bluuebunny/crossref_metadata_2025 huggingface dataset:
Comments on ‘‘An analytical study of the p-n junction space-charge region under high forward voltage’’ [J. Appl. Phys. 6
2, 948 (1987)]
Authors: van den Biesen J. J. H.
Published: July 2002

The recent findings of Park, Lindholm, and Neugroschel [J. Appl. Phys. 62, 948 (1987)] regarding the depletion capacitance of p-n junctions of the symmetrical-step type and of the linearly graded type under high-forward voltage are compared to the results of an earlier analysis of the same subject. The difference in the method of solution and the role of a characteristic length in linearly graded junctions is briefly discussed.
Ion beam mixing of aluminum and titanium
Authors: Borgesen P. , Lilienfield D. A. , Johnson H. H.
Published: July 2002

The ion beam mixing of Al and Ti by 600 keV Xe ions was studied at room temperature and near 80 K. In view of recent observations of large differences between bilayer and multilayer mixing rates in the Fe-Ti, Ni-Ti, and Cu-Ti systems, both bilayer and buried-layer samples were investigated. Results obtained with the various sample configurations were in good mutual agreement. Comparison to literature data on marker experiments in Al suggested no significant dependence on layer thickness above ∼5 Å. At room temperature, the mixing rate is in excellent agreement with previous multilayer mixing experiments. The initial mixing rate was found to vary by less than 20% between 80 and 300 K. The results are discussed in terms of theoretical models for the mixing mechanisms together with published data on comparable systems. In spite of the low Z values involved, the mixing rate is in good agreement with an expression based on a thermal spike mechanism. At large fluences, a 1260-Å-thick surface layer of Al would suddenly start to degrade quite rapidly.
Ga vacancy-assisted diffusion of Si in GaAs
Authors: Kahen K. B.
Published: July 2002

A model for Si diffusion into GaAs based on the formation of Si+Ga-V−Ga pairs is developed. The model follows the formalism developed by M. E. Greiner and J. F. Gibbons [Appl. Phys. Lett. 44, 750 (1984)]. Using recently derived values for the Ga vacancy diffusivity, it is shown that the pair diffusion coefficient is approximately equal to three-quarters its value. The results of the model are demonstrated to be in good agreement with the Si diffusion data.
Titanium-related deep levels in silicon: A reexamination
Authors: Mathiot D. , Hocine S.
Published: July 2002

Deep-level transient spectroscopy is used to determine the energetic positions of the deep levels induced by titanium in the silicon band gap. The experimental results confirm that titanium is an amphoteric center with an acceptor level at Ec–0.09 eV and two donor levels at Ec−0.30 eV and Ev+0.26 eV. The properties of the first donor level are analyzed in more detail, and an explanation is proposed for the absence of the Poole–Frenkel effect at this level.
Ultraviolet induced defect creation and annihilation in low-temperature-deposited SiO2
Authors: Devine R. A. B. , Francou J-M.
Published: July 2002

Continuous Xe arc and pulsed KrF excimer laser ultraviolet radiation induced modification of the density of oxygen-vacancy defect centers in unannealed, low-temperature-deposited SiO2 has been studied. In lamp-irradiated samples, the density grows from an initial value ∼2×1016 cm−3 to 1017 cm−3. Laser radiation using pulses 40 mJ cm−2 reduces the defect density 6.3×1013 defects cm−3 J−1 cm2 while 200 mJ cm−2 pulses reduce the defect density ∼5.2×1012 defects cm−3 J−1 cm2. Lamp irradiation (EPhoton<4 eV) transforms existing defect precursors while laser radiation annihilates existing defects by a process of trapping of electrons excited from the valence-band edge. Evidence for new defect creation due to two-photon processes is presented.
Fiber-optic-based evanescent field chemical sensor using tunable diode lasers for the midinfrared spectral region
Authors: Schnitzer I. , Katzir A. , Schiessl U. , Riedel W. J. , Tacke M.
Published: July 2002

A new fiber-optic sensor system, comprised of an IR tunable diode laser source and an unclad multimode IR fiber, is described. Design considerations, theoretical predictions, and experimental verification of the sensor performance are presented. This sensor has a relatively high sensitivity, and it will be very useful for monitoring and controlling in situ and in real time, concentrations and chemical transformations of liquids and pastes.
Selective growth and optical properties of an AlGaAs layer on V-grooved Si substrates
Authors: Hashimoto A. , Fukunaga T. , Watanabe N.
Published: July 2002

Selective growth and optical properties of GaAs and AlXGa1−X As (X≂0.3) layers on V-grooved Si substrates by low-pressure metalorganic vapor-phase epitaxy are studied. In the microscopic Auger electron spectroscopy measurement, the As and Ga atoms were not observed on the {111} Si sidewalls of the V-grooved Si substrates. This result clarifies that the GaAs and AlXGa1−X As layers grew only on the {100} planes. The cross-sectional shapes of the selectively grown layer depended on the crystal directions due to the different chemical reactions on the different planes. Spectra of the microscopic photoluminescence and Raman scattering measurements from selectively grown layers showed the significant positional dependence. These spectral changes are interpreted as the impurity and/or the strain distributions in the selectively grown layers.
Influence of luminescence self-absorption on photoluminescence decay in GaAs
Authors: Bensaid B. , Raymond F. , Leroux M. , Vèrié C. , Fofana B.
Published: July 2002

In direct-gap semiconductors, self-absorption processes are known to increase minority carrier lifetimes. In this paper, an original method is developed to solve the dynamic continuity equation with the inclusion of self-absorption phenomena. Also named photo recycling, this process is treated in a model which takes into account the experimental conditions, together with geometrical and optical characteristics of the sample. This method is used to analyze photoluminescence decay experiments on angle-lapped GaAs/Ga0.15Al0.85As double heterostructures. The inclusion of the reabsorption effects is shown to improve the global fit of calculated luminescence with experimental data. This leads to a more accurate determination of key electronic parameters such as diffusion coefficient, surface recombination velocities, and nonradiative lifetime of minority carriers.
Ellipsometric study of Al2O3/Ag/Si and SiO2/Ag/quartz ashed in an oxygen plasma
Authors: De Bhola N. , Woollam John A.
Published: July 2002

Using monolayer-sensitive variable angle of incidence spectroscopic ellipsometry, the silver oxide growth on a silver mirror, coated with an Al2 O3 or SiO2 protective layer, was investigated. The oxidation was done in a pure oxygen plasma asher. The resulting silver oxide growth was monitored accurately as a function of exposure time in the plasma asher. It was found that silver was converted to silver oxide under the protective coating, during ashing of a sample. The optical constants of a dense silver oxide thin film, created by oxidizing in the asher, were also measured.
Electrical studies on plasma and reactive-ion-etched silicon
Authors: Henry A. , Awadelkarim O. O. , Lindström J. L. , Oehrlein G. S.
Published: July 2002

The effect of reactive-ion etching (RIE) and plasma etching (PE) using deuterium on the electrical properties of boron-doped p-type silicon has been studied employing junction capacitance measurements on Schottky diodes. Deep-level transient spectroscopy (DLTS) measurements on the treated samples revealed the presence of a number of previously unreported near-surface traps. These comprise hole traps H(0.44) and H(0.54) at 0.44 and 0.54 eV above the valence band, respectively, and an electron trap E(0.46) at 0.46 eV below the conduction band. The H(0.44) observed directly after the RIE treatment increases in concentration as the sample is annealed to 200 °C, whereas the E(0.46) and H(0.54) are detected in the PE samples directly after etching and annealing at 100 °C, respectively. The depth profiles of the observed traps have been determined, and their annealing behavior is studied up to 200 °C. E(0.46) and H(0.54) are tentatively associated with strain-induced defects resulting from hydrogen platelet formation, whereas H(0.44) is attributed to a vacancy-related defect complex. Other broader DLTS signals following annealing ≥200 °C are explained in terms of additional trap levels closely positioned in the band gap and/or extended defect clusters. Also, the capacitance-voltage (C-V) data on the diodes were modeled to extract the boron deactivation depth profile of the samples after plasma exposures and upon annealing at 200 °C. For both RIE and PE, annealing at 200 °C for 60 min caused the shallow boron acceptor concentration in the samples to almost recover to its preetched value.
A deep level in Zn-doped InGaAlP
Authors: Nozaki Chiharu , Ohba Yasuo
Published: July 2002

A deep level in Zn-doped In0.5(Ga1−xAlx)0.5P (x=0–1.0) has been studied by using pulsed-bias transient capacitance measurements and photocapacitance measurements. One major deep level was found for the entire alloy composition range (x=0–1.0). The deep-level concentration was proportional to Zn concentration for x=0.4. The ratio of the deep-level concentration to Zn concentration increased slightly with x. The energy depth from the valence-band maximum increased with x, from 0.04 eV at x=0 to 0.42 eV at x=1.0. The energy position, referred to as the vacuum state, is essentially invariable for 0<x<1. This level was considered to have a small lattice relaxation. It seemed that this level originates from Zn-related defects.
Electronic transport in gratinglike potential modulated inversion layers
Authors: Vettese F. , Sicart J. , Robert J. L. , Vincent G. , Vareille A.
Published: July 2002

We propose a quantitative approach to the long-range potential fluctuation model previously developed in disordered 3-D semiconductors. To study how potential modulation modifies the conduction processes in 2-D electron gas, metal-oxide-semiconductor field-effect transistor structures were irradiated through the gate oxide by an electron beam (20-keV microfabricator) scanning lines parallel or perpendicular to the drain-source axis. The samples were irradiated at various doses for different periods. Irradiation led to a modulation of the oxide and interface charge, resulting in potential valleys and barriers. A shift in the threshold voltage was measured, which depended on the irradiation dose and also on the direction of the lines. The change in electrical properties (threshold voltage VT, mobility) is simply interpreted by a model based on the existence of a conduction threshold. Thus both the range and magnitude of potential fluctuations are investigated using structures with controllable disorder.
Energy deposition in O+ by high-energy electron beams
Authors: Taylor R. D. , Ali A. W. , Slinker S. P.
Published: July 2002

A discrete, time-dependent energy-deposition model is used to study high-energy electron-beam (100 eV–10 MeV) deposition in O+. Both time-dependent and steady-state secondary electron distributions are computed. The distribution functions, production efficiencies, loss function, and mean energies per electron-ion pair (W) are presented for a wide range of energies. The model predicts W to be approximately 72 eV for O+ over a wide range of beam energies when inner-shell ionization is neglected. The results change when inner-shell ionization, followed by the accompanying emission of an Auger electron, is included. The model also includes inner-shell excitation to high Rydberg states. Changes resulting from these processes are noted and discussed.
Beryllium diffusion in GaInAs grown by molecular beam epitaxy
Authors: Scott E. G. , Wake D. , Spiller G. D. T. , Davies G. J.
Published: July 2002

The diffusion of Be from buried Be-doped layers in GaInAs has been studied for temperatures between 600 and 700 °C. An interstitial-substitutional model is proposed for the diffusion mechanism, which is dependent on growth conditions and consistent with the data presented. Under growth conditions where Be transport is minimized GaInAs junction field-effect transistors have been produced with transconductances in excess of 200 mS mm−1 for a 1-μm gate length.
Nucleation kinetics of molecular-beam epitaxially grown (001) ZnTe and CdTe surfaces
Authors: Benson J. D. , Summers C. J.
Published: July 2002

Reflection high-energy electron diffraction desorption studies have been performed on epitaxial (001) ZnTe surfaces. The desorption of Cd and Te were observed to follow a simple first-order rate law, while the desorption of Zn was more complicated. Activation energies of 3.7, 1.8, and 3.9 eV were found for Zn, Cd, and Te, respectively, on the ZnTe surface. The congruent evaporation temperature was determined to be 400 °C. The nucleation kinetics of (001) ZnTe and (001) CdTe are compared. A theoretical model was employed to predict a method for growing high-quality ZnxCd1−xTe .
Reduced Al/PtSi reaction up to 600 °C using an amorphous carbon barrier layer
Authors: Chang Chin-An
Published: July 2002

An amorphous carbon barrier layer is used to reduce the reaction between PtSi and Al for interconnect application. Using a carbon layer of 1000 Å and a structure of Al/C/PtSi (2000 Å/1000 Å/850 Å/Si substrate), the preformed PtSi is shown to remain stable after a 30-min anneal at 600 °C in a N2-H2 ambient, with no PtAl2, the reaction product between Al and PtSi, detected. The Al-PtSi reaction is nearly completed after an anneal of 30 min at 650 °C. Sheet resistance measurement confirms the low resistance of the top Al layer at these temperatures. The much reduced reaction between Al and PtSi using an amorphous carbon barrier layer, with similar results on the Al/Pd2Si reaction, makes carbon a promising barrier between Al and silicide contacts.
Effects of coexisting nonsuperconducting phase on the superconductivity of YBa2Cu3O7
Authors: Itoh Takao , Uchikawa Hiroshi
Published: July 2002

The effects of coexisting nonsuperconducting phases (BaCuO2, Y2 Cu2 O5 and Y2 BaCuO5 ) on the superconductivity of YBa2 Cu3 O7 have been investigated by measuring the temperature-dependent resistivity and ac susceptibility. As the fraction of the nonsuperconducting phase is increased in the YBa2 Cu3 O7 sample (1) the onset and apparent zero Tc in the R-T curves shift to a lower temperature, (2) the temperature region of the resistive transition becomes broad, and (3) the behavior of the resistivity changes from metallic to semiconductorlike at temperatures above Tc. The resistivity measured as a function of temperature is simulated using a paralleled-circuit model. The model reproduces well the observed R-T curves and in all the observations stated above.
Electron beam flash evaporation for YBaCuO and BiCaSrCuO thin films
Authors: Davis Matthew F. , Wosik Jaroslaw L. , Wolfe J. C.
Published: July 2002

An electron beam flash evaporation technique is described which reproduces the stoichiometry of superconducting YBa2Cu3Ox (123), Bi2CaSr2Cu2Oy (2122), and Bi2Ca2Sr2Cu3Oz (2223) source powders. Films of each material deposited with this technique exhibit zero resistance temperatures of 78 K or above when furnace annealed; 75 K zero temperatures are obtained for 123 films in situ annealed with atomic oxygen at 775 °C. Transport critical current densities are 1×104 A/cm2 in 25-μm stripes patterned from 123 films, and 6×104 A/cm2 in 1-mm stripes of 2122 and 2223 films using a 1-μV/mm measurement criteria. Typical normal state resistivities are 700 μΩ cm for 2122 and 2223 films and 5 mΩ cm for 123 films. The 2122 films are highly textured with the c axis normal to the substrate. All results are for films deposited on MgO.
Determination of stress in GaAs/Si material
Authors: Li Chaorong , Mai Zhenhong , Cui Shufan , Zhou Junmin , Ding Aiju
Published: July 2002

The stresses in GaAs/Si samples which were prepared under different growing conditions were determined by the x-ray diffraction method. The results show that the stress in GaAs/Si samples is reduced by improving the homogeneity of the thermal field. As the thickness of the epitaxial film increases, the curvature of the sample increases, but the stress remains in the same order.
Chemical shifts of impurities in quantum wells
Authors: Trzeciakowski Witold
Published: July 2002

The ground state of an impurity in the center of a quantum well is calculated variationally, including both the Coulomb and the short-range potential V S in the presence of a perpendicular magnetic field. The chemical shifts ΔE due to V S are determined together with the wave function at the impurity site ‖F(0,0)‖2. Both of these quantities show a significant increase (over an order of magnitude for donors in GaAs) when the well width is reduced. The increase in ΔE should be observable in far-infrared impurity spectra while the increase in ‖F(0,0)‖2 should appear in the electron-spin-resonance linewidths. Large chemical shifts in quantum wells might be helpful in identifying the chemical nature of residual donors.
Effects of multiband electron-hole scattering and hole wave-function symmetry on minority-electron transport in GaAs
Authors: Sadra K. , Maziar C. M. , Streetman B. G. , Tang D. S.
Published: July 2002

A Monte Carlo investigation of the effect of multiband electron-hole scattering on steady-state minority-electron transport in room-temperature p-GaAs is reported. A comparative study of the strength of such scattering mechanisms is presented and shows that a careful treatment of these processes is indispensible for a quantitative microscopic understanding of minority-electron behavior. The effect of the p-type symmetry of hole wave functions on multiband processes and minority-electron transport is also described. Finally, we discuss several additional issues, which we believe must be carefully investigated before present Monte Carlo treatments of electron-hole scattering can provide reliable quantitative information.
Modulated reflectance study of strain in epitaxial GaAs on silicon
Authors: Kallergi M. , Aubel J. , Sundaram S.
Published: July 2002

The electrolyte electroreflectance technique was used to study the nature of the strain in epitaxial layers of GaAs grown by laser-assisted metalorganic chemical vapor deposition on (100) Si substrate. The GaAs epilayer, about 140 nm thick, was chemically etched in steps of about 20 nm and spectra of the differential reflectivity (ΔR/R) versus energy were recorded in the 2.4–4.0 eV region immediately following each etch procedure. The E1 and E1+Δ1 transitions of GaAs and their broadening parameters were calculated using the low-field analysis of the electrolyte electroreflectance line shapes. The uniformity of carriers and the effects of the etching procedure were studied with three-dimensional amplitude maps. The variations of the spectral characteristics are interpreted in terms of strains and electronic changes as one approaches the GaAs-Si interface.
Range profiles of Hg+, Hg2+, and Hg3+ in polymer polyvinylalcohol
Authors: Wang Ke-Ming , Shi Bo-Rong , Liu Ji-Tian , Liu Xiang-Dong , Yao Ke-Jun
Published: July 2002

Depth profiles of Hg+, Hg2+, and Hg3+ implanted in polymer polyvinylalcohol at energies from 50 to 600 keV are measured by 2.1-MeV 4He2+ Rutherford backscattering. Based on Biersack’s angular diffusion model, a computer program is written for comparison with the experimental values. The result shows that the measured projected range is in good agreement with the calculated value for first-order treatment. The experimentally determined range straggling is still higher than the calculated value after considering the second-order energy loss. The Monte Carlo simulation shows that the Hg profile is not described by an ionization or nuclear damage profile, but rather is described by a classical predicted implantation profile.
Wide-bandwidth and high-power InGaAsP distributed feedback lasers
Authors: Dutta N. K. , Wang S. J. , Piccirilli A. B. , Karlicek R. F. , Brown R. L. , Washington M. , Chakrabarti U. K. , Gnauck A.
Published: July 2002

The fabrication and performance characteristics of a wide-bandwidth InGaAsP laser diode structure are described. The wide bandwidth is achieved using semi-insulating Fe-doped InP current blocking layers around the active region. The lasers have a bandwidth of 18 GHz at 20 mW, emit 50 mW in a single transverse and longitudinal mode, have rise and fall times of less than 40 ps, have low chirp (FWHM<1 Å) under modulation, and exhibit harmonic distortion characteristics in agreement with fundamental calculations using a rate equation model. Error-free transmission with no dispersion penalty has been obtained using these lasers in a transmission experiment at 8 Gb/s over 76 km of fiber.
Thermal stresses in multilayer optical-storage media
Authors: Nkansah M. A. , Evans K. E.
Published: July 2002

Previously, it has been shown that thermal stresses may have a significant role to play in optical-storage media. Calculations have shown that thermal stresses are produced in single-layer optical-storage thin films sufficient to cause interlayer failure and blister formation. In this paper, more realistic multilayer thin films are modeled and it is shown that considerably higher stresses can be produced depending on the layer geometry and material properties. These effects are important both in the initial writing process and in subsequent reading or writing processes, and may result in long-term-accumulated, stress-induced damage.
Defect studies of electrothermal stress of InP metal-oxide-semiconductor structures
Authors: Tin C. C. , Barnes P. A.
Published: July 2002

We have carried out deep-level transient spectroscopy (DLTS) studies of traps that are generated in InP metal-oxide-semiconductor (MOS) structures by applying combinations of high reverse bias and high temperature (electrothermal stress). The MOS samples were prepared using different methods of oxidation. The defect levels in freshly made samples (before stress treatment) were found to be at 0.59, 0.54, and 0.45 eV below the conduction-band edge. After electrothermal stress treatment, traps at (Ec −0.35) and (Ec −0.22) eV were observed and these were found to be similar to the traps caused by electron injection and irradiation of InP. Both large- (filling pulse=1.2 V) and small-pulse (filling pulse=0.2 V) DLTS experiments were carried out to determine the variation of these traps with bias. We have proposed a simplified mechanism to account for the electrothermal stress-induced electron traps. This mechanism involves the concept of recombination-enhanced defect reaction and is general enough that it can be applied to all metal-insulator-semiconductor system.
Oxidation of silicon: Is there a slow interface reaction?
Authors: Doremus Robert H.
Published: July 2002

Chemical analysis of the surface of an oxidized silicon-germanium mixture by Rutherford backscattering reported recently showed that the silicon is oxidized, but not the germanium. This result provides evidence that the effective oxygen concentration at the silica-silicon interface is low, which is contrary to a slow interface reaction. Strain in the oxide film can result in linear-parabolic oxidation kinetics without a slow interface reaction.
Instabilities in laser cutting of soft media
Authors: Frenz M. , Romano V. , Zweig A. D. , Weber H. P. , Chapliev N. I. , Silenok A. V.
Published: July 2002

Laser cutting of biological matter is explained by a combined action of evaporation and ejection of liquid. It is shown that when the depth of the incision is larger than its diameter and when a certain critical value of the intensity is exceeded, a new effect, a turbulent flow of the liquid layer, emerges as a result of the increased vapor pressure gradient. This turbulent flow is accompanied by the appearance of a number of additional effects. These are the occurrence of a local minimum in the dependence of the normalized recoil momentum as a function of the position of the beam focus, the formation of bumps and, connected with this, a change in the extent and velocity of the ejection. These effects are experimentally studied in the present investigation. In addition, it is shown that for cutting soft tissue the accuracy of focusing has a crucial influence on the depth of the generated incision and the extension of the created thermal damage zone.
Self-cleaning effect in partially ionized beam deposition of Cu films
Authors: Yang G.-R. , Bai P. , Lu T.-M. , Lau W. M.
Published: July 2002

We have shown that high-purity Cu films can be deposited on the Si substrate at room temperature in a conventional vacuum condition using the partially ionized beam technique. The beam contains about 2% of Cu self-ions and a bias potential of 1 kV is applied to the substrate during deposition. By using the secondary ion mass spectrometry technique we show that the Cu/Si interface is free of contaminants such as oxygen, carbon, and hydrogen, despite the fact that no in situ surface cleaning has been performed on the substrate prior to deposition. These phenomena are attributed to the self-cleaning effect induced by the energetic Cu ions bombardment during deposition.
Electrical properties of highly boron-implanted polycrystalline silicon after rapid or conventional thermal annealing
Authors: Almaggoussi A. , Sicart J. , Robert J. L. , Chaussemy G. , Laugier A.
Published: July 2002

Conductivity and Hall measurements were carried out on highly boron-implanted (5×1015 cm−2) low-pressure chemical vapor deposited silicon films. Polycrystalline films were annealed using a rapid thermal annealing (RTA 10 and 20 s) at 950, 1050, and 1150 °C, or standard furnace annealing [conventional thermal annealing (CTA) 950 °C, 30 min]. The Hall mobility and carrier density of the RTA films were higher than those of CTA films. Moreover, the temperature dependence of the mobility in RTA films showed a very striking behavior at high temperatures, i.e., the mobility decreased with increasing temperature, whereas CTA films showed thermally activated mobility. These results are analyzed in terms of the electrical activity of grain boundaries.
Quenching cross sections of neon metastable atoms by light molecules
Authors: Ortiz M. , García G. , Martín P. , Cabrera J. A. , Campos J.
Published: July 2002

The quenching cross sections of Ne metastable levels by N2 and CO were measured to be (in Å2 units): 8.3±0.4, 8.7±0.4 for 3s(3/2)2 level and 8.0±0.4, 9.1±0.4 for 3s(1/2)0 level, respectively, at 443 K. The metastables are produced by a pulsed electron beam and their population was monitored by fluorescence induced by a cw dye laser.
Preparation and characterization of the filled tetrahedral semiconductor LiZnP film on quartz
Authors: Kuriyama K. , Katoh T. , Tsuji S.
Published: July 2002

A direct wide-gap semiconductor LiZnP has been prepared by rapid evaporation onto a quartz substrate. Various characterization techniques such as x-ray analysis, Rutherford backscattering analysis, and scanning electron microscopy were used to evaluate the quality of the films. Single-phase films were obtained by annealing during 40 min at substrate temperatures ranging from 400 to 440 °C. The grains in the films were oriented preferentially to the 〈111〉 direction with increasing substrate temperature. The optical transmission of the LiZnP films was observed to the short wavelength beyond an absorption edge (∼600 nm) of bulk materials. This suggests the existence of the imperfection such as accumulated impurities at grain boundaries.
On the propagation of transverse disturbances in free-molecule flow
Authors: Yang H. T.
Published: July 2002

It is shown that the propagation of transverse disturbances in free-molecule flow could be either diffusive or wave-type dependent upon the averaging process. Parallel to the reasoning in the continuum limit, we conclude that the process is governed by the classical transverse wave equation with the isothermal speed of sound as the propagation speed. Furthermore, the governing equation is invariant under Galilian transformation.
Enhancement of oxygen precipitation in quenched Czochralski silicon crystals
Authors: Hara Akito , Fukuda Tetsuo , Miyabo Toru , Hirai Iesada
Published: July 2002

The effect of cooling rates from solution annealing (>1270 °C) on oxygen precipitation in Czochralski silicon crystals was studied. The higher the cooling rate, the more oxygen precipitated. There was a lot of oxygen precipitation in quenched silicon after solution annealing, but not much in quenched silicon after solution annealing followed by solution annealing and then slow cooling. When slowly cooled silicon is quenched after solution annealing, the amount of oxygen precipitation was large again. This indicates that quenching from high temperature introduces defects which enhance oxygen precipitation. We assume that the defects are related to intrinsic point defects. We found that these defects disappear above 900 °C. Nitrogen impurities diffused into silicon during high-temperature annealing also enhance oxygen precipitation.
Experimental and theoretical characterization of trap-related transfer loss in acoustic charge transport devices
Authors: Janes D. , Hoskins M. J.
Published: July 2002

The behavior of trap-related transfer loss in acoustic charge transport devices is characterized experimentally through measurements of pulse degradation and frequency response rolloff. A theoretical loss analysis which incorporates a physical model of the charge packets in the device and the characteristics of electron traps in the GaAs epitaxial layers is presented and correlated with experimental results. It is found that the trap-related loss cannot be described by a proportional loss model. Good qualitative agreement is found between theoretical predictions and experimental results; however, the time constants observed experimentally in pulse measurements are 50–100 times faster than the theoretical predictions. Additional loss due to traps with long time constants is predicted theoretically but not observed experimentally.
Effective dielectric constant and magnetic permeability of a simple cubic lattice populated by two species of conducting magnetic spheres
Authors: Lam John
Published: July 2002

The effective dielectric constant and the effective magnetic permeability are calculated for a mixture of two species of general conducting magnetic spheres occupying alternate sites of a simple cubic lattice. The problem is formulated exactly with a pair of coupled linear matrix equations which contains all the multipole interactions within and between the two species of spheres. The matrix equations are solved analytically by iteration. Analytical formulas are derived for the effective dielectric constant and the magnetic permeability as series expansions in fractional powers of the volume fractions of the spheres, the expansion coefficients being explicit functions of the constitutive parameters of the spheres. The analytical solution of the two-species problem embodies those for a simple cubic lattice and a face-centered-cubic lattice of one species of spheres as limit cases.
Toward an analytical solution of the hydrogenated amorphous silicon p-i-n structure: Hyperbolic approximation of nonuniform electric field
Authors: Irrera Fernanda , Palma Fabrizio
Published: July 2002

An approximated expression of the electric field spatial dependence in the intrinsic region of amorphous silicon p-i-n solar cells has been introduced, leading to analytical solutions for carrier distributions in the family of Bessel functions. Autoconsistent determination of the parameters involved in the field expression is discussed, on the basis of physical considerations, minimizing the error related to the hyperbolic approximation. A new analytical transport model for the p-i-n device is adopted in the solution: in this model the continuity equation is solved for both the majority and minority carrier in the whole structure, and photogeneration is introduced in the equations as an analytical, nonhomogeneous term. Rigorous boundaries conditions on carriers and currents at the interfaces can thus be imposed.
Silicon nitride films prepared using a SiH4/NH3 microwave multipolar plasma
Authors: Boher Pierre , Schneider Jacques , Renaud Monique , Hily Yves , Bruines Joop
Published: July 2002

Silicon nitride films have been prepared at room temperature using a microwave multipolar plasma chemical vapor deposition system. In situ kinetic ellipsometry during deposition and ex situ measurements such as infrared absorption or spectroscopic ellipsometry have been used to investigate the dependence of film composition and properties on the flow ratio SiH4/NH3 and on the total pressure. Depending on the silane partial pressure, the films contain a variable amount of oxygen or amorphous silicon which directly affects the electrical properties.
Nonresonant third-order optical nonlinearity of quantum-confined CdS clusters: A third harmonic generation study
Authors: Cheng Lap-Tak , Herron Norman , Wang Ying
Published: July 2002

We report the first study, to the best of our knowledge, of the nonresonant third-order optical nonlinearity of quantum-confined CdS clusters using third harmonic generation from 1.91 to 0.64 μm. We observe that the nonlinearity increases with the increase in the cluster size. The intrinsic, nonresonant χ(3)CdS for ∼30, ∼15 Å thiophenolate-capped CdS clusters and [Cd10S4(SPh)16]−4 molecular clusters are 3.3×10−10, 2.5×10−11, 4.7×10−12 esu, respectively. To utilize this large nonresonant nonlinearity it is necessary to incorporate these clusters into a sample in high concentrations.
Temperature-dependent characteristics of GaAs/AlGaAs multiple-quantum-well optical modulators
Authors: Bailey R. B. , Sahai R. , Lastufka C. , Vural K.
Published: July 2002

Transmission versus voltage operating characteristics of a GaAs/AlGaAs multiple-quantum-well light modulator have been measured at temperatures between 4.3 and 290 K. At 4.3 K, the linewidth of the heavy-hole exciton absorption is 1.3 meV, and the modulation ratio is greater than 1000 at a 9-V bias. At room temperature, the exciton resonance is broadened to 5.3 meV by phonon scattering and the maximum modulation ratio is 4.93 at 12 V. The measured temperature and voltage dependence of the exciton absorption energies, linewidths, and intensities have been used with a simple model for the modulator’s optical transmission to calculate the operating characteristics as a function of material quality. The upper limit on the room-temperature transmission modulation ratio is estimated to be 5.4 for a device fabricated from 100 quantum wells of width 100 Å.
The influence of the insulator surface in the plasma focus behavior
Authors: Feugeas J. N.
Published: July 2002

The insulator (Pyrex glass pipe in our system) surface alteration suffered due to successive plasma focus discharges was found to be responsible for the improvement in stabilization in the plasma focus behavior. The development of microscopic conductive sites (∼1 μm in size), observed on the insulator surface due to the accumulation of successive discharges, increases the efficiency, by a metal-insulator-metal process, on current sheath buildup with an increment in current density during the breakdown. The influence of the surface in the early stage of the discharge, and its correlation with the intensity of the pinch, was studied by analyzing the Si concentration on the surface of the targets of AISI 304 exposed to the plasmas and ion beams generated in the discharge for different experimental situations.
On the mixing of Cu and Y by Xe ions
Authors: Bo/rgesen P. , Lilienfeld D. A.
Published: July 2002

As part of an ongoing effort to produce high-Tc superconducting layers by ion-beam mixing, the mixing of Cu and Y was studied at both liquid nitrogen and room temperature, using 600-keV Xe ions and Y film thicknesses representative of multilayer mixing experiments. At low temperatures the mixing rate was found to agree with predictions based on thermal spike effects. At higher temperature the mixing is dominated by the rapid formation of the Cu7 Y phase.
Valence-band barrier formation in graded Hg1−xCdxTe heterojunctions with a valence-band offset included
Authors: Madarasz Frank L. , Szmulowicz Frank
Published: July 2002

In two previous papers [J. Appl. Phys. 62, 3267 (1987); 64, 6373 (1988)], we used a highly accurate numerical model to solve the problem of equilibrium barrier formation in graded Hg1−xCdxTe heterojunctions. However, we concentrated solely on narrow-gap p on wide-gap n heterojunctions in which the barrier forms in the conduction band. The present calculation is an extension of that work, but with emphasis on wide-gap p on narrow-gap n heterojunctions. We perform a full parametric study, varying doping concentrations (symmetric and asymmetric), cadmium compositions, and cadmium grading widths. All band profiles are calculated with and without a valence-band offset. Clear trends are observed. Without the valence-band offset, for the larger grading widths, there is a tendency for the valence band to bow down on the n side. The band bowing acts as a potential barrier for the minority carriers. When the valence-band offset is included though, the existence of a barrier to minority carriers depends on the grading width. For the most narrowly graded junctions, a potential well for the minority carriers is present. In the present study, we assume a valence-band offset of 300 meV for HgTe:CdTe. The effects of elevated temperatures and interdiffusion of dopants are also studied, but appear to be inconsequential for the present cases.
Structural properties of Hg1−xZnxTe-CdTe strained layer superlattices and the reduction of threading dislocations from a CdTe buffer layer
Authors: Petruzzello J. , Olego D. , Chu X. , Faurie J. P.
Published: July 2002

Hg1−xZnxTe-CdTe strained layer superlattices were grown by molecular-beam epitaxy. Their structural properties and interplay with a CdTe buffer layer were investigated with transmission electron microscopy. There is an order of magnitude reduction in the density of threading dislocations in the superlattice compared with the CdTe buffer layer. The reduction is accomplished by using the lattice-mismatch-induced strain to bend threading dislocations over into the superlattice-buffer layer interface. The magnitude of the reduction agrees well with predicted values for this system.
Amorphization of stainless steels by carbon implantation
Authors: Follstaedt D. M. , Knapp J. A. , Pope L. E.
Published: July 2002

The ion implantation of C has been discovered to amorphize stainless steels, in contrast to the formation of crystalline carbides for pure Fe. Examination of C-implanted Fe(Cr) alloys indicates that the amorphous phase is stabilized by 12–18 at. % Cr in the steels. Reduced friction is found for C-implanted stainless steels, but an amorphous layer with C alone is more easily worn away than one with both Ti and C. This and other comparisons indicate that both Ti and C are essential for the extended wear resistance and low friction of amorphous Fe(Ti,C) surface alloys.
F center deexcitation induced by local vibration tunneling
Authors: Gomes L. , Morato S. P.
Published: July 2002

A new concept of electronic deexcitation of defects has been developed for systems where the electron couples very strongly with a local lattice mode. The model is based on a classical-quantum description of the configuration curve diagram and proposes that an electronic transition may be induced when the wave packets of the lattice oscillators in the upper and lower states involved overlap. It was successfully applied to the F-center system, at low temperature, in almost all the alkali halides. The luminescence efficiency derived from the model explains very well the observations, even the fact that the F* electron always reaches the relaxed excited state.
Finite-size effects in the frequency response of piezoelectric composite plates
Authors: Alippi A. , Craciun F. , Molinari E.
Published: July 2002

The resonance spectrum of composite plates made of alternating piezoelectric ceramic and epoxy elements is studied both theoretically and experimentally in the frequency range below the thickness resonance. The transmissivity of the finite structure to plate modes is calculated, taking into account the effective plate velocities of the two constituent materials and the finite number of elements in the structure. The results are in excellent agreement with the electrically excited acoustical resonances of samples with different geometry and number of elements. In particular, the effects of the finite size on the number and frequency of modes, as well as their selection rules in the given experimental setup, are successfully interpreted. New ‘‘surface’’ resonances, attributed to the end elements, are observed in the stopbands when the surface elements have lower impedance.
Annealing behavior of strain-induced anion antisites in semi-insulating GaAs
Authors: Benakki S. , Christoffel E. , Goltzené A. , Schwab C. , Wang Guangyu , Wu Ju
Published: July 2002

The decay of the anion-antisite-related electron paramagnetic resonance quadruplet has been studied both quantitatively (resonance parameters) and qualitatively (photoquenchability, microwave saturability) as a function of annealing temperature in plastically deformed semi-insulating GaAs. The AsGa characteristics remain practically unaffected during thermal treatment, wheras the resonance parameters strongly depend on microwave power level. After comparison with similar data on particle-irradiated materiak, this behavior is explained by the kinetics of formation and dissociation of AsGaVAsVGa complexes.
Dislocation luminescence in HgI2 single crystals
Authors: Petroff P. M. , Hu Yu Peng , Milstein Frederick
Published: July 2002

Cathodoluminescence (CL) spectra and spectrally resolved CL images were obtained from a single crystal of mercuric iodide (HgI2) in the neighborhood of Knoop microhardness indentations. We report on a dislocation enhanced luminescence band and a novel elastic strain field effect on the luminescence of HgI2.
Laser gain on 3p-3d and 3s-3p transitions and x-ray line ratios for the nitrogen isoelectronic sequence
Authors: Feldman U. , Seely J. F. , Bhatia A. K.
Published: July 2002

The populations of the 72 levels belonging to the 2s22p3, 2s2p4, 2p5, 2s22p23s, 2s22p23p, and 2s22p23d configurations of the N i isoelectronic sequence have been calculated for the ions Ar xii, Ti xvi, Fe xx, Zn xxiv, and Kr xxx and for electron densities up to 1024 cm−3. Electron collisional monopole excitation from the 2s22p3 ground configuration to the 2s22p23p configuration contributes significantly to the populations of the excited levels and results in relatively large 2s22p23p populations. The population inversions and laser gain for transitions between the 2s22p23s and 2s22p23p configurations are calculated. It is also found that large population inversions and gain occur between levels in the 2s22p23p configuration and levels in the 2s22p23d configuration that cannot decay to the ground configuration by an electric dipole transition. For these potential laser transitions of the type 2s22p23p-2s22p23d, the reabsorption of the radiation from the lower laser level is less of a problem than for the 2s22p23s-2s22p23p laser transitions. The 2s22p23p 4P5/2-2s22p23d 4D7/2 and 2s22p23p 2F7/2-2s22p23d 2G9/2 transitions represent promising transitions for overcoming some of the problems of opacity in dense plasmas. At high electron densities where the excited levels become collisionally mixed, the intensities of the x-ray transitions from the 2s22p23p levels to the 2s2p4 levels decrease relative to the x-ray transitions from the 2s22p23s and 2s22p23d levels. The density dependence of these x-ray line ratios is presented.
The plasma oxidation of titanium thin films to form dielectric layers
Authors: Burns G. P. , Baldwin I. S. , Hastings M. P. , Wilkes J. G.
Published: July 2002

A remote indicatively coupled radio frequency plasma has been used to oxidize titanium thin films evaporated onto silicon substartes. The substrate was heated during oxidation to temperatures between 200 and 500 °C using a resistively heated furance. Titanium dioxide layers were formed of thicknesses from 53 to 150 nm. The crystal structure was shown to be rutile by x-ray diffraction for oxidation temperatures of 500 °C. These samples were also seen to have a thin interfacial silicon dioxide layer. Measurements on 1-mm Al dot capacitors showed the leakage current of a 53-nm film oxidized at 500 °C to be below 10−8 A at a 2-V bias. Good capacitance-voltage characteristics were observed for high oxidation temperatures, with a dielectric constant of between 15 and 22 for the TiO2/SiO2 layers. The refractive index of the layers was measured by ellipsometry to be 2.5–2.6. Plasma oxidation thus provides a low-temperature method of forming titanium dixoide thin films.
Low resistivity quasi-epitaxial Mo-Ta alloy and high-quality anodic oxide for a-Si thin-film transistor liquid-crystal display
Authors: Ikeda M. , Dohjo M. , Oana Y.
Published: July 2002

Sputtered Mo-Ta alloy and its anodic oxide have been studied in a Mo composition range from 0 to 30 at. %. Resistivity abruptly changed as Mo composition increased above 10 at. % from 185 μΩ cm to about 35 μΩ cm. The crystal structure transformed from tetragonal to cubic at this Mo composition. For higher Ta compositions, the crystal structure varied according to the under-layer polycrystalline film crystal structure, which may be denoted as quasi-epitaxial deposition, and the resistivity decreased to as low as 22 μΩ cm. Anodic oxide films of Mo-Ta alloy were superior to conventional Ta anodic oxide films in regard to resistivity and breakdown field, and the best insulator was obtained at Ta 95 at. %. This quasi-epitaxial Mo-Ta alloy and anodic oxide were applied for thin-film transistor matrix substrates.
Consequences of valley filtering on abrupt junction AlGaAs/GaAs heterojunction bipolar transistors
Authors: Das Amitava , Lundstrom Mark
Published: July 2002

Electron transport in AlGaAs/GaAs heterojunction bipolar transistors with compositionally abrupt emitter-base junctions is examined. Transport across the abrupt emitter-base heterojunction is treated quantum mechanically, and the Monte Carlo technique is used to study transport through the base. Although there is a sizeable population of upper-valley electrons in the bulk emitter, the AlGaAs/GaAs heterojunction is found to favor the injection of Γ-valley electrons into the base. This valley filtering effect enhances device performance by reducing base transit time, but quantum mechanical tunneling lowers the average energy of the injected flux which increases base transit time. The design of a heterojunction bipolar transistor for minimum base transit time involves a careful tradeoff between these competing factors. We examine the influence of varying aluminum fraction and bias on base transit time. The results suggest that a moderately doped emitter with high aluminum mole fraction produces the shortest base transit time.
Steady-state space-charge fields in photorefractive materials for volume holographic interconnections
Authors: Lee Hyuk , Baek Woon Sik
Published: July 2002

Criteria for optimal implementation of the volume holographic interconnections utilizing photorefractive materials are presented. To study the photorefractive recording mechanism which yields optimal implementation of the volume holographic interconnections, analytic solutions of the steady-state space-charge fields in photorefractive crystals are derived for small laser intensity at large modulation depth. Numerical solutions for the photorefractive crystal BSO are obtained without the assumption of small laser intensity, and they are compared with the analytic solutions. The data regions which can be applied to optimize the volume holographic interconnections are obtained.