bluuebunny/crossref_metadata_2025 huggingface dataset:
Auger recombination in HgCdTe quantum wires and quantum boxes
Authors: Jiang Y. , Teich M. C. , Wang W. I. , Meyer J. R.
Published: July 2002

Quantum-wire and quantum-box structures for narrow-gap materials with small effective masses, such as HgCdTe, can readily be fabricated using current lithographic techniques. In this article, we calculate the Auger-recombination carrier lifetimes in HgCdTe quantum-wire and quantum-box structures, with band gaps in the 2–5 μm wavelength range. Quantum confinement is generally believed to increase the carrier lifetimes. However, we find the Auger recombination lifetime in a HgCdTe quantum wire is shorter than that in a quantum well, and it decreases as the wire width decreases because of the corresponding increase in the density of states. On the other hand, band-to-band Auger recombination is zero in a quantum box because the overlap functions vanish and because of the discrete nature of the energy levels. Therefore, within the confines of our model, we can expect improved temperature performance from long-wavelength quantum-box lasers but not from quantum-wire lasers. Furthermore, these conclusions are applicable for all types of band-to-band Auger processes and semiconductor materials.
Analysis of a magnetization process based on a two sublattice model
Authors: Zhang Zhi-dong , Zhao Tong , Sun X. K. , Chuang Y. C.
Published: July 2002

A computer simulation program, based on a two sublattice model, is performed to analyze the magnetization process of ferromagnetic materials (like, for instance, RCo5 and R2Fe14B compounds). Without using the assumption of the existence of a small canting angle between the two sublattices, as has been used in the analysis of S. Rinaldi and L. Pareti [J. Appl. Phys. 50, 7719 (1979)], the magnetization curve as well as its derivative curves are studied for the two sublattice system with high competing single-ion anisotropies. In the present work, a peak in the low field range of the second curve of magnetization is reported and the magnetic process is correspondingly discussed in terms of both the exchange energy and the anisotropy.
Magnetic properties of Ag/Ni multilayered films
Authors: Peng Chubing , Cao Yang , Dai Daosheng
Published: July 2002

The magnetic properties of Ag/Ni multilayered films, prepared by the vacuum evaporation method, as a function of different thicknesses of Ni and Ag layers have been studied. It has been found that the magnetic moment of the Ni layer decreases greatly with increase of the thickness of the Ag layer. The temperature dependence of magnetization exhibits the features of Bloch’s T3/2 law with a large value of the Bloch coefficient, B3/2, which also depends on the thickness of the Ag layer when the thickness of the Ni layer is fixed at 30 Å. These phenomena can be explained by means of the itinerant electron theory. Furthermore, the magnetic size effect of Ag/Ni multilayered films, such as a reduced Curie temperature as a function of the thickness of the Ni layer tNi and a linear dependence of magnetization on temperature for T<175 K when tNi=10 Å, have been discussed.
Hole trap level generation in silicon during rapid thermal annealing: Influence of substrate type and process conditions
Authors: Chabane-Sari N.-E. , Thibaud L. , Kaddour S. , Berenguer M. , Barbier D.
Published: July 2002

Hole trap level generation in boron-doped silicon by rapid thermal annealing between 900 and 1100 °C has been studied using deep level transient spectroscopy, with emphasis on the effects of substrate type and process parameters. A dominant hole trap level at Ev+0.30 eV and two accompanying hole trap levels at Ev+0.22 eV and Ev+0.40 eV in lower concentrations have been systematically detected in Czochralski, float zone, and epitaxial substrates, in a less than 5-μm-thick surface layer. The defect state concentrations were observed to increase monotonically with both the annealing temperature and the cooling rate. Higher concentrations of hole trap levels were measured in the Czochralski and epitaxial substrates than in the float zone substrate. Finally, both a silicidation and an oxidation reaction during the high-temperature plateau totally inhibited the formation of defect states. We suggest that the defect centers responsible for the observed hole trap levels could be formed during the high-temperature plateau with the participation of dissolved as-grown impurities and metal contaminants diffused from the wafer surface.
Observation of current filaments in GaAs/AlxGa1−xAs heterostructures using a time-resolved imaging technique
Authors: Zwaal E. A. E. , Vermeulen M. J. M. , Hendriks P. , Haverkort J. E. M. , Wolter J. H.
Published: July 2002

We developed a time-resolved optical beam induced current (TROBIC) technique, and performed time-resolved current imaging experiments on GaAs/AlxGa1−xAs heterostructures under high electric field conditions. These experiments are the first time-resolved imaging experiments of current patterns in a two-dimensional semiconductor structure. We attribute the current patterns observed in the TROBIC images to the formation of current filaments in the AlxGa1−xAs layer, parallel to the two-dimensional electron gas (2DEG). We show that even in samples where the two-dimensional electron gas and the contacts to the 2DEG are perfectly ohmic and homogeneous, current filaments can still develop in high electric fields. These temporal and spatial instabilities in the AlxGa1−xAs layer strongly affect the high-field transport properties of the heterostructure.
Electrode shapes for high-power diodes with non-space-charge-limited flow
Authors: Peter William
Published: July 2002

Electrode shapes appropriate to diodes with non-space-charge-limited flow (e.g., laser-irradiated photocathodes) and high-power (eV0 ≳ mc2) are derived. The electrode shapes are designed to keep the electron beam rectilinear, and generalize the shapes derived by Pierce for space-charge-limited cathodes in low-power diodes.
Excitation of nonlinear ionization waves caused by three-wave interaction in He positive columns
Authors: Ohe K. , Itani H.
Published: July 2002

Three-wave interactions among self-excited nonlinear ionization waves in a diffusion-controlled He positive column are investigated. Observations of the bispectrum and bicoherence spectrum show nonlinear interaction among three modes which are composed of a self-excited backward ionization wave, a low frequency forward one and one excited in causing the modulational instability.
The beam breakup instability in quadrupole and solenoidal electron-beam transport systems
Authors: Bosch R. A. , Menge P. R. , Gilgenbach R. M.
Published: July 2002

Dispersion relations are derived to determine the growth rate, dominant wavelength, and group velocity of disturbances caused by the beam breakup instability. Considerations include weak and strong focusing, x-y coupling in solenoidal transport, the spacing of accelerator cavities, and periodically pulsed beams. Beam breakup growth is minimum when the cavity spacing equals an integral number of half-betatron wavelengths for quadrupole focusing, and an integral number of betatron wavelengths for solenoidal focusing. Minimum growth is also found for periodic pulses separated by an integral number of half-periods of the TM110 cavity mode. Expressions for beam breakup growth at the minima are obtained.
Homogenization of EL2 defect concentration of dislocation-free liquid-encapsulated-Czochralski GaAs:In in its growth direction
Authors: Kitagawara Y. , Takenaka T.
Published: July 2002

Homogenization of EL2 point defect concentration is attempted for dislocation-free In-doped liquid-encapsulated-Czochralski (LEC) GaAs in its growth axial direction. The investigation reveals first the existence of characteristic axial distributions of [EL2] and resistivity which reflect a thermal history of dislocation-free as-grown crystal ingot. The variations of these quantities are small but cannot be homogenized even after a postgrowth heat treatment at 950 °C. The origin of the axial inhomogeneity is shown to be caused by inhomogeneous distribution of As precipitates in the growth direction. The arsenic (As) precipitates in the bulk crystal, which were formed during the LEC growth, are found to be dissolved by a heat treatment at 1200 °C followed by a fast cooling. After the 1200 °C heat treatment and the succeeding heat treatment at 950 °C to stabilize the EL2 defect concentration, a highly improved axial homogeneity is achieved in the distributions of both [EL2] and resistivity. From the amount of [EL2] change induced by the dissolution of the As precipitates, the amount of precipitated As in an as-grown crystal is estimated to be equivalent to an EL2 concentration on the order of 1015 cm−3 at the seed end and nearly zero at the tail end of the crystal ingot. Also discussed is a mechanism to produce the characteristic axial distribution of the As precipitates in an as-grown crystal ingot.
Thermally assisted solid state amorphization of rod milled Al50Nb50 alloy
Authors: El-Eskandarany M. Sherif , Aoki Kiyoshi , Suzuki Kenji
Published: July 2002

Differential thermal analysis, differential scanning calorimetry, optical metallography, scanning electron microscopy, and transmission electron microscopy were used to study the amorphization and crystallization processes of mechanically alloyed Al50Nb50 powder prepared by the rod-milling technique. The results have shown that the crystalline-to-amorphous transformation occurs in three stages. At the intermediate stage of milling, the transformation from crystalline into amorphous was conducted by heating the alloy to 800 K. This transformation has occurred due to a thermally assisted solid-state amorphization between the layers of the elemental starting material of the composite particles. At the final stage of milling, the mechanical driving force which was generated by the rods causes the formation of a homogeneous and uniform amorphous alloy. The amorphization temperature, Ta, and the crystallization temperature, Tx, are determined to be 650 and 1105 K, respectively. Moreover, the enthalpy change of amorphization, ΔHa, and the enthalpy change of crystallization, ΔHx, were evaluated to be −1.80 kJ/mol and −13 kJ/mol, respectively. Furthermore, the activation energy of amorphization, Ea, was calculated to be 170 kJ/mol.
Analytic time domain characterization of p-i-n photodiodes: Effects of drift, diffusion, recombination, and absorption
Authors: Lee JaWoong , Kim Dae M.
Published: July 2002

An analytic impulse response function of high-speed p-i-n photodiodes is given in direct time domain, incorporating the effects of drift, diffusion, recombination, and absorption. In the limit of no carrier diffusion and large excess carrier lifetime, the result reduces to the well-known theory of Lucovsky et al. [J. Appl. Phys. 35, 622 (1964)]. In this analysis the output photocurrent is obtained in terms of photogenerated carrier concentrations from the energy balance consideration. The excess carrier transport is described by a Green’s function method. Additionally the internal electric field is explicitly examined. The present formulation is a generalization of Yariv’s one-carrier-current model which ascribes the externally detected current to the time-varying induced charge on the electrodes.
A new route to high-T
c superconducting Bi–Sr–Ca–Cu–O thin films: Improved deposition efficiency and film morphology using ammonia–argon mixtures as the carrier gas
Authors: Zhang J. M. , DiMeo F. , Wessels B. W. , Schulz D. L. , Marks T. J. , Schindler J. L. , Kannewurf C. R.
Published: July 2002

Highly oriented films of the high-Tc superconductor Bi2Sr2CaCu2Ox have been prepared by a low-pressure organometallic chemical vapor deposition process using a mixture of ammonia and argon as the carrier gas together with Sr(dpm)2 (dpm-dipivaloylmethanate), Ca(dpm)2, Cu(acac)2 (acac-acetylacetonate), and triphenylbismuth as the organometallic precursors. By introducing ammonia into the carrier gas, a significant improvement in the volatility and thermal stability of both Sr(dpm)2 and Ca(dpm)2 is observed. Typical required source temperatures for Sr(dpm)2 and Ca(dpm)2 with the introduction of ammonia are about 40–50 °C lower than the source temperatures of the precursors without the introduction of ammonia. Enhancement of source volatility for Cu(acac)2 is also observed. After annealing at 865 °C in flowing oxygen, the films consist predominantly of the Bi2Sr2CaCu2Ox phase and exhibit high preferential orientation of the crystallite c axes perpendicular to the substrate surface. Four-probe resistivity measurements indicate the onset of film superconductivity at ∼110 K and zero resistivity achieved at 74 K.
Enhancement of magneto-optical Faraday rotation by bismuth substitution in bismuth and aluminum substituted yttrium–iron–garnet single-crystal films grown by coating gels
Authors: Matsumoto Koji , Sasaki Satoshi , Haraga Ken’ichi , Yamaguchi Kazuhiro , Fujii Toshitaka , Asahara Yousuke
Published: July 2002

The effect of bismuth substitution on the magneto-optical Faraday rotation of bismuth and aluminum substituted yttrium–iron–garnet (Y3−xBixFe4.2Al0.8O12, x=0 to 2.8) single-crystal films was investigated, where the films were prepared by coating gels involving the constituent metallic ions on single-crystal (GdCa)3(GaMgZn)5O12 garnet plates. The maximum amount of bismuth substitution that yields solely the garnet phase was x=2.5. The onset and the completion temperatures for crystal growth of garnet were decreased by bismuth substitution and were, respectively, 500 and 560 °C for x=2.5. A marked increase in the Faraday rotation θF was observed at heavy substitution x≥2.0 and θF at 3.06 eV (λ=405 nm) was 36.6 deg/μm, but no substantial improvement in the figure of merit for Faraday effect θF/α, where α is the absorption coefficient, was recognized.
Alloy inhomogeneities in InAlAs strained layers grown by molecular-beam epitaxy
Authors: Peiró F. , Cornet A. , Morante J. R. , Clark S. A. , Williams R. H.
Published: July 2002

Transmission electron microscopy studies have been performed to characterize InxAl1−xAs layers grown by molecular-beam epitaxy on (100) InP substrates. The first observations of compositional nonuniformities in strained InAlAs layers are reported. The coarse quasiperiodic structure present in each sample has been found to be dependent upon the growth parameters and the sample characteristics.
Synthesis of Tl-based ‘‘2234’’ superconductors
Authors: Kaneko Tetsuyuki , Hamada Kazuyuki , Adachi Seiji , Yamauchi H. , Tanaka Shoji
Published: July 2002

Nearly single-phase samples of superconducting Tl–Ba–Ca–Cu–O ‘‘2234’’ were successfully synthesized. The sample sintered in air had Tc of 112 K. Post-annealing of the sintered sample in a high-pressure oxygen gas made its Tc increase up to 115 K. The sample sintered in argon gas had Tc of 90 K. The thermoelectric power (TEP) of the sample was also measured. All the samples showed positive TEP signals. The magnitude of TEP signal decreased as Tc increased. Thus, it was likely that the as-sintered 2234 phase was in an under-doped state with respect to the optimum carrier concentration.
Effect of silver solubility on microstructure and superconducting properties of YBa2Cu3−xAgxO7−δ superconductors
Authors: Joo J. , Singh J. P. , Poeppel R. B. , Gangopadhyay A. K. , Mason T. O.
Published: July 2002

The effect of silver (Ag) solubility on microstructure and superconducting properties of YBa2Cu3−xAgxO7−δ (0≤x≤0.5) superconductors has been evaluated. The solubility limit of Ag for copper sites in YBCO at ambient conditions (room temperature, atmospheric pressure) was evaluated to be x≂0.06. Analysis revealed the Ag content (x) of YBCO grains to be lower than the nominal Ag content (xn) used for fabrication, probably due to processing-related problems. Part of the Ag used for fabrication segregates on the YBCO grain boundaries. The segregated Ag particles are believed to pin YBCO grains, resulting in fine-grain microstructures. For low nominal Ag content, xn<0.2, critical current density (Jc) increased from 98 to 160 A/cm2 as a function of increasing Ag content. These improvements are believed to be due to the increased oxygen content and associated microstructural changes in the YBCO. For higher nominal Ag content, xn≳0.2, however, Jc decreased rapidly with the increasing Ag content due to the precipitation of nonsuperconducting phases.
Measuring linear polarization of photoluminescence and photoluminescence excitation using a photoelastic modulation technique
Authors: Wassermeier M. , Weman H. , Miller M. S. , Petroff P. M. , Merz J. L.
Published: July 2002

Polarization modulation is used to investigate the polarization dependencies in the low-temperature photoluminescence (PL) and the photoluminescence excitation (PLE) of GaAs/AlGaAs quantum wire arrays. The modulation technique employing a photoelastic modulator is described and its implementation in the experimental setup of the PL and PLE experiments is presented. In the PL experiment the technique is used to analyze the emitted light with respect to its polarization, whereas for the PLE experiment the polarization of the exciting light is modulated, probing the polarization dependence of the absorption of the light. Since the modulation of the light is restricted to the polarization, the polarization dependence can be measured simultaneously with the PL or PLE intensity. The versatility and the sensitivity of the technique is exemplified by presenting results of polarized PL and PLE obtained on quantum wire samples grown on the vicinal (100) surface of GaAs by molecular-beam epitaxy that show a considerable anisotropy in the linear polarization for both the PL and PLE.
Resolution limits of ion milling for fabricating Y1Ba2Cu3Ox nanostructures
Authors: Fong F-O. , Deshmukh S. C. , Davis M. F. , Stumbo D. P. , Wolfe J. C. , Economou D. J.
Published: July 2002

A process is described for fabricating 0.23-μm-wide lines in Y1Ba2Cu3Ox thin films where patterns are defined in a commercial, negative tone, epoxy-based resist by masked ion beam lithography and transferred to the superconducting film by argon ion milling. Lines in 80-nm-thick films had the same zero-resistance temperature (89 K) as the starting films, and a critical current density of 0.7×106 A/cm2 at 77 K, representing a threefold reduction from the starting value. A consistent interpretation of these results is that the line consists of a superconducting core 70 nm in width with the critical current density of the starting film and with 80-nm-wide nonsuperconducting sidewalls. The results were reproducible in lines which did not cross outgrowths in the superconducting film.
Investigation of deep levels in Zn-doped InSe single crystals
Authors: Micocci G. , Tepore A. , Rella R. , Siciliano P.
Published: July 2002

Deep levels in p-InSe single crystals doped with zinc have been investigated by resistivity, Hall-effect, photoinduced-current transient spectroscopy, and space-charge-limited-current measurements. Hole traps located about 0.59 eV above the valence band have been detected and the corresponding thermal capture cross sections evaluated. These trapping levels are probably associated with defects due to dopant atoms in the interlayer regions.
Structural and electrical characterization of gold/chemically vapor deposited diamond contact
Authors: Gomez-Yanez C. , Alam M.
Published: July 2002

Structural and electrical characteristics of a gold contact to chemically vapor deposited diamond film were investigated. The film was polycrystalline with defective crystals of octahedral morphology, contained nondiamond forms of carbon, silicon, tungsten, and gold, and also incorporated other defects such as vacancies. The silicon/diamond interface contained voids of different sizes. The contact exhibited rectifying characteristics with a breakdown voltage of about 30 V. The ideality factor calculated on the basis of a thermionic emission model is rather large for other mechanisms beside thermionic emission to be operative. Electrical conduction can be explained by the space charge limited current in the presence of exponential trap distribution. The trap distribution is characterized by two different sets of parameters, one at low voltages (up to 4.2 V) and the other at higher voltages (greater than 4.2 V).
Pulsewidth dependence of time-resolved two-photon absorption with picosecond pump–probe excitation
Authors: Tomita Yasuo , Shibata Masa-aki , Bergquist Johan
Published: July 2002

Pulsewidth dependence of time-resolved two-photon absorption with picosecond pump–probe excitation is investigated. It is shown theoretically that the time-resolved probe transmittance change by two-photon absorption almost follows a temporal autocorrelation of the pump and probe pulses. Time-resolved two-photon absorption measurements of 1.064 μm, 29 ps pulses with semi-insulating undoped GaAs are also performed. The comparison of the experimental results with second harmonic generation autocorrelation measurements confirms the theory.
A study of nonlinear reflection and optical switching in indium antimonide
Authors: Feng S. T. , Irene E. A.
Published: July 2002

Bistability in the reflected light from an InSb surface has been observed without the use of a resonance cavity, and is explained by an increasing absorption positive feedback mechanism. Relying on this mechanism, a novel InSb optical switch is demonstrated that uses only the surface reflection and operates at room temperature using a pulsed CO2 laser as the pump beam. The polarity of the switched-out signal, the probe beam, was found to depend on the wavelength of the probe beam in the visible and near-infrared range. This novel spectral dependence was used to demonstrate several optical logic elements.
Direct writing in polymethyl methacrylate films using near-ultraviolet light of Ar+ laser
Authors: Bozhevolnyi S. I. , Potemkin I. V. , Svetovoy V. B.
Published: July 2002

Direct laser writing of micron-wide grooves in polymethyl methacrylate (PMMA) films with the scan speed of up to 100 μm/s is demonstrated using cw near ultraviolet radiation at 351 and 363 nm. For the PMMA film on a silicon substrate we have found that the light energy required for complete ablation increases with the decreasing of incident beam power and extremely rises up when the power becomes less than 10 mW. It is shown that the groove profile depends on the process parameters and nearly vertical resist walls can be obtained.
Carrier injection characteristics of the metal/organic junctions of organic thin-film devices
Authors: Egusa Syun , Gemma Nobuhiro , Miura Akira , Mizushima Koichi , Azuma Makoto
Published: July 2002

The junction characteristics of metal/organic thin film (M/Org) interfaces were investigated by measuring the displacement currents for the structure of M/Org/SiO2/Si devices. The observed currents were ascribed to the carriers injected from metal electrodes into organic films, which were markedly dependent both on metals and organic materials employed. The threshold bias for carrier injection was also found to be dependent on the metal work function. The results can thus provide some detailed information about the junction properties including the potential barriers formed at the M/Org interfaces.
Laser-induced reflectivity changes as a general method for Q switching: Q switching at soft-x-ray wavelengths
Authors: Dharamsi A. N.
Published: July 2002

A new technique for Q switching lasers by inducing reflectivity changes in one of the cavity’s multilayer-coated mirrors is discussed. This mirror is such that, under normal operation, the constructive interference condition is not satisfied, and it therefore has a low reflectivity. Towards the end of the laser gain-pumping pulse, suitably tuned radiation from a short-pulse visible/uv laser is shone upon the mirror, resulting in changes in layer thicknesses and layer indices of refraction, such that the interference condition is satisfied. In this manner, the cavity Q may be switched in a short time interval (picoseconds) from a low to a high value. The mechanisms by which the induced changes occur are discussed, and calculations of reflectivity as a function of layer thicknesses and indices of refraction are presented. A general design criterion for successful implementation of the technique is given, along with some specific examples. Estimates of the required characteristics of the external, change-inducing laser are also provided. In principle, the method can be applied to any laser cavity, including the recently demonstrated soft-x-ray multipass laser cavities, and would find use in many other situations where currently available techniques do not work. The lower bound on the wavelength of the laser line which can be Q switched in this manner is found to be between 200 and 400 Å.
Band structure of InAsSb strained-layer superlattices
Authors: Liu Lifeng , Lee G. S. , Marshak A. H.
Published: July 2002

Band structures of relaxed InSb/InAs1−xSbx strained-layer superlattices (SLSs) were calculated based on Herman-Skillman neutral atom ionization energies, effective dipole theory, and strain shift of band edges. The conduction-band minimum and the valence-band maximum of InAs1−xSbx are lower in energy than those of InSb, respectively. The band structures of InSb/InAs1−xSbx are type II SLSs and an extreme type II superlattice is predicted for x<0.82. This extreme type II superlattice with a proper structure factor can have favorable properties for infrared detectors covering the 8–12 μm wavelength range. The requirement for layer thickness of InSb/InAs1−xSbx SLSs with different absorption mechanisms was discussed.
Photoresponse of shallow step, weak-link bridges using inverted cylindrical magnetron-sputtered Y1Ba2Cu3O7−x thin films
Authors: Cukauskas E. J. , Allen L. H. , Holm R. T. , Sherrill G. K. , Van Damme P. K.
Published: July 2002

The photoresponse of Y1Ba2Cu3O7−x step, weak-link devices on MgO substrates has been measured using a He-Ne laser light source. The temperature and magnetic-field dependencies of the device critical current density were investigated. Single-step and multistep devices were fabricated and found to have a bolometric response in the resistive region and weak-link, video-detection response in the superconducting region. These devices are suitable for operation over a wide range of temperatures from 4 to 90 K. Responsivities greater than 1000 V/W were measured at low temperature for some devices.
High-pressure thermoluminescence and photoluminescence study of ZnS:Mn:Cu:Cl phosphor
Authors: Lang J. M. , Dreger Z. A. , Drickamer H. G.
Published: July 2002

The effect of pressure has been studied on the thermoluminescence and photoluminescence of a well-characterized sample of ZnS:Mn:Cu:Cl. The thermoluminescence was particularly revealing. Initially two traps were present. As they increased in depth with increasing pressure new shallower traps appeared. The pressure dependence of four traps was established. By comparison with pressure measurements on ZnS doped only with Mn+2 and only with Cu+ and Cl−, we established that the deepest trap is associated with defects introduced by Mn+2, while the two traps next lower in energy are associated with defects introduced by Cl−. The shallowest trap could not be assigned to a specific defect. The photoluminescence emission (from the 4T1, to the 6A1 energy level of Mn+2) shifted to lower energy at a rate identical to that previously reported for a less well-characterized ZnS:Mn sample. The shift could be described quantitatively in terms of changes in the ligand field parameters.
Suppression mechanisms for oxidation stacking faults in silicon on insulator
Authors: Guillemot N. , Tsoukalas D. , Tsamis C. , Margail J. , Papon A. M. , Stoemenos J.
Published: July 2002

Oxidation of the Si overlayer in silicon separated by oxygen (SIMOX) is expected to form oxidation stacking faults (OSF) since this process generates Si interstitials into the active Si layer. In spite of this process, recent experiments reveal that the density of OSF is very low. A possible mechanism to explain the absence of OSF in SIMOX is that Si interstitials rejected from the Si-overlayer/SiO2 interface could react with the SiO2 of the buried layer to form SiO molecules (Si+SiO2=2SiO). These species, which can diffuse four orders of magnitude faster than Si through the SiO2 buried layer, are recombined by the reverse reaction at the back interface due to the absence of Si-interstitial supersaturation. Since the activation energy for this process is 4.4 eV, OSF can be generated if the Si overlayer is subjected to a preoxidation treatment that introduces a high density of stacking fault (SF) nucleation sites, because the activation energy for heterogeneous generation of OSF is only 2.3 eV. In this case 0.21×10−3 of Si interstitials are incorporated in OSF over the total Si atoms that are consumed during the oxidation. This value agrees with the proportion of Si interstitials incorporated in OSF when the SiO2 buried layer is replaced by a Si3N4 buried layer since this layer is a barrier for the Si-interstitial migration to the substrate. The value 0.21×10−3 is very close to the expected theoretical value revealing that almost all the Si interstitials were captured by the OSF.
Solid phase epitaxy of stressed and stress-relaxed Ge-Si alloys
Authors: Hong Q. Z. , Zhu J. G. , Mayer J. W. , Xia W. , Lau S. S.
Published: July 2002

Solid phase epitaxy of 3500-Å-thick GexSi1−x (0.04≤x≤0.12) films on (100) Si substrates has been investigated. The thickness of regrown layers increased linearly with annealing time in the temperature range of 475–575 °C. The regrowth rates of stressed alloys were less than those of pure Si, while stress-relaxed alloys have larger rates than Si. The difference in regrowth rates was explained by the activation-strain tensor model (Aziz, Sabin, and Lu, to be published in Phys. Rev. B). The first element of the activation-strain tensor obtained in this experiment was in excellent agreement with that deduced by Aziz et al. For low Ge concentrations (x<0.08), the recrystallized region was of good crystalline quality. However, threading dislocations were observed in a stressed Ge0.1Si0.9 alloy after complete recrystallization. During the regrowth at 550 °C, the Ge-Si alloy first regrew coherently up to 300 Å, above which threading dislocations started to nucleate. On the other hand, no dislocations were detected in the regrown layer of a stress-relaxed Ge0.1Si0.9 alloy sample.
Oxidation of alkoxide-derived YBa2Cu3O7−x films using dinitrogen monoxide
Authors: Katayama Shingo , Mizushima Yasuyuki , Sekine Masahiro
Published: July 2002

Oxidation of YBa2Cu3O7−x was studied to improve superconductivity in films prepared by a chemical process using metal alkoxides. YBa2Cu3O7−x films prepared by firing of gel films at 700 °C for 6 h under argon were annealed under N2O or O2. The films annealed under N2O at 500 °C for 3 h showed Tc(zero)=76 K, whereas the ones annealed under O2 showed Tc(zero)=41 K. The impressive effect of annealing under N2O for increasing Tc(zero) was observed. The effective annealing temperature using N2O was consistent with the decomposition temperature of N2O on YBa2Cu3O7−x. The effect of N2O on the oxidation of YBa2Cu3O7−x is thought to be due to active oxygen atoms formed by the decomposition of N2O on the surface of YBa2Cu3O7−x films.
Non-self-limiting nature of silicon reduction of WF6 in cold wall systems
Authors: Joshi R. V. , Prasad V. , Yu M. L. , Scilla G.
Published: July 2002

This paper addresses the kinetics and related mechanisms of non-self-limiting nature of Si reduction of WF6 in cold wall systems for the first time. The growth of such films in low-pressure chemical-vapor deposition (LPCVD) and ultrahigh vacuum (UHV) systems is compared. Both systems produce non-self-limiting, uniform, controllable, nonporous films. The growth is controlled by process parameters such as the wafer temperature and WF6 concentration at the wafer surface. The order of the Si reduction reaction is 0.5 in the concentration of WF6. The tungsten films deposited in the LPCVD system contaminated with water vapor are thicker than the films grown in the UHV system even when the temperature is below 450 °C. Such thicker films are produced as a result of the formation of an amorphous W-O layer. From the thermodynamic considerations, the origin of W-O layer is attributed to a parallel reaction between water vapor, WF6, and substrate Si. The beneficial role played by the W-O layer is that it prevents any volume shrinkage of the converted layer and restricts lateral encroachment. In the absence of such a layer as in the case of the UHV system, severe volume shrinkage and encroachment are observed. A theoretical model together with physical mechanisms explaining the non-self-limiting phenomenon are proposed. The mechanism suggests that a fine-grained W structure surrounded by a W-O layer, formed in the LPCVD system, assists faster out-diffusion of Si through the tungsten films compared to the UHV system. The higher values of the diffusion coefficient for Si out-diffusion through films grown in the LPCVD system as compared with the UHV system support this mechanism. The out-diffused Si is substituted to W by reduction reaction to complete the film growth.
Transient boron diffusion in medium dose germanium-implanted silicon
Authors: Peterström S. , Svensson B. G.
Published: July 2002

The transient enhanced diffusion of implanted boron has been examined by secondary ion mass spectrometry in crystalline silicon, in germanium preamorphized silicon, and in germanium amorphized and epitaxially regrown material. The total germanium dose used for amorphization of the silicon crystal was 1.2×1015 ions/cm2. The transient enhanced diffusion in regrown material was merely one-third of the diffusion in original crystalline silicon while the enhanced diffusion in preamorphized silicon had been retarded to 70% of the crystalline silicon value. This shows that a medium germanium implantation dose is sufficient to reduce the depth of the boron doping profile during furnace high-temperature annealing.
Novel equiaxed magnetite media with high coercivity and thermal stability
Authors: Chin Tsung-Shune , Deng Ming-Cheng
Published: July 2002

Equiaxed magnetite media with coercivity of up to 1560 Oe, saturation and residual magnetizations of up to 83 and 50 emu/g, respectively, and squareness ratio of up to 0.61 have been developed by the modification of Mn and Co, and by proper annealings. They were prepared by coprecipitation of Fe, Mn, and Co ions from an aqueous solution, by suitable alkali such as triethylamine, to adjust the pH, followed by calcination, reduction, oxidation, step-annealings, and final reduction. Oxidation leads to a defect spinel ferrite structure, whose coercivity can be greatly enhanced by a step-annealing treatment, and high coercivity can be retained after the final reduction to magnetite, whose coercivity can not be raised at all by the step-annealing. These media have a temperature coefficient of coercivity as low as 0.20–0.33%/°C, hence are potential candidates for high density recording.
Thermal stability of the (100) Cu-Ni superlattices with reversed magnetic anisotropy
Authors: Chang Chin-An
Published: July 2002

The (100) Cu(100 Å)-Ni(25 Å) superlattice structure, grown on Cu/Si(100), that shows a reversed magnetic anisotropy between the in-plane and normal-to-plane magnetizations, has been heated to 400 °C, and the magnetic and structural changes investigated. The periodic structure remains mostly intact up to a 30-min heating at 300 °C, and partially so after heating at 400 °C. The reversed anisotropy, with a hysteresis loop seen for the field perpendicular to the film plane, but not for that parallel to the film plane, remains seen up to 400 °C. This is compared with two (100) Cu/Ni/Cu structures containing 50- and 500-Å Ni, respectively, with two 1000-Å Cu layers each. The former structure, with a completely reversed magnetic anisotropy, lost both the Ni layer and the magnetic characteristics after heating at 200 °C. The latter structure retained its magnetic properties up to 300 °C, and lost both the Ni layer and the magnetic characteristics after heating at 400 °C. The different reactions involved are discussed, including that with Si and mixing between Cu and Ni.
Spatial harmonics of photorefractive gratings in a barium titanate crystal
Authors: Lee Yeon H. , Hellwarth R. W.
Published: July 2002

Calibrated optical Bragg-scattering measurements of the fundamental steady-state space-charge-field amplitude, and of two higher spatial harmonics, in photorefractive p-type barium titanate excited by a light intensity pattern that is a simple sine function of distance are reported. These measurements are performed over the entire range (0<m<1) of intensity modulation index m when the modulation period is both much larger than, and comparable to, the smallest characteristic (Debye screening) length involved in the photoconduction process. There is no externally applied electric field. The measurements are compared to numerical solutions of the standard single-carrier band-conduction model of photoconductivity, and good agreement is found except for large unexplained differences at high modulation index (∼0.8<m<1). Phenomenological analytic expressions are also given for the fundamental and two higher field-grating harmonics that are useful approximations to the numerical solutions of the standard model equations for all m and for (small, intermediate, and large) grating periods.
Characterization and thermal instability of low-resistivity carbon doped GaAs grown by low-pressure organometallic vapor phase epitaxy
Authors: Enquist P.
Published: July 2002

Heavily carbon (C)-doped GaAs grown by low-pressure organometallic vapor phase epitaxy using carbon tetrachloride exhibits a lifetime significantly lower than that obtained by zinc doping in previous work and does not exhibit strain relaxation for thicknesses above twice the critical thickness for misfit dislocation formation (hc). GaAs:C+ is shown to be thermally unstable to annealing cycles as brief as 600 °C for 4 min. The instability is manifest in conductivity, photoluminescence intensity, and lattice contraction reduction for carbon concentrations above 7×1019 cm−3. This reduction is not alleviated by reducing the layer thickness below hc or adding indium to increase hc above the layer thickness. This suggests that either hc is not an adequate measure of misfit dislocation formation during annealing or misfit dislocation generation is in general not responsible for the thermal instability of GaAs:C+.
Admittance properties of thin/thick metal-oxide-semiconductor structures. II. Exact modeling by two-dimensional simulation
Authors: Wachutka G. , Fahrner W. R.
Published: July 2002

In the foregoing part of this article, the admittance characteristics of stepped oxide structures have been discussed using an equivalent network analysis. This approach proves to work satisfactorily as long as the thin/thick oxide thickness ratio is sufficiently large (≥0.3 typically); however, it seems to become increasingly problematic when this ratio tends to assume smaller values. Since we guessed that the discrepancies were caused by two-dimensional effects, exact two-dimensional admittance simulations have been performed to clarify the situation. These calculations allow a detailed interpretation of the individual C(V) features in terms of the spatial distribution of the charge carriers in the interior of the device under test. They largely justify the equivalent network, but also indicate the shortcomings introduced by this approach.
Heteroepitaxial GaAs layers on InP substrates: Radiative recombinations, strain relaxation, structural properties, and comparison with InP layers on GaAs
Authors: Olego D. J. , Okuno Y. , Kawano T. , Tamura M.
Published: July 2002

GaAs layers grown on (001) InP surfaces by low-pressure metalorganic chemical vapor deposition were investigated with photoluminescence spectroscopy, x-ray diffraction, Raman scattering, and transmission electron microscopy. Correlations between the optoelectronic properties, the strain relaxation, and the structural defects were established for layer thickness D ranging between 0.1 and 3.0 μm. A comparison with the case of InP layers grown on GaAs substrates is presented. Radiative recombinations to split light- and heavy-hole valence bands near the zone center are seen at 12 K in the photoluminescence spectra. The splitting is due to a biaxial tensile strain. With increasing temperature, the heavy-hole transitions gain intensity and at around 140 K they are the only features in the spectra. In the 12–50 K temperature range the intensity ratio between the heavy- and light-hole transitions also depends on laser power. The hole activation energy determined from the temperature dependence of the intensity ratio above 50 K agrees with the valence-band splitting. The strain for D≳0.3 μm arises from differences in linear thermal expansion and has contributions from the lattice mismatch in thinner layers. The strain values yielded by x-ray diffraction are smaller than those obtained from the valence-band splitting measured with photoluminescence. The difference is attributed to a temperature dependence of the linear thermal expansion, which was corroborated by the shifts of the longitudinal optical phonon frequencies measured with Raman spectroscopy at 300 and 12 K. A comparison is made of the absolute magnitude of the strain and the x-ray diffraction linewidths for heteroepitaxial GaAs and InP layers on InP and GaAs substrates, respectively. The contribution to the strain from the lattice mismatch relaxes in GaAs faster than in InP and the GaAs x-ray linewidths are narrower for D<1.0 μm. These results are understood in terms of the growth habit and the behavior of threading and interfacial dislocations.
Electromigration-induced vacancy behavior in unpassivated thin films
Authors: Lloyd J. R. , Koch R. H.
Published: July 2002

A model is constructed where a nonequilibrium vacancy concentration resulting from electromigration-induced mass flux divergences is responsible for damage in the form of wedge-like and/or crack-like voids as well as thinning of extended areas. The damage morphology is primarily a function of temperature.
Anisotropy in the optical absorption of Ag–SiO2 thin films with oblique columnar structures
Authors: Suzuki Motofumi , Taga Yasunori
Published: July 2002

An attempt has been made to clarify the anisotropy in the optical absorption and nanostructure of thin films prepared by oblique codeposition of Ag and SiO2. At a low concentration of Ag, the columnar structure grows toward the incident direction of vapor flux of SiO2, and Ag is dispersed in that structure as small metallic particles. An inhomogeneous distribution of Ag particles is obtained when Ag is deposited from the side of the normal to the film surface opposite to that of the incident direction of SiO2 flux. The optical transmittance is strongly dependent on the angle of incidence and the polarization of the incident light due to the effects of the small Ag particles embedded in the oblique columnar structure. The anisotropic optical absorption of Ag and SiO2 hybrid films can be used as an inorganic polarizer.
Thermally stimulated current of Si-ion-implanted GaAs
Authors: Lee Y. H. , Kang T. W. , Kim T. W.
Published: July 2002

A thermally stimulated current technique has been carried out to investigate the defect levels in Si-ion-implanted GaAs. Thermally stimulated current measurements have been performed in the temperature range of 90–300 K, and five deep traps with activation energies of 0.18, 0.20, 0.31, 0.40, and 0.43 eV have been observed. It is considered that the one of the traps (Ea=0.18 eV) shows the optical quenching effect and another trap (Ea=0.20 eV) is related to the damage due to the implanted ions.
A method for doping fluctuations measurement in high resistivity silicon
Authors: Castoldi A. , Chinnici S. , Gatti E. , Longoni A. , Sampietro M. , Vacchi A. , Rehak P.
Published: July 2002

This paper presents a method for the measurement of doping fluctuations in high resistivity silicon wafers. Spatial fluctuations of doping are derived from the knowledge of the electrostatic potential in a completely depleted semiconductor bulk. The potential variations are indirectly measured through the analysis of the trajectories of majority carriers drifting within the depleted semiconductor material. Regions of semiconductors up to the full wafer can be investigated. An example of mapping along parallel lines of a floating zone 2 K Ω cm silicon wafer over an area of 0.4×0.8 cm2 is presented. The relative sensitivity of the method is better than 1%.
Laser-induced fluorescence and emission spectroscopic study of magnetic field effects in a low-pressure etch plasma
Authors: Heinrich Friedhelm , Hoffmann Peter
Published: July 2002

The influence of a magnetic volume field B on the chemical and physical properties of a 13.56-MHz CF4 plasma was studied by laser-induced fluorescence (LIF) and by optical emission spectroscopy (OES) at typical low-pressure etching conditions. The measurements were carried out in a commercial magnetron with a modified magnetic field configuration allowing a continuous variation of B up to a maximum field strength of 80 G. As indicated by LIF the densities of the CF2 radicals in the electronic and vibrational ground state increased by about a factor of 3 when the maximum B field was applied. No concentration gradients were detected by spatially resolved LIF. A similar increase as for CF2 was observed for actinometrically normalized F emission intensities. The ratios of CF2 LIF and CF2 OES signals are compared with the emission intensity behavior of argon, admixed to a small percentage, which suggest an increase of the electron induced production rates (electron densities) significantly stronger than that of the radical concentrations. This phenomenon is explained by simple considerations concerning B dependent production and losses of ions and radicals.
Laser chemical vapor deposition of cobalt thin films
Authors: Schulmeister K. , Lunney J. G. , Buckley B.
Published: July 2002

Smooth cobalt thin films have been deposited by decomposing dicobalt octacarbonyl [Co2(CO)8] with 248 nm excimer laser radiation. Area selective deposition has been achieved by imaging a mask onto soda-lime glass and Suprasil quartz substrates. The decomposition has been found to be partially due to thermal decomposition of the cobalt carbonyl on the laser-heated surface and partially due to photolysis of adsorbed cobalt carbonyl molecules. The crystalline structure of the cobalt films was found to depend on the laser fluence. For a fluence below 115 mJ cm−2 per pulse, the hcp phase was produced, but for higher fluences the fcc phase was formed, and was found to be stable at room temperature. Examination of the optically smooth surface of the low fluence films showed nanometer scale ridges parallel to the gas flow direction.