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  • American Institute of Physics (AIP)  (49,883)
  • American Association for the Advancement of Science (AAAS)  (8,860)
  • 1995-1999  (58,743)
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  • 1
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    American Association for the Advancement of Science (AAAS)
    In:  Science, 284 (5411). pp. 118-120.
    Publication Date: 2019-05-10
    Description: A coral reef represents the net accumulation of calcium carbonate (CaCO3) produced by corals and other calcifying organisms. If calcification declines, then reef-building capacity also declines. Coral reef calcification depends on the saturation state of the carbonate mineral aragonite of surface waters. By the middle of the next century, an increased concentration of carbon dioxide will decrease the aragonite saturation state in the tropics by 30 percent and biogenic aragonite precipitation by 14 to 30 percent. Coral reefs are particularly threatened, because reef-building organisms secrete metastable forms of CaCO3, but the biogeochemical consequences on other calcifying marine ecosystems may be equally severe.
    Type: Article , PeerReviewed
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  • 2
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4930-4935 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Room-temperature recrystallization (self-annealing) of electroplated copper (Cu) films is investigated using three kinds of seed/barrier layers with nontexture and (111) texture. The as-plated films have almost the same texture as the seeds. The texture changes during self-annealing depend on the seed texture. The (111) texture of the self-annealing films increases for the film deposited on the nontexture seed layer, but decreases for the film deposited on (111) texture seed layers. For all the plated films, tensile stress increases after self-annealing, which corresponds to the film shrinkage. Recrystallization rate of the Cu film plated on the nontexture seed layer is higher than the one on the (111) texture seed. It is postulated that the reduction of grain boundary energy is the major driving force for film self-annealing and grain growth. © 1999 American Institute of Physics.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated the effect of C49-to-C54 conversion behavior on the agglomeration of Ti-silicide fabricated on subquarter micron polycrystalline Si lines by comparing pre-amorphized samples with conventional ones. Pre-amorphization of polycrystalline Si enhances the C49-to-C54 transformation on subquarter micron linewidths, however, it results in the early development of macroscopic grooves during the second rapid thermal annealing. From these results, we suggest the existence of an extra thermal budget during the second rapid thermal annealing of the pre-amorphized samples, which deteriorates the thermal stability of the C54-TiSi2 featured line. It is also shown that C49-to-C54 transformation on a 0.2 μm linewidth in the conventional samples has two kinds of competing factors when postannealing is added. One is the tendency of C54 transformation and the other is agglomeration of C49-TiSi2 grains. During high temperature annealing (〉850 °C), C49-TiSi2 has been agglomerated by a thinning mechanism instead of transformation into the C54 phase. © 1999 American Institute of Physics.
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  • 4
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5065-5069 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transport in an anisotropic material can create potentially large induced transverse fields which reduce the measured electric and thermal conductivities relative to those computed without the induced fields. These affect the thermoelectric figure of merit ZT modestly. The induced electric field in n-type Bi2Te3 is predicted to be as much as 76% of the external one and can lower the measured electrical conductivity by up to 60%. In Hg1−xCdxTe superlattices, the anisotropy may be increased by varying the composition and width of the barrier and well to give induced fields much larger than the applied one. These effects should be easily observable. The present work utilizes general results applied to a microscopic model relevant for multivalleyed materials within the effective-mass and relaxation-time approximations. © 1999 American Institute of Physics.
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  • 5
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5075-5078 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on the results of measurements of low frequency noise in n-type gallium nitride (GaN) grown on sapphire with 300 K electron mobility of 790 cm2/V s. The noise spectra have the form of 1/f noise with a Hooge parameter α of approximately 5×10−2. This value of α is two orders of magnitude smaller than that observed before in n-GaN. The obtained results show that the level of flicker noise in GaN, just like that in GaAs and Si, strongly depends on the structural perfection of the material (the amplitude of the 1/f noise is much smaller in material with high mobility). The effects of band-to-band illumination on the low-frequency noise show that 1/f noise in GaN might be caused by the occupancy fluctuations of the tail states near the band edges. This mechanism of the 1/f noise is similar to that in GaAs and Si. © 1999 American Institute of Physics.
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  • 6
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5085-5093 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A Wigner transport equation taking account nonparabolic energy band structures of electrons is formulated using the expanded power series dispersion relation in the kinetic energy term in the Hamiltonian. Numerical simulations for GaAs/AlGaAs resonant tunneling diodes are performed based on this model. In the analysis of steady-state current–voltage characteristics, the introduction of nonparabolicity gives overall reduced current densities. However, as in the case of mass correlation terms, the tunneling current when we include the correlation of spatially varying nonparabolicity parameter is bigger than that with constant nonparabolicity parameter. In the transient response analysis, it gives a damping effect which reduces the oscillatory behavior of current and electron densities. © 1999 American Institute of Physics.
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  • 7
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5103-5108 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Conductivity of wires with thickness less than the screening length is shown to be very sensitive to any kind of inhomogeneity causing a long-range carrier redistribution along the wire. This deviation from quasineutrality depends on the applied voltage and results in a nonlinear current–voltage characteristic and a noticeable frequency dispersion of the wire conductivity. These effects were analyzed in detail for the two different models: (i) wires with nonuniform doping, (ii) uniform wires separated from a contact by a short high-resistive (e.g., tunnel) region. The second model describes also the Coulomb blockade effects in wires. The effects can be large in spite of the large static capacity of wires, since at the high frequencies responsible for a Coulomb blockade, the capacity drops to the values comparable with those of quantum dots. © 1999 American Institute of Physics.
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  • 8
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5131-5140 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A unified model explaining the wear-out and the breakdown of thin and ultrathin films of silicon dioxide when subjected to electrical stressing is proposed. The suggested breakdown model is based on the ability of charge trapped inside the dielectric to increase locally the effective dielectric permittivity (ε) of the material by increasing the polarization locally. The impact of this local perturbation to the macroscopic characteristics of the oxide is investigated. Breakdown is correlated with the existence of a fixed amount of trapped charge inside the oxide. Moreover, the dependence of this bulk oxide trapped charge at breakdown with respect to the oxide thickness has been justified by the suggested mechanism and has been found to have excellent agreement with the experimental data. © 1999 American Institute of Physics.
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The new trilayer system NiMnSb/V/NiMnSb on MgO(001) was investigated by means of vibrating sample magnetometry (VSM), x-ray, and neutron reflectivity. VSM revealed a coercive field Hc=23 Oe and a hysteresis loop similar to that of an uncoupled ferromagnet. The x-ray and neutron reflectivity data proved that interface roughnesses of 10 Å are present. A detailed analysis yielded significant interdiffusion at the NiMnSb/V interfaces which is one possible explanation for the weak magnetoresistance effect measured in similar NiMnSb-based multilayer systems. © 1999 American Institute of Physics.
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  • 10
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    Journal of Applied Physics 86 (1999), S. 5152-5156 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of Mn substitution for Fe on the structure and magnetic properties of Pr2Fe17−xMnx compounds with 0≤x≤9 was investigated. X-ray diffraction indicates that all samples are single phase with the rhombohedral Th2Zn17-type structure. The unit cell volume V remains nearly constant with increasing manganese content up to x=2, then increases linearly at a rate of about 2.5 Å3 per Mn atom up to x=8 and there is a large increase of cell volume at x=9. The Curie temperature increases a little from 298 K at x=0 to 308 K at x=1, and then decreases to 37 K at x=9 quickly. The saturation magnetization at 5 K was found to decrease monotonously with increasing Mn concentration. The thermal magnetization curves M(T) of the compounds with x=1–9 show a strong decrease below TC with decreasing temperature. Also it presents considerable magnetic hardness at low temperature. This can be attributed to the presence of narrow Bloch walls. © 1999 American Institute of Physics.
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  • 11
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    Journal of Applied Physics 86 (1999), S. 5179-5184 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Highly oriented perovskite films of PbMg1/3Nb2/3–PbTiO3 and PbSc1/2Nb1/2O3–PbTiO3 with compositions near the morphotropic phase boundary were formed by pulsed laser deposition on La0.5Sr0.5CoO3/MgO (100). The dielectric properties of the films were studied over the frequency range of 100 Hz–1 MHz in the temperature range 20–350 °C. The room temperature polarization and dielectric permittivity of 250-nm-thick films were close to those in bulk ceramics. The films exhibited relaxor-type behavior with thermal hysteresis and with the temperatures of the dielectric peaks corresponding to those in the bulk. The width of the transition in the films was larger than in bulk ceramics. The properties of the films were found to be influenced by the small grain size rather than by the interfaces of the films. © 1999 American Institute of Physics.
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  • 12
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 4922-4929 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Mechanical properties of sputtered AlCu(0.5 wt %) thin films, 0.2–2.0 μm thick, were determined by tensile testing. For comparison, tensile tests were also performed on bulk samples of the same composition. The films were deposited on thin polyimide foils. They were characterized with respect to the surface, microstructure, residual stress, and concentration of copper and oxygen. Stress-strain curves of the films were obtained by separating the force working on the polyimide foil from that working on the metal-polyimide compound. Young's modulus of the films almost corresponded to the bulk value. Films with a thickness 〉1.5 μm broke by formation of macrocracks while thinner films showed formation of microcracks. The Hall–Petch model, additional strengthening by small grain size, and the role of grain boundary sliding for crack formation are discussed. © 1999 American Institute of Physics.
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  • 13
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    Journal of Applied Physics 86 (1999), S. 4936-4942 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coefficient of thermal expansion (CTE), biaxial modulus, and stress of some amorphous semiconductors (a-Si:H, a-C:H, a-Ge:H, and a-GeCx:H) and metallic (Ag and Al) thin films were studied. The thermal expansion and the biaxial modulus were measured by the thermally induced bending technique. The stress of the metallic films, deposited by thermal evaporation (Ag and Al), is tensile, while that of the amorphous films deposited by sputtering (a-Si:H, a-Ge:H, and a-GeCx:H) and by glow discharge (a-C:H) is compressive. We observed that the coefficient of thermal expansion of the tetrahedral amorphous thin films prepared in this work, as well as that of the films reported in literature, depend on the network strain. The CTE of tensile films is smaller than that of their corresponding crystalline semiconductors, but it is higher for compressive films. On the other hand, we found out that the elastic biaxial modulus of the amorphous and metallic films is systematically smaller than that of their crystalline counterparts. This behavior stands for other films reported in the literature that were prepared by different techniques and deposition conditions. These differences were attributed to the reduction of the coordination number and to the presence of defects, such as voids and dangling bonds, in amorphous films. On the other hand, columnar structure and microcrystallinity account for the reduced elasticity of the metallic films. © 1999 American Institute of Physics.
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  • 14
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Carbon nitride thin films were deposited on silicon wafers by pulsed KrF excimer laser (wavelength 248 nm, duration 23 ns) ablation of graphite with assistance of nitrogen ion beam bombardment. X-ray photoelectron spectroscopy, Raman spectroscopy, and ellipsometry were used to identify the binding structure, nitrogen content, and optical properties of the deposited thin films. The influence of the nitrogen ion beam energy on the compositional, electronic, and optical properties of the deposited thin films was investigated. The thin films deposited with nitrogen ion bombardment had an N/C ratio of 0.43. Raman spectroscopy measurements indicated the formation of CN triple bonds in the deposited thin films. The optical band gap Eopt was observed to decrease with the nitrogen ion energy. A nitrogen ion energy between 50 and 100 eV was deduced to be the optimal condition for depositing the carbon nitride thin films. © 1999 American Institute of Physics.
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  • 15
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    Journal of Applied Physics 86 (1999), S. 4959-4963 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The alteration of the organic/electrode interface is partially responsible for the deterioration of the electrical efficiency of some molecular electronic devices. We used the picosecond ultrasonics to investigate the changes that occur at the interface copper-phthalocyanine/M (M=Al or Au) after the electrode deposition: the absorption of an ultrashort laser pulse sets the heterostructure into vibration and the nature of the interface is deduced from the photoelastic response of the samples. We show that a broad interfacial layer is formed, the thickness of which is estimated. We show also that the slow migration of metallic particles within the organic layer leads, after a few weeks, to a broadening of the interfacial region. © 1999 American Institute of Physics.
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  • 16
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The photoluminescence (PL) of hydrogenated amorphous carbon nitride films and its behaviors due to ultraviolet (UV) light irradiation and thermal annealing have been investigated. The films were produced using an electron cyclotron resonance plasma with various mixtures of N2 and CH4 gases. The broad PL spectra centered around 2.3 eV have been observed in air at room temperature and the PL intensity is inversely proportional to the concentration of nitrogen in the film. The UV irradiation results in the modification of configuration and increase of the PL intensity. Moreover, a new luminescence center around 2.76 eV occurs in the film with higher nitrogen content. The changes in film properties due to UV irradiation correlate with the incorporation of nitrogen in the film. Different from the effects of UV irradiation, thermal annealing promotes graphitization of the film. The PL intensity decreases with red shift as annealing temperature increases and is completely quenched when the temperature is over 400 °C. The changes of PL spectra are discussed on the basis of a model in which the sp2 clusters are considered as luminescence centers. © 1999 American Institute of Physics.
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  • 17
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    Journal of Applied Physics 86 (1999), S. 4813-4820 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Characteristics of chlorine, transformer-coupled pulsed plasmas are reported. Time dependencies of electron (ne), positive ion (ni+), and negative ion (ni−) densities and electron temperatures (Te) were measured with a Langmuir probe and microwave interferometry at 240 and 500 W input powers, and pressures between 3 and 20 mTorr. During the OFF portion of the power modulation, ne decreases rapidly as Cl− is formed by dissociative attachment of Cl2. The formation of Cl− is accelerated at high Cl2 densities (at high pressures and low powers). At 10 mTorr and higher pressures, an ion–ion plasma forms near the end of the OFF portion of the cycle, the sheath collapses, and Cl− reaches the wafer. Te decays rapidly in the OFF period and increases with a similar time constant at the beginning of the ON cycle if electrons are present at a sufficiently high level. If ne is very low at the beginning of the ON cycle, such as at high pressure (10 mTorr), then Te exhibits a spike at the beginning of the ON period. In a comparison study, plasma induced damage is reduced when aluminum is etched under similar source power modulation conditions. © 1999 American Institute of Physics.
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  • 18
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    Journal of Applied Physics 86 (1999), S. 4821-4824 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A dc glow discharge source with controlled plasma potential was developed for application in plasma immersion ion implantation processing of materials surfaces. This type of ion implantation system allows cost effective surface modification of workpieces with complex shapes. The effects of the nitrogen plasma etching during the plasma immersion ion implantation process was studied using Si wafers as monitors, as we varied the externally controlled plasma potential between 0 and 350 V. When the plasma potential is controlled below 70 V, the ion implantation is dominant, otherwise the etching overtakes. The nitrogen implanted silicon wafers were analyzed by high resolution x-ray diffraction and Auger electron spectroscopy which revealed successful implantation of ions with accumulated nitrogen dose of 1.5×1017 cm−2, for the low potential case. © 1999 American Institute of Physics.
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  • 19
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In plasma etching and deposition processes, the energy distribution of ions incident onto the substrate strongly affects the surface reactions and the film deposition and etching rates. The magnitude and frequency of the rf-bias power applied to the substrate electrode determines the spatiotemporal variations of the sheath potentials and hence the energy distribution of the ions impinging upon the substrate. A self-consistent dynamic model of the sheath, capable of predicting ion energy distributions impinging on a rf-biased electrode, was developed. The model consists of equations describing the charge transport in the sheath coupled to an equivalent circuit model of the sheath to predict the spatiotemporal charge and potential distributions near the surface. Experimental measurements of the energy distributions of ions impinging on a rf-biased electrostatic chuck have also been made in a high density transformer coupled plasma reactor through Ar and Ne plasmas. The predicted ion energy distributions and sheath profiles are in very good agreement with the experimental measurements. © 1999 American Institute of Physics.
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  • 20
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have investigated the operating conditions that result in the greatest utilization efficiencies (UEs) of NF3, CF4, and C2F6 in a capacitively coupled GEC reference cell. We have also independently measured the rf electrical characteristics and optical emission spectra of the plasmas. To avoid inadvertently attributing changes in the UE, discharge impedance, rf currents, or atomic emission intensities to parasitic losses in the matching network or rf delivery system, the rf generator was adjusted to ensure that the same amount of power was dissipated within each discharge. For the NF3 plasmas, argon was used as a diluent and both the NF3 concentration and reactor pressure were varied. For the CF4 and C2F6 based plasmas, the gas compositions were fixed (86 mol % CF4/O2 and 50 mol % C2F6/O2) and the reactor pressure was varied. The greatest NF3 UEs occurred within a narrow range of NF3 partial pressures. The greatest CF4 and C2F6 UEs occurred within a narrow range of reactor pressures. For all mixtures, operating conditions that yielded the highest UEs also yielded the brightest plasmas, the lowest impedance magnitudes, the greatest fraction of current flowing to the grounded electrode, and impedance phase angles within a narrow window centered near φpe=−40°. Within this region, plasma power is most efficiently utilized to dissociate the source gas and excite the atoms that emit light. Collapsed plasmas, observed for high pressure highly electronegative conditions, exhibited very low UEs. At optimal operating conditions the UE of the fluorinated source gases were found to decrease in the order: NF3〉C2F6〉CF4. The results of this study suggest that the baseline corrected fluorine atom emission intensity (703.7 nm), the magnitude of the discharge impedance, or phase angle of the discharge impedance could be monitored to determine the relative fluorinated source gas UE in an arbitrary plasma reactor as the operating conditions are varied. The concept of an ideal NF3 partial pressure could prove to be a useful strategy to prevent the formation of collapsed plasmas at high reactor pressures while maintaining high NF3UEs. © 1999 American Institute of Physics.
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  • 21
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    Journal of Applied Physics 86 (1999), S. 4843-4846 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report on a light-induced phenomenon in dye-doped liquid crystals (LCs) with the distinctive features of molecular transport and assembly at micron scales. Under single-beam laser irradiation, the dye molecules phase separate from the LC host and assemble onto the cell substrate. Although the intensity of incident light is uniform within the irradiated area, the density of the adsorbed dye is modulated in accord with the director modulation of the LC. The dye molecules form a surface imprint that portrays orientational distortions of the LC host. © 1999 American Institute of Physics.
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  • 22
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    Journal of Applied Physics 86 (1999), S. 4160-4165 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of helium induced cavities in silicon during short-time annealing is analyzed by spectroscopic ellipsometry. Specimens implanted with 40 keV He+ ions to a dose of 5×1016 cm−2 are heat treated at 800 °C for times of 1–1200 s by rapid thermal annealing. Spectroscopic ellipsometry is employed to obtain quantitative information on the cavity volume depth profiles. A newly developed formula is used to model the optical multilayer depth profiles. The cavity volume is found to increase during annealing for about 300 s and to decrease for longer annealing times. Over this characteristic time a marked change in the He loss occurs, which has been reported only recently. Swelling of the helium implanted and annealed silicon is analyzed using an atomic force microscope. Step heights are consistent with the cavity volume per unit area obtained from spectroscopic ellipsometry data analysis. The number density of cavities after annealing for 600 s is calculated to be (approximate)1.16±0.27×1017 cm−3 and is found to be largely independent of depth in the central part of the cavity layer. © 1999 American Institute of Physics.
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  • 23
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    Topics: Physics
    Notes: Implantation of C ions with an energy of 195 keV into Si wafers heated up to 800 °C results in an elastic distortion of the Si host lattice and in the formation of crystalline SiC particles or their prestages depending on implantation dose and temperature. Synchrotron x-ray diffraction at the Rossendorf beamline in Grenoble was used to reveal phase formation and the correlated lattice strain changes. Only a Si lattice deformation without growth of SiC was observed if the fluence did not exceed 5×1015 C ions/ cm2. After implantation of C ions up to 4×1017 cm−2 at a temperature of 500 °C, agglomerations of Si–C and an altered state of Si lattice deformation are found. By implantation of 4×1017 ions/cm2 at 800 °C, particles of the 3C–SiC (β-SiC) phase grow, which are aligned with the Si matrix. They are aligned in such a way with the Si matrix that the cubic crystallographic axes of matrix and particles coincide with an accuracy of 3°. © 1999 American Institute of Physics.
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  • 24
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    Journal of Applied Physics 86 (1999), S. 4166-4175 
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    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe conventional and high-resolution transmission electron microscopy (HRTEM) characterization of the microstructure of sputtered NiFe/Cu giant magnetoresistance spin valves (Cu/FeMn/NiFe/Cu/NiFe) sandwiched between thick Nb contact layers. Six spin valves, sputtered at different temperatures, three with thin (3 nm) and three with thick (24 and 30 nm) NiFe layers, were studied. All of the spin-valve layers were smooth and continuous, consisting of columnar grains generally 20–90 nm wide. In most cases, the grains had grown epitaxially from the bottom contact, through the entire multilayer, to the top contact layer. The columnar grains grew on the closest-packed planes (i.e., {110} planes for bcc Nb and {111} planes for fcc Cu, FeMn, and NiFe spin-valve components). This epitaxial growth yields an apparent Kurdjumov–Sachs {111}fcc(parallel){110}bcc; 〈110〉fcc(parallel)〈111〉bcc orientation relationship. However, HRTEM imaging supported by fast Fourier transform analysis reveals that in some of the columnar grains the Cu, FeMn, and NiFe layers take up a nonequilibrium bcc structure. In these cases, the bcc Cu, FeMn, and NiFe layers grow on {110} planes and are epitaxial with the Nb contacts for the individual grain columns. While bcc Cu has been observed elsewhere, the length scale of the nonequilibrium bcc phases reported here is an order of magnitude greater than previously observed. © 1999 American Institute of Physics.
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  • 25
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    Journal of Applied Physics 86 (1999), S. 4176-4183 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the formation of surface blisters in 〈100〉 n-type silicon following co-implantation with boron and hydrogen. The silicon substrates had four different n-type dopant levels, ranging from 1014 to 1019 cm−3. These substrates were implanted with 240 keV B+ ions to a dose of 1015 cm−2, followed by a rapid thermal anneal at 900 °C for 30–60 s to force the boron atoms into substitutional lattice positions (activation). The samples were then implanted with 40 keV H+ to a dose of 5×1016 cm−2. The implanted H+ distribution peaks at a depth of about 475 nm, whereas the distribution in the implanted B+ is broader and peaks at about 705 nm. To evaluate the role of the B+ implantation, control samples were prepared by implanting with H+ only. Following the H+ implantation, all the samples were vacuum annealed at 390 °C for 10 min. Blisters resulting from subsurface cracking at depths of about 400 nm, were observed in most of the B+ implanted samples, but not in the samples implanted with H+ only. This study indicates that the blistering results from the coalescence of implanted H into bubbles. The doping with B facilitates the short-range migration of the H interstitials and the formation of bubbles. A comparison of the observed crack depth with the depth of the damage peak resulting from the H+ implantation (evaluated by the computer code TRIM) suggests that the nucleation of H bubbles occurs at the regions of maximum radiation damage, and not at the regions of maximum H concentration. For given values of B+ and H+ doping, the blister density was found to decrease with increasing n-type doping, when the boron is activated. Blister formation was also observed in B+ implanted samples which had not been activated. In this case, the blister density was found to increase with increasing value of n-type doping. © 1999 American Institute of Physics.
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  • 26
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    Journal of Applied Physics 86 (1999), S. 4188-4191 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the effect of lattice stress relaxation on the microstructures of epitaxial thin films by domain structure studies of epitaxial SrRuO3 thin films grown on vicinal (001) SrTiO3 substrates. X-ray diffraction analysis revealed that the as-grown films are single domain and have a strained lattice due to the lattice mismatch with the substrate. In contrast, plan-view transmission electron microscopy (TEM) images obtained from the same films showed the coexistence of domains with three different crystallographic orientations. The discrepancy is attributed to the lattice stress relaxation occurring on the TEM specimens as the substrate material is eliminated by ion milling or etching, resulting in the formation of elastic domains with different crystallographic orientations. These studies directly reveal a crucial effect of the lattice strain relaxation on the microstructures and properties of epitaxial thin films when the substrate material is removed. © 1999 American Institute of Physics.
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  • 27
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    Journal of Applied Physics 86 (1999), S. 5256-5262 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ion channeling in the low-keV energy range is demonstrated by means of the technique of time-of-flight scattering and recoiling spectrometry. The predictions of the Lindhard string model of ion channeling are compared with the experimental findings. Qualitative agreement was obtained between the experimentally measured critical angles and the predictions of the model. The technique of low-energy ion channeling is shown to be capable of quantitatively probing the positions of light elements on heavy substrates with analysis by simple geometrical constructs. Classical ion trajectory simulations using the scattering and recoiling imaging code were used to observe the details of the ion trajectories. Quantitative analysis of the Pt(111)-(1×1)-H surface using 5 keV Ne+ shows that the hydrogen atoms preferentially populate the threefold fcc sites with a height of 0.9±0.1 Å above the first-layer Pt atoms and a corresponding Pt–H bond length of 1.9±0.1 Å. © 1999 American Institute of Physics.
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  • 28
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 5270-5273 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermal annealing effects on optical and structural properties of Ge-doped SiO2 thin films prepared by the chemical vapor deposition and flame hydrolysis deposition methods were investigated. The thin film prepared by the former method showed inhomogeneous Ge distribution, and Ge oxygen-deficient centers were observed. When it was thermally annealed at temperatures higher than 800 °C, the Ge distribution became uniform. The concentration of oxygen deficient centers was found to decrease with the thermal annealing in an O2 atmosphere, while it increased with the thermal annealing at 1000 °C in N2. This suggests that improvement of the film quality can be achieved by thermal annealing. On the other hand, neither inhomogeneity of Ge distribution nor the appearance of oxygen deficient centers was observed in the film prepared by the latter method, and its film quality was scarcely affected by the thermal annealing. © 1999 American Institute of Physics.
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  • 29
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    Journal of Applied Physics 86 (1999), S. 5274-5278 
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    Source: AIP Digital Archive
    Topics: Physics
    Notes: A fabrication technology of three-dimensionally buried porous silicon (PS) optical waveguide with an extremely high refractive index contrast is presented, including its fundamental properties. The origins of attenuation losses are investigated by experimental and theoretical analyses in terms of microscopic observations, edge emission measurements, polarization mode determination of guided wave, and evaluation of bending loss. The results of these studies indicate that attenuation losses in PS waveguides are due to self-absorption by residual silicon, structural and optical inhomogeneities in the core region, and roughness at interfaces between the core and the cladding layers. Some possible ways for reducing these attenuation losses are discussed. It is also demonstrated that a buried bent PS waveguide with an extremely small curvature of 250 μm can be fabricated by simple planar processing, and that a visible optical wave propagates along it owing to a significantly high refractive index contrast between the core and the cladding layers. © 1999 American Institute of Physics.
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  • 30
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    Topics: Physics
    Notes: Synthesis of ultrafine nanosize powders by ion beam evaporation (IBE) has been studied numerically and experimentally. Theoretical models have been developed, which involve such physical processes as beam-target interaction, plasma expansion, and the synthesis of powders. The macroscopic properties of the ultrafine powders have been predicted. As an application of our models, the macroscopic properties of AlN powders synthesized by IBE with an AlN target have been predicted. The energy density, pulse width, and spot size of the ion beam are 20 J/cm2, 70 ns, and 1 cm2, respectively. The main results have shown that the particle size distribution is log normal and that 70% of all particles exist between 20 and 40 nm. The average diameter and the specific surface area are ∼30 nm and ∼50 m2/g, respectively. Experimentally, the ultrafine AlN powders have been successfully synthesized by IBE, which has been verified by x-ray diffraction and transmission electron diffraction. Furthermore, particle size distributions have been obtained by transmission electron microscopy. The experimental results are found to be in a reasonable agreement with the numerical studies. © 1999 American Institute of Physics.
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  • 31
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    Journal of Applied Physics 86 (1999), S. 5293-5295 
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    Source: AIP Digital Archive
    Topics: Physics
    Notes: Abnormal junction leakage characteristics in titanium-capped cobalt disilicide were investigated. The cobalt silicide n+-p junctions, fabricated with different capping layers, were characterized by current–voltage measurements and transmission electron microscopy. The reverse junction leakage currents of Ti-capped 13.5-nm-thick cobalt disilicide (CT) are higher than those of TiN-capped samples. The activation energy of CT at temperatures below 80 °C is 0.41 eV, and its dominant leakage mechanism is consistent with phonon-assisted tunneling. Transmission electron microscopy analysis indicates the existence of island phases and precipitates located at the silicide/Si interface, which are titanium disilicide and CoxTi1−xSi2 phases, as evidenced by energy dispersive spectroscopy. As a result, for the case of CT, the reasons for higher junction leakage currents and their field dependence appear to be the result of the diffusion of Ti atoms into CoSi2 grain boundaries and the resulting formation of TiSi2 and CoxTi1−xSi2 phases, which gives rise to a rougher silicide interface and a close spacing between silicide and the junction. © 1999 American Institute of Physics.
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  • 32
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    Topics: Physics
    Notes: Low-pressure metalorganic vapor-phase epitaxy growth conditions of AlxGa1−xN epilayers on c-oriented sapphire have been optimized for aluminum mole fractions x lying in the 0–0.35 range both on GaN and AlN nucleation layers, with a view to application in visible blind UV photodetectors. Good structural, electrical, and optical properties were obtained for undoped and n-type doped AlGaN alloys on (0001)-oriented sapphire substrates. A typical full width at half maximum of 670–800 arc s is measured for the (0002) x-ray double-diffraction peak in the ω mode of 1-μm-thick AlGaN epilayers grown on a GaN nucleation layer. Room-temperature electron mobilities up to 90 cm2/V s are measured on n-type (1018 cm−3) AlGaN epilayers. The low-temperature photoluminescence (T=9 K) performed on nonintentionally doped AlGaN epilayers with low-Al content (10% and 14%) exhibits reproducibly a sharp exciton-related peak, associated with two phonon replica and does not exhibit any low-photon energy transitions. Optical transmission as well as absorption coefficient measurements using photothermal deflection spectroscopy have been used to study the variation of the T=300 K energy gap of AlGaN with the aluminum concentration. Visible-blind AlGaN(Si)-based photoconductors and Schottky barrier photodiodes with good operating characteristics have been fabricated with these materials. © 1999 American Institute of Physics.
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  • 33
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    Topics: Physics
    Notes: Titanium nitride (TiNx) thin films, ∼100 nm thick, were deposited on Si(100) substrates by dc reactive magnetron sputtering. The effects of the substrate bias voltage and deposition temperature on their optical, electrical, and mechanical properties have been studied. It was found a strong correlation between the electrical and mechanical properties of the films which are significantly improved with increasing the substrate bias voltage and the deposition temperature. The low resistivity (43 μΩ cm), combined with the high hardness and elastic modulus values, suggest the TiNx as a promising metallization material in Si technology. © 1999 American Institute of Physics.
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  • 34
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    Journal of Applied Physics 86 (1999), S. 5305-5307 
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    Topics: Physics
    Notes: A deep photoluminscence band at 0.95 eV was studied in CuGaTe2 crystals. The shape of this band did not change with laser power and no j shift was detected. This band shifts towards higher energy with increasing temperature and its shape becomes more asymmetric. The activation energy of this band was ET=0.20 eV as measured with thermal quenching. The possible association of the 0.95 eV band with grain boundaries or dislocations is discussed. © 1999 American Institute of Physics.
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  • 35
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    Topics: Physics
    Notes: The rotational temperature of a low energy (0.09 eV), C2 Swan band state (a 3Πu), obtained by white light absorption, is compared to the rotational temperatures of three electronic excited states [C2(d 3Πg),CH(A2Δ) and CN(B 2Σ+)] in a high power, H2/CH4 microwave plasma used for diamond deposition. All temperatures are measured at 50 mbar, and both continuous (as a function of microwave power) and pulsed (as a function of time after the pulse) modes of operation are investigated. The rotational temperature of C2's excited state is found to be higher than that of the low energy state (assumed equal to the gas temperature), indicating that the excitation of C2 is to a large extent the result of chemical reactions (chemiluminescence) rather than electronic excitation. The rotational temperatures of CH(A 2Δ) and CN(B 2Σ+) excited states are also higher than that for C2's low energy state temperature. © 1999 American Institute of Physics.
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  • 36
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    Topics: Physics
    Notes: A series of samples consisting of a strained layer of GaNxAs1−x of different thickness, covered by a GaAs cap layer of 100 nm were grown by molecular-beam epitaxy. The samples have been characterized by high-resolution x-ray diffraction and simulations based on the dynamical theory in order to determine the strain relaxation in GaNxAs1−x layers. It is found that there is a huge difference between the critical thickness determined by x-ray diffraction and the theoretical calculations according to the Matthews and Blakeslee model. The critical thickness of GaNxAs1−x on GaAs is ten times smaller than the theoretical value. The strain relaxation is a crucial point that affects the quality of GaNAs. Photoluminescence measurements are in good agreement with the x-ray diffraction results. The optical properties degraded rapidly when the GaNxAs1−x thickness exceeded the critical thickness determined above. © 1999 American Institute of Physics.
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  • 37
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    Topics: Physics
    Notes: Similarity among the thermally stimulated luminescence glow curves of undoped Lu2SiO5 and Ce3+-doped oxyorthosilicates possessing the monoclinic C2/c structure strongly suggests the luminescence traps are intrinsic in origin. They are most likely associated with the configuration of oxygen ions in the vicinity of not only the Ce3+ ion, as suggested in previous work, but also the host lanthanide ion. The optical absorption spectrum of pristine Lu2SiO5 shows the presence of intrinsic absorption centers that are enhanced upon x irradiation as seen in other oxides containing oxygen related point defects. © 1999 American Institute of Physics.
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  • 38
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    Journal of Applied Physics 86 (1999), S. 5317-5317 
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  • 39
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    Notes: Modulated thermoreflectance microscopy is applied to a complete thermal characterization of a thin film of gold (78 nm) or YBaCuO (300 nm) on a LaAlO3 substrate. The phase profile, measured at several modulation frequencies covering an appropriate range, is fitted with a rigorous thermal diffusion model. This leads to a simultaneous estimation of the thermal diffusivities of the film and the substrate, as well as of the thermal film/substrate boundary resistance. The estimated values for the gold film sample are, respectively, 4.3×10−6 m2 s−1 (substrate diffusivity), 1.0×10−4 m2 s−1 (film diffusivity), and 1.0×10−8 m2 KW−1 (thermal boundary resistance), while for the thermally anisotropic YBaCuO film sample are, 4.1×10−6 m2 s−1, 3.5×10−6 m2 s−1 (in-plane diffusivity), and 8.0×10−8 m2 KW−1, respectively. © 1999 American Institute of Physics.
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  • 40
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    Topics: Physics
    Notes: Molybdenum (Mo) doped vanadium dioxide thin films were synthesized using a Mo striped vanadium (V) target during pulsed laser ablation process. The film structure was characterized by high resolution x-ray diffraction, x-ray rocking curve and Rutherford backscattering/channeling measurements. The results show that the full width at half magnitude of the x-ray rocking curve is as narrow as 0.0074°, comparable to that of the (0001) sapphire substrate, 0.0042°, in this study. The ratio of the aligned-to-random backscattered yield reaches 5%, implying that the growth is that of the single crystalline epitaxy. The result of angular scans for both V and Mo atomic channelings reveals that Mo atoms successfully take sites of the V sublattice as a substitutional dopant. It has been noted that the degradation of the phase transition properties of the film upon doping is closely related to the conductivity in the semiconductor phase. © 1999 American Institute of Physics.
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  • 41
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    Journal of Applied Physics 86 (1999), S. 5318-5318 
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  • 42
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    Notes: Vertical stacking of organic light emitting devices (OLEDs) that emit the three primary colors is a means for achieving full-color flat panel displays. The physics, performance, and applications of stacked OLEDs (SOLEDs) are discussed in this and the following paper (Papers I and II, respectively). In Paper I, we analyze optical microcavity effects that can distort the emission colors of SOLEDs if not properly controlled, and describe design principles to minimize these parasitic effects. We also describe the fabrication and operating characteristics of transparent contacts that are an integral part of SOLEDs. We demonstrate that both metal-containing and metal-free transparent electrodes can serve as efficient electron and hole injectors into the stacked organic semiconductor layers. Two different transparent SOLED structures (metal-containing and metal-free) that exhibit sufficient performance for many full-color display applications will be discussed in Paper II. © 1999 American Institute of Physics.
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  • 43
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    Topics: Physics
    Notes: Synchrotron x-ray back reflection section topographs of epitaxial lateral overgrown (ELO) GaAs samples grown on (001) GaAs substrates show images of the GaAs layers bent due to the interaction between the layer and the SiO2 mask. The topographs are simulated under the assumption of orientational contrast. Using the same data the measured x-ray diffraction curve is simulated. The calculations, which are in good agreement with the measurements, are used to gain information on the tilted (001) lattice planes in each ELO layer. We show that the bending of ELO lattice planes reaches a maximum at the center of the ELO stripes, where misorientation is at a minimum, and decreases towards the edges of the stripes, where misorientation reaches a maximum. © 1999 American Institute of Physics.
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  • 44
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    Journal of Applied Physics 86 (1999), S. 4273-4281 
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    Topics: Physics
    Notes: It has been shown that significant changes in the course of solid state reactions can be realized by decreasing length scale, temperature, or by varying parent microstructures. In the case of the formation of Cu3Si by interdiffusion of Cu and Si, previous research has shown that over a large temperature range reaction rates are determined by the rate of grain boundary diffusion of Cu through the growing Cu3Si phase. We have examined the effect of replacing crystalline Si with amorphous Si (a-Si) on these solid state reactions, as well as the effect of decreasing the temperatures and length scales of the reactions. Multilayered thin film diffusion couples of Cu and a-Si were prepared by sputter deposition, with most average composite stoichiometries close to that of the equilibrium phase Cu3Si. Layer thicknesses of the two materials were changed such that the modulation (sum of the thickness of one layer of Cu and a-Si), λ, varied between 5 and 160 nm. X-ray diffraction analysis and transmission electron microscopy analysis were used to identify phases present in as prepared and reacted diffusion couples. Complete reactions to form a single phase or mixtures of the three low temperature equilibrium silicides (Cu3Si, Cu15Si4, and Cu5Si) were observed. Upon initial heating of samples from room temperature, heat flow signals were observed with differential scanning calorimetry corresponding to the growth of Cu3Si. At higher temperatures (〉525 K) and in the presence of excess Cu, the more Cu-rich silicides, Cu15Si, and Cu5Si formed. Based on differential scanning calorimetry results for samples with average stoichiometry of the phases Cu3Si and Cu5Si, enthalpies of formation of these compounds were measured. Considering the reaction of these phases forming from Cu and a-Si, the enthalpies were found to be −13.6±0.3 kJ/mol for Cu3Si and −10.5±0.6 kJ/mol for Cu5Si. The growth of Cu3Si was found to obey a parabolic growth law: x2=k2t, where x is the thickness of the growing silicide, k2 is the temperature dependent reaction constant, and t is the reaction time. Also, the form of the reaction constant, k2, was Arrhenius: k2=k0 exp(−Ea/kbT) with kb being Boltzmann's constant and the prefactor, k0=1.5×10−3 cm2/s, and activation energy, Ea=0.98 eV. These results indicate a much slower reaction to form Cu3Si in thin film Cu/a-Si diffusion couples than indicated by previous researchers using mostly bulk samples of Cu and crystalline Si (x-Si). © 1999 American Institute of Physics.
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  • 45
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    Journal of Applied Physics 86 (1999), S. 4312-4315 
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    Topics: Physics
    Notes: The redistribution of Be in highly doped AlxGa1−xAs layers and AlxGa1−xAs/AlAs(GaAs) short period superlattices (SPSL) during molecular beam epitaxy was investigated by secondary ion mass spectrometry (SIMS) depth profiling. Be outdiffuses significantly from these layers and, additionally, segregates in growth direction. Conversely, Be is depleted and incorporated only up to a solid-solubility limit depending on the Al content. SPSLs with shorter period are disordered and show the solid-solubility limits of homogeneous AlxGa1−xAs layers with the same average composition. Be solid-solubility limits in AlxGa1−xAs layers covering the whole range from GaAs to AlAs are derived from the SIMS depth profiles. © 1999 American Institute of Physics.
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  • 46
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    Journal of Applied Physics 86 (1999), S. 4304-4311 
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    Topics: Physics
    Notes: One of the most used metallization schemes on silicon is the TiN/TiSi2/Si structure, since it has taken advantage of good electrical contact between Si and TiSi2 and the property as a diffusion barrier of TiN. In the present study, this structure has been realized by sputter depositing different layers of TiN/Ti onto silicon (100) substrate and annealing them in nitrogen ambient at different temperatures. Transmission electron microscopy as well as grazing incidence x-ray diffraction have been employed to study the morphology and the crystallographic properties of the formed layers. Initial stage of the C-49 TiSi2 formation has been investigated at 590 °C and complete formation of C-54 TiSi2 phase observed at 710 °C for higher thickness samples. Our attention has been focused on the TiN/TiSi2/Si structures obtained after annealing the deposited films at 710 and 850 °C. We demonstrate that at the annealing temperature of 850 °C as the thickness of the TiN/Ti deposited films is decreased from 600/560 to 175/30 Å, the formation of TiSi2 (C-54) phase is almost inhibited due to a faster consumption of Ti in the formation of TiN.© 1999 American Institute of Physics.
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  • 47
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    Notes: The kinetics changes in the growth of GaN induced by the presence of In segregated on the surface have been investigated in situ by using reflection high energy electron diffraction intensity oscillations. Two types of surfaces have been studied, namely, Ga-polar (0001) wurtzite, and (001) zinc blende. It has been found that In influenced both Ga and N surface kinetics, leading to a change in the growth rate associated with a change in the amount of Ga and N effectively available for the GaN growth. © 1999 American Institute of Physics.
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  • 48
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    Notes: Silicon dioxide (SiO2)/silicon carbide (SiC) structures annealed in nitric oxide (NO) and argon gas ambiences were investigated using x-ray photoelectron spectroscopy (XPS). The XPS depth profile analysis shows a nitrogen pileup of 1.6 at. % close to the NO annealed SiO2/SiC interface. The results of Si 2p, C 1s, O 1s, and N 1s core-level spectra are presented in detail to demonstrate significant differences between NO and Ar annealed samples. A SiO2/SiC interface with complex intermediate oxide/carbon states is found in the case of the Ar annealed sample, while the NO annealed SiO2/SiC interface is free of these compounds. The Si 2p spectrum of the Ar annealed sample is much broader than that of the NO annealed sample and can be fitted with three peaks compared with the two peaks in the NO annealed sample, indicating a more complex interface in the Ar annealed sample. Also the O 1s spectrum of the NO annealed samples is narrow and symmetrical and can be fitted with only one peak whereas that of the Ar annealed sample is broad and asymmetrical and is fitted with two peaks. It is evident that the Ar annealed sample contains some structural defects at the interface, which have been removed from the interface by NO annealing as shown by O 1s spectra. The C 1s spectra at the interface reveal the subtle difference between NO and Ar annealed samples. An additional peak representing the interface oxide/carbon species is observed in the Ar annealed sample. At the interface, the N 1s spectrum is symmetrical and can be fitted with one peak, representing the strong Si(Triple Bond)N bond. However, the N 1s and C 1s XPS spectra acquired in the bulk of the dielectric showed not only the Si(Triple Bond)N bond but also a trace amount of the N–C bond. © 1999 American Institute of Physics.
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  • 49
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    Notes: The sheet carrier concentration (Ns) of channel layers in modulation-doped InAlAs/InGaAs heterostructure field-effect transistor (HFET) structures with n+InGaAs contact layers has been successfully and nondestructively determined using the room-temperature photoluminescence (PL) method. It is found that the spectral energy width between the maximum position of the main PL peak around 0.8 eV and the half-maximum position on the higher energy side has a good positive linear correlation with the Ns of the channel measured by the van der Pauw method. The scattering of the data is less than ±3×1011 cm−2. The determination of Ns is effective even if the HFET structures have not only n+InGaAs contact layers but also layers for InAlAs Schottky level-shift diodes. From a comparison with low-temperature PL spectra, the main PL peak is attributed to the e2h transition in the quantum well of the channel. It is considered that the slope of the peak stretches further to the high energy as the Fermi energy in the channel become higher, i.e., as the Ns becomes larger. © 1999 American Institute of Physics.
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  • 50
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    Journal of Applied Physics 86 (1999), S. 4326-4332 
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    Topics: Physics
    Notes: The spatial resolution and the near-field signal detection efficiency obtained in scanning near-field cathodoluminescence microscopy (SNCLM) are theoretically evaluated in the case of semiconductor investigation. The effect of the electron-beam interaction volume, the surface recombination velocity, and the energy diffusion is taken into account. The lateral resolution of the SNCLM, because of the near-field collection mode, is not energy-transfer dependent. A good lateral resolution can be obtained even when the surface recombination velocity is low and the minority-carrier diffusion length is large [this is the advantage of the near-field collection mode with respect to the tip illumination/far-field collection mode generally used in photoluminescence (PL) imaging]. Further, it is shown that the radiative recombination centers situated far from the tip can perturb the near-field detection efficiency, particularly for large nonradiative surface recombination velocities and low diffusion lengths. Nevertheless, the short range of the electron energy loss limits the contribution of these luminescent centers. Consequently, the near-field/far-field contribution ratio in cathodoluminescence experiments is better than that of PL experiments done in the far-field illumination/tip collection mode for which the far-field signal is more important because of the large laser-beam excitation area. © 1999 American Institute of Physics.
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  • 51
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    Notes: Electroplated copper exhibits some surprising changes at room temperature in sheet resistance, stress, and microstructure. This behavior, now known as self-annealing, is shown here to be intimately linked to the composition of the plating bath and the resulting incorporation of organic additives in the Cu layer. Their addition is a necessary condition for self-annealing to occur, but slows down the process for higher concentrations. The phenomenon also depends critically on film thickness, showing an accelerated transformation when film thickness increases. This dependence is explained in terms of a very rapid primary crystallization from the top surface down just after deposition, followed by a slower lateral recrystallization producing large secondary grains. The stress and sheet resistance during recrystallization are identified as two noncorrelated variables. © 1999 American Institute of Physics.
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  • 52
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    Notes: Low-temperature deposition of TiN by reactive evaporation or sputter deposition onto amorphous substrates leads to highly underdense layers which develop mixed 111/002 orientations through competitive growth. In contrast, we demonstrate here the growth of low-temperature (450 °C) fully dense polycrystalline TiN layers with complete 111 texture. This was achieved by reactive magnetron sputter deposition using a combination of: (1) highly oriented 25-nm-thick 0002 Ti underlayers to provide 111 TiN orientation through texture inheritance (local epitaxy) and (2) high flux (JN2+/JTi=14), low-energy (EN2+(similar, equals)20 eV), N2+ ion irradiation in a magnetically unbalanced mode to provide enhanced adatom diffusion leading to densification during TiN deposition. The Ti underlayers were also grown in a magnetically unbalanced mode, in this case with an incident Ar+/Ti flux ratio of 2 and EAr+(similar, equals)11 eV. All TiN films were slightly overstoichiometric with a N/Ti ratio of 1.02±0.03. In order to assess the diffusion-barrier properties of dense 111-textured TiN, Al overlayers were deposited without breaking vacuum at 100 °C. Al/TiN bilayers were then annealed at a constant ramp rate of 3 °C s−1 to 650 °C s−1 and the interfacial reaction between Al and TiN was monitored by in situ synchrotron x-ray diffraction measurements. As a reference point, we find that interfacial Al3Ti formation is observed at 450 °C in Al/TiN bilayers in which the TiN layer is deposited directly on SiO2 in a conventional magnetically balanced mode and, hence, is underdense with a mixed 111/002 orientation. However, the onset temperature for interfacial reaction was increased to 610 °C in bilayers with fully dense TiN exhibiting complete 111 preferred orientation. © 1999 American Institute of Physics.
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  • 53
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    Journal of Applied Physics 86 (1999), S. 3655-3660 
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    Topics: Physics
    Notes: The presence of a small amount of Mo was shown to have a significant effect on the C49–TiSi2 to C54–TiSi2 phase transformation in the Ti–Si reaction. The formation of the C54–TiSi2 phase was facilitated when an ultrathin layer of either Mo or α-MoSix was inserted at or close to the Ti/Si interface. Mo deposited on the surface of Ti had no beneficial effect on the Ti–silicide reaction; neither did Mo implanted into preexisting C49–TiSi2 films. The optimum thickness of interfacial Mo and α-MoSix layers was found to be less than 0.3 nm. Transmission electron microscopy and diffraction investigations demonstrated that Mo did not alter the sequence of the Ti–Si reaction, as proposed in recent studies. Rather, the most obvious effect of molybdenum was a reduction of the grain size of the C49–TiSi2 phase, which could lead to an increase in the nucleation density of the desired C54–TiSi2 phase and account for the observed reduction in formation temperature. © 1999 American Institute of Physics.
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  • 54
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    Topics: Physics
    Notes: CNx films were deposited on Si(100) substrates at a substrate temperature of 600 °C using dc magnetron sputtering of a high-purity graphite target in pure nitrogen. The film characteristics were primarily controlled by the pressure, p, (0.05–5 Pa), the discharge current on the magnetron target, Im, (0.5–3 A), and the rf induced negative substrate bias voltage, Ub, (−300 to −1200 V). The films, typically 1–2 μm thick, were found to be amorphous, and they possessed the N/C atomic concentration ratio up to 0.35, the hardness up to 40 GPa, the elastic recovery up to 85%, and good adhesion and promising tribological properties. The energy and flux of ions bombarding the target and the growing films were evaluated on the basis of the discharge characteristics measured for both the dc magnetron discharge and the rf discharge in the deposition zone. Optical emission spectroscopy was used to study the behavior of significant atomic and molecular species, such as N, N2, N+, N2+, CN, C, and C2, near the substrate and in the plasma bulk. The measurements indicated that both dc and rf discharges are mutually coupled. We confirmed that CN radicals and N atoms are the principal precursors for reactive magnetron sputtering of the CNx films. Good correlation between the N/CN concentration ratio in the deposition zone and the N/C atomic ratio in the films was found over a wide range of the investigated process parameters. We have shown that the CNx films have a high hardness only when the energy and flux of the nitrogen ions are sufficiently high for effective incorporation of nitrogen in the layers; such conditions require the pressures lower than 0.5 Pa and the Ub values between −500 and −700 V. It has been proved that the frequently used deposition parameters such as Im, Ub, p, and Ts, do not generally suffice to satisfactorily characterize the film growth process. © 1999 American Institute of Physics.
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  • 55
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    Journal of Applied Physics 86 (1999), S. 3661-3669 
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    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two tools for the analysis of facets as detected by scanning-probe microscopy (SPM) images are proposed. One tool is an adaptation of the radial-histogram transform proposed by D. Schleef et al. in Phys. Rev. B. 55, 2535 (1997). In this article the local slopes in the SPM image are in the present version determined by Savitsky–Golay filters with variable lengths [A. Savitsky and M. J. E. Golay, Anal. Chem. 36, 1627 (1964)]. These variable length filters turn out to be important to suppress the influence of noise obscuring the possibility to detect facets and to analyze corrugations with different length scales in SPM images, e.g., surface reconstructions. The other tool allows the direct quantitative determination of the orientation (with a standard deviation) of user-specified parts of facets. It makes use of a Savitsky–Golay filter as well. Both tools were applied to an artificially constructed SPM image and several experimental SFM images showing (ionic) MnO precipitates protruding out of a (metallic) Cu surface. It is shown that the Miller indices of the facets can be derived experimentally. © 1999 American Institute of Physics.
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  • 56
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    Journal of Applied Physics 86 (1999), S. 4498-4508 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser-induced surface deformation and surface relief grating formation at different intensity levels on azobenzene-functionalized polymer films were investigated. The surface deformation profile induced by a Gaussian laser beam at low intensities reveals strong polarization dependence and establishes that an optical-field component in the direction of the optical-field gradient is essential for this deformation process. A theoretical analysis based on the optical-field gradient force model is presented to account for the deformation behavior at low intensities. In the higher-intensity regime, however, a different mechanism is found to dominate the surface deformation process. Simultaneous formation of two different types of topographic gratings is observed in a two-beam interference experiment. The phase relationship between these surface relief gratings and the interference intensity pattern was deduced based on the results from the single-beam experiments. The erasing behaviors of the two distinct surface relief gratings were experimentally investigated to highlight the two mechanisms involved in these grating recordings. © 1999 American Institute of Physics.
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  • 57
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    Journal of Applied Physics 86 (1999), S. 3676-3681 
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    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamical process of surface band bending induced by ion bombardment as a function of ion fluence and energy has been studied with a special low energy ion beam system and an x-ray photoelectron spectrometer. It was found that 10 and 100 eV Ar+ bombardment of n- and p-InP (110) samples, which were prepared in ultrahigh vacuum by in situ cleavage of InP (100) bars, moved their surface Fermi levels to a common pinning position 0.95 eV above the valence-band maximum. The observed surface band bending was attributed to the displacement damage in the near-surface region induced by the ion bombardment. A quantitative analysis of the band bending data as a function of ion fluence showed that for the 10 eV Ar+ bombardment the formation of ionized surface states at a density of about 1×1012/cm2 in the band gap of InP was induced by an ion fluence of 5×1016/cm2. As expected, an increase of bombardment energy from 10 to 100 eV greatly raised the formation probability of surface defects. The results imply that very brief plasma exposure is sufficient to cause surface damage to a semiconductor that is severe enough to affect the device performance of the semiconductor. © 1999 American Institute of Physics.
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  • 58
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    Journal of Applied Physics 86 (1999), S. 3682-3687 
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    Source: AIP Digital Archive
    Topics: Physics
    Notes: The destabilization of a planar solid/liquid interface during resolidification of the molten surface layer of Si–Sn alloys is investigated. Experimental data are compared with the results of a transient numerical stability analysis. In that analysis the time evolution of an infinitesimal sinusoidal perturbation of a planar interface is investigated. For this the concentration profile in the melt as well as the temperature distributions in the melt and solid are divided into a base state and a state due to the perturbation. The highly nonuniform Sn profiles implanted in (100) silicon samples serve as initial conditions for the numerical calculations. Deviations from thermal equilibrium at the solid/liquid interface are considered. The critical concentration for breakdown is calculated as a function of solidification velocity and compared with the results of the analytical analysis of Huntley and Davis [Acta Metall. Mater. 41, 2025 (1993)]. It is further investigated whether an analytical steady-state stability analysis can be used to approximately describe the experiments considered. © 1999 American Institute of Physics.
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  • 59
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    Journal of Applied Physics 86 (1999), S. 3694-3698 
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    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical investigation of plane-wave electromagnetic scattering in active dielectric sphere predicted the existence of anomalous resonances that occur at discrete wavelengths. These resonances may be understood from a leaky wave phase matching boundary conditions, in which the gain in the dielectric exactly makes up for the radiative loss of a mode. This results in a radiative mode that does not decay in time, therefore it is described as a lossless radiative mode. Experiments have been performed to verify the existence of these resonances. Optical pumping was used to provide the gain, and the threshold of each resonant mode was found to be a function of the dye concentration and the radius of the dielectric sphere. © 1999 American Institute of Physics.
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  • 60
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    Journal of Applied Physics 86 (1999), S. 3688-3693 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Structures and crystal transformation of the newly synthesized vinylidene fluoride (VDF) oligomer with large electric dipoles evaporated on KCl (001) at various substrate temperatures have been investigated by an energy dispersive–grazing incidence x-ray diffraction system, Fourier transform infrared spectroscopy, and atomic force microscope (AFM). It was revealed that the molecules grow epitaxially and are influenced greatly by forces of the crystal surface field in terms of van der Waals or electrostatic potentials, and found that the phase transformation from form II (α phase) to form I (β phase) is induced by raising the temperature of the substrate from 50 to 80 °C, accompanying the alternation in the crystal axes on the substrate from the a axis of form II to the polar b axis of the form I crystal. This fact suggests that the molecular chain of VDF oligomers aligns their c axes along the 〈110〉 row of K+ or Cl− with the aid of electrostatic interaction under enough thermal movement. Moreover, in the transformation process, a pair of "rod-like" crystals, suggesting ferroelectric activity, were observed by AFM. © 1999 American Institute of Physics.
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  • 61
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    Topics: Physics
    Notes: Hetero- and homoepitaxial Nd3+-doped LaF3 thin films have been grown by molecular beam epitaxy. Two different orientations of CaF2 substrates, (111) and (110), have been used for the heteroepitaxial structures. High-resolution emission and excitation spectra as well as the decay time of the emission have been measured. The spectroscopic measurements demonstrate that one Nd3+ site is present in the LaF3 layers grown on CaF2(111) substrates but two slightly different Nd3+ centers are resolved in the films on CaF2(110) substrates. One Nd3+ site has been found in the homoepitaxial sample. Slight differences are observed between the centers found in the LaF3 layers and the one observed in the Nd3+-doped LaF3 bulk crystal. For the homoepitaxial layer, the linewidths are similar to those of the bulk crystals, whereas for the heteroepitaxial layers, a broadening is observed. © 1999 American Institute of Physics.
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  • 62
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    Journal of Applied Physics 86 (1999), S. 3705-3708 
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    Topics: Physics
    Notes: The bulk amorphous-like (a-) semiconductor, a-ZnIn2Te4, is prepared by the melt-quench technique. The pseudodielectric-function spectra, 〈ε(E)〉=〈ε1(E)〉+i〈ε2(E)〉, of a-ZnIn2Te4 are measured by spectroscopic ellipsometry in the 1.2–5.3 eV photon-energy range at room temperature. The measured 〈ε(E)〉 spectra strongly resemble those of amorphous tetrahedrally bonded semiconductors. These spectra are analyzed using a simplified model of the interband optical transitions. Dielectric-related optical constants, such as the complex refractive index, absorption coefficient, and normal-incidence reflectivity, of a-ZnIn2Te4 are also been presented. © 1999 American Institute of Physics.
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  • 63
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    Journal of Applied Physics 86 (1999), S. 3714-3720 
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    Topics: Physics
    Notes: AlGaN/GaN quantum well (QW) structures are grown on c-plane sapphire substrates by molecular beam epitaxy. Control at the monolayer scale of the well thickness is achieved and sharp QW interfaces are demonstrated by the low photoluminescence linewidth. The QW transition energy as a function of the well width evidences a quantum-confined Stark effect due to the presence of a strong built-in electric field. Its origin is discussed in terms of piezoelectricity and spontaneous polarization. Its magnitude versus the Al mole fraction is determined. The role of the sample structure geometry on the electric field is exemplified by changing the thickness of the AlGaN barriers in multiple-QW structures. Straightforward electrostatic arguments well account for the overall trends of the electric-field variations. © 1999 American Institute of Physics.
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  • 64
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    Topics: Physics
    Notes: Time resolved photoluminescence and deep level transient spectroscopy have been used to monitor the effect of rapid thermal annealing on bulk GaInP and GaInP/AlGaInP quantum wells grown by solid source molecular beam epitaxy similar to those used in 650 nm range lasers. Following rapid thermal annealing at temperatures up to 875 °C, reductions in the concentration of several deep level traps are observed. Correlation of these data with photoluminescent intensity and lifetime measurements indicate that the defect labeled N3, 0.83 eV below the conduction band, is the dominant recombination center. The combination of these two transient spectroscopy measurement techniques is therefore not only able to measure the change in deep level concentration, but also to correlate this change with improved carrier lifetimes and, ultimately, reduced threshold current densities in quantum well lasers. There is also evidence to suggest that this same defect, possibly a phosphorous vacancy or a related complex, plays an important role in other GaInP based devices. © 1999 American Institute of Physics.
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  • 65
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    Topics: Physics
    Notes: This work discusses the temperature behavior of the various photoluminescence (PL) transitions observed in undoped, n- and p-doped GaN in the 9–300 K range. Samples grown using different techniques have been assessed. When possible, simple rate equations are used to describe the quenching of the transitions observed, in order to get a better insight on the mechanism involved. In undoped GaN, the temperature dependence of band edge excitonic lines is well described by assuming that the A exciton population is the leading term in the 50–300 K range. The activation energy for free exciton luminescence quenching is of the order of the A rydberg, suggesting that free hole release leads to nonradiative recombination. In slightly p-doped samples, the luminescence is dominated by acceptor related transitions, whose intensity is shown to be governed by free hole release. For high Mg doping, the luminescence at room temperature is dominated by blue PL in the 2.8–2.9 eV range, whose quenching activation energy is in the 60–80 meV range. We also discuss the temperature dependence of PL transitions near 3.4 eV, related to extended structural defects. © 1999 American Institute of Physics.
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  • 66
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    Topics: Physics
    Notes: Long lasting phosphorescence (LLP) and photostimulated luminescence (PSL) were found in reduced calcium aluminate glasses activated with Tb3+ ions. The LLP from Tb3+ was observed by illuminating the Tb3+ 4f→5d charge transfer band with ultraviolet (UV) 254 nm light, while the PSL was seen by stimulating the UV-illuminated glasses with 633 nm light. The decay curve of the LLP was fitted with a second-order kinetic for the initial period (0〈t〈20 min) and a first-order kinetic for the later (t〉30 min). An electron paramagnetic resonance (EPR) signal, which is attributed to an F+-like center associated with Ca2+ ions, was induced by illumination with UV light and its intensity decay was fitted with a first-order kinetic similarly to the later stage of the LLP. The appearance of the PSL by illumination is accompanied by a distinct intensity reduction of the EPR signal due to the F+-like center. The thermoluminescence spectra of the specimen illuminated with UV light at 77 K consist of two components peaking at ∼240 and ∼390 K. The low temperature component and the high temperature component were attributed to an F-like center and an F+-like center, respectively. These results lead to a conclusion that electrons of the F-like center and the F+-like center contribute predominantly to the emergence of the LLP and the PSL, respectively. © 1999 American Institute of Physics.
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  • 67
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    Journal of Applied Physics 86 (1999), S. 3745-3750 
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    Topics: Physics
    Notes: The complex refractive index of a LiF crystal surface layer irradiated by low-energy electrons is modified by the stable formation of color centers embedded in it. A simplified dipole-electromagnetic field interaction model has been adopted in order to estimate the dispersion curves of colored LiF from a single optical transmittance measurement. The excellent agreement with the corresponding experimental curves (obtained by means of spectrophotometry and ellipsometry) demonstrates this to be a promising approach for LiF-based optical waveguide characterization.© 1999 American Institute of Physics.
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  • 68
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    Notes: Pump-probe experiments in GaAs/AlGaAs multiple quantum well samples are described using both picosecond and femtosecond laser pulses in different polarization configurations. The excitonic and free carrier components of exciton absorption saturation were analyzed as a function of well width. The relative importance of phase space filling, Coulomb screening and broadening contributions was determined from polarization and laser bandwidth dependencies via spin-dependent and spin-independent components. A five-level model was used to fit the data and nonlinear coefficients for the individual contributions were determined for each well width. The Coulomb contributions arising from screening and broadening of the excitons was found to dominate the absorption bleaching using picosecond pulses, whereas phase space filling was largest in the femtosecond regime. Exciton phase space filling was found to be four times larger than free carrier phase space filling at narrower well widths. A sublinear dependence of exciton broadening with carrier density was observed. © 1999 American Institute of Physics.
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  • 69
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    Journal of Applied Physics 86 (1999), S. 3751-3757 
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    Topics: Physics
    Notes: Two different types of structure called X1 and X2 are existing in Y2SiO5 at normal conditions. In X1 type, Y3+ ions occupy two sites where they are surrounded respectively by nine and seven oxygen ions, while in X2 structure, only six and seven oxygen ions are involved. Nanometric scale X1-Y2SiO5 crystals were prepared by sol-gel method with particle size around 50 nm. Site selective excitation at low temperature has shown four different luminescent centers. Two of them belong to Eu3+ embedded in X1-Y2SiO5, the other two are attributed to Y2O3:Eu phase and to a particular site on the surface. The occurrence of the latter site may be related to the nanometric size of the sample. A pronounced excitation energy transfer from site 2 to site 1 was also observed on excitation spectra. The energy transfer rate increases rapidly with increasing Eu3+ concentration and for x=0.7 in Y2−xSiO5:Eux, no fluorescence takes place in site 2 at 15 K. The lifetimes of the 5D0 levels of Eu3+ in the two sites were measured as a function of Eu3+ concentration. The results have shown that the lifetime of the 5D0 level of Eu3+ in site 2 decreases with increasing Eu3+ concentration. The energy transfer rate dependence upon temperature was studied in detail and compared to a theoretical simulation. © 1999 American Institute of Physics.
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  • 70
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    Notes: First principles, total energy methods have been applied to predict the relative stabilities of the four experimentally verified MoC phases: the cubic δ(NaCl) phase and the three hexagonal γ(WC), η and γ′(TiAs) phases. The effect of vacancies on the relative stability of these four phases was investigated using a model structure with ordered vacancies within the carbon sublattice. For stoichiometric MoC, the γ phase was found to be the most stable followed by γ′, δ, and η, but for substoichiometric MoC0.75, the order of relative stability was changed and the substoichiometric δ phase was found to have the lowest energy followed by γ′ and γ. A study of the electronic structure revealed vacancy induced peaks in the density of state and the electron density attached to these peaks was analyzed and found to emanate from unscreened Mo–Mo bonds through the carbon vacancy site. Finally, the oxygen stabilization of the γ′ MoC phase was studied. © 1999 American Institute of Physics.
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  • 71
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    Journal of Applied Physics 86 (1999), S. 3768-3772 
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    Topics: Physics
    Notes: Using a semi-empirical pseudopotential method, a set of band-structure calculations are performed on a range of GaInN and GaAlN alloys in both the zinc-blende and wurtzite structures. Pseudopotentials for the bulk materials are described by suitable V(q) functions, and these are used to construct the alloy pseudopotentials. The band gap as a function of alloy composition is studied, and it is found that there is no significant bowing in the case of GaAlN. The bowing is larger for GaInN, although heavily dependent on the strain present. A more detailed study of the wurtzite alloys is carried out for low Al and In fractions. Wurtzite k⋅p parameters for several alloys at concentrations commonly used in devices are obtained from the semi-empirical band structure using a Monte Carlo fitting procedure. © 1999 American Institute of Physics.
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  • 72
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    Topics: Physics
    Notes: An exact method is introduced to determine the electric potential in an infinite rectangular lattice of particles described by curvilinear coordinates in which Laplace's equation separates. The potential is expanded in harmonic functions, and suitable auxiliary functions are used to obtain an infinite system of linear algebraic equations for the expansion coefficients. Special attention is paid to lattices of spheres and prolate spheroids. For these cases, the truncated system converges very rapidly as the number of terms in the truncation series increases. The method works well for calculating the effective conductivity for dense or sparse inclusions, and for highly conducting lattices or lattices of cavities. Numerical results for the effective conductivity are given and compared with data obtained by other methods. © 1999 American Institute of Physics.
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    Journal of Applied Physics 86 (1999), S. 3787-3791 
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    Topics: Physics
    Notes: We report on the observation of quantized jumps due to single-carrier trapping and detrapping at defect states in silicon photoconductors of 103 μm3 in volume. A specifically designed electrical test structure in a low-doped (2×1014 cm−3) silicon crystal was fabricated. It consists in four substrate resistances connected in a Wheatstone bridge. After the exposure to light, the bridge offset voltage recovers its equilibrium value with steps of 5–10 μV, corresponding to the emission or capture of a single carrier. Such structures also display random telegraph signals in the dark, with steps of similar amplitude. This behavior is observed with structures processed on Czochralski-grown substrates and not with those processed on float-zone substrates. Simple calculations based on quantized free carrier concentration variations corroborate the above measurements. © 1999 American Institute of Physics.
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  • 74
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    Notes: Based on semiempirical quantum-chemical calculations, the electronic band structure of β-Ga2O3 is presented and the formation and properties of oxygen vacancies are analyzed. The equilibrium geometries and formation energies of neutral and doubly ionized vacancies were calculated. Using the calculated donor level positions of the vacancies, the high temperature n-type conduction is explained. The vacancy concentration is obtained by fitting to the experimental resistivity and electron mobility. © 1999 American Institute of Physics.
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