bluuebunny/crossref_metadata_2025 huggingface dataset:
Four-domain twisted nematic liquid crystal display fabricated by reverse rubbed polyimide process
Authors: Chen J. , Bos P. J. , Johnson D. L. , Bryant D. R. , Li J. , Jamal S. H. , Kelly J. R.
Published: July 2002

In Appl. Phys. Lett. 67, 1990 (1995), we proposed a particularly simple four-domain (4-D) twisted nematic(TN) liquid crystal display(LCD) device, which is composed of two left-handed and two right-handed TN subpixels. The two members of each pair of same handedness subpixels are rotated 180° with respect to each other, resulting in four domains that spatially average one another optically to provide a wide angle of viewing with no gray scale inversion. The optical performance of the 4-D TN LCD was confirmed by studies of a test cell fabricated by a two-step SiOx oblique evaporation technique. In this article, we report the realization of our four-domain TN display by a reverse rubbing technique that should be suitable for mass production in the display industry. The optical simulation of our 4-D TN cell was performed and the effect of disclinations at subpixel boundaries on display contrast investigated. A simple model was developed to evaluate the stability of our 4-D structure.
Nitrogen doping concentration as determined by photoluminescence in 4H– and 6H–SiC
Authors: Ivanov I. G. , Hallin C. , Henry A. , Kordina O. , Janzén E.
Published: July 2002

Low-temperature photoluminescence (PL) spectroscopy is used for determination of the nitrogen doping concentration in noncompensated 4H– and 6H–SiC by comparing the intensity of nitrogen-bound exciton (BE) lines to that of the free exciton (FE), the latter being used as an internal reference. The results are compared with a previous work performed for the case of 6H–SiC only. A line-fitting procedure with the proper line shapes is used to determine the contribution of the BE and FE lines in the PL spectrum. The ratio of the BE zero-phonon lines (R0 and S0 in 6H, Q0 in 4H) to the FE most intensive phonon replica around 77 meV exhibits very well a direct proportional dependence on the doping as determined by capacitance–voltage (C–V) measurements for both polytypes. The use of fitting procedure which takes into account the real line shapes, the influence of the spectrometer transfer function, and the structure of the PL spectrum in the vicinity of the FE replica allows us determination of the N-doping concentration by PL for doping levels in the region 1014 cm−3–3×1016 cm−3 for 4H– and 1014 cm−3–1017 cm−3 for 6H–SiC. Above these levels the free-exciton related emission is not observable.
Diagnosis of high-brightness ion beams produced in point pinch diodes
Authors: Masugata Katsumi , Okuda Hisato , Yatsui Kiyoshi , Tazima Teruhiko
Published: July 2002

Diagnosis and evaluation have been carried out of the ion beam and anode plasma produced in a ‘‘point pinch diode.’’ From the measurement of a highly resolved Thomson-parabola mass spectrometer, the ions accelerated in the diode gap contain (a) protons, (b) highly ionized carbon and oxygen ions, and (c) singly ionized medium mass ions such as carbon, oxygen, CO+2, OH+, H2O+. Time-integrated x-ray and particle pinhole images show the spot size of the electron beam on the plasma to be less than 0.5 mm in diameter, in which fine structures are found with size less than 0.1 mm. A Kα satellite line of Al V is observed with a crystal spectrograph, which indicates the existence of Al4+ in the plasma.
Microstructural and physical properties of layered manganites oxides related to the magnetoresistive perovskites
Authors: Laffez P. , Tendeloo G. Van , Seshadri R. , Hervieu M. , Martin C. , Maignan A. , Raveau B.
Published: July 2002

A structural and magnetoresistance study of layered manganites with nominal formula Ln2−yA1+yMn2O7 (Ln=Nd, Pr) (A=Ca, Sr, Ba) is presented. A combination of electron diffraction and high resolution microscopy allows us to propose a structural model where two perovskite blocks are intergrown with one rock salt type layer. The average structure crystallizes in a tetragonal unit cell with lattice parameters a≊b≊ap c≊19.3 Å. Moreover, an orthorhombic distortion of the tetragonal cell with lattice parameters a≊b≊√ap and c≊19.3 Å has been evidenced for the calcium-based oxides. Different variants of the fundamental structure and intergrowth with the pseudocubic perovskite structure as well as stacking deviations are easily formed. The magnetoresistance effect is discussed in relation to the crystallographic data.
Radiation damage profiles of the refractive indices of He+ ion-implanted KNbO3 waveguides
Authors: Pliska Tomas , Solcia Carlo , Fluck Daniel , Günter Peter , Beckers Lutz , Buchal Christoph
Published: July 2002

The refractive index profile of na of ion-implanted potassium niobate (KNbO3) planar waveguides is evaluated for waveguides fabricated with ion energies between 2.0 and 3.5 MeV and doses between 7.5×1014 cm−2 and 3.0×1015 cm−2. The measured mode index values are fitted to a quantitative model that correlates the index profile with the irradiation parameters. The reconstructed profile of na is compared to the profiles of nb and nc which have been determined previously.
Photoelectric properties of GaSb Schottky diodes
Authors: Rotelli B. , Tarricone L. , Gombia E. , Mosca R. , Perotin M.
Published: July 2002

Electrical and photoelectrical properties of GaSb Schottky diodes obtained by evaporating gold metal dots on sulphur treated or chemically etched surfaces of Te-doped n-GaSb crystals (grown from melt by Czochralski method), with Hall carrier density in the range of 1.8–6.5×1017 cm−3, were studied. J/V characteristics with an ideality factor ranging between 1.17 and 1.22 were measured on Schottky diodes prepared on sulphur passivated surfaces. After image force effect correction, photoelectric determination of the barrier height (qΦb=0.598±0.006 eV) has been found to be independent of the surface treatment and, in the case of the sulphur-treated diodes, in good agreement with the value obtained through C−2 vs reverse bias measurements (qΦb=0.6±0.01 eV). Through spectral response analysis of Schottky diodes, an estimation of minority carrier diffusion length value is given. A major role of sulphur passivation on preparation of Schottky barrier with good and well reproducible electrical properties is confirmed.
Capillary instabilities of a catenoidal hole in a solid film
Authors: Wong Harris , Voorhees Peter W. , Miksis Michael J. , Davis Stephen H.
Published: July 2002

Holes formed in a solid film during annealing can grow and lead to the formation of many isolated islands. The morphological evolution of holes is thus of primary importance in the production of planar films. This work studies the linear instability of a stationary axisymmetric hole in a film with zero surface mean curvature. At the hole, the film forms a contact angle α with the substrate at a circular contact line of radius a0. The film is bounded by an outer wall at a distance a0L from the center. An infinitesimal disturbance in the form of a normal mode is applied and its stability analyzed for 0⩽α⩽180° and 1⩽L<∞. Capillarity-driven surface diffusion is taken to dominate the mass transport. As L→1, the film is a ring that is unstable to periodic disturbances along the ring. For an unbounded film with L→∞, only axisymmetric disturbances can grow, and the growth rates become independent of L or the boundary conditions at the outer wall. This instability persists even when the film is “flat” in the limit α→0, in contrast to the stability results of a uniform film without a hole. The growth rates agree qualitatively with those observed in experiments.
Shapes of agglomerates in plasma etching reactors
Authors: Huang Fred Y. , Kushner Mark J.
Published: July 2002

Dust particle contamination of wafers in reactive ion etching (RIE) plasma tools is a continuing concern in the microelectronics industry. It is common to find that particles collected on surfaces or downstream of the etch chamber are agglomerates of smaller monodisperse spherical particles. The shapes of the agglomerates vary from compact, high fractal dimension structures to filamentary, low fractal dimension structures. These shapes are important with respect to the transport of particles in RIE tools under the influence electrostatic and ion drag forces, and the possible generation of polarization forces. A molecular dynamics simulation has been developed to investigate the shapes of agglomerates in plasma etching reactors. We find that filamentary, low fractal dimension structures are generally produced by smaller (<100s nm) particles in low powered plasmas where the kinetic energy of primary particles is insufficient to overcome the larger Coulomb repulsion of a compact agglomerate. This is analogous to the diffusive regime in neutral agglomeration. Large particles in high powered plasmas generally produce compact agglomerates of high fractal dimension, analogous to ballistic agglomeration of neutrals.
Anisotropic magnetoresistance in sputtered Co48Ag52 granular films
Authors: Mendes J. A. , Amaral V. S. , Sousa J. B. , Thomas L. , Barbara B.
Published: July 2002

Co 48 Ag 52 films prepared by sputtering at 77 K were characterized by magnetoresistance (MR) and magnetization. MR measurements give evidence for an important positive anisotropic magnetoresistance (AMR) in the as-deposited samples that reaches ∼11% at 15 K and saturates at H≈2 kOe. For higher applied fields the magnetoresistance is reversible and well described by a square Langevin function indicating a giant magnetoresistance behavior mostly due to superparamagnetic particles. The positive AMR becomes negligible after annealing at 350 °C for 10 min, probably due to stress relief.
Assembly and imaging of submicron ferromagnets in GaAs (invited)
Authors: Shi Jing , Awschalom D. D. , Petroff P. M. , Babcock K.
Published: July 2002

Submicron room-temperature ferromagnets are formed in GaAs semiconductors through a simple process of ion implantation and subsequent heat treatment. The ferromagnetic structures are studied using magnetic force microscopy. Magnetization switching of single-domain particles has been directly imaged in applied magnetic fields. In order to understand the images of magnetic structures taken under external fields, we have characterized the magnetic force microscopy (MFM) probes by imaging microfabricated current-carrying strips in applied magnetic fields. Patterned micrometer scale lines containing submicron magnetic structures on GaAs are fabricated using lithography in conjunction with broad beam ion implantation.
From demagnetizing to magnetizing interactions in CoFe–AgCu granular films
Authors: Franco V. , Batlle X. , Labarta A. , Watson M. L. , O’Grady K.
Published: July 2002

CoFe–AgCu granular films of compositions ranging from 0.17–0.44 ferromagnetic atomic concentration were prepared by rf sputtering. The microstructure and the transport and magnetic properties suggested that this family of samples can be classified into two groups with a crossover concentration at about 32 at. %. The experimental results for samples Co34Fe8Ag54Cu4 and Co18Fe8Ag70Cu4, which are representative of both different behaviors, are discussed. For the as-prepared sample with higher CoFe content, an uncompensated out-of-plane antiferromagneticlike microstructure with dominant demagnetizing interactions was observed. The particle growth through the annealing led to large in-plane ferromagneticlike clusters with dominant magnetizing interactions. The thermal dependence of the remanence-to-saturation ratio of the as-prepared and annealed samples indicated the existence of a high degree of magnetic correlations leading to a very low magnetoresistivity: In none of the cases was a Stoner–Wohlfarth behavior observed. On the contrary, for the sample with lower CoFe content, the magnetoresistivity change was much higher, and the remanence followed the expected behavior, since magnetic correlations were strongly reduced through dilution.
Stability of sulfur-treated InP surface studied by photoluminescence and x-ray photoelectron spectroscopy
Authors: Han I. K. , Kim E. K. , Lee J. I. , Kim S. H. , Kang K. N. , Kim Y. , Lim H. , Park H. L.
Published: July 2002

The degradation behavior of the sulfur-treated InP surface at relatively low temperature has been investigated with x-ray photoelectron and photoluminescence (PL) spectroscopy. The results showed that the treated surfaces were oxidized to In2O3, InPO3, and InPO4 at 250 °C and in a vacuum of 10−3 Torr for 20 min. As the holding time for S-treated InP under a vacuum of 10−3 Torr increased, the PL peak caused by the band edge transition decreased without the formation of oxides. It was therefore suggested that the decrease of the PL intensity for S-treated InP is only related to the generation of phosphorous vacancies at the surface, not to oxide formation. The usefulness of a thin S overlayer on III–V semiconductors was also discussed.
Anisotropies, cone states, and stripe domains in Co/Pt multilayers
Authors: Stamps R. L. , Louail L. , Hehn M. , Gester M. , Ounadjela K.
Published: July 2002

We present results for perpendicular uniaxial anisotropies obtained using torque magnetometry and magnetic force microscopy on epitaxially grown Co/Pt multilayers. A strong dependence of the two lowest order uniaxial anisotropies on Pt film thickness and temperature were observed. The possibility of an interfacial strain origin for the anisotropies due to lattice mismatch between the Co and Pt is discussed. A surprising result is the appearance of magnetic orientations at oblique angles with respect to the film plane and the surface normal. These orientations are identified as “cone states” and found to exist in limited ranges of Pt film thickness and temperatures. The temperature dependence is very unusual and controlled through the behavior of the lowest order perpendicular uniaxial anisotropies. The magnetization process was also examined in terms of saturation fields and domain formation. Narrow stripe domains with periods less than 100 nm were observed in the demagnetized state using magnetic force magnetometry and multilayer effects on the domain period and associated saturation fields were founds.
Piezoresistivity of polycrystalline p-type diamond films of various doping levels at different temperatures
Authors: Wang W. L. , Jiang X. , Taube K. , Klages C.-P.
Published: July 2002

The piezoresistivity of polycrystalline p-type diamond films has been studied. The films were grown by microwave plasma assisted chemical vapor deposition and in situ doped with different concentrations of boron. A four-point electrical measurement was performed to evaluate the film resistivity change upon straining in a four-point bending beam setup. Films were glued directly onto a stainless steel beam and the silicon substrates were selectively removed. A gauge factor (relative change of the resistivity divided by the elastic strain) of about 690 under 100 microstrains was obtained at room temperature for a film doped with 32 ppm boron. With increasing temperature and dopant concentration the gauge factor increases. The experimental results obtained are discussed.
Supercurrent distributions and flux penetration in YBa2Cu3O7–YBa2C o0.15Cu2.85O7–YBa2Cu3O7 edge junctions
Authors: Gausepohl S. C. , Lee Mark , Berkowitz S. J. , Mallison W. H.
Published: July 2002

We report the measurement and analysis of critical current (Ic) modulation and microwave response in magnetic field for a set of YBa2Cu3O7-YBa2Co0.15Cu2.85O7-YBa2Cu 3O7 ramp-edge Josephson junctions. These junctions have been fabricated with various widths w to span the transition from the moderately small (w<2λJ) to the moderately large (w>2λJ) junction limit at 77 K. As w increases, both the Ic modulation and microwave absorption behavior independently suggest a growing contribution from edge supercurrents. The addition of a superconducting ground plane was shown to reduce the edge supercurrent effects.
Deep electron states in n-type Al-doped ZnS1−xTex grown by molecular beam epitaxy
Authors: Lu Liwu , Ge Weikun , Sou I. K. , Wang Y. , Wang J. , Ma Z. H. , Chen W. S. , Wong G. K. L.
Published: July 2002

Capacitance–voltage, photoluminescence (PL), and deep level transient spectroscopy techniques were used to investigate deep electron states in n-type Al-doped ZnS1−xTex epilayers grown by molecular beam epitaxy. The integrated intensity of the PL spectra obtained from Al-doped ZnS0.977Te0.023 is lower than that of undoped ZnS0.977Te0.023, indicating that some of the Al atoms form nonradiative deep traps. Deep level transient Fourier spectroscopy (DLTFS) spectra of the Al-doped ZnS1−xTex (x=0, 0.017, 0.04, and 0.046, respectively) epilayers reveal that Al doping leads to the formation of two electron traps 0.21 and 0.39 eV below the conduction band. DLTFS results suggest that in addition to the roles of Te as a component of the alloy as well as isoelectronic centers, Te is also involved in the formation of an electron trap, whose energy level with respect to the conduction band decreases as Te composition increases. Our results show that only a small fraction of Al atoms forms nonradiative deep defects, indicating clearly that Al is indeed a very good donor impurity for ZnS1−xTex epilayers in the range of Te composition being studied in this work.
Imaging flaws in magnetically permeable structures using the truncated generalized inverse on leakage fields
Authors: Bruno A. C.
Published: July 2002

In order to image the magnetic source distribution inside a flawed magnetically permeable structure, the truncated generalized inverse and singular value decomposition were used. These techniques were applied to the magnetic flux leakage generated when the structure is magnetized. The leakage field from different flaw shapes was simulated by placing magnetic dipoles at the boundary surfaces, which reduces the flux density in the flawed structure. A criterion to establish the generalized inverse truncation index is proposed, by using the two-dimensional correlation coefficient between the original image and the reconstructed image. Others aspects such as the measurement signal-to-noise ratio, and density of the model source distribution are also discussed. This imaging technique was successfully applied to a number of different model flaw sources.
Electrical conductance simulation of two-dimensional directional site percolated networks for porous silicon structures
Authors: Yeh Everett C.-C. , Hsu Klaus Y.-J.
Published: July 2002

Two-dimensional porous silicon structures were modeled as two-dimensional directional site percolated networks (2D-DSPNs). In the present work, the 2D-DSPNs were modeled as resistive networks, and the electrical conductance values were numerically calculated. The effects of porosity and geometrical connection on the electrical conduction behavior were isolated and identified. It was shown that the geometrical connection of 2D-DSPNs makes the conduction behavior distinctly different from that in traditional random networks. A geometry anisotropic random walk model was developed to microscopically understand the macroscopic conduction behavior of 2D-DSPNs.
Growth of aluminum nitride on (111) silicon: Microstructure and interface structure
Authors: Bourret A. , Barski A. , Rouvière J. L. , Renaud G. , Barbier A.
Published: July 2002

The growth of hexagonal aluminum nitride directly on (111) silicon has been studied by grazing incidence x-ray diffraction and high resolution electron microscopy as a function of film thickness. Two epitaxial relationships were observed: (1) AlN (0001) [211¯0]//Si(111) [022̄], which prevails at deposition temperatures larger than 650 °C, and (2) AlN (0001) [101̄0]//Si(111) [022̄]. For a 40 Å thick layer, the average in-plane crystallite size is 162 Å, the in-plane rotation is ∼2° and the dislocations induce an average strain distribution of 0.8%. The Si/AlN interface is very sharp and complete relaxation (down to ∼0.2%) occurs within one bilayer. No long range order was observed at the interface. This implies a low mobility of the AlN species on Si, inhibiting any structural rearrangement. In particular the in-plane rotations originate from the early stage of the layer growth and decrease with the layer thickness, especially for thicknesses larger than 250 Å.
Phase profiles of microwave magnetic envelope solitons
Authors: Nash J. M. , Kabos P. , Staudinger R. , Patton C. E.
Published: July 2002

A new method for the analysis of microwave magnetic envelope (MME) solitons has been developed. This method is based on the determination and analysis of output microwave pulse phase profiles. Simple analytical results based on the nonlinear Schrödinger equation show that MME soliton phase profiles contain the necessary and sufficient information needed to define a particular pulse as a linear dispersive pulse or a fully formed soliton. The effects are demonstrated both theoretically and experimentally for magnetostatic backward volume wave and magnetostatic surface wave pulse signals. Theoretical phase profiles are considered for Gaussian, hyperbolic secant, and rectangular pulse shapes. Experimental profiles are obtained for rectangular input pulses. The measured phase profiles compare favorably with the numerical results. Both the data and the theory show that a constant phase profile across the pulse provides a consistent and quantitative criterion for an MME soliton.
Optical absorption in Hg1−xCdxTe
Authors: Nathan Vaidya
Published: July 2002

The theory of optical absorption due to interband transitions in direct-gap semiconductors is revisited. An analytical expression for the linear absorption coefficient in narrow-gap semiconductors is obtained by including the nonparabolic band structure due to Keldysh [Sov. Phys.–JETP 6, 763 (1958)] and Burstein–Moss shift. Numerical results are obtained for Hg1−xCdxTe for several values of x and temperature, and compared with recent experimental data. The agreement is found to be good.
NbN–Nb–Al superconducting tunnel junctions as photon counting detectors
Authors: Rando N. , Verhoeve P. , Poelaert A. , Peacock A. , Goldie D. J.
Published: July 2002

Asymmetric NbN–Nb–Al–AlOx-Al–Nb superconducting tunnel junctions have been investigated as photon counting detectors at x-ray and ultraviolet (UV)-visible wavelengths. The inclusion of a thin NbN passivation layer on the top electrode of the devices in place of the natural niobium oxides has reduced the quasiparticle loss rates, thereby enhancing the probability of multiple tunnel processes. As a consequence, the detector responsivity has increased from 900e−/eV, up to values in excess of 2000e−/eV in the temperature range 0.3–0.8 K. Such a responsivity level has allowed single photon counting performance at wavelengths as long as 700 nm and at operating temperatures as high as 830 mK. The devices show a linear response in the UV-visible range, while at 6 keV the expected nonlinearities in the energy response and moderate energy resolution similar to that found in Nb–Al junctions are observed.
Differential Preisach model for the description of dynamic magnetization processes
Authors: Andrei P. , Stancu Al. , Caltun O.
Published: July 2002

A differential dynamic Preisach model developed by us and introduced as an idea suggested by Bertotti is generalized. The starting point of this model is that the instantaneous excess field due to the moving and dynamic processes can be approximated as a function of M and it’s variation rate dM/dt: F(M,dM/dt). Thus, we determine a differential equation for the magnetic susceptibility. The model’s parameters are found by an original identification method. As an application we simulate a simple electrical circuit and compare the results with the experimental data. A very good agreement between the measured and simulated data is observed.
Numerical study on localized defect modes in two-dimensional triangular photonic crystals
Authors: Sakoda Kazuaki
Published: July 2002

The eigenfrequencies and eigenfunctions of localized defect modes in two-dimensional triangular photonic crystals composed of circular dielectric rods were calculated by means of the numerical simulation of the radiation process of a virtual oscillating dipole moment. In addition to the excellent agreement between our result and the experimental observation by Smith et al. [J. Opt. Soc. Am. B 10, 314 (1993)], we could evaluate the dependence of the eigenfrequency on the size of the supercell used in the numerical calculation. The result was also compared with that of the plane-wave expansion method.
Small inductance approximation of phase locking in multijunction SQUIDs
Authors: Frank B. , Krech W. , Platov K. Yu.
Published: July 2002

We present a theoretical analysis of the dynamics of multijunction superconducting quantum interference devices (SQUIDs). The small inductance approximation allows to get analytical expressions for the Josephson phases and voltages, taking into account a finite value of the inductance of the SQUID cells. Contrary to most theoretical investigations which exploited the first-harmonic approximation approach, our results describe the behavior of the circuit for small values of the Josephson frequency as well. Analytical results have been shown to be in a good agreement with numerical simulations.
Effect of SiOx buffer layer on propagation loss in LiNbO3 channel waveguides
Authors: Lee Ching-Ting , Huang Chang-Ting , Chen Jieng-Yue
Published: July 2002

SiO x buffer layer is widely employed in metal-clad Z-cut LiNbO3 optical waveguides to prevent excessive propagation loss and disturbances induced by the direct loading of the metal on the guiding layer. The dependence of propagation loss in proton-exchange LiNbO3 channel waveguides induced by a SiOx buffer layer on the annealing time is studied using a nondestructive measurement method. These studies reveal that the propagation loss is degraded for annealing times of less than 3 h, while it can be improved by about 0.08 dB/cm for annealing times longer than 6 h. By extending the annealing time to 8 h, we demonstrate a propagation loss reduction of 0.09 dB/cm. The physical mechanisms, including surface roughness, refractive index changes, oxidation of the SiOx buffer layer, optical confinement, and surface scattering of the LiNbO3 channel waveguide are also investigated.
Nucleation processes during metalorganic vapor phase epitaxy of ZnSe on GaAs(001)
Authors: Funato Mitsuru , Aoki Satoshi , Fujita Shizuo , Fujita Shigeo
Published: July 2002

We investigate the nucleation processes of ZnSe grown on GaAs(001) by metalorganic vapor phase epitaxy (MOVPE). The growth of ZnSe begins with an initial exposure of GaAs to either a Zn or a Se precursor. The Zn-initiated growth initially develops through formation of anisotropic two-dimensional (2D) islands and then exhibits a transition to 2D layer-by-layer growth. In the Se-initiated growth, on the other hand, the initial 2D islands are isotropic and the thickness at which the growth mode changes to the layer-by-layer mode is thicker than that in the Zn-initiated growth. Three-dimensional growth does not occur in the present MOVPE, which is remarkably different from molecular beam epitaxy. The observed variation of the nucleation is explained in terms of the interface structures. On thick ZnSe layers, where the growth is free from the influence of the interface, several stages during 1 monolayer formation through 2D layer-by-layer growth are clearly observed.
Characterization of border trap generation in rapid thermally annealed oxides deposited using silane chemistry
Authors: Bhat Navakanta , Saraswat Krishna C.
Published: July 2002

The border trap generation under high field stressing has been characterized in rapid thermal annealed low pressure chemical vapor deposited gate oxides. The hysteresis in high frequency capacitance–voltage curve is used to characterize the border traps. It is shown that at least some of the border traps are not associated with trapped positive charge. The border traps are charged and discharged through electrons tunneling from and to the substrate. The hysteresis is independent of temperature confirming the tunneling model. The effects of different annealing ambients suggest that the border trap generation depends on the physical stress at the substrate interface, which is qualitatively measured using Fourier transform infrared spectroscopy. The border trap generation is attributed to bond breaking at the substrate interface by energetic electrons.
A least squares method for fitting diffusion data to the Whipple/Suzuoka equations for grain boundary diffusion
Authors: Shaw D. , Shaw T. L.
Published: July 2002

A least squares computational method, GBFIT, of fitting experimental diffusion data to the Whipple/Suzuoka equations for grain boundary diffusion is described. The basic equations have been extended to include diffusion within the grain boundary so that GBFIT is applicable to Harrison’s type B and/or C kinetics. GBFIT contains no approximations or assumptions, other than those made by Whipple, and requires the grain boundary half-width, a, the volume diffusivity, D, and anneal time, t, to be specified for a given data set. The fitting parameters are L, the half distance between parallel grain boundaries, and D′/D where D′ is the diffusivity in the grain boundary. Examples of the use of GBFIT are presented in which experimental diffusion profiles in polycrystals and bicrystals, taken from the literature, are analyzed.
Improved Monte Carlo method for the study of electron transport in degenerate semiconductors
Authors: Borowik Piotr , Thobel Jean-Luc
Published: July 2002

Standard Lugli–Ferry method for including Pauli principle in Monte Carlo simulations yields unphysical results when the system is strongly degenerate. For example, one finds that distribution function is higher than unity in low energy region. In this article we explain the origin of these errors. We propose simple correction in order to overcome these problems without significant increase of required computational resources. We applied our method to the study of electron transport in degenerate In0.53Ga0.47As at 77 K. We found good agreement between obtained results and theoretical Fermi–Dirac distribution in zero field limit.
In-plane uniaxial stress effects of AlGaAs/GaAs modulation doped heterostructures characterized by the transmission line method
Authors: Fung A. K. , Albrecht J. D. , Nathan M. I. , Ruden P. P. , Shtrikman H.
Published: July 2002

Transmission line method patterns were fabricated on AlGaAs/GaAs heterostructures to measure the effect of uniaxial stress on the heterojunction two-dimensional electron gas resistivity and the contact resistance. Uniaxial compressive stress was applied in the [110] and [11̄0] directions of heterojunctions fabricated on (001)-oriented GaAs substrates. Fitting the measured data to a lumped resistor model yielded normalized sheet resistivity stress coefficients of −3.2%/kbar and 12.6%/kbar for stress in the [110] and [11̄0] directions, respectively. From these coefficients we obtain a value for the piezoelectric constant e14 of Al0.4Ga0.6As to be −0.26 C/m2, which when linearly extrapolated to AlAs gives −0.40 C/m2 compared to the value −0.225 C/m2 calculated by Hübner [Phys. Status Solidi B 57, 627 (1973)].
Influence of temperature and phase transitions on the Urbach’s tails of absorption spectra for TlInS2 single crystals
Authors: Abay B. , Güder H. S. , Efeoǧlu H. , Yoǧurtçu Y. K.
Published: July 2002

Optical absorption spectra of TlInS2 single crystals were investigated in the temperature range of 10–340 K. The exponentially increasing absorption tails were explained as Urbach tails. TlInS2 single crystals exhibited five different convergent groups of lines ln α(E,T) having different convergence points of E0 and α0 between 120 and 340 K. Characteristic Urbach’s parameters such as steepness parameter [σ(T)], Urbach’s energy [Eu(T)], and effective phonon energy (hνp) were obtained as a function of temperature. σ(T) and Eu(T) exhibited a number of jump-like trends at the identified temperature regions. Jump-like changes of σ(T) and Eu(T) were explained to be due to the phase transitions (PTs) and contributions of electron–(exciton)–phonon interaction caused by exciton dissociation. The temperature dependence of the band gap (BG) exhibited six clearly distinct regions and differs from the temperature dependent BG behavior of known semiconductors. Absorption edge and band gap anomalies in TlInS2 samples at PT were interpreted using the theory proposed by Zametin [Phys. Status Solidi B 124, 625 (1984)]. Measured BG jumping values, ΔEgα, are greater than those calculated from this theory in the 340–200 and 175–120 K regions, while one of them is smaller than that of the calculated in the 198–180 K region. These differences were explained as due to PTs and simultaneous influence of phonon coupling with electrons (excitons) induced by exciton dissociation, and the existence of the chaotic states caused by the coexistence of different phases which have opposite sign contributions below the ferroelectric phase transition, respectively.
Back-channel-oxidized a-Si:H thin-film transistors
Authors: Takechi Kazushige , Hirano Naoto , Hayama Hiroshi , Kaneko Setsuo
Published: July 2002

We have developed a back-channel-oxidized thin-film transistor (TFT) structure which does not require the conventional etching of the n+-a-Si:H layer from the channel region. Key processes in the fabrication of this structure are the deposition of a very thin (less than 10 nm) n+-a-Si:H layer with low resistivity (∼50 Ω cm), and an oxygen plasma treatment to change the n+-a-Si:H layer above the channel region into dielectric oxide. With a thin (∼50 nm) a-Si:H layer, the back-channel-oxidized TFT structure makes it possible to obtain much better “ON” characteristics than are obtained with conventional channel-etched TFTs. To gain insight into the underlying physical mechanism we investigated the back-channel electrical characteristics of both types of TFTs as a function of temperature, and found that back-channel-oxidized TFTs had much better back-channel characteristics than channel-etched TFTs, which is due to a lower density of back-channel interface states.
Coplanar amorphous silicon thin film transistor fabricated by inductively coupled plasma chemical vapor deposition
Authors: Kim Sung Ki , Choi Young Jin , Cho Kyu Sik , Jang Jin
Published: July 2002

The electrical and optical properties of the hydrogenated amorphous silicon (a-Si:H) films deposited by inductively coupled plasma (ICP) chemical vapor deposition (CVD) have been investigated. The ICP-CVD a-Si:H films deposited at the pressure of 30 mTorr exhibited the hydrogen content of 17 at. %, a photosensitivity of 106 at 100 mW/cm2 and a conductivity activation energy of 0.9 eV. A novel coplanar self-aligned a-Si:H thin film transistor was fabricated using Ni-silicide gate and source/drain electrodes. The simultaneous Ni-silicide formation of gate and source/drain regions using the stacked layers of thin a-Si:H, silicon nitride (SiNx) and a-Si:H reduces the offset length between gate and source/drain, which leads to the coplanar a-Si:H thin film transistor (TFT). This self-aligned a-Si:H TFT exhibited a field effect mobility of 0.44 cm2/V s, threshold voltage of 5.3 V and subthreshold slope of 0.5 V/dec. The coplanar geometry reduces the parasitic capacitance and parasitic resistance compared with those of conventional staggered a-Si:H TFTs.
Surface structures and electronic states of clean and (NH4)2Sx-treated InAs(111)A and (111)B
Authors: Ichikawa S. , Sanada N. , Utsumi N. , Fukuda Y.
Published: July 2002

The surface structures, unoccupied and occupied electronic states, and chemical states of surface atoms for clean and (NH4)2Sx-treated InAs(111)A and (111)B surfaces have been studied using low-energy electron diffraction (LEED), inverse photoemission spectroscopy (IPES), and (x-ray and ultraviolet) photoemission spectroscopy (PES). Thermal stability of the treated surfaces upon annealing in an ultrahigh vacuum is also investigated. A diffuse (1×1) LEED pattern appears for the treated -(111)A and -(111)B surfaces annealed at 230 and 330 °C, respectively, Upon annealing the (111)B sample at 380 °C, the (1×1) structure remains and the LEED spots become clearer. For the (111)A annealed at 380 °C, the pattern changes to a clear (2×2) structure which is found for the first time for sulfurized (111) surfaces of III–V compounds. Sulfur is completely desorbed from both the (111)A and (111)B surfaces at 440 °C, exhibiting the (2×2) and (1×1) structures, respectively. IPES and PES results indicate that unoccupied and occupied dangling bonds disappear for the sulfur-adsorbed (111)A-(2×2) and (111)B-(1×1) surfaces, respectively. S 2p spectra show that sulfur is bonded to both indium and arsenic on the (111)B surface annealed at less than 340 °C and bonded only to indium at 420 °C. On the other hand, it is bonded solely to indium on the (111)A surface with and without annealing. Surface core-level shifts of In 4d and adsorption sites of sulfur are discussed.
Bulk oxide traps and border traps in metal–oxide–semiconductor capacitors
Authors: Fleetwood D. M. , Winokur P. S. , Riewe L. C. , Reber R. A.
Published: July 2002

Thermally stimulated current (TSC) and capacitance–voltage measurements are combined via a newly developed analysis technique to estimate positive and negative oxide-trap charge densities for metal–oxide–semiconductor (MOS) capacitors exposed to ionizing radiation or subjected to high-field stress. Significantly greater hole trapping than electron trapping is observed in 3% borosilicate glass (BSG) insulators. Two prominent TSC peaks are observed in these BSG films. A high-temperature peak near 250 °C is attributed to the Eγ′ defect, which is a trivalent Si center in SiO2 associated with an O vacancy. A lower temperature positive charge center near 100 °C in these films is likely to be impurity related. The higher temperature Eγ′ peak is also observed in 10, 17, and 98 nm thermal oxides. A much weaker secondary peak is observed near ∼60 °C in some devices, which likely is due to metastably trapped holes in the bulk of the SiO2. Negative charge densities in these thermal oxides are primarily associated with electrons in border traps, which do not contribute to TSC, as opposed to bulk electron traps, which can contribute to TSC. Ratios of electron to hole trap densities in the thermal oxides range from ∼30% for radiation exposure to greater than 80% for high-field stress. It is suggested that the large densities of border traps associated with trapped holes in these devices may be due to high space-charge induced electric fields near the Si/SiO2 interface. In some instances, border traps can reduce near-interfacial electric fields by local compensation of trapped positive charge. This may provide a natural explanation for the large densities of border traps often observed in irradiated or electrically stressed MOS capacitors.
Sheath overlap during very large scale plasma source ion implantation
Authors: Cluggish B. P. , Munson C. P.
Published: July 2002

Measurements of plasma source ion implantation have been performed on a large target of complex geometry. The target consists of 1000 aluminum, automotive piston surrogates mounted on four racks; total surface area is over 16 m2. The four racks are positioned parallel to each other, 0.25 m apart, in an 8 m3 vacuum chamber. The racks of pistons are immersed in a capacitive radio frequency plasma, with an argon gas pressure of 20–65 mPa. Langmuir probe measurements indicate that the plasma density profile is highly nonuniform, due to particle losses to the racks of pistons. The plasma ions are implanted into the pistons by pulse biasing the workpiece to negative voltages as low as −18 kV for up to 20 μs. During the voltage pulse, the high-voltage sheaths from adjacent racks of pistons converge towards each other. At plasma densities less than 109 cm−3 the sheaths are observed to overlap. Measurements of the sheath overlap time are compared with standard analytic theory and with simulations run with a two-dimensional particle-in-cell code.
Junction properties of homoepitaxial diamond films grown by step–flow mode
Authors: Yamanaka S. , Watanabe H. , Masai S. , Kawata S. , Hayashi K. , Takeuchi D. , Okushi H. , Kajimura K.
Published: July 2002

Homoepitaxial diamond films with atomically flat surface were reproducibly grown by step–flow mode under the condition of less than 0.1% CH4/H2. Using these diamond films, high-quality Schottky junctions between Al and high-conductivity layer near the surface of the films have been successfully made. At 400 K, the ideality factor and the barrier height of the Schottky junctions, which are defined by the conventional junction theory, estimated from the current–voltage (I–V) characteristics are about 1.1 and 1.5–1.6 eV, respectively. Under the condition of more than 0.1% CH4/H2, however, many unepitaxial crystallites (UC) and pyramidal hillocks (PH) are often formed on the surface of the films which are even mainly grown by the step–flow mode. The Schottky junction properties become worse with an increase in the density of UC and PH. In particular, the increase in the saturation current, which was obtained by extrapolating the straight line to V=0 in a plot of ln I against V, correlated with Schottky barrier height is more sensitive than that of the ideality factor to the density of UC and PH. It is concluded that diamond films grown by the step–flow mode without UC and PH is essential to obtain an ideal Schottky junction.
Analytic framework for the modeling of effective media
Authors: Diaz Rodolfo E. , Merrill William M. , Alexopoulos Nicolaos G.
Published: July 2002

Synthetic materials in which new electromagnetic properties are obtained from the combination of two or more materials have been of theoretical and practical interest for nearly a century. The ability to explain and predict the properties of these materials has traditionally relied on combining physicomathematical models of the effective environment seen by the various constituents of the mixture with some assumptions about the way these microscopic properties should translate into macroscopic homogeneous parameters. Thus, even in the simplest case of the binary mixture, with every new set of assumptions, a new effective medium theory (EMT) results, and, with each new theory, stronger claims of correctness and applicability are made. This issue of correctness becomes critical when the properties of one of the constituents is unknown a priori and the claim is made that by inverting a fit of experimental results to the EMT model those properties can be ascertained. For this inverse procedure to be possible, the EMT theory should not only be correct, it should be unique in the analytic sense. In this article, a generalized framework is developed through which the analytic properties of all binary mixture EMTs can be deduced and compared. In the process it is shown that in the complex plane of the variable u=i/(εeff−1), it is straightforward to separate the morphology dependent properties of the EMT from its dependence on the susceptibilities of the components. The frequency dependence of the EMT model as a function of the arbitrary complex properties of the filler is easily summarized as a compact sum of the poles of a complex function. This process is demonstrated for a number of common EMTs.
The piezoresistance of aluminum alloy interconnect structures
Authors: Reilly Christopher J. , Sanchez John E.
Published: July 2002

The effects of applied strain on the resistivity of Al thin film metallization interconnects have been measured with a novel methodology that uses thermal expansion mismatch to produce the strain. The interconnect volumetric strain is induced by thermal cycling of passivated and unpassivated interconnects between ≈70 and 373 K. The coefficient of piezoresistivity, defined as dρ/dεv, where ρ=resistivity and εv=volumetric strain, is determined by properly accounting for the degree of interconnect constraint and thermal expansion mismatch strain induced during temperature changes. The volumetric strains are calculated for unpassivated and passivated lines of varying thickness and width. A model which incorporates the geometrical and piezoresistance effects on the measured interconnect resistance during temperature changes is described. The coefficient of piezoresistivity is calculated by a fitting procedure which provides an accurate and consistent fit for both unpassivated and passivated interconnects of different geometries and different strain states. The measured coefficient dρ/dεv is 2.0×10−5 Ω cm in tension, similar to earlier results in bulk Al samples measured in compression but significantly higher than values recently measured in Al interconnects. The application of the calibrated coefficient of piezoresistivity for the measurement of electromigration-induced stresses in novel interconnect test structures will be described.
Growth and characterization of PbSe and Pb1−xSnxSe on Si (100)
Authors: Sachar H. K. , Chao I. , McCann P. J. , Fang X. M.
Published: July 2002

PbSe and Pb1−xSnxSe layers, with thicknesses ranging from 1 to 5 μm, were grown by liquid phase epitaxy on Si (100) substrates using PbSe/BaF2/CaF2 buffer layers grown by molecular beam epitaxy. Optical Nomarski characterization revealed excellent surface morphologies and good growth solution wipeoffs. Although most PbSe layers were free of cracks over the entire 8×8 mm2 substrate area, ternary Pb1−xSnxSe layers exhibited varying crack densities ranging from zero in the center of samples to over 30 cracks/cm at the edges. High resolution x-ray diffraction (HRXRD) measurements of crack-free PbSe layers showed a residual in-plane tensile strain of 0.21% indicating that most of the 0.74% thermal expansion mismatch strain was absorbed by plastic deformation. HRXRD full width half maxima values of less than 200 arc sec showed that these layers also had high crystalline quality. Fourier transform infrared transmission measurements at room temperature and 110 K showed absorption edges in the range of 270–80 meV, depending on temperature and tin content. This work shows that these materials should be suitable for fabrication of mid-infrared devices covering the 4.6–16 μm spectral range.
Confocal micro-Raman characterization of lattice damage in high energy aluminum implanted 6H-SiC
Authors: Campos F. J. , Mestres N. , Pascual J. , Morvan E. , Godignon P. , Millán J.
Published: July 2002

High energy (MeV) and low dose aluminum implants were performed in p-type 6H-SiC at room temperature. The material was characterized by means of Rutherford backscattering in channeling configuration and confocal micro-Raman scattering. The damage induced changes in the optical absorption coefficient of the implanted layer can be extracted from the depth profiling of the first order Raman intensity of the undamaged portion of the sample, using a confocal microprobe setup. Optical modeling indicates the formation of two layers: an outermost and low absorbing layer with thickness proportional to the energy of the bombarding ions, and a more highly damaged and absorbing layer. Since the damage level is low, the disorder can be essentially removed by annealing at relatively low temperatures.