bluuebunny/crossref_metadata_2025 huggingface dataset:
Control of Zn diffusion in InP/InGaAs heterojunction bipolar transistor structures grown by metalorganic vapor phase epitaxy
Authors: Kurishima Kenji , Kobayashi Takashi , Ito Hiroshi , Gösele Ulrich
Published: July 2002

It is known that high n+ doping in the cap layers of heterojunction bipolar transistor structures induces anomalous Zn diffusion in the base region during metalorganic vapor phase epitaxial growth. This phenomenon has been explained in terms of nonequilibrium group III interstitials generated in the n+ cap layer, which create highly diffusive Zn interstitials via the kick-out mechanism. In this article, we show that low-temperature growth (550 °C) is effective in alleviating the influence of the n+ cap layer. Due to a large time constant for the recovery of thermal point-defect equilibrium, the last-to-grow n+ cap layer cannot inject the excessive group III interstitials into the base region within a growth sequence. Under the low-temperature growth, however, the first-to-grow n+ subcollector produces group III interstitials during the whole growth sequence and thereby causes anomalous Zn diffusion. To prevent this effect, we propose interrupting the growth for a long time period (30 min) before growing the base layer, and growing the n+ subcollector at a higher temperature (600 °C). These growth techniques are shown to be effective in purging the subcollector of the undesirable group III interstitials before base-layer formation.
Resonant Raman scattering and photoluminescence studies of porous silicon membranes
Authors: Guha Soumyendu , Steiner Peter , Lang Walter
Published: July 2002

Raman scattering measurements as a function of excitation wavelength are conducted on a 55-μm-thick porous silicon (PS) membrane of an approximate porosity of 70%. A narrowing of the Si–Si phonon peak with increasing excitation wavelength is observed. We attribute this to a resonance of the excitation energy with the electronic states of nanocrystallites in PS. We estimate the size of silicon particles from the shift and broadening of the phonon band. The absorption band edge is next blue shifted by annealing the sample at 300 and 500 °C. A collapse of the nanostructure with a decrease in particle size is observed. The photoluminescence (PL) spectra exhibit a red shift of the PL band upon annealing. We also estimate the size of silicon particles from the PL peak.
Influence of radiation interference on the shape of Raman spectra for amorphous hydrogen-free diamondlike carbon films
Authors: Khriachtchev L. Yu. , Räsänen M. , Lappalainen R.
Published: July 2002

The influence of interference on the shape of Raman spectra from thin films is considered. High refractive index, low absorption and sufficient film thickness combined with high reflection from a substrate surface are the conditions to enhance the interference distortion of the Raman spectra. In the case of an amorphous hydrogen-free diamondlike carbon film deposited onto a highly reflecting aluminum layer, the interference dramatically distorts the ratio of Raman intensities at 500 and 1550 cm−1, by about a factor of four when the spectra are registered by using a conventional backscattering geometry. The effect is smaller but clearly noticeable for ordinary silicon-substrate samples as well. The magnitude of the interference modification is strongly influenced by geometrical factors such as the direction and polarization of the detected Raman scattered light.
Study of subband electronic structure of Si δ-doped GaAs using magnetotransport measurements in tilted magnetic fields
Authors: Li G. , Hauser N. , Jagadish C. , Antoszewski J. , Xu W.
Published: July 2002

Si δ-doped GaAs grown by metal organic vapor phase epitaxy (MOVPE) is characterized using magnetotransport measurements in tilted magnetic fields. Angular dependence of the longitudinal magnetoresistance (Rxx) vs the magnetic field (B) traces in tilted magnetic fields is used to examine the existence of a quasi-two-dimensional electron gas. The subband electron densities (ni) are obtained applying fast Fourier transform (FFT) analysis to the Rxx vs B trace and using mobility spectrum (MS) analysis of the magnetic field dependent Hall data. Our results show that (1) the subband electron densities remain roughly constant when the tilted magnetic field with an angle <30° measured from the Si δ-doped plane normal is ramped up to 13 T; (2) FFT analysis of the Rxx vs B trace and MS analysis of the magnetic field dependent Hall data both give the comparable results on subband electron densities of Si δ-doped GaAs with low δ-doping concentration, however, for Si δ-doped GaAs with very high δ-doping concentration, the occupation of the lowest subbands cannot be well resolved in the MS analysis; (3) the highest subband electron mobility reported to date of 45 282 cm2/s V is observed in Si δ-doped GaAs at 77 K in the dark; and (4) the subband electron densities of Si δ-doped GaAs grown by MOVPE at 700 °C are comparable to those grown by MBE at temperatures below 600 °C. A detailed study of magnetotransport properties of Si δ-doped GaAs in the parallel magnetic fields is then carried out to further confirm the subband electronic structures revealed by FFT and MS analysis. Our results are compared to theoretical calculation previously reported in literature. In addition, influence of different cap layer structures on subband electronic structures of Si δ-doped GaAs is observed and also discussed.
An improved method, based on Whipple’s exact solution, for obtaining accurate grain-boundary diffusion coefficients from shallow solute concentration gradients
Authors: Chung Yong-Chae , Wuensch Bernhardt J.
Published: July 2002

An equation developed by Le Claire is widely used to obtain a grain-boundary diffusion product, aD′, from the measured solute concentration gradients produced under conditions of constant surface concentration in grain-boundary diffusion experiments. However, a numerical assessment of the accuracy of Le Claire’s equation has revealed errors as large as 70% when applied outside of its range of validity to the shallow gradients (∼102 nm) that are provided by high-resolution analytical methods. To provide a relation applicable to this region, a numerical analysis of the variation of computed values of ∂ ln C̄/∂η6/5 with β has been used to develop a new and greatly improved expression of the form aD′=D3/2t1/2[10A(−∂ ln C̄/∂η6/5)B ], where A and B are parameters whose value depends on the experimental value of ∂ ln C̄/∂η6/5. The relation is valid for the experimentally useful range of solute penetrations 6√Dt∼10√Dt and for 1≤β≤105, and has been shown to produce a grain-boundary diffusion product accurate to within 1% throughout this domain. As the accuracy of the relation does not change systematically with η or β, it avoids introduction of an error in the activation energy for boundary diffusion that would result from inappropriate use of Le Claire’s equation in this region.
Simulation of reactive flow in filament-assisted diamond growth including hydrogen surface chemistry
Authors: Ruf B. , Behrendt F. , Deutschmann O. , Warnatz J.
Published: July 2002

One-dimensional reactive-flow simulations of a hot-filament chemical vapor deposition-system including surface reactions of H atoms and H2 molecules are reported. The corresponding governing equations of mass, momentum, chemical species, and energy are solved assuming a stagnation-point flow. In the model, the filament is catalytically active to dissociate H2 molecules, and the net surface reaction is the recombination of H atoms to H2 molecules. It is shown that the surface chemistry strongly influences the H and CH4 concentration profiles, whereas only a minor influence on CH3 and C2H2 concentrations—possible candidates as precursors for diamond growth—is observed. The influence of the surface temperature on gas-phase species concentration is discussed. At surface temperatures below 1000 K, the CH3-concentration dependence on the substrate temperature can be characterized by an activation energy of 14 kJ/mol which is in good agreement with experiment. The simulations show that this activation energy is a pure gas-phase effect due to recombination of methyl radicals and H atoms to methane in the cool gas layer near the substrate.
Effect of the oxidation of TiN on the stability of the Al/TiN interface
Authors: Gagnon G. , Gujrathi S. C. , Caron M. , Currie J. F. , Tremblay Y. , Ouellet L. , Biberger M. , Reynolds R.
Published: July 2002

The stability of TiN barriers deposited between Si or SiO2 substrates and AlSiCu metallic alloy contacts was investigated as a function of the sintering temperature and of the application of an oxidation step to the barrier. It was found that Al penetrates the barrier during the sintering at 450 °C for 1 h, which also results in the diffusion of Ti inside the Al alloy. This mutual interdiffusion increases with temperature but when oxygen is present at the barrier surface, the intensity of diffusion processes decreases considerably. It is also established that the barrier remains more stable on SiO2 than on the Si substrate. It is suggested that the better reaction resistance of oxidized TiN compared with oxygen-free nitride may be due to the blocking of fast-diffusion paths of Al diffusion by oxygen and subsequently the formation of Al2O3, AlN, and TiAl3 phases during sintering.
Photoluminescence and x-ray photoelectron spectroscopy study of S-passivated InGaAs(001)
Authors: Geelhaar L. , Bartynski R. A. , Ren F. , Schnoes M. , Buckley D. N.
Published: July 2002

The influence of sulfur passivation on the surface composition of In0.53Ga0.47As(001) was investigated with photoluminescence (PL) and x-ray photoelectron spectroscopy (XPS). Films of In0.53Ga0.47As(001), epitaxially grown on InP(100) substrates, were S passivated using a dry electron cyclotron resonance (ECR)-plasma deposition process and were either passivated as-prepared, or exposed to a BCl3 pre-etch prior to passivation. In the spectral range from 1450 to 1750 nm, S passivation enhances the PL yield by approximately an order of magnitude. XPS shows that S binds both to In and As, although preferably to In, and that oxidation is essentially eliminated by the passivation process. The In–S bonds are more stable upon annealing than are the As–S bonds. Furthermore, the pre-etched+H2S treatment enhances the PL yield beyond that of the H2S passivation treatment alone and produces a higher ratio of In–S to As–S bonds at the surface. In a second set of experiments, the influence of the ECR power applied to the sample during passivation was examined. The variation of this processing parameter has little effect on the surface composition.
Analysis of lattice vibration in fine particles of barium titanate single crystal including the lattice hydroxyl group
Authors: Noma Tatsuo , Wada Satoshi , Yano Mamoru , Suzuki Takeyuki
Published: July 2002

Fine particles of barium titanate single crystal with an average particle size of about 66 nm were prepared by a hydrothermal method. In the as-prepared sample, there was a large amount of the hydroxyl group and barium vacancy, and its crystal structure was assigned to cubic with an expanded lattice using a Rietveld method. The hydroxyl group desorbed with increasing calcination temperature, especially desorbing remarkably in the range from 200 to 300 °C. Above 700 °C, there was no hydroxyl group in the particle, and the crystal structure of the sample treated at 800 °C was assigned to tetragonal with tetragonality of 1.001 using a Rietveld method. The state of the lattice vibration was measured by an infrared reflection method, and analyzed using a nonlinear least-squares method with a four-parameter semiquantum model. As the result, the crystal structure of the as-prepared sample estimated using Fourier transform infrared and Raman was assigned to tetragonal. On the O6 octahedra deformation mode, the resonance frequency was independent of the concentration of the lattice hydroxyl group while the damping factor decreased with decreasing concentration of the lattice hydroxyl group. The role of the lattice hydroxyl group on the O6 octahedra deformation mode is discussed.
Optical amplification in Er3+-doped P2O5–SiO2 planar waveguides
Authors: Hattori Kuninori , Kitagawa Takeshi , Oguma Manabu , Okazaki Hisaaki , Ohmori Yasuji
Published: July 2002

The small signal gain of Er3+-doped P2O5–SiO2 planar waveguides is described with a homogeneous upconversion model. The homogeneous upconversion process accurately describes the absorption saturation at a wavelength of 0.98 μm. Interpretation of the absorption saturation provides homogeneous upconversion coefficients of 4×10−15 cm3 s−1 for a 0.54 wt % Er3+-doped 14.6 wt % P2O5 codoped silica waveguide and 6×10−18 cm3 s−1 for a 0.46 wt % Er3+-doped 21.6 wt % P2O5 codoped silica waveguide. The upconversion process occurs in the Er3+ ion rich phase in the P2O5–SiO2 core glass. A calculation that includes the homogeneous upconversion process proves that the gain can be enhanced by codoping the planar waveguide with P2O5. A gain of 20 dB is calculated with an Er3+ ion concentration of 0.4–0.7 wt % and a waveguide length of 40 cm when the pump power is 100 mW and 20 wt % P2O5 codoped Er3+-doped silica-based planar waveguides are used.
Characterization of textured polycrystalline diamond by electron spin resonance spectroscopy
Authors: Graeff C. F. O. , Nebel C. E. , Stutzmann M. , Flöter A. , Zachai R.
Published: July 2002

Electron spin resonance (ESR) is shown to be a useful and versatile technique for the detection and characterization of preferred orientation effects in polycrystalline diamond films. A nitrogen related center known as P1 is used for this purpose. The ESR signal coming from this center is composed of a central line and hyperfine satellite lines. It is found that crystallite disorientation causes a linewidth broadening of the satellite lines, which can thus be used to quantitatively characterize the diamond film texture. It is shown that the method is able to separate contributions of disorder induced by rotations of the crystallites around the growth direction from other contributions. The general conditions in which the method can be applied, and its applicability to other materials, are discussed.
Relative atomic chlorine density in inductively coupled chlorine plasmas
Authors: Hebner G. A.
Published: July 2002

Atomic chlorine is an important chemical species in plasma processing of silicon and III–V compound semiconductors. Two-photon laser-induced fluorescence (LIF) has been used to measure the relative atomic chlorine density in an inductively driven, rf discharge in chlorine gas. The Cl density in the center of the discharge was independent of rf power in the range of 150–400 W and increased a factor of 2 when the pressure was increased from 15 to 50 mTorr. LIF measurements performed on both levels of the chlorine spin-split ground state indicate similar trends for both energy levels in the inductive plasma mode.
Laser-induced forces on small objects in a resonant background gas
Authors: van Duijn E. J. , Cornelisse L. N. , Chapovsky P. L. , Hermans L. J. F.
Published: July 2002

A laser tuned into the Doppler wing of an absorption line in a low-pressure gas creates a flux of excited molecules. If these deexcite on the surface of a suspended micrometer-sized particle, internal-to-translational energy conversion produces a recoil force on the micro-particle. This new type of force is investigated in a pilot experiment. As a resonant gas we use HF or CH3F. An odd-in-detuning force on a 20 μm diameter probe wire simulating the particle is indeed observed. Possible applications are discussed.
Effect of implant temperature on transient enhanced diffusion of boron in regrown silicon after amorphization by Si+ or Ge+ implantation
Authors: Jones K. S. , Moller K. , Chen J. , Puga-Lambers M. , Freer B. , Berstein J. , Rubin L.
Published: July 2002

Si wafers were preamorphized by either Si+ or Ge+ ions at temperatures between 5 and 40 °C. The diffusion of low energy (4 keV) B+ implants into the preamorphized Si was studied in order to monitor the flux of interstitials from the end of range (EOR) region toward the surface. Transient enhanced diffusion (TED) in the regrown silicon was observed for all implants. Increasing the implantation temperature of the Si+ implant by as little as 15 °C can result in a marked decrease in the magnitude of the interstitial flux flowing from the EOR region toward the surface. This sensitivity to implant temperature appears to be even greater for Ge+ implants. In order to better understand this effect, detailed transmission electron microscopy (TEM) studies were conducted. As-implanted cross-sectional TEM micrographs indicate a measurable decrease in the thickness of the amorphous layer (up to 300 Å) occurs when the implantation temperature increases from 5 to 40 °C as a result of ion beam induced epitaxial recrystallization. Upon 800 °C annealing, two types of defects are observed in the EOR region: {311} defects and dislocation loops. The {311} defects are unstable and the comparison of secondary ion mass spectroscopy and TEM data for annealed samples indicating the dissolution of these {311} defects is at least one of the sources of interstitials for TED in the regrown Si at 800 °C. The EOR dislocation loops are stable for the annealing conditions used in this study (800 °C for 15 min) and there appears to be an exponential dependence of the TED that occurs in regrown Si on the density of the EOR dislocation loops.
Quantum coherent networks: A theoretical study
Authors: Sheng Wei-Dong
Published: July 2002

Electron transport in quantum coherent networks (interacting quantum waveguide arrays) is investigated theoretically with use of the scattering-matrix method. The scattering matrix for the basic unit of networks, the cross junction with square or rounded corners, is derived using the mode-matching technique. The overall scattering matrix for the network is obtained by the composition of the scattering matrices associated with each unit of the network. For a uniform network, the transmission spectra are calculated in the single-mode regime and are found notably dependent on the junction geometry. Small reflection for the input terminal and uniform output for some output ports are obtained, which means that the quantum coherent network can be used as a distributing net for the electron waves. Cross junctions with rounded corners of large radii are found to play a negative role in the device application of quantum coherent networks.
Dependence of the interlayer coupling on anneal temperature in Ni–Fe/Cu evaporated multilayers
Authors: Borchers J. A. , Gehring P. M. , Majkrzak C. F. , Zeltser A. M. , Smith N. , Ankner J. F.
Published: July 2002

Resistivity and magnetization studies of [Ni83Fe17(27 Å)|Cu(37 Å)]10 multilayers, grown by electron-beam evaporation, reveal that the magnetoresistance (ΔR/R) increases from <0.3% to 4.4% following a heat treatment at 325 °C. Polarized neutron reflectivity measurements on annealed samples show that the interlayer coupling changes from ferromagnetic to antiferromagnetic, confirming the conclusions of the bulk studies. Data for the 300 and 325 °C annealed samples in small fields show a magnetic peak at half-order that is absent for the as-deposited and 275 °C annealed multilayers. Some of the Ni–Fe spins in the annealed multilayers are thus ordered in large (>100 μm) in-plane domains aligned antiparallel across the Cu layers. An increase in the magnetic scattering at low angles indicates that some of the remaining Ni–Fe moments are randomly oriented from one layer to the next.
Characterization of films of La1−xSrxMnO3−δ grown by means of metal organic chemical vapor deposition
Authors: Heremans J. J. , Carris M. , Watts S. , Yu X. , Dahmen K. H. , von Molnár S.
Published: July 2002

An effort to develop La manganites for possible sensor applications has led to the successful growth of La1−xBxMnO3−δ (B=Sr, Ca) thin films on single crystal MgO, Al2O3, and LaAlO3 substrates. Here we concentrate on Sr-doped material on LaAlO3 with Curie temperature Tc=262±2 K. Tc was determined from magnetization measurements using Arrott plots, and agrees well with the observed resistivity peak in zero applied magnetic field (H). This Tc corresponds closely to a Sr content x=0.17 reported in bulk materials. At H=60 kOe the maximum magnetoresistance Δρ/ρ≈0.95. No discernible hysteresis, as might be expected for structural phase transitions, was observed. When plotted as a function of reduced temperature T/Tc, the magnetization extrapolated to zero H is best fit by a Brillouin function with an effective spin value 〈S〉 much larger than the 〈S〉=1.9 indicated by the composition. This may be indicative of magnetic polaron formation, especially near the magnetic and transport transition temperatures. At temperatures far below Tc there is an increase in resistivity of the thin films, which is considerably modified by the application of a field of 50 kOe. The conductivity, however, remains finite as the temperature approaches zero, indicating transport in states close to but above the mobility edge.
Ferromagnetic antiresonance in La0.7Ba0.3MnO3 traced out by temperature variation
Authors: Bhagat S. M. , Lofland S. E. , Kim P. H. , Schmadel D. C. , Kwon C. , Ramesh R. , Tyagi S. D.
Published: July 2002

Using the phenomenon of ferromagnetic antiresonance (FMAR) in ceramic samples of La0.67Ba0.33MnO3 at 10 GHz, we report a large magneto-impedance MI=Rs(H∥)−Rs(H⊥)]/Rs(H∥), where Rs is the microwave surface resistance and H the applied field. The MI reaches 30% at a field of 30 mT near room temperature. The FMAR also lets us measure M(T) by following Rs as a function of T and H.
Improvement of 〈indium-tin-oxide/silicon oxide/n-Si〉 junction solar cell characteristics by cyanide treatment
Authors: Kobayashi H. , Tachibana S. , Yamanaka K. , Nakato Y. , Yoneda K.
Published: July 2002

The performance of 〈indium-tin-oxide (ITO)/silicon oxide/n-Si(100)〉 junction solar cells is improved by immersing Si wafers in a potassium cyanide solution before the ITO deposition. It is found from x-ray photoelectron spectroscopy measurements that about 3% monolayer cyanide (CN−) ions are present on the Si surface after the cyanide treatment. The temperature dependence of the current–voltage curves shows that the band bending in n-Si is increased by the cyanide treatment. The increase in the band bending is attributed to an upward Si band edge shift caused by the presence of CN− ions at the oxide/Si interface and/or in the oxide layer. Conductance–voltage measurements show that the density of trap states considerably decreases after the cyanide treatment. The conductance decrease is attributed to the passivation of interface states by the adsorption of CN− ions on Si dangling bonds.
The structural dependence of the effective mass and Luttinger parameters in semiconductor quantum wells
Authors: Long Fei , Hagston W. E. , Harrison P. , Stirner T.
Published: July 2002

A detailed comparison of the empirical pseudopotential method with single and multiple band calculations based on the envelope function and effective mass approximations are presented. It is shown that, in order to give agreement with the more rigorous microscopic approach of the pseudopotential method, structural dependent effective masses and Luttinger parameters must be invoked. The CdTe/Cd1−xMnxTe system has been employed as an example, and the first pseudopotential calculations of quantum wells and superlattices in this material are presented. It is shown that the electron, light- and heavy-hole effective masses tend towards twice their bulk values in the limit of narrow quantum wells.
Photoluminescence studies of hydrogenated amorphous carbon and its alloys
Authors: Liu S. , Gangopadhyay S. , Sreenivas G. , Ang S. S. , Naseem H. A.
Published: July 2002

In this article, we have studied the photoluminescence (PL) behaviors of a-C:H and its alloys (a-C:H,N,F). The samples were deposited in a radio frequency plasma enhanced chemical vapor deposition system with various mixtures of CH4, N2, and NF3 gases. For this work, the effects of doping and excitation energy on PL peak position and bandwidth were investigated in detail. It was found that with the decrease in Tauc gap, the PL peak shifts to lower energy and the bandwidth is narrowed. If the excitation energy is below a certain energy, the PL peak shifts to lower energy and the bandwidth is reduced through a cutoff of the high energy region. If the excitation energy is above a certain energy, the PL becomes saturated and the shape remains almost the same. Our results support the cluster model proposed by Robertson that a-C:H contains both sp2 and sp3 sites, with sp2 clusters embedded in a sp3 bonded matrix. Our PL data are explained by the distribution function of cluster gaps.
Effect of “bamboo” grain boundaries on the maximum electromigration-induced stress in microelectronic interconnect lines
Authors: Gleixner R. J. , Nix W. D.
Published: July 2002

A model which describes the steady-state mechanical stresses resulting from electromigration in microelectronic interconnect lines is presented. This model is valid when sidewall and grain boundary interface diffusion are the dominant transport paths, and accounts for the two-dimensional microstructure present in such lines. By applying the model to simulated line microstructures, we find that bamboo grain boundaries may substantially increase the maximum electromigration stress. Furthermore, microstructural simulations on bounded interconnect segments show that variations in grain size may lead to a large scatter in the maximum stress, particularly as line length decreases.
Structural evolution and characterization of crystallized luminescent Sr1−xCaxWO4 solid-solution films prepared by an electrochemical method at room temperature
Authors: Cho Woo-Seok , Yoshimura Masahiro
Published: July 2002

A complete series of well-crystallized solid-solution oxide films, Sr1−XCaXWO4 (0⩽X⩽1), has been prepared on a tungsten substrate in an electrolytic solution containing Sr2+ and Ca2+ ions by electrochemical anodization of tungsten substrates at room temperature (25 °C). The composition of the solid-solution oxide films was investigated using Vergard’s law and x-ray photoelectron spectroscopy. The peak positions of excitation and emission of the films were independent of the Ca content. However, there were variations in the intensities of the emissions: the Ca-rich films showed an extremely strong luminescence, while the Sr-rich films showed a much fainter emission. The crystallization of the films was apparently characterized by three-dimensional nucleation and growth. A model is proposed for the mechanism for formation and growth of the films.
Angle-resolved x-ray photoelectron spectroscopy comparison of copper/Teflon AF1600 and aluminum/Kapton metal diffusion
Authors: Popovici D. , Piyakis K. , Meunier M. , Sacher E.
Published: July 2002

We use angle-resolved x-ray photoelectron spectroscopy to study metal diffusion in the cases of evaporated Cu on Teflon AF1600 and evaporated Al on Kapton polyimide. Although minimal diffusion is essential for long term stability and reliability of microelectronic devices, neither the presently used Al/polyimide nor any new candidates, such as Cu/fluoropolymer, has been sufficiently characterized and compared. Diffusion constants for infinite dilution in both cases were evaluated supposing Fickian diffusion as a first approximation. For the Al/polyimide interface, we found little, if any, diffusion after annealing for 30 min at 150 °C. In the case of the Cu/Teflon AF1600 interface, the same annealing induces significantly more copper diffusion. These results are discussed with respect to the diffusion equation, and it is shown that the experimental results indicate a concentration-dependent diffusion coefficient; experimental values, measured at infinite dilution of metal in polymer, are also reported.
Behavior of hot hole stressedSiO2/Si interface at elevated temperature
Authors: Zhang J. F. , Al-kofahi I. S. , Groeseneken G.
Published: July 2002

The behavior of hot hole stressed SiO2/Si interface at elevated temperature is investigated. Although an exposure to an elevated temperature does not affect a fresh device, considerable damages occur in a stressed device for temperature above 300 °C. The damage is caused by two thermally activated processes, which are triggered by hole injection and continued after the injection. One of them is the post-stress interface state generation and the other is the unexpected creation of interface state precursors. These new precursors can only be electrically detected when the device is stressed again. The effects of temperature, exposure time and hole injection time on these processes are studied. At 400 °C, annealing of interface states is also significant. It is found that the annealing of the states created post-stress is much faster than the annealing of the states generated during the hole injection, indicating these two have different structures. Roles played by electron injection and hydrogen in the annealing are studied and the hole detrapping process is addressed. The precursor generation follows the first order kinetics with a single characteristic time. The generated precursor is found to be different from the original one existed in a fresh device. These new precursors enhance the degradation in the subsequent stress.
Influence of the doping element on the electron mobility in n-silicon
Authors: Kaiblinger-Grujin G. , Kosina H. , Selberherr S.
Published: July 2002

We present a theoretical approach to study the dependence of the electron mobility on the dopant species in n-doped silicon under low electric fields. The electron charge distribution of the impurities is calculated by the Thomas–Fermi theory using the energy functional formulation. Ionized impurity scattering has been treated within the Born approximation. Our model accounts for degenerate statistics, dispersive screening and pair scattering, which become important in heavily doped semiconductors. The dielectric function is accurately approximated by a rational function. A new expression for the second Born amplitude of a Yukawa-like charge distribution is derived, which now depends on the atomic and electron numbers of the impurity ion. Monte Carlo simulations including all important scattering mechanism have been performed in the doping concentration range from 1015 to 1021 cm−3. The agreement with experimental data is excellent. The results confirm the lower electron mobility in As-doped silicon in comparison to P-doped silicon.
Electroluminescence of strained SiGe/Si selectively grown above the critical thickness for plastic relaxation
Authors: Stoica T. , Vescan L. , Goryll M.
Published: July 2002

Electroluminescence of strained Si0.80Ge0.20/Si(001) pin diodes has been investigated experimentally and by quantitative modeling. The key aspect of this investigation was that by selective epitaxial growth the experimental critical thickness for plastic relaxation (80 nm at Tepi=700 °C and large areas) could be increased in finite pads. SiGe layers with thickness of 60, 72 or 370 nm have been grown within the intrinsic i region of pin structures. Samples free of misfit dislocations revealed electroluminescence with the SiGe no-phonon peak and its transversal optical–phonon replica corresponding to interband transitions. It was found that by increasing the thickness of the SiGe layer the drop in the electroluminescence with increasing temperature could be shifted to higher temperature, so that for the 370 nm thick SiGe sample the emission was observed to persist still at 300 K. Modeling based on drift-diffusion and carrier recombination equations was used to simulate the current–voltage characteristics of the pin diodes and their band gap electroluminescence. It was found that the modeling results can account for the temperature and thickness dependence of the electroluminescence. Hole and electron Shockley–Read–Hall recombination times could be evaluated.
Space- and time-resolved optical spectroscopy of plumes generated by laser ablation of NiO in a vacuum
Authors: Tanaka M. , Fujisawa Y. , Nakajima T. , Tasaka Y. , Ota K. , Usami S.
Published: July 2002

Laser ablation of NiO at 266 nm has been studied by measuring absorption spectra and emission spectra which are resolved both temporally and spatially. The spectra were measured at several points 1 mm apart from the laser spot and with several detection angles. Ablated species in different electronic states such as the ground state, lower lying states, and excited states are distinguished from absorption and emission spectroscopy. Time-of-flight spectra of these species and their angular dependence are obtained. It is revealed that excited Ni neutrals are generated mainly by the recombination of Ni+ ions with electrons, and Ni+ ions ejected nearly normal to the surface are exclusively excited due to multiple collisional effect. The isotropic angular dependence of most probable velocities of Ni+ ions and Ni neutrals are explained by ambipolar diffusion of the plume. The mechanism of species ejection is also discussed.
Two types of growth mode for Ge clusters on Si(100) substrate with and without atomic hydrogen exposure prior to the growth
Authors: Tezuka Tsutomu , Sugiyama Naoharu
Published: July 2002

The growth mode of Ge clusters on a Si(100) surface was found to depend on whether the initial Si surface was hydrogenated or not. The Ge clusters, grown by ultrahigh vacuum chemical vapor deposition, were characterized by atomic force microscopy and cross-sectional transmission electron microscopy. Dome-shaped clusters were formed when the Si buffer layer had been exposed to atomic hydrogen. On the other hand, hut-shaped clusters were grown when there was no hydrogen exposure, and they were more than an order of magnitude smaller than the dome-shaped clusters. Thermal desorption spectroscopy measurements revealed that the Si surface exposed to atomic hydrogen was partially hydrogenated into the monohydride phase. It was concluded that hydrogen termination of the Si(100) surface plays an important role in the successive growth of Ge clusters.
The amorphization kinetics of GaAs irradiated with Si ions
Authors: Brown R. A. , Williams J. S.
Published: July 2002

The critical relationship between ion flux and substrate temperature which defines the threshold conditions for the formation of amorphous layers in GaAs at constant ion fluence is measured for the first time. At elevated temperatures, amorphous layers are formed in GaAs by a collapselike process when a critical free energy value is exceeded. The threshold conditions for amorphization are shown to be thermally activated, with an activation energy of 0.9±0.1 eV. However, specific defects and/or processes giving rise to this value are not yet known.
Magnetooptical properties of Sc-substituted erbium–iron–garnet single crystals
Authors: Ostoréro J. , Guillot M.
Published: July 2002

The magnetooptical properties of Er3Fe5−zSczO12 (z=0.10 and 0.30) single crystals are presented and compared to those of pure ErIG. Faraday rotation (FR) measurements at 1152 nm wavelength were performed in the 6–600 K temperature range under a magnetic field of up to 20 kOe applied parallel to the [100] and [111] crystallographic axes of the crystals. The compensation temperature Tcomp is shifted from 80 (z=0) to 51 K (z=0.30). Below Tcomp, the diamagnetic Sc3+ substitution in the octahedral Fe3+ sublattice also has a strong influence on FR anisotropy: both spontaneous FR Φs and FR susceptibility χF=dΦ/dH show that the “easy” FR axis changes from [111] in ErIG (z=0) to [100] for z=0.30. The FR isotherms (z=0.30) for the [111] direction show a nonlinear behavior in the 20 K–Tcomp temperature region.
Mechanism of composition change in sputter deposition of barium ferrite films with sputtering gas pressure
Authors: Suzuki E. , Hoshi Y. , Naoe M.
Published: July 2002

In this study, we used computer simulation to investigate changes in the composition of hexagonal barium ferrite films with sputtering gas pressure obtained by the sputter-deposition processes. The iron content in the film deposited by facing target sputtering increased as the sputtering gas pressure increased and reached a maximum value at a certain gas pressure. These changes in the film composition were explained as follows: sputtered particles scatter when they collide with sputtering gas atoms, and this scattering changes the ratio of the particles reaching the substrate. When the substrate was located to the side of the target, as in a facing target sputtering system, this scattering resulted in an increase in the amount of sputtered particles arriving at the substrate, although too much scattering caused the amount to decrease. When a magnetron sputtering system is used for the film preparation, this gas scattering leads to a decrease in the amount of sputtered particles arriving at the substrate which is located opposite the target. Since this gas scattering depends significantly on the atomic mass of the sputtered particles, the gas pressure dependence of the amount of iron atoms arriving differs considerably from that of the amount of barium atoms arriving. This difference leads to the changes in film composition.
Effect of electric fields on adhesion of ice to mercury
Authors: Petrenko Victor F.
Published: July 2002

We report a strong and fully reversible effect of a small dc bias (−6 to +6 V) on ice adhesion to mercury. The effect was observed in ices doped with KOH, HF, and NaCl and was absent in very pure ice grown from deionized water. The ac voltage of up to 40 V did not cause any noticeable changes in ice adhesion. Different physical mechanisms of ice adhesion to metals and possible explanations of the effect are discussed. The phenomenon was used to estimate the contribution of electrostatic interactions to ice adhesion to metals.
Effects of hydrogen plasma treatment on the 1.54 μm luminescence of erbium-doped porous silicon
Authors: Dejima Tohru , Saito Riichiro , Yugo Shigemi , Isshiki Hideo , Kimura Tadamasa
Published: July 2002

Well resolved, sharp photoluminescence (PL) peaks of Er3+ (4f11) ions at ∼1.54 μm are obtained from Er-doped porous silicon (PS:Er) on which a hydrogen plasma treatment is carried out after electrochemical incorporation of Er3+ions into porous silicon. The full width at half maximum (FWHM) of the 1.538 μm main peak at 20 K is less than 1 nm, which is much smaller than that obtained from PS:Er samples annealed in a H2 or O2 flow (FWHM 7–10 nm), and is comparable to that of Er-doped crystalline silicon. The thermal quenching of the PL intensity is, however, relatively small, the PL intensity decreasing only by a factor of 10 from 20 to 300 K.
Fundamental efficiency limit of solar power plants
Authors: Graf Th.
Published: July 2002

The second law of thermodynamics is applied to the entropy fluxes going into and out of solar power plants. It is discussed how clouds affect the entropy flux coming from the sun by redistributing the photons on a larger number of electromagnetic modes and thereby reduce the efficiency of the energy conversion in power plants. Under direct illumination the fundamental efficiency limit corresponds to the Carnot efficiency which is 94.8%. With isotropically scattering clouds the efficiency is reduced to a spectral average of 72.3%.
Reconstruction theory of thermal conductivity depth profiles by the modulated photoreflectance technique
Authors: Xu M. H. , Cheng J. C. , Zhang S. Y.
Published: July 2002

A reconstruction theory of thermal conductivity depth profiles from modulated photoreflectance data has been reported. This theory is based on the pulsed spectrum technique and a regularization method. The performance of this approach is illustrated by numerical simulations.
Effect of Al3Ti intermetallic compound on electromigration lifetime of Al alloy interconnections
Authors: Kouno T. , Hosaka M. , Niwa H. , Yamada M.
Published: July 2002

The dependence of the electromigration (EM) lifetime and the cross-sectional structure of interconnections after EM tests on linewidths was investigated in multi-level and single-level Al alloy interconnections consisting of a top–TiN/Ti/Al–0.5%Cu/TiN/Ti–bottom stack. In this study, an almost uniform Al3Ti intermetallic compound layer was formed by a well-known reaction between the Ti and Al. We found the following anomalous behavior: the mean time to failure (MTF) of EM in the multi-level interconnections with tungsten diffusion barriers decreased by increasing the linewidth. We also found that in the multi-level interconnections after EM tests, independent of linewidths, a local Al thickening formed near the anode end of the line and voids formed near the cathode end. On the other hand, in the single-level interconnections with bonding pads, the MTF of EM increased by increasing the linewidth and, after EM tests, a local Al thickening formed near the anode end even though no voids were observed near the cathode end. This directly opposed EM lifetime dependency on linewidth found in the multi-level and single-level interconnections and the observed Al thickening correlate closely with the fast diffusitivity of Al atoms at the interface between the Al3Ti and Al and/or between the Al3Ti and TiN.
Structural analysis of annealed Al/n-InP(100) interfaces: Different types of indium heteroepitaxial growth on InP(111)A and InP(111)B planes
Authors: Kečkéš J. , Ortner B. , Jakabovič J. , Kováč J.
Published: July 2002

Al /n- InP (100) structures, prepared as Schottky contacts, are provided by Al thermal evaporation at 28 °C and subsequent annealing in the range of 200–750 °C for 3 min. Annealing at temperatures above 500 °C causes the formation of metallic indium at the interfaces. The orientation relationship between In and the substrate is revealed by x-ray diffraction texture analysis. For samples annealed below the melting point of Al (660.1 °C), an epitaxy is formed with In(101)∥InP(111)A and In[010]∥InP[1̄10]. For samples annealed at temperatures above the melting point of Al, the same epitaxy occurs besides two further epitaxies of indium growing on InP(111)B planes. Their orientation relationships are In(001)∥InP(111)B and In[010]∥InP[1̄10] and, for the second type, In(110)∥InP(111)B and In[1̄13]∥InP[1̄10].
Device model investigation of single layer organic light emitting diodes
Authors: Crone B. K. , Davids P. S. , Campbell I. H. , Smith D. L.
Published: July 2002

We present calculations of single layer organic light emitting diode (LED) characteristics using a device model which includes charge injection, transport, recombination, and space charge effects in the organic material. Contact limited and ohmic contacts, high and low carrier mobilities, and device thicknesses from 5 to 200 nm are considered. The scaling of device current with applied voltage bias and organic film thickness is described for contact limited and ohmic contacts. Calculated device current, light output, and quantum and power efficiency are presented for representative cases of material and device parameters. These results are interpreted using the calculated spatial variation of the electric field, charge density, and recombination rate density in the devices. We find that efficient single layer organic LEDs are possible for a wide range of organic material and contact parameters.
Microstructural and electrical investigation of Pd/Ge/Ti/Au ohmic contact to pseudomorphic high electron mobility transistor with undoped cap layer
Authors: Kim Yi-Tae , Lee Jong-Lam , Lee Byung-Teak
Published: July 2002

Microstructural reactions of Pd/Ge/Ti/Au contact to AlGaAs/InGaAs pseudomorphic high electron mobility transistor with an undoped GaAs/AlGaAs cap layer have been investigated using cross-sectional transmission electron microscopy, and the results are used to interpret the electrical properties of the ohmic contact. In the as-deposited state, a quaternary phase of PdxAlGaAs containing excess Ge atoms is formed at the interface of Pd/AlGaAs and some microvoids exist at the Pd layer in the vicinity of the interface. When the ohmic metals deposited on the undoped cap layer were annealed, the lowest contact resistivity of 9.1×10−5 Ω cm2 is obtained at 380 °C. AuGa compound is formed at the PdGe/undoped-AlGaAs interface as a result of the reaction between the ohmic metal and the undoped GaAs cap. This is due to the fast in-diffusion of Au toward the undoped AlGaAs through grain boundaries of the PdGe compound. The layer structure is changed to TiO/AuGa/PdGe/AuGa(TiAs+epi-Ge)/undoped-AlGaAs. The AuGa compound enhances the creation of group III vacancies, and the in-diffused Ge atoms occupy the vacancies. Thus, a number of electrons are produced below the contact, which plays a role in reducing the contact resistivity. For the ohmic metals deposited on n-AlGaAs by removing the undoped cap layer, the annealing temperature at which the contact resistivity has the minimum value of 2.3×10−6 Ω cm2 increases to 460 °C. The Au2Al is additionally observed at the PdGe/n-AlGaAs interface. Consequently, the layer structure is changed to TiO/AuGa/PdGe/AuGa+Au2Al(TiAs+epi-Ge)/n-type AlGaAs. The formation of Au2Al at the PdGe/n-AlGaAs interface creates more group III vacancies. Thus, the contact resistivity is further reduced by the incorporation of the in-diffused Ge into the group III vacancies. The InGaAs channel layer is observed to be intermixed in the annealed sample. This evidences the production of a large number of the group III vacancies via electrons below the contact.
Structure and magnetoresistance effect in granular Ag–Ni alloys prepared by gas flow condensation technique
Authors: Dimesso L. , Hahn H.
Published: July 2002

Giant magnetoresistance (GMR) effect in heterogeneous granular Ag–Ni alloys, prepared by utilizing coevaporation of the metals in continuous He flow, is reported. The average grain size, determined from x-ray diffraction (XRD) data, increases from 11 to 28 nm with increasing He pressure. The transmission electron microscope analysis revealed the presence of Ag and Ni isolated grains which give rise to coalescence. The nitrogen adsorption measurements show a decrease of the surface area with increasing pressure confirming the XRD data. Electrical measurements revealed a GMR effect as large as 7%, at room temperature and a magnetic field H=1 T, on the specimen prepared with a final pressure of 800 Pa.
An atomistic simulator for thin film deposition in three dimensions
Authors: Huang Hanchen , Gilmer George H. , Dı́az de la Rubia Tomas
Published: July 2002

We describe an atomistic simulator for thin film deposition in three dimensions (ADEPT). The simulator is designed to bridge the atomic and mesoscopic length scales by using efficient algorithms, including an option to speed up surface diffusion using events with multiple diffusion hops. Sputtered particles are inserted and assigned ballistic trajectories with angular distributions appropriate for magnetron sputtering. Atoms on the surface of the film execute surface diffusion hops with rates that depend on the local configuration, and are consistent with microscopic reversibility. The potential energies are chosen to match information obtained from a database of first principles and molecular dynamics (MD) calculations. Efficient computation is accomplished by selecting atoms with probabilities that are proportional to their hop rates. A first implementation of grain boundary effects is accomplished by including an orientation variable with each occupied site. Energies and mobilities are assigned to atoms in grain boundaries using values obtained from MD. In this article we describe simulations of the deposition of aluminum. The film atoms occupy face centered cubic lattice sites of a single crystal. Three-dimensional films deposited on vias and trenches up to 0.05 μm in size have been simulated. We discuss these films in the context of step coverage issues, and scaling to macroscopic sizes. Texture development is discussed in the light of simulations showing anisotropic crystal growth. Future versions of ADEPT will include a more complete model of grain development in thin films.