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Journal of Applied Physics

Issue 11 • Date Jun 1987

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Displaying Results 1 - 25 of 46
  • The stability of a sample in a diamond anvil cell

    Page(s): 4951 - 4954
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    We have performed a theoretical analysis of the stability of a gasketed sample in a diamond anvil cell. Our analysis shows the stability of the sample depends principally on the yield strength and the thickness of the gasket, the bulk modulus and the radius of the sample, and the geometry of the culet. Our results yield a simple methodology that can be used to obtain stable samples in a diamond anvil cell. View full abstract»

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  • Generation of lithium negative ions in a volume source with optical pumping

    Page(s): 4955 - 4963
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    An experiment is described in which a high density of lithium negative ions (1×1010 cm-3) is generated by dissociative attachment of electrons to optically pumped lithium molecules in a supersonic expansion. During a 3‐μs period up to 7% of electrons are attached. A measurement of the lithium vibrational temperature is also reported. Theoretical aspects of Li- production in both a static multicusp source and a supersonic beam source are discussed. The optical pumping requirements for a continuous Li- supersonic beam source are derived. View full abstract»

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  • Transfer‐matrix method applied to multiregion cylindrical induction devices with two‐dimensional current excitation

    Page(s): 4964 - 4969
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    A theory is presented here to obtain the electromagnetic field in a multiregion cylindrical induction device with arbitrary two‐dimensional current sheet excitation. This theory is based on the transfer‐matrix method and provides a closed‐form solution. It applies also to the case of one‐dimensional excitation where it reduces to the known results presented by Freeman [Freeman, IEE Proc. 121, 1117 (1974); Greig and Freemen, IEE Proc. 114, 1681 (1967); Freeman and Blank, IEE Proc. 123, 149 (1976)]. A numerical example is shown, and it is in good agreement with published data. View full abstract»

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  • The design and simulation of high‐voltage Applied‐B ion diodes for inertial confinement fusion

    Page(s): 4970 - 4977
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    We present the design of the high‐voltage (30 MV) Applied‐B ion diode that is now being tested on the PBFA‐II accelerator at Sandia National Laboratories. This diode design is the first application of a new set of numerical design tools that have been developed over the past several years. Furthermore, this design represents significant departures from previous designs due to much higher voltage and the use of a nonprotonic ion, Li+. The higher voltage increases the magnetic field strength required to insulate the diode from 1 to 2 T of previous diodes to 3–7 T. This represents a very large increase in the magnetic field energy and the magnetic forces exerted on the field‐coil structures. Our new design incorporates changes in the field‐coil locations to significantly reduce the field energy and the forces on the field‐coil structures. The use of nonprotonic ions introduces a new complication in that these ions will be stripped when they penetrate material, i.e., the gas cell membrane. The importance of current neutralization, charge‐exchange reactions, and the conservation of canonical angular momentum are discussed in the context of designing light ion diodes suitable as drivers for inertial confinement fusion. We have simulated the performance of this diode design using the electromagnetic particle‐in‐cell code, magic. We find that the most sensitive point in the power flow is the transition from the self‐magnetically insulated transmission line to the applied field region of the diode. View full abstract»

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  • Axisymmetric instability model for shaped charge jets

    Page(s): 4978 - 4985
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    As a shaped charge jet stretches it breaks up into a series of particles along the jet axis of symmetry. These particles are frequently of approximately the same length, suggesting the existence of a critical wavelength for which the growth of an initial surface disturbance is greatest. Following the failure of earlier one‐dimensional models to reproduce this critical wavelength effect, this paper addresses the problem using the axisymmetric equations of motion and boundary conditions of continuum mechanics. Certain simplifying assumptions are made, which enable the analysis of the growth of a small initial sinusoidal disturbance for a range of wavelengths including that suggested by observation of break‐up by flash radiographic experiments. The disturbance growth equation derived is of a complicated and singular nature. Under certain initial conditions it can approximately predict from the experimental data the observed critical wavelength. View full abstract»

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  • A potential fall produced by a space‐charge dipole layer moving in an oxygen glow discharge

    Page(s): 4986 - 4991
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    A potential fall created by a space‐charge dipole layer that moves as a solitary wave with a velocity close to that of an electron in the positive column at higher pressure in oxygen is shown. Sometimes only one potential fall exists between electrodes. The number of the potential fall changes with discharge current, by which the hysteresis phenomenon is found. Since the width of a potential fall is much larger than the electron mean‐free path, both ionization and attachment play an important role in the potential fall for the formation of a dipole layer. The shape of the small current change when a dipole layer arrives at an anode is examined, suggesting what is existent in a dipole layer. The nature of the self‐excitation of a dipole layer in the positive column cannot be found. The reason why a dipole layer appears and how it is maintained in the positive column of the oxygen glow discharge are explained. View full abstract»

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  • Influence of metal‐insulator junction on surface flashover in vacuum

    Page(s): 4992 - 4999
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    The influence of the metal‐dielectric junction on the electric field distribution along the solid insulator‐vacuum interface is analyzed in detail in two widely used electrode‐insulator geometries: (1) a cylindrical solid insulator with metal inserts at both ends and (2) a cylindrical solid insulator placed in recessed electrodes at both ends. The effects of the length of the metal inserts and the angle ψ between the solid insulator and the recessed electrode on the electric field and the flashover voltage have been theoretically investigated and experimentally validated. The permittivity of the solid insulator materials used is varied from 2.1 to 100. The surface flashover voltages of Macor glass ceramic and Teflon are measured in vacuum (≪10-8 Torr) in different electrode‐insulator contact geometries using dc, ac (60 Hz), and 1.2/50‐μs lightning impulse. The measurements show good qualitative agreement with the behavior predicted from the computation. View full abstract»

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  • The role of cesium‐ion bombardment in the formation of negative hydrogen ions on a converter surface

    Page(s): 5000 - 5011
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    A fundamental study of the formation of negative hydrogen ions via surface conversion is presented. Employed is a novel type of converter, namely a porous tungsten button with liquid cesium flowing through it towards the side which is in contact with the plasma. A high cesium coverage, i.e., a small work function, can easily be maintained with this approach. This is related to the high flux of neutral cesium atoms to which the converter is exposed and to the small cesium density in the discharge. Despite the small work function, we obtain negative‐ion yields which are an order of magnitude smaller than is usually found in more conventional experiments, in which the converter is cesiated via injection of cesium vapor into the discharge. Furthermore, our energy distributions show that no negative ions are formed via desorption by cesium‐ion impact. This gives a strong indication that the extracted negative hydrogen ions are primarily formed via this process in cesium seeded discharges. Our view is confirmed by the observation that the negative‐ion yield increases with an order of magnitude when a small amount of argon gas is injected into the discharge. View full abstract»

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  • Deposition of new piezoelectric Ta2O5 thin films and their surface acoustic‐wave properties

    Page(s): 5012 - 5017
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    A new technique for the deposition of the crystallized Ta2O5 thin films is described. Crystallized Ta2O5 thin films have been deposited on fused quartz substrates by reactive dc‐diode sputtering. Crystalline structure and piezoelectric properties of the Ta2O5 thin film were investigated. Surface acoustic‐wave properties, including a phase velocity, coupling coefficient, temperature coefficient of delay, and propagation loss, were measured. View full abstract»

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  • Consistent perturbation expansion for phase‐changing material in a finite domain

    Page(s): 5018 - 5022
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    A self‐consistent perturbation expansion is developed for the case of a finite slab of phase‐changing material with constant boundary conditions corresponding to a ‘‘two‐phase’’ problem. Consistency is achieved by a power‐series expansion in functions of both solid and liquid Stefan numbers. Terms through third order are calculated. View full abstract»

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  • The effects of In doping on the heteroepitaxial growth of ZnS on GaP substrates

    Page(s): 5023 - 5026
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    Single‐crystal layers of ZnS have been grown on GaP substrates in a hydrogen transport system. In order to clarify the doping effects of In on the growth behavior, some In‐doping experiments with various doping processes are performed. The reversal in the orientation dependence of the growth rate and the improvement of the crystallinity of the epitaxial layers are caused by the existence of In atoms and/or In compounds at the growing surface of ZnS. The In atoms and/or In compounds which exist at the interface between the GaP substrate and ZnS epitaxial layer are shown to have no significant effect on the growth behavior. View full abstract»

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  • Kinetics and moving species during Co2Si formation by rapid thermal annealing

    Page(s): 5027 - 5030
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    We have investigated the growth kinetics and identified the moving species during Co2Si formation by rapid thermal annealing (RTA). For the kinetics study, samples which consisted of a thin Co film on an evaporated Si substrate were used. To study which species moves, samples imbedded with two very thin Ta markers were employed. Upon RTA, only one silicide phase, Co2Si, was observed to grow before all Co was consumed. The square root of time dependence and the activation energy of about 2.1±0.2 eV were observed during the Co2Si formation up to 680 °C. The marker study indicated that Co is the dominant mobile species during Co2Si formation by RTA. We conclude that Co2Si grows by the same mechanisms during RTA and conventional thermal annealing. View full abstract»

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  • Structural studies of low‐temperature low‐pressure chemical deposited polycrystalline silicon

    Page(s): 5031 - 5037
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    Structural studies were performed on Si films formed by chemical‐vapor deposition on SiO2 films using silane under pressures below 150 mTorr and temperatures below 640 °C. The mode of growth of these films was found pressure dependent. Films grown at pressures below 10 mTorr were found to have a columnar structure with a (001) preferred orientation ending at a curved surface. The radius of the crystallites increases and the radius of curvature of their free surface decreases as the pressure decreases, while the converse is true for the temperature dependence. Transition from this mode is associated with diminishing of the capillarity effects. For pressures above 10 mTorr the structure is striated with a 〈111〉 twin texture almost perpendicular to the substrate. At pressures above 100 mTorr the structure is similar to the previous one but with a tufty appearance. This structure is associated with compressive and dilatational strain. The size of initial crystallites was found also pressure dependent increasing with pressure. View full abstract»

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  • Stresses in TaSix films sputter deposited on polycrystalline silicon

    Page(s): 5038 - 5046
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    Stress in thin TaSix films sputtered on polycrystalline silicon was studied as a function of temperature. A dual laser‐beam apparatus was used to measure wafer curvature in situ. Stress was studied in the TaSi2/undoped polysilicon structure, in TaSi2 on polysilicon doped with either phosphorus, arsenic, or boron, and in films with a deposited Si/Ta ratio of more than 2. Several observations of stress‐temperature behavior in TaSi2 were made. Tensile stress in TaSi2/undoped polysilicon increases to 1.2×1010 dyn/cm2 at 450 °C during the postdeposition anneal, decreases to near 0 at 900 °C, and linearly increases as temperature is subsequently lowered. Both doping and stoichiometry affected the stress‐temperature behavior. N‐type dopants decreased tensile stress and boron did not. Raising the Si/Ta ratio increased tensile stress at high temperatures. The stress‐temperature measurements were combined with results from other characterization techniques to draw conclusions about the influence of temperature on the film. TaSi2 compound formation was found to occur at less than 400 °C in these films. View full abstract»

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  • Evidence for EL6 (Ec- 0.35 eV) acting as a dominant recombination center in n‐type horizontal Bridgman GaAs

    Page(s): 5047 - 5050
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    Horizontal Bridgman grown n‐type GaAs is shown to contain two important electron traps EL6 (0.35 eV) and EL2 (0.80 eV) in the 1015 cm-3 concentration range. A heat treatment at 800 °C for 1 h results in the reduction of EL6 to about 1013 cm-3 to a depth of at least 10 μm and an increase in EL2 by an amount about equal to the reduction of EL6. Measurement of the minority‐carrier (hole) diffusion lengths in this depth range by an electron beam induced current (EBIC) technique shows an inverse correlation with the concentration of the EL6 trap. The results may be explained if EL6 is assumed to be VGa‐VAs, EL2 to be AsGa‐VAs, and the interaction between the two traps to involve Asi. View full abstract»

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  • C‐induced deep levels in crystalline Si

    Page(s): 5051 - 5054
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    A study of deep traps in the depletion regions of Schottky barrier junctions on silicon was made using deep level transient spectroscopy (DLTS). The Si samples, which had different carbon contents (C), were exposed to several annealing processes. The measurements show that depending on the C concentration and the annealing process employed C‐induced deep traps with activation energies of 355, 290, and 216 meV appear above the valence band. The density, the trap levels, and the capture cross sections of these C‐induced traps were determined from the DLTS data. The deep trap densities are correlated with the behavior of the diffusion length of the minority carriers in the different Si materials. View full abstract»

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  • Effect of the capture coefficient in deep‐level transient spectroscopy measurements

    Page(s): 5055 - 5061
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    Underlying the conventional deep‐level transient spectroscopy (DLTS) method is the assumption of an exponential capacitance transient to the equilibrium state as a result of the thermal emission rate of free carriers from a filled trap energy level. This exponential capacitance transient may prove to be a good approximation for specific cases but, in general, the transient capacitance decay to the equilibrium state following a capture pulse is nonexponential. In this study nonexponential capacitance transients are shown to be encouraged by the presence of the free‐carrier tail which spills over abundant free mobile carriers into the space‐charge region thus negating the abrupt junction depletion approximation and favoring both capture and emission of carriers. An upper limit for this effect is obtained here by assuming the carrier concentration in the relevant part of the space‐charge region which one has in the neutral region. This reduces the thermal emission rate by several orders of magnitude from what one would find with the assumption of pure exponential transient and neglecting spillover, as in the normal DLTS method. A particular case is considered, where both capture and thermal emission processes occur simultaneously in the Shockley–Read–Hall kinetic equation for a single‐trap energy level. The variation of carrier occupancy with respect to time leads to a nonexponential capacitance transient decay to the equilibrium state. View full abstract»

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  • Electron traps in AlGaAs grown by molecular‐beam epitaxy

    Page(s): 5062 - 5069
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    Using deep‐level transient capacitance spectroscopy we have investigated deep electron traps in n‐AlGaAs grown by molecular‐beam epitaxy (MBE). The thermal activation energies of seven traps, labeled ME1–ME7, observed in this study increase with increasing Al content(x) up to the direct‐indirect crossover point (x∼0.42), but show only a small change with further increases in Al content. Traps ME4–ME7 are dominant in samples with x≤0.2. Traps ME4–ME6 strongly depend on the growth ambient. The concentration of ME7 is almost independent of the ambient in the growth chamber but decreases rapidly with increasing growth temperature. ME7 is a native defect and can almost certainly be identified with the trap EL2 observed in bulk and vapor‐phase epitaxially grown GaAs. Traps ME4–ME6 are probably formed by impurities involving oxygen such as CO, H2O, and AsO in the growth ambient. All of the traps, ME5–ME7 are clearly responsible for a decrease in the photoluminescence intensity of MBE grown AlGaAs. View full abstract»

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  • Surface‐depletion effect correction to nonuniform carrier distributions by Hall measurements

    Page(s): 5070 - 5075
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    Significant errors in the determination of carrier profiles obtained by the Hall‐effect method result if the depletion effect at a semiconductor surface is not taken into account. A practical procedure for correcting the apparent measured carrier profiles for this surface‐depletion effect is described for nonuniformly doped semiconductors. This correction method is then applied to Si‐implanted GaAs and the results are compared with those of capacitance‐voltage measurements. The number of total trapped charges in free‐surface states are estimated to be about 1×1012 cm-2. View full abstract»

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  • Electrical and stoichiometric characteristics of CdTe films deposited by the hot‐wall flash‐evaporation technique

    Page(s): 5076 - 5079
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    The electrical and stoichiometric characteristics of polycrystalline CdTe films deposited by the hot‐wall flash‐evaporation technique are reported for different deposition parameters. The crystallites in these films grow in a columnar type of grain. The stoichiometry of the films is largely dependent on substrate (Ts) and wall temperatures (Tw) during deposition. At low values of Ts and Tw (∼92 and 425 °C, respectively) a large excess of Te is present (∼30 at. %). At Ts≂192 °C and Tw≂560 °C, nearly stoichiometric films were obtained. The electrical characteristics were strongly dependent on the amount of excess Te present in the samples. A change in the resistivity of up to seven orders of magnitude was measured between the samples with ∼30 at. % of excess Te and those with a stoichiometry close to 1:1. Also a large difference in the resistivity measurements was observed on the surface and across the samples for the different deposition conditions studied. The behavior of the resistivity with temperature in the 100–500 K range is also discussed. View full abstract»

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  • Thermoelectric power of two‐dimensional electron gas in heterojunctions at low temperatures

    Page(s): 5080 - 5083
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    The low‐temperature thermopower of two‐dimensional electron gas has been calculated by using the expression obtained from the Boltzmann equation. The relevant scattering mechanisms are taken into account. It is found that the calculated thermopower increases almost linearly with temperature in the GaAs‐AlGaAs and InGaAs‐InP structures, but in all cases the results differ widely from the values given by the Mott formula and also from the experimental values. The results are not influenced by phonon scattering and are slightly affected if the impurity density is changed by the order of magnitude. For high‐mobility samples, the experimental values are higher than the theoretical ones and it seems that phonon drag thermopower may account for the difference. For low‐mobility samples, however, the experimental values are lower and in some cases decrease with temperature. The present model is then inadequate. Possible refinements of the theory are suggested. View full abstract»

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  • Silicided shallow junction formation by ion implantation of impurity ions into silicide layers and subsequent drive‐in

    Page(s): 5084 - 5088
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    We have developed a technique for the fabrication of shallow, silicided n+-p and p+-n junctions with good electrical characteristics. The technique utilizes the ion implantation of dopants into silicide layers previously formed by ion‐beam mixing with Si ions and low‐temperature annealing, and the subsequent drive‐in of implanted dopants into the Si substrate to form shallow junctions. This technique can be applied to the fabrication of metal‐oxide‐semiconductor field‐effect transistor in a self‐aligned fashion and can have a significant impact on complementary metal‐oxide‐semiconductor devices. View full abstract»

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  • Auger electron spectroscopy, transmission electron microscopy, and scanning electron microscopy studies of Nb/Al/Nb Josephson junction structures

    Page(s): 5089 - 5097
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    Al films deposited on Nb can be oxidized and used to make Josephson junction devices. We studied the structure of Al films deposited under ‘‘warm’’ (estimated to be near 200 °C) and ‘‘cold’’ (near room temperature) conditions because the cold films produced better Josephson junction devices. For the warm case, the Al film was composed of islands with open channels between them, which we attribute to a high mobility of the Al atoms that lowers the island nucleation density. The Nb surface was extremely flat, which we ascribe to the high surface atom mobility at the higher deposition temperature. The cold Al film was of uniform thickness which can be explained by a high island nucleation density. The cold Nb films had an undulating surface, caused by the lack of surface atom mobility during deposition. There was no evidence of Al‐Nb interdiffusion, even after postdeposition heating to 300 °C. Auger spectroscopy, transmission electron microscopy, and scanning electron microscopy were needed to obtain these definitive conclusions. View full abstract»

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  • Detection of singularities in the reversible transverse susceptibility of an uniaxial ferromagnet

    Page(s): 5098 - 5101
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    The reversible transverse susceptibility χt of a ferromagnet having a positive uniaxial anisotropy has been measured as a function of the applied magnetic field. The presence of peaks in the χt (H) curve of a polycrystal was predicted by theoretical calculations based on the Stoner and Wohlfarth model [A. Aharoni, E. M. Frei, S. Shtrikman, and D. Treves, Bull. Res. Counc. Isr. A 6, 215 (1957)]. Unlike previous measurements, our data verify the predictions of such a theory. An explanation for the failure of previous attempts to detect the peaks in the χt (H) curve is given. It is also experimentally shown that the χt (H) measurement allows a precise determination of both coercive and anisotropy fields in a uniaxial ferromagnet provided it is made by single domain particles. View full abstract»

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  • Effect of fluorine in chemical‐vapor‐deposited tungsten silicide film on electrical breakdown of SiO2 film

    Page(s): 5102 - 5109
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    The effect of fluorine in chemical‐vapor‐deposited tungsten silicide film on electrical breakdown of SiO2 film was investigated. Fluorine diffuses into the SiO2 film through the upper layer of poly Si above 800 °C. At 1000 °C, fluorine diffuses into the SiO2 film to a concentration on the order of 1020 cm-3. Electrical breakdown field of the SiO2 film degrades remarkably at 1000 °C. However, it was clear that the diffusion of fluorine was blocked by a thin chemical‐vapor‐deposited Si3N4 layer on the SiO2 film. In this case, the degradation of SiO2 film was not observed. From the above results, it is concluded that the diffusion of fluorine included in the chemical‐vapor‐deposited tungsten silicide film is one of the causes in degradation of electrical breakdown of the SiO2 film when the chemical‐vapor‐deposited tungsten silicide film was used as a gate electrode in metal oxide semiconductor integrated circuits. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory