Liu L. , Wang J. Y. , Su Q. D.
Published: July 2002

The quantum size and composition effects on the optical properties of FexZr1−xO2 (x=0, 7.5, 15, and 35 wt %, respectively) clusters were studied by measuring their photoacoustic spectra at room temperature. We observed a concomitant smearing of the band gap, narrowing the effective gap of the grains with increasing iron content. These phenomena are attributed partly to the formation of a separate Fe2O3 phase, likely residing at the grain boundaries. The appearance of five spectral bands may be ascribed to the electronic transition of the Fe3+ centers in the samples from the ground level to five excitation states. The exciton peaks occur and shift towards blue, which can be explained by the quantum size effect. The absorption edges exhibit a red shift with increasing Fe content due to the Burstein’s effect.
The interface formation of copper and low dielectric constant fluoro-polymer: Plasma surface modification and its effect on copper diffusion
Authors: Du M. , Opila R. L. , Donnelly V. M. , Sapjeta J. , Boone T.
Published: July 2002

The bulk and surface diffusion of Cu deposited on a treated low dielectric constant fluoropolymer (FLARE™ 1.0, AlliedSignal) was studied using x-ray photoelectron spectroscopy. Copper was found to be relatively unreactive on untreated, N2 and O2 plasma treated, and Ar+ sputtered surfaces. Shifts in the Cu 2p3/2 binding energy showed that larger Cu islands formed when Cu was evaporated on the untreated surface. Because sputter deposition of Cu damaged the fluoropolymer and formed nucleation sites for Cu islands, many smaller islands were found for Cu sputter deposited on untreated polymer. The competition between bulk and surface diffusion also plays a role in Cu island size: Plasma treatments and sputtering limit diffusion of Cu into the bulk of the polymer below the glass transition temperature Tg. The plasma treatments increase the surface reactivity and the plasma treatments and sputtering increase the cross linking in the surface region. Above Tg, no treatment was found to effectively limit diffusion into the bulk. Bulk diffusion during Cu deposition, however, is found to limit island size.
Electrical and optical characterization of Er-doped silicon grown by liquid phase epitaxy
Authors: Cavallini A. , Fraboni B. , Pizzini S. , Binetti S. , Sanguinetti S. , Lazzarini L. , Salviati G.
Published: July 2002

We have carried out deep level transient spectroscopy (DLTS), optical DLTS, and capacitance–voltage measurements on liquid phase epitaxy-grown Er-doped Si to characterize the deep levels present in the material and to identify those related to dislocations and involved in the luminescence activity. The optical properties of the material have been studied by photoluminescence, cathodoluminescence investigations, and two emission lines, labeled A and B, have been found, line A being located at 0.806 eV. We have observed that an actual interaction occurs between dislocations and Er-related emitting centers.
Modeling the optical properties of fluorescent powders: Y1.91Eu0.09O3
Authors: Konrad A. , Almanstötter J. , Reichardt J. , Gahn A. , Tidecks R. , Samwer K.
Published: July 2002

A numerical model is developed to study the optical properties of phosphor powder coatings. The method derived uses a combination of ray tracing and Monte Carlo modeling which allows us to calculate the absorption, reflection, and transmission for the exciting ultraviolet radiation as well as for the emitted visible light. Size, shape, morphology, density of packing of the phosphor grains, and the roughness of the coating can be studied in detail with our model. Calculations for Y1.91Eu0.09O3 red phosphor powder layers used in commercial fluorescent lamps are presented. Good agreement with experiment was found.
Structural characterization of a lamellar W/Si multilayer grating
Authors: Jergel M. , Mikulı́k P. , Majková E. , Luby Š. , Senderák R. , Pinčı́k E. , Brunel M. , Hudek P. , Kostič I. , Konečnı́ková A.
Published: July 2002

A lamellar multilayer grating of the nominal normal and lateral periods 8 and 800 nm, respectively, was obtained by etching a planar amorphous W/Si multilayer up to the substrate. The specular reflectivity, grating truncation rods of nonzero orders, and a reciprocal space map of the scattered intensity close to the total external reflection were measured using the Cu Kα radiation. We demonstrate an extraction of real structural parameters of a fully etched periodic multilayer grating from fitting the measured truncation rods based on the matrix modal eigenvalue approach to the dynamical theory of reflectivity by gratings.
Modeling the optical constants of GaP, InP, and InAs
Authors: Djurišić Aleksandra B. , Rakić Aleksandar D. , Kwok Paul C. K. , Li E. Herbert , Majewski Martin L.
Published: July 2002

An extension of the Adachi model with the adjustable broadening function, instead of the Lorentzian one, is employed to model the optical constants of GaP, InP, and InAs. Adjustable broadening is modeled by replacing the damping constant with the frequency-dependent expression. The improved flexibility of the model enables achieving an excellent agreement with the experimental data. The relative rms errors obtained for the refractive index equal 1.2% for GaP, 1.0% for InP, and 1.6% for InAs.
Dependence of tunneling magnetoresistance on ferromagnetic electrode thickness and on the thickness of a Cu layer inserted at the Al2O3/CoFe interface
Authors: Sun J. J. , Freitas P. P.
Published: July 2002

The dependence of the spin tunneling magnetoresistance (TMR) on the ferromagnetic electrode thickness, tCoFe, and on the thickness of a Cu layer inserted at barrier/ferromagnetic (Al2O3/CoFe) interface is reported. Junctions were fabricated through contact shadow mask or microlithography. Junction TMR increases sharply from zero to a maximum value of 16.4% (shadow masks) with increasing tCoFe from 10 to 30 Å, or to 22% (microlithography) with increasing tCoFe from 6 to 20 Å, and then varies slightly up to tCoFe of 500 Å. The initial increase of TMR with tCoFe up to 30 Å results from the spin-polarization increase in CoFe. This is supported by the magnetization measurement of (Ta 150 Å/CoFe tCoFe)×n multilayers, where the magnetization of CoFe increases from near zero to its bulk value with increase of CoFe thickness from 10 to 40 Å. The incorporation of Cu layers at the Al2O3/CoFe (top electrode) interface decreases the TMR. However, junctions with a 40 Å thick Cu layer added at the Al2O3/CoFe interface still maintain a TMR signal of 1%. The bias voltage dependence of TMR does not vary with the Cu layer thickness added at Al2O3/CoFe interface, implying that it is not significantly dependent on the barrier/ferromagnetic interface.
Measurements of media jitter down to 0.2 μm track widths
Authors: Champion Eric J. , Tarnopolsky Giora J.
Published: July 2002

The design of high areal density recording systems requires a detailed understanding of how the signal-to-noise ratio depends on the system geometry. We have made measurements using various head-media combinations of the variation of the media jitter with recorded track width. An analogy is made between the width of these recorded micro tracks and an equivalent reader width. The results are then compared with the recording theory expectation that the jitter varies as the inverse square root of the read track width. For the two head-media combinations discussed in this article, the jitter exponents are found to be −0.34 and −0.43, respectively. The deviation from a −0.5 exponent can be correlated to nonuniformities in the micro-track profiles of the heads used in the measurement.
Experimental study of nonlinear transition shift and error rate degradation caused by thermal decay
Authors: Taratorin A. , Cheng D. , Marinero E.
Published: July 2002

It is demonstrated that the nonlinear transition shift (NLTS) increases with time in a thermally unstable medium. The measurements were performed using an experimental medium with low magnetic moment. The increase of NLTS during thermal decay can be explained by the density dependence of the decay rates. This density dependence of thermal decay rates is caused by demagnetization field from adjacent transitions. A random magnetization pattern demonstrates different amplitude decay at high and low densities, and an increased level of NLTS. Error rates of PRML channel were estimated before and after the thermal decay.
The effect of the switching rate dependence of coercivity on recording performance
Authors: Wachenschwanz David , Alex Michael
Published: July 2002

A technique was developed to determine the dynamic remanent coercivity, Hc,r, of the writing process using a spin stand to measure the fundamental signal harmonic as a function of write current. The technique also provides a measurement of the remanent-moment-thickness product, Mrt, as well as coercive squareness, S*. These measurements were compared with measurements done with a Kerr-effect magnetometer for various media having different alloy compositions and/or processing conditions. It was found that recording parametrics such as PW50 and media jitter correlated well with the dynamic coercivity at actual recording field switching rates. Measurements of adjacent track interference or “squeeze” were also found to have excellent correlation with the dynamic media coercivity.
Optical signatures from magnetic two-dimensional electron gases in magnetic fields to 60 T
Authors: Crooker S. A. , Rickel D. G. , Smorchkova I. P. , Samarth N. , Kikkawa J. M. , Awschalom D. D.
Published: July 2002

We present experiments in the 60 T long-pulse magnet at the Los Alamos National High Magnetic Field Lab focusing on the high-field, low temperature photoluminescence (PL) from modulation-doped ZnSe/Zn(Cd,Mn)Se single quantum wells. High-speed charge-coupled array detectors and the long (2 s) duration of the magnet pulse permit continuous acquisition of optical spectra throughout a single magnet shot. High-field PL studies of the magnetic two-dimensional electron gases at temperatures down to 350 mK reveal clear intensity oscillations corresponding to integer quantum Hall filling factors, from which we determine the density of the electron gas. At very high magnetic fields, steps in the PL energy are observed which correspond to the partial unlocking of antiferromagnetically bound pairs of Mn2+ spins.