bluuebunny/crossref_metadata_2025 huggingface dataset:
Method for determining effective nonradiative lifetime and leakage losses in double-heterostructure lasers
Authors: van Opdorp C. , ’t Hooft G. W.
Published: February 2003

Carrier losses in double-heterostructure lasers are twofold: (i) nonradiative recombination through killers in the bulk of the active region and at all its boundaries (interfaces and surfaces), and (ii) leakage out of the active region. A simple theory shows the following. In the high-injection regime (p?n) all processes under (i) are directly proportional to n. Consequently their contributions can be lumped together in a single effective nonradiative carrier lifetime τnr ; this τnr is constant (i.e., independent of n) owing to the constant degree of occupation of all killers in the mentioned regime. On the other hand, the leakage losses (ii) are superlinear in n. This provides a well-grounded basis for disentangling the contributions of (i) and (ii) in a given sample. Further, a simple method is presented for accurately determining τnr from data of the external quantum efficiency ηext measured as a function of current I in the spontaneous high-injection regime below the laser threshold. Knowledge of the light-extraction factor (i.e., the ratio of external and internal quantum efficiencies) is essentially unnecessary with this method. However, optionally it can be determined easily from a slight extension of the method. For illustration the method of determining τnr, which is also applicable to double-hetero LED’s, has been applied to some thirty LPE and metal-organic VPE GaAs-(Ga,Al)As lasers of widely varying qualities. The values found vary between 0.8 and 55 ns. From the measured values of τnr it follows that the upper limit for the interface recombination velocity in the best samples is 270 cm/s. For most samples τnr cannot account for all electrical losses at laser threshold. The superlinear  excess  losses are ascribable to leakage.
On the spatial mode stability of oxide stripe cw lasers during accelerated aging at 70 °C
Authors: Ettenberg M.
Published: February 2003

The spatial mode stability of state-of-the-art (AlGa)As oxide stripe cw lasers during aging at 70 °C has been studied. These routinely fabricated devices exhibited reproducible fundamental spatial mode operation and had a median time to failure at 70 °C of 7000 h. While there was wandering of the farfield beam pattern of up to 10° during aging, operation in an essentially fundamental spatial mode continued until very close to the end of life.
e-beam preionized mercury bromide dissociation laser
Authors: Burnham R. , Whitney W. T.
Published: February 2003

An HgBr2/HgBr dissociation laser has been excited in an e-beam preionized, self-sustained discharge. Laser output of 100 mJ at 502 and 504 nm has been obtained with an overall efficiency of 0.5%. The steady-state efficiency for formation of the HgBr (B) state in the Ne/N2/HgBr2 discharge is determined to be 4%. An optical gain to loss ratio of ∼ 14 at the laser wavelength is inferred.
UV-sustained CO laser discharge II. Discharge studies
Authors: Suhre D. R. , Wutzke S. A.
Published: February 2003

A high-pressure (2×4×77) cm3 UV-sustained discharge was operated in a (1:3:9, CO:N2:He) gas mixture doped with either NO or C2H4. The electrical energy loading into the gas was parameterized with respect to the UV source energy, additive density, reduced temperature, and sustainer voltage. All the results were consistent with a discharge operated below the glow voltage and sustained entirely by photoionization. A maximum energy loading of about 400 J/liter was achieved.
Optical generation of tunable ultrasonic waves
Authors: Nelson Keith A. , Miller R. J. Dwayne , Lutz D. R. , Fayer M. D.
Published: February 2003

A convenient method of optically exciting and monitoring coherent acoustic waves in transparent or light-absorbing liquids and solids is described. The acoustic frequency is easily and continuously tunable from ≊3 MHz to at least 30 GHz with our experimental apparatus and in principle over a considerably wider range. In anisotropic materials any propagation direction can be selected. The optically generated acoustic waves can be optically amplified, cancelled, or phase shifted.
Experimental determination of 6 3P–6 3P collisional excitation cross sections for line emission in the positive column of dc mercury discharges
Authors: van de Weijer P. , Cremers R. M. M.
Published: February 2003

The absolute emission intensities of lines originating from highly excited mercury levels in the positive column of a dc mercury discharge have been determined for various discharge conditions. For the same conditions, the densities in the 6 3P states have been determined with the hook method. From these experimental data the 6 3P− 6 3P collisional excitation cross sections for line emission can be derived for nine transitions. Generally, these cross sections are much smaller than those determined in previous experiments.
X-ray measurements of imploding wire plasmas
Authors: Clark W. , Wilkinson M. , Rauch J. , LePage J.
Published: February 2003

The 6-TW, 0.4-Ω pulse generator at Maxwell Laboratories, Inc., was used to create hot, dense plasma pinches by imploding cylindrical arrays of fine aluminum wires. These plasmas have been diagnosed by observing their x-ray emission at energies above hν∼1 keV. The results of various x-ray measurements including x-ray streak photography are presented.
Defects in hydrogenated amorphous silicon-carbon alloy films prepared by glow discharge decomposition and sputtering
Authors: Morimoto A. , Miura T. , Kumeda M. , Shimizu T.
Published: February 2003

Properties of hydrogenated amorphous silicon-carbon alloy (a-Si1−xCx :H) films prepared by radio frequency (rf) glow discharge decomposition and rf sputtering have been investigated by means of electron spin resonance (ESR), infrared absorption, optical absorption, and photoconductivity measurements. Although the number of C-H per C atom [C-H]/[C] is larger than that of Si-H per Si atom [Si-H]/[Si], the ESR spin density increases greatly with the C content. The increase in the density of dangling bonds may be related to the fact that the number of H atoms in gathered phase increases with an increase in x. ESR measurements also give useful information about the preferential formation of C or Si dangling bonds and the atomic distribution of Si and C through a compositional dependence of the g value. A remarkable feature for a-Si1−xCx :H film is that the presence of C atoms in the amorphous network makes the Si-H bond in a-Si1−xCx :H more stable than that in a-Si:H.
A dynamic approach to study variable diffusion coefficients in nematic liquid crystals
Authors: Hakemi H.
Published: February 2003

In mass transport studies of nematic liquid crystals by the optical method, where the textural appearance of the diffusion profile provides the analysis of concentration distributions, it was feasible to study the diffusion processes as a function of time. With such a dynamic approach, we determined the values of diffusion coefficients in an oriented nematic film at various diffusant concentration ranges within the profile and estimated the value of self-diffusion coefficient by extrapolation to zero concentration.
Comment on ’’Generalized Hall-effect measurement geometries and limitations of van der Pauw-type Hall-effect measurements’’
Authors: Beck W. A.
Published: February 2003

The general validity of the van der Pauw-Hall measurement technique for arbitrarily shaped samples has recently been disputed, and the claim has been made that the samples must have mirror symmetry. Here, it is shown that the analysis leading to the mirror symmetry requirement is more restrictive than necessary and that arbitrary shapes can be used. It is also shown that even with nonsymmetric shapes, magnetoresistance effects are eliminated by reversing the magnetic field and averaging the data.
Thermal stability of Pb-alloy Josephson junction electrode materials. V. Effects of repeated cycling between 298 and 4.2 K of Pb-Bi counter electrode
Authors: Murakami Masanori , Basson J. H.
Published: February 2003

Changes in the microstructure of ε-phase Pb-Bi films with various thicknesses that were deposited onto oxidized Si substrates and then repeatedly thermally cycled between 298 and 4.2 K were studied using x-ray diffraction, transmission, and scanning electron microscopy. The level of strain supported elastically by the films had a strong dependence on the film thickness. For 0.2-μm-thick films, almost all of the strain was supported elastically. For 1.0-μm-thick films most of the strain was relaxed upon cooling to 4.2 K, and grain rotation, hillock formation, and dislocation slip steps were observed after repeated cycling. For 0.4-μm-thick films in which about 0.1% of the strain was relaxed upon cooling to 4.2 K, such changes in the microstructure were observed after ∼200 cycles. Although these changes were significantly suppressed by 0.6-μm-thick SiO layers coated onto the films, the grain rotation and hillock formation were observed after 400 cycles for SiO-coated, 0.4-μm-thick films similar to those used for the counter electrodes of Pb-alloy Josephson junctions.
Optimal paths for thermodynamic systems: The ideal Otto cycle
Authors: Mozurkewich Michael , Berry R. Stephen
Published: February 2003

We apply the method of optimal control theory to determine the optimal piston trajectory for successively less idealized models of the Otto cycle. The optimal path has significantly smaller losses from friction and heat leaks than the path with conventional piston motion and the same loss parameters. The resulting increases in efficiency are of the order of 10%.
Electron paramagnetic resonance study of the role of CuO additives in altering phase transition behavior of ammonium nitrate
Authors: Owens F. J.
Published: February 2003

The role of CuO in reducing the volume change and altering the transition temperature of structural phase transitions in ammonium nitrate is studied by electron paramagnetic resonance (EPR). At room temperature, two distinct EPR spectra, indicative of two chemical forms of copper were observed in ammonium nitrate heated from the melt containing 5% by weight of CuO and through which NH3 gas was bubbled. One spectrum having an orthorhombic g tensor with principle components g1 = 2.185, g2 = 2.109, and g3 = 2.055 is assigned to the Cu(NH3)2+4 complex. The other spectrum, also having orthorhombic symmetry, with g1 = 2.315, and g2 = 2.264, is tentatively assigned to a Cu2+ ion either interstitial or substitutional in the lattice. The g values of this spectrum were quite sensitive to temperature and change substantially during the structural phase transition at 60 °C. Heating ammonium nitrate to 160 °C for an hour changed the tetramine copper complex into a new spectrum which is identified as the diamine complex of copper. At room temperature this spectrum slowly returned to the tetramine complex. The role of these forms of copper in reducing the volume change associated with the above room-temperature phase transition is discussed.
Nonlinear coupled-mode theory for surface acoustic waves
Authors: Vlannes Nickolas P. , Bers Abraham
Published: February 2003

A general coupled amplitude equation is developed for surface acoustic waves (SAW) from coupled-mode theory. The derivation accounts for the surface propagating character and bulk decay pattern of the uncoupled modes. The general equation is applied to interactions arising from the weak nonlinearities of the materials supporting SAW’s. Coupling contants K of the nonlinear interactions are shown to be determined from the nonlinear material constants and normalized particle velocity, electric, and strain fields of the linear normal modes. For conservative coupling, a single coupling constant describes a given three-wave interaction. For a given mode α, the coupling constant to two other modes (β,γ) scales as the product of the frequencies of modes β and γ (ωβωγ ). Theory shows how one-dimensional single-nonlinear-parameter models can approximately account for multiharmonic generation on YZ-LiNbO3. Applying the theory to experiments on second-harmonic generation, we find the nonlinear coupling constant for YZ-LiNbO3 is ‖K‖≊1.1×109 m/sec2 W1/2 at 50 MHz. Similarly for (11̄0)-(001) Bi12GeO20, we find ‖K‖≊1.4×108 m/sec2 W1/2 at 50 MHz and ‖K‖≊5.3×108 m/sec2 W1/2 at 100 MHz. The nonlinear coupling constant units are for interacting field amplitudes normalized to the square root of action density integrated over depth (W sec2/m)1/2.
Characterization of low-pressure chemical-vapor-deposited and thermally-grown silicon nitride films
Authors: Habraken F. H. P. M. , Kuiper A. E. T. , Oostrom A. v. , Tamminga Y. , Theeten J. B.
Published: February 2003

Low-pressure chemical vapor-deposited (LPCVD) silicon nitride films on silicon have been characterized by means of Rutherford backscattering (RBS), Auger electron spectroscopy (AES) combined with ion sputtering, and spectroscopic ellipsometry. It appeared that all LPCVD samples in the examined thickness range of 50 –500 Å had an oxygen-containing layer equivalent to 15–20 Å of SiO2 at the nitride-silicon interface. This interfacial layer originates from the native silicon oxide present at the silicon substrate when the deposition of nitride is started. For comparison, oxide-free silicon substrates were nitrided in ammonia at temperatures between 800–1160 °C. The thermal nitride films were found to be very thin, at the most 30 Å, even after 5 h of nitridation. Both the LPCVD and thermal nitride films oxidize slightly when transferred into the ambient; a surface layer equivalent to 8 Å of SiO2 was detected. Auger and RBS results agree very well for all nitride films investigated. It is shown that RBS can be made a very sensitive probe for such thin multilayer structures by performing glancing-angle scattering experiments under channeling conditions. Spectroscopic ellipsometry proves to be more sensitive to the interface structure than to the surface composition. Although quantitatively deviating results were obtained, in the extremely thin thermal nitrides this optical technique traces chemical intermediates, not perceived with RBS or AES.
X-ray diffraction studies of sputtered thin films of platinum
Authors: Hecq M. , Hecq A. , Langford J. I.
Published: February 2003

The microstructure of sputtered thin films of platinum, deposited on glass substrates in the presence of argon, is investigated by x-ray diffraction. (111) layers tend to align parallel to the substrate surface and the degree of orientation depends on the film thickness, deposition rate, gas pressure, and cathode potential. These parameters can be optimized to give maximum orientation or crystallinity. From an analysis of the breadths of the (111) and (222) reflections by the variance and Fourier (Warren-Averbach) methods and from peak asymmetries, the domain size, strain, dislocations density, and faulting probability are obtained for as-prepared and annealed films. It is found that annealing decreases the strain due to dislocation. Large domain sizes with low fault and dislocation densities occur at high deposition rates and low pressures, and structural perfection is greatest when the ratio of the deposition rate to the pressure is in the region of 2000 Å min−1 Torr−1. It appears that some annealing due to particle bombardment takes place during deposition.
Effect of donor impurities on the conduction and valence bands of silicon
Authors: Lowney Jeremiah R. , Bennett Herbert S.
Published: February 2003

The energy shifts of valence and conduction band states in silicon due to the interaction of electrons and holes with ionized donors have been calculated by performing a partial wave analysis. The potential is modeled by the Yukawa form with the screening radius determined self-consistently by the Friedel sum rule. The results show that this effect is an important part of the optically measured band-gap narrowing. The variation of the Fermi energy due to this phenomenon is also calculated.
Ultraviolet bleaching and regeneration of ⋅Si≡Si3 centers at the Si/SiO2 interface of thinly oxidized silicon wafers
Authors: Caplan Philip J. , Poindexter Edward H. , Morrison S. Roy
Published: February 2003

The ⋅Si≡Si3 defect revealed by electron spin resonance (ESR) at the Si/SiO2 interface has been found to be very sensitive to ultraviolet (UV) radiation at 2537 A. With native oxides or very thin thermal oxides, UV bleached the signal, which then recovered slowly in room temperature air, or rapidly upon water immersion. Details of the bleaching suggest outer-oxide surface trapping by adsorbed oxygen, rather than bulk oxide traps. In HF-stripped silicon, an opposite uv effect was observed, i.e., an accelerated growth of ⋅Si≡Si3 centers. The physico-chemical responses of ⋅Si≡Si3 reflected several stages in the development of nascent oxides on silicon wafers. The uv trapping phenomenon further offers a potential method for determination of the energy levels of the ⋅Si≡Si3 defect, and thus for clarification of its role in interface trapping.
A sensitive method for measuring surface conductivity of insulators
Authors: Heimann P. A. , Olsen J. E.
Published: February 2003

A method is described for measuring the surface conductivity of insulating thin films. The conductivity is determined by observing the current transients while charging a capacitor whose dielectric is the insulating material and part of whose top electrode is the insulator surface. No elaborate sample preparation or experimental apparatus is required. Results are presented for oxide thermally grown on silicon, where sheet resistances between 1016 and 1020 Ω/⧠ were obtained for different values of relative humidity. The method can also be applied to a thin conducting layer on top of a thicker insulating film.
ac losses of superconducting solenoidal coils
Authors: Kuroda Kunishige
Published: February 2003

ac losses of superconducting solenoidal coils were investigated with a calorimetric method while applying a current or uniform magnetic field of 50 Hz with a sinusoidal wave form. The peak value of the ac current was varied from 0 to 15 rms A and that of the ac magnetic field from 0 to 0.02 T. These experimental conditions are for a practical regime where loss theories are difficult to apply and empirical data of the type generated are directly useful. Nine coil samples of various sizes were constructed with different fine multifilamentary superconducting wires. The ac losses observed are proportional to the square of the amplitude of an applied ac magnetic field or an applied ac current and appear to be mainly eddy current losses. The ac losses of coils of the same size caused by an applied ac current were the same regardless of the kind of wire used. All losses in the superconducting coils appeared to be equivalent to those expected from eddy currents in solid copper wires 0.72 times the diameter of the wires used, independent of the wire size and internal configuration.
Piezoelectricity in polymer electrets
Authors: Strathdee J. , Robinson W. H.
Published: February 2003

The model of Mopsik and Broadhurst for piezoelectricity in polymer electrets is reconsidered and further developed. The main features of the model are reviewed with particular attention directed to tensorial aspects of the piezoelectric effect. A characteristic difference is pointed out in the patterns of piezoelectric response attributed to two distinct sources: (1) the strain dependent residual polarization associated with the alignment of electric dipoles, and (2) the presence of trapped charge injected during the poling process. Trapped charge contributes to the piezoelectric shear stress constants e15, e24 whereas the oriented dipoles do not (unless electrostrictive anisotropy is important).
Dynamic fatigue of optical fiber under repeated stress
Authors: Katsuyama Yutaka , Mitsunaga Yutaka , Kobayashi Hirokazu , Ishida Yukinori
Published: February 2003

In this paper we present dynamic fatigue of fused silica optical fibers. Time-to-failure of the fibers under repeated stress has been investigated theoretically and experimentally, and the results have been compared with the time-to-failure under constant stress and increasing stress at a constant rate. As a result, it is found that the time-to-failure under repeated stress is related to the maximum stress with the same parameter n as those representing the times-to-failure by the other tests. The lifetime under repeated stress can be predicted by using two constants measured by the increasing test stress at a constant rate.
Local inertial effects in dynamic fragmentation
Authors: Grady D. E.
Published: February 2003

A general definition of dynamic fragmentation can encompass any impulsive process which partitions a body of material into discrete domains. Two examples are fragmentation due to brittle fracture under impact loading and fragmentation due to shear banding in shock-compression plastic deformation. In application, prediction of fragment size or shear band spacing is frequently either the objective, or else requisite to understanding the process. An approach is presented whereby surface or interface area created in the fragmentation process is governed by an equilibrium balance of the surface or interface energy and a local inertial or kinetic energy. Fragment size can be approximately related to surface or interface area. Relations provided by the analysis compare well with experimental dynamic fracture and shock-wave shear-band results.
Thermal stability of Pb-alloy Josephson junction electrode materials. III. Correlation of microstructure and strain in Pb-In-Au base electrodes
Authors: Murakami Masanori , Serrano Carlos M.
Published: February 2003

Upon cooling typical Pb-alloy Josephson junction devices from 300 to 4.2 K, strain is introduced into the junction electrode films due to the thermal expansion coefficient mismatch between the films and their underlying Si substrates. To reduce the probability of device failure, it is desirable for the strain to be supported elastically by the electrodes. Studies were undertaken by transmission electron microscopy and x-ray diffraction to correlate film microstructure with the elastic strain that can be supported at 4.2 K by Pb-alloy films containing Au and/or In. Grain size was confirmed to be one of the key factors that control the level of the elastic strain supported at 4.2 K when the films contained no misfit dislocations. The critical grain size (gc) (the value larger than which strain relaxation occurs upon cooling to 4.2 K) was found to be ∼0.6 μm for the Pb and Pb-alloy films prepared at 298 K by nucleating them on an ultrathin Au or oxidized In layer in a vacuum lower than 1×10−7 Torr. The Pb-alloy films prepared at 77 K supported more strain elastically; no strain relaxation was observed when their grain sizes were about a factor of two larger than the gc. When films contained misfit dislocations as observed at Pb/In interfaces in Pb-In and Pb-In-Au alloy films prepared at 298 K, strain relaxation by the dislocation glide was observed even though the average grain sizes were smaller than gc. No evidence was obtained that Pb3Au and AuIn2 intermetallic compounds observed in Pb-Au and Pb-In-Au films, respectively, control the level of elastic strain they can support at 4.2 K. However, these compounds were found to retard grain growth of the Pb-alloy films and to improve their grain size uniformity.
Nonaxisymmetric wave propagation in pulsed power machines
Authors: Waisman Eduardo M. , Wilson Andrew
Published: February 2003

We analyze, in the absence of space charge, nonaxisymmetric wave propagation in pulsed power machines in the long wavelength limit (λ≫anode-cathode gap dimensions). The conditions for generalized TEM waves are derived for both straight (coaxial) and convergent (double-disk) transmission lines. We examine the asymmetries resulting from the lack of switch synchronization as it affects the wave propagation and power delivery to a small radius symmetric imploding load. We apply the long wavelength equations to the output water line and vacuum feed sections of a machine resembling BLACKJACK V and calculate the reduction in power delivered to the load as a function of the degree of synchronization. An important, but simple, consequence of the theory is that for a small symmetric load the angular average of the voltage at the switches is approximately the effective driver of the power reaching the load.
Effects of Ga(As,Sb) active layers and substrate dislocation density on the reliability of 0.87-μm (Al,Ga)As lasers
Authors: Anthony P. J. , Hartman R. L. , Schumaker N. E. , Wagner W. R.
Published: February 2003

Reliability data are presented for (Al,Ga)As double-heterostructure lasers that emit light near 0.87 μm. Devices were grown with and without small additions of Sb to the active layer, with some devices grown on high dislocation density substrates. The reliability is more than an order of magnitude better for lasers with GaAs1−ySby active layers with y≊0.01 than for lasers with GaAs active layers. The rate of formation of dark line defects is reduced in the Ga(As,Sb) active layer lasers such that not all devices fail due to dark line defects. However, for Ga(As,Sb) active layer lasers grown on high dislocation density substrates, dark line defects formed very rapidly. An increase of roughly an order of magnitude in the substrate dislocation density resulted in a nearly three orders of magnitude decrease in the 70 °C lifetimes of Ga(As,Sb) active layer lasers.
Electrical conductivity of synthetic and natural quartz crystals
Authors: Jain H. , Nowick A. S.
Published: February 2003

Electrical conductivity of α quartz is ionic, the current being carried by alkali ions (M+) moving in channels parallel to the c axis. A study was made of conductivity σ of one natural and three synthetic crystals in order to better understand these ionic defects. ac measurements were made over a wide range of frequencies, and complex-impedance analysis was used to separate out the bulk conductivity from electrode effects. The activation energy E for the synthetic crystals was always close to 1.36 eV and the pre-exponential A was in the range of 106 K/Ω cm. A decrease in σ resulted from electrodiffusion (sweeping) in hydrogen. For the as-received natural crystal, the value of E was 0.82 eV, but this E value increased appreciably after hydrogen sweeping or after irradiation plus high-temperature anneal. The principal observations could not be interpreted in terms of the conventional theory in which the Al3+-M+ pair and its dissociation products are the only defects involved. A modified theory, in which additional unassociated Al is present as compensation either for H+ or for oxygen vacancies, allows a detailed interpretation of the results. Supporting data are also obtained from infrared measurements.
Electrical properties of lightly doped polycrystalline silicon
Authors: Lee J. Y. M. , Cheng I. C.
Published: February 2003

The electrical properties of lightly doped polycrystalline silicon as a function of temperature have been investigated. The polycrystalline silicon was deposited by low-pressure CVD and doped by phosphorus with ion implantation. The I-V characteristic was measured over the temperature range of 20–300 K. Comparison was made between experimental data and an electrical conduction model including both thermionic emission and thermionic field emission at the grain boundaries. The grain boundary potential barrier height was found to be an increasing function of temperature below 300 K. The effect of geometrical size on the sheet resistance of these polycrystalline silicon resistors was also measured and discussed.
Mg diffused zinc phosphide n/p junctions
Authors: Bhushan M.
Published: February 2003

Heating a Mg/Zn3P2 Schottky solar cell in air results in the formation of an n/p junction due to the diffusion of Mg in Zn3P2. The cells are fabricated on large grain polycrystalline Zn3P2 wafers. The junction depth is determined from the change in the measured collection efficiency of the cell after heating and follows a (time)1/2 dependence. The diffusion coefficient has been measured in the temperature range of 75–150 °C. The short-circuit current and open-circuit voltage of the homojunction qualitatively follow the theoretical predictions. A diffusion voltage of 1.2 V and a maximum open-circuit voltage of 0.6 V have been achieved.
A detailed analytical potential calculation strategy for complex electron optical systems with rotational symmetry
Authors: Heerens W. Chr.
Published: February 2003

An analytical potential calculation strategy is worked out, using the analytical solution of Laplace’s equation in cylindrical and toroidal configurations with rectangular sectional shape and rotation symmetrical boundary conditions. This strategy makes it possible to calculate the potential distribution to any desired rate of accuracy, even in very complex rotation symmetrical lens systems, and serves as a basis for the calculation of charged particle trajectories. These calculations only have to be done in places or areas where the shapes of the particle trajectories are of interest, while only and in a direct way the potential distribution on the boundaries of the potential volume is used in the calculations. Even in regard to the commonly used charge density method, this analytical calculation procedure saves a great amount of computer memory and calculation time, since no matrix inversions are required anymore.
A system for measuring deep-level spatial concentration distributions
Authors: Wang K. L.
Published: February 2003

A deep-level defect distribution profiling system using both analog and digital data-acquisition concepts is described. Analog circuits and digital data processing are used to provide high-speed acquisition and a high dynamic range, respectively. The implementation has an advantage of easy adaptation with an existing deep-level transient spectroscopy system having minimal software development. Additional advantages are the capabilities of eliminating long-term system drifts and superposition of data taken subsequently for averaging in order to conveniently achieve a desirable signal-to-noise margin. Several examples using ion-implanted n-type and p-type Si Schottky diodes are given. In addition, a metal-oxide-semiconductor field-effect transistor after a Si+ implant and annealing at 600 C is illustrated to indicate a high surface-defect concentration due likely to the recoiling process.
Photoacoustic measurements of thermal diffusivity description of the ’’drum effect’’
Authors: Charpentier P. , Lepoutre F. , Bertrand L.
Published: February 2003

Thermal diffusivities of metals can be accurately measured by the photoacoustic method. It is necessary, however, to use rear-surface illumination and to work at sufficiently high modulation frequency. Furthermore, to prevent mechanical vibrations of the sample due to its periodic dilatation (’’drum effect’’), this sample must be carefully fixed on the backing.
Optical properties of In1−xGaxP1−yAsy, InP, GaAs, and GaP determined by ellipsometry
Authors: Burkhard H. , Dinges H. W. , Kuphal E.
Published: February 2003

Refractive indices and absorption coefficients of In1−x Gax P1−yAsy for y = 0 to 1 lattice matched to InP and of GaAs and GaP have been measured by ellipsometry in the wavelength range between 365 and 1100 nm. The high-purity layers (7×1014<n<2×1016 cm−3) used here were grown by liquid phase epitaxy. The quaternary refractive indices were also calculated from the measured indices of the constituent binary compounds by averaging the quantity (ε−1)/(ε+2). The ε values were all taken at the same energy separation from the respective band gaps. The results of this new averaging procedure are compared with the measured indices and with the refractive index steps to InP deduced from lasers. In addition, the absorption coefficient of InP near the band gap was measured as a function of the doping level. Finally, the temporal growth of the natural oxide layer thickness dox on various InP and GaAs samples was determined by ellipsometry. For InP, the increase of dox is 0.39 nm per decade of time.
CO2 laser annealing characteristics of high-dose boron- and arsenic-implanted silicon
Authors: Tsien P. H. , Götzlich J. , Ryssel H. , Ruge I.
Published: February 2003

The CO2 laser annealing characteristics of high-dose boron- and arsenic-implanted silicon were studied by isothermal annealing experiments. A different annealing behavior at different annealing temperatures was found. At high annealing temperatures, a complete electrical activation was achieved, but after a prolonged annealing time, a relaxation of metastable concentrations takes place. At low doses, this phenomenon does not occur. The electrical activation energy is 5.8 eV for boron-implanted silicon (1.3×1016 cm−2, 120 keV), for annealing temperatures between 1045 and 1140 ° C.
Containerless undercooling and solidification of bulk metastable Nb3Ge alloys
Authors: Lacy L. L. , Rathz T. J. , Robinson M. B.
Published: February 2003

A containerless low-gravity environment, produced within a 32-m drop tube has been used to undercool and solidify Nb(1−x) Gex alloys for 0.13⩽x⩽0.27 with sample diameters in the range of 2–4 mm. Even for modest undercoolings of 100 K, evidence is found for the formation of metastable Nb3Ge. For major undercoolings in the range of 300–500 K, the x-ray diffraction studies on these samples revealed the A-15 structure with lattice constants consistent with the values obtained on chemical vapor deposited films. The instabilities of Nb3Ge at temperatures near the solidification temperature are revealed by quenching the samples in oil. The Tc widths vary from broad, similar to splat-solidified specimens, to narrow, similar to thin-film values, depending upon the high temperature solid state quenching rates in oil. The importance of maintaining a stoichiometric composition near 25 at. % Ge and the requirements for longer processing times are also revealed in the experiment.
The improvement of fatigue life in Ti-6Al-4V by ion implantation
Authors: Vardiman R. G. , Kant R. A.
Published: February 2003

The alloy Ti-6Al-4V has been implanted with carbon and nitrogen ions. The microstructure produced by these implants is found to contain fine particles of TiC and TiN, respectively. Rotating beam fatigue tests show improved fatigue life for both implants, with the superior carbon implantation giving a 20% increase in endurance limit and a factor of 4–5 lifetime increase at higher stresses over unimplanted material. A dose of 1×1017 at./cm2 is required to obtain the maximum effect. Fatigue cracks have been observed to originate up to 150 μm below the surface, indicating a complex interaction between the implanted layer and the fatigue failure process.
Some properties of dc glow discharge amorphous silicon solar cells
Authors: Wiesmann H. , Coleman C. , Ghosh A.
Published: February 2003

A study of the internal yield, depletion width, and absorption constant is presented for dc glow discharge P-I-N amorphous silicon films. Internal yields of ∼0.9 at 475 nm and depletion widths as large as 0.37 μm were observed at low illumination levels and were characteristic of the better cells. The absorption constant as a function of wavelength showed no anomalies and was comparable to rf glow discharge films with an optical gap of 1.68 eV. A unique aspect of these cells is that the top P layer is amorphous boron.
A new method for determination of particle-size distribution function from small angle scattering data
Authors: Re Fiorentin S.
Published: February 2003

A new numerical method is presented for calculating the particle-size distribution function of dilute particle systems from Small Angle Scattering data. The size distribution function, in order to be always positive, is approximated by the square of a combination of cubic B-splines. The coefficients of the combination are calculated in reciprocal space using the weighted least squares principle, which leads to a variational problem, solved by a Newton-Gauss-Marquardt iterative technique. A strategy is presented to enhance resolution in correspondence to the peaks of the distribution. Some results obtained on simulated and experimental points are presented, showing the accuracy of the method.
Electron mobility in n-type GaAs at 77 K: Determination of the compensation ratio
Authors: Walukiewicz W. , Lagowski J. , Gatos H. C.
Published: February 2003

Electron-mobility values in n-type GaAs at 77 K were computed utilizing a variational procedure and taking into account all major scattering mechanisms. Mobility values are tabulated as a function of electron concentrations, providing a convenient means for the determination of the compensation ratio, i.e., the determination of the total concentration of ionized impurities.
Low-temperature sintered AuGe/GaAs ohmic contact
Authors: Aina O. , Katz W. , Baliga B. J. , Rose K.
Published: February 2003

Ohmic contacts with low specific-contact resistivity and with contact morphology superior to conventionally alloyed contacts have been made to n-type GaAs by sintering AuGe films on GaAs at 315 and 330 °C for several hours. The specific contact resistivities were found to decrease with sintering time and values as low as 3×10−6 Ω cm2 were obtained for contacts on GaAs (doped with silicon to a concentration of 1018 cm−3) after sintering at 330 °C for 1 h. Secondary Ion Mass Spectrometry profiling of the sintered films has been used to show that the ohmic contact formation is due to an enhanced diffusion of Ge into GaAs.
Properties of AlxGa1−xN films prepared by reactive molecular beam epitaxy
Authors: Yoshida S. , Misawa S. , Gonda S.
Published: February 2003

Single-crystal films of the solid solution AlxGa1−xN of the entire composition range have been fabricated on sapphire and silicon substrates by reactive molecular beam epitaxy (MBE) at 700 °C. The properties of the films have been studied by the reflection high energy electron diffraction technique, x-ray diffraction, and electrical and optical measurements. The lattice constant of the film is not a linear function of the composition, and the fundamental absorption edge also shows nonlinear dependence on the composition. The narrow intense peak of the cathodoluminescence concerned with the band to band or shallow impurity band transition, varies from 3.4 to 6 eV with the composition, which suggests the feasibility of AlxGa1−xN films grown by reactive MBE for optical devices in the ultraviolet spectral region.
Ion-beam-induced metastable Pt2Si3 phase. III. Structure and diffusion in amorphous Pt2Si3
Authors: Graczyk J. F. , Tu K. N. , Tsaur B. Y. , Mayer J. W.
Published: February 2003

We have used electron microscopy, scanning electron diffraction, and structure modeling techniques to investigate crystallization behavior and structure of ion-mixed and codeposited films of Pt-Si of various compositions deposited on Si and on NaCl. We have determined that the amorphous alloys of ion-mixed Pt2Si3 have lateral compositional fluctuations on the atomic scale of 80–160 Å in diameter. We show that the amorphous phase of Pt2Si3 is a new phase which cannot be fully described by the simple binary dense random packing of hard spheres model (DRPHS). We propose, but do not prove unequivocably, that the amorphous structure can be described by a DRPHS model with lateral compositional fluctuations on the atomic scale of 80–160 Å, which contains very small nuclei on the order of 5–7 Å in size. We further propose that these nuclei have a composition exactly equal to the metastable crystalline Pt2Si3 phase, and that they cannot grow without a high temperature annealing because of the surrrounding amorphous material of slightly different composition. We find a long range diffusion process for amorphous Pt2Si3 at temperatures below crystallization. The activation energy for the process is 1.56±0.2 eV, with an average 〈D〉=2.0×10−15 cm2/sec at 385 °C. The process can relax and homogenize the amorphous structure by atomic displacements over a distance of 80–160 Å, and is probably possible because of micropores in the film. The structures of Pt62Si38 and Pt26Si74 on NaCl were amorphous, while that of Pt80Si20 was microcrystalline.
Effects of imperfections in InP avalanche photodiodes with vapor phase epitaxially grown p+-n junctions
Authors: Susa Nobuhiko , Yamauchi Yoshiharu , Ando Hiroaki
Published: February 2003

The influences of growth conditions, substrate dislocation, and misfit dislocation on characteristics of p+-n junctions, which have been prepared by vapor phase epitaxy (VPE) growth, are studied. The gas flow rate ratio of InC1 and PH3 in the hydride VPE growth affects junction properties. One-to-one correlation does not exist between dislocation and fatal junction degradation for the grown junctions. Dislocation affects junction properties at low dislocation densities only near the breakdown, where photocurrent is multiplied by a factor of several tens. The results obtained suggest that other crystal defects are responsible for destructive junction failure at low dislocation densities.
Theory of generation-recombination noise in intrinsic photoconductors
Authors: Smith D. L.
Published: February 2003

A theory of generation-recombination (g-r) noise is presented for intrinsic photoconductors, such as Hg1−xCdxTe. It includes, for the first time, effects of both diffusion and drift of carriers into the high recombination region near the contacts and combined with Rittner’s equation for responsivity gives a correspondingly complete expression for the detectivity, D*. Additionally, it includes the effect of the spatial correlation between the probability of a density fluctuation occurring and the lifetime of the fluctuation, rather than using spatial averages. The derived expression for the g-r noise consists of a thermal component and a background component which add in quadrature. The bias field and frequency dependence of these two components are different and thus the behavior of the total g-r noise and of D* depends on their relative contributions. In particular D* increases with increasing bias field when the background contribution dominates. The results of calculations for noise voltage and D* for a X=0.21 Hg1−xCdxTe photoconductor are presented.
Surface segregation model for Sn-doped GaAs grown by molecular beam epitaxy
Authors: Rockett A. , Drummond T. J. , Greene J. E. , Morkoc H.
Published: February 2003

A segregation model is presented which accounts for the accumulation of Sn at the growing film surface and the corresponding Sn depletion near the film-substrate interface during the deposition of Sn-doped GaAs by molecular beam epitaxy. Calculated Sn profiles were found to provide a good fit to experimental data obtained by secondary ion mass spectrometry.
Reduced Cu-Cr mixing and reduced Pt-Cu interdiffusion by oxygen in Cu/Cr and Pt/Cu/Cr thin films
Authors: Chang Chin-An
Published: February 2003

The effects of oxygen on the Cu-Cr mixing and Pt-Cu interdiffusion have been studied using Cu/Cr and Pt/Cu/Cr thin film structures. Both processes are reduced by oxygen, in agreement with the predicted effects of oxygen by the surface potential model. The Pt-Cu interactions provide another example of competing ambient effects dominated by the more electronegative species Pt.
Charge pumping measurements on stepped-gate metal-nitride-oxide-silicon memory transistors
Authors: Maes H. E. , Usmani S. H.
Published: February 2003

Charge pumping measurements using a variable pulse base level and a constant voltage amplitude are shown to be best suited for the direct determination of surface state densities in the different regions of stepped gate metal-nitride-oxide-silicon memory transistors. The effect of hydrogen annealing on the reduction of the surface state densities in the different regions can be directly demonstrated by using this technique. Finally the technique is very helpful in the study of Write/Erase degradation in these memory devices.
Rapid annealing of silicon with a scanning cw Hg lamp
Authors: Stultz T. J. , Sturm J. , Gibbons J. F. , Ichiki S. K.
Published: February 2003

A scanning arc lamp annealing system has been built using a 3-in.-long mercury arc lamp with an elliptical reflector. The reflector focuses the light into a high intensity narrow line source. Silicon wafers implanted with 100-KeV 75As+ to 1×1015 cm−2 have been uniformly annealed with a single scan, resulting in complete activation and negligible redistribution of the implanted species. Using a scan rate of 1 cm/s, entire 3-in. wafers have been annealed in less than 10 sec with this system.
Electrical properties and their thermal stability for silicon nitride films prepared by plasma-enhanced deposition
Authors: Maeda Masahiko , Arita Yoshinobu
Published: February 2003

The structural and electrical properties for plasma chemical vapor deposition amorphous silicon nitride films prepared from SiH4-N2-Ar mixtures have been investigated. Substrate temperature varied between 250 and 350 °C, and rf power density was set up in a range between 0.51 and 1.19 W/cm2 (13.56 MHz). Film composition changes toward a Si rich state with increasing substrate temperature or decreasing rf power density. Film density increases with increasing substrate temperature and rf power density. Film with a high degree of perfection (N/Si ratio=1.33 and density=3.2 g/cm3), is obtained at 350 °C and 1.19 W/cm2. Average electronic polarizability, dielectric strength, and Poole-Frenkel barrier height become smaller, stronger, and larger, respectively, when film structure approaches perfection. The electrical properties are degraded largely by annealing (700 °C, in a N2 gas), when as-grown films structure is far from perfection. This instability of electrical properties is attributed to the increase of trap density due to dehydrogenation and densification.
Hot electrons in a GaAs heterolayer at low temperature
Authors: Price Peter J.
Published: February 2003

The theory of hot electrons is developed for high-mobility GaAs heterolayers at low temperature, where the electron system is two-dimensionally itinerant with a highly degenerate distribution, and the scattering is predominantly elastic. The inelastic scattering which controls the electron heating is by acoustic-mode phonons, with both deformation and piezoelectric coupling to the electrons. Both ‘‘equipartition’’ and ‘‘Bloch’’ temperature ranges are considered. The assumption of an electron temperature, for the hot distribution, is critically investigated.
Electrical permittivity and conductivity of carbon black-polyvinyl chloride composites
Authors: Chung K. T. , Sabo A. , Pica A. P.
Published: February 2003

Electrical conductivity and permittivity of carbon black-polyvinyl chloride composites were studied over a wide frequency spectrum (dc, 1.3 GHz). Conductivity of the bulk composites increases with higher volume fraction of carbon black as expected. However, the functional dependence of the increasing conductivity with carbon black loading is different below and above the percolation threshold because of the different mechanisms involved. Bulk electric permittivity increases until the composite percolation is reached and then decreases to zero after fully connected conductive paths have been established. Such highly loaded composites showed a metal-like electrical behavior. Different electrical percolation threshold of the composites were found for different species of carbon black. Carbon blacks with the lowest packing efficiency reach the percolation threshold with the least volume fraction of carbon black loading. The percolation behavior of spherical carbon blacks showed good agreement with Bruggeman’s effective-medium theory in terms of both the percolation threshold and frequency dependence of conductivity at percolation.