bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensing characteristics of SnO2 thin film gas sensor
Authors: Oyabu Takashi
Published: February 2003

The Pd-doped SnO2 thin film detector for gaseous components has been developed, whose detection is based on the fact that the adsorption and desorption of gases cause the remarkable change in electrical resistivity of the semiconductor. This property of SnO2 film is applicable to the preferential detector for gaseous components, especially ethanol gas. SnO2 thin film was prepared on the polished ferrite substrate which SiO was precoated. Both the preparation and the precoating were done by vacuum deposition. Subsequently the oxidation for SnO2 film in air was done at 500–550 °C for 30–60 min. The rise rate and fall rate of temperature were 2.5 and 1.7 °C/min, respectively. The thickness of SnO2 film was about 0.3–0.35 μm.
Infrared absorption and defects in Al-doped ZnSe
Authors: Ko J. S. , Spitzer W. G.
Published: February 2003

It is suggested that the infrared absorption spectrum of the localized vibrational modes of Al-doped ZnSe can be explained by two Al defects: AlZn and an Al dimer, possibly 2AlAn-VZn , where the 2AlZn and the VZn are all second-nearest neighbors.
Interaction between n-type amorphous hydrogenated silicon films and metal electrodes
Authors: Ishihara S. , Hirao T. , Mori K. , Kitagawa M. , Ohno M. , Kohiki S.
Published: February 2003

The interactions of Al and NiCr electrodes with hydrogenated n-type amorphous silicon films have been investigated in a temperature range of 100–350 °C. It was found that pits were produced in the a-Si films at temperatures above 170 °C in the case of Al electrodes, while they were not observed in the case of NiCr electrodes even if heat-treated at a temperature of 350 °C. From the Auger electron spectroscopy measurements, it was shown that a marked interdiffusion of Al and Si occurs. The sheet resistance of the a-Si films began to increase at temperatures above 170 °C. The contact resistivity between the a-Si films and Al electrodes could not be determined in the case of a-Si films with usual low conductivity. For the specimens with high conductivity [σ∼1(Ω cm)−1], the value of about 1×10−3Ω cm2 was obtained.
An effect of back-surface boron implantation on silicon solar cells
Authors: Spitzer Mark B. , Solomon Stanley J. , Younger Peter R.
Published: February 2003

An experiment was carried out to isolate the effect responsible for Voc enhancement in back-surface ion-implanted Si solar cells. It is shown that open circuit voltage enhancement from back-surface boron implantation is due to the formation of an effective back surface field rather than to lifetime enhancement that results from damage-induced gettering. Comparison of boron-implanted cells is made to cells that had no boron implants and to cells with the boron implant removed by etching.
Optical constants for silicon at 300 and 10 K determined from 1.64 to 4.73 eV by ellipsometry
Authors: Jellison G. E. , Modine F. A.
Published: February 2003

Polarization modulation ellipsometry has been used to determine the optical constants of Si for photon energies from 1.64 to 4.73 eV (755 to 262 nm) at 300 as well as 10 K. The results were interpreted using a 2-boundary, 3-layer model (air-SiO2-Si); the inclusion of an interface layer between the SiO2 and Si did not greatly affect the derived optical constants below ∼3.5 eV. The accuracy of the results has been carefully evaluated, the error in the index of refraction (n) being < 1%, while the error in the extinction coefficient (k) or the absorption coefficient (α) being dependent upon the magnitude, ∼15% at α = 104 cm−1, ∼6% at α = 105 cm−1, and ∼1.5% at α = 106 cm−1. The room temperature absorption coefficient results represent the best spectroscopically available values from ∼2.5 to ∼3.5 eV (∼350 to 500 nm), while results at 10 K represent the best values available over the entire wavelength region measured. A comparison with previously published data is presented.
Photothermal ionization spectroscopy of acceptors in high purity germanium
Authors: Darken L. S.
Published: February 2003

The results obtained by photothermal ionization spectroscopy on acceptors in high-purity germanium are presented. The distribution of the residual acceptor impurities, boron and aluminum, in high-purity germanium crystals are studied by lightly doping the crystals with gallium, and using semiconductor statistics to determine the relative concentrations of the shallow acceptors from their relative peak heights in the spectra. Under the conditions of growth (SiO2 crucible, H2(g) ambient) the distributions of aluminum and boron do not follow the equation for normal segregation The distribution profiles of aluminum indicate that it is being removed from the melt during growth while the distribution profiles of boron are usually consistent with boron being added to the melt during growth. Data were taken with a high resolution (0.10 cm−1) Fourier transform spectrometer. Transition energies are tabulated for the acceptors observed. Three new shallow acceptors are reported. Two have D transitions at 60.20 and 64.69 cm−1, respectively. The other acceptor has a split ground state with D transitions at 69.12 and 73.77 cm−1. The deepest acceptor observed was neutral copper with a binding energy measured to be 348.9 cm−1 (43.27 meV).
Comparison of excitation spectra of 1.2- and 2.0-eV photoluminescence bands in Cd1−xMnx Te for 0.4<x≲0.7
Authors: Tao R. Y. , Moriwaki M. M. , Becker W. M. , Galazka R. R.
Published: February 2003

The excitation spectra of the 1.2- and 2.0-eV emissions in Cd1−xMnx Te were measured using a dye laser, and various lines from an Argon ion laser. Both emissions have their excitation thresholds near the Mn2+ 6A1(6S)→4T1(4G) absorption edge. For x∼0.7, the excitation spectra at higher energies are similar for both emissions and are related to the Mn2+ 6A1(6S)→4T2(4G) transition. For all x in this range, there is a drop of intensity above the Mn2+ absorption edge, ascribed here to competitive intrinsic absorption, which does not lead to Mn2+ emission. Details of these behaviors are reproduced by a model which assumes separate Urbach tails for the Mn2+ and intrinsic absorptions.
Laser writing on metal-silicon bilayers for optical storage. I. Optical properties
Authors: Ahn K. Y. , Di Stefano T. H. , Mazzeo N. J. , Herd S. R. , Tu K. N.
Published: February 2003

Various bilayer structures consisting of metal and silicon were investigated as possible candidates for the optical recording medium. The silicon-on-metal bilayers offer tunability with a reasonable thickness of Si in the visible spectrum with a typical reflectivity less than 5%. Of the two possible writing processes, the low-power process of silicide formation has a threshold power of 30 mW for a Rh-Si bilayer which provides a reflectivity change in excess of 40%. The absence of raised rims around the written spots offers a smooth morphology that is compatible with encapsulation.
Probing aerosols by photoelectric charging
Authors: Burtscher H. , Scherrer L. , Siegmann H. C. , Schmidt-Ott A. , Federer B.
Published: February 2003

Particles suspended in a gas may emit photoelectrons upon irradiation with ultraviolet light. It is shown that photoemission from small particles involves material and surface dependent physical processes that yield new information, especially on ultrafine particles not accessible to the well-known diffusion charging. An apparatus is presented for the measurement of the electric mobility and the charge generated on particles in the atmosphere using a monochromatic low-pressure Hg arc. Particles generated by combustion of organic material, e.g., auto exhaust, are charged with high efficiency. This offers a new way to detect and/or remove such particles from the air. In outside air the concentration of photoelectrically active particles has a diurnal cycle which also depends on the meteorological conditions. Surprisingly, highly mobile particles are detectable even during rainfall.
Reaction of atomic fluorine with silicon: The gas phase products
Authors: Vasile M. J. , Stevie F. A.
Published: February 2003

SiF2 and SiF4 have been identified as gas phase products of the reaction between atomic fluorine and silicon. Atomic fluorine is supplied by a low density molecular beam hitting a silicon target in a high vacuum. Reaction products were detected by mass spectrometric measurements. Activation energies for the production of SiF2 and SiF4 were found to be 0.09±0.02 and 0.15±0.02 eV/°K, respectively, in good agreement with the values measured by flowing afterglow techniques. The reaction probability for the reaction 4F+Si→SiF4 was found to be 0.016 at 100 °C.
Properties of metal-oxide-semiconductor structures with buried layers as deduced from nonequilibrium C(V) measurements
Authors: Bach H. G. , Fahrner W. R.
Published: February 2003

An n-type buried channel in a p-type metal-oxide-semiconductor ( p-MOS) structure is created by phosphorus implantation. The 1-MHz capacitance is measured at fast bias sweep rates so that nonequilibrium punchthrough occurs. The various portions of this curve are discussed. The depth of the p-n space-charge layer is increased with an external layer voltage, and so is the punchthrough depth. The variation of the punchthrough depth underneath the gate with the gate voltage is exploited for substrate doping profiling, so that a complete doping profile of the layer and the substrate up to a depth of ⩾3 μm is now available. The average generation rate in the depleted silicon is determined as a function of temperature and the activation energy of generation is determined to be 0.45 eV.
Transient response of n-channel metal-oxide-semiconductor field-effect transistors during turnon at 10–25 °K
Authors: Tewksbury S. K.
Published: February 2003

The transient, excess source-drain current which occurs under freeze-out conditions when a metal-oxide-semiconductor field-effect transistor (MOSFET) is switched into a conducting state is described. The major features of the observed transient response for n-channel MOSFET’s in the temperature range 10–25 °K are explained in terms of a simple one-dimensional model. The transient response is largely independent of both temperature (in this range) and the static current level, except for the variation of relaxation rate with temperature. The transient response waveform and the temperature dependence of the relaxation rate for n-channel MOSFET’s differ greatly from previously reported results on p-channel MOSFET’s.
Defect trapping of ion-implanted deuterium in nickel
Authors: Besenbacher F. , Bo/ttiger J. , Myers S. M.
Published: February 2003

Trapping of ion-implanted deuterium by lattice defects in nickel has been studied by ion-beam-analysis techniques in the temperature range between 30 and 380 K. The deuterium-depth profiles were determined by measuring either the α particles or the protons from the 3He-excited nuclear reaction D(3He,α)p, and the deuterium lattice location was obtained by means of ion channeling. Linear-ramp annealing (1 K/min) following a 10-keV D+ implantation in nickel produced two annealing stages at 275 and 320 K, respectively. The release-vs-temperature data were analyzed by solving the diffusion equation with appropriate trapping terms, yielding 0.24 and 0.43 eV for the trap-binding enthalpies associated with the two stages, referred to as an untrapped solution site. The 0.24-eV trap corresponds to deuterium close to the octahedral interstitial site where it is believed to be trapped at a vacancy, whereas it is suggested that the defect correlated with the 0.43-eV trap is a multiple-vacancy defect. The previously air-exposed and electropolished nickel surface was essentially permeable; the surface-recombination coefficient was determined to be K≳10−19 cm4/s at 350 K.
Determination of the primary elastic constants from thin foils having a strong texture
Authors: Baral D. , Hilliard J. E. , Ketterson J. B. , Miyano K.
Published: February 2003

A new method is described for determining the primary elastic constants (stiffnesses cij’s and compliances sij’s) with respect to the crystallographic axes. Although we will consider only cubic materials the method can be applied to materials of lower symmetry. The method utilizes the symmetry present in a textured (preferred growth) foil and can be used for cases when bulk single crystals are difficult to prepare for ultrasonic experiments. The method involves the use of expressions, that have not been previously derived, relating the biaxial, flexural, Young’s and shear modulus to the primary elastic constants for textured foils. The agreement of the experimentally observed moduli with ones calculated from the expressions to be presented demonstrates that the accuracy is comparable with existing methods.
Critical stress in silicon brittle fracture, and effect of ion implantation and other surface treatments
Authors: Hu S. M.
Published: February 2003

We introduce a method, which is free of specimen edge effect, for the determination of critical stress in material brittle fracture. Using this method, we have investigated the critical stress in silicon brittle fracture. Silicon wafers polished with silica gel showed an average fracture stress of 2.8 GPa, with a standard deviation of 1.2 GPa and a maximum observed value of 6.9 GPa. We have also investigated effects of various surface treatments on the critical stress. Mechanically lapped surfaces, with damage penetrating deeper than ∼3 μm, reduced the fracture strength to 0.3–0.4 GPa (damage surface placed in tension). Both polysilicon and quartz overlays reduced the silicon fracture strength only very slightly, while argon implantation (at 150 keV, with a dose of 1×1016 cm−2) did not show a detectable effect. However, anneal of the argon implanted samples at 900 °C in nitrogen for one hour significantly increased the silicon fracture strength, conceivably as a consequence of the removal of existing surface flaws by an epitaxial regrowth of the implantation-amorphized surface layer. The last finding is both of basic interest and of practical significance. Silicon wafers of (100) orientation showed a ∼50% higher fracture strength than wafers of (111) orientation.
Dislocations in shocked and recovered LiF
Authors: Vorthman John E. , Duvall George E.
Published: February 2003

Magnesium doped single-crystal LiF was shocked above the critical shear stress necessary for rapid precursor decay. Post-shock analysis of the samples indicate that the dislocation density in the shock front is not significantly greater than the preshot value.
Photoelectric memory effect in GaAs
Authors: Vincent G. , Bois D. , Chantre A.
Published: February 2003

Experimental data are reported for the persistent photocapacitance quenching observed at 77 K in GaAs. This effect, which arises on the so-called oxygen (or EL2) center in gallium arsenide, is explained by the existence of two states of this center. The physical parameters of these stable and metastable states are given: optical cross section, annealing, and electrical deexcitation. Assuming a large lattice relaxation for the metastable one, a physical model is given with a possible microscopic origin. Other striking memory effects, and especially photoconductivity, are shown to be simply explained by our model.
Electrical properties of Si heavily implanted with boron molecular ions
Authors: Fuse G. , Hirao T. , Inoue K. , Takayanagi S. , Yaegashi Y.
Published: February 2003

High dose implantations of boron molecular ions such as BF+2 and BCl+2 ions in Si have been investigated in an attempt to form shallow P+ layers in the dose range 1×1015–1×1016 ions/cm2, in comparison with those of boron. For BF+2 implants it was found that both the effective surface carrier density Ns and junction depth Xj in Si after 1000°C anneal tend to completely saturate at doses above 5×1015 ions/cm2, while they tend to increase for B+ implants. From profile measurements of total and electrically active boron it was clarified that the additional implantation of BF+2 ions in excess of 5×1015 ions/cm2 results in the accumulation of inactive boron atoms particularly around the surface region. Junction depths in Si resulting from BF+2 implants are generally shallower than those resulting from B+ implants. For BCl+2 implants the values of Ns are generally much lower than those for BF+2 and B+ implants.
Hydrogen donors in α-Al2O3
Authors: El-Aiat M. M. , Kröger F. A.
Published: February 2003

Annealing of acceptor dominated α-Al2O3 at Tsat = 1100–1500 °C in atmospheres containing hydrogen leads to dissolution of hydrogen, changing the material from p- to n-type when the concentration of hydrogen donors is larger than that of the acceptor impurities present. If oxygen equilibrium is maintained, the concentration of ionized donors depends on pH2 as well as pO2 (or pH2O). In measurements of dc conductivity in atmospheres not containing hydrogen, a contribution to the conductivity by mobile protons rapidly disappears as a result of polarization. Analysis of the rate of polarization leads to values for the concentration and mobility of mobile protons. In measurements in atmospheres with well-defined hydrogen and oxygen fugacities, protons, native ions, and electrons and holes contribute continuously to the conductivity. Transference numbers of the various species and the corresponding partial conductivities were determined by emf measurements. The amount of dissolved hydrogen increases with decreasing temperature of saturation, increasing hydrogen pressure, and increasing oxygen pressure. Attempts to find detailed defect models explaining the results were only partially successful.
Photocurrent in thermal SiO2 under x-ray irradiation: Significance of contact injection
Authors: Chin M. R. , Ma T. P.
Published: February 2003

The x-ray induced photocurrent in the thermal SiO2 layer of a Metal-SiO2-Si (MOS) structure consists of two components: (1) contact photoinjection and (2) bulk generation. It has been found, both theoretically and experimentally, that the relative importance of the contact photoinjection component increases with decreasing oxide thickness. For a 500-Å SiO2, the contact photoinjection is approximately equal to the bulk generation over a wide range of oxide fields (105–2×106 V/cm) and starts to dominate for oxides thinner than 300 Å. The earlier internal photoemission theory developed for UV photon energies below the SiO2 band gap can be used to describe the observed voltage dependence of the contact photoinjection current under x-ray irradiation, and good agreement between the theory and the experiment has been established. Onsager’s theory of geminate recombination is shown to satisfactorily explain the field dependent generation rate in SiO2 over the field range 105–2×106 V/cm. These findings are important to the understanding of the ionizing radiation effects in MOS structures where carrier injection and generation play an essential role.
Characteristics and analysis of channeled substrate narrow stripe GaAs/GaAlAs lasers
Authors: Curtis J. P. , Plumb R. G. , Goodwin A. R. , Kirkby P. A.
Published: February 2003

An optimization of channeled substrate narrow stripe GaAs/GaAlAs lasers for operation in the zero-order transverse mode to output powers of 10 mW is described. A correlation between zero-order mode power and substrate-induced optical loss is demonstrated. The devices fabricated have threshold currents around 30 mA, highly linear transfer characteristics, and exhibit quasisingle longitudinal mode behavior. Transient response measurements show device suitability for G bit/s optical communication systems. Preliminary lifetest results indicate a median life of over 10 000 h at 70 °C and 2-mW output. A computer model of liquid phase epitaxial growth over channels and a theoretical analysis of the waveguide structure grown show good agreement with experiment.
A strongly nonlinear analytic model for microwave electron devices
Authors: Thomas Gary E.
Published: February 2003

In this paper, a description of a new method for obtaining a strongly nonlinear analytic model for nonlinear electron devices is given. Specific examples include crossed-field amplifiers and gyro-travelling wave tubes. This method is an extension of previous work where a nonlinear partial differential equation is derived and reduced by a multiple time scales perturbation technique to a nonlinear Schrodinger equation. The extension of the above approach to a strongly nonlinear regime is accomplished by including ErfxB0 (rf electric and dc magnetic field) effects in the linear dispersion relation in an approximate manner. The inclusion of these ErfxB0 terms results in nonlinear coefficients (i.e., dependence upon Erf ) of the nonlinear Schrodinger equation. The importance of these rf related terms is discussed for the crossed-field amplifier and the gyro-travelling wave tube.
Spatial structure and coherence properties of Brillouin scatter from CO2 laser-target interaction
Authors: Mitchel G. R. , Grek B. , Johnston T. W. , Pépin H. , Church P. , Martin F.
Published: February 2003

The spatial structure and coherence properties of 10.6-μm light scattered from CO2 laser-target interactions in oblique incidence show many unexpected features. It is found that the Brillouin backscatter is neither a phase conjugate nor a ray retrace of the incident beam. Rather, it shows a preference for scattering directions other than those exactly antiparallel to the incident beam, apparently related to the angular distribution of the scattering source and also of the plasma corona that serves as the Brillouin amplifying medium. As well, the backscatter phasefront is strongly perturbed with respect to the incident phasefront. This is an indication of turbulence in the corona and/or memory of the structure in the source that is then amplified. Small-scale structures seen in the reimaged backscatter are due to phase perturbation and cannot be simply interpreted as geometric images of a (filamented) source. The phasefront of light that is scattered obliquely from the plasma is much more coherent.
Structural changes in Se-Te bilayers by laser writing
Authors: Herd S. R. , Ahn K. Y. , von Gutfeld R. J. , Vigliotti D. R.
Published: February 2003

Transmission electron microscopy is used to characterize the hole-formation process due to laser writing in evaporated and sputtered Te thin films and in a Se-Te bilayer. Bilayers, with Se as the top layer, combine the effect of an antireflective coating with protection against oxidation and provide the advantage of alloy formation during spot writing. Solidification of the melt in the Se-Te spot takes place as an amorphous alloy resulting in smooth-rimmed, clean holes. In contrast, Te crystallizes from the melt, giving rise to uneven rims and debris inside the spot.
Deformation of amorphous Fe40Ni40P14B6 under compression to 250 kbar
Authors: Kimura H. , Ast D. G. , Bassett W. A.
Published: February 2003

Amorphous Fe40Ni40P12B6 was compressed in the diamond anvil cell up to a 250 kbar pressure, and the pressure was measured as a function of position with the ruby fluorescence method. Analysis of the spatial distribution of the pressure indicates that the flow stress σy of the material varies as σy = 17 exp(0.004 P), with σy and P expressed in units of kbar. The increase in the flow stress with pressure corresponds to an activation volume of 0.16 Å.3 The pre-exponential factor represents the flow stress of the material at zero pressure. Because the material in a diamond cell is subjected to a very extensive plastic flow before the pressure distribution is established, this value is not necessarily identical to the flow stress measured with more conventional methods, involving no or very little prior plastic deformation. The latter methods tend to measure higher values for σy, indicating that metallic glasses undergo work softening when deformed extensively.
Hydrogen passivation of a bulk donor defect (E
c −0.36 eV) in GaAs
Authors: Pearton S. J.
Published: February 2003

The passivation of a bulk donor defect (Ec –0.36 eV) in polycrystalline GaAs by reaction with atomic hydrogen has been observed using deep level transient spectroscopy. The concentration profile of the defect is presented as a function of the duration and temperature of the exposure to atomic hydrogen—when exposed for 3 h at 250 °C, 3×1015 donor defects cm−3 were passivated to a depth of ∼1.1 μm.
Shock temperatures in fused silica measured by optical technique
Authors: Sugiura H. , Kondo K. , Sawaoka A.
Published: February 2003

Shock temperatures of fused silica were determined using radiance intensity measurements at two color bands of 620 and 810 nm. The shock temperature increased from 2.0×103 to 3.3×103 K in the pressure range between 31.8 and 40.5 GPa, and up to 4.2×103 K in the range up to 65.1 GPa. The rate of increase of temperature with pressure decreased at ∼40 GPa. The low gradient above 40 GPa suggests that a shock-induced phase transformation of fused silica begins at ∼40 GPa.
Filamentation of helicon waves in semiconductors
Authors: Salimullah Md. , Alam M. N.
Published: February 2003

This paper presents a theoretical investigation of the filamentation instability of high power helicon waves in magnetoactive semiconductors. Fluid equations have been used to find the nonlinear response of the low-frequency electrostatic space-charge density perturbation in a semiconductor. The low-frequency nonlinearity arises through the ponderomotive force on electrons, whereas the high-frequency nonlinearity arises through the equation of continuity. For typical parameters in n-InSb: εL = 16 at 77 °K, n00 ?2×1014/cm3, Bs ?0.8 kG, ν0 = 5×1010 rad/sec, ω0 = 1010 rad/sec, and for the power density of the incident helicon beam ?30.27 KW/cm2, the growth rate of the instability turns out to be ∼1.71×106 rad/sec.
Dielectric behavior of MgO:Li+ crystals
Authors: Puma M. , Lorincz A. , Andrews J. F. , Crawford J. H.
Published: February 2003

Measurements of the dielectric constant in crystals of MgO doped with Li+ ions have been carried out after quenching from anneals at 1300 °C in static air. Prior to heat treatment, the crystals showed no discernible dielectric loss, but afterwards, the loss tangent exceeded 0.4. For 10-min anneals, the dielectric relaxation is very close to a Debye process, and the temperature dependence of the maximum of the loss peak corresponds to an activation energy of 0.724 eV. When plotted in the form of a Cole-Cole arc, the data indicate that deviation from a Debye relaxation amounts to a distribution of relaxation time no greater than that which can be accounted for with a distribution of activation energies of only 0.007 eV. For longer heating times, overlapping relaxation processes appear. The lack of broadening of the loss peak, and the magnitude of the relaxation time, yield clues as to possible loss mechanisms.
Chemiluminescent reaction of SiF2 with fluorine and the etching of silicon by atomic and molecular fluorine
Authors: Mucha John A. , Flamm Daniel L. , Donnelly Vincent M.
Published: February 2003

The homogeneous reaction between F or F2 and SiF2, the latter formed by the high-temperature reaction of solid silicon with SiF4, is accompanied by an intense chemiluminescent ’’flame’’ with the spectrum previously observed during silicon etching by F and F2. This experiment provides direct confirmatory evidence that chemiluminescence from both reactions arises from the homogeneous reaction between SiF2 and fluorine atoms or molecules.
A numerical model for Barkhausen coercivity
Authors: Della Torre E. , Torfeh-Isfahani M.
Published: February 2003

The well-known Barkhausen effect occurs when a domain wall moving through a crystal gets pinned at imperfections. A numerical model is described here that gives a possible mechanism for this effect. It is assumed that the imperfection is a spherical nonmagnetic ’’hole’’ in an otherwise perfect ferromagnetic material which generally repels the approaching wall. The equilibrium wall shapes, as the applied field is slowly increased, are successively computed. When either the wall ’’touches’’ the hole, causing a reduction in the induced pole strength, or the wall closes about the hole, a sudden irreversible change is triggered. The field strength at which this takes place is the coercive force.
Temperature distributions produced in a two-layer structure by a scanning cw laser or electron beam
Authors: Burgener M. L. , Reedy R. E.
Published: February 2003

We derive the Green’s function solution to the heat equation for a two-layer structure and describe how to extend the technique to derive the Green’s function for N-layer structures. The Green’s function is applied to the interaction of a two-layer structure with scanning circular energy beams. The mathematics necessary to reduce the resultant solutions from a quintuple integral to a double integral are presented. Numerical integration of the remaining integrals leads to temperature profiles generated during laser irradiation of two-layer structures. These profiles are shown to reduce, in the appropriate limits, to previously reported profiles for the single-material case. Normalized linear temperature profiles as well as actual temperature profiles for silicon on sapphire are presented and discussed.
Silicon doping and impurity profiles in Ga0.47In0.53As and Al0.48In0.52As grown by molecular beam epitaxy
Authors: Cheng K. Y. , Cho A. Y.
Published: February 2003

Silicon-doped n-type Ga0.47In0.53As and Al0.48In0.52As epitaxial layers lattice matched to InP substrates have been grown by molecular beam epitaxy. Doping levels up to 7×1018 cm−3 vary proportionally with the arrival rate of Si. For the same Si arrival rate, the carrier concentrations in both ternary epitaxial layers are identical. Mobility studies showed that the variations of electron mobility as a function of carrier concentration in Si-doped Ga0.47In0.53As are in good agreement with the theoretically calculated results involving the alloy scattering mechanism at both 77 and 300 K. This alloy scattering mechanism is attributed to the defects induced at lower growth temperature. Doping profile measurements by the differential capacitance technique show that very abrupt changes in carrier concentration can be realized in Si-doped Ga0.47In0.53As and Al0.48In0.52As and Sn-doped Al0.48In0.52As. In the case of Sn-doped Ga0.47In0.53As, the sharpness of the doping profile is limited by the surface segregation of Sn. Schottky barrier height on Ga0.47In0.53As was enhanced with the aid of a thin n-type Al0.48In0.52As surface layer.
Electrochemichromism of rf reactively sputtered tungsten-oxide films
Authors: Kaneko H. , Miyake K. , Teramoto Y.
Published: February 2003

Electrochemichromic proerties of tungsten-oxide films prepared by rf reactive sputtering from a metallic tungsten target have been investigated. The films, approximately 5200-6800-Å thick, were deposited on the substrate at 200 °C under a constant total operating pressure of 5×10−3 or 4×10−2 Torr using a mixture of Ar and 4-50% O2. Electrochromic properties of the reactively sputtered tungsten-oxide films depend considerably on the total operating pressure and oxygen concentration of the sputtering atmosphere. The transparent tungsten-oxide films, with a resistivity of approximately 106−1010 Ω cm and prepared under a total operating pressure of 4×10−2 Torr in an atmosphere containing more than 5% O2, have good electrochromic properties similar to those of the vacuum evaporated films form WO3 powder. But, the transparent oxide films, formed under a total operating pressure of 5×10−3 Torr in an atmosphere containing more than 16% O2, show a poor electrochromic property, although these films have a resistivity of approximately 107−1011 Ω cm. Upon electrochromic coloration, the optical spectra of tungsten-oxide films with a good electrochromic property show increased absorption in the visible and near infrared region, with the absorption band centered at ∼0.95 μm.
On the mechanism of degradation in Si/SiOx/Ag metal oxide semiconductor solar cells
Authors: Kar S. , Varghese R.
Published: February 2003

The mechanism of degradation in metal oxide semiconductor solar cells with Ag as the barrier metal has been investigated. Si/SiOx /Ag cells were fabricated with different oxide thicknesses but with no protective or antireflection coating. These cells were aged in the atmosphere and their current-voltage and capacitance-voltage characteristics were monitored. These electrical measurements and transmission electron micrographs of the ultrathin Ag films indicate the following mechanisms to be responsible for degradation. The ultrathin Ag films are discontinuous and consist of interconnected islands. Lateral migration of Ag takes place as the cells age, leading to disruption of interconnections between the islands. Consequently, the active area of the cell decreases and the series resistance increases resulting in poorer fill factor and a decrease in the short-circuit current. Ag may also be diffusing to the interface, creating interface states, which may be contributing to the reduction in open-circuit voltage. Oxygen/water vapor also diffuses to the interface, as the cells age, leading to a growth of the interfacial oxide layer. If the initial oxide is thinner than the optimal, the open-circuit voltage will increase; however, when the oxide becomes thicker, drastic photocurrent suppression will occur with a simultaneous decrease in fill factor and open-circuit voltage.
Hall measurement studies and an electrical conduction model of tin oxide ultrafine particle films
Authors: Ogawa Hisahito , Nishikawa Masahiro , Abe Atsushi
Published: February 2003

The Hall effect has been measured for ultrafine particle films of tin oxide (particle size 50–200 Å) in contact with reducing gases. Both the carrier concentration and mobility increased with an increasing concentration of reducing gas. As a result, conductivity, the product of the carrier concentration and mobility, shows a large gas concentration dependence. This means the ultrafine particle films are highly sensitive to gases. The variation of the carrier mobility with the gas concentration is interpreted in terms of a model in which the width of a long, thin channel, determined by particle size and Debye length, increases with a decrease in the number of O− ions desorbed by a chemical reaction with the reducing gases.
Plasma diagnostics with computer-imaged microwave holography
Authors: Iizuka Keigo , Steiner George , Wong Alfred , Santoru Joseph
Published: February 2003

The aplication of computer-imaged microwave holography to plasma diagnostics is mathematically formulated, a system is constructed and performance evaluated, and tested experimentally in a plasma chamber. The initial results of the project indicate potentials of the holographic technique in the area of non-interference versatility and simplicity of operation.
A study of thin silicon dioxide films using infrared absorption techniques
Authors: Boyd I. W. , Wilson J. I. B.
Published: February 2003

Infrared transmission spectra of a series of silicon dioxide (SiO2) films grown on silicon wafers from a HCl and O2 gas mixture at 850 °C, have been studied for film thicknesses down to 28 Å. The validity of Lambert-Bouguer’s Law for such thin films has been confirmed, and the apparent absorption coefficient calculated for the absorption at 1065 cm−1 is in good agreement with previously published data for thicker, vapor-deposited, and thermally grown films. A continuous shift of the absorption near 1065 cm−1 has been found, moving from an asymptotic limit maximum of ∼1070 cm−1 for thick films towards smaller wave numbers for thinner films. Various possibilities for the origin of this shift are discussed.
Effects of humidity on stress in thin silicon dioxide films
Authors: Blech I. , Cohen U.
Published: February 2003

The stresses of thermally grown as well as chemically vapor deposited (CVD) silicon dioxide were measured by the cantilever beam technique using x-ray diffraction. Thermally grown oxide shows reversible stress changes upon heating or cooling of the films. The linear thermal expansion of such films is similar to that of bulk vitreous silica, 5×10−7 °C−1, the biaxial elastic modulus was found to be 6.3×1011 dyn/cm2. CVD oxides show extensive hysteresis in the stress-temperature curves when tested in ambient air. From stress measurements of such films, deposited on Si and GaAs, it was concluded that their average linear thermal expansion coefficient in the temperature range of −170–115 °C is 4×10−6 °C−1, much higher than that of thermally grown oxide, while their biaxial elastic modulus is only 4.6–5.1×1011 dyn/cm2. The stress in such films was found to increase when the films were exposed to a dry ambient or vacuum. The time constant for this change was found to be several minutes at room temperature.
The Born approximation for the scattering theory of elastic waves by two-dimensional flaws
Authors: Jain D. L. , Kanwal R. P.
Published: February 2003

First, we present formal aspects of the scattering of plane elastic waves by a single elastic cylindrical inclusion or a cavity of an arbitrary cross section embedded in an isotropic homogeneous elastic medium of different properties. An integral equation is used to derive expressions for the displacement field valid in the entire domain. Thereafter the Born approximation for the solution is derived. Formulas for the scattered amplitudes and the scattering cross sections are presented. The validity of the approximation is examined by comparing the results with those of the simple bodies for which the exact solutions are available in the literature. Some new results for the corresponding three-dimensional case are also presented.
Torsional velocity measurements in wire, with application to metal-matrix composites
Authors: Frost H. M. , Prout J. H. , Reed Robert W.
Published: February 2003

A technique is described for measuring torsional wave velocity in (nonferromagnetic) wire with diameters of less than 1 mm. Transduction is noncontacting, via Lorentz forces acting across a gap between transducer and wire, so that velocity can be ’’scanned’’ along the length of the wire. A double-receiver approach permits the scan to be made in a ’’point-by-point’’ fashion. The wires are a metal-matrix composite of 6061 aluminum and pitch mesophase graphite. Some data are presented, together with a discussion of the effects of metal-matrix-composite parameters, such as graphite content and porosity, on torsional velocity. An extrapolation of our metal-matrix- composite data yields a value for c44, of the graphite fiber, that was within 1% of a value determined from data of Fischbach and Scrinivasagopalan. Good predictions of experimental results were obtained through use of theory of Hashin and of Achenbach and Herrmann. Some differences, and their implications, between torsional and longitudinal waves propagating in metal-matrix-composite wire are described.
Magnesium- and calcium-doping behavior in molecular-beam epitaxial III-V compounds
Authors: Wood C. E. C. , Desimone D. , Singer K. , Wicks G. W.
Published: February 2003

Residence lifetimes of Mg on GaAs surfaces were observed using 10 KV reflection electron diffraction and Auger electron spectroscopy to decrease from ∼120 s at 550 °C to ∼1 s at 600 °C. The electrical incorporation coefficient is ∼0.3 at and below 500 °C decreasing to ∼3×10−4 at 600 °C at the expense of desorption. Hole mobilities of uniformly Mg-doped samples are as good as those for equivalently Be-doped GaAs samples. Calcium does not behave as a shallow acceptor in GaAs grown by molecular-beam epitaxy.
Ion beam exposure characteristics of resists: Experimental results
Authors: Hall T. M. , Wagner A. , Thompson L. F.
Published: February 2003

The exposure characteristics of six polymer resists to 1.5 MeV H+, He+, and O+ ions and to 20 keV electrons were measured. The resists used were polystyrene (PS), polymethyl methacrylate (PMMA), PMMA mixed with 20% of a copolymer of vinyl acetate and vinyl chloride (VMCC), poly(glycidyl methacrylate-co-3-chlorostyrene) (GMC), poly(butene-1-sulfone) (PBS), and a novolac. The deposited energy per unit volume required to expose a resist was found to be a function of the spatial energy dissipation rate of the ion in the resist. This has been accounted for in terms of the nature of the energy distribution around the primary particle track in conjunction with whether the resist requires the activation of a single site or two adjacent sites to produce exposure.
Accelerated facet degradation of InGaAsP/InP double-heterostructure lasers in water
Authors: Morimoto M. , Takusagawa M.
Published: February 2003

Facet degradation of InGaAsP/InP double-heterostructure (DH) lasers in accelerating environment of water was studied from the standpoint of quantitative comparison with GaAlAs DH lasers. Facet degradation of InGaAsP/InP DH lasers proceeds by oxidation mechanism and its degradation rate is 2–3 orders below that of GaAlAs DH lasers. The difference of oxidation behavior between InGaAsP/InP and GaAlAs DH lasers was examined by using large wafers having the same composition as lasers. The following results were obtained: the oxidation proceeds with the inward diffusion of molecule water through the oxide film, the oxidation rate of n-InP is more than two orders of magnitude lower than that of n-GaAs, In oxide and P oxide were uniformly distributed in the depth profile of the oxide for InP and InGaAsP, and As oxide has the abnormally depleted distribution in the front layer of the oxide for GaAs and GaAlAs. The facet degradation rate is influenced by some experimental factors, i.e., the optical output power, the injection current in dc-biased experiment, and the water temperature in unbiased experiment. To explain the degradation behavior caused in dc-biased and unbiased experiment under identical mechanism, we attempted to evaluate the degradation rate as a function of the facet temperature; the optical output power and the injection current in dc-biased experiment were assumed to contribute to the supplying source of carriers, which rapidly recombine nonradiatively, raise the facet temperature, and finally promote the diffusion of molecule water through oxides and the reaction rate at oxide-facet interface. Combining these results with the fact that the oxidation rate varies in proportion to the partial pressure of a molecule water in the operation environment, we estimated the degradation rate of InGaAsP/InP DH lasers operated under 6.7 mW/μm2 at 70 °C in a nearly dry nitrogen environment (relative humidity of 1–10%).
Plasma KrF laser pulse compressor
Authors: Capjack C. E. , James C. R. , McMullin J. N.
Published: February 2003

The use of a plasma medium for the compression of KrF laser light to pulse widths suitable for laser-driven fusion applications is described. The results indicate that efficient pulse compression can be realized. A particular feature is the absence of the troublesome backward second-Stokes wave found in gas cell compressors.
Temperature dependence of the refractive index of strontium titanate and prism coupling to lithium niobate optical waveguides
Authors: Schneider E. , Cressman P. J. , Holman R. L.
Published: February 2003

The temperature dependence of the refractive index of SrTiO3, near room temperature, has been found to be −5.1×10−5 °C−1 at 632.8 nm by a variation of the minimum deviation prism method. We found that this temperature dependence had to be included to account correctly for the observed temperature sensitivity of coupling light to lithium niobate optical waveguides with strontium titanate prisms.
Quantitative measurements of laser-generated acoustic waveforms
Authors: Dewhurst R. J. , Hutchins D. A. , Palmer S. B. , Scruby C. B.
Published: February 2003

The generation of acoustic waves in metals by pulsed laser irradiation over a wide range of material conditions has been studied. Capacitance transducers have been used to obtain quantitative measurements of the amplitude of bulk acoustic waveforms where the laser beam was directed onto free metal surfaces in the presence and absence of surface plasmas, and onto modified metal surfaces. The application of acoustic wave propagation theory has allowed theoretical waveforms to be determined. By combining data for thermoelastic and normal force sources, waveforms have been produced that follow closely those measured experimentally.
Studies of three-cylinder electrostatic mirrors and lenses
Authors: Berger Colette , Baril Marcel
Published: February 2003

With the aim of using it in mass spectrometry, we have tried to find an axisymmetric electrostatic system with very particular characteristics, viz. reduced spherical and chromatic aberrations. We chose a system made up of three coaxial cylinders of radius ρ. The inner electrode is 0.90 ρ long and is separated from the outer cylinders (which are taken to be of infinite length) by two identical gaps of 0.40 ρ. This system has been studied from both the mirror and the lens point of view. The mirror is studied using two electrostatic parameters. The potentials of the three cylinders are reffered to as V1, V2, and V3. The first parameter used is Rd=100 (V1−V2)/(V1−V3) and the second is V3/V1. For six values of Rd, ranging from 100 to 74, we examine the paraxial characteristics and the coefficients of spherical and chromatic aberration as a function of V3/V1. We only deal with the area where the mirrors are convergent and where the radii of curvature do not exceed 10ρ. For the values of Rd studied, other than 100, we use a field of variation from −0.10 to −0.50 for V3/V1. When we study the lens, we deal with the area where the outer potentials V1 and V3 are identical. There is thus only one variable, the ratio V2/V1 of the potentials of the first two cylinders. We consider two cases: V2/V1≳1 and V2/V1<1. Among the results obtained, we have chosen two groups of mirrors for which the chromatic aberration coefficient Cc is null and whose radii of curvature are greater than 6.60 ρ, a group of mirrors for which the spherical aberration coefficient Cs is null and where Cc is greatly reduced (here the radii of curvature are greater than 4.00 ρ), and a mirror for which both Cc and Cs are null and which has a radius of curvature of 7.28 ρ.
Kinetics of growth of the oxidation stacking faults: The capture of interstitials by partial dislocation
Authors: Leroy Bernard
Published: February 2003

All models of oxidation stacking fault (OSF) growth previously published depict the stacking fault as a circular sink of interstitials the concentration of which has been maintained at a value Cs very far from the OSF. This geometry is not correct. The silicon-oxide interface provides the interstitials, and the partial dislocation surrounding the OSF emerges at this interface. The model presented in this article takes into account the actual geometry, and thus it can be deduced that the OSF’s are elongated semiellipses rather than semicircles. The activation energy for the capture of interstitials by partial dislocation ΔH is small or negative (ΔH<0.1 eV). The dependence of the length of the OSF’s with respect to the distance between them d is small when this distance is more than 260 nm in our experiments. The minor axes of the OSF’s may be reduced if their distance d is less than half their length.
Laser-initiated vacuum plasma shutters using a dielectric aperture for retropulse isolation
Authors: Sheheen T. W. , Czuchlewski S. J. , Hyde J. , Ainsworth R. L.
Published: February 2003

It is demonstrated that sintered LiF spatial-filter apertures may be used in a vacuum environment of 10−6 Torr as laser-initiated plasma shutters for retropulse isolation in high-energy laser fusion systems. In the experimental data presented, a 1.1-ns duration pulsed CO2 laser at 10.6-μm wavelength with an energy of 3.0 J is used for plasma initiation. A chopped cw CO2 laser tuned to 9.6 μm is used as a probe laser in determining the time the plasma blocks transmission of a CO2 laser beam. Both the 10.6- and the 9.6-μm transmission were measured as a function of pulsed laser fluence on the aperture edge, up to 240 J/cm2. Blocking times in excess of 1.0 μs were observed for an aperture diameter of 800 μm, for a Gaussian beam with a diameter of 1.2 mm determined at the 1/e2 intensity points.