bluuebunny/crossref_metadata_2025 huggingface dataset:
Gallium arsenide passivation through nitridation with hydrazine
Authors: Vogt Kirkland W. , Kohl Paul A.
Published: July 2002

Passivating films were grown on gallium arsenide by direct nitridation with hydrazine at 300–400 °C. Auger electron spectroscopy and x-ray photoelectron spectroscopy analysis show that the films are primarily gallium nitride with an oxide impurity. The oxide content is a function of the surface pretreatment, reaction temperature, and water concentration in the hydrazine. Improvements in the band gap photoluminescence with nitridation indicate a lower surface state density and reflect an improvement in the termination of the semiconductor lattice.
Band-edge optical absorption spectra of GaAs quantum wires calculated by multiband effective mass theory
Authors: Ando Hiroaki , Nojima Shunji , Kanbe Hiroshi
Published: July 2002

Optical absorption spectra of quasi-1D GaAs quantum well wires are theoretically investigated within the framework of multiband effective mass theory. In the calculation, the mixing of heavy-hole and light-hole bands resulting from both 1D quantum confinement and electron-hole Coulomb interaction is considered. Detailed excitonic structures in the absorption spectrum near the band edge are clarified by taking into account Coulombic bound states and unbound continuum states. Polarization dependence of the optical absorption spectra is discussed in terms of the band mixing effects.
Resonant tunneling structures with local potential perturbations
Authors: Burgnies L. , Vanbesien O. , Sadaune V. , Lippens D. , Nagle J. , Vinter B.
Published: July 2002

Self-consistent Schrödinger–Poisson model has been used to handle band-bending effects in resonant tunneling heterostructures with local potential perturbations. Simulation results are presented for a high-quality In0.1Ga0.9As/AlAs/GaAs double-barrier heterostructure in a triple well configuration which we also fabricated and tested. The samples exhibit state-of-the-art conduction characteristics for this material system with a peak-to-valley current ratio as high as 7:1 and a peak current density of 50 kA cm−2. These conduction characteristics are analyzed in terms of tunneling transitions between highly coupled quantum wells by calculating numerically the change in the local density of states due to a bias. Also, we discuss the validity of the Thomas–Fermi screening model which leads to unphysical jumps in the carrier density at heterointerfaces.
Impact ionization model for full band Monte Carlo simulation
Authors: Kamakura Y. , Mizuno H. , Yamaji M. , Morifuji M. , Taniguchi K. , Hamaguchi C. , Kunikiyo T. , Takenaka M.
Published: July 2002

The impact ionization rate in silicon is numerically derived from wave functions and energy band structure based on an empirical pseudopotential method. The calculated impact ionization rate is well fitted to an analytical formula with a power exponent of 4.6, indicating soft threshold of impact ionization rate, which originates from the complexity of the Si band structure. The calculated impact ionization rate shows strong anisotropy at low electron energy (ε<3 eV), while it becomes isotropic at higher energy. Numerical calculation also reveals that the average energy of secondary generated carriers depends linearly on the primary electron energy at the moment of their generation. A full band Monte Carlo simulation using the newly derived impact ionization rate demonstrates that calculated quantum yield and ionization coefficient agree well with reported experimental data.
Tail broadening of photocurrent transients in molecularly doped polymers
Authors: Borsenberger P. M. , Bässler H.
Published: July 2002

Tail broadening of nondispersive photocurrent transients has been measured in 1,1-bis(di-4-tolylaminophenyl)cyclohexane-doped polystyrene over a range of concentrations, fields, and temperatures. The results are described by the parameter W, defined as W=(t1/2−t0)/t1/2, where t1/2 is the time for the transient to decay to one-half of its plateau value and t0 the time defined by the intersection of asymptotes of the plateau and trailing edge of the transient. The interpretation of the experimental results leads to the conclusion that energetic disorder is the principal source of broadening of the transients.
Initial permeability of composite-anisotropy multilayer films
Authors: Shimada Yutaka , Sugawara Eishu , Fujimori Hiroyasu
Published: July 2002

Initial permeabilities of composite-anisotropy multilayer films were theoretically investigated. Calculation based on the Landau–Lifshitz relation predicts that the dipole-dipole coupling between the magnetic layers works in favor of Ku (in-plane uniaxial anisotropy) in each magnetic layer and that the initial permeability increases gradually as the spacer increases in thickness along with the gradual decrease of the resonance frequency. This calculation indicates that the dipole-dipole interaction suppresses fluctuation of the initial permeability caused by thermal change of Ku. These predictions are in agreement with the experimental results.
Steady state model for facet heating leading to thermal runaway in semiconductor lasers
Authors: Schatz R. , Bethea C. G.
Published: July 2002

A steady state model is presented which provides new insight into the thermal runaway process that leads to catastrophic damage of semiconductor lasers. We show that thermal runaway is preceded by a situation where two self consistent thermal steady state solutions exist at low output power, one stable and one unstable. When the output power is increased, the two solutions degenerate and disappear which means that the laser will enter thermal runaway. The steady state model consists of two parts: a three dimensional thermal model and a one dimensional model for the carrier diffusion towards the facet. The temperature dependence of both the heat sources and the thermal conductivity play the crucial role. Also ordinary bulk heating is shown to be an important factor. Both 0.88 μm GaAs lasers and 1.5 μm InGaAsP lasers are discussed and minimum values of surface recombination and output power needed for thermal runaway are given. Thermal runaway in GaAs lasers can be explained by the model for realistic values of surface recombination. However, the calculated values of needed output power are significantly higher than what is experienced in reality. Possible explanations for this discrepancy are given.
Properties of GaN films grown under Ga and N rich conditions with plasma enhanced molecular beam epitaxy
Authors: Botchkarev A. , Salvador A. , Sverdlov B. , Myoung J. , Morkoç H.
Published: July 2002

GaN growth mediated by electron cyclotron resonance activated nitrogen has been investigated under Ga and nitrogen rich conditions in a substrate temperature range of 650–850 °C. A biasable grid installed between the substrate and nitrogen flux allowed control of the nitrogen species participating in the growth process. The absence of high energetic ions resulted to films with increased photoluminescence signals in the 480–650 nm spectral range. In the Ga rich conditions, the Ga and N ion flux values used were 5×1014 and 3.5×1014 cm−2 s−1, respectively. The nitrogen rich conditions were achieved by increasing the N flux first to 8×1014 and then to 1.2×1015 cm−2 s−1. Both types of samples exhibited strong band edge photoluminescence signal at room temperature, with N rich conditions leading to better mobilities and lower carrier concentrations. The best films were obtained when the substrate temperature was 750 °C.
Line shape, linewidth and configuration coordinate diagram of the Cu band (1.21 eV) in InP
Authors: Pal D. , Bose D. N.
Published: July 2002

Photoluminescence (PL) measurements carried out between 10 and 140 K on Cu-diffused InP showed the presence of the Cu band at 1.216 eV. From the temperature variation of PL intensity the activation energy for the quenching was found to be 77.4 meV. The line shape, linewidth, and configuration coordinate diagram of the defect band have been calculated. The vibration energy of the excited state was found to be 14 meV from linewidth analysis. A coupled phonon energy of 38 meV and a Huang–Rhys factor of 2.13 were obtained from line-shape analysis. The displacement of the excited state minimum from the ground state was found to be 0.079 Å which showed that the lattice relaxation of the Cu-related defect in InP is small.
Hot-electron and thermal effects on the dynamic characteristics of single-transit SiC impact-ionization avalanche transit-time diodes
Authors: Joshi R. P. , Pathak S. , Mcadoo J. A.
Published: July 2002

We report our simulation results for the dynamic characteristics of single-transit SiC SiC impact-ionization avalanche transit-time (IMPATT) diodes. An iterative Monte Carlo–Crank-Nicholson technique has been used to solve the coupled electron transport-heat conduction problem. This procedure allows for accurate computation of both the device current as a function of temperature, time, and position, and the internal heat generation. The technique is quite general, has not been used before, and can be applied for the analysis of any power device. Our results show that the internal power generation profile within the SiC IMPATT device can have a very nonuniform axial distribution. The internal heating is seen to significantly degrade the device efficiency and optimum operating frequency. With thermal effects the output current values are lower and the transit time is increased.
Influence of thermal annealings in different atmospheres on the band-gap shift and resistivity of CdS thin films
Authors: Tomás S. A. , Vigil O. , Alvarado-Gil J. J. , Lozada-Morales R. , Zelaya-Angel O. , Vargas H. , Ferreira da Silva A.
Published: July 2002

We study by photoacoustic spectroscopy the band-gap shift effect of CdS films. The CdS films were grown by chemical bath deposition and exposed to different annealing atmospheres over a range of temperature in which the sample structure changes. We show the band-gap evolution and resistivity as a function of temperature of thermal annealing and determine the process that produces the best combination of high band-gap energy and low resistivity.
Energy transfer processes in Er3+- and Yb3+-doped infrared upconversion materials
Authors: Mita Yoh , Yamamoto Hajime , Katayanagi Kenji , Shionoya Shigeo
Published: July 2002

Luminescence characteristics in Er3+-ion activated, Yb3+-ion sensitized infrared upconversion materials have been investigated, especially for their energy back transfer processes from Er3+ to Yb3+ ions. Decay characteristics of Er3+ ion green emission have been examined in various fluoride crystals and fluoride glasses for the purpose of elucidating the energy transfer processes involved in the upconversion phenomena. It has been shown that decay characteristics of the green emission are sensitive to the host materials as well as Yb3+ concentration. The decay characteristics have been analyzed with a model taking into account configurations of Yb3+ ions around an Er3+ ion. It has been shown that the analyses present useful methods for characterizing energy transfer processes in materials containing higher amount of Yb3+ ions.
Arrhenius parameters and the compensation effect in crystallization and diffusion in amorphous Si:H(F) in the presence or absence of metal contacts
Authors: Khait Yu. L. , Weil R.
Published: July 2002

A kinetic many-body electron-related model of crystallization in a-Si:H(F) in the presence and absence of metal contacts is proposed. The model expresses the parameters of the formation of crystalline nuclei in terms of atomic and electronic material characteristics. The model is based on the kinetic electron-related theory of thermally activated rate processes in solids. The model considers picosecond atomic and electronic phenomena occurring in the nanometer vicinity of strongly fluctuating Si atoms executing diffusionlike jumps over energy barriers to more ‘‘ordered’’ positions which are associated with the formation of crystalline nuclei. The influence of random picosecond fluctuational heatings (coolings) in the nanometer vicinity of hopping atoms on the nucleation (crystallization) rate is considered. The following main results are obtained. (i) The Arrhenius-like equations for the nucleation time tN linking it with the Si self-diffusion in the metal/semiconductor interface are found from the kinetic consideration of the crystallization process, and are in agreement with experimental data. (ii) The Arrhenius activation energy ΔE and the pre-exponential factor t0N of the nucleation process are calculated.

They are expressed in terms of local parameters that characterize picosecond atomic and electronic processes which occur in the nanometer neighborhood of the hopping Si atoms. (iii) The ‘‘abnormally’’ large variations in the prefactor t0N (about 11 orders of magnitude) and the activation energy ΔE (a factor of 7.5) caused by metal contacts are explained. (iv) An explanation for a linear dependence between ln t0N and ΔE found experimentally in the crystallization in a-Si:H and a-Si:F is suggested. This dependence is known as the compensation effect (CEF). (v) Coefficients in the CEF equation and other kinetic parameters are calculated and expressed in terms of material characteristics, and are in good agreement with experimental data. (vi) An explanation for the large observed differences in the rate of nucleation in a-Si:H and a-Si:F is suggested. (vii) Causes for observed considerable differences in the effects of metals not forming and forming silicides on the crystallization are discussed. (viii) Si self-diffusion coefficients are calculated from the nucleation parameters in a-Si:H, a-Si:F, and in the metal/a-Si:H(F) interface for the following systems: a-Si:H/Al; a-Si:H/Pd; a-Si:F/Al; and a-Si:F/Pd.
CO2 laser-assisted removal of submicron particles from solid surfaces
Authors: Héroux J. B. , Boughaba S. , Ressejac I. , Sacher E. , Meunier M.
Published: July 2002

A CO2 laser-based system was used to provoke the vapor-assisted removal of contaminating particles from different kinds of surfaces. Particles of alumina, silicon carbide, boron carbide, and cerium dioxide, with a size as small as 0.1 μm, have been efficiently removed from silicon, gold, and silicon dioxide surfaces. The dependence of the cleaning efficiency on the laser fluence was investigated; a threshold was found at 0.65 J/cm2 and the efficiency was highest for a fluence ranging from 2.9 to 3.2 J/cm2 for silicon, and 3.2 J/cm2 for gold and silicon dioxide surfaces. The amount of the water vapor which condenses at the surface was also found to play a major role, the best results being obtained with a condensed thickness calculated to be 6 μm. The zeta potential value of the contaminant particles with respect to that of the surface greatly influences the cleaning process.
A magnetoelastic torque transducer utilizing a ring divided into two oppositely polarized circumferential regions
Authors: Garshelis I. J. , Conto C. R.
Published: July 2002

Significant improvements in both transducer performance and constructional simplicity is achieved by dividing a single ring into two equal width regions having oppositely directed circumferential magnetizations. The square hysteresis loop associated with the uniaxial anisotropy in the ring enables this magnetization arrangement to be readily instilled by rotating the shaft/ring assembly in the dipole fields of a set of axially separated permanent magnets having opposing polarizations. Following the removal of the magnets, each such region effectively becomes a single domain separated from the other only by a centrally located 180° domain wall. Unchanging performance of the transducer throughout nearly 107 torque cycles, severe overloads, and a wide range of thermal environments attest to the stability of both the remanent magnetizations in each region and the position of the domain wall.
Dynamical micromagnetics of a ferromagnetic particle: Numerical studies
Authors: Yang Bo , Fredkin Donald R.
Published: July 2002

We have developed a general purpose dynamical micromagnetic code to solve the damped Gilbert equation using the finite element method. We report a study of magnetization switching in a ferromagnetic prolate ellipsoid with aspect ratio of 4.6:1. Switching starts with curling at the middle of the particle, then continues with more complex magnetization configurations, heavily influenced by the damping constant. In general, lighter damping produces more sharply defined domain walls. The critical field for switching has a mild dependence on the damping constant.
The effect of dislocations on the optical absorption of heteroepitaxial InP and GaAs on Si
Authors: Iber H. , Peiner E. , Schlachetzki A.
Published: July 2002

The optical absorption of heteroepitaxial InP and GaAs layers grown on exactly [001]-oriented Si substrates was investigated by spectroscopic ellipsometry combined with anodic stripping. In the wavelength range above the band-gap-equivalent wavelength considerable absorption was found which depends on the dislocation density in the layer. A theoretical model based on the electric microfield of charged dislocations was developed which agrees closely with the experimental results. After calibration differential spectroscopic ellipsometry was used to determine the dislocation-density profile in the InP and GaAs layers. Thus, the dislocation density could be determined in the region of a few tens of nm to the heterointerface of InP on Si where the identification and counting of dislocations is impossible by other methods.
An electronegative inductive discharge instability
Authors: Tuszewski M.
Published: July 2002

An instability has been observed with Langmuir probes in cylindrical inductive discharges operated with low electronegative gas pressures. The instability consists of ion density modulations that propagate axially and radially at the ion acoustic speed. Measurements and calculations of negative ion concentrations in oxygen discharges suggest that the radial distribution and the magnitude of the density drops are consistent with the negative ion population. The instability appears to be a periodic expulsion of most negative ions from the plasma core. The cause of the modulations remains to be clarified. The instability may provide valuable information on negative ion concentrations and temperatures in a low pressure regime where measurements of those parameters are difficult.
Raman scattering study of GaN films
Authors: Kirillov Dimitry , Lee Heon , Harris James S.
Published: July 2002

Raman spectra of GaN films grown by molecular-beam epitaxy and hydride vapor-phase epitaxy on GaAs and Al2O3 substrates have been studied. It was found that longitudinal phonon modes disappear from the spectra of n+ films due to screening by free carriers, but coupled plasmon phonon modes of the higher-energy branch are not observed because of strong damping of plasmons. Precise values for phonon frequencies and linewidths are presented. No differences in phonon frequencies for the films of different thicknesses grown on different substrates have been found which indicates that the strain due to lattice and thermal-expansion mismatch is relaxed by the formation of the dislocations very close to the substrate–film interface.
Amorphous {100} platelet formation in (100) Si induced by hydrogen plasma treatment
Authors: Hwang Ki-Hyun , Park Jin-Won , Yoon Euijoon , Whang Ki-Woong , Lee Jeong Yong
Published: July 2002

The defect formation in (100) Si at low temperatures during electron cyclotron resonance hydrogen plasma treatment has been studied. The temperature effect on crystalline defect morphology is studied by transmission electron microscopy and high resolution transmission electron microscopy. A high density of hydrogen-stabilized {111} platelets is observed at 240 °C, whereas a large number of amorphous {100} platelets is observed at 385 °C. The formation of amorphous {100} platelets without {111} platelets at 385 °C is reported. The amorphous {100} platelet at 385 °C results from the precipitation of oxygen promoted by hydrogen-enhanced oxygen diffusion. The low-temperature photoluminescence study and the spreading resistance profiles for the hydrogenated Si support the proposed mechanism of the amorphous {100} platelet.
Fluorescence line narrowing spectroscopy of Sm2+ and Eu3+ in sodium borate glasses
Authors: Fujita Koji , Tanaka Katsuhisa , Hirao Kazuyuki , Soga Naohiro
Published: July 2002

A fluorescence line narrowing technique was carried out for sodium borate glasses containing a Sm2+ ion and its isoelectonic Eu3+ ion under a pulsed tunable dye laser excitation. In order to obtain site-dependent information, measurements were made by exciting the inhomogeneously broadened D05-F07 transition at 10 K. Line-narrowing fluorescence of the D05→F17 transition and the temporal changes of the emission lines were investigated as a function of excitation energy, and the dynamics of excited states for both ions were compared with each other. The results indicate that the site-to-site variations of the inhomogeneous broadening of D05-F07 transitions are attributed to the apparent difference in local environment between the Sm2+ and Eu3+ ions doped in borate glasses with Na2O content from 10 to 20 mol %. Also, a decrease in concentration of rare-earth ions causes a more significant effect on Eu3+ ions than on Sm2+ ions in the high-excitation-energy range. It is concluded that the difference in the local environment between Sm2+ and Eu3+ is mainly ascribable to the difference in the valence and in the ionic radius.
On the origin of the nonlinear and chaotic behavior of the magnetoelastic resonance
Authors: Garcı́a-Arribas A. , Barandiarán J. M. , Gutiérrez J. , Sagastabeitia I.
Published: July 2002

The nonlinear shape of the hysteresis loop M(H) and the dependence of the elastic constants on the magnetic state of the sample (ΔE effect) are shown to be two important sources of nonlinear effects that appear in magnetoelastic resonance experiments. The magnitude of these effects increases with the amplitude of the driving field and also is greatly dependent on the magnetic state at which the sample is biased, being more intense in the proximity of the anisotropy field (or saturation field) where both M(H) and E(H) curves change steeply. The influence of both factors is further studied by solving numerically a differential equation that accounts for the frequency response of the magnetoelastic resonance. We force the solution to follow simplified models for M(H) and E(H), obtaining frequency dependencies in good agreement with the experimental results.
Magnetic field induced crossover to chiral ordering in the easy-axis triangular antiferromagnet CsNiCl3 (abstract)
Authors: Visser D. , Monteith A. R. , Carling S. G. , Zeiske Th.
Published: July 2002

The easy-axis triangular antiferromagnet CsNiCl3 undergoes a magnetic phase transition to a triangular chirally ordered 120° type magnetic structure in an applied magnetic field of 2 T directed along the c axis. We studied by means of elastic neutron diffraction the crossover to chiral ordering. At B=2 T, the exponent of the sublattice magnetization β=0.25, which confirms the creation of the chirally ordered state. Data taken at B=1.75 T indicate that the crossover may be smeared out in B or is due to a slight misorientation of the applied field. The induced change in the magnetization direction of the ordered moments was also studied by means of SQUID magnetometry.
The influence of electron temperature on pattern-dependent charging during etching in high-density plasmas
Authors: Hwang Gyeong S. , Giapis Konstantinos P.
Published: July 2002

The effect of the electron temperature (Te) on charging potentials that develop in trenches during plasma etching of high aspect ratio polysilicon-on-insulator structures is studied by two-dimensional Monte Carlo simulations. Larger values of Te cause the potential of the upper photoresist sidewalls to become more negative; thus, more electrons are repelled back and the electron current density to the trench bottom decreases. The ensuing larger charging potential at the bottom surface perturbs the local ion dynamics so that more ions are deflected towards the polysilicon sidewalls causing (a) more severe lateral etching (notching) and (b) larger gate potentials, thereby increasing the probability of tunneling currents through the underlying gate oxide. The simulation results capture reported experimental trends and offer new insight into the nature of charging damage.
Interference phenomenon determines the color in an organic light emitting diode
Authors: Granlund Thomas , Pettersson Leif A. A. , Anderson Mats R. , Inganäs Olle
Published: July 2002

We report on electroluminescence from two-layer organic diodes made of poly(3-methyl-4-octylthiophene) and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,2,4-oxadiazole films between electrodes of indium tin oxide and Ca/Al. The diodes emitted light in the green-blue range; the electroluminescence spectra varied between diodes with different thicknesses of the polymer and molecular layers. The optical phenomena were simulated with a model accounting for interference effects; simulated results showed that the electroluminescence from the organic diode can be due neither to luminescence of the polymer nor of the molecular layer. These model simulations, together with electrochemical measurements, can be interpreted as evidence for an indirect optical transition at the polymer/molecule interface that only occurs in a strong electric field. We label this transition an electroplex.
Experimental determination of the frequency factor of thermal annealing processes in metal–oxide–semiconductor gate-oxide structures
Authors: Saigné F. , Dusseau L. , Albert L. , Fesquet J. , Gasiot J. , David J. P. , Ecoffet R. , Schrimpf R. D. , Galloway K. F.
Published: July 2002

Radiation-induced trapped charge annealing processes in the gate and field oxides of metal–oxide–semiconductor field-effect transistors are thermally activated. The activation energy and the frequency factor are related to the relaxation time constant by an Arrhenius law. A simple measurement of the relaxation time constant defines the activation energy, frequency factor (E,ν) pair. Choosing arbitrarily a “realistic” frequency factor corresponds to determining a characteristic energy, on which depends any subsequent annealing prediction. A controversy exists about the appropriate value of ν for silicon dioxide, with published values ranging from 1×107 to 1×1014 s−1. In this paper, a new method is presented that yields values for both frequency factor and activation energy. This method leads to an unexpectedly low (but consistent) value of ν (about 1×107 s−1) when applied to three different devices, obtained from three different manufacturers. The experimental procedure and the results for all three cases are presented and discussed.
Detonation waves in triaminotrinitrobenzene
Authors: Tarver Craig M. , Kury John W. , Breithaupt R. Don
Published: July 2002

Fabry–Perot laser interferometry is used to obtain nanosecond time resolved particle velocity histories of the free surfaces of copper, tantalum, or magnesium disks driven by detonating triaminotrinitrobenzene (TATB)-based charges and of the interfaces between detonating TATB and transparent salt crystals. Detonation reaction zone profiles are measured for self-sustaining detonation waves propagating through various thicknesses of LX-17 (92.5% TATB and 7.5% KelF binder) and pure ultrafine particle size TATB. The experimental records are compared to particle velocity histories calculated with the DYNA2D hydrodynamic code using the ignition and growth reactive flow model. The calculations yield excellent agreement with the experimental records for LX-17 using an unreacted von Neumann spike pressure of 33.7 GPa, a reaction rate law which releases 70% of the chemical energy within 100 ns, and the remaining 30% over 300 additional ns, and a reaction product equation of state fit to cylinder test and supracompression data with a Chapman–Jouguet (C–J) pressure of 25 GPa. The late time energy release is attributed to diffusion controlled solid carbon particle formation. Ultrafine TATB, pressed to a lower density (1.80 g/cm3) than LX-17 (1.905 g/cm3), exhibits lower unreacted spike and C–J pressures than LX-17 but similar reaction rates.
Ion-beam annealing of electron traps in n-type Si by post-H+ implantation
Authors: Ito A. , Tokuda Y.
Published: July 2002

The effects of post-H+ implantation on electron traps that are induced by P+ implantation (300 keV, 1×109 cm−2) has been studied by deep-level transient spectroscopy. H+ implantation is performed at room temperature to a dose of 2×1010 cm−2 in the range 30–120 keV. The post-H+ implantation partly decreases the concentration of the electron traps induced by P+ implantation, although it increases the concentrations around the projected range of H+. The annealing effect is ascribed to the reaction of preexisting defects with point defects induced by postimplantation. Peaks are observed in the reduction ratio profiles of the preexisted trap concentrations versus the distance from the projected ranges of postimplantation. The highest values of the reduction ratios in each postimplantation tend to decrease with increasing distance between the projected ranges of P+ and H+. This is due to the decrease of the supply of point defects caused by postimplantation with increasing distance. We compare the reduction ratio profiles of the dominant three electron traps (Ec−0.12, 0.15, and 0.39 eV).
Self-organized mesoscopic magnetic structures
Authors: Sugawara Akira , Hembree G. G. , Scheinfein M. R.
Published: July 2002

Three types of mesoscopic magnetic microstructure have been formed using self-organization: linear arrays of nanometer diameter islands, nanometer width lines, and undulating, continuous films. These structures were produced by annealing NaCl (110) and (111) surfaces in situ to produce patterned templates with 10–100 nm periodicity. Growth parameters such as groove spacing, substrate temperature and total deposit thickness can be varied in order to define specific mesoscopic magnetic structures. The microstructural evolution during growth is discussed in the context of nucleation and coalescence kinetics. The resulting magnetic properties are described, and their connection to the underlying microstructure elucidated.
Improved quality GaN by growth on compliant silicon-on-insulator substrates using metalorganic chemical vapor deposition
Authors: Cao J. , Pavlidis D. , Park Y. , Singh J. , Eisenbach A.
Published: July 2002

The use of compliant silicon-on-insulator (SOI) substrates instead of Si substrates is shown to improve the quality of epitaxial GaN layers by releasing the strain and absorbing the generated threading dislocations in the thin Si overlay of the SOI substrate. GaN layers have been grown on SOI substrates by low-pressure metalorganic chemical vapor deposition and various growth conditions and compared with GaN layers grown on Si substrates. Crystal uniformity, surface morphology, and number of threading dislocations of GaN layers grown on SOI substrates are improved compared to layers grown directly on Si substrates as evidenced by x-ray diffraction spectroscopy (XRD) and transmission electron microscopy. Full width at half maximum XRD values improved from 672 to 378 arcsec by growth on SOI instead of Si substrates. The GaN layers grown directly on Si substrates are highly resistive while all as-grown GaN layers on SOI substrates are unintentionally n type. For a 1–2 μm thick GaN layer grown on SOI, the electron mobility is typically in the order of 102 cm2/V s with a background carrier concentration in the range of 1.5–5.0×1017 cm−3.
Stress evaluation of radio-frequency-biased plasma-enhanced chemical vapor deposited silicon nitride films
Authors: Maeda Masahiko , Ikeda Koichi
Published: July 2002

Stress is evaluated for silicon nitride films prepared by rf-biased plasma-enhanced chemical vapor deposition. The total stress of the films shows a change from tensile to compressive with increasing applied rf bias during film deposition. The biaxial elastic moduli and linear thermal expansion coefficients of the silicon nitride films are determined by measuring the temperature dependence of the total stress of films deposited on two different substrate materials. Both the biaxial modulus and linear thermal expansion coefficient are dominantly related to film density. The intrinsic stress of the silicon nitride films calculated using these values is very close to the total stress. The intrinsic tensile stress originates from spontaneous densification during film growth, while the compressive stress results from incorporated atoms that are accelerated and implanted into the films by rf-bias induced plasma potential.
Microphotoluminescence characterization of cleaved edge overgrowth T-shaped InxGa1−xAs quantum wires
Authors: Yoshita Masahiro , Akiyama Hidefumi , Someya Takao , Sakaki Hiroyuki
Published: July 2002

Microphotoluminescence (micro-PL) characterization was performed for T-shaped InxGa1−xAs quantum wires (T-QWRs) fabricated by the cleaved edge overgrowth method with molecular beam epitaxy. The spatial distribution of optical properties in InxGa1−xAs T-QWRs was examined by means of PL intensity imaging and scanning micro-PL spectroscopy with about 1 μm spatial resolution. In the successfully fabricated 3.5-nm-scale In0.17Ga0.83As T-QWRs with Al0.3Ga0.7As barriers, uniform PL image and PL spectra from QWRs along the wire direction were observed, which indicates spatially uniform and high quality QWRs were formed. The effective lateral confinement energy of one-dimensional excitons was found to be 34 meV, showing the usefulness of InxGa1−xAs as a well material in T-QWR structures. On the other hand, in the unsuccessfully fabricated 4-nm-scale In0.09Ga0.91As T-QWRs with Al0.3Ga0.7As barriers, PL image and spectra were inhomogeneous. These results demonstrate the importance of flat cleaved surface and optimized overgrowth condition to fabricate uniform T-QWRs.
Ultrathin silicon oxynitride films grown by Ar/N2O remote plasma processing
Authors: Smith Bradley C. , Lamb H. Henry
Published: July 2002

On-line Auger electron spectroscopy, secondary ion mass spectroscopy, and angle-resolved x-ray photoelectron spectroscopy (ARXPS) were employed to determine the concentration, spatial distribution, and local chemical bonding of nitrogen in ultrathin oxynitride films grown by Ar/N2O remote plasma processing. Nitrogen incorporation in the films occurs primarily at the Si–SiO2 interface irrespective of rf power (5–50 W); however, the interfacial nitrogen concentration increases with rf power. Up to 0.6 monolayers of nitrogen atoms, bonded as (Si–)3N, are incorporated at the interface. Atomic oxygen generated in N2O plasma decomposition scavenges nitrogen from the bulk of the film, effectively confining nitrogen to a very narrow region near the substrate. A very small concentration of nitrogen, bonded as (Si–)2N–O, is detected on the top surface of the film by ARXPS.
Determination of effective energy loss functions and x-ray photoelectron spectroscopy source functions for Si 2p photoelectrons from clean Si(111), oxygen-adsorbed Si(111) and SiO2 surfaces
Authors: Nagatomi Takaharu , Kawano Takashi , Shimizu Ryuichi
Published: July 2002

Effective energy loss functions for Si 2p photoelectrons were determined for the thermally cleaned Si(111), oxygen-adsorbed Si(111) and SiO2 surfaces by the analysis of the reflection electron energy loss spectroscopy (REELS) spectra using the extended Landau theory. The background subtraction of the Si 2p x-ray photoelectron spectroscopy (XPS) spectra using these effective energy loss functions has enabled the XPS source functions to be derived with considerable effectiveness. This result has indicated that the effective energy loss functions derived for the clean Si(111) surface are significantly affected by the oxygen adsorption and the XPS source functions from the clean and oxygen-adsorbed Si(111) surfaces show a small hump due to the chemical shift by the oxygen adsorption appearing at the tail of the lower kinetic energy side of the Si 2p peak from the oxygen-adsorbed Si surface. On the SiO2 surface, the analysis of the REELS spectrum has yielded the effective energy loss function reflecting the fine structures which were not as clearly observed in the measured REELS spectrum. The Si 2p XPS source function determined for the SiO2 surface at two different measuring geometries showed very good agreement with each other. This study strongly suggests that the present analysis is very informative for the study of the initial oxidation of the silicon surface.
Gap dependence of the tip-sample capacitance
Authors: Kurokawa Shu , Sakai Akira
Published: July 2002

The tip-sample capacitance has been studied in the nontunneling regime and the capacitance-distance characteristics and its dependence on the tip geometry have been determined for the gap distance 1<s<600 nm. Measurements were carried out in ultrahigh vacuum on a capacitor formed between a metal tip (W or Pt–Ir) and a clean Au(111) surface. Tips of different tip radius R=30∼4000 nm were used to investigate the influence of tip geometry on the capacitance. When the gap distance is reduced, the capacitance increases while its gap sensitivity |∂C/∂s| decreases with the gap distance. The capacitance therefore shows no 1/s divergence. The magnitude of the capacitance change is found to depend on the tip geometry: blunt tips (R>1000 nm) show larger capacitance increase than that for sharp tips (R⩽100 nm). The effective tip radius Reff estimated from the C−s characteristics agrees with the real tip radius in a limited distance range which varies with the tip geometry. At small distances (s<30 nm), Reff≃R for sharp tips but Reff200 nm), the relation is reversed, Reff>R for sharp tips while Reff∼R for blunt tips. These results on Reff can be explained by the field concentration to the tip apex and the change of capacitance-contributing tip area with the gap distance. Capacitance calculations indicate that the capacitance of the “truncated cone + half sphere” tip well reproduces the observed C−s characteristics and its dependence on the tip geometry.
An analytic method for tunneling lifetime in the double-barrier quantum well
Authors: Kim J. U. , Lee Hong H.
Published: July 2002

An analytic method is presented for solving the time-dependent Schrödinger equation for double-barrier quantum well problems that allows for the presence of incident waves. A simple method is devised for determining the tunneling lifetime based on the analytic method.
Film thickness effects in the Co–Si1−xGex solid phase reaction
Authors: Boyanov B. I. , Goeller P. T. , Sayers D. E. , Nemanich R. J.
Published: July 2002

The thickness dependence of the reaction of cobalt with epitaxial silicon–germanium alloys (Si1−xGex) has been studied. The reaction products of Co with (100)-oriented Si0.79Ge0.21 after annealing at 800 °C depended on the thickness of the Co film. Complete conversion to CoSi2 occurred only when the thickness of the Co layer exceeded 350 Å. Interface reactions with Co layers thinner than 50 Å resulted in CoSi formation, while a mixture of CoSi and CoSi2 was formed at intermediate thicknesses. X-ray diffraction and extended x-ray absorption fine structure measurements indicated no measurable incorporation of Ge had occurred in either the CoSi or CoSi2. The threshold thickness for nucleation of CoSi2 on (100)-oriented Si1−xGex was determined in the range 0⩽x⩽0.25. The threshold thickness increased superlinearly with the Ge concentration x, and did not depend on the doping of the Si(100) substrate or the strain state of the Si1−xGex film. The observed thickness effect was attributed to preferential Co–Si bonding in the reaction zone and the energy cost of Ge segregation, which accompanies the formation of CoSi and CoSi2 during the reaction of Co with Si1−xGex.
Secondary electron enhanced discharges in plasma source ion implantation
Authors: Cluggish B. P. , Munson C. P.
Published: July 2002

The first published measurements of a plasma discharge enhanced by secondary electrons during plasma source ion implantation are presented. The ion implantation 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. Each plasma ion implanted into the target results in the emission of multiple secondary electrons. Langmuir probe measurements indicate that at high enough gas pressures, the energy of the secondary electrons can couple to the plasma, increasing the rate of ionization. Two different coupling mechanisms are observed. In the first, the secondary electrons directly ionize the background gas. In the second, the secondary electrons couple to the thermal electrons through a beam-plasma instability. Measurements of the instabilities are in agreement with two-dimensional particle-in-cell simulations.
Correlation for the glass forming ability of Pd83.5−xCuxSi16.5 with crystalline-compound/solid-solution formation
Authors: Chua L. F. , Kui H. W.
Published: July 2002

Molten Pd83.5−xCuxSi16.5 alloys, where 0⩽x⩽27, were allowed to crystallize at temperatures not too far removed from their liquidus T1. The crystalline phases in the as-crystallized specimens were then identified. An attempt was made to correlate the glass forming ability of Pd83.5−xCuxSi16.5 alloys with the crystalline phases formed upon their solidification from the molten state.
Electrical characteristics of metal-dielectric-metal and metal-dielectric-semiconductor structures based on electron beam evaporated Y2O3, Ta2O5 and Al2O3 thin film
Authors: Mikhaelashvili V. , Betzer Y. , Prudnikov I. , Orenstein M. , Ritter D. , Eisenstein G.
Published: July 2002

This work examines the electrical properties of metal-dielectric-semiconductor (Au/Ti–D–pSi) and metal-dielectric-metal (Au/Ti–D–Pt/Ti–pSi) capacitors which incorporate as dielectrics Y2O3, Al2O3 and Ta2O5 films evaporated by an electron beam at room temperature. The emphasis of the results is twofold: the first is the high quality of the investigated films as evidenced by the small measured values of loss factor, flatband voltages, and surface states density as well as the low dispersion of the relative dielectric constants. The second is an analytical procedure for discrimination of current flow mechanisms, under different regimes of applied voltage. A detailed study of the power exponent parameter α=d(Log I)/d(Log V) was found to be superior to conventional graphical representation of I–V data. The dominant mechanisms of charge transport through the metal-dielectric-metal structures was found to be the Schottky emission for Y2O3 and Al2O3 at low electrical fields. For structures with Y2O3 and Ta2O5 films operating in the high field regime, the charge transport mechanism is mainly space charge limited current.
Compositional dependence of electrical characteristics of SrBi2(Ta1−xNbx)2O9 thin-film capacitors
Authors: Furuya Akira , Cuchiaro Joe D.
Published: July 2002

Ferroelectric capacitors using SrBi2(Ta1−xNbx)2O9 (SBTN) were compositionally altered varying Nb concentration from 0 to 1, the corresponding I–V and P–E electrical characteristics evaluated from room temperature to 145 °C. These temperature evaluations reveal that the leakage current will increase with larger Nb concentration and the dominant conduction mechanism changes from Schottky to Frenkel–Poole emission. The ferroelectric hysteresis curve shifts in the direction of negative polarization as the temperature or the concentration of Nb increases. Concentration increases in Nb reduces the temperature dependence of remnant polarization and coercive field. Film resistance to imprint and degradation from elevated temperature improves. Substituting b-site Nb for Ta allows imprinted capacitors to recover by application of either bipolar fatigue pulses at room temperature (RT) or, cycling P–E measurement pulses at elevated temperature. Due to this asymmetrical tradeoff of film ferroelectric properties, there is an optimum identifiable range of Nb concentrations (0.25–0.5) capable of achieving memory performance. Optimized SBTN ferroelectric films will suitably perform in integrated circuit memory function applications provided that the leakage current incurred at higher Nb concentrations can be reduced.
Comparison of the temperature dependence of optical poling between guest-host and side-chain polymer films
Authors: Xu Gang , Si Jinhai , Liu Xuchun , Yang Q. G. , Ye Peixian , Li Zhao , Shen Yuquan
Published: July 2002

A comparison of temperature-dependent optical poling between two azopolymers, a side-chain polymer system (disperse red 19-functionalized polyimide polymer) and a guest-host polymer (dispersed red 1-doped polymethyl methacrylate), has been performed at various poling temperatures ranging from 25 to 70 °C. The observed saturation levels of induced second-order nonlinear susceptibility in all cases could be resolved into two components with a faster and a slower decay process after poling, which were respectively attributed to the cis-to-trans isomerization and the loss of induced polar order by orientational diffusion of azo chromophores. The saturation level and its slower decay component were observed to increase with the increase of poling temperature in the side-chain polymer, but to decrease in the guest-host system. The faster decay components were observed to decrease with poling temperature in both the systems. The decay times of the faster component decreased with temperature in the two polymers. The decay times of the slower component in the guest-host polymer, which were much smaller than those in the side-chain polymer, also decreased with temperature. All the observations have been explained physically.
Absolute atomic hydrogen densities in a radio frequency discharge measured by two-photon laser induced fluorescence imaging
Authors: Chérigier L. , Czarnetzki U. , Luggenhölscher D. , Schulz-von der Gathen V. , Döbele H. F.
Published: July 2002

Absolute atomic hydrogen densities were measured in the gaseous electronics conference reference cell parallel plate reactor by Doppler-free two-photon absorption laser induced fluorescence spectroscopy (TALIF) at λ=205 nm. The capacitively coupled radio frequency discharge was operated at 13.56 MHz in pure hydrogen under various input power and pressure conditions. The Doppler-free excitation technique with an unfocused laser beam together with imaging the fluorescence radiation by an intensified charge coupled device camera allows instantaneous spatial resolution along the radial direction. Absolute density calibration is obtained with the aid of a flow tube reactor and titration with NO2. The influence of spatial intensity inhomogenities along the laser beam and subsequent fluorescence are corrected by TALIF in xenon. A full mapping of the absolute density distribution between the electrodes was obtained. The detection limit for atomic hydrogen amounts to about 2×1018 m−3. The dissociation degree is of the order of a few percent.
Search for radiation-induced electrical degradation in ion irradiated sapphire and polycrystalline Al2O3
Authors: Kesternich W.
Published: July 2002

An international discussion is being carried out on whether radiation-induced electrical degradation in ceramic insulators does or does not exist. In the present experiments on radiation-induced conductivity and radiation-induced electrical degradation in high purity polycrystalline Al2O3 and sapphire all interfering effects resulting from surface conductances have been eliminated. The results have not confirmed a permanent degradation of the volume conductivity. Radiation-induced conductivity values were observed to decrease with dose. A transient in the electrical conductivity after ion beam off was discovered.