bluuebunny/crossref_metadata_2025 huggingface dataset:
Nuclear-magnetic-resonance characterization of doped SiO2 films used in integrated circuits
Authors: Schilling Frederic C. , Steiner Kurt G. , Obeng Yaw S.
Published: July 2002

Phosphorus-doped silicon dioxide dielectric films, prepared by plasma-enhanced chemical-vapor deposition at low temperature (400 °C), play a critical role in the reliability of very large scale integration devices. The phosphorus in the phosphosilicate glass (PSG) neutralizes the effect of mobile ion species and improves the glass flow, resulting in better gap filling and improved planarization. To extract the maximum contribution from this and other doped films (boron and germanium doped) in advanced sub-0.5 μm complimentary metal-oxide-semiconductor technologies, it is necessary to understand dopant incorporation and the effects of variation in the exposure to water, dopant concentration, and high-temperature annealing. An analysis of PSG by 1H, 29Si, and 31P solid-state nuclear magnetic resonance establishes the chemistry of the phosphorus dopant incorporation and the effect of moisture on the glass structures. Exposure to water results in a depolymerization of the PSG structures and a concurrent decrease in the crosslink density of the glass network. Similar concentrations of silanols are observed in both doped and undoped samples of SiO2. An increase in silanol concentration is found in P-doped glass after exposure to moisture in air. The level of exposure to water will determine the extent of structural changes in the dielectric film. Variations in this exposure can be expected to produce variability in the glass flow and other properties of the dielectric.
The low electric field conduction mechanism of silicon oxide-silicon nitride-silicon oxide interpoly-Si dielectrics
Authors: Maruyama T. , Shirota R.
Published: July 2002

A model for the leakage current of silicon oxide-silicon nitride-silicon oxide (ONO) dielectrics at low electric fields (≂2 MV/cm) was successfully developed. It is proposed that two transition mechanisms occur simultaneously. One is the detrapping of electrons from the silicon dangling bond in amorphous silicon nitride (SiN), which corresponds with the transition of dangling bonds among three possible charge states. The second is the direct tunneling of the detrapped electrons from the SiN to the gate through the thin silicon oxide. Both the location and the energy levels of the defect state are taken into account. The energy level, and the intrinsic time constant of the Si dangling bond and the uniform trap density in SiN, can be obtained by comparing the experimental results of the ONO discharge current with the calculated ones based on the above model. It can be found that the energy levels for negatively charged and neutral Si dangling bonds (E− and E0), with respect to the SiN conduction band, are 1.2 and 2.0 eV, respectively, the intrinsic time constants t− and t0 are 1.0×10−14 and 4.0×10−13 s, respectively, and the uniform trap density is 4.0×1019/cm3. From the energy level difference between E− and E0, we can conclude that the effective correlation energy of the Si dangling bonds in SiN is 0.8 eV, which is consistent with Robertson’s results based on a tight binding calculation.
Diamond deposition on tungsten wires by cyclic thermal plasma chemical vapor deposition
Authors: Yin Huaqing , Eguchi Keisuke , Yoshida Toyonobu
Published: July 2002

Deposition of diamond on tungsten wires were tried by means of cyclic thermal plasma chemical vapor deposition. Deposition rate, morphology, and uniformity were found to be strongly dependent upon the wire size and its heating history estimated using a simple model based on the heat balance equation. Relatively uniform coatings were obtained on wires with a diameter of 0.2 mm at a rotation speed of 450 rpm. This was not the case with larger wires with a diameter of 0.7 mm at 200 rpm. This effect is attributed to the disturbance of the flow pattern around the large wire. Under the best conditions, 1 μm uniform highly quality diamond film could be deposited on 0.2-mm-diam tungsten wires over a total run time of 75 min. The corresponding depositing duty time is calculated to be about 2 min.
Exposure of space material insulators to energetic ions
Authors: Tahara Hirokazu , Zhang Lulu , Hiramatsu Miki , Yasui Toshiaki , Yoshikawa Takao , Setsuhara Yuichi , Miyake Shoji
Published: July 2002

To understand degradation of materials due to ion bombardment in a space plasma environment, polymers of polyimide, polyetheretherketone and perfluoroalkoxy, and glasses coated with MgF2 were exposed to ion beams of oxygen and nitrogen with energy levels ranging from 600 eV to 5 keV. For the polymers, x-ray photoelectron spectroscopic analysis showed that the addition reaction of oxygen or nitrogen atoms or the disruption or separation of various structural compounds occurred depending on ion energy and dose. For the glass plate, the coating layer of MgF2 was drastically sputtered.
Recovery of electric resistance degraded by electromigration
Authors: Ohfuji Shin-ichi , Tsukada Mitsuo
Published: July 2002

Electric resistance degraded by electromigration at low temperatures is investigated by sweeping temperatures up to 400 K at a constant rate. Recovery (decrease) of the resistance is found and a first-order reaction model is applied to evaluate the activation energy spectra for this recovery. The energy spectra are found to broaden up to 1.1 eV. A comparison of the spectra with both the activation energy for the motion of vacancies and the spectra for as-deposited films prepared by electron-beam evaporation and dc sputtering indicates that the recovery comprises multienergy processes. The relaxation of mechanical stress gradients built up during the dc stress tests, the relief of microstructural changes by bulk diffusion involving the cooperative motion of large groups of atoms, and the formation of vacancy–hydrogen complexes as intermediates are discussed as possible factors contributing to the broad activation energy spectra of the recovery.
The effect of interaction between supported Au clusters on the conductance resonance
Authors: Chen Xiaoshuang , Zhao Jijun , Liu Fengqi , Sun Qing , Wang Guanghou
Published: July 2002

Conductance resonance of tunneling structure with a few Au clusters, deposited on an insulating film, is studied by the generalized Breit–Wigner formula in a tight-binding approximation. We find that in the conductance resonance the multiple peak structure may come from the interaction between supported Au clusters on an insulating film and the different arrangements of Au clusters may cause difference of the conductance resonance peaks. The experimental observation of multiple peak structure can be explained by generalizing our model to the system of a few quantum dots. Therefore, it is possible to predict the effect of interaction between metal clusters on the conductance resonance and develop some new microelectronic devices by artificially arranging metal clusters onto the surface of the insulating film.
The frequency and temperature dependence of noise in YBa2Cu3O7 multijunction flux-flow amplifiers
Authors: Macfarlane J. C. , Hao L. , Kuznik J. , Pegrum C. M.
Published: July 2002

Measurements of the absolute noise power of high Tc multijunction flux-flow amplifiers in the frequency range 0.1 Hz–60 kHz are reported. The noise is found to have maxima at the operating points corresponding to optimum transresistance and gain, and is consistent with existing models of critical current fluctuations as found in single grain boundary junctions. The frequency dependence of the noise power is usually close to 1/f, although a Lorentzian term is sometimes observed. The normalized values of measured critical current fluctuations are approximately temperature independent as previously found for single junctions prepared by similar techniques.
Oxidation enhanced diffusion of boron in silicon at 650–750 °C using steam in the range 1–15 atmospheres
Authors: Lever R. F. , Griffin P. B. , Rausch W. A.
Published: July 2002

Buried boron layers were epitaxially grown on single crystal silicon substrates and subjected to steam oxidation at 650–750 °C and pressures of 1, 5, and 15 atm. The layers were approximately 200 nm thick and capped by 400 nm of undoped silicon. The boron concentration varied from 8×1017 to 4×1018 atoms/cm3. The ensuing enhanced boron diffusion was modeled on the assumption that the oxidation maintained a supersaturation of interstitials at the surface which was proportional to the square root of the oxidation rate. Fully coupled dopant-defect diffusion equations were necessary to accurately model the oxidation enhanced diffusion.
Crystallographic microstructure and electrical characteristics of Au/Pt/Ti/Ni ohmic contacts on p-type (001) ZnTe layers
Authors: Mochizuki Kazuhiro , Terano Akihisa , Momose Masayuki , Taike Akira , Kawata Masahiko , Gotoh Jun , Nakatsuka Shin-ichi
Published: July 2002

The crystallographic microstructure and electrical characteristics of Au/Pt/Ti/Ni ohmic contacts on p-type (001) ZnTe layers are investigated as a function of annealing temperature, by using the transmission line model method, cross-sectional transmission electron microscopy, and Auger electron spectroscopy. The specific contact resistance decreases when the annealing temperature is increased and reaches a minimum at 300 °C. A minimum value of 1.1×10−6 Ω cm2 is obtained for a hole concentration of 3×1019 cm−3. The epitaxial NiTe2 that formed at the metal/semiconductor interface due to annealing is considered to play an important role in lowering the contact resistance. The excess Zn atoms created by the reaction between Ni and ZnTe are found to diffuse upward and to segregate at the Pt/Ni interface. A contact stability test performed at 102 °C suggests that these ohmic contact structures are stable even under high-current injection.
Effect of amorphous carbon film structure on diamond nucleation
Authors: Feng Z. , Komvopoulos K. , Brown I. G.
Published: July 2002

The effect of the structure of amorphous carbon films on diamond nucleation was investigated with a microwave plasma-enhanced chemical-vapor-deposition system. The films were synthesized on smooth silicon surfaces using a vacuum arc technique. Different film structures were obtained by varying the negative pulsed bias voltage from approximately zero to −1.0 kV. The maximum film density and etching resistance in a pure hydrogen plasma were obtained for a pulsed bias voltage equal to −200 V. It was determined that these films contained the highest percentage of tetrahedrally bonded (sp3) atomic carbon configurations. The carbon-coated substrates were first exposed to a low-temperature high-methane-concentration hydrogen plasma before initiating the diamond nucleation experiments. The higher nucleation density (∼3×109 cm−2) and better quality of diamond films corresponded to a pulsed bias voltage of −200 V. Increasing the magnitude of the negative pulsed bias voltage resulted in significantly lower nucleation densities and the formation of relatively larger particles. The enhancement of the diamond nucleation density for a pulsed bias voltage of −200 V is attributed to both the inherent high etching resistance of the produced amorphous carbon films, resulting from the high content of sp3 bonds, and the pretreatment process which yielded a high density of high-surface free-energy nucleation sites.
A monolithic nonlinear transmission line system for the experimental study of lattice solitons
Authors: Shi H. , Domier C. W. , Luhmann N. C.
Published: July 2002

We describe a new method, applying molecular beam epitaxial (MBE) growth and microfabrication techniques, to experimentally model nonlinear phenomena. Specifically, we have built a periodically loaded monolithic nonlinear transmission line which has been fabricated on a specially designed MBE GaAs wafer to duplicate a theoretical physics model, the one-dimensional exponential lattice, which was proposed by Toda. An advantage of the current approach over previous lumped element circuits is that it precisely reproduces the physics of the model without depending upon mathematical manipulations and corrections. To accomplish this, the line capacitance and parasitic capacitance were canceled by proper design of the MBE wafer profile. The conditions required to apply this approach to other nonlinear systems have also been studied. The experimentally measured pulse shapes for the Toda soliton system were compared against calculated results, with good agreement.
Atomic transport and phase formation in the Sb/Al system induced by heavy-ion bombardment
Authors: Shi Fenying , Bolse Wolfgang , Lieb Klaus-Peter
Published: July 2002

Antimony/aluminium films in bilayer and multilayer geometries were irradiated at liquid-nitrogen temperature with 50–900 keV ion beams ranging in mass from 20Ne to 208Pb. Depth profiling of the element concentrations was carried out via Rutherford backscattering spectroscopy. The formation of intermetallic phases and phase segregation was analyzed by means of x-ray diffraction, cross-section transmission electron microscopy, and scanning electron microscopy. From the low-dose irradiation data, the mixing rates k were obtained and found to depend linearly on the energy density FD deposited at the interface. The mixing efficiency of Sb/Al bilayers, k/FD=296(30) Å5/eV, supports the local thermal spike model. After high-fluence irradiations of Sb/Al bilayers with 550 keV Xe++ ions, a reacted layer of crystalline SbAl (B3 phase) at the interface was observed. Sb/Al multilayers irradiated with 900 keV Xe++ ions were found to become amorphous. Phase formation was studied as a function of the ion fluence, irradiation energy, and ion mass, and was found to start at that fluence, where cracking and shrinking of the Sb top layer and an increase of the sputtering yield were also observed.
Single crystal diamond deposition by laminar and turbulent acetylene-oxygen flames
Authors: Schermer J. J. , Giling L. J. , Alers P.
Published: July 2002

The homoepitaxial deposition of diamond layers on {111} and {001} type-IIa natural diamond substrates, by both laminar and turbulent acetylene-oxygen flames, is described. Using the same gas flows, temperatures, and supersaturations of 4%, a higher growth rate was obtained on a {001} substrate with a turbulent flame than with a laminar flame. Layers grown at the same temperature on {111} substrates with a supersaturation of 3% show no significant difference in growth rate. Due to the large differences in geometry between both types of flames it is not possible to relate the substrate positions in the acetylene feathers to each other and compare the growth results at any location. However, it is shown that the application of turbulent flames for single-crystal growth does not lead to a dramatic change in quality of the diamond as was previously reported in the literature. It is demonstrated by microscopic and spectroscopic techniques that the crystallographic orientation of the substrates, the deposition temperature, and the gas velocity all have a larger influence on the crystal morphology and impurity incorporation of the grown single crystals than the introduction of turbulence.
Cathodoluminescence characterization of Ge-doped CdTe crystals
Authors: Pal U. , Fernández P. , Piqueras J. , Sochinskii N. V. , Diéguez E.
Published: July 2002

Cathodoluminescence (CL) microscopic techniques have been used to study the spatial distribution of structural defects and the deep levels in CdTe:Ge bulk crystals. The effect of Ge doping with concentrations of 1017 and 1019 cm−3 on the compensation of VCd in CdTe has been investigated. Dependence of the intensity distribution of CL emission bands on the dopant concentration has been studied. Ge doping causes a substantial reduction of the generally referred to 1.40 eV luminescence, which is often present in undoped CdTe crystals, and enhances the 0.91 and 0.81 eV emissions.
Segregation behavior during silicon single-crystal growth from the melt
Authors: Izumi Teruo
Published: July 2002

The dependence of the effective segregation coefficient (ke) on the growth rate (R) has been investigated by the necking method using phosphorous as an impurity in the silicon melt growth process. The investigations were carried out for two different growth orientations of the silicon crystal, 〈100〉 and 〈111〉. The coefficient increased with increasing growth rate for both crystal orientations. The behavior in the relatively lower growth rate region is explained by the BPS model. However, the coefficient in the higher growth rate region is larger than that expected by the BPS theory. Additionally, the critical growth rate (R*), where the value of the coefficient deviates from the theory, depends on the growing crystal orientation. The R* in the 〈111〉 crystal is lower (∼0.5 mm/min) than that in the 〈100〉 crystal (∼3.0 mm/min).
Absolute magnetometer based on the high-frequency modulation of the kinetic inductance of a superconducting thin film
Authors: Ayela F. , Bret J. L. , Chaussy J.
Published: July 2002

The high-frequency thermal modulation of a superconducting closed loop just below its critical temperature gives rise to a spectacular divergence of its kinetic inductance. It is shown that this periodic divergence due to that of the London penetration length λ permits very fine magnetic measurements. A superconducting magnetometer has been designed that can detect the absolute intensity of weak magnetic fields, with a noise level of 10−12 T/√Hz. This absolute level was reached by the double thermal modulation of a superconducting disk around its critical temperature and of a neighboring superconducting closed loop. As a consequence of the Meissner effect, the superconducting disk gives an estimation of the applied perpendicular magnetic field and removes any incertitude about the number of flux quantums inside the loop. Then, the modulation of the temperature of the loop increases the absolute sensitivity. The detection is performed by a very low-loss superconducting LC resonator set at the input of a cryogenic preamplifier. The thermal modulation is performed by pigtailed laser diodes. Practical limitations and further improvements are discussed.
Statistical properties of Langmuir-probe and Thomson scattering data reduction provided by an appropriate curve fitting in the mathematical frame of the regularization procedure
Authors: Chegotov M. V.
Published: July 2002

A self-consistent data reduction of statistical sets of electron probe currents and Thomson scattering spectra is carried out with the help of the strictly determined curve fitting in the mathematical frame of a new regularization procedure [M. V. Chegotov, J. Phys. D 27, 54 (1994)]. Both the stability and high speed of the present procedure enable one to process without averaging every electron probe current characteristic or Thomson spectrum of the statistical set at a practically arbitrary noise level and to obtain not only the averaged electron velocity distribution function (EVDF) but even its standard deviation at every point. An algorithm is described which enables one to establish the highest feasible energy resolution EVDF for the given statistical sets of electron probe currents or scattering spectra. These features make this algorithm rather flexible and convenient in particular for the processing of Langmuir-probe and Thomson scattering measurements.
Multipacting discharges: Constant-k theory and simulation results
Authors: Gilardini Aldo L.
Published: July 2002

Multipacting discharge conditions in a parallel geometry are first reconsidered according to the so-called constant-k theory of Gill and von Engel [Proc. R. Soc. London A 192, 446 (1948)]. Four dimensionless variables are introduced: two for representing in a normalized form the peak value of the applied voltage and its frequency, two for characterizing the emission of secondary electrons from the electrodes. Numerical solutions of the equations developed by the author in a previous article [J. Appl. Phys. 71, 4629 (1992)] show the existence, when the constant-k postulate is valid, of a larger than previously known set of possible multipacting resonance modes. The effects on them of the electron phase-focusing requirements for a stable discharge are outlined. A procedure for determining breakdown voltages of the multipacting discharge through Monte Carlo simulations is then described. A set of simulation results is presented and compared with the corresponding data obtained from the constant-k theory: Except for the cutoff frequency values, the agreement is very good for the lowest-mode breakdown. In the presence of higher modes, breakdown voltages obtained from simulations are higher than the corresponding minimum breakdown values from the constant-k theory, but the transitions between successive modes, when the frequency is increased, can generally be recognized. These results confirm also the main features which are found in the plots of the experimental data reported by various authors, and particularly, at the highest frequencies, the linear dependence of the breakdown voltage on the product of frequency times electrode separation. In addition to breakdown voltages, Monte Carlo simulations provide the corresponding distributions of electron crossing times. These distributions prove the existence, under well-simulated physical conditions, of the breakdown mode first reported in the author’s previous article.
Coercivity and its dependence on the strength of alignment magnetic field in Nd-Fe-B sintered magnets
Authors: Gao Ruwei , Zhang Deheng , Li Hua , Jiang Shouting , Zhou Shouzeng , Li Fobiao , Zhang Lidong
Published: July 2002

The coercivity mechanism of Nd-Fe-B sintered magnets is investigated using a continuously varying model for a single variable K. The results show that the starting field Hs (which includes the critical field H0 and the expanding field He) is greater than the nucleation field Hn and is the main element that controls the coercive force in Nd-Fe-B sintered magnets. The comparison between theory and experiment on the dependence of coercivity on the field strength aligning the grains Ha indicates that the starting field theory is in better agreement with the experimental result than other theories discussed.
Characterization of thin amorphous silicon films with multiple internal reflectance spectroscopy
Authors: Fameli Giuseppe , della Sala Dario , Roca Francesco , Pascarella Francesco , Grillo Pietro
Published: July 2002

Infrared multiple internal reflection (MIR) spectroscopy has been applied here to the characterization (ex situ) of thin amorphous silicon layers on crystalline silicon substrates. The specimens are tightly clamped against a Ge prism with 45° bevel angle for the entrance and exit sides, allowing for up to 25 multiple internal reflections. This greatly enhances the thin-film absorption, and the stretching bands of SiHn bonds in amorphous Si are detected in a range of film thickness from 3 to 600 nm. Very thin films (with thickness less than 50 nm) exhibit a different hydrogen bonding compared to the thin ones, due to hydrogenated sublayers that are not visible in IR spectra for larger film thickness. Sublayers are found both at the film/substrate interface and at the film free surface. Another transitional layer, with increased concentration of SiH2 groups and considerably less than 30 nm, is found at the film/substrate interface. MIR is also applied to study the step-by-step etching in CF4/O2 of a 70-nm-thick amorphous silicon layer. This experiment is able to define the location of the sublayers.
Capacitance–voltage and current–voltage characterization of AlxGa1−xAs–GaAs structures
Authors: Passlack M. , Hong M. , Mannaerts J. P. , Chiu T. H. , Mendonca C. A. , Centanni J. C.
Published: July 2002

AlxGa1−xAs–GaAs structures with thin (400–1000 Å) Cr-doped or unintentionally doped AlxGa1−xAs layers (0.3≤x≤1) were grown on n+ GaAs substrate by molecular-beam epitaxy. The AlxGa1−xAs–GaAs interface and the insulating properties of thin AlxGa1−xAs layers at 300 K have been studied by capacitance–voltage and current–voltage measurements, respectively. An AlxGa1−xAs–GaAs interface state density in the lower 109 eV−1 cm−2 range was obtained. The insulating properties of thin AlxGa1−xAs layers were found to be controlled by AlxGa1−xAs–GaAs interface band offsets (ΔEo,ΔEv) and metal–AlxGa1−xAs barrier height ΦBn in accumulation and deep depletion, respectively, rather than by AlxGa1−xAs bulk properties such as specific bulk resistivity. Furthermore, required electrical properties of insulating layers employed in metal–insulator–semiconductor structures are discussed using a self-consistent heterostructure model based on Poisson’s equation and current continuity equations. Finally, a fundamental equation for the formation of inversion channels has been derived.
Raman scattering from longitudinal-optical phonon-plasmon-coupled mode in carbon-doped p-type InGaAs
Authors: Qi Ming , Konagai Makoto , Takahashi Kiyoshi
Published: July 2002

The Raman scattering by longitudinal-optical (LO) phonon-plasmon-coupled (LOPC) mode in carbon-doped p-type InGaAs with indium composition x≊0.3 and hole concentration from 1017 to 1019 cm−3 grown by metalorganic molecular beam epitaxy was studied experimentally. Only one LOPC mode appears between the GaAs-like and InAs-like LO modes was observed. The peak position of the LOPC mode is near the GaAs-like transverse-optical mode frequency and is insensitive to the hole concentration. The linewidth and intensity of the LOPC mode are dependent strongly on the carrier concentration, while the two LO modes decrease and become invisible under the high doping level. It was shown that the plasmon damping effect plays a dominant role in Raman scattering by LOPC mode for the p-type InGaAs.
Electron-stimulated desorption of positive and negative oxygen ions from YBa2Cu3O7 surfaces
Authors: Hoffman A. , Moss S. D. , Paterson P. J. K. , Petravic M.
Published: July 2002

Electron-stimulated desorption of positive and negative oxygen ions from YBa2Cu3O7 surfaces has been studied as a function of electron kinetic energy in the 70–600 eV range. It has been found that the threshold electron kinetic energy needed to induce positive oxygen ion desorption occurs at 260±5 eV, whereas that associated with negative oxygen ion desorption was found to be 100±5 eV. These electron kinetic energies correspond to Cu, Y, and Ba core-level binding energies. These results suggest that negative and positive oxygen ion desorption may be initiated via a primary core level ionization.
The effect of focused ion-beam implantation on the threshold voltage of short-channel silicon metal–oxide–semiconductor field-effect transistors
Authors: Ahmed Amer , Noor Mohammad S. , Carter Ronald L.
Published: July 2002

A theoretical modeling of the threshold voltage of short-channel silicon metal–oxide–semiconductor field-effect transistors (MOSFETs) taking into consideration the focused ion-beam technology for the direct implantation of dopants into semiconductor substrates has been performed. Based on a quasitwo-dimensional solution of Poisson’s equation, the surface potential distribution along the channel of a MOSFET has been derived. For this, implanted channel doping concentration is varied linearly along the channel and in a Gaussian-type fashion in a direction perpendicular to the channel. The threshold voltage has been determined from a knowledge of the minimum surface potential in the channel. The effects of finite source and drain junction depths have been included by modifying the depletion capacitance beneath the gate. Short-channel effects on the threshold voltage are thus taken into consideration. The model provides important insight of the physics controling the threshold voltage of a MOSFET. It is noted that a nonuniform doping with density lower in the drain end of the channel and higher in the source end of the channel, and a proper tailoring of the doses, straggles, and energy of implantation are keys to the improvement of the electrical characteristics of a MOSFET.
Optical study of strained and relaxed epitaxial InxGa1−xAs on GaAs
Authors: Andreani L. C. , De Nova D. , Di Lernia S. , Geddo M. , Guizzetti G. , Patrini M. , Bocchi C. , Bosacchi A. , Ferrari C. , Franchi S.
Published: July 2002

Photoreflectance (PR) at different temperatures and spectroellipsometry (SE) at room temperature were used to study, in a systematic and complementary way, the optical response of a series of strained and relaxed InxGa1−xAs (x<0.15) epilayers. All the samples were grown by molecular-beam epitaxy on GaAs, both with and without a GaAs cap layer, which in the thinnest samples determines a single-quantum-well configuration. The effects of the strain on the optical structures E0, E1, and E1+Δ1 observed in the 1.2–3.3 eV photon-energy range were analyzed by fitting standard critical points (CP) line shapes to the PR and SE spectra. The CP experimental energies versus x were compared with the relations obtained in the framework of the elastic strain theory and, in the quantum-well structures, of the envelope-function scheme. The excellent agreement between experiment and theory allowed us to determine, independently and only by optical techniques, the strain ε and the composition x values, which compare well with those measured by x-ray diffraction. Additional information concerning the critical thickness for the pseudomorphic growth and the residual strain in quasirelaxed layers was achieved.
Microscopically inhomogeneous GaAs/InGaP/n+InGaAs epilayer qualities induced by Si implantation and annealing
Authors: Watanabe Kazuo , Hyuga Fumiaki , Yamazaki Hajime , Nittono Takumi , Takaoka Hidetoshi
Published: July 2002

We investigate the effect of Si ion implantation and subsequent rapid thermal annealing (RTA) on the homogeneity of the crystal quality of metalorganic chemical-vapor-deposited GaAs (150 Å)/InGaP (100 Å)/n+InGaAs:Si (150–200 Å)/GaAs (800 Å) epilayers, which is the structure for heterostructure metal–semiconductor field-effect transistors. It is found that ion implantation to a dose higher than 3×1013 cm−2 at energies between 30 and 90 keV and RTA causes the appearance of dark regions in and near the InGaP layers and the disappearance of the InGaP ordered structure in the lattice images taken with a transmission electron microscope. In the dark regions, the interfaces between the InGaP layer and the GaAs and InGaAs layer become indistinct. An energy-dispersive x-ray analysis shows that compositional atoms intermix through these interfaces. The intermixing seems to be enhanced by implantation damage rather than by the interactions of Si impurities. On the other hand, 1×1013 cm−2 implantation causes no dark regions.
Biquadratic coupling in Fe/Au/Fe trilayers: Experimental evidence for the magnetic-dipole mechanism
Authors: Rücker U. , Demokritov S. , Tsymbal E. , Grünberg P. , Zinn W.
Published: July 2002

We have compared the biquadratic coupling in epitaxially grown Fe/Au/Fe(100)-systems with different interface roughness. The profound short-period oscillations observed on the smooth samples are found to be wiped out for the sample with rougher interfaces. In addition, a stronger biquadratic coupling has been observed. For all measured Au-interlayer thicknesses (1.3–2.4 nm) the biquadratic coupling dominates the antiferromagnetic and ferromagnetic coupling, in contrast to the measurements of the samples with smooth interfaces. The observed increase in biquadratic coupling can be explained in the frame of the currently proposed magnetic-dipole mechanism. The experimental results are in a good agreement with the calculation based on this mechanism, which used the roughness parameters obtained by scanning tunneling microscopy and which did not need any fitting parameters. Thus the existence of the magnetic-dipole coupling mechanism has been confirmed experimentally.
Deterministic modeling of impact ionization with a random-k approximation and the multiband Boltzmann equation
Authors: Wu Yu-Jen , Goldsman Neil
Published: July 2002

We present here an approach for determining impact ionization coefficients for the spherical multiband model in silicon. Using random-k approximation, the impact ionization rate is determined to reflect the multiband density of states in silicon. To account for the actual density of states, we have solved four coupled Boltzmann transport equations by combining a generalized Legendre polynomial expansion method with numerical techniques using finite differences and sparse matrices. Calculated values for the impact ionization coefficients agree with experiments for electrons in silicon, while being obtained in significantly less CPU time than required by analogous Monte Carlo calculations. Different multiband transport parameter sets are also compared.
Cross sections for 16O(He,He)16O resonant elastic scattering and application to elemental analysis of YBa2Cu4O8 and Nd1+xBa2−xCu3O7−δ films grown on SrTiO3
Authors: Nishimura T. , Kido Y. , Badaye M. , Yoshida Y. , Wang F. , Morishita T. , Kumagai M.
Published: July 2002

The differential cross sections for 16O(He,He)16O resonant elastic scattering at 3.034 and 3.078 MeV have been measured using stoichiometric thin (100 Å) and thick (6000 Å) SiO2 layers formed on Si(100) wafers by thermal oxidation at 900 °C under H2 and O2 flows. We have determined the resonance widths (Γ) and interaction radii (a), which are the parameters defining the cross sections in the partial wave analysis, by best fitting the angular and energy dependent scattering yields from oxygen. A computer simulation program for Rutherford backscattering including the 16O(He,He)16O resonant scattering has been synthesized and applied to the elemental analysis of thin YBa2Cu4O8 and Nd1+xBa2−xCu3O7−δ films grown on SrTiO3 substrates. The present elemental analysis is compared with the transition temperatures of superconductivity (Tc) in the context of the oxygen deficiency. The accuracy of oxygen content is estimated to be better than 0.1 (a few %). How to improve the accuracies of the elemental analysis, in particular the oxygen content, is discussed in detail.
On the different physical roles of hysteresis and intrinsic oscillations in resonant tunneling structures
Authors: Woolard D. L. , Buot F. A. , Rhodes D. L. , Lu X. J. , Lux R. A. , Perlman B. S.
Published: July 2002

Electronic sources based upon resonant tunneling diodes (RTDs) usually generate power by establishing limit cycles which exchange energy with storage elements in an external biasing circuit; hence, the output power in this type of implementation will always be limited by extrinsic effects. We verify the presence of multiple energy-storage mechanisms solely within the RTD and characterizes the interdependencies necessary to induce intrinsic oscillations observed in quantum mechanical simulations. Specifically, we show that a nonlinear ‘‘access’’ resistance and quantum-well inductance is responsible for the hysteresis, ‘‘plateaulike’’ behavior, and bistability associated with the intrinsic current–voltage (I–V) characteristic. Furthermore, a new circuit-level representation which accurately incorporates the nonlinear dependencies into these heretofore ‘‘linear’’ equivalent-circuit elements is used to demonstrate the different roles, as well as the degree of cooperative interplay, of the intrinsic oscillations and hysteresis in determining the overall I–V characteristics of the RTD.
Stress sensitivity of electromagnetic resonances in circular dielectric disks
Authors: Lee P. C. Y. , Yang J. S. , Yu J. D. , Ballato A.
Published: July 2002

A formula for predicting the stress effect on the electromagnetic resonances of dielectric resonators is obtained by applying a perturbation method to the three-dimensional Maxwell’s equations in which the dielectric permittivity tensor is perturbed by the applied stress (or strain) field through the piezo-optic effect. The dielectric resonator, which is surrounded by infinite free space, can be isotropic or anisotropic and of arbitrary shape. By using previously obtained two-dimensional closed-form solutions as the approximate unperturbed solutions, stress effect on the electromagnetic resonances in a dielectric circular disk is studied. Frequency changes of both the transverse electric and transverse magnetic modes are computed for disks of gallium arsenide and under three cases of loading: (1) a pair of diametral forces, (2) steady vertical acceleration, and (3) steady horizontal acceleration. In the latter two cases, the bottom face of the disk is supported by a rigid base.
Analytical solution of the breakdown voltage for 6H-silicon carbide p+n junction
Authors: Byeon Dae-Seok , Han Min-Koo , Choi Yearn-Ik
Published: July 2002

An analytical solution of the breakdown voltage for 6H-silicon carbide p+n junction has been derived by employing an effective ionization coefficient. The breakdown voltage extracted from our analytical model agrees fairly well with the experimental data in the range of 1016–1018 cm−3 doping levels.
Dislocation formation and B transient diffusion in C coimplanted Si
Authors: Cacciato A. , Klappe J. G. E. , Cowern N. E. B. , Vandervost W. , Biró L. P. , Custer J. S. , Saris F. W.
Published: July 2002

Suppression of dislocation formation and boron transient diffusion by carbon coimplantation is studied by means of transmission electron microscopy, secondary-ion-mass spectrometry, photoluminescence spectroscopy, and high-resolution x-ray diffraction. It is shown that both the effects are due to the formation of C-related damage which acts as a trap for Si interstitials. Quantitative simulations indicate that this damage is probably formed by coprecipitation of Si and C atoms in Si1.15C complexes. These complexes also deteriorate the electrical properties of the implanted layer. They dissolve at annealing temperatures higher than 900 °C. When this occurs, the effect of C is reduced and both B transient diffusion and dislocations, as well as the recovery of the electrical properties, are observed.
Optical properties of wurtzite GaN grown by low-pressure metalorganic chemical-vapor deposition
Authors: Shan W. , Schmidt T. , Yang X. H. , Song J. J. , Goldenberg B.
Published: July 2002

We present the results of optical studies on the properties of GaN grown by low-pressure metalorganic chemical-vapor deposition, with emphasis on the issues vital to device applications such as stimulated emission and laser action as well as carrier relaxation dynamics. By optical pumping, stimulated emission and lasing were investigated over a wide temperature range up to 420 K. Using a picosecond streak camera, the free and bound exciton emission decay times were examined. In addition, the effects of temperature and pressure on the optical interband transitions and the transitions associated with impurity/defect states were studied using a variety of spectroscopic methods, including photoluminescence and photoreflectance. The fundamental band gap of GaN was mapped out as a function of temperature using the empirical Varshni relation. The pressure coefficient of the gap was determined using diamond-anvil pressure-cell technique. The hydrostatic deformation potential for the direct Γ band gap was also derived from the experimental results.
Electron swarm parameters in ramp electric fields
Authors: Date H. , Ventzek P. L. G. , Shimozuma M. , Tagashira H.
Published: July 2002

The behavior of electron swarms in gases in time-varying ramp electric fields is investigated using a Monte Carlo simulation. In particular, we consider the case of swarms in chlorine gas. Swarm parameters as a function of instantaneous E/N(E is the electric field and N is the gas number density) for different dE/dt are determined. At higher dE/dt, all the parameters as a function of E/N are shifted to larger E/N when compared to the steady-state case. The drift velocity curve develops a peak which shifts to higher E/N and increases in magnitude as dE/dt is increased. Next, we pay attention to the definition of the swarm parameters, where the parameters derived from kinetic theory and by analogy to experiment are compared. For the high dE/dt cases, differences in the swarm parameters at the same E/N values are caused by the inertia of the electrons and their transient beam-like high drift velocity, while discrepancies due to the difference between the definitions in the kinetic theory and in the analogy to experiment appear significantly.
Stable nanostructuring of ultrathin porous silicon films by scanning tunneling microscopy
Authors: Enachescu M. , Hartmann E. , Koch F.
Published: July 2002

The capability of producing electronically induced modifications in ultrathin (∼20 nm) light-emitting porous silicon (PS) films by use of a scanning tunneling microscope (STM) operated in a high-vacuum environment is demonstrated. Upon increasing the tunnel current to 2 nA and the tunnel voltage beyond a threshold value of ∼7 V, structures 20–50 nm in width can be created to any desired pattern. These nanopatterns are stable at least for four days at room temperature. Experiments with both voltage polarities but equal power densities reveal that these structures can only be induced by directing the intense electron beam provided by the STM tip towards the sample surface, excluding pure thermal effects for the layer modifying process. These observations can be well explained by a model which includes a local increase in the density of defect states in deep-layer regions of the PS layer, which might be accompanied by a local quenching of the photo- or electroluminescence activity.
The macroscopic ferri-ferromagnetic transition in amorphous Y–Co/Gd–Co bilayers
Authors: Yonamine T. , Souche Y. , Santos A. D.
Published: July 2002

We developed a model to completely explain the domain wall existing at the interface of an amorphous Y–Co/Gd–Co bilayer. Samples produced by sputtering, were characterized by Rutherford backscattering spectrometry and transverse magneto-optical Kerr effect. From the experimental parameters we determined the thickness (δ) and relative position (Δ) of the domain wall, and also the exchange constant (A) for the Co–Co atom pair. The room temperature value of A was found to be (4.8±1.4)×10−8 erg/cm.
59Co nuclear magnetic resonance studies of the effect of annealing molecular beam epitaxy grown Co/Cu(111) multilayers
Authors: Thomson T. , Riedi P. C. , Hickey B. J.
Published: July 2002

59Co NMR, magnetotransport and grazing incidence x-ray scattering studies have been undertaken on a series of Co/Cu(111) multilayers, grown by molecular beam epitaxy (MBE), and subsequently annealed. Magnetotransport measurements showed that the magnetoresistance (Δρ/ρ) decreased only slightly as the annealing temperature was increased, but both the resistivity ρ and the change in resistivity Δρ doubled. NMR measurements showed that the strain in the interior of the Co layers relaxed slightly as a result of annealing while the strain at the interfaces remained constant. A small increase in the ratio of the area under the main NMR line to the area under the interface line, together with a reduction of interface line area, suggests a slight deterioration in the quality of the interfaces as a result of annealing. These observations are consistent with the model that MBE grown multilayers require good quality interfaces for large magnetoresistance (MR). Data from x-ray measurements showed that the increase in resistivity could be explained as a result of alloying between the top Cu layer of the multilayer and the Au capping layer.
Experimental study to validate a model of hillock’s formation in aluminum thin films
Authors: Génin F. Y. , Siekhaus W. J.
Published: July 2002

The growth of holes and hillocks in thin films has been reported extensively and for a multitude of film–substrate systems. A recently developed model [F. Y. Génin, J. Appl. Phys. 77, 5130 (1995)] which analyzes the formation of a ridge at a traveling grain boundary due to stress and capillarity driving forces provides a quantitative description of the growth of the hillocks. In order to test the model, the surface morphology of aluminum thin films deposited on oxidized silicon substrates and annealed at 450 °C in argon is investigated; the profiles of thermal hillocks are measured by atomic force microscopy. The comparison shows excellent agreement between modeled and experimental profiles.
Improved current transport properties of post annealed Y1Ba2Cu3O7−x thin films using Ag doping
Authors: Clausen T. , Skov J. L. , Jacobsen C. S. , Bukh K. R. , Bollinger M. V. , Tobiasen B. P. , Sager M. P. , Chorkendorff I. , Larsen J.
Published: July 2002

The influence of Ag doping on the transport properties of Y1Ba2Cu3O7−x thin films prepared by Y, BaF2, and Cu co-evaporation and optimized ex situ post annealing has been investigated. Both undoped and Ag doped films have values of Tc above 90 K, but Jc (77 K) is highly dependent on the nominal thickness (tnom) of the as-deposited film. For undoped films with tnom≤300 nm Jc (77 K) (≫106 A/cm2) decreases monotonically with increasing film thickness. Above 300 nm Jc (77 K) decreases rapidly to values below 5×105 A/cm2. Ag doped films with tnom≥200 nm have higher Jc (77 K) values than those of undoped films. Ag doped films have a maximum in Jc (77 K) around 250 nm. As for the undoped films, there is a large decrease in Jc (77 K) for Ag doped films with tnom≥300 nm. It was found that the higher values of Jc (77 K) for the Ag doped films were due to a better epitaxial growth of the YBCO compound. The low values of Jc (77 K) for both undoped and Ag doped single layer films with tnom≥300 nm were found to be due to the absence of 1–2–4 inclusions in these films. Based on these findings high Jc (77 K) films with tnom≳300 nm were grown by successive deposition and annealing of films with tnom<300 nm on top of each other. A 2×150 nm undoped film was found to have a Jc (77 K) value of 4, 1×106 A/cm2. This is almost a doubling of the Jc (77 K) value as compared to the value for the 300 nm single layer undoped film (2,2×106 A/cm2). Ag doped double layer films of 2×150 nm and 2×215 nm had comparable Jc (77 K) values (5,8×106 and 5,6×106 A/cm2, respectively). In comparison with the undoped 2×150 nm film Jc (77 K) is thus further increased (by about 50%) when doping with Ag.
Depth dependence of residual strains in polycrystalline Mo thin films using high-resolution x-ray diffraction
Authors: Malhotra S. G. , Rek Z. U. , Yalisove S. M. , Bilello J. C.
Published: July 2002

The magnitude of the stress in a thin film can be obtained by measuring the curvature of the film–substrate couple. Crystal curvature techniques yield the average stress throughout the film thickness. On a microscopic level, the details of the strain distribution, as a function of depth through the thickness of the film, can have important consequences in governing film quality and ultimate morphology. A new method, using high-resolution x-ray diffraction to determine the depth dependence of strain in polycrystalline thin films, is described. The technique requires an analysis of the diffraction peak shifts of at least six independent {hkl} scattering vectors, at a variety of penetration depths from the free surface of the film. The data are then used to determine the magnitude and directions of the strain eigenvalues in a laboratory reference frame for each penetration depth from the free surface of the film. A linear elastic model was used to determine the strains in successive slabs of the film. Results are reported for two Mo films, with nominal thicknesses of 50 and 100 nm, which were deposited by planar magnetron sputtering onto Si (100) substrates. This technique can provide quantitative insight into the depth variation of residual strains (stresses) in thin films and should work with a wide variety of materials.