bluuebunny/crossref_metadata_2025 huggingface dataset:
On Schottky barrier inhomogeneities at silicide/silicon interfaces
Authors: Aboelfotoh M. O.
Published: July 2002

The Schottky-barrier heights of several silicides on both n- and p-Si(100) have been measured in the temperature range 77–295 K. The results deviate significantly from the predictions of a recent model based on the assumption of barrier height inhomogeneities at such interfaces. For all these interfaces, the sum of the barrier heights to n- and p-Si(100) is always equal, within the experimental accuracy, to the indirect band gap of Si. Furthermore, the temperature dependence of the barrier height suggests that the Fermi level at these interfaces is pinned relative to the Si valence-band edge.
Analysis of the strain profile in thin Au/Ni multilayers by x-ray diffraction
Authors: Chaudhuri J. , Gondhalekar V. , Jankowski A. F.
Published: July 2002

The strain relaxation in Au/Ni multilayers was analyzed in detail using a dynamical theory of x-ray diffraction. The depth profile of strain in the modulation direction was determined by an iterative fitting of the calculated rocking curve with the experimental one. The repeat periods of Au/Ni multilayers used in this study range from 0.82 to 9.0 nm. The analysis indicates that the theoretical x-ray patterns are extremely sensitive to the amount of strain at the interface.
Three-dimensional simulation of dye laser amplifiers
Authors: Takehisa K. , Nishimura H. , Miki A.
Published: July 2002

A time-dependent and three-dimensional dye laser amplifier simulation is presented. Its amplified spontaneous emission (ASE) is simulated by distinguishing the propagating directions of the angularly divided ASE, which makes it possible to simulate both the laser and ASE. Strong generation of the ASE is seen from the part of the excited volume where there is no input signal, indicating that ASE greatly depends on the input-beam geometrical profile, as well as its temporal matching with the pumping beam.
Modeling of agglomeration in polycrystalline thin films: Application to TiSi2 on a silicon substrate
Authors: Nolan T. P. , Sinclair R. , Beyers R.
Published: July 2002

An equilibrium model for agglomeration in polycrystalline thin films which considers the energy balance between the grain boundary energy and both surface and substrate interface energies is presented. It predicts that small grain size, low grain boundary energy, and high film surface and interface energies should promote resistance to agglomeration, and shows that the substrate-film interface can play a significant role in the process. It also predicts a critical grain size limiting formation of a discontinuous island structure. This easily calculable value is significantly smaller than that found in previous modeling. The critical grain size, the importance of the substrate interface, and some of the assumptions are shown to be consistent with transmission microscope observations of TiSi2 thin films deposited on Si substrates.
Crystallization and structural relaxation of amorphous FeNiSiB alloys due to rapid heating
Authors: Kopcewicz Michal/ , Jackiewicz Ewa , Zal/uski Leszek , Zal/uska Alicja
Published: July 2002

The unconventional method of annealing of amorphous metals makes use of the Joule heat produced by passing electric current pulses. The effects induced in amorphous FexNi75−xSi10B15 and Fe80B20 alloys by rapid heating with a heating rate of 104 K/s are studied in detail as a function of alloy composition. The structural relaxation and the formation of crystalline phases were characterized by Mössbauer spectroscopy. Various crystalline phases were formed as a result of pulse heating in dependence on the relative contents of iron and nickel in the amorphous phase. The crystallization caused by pulse heating leads to crystallization products that usually differ considerably from those formed in conventional annealing. In particular the micro- and nanocrystalline materials can be formed in this way.
Exciton binding energy as a function of the well width
Authors: Hrivnák Ľ.
Published: July 2002

An empirical formula for the binding energy of an electron-heavy-hole exciton is proposed which modifies the known formula for the Wannier exciton binding energy in the case when the well width is smaller than the bulk diameter of the exciton. This formula is utilized in calculations of the peak wavelengths in photoluminescence spectra which correspond to the ground-state electron-heavy-hole exciton recombinations in Al0.3Ga0.7As/GaAs single quantum wells of various widths.
Re-evaluation of the derivatives of the half order Fermi integrals
Authors: Smith A. W. , Rohatgi A.
Published: July 2002

The Fermi integrals of half orders are important in the simulation of semiconductor transport processes. Several of these integrals (−1/2, 1/2, 3/2, 5/2) have been recently retabulated since the 1938 study by McDougall and Stoner [Phil. Trans. Roy. Soc. A 237, 67 (1938)], but the derivatives were not re-evaluated. The original integral values were calculated without the aid of high speed computers by using approximate series evaluation and tabulations of exponentials and zeta functions. In addition, a discrepancy was found in the literature since the original study in 1938. The second derivative of F1/2 has been mistakenly represented as being proportional to a Fermi integral of another order. This article tabulates the half order Fermi integrals from −1/2 to 5/2 over the reduced energy range −5 to 20 in 0.25 increments. The first two derivatives of F−1/2 are also calculated by numerical integration and tabulated to aid in interpolation. It is shown that the second derivative of F1/2 is not proportional to another Fermi integral. A suitable interpolation scheme is proposed to calculate the values of the Fermi integrals of various order to high accuracy over the total reduced energy range.
Determination of the zirconium site in zirconium-substituted Nd2Fe14B
Authors: Capehart T. W. , Mishra R. K. , Pinkerton F. E.
Published: July 2002

We report a direct determination of the Zr site in pseudoternary alloys with a nominal composition of Nd1.6Zr0.4Fe14B using extended x-ray absorption fine structure (EXAFS). Comparing the Zr EXAFS from these alloys to the Y EXAFS from Y2Fe14B and the Fe EXAFS from Nd2Fe14B reveals that the local Zr and Y environments are nearly identical, and quite disparate from the Fe environment. This finding, and results from x-ray diffraction and electron microscopy, lead to the conclusion that Zr is incorporated as a substituent for Nd in the Nd2Fe14B structure.
Effect of deep traps on the capacitance-voltage plots of Schottky barrier diodes: Application to the study of sputter-etched Ti-W/n-Si diodes
Authors: Bauza D.
Published: July 2002

Capacitance-voltage (C-V) plots in the form of 1/C2 versus voltage plots are universally used to extract the doping concentration and the barrier height of Schottky barrier diodes. These quantities are obtained assuming ideal conditions for the metal-semiconductor contact and a perfectly crystalline semiconductor. However, during processes such as sputter-metal deposition, sputter etching, or reactive-ion etching, the silicon surface is subjected to the bombardment of energetic particles which induces donorlike traps in the near–metal-silicon interface region. The effect of such traps on the meaning of the 1/C2-V plots is studied for the case of n-type silicon. The slope and the voltage axis intercept are evaluated as function of the parameters of the traps. The concentration of the traps will be assumed to decrease exponentially with the semiconductor depth, as widely observed for sputter-induced deep traps. It is found that the traps which neutralize at reverse bias induce distortion of the 1/C2-V plots so that the apparent doping concentration is reduced and the barrier height is overestimated. At large reverse bias, when the traps are ionized, the plot is simply shifted towards the negative voltages and the barrier height is lower than the real value. Experimental results obtained on Ti-W/n-Si Schottky barrier diodes sputter etched before metal deposition confirm the above results. It is also shown that the 1/C2-V plots allows the damage in the semiconductor to be evaluated.
Annealing of Cd-implanted GaAs: Defect removal, lattice site occupation, and electrical activation
Authors: Moriya N. , Brener I. , Kalish R. , Pfeiffer W. , Deicher M. , Keller R. , Magerle R. , Recknagel E. , Skudlik H. , Wichert Th. , Wolf H. ,   ISOLDE Collaboration
Published: July 2002

A systematic investigation of the behavior of Cd-implanted GaAs after rapid thermal annealing is presented. The use of various experimental techniques gives a detailed picture regarding the annealing process in the low-dose regime (1012 and 1013 cm−2) on a microscopic as well as on a macroscopic scale. Perturbed angular correlation experiments, using the radioactive probe 111mCd, yield information on the immediate environment of the Cd implant on an atomic scale. Rutherford backscattering channeling and photoluminescence spectroscopy give complementary information concerning the overall damage level in the implanted layer, Hall measurements are used to determine the degree of electrical activation of the implanted Cd acceptors. The outdiffusion of the implanted radioactive Cd atoms is also investigated. The removal of defects in the next-nearest neighborhood of the Cd atoms takes place after annealing at 700 K and is accompanied by a general recovering of the crystal lattice. Between 600 and 900 K more distant defects are removed. The observed outdiffusion of about one-third of the dopant atoms after annealing above 600 K is discussed in context with their partial incorporation in extended defects. Although already at 700 K, 80% of the implanted Cd atoms are on substitutional lattice sites with no defects in their immediate environment, an annealing temperature in excess of 1000 K is necessary to obtain electrical activation of the implants. It is concluded that compensating defects, present in ion-implanted GaAs, are the reason for the significantly higher temperature required for electrical activation as compared to the incorporation of the dopants on defect-free, substitutional lattice sites.
Cooperative behavior during ferroelectric transitions in KNO3 powder
Authors: Westphal M. J.
Published: July 2002

Experimental evidence of cooperative behavior during the ferroelectric phase transitions in granular and powder KNO3 at atmospheric pressure is presented. Three different experimental studies were performed in which phase transitions were detected and characterized by heat flow calorimetry: (1) the distribution of SiC powder in granular KNO3 was varied; (2) the volume fraction of SiC in powdered KNO3 was varied; and (3) pure KNO3 powder was thermally cycled. All three studies provided evidence of cooperative behavior between the KNO3 particles during the III-II phase transition. The cooperative behavior reduced the temperature range of phase III stability from ∼97–124 °C to that characteristic of bulk material (∼110–124 °C). Separate KNO3 particles behaved as individual ferroelectric domains, with each particle making the phase transition independently near the expected Curie temperature. Particles of KNO3 in intimate physical contact tended to behave cooperatively as a single large ferroelectric domain leading to sharper phase transitions more characteristic of single crystals. The degree of cooperative behavior was dependent upon the extent to which the individual particles were in physical contact. The absence of the III-II phase transition in KNO3 powder that has been reported in the literature can be understood from the results obtained using SiC powder to separate KNO3 particles during heat flow calorimetry measurements.
Energy distribution of slow trapping states in metal-oxide-semiconductor devices after Fowler–Nordheim injection
Authors: Kerber Martin
Published: July 2002

Slow trapping charges in metal-oxide-semiconductor capacitors resulting from Fowler–Nordheim injection are investigated by an improved static capacitance method which provides direct experimental evidence for slow charging traps and their energy distribution. After the initial clearing of charges directly caused by the stress condition, a significant amount of slow traps are left which can be charged and discharged by alternating the gate bias. The number of trap sites is found to slightly decrease during repeated charging and discharging. The prominent peak of slow traps is energetically located around that of conventional interface traps, indicating a close correlation of both types of traps.
Experimental and theoretical photoluminescence study of heavily carbon doped GaAs grown by low-pressure metalorganic chemical vapor deposition
Authors: Kim Seong-II , Kim Moo-Sung , Min Suk-Ki , Lee Choochon
Published: July 2002

Carbon (C) doped GaAs epilayers grown by low-pressure metalorganic chemical vapor deposition have been analyzed by photoluminescence as functions of hole concentration and temperature. We have obtained an empirical relation of the effective band gap shrinkage for C doped GaAs as a function of hole concentration, ΔEg=−2.17×10−8p1/3. The temperature dependent band gap energy of C doped GaAs with a hole concentration of 9.0×1019 cm−3 has been analyzed. The resulting band gap at 0 K is (1.422±0.005) eV. The photoluminescence spectra have been analyzed on the bases of the Halperin and Lax bandtail model and an effective energy dependent optical transition matrix element. We have shown that the intensity distribution position of the photoluminescence spectrum of the conduction band to the heavy hole valence band transition is clearly separated from the intensity distribution of the conduction band to the light hole valence band transition. The conduction band to the light hole valence band transition is very prominent in the photoluminescence emission spectra of heavily C doped GaAs, and particularly at low temperatures. We have suggested that the shoulder peak which appears on the higher energy side of photoluminescence spectra is mainly due to the conduction band to the light hole valence band transition. At room temperature, the shoulder peak disappears and the full width at half maximum of the photoluminescence spectra increases; this is in good agreement with experimental results.
On the relation between the Hugoniot elastic limit and the yield strength of brittle materials
Authors: Rosenberg Zvi
Published: July 2002

We derive a new relation between the Hugoniot elastic limit (HEL) of brittle materials and their compressive strength (Yc). This relation is based on Griffith’s yield criterion [Proceedings of the 1st Conference on Applied Mechanics, Delft, Holland (1924), p. 55] for brittle behavior in contrast with the traditional relation, which is based on the criteria of Tresca or von Mises. Our newly derived relation results in a larger ratio between the HEL and Yc, in agreement with all the experimental observations on polycrystalline ceramics.
Computer simulation of electromigration in thin-film metal conductors
Authors: Trattles J. T. , O’Neill A. G. , Mecrow B. C.
Published: July 2002

A model is presented for simulating electromigration in thin-film metal conductors. The backfluxes are calculated explicitly in each of the grain boundaries using concentration and stress gradients resulting from the initial electromigration flux. The stress-dependent diffusivity term is also directly included in the formulation. It is assumed that the main cause of the flux divergence is the grain structure of the conductor and that these divergences occur at the triple-point junctions of the grain boundaries. Time-to-failure and classic resistometric analyses of five conductors are performed. Results indicate that current-density exponent of n≊2 should be used in time-to-failure analysis. This is due to the localized stress migration and diffusion acting against the electromigration force throughout the period of the conductor lifetime. A direct correlation between the time to failure (TTF) and relative rate of resistance change Rrc was found when all conductors and stress conditions were considered together. This relationship is of the form TTF=0.223R−1.11rc and indicates that resistance measurements can be used in producing lifetime parameters for use in providing reliability rules for conductor design.
Ferromagnetism of YFe2Hx
Authors: Kanematsu Kazuo
Published: July 2002

Isothermal hydrogen absorption of YFe2 at several temperatures forms four types of hydrides: δ, γ, β1, and β2. The δ hydrides with an orthorhombic MgCu2-type structure, YFe2H4.1, are ferromagnets of 3.8μB/f.u. (YFe2H4.1) and Tc=310 K. The Mössbauer spectrum is analyzed with the direction of magnetization along [111]. The γ hydride YFe2H2.4 is a rhombohedral-type ferromagnet of 3.5μB/f.u. and Tc=500 K. The spectrum is analyzed with the direction of magnetization along the c axis. Both β1 hydride YFe2H1.9 and β2 hydrides YFe2H1.3 are rhombohedral-type ferromagnets of 3.5μB/f.u. and Tc=570 K. The β1 hydride shows a smooth decrease of magnetization but the β2 hydride shows a large decrease of magnetization between 200 and 400 K. The Mössbauer spectra of both hydrides are analyzed with the direction of magnetization in the c plane. The magnetization decrease in the β2 hydride is discussed, assuming high- and low-magnetization phases.
Calculation of the temperature dependence of the giant MR and application to Co/Cu multilayers
Authors: Duvail J. L. , Fert A. , Pereira L. G. , Lottis D. K.
Published: July 2002

Most theoretical models of the giant magnetoresistance (GMR) in metallic magnetic multilayers developed up to now are for the zero-temperature limit, thus neglecting the spin-flip scattering arising from spin fluctuations (magnons), as well as other scatterings from thermal excitations. To account for the temperature dependence of the GMR, we have introduced electron–magnon and electron–phonon scattering terms in a Camley–Barnas-like semi-classical model. We apply our calculation to the interpretation of the temperature dependence of the resistivity and GMR in Co/Cu.
Plasma-deposited silicon nitride on ultrathin silicon oxide films investigated by infrared grazing internal reflection spectroscopy
Authors: Balz T. , Brendel R. , Hezel R.
Published: July 2002

Ultrathin silicon nitride films of 0.4–4.0 nm thickness prepared by remote plasma-enhanced chemical-vapor deposition (RPECVD) and direct plasma-enhanced CVD (DPECVD), respectively, are investigated by infrared grazing internal reflection spectroscopy. The ultrathin silicon nitride films are deposited on top of a 1.3 nm silicon oxide film thermally grown on crystalline silicon. From the spectra it is concluded that the vibrational properties of the 1.3 nm silicon oxide layer have strongly changed after deposition of a thin DPECVD silicon nitride, while the vibrational properties of the 1.3 nm oxide are nearly unchanged after deposition of a RPECVD silicon nitride film. The infrared spectra are analyzed by simulating the measured spectra with a dielectric function model that accounts for the amorphous film structure. An analytic formula for this dielectric function model is derived.
Pseudomorphic high electron mobility transistor channel sheet charge measured by photoluminescence
Authors: Parsons C. A. , Kim M. H. , Quinn W. E. , Herrmann H. B. , Swirhun S. E. , Brierley S. K.
Published: July 2002

Nondestructive room temperature photoluminescence of the InGaAs channel of a pseudomorphic high electron mobility transistor is presented as a function of bias applied to a semitransparent gate. The channel electron sheet concentration is evaluated via line-shape fitting of the photolumin- escence spectrum. Excellent agreement with electrically derived values of the channel charge was found. Information on the symmetry of the channel potential is also provided by the results of the photoluminescence line-shape fit.
Ar+-ion milling characteristics of III-V nitrides
Authors: Pearton S. J. , Abernathy C. R. , Ren F. , Lothian J. R.
Published: July 2002

Ion milling of thin-film GaN, InN, AlN, and InGaN was performed with 100–500 eV Ar+ ions at beam angles of incidence ranging from 0° to 75° from normal incidence. The mill rates normalized to the Ar+ beam current for the single-crystal GaN, AlN, and InGaN were typically a factor of 2 lower than for GaAs and InP. For the polycrystalline InN, the mill rates were similar to those of GaAs and InP. The surface morphology of the ion-milled nitrides was smooth even at 500 eV Ar+ energy, with no evidence for preferential sputtering of the N, a result confirmed by Auger electron spectroscopy. The surface region was not amorphized by extended ion milling (35 min) at 500 eV with the samples held at 10 °C, as determined by Rutherford backscattering. Since the ion mill rates are slow for single-crystal nitrides and less than the mill rates of common masking materials (SiO2, SiNx, photoresist) it appears this technique is useful only for shallow-mesa applications, and that dry etching methods involving an additional chemical component or ion implantation isolation are more practical alternatives for device patterning.
Schottky diodes with high series resistance: Limitations of forward I-V methods
Authors: Aubry V. , Meyer F.
Published: July 2002

Some methods have been proposed to deduce the value of Schottky parameters from forward I-V characteristic even in the presence of a large series resistance. In this paper, some well-known methods have been applied to experimental data of a real diode and to computer calculated curves. A comparison is made between these methods and the standard procedure. Some indications are given on the validity and the main limitations of all these techniques.
Magnetic force microscope study of local pinning effects
Authors: Barnes J. R. , O’Shea S. J. , Welland M. E.
Published: July 2002

A magnetic force microscope is used as a highly localized probe of the magnetic properties of Co-Pd multilayer films. The stray field from the magnetic tip is used to induce magnetization changes in the sample on a scale of the order of ∼100 nm. These changes are characterized by discontinuous jumps in the force or force gradient acting on the tip due to its interaction with the magnetostatic stray field from the sample. Both reversible and irreversible domain-wall motion is seen.
Optoelectronic characterization by photothermal deflection: Single-crystalline semiconductors
Authors: Grunow P. , Kunst M.
Published: July 2002

The use of the photothermal deflection (PD) technique for the characterization of semiconductors is investigated by measurements on crystalline silicon and CdS. The influence of the absorption profile and recombination at the back side is involved in the theoretical description and compared with experimental results. It is shown that reliable values for the electronic transport parameters can be determined. PD signals are relatively specific and enable one to assess the suitability of electronic transport models. The presence of nonlinear surface recombination due to space-charge fields can be deduced from the measurements of the deflection signal. Also, the inadequacy of linear volume recombination as a description for excess carrier decay in CdS is clearly observed.
Reduction of deep defect concentration in chlorine-doped ZnSe by after-growth thermal treatment
Authors: Hu B. , Karczewski G. , Luo H. , Bindley U. , Furdyna J. K.
Published: July 2002

Deep-level transient spectroscopy was applied for investigating the effect of after-growth annealing on the concentration of deep defects in Cl-doped ZnSe epilayers. The samples were grown by molecular beam epitaxy on (100)-GaAs substrates, employing ZnCl2 as the dopant source. The ZnSe:Cl epilayers were annealed in Zn-rich atmosphere at temperatures 400–650 °C for 18–60 h, respectively. As a consequence of the thermal treatment, the total concentration of deep defects in the material was significantly reduced. In particular, annealing almost completely eliminated the dominant defects in the as-grown material (located 0.51 eV below the edge of the conduction band), which strongly supports the identification of the origin of these defects as zinc-vacancy complexes. We also note that the annealing process introduces a small concentration of new defects. The activation energies for electron emission and capture of these traps are 0.24 and 0.17 eV, respectively, indicating that this level lies at 0.07 eV below the conduction band.
Structural and magnetic studies of FexCo1−x(001) alloy films on MgO(001) substrates
Authors: Mühge Th. , Zeidler Th. , Wang Q. , Morawe Ch. , Metoki N. , Zabel H.
Published: July 2002

Thin epitaxial FexCo1−x alloy films sputtered on MgO(001) substrates were studied by x-ray scattering and by the magneto-optical Kerr effect in order to investigate the structural phase stability induced by the substrate and to relate the magnetic properties to the alloy film structure. Alloy films with a thickness of about 20 nm and concentrations from x=1 to x=0.3 exhibit a bcc (001) growth with the in-plane [100] axis parallel to the MgO[110] axis. For pure Co (x=0) a fcc (001) structure with the Co[100] axis parallel to the MgO[100] axis was obtained. For x=0.15 no out-of-plane or in-plane Bragg peak could be observed, possibly due to the bcc-fcc structural phase transition. Kerr rotation angles in saturation as a function of x reveal a shape similar to the Slater–Pauling curve. Magnetic hysteresis measurements reveal a fourfold anisotropy with easy axes parallel to the FexCo1−x[100] crystal axis for 1≥x≥0.8, and parallel to the FexCo1−x[110] crystal axis for 0.7≥x≥0.3. In pure Co the easy axis lies parallel to the fcc-Co[110] crystal axis. Finally, for x=0.28 a step in the magnetic hysteresis in the FexCo1−x[11̄0] direction indicates an overlap of a fourfold and twofold magnetic anisotropy.
Reduction of surface particles on YBa2Cu3O7−∂ thin films through the use of nonstoichiometric sputtering targets and N2O in the sputtering gas
Authors: Johnson C. N. L. , Helmersson U. , Madsen L. D. , Rudner S. , Wernlund L.-D.
Published: July 2002

High quality YBa2Cu3O7−∂ (YBCO) thin films that combine good electrical properties and smooth surfaces without particles are important for many future applications. Today most films with good electrical properties have secondary phases in the form of copper-rich surface particles and small Y2O3 inclusions in the film. This work investigates how the surface particle coverage and superconducting properties of dc-magnetron sputtered thin films change as a function of target stoichiometry and the use of Ar:O2 or Ar:O2:N2O as sputtering gases. In an attempt to eliminate the copper-rich surface particles, sputtering was performed using targets deficient in copper (by up to 28%). However, only a small reduction in the number of the surface particles was achieved with an Ar:O2 sputtering gas mixture and little change in the superconducting properties was found. No new secondary phases could be detected. When nitrous oxide (N2O) was added to the sputtering gas, the superconducting properties deteriorated and Ba2CuO3 precipitates formed. To compensate for the usual Y2O3 formation in YBCO, yttrium-rich targets were also investigated. A significant reduction in the number of copper-rich surface particles was achieved when an Ar:O2 sputtering gas mixture was used and an yttrium-rich phase (possibly Y2BaCuO5) was detected. By incorporating N2O in the sputtering gas, the formation of copper-rich surface particles and the precipitates of the yttrium-rich phase was avoided and hence smooth films were deposited. No deterioration of the superconducting properties was observed in this case. It is concluded that the use of yttrium-rich targets and N2O in the sputtering gas may be a reliable way to achieve smooth films without surface particles and with satisfactory superconducting properties. It appears that the excess yttrium in the target compensates for the usual formation of Y2O3 inclusions and the N2O is needed to avoid barium desorption.
Deep-level transient spectroscopy and electrical characterization of ion-implanted p-n junctions into undoped InP
Authors: Martin Jaime M. , García S. , Mártil I. , González-Díaz G. , Castán E. , Dueñas S.
Published: July 2002

Current-voltage, small-signal measurements, and deep-level transient spectroscopy (DLTS) spectra of p-n junctions made by Mg implantation into undoped InP are described. The I-V characteristics show that the dominant conduction mechanism at forward bias is recombination in the space-charge zone, whereas a thermally activated tunneling mechanism involving a trap at 0.32 eV dominates at reverse bias. Five deep levels located in the upper-half of the band gap were detected in the junctions by DLTS measurements, three of which (at 0.6, 0.45, and 0.425 eV) were found to appear due to rapid thermal annealing. The origin of the other two levels, at 0.31 and 0.285 eV, can be ascribed to implantation damage. Admittance spectroscopy measurements showed the presence of three levels at 0.44, 0.415, and 0.30 eV, all in agreement with those found by DLTS. The DLTS measurements showed that the concentration of deep levels decreased after longer annealing times, and that the concentration of deep levels due to the implantation increased after additional P or Si implantations. This explains the influence of annealing time and additional implantations on the I-V characteristics of the junctions.
Photocurrent spectroscopy of 5-nm-wide InGaAs/InAlAs quantum wells and quadratic dependence of optical transition energies on quantum numbers
Authors: Kotera N. , Tanaka K. , Nakamura H.
Published: July 2002

A series of optical transitions between higher conduction subbands and higher heavy-hole subbands have been observed between 77 K and room temperature in photocurrent spectra of p-i-n photodiodes including 5-nm-wide InGaAs/InAlAs multi-quantum wells. The quadratic dependence of the transition energy on the heavy-hole quantum number, l=1,2 and 3, has been clarified for each conduction-electron quantum number, n=1 and 2. This experiment evidences the applicability of a particle-in-a-box model to the energy level determination. The carrier effective masses in InGaAs wells and the related band discontinuities were analyzed.
A mild electrochemical sulfur passivation method for GaAs(100) surfaces
Authors: Li Z. S. , Hou X. Y. , Cai W. Z. , Wang W. , Ding X. M. , Wang Xun
Published: July 2002

We have developed a mild electrochemical sulfurization technique which can form a very thick sulfide layer on GaAs(100) surface. This sulfide layer is quite stable in air. The photoluminescence spectrum of such anodic sulfurized GaAs surface shows a large intensity enhancement as compared with that of as-etched GaAs samples. No visual intensity decay occurs under the laser beam illumination after the sample has been maintained in air for more than seven months. The structure and composition of the passivation layers are investigated by x-ray photoelectron spectroscopy and the mechanism of layer formation is discussed.
Influence of negatively and positively charged scattering centers on electron mobility in semiconductor inversion layers: A Monte Carlo study
Authors: Gámiz F. , López-Villanueva J. A.
Published: July 2002

The effects of the presence of charged centers of different sign on the electron mobility in n-channel metal-oxide-semiconductor transistors are studied by a Monte Carlo simulation. By solving the Poisson equation for the potential fluctuations, an expression for the Coulomb-scattering rate when there are charged centers of different sign is provided. In addition, it is shown that, when charges of different sign exist in the structure, local band-bending fluctuations are greater, thus resulting in lower electron mobility. In contrast, since in this case the potential mean value is lower, the influence of the charged centers on the threshold voltage is lesser. The electron mobility in compensated substrates is also analyzed.
Electromagnetic scattering and absorption by finite wires
Authors: Waterman P. C. , Pedersen J. C.
Published: July 2002

The scattering from a thin conducting wire is computed by representing the induced current as a sum of driven and resonant terms, the latter with complex propagation constant mk perturbed from its free space value k. Using Galerkin’s method, the central problem of determining m reduces to a minimization problem. For the limiting cases of highly conducting or highly absorbing wires simplifications are found. For short wires the Rayleigh cross sections are obtained; for longer wires with high absorption, accurate cross section formulas are constructed based on the unperturbed infinite wire currents. For general wire lengths and conductivities the method is computationally very simple and results are in excellent agreement with independent computations of both current and far field quantities, as well as experimental measurements.
Critical thickness of InAs grown on misoriented GaAs substrates
Authors: Nabetani Y. , Wakahara A. , Sasaki A.
Published: July 2002

We grow InAs layers on (001) on-axis and misoriented GaAs substrates by molecular beam epitaxy, respectively. The critical thickness of each InAs layer is investigated with photoluminescence spectroscopy and transmission electron microscopy (TEM). We show that the critical thickness is significantly influenced by the substrate misorientation. The critical thickness of the InAs layer grown on the GaAs substrate misoriented toward the [11̄0] direction becomes thicker [5 monolayers (ML)] than that (3 ML) of the InAs layers grown on the GaAs substrates (001) on-axis or misoriented toward the [110] direction. The plan-view TEM images show that the islands grown coherently do not coalesce even beyond the on-axis critical thickness (3 ML). The strain energy is calculated based on valence-force-field model to investigate the interaction between dislocation and step in case on misoriented substrate. As results, we show that dislocation has the minimum length above which dislocation can stably exist and that the extra strain energy generated at the cross point of dislocation and step plays an important role in dislocation generation.
Pulsed laser ablation: A new route to synthesize novel superconducting compounds as oriented films
Authors: Gnanasekar K. I. , Sharon M. , Pinto R. , Pai S. P. , Rao M. S. R. , Apte P. R. , Tamhane A. S. , Purandare S. C. , Gupta L. C. , Vijayaraghavan R.
Published: July 2002

We report here the significance of the pulsed laser ablation technique in stabilizing strained lattices that do not form by the conventional ceramic method and show that the technique offers unique possibilities to probe the structure property relationship in complicated systems. One of such systems is LuBa2Cu3O7−δ; a systematic investigation of structural (in)stability of its superconducting phase is presented here. Our analysis suggests that the system suffers from internal strain due to lower ionic radius of Lu3+; however, the structure can be stabilized only as oriented films on 〈100〉 LaAlO3, 〈100〉 SrTiO3, and 〈100〉 MgO, with excellent superconducting properties (Jc≊5.0×106 A cm−2 at 77 K). We have also investigated similar compounds having their stability close to their crystallographic limit. The important feature of these metastable phases is that they grow only as oriented films. Free energy of epitaxial growth of strained films are investigated and a simple growth model is proposed based on our observation. Importance of this growth model in explaining the superconductor–normal-metal–superconductor type of junctions, observed in high-Tc superconductors is highlighted.
Nanomechanical basis for imaging soft materials with tapping mode atomic force microscopy
Authors: Howard A. J. , Rye R. R. , Houston J. E.
Published: July 2002

The surfaces of virgin and chemically etched poly(tetrafluoroethylene) (PTFE) have been studied using scanning electron microscopy (SEM), and atomic force microscopy (AFM) in both contact and tapping modes. Contact mode AFM images of this relatively soft polymeric material are dominated by tip-induced imaging artifacts. When subsequent, AFM imaging was performed in tapping mode these artifacts were eliminated, and comparable tapping mode AFM and SEM images were obtained for even the highly porous, unstable surface that results from sodium naphthalenide etching. Interfacial force microscopy force versus displacement, and creep experiments were performed to determine the nanomechanical nature of virgin PTFE. These experiments show that virgin PTFE is a viscoelastic material which is capable of supporting large forces on the millisecond time scale but creeps dramatically at longer times. Clearly, with scanning probe techniques which utilize constant probe force feedback, one should expect image distortions, as we observe, with soft materials such as virgin or etched PTFE. Conversely, with tapping mode AFM, rational images require contact times (μs) that are much shorter than creep times (ms). Thus, viscoelastic material characteristics determine the need for tapping mode AFM over contact mode AFM. By comparing tapping mode AFM images of virgin and etched PTFE surfaces, we can understand the three-dimensional character of the etched surface necessary for mechanical interlocking and resultant strong metal adhesion.
Analysis of current fluctuations in silicon pn+ and p+n homojunctions
Authors: Martín M. J. , Velázquez J. E. , Pardo D.
Published: July 2002

A detailed study of bipolar transport under forward-bias conditions is evaluated by Ensemble Monte Carlo simulation in two structures (p+n and pn+ junctions). The static characteristics of both structures are presented. In particular, this study focuses on a microscopic analysis of current fluctuations. A decomposition of the autocorrelation function of the total current fluctuations in electron, hole and crossed contributions is performed. In this way, the importance of each type of carrier in the spectral density of current fluctuations in both structures for a wide frequency range is determined. In the low frequency range, the presence of shot, thermal and excess noise was found. The Ensemble Monte Carlo method also permits ready evaluation of the noise equivalent temperature in both structures.
High-frequency magnetic properties in metal–nonmetal granular films (invited)
Authors: Ohnuma S. , Fujimori H. , Mitani S. , Masumoto T.
Published: July 2002

The structure and properties of Co–N and Co–O based films, prepared by rf magnetron reactive sputtering using nitrogen or oxygen and argon gases, have been studied. Transmission electron microscopy (TEM) observation reveals that each Co–(Al or Si)–(N or O) film is a typical film with granular structure, with grain size less than 5 nm. It is found by micro-focused energy-dispersive x-ray and electron energy loss spectroscopy analysis that the grains are mainly composed of Co and the intergranular regions are ceramics of N or O. In Co–N based films, soft magnetic properties are found in both Si and Al containing films over a wide range of film preparation conditions and compositions. Only the films with Al show soft magnetic properties in Co–O based films, which have ρ of 500–1000 μΩ cm, Hk of about 80 Oe and Bs of about 10 kG. By adding about 10 at. % Pd, the soft magnetic properties and Hk of Co–O based films are significantly improved, with Hk more than 180 Oe. These films exhibit a remarkable constant frequency response of the permeability up to around 500 MHz, which is approximately explained by the Landau–Lifshitz formula.
59Co and 55Mn NMR of CoMn alloys and multilayers
Authors: Thomson T. , Riedi P. C. , Wang Q. , Zabe H.
Published: July 2002

59Co and 55Mn NMR measurements have been made on a range of CoMn materials: dilute powder alloy, thin-film alloys, and multilayers. Our results suggest that in dilute alloys isolated atoms of Mn couple both ferro and antiferromagnetically to the Co host, with the latter producing a reduction in the magnitude of the Co hyperfine field of 17%. This reduction of hyperfine field appears similar for both the fcc and hcp phases of Co. NMR on Co/Mn sputtered multilayers shows large changes in the hyperfine field distribution between a film with Mn layers of 10 Å and Mn layers of 30 Å.
Effect of layered structures on the location of emissive regions in organic electroluminescent devices
Authors: Aminaka Ei-ichiro , Tsutsui Tetsuo , Saito Shogo
Published: July 2002

Effect of layered structures on the location of emissive regions was studied in four types of organic electroluminescent (EL) devices: a single-layered (SL) device consisting only of an emissive layer (EML), two types of double-layered (DL-H and DL-E) devices in which a hole-transport layer (HTL) or an electron-transport layer (ETL) is attached to an EML, and a triple-layered (TL) device in which an EML is sandwiched between a HTL and an ETL. As EML, HTL and ETL material, 9, 10-bis[4-(diphenylamino)styryl]anthracene, 4,4′-bis[(3-methylphenyl)phenylamino]biphenyl and 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxadiazolyl]phenylene, respectively, were used. Within EML layers, a thin sensing layer doped with a squarilium dye, 2,4-bis[4-diethylamino)-2- hydroxyphenyl]cycrobutenediylium-1,3-dioxide was inserted. The change in emission intensity from the dopant, when the location of the sensing layer was systematically varied, gave information on emissive regions in each type of EL device. The emissive region in the SL device extended through the EML, and that in the DL-H device resided near the HTL/EML boundary. On the contrary, those in the DL-E and TL devices were located within a 10-nm-wide region adjacent to the EML/ETL boundary. Moreover, the emission efficiencies of the DL-E and TL devices were found to be higher than those of the SL and DL-H devices. It was experimentally demonstrated that the carrier recombination within the narrow region adjacent to the EML/carrier transport layer boundary gave high emission efficiency.
Luminescence properties of heavily carbon doped GaAs
Authors: Lee Jeong-Seok , Kim In , Choe Byung-Doo , Jeong Weon Guk , Sin Y. K. , Min W. S.
Published: July 2002

Carbon-doped GaAs epilayers with concentrations as high as 1.8×1020 cm−3 were studied by photoluminescence (PL) spectroscopy. A shoulder is observed at 1.495 eV in 17 K PL spectrum of the heavily C-doped sample grown on semi-insulating substrate. But the shoulder occurs at different energies when the substrate conductivity is changed. The shoulder is found to originate from the substrate luminescence. Identifying the origin of the shoulder, the true Fermi level of p+-GaAs is determined and the band gap narrowing due to heavy doping is quantified.
Free to bound transition-related electroluminescence in 3C and 6H SiC p+–n junctions at room temperature
Authors: Yoganathan M. , Choyke W. J. , Devaty R. P. , Neudeck P. G.
Published: July 2002

The room temperature electroluminescence spectra of moderately nitrogen doped (1×1017 cm−3) 3C and 6H SiC p+–n junctions are studied as a function of forward current. The free to bound transition due to the unintentional, deep boron (defect) center is dominant at low forward bias, while the free to bound transitions due to nitrogen donors and aluminum acceptors are dominant at higher forward biases. These results can be explained using Shockley–Read–Hall analysis of the recombination rate as a function of bias. The origin of boron related electroluminescence is suggested to be primarily from recombination within the depletion region, while aluminum and nitrogen related electroluminescence is attributed to recombinations in the minority carrier injection regions.
Stability of Zn doping profile in modulation-doped multiple quantum well structure
Authors: Otsuka Nobuyuki , Ishino Masato , Matsui Yasushi
Published: July 2002

Stability of the Zn doping profile in InGaAs/InGaAsP modulation-doped multiple quantum well (MD-MQW) structures grown by low-pressure metalorganic vapor-phase epitaxy (MOVPE) has been investigated by secondary ion mass spectrometry and transmission electron microscope with wedge-shaped samples. Although excellent stability of Zn profile is confirmed in an as-grown sample with modulation doping (d=3 nm CZn=1×1018 cm−3), the modulation-doping structure diminishes after the second epitaxial regrowth of a p-InP layer (CZn=1×1018 cm−3) carried out by either liquid phase epitaxy or MOVPE, which is applicable for buried heterostructure lasers. However, the modulation-doping profile is successfully preserved even after regrowth of the p-InP layer for 90 min in a sample constructed of an undoped InP clad layer instead of a p-InP clad layer superposed on the MD-MQW layers. A Zn diffusion coefficient in the modulation-doped region is extremely small, having a value of less than 7×10−18 cm2/s. The maximum Zn concentration in the modulation-doped region in barrier layers was found to be 2×1018 cm−3 for obtaining a stable modulation-doping structure. It is proposed that the suppression of both interstitial Zn atoms and subsequently produced interstitial group III atoms, which are generated in the p-InP clad layer via a kick-out mechanism and diffuse into the MD-MQW region, is important for preserving modulation-doping structure.
Properties of TiN films deposited at low temperature in a new plasma-based deposition system
Authors: Hoang Nguyen Huy , McKenzie D. R. , McFall W. D. , Yin Y.
Published: July 2002

Stoichiometric titanium nitride (TiN) films were deposited at less than 130 °C in a new configuration of the helicon activated reactive evaporation system. An in situ ellipsometer was used to monitor the optical properties of the films during growth. The film stress, lattice parameter, surface roughness, crystallite size, and preferred orientation were investigated as a function of substrate bias and hence ion energy of the incident species. The intrinsic stress dependence on ion energy shows the expected result also shown by a variety of materials and is in good agreement with the theoretical model of Davis [Thin Solid Films 226, 30 (1993)]. The high stress level at −50 V bias is confirmed by measurement of lattice parameter. X-ray-diffraction measurements show that the (111)-preferred orientation normal to the substrate surface correlates strongly with the stress level of the films. By correlating our results with those from a number of other reported studies at higher substrate temperature we conclude that the observed preferred orientation in TiN films can be explained from the viewpoint of the energy minimization principle. Kinetic factors are of less importance except possibly at the highest bombardment energies.
Giant magnetoimpedance effect in nanocrystalline Fe74SixB22−xCu1Nb3 ribbons
Authors: Ueda Y. , Ikeda S. , Takakura W.
Published: July 2002

We investigated the magnetoimpedance (MI) effect for the soft magnetic nanocrystalline Fe74SixB22−xCu1Nb3 (x=4–18) alloys, and also the relationship between the magnetic properties and the MI effect. The annealing temperature dependence of the MI ratio corresponds to that of the permeability of longitudinal direction of the samples. However, the Si concentration dependence of the longitudinal permeability is different from that of the MI ratio. The maximum MI ratio and the highest field sensitivity for the sample with x=16 after annealing at 570 °C for 1 h are 67% and 23%/Oe, respectively. The MI effect is affected by the magnetic uniaxial anisotropy which is along the longitudinal direction of the ribbon samples.
Monte Carlo simulation of pulsed laser ablation from two-component target into diluted ambient gas
Authors: Itina T. E. , Marine W. , Autric M.
Published: July 2002

Laser ablation from a binary target into a diluted gas background is studied by means of a Monte Carlo simulation. The influence of the ambient gas on the spatial and mean energy distribution of particles deposited at the distant detector is considered. Thermalization of the particles, the random scattering effect and the backscattering of particles were observed. Considerable modification of the deposited film thickness profiles due to collisions of the ablated particles with the ambient gas is shown. The increase of the ambient gas pressure was found to affect the stoichiometry distribution of deposited and backscattered particles. The study is of a particular interest for the development of the thin film growing technique known as pulsed laser deposition.