bluuebunny/crossref_metadata_2025 huggingface dataset:
Low- and high-field transport properties of pseudomorphic InxGa1−xAs/InP (0.73≤x≤0.82) p-type modulation-doped single-quantum-well structures
Authors: Mesquida Küsters A. , Kohl A. , Heime K. , Schäpers Th. , Uhlisch D. , Lengeler B. , Lüth H.
Published: July 2002

The transport properties of three p-type modulation-doped InxGa1−xAs/InP (0.73≤x≤0.82) single-quantum-well structures grown by metalorganic chemical-vapor deposition are reported. High carrier mobilities of μH=7800 cm2/V s coupled with total carrier concentrations of pS=2.1×1012 cm−2 were reached, for example, for x=0.73 at 5 K. Shubnikov–de Haas and quantum Hall-effect measurements at 50 mK showed the population of two spin-split V3/2 subbands. Using p-modulation-doped field-effect transistors with a gate length of LG=1 μm, fabricated on the same samples, the carrier transport at moderate and high fields was investigated at 77 K. Thereby, the population of the heavy-hole subband and, above a critical field, also the occupation of the light-hole subband were verified. With the help of dc transconductance (gmext-VGS) and magnetotransconductance measurements a decoupling between both subbands at cryogenic conditions and moderate fields was observed, resulting in two clearly defined conducting channels. Further analysis of the measured mobility-voltage (μ-VGS) and velocity-field (vavg-Eavg) profiles revealed that carrier transport in compressively strained two-dimensional hole gas (2DHG) systems is strongly affected by intersubband scattering and shows a nonlinear behavior at low fields, caused by the zone-center degeneracy of their E-k∥ distribution.
Self-defocusing of nanosecond laser pulses in ZnTe
Authors: Ji W. , Kukaswadia A. K. , Feng Z. C. , Tang S. H.
Published: July 2002

We report the observation of self-defocusing in ZnTe across a range of wavelengths just below the band edge. By using nanosecond laser pulses, the transmitted spatial profiles and the optical limiting behavior are measured. We also compare the experimental results to a theory, which assumes that the self-refraction is caused by free carriers created by single-photon absorption. By fitting this theory to the experimental findings, the nonlinear refractive cross-sections are deduced. We find that the values of the nonlinear refractive cross-sections are in agreement with a band-filling model.
Characteristics of conduction minibands of Si/Si1−xGex superlattices
Authors: Cho Sung M. , Lee Hong H.
Published: July 2002

Examined here are the characteristics of conduction bands of Si/Si1−xGex superlattices as affected by the type of well and barrier making up the superlattices and their individual layer thicknesses. Common to all five basic structures studied is the presence of islands in the middle of minibands that are forbidden energy gaps. Optical transitions across the islands can be utilized for photodetection in the very far infrared range. Merging of minibands of two adjacent states into a single one is a distinct feature of double well-and-barrier superlattices.
Luminescence and photomodulated transmission measurements in InGaAs/GaAs modulation doped single quantum wells
Authors: Iikawa F. , Bernussi A. A. , Soares A. G. , Plentz F. O. , Motisuke P. , Sacilotti M. A.
Published: July 2002

Photoluminescence and photomodulated transmission measurements on In0.2Ga0.8As/ GaAs/Al0.3Ga0.7As modulation doped pseudomorphic single quantum wells are presented. Photomodulated transmission spectra at low temperatures showed sharp lines that are separated with respect to the luminescence peaks due to the Stokes shift. From the Stokes shift we estimated the Fermi energy and the two-dimensional electron gas density. The obtained results are in good agreement with Shubnikov–de-Haas data. The temperature dependence of the optical spectra was also investigated. The photomodulated transmission technique is shown to be a good tool to evaluate the electronic properties of modulation doped single quantum well structures, including an estimation of the Fermi energy and the two-dimensional electron gas density.
New nonstationary velocity overshoot phenomenon in submicron gallium arsenide field-effect transistors
Authors: Jyegal J. , DeMassa T. A.
Published: July 2002

The gallium arsenide metal-semiconductor field-effect transistor (GaAs MESFET) with a gate length of 0.3 μm is numerically simulated in two dimensions using a semiclassical hot-electron transport model. A new type of nonstationary velocity overshoot is predicted in submicron devices. This new velocity overshoot phenomenon occurs in the drain region when the applied drain voltage is sufficiently large, so that a strong stationary high-field domain extended near the drain is developed in the region between the gate and the drain. The mechanism is found to be associated with a large mobility change by macroscopic intervalley transfer from the low-mobility higher energy satellite valleys to the high-mobility lower energy central valley in GaAs. In submicron GaAs MESFETs, this situation occurs as the electrons are rapidly cooled from the higher energy satellite valleys below the threshold energy during their transport across the depletion layer that developed near the drain electrode under large drain-bias conditions. Even though the mechanism involves initially heavy electrons under decreasing electric field conditions, it is found that a substantially high velocity overshoot is exhibited. The peak drift velocity attained reaches twice the maximum drift velocity obtainable under stationary conditions.
Initial stages of epitaxial growth of Y-stabilized ZrO2 thin films on a-SiOx/Si(001) substrates
Authors: Bardal A. , Matthée Th. , Wecker J. , Samwer K.
Published: July 2002

The initial stages of crystallization and growth of epitaxial Y-stabilized ZrO2 (YSZ) thin films on Si (001) substrates covered with amorphous native oxide were investigated by transmission electron microscopy (TEM) and reflection high-energy electron diffraction (RHEED). The YSZ crystallizes by solid-phase epitaxy with an initial thickness of 1 nm. The crystallization is initially incomplete, yielding both epitaxial and disordered regions of the YSZ film. In situ RHEED measurements showed the lattice parameter of the YSZ gradually decreased during growth, reaching the bulk value at a film thickness of 5–7 nm. For a larger thickness, the film is fully elastically relaxed. TEM revealed misfit dislocations at the YSZ/Si interface. The average spacing between misfit dislocations with Burgers vector b=1/2 〈110〉 was measured as 8.3 nm, showing epitaxial misfit strain to be fully accommodated by misfit dislocations. Thermal strain introduced during cooldown from the deposition temperature is fully elastically accommodated. For YSZ thicknesses below 7 nm, the thickness of the regrown layer of silicon oxide at the YSZ/Si interface is 0–0.5 nm.
Fine structure in the χ(2) signals of inorganic-organic nanocomposites
Authors: Kador L. , Fischer R. , Kasemann R. , Brück S. , Dürr H.
Published: July 2002

Thin films of organically modified ceramics with nonlinear-optical-active chromophores produced in a sol-gel process exhibit Maker fringe signals which are superimposed by a periodic fine structure. The fine structure is shown to be due to Fabry–Perot resonances of the second-harmonic light which are stronger as compared to the amplitude corresponding to the regular Fresnel surface reflectivity by one to two orders of magnitude. The effect which is also observed on unpoled samples is tentatively ascribed to an accumulation and partial spontaneous orientation of the chromophores at the film surfaces.
Photoluminescence of GaAs doped with dimethylaluminum methoxide during organometallic vapor phase epitaxy
Authors: Park Y. , Skowronski M.
Published: July 2002

Photoluminescence (PL) measurements of GaAs doped with dimethylaluminum methoxide during organometallic vapor phase epitaxy are reported. The near-band-edge luminescence intensity decreases by at least a factor of 104 at low growth temperatures, which correlates well with the incorporation of oxygen. Concomitantly, several new PL peaks appeared at 72, 97, 150, 410, and 510 meV below the band edge. Based on the dependence of PL peak position on excitation power density, these bands have been interpreted as due to donor-acceptor type transitions involving deep oxygen-related levels. The intensity of near-band-edge emission was not affected by the annealing of doped layers at 800 °C under arsenic overpressure, which indicates that the doping-induced deep centers are thermally stable.
Atomic layer epitaxy and structural characterization of InP and InAs/InP heterostructures
Authors: Tran C. A. , Masut R. A. , Brebner J. L. , Jouanne M.
Published: July 2002

We report the growth and structural properties of InP, InAs/InP strained single quantum wells and short-period InAs/InP strained layer superlattices by atomic layer epitaxy. A self-limiting growth close to 1 monolayer/cycle has been obtained for InP and for InAs with low substrate temperatures between 350 and 360 °C. The samples were grown on InP (001) substrates and characterized by high resolution x-ray diffraction, grazing-incidence x-ray reflectometry, and Raman spectroscopy. The interference of x-ray wave fields in the grown structures observed by both types of x-ray measurements can be used to measure nondestructively the thickness of the deposited films with relatively high precision. High resolution x-ray diffraction and grazing-incidence x-ray reflectometry of the InAs/InP superlattices confirm the periodicity of the structures in agreement with theoretical predictions. Raman spectroscopy shows doublets of folded acoustic modes as well as InAs-like and InP-like confined longitudinal optical phonons in the InAs/InP superlattices. Results indicate that, despite the 3.2% lattice mismatch, atomic layer epitaxy is a powerful method for fabricating highly strained structures with atomically controlled heterointerfaces.
Study of the crystal growth of a (15,17,1) vicinal plane on a Si(110) surface using high-temperature scanning tunneling microscopy
Authors: Yamamoto Youiti , Sueyoshi Takashi , Sato Tomoshige , Iwatsuki Masashi
Published: July 2002

High-temperature scanning tunneling microscopy was used to study the crystal growth of a (15,17,1) vicinal plane on a Si(110) surface, and the dynamic behavior of surface Si atoms at high temperature was directly observed. It was found that an impurity hillock, which may be SiC on the surface, pins step flows and bunches them together to form a vicinal plane such as (17,15,1), (17,15,1̄), (15,17,1), and (15,17,1̄) at 710 °C. The vicinal plane has a faceted structure and is formed by a periodic arrangement of monolayer steps and has a terrace of 2.5 nm in the 〈111〉 direction. The step-edge direction is 〈112〉. At 695 °C, it was also found that the 16 structure was formed on a flat area. It was confirmed that the 16 structure and the vicinal plane (15,17,1) coexisted in a temperature range of about 700 °C to room temperature.
The metastable Al-Zr alloy thin films prepared by alternate sputtering deposition
Authors: Ho Jin-Kuo , Lin Kwang-Lung
Published: July 2002

Al-Zr alloy thin films are prepared via alternate sputtering deposition. The as prepared films exhibit metastable phases including amorphous, cubic ZrAl3(L12), supersaturated Al-in-Zr close-packed hexagonal structures, and Zr-in-Al face-centered cubic solid solutions with uniform composition distribution. The amorphous phase occurs in the compositions ranging from 16.8 to 69.9 at. % Al. The formation of amorphous structure is considered to follow the mechanism of solid state reaction amorphization or surface diffusion induced mixing. Additionally, the formation of a metastable cubic ZrAl3 intermetallic compound is attributed to its low nucleation energy barrier with respect to the stable tetragonal ZrAl3 (DO23). The heat of crystallization of the amorphous phase is also measured to investigate the metastability of the amorphous phase.
The double resonant enhancement of optical second harmonic susceptibility in the compositionally asymmetric coupled quantum well
Authors: Lien Chenhsin , Huang Yimin , Lei Tan-Fu
Published: July 2002

The second harmonic susceptibility due to the intersubband transitions in the three-level GaAs/AlxGa1−xAs/AlyGa1−yAs compositionally asymmetric coupled quantum well (CACQW) under the influence of the applied electric field is investigated theoretically. The subband eigenenergy En of the CACQW structure could be designed to form an equally spaced energy-level ladder. Since the eigenenergy spacing could be designed to resonate with the pumping source, the second harmonic susceptibility could be greatly enhanced through the double resonance. Based on the theoretical calculations, the second harmonic susceptibility as high as 220 nm/V can be achieved for the CACQW. This is a more than three orders of magnitude enhancement as compared to that of the bulk GaAs. In addition to the design of CACQW structure, the double resonance can also be achieved by biasing the CACQW under a proper electric field. The extinguishment of the second order nonlinear optical effect by the applied electric field has also been studied. This phenomenon is attributed to the symmetry restoration of envelope wave functions of the CACQW structures under the quenching electric field ℰoff. A simple physical model to estimate the ℰoff has also been developed.
Spectroscopic characterization of band discontinuity in free-standing CdZnS/ZnS strained layer superlattices
Authors: Yokogawa T. , Ishikawa T. , Merz J. L. , Taguchi T.
Published: July 2002

We present the results of luminescence studies for free-standing CdZnS/ZnS strained layer superlattices (SLSs). The band discontinuity is estimated by an analysis of the luminescence results in terms of a finite-potential well model. CdZnS/ZnS SLSs are grown by metal-organic vapor phase epitaxy at 350 °C on (100) GaAs. Photoluminescence (PL) measurements of the CdZnS/ZnS SLS at 1.4 K show intense, sharp excitonic emission in the blue-ultraviolet spectral region. With decreasing CdZnS well width, the PL peaks shift to higher energy. The quantum transition energies are calculated, including the effect of exciton binding energy and elastic strain. A free-standing SLS is assumed. In a Cd0.3Zn0.7S/ZnS SLS, the analysis of the data yields a zero-stress band discontinuity of ΔEc=461 meV and ΔEv=88 meV, which is in extremely good agreement with the data calculated from Harrison’s model (465 and 84 meV, respectively). The band discontinuity over the entire Cd composition range is also estimated.
Combined experimental and modeling studies of laser-assisted chemical vapor deposition of copper from copper(I)-hexafluoroacetylacetonate trimethylvinylsilane
Authors: Han Jaesung , Jensen Klavs F.
Published: July 2002

We describe laser-assisted chemical vapor deposition of copper from copper(I)- hexafluoroacetylacetonate trimethylvinylsilane onto silicon and metal substrates. The deposition process was driven thermally with 514.5 nm radiation from an argon ion laser. The relationship between operating parameters and the materials properties of deposited copper lines was investigated experimentally and interpreted through models of the deposition process. The as-deposited Cu lines were of high purity, showing no detectable carbon and oxygen contamination, and at optimal conditions, the resistivity of the lines was comparable to that of bulk copper. The line morphology was strongly dependent upon laser power with volcano shapes appearing at higher powers, as well as spatially periodic structures occurring in a narrow range of laser powers and scanning speeds. A mathematical model was developed for the laser heating and deposition processes to provide insight into the fundamental processes underlying the observed phenomena. Optical and thermophysical property changes caused by the continuously growing deposit were included, thereby enabling accurate predictions of the laser induced temperature distributions. The surface temperature distribution and the maximum temperature rise at the center of the laser beam were significantly affected by the deposit. The model further allowed identification of kinetic parameters for the deposition process. The volcano-shaped deposits were attributed to enhanced desorption of precursors in the center of the irradiated spot, and the periodic structures were interpreted in terms of a nonlinear coupling between heat conduction and chemical kinetics.
Long Josephson junctions with uniform dc and rf driving currents: General results for the phase-locked regimes
Authors: Cirillo M. , Cocciolo P. , Merlo V. , Gro/nbech-Jensen Niels , Parmentier R. D.
Published: July 2002

We investigate the dynamics of a long overlap Josephson junction in the presence of constant and sinusoidally time-varying currents on a finite-length spatial interval imposing open circuit boundary conditions at the ends. We scan the behavior of the system in parameter plane regions where the phase locking between the fluxon oscillations in the junction and the external time-varying field is possible. This scanning is performed for different values of the dc driving term and for lengths of the spatial interval ranging from 3.8 up to 15 and dissipation parameters ranging from 0.025 to 0.25. In spite of the complexity of the system and of the broad range of parameters investigated we find that the response to the rf excitation presents general features that can be well understood in terms of current-voltage characteristics of the junctions (and related experimental parameters). The results are compared with a recent theoretical model based on a perturbation approach of the sine-Gordon Hamiltonian.
Superconducting and structural properties of Nd2−xCexCuO4−y thin films on perovskite and fluorite substrates
Authors: Mao S. N. , Xi X. X. , Li Qi , Venkatesan T. , Beesabathina D. Prasad , Salamanca-Riba L. , Wu X. D.
Published: July 2002

High quality epitaxial Nd2−xCexCuO4−y (NCCO) thin films were fabricated on various substrates by pulsed-laser deposition using N2O reactive gas. The similarities and dissimilarities of the superconducting and structural properties of NCCO films, on perovskite-type substrates such as LaAlO3, NdGaO3, and SrTiO3 and on a fluorite-type substrate of yttria-stabilized zirconia (YSZ), were investigated systematically as a function of film thickness by transport measurements and structural analysis. A remarkable reduction of Tc was observed when the film was thinner than a critical thickness, which strongly depends on the substrate. The critical thicknesses for which Tc is 80% of Tc max are 1200, 1000, 600, and 450 Å for LaAlO3, NdGaO3, SrTiO3, and YSZ, respectively. YSZ turns out to be the best candidate for the growth of very thin NCCO films among the substrates studied. These results show a strong correlation between the strain and Tc in NCCO thin films and point the way to the fabrication of n-type superconducting electric field devices using ultrathin NCCO films.
Structural characterization of a CuO/MgO artificially superstructured film by the x-ray diffraction method
Authors: Sohma M. , Kawaguchi K. , Fujii Y.
Published: July 2002

A CuO/MgO epitaxial artificially superstructured film [CuO(50 Å)/MgO(40 Å)]40 was successfully grown and its structure was studied by x-ray diffraction (XRD). The film was found to have a texture in which the (111) planes of monoclinic CuO and the (001) planes of cubic MgO were layered perpendicular to the film plane. Its lateral structure was revealed by precession photographs where the CuO [101̄] axis is oriented approximately along the MgO [100] axis in the film plane. The XRD pattern, observed over a wide range of scattering vectors perpendicular to the film plane, was carefully analyzed by an extended step model. The fluctuation of the superlattice period was estimated to be as small as 1 Å.
Investigation of the lateral magnetic force and stiffness between a high-T
c superconductor and magnet of rectangular shapes
Authors: Johansen T. H. , Mestl H. , Bratsberg H.
Published: July 2002

A new experimental setup has been designed to measure with high-resolution the horizontal force between a permanent magnet levitating over a high-temperature superconductor. We have studied the lateral stability as well as elastic stiffness associated with small-amplitude (<10 μm) vibrational motion both as functions of levitation height and relative horizontal displacements. The results, obtained for a sintered sample of YBa2Cu3Ox and a NdFeB magnet of rectangular geometry, are found to agree well with a recent quantitative theory applicable to granular superconductors.
H
K
distributions and H
C calculations for magnetic recording particles
Authors: Parker F. T. , Berkowitz A. E. , Slade S. B.
Published: July 2002

Magnetization vs applied magnetic field data for several different classes of particulate magnetic recording media have been analyzed by fitting the first quadrants to log-normal distributions in anisotropy fields using the Stoner–Wohlfarth assumptions. Materials examined included small and large particle γ-Fe2O3 and partially reduced γ-Fe2O3 (precursor), Co-adsorbed precursor, CrO2, Fe metal, pure Ba ferrite, and Co–Ti substituted Ba ferrite. Measurement temperatures ranged from 4.2 to 296 K. Of the two distribution parameters, 〈HK〉G (geometric mean anisotropy field) and σ (standard deviation), σ generally shows little thermal variation. 〈HK〉G generally exhibits the expected temperature response, but shows an anomalous linear temperature dependence for the small spinel particles (which is related to spin canting), and a modest jump at low temperatures for the Fe particles (which is due to interaction with the Fe oxide outer layer). Substituted Ba ferrite shows strong temperature dependence of both parameters, due to a large K2 anisotropy constant, which the Stoner–Wohlfarth analysis does not properly account for. Moments additive to the distribution calculations were found for CrO2 and the small spinels. From the observed temperature dependence, the additional moment for the former arises from superparamagnetism, and for the latter from spin canting. Extension of the modeled first quadrant moments into the second quadrant yields coercivities much closer to experimental values than those predicted by mean anisotropy fields or by curling models. Thus, coherent rotation is close to, if not the easiest, reversal mode in these particles.
Magnetization reversal in SmFeTi (002) textured films with the ThMn12 structure
Authors: Panagiotopoulos I. , Zouganelis G. , Niarchos D.
Published: July 2002

SmFeTi films with the ThMn12 structure were prepared with a rf magnetron technique. The magnetization reversal mechanisms are studied by magnetization measurements. The results indicate a domain wall pinning mechanism.
Mechanical alloying process of Cu-Zn system studied by 63Cu nuclear magnetic resonance
Authors: Li Bai-Qin , Wang Ye-Ning
Published: July 2002

The process of mechanical alloying (MA) and the phase transformations that accompany ball milling the elemental Cu and Zn powder mixtures have been investigated by 63Cu nuclear magnetic resonance spectrometry and x-ray diffractometry. The 63Cu Knight shifts in mechanically alloyed clusters of α, β, γ, or ε phases show significantly different from that of heavily deformed pure copper, indicating a reduction of s-like electron density. The wave functions around the Cu atoms are likely to assume a greater ‘‘p’’ character when Zn is added. The formation and development of alloyed clusters are caused by the strong bonding interactions between Cu and Zn when the mixtures are ball milled. Under present conditions the alloying reaction is accomplished after milling about 15 h for Cu-39 at. % Zn, and it is faster when the Zn content is smaller. No amorphous phase was detected in the Cu-Zn system. The local atom rearrangement in the alloyed clusters is facilitated by the onset of the internal stress induced by MA. This might prevent the retaining of amorphous phase even if partial amorphization may occur during the MA process.
Direct determination of group velocity surfaces in a cuspidal region in zinc
Authors: Kim Kwang Yul , Sachse Wolfgang
Published: July 2002

A direct determination of group velocity surfaces of zinc from the group velocities measured in various directions within and without a cuspidal region is described. A zinc crystal disk oriented in the symmetry direction [0001] is used as a specimen. Quasilongitudinal (QL) and quasitransverse (QT) elastic pulses propagating in a wide range of directions are generated by a broadband pointlike source activated by the fracture of a tiny glass capillary on the surface of the specimen and they are detected at epicentral and off-epicentral positions on the opposite face by a miniature capacitive transducer which senses a displacement normal to the surface. The group velocities associated with QL and QT modes are directly measured from the detected signals. The QL mode arrival is easily identified as the first point from which the signal jumps from the noise level. In the cuspidal region, there are three branches of QT group velocity: fast QT (FQT) ray branch, intermediate speed QT (IQT) ray branch, and slow QT (SQT) ray branch. It is observed that the arrivals of FQT, IQT, and SQT rays correspond to the first zero crossing, to the first negative minimum, and to the second local minimum, respectively, in the displacement signal. In the epicentral signal, both IQT and SQT rays coincide, whose arrivals correspond to single sharp negative minimum, and the FQT ray arrival is found at the first zero crossing after the arrival of a longitudinal wave. Outside the cuspidal region, both FQT and IQT branches disappear and so do their corresponding characteristics, i.e., the zero crossing and sharp negative minimum in the displacement curve. The SQT ray arrival outside the cuspidal region is observed at the first sharp minimum in the displacement signal. Finally, the group velocities of pure transverse waves with shear horizontal polarization propagating in various directions of a [0001] zonal section within and without the cuspidal region are measured with the miniature piezoelectric shear transducer (PZT) source and shear PZT detector.
Small-angle x-ray scattering study of anodically oxidized porous silicon layers
Authors: Naudon A. , Goudeau P. , Halimaoui A. , Lambert B. , Bomchil G.
Published: July 2002

Small-angle x-ray scattering was used to investigate the microstructural change induced by electrochemical oxidation of porous silicon (PS) layers. It is shown that when the oxidation level increases, the size of the crystalline Si domains, which constitute the PS layer, decreases. This size reduction is correlated to the blue-shift observed in the photoluminescence spectra when the oxidation level is increased. Moreover, we found that a ‘‘fuzzy’’ surface appears between pores (voids) and matter when the samples are electrochemically oxidized. This interface is found very sharp for the as-prepared and nonoxidized PS layers.
Contact-related deep states in the Al-GaInP/GaAs interface
Authors: Huang Z. C. , Wie C. R.
Published: July 2002

Deep levels have been measured in a molecular beam epitaxy grown Ga0.51In0.49P/GaAs heterostructure by double correlation deep level transient spectroscopy. Gold (Au) and aluminum (Al) metals were used for a Schottky contact. A contact-related hole trap with an activation energy of 0.50–0.75 eV was observed at the Al/GaInP interface, but not at the Au/GaInP interface. To our knowledge, this contact-related trap has not been reported before. We attribute this trap to oxygen contamination, or a vacancy-related defect, VIn or VGa. A new electron trap at 0.28 eV was also observed in both Au- and Al-Schottky diodes. It depth profile showed that it is a bulk trap in a GaInP epilayer. The temperature dependent current-voltage characteristics show a large interface recombination current at the GaInP surface due to the Al contact. The energy distribution of the interface state density showed a maximum at EV+0.85 eV within the band gap. Concentration of the interface trap and the magnitude of recombination current are both reduced by a rapid thermal annealing at/or above 450 °C after aluminum deposition. The Al Schottky barrier height also increased after a 450 °C annealing.
Nonperturbative ion etching of YBaCuO thin films
Authors: Xavier P. , Fournier T. , Chaussy J. , Richard J. , Charalambous M.
Published: July 2002

Conventional Ar ion etching deteriorates the features of YBaCuO superconducting thin films, because of heating and ion damage. We demonstrate here the interest of two other approaches: Ar ion etching with liquid nitrogen cooling and Xe ion etching.
Effect of alloy scattering on the longitudinal hot electron drift velocity in n-Hg0.8Cd0.2Te in the extreme-quantum-limit magnetic fields at low temperatures
Authors: Banerji Pallab , Sarkar C. K.
Published: July 2002

Longitudinal hot electron drift velocity in n-Hg0.8Cd0.2Te in the extreme quantum limit has been investigated at low temperatures using displaced Maxwellian approximation. The model includes various complexities such as band nonparabolicity, quantum screening due to magnetic quantization, and Landau level broadening due to impurity fluctuations. The influence of alloy scattering on the drift velocity has been examined. The field dependences of hot electron drift velocity in n-Hg0.8Cd0.2Te have also been studied.
Comment on ‘‘Inverse problem for the nonexponential deep level transient spectroscopy analysis in semiconductor materials with strong disorder: Theoretical and computational aspects’’ [J. Appl. Phys. 74, 291 (1993)]
Authors: Eiche C. , Maier D. , Weese J. , Honerkamp J. , Benz K. W.
Published: July 2002

It is shown that a recently proposed analysis of deep level transient spectroscopy signals with a regularization method by Batovski et al. [J. Appl. Phys. 74, 291 (1993)] can be simplified significantly by calculating the relaxation time spectrum of the capacitance transient with a regularization method directly.
Acousto-optic actively mode-locked frequency-doubled continuous-wave Nd:YAG laser
Authors: Bai Jintao , Qiao Xueguang , Wang Shuicai
Published: July 2002

We report a 200-MHz ultrahigh frequency acousto-optic mode-locked and KTiOPO4 stable intracavity frequency-doubled Nd:YAG laser pump source, which included a single-lens telescopic and L-type folded-arm resonator. 20 W high average mode-locked power and 2.0 W average mode-locked doubled green light power achieved at 4.0 kW single lamp pumped power, respectively. The instability of second-harmonic light output power was effectively suppressed by inserting a quarter wave plate at the fundamental laser wavelength inside the cavity.
Threshold characteristics of multimode semiconductor lasers
Authors: Casperson Lee W. , Khoshnevissan Mehdi
Published: July 2002

The effects of spontaneous emission on the threshold characteristics of multimode laser oscillators with mixed line broadening are considered in detail. Most previous studies of multimode laser operation have emphasized the two limits of homogeneous and inhomogeneous broadening. With homogeneous broadening there is a tendency for oscillation in a single longitudinal mode, while in the inhomogeneous limit oscillation over much of the gain spectrum is expected. All practical lasers are somewhere between these limits, and this study explores the mode characteristics of lasers with mixed line broadening. Special attention is given to the important practical case of semiconductor diode lasers, and band-to-band absorption is fully included.
Computer simulation of thin-film media noise using an autocorrelation function along the track direction
Authors: Yoshida Kazuetsu , Hara Miki , Uesaka Yasutaro , Nakatani Yoshinobu , Hayashi Nobuo
Published: July 2002

The causes of thin-film media noise are discussed by deriving a formula which shows a direct relationship between the noise spectrum and the magnetization configuration of a thin-film medium. This formula is derived by Fourier-transforming the autocorrelation function of jMx-Mz along the track direction, where Mx and Mz are the longitudinal and vertical components of magnetization, respectively. Noise and signal spectra are computed by means of this formula. The computed noise spectra are the maximum for a relatively long wavelength. Their form and intensity are shown to be strongly affected by the anisotropy constant and the axis orientation of easy magnetization.
Two-zone equilibria of Tl-Ca-Ba-Cu-O superconductors
Authors: Aselage T. L. , Venturini E. L. , Van Deusen S. B.
Published: July 2002

Phase equilibria in the Tl-Ca-Ba-Cu-O system have been studied at sample temperatures that are near, but below, the onset of melting. Independent control of the partial pressures of oxygen P(O2) and thallous oxide P(Tl2O) was achieved through the use of a two-zone furnace. Stable ranges of P(Tl2O), P(O2), and sample composition for individual Tl superconductors, including 2122, 2223, 1122, and 1223 (the latter intergrown with about 10% 2223) have been determined. A qualitative understanding of these stable ranges, based on the relative Tl content and formal oxidation state of the cations within a structure type, has been developed. From this information, equilibrium phase diagrams for Tl superconductors with Ca:Ba:Cu ratios of 1:2:2, 2:2:3, and 3:2:4 are proposed. These diagrams provide process information for the two-zone synthesis of bulk materials and thin and thick films. The superconducting transition temperatures of the individual phases produced by near-equilibrium processing are both reproducible and relatively insensitive to changes in the process conditions.
Resistive measurement of the temperature dependence of the penetration depth of Nb in Nb/AlOx/Nb Josephson junctions
Authors: Kim D. H. , Gray K. E. , Hettinger J. D. , Kang J. H. , Choi S. S.
Published: July 2002

The temperature dependence of the penetration depth of Nb films was determined from resistive transitions of Nb/AlOx/Nb Josephson junctions in a constant magnetic field applied parallel to the junction planes. Distinct resistance peaks were observed as temperature decreases and those peaks were found to appear when the total flux threading the junction equals an integral multiple of the flux quantum. From this condition, the penetration depth at those peak positions has been determined. The temperature dependence was well described by either the dirty local limit or the two-fluid model. This method can be useful for a highly fluctuating system such as high-temperature superconductors.
Modeling of suppressed dopant activation in boron- and BF2-implanted silicon
Authors: Kinoshita H. , Huang T. H. , Kwong D. L.
Published: July 2002

The diffusion and activation of boron following the rapid thermal annealing (RTA) of ion-implanted boron and BF2 are investigated. The early stage of RTA is characterized by the enhancement of boron diffusion and the suppression of dopant activation throughout the impurity depth profile. This phenomenon is explained and modeled by considering the reaction kinetic between the electrically activated boron species and the inactive boron-silicon interstitialcy. The self-interstitial supersaturation created by ion implantation damage is believed to lower the boron activation during RTA by forming electrically inactive boron interstitialcies. A model that accurately predicts both the enhanced diffusion and the suppressed activation of boron during RTA is presented.
Structural and electrical properties of rf magnetron-sputtered Ba1−xSrxTiO3 thin films on indium-tin-oxide-coated glass substrate
Authors: Kim Tae Song , Kim Chong Hee , Oh Myung Hwan
Published: July 2002

Structural and electrical properties of rf magnetron-sputtered Ba1−xSrxTiO3 thin films (x=0, 0.25, 0.5, 0.75, 1) on indium-tin-oxide-coated glass substrate were studied. The dense Ba1−xSrxTiO3 thin films sputtered from five different targets at the deposition temperature of 550 °C had individual orientations. The results of compositional analysis in films showed the deviation from the stoichiometry [(Ba+Sr)/Ti=1.009−1.089] with the increase of SrTiO3 content in the targets. The tetragonality in crystallographic structure of Ba1−xSrxTiO3 thin films was not observed even in the case of <x=0.3. The large frequency and composition dependence of ε′ and tan δ were also observed. There were no significant changes in ε′ up to x=0.5; however, the maximum value (ε′=204 at 100 kHz) around x=0.25 was in accordance with the results of bulk Ba1−xSrxTiO3 except at 1000 kHz. Above x=0.5, however, larger decreases of the dielectric constant were observed. The maximum values of ε′ in x=0.25, 0.5, 0.75 were shown around the measuring temperatures of 50, 25, −20 °C, respectively, indicating the diffuse phase transition in Ba1−xSrxTiO3 thin films. The observed increases in ε′ and tan δ above 125 °C are well explained with the barrier model. Nonlinear current-voltage characteristics in Ba1−xSrxTiO3 thin films showed that the lower the SrTiO3 content, the leakier Ba1−xSrxTiO3 thin films became, and the increase of SrTiO3 content leads to the increase of the breakdown fields from 1.7 to 2.7 MV/cm.
Increase of multilayer x-ray reflectivity induced by pulsed laser heating
Authors: Zigler Arie , Fraenkel Moshe , Henis Zohar , Kolka Eyal , Eliezer Shalom
Published: July 2002

The reflectivity of tungsten-carbon (W-C) multilayers, heated by 7 ns Nd-YAG laser pulses was measured using soft x-ray radiation at 4.4 nm. The reflectivity permanently increased and the Bragg angle decreased after heating the multilayer at fluences of 0.3 J/cm2. The reflectivity increase was achieved in a narrow domain of heating fluences. A quantitative model based on laser absorption and heat transport, that explains the melting phenomenon of tungsten and the heating to a temperature where graphitization is possible in the carbon layers, is presented. The two phenomena: (a) increase in x-ray reflectivity and (b) expansion of the multilayer mirror can be explained by the laser heating. The improvement of reflectivity is caused by the smoothening of the tungsten layers due to melting, while the change in the spacing is attributed to the carbon phase transition (graphitization).
YBa2Cu3O7−x films on yttria-stabilized ZrO2 substrates: Influence of the substrate morphology
Authors: Brorsson G. , Olsson E. , Ivanov Z. G. , Stepantsov E. A. , Alarco J. A. , Boikov Yu. , Claeson T. , Berastegui P. , Langer V. , Löfgren M.
Published: July 2002

c-axis-oriented YBa2Cu3O7−x (YBCO) thin films were laser deposited on (001) yttria-stabilized ZrO2 (YSZ) substrates with different surface morphologies. The in-plane orientation of the films on smooth substrates was sensitive to the deposition conditions, often resulting in mixed orientations. However, a strongly dominating [110]YBCO//[110]YSZ orientation was obtained at a deposition temperature of 770 °C. Films on substrates with surface steps, induced by depositing a homoepitaxial buffer layer or by thermally annealing the substrate, had a [110]YBCO//[100]YSZ orientation when deposited at the same temperature. It was concluded that the [110]YBCO//[100]YSZ orientation was promoted by a graphoepitaxial mechanism. Films prepared under identical conditions on smooth and stepped substrates grew with extended c axes on the former. It is proposed that the extension can be induced by disorder, invoked by a low oxygen pressure and a low density of adsorption sites. The disorder may be eliminated by either an increase of the oxygen pressure or an increase of the density of adsorption sites in the form of steps. The film microstructure influenced the microwave surface resistance, which was similar for films with one exclusive in-plane orientation and higher for films with mixed orientations. The films on the stepped surfaces had superior superconducting properties; inductive measurements gave a Tconset of 88 K, a ΔT(90%–10%)c of 0.2 K, and the transport jc was 1.5×106 A/cm2 at 83 K, for films on substrates with homoepitaxial buffer layers.
Study of interdiffusion in Pd/Cu multilayered films by Auger depth profiling
Authors: Jeon I. J. , Hong J. H. , Lee Y. P.
Published: July 2002

In thin films, diffusion phenomena play an important role for the growth process, and in the understanding of the mechanical, electrical and magnetic properties. The change in the concentration profile due to the interdiffusion by annealing was investigated using Auger electron spectroscopy depth-profiling technique on Pd/Cu multilayered films. It was observed that the initial concentration distributions, which were almost rectangular in the unheated samples, were changed into sinusoidal ones in the annealed films at various temperatures. The concentration-independent interdiffusion coefficients were calculated from the amplitudes of sinusoidal distributions. The activation energy was determined to be 1.66±0.23 eV from the Arrhenius plot. The concentration-dependent interdiffusivity at 150 °C was also estimated using Boltzmann–Matano method.
High frequency capacitance behavior of metal-oxide-semiconductor tunnel structures
Authors: Bredimas Vassiliki
Published: July 2002

We use a simple model based on the steady-state balance of current flowing by tunneling across a Si-SiO2-metal structure. The recombination current is not taken into account. This model yields analytical expressions for the positions of the quasi-Fermi levels at the Si-SiO2 interface which govern the shape of current-voltage and capacitance-voltage characteristics. In particular, the knee which appears in the capacitance-voltage curves of inverse-biased structures and the corresponding plateau or the break in the slope of the 1/C2 versus applied voltage curve is correctly described. Measuring the slopes before and after the plateau or breaking, which marks the boundary of the tunneling domain, could provide information on the surface states when the surface parameters are known or vice versa. The main feature in the interpretation of the curves obtained is the degree of communication between metal and semiconductor, which is dominated by the tunnel transmission coefficient. The main parameters are therefore the oxide thickness and the minority barrier height for reverse polarization and the majority barrier height for forward bias polarization. It turns out that actual structures never have the predicted values for these barriers but notably lower ones when one assumes a perfect oxide layer. This fact may be due to defects in the oxide layer.
Many-body effects on temperature dependence of the interband absorption in quantum wells
Authors: Gumbs Godfrey , Huang Danhong , Fessatidis Vassilios
Published: July 2002

A theory, which includes many-body effects, is presented for the interband absorption in a pseudomorphic Ga1−yAlyAs/InxGa1−xAs/GaAs modulation-doped quantum well. The electron-electron interaction in a degenerate Fermi sea is calculated in the self-consistent Hartree approximation. In addition, the binding energy within an electron-hole pair is included in the ladder approximation as a vertex correction to the response function. Due to the subband structure arising from the quantization by the quantum well, there are different types of excitons associated with the electrons and holes in different subbands. In the theory, the coupling between excitons is calculated in the random-phase approximation. The numerical results for the temperature dependence of the absorption peaks at the Fermi edge (low temperature) and the band edge (room temperature) compare well with available experimental data which was obtained in electric-field modulated photoreflectance experiments. At low temperatures, the theory shows that there are important modifications to the single-particle model. The Fermi energy is extracted by fitting the calculated results to the thermally broadened line shape of the absorption spectrum. As a consequence, the electron density of the quantum wells can be accurately determined by means of this contactless, nondestructive, rapid and simple characterization method. Moreover, information on the alloy composition, built-in electric field, and the interface stress can also be obtained.
Double-grating thin-film devices based on second-order Bragg interaction
Authors: Kasraian Masoud
Published: July 2002

Four coupled-mode equations describing the characteristics of the second-order Bragg interaction are derived for the transverse electric mode of a dielectric film waveguide with periodic corrugations on both the film-cover and the film-substrate interfaces. The characteristics of the frequency-selective filter, output coupler, input coupler, and distributed feedback laser are obtained. Proper choice of the design parameters leads to a frequency-selective filter radiating neither in the cover nor in the substrate, a highly efficient output coupler radiating only in the cover, and an efficient input coupler exciting a guided wave only in one direction. Similarly, in the distributed feedback laser, a suitable choice of the parameters of the two gratings provides a mechanism for controlling the oscillation characteristics of the laser. The attractive feature of the double-grating design is that the characteristics of the thin-film devices are not very sensitive to small deviations of the grating parameters from their designed values.
Elastic and elasto-optic properties of thin films of poly(styrene) spin coated onto Si(001)
Authors: Sun L. , Dutcher J. R. , Giovannini L. , Nizzoli F. , Stevens J. R. , Ord J. L.
Published: July 2002

Brillouin light scattering (BLS) has been used to study a series of three thin films of poly(styrene) spin coated onto Si(001) wafers. Poly(styrene) molecular weights M̄w of 30 000 and 600 000 were used, and the film thicknesses h were in the range 1730 Å<h<3750 Å. It was found that the poly(styrene) films have isotropic elastic symmetry and that all of the films can be described by the same set of two independent elastic constants c11=5.7±0.15 GPa and c44=1.39±0.03 GPa. Both c11 and c44 were determined unambiguously using a least-squares-fitting procedure by observation of the longitudinal guided and Rayleigh modes of the poly(styrene) films. Calculations have been performed of the BLS spectra which include both surface ripple and elasto-optic light scattering mechanisms. From comparisons of the relative mode intensities in the measured and calculated BLS spectra, it is found that the values of the elasto-optic coefficients for poly(styrene) are k11=−1.4±0.4 and k12=−1.6±0.4.
Electrical and optical properties of amorphous (Se0.7Te0.3)100−xInx system
Authors: Mehra R. M. , Ganjoo Ashtosh , Mathur P. C.
Published: July 2002

The effect of In impurity on the dark and photoconductivity and the optical band gap of amorphous (Se0.7Te0.3)100−xInx has been studied. The activation energy ΔE and the pre-exponential factor σ0(0,T) which appear in the dc conductivity are found to increase with increasing In content. The photocurrent, as a function of illumination intensity and time of illumination, has been measured at around room temperature. The bimolecular recombination mechanism is found to be predominant at steady state in all the samples near room temperature. The nonexponential decay, after stopping the illumination, has been explained in terms of localized-localized recombination. The data have been analyzed in terms of the dispersive diffusion controlled recombination and monomolecular recombination is found to be dominant in the transient state. The optical band gap is found to decrease with increasing In content. This decrease has been explained on the basis of metallic bonding due to incorporation of In.