bluuebunny/crossref_metadata_2025 huggingface dataset:
2.5 kHz high repetition rate XeCl excimer laser
Authors: Takagi S. , Okamoto N. , Kakizaki K. , Sato S. , Goto T.
Published: July 2002

An XeCl excimer laser was operated at the high repetition rate of 2.5 kHz, which can circulate the laser gas uniformly and efficiently. The characteristics of the gas flow rate and the average laser power versus the repetition rate were investigated in both He and Ne buffer gas mixtures. In He buffer gas, the average laser power saturates at 1.3 kHz and, thereafter, drops abruptly. On the other hand, stable operation at the highest repetition rate, 2.5 kHz, has been attained in Ne buffer at a gas flow rate of 54 m/s with an average laser power of 87 W.
Electroabsorption studies on InGaAs/InGaAsP quantum-well laser structures
Authors: Satzke K. , Vestner H. G. , Weiser G. , Goldstein L. , Perales A.
Published: July 2002

Field-induced changes of the transmittance of quantum-well laser structures with five ternary wells and quaternary barriers and waveguides, grown on InP substrates, have been investigated at low temperatures. The method selectively picks up states in undoped regions that are particularly sensitive to electric fields: the heavy-hole exciton in quantum wells, responding by the quantum confined Stark effect, and the band gap of the thicker waveguides which responds by the Franz–Keldysh effect. Both effects are used to determine the transition energies and the electric field in the respective regions. It is found that in typical laser structures electrons and holes are localized to single wells as their coupling is overcome by the internal field. The internal field corresponds approximately to the ratio of the gap energy of the waveguide material and the thickness of undoped regions. Stark localization persists even if the internal field is reduced by forward bias down to a level where diffusion currents lead to electroluminescence. The narrow linewidth of the response of the localized heavy-hole excitons allows to resolve small splitting due to inhomogeneities of the wells. The evolution of the spectra with bias voltage and the comparison of the fields derived for quantum-well and waveguide regions, yield information on the distribution and on the homogeneity of the field, giving access to space charges.
Magnetic measurements with a SQUID magnetometer: Possible artifacts induced by sample-holder off-centering
Authors: Casañ-Pastor Nieves , Gomez-Romero Pedro , Baker Louis C.W.
Published: July 2002

Asymmetries in sample holders used for magnetic measurements on magnetometers based on induction methods, such as those equipped with SQUID sensors, can lead to substantial errors and/or important artifacts which resemble phase transitions. They occur under the conditions for which sample and/holder have signals of opposite sign, but are nearly equal in magnitude. The most serious errors can occur often, but not exclusively, for compounds having intermediate magnetic dilution. We present here a general discussion of the problem illustrated by measurements of a polyoxometallate with the known Keggin structure K6[Fe(III)W12O40]⋅nH2O, done on a SHE VTS model 905. While one of the obvious solutions to this problem is the use of holders with a signal much smaller than that of the sample, it would be preferable if, in addition, the holder had a response of the same sign as that of the sample, for all temperatures and fields measured.
Electrical conductivity of a suspension of charged spherical particles in electrolyte solution
Authors: Gu Guoqing , Yu K. W.
Published: July 2002

We investigate the influence of interaction between dispersed particles to ac conductivity of suspension of charged particles immersed in electrolyte solution. Using the Rayleigh technique, we establish an identity for charged suspensions, and derive a formula for effective complex conductivity of the systems. A useful scheme for computation of effective constants of composite media is proposed.
Electronic properties of multiple Si δ doping in GaAs
Authors: Degani Marcos H.
Published: July 2002

The subband structure of multiple Si δ-doped layers in GaAs is calculated within the local-density-functional approximation for several doping periods. The diffusion effect of donors impurities are investigated. The physical properties of the present multiple δ doping depend strongly on the period length, reflecting a transition from quantum well to superlattice.
Linear and quadratic magnetoelectric (ME) effect in Ni-Cl boracite
Authors: Rivera J.-P. , Schmid H.
Published: July 2002

Quasistatic and dynamic measurements of the magnetic field induced magnetoelectric polarization (MEH effect) have been performed in the weakly ferromagnetic/ferroelectric/ferroelastic phase of point group m′m2′ of Ni-Cl boracite between 1.8 and 9 K (=TC) and above. For the first time the quadratic MEH effect of Ni-Cl boracite has been measured and separated from the linear one. The results allow us to discard the existence of a previously assumed antiferromagnetic phase mm2 between 9 and 25 K. Above 9 K, the phase is paramagnetic (mm21′). The coefficients of the linear (α23, α32) and quadratic (β311, β322, β333, and β223) MEH effect are given for 4.2 K. α32 and β322 are also given vs temperature.
Photorefractive damage in KTP used as second-harmonic generator
Authors: Tyminski Jacek K.
Published: July 2002

A common application of KTP is as a second-harmonic generator. However, scaling up second-harmonic efficiencies of KTP is limited by generation of ‘‘dark tracks.’’ It is possible to circumvent the problem of dark tracking by raising the crystal temperature. The heating extends the life time of the nonlinear medium and permits an increase of the second harmonic efficiency. At 170 °C an astigmatic beam distortion of the harmonic beam was observed. The astigmatism was strongly dependent on the beam intensities. The direction of the astigmatic distortion was parallel to the z crystallographic direction. The development of the beam distortion resulted from optically induced nonuniformity of the nz refractive index of KTP. It represented photorefractive damage to KTP. Analysis of the astigmatic distortion versus second-harmonic power indicates that the photorefractive damage resulted from multiphoton absorption involving fundamental and harmonic photons.
Growth and characterization of indium antimonide doped with lead telluride
Authors: Partin D. L. , Heremans J. , Thrush C. M.
Published: July 2002

A PbTe dopant source has been used to grow n-type InSb using the molecular beam epitaxy growth technique. From Auger electron spectroscopy studies, no surface segregation of tellurium is observed up to ∼1019 cm−3 doping levels. The correlation between the PbTe flux used during growth and the electron density in the grown films is very good, suggesting that the incorporation of tellurium is near unity. From secondary-ion mass spectroscopy (SIMS) studies, no lead could be detected in the films, even when grown at temperatures as low as 280 °C. This suggests that the lead rapidly re-evaporates from the surface during growth. SIMS depth profiles of tellurium show evidence of solid-state diffusion at 360 °C with a diffusion coefficient ∼10−13 cm2 s−1. Six-probe Hall measurements of carrier transport gave room-temperature mobilities as high as 51 300 cm2 V−1 s−1 at an electron density of 2.9×1016 cm−3 (54 300 at an electron density of 1.9×1016 cm−3 at 110 K) for a film of 4.0-μm thickness on an InP substrate. Our experiences with selenium contamination from previous PbSe evaporations in the same chamber and from impure Sb source material are described as well as the technique used to make the PbTe source material.
The concentration dependence of the hole mobility of 1,1-bis(di-4-tolylaminophenyl)cyclohexane doped bisphenol-A-polycarbonate
Authors: Borsenberger P. M.
Published: July 2002

Hole mobilities of 1,1,-bis(di-4-tolylaminophenyl)cyclohexane (TAPC) doped bisphenol-A- polycarbonate have been measured over a range of concentrations. The mobilities are strongly concentration dependent, increasing with increasing TAPC concentration. The results are described within the framework of the disorder formalism, due to Bässler and co-workers. The formalism is based on the assumption that charge propagation occurs by hopping through a manifold of states subject to concurrent energetic and positional disorder. The results show that both energetic and positional disorder increase with decreasing TAPC concentration. The increase in energy disorder is attributed to dipole moments of the carbonyl groups associated with the polycarbonate while the increase in positional disorder is suggested as due to packing constraints induced by the polymer host.
Frequency shifting of electromagnetic radiation by sudden creation of a plasma slab
Authors: Kalluri D. K. , Goteti V. R.
Published: July 2002

The effect of switching a plasma medium of finite width (slab) on a time-harmonic plane electromagnetic wave propagating in free space is considered. The transient solution is obtained through the use of Laplace transforms. The solution is broken into two components: A component which in steady state has the same frequency as the incident wave frequency (ω0) and a B component which has an upshifted frequency ω1 =√ω20+ω2p. Here ωp is the plasma frequency of the switched plasma slab. Numerical results are presented to show the effect of the slab width on the reflected and transmitted waves. A proper choice of ω0, ωp and the slab width will yield a transmitted electromagnetic pulse of significant strength at the upshifted frequency.
Scattering mechanisms affecting hole transport in remote-doped Si/SiGe heterostructures
Authors: Emeleus C. J. , Whall T. E. , Smith D. W. , Kubiak R. A. , Parker E. H. C. , Kearney M. J.
Published: July 2002

Boron modulation-doped Si/SiGe heterojunctions have been grown by molecular beam epitaxy. The two-dimensional hole gas formed along the heterojunction, just inside the alloy, has a sheet density in the range 2–5×1011 cm−2 and a typical mobility at 5 K of 2000 cm2 V−1 s−1. An explanation for the magnitude of the mobility is sought by considering likely scattering mechanisms, namely those due to remote impurities, interface roughness, alloy disorder, and interface impurities. A self-consistent model is used to determine the sheet density in terms of structural and energy parameters and dopant concentrations in the heterostructure. It is shown that the presence of negatively charged impurities at the heterojunction provides the basis for a consistent interpretation of the experimental results.
Characterization of Ca1−xErxF2+x solid solution thin films grown on Si(100) substrates
Authors: Barrière A. S. , Mombelli B. , Porté B. , Raoux S. , Guégan H. , Réau M. , L’Haridon H. , Moutonnet D.
Published: July 2002

Erbium-substituted Ca1−xErxF2+x calcium trifluoride layers were grown on Si(100) substrates by sublimation under ultrahigh vacuum of high purity solid solution powders. X-ray diffraction and scanning electron microscopy techniques were performed to study the texture and the structure of the layers. Their composition was mainly deduced from Rutherford backscattering of α particles and particle induced x-ray emission. For an erbium substitution rate, x, lower than 0.2, it has been shown that the film compositions are analogous with that of the sintered material and quite homogeneous. A Rutherford backscattering study in channeling conditions showed that heteroepitaxial Ca1−xErxF2+x/Si(100) structures can be grown for a substrate temperature of 550 °C.
Behavior of elastic constants, refractive index, and lattice parameter of cubic zirconia at high temperatures
Authors: Botha P. J. , Chiang J. C. H. , Comins J. D. , Mjwara P. M. , Ngoepe P. E.
Published: July 2002

Acoustic mode frequency, lattice parameter, and refractive index measurements have been carried out on single crystals of cubic stabilized zirconia, ZrO2(xY2O3), in the temperature range 300 to 1450 K, using Brillouin scattering, x-ray diffraction, and interferometric methods, respectively. Elastic constants Cij and associated quantities such as the bulk modulus B=(C11+2C12)/3, the anisotropy ratio A=2C44/(C11−C12), and the Cauchy relation failure Δ=(C12−C44) have been determined from these measurements. The results show a linear reduction in C11 , C12 , and C44 until a characteristic transition temperature Tc, which depends on the dopant concentration x. The linear decrease is understood in terms of normal thermal expansion. Above Tc (1300 K for x=9.4 mol % and 1050 K for x=24 mol %) there are elastic anomalies; significant reductions in C11, (C11-C12)/2 and C44 occur, with an increase in C12 . These effects are considered to result from thermally generated disorder. Detailed examination of the temperature dependence of the Cij as well as B, A, and Δ show some similarities, but also significant differences in comparison with the anomalous elastic behavior corresponding to the high-temperature superionic state of fluorites. The thermally created defect structures formed at high temperatures in cubic zirconia are thus considered to be different from the anion Frenkel disorder formed in fluorites; this is in accord with recent results from computational simulations and high-temperature neutron scattering.
Reverse-ballistic impact study of shear plug formation and displacement in Ti6Al4V alloy
Authors: Holt W. H. , Mock W. , Soper W. G. , Coffey C. S. , Ramachandran V. , Armstrong R. W.
Published: July 2002

Gas-gun reverse-ballistic experiments have been performed in which Ti6Al4V alloy disks were impacted onto smaller diameter, hardened steel rods to push out shear plugs from the disk material. The range of disk velocities was 219–456 m/s. For each experiment, the disk, plug, and rod were soft recovered after impact. Below 290 m/s, the plugs were pushed only partway through the disks, but localized shear bands outlining the plug shapes were easily recognized in metallographic sections. Optical and scanning electron microscopies were used to determine shear zone widths and to describe microstructural details associated with the primary shear zones. There is evidence for appreciable adiabatic heating and consequent thermal softening and melting of material in the main shear zone. A simple model is used to relate the observed plug displacements to the impact velocities and to provide estimates of several features: the shear zone strength, the threshold energy for shear plug displacement, and the threshold energy for shear plug separation. Clear evidence is presented of molten material having been produced as part of the plug separation process.
The analysis of the temperature dependence of photoconductive frequency-resolved spectroscopy in the presence of carrier trapping: Application to polycrystalline silicon
Authors: Lourenço M. A. , Homewood K. P. , McLellan R. D.
Published: July 2002

The analysis of photoconductive frequency-resolved spectroscopy is developed for variable temperature measurements. It is shown that when the excess carrier kinetics is dominated by carrier trapping the technique can be used to obtain the major trap parameters. This analysis is applied as an example to polycrystalline silicon on insulator on silicon films and a dominant trap with an activation energy of 70 meV is identified.
Vacancy-type defects in crystalline and amorphous SiO2
Authors: Dannefaer S. , Bretagnon T. , Kerr D.
Published: July 2002

Positron lifetime spectroscopy and two-dimensional angular correlation of annihilation radiation have been used to investigate grown-in vacancy structures in synthetic crystalline α-SiO2, synthetic fused quartz, and in a 60-μm-thick chemical-vapor-deposited amorphous SiO2 film. For α-SiO2 a ∼300 ps lifetime component suggests trapping by either silicon monovacancies or by oxygen divacancies (or both). The vacancies are neutral and present at a concentration level of 1017/cm3. The positron bulk lifetime for α-SiO2 is estimated to be ∼238 ps in good agreement with semiempirical predictions. In the fused quartz significant positronium formation is found (80%) and the remaining positrons annihilate in voids yielding a lifetime of ∼500 ps. The amorphous SiO2 film contains a mixture of small vacancy clusters and voids and ∼30% of the positrons form positronium. Heat treatment above 950 °C results in a substantial reduction in defect concentration, but up to 1100 °C a small vacancy cluster contribution persists. The positron data indicate that positronium formation in the fused quartz and in the amorphous film takes place in the voids.
Characteristics of secondary electron emission from CsI induced by x rays with energies up to 100 keV
Authors: Gibrekhterman A. , Akkerman A. , Breskin A. , Chechik R.
Published: July 2002

A microscopic model for low energy electron interaction in alkali halides was used to simulate secondary electron emission from CsI induced by x rays with energies up to 100 keV. The integral ‘‘current’’ and ‘‘pulse’’ yields were calculated as function of the x-ray energy, CsI convertor thickness, and angle of incidence. We observe a decrease in true low energy (<50 eV) secondary electron yields at increasing x-ray energies and discuss the effectiveness of CsI convertors coupled to gaseous electron multipliers developed for fast, high resolution x-ray imaging.
Analysis of excitation and coherent amplitude enhancement of surface acoustic waves by the phase velocity scanning method
Authors: Yamanaka Kazushi , Kolosov O. V. , Nagata Yoshihiko , Koda Toshio , Nishino Hideo , Tsukahara Yusuke
Published: July 2002

We present a general theoretical formulation for the characteristics of surface acoustic waves (SAW) generated by the phase velocity scanning (PVS) method that employs a scanning single laser beam (SSB) or a scanning interference fringes (SIF). In the SSB approach, a broad band SAW pulse is generated and its amplitude is coherently enhanced when the laser scanning velocity V is equal to the phase velocity νR of the SAW. The amplitude of the SAW follows a resonance curve represented by a sinc function of the scanning velocity V, but different spatial frequency components in the SSB significantly suppress the side lobes of the resonance curve. In the SIF approach, the scanning velocity νf of the fringes is determined by the intersection angle and the frequency difference ωa of the laser beams. A narrow band tone burst of SAW with frequencies higher than 100 MHz can be excited. The SAW frequency ω depends upon a characteristic time t*, defined as a propagation time of the SAW across the laser beam spot. The SAW frequency ω is identical to the frequency difference ωa when the laser pulse width T is longer than the characteristic time t*. But, the SAW frequency ω is determined as a product kfνR of the wave number of the SIF and the SAW velocity when the laser pulse width is shorter than the characteristic time. Precise frequency measurement provided by the amplitude enhancement effect and the narrow frequency bandwidth in the SIF approach make the PVS method particularly promising for the noncontact SAW velocity measurement.
Kinetic-energy distributions of ions sampled from argon plasmas in a parallel-plate, radio-frequency reference cell
Authors: Olthoff J. K. , Van Brunt R. J. , Radovanov S. B. , Rees J. A. , Surowiec R.
Published: July 2002

Kinetic-energy distributions are presented for ions sampled from 13.56-MHz discharges in argon in a capacitively-coupled, parallel-plate, Gaseous Electronics Conference (GEC) radio-frequency reference cell. The cell was modified to allow sampling of ions through an orifice in the grounded electrode. Kinetic-energy distributions are presented for Ar+, Ar++, Ar+2, ArH+, and several trace ions for plasma pressures ranging from 1.3 Pa, where ion-atom collisions in the plasma sheath are not important, to 33.3 Pa, where collisions are important. Applied peak-to-peak radio-frequency (rf) voltages of 50, 100, and 200 V were used, and the current and voltage waveforms at the powered electrode were measured. Dependences of the ion fluxes, mean energies, and kinetic-energy distributions on gas pressure and applied rf voltage are interpreted in terms of possible ion-collision processes. The results agree with previously measured kinetic-energy distributions of ions sampled from the side of the plasma through a grounded probe for similar discharge conditions, verifying that ion kinetics are characteristic of the plasma sheath independent of where it is formed [J. K. Olthoff, R. J. Van Brunt, and S. B. Radovanov, J. Appl. Phys. 72, 4566 (1992)].
Tentative anatomy of ZnS-type electroluminescence
Authors: Bringuier E.
Published: July 2002

The paper reviews the electrical and optical mechanisms at work in sulfide-based thin-film electroluminescence display devices within the framework of general semiconductor physics. The electrical problem is twofold: (i) charge carriers are sourced at high electric field in a nominally insulating material, the carrier density increasing by almost eight orders of magnitude; (ii) the carriers are transported at high field, with an average energy largely exceeding the thermal one. (i) Carrier sourcing is best understood from direct-current-driven ZnS films, and is ascribed to partly filled deep donors transferring electrons to the conduction band by Fowler–Nordheim tunneling. The deep donors also act as carrier sinkers, and evidence for space charge is afforded by small-signal impedance analysis disclosing a markedly inductive behavior. The conduction picture obtained from dc-driven films is then used to clarify the operation of alternating-current electroluminescence structures where the sulfide is sandwiched between two blocking oxide layers. The electrostatics of the ac structure is investigated in detail including space charge and field nonuniformity, and external observables are related to internal quantities. The simple model of interfacial carrier sourcing and sinking is examined. (ii) High-field electronic transport is controlled by the electron-phonon interaction, and the modeling resorts to numerical simulations or the lucky-drift concept. At low electron energies the interaction with phonons is predominantly polar, while at optical energies it proceeds via deformation potential scattering.

In spite of the uncertainties in transport models in that range, it is likely that ∼50% of the electrons overtake 2 eV at the usual operating fields in ZnS. Light emission is associated with impurity luminescence centers embedded in the sulfide host. They are excited while current is flowing, and the ensuing relaxation is partly radiative. We describe the two ways in which an impurity may be excited electrically, namely, impact excitation (internal promotion of the center to a state of higher energy) or impact ionization (with an electron released to the host conduction band). The actual excitation mechanism depends on the position of the impurity excited level relative to the host energy bands. A calculation of the excitation yield (number of excited centers per transferred electron) is detailed in the case of impact excitation. Lastly, a phenomenological description of the various relaxation channels is given in terms of formal kinetics, and the relative importance of radiative relaxation is assessed by means of the deexcitation yield (fraction of centers decaying radiatively), which is defined in the case of the impulse response.
Deep levels of chromium-hydrogen complexes in silicon
Authors: Sadoh T. , Watanabe M. , Nakashima H. , Tsurushima T.
Published: July 2002

Deep levels related to chromium in n-type silicon have been investigated using deep level transient spectroscopy (DLTS) and concentration profile measurements. The DLTS measurement reveals four electron traps of EC−0.22, EC−0.28, EC−0.45, and EC−0.54 eV in chromium-doped samples. The trap of EC−0.22 eV is a donor due to interstitial chromium. The other three traps are observed near the surface region of samples etched with an acid mixture containing HF and HNO3 and annihilate after annealing at 175 °C for 30 min. The origin of these traps has been studied by isochronal annealing and various chemical treatments. It is demonstrated that the three electron traps are due to complexes of interstitial chromium and hydrogen.
Effective density-of-states distributions for accurate modeling of polycrystalline-silicon thin-film transistors
Authors: King Tsu-Jae , Hack Michael G. , Wu I-Wei
Published: July 2002

The effective density-of-states (DOS) distributions in unhydrogenated and hydrogenated polycrystalline silicon (poly-Si) thin films have been determined from field-effect conductance measurements of n- and p-channel thin-film transistors (TFTs) fabricated in these films. These results are compared with those obtained through device simulation as well as with trap-state densities obtained by Levinson’s method. Variations in TFT fabrication process conditions and device architecture are shown to significantly impact the DOS distribution and to correspondingly affect device performance. Hydrogenated low-temperature-processed (600 °C) films have relatively high midgap-state and valence-band tail-state densities and Fermi levels located above midgap, in contrast to high-temperature-processed (950 °C) films that have low midgap-state densities and Fermi levels located below midgap. The field-effect conductance analysis method provides realistic gap-state density information and can thereby facilitate the accurate modeling and simulation of TFT device and circuit behavior.
Response to ‘‘Comment on ‘Inverse problem for the nonexponential deep level transient spectroscopy analysis in semiconductor materials with strong disorder: Theoretical and computational aspects’ ’’ [J. Appl. Phys. 75, 1242 (1994)]
Authors: Batovski D. A. , Hardalov Ch. M.
Published: July 2002

It is shown that a recently proposed comment on our paper [J. Appl. Phys. 74, 291 (1993)] cannot be considered as a significant simplification by obtaining the deep level energy spectrum D(E).
Parallel pumping fine structure at 9.4 GHz for in-plane magnetized yttrium iron garnet thin films
Authors: Wiese G. , Buxman L. , Kabos P. , Patton C. E.
Published: July 2002

A fine structure in the parallel pumping spin wave instability absorption has been observed. The data were obtained at 9.4 GHz on a narrow linewidth in-plane magnetized yttrium iron garnet film with a magnetic layer thickness of 15.9 μm. The standard butterfly curve of the spin wave instability threshold microwave field amplitude hcrit versus external static magnetic field Hext was constructed from hcrit determinations obtained by sweeping the static field at different microwave power levels and measuring the change in microwave loss. For values of Hext below the minimum, hcrit position, the loss versus Hext profiles showed a characteristic fine structure previously observed only in spheres. The fine structure spacing was on the order of 5 Oe and the square of the spacing decreased linearly with increasing static field. These fine structure results are in accord with predictions from theory for critical modes at one-half the pump frequency, with the critical mode wave vectors aligned perpendicular to the film plane, and with the wave numbers for these modes quantized as standing spin wave modes for a thin film. Analysis of the fine structure data gives a spin wave exchange stiffness parameter Dfs=(6.0±0.9)×10−9 Oe cm2, which agrees within experimental error with the value D=(5.4±0.2)×10−9 Oe cm−2 obtained from Brillouin light scattering measurements on YIG spheres. The standing wave critical modes are explained in terms of cooperative volume dipole-dipole and shape demagnetizing induced ellipticity for the modes.
Power dissipation measurements in a low-pressure N2 radio-frequency discharge
Authors: Baggerman J. A. G. , Visser R. J. , Collart E. J. H.
Published: July 2002

Energy-flux density measurements using silicon substrates were performed on various parts of a parallel-plate etch reactor in contact with a low-pressure nitrogen radio-frequency discharge. The energy flux consists of contributions of ions, electrons, atoms, photons, and excited particles. Experimental results on the reaction kinetics of N+2 and atomic oxygen, and some additional model calculations of the excitation rates of molecular nitrogen (N2 X 1Σ+g) to excited electronic states were used to determine the rates of ionization and dissociation, and of vibrational, rotational, translational, and electronic excitation of molecular nitrogen. On the basis of these rates the contribution of various particles to the measured energy flux density on the powered and grounded electrode is discussed. It is shown that for a nitrogen discharge at a pressure of 30 Pa and a rf power setting of 300 W the energy flux density of the energetic particles, which are ions and energetic neutrals formed by charge-exchange and elastic collisions in the sheath, accounts for 93% of the measured energy flux on the powered electrode. The remaining energy flux density is caused by recombination of atomic nitrogen and fluxes of thermal electrons, photons and excited particles. The contributions of thermal electrons in the plasma and the acceleration of secondary electrons and ions in the sheaths to the power dissipation of the rf discharge were determined from experimental results and some additional model calculations.
Electron-beam-induced patterned deposition of allylcyclopentadienyl palladium using scanning tunneling microscopy
Authors: Saulys D. S. , Ermakov A. , Garfunkel E. L. , Dowben P. A.
Published: July 2002

Scanning tunneling microscopy has been used to study the electron-induced decomposition of allylcyclopentadienyl palladium [Pd(η3-C3H5)(η5-C5H5)] and subsequent deposition on a Si(111) surface. Deposition occurs via an electron impact mechanism on either the tip or surface, depending on the bias polarity, and is observed with voltages of ≥2.75 V. This is close to the predicted condensed phase dissociation energy of 2.3 eV for Pd(η3-C3H5)(η5-C5H5)→Pd+C3H5+C5H5. Metallic deposits of nanometer dimensions can be written on the surface. Deposition onto an electrochemically etched tip results in a narrow conductive secondary tip which gives improved spatial resolution when imaging high-aspect ratio features on the surface.
Solid state reaction of Co,Ti with epitaxially-grown Si1−xGex film on Si(100) substrate
Authors: Qi Wen-Jie , Li Bing-Zong , Huang Wei-Ning , Gu Zhi-Guang , Lu Hong-Qiang , Zhang Xiang-Jiu , Zhang Ming , Dong Guo-Sheng , Miller David C. , Aitken Robert G.
Published: July 2002

The solid state reaction of Co,Ti with an epitaxially grown Si1−xGex strained layer is investigated in this article. The reaction was performed in a rapid thermal annealing system. The resulting films were characterized by Rutherford backscattering, Auger electron spectroscopy, x-ray photoelectron spectroscopy, x-ray diffractometry, and scanning electron microscopy. The electrical resistivity and Hall effect were measured in the temperature range of 77–300 K. Rapid thermal annealing of Co/Si0.8Ge0.2 at 650 °C results in a Co(Si0.9Ge0.1) film with cubic crystalline structure. At higher temperature CoSi2 is formed with Ge segregation towards the surface. After a multi-step annealing, a highly oriented CoSi2 layer can be grown. For TiN/Ti/SiGe, the ternary phase of Ti(Si1−yGey)2 is formed, with a smooth surface and with resistivity comparable to the lowest value exhibited by TiSi2. The Co/Ti/SiGe/Si reaction is studied for the first time, demonstrating that the uniformity of Co/SiGe reaction is improved by applying the Co/Ti bilayer. A TiN(O)/CoSi2(Ge)/Si multilayer structure is formed, and the CoSi2(Ge) layer exhibits a strongly textured structure. Low temperature measurement reveals that the CoSi2(Ge) layer has a re?istivity slightly higher than that of CoSi2.
Effects of hydrostatic pressure on dopant diffusion in silicon
Authors: Park Heemyong , Jones Kevin S. , Slinkman Jim A. , Law Mark E.
Published: July 2002

A point-defect-based model for the stress effects on dopant diffusion in silicon is presented. Variations in binding energies and diffusivities of dopant-defect pairs under hydrostatic pressure are modeled, and a pressure-dependent dopant diffusion equation is derived. New experimental work was performed on boron pileup near dislocation loops, and compared to the model. Qualitative agreement is possible, which suggests that stress might be a significant effect in scaled modern device structures.
Structural characterization of ion-beam synthesized NiSi2 layers
Authors: Wu M. F. , De Wachter J. , Van Bavel A.-M. , Moons R. , Vantomme A. , Pattyn H. , Langouche G. , Bender H. , Vanhellemont J. , Temst K. , Bruynseraede Y.
Published: July 2002

NiSi2(111) and NiSi2(100) layers with good crystalline quality have been formed by ion-beam synthesis. An unusual Ni atom distribution showing two completely separated layers during a single implantation step has been observed by Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). The orientation, strain, and stiffness of the NiSi2 layers have been studied by RBS/channeling, x-ray diffraction, and TEM. The results show that the continuous NiSi2 layers have type-A orientation with a parallel elastic strain larger than the theoretical value of 0.46% for pseudomorphic growth. The perpendicular strain of the NiSi2(111) layers is apparently smaller than that of NiSi2(100) layers, indicating a higher stiffness in the 〈111〉 direction.
Ion implantation damage in Al0.6Ga0.4As/GaAs heterostructures
Authors: Turkot B. A. , Forbes D. V. , Robertson I. M. , Coleman J. J. , Rehn L. E. , Kirk M. A. , Baldo P. M.
Published: July 2002

The damage produced at the interfaces in a sample of GaAs/Al0.6Ga0.4As/GaAs that has been subjected to ion implantation at 77 and 293 K with 1 MeV Kr+ ions has been investigated using a combination of ion channeling and transmission electron microscopy (TEM) techniques. Low temperature ion-channeling spectra obtained from samples implanted at 77 K, to an ion dose of 1014 ions cm−2, were similar to the random spectrum, indicating that the GaAs and Al0.6Ga0.4As layers had sustained a considerable degree of damage. An asymmetric signal developed in the He+ ion-channeling spectrum as the sample warmed to room temperature. The backscattering yield corresponding to the bottom interface (i.e., Al0.6Ga0.4As grown on GaAs) resembled that of the random yield, whereas that from the top interface (GaAs grown on Al0.6Ga0.4As) decreased, shifting toward the unirradiated channeled spectrum. This observation suggests that the damage produced near the top of the Al0.6Ga0.4As layer is thermally unstable. Cross-sectional TEM images reveal a greater amount of damage in the form of extended defects and amorphous regions at the bottom interface than at the top one. This difference is sufficient to account for the observed asymmetry in the channeling spectra. Increasing the ion dose to 1015 ions cm−2 produced a damage state throughout the Al0.6Ga0.4As layer that was stable at both 77 and 293 K. TEM examination revealed that at this ion dose the GaAs and Al0.6Ga0.4As layers were both amorphous. Room-temperature implantation to a dose of 1×1016 ions cm−2 was also performed. Planar defects were observed at both interfaces, although their density appeared to be greater near the bottom interface.

In addition, the bottom interface was rougher than the top. The difference in the damage states at the bottom and top interfaces can be attributed to a variation in the number of displacement cascade events as a function of depth through the Al0.6Ga0.4As layer. This variation in the number of cascades results in different amounts of ion mixing at the top and bottom interfaces.
Study of structural changes in amorphous germanium–nitrogen alloys by optical techniques
Authors: Zanatta A. R. , Chambouleyron I. , Santos P. V.
Published: July 2002

Thin films of amorphous germanium–nitrogen (a-GeN) alloys prepared by the rf sputtering deposition technique have been studied by Raman scattering spectroscopy. The nitrogen content of the samples varies between zero and ≊3×1022 atoms cm−3, as determined from nuclear reaction analysis data. Modifications of the structural characteristics of the Ge–N alloys, probed through their phonon density, were investigated as a function of the nitrogen concentration. In addition to an increase of the network’s topological disorder, nitrogen is responsible, at relatively high concentrations, for a structural transition in the a-Ge host. The optical and electronic characterization of the samples confirm these changes which are highly dependent on the nitrogen concentration.
Spin-dependent transmission of free electrons through ultrathin cobalt layers (invited)
Authors: Drouhin H.-J. , van der Sluijs A. J. , Lassailly Y. , Lampel G.
Published: July 2002

We present an original technique to investigate spin-dependent electron interactions in ferromagnetic metals, and place it in the context of previous studies. Our technique is based on spin-polarized electron transmission through ultrathin, free-standing, metal foils. A longitudinally spin-polarized, quasimonoenergetic, free-electron beam impinges onto a ferromagnetic target consisting of a few atomic layers of cobalt sandwiched between gold layers, for an overall thickness of the order of 25 nm. It is remanently magnetized perpendicular to the film plane. The current transmitted through the foil is energy analyzed and its dependence on the relative orientation between the spin polarization of the primary beam and the magnetization direction of the cobalt layer is measured. The experiments are performed over a wide primary energy range, starting from the vacuum level of the target; the work function of the target can be lowered down to 2 eV by cesium deposition. We demonstrate a spin-filter effect, favoring the transmission of majority electrons. It is very large at low primary energy, when the electrons travel close to the 3d bands. Perspectives for compact and highly discriminative spin detectors are discussed.
Steps in the hysteresis loops of a high-spin molecule
Authors: Friedman Jonathan R. , Sarachik M. P. , Tejada J. , Maciejewski J. , Ziolo R.
Published: July 2002

We report the first observation of steps in the hysteresis loop of a high-spin molecular magnet. We propose that the steps, which occur every 0.46 T, are due to thermally assisted resonant tunneling between different quantum spin states. Magnetic relaxation increases dramatically when the field is in the neighborhood of a step. A simple model accounts for the observations and predicts a value for the anisotropy barrier consistent with that inferred from the superparamagnetic blocking temperature.
Thermal stability of W ohmic contacts to n-type GaN
Authors: Cole M. W. , Eckart D. W. , Han W. Y. , Pfeffer R. L. , Monahan T. , Ren F. , Yuan C. , Stall R. A. , Pearton S. J. , Li Y. , Lu Y.
Published: July 2002

W was found to produce low specific contact resistance (ρc∼8.0×10−5 Ω cm2) ohmic contacts to n+-GaN (n=1.5×1019 cm−3) with limited reaction between the metal and semiconductor up to 1000 °C. The formation of the β–W2N and W–N interfacial phases were deemed responsible for the electrical integrity observed at these annealing temperatures. No Ga out-diffusion was observed on the surface of thin (500 Å) W contacts even after 1000 °C, 1 min anneals. Thus, W appears to be a stable contact to n+-GaN for high temperature applications.
Hall factor and drift mobility for hole transport in strained Si1−xGex alloys
Authors: Joelsson K. B. , Fu Y. , Ni W.-X. , Hansson G. V.
Published: July 2002

Hole transport in B-doped strained Si1−xGex has been studied using Hall measurements for boron concentrations from 2×1018 to 7.5×1018 cm−3 with Ge content 0⩽x⩽0.36. By keeping the B flux constant during the molecular beam epitaxy growth of sets of samples and only varying the Si and Ge fluxes, we were able to prepare samples for an accurate determination of the Hall factor based on using the established relationship between B-doping concentration and resistivity for pure Si. It was found that the Hall factor drops considerably when the Ge content is increased. Determined Hall factor values are compared with calculated values taking into account the full valence band structure and various scattering mechanisms. The hole drift mobility has been derived from our measured Hall mobility using the determined Hall factor for the corresponding Ge content. We find that, depending on the doping concentration, the drift mobility can be higher for strained layers containing Ge. The grown layers were also characterized using x-ray diffraction, where the Ge contents and layer thicknesses could be confirmed. Temperature dependent measurements from 50 K to room temperature have also been made.
Transport of positrons in the electrically biased metal-oxide-silicon system
Authors: Clement M. , de Nijs J. M. M. , Balk P. , Schut H. , van Veen A.
Published: July 2002

This paper describes a study of the effect of an external electric field on the behavior of positrons in metal-oxide-silicon (MOS) systems. Doppler broadening measurements of the annihilation radiation were performed on capacitors with identical thermally grown SiO2 layers and with Al, W and Au layers as a gate. The data were analyzed by the combined use of the shape- and wing-parameters of the photo peak. The observed effects of the electric field are due to the field-driven transport of positrons through the SiO2, silicon and the interfaces. By applying a field of the order of 1 MV/cm the positrons can be efficiently transported through the approximately 100 nm thick SiO2 layer. From the transport behavior of the positrons it is concluded that the positron affinity is higher for SiO2 than for silicon and for the gate metal. By properly choosing the direction of the field, the positrons implanted into the SiO2 layer are collected either at the Si/SiO2 interface or at the SiO2/gate interface. For negative gate bias the positrons implanted into the substrate, that diffuse back to the SiO2, are transported through the oxide layer and injected into the gate metal. This is the first time that field-assisted transport of positrons across an insulating layer has been demonstrated.
High tunability of the permittivity of YBa2Cu3O7−∂/SrTiO3 heterostructures on sapphire substrates
Authors: Boikov Yu. A. , Claeson T.
Published: July 2002

The combination of a low loss, high-Tc superconductor and a polarizable dielectric looks interesting from the point of tunable, high Q filters for cellular communication. Epitaxial heterostructures of YBa2Cu3O7−∂/SrTiO3/YBa2Cu3O7−∂/CeO2 and SrTiO3/YBa2Cu3O7−∂/CeO2 were grown on sapphire substrates in this study. Superconducting transition temperatures of 88–90 K and a critical current density of about 2×106 A/cm2 at 77 K were determined for YBa2Cu3O7−∂ films on CeO2 buffered sapphire. An effective permittivity of 340 at 300 K was measured capacitively for the SrTiO3 layer between YBa2Cu3O7−∂ electrodes; it increased three times at 50 K. The dielectric constant of SrTiO3 was observed to decrease a factor of 2 as a dc bias voltage of ±2.5 V was applied between the electrodes. Much smaller nonlinearities and temperature dependences of the dielectric constant were noted if the top YBa2Cu3O7−∂ electrode was replaced by an Ag one.
Thermal stability of the electrical isolation in n-type gallium arsenide layers irradiated with H, He, and B ions
Authors: de Souza J. P. , Danilov I. , Boudinov H.
Published: July 2002

The stability of the electrical isolation in n-type GaAs layers irradiated with ions of different mass is compared. The irradiations were performed with proper doses of H+1, He+4, or B+11 ions to create specific damage concentration level which lead to: (i) the trapping of practically all the carriers (Rs ≈108 Ω/□), (ii) the onset of hopping conduction (Rs ≈108 Ω/□), and (iii) a significant hopping conduction (Rs ≈106 Ω/□). Irrespectively of the ion mass, the temperature range for which the isolation is preserved, i.e., Rs >108 Ω/□, extends up to 200 or ≈ 600 °C, respectively, for the cases (i) and (ii). In case (iii), this range comprises temperatures from ≈ 400 to 650 °C. Annealing stages at 200 and 400 °C recover in a great extent the conductivity and improve the carrier mobility in low dose irradiated samples [case (i)]. In samples irradiated to higher doses [cases (ii) and (iii)], the conductivity recovers in a single stage.
Langmuir probe measurements of plasma parameters in the late stages of a laser ablated plume
Authors: Hendron J. M. , Mahony C. M. O. , Morrow T. , Graham W. G.
Published: July 2002

A simple Langmuir probe technique has been used to measure the electron density, electron temperature, and plasma potential in the late stages (>5 μs) of a laser ablated plasma plume. In the plasma, formed following 248 nm laser irradiation of a copper target, in vacuum at a laser fluence of 2.5 J cm−2, electron densities of ∼1018 m−3 and temperatures of ∼0.5 eV were measured. These values are comparable with those reported previously using Faraday cup detectors and optical emission spectroscopy, respectively.
Magnetic and transport properties of the itinerant electron system Hf1−xTaxFe2
Authors: Duijn H. G. M. , Brück E. , Menovsky A. A. , Buschow K. H. J. , de Boer F. R. , Coehoorn R. , Winkelmann M. , Siemensmeyer K.
Published: July 2002

Magnetization and resistivity measurements of poly- and single-crystalline samples of Hf1−xTaxFe2 are presented. At the antiferromagnetic to ferromagnetic transition we find a large change of resistance which can be induced as a function of temperature as well as field. For single-crystalline Hf0.86Ta0.14Fe2 we observe at room temperature a giant magnetoresistance effect of 6%. From neutron-powder-diffraction measurements, possible magnetic structures in the different magnetic states are constructed.
The composition of ultrathin silicon oxynitrides thermally grown in nitric oxide
Authors: Gusev E. P. , Lu H. C. , Gustafsson T. , Garfunkel E. , Green M. L. , Brasen D.
Published: July 2002

The thermal oxynitridation of Si(100) in nitric oxide (NO) has been studied by high resolution medium energy ion scattering for ultrathin films. The nitrogen depth distribution and the composition of the films have been accurately determined. It is observed that for NO-grown films the nitrogen is distributed relatively evenly in the film, unlike the sharply peaked distribution observed in the case of SiO2 films that were subsequently annealed in NO. The width of the nitrogen distribution, as well as the oxynitride thickness, increase with temperature. It is further found that the total amount of nitrogen in the film and the ratio of nitrogen to oxygen increases with increasing oxynitridation temperature. These results have significant impact on our understanding of how nitrogen can be positioned in next-generation gate dielectrics.
Dependence of optical gain on crystal orientation in wurtzite–GaN strained quantum-well lasers
Authors: Ohtoshi T. , Niwa A. , Kuroda T.
Published: July 2002

Optical gains in wurtzite–GaN strained quantum-well (QW) lasers are estimated theoretically for various crystallographic directions. The calculation of the valence subbands is based on the k⋅p theory, where deformation potentials are determined by a semiempirical tight-binding method. It is found that the gains in GaN strained QW lasers with non-(0001) orientations, particularly around the (101̄5) orientation, are markedly high and anisotropic, unlike those in (0001)-oriented lasers.