bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical and optical characterization of Er-implanted Si: The role of impurities and defects
Authors: Priolo F. , Coffa S. , Franzò G. , Spinella C. , Carnera A. , Bellani V.
Published: July 2002

The electrical and optical properties of Er-implanted Si are shown to be critically dependent on the presence of impurities and defects. A large enhancement in the electrical activation of Er (up to three orders of magnitude) is obtained by coimplanting Er with O or C at 300 °C. The use of C also allows one to obtain a good quality crystal after implantation and annealing. This is shown to be crucial in the photoluminescence process. In fact, in spite of the large amount of active Er atoms, photoluminescence is inhibited in the presence of the high concentration of precipitates and crystallographic defects which are left after annealing of the Er and O coimplants. The photoluminescence intensity is, on the other hand, enhanced by the high concentration of active Er atoms in the defect-free crystal which is left after annealing of the Er and C coimplants. Moreover, a clear shift in the main photoluminescence peaks is observed in Er- and C-coimplanted samples as a result of the different surroundings experienced by the Er atoms.
Monte Carlo simulation of phase separation during thin-film codeposition
Authors: Adams C. D. , Srolovitz D. J. , Atzmon M.
Published: July 2002

The results of Monte Carlo simulation of phase separation during binary film coevaporation are presented for a range of deposition conditions. The model employed assumes that phase separation occurs through surface interdiffusion during deposition, while the bulk of the film remains frozen. Simulations were performed on A-B alloy films having compositions of 10 and 50 vol % solute. For both film compositions, the lateral scale of the domains at the film surface evolves to a steady-state size during deposition. A power-law dependence of the steady-state domain size on the inverse deposition rate is obtained. Simulation microstructures at 50 vol % compare favorably with those obtained in a previous experimental study of phase separation during coevaporation of Al-Ge films of the same composition. Results of simulations performed at 10 vol % are compared with the predictions of a theoretical model based on the above assumptions. The power-law exponent obtained from simulations at 10 vol % is different than that predicted by the theoretical model. The reasons for this difference are discussed.
Generation of interface states at the silicon/oxide interface due to hot-electron injection
Authors: Wong H. , Cheng Y. C.
Published: July 2002

By considering the decomposition of water-related bonds at the silicon/oxide interfaces, theoretical expressions for the hot-electron induced interface state generation and threshold-voltage shift are developed. Results demonstrate that the relation between the threshold-voltage shift and the hot-electron fluence needs not follow the power law. The developed expression of the threshold-voltage shift is a function of the initial interface trap density, interface hardness, density of water-related chemical bond, and the capture cross section of interface trap and can be used to explain most of the reported experiments. When the trapping rate and the generation rate are close to each other, a power law dependence of the threshold-voltage shift will be observed in a wide range of injection fluence. However, if the trapping rate is greater than the generation rate or for a sample with large hardness and small initial trap density, a quasi-saturation region is observed because of most of the interface trap being filled and the small amount of generated traps. Saturation of the threshold-voltage shift will occur when most of the water-related bonds are dissociated and the created traps are filled.
Microstructural investigations of barium ferrite longitudinal thin-film media
Authors: Wong B. Y. , Sui X. , Laughlin D. E. , Kryder M. H.
Published: July 2002

Crystalline barium ferrite films with in-plane magnetic anisotropy have been obtained by postdeposition annealing of amorphous sputtered films. The magnetic properties, the crystallographic texture, and the microstructure are very sensitive to the sputtering and postdeposition annealing conditions. It was found that both Hc and the grain size decrease with the addition of Co and Ti ions. However, an excessive amount of dopants leads to a loss in the in-plane anisotropy. Barium ferrite films produced by this technique contain physical voids or channels separating the grains which help to decrease the exchange coupling between grains.
Self-induced laterally modulated GaInP/InAsP structure grown by metal-organic vapor-phase epitaxy
Authors: Ponchet A. , Rocher A. , Ougazzaden A. , Mircea A.
Published: July 2002

Zero-net strained multilayer alternating tensile GaInP and compressive InAsP have been grown on (001)InP by metal-organic vapor-phase epitaxy. A structural analysis using transmission electron microscopy (TEM) is reported. A remarkably regular laterally modulated structure has been observed. GaInP- and InAsP-rich vertical zones alternate with a periodicity of 0.28 μm along the lateral [110] direction, thus balancing the mismatch along the [110] rather than the [001] growth direction. TEM experiments suggest that each vertical zone is partially elastically relaxed.
Low-level leakage currents in thin silicon oxide films
Authors: Dumin D. J. , Cooper J. R. , Maddux J. R. , Scott R. S. , Wong D.-P.
Published: July 2002

The low-level leakage currents in thin silicon oxide films were measured before and after the oxides had been stressed at high voltages. Four components of current were identified. These components were the tunneling current, the capacitive current associated with the measurement sweep rate, a negative differential current associated with the voltage sweep through the changing oxide C-V characteristic, and an excess current that occurred after the high-voltage stress. The excess current was due to the charging and discharging of traps generated inside of the oxide by the high-voltage stress. The excess current was proportional to the number of traps generated in the oxide. The magnitude of the excess current could be changed by changes in the measurement procedures due to the charging and discharging of traps. A major portion of the stress-generated excess low-level leakage current may not be a current that flowed through the oxide, but may be a trap charging/discharging current. This paper will concentrate on describing the low-level pretunneling leakage currents and the measurement techniques needed to determine the properties of the excess leakage currents associated with the traps generated inside of the oxide.
Non-ohmic characteristics of ZnO-V2O5 ceramics
Authors: Tsai Jyh-Kuang , Wu Tai-Bor
Published: July 2002

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.
The effective transverse thermal conductivity of amorphous Si3N4 thin films
Authors: Griffin A. J. , Brotzen F. R. , Loos P. J.
Published: July 2002

The effective transverse thermal conductivity of Si3N4 thin films is determined as a function of film thickness. Results indicate that the effective thermal conductivity behavior of Si3N4 thin films is similar to that exhibited by amorphous SiO2 films; that is, there is no significant difference between the thermal conductivity of amorphous Si3N4 and amorphous SiO2 thin films as a function of thickness or temperature. The average effective transverse thermal conductivity decreases drastically as the film thickness is reduced. This strong thickness dependence is ascribed to a thermal resistance that is localized at the amorphous film/Si-substrate interface. Within the narrow temperature range studied, the interfacial thermal resistance and the intrinsic conductivity of amorphous films increase with temperature; however, the interfacial resistance dominates as the film thickness is reduced. In light of the observed similarities between the Si3N4 results and those previously obtained on SiO2, the reduction in the effective thermal conductivity of amorphous thin films with decreasing thickness is discussed in terms of both interfacial thermal resistance and scattering mechanisms in amorphous solids.
Flat band current-voltage-temperature method for band-discontinuity determination and its application to strained InxGa1−xAs/In0.52Al0.48As heterostructures
Authors: Huang J.-H. , Chang T. Y.
Published: July 2002

A method that combines capacitance-voltage and current-voltage-temperature measurements of a n+-i-n− (or p+-i-p−) heterobarrier structure for reliable determination of the band discontinuity is described. Experimental and analytical procedures for the extraction of the Fermi energies in the doped layers, the location of the flat band condition, and the determination of the barrier height at flat band are given. The effects of nonparabolicity and strain are also considered. Some potential sources of errors encountered in the conventional procedure that is based on the barrier height at zero bias are avoided in this flat band method. The application of this method and other experimental considerations are illustrated by using the strained InxGa1−xAs/In0.52Al0.48As heterointerface as a specific example. The results show that the conduction-band offset ratio, Qc, is nearly constant at 0.71 for x≤0.54 but appears to change quite abruptly to a fairly constant value of 0.82 for x≥0.58.
Interaction of hydrogen, methane, ethylene, and cyclopentane with hot tungsten: Implications for the growth of diamond films
Authors: Winters Harold F. , Seki Hajime , Rye Robert R. , Coltrin Michael E.
Published: July 2002

Modulated-beam mass spectrometry and x-ray photoelectron spectroscopy (XPS) have been used to investigate the interaction of CH4, C2H4, C5H10, and H2 with carburized and uncarburized tungsten. It is shown that significant evaporation of C1, C2, and C3 occurs for carburized tungsten at temperatures above 1900 °C. The temperature dependence of the carbon evaporation rate was found to be similar to the temperature dependence of the diamond film deposition rate observed in chemical vapor deposition (CVD) reactors, similar to the temperature dependence for the carbon deposition rate observed in the present experiments, and similar to the expected evaporation rate of carbon from graphite and tungsten carbide. The desorption of hydrocarbon species (other than the incident gas) was not clearly observed under any conditions for methane or ethylene. In contrast, it is quite likely that cyclopentane decomposes at the surface to produce new species which are subsequently desorbed into the gas phase. The reaction of ethylene with tungsten is believed to result in complete decomposition with the hydrogen being desorbed as atoms or molecules while the carbon remains on the surface where there is competition between carburization and evaporation. The reaction probability of ethylene with tungsten was found to be close to unity while the reaction probability of methane was small. The removal of carbon from carburized tungsten via an etching reaction involving hydrogen was not observed.

The production of hydrogen atoms from H2 was found to be largest on clean tungsten, less on carburized tungsten, and not observable on graphite. Evaporation of tungsten from carburized tungsten was seen at temperatures below 2500 °C but not below 2200 °C. XPS measurements indicated that slightly carburized tungsten contained some graphite in the surface region while heavily carburized tungsten contained much more graphite. The surface concentration of carbon was found to depend in a complicated manner on the balance between carbide and graphite growth and carbon evaporation. The reaction probability of the incident gas is also a determining factor. In addition, computer simulations were used to calculate the concentrations of various species in the gas phase under conditions which are typical of those used in diamond hot-filament CVD reactors. Calculated gas-phase species distributions near the substrate for carbon-atom/H2 mixtures are found to be similar for most species to those calculated for CH4/H2 mixtures. It appears that the fast H2 and H chemistry determines the equilibrium mixture and that it is nearly independent of the type of carbon containing species introduced near the filament. Literature results obtained in typical diamond hot-filament CVD reactors are compared and interpreted on the basis of the present data.
Magnetic and structural properties of vapor-deposited Fe-Co alloy particles
Authors: Gangopadhyay S. , Yang Y. , Hadjipanayis G. C. , Papaefthymiou V. , Sorensen C. M. , Klabunde K. J.
Published: July 2002

The structural and magnetic properties of two Fe-Co alloy particles with composition Fe100−xCox(x=45,65) were studied using x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, superconducting quantum interference device magnetometry, and Mössbauer spectroscopy. The particles were nearly spherical in shape with an average particle size around 350 Å. Particles formed long chains and showed a core/shell particle morphology. X-ray diffraction and Mössbauer studies showed the presence of bcc α-Fe-Co and CoFe2O4 phases with the former as the majority phase in Fe55Co45 and the latter the majority phase in Fe35Co65. The room-temperature coercivities of both of these samples were much higher than those in Fe particles with values exceeding 2.2 kOe. The Fe35Co65 sample showed a drastic temperature dependence of coercivity from 1.5 kOe at 300 K to 15 kOe at 10 K. The structural and magnetic data suggest a core/shell morphology with the surface oxide layer having a very important impact on both the magnitude and temperature dependence of the coercivity of the whole particle.
Co/CoAl magnetic superlattices on GaAs
Authors: De Boeck J. , Bruynseraede C. , Bender H. , Van Esch A. , Van Roy W. , Borghs G.
Published: July 2002

Co/CoAl multilayers are grown by molecular beam epitaxy on AlAs/GaAs (001). CoAl is used as a template for the epitaxy of Co. From RHEED and lattice matching considerations bcc Co is expected, but thicker Co layers are probably fcc with stacking faults. The crystallographic structure of the Co layers is unclear at present. Room-temperature magnetization and magnetoresistance data are presented. Co/CoAl multilayers with various CoAl thickness all show in-plane magnetic anisotropies along 〈110〉. Uniaxial anisotropy along 〈110〉 is found to increase with increasing thickness of the CoAl layers in the multilayers. The magnetoresistive effect as a function of the orientation of the current path and the applied field is ascribed to domain-wall effects and internal Lorentz magnetoresistance.
Room- and low-temperature assessment of pseudomorphic AlGaAs/InGaAs/GaAs high-electron-mobility transistor structures by photoluminescence spectroscopy
Authors: Gilpérez J. M. , Sánchez-Rojas J. L. , Muñoz E. , Calleja E. , David J. P. R. , Reddy M. , Hill G. , Sánchez-Dehesa J.
Published: July 2002

The use of room- and low-temperature photoluminescence (PL) spectroscopy for the assessment of n-type pseudomorphic AlGaAs/InGaAs/GaAs high-electron-mobility transistor structures is reported. We describe a method to determine the InAs mole fraction x, the channel layer thickness L, and the confined two-dimensional electron gas density (ns), based on the comparison between the PL transitions and the recombination energies derived from self-consistent calculations of the subband structure. A detailed analysis of the optical transitions and their dependence on the Fermi level position and temperature is performed. It is shown that, in real devices, the high sensitivity of the recombination energies and intensities on small changes of the parameters x, L, and ns allows us to detect deviations from their nominal structural parameters within the uncertainty of the molecular beam epitaxy growth technique. The present assessment procedure has been applied to a significant number of samples, and it has been backed by independent measurements of these parameters by more sophisticated techniques such as Shubnikov–de Haas and PL excitation in standard and gated samples, and by physical techniques like transmission electron microscopy and Auger spectroscopy.
Band alignment and carrier injection at the porous-silicon–crystalline-silicon interface
Authors: Ben-Chorin M. , Möller F. , Koch F.
Published: July 2002

The current-voltage characteristics and the photoresponse of metal-porous Si–p-type Si heterostructures have been studied. It is shown that the common interpretation of the current-voltage characteristics, which assumes that the current is limited by the Schottky barrier at the metal-porous Si interface, is wrong. An alternative explanation based on the electric-field dependence of the porous Si conductivity is suggested. It is shown that the rectifying behavior originates from a depletion inside the c-Si substrate at its interface to the porous Si.
Monte Carlo calculations of the temperature- and field-dependent electron transport parameters for 4H-SiC
Authors: Joshi R. P.
Published: July 2002

Monte Carlo simulation results for the field- and temperature-dependent electronic mobilities, drift velocities, and diffusion coefficients in 4H-SiC are presented. The calculations include crystal anisotropy, and values are obtained for field orientations both parallel and transverse to the c axis of the hexagonal structures. The simulations are based on electron effective mass data that has only recently become available. Our theoretical predictions of the electron mobilities and their anisotropy ratios compare very well with available experimental data at 300 K. A room-temperature velocity of 2.7×107 cm/s was obtained in 4H-SiC for transport parallel to the c axis. This value is found to be larger than both 6H and 3C material. Finally, our calculations for the longitudinal and transverse diffusion coefficients at 300 K indicate that both have appreciable field dependences and exhibit a ‘‘soft’’ threshold.
Growth and characterization of PbS deposited on ferroelectric ceramics
Authors: Pintilie I. , Pentia E. , Pintilie L. , Petre D. , Constantin C. , Botila T.
Published: July 2002

The growth and properties of PbS thin films, chemically deposited on bulk lead titano-zirconate ceramics, are investigated. Scanning electron microscopy photographs reveal that the medium size of crystallites is much larger for PbS films grown on poled ferroelectric substrates than for the films grown onto glass or onto unpoled ferroelectric substrates. In the first case the medium size of crystallites is about 1–1.5 μm while in the second case it is less than 0.3 μm. Spectral distribution of photoconductivity and thermally stimulated currents (TSC) measurements were performed on all samples. Experimental results indicate that the properties of the PbS films can vary, depending on the substrate nature and in the case of poled ferroelectric substrates, on the polarity. The photoconductive signal is usually larger, the dark resistivity is smaller, and the TSC current value is higher for PbS films deposited on the positive face of the ferroelectric substrate than for those deposited on the negative face.
Thermoelectric properties of CoSb3 and related alloys
Authors: Sharp J. W. , Jones E. C. , Williams R. K. , Martin P. M. , Sales B. C.
Published: July 2002

Seebeck, electrical, and thermal conductivity data are reported on CoSb3, and doped and undoped alloys of Co1−xIrxSb3−yAsy from 20 to 700 K. n-type semiconductors were obtained by doping with Ni, Te, or Pd, and the hole concentration in p-type samples was increased by substitution of Fe, Ru, Os, and Ge. An estimated maximum value for ZT of 0.6 (Z is the figure of merit) was found for a Te-doped (n-type) alloy at 700 K. For p-type alloys, the maximum value of ZT was found to be 0.3 at 550 K. Electrical and thermal transport data also are reported for CoAs3, RhSb3, and IrSb3. Most of the samples investigated were polycrystalline, but a few measurements on CoSb3 single crystals also are discussed.
A detailed experimental study of the wet oxidation kinetics of AlxGa1−xAs layers
Authors: Nickel H.
Published: July 2002

We have studied the oxidation in water vapor of thick (0.5–2 μm) AlGaAs layers with aluminum contents ranging from 48% to 78% grown by molecular beam epitaxy. The oxidation rate was measured as a function of the aluminum content, the temperature and the flow rate of the N2 carrier gas supplying the water vapor. The oxide films proved to be mechanically very stable and the growth was found to be linear with time also in the case of an excessive supply of water vapor. The activation energies for the wet oxidation of AlGaAs were determined to increase from 1.1 to 1.8 eV for the Al contents decreasing from 78% to 48%.
Raman scattering study of antimony-based skutterudites
Authors: Nolas G. S. , Slack G. A. , Caillat T. , Meisner G. P.
Published: July 2002

Raman spectra of single-crystal CoSb3 and RhSb3 and of polycrystalline IrSb3 have been studied. We have also studied four different polycrystalline-filled skutterudite samples, Ir4LaGe3Sb9, Ir4NdGe3Sb9, Ir4SmGe3Sb9, and Fe4CeSb12, where rare-earth ions occupy the voids in the skutterudite structure. These void-filling ions interact with some of the lattice vibrations in this structure and produce a shift and broadening of the observed lines. The most prominent lines in all of the samples are the Sb4 ring-breathing modes.
Atomic layer epitaxy of CdTe and MnTe
Authors: Hartmann J. M. , Feuillet G. , Charleux M. , Mariette H.
Published: July 2002

Atomic deposition techniques are investigated for binary semiconductors of the telluride family, namely CdTe and MnTe. An original method for directly determining the CdTe atomic layer epitaxy (ALE) growth rate—in monolayers/cycle—is proposed, consisting in monitoring the reflection high-energy electron diffraction (RHEED) sublimation intensity oscillations of an ALE grown CdTe layer deposited on a MgTe buffer layer. The ALE CdTe autoregulated growth rate at 0.5 monolayer/cycle (in the substrate temperature domain between 260 and 290 °C) is accounted for on the basis of an atomic model which relies on the alternating c(2×2) Cd and (2×1) Te surface reconstructions during the ALE cycle. RHEED studies on MnTe atomic deposition, together with x-ray diffraction and transmission electron microscopy on ALE grown CdTe/MnTe superlattices reveal that all deposited Mn atoms are incorporated so that no autoregulated growth can be achieved. Furthermore, less than one or just one monolayer of Mn must be sent on the surface per ALE cycle to obtain well controlled superlattices with abrupt interfaces.
Thickness-shear and flexural vibrations of contoured crystal strip resonators
Authors: Lee P. C. Y. , Wang J.
Published: July 2002

A system of two-dimensional equations of motion of successively higher-order approximations for contoured crystal plates are deduced from the three-dimensional equations of elasticity by expansion of displacements in a series of trigonometrical functions of the thickness coordinate of the plates. By removing the first-order thickness-stretch mode and the first-order x2x3 (or fast) thickness-shear mode and all the higher ones, a set of first-order equations of motion is obtained for contoured crystal plates and for frequencies up to and including those of the fundamental x1x2 (or slow) thickness-shear mode. The coupled thickness-shear and flexural vibrations are studied for contoured quartz strip resonators having the shape of (a) a double wedge and (b) a plate with beveled edges. Exact solutions in terms of infinite power series are obtained by Frobenius method for the plates with linearly varying thickness in the x1 direction. Frequency spectra and mode shapes are computed for both types of resonators. The effects of the contour on the frequencies and modes are examined.
Growth and structural properties of epitaxial Pb(ZrxTi1−x)O3 films and Pb(ZrxTi1−x)O3-cuprate heterostructures
Authors: Triscone J.-M. , Frauchiger L. , Decroux M. , Miéville L. , Fischer O/. , Beeli C. , Stadelmann P. , Racine G.-A.
Published: July 2002

We report on the epitaxial growth and structural properties of Pb(ZrxTi1−x)O3 (PZT) thin films and of epitaxial heterostructures containing metallic DyBa2Cu3O7 (DyBCO) and ferroelectric PZT layers grown using an off-axis rf reactive sputtering technique. On (100) and (110) SrTiO3 substrates, tetragonal (001) and (011) epitaxial Pb(Zr0.52Ti0.48)O3 films have been obtained. Extensive characterization on (001) PZT films using x-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), Rutherford backscattering spectroscopy, and atomic force microscopy reveal a very high degree of structural quality, and very smooth surfaces with a root-mean-square roughness of 3 Å for a 0.5 μm×0.5 μm scan on a 1000 Å thick film. TEM studies on DyBCO–PZT structures reveal sharp and clean interfaces without traces of intermixing. Primary dislocations are observed at the DyBCO–PZT interface, which do not propagate through the PZT layer. [101]-type dislocations are also seen, possibly related to subgrains in the PZT layer, and they show an extended strain field throughout the PZT layer. The possible relation between these structural defects and the nonlinear current–voltage characteristics observed in DyBCO–PZT–Au structures is discussed.
Efficient excimer ultraviolet sources from a dielectric barrier discharge in rare-gas/halogen mixtures
Authors: Zhang Jun-Ying , Boyd Ian W.
Published: July 2002

The generation of excimer radiation in mixtures of the rare-gases Kr or Xe together with chlorine gas has been investigated by a dielectric barrier discharge. The characteristics of the emission spectra of the excimers formed, centered around 222 and 308 nm, were obtained for different gas mixtures and total gas pressures using an ultraviolet (UV) monochromator. The influence of the gas mixture, chlorine gas concentration, total gas pressure, and buffer gas dependence of the UV intensity has been investigated using chemical actinometry. Conversion efficiencies (from input electrical to output optical energy) as high as 15% can be achieved under optimal conditions. This low-cost and high-power excimer lamp system can provide an interesting alternative to conventional UV lamps for industrial large-scale UV processes.
Internal stress and strain in heavily boron-doped diamond films grown by microwave plasma and hot filament chemical vapor deposition
Authors: Wang W. L. , Polo M. C. , Sánchez G. , Cifre J. , Esteve J.
Published: July 2002

The internal stress and strain in boron-doped diamond films grown by microwave plasma chemical vapor deposition (MWCVD) and hot filament CVD (HFCVD) were studied as a function of boron concentration. The total stress (thermal+intrinsic) was tensile, and the stress and strain increased with boron concentration. The stress and the strain measured in HFCVD samples were greater than those of MWCVD samples at the same boron concentration. The intrinsic tensile stress, 0.84 GPa, calculated by the grain boundary relaxation model, was in good agreement with the experimental value when the boron concentration in the films was below 0.3 at.%. At boron concentrations above 0.3 at.%, the tensile stress was mainly caused by high defect density, and induced by a node-blocked sliding effect at the grain boundary.
Structural and electrical characteristics of rapid thermally processed ferroelectric Bi4Ti3O12 thin films prepared by metalorganic solution deposition technique
Authors: Joshi P. C. , Desu S. B.
Published: July 2002

Polycrystalline Bi4Ti3O12 thin films having layered perovskite structure were fabricated by metalorganic solution deposition technique on both Pt-coated Si and bare Si substrates at a temperature as low as 500 °C. The effects of post-deposition rapid thermal annealing on the structural and electrical properties were analyzed. The electrical measurements were conducted on metal–ferroelectric–metal capacitors. The typical measured small signal dielectric constant and dissipation factor at 100 kHz were 184 and 0.018 and the remanent polarization and the coercive field were 4.4 μC/cm2 and 84 kV/cm, respectively. The films exhibited high resistivity in the range 108–1012 Ω cm for films annealed at temperatures of 500–700 °C for 10 s. The I–V characteristics were found to be Ohmic at low fields and space-charge-limited at high fields. A V3/2 dependence of the current was observed in the space-charge region. This could be explained by assuming the mobility to be field dependent since in thin films the electric fields are invariably high even at low applied voltages.
Deep-center hopping conduction in GaN
Authors: Look D. C. , Reynolds D. C. , Kim W. , Aktas Ö. , Botchkarev A. , Salvador A. , Morkoç H.
Published: July 2002

Molecular-beam-epitaxial GaN layers change from strongly conductive (ρ≂10−2 Ω cm at 300 K) to semi-insulating (ρ≂106 Ω cm) as the N flux is increased. Layers grown at low fluxes show strong n-type conduction, with transport in the conduction band at high temperatures and in a shallow donor band at low temperatures. For layers grown at high N fluxes, the Hall coefficients become too small to measure, suggesting hopping conduction among deep centers. The temperature-dependent resistivity data are most consistent with multiphonon, rather than single-phonon, hopping.
Structural and optical characterization of InAs/InGaAs self-assembled quantum dots grown on (311)B GaAs
Authors: Nishi Kenichi , Mirin Richard , Leonard Devin , Medeiros-Ribeiro Gilberto , Petroff Pierre M. , Gossard Arthur C.
Published: July 2002

InAs/InGaAs self-assembled quantum dots (SADs) are fabricated on (311)B GaAs by molecular-beam epitaxy using the Stranski–Krastanow growth mode. The critical thickness for the SAD formation on (311)B substrates is almost the same as that on (100) surface, characterized by in situ reflection high-energy electron-diffraction pattern changes. Atomic force microscopy observation on In0.5Ga0.5As SADs showed uniform nanometer scale quantum dots with a typical dot diameter of around 25 nm ±2 nm and a typical height of 13.7 nm ±2.2 nm. In photoluminescence measurements, an intense peak from the SADs is observed with a sharp luminescence from the wetting layer that exists two-dimensionally underneath the SAD structure. A compound SAD structure is proposed where the composition of the wetting layer and the SAD layer are different. This is intended to suppress the luminescence from the wetting layer. The narrowest full widths at half-maximum of the luminescence from the compound SADs on (311)B are about 35 meV at 2 K and 41 meV at room temperature, respectively, which are much narrower than those measured from reference (100) SADs. The PL linewidth is not strongly affected by the measurement temperature, indicating that the linewidth is mainly governed by inhomogeneous broadening due to the dot size distribution. These narrow PL spectra demonstrate an advantage of using (311)B substrates for SAD formation in molecular-beam epitaxy. A shoulder peak distinctly observed in the SAD luminescence corresponds to the transition between the second quantum level in the SADs, as estimated from a simple calculation of the quantum confinement energy as well as excitation-intensity-dependent photoluminescence measurements.
Combined surface Brillouin scattering and x-ray reflectivity characterization of thin metallic films
Authors: Beghi M. G. , Bottani C. E. , Ossi P. M. , Lafford T. A. , Tanner B. K.
Published: July 2002

The structural and elastic properties of a thin gold film alloyed with Cu and Ni have been studied by surface Brillouin scattering, x-ray reflectivity and low angle x-ray diffraction. The role of guided (Sezawa) acoustic modes to determine precise values of the elastic constants has been ascertained. Although weak, the hardening effect of alloying elements has been clearly detected.
Analysis of picosecond mid-infrared pulses by two-photon absorption in germanium
Authors: Rauscher C. , Laenen R.
Published: July 2002

We report on the observation of two-photon absorption for the direct gap in intrinsic germanium at room temperature using two independently tunable picosecond, mid-infrared light pulses. The two-photon absorption coefficient is determined for different wavelengths, and carrier densities down to about 1013 cm−3 could be detected at a sample length of 700 μm. Two-photon absorption in germanium is demonstrated to be a versatile tool for zero-point determination in time resolved pump-probe investigations and permits a precise measure of the time resolution of the laser system.
Physical mechanisms of transient enhanced dopant diffusion in ion-implanted silicon
Authors: Stolk P. A. , Gossmann H.-J. , Eaglesham D. J. , Jacobson D. C. , Rafferty C. S. , Gilmer G. H. , Jaraíz M. , Poate J. M. , Luftman H. S. , Haynes T. E.
Published: July 2002

Implanted B and P dopants in Si exhibit transient enhanced diffusion (TED) during annealing which arises from the excess interstitials generated by the implant. In order to study the mechanisms of TED, transmission electron microscopy measurements of implantation damage were combined with B diffusion experiments using doping marker structures grown by molecular-beam epitaxy (MBE). Damage from nonamorphizing Si implants at doses ranging from 5×1012 to 1×1014/cm2 evolves into a distribution of {311} interstitial agglomerates during the initial annealing stages at 670–815 °C. The excess interstitial concentration contained in these defects roughly equals the implanted ion dose, an observation that is corroborated by atomistic Monte Carlo simulations of implantation and annealing processes. The injection of interstitials from the damage region involves the dissolution of {311} defects during Ostwald ripening with an activation energy of 3.8±0.2 eV. The excess interstitials drive substitutional B into electrically inactive, metastable clusters of presumably two or three B atoms at concentrations below the solid solubility, thus explaining the generally observed immobile B peak during TED of ion-implanted B. Injected interstitials undergo retarded diffusion in the MBE-grown Si with an effective migration energy of ∼3.5 eV, which arises from trapping at substitutional C. The concept of trap-limited diffusion provides a stepping stone for understanding the enormous disparity among published values for the interstitial diffusivity in Si. The population of excess interstitials is strongly reduced by incorporating substitutional C in Si to levels of ∼1019/cm3 prior to ion implantation. This provides a promising method for suppressing TED, thus enabling shallow junction formation in future Si devices through dopant implantation. The present insights have been implemented into a process simulator, allowing for a significant improvement of the predictive modeling of TED.
Ordered structures in Fe3O4 kerosene-based ferrofluids
Authors: Hong Chin-Yih , Jang I. J. , Horng H. E. , Hsu C. J. , Yao Y. D. , Yang H. C.
Published: July 2002

The patterns of kerosene-based ferrofluid films in applied parallel and perpendicular magnetic fields were studied. The time dependence of quasiperiodic chains in a parallel magnetic field, the perfect hexagonal crystal structure in a weaker perpendicular field, and the labyrinthine pattern in a stronger perpendicular field were observed. The Fe3O4 kerosene-based ferrofluids that we used in this study were synthesized by the coprecipitation method. As the parallel external magnetic field was applied to a ferrofluid film, the ordered quasiperiodic chains were obtained. On the other hand, the initial nonequilibrium disordered quantum columns were formed in an applied perpendicular magnetic field, and an equilibrium hexagonal structure with columns occupying its vortices was formed after two hours. The distance between these columns decreases as the strength of the applied magnetic field increases, and hence, the patterns change gradually from the hexagonal structure to a labyrinthine pattern with the strength of the perpendicular field above a critical value. Thus, a phase transition exists in the ferrofluid film system as the field strength increases.
Laser cleaning of etch-induced polymers from via holes
Authors: Lu Y. F. , Lee Y. P. , Zhou M. S.
Published: July 2002

The demand for new wafer cleaning technology after plasma etching increases as the industry enters into submicron processes. The success of low-resistance interconnecting high-density ultralarge-scale integrated devices depends on the cleanliness of via holes. A new approach in removing the sidewall and bottom polymers resulting from reactive ion etching of via holes, using a noncontact dry laser cleaning technique is reported and investigated in this study. Pulsed excimer laser irradiation at 248 nm is found to be capable of removing the polymers by subthreshold ablation, even at fluences limited by the damage threshold of the underlying Al–Cu metal film with titanium nitride (TiN) antireflective coating of 250–280 mJ cm−2. The various mechanisms possibly involved in the laser removal of the via-etch-induced polymer below its ablation threshold are discussed. Experimental results also show that the ablation rate when irradiating at an angle is not only comparable to that at vertical incidence, but even register higher values for most of the ablation rate data obtained. Thus the performance in terms of ablation rate does not slacken when the incident radiation is done at an angle to expose the sidewall polymers of the via holes to laser irradiation. Comparing ablation results obtained using Nd-YAG laser and excimer laser shows that although the shorter 7 ns Nd-YAG laser pulse gives a greater etch thickness than the 23 ns excimer laser pulse, it also tends to damage the metal films and the silicon substrates of the via wafers more easily. The damage threshold using the third and fourth harmonics of the Nd-YAG laser at 355 and 266 nm was just above 100 mJ cm−2 after 20 pulses.
Theory of two magnon scattering microwave relaxation and ferromagnetic resonance linewidth in magnetic thin films
Authors: Hurben M. J. , Patton C. E.
Published: July 2002

A detailed analysis of the two magnon scattering contribution to the microwave relaxation and ferromagnetic resonance linewidth in isotropic and anisotropic films and disks has been made. The analysis is based on the Sparks, Loudon, and Kittel (SLK) theory for the scattering of uniform mode magnons into degenerate spin wave states for isotropic spherical samples in the presence of magnetic inhomogeneities in the form of spherical voids or pores. The SLK theory has been extended to include: (i) thin film and thick film samples magnetized in an oblique out-of-plane direction; (ii) uniaxially anisotropic materials with either easy-axis or easy-plane anisotropy and an anisotropy axis perpendicular to the disk plane; (iii) a modified density of degenerate states to account for the nonzero relaxation rate of the scattered spin waves; and (iv) two limiting cases of the scattering interaction: (a) the original SLK case where the inhomogeneities are modeled as spherical voids and the coupling to the degenerate spin waves varies with the spin wave propagation direction and (b) an isotropic scattering model where the coupling is independent of the propagation direction. The formulation is valid for thick films for which the discrete nature of the spin wave modes may be neglected. The two magnon linewidth as a function of field orientation is calculated for three classes of material parameters corresponding to yttrium iron garnet and barium M-type and zinc Y-type hexagonal ferrites. The linewidth versus static field angle profiles show characteristic profiles which depend on the crystalline anisotropy, the sample dimensions, the nature of the scattering interaction, the inhomogeneity size, and the inhomogeneity volume fraction. These parameters, as well as the shape and evolution of the spin wave band as a function of the field angle under ferromagnetic resonance conditions, play critical roles in determining the linewidth versus angle profiles.
Surface instability of multipulse laser ablation on a metallic target
Authors: Ang L. K. , Lau Y. Y. , Gilgenbach R. M. , Spindler H. L. , Lash J. S. , Kovaleski S. D.
Published: July 2002

Large scale wavelike patterns are observed on an aluminum surface after it is ablated by a series of KrF laser pulses (248 nm, 40 ns, 5 J/cm2). These surface structures have a wavelength on the order of 30 μm, much longer than the laser wavelength. We postulate that these wave patterns are caused by the Kelvin–Helmholtz instability at the interface between the molten aluminum and the plasma plume. A parametric study is given in terms of the molten layer’s thickness and of the spatial extent and kinetic energy density in the laser-produced plasma plume. Also included is an estimate of the cumulative growth in a multipulse laser ablation experiment. These estimates indicate that the Kelvin–Helmholtz instability is a viable mechanism for the formation of the large scale structures.
Magnetohydrodynamic calculation for free surfaces
Authors: Fujisaki Keisuke , Ueyama Takatsugu
Published: July 2002

A magnetohydrodynamic calculation for free surface is used in the design and evaluation of a cold-crucible or initial solidification such as stirring phenomena commonly found in the metal processing industry. A direct calculation of both the electromagnetic field and the fluid dynamics field for the surface of a molten metal that changes with time requires significant computing times, especially for three-dimensional models. An approximate calculation method, the shadow method, is one which uses a fixed mesh. Results obtained by the shadow method show that the shape of molten metal does not collapse under gravity as observed experimentally.
Polarized Raman and photoluminescence study on silicon quantum wires
Authors: Papadimitriou D. , Nassiopoulou A. G.
Published: July 2002

A detailed Raman and photoluminescence study was performed on Si quantum wires fabricated on crystalline silicon (100). A shift of the phonon frequency was observed indicative of a compressive stress of about 9.5 kbar, possibly originating from the oxide skin grown on the wire surface by high temperature thermal oxidation. A splitting of the Raman phonon was also observed and interpreted as originating from the existing stress and/or from the excitation of phonons polarized parallel and normal to the direction of confinement. The photoluminescence emission was found to depend on the excitation wavelength and on the polarization of the laser beam. The energy and efficiency of the emitted luminescence increased with decreasing laser wavelength. This was interpreted as an effect due to the size distribution of the studied wires, since thin wires with a higher band gap than thick wires can be excited by shorter laser wavelengths. The photoluminescence efficiency was significantly higher when the laser beam was polarized in the direction of confinement in agreement with theoretical predictions. The emitted luminescence was also polarized preferentially in the direction of confinement. This resulted in depolarization of the emitted light when the laser beam was polarized along the wire axis, normal to the direction of confinement.
Resolution and contrast in Kelvin probe force microscopy
Authors: Jacobs H. O. , Leuchtmann P. , Homan O. J. , Stemmer A.
Published: July 2002

The combination of atomic force microscopy and Kelvin probe technology is a powerful tool to obtain high-resolution maps of the surface potential distribution on conducting and nonconducting samples. However, resolution and contrast transfer of this method have not been fully understood, so far. To obtain a better quantitative understanding, we introduce a model which correlates the measured potential with the actual surface potential distribution, and we compare numerical simulations of the three-dimensional tip–specimen model with experimental data from test structures. The observed potential is a locally weighted average over all potentials present on the sample surface. The model allows us to calculate these weighting factors and, furthermore, leads to the conclusion that good resolution in potential maps is obtained by long and slender but slightly blunt tips on cantilevers of minimal width and surface area.
Characterization of cubic SiC films grown on thermally oxidized Si substrate
Authors: Sun Yong , Miyasato Tatsuro
Published: July 2002

The growth of cubic SiC films on the thermally oxidized Si substrate is studied by means of hydrogen plasma sputtering of a SiC target. The cubic SiC film without the hollow voids at the film/substrate interface can be grown on the SiO2 layer/Si substrate at 650 °C. The film has stoichiometric composition, and showed well-defined (111) growth at that temperature. There is an etching effect of hydrogen plasma on the substrate before a continuous film is formed over the substrate, and the etch rate depends strongly on the substrate temperature. The plasma etching results in both the breakage of the SiO2 layer and the loss of the substrate Si leading to the hollow voids at the film/substrate interface. There is also an atom migration process between the SiC film, the SiO2 layer, and the Si substrate during the growth of the films. At the substrate temperatures above 750 °C, the adsorbed C atoms diffuse into the Si substrate by different mechanisms, and result in the SiC islands in the Si substrate.
Influence of net strain, strain type, and temperature on the critical thickness of In(Ga)AsP-strained multi quantum wells
Authors: Ogasawara Matsuyuki , Sugiura Hideo , Mitsuhara Manabu , Yamamoto Mitsuo , Nakao Masashi
Published: July 2002

We examined the critical thickness of strained multi quantum wells (MQWs) consisting of InAsP/InGaAsP and InGaAsP/InGaAsP. More than 50 MQWs with different total thicknesses, well strain, and well thicknesses were prepared by metalorganic molecular beam epitaxy (MOMBE) or metalorganic vapor phase epitaxy (MOVPE) to study the influence of net strain, strain type, and temperature on critical thickness. The microscopic photoluminescence method was used mainly to observe misfit dislocations in the MQWs. Three kinds of net strain-critical thickness curves were experimentally determined, i.e., the curves for compressive as well as tensile strained MQWs grown by MOMBE and that for compressive strained MQWs grown by MOVPE. We found that the above three curves coincide with each other and differ greatly from the Matthews’ [J. W. Matthews and A. E. Blakeslee, J. Cryst. Growth 27, 118 (1974)] theoretical curve in a low-net strain range of less than 0.5%.
Thermal effects in quantum dot lasers
Authors: Patanè A. , Polimeni A. , Henini M. , Eaves L. , Main P. C. , Hill G.
Published: July 2002

The thermal behavior of lasers based on In0.5Ga0.5/As/GaAs self-aggregated quantum dots is investigated. Increasing temperature from 10 to 290 K produces a narrowing of the dot laser mode distribution. This effect is explained in terms of carrier relaxation between dots and carrier thermal escape from dots to nonradiative recombination centers. The thermal dependence of the threshold current and the differential quantum efficiency is also discussed.