bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoresist gratings on reflecting surfaces
Authors: Kapon E. , Katzir A.
Published: February 2003

The fabrication of photoresist gratings on reflecting surfaces is considered both theoretically and experimentally. We show that it is important to take into account the actual phase shift of the waves reflected from the surface. It is found that the intensity at the photoresist-surface boundary may be significantly larger than that at the standing-wave minimum. The theory is confirmed by the examination of the profiles of photoresist gratings made on PbSnTe, in comparison to GaAs. This phenomenon may have wider applications when the photolithographic fabrication of fine features on reflecting surfaces is considered.
The laser-initiated, gas-embedded z-pinch: Two-dimensional computations
Authors: Lindemuth I. R. , Brownell J. H. , Oliphant T. A. , Weiss D. L.
Published: February 2003

A high-density, laser-initiated, gas-embedded Z-pinch is modeled computationally in two dimensions. All aspects of an actual experiment are modeled: the computer model includes a laser optics package, a Marx-bank/transmission line package, an electron avalanche prescription, and two-dimensional magnetohydrodynamics. The experimental observations are reproduced to a very satisfactory degree. Predictions of performance in nonstandard operating modes are given.
Pulsed electron beam annealing of arsenic-implanted silicon
Authors: Yamamoto Y. , Inada T. , Sugiyama T. , Tamura S.
Published: February 2003

Pulsed electron beam with an energy fluence of 1.0 J/cm2 was irradiated on (100) and (111) Si implanted with 1×1016 As+/cm2 at 40 keV. Highly doped n+ layers with peak carrier concentrations of 8×1020/cm3 and 7×1020/cm3 for (100) and (111) samples were obtained, respectively, after electron beam irradiation. The effect of additional thermal treatment on electrical behaviors and crystalline quality of electron-beam annealed samples has been investigated. Carrier concentration decreased with increasing additional annealing temperature up to 800 °C and it increased above 800 °C, where the system approached a thermal equilibrium and at the same time thermal diffusion of As occurs. Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM) observations revealed that no residual damage remained after electron beam irradiation but dislocation loops were formed during the course of additional thermal annealing.
Measurements of intense ion beams by a novel diagnostic method
Authors: Blaugrund A. E. , Stephanakis S. J. , Goldstein Shyke A.
Published: February 2003

A new diagnostic method capable of measuring beam profiles and trajectories of intense ion beams as a function of time has been developed. The technique employs fast photography in conjunction with fast scintillators. Prior to detection, the excessive intensity of the direct ion beam is reduced by means of Rutherford scattering. A time resolution of a few nanoseconds and a spatial resolution of a few millimeters has been achieved. Using this technique focusing properties of planar and spherical pinch reflex diodes have been investigated. A low energy electron beam precursor has been detected. A simple model for its production is presented.
Unusual microstructures in TiO2 ceramic pellets with asymmetrical electrical conductivity
Authors: Shinozaki S. S. , Donlon W. T. , Meitzler A. H.
Published: February 2003

Ceramic pellets of TiO2 (rutile), with embedded Pt wire electrodes, have been heat treated in a manner that changed the normal electrical properties of rutile at room temperature from those of an insulator to those of a semiconductor with rectifying characteristics. This change in electrical properties was accompanied by the development of unusual microstructures in the rutile grains which were analyzed by a combination of techniques including transmission electron microscopy and scanning transmission electron microscopy. These analyses indicated that, under the applied conditions of heat treatment, Pt diffused into the rutile and reacted initially with the TiO2 at oxygen vacancy sites to form point-defect agglomerates and that these point defects blocked the normal formation of crystallographic shear planes. As the process proceeded by continued Pt diffusion, thin planar precipitates of PtTi3 were formed in epitaxial relation to the surrounding rutile matrix.
Barrier heights to silicon, of ruthenium and its silicide
Authors: Donoval D. , Stolt L. , Norde H. , de Sousa Pires J. , Tove P. A. , Petersson C. S.
Published: February 2003

The Schottky barrier height between as-deposited, as well as heat-treated samples of Ru metal deposited onto n-type silicon was determined, using forward IV data and photoelectric response measurements. When no silicide formation was observed (using Rutherford backscattering analysis) a barrier height of φBo = 0.79±0.01 eV was found. Where heat treatment resulted in formation of RuSi1.5 (reported to be semiconducting), the barrier height varied in the range 0.70– 0.74 eV. We included recent barrier-height data for the other 4d-series elements with our results and found a trend of increase of barrier height with work function, similar to that found for the 5d series.
Composite-processed Nb3Sn with titanium addition to the matrix
Authors: Tachikawa K. , Sekine H. , Iijima Y.
Published: February 2003

The effects of a titanium addition to the matrix on the superconducting properties and the metallurgical aspects of the composite-processed Nb3Sn have been studied. The titanium added to the matrix is found to diffuse readily into the Nb3Sn layer. The small amount of the titanium addition to the matrix significantly increases the growth rate and the critical current density Jc in high magnetic fields of the Nb3Sn layer. A Jc(Nb3Sn layer) of over 1×105 A/cm2 has been obtained at 16 T for the Nb/Cu-7 at. % Sn-0.35 at. % Ti composite wire reacted at 750 °C for 100 h. The titanium addition to the matrix may be practically more promising than the titanium addition to the core.
Effects of high-current pulses on polycrystalline silicon diode with n-type region heavily doped with both boron and phosphorus
Authors: Kim O-Hyun , Kim Choong-Ki
Published: February 2003

A new phenomenon in polycrystalline silicon lateral diodes with very high doping concentrations is observed experimentally. The impurity concentrations of the experimental devices are greater than 1020 cm−3 in both n- and p-type regions, and the n-region is doped with both boron and phosphorus. When current pulses of 106 A/cm2 or larger are applied, abrupt transition of the current-voltage characteristics from those of a diode to those of a resistor is observed.
Tensile stresses in copper and aluminum under dynamic tension
Authors: Maron Y. , Blaugrund A. E.
Published: February 2003

The behavior of copper and aluminum slabs under tension, resulting from the detonation of a slab of explosive in contact with them, was studied. A new technique, based on microwave interferometry, was employed for continuous observation of the free-surface velocity. Retrieved metal discs were scanned for microfractures. Tensile stresses, especially in regions where no observable damage occurred, were studied. They were found to be significantly lower than the negative pressures calculated by the common codes, already at early times of tension. This discrepancy increases in a gradual fashion with increased duration of tension. Observable damage appears only after a considerable reduction in the tensile stresses has already taken place. Elastic behavior of copper was studied by observing successive shock wave reverberations in the metal.
Experimental study of nonlinear interactions for noncollinear surface acoustic waves
Authors: Vlannes Nickolas P.
Published: February 2003

An experiment was carried out to measure the magnitude of the nonlinear coupling constant for a noncollinear surface-wave interaction on Y-cut LiNbO3. the resonant interaction was an upconversion interaction in which two surface acoustic waves with frequencies of 36 and 214 MHz interacted to produce a 250-MHz wave. The 36-MHz wave was launched with a phase velocity in the Z direction, and the 214-MHz wave was launched with its phase velocity 10° off the Z direction. The magnitude of the coupling constant was found to be: (2.8±0.6)×109 m/sec2W1/2.
Some observations on the amorphous to crystalline transformation in silicon
Authors: Drosd R. , Washburn J.
Published: February 2003

An atomistic model for the transformation of amorphous (α) to crystalline silicon films while in contact with a crystalline substrate is presented. The atomic structure of the {100}, {110}, and {111} surfaces is examined and related to the observed interface migration rates. The assumption that for an atom to attach successfully to the crystal it must complete at least two undistorted bonds, leads to the prediction that the {100} amorphous/crystalline interface should advance fastest and the {111} slowest. The origin of crystal defects is discussed in terms of the atomistic recrystallization mechanism. Microtwins are found to be a logical consequence of crystallization on the {111} surfaces but are not expected to form on any other interface. Once microtwins are formed they can increase the recrystallization rate of a {111} surface. This phenomenon is both described in the model and experimentally observed.
Composite oxide films formed by dc plasma anodization of Al/GaAs
Authors: Pu N. F. , Robinson G. Y.
Published: February 2003

Insulating films consisting of both aluminum oxide (Al2O3) and native oxide (Ga-As-O) have been grown anodically on p- and n-type GaAs in a dc oxygen plasma. Films were grown at a constant anodization current up to 2000 Å in thickness using GaAs wafers precoated with 50 to 150 Å of Al. Auger analysis using ion milling for depth profiling revealed Al2O3 mixed with native oxide in the upper 1000 Å and only native oxide at the GaAs interface. It was found that the presence of the Al2O3 did not prevent the buildup of As at the GaAs interface during anodization. The composite films were found to be ohmic with a resistivity of 1015 Ω-cm for electric fields below about 6×105 V/cm. The presence of the Al2O3 increased the breakdown strength to about 4×106 V/cm. An analysis of the capacitance-voltage characteristics of metal-oxide-GaAs devices measured from 100 to 1 MHz showed a typical interface-state density of 2–6×1012 cm−2 eV−1 in the lower half of the GaAs band gap. In contrast to earlier reports, the addition of Al2O3 to the anodic oxide did not alter the As and Ga distributions in the native oxide adjacent to the GaAs substrate nor did it appreciably improve the electrical properties of the oxide-GaAs interface.
Effect of impurity pairs on the disappearance of impurity levels in silicon
Authors: Kahn Arnold H. , Lowney Jeremiah R.
Published: February 2003

We report calculations of the binding energy of an electron to a pair of charged donor ions in the presence of screening by free carriers. The effective-mass approximation was assumed. We used a two-dimensional finite-element analysis to obtain numerical solutions, as we did in a previous study of the screening of single donor ions. The ground state was found to disappear into the conduction band at a doping level of 1.27×1019 cm−3, at 300 K, with a uniform distribution of donors. The results support the conclusion that at doping levels of 2×1019 cm−3 or higher, the density of electronic states in silicon contains no contribution from localized bound impurity levels.
Implications of the change in work function of chromium by the presence of hydrogen on the properties of electrical contact between chromium and hydrogenated amorphous silicon
Authors: Szadkowski A. J. , Kalnitsky A. , Ma K. B. , Zukotynski S.
Published: February 2003

The decrease of the work function of chromium and stainless steel due to hydrogenation has been observed. The consequences of hydrogenation of metals, which occurs when they are used as electrical contacts in solar cells made from hydrogenated amorphous silicon, are discussed.
Behavior of the Si/SiO2 interface observed by Fowler-Nordheim tunneling
Authors: Maserjian J. , Zamani N.
Published: February 2003

Thin-oxide (40–50 Å) metal oxide semiconductor (MOS) structures are shown to exhibit, prior to large levels of electron tunnel injection, the near-ideal behavior predicted for a uniform trapezoidal barrier with thick-oxide properties. The oscillatory field dependence due to electron-wave interference at the Si/SiO2 interface indicates an abrupt, one-monolayer barrier transition (∼2.5 Å) consistent with earlier work. After tunnel injection of 1017 –5×1018 electrons/cm2, the barrier undergoes significant degradation leading to enhanced tunneling conductance, with reproducible behavior observed among different samples. This effect is consistent with the generation of positive states in the region of the oxide near the Si/SiO2 interface (<20 Å), where the tunneling electrons emerge into the oxide conduction band. Densities of positive-charge and interface-state buildup are also observed from capacitance-voltage (C-V) measurements and are found to be consistent with the observed tunneling dependence on positive-state generation. We suggest that the interface-state buildup may be identical to the positive-state generation observed by tunneling. The generated oxide states are shown to anneal slowly at room temperature, and more rapidly at 100 °C. Comparisons are made between wet, wet/annealed, and dry oxidation processes, with wet oxides exhibiting the largest densities of state generation, and dry oxides the smallest. The results are consistent with other work on the effect of water-related defects in oxides, and with x-ray photoelectron spectroscopy results, showing that breaking of strained Si-O-Si bonds is responsible for state generation during stress. The tunneling data also indicate that, prior to stress, very few positive states reside in the oxide (?1010 cm−2), even though appreciable interface-state desities are observed from C-V data. We therefore conclude that these initial interface states must be associated primarily with the monolayer transition layer and disorder in the underlying silicon, and are not distributed into the oxide near the interface.
Some analytical and intuitive results in the quantum theory of mixing
Authors: Feldman M. J.
Published: February 2003

This paper is an elaboration upon Tucker’s quantum theory of mixing, which has proven very valuable in interpreting recent experiments in superconducting quasiparticle mixing. Tucker’s formula for the conversion gain of a three-frequency quantum mixer in the low intermediate frequency (IF) limit is generalized to include arbitrary source reactance; one choice of source reactance is found to resonate out the quantum reactance in the conversion expression. The signal reflection gain is evaluated; it becomes infinite simultaneously with the IF conversion gain. Infinite gain occurs only within the region of negative dc differential resistance. A number of relationships among the complex elements of the small-signal admittance matrix is presented; the nonlinear reactive elements are shown to be small under certain conditions when the conversion gain is maximized. The local oscillator (LO) power required for quantum mixing is calculated and found to be related to the gain denominator. This implies that certain quantum mixers at high gain will exhibit a constant gain-powerwidth product and a gain-proportional noise temperature component. A particularly simple expression for the conversion gain of an optimized quantum mixer is developed, which agrees with previous experiments. The origin of nonclassical behavior, including conversion gain and the nonlinear quantum reactance, is discussed. We conclude that the nonlinear quantum reactance, though it certainly must exist, is not itself responsible for conversion gain and has a minor, perhaps insignificant, effect upon the properties of a quantum mixer.
Anomalous magnetization loop in a nickel thin film with oblique magnetic anisotropy
Authors: Okamoto Kensho
Published: February 2003

The magnetization characteristics of a nickel thin film deposited onto a glass substrate with oblique incidence are studied by the measurement of its extraordinary Hall effect (spin Hall effect). The results show that the Hall loop which corresponds to the M-H loop is anisotropic with respect to the direction of the applied field, and that the loop varies from normal type to anomalous type reversibly with the angle between the applied field H and the film normal in a plane containing both the film normal and the easy axis.
The response of solids to elastic/plastic indentation. I. Stresses and residual stresses
Authors: Chiang S. S. , Marshall D. B. , Evans A. G.
Published: February 2003

A new approach for analyzing indentation plasticity and for determining indentation stress fields is presented. The analysis permits relations to be established between material properties (notably hardness, yield strength, and elastic modulus) and the dimensions of the indentation and plastic zone. The predictions are demonstrated to correlate with observations performed on a wide range of materials. The indentation stress fields are computed along trajectories pertinent to three dominant indentation crack systems: radial, median, and lateral cracks. The peak load and residual tensile stresses are shown to be consistent with observed trends in indentation fracture.
Vacuum transmission lines in the presence of a resistive cathode plasma
Authors: Waisman Eduardo , Chapman Milt
Published: February 2003

A model is introduced to describe the transverse electromagnetic propagation of power in high-voltage vacuum transmission lines in the presence of a resistive cathode plasma. The model consists of the transmission line equations complemented with a one-dimensional model for calculating local shunting currents. These equations are self-consistently solved in the presence of a cathode plasma expanding against the magnetic field. The plasma motion, considered to start at a given point when the local electric field reaches the selected threshold value of 0.3 MV/cm, is described by using one-dimensional magnetohydrodynamic equations in which the plasma properties at each position along the length of the line are assumed to depend only on the cross cathode-anode direction. Magnetic diffusion is taken into account in the plasma as well as in the metal cathode. The model is applied to a system for which experimental results are available: a 2-m vacuum coaxial line of Al walls, driven by a voltage pulse of 130-ns duration and 0.5-MV peak, of 6.2-cm radius and 0.5-cm gap terminated by an 18-nH inductive load. Several calculations with different initial temperatures and densities were performed assuming an Al plasma in local thermal equilibrium of variable degree of ionization z̄. For the highest initial values of temperature and areal density used, T = 5 eV, μ = 8.7×10−7 g/cm2, the average plasma front velocity was 2.4×106 cm/s. For this case the plasma is found to carry about 50% of the line current once its size is of the order of 1 mm, and it is almost stopped by the magnetic field, which reaches 25 kG at 130 ns. The calculated values of the line and shunting currents at different positions along the coax are compared with the experimental values. It is shown that the line currents are higher than if no plasma were present and lower than if it were a moving perfect conductor. For lower temperatures and densities, the average plasma front velocities are lower, of the order of 2×106 cm/s. To assess the possible influence of anomalous effects an ad hoc model for resistivity, in which it is equal to the inverse of the electron plasma frequency, is introduced. For T = 5 eV and μ = 8.7×10−7 g/cm2, this ad hoc model which clearly underestimates the influence of the magnetic field in slowing down the plasma, gives average plasma front velocities of 3.5×106 cm/s. On the basis of these calculations, it is concluded that for the type of experimental setup under consideration, no plasma closure should be observed, even when active loads are used, within the framework of the physical phenomena considered here. The importance of considering magnetic diffusion and joule heating in the motion of the cathode plasma as it influences the electrical properties of vacuum lines is demonstrated.
Transient analysis of low-hysteresis Josephson interferometer with feedback
Authors: Slusky S. E. G. , Jackel L. D.
Published: February 2003

We have performed a transient analysis of a Josephson interferometer in which feedback has been introduced to sharpen the transfer function. We examine the case for junctions with small, but finite, capacitance, so that the junction I-V characteristics have a small hysteresis. We find that no significant changes in switching times occur when feedback is introduced. The transfer function for the interferometer calculated in our ac analysis, which includes finite junction capacitance, is somewhat different from the one determined by a simple dc analysis that assumed zero capacitance.
The case for Auger recombination in In1−xGaxAsyP1−y
Authors: Dutta N. K. , Nelson R. J.
Published: February 2003

The possible Auger recombination mechanisms in direct-gap semiconductors are investigated. These include band-to-band processes, phonon-assisted processes, and Auger recombination via shallow traps. The band-to-band Auger rates are calculated including Fermi statistics, nonparabolic bands, and screening effects both for n-type and p-type semiconductors. The nonparabolicity is calculated using the Kane-band model. The band-to-band Auger processes are characterized by a strong temperature dependence, the Auger rate decreasing rapidly with decreasing temperature. The phonon-assisted and the trap processes do not exhibit such a strong temperature dependence. This is because the additional momentum conservation for the four-particle states in band-to-band processes gives rise to a ’’threshold energy’’ for the process. For the same reason, the band-to-band Auger rate decreases rapidly with increasing band gap. In large-band-gap semiconductors the weakly temperature-dependent phonon-assisted processes are expected to dominate. The Auger recombination rate via shallow-trap levels increases with increasing trap depth. A numerical computation is carried out for the quaternary alloy In1−xGaxAsyP1−y. We find that the calculated Auger rate is significant enough to account for the observed temperature dependence of threshold current of 1.3- and 1.55-μm InGaAsP-InP double heterostructure lasers.
Detailed characterization of deep centers in CdTe: Photoionization and thermal ionization properties
Authors: Takebe T. , Saraie J. , Matsunami H.
Published: February 2003

Electronic properties of four defect centers (designated as E7, E8, I, and IV) in A1-doped n-CdTe single crystals annealed under various Cd vapor pressures ( pCd) have been investigated by a combined use of photocapacitance, deep level transient spectroscopy (DLTS), and thermally stimulated capacitance techniques. Electron trap E7 at Ec−0.68 eV, a dominant deep defect center in samples quenched after annealing under high pCd, has shown a strong interaction with the lattice vibrations (S≳30, S: electron-phonon coupling parameter). The photoionization threshold energy for electrons E0n for the purely electronic transition has been estimated to be larger than 1.30 eV. Temperature dependence of the capture cross section for electrons σtn has been found to be very weak. The configuration coordinate diagram for E7 has suggested that E7 will nonradiatively capture the free electron. On the other hand, recombination center E8 at Ec−0.74 eV, a dominant deep defect center in samples annealed under low pCd, has shown only a negligible interaction with the lattice vibrations (S∼4) and has the photoionization threshold energies for electrons E0n ( = 0.80 eV) and for holes E0p ( = 0.95 eV) close to the thermal ionization energies for electrons Etn ( = 0.74 eV) and for holes Etp ( = 0.83 eV), respectively. The configuration coordinate diagram for E8 has revealed that E8 can radiatively capture the free electron and the free hole and can emit photons of ∼0.66 and ∼0.75 eV, respectively. E7 and E8 have been proposed to be identical with the levels previously reported as the doubly ionized Cd interstitial and the doubly ionized Cd vacancy, respectively. As to true origins of these centers, the data obtained in this study have suggested that both E7 and E8 may be donorlike complex centers including native defects, or impurities whose solubilities or stable sites in the lattice are strongly dependent on pCd. Hole trap IV at Ev +0.48 eV, which gradually decreases in concentration with decreasing pCd, has shown a weak interaction with the lattice vibrations (S∼6.7). It has been revealed that level IV can capture the free electron with emission of the photon of ∼1.0 eV. This level has been attributed to an impurity whose solubility in the crystal is moderately dependent on pCd. Electron trap I, which exists only in samples quenched after annealing under the highest pCd and have an electron-repelling barrier, has shown a very strong interaction with the lattice vibrations.
The theory of the Shockley-Haynes experiment: Contact effects
Authors: Duggan G. , Berz F.
Published: February 2003

Theoretical expressions are derived which describe the excess minority carrier distribution one can expect to observe when a Shockley-Haynes measurement is performed in the presence of a contact. The contact has been modelled by postulating the existence of an interface recombination velocity (S) at the contact/semiconductor boundary. An ohmic contact (S = ∞) and the general case of a finite S contact have both been considered. The variation in minority carrier distribution with S is illustrated using the derived expressions and the material parameters appropriate to a short wavelength (3–5 μm) Cadmium Mercury Telluride photodetector. The applied electric field (E) has been taken equal to 100 V cm−1 and the width of the read-out region, l = 40  μm. It has been shown that in this case an ohmic contact scarcely affects the average carrier distribution in the read-out region, and therefore the ’’classical’’ theory can be applied to derive the mobility ( μ) and diffusion constant (D), from the evolution with time of the conductivity modulation in the read-out region. The same procedure, when applied to a less recombining contact, still leads to a fairly reliable value of μ, but gives an appreciable overestimate of D, due to the broadening of the observed pulse.
Radiation-induced conductivity in quartz crystals
Authors: Jain H. , Nowick A. S.
Published: February 2003

Following room-temperature irradiation of quartz crystals by x rays or γ rays, a transient enhancement of electrical conductivity is observed which decays over a period of several hours. This enhanced conductivity is produced by alkali ions (M+) which are liberated during the irradiation. By freezing in this transient conductivity of synthetic crystals to temperatures below 270 K, the activation energy Em for migration of free alkali ions along c-axis channels of the crystal is shown to be 0.14±0.01 eV. The activation energy for the annealing process is ∼0.5 eV, showing that annealing is not controlled by Em. Results on natural crystals following irradiation are quite different from those of the synthetics; the differences are explained in terms of the presence of shallow traps for free M+ ions in natural crystals. Finally, the transient conductivity is compared with other transient phenomena following irradiation, viz., the frequency change and internal friction of quartz-controlled oscillators.
Photovoltaic investigation of minority carrier lifetime in the heavily-doped emitter layer of silicon junction solar cell
Authors: Ho Ching-Tao
Published: February 2003

The minority carrier lifetime in a phosphorous-diffused layer of a conventional N+/P silicon photocell has been investigated experimentally. The photovoltages have been measured as a function of photon flux density from low to medium illumination levels. From the quasi-Fermi level analysis of Gray-Kao-Schroder, we have determined the carrier recombination lifetime as a function of the photogeneration rate 〈G〉 in the heavily-doped N+ layer. When the band gap narrowing effect is taken into consideration, the recombination processes can be described by (i) a ’’positive-field controlled’’ Shockley-Reed-Hall recombination at low photo injection level, (ii) a ’’positive-field influenced’’ Auger recombination at the medium injection level, and (iii) a ’’negative-field controlled’’ Auger recombination at the high injection level. Under a very high photoexcitation condition, the magnitude of the saturated open circuit voltage of the cell is limited by the recombination lifetime at the surface contact region.
Intrinsic density n
i (T) in GaAs: Deduced from band gap and effective mass parameters and derived independently from Cr acceptor capture and emission coefficients
Authors: Blakemore J. S.
Published: February 2003

Prior attempts at determination of the intrinsic density in GaAs are reviewed, and this quantity is then deduced anew from the temperature dependences of the intrinsic gap and of the valence and conduction band system statistical weights. The nonparabolicity of the lowest conduction band, and the effects of the next two conduction bands, are taken into account in deducing ni (T) for the range 250–1500 K. That procedure gives a room-temperature value ni (300) = 2.1×106 cm−3, which can be compared with prior values from various experimental methods. The magnitude and temperature dependence of ni are then calculated by a different and entirely new method, which utilizes experimental data of the electron and hole emission and capture coefficients associated with Cr2+?Cr3+ transitions of the substitutional CrGa deep-level impurity in GaAs. Recent data of Martin et al. concerning these coefficients permits a deduction of ni(T) = 1.05 ×1016 T3/2 exp(−0.802/kT) cm−3 for 300<T<475 K, a range in which ni increases from 2×106 cm−3 to 3×1011 cm−3. Throughout that range, the procedure gives ni lying within ±15% of that calculable ’’directly’’ from band gap and effective mass parameters.
Electron mobility and carrier concentration of heteroepitaxial zinc selenide
Authors: Leigh W. B. , Besomi P. , Wessels B. W.
Published: February 2003

The Hall mobility and carrier concentration have been measured on low-resistivity ZnSe epitaxial films in the temperature range of 77–300 K. Both undoped and indium doped materials were studied. Resistivities of the as-grown films varied from 10−1 to 105 Ω cm. Electron mobility was of the order of 10–200 cm2 V−1 s−1 and was limited by ionized-impurity scattering. Analysis of the temperature dependence of the carrier concentration and Hall mobility indicated that the n-type films were heavily compensated having acceptor concentrations NA≳1018 cm−3. It was found that the acceptor and donor concentrations were essentially independent of Zn/Se pressure ratio present during growth.
Finite time thermodynamics: Optimal expansion of a heated working fluid
Authors: Band Yehuda B. , Kafri Oded , Salamon Peter
Published: February 2003

We determine the solution to the prototype problem: Given a finite amount of time, what is the optimal motion of a piston fitted to a cylinder containing a gas pumped with a given heating rate and coupled to a heat bath? The optimal motion is such as to maximize the work obtained via the piston in a specified period of time. This problem is solved for various end-point constraints, including constraints on final volume, final energy, or final volume and energy. We consider several associated problems including constraints on the rate of change of volume, piston friction, piston mass, and inertial effects of the gas. Explicit thermodynamic analyses of the solutions are carried out for various examples. The efficiency and the gain over nonoptimal paths are studied. Significant improvement over the bound on the efficiency is obtained as calculated by (infinite time, reversible) thermodynamics. The nature of the limit of the optimal solution as the time approaches infinity is determined. For a finite heating rate the optimal path is irreversible even as the time approaches infinity.
Loss calculations of the hollow-core, oxide-glass-cladding, middle-infrared optical waveguides
Authors: Hidaka T.
Published: February 2003

The loss characteristics of hollow-core, oxide-glass-cladding, middle infrared (near 1000 cm−1) optical waveguide is calculated numerically for TE01, TM01, and HE11 modes. The oxide-glass cladding used has its refractive index nr less than unity; their transmission losses of the waveguide are relatively small due to total reflection effect. The necessity condition of complex refractive index nr -ik of the cladding is clarified to be used with such hollow-core optical waveguides.
Photoacoustic study of two-photon absorption in hexagonal ZnS
Authors: Bae Y. , Song J. J. , Kim Y. B.
Published: February 2003

Photoacoustic detection technique is employed to investigate two-photon absorption (TPA) effects in ZnS over a wide frequency range with polarized 5 nsec dye laser pulses. By analyzing the dispersion and polarization dependence of TPA, we find that near the band gap, the TPA in ZnS occurs via allowed-forbidden type one-step, two-photon transitions.
Photoluminescence and infrared absorption studies of liquid encapsulated Czochralski-grown InP single crystals
Authors: Yamaguchi Masafumi , Yamamoto Akio , Shinoyama Seiji , Sugiura Hideo
Published: February 2003

Photoluminescence and infrared absorption in liquid encapsulated Czochralski-grown InP single crystals are discussed. Photoluminescence intensities, intensity ratio, and half-width due to donor-valence band and conduction band-acceptor transitions are clarified at 77 K as functions of carrier concentration. Acceptor binding energies of Zn, Cd, and Hg impurities are determined. Correlations between free-carrier absorption coefficient and carrier concentration to mobility ratio are also examined. It is concluded that carrier concentration, compensation ratio, and mobility in InP single crystals can be determined nondestructively by combining their photoluminescence and infrared absorption spectroscopies.
A simple model for the hysteretic behavior of ZnS:Mn thin film electroluminescent devices
Authors: Howard W. E. , Sahni O. , Alt P. M.
Published: February 2003

A model is proposed for the observed hysteretic behavior of ac-coupled ZnS:Mn thin-film electroluminescent devices. The following mechanisms are invoked: (1) tunnel injection from ZnS-dielectric interfaces (ℰ4106 V/cm), (2) electron-hole pair generation, (3) deep trapping of holes, leading to space-charge formation, (4) charge storage at the ZnS-dielectric interfaces, and (5) direct recombination of injected electrons and trapped holes. When these mechanisms are combined in a self-consistent numerical simulation model, a bistability of charge transfer versus applied voltage is obtained which exhibits many of the characteristics of the observed device behavior. Experimental evidence in support of the individual assumptions is also discussed.
Extension of Maxwell-Garnett theory for granular surfaces
Authors: Bosi Giulio , Girouard Fernand E. , Truong Vo-Van
Published: February 2003

The Maxwell-Garnett theory is generally used to describe the optical behavior of aggregated metallic films. This theory is, however, restricted to ultrafine particles whose main dimension can be considered very small compared to that of the wavelength. With particle dimensions in experiments generally larger than 10 nm, this approach is no longer valid for many metals. The purpose of the present work is, therefore, to revise the dipole approximation to include frequency-dependent terms. The theory is also extended to quadrupolar terms, in order to assess the relative importance of these latter when the aggregates are no longer very small compared to the wavelength. Applications to real metals are discussed.
Thermal gradient migration of brine inclusions in synthetic alkali halide single crystals
Authors: Olander D. R. , Machiels A. J. , Balooch M. , Yagnik S. K.
Published: February 2003

An apparatus consisting of an optical microscope with a hot stage attachment capable of simultaneously nonuniformly heating and mechanically loading small single crystals of salt was used to measure the velocities of all-liquid inclusions NaC1 and KC1 specimens under various conditions of temperature, temperature gradient, and uniaxial stress. The rate-controlling elementary step in the migration of the inclusions was found to be associated with interfacial processes, probably dissolution of the hot face. Dislocations are required for this step to take place. The small number of dislocation intersections with small inclusions in nearly perfect crystals causes substantial variations in the velocity, a sensitivity of the velocity to mechanical loading of the crystal, and a velocity which varies approximately as the second power of the temperature gradient.
Classical excitation energies for a finite-length sine-Gordon system
Authors: DeLeonardis R. M. , Trullinger S. E. , Wallis R. F.
Published: February 2003

We present simple analytic expressions for the classical energies of previously obtained nonlinear-standing-wave and single-soliton solutions to the sine-Gordon equation for a finite-length system with fixed- and free-boundary conditions. Plots of these energies are presented for several system lengths and the energy expressions are shown to reduce to those appropriate to familiar solutions in the infinite system as the length approaches infinity.
Auger electron spectroscopy investigation of degradation effect in GaAs metal-insulator-semiconductor solar cells
Authors: Pandelišev Kiril A. , Wang Edward Y.
Published: February 2003

Au-interfacial oxide layer (GeO2, Sb2O3, Bi2O3, SnO2 and native oxide mixture of AS2O3 and Ga2O3)-semiconductor (GaAs) structures were investigated by the Auger Electron Spectroscopy Method. The results of depth profiling with Ar+-ion sputtering are presented for all metal-insulator-semiconductor (MIS) structures. ’’Metal’’ atoms from deposited interfacial oxide layers (Ge from Ge2O3, Sb from Sb2O3, Bi from Bi2O3, and Sn from SnO2) were observed on the surface. Only As atoms were observed for the native oxide mixture of As2O3 and Ga2O3 interfacial layer. These findings suggest that As2O3 is the dominating oxide at the metal-oxide interface for native oxide GaAs MIS solar cells. The interfacial reaction takes place between Au and the interfacial layer at room temperature. The ’’diffusion’’ of metal atoms from the interfacial layer towards the surface is suspected to play a role in degradation effect in GaAs MIS solar cells.
Electrical properties of Zn in metalorganic chemical vapor deposition Ga1−xAlxAs
Authors: Yang Jane J. , Simpson William I. , Moudy Lavada A.
Published: February 2003

The Ga(1−x)AlxAs ternary semiconductor alloys have important applications for optoelectronic devices such as lasers and solar cells; hence electrical properties have been investigated extensively. However, little information is available about the behavior of Zn in metalorganic chemical vapor deposition (MO-CVD)Ga(1−x)AlxAs. In this paper the electrical properties of Zn-doped, p-type Ga(1−x)AlxAs films (0⩽x⩽1.0) grown by MO-CVD on GaAs:Cr substrates were studied using Hall measurements over a wide range of temperature (77 to 420 °K). The electrical activation energies were determined by measuring the variation of the carrier concentration of Ga(1−x)AlxAs films with temperature. The results indicate that activation energies increase with increasing Al composition (from 23∼26 meV for x = 0 to 140 meV for x = 1.0). The experimental results have been compared with theoretical data calculated from the modified hydrogenic model, and agreement is excellent for x⩽0.5.
Mobility and carrier-concentration profiles of P+ ion-implanted, isothermally annealed silicon crystals
Authors: Mitsuishi T. , Sasaki Y. , van Thieu Huynh , Yoshihiro N.
Published: February 2003

Experimental data of carrier mobility and carrier concentration profiles in depth from the surface of silicon wafers implanted with 50 keV P+ ions of various doses, isothermally annealed at 480 °C, are reported. Generation and annihilation of mobility controlling defects and carrier trapping centers are discussed with these data. A comment on the carrier recovery of heavily dosed specimens is given.
Optical emission: A probe of neutral atoms in liquid-metal ion sources
Authors: Venkatesan T. , Wagner A. , Barr D.
Published: February 2003

The optical emission close to the Taylor cone tips of liquid gallium and gold ion sources has been studied as a function of wavelength and ion current. The optical emission may be interpreted as due to excitations caused by binary collisions, among which Ga-Ga+ collisions play a dominant role. The release rate of neutrals from the source inferred from the optical-emission curves is consistent with the idea of contributions to the total ion current from field evaporation and field ionization, with the latter becoming increasingly important at higher currents. It is difficult to account for the origin of the neutrals by thermal evaporation at the tip.
Crystalline quality improvement of silicon on sapphire film by oxygen implantation and subsequent thermal annealing
Authors: Yamamoto Y. , Sugiyama T. , Hara A. , Inada T.
Published: February 2003

Rutherford backscattering measurements have revealed that the buried amorphous layer formed in the silicon-on-sapphire (SOS) film by oxygen implantation with a dose of 1×1015/cm2 at 130 K reorders epitaxially from the surface, and crystalline quality is improved in the entire region of the SOS film after annealing at 1000 °C for 20 min in N2. But in the case of implantation with a dose of 1×1016/cm2 at room temperature, the high concentration of oxygen prevents the reordering and as a result the crystalline quality improvement is limited only in the surface region. Energy dependence of the dechanneled fraction shows that the type of defects in Si near the Si/sapphire interface has changed probably from microtwins or stacking faults to dislocation loops after reordering.
Oxide charges induced in thermal silicon dioxide by scanning electron and laser beam annealing
Authors: Razouk R. R. , Delfino M. , Fulks R. T. , Powell R. A. , Yep T. O.
Published: February 2003

Oxide charge generation resulting from the exposure of Si/SiO2 structures to scanning electron and laser beams during the anneal of ion implantation damage was investigated. Fixed oxide charge, interface trapped charge, and oxide trapped charge densities were measured by use of high-frequency, quasistatic C-V, and avalanche carrier injection techniques. The effective density of traps induced by the exposure of thin oxides to electron beam fluences of 0.39–3.10×10−2 C/cm2 at 5 kV was found to be an order of magnitude larger than in control wafers. This effect was primarily due to neutral trap formation. Although interface charges could be reduced to an acceptable level by a post-irradiation anneal (400 to 500 °C) in forming gas, neutral traps could not be annealed satisfactorily. It was also found that scanned electron-beam annealing from the backside of the wafer or laser annealing constitute viable alternatives with minimal effects on the densities of fixed oxide charges in the silicon dioxide layer.
Prussian-blue-modified electrodes: An application for a stable electrochromic display device
Authors: Itaya Kingo , Shibayama Kimio , Akahoshi Haruo , Toshima Shinobu
Published: February 2003

An electrochromic display based on a Prussian-blue-modified electrode is described. Prussian blues are deposited electrochemically in a solution of ferric-ferricyanide. Current flow at +0.2 and +1.0 V is due to the reduction of Fe3+ and the oxidation of Fe2+ in the Prussian-blue coating, respectively. The result is a display that switches from clear to blue, has high stability, and has a response of less than 100 ms.
Isothermal enthalpy studies of poly(methyl methacrylate) stereoisomers and their blends
Authors: White A. J. , Filisko F. E.
Published: February 2003

The residual enthalpies of slow cooled atactic and isotactic poly(methyl methacrylate) were measured as a function of temperature. The samples were found to contain exothermic amorphous heats which decreased linearly with temperature below their respective Tg ’s. Blends of atactic and isotactic poly(methyl methylcrylate) were found to be one or two phase by differential scanning calorimetry depending on the method of preparation. The redisual enthalpies of the blends were lower than the pure components for the one-phase blend and a weight average of the pure components for the one-phase blend and a weight average of the pure components for the two-phase blend. Polymer-polymer heats of mixing were calculated by comparing the residual enthalpies of the blends to that of the pure components. The magnitude of the polymer-polymer heat of mixing is shown to be a measure of the extent of interaction of the blend relative to the pure components.
cw-laser annealed solar cells
Authors: Matsumoto S. , Gibbons J. F. , Wu F. C.
Published: February 2003

A technique combining ion implantation and cw-laser annealing has been applied to fabricate solar cells in single-crystal, metallurgical grade (MG) polycrystalline, and Wacker-cast polycrystalline silicon materials. cw-laser processing can produce solar cells with a high fill factor in all materials used. The best AM1 conversion efficiencies for MG Si and Wacker-cast Si cells were 10.3% and 10.5%, respectively, without an antireflecting coating.
Fluxon propagation in Josephson junction transmission lines coupled by resistive networks
Authors: Newman H. S. , Davis K. L.
Published: February 2003

The transmission, reflection, and absorption characteristics for fluxons propagating in long Josephson junction transmission lines which are connected by resistive networks have been studied by means of computer simulation. Although fluxon scattering behavior is qualitatively similar to that expected for electromagnetic waves, the existence of threshold resistances which depend upon applied bias current and junction loss is observed. For the case of two long junctions coupled by a serious resistor, it is found that variations in bias current, junction loss, and resistor value determine whether a fluxon incident on the resistor is either absorbed, or produces a reflected fluxon, a transmitted fluxon, or both a reflected and a transmitted fluxon. It is found that three junction segments can be connected in a configuration which functions as a fluxon multiplexer. Finally, the time delay (that is, the time required for a fluxon to attain steady state energy) in a typical low-loss tunnel junction line is found to be comparable to the delay in lines having a linear shunt conductance.
Interface investigation using transparent conductor-oxide-silicon structures
Authors: Kar S. , Varma S. , Saraswat P. , Ashok S.
Published: February 2003

Transparent conductor-oxide-silicon (TCOS) structures were fabricated, with oxide thicknesses ranging between 0 and 400 Å, by depositing indium oxide by spray hydrolysis on thermally oxidized silicon. Measurements and analysis show that the TCOS structures possess admittance characteristics identical to those of metal-oxide semiconductor. Hence, degenerate oxide semiconductors such as SnO2 and In2O3, are superior to semitransparent metals as the transparent gate for the application of optical illumination to extending the capability of the surface admittance techniques, especially in case of thin oxide structures with measurable leakage currents. A procedure has been outlined for obtaining the interface state density distribution from the capacitance-voltage characteristics measured under illumination.