bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogenation during thermal nitridation of silicon dioxide
Authors: Kuiper A. E. T. , Willemsen M. F. C. , Theunissen A. M. L. , van de Wijgert W. M. , Habraken F. H. P. M. , Tijhaar R. H. G. , van der Weg W. F. , Chen James T.
Published: July 2002

The incorporation of nitrogen and hydrogen during nitridation of SiO2 was studied over the temperature range of 800–1000 °C and for ammonia pressures of 1, 5, and 10 atm. The nitrogen content of the nitrided films was determined with Rutherford-backscattering spectrometry and elastic-recoil detection. Nitrogen in-depth profiles were obtained applying Auger analysis combined with ion sputtering. Hydrogen profiles in the films were measured using nuclear-reaction analysis. Both the nitrogen and hydrogen incorporation were found to increase with temperature in this range. A higher ammonia pressure primarily increases nitridation of the bulk of the oxide films. Depending on the nitridation conditions, up to 10 at.% of hydrogen may be incorporated. As distinct from the nitrogen profiles, the hydrogen in-depth profiles are essentially flat. The concentration of hydrogen in the films, however, was always found to be smaller than that of nitrogen: measured H/N ratios varied between 0.25 and 0.85, the smaller values being obtained for the thinner oxides and higher nitridation temperatures. The model previously postulated to explain the nitrogen incorporation during atmospheric nitridation of SiO2 proves to be valid at higher pressures as well. By considering the role of OH as a reaction product of the nitridation process, the hydrogen results can be accommodated within the same concept. The model predicts a low H/N-incorporation ratio for a thin surface and interface layer and a substantially larger ratio for the bulk of the film. If this prediction is correct, which seems to be indicated by the etch-rate behavior of the nitrided oxides, then this would have considerable importance for the electrical properties of this material.
Crystalline oxide tunnel barriers formed by thermal oxidation of aluminum overlayers on superconductor surfaces
Authors: Braginski A. I. , Talvacchio J. , Janocko M. A. , Gavaler J. R.
Published: July 2002

Crystalline oxide tunnel barriers were formed by thermal oxidation of thin Al overlayers on single-crystal and polycrystalline films of four refractory superconductors: Nb, Mo-Re, Nb3Sn, and NbN. Tunnel junctions were fabricated mostly with Pb-Bi and also with Nb, Mo-Re, and NbN counterelectrodes. Differences in the base electrode crystallinity, surface roughness, oxygen affinity, and native oxide properties influenced the average barrier height, the subgap and normal (above-gap) conductance and the occurrence of microshorts. An effect of the overlayer deposition method (evaporation versus sputtering) was also noticed. The comparison of properties of barriers obtained on different base electrodes and of those amorphized by ion milling lead to the observation that amorphous barriers are more uniform and representative of Al2O3 than the crystalline and epitaxial barriers. The properties of the latter are defined, in part, by the shunting native oxide channels which result from a nonuniform coverage of the base electrode.
Interface formation and microstructural evolution in a-Si:H/a-SiNx:H heterostructures
Authors: Collins R. W.
Published: July 2002

I n situ ellipsometry measurements have been used to determine the optical structure of interfaces during the growth of a-Si:H/a-SiNx:H heterostructures. We have observed significant deviations of the ellipsometry data from calculations which assume both uniform growth and abrupt interfaces. For the growth of a-SiNx:H on a-Si:H such deviations are attributed to a 40 Å layer, less absorbing than bulk a-SiNx:H, which is left behind at the interface. This layer appears to result from a higher void density or enhanced N incorporation in the initial 20 s of a-SiNx:H growth. It is also possible, however, that a thin layer on the a-Si:H surface is converted to a transparent nitride. In support of the latter possibility, the a-Si:H surface is found to be highly reactive in a N2 plasma: a 150 Å nitride layer is formed during a 10-min exposure time at the same plasma power used for a-SiNx:H growth. For the growth of a-Si:H on a-SiNx:H, we have found that the interface structure is sensitive to the nitride preparation technique. The evolution of the surface roughness on a-Si:H alternate layers is obtained in real time during the preparation of an a-Si:H/a-SiNx:H multilayer structure. The implications of these observations for recent interpretations of optical measurements on multilayer structures is treated in detail.
Effects of heavy ion irradiation on amorphous hydrogenated (diamondlike) carbon films
Authors: Prawer S. , Kalish R. , Adel M. , Richter V.
Published: July 2002

Energetic ion-beam irradiation of diamondlike carbon thin films induces a decrease of 5–6 orders of magnitude in the resistivity of the films from their as-grown value of 107 Ω cm. Diagnostics used to characterize the nature of the transformation included optical absorption measurements (band gap), Raman spectroscopy (microcrystalline structure), Rutherford backscattering spectroscopy (hydrogen content of the films), and measurements of the temperature dependence of the conductivity (electronic structure). It was found that the initial decrease in resistivity with an increasing ion dose is due to the loss of hydrogen from the films, with a concomitant decrease in the optical band gap. Heating the films during the irradiation greatly accelerates the rate of hydrogen loss as a function of dose. Once the hydrogen removal is complete, further irradiation increases the film conductivity by inducing the growth of microcrystallites of graphite.
Spark propagation mechanisms in ambient air at the surface of a charged dielectric. I. Experimental: The main stages of the discharge
Authors: Larigaldie S.
Published: July 2002

The fast propagation (v≊106 ms−1) of an ionized and thermalized channel (ne≊1018 cm−3, T≊2.8×104 K) is studied in ambient air at atmospheric pressure, using gliding discharges produced over a charged dielectric slab. For surface voltages of about 100 kV, 1-m-long gliding sparks follow a straight line without any preionization of the gas. In this way, the discharges can be investigated with full diagnostics, including measurements of the current and of the propagation velocity, recording of the light emission (electronic image converter, spectroscopy, Lichtenberg figures), holographic interferometry of the spark channels, and detection of transient electric fields by capacitive probes. The various measurements are synchronized from optical fiber devices located close to the sparks. The study shows that the thermalized spark channel is produced by the three following stages: (a) a predischarge stage where the electron temperature Te≊2 eV is much greater than the gas temperature T0<1500 K; (b) a transient arc stage, lasting about 10 ns where energy is transferred from the electric field to the gas ionization; and (c) a heating stage, lasting from 25 to 60 ns, where the electric field has been largely reduced.
Determination of valence and conduction-band discontinuities at the (Ga,In) P/GaAs heterojunction by C-V profiling
Authors: Rao M. A. , Caine E. J. , Kroemer H. , Long S. I. , Babic D. I.
Published: July 2002

The valence and conduction band discontinuities for the lattice matched (Ga,In)P/GaAs heterojunction have been determined by capacitance-voltage (C-V) profiling. Both p-p and n-n heterojunctions were profiled, in order to obtain separate and independent values for both the valence-band-edge discontinuity (ΔEv) and the conduction-band discontinuity (ΔEc). The band lineup is found to be of the straddling type with the valence- and conduction-band discontinuities 0.24 and 0.22 eV, respectively, with an estimated accuracy of ±10 meV. Computer reconstruction of the C-V profiles was used to check the consistency of the data. The band offset data indicate that the (Ga,In)P/(Al,Ga)As system should be staggered for a certain range of Al compositions.
Multipulse laser damage of GaAs surfaces
Authors: Sardar Dhiraj K. , Becker Michael F. , Walser Rodger M.
Published: July 2002

An in-depth study of the single and multiple-pulse laser (10 ns, 10 Hz, and 1064 nm) damage of (100) single-crystal gallium arsenide surfaces is presented. The surface morphologies resulting from both chemical etching and laser-induced damage are discussed. The damage behavior is determined from the damage probability and accumulation curves. The dependence of damage on accumulated incident energy in multipulse experiments is determined and compared with the behavior of other semiconductor and metal surfaces. Finally, Auger electron spectroscopy is employed to measure the elemental depth composition of GaAs wafers using Ar+ ion sputter etching. This technique is used to study the changes in elemental depth profiles caused by the laser-induced damage.
The effects of oxygen dose on the formation of buried oxide silicon-on-insulator
Authors: Mao B.-Y. , Chang P.-H. , Chen C.-E. , Lam H. W.
Published: July 2002

The effects of the oxygen dose on the microstructure and the dielectric properties of the buried oxide in oxygen implanted silicon-on-insulator (SOI) structures have been studied. Cross-sectional transmission electron microscopy analyses show that the density of oxygen precipitates at the silicon/buried-oxide interface increases with a decreasing oxygen dose when identical annealing processes are employed. Annealing studies reveal that 1275 °C anneals annihilate the oxygen precipitates. A longer annealing time is required to achieve an oxygen-precipitate-free silicon layer in an SOI substrate implanted with a lower oxygen dose. The inverse relationship between oxygen content in the silicon film and oxygen dose is attributed to the redistribution of oxygen during implantation. In the oxygen dose range studied, the thickness and the breakdown voltage of the buried oxide layer increase with increasing oxygen dose. Higher postimplant annealing temperature improves the isolation properties of the buried oxide layer.
Doping and composition profiling in Hg1−xCdxTe by the graded capacitance-voltage method
Authors: Rosbeck J. P. , Harper M. E.
Published: July 2002

A capacitance-voltage (C-V) technique is established to simultaneously profile both the band gap (i.e., composition or x value) and doping levels in Hg1−xCdxTe material grown by liquid-phase epitaxy. A photochemical SiO2 passivation/dielectric (PHOTOX©) is used to fabricate metal-oxide-semiconductor devices along the surface of taper etched samples to permit measurement as a function of depth into the layer. In this manner, a depth resolution near 200 Å is feasible. Surface state densities generally in the 1010 cm−2 eV−1 range are achieved with the PHOTOX© passivation, making possible analysis by low- and/or high-frequency C-V methods. Both the x value and doping levels throughout multiple layer samples of changing material type, composition, and doping level are established. Material with band gaps ranging from about 0.1 to 0.3 eV, and doping levels from 3×1015 to 2×1017 cm−3, are examined. The measured composition results on bulk material samples are found to be in good agreement with other methods of anlysis, namely, visible light reflectance, infrared transmittance, and energy dispersive x ray.
Degradation of metal-oxide-semiconductor devices caused by iron impurities on the silicon wafer surface
Authors: Takizawa Ritsuo , Nakanishi Toshiro , Ohsawa Akira
Published: July 2002

A reliable method of controlling iron impurities on the silicon wafer surface at low levels has been developed by using an iron-contaminated HNO3 solution. Iron ions are thought to react with the silicon native oxide to form an Fe(III)-O complex in proportion to the iron concentration in the solution. Using this method, we have quantitatively investigated the influence of iron impurities on metal-oxide-semiconductor device characteristics. The drastic degradation of generation lifetime, surface generation velocity, and dielectric breakdown strength of SiO2 have been observed above the surface iron concentration of 1×1012, 5×1012, and 1×1013 cm−2, respectively.
Hot-electron transport in selectively doped n-type AlGaAs/GaAs heterojunctions
Authors: Hirakawa Kazuhiko , Sakaki Hiroyuki
Published: July 2002

We investigate the high-field transport of two-dimensional (2D) electrons in selectively doped AlGaAs/GaAs heterojunctions. The dependencies of mobilities on external applied electric fields are systematically studied by pulsed Hall measurements up to 1.5 kV/cm on various samples with mobilities ranging from 4×104 to 1.3×106 cm2/V s. Measured dependencies of mobilities on electric fields are compared with theories. It was found that the simple theoretical approach based on the electron temperature model is insufficient, and that the measured mobilities are in excellent agreement with the recent theoretical results of Lei et al. [Phys. Rev. B 33, 4382 (1986)]. The high-field descreening effect is found to be more responsible for the reduction of 2D electron mobilities than the electron heating. At very high fields (several kV/cm), drift velocities of electrons determined by two-terminal I-V measurements are found to saturate gradually with increasing electric fields. Measured saturation velocities do not depend sensitively on electron densities and low-field mobilities, and are (2.0±0.2)×107 cm/s at both 4.2 and 77 K, and (1.2±0.1)×107 cm/s at 295 K. The lattice-temperature dependence of saturation velocities is compared with a crude estimation which takes into account the polar optical phonon scattering, and is found to be in rather good agreement. Consequently, it is clarified that high electron mobility transistors are superior to Si metal-oxide-semiconductor field-effect transistors in the ultimate switching speed at least by a factor of 2.5 at 77 K and 1.8 at 300 K.
Mechanism for radiation resistance of InP solar cells
Authors: Yamaguchi Masafumi , Ando Koushi
Published: July 2002

Photovoltaic properties of InP solar cells and defect behaviors of InP single crystals irradiated with 1-MeV electrons have been studied in order to clarify the superior radiation resistance of InP solar cells compared to Si and GaAs solar cells. It is confirmed that the excellent radiation tolerance of the InP cells is originated from the room-temperature annealing and minority-carrier injection-enhanced annealing phenomena of major radiation-induced defects in InP. The main defects in InP induced by irradiation at room temperature are thought to be due to a Frenkel pair of phosphorus vacancy and interstitial. They are much more mobile than those in GaAs.
Optical properties of In2S3:Co2+ single crystals
Authors: Kim Wha-Tek , Lee Wang-Sub , Chung Chang-Sub , Kim Chang-Dae
Published: July 2002

β⋅In2 S3 and β⋅In2S3 :Co2+ single crystals were grown by the chemical transport reaction method. The optical absorption and photoconductivity measurements carried out at the temperature region 20–300 K and the photoacoustic spectrum was done at 292 K. The results showed that the structural defects of the β⋅In2 S3 single crystal decreased as cobalt was introduced into the samples and that the cobalt atoms were located at the Td symmetry site of the β⋅In2 S3 host lattice as Co2+ ion.
A lumped circuit model for transient arc discharges
Authors: Robiscoe R. T. , Kadish A. , Maier II William B.
Published: July 2002

Electrical breakdown of highly charged insulating systems can result in an arc discharge, i.e., a sudden, intense pulse of current. We model such arcs by a simple circuit: the discharge of a capacitor C (related to the initial charge reservoir) through a series inductor L and resistor R. For R=V*/‖Ia‖, where V* is a positive constant and Ia is the arc current, an essentially arbitrary dependence for L=L(Ia), a constant capacitance, and a circuit starting voltage V0, we establish four remarkable results for the subsequent arc discharge: (1) no discharge occurs at all unless ‖V0‖>V*; (2) if n is the largest non-negative integer for which ‖V0‖≥(2n+1)V*, then the arc current will reverse sign precisely n times and will decline in amplitude by 2V* at each extreme; (3) the discharge stops abruptly at a final voltage Vf=(−1)n+1[V0−(n+1)2V* sgn V0]; (4) maxima and minima in Ia occur at voltages V=±V*. Results (1) and (3) provide the threshold condition and finite final potential necessary for any realistic arc discharge theory, while result (2) suggests an experiment to look for a finite number of current oscillations in a highly driven arc. Result (4) suggests an experimental method for determining V*. Finally, the empirical areal scaling laws for arcs are reproduced with this model. The usual phenomenological treatments of arc start and stop voltages, current ringing, and areal scaling are thus modeled by a single parameter, V*. These results are generalized to voltage-dependent capacitance, C(V).
Zinc diffusion in InGaAsP
Authors: van Gurp G. J. , Tjaden D. L. A. , Fontijn G. M. , Boudewijn P. R.
Published: July 2002

Ampoule diffusion of Zn in undoped liquid phase epitaxial InGaAsP layers between 425 and 525 °C shows the Zn solubility, as measured with secondary ion mass spectrometry, to be much larger than in InP and to be slightly less than in GaAs. The acceptor concentration, as determined by capacitance-voltage measurements, is 60%–90% of the Zn concentration. Incorporation and diffusion of Zn can be described with the interstitial-substitutional model. The difference between the acceptor and Zn concentrations can be explained by compensating Zn interstitial donors or by neutral Zn-vacancy complexes. The diffusion depth is slightly smaller than in InP and much larger than in GaAs. In n-type InGaAsP, profiles are found with a cut-off similar to the behavior in InP. The solubility is higher than in undoped InGaAsP.
Nonlinear properties of Rayleigh and Stoneley waves in solids
Authors: Shui Yongan , Solodov Igor Yu.
Published: July 2002

Bulk wave reflection formulas are extended to the surface-wave case, considering Rayleigh and Stoneley waves in terms of refracted inhomogeneous longitudinal and transversal waves, linked by the surface coupling. In this manner, a physical mechanism of second-harmonic generation process is clearly shown. The analytical expressions and physical pictures of Rayleigh- and Stoneley-wave harmonic generation have been derived in a second-order approximation. The solution shows that the second-harmonic surface waves have a field structure different from the fundamental ones and varying with the propagation distance. Some parameters were defined to characterize the elastic surface-wave second-harmonic generation efficiency. Numerical data for some isotropic materials are present. The steady-state form of finite amplitude surface wave is described and explained by a clear physical model.
Growth of ZnSe/ZnS strained-layer superlattices on Si substrates
Authors: Yokogawa Toshiya , Sato Hisanao , Ogura Mototsugu
Published: July 2002

The high-quality ZnSe-ZnS strained-layer superlattices (SLSs), as well as the ZnS layers, were successfully grown for the first time on Si substrates. Photoluminescence (PL) spectra of ZnS layers grown on Si showed an intense excitonic-emission line. In transmission electron microscopy analyses, no misfit dislocations and no moiré fringes were observed on the ZnS layer with a thickness of less than about 500 Å. We have also characterized ZnSe-ZnS SLSs grown on Si substrates. By the PL measurements, an intense excitonic-emission line, and no emissions due to deep levels, were observed. As the ZnSe well-layer thickness decreased, the peak of the line largely shifted towards the higher-energy side. This behavior may be related to the quantum size effect. In the temperature dependence of PL intensity, there appeared the thermal quenching process, which may be related to the thermal release of excitons in quantum wells. As the thickness of the ZnSe well-layer decreased, the activation energy abruptly increased at a ZnSe thickness of less than the three-dimensional exciton Bohr radius in bulk ZnSe. It is proposed that the dependence of the activation energy is due to the two-dimensional exciton behavior in quantum wells.
Mechanism for nearly ohmic behavior in annealed Au/n-GaAs Schottky diodes
Authors: Leon R. P. , Newman N. , Liliental-Weber Z. , Weber E. R. , Washburn J. , Spicer W. E.
Published: July 2002

The origin of the ohmic behavior observed after annealing Au/n-GaAs {110} Schottky diodes was investigated by electron-beam-induced current (EBIC) measurements of diode plan views and cross sections, combined with standard scanning electron microscopy and transmission electron microscopy techniques. The large leakage currents responsible for this behavior arise at the periphery of the deposited gold films, where elongated gold crystallites which lie on the GaAs surface are observed after heat treatment. These crystallites are typically 2–5 μm long, 500–2000 Å wide, and are crystallographically oriented along the GaAs [110] direction. EBIC imaging demonstrated that a space-charge region was present under the peripheral area showing the gold crystallites. Comparison of current collection as measured with EBIC between annealed and unannealed diodes shows a large reduction in current collection under and around the periphery of the annealed diodes. These data allow attribution of the ohmic behavior to a recombination current. Experiments done with overlapping Au evaporations show that recombination on the bare GaAs surface between the observed crystallites surrounding each annealed diode is the main component of this recombination current, and thus of the large leakage current.
Systematic studies on the effect of growth interruptions for GaInAs/InP quantum wells grown by atmospheric pressure organometallic vapor-phase epitaxy
Authors: Wang T. Y. , Reihlen E. H. , Jen H. R. , Stringfellow G. B.
Published: July 2002

GaInAs/InP quantum wells were grown by using atmospheric pressure organometallic vapor-phase epitaxy with and without interruptions at the interfaces. The growth schedule has a major effect on the optical properties of the quantum wells. For approximately 10-Å-thick wells, the ground-state energy as determined by 10-K photoluminescence decreases in the following order: continuous growth, an interruption at the second interface, and interruptions at both interfaces. It is demonstrated that As is effective in substituting for P atoms on the InP surface during AsH3 purge. Varying the AsH3 flow rate during growth of the GaInAs well layer significantly influences the emission energies for samples grown continuously or with an interruption at the second interface. However, the emission energies of quantum wells grown with interruptions at both interfaces are found to be independent of the AsH3 flow rate, indicating insignificant substitution of As for P in the InP barriers. An interfacial layer of InAsxP1−x may play a dominant role in determining the emission energies for quantum wells thinner than 50 Å.
On the origin of rapid thermal process induced recombination centers in silicon
Authors: Eichhammer W. , Vu-Thuong-Quat  , Siffert P.
Published: July 2002

The recombination centers induced by rapid thermal processing are characterized by measurements of the minority-carrier diffusion lengths using the surface photovoltage technique. It is shown that transition metals originating from the ambient, especially the furnace and handling, as well as residual metal impurities in the starting material are important factors for the final diffusion length in rapid thermal processed virgin silicon. The preparation of the surface has equally an influence on the diffusion length. The strong degradation of ion-implanted samples is a result of coimplanted metallic impurities which are due to sputtering on metallic parts of the implantation system (apertures), and which are activated by the quenching step. Most of our data presented for quenching-induced recombination centers are in agreement with a model of isolated metallic impurities which are activated by the quenching. The puzzling deep-level transient spectroscopy data on quenched-in defects, however, and some experimental results give hints that the nature of these centers may be a complex one.
Effects of Hartree, exchange, and correlation energy on intersubband transitions
Authors: Bloss Walter L.
Published: July 2002

We calculate the effects of the Hartree and the exchange-correlation potential on the subband levels of a doped GaAs/AlxGa1−xAs quantum well within the local density approximation. The intersubband transition energy appropriate to infrared detectors is calculated including both exciton and depolarization shifts. These effects are all known to be very important in the Si inversion layer and are shown here to be significant for the intersubband transitions in doped quantum wells. The effects of an applied electric field on these energy levels is explicitly included in the calculation. The Hartree potential is shown to effectively screen the electric field significantly reducing the Stark effect.
Stability of electrical properties of nitrogen-rich, silicon-rich, and stoichiometric silicon nitride films
Authors: Lau W. S. , Fonash S. J. , Kanicki J.
Published: July 2002

Metal-nitride-silicon capacitors were used to explore the stability of the electrical properties of silicon nitride films of various stoichiometries. Silicon-rich silicon nitride films were found to display a large and symmetric hysteresis loop in the capacitance-voltage curve, a large flat-band voltage shift approximately symmetric with respect to the polarity of the voltage under bias temperature stress, and a current density-voltage characteristic which is approximately symmetric with respect to polarity. It is argued that in these silicon-rich silicon nitride films the dominant defects are silicon dangling bonds which can trap either electrons or holes. A different class of behavior was observed, however, for nitrogen-rich silicon nitride films deposited by plasma enhanced chemical vapor deposition. These films have a much smaller and asymmetric hysteresis loop in the capacitance-voltage curve, an asymmetric flat-band voltage shift under bias temperature stress, and an asymmetric current density-voltage characteristic. In addition, the breakdown electric field was found to be higher for these films for positive than negative gate biases. Our proposed explanation for these observations is that silicon dangling bonds, which can trap either electrons or holes, are greatly reduced in nitrogen-rich films and the dominant residual traps are hole traps.
Strain effects and band offsets in GaAs/InGaAs strained layered quantum structures
Authors: Arent D. J. , Deneffe K. , Van Hoof C. , De Boeck J. , Borghs G.
Published: July 2002

Strained single quantum wells composed of GaAs/InGaAs/GaAs were grown by molecular beam epitaxy and characterized at room temperature by photoreflectance and at 6 and 77 K by photoluminescence spectroscopy. For the InGaAs/GaAs heterojunction, utilizing a band offset ratio of 85:15 (conduction band:valence band) for the intrinsic (nonstrained) interface and a contribution of the hydrostatic compression to the valence band movement corresponding to the pressure sensitivity of the spin orbit band, excellent agreement is found between calculated excitonic transition energies and those found by experiment at all temperatures studied. Our analysis indicates that material parameters and the combined strain components used to calculate band structure are not temperature dependent to our degree of sensitivity. An empirical equation, which differs slightly from that for bulk InGaAs crystals, describing the nonstrained band-gap energy as a function of In fraction at 77 K is presented. The difference between band offset ratios for the intrinsic and strained heterojunction are found to be significant and the relative merits of each are discussed.
Reverse-bias current reduction in low-temperature-annealed silicon p
n junctions by ultraclean ion-implantation technology
Authors: Nitta T. , Ohmi T. , Ishihara Y. , Okita A. , Shibata T. , Sugiura J. , Ohwada N.
Published: July 2002

Reduction in the reverse-bias current in low-temperature-annealed silicon pn junctions has been studied. It has been shown that the transition region existing underneath the ion-implantation-generated amorphous layer and the contamination incorporated into this region play a decisive role in determining the reverse current level. In order to minimize the contamination involvement into the transition region, ultraclean ion-implantation technology has been developed. Ion implantation was carried out under a UHV (5×10−10 Torr) condition in order to minimize the recoil implantation of adsorbed contamination at the surface. The contamination due to the high-energy ion-beam sputtering of component parts in the ion implanter has also been suppressed. As a result, a low reverse-bias current level of about 1.2×10−7 A/cm2 has been obtained for arsenic-implanted n+p junctions annealed at 550 °C, which is more than two orders of magnitude smaller than that previously reported. The stress compensation technology employing combined implantation of phosphorus and arsenic has also been shown to be very effective in reducing the lattice strain and in suppressing the damage generation.
A distributed parameter wire model for transient electrical discharges
Authors: Maier II William B. , Kadish A. , Sutherland C. D. , Robiscoe R. T.
Published: July 2002

A model for freely propagating transient electrical discharges, such as lightning and punch-through arcs, is developed in this paper. We describe the electromagnetic fields by Maxwell’s equations and we represent the interaction of electric fields with the medium to produce current by ∂J/∂t=ω2(E−E*Ĵ)/4π, where ω and E* are parameters characteristic of the medium, J≡current density, and Ĵ≡J/‖J‖. We illustrate the properties of this model for small-diameter, guided, cylindrically symmetric discharges. Analytic, numerical, and approximate solutions are given for special cases. The model describes, in a new and comprehensive fashion, certain macroscopic discharge properties, such as threshold behavior, quenching and reignition, path tortuosity, discharge termination with nonzero charge density remaining along the discharge path, and other experimentally observed discharge phenomena. Fields, current densities, and charge densities are quantitatively determined from given boundary and initial conditions. We suggest that many macroscopic discharge properties are properly explained by the model as electromagnetic phenomena, and we discuss extensions of the model to include chemistry, principally ionization and recombination.
An annealing study of strain relaxation and dislocation generation in Si1−xGex/Si heteroepitaxy
Authors: Timbrell P. Y. , Baribeau J.-M. , Lockwood D. J. , McCaffrey J. P.
Published: July 2002

The generation of interface misfit dislocations, and the accompanying strain relaxation, in a molecular-beam epitaxy grown 0.17 μm thick metastable Si0.82Ge0.18/Si(100) strained epilayer have been studied in detail as a function of rapid thermal annealing treatments over the 500–850 °C temperature range. Charge collection and transmission electron microscopy were used to determine the onset of relaxation by directly imaging misfit dislocations and to investigate the variation in dislocation density with increasing anneal temperature. The strain variation in the epilayer was carefully monitored using double-crystal x-ray diffraction and Raman spectroscopy, and the annealing induced changes in strain related to the electron microscopy observed density of interface misfit dislocations. The relative merit of each experimental technique is discussed in the light of these results. The generation of strain relieving dislocations was found to be an activated process, with an activation energy on the order of 1.5 eV for the Si0.82Ge0.18 epilayer. Preferential surface streaking, along one of 〈110〉 directions, was observed in the relaxed samples despite a nondirectional uniform network of interface misfit dislocations.
Stress measurements of Pt/Ti/InP and Pt/Ti/SiO2/InP systems: I
n s
i
t
u measurements through sintering and after rapid thermal processing
Authors: Katz A. , Dautremont-Smith W. C.
Published: July 2002

The stresses induced in an evaporated Pt(75 nm)/Ti(50 nm) bilayer metallization scheme on InP and SiO2 (300 nm)/InP substrates, as well as the stress in a SiO2 layer (300 nm) on an InP substrate, were measured in situ during sintering at temperatures of 25 to 500 °C and after rapid thermal processing (RTP) at temperatures of 400, 450, and 500 °C for 30 s. The as-deposited highly tensile Pt/Ti bilayer structure on InP (5×109 dyn cm−2) was found to be stress-free when heated to 400 °C and to have relatively low tensile stress after cooling back to room temperature. The as-deposited Pt/Ti/SiO2 structure on InP was found to be only moderately tensile stressed (3×109 dyn cm−2) and became more tensile as a result of heating to 500 °C (5×109 dyn cm−2). The high tensile stress was preserved even after cooling back to room temperature. This is mostly due to the tendency of the plasma-enhanced chemical vapor deposited (PECVD) SiO2 layer to undergo densification and switch its as-deposited compressive stress (−2.5×109 dyn cm−2) to tensile (2×109 dyn cm−2) when heated to 500 °C. The measured stresses after rapid thermal processing (RTP) revealed no observable difference from the in situ measured stresses. This suggests a negligible influence of the speed of heating and cooling through the RTP on the overall stresses induced in the thin layers. The previously unknown coefficient of thermal expansion and the biaxial elastic moduli of the PECVD SiO2 and the evaporated Ti and Pt thin films were determined by in situ stress measurements of the above-mentioned structure as well as systems composed of the same thin layers deposited on Si, GaAs, GaP, and InAs substrates.
Effects of silver doping in the high-T
c superconductor system Y-Ba-Cu-O
Authors: Kao Y. H. , Yao Y. D. , Jang L. Y. , Xu F. , Krol A. , Song L. W. , Sher C. J. , Darovsky A. , Phillips J. C. , Simmins J. J. , Snyder R. L.
Published: July 2002

Changes in various superconducting properties as a function of silver substitution in the bulk granular high-Tc system Y-Ba-Cu-O have been investigated. In the low doping limit, Ag impurities behave as an excellent oxygen stabilizer and the critical current density is enhanced by an order of magnitude while the Tc remains practically unchanged. When the Ag content is increased to above 20%, the Tc starts to drop and the effects of Ag clusters as well as impurity phases become more important. However, the compound is still a superconductor with a Tc around 20 K by full substitution of Ag for Cu. The problems concerning the location of Ag atoms and formation of Ag clusters are examined with measurements of x-ray absorption fine structure using synchrotron radiation. Our results indicate that at least some Ag atoms occupy the Cu(1) and Cu(2) sites in the material. Magnetic field dependence shows that the critical current density of a bulk sintered high-Tc superconductor below a characteristic value H′c is mainly controlled by intergranular weak-link coupling. A shift of Hc with the addition of Ag helps explain the variation of critical current density in this compound system.
EL2 trends in As-rich GaAs grown by close-spaced vapor transport
Authors: Lombos B. A. , Bretagnon T. , Jean A. , Le Van Mao R. , Bourassa S. , Dodelet J. P.
Published: July 2002

Deep level transient spectroscopy and transport properties measurements were performed on close-spaced vapor transport deposited epitaxial GaAs. The deep EL2 donor level was consistently observed in all of the layers. A side band at around 300 K was found to be present in relatively high concentration close to the as-grown surface of the epitaxial films. The multilevel impurity model treatments suggest the existence of an off-stoichiometry-induced deep acceptor level, related to possible gallium vacancies, in As-rich GaAs.
Viable strained-layer laser at λ=1100 nm
Authors: Waters R. G. , York P. K. , Beernink K. J. , Coleman J. J.
Published: July 2002

In0.45Ga0.55As/GaAs/AlGaAs quantum well lasers emitting at 1100 nm have been fabricated and evaluated. These devices, which employ a highly strained quantum well region, exhibit low- (250 A/cm2) threshold current density and excellent reliability both of which were hitherto unattainable at such high In mole fractions.
Barkhausen jump correlations in thin foils of Fe and Ni
Authors: Swartzendruber L. J. , Bennett L. H. , Ettedgui H. , Aviram I.
Published: July 2002

The Barkhausen noise emanating from the surface of thin foils of nearly pure iron and nickel was obtained by digitizing the noise signal over a complete hysteresis loop. This digitized signal is used to analyze various attributes of the noise such as the autocorrelation, power density spectrum, jump amplitude spectrum, and jump amplitude correlation. For thin foils (25 μm) the power density exhibits a peak in the low-frequency range, contrary to what is predicted for a series of statistically independent Barkhausen jumps. Return maps and plots of jump amplitude versus time between jumps show no evident deviation from random noise behavior. Thus jump correlations or clustering do not explain the power density spectra, and an additional mechanism for the loss of low-frequency power is required.
Instabilities of metal-oxide-semiconductor transistor with high-temperature annealing of its gate oxide in ammonia
Authors: Wong H. , Cheng Y. C.
Published: July 2002

This paper deals with the instabilities of the metal-oxide-semiconductor (MOS) transistors with nitrided oxides as gate insulators. In order to relate, and to trade off among, the instabilities, the noise behaviors, and other electrical characteristics in these devices, extensive investigations on the electrical properties—including the flatband-voltage shift, fixed-oxide charge, interface-state density, surface mobility, transconductance, and the electronic conduction in the insulating layer—were conducted with various amounts of hot-electron injections. From the noise-temperature and the interface-state density measurements, we found that the electronic trap density at the nitrided-oxide/silicon interface is significantly enhanced at around an energy level of 0.43 eV below the conduction-band edge of silicon. On the other hand, results also suggest that the nitridation of the gate insulator in a MOS transistor can improve the stabilities again by hot-electron bombardment, but suppresses the electron conduction in the inversion layer and enlarges the noise level remarkably under normal operation conditions. In addition, the degradation of the electrical characteristics of MOS transistors subjected to hot-electron stressing seems to be due to the interface-state generation rather than electron trapping.
A new magnetic multilayer system: Iron-bismuth
Authors: Cui F. Z. , Fan Y. D. , Wang Y. , Vredenberg A. M. , Draaisma H. J. G. , Xu R.
Published: July 2002

Magnetic Fe-Bi multilayers have been, for the first time, synthesized by using electron-beam evaporation at 140 K. The relationships between film structure and magnetic properties were investigated by means of measurements of magnetization, x-ray diffraction, electron diffraction, and Mössbauer spectra. Films are ferromagnetic or paramagnetism, depending on Fe layer thickness, tFe. Films with tFe of about 1 nm exhibit perpendicular magnetic anisotropy while these with the thicker tFe have in-plane magnetism. Temperature dependence of magnetization in the Fe-Bi multilayers was also studied in the temperature range of 77–600 K.
Absolute x-ray power measurements with subnanosecond time resolution using type IIa diamond photoconductors
Authors: Kania D. R. , Pan L. S. , Bell P. , Landen O. L. , Kornblum H. , Pianetta P. , Perry M. D.
Published: July 2002

Photoconductive devices have been fabricated from type IIa diamonds. The sensitivity of these devices is independent of photon energy from 200 to 2200 eV. The dynamic range is 105. The large band gap of the diamond greatly reduces the sensitivity to photons with an energy less than 5.5 eV which is an attractive feature for many applications. The carrier lifetime in the material is 90 ps and the mobility is 1650 cm2/V/s at 106 V/m.
Optical studies of heat-treated Si-doped GaAs bulk crystals
Authors: Suezawa M. , Kasuya A. , Nishina Y. , Sumino K.
Published: July 2002

The effect of heat treatments on optical properties of Si-doped GaAs was investigated. Special care was taken to avoid the evaporation of As during heat treatment. Several kinds of photoluminescence peaks were found to be developed, depending on the Si concentration of the crystal and the temperature of the heat treatment. In crystals of high concentrations of Si a broad photoluminescence peak centered at about 1040 nm in wavelength was observed. The intensity and position of the peak were found to depend on the temperature of the heat treatment for a crystal in which the Si concentration was higher than 3.8×1018 atoms/cm3. The change in the peak position was accompanied by the changes in the optical absorptions related to SiGa-SiAs and SiAs-VGa pairs and also by the change in the concentration of free electrons. The characteristics of the observations were well interpreted with the idea that the photoluminescence peak was related to clusters of Si atoms and that clustering of Si atoms took place during heat treatment. Such clustering of Si atoms did not take place appreciably in a crystal of a Si concentration lower than 3.0×1018 atoms/cm3. The origins of other photoluminescence peaks related to shallow levels were identified, while those related to deep levels are not known at the present moment.
Experimental analysis of temperature dependence of deep-level capture cross-section properties at the Au oxidized InP interface
Authors: Telia A. , Lepley B. , Michel C.
Published: July 2002

Deep levels in unintentionally doped InP liquid encapsulated Czochralsky material have been studied by deep-level transient spectroscopy (DLTS) technique. Five electron traps are observed between 80 and 270 K labeled T1, T3, T4A, T4B, and T5. Trap concentrations are generally below 1013 cm−3. The capture cross sections for levels T1, T3, and T5, determined assuming an exponential time dependence of the capacitance transient, show a quite large variation with temperature which is consistent with the multiphonon emission process. In each case under this process, the binding energy term is much lower than the capture activation energy term. An unusual increase of the DLTS peak magnitude as the emission rate decreases leads us to analyze the capacitance signal as a multi-exponential transient. Each DLTS peak is then decomposed into two components from which the specific parameters have been extracted, activation energy, binding energy, and the experimental dependence of the capture cross section versus temperature for each contribution. The agreement between the theoretical model and experimental results is very good for the three levels T1, T3, and T5 under all experimental conditions, including the incomplete capture.
Majority and minority electron and hole mobilities in heavily doped GaAs
Authors: Lowney Jeremiah R. , Bennett Herbert S.
Published: July 2002

The majority electron and minority hole mobilities have been calculated in GaAs for donor densities between 5×1016 and 1×1019 cm−3. Similarly, the majority hole and minority electron mobilities have been calculated for acceptor densities between 5×1016 and 1×1020 cm−3. All the important scattering mechanisms have been included. The ionized impurity and carrier–carrier scattering processes have been treated with a phase-shift analysis. These calculations are the first to use a phase-shift analysis for minority carriers scattering from majority carriers. The results are in good agreement with experiment, but predict that at high dopant densities minority mobilities should increase with increasing dopant density for a short range of densities. This effect occurs because of the reduction of plasmon scattering and the removal of carriers from carrier–carrier scattering because of the Pauli exclusion principle. Some recent experiments support this finding. These calculations do not treat the density-of-states modifications due to heavy doping, which should have only a small effect on the mobility at room temperature. The results are important for device modeling because of the need to have values for minority mobilities.
Structure and optical absorption of LiyV2O5 thin films
Authors: Talledo A. , Andersson A. M. , Granqvist C. G.
Published: July 2002

Thin films of LiyV2O5 (0<y<1) were made by reactive dc magnetron sputtering of V followed by electrochemical treatment in LiClO4. X-ray diffractometry showed an orthorhombic structure that varied from nanocrystalline (n-X ) for unheated substrates to polycrystalline (p-X ) for substrates at 180 °C. Optical absorption was measured at 0.3<λ<2.5 μm. The semiconductor bandgap lay fixed at ∼0.5 μm for p-X  LiyV2O5 and appeared blue-shifted in proportion with y for n-X Liy V2O5. At λ>0.5 μm there are absorption peaks associated with V4+ ions both for p-X and n-X materials, and a broad absorption feature for p-X Liy V2O5 that is tentatively ascribed to electron hopping in the crystallographic b direction. The absorption goes up for increased y, as expected from the higher V4+ density.
Strain in porous Si with and without capping layers
Authors: Kim Kun Ho , Bai G. , Nicolet Marc-A. , Venezia Abraham
Published: July 2002

The strain of porous Si formed on p+-Si wafers without and with GeSi or CoSi2 capping layers were analyzed by double crystal x-ray diffractometry, MeV 4He backscattering spectrometry, and Auger electron spectroscopy. The parallel strain is zero for all the samples. The perpendicular strain of uncapped porous Si is positive, and decreases from ∼0.3% to ∼−0.6% upon vacuum annealing at 600 °C for 30 min. That of GeSi-capped porous Si is negative (∼−0.1%) and remains unchanged upon the same annealing. The perpendicular strain of CoSi2-capped porous Si also decreases due to the pinholes in the CoSi2 layer. We propose that the decrease of strain upon thermal annealing in vacuum is a result of the desorption of physisorbed gas molecules from the native oxide of the pore walls in the porous Si layer. The strain of annealed uncapped-porous Si increases again when stored in ambient air at room temperature, with a time constant on the order of days, while no change was detected for the annealed GeSi-capped porous Si. A little increase was observed for the annealed CoSi2-capped porous Si due to the existence of the pinholes. We attribute the increase of strain to adsorption of gas molecules (H2O in particular) from air.
Current transport characteristics of P+/N AlxGa1−xAs homojunction diodes
Authors: Lin Hao-Hsiung , Liu Yean-Shin
Published: July 2002

This paper reports a current transport study on the P+/N AlxGa1−xAs homojunction diodes with the AlAs mole fraction, x, ranging from 0 to 0.66. From the 2-kT surface recombination current behavior, the surface state density is nearly independent of x as x is smaller than 0.2. On the other hand, as x is larger than 0.2, the surface state density decreases as x increases. A photocurrent-aided method is proposed to extract the embedded 1-kT current out of the series resistance effect. It is found that the 1-kT current follows Shockley diffusion theory, and the hole diffusion length has a drastic change in the transition region from direct to indirect band. A three-band diffusion model considering the Γ-band-electron-concentration-dependent hole lifetime has been proposed to explain the experimental results successfully.
Inhomogeneous thermoelectrics
Authors: Mahan G. D.
Published: July 2002

Theoretical calculations show that inhomogeneous doping can increase the efficiency of thermoelectric generators and refrigerators.