bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of electromigration-induced mass divergences in multilayer interconnects by energy-dispersive x-ray spectroscopy
Authors: Lee C.-C. , Machlin E. S. , Rathore H.
Published: July 2002

A nondestructive technique, based on energy-dispersive x-ray spectroscopy, was applied to characterize mass divergences in multilayer interconnects. The technique was used to reveal less than 0.5-μm-diam subsurface voids, precipitates, local changes in thickness of subsurface conducting layer, electromigration-induced mass divergences at conjugate mass source and sink in both the Al-Cu conducting layer and intermetallic compound overlayer, and a thin, hairline crack in the surface layer that is hardly visible in scanning electron microscopy.
Random successive nucleation model for simulating multiple fractal formation in a-Ge/Au bilayer films
Authors: Wang Dai-mu , Zhao Ya-dun , Wu Zi-qin
Published: July 2002

Multiple fractal formation in a-Ge/Au bilayer films has been simulated by use of the random successive nucleation model in which cluster is grown by the random nucleation generation after generation and no long-range diffusion is necessary. The random successive nucleation process is stimulated by the local temperature rise after releasing the latent heat during crystallization, if the short-range effect from the nearby nuclei related to the interdiffusion and the strain energy release are lower than a certain level.
Epitaxial and interface properties of InAs/InGaSb multilayered structures
Authors: Zborowski J. T. , Fan W. C. , Golding T. D. , Vigliante A. , Chow P. C. , Shih H. D. , Anthony J. M.
Published: July 2002

We have used the technique of molecular beam epitaxy to grow InAs on GaSb, GaSb on InAs, and InAs/InxGa1−xSb (0≤x≤0.4) multilayered structures and have performed a detailed investigation of the layers and resultant interfaces. The structures were grown on (100) oriented GaSb or GaAs substrates. Combined reflection high energy electron diffraction, x-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) studies indicate that Sb is persistently present on the InAs growth surface. XPS and AES analysis of InAs/GaSb heterojunctions indicates no compound formation at either the InAs/GaSb or GaSb/InAs interface. Secondary ion mass spectroscopy (SIMS) and XPS extinction profiles reveal the presence of approximately 5–10% As in the nominally pure GaSb layers. Analysis of InAs/GaSb/GaSb (100) structures by SIMS indicates that the As is incorporated during growth. The multilayer structures have been characterized by double crystal x-ray diffraction and the data has been modeled using kinematic formulations. We find that the experimental data is fitted by assuming atomically abrupt composition changes across the interfaces.
Effects of amorphous titanium silicide on subsequently formed crystalline compound prepared by two-step thermal process
Authors: Nam H. G. , Chung I. , Bene R. W.
Published: July 2002

Titanium silicides prepared by codeposition at intermediate substrate temperatures with subsequent high temperature annealing were studied. It was found that coevaporation with Si/Ti ratio of 2.5 at the substrate temperature (Ts) of 120 °C results in the formation of an amorphous phase. On the other hand, samples prepared at Ts of 300 °C resulted in crystalline TiSi2(C49). However, the amorphous phase was still present at the silicide/substrate interface. Considerable grain growth was observed to start at the silicide/Si interface even though the interfacial amorphous phase was the last to crystallize. It was suggested that Si diffusion is much more rapid through the amorphous silicide than crystalline TiSi2. This difference in kinetics was shown successful in explaining the dependency of the film properties of annealed samples on the structure of the product of the initial reaction.
Propagation of several waves in a nonlinear medium displaying an optical activity: Application to four-wave mixing in Bi12(Ge;Si)O20 crystals
Authors: Sylla M. , Nguyen P. X. , Rouede D. , Rivoire G.
Published: July 2002

A set of coupled-wave equations relative to degenerate four-wave mixing is derived and solved for optically active Bi12(Ge;Si)O20 cubic crystals. Nonlinear absorption is taken into account. Circular polarized waves are used. The calculated results concerning phase conjugation efficiency are compared to the experimental ones.
Electronic surface state (Tamm state) under electric field in semiconductor superlattices
Authors: Huang F. Y. , Morkoç H.
Published: July 2002

The tunneling resonance technique is used to study the electronic surface state (Tamm state) [Phys. Rev. Lett. 64, 2555 (1990)] under external electric field in semiconductor superlattices. The localization characteristics of the confined surface states depend on the direction and strength of the applied electric field. In the weak-field regime the surface states behave delocalized due to the distortion of the periodic medium by the applied field. The calculations presented can provide eigenenergy, wave function, and lifetime for the quasibound surface states, which are related directly to the optical properties of surface states under an electric field.
Elastic scattering of electrons and positrons by bound phosphorus, indium, and antimony atoms
Authors: Öztürk N. , Williamson W. , Antolak A. J.
Published: July 2002

Elastic differential and total cross sections of electrons and positrons scattered by bound phosphorus, indium, and antimony atoms have been calculated using the method of partial waves. The interaction potential consists of an electrostatic potential, a Buckingham-type polarization potential, and, in case of electron impact, the Mittleman–Watson exchange potential. The incident energies range from a few eV to 10 keV. A parameterization of the computed partial-wave total cross sections in terms of the screened Rutherford total cross section is presented.
Organometallic vapor-phase epitaxy of Hg1−xCdxTe on {211}-oriented substrates
Authors: Bevan M. J. , Doyle N. J. , Temofonte T. A.
Published: July 2002

Hg1−xCdxTe layers have been grown by organometallic vapor-phase epitaxy at 350 °C on {211}-oriented substrates, including CdTe, (CdZn)Te, and GaAs, with the emphasis on lattice matching for improved structural quality films. Characterization included optical microscopy, x-ray diffraction, Fourier transform infrared spectroscopy, and detailed field and temperature Hall measurements. The (211)B-oriented epilayers combine the structural quality of (100) including the absence of twinning with the flat topography of (111)B-oriented films. The crystal quality improved to that of the substrate with the closer lattice matching of (CdZn)Te, the mismatch taken up with lattice inclination on the high step density surface. A tighter control of the substrates’ Zn content than exists at present is required for ultimate lattice matching to Hg0.2Cd0.8Te. As-grown Hg1−xCdxTe on (CdZn)Te (211)B substrates is p type with carrier levels in the 1–6 × 1016-cm−3 range for compositions greater than 0.20 and with no indication of mixed conduction behavior due to inversion layers or growth-related surface or interface layers.
Beam divergence effects on nonlinear frequency mixing
Authors: Wong S. K. , Fournier G. , Mathieu P. , Pace P.
Published: July 2002

The effects of the beam divergence of the input pump laser beams on the nonlinear frequency mixing process in a dielectric medium is discussed. The divergent laser beams have finite angular spreads so that all of the interactions between the two input beams can never satisfy the phase-matching condition exactly. A numerical model is developed to investigate the effects of input beam divergence on conversion efficiency. The angular spread of each of the input beams is represented by a set of plane waves having a distribution of propagation directions. Each of the plane-wave components from one input beam is allowed to interact with all the plane-wave components of the second input beam. This model is applicable to processes such as sum frequency generation, difference frequency generation, and optical parametric amplification. Second-harmonic generations as a special case of sum frequency generation is used as an example in the numerical studies. Results indicate that the conversion efficiency is dependent on the amount of beam divergence, the input intensity, and the length of the nonlinear medium. These parameters must be optimized with respect to one another to maximize the conversion. The optimization is especially critical in high-power systems where high conversion efficiency is sought.
Determination of the polarization-depth distribution in poled ferroelectric ceramics using thermal and pressure pulse techniques
Authors: De Reggi Aimé S. , Dickens Brian , Ditchi Thierry , Alquié Claude , Lewiner Jacques , Lloyd Isabel K.
Published: July 2002

This paper is the first of a series with the common theme of comparing thermal and acoustic pulse methods of measuring charge or polarization profiles across the thickness of slab-shaped samples that are representative of different types of materials. In this paper, thermal and pressure pulse measurements are reported of the polarization distribution in poled, ferroelectric ceramic samples. The results obtained from both methods are complementary so that there is a benefit to using both. The results also demonstrate that large deviations from uniform polarization can be induced by processing differences.
The negative differential resistance behavior in delta-doped GaAs structure due to resonant interband tunneling
Authors: Houng M. P. , Wang Y. H. , Chen H. H. , Wei H. C. , Lee Y. H.
Published: July 2002

A GaAs delta-doped tunneling diode having a δn+-i-δp+-i-δn+ structure is investigated. A negative differential resistance behavior with peak-to-valley ratio as high as 3.1 and a peak current density of 3 kA/cm2 is exhibited when the device is operated at room temperature. It becomes resistor-like at the temperature of 77 K. Theoretical analysis, based on envelope wave function approximation, indicates that the resonant interband tunneling process is responsible for room-temperature characteristics, while the band-gap widening effect is responsible for low-temperature behavior. Furthermore, the dependence of device performance on such structure parameters as doping level, and the physical dimension of the delta-doped region, etc., is discussed, and found to agree well with experimental results.
Grain-size distribution in ion-irradiated amorphous Si films on glass substrates
Authors: Oyoshi Keiji , Yamaoka Tomonori , Tagami Takashi , Arima Yasunori , Tanaka Shuhei
Published: July 2002

Amorphous Si films containing crystal seeds can be converted to a polycrystal by an ion beam with heating at 350 °C on silica glass substrates, and the density of the crystal grain is almost the same as that of the initial seed. However, the size and density of the crystal seed decrease when the ion irradiation is performed without external heating. The average grain size in the completely crystallized film can be controlled by decreasing the crystal seed density before crystallization. The growth process of crystal grains (average grain diameter R and standard deviation σR) is reported and the gradient ΔσR/ΔR is estimated to be about 0.15. A model calculation is performed to estimate the gradient on the assumption that the growth rate is governed by the plane (111) crystallization and the calculated value is 0.05.
Smectic layer orientation during switching of surface stabilized cells filled with fluorinated ferroelectric liquid crystals
Authors: Chen Li , Kumar Satyendra , Tristani-Kendra Miguel , Janulis Eugene P.
Published: July 2002

X-ray diffraction study of smectic-C* layer orientation in surface stabilized cells filled with fluorinated ferroelectric liquid crystals show chevron layer structure. The chevrons remain unperturbed up to a field of 12.5 × 106 V/m while optical observations suggest uniform switching at low fields, and nucleation and growth mediated switching at high-field strengths.
Plasma cleaned Si analyzed in situ by x-ray photoelectron spectroscopy, secondary ion mass spectrometry, and actinometry
Authors: Delfino M. , Salimian S. , Hodul D. , Ellingboe A. , Tsai W.
Published: July 2002

Silicon surfaces are cleaned in an electron cyclotron resonance excited hydrogen plasma and characterized by in situ x-ray photoelectron spectroscopy and in situ static secondary ion-mass spectrometry. Emission spectroscopy and actinometry are used to characterize the hydrogen plasma. Exposure to the plasma for 3 to 4 minutes without applying heat or bias to the substrate completely removes the native silicon oxide resulting in a hydrogen terminated surface that is resistant to reoxidation. Adventitious hydrocarbon, when present on the surface, is also completely removed by the plasma. A shift in the isotope ratios of silicon suggests that a clean 〈100〉 silicon surface is monohydride terminated, whereas a 〈111〉 silicon surface appears largely dihydride terminated. A depth profile of the silicon isotope ratios shows a temporal instability, which with the assignment of a H 1s state in the valence-band spectra provides evidence that the hydrogen is concentrated at the surface and has not diffused deep into the silicon lattice. The oxygen removal rate has the following characteristics: two distinct microwave operating regimes separated by a discontinuity in power around 600 W; a singularity corresponding to rapid oxygen removal at 2.5 mTorr; an abrupt and near monotonic decrease in oxygen removal above 14 mTorr; and an invariance of the removal rate to ion-energy from about 10 to 100 eV. The density of hydrogen excited species and the ground state hydrogen atom density are correlated with the oxygen removal rate under all conditions except high pressure, where the density of hydrogen ions is low. This suggests an ion-induced etching mechanism whereby the native silicon oxide removal is enhanced with low-energy hydrogen ion bombardment.
Comparison of band structure calculations and photoluminescence experiments on HgTe/CdTe superlattices grown by molecular beam epitaxy
Authors: Kraus M. M. , Regnet M. M. , Becker C. R. , Bicknell-Tassius R. N. , Landwehr G.
Published: July 2002

We have grown HgTe/CdTe superlattices by molecular beam epitaxy; barrier thicknesses were in the range from 15 to 91 Å and the well thickness was maintained at a constant value of 30 Å. The infrared photoluminescence was investigated by means of Fourier transform infrared spectroscopy in the temperature range from 4.2 to 300 K. All superlattices showed pronounced photoluminescence at temperatures up to 300 K. To gain more detailed insight into the band structure of the HgTe/CdTe superlattices, band structure calculations were performed. The concept of the envelope function approximation was followed. Employing the transfer matrix method, the calculations were completed taking into account an eight band k⋅p model. An important parameter in these calculations is the natural valence band offset (VBO) between the well and barrier materials. As a general trend, the value for the direct gap decreases with increasing VBO. The experimentally determined energies of the band gap are in reasonable agreement with the values obtained by the theoretical calculations. A comparison between theory and experiment shows that the observed transition energies are closer to calculations employing a large offset (350 meV) as opposed to a small VBO (40 meV).
The effect of the laser mode structure on the sideband spectrum of stored ions
Authors: Lakkaraju H. S. , Walian P. J. , Schuessler H. A.
Published: July 2002

The optical absorption spectrum of ions oscillating in a three-dimensional harmonic trap is calculated for laser excitation. The effect of the mode structure of the laser beam employed, in particular the case of the TEM00 mode used in most experiments is considered. The spectrum contains many sidebands, besides the central transition frequency, generated by all combinations of the ion oscillation frequencies in the three orthogonal directions of motion, even when the laser is directed along the trap axis or is incident in the radial plane, and even when perfect symmetry of the trapping fields is assumed. It is shown that this coupling between the axial and radial frequencies is due to the Gaussian mode structure of the laser beam. In laser spectroscopy of ions trapped in a real radio frequency (rf) trap, energy transfer between the ion motional degrees of freedom is therefore caused by the mode structure of the laser beam and, as previously assumed, by asymmetries of the pseudopotential well and for more than one ion in the trap by ion space charge fields. The ion motion coupling due to the laser mode structure is of particular significance during the initial phases of laser cooling experiments when comparatively hot ions sample a distance comparable to the waist of the collimated laser beams and when this distance is of the order of the optical wavelength.
Site transfer of Si in GaAs after heavy ion MeV implantation and annealing
Authors: Moore F. G. , Klein P. B. , Dietrich H. B.
Published: July 2002

The electrical and optical properties of n-type and p-type epitaxial GaAs layers have been studied after MeV implantation of heavy (Xe and Er) ions. All implanted layers were highly resistive immediately after implantation. Annealing to only moderate temperature (725 °C) recovered the as-grown electrical properties of beryllium-doped p-type layers. However, after annealing silicon-doped n-type layers, we observe a dramatic change from the as-grown carrier profiles. After anneal, the silicon-doped, n-type layers became conductive but the carrier profiles were markedly different from the as-grown material. A significant thickness of the implanted portion of the epitaxial layers shows distinct p-type conductivity after annealing. We have correlated this p-type activity with a transfer of silicon from the gallium sublattice (SiGa) to the arsenic sublattice (SiAs). The site transfer is viewed to result from the altered thermodynamics governing site occupancy during annealing of Si in GaAs under the unique damage conditions produced by heavy ion MeV implantation. Additionally, the observed thermal stability of the site transfer process above 875 °C may have implications for implantation isolation techniques.
Diffusion barrier properties of TiN films for submicron silicon bipolar technologies
Authors: Kobeda E. , Warnock J. D. , Gambino J. P. , Brodsky S. B. , Cunningham B. , Basavaiah S.
Published: July 2002

We have studied the properties of reactively sputtered TiN films used as diffusion barriers for Al-Cu metallization in submicron bipolar transistors. Emitter-base diodes with shallow junctions were fabricated to monitor the integrity of the barrier via junction leakage measurements. Scanning and transmission electron microscopy were used to study the morphology and step coverage of these films, and also for barrier failure analysis. The effectiveness of the barrier depends on both the nominal thickness of the TiN layer and on the device dimensions. For thin TiN layers (∼47 nm), high junction leakage was observed on narrow emitters (0.5 μm) but not on wide emitters (5 μm). These observations highlight the reliability and yield concerns associated with the use of sputtered TiN films for deep submicron technologies. In some cases, low-temperature (500 °C) epitaxial alignment of the emitter polysilicon was observed, associated with Al penetration of the barrier. This indicates that the Al provides an enhancement of the tendency towards epitaxial alignment of the polysilicon grains. For thicker TiN layers (∼83 nm), low leakage was observed on both narrow and wide emitters, and no unusual epitaxial alignment was observed.
Observation and prediction of first phase formation in binary Cu-metal thin films
Authors: Li Jian , Strane J. W. , Russell S. W. , Hong S. Q. , Mayer J. W. , Marais T. K. , Theron C. C. , Pretorius R.
Published: July 2002

First phase formation has been determined in Cu binary thin film systems with Ti, Zr, Mg, Sb, Pd, and Pt using transmission electron microscopy and Rutherford backscattering spectrometry. CuTi, CuZr, CuMg2, Cu2Sb, Cu3Pd, and Cu3Pt are the first phases to form upon annealing the Cu/metal bilayers. The effective heat of formation model is used to predict first phase formation in 14 Cu/metal systems.
Temperature rise during silicon-on-glass recrystallization produced by ac magnetic fields
Authors: Hayama Hiroshi , Saito Takeshi
Published: July 2002

Studied here is the temperature rise in thin films during heating produced by ac magnetic fields. Eddy currents induced by ac magnetic fields in tantalum foils and silicon thin films are calculated for previously reported recrystallization equipment. Two kinds of transient temperature rise, produced by the power loss resulting from the eddy currents, are calculated on the basis of a one-dimensional variation of Fourier’s thermal equation. The first calculation, along the r axis of a cylindrical coordinate system centered at the equipment coil center, shows that temperature is strongly dependent on distance from the coil center. The calculation further suggests that tantalum can be successfully heated to over 1000 °C in a short time with the equipment, and that undoped silicon can be heated only when the effective initial temperature is over 500 °C. The second calculation along the z axis perpendicular to a SOG (silicon on glass) wafer surface, shows that undoped silicon thin film can be heated to over 500 °C in a short time when the Ta-foil/SOG-wafer gap is kept within a 0.1–1 mm range. Calculated temperature distributions agree well with those measured experimentally on Ta-foil surfaces. The results of these calculations contribute to an understanding of the recrystallization process and provide important suggestions for improving the SOG recrystallization produced by ac magnetic fields.
Evaluation of local vibrational mode absorption caused by carbon in GaAs
Authors: Saban S. B. , Blakemore J. S. , Nordquist P. E. R. , Henry R. L. , Gorman R. J.
Published: July 2002

Room temperature measurements are reported of the mid-infrared local vibrational mode (LVM) absorption caused by CAs acceptors in GaAs. A 30:1 range of carbon content was found among a group of 33 samples of melt-grown semi-insulating GaAs. The LVM absorption band area is compared with the dip ΔT this band makes in a transmittance spectral trace. The ratio (ΔT/t) of transmittance dip to sample thickness shows a useful correlation with the integrated LVM band area.
The lifetime of a surface plasma wave on a semi-infinite air/metal interface
Authors: Chang Keh-su , Chou Chien , Lee Chih-hung
Published: July 2002

The lifetime of a surface plasma wave (SPW) on a semi-infinite air/metal interface is calculated. The calculation is based on the assumption that SPW has a real frequency and a complex propagation constant. Thus the lifetime of the SPW can be calculated in a wide spectrum range from 0.1 to 10 μm. Two different metals (aluminum and silver) have been used separately as the media for generating the SPW. Within the spectrum of visible light, the lifetime of the SPW on the air/metal interface is in subpicoseconds.
Electronic properties of the hydrogen-carbon complex in crystalline silicon
Authors: Endrös A. L. , Krühler W. , Koch F.
Published: July 2002

The electronic properties of hydrogen in carbon-doped n-type silicon have been studied using deep-level transient spectroscopy. It is demonstrated that hydrogen (H) in the presence of substitutional carbon (C) forms an H-C complex with an energy level located ≊0.16 eV below the edge of the conduction band. The H-C complex is a deep donor which is only stable in the positively charged state and dissociates after capture of free electrons for temperatures T≥300 K. The H-C dissociation kinetics yield an activation energy of 0.73 eV.
Correlation between hole carrier densities and a Raman spectrum in polycrystalline silicon doped with boron
Authors: Nakano Noboru , Marville Louis , Reif Rafael
Published: July 2002

Hole carrier densities and Raman spectra were measured in polycrystalline silicon doped with boron. After increasing the annealing temperature and the dopant dose, spectral broadening was observed in the high-energy side of the Si peak. The fraction of boron at the substitutional position was estimated by the intensity ratio between the Si-B local mode and the Si optical phonon mode. This ratio was proportional to the hole carrier densities, and, as a result, estimation of the hole carrier densities was also possible. Raman scattering is applicable for the estimation both of boron at the substitutional position and of hole carrier densities.
Measurement of electron impact ionization coefficient in bulk silicon under a low-electric field
Authors: Takayanagi Isao , Matsumoto Kazuya , Nakamura Jun-ichi
Published: July 2002

The electron impact ionization coefficient, αn, in bulk silicon, was extracted using a new method that is applicable for the low-electric fields. In this method, αn can be simply estimated from the multiplication factor of an n-type static induction transistor, and a structurally determined depletion layer thickness. Values of αn, as low as 1×10−4 cm−1, have been obtained at 300 and 77 K, and they agreed approximately with previously reported data that covered relatively high electric fields.
Silicon-carbide-enhanced thermomigration
Authors: Abbasi Masoud , Johansson Torbjorn , Normann Richard A.
Published: July 2002

The widespread acceptance of thermomigration technology to produce through-chip interconnects has been impaired by (i) a random walk of the Si-Al liquid eutectic inclusion as it traverses the wafer, and (ii) a ‘‘surface barrier’’ which allows thermomigration of only relatively large inclusions. In this paper it is shown that these problems can be mitigated by thermomigrating at high wafer temperatures and with large temperature gradients through the wafer. It has been possible to achieve these high wafer temperatures and large gradients using a bank of infrared lamps and a bilaminar structure of silicon carbide powder compressed onto the top of a silicon wafer. This increases the delivery of energy to the wafer and reduces the random walk of the liquid inclusion. Further, the high wafer temperatures and enhanced temperature gradients created with this bilaminar silicon carbide structure allow relatively small, square aluminum pads (35 μm on a side) to thermomigrate through a 16-mil-thick silicon wafer.
Influence of compensation on 77 K free carrier absorption in n-ZnS
Authors: Ruda H. E.
Published: July 2002

Quantum theory is applied to calculate the free carrier absorption coefficients in n-ZnS. This treatment includes all major scattering mechanisms and screening. We present the results of calculations of 77 K free carrier absorption and derivative logarithmic absorption coefficients, as a function of the free carrier concentration and compensation ratio, at 10 μm. We discuss the unambiguous determination of both free carrier concentration and compensation ratio for unknown samples.
Low-loss optical channel waveguides in KNbO3 by multiple energy ion implantation
Authors: Fluck D. , Günter P. , Fleuster M. , Buchal Ch.
Published: July 2002

Permanent optical channel waveguides in single crystals of KNbO3 are formed with low-dose MeV He ion irradiation. A single energy implantation forms a confinement barrier at the projected range of the ions whereas multiple energy implantations combined with a positive shielding mask form the side walls. Guiding modes are produced and propagation losses as low as 1.0 dB/cm are measured without the need for any annealing. The irradiation induced refractive index changes that define the boundaries of the waveguiding channels are made visible with cross-polarized light microscopy.
Effect of ohmic contact conductance on the distribution of surface and bulk currents in semiconductor planar devices
Authors: Huo Chong-ru , Gu Ben-yuan , Coluzza C.
Published: July 2002

We investigate the effect of the ohmic contact conductance on the current distribution in the surface and bulk layers in semiconductor planar devices. In particular we analyze the current-voltage characteristics in the three-probe configurations, where probe one is the injecting contact and probes 2 and 3 are the drains. We find that the current distribution is substantially affected by the contact conductance and the ratio between the shunt currents from probes 1 to 2, and from 1 to 3 is mainly dominated by the contact and surface conductivities in the sample. This ratio is less sensitive to the change of the bulk conductivity. We also show the effect of the geometric parameters of the sample on the current distribution. In addition, the lines of current from probes 1 to 2 are concentrated within a thin surface layer. Therefore, the current through probe 2 is determined by the bulk and surface conductances as well as by the contact conductivity. On the other hand, the current through probe 3 is primarily controlled by bulk and contact conductivity. This makes it possible to simultaneously measure surface and bulk conductances in semiconductors if the contact conductivity is known.
Longitudinal optical phonon modes in a ZnSe-ZnTe strained-layer superlattice
Authors: Cui Jie , Wang Hailong , Gan Fuxi
Published: July 2002

We have observed by off-resonance Raman scattering confined longitudinal optical phonon modes in the ZnSe layer of a ZnSe-ZnTe strained-layer superlattice which has a lattice mismatch as large as 7.3% at room temperature. We have calculated the red shifts of phonon frequencies due to confinement and the shifts induced by the elastic strains, which are much larger than the red shifts due to confinement. The red shifts induced by tensile strain in the ZnSe layer and the blue shifts induced by compressive strain in the ZnTe layer caused some confined LO modes in two individual layers overlap. Therefore, the folded LO mode has been observed in the ZnSe-ZnTe strained-layer superlattice.
Resolution limitations in focused ion beam damage-induced masking for photoelectrochemical etching of GaAs
Authors: Khare Reena , Hu Evelyn
Published: July 2002

The use of ion beam damage to locally suppress photoelectrochemical etching of GaAs has been previously described. This study examines the limitations on the resolution of patterns formed by this technique, using a focused ion beam. Directly written patterns of damage were formed in Si-doped n+ GaAs (1×1018 cm−3) by implantation with a 120 keV focused beam of Ga ions. Photoelectrochemical etching of the substrate was suppressed, not only in the implanted regions themselves, but also within a region extending a few micrometers beyond the implanted region. This suppression distance limits the smallest pattern feature or resolution achievable with this technique. The resolution was examined as a function of incident laser intensity, implant dose, the dimensions of the damaged areas, and distance between the damaged areas. A simple one-dimensional model suggests that the diffusion of the photogenerated carriers, relative to their reaction rate at the surface, determines the resolution achievable.
Simultaneous disordering and isolation induced by ion mixing in InGaAs/InP superlattice structures
Authors: Pappert S. A. , Xia W. , Zhu B. , Clawson A. R. , Guan Z. F. , Yu P. K. L. , Lau S. S.
Published: July 2002

The phenomenon of simultaneous compositional disordering and the formation of electrical resistive layers induced by oxygen implantation in InGaAs/InP superlattices has been investigated. The disordering characteristics have been studied as a function of implantation temperature and ion dose. It was found that implantation at elevated temperatures (referred to as the IM or ion mixing process) usually leads to much more efficient disordering compared to implantation at room temperature followed by annealing at the same elevated temperature (referred to as the implantation plus annealing process). Of particular interest is the observation that ion mixing at 550 °C with 1×1013 O+/cm2 leads to significantly more disordering than implantation with the same dose at room temperature followed by annealing at 550 °C for the same period of ion mixing time. In addition, the electrical resistance of the ion-mixed layer at 550 °C increases 2600 times for the p-type InGaAs/InP superlattice structure, whereas the sample implanted at room temperature and annealed at 550 °C showed only a 20 times increase in electrical resistance. These results indicate a distinct advantage for the IM process in achieving simultaneous compositional disordering and electrical isolation for optoelectronic applications.
High-resistivity GaAs grown by high-temperature molecular-beam epitaxy
Authors: Polyakov A. Y. , Stam M. , Milnes A. G. , Wilson R. G. , Fang Z. Q.
Published: July 2002

It is shown that when grown by molecular-beam epitaxy at high temperatures around 700 °C, undoped GaAs layers display high resistivity. Preliminary results seem to imply that Ga-related inclusions that produce internal Schottky diodes might be responsible for this effect rather than the presence of deep centers. It is proposed that Ga-related inclusions that produce internal Schottky diodes might possibly be responsible for this effect rather than the presence of deep centers.
Photobehavior of paramagnetic anion antisites in plastically deformed GaAs
Authors: Benchiguer T. , Mari B. , Schwab C. , Wu Ju , Wang Guangyu
Published: July 2002

We investigate the behavior of paramagnetic AsGa+-related defects under 1.2 eV illumination at 4.2 K in plastically deformed bulk semi-insulating GaAs. We find them identical to the grown-in antisites with a similar photoquenchability and analogous parameters. Further, there is effective generation of additional AsGa centers after deformation. The photobehavior can be interpreted by a charge transfer model, where the metastability involved with the AsGa+ signal decay is not a defect inherent feature.
Characterization of ultrathin oxide prepared by low-temperature wafer loading and nitrogen preannealing before oxidation
Authors: Wu S. L. , Lee C. L. , Lei T. F. , Liang M. S.
Published: July 2002

In this study, we report a high-performance ultrathin oxide (≊80 Å) prepared by a low-temperature wafer loading and N2 preannealing before oxidation. This recipe can reduce native oxide thickness and thermal stress compared to the conventional oxidation recipe. The high-resolution transmission electron microscopy reveals that the SiO2/Si interface is atomically flat, and a thin crystalline-like oxide layer about 7 Å exists at the interface. Oxides prepared by the proposed recipe show a very high dielectric breakdown field (≥16 MV/cm) and a very low interface state density (Nit ≊ 3 × 109 eV−1 cm−2 at midgap). The effective barrier height at cathode derived from the slopes of log(Jg/E2ox) vs 1/Eox and tbd vs 1/Eox plots is about 3.9 eV, instead of 3.2 eV for the control sample. It also shows a better immunity to the charge trapping and interface state generation under high-field stressing, and superior time-dependent dielectric breakdown characteristics.
The identification of Si donor states in AlxGa1−xAs by photoluminescence
Authors: Kang Junyong , Huang Qisheng
Published: July 2002

Photoluminescence (PL) had been performed on n-type Si-doped AlxGa1−xAs layers with alloy composition 0.2<x<0.95. By analyzing the PL spectra in various excitation densities, doping levels, and temperatures, the donor-acceptor pair (D-A) emissions near band edge are identified as Si donor states of DΓ, D2, and D3 to carbon acceptor transitions. The composition dependencies of energy positions for the donor states and the normalized emission intensities for D-A suggest that DΓ is a shallow donor state bound to the Γ band, and D2 and D3 are deep donor states mainly bound to the L and X bands, respectively.
Effect of layer thickness variations on the performance of asymmetric Fabry–Perot reflection modulators
Authors: Law K-K. , Merz J. L. , Coldren L. A.
Published: July 2002

We present a study of the effect of the active cavity layer thickness variations on the operating characteristics of normally on low voltage high performance asymmetric Fabry–Perot modulators. For a modulator consisting of 25.5 periods of 100 Å GaAs quantum wells confined by 45 Å (GaAs/AlAs) short period superlattices with 5 pairs and 20.5 pairs of top and bottom quarter-wave stacks, respectively, and assuming only layer thickness variation caused by Ga flux nonuniformity, the shift of the Fabry–Perot mode wavelength with respect to the fractional change of GaAs thickness inside the active cavity is ∼6 times that of the quantum well heavy hole exciton. This affects the relative distance between the wavelengths of the quantum well exciton and the Fabry–Perot resonance, and hence the performance of the modulators. Also, the tolerable percentage change of the Fabry–Perot mode wavelength should be less than 0.13% in order that such modulator arrays have at least 10:1 contrast ratios at a fixed optimum operating wavelength. This defines the epitaxial growth tolerance and precision with which we can obtain a desired operating wavelength, and the uniformity requirement on the two-dimensional arrays of such kind of modulators.
Local hydrogen hopping and long-range diffusion in Nb films: An electrical noise study
Authors: Nevins B. D. , Weissman M. B.
Published: July 2002

The low-frequency resistance noise of thin Nb films was studied at temperatures from 60 to 400 K. This resistance noise came predominantly from hydrogen-ion motions, as can be shown by draining ions out of the sample with an electric field. In addition to the long-range diffusion noise and the large-scale collective motion noise, which have been described previously, noise was found near 150 K, due to local hydrogen hopping motions, similar to that observed in several other materials. However, unlike in some other materials, the local hopping noise came from a different type of motion than those that give the long-range diffusion.
High critical current densities reproducibly observed for hot-isostatic-pressed PbMo6S8 wires with Mo barriers
Authors: Yamasaki H. , Umeda M. , Kosaka S.
Published: July 2002

Fabrication process, critical current densities (Jc), and microstructure of the superconducting PbMo6S8 wires with Mo barriers have been investigated. Reducing the volume fraction of the Mo barrier and using electron-beam-melted Mo with less deformation resistance than that of conventional powder-metallurgy-processed Mo, facilitate the densification of PbMo6S8 and Jc improvement by the hot-isostatic-pressing (HIP) treatments. We have succeeded in obtaining reproducibly HIP treated PbMo6S8 wires with homogeneously high Jc≥108 A/m2 at 22 T and 4.2 K, which is promising for the production of future high field (≳20 T) superconducting magnets.
Calculation of point defect concentrations in GaAs grown by molecular beam epitaxy
Authors: Ichimura Masaya , Wada Takao
Published: July 2002

Thermodynamic chemistry of native defects is applied to molecular beam epitaxial (MBE) growth of GaAs. Following the model of Stringfellow [J. Cryst. Growth 70, 133 (1984)], we assume that the equilibrium is established at the solid-vapor interface. Calculated results show that the defect concentration is rather low, less than 1015 cm−3 under usual growth conditions and that MBE GaAs is less As-rich than those grown by organometallic vapor phase epitaxy or halogen transport vapor phase epitaxy.
The interfaces of NbN-MgO-NbN tunnel junctions
Authors: Wessely B. , Hebrank F. , Voss M. , Gross R. , Huebener R. P. , Schmeisser D. , Göpel W.
Published: July 2002

The chemical composition of the surfaces and interfaces of NbN-MgO-NbN trilayers has been studied by x-ray photoelectron spectroscopy during the fabrication of the trilayer without breaking the vacuum. The NbN and MgO layers were prepared by rf magnetron sputtering. The results of the chemical analysis have been correlated to the electrical characteristics of the completed NbN-MgO-NbN tunnel junctions. During the deposition of the MgO barrier layer the presence of a high amount of energetic oxygen ions and atoms in the sputtering plasma results in a strong plasma oxidation of the NbN base electrode and, hence, in mixed Nb2O5-MgO barriers. The oxygen ions and atoms are generated by the dissociation of the target material and the water of the background pressure. Their amount was found to increase with increasing argon pressure during the MgO sputtering process. Also, adsorption layers of hydroxides on the MgO-target result in the formation of an uncontrollable amount of niobium oxide components at the interface between the NbN base electrode and the MgO barrier. The current-voltage characteristics of tunnel junctions with such barriers show large subgap leakage currents. Pure MgO barriers can be prepared by reducing the oxygen bombardment of the NbN films during the MgO deposition. Pure MgO barriers are oxygen deficient and easily adsorb hydroxides. These hydroxides react with the first layers of the NbN top electrode to NbO2 and NbO thereby reducing and broadening the sumgap value of the tunnel junctions. Tunnel junctions with pure MgO barriers of a nominal thickness of less than 2 nm usually have current-voltage characteristics indicative for microshorts. A special annealing procedure of the NbN-MgO bilayers prior to the deposition of the top electrode desorbs the hydroxides, transforms Mg(OH)2 to MgO without forming metallic magnesium and prevents the formation of intermediate layers of niobium suboxides and metallic shorts.
Effect of low pressure dc plasma discharge on laser ablated ferroelectric Pb(Zr,Ti)O3 thin films
Authors: Krupanidhi S. B. , Roy D.
Published: July 2002

Ferroelectric thin films of PZT [Pb(Zr,Ti)O3] were deposited on platinum coated silicon and bare silicon by excimer laser (248 nm) ablation and were in situ crystallized, with and without an oxygen discharge. Films deposited at various oxygen discharge voltages exhibited variations in polarization switching, dielectric constant, and loss, and current-voltage (I-V) characteristics. Crystalline perovskite PZT films deposited with a discharge voltage of +300 V offered stoichiometric and crystalline films, with a dielectric constant of 850, a remnant polarization of 22 μC/cm2, and a coercive field of 40 kV/cm, a resistivity of about 1012 Ω cm and a charge storage density of as high as 100 fC/μm2 at 5 V. Besides the property enhancement, the presence of O2+ discharge plasma appeared to have reduced the deposition temperature to relatively lower values (500 °C).
Investigation of epitaxial lateral overgrowth by x-ray topography
Authors: Köhler R. , Jenichen B. , Bauser E. , Bergmann R.
Published: July 2002

Epitaxial lateral overgrowth by liquid phase epitaxy of silicon over SiO2 has been investigated by x-ray double crystal topography. A large number of lamellae was free of crystallographic defects, but all of the lamellae showed growth striations. For the lamellae grown from indium solutions growth striations with indium concentration differences of about 1016–2 × 1017 cm−3 were detected. A considerable part of the indium impurities in the lamellae seemed to be electrically inactive. The tilt of the defect free lamellae against the substrate is of the order of 10−6. Some of the lamellae showed single dislocations parallel to the sample surface. These dislocations originated at the edges of the seeding windows and ended in reentrant corners at the outer edge of the lamellae. In most of the defective lamellae the dislocations formed a dense network.
Opto-optical switching using field enhancing effect in Bi12SiO20
Authors: Liu Liren , Liu Xiaoben
Published: July 2002

The opto-optical Bi12SiO20 switching described in this article is caused by the photocharge created by the control beam and the resultant electric-field enhancement. The field enhancing effect and the electro-optical modulation with both the Pockels effect and the optical activity are analyzed. On this basis, the design considerations for switches are given. Experimental results are demonstrated.
Photovoltaic output limitation of n-FeS2 (pyrite) Schottky barriers: A temperature-dependent characterization
Authors: Büker K. , Alonso-Vante N. , Tributsch H.
Published: July 2002

Metal/n-pyrite (metal=Pt, Au, Nb) Schottky barrier type diodes were fabricated on electrochemically reduced either synthetic or natural (100) and (111) surfaces of single crystalline n-FeS2. The temperature dependence of I-V curves in darkness were analyzed in the range of 200–350 K on the basis of thermionic emission and recombination models. The calculated effective barrier height was ∼0.60 eV and the activation energy for recombination ∼0.50 eV for all investigated n-FeS2/Pt samples. The doping density and the extrapolated potential (pseudo flatband situation) from the Mott–Schottky plot, obtained from capacities deduced from potentiostatic complex impedance measurements, were 2.0×1016 cm−3 and 0.25 eV vs Pt for the synthetic n-pyrite crystal, respectively. From the donor density and barrier height a band bending of 0.5 eV was deduced. Photovoltaic parameters like open-circuit photovoltage and short-circuit photocurrent were studied down to temperatures of 200 K. The main phenomenon preventing the generation of a photopotential approaching the band bending (0.50 eV) appears to be the pinning of the Fermi-level by recombination centers located in the middle of the band gap (Eg=0.95 eV) of pyrite.
High critical current density obtained by focused ion beam patterning of high temperature superconducting thin films
Authors: Zaquine I. , Assayag G. Ben , Gierak J. , Dessertenne B. , Marcilhac B. , Mercandalli M. , Mage J. C.
Published: July 2002

In an attempt to pattern microbridges in a superconducting line by focused ion beam milling, we have obtained a very high critical current density: 6 × 108 A/cm2 at 77 K. Direct focused ion milling leads to microbridge structures as narrow as 200 nm. Ultrahigh current densities have already been reported by H. Jiang [Phys. Rev. Lett. 66, 1785 (1991)] in such ‘‘nanobridges.’’ We have also measured size-dependent critical current densities. We take into account the electrical field criterion and give a very simple interpretation of our experimental results based on the possibility of strong pinning in a very narrow bridge and the inhomogeneity of our films at a submicronic scale.
Incorporating susceptibility changes in a general thermally-stimulated polarization process
Authors: Ferreira G. F. Leal
Published: July 2002

Generalization of a previously given expression dealing with processes in which temperature and electric field are simultaneously varied is proposed in order to include also susceptibility changes.
Effects of BF2+ implants on titanium silicide formation by rapid thermal annealing
Authors: Choi J. S. , Hwang Y. S. , Paek S. H. , Oh J. E. , Sim T. U. , Lee J. G.
Published: July 2002

The formation of titanium silicides on Si implanted with different BF2+ dosages has been studied by secondary ion mass spectrometry and transmission electron microscopy measurements. The thickness of the silicide layer formed in the temperature ranging from 600 to 800 °C has been investigated as a function of the implanted BF2+ dosage up to 1×1016 cm−2. Annealing at 700 °C results in conversion of the titanium film into predominantly C49 TiSi2, and most of it is transformed into the C54 phase at 800 °C or higher, resulting in a lower sheet resistance (16 μΩ cm). The titanium silicide thickness formed after the rapid thermal annealing (RTA) treatment depends on the implanted BF2+ dosage, caused by the native oxide enhanced by increased damage. Boron is redistributed into the silicide layer up to the solid solubility limit during annealing, leading to an accumulation at the silicide/silicon interface. The lowest contact resistance (with a size of 0.7 μm×0.7 μm) of 35 Ω is obtained at the annealing temperature of 700 °C.