bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of surface recombination velocity at a grain boundary using electron-beam-induced current
Authors: Burk D. E. , Kanner S. , Muyshondt J. E. , Shaulis D. S. , Russell P. E.
Published: February 2003

In order to determine the surface recombination velocity at a grain boundary surface, computer-aided calculations of the theoretical electron-beam-induced-current response to a point source excitation are fitted to data taken as a function of distance from the grain boundary. It is demonstrated that the data is in good agreement with this theoretical response for distances greater than two maximum penetration depths of the incident electron beam.
Microscopic location of electron traps induced by arsenic implantation in silicon dioxide
Authors: Alexandrova S. , Young D. R.
Published: February 2003

The microscopic location of implanted arsenic (As) atoms in a silicon dioxide (SiO2) matrix was studied using the avalanche injection technique. For samples annealed in nitrogen (N2), two trapping centers were observed with capture cross sections of (2–3)×10−16 cm2 and (1.5–2)×10−15 cm2. This is consistent with earlier results. Since silicon (Si) implantation reduces the density of these traps, we have concluded that they are due to As located substitutionally for Si in the SiO2 rather than in oxygen (O) sites suggested by earlier workers. The dominant trap for the samples annealed in an O2 ambient has a capture cross section of 1×10−15 cm2. It is suggested that this trap is due to an As-O complex formed through a reaction of O with interstitial As.
The mechanism of the enhancement of divacancy production by oxygen during electron irradiation of silicon. II. Computer modeling
Authors: Oehrlein G. S. , Krafcsik I. , Lindström J. L. , Jaworowski A. E. , Corbett J. W.
Published: February 2003

Numerical tests of possible models for the oxygen dependence of the divacancy introduction rate in silicon electron irradiated at room temperature were performed on a computer. Only the model in which oxygen traps Si self-interstitials can reproduce all the experimental data. Our modeling results (in conjunction with the experimental data) imply that during room-temperature electron irradiation of Si the indirect production of divacancies can be more important than the direct production of V2 via the single-collision process.
High-power microwave energy coupling to nitrogen during breakdown
Authors: Bollen W. M. , Yee C. L. , Ali A. W. , Nagurney M. J. , Read M. E.
Published: February 2003

Microwave energy coupling to nitrogen for breakdown conditions has been investigated. The experiments were performed in 25-Torr nitrogen using a 35-GHz 1-μs microwave pulse focused to 33 kW/cm2. The plasma created during breakdown was observed to travel towards the source with a velocity of 4.6×106 cm/s. Spectroscopic measurements using a nitrogen-helium mixture indicate the average electron density over a 2-cm chord to be 4.4×1012 cm−3, and the electron temperature to be 3.8 eV. Microwave cutoff was observed photographically, and suggests the peak electron density to be the collisional critical density. Computer simulations were also performed, and their results are in accord with the experimental results.
Photo-deep level transient spectroscopy: A technique to study deep levels in heavily compensated semiconductors
Authors: Mooney P. M.
Published: February 2003

Photo-deep level transient spectroscopy (photo-DLTS), a new technique to study deep levels in high-resistivity semiconductors, is described, and results of experiments on electron-irradiated n-type silicon are presented. In addition to the usual parameters, such as thermal activation energy and capture cross section, the photoionization energy for some defects was also measured. Thus optical and thermal parameters are measured for the same defects in the same sample. This technique should be useful for studying deep levels in materials made semi-insulating by the introduction of deep levels as compensating centers.
Ballistic and overshoot electron transport in bulk semiconductors and in submicronic devices
Authors: Ghis A. , Constant E. , Boittiaux B.
Published: February 2003

The possibility of ballistic and overshoot transport in bulk semiconductor and submicronic devices are discussed using both simple analytical calculation and more exact Monte Carlo simulation. Assuming a homogeneous semiconductor, it appears possible, using a really ballistic motion of electrons to achieve over very short distances (a few tenths of a micron) higher velocities than in the overshoot motion. The influence of the doping concentration and of the operating temperature, as well as the improvement which could be achieved by using other materials, is also discussed. The potential of such ballistic motion and velocity overshoot in a real submicronic device is then assessed; it is shown that, due to spatial nonuniformities, additional phenomena occur which might considerably change, and often reduce, the velocity of the carriers.
Study of the atomic models of three donor-like traps on oxidized silicon with aluminum gate from their processing dependences
Authors: Sah Chih-Tang , Sun Jack Yuan-Chen , Tzou Joseph Jeng-Tao
Published: February 2003

The effects of processing on the generation of three donor-like traps, i.e., the bulk compensating donor, the donor-like turn-around trap, and the peaked interface donor in boron doped p-Si aluminum-gate metal-oxide-semiconductor capacitors, are reported. After a possible initial delay, the generation of the bulk compensating donor follows first-order kinetics with a final density always approaching the initial boron concentration over the present experimental range 2.5×1016–1.5×1017 boron/cm3. The initial delay and the generation cross section of the bulk compensating donor and the generation cross sections and the densities of the turn-around and peaked interface donors are process dependent. Experimental evidence indicates that the three traps are water related. The close correlation of their generation-annealing kinetics suggests that they may be from the same water-related mobile impurity species, such as atomic hydrogen, released by the avalanche injected hot electrons. The generation kinetics of the three donors could involve (i) bond breaking and release of some water-related species, such as atomic hydrogen, at the Al–SiO2 interface or in the oxide, (ii) transport of the species through the oxide, (iii) modification of the peaked interface donor and the donor-like turn-around trap when the species reached the oxide–silicon interface, and (iv) formation of the bulk compensating donor when the species penetrate the silicon surface space charge layer.
Phase study and magnetic behavior of a new series of ternary borides (RE1−xRhx)Rh3B2 (RE=Y, La, Nd, Sm, Gd, Tb, Dy, Ho, Er)
Authors: Ohtani T. , Chevalier B. , Lejay P. , Etourneau J. , Vlasse M. , Hagenmuller P.
Published: February 2003

A new series of ternary borides with the formula (RE1−xRhx)Rh3B2 (RE=Y, La, Nd, Sm, Gd, Tb, Dy, Ho, Er) has been prepared. Their crystal structure which derives from the CeCo3B2-type is hexagonal with the P6̄2m space group. A large homogeneity range is observed (i.e., 0.29≤x≤0.52 for the Nd compounds). The Y and La compounds show for x=0.43 a strong itinerant-electron ferromagnetism (TC≂12–14 K). A great enhancement of μeff and θp occurs in the Y compound doped with 0.5 at. % Fe. The compounds with magnetic rare earth ions are ferromagnetic with TC growing up to 15 K and show a large increase of μeff due to a superimposed itinerant-electron paramagnetism. This itinerant magnetism can be attributed to the 4d conduction electrons of rhodium.
Linear and nonlinear intensity dependent refractive index of Hg1−xCdxTe
Authors: Jensen B. , Torabi A.
Published: February 2003

The index of refraction n is calculated as a function of frequency and mole fraction x for the ternary compound Hg1−xCdxTe in terms of known experimental parameters and compared with recent experimental results. The theoretical result for n is obtained from a quantum mechanical calculation of the dielectric constant of a compound semiconductor, which has been successfully applied to a number of III–V and II–VI binary, ternary, and quaternary compounds for which experimental data are available. The refractive index is calculated in terms of basic material parameters only, with no adjustable constants. These material parameters consist of band-gap energy, effective electron mass, and effective heavy hole mass at the band edge, the lattice constant, the spin-orbit splitting energy, and the carrier concentration for n-type of p-type materials. If these parameters are known as functions of mole fraction x and temperature, the refractive index is completely determined as a function of frequency below the fundamental absorption edge. The change in refractive index with increasing temperature depends mainly on the change in band-gap energy with temperature and is expected to be positive for x>0.529 and negative for x<0.529 for Hg1−xCdxTe . A negative change in the refractive index at the absorption edge proportional to I1/3, where I is the incident radiation intensity, is predicted on passing radiation through a crystal if the change in carrier concentration of the initially unoccupied conduction band is assumed proportional to I.
Pulsed Raman measurements of lattice temperature: Validity tests
Authors: Compaan A. , Lee M. C. , Lo H. W. , Trott G. J. , Aydinli A.
Published: February 2003

We measure the temperature dependence of the Raman correction factors and present data on the spot size and transverse beam quality of lasers used in the pulsed Raman measurements of lattice temperature in Si. Recent criticisms are also evaluated and shown to be inappropriate or in error. Finally we measure the shift of the 520-cm−1 Raman line and find it also to be consistent with the observed Stokes/anti-Stokes ratios indicating optic phonon populations characteristic of ∼450 °C.
Photoluminescent properties of n-GaAs electrodes: Applications of the dead-layer model to photoelectrochemical cells
Authors: Hobson William S. , Ellis Arthur B.
Published: February 2003

Single-crystal samples of n-type GaAs have been used as electrodes in photoelectrochemical cells (PECs) employing aqueous ditelluride electrolyte. Photoluminescence (PL) from the electrodes can be quenched by the electric field present in the semiconductor during PEC operation. The extent of PL quenching, studied as a function of carrier concentration, excitation wavelength, and applied potential, is consistent with the dead-layer model previously used to describe PL quenching in semiconductor/metal, Schottky-barrier systems. PL quenching curves calculated by assuming that the dead-layer thickness varies with applied potential in the same manner as the depletion width differ from the experimental data, particularly in the region near the flat-band potential. Sources of these discrepancies are discussed, including the possibility that relative PL intensity reflects the manner in which applied potential is partitioned across the semiconductor–electrolyte interface.
Silicon etching mechanism and anisotropy in CF4+O2 plasma
Authors: Lee Young H. , Chen Mao-Min
Published: February 2003

From measurements of optical emission and silicon etch rate, we are able to separate contributions due to the chemical etching and the ion-bombardment enhanced etching in the CF4+O2 reactive ion etching process. The chemical etching part of undoped polysilicon etch rates is linearly proportional to the ground state fluorine population and the ion bombardment part is proportional to the dc self-bias voltage (V2.3bi). The chemical etching predominates during plasma etching, giving rise to the isotropic etch profile, while both the chemical etching and the ion-bombardment enhanced etching mechanisms coexist during reactive ion etching. A degree of the etch anisotropy in reactive ion etching is determined by competition between the chemical etching and the ion-bombardment enhanced etching, and can be expressed by an equation which only involves two physical quantities, etch rate and fluorine concentration, experimentally measurable in plasma etching and reactive ion etching. The silicon loading effect leads to a substantial decrease in a number density of the ground state fluorine and consequently makes an etch profile more directional by reducing a contribution due to the chemical etching. Also, we have identified important process parameters which influence etch profiles.
Crystallographic etching of GaAs with bromine and chlorine plasmas
Authors: Ibbotson Dale E. , Flamm Daniel L. , Donnelly Vincent M.
Published: February 2003

We report results that show (100)GaAs can be crystallographically etched by a bromine or chlorine plasma. Specifically, {110}, {100}, and {111}A crystal facets develop under masked portions when the substrate is etched under ‘‘isotropic’’ or chemical plasma etching conditions (0.15–0.30 Torr, 0.1–14 MHz, ≲0.5 W cm−2). The etch rate of GaAs(100) is ∼20 to ∼70 μ/min in a pure Br2 discharge under these conditions. Absolute Br and Br2 concentrations were measured as a function of applied frequency by absorption spectroscopy. Relative optical emission from Br, Br+, and Br+2 was also recorded. The relationship between Br emission at 700.5 nm and Br concentration is quantitatively accounted for by an increase in the population of electrons above 13.5 eV with discharge frequency. The etch rate of GaAs(100) is directly proportional to Br concentration, and increases by a factor of 2.0 between 0.1 and 14 MHz.
Effects of surface preparation on the properties of metal/CdTe junctions
Authors: Werthen J. G. , Häring J.-P. , Fahrenbruch A. L. , Bube R. H.
Published: February 2003

The effects of surface preparation on the properties of single crystal CdTe junctions have been investigated through characterization of metal/CdTe junctions. Oriented surfaces include air-cleaved (110) surfaces, bromine-in-methanol etched (110) and (111) surfaces, and bromine-in-methanol etched surfaces subjected to a hydrogen heat treatment. Surface photovoltage measurements of the surfaces indicate larger band bending on the etched surfaces than on the cleaved and heat treated surfaces. X-ray photoelectron spectroscopy analysis verifies that excess Te remains after bromine-in-methanol etching and that cleaving leaves a stoichiometric surface. Hydrogen heat treatment of an etched CdTe surface restores a stoichiometric cleaved-like surface from that altered by the etching process. The barrier height for metal/CdTe junctions formed on cleaved surfaces depends on metal work function and reaches 0.99 V in an Al/CdTe junction and 0.87 V in a Cr/CdTe junction. Junctions formed with different metals on etched (110) surfaces result in barrier heights of 0.55–0.65 V with no dependence of the barrier height on the metal work function being observed, due to the presence of an etch-induced layer that partially governs the properties the surface. Heat treatment of an etched surface results in metal/CdTe junctions with characteristics similar to those of junctions formed on cleaved surfaces, and dependence of barrier height on metal work function is again observed, indicating the removal of an etch-induced layer by the heat treatment and the production of a junction similar to that on the cleaved surface.
Estimation of thermal accommodation coefficients for inert gases on nuclear materials
Authors: Dharmadurai G.
Published: February 2003

A simple method considering phononic thermal transport from a hot solid into a gaseous medium in conjunction with a phenomenological consideration of the contribution from the adsorbed molecules at the surface sites is proposed for estimating the thermal accommodation coefficients (TAC) of inert gases on various nuclear materials. The present estimates are consistent with TAC determined from recent measurements at ambient temperatures and offer a qualitative explanation for the observed trend of monotonous decrease in TAC at higher temperatures. In addition, the present evaluations indicate the conditions under which the different values of TAC used in some nuclear reactor fuel behavior computer codes could be valid.
Bulk minority carrier diffusion length and photogenerated carrier profile in silicon photovoltaic cells
Authors: Ho C. T. , Mathias J. D.
Published: February 2003

The bulk minority carrier diffusion length of single-crystal and polycrystalline ribbon silicon photocells was measured with monochromatic light of various wavelengths and flux densities. We noted that the diffusion length shows a gradual reduction as the illumination wavelength becomes shorter in both types of cells. In addition, the light enhancement phenomenon of the diffusion length in the ribbon cells diminished when shorter wavelength lights were used. In the single-crystal cells, however, no enhancement effect was observed for any wavelength. The interpretation of these results is based on the examination of the photogenerated minority carrier profile as a function of diffusion length and wavelength in the bulk region of the cell. We correlate the measured diffusion length with the depth in which a positive minority carrier concentration gradient exists.
Analysis of picosecond optoelectronic cross-correlation switches
Authors: Moss D. J. , van Driel H. M.
Published: February 2003

We analyze the use of tandem, photoconducting gates in a biased transmission line for picosecond, optoelectronic cross-correlation measurements. In general the integrated photoinduced current is a function of the time delay between excitation pulses and is the sum of the cross correlation of the induced conductivities and a constant background. We consider two possible circuits, which differ in that one contains an isolation attenuator between the two switches which helps improve the contrast ratio of the cross correlation and dc outputs. We obtain the contrast ratios and the absolute outputs of the two circuits as a function of circuit parameters. We show that gate transmission saturation leads to distortions in the cross-correlation function and induced asymmetries which reflect the different functions performed by the two switches. Certain elements of the theory are compared with experimental results on the picosecond photoconductive response of semiconducting diamond. We, thereby, also illustrate the use of tandem photoconductivity gates in analyzing low resistivity semiconductors.
Extension of the spectral coverage range of frequency modulation spectroscopy by double frequency modulation
Authors: Lotem Haim
Published: February 2003

The performance of frequency modulation spectroscopic techniques is limited by the modulation cutoff frequency of optical phase modulators. A method which allows for overcoming this limit by using high order sidebands in a double-frequency modulation scheme is proposed. The usefulness of the proposed technique in relation with a recently developed frequency modulation spectroscopy is discussed in detail.
The spectral characteristics of an atomic cesium resonance filter
Authors: Flusberg A.
Published: February 2003

It is shown that the excitation spectrum of atomic Cs vapor around 455.5 nm (21947 cm−1), observed by Marling et al., contains 0.1 cm−1 structure which is not expected on the basis of hyperfine constants previously reported in the literature. If this structure is extraneous it follows that a Cs vapor resonance ‘‘filter’’ designed to fluoresce in the red when irradiated on its blue (455.5 nm) resonance can suppress background light better than has heretofore been thought. Additional experiments to determine the origin and relevance of this structure are therefore recommended.
Radial distribution studies of amorphous Fe–W and Ni–P at high pressure
Authors: Munro R. G. , Mauer F. A. , Piermarini G. J. , Block S.
Published: February 2003

The procedure for the determination of a radial distribution function of an amorphous material contained in a diamond anvil pressure cell is discussed. The details of the method of computation are presented, and the results for two amorphous metals, Fe–W (72 at. % Fe) and Ni–P (75 at. % Ni), are presented and critically discussed. For the reduced structure function and its Fourier transform, the differential radial distribution function, amplitudes are not well determined, and maxima and minima are located with an absolute accuracy not better than 3%. However, for a single experimental configuration and sample, the relative changes in the first neighbor distance as a function of pressure are readily detectable, even for variations on the order of 0.5%. Measurements at 0, 0.3, 3.6, 7.5, and 10.5 GPa and room temperature indicate that Fe–W (72 at. % Fe) has a bulk modulus of about 170 GPa and has a volume compression of about 6% at 10.5 GPa. Measurements at 0.15, 2.80, and 5.50 GPa indicate that Ni–P (75 at. %Ni) has a bulk modulus of about 370 GPa at room temperature and has a volume compression of about 1.5% at 5.50 GPa.
Extremely high corrosion resistance in amorphous Cr–B alloys
Authors: Ruf R. R. , Tsuei C. C.
Published: February 2003

Amorphous Cr–B alloy films containing 40 to 80 at. % Cr are prepared by rf and dc sputtering onto liquid nitrogen and water cooled substrates. Amorphous Cr–B alloys with Cr ≥60 at. % do not corrode in concentrated solutions of HCl (12N), 3/1 volume ratio HC1/H2O2, 1/1 HNO3/HCl, 1/1 H2O/H2SO4, and NH4 OH. For example, amorphous Cr80B20 and Cr60B40 films (∼4000 Å) can be immersed in concentrated (12N) HCL for over 3 months with no detectable change in thickness. By comparison, pure polycrystalline Cr dissolves at ∼700 μm/day. Corrosion properties of these new materials are investigated by electrochemical and immersion techniques as a function of alloy composition and thermal annealing. The corrosion tests are supplemented by measurements of electrical resistivity, and hardness and scanning electron microscopy observations. The main results of these studies are (1) high corrosion resistance is observed in 12N HCl only when Cr content is ≥60 at. %, (2) the corrosion rate is strongly dependent on surface smoothness and/or microstructural size only when Cr concentration is ≥60 at. %, and (3) at potentials above 1 V (SCE) the crystallized Cr–B alloy films corrode by pitting, while their amorphous counterparts exhibit slow and uniform dissolution. These results indicate that it takes both high Cr content and a smooth surface, as provided by the amorphous Cr–B films, to form a continuous, uniform passive oxide which is essential to the extremely high corrosion resistance in concentrated acids.
Pressure-induced alpha-omega transformation in titanium: Features of the kinetics data
Authors: Singh A. K. , Mohan Murali , Divakar C.
Published: February 2003

The increase in the electrical resistance of the specimen, associated with the α→ω transformation in Ti, has been used to obtain the fraction ζ of the ω phase as a function of time under isobaric–isothermal conditions in the pressure range 4–9 GPa and at 300±3 K. In the entire pressure range ζ–t data fit an equation of the form: ζ=1−exp−(t/τ)n, where τ and n are constants at a given pressure. The results indicate that τ decreases rapidly and n slightly with increase in pressure. An analysis of τ–p data shows that (i) the activation free energy for the total process is very high at low pressures and decreases rapidly with increasing pressure, and (ii) the activation volume in the 6–9 GPa range is −4.3 cm3 mol−1. The activation enthalpy has been obtained by measuring τ at different temperatures, and the average value in the pressure range 5–8 GPa is 12±0.5 kCal mol−1.
Diffusion of silicon into amorphous FexB100−x
Authors: Luborsky F. E.
Published: February 2003

The diffusion of silicon into FexB100−x amorphous alloys for 74<x<88 has been determined at two temperatures—297.6 and 373 °C—using composition-depth profiles determined from Auger-ion milling analysis. The value of the diffusion constant at 298 °C was 4.4×10−23 m2/s and at 373 °C was 2.8×10−21 m2/s, both independent of composition. This result indicates that the rate limiting process in diffusion of Si is independent of any structural changes occurring as the composition of Fe–B varies. The diffusion of silicon into Fe82B18 has also been studied as a function of temperature giving an activation energy of 2.0±0.4 eV/atom with a preexponential constant of 5.7×10−4 m2/s. No effect on the shape of the interface or the value of D was found for various surface polishing procedures or for preannealing the amorphous alloy before depositing the silicon. It has been concluded that the rate limiting step in the diffusion of Si in amorphous Fe–B alloys is different than the mechanism involved in stress relaxation and in crystallization but may be the same as is involved in the formation of the induced magnetic anisotropy. On the basis of the atomic size dependence for diffusion of various species through a variety of amorphous metal-metalloid alloys it is postulated that the diffusion of silicon proceeds by a mechanism similar to interstitial diffusion assumed for boron diffusion.
The effects of processing conditions on the out-diffusion of oxygen from Czochralski silicon
Authors: Heck D. , Tressler R. E. , Monkowski J.
Published: February 2003

The out-diffusion profiles of oxygen from Czochralski grown (Cz) silicon were measured with secondary ion mass spectrometry for several processing conditions. The diffusivity of oxygen was found to be retarded under oxidizing conditions. This effect, however, is eliminated with the addition of 2% HCl to the oxidizing ambient. Both in-diffusing boron and in-diffusing phosphorus enhance the diffusivity of oxygen. These observations are consistent with a vacancy dominant diffusion mechanism for oxygen in silicon. The surface concentration of oxygen Cs varies considerably with processing conditions. An increased concentration of oxygen at the surface was observed under oxidizing conditions. Under inert or reducing conditions, Cs was lower than oxidizing conditions but did not approach as low a value as was expected. The lowest values of Cs were obtained for the phosphorus diffusion, boron diffusion, and for the 10% HCl oxidation.
Reactive sputtering of amorphous silicon in Ne, Ar, and Kr
Authors: Ross R. C. , Messier R.
Published: February 2003

We have characterized hydrogenated amorphous silicon films prepared by rf diode sputtering in varying partial pressures of Ne, Ar, and Kr. The mechanisms of ion bombardment of growing film surface due to large negative floating potentials at low gas pressures can explain the observed film characteristics. These inert gas effects are in contrast to those seen in inert gas dilution studies of glow discharge decomposition of SiH4. These differences are examined and lead to general conclusions about the effect of bombardment in minimizing microstructure, and in producing electronically-active defects. Other bombardment processes are also discussed.
Thermal and ion-induced reaction of Ni–Au dilute alloys on Si
Authors: Hung L. S. , Zheng L. R. , Mayer J. W.
Published: February 2003

Redistribution of Au in Ni silicide formation by thermal annealing or ion beam mixing of Ni films with 1.4 at. % Au deposited on 〈100〉 Si was investigated using Rutherford backscattering spectrometry and glancing-angle x-ray diffraction. Annealing at temperatures of 300–350 °C results in the formation of Ni2Si with accumulation of Au at the Ni2Si/Ni interface. A similar redistribution of Au has also been found when the samples are irradiated with Xe ions at doses ≥2×1015 ions/cm2. This accumulation is contrary to the dispersion that one would anticipate in ballistic collisions and we believe that the Au accumulation is a result of thermodynamic forces in ion-induced reactions. In thermal annealing, the accumulation of Au impedes the supply of Ni and the second phase NiSi begins to form before the Ni film is consumed. With ion beam mixing, however, the accumulation of Au does not block silicide formation and Ni2Si continues to grow. We attribute the continued growth of Ni2Si to Au–Ni demixing within the collision cascade.
Thermal stability of Pb-alloy Josephson junction electrode materials. IX. Multilayered Pb–In–Au electrodes
Authors: Murakami Masanori , Alessandrini E. I. , Magerlein J. H.
Published: February 2003

Effects of substrate temperature, deposition sequence, and number of layers on the microstructure of Pb-12 wt. % In-4 wt. % Au films were studied using x-ray diffraction and transmission and scanning electron microscopy before and after repeated thermal cycling between 298 and 4.2 K. Significant grain size reduction and smooth film surfaces were obtained when the film deposition was carried out at substrate temperatures below 200 K. The deposition sequence strongly affected the rate of grain growth that occurred during warming from the deposition temperature to ambient temperature. It was found that the sequential Au and In depositions were essential in order to suppress grain growth. Strain introduced into films upon cooling from 298 to 4.2 K due to a thermal expansion coefficients mismatch between the films and Si substrates was also measured. The strain supported elastically by 0.35-μm-thick multilayered films was increased by reducing the thickness of each layer. By studying dependence of thickness of each layer on strain at 4.2 K, the critical grain size, smaller than which strain is not relaxed by dislocation glide, was determined to be ∼90 nm. This size agrees well with the previously measured mean spacing between misfit dislocations. Based on the present study, 10-layered Pb-In-Au films prepared at 200 K were developed for use as Josephson junction electrodes. The films had smooth surfaces and showed no undercut at the edges of lift-off patterned films. After 400 thermal cycles between 298 and 4.2 K, no microstructure changes such as hillock formation, dislocation slip steps, and grain rotation, were observed. These films can be used both as base electrode films for Pb-alloy Josephson junctions and as counterelectrodes for Nb/Pb-alloy junctions.
Tests of Gaussian statistical properties of 1/f noise
Authors: Restle P. J. , Weissman M. B. , Black R. D.
Published: February 2003

Two statistical tests of 1/f noise—histograms of noise power in time-frequency windows and covariance matrices of noise power in separate octave bands—were used to determine deviations from Gaussian statistics. In silicon, bismuth, and some carbon granule resistors no non-Gaussian effects were found. One carbon resistor showed clear non-Gaussian behavior. The significance of the results for models of the origins of 1/f noise is discussed.
Theoretical modeling of amorphous silicon-based alloy p-i-n solar cells
Authors: Hack M. , Shur M.
Published: February 2003

We have developed a computer model of amorphous silicon based alloy p-i-n solar cells based on the solution of the electron and hole continuity equations, together with Poisson’s equation. This model takes into account the spatial and energy variations of the localized state spectrum, nonuniform doping profiles, and nonuniform optical excitation. Heavily doped p+ and n+ regions are used as contacts, and these enable us to realistically set up the boundary conditions. Appropriate boron profiles have been added to the intrinsic layer, with the density of states being dependent on the doping concentration. The computed dark and light current–voltage characteristics are in good agreement with experimental data. In particular, our results indicate the importance of residual boron doping in the intrinsic layer for cells illuminated through the n+ layer, and show that for optimized p-i-n devices carrier back diffusion is not a significant effect and that the open circuit voltage is determined by the recombination current.
Chain scission and mechanical failure of polyethylene
Authors: Fanconi Bruno M.
Published: February 2003

The role of chain scission in the mechanical degradation of polyethylene has been examined using Fourier transform infrared spectroscopy to measure changes in molecular end group concentrations. The increase in chain scission concentration during cyclic fatigue of ultrahigh molecular weight polyethylenes has been investigated by this technique. The concentration of chain scissions at macroscopic failure was independent of the peak stress and time to failure in the fatigue experiment, but dependent on fatigue test frequency and molecular weight.
Preexisting polarization and influence of electrode materials on PVF2 electrets as determined by thermal pulse and pyroelectric methods
Authors: Lang Sidney B. , DeReggi A. S. , Mopsik F. I. , Broadhurst M. G.
Published: February 2003

A number of polyvinylidene fluoride (PVF2) electrets were prepared with different permutations of gold and aluminum electrodes and poled with dc fields up to 160 MV m−1 at room temperature. Polarization distributions were measured by the thermal pulse method and pyroelectric coefficients were determined. Quantitative measurements were made of a significant level of polarization in nominally unpoled PVF2 and a contact electrification mechanism was proposed. No consistent effects of electrode materials on polarization distribution were found. PVF2 poled at room temperature has its highest polarization near the center of the thickness in contrast to the results on samples poled at elevated temperatures and cooled inhomogeneously with the field applied.
Specular reflection cancellation in an interferometer with a phase-conjugate mirror
Authors: Drummond P. D. , Friberg Ari T.
Published: February 2003

An ordinary mirror placed in front of a phase-conjugate mirror forms a type of Fabry–Perot interferometer with unusual reflection properties. The specularly reflected and phase-conjugate reflected intensities are analyzed for arbitrary reflection coefficients, given an incident monochromatic linearly polarized plane wave. It is shown that if the ordinary mirror is lossless and the phase-conjugate reflectivity is unity, the specularly reflected wave disappears completely. This leaves only the phase-conjugate reflected wave that propagates in the direction opposite to that of the incident wave. The above result is independent of the reflectivity of the ordinary mirror and the separation between the two interferometer mirrors. Some of the main effects due to absorption in the ordinary mirror are briefly discussed.
Narrow-linewidth gain and saturation measurements of a KrF discharge laser
Authors: Fedosejevs R. , Tomov I. V. , McKen D. C. D. , Arnfield M. , Domier C. , Offenberger A. A.
Published: February 2003

The gain and output characteristic of a KrF discharge laser module have been studied using a 0.1-cm−1 linewidth probe pulse generated from an etalon-narrowed injection-locked oscillator-amplifier system. A small signal gain coefficient of 0.115 cm−1 was measured. Saturation of the output intensity could be accurately modelled by assuming steady state conditions including a nonsaturable absorption of 0.01 cm−1 which yields a saturation intensity of 1.7 MW/cm2.
Criterion for exciton lasing in pure crystals
Authors: Liu K. C. , Liboff Richard L.
Published: February 2003

A scheme for lasing action involving excitons in a pure crystal is described. The lasing mechanism depends on the nonboson quality of excitons. We find this property to be exhibited at high exciton density. A criterion for lasing under these conditions is obtained.
Aspect of nonlinear parametric interaction in a piezosemiconductor
Authors: Pal R. K. , Gupta M. , Sinha D. K.
Published: February 2003

The present paper is an attempt to investigate the nonlinear parametric interaction of acoustic waves propagating through a piezosemiconductor which is subjected to a dc electric field as well as acted upon by a mechanical body force. The analysis indicates that it is always possible to obtain a gain in the energy of the signal wave by suitable body force(s). Numerical computations are resorted to so as to obtain a better understanding of the theoretical results arrived at. Also, graphs are used to illustrate the results involved. The numerical computations bring out fairly close agreement with theoretical conclusions.
Optimization of corona-discharge photoionization sources for CO2 lasers
Authors: Marchetti R. , Penco E. , Armandillo E. , Salvetti G.
Published: February 2003

The results of an experimental study of ultraviolet photoionization produced by a corona discharge in CO2 laser gases are reported. The influence of corona discharge physical and electrical parameters on the produced photoelectron density is investigated so that an optimized design of these types of photoionization sources can be achieved.
Longitudinal acoustic mode in polymers: Influence of defects
Authors: Chang Chih , Krimm S.
Published: February 2003

Normal mode calculations have been done on planar zigzag chains Cn (n=22 to 82), terminated or connected by various fold structures and subjected to force and mass perturbations, to determine how the longitudinal acoustic mode (LAM) is influenced by such defects. We find that in general LAM-like displacements are distributed over a frequency range (depending on the stem length), with a total intensity smaller than that for the unperturbed case. Only when the fold comprises ∼3% or less of the mass of the stem does it behave like a point mass perturbation. These results show that the perturbed elastic rod model has limited validity and that caution is necessary in attributing the shape of a LAM band entirely to a distribution of stem lengths.
Effect of damage dissemination on crack propagation in polypropylene
Authors: Chudnovsky A. , Moet A. , Bankert R. J. , Takemori M. T.
Published: February 2003

Kinematic measurements of Fatigue Crack Propagation (FCP) in thick compact tension polypropylene specimens shows that the rate of FCP does not increase monotonically as predicted by conventional laws of fracture mechanics. Specifically, crack deceleration occurs with increasing crack length. Microscopic examination indicates that crazes (damage) disseminate around and ahead of the main crack, thus controlling its rate of propagation. Accounting for damage dissemination, in terms of the crack layer theory, shows that the rate of FCP is controlled by the shape of the active zone and by its size, in addition to the crack length. Abrupt changes in the first two parameters are directly related to the observed crack deceleration.
A Raman study of Si-implanted silicon on sapphire
Authors: Ohmura Y. , Inoue T. , Yoshii T.
Published: February 2003

It has been demonstrated by Raman scattering spectroscopy that an Si implantation technique to improve the crystalline quality of silicon on sapphire (SOS) also changes the strain state of SOS. Optical phonon (OP) frequencies from the surface crystalline region in as-implanted SOS shift larger than those for heavily implanted bulk silicon, which may be due to a superposition of implantation-induced compressive stress and thermal expansion coefficient difference-induced compressive strain. These highly shifted OP frequencies (∼10 cm−1 from the bulk) decrease relatively abruptly as the recrystallization proceeds, and the surface implantation-induced damage is reduced. After the recrystallization is completed, the OP frequencies are close to those which are determined by the expansion coefficient difference-induced strain between annealing and room temperatures, as though the silicon film were grown at the annealing temperature. The newly formed low strain at 600 °C, however, again becomes high by subsequent annealing above 1000 °C, which implies that the new bond of silicon to sapphire is not strong enough to stand the 400 °C difference of thermal expansion.
Photoluminescence from CdTe/sapphire films prepared by molecular beam epitaxy
Authors: Edwards S. T. , Schreiner A. F. , Myers T. M. , Schetzina J. F.
Published: February 2003

Photoluminescence studies at 77 K are reported for CdTe/sapphire films prepared by molecular beam epitaxy. The CdTe/sapphire epilayers exhibited very bright photoluminescence spectra that were dominated by the near-edge emission band at 1.58 eV. The best CdTe/sapphire film proved to be the brightest source of luminescence of any CdTe specimen studied in our laboratories, including homoepitaxial films and bulk hydroplane polished samples. The CdTe/sapphire films also exhibited the best lateral uniformity as manifested by a nearly constant luminescence intensity over their surfaces. These results provide new evidence that high quality CdTe epitaxy on sapphire has been achieved.
Photoenhanced oxidation of gallium arsenide
Authors: Bermudez Victor M.
Published: February 2003

Auger electron spectroscopy has been used to observe the influence of low-intensity visible/near-ultraviolet radiation on the oxidation of n- and p-type GaAs (110). Irradiation increases the rate of formation of the first monolayer by factors of 5–10 for p-type and 10–20 for n-type material. Kelvin-probe measurements of the change in work function with O2 exposure have also been carried out. The results suggest a model in which defects present on the clean surface pin the Fermi level at midgap, bending the bands sufficiently to allow stabilization of photogenerated broken Ga–As bonds. Similar experiments for physisorbed CO and H2O gave no photoeffect. This indicates that chemisorption (as in the case of O2) is necessary to weaken (or break) the intramolecular bond. Subsequent oxidation of GaAs is then accelerated by photoenhanced breaking of Ga–As bonds. Experiments with NO indicate a smaller sticking coefficient and a much smaller photoeffect than for O2.
Oxidation induced stresses and some effects on the behavior of oxide films
Authors: Hsueh C. H. , Evans A. G.
Published: February 2003

The elastic and viscoelastic stresses created during the oxidation of curved surfaces are calculated. The stress state and amplitude are shown to depend sensitively upon the oxidation site (interface or surface) and the oxidation strain (uniaxial or dilational). The viscoelastic stresses depend, in addition, on the rate of oxidation, vis-a-vis the viscosity of the oxide. In most cases, the stresses increase rapidly as the radius of curvature of the surface decreases. The influence of the stresses on several important oxidation phenomena are discussed. Specifically, corner effects on the oxidation rate, cracking and spalling of the oxide, and plastic deformation of the substrates are briefly addressed.
Calculations on the role of carbon monoxide in tungsten–halogen bulbs containing dibromomethane
Authors: Sell J. A.
Published: February 2003

Previously, Maier at Osram made tungsten–halogen bulbs with a fill gas mixture of dibromomethane in argon and various levels of carbon monoxide. He found that after the bulbs were burned the walls blackened in the bulbs with less than 267 ppm of carbon monoxide, but stayed clear at higher carbon monoxide levels. This report describes a chemical equilibrium calculation which explains these results, and identifies WO2Br2 as the compound that forms near the bulb walls and keeps them clear.
The reaction probability of XeF2 with silicon
Authors: Vasile M. J.
Published: February 2003

The plasma etching of silicon has been simulated with experiments using atomic fluorine sources or with the dissociative adsorption of XeF2. Atomic fluorine is known to be the species responsible for etching silicon in a plasma, and it is reasonable to question whether XeF2 and atomic fluorine are equivalent reactants with silicon. One means to compare these two reactants is through their reaction probabilities to form SiF4 from a silicon surface. The reaction probability of XeF2 with silicon was measured in the same molecular beam apparatus used to measure the reaction probability of atomic fluorine with silicon. The value for XeF2 is between 1 and 3×10−3 under the conditions employed, and it is a factor of 10 lower than the value obtained for atomic fluorine. Examination of the products obtained from the reaction of XeF2 with silicon shows that there is a range in experimental conditions where the reaction probability is not a unique parameter. The values measured in this experiment represent a lower limit for the reaction probability of XeF2 with silicon. Reactions of XeF2 with silicon are effectively inhibited by a thin surface oxide which must be removed by ion bombardment. No significant differences in reactivity of XeF2 with either single crystal silicon or electron beam evaporated silicon were found.
Degradation of a CuxS/CdS solar cell in hot, moist air and recovery in hydrogen and air
Authors: Partain L. D. , McLeod P. S. , Duisman J. A. , Peterson T. M. , Sawyer D. E. , Dean C. S.
Published: February 2003

A polycrystalline, thin-film CuxS/CdS solar cell was exposed to air saturated with water vapor at temperatures between 27 and 67 °C for up to 6 1/2 h. The short-circuit current decreased progressively from 11.7 to 1.02 mA/cm2. Subsequent heating in hydrogen at 150 °C for 680 h and in 170 °C air for 5 h restored the short-circuit current to 14.4 mA/cm2. Modeling of the measured quantum yield indicates that the degradation could be quantitatively explained by two effects: (1) the CuxS minority carrier electron diffusion length decreasing from 0.23 to 0.02 μm (±20%) and (2) the CuxS optical band gap increasing from 1.16 to 1.46 eV (±3%). The recovery was quantitatively modeled by the CuxS diffusion length increasing back to 0.24 μm and the CuxS band gap returning to 1.16 eV. A Burstein–Moss analysis shows the band-gap shift is due to the Fermi level penetration of the valence band as the measured hole concentration increased from 1.03(1020) cm−3 to 4.62(1021) cm−3 during degradation. A new band structure is proposed with six equivalent, indirect, valence band maxima located at 1.16 eV (±3%) below the conduction band edge followed by two direct maxima located at 1.28 and 1.8 eV (±3%) below the conduction band edge. A density-of-states effective mass ratio for holes of 2.0 (±30%) is found. The sharp decrease and recovery in diffusion length is explained by a transition between phonon-assisted and direct minority carrier recombination with changes in CuxS hole concentration.
Limiting efficiencies for multiple energy-gap quantum devices
Authors: Wu Cheng-Hsiao , Williams Richard
Published: February 2003

We have used a thermodynamic model to calculate theoretical limiting efficiencies for simple and multiple gap solar cells. The limiting efficiency is 26% for a simple solar cell of hydrogenated amorphous silicon, operating at one Sun sensitivity. For a multiple gap cell made from hydrogenated amorphous silicon, together with a second cell, made from a material with lower band gap, it is 38%. The optimum band gap for the second material is 1.0 eV.
Equivalence of different solutions of the vector potential for a thick solenoid
Authors: Caldwell J. , Zisserman A.
Published: February 2003

It is shown that the integral representation of the vector potential A for a thick solenoid may be evaluated, in certain situations, to give results identical to those obtained from a differential formulation and a Legendre polynomial expansion.
Temporal and spatial growth of ionization currents in nitrogen below Paschen’s minimum
Authors: Govinda Raju G. R.
Published: February 2003

On the basis of the temporal and spatial growth of ionization currents formative time lags are calculated in nitrogen at Nd values below Paschen’s minimum and compared with the measured values. The secondary ionization coefficient is observed to be entirely due to positive ions and an over voltage of more than 100% is required to obtain 5% contribution from the photoelectric action to the total secondary ionization coefficient.
Dependence on hydrostatic pressure of the crystal structure of ruby
Authors: Kottke T. , Williams F.
Published: February 2003

We show from application of elasticity theory that the rhombohedral angle of ruby changes with hydrostatic pressure. The predicted change is found on reanalysis of published x-ray diffraction data on ruby. The importance of these structural changes with pressure to the application and evaluation of the theories of the effects of pressure on optical properties is emphasized.