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1 May 1997

Volume 81, Issue 9, pp. 5821-6494

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The physics and technology of gallium antimonide: An emerging optoelectronic material

P. S. Dutta, H. L. Bhat, and Vikram Kumar

J. Appl. Phys. 81, 5821 (1997); http://dx.doi.org/10.1063/1.365356 (50 pages) | Cited 205 times

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Recent advances in nonsilica fiber technology have prompted the development of suitable materials for devices operating beyond 1.55 μm. The III–V ternaries and quaternaries (AlGaIn)(AsSb) lattice matched to GaSb seem to be the obvious choice and have turned out to be promising candidates for high speed electronic and long wavelength photonic devices. Consequently, there has been tremendous upthrust in research activities of GaSb-based systems. As a matter of fact, this compound has proved to be an interesting material for both basic and applied research. At present, GaSb technology is in its infancy and considerable research has to be carried out before it can be employed for large scale device fabrication. This article presents an up to date comprehensive account of research carried out hitherto. It explores in detail the material aspects of GaSb starting from crystal growth in bulk and epitaxial form, post growth material processing to device feasibility. An overview of the lattice, electronic, transport, optical and device related properties is presented. Some of the current areas of research and development have been critically reviewed and their significance for both understanding the basic physics as well as for device applications are addressed. These include the role of defects and impurities on the structural, optical and electrical properties of the material, various techniques employed for surface and bulk defect passivation and their effect on the device characteristics, development of novel device structures, etc. Several avenues where further work is required in order to upgrade this III–V compound for optoelectronic devices are listed. It is concluded that the present day knowledge in this material system is sufficient to understand the basic properties and what should be more vigorously pursued is their implementation for device fabrication. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Ey III-V and II-VI semiconductors
72.40.+w Photoconduction and photovoltaic effects
71.55.Eq III-V semiconductors
81.65.Rv Passivation
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.60.Gz Photodetectors (including infrared and CCD detectors)
84.60.Jt Photoelectric conversion
01.30.Rr Surveys and tutorial papers; resource letters

Influence of aperture diameter on image contrast and resolution in scanning near-field optical microscopy

J. Schöfer, M. J. Gregor, P. G. Blome, and R. G. Ulbrich

J. Appl. Phys. 81, 5871 (1997); http://dx.doi.org/10.1063/1.364373 (7 pages) | Cited 4 times

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The influence of aperture diameter on image contrast and resolution in scanning near-field optical microscopy has been investigated. Evanescent standing wave fields at glass–air interfaces were probed with well-characterized aluminum-coated fiber tips. A strong decrease in image contrast was found when the aperture diameter exceeds a critical value. Numerical simulations with the concept of an intensity transfer function using the axial component of the Poynting vector inside the probe demonstrate that this phenomenon is the result of the increasing influence of higher-order waveguide modes on power transmission through the probe. It has been shown that standing wave patterns are convenient and reliable reference devices for individual probe characterization and quantification of their resolving power. © 1997 American Institute of Physics.
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07.79.Fc Near-field scanning optical microscopes
42.30.Va Image forming and processing

Observation of microstructure and damage in materials by phase sensitive radiography and tomography

P. Cloetens, M. Pateyron-Salomé, J. Y. Buffière, G. Peix, J. Baruchel, F. Peyrin, and M. Schlenker

J. Appl. Phys. 81, 5878 (1997); http://dx.doi.org/10.1063/1.364374 (9 pages) | Cited 173 times

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The novel possibilities of phase feature detection in radiography at a third generation synchrotron radiation source are used to image, both in projection and in computed tomography, a cracked silicon single crystal and metal matrix composites strained in tension. Through an instrumentally very simple technique, based on Fresnel diffraction, phase jumps related to the interface between the matrix and the reinforcing phases of the composites are detected even when these phases show very similar x-ray attenuation. Strain-induced cracks with openings below the micrometer range are also visible through the phase modulation they introduce, illustrating the potential of the technique for assessing damage in materials with improved resolution and sensitivity. © 1997 American Institute of Physics.
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81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
81.05.Cy Elemental semiconductors
61.72.-y Defects and impurities in crystals; microstructure
81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
07.85.-m X- and γ-ray instruments

Radiographic imaging with image plates: The influence of the readout intensity on the image quality

M. Thoms and H. von Seggern

J. Appl. Phys. 81, 5887 (1997); http://dx.doi.org/10.1063/1.364375 (9 pages) | Cited 4 times

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The image quality of radiographic images from image plate detectors is limited by two factors: first, the quality of the image plate itself and, second, the scanning procedure of the individual scanning device. In this study the impact of the latter on the image quality is investigated. A method to calculate the spatial resolution in the form of the line-spread function and the photostimulated luminescence intensity for various scanning laser beam intensities is presented. Theoretical results are compared to experimental ones obtained from a commercially available image plate. It is shown experimentally that the spatial resolution is reduced with increasing laser intensity of the readout beam, that the detected information shifts spatially and that the response of the photostimulated luminescence does not vary linearly with the intensity of the laser light. The results are explained by light scattering in the phosphor layer of the image plate and information bleaching during the readout procedure. © 1997 American Institute of Physics.
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42.79.Pw Imaging detectors and sensors
78.55.-m Photoluminescence, properties and materials
07.85.-m X- and γ-ray instruments
81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing
87.59.B- Radiography
42.62.-b Laser applications
42.25.Fx Diffraction and scattering

Generation of energetic He atom beams by a pulsed positive corona discharge

Shui-Yin Lo, Julio D. Lobo, Seth Blumberg, Theodore S. Dibble, Xu Zhang, Chun-Cheng Tsao, and Mitchio Okumura

J. Appl. Phys. 81, 5896 (1997); http://dx.doi.org/10.1063/1.364376 (9 pages) | Cited 2 times

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Time-of-flight measurements were made of neutral helium atom beams extracted from a repetitive, pulsed, positive-point corona discharge. Two strong neutral peaks, one fast and one slow, were observed, accompanied by a prompt photon peak and a fast ion peak. All peaks were correlated with the pulsing of the discharge. The two types of atoms appear to be formed by different mechanisms at different stages of the corona discharge. The fast atoms had energies of 190 eV and were formed at the onset of the pulsing, approximately 0.7 μs before the maximum of the photon peak. The slow peak, composed of electronically metastable He atoms, originated 30–50 μs after the photon pulse, and possessed a nearly thermal velocity distribution. The velocity distribution was typical of an undisturbed supersonic expansion with a stagnation temperature of 131 K and a speed ratio of 3.6. Peak intensities and velocities were measured as a function of source voltage, stagnation pressure, and skimmer voltage. © 1997 American Institute of Physics.
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37.20.+j Atomic and molecular beam sources and techniques
52.80.Hc Glow; corona
07.77.Gx Atomic and molecular beam sources and detectors
31.50.Df Potential energy surfaces for excited electronic states

Comparison between the optical limiting behavior of chloroaluminum phthalocyanine and a cyanine dye

S. Hughes, G. Spruce, B. S. Wherrett, and T. Kobayashi

J. Appl. Phys. 81, 5905 (1997); http://dx.doi.org/10.1063/1.364377 (8 pages) | Cited 12 times

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The picosecond optical limiting characteristics of the optical limiting dyes hexamethylindotricarbocyanine iodide (HITCI) and chloroaluminum phthalocyanine (CAP) are compared and contrasted at 532 nm. From single pulse transmittance experiments, HITCI is shown to possess a serious limitation in its optical limiting behavior, where the regime of induced absorption becomes one of induced transmission for high irradiances. CAP, on the other hand, although possessing a smaller ratio of the excited-state to ground-state absorption cross-section, continues to exhibit optical limiting over a much broader dynamic range. From cross-polarized time-resolved excitation-probe measurements, HITCI exhibits a sharp negative spike around zero delay which originates from orientational coherent grating effects, while CAP does not exhibit any spike. These nonlinearities are explained theoretically as a complex interplay between a series of excited manifolds for the dyes and the radiation properties of the interacting laser pulse. © 1997 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.47.-p Spectroscopy of solid state dynamics
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Quantitative model of volume hologram formation in photopolymers

V. L. Colvin, R. G. Larson, A. L. Harris, and M. L. Schilling

J. Appl. Phys. 81, 5913 (1997); http://dx.doi.org/10.1063/1.364378 (11 pages) | Cited 87 times

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A quantitative model is presented to describe the formation of volume holograms in a polymeric medium containing photopolymerizable acrylate monomers that undergo spatially modulated gelation as a result of exposure to a visible “write” beam. The model refines the simple diffusion model of Zhao and Mouroulis [J. Mod. Opt. 41, 1929 (1994)], by including cure dependence of both the photoreaction kinetics and the monomer diffusivity. These dependences are determined by experimental measurements, using near infrared spectroscopy to quantify the degree of cure and the time dependence of the hologram formation to infer the cure-dependent diffusivity. The cure-dependent diffusion coefficient can be fit by an expression from a free-volume theory, and the cure-dependent reaction rate coefficient is found to be proportional to the diffusivity, showing the reaction rate to be diffusion limited. With the model parameters determined experimentally, predictions are then made of the first, second, and third harmonics of the grating profile, and these are found to be in good agreement with the measured values. The results show the validity of the model and its usefulness in predicting the optimal exposure conditions and performance of a given holographic material. © 1997 American Institute of Physics.
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42.70.Ln Holographic recording materials; optical storage media
42.70.Jk Polymers and organics
42.40.Ht Hologram recording and readout methods
42.70.Gi Light-sensitive materials
82.35.-x Polymers: properties; reactions; polymerization
82.50.-m Photochemistry
82.20.Hf Product distribution
78.35.+c Brillouin and Rayleigh scattering; other light scattering
42.40.Eq Holographic optical elements; holographic gratings
42.79.Dj Gratings
82.20.Pm Rate constants, reaction cross sections, and activation energies

Reflective twisted nematic liquid crystal displays. I. Retardation compensation

S. T. Tang, F. H. Yu, J. Chen, M. Wong, H. C. Huang, and H. S. Kwok

J. Appl. Phys. 81, 5924 (1997); http://dx.doi.org/10.1063/1.364379 (6 pages) | Cited 21 times

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Reflective twisted nematic displays where the output polarizer is eliminated are analyzed and demonstrated. The absence of the rear output polarizer has many advantages, including much higher brightness and higher resolution. In this article, we examine the solution space for the design of such reflective displays. Both the cases of a simple reflective display and the use of a retardation film within the display to compensate for color dispersion are explored. It is shown that excellent black and white displays can be obtained using film compensation. Experimentally, over 90% reflectance from a compensated reflective display has been obtained with low color dispersion. The optical response of this reflective display was also found to be quite fast and suitable for video rate applications. © 1997 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
85.60.Pg Display systems

Optimizing AlxGa1−xN separate confinement heterostructure lasers with large band discontinuities

Pankaj Shah and Vladimir Mitin

J. Appl. Phys. 81, 5930 (1997); http://dx.doi.org/10.1063/1.364380 (5 pages) | Cited 4 times

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Two-dimensional simulations were performed to optimize the waveguiding region’s aluminum composition of an AlGaN/GaN separate confinement heterostructure (SCH) laser with large band discontinuities. Results demonstrate that the active region’s thickness, waveguiding regions’ thickness, and the material composition of the waveguiding region should be optimized, based on losses of the materials in the structure. Results also demonstrate that the threshold current of a SCH laser may be larger than that of a double heterostructure laser. The increase is caused by a competition between the active region and the waveguiding region which has a parasitic effect on the laser’s modal gain because of the waveguiding region’s slightly larger band gap, so that below the lasing threshold, photon emission and population inversion can occur in both regions. At the minimum threshold current the structure is optimized to strongly confine both the guided optical mode and the charge carriers responsible for the gain. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Boltzmann equation analysis of spatiotemporal electron swarm development

M. Ould Mohamed Mahmoud and M. Yousfi

J. Appl. Phys. 81, 5935 (1997); http://dx.doi.org/10.1063/1.364381 (10 pages) | Cited 7 times

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A powerful and a stable numerical method is developed to solve the Boltzmann equation of electrons moving under the action of an electric field in weakly ionized gases involving space and time gradients. It is based on the classical two term development of the distribution function and on a strongly implicit procedure following position and energy axis and an explicit approach along the time axis. This numerical algorithm is successfully applied to determine the spatiotemporal variation of the electron distribution function and the associated swarm parameters (mean energy, drift velocity, ionization and attachment coefficients, etc.) in the case of nonthermal electrical discharges in different gases (He, Ar and O2) under different applied electric fields and initial and boundary conditions. The transient phase, the following steady state phase and also the electrode effects are clearly emphasized and analyzed for each gas discharge studied. © 1997 American Institute of Physics.
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52.80.Tn Other gas discharges
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
05.60.-k Transport processes

Doppler spectroscopic measurements of sheath ion velocities in radio-frequency plasmas

B. K. Woodcock, J. R. Busby, T. G. M. Freegarde, and G. Hancock

J. Appl. Phys. 81, 5945 (1997); http://dx.doi.org/10.1063/1.364382 (5 pages) | Cited 8 times

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We have measured the distributions of N2+ ion velocity components parallel and perpendicular to the electrode in the sheath of a radio-frequency nitrogen reactive ion etching discharge, using pulsed laser-induced fluorescence. Parallel to the electrode, the ions have throughout a thermal distribution that is found to be consistent with the rotational temperature of 355 K. In the perpendicular direction, we see clearly the acceleration of the ions towards the electrode, and our results agree well with theoretical predictions although an unexpected peak of unaccelerated ions persists. We have also determined the absolute ion concentrations in the sheath, which we have calibrated by analyzing the decay in laser-induced fluorescence in the plasma bulk after discharge extinction. At 20 mTorr, the bulk concentration of 1.0×1010 cm−3 falls to around 2×108 cm−3 at 2 mm from the electrode. © 1997 American Institute of Physics.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
33.50.Dq Fluorescence and phosphorescence spectra
52.25.Fi Transport properties
52.80.Pi High-frequency and RF discharges

Ion energy and angular distributions in inductively driven radio frequency discharges in chlorine

J. R. Woodworth, M. E. Riley, P. A. Miller, G. A. Hebner, and T. W. Hamilton

J. Appl. Phys. 81, 5950 (1997); http://dx.doi.org/10.1063/1.364383 (10 pages) | Cited 44 times

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In this article, we report values of ion energy and angular distributions measured at the grounded electrode of an inductively coupled discharge in chlorine gas. The inductive rf drive in our cell produced high plasma densities (1011/cm3 electron densities) and stable plasma potentials. As a result, ion energy distributions typically consisted of a single peak well separated from zero energy. Mean ion energy varied inversely with pressure, decreasing from 13 to 9 eV as the discharge pressure increased from 20 to 60 mTorr. Half-widths of the ion angular distributions in these experiments varied from 6° to 7.5°, corresponding to transverse energies from 0.13 to 0.21 eV. During the course of the experiment, ion energies gradually decreased, probably due to the buildup of contaminants on the chamber walls. Cell wall temperature also was an important variable, with ion fluxes to the lower electrode increasing and the ion angular distribution narrowing as the cell temperature increased. © 1997 American Institute of Physics.
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52.80.Pi High-frequency and RF discharges

Shapes of agglomerates in plasma etching reactors

Fred Y. Huang and Mark J. Kushner

J. Appl. Phys. 81, 5960 (1997); http://dx.doi.org/10.1063/1.364384 (6 pages) | Cited 17 times

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Dust particle contamination of wafers in reactive ion etching (RIE) plasma tools is a continuing concern in the microelectronics industry. It is common to find that particles collected on surfaces or downstream of the etch chamber are agglomerates of smaller monodisperse spherical particles. The shapes of the agglomerates vary from compact, high fractal dimension structures to filamentary, low fractal dimension structures. These shapes are important with respect to the transport of particles in RIE tools under the influence electrostatic and ion drag forces, and the possible generation of polarization forces. A molecular dynamics simulation has been developed to investigate the shapes of agglomerates in plasma etching reactors. We find that filamentary, low fractal dimension structures are generally produced by smaller (<100s nm) particles in low powered plasmas where the kinetic energy of primary particles is insufficient to overcome the larger Coulomb repulsion of a compact agglomerate. This is analogous to the diffusive regime in neutral agglomeration. Large particles in high powered plasmas generally produce compact agglomerates of high fractal dimension, analogous to ballistic agglomeration of neutrals. © 1997 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning
52.25.Fi Transport properties
52.25.Vy Impurities in plasmas
02.70.Ns Molecular dynamics and particle methods
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Model for noncollisional heating in inductively coupled plasma processing sources

Shahid Rauf and Mark J. Kushner

J. Appl. Phys. 81, 5966 (1997); http://dx.doi.org/10.1063/1.364385 (9 pages) | Cited 38 times

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Low pressure (<10 mTorr) inductively coupled plasma sources are being developed for etching and deposition of semiconductors and metals. In models for these devices, plasma dynamics are typically coupled to the electromagnetic fields through Ohm’s law, which implies that collisional heating is the dominant power transfer mechanism. In this article, we describe an algorithm to couple plasma dynamics to electromagnetic field propagation which self-consistently includes noncollisional heating effects as well. The algorithm makes use of kinetic information available from an electron Monte Carlo simulation to compute plasma currents that are then used in computation of the electromagnetic field. Results for plasma density and electric field amplitude are presented as a function of power and pressure, and are compared to results from models that consider only collisional heating. We find that noncollisional heating effects are important at pressures of less than 10–20 mTorr, a range that depends both on gas mixture and geometry. Noncollisional heating effects allow the wave to couple more efficiently to the plasma. As a result, the electric field amplitude required to deposit a given amount of power in the plasma is smaller than that needed when only collisional heating is considered. For a constant power deposition, this generally leads to lower plasma densities. © 1997 American Institute of Physics.
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52.50.Dg Plasma sources
52.20.-j Elementary processes in plasmas
52.25.Dg Plasma kinetic equations
52.65.Pp Monte Carlo methods
52.50.Gj Plasma heating by particle beams

Influence of ultraviolet illumination on microdischarge behavior in dry and humid N2, O2, air, and Ar/O2: The Joshi effect

Zoran Falkenstein

J. Appl. Phys. 81, 5975 (1997); http://dx.doi.org/10.1063/1.364386 (5 pages) | Cited 10 times

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The influence of UV illumination on the behavior of silent electrical discharge streamers (microdischarges) in dry and humid gases (nitrogen, oxygen, air, and Ar/O2 mixtures) is presented. A commercial low-pressure mercury lamp, which was spectrally calibrated, provides UV light. The UV irradiance power coupled into the discharge cell is also calculated. The transferred charge per mean microdischarge (in a voltage half-cycle) was measured for a pin electrode assembly, configured to deliver either M−G+ transitions (electrons going from metal towards dielectric) or M+G− transitions (electrons going from dielectric to metal). The total transferred charge is recorded by monitoring a charge versus voltage plot (Lissajous figure). When illumination is restricted to the gas alone, both the total transferred charge and the individual-microdischarge transferred charge remain constant for either transition (M−G+ or M+G−). However, when the dielectric is illuminated, a marked decrease in the individual-microdischarge transferred charge is observed for M+G− transitions in some gases. For this case, a greater number of microdischarges must occur in a half-cycle to keep the total transferred charge constant, thereby creating more homogeneous discharge conditions. © 1997 American Institute of Physics.
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52.80.Hc Glow; corona
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
34.70.+e Charge transfer
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light

Soft x-ray emission produced by a sub-picosecond laser in a single- and double-pulse scheme

J. F. Pelletier, M. Chaker, and J. C. Kieffer

J. Appl. Phys. 81, 5980 (1997); http://dx.doi.org/10.1063/1.364387 (4 pages) | Cited 14 times

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The interaction of a high-contrast, 400 fs, 5×1017 W/cm2 laser pulse with a preformed tantalum plasma produced in a double-pulse configuration is investigated. The x-ray emission characteristics are studied for different time delays between the two laser pulses. A time-resolved transmission grating spectrometer is used to measure the x-ray conversion efficiency and emission duration in the 0.2–1.2 keV energy range. Our results show that it is possible to increase the x-ray source conversion efficiency by an order of magnitude simply by optimizing the delay between the laser pulses. To give an overview of the performances available from such laser-plasma x-ray sources, these results are compared those obtained with a single laser pulse in different interaction regimes. © 1997 American Institute of Physics.
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42.55.Vc X- and γ-ray lasers
78.70.En X-ray emission spectra and fluorescence
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Dependence of the electro-optical properties of polymer dispersed liquid crystals on the photopolymerization process

J. D. LeGrange, S. A. Carter, M. Fuentes, J. Boo, A. E. Freeny, W. Cleveland, and T. M. Miller

J. Appl. Phys. 81, 5984 (1997); http://dx.doi.org/10.1063/1.364388 (8 pages) | Cited 22 times

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We have studied the dependence of the electro-optical properties of polymer dispersed liquid crystals (PDLC) on the ultraviolet (UV) cure of the solution of monomer and liquid crystal. The kinetics of UV polymerization and its effect on the morphology of the phase separated droplets of liquid crystal determine the switching voltage, response time, and luminance of the PDLC. Using a series of statistically designed experiments, we have mapped the dependence of these responses on the weight fraction of liquid crystal, the temperature of the cell during cure, and light intensity. Temperature and composition are strongly coupled parameters that influence switching voltage, luminance, and response times. Switching voltages are minimized at 4–5 V for an 8 μm cell gap over a large region of temperature-composition space. An abrupt transition line occurs through that space. On one side of the transition line, voltage increases linearly either as temperature increases or composition decreases, and on the other side of the line, voltage is constant. Analyses of decay times, the slower response time of the PDLC, show that the times peak along a line of points in temperature-composition space that is close to the transition line for increasing switching voltages. We present these results as contours on the same graphs and relate them to our understanding of the phase separation process in the PDLC mixture. © 1997 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
61.30.-v Liquid crystals
78.20.Jq Electro-optical effects
82.35.-x Polymers: properties; reactions; polymerization
42.70.Jk Polymers and organics
85.60.Pg Display systems

Dependence of the morphology of polymer dispersed liquid crystals on the UV polymerization process

S. A. Carter, J. D. LeGrange, W. White, J. Boo, and P. Wiltzius

J. Appl. Phys. 81, 5992 (1997); http://dx.doi.org/10.1063/1.364447 (8 pages) | Cited 41 times

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Using confocal microscopy, we have studied the morphology of polymer dispersed liquid crystals (PDLC) as a function of polymer/liquid crystal composition, polymer cure temperature, and ultraviolet (UV) curing power and determined how this morphology affects the electro-optical properties. The PDLC morphology consists of a spongelike texture where spherically shaped liquid crystalline domains are dispersed in a polymer matrix. These domains grow as the fraction of liquid crystal increases and as the UV curing power decreases. We observe no significant changes in domain size with changes in the curing temperature. Instead, high-temperature cures result in coalescence and the formation of elliptical-shaped liquid crystal domains. The temperature at which this coalescence starts to be observed marks a threshold temperature Tth, above which the switching properties are strongly dependent on morphology. Below Tth the switching properties are largely independent of morphology. © 1997 American Institute of Physics.
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82.35.-x Polymers: properties; reactions; polymerization
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.
42.79.Kr Display devices, liquid-crystal devices
78.20.Jq Electro-optical effects

Neutron depolarization study of internal stresses in amorphous Fe40Ni40B20

M. de Jong, J. Sietsma, M. Th. Rekveldt, and A. van den Beukel

J. Appl. Phys. 81, 6000 (1997); http://dx.doi.org/10.1063/1.364448 (13 pages) | Cited 2 times

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The magnetic domain structure of amorphous ferromagnets with nonzero magnetostriction is mainly determined by the internal stress state because of the magneto-elastic coupling. The stress and field dependence of the domain structure contains important information on the internal stresses in the material. The three-dimensional neutron depolarization technique has been used to study the stress- and field-dependence of the bulk domain structures in both as-quenched and annealed ribbons of the metallic glass Fe40Ni40B20. A three-layer domain structure model corresponding to compressive and tensile internal stresses is presented to explain the measured data. The influence of surface roughness on the interpretation of neutron depolarization measurements in amorphous ribbons is discussed. Finally, the internal stress relaxation due to the annealing is explained in terms of the viscous behaviour of the glass. © 1997 American Institute of Physics.  
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75.50.Bb Fe and its alloys
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ch Domain walls and domain structure
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
68.35.B- Structure of clean surfaces (and surface reconstruction)
75.70.Rf Surface magnetism

Correlations for damage in diffused-junction InP solar cells induced by electron and proton irradiation

Masafumi Yamaguchi, Tatsuya Takamoto, Stephen J. Taylor, Robert J. Walters, Geoffrey P. Summers, Dennis J. Flood, and Masamichi Ohmori

J. Appl. Phys. 81, 6013 (1997); http://dx.doi.org/10.1063/1.364449 (6 pages) | Cited 7 times

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The damage to diffused-junction n+-p InP solar cells induced by electron and proton irradiations over a wide range of energy from 0.5 to 3 MeV and 0.015 to 20 MeV, respectively, has been examined. The experimental electron and proton damage coefficients have been analyzed in terms of displacement damage dose, which is the product of the particle fluence and the calculated nonionizing energy loss [G. P. Summers, E. A. Burke, R. Shapiro, S. R. Messenger, and R. J. Walters, IEEE Trans. Nucl. Sci. 40, 1300 (1993).] Degradation of InP cells due to irradiation with electrons and protons with energies of more than 0.5 MeV show a single curve as a function of displacement damage dose. Based on the deep-level transient spectroscopy analysis, damage equivalence between electron and proton irradiation is discussed. InP solar cells are confirmed to be substantially more radiation resistant than Si and GaAs-on-Ge cells. © 1997 American Institute of Physics.
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84.60.Jt Photoelectric conversion
61.80.Fe Electron and positron radiation effects
61.80.Jh Ion radiation effects
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
71.55.Eq III-V semiconductors

Delayed failure in shocked silicon carbide

Neil Bourne, Jeremy Millett, and Ian Pickup

J. Appl. Phys. 81, 6019 (1997); http://dx.doi.org/10.1063/1.364450 (5 pages) | Cited 25 times

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Plate impact and split Hopkinson pressure bar (SHPB) experiments have been conducted on three grades of silicon carbide produced by different routes. Data are presented which indicate that the failure of the materials was delayed for some time after the maximum stress had been achieved. In particular, the measured lateral component of the stress in plate impact was found to increase across a front which traveled behind the shock. This phenomenon is akin to the failure wave which has been observed to occur in glasses but has not previously been reported in polycrystalline materials. Hopkinson bar experiments have revealed significant differences in the behaviors between the three materials. These may be related to the effects observed in the plate impact experiments. These results explain the anomalous ballistic phenomena that have been reported for the penetration behavior of SiC. Additionally the Hugoniot elastic limit (HEL) and shear strength were found to vary with the production route used. © 1997 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep

The thermodynamics of amorphous phases in immiscible systems: The example of sputter-deposited Nb–Cu alloys

C. Michaelsen, C. Gente, and R. Bormann

J. Appl. Phys. 81, 6024 (1997); http://dx.doi.org/10.1063/1.364451 (7 pages) | Cited 24 times

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Amorphous metallic alloys, frequently observed to occur in systems with large negative heats of mixing, are much less common in systems which are immiscible in the equilibrium solid state, such as Nb–Cu. However, amorphous Nb–Cu alloys can be produced over a wide composition range by sputtering. Using isothermal and nonisothermal differential scanning calorimetry, both the kinetics and the thermodynamics of these amorphous Nb–Cu alloys were characterized quantitatively. It was found that the formation enthalpies of the amorphous alloys amounted to only 4.5–7.6 kJ/g atom. These data were combined with a modeling of the thermodynamic functions of the system. The unexpected low enthalpies and Gibbs energies of the amorphous phase demonstrate the thermodynamic stabilization of the liquid phase which develops with undercooling. This is connected with a change of sign in the heat of mixing of the liquid phase, which is positive at high temperatures and negative at low temperatures. © 1997 American Institute of Physics.
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65.20.-w Thermal properties of liquids
65.40.gd Entropy
82.60.Cx Enthalpies of combustion, reaction, and formation
64.75.-g Phase equilibria
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
81.05.Kf Glasses (including metallic glasses)
81.05.Bx Metals, semimetals, and alloys

Physical mechanisms of transient enhanced dopant diffusion in ion-implanted silicon

P. A. Stolk, H.-J. Gossmann, D. J. Eaglesham, D. C. Jacobson, C. S. Rafferty, G. H. Gilmer, M. Jaraíz, J. M. Poate, H. S. Luftman, and T. E. Haynes

J. Appl. Phys. 81, 6031 (1997); http://dx.doi.org/10.1063/1.364452 (20 pages) | Cited 313 times

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Implanted B and P dopants in Si exhibit transient enhanced diffusion (TED) during annealing which arises from the excess interstitials generated by the implant. In order to study the mechanisms of TED, transmission electron microscopy measurements of implantation damage were combined with B diffusion experiments using doping marker structures grown by molecular-beam epitaxy (MBE). Damage from nonamorphizing Si implants at doses ranging from 5×1012 to 1×1014/cm2 evolves into a distribution of {311} interstitial agglomerates during the initial annealing stages at 670–815 °C. The excess interstitial concentration contained in these defects roughly equals the implanted ion dose, an observation that is corroborated by atomistic Monte Carlo simulations of implantation and annealing processes. The injection of interstitials from the damage region involves the dissolution of {311} defects during Ostwald ripening with an activation energy of 3.8±0.2 eV. The excess interstitials drive substitutional B into electrically inactive, metastable clusters of presumably two or three B atoms at concentrations below the solid solubility, thus explaining the generally observed immobile B peak during TED of ion-implanted B. Injected interstitials undergo retarded diffusion in the MBE-grown Si with an effective migration energy of ∼3.5 eV, which arises from trapping at substitutional C. The concept of trap-limited diffusion provides a stepping stone for understanding the enormous disparity among published values for the interstitial diffusivity in Si. The population of excess interstitials is strongly reduced by incorporating substitutional C in Si to levels of ∼1019/cm3 prior to ion implantation. This provides a promising method for suppressing TED, thus enabling shallow junction formation in future Si devices through dopant implantation. The present insights have been implemented into a process simulator, allowing for a significant improvement of the predictive modeling of TED. © 1997 American Institute of Physics.
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66.30.J- Diffusion of impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uf Ge and Si
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.05.Cy Elemental semiconductors
73.61.Cw Elemental semiconductors
72.80.Cw Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.Cc Kinetics of defect formation and annealing

Effect of implant temperature on transient enhanced diffusion of boron in regrown silicon after amorphization by Si+ or Ge+ implantation

K. S. Jones, K. Moller, J. Chen, M. Puga-Lambers, B. Freer, J. Berstein, and L. Rubin

J. Appl. Phys. 81, 6051 (1997); http://dx.doi.org/10.1063/1.364391 (5 pages) | Cited 25 times

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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. © 1997 American Institute of Physics.
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66.30.J- Diffusion of impurities
81.05.Cy Elemental semiconductors
72.80.Cw Elemental semiconductors
61.72.uf Ge and Si
61.72.S- Impurities in crystals

Interdiffusion studies in GaAsP/GaAs and GaAsSb/GaAs superlattices under various arsenic vapor pressures

U. Egger, M. Schultz, P. Werner, O. Breitenstein, T. Y. Tan, U. Gösele, R. Franzheld, M. Uematsu, and H. Ito

J. Appl. Phys. 81, 6056 (1997); http://dx.doi.org/10.1063/1.364453 (6 pages) | Cited 7 times

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Interdiffusion coefficients on the group V sublattice of GaAs were determined in GaAsP/GaAs and GaAsSb/GaAs superlattices. Strained GaAs0.86P0.14/GaAs, GaAs0.8P0.2/GaAs0.975P0.025 and GaAs0.98Sb0.02/GaAs superlattices were annealed between 850 °C and 1100 °C under different arsenic vapor pressures. The diffusion coefficient was measured by secondary ion mass spectroscopy and cathodoluminescence spectroscopy. The interdiffusion coefficient was higher under arsenic-rich conditions than under gallium-rich conditions, pointing to an interstitial-substitutional type of diffusion mechanism. © 1997 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Fd III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.J- Point defects and defect clusters
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