bluuebunny/crossref_metadata_2025 huggingface dataset:
Fine line structures of ceramic films formed by patterning of metalorganic precursors using photolithography and ion beams
Authors: Hung L. S. , Zheng L. R.
Published: July 2002

Fine line structures of ceramic thin films were fabricated by patterning of metalorganic precursors using photolithography and ion beams. A trilevel structure was developed with an outer resist layer to transfer patterns, a silver delineated layer as an implantation mask, and a planar resist layer protecting the precursor film from chemical attacking and sputtering. Ion irradiation through the Ag stencil rendered metal carboxylates insoluble in 2-ethylhexanoic acid, permitting patterning of the precursor film with patterning features on micron scales. The potential of this technique was demonstrated in patterning of Bi2Sr2CaCu2O8+x and Pb(Zr0.53Ti0.47) thin films.
Preparation of an oxide film through a hydroxide compound layer
Authors: Morita Kazuhide , Kambe Shiro , Ohshima Shigetoshi , Okuyama Katsuro
Published: July 2002

The preparation of an oxide film through a hydroxide layer is studied. A (001) oriented Ca(OH)2 film is formed on a MgO substrate by the spray method. By heating this film at 600–800 °C for dehydration, a (111) oriented CaO film is formed. The change of the orientation from (001) to (111) is discussed in connection with a topotaxy mechanism. This result shows the possibility of ‘‘hydrogen bond epitaxy,’’ that is, atomic layer epitaxy through a layer hydroxide.
Chemical and electrical characterization of AlGaAs/GaAs heterojunction bipolar transistors treated by electron cyclotron resonance plasmas
Authors: Li P. W. , Wang Q. , Yang E. S.
Published: July 2002

The effects of electron cyclotron resonance (ECR) hydrogen, nitrogen, and ammonia plasma have been studied by x-ray photoelectron spectroscopy. Experimental evidence shows that the ECR hydrogen plasma removes the native oxide on the GaAs surface and recovers the surface order. A mixed nitride-oxide surface layer is formed after nitrogen and ammonia plasma treatments. The appearance of the nitride layer correlates with the passivation of the GaAs surface and the much improved I-V characteristics of AlGaAs/GaAs heterojunction bipolar transistors.
Polarization independent narrow band Bragg reflection gratings made with silica-on-silicon waveguides
Authors: Adar R. , Henry C. H. , Kistler R. C. , Kazarinov R. F.
Published: July 2002

We report polarization independent Bragg reflectors, centered at 1.55 μm and made with silica-on-silicon waveguides. Gratings are etched into the upper core surface and glass doped with boron and phosphorus is used to fill in the grating corrugation and for the top cladding. The Bragg coupling length in these gratings is independent of polarization. Post-processing anneals at temperatures above 780 °C weaken the gratings and can be used to tailor the reflection stop band in the range 15–1.5 Å. By etching trenches along the sides of the waveguides, the strain induced birefringence in practically eliminated and the TE and TM reflection peaks overlap to within 0.4 Å.
Differential optical absorption spectroscopy in Ge-Si superlattices
Authors: Pearsall T. P.
Published: July 2002

We have used a differential spectroscopy technique to measure and characterize the optical absorbance spectra of Ge-Si superlattices. Because of the fundamental nature of the band-edge electronic structure, it is argued that the conventional models for absorption versus photon energy in bulk semiconductors may not apply to these Ge-Si superlattices. Results obtained on superlattices grown on Si show localized levels near the band edge, in contrast to those grown on Ge which display a band to band absorption spectrum. The superlattices grown on (001) Ge show more than 100 times the absorbance of those grown on Si, and the absolute magnitude of the absorption corresponds to a band-edge absorption coefficient greater than 103 cm−1.
25.2% efficiency (1-sun, air mass 0) AlGaAs/GaAs/InGaAsP three-junction, two-terminal solar cell
Authors: Chung B.-C. , Virshup G. F. , Klausmeier-Brown M. , Ristow M. Ladle , Wanlass M. W.
Published: July 2002

A 25.2% efficiency measured under 1 sun, air mass 0 illumination has been achieved in a two-terminal AlGaAs/GaAs/InGaAsP three-junction solar cell. The cascade cell consists of a monolithic AlGaAs (Eg=1.93 eV)/GaAs two-junction mechanically stacked on an InGaAsP (Eg=0.95 eV) single-junction cell. The component cell of the AlGaAs/GaAs two-junction structure were electrically connected using a metal interconnect fabricated during post-growth processing. To minimize the obscuration effect introduced by the grid lines and metal interconnect, a prismatic cover glass was bonded to the AlGaAs/GaAs cascade cell. The results obtained with this structure represent the highest 1-sun, air mass 0 efficiency achieved in any solar cell operating under a two-terminal configuration. The implications of achieving this high efficiency in a two-terminal, three-junction solar cell for terrestrial and space applications are described as well.
Spatial distributions of x-ray lasing spectral linewidth and electron density in a lithiumlike silicon plasma
Authors: Lu Pei-xiang , Zhang Zheng-quan , Xu Zhi-zhan , Fan Pin-zhong , Chen Shi-sheng , Shen Bai-fei
Published: July 2002

The spatial distribution of the spectral linewidth of lithiumlike silicon ions in the 5f-3d transition line at 88.84 Å is presented in this letter, and it shows that Stark broadening is the dominant line-broadening mechanism for lithiumlike Si11+ ions on recombination x-ray lasers. Spatial distribution of the electron density of the x-ray lasing gain medium is calculated using the linear Stark theory, which shows that the electron density is ∼1019/cm3 in the gain region. A large linewidth at the gain peak (i.e., at 450 μm from the target surface) is 0.21 Å and the corresponding electron density and population inversion are 2.9×1019/cm3 and 5.5×1016/cm3, respectively.
High resolution electron microscopy of crystalline–amorphous interface: An indication to Eden aggregate
Authors: Lereah Y. , Pénisson J. M. , Bourret A.
Published: July 2002

The interface between crystalline and amorphous phases in partially crystallized Al:Ge amorphous thin films was examined by high resolution electron microscopy and by nanoprobe analysis. The interface shows no smoothness at any scale down to the atomic scale. No gradient of concentration was found in the amorphous phase even at irregularities, but pockets of amorphous phase were found in the crystalline scale. These results indicate that no long range atomic mobility exists during crystallization, thus no diffusion in the amorphous phase nor surface diffusion in the crystal interface. The Eden model for growth is well suited to describe the interface morphology.
Study of the defects induced by low-energy (100 eV) hydrogen-ions on amorphous silicon dioxide
Authors: Fortunato G. , Mariucci L. , Pecora A. , Fanfoni M. , Priori S.
Published: July 2002

The low-energy (100 eV) hydrogen-ion bombardment effects on a-SiO2 have been investigated by using synchrotron radiation photoemission spectroscopies. The argon bombardment effects have also been studied, in order to discriminate between physical and chemical characters in the hydrogen/a-SiO2 interaction. Our results show that hydrogen treatment produces predominantly Si-H defects, which are observed to induce gap states in a-SiO2.
High Q YBa2Cu3Ox cavities
Authors: Button T. W. , Alford N. McN.
Published: July 2002

Melt-processed YBa2Cu3Ox thick film components for resonant cavities have been produced on yttria stabilized zirconica substrates. A variety of cavities have been constructed incorporating both copper and superconducting components and the TE011 modes have been examined. The highest unloaded Q factor measured was 715 688 for the TE011 mode of an all superconducting cavity at 77 K and 5.66 GHz in the Earth’s magnetic field. This corresponds to a surface resistance of 1.09 mΩ over a total surface area in excess of 230 cm2. Cooling this cavity within a mumetal shield increased the unloaded Q factor by approximately 5%.
Mode locking of room-temperature cw thulium and holmium lasers
Authors: Heine Frank , Heumann Ernst , Huber Günter , Schepler Kenneth L.
Published: July 2002

We report the generation of ultrashort light pulses from cw-pumped Cr, Tm:YAG and Cr, Tm, Ho:YAG lasers actively mode-locked by an acousto-optic modulator. The pulse duration obtained from Tm:YAG was 45 ps which was approximately two times the bandwidth limit. Mode-locked pulses less than 800 ps were also produced in Cr, Tm, Ho:YAG.
Ultrasonic Newton’s rings
Authors: Hsu David K. , Dayal Vinay
Published: July 2002

Interference fringes due to bondline thickness variation were observed in ultrasonic scans of the reflected echo amplitude from the bondline of adhesively joined aluminum skins. To demonstrate that full-field interference patterns are observable in point-by-point ultrasonic scans, an optical setup for Newton’s rings was scanned ultrasonically in a water immersion tank. The ultrasonic scan showed distinct Newton’s rings whose radii were in excellent agreement with the prediction.
Kinetic diffusion model of ion-implanted boron during rapid thermal annealing
Authors: Kinoshita H. , Kwong D. L.
Published: July 2002

The diffusion of ion-implanted B during rapid thermal annealing (RTA) has been modeled by studying the reaction kinetics between eight species including boron, Si self-interstitials, and vacancies in multiple-charge states. Monte Carlo generated point-defect profiles are used to include the effects of ion-implant damage on the enhanced diffusion of B. Accurate diffusion modeling of high-dose implantation has been achieved with the addition of an extended defect model. The extended defect model describes the absorption and release of Si interstitials corresponding to extended defect formation and annealing, which give rise to the transient-enhanced diffusion of B. Good agreement between the model and experimental results for RTA of ion-implanted B at a dose range of 1×1014–2×1015 cm−2 has been obtained.
Shallow, titanium-silicided p+n junction formation by triple germanium amorphization
Authors: Dehm Christine , Gyulai J. , Ryssel H.
Published: July 2002

TiSi2 contacts were fabricated using self-aligned silicidation technology by ion-beam mixing with germanium. Shallow p+n junctions of 170 nm depth with low leakage currents of 10 nA and an ideality factor of 1.08 could be formed by 13 keV boron implantation in silicided silicon substrates preamorphized by germanium implantation. For germanium amorphization, three implantation energies were chosen to check the influence of the overlap between implantation produced interstitial-rich and vacancy-rich areas on transient diffusion of the boron and on formation of end-of-range disorder. Using this triple germanium amorphization, end-of-range defect concentrations could be appreciably reduced compared to conventional substrate amorphization, leading also to improved electrical characteristics and to somewhat shallower junction depths.
Surface-interface states and a model for surface effects in semi-insulating bulk GaAs
Authors: Miller W. R. , Stillman G. E.
Published: July 2002

Surface-related effects in undoped and Cr-doped semi-insulating (SI) liquid-encapsulated Czochralski (LEC) GaAs, as seen in Hall effect and resistivity measurements, are shown to be caused by mixed conduction due to a p-type surface space-charge layer, as predicted by theoretical calculations employing a surface-interface state model recently developed to explain surface-potential changes in epitaxial GaAs. Wet chemical treatments with ammonium hydroxide were used to induce especially large surface effects and are shown to form a substantial hole concentration at the surface. The excellent agreement between the theoretical results and experimental data provides strong support for the surface-interface state model used and demonstrates its utility as the first ‘‘working’’ mathematical model of surface-interface states in GaAs. In addition, wet chemical treatment in hydrogen peroxide is shown to minimize the surface layer and thereby allow accurate as well as stable and repeatable electrical characterization of the n-type bulk.
Oriented lead germanate thin films by excimer laser ablation
Authors: Peng C. J. , Roy D. , Krupanidhi S. B.
Published: July 2002

c-axis-oriented lead germanate thin films were fabricated, to our knowledge for the first time, by pulsed excimer laser ablation. Composition analysis indicated that the films are stoichiometric and very close to the target composition. The orientation of the films along the unique polar axis (c axis) appeared to have been influenced by the ablation fluence via the energy of the ablated species and by the nature of substrates. Films were found to be ferroelectric at room temperature, with a remanent polarization of about 2.5 μC/cm2 at a coercive field of 55 kV/cm. The (003)-oriented films also showed a clear onset of ferro–paraelectric phase transition at about 175 °C close to that of single crystals.
Excimer laser mixing of Ti layers on Si3N4 ceramic substrates
Authors: Jervis T. R. , Nastasi M. , Hubbard K. M.
Published: July 2002

We have used pulsed excimer laser radiation at 248 nm to mix Ti layers into Si3N4 substrates. Mixed layers show formation of small grain TiN in a Si3N4 but no evidence of Ti-Si compounds or free Si. Low fluence (∼1.0 J cm−2) processing results in minimal mixing as TiN formation at the interface impedes further diffusion. At higher fluence (≳2 J cm−2) complete and quite uniform mixing occurs. The mixed layer is of the order of 0.5 μm thick.
New all-optical reflection modulator based on a doubly resonant hetero-nipi saturable Bragg reflection
Authors: Poole P. J. , Phillips C. C. , Hughes O. H.
Published: July 2002

Very large fractional reflectivity changes (30%) under optical pump densities of ≊3 mW/cm2 are found in a novel GaAs/Al0.35Ga0.65As hetero-nipi structure grown by MBE. This high sensitivity originates in the interaction between the n=1 heavy-hole excitonic resonances in the hetero-nipi and an optical Bragg resonance, designed into the structure through its optical periodicity. The dynamics of the nonlinearity are shown to be dominated by the ‘‘giant ambipolar diffusion’’ mechanism for in-plane carrier transport, and the implications of this for device applications are discussed.
High-field electron velocity measurement in GaAs/AlGaAs multiple-quantum wells
Authors: Shigekawa Naoteru , Furuta Tomofumi , Arai Kunihiro , Tomizawa Masaaki
Published: July 2002

We measured the electron velocity versus electric field (v-E) relationships for GaAs/AlGaAs multiple quantum wells with different well-layer thicknesses (50, 100, and 200 Å). No clear dependences on the well thickness have been observed in the measured v-E’s, which indicate that the confinement of electrons in well layers does not induce strong effects on the momentum relaxation and the energy loss rate. The results of the measurement were also compared with those derived by the Monte Carlo calculation, and a remarkable discrepancy between measured and calculated results was found in the well thickness dependence of the electron peak velocity.
Transient response of a high T
c superconducting thin film
Authors: Dhali Shirshak K. , Wang Lei
Published: July 2002

The transient response of a YBCO thin film to a current pulse is reported. The measured rate of change of resistance across the superconductor is consistent with the thermal propagation of a normal region in a thin superconducting film. It appears that the normal region occurs at an ohmic contact and propagates across the length of the film, thus switching the film from its superconducting state to its normal state. The rate of resistance change shows a strong dependence on the bias temperature and current.
Low-loss metallic hollow waveguides coated with durable and nontoxic ZnS
Authors: Matsuura Yuji , Miyagi Mitsunobu
Published: July 2002

ZnS-coated Ag hollow waveguides are newly proposed and fabricated to realize a durable and nontoxic waveguide for CO2 laser light transmission. The fabrication method is based on rf-sputtering and electroplating techniques and a polyimide tube is used as a hollow mandrel. As a result of measurements, low-loss property of the ZnS-coated waveguide is shown and the beam profile with a sharp energy peak is obtained. The result of the aging test proves good durability of the ZnS-coated Ag waveguide.
Tungsten metallization onto InP prepared by rapid thermal low-pressure chemical vapor deposition of WF6 and H2
Authors: Katz A. , Feingold A. , El-Roy A. , Pearton S. J. , Lane E. , Nakahara S. , Geva M.
Published: July 2002

Tungsten (W) films were deposited onto InP in a cold wall, rapid thermal low-pressure chemical vapor deposition (RT-LPCVD) reactor, using a tungsten hexafluoride (WF6) gas reduced by hydrogen (H2). W films of thickness 50–450 nm were deposited in the temperature range of 350–550 °C, pressure range of 0.5–4.5 Torr, and deposition rates up to 4 nm/s with an apparent activation energy of about 1.12 eV. The film stress varied depending on the deposition pressure, from low compressive (deposition at 0.5 Torr) to moderate tensile (deposition at about 4.5 Torr). Post-deposition sintering of the W films at temperatures up to 600 °C led to reduction of the resistivity with a minimum value of about 55 μΩ cm as a result of heating at 500 °C.
Anomalies in the pressure response of the Raman modes in (211)-oriented InxGa1−xAs/GaAs strained-layer superlattices
Authors: Lemos V. , Ritter T. , Weinstein B. A.
Published: July 2002

The phonon spectra of InxGa1−xAs/GaAs strained-layer superlattices grown on (100), or either one of the two inequivalent (211)A and B surfaces of GaAs were obtained by Raman scattering for pressures ranging from 1 atm to 13.0 GPa. The measurements show that phonon frequencies are discontinuous functions of pressure for (211)A superlattices in contrast to the continuous behavior observed for (100) and (211)B-oriented superlattices. These discontinuities are discussed in terms of pressure induced increase in the density of heterointerface dislocations.
Planar microwave biased radio frequency SQUIDs with a cryogenic preamplifier
Authors: Mück M. , Hallmanns G. , Heiden C. , Fontana G. , Cerdonio M. , Mezzena R. , Vitale S.
Published: July 2002

We report on the design and performance of a planar microwave rf-SQUID readout by a cryogenic preamplifier. The SQUID-sensor consists of a planar half-wavelength microstrip resonator, into which the SQUID-loop is integrated. The pump frequency is 1.7 GHz. The cryogenic preamplifier employs a microwave high electron mobility transistor (HEMT), located close to the SQUID sensor. Measurements of the flux noise and the fractional step rise parameter were carried out in the temperature range between 4.2 and 1.5 K. In an open loop white flux noise values of 2×10−6 Φ0/√Hz were obtained at 4.2 K.
Fast high-efficiency integrated waveguide photodetectors using novel hybrid vertical/butt coupling geometry
Authors: Soole J. B. D. , Silberberg Y. , Scherer A. , LeBlanc H. P. , Andreadakis N. C. , Caneau C. , Schumacher H. , Erben U.
Published: July 2002

We report a novel coupling geometry for integrated waveguide photodetectors−a hybrid vertical coupling/butt coupling scheme that allows the integration of fast, efficient, photodetectors with conventional double heterostructure waveguides. It can be employed to yield a planar, or pseudo-planar, surface that supports further levels of integration. The approach is demonstrated with a 25-μm-long p-i-n detector integrated with an InP/InGaAsP/InP waveguide, which displays a high (∼90%) efficiency and large (∼15 GHz) bandwidth. This is the fastest high-efficiency integrated waveguide photodetector reported to date.
Regrowth of a thin InP surface covering layer in the Au/InP system during annealing
Authors: Pécz B. , Radnóczi G. , Barna P. B. , Zsoldos Éva
Published: July 2002

Au(100 nm)/InP(111) samples were annealed at 500 °C in a forming gas for 10 min. Au9In4 and AuIn2 phases formed during the heat treatment. Besides the formation of Au-In phases, a thin (about 20 nm thick), polycrystalline, continuous InP layer was observed on the top of the sample.
Bistable hot electron transport in InP/GaInAs composite collector heterojunction bipolar transistors
Authors: Ritter D. , Hamm R. A. , Feygenson A. , Temkin H. , Panish M. B. , Chandrasekhar S.
Published: July 2002

The transport mechanism of electrons across an energy barrier in the collector of a heterojunction bipolar transistor is studied and identified as hot electron thermionic emission. Bistability between tunneling and thermionic emission was observed at 77 K and room temperature. The bistability can be suppressed by n-type doping of the heterointerface vicinity.
Inhibition of etching in oxygen-implanted AlGaAs
Authors: Reynolds C. L. , Lengle S. E. , Ahrens R. E. , Parker S. M.
Published: July 2002

Ion bombardment for the formation of thermally stable, high resistivity layers in GaAs and AlGaAs is well known. The impact of this device isolation scheme on subsequent processing steps is less understood. Here, we report on an inhibition of etching in oxygen-implanted AlGaAs at an ion dose of 1×1014/cm2. Speculation on potential applications is given.
Low residual impurities assessment by photoluminescence in multistep wafer-annealed semi-insulating Czochralski-grown GaAs
Authors: Ka O. , Oda O. , Makita Y. , Yamada A.
Published: July 2002

Multistep wafer-annealed semi-insulating GaAs wafers (MWA) are characterized using photoluminescence (PL). The PL spectra present well-resolved near-band-edge transitions, including the doublet of the neutral acceptor-bound exciton. A detailed investigation using selective pair luminescence of samples submitted to different annealings, i.e., wafer- or ingot-annealing, single or multistep, shows that carbon is the main shallow acceptor. However, for the wafer-annealed samples, two other residual impurities found in the as-grown or ingot-annealed crystals have their estimated concentrations noticeably reduced, for Zn (e.g., around 1013 cm−3 in MWA), or are unresolved for Si. This reduction of background impurities may have direct consequences for device applications.
Role of hydrogen in the growth of Y1Ba2Cu3O7 on MgO substrates by off-axis magnetron sputtering
Authors: Cukauskas Edward J. , Allen Laura H. , Sherrill Gregory K. , Holm R. T.
Published: July 2002

Y1Ba2Cu3O7 thin films have been grown on MgO by off-axis magnetron sputtering using mixtures of argon, oxygen, and hydrogen. Reduction in film transition temperature resulting from cumulative target sputtering time (target degradation) is minimized by adding hydrogen to the sputtering gas. Without hydrogen, new targets which had produced films with 87.5 K transition temperatures degraded with deposition time and produced films with transition temperatures of only 82 K. After addition of hydrogen, these targets produced films with transition temperatures of nearly 89 K. Critical-current densities for the films made at optimum hydrogen flow were greater than 3×106 A/cm2 at 4 K. With the addition of hydrogen, we observed a significant increase in the sputtergun cathode voltage and a dramatic increase in the deposition rate. The films were predominantly c-axis oriented, and we observed a minimum c-axis lattice parameter for optimum hydrogen flow. We attribute these improvements in material properties to the catalytic effect of hydrogen in maintaining atomic oxygen in the plasma, allowing more oxygen to be incorporated into the target and the film during growth.
Organometallic vapor phase epitaxy of CoGa on (100)GaAs
Authors: Maury F. , Talin A. A. , Kaesz H. D. , Williams R. S.
Published: July 2002

We report the first epitaxial growth of CoGa thin films on (100)GaAs substrates by organometallic chemical vapor deposition. The separate sources (η5-C5H5)Co(CO)2 and Et3Ga were mixed in a stream of carrier gas and decomposed in a conventional cold wall epitaxial reactor between 260 and 300 °C under atmospheric pressure. A typical growth rate of 1 μm/h was achieved and the film composition could be directly monitored from the gas phase composition. The Co-rich films have the α-Co metal structure and react with GaAs at 500 °C to form CoAs. By contrast, Ga-rich β-CoGa films were lattice matched on (100)GaAs and were found to be thermodynamically stable at 500 °C. This work demonstrates that organometallic vapor phase epitaxy is also a suitable technique for the fabrication of buried metal/semiconductor heterostructures.
Nitrogen-induced amorphization of Ti-Zr powders during mechanical alloying
Authors: Aoki K. , Memezawa A. , Masumoto T.
Published: July 2002

A mixture of elemental powders of Ti and Zr, which exhibit the complete solid solubility, has been mechanically alloyed by a high-energy ball mill, at room temperature, under a controlled nitrogen atmosphere. The products were characterized by x-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and chemical analysis. Nanocrystalline fcc type c-TiZrN0.9 powders were prepared by MA in 2 MPa of nitrogen gas. On the contrary, amorphous a-TiZrN0.3 alloy powders were synthesized by MA in 0.04 MPa of nitrogen gas.
Laser-driven boron diffusion into a Si epitaxial layer from a p+ boron-doped Si substrate
Authors: Kim K. M. , Mei S. N. , Saccamango M. J. , Chu S. F. , von Gutfeld R. J. , Vigliotti D. R.
Published: July 2002

Experiments are described in which ∼0.2-s-wide argon laser pulses are incident on a 6-μm-thick n− Si epitaxial layer. Local melting and refreezing of both the layer and a small volume of the underlying p+ boron-doped Si substrate occur. In the molten phase, boron diffusion from the substrate is sufficient to make a low resistance path between the front surface and the substrate, with a nearly uniform dopant concentration of 5×1018/cm3. The melted/recrystallized front surface diameter is ∼50 μm. Unique features and applications of this type of substrate contacting are discussed.
Anisotropic strain relaxation in GaAs layers grown on Si(100) substrates by post-growth patterning
Authors: Tsukamoto Nobuo , Yazawa Yoshiaki , Asano Junko , Minemura Tetsuroh
Published: July 2002

Strain relaxation in stripe-shaped GaAs layers on Si(100) substrates by post-growth patterning has been investigated by photoluminescence (PL) measurements. PL spectrum for the GaAs stripes along [001] showed peaks positioned at shorter wavelength than those for stripes along [011] and [01̄1]. The stripe-orientation dependence was regarded as the crystallographic anisotropy of strain relaxation in the stripe-shaped GaAs layers. The PL results, therefore, showed that the stripes along [001] were superior to those along [011] and [01̄1] for reducing residual strain in the GaAs layers.
Determination of low temperature impact ionization coefficients in GaAs by electroluminescence measurements on single barrier tunneling structures
Authors: Cockburn J. W. , Skolnick M. S. , David J. P. R. , Grey R. , Hill G. , Pate M. A.
Published: July 2002

Measurements of the absolute intensity of electroluminescence (EL) due to impact ionization in n-type GaAs/AlGaAs single barrier tunneling structures are reported. These measurements yield values for the impact ionization coefficient (α) for electrons in GaAs as a function of electric field at a temperature of 5 K. Structures with undoped high field regions of length 100, 150, and 200 nm are shown to give very similar quantitative results for α. Very good agreement is obtained with the results of low temperature carrier multiplication measurements, carried out independently on a bulk GaAs p-i-n diode, thus establishing EL studies as a reliable quantitative probe of impact ionization phenomena.
Carrier lifetime in HgTe/CdTe superlattices grown by photoassisted molecular beam epitaxy
Authors: Reisinger A. R. , Harris K. A. , Myers T. H. , Yanka R. W. , Mohnkern L. M. , Hoffman C. A.
Published: July 2002

We report excess carrier lifetimes of several hundred nanoseconds in HgTe/CdTe superlattices grown by photoassisted molecular beam epitaxy. The structures were doped either n-type in the low 1015 cm−3 range or p-type in the low 1016 cm−3 range, and were designed for peak response in the long-wave infrared regime. The measured lifetimes, recorded by the transient photoconductivity technique, approach values calculated for alloys of equivalent band-gap energy. They indicate that recombination at the superlattice interfaces has been substantially reduced and underscore the recent progress achieved in superlattice growth technology.
Correlation between the exciton mobility and the excitonic linewidth in shallow InxGa1−xAs/GaAs quantum wells
Authors: Bacher G. , Schweizer H. , Kovac J. , Nickel H. , Schlapp W. , Lösch R.
Published: July 2002

Using time-resolved photoluminescence (PL) spectroscopy with high spatial (0.1 μm) and temporal (50 ps) resolution, we have investigated exciton scattering in a set of strained InxGa1−xAs/GaAs quantum wells as a function of well width Lz and In content x. Summarizing the results, a strong correlation between the exciton mobility and the emission linewidth (LW) is found: High mobilities correspond to small luminescence LWs, indicating reduced exciton scattering. From the dependence of the excitonic mobility on temperature and In content x, we conclude, that interface roughness scattering and alloy scattering, respectively, are the dominant processes controlling the mobility as well as the PL LW at low temperatures.
Two wavelength optically controlled latch and AND gate
Authors: An X. , Geib K. M. , Hafich M. J. , Crumbaker T. E. , Silvestre P. , Beyette F. R. , Feld S. A. , Robinson G. Y. , Wilmsen C. W.
Published: July 2002

A new optical device which functions either as a gated latch or an AND gate is demonstrated. This device utilizes two different wavelengths of input light and is composed of two heterojunction phototransistors (HPTs) vertically integrated with a light emitting diode. The collector-base regions of the two HPTs are fabricated from different band-gap materials and thus, respond to different wavelengths of input light. The device structure was fabricated from InGaAsP/InP epitaxial layers grown by gas source MBE. The gated latch and AND gate are shown to have an on/off contrast ratio of 12 and 6, respectively.
Thermal wave measurement of ion implanted semiconductors in the mirage effect geometry
Authors: Glazov A. L. , Muratikov K. L. , Suvorov A. V.
Published: July 2002

The effect of ion implant processes on an amplitude and phase of thermal wave signals from semiconductors was analyzed. It is experimentally shown for InP and GaAs that the ion implantation results in a considerable increase of the signal amplitude when using Nd:YAG pump laser at 1.06 μm wavelength. It was found out that the nature of spatial oscillations observed in a signal behavior is forced by pump radiation interference due to the internal reflection from a rear sample surface.
Production of substantially stable Nd-Fe-B hydride (magnetic) powders using chemical dissociation of water
Authors: Ram S. , Joubert J. C.
Published: July 2002

Finely divided loose Nd2Fe14BHx, x≤5, hydride powder (particle size ≤1 μm is synthesized by washing Nd2Fe14B crystallites embedded in calcium and other by-products (during a reduction-diffusion-reaction performed using excess calcium) in water. The calcium reacts thereby with the water and produces, Ca+H2O■CaO+H2, native hydrogen, which very intimately reacts the alloy and forms the hydrided alloy. The particles are passivated forming a thin but rather hydrogen proof (and probably amorphous) layer of oxide and hydroxide species on the surface. Consequently, peculiarly, they are stable, stand against high corrosion, and can be stored in laboratory air atmosphere at room temperature for extended periods of time with no apparent further loss in structural or magnetic properties.
Microwave resonators from YBa2Cu3O7−δ thin films made by plasma-enhanced metalorganic chemical vapor deposition
Authors: Young K. H. , Robinson McD. , Negrete G. V. , Zhao J. , Chern C. S. , Li Y. Q. , Norris P. E.
Published: July 2002

Epitaxial YBa2Cu3O7−δ thin films on LaAlO3 deposited by plasma-enhanced metalorganic chemical vapor deposition were tested in a 100 GHz microwave cavity and as patterned 5.6 GHz resonators. Two films, both having high critical temperature (≳90 K) and high critical current density (≳106 A/cm2), exhibited low-power Q’s of 5400 and 8000 as 5.6 GHz microstrip resonators when operated at 77 K. The equivalent surface resistances at 10 GHz are 1.7 and 1 mΩ, respectively. Despite the fact that these films are thinner than typical laser ablation films, the results are within a factor of 2 of the best laser ablation prepared YBa2Cu3O7−δ films.
Boron-enhanced low-temperature Si epitaxy by rapid thermal processing chemical vapor deposition
Authors: Hsieh T. Y. , Jung K. H. , Kwong D. L. , Kim Y. M. , Brennan R.
Published: July 2002

We demonstrate that epitaxial growth temperatures can be lowered by in situ boron incorporation using rapid thermal processing chemical vapor deposition (RTPCVD). Heavily boron-doped epitaxial layers with very abrupt dopant transition profiles have been grown at 800 °C. Carrier concentrations as high as 5×1019 cm−3 were obtained with defect densities of the order of 102–103 cm−2. The film quality and surface morphology were closely related to dopant concentration. Higher dopant concentrations improved surface morphology.
Low resistance tungsten films on GaAs deposited by means of rapid thermal low pressure chemical vapor deposition
Authors: Katz A. , Feingold A. , Nakahara S. , Pearton S. J. , Lane E.
Published: July 2002

Low resistance tungsten (W) films were deposited onto GaAs substrates by means of rapid thermal low pressure chemical vapor deposition (RT-LPCVD), using tungsten hexafluoride (WF6) gas reduced by hydrogen (H2). Deposition temperatures up to 550 °C for durations of up to 30 s were explored, resulting in deposition of relatively pure W films (containing less than 2% O2 and C). Post-deposition sintering of the layers led to significant reduction of the resistivity to values as low as 50 μΩ cm. The efficiency of the deposition improved upon increasing the H2 flow rate up to 1250 sccm resulting in a deposition rate of about 10 nm/s at a total chamber pressure of 3.5 Torr and temperature of 500 °C. The films appeared to be polycrystalline with a very fine grain structure, regardless of the deposition temperature with good morphology and underwent a limited reaction with the underlying GaAs substrates.
Theory of stability in a nonlinear resistive network
Authors: Uenoyama T. , Esaki L. , Kotera H.
Published: July 2002

In a nonlinear resistive network, Kirchhoff’s laws and branch equations generally give several solutions as operating points. We have studied the condition of the stability of the solutions, taking into account the curvature of the total power in voltage-current space. Since the power of each element is expressed by integration over the voltage and current as independent functions, this new expression makes a geometrical representation of the total power. It is shown that the differentiable and minimum points correspond to the physical operating points of the network.
Use of electron-beam charging for in-process inspection of silicide complementary metal-oxide-semiconductor gate electrode isolation
Authors: Jenkins K. A. , Agnello P. D. , Bright A. A.
Published: July 2002

Inspection of complementary metal-oxide-semiconductor circuits by electron-beam charging is demonstrated. Isolation of the gate electrodes used in the actual circuits is verified. The inspection is done entirely without contact, without removing wafers from the clean room, and prior to metal and interlevel dielectric deposition.
High-performance planar native-oxide buried-mesa index-guided AlGaAs-GaAs quantum well heterostructure lasers
Authors: Caracci S. J. , Kish F. A. , Holonyak N. , Maranowski S. A. , Smith S. C. , Burnham R. D.
Published: July 2002

High-performance planar ‘‘buried-mesa’’ index-guided AlGaAs-GaAs quantum well heterostructure (QWH) lasers have been fabricated by oxidation (H2O vapor+N2 carrier gas, 425–525 °C) of a significant thickness of the high composition AlxGa1−xAs upper confining layer (outside the active stripe). The oxide provides excellent current confinement for low-threshold laser operation and a low refractive index (n∼1.6) for transverse optical confinement and index guiding. Laser diodes with ∼4 μm-wide active regions exhibit 300 K continuous (cw) laser thresholds of 8 mA, with single longitudinal mode operation to 23 mW/facet, and maximum output powers of 45 mW/facet (uncoated). Devices fabricated on a lower confinement AlxGa1−xAs-GaAs QWH crystal (x≲0.6 instead of x≳0.8) with ∼4 μm-wide active stripes exhibit 300 K cw thresholds of 9 mA and total external differential quantum efficiencies of 66%. Peak output powers ≳80 mW/facet (uncoated) with linear L-I characteristics over the entire operating range are observed. In limited ‘‘lifetest’’ these laser diodes have been operated ≳500 h without significant degradation.
Measurement of elastic relaxation in cross-sectional transmission electron microscopy of GexSi1−x/Si strained-layer superlattices
Authors: Duan X. F.
Published: July 2002

Two types of relaxation occur in the cross-sectional transmission electron microscopy samples of the GexSi1−x/Si strained-layer superlattices (SLS) by large-angle convergent-beam electron diffraction (LACBED) and imaging technique which gives a good LACBED pattern superimposed on a high spatial resolution shadow image of the SLS. One type of relaxation occurs between the Si and the GeSi layers. It is negligible in the convergent-beam electron diffraction (CBED) case for the larger value of the ratio of the sample thickness to the SLS wavelength. Another type occurs between the superlattice as an average crystal and the Si substrate. The relaxation of the SLS can be measured by the shift of the Kikuchi line in the SLS from that in the Si substrate.
Conversion loss of a YBa2Cu3O7 grain boundary mixer at 20 GHz
Authors: Butler Donald P. , Yang Wiyi , Wang Jianglin , Bhandari Anil , Celik-Butler Zeynep
Published: July 2002

We have measured the conversion gain of a YBa2Cu3O7 annealed grain boundary microbridge mixer by operating the device as a lower side-band down-converter from an 18.5 GHz radio frequency to a 1.5 GHz intermediate frequency under the action of a 20.0 GHz local oscillator. We have found the conversion gain to be relatively independent of bias up to a current density which marks the onset of the flux flow resistance. Above the onset of flux flow resistance, the gain decreased dramatically. A maximum conversion gain of −8±4 dB was measured at 25 K. The mixer was operated with a local oscillator power of only −60 dBm. The results demonstrate that high Tc superconductor mixers are capable of delivering comparable conversion gains to Schottky diode mixers while requiring substantially lower power local oscillators.
Microwave oscillation in InAs p-n junctions
Authors: Kamakura Katsutoshi
Published: July 2002

Continuous coherent microwave oscillation has been observed in InAs p-n junctions under the application of a dc reverse bias voltage and an external magnetic field in the region of avalanche breakdown at room temperature. The observed oscillation frequency varies with the sample current of the p-n junction and the magnetic field.
Observation of the dispersion behavior of surface acoustic waves in a wedge waveguide by laser ultrasonics
Authors: Jia X. , de Billy M.
Published: July 2002

Wedge (or line) acoustic waves, propagating along the tip of an elastic wedge waveguide, are generated by pulsed YAG laser impact and detected by a wideband optical interferometer. In an ideal infinitely sharp and tall wedge guide, the antisymmetrical flexural (ASF) modes are nondispersive and their energies are mostly confined near the wedge tip. The displacement measurements with the optical probe on metallic wedges show broadband pulsed wave forms of ASF modes. Dispersive behavior of these wave forms, which are not predicted by the theoretical models, are clearly demonstrated. The dispersion curves of the phase velocity are quantitatively deduced by a phase analysis method.
Crystallization and phase transitions in C60
Authors: Byszewski P. , Diduszko R. , Kowalska E. , Fink-Finowicki J. , Witowski A.
Published: July 2002

C60 fullerites were condensed from solution using various techniques. The phase transitions were monitored by derivative scanning calorimetry measurements performed in various gases. Two phase transitions were observed in C60 crystals at 245 and 260 K. The low temperature one results from the molecules’ reorientation in the lattice and disappears for poorly crystallized material. The high temperature one is observed in all samples and results from molecules libration. The gas dissolved in C60 crystals strongly influences observed phase transitions.
Wavelength control and residual oxygen in AlGaAs/InGaAs strained quantum-well heterostructures grown by molecular beam epitaxy
Authors: Chand Naresh , Fitzgerald E. A. , Geva M.
Published: July 2002

We have studied the residual oxygen in AlGaAs/GaAs/InGaAs heterostructures, and the effects of As2 and As4 species and growth temperature (TS) on optical properties of InGaAs quantum wells (QW) for AlGaAs/InGaAs strained QW lasers. In clean growth conditions, the optical properties of InGaAs QWs are insensitive to the As beam used, and the luminescence intensity does not increase with increasing TS from 570 to 630 °C or by postgrowth thermal annealing. Because of the very strong dependence of In sticking coefficient on TS, the TS needs to be precisely controlled to obtain the desired emission wavelength. A solubility limit of ∼8×1017 cm−3 for Be is measured in AlAS at 700 °C growth temperature. The residual oxygen level in undoped and Be-doped AlxGa1−xAs with x=0.35 was found to be higher by a factor 2 than in x=0.5, 0.6, and 1.0 compositions. In Si-doped AlxGa1−xAs, the O level is the lowest with no variation with x.
Selective growth of Si/SiGe resonant tunneling diodes by atmospheric pressure chemical vapor deposition
Authors: Zaslavsky A. , Grützmacher D. A. , Lee Y. H. , Ziegler W. , Sedgwick T. O.
Published: July 2002

Atmospheric pressure chemical vapor deposition is used to grow p-type Si/Si1−xGex double-barrier resonant tunneling structures on unstrained substrates, with a Si0.75Ge0.25 well clad by Si barriers. The current-voltage I(V) characteristics at T=77 and 4.2 K exhibit current peaks and negative differential resistance regions corresponding to resonant tunneling through well-resolved heavy- and light-hole subbands in the well. Device quality is comparable to Si/SiGe resonant tunneling structures grown by molecular beam epitaxy. The in situ substrate cleaning and selective growth capabilities of atmospheric pressure chemical vapor deposition are used for the first successful selective growth of resonant tunneling structures through an oxide mask. The resulting diodes exhibit good resonant tunneling characteristics. The selective growth process is promising for the fabrication of small vertical heterostructure devices.
Structure and magnetic properties of anisotropic Sm2Fe17Nx powders
Authors: Ding J. , McCormick P. G. , Street R.
Published: July 2002

Anisotropic powders of Sm2Fe17Nx were prepared by the mechanical milling of Sm2Fe17 and nitriding. The effects of milling time, ball size, and heat treatment on the structure and magnetic properties have been studied. Short milling times resulted in particle attrition; disproportionation into a mixture of Fe and an amorphous Fe-Sm phase occurred above a critical milling time. Maximum energy products of up to 21 MGOe were obtained in aligned samples of mixed structure which were milled for intermediate times and heat treated prior to nitriding.
Enhanced long wavelength response in a GaAs photodetector
Authors: Nakajima Kazutoshi , Sugimoto Kenichi , Hirohata Toru , Mizushima Yoshihiko
Published: July 2002

A metal-semiconductor-metal photodetector (MSM-PD) fabricated on a semi-insulating GaAs has a long wavelength response beyond the energy gap. It is enhanced by applying a second bias voltage to the bottom electrode. When the bias is 100 V, the responsivity exceeds the unit quantum efficiency, which indicates that a photoconductive amplification function exists. Since the dark current is as small as 0.2 nano-amperes, it may be more suitable than an InGaAs or a Ge photodiode for long wavelength detection.
Cross-sectional structures of CoNiCr/Cr bilayer and multilayer thin films
Authors: Wong B. Y. , Laughlin E. E.
Published: July 2002

The cross-sectional structure of CoNiCr/Cr bilayer and multilayer thin films is investigated by HRTEM. Results showed that the orientation relationship between CoNiCr and Cr and the crystallographic orientation of CoNiCr is controlled by the orientation of the Cr column. Similar results are found for the multilayer film. The crystallographic orientation of the Cr interlayer and the second CoNiCr layer is identical to that of the Cr underlayer and the first CoNiCr layer. The misfit at the interface is partially relieved by misfit dislocations and the rest remains as elastic strain.
Atomic scale imaging of hydroxyapatite and brushite in air by force microscopy
Authors: Siperko Lorraine M. , Landis William J.
Published: July 2002

A method for obtaining atomic scale images of powder samples by force microscopy has been used to determine surface structures of hydroxyapatite and brushite. From isolated hydroxyapatite crystal clusters, two crystal planes have been identified. The 〈001〉 and 〈110〉 spacings obtained agree well with published crystallographic values. Groups of brushite platelets yielded atomic spacings which are presumed to be those of the 〈110〉 crystal plane.
Heterostructure field-effect transistor optical modulator in the InGaAs/AlGaAs material system
Authors: Vang T. A. , Taylor G. W. , Evaldsson P. A. , Cooke P.
Published: July 2002

The heterostructure field-effect transistor optical modulator is demonstrated in a waveguide geometry using strained InGaAs quantum wells. A 20 μm×300 μm device is shown to have a contrast ratio of 35:1 using a 2 V swing from −1 to +1 V, which results in a figure of merit of 25.7 dB/V mm for this device. A Kramers–Kronig transformation is used to show the potential low chirp available at maximum contrast ratio for this device. Wavelength compatibility with a 5 μm×400 μm heterostructure field-effect laser from the same wafer is demonstrated, and the corresponding heterostructure field-effect transistor is also demonstrated from the same wafer with a transconductance of 120 mS/mm for a 1 μm gate length.
YBa2Cu3O7 thin films grown on sapphire with epitaxial yttria-stabilized zirconia buffer layers
Authors: Chen L. F. , Chen P. F. , Li L. , Li S. L. , Jing X. N. , Pan S. J. , Guo Y. H.
Published: July 2002

Epitaxial yttria-stabilized zirconia (YSZ) buffer layers were grown successfully on sapphire (112̄0) substrates by using rf magnetron sputtering method. The films were cubic in structure with their (100) orientation normal to the substrate surface. YBa2Cu3O7 thin films were deposited on the YSZ/sapphire substrates by the in situ dc magnetron sputtering method. X-ray diffraction analysis showed they were highly c-axis oriented with the zero resistance temperature TCO=92 K and critical current density Jc=1.6×106 A/cm2 at 77 K.
Multiple photochemical switching device based on Langmuir–Blodgett films
Authors: Tachibana Hiroaki , Manda Eiichiro , Azumi Reiko , Nakamura Takayoshi , Matsumoto Mutsuyoshi , Kawabata Yasujiro
Published: July 2002

We have demonstrated that the multiple photochemical switching device can be fabricated by successive deposition of two different photochemical switching Langmuir–Blodgett (LB) films consisting of molecules with switching, transmission, and working units, each corresponding to azobenzene derivatives, alkyl chain, and conductive pyridinium (TCNQ)2 complex, respectively. The photoisomerization of switching units causes a change in conductivity of the LB films, which is associated with working units. When molecules with different switching units are used to assemble the device, its conductivity can be controlled by the irradiation with four types of control light.