bluuebunny/crossref_metadata_2025 huggingface dataset:
Backscattering spectrometry and ion channeling studies of heavily implanted As+ in silicon
Authors: Brizard C. , Regnard J. R. , Allain J. L. , Bourret A. , Dubus M. , Armigliato A. , Parisini A.
Published: July 2002

Backscattering and ion channeling measurements have been carried out on 〈100〉 silicon wafers implanted with a dose of 3×1016 As+/cm2. These samples have been submitted to laser annealing and then to various thermal annealings in the 350–1000 °C temperature range. Three different crystallographic directions, 〈100〉, 〈110〉, and 〈111〉, have been explored. The deactivated As atom displacement with respect to the lattice sites has occurred already by the first stage of electrical deactivation at 350 °C. The average displacement is constant in the considered temperature range and has been found equal to 0.23±0.06 Å making an angle of 23±8° with the [100] direction. By comparing this finding with the local atomic As arrangement, deduced from previously reported extended x-ray absorption fine structure measurements performed on the same samples, new cluster models are presented. These models consist of As2V and As4V clusters during the very early stage of deactivation, and of several As4V clusters grouped together giving rise to larger AsmVn agglomerates (m up to 12 and n up to 5). In this context, the average As displacement mainly results from the combined displacements of As atoms inside the clusters. The thermal evolution of the As agglomerates at higher temperatures is also discussed.
TeSeF films by TeSe-SeF6/Ar reactive sputtering for ablative optical recording
Authors: Horie Michikazu , Tamura Takanori , Ohgaki Mitsuaki , Yoshida Hidemi , Kisaka Yoshiyuki , Kobayashi Yoshimitsu
Published: July 2002

A TeSeF film with fine polycrystalline structure with a grain size of less than about 1000 Å had desirable properties as a recording layer for an ablative write-once medium. Low media noise, and uniform and regular pit shape were achieved. The TeSeF film was prepared by reactive sputtering of TeSe in a gaseous mixture of Ar and SeF6. The fluorine-doping effect on the crystallinity of TeSe alloy films and a reactive sputtering process with TeSe alloy target in a gaseous mixture of SeF6 and Ar were studied. With SeF6 flow, polycrystalline films with a large grain size of more than a few thousand Å became amorphous in an as-deposited state. After annealing below 100 °C, the amorphous films became fine polycrystalline with a 500–1000 Å grain size. This crystallinity change was due to 20–30 at. % of fluorine incorporating into TeSe networks in a hexagonal structure. Most of fluorine was unstable and evolved immediately during annealing even below 100 °C. But the residual a few at. % of fluorine was strongly incorporated into TeSe networks and constrained grain growth up to about 300 °C. The mechanism of fluorine incorporation in a SeF6/Ar reactive sputtering plasma was investigated by mass spectrometry. Most of fluorine must be incorporated into a TeSe film as a form of TeFx and SeFx which are products of SeF6 fragmentation and a reaction on a TeSe target surface.
Infrared transitions in strained-layer GexSi1−x/Si
Authors: Kahan A. , Chi M. , Friedman L.
Published: July 2002

We present a detailed procedure for calculating confined energy levels of strained-layer GexSi1−x/Si valence-band quantum wells as a function of Ge concentration x and well width L. The method assumes noncoupled wells and takes into account strain and spin-orbit-induced band shifts and splitting. We illustrate the method and find the heavy-hole (hh), light-hole (lh), and spin-orbit split-off (so) subband energy levels for wells deposited on Si(001) and Si(111) oriented substrates. We show results for L=40 Å and Ge concentrations between x=0.0 and x=0.8, and for composition x=0.25 and well widths between L=0.0 and L=100 Å. We plot (x,L) sets which give transition wavelengths between 10 and 11 μm, the central region of an atmospheric transmission window of interest to infrared detector applications. We find that hh ground to excited-state transitions are more sensitive to well width variations, whereas hh to lh or hh to so transitions are more composition dependent. There are (x,L) combinations which permit both hh ground to excited state and hh to lh transitions. Such regions may possess strong absorption cross sections both for excitation at normal incidence and for illumination at an angle. Energy levels for the two substrate orientations are qualitatively similar, but for Si(111) the corresponding transitions occur at smaller x and L. The smaller L minimizes strain relaxation effects.
Dopant electrical activity of Si and Si1−xGex multilayer structures doped with δ-like boron spikes at different temperatures
Authors: Gaworzewski P. , Krüger D. , Kurps R. , Rücker H. , Zeindl H. P.
Published: July 2002

Boron spikes within multilayer structures of Si and of Si1−xGex deposited by means of molecular-beam epitaxy (MBE) at different temperatures have been investigated by secondary-ion-mass spectrometry (SIMS), spreading resistance, and Hall-effect measurements. For a Ge amount of x=7% it is shown that segregation effects, electrical activity of B, steepness of B spikes, and solid solubility of B differ in Si and Si1−xGex at the same deposition temperatures. For Si1−xGex growth the surface segregation is significantly reduced in comparison to the growth of Si layers. Steeper B profiles can be obtained at same temperatures but the amount of electrically inactive B is higher. Calculations of the charge-carrier distributions near the spikes have been performed using classical and quantum mechanical approaches to find out reasons for deviations of the concentration profiles of B and of holes obtained from SIMS and from spreading resistance measurements, respectively.
New insights into the compensation mechanism of Fe-doped InP
Authors: Zach F. X.
Published: July 2002

We have investigated iron-doped semi-insulating and conducting InP using a variety of characterization techniques. The occupation of the iron acceptor level was determined from measurements of the Fe2+ intracenter absorption and the Fe3+ electron paramagnetic resonance signal. These iron concentrations were then related to the total iron content, the free carrier concentration, and the net donor concentration as determined from an impurity analysis. When comparing the sum [Fe2+]+[Fe3+] with the total iron content of the samples measured by glow discharge mass spectroscopy we find that below about 1×1017 cm−3 no significant formation of precipitates occurs. Analysis of the free carrier concentration in semi-insulating crystals allows us to determine the temperature shift of the iron acceptor level with respect to the conduction band. We obtain a value of 4.7×10−4 eV/K somewhat larger than the band-gap shift of InP (3.8×10−4 eV/K). Due to this temperature shift the thermodynamic position of the iron acceptor level at room temperature is about 0.49 eV below the conduction band. This value is significantly smaller than the low temperature value of 0.63 eV. We believe that the temperature shift of deep electronic levels provides insight into the local electron-phonon coupling. Finally we find that the net donor concentration determined by an impurity analysis appears to be too low to account for the observed [Fe2+] concentrations. We present evidence that the missing donor is related to the well-known hydrogen related local vibrational mode at 2315 cm−1. These results indicate that both hydrogen passivation and native defects are necessary for a quantitative understanding of the compensation mechanism in semi-insulating InP.
Fast crystallizing GeSb alloys for optical data storage
Authors: Solis J. , Afonso C. N. , Trull J. F. , Morilla M. C.
Published: July 2002

A systematic study is presented on the optical and structural transformations induced in amorphous Ge1−xSbx alloys with Sb contents in the 0.71≤x≤0.91 range by irradiation with 250 ns laser pulses. The results show that only those films richer in Sb than the eutectics (x=0.85) show appreciable optical contrast upon irradiation. The dominant role of Sb in the performances of this family of alloys is analyzed. The transition from a low-reflectivity amorphous phase to a high-reflectivity extended solid solution of Ge in crystalline Sb is shown to be the key for a new generation of fast reversible optical storage materials in which amorphous-crystalline cycling using ultrashort laser pulses is feasible.
Inverted hysteresis in magnetic systems with interface exchange
Authors: O’Shea M. J. , Al-Sharif A.-L.
Published: July 2002

The effects of interface exchange on magnetic hysteresis are considered for a variety of situations in a two-phase model in which the phases are coupled antiferromagnetically. This work is motivated by studies of Co-CoO nanophase systems where inverted hysteresis loops, a phenomenon closely related to shifted hysteresis loops, are obtained. Some previous examples of systems with inverted hysteresis loops are reviewed and a two-phase model with uniaxial anisotropy and interface exchange is considered. It should be emphasized that this model cannot completely explain inverted hysteresis loops, but it does show that partially inverted loops can be obtained. Cases where H is not along an anisotropy axis are discussed; it was concluded that some alignment of H with the axis of the stronger anisotropy phase is necessary to obtain partially inverted hysteresis.
Resistivity anomaly in nonmagnetic metals with ferromagnetic insulator proximity layers
Authors: Roesler G. M. , Idzerda Y. U. , Broussard P. R. , Osofsky M. S.
Published: July 2002

Epitaxial bilayers and multilayers were prepared using the ferromagnetic insulator EuO and the metals V and Ag. For metal films of thickness 10 nm or less, there is a sharp change in the slope of the resistivity versus temperature, which occurs at 86 K for EuO/V specimens and at 50 K for EuO/Ag specimens. Soft x-ray magnetic circular dichroism measurements showed a clear dichroism for Eu but none for V. Therefore, the dR/dT discontinuity is attributed to a change in spin-dependent surface scattering at the insulator/metal interface caused by the magnetization of the surface layer of Eu++ ions. The difference in temperature between the dR/dT discontinuities between the two metals (and from the bulk EuO Curie temperature of 70 K) is tentatively attributed to the influence of the Ruderman–Kittel–Kasuya–Yosida (RKKY) mechanism.
Investigations of cathode phenomena in pseudospark discharges
Authors: Felsner P. , Stetter M. , Hartmann W. , Linsenmeyer A. , Christiansen J. , Frank K.
Published: July 2002

The cathode phenomena during the conduction phase of a pseudospark discharge are investigated with different cathode materials: Cu, Mo, Ni, Ta, and W/Re. The discharge gas was hydrogen with a gas pressure of 40 Pa. At a pulse duration of 2.7 μs and a maximum current of 9 kA, i.e., at a transferred charge of 11 mC/discharge, mass erosion rates of the cathode materials showed no significant material dependence after 106 discharges. Fast framing photography (end-on, exposure time: 5 ns) of the light emission from the cathode surface revealed several small spots simultaneously, distributed over a cathode surface of 1 cm2. The distribution of metal and hydrogen spectral lines at the cathode surface and in the gap were compared. Metal lines are localized on the cathode surface, whereas the hydrogen Balmer β-line is diffuse over the electrodes surfaces and the gap. Polished electrodes showed, after a single pulse, about 107 craters with 0.5–5 μm in diameter. This is leading to a local current density of about 108 A/cm2 in a single crater.
Analysis of lattice defects induced by ion implantation with photo-acoustic displacement measurements
Authors: Sumie Shingo , Takamatsu Hiroyuki , Morimoto Tsutomu , Nishimoto Yoshiro , Kawata Yutaka , Horiuchi Takefumi , Nakayama Hiroshi , Kita Takashi , Nishino Taneo
Published: July 2002

Subsurface lattice defects in silicon induced by ion implantation were studied by the use of the photo-acoustic displacement (PAD) method based on the sensitive measurements of the surface displacement due to the absorption of laser-light energy. A definite correlation between PAD and displaced atoms density (DAD) was found because PAD reflects the change in thermal conductivity associated with the net amount of displaced atoms in the crystal lattice beneath the surface. According to the linear dependence of 1/PAD on DAD, defects below a DAD of 1014/cm2 (corresponding to implant doses of 2×1011, 8×1010, and 6×1010 ions/cm2 for 100 keV B+, P+, and As+, respectively) were concluded to be point defects. After the DAD reached 1014/cm2, the PAD showed a gentle increase, and this can be attributed to the growth of point-defect clusters. A marked dependence of the PAD on the DAD was not observed beyond a DAD of 1016/cm2. In this region, the presence of an amorphous layer was observed by cross-sectional transmission electron microscopy. Annealing behavior due to low-temperature heating was studied by the change in temperature dependence curves of the PAD, and the results reflected the characteristics of the defects described above.
Photoemission measurement of equilibrium segregation at GeSi surfaces
Authors: Rowe J. E. , Riffe D. M. , Wertheim G. K. , Bean J. C.
Published: July 2002

Photoemission spectroscopy is used to demonstrate that Ge segregates to the first atomic layer of Ge0.5Si0.5(100)2×1 and that the second layer is predominantly Si. Comparison of the resolved signals from the dimer atoms of the reconstructed (100)2×1 surfaces of Ge, Si, and equiatomic Ge-Si alloy shows that the surface layer of the alloy is extremely Ge rich and the second layer is occupied mainly by Si atoms. This result is in good agreement with theoretical predictions.
Experimental verification of the smooth-approximation theory for a space-charge dominated beam in an axisymmetric periodic focusing channel
Authors: Suk H. , Reiser M. , Wang J. G. , Wang D. X.
Published: July 2002

The predictions of the smooth-approximation theory for the effective radius of a space-charge dominated beam in a periodic solenoid focusing channel were checked experimentally over a wide range of focusing conditions. Electron beams with an energy of 5 keV and currents of 50 to 70 mA were transported through a 5-m-long periodic channel and beam radii were measured by an axially moveable phosphor screen and a charge-coupled device camera. The phase advance of betatron oscillation per period without space-charge, σ0, was varied from σ0=45° to σ0=90°. The tune depression due to space-charge, σ/σ0, was in the range of 0.2–0.3. The theoretical results for average beam radius R̄ over one period and the ratio R̄/Rmax were found to agree with the experimental data to better than 5% when a correction due to spherical aberration was taken into account.
An efficient method for the numerical evaluation of resonant states
Authors: Fernando Chenjing L. , Frensley William R.
Published: July 2002

An efficient technique is presented for numerically evaluating the resonant states of semiconductor heterostructures with an arbitrarily complex potential. It employs the modified quantum transmitting boundary method to couple the boundary conditions into the construction of a non-Hermitian discrete Hamiltonian matrix. The resonances are the complex-valued eigenvalues of the corresponding matrix. The boundary terms are energy dependent; therefore the eigenvalue problem is nonlinear. The eigenvalues are located by using a combination of partial-shift tridiagonal LR algorithm for the initial evaluation of eigenvalues and Newton iteration for refinement of the eigenvalues. For one-dimensional problems, this technique is efficient and fast enough to be used in an interactive mode, and it has been incorporated into a general-purpose interactive heterostructure modeling program.
Effect of buried Si-SiO2 interfaces on oxidation and implant-enhanced dopant diffusion in thin silicon-on-insulator films
Authors: Crowder S. W. , Hsieh C. J. , Griffin P. B. , Plummer J. D.
Published: July 2002

The diffusion behavior of phosphorus and boron was used to study point defect kinetics in silicon-on-insulator (SOI) material. Phosphorus marker layers were used to study oxidation enhanced diffusion in bulk and bonded and etched-back silicon-on-insulator (BESOI) material under oxidizing conditions at 750, 800, and 850 °C. An effective interstitial recombination velocity Kox for the buried Si-SiO2 interface in the BESOI material was extracted by fitting the experimentally obtained phosphorus profiles with suprem−iv simulation results. The data can be modeled with a time-independent interface recombination velocity. The same parameter set incorporating this extracted recombination velocity was used to accurately model the implant enhanced diffusion of boron marker layers at 750 and 800 °C in thin SOI films, implying the recombination velocity is independent of the interstitial supersaturation. The expression Kox/DI=4.7×10−3 exp(+1.34/kT) fits this work and also a wide range of literature results at higher temperatures.
Characterization of fluorinated hydrogenated amorphous silicon nitride (a-SiNx:H) alloys
Authors: Shen J. M. , Palsule C. , Gangopadhyay S. , Naseem H. A. , Kizzar S. , Goh Freddy H. C.
Published: July 2002

Fluorinated a-SiNx:H(0≤x≤0.19) alloys prepared using glow discharge decomposition of NF3 and SiH4 have been characterized using infrared absorption and the constant photocurrent method (CPM). The bonding configurations and the oscillator strengths of various bonds in these alloys have been obtained from the infrared-absorption spectra. The density of defects and their distribution in the band gap have been obtained without making any assumptions about the form of the distribution. It is found that in this composition range the main defect is the neutral silicon dangling bond and the concentration of charged dangling bonds is either too low or they are not present in these alloys. The possible role of fluorine in these alloys is also discussed.
Blue photoluminescence from rapid thermally oxidized porous silicon following storage in ambient air
Authors: Loni A. , Simons A. J. , Calcott P. D. J. , Canham L. T.
Published: July 2002

We have studied the temporal variation of the visible photoluminescence from rapid thermally oxidized porous silicon prepared from n+ substrates. In contrast to the red (slow band) emission, which is observable immediately after high-temperature oxidation, the blue (fast band) emission is shown to become prevalent only after samples are stored in ambient air. The intensity of the blue emission increases with progressive aging, the magnitude of the increase being dependent on the temperature at which the material is oxidized. Thermal treatment of aged rapid thermally oxidized material can reduce and even quench the blue photoluminescence. Quenching is reversible in that the photoluminescence re-appears after further aging at room temperature.
B-doped Si(001) grown by gas-source molecular-beam epitaxy from Si2H6 and B2H6:B incorporation and electrical properties
Authors: Lu Q. , Bramblett T. R. , Lee N.-E. , Hasan M.-A. , Karasawa T. , Greene J. E.
Published: July 2002

B-doped Si(001)2×1 films were grown on Si(001) substrates by gas-source molecular beam epitaxy using Si2H6 and B2H6. B concentrations CB (5×1016–5×1019 cm−3) were found to increase linearly with increasing flux ratio JB2H6/JSi2H6 (9.3×10−5–2.5×10−2) at constant film growth temperature Ts (600–950 °C) and to decrease exponentially with 1/Ts at constant JB2H6/JSi2H6 ratio. The B2H6 reactive sticking probability ranged from ≂6.4×10−4 at Ts=600 °C to 1.4×10−3 at 950 °C. The difference in the overall activation energies for B and Si incorporation at Ts=600–950 °C is ≂0.34 eV. A comparison of quantitative secondary-ion mass spectrometry (SIMS) and temperature-dependent Hall-effect measurements showed that B was incorporated into substitutional electrically active sites over the entire B concentration range investigated. SIMS B depth profiles from modulation-doped samples were abrupt with no indication of surface segregation to within the instrumental resolution limit and initial δ-doping experiments were carried out. Structural analysis by in situ reflection high-energy electron diffraction combined with post-deposition high-resolution plan-view and cross-sectional transmission electron microscopy showed that all films were high-quality single crystals with no evidence of dislocations or other extended defects. Temperature-dependent (20–300 K) hole carrier mobilities were equal to the best reported bulk Si:B values and in good agreement with theoretical maximum values.
Effect of substrate preparation on smectic liquid crystal alignment. II. Further results and modeling
Authors: Smela Elisabeth , Martínez-Miranda Luz J.
Published: July 2002

X-ray-diffraction measurements were performed on smectic A octylcyanobiphenyl liquid-crystal (LC) films deposited on glass and silicon gratings with periods between 664 nm and 200 μm. The film’s two interfaces, air-LC and LC-grating, imposed boundary conditions that required different alignments for the minimum energy configuration; the competition between these two forces was studied in thick (30+ μm) films. Consistent with earlier work, gratings with periods on the order of 10 μm and depths of 1.5–3 μm induced a portion of the film into homogeneous alignment in the direction of the grooves. As expected from theory, longer-period 200 μm gratings with the same depth showed an inconsistent ability to produce an inplane alignment; however, contrary to theory, shallower 664 nm gratings also failed to consistently induce in-plane alignment and did not produce an azimuthal preference. The results from the x-ray scans were fit with a multilayer model to give estimates of the thicknesses, orientations, and mosaic spreads of the different regions in the films. Films having an in-plane component were estimated to have a 5–10-μm-thick homeotropic skin at the surface. On 9 and 15 μm gratings, the in-plane scattering arose from a single homogeneous region in which the molecules had a small tilt (up to 5°) with respect to the plane of the substrate. The director was not exactly parallel to the grooves but was offset by up to 20°, and the mosaic spread in the azimuthal direction was typically 20°. In some films there was an additional region that appeared to be disordered.
Short-period transient grating measurements of perpendicular over-barrier diffusion in GaAs/AlGaAs multiple quantum wells
Authors: Norwood D. P. , Smirl Arthur L. , Swoboda H.-E.
Published: July 2002

A short-period transient grating technique is used to study perpendicular (or cross-well) transport as a function of lattice temperature in a GaAs/Al0.3Ga0.7As multiple quantum well with barriers that are sufficiently thick (10 nm) to ensure that tunneling is negligible. The grating decay time is observed to increase dramatically as the temperature is decreased, consistent with the need to thermally activate carriers from the wells; however, thermal activation alone will not account for the observed temperature dependence. The measured temperature dependence of the perpendicular transport, however, can be fit by including the temperature dependence of the above-barrier diffusion coefficients as well as the temperature dependence of the thermal activation. These fits to the data, which assume diffusion limited by polar-optical-phonon scattering, yield diffusion coefficients typical of those measured in AlGaAs alloys.
Pulsed dielectric breakdown of pressurized water and salt solutions
Authors: Jones H. M. , Kunhardt E. E.
Published: July 2002

The dielectric breakdown of pressurized water and salt solutions subjected to high amplitude electric fields of submicrosecond duration has been investigated. Well-defined pulses (80 kV, 3 ns rise time, 100 ns duration) have been applied to a gap (0.04–0.21 cm), between Rogowski profile electrodes, containing de-ionized, nondistilled water; de-ionized, distilled water; sodium chloride solutions (0.001–1.0 M); or magnesium sulfate solutions (0.01–0.1 M). Breakdown in these liquids has been studied at pressures up to 400 atm. Calibrated voltage dividers situated on the source and load sides of the test gap permitted measurement of the interelectrode potential and the current response. From these measurements, the time lag to breakdown, breakdown voltage, power input to the liquid, and temporal characteristics of the breakdown process have been determined. The breakdown time lag increases with increasing pressure and gap width, and decreases with increasing field. Moreover, it is weakly dependent on the conductivity of the liquid. A dynamical model has been developed to explain these results. In this model, field emission currents heat the liquid and create a region with density below the critical density for the formation of electron avalanches. An ionizing wave front subsequently develops and propagates via a sequence of processes occurring in the region ahead of the front; namely, heating by electron injection, lowering of the liquid density, and avalanche growth and retardation. The time for nucleation of the low density region has been experimentally determined and is in good agreement with theory.
In situ studies of the crystallization kinetics in Sb–Ge films
Authors: Petford-Long Amanda K. , Doole R. C. , Afonso C. N. , Solís J.
Published: July 2002

The crystallization process in SbxGe1−x alloy films has been observed during in situ annealing in a transmission electron microscope. Results are presented for two films with x=0.89 (89 at. % Sb) and x=0.71 (71 at. % Sb), which lie on either side of the eutectic composition (x=0.85). In the former films radial crystals are observed to grow rapidly from discrete nuclei, whereas in the latter films the crystallization process occurs through a near-planar front. In addition, quantitative data obtained from these experiments show that the Sb0.89Ge0.11 films have a higher activation energy for crystal growth and a lower temperature for the nucleation of crystals. Significant differences are observed between the crystallization processes for the two films studied, with the Sb0.89Ge0.11 film showing better potential for development as an ultrafast optical phase-change storage medium.
Spin-glass behavior of spinel iron oxide particles on iron metal particle recording media
Authors: Parker F. T. , Spada F. E. , Cox T. J. , Berkowitz A. E.
Published: July 2002

Small (30 Å diameter) spinel iron oxide particles which form the protective layer on acicular iron metal particle recording media are found to exhibit no observable magnetization. The typical experimental decrease in sample magnetization for several media specimens is about 3% from 5 to 300 K. This change is the same as the thermal decrease in metal core magnetization, determined by Mössbauer spectroscopy. The predicted decrease in sample magnetization assuming normal spinel oxide behavior is typically about 20%. Two intraparticle models for reduced magnetization in oxide nanoparticles are found to be incompatible with the magnetization data. An interparticle ‘‘super-spin-glass’’ model is compatible with the magnetization data. The alignment between adjacent oxide nanoparticle moments is hypothesized to depend on the particular sublattices in contact, since the sublattice exchange interactions are all antiferromagnetic. An inverse particle size dependence is thus expected, in agreement with spinel oxide magnetization reduction and other phenomena seen in a wide range of studies on larger oxide particles and films.
Moduli determination in polyimide film bilayer systems: Prospects for depth profiling using impulsive stimulated thermal scattering
Authors: Dhar Lisa , Rogers John A. , Nelson Keith A. , Trusell Fred
Published: July 2002

A laser-based ultrasonic technique, impulsive stimulated thermal scattering (ISTS), is used to characterize the acoustic waveguide behavior in a series of silicon-supported and free-standing polyimide bilayer structures. The experimental results demonstrate that multilayer structures are characterizable using ISTS measurements. In addition, simulations of acoustic waveguide behavior in coatings with very thin interfacial layers adjacent to the substrate and in films with continuously changing elastic properties are presented. The results indicate depth-profiling possibilities using ISTS.
Crystallization process of amorphous GaSb films studied by Raman spectroscopy
Authors: Dias da Silva J. H. , da Silva S. W. , Galzerani J. C.
Published: July 2002

Thermal annealings of amorphous gallium antimonide films were accompanied using Raman spectroscopy, both for stoichiometric and nonstoichiometric compositions. The films were prepared by flash evaporation on silicon substrates. Structural changes were induced by the heat treatments: an increasing degree of crystallization as a function of the annealing temperature is observed. Sb clusters are found to crystallize before GaSb does, and the dependence of the corresponding Raman peak intensity with the annealing temperature (occurring in two regimes) is explained. A mechanism for the crystallization of the amorphous GaSb is proposed, based on the prior migration of the Sb excess outside the GaSb region to be crystallized.
Photoluminescence and photoconductivity in CdIn2Te4
Authors: Couturier G. , Jean B. , Salardenne J.
Published: July 2002

Photoluminescence, photoconductivity, and Hall measurements were performed over a large range of temperature (13–300 K) for various crystals of the electro-optical semiconductor CdIn2Te4. Crystals are compensated semiconductors with a high donor–acceptor pair concentration assigned to the disorder in the cation sublattice. The inhomogeneities in the distribution of the donor–acceptor pairs and point defects, due to the lack of stoichiometry, result in band fluctuations, and thus in carrier localization effects, at low temperature. This is suggested by the photocurrent transient responses and the dependence of the luminescence intensity versus the excitation level. The nonhomogeneous distribution of point defects in off-stoichiometry crystals is observed by the deep level transient spectroscopy technique.
Enhanced photoluminescence detection of oxygen in silicon crystal by formation of a carbon–oxygen complex through carbon implantation and electron irradiation
Authors: Nakamura M. , Byrne A. S. , Kitamura E. , Suzuki T. , Nagai S. , Sunaga H. , Aoki Y. , Naramoto H.
Published: July 2002

In order to develop a method to detect low-level oxygen in thin silicon crystals by photoluminescence (PL), a radiative carbon–oxygen center (C center: 0.79 eV) is formed in silicon crystals through carbon introduction by ion implantation. The PL intensity of the C center of the implanted sample is significantly increased by annealing the sample at 1000 °C followed by electron irradiation. The possibility of detecting a low concentration of oxygen (below 1×1015 atoms/cm3) in a layer thinner than 1 μm thick is seen.
The effects of oxygen and defects on the deep-level properties of Er in crystalline Si
Authors: Libertino S. , Coffa S. , Franzó G. , Priolo F.
Published: July 2002

We have investigated the electronic properties of Er in crystalline Si using deep-level transient spectroscopy and capacitance-voltage measurements. Erbium was incorporated by ion implantation in a p+-n junction structure. In order to explore the role of oxygen and defects some samples were coimplanted with O and the annealing behavior of the deep-level spectra was explored in the temperature range 800–1000 °C for annealing times ranging from 5 s to 30 min. We show that O-codoping produces large modifications in the Er-related deep-level spectra and, in particular, a promotion from deep to shallow levels, thus enhancing the donor behavior of Er in Si. For erbium implanted in pure crystalline Si the spectrum is dominated by deep levels arising from Er-defect complexes which are easily dissociated upon thermal annealing. In O-coimplanted samples the formation of Er-O complexes with a characteristic level at EC−0.15 eV is observed. These complexes form upon thermal annealing and are stable up to 900 °C. These results are presented and possible implications for our current understanding of the mechanisms of Er photoluminescence in Si are discussed.
Low-temperature photochromic response of phosphorus-doped bismuth silicon oxide
Authors: McCullough J. S. , Harmon Angela , Martin J. J. , Martin J. J. , Harris M. T. , Larkin J. J.
Published: July 2002

Phosphorus is one of several dopants that electronically compensate the native deep donor responsible for the yellow coloration observed in bismuth silicon oxide (BSO). Low-temperature optical absorption measurements of a series of Czochralski-grown P-doped BSO crystals show that ∼0.1–0.15 at. % P is needed in the sample to fully remove the yellow coloration. The absorption cutoff in the fully compensated P-doped sample was at 3.2 eV while compensated Al- and Ga-doped samples cutoff at 3.35 eV. Excitation at 10–15 K with near band-edge light produces photochromic absorption bands. In the lightly-doped (partially bleached) samples these bands were identical to those observed in undoped BSO. In the fully bleached sample a new spectrum was observed. Its major contribution was a band centered near 1.8 eV with a weaker absorption in the blue-green. By comparison with the spectra observed in undoped and in Al-doped material before and after photoexcitation it is believed that the 1.8 eV band is due to the [PO4]− center and that the broad 2.45 eV band observed in Al- and Ga-doped BSO is due to the [BiO4]0 center.
Degradation and annealing of electron-irradiated diffused junction InP solar cells
Authors: Walters R. J. , Summers G. P.
Published: July 2002

The degradation and annealing properties of 1 MeV electron-irradiated n+p diffused junction InP solar cells are reported in detail. The solar cells were characterized through current–voltage measurements under simulated solar illumination at 1 sun, AM0. The radiation-induced defect spectra were characterized through deep level transient spectroscopy. At fluences up to 1015 cm−2, cell degradation was primarily due to a decrease in the short-circuit current Isc which occurred during the introduction of the hole trap, H4. Most of this degradation could be removed by minority-carrier injection annealing of the H4 defect at temperatures as low as 225 K. At higher irradiation fluences, up to 1016 cm−2, cell degradation was dominated by a decrease in both the open-circuit voltage Voc and the fill factor. This degradation was caused by a large radiation-induced recombination current and by carrier removal which was associated with the introduction of the hole trap H5 and the electron traps EA, EC, and ED. Most of the effects of the recombination current and some of the carrier removal were removed by concurrent injection and thermal annealing between 373 and 400 K where the residual H4 defect concentration and the H5 defect were removed. Essentially full cell recovery was achieved after subsequent annealing between 450 and 500 K where the electron traps also showed a partial annealing stage. Thermal annealing without illumination in the range of 350–500 K showed the same defect annealing stages suggesting that the cell recovery in this temperature range is due solely to thermal annealing. The data are summarized to give a model for the radiation-induced degradation and annealing of these InP solar cells.
Characterization of the transport properties of channel delta-doped structures by light-modulated Shubnikov–de Haas measurements
Authors: Mena R. A. , Schacham S. E. , Haugland E. J. , Alterovitz S. A. , Young P. G. , Bibyk S. B. , Ringel S. A.
Published: July 2002

The transport properties of channel delta-doped quantum-well structures were characterized by conventional Hall effect and light-modulated Shubnikov–de Haas (SdH) effect measurements. The large number of carriers that become available due to the delta doping of the channel, leads to an apparent degeneracy in the well. As a result of this degeneracy, the carrier mobility remains constant as a function of temperature from 300 down to 1.4 K. The large amount of impurity scattering, associated with the overlap of the charge carriers and the dopants, resulted in low carrier mobilities and restricted the observation of the oscillatory magnetoresistance used to characterize the two-dimensional electron gas by conventional SdH measurements. By light modulating the carriers, we were able to observe the SdH oscillation at low magnetic fields, below 1.4 T, and derive a value for the quantum scattering time. Our results for the ratio of the transport and quantum scattering times are lower than those previously measured for similar structures using much higher magnetic fields.
Scattering from strain variations in high-mobility Si/SiGe heterostructures
Authors: Feenstra R. M. , Lutz M. A.
Published: July 2002

Computations of scattering rates from strain variations in high-mobility n-channel Si/SiGe heterostructures are presented, and the results compared with experiment. Two sources of strain variation are considered—interface roughness and misfit dislocations—both of which form to relieve strain in the Si channel layer which is under tension. Strain variations induced by interface roughness are demonstrated to provide a source of scattering which, for highly strained systems of the type considered here, is significantly larger than conventional geometrical roughness scattering. Misfit dislocations provide a source of localized scattering centers, and an appropriate formalism is developed to describe this case. For both types of scattering, reasonable agreement with measured mobilities is found for various values of channel thickness.
Properties of SiGe oxides grown in a microwave oxygen plasma
Authors: Mukhopadhyay M. , Ray S. K. , Maiti C. K. , Nayak D. K. , Shiraki Y.
Published: July 2002

Thin oxide on strained Si1−xGex surface has been grown using a nonelectron cyclotron resonance mode microwave plasma at low temperatures (150–200 °C). An optimized post-oxidation and post-metal annealing cycle has resulted in very low fixed oxide charge density (1.78×1010/cm2) and moderately low interface trap density (2.9×1011/cm2 eV). A controlled in situ hydrogen-plasma treatment to Si1−xGex has been found to be useful in improving the electrical properties of the oxide. The high electron injection phenomena of metal oxide semiconductor capacitors has been used for charge trapping studies of sites normally present in the SiGe oxides. From the position and the extent of current ledge observed as a function of ramped gate voltage, the capture cross section and the total number of traps have been determined.
Analysis of the operating regimes of microsecond-conduction-time plasma opening switches
Authors: Cassany B. , Grua P.
Published: July 2002

A theoretical model for the microsecond-conduction-time plasma opening switch (POS) based on magnetohydrodynamics is presented. The operating processes are associated with the magnetic field transport in the switch. The concept of the freezing-in of magnetic field in fluids is used to analyse the dynamics of this field in the plasma. One-dimensional and two-dimensional numerical simulations lead to the identification of two operating regimes, related to the Hall and the snowplow effects. The transition between these two regimes is determined by the plasma density. Scaling relations are developed from this model. In particular the electrical charge Q, conducted by the POS during the conduction time, provides a useful tool for comparisons between theory and experiments; it is shown to be the essential parameter for the switch design.
Theory of ‘‘supercurrents’’ and their influence on field quality and stability of superconducting magnets
Authors: Krempasky L. , Schmidt C.
Published: July 2002

Unexpected periodic variations of the magnetic field were recently found along the axes of superconducting accelerator magnets. This modulation, which reduces the field quality of the magnets, shows a complex space and time dependence containing very long time constants. We show in this article that the variation of the field rate dB/dt along the length of a superconducting cable induces superposed coupling currents which flow over a long length. The space and time dependence of these ‘‘supercurrents’’ for a two-wire cable model is obtained by the solution of the diffusion equation with the diffusivity given by the cable parameters. The existence of supercurrents explains the observed effects in accelerator magnets. It is furthermore shown that supercurrents can lead to a highly inhomogeneous current distribution over the cable cross section and to additional coupling losses, even in sections of the magnet where dB/dt=0. Both these effects can reduce the stability of magnets, which may explain the ramp rate limitation found in accelerator magnets as well as in large magnets for fusion research.
Nondestructive propagation loss and facet reflectance measurements of GaAs/AlGaAs strip-loaded waveguides
Authors: Park K. H. , Kim M. W. , Byun Y. T. , Woo D. , Kim S. H. , Choi S. S. , Chung Y. , Cho W. R. , Park S. H. , Kim U.
Published: July 2002

A modified Fabry–Perot resonance technique using a single cavity was proposed to obtain the propagation loss of the optical waveguide. The propagation loss as well as the facet reflectance were measured without sequential cleavage for a GaAs/AlGaAs strip-loaded waveguide based on the contrast ratios of the reflected and transmitted interference patterns.
Structural, magnetic, and electrical properties of (Pr0.5Er0.5)2Fe17−xAlx
Authors: Suresh K. G. , Rama Rao K. V. S.
Published: July 2002

An x-ray diffraction study of (Pr0.5Er0.5)2Fe17−xAlx (0≤x≤10) shows an expansion of its unit cell with x. The crystal structure changes from hexagonal Th2Ni17 to rhombohedral Th2Zn17 at x=6. The magnetic moment decreases by increasing the Al concentration. This effect may be due to the charge transfer from Al to the 3d band of Fe. The Curie temperatures are found to increase with Al up to x=3 and then decrease up to x=10, and the possible underpinning mechanisms are discussed. X-ray diffractograms of the magnetically aligned samples indicate that the easy magnetization directions of the samples with x=1,2,3, and 4 lie on a cone about the c axis. Electrical resistivity measurements show that the residual resistivity increases drastically with the Al concentration. The temperature coefficient of resistivity becomes almost zero for intermediate Al concentrations.
Optically pumped GaN/Al0.1Ga0.9N double-heterostructure ultraviolet laser
Authors: Aggarwal R. L. , Maki P. A. , Molnar R. J. , Liau Z.-L. , Melngailis I.
Published: July 2002

Molecular-beam epitaxy was used to grow a 100 nm Al0.1Ga0.9N/100 nm GaN/500 nm Al0.1Ga0.9N double heterostructure on a 10-μm-thick GaN buffer layer grown with hydride vapor phase epitaxy on (0001) sapphire. Lasing from the 100 nm GaN active layer has been obtained at ∼359 nm at liquid-nitrogen temperature (77 K) and at ∼365 nm at room temperature (295 K), using transverse optical pumping at 337.1 nm with a 600 ps transversely excited atmospheric pressure pulsed nitrogen laser. Threshold pump fluences were measured to be 0.3 and 0.5 mJ/cm2 at 77 and 295 K, respectively, for a laser with 65 μm cavity length. In a laser of 23 μm cavity length, longitudinal cavity modes were observed with 0.56 nm spacing, corresponding to a group refractive index of 5.0 at the lasing wavelength.
Characterization of strained quantum wells by high-resolution x-ray diffraction
Authors: Finkelstein Y. , Zolotoyabko E. , Blumina M. , Fekete D.
Published: July 2002

The GaAs/GaInAs/GaAs quantum-well structures grown by metalorganic chemical vapor deposition were studied using high-resolution x-ray diffractometry and photoluminescence techniques. Diffraction profiles were fitted to experimental rocking curves by a simulation procedure, based on the direct summation of scattered waves. The analytical expressions obtained shed light on various relevant parameters and, together with a specific growth procedure, permitted determination of the thickness and composition of strained quantum wells. By following fine interference effects in the x-ray diffraction spectra quantum wells as thin as 1.4 nm could be characterized. In order to check the validity of the procedure, the obtained quantum-well parameters were used to calculate the peak positions in luminescence spectra and good agreement with experimental data was found.
Optical band gap and Urbach tail in Y-doped BaCeO3
Authors: He T. , Ehrhart P. , Meuffels P.
Published: July 2002

Optical processes at the absorption edge in Y-doped BaCeO3 films with thicknesses of 160 and 4600 nm have been studied in the temperature region between 20 and 1000 °C. For the first time, optical band-gap energies of Y-doped BaCeO3 were determined with a room temperature value of 4.1 eV and a temperature coefficient of −3.88×10−4 eV/K. It was found that the optical absorption coefficient below the band–band transition exhibits an exponential dependence on photon energy following Urbach’s rule, and the Urbach tail is dependent on oxygen partial pressures, i.e., on lattice defects. The corresponding Urbach edge parameters and their temperature dependence were investigated. The data are discussed within the model of structural and thermal disorder and a characteristic phonon energy of 46 meV was obtained according to this disorder model.
Nondestructive inspection of a fractured nickel bar by Barkhausen and magnetoacoustic emissions
Authors: Yu C. C. , Qin C-D. , Ng D. H. L.
Published: July 2002

Barkhausen emission (BE) and magnetoacoustic emission (MAE) measurements have been made on a nickel bar before and after it is torn apart by a tensile stress. The BE and MAE profiles obtained are all single-peaked. The peaks obtained after fracture are found at the lower field regions of the profiles, and this suggests that the field required for the domain wall motion in the fractured bar has been lowered. In the BE measurement, the signals show an increase of 44% (away from fracture end) to 144% (at fracture end); on the contrary, the MAE signals show a reduction of 43% (away from fracture end) to 14% (at fracture end). As the nickel bar is fractured, we find that in the broken pieces, the grains have been elongated in the stressed direction, and there is an increase of defects such as dislocations, voids and microcracks, especially near the fracture end of the bar. BE which is sensitive to these factors, has therefore been intensified. On the other hand, the plastically elongated grains, which have a lower absolute magnetostriction, enhance the reduction of MAE activity. The results measured from the nickel bar will be compared with those obtained from a fractured mild steel bar, which has different magnetostriction and other magnetic properties.
Spectrally resolved near-field mode imaging of vertical cavity semiconductor lasers
Authors: Hörsch I. , Kusche R. , Marti O. , Weigl B. , Ebeling K. J.
Published: July 2002

The transversal mode properties of vertical cavity surface emitting lasers (VCSELs) are studied by spectrally resolved scanning near-field optical microscopy. In contrast to classical optical microscopy techniques, our method is able to simultaneously decompose lasing transversal modes by their wavelength with lateral superresolution. As the tip-sample distance is controlled by the well-established shear-force detection, additional topographical information showing the surface structure of the laser is provided. Therefore, near-field spectroscopy allows the detailed analysis of the spatial light distribution emitted by the laser with respect to the current injection contact, making it a promising tool for the characterization and optimization of VCSELs.