Volume 91, Issue 10, 15 May 2002
- applied physics reviews
- lasers, optics, and optoelectronics (pacs 42)
- plasmas and electrical discharges (pacs 51-52)
- structural, mechanical thermodynamic, and optical properties of condensed matter (pacs 61-68, 78)
- electronic structure and transport (pacs 71-73)
- magnetism and superconductivity (pacs 74-76)
- dielectrics and ferroelectricity (pacs 77)
- nanoscale science and design
- device physics (pacs 85)
- interdisciplinary and general physics (pacs 1-41, 43-47, 79, 81-84, 89-99)
- 46th annual conference on magnetism and magnetic materials
- inductive recording heads and materials
- high magnetic anisotropy and patterned media
- quantum dots, nano-wires, and layers
- exchange biasing i
- micromagnetic modeling i
- domain observation and control
- particle arrays i
- power, magnetic shielding, and separation
- new applications
- spin polarized tunneling
- particle arrays ii
- longitudinal thin film media and related i
- spin valves
- molecular magnets i
- multilayers and ultrathin films
- exchange biasing ii
- mram--overview and new developments
- spin injection in ferromagnetic/semiconductor materials
- magnetoresistive heads i
- magneto-optic materials i
- patterned films i
- magnetic microscopy and imaging i
- electronic structure
- ferrites i
- molecular magnets ii
- cmr i: magnetotransport
- anisotropic magnetoresistance, magnetoimpedance, hall effect, and devices
- thermal magnetic stability of nano-sized magnetic devices
- magnetic tunnel junction--metals and semiconductors
- magnetic semiconductors i
- cmr ii: fundamental and optical properties
- multilayer films and superlattices
- micromagnetic modeling ii
- head/media interface and tribology i
- ferrites ii
- microwave and millimeter wave devices
- hysteresis modeling
- novel superconductivity and magnetism
- longitudinal thin film media and related ii: afc
- cmr iii: thin films
- exchange biasing iii
- magnetic sensors
- magnetoelastic materials i
- crystalline alloys
- rare earth magnetic materials
- magnetic semiconductors and half-metallics
- cmr iv: spectroscopy
- magnetic tunnel junction i
- patterned films ii
- aspects of perpendicular recording
- spin dynamics i
- perpendicular recording i
- magnetic semiconductors ii
- giant magnetoresistance
- strongly correlated electron systems
- ultrathin films and surface effects i
- rare earth nanostructures
- soft magnetic materials
- magnetoelastic and magneto-optic materials
- fundamental magnetism i
- micromagnetic modeling iii
- numerical methods i
- head/media interface and tribology ii
- spin polarization in half-metals
- perpendicular recording ii
- spin glasses, frustration, and quantum magnetism
- magnetoelectronic devices
- melt spun and splat quenched materials
- planar inductors: materials and devices
- copt, fept, and other hard magnetic materials
- new magnetic materials
- magnetic fluids, biomagnetism, and magnetochemistry
- giant magnetoresistance and spin valves i
- giant magnetoresistance and spin valves ii
- longitudinal thin film media and related iii
- spin dynamics ii
- printed media and recording systems
- numerical methods ii
- particulate media and me tape
- ultrathin films and surface effects ii
- magnetoresistive heads ii
- magnetic tunnel junctions ii
- permanent magnets, processing, and applications
- magnetic microscopy and imaging ii
- fundamental magnetism ii
- instrumentation and measurement techniques
- cmr v
Index of content:
- APPLIED PHYSICS REVIEWS
91(2002); http://dx.doi.org/10.1063/1.1467950View Description Hide Description
The use of adhesive bonding in joining of materials with different characteristics is of major importance in a variety of microelectronic and photonic applications. The curing of such adhesives is also of great consequence, with the use of optical radiation for adhesive curing becoming the method of choice in various applications, especially bonding of components in microelectronics and fiber–optic assembly. This article reviews recent advances in the development of adhesives, their applications, and their curing methods using optical radiation; it also includes a brief overview of the adhesion mechanisms.
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
91(2002); http://dx.doi.org/10.1063/1.1467404View Description Hide Description
Gain quenched lasers can satisfy the requirements for all-optical switches in communications and computing systems. Hitherto, these devices have lacked optical gain between the input beam and output beam, and have been limited to switching amplitude modulated optical signals. A simple model based on the laser rate equations demonstrates that quenched devices can convert wavelength modulated signals into amplitude modulated ones with programmable optical gain. The discussion includes the effect of carrier injection, laser construction, and type of heterostructure.
91(2002); http://dx.doi.org/10.1063/1.1469664View Description Hide Description
The effects of nitrogen on GaAsP light-emitting diodesgrown by hydride vapor phase epitaxy are described. Nitrogen acts as an isoelectronic trap and this localized state makes GaAsP a widely used material for from-yellow-to-red visible light-emitting diodes. The photoluminescence and electroluminescencespectra,brightness, and reliability were investigated systematically in line with the function of nitrogen concentration, from 0 (without nitrogen) to When the nitrogen concentration reached the total emission in the photoluminescencespectrum at 4.2 K showed a redshift. The study provides clarification of the effects of nitrogen on the diodes and demonstrates that the characteristics of the diodes strongly depend on the nitrogen concentration.
91(2002); http://dx.doi.org/10.1063/1.1473677View Description Hide Description
An efficient and versatile many-body nonequilibrium approach is formulated for computation of photocurrent and photoexcited properties of device structures where quantum effects dominate. This method, based on nonequilibrium Green’s functionquantum transport equations, makes it possible to consider open systems of arbitrary dimensionality having complex potentials, complex geometries, and multiple terminals. In contrast to other approximate computational approaches, no a priori assumptions regarding the particular nature of the phototransitions are required (i.e., bound-to-bound, bound-to-continuum, or continuum-to-continuum). Furthermore, if desired, electron–phonon and electron–electron interactions can also be rigorously accounted for within the same formalism. In this article, the method is applied to two typical resonant-tunneling infrared detector heterostructures as examples: (1) a single-quantum-well structure, and (2) a multiperiod superlattice structure.
- PLASMAS AND ELECTRICAL DISCHARGES (PACS 51-52)
91(2002); http://dx.doi.org/10.1063/1.1468256View Description Hide Description
A one-dimensional fluid model was developed to investigate the time evolution of a positive ion-negative ion (ion-ion) plasma after the application of a direct current (dc) bias voltage. The ion mass and momentum continuity equations were coupled to the Poisson equation for the electric field. The applied bias is shielded and space charge sheaths are formed within the time scale of ion response (ion plasma frequency). When the ion collision frequency is low compared to the ion plasma frequency, electric fieldoscillations develop in the bulk due to the ion inertia (overshoot). The net charge density in the sheath, the sheathelectric field, and the flux and energy of ions bombarding the electrodes all go through maximum values at a time comparable to the ion plasma frequency. Over long time scales the sheaths are in quasiequilibrium with the bulk plasma. At this time, the ion flux on each electrode is twice the free diffusion flux.
Spatially resolved electron temperatures, species concentrations, and electron energy distributions in inductively coupled chlorine plasmas, measured by trace-rare gases optical emission spectroscopy91(2002); http://dx.doi.org/10.1063/1.1467398View Description Hide Description
Determining the spatial dependence of charged and neutral species concentrations and energies in inductively coupled plasmas(ICP) is important for understanding basic plasma chemistry and physics, as well as for optimizing the placement of the wafer with respect to the ICPsource to maximize properties such as etching rate uniformity, while minimizing charging-induced damage and feature profile anomalies. We have determined the line-integrated electron temperature and Cl-atom number density as a function of the axial distance (z) from the wafer in a chlorine ICP, using trace rare gases optical emission spectroscopy (TRG-OES). By selecting rare gas lines that are either (a) excited mostly from the ground states, or (b) excited mainly from the metastable states we were also able to obtain approximate electron energy distributions functions(EEDFs). The gap between the wafer and the window adjacent to the flat coil inductive source was fixed at 15 cm. The pressure was 2, 10, or 20 mTorr (95% 1% each of He, Ne, Ar, Kr, Xe) and the inductive mode source power was 340 or 900 W. measured by TRG-OES, mostly characteristic of the high-energy (>10 eV) part of the EEDF, peaked near the source under all conditions except 2 mTorr and 900 W, where a maximum of 5.5 eV was observed at midgap. The falloff in this high-electron-energy away from the source is mainly due to a preferential loss of high-energy electrons, which can be explained by an increasingly depleted (with increasing energy) EEDF, combined with the nonlocal effect: electrons lose kinetic energy as they approach the higher potential energy regions of lower electron density near the wafer. At 20 mTorr and 340 W, the mean free path for inelastic scattering by high-energy electrons becomes comparable to the reactor dimensions, causing added cooling of the EEDF near the wafer. TRG-OES EEDFsmeasured at a distance of 3 cm from the wafer and 900 W are in excellent agreement with previous Langmuir probe measurements. increased with power and was highest at 900 W in the region between midgap and the ICP window, reaching a level corresponding to a high degree of dissociation of
Comparison of a one-dimensional particle-in-cell–Monte Carlo model and a one-dimensional fluid model for a capacitively coupled radio frequency discharge91(2002); http://dx.doi.org/10.1063/1.1461895View Description Hide Description
A one-dimensional particle-in-cell–Monte Carlo (PIC–MC) model was developed for a capacitively coupled rf discharge in a mixture of and The electron behavior is kinetically simulated by solving Newton’s equations and treating the electron collisions with the Monte Carlo algorithm, whereas the behavior of the ions and radicals is treated by a set of continuity equations. The distinctive feature of this model is its self-consistency, i.e., the motion of the electrons is considered in the real electric field calculated from the Poisson equation, and not in the time-averaged electric field. The PIC–MC results were compared with the data calculated by means of a pure fluid model. In both models, exactly the same type of species, reactions, and cross sections are used. The results of both models, such as the electron energy distribution function, the average electron energy, and the densities of the various plasma species, are compared at a gas pressure of 0.14 Torr and a discharge frequency of 13.56 MHz, for the power ranging from 0.5 to 25 W. The nonstationary and nonlocal features of the electron energy distribution function are shown in the PIC–MC calculations. The effect of accumulation of low-energy electrons in the center of the discharge at higher input power W is observed in the PIC–MC model, in contrast with the fluid model. The mechanisms causing the accumulation of low-energy electrons, and the processes defining the stationary state of the discharge are analyzed. The applicability of the fluid model for the calculation of the density of different hydrocarbon radicals is discussed.
Measurements and modeling of ion energy distributions in high-density, radio-frequency biased discharges91(2002); http://dx.doi.org/10.1063/1.1467403View Description Hide Description
Models of ion dynamics in radio-frequency (rf) biased, high-density plasma sheaths are needed to predict ion bombardment energies in plasma simulations. To test these models, we have measured ion energy distributions (IEDs) in pure discharges at 1.33 Pa (10 mTorr) in a high-density, inductively coupled plasma reactor, using a mass spectrometer equipped with an ion energy analyzer. IEDs of and ions were measured as a function of bias frequency, bias amplitude, and inductive source power. Simultaneous measurements by a capacitive probe and a Faraday cup provide enough information to determine the input parameters of sheathmodels and allow direct comparison of calculated and measured IEDs. A rigorous and comprehensive test of one numerical sheathmodel was performed. The model, which includes a complete treatment of time-dependent ion dynamics in the sheath, was found to predict the behavior of measured IEDs to good accuracy over the entire range of bias frequency, including complicated effects that are observed when the ion transit time is comparable to the rf bias period.
91(2002); http://dx.doi.org/10.1063/1.1465102View Description Hide Description
The influence of the noble gas mixture composition on the plasma display panel performance is investigated in test panels with a design which resembles the one used in commercial panels. Single gases and binary and ternary mixtures of He, Ne, Ar, Kr, and Xe are applied, where the Xe concentration is varied from 0% to 100%. The performance is characterized in terms of the panel luminance, efficacy, and discharge voltages. It is found that while an increase in efficacy and luminance can be achieved in several multicomponent mixtures it is necessary to examine the associated increase in the firing voltage, If one considers the luminance versus dependence, then binary mixtures are optimal to achieve the highest efficacy values at the lowest The maximum efficacy gain factor in high Xe partial pressure mixtures is about a factor of 3 with respect to the mixture applied in default commercial panels.
91(2002); http://dx.doi.org/10.1063/1.1473670View Description Hide Description
This article presents experimental evidence of a coupling of power between the rf supply and a collisionless plasma in a capacitively coupled plasma reactor. The reactor is driven in plasma sheath resonance to let high rf currents circulate in the system. These currents allow the formation of strong rf fields inside the nonuniform plasma leading to a double layer with a mechanism similar to the rf plasma sheath at the electrodes. Electrons accelerated by the double layer are very effective in ionizing, because of the increased cross section, and create a dense plasma at low pressures. The power is consequently transferred by the ions accelerated in the electrodesheath to the substrate to be processed with high improvement in both performance and process rate. Diagnostics include a retarding field analyzer on the grounded electrode to measure the energy spectrum of ions hitting the substrate and a capacitive probe to obtain the rf potential variations in the plasma.
- STRUCTURAL, MECHANICAL THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER (PACS 61-68, 78)
91(2002); http://dx.doi.org/10.1063/1.1470258View Description Hide Description
In order to investigate the nature of defects produced by ion irradiation through a heterostructure, a silicon-on-insulator substrate with a buried layer at a depth of ∼1.5 μm was irradiated. The implantation was done using 2 MeV ions in the dose range of The subsequent defect analysis was performed using the Au labeling technique. Besides the presence of an expected excess of vacancy-type defects in the Si overlayer an additional vacancy excess peak was observed at the frontside of the buried interface The is found to increase linearly with increasing dose of the high-energy implant. The presence of this peak near the interface is also predicted by the TRIM Monte Carlo code. Additional Monte Carlo simulations of damage production via high-energy implantation in -type structures show that the nature of the defects at the front interface can be changed from vacancy to interstitial-type by increasing the mass of atoms in the buried thin-film,X. These experiments provide quantitative verification of nonuniform defect production at an ion-irradiated buried interface in Si.
Analytical model for intrinsic residual stress effects and out-of-plane deflections in free-standing thick films91(2002); http://dx.doi.org/10.1063/1.1470257View Description Hide Description
An analytical model for the influence of residual stress on the out-of-plane deflection in a free-standing thick diamondfilm (the bowing phenomenon) is presented. The variation in residual stress with film thickness is usually believed to cause the bowing. In this study, the stress variation is assumed to be produced by a gradual increase in substrate deformation resulting from layer-by-layer deposition of the film. The model uses the infinitesimal plate-bending theory to describe the layer-by-layer film growth more exactly, considering the two deformation modes of contraction or expansion and bending. To verify the suggested model, thick diamondfilms were fabricated on Si, Mo, and W substrates of varying thicknesses by microwaveplasma assisted chemical vapor deposition. The model’s predictions on bowing, based on the intrinsic stress value measured by the curvature method, were in good agreement with the bowing curvature of the as-released films measured by a profilometer. This confirms that the bowing of thick films depends on the intrinsic stress variation of the film associated with a gradual increase in substrate deformation. A method of eliminating bowing by depositing different layers with different intrinsic stresses is discussed.
91(2002); http://dx.doi.org/10.1063/1.1467608View Description Hide Description
We determined all the independent components of the acoustical physical constants (elastic constant, piezoelectric constant,dielectric constant, and density) of and crystals grown from the melts of three different starting materials with the contents set to 48.0, 48.5, and 49.0 mol %, and obtained the chemical composition dependences of the constants of each single crystal around the congruent composition. All the constants as well as the measured longitudinal, shear, and leaky surface acoustic wave (LSAW) velocities varied linearly with the composition ratios in the experimental range. The composition dependences of the LSAW velocities for the and substrates, previously obtained by line-focus-beam acoustic microscopy, were well matched with the calculated ones using the constants determined. Therefore the data of the composition dependences of the determined constants enable us to easily prepare the calibration lines for evaluating the crystals for any arbitrarily cut specimen surfaces, wave propagation directions, and modes by numerical calculations.
91(2002); http://dx.doi.org/10.1063/1.1461894View Description Hide Description
Refractive index change is shown to be induced by the irradiation of ultraviolet photons in hydrogenated amorphous silicon oxynitride films prepared by plasma-enhanced chemical vapor deposition. The mechanism of the index change and its dependence on the nitrogen content were investigated by electron spin resonance and scanning electron microscopy. It is concluded that the index change is due mainly to densification, and that the contribution of the formation of paramagnetic defects is only slight. To demonstrate the versatility of this refractive index change, a planar diffraction grating was fabricated.
91(2002); http://dx.doi.org/10.1063/1.1468891View Description Hide Description
4H-SiC commercial wafers and sublimationgrownepitaxial layers with a thickness of 100 μm have been studied concerning crystalline structure. The substrates and the epitaxial layers have been separately investigated by high-resolution x-ray diffraction and synchrotron white beam x-ray topography. The results show that the structural quality was improved in the epitaxial layers in the and directions, concerning domain distribution, lattice plane misorientation, mosaicity, and strain, compared with the substrates. Misoriented domains have merged together to form larger domains while the tilt between the domains was reduced, which resulted in nonsplitting in diffraction curves. If the misorientation in the substrate is large, we can only see a slight decrease in the misorientation in the epilayer. At some positions on the substrates block structures (mosaicity) were observed. ω-rocking curves showed smaller full width at half maximum values and more uniform and narrow peaks, while the curvature was almost the same in grown epilayers compared with the corresponding substrates. We show that threading edge dislocations along the c axis in siliconcarbidegrown crystals transform to deflected dislocations in the epilayer. A formation mechanism for deflected dislocations and supporting facts are presented. We further show that these deflected dislocations are one possible source for the creation of stacking faults that recently has been reported to cause degradation in processed SiC bipolar diodes.
91(2002); http://dx.doi.org/10.1063/1.1469691View Description Hide Description
AISI 304L austenitic stainless steel was implanted at 400 °C with 1.2 keV nitrogen ions using a high beam current density of 1 mA/cm2. The nitrogen depth profile, structure, and chemical composition in the modified surface layer were determined by nuclear reaction analysis (NRA) and x-ray diffraction(XRD). The chemical bonding of Fe, Cr atoms with nitrogen was investigated by x-ray photoelectron spectroscopy(XPS). For a treatment time of 1 h, the formation of a thick nitrided layer of about 3.5 μm with a high nitrogen content (∼20 at. %) is observed by NRA. The nitrogen depth profile is characterized by a nearly flat shape over a thickness of 2.5 μm followed by an abrupt decrease. XRD spectra show the formation in the nitrided layer of a phase usually called expanded austenite which corresponds fairly well with a nitrogen solid solution of the fcc structure containing a high density of stacking faults. The XPS study of the and binding states indicate clearly the preferential bonding of chromium with nitrogen with a binding energy of about 1 eV. This value, which is lower than the expected one for chromium nitride CrN, would be characteristic of the binding energy of nitrogen with Cr in the expanded austenite phase. Moreover, it has been found that the atomic ratio N/Cr in the nitride layer deduced from both NRA and XPS is very close to 1. These experimental results support the specific role of chromium in the mechanisms of atomic transport of nitrogen over long distances at moderate temperature in austenitic stainless steels.
91(2002); http://dx.doi.org/10.1063/1.1466879View Description Hide Description
We report the dynamics of amplified spontaneous emission(ASE) in thin organic films of tris-(8-hydroxyquinoline)-aluminum doped with small amounts of the laser dye 4-dicyanmethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). The energy transfer from the initially photoexcited to the DCM molecules affects the high excitation density dynamics significantly. The time delay between pulsed photoexcitation and the ASE burst depends on the pumping level. For higher pumping levels the competition between depopulation by ASE and refilling of the DCM states via energy transfer leads to an oscillatory emission with a fundamental frequency of up to 0.2 THz.
91(2002); http://dx.doi.org/10.1063/1.1466876View Description Hide Description
Within the study of oxide materials,high pressure bulk growth has generated a number of new and interesting materials. More recently, attention has been paid to using epitaxy to stabilize these high pressure oxide materials as thin films. In this article we report on the molecular beam epitaxial growth of a high pressure, highly correlated, model oxide. We find that the choice of substrate can significantly alter not only the structure but also the chemistry of the resulting film. For growth on substrates the epitaxially stabilized structure for single phase films with a composition is based on a tetragonal unit cell. For identical growth conditions, but on a substrate, a single phase film with the composition and structure of the infinite layer material is formed. We also review the literature for the successes and failures of epitaxy to stabilize high pressurestructures.
Elastic and piezoelectric fields in substrates GaAs (001) and GaAs (111) due to a buried quantum dot91(2002); http://dx.doi.org/10.1063/1.1468906View Description Hide Description
In this article we present a rigorous study on the elastic and piezoelectric fields in substrates GaAs (001) and GaAs (111) due to a buried quantum dot(QD) using an efficient and accurate continuum mechanics model. It is based on a Green’s function solution in anisotropic and linearly piezoelectric half space combined with the generalized Betti reciprocal theorem. To address the effect of material anisotropy, two other substrates, Iso (001) and Iso (111), are also examined and they are assumed to be elastically isotropic. For a point QD with hydrostatic misfit strain in volume where and at depth below the surface, we have observed the following features. (1) The simplified elastically isotropic model should, in general, not be used for predicting elastic and piezoelectric fields in the semiconductor GaAs. (2) The magnitude of the QD-induced piezoelectric potential on the surface of GaAs (111) or GaAs (001) is comparable to, or even larger than, the direct potential. (3) Large horizontal and vertical electric fields, on the order of can be induced on the surface of GaAs (001) and GaAs (111). (4) The elastic field induced on the surface of GaAs (001) has rotational symmetry of order (i.e., the elastic field remains the same after rotation of 2π/4 around the  axis), while the corresponding piezoelectric field has rotational symmetry of order On the other hand, both the elastic and piezoelectric fields on the surface of GaAs (111) have rotational symmetry of around the  axis. (5) The magnitude of the elastic and piezoelectric quantities on the surface of GaAs (111) is, in general, larger than that of the corresponding quantities on the surface of GaAs (001). (6) Under different electric surface conditions (insulating or conducting), the surfacepiezoelectric fields induced are quite different.
Damage evolution and recovery on both Si and C sublattices in Al-implanted 4H–SiC studied by Rutherford backscattering spectroscopy and nuclear reaction analysis91(2002); http://dx.doi.org/10.1063/1.1469204View Description Hide Description
Damage evolution and subsequent recovery in 4H–SiC epitaxial layers irradiated with 1.1 MeV molecular ions at 150 K to ion fluences from to were studied by Rutherford backscatteringspectroscopy(RBS) and nuclear reactionanalysis (NRA) using a 0.94 MeV deuterium beam in channeling geometry. Disorder on both the Si and C sublattices was measured simultaneously from the RBS scattering and NRA reaction yields. The relative disorder on both sublattices follows a nonlinear dependence on ion fluence that is consistent with a model based on simple defect accumulation and a direct-impact, defect-stimulated process for amorphization. At low ion fluences, the relative disorder on the C sublattice is higher than that on the Si sublattice. Isochronal annealing up to 870 K revealed the existence of three distinct recovery stages at ∼350, 520, and 650 K for low to intermediate damage levels. In highly damaged samples, where a buried amorphous layer is produced, the onset of a fourth recovery stage appears above 800 K. Similar recovery behaviors on both the Si and C sublattices suggests some coupling of recovery processes for Si and C defects.