bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of a biased probe on the afterglow operation of an ECR4 ion source
Authors: Hill C. E. , Küchler D. , Wenander F. , Wolf B. H.
Published: July 2002

Various experiments have been performed on a 14.5 GHz ECR4 in order to improve the ion yield. The source runs in pulsed afterglow mode, and provides currents ∼120 eμA of Pb27+ to the CERN Heavy Ion Facility on an operational basis. In the search for higher beam intensities, the effects of a pulsed biased disk on axis at the injection side were investigated with different pulse timing and voltage settings. No proof for absolute higher intensities was seen for any of these modifications. However, the yield from a poorly tuned/low-performing source could be improved and the extracted pulse was less noisy with bias voltage applied. The fast response on the bias implies that increases/decreases are not due to ionization processes. A good tune for high yield of high charge states during the afterglow coincides with a high plasma potential.
Production of highly charged ions in electron cyclotron resonance ion sources using an electrode in two modes
Authors: Biri S. , Kenéz L. , Valek A. , Nakagawa T. , Kidera M. , Yano Y.
Published: July 2002

One of the most known ways to obtain higher beam intensities in electron cyclotron resonance (ECR) ion sources is to install an electrode (usually disk) into the plasma chamber. We found that a majority of the groups observed the beam intensity improvement by supplying a suitable biased voltage to the electrode and an electron current was injected into the plasma. A few groups observed the enhancement, however, when the electrode operated at floating potential—without being an electron donor. In spite of the great success of the “biased disk” method, the mechanism is still not completely clear. In this contribution, as a step toward of understanding, we examined the above mentioned two modes. The experiments were performed at the 18 GHz RIKEN and at the 14.5 GHz ATOMKI ECR ion sources.
Tornado-type closed magnetic trap for an electron cyclotron resonance ion source
Authors: Abramova K. B. , Smirnov A. N. , Voronin A. V. , Zorin V. G.
Published: July 2002

We propose to use a Tornado-type closed magnetic trap for creation of a source of multicharged ions with plasma heating by microwave radiation. Plasma loss in closed traps is determined by diffusion across the magnetic field, which increases substantially plasma confinement time as compared to the classical mirror trap. The Tornado trap also possesses merits such as: an opportunity to produce high magnetic fields up to 3 T, which makes possible heating and confinement of plasma with a high density of electrons; an opportunity to use supplementary coils for ion extraction; plasma stability to magnetohydrodynamic perturbations because the magnetic field structure corresponds to the “min B” configuration; and relatively low costs. All estimates and calculations were carried out for the existing Tornado-322 pulse installation (maximal magnetic field 2.8 T) with plasma heating at 53 GHz frequency. The numerical simulation has shown that, by the end of the magnetic field pulse, ion distribution over charge states may reach a maximum at Ar+16 for the plasma density of 1013 cm−3. The current density of ions Ar+16 can be varied from 10 mA/cm2 to approximately 1 A/cm2.
Development of high intensity deuteron ion source for the fusion intense neutron source
Authors: Kinsho M. , Sugimoto M. , Seki M. , Oguri H. , Okumura Y.
Published: July 2002

A high intensity deuteron ion source has been developed in order to increase the neutron flax from the D–T neutron source for Fusion Neutronics Source at JAERI. It is possible to extract more than 50 mA of deuteron beam at the beam energy of 50 keV. The lifetime of the tungsten filaments utilized in the ion source has been achieved in over 300 h with continuous operation. The high intensity deuteron ion source for the International Fusion Material Irradiation Facility is being designed on the basis of the experimental results and the experience obtained from the present ion source.
Experiments with a microwave plasma as a cathode for cold or hot reflex discharge ion source
Authors: Cojocaru G.
Published: July 2002

A microwave plasma cathode (MPC) was developed to replace the thermionic filaments of the cold or hot reflex discharge ion source (CHORDIS) ion source for operation with reactive gases. Experiments with our MPC showed its long lifetime and its capability of high-current electron emission. Two new types of antennae are presented. Different electron extraction apertures were used, but the best results were obtained with an extraction aperture of 6 mm in diameter. Ion beam currents for different oxygen pressures and different discharge voltages are presented and discussed. The gas pressure proved to be a critical parameter in respect to the extracted ion beam densities and beam noise. Total ion current densities of 16.8 mA/cm2 were obtained for oxygen. We are also presenting an experiment where the MPC-CHORDIS system was used as a tool to study the influence of the beam noise on the space charge compensation at the GSI Darmstadt injection beam line.
MgO thin film formation by ion enhanced deposition processes
Authors: Hashimoto M. , Onozaki Y. , Uchida H. , Matsumura Y.
Published: July 2002

MgO thin films were prepared by ion plating systems and by an ion beam sputtering system with a plasma filament type ion source. Triode-type and rf ion plating processes were employed. MgO films were prepared with various oxygen partial pressures ranging from 10−3 to 10−2 Pa. In the triode-type ion plating process, the MgO(200) was the preferred growth orientation of film. In the rf ion plating process, MgO(111) and (220) reflection peaks appeared in the x-ray diffraction patterns of films. The films were transparent, and those values of transmittance of ultraviolet region were increased as increasing oxygen partial pressure. In the ion beam sputtering process, the film showed amorphous structure and low transmittance.
Hydrogen negative ion source with LaB6 inserts
Authors: Belchenko Yu. I. , Kuznetsov G. I. , Grigoryev E. A.
Published: July 2002

The compact negative ion source having a semiplanotron discharge geometry and the two independently heated LaB6 cathode inserts was developed and studied. The hot LaB6 cathode insert supports discharge ignition and operation at low hydrogen pressure, while the cold one provides the glow discharge concentration in its vicinity. The stable production of H− beams with the current density in the emission hole in the range of about 0.1 A/cm2 was obtained in the pure hydrogen discharge. Negative ion yield at the different parts of the composite source cathode was measured. It was maximal in the glow region. An enhanced H− yield was recorded due to discharge concentration near the LaB6 inserts. LaB6 with a decreased work function does not produce a sizable income of surface-produced negative ions to the beam, extracted from the pure hydrogen discharge. The use of LaB6 inserts as a reliable source of electrons to form the discharge simplifies the surface-plasma source use.
Bipolar extraction neutralization: Time resolved characterization
Authors: Korzec D. , Dahlhaus R. , Engemann J.
Published: July 2002

By switching the polarization of the screen and accelerator grid of a two grid extraction system, an ion or electron beam can be extracted from the same gas discharge. Such ion source operation mode, called bipolar extraction neutralization (BEN), allows a filamentless current neutralization of electrically insulated substrates. In this study BEN was used for a broad (12 cm), high current (0.36 A) ion beam from an electron cyclotron resonance ion source. The neutralization process is controlled by the duty cycle and frequency of the electron extraction pulses. An electrostatic monitor was positioned in the vicinity of the sputter target and used for monitoring the beam plasma potential and control of the neutralization parameters. The beam potential and extraction grid currents are presented time resolved for neutralization frequency from 20 to 80 kHz and duty cycle from 10% to 80%. This kind of monitoring allows not only control of the ion/electron extraction but also determination of the ion time of flight between the extraction grid and the substrate.
Energy analysis of negative hydrogen ions using detached electrons
Authors: Takahashi M. , Yoshimoto M. , Shinto K. , Takagi A. , Ikegami K. , Mori Y.
Published: July 2002

An electron of a negative hydrogen ion (H−) can be easily detached by collisions with an external laser beam or residual gas molecules in the beam line, because its electron affinity is small (0.754 eV). The detached electrons provide information about the original negative hydrogen ions and should have the same velocity as the original hydrogen ions. By measuring the energy of the detached electrons, the energy of a negative hydrogen-ion beam can be estimated. A preliminary experimental result of an energy analysis of a H− beam using detached electrons is presented.
Electron cyclotron resonance ion trap: A hybrid magnetic system with very high mirror ratio for highly charged ion production and trapping
Authors: Biri S. , Simons L. , Hitz D.
Published: July 2002

In the Paul Scherrer Institute [PSI Switzerland] an experimental program was started to measure the ground state shift and width of pionic hydrogen. To calibrate the crystal spectrometer x-ray transitions in hydrogen-like heavy ions (e.g., Ar17+), produced by electron cyclotron resonance (ECR) ion sources, are necessary. In PSI a superconducting cyclotron trap magnet, originally developed for particle physics experiments, will be transformed into an ECR ion trap (ECRIT). The SC magnet can deliver more than 4 T magnetic fields with a mirror ratio of 2. A careful calculation showed this mirror ratio can be increased upto 10 and the trap can operate with frequencies between 5 and 20 GHz. To form a closed resonance zone an open structure NdFeB hexapole will be applied. The first tests will be performed at 6.4 GHz. Later higher frequencies and the two-frequency heating (6.4+10, 6.4+14.5, or 10+14.5 GHz) are planned to be applied to get enough quantity of H-like heavy ions. The ECRIT will operate at ground potential while a simple 90° beamline (at negative potential) will help the fine tuning of the plasma for very high charge states.
Discharge characteristics of a long pulse ion source for the Korea Superconducting Tokamak Advanced Research neutral beam system
Authors: Oh B. H. , Kim K. R. , Choi B. H.
Published: July 2002

The discharge characteristics of a prototype ion source for the Korea Superconducting Tokamak Advanced Research neutral beam system, which has been developed to meet the specification of 120 keV and 65 A beam during 300 s, were investigated. The relationships between the operation conditions, such as the filament current, the arc current (up to 1200 A), the pressure of the ion source, and the measured plasma parameters were studied, and the possibility of steady-state operation was checked. Langmuir probes were used in measuring the plasma parameters and the density distributions. The hydrogen ion density was 2.0×1011 cm−3, the electron temperature was lower than 5 eV, and the plasma uniformity around the bucket was within 30% in the optimum operation conditions.
Design and performance of a versatile, cost-effective microwave electron cyclotron resonance plasma source for surface and thin film processing
Authors: Anton R. , Wiegner Th. , Naumann W. , Liebmann M. , Klein Chr. , Bradley Chr.
Published: July 2002

A plasma source has been developed, which makes use of electron cyclotron microwave resonance conditions without cost-intensive tuning or other active elements. A magnetron typical of domestic microwave ovens is coupled to a cylindrical resonator of fixed dimensions. A high density plasma is maintained with permanent magnets. Sources have been designed for both high vacuum and ultrahigh vacuum environments. In the latter, microwaves are conducted by a coaxial feedthrough from the resonator to a ceramic plasma cup inside the vacuum chamber. This permits shorter working distances, resulting in higher beam densities at the sample. Ions are extracted from the plasma by grid assemblies. Beam energies are in the range from 30 to 2000 eV, with densities from a few μA/cm2 up to 10 mA/cm2, respectively. Predominantly neutral species are emitted using a specially designed, ceramic grid. Operating with O2 gas, a flux of neutral monomers of 2×1016/cm2 s has been measured by the oxidation of Ag films. The performance of the source is demonstrated in various surface and thin film processes, like ion beam sputtering, reactive ion beam deposition, as well as sputter cleaning and reactive etching of semiconductor materials.
Matching the injected ion beam into an rf Linac for a high-energy, high-current ion implanter
Authors: Saadatmand Kourosh
Published: July 2002

Over the last several years, high-energy (in the MeV range) ion implantation has become an integral part of mainstream semiconductor device manufacturing. The rapid growth in the use of the high-energy ion implanters has been driven by device engineering process requirements. At Eaton, we have developed an rf Linac based high-energy implanter, NV-GSD/VHE, capable of delivering 1.7 MeV B+ beam in excess of 1 mA. However, as high-dose buried layers and 300 mm substrates emerge for mainstream integrated circuit processing, a need for a significantly higher B+ beams up to 2 MeV is on the horizon. To maximize the beam transmission, optimizing the match between the injected ion beam and the Linac acceptance is essential. A pepper-pot emittance measurement apparatus is used to measure the beam emittance down stream of the ion source extraction optics. The ion source beam emittance requirement, its measured and theoretical values for our ion source will be discussed.
Optically pumped polarized H− ion source for RHIC spin project
Authors: Mori Y. , Ikegami K. , Takagi A. , Zelenski A. N. , Dutto G. , Kadantsev S. , Levy C. D. P. , Wight G. W. , Alessi J. , Okamura M.
Published: July 2002

In the RHIC spin experiment, the high intensity polarized H− ion source is requested. The required 2×1032/s cm2 luminosity in RHIC can be obtained with a 0.5 mA injected H− ion beam intensity. In order to realize such beam intensity, a KEK optically pumped polarized H− ion source is being upgraded at TRIUMF for future installation at RHIC. The first results of polarization measurements are presented here.
A W–InSb point contact diode for harmonic generation and mixing in the visible
Authors: Moretti A. , Maccioni E. , Nannizzi M.
Published: July 2002

Metal–oxide–metal (MIM) and Schottky barrier diodes are widely used as harmonic generators and mixers and for frequency measurements from far infrared to visible. MIM diodes have a low cost of fabrication and are very easy to handle, while Schottky diodes are mechanically more stable and long lived. In this article we present the performance of a W–InSb point contact diode for radiation at visible wavelength; the device is very simple, easy to fabricate and costless, has the advantages of MIM as well as of Schottky diodes, and has proved to be very effective as both detector and mixer.
Surface photoabsorption studies of the chemical structure of GaInP grown by organometallic vapor phase epitaxy
Authors: Murata H. , Ho I. H. , Hsu T. C. , Stringfellow G. B.
Published: July 2002

The surface structure of Ga0.52In0.48P was studied by surface photoabsorption. An absorption peak due to P dimers on Ga0.52In0.48P was observed at ∼400 nm, shorter than for InP (430 nm). From comparison with results for GaAs and InP, the data are interpreted to indicate that at a tertiarybutylphosphine (TBP) pressure of 50 Pa for temperatures below 670 °C, the P-stabilized surface has P dimers aligned along the [1̄10] direction, i.e., it has a (2×4)-like structure. Above 670 °C, the 400 nm peak due to the P-dimer structure disappears because of P desorption from the surface at this TBP partial pressure. Epitaxial Ga0.52In0.48P layers grown using TBP, trimethylgallium and ethyldimethylindium are nearly disordered at 670 °C and highly ordered at 620 °C. These data suggest a correlation between surface structure and ordering.
Intersubband second-harmonic generation with voltage-controlled phase matching
Authors: Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Ram-Mohan L. R.
Published: July 2002

We propose an intersubband-based frequency-mixing device in which phase matching is imposed electrically. The dynamic tuning considerably relaxes fabrication tolerances, allows compensation for the intensity dependence of the index, and enables phase-matched operation at a range of degenerate and nondegenerate pump wavelengths.
Tritertiarybutylaluminum as an organometallic source for epitaxial growth of AlGaSb
Authors: Wang C. A. , Finn M. C. , Salim S. , Jensen K. F. , Jones A. C.
Published: July 2002

A new organometallic source, tritertiarybutylaluminum (TTBAl), has been used in growth of AlxGa1−xSb epilayers by low pressure organometallic vapor phase epitaxy. Ternary alloys were grown over the whole composition range 0<x≤1 on GaSb and GaAs substrates from TTBAl, triethylgallium, and triethylantimony (TESb) or trimethylantimony (TMSb). All layers exhibited mirror surface morphologies. Photoluminescence was observed for layers with x<0.2, the composition that corresponds to the indirect transition. The background of C and O in AlSb grown with TESb was ∼2×1018 and ∼6×1019 cm−3, respectively, and ∼1.5×1019 and ∼1.5×1019 cm−3, respectively, for AlSb grown with TMSb. All layers exhibited p-type conductivity with hole concentration increasing with x, and saturating ∼5×1018 cm−3 for x=1, which is about 10 times lower compared to layers grown with conventional Al sources.
A spectroscopic study on the luminescence of Er in porous silicon
Authors: Hömmerich Uwe , Namavar Fereydoon , Cremins Annmarie , Bray Kevin L.
Published: July 2002

We report a spectroscopic study on the photoluminescence (PL) of erbium implanted into porous silicon (Er:PSi). Two different porous Si samples were implanted with a dose of 1015 Er/cm2 at 380 keV and annealed at 650 °C for 30 min under identical conditions. Both samples exhibited Er3+ luminescence at 1.54 μm, which was quenched by less than a factor of two between 15 K and room temperature. Visible PL studies of Er implanted and annealed porous Si samples showed broad spectra which peaked at ∼700 nm for sample A and peaked at ∼660 nm for sample B. Sample A showed a four times stronger Er3+ luminescence than that observed from sample B. In contrast, temperature quenching of the Er3+ luminescence was found to be similar or slightly weaker from sample B than from sample A. The spectroscopic data will be discussed in terms of the excitation mechanisms of Er3+ in porous Si nanostructures.
Planar native-oxide-based AlGaAs-GaAs-InGaAs quantum well microdisk lasers
Authors: Ries M. J. , Chen E. I. , Holonyak N. , Iovino G. M. , Minervini A. D.
Published: July 2002

Data are presented on the 300 K photopumped (pulsed) laser operation of ultrathin (∼0.15 μm) planar microdisk lasers. The tiny lasers employ the wet oxidation of an AlGaAs layer beneath the disks to form semiconductor cavities that are in solid contact but optically isolated from the GaAs substrate. The resulting microcavity lasers operate at low pump intensities and exhibit spectra characteristic of whispering gallery mode microdisk lasers.
Silicon interstitial trapping in polycrystalline silicon films studied by monitoring interstitial reactions with underlying insulating films
Authors: Tsoukalas D. , Kouvatsos D.
Published: July 2002

Oxidation experiments on structures of polycrystalline silicon on thin oxides indicate that the generated interstitials are partially trapped within the polycrystalline silicon layer and partially escape, diffuse through the underlying thin oxide, and affect pre-grown oxidation-induced stacking faults in the silicon. The trapping efficiency of the polycrystalline silicon film has been found to increase with decreasing grain size or increasing film thickness. This indicated that grain boundary traps are primarily responsible for interstitial trapping within the polycrystalline silicon. The larger trapping efficiency of smaller grain size films was attributed to the larger surface of grain boundaries and the larger grain boundary trap concentration in that case. In all cases, polycrystalline silicon films trap more interstitials than crystalline silicon films of the same thickness that were used as a reference in this study.
Electrical detection of electron nuclear double resonance in silicon
Authors: Stich B. , Greulich-Weber S. , Spaeth J.-M.
Published: July 2002

Electrical detection of electron nuclear double resonance (EDENDOR) is demonstrated using shallow P donors in silicon. The EDENDOR spectra are compared with conventional ENDOR spectra. With EDENDOR, both the 31P hyperfine as well as 29Si superhyperfine interactions could be resolved. The sensitivity of EDENDOR seems higher compared to conventional ENDOR, especially for the 29Si ligands. EDENDOR is particularly suitable for the study of the microscopic structure of point defects in semiconductors, especially for detection of paramagnetic centers that are present in low concentrations and in small volumes.
A study of the effects of post-deposition treatments on CdS/CdTe thin film solar cells using high resolution optical beam induced current
Authors: Galloway S. A. , Brinkman A. W. , Durose K. , Wilshaw P. R. , Holland A. J.
Published: July 2002

The optical beam induced current (OBIC) technique was applied using a scanning optical microscope (SOM) to study n-Cds/p-CdTe thin film solar cells which had been subjected to different post-deposition treatments. High spatial resolution maps were obtained of the current collection with and without an applied reverse bias. The quantum efficiency of the devices was also measured with high spatial resolution. The results both quantify and illustrate vividly the manner in which the well known CdCl2 treatment increases collection efficiency. The high uniformity in the best cells indicates that grain boundaries do not play a substantial role in limiting collection efficiency.
Electron cyclotron resonance etching characteristics of GaN in SiCl4/Ar
Authors: Zhang L. , Ramer J. , Brown J. , Zheng K. , Lester L. F. , Hersee S. D.
Published: July 2002

Electron cyclotron resonance (ECR) plasma etching characteristics of gallium nitride (GaN) are investigated using low pressure (4–10 mTorr) SiCl4/Ar ECR discharges. The purpose of this effort is to examine the dry etching processes of GaN that do not require hydrogen, which is known to cause carrier compensation in GaN. A maximum etching rate of 960 Å/min and good surface morphologies are obtained. The etch rate is found to increase near-linearly with increasing dc bias, and a minimum dc bias of 100 V is required to initiate etching. Enhanced etching rates are obtained as the fraction of active chemical etchant species (SiCl4) in the discharge is increased. We have also found that the material quality significantly affects the etch rate. The latter decreases with x-ray rocking curve half-width and increases with defect density.
The mechanism of iron gettering in boron-doped silicon
Authors: Stolk P. A. , Benton J. L. , Eaglesham D. J. , Jacobson D. C. , Cheng J.-Y. , Poate J. M. , Myers S. M. , Haynes T. E.
Published: July 2002

High-energy B implantation was used to introduce gettering layers into float-zone Si wafers contaminated with 2×1014 Fe/cm3. Secondary ion mass spectrometry shows that about 5% of the Fe contamination is collected at the 4 μm deep peak of a 4×1014/cm2, 3.3 MeV B implant after annealing at 1000 °C for 1 h. Deep level transient spectroscopy demonstrates that increasing the gettering B dose from 4×1012 to 4×1014/cm2 reduces the Fe concentration from 3×1012 to below ∼1010/cm3 in the 1–3 μm deep region from the surface, indicating very efficient gettering. Measurements of the Fe depth profile imply that the depletion of Fe near the gettering layer occurs upon cooling down from 1000 °C. The gettering behavior can be qualitatively understood in terms of a Fermi-level-enhanced pairing reaction between Fe and B.
Hall coefficients in the superconductor-insulator transition of Bi2+xSr2−xCuOy: Measurement of Hall-bar shaped single crystals fabricated by excimer-laser cutting
Authors: Inagaki K. , Tanda S. , Sajiki K.
Published: July 2002

Hall coefficients and resistivities of a series of Bi2+xSr2−xCuOy single crystals were measured to investigate the relation between the carrier concentration and the disorder of the system in the superconductor-insulator transition. Excimer-laser cutting technique was applied to fabricate the Hall-bar shaped samples in order to determine precisely the transport properties of the single crystals. The Hall coefficients were found to be independent of the temperature, which suggests Coulomb interaction was negligible in the localized regime of Bi2+xSr2−xCuOy. We found the Ioffe–Legel condition kFl∼1 laid around n0∼8×1020 cm−3 in this system, and the carriers in the localized regime were essentially ‘‘metallic.’’
Local electron field emission characteristics of pulsed laser deposited diamondlike carbon films
Authors: Chuang F. Y. , Sun C. Y. , Chen T. T. , Lin I. N.
Published: July 2002

Local electron field emission properties of diamondlike carbon (DLC) films were measured by a probe method in 1 atmosphere ambient pressure, using the modified scanning tunneling microscopic (STM) system, and the diode method. In the STM probe method, the field emission was turn on at a low bias as +2.67 V. A large emission current of 40 nA was attained at +7 volt bias voltage and the emission current density was estimated as Jt=5 A/cm2. By contrast, the current–voltage (I–V) characteristics of the same DLC films measured by diode method in 10−6 Torr ambient pressure revealed that the electron field emission was produced for a 13.2 V/μm electric field, and a high emission current density of J=160 μA/cm2 was obtained for a E=20 V/μm electric field. The geometrical enhancement factor (α), evaluated from the Fowler–Nordheim plot was around α=30, which is larger than what would be expected from a planar surface. This can be interpreted as the evidence that electrons are emitted locally from spherical SP3 clusters.
Orientational relationship among polyimide alignment layer, liquid crystal monolayer, and bulk pretilt angle
Authors: Shirota Koichiro , Yaginuma Michio , Sakai Takahiro , Ishikawa Ken , Takezoe Hideo , Fukuda Atsuo
Published: July 2002

We have determined the orientational distribution function (ODF) of side chains of rubbed polyimide (PI) films and liquid crystal (LC) monolayers on those films (PI & LC) by optical second-harmonic generation (SHG). To separate the SHG signal of the LC monolayer from that of the (PI & LC) film, the phase difference between the SHG signals from PI and (PI & LC) was measured by an interference method. We found that the ODFs of PI and LC films are quite different. However, serious changes in these ODFs occur at the same rubbing strength, where the pretilt angle also shows a remarkable change.
Far-infrared ellipsometry of depleted surface layer in heavily doped n-type GaAs
Authors: Humlíček J. , Henn R. , Cardona M.
Published: July 2002

Far-infrared ellipsometric spectra of n-type (100) GaAs display sharp features in the range of the longitudinal optical phonon of intrinsic material, originating in the surface depletion region. We compare measured relative ellipsometric phase shifts with model calculations of the graded depletion layer. A very good agreement is observed, enabling us to determine the surface potential.
Oxygen contamination of low temperature ultrahigh vacuum-deposited Ge films on GaAs
Authors: Dubey Madan , Lareau Richard T. , Cole Melanie W. , Jones Kenneth A. , West Lawrence C. , Roberts Charles W. , Piscani Emil
Published: July 2002

The Fourier transform infrared absorption spectrum for the range of 500–4000 cm−1 wave numbers was measured for several Ge films deposited on GaAs using ultrahigh vacuum e-beam deposition at various substrate temperatures ranging from room temperature (RT) to 500 °C. Spectra indicate oxygen incorporation at low deposition temperatures whether or not the native oxide was removed from the substrate prior to film deposition. Using transmission electron microscopy, we show that Ge films deposited at RT and 100 °C on a (100) GaAs surface that did not have the oxides removed are amorphous while those deposited at 100 °C with the oxide removed are crystalline, but are highly defective. Secondary ion mass spectroscopy (SIMS) measurements show that the amorphous films at RT contain more than two orders of magnitude more oxygen than the films deposited at 100 °C or a single crystal film deposited at 400 °C. Oxygen-18 diffusion studies definitively show that the excess oxygen in the amorphous films percolates in from the atmosphere. SIMS studies further reveal that thermally removing the GaAs substrate surface oxide or depositing an Au film on top of the Ge film has little effect on the incorporation of oxygen.
Surface discharge plasma induced by spontaneous polarization switching
Authors: Shur D. , Rosenman G. , Krasik Ya. E.
Published: July 2002

A flashover plasma has been induced by spontaneous polarization switching on a polar surface of the ferroelectric crystal triglycine sulphate (TGS). The effect has not been observed in the paraelectric phase. The threshold switching voltage for a surface flashover ignition was as low as 100 V for pulsed and ac voltage. A mechanism of plasma initiation on a ferroelectric surface is proposed. It is assumed that the plasma is ignited by electron emission initiated by polarization switching. Subsequent electron avalanching occurs as a result of the high potential gradient along the ferroelectric surface caused by inhomogeneous polarization switching. Electrons and ions with energies up to several hundreds of eV were been recorded due to a high surface potential of the switched ferroelectric.
A high strain two-stack two-color quantum well infrared photodetector
Authors: Tidrow M. Z. , Chiang J. C. , Li Sheng S. , Bacher K.
Published: July 2002

A high strain two-stack, two-color, InGaAs/AlGaAs and AlGaAs/GaAs quantum well infrared photodetector for midwavelength infrared (MWIR) and long wavelength infrared (LWIR) detection has been demonstrated. Each stack is designed to have detection in one of the two atmospheric windows, 3–5 μm and 8–12 μm, respectively. The MWIR stack has employed 35% of indium in the InGaAs well, which not only achieved peak wavelength at 4.3 μm, but also obtained very high peak responsivity of Rp=0.65 A/W, using 45° light coupling. Normal incidence without grating coupling also has high responsivity with 40%–50% in the MWIR stack and 35%–45% in the LWIR stack, respectively, compared with the 45° incidence. Despite the large in-plane compressive strain induced by the high indium concentration, the device is highly uniform and has very low dark current in the MWIR stack. The background limited temperature is 125 K for the MWIR stack with a cutoff wavelength λc=4.6 μm, and is 70 K for the LWIR stack with λc=10 μm.
Ultra bright surface emission from a distributed Bragg reflector hot electron light emitter
Authors: O’Brien A. , Balkan N. , Roberts J.
Published: July 2002

Hot electron light emitting and laser semiconductor heterostructure (HELLISH-1) is a novel surface emitting device. It utilizes longitudinal transport where electric fields heat up electrons and holes in their respective channels simultaneously. Hot electrons and holes are then captured by mainly tunnelling and thermionic emission in the quantum well where radiative recombination occurs. In this work, we demonstrate and compare the operation of HELLISH-1 and ultrabright HELLISH-1 (UB-HELLISH-1). The latter is an improved version of HELLISH-1 which incorporates a distributed Bragg reflector allowing detection of super radiant emission with a vastly improved full width at half-maximum. It is also shown that the emitted light intensity in the UB-HELLISH-1 device is enhanced by about two orders of magnitude compared with the simple structure.
Dual mode electron emission from ferroelectric ceramics
Authors: Shannon D. N. J. , Smith P. W. , Dobson P. J. , Shaw M. J.
Published: July 2002

Two modes of electron emission have been observed from the ferroelectric ceramic PLZT when subjected to a high voltage bipolar pulse. One mode is always associated with bright visible plasma on the emitting surface, while the other occurs with no visible emission. Emitted current wave forms are consistent with two distinct mechanisms for emission: surface plasma in the first case and polarization switching in the second.
Wet oxidation of AlxGa1−xAs: Temporal evolution of composition and microstructure and the implications for metal-insulator-semiconductor applications
Authors: Ashby Carol I. H. , Sullivan John P. , Newcomer Paula P. , Missert Nancy A. , Hou Hong Q. , Hammons B. E. , Hafich Michael J. , Baca Albert G.
Published: July 2002

Three important processes dominate the wet thermal oxidation of AlxGa1−xAs on GaAs: (1) oxidation of Al and Ga in the AlxGa1−xAs alloy to form an amorphous oxide, (2) formation and elimination of crystalline and amorphous elemental As and of amorphous As2O3, and (3) crystallization of the amorphous oxide film. Residual As can lead to strong Fermi-level pinning at the oxidized AlGaAs/GaAs interface, up to a 100-fold increase in leakage current, and a 30% increase in the dielectric constant of the oxide layer. Thermodynamically favored interfacial As may impose a fundamental limitation on the use of AlGaAs wet oxidation in metal-insulatorsemiconductor devices in the GaAs material system.
Cd
1−x
Mn
x
Te
magneto-optical waveguide integrated on GaAs substrate
Authors: Zaets W. , Watanabe K. , Ando K.
Published: July 2002

The refractive indices of diluted magnetic semiconductor Cd1−xMnxTe films on sapphire substrates have been determined by m-line spectroscopy to precision 0.001 at the wavelengths λ=670, 785, and 1150 nm. Using these data, we designed double-layer Cd1−xMnxTe structures on a GaAs substrate, achieving the integration of the magneto-optical waveguide on a semiconductor substrate. Good optical confinement of the waveguide mode was confirmed.
Absolute photoyield from chemical vapor-deposited diamond and diamond-like carbon films in the UV
Authors: Breskin A. , Chechik R. , Shefer E. , Bacon D. , Avigal Y. , Kalish R. , Lifshitz Y.
Published: July 2002

The absolute photoyields of chemical vapor deposited (CVD) diamond and amorphous hydrogen-free diamondlike carbon (DLC) films, in the range of 140–300 nm, are reported. CVD diamond films exhibit a large photoyield, of a few percent in the range 140–180 nm. DLC films have a 20–50 times lower yield. Post growth hydrogenation is found to substantially increase the photoyield of CVD diamond films. We discuss the applicability of these films as UV photocathodes coupled to electron multipliers based on gaseous charge multiplication.
Radiation damage and implanted He atom interaction during void formation in silicon
Authors: Raineri V. , Saggio M.
Published: July 2002

He was implanted in silicon wafers to several doses (5×1015–4×1016 cm−2) at different temperatures (from −196 up to 400 °C). Void formation and evolution was observed by cross-sectional and plan view transmission electron microscopy analyses. We observed that void density and morphology are strictly related to substrate temperature during He implantation. Experiments show that for substrate temperature between 10 and 90 °C or higher than 150 °C, void formation is inhibited; when voids are observed, a few degrees of difference significantly change their density. The results can be interpreted by considering the interaction between He and the radiation damage produced during He implantation that forms stable bubbles.
Mechanism for Si island retention in buried SiO2 layers formed by oxygen ion implantation
Authors: Afanas’ev V. V. , Stesmans A. , Revesz A. G. , Hughes H. L.
Published: July 2002

The density of silicon islands trapped in buried SiO2 layers produced by the implantation of oxygen into (001)Si substrates is monitored by atomic force microscopy for the oxygen dose range just above that required for continuous oxide formation. In addition to an exponential increase in the Si island density with oxygen dose, the regularly shaped remnants of an SiO2 phase with a reduced HF etch rate were found. The formation of this additional oxide phase as a result of enhanced internal pressure inside the Si crystal is proposed to account for the retention of Si islands in the buried oxide.
Dynamics of photoexcited holes in n-doped InGaAs/GaAs single quantum well
Authors: Dao L. V. , Gal M. , Li G. , Jagadish C.
Published: July 2002

We have measured the temporal evolution of the photoluminescence (PL) of a Si δ-doped In0.2Ga0.8As/GaAs quantum wells using the PL up-conversion technique. The luminescence spectrum of this sample displayed the characteristic features of the Fermi edge singularity. The temporal evolution of the luminescence is described in terms of the dynamics of the hole population. From the experiments, we have determined the effective hole capture time (15 ps), the interband relaxation time (3 ps), and the radiative decay time (>1 ns) at T=8 K. We have found that the radiative decay time decreases dramatically with increasing temperature (τr=45 ps at T=125 K) which, we believe, is the result of the smearing of the Fermi edge and the delocalization of the holes that are responsible for the luminescence.
Operating stability of light-emitting polymer diodes based on poly(p-phenylene vinylene)
Authors: Carter J. C. , Grizzi I. , Heeks S. K. , Lacey D. J. , Latham S. G. , May P. G. , Ruiz de los Paños O. , Pichler K. , Towns C. R. , Wittmann H. F.
Published: July 2002

We have developed modified poly(p-phenylene vinylene) (PPV) to improve its performance in organic electroluminescent devices. Encapsulated single-layer devices with this PPV on indium–tin oxide and a calcium cathode have been operated in air for >7000 h at 20 °C and >1100 h at 80 °C without noticeable degradation. Devices fabricated with this PPV, a conducting polymer layer as anode, and a sputtered low work-function alloy as cathode have efficiencies of over 2 lm/W, brightnesses of >600 Cd/m2 at 4 V, and lifetimes of >1400 h driven at ∼100 Cd/m2 initial brightness.
An optically addressed modulator based on low-temperature-grown multiple quantum well GaAlAs
Authors: Tayebati Parviz , Hantzis Christos , Canoglu Ergun , Sacks Robert N.
Published: July 2002

We report an optically addressed multiple quantum well spatial light modulator with large modulation gain which can be used in applications such as amplified incoherent-to-coherent conversion. The novel device design utilizes separate detector and modulator regions to obtain large gain. The design also incorporates low-temperature-grown quantum wells in the modulator region to reduce the effects of high-intensity readout. Our preliminary data show that modulation gain of 45 and modulation depth of 40% can be obtained by simply applying a dc bias. However, our data also show that the modulation gain decreases at higher writing frequencies, indicating that refreshing the device is required after each write-read operation.
Microstructure studies of Zr41Ti14Cu12.5Ni10Be22.5 bulk amorphous alloy by electron diffraction intensity analysis
Authors: Wang Wei-Hua , Wei Qing , Friedrich S. , Macht M. P. , Wanderka N. , Wollenberger H.
Published: July 2002

Reduced density function analyses for the bulk amorphous alloy Zr41Ti14Cu12.5Ni10Be22.5 and its decomposition and crystallization have been made by means of electron diffraction intensity measurement with imaging plate. The local atomic structure of the amorphous alloy as well as its development in the course of the decomposition and crystallization is described from the analysis of the atomic distribution function. The origin of the high thermal stability and the large glass forming ability of the alloy as well as the effect of the decomposition on the crystallization is discussed from the viewpoint of the local atomic structure characteristics of the alloy.
Effect of antiferromagnetic grain size on exchange-coupling field of Cr70Al30/Fe19Ni81 bilayers
Authors: Uyama Hiroko , Otani Yoshichika , Fukamichi Kazuaki , Kitakami Osamu , Shimada Yutaka , Echigoya Jun-ichi
Published: July 2002

The exchange-coupling mechanism of Cr70Al30/Fe19Ni81 bilayer films was investigated in terms of the crystallographic orientation, the interface roughness, and the grain size. The exchange-coupling field Hex appears when the Cr70Al30 layer is thick enough to accommodate an antiferromagnetic domain wall. The value of Hex was found to increase with decreasing the grain size in association with the [110] orientation. This tendency can be explained by considering the exchange-coupling field evaluated from the random field approximation.
Magneto-optical properties of sputter-deposited NiMnSb thin films
Authors: Caballero J. A. , Geerts W. J. , Childress J. R. , Petroff F. , Galtier P. , Thiele J.-U. , Weller D.
Published: July 2002

High-quality thin-film of NiMnSb with the Clb crystal structure can be grown by low-power sputtering, at substrate temperatures as low as 250 °C. Structural and magneto-optical properties of these films are similar to those of bulk material prepared at high temperatures, which suggest that the predicted 100% spin-polarized behavior of NiMbSb may also be found in these films. The magneto-optical Kerr spectra have been measured, and they are found to be very sensitive to the preparation condition. The spectrum of the bulk alloy is closely reproduced only in the case of optimized films. This suggests that, in the optimized case, the electronic band structure is bulklike.
Electron pump current by two pulses with phase delay
Authors: Tsukagoshi Kazuhito , Nakazato Kazuo
Published: July 2002

Electron packet transport through two nodes built between three multiple-tunnel junctions (MTJs) was investigated. Two trapezoidal voltage pulses were applied to each node to transfer the electron packet. A pump current due to sequential transport of the electron packets was observed at a particular phase delay where the backward tail of the first pulse just overlapped the forward tail of the second pulse, whereas synchronized pulses could not carry the current. A dependence on pulse shape was also investigated.
Rapid thermal chemical vapor deposition of in situ boron-doped polycrystalline silicon-germanium films on silicon dioxide for complimentary-metal-oxide-semiconductor applications
Authors: Li V. Z-Q , Mirabedini M. R. , Kuehn R. T. , Wortman J. J. , Öztürk M. C. , Batchelor D. , Christensen K. , Maher D. M.
Published: July 2002

In situ boron-doped polycrystalline Si1−xGex (x>0.4) films have been formed on the thermally grown oxides in a rapid thermal chemical vapor deposition processor using SiH4-GeH4-B2H6-H2 gas system. Our results showed that in situ boron-doped Si1−xGex films can be directly deposited on the oxide surface, in contrast to the rapid thermal deposition of undoped silicon-germanium (Si1−xGex) films on oxides which is a partially selective process and requires a thin silicon film pre-deposition to form a continuous film. For the in situ boron-doped Si1−xGex films, we observed that with the increase of the germane percentage in the gas source, the Ge content and the deposition rate of the film are increased, while its resistivity is decreased down to 0.66 mΩ cm for a Ge content of 73%. Capacitance-voltage characteristics of p-type metal-oxide-semiconductor capacitors with p+-Si1−xGex gates showed negligible polydepletion effect for a 75 Å gate oxide, indicating that a high doping level of boron at the poly-Si1−xGex/oxide interface was achieved.
In situ
imaging of polymer melt spreading with a high-temperature atomic force microscope
Authors: Glick D. , Thiansathaporn P. , Superfine R.
Published: July 2002

We have developed a method of imaging at high temperatures with atomic force microscopy using a laser to deliver heat to an area localized around the AFM tip–sample junction. We couple approximately 75 mW from an argon-ion laser into the active region to raise the temperature of a 100 nm gold film to around 225 °C. As a sample, we use 1.2 μm polystyrene spheres adsorbed onto the film. We image the flow of these spheres, in situ, over the course of an hour. The dynamics of the polymer spreading is shown to be consistent with the dry spreading of a precursor film.
Bright-line defect formation in silicon carbide injection diodes
Authors: Konstantinov A. O. , Bleichner H.
Published: July 2002

Irreversible formation of a network of linear defects has been observed for images showing recombination luminescence from injection diodes in hexagonal silicon carbide. The defects are related to dislocations that are initially formed as a result of thermal stress near the tip of the contact probe and subsequently propagate through the diode area. The dislocation network appears in the images of the electroluminescence as bright-line defects, in contrast to the well-known dark-line defects due to degradation of gallium–arsenide-based light-emitting devices. Higher forward currents are found to promote the dislocation growth.
Visible luminescence from Pr-doped sulfide glasses
Authors: Tikhomirov V. K. , Iakoubovskii K. , Hertogen P. W. , Adriaenssens G. J.
Published: July 2002

Room-temperature visible luminescence from Pr3+ ions embedded in germaniumsulfide glass hosts is reported along with edge luminescence from these hosts. The important role of energy transfer processes between the host and Pr ions is demonstrated experimentally through the dependencies of photoluminescence on excitation wavelength, temperature, and polarization.
Electron-beam damage of C60 films on hydrogen-passivated Si(100)
Authors: Hunt Michael R. C. , Schmidt Jens , Palmer Richard E.
Published: July 2002

We report the effects of medium-energy (3.5 keV) electron-beam irradiation of C60 films between 1 and 4 ML thick grown on Si(100) 2×1-H studied by high-resolution electron energy-loss spectroscopy. Electron irradiation leads primarily to molecular fragmentation. Initially, molecular fragments are discrete, and saturated with hydrogen, but continued irradiation leads to the formation of a disordered material with a graphitic local structure. Experiments performed on a single monolayer of C60 show that under irradiation, fragments can bond to the substrate via displacement or desorption of the hydrogen atoms bonded to the Si substrate.
High bandwidth-efficiency resonant cavity enhanced Schottky photodiodes for 800–850 nm wavelength operation
Authors: Ünlü M. S. , Gökkavas M. , Onat B. M. , Ata E. , Özbay E. , Mirin R. P. , Knopp K. J. , Bertness K. A. , Christensen D. H.
Published: July 2002

High-speed resonant cavity enhanced Schottky photodiodes operating in 800–850 nm wavelength region are demonstrated. The devices are fabricated in the AlGaAs/GaAs material system. The Schottky contact is a semitransparent Au film which also serves as the top reflector of the Fabry–Perot cavity. The detectors exhibit a peak quantum efficiency of η=0.5 at λ=827 nm wavelength and a 3 dB bandwidth of more than 50 GHz resulting in a bandwidth-efficiency product of more than 25 GHz.
Coherent-to-incoherent transition in surfactant mediated growth of InAs quantum dots
Authors: Neves B. R. A. , Andrade M. S. , Rodrigues W. N. , Sáfar G. A. M. , Moreira M. V. B. , de Oliveira A. G.
Published: July 2002

In this letter, we present an atomic force microscopy study of a series of Te-mediated InAs/GaAs samples with InAs coverage ranging from 1.5 to 3 monolayers. We were able to directly identify the growth mode transition and the mechanism of relaxed island formation. At the limit of coherent growth mode, strained quantum dots aggregate, forming twin quantum dots (TQDs), which are structures of two, or more, dots virtually bonded together, separated by less than 3 nm. The onset of the incoherent mode is then unambiguously characterized by the coalescence of individual TQDs forming initially small, and then larger, relaxed islands.