bluuebunny/crossref_metadata_2025 huggingface dataset:
Low temperature magnetization and thermoremanence of FeCl2⋅H2O
Authors: DeFotis G. C. , Cinquina C. C. , Hammann J.
Published: July 2002

The latest member of the new series of transition metal dichloride monohydrates to exhibit novel magnetic behavior is FeCl2⋅H2O. Reported here are field cooled and zero-field cooled magnetizations (MFC and MZFC, respectively) for different fields as a function of temperature, and time-dependent thermoremanent magnetizations (TRM) for different temperatures and wait times. Near 20.4 K a peak appears in both MFC and MZFC using H=106 G, as seen previously. In the smaller fields of 26.5 and 0.1 G, MFC is more nearly constant for temperatures below the 20.4 K peak in MZFC which still appears. The irreversible magnetization, MFC−MZFC, is more pronounced for lower measuring field. Unusual behavior is seen in the temperature and wait-time (tw) dependence of TRM(t). Data at 4.4 K (0.22Tc) show no wait time, or aging, effects, using a cooling field of 9.95 G. At 15.1 K (0.74Tc), for the same cooling field, differences occur among TRM(t) data for tw=10, 100, and 500 min. The data become essentially coincident, however, if the measuring time is scaled by the wait time. Although the general behavior is similar at 18.0 K (0.88Tc), there is a noticeable shift of the tw=500 min data in this case. The results suggest that below the critical temperature the system must equilibrate among a huge number of metastable states. It takes an almost infinite time to probe all these states below 0.88Tc, which explains the t/tw scaling. At 0.22Tc, the system remains stuck in one specific state and the aging disappears. Two different time scales appear to control the relaxation. The observed properties are not altogether typical of spin glasses, and the system may better be viewed as a weakly and randomly coupled array of ferromagnetic chains, in which dynamic domains readily form and evolve, and in which the aging effects are associated with domain wall growth.
Deposition conditions of magnetoresistance in La0.67Ca0.33MnO3−δ thin film
Authors: Guo J. Q. , Takeda H. , Kazama N. S. , Fukamichi K. , Tachiki M.
Published: July 2002

Magnetoresistance of the La0.67Ca0.33MnO3−δ thin films was investigated. The magnetoresistance depends on ablation conditions such as the substrate temperature and oxygen pressure and has a relation with the lattice constants of the thin films. A colossal magnetoresistance ratio with 4.79×106% was obtained at 70 K and a magnetic field of 5.5 T. The resistivity of the thin films has a close relation with the substrate temperature and the oxygen pressure. When the substrate temperature is fixed, the resistivity shows double peaks in the oxygen pressure range of 1×10−7 to 1 Torr.
The physics and technology of gallium antimonide: An emerging optoelectronic material
Authors: Dutta P. S. , Bhat H. L. , Kumar Vikram
Published: July 2002

Recent advances in nonsilica fiber technology have prompted the development of suitable materials for devices operating beyond 1.55 μm. The III–V ternaries and quaternaries (AlGaIn)(AsSb) lattice matched to GaSb seem to be the obvious choice and have turned out to be promising candidates for high speed electronic and long wavelength photonic devices. Consequently, there has been tremendous upthrust in research activities of GaSb-based systems. As a matter of fact, this compound has proved to be an interesting material for both basic and applied research. At present, GaSb technology is in its infancy and considerable research has to be carried out before it can be employed for large scale device fabrication. This article presents an up to date comprehensive account of research carried out hitherto. It explores in detail the material aspects of GaSb starting from crystal growth in bulk and epitaxial form, post growth material processing to device feasibility. An overview of the lattice, electronic, transport, optical and device related properties is presented. Some of the current areas of research and development have been critically reviewed and their significance for both understanding the basic physics as well as for device applications are addressed. These include the role of defects and impurities on the structural, optical and electrical properties of the material, various techniques employed for surface and bulk defect passivation and their effect on the device characteristics, development of novel device structures, etc. Several avenues where further work is required in order to upgrade this III–V compound for optoelectronic devices are listed. It is concluded that the present day knowledge in this material system is sufficient to understand the basic properties and what should be more vigorously pursued is their implementation for device fabrication.
Quantitative analysis of the nitrogenation process in Y2Fe17Nx based on a two-region configuration
Authors: Yang D. P. , Zhang Y. D. , Hines W. A. , Budnick J. I.
Published: July 2002

A quantitative analysis has been carried out for the nitrogenation process using two groups of Y2Fe17Nx samples, one obtained by successively allowing longer nitrogenation times and the other by systematically varying the particle size. A detailed calculation using the two-region model results in an analytical solution for the nitrogen distribution as a function of nitrogenation time and particle size, which agrees with the observations in both groups of samples. This model describes the entire nitrogenation process (usually longer than 10 h), and predicts a diffusion parameter D0 with the correct order of magnitude (∼10−6 m2/s).
Local field and quantum effects for current perpendicular to planes in multilayers
Authors: Zhang X.-G. , Butler W. H.
Published: July 2002

The calculation of giant magnetoresistance and in general, of electron transport for multilayers in the case of current perpendicular to the planes (CPP) requires both the two-point conductivity and the solution to the local field problem. In this paper we present a solution to the local field problem at an interface using two approaches. In the first approach we find the semiclassical solution for the local field when there is a band mismatch between two sides of an interface, and examine the deviation of the total resistance from the result of “self-averaging,” in the lowest order of the value of the potential step. In the second approach, we solve for the quantum correction to the local field through a numerical iterative scheme. The oscillations due to the quantum correction are surprisingly large, but their correction to the total resistance is remarkably small. Our results imply that the “self-averaging” of the resistance, which is usually assumed in analysis of CPP, is only approximate.
A model of hole trapping in SiO2 films on silicon
Authors: Lenahan P. M. , Conley J. F. , Wallace B. D.
Published: July 2002

We demonstrate that hole trap densities and hole trapping in SiO2 films on silicon can be predicted quantitatively using a physically based model of intrinsic oxide trapping centers.
Strain and relaxation effects in InAsP/InP multiple quantum well optical modulator devices grown by metal-organic vapor phase epitaxy
Authors: Yip R. Y.-F. , Aït-Ouali A. , Bensaada A. , Desjardins P. , Beaudoin M. , Isnard L. , Brebner J. L. , Currie J. F. , Masut R. A.
Published: July 2002

Strained-layer multiple quantum well (MQW) InAsP/InP optical modulators have been fabricated from layers grown by metal-organic vapor phase epitaxy. The devices are a series of p-i(MQW)-n photodiodes in which the active core regions consist nominally of 25 periods of 10 nm InAsP quantum wells of 4.4%, 10.0%, 15.6%, and 26.4% As composition separated by 10 nm InP barriers. Structural parameters for the samples were obtained using high-resolution x-ray diffraction rocking curves and transmission electron microscopy. The series contains samples with both coherently strained and partially relaxed multi-layers where the relaxation is characterized by misfit dislocations. The band offsets for the heterostructures were determined by fitting the energy positions of the optical absorption peaks with those computed using the Marzin–Bastard model for strained-layer superlattices [as in M. Beaudoin et al., Phys. Rev. B 53, 1990 (1996)]. The conduction band discontinuities thus obtained are linear in the As composition (7.56±0.08 meV per As % in the InAsP layer) at low and room temperature for As concentrations up to 39%, and up to 17% average relaxation. Comparisons between the coherently strained and partially relaxed samples demonstrated a broadening of optical transition linewidths due to relaxation which appears to be of minor consequence for optical modulator devices as the essential optical and electrical properties remain intact. The electric field-dependent red-shift of the n=1 electron-heavy hole transition was measured by a photocurrent method and found to be enhanced in structures with lower barrier heights.
Intermodulation and quality factor of high-Tc superconducting microstrip structures
Authors: Dahm T. , Scalapino D. J.
Published: July 2002

The intermodulation power and quality factor Q of high-Tc superconducting microstrip resonators with different shapes is calculated. Acute corners increase the losses and the intermodulation power. The influence of normal conducting regions is investigated. The case of two microstrips carrying in phase or out of phase currents is also studied. The losses and the intermodulation power are significantly reduced if the currents are in phase in the two microstrips compared to the mode with out of phase currents.
Temperature dependence of photoluminescence intensity from AlGaInP/GaInP-quantum well structures
Authors: Ishitani Yoshihiro , Minagawa Shigekazu , Hamada Hiroshi , Tanaka Toshiaki
Published: July 2002

The photoluminescence (PL) intensity of AlGaInP/GaInP-quantum well structures under a continuous excitation condition was measured as a function of the crystal temperature (10–450 K). The thermal emission of carriers from the well layers to the barrier layers was investigated by generating the carriers only in the wells. The dependence of the PL intensity on the crystal temperature was analyzed by fitting a model function to the experimental results. The rapid decrease in PL intensity at temperatures higher than 200 K was found to be probably due to the emission of carriers into the barrier layers. The effective barrier heights obtained by the fitting are in good agreement with the band-energy alignment schemes of these crystals. When AlInP barrier layers were inserted directly beside the quantum wells, the emission of carriers to the quaternary layers through the AlInP layers was reduced, resulting in stronger PL intensity at higher temperatures and a larger effective barrier height.
Atomic force microscopy for the determination of refractive index profiles of optical fibers and waveguides: A quantitative study
Authors: Huntington S. T. , Mulvaney P. , Roberts A. , Nugent K. A. , Bazylenko M.
Published: July 2002

The use of preferential etching and atomic force microscopy to measure refractive index profiles of optical fibers is investigated. Both the etch rate and the position of lateral features are shown to be independent of etch time. An elliptical core fiber was studied and the resultant profile was found to be in qualitative agreement with the preform index profile. It is shown, however, that the ellipticity of the core has changed during the drawing process. The method was extended to fluorine and germanium doped planar waveguides and the results correlated with the fabrication process.
Optical content and resolution of near-field optical images: Influence of the operating mode
Authors: Carminati R. , Madrazo A. , Nieto-Vesperinas M. , Greffet J.-J.
Published: July 2002

Recent experimental work has shown that the contrast of near-field optical images depends on the path followed by the tip during the scan. This artifact may misguide the interpretation of the images and the estimation of the optical resolution. We provide a rigorous theoretical study of this effect based on three-dimensional perturbation theory and two-dimensional exact numerical calculations. We quantitatively study the dependence of the artifact on the illumination/detection conditions and on the scattering potential of the sample. This study should provide guidelines for future experimental work.
Density of ultradry ultrathin silicon oxide films and its correlation with reliability
Authors: Yamada Hiroshi
Published: July 2002

To clarify the structure of ultrathin silicon oxide gate films less than about 5 nm thick, densities of the films grown on Si(100) at 800–950 °C by the recently proposed rigorous ultradry oxidation process were determined by charged-particle activation analysis. The density curve plotted as a function of oxidation temperature shows a peak, i.e., the density of the 850 °C grown films is largest of all, about 2.38 Mg/m3. Interestingly, a similar relationship is confirmed in the time-dependent dielectric breakdown lifetime characteristic curve, which is the most fundamental index of reliability for the oxide. This suggests that the reliability is closely related to the density. That is, since the density reflects the atomic arrangement of the films, the lifetime enhancement near the same oxidation temperature is possibly caused by changes in the films’ microscopic structure.
Analytic and numerical two-dimensional micromagnetic calculations of thin films with a laterally oscillating interface coupling
Authors: Dekker Martijn J. , Ramstöck Klaus
Published: July 2002

The effects of a laterally oscillating interface energy competing with the exchange energy and uniaxial volume anisotropy were studied both analytically and numerically. The analytic prediction for the magnetization and the total energy in the ground state is expressed as a power series expansion in the interface coupling strength. The first three terms of this expansion are constructed explicitly. The results compare well with results of micromagnetic simulations within the expected range of applicability of the series expansion. The analytic solution can serve as a valuable benchmark for micromagnetic simulations.
Scanning tunneling microscopy study on the surface and interface of Si(111)/SiO2 structures
Authors: Fujita Ken , Watanabe Heiji , Ichikawa Masakazu
Published: July 2002

Scanning tunneling microscopy was used to investigate the surface and interface of Si(111)/SiO2 structures. The oxide thickness ranged from 0.3 to 1.7 nm. The surface was observed using a sample bias larger than 4.0 V. Fourier transform spectra of the surface images showed clear seventh order spots originating from the Si(111)7×7 reconstruction, indicating that 2.7 nm periodicity of the reconstruction remains on the oxide surface. At a sample bias of less than 4.0 V, a Si(111)/SiO2 interface was observed when 0.3-nm-thick oxide was partially left on the Si surface.
Amorphous silicon based nipiin structure for color detection
Authors: Knipp D. , Stiebig H. , Fölsch J. , Finger F. , Wagner H.
Published: July 2002

Hydrogenated amorphous silicon based nipiin three color detectors with a bias voltage controlled spectral response have been fabricated. These band-gap and mobility-lifetime product engineered structures employed as two terminal devices exhibit a dynamic range above 95 dB. The maximum of the spectral response shifts by variation of the applied voltage. Three linearly independent spectral response curves can be extracted to generate a red-green-blue signal. Conventional spatial color separation with optical filters is transferred into a voltage multiplexed read out sequence. Bias voltage switching under different monochromatic illumination and illumination switching-on transients for different bias voltages are carried out to investigate the time dependent behavior of the photocurrent. Based on these results optimization criteria to accelerate the transient behavior and to determine the maximum frame rate for color detection are presented.
A Mössbauer spectral study of Nd6Fe13X, where X is Cu, Ag, and Au and of the spin reorientation in Nd6Fe13Si
Authors: Hautot Dimitri , Long Gary J. , Grandjean F. , de Groot C. H. , Buschow K. H. J.
Published: July 2002

The Mössbauer spectra of Nd6Fe13X, where X is Si, Cu, Ag, and Au, have been measured between 80 and 500 K. A model corresponding to a basal alignment of the magnetic moments leads to excellent, internally consistent, fits for the Cu, Ag, and Au compounds. The resulting temperature dependences of the spectral hyperfine parameters are uniform and reveal for each Fe site the expected correlations between the isomer shift and the Wigner–Seitz cell volume and the hyperfine field and the number of Fe near neighbors. For Nd6Fe13Si, a different model must be used because of the presence of a spin reorientation below 155 K. Above 155 K, because of the axial alignment of the moments, and in agreement with the 295 K powder neutron diffraction results, the spectra can be analyzed with four sextets. Below 155 K, five additional sextets are required to fit the spectra because of a progressive transition towards a basal alignment of the Fe moments. At 80 K the mixed magnetic phase is 75% basal and 25% axial, whereas at 110 K the mixture is 50:50. The hyperfine parameters of the basal and axial sextets found for Nd6Fe13Si are consistent with those found for the basal Cu, Ag, and Au compounds and those observed for basal Nd6Fe13Sn. The lattice properties of the compounds, obtained from the temperature dependences of the isomer shift and the spectral absorption area, are consistent with the Wigner-Seitz cell volumes and the bonding of each crystallographically distinct Fe site. The magnetic anisotropy of a variety of Nd6Fe13X compounds is controlled by the s-p hybridization of the Nd–X bonds, a hybridization which is very sensitive to the electronic configuration of X.
Strain and surface morphology in lattice-matched ZnSe/InxGa1−xAs heterostructures
Authors: Heun S. , Paggel J. J. , Sorba L. , Rubini S. , Bonanni A. , Lantier R. , Lazzarino M. , Bonanni B. , Franciosi A. , Bonard J.-M. , Ganière J.-D. , Zhuang Y. , Bauer G.
Published: July 2002

Lattice-matched ZnSe/InxGa1−xAs heterostructures were fabricated by molecular beam epitaxy on GaAs(001)2×4 surfaces. We find that the partial character of the strain relaxation within the ternary layer can be compensated by a suitable excess in the In concentration to match the free-surface lattice parameter to ZnSe. The surface of the II–VI epilayer, however, exhibits a cross-hatched pattern of surface corrugations oriented along orthogonal 〈110〉 directions. This complex surface morphology reflects the formation of surface slip steps during the nucleation of dislocation half-loops at the surface and the establishment of the misfit dislocation network at the InxGa1−xAs/GaAs interface.
Theory of electron transport in small semiconductor devices using the Pauli master equation
Authors: Fischetti M. V.
Published: July 2002

It is argued that the Pauli master equation can be used to simulate electron transport in very small electronic devices under steady-state conditions. When written in a basis of suitable wave functions and with the appropriate open boundary conditions, this transport equation removes some of the approximations which render the Boltzmann equation unsatisfactory at small length scales, permitting the inclusion of tunneling, interference effects, arbitrary “steep” potentials, and intracollisional field effects. However, the master equation is based on the same weak-scattering and long-time limits on which also the Boltzmann equation rests and cannot provide the complete solution of time dependent quantum transport problems. The main problems consist in describing the interaction of the system with the reservoirs—here treated phenomenologically—and in assessing the range of validity of the equation: Only devices smaller than the size of the electron wave packets injected from the contacts can be handled, and this constitutes the interesting range of sub-50 nm devices. Three one-dimensional examples solved by a simple Monte Carlo technique are finally presented.
On the origins of the Franz–Keldysh oscillations observed in the electromodulation spectra of graded emitter Ga1−xAlxAs/GaAs heterojunction bipolar transistor structures
Authors: Sun W. D. , Pollak Fred H.
Published: July 2002

We have derived expressions for the origins of the Franz–Keldysh oscillations (FKOs), observed in electromodulation, associated with the fields in the Ga1−xAlxAs emitter and GaAs collector regions of graded band gap heterojunction bipolar transistor structures. We show that while the latter FKOs are a measure of the maximum collector space charge field at the collector/base junction the former FKOs are determined by both the space-charge field and the “field” due to the grading in the emitter region. The special case of the abrupt emitter/base junction also is considered. Our expressions are general and can easily be applied to any graded (or abrupt) emitter structure. The results will be compared with experiment, including the photovoltaic effect.
Molecular dynamics simulations of low-energy (25–200 eV) argon ion interactions with silicon surfaces: Sputter yields and product formation pathways
Authors: Kubota Nawoyuki A. , Economou Demetre J. , Plimpton Steven J.
Published: July 2002

The etch yield and subsurface damage are important issues in low energy (200 < eV) ion interactions with surfaces. In particular, atomic layer etching requires etching of electronic materials with monolayer precision and minimal interlayer atomic mixing. In this study, the molecular dynamics technique is used to simulate the impact of argon ions on chlorine-free and chlorine-passivated silicon surfaces, under conditions relevant to atomic layer etching. Thousands of individual ion impact simulations are performed on a massively parallel supercomputer. The silicon sputter yield is obtained for Ar ion energies ranging from 25 to 200 eV. Where possible, simulation results are compared to available experimental data. Volatile product formation during ion bombardment of ordered surfaces tends to follow distinct local trajectories. For example, the formation of products due to 120 eV Ar ions impacting onto Si(001)(2×1) at normal incidence has been found to occur mainly by a mechanism in which the Ar ion impacts directly in-between a surface silicon dimer pair. The energetic recoiled silicon atoms undercut nearby silicon atoms resulting in product formation. Several other product formation pathways have also been observed.
Spatial distributions of atomic hydrogen and C2 in an oxyacetylene flame in relation to diamond growth
Authors: Klein-Douwel R. J. H. , ter Meulen J. J.
Published: July 2002

Two-dimensional laser induced fluorescence measurements are applied to the chemical vapour deposition of diamond by an oxyacetylene flame to visualize the distributions of atomic hydrogen and C2 in the gas phase during diamond growth. Experiments are carried out in both laminar and turbulent flames and reveal that atomic hydrogen is ubiquitous at and beyond the flame front. Its presence extends to well outside the diamond deposition region, whereas the C2 distribution is limited to the flame front and the acetylene feather. The diamond layers obtained are characterized by optical as well as scanning electron microscopy and Raman spectroscopy. Clear relations are observed between the local variations in growth rate and quality of the diamond layer and the distribution of H and C2 in the boundary layer just above the substrate. These relations agree with theoretical models describing their importance in (flame) deposition processes of diamond. Three separate regions can be discerned in the flame and the diamond layer, where the gas phase and diamond growth are predominantly governed by the flame source gases, the ambient atmosphere, and the interaction of both, respectively.
Phonon-limited electron mobility in ultrathin silicon-on-insulator inversion layers
Authors: Gámiz F. , Roldán J. B. , López-Villanueva J. A.
Published: July 2002

Phonon-limited mobility in ultrathin silicon-on-insulator inversion layers has been calculated by the Monte Carlo method both at room and at lower temperatures. The phonon-scattering rate has been shown to increase as a consequence of the greater confinement of electrons as the top silicon film thickness shrinks below a determined value. This fact helps to explain the mobility decrease that appears experimentally in these devices.
The magnetic properties of Cu-doped Sm–Fe–Si–C ribbons prepared by melt spinning
Authors: Zhang Hong-wei , Zhang Shao-ying , Shen Bao-gen , Zhang Li-gang
Published: July 2002

We studied magnetic properties of Cu-doped Sm–Fe–Si–C compounds with the Th2Zn17-type structure prepared by melt spinning. Substituting small amounts of Cu for Fe does not change the unit cell volume v, Curie temperature TC, and magnetocrystalline field HA of these materials, while the saturation magnetization Ms decreases slightly. A drastic increase in the coercivity has been observed upon Cu addition. The highest intrinsic coercivity μ0iHc=1.32 T and 1.47 T at room temperature was obtained in Sm2Fe14CuSi2C and Sm2Fe14CuSi2C1.5 ribbons prepared at a wheel speed of 15 m/s, respectively. The large coercivity can result from the atoms Cu precipitated in the grain boundaries, which has a pinning domain wall effect. The coercivity mechanism is mainly controlled by the nucleation of reversed domains. The microstructural parameter αk and the averaged local effective demagnetization factor Neff were derived from the temperature dependence of coercivity.
First-principles theory of magnetoelastic coupling and magnetic anisotropy strain dependence in ultrathin Co films on Cu(001)
Authors: Shick A. B. , Novikov D. L. , Freeman A. J.
Published: July 2002

The magnetoelastic coupling and magnetic anisotropy energy (MAE) of (i) an uncovered and (ii) a Cu-capped Co overlayer on Cu(001) are determined employing a self-consistent relativistic spin-polarized version of the total-energy full-potential linearized augmented plane-wave (FLAPW) method and the magnetic torque method. Layer-resolved contributions to the magnetoelastic coupling and MAE are obtained. We find surface magnetoelastic coupling coefficients to be positive for the Co layer and negative for the Cu substrate and cap layers. A substantial difference of magnetoelastic coupling coefficients for thin films as opposed to bulk is demonstrated, which causes a negative magnetostriction coefficient (λ001) for uncovered Co overlayer and a positive λ001 for the Cu-capped Co overlayer on Cu(001).
Radiation enhanced diffusion in MgO
Authors: Van Sambeek A. I. , Averback R. S. , Flynn C. P. , Yang M. H. , Jäger W.
Published: July 2002

Radiation enhanced diffusion and ion beam mixing of O18, Ca, and Zn buried tracer layers in MgO, grown by molecular beam epitaxy, have been measured following irradiation with 2.0 MeV Kr+ and 1.0 MeV Ne+, He+, and H+ from 30 to 1500 °C. The ion beam mixing parameter varied between 1.0 and 5.0 Å5 eV−1 for the different tracers at 30 °C and increased slowly with increasing temperature. These results are consistent with ballistic mixing. In the highest temperature range investigated, 1350–1500 °C, the radiation enhanced diffusion coefficient for O18 was proportional to the square root of the irradiation flux and displayed an apparent activation enthalpy of 1.2 eV. These dependencies on flux and temperature are indicative of recombination-limited kinetics, with the measured activation enthalpy representing one-half the migration enthalpy of anion vacancies. From 1150 to 1350 °C an activation enthalpy of 4.1 eV was obtained. The unexpectedly high value is attributed to the dissociation energy of small vacancy clusters. Measurements on the cation sublattice were limited to temperatures below 900 °C owing to the excessive thermal diffusion associated with extrinsic vacancies, which are present for trivalent impurity charge compensation.
Optimization of plasma-enhanced chemical vapor deposition of hydrogenated amorphous silicon
Authors: Oversluizen G. , Lodders W. H. M.
Published: July 2002

An experimental study of the optimization of plasma-enhanced chemical vapor deposition of hydrogenated amorphous silicon is presented. The correlations between deposition parameters and layer properties are discussed. The conditions involve two deposition regimes, collisional “wave riding” at the sheath boundaries (the so-called α-regime) and “Joule heating” in the bulk (the so-called γ′-regime). For low growth rates in the α-regime optimum density of states values and the lowest microvoid densities are obtained in layers with a high compressive stress. For high growth rates in the γ′-regime, layers with a high density of states and a high microvoid density are obtained. The stress in these layers is tensile and correlates with the microvoid density. For moderate growth rate hydrogen-diluted deposition conditions in the γ′-regime near optimum density of states values and low microvoid densities can be obtained in layers with a low compressive stress. Furthermore, using hydrogen-diluted growth, an improved reproducibility and layer-thickness uniformity is obtained in a wider process window. For device applications, a design adapted for the use of hydrogen-diluted growth in the γ′-regime is recommended.
Optical absorption of vanadium doped ZnGa2Se4 single crystals
Authors: Kim Yong-Geum , Lee Chomsik
Published: July 2002

Vanadium doped ZnGa2Se4 single crystals were grown by the chemical vapor transport method. Optical absorption peaks in the measurement of the vanadium doped ZnGa2Se4 single crystal absorption spectrum at 6020, 9319, 12716, and 15290 cm−1 bands are found to be the electron transition of V3+ ion with Td symmetry from ground state A32(F3) to excited states T32(3F),3T1(3F),3T1(3P), and E1(G1). Crystal-field parameter and Racah parameters, which were obtained from the optical-absorption peaks, are found to be `Dq=602 cm−1, B=265 cm−1, and C=5294 cm−1, respectively. We also found the value of B is reduced 70% compared to the V3+ free ion. The V3+ ion splits into three states: Γ3+Γ5, Γ4, Γ1 by the first-order spin-orbit coupling effect. Hence, the spin-orbit coupling constant is λ=−312 cm−1.
All-optical double-sideband suppressed-carrier modulation of semiconductor lasers
Authors: Varangis P. M. , Gavrielides A. , Kovanis V. , Erneux T. , Lester L. F.
Published: July 2002

We demonstrate theoretically and verify experimentally that injection locking may be used to achieve double-sideband suppressed-carrier modulation of semiconductor lasers. Our theoretical investigation explains the suppression of the optical carrier and illustrates the dominant role of the phase in prescribing the response of the injected laser.
Correlation between microstructure and localized band gap of GaN grown on SiC
Authors: Bangert U. , Harvey A. , Davidson J. , Keyse R. , Dieker C.
Published: July 2002

Transmission electron microscopy and localized electron energy loss (EEL) spectroscopy in the band gap energy regime were conducted in the GaN/3C–SiC system. Though grown on a cubic substrate, the GaN film exhibits hexagonal phases of two different orientation relationships with the substrate. One of these has transformed in parts into a cubic phase via sequential faulting. The band gap was determined in local regions of good crystallinity, in the proximity of stacking faults, dislocations, grain boundaries, and heterointerfaces. Extrapolation of the low EEL spectra gives a band gap value of 3.4 eV for the unfaulted hexagonal-close-packed (hcp) phase, which ties in with the predicted value. The band gap itself in the EEL spectra is heavily masked by near band edge states around 3.2 and 3.3 eV in particular in the faulted grains. Local variations in the midgap and near band edge density of states in the EEL spectra were found to relate to different amounts and kinds of microstructural defects in the GaN film. Accordingly photoluminescence measurements at 6 K do not reveal the bound exciton at around 3.47 eV, but instead suggest the presence of donor acceptor pairs at 3.27 eV. EEL spectra of the cubic portions reveal a tail of the scattering intensity, which can be fitted by a parabolic density of states curve extending to 3.2 eV, the predicted value of the cubic band gap. These transitions are, however, of surprisingly low intensity, considering the crystallographic perfection of the material in the cubic portions.
Theoretical stability of the polarization in insulating ferroelectric/semiconductor structures
Authors: Watanabe Yukio
Published: July 2002

Stability of the polarization in a thin ferroelectric film on a semiconductor is theoretically investigated using an insulating homogeneous Ginzburg–Landau theory. Dependence of the stability on various parameters such as the ferroelectric thickness, the materials (BaTiO3, KNbO3, PbTiO3, Bi4Ti3O12), the interfacial defects, the work function difference, the epitaxial orientation, and the buffer insulator thickness is numerically and analytically studied, and the results are qualitatively compared with the past experiments on ferroelectric field effect devices. The spontaneous polarization in a ferroelectric single-domain on a semiconductor is shown to be bistable in agreement with recent experiments. Furthermore, its thickness limit of the ferroelectric stability is found to be very small, implying a great potential of this structure for the miniaturization. The single-domained spontaneous polarization is destabilized when even a very thin insulating layer exists between the ferroelectric and the semiconductor. The formation of the multidomain is found to be insufficient to stabilize the spontaneous polarization in thin ferroelectrics used in experiments. The spontaneous polarization can be stabilized at one polarity by the defects or the surface states at the ferroelectric/insulator interface, which explains its temporary stability experimentally suggested. The thermodynamic liner susceptibility is crucial for the stability, while the ferroelectric stability is predicted to be enhanced by modifying it effectively by changing the epitaxial orientation of the ferroelectric film. An addition of metallic layer between the ferroelectric and the insulator changes this restriction, although this invites another instability of the conductance modulation. To explain the experimental instabilities, they are classified into four categories. The present study suggests also a limitation of the assumption of an insulating ferroelectric under a very large depolarization field.
Glass and silicon probes: A comparative theoretical study for near-field optical microscopy
Authors: Castiaux A. , Danzebrink H. U. , Bouju X.
Published: July 2002

Glass fibers, chemically etched at their extremities and covered with a thin metal coating, are often present in near-field optical microscopy. Such elongated systems can be used to either probe the evanescent components of the electromagnetic field at the surface of a sample, or locally couple this sample with optical evanescent waves. In this article, we analyze theoretically an alternative tip design made with a silicon core. This kind of probe could be very useful when infrared properties of a surface are to be investigated. The advantages of using such a material for near-field optical detection will be stressed and compared with the performances of a bulk glass fiber.
Reactivation kinetics of the Cu and Fe hole traps in hydrogenated p-type GaAs
Authors: Radue C. , Conibear A. B. , Ball C. A. B.
Published: July 2002

Deep level transient spectroscopy has been used to investigate hydrogen passivated p-type GaAs. Annealing studies have shown reactivation of the passivated CuB and Fe2+/3+ defects under differing bias conditions. The dissociation energies and dissociation attempt frequencies of these defects have been determined. It has been found that Fe–H has dissociation energies of 1.37 eV under zero bias annealing and 0.83 eV under reverse bias annealing. The CuB–H defect only displays measurable reactivation under reverse bias conditions, and has a dissociation energy of 1.57 eV. The passivated CuA defect does not show reactivation, even after extended periods of annealing at high temperatures.
Reflection characteristics of obliquely incident surface acoustic waves from groove and aluminum gratings on {100}-cut gallium arsenide
Authors: Cameron T. P. , Hunt W. D.
Published: July 2002

In this article we present an experimental study of the surface acoustic wave behavior of a slanted reflector array on {100}-cut, 〈110〉-propagating GaAs. The thorough examination of both Al stripes and grooves on GaAs unveiled previously unknown information about the behavior of slanted gratings on {100}-cut GaAs. We discovered that etched grooves provide a strong reflection coefficient (C=0.29) while Al stripes do not (C=0.014). These data were obtained from measurements of the reflection characteristics for slanted gratings on GaAs. Potential device applications include an ultralow power acoustic charge transport device which does not require an interdigital transducer.
Determination of the defect depth profile after saw cutting of GaAs wafers measured by positron annihilation
Authors: Börner F. , Eichler S. , Polity A. , Krause-Rehberg R. , Hammer R. , Jurisch M.
Published: July 2002

Positron lifetime measurements and Doppler broadening spectroscopy using slow positrons were combined to investigate open-volume defects created by sawing wafers from GaAs ingots by a diamond saw cutter. It was found during step-by-step polishing that the depth distribution represents a wedgelike profile. The depth and the concentration of the defects introduced by the diamond saw depend on the advance of the saw blade. An isochronal annealing experiment was carried out to study the thermal stability of the observed defects. The positron lifetime of the dominant open-volume defect was estimated to be larger than 330 ps. It was concluded from this lifetime value and from the Doppler broadening parameters as well as from the annealing behavior that vacancy aggregates consisting of at least two vacancies are created by the sawing procedure. More extended defects such as microcracks were analyzed by scanning electron microscopy.
Simulations of step responses of electronegative radio-frequency capacitively coupled discharges
Authors: Yang Jing , Ventzek Peter L. G. , Sakai Y. , Date H. , Kitamori K. , Tagashira H. , Meyyappan M.
Published: July 2002

The transient response of electronegative radio-frequency glow discharges is important for process control, charge free etching, and highly selective etch applications. The step response of typical electronegative process gases (silane at 1 Torr and chlorine at 100 mTorr) is studied using a drift-diffusion model for silane and a three-moment model for chlorine. The silane simulations include a blocking capacitor whereas the chlorine results do not. For the silane results with a blocking capacitor in series with the plasma, it is found that there are three types of transients. Depending on the final steady-state value of the source rf voltage, the step response can be characterized either by smooth transitions in the number densities of species in the discharge from one steady state to the next, temporary extinction of the discharge or a discharge mode characterized by temporary extinction and reignition of the discharge. In the case of silane definite thresholds separate the phenomena. The step response of the chlorine discharges is always characterized by a smooth transition from one steady state to the next. Smooth transitions from one steady state to the next in the case of step decreases in the source voltage are possible since decrease of the negative ion density in the bulk is controlled by ion–ion recombination. It appears that the temporary extinction of the discharge and natural pulsed steady state is the consequence of how the voltage is divided between the gap and the blocking capacitor during the transient and the fact that the attachment coefficient becomes larger than the ionization coefficient at low values of reduced electric field.
Escape length of ultraviolet induced photoelectrons in alkali iodide and CsBr evaporated films: Measurements and modeling
Authors: Boutboul T. , Akkerman A. , Breskin A. , Chechik R.
Published: July 2002

The escape length of electrons photoinduced from thin CsI, KI, RbI, NaI, and CsBr evaporated films was measured in the 140–180 nm photon spectral range. Theoretical model predictions of the escape length value are in fair agreement with the experimental results. They vary between 10 and 40 nm, the highest values being for CsI, RbI and CsBr. For CsI, measured and calculated ultraviolet-induced escape length values are consistent with that determined from x-ray photoemission quantum yield data. Post-evaporation annealing of the films had no major impact on the measured electron transport properties.
Measurement of the Hg distribution in a high-pressure arc lamp by x-ray absorption
Authors: Curry J. J. , Sakai M. , Lawler J. E.
Published: July 2002

We have used an x-ray absorption technique to measure the distribution of Hg atoms in a pure-Hg high-pressure arc lamp. The x rays are obtained from a molybdenum-anode x-ray tube at an accelerating potential of 25.3 kV. The spectral distribution of x rays which produce the absorption signal consists mainly of the Mo Kα and Kβ fluorescence peaks at 17.5 and 19.6 keV, respectively. Plane-wave illumination of the lamp and two-dimensional detection of the transmitted x rays allow us to probe the Hg atom density in all regions of the lamp, simultaneously, with a spatial resolution of 170 μm. A complete two-dimensional map of the density is obtained by Abel inversion of the absorption data. This map extends all the way out to the arc-envelope boundary and includes the cold regions of the discharge behind the electrodes. A temperature map of the discharge is obtained by combining the density information with an optical emission measurement of the core temperature at a single axial location.
Simultaneous determination of the compositions and thicknesses of a multilayer film using spectroreflectometry
Authors: Weyburne David W. , Paduano Qing S.
Published: July 2002

In the growth of III–V epitaxial layers, spectroreflectometry is a fast, convenient method for measuring layer thickness. The experimentally measured optical thickness is the product of the composition-dependent refractive index and the layer thickness. In the past, the thickness of a ternary layer was uniquely determined by fixing the composition using photoluminescence or x-ray measurements. In this article, we show that the decoupling can be accomplished by measuring and fitting the spectroreflectance in a wavelength range where there is significant variation of the refractive index, for example, near the semiconductor band gap. The technique is demonstrated by the simultaneous measurement of the compositions and thicknesses of multilayered AlGaAs/GaAs films incorporating up to three different AlGaAs compositions.
Electrical characterization of silicon carbide n+pp+ diodes with an N-implanted n+ emitter
Authors: Raynaud C. , Ghaffour K. , Ortolland S. , Locatelli M.-L. , Souifi K. , Guillot G. , Chante J.-P.
Published: July 2002

Silicon carbide bipolar diodes fabricated by nitrogen implantation with a subsequent annealing at 1100 °C and passivated with a deposited oxide have been characterized. Capacitance– and current–voltage measurements have been made to analyze the quality of the junction. Admittance spectroscopy shows the presence of three peaks: two correspond to nitrogen and aluminum shallow levels; the third one has been more precisely studied by deep level transient spectroscopy. It presents an activation energy of Ev+0.49 eV and is probably due to a hole trap created by the nitrogen implantation.
Simulation of a quantum-dot flash memory
Authors: Iannaccone G. , Trellakis A. , Ravaioli U.
Published: July 2002

We present the simulation of a flash memory in which the floating gate is replaced by a silicon quantum dot. Unlike conventional flash memories, this device promises the advantage of self-limited direct charging of the floating gate with a low writing voltage, thus allowing one to overcome hot carrier degradation problems. Due to the small dimensions of this memory device, quantum effects are expected to play an important role. To estimate their magnitude, we compare a semiclassical simulation based on the solution of Poisson’s equation with a quantum computation solving the complete system of Schrödinger’s and Poisson’s equation. Despite the three-dimensional nature of the problem, a two-dimensional computational mesh proved to be sufficient to provide good agreement with experimental results, after three-dimensional corrections were included.
Enhanced exchange anisotropy of Ni–Fe/Mn–Ni bilayers fabricated under the extremely clean sputtering process
Authors: Tsunoda Masakiyo , Uneyama Kazuhiro , Suzuki Toshihiro , Yagami Kojiro , Takahashi Migaku
Published: July 2002

In order to clarify the influence of the impurities in the sputtering atmosphere on the exchange anisotropy of ferromagnet/antiferromagnet bilayers, Ni–Fe/Mn–Ni films were prepared under different purities of the sputtering atmosphere by changing the base pressure from 10−11 Torr [extremely clean (XC) process] to 10−7 Torr [lower grade (LG) process]. The correlation between the exchange anisotropy and the microstructure of the films is discussed. As a result, we found that: (1) The exchange anisotropy was enhanced in the XC processed films comparing to the LG processed ones, especially when the thicknesses of both the ferromagnetic and antiferromagnetic layers were very thin. (2) The critical thicknesses of the antiferromagnetic layers were 110 and 150 Å for the XC and the LG processed films, respectively. (3) In the XC processed films, the fcc-[111] direction of the Ni–Fe grains were highly oriented perpendicularly to the film plane and an enlargement of antiferromagnetic grains was observed. We conclude that the enhancement of exchange anisotropy is caused by the enlargement of antiferromagnetic grains in the XC processed films.
Growth of ultrathin SiO2 on Si by surface irradiation with an O2+Ar electron cyclotron resonance microwave plasma at low temperatures
Authors: Liu Y. C. , Ho L. T. , Bai Y. B. , Li T. J. , Furakawa K. , Gao D. W. , Nakashima H. , Muroaka K.
Published: July 2002

Ultrathin SiO2 films were grown by Si surface irradiation with an O2+Ar electron cyclotron resonance (ECR) microwave plasma at low temperatures. These films without hydrogen and silicon deposition were easily grown in a few minutes at low temperatures and at relatively low working pressures (1.0–3.9×10−1 Pa). The promoting growth process of an ultrathin oxidized layer (1–9 nm) was analyzed by in situ Fourier transform infrared reflective absorption spectroscopy. By using the sputter erosion technique, the dependence of x-ray photoelectron spectroscopy on the depth profiling of the films was obtained. The compositional deviations of the films from the stoichiometric SiO2 were also discussed in the interface region of Si/SiO2. This study indicated that an O2 ECR microwave plasma was efficient to form controlled ultrathin SiO2 dielectric films. The dependence of the film quality on the working pressure and gas flow rate ratios of the O2 to Ar was discussed.
Electrostatic Aharonov–Bohm effect in solids revised
Authors: Figielski T. , Wosiński T.
Published: July 2002

We consider the Aharonov–Bohm [Phys. Rev. 115, 485 (1959)] interferometer (or a hypothetical quantum interference transistor) that consists of a single-channel quantum wire split into a mesoscopic loop, whose conductance is controlled by a voltage applied between a gate electrode coupled capacitively to one branch of the loop and the wire. It is deduced from fundamental properties of one-dimensional conductors that putting a single elementary charge on the gate–wire capacitor dramatically alters the interference conditions in the device by introducing the phase shift π/2. This surprising result means that the electrostatic Aharonov–Bohm effect belongs in fact to the category of single-electron phenomena in solids and that inherent charge fluctuations can make its clear observation impossible.