bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient analysis of a step wave propagating in a lossy dielectric
Authors: Hechtman Charles D. , Hsue Ching-Wen
Published: July 2002

A transverse electromagnetic wave propagating through a lossy dielectric is studied. We propose rational functions to describe the general behavior of the permittivity as a function of frequency. The impulse response of the system is found in closed form. The step response is found in terms of a small argument series and an asymptotic expansion. Rise times may be calculated with a nominal number of terms. Pulses may be formed as the superposition of this solution.
The frequency response of an attenuated total reflection modulator
Authors: Chiao Ding-Liang , Lee Cheng-Min
Published: July 2002

A method using attenuated total reflection (ATR) as an intensity modulator to excite the surface plasma wave on the interface is proposed by Sinorbox and Gordon [Appl. Opt. 20, 1491 (1981)]. The characteristics of this intensity modulator can be described in detail by using the dispersion relation and conservation of momentum. The cutoff frequency response of the ATR modulator is limited by the temporal damping, i.e., the reciprocal of lifetime of the surface plasma waves. Meanwhile, the response of this modulator depending on the variation of the depth of an air gap with fixed bias is also discussed.
Spatial-frequency selection using downconversion optical parametric amplification
Authors: Laferriere Paul A. , Wetterer Charles J. , Schelonka Lee P. , Kramer Mark A.
Published: July 2002

We have observed spatial-frequency selection using downconversion optical parametric amplification in lithium iodate. A mode-locked Nd:YAG laser with a second harmonic generator provided the pump beam at 532 nm and the signal beam at 1064 nm. An image was placed on the signal beam and spatial frequencies from 0 to 60 lines/mm were selectively amplified from the image by rotating the lithium iodate crystal 0°–0.77° from the phase-match angle. The optical parametric amplifier’s passband behavior was in excellent agreement with the existing theory.
Bistability and hysteresis in a laser beatwave excited relativistic Langmuir wave
Authors: Ma Jin-xiu , Xu Zhi-zhan
Published: July 2002

It is shown that the large amplitude Langmuir wave driven by two collinear laser beams with a frequency difference approximately equal to the plasma frequency exhibits bistability and hysteresis. The threshold pump intensity for the occurrence of the bistability is rather low compared to most laser-plasma experiments. By using the hysteretic effect, relatively weak pump intensities can result in a very large amplitude of the Langmuir wave.
Hydrogenation kinetics and defect termination of post-plasma-treated chemical-vapor-deposited amorphous silicon film
Authors: Nakamura Minoru , Ohno Toshiyuki , Miyata Kenji , Konishi Nobutake , Suzuki Takaya
Published: July 2002

In order to study hydrogenation kinetics of post-plasma-treated chemical-vapor-deposited amorphous Si film, changes in bonding of Si and H, content of bonded hydrogen, the hydrogen profile in the depth direction of the film, and spin elimination were measured as functions of plasma exposure time and temperature (Tp) and film thickness. The activation energy of hydrogen diffusion estimated from the change of hydrogen content with Tp and exposure time was small, i.e., 0.2–0.4 eV in comparison with that of bond breaking diffusion (∼1.5 eV). Accordingly, bond breaking diffusion was minor for the post-hydrogenation of Si film by hydrogen plasma. All the observed physical quantities in this study could be explained by the fast diffusion of atomic hydrogen through weakly bound sites such as interstitials and its capture by reactive sites such as dangling bonds and weak SiSi bonds. For the capture process, preferential capture of the hydrogen by dangling bonds always occurred. The surface etching of the film, often observed in plasma hydrogenation experiments, was attributable to the evaporation of hydrosilane molecules created by adding hydrogen to the SiSi bond in the surface region.
Atomic and carrier profiles of 1-, 2-, 4-, and 6-MeV 30Si implanted into GaAs
Authors: Thompson Phillip E. , Wilson Robert G. , Ingram David C. , Pronko Peter P.
Published: July 2002

3 0Si has been implanted in GaAs at energies of 1, 2, 4, and 6 MeV. We have measured atomic concentration profiles using secondary ion mass spectroscopy (SIMS) and carrier concentration profiles using an electrolytic capacitance-voltage procedure. Theoretical atomic profiles have been calculated using the computer code TRIM-86. The range statistics and profile shape factors: Rm, Rp, ΔRp, skewness (γ1), kurtosis (β2), and maximum Si density (Nmax) have been determined from the SIMS data. The first two moments (Rp and ΔRp) were also obtained from the carrier profiles and the theoretical profiles. The range and standard deviation obtained by the separate techniques have a maximum difference of only 15%, and the difference is usually less than 10%. This is less than the mutual experimental uncertainty of 17%. The samples were activated using a furnace anneal (800 °C, 15 min) with a Si3N4 cap and using rapid thermal anneal (1000 °C, 10 s) with and without a cap. No redistribution of Si was observed for any of the anneal conditions.
Cold shock waves in semiconductors and insulators
Authors: Dharamsi A. N. , Hassam A. B.
Published: July 2002

It is proposed that ultrahigh density shock waves could be generated in solids by inducing changes in the lattice constant upon laser irradiation. Moreover, for appropriately chosen semiconductors and insulators the initial shock is cold in that the laser energy is converted directly into the compression, with no thermal energy generated initially. Density amplification factors in the hundreds corresponding to transient pressures of gigabars, could be obtained by picosecond, 1-mJ laser pulses. With smaller laser peak powers, the lattice constant variation may be exploited to generate picosecond optoacoustic pulses.
Optical-emission-spectroscopic studies of the sputtering of Y-Ba-Cu-oxide thin films
Authors: Fleddermann C. B.
Published: July 2002

Optical emission spectroscopy is used to determine the identity of species ejected during sputtering of a composite Y-Ba-Cu-oxide target. In this experiment, Y, Ba, Cu, Ba+, and YO were detected near the surface of the target, indicating that oxygen is transported to the substrate during sputtering. Varying of the sputter ion energy caused some variation in relative peak heights, but changing the gas mixture in the system did not significantly alter the spectra.
Structure, composition, and surface topography of cadmium telluride films fabricated by a new nonaqueous electroplating technique
Authors: Gore R. B. , Pandey R. K. , Kulkarni S. K.
Published: July 2002

A new electroplating technique for growing cadmium telluride films in a nonaqueous medium is reported. The influence of the deposition conditions on the structure, stoichiometry, and surface topography of the CdTe films has been discussed in light of the x-ray diffraction analysis, x-ray photoelectron spectroscopy, and scanning electron microscopy studies. Higher bath temperatures have been found to favor larger grain growth with a certain amount of orientation. The CdTe formation is not favored at temperatures <130 °C. The compositional analysis using x-ray photoelectron spectroscopy indicated that the films deposited under galvanostatic conditions are generally richer in cadmium. Nearly stoichiometric films can be deposited under potentiostatic conditions at a deposition potential of −0.8 V (with respect to Pt neutral electrodes). A uniform and regular growth of CdTe films with no sign of cracking was also observed in the surface investigations by a scanning electron microscope.
Crystallinity of InGaPAs epitaxial layers revealed in equal thickness fringes in transmission electron microscopy
Authors: Kondow Masahiko , Kakibayashi Hiroshi , Nishino Taneo , Hamakawa Yoshihiro
Published: July 2002

Crystallinity of InGaPAs layers grown on GaAs substrates by liquid phase epitaxy has been examined by observing equal thickness fringes in transmission electron microscopy. Even InGaPAs layers within the theoretically immiscible composition region are found to be of one phase without compositional fluctuation. Phase separation, which can theoretically occur, is not found. However, crystallinity is generally inferior, and this inferiority increases as the epitaxial layer grows. The substrate-induced stabilization effect seems to produce high quality crystals in the immiscible region only in the initial stage of epitaxial growth. It is also found that immiscibility affects InGaPAs layers grown on GaAs substrates to a greater extent than those grown on InP substrates.
Nonconventional electron diffusion current in GaAs/AlxGa1−xAs N-p-n heterojunction bipolar transistors with heavily doped base layers
Authors: de Lyon T. J. , Casey H. C. , SpringThorpe A. J.
Published: July 2002

Measurements of collector current density in a GaAs/AlxGa1−xAs N-p-n heterojunction bipolar transistor with a p-type base doping of 6×1018 cm−3 are compared with the conventional expression for electron transport by diffusion across the base layer. The experimental collector current density exceeds the conventional diffusion theory result by more than a factor of 4, even after band-gap shrinkage and bandtailing due to the heavy p-type base doping are taken into account in the determination of the thermal equilibrium electron density in the base. The potential necessity of retaining an additional term in the fundamental electron current density equation to account for the experimental collector current is stressed. The form of this additional current-driving term is exhibited equivalently in both an electron activity coefficient formalism and in terms of a spatial gradient of the conduction-band density of states. A conclusive assessment of the relative importance of this additional term will require a theoretical treatment of the influence of excess minority-carrier electron concentrations on the density of states and electron activity coefficient for excited p-type GaAs.
Nonlinear liquid-crystal fiber-fiber coupler for optical switching and gating operations
Authors: Khoo I. C. , Normandin R.
Published: July 2002

Using well-aligned nematic liquid-crystal film as nonlinear optical coupling of two single-mode optical fibers, we have experimented with cw and pulsed 1.06- and 1.32-μm Nd:YAG laser and observed interesting optical nonlinear transmission and opto-optical switching effects.
Continuous Al5 Nb3Ge superconducting tapes via the amorphous state
Authors: Manzur Tariq , Clapp Mireille Treuil
Published: July 2002

Alloys of Nb75Ge24.5B0.5 were rapidly solidified into amorphous ribbons using the melt-spinning technique. After annealing continuous Al5 tapes were obtained with an average grain size of 30 nm. It was not possible to form a continuous tape by melt spinning directly into the Al5 structure since only brittle fragments were obtained. The amorphous annealed Al5 phase was close to stoichiometry with a lattice parameter of 0.514 nm and a superconducting transition temperature of 18 K. The critical current densities were 5×1010 and 8×108 A/m2 at magnetic fields of 0 and 15 T, respectively. This processing technique could be the initial step in the fabrication of multifilamentary Nb3Ge superconducting composites.
Quasi-donor-acceptor pair photoluminescence emission in GaxIn1−xAs/InP
Authors: Yu P. W. , Peng C. K. , Morkoç H.
Published: July 2002

The low-temperature properties of the excitation-dependent photoluminescence emission, in nominally undoped n-type GaxIn1−x As (0.44≤x≤0.48) layers grown on InP by molecular-beam epitaxy, are investigated with changes of temperature and excitation intensity. The excitation-dependent emission is attributed to the quasi-donor-acceptor pair transition in impure compensated crystals. The random impurity potential arising from residual impurities causes a larger energy shift than expected for the usual donor-acceptor pair transition.
Preparation of highly photoconductive hydrogenated amorphous silicon carbide films with a multiplasma-zone apparatus
Authors: Asano A. , Ichimura T. , Sakai H.
Published: July 2002

Highly photoconductive hydrogenated amorphous silicon carbide (a-SiC:H) films were prepared by alternating monolayer deposition and hydrogen passivation by the plasma-assisted chemical vapor deposition technique with a multiplasma-zone apparatus. With this apparatus, the hydrogen-coverage factor of the growing film surface was increased by the hydrogen plasma in the H-passivation zone. The a-SiC:H films grown by repeating deposition of the 3-Å-thick layer on the hydrogen-covered surface showed lower densities of spin and tail states than those of continuously deposited films. Infrared spectra showed that absorption intensities of the carbon polyhydride modes (2890 and 2940 cm−1) decreased and those of the silicon monohydride mode (2000 cm−1) increased with decreasing stacking layer thickness, which suggested formation of a dense network structure. The hydrogen-coverage factor of the growing film surface was estimated from the dependence of carbon content in the film on the hydrogen-passivation time and the stacking layer thickness. Under optimized conditions, the film with a photoconductivity of 3×10−5 S/cm and an optical gap of 1.91 eV was prepared.
Effects of high pressure on silicon metal-oxide-semiconductor structures
Authors: Crumbaker T. E. , Sites J. R. , Spain I. L.
Published: July 2002

The frequency and bias dependence of capacitance in a planar silicon metal-oxide-semiconductor structure has been successfully measured in a diamond anvil high-pressure cell. Electrical contact was achieved with gold ribbon leads passed between one diamond and an insulator-coated pressure seal. Pressure effects on the SiO2 thickness and the silicon surface state profile were separated from changes in lead capacitance and leakage. As the pressure was increased to 30 kbar, SiO2 was compressed 12% normal to the planar surface, but only partially relaxed on a time scale of days after pressure release. The surface state profile, with a minimum at 1×1012 cm−2  eV−1, was essentially unaffected by pressure. Above 30 kbars leakage currents severely limited capacitance interpretation.
Anomalous dielectric behavior of some ferrites
Authors: Murthy S. S. N. , Murthy V. R. K. , Sobhanadri J.
Published: July 2002

The dielectric behavior of some powdered polycrystalline samples has been studied in the frequency range of 200 Hz–100 kHz. It is shown that the dielectric behavior in these systems below the Curie temperature is not purely relaxational in its character and cannot be described by any of the models of the dielectric relaxation hitherto put forward. It is also shown that ‘‘isolation’’ of the particles in the powder samples plays a very important role. The origin of this abnormality is thought to be due to the mechanical resonance arising out of the magnetostrictive property of the material.
The role of damage in post-emission of electrons from cleavage surfaces of single-crystal LiF
Authors: Mathison J. P. , Langford S. C. , Dickinson J. T.
Published: July 2002

It has been previously reported that the cleavage of single-crystal LiF produces intense, long-lasting electron emission persisting several minutes after fracture (called post-emission). We find that this contrasts dramatically with the weak, rapidly decaying emission accompanying LiF fracture in three-point bend or tension. We examine the dependence of intensity and duration of the electron emission produced by LiF cleavage on the interaction of the cleavage blade with the LiF crystal. We show that the damaged region where the cleavage blade and crystal come into contact is by far the major source of the post-emission. Macroscopic particles (‘‘ejecta’’) from the damaged region which frequently cling to the fracture surface are also shown to be highly emissive. In contrast, the ‘‘untouched’’ cleavage surface emits little, if any, post-emission (on the time scale of several seconds). We propose that the high intensity emission originates from defects created during the production of higher index plane fracture surfaces.
On the electromigration failure under pulsed conditions
Authors: Hummel Rolf E. , Hoang Hoang H.
Published: July 2002

Pulsed electromigration experiments on a series of Al-1% Si test stripes deposited on 0.5 μm SiO2 have been performed applying a frequency of 10 kHz and various duty cycles. A model was developed which takes the intermittent cooling of the metallization and a partial backstreaming of the vacancies during off times into consideration. Experiments and calculations both show an enhanced lifetime and are in good agreement for the conditions examined.
A hydrodynamic model of plasma initiation off irradiated metallic aerosols in vacuum: The diffusive regime
Authors: Chitanvis Shirish M.
Published: July 2002

We exploit the analogy between chemical reactions and cascade ionization to study the spatial and temporal dynamics of plasma formation in the vapor that is formed off a metallic aerosol that is being irradiated by a high-energy laser beam, in vacuum. Our hydrodynamic model is valid for relatively low laser fluences (103 J/cm2 for aluminum aerosols) and pulses of the order of nanoseconds or less, when the diffusive approximation may be safely invoked. The main result of our paper is to show that the laser-induced plasma layer around aerosols shows a crossover, from being transparent to being opaque, as the fluence incident upon the aerosol is increased. We use our model of cascade ionization to show that for the laser fluxes for which the model is valid, the plasma in the vapor layer surrounding an aluminum metallic sphere is not dense enough to obscure the laser beam. But for flux levels of 1011 W/cm2 or higher and pulse lengths of 10 ns or longer, the plasma around individual aluminum aerosols becomes very absorbing.
Titanium and carbon coimplantation into sintered α-SiC and hot-pressed Si3N4
Authors: Bhattacharya R. S. , Rai A. K. , Williams J. M.
Published: July 2002

Sintered α-SiC and hot-pressed Si3N4 were coimplanted with 175 keV Ti+ and 46 keV C+ at doses of 1×1017 cm−2. Energies of Ti+ and C+ were such that the depth distributions match closely. The samples were annealed at 1200 °C for 2 h in flowing Ar. The samples were characterized by Rutherford backscattering and cross-section transmission electron microscopy. The distribution of Ti in α-SiC remained unaltered after the anneal whereas significant redistribution occurred in Si3N4. Cross-section transmission electron microscopy revealed the formation of TiC precipitates in the recrystallized surface layer of SiC. Although some precipitates were found to be present in the recrystallized surface layer of Si3N4, the diffraction analysis revealed that these are not TiC.
Long and middle wavelength infrared photodiodes fabricated with Hg1−x CdxTe grown by molecular-beam epitaxy
Authors: Arias J. M. , Shin S. H. , Pasko J. G. , DeWames R. E. , Gertner E. R.
Published: July 2002

Long and middle wavelength infrared (LWIR, MWIR) p+-n photodiodes have been fabricated with Hg1−xCdxTe (0.20<x<0.30) grown by molecular-beam epitaxy (MBE). The epilayers were grown on (211)B lattice-matched ZnCdTe substrates. The surface morphology was smooth and free of in-plane twins. The Cd concentration (x) was uniform across the wafer, with standard deviations (Δx) as low as 0.0017. Structural properties were measured by double-crystal x-ray rocking curve and dislocation etching; FWHM values as low as 34 arcsec and etch pit density values as low as 1×105 cm−2 were measured. p+ -n homojunctions were formed by arsenic diffusion; unpassivated mesa photodiodes were fabricated by standard photolithographic techniques. MWIR and LWIR photodiodes fabricated with MBE material exhibited good diode performance, comparable to that obtained on photodiodes fabricated with the more matured technique of liquid-phase epitaxy. 77-K R0A products of the diodes measured were 6.35×107, 22.3, and 1.76 Ω cm2 with cutoff wavelengths of 4.66, 9.96, and 12.90 μm, respectively. The R0A product for a VLWIR photodiode was 1.36×102 Ω cm2 with a cutoff wavelength of 16.23 μm at 35 K. LWIR diodes with no antireflection coating had a quantum efficiency of 48.6%. The present results represent a significant step toward the demonstration of MBE as a viable growth technique for the fabrication of large infrared focal plane arrays.
Infrared and x-ray photoelectron spectroscopic study of photostructural changes in amorphous P-Ge-Se thin films
Authors: Kumar Ajay , Malhotra L. K. , Chopra K. L.
Published: July 2002

The structure of thin films of P40−xGexSe60 glasses deposited at various angles of incidence and the photostructural changes occurring therein on illumination with UV light have been studied by far-infrared (IR) spectroscopy and x-ray photoelectron spectroscopy (XPS). IR spectra reveal the absorption bands due to P=Se, P-Se-P, Ge-Se, and -Se-Se- group vibrations. The coexistence of various types of structural units (SePSe3/2, PSe3/2, GeSe4/2, -Se-Se-) in these films is supported by XPS and IR results. The photostructural changes are a consequence of the changes in the relative concentration of these structural units. Annealing of the films also causes a change in the concentration of these structural units, which in turn gives rise to a partial reversibility of the photoeffects. It has been established that the magnitude of the photostructural changes is maximum for the composition (P20Ge20Se60) having maximum concentration of fourfold coordinated units.
Brightness degradation and its mechanism in Tb-doped ZnS thin-film electroluminescent devices
Authors: Okamoto Kenji , Yoshimi Takuya , Miura Shoshin
Published: July 2002

We investigated the origin and mechanism of brightness degradation in Tb-doped ZnS thin-film green electroluminescent devices. We concluded that the increased number of TbF bond breaking, acting as nonradiative emission centers for Tb emission, is responsible for the degradation. The recombination energy of electron-hole pairs generated by hot-electron impact at the Tb-doping site breaks the TbF bond, which is vital to efficiency. We found that high-temperature annealing reduces the generation rate of nonradiative recombination centers, resulting in long device life.
Cobalt related levels in P and (P+B) doped n-type silicon: Possible observation of the (CoB) pair
Authors: Mathiot Daniel
Published: July 2002

The deep levels observed in n-type silicon containing cobalt depend strongly on the detailed experimental process, as well as on the substrate characteristics. In fast-quenched boron-counterdoped samples three acceptor levels—E(0.48), E(0.26), and E(0.21)—are observed if the electron density is not too high, whereas no level is present in samples doped with phosphorus only. After furnace annealing (low quenching rate) two other levels, E(0.58) and E(0.17), are observed in the most heavily doped samples. It is shown that E(0.48) and E(0.26) are two levels of a single defect, tentatively identified as the (CoB) pair, whereas E(0.21) is proposed to be the acceptor level of interstitial cobalt.
Electro-optical effects of Cd1−xMnxTe films prepared by ionized-cluster beams
Authors: Nakamura Kimio , Koyanagi Tsuyoshi , Yamano Koji , Matsubara Kakuei
Published: July 2002

We report the first investigation of electro-optical properties of Cd1−xMnxTe films, prepared by the ionized-cluster beam deposition technique. Measurements of the birefringence Δn of the films were performed under applied electric field in the wavelength region from 800 to 450 nm. Major results obtained are as follows: The value of Δn rises to second power against the applied electric field, and for a film with x=0.77 a large quadratic electro-optical coefficient of 3.5×10−12 cm2/V2 is obtained at 633 nm. The wavelength dispersion of Δn is observed near its band gap, suggesting that the electro-optical properties of these films are caused by the Franz–Keldysh effect.
Monte Carlo simulation of Si and GaAs avalanche electron emitting diodes
Authors: Higman J. M. , Kim K. , Hess K. , van Zutphen T. , Boots H. M. J.
Published: July 2002

Results of Monte Carlo simulations of Si and GaAs p-n electron emitters are presented. A single-electron Monte Carlo transport simulation is used to obtain the total number, including avalanche multiplication, of electrons which reach the surface of the semiconductor, as well as the fraction of these which overcome the work function and are emitted into the vacuum. The distribution function is obtained, as well as ensemble average of quantities such as the ionization coefficient. The efficiency of the device is calculated as a function of both the work function and the top conducting channel thickness. The potential performance of GaAs devices is explored via the Monte Carlo simulation, and calculated results for the Si device are compared to published experimental data.
Deposition of zinc ferrite (ZnxFe3−xO4) films by pulsed laser evaporation process
Authors: Ogale S. B. , Nawathey Rashmi
Published: July 2002

Zinc ferrite (ZnxFe3−xO4) films have been deposited on a single-crystal Al2O3 substrate by pulsed ruby laser-induced vaporization from a sintered ZnFe2O4 pellet. The film structure has been determined by small-angle x-ray diffraction measurements, and the film morphology by scanning electron microscopy. The microstructural features have been brought out by conversion electron Mössbauer spectroscopy. The dependence of the film properties on the oxygen partial pressure and substrate temperature during deposition is studied to explore optimized conditions for deposition of near single-phase stoichiometric films.
On the nature of the silicon activation efficiency in liquid-encapsulated Czochralski-grown GaAs by photoluminescence
Authors: Bindal A. , Wang K. L. , Chang S. J. , Kallel M. A. , Stafsudd O. M.
Published: July 2002

The shallow defect evolution in Si-implanted and -annealed liquid-encapsulated Czochralski-grown GaAs is investigated by photoluminescence experiments. Three major emission lines are found. The first emission line located at 1.492 eV corresponds to the SiGa-CAs radiative recombination. The remaining two lines located at 1.44 and 1.40 eV are shown to correspond to GaI-SiAs and VAs-SiAs radiative recombinations, respectively. The effects of these three shallow centers on the silicon activation efficiency are discussed with respect to different annealing and implantation conditions.
Comment on ‘‘An alternating-gradient magnetometer’’ [J. Appl. Phys. 6
3, 3940 (1988)]
Authors: Richter H. J.
Published: July 2002

In a recent article, an alternating field-gradient magnetometer was described [P. J. Flanders, J. Appl. Phys. 63, 3940 (1988)]. For calibration of the system, a calculation was carried out. Here, the treatment of the extension rod of that system and the considerations concerning the piezoceramic are criticized.
Electromigration early-failure distribution
Authors: Hoang H. H. , Nikkel E. L. , McDavid J. M. , MacNaughton R. B.
Published: July 2002

This work investigates the functional form of the electromigration early-failure distribution in thin Al-1% Si metal films. In a very-large-scale experiment with 28 320 packaged samples, an early-failure group was identified and found to correspond to a log-normal distribution, but with a larger dispersion than that which was typical of the primary, or wear-out, distribution. The total distribution for the failures is approximately bimodal, with the more disperse background distribution dominating at early times. Scanning electron micrographs were obtained to characterize the typical failure mode, which had the same appearance for both groups. Evidence for a test-condition stress-level effect on the form of the accelerated lifetime distribution is also presented.
Measurements and simulation of the spatial charge distribution in electron-beam-irradiated polymers
Authors: Maeno T. , Futami T. , Kushibe H. , Takada T.
Published: July 2002

The amount and profile of the charge distribution in a polymethyl methacrylate plate of 7.9-mm thickness were measured after electron beam irradiation. When the plate was irradiated by a beam whose energy was 1 MeV and the total dose was 3 kGy, a spatial charged layer was produced at approximately 2.5 mm from the irradiated side. The maximum charge density was 1.7 μC/cm3 . The charges of the irradiated side decayed faster than the charges which accumulated at positions further away from the irradiated side in the specimen. Computer simulations were carried out to study the charge decay phenomena, assuming that shallow trap levels were created at the irradiated side by the electron beam. The time dependence of the accumulated charge distribution agreed well with the experimental results.
Surface barrier junctions: Majority- and minority-carrier currents
Authors: El Guibaly Fayez
Published: July 2002

The continuity equations for electrons and holes in an illuminated Schottky-barrier junction are analyzed in the presence of surface recombination. The results are derived for an n-type semiconductor, but are equally valid for a p-type semiconductor. The analysis is also valid for the case of semiconductor-electrolyte solar cells by proper substitution of the currents describing charge transfer kinetics at the interface. The net current due to each type of carrier in the junction is shown to depend on the two characteristic currents: the semiconductor saturation current and the exchange current at the interface. Electrons and holes contribute to the total current through the exchange process between the metal and the conduction and valence bands, respectively. For solar cell applications, only the minority carriers generate the useful current component for energy conversion. The results of the model indicate that an efficient solar cell must have (a) little communication between the conduction band and the metal, (b) good communication between the valence band and the metal, (c) little surface recombination, (d) strong light absorption properties, (e) wide depletion region, and (f) large hole diffusion length.
A non-Markovian model of avalanche gain statistics for a solid-state photomultiplier
Authors: LaViolette Randall A. , Stapelbroek M. G.
Published: July 2002

A solid-state photomultiplier (SSPM) capable of continuously detecting individual photons of wavelength between 0.4 and 28 μm has recently been disclosed [Petroff et al., Appl. Phys. Lett. 51, 406 (1987)]. The initial response of the SSPM to a single photon is a fast, high-amplitude current pulse of between 104 and 105 electrons. The distribution of the pulse amplitudes possesses a strikingly and unexpectedly narrow dispersion. We present a phenomenological model of the SSPM avalanche process which successfully predicts the shape of the observed pulse-amplitude distribution by including small history-dependent effects on the carrier transport, effects heretofore ignored in the traditional (Markovian) treatments. The model clarifies the consequences of the electric field strength and the scattering of the electrons for the development of the avalanche in the SSPM.
The effect of molecular-beam-epitaxial growth conditions on the electrical characteristics of In0.52Al0.48As/In0.53Ga0.47As resonant tunneling diodes
Authors: Oh J. E. , Mehdi I. , Pamulapati J. , Bhattacharya P. K. , Haddad G. I.
Published: July 2002

We have investigated the dependence of the performance characteristics of In0.52 Al0.48As/ In0.53 Ga0.47 As resonant tunneling diodes upon molecular-beam-epitaxial growth parameters. The roughness of the growth front, leading to intrawell-size fluctuations and the V/III flux ratio at a fixed growth temperature are found to be important parameters affecting the performance of these devices. By means of a simple model, we have semiquantitatively related the peak current to the interface roughness. Defects and traps in the In0.52 Al0.48 As barriers, on the other hand, produced partially by nonoptimal V/III flux ratios, may produce shunt paths for tunneling, again reducing the resonant tunneling current peak-to-valley ratio. Under optimum growth conditions we have measured current peak-to-valley ratios of 6.1 and 21.6 at 300 and 77 K, respectively. These are the best values reported so far for this heterostructure system.
Interface formation and thermal stability of Sn overlayers grown on cubic SiC(100)
Authors: Niles David W. , Höchst Hartmut , Zajac G. W. , Fleisch T. H. , Johnson B. C. , Meese J. M.
Published: July 2002

We present an angle resolved synchrotron radiation photoemission study in the photon energy range hν=40–140 eV of the Sn/SiC(100) interface formation. Valence-band and core level photoemission spectra suggest that the first monolayer of Sn grows as a two-dimensional layer in the tetrahedrally bonded α phase. Subsequent layers grow as metallic β-Sn in a three-dimensional cluster mode. Heating a 60 Å Sn/SiC(100) interface grown at room temperature to 400 °C leads to a Sn-Si reaction with a breakdown of the α phase and qualitative changes in the sizes and/or shapes of the Sn overlayer clusters. Heating to 1000 °C accelerates the Sn-Si reaction but does not seem to completely remove the β-Sn clusters.
Plasma deposition of hydrogenated amorphous silicon: Effect of rf power
Authors: Kuznetsov V. I. , van Oort R. C. , Metselaar J. W.
Published: July 2002

The experimentally determined growth rate power dependence of plasma-enhanced chemical-vapor-deposited amorphous silicon was compared with the predicted dependence for the case when the SiH3 radicals are the dominant contributors to film growth. The higher experimental growth rate compared to its calculated value can be explained by the influence of Si2H6 produced in the discharge. The maximum of the growth rate was found to be around 50 mW/cm3 . The decrease of the growth rate at powers exceeding 50 mW/cm3 can be explained by the increased influence of hydrogen, which is consistent with the measurements of the refractive index of the deposited films.
Microstructure and superconductivity in a new superconductor series: (Tl,Pb)1Sr2Can−1CunO2n+3−δ
Authors: Barry J. C. , Iqbal Z. , Ramakrishna B. L. , Sharma Renu , Eckhardt H. , Reidinger F.
Published: July 2002

The synthesis procedure and superconducting properties of the first two members of the new series of superconductors of a general formula: (Tl, Pb)1 Sr2 Can−1 Cun O2n+3−δ , are reported. The detailed atomic level microstructure of the compounds have been determined and computer simulated with structural models. Tc increases with n, the number of Cu-O2 layers per unit cell, as in the single Tl-layer Tl-Ba-Ca-Cu-O compounds, but the new materials have higher Tc ’s for the same value of n.
A simple measure of defect concentration in heavily compensated semiconductor
Authors: Boddaert X. , Deresmes D. , Stievenard D. , Bourgoin J. C.
Published: July 2002

We propose a simple capacitance technique to measure the concentration NT of defects in the case where NT is not negligible compared to the concentration ND of the dopant. The technique avoids the use of the so-called deep-level transient spectroscopy which needs, in such a case, a complicated analysis.
Two-dimensional electric (magnetic) field of corrugated sheets and planes containing protrusions or grooves
Authors: Owen D.
Published: July 2002

The electric (magnetic) field of planes containing protrusions or grooves and corrugated sheets or systems, consisting of plane-opposite corrugated sheets, are examined using modified Schwarz–Christoffel formulas. The conductors are of general shapes.
Intersubband optical absorption in a biased superlattice
Authors: Leo J. , Movaghar B.
Published: July 2002

The experimental study of optical absorption in multiple quantum well and superlattice structures in the presence of an electric field has been very important. It has not only allowed the energy levels and the wave functions to be probed with great sensitivity but the possibility also exists of using these sytems as infrared detectors. In view of this work, this paper constitutes a theoretical study of optical absorption in a biased superlattice where the energy levels lie on a Stark ladder.
Dual frequency addressing of polymer-dispersed liquid-crystal films
Authors: Vaz Nuno A. , Montgomery G. Paul
Published: July 2002

We report the feasibility of using dual frequency addressing (DFA) to switch polymer-dispersed liquid crystal (PDLC) films between their on- and off-states. In this scheme, the on-state is activated with an applied voltage of low frequency while the off-state is activated with a high-frequency voltage. We find that DFA increases the forward-scattering efficiency of PDLC films in the off-state without decreasing their on-state transmittance. Consequently, DFA can be used to improve the contrast ratio of PDLC films in projection displays and similar devices. We also find that the addressing frequency required to activate the off-state in a PDLC film has the same exponential temperature dependence observed in conventional liquid-crystal devices not employing microdispersed liquid crystals; this limits the use of DFA in PDLC films to applications which do not require operation over a wide temperature range.
The influence of an external dc substrate bias on the density of states in hydrogenated amorphous silicon
Authors: Alvarez F. , Prieto P. , Florez A. , Tirado L. , Castro L. F.
Published: July 2002

We report a study of the dependence of the density of states in hydrogenated amorphous silicon produced under different dc substrate biases. A dependence of the density of states in materials deposited simultaneously onto indium-tin-oxide-coated glass and stainless steel has been found. The same is attributed to sheath plasma differences at the top surface of the growing film. The density of states was determined by the space-charge-limited current method. The universal scaling law is tested for samples having a similar density of states. Attempts were made to correlate the product of the hole mobility and the recombination time for samples deposited in conditions similar to those used in the space-charge-limited current experiments.
Surface magnetic properties of Nd-Fe-B sintered magnets
Authors: Fukuno Akira , O’Handley R. C.
Published: July 2002

The magneto-optic Kerr effect has been used in conjuction with vibrating sample magnetometry to distinguish the surface magnetic response (20 nm) from that of the bulk in sintered magnets. Three Fe-Nd-B compositions having low, medium, and high coercivity (13, 14, and 15 at. % Nd, respectively) were studied. Bulk magnetization as a function of applied field suggests that intragranular pinning is weak. The high coercivity is ascribed to magnetization reversal limited by nucleation in saturated grains or, equivalently, by pinning of domain walls as they cross from one grain to the next. We find the surface to be more easily magnetized than the bulk and, after bulk saturation, the surface shows a lower coercivity than the bulk for the medium- and high-Hc compositions. When the bulk is not saturated, its coercivity can be as low as that of the surface. Thus, the soft surface only degrades the bulk properties of the samples less rich in Nd.
Deep traps at the interface of SiO2 and InP grown by molecular-beam epitaxy
Authors: Iliadis A. A. , Laih S. C. , Martin E. A. , Ioannou D. E.
Published: July 2002

Deep level transient spectroscopy (DLTS) was employed to study for the first time the interface between deposited SiO2 and n-InP(100) grown by molecular-beam epitaxy (MBE). The DLTS spectra exhibited three well-defined interface peaks I1, I2, and I3. Comparison between MBE grown layers and bulk samples clearly showed a different interface trap configuration, with I1 being common to both types of samples and I2 and I3 being characteristic of the MBE samples. Two different thicknesses of SiO2 were found to produce no observable change in the DLTS signatures of the MBE samples. Peaks I2 and I3 were associated with the nonequilibrium processes of MBE growth, and the data suggested that these interface traps were derived from the semiconductor side of the interface.
Effects of operating temperature on optical-absorption coefficient and optical band gap of hydrogenated amorphous silicon
Authors: Park Jin Seok , Han Min Koo
Published: July 2002

This communication reports experimental results concerning the effects of the operating temperature on the optical properties of doped and undoped hydrogenated amorphous silicon films prepared by rf glow discharge. Optical-absorption coefficients of those films increased by about 10%–18% and their optical band gaps decreased linearly by about 4–8×10−4 eV/K with increasing temperature from about 20 to 100 °C.
Optical velocimetry correction in Fabry–Perot measurements taken through cylindrically expanding shocked fluids with no dispersion
Authors: Goosman D. R.
Published: July 2002

A correction is needed in interpreting optical velocity measurements made by reflected frequency versus time measurements through cylindrically expanding air or fluids. The reflected frequency seen by the velocimeter will be higher than it would be in a planar geometry, even if the fluid obeys the Gladstone–Dale model for the index of refraction versus compression. This has been pointed out by Wackerle, Stacy, and Dallman [Proc. Int. Soc. Opt. Eng. 832, 72 (1987)], who develop a general Lagrangian treatment of one-dimensional planar, cylindrical, and spherical geometries. Our work, developed independently, uses a different, very simple, and rigorous treatment for a special case of cylindrical geometry. It also provides physical insight into the processes that lead to this frequency change. The magnitude of the correction is very small for air, but for a realistic constant density versus radius model is about 5%–10% for fluids such as water, for cylindrically expanding shocks with radii of curvature near 3 cm.
Photoluminescence and photoluminescence excitation spectroscopy in a magnetic field for GaAs grown on a Si substrate
Authors: Zemon S. , Lee J. , Lambert G.
Published: July 2002

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy in an applied magnetic field are reported for GaAs grown directly on a Si substrate by organometallic vapor-phase epitaxy. PLE features associated with interband Landau level transitions and excitonic transitions are identified. The magnetic field dependencies of the interband features are found to be in qualitative agreement with theoretical calculations. A narrow, Raman-like feature (spectral width ≤0.5 meV), observed both in PL and PLE, is identified with a process in which a donor is excited from the 1s ground state to a 2p−1 final state.
Proximity effect correction for high-voltage electron beam lithography
Authors: Abe Takayuki , Takigawa Tadahiro
Published: July 2002

A new proximity effect correction method using an approximate dose correction formula has been developed. The method is especially effective for a high acceleration voltage. In the case of an acceleration voltage of 40 kV, the correction error for the energy deposition in the resist was estimated analytically to be less than ±7%. The deviations of the line and space pattern dimensions were also evaluated experimentally to be less than ±0.03 μm. The calculation time for correcting a 4-Mbit dynamic random access memory (DRAM) was only 0.7 h using a large-scale computer of 15 MIPS (mega instructions per second). Even if the LSI patterns have no hierarchical structure, in an application specific integrated circuit (ASIC) pattern the calculation time would be 1 h or so. A 4-Mbit DRAM pattern can be written using the electron beam direct-writing system EX-7 with sufficient accuracy. These results suggest that the method is practical.
A metal-oxide-silicon field-effect transistor made by means of solid-phase doping
Authors: Gong S. F. , Hentzell H. T. G. , Robertsson A. , Strandberg J. , Hagel J.
Published: July 2002

Solid-phase doping has currently been receiving attention because of the demand for further decreasing geometrical dimensions in integrated circuits. In this paper, we report our implementation of a metal-oxide-silicon (MOS) field-effect transistor using Sb-doped polycrystalline silicon, which is obtained by annealing amorphous Si and Sb thin films, as a diffusion source and also as active elements. Good characteristics of the transistor are obtained, which confirms the applicability of using solid-phase doping in making devices. The technique and the configuration of the device suggest the possibility of reducing the number of processing steps of MOS integrated circuits and achieving small dimension and high-speed devices.
Plasma flow characteristics through small orifices
Authors: Tao Jin , Beardsley Kelly , Seyhoonzadeh Amir , Tai Kim , Forsling Peter , Lonngren Karl E.
Published: July 2002

Experiments have been performed to investigate the two-dimensional characteristics of a time-independent plasma flowing through small orifices (a narrow slit or a small hole) in a flat object. The observed phenomena are modeled with a self-similar quasineutral plasma fluid description that describes the cylindrical or spherical expansion of a fixed number of plasma particles into an underdense plasma.
The dynamics of free, straight dislocation pairs. II. Edge dislocations
Authors: Eykholt R. , Srolovitz D. J.
Published: July 2002

We present a detailed analysis of the relative motion of a pair of edge dislocations with parallel line directions due to their mutual interactions in the overdamped limit. In particular, we derive analytic expressions for the trajectories in the three cases of parallel, antiparallel, and perpendicular Burgers vectors for both zero climb and finite climb. In each of these cases, we find attracting (stable) or repelling (unstable) equilibria, and this allows a simple characterization of the motion. For all other orientations, no such equilibria exist, and the two dislocations either come together or escape to infinity. In addition, we give the equations of motion for the trajectories in the presence of an external stress.
Deep levels produced by triplet vacancy-impurity complexes in GaP
Authors: Shen Yu-Tang , Myles Charles W.
Published: July 2002

A theory of the deep energy levels produced by triplet vacancy-impurity complexes in GaP is outlined. The major chemical trends in the deep levels of a1, b1, and b2 symmetry are predicted for 56 such complexes in this material. These calculations show that a triplet vacancy-impurity complex can produce deep levels at energies where neither the corresponding vacancy-impurity pair nor the isolated impurity produce any.
Impact ionization coefficient and energy distribution function at high fields in semiconductors
Authors: Chen Y.-Z. , Tang T.-W.
Published: July 2002

Impact ionization coefficients in semiconductors are numerically calculated following Keldysh’s method [Sov. Phys. JETP 21, 1135 (1965)]. This requires deriving expressions for an energy-dependent mean free path l(ε) and an energy-dependent impact ionization scattering rate rii(ε). In the derivation of rii(ε), a nonparabolic ε-k relation as well as a smooth transition from the phonon-assisted impact ionization to the phononless impact ionization are considered. Numerically calculated impact ionization coefficients for electrons and holes in Ge, Si, and GaAs agree very well with experimental data. The calculated Keldysh energy distribution function is also compared with the standard Maxwellian distribution. The average mean free path l̄, which is a function of the electric field, has values within the range often quoted in the literature.