bluuebunny/crossref_metadata_2025 huggingface dataset:
The diffusivity, mobility, and correlation factor for solute vacancy diffusion in an edge dislocation in a face-centered-cubic crystal
Authors: Stark J. P.
Published: July 2002

An edge dislocation in a face-centered-cubic crystal is considered for the basis of a transport model of solute diffusion by a vacancy mechanism. The Burgers vector for the dislocation is b=a/2[110], and the solute moves along the edge of the extra half plane of atoms within the compressed region of the core. When the vacancy is tightly bound to the dislocation, self-diffusion yields the correlation factor approaching infinity because the number of available vacancies for diffusion becomes large, and the mobility for electromigration divided by the diffusivity becomes infinite because the vacancy wind diverges faster than the diffusivity. When the solute repels the vacancy, the diffusivity becomes small; however, the mobility still becomes large. With solute vacancy attraction, the diffusivity remains of magnitude of unity and the mobility to diffusivity ratio becomes large.
Photoluminescence in electrically reversible (semiconducting to semi-insulating) bulk GaAs
Authors: Yu P. W. , Look D. C. , Ford W.
Published: July 2002

A photoluminescence study has been made of electrically reversible, bulk, liquid-encapsulated Czochralski GaAs at temperatures 2–300 K. The reversibility from the semiconducting to the semi-insulating state is made by slow or fast cooling, respectively, following a 5-h, 950 °C heat treatment in an evacuated quartz ampoule. A donor level at Ec−0.13 eV and two acceptor levels at Ev+0.069 eV and Ev+0.174 eV are produced after the heat treatment. Only the acceptor levels were detected by photoluminescence. A tentative model assigning the acceptor to the intrinsic defect pair VGa-GaAs is discussed.
The integro-differential equations for time-dependent space-charge decay currents in media between radially symmetrical electrodes
Authors: Henson Bob L.
Published: July 2002

Using a single charge-carrier species with a field-independent mobility model, dimensionless, nonlinear integro-differential equations have been derived whose solutions would exactly predict the time-dependent current produced by the drift and collection of space-charge swarms in media between electrodes with cylindrical and spherical symmetries. The equations are the one-dimensional solutions of the mathematical problems involving arbitrary initial space-charge distributions whose initial currents may or may not be space-charge limited. In principle, if the initial charge distributions were known, the solutions would reduce to first-order, nonlinear differential equations which then could be numerically integrated. The general equations are applied to a specific example of a charge-density distribution which is important in scientific and technological applications.
Distribution functions in linear viscoelastic theory
Authors: Gross Bernhard
Published: July 2002

The relaxation function of stress can be interpreted in terms of the distribution function of relaxation times. The retardation function of strain can be interpreted in terms of the distribution function of strain. The two distribution functions, or spectra, belonging to the same physical system are related by integral transforms. These transforms have been discussed in earlier papers. However, the discussion was not entirely satisfactory because it missed the appearance of single lines associated with truncated spectra, and because it employed integrals over improper and ill-defined functions. This paper gives an alternative treatment which is believed to be more satisfactory mathematically. The distribution functions are found to be the imaginary components of two complex, analytical functions which are the generating functions of all other functions of viscoelastic theory.
Near-edge fine-structure analysis of core-shell electronic absorption edges in silicon and its refractory compounds with the use of electron-energy-loss microspectroscopy
Authors: Skiff W. M. , Carpenter R. W. , Lin S. H.
Published: July 2002

Core-shell electronic absorption edges from thin specimens of silicon, α-silicon carbide, β-silicon nitride, and amorphous silica are studied by using electron-energy-loss spectroscopy in a transmission electron microscope. The elemental and chemical effects in the near-edge regions of the Si L2,3 and C, N, and O K edges are calculated by using some semiempirical models. The chemical effects in the region of the edges near-edge onset are due to valence-shell excited states, which we have modeled as linear combinations of atomic orbitals using the extended Hückel method, with the effects of translational periodicity in crystals included by using Bloch wave functions. Population analyses of valence-shell electronic structure and cross sections for bound→bound atomic transitions are used to interpret and calculate theoretical near-edge fine structure for direct comparison with experiment. The near-edge ionization region is calculated by using a plane-wave excited state to account for elemental effects. Chemical effects in the ionization region are accounted for by including contributions from the elastic backscattering of outgoing waves by the atoms that neighbor the excited atom. The elemental and chemical effects in the edges are shown to be separable to a large extent by using these models, and calculated cross sections are in good semiquantitative agreement with experimental results.
Excimer-laser annealed ohmic contacts to n-GaAs substrates through an ultrathin reacted layer
Authors: Imanaga Syunji , Kawai Hiroji , Kajiwara Kazuo , Kaneko Kunio , Watanabe Naozo
Published: July 2002

An excimer laser has been employed to form ohmic contacts to n-GaAs substrates through an ultrathin reacted layer. An eutectic AuGe alloy, Ni/AuGe (/n-GaAs), and AuGe/Ni (/n-GaAs) were used as ohmic metals. The lowest specific contact resistance ρc measured using the transmission line method was 6.2×10−7 Ω cm2, 2×10−6 Ω cm2, and 1.5×10−6 Ω cm2 for AuGe, Ni/AuGe and AuGe/Ni, respectively. Good surface morphology was also obtained. Depth profiles of the contacts analyzed by an Auger electron microscope show that the thickness of the transition region between the ohmic metal and GaAs was about 100 Å for AuGe and Ni/AuGe, and 300–400 Å for AuGe/Ni.
Photoinduced effects in a mordenite-AgI inclusion compound
Authors: Hirono Takushi , Kawana Akio , Yamada Tomoaki
Published: July 2002

This paper describes the photoinduced effects in a mordenite-AgI inclusion compound due to Ar laser light. Its photosensitization has an irradiation power density threshold instead of the energy density threshold usually observed in many photosensitive materials. The threshold decreases as the temperature decreases. After a certain period of irradiation, the photoinduced reaction occurs accompanied by transitory luminescence. The above characteristics are not observed in pure AgI. To explain these characteristics a model is presented in which Ar laser irradiation makes a photoinduced intermediate state of AgI in mordenite.
Viscoelastic behavior of polymer layers with inclusions
Authors: van der Linden J. H. M. , Wierenga P. E. , Honig E. P.
Published: July 2002

The viscoelastic properties of very thin layers of a composite, consisting of TiO2 particles in a polyester-urethane binder, were determined by dynamic indentation measurements. Air inclusions appear to have a great influence on the viscoelastic properties. Application of Honig, Wierenga, and van der Linden’s extended theory [J. Appl. Phys. 62, ▪▪▪▪ (1987)] to our composite with two types of inclusions, pigment and air, yields a modulus of elasticity that is in agreement with the experimental values up to a pigment volume concentration (c1) of 0.4. The experimentally found maximum in the curve of the modulus of elasticity as a function of c1 is also predicted with this model. The experiments show a more or less constant loss tangent, in accordance with the theoretical prediction that the loss tangent is independent of c1.
Observations of high-current electron beam transport in a curved system with periodic solenoid lenses
Authors: Humphries S. , Len L. K.
Published: July 2002

Experiments were performed on high-vacuum transport of a relativistic electron beam (130 A, 300 keV) through a 180° section of a curved transport system. The system was constructed for high-current betatron experiments. The electron beam was directed by a sector-type bending field and focused by an array of 18 solenoidal lenses. The lenses could be operated with the same field polarity (modulated toroidal field) or with alternating polarity (cusp array). The reversing field of the cusp array canceled beam drift motions. Consequently, the beam was quite stable and could tolerate vertical field errors of ±100%. In contrast, beam motion in the toroidal field was dominated by drifts. After propagation through the 3.2-m-long transport tube, significant beam loss was observed with only an 8% vertical field error. Measured displacements of the beam centroid at the end of the transport system were well described by theory in both field geometries.
Electron traps in GaAs0.6P0.4 p+n diodes fabricated by Zn implantation and rapid thermal annealing
Authors: Tokuda Yutaka , Usami Akira , Shiraki Hiroyuki , Wada Takao
Published: July 2002

Majority-carrier traps in p+n diodes fabricated by rapid thermal annealing (RTA) of Zn-implanted GaAs0.6P0.4:Te and in Schottky diodes fabricated on GaAs0.6P0.4:Te after only RTA were studied using deep-level transient spectroscopy (DLTS). RTA using halogen lamps was performed in the temperature range 830–1000 °C for approximately 6 s without any encapsulant. Two electron traps E1 and E2 were observed for both p+n and Schottky diodes and were found to have thermal emission activation energies of 0.20 and 0.36 eV, respectively. The broadened DLTS spectrum was observed and reproduced using the Gaussian distribution for thermal emission activation energies of these traps. Furthermore, traps E1 and E2 have thermal activation energies of 0.09 and 0.24 eV for electron capture, respectively. It is considered that these traps are native defects and may belong to donor-related (DX) centers. Depth profiles of shallow donors and traps were determined using capacitance-voltage measurements because of anomalously high concentrations of these traps. Shallow donor and trap concentrations were found to decrease over several μm from the surface for RTA Schottky diodes above ∼900 °C, but were observed to be uniform for RTA  p+n diodes. The concentrations calculated for shallow donors and trap E2 by RTA at 1000 °C decreased exponentially with depth. The difference between p+n and Schottky diodes, and the possible mechanism for the decrease of shallow donor and trap concentrations by RTA are discussed. It is possible that the decrease of shallow donor and trap concentrations by RTA is due either to their interaction with vacancies produced near the surface or to their out-diffusion.
Ionization and radiation dynamics of carbon ablation plasmas
Authors: Thornhill J. Ward , Duderstadt James J. , Duston Dwight P.
Published: July 2002

A computational model that can be used for studying the ablation physics of medium z targets by ion beams is presented. In particular, the interaction of a proton beam as it heats and ablates a carbon target is analyzed. Because the radiation emitted during the interaction can carry away a significant amount of the total target energy, the radiation and ionization dynamics is treated carefully. This is accomplished by incorporating a collisional-radiative equilibrium model into the ionization dynamics package of a one-dimensional hydrodynamics model. Cold target energy deposition is assumed, thus eliminating the need for resolving the energy deposition after each time step. The errors incurred by this assumption are discussed. The computer simulation is applied to a general parameter study that involves varying the initial beam conditions to see effects upon the evolution of the target. In addition, the amount of Kα radiation produced by the direct interaction of the beam particles with the individual target atoms is calculated. This information is useful for diagnostic purposes since it is highly dependent upon the ionization state of the target.
Raman scattering studies of metalorganic chemical vapor deposition grown GaAs/AlAs superlattices
Authors: Hark S. K. , Weinstein B. A. , Burnham R. D.
Published: July 2002

We have used Raman backscattering to characterize GaAs/AlAs superlattices grown by metalorganic chemical vapor deposition technique. Diffusion across the GaAs and AlAs interfaces can be observed by studying the optic and folded acoustic phonon scattering. Observation of light scattering from folded acoustic phonons in metalorganic chemical vapor deposition grown samples suggests the ability of the technique in monitoring the layer-to-layer uniformity of superlattices. Using a simple, analytic model we estimate the interfacial width to be 20 Å.
Theoretical approach to the optimal preheating temperature for cw CO2 laser annealing of semiconductors
Authors: Liu Youfan , Wang Enge
Published: July 2002

Using the classical and semiclassical theory, we first give the precise formula of the light absorptance β(T) in semiconductors. As an example, the results for p-type Si wafers are calculated numerically. The absorptance β(T), the absorption coefficient α(T), and the reflectance R(T) of a cw CO2 laser in p-type Si wafers are shown as a function of temperature. By using these relations some important results are found: (1) The optimal preheating temperature range for cw CO2 laser annealing is determined; (2) a conclusion is reached that annealing efficiency is higher for laser irradiation from the back surface, in agreement with experimental observations; and (3) it is shown that to discuss the problem of light absorption by means of the light-absorption coefficient is not sufficient. In this paper a theoretical method of determining the optimal preheating temperature for cw CO2 laser annealing of semiconductors is proposed.
Catalyzed gaseous etching of silicon
Authors: Selamoglu Nur , Mucha John A. , Flamm Daniel L. , Ibbotson Dale E.
Published: July 2002

Traces of copper and silver are shown to accelerate the etching of silicon by molecular fluorine. Copper residue formed by aqueous HF etching of sputter-deposited aluminum (0.5% Cu) produces a 100-fold increase in the etching rate of an underlying (100) silicon, compared to unmetallized samples, at temperatures above 80 °C. Above 180 °C, F2 exhibits a higher absolute etch rate than equivalent concentrations of fluorine atoms. The temperature dependence of the reaction is interpreted in terms of a Cu-CuF(x=1,2) catalytic cycle in which CuF(x=1,2) is the active intermediate. Preliminary results for other gases and metals are presented, and the origin of discrepancies in published rate data for the F2/Si reaction are discussed.
Diffusion and electromigration in lead alloys. I. Nickel as a mobile element
Authors: Mei Shao-ning , Shi Jinghong , Huntington H. B.
Published: July 2002

Studies of bulk diffusion and electromigration of Ni in Pb-Sn-Ni ternary alloys and in Pb-In alloys have been carried out by the standard sequential-sectioning technique and steady-state method, respectively. From a trapping approach, it was found that the binding energy of Ni with Ni and with In are of the order of 0.17 and 1.1 eV, respectively. The close agreement of the prediction of the model with the experiments implied that the Sn atoms trapped only single Ni atoms. The measurement of chemical diffusivity of Ni in Pb showed that the thermodynamic factor had a strong influence on the Z*a value of Ni in Pb-Ni alloys. The thermodynamic factor of Ni in Pb was determined to be about 7×10−2 at 50-ppm Ni and 3×10−2 at 200-ppm Ni. This rapid decrease also showed its effect in the increase of the Z*a of Ni with higher Ni concentration at lower temperatures. Introduction of Sn trapping atoms reduced this effect, as might be expected. On the other hand, addition of indium increased the Z*a value of Ni, present in tracer amount, over the value in pure lead.
Diffusion and electromigration in lead alloys. II. Ag, Au, and Cu in lead-indium
Authors: Shi Jinghong , Mei Shao-ning , Huntington H. B.
Published: July 2002

As a sequel to certain studies of ‘‘fast diffusers’’ in lead-tin alloys, we have carried out a comparable program for lead-indium alloys with silver, gold, and copper as mobile elements. It has been found that the addition of In greatly increased DAg up to 60 times, but made the electromigration parameter Z*a,Ag more negative and it eventually became zero. On the other hand, DAu drops quickly with the addition of In, indicating an Au-In binding energy of about 0.5 eV. The comparable binding energy of Ni with In was found to be 1.1 eV. For the mobile copper, DCu decreased when In was introduced at low concentration but started increasing when In concentration was 7 at. %. Measurements of electromigration of Au and Cu indicated that the added In has little influence on Z*a.
Deposition mechanism of SiO2 film by low-pressure microwave-discharged plasma
Authors: Murakami Eiichi , Kimura Shin-ichiro , Miyake Kiyoshi , Warabisako Terunori , Wada Yasuo
Published: July 2002

Deposition mechanism of SiO2 film by low-pressure microwave-discharged plasma is qualitatively investigated. Film deposition is performed by a newly developed activated reactive evaporation system in which Si atoms are evaporated in O2 gas or in oxygen plasma ambient, and with or without ion bombardment in the plasma. The most important factor in obtaining high-quality SiO2 film is not low-energy (10–20 eV) ion bombardment but enhancement of Si-O reaction and reduction of Si-O2 reaction. These two types of reactions explain simultaneous deposition of high- and low-quality films commonly observed in systems using this type of plasma.
Electromigration-induced short-circuit failure in aluminum underlaid with chemically vapor deposited tungsten
Authors: Broadbent Eliot K. , Towner Janet M. , Towsend Paul H. , Vander Plas Hubert A.
Published: July 2002

Electromigration was studied in Al conductors underlaid with chemically vapor deposited W, and the results compared to the more conventional Al/TiW metallization. In Al/TiW conductors electromigration results in Al whisker growth, causing metal short rather than open-circuit failure. Contrary to expectations, the Al/W metallization was found to be more susceptible to the formation of whiskers during current stress, with Al/W lifetimes reduced by about one-half compared with Al/TiW. The temperature and current density failure dependencies were not significantly affected by the composition of the underlayer. The mechanical stress in the underlayer was not found to significantly affect the stress distribution in the overlying Al film.
Scanning electron microscopy study of seeded recrystallization of silicon-on-insulator layers with either polycrystalline or epitaxially deposited silicon in the seed windows
Authors: Smith D. A. , McMahon R. A. , Ahmed H. , Barfoot K. M. , Peters T. B. , Hopper G. F. , Godfrey D. J.
Published: July 2002

Silicon-on-insulator layers have been produced under conditions which are compatible with three-dimensional device integration. The layers were formed by zone melting recrystallization of two types of seeded silicon films in a dual electron beam system. High-resolution scanning electron microscopy was used to observe the starting materials and the stages of recrystallization from unseeded regrowth through seeded regrowth to under oxide melting. With the standard structure, which has an overall layer of polycrystalline silicon, good seeding requires melting into the bulk. However, when the silicon is deposited under conditions which give epitaxial growth in the seed windows, seeded recrystallization does not require melting in the substrate or even across the complete width of the window. A study of the silicon mass flow for the various stages is presented and the processing conditions for the minimum thickness variation of the silicon film are reported.
Theory of potential distributions in abrupt heterojunction crystalline semiconductor devices: Treatment of Schottky barriers and rectifiers
Authors: Mohammad S. Noor
Published: July 2002

A theoretical method for potential distribution in abrupt heterojunctions (HJs) made of uniformly doped degenerate semiconductors has been developed. The method reduces automatically to that in HJs from nondegenerate semiconductors in the limits of low carrier concentrations. For the development of the method the rigid band approximation of degenerate semiconductors has been considered to be valid. The transport equations of Marshak and Van Vliet [Solid-State Electron. 21, 417 (1978)] and an analytical approximation for the Fermi–Dirac

integral of order half by the present author [Solid-State Electron. 30, 713 (1987)] have been employed for the formulation. The average of the scattered experimental data for band-gap narrowing of n-Si, n-Ge, p-GaAs, and n-InP have been fitted to the same form as that for the Fermi–Dirac integral of order 1/2 to ease this formulation. Local electrostatic field and local electrostatic potentials obtained from the formulation reduce to those of Chatterjee and Marshak [Solid-State Electron. 24, 1111 (1981)], Cserveny [Int. J. Electron. 25, 65 (1968)], and Kroemer [J. Appl. Phys. 52, 873 (1981)] under special conditions. It is noted that band-gap narrowing and consideration of Fermi–Dirac statistics represent opposite effects for effective intrinsic carrier concentration and local electrostatic field. At some critical concentration belonging to the degenerate limit of a semiconductor, these two effects cancel the influence of each other on effective intrinsic carrier concentration of the semiconductor and on transition region properties of an HJ. Below this critical concentration, band-gap narrowing rather than a consideration of Fermi–Dirac statistics dominantly influences the device properties. However, above this critical concentration, consideration of Fermi–Dirac statistics dominates over the other. Applications of electrostatic field and electrostatic potential to isotype and anisotype HJs have been discussed. On the basis of present formulas a general form for potential distribution in Schottky barriers has been derived. The relation reduces to that of Gummel and Scarfetter [J. Appl. Phys. 38, 2148 (1967)] under special conditions. Theoretical reasons underlying the lack of rectification in various n-N HJs have been analyzed. In light of this analysis, a theoretical model in terms of many-body electron-electron and electron-donor interactions, and in terms of lowering of band edge in the vicinity of transition region, has been proposed. Numerical results obtained from this model for n-GaAs agree remarkably with observations from experimental measurements.
Ga0.5In0.5P/GaAs interfaces by organometallic vapor-phase epitaxy
Authors: Bour D. P. , Shealy J. R. , McKernan S.
Published: July 2002

Organometallic vapor phase epitaxial growth of most III–V compounds is normally performed under group-V-rich conditions, making it difficult to form an abrupt interface during a change of group V species. The Ga0.5In0.5P/GaAs interface is of interest because it offers a potential advantage over AlGaAs/GaAs selectively doped structures by reducing the deep-level donor problem. In this communication, formation of the Ga0.5In0.5P/GaAs interface during low-pressure organometallic vapor phase epitaxial growth is studied by comparing a series of three superlattices grown using different interface formation techniques. Continuous growth, growth stop under group V gas, and growth stop followed by a purge of all reactants are analyzed by Raman scattering, transmission electron microscopy (TEM), and 4-K photoluminescence. All superlattices show good TEM contrast between layers. The growth stop is found to reduce both P and In intermixing into the GaAs layers, relative to the continuously grown superlattice. The purging step further reduces In intermixing, but also results in decomposition of the Ga0.5In0.5P layers, which increases P carryover into the GaAs layers.
Interactions between interstitial atoms in silicon: Arsenic-argon-boron and boron-argon-phosphorus
Authors: Aronowitz S.
Published: July 2002

Experiments were performed that examined the behavior of overlapping populations of two triplet combinations of implanted dopants in silicon: arsenic-argon-boron and boron-argon-phosphorus. It was found that the chemical profile and electrical activity of arsenic could be adjusted practically at will. Anomalous behavior was observed with boron. Similar control was displayed with boron and phosphorus when argon was present. The experimental results are both consistent with and supportive of calculations on a model silicon lattice that predict complex formation; arrangements of these triplets in close proximity are more stable energetically than when they are sufficiently separated that interactions are minimal.
A novel heteroepitaxy method of Ge films on CaF2 by electron beam exposure
Authors: Kanemaru Seigo , Ishiwara Hiroshi , Furukawa Seijiro
Published: July 2002

A novel heteroepitaxy method of Ge films on CaF2/Si(111) structures is presented, in which two successive processes of electron beam (e-beam) exposure and predeposition of thin Ge layers at room temperature are done prior to the growth of thick Ge films at elevated temperatures. It was found in the e-beam exposed region that the island growth of the predeposited Ge layer was prevented and the surface morphology and crystalline quality of the Ge overlayer grown at 600  °C were dramatically improved. These results were virtually independent of the sequence of the predeposition and exposure processes. From discussion on the growth mechanism of this method, a most plausible model that e-beam dissociates the surface composition of CaF2 and improves the wettability between Ge and CaF2 is proposed.
Deep-level analysis in Te-doped GaAs0.62P0.38
Authors: Kaniewska M. , Kaniewski J.
Published: July 2002

Deep-level transient spectroscopy and photocapacitance techniques have been used to study the features of the main electron trap, with thermal activation energy equal to ΔEB=0.39 eV, present in Te-doped GaAs0.62P0.38, obtained by vapor-phase epitaxy. Nonexponential behavior of this trap in thermal emission and capture has been interpreted using a model based on the alloy broadening effect. Good agreement of the deep-level parameters determined from the emission and capture data has been obtained, and additionally confirmed by results of independent measurements of the transition region width. The influence of this level on the luminous intensity of light emitting diodes suggests that it can be an effective nonradiative recombination center.
Breakdown mechanisms of thermally grown silicon dioxide at high electric fields
Authors: Klein N.
Published: July 2002

Examination of breakdown observations in oxides roughly thicker than 10 nm shows that the impact ionization-recombination (IIR) model interprets fast breakdowns on constant voltage tests by the growth of positive charge at the cathode at fields larger than a critical field Fr . Breakdown events of longer duration at fields slightly below the critical field can be observed on constant current tests. Such breakdown cannot be explained by the IIR model. It is suggested that it results from changes produced in the oxide prior to the breakdown by the generation of a large density of electron trap states of the order of 1019 cm−3. The mechanism of such breakdowns has not been identified yet. Resonant tunneling via trap states near the cathode, or degradation of the injection barrier, or transition of the oxide from an insulating to a conducting state may be processes producing breakdown in constant current tests.
A mass spectrometric study of small aluminum clusters formed by a single-state free-jet expansion
Authors: Hawley J. H. , Ficalora P. J.
Published: July 2002

Small Aln clusters (n≤6) formed in a free-jet expansion were observed. Species of n>2 have never been observed above a Knudsen cell by mass spectrometry. Since the pressure of the Al vapor in the crucible was found to be subsaturated, a heterogeneous nucleation mechanism is proposed.
Influence of the calcining temperature on the superconducting transition and critical current of Y-Ba-Cu-oxide compound
Authors: Lee H. K. , Kwon H. C. , Kim I. S. , Park J. C.
Published: July 2002

Superconducting transition and critical current of a Y-Ba-Cu-oxide compound prepared by ceramic technique have been studied for the samples which have the same nominal composition and sintering conditions, while systematically varying the calcining temperature from 850 to 1000 °C. It was observed that the shape of the superconducting transition in resistivity measurement markedly depends on the calcining temperature. All samples showed metallic behavior in normal state and samples which have lower resistivity showed higher critical current density. The resistivity just above onset temperature decreased with increasing the calcining temperature up to 950 °C, but above 975 °C the opposite behavior was observed. This behavior was discussed in connection with x-ray diffraction patterns of the samples.
Optical phase conjugation in narrow direct-gap semiconductors
Authors: Sen P. K. , Sen P.
Published: July 2002

Optical phase conjugation processes via degenerate four-wave mixing mechanisms have been investigated analytically in narrow direct-gap semiconductors duly irradiated by low-power near resonant lasers. The role of linear absorption phenomena is introduced intrinsically into the electromagnetic equations through complex first-order optical susceptibility of the crystal. A coherent radiation-exciton interaction model is employed to obtain the intensity-dependent crystal optical susceptibility. The band-to-band optical transitions into the true continuum above the fundamental absorption edge are considered. We have estimated qualitatively the conversion efficiency η for important III-V crystals like InSb, GaSb, and GaAs. The nature of variation of η with respect to detuning as well as excitation intensity are found to be in very good agreement with the experimental observations in ammonia, and in semiconductors like Si, Ge, and Hg1−xCdxTe. The analyses also reveal that large η can be derived by using submicrometer sized crystals. InSb is established as the most promising III-V semiconductor for optical phase conjugation device technology at very low cw resonant laser irradiation.
Thermal degradation effects in InP
Authors: Sartorius B. , Schlak M. , Rosenzweig M. , Pärschke K.
Published: July 2002

Thermal degradation in InP has been regarded to be equivalent to surface deformation. By means of luminescence microscopy we discovered a much larger scale of degradation effects. Crystallographic defects of several geometrical characteristics have been observed although the surfaces seemed to be perfectly smooth. The standard methods of protection against degradation used in liquid phase epitaxy turned out to be unreliable concerning the invisible degradation effects. We propose a model which describes the evolution of degradation starting with invisible crystallographic defects. An extreme loss of phosphorus concentrated around dislocations causes local melting representing the final and visible stage of degradation. We suppose that P vacancies which have never been noticed before are responsible for inhomogeneities affecting processing and the reliability of optoelectronic devices.
Excess gate-leakage current of InGaAs junction field-effect transistors
Authors: Ohnaka K. , Shibata J.
Published: July 2002

The excess gate-leakage current of InGaAs junction field-effect transistors (JFET), which is about 106 times that of the Si JFET, is attributed to hole-electron-pair generation produced by impact ionization of the high electric field in the JFET channel. The impact-ionization rate α is estimated from the excess gate-leakage current of the InGaAs JFET. At 77 K, the impact-ionization rate is about one-half compared with that of 300 K, and the difference between these two temperatures agrees with the calculated polar optical-phonon scattering rate. The excess gate-leakage current can be reduced by a factor of 7 by the introduction of a thin n-InP layer at the interface between the InGaAs channel and semi-insulating InP substrate.
Interaction of low-energy electrons with the electron beam resist poly(butene-1-sulfone)
Authors: Ashley J. C.
Published: July 2002

An insulator model, with parameters fixed by fits to optical data, is used to determine the energy-loss function describing the response of valence electrons in poly(butene-1-sulfone). Generalized oscillator strengths describe the response of the inner shell electrons. This theoretical information is employed to calculate inelastic mean free paths and stopping powers in poly(butene-1-sulfone) for electrons with energies ≤10 keV.
Properties of Pb1−xEuxTe films prepared by hot-wall epitaxy
Authors: Ishida A. , Matsuura S. , Mizuno M. , Sase Y. , Fujiyasu H.
Published: July 2002

Pb1−xEuxTe films were prepared by hot-wall epitaxy, evaporating PbTe, Eu, and Te from the same quartz-tube furnace onto BaF2 (111) substrates. Good crystalline films were obtained by preparing the films in excess Te vapor. Dependence of the energy band gaps and lattice constants of the Pb1−x EuxTe films on the EuTe content was measured through the optical absorption, x-ray diffraction, and x-ray microanalysis. Temperature dependence of the energy band gap was also measured. Single-phase films with Eg ≤0.83 eV and x≤0.26 were obtained. Derivatives of the band gap with respect to the EuTe content x(dEg/dx) were 3.5 eV at 300 K and 4.5 eV at 77 K up to x=0.06, and the value decreased for x>0.06. Electrical properties of the Pb1−xEuxTe films were also measured. Bi and Tl were used as donor and acceptor impurities, respectively. High carrier concentration (n, p≥1018 cm−3) and low resistivity films were obtained up to x=0.06 (Eg =0.55 eV).
The electrical resistance of Cr films
Authors: Lourens J. A. J. , Arajs S. , Helbig H. F. , Cheriet L. , Mehanna El-Sayed A.
Published: July 2002

Measurements of the thickness dependence of the electrical resistance of two very thin Cr films deposited at substrate temperatures of 385 and 360 °C and pressures of 4×10−7 and 10−6 Torr are reported. Preliminary measurements of the thickness dependence of the Néel temperature (TN) of the film deposited at 360 °C at thicknesses ≥10 nm are also presented. In these two films the resistance in the thickness region 2≤d≤7.5 nm can be very well described by R∝[(d/dc)−1 ]−t with dc equal to 1.64±0.20 and 1.03±0.20 nm, respectively, and t=1.34±0.11. The Néel temperatures show a turning point around 14 nm in agreement with the known thickness dependence of the stress. dTN/dSt has been found to be ∼100 K/kbar where St is the internal tensile stress in the film.
Electrical quality of low-temperature (Tdep≤800 °C) epitaxial silicon: The effect of deposition temperature
Authors: Burger W. R. , Reif R.
Published: July 2002

The results of an investigation of the effects of temperature, during both the in situ argon sputter clean and the deposition, on the electrical properties of low-temperature (Tdep≤800 °C) expitaxial silicon films are presented. The data indicate that the electrical quality does not depend on the sputter temperature, at least for temperatures in the 750–800 °C temperature range. The electrical quality is a strong function of the deposition temperature, however. Epitaxial layers deposited at 800 °C have electrical characteristics comparable or superior to bulk silicon. However, reducing the deposition temperature to 750 °C results in a significant degradation in the film electrical properties. The electrical quality is stable to further annealing for temperatures in the 750–950 °C range. The mechanism responsible for the dependence of the film electrical quality on the deposition temperature is described.
Photoluminescence study on the interface of a GaAs/AlxGa1−xAs heterostructure grown by metalorganic chemical vapor deposition
Authors: Akimoto Katsuhiro , Tamamura Koshi , Ogawa Junko , Mori Yoshifumi , Kojima Chiaki
Published: July 2002

The interface of a GaAs/AlxGa1−xAs heterostructure grown by metalorganic chemical vapor deposition has been studied by photoluminescence spectroscopy by using a step-etching technique. Luminescence peaks associated with vacancy complexes emitted from both GaAs and AlxGa1−xAs layers were observed, and these peaks were remarkably intense on both sides of the GaAs/AlxGa1−xAs interface region. This result can be explained by the accumulation of vacancies in the interface region. The cause of this vacancy accumulation at the interface is discussed.
Photoluminescence study on local atomic arrangements in InGaP and GaAsP alloys using Co deep impurity
Authors: Shirakata S. , Nishino T. , Hamakawa Y.
Published: July 2002

Low-temperature photoluminescence (PL) related to Co deep impurities in In1−x GaxP (0.74≤x≤1) and GaAs1−x Px (0.65≤x≤1) alloys has been studied. Broad PL bands with some structures have been observed in the 2.3-μm region for both the alloys. The results of time-resolved PL measurements have shown that the PL bands are due to the intracenter transitions 4T2(4F)→4A2(4F) in a substitutional Co2+ ion in the zinc-blende lattices. These Co-related PL spectra have been analyzed in terms of the local atomic arrangements around the Co luminescent center. As a result, it has been found that these Co-related PL spectra in InGaP and GaAsP alloys are composed of several bands closely related to the local arrangement of atoms around the Co center.
The effect of radiative heat lost on laser material damage
Authors: Chan C. L. , Mazumder J.
Published: July 2002

A one-dimensional steady-state model describing the damage caused by materials removal vaporization and liquid expulsion due to laser material interaction are presented. The effect of the radiative heat loss is investigated. Gray and diffusive radiative heat loss is assumed. It is found that the radiation plays an insignificant role in determining the surface temperature, rate of materials removal both in vapor and liquid form, and the exit plane Mach number. Results with radiative heat loss are obtained and compared to those without radiative heat loss.
Studies of boron on the arsenic site in electron-irradiated GaAs
Authors: Moore W. J. , Hawkins R. L.
Published: July 2002

The introduction of boron on the arsenic site in gallium arsenide, as monitored by the strength of its local vibrational modes (LVM) at 601.7 and 628.3 cm−1, has been observed as a function of 2 MeV electron fluence. Simultaneous monitoring of the strength of the 1S-2P electronic transitions of the neutral shallow acceptors and of the neutral 78 meV acceptor and its singly ionized 203 meV level provides an accurate knowledge of the position of the Fermi level throughout most of the irradiation sequence. The results are inconsistent with previous models for the formation of boron on the arsenic site. We propose a model based on enhanced boron diffusion when the Fermi level lies above 78 meV. A compensation rate for electron irradiation, an introduction rate for the BAs center, and an infrared cross section for the BAs LVM are determined.
Reverse annealing and low-temperature diffusion of boron in boron-implanted silicon
Authors: Huang J. , Fan D. , Jaccodine R. J.
Published: July 2002

Low-temperature annealing (525 °C–800 °C) of 50-keV, 1×1015-cm−2, boron-implanted silicon was studied with the emphasis on the mechanisms responsible for the reverse annealing as well as the enhanced diffusion of the implanted boron. The electrical properties of boron-implanted silicon were analyzed with Hall measurement. Boron depth profiles were also measured using secondary-ion mass spectrometry. These results were then correlated with cross-section transmission electron microscopy studies and deep-level transient spectroscopy studies. It is shown that reverse annealing is possibly due to boron-silicon interstitial complexes, rather than the formation of the commonly observed rodlike defects or precipitates. On the other hand, the enhanced tail diffusion of boron is found to be most likely associated with self-interstitials. Consequently, vacancy trapping of the silicon interstitial component may account for both the charge carrier recovery and the ending of the enhanced tail diffusion of implanted boron.
Field effects in semiconductor double-injection devices
Authors: Stawski R. , Ashley K. L.
Published: July 2002

An analysis of high-field effects in semiconductor double-injection devices is presented. Exact and approximate numerical solutions are developed, which include the electric field dependence of carrier mobilities and capture coefficients. The model assumes that the current is entirely field driven and that charge neutrality applies. The current-voltage characteristics are obtained in the square-law and threshold voltage regions. A comparison is made between the present analysis and a previous, more approximate, analytical formulation which was similarly based on a modification of the square law. The validity of approximations made in the development of the models is discussed. The conditions, under which high-field effects have a significant influence on the current-voltage characteristics, are determined.
Distributed Bragg reflector Pb1−xSnxSe/Pb1−x−yEuySnxSe diode lasers with a broad single-mode tuning range
Authors: Shani Y. , Rosman R. , Katzir A. , Norton P. , Tacke M. , Preier H. M.
Published: July 2002

Distributed Bragg reflector Pb1−xSnxSe/Pb1−x−yEuySnxSe double heterostructure stripe geometry diode lasers were fabricated using molecular-beam epitaxy. Single-mode cw operation at about 7.8 μm was obtained for heat-sink temperatures in the range 25–75 K. the single-mode continuous tuning range was 10 cm−1. Tuning the diodes via the injection current, a range of 24 cm−1 was completely covered with single-mode emission. The reason for this wide tuning range was mode hopping to lower frequencies rather than the usual hopping to higher frequencies.
Coupled plasmon–LO-phonon excitations in semiconductor superlattices
Authors: Kushwaha Manvir S.
Published: July 2002

The intrasubband collective excitations in semiconductor superlattice systems have been investigated within a simple model theory with the use of a two-dimensional δ function for the charge-density profiles. In particular, the coupling of the plasmons to the LO (longitudinal optical) phonons is accounted for. The coupling effect modifies the plasmon dispersion and generates additional (bulk and surface) modes above ωL (LO-phonon frequency). This can give rise to some interesting observable effects, particularly because the interaction effects on the physical properties are usually enhanced in systems of lower dimensionality.
Generation of spatial subharmonics by two-wave mixing in a nonlinear photorefractive medium
Authors: Mallick S. , Imbert B. , Ducollet H. , Herriau J. P. , Huignard J. P.
Published: July 2002

Self-generation of spatial subharmonics when two coherent, almost collinear, pump beams propagate in a nonlinear photorefractive crystal of Bi12 SiO20, is reported. The intensity of the self-generated light beam at the half-angle between the two pumps is as high as 40% of the pump beam intensity. This phenomenon is probably a spatial analog of the temporal subharmonics obtained in a cavity containing a nonlinear medium. Application of the subharmonic of half-spatial frequency to collinear Bragg diffraction of a near infrared beam is demonstrated.
Spectral shape analysis of selective pair luminescence in GaAs
Authors: Iino Takayuki , Tajima Michio , Ishida Koichi
Published: July 2002

We have analyzed the spectral shape of the selective pair luminescence (SPL) in undoped semi-insulating Czochralski grown GaAs. The shape of the SPL spectra, consisting of sharp peaks and a broadband, depends strongly on the excitation photon energy, the excitation intensity, and the acceptor concentrations. The characteristic spectral variations are successfully explained by a simple model in which the probability density function of separation for photoexcited donor acceptor pairs are calculated under the various experimental conditions. On the basis of the theoretical calculation the improvement of the higher and lower detection limits for acceptor impurities is demonstrated.
High-resolution transmission electron microscopy and x-ray study of colloidal cobalt ferrite particles
Authors: Nunes Anthony C. , Hall Ernest L. , Berkowitz Ami E.
Published: July 2002

High-resolution transmission electron micrographs, including high-resolution structure images, and x-ray powder diffraction patterns have been observed of oleic acid-coated colloidal particles of cobalt ferrite. Particles were prepared by grinding. Particle defect content, size distribution and aspect ratio, and crystallite size and lattice constant were determined. Particles are irregularly shaped of log normally distributed dimension peaking near 5 nm and with an average aspect ratio of 1.3. They appear to be single crystals with few volume defects. Their lattice constant (0.8393±0.0003 nm) is indistinguishable from that of the bulk material. This supports earlier assertions that the anomalous magnetic behavior of these particles originates at their surface or the ferrite-surfactant interface.
An analysis of the coefficients of a perturbed nonlinear Schrödinger equation for femtosecond behavior in an optical waveguide
Authors: Potasek M. J.
Published: July 2002

An analysis is made for higher-order terms in an extended nonlinear Schrödinger equation. The analysis is in reasonable agreement with recent experiments involving femtosecond pulses in optical fibers.
Photoemission optogalvanic spectroscopy: An i
n s
i
t
u method for plasma electrode surface characterization
Authors: Downey S. W. , Mitchell A. , Gottscho R. A.
Published: July 2002

Photoemission optogalvanic spectroscopy (POGS) is shown to be useful for plasma electrode surface characterization. A pulsed ultraviolet laser is used to induce photoemission from the electrode surface in a radio frequency plasma reactor and the increase in plasma current is detected. The photoemission process is first characterized in vacuum and then compared to that in several plasma gases using Al and Si electrodes. In vacuum, the laser-induced photoemission signal is generally consistent with space-charge-limited current. When below the space-charge limit, the magnitude of the photoemission signal depends upon laser wavelength and power, surface composition, and film thickness. The removal of SiO2 from Si and the contamination of Al in fluorine-containing plasmas is monitored using this technique. A large increase in the POGS signal is observed as the oxide is removed from Si or when a fluorinated Al surface is exposed to an O2 plasma. The POGS signal decreases with fluorine exposure with both Al and Si. We are continuing to explore the utility of this technique as an endpoint detector and in situ contamination monitor.