bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth kinetics of solid-state-reacted Fe-Zr multilayer films
Authors: Paesano A. , Teixeira S. R. , Amaral L.
Published: July 2002

Multilayers of Fe0.33Zr0.67, prepared by electron beam evaporation, have been characterized by conversion electron Mössbauer spectroscopy, Rutherford backscattering spectroscopy, and x-ray diffraction. Two phases, one amorphous and another crystalline (FeZr3), occur by solid-state reaction. For temperatures of 350 and 500 °C and annealing times ranging from 10 min to 72 h the growth rates of both phases had been obtained. From these results we suggest a model to describe the phase growth kinetics of the amorphous-crystalline Fe0.33Zr0.67 multilayer thin film.
The localization of energy and plastic deformation in crystalline solids during shock or impact
Authors: Coffey C. S.
Published: July 2002

When crystalline solids are subjected to shock or impact the resulting plastic shear deformation is often concentrated in narrow-band-like regions. These regions are the sites of considerable energy localization and often determine the response of the crystal to the rapid deformation. Here, a theoretical account is given of this energy-localization plastic-deformation process. It is shown that the process is distinctly quantum mechanical. For mild shocks or impacts the energy dissipated within the bands can cause heating, material failure, and, where appropriate, chemical reactions. For high-amplitude shocks rapid multiphonon-stimulated internal molecular excitation can occur. This energy localization is responsible for both the initiation of chemical reaction in explosive crystals subjected to mild impact and the transition to detonation in these same crystals during high-amplitude shock loading.
A model of fluid, heat flow, and electromagnetic phenomena in a nontransferred arc plasma torch
Authors: Westhoff R. , Szekely J.
Published: July 2002

A mathematical model is presented to describe the electromagnetic, heat flow, and fluid flow phenomena within a nontransferred arc plasma torch and in the resultant plume. In the development of the model allowance is made for the conservation of mass, momentum, thermal energy, and the continuity of the current. An important, novel feature of the model is that it can predict both the pattern of heat generation within the torch and the electromagnetic forces, thus providing a fundamental basis for predicting plume behavior. Specific calculations are presented for a pure argon system (i.e., an argon plasma discharging into an argon environment), operating in a laminar mode, and the theoretical predictions appear to be in quite good agreement with experimental measurements. An important finding of the work is that the electromagnetic forces may markedly modify the velocity profiles and may significantly affect the swirl of the plasma gas exiting the torch. In addition, swirl is shown to have a significant affect on the behavior of the arc and thus affects the resulting plume.
Interdiffusion, hardness and resistivity of Cr/Cu/Co/Au thin films
Authors: Madakson Peter
Published: July 2002

The effects of interdiffusion and microstructure on the hardness and resistivity of Cr/Cu/Co/Au thin films were studied at temperatures ranging from 25 to 600 °C. Cobalt was found to be a very effective diffusion barrier between Cu and Au at temperatures of ≤400 °C for annealing times greater than 2 h. As a result, little or no change in hardness or resistivity of the Cr/Cu/Co/Au structure occurs. Above 400 °C, the Co layer breaks down, and there is massive interdiffusion of Cu and Au, which is associated with grain growth, grain boundary precipitation and surface roughening of the films. The observed changes in the hardness and resistivity correlate with the degree of interdiffusion of Cu and Au for temperatures ≤500 °C. The activation energy for interdiffusion is 1.65 eV and that for Au diffusion into Cu via the Co layer is 1.91 eV. These values are consistent with those reported for grain boundary diffusion in thin films.
Structural and electrical characteristics of metal-insulator-semiconductor diodes based on Y2O3 dielectric thin films on silicon
Authors: Rastogi A. C. , Sharma R. N.
Published: July 2002

Metal-insulator-semiconductor (MIS) diodes with an electron-beam-deposited and oxygen-annealed thin (≊80 nm) Y2O3 dielectric layer on p-Si(100) show metal-oxide-semiconductor capacitor action. As-deposited Y2O3 films are oxygen-deficient amorphous and show low 5×10−9 A leakage currents for a capacitor area of 0.785 mm2 and breakdown fields of 1.0 MV/cm. Amorphous Y2O3 film crystallizes to a bcc phase by annealing at 400 °C causing increased conduction due to asperities related localized high-field regions at contacts while its dielectric constant increases from a low value of 9.0ε0 to 27ε0. Annealing the Y2O3 film on Si above the crystallization temperature in the range 425 °C<Ts < 650 °C leads to growth of an about 5-nm-thick intermediate SiO2 layer at the Y2O3/SiO2 interface. A remarkable two orders of magnitude decrease in leakage current to 2×10−11 A and increase in breakdown field to 2.0 MV/cm is observed for MIS diodes with composite Y2O3/SiO2 dielectric. Current-voltage behavior in the inversion mode demonstrates existence of positive charge trapping states at the Y2O3/SiO2 interface region. The current transport in Y2O3 and Y2O3/SiO2 insulator layers is dominated by bulk conduction behavior of Y2O3 through the Poole–Frenkel mechanism.
Structure property anisotropy in lattice-mismatched single heterostructures
Authors: Morris D. , Sun Q. , Lacelle C. , Roth A. P. , Brebner J. L. , Simard-Normandin M. , Rajan K.
Published: July 2002

Anisotropic optical, electrical, and structural properties have been observed in thick InxGa1−xAs/GaAs single heterostructures grown by low-pressure metal-organic vapor phase epitaxy on (001) and slightly misoriented GaAs substrates. The luminescence of the (001) samples is polarized and the electron mobility is higher along one of the 〈110〉 directions. Asymmetric distributions of surface ridges and misfit dislocations have been observed in secondary electron micrographs (SEMS) of the surfaces and in transmission electron micrographs. Strong anisotropy and a clear correlation between the anisotropic optical, electrical, and structural properties have been observed for samples grown on (001) oriented substrates. For (001) samples, the results indicate that the anisotropic properties are induced by nonuniform strain relaxation. For samples grown on misoriented substrates, SEM and micro-Raman spectroscopy indicate a better crystal quality. The anisotropic properties are found to be reversed and the degree of anisotropy is significantly reduced. The results suggest the improvement of interfacial coherency owing to the mechanism of nucleation on a substrate presenting a series of steps and ledges. The reduction of defects within the epilayer can be partly due to a faster strain relief in vicinal (001) epilayers.
Thermal runaway in microwave heated ceramics: A one-dimensional model
Authors: Kriegsmann Gregory A.
Published: July 2002

The heating of a ceramic slab under TM-illumination is modeled and analyzed in the small Biot number regime. The temperature distribution is almost spatially uniform in this limit and its evolution in time is governed by a first-order nonlinear amplitude equation. This equation admits a time independent solution which is a multivalued function of the microwave power. The graph of this steady temperature as a function of the microwave power gives an S-shaped response curve when the electrical conductivity is modeled either as an exponential function of temperature or an Arranius law. The dynamics of the heating process are deduced from the amplitude equation and the multivalued response, and are dependent upon the microwave power and initial conditions. For certain initial conditions and power levels the system evolves to the upper branch of the response curve which corresponds to thermal runaway. Other initial conditions and power levels force the system to evolve to the lower branch and a safe sintering temperature. This heating process can be controlled in some sense by varying the microwave power in time at a rate commensurate with the thermal changes. Specifically, the power is allowed to change in an exponential fashion from a higher to a lower power level. This relationship is turned into a differential equation, which is appended to the amplitude equation to form an autonomous system of the second order. This system is analyzed using a phase-plane method. The analysis shows the existence of a stable manifold which divides the phase plane into two parts: Trajectories in the region above this curve correspond to runaway heating while those below yield stable sintering. Various heating scenarios are presented and discussed.
Effect of contact barrier heights on a-Si:H p-i-n detector and solar-cell performance
Authors: Rubinelli F. A. , Arch J. K. , Fonash S. J.
Published: July 2002

The transport-simulation computer program amps has been used to examine the role of contact barrier heights in determining the performance of a-Si:H p-i-n homojunction detector and solar-cell devices. Current-voltage performance, with and without illumination present, is considered. It is determined that for p and n layers that are sufficiently thick and sufficiently doped, the reverse bias currents, both in the dark and under illumination, do not depend or depend only weakly on the barrier heights of the contacts to the doped layers. However, these contact barrier heights can strongly influence both the dark and illuminated currents in forward bias. Thus, it is determined that the quality of the contacts to the doped layers does not affect the performance of a-Si:H p-i-n detector structures, but it can strongly influence the performance of a-Si:H p-i-n solar-cell structures.
Optical and structural properties of ternary alloy AlxGa1−xAs/AlAs multiple-quantum-well structures
Authors: Dabbicco M. , Cingolani R. , Ferrara M. , Tapfer L. , Fischer A. , Ploog K.
Published: July 2002

The linear and nonlinear optical properties of a series of ternary alloy AlxGa1−xAs/AlAs multiple-quantum-well structures have been investigated and related to the multilayer configuration. The direct energy gap was found to scale with the AlAs mole fraction as predicted by Lee and Yuravel [Phys. Rev. B 21, 659 (1980)] and the band offset ratio to depend on the alloy composition. Exciton absorption bleaching was observed at room temperature and the nonlinear absorption cross sections were estimated for the first two confined excitonic states. Finally, the possibility of achieving optical gain for the type-II band alignment along the growth direction as well as in the layer plane is demonstrated.
Enhanced oxygen precipitation in electron irradiated silicon
Authors: Hallberg Tomas , Lindström J. Lennart
Published: July 2002

The precipitation of oxygen has been investigated for 2 MeV electron irradiated silicon samples, with irradiation doses 1015–1018 cm−2, at an annealing temperature of 900 °C for up to 444 h. The samples initially contained either different concentrations of the vacancy-oxygen (VO) center created at the irradiation, or the vacancy-dioxygen (VO2) center created by annealing at 350 °C after the irradiation. It was found that the incubation time and oxygen decay rate for the precipitation process was irradiation dose dependent. Among the VO samples this could be caused by a supersaturation of vacancies, which would both decrease the critical precipitate radius and enhance oxygen diffusion. It was also found that an enhanced precipitation among VO samples appeared as a transient process, which has not been observed at this high temperature before. A different mechanism could account for the enhanced precipitation rate for samples with VO2. For these samples results from transmission electron microscopy studies, Wright etching, and growth of precipitate related infrared (IR)-absorption bands all indicate increased precipitate number densities. High temperature rapid thermal annealing shows that VO2 develops into VO2+Oi. It is therefore suggested that the VO2 center is a nucleus for oxygen precipitation. Different incubation times were observed for the growth of the precipitate IR bands, which is explained by the appearance of differently shaped precipitate particles.
Electronic and gaseous processes in the prebreakdown phenomena of dielectric liquids
Authors: Beroual A.
Published: July 2002

The article shows experimentally the simultaneous influence of electronic scavenger additives and the hydrostatic pressure on the current and emitted light by streamers, especially in cyclohexane under negative polarity. This suggests that both electronic and gaseous mechanisms do not act singly in the prebreakdown phase of dielectric liquids. A relationship between the streamer current, the electrical charge, the velocity, and the propagation mode of streamers is discussed. Based on energy considerations, we establish a mathematical expression allowing us to evaluate the velocity of streamers and to explain the propagation modes. The streamer the current of which consists of discrete pulses moves by steps. The higher the number and/or the amplitude of the current pulses, the shorter the durations between these steps and the higher the average velocity of the streamers; its propagation tends to become continuous. That is the case of the slow streamers in the presence of electronic scavenger additives. On the other hand, the streamer becomes rapid then more energetic and the hydrostatic pressure necessary for its disappearance increases. That is why it is thought that both gaseous and electronic processes simultaneously act in the prebreakdown phase even if one of them is dominant in one case and the second in another.
Simulation program suitable for hot carrier studies: An efficient multiband Monte Carlo model using both full and analytic band structure description for silicon
Authors: Wang Xiaolin , Chandramouli V. , Maziar Christine M. , Tasch Al F.
Published: July 2002

An efficient Monte Carlo model using both the full electronic band structure calculated from the empirical pseudopotential method and fitted, anisotropic, analytic bands is described. With the simulation program suitable for hot carrier studies, electron dynamics (i.e., scattering processes) are treated using the pseudopotential bands, where the accuracy of the band structure is most critical, while the electron kinetics (i.e., electron free flight between scattering and postscattering momentum selection) is treated using the fitted, analytic bands in order to greatly enhance the computational efficiency of the simulator. The analytic, multiband, multivalley model has 65 ellipsoidal, nonparabolic valleys and fits both the density of states and the electron E(k) dispersion relations of the pseudopotential band. The scattering ‘‘matrix elements’’ effect is also explored and an efficient model for this was developed and implemented for the first time in the framework of an analytic band. With this model, it is possible to include band-structure effects with greatly enhanced physical accuracy and central processing unit times comparable to other fitted band models. Excellent agreement is obtained between results using this new model and those from experiments and computationally more demanding simulators.
Energy of arrays of nonperiodic interacting dislocations in semiconductor strained epilayers: Implications for strain relaxation
Authors: Jain Uma , Jain S. C. , Atkinson A. , Nijs J. , Mertens R. P. , Van Overstraeten R.
Published: July 2002

The interaction energy EirrI of arrays of dislocations with nonperiodic (or irregular) distribution is calculated. The calculations have been made for uniform-random and Gaussian distributions of dislocations. The method used is, however, general and can also be applied to any arbitrary or an observed distribution of dislocations. The results for several values of average spacing p̄ and standard deviation σ are given and are compared with the energy EI of periodic arrays with spacing p=p̄. The total energy EirrT of strained layers containing nonperiodic dislocation arrays is also calculated. The results for both 90° and 60° dislocations are given. For sufficiently large numbers of dislocations, EirrI is always larger than EI. The difference between the energies EirrI and EI increases rapidly as the standard deviation σ of the nonperiodic distribution increases. The equilibrium strain relaxation in thick layers and the strain relaxation on annealing the metastable layers are usually calculated by modeling the nonperiodic array as an equivalent periodic array with p=p̄. It is found that this procedure for the calculation of the strain relaxation is not valid.
A quantum statistical theory of linewidths of radiative transitions due to compositional disordering in semiconductor alloys
Authors: Lee S. M. , Bajaj K. K.
Published: July 2002

A quantum statistical formalism has been developed for the excitonic luminescence linewidths and line shapes in semiconductor binary alloys due to band-gap fluctuations caused by the random distributions of the alloy components in an applied magnetic field. The virtual crystal approximation is used to estimate the local band-gap variations. The shifts of the excitonic transition energy due to the band-gap fluctuations are obtained using the first-order perturbation theory. A Gaussian line shape is obtained for the excitonic transition using standard statistical techniques. This formalism is applied to calculate the linewidths and line shapes associated with the ground-state excitonic transition as a function of alloy composition and magnetic-field strength in AlxGa1−xAs and InxGa1−xP alloys. The resulting linewidths and line shapes are in good agreement with the available low-temperature photoluminescence data; however, the calculated linewidths are consistently smaller than the measured values. The possible mechanisms responsible for this discrepancy are discussed. A comparison of excitonic linewidths obtained from the present theory with those calculated earlier is also presented.
Oxygen on the (100) CdTe surface
Authors: Wu Y. S. , Becker C. R. , Waag A. , Schmiedl R. , Einfeldt S. , Landwehr G.
Published: July 2002

We have investigated oxygen on CdTe substrates by means of x-ray photoelectron spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED). A Te oxide layer that was at least 15 Å thick was found on the surface of as-delivered CdTe substrates that were mechanically polished. This oxide is not easily evaporated at temperatures lower than 350 °C. Furthermore, heating in air, which further oxidizes the CdTe layer, should be avoided. Etching with HCl acid (15% HCl) for at least 20 s and then rinsing with de-ionized water reduces the Te oxide layer on the surface down to 4% of a monoatomic layer. However, according to XPS measurements of the O 1s peak, 20%–30% of a monoatomic layer of oxygen remains on the surface, which can be eliminated by heating at temperatures ranging between 300 and 340 °C. The RHEED patterns for a molecular beam epitaxially (MBE)-grown CdTe film on a (100) CdTe substrate with approximately one monoatomic layer of oxidized Te on the surface lose the characteristics of the normal RHEED patterns for a MBE-grown CdTe film on an oxygen-free CdTe substrate.
Giant magnetoresistance in Co/Cu superlattices with mixed interfaces
Authors: Suzuki Motofumi , Taga Yasunori
Published: July 2002

Magnetoresistance, antiferromagnetic coupling, and crystallographic orientation of Co/Cu superlattices with intentionally mixed interfaces have been studied as a function of the thickness of the mixed region. The antiferromagnetic coupling is weakened, and spin-independent scattering of free electrons is enhanced with increasing thickness of the mixed region, although the morphology and the superlattice period remain unchanged. Saturation magnetoresistance is reduced from 27% to 4% as the result of the formation of a 0.15 nm mixed region at the interfaces. Moreover, the crystallographic orientation of Co/Cu superlattices is also found to be varied by formation of the mixed region. Giant magnetoresistance, antiferromagnetic coupling, and the crystallinity of Co/Cu superlattices are governed by the events in the thin region at the interfaces less than 1 monolayer.
Optical and electrical properties of layer semiconductor p-GaSe doped with Zn
Authors: Shigetomi S. , Ikari T. , Nakashima H.
Published: July 2002

Zinc (Zn) is doped into GaSe single crystals grown by the Bridgman technique in a wide range from 0.005 to 0.5 at. % to the stoichiometric melt. Radiative recombination mechanisms have been investigated by using photoluminescence (PL) measurements. The PL spectra in Zn-doped samples at 77 K are dominated by three emission bands at 1.75, 1.63, and 1.27 eV. The 1.63 and 1.27 eV emission bands are enhanced with the increase in the amount of Zn. In addition to the results of Hall effect measurements, it is found that the 1.63 and 1.27 eV emission bands are associated with the acceptor levels at 0.12 and 0.3 eV above the valence band, respectively. For the 1.27 eV emission band, the temperature dependences of the PL intensity, peak energy, and half-width are characterized by the configurational coordinate model.
Charge and energy transport by tunneling thermoelectric effect
Authors: Marschall Jochen , Majumdar Arun
Published: July 2002

Computational predictions, based upon conventional one-dimensional tunneling theory, are presented for charge and energy transport by electron tunneling thermoelectric effect. It is shown that a temperature difference across a tunnel junction connected in an open electrical circuit produces a thermopower S and a heat conductance HV. In a closed circuit, the temperature difference drives a tunnel current which is quantified by a current conductance Q =‖ Jth/ΔT‖LimΔT■0 (where Jth is the current density) and a heat conductance HJ. The thermopower S is shown to be relatively insensitive to image potentials and barrier thickness, whereas the transport coefficients Q, HJ, and HV are highly sensitive to junction parameters. The calculations for a ‘‘generic’’ Al-Al2O3-Al junction with a 25 Å barrier thickness indicate that S and Q could be measurable, whereas HV and HJ are probably below the limits of detection. Although S might be measured by a scanning tunneling microscope, it is not clear at present how tip geometry would influence the measurement.
Highly resolved separation of carrier- and thermal-wave contributions to photothermal signals from Cr-doped silicon using rate-window infrared radiometry
Authors: Mandelis A. , Bleiss R. , Shimura F.
Published: July 2002

It is shown that the new photothermal technique of lock-in rate-window infrared radiometry is capable of completely separating out photoexcited free-carrier-wave and thermal-wave contributions to the photothermal signal from an n-type, Cr-doped Si wafer with a simple experimental procedure, and with superior temporal resolution in the determination of the electronic lifetime and thermal transport time constant.
Correlation between Schottky-barrier height and the heat of formation of transition-metal silicides
Authors: Kikuchi Akira
Published: July 2002

The intrinsic Schottky-barrier height obtained from an interface-defect-free model has the close correlation with the heat of formation of transition-metal silicides. This linear correlation includes previously anomalous values reported for PtSi and IrSi.
Effects of dopants on dynamic behavior of dislocations and mechanical strength in InP
Authors: Yonenaga Ichiro , Sumino Koji
Published: July 2002

The dynamic behavior of α, β, and screw dislocations in both undoped and doped InP is investigated. The generation of dislocations from a surface scratch is suppressed in doped InP. This effect is attributed to the immobilization of dislocations due to locking by impurities similar as observed in GaAs. Isovalent Ga and As dopants are found not to affect the dislocation velocity. Zn acceptors strongly reduce the dislocation velocities of all type of dislocations while S donors enhance the velocity of α dislocations and reduce the velocity of β and screw dislocations. Such impurity effects are in contrast with those observed in GaAs. The measured dislocation velocities are expressed with a simple empirical equation as a function of stress and temperature. The mechanical strength of InP reflects the above dynamic behavior of individual dislocations. An increase in the yield strength results from a decrease in the dislocation velocity in Zn-doped InP. On the other hand, an increase in the strength at high temperatures results from dislocation immobilization in Zn- or S-doped InP.
Molecular-dynamics simulation of mechanical alloying for the Al50Ti50 alloy
Authors: Lu J. , Szpunar J. A.
Published: July 2002

The structural ordering development during mechanical alloying of the Al50Ti50 alloy was investigated by using molecular-dynamics computer simulations. Random external forces with both random orientations and magnitudes were used to simulate the mechanical alloying processes and pseudopotential was used as a model for the interaction between the atoms. The results indicate that the final nonequilibrium phase obtained through simulation of mechanical alloying is an amorphous state which can be formed experimentally in the laboratory. The transformation from crystals to amorphous state may locally be a first-order-like phase transition, but statistically it is a gradual phase transition due to the characteristics of random external forces which help atoms to overcome their energetic barrier during the mechanical alloying. This means that the transformation occurs in random sites and is discontinuous.
Pulsed laser-induced melting followed by quenching of silicon films
Authors: Sameshima T. , Usui S.
Published: July 2002

Amorphization and crystallization were studied through laser-induced melting of silicon films formed on quartz substrates induced by irradiation with a 30 ns XeCl excimer laser. Homogeneous and rapid solidification occurs and amorphous solid state can be formed when the melt duration is long enough to make the temperature gradient in liquid silicon lower than 1×105 K/cm at the Si/quartz interface. The solid state after homogeneous solidification is governed by recalescence caused by latent heat released at solidification. A completely amorphous state is formed when film thickness is thinner than 24 nm because latent heat reduces as film thickness decreases. Both crystalline and amorphous states were observed for film thickness above 24 nm because recalescence can cause crystalline grain growth. Complete crystallization occurs through interface controlled growth when the temperature gradient is higher than 1×105 K/cm. The velocity of liquid/solid interface is 0.6 m/s, which is too low to cause amorphization.
The dependence of Si and SiO2 electron emission on the angle of ion incidence
Authors: Jacobsson Harald , Holmén G.
Published: July 2002

The electron emission from Si and SiO2 was measured as a function of the angle of ion incidence for 200–300 keV H+, N+, Ar+ and Xe+ ions. For Si, the angular variation of the electron emission was found to approximately follow the angular variation of the electronic energy deposition, provided that recoil ionization was taken into account. For SiO2, the electron emission increased much more slowly with the angle of the ion incidence than expected, but the data are reasonably well represented by a single function of the expected electronic energy deposition to the power of 0.73. It is suggested that the holes left behind by the electron cascades of individual ions in SiO2 may attract the liberated electrons and cause the probability of escape to decrease with increasing electronic energy deposition. Measurements of the dependence of the electron emission on the angle of ion incidence were found to be a powerful tool in sorting out various mechanisms that could possibly influence electron emission.
Thermal and direct etching mechanisms of Si(100) with a hyperthermal chlorine beam
Authors: Szabó András , Farrall Paul D. , Engel Thomas
Published: July 2002

The etching of Si(100) with hyperthermal beams of atomic and molecular chlorine has been studied in the temperature range between 130 and 200 K. The dominant etch product, SiCl4, is evolved in two parallel reaction pathways, only one of which is thermally activated. It is shown that the nonactivated pathway, which has an appreciable rate only when hyperthermal chlorine atoms are incident upon the surface, is due to collision-induced desorption of weakly bound SiCl4. By increasing the normal component of the chlorine incident translational energy, the efficiency of converting incident Cl into SiCl4 can be increased to 0.6% in the nonthermal channel, at temperatures for which the thermal etching rate is negligible. The normal energy scaling and the observed energy threshold suggest that this process should result in highly anisotropic etching.
Magnetic neutron scattering (invited)
Authors: Lynn J. W.
Published: July 2002

The application of neutron scattering techniques to magnetic problems is reviewed. We will first discuss diffraction techniques used to solve magnetic structures, as well as to measure magnetic form factors, order parameters, critical phenomena, and the scattering from low-dimensional systems. We will also discuss inelastic scattering techniques, including polarized beam methods, utilized to determine the spin dynamics of various materials. Information will be provided about the types of spectrometers available at the user-oriented national facilities located at Argonne National Laboratory, Brookhaven National Laboratory, Los Alamos National Laboratory, The National Institute of Standards and Technology, and Oak Ridge National Laboratory, as well as the spectrometers at the Missouri University Research Reactor.
Annealing effects on Si-doped GaAs grown on high-index planes by molecular-beam epitaxy
Authors: Harrison I. , Pavesi L. , Henini M. , Johnston D.
Published: July 2002

A photoluminescence study of the effects of annealing on Si-doped (∼1016 cm−3) GaAs grown on (311)A-, (111)A-, (111)B-, and (100)-oriented substrates by molecular-beam epitaxy has been performed. The anneal temperatures were 873, 973, and 1098 K. All the anneals were of 24 h duration. Detailed assessment of the low-temperature photoluminescence spectra suggests that site switching (Si switching from Ga site to As site) only occurs in the n-type samples [(100) and (111)B samples] and not in the p-type ones [(111)A and (311)A samples].
Influence of metal/n-InAs/interlayer/n-GaAs structure on nonalloyed ohmic contact resistance
Authors: Shiraishi Y. , Furuhata N. , Okamoto A.
Published: July 2002

We have investigated in detail the influence of interlayer structures on nonalloyed ohmic contact resistance (ρc), in terms of the crystalline defects and the potential barrier at the interlayer/GaAs interface. The interlayer structures are a graded-band-gap InAs/GaAs strained-layer superlattice (graded SLS), a graded-band-gap InGaAs, and conventional SLSs without graded band gaps. A two-layer transmission line model indicates that the barrier resistance in the interlayer highly depends on the interlayer structure: ≤5×10−8 Ω cm2 for the graded SLS and graded InGaAs interlayers and 10−5–10−6 Ω cm2 for the conventional SLS interlayers. To explain the large dependence of the interlayer structure, first, the density and distribution of the misfit dislocations and stacking faults caused by the large lattice mismatch between InAs and GaAs have been investigated in detail by high-resolution transmission electron microscopy. In the graded SLS and conventional SLS interlayers, the influence of the high-density depletion regions spread near the crystalline defects is found to be negligible because of the high doping concentrations (∼1019 cm−3) in the interlayers. Second, the potential barrier at the interlayer/GaAs interface has been investigated by simulating the barrier resistance. The potential barrier profile is calculated self-consistently with Poisson’s equation and the Schrödinger equation. Tunneling current through the barrier is analyzed using the Wentzel–Kramers–Brillouin approximation or the numerical wave solution to the Schrödinger equation. The graded SLS interlayer has the effectively smooth conduction band profile without the barriers, which is similar to that of the graded InGaAs interlayer, because of its short period SLS. In the conventional SLS interlayers, the reasonable barrier heights of 0.14–0.26 eV obtained by this simulation indicates that these barriers are the dominant factor which increases the contact resistances. For the low-resistance nonalloyed ohmic contact, therefore, a smooth conduction band profile without band discontinuity is more predominant than the reduction in the crystalline defect density.
Calculation of hole mobility in doped SiGe alloys using a Monte Carlo method with a bond orbital band structure
Authors: Liou Tsyr-Shyang , Wang Tahui , Chang Chun-Yen
Published: July 2002

Hole mobility in strained Si1−xGex/Si(001) layers is calculated as functions of temperature and doping concentration for various Ge contents using a Monte Carlo technique. In the Monte Carlo simulation, the band structure is computed by using a bond orbital model, which combines the k⋅p and the tight-binding methods with a strain Hamiltonian. The Fermi–Dirac distribution is employed for heavily doped impurity scattering. The alloy interaction potential of 1.0 eV for the Monte Carlo model is obtained by fitting the measured velocity-field characteristics in strained Si1−xGex alloys. The calculated hole mobilities compare well with experimental results. The strain effect on hole transport is also evaluated.
Multiphonon-assisted energy transfer between Yb 4f shell and InP host
Authors: Taguchi Akihito , Takahei Kenichiro , Horikoshi Yoshiji
Published: July 2002

The energy transfer mechanism between an Yb 4f shell and an InP host was investigated, assuming that a nonradiative multiphonon process assists the energy transfer. The values of the energy involved in the energy transfer were determined from the results of optical and electrical experiments. Rate equations were solved to obtain the temperature dependence of the Yb intra-4f-shell luminescence decay time. The calculated results and the experimentally obtained temperature dependence agree well. The calculated temperature dependence of the Yb intra-4f-shell luminescence intensity also agrees with the experimental measurements. These results strongly suggest that phonon absorption and emission compensate the energy mismatch in the energy transfer processes. The calculations also indicate that the thermal quenching phenomenon is mainly determined by the energy mismatch between the recombination energy of an electron and a hole and the Yb 4f-shell energy between the excited and ground states. On the basis of the above formulation, the Yb intra-4f-shell luminescence intensity under hydrostatic pressure was also investigated theoretically and compared with experimental results. The 4f-shell luminescence recovery at elevated temperature under hydrostatic pressure was qualitatively explained in the framework of the present model. The characteristic behavior of the thermal quenching in other rare-earth doped semiconductors could also be explained qualitatively assuming that the energy transfer mechanism is similar to the one for InP:Yb.
Nuclear magnetic resonance study of the magnetic behavior of ultrafine Co clusters in zeolite NaY
Authors: Zhang Y. D. , Hines W. A. , Budnick J. I. , Zhang Z. , Sachtler W. M. H.
Published: July 2002

59Co spin-echo nuclear magnetic resonance (NMR) experiments have been carried out at 1.3 and 4.2 K, for external magnetic fields up to 9 kOe, in order to study 6–10 Å, single-domain Co clusters isolated inside zeolite NaY supercages. The magnetic behavior is characterized by a superparamagnetic blocking temperature, relaxation time behavior for increasing and decreasing fields, and a dependence on the magnetic history. The observed NMR spectra are broad with structural features characteristic of both fcc- and hcp-like short-range order. Unlike bulk materials, the application of fields up to 9 kOe causes a dramatic increase in the signal intensity. The results are discussed in terms of the particle-size distribution and crystalline anisotropy, and their relationship to the temperature and field dependence of the superparamagnetic/ferromagnetic behavior.
Formation and optical characterization of nanometer dimension colloids in silica formed by sequentially implanting In and Ag
Authors: Magruder R. H. , Zuhr R. A.
Published: July 2002

The optical properties of a series of In then Ag sequentially implanted silica samples are examined as a function of the relative concentrations of implanted In and Ag. The doses used were in ratios, In to Ag, of 9:3, 6:6, and 3:9. Energy of implantation was 320 keV for the In and 305 keV for the Ag. Nominal total doses as determined by current integration for the three samples were 12×1016 (In+Ag) ions/cm2. The depth profile of the implanted ions and optical absorption were found to be a function of the relative doses and to differ significantly from samples implanted separately with either In or Ag.
The effect of subwafer dielectrics on plasma properties in plasma etching reactors
Authors: Hoekstra Robert J. , Kushner Mark J.
Published: July 2002

Nonplanar electrode topographies in plasma etching reactors are known to perturb plasma properties. In this article results from a computational study of plasma etching reactors having nonuniform dielectric structures below the wafer are presented. The system is an inductively coupled plasma reactor having a 13.56 MHz bias applied to the substrate. The model we have used is a hybrid simulation consisting of electromagnetics, electron Monte Carlo and fluid kinetics modules, and an off-line plasma chemistry Monte Carlo simulation. We found that the subwafer dielectric adds a series capacitance to the sheath and wafer resulting in voltage division of the applied potential between the sheath, wafer, and dielectric. This produces a smaller sheath potential and smaller sheath thickness above the dielectric. The ion energy distribution is therefore depressed in the vicinity of the dielectric. The effect is more severe at high plasma densities where the capacitance of the sheath is larger compared to the subwafer dielectric.
Influence of fluorine implant on boron diffusion: Determination of process modeling parameters
Authors: Vuong H.-H. , Gossmann H.-J. , Rafferty C. S. , Luftman H. S. , Unterwald F. C. , Jacobson D. C. , Ahrens R. E. , Boone T. , Zeitzoff P. M.
Published: July 2002

The effects of low-dose ion implants with Si+, Ne+, and F+ on the transient enhanced diffusion of B in silicon after annealing at 900 °C for 30 min have been investigated. Processing conditions such as implant dose (3.5×1013 cm−2) and energy (30–60 keV) were chosen to simulate the lightly doped drain implant in a 0.35 μm complementary metal-oxide-semiconductor technology. An epitaxially grown B-doping superlattice is used to extract directly depth profiles of average Si self-interstitial concentration after processing. For Si+ the transient enhanced diffusion of B increases with the energy of the implanted ion. Ne+ implanted with the same energy as Si+ causes more transient enhanced diffusion, while Ne+ implanted with the same range as Si+ causes slightly less. Implantation of F+ enhances the B diffusivity considerably less than Si or Ne implantation. These effects were modeled using simulations of defect diffusion in the presence of traps. A trap concentration of (2.4±0.5)×1016 cm−3 gave good agreement in all situations except F+ implantation, where (6.6±0.6)×1016 cm−3 traps were necessary. It is proposed that this is caused by additional traps for Si interstitials that are related to F+.
Semiconducting rhenium silicide thin films on Si(111)
Authors: Nguyen Tan T. A. , Veuillen J. Y. , Muret P. , Kennou S. , Siokou A. , Ladas S. , Lahatra Razafindramisa F. , Brunel M.
Published: July 2002

The crystallographic, electronic, and optical properties of thin ReSi2 films (∼20–300 Å) have been investigated in situ by low energy electron diffraction (LEED) and photoelectron spectroscopy (XPS and UPS), ex situ by glancing incidence x-ray diffraction (GIXD), and optical absorption measurements. Thin Re layers were evaporated under ultrahigh vacuum on Si(111) (7×7) surfaces, maintained at room temperature, or heated at 650 °C. The films were subsequently annealed at increasing high temperature and the silicide formation was followed by in situ surface techniques. For very thin films (≲35 Å) LEED shows a faint (1×1) pattern after annealing at 750 °C, which improves slightly up to ∼900 °C. For thick films (∼50–300 Å) only a bright background is observed. XPS indicates that the ReSi2 composition is attained upon annealing at 600 °C. In the Re-Si bonding the charge transfer is negligible: the energy positions of the corelevels (Si 2p and Re 4f) are the same in the compound and in the elements. As the energy shift of the Si KLL Auger is negligible also, the extra-atomic relaxation energy for Si atoms is the same in silicide as in silicon, indicating that ReSi2 has a semiconducting character. UPS results confirm this assumption: the density of states near EF decreases strongly upon ReSi2 formation and at the same time the valence band edge shifts from EF to lower binding energy. GIXD gives sharp diffraction peaks, characteristic of ReSi2 (110) in epitaxy on Si(111). This technique also reveals that the films present an additional orientation near the interface. Optical absorption measurements performed on ReSi2 films of ∼300 Å thick indicate that this silicide is a semiconductor with an indirect energy gap of 0.15 eV, in agreement with previous studies.
Al2Cu precipitate distribution in AlCu interconnects after electromigration stressing: A study by Auger microscopy and ion beam bevelling
Authors: Barkshire I. R. , Prutton M.
Published: July 2002

The York multi-spectral Auger microscope has been used to study unpassivated AlCu interconnects on silicon, which have undergone electromigration stressing. Auger, energy dispersive x-ray, and backscattered electron images have been obtained simultaneously from a sample which has been bevelled using Xe+ ions. The exposed surface on the bevel makes an angle of about 10−3 rad with the virgin surface so exposing laterally the depth distribution of the elements in the material. Cu-rich precipitates are observed in the tracks. The combination of Auger, energy dispersive x-ray, and backscattered electron imaging allows the determination of the location of both surface and subsurface AlCu precipitates. The faceted character of the particles can lead to an apparent excess of oxygen in their surfaces. The backscattered electron images are used to correct the Auger images for these topographical artifacts.
Homojunction internal photoemission far-infrared detectors: Photoresponse performance analysis
Authors: Perera A. G. U. , Yuan H. X. , Francombe M. H.
Published: July 2002

The concept of homojunction internal photoemission far-infrared (FIR) detectors has been successfully demonstrated using forward biased Si p-i-n diodes at 4.2 K. The basic structure consists of a heavily doped IR absorber layer and an intrinsic (or lightly doped) layer. An interfacial workfunction between these regions defines the long-wavelength cutoff (λc) of the detector. Three types of detectors are distinguished according to the emitter layer doping concentration level. Our model shows that high performance Si FIR detectors (≳40 μm) can be realized using the type-II structures with a tailorable λc, in which the absorber/emitter layer is doped to a level somewhat above the metal-insulator transition value. Analytic expressions are used to obtain the workfunction versus doping concentration, and to describe the carrier photoemission processes. The photoexcitation due to free-carrier absorption, emission to the interfacial barrier, hot-carrier transport, and barrier collection due to the image force effect, are considered in calculating the spectral response and quantum efficiency as functions of device parameters for Si n+-i structures, leading to a detailed photoresponse analysis of type-II detectors. These results are useful for the design and optimization of type-II detectors.
Orientation selection in thin platinum films on (001) MgO
Authors: McIntyre P. C. , Maggiore C. J. , Nastasi M.
Published: July 2002

Orientation selection in platinum films of ∼20 nm thickness deposited onto (001) MgO substrates by e-beam evaporation was investigated through ion beam channeling and x-ray diffraction. A mixture of crystallites having (111) and (001) orientation was observed in Pt films deposited over a range of substrate temperatures from 25 to 700 °C, with the (111) orientation dominant at low temperatures. The (111) orientation was present in these evaporated films at significantly higher substrate temperatures than reported for Pt films deposited by sputtering or pulsed laser deposition. Both orientations had strongly preferred in-plane orientations: [110] Pt//[110] MgO for the (001)-oriented crystallites and [110]Pt//[110] MgO for the (111). The orientation selection process was rationalized based on the expected relative interfacial energies for these two orientations.
Geometry and structure of sputter-induced cones on nickel-seeded silicon
Authors: Fujimoto Y. , Nozu M. , Okuyama F.
Published: July 2002

Microprotrusions, or cones, grown on monocrystalline Si obliquely sputtered with Ar+ ions, while being supplied with Ni ‘‘seeds’’ by sputtering, were observed by scanning and transmission electron microscopy. At temperatures lower than 400 °C, Ni atoms were deposited on the upper cone slope receiving the high fluxes of seeds, resulting in the development of ‘‘delta-winged’’ cones. Seed layers were Ni for substrate temperatures below 200 °C and nickel silicide for temperatures above 200 °C, and they were silicidized to NiSi2 above 300 °C, suggesting that Ar+ bombardment activated the NiSi2 formation at the growth front of seed-layer tip. Cones were grown heteroepitaxially at 400 °C, consisting of alternating NiSi2 and Si layers. We thus consider that a controlled particle supply process was involved in Ar+ bombardment at 400 °C. Evidence is also presented that impacting Ar+ ions induced an eutectic reaction between Ni and Si around 500 °C.
Reaction probability and reaction mechanism in silicon etching with a hot Cl2 molecular beam
Authors: Suzuki Keizo , Hiraoka Susumu
Published: July 2002

Reaction products in Si etching with a hot Cl2 (Cl2*) molecular beam were measured by a quadrupole mass spectrometer. A major part of the product was shown to be SiCl4, and the reaction probability of Cl2* on a Si surface was obtained. It was found that the reaction probability increases rapidly with the increase in furnace temperature for Cl2* formation, and high reactivity of Cl2* was demonstrated. A reaction model (the activated complex Arrhenius model) is proposed to explain the experimental results, and the model parameters are determined. This model takes into account the effects of the translational and vibrational energies of a Cl2* molecule on the activation energy and the frequency factor in the ordinal Arrhenius model.
Electron-paramagnetic-resonance spectra in as-grown CdGeAs2
Authors: Halliburton L. E. , Edwards G. J. , Schunemann P. G. , Pollak T. M.
Published: July 2002

Electron-paramagnetic-resonance (EPR) has been used to investigate point defects in a single crystal of as-grown CdGeAs2. Spectra taken at 17 K with the magnetic field parallel to the c axis show a broad signal (∼165 Gauss wide) centered on gc=2.018 and a sharper signal (∼56 G wide) centered on gc=2.015. Together, these signals represent an unpaired-spin concentration of approximately 5×1019 cm−3. A single broad signal (∼165 G wide) centered on ga=1.995 is observed at 17 K when the magnetic field is along the a axis. It is suggested that these dominant EPR-active defects in CdGeAs2 consist of either a cation vacancy or an antisite cation with the unpaired spin shared by the four neighboring As ions. Additional weak EPR lines appear when the temperature is increased (from 17 to 40 K) and the microwave power is decreased (from 7 to 2.3 mW).