bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement of the H− thermal energy in a volume ion source plasma
Authors: Bacal M. , Berlemont P. , Bruneteau A. M. , Leroy R. , Stern R. A.
Published: July 2002

The H− negative ion thermal energy measured using the two-laser-pulse photodetachment technique is reported to be in the range from 0.1 to 0.7 eV for various conditions of volume ion source operation (pressure−from 2 to 7 mTorr, discharge current−from 1.5 to 20 A). The hydrogen pressure has a significant effect in lowering the negative ion temperature, while the increase of the discharge current leads to a rise in T−. It is found that T− is a fraction of the electron temperature, Te. This fraction is strongly dependent on the gas pressure. T− scales linearly with the electron temperature and exceeds the highest values predicted by the theory of dissociative attachment. The possible mechanisms for H− ion heating are discussed.
Mössbauer determination of cobalt substitution in iron-based intermetallics
Authors: Liao L. X. , Ryan D. H. , Altounian Z.
Published: July 2002

A Mössbauer source technique has been used in studies of cobalt site preferences in the intermetallic compounds Er6Fe23 and Nd2Fe17. Data quality has been improved by the construction of a resonant conversion electron detector. This detector provides a tenfold increase in signal and allows measurements to be made with the source at reduced temperatures. Results for Er6Fe23 show a strong tendency for cobalt to occupy the f2 site and to avoid the f1 site. For Nd2Fe17, our results reveal that cobalt while it occupies preferentially the h and d sites, is almost completely absent from the c site, and it tends to avoid the f site.
Carrier transport mechanisms of p-type amorphous–n-type crystalline silicon heterojunctions
Authors: Mimura Hidenori , Hatanaka Yoshinori
Published: July 2002

Measured current–voltage characteristics of undoped and p-type hydrogenated amorphous silicon (a-Si:H)/n-type crystalline silicon (c-Si) heterojunctions are used to discuss the carrier transport mechanisms. The forward current was characterized by two parts: The forward current increased with applied voltage exponentially (region 1), and nonexponentially (region 2). In region 1, it was found that the current was dominated by the tunneling process in which electrons tunneled from the c-Si into gap states in the a-Si:H and recombinated holes captured by the gap states in the a-Si:H. In region 2, the current was found to be a space-charge-limited current due to both electrons injected from the c-Si and holes injected from an ohmic contact. The carrier transport mechanism of reverse currents depended on the magnitude of boron doping in the a-Si:H. The reverse current was considered to be mainly generated in the depletion layer of the a-Si:H for the heterojunction with undoped a-Si:H, generated in the depletion layer of both the a-Si:H and the c-Si for that with boron-doped a-Si:H of B2H6/SiH4=1×10−5, and generated in the depletion layer of the c-Si for that with boron-doped a-Si:H of B2H6/SiH4=1×10−4.
Real-time optical characterization of surface acoustic modes of polyimide thin-film coatings
Authors: Duggal Anil R. , Rogers John A. , Nelson Keith A.
Published: July 2002

A modification of the optical technique of impulsive stimulated thermal scattering that allows real-time data acquisition is introduced. The method is used to characterize the pseudo-Rayleigh acoustic modes of thin (∼1 μm) polyimide films attached to silicon substrates and its potential use as a means for extracting the elastic constants of thin-film coatings is demonstrated.
Adding a heat bypass improves the thermal characteristics of a 50 μm spaced 8-beam laser diode array
Authors: Murata Setsuko , Nakada Hiroshi
Published: July 2002

Because heat transferred between closely spaced elements in a compact laser diode array shortens array lifetime and affects the elements’ operating characteristics, we evaluated the effect of a heat-bypass structure by measuring the thermal resistance of array elements. We estimated thermal resistance by measuring differences between junction voltage before and after injecting subthreshold current pulses. The thermal resistances due to self heating were more than 20% lower after adding the heat-bypass structure. This effect was greatest for elements whose thermal resistance was initially highest, and it was proportional to the number of operating elements. The bypass structure therefore also reduced the thermal resistance resulting from simultaneous operation of all eight elements by more than 40%. The resultant reduction in the junction temperature of array elements operating at 100 mW would increase array lifetime at least threefold.
Surface-diffusion model in selective metalorganic chemical vapor deposition
Authors: Yamaguchi Ko-ichi , Ogasawara Masaaki , Okamoto Kotaro
Published: July 2002

Selective epitaxial growth of GaAs was carried out by atmospheric pressure-metalorganic chemical vapor deposition using W and SiO2 masks, and a deposition-free region was clearly observed along the edge of the masks. The surface concentration of the reactant species on the masks was analyzed by a surface-diffusion model and a new method to estimate the surface-diffusion length on the masks was proposed. The surface-diffusion length on SiO2 and W masks were 0.45 and 0.07 μm at 610 °C, respectively. The surface-diffusion length increased with decreasing the substrate temperature and became longer on the masks irradiated by an atom beam.
A simple model for the etching of photoresist with plasma-generated reactants
Authors: Koretsky Milo D. , Reimer Jeffrey A.
Published: July 2002

The neutral heterogeneous chemistry between reactive species formed in a glow discharge plasma and a polymer surface is investigated. Oxygen and fluorine atom concentrations in an O2/CF4 plasma afterglow are measured by gas phase electron resonance spectroscopy. These atom concentrations are correlated to etch rate data via a simple heterogeneous model which divides the etching process into three steps: initiation, etching, and passivation. The model predicts etch rate data well using measured atom concentrations. When the substrate temperature is changed, the etching step is affected most, presumably limited by product desorption. Dilution of the discharge with argon enhances the etch rate in two ways. First, the homogeneous chemistry is altered, most notably affecting the fluorine atom concentration. The homogeneous effects are taken into account through measured atom concentrations. Second, the argon metastables play a role in the heterogeneous chemistry, enhancing the etching step. From an estimation of this enhancement based on the shift in etch rate maximum, the magnitude of etching in an argon diluted discharge can be predicted.
Planar laser-induced fluorescence imaging of Cu atom and Cu2 in a condensing laser-ablated copper plasma plume
Authors: Sappey Andrew D. , Gamble Thomas K.
Published: July 2002

Planar laser-induced fluorescence (PLIF) is used to monitor Cu atoms and Cu2 produced by excimer laser ablation of a copper target (308 nm, ≳10 J/cm2, 1–3 GW/cm2) expanding rapidly into helium background gas at pressures ranging from 10 to 100 Torr. The Cu2 results from gas phase condensation of the copper atoms ablated from the target in the regions of highest Cu atom density as expected, but the maximum Cu2 laser-induced fluorescence (LIF) signal occurs significantly after the maximum of the Cu signal. Rotationally resolved excitation scans of Cu2 utilizing the A–X (0,0) transition indicate that the Cu2 has reached equilibrium with the 300 K background gas. An extensive search for Cu3 via LIF failed, indicating that Cu3 is present only in very low ‘‘steady state’’ number density in the plume. This data is explained qualitatively by a simple kinetic model. In addition to the kinetic information, it is clear from the PLIF images that viscous eddy formation becomes more pronounced as the backing gas pressure increases; however, we see no evidence of turbulence in the plume even at the highest backing gas pressure studied. The PLIF technique allows us to observe the onset of condensation directly as well as to obtain information about the expansion dynamics of the plume not easily obtainable by other means.
Temperature measurements of polyimide during KrF excimer laser ablation
Authors: Brunco D. P. , Thompson Michael O. , Otis C. E. , Goodwin P. M.
Published: July 2002

The temperature at the interface between a thin polyimide film and a quartz substrate was monitored as a function of time during KrF (248 nm) laser-induced heating and ablation using thin film NiSi thermistors. These experimental temperature measurements were coupled with heat flow simulations to obtain time-resolved temperature profiles in the polyimide. Thermal properties of the polyimide were estimated by requiring that the simulations reproduce experimental temperature profiles. The peak surface temperature of the polyimide at the onset of ablation was subsequently estimated from these constrained simulations and a value of 1660±100 K was obtained for the observed ablation threshold fluence of 36 mJ/cm2.
Perpendicular magnetic anisotropy in epitaxial ultrathin films of Fe and Co on Cu(100), Cu(110), and Cu(111)
Authors: Kief M. T. , Egelhoff W. F.
Published: July 2002

We report studies of the perpendicular magnetic anisotropy of Fe and Co on Cu(100), Cu(110), and Cu(111) using the magneto-optic Kerr effect. In general, the perpendicular anisotropy in the Fe films is enhanced for growth at low temperature, 80 K. Perpendicular remanence has been observed below a critical thickness of about 5–6 ML for fcc Fe(100)/Cu(100), fcc Fe(110)/Cu(110), and bcc Fe(110)/Cu(111). In contrast, a perpendicular remanence has been observed only for fcc Co(111)/Cu(111) and not in the as-grown state. These results are shown to be inconsistent with standard empirical theories of magnetocrystalline, magnetoelastic, and magnetostatic surface anisotropies and suggest a common magnetic interface anisotropy.
Refractive indices of lithium niobate as a function of wavelength and composition
Authors: Schlarb U. , Betzler K.
Published: July 2002

An interferometric method is applied to determine the refractive indices of lithium niobate single crystals over a wide wavelength and composition range. A generalized two term Sellmeier equation is proposed that describes the refractive indices as a function of wavelength and stoichiometry. On the basis of this generalized Sellmeier equation the parameters of nearly all optical characterization methods for LiNbO3 can be calculated. By means of a Kramers–Kronig analysis the shift in the UV absorption edge and the change in the extraordinary refractive index with the composition can be referred to each other. Excellent agreement is found with the respective experimental values.
A positron annihilation study of defects in neutron transmutation-doped float-zone (Ar)-Si
Authors: Puff Werner , Meng Xiang-ti
Published: July 2002

Annealing of defects introduced by neutron transmutation doping of float-zone silicon has been investigated by positron lifetime spectroscopy and Doppler-broadening measurements. It is shown that the main defects anneal out at about 150 and 500 °C. During annealing, the formation of bigger defect complexes can be seen.
Alternating gradient force magnetometry: Applications and extension to low temperatures (invited)
Authors: O’Grady K. , Lewis V. G. , Dickson D. P. E.
Published: July 2002

This paper describes the results of a study undertaken to determine the sensitivity and reproducibility of a commercially produced alternating gradient force magnetometer. A noise base of 2×10−8 emu is achievable with an averaging time of 1 s. Reproducibility was found to be within 6% for most samples, but increases to 20% with low moment samples. The effect of the alternating field gradient on magnetic measurements has been fully investigated. The alternating field gradient is found to have significant effects on samples with a low fluctuation field and low coercivity. A low temperature system (4–300 K) is described and modifications to improve the sensitivity and base temperature are discussed.
Microscopic study of cluster formation in the Ga on GaAs(001) system
Authors: Lowes T. D. , Zinke-Allmang M.
Published: July 2002

A microscopic study of the cluster morphology for the system Ga on GaAs(001) is presented. Clusters are shown to have significant volume fractions below the surface level of the surrounding substrate. A thermodynamic model qualitatively describes this phenomena based on a comparison between (a) arsenic desorption from the GaAs surface, limited either by bulk diffusion of arsenic or surface diffusion of gallium to the nearest cluster and (b) dissolution of GaAs in Ga clusters with subsequent diffusion of the As to the cluster surface and desorption. A quantitative rate prediction based on this model is in an order of magnitude agreement with the experimental data.
Optical properties of mixed silver halide crystals and fibers
Authors: Nagli L. , Bunimovich D. , Shmilevich A. , Kristianpoller N. , Katzir A.
Published: July 2002

The dependence of the bulk (βb) and surface (βs) absorption coefficients of AgClxBr1−x crystals and of polycrystalline fibers at 10.6 μm on the composition (x) of the material were investigated. The bulk coefficient βb for AgBr was about 0.5×10−4 cm−1 and increased gradually with increasing molar concentration x of the Cl− ions up to 2.5×10−4 for pure AgCl crystals. Luminescence properties of these crystals as well as effects of thermal treatments on the absorption, luminescence, and conductivity were also investigated. A correlation was found between the effects of these treatments on the infrared (IR) absorption, the luminescence, and conductivity of the various samples. Experimental results indicate that the absorption of the silver halide crystals at 10.6 μm is mainly due to cation vacancies bound to dislocations. The absorption of the fibers was found to be greater than that of the crystals of the same composition. This is apparently due to defects induced by the heating under pressure, applied during the production of the fibers by extrusion, and the subsequent fast quenching to room temperature. A simple method for reduction of the IR absorption is proposed.
Transition between Ge segregation and trapping during high-pressure oxidation of GexSi1−x/Si
Authors: Frey E. C. , Yu N. , Patnaik B. , Parikh N. R. , Swanson M. L. , Chu W. K.
Published: July 2002

A transition from Ge segregation to trapping during high-pressure oxidation of GexSi1−x alloys has been observed. The atomic fraction x of Ge was varied from 0.4% to 26%, and oxidations were performed at 740 °C under 102 atm of dry O2. It was observed that the effect of oxidation on the Ge distribution could be divided into three stages. In the initial stage of the oxidation, Ge was segregated from the growing oxide and accumulated in a Ge-rich layer at the oxide/alloy interface. For alloys with high Ge content this initial stage was very short. In the second stage of oxidation, after a critical quantity of Ge had accumulated at the interface, there was a transition from segregation to trapping of Ge in the oxide. In the third stage, the critical amount of Ge remained segregated at the interface, and the final oxide layer was Ge free. A kinetic model based on a steady-state equilibrium between the diffusive flux of Si across the Ge-rich layer and the rate of Si consumption by the oxidation reaction predicts, with reasonable agreement, the critical quantity of segregated Ge for the onset of trapping.
Nonlinear transition shifts in magnetic recording due to interpattern proximity effects
Authors: Tang Yaw-Shing , Tsang Ching
Published: July 2002

A high-precision measurement of the proximity shift on a magnetic transition due to the presence of an old transition in the background is presented. Using peak detection electronics, this interpattern shift was deduced by measuring the distance between a reference and a test transition in a multibit pattern, with and without a background transition in the vicinity of the test transition. The measurement process was carefully designed to achieve high accuracy. The proximity shift of a 3380-type write head on disks with different remenent-thickness product for cases of both easy and hard transition types was measured for both the background and the data transitions. Results showed three distinct transition-shift behaviors depending on the background-to-test intertransition distance: a gradual decay in the far region (≳2 μm), a rapid rise in the intermediate region, and asymptotic saturation at the near region when the two transitions are almost on top of each other. The asymptotic shift magnitude agrees well with independently measured hard-transition shifts, and good agreement with theoretical modeling is obtained for shifts in the far and intermediate regions.
Determining the lattice relaxation in semiconductor layer systems by x-ray diffraction
Authors: Fewster Paul F. , Andrew Norman L.
Published: July 2002

This paper illustrates the procedure for extracting structural information available from x-ray diffraction space mapping and topography. The methods of measuring, the residual strain, macroscopic tilts, microscopic tilts and their lateral dimensions, and the strain field disruption emanating from the interfacial defects are presented. Partially relaxed thick InGaAs layers on GaAs substrates were studied and it was concluded that the relaxation and macroscopic tilting were anisotropic, the microscopic tilting reduced with thickness, and the interfacial disruption did not continue to increase with increasing relaxation. A ‘‘mosaic grain growth’’ model is postulated to account for the diminishing microscopic tilt spread and increasing topographic contrast with layer thickness.
Diffusion of dopants in B- and Sb-delta-doped Si films grown by solid-phase epitaxy
Authors: Gossmann H.-J. , Vredenberg A. M. , Rafferty C. S. , Luftman H. S. , Unterwald F. C. , Jacobson D. C. , Boone T. , Poate J. M.
Published: July 2002

The diffusion of δ-function-shaped B- and Sb-dopant spikes in thin Si films grown by solid-phase-epitaxy [(SPE), growth of amorphous film by molecular-beam epitaxy (MBE) at room temperature and subsequent regrowth in situ] during annealing in vacuum is compared to diffusion in films grown by low-temperature (LT) MBE. Diffusion temperatures from 750 to 900 °C, and two-dimensional concentrations of 0.7–1.6×1014 cm−2 have been investigated. The diffusive behavior of dopants in SPE films is found to be qualitatively different from that in films grown by LTMBE. This is related to the vacancylike defects that are intrinsic to growth by SPE but not to growth by LTMBE. Dopant profiles widen significantly during SPE regrowth, making the achievement of δ-function dopant spikes impossible. After a vacuum anneal the diffusion coefficients for both n- and p-type dopants are lower in SPE films than the corresponding values in films grown by LTMBE by up to one order of magnitude. The diffused depth profile of the dopant in LTMBE films shows the characteristic deviation from a pure Gaussian that is expected due to the concentration dependence of diffusion, i.e., a flat top and steep shoulders. In contrast, dopant depth profiles of SPE-grown material show after diffusion a central spike and relatively flat shoulders. The width of the central spike is, after an initial transient that it was not possible to resolve, independent of diffusion time and temperature. This indicates that the SPE material is defective, with the defects acting as traps during diffusion.
Raman scattering from In1−xAlxSb metastable epilayers
Authors: Gnezdilov V. P. , Lockwood D. J. , Webb J. B. , Maigné P.
Published: July 2002

Raman scattering has been used to investigate the optical phonons in thick compositionally uniform epilayers of In1−xAlxSb (x<0.65) grown by magnetron sputter epitaxy on (001)InSb. An analysis of the stress-induced changes in the frequencies of the two optical phonon modes found in the epilayers was performed, and the stress factors and phonon mode behaviors for bulk material were evaluated. It was found that some epilayers with low x values were coherently strained, even though their thicknesses far exceeded the mechanical-equilibrium critical thickness limit.
Effect of milling on the magnetic and microstructural properties of Sm2Fe17Nx permanent magnets
Authors: Wendhausen P. A. P. , Gebel B. , Eckert D. , Müller K.-H.
Published: July 2002

By ball milling Sm2Fe17Nx the coercivity can be increased from 0.3 to 1.5 T. The coercivity increases continuously during milling up to a time of about 600 min, and then decreases for too intensive ball milling. This is connected to particle size reduction and other effects like the increase in oxygen content, introduction of mechanical stresses, formation of new grain boundaries, and amorphization of the material. Magnetic measurements, scanning electron microscopy, as well as domain wall observations indicate that long-time milled material is mainly constituted of single domain particles and isotropic polycrystalline particles with small grains.
Origin of deep donors in AlSb grown by molecular beam epitaxy
Authors: Furukawa A. , Ideshita S.
Published: July 2002

The origin of deep donors in not intentionally doped AlSb grown by molecular beam epitaxy (MBE) has been investigated. It was found that the origin of deep donor is oxygen incorporated during growth of AlSb, and that oxygen comes mainly from the Sb source material used in MBE growth. Decreasing oxygen density in Sb reduced the deep donor density to 5.5×1015 cm−3 in AlSb and reduced the electron density to about 2.5×1011 cm−2 in the InAs/AlSb quantum well.
High-speed scanning tunneling microscopy: Principles and applications
Authors: Mamin H. J. , Birk H. , Wimmer P. , Rugar D.
Published: July 2002

A fast scanning tunneling microscope (STM) for scanning micron-sized areas of atomically rough surfaces has been developed. The response time of the feedback loop controlling the tip-sample spacing is roughly 5 μs, and the maximum scan velocity is 1 mm/s. The instrument uses fast electronics and a novel mechanical design to achieve the high bandwidth. The high bandwidth makes the STM capable of nearly real-time panning and zooming, allowing for rapid searches over the surface of the sample. The instrument has been used in air to study wear of atomic layers, and also to perform nanowriting while scanning. In the case of the wear study, it was found that step edges not only can retreat during wear, but can also advance.
Study of the factors affecting the broadening of the photoluminescence spectra of InGaAs/InP quantum wires
Authors: Notomi M. , Okamoto M. , Tamamura T.
Published: July 2002

The origin of the observed large half width of photoluminescence spectra for InGaAs/InP quantum wires fabricated by electron beam lithography and reverse-mesa wet etching have been investigated. First, we studied size fluctuations in the fabricated wires using an atomic force microscope. We also studied other factors that can affect the photoluminescence half width. We found that the interface carrier concentration and size fluctuations play dominant roles in shaping the luminescence spectrum for wires narrower than 200 Å. For wider wires, the carrier concentration was found to be a factor in the broadening. These results indicate that a large half width itself does not directly mean a degradation of device performance, but the amount of size fluctuations limits it.
Growth of aluminum nitride thin films on Si(111) and Si(001): Structural characteristics and development of intrinsic stresses
Authors: Meng W. J. , Sell J. A. , Perry T. A. , Rehn L. E. , Baldo P. M.
Published: July 2002

We have grown aluminum nitride thin films by ultrahigh vacuum reactive sputter deposition on Si(111) and Si(001) substrates. We show results of film characterization by Raman scattering, ion beam channeling, and transmission electron microscopy, which establish the occurrence of epitaxial growth of wurtzitic aluminum nitride thin films on Si(111) at temperatures above 600 °C. In contrast, microstructural characterization by transmission electron microscopy shows the formation of highly oriented polycrystalline wurtzitic aluminum nitride thin films on Si(001). Real-time substrate curvature measurements reveal the existence of large intrinsic stresses in aluminum nitride thin films grown on both Si(111) and Si(001) substrates.
Optical generation of high-frequency acoustic waves in GaAs/AlxGa1−xAs periodic multilayer structures
Authors: Basséras P. , Gracewski S. M. , Wicks G. W. , Miller R. J. D.
Published: July 2002

A picosecond study of ultrahigh-frequency acoustic phonons in specifically engineered GaAs/AlxGa1−xAs periodic multilayer structures is presented. The lattice-matched boundary conditions for photothermal acoustic generation and optical properties of these materials make these structures ideal for sound-wave generation in the 100 GHz to THz range. The acoustics are generated using ultrashort-laser-pulse excitation and detected in real time by measuring the strain-induced change in reflectivity with the pump-probe technique. By using 12 nJ, 90 fs pulses from a Ti:sapphire laser source, the generation and detection of ∼50 GHz acoustics in a 6-bilayer, [001]-oriented GaAs/Al0.4Ga0.6As structure, 500 Å thickness per layer, on a GaAs substrate, are successfully demonstrated. The structure was specifically designed to give the maximum sensitivity to the acoustics through étalon-induced modulations in the reflectivity spectrum. With similarly designed multilayer structures, the upper frequency limit can be achieved for the thermoelastic generation of coherent acoustic phonons, that is, ∼300 GHz in GaAs for ∼1 eV above band-gap-energy photons.
Detecting laser-induced phase change at the surface of solids via latent heat of melting with a photothermal deflection technique
Authors: Shannon Mark A. , Rubinsky Boris , Russo Richard E.
Published: July 2002

The detection of laser-induced melt at the surface of a solid in real time is demonstrated using a photothermal deflection (PTD) technique. Experimental results for indium and tin show that a local maximum and minimum pair can occur in the temporal profile of the PTD signal when melt occurs. A local minimum does not occur without phase change. Analytical work is presented which explicitly shows the effect of the latent heat of melting, thermal properties, and probe-beam size and offset on the shape of a PTD signal. Results are presented which demonstrate that the observed change in shape will not occur with planar heating, with or without phase transition. However, results derived for point-source heating show that it is possible for the maximum/minimum pair to occur when melting with a focused laser beam. The ratio of the sensible heat to the latent heat, and the ratio of the thermal diffusivities of the target and deflecting medium are the key factors which govern the deflection response. Computations for a general class of materials are given to show when the effect of latent heat can be observed at a surface. Results are also given which consider the probe-beam size and offset on the observations.
Generation aspects of the delocalized intrinsic EX defect in thermal SiO2
Authors: Stesmans A. , Scheerlinck F.
Published: July 2002

A K-band electron-spin-resonance study of the appearance of the delocalized intrinsic EX center in dry thermal SiO2 was performed on (001) and (111) Si/SiO2. The defect is found in both structures in nearly identical spin densities, 1.2×1012 cm−2 being the maximum areal density. Variation of Si precleaning treatments showed the center’s generation to depend on the initial surface condition of the c-Si substrate. For fixed initial surface conditions, however, systematic variation of the oxidation temperature (760–930 °C), oxidation time (a few min up to 24 h), and oxygen pressure (∼24 and ∼110 kPa), in combination with stylus profilometry, revealed the EX areal density to be solely determined by the grown oxide thickness (dox), EX being detectable from dox≊70 Å onwards, with a maximum intensity at dox≊125 Å. Etch back experiments showed the defects to reside in the top 45 Å of the oxide layer, with the largest local volume density (∼3×1018 cm−3) occurring near the ambient/SiO2 interface. With growing oxide thickness, the spatial profile remains largely unchanged, the mere effect being changes in the overall EX areal density. Alternated isochronal anneals in H2 and vacuum revealed the defect’s thermochemical properties to be dominated by the interaction with H2, in a very similar fashion as for the Pb center at the (111)Si/SiO2 interface. Possible hints of these growth aspects as to the nature of the EX defect are discussed.
Determination of the band offset in semimagnetic CdTe/Cd1−xMnxTe quantum wells: A comparison of two methods
Authors: Kuhn-Heinrich B. , Ossau W. , Litz T. , Waag A. , Landwehr G.
Published: July 2002

We present a comparative study of two different spectroscopic techniques in order to determine the valence band offset in CdTe/Cd1−xMnxTe quantum wells. The energy difference between heavy- and light-hole excitons as a function of the heavy-hole transition energy is known as a sensitive tool for the determination of the valence band potential height. In the present study we have employed this technique to CdTe/Cd1−xMnxTe quantum wells. A valence band offset around Qv=0.30 is determined, which is found to be valid in the whole range of investigated Mn contents up to x=0.27. In semimagnetic quantum wells the tuning of potential heights in external magnetic fields offers the possibility to evaluate the valence band offset. This technique has been widely employed to CdTe/Cd1−xMnxTe, but no consensus has been reached yet. We have analyzed the Zeeman splitting of the heavy-hole exciton in CdTe/Cd1−xMnxTe quantum wells with different Mn contents. Using the valence band offset as an adjustable parameter, a smaller valence band offset is determined for quantum wells with higher Mn content in the barrier. The published data derived from magneto-optical experiments show this behavior too. Only at low Mn contents (x<0.05) the results of both spectroscopic techniques coincide. The underestimation of the valence band offset derived from the Zeeman splitting at higher Mn contents is explained by an enhanced paramagnetic contribution arising at the heterointerface of semimagnetic quantum wells.
Theoretical study of magnetostriction in FeTaN thin films
Authors: Cates James C. , Alexander Chester
Published: July 2002

Single layer films of FeTaN have been deposited by dc magnetron sputtering, and the relationships between the magnetostriction and film composition have been studied. A linear increase in magnetostriction with nitrogen content has been explained by the dependence of λ100 on nitrogen concentration. The form of this dependence has been derived based on a theory developed by De Vries for describing the magnetic after effect in iron films with interstitial nitrogen. At room temperature, the best fit for the experimental magnetostriction data was found for an interstitial interaction constant of D=4.18×106 J/m3. The total magnetic anisotropy energy per grain, U110, has also been calculated as a function of the strain for FeN films with a (110) orientation under a tetragonal deformation. This calculation used the results derived for the dependence of the magnetostriction constant, λ100, on nitrogen concentration. The calculated U110 value shows a minimum at a lattice strain value of ε11=0.0029, in close agreement with a maximum in permeability at Δd110/d110=0.0028 previously reported for FeN films.
Hot electron spin-valve effect in coupled magnetic layers
Authors: Celotta R. J. , Unguris J. , Pierce D. T.
Published: July 2002

SEMPA observations of magnetic exchange coupling in the Fe/Ag/Fe, Fe/Au/Fe, and Fe/Cr/Fe systems reveal an intensity variation in the emitted secondary electron signal that depends only on whether the Fe layers are coupled in a ferromagnetic or antiferromagnetic sense. We ascribe this new effect to spin dependence in the transport of electrons between the two magnetic layers.
Oscillatory interlayer coupling through (111) oriented noble metal spacers
Authors: Keavney D. J. , Storm D. F. , Freeland J. W. , Walker J. C. , Pini M. G. , Politi P. , Rettori A.
Published: July 2002

We use a surface-sensitive Mössbauer spectroscopy technique to examine the spin-wave spectrum, at the Fe(110)/NM(111) interface only, of a multilayer structure with a noble metal (NM) interlayer. We find that the temperature dependence of the hyperfine field follows a Bloch law (1−BT3/2), and use spin-wave calculations to connect the surface spin-wave stiffness parameter, B, to the interlayer exchange coupling. Films grown with Ag(111) interlayers show clear oscillations with a period of 6 ML, in good agreement with recent predictions.
Electrical and optical properties of Li-doped LiBO2 and LiNbO3 films
Authors: Can Nguyen , Ashrit P. V. , Bader G. , Girouard F. , Truong Vo-Van
Published: July 2002

Li-doped LiBO2 and LiNbO3 thin films have been studied and their optical and electrical properties determined. With doping the ionic conductivity of the films was found to increase substantially. The highest conductivity obtained with the doped films was about 4.5×10−6 S cm−1. All the films exhibited a high degree of transmission in the spectral region from 350 to 2500 nm. The remarkable increase in the ionic conductivity coupled to the preservation of a high optical transmission makes this doping technique highly attractive for devising ion conductors that can be used in transmissive solid-state electrochromic systems or the so-called ‘‘smart windows.’’
Theoretical studies of the optical characteristics of the resonant tunneling light-emitting diode
Authors: Fu Y. , Willander M.
Published: July 2002

We have developed a simple empirical way for future device design to obtain the energy band diagram of the resonant tunneling light-emitting diode based on our self-consistent numerical Hartree–Fock calculations. From analysis of the light emission it is found that the transverse component (perpendicular to the sample growth direction) of the photon vector potential is very small due to translational symmetry. The optical transition between electron and hole states involves both the transitions between the conduction and valence bands and between electron and hole subbands in the quantum well. For high optical transitions, a large electric field inside the quantum well is preferred.
Epitaxial GaAs growth using atomic hydrogen as the reactant
Authors: Silva-Andrade F. , Chávez F. , Gómez E.
Published: July 2002

Epitaxial GaAs films are grown by the close space vapor transport technique, using atomic hydrogen as the initial reactant. Measurements of concentration and mobility of majority carriers reveal that the grown films are n type, with donor concentrations ND≊1017 cm−3, and mobilities at 300 K of μn≊3600 cm2 V−1 s−1. The growth and etching rates versus inverse temperature plots show an Arrhenius dependence with an activation energy of 36 kcal mol−1 in both cases.
Target compression by working fluids driven with solid liner implosions
Authors: Chiang P-R. , Lewis R. A. , Smith G. A. , Dailey J. M. , Chakrabarti S. , Higman K. I. , Bell D. , Degnan J. H. , Hussey T. W. , Mullins B. W.
Published: July 2002

Compression by a spherical solid liner of a gold target surrounded by a hydrogen plasma is simulated. Two-dimensional simulations that treat only a subset of the physics included in the one-dimensional code were performed in an attempt to assess multidimensional effects. A one-dimensional numerical code has been developed to study the effects of thermal radiation and conduction. Results of pressure, density, and energy deposited for different initial plasma conditions are presented and discussed. Results from both one- and two-dimensional codes show that the average target density at peak compression is 39–43 g/cm3, using the SHIVA Star facility at 90 kV discharge.
Preparation and applications of magnetostrictive thin films
Authors: Quandt E. , Gerlach B. , Seemann K.
Published: July 2002

Amorphous magnetostrictive films of the binary compound SmxFe1−x as well as of the ternary compound (TbyDy1−y)xFe1−x were prepared by rf or dc magnetron sputtering using either a multitarget arrangement with pure element targets or cast composite-type targets. The magnetostrictive properties of (Tb0.3Dy0.7)0.4Fe0.6 and Sm0.4Fe0.6 films were investigated in relation to their preparation conditions. Depending upon these conditions (especially upon the deposition rate, the bias voltage, and the Ar sputtering pressure) amorphous films with a giant magnetostriction of about 250 ppm (−220 ppm) at 0.1 T and 400 ppm (−300 ppm) at 0.5 T for the TbDyFe (SmFe) and an in-plane magnetic easy axis could be prepared. In view of applications in microsystem technologies (e.g., pumps, valves, positioning elements) these films have been tested in a simple cantilever arrangement and the predicted deflection of a magnetostrictive actuated membrane has been calculated.
High resolution method for the analysis of admittance spectroscopy data
Authors: Maier D. , Hug P. , Fiederle M. , Eiche C. , Ebling D. , Weese J.
Published: July 2002

There are several experimental methods which give information about the thermal relaxation times of the deep levels in a semiconductor. Analyzing the temperature dependence of the relaxation times, the activation energy and the cross section of the corresponding deep levels can be determined. An essential problem of such methods is the identification of the relaxation times in the measured signal. In the context of time-dependent measurements such as photoinduced current transient spectroscopy and deep level transient spectroscopy, Tikhonov regularization was recently proposed as a high resolution method for this purpose. In this contribution it is proposed to apply Tikhonov regularization in order to identify the thermal relaxation times in admittance spectroscopy data. The method is tested and discussed using simulated data. Finally, admittance spectroscopy data of a GaAs diode are analyzed. The results demonstrate that the resolution of an ordinary admittance spectroscopy setup can considerably be improved by the application of Tikhonov regularization.
Persistent photoconductance in n-type 6H-SiC
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C.
Published: July 2002

Defects in n-type 6H-SiC have been studied using optical admittance spectroscopy. Six conductance peaks, which correspond to photoexcitation of electrons into the conduction band from defects and the valence band at different wavelengths, were clearly identified. Persistent photoconductance (PPC) due to a defect 1.07 eV below the conduction band was studied. The decay kinetics of the PPC follow the stretched exponential form. The relaxation time constant τ and the stretching factor β were systematically measured as functions of temperature. The thermal capture barrier of 61 meV was determined from these results. It was also found that the PPC can be quenched optically by illumination with sub band gap radiation. This is the first reported observation of optical quenching of PPC in n-type 6H-SiC. The lattice relaxation model is used to qualitatively explain these experimental results.
Electrical properties of CdTe films prepared by close-spaced sublimation with screen-printed source layers
Authors: Chung Gil Yong , Park Sung Chan , Cho Kurn , Ahn Byung Tae
Published: July 2002

CdTe films have been deposited by a close-spaced sublimation process with screen-printed CdTe layers as a new source. The source-layers were fabricated by screen printing and sintering slurries consisting of propylene glycol, CdCl2 and either CdTe powder or (Cd+Te) powder. When CdTe powder was used as a starting material for the source-layer, the electrical resistivity of the CdTe film deposited in O2 was about one-tenth lower than that of the film deposited in He. AES, EDS and PIXE analysis showed that the Cd content in the CdTe films deposited in O2 was smaller than that in the CdTe films deposited in He. Especially, no oxygen element was detected in the CdTe films deposited in O2. It turned out that the sublimated Cd(g) and CdTe(g) from the source-layer formed cadmium oxides in O2 and as a result the overall composition of vapor source became more Cd-deficient. The CdTe film with less Cd content increased cadmium vacancy defects (VCd2−Cl+ and VCd2−) and hole concentrations. As the Cd/Te ratio in the starting (Cd+Te) powder decreased, the resistivity of the CdTe films decreased and reached at a constant value of about 3x104 Ω⋅cm, regardless of deposition atmosphere. In addition, the resistivity decrease by O2 treatment was diminished when the Cd/Te ratio was below 0.7, where the composition of CdTe film might be limited by solid solubility (Cd0.92Te1.0). The above results indicated that the resistivity decrease of CdTe films deposited in O2 was not due to the effect of previously-known oxygen doping but due to the effect of Cd/Te compositional change.
Si acceptor excited states in ion-implanted InP
Authors: Ka O. , Yamada A. , Yoshinaga H. , Makita Y.
Published: July 2002

Photoluminescence has been used to investigate the behavior of Si-implanted InP, submitted to a postimplantation rapid thermal annealing. Compared with the non-implanted material, the implanted crystal displays a new broad band around 1.382 eV, in the low temperature (2 K) spectra. This band appears to be made of two unresolved recombination paths ascribed to the electron–acceptor (e,A°) and donor–acceptor pair recombinations of the silicon acceptor impurity substituted on phosphorus site. Besides the Zn-related transitions to s and p excited states, the selective excitation of the donor–acceptor pairs reveals additional recombination paths, ascribed to transitions to 2s3/2 and 2p5/2 (Γ7 and Γ8) excited states of silicon. The acceptor behavior of Si in InP is hence given a definite support by this work.
Anisotropic elasticity study of the critical thickness of an epilayer on a substrate with different elastic constants
Authors: Zhang Tong-Yi
Published: July 2002

The critical thickness of an epilayer on a substrate with different elastic constants is investigated by following Stroh’s treatment of anisotropic elasticity [Philos. Mag. 3, 625 (1958)]. A closed formula is derived to calculate the critical thickness and an exact solution may involve numerical evaluation of the equation. The results indicate that the self-energy of the dislocation is controlled by the soft phase between the epilayer and the substrate, while the interaction energy depends only on the elastic constants of the thin film. It is easier for a dislocation to be formed if the substrate is softer than the film, and consequently the critical thickness is smaller. On the other hand, a soft epilayer can have a large thickness without any mismatch dislocation. Explicit equations are given here for the {100}, {110}, and {111} epitaxial planes. The system of a GexSi1−x epilayer on a Si substrate was taken as an example to demonstrate the influence of the difference in elastic constants on the critical thickness. Even though the difference between the elastic constants of the epilayer and the substrate is not very large, ignoring this difference can cause a relative error over 20% in calculation of the critical thickness. For this system, a simplified equation yields sufficiently accurate results.
Optimization and characterization of interfaces of InGaAs/InGaAsP quantum well structures grown by gas-source molecular beam epitaxy
Authors: Bi W. G. , Tu C. W.
Published: July 2002

We report a study of the interfaces of InGaAs/InGaAsP quantum wells (QWs) grown by gas-source molecular beam epitaxy. By optimizing the group-V source supply sequence, a photoluminescence (PL) linewidth as narrow as 6.6 meV has been observed from a 2 nm wide single QW. The PL linewidths have been analyzed to evaluate the contributions of alloy compositional scattering and interface roughness. The analysis shows that for QW structures grown with the optimized growth sequence, the PL linewidth is mainly due to alloy compositional variations, whereas the contribution from interface roughness is small, indicating a good interface control. By considering the strain effect on the band alignment of the InGaAs/InGaAsP heterojunction, theoretical transition energies of QWs have been calculated using the envelope-function approximation, and the results agree well with the experimental data.
Nonstationary current in bipolar photoconductor with slow photoconductivity relaxation
Authors: Korneev N. , Mansurova S. , Stepanov S.
Published: July 2002

We show that a photoconductivity relaxation can strongly influence the magnitude of the ac current induced in a bipolar photoconductor by a vibrating pattern of interference fringes. This occurs for low pattern vibration frequencies if the time of the photoconductivity relaxation is much greater than the dielectric relaxation time. The features predicted by the theory were observed in semi-insulating GaAs illuminated by a He–Ne laser (λ=633 nm) for vibration frequencies lower than 20 kHz.
Site-selective spectroscopy and determination of energy levels in Eu3+-doped strontium fluorophosphate
Authors: Wright Andrew O. , Seltzer Michael D. , Gruber John B. , Chai Bruce H. T.
Published: July 2002

Absorbance and site-selective fluorescence studies of Eu3+:Sr5(PO4)3F (Eu:SFAP) provide a nearly complete characterization of the Eu3+ energy levels. These results are compared with calculated energies generated by lattice-sum analysis. Eu3+ is found to occupy one site predominantly, but numerous minority sites are also evident; polarization studies of absorption and fluorescence lines provide evidence for the principle site having Cs symmetry. Vibronic transitions occur in spectra as well. Interpretation of the lattice location and charge compensation mechanism for the principal site is discussed in the context of obstacles arising from spectral interpretation, high crystal fields in SFAP, low site symmetry, low J-numbers in Eu3+ energy manifolds, and lattice covalency. Eu2+ emission upon ultraviolet excitation is also demonstrated; valleys in the emission profile are attributed to intracrystal absorption by Eu3+.
The complete electromagnetic field of a three-phase transmission line over the earth and its interaction with the human body
Authors: King Ronold W. P. , Wu Tai T.
Published: July 2002

The electromagnetic field at all points near a high-voltage transmission line is determined in analytical form. Account is taken of the presence of the earth below the three-wire, three-phase power line. The electric and magnetic fields, the total axial current, and the current and power densities in the interior of a human body are determined when the body is standing on the ground under or near the line, is in an elevated basket under the line, or is reclining in bed near the height of the line. The fields are very weak and the current and power densities so small that thermal effects are ignorable, but not necessarily possible effects on nerve action, the functioning of cells, or on certain secretions.