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  • American Institute of Physics (AIP)  (46,193)
  • 1990 - 1994  (46,193)
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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4935-4982 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the past few years, there has been rapid growth in the positron annihilation spectroscopy (PAS) of overlayers, interfaces, and buried regions of semiconductors. There are few other techniques that are as sensitive as PAS to low concentrations of open-volume-type defects. The characteristics of the annihilation gamma rays depend strongly on the local environment of the annihilation sites and are used to probe defect concentrations in a range inaccessible to conventional defect probes, yet which are important in the electrical performance of device structures. We show how PAS can be used as a nondestructive probe to examine defects in technologically important Si-based structures. The discussion will focus on the quality of overlayers, formation and annealing of defects after ion implantation, identification of defect complexes, and evaluation of the distribution of internal electric fields. We describe investigations of the activation energy for the detrapping of hydrogen from SiO2−Si interface trap centers, variations of interface trap density, hole trapping at SiO2−Si interfaces, and radiation damage in SiO2−Si systems. We also briefly summarize the use of PAS in compound semiconductor systems and suggest some future directions.
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  • 2
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5070-5078 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fractal dimensions of five fractional Brownian motion (fBm) surfaces of 257×257 pixel size, with Hurst exponent H ranging from 0.1 to 0.9, were computed by profile, contour, and surface area analyses. A technique was deemed reliable if it demonstrated accuracy, consistency and sensitivity. Of all the techniques examined, surface area analysis methods, namely, two-dimensional pyramid and Peleg methods, were found to be most reliable and efficient for the data size studied. Hence, these were employed in a preliminary fractal analysis of poly(methyl methacrylate) and poly(styrene) fracture surfaces. The surfaces were imaged at scan sizes ranging from 1–6.5 μm by atomic force microscopy (AFM). The images indicated the existence of fractal structure and a high degree of roughness at microstructural scales for both the surfaces. These observations were supported by the results of the two surface area analysis techniques. A more conclusive study was prevented by severe scoring of the surfaces by the AFM tip at smaller scan sizes and the availability of only a narrow range of scan sizes.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A detailed study of Fe implantation and damage annealing in indium phosphide is presented. The technological goal was to obtain thermally stable semi-insulating layers in n-type InP. Different characterization techniques were employed, including structural (x-ray diffraction, Rutherford backscattering spectrometry, and transmission electron microscopy), chemical (secondary ions mass spectrometry), and electrical (current-voltage) measurements. Both undoped and n-type (Sn) doped substrates were implanted with Fe doses ranging from 5×1011 to 2.2×1014 cm−2 and annealed at a temperature of 650 °C. The high doses used to compensate n+ doping caused amorphization of the material. The reordering process of the amorphous layers and its influence on the Fe redistribution properties were studied in detail. The activation of the implanted Fe atoms after annealing was derived. Although the recovery process of the amorphized layer appears to be rather complex, our results show that good crystal quality and full compensation can be reached also for n+ doped substrates, leading to resistivity values above 2×107 Ω cm, even starting from an initial doping level as high as 1.4×1018 cm−3.
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  • 4
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5099-5110 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated in detail the influence of interlayer structures on nonalloyed ohmic contact resistance (ρc), in terms of the crystalline defects and the potential barrier at the interlayer/GaAs interface. The interlayer structures are a graded-band-gap InAs/GaAs strained-layer superlattice (graded SLS), a graded-band-gap InGaAs, and conventional SLSs without graded band gaps. A two-layer transmission line model indicates that the barrier resistance in the interlayer highly depends on the interlayer structure: ≤5×10−8 Ω cm2 for the graded SLS and graded InGaAs interlayers and 10−5–10−6 Ω cm2 for the conventional SLS interlayers. To explain the large dependence of the interlayer structure, first, the density and distribution of the misfit dislocations and stacking faults caused by the large lattice mismatch between InAs and GaAs have been investigated in detail by high-resolution transmission electron microscopy. In the graded SLS and conventional SLS interlayers, the influence of the high-density depletion regions spread near the crystalline defects is found to be negligible because of the high doping concentrations (∼1019 cm−3) in the interlayers. Second, the potential barrier at the interlayer/GaAs interface has been investigated by simulating the barrier resistance. The potential barrier profile is calculated self-consistently with Poisson's equation and the Schrödinger equation. Tunneling current through the barrier is analyzed using the Wentzel–Kramers–Brillouin approximation or the numerical wave solution to the Schrödinger equation. The graded SLS interlayer has the effectively smooth conduction band profile without the barriers, which is similar to that of the graded InGaAs interlayer, because of its short period SLS. In the conventional SLS interlayers, the reasonable barrier heights of 0.14–0.26 eV obtained by this simulation indicates that these barriers are the dominant factor which increases the contact resistances. For the low-resistance nonalloyed ohmic contact, therefore, a smooth conduction band profile without band discontinuity is more predominant than the reduction in the crystalline defect density.
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  • 5
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5095-5098 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We applied dynamic force microscopy in a liquid environment to silanized and derivatized glass surfaces, InGaAs, as well as to biological materials such as hexagonally packed intermediate layers of deinococcus radiodurans. The vertical and lateral resolution were estimated to be <1 A(ring) and 7–10 nm, respectively. Upon immersing the cantilever into water, the resonance frequency was found to be reduced by a factor of two and the Q factor was lowered to 20–30. The experimental working distance between sensor and sample was determined with approach curves indicating that the range of interaction in water is much shorter compared to air.
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  • 6
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5111-5117 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The procedure for analyzing the discrimination of fundamental peaks in x-ray-diffraction measurements of strained-layer superlattice (SLS) structures is generalized and refined for application to more complex structures, including both lattice-relaxed and coherently strained layers. Two criteria are proposed for investigating lattice relaxation and coherent deformation of relevant layers. A ZnCdSe/ZnSe SLS grown on a GaAs substrate with a ZnSe buffer layer is structurally analyzed by the generalized procedure with the two criteria, demonstrating its effectiveness in analyzing such complex structures. It is revealed from this analysis that the ZnSe buffer layer is almost totally lattice relaxed relative to the GaAs substrate and that the ZnCdSe/ZnSe SLS layer is coherently strained relative to the relaxed ZnSe buffer layer. Quantitative analysis with a kinematical step model also confirms the above results in terms of peak position and peak intensity profile. The full width at half-maximum of the SLS peaks in the experimental profiles, however, is much broader than that of the calculated profiles. Based on this difference, some consideration of the peak broadening mechanism is offered from the viewpoint of broadening symmetry, revealing that this analysis works as a simple checking method on the peak broadening mechanism.
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  • 7
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5122-5131 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tunneling spectroscopy of sulfur- and oxygen-terminated n- and p-type GaAs (110) surfaces is reported for air and ultrahigh-vacuum conditions. Simulations of the complete I-V characteristics with explicit inclusion of surface states within the planar junction theory are described and compared to experiment. These results provide a comprehensive understanding of the interplay between tip-induced and surface-state-induced band-bending effects observed in the tunneling spectra of passivated semiconductor surfaces.
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Degradation of top electrodes is one of the most important factors to determine the lifetimes of organic electroluminescence (EL) devices. An organic EL device [indium thin oxide (ITO)/N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4, 4'-diamine (TPD)/tris(8-hydroxy- quinoline)aluminum (Alq3)/Al] was prepared and a morphological change of the Al top electrode was observed during and/or after applying voltage by atomic force microscopy and scanning electron microscopy (SEM). The change in the electrode surface, i.e., the increase in surface roughness was observed during the current flow. The degradation process started from faint dark core parts and propagated into disks with different rates depending on the magnitude of applied voltage. Degraded sites of the Al electrode, which were analyzed as aluminum oxide by Auger electron spectroscopy, protruded into the air on the organic layers. In SEM images of a life-end electrode, discontinuities due to crevasse formation in the organic layers sandwiched by the ITO base and the metal top electrodes were observed in many places. These results confirm that one of the most crucial factors of the degradation process was deformation of metal and organic layers due to heat, gas evolution, and oxidation caused by applied voltage.
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A redistribution of nitrogen atoms towards a buried carbon-rich layer is observed for thin iron films implanted at 250 °C. The effect is attributed to the formation of ε-Fe3−x(C,N) iron carbonitride. Above 300 °C the ε-carbonitride phase becomes unstable and consequently the redistribution effect vanishes leading to well-separated profiles of nitrogen and carbon atoms.
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  • 10
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5136-5142 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fracture characteristics of metal/polymer line structures formed by depositing Au/Cr lines on a semiflexible polyimide, pyromellitic dianhydride-oxydianiline (PMDA-ODA), substrate have been investigated using a stretch deformation technique. The delamination behavior, fracture morphology, fracture energy, and energy dissipation rate have been determined as a function of line width and thickness. The metal dimension was found to influence the crack formation mode and morphology. The experimental studies were supplemented by finite-element analysis to evaluate the stress distribution and deformation energetics of the line structure, which takes into account the plastic deformation of the metal and the polymer. Results from this analysis show that the observed fracture characteristics can be attributed to the edge and thickness effects induced by metal confinement. Essentially, the deformation behavior is determined by the mechanical environment induced by metal confinement at the interface. Plastic deformation of both metal and polymer plays an important role in controlling the stress distributions as well as the deformation energetics. The fracture energy of the metal-polyimide interface determined by an overall energy balance method was consistent with that obtained from energy dissipation rate. The average value is 25 J/m2 for the Au/Cr/PMDA-ODA line structure.
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  • 11
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5143-5148 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The fracture behavior of the Au/Cr line structures formed on a rigid-rodlike polyimide, biphenylenetetracarboxylic dianhydride-phenylenediamine (BPDA-PDA), film substrate has been investigated using a stretch deformation technique and compared with that of the Au/Cr line structures formed on a semiflexible polyimide, pyromellitic dianhydride-oxydianiline. In general, the effects of metal line dimensions on the deformation behavior can be attributed to the changes in the mechanical environment induced by metal confinement at the line interface. This gives rise to a fracture behavior and geometrical dependence of these two polyimide structures which are qualitatively similar in most aspects. However, the fracture energy and crack propagation rate of these two polyimide line structures are quantitatively different, with values about twice higher for the BPDA-PDA line structures. This cannot be accounted for solely by the different chemical bonding; instead, the high fracture toughness of the BPDA-PDA structure has to be attributed to its superior mechanical properties, particularly its plastic deformation characteristics, which are related to its molecular structure.
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  • 12
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5149-5153 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method is introduced to a measure the free-energy barrier W*, the activation energy, and activation entropy to nucleation of crystallites in amorphous solids, independent of the energy barrier to growth. The method allows one to determine the temperature dependence of W*, and the effect of the preparation conditions of the initial amorphous phase, the dopants, and the crystallization methods on W*. The method is applied to determine the free-energy barrier to nucleation of crystallites in amorphous silicon (a-Si) thin films. For thermally induced nucleation in a-Si thin films with annealing temperatures in the range of from 824 to 983 K, the free-energy barrier W* to nucleation of silicon crystals is about 2.0–2.1 eV regardless of the preparation conditions of the films. The observation supports the idea that a-Si transforms into an intermediate amorphous state through the structural relaxation prior to the onset of nucleation of crystallites in a-Si. The observation also indicates that the activation entropy may be an insignificant part of the free-energy barrier for the nucleation of crystallites in a-Si. Compared with the free-energy barrier to nucleation of crystallites in undoped a-Si films, a significant reduction is observed in the free-energy barrier to nucleation in Cu-doped a-Si films. For a-Si under irradiation of Xe2+ at 105 eV, the free-energy barrier to ion-induced nucleation of crystallites is shown to be about half of the value associated with thermal-induced nucleation of crystallites in a-Si under the otherwise same conditions, which is much more significant than previously expected. The present method has a general kinetic basis; it thus should be equally applicable to nucleation of crystallites in any amorphous elemental semiconductors and semiconductor alloys, metallic and polymeric glasses, and to nucleation of crystallites in melts and solutions.
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  • 13
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5154-5160 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of pressure gradients that develop in diffusion systems consisting of particulates dispersed in a continuous fluid is considered. It is shown that the gradient of chemical potential which drives the diffusion flux induces a pressure gradient that opposes this flux. This effect, which exists in addition to the induced bulk flow, is expressed in terms of a diffusive buoyancy force (DBF). For dispersions consisting of monodisperse particulates in a single-component fluid, the net driving force is the negative product of the volume fraction occupied by the fluid and the gradient of the chemical potential of the particulates. For polydisperse particulates, the DBF is the negative product of the total volume fraction occupied by the particulates and the expectation of gradient of their chemical potential. The joint effect of the DBF and the hydrodynamic hindrance is expressed in terms of a concentration-dependent diffusion coefficient. It is shown that the effect of the DBF yields a fundamental diffusion coefficient Dφ, which is the product of the volume fraction occupied by the fluid 1−φ, and the Stokes–Einstein diffusion coefficient D. The intrinsic diffusion coefficient, which is defined as the product of 1−φ and Dφ, thus becomes the product of the square of 1−φ and D. At steady state the concentration profile cannot be analytically linear unless the buoyancy and hydrodynamic effects are offset by changes of size, energy per particulate and the activity coefficient. Finally, implications regarding the diffusion equation and effects of combined fields on the DBF are considered.
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  • 14
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5171-5178 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Local structural information has been obtained from extended x-ray-absorption fine-structure measurements on samples of porous silicon produced under various conditions, and these have been correlated with photoluminescence emission and excitation spectra. The x-ray near-edge structure (XANES) shows the existence of a feature in between those assigned to Si—Si and Si—O bonding. Laser-induced mass analysis indicates that the presence of various silicon hydroxides correlates strongly with the strength of this peak. In addition, although porous silicon consists of a surface whose roughness is of the order of nm, it has been possible to obtain depth-profiling reflected x-ray-absorption fine structure (REFLEXAFS) and reflectivity from some samples. The REFLEXAFS XANES again shows the additional feature, the strength of which increases with the intensity of the Si-Si peak, that is, with depth.
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  • 15
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In situ resistance measurements, x-ray diffraction, Rutherford backscattering spectrometry, transmission electron microscopy, isothermal and constant heating rate differential scanning calorimetry and Auger electron spectrometry depth profiles have been used to investigate the interactions in copper and magnesium thin films leading to the growth of Cu2Mg and CuMg2 intermetallics. The effect of exposing the reacting interfaces to controlled exposure of oxygen on the nucleation and growth kinetics of such intermetallics was also investigated. It is found that the first phase to form is CuMg2, at about 200–215 °C. It is determined that the formation of CuMg2 occurs by a two step process consisting of nucleation and growth. The nucleation of CuMg2 takes place in a region composed of a Cu/Mg solid solution. The nuclei form at certain preferred sites and grow in directions both parallel and perpendicular to the surface, eventually leading to a continuous CuMg2 layer. The growth of CuMg2 nuclei in the plane of the original interface occurs at a constant rate, whereas the growth in a direction perpendicular to the original interface is found to be diffusion limited. In the presence of excess copper Cu2Mg forms at higher temperatures, with complete conversion to Cu2Mg occurring at about 380 °C. When the Cu surface is dosed with oxygen prior to Mg deposition, ramp rate differential scanning calorimetry (DSC) shows that the nucleation and growth of CuMg2 as well as the growth of Cu2Mg are not disturbed. Dosing the Mg surface with oxygen results in significant changes in the growth of the two phases. In this case a thin MgO layer is formed at the oxygen dosed surface, lateral growth of CuMg2 is unaffected, but vertical growth of CuMg2 across the oxygen dosed interfaces is delayed by 25–30 °C. The growth of Cu2Mg is also shown to be delayed, by 22–54 °C due to the interfacial oxygen dose.
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  • 16
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5190-5194 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The energetics of the CoSi2-Si interface and the CoSi2 surface have been investigated by analyzing the equilibrium shapes of isolated silicide precipitates. CoSi2 precipitates grown by heating 2 A(ring) of Co on a clean, reconstructed Si{100} surface formed with a number of orientations that remained stable upon annealing to high temperatures. Precipitates buried by a Si capping layer were shown to form along {111} and {100} interfaces. A ratio of the CoSi2-Si interfacial free energies has been measured from the shapes of a large number of buried precipitates indicating that γ{100}/γ{111}=1.43±0.07. It is suggested that the shape of CoSi2 equilibrated within vacuum consists of {111}, {100}, and {110} facets.
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  • 17
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermal stability and crystallization of amorphous Si:P alloy thin films consisting of 20–44 at. % P have been studied in this work. The results show that the alloys have crystallization temperatures ranging from 850 to 1150 °C, which are all higher than that of pure amorphous Si, and that the variation of resistivity of the alloys during the 120 h aging at 300 °C is small (0.6%). These results indicate that the alloys have a high thermal stability, which is in agreement with the thermodynamic prediction we have made. It has also been observed that the crystallization products for these alloys are different. A new silicon phosphide phase has been observed in the 30 at. % alloy sample and suggested to be possibly a hexagonal Si7P3 phase which has lattice parameters a=5.32 A(ring) and c=13.3 A(ring). The alloy films were deposited onto quartz substrates and Si wafers by coevaporation of Si and P. X-ray diffractometry and transmission electron microscopy were utilized to investigate the crystallization temperature and product of the amorphous alloys.
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  • 18
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5185-5189 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The kinetics associated with the breakdown of epitaxy at low temperatures are studied for growth onto a number of Si surfaces, including (001), (117), (115), and (113). These surfaces are all initially generated at trench edges on a single patterned substrate. Growth on each of these surfaces at low temperatures is shown to result in a well-defined crystalline-to-amorphous transition. The epitaxial thicknesses hepi have been measured over a range of substrate temperatures below 280 °C, and activation energies characteristic of this transition were determined. In general, the breakdown in epitaxy occurs such that hepi(001)(approximately-greater-than)hepi(117)(approximately-greater-than)hepi(115)(approximately-greater-than)hepi(113). Growth at slightly higher temperatures, Tsubstrate(approximately-greater-than)300 °C, shows a different microstructure than that at lower temperatures. Epitaxial growth continues for longer times on (113) facets, as compared with (001). These results are discussed in terms of a recently proposed model explaining the breakdown of epitaxy at lower temperatures and an epitaxial temperature for Si.
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  • 19
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5202-5207 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A rate equation model based on the master equation approach is developed for the study of molecular-beam-epitaxy doping kinetics. The model includes elementary surface processes such as adsorption, evaporation, and migration of atoms. The model is applied to the study of the surface segregation phenomenon during In doping of Si. The doping studies were performed for the following growth conditions: T in the range 500–750 °C; a growth rate of 1 μm/h; and a flux ratio JIn/JSi equal to 2.0×10−4. The predicted sticking coefficient of In versus 1/T shows excellent agreement with experiments. The sticking coefficient decreases with T due to surface segregation aided evaporation of In at higher temperature. The predicted dopant depth profile also shows excellent qualitative agreement with experiments. The surface segregation of In occurs due to a strong repulsive interaction between In and the host lattice. The results of this study show that there is a dopant-depleted zone (DDZ) where the In concentration is lower than both the bulk and the top surface layer. The observed DDZ qualitatively matches that observed in experiments. The time and growth rate dependencies of the phenomenon are studied and found to be in good agreement with experiments. The model was used to study δ doping of dopants in the range of 673 to 973 K. The results are in qualitative agreement with experimental results. With an increase in temperature, the dopant profiles become sharper. This is caused by a smoother growing surface at higher temperatures.
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  • 20
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5195-5201 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin-film reactions between nickel and silicon are investigated by differential scanning calorimetry and transmission electron microscopy on evaporated bilayers with different compositions and thicknesses. The thermograms are interpreted by a computer modeling, based on diffusion-controlled growth. Experiments and simulation reveal the simultaneous formation of crystalline Ni2Si and of an amorphous phase of composition probably near NiSi. The derived kinetic data confirm literature values from isothermal experiments.
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  • 21
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrogenated amorphous silicon (a-Si:H) films were deposited at high growth rates by increasing the rf power density in a (SiH4+H2) discharge, while powder formation due to gas phase polymerization was controlled by heating the cathode together with the anode. A combination of Raman scattering, infrared absorption, and small angle x-ray scattering experiments was used to study the short-range order and microstructure of films deposited in different (dusty or otherwise) plasma conditions. The results were correlated with initial and light-soaked photoresponse to demonstrate that films with more microstructure and less short-range order were generally poorer.
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  • 22
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Polar angle distributions of core level photoemission intensities recorded on YbAs/GaAs(001) and ScAs/GaAs(001) heterostructures are presented. They allow first the surface roughness of thin YbAs overlayers to be seen, second to estimate the tetragonal distortion of a strained ScAs film and, third, the most interesting point, to demonstrate in a direct fashion that the mixed (Yb-As) (010) planes of YbAs grow in the prolongation of the As planes of GaAs. The results are compared to those obtained by other authors with various techniques. The main advantage of the photoelectron diffraction method over the other techniques is that it can be performed on very thin epitaxial films (some monolayers) directly in situ under ultrahigh vacuum.
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  • 23
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of Ar dilution in a N plasma source has been used to achieve control of both electrical and optical properties of p-type ZnTe:N grown by molecular-beam epitaxy. Photoluminescence data are presented that show the transition from "pure'' ZnTe emission to that indicative of heavily N-doped ZnTe. A new principal bound-exciton line associated with N impurities is observed at 2.3685 eV. An anomalous red shift in the corresponding donor-acceptor pair peak energy with increasing N concentration is observed at high N concentration and is attributed to the effects of N impurity banding. Trends in p-type conductivity confirmed the ability to control hole concentrations using Ar dilution.
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  • 24
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rapid thermal oxidation of Czochralski-grown silicon in either O2 or N2O atmospheres have been studied using spectroellipsometry and Auger electron spectroscopy. Multiwavelength ellipsometric data were processed in order to separately derive the thicknesses and refractive indexes of rapid thermal dielectrics. Results revealed a significant increase of the mean refractive index as the film thickness falls below 20 nm for both O2 or N2O oxidant species. A multilayer structure including an about 0.3-nm-thick interfacial region of either SiOx or nitroxide in the case of O2 and N2O growth, respectively, followed by a densified SiO2 layer, was found to accurately fit the experimental data. The interfacial region together with the densified state of SiO2 close to the interface suggest a dielectric structure in agreement with the continuous random network model proposed for classical thermal oxides. Auger electron spectroscopy analysis confirmed the presence of noncrystalline Si—Si bonds in the interfacial region, mostly in the case of thin oxides grown in O2. It was speculated that the initial fast growth regime was due to a transient oxygen supersaturation in the interfacial region. Besides, the self-limiting growth in N2O was confirmed and explained in agreement with several recently published data, by the early formation of a very thin nitride or oxynitride membrane in the highly densified oxide beneath the interface. The beneficial effect of direct nitrogen incorporation by rapid thermal oxidation in N2O instead of O2 for the electrical behavior of metal-oxide-semiconductor capacitors is likely a better SiO2/Si lattice accommodation through the reduction of stresses and Si—Si bonds in the interfacial region of the dielectric.
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  • 25
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5249-5252 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrical conductivities of n-doped silicon and, in particular Si:Bi, have been investigated for doping levels greater than the impurity critical concentration Nc for the metal-nonmetal transitions. A general feature of the conductivity for concentration normalized to Nc is presented in the order σ(Bi)(approximately-greater-than)σ(As)(approximately-greater-than)σ(P)(approximately-greater-than)σ(Sb). For Si:Bi, the value of Nc is calculated for different criteria. The mobility of electrons presents a lower value compared to Si:P. The results for Si:P and Si:As are compared to the experimental data available in the literature.
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  • 26
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5253-5259 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of operating temperature and current density on the resistivity of low-pressure chemical-vapor-deposition polycrystalline silicon heavily doped with different impurities, phosphorous (3.1×1020 cm−3), arsenic (4.6×1020 cm−3), or boron (3.1×1020 cm−3), were studied. The resistivity of the films was measured over a wide range of temperatures (15–195 °C) and current levels (1–20 mA). The arsenic-doped polycrystalline silicon results agree with the widely used thermionic emission model; however, unexpected results were obtained for the phosphorous- and boron-doped samples where the resistivity increases with temperature and current density. For the phosphorous and boron-doped materials, an empirical model based on carrier mobility that can predict the resistivity of the polycrystalline silicon over a wide range of operating temperatures and current densities has been developed; the agreement between the model predictions and the experimental data is good.
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  • 27
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5232-5241 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Ar-ion-beam mixing of Fe/Zr multilayers is studied in detail by conversion electron Mössbauer spectroscopy (CEMS) and x-ray diffraction (XRD). The dependence of the ion-beam induced amorphization and interfacial mixing on the sublayer thickness and ion dose (1×1013–2×1016 Ar/cm2) is studied systematically for samples with Fe to Zr thickness ratios dFe/dZr=1 and 0.5 and modulation wavelengths Λ=dFe+dZr of 5–80 nm and 7.5–90 nm, respectively. The CEMS results allowed the evaluation of the mixing efficiency from the thickness of the mixed layers. The experimentally determined mixing efficiency was compared with theoretical estimates based on the ballistic collision and thermal spike models, showing good agreement with the predictions of the modified ballistic collision model. For high degrees of amorphization the composition of the amorphous phase formed due to ion-beam mixing is close to the nominal composition of the sample, as revealed by CEMS measurements. These results were compared with those obtained for amorphous Fe-Zr alloys formed by vapor deposition. The XRD results fully agree with CEMS measurements and show that due to ion irradiation the amorphous Fe-Zr phase is formed. The XRD results show that a change of texture occurs from Zr(002) to Zr(100) in the samples with small Λ irradiated with high ion dose. XRD reveals in these samples the formation of the ZrO2 phase.
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  • 28
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical absorption spectroscopy has been applied to measure the absolute population densities of the first excited levels of atomic hydrogen H*(n=2) and argon Ar*(4s) in an expanding cascaded arc plasma in hydrogen-argon mixture. It is demonstrated that the method allows us to determine both H*(n=2) and Ar*(4s) absolute density radial profiles for H2 admixtures in Ar ranging from 0.7% to 10% with good accuracy. The measured H*(n=2) densities are in the 1014–1016 m−3 range, and Ar*(4s) densities are in the range of 1015–1018 m−3. It has been shown, that the density of hydrogen excited atoms H*(n=2) serves as an indicator of the presence of argon ions and hydrogen molecules in the expanding plasma. A kinetic model is used to understand evolution of H*(n=2) density in the expansion, and to estimate the total atomic hydrogen population density and hydrogen dissociation degree in sub- and supersonic regions of the plasma.
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  • 29
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4524-4532 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The application of the elastic recoil detection technique utilizing heavy ions for the analysis of semiconductor samples is demonstrated. With this technique the depth profiles of the primary constituents as well as profiles of all impurities can be measured in one spectrum. Depending on the target material, a depth resolution down to 20 nm can be achieved. All elements except hydrogen can be detected with almost the same sensitivity, namely ∼1×1015 at/cm2 with 136 MeV I in a 30° recoil geometry. For hydrogen, the sensitivity is about four times better.
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  • 30
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4516-4523 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Abnormal (100) grain growth has been characterized in predominantly (111)-textured Cu thin films as a function of deposition temperature, annealing temperature and the presence of a Ta or W underlayer. For films deposited at room temperature, bimodal grain size distributions are observed at annealing temperatures at or above 150 °C for Cu on Ta and 100 °C for Cu on W. Suppression of (100) abnormal grain growth was achieved by depositing Cu on either barrier layer at 150 °C. A bimodal grain size distribution was still observed for the film deposited on W at 150 °C but the large grains forming this distribution were found to be (111) oriented. These results are explained as the result of competition between strain energy minimization and surface and interface energy minimization. The (100) growth is shown to be driven by a reduction of the orientation-dependent strain energy that builds up due to the elastic anisotropy of Cu. Films deposited at higher temperatures have a lower yield stress which limits the achievable strain energy driving force, thereby suppressing the (100) growth. Surface energy minimization drives the (111) abnormal growth.
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  • 31
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The characteristics of Cu precipitation on various types of defects associated with oxygen precipitation in Czochralski-grown silicon are investigated by transmission electron microscopy and the electron-beam-induced-current technique. Specimens containing dominantly either punched-out dislocations or bulk stacking faults were intentionally contaminated with Cu at various temperatures and cooled at three different rates. Colonies of Cu precipitates developed irrespective of cooling rate, apparently originating from punched-out dislocations developed around oxygen precipitates. In heavily contaminated specimens cooled fast from the contamination temperature, Cu also precipitates on Frank partial dislocations bounding stacking faults. During slow cooling, precipitation of Cu takes place on Frank partials only in lightly contaminated specimens but never in heavily contaminated specimens. Cu precipitates in colonies are thermally more stable than those formed on Frank partials. It is concluded that punched-out dislocations are more favorable precipitation sites for Cu than Frank partials.
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  • 32
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanometer size crystalline particles of α-Fe, γ-Fe, Ni, β-Co, and Co3C encapsulated in multiwalled carbon cages are synthesized by a standard dc arc evaporation of composite anodes containing 10–15 wt. % each of the metals or their compounds. The typical particle size is ∼10 nm. Elemental analysis is made by x-ray energy dispersive spectroscopy. The spectra show only the peaks associated with the respective metal and carbon. The stoichiometry and phase of the crystals are assigned from the characteristic lattice spacings obtained by high-resolution transmission electron microscopy and x-ray diffractometry. Particle size distribution is obtained from a statistical survey of electron micrographs. A statistical growth model is adequate for explaining the crystalline particle size distribution of the encapsulated crystals consisting of α-Fe and γ-Fe smaller than 15 nm. Significant deviation from the model is found for the encapsulated crystals consisting of α-Fe and γ-Fe larger than 15 nm, those of Ni larger than 4 nm, and those consisting of β-Co and Co3C larger than 6 nm. The deviation is discussed in terms of encapsulation effect on the particle growth mechanism.
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  • 33
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4547-4552 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model for the growth and shrinkage of stacking faults in silicon is presented. It accounts for interstitial traps and a nonuniform concentration of intrinsic point defects. The complete system of balance equations of intrinsic point defects is solved numerically to simulate the kinetics of stacking faults during oxidation under the assumption that float-zone silicon contains less interstitial traps than Czochralski silicon. Investigation of the influence of different interstitial trap concentrations on the growth and shrinkage of surface stacking faults shows that the kinetics of surface stacking faults is not strongly affected by the presence of interstitial traps. Surface stacking faults are expected to grow in float-zone and Czochralski silicon in a similar way.
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  • 34
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 5586-5588 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spin wave resonance spectra have been observed in yttrium iron garnet films. The spectra exhibit as many as 120 strongly excited modes with large deviation from quadratic spacing, which are interpreted in terms of a thickness variation of the effective magnetization 4πM(x) depending both on the magnetization and the anisotropy field. Profiles of 4πM(x) are calculated from the spectra measured both in parallel and in perpendicular bias magnetic fields. It has been shown that the films tested have monotonic variations of the effective magnetization. The difference 4πΔM between upper and lower 4πM(x) values is as large as 330 G. It is shown that exchange-dominated spin waves (ESW) with the maximum wave number of 2.5×105 cm−1 have been excited under experiment conditions. Microwave pulse delay due to ESW propagation across the film thickness has been observed. Delay versus frequency characteristics strongly depend on the profile M(x) and the direction of the applied magnetic field. Profiles M(x) have been calculated to provide both constant and linear delay-versus-frequency characteristics.
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  • 35
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4560-4566 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Mie–Grüneisen equation of state (EOS) is further examined for restrictions upon the form of the Grüneisen parameter, which is given as a function of volume and relates the pressure and energy changes at constant volume. Employing basic thermodynamic rules and applying them to the Mie–Grüneisen EOS, a more restrictive condition is offered for the Grüneisen parameter, which extends previous work on the subject.
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  • 36
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Age-momentum measurements and positron lifetime measurements were carried out in order to investigate vacancy-type defects produced in 3 MeV electron irradiated synthetic silica glasses, in which 1 ppm and 300 ppm of –OH bonds were contained. A high formation probability of positronium (Ps) was found for unirradiated specimens. These Ps atoms were considered to be formed in open-volume defects (∼7×10−2 nm3). The formation probability of Ps was drastically decreased by the electron irradiation, especially for the specimens which contained 1 ppm of –OH bonds, even though the size of the open-volume defects and the momentum distribution of electrons at the open-volume defects are independent on the –OH concentration and on the electron irradiation. Since the values of second lifetime components of positron lifetime spectra were ∼300 ps and very close to the estimated value of the lifetime of the positrons which are considered to be trapped in the mono- or divacancies, the decrease of formation probability of Ps can be attributed to an increase of positron annihilation in vacancy-type defects generated by the electron irradiation. Positrons were suspected to be trapped in such defects.
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  • 37
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4567-4570 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coefficient of thermal expansion of electrodeposited Ni/Cu multilayers was obtained by measuring the evolution of membrane resonances and hence the tension as a function of temperature. The apparent thermal expansion coefficient of the multilayer membranes increases as the interface density of the multilayers increases. This increase is analyzed in terms of stress relaxation resulting from sliding of nonperfectly bonded interfaces. The analysis permits the normalization of all thermal expansion data of the Cu/Ni multilayers with layer thicknesses ranging from 20 to 800 nm but not of the thinnest layers, 2 nm thick. The results are consistent with the idea that interfacial adhesion improves as the layer thickness becomes very small, favoring epitaxial growth.
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  • 38
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A local structural investigation has been carried out on the 10 A(ring) InAsxP1−x layer in ad hoc grown InAsxP1−x/InP epitaxial multistructures deposited by low pressure metallorganic chemical vapor deposition by means of extended x-ray absorption fine structure spectroscopy, high resolution transmission electron microscopy, and high resolution x-ray diffraction analyses. The goal was to characterize the local structure of the unwanted, strained, interface layers of InAsxP1−x produced by the exposure of the InP surface to AsH3 as occurs during the growth of InP/In0.53Ga0.47As heterostructures optimized for photonics. High resolution x-ray diffraction and high resolution transmission electron microscopy confirm the high crystalline perfection of the investigated interfaces. As K-edge extended x-ray absorption fine structure analysis shows, the first shell environment of As at these interfaces is similar to that found in bulk InAsxP1−x alloys of similar composition, as determined experimentally and by comparison with recent theories of bond lengths in semiconductor alloys. In particular we measure an As—In bond length which varies at most 0.02 A(ring) with As concentration at the interface; this implies that epitaxy with InP is accompanied by local structural distortions, such as bond angle variations, which accommodate the nearly constant As—In bond length.
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  • 39
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hot-stage high-voltage (1.5 MeV) transmission electron microscopy was used to directly observe CdS nanocrystals precipitated in a silicate glass and a theoretical framework of nanocrystal coarsening kinetics more appropriate than the popularly used Lifshitz–Slyozov–Wagner theory was developed. Nanocrystallite nucleation and coarsening were monitored in situ by video taping of bright-field images of the edges of thin (less than 2 μm) glass fragments heated in the hot stage; crystallite size distribution was obtained from the taped experimental observations. The effects of electron-beam heating and diffusion out of the nanocrystals were included in developing the theoretical analysis of coarsening kinetics which were used, in turn, to interpret the experimental size distribution curves.
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  • 40
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface properties of an underlying Si substrate after reactive ion etching of SiO2 in CHF3/C2F6 gas plasmas have been studied using x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry, Rutherford backscattering spectroscopy, and high resolution transmission electron microscopy (HRTEM). A 50-nm-thick silicon layer that contains carbon and fluorine and a 4-nm-thick uniform residue layer composed entirely of carbon, fluorine, oxygen, and hydrogen on the silicon surface have been observed. The residue film has nine different kinds of chemical bonds. At the surface, O—F bond is found on C—F polymer that contains C—CFx (x≤3), C—F1, C—F2, and C—F3 bonds. Between the C—F polymer layer and the silicon substrate, C—C/H, Si—C, Si—O, and Si—F bonds exist. Neither point defect clusters nor distinct planar defects are found in cross-sectional HRTEM images of the silicon substrate. The changes of peak shapes for C, Si, O, and F in the residual film have been analyzed through an in situ resistive anneal under ultrahigh vacuum condition. C—F1, C—F2, and C—F3 bonds decompose and form C—CFx bonds above 200 °C. Above 400 °C, C—CFx bonds also decompose to C—C/H bonds. For removal of the silicon surface residue, reactive ion etched specimens have been exposed to O2, NF3, Cl2, and SF6 plasmas. By XPS analysis, NF3 treatment has been revealed to be the most effective. With 10 s exposure to NF3 plasma, the fluorocarbon residue film decomposes and the remaining fluorine is mostly bound to silicon. The fluorine completely disappears after wet cleaning.
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  • 41
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental observations of dopant diffusion and defect formation are reported as a function of implant temperature in Si implanted GaAs. The diffusion of Si during post-implant annealing decreases by a factor of 2.5 as the implant temperature increases from −2 to 40 °C. In this same temperature range, the maximum depth and density of extrinsic dislocation loops increase by factors of 3 and 4, respectively. Rutherford backscattering channeling measurements indicate that Si implanted GaAs undergoes an amorphous to crystalline transition at Si implant temperatures between −51 and 40 °C. A unified explanation of the effects of implant temperature on both diffusion and dislocation formation is proposed based on the known differences in sputter yields between crystalline and amorphous semiconductors. The model assumes that the sputter yield is enhanced by amorphization in the lower temperatures, thus increasing the excess vacancy concentration. Estimates of excess vacancy concentration are obtained by simulations of the diffusion profiles and are quantitatively consistent with a realistic sputter yield enhancement.
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  • 42
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Barium titanate thin films were fabricated by the sol-gel technique from two different precursors, one using barium 2-ethyl haxanoate and other using barium hydroxide dissolved in methoxy ethanol as barium source. The films were examined at different curing temperatures using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy, optical transmission spectroscopy, and x-ray diffraction. The films prepared from an ethyl hexanoate precursor were found to crystallize around 550 °C into tetragonal polycrystalline form, whereas those prepared from a barium hydroxide precursor were crystallized into cubic form around 600 °C. The films prepared from the ethyl hexanoate precursor showed larger shrinkage during heat treatment and were more porous than those made from the hydroxide precursor. The changes in thickness, refractive index, and band gap of the films annealed at different temperatures were correlated with chemical modifications of the precursor film as well as structural and microstructural changes occurring during the formation of the final barium titanate thin film. FTIR spectroscopy and electron microscopy were used to support these observations.
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  • 43
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure and texture of thin Mo films sputtered onto the native oxide of Si(100) wafers were investigated with both conventional reflection x-ray pole figures, and transmission electron microscopy and diffraction. Films were grown at two deposition rates (powers), 34 nm/min (1.5 kW) and 67 nm/min (3.9 kW), onto both moving and stationary substrates, under otherwise identical experimental conditions. The microstructure of the Mo films evolved into a zone 2 microstructure within the first 2 μm of growth. The development of both out-of-plane and in-plane textures was found to be influenced by deposition rate and geometry. Films grown at the lower deposition rate exhibited predominantly {110} textures, while films grown at the higher rate exhibited predominantly {110} textures up to a film thickness of ∼0.5 μm and {111} textures above a film thickness of ∼1 μm. Films with the {110} textures developed grains with elongated footprints and faceted surfaces, while films with the {111} textures developed grains with elongated triangular footprints and faceted surfaces. In all of the films deposited onto moving substrates, an alignment of the grains normal to the tangent plane (defined by the substrate normal and the direction of platen rotation) was observed. In all of the films deposited onto stationary substrates, the development of an in-plane texture was suppressed. These results suggest that a combination of geometric, energetic, and kinetic mechanisms are contributing to the evolution of the microstructure and texture in the Mo films.
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  • 44
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The scaling of dry thermal oxides into the thin (<400 A(ring)) range continues to motivate studies of the rapid initial oxidation rate of silicon unaccounted for by a linear-parabolic model. In this paper, silicon oxidation kinetics in this unresolved regime are studied by the incremental reoxidation of thin thermally grown and deposited silicon oxide layers on silicon. It is found that the reoxidation rates of thermally grown oxides in the thin regime rapidly decrease with increasing oxide thickness. In contrast, the reoxidation rates of deposited oxides are faster, and nearly thickness independent. It is also found that the reoxidation rates of thin thermal oxides can be significantly increased by inert thermal annealing. Existing thin-regime oxidation models are evaluated in light of these experimental findings, and it is concluded that only models invoking stress suppression of early oxidation kinetics can reconcile all experimental observations. In further support of a stress argument, the time and temperature effects of inert annealing are shown to be quantitatively consistent with a Maxwellian model for stress relaxation. Kinetic parameters extracted from experimental data are utilized to isolate specific mechanisms for the suppression of oxidation rate during the initial stages of silicon oxidation.
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  • 45
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4625-4629 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The initial stages of strain relaxation in two (SimGen)p short period superlattices grown on Si have been studied by transmission electron microscopy. Relaxation occurs by the formation of 60° dislocations which terminate at heterogeneous sources close to the surface of the sample. The rate of strain relaxation in the short period superlattices has been compared to the rate in homogeneous Si1−xGex layers grown in the same chamber and having equivalent effective stresses to drive the dislocations. The rate of dislocation nucleation was observed to be much higher in the short period superlattices. This was attributed to the tendency for Ge island formation during the growth of the superlattices, leading to localized strain centers which act as easy dislocation sources on annealing.
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  • 46
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4656-4662 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model of electron transport in alkali halides, below 10 eV, is described. It is based on theoretically calculated microscopic cross sections of electron interactions with lattice phonons. Both acoustic and optical scatterings are taken into account, the former being also treated as a quasielastic process that randomizes the electron motion. Monte Carlo calculations based on the model simulate the UV-induced photoelectron emission from CsI. The calculated quantum efficiency and energy spectra are in good agreement with experimental data, in the photon energy range of 6.3–8.6 eV. The probability for an electron to escape from CsI, NaCl, and KCl is provided as a function of its energy and creation depth. A comparison is made between our approach and other phenomenological models.
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  • 47
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of finite surface recombination velocity on the proper interpretation of photoconductive decay (PCD) transients in semiconductors is discussed. The limitations of simple analytical equations which relate the observed effective lifetime to the material parameters are considered. It is shown that, under most circumstances, the correct application of the appropriate analytical expression requires some prior knowledge of the material parameters under investigation. Several methods are proposed to extract useful information from PCD experiments. Finally, the practicality of these methods is investigated by measuring the effective lifetimes of high-purity germanium and float-zone silicon using a noncontact PCD technique.
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  • 48
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4670-4675 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Acoustic phonon modes in isotropic cubic media are derived for a number of quantum-wire and quantum-dot geometries of significant interest in nanoelectronics and optoelectronics. In each case, the mode amplitude is determined by requiring that the mode energy be given by that of the properly quantized phonon. For the case of cylindrical quantum wires and quantum dots with rectangular faces, the Hamiltonians for the deformation potential interactions are derived. These quantized acoustic modes and the associated deformation potential Hamiltonians provide a basis for modeling carrier-acoustic-phonon interactions in a variety of mesoscopic devices. Our new results supplement previous treatments of related piezoelectric effects in cylindrical quantum wires.
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  • 49
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Charging and discharging currents flowing through polyethylene terephthalate (PET) ultrathin films (1.5–12 μm) were measured by the use of a two-electrode configuration involving opposite lateral contacts. A study of the influence of electrification time, applied electric field, film thickness, nature of electrodes, and water content was carried out on both transient and steady-state conduction. The transient behavior can be interpreted in terms of dipolar orientation and relaxation processes while steady-state conductivity can be mainly accounted for in terms of Schottky emission. A comparison between PET and polyethylene naphthalate films is also reported.
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  • 50
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of various heat treatments performed before or after the vacuum deposition of aluminum electrodes on the charging currents flowing through polyethylene terephthalate (PET) thin films (6 and 12 μm) were studied. The amorphous phase of the PET films was characterized by the use of thermally stimulated current/relaxation map analysis spectrometry, allowing precise determination of thermodynamic and thermokinetic parameters. Density measurements were used to calculate the rate of crystallinity achieved after annealing. A correlation was found between the relaxation parameters of the α dipolar relaxation of PET, the rate of crystallinity, and the properties of the charging currents observed from room temperature to 200 °C. Strain-induced crystallization has been put forward to account for the experimental evidences.
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  • 51
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4713-4718 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electrical properties of Pd/Zn/Pd/Au ohmic contacts to p-type In0.47Ga0.53As/InP have been investigated as a function of the ratio of the interfacial Pd and Zn layers and the annealing treatment. For as-deposited contacts, the presence of an increasing thickness of interfacial Zn and Pd to ∼300 A(ring) in the metallization resulted in a reduction in specific contact resistance, ρc, to a low value of 1.2×10−5 Ω cm2. Annealing of all of the contact configurations except the Zn=0 and 20 A(ring) structures produced a reduction in ρc to a minimum value of 7.5×10−6 Ω cm2 at 500 °C. A critical thickness of the Zn≥50 A(ring) and Pd≥100 A(ring) interfacial layers was required in order to produce a significant reduction in ρc during annealing. These results have been interpreted in terms of the reaction between Pd and In0.47Ga0.53As and an associated doping at the near surface region by Zn atoms. Annealing of the contacts at temperatures of ≥450 °C resulted in significant intermixing of the metal layers and the In0.47Ga0.53As as revealed by Rutherford backscattering spectrometry and Auger depth profiling.
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  • 52
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4719-4723 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Silicon dioxide (SiO2) insulator layers on indium antimonide (InSb) have been prepared by direct photochemical-vapor deposition at low temperature below 200 °C using 2537 A(ring) UV light. Ellipsometric studies prove that the refractive index and deposition rate of the photo-oxide films depend on the substrate temperature and gas ratio. The films evaluated by Auger electron spectroscopy (AES) depth profile showed that composition atoms were distributed uniformly throughout the oxide film. The AES analysis found the dominant components of the oxide film are silicon and oxygen. Fourier transform infrared spectroscopy absorption shows that the grown film has strong Si—O bonds with few Si—H bonds. The chemical x-ray photoelectron spectroscopy depth profile shows that the constituents of the semiconductors' outdiffusion into the oxide are few. Metal-oxide-semiconductor (MOS) capacitors were constructed on InSb substrates. Capacitance voltage (C-V) characteristics of the MOS capacitors were measured at 77 K. The interface-state density is of the order of 1011 cm−2 eV−1, and distributed in a very good U shape within the midgap. C-V curves showed almost no hysteresis and smaller flatband voltage. The current-voltage curve shows the leakage current is about 1 nA at 0.8 V, and the breakdown voltage is about 0.8 MV/cm.
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  • 53
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4787-4792 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rectangular current pulses of duration 0.14 μs, flowing across Bloch domain walls in Ni81Fe19 films, cause displacements Δx of these walls, observable by Kerr-contrast microscopy. In zero magnetic field, Δx reaches (approximately-equal-to)14 μm/pulse at current densities (approximately-equal-to)30% above the value jc where wall motion starts. This critical current density is jc(approximately-equal-to)1.2×1010 A/m2 for a film thickness w=263 nm. We have measured jc versus film thickness for w=120–740 nm, and find jc∝w−2.1. This suggests strongly that the observed wall motion is associated with an S-shaped distortion of the wall by the circumferential magnetic field of the current. This wall distortion is limited by the wall surface tension. The wall structure becomes that of the so-called asymmetric Néel wall. Through wall distortion, the current pulse pumps kinetic energy and momentum into the wall. This kinetic energy is then dissipated during ballistic wall motion happening largely after the end of the pulse. We also find jc to be independent of pulse duration.
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  • 54
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4800-4804 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: p-type porous silicon is studied by electron paramagnetic resonance which shows an anisotropic hyperfine structure due to 11B and a weak isotropic signal at room temperature corresponding to an amorphous phase in porous silicon. The weaker isotropic signal is found overlapped with the strong anisotropic dangling bond signal when the porous silicon-containing wafer is scanned. It is argued that the large hyperfine splitting of 11B is predominantly due to the interaction of quantum-confined carriers with boron nuclei.
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  • 55
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Oriented PbTiO3 (PT) thin films, approximately 2000 A(ring) thick, have been successfully grown on Si(100) using a low-pressure, cold-wall metalorganic chemical vapor deposition technique at temperatures as low as 450 °C. Titanium isopropoxide, Ti(C3H7O)4, tetraethyl lead, Pb(C2H5)4, and pure oxygen were used as precursor materials in this work. The dependence of film texture and microstructure on the Pb/Ti source flow ratio and growth temperature is described. With proper growth conditions, stoichiometric PbTiO3 films can be produced. Two types of polycrystalline PbTiO3 films, including multi-oriented and single-oriented textures, were obtained. At growth temperatures above the Curie point (cubic-to-tetragonal transition temperature), multi-oriented textures were found. On the other hand, oriented films were fabricated at growth temperatures in the range of 450–475 °C. It is hypothesized that the preferred orientation is due to the combined effects of thermal stress and anisotropic growth rates along different crystal directions. Microstructure examinations using scanning electron microscopy showed visible grain boundaries for all crystalline samples, as well as the non-columnar cross-section morphology, which indicates highly dense and uniform structures. Using the transmission electron microscopy technique, these grains were found to consist of many fine crystalline particles (10–50 nm). Selected area electron diffraction patterns from these crystalline particles have been indexed in terms of the tetragonal PbTiO3 phase.
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  • 56
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4817-4822 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The densification behavior, microstructure, and electrical properties of ZnO-V2O5 ceramics were studied with V2O5 as the only additive ranging from 0.01 to 1.0 mol %. The addition of V2O5 to zinc oxide shows a tendency to enhance the densification rate and promote grain growth. However, a microstructure that consisted of anomalously grown grains was found for the specimens containing V2O5≥0.05 mol % when sintered at 1100 °C for 2 h. The x-ray diffraction and SEM-EDS microanalysis revealed that the sintered specimens had a two-phase microstructure, i.e., a vanadium-rich intergranular phase formed between ZnO grains. The formation of the grain boundary barrier layer was confirmed by the non-ohmic I-V behavior and the quick drop of apparent dielectric constant with increasing frequency of the ceramics. A nonlinearity coefficient of 2.4–2.8 was obtained at a current density of 10 mA/cm2 for a series ZnO-V2O5 ceramics, and a Schottky barrier height of 0.44–0.47 eV (at 25 °C) was determined from the I-V and C-V experimental data, based on the thermionic emission theory, and the model of back-to-back double Schottky barriers.
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  • 57
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4766-4771 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model which describes the creep of finite size superconductive samples with anisotropic U0's and Jc's has been completed. The 2D model developed assumes anisotropic values of these parameters are associated with two orthogonal directions. The effective creep rate is found to be intermediate between these two creep rates, and is significantly influenced by sample geometry. This model is applied to measurements of magnetization creep in the proximity effect coupled NbTi/Cu multifilamentary superconductive composites. Creep measurements as a function of field at T=4.2 K were made for untwisted samples of various lengths. With the aid of this model, pinning potentials for the proximity effected matrix from 5.3 to 10 meV are extracted for these samples. PE creep for longer, twisted samples was also measured. It is suspected that end effects influence creep in the twisted as well as the untwisted strands.
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  • 58
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4836-4846 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photoluminescence spectra of Yb-implanted InP samples were studied under pulsed and cw excitations using an Ar+-ion laser (above band-gap excitation) at different temperatures and excitation intensities. The photoluminescence spectrum of the 4f transitions 2F5/2–2F7/2 consists of a sharp peak at 1001 nm and broader peaks in the spectral range between 1002.5 and 1010 nm. Time-resolved spectra were recorded at different temperatures. Using a tunable Ti:sapphire laser (above and below band-gap excitation) the photoluminescence excitation spectra were investigated for different emission lines. Study of the rise and decay time under intrinsic excitation (band to band) show that the rise time is a function of excitation intensity, which reflects an indirect excitation process for Yb3+. The experimental data are explained using a kinetics model of energy transfer from the host lattice to the localized core excited states of rare-earth isoelectronic structured traps. The numerically simulated luminescence rise and decay times show a good general quantitative agreement with experimental data, over a wide range of generation rates. The photoluminescence spectra and decay time were also studied as a function of temperature. A quenching mechanism of ytterbium luminescence involving Yb and Fe ions is proposed. Finally, the electric-field quenching of InP:Yb photoluminescence is investigated.
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  • 59
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4853-4856 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The change in electromagnetic impedance of a conductor due to the presence of a long, perpendicular surface-breaking crack in a normally incident, uniform electric field is calculated in closed form in the high-frequency limit. At high frequencies, where the skin depth is much smaller than the depth of the crack, the fields near the edge and corners of the crack are effectively decoupled. This means that the solution may be formulated as the sum of contributions from the corners, faces, and edge of the crack. Simple analytical expressions for the electric field are found and used to calculate the impedance due to the crack in the high-frequency limit without resorting to numerical methods.
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  • 60
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dye molecules were selectively incorporated on the laser fabricated surface of poly(methyl methacrylate) by soaking the irradiated sample in an aqueous solution of dye molecules. The selectivity depended on the laser fluence. Dye molecules were observed only on the area irradiated at a laser fluence of 40 mJ cm−2 pulse−1, while at 570 mJ cm−2 pulse−1, dye molecules were not introduced on the ablated surface but were observed on the nonirradiated part hidden with a mesh mask. The spatial resolution of the simultaneous fabrication and chemical modification was a few micrometers. Multistep incorporation of dye molecules was also demonstrated. A metastable molecular species of a propagating radical was detected in the irradiated sample by ESR. X-ray photoelectron spectroscopy of the surface fabricated at 40 mJ cm−2 pulse−1 revealed the existence of oxygen-containing components. Contact angle measurements showed that the surface fabricated at low laser fluence was more hydrophilic than that at high fluence. Morphological changes of the surface were also considered to be responsible for the incorporation of the dye molecules. Among the various kinds of dye molecules, only the cationic molecules were incorporated, probably because of the interaction with polar chemical species on the fabricated surface. On the basis of these results, the incorporation mechanism was discussed.
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  • 61
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4340-4343 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Below-gap structures in photoreflectance spectra of semi-insulating GaAs were observed originating from electroabsorption of light reflected from the back surface. The peak amplitude of these structures was strongly temperature dependent within the range (78–290) K. The different lineshape at low temperature in comparison to that at room temperature suggested different physical mechanisms. This conclusion was proven experimentally using a two phase lock-in technique by which a fast (X) and slow (Y) component of the spectra could be separated. A fit procedure provides the pure back surface reflection effect for both components. The X mode dominating at low temperatures is attributed to electromodulation of the field-broadened excitonic absorption tail whereas the Y mode originates from the Franz–Keldysh electroabsorption.
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  • 62
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4344-4350 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microscopic structure and formation processes of porous Si layers (PSLs) have been studied by infrared absorption and Raman scattering. How the concentration of HF used during formation affects the vibrational spectra of PSLs has been examined. The IR spectra of as-anodized PSL in the Si-Hx vibration region are quite similar to those of Si(111) or (100) surfaces etched in HF solutions of pH∼2. The amount of dihydrogen adsorbed on the surface increases for lower HF concentrations relative to that of monohydrogen. Fluorine and oxygen are found on PSLs anodized for a long period. The size of the Si particle (or column) is a few nanometers for samples anodized with the solution of HF:H2O=1:1 as estimated from Raman data, and it decreases with a decrease in the HF concentration. No Si nanostructures are detected in the Raman data for the case of HF:H2O:ethanol=1:1:8. The HF concentration dependence of the IR spectra is explained in terms of the change in the size of columns or particles in the PSL. The Si—Si back bond for the surface Si atom terminated by dihydrogen is more stable against oxidation in air than the bond for the atom terminated by monohydrogen. The HF concentration dependence of the electrochemical process is discussed in connection with the relative contribution of electropolishing and pore formation processes. The relation between the photoluminescence intensity and the surface structure is also discussed.
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  • 63
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4362-4366 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A refrigerator is described that is based upon thermionic emission. Room-temperature refrigeration is efficient when the work function of the anode is about 0.3–0.4 eV but those low values are unattainable. The refrigerator only operates at higher temperatures.
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  • 64
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Alternating current driven ZnS thin-film electroluminescent devices (ACTFELDs) have been investigated under continuous-wave ultraviolet (UV) irradiation. Under specific experimental conditions, UV irradiation can erase the residual polarization between two electric pulses which is caused by stored charges in the semiconductor and the semiconductor-insulator interfaces. No photodielectric effects have been observed. The reduction of the residual polarization allows one to investigate the role of the space charge in ACTFELDs, by comparing the excitation efficiencies with and without UV irradiation.
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  • 65
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a measurement of the total photoelectron yield of gold as a function of the incident x-ray polarization. Polarized x rays with energies of 2.5, 2.7, and 4.0 keV were used to excite a gold photocathode at a glancing incidence angle between 5° and 50°. Contrary to a previous report, we found no measurable polarization dependence for all three x-ray energies. We conclude that the modulation factor, i.e., the fractional change of the total yield when the polarization state is varied, is less than 4%.
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  • 66
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4367-4371 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We study the efficiency of using multilayer structures as an etch-stop mechanism in the ablation of polyimide films by ultraviolet lasers. The study is done using a photothermal model that includes the light absorption by the decomposed fragments, which shield the polymer from the laser beam, an intermediate zone in which the polymer is suffering a phase transition and the underlying unburned material. The layers are differentiated from each other through their optical properties. Variation in the optical properties of polyimide has been achieved by a proper selection of impurities. From our modeling work, we conclude that optically thin foils may be used as etch stop in the ablation process when the penetration depth of the middle layer is around three times larger than the penetration depth of the surrounding layers, this for fluences below 200 mJ/cm2. We also present some experimental results.
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  • 67
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Homoepitaxy of silicon at low temperature has been achieved using low-energy mass selected silicon ion beams. Reflection high-energy electron diffraction and Rutherford backscattering spectrometry have been utilized to assess the quality of silicon films deposited from 15 eV 28Si+ beams in the temperature range of 50–350 °C. Auger electron spectroscopy was used to monitor the contaminant levels on the surfaces. The films deposited at 350 °C are epitaxial and of a quality near that of the original substrate. The growth rate at 350 °C is ≈200 times faster than that for solid phase epitaxy. At 50 and 200 °C layer-by-layer epitaxial growth was inhibited and evidence for formation of three-dimensional islands in the early stage of growth followed by transition to an amorphous phase was observed. The transition to an amorphous phase occurred at lower film thickness (smaller ion dose) for lower temperatures. It is shown that small amounts of N+2 impurity in the 28Si+ beam, sufficient to add 1.4 at. % N to the silicon film, result in amorphous films, even at the highest temperature used, 350 °C. The effects of substrate temperature, contamination, and surface damage on the growth mechanism are discussed.
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  • 68
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of a low oxidation state Ti compound, cyclopentadienyl cycloheptatrienyl titanium, (C5H5) Ti(C7H7) (CPCHT), as a potential source for TiN and Ti in plasma enhanced chemical vapor deposition processes has been investigated. This precursor provides us with a new chemical vapor deposition route to TiN films that offer an interesting contrast to films deposited from Ti(IV) precursors. Film depositions were carried out by introducing CPCHT, with H2 carrier gas, into the downstream region of a NH3, N2, H2, or mixed H2/N2 plasma. Low resistivity (100–250 μΩ cm) nitrogen-rich TiN films with little carbon or oxygen incorporation and good conformality were deposited with activated N2 or NH3 at deposition temperatures of 300–600 °C, inclusive. Mixed H2/N2 plasmas resulted in more stoichiometric TiN films with similar properties. The most striking feature of these films is the absence of columnar grain growth, in contrast to TiN films deposited using TiCl4 or Ti(NR2)4. Although the film texture was influenced by the plasma gas, the average grain size of the films deposited using activated N2 and NH3 was similar. The TiN films that we deposited were effective diffusion barriers between aluminum and silicon up to 575 °C. Depositions using activated H2 resulted in films with significantly less carbon than CPCHT, but still having a minimum of 2.7:1 C:Ti. The lower oxidation state of the precursor did not facilitate the deposition of a Ti-rich film. No depositions were observed with any of the reactant gases in the absence of plasma activation.
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  • 69
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4372-4376 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have exploited the excimer light generation principle to generate large photon fluxes over a narrow band of very short wavelengths around 172 nm. By irradiating gas mixtures of silane and oxygen with this light, we have succeeded in directly photodepositing silicon dioxide films. Very high deposition rates (500 A(ring)/min) have been obtained for substrate temperatures as low as 300 °C. The deposited films have been characterized using ellipsometry and Fourier transform infrared spectroscopy. The influence of the deposition parameters on the film properties and their optimization are discussed. In particular, we describe the minimization of hydrogen incorporation in the films, rendering this new technique promising for applications in optical and electronic thin film processing.
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  • 70
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4390-4392 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin films of carbon nitride have been grown on various substrates using low power radio frequency reactive sputtering of graphite in pure nitrogen plasma. A quantitative composition analysis using Rutherford backscattering spectrometry shows that the film contains about 51 at. % C, 44 at. % N, and 5 at. % O. The study of the microstructure of the films using cross-sectional scanning electron microscopy reveals highly oriented columnar structures.
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  • 71
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4393-4398 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amplification studies of a two-cavity second harmonic gyroklystron with a coaxial input cavity and drift tube are reported. The inner conductor is supported by tungsten pins which intercept the beam, and it utilizes lossy dielectric rings to enhance mode suppression. A double-anode magnetron injection gun produces a 440 kV, 200–268 A, 1 μs beam with an average perpendicular-to-parallel velocity ratio near one. The TE011 input cavity is driven near 9.886 GHz and the TE021 output cavity resonates near 19.772 GHz. Peak powers near 30 MW have been achieved, although more easily reproducible peak powers hover closer to 20 MW. While stability is improved over previous devices, beam interception reduces the accessible range in parameter space and thus degrades amplifier performance. Pin erosion is also evident and qualitatively agrees well with theoretical predictions.
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