bluuebunny/crossref_metadata_2025 huggingface dataset:
Exchange and crystalline electric fields at R sites in R2Fe14B (R=Tb, Dy, Ho, Er, and Tm)
Authors: Zhao T. S. , Lee Jae Il
Published: July 2002

The R-Fe exchange field and the crystalline-electric-field (CEF) parameters at f and g sites in the R2Fe14B compounds (R=Tb, Dy, Ho, Er, and Tm) are determined by analyzing inelastic neutron-scattering spectra and high-field magnetization curves at low temperatures. The determined R-Fe exchange field and CEF parameters vary monotonously across the series. Different values for the R-Fe exchange field at f and g sites with a ratio of about 1.2 and for the second-order CEF parameter A02 at f and g sites with a ratio of 1.24 have been deduced. By using the determined parameters, our calculations reproduce well the observed first-order magnetization process along the [100] direction in Er2Fe14B and Tm2Fe14B at low temperatures.
Line-shape analysis of reflectance spectra from ZnSe/Zn0.99Fe0.01Se spin superlattices
Authors: Chern-Yu K. , Chou W. C. , Twardowski A. , Yu W. Y. , Lee S. T. , Petrou A. , Warnock J. , Jonker B. T.
Published: July 2002

Line-shape analysis of magnetoreflectance spectra from ZnSe/Zn0.99Fe0.01Se quantum well structures was performed using a classical dielectric function model. This model explains the spectral dependence on the sample geometry, as well as providing additional evidence of spin superlattice formation in ZnSe/ZnFeSe heterostructures.
NiGe-based ohmic contacts to n-type GaAs. II. Effects of Au addition
Authors: Kawata Hirotaka R. , Oku Takeo , Otsuki Akira , Murakami Masanori
Published: July 2002

Our efforts have been continued to improve the electrical properties of NiGe ohmic contacts by adding a small amount of a third element to the NiGe contacts without deteriorating thermal stability and surface smoothness. In the present study, Au was chosen as the third element, and the optimum conditions to produce thermally stable, low resistance ohmic contacts were determined by preparing a variety of contacts with different thickness ratios of the Ni, Ge, and Au layers. The best ohmic contact was prepared by depositing sequentially Ni (40 nm), Au (5 nm), and Ge (100 nm) onto the n-type GaAs substrate, and annealing at 450 °C for 5 s. This contact provided the contact resistance of about 0.2 Ω mm, which is lower than that of the NiGe(In) contacts. The present contact had smooth surface after contact formation and showed excellent thermal stability during isothermal annealing at 400 °C. The cross-sectional observation using high-resolution electron microscopy indicated that the GaAs/metal interface was uniform and the diffusion depth of the contact metal to the GaAs substrate was shallow (∼20 nm). These contact properties are desirable for future GaAs very large scale integration devices.
Improvement of the SiO2/Si interface of metal-oxide-semiconductor devices using gate dielectrics formed by NF3-aided oxidation and N2O post-annealing
Authors: Huang Jenn Gwo , Jaccodine Ralph J. , Young Donald R.
Published: July 2002

With the increasing requirement for ultrathin gate dielectrics in advanced metal-oxide-semiconductor structures, a low thermal budget process to grow thin dielectric film is vital, while at the same time maintaining the good interface quality and thin film reliability. In this article, thermal nitridation of fluorinated oxide in N2O ambient was investigated. While fluorinated oxides provide a lower thin film stress and better interface than conventional oxides, an excess amount of fluorine in the starting oxide has an adverse effect on the high field stability. For N2O-nitrided oxide, high temperature and prolonged nitridation time reduce the interface state generation ΔDit resulting from avalanche electron injection at the expense of increasing the flatband voltage shift ΔVfb. The electrical properties are strongly process dependent. The best operating window of N2O nitridation of fluorinated oxide (F-ox), grown at 900 °C with a 100 ppm NF3 additive, lies between 30 and 120 min at 950 °C. With careful control of fluorinated oxide growth parameters and N2O annealing, we have demonstrated an excellent way to fabricate dielectric thin films for future applications.
Signal and noise with a magnetic circular dichroism detection system in optical data storage
Authors: Schlichting W. , Milster T. D. , Wang M. S. , Brucker C.
Published: July 2002

A magneto-optical head with circular polarized light incident on a Co/Pt superlattice medium is studied. Differential absorption due to magnetic-circular-dichroism (MCD) is used for erasable data detection. This MCD detection system utilizes an optical isolator to minimize the feedback to the laser. The tradeoff for its reduced complexity is the loss of the common mode noise reduction capability. A disk is tested dynamically with the MCD detection system. With a linear medium velocity of 7.56 m/s and a frequency of 5 MHz a carrier-to-noise ratio of 40 dB is demonstrated.
Spectroscopy of Nd3+ in KLiYF5 and KLiGdF5
Authors: Summers P. L. , Weidner H. , Peale R. E. , Chai B. H. T.
Published: July 2002

High-resolution Fourier-transform absorption and photoluminescence spectroscopy with site-selective excitation reveal two sites for Nd3+ ions in each of the two new crystals KLiYF5 and KLiGdF5. Energy levels for the 4I multiplets and the 4F3/2 multiplet have been determined separately for each site in each crystal. Comparison of spectra and levels indicates that the crystal fields in each of the two materials are nearly identical. This suggests that KLiGdF5 is isostructural to KLiYF5.
Backpropagation (neural) networks for fast pre-evaluation of spectroscopic ellipsometric measurements
Authors: Fried Miklós , Masa Péter
Published: July 2002

We show that a certain type of artificial neural systems or neural networks, more specifically the backpropagation network (BPN), can be an efficient tool in fast, approximate pre-evaluation of spectroscopic ellipsometric (SE) measurements. The BPN is a multilayer, feedforward network which can perform nontrivial mapping functions. We demonstrate the method on separation by implantation of oxygen (SIMOX) structure and ion implantation caused damage depth profile evaluation. The results are compared with others from independent measurements.
Molecular beam epitaxial growth of single domain ZnSe on Ge
Authors: Li L. K. , Wang Y. , Jurkovic M. , Wang W. I.
Published: July 2002

High quality ZnSe epilayers have been successfully grown on a Ge (311) substrate by molecular beam epitaxy. Reflection high energy electron diffraction indicated antiphase domain free growth. The x-ray diffraction rocking curve demonstrated a full width at half maximum as narrow as 198 arcsec, which is the narrowest linewidth reported to date for a ZnSe/Ge heteroepitaxy. Our results indicate that ZnSe/Ge heterostructures are promising for optoelectronic device applications.
Interface states characterization by conductance measurements of Au/Cr Schottky barriers to sulfur-treated GaAs
Authors: Sawant Nilima M. , Srinivasa R. S.
Published: July 2002

Conductance measurements are presented for sulfur-treated and untreated Au/Cr/GaAs Schottky diodes. The presence of large numbers of surface states limit the performance of GaAs devices. Sulfur treatment was carried out using H2S(g). ‘‘Passivation’’ using sulfur has been extensively studied and has been found to be effective in reducing the surface state density. Au-GaAs contact is popularly used as a Schottky gate in the metal-semiconductor field-effect-transistors. The adhesion of gold to GaAs is poor, so chromium is used as an interlayer. Chromium is highly reactive and could lead to various phases at the interface both for untreated and sulfur-treated diodes. We report here the defect levels identified for these diodes by conductance measurements. We correlate here the presence of different phases at the interface with the various defects identified. In our case the statistical model is found to most accurately fit the interface state conductance response. The density of states for these defect energy levels is considerably high which could be the reason for the poor electrical performance of both types of Schottky diodes.
Brillouin scattering determination of magnetic and elastic constants in Invar-type La(FexAl1−x)13 amorphous alloy films
Authors: Yoshihara Akira , Shimada Yutaka , Chiang Te-Hsuan , Fukamichi Kazuaki
Published: July 2002

Magnetic and elastic constants of Invar-type La(FexAl1−x)13 amorphous alloy films (x=0.8–0.95) have been determined by Brillouin scattering at 290 K. Observation of the well-defined standing spin waves up to fourth order allowed us to determine the spin wave stiffness at T/Tc∼0.76, as 63±10 meV A2 for the x=0.8 alloy film. Young’s modulus and Poisson’s ratio as a function of the Fe concentration x have been determined from the surface phase velocities of the Rayleigh and Sezawa waves. Here E(x)=1.08−0.93(1−x)1012 dyn/cm2 for Young’s modulus and σ(x)=0.34±0.2 for Poisson’s ratio have been obtained through numerical analyses for the surface acoustic wave dispersions.
Influence of plasma conditions on the defect formation mechanism in amorphous hydrogenated silicon
Authors: Kounavis P. , Mataras D. , Spiliopoulos N. , Mytilineou E. , Rapakoulias D.
Published: July 2002

The variation of a-Si:H film quality, deposited by a rf glow discharge of pure silane, is examined as a function of the interelectrode distance for two different pressures. Constant photocurrent and modulated photocurrent methods are used to estimate the magnitude and the shape of the defect states in the valence band and the conduction band, respectively. An effort is made to correlate the film quality parameters and the defect formation with the plasma macroscopic and microscopic parameters. The results suggest that, at low interelectrode distances, high sticking coefficient radicals modify the film growth and the defect formation mechanisms, leading to the deterioration of the film quality. The conclusions drawn are compared with the predictions of recent theoretical models concerning the defect formation in a-Si:H.
n-type doping of the wide gap ternary alloy (CdMg)Te during molecular beam epitaxy
Authors: Waag A. , Fischer F. , Gerschütz J. , Scholl S. , Landwehr G.
Published: July 2002

We report on the n-type doping of the wide gap II-VI semiconductor CdMgTe. Bromine and chlorine have been used as dopants during molecular beam epitaxy. For the CdTe base material both bromine and chlorine give shallow donors, and free carrier concentrations of up to 2.8×1018 cm−3 have been reached. For increasing Mg concentration, however, deep donors are created, limiting the free carrier concentration at room temperature. This is demonstrated by Hall effect measurements at different temperature. The deep donors can be converted to metastable shallow donors by light illumination at temperatures below about 180 K, which results in persistent photoconductivity. We interpret our results in terms of a DX-like state, which is introduced by both the chlorine and bromine doping, and which moves into the band gap with increasing Mg concentration. We conclude that the limit in the n-type doping of CdMgTe, the band gap of which can easily be tuned through the whole visible range, is an intrinsic property of the dopants used, and not due to self-compensation caused by nonideal growth conditions.
Beam breakup growth and reduction experiments in long-pulse electron beam transport
Authors: Menge P. R. , Gilgenbach R. M. , Lau Y. Y. , Bosch R. A.
Published: July 2002

The results of an experimental program whose sole objective is to investigate the cumulative beam breakup instability (BBU) in electron beam accelerators are presented. The BBU growth rate scalings are examined with regard to beam current, focusing field, cavity Q, and propagation distance. A microwave cavity array was designed and fabricated to excite and measure the cumulative BBU resulting from beam interactions with the deflecting TM110 cavity mode. One phase of this experiment used high Q(≊1000) cavities with relatively large frequency spread (Δf/f0≊0.1%). The observed TM110 mode microwave growth between an upstream (second) and a downstream (tenth) cavity indicated BBU growth of 26 dB for an electron beam of kinetic energy of 750 keV, 45 A, and focused by a 1.1 kG solenoidal field. At beam currents of less than 100 A the experiments agreed well with a two-dimensional continuum theory; the agreement was worse at higher beam currents (≳100 A) due to beam loading. The second-phase experiments used lower Q(≊200) cavities with relatively low frequency spread (Δf/f0≊0.03%). Theory and experiment agreed well for beam currents up to 220 A. Distance scaling experiments were also performed by doubling the propagation length. Instability growth reduction experiments using the technique of external cavity coupling resulted in a factor of four decrease in energy in BBU growth when seven internal beam cavities were coupled by microwave cable to seven identical external dummy cavities. A theory invoking power sharing between the internal beam cavities and the external dummy cavities was used to explain the experimental reduction with excellent agreement using an equivalent circuit model.
The two carriers’ mobility-lifetime products and their light intensity dependencies in hydrogenated amorphous silicon
Authors: Balberg I.
Published: July 2002

The effect of the equilibrium (or dark) occupation of the recombination centers on the majority-carrier mobility-lifetime μτ product and its light intensity dependence have been discussed by Rose many years ago [Concepts in Photoconductivity and Allied Problems (Wiley Interscience, New York, 1963), p. 22]. The corresponding theory is extended and it is discussed in terms of the energy separation between the equilibrium Fermi level and the energy levels of the recombination centers. The theory is then generalized to include the corresponding dependencies of the minority-carrier μτ product. The results are shown to be useful in analyzing the available phototransport data of hydrogenated amorphous silicon, a-Si:H, indicating that the ‘‘standard defect’’ model, which is widely used for the description of the electronic structure and the recombination processes in this material, cannot account for the phototransport data associated with the minority carrier. On the other hand the ‘‘defect pool’’ model, suggested more recently, is shown to be in accord with the available data.
Cu-Mo contacts to CuInSe2 for improved adhesion in photovoltaic devices
Authors: Yang L.-Chung , Rockett A.
Published: July 2002

An electrical contact material consisting of an initially metastable solid solution of Cu in Mo is shown to provide improved adhesion to CuInSe2 when the Cu content exceeds ∼30 at. %. During physical-vapor deposition of CuInSe2 on these Cu-Mo solutions at elevated temperatures, phase separation occurs and Cu is released into the CuInSe2 layer. The Cu release begins at approximately 450 °C and increases in rate with increasing temperature. The release of Cu into the film along with consequent changes in the back contact are responsible for the improved adhesion. Similar adhesion improvements were obtained using annealed Cu-Mo layers in which phase separation occurred before CuInSe2 growth. Photovoltaic devices based on CuInSe2 on Cu0.3Mo0.7 back contacts showed improved performance and uniformity.
High-power proton beam-matter interaction diagnostics by analysis of the hydrodynamic response of solid targets
Authors: Baumung K. , Karow H. U. , Rusch D. , Bluhm H. J. , Hoppé P. , Kanel G. I. , Utkin A. V. , Licht V.
Published: July 2002

The hydrodynamic response of thin planar targets to the ablative pressure pulse induced by a high-power proton beam has been investigated experimentally at the Karlsruhe Light Ion Facility using time-resolved laser-Doppler velocimetry. An analytical acoustic model was established which allows a semiquantitative interpretation of the phenomena observed. Details in the measured ablation pressure history could be explained by the particularities of the proton beam. The evolution in time of the depth of the energy deposition zone deduced from our experiments is in good agreement with the proton energy and stopping range increase during the voltage rise of the generator pulse.
Temperature-dependent kinetic inductance of YBa2Cu3O7−δ thin films predicted by the coupled grain model in the strong-coupling limit
Authors: Fagerberg R. , Grepstad J. K.
Published: July 2002

The introduction of a temperature dependence to the effective penetration depth as calculated in the strong-coupling limit of the coupled grain model is discussed. Assuming a phenomenological Gorter–Casimir behavior for the intrinsic penetration depth of YBa2Cu3O7−δ (YBCO) and a simple model for the temperature-dependent intergrain critical current density, the coupled grain model is found to predict a kinetic inductance which accurately fits the relative phase velocity, vφ(T)/vφ(T0), measured on coplanar YBCO transmission lines. This indicates that the coupled grain model provides an adequate physical interpretation of the empirical penetration depth proposed by, e.g., Rauch et al. [J. Appl. Phys. 73, 1866 (1993)] and suggests that the kinetic inductance is strongly influenced by boundaries between grains with minor relative misalignment. The average grain size and critical current density of the grain boundaries were estimated at a=140–240 nm and Jgc(0)=3.5×1010–1×1011 A m−2, respectively. We argue that the coupled grain model may prove suitable for implementation in microwave circuit design software, as thin film preparation techniques mature in the sense of providing samples with highly reproducible properties.
Compensation of field distortion with ferromagnetic materials and permanent magnets
Authors: Abele Manlio G. , Rusinek Henry , Bertora Franco , Trequattrini Alessandro
Published: July 2002

This paper discusses a technique for improving the homogeneity of the magnetic field in structures of permanent magnets designed for magnetic resonance imaging, achieved by inserting layers of ferromagnetic plates and permanent magnets along the cavity of the structure. The analysis of the field in the magnet is performed using a boundary integral equation method. An example of optimization of the geometry and the amount of the magnetic material is presented.
Pinned domain-wall structure in magnetic field
Authors: Teh Chai Tak , Huang Huei Li , Sobolev Vladimir L.
Published: July 2002

The pinned domain-wall (DW) structure is investigated using a perturbational approach in terms of the inverse quality factor 1/Q and the ratio of H∥/Hk (H∥ being the component magnetic field parallel to the anisotropy axis, Hk being the anisotropy field). The parallel component field gives rise to asymmetric boundary conditions which asymmetrize the DW structure. Dependence of the DW energy, static DW structure, and width on the orientation and the strength of the magnetic field has been evaluated and the corresponding Kondorsky function obtained.
Design and performance of magneto-optic enhanced Co/Pt-based trilayers having zero Kerr ellipticity
Authors: Atkinson R. , Grundy P. J. , Hanratty C. M. , Pollard R. J. , Salter I. W.
Published: July 2002

The design philosophy and objectives for producing phase-optimized trilayer structures for magneto-optic enhancement of the polar Kerr effect is outlined. A number of alternative designs is presented based on glass/Co-Pt/SiO2/Al. The performance of an actual device, as a function of the wavelength of the incident radiation, and of angle of incidence, for both of the principal polarization states, has been evaluated experimentally and theoretically. Results indicate excellent agreement and demonstrate the ease with which devices can be designed and fabricated.
Magneto-optical properties of (BiGdY)3Fe5O12 for optical magnetic field sensors
Authors: Kamada O. , Minemoto H. , Itoh N.
Published: July 2002

The temperature dependent sensitivity characteristic in the zeroth-order diffraction beam from the multidomain materials of BiXGdYY3−(X+Y)Fe5O12 films grown by a conventional liquid-phase-epitaxial method are studied. By measuring the variation of the sensitivity with temperature, it was found that films with X=1.3 and Y=0.43 show the minimum value of ±0.5% between 253 and 353 K. The contribution of the Gd substitution on the improvement of the temperature dependence of the sensitivity was explained by a simple theoretical calculation.
Two-band model for Kondo insulators: Thermodynamic and scaling properties
Authors: Continentino M. A. , Japiassu G. M. , Troper A.
Published: July 2002

Recently a new family of heavy fermions (e.g., Ce3Bi4Pt3) has been discovered which is characterized by an insulating ground state. Similar behavior has been found in some transition metal compounds like FeSi. We introduce a two-band model to describe the physical properties of these systems. Coulomb correlations in the narrow band are treated beyond the mean field approach. We find that a critical value of the hybridization Ṽc is required to open a gap that produces an insulating ground state. We discuss the scaling properties of these systems close to Ṽc. The temperature-dependent magnetic susceptibility calculated in our model is in good agreement with experimental results.
Magnetic properties of epitaxial MnAl/NiAl magnetic multilayers grown on GaAs heterostructures (invited)
Authors: Cheeks T. L. , Harbison J. P. , Tanaka M. , Hwang D. M. , Sands T. , Keramidas V. G.
Published: July 2002

New ultrathin epitaxial magnetic multilayers consisting of ferromagnetic τMnAl and nonmagnetic NiAl have been prepared on GaAs by molecular beam epitaxy. The magnetic and magneto-optic properties of these multilayers and the effect of incorporating nonmagnetic NiAl into the structure have been investigated. Perpendicular magnetization was confirmed and the remnant magnetization and coercivity were improved compared to τMnAl thin films. In addition, by systematically changing the thickness of the NiAl layer the magnetic properties could be controlled. We discuss these issues and compare the magnetic and magneto-optic properties of these structures with other epitaxial magnetic structures.
High-field polar MOKE magnetometry as a probe of interlayer exchange coupling in MBE-grown Co/Cu/Co(111) and Fe/Cr/Fe(001) wedged trilayers
Authors: Ives A. J. R. , Hicken R. J. , Bland J. A. C. , Daboo C. , Gester M. , Gray S. J.
Published: July 2002

We discuss the use of room temperature polar magneto-optic Kerr effect (MOKE) measurements at high field (≤7 T) in investigating antiferromagnetic (AFM) and ferromagnetic (FM) exchange coupling in MBE-grown wedged trilayers. In the case of Co/Cu/Co(111), the polar MOKE revealed the first AFM coupling peak at 9 Å Cu thickness and the second weaker AFM coupling peak at 20 Å. This is an important result because it helps in resolving the present controversy over whether oscillatory coupling exists in (111) oriented MBE-grown Co/Cu/Co structures. For Fe/Cr/Fe(001), polar MOKE is found to be less sensitive than in-plane MOKE for extracting the detailed form of the coupling. However, polar MOKE reveals additional variations in the perpendicular saturation fields as a function of interlayer thickness, which are not found in the in-plane MOKE saturation fields.
Anisotropy studies of molecular-beam-epitaxy-grown Co(111) thin films by ferromagnetic resonance
Authors: Schreiber F. , Soliman A. , Bödeker P. , Meckenstock R. , Bröhl K. , Pelzl J. , Garifullin I. A.
Published: July 2002

The magnetic anisotropy of Co/Cu(111) thin films has been investigated using the ferromagnetic resonance (FMR) technique. The films were prepared by molecular-beam epitaxy in ultrahigh vacuum on sapphire substrates with niobium as a buffer layer. In situ RHEED investigations, ex situ x-ray low-angle reflectivity measurements, and high-angle Bragg scans confirm the structural quality of the films. Angular dependent FMR measurements are performed in the plane of the films and out-of-plane. The angular dependence of the line positions in-plane shows a competition between the sixfold anisotropy, which is expected for bulk Co, and a twofold anisotropy contribution. It is demonstrated that by FMR one can detect even small values of the higher-order anisotropy terms. In the analysis, we put emphasis on the relationship between magnetic and structural properties.
Magnetic and magneto-optic properties of sputtered Co/Ni multilayers
Authors: Zhang Y. B. , He P. , Woollam J. A. , Shen J. X. , Kirby R. D. , Sellmyer D. J.
Published: July 2002

We have investigated the magnetic and magneto-optic properties of Co/Ni multilayers deposited on Ag and Au buffer layers. The samples with Au buffer layers show perpendicular magnetic anisotropy, but those with Ag buffer layers do not. The structure and degree of crystalline alignment of the buffer layer are evidently crucial to development of perpendicular magnetic anisotropy. We also present the results of polar Kerr rotation measurements as a function of wavelength and layer thickness of the multilayers.
Stress sensitivity of resonances of transverse electric modes in circular disk dielectric resonators
Authors: Lee P. C. Y. , Yang J. S. , Ballato A.
Published: July 2002

Two-dimensional governing equations for guided electromagnetic waves in isotropic or cubic crystal dielectric plates are extended to include the piezo-optic effect in the constitutive equations. These equations are then employed to study the frequency shifts of transverse electric modes caused by stresses in circular disk dielectric resonators under three cases of loading conditions: (1) a pair of diametral forces, (2) steady vertical acceleration, and (3) steady horizontal acceleration. In the latter two cases, the bottom face of the disk is bounded to a rigid supporting base.
Spectral linewidth in microcavity surface-emitting lasers
Authors: Vurgaftman Igor , Singh Jasprit
Published: July 2002

The Schawlow–Townes expression for the laser linewidth predicts a substantial cw linewidth enhancement in microcavity lasers, in which a large fraction of spontaneous emission is directed into the lasing mode, in contrast with conventional semiconductor lasers, in which the lasing mode accepts only a tiny fraction of spontaneously emitted photons. By performing a theoretical analysis of rigorous solutions of the wave equation in the surface-emitting cavity and of the band structure in the active region, it is shown that the increase in the linewidth is much slower than the increase in the spontaneous-emission factor β because of reductions in the total spontaneous emission rate, the threshold carrier density, and the linewidth enhancement factor and an increased slope of the light-current characteristic obtained for the microcavity laser in steady state. Also much smaller driving currents in a microcavity laser are required to achieve the same power output compared with conventional semiconductor lasers, resulting in a linewidth of the order of several hundred MHz at moderate driving currents for the former. We also discuss the various factors influencing the linewidth in microcavity and strained quantum well lasers and the relation between lasing threshold and spectral linewidth in both macroscopic and microscopic cavity lasers.
Photorefractive effect in Cu- and Ni-doped KNbO3 in the visible and near infrared
Authors: Medrano C. , Zgonik M. , Sonderer N. , Beyeler Ch. , Krucker S. , Seglins J. , Wüest H. , Günter P.
Published: July 2002

Nickel- and copper-doped KNbO3 crystals were grown in order to investigate the photorefractive response in the visible and near infrared. Optical absorption, photoconductivity, and two-beam coupling experiments between 515 and 1064 nm are reported. A two-beam coupling constant at 860 nm of 1.4 and 3.2 cm−1 was measured in the nickel- and copper-doped crystals, respectively.
Recombination via radiation-induced defects in field-effect transistor
Authors: Le Bras Luc , Bendada Matti , Mialhe Pierre , Blampain Eloi , Charles Jean-Pierre
Published: July 2002

Modeling techniques of P-N junctions have been applied for studying charge transport phenomena in metal-oxide semiconductor field-effect transistor structures. A parameter extraction method provides a precise description of the changes in conduction processes due to radiation damage in the integral body-drain junction. A large increase of the space charge recombination current is related to band-gap localized radiation-induced defects.
Discontinuities in finite-potential and gate-induced electron waveguides
Authors: Wilson Daniel W. , Glytsis Elias N. , Gaylord Thomas K.
Published: July 2002

Ballistic electron wave propagation through discontinuous finite-potential electron waveguides is analyzed. The wave function in each uniform waveguide section surrounding a discontinuity is represented as a sum of the local eigenmodes of that section, and both propagating and evanescent modes arising from bound and discretized continuum states are included in the expansion. The local eigenmodes are found using a transfer-matrix technique that allows the mode-matching across discontinuities to be calculated efficiently. A scattering matrix formalism is used to cascade multiple discontinuities and extract the current reflection and transmission characteristics. The method is shown to be accurate and efficient. The discontinuity analysis is applied to waveguides induced by split gates over two-dimensional electron gases. An analytical method is developed to approximate the potential energy profile produced by arbitrary-shaped gates as a function of gate voltage and material parameters. Simulation of a gate-induced constriction (quantum point contact) shows that the conductance as a function of gate voltage exhibits smooth quantized steps without oscillations in agreement with published experimental results.
Effect of bias annealing on Au/n-Si Schottky barrier with hydrogen incorporation
Authors: Yuan M. H. , Jia Y. Q. , Qin G. G.
Published: July 2002

The Au/n-Si Schottky barrier (SB) which contains hydrogen has a 0.10 eV lower SB height (SBH) than that without hydrogen. For the hydrogen-containing SB, zero bias annealing (ZBA) decreases the SBH while reverse bias annealing (RBA) increases it. In addition, ZBA and RBA cycling experiments have been made which reveal a reversible change of the SBH within at least four cycles. The annealing temperature of ZBA and especially of RBA influences the SBH. We interpret the above effect in terms of an interaction between hydrogen and metal-semiconductor interface states.
Scanning tunneling microscopy/spectroscopy studies of conducting polymer polypyrrole
Authors: Wakabayashi Shigemi , Kato Hitoshi , Tomitori Masahiko , Nishikawa Osamu
Published: July 2002

Ultrahigh-vacuum scanning tunneling spectroscopy and tunneling spectroscopy measurements of polypyrrole-vacuum-metal and polypyrrole-vacuum-polypyrrole tunneling junctions indicates the existence of three characteristic energy levels, 0.60, −0.40, and −0.65 eV near the Fermi level of an as-grown polypyrrole films. The measured energy levels of −0.40 and −0.65 eV could be attributed to localized filled states and mobility edge, respectively.
n-type polycrystalline silicon films obtained by crystallization of in situ phosphorus-doped amorphous silicon films deposited at low pressure
Authors: Sarret M. , Liba A. , Le Bihan F. , Joubert P. , Fortin B.
Published: July 2002

The low-pressure chemical-vapor deposition of phosphorus-doped silicon film on glass at 550 °C was investigated as a function of silane pressure (1–100 Pa) and phosphine/silane mole ratio ranging between 4×10−6 and 4×10−4. At this low temperature the film is homogeneous in thickness and the silicon is amorphous except for low pressure (1 Pa). Phosphorus concentration varies linearly with mole ratio in amorphous deposited films. The resistivity of films annealed at 600 °C decreases while the incorporation of phosphorus (mole ratio) increases, and varies with phosphorus concentration from 101 to 10−3 Ω cm. For the same phosphorus content, the resistivity is lower if the silicon film is amorphous deposited and subsequently crystallized, than if the film is polycrystalline deposited. Carrier concentration and mobility are measured using the Hall method. Doping efficiency and electrical properties are discussed.
Control of nitrogen incorporation in ZnTe:N grown by molecular-beam epitaxy using Ar dilution in a N plasma source
Authors: Duddles N. J. , Dhese K. A. , Devine P. , Ashenford D. E. , Scott C. G. , Nicholls J. E. , Lunn B.
Published: July 2002

The use of Ar dilution in a N plasma source has been used to achieve control of both electrical and optical properties of p-type ZnTe:N grown by molecular-beam epitaxy. Photoluminescence data are presented that show the transition from ‘‘pure’’ ZnTe emission to that indicative of heavily N-doped ZnTe. A new principal bound-exciton line associated with N impurities is observed at 2.3685 eV. An anomalous red shift in the corresponding donor-acceptor pair peak energy with increasing N concentration is observed at high N concentration and is attributed to the effects of N impurity banding. Trends in p-type conductivity confirmed the ability to control hole concentrations using Ar dilution.
Analytical and numerical analysis of Debye–Ramm’s equation for the polarization density distribution in polar materials
Authors: Ardi M. Safari , Andersson S. I. , Kubát J.
Published: July 2002

Due to dipole interaction, the molecular polarization brought about by an external field is significantly lower in condensed matter (liquids) than in a gas. In addition to this, the response of interacting dipoles to stepwise changes of the external field does not follow a simple time exponential. Instead, a spectrum of relaxation times is required to describe such a response. Debye and Ramm [Ann. Phys. 28, 28 (1937)] have attempted to describe the effects associated with rotational hindrances due to dipole-dipole interaction by the following differential equation: ∂f/∂t =(kT/ρ)Δf+(1/ρ)div(f grad u), where f denotes the distribution function specifying the number of dipoles pointing in a certain solid angle, t the time, ρ a friction coefficient, and u the potential of the forces acting on the dipoles. The latter quantity depends both on the external field and on the contribution from the dipole-dipole interaction (internal field). Although unable to solve the above equation explicitly, Debye and Ramm (DR) made some predictions about the solution, concluding, among other things, that the inclusion of an internal field E would yield a process with a discrete spectrum of relaxation times. Finding such prospect highly interesting, we subjected the DR equation to a close study using some advanced mathematical tools (Fourier integral operators etc.). Contrary to the conclusions of DR, we found that the above equation cannot be solved in the way originally described, and that the conjectured eigenfunctions and eigenvalues do not exist. Furthermore, we show that, in contrast to DR’s statements, the above equation is not solved by certain classical expressions relating to free-rotating dipoles (no internal field). The lack of physical content of this equation appears to be due to a number of not permissible simplifications.
Local structure of porous silicon
Authors: Bayliss S. C. , Anstee P. , Hutt D. A. , Zhang Q. , Danson N. , Bates J. , Waddilove A.
Published: July 2002

Local structural information has been obtained from extended x-ray-absorption fine-structure measurements on samples of porous silicon produced under various conditions, and these have been correlated with photoluminescence emission and excitation spectra. The x-ray near-edge structure (XANES) shows the existence of a feature in between those assigned to Si—Si and Si—O bonding. Laser-induced mass analysis indicates that the presence of various silicon hydroxides correlates strongly with the strength of this peak. In addition, although porous silicon consists of a surface whose roughness is of the order of nm, it has been possible to obtain depth-profiling reflected x-ray-absorption fine structure (REFLEXAFS) and reflectivity from some samples. The REFLEXAFS XANES again shows the additional feature, the strength of which increases with the intensity of the Si-Si peak, that is, with depth.
Thermal stability and crystallization products of amorphous Si:P alloy thin films made by coevaporation of Si and P
Authors: Li X.-H. , Carlsson J. R. A. , Gong S. F. , Hentzell H. T. G.
Published: July 2002

Thermal stability and crystallization of amorphous Si:P alloy thin films consisting of 20–44 at. % P have been studied in this work. The results show that the alloys have crystallization temperatures ranging from 850 to 1150 °C, which are all higher than that of pure amorphous Si, and that the variation of resistivity of the alloys during the 120 h aging at 300 °C is small (0.6%). These results indicate that the alloys have a high thermal stability, which is in agreement with the thermodynamic prediction we have made. It has also been observed that the crystallization products for these alloys are different. A new silicon phosphide phase has been observed in the 30 at. % alloy sample and suggested to be possibly a hexagonal Si7P3 phase which has lattice parameters a=5.32 Å and c=13.3 Å. The alloy films were deposited onto quartz substrates and Si wafers by coevaporation of Si and P. X-ray diffractometry and transmission electron microscopy were utilized to investigate the crystallization temperature and product of the amorphous alloys.
Characterization of texture and microstructure of oriented PbTiO3 thin films grown by metalorganic chemical vapor deposition on Si(100)
Authors: Yen Bi Ming , Liu Donhang , Bai Guo Ren , Chen Haydn
Published: July 2002

Oriented PbTiO3 (PT) thin films, approximately 2000 Å thick, have been successfully grown on Si(100) using a low-pressure, cold-wall metalorganic chemical vapor deposition technique at temperatures as low as 450 °C. Titanium isopropoxide, Ti(C3H7O)4, tetraethyl lead, Pb(C2H5)4, and pure oxygen were used as precursor materials in this work. The dependence of film texture and microstructure on the Pb/Ti source flow ratio and growth temperature is described. With proper growth conditions, stoichiometric PbTiO3 films can be produced. Two types of polycrystalline PbTiO3 films, including multi-oriented and single-oriented textures, were obtained. At growth temperatures above the Curie point (cubic-to-tetragonal transition temperature), multi-oriented textures were found. On the other hand, oriented films were fabricated at growth temperatures in the range of 450–475 °C. It is hypothesized that the preferred orientation is due to the combined effects of thermal stress and anisotropic growth rates along different crystal directions. Microstructure examinations using scanning electron microscopy showed visible grain boundaries for all crystalline samples, as well as the non-columnar cross-section morphology, which indicates highly dense and uniform structures. Using the transmission electron microscopy technique, these grains were found to consist of many fine crystalline particles (10–50 nm). Selected area electron diffraction patterns from these crystalline particles have been indexed in terms of the tetragonal PbTiO3 phase.
Nonlinear interface stability analysis of alloy solidification including effects of surface energy
Authors: Schlitz Lei Z. , Garimella Suresh V.
Published: July 2002

The morphological stability of the solid-liquid interface in the solidification of a dilute binary alloy is analyzed using linear and nonlinear perturbation analyses. The energy-balance condition at the interface is modified to incorporate the effects of surface excess energy. The Landau coefficient, which represents the nonlinear growth rate, is calculated using the direct method of undetermined coefficients. The results are applied to practical metallic and nonmetallic systems. The proposed surface energy correction is found to be significant at large growth velocities and low frequencies of interface perturbation: Linear stability is obtained over a larger range of frequencies and velocities; while the correction restricts the frequency range of nonlinear stability, the Landau coefficients obtained are larger and indicate greater stability over this range.
Diamond film deposited on a silica substrate with a ZnO:Al intermediate layer by hot-filament chemical vapor deposition
Authors: Sun Z. , Zheng Z. , Xu N. , Sun Y. , Ji R. , Zhao W.
Published: July 2002

Diamond films were deposited on ZnO:Al thin-film silica substrates by hot-filament chemical vapor deposition. Ultrasonic irradiation in a diamond suspension enhanced the diamond nucleation density on a ZnO:Al-silica substrate. The nucleation density and the growth rate of diamond film deposited on ZnO:Al thin film is higher than on the silica. The cracks on a ZnO:Al-silica substrate occurred during the diamond deposition process. It is proposed that the cracks were caused by the stress in ZnO:Al film and diamond film, and the peak frequency shift of the Raman line of diamond indicates the presence of compressive stress in the diamond film.
Tribochemical wear of carbon films in oxygen
Authors: Strom B. D. , Bogy D. B. , Walmsley R. G. , Brandt J. , Bhatia C. S.
Published: July 2002

Gases sampled directly from the sliding interface of a carbon-coated thin-film magnetic recording disk and a conventional read/write head show that carbon dioxide is generated during sliding in both dry-nitrogen and dry-oxygen environments. The generation rate is approximately ten times greater when sliding in oxygen rather than nitrogen. A novel pressure interface and sampling system was developed for the experiments.
Electrical and structural properties of rapid thermally annealed boron-doped silicon films deposited by plasma-enhanced chemical-vapor deposition
Authors: Jeanjean P. , Sicart J. , Sellitto P. , Robert J. L. , Bustarret E. , Grieshaber W. , Cali J. , Le Berre M. , Lemiti M. , Pinard P. , Conedera V.
Published: July 2002

The structural, electrical, and piezoresistive properties of in situ boron-doped thin silicon layers deposited by plasma-enhanced chemical-vapor deposition at 320 °C on oxidized silicon substrates and subjected to a rapid thermal anneal (1100 °C for 20 s) have been investigated. Macroscopic electrical parameters derived from resistivity and Hall-effect measurements were compared to microscopic characteristics deduced from optical data to explain the low-temperature coefficients of resistance measured on this polycrystalline material. Finally, the piezoresistivity gauge factors of these heavily doped layers are discussed in view of their internal stress state and of other structural characteristics.
Electron paramagnetic resonance in heat-treated porous silicon
Authors: Laiho R. , Vlasenko L. S. , Afanasiev M. M. , Vlasenko M. P.
Published: July 2002

Electron paramagnetic resonance (EPR) of centers produced in porous silicon (PS) by heat treatment in air is investigated. The properties of these centers are compared with the defects present in as-prepared PS or activated by treatment of the specimens with ethanol. The native defects of PS and those produced by thermal annealing show different saturation behavior of the EPR spectra when the microwave power is increased. Also, their spin-dependent recombination processes are different. The dependence of the EPR line intensity on the thermal annealing time at temperatures of 150–500 °C obeys a law characteristic to a diffusion process with an activation energy of 0.9 eV. This value is close to the activation energy of oxidation of crystalline silicon surfaces with atomic oxygen.
Properties of shielded microstrip line resonators made from double-sided Y1Ba2Cu3Ox films
Authors: Miura S. , Yoshitake T. , Tsuge H. , Inui T.
Published: July 2002

Double-sided Y1Ba2Cu3Ox films are prepared on MgO(100) substrates for KrF excimer laser deposition and their electrical properties, both direct current and microwave frequencies, are examined. Double-sided Y1Ba2Cu3Ox films show zero resistivity at temperatures higher than 88 K and ρ(300K)/ρ(100 K) higher than 2.7. Using a niobium shield, a double-sided Y1Ba2Cu3Ox films microstrip line resonator at 5.7 GHz shows an unloaded Q value of 2.6×104 at 77 K and 1.1×105 at 4.2 K. These are the highest class of unloaded Q known to be reported for planar-type resonators.
Superconducting fast microbolometers operating below their critical temperature
Authors: Langlois P. , Robbes D. , Lam Chok Sing M. , Gunther C. , Bloyet D. , Hamet J. F. , Desfeux R. , Murray H.
Published: July 2002

The bolometric nature of the optical sensitivity of YBCO (YBa2Cu3O7−δ) thin-film microstrips in the superconducting state is demonstrated. Below the critical temperature Tc the critical current temperature dependence of the device provides a suitable temperature sensor. A theoretical thermal model that gives reliable forecasts for the sensor time constant and sensitivity over the 10–90 K temperature range has been developed. Sensitivity measurements on high-quality YBCO films deposited on MgO are in quite good agreement with the model, showing that the observed signals are entirely bolometric. The effective heat capacity of the sensor is that of the film in the irradiated area. Owing to the high thermal conductivity of MgO, the substrate stays at the heat sink temperature and the main resistance to heat flow is the film/substrate interface. The heat capacity of the irradiated area of the film, strongly coupled to the heat sink through the thermal boundary resistance gives high-speed bolometers behaving as first-order systems. For SrTiO3 or ZrO2 substrates, their lower thermal conductivity would lead to higher time constants and more complicated behaviors. The precise origin of the measured sensor noise has still to be established. On a 0.2×10×15 μm3 microbridge at 85 K (below the critical temperature), a noise equivalent power of 120 p. W√Hz and a time constant τ of 20 ns were measured; this corresponds to a noise equivalent temperature of 60 nK√Hz and a specific detectivity D* of 1.8×106 cm√HzW. A more relevant criterion for comparing optical sensors is the D*√τ ratio. In the case presented, this ratio is equal to 1.3×1011 cm/J which is one of the best values published at this time. Such performances should give competitive composite or antenna coupled bolometers compared to existing sensors for wavelengths greater than 20 μm.
Modeling of Tamm-like states in superlattices from a simple tight-binding method
Authors: Chowdhury Andalib A. , Maziar C. M.
Published: July 2002

Superlattices provide an excellent experimental tool for the study of surfacelike behavior in periodic structures such as a semiconductor crystal. Superlattices permit the construction of an arbitrary model surface for a particular study. A simple tight-binding model describing the existence of Tamm-like states in superlattices is presented. Using this method it is possible to derive the energy levels and the envelope wave functions of the surfacelike states in an analytical form.
Metal/insulator/semiconductor tunnel diodes formed by the oxidation of polycrystalline diamond films
Authors: Gonon P. , Deneuville A. , Gheeraert E. , Fontaine F. , Lenormand F.
Published: July 2002

Polycrystalline diamond films have been annealed under O2 at 600 °C, or have been dipped in a H2SO4/CrO3 solution. Both treatments result in the formation of a thin electrically insulating layer at the top of the films. Subsequent metallization results in the formation of a metal/insulator/diamond tunnel diode with a potential barrier for holes of 0.85 eV, and with a Fermi level localized at about 0.45 eV above the diamond valence band.