bluuebunny/crossref_metadata_2025 huggingface dataset:
Nd:CaYAlO4—a new crystal for solid-state lasers emitting at 1.08 μm
Authors: Verdún Horacio R. , Thomas Leonard M.
Published: July 2002

Crystals with the K2 NiF4 structure are good hosts for transition metal and rare-earth ions. Continuous-wave room-temperature laser action in a neodymium-doped crystal with this structure, CaYAlO4 , was observed using a GaAlAs diode laser array for end pumping of the laser rod. The free-running laser operated at a wavelength of 1080.6 nm.
Quantitative, all-optical prediction of the carrier density in semi-insulating GaAs
Authors: Steiner T. W. , Zhang Yu. , Thewalt M. L. W. , Maciaszek M. , Bult R. P.
Published: July 2002

We have used a series of all-optical measurements to determine shallow acceptor, shallow donor, and midgap donor (EL2) concentrations. The validity of these measurements was then tested by comparing the predicted electron density to the measured Hall density. Resonant pumping of the first excited state of the polariton sharpened the photoluminescence spectrum sufficiently to allow a reliable measurement of the shallow donor to acceptor ratio. The absolute shallow acceptor, donor, and EL2 concentrations were determined by a series of absorption and luminescence measurements. The Fermi level and hence the carrier concentration was then deduced using the three-level model of semi-insulating behavior.
Column III-column V sublattice interaction via Zn and Si impurity-induced layer disordering of 13C-doped AlxGa1−xAs-GaAs superlattices
Authors: Guido L. J. , Major J. S. , Baker J. E. , Holonyak N. , Cunningham B. T. , Stillman G. E.
Published: July 2002

Experiments are described employing secondary-ion mass spectroscopy (SIMS) to study the stability of 13C-doped Al0.5Ga0.5As-GaAs superlattices against Zn and Si impurity-induced layer disordering (IILD). The modulation depth of the SIMS 27Al and 13C signals is used as a sensitive probe of column III and column V sublattice interdiffusion. The data show that CAs is much more stable against Zn and Si IILD than the column III superlattice host crystal itself. The minor enhancement of CAs diffusion via the column III disordering agents, which is present to a significant extent for Si IILD but almost nonexistent for Zn IILD, suggests that there is no direct interchange of column III and column V sublattice atoms. The Zn and Si enhancement of carbon diffusion is probably caused by local Coulombic interaction between the diffusing Zn+i and Si+III species and the C−As acceptor.
A Si0.7Ge0.3 strained-layer etch stop for the generation of thin layer undoped silicon
Authors: Godbey D. , Hughes H. , Kub F. , Twigg M. , Palkuti L. , Leonov P. , Wang J.
Published: July 2002

The use of a Si0.7Ge0.3 strained layer as an etch stop in silicon-based materials is reported. The etch rates were characterized through silicon and a 60 nm Si0.7Ge0.3 strained layer. The etch rate through undoped silicon was 17–20 nm/min, while the etch rate through the Si0.7Ge0.3 layer was 1 nm/min. After annealing the wafer to 850 °C for 30 min, transmission electron microscopy was used to show that strain in the alloy layer was only partially relieved, and that generated misfit dislocations were confined to the strained Si0.7Ge0.3 layer. The etch rate through the strained layer increased to 1.7 nm/min after this treatment, and was still perfectly functional as an etch stop.
Influence of slip direction on the photoplastic effect in cadmium sulfide
Authors: Garosshen T. J. , Kim C. S. , Galligan J. M.
Published: July 2002

Studies of the photoplastic behavior of CdS single crystals show that when slip occurs on the basal plane, a large increase in flow stress is observed in the presence of incident light. However, when the crystal is oriented for slip on the prismatic planes, a very small photoplastic effect is observed. Measurements of the current associated with dislocation motion on the active slip systems indicate that the photoplastic effect is proportional to the charge on the dislocations in the respective slip planes.
Changes in refractive index of fluoride glass fibers during fiber fabrication processes
Authors: Nakai T. , Norimatsu N. , Noda Y. , Shinbori O. , Mimura Y.
Published: July 2002

Refractive indices of fluoride glass fibers were measured for the first time and a remarkable decrease in the refractive index during fiber fabrication processes has been observed. This decrease is most likely due to the change in the glass structure during fiber drawing and due to the stress induced during preform fabrication processes.
Enhanced diffusion of Si due to He ion implantation in Si-delta doped GaAs layers
Authors: Tell B. , Brown Goebeler K. F. , Cunningham J. E. , Chiu T. H. , Jan W. Y.
Published: July 2002

Enhanced diffusion of Si due to He ion implantation in Si-delta doped GaAs layers has been observed by the capacitance-voltage technique. After an 800 °C anneal, an increase as large as an order of magnitude in the diffusion coefficient compared to thermal diffusion was observed. We also observe a decrease in the integrated sheet carrier concentration as a result of the He implants, and the decrease appears independent of annealing time.
Heterojunction bipolar transistor fabrication using Si1−xGex selective epitaxial growth by gas source silicon molecular beam epitaxy
Authors: Hirayama Hiroyuki , Hiroi Masayuki , Koyama Kazuhisa , Tatsumi Toru
Published: July 2002

B doping in Si1−xGex was successfully achieved using HBO2 cell in gas source Si molecular beam epitaxy (Si-MBE). Combining this B doping method and selective epitaxial growth of Si1−xGex by gas source Si-MBE, B-doped Si1−xGex selective epitaxial growth was found to be possible. This B-doped Si1−xGex selective epitaxial growth was applied to Si1−xGex/Si heterojunction diode and Si1−xGex base heterojunction bipolar transistor (HBT) fabrications. The Si1−xGex base HBT (x=0.16, 0.22, 0.31) showed higher hFE in as-grown condition than that for a homojunction transistor. The band-gap difference between the Si1−xGex base and the Si emitter was estimated by the temperature dependence of the collector current ratio between the HBT and the homojunction transistor.
1.5 μm InGaAsP/InP buried crescent superluminescent diode on a p-InP substrate
Authors: Chen T. R. , Zhuang Y. H. , Xu Y. J. , Yariv A. , Kwong N. S.
Published: July 2002

An InGaAsP/InP superluminescent diode (SLD) emitting at 1.54 μm has been fabricated. The device uses a buried crescent structure on a p-InP substrate. The parameters were optimized for high output power, small spectral modulation, and smooth far-field operation. The coherence function of the SLD emission was studied systematically. An output power of 5 mW, a coherence length of 41 μm, and a second coherence peak suppression ratio of 22 dB were obtained.
Improved minority-carrier lifetime in Si/SiGe heterojunction bipolar transistors grown by molecular beam epitaxy
Authors: Higashi G. S. , Bean J. C. , Buescher C. , Yadvish R. , Temkin H.
Published: July 2002

Noncontact-probe photocarrier lifetime measurements have been used to give rapid feedback on minority-carrier lifetimes of epitaxial Si/SiGe layers grown by molecular beam epitaxy (MBE). In this manner, problems with impurity incorporation during the crystal growth can be rapidly diagnosed in a device-processing-independent fashion. These improvements in minority-carrier lifetime translate directly into high gains in the heterojunction bipolar transistors (HJBTs). HJBT test devices fabricated from the MBE-grown Si/SiGe layers show current gains as high as 800. The homojunction gain of this device is estimated to be ∼6, making the heterojunction gain on the order of 130.
Optical generation of picosecond electrical pulses in asymmetric quantum well structures placed in a transverse magnetic field
Authors: Khurgin J.
Published: July 2002

New technique for optical generation of ultrashort electrical pulses in semiconductor heterostructures is proposed. It is shown that in asymmetric quantum well structures placed in a transverse magnetic field, optically excited carriers have an asymmetrical distribution in k-vector space, and therefore, they have finite drift velocity in the direction perpendicular to both growth direction and field direction. It results in photogenerated voltage along the quantum well plane. The temporal response and sensitivity of the proposed scheme are evaluated, and possible applications are suggested in ultrafast detectors or as a tool for generation and study of hot carriers.
Arsenic influence on extended defects produced in silicon by ion implantation
Authors: Coffa S. , Calcagno L. , Catania M. , Rimini E.
Published: July 2002

Ge ions at 400 keV were implanted on 〈100〉 undoped silicon and on arsenic-doped silicon wafers maintained at 250 °C. The arsenic concentration ranged between 1.0×1019 and 1.0×1020 atom/cm3. The residual damage is mainly in the form of dislocation loops as measured by channeling and transmission electron microscopy. The amount of extended defects is lower in the arsenic-doped than in the undoped samples and it is reduced by a factor of 2 at a dopant concentration of 1×1019 atom/cm3. The experimental data are accounted for by a simple model which assumes an enhanced recombination of point defects created by the ion beam, through the formation of arsenic-point defect pairs in the doped samples.
Magnetically filtered low-loss scanning electron microscopy
Authors: Wells Oliver C. , LeGoues Francoise K. , Hodgson Rodney T.
Published: July 2002

The resolution of the scanning electron microscope can be improved by mounting the sample in the high-field region of a condenser-objective lens. Low-loss electrons (LLEs) are scattered from the sample with an energy loss of less than a few percent of the incident energy. In the past, LLEs have been collected with a retarding-field energy filter. A way has been found to collect LLEs using a detector located within the magnetic field of the condenser-objective lens which provides the required energy-filtering action. This greatly simplifies the apparatus and makes it possible to obtain LLE images with less tilt of the specimen and with a higher beam energy than before.
Wavelength and polarization insensitive 3 dB cross-coupler power dividers by ion exchange in glass
Authors: Hussell Christopher P. , Ramaswamy Ramu V. , Srivastava Ramakant , Jackel Janet L.
Published: July 2002

We have fabricated fiber-compatible, low-loss, wavelength and polarization insensitive 3 dB 2×2 cross couplers by Ag+-Na+ ion exchange in glass. The couplers were designed using the adiabatic invariance condition for graded-index channel waveguides. An excellent agreement between theory and experiment is demonstrated.
Lasing characteristics of a continuous-wave operated folded-cavity surface-emitting laser
Authors: Takamori Takeshi , Coldren Larry A. , Merz James L.
Published: July 2002

Room-temperature continuous-wave operation of a folded-cavity surface-emitting AlGaAs/GaAs laser with transverse junction stripe structure, which has a dry-etched 45° internal mirror, is demonstrated for the first time. A threshold current of 42 mA and a differential external quantum efficiency of 19% per facet were obtained. A single far-field lobe and single longitudinal mode emission were also observed.
Microwave surface resistance of magnetron-sputtered Tl-Ba-Ca-Cu-O films on silver substrates
Authors: Cooke D. W. , Gray E. R. , Arendt P. N. , Reeves G. A. , Houlton R. J. , Elliott N. E. , Brown D. R.
Published: July 2002

Surface resistance measurements on Tl-Ba-Ca-Cu-O thick films (∼15 μm) magnetron sputtered onto BaF2-buffered, silver-based (Consil 995) substrates have been made at a microwave frequency of 22 GHz. The relatively large-area films (∼5 cm2) are characterized by surface resistance values of 6.9±2 mΩ at 11.3 K and 30.2±1 mΩ at 77 K; the corresponding values for Cu are 10 and 22 mΩ, respectively. These results demonstrate that Tl-Ba-Ca-Cu-O can be deposited onto large-area, metallic substrates with characteristic surface resistance values lower than Cu at 4 K. Orientation of the film should improve the surface resistance at 77 K, thereby making the fabrication of microwave cavities that are superior to Cu possible.
Misfit In0.18Ga0.82As/GaAs metal-semiconductor field-effect transistors with improved Schottky gate characteristics
Authors: Wang G. W. , Kaliski R. , Kuang J. B.
Published: July 2002

In0.18Ga0.82As epitaxial layers having a thickness much greater than the established critical thickness of pseudomorphic layers have been grown on GaAs substrates. 0.25 μm gate metal-semiconductor field-effect transistors (MESFETs) are fabricated by silicon ion implantation into the epitaxial wafers. In spite of the large lattice mismatch and the high defect density, the devices show excellent device performance with a maximum extrinsic transconductance of 620 mS/mm and a current-gain cutoff frequency fT of 92.8 GHz. Furthermore, the Schottky gate characteristics of this device are shown to be comparable to those of GaAs MESFETs.
Time-resolved investigations of sidewall recombination in dry-etched GaAs wires
Authors: Mayer G. , Maile B. E. , Germann R. , Forchel A. , Grambow P. , Meier H. P.
Published: July 2002

We have investigated the sidewall recombination in dry-etched GaAs/GaAlAs wires with widths between 12 μm and 300 nm using picosecond spectroscopy. The wires were fabricated with electron beam lithography and different reactive ion etching processes. The excitonic lifetimes decrease strongly with decreasing wire widths due to sidewall recombination. Using a model calculation to fit the experimentally observed width dependence of the lifetimes the surface recombination velocity is determined to be S=2×106 cm/s at 50 K. S increases with temperature and is independent of the etching process.
Effect of a magnetic field on the gate current in heterostructure field-effect transistors
Authors: Chen You-jun , Dahlberg E. Dan , Shur M. , Akinwande A.
Published: July 2002

We report the effect of relatively weak (classical) magnetic fields on the gate current in heterostructure field-effect transistors. With a three-terminal device using the measured dependences, we deduce an average electron velocity and the average concentration of the two-dimensional (2-d) electron gas in the channel. In addition, our results clearly show the onset of velocity saturation in high electric field. The value of the effective saturation velocity in the channel is of the order of 105 m/s, in agreement with the values deduced from device transconductance.
Efficient techniques for computer simulations of heteroepitaxial growth
Authors: Carson C. L. , Bernholc J. , Faux D. , Hall C. K.
Published: July 2002

A new discrete Monte Carlo technique suitable for simulations of the kinetics of heteroepitaxial crystal growth has been developed and tested on a 103 atom system. The technique offers sizable speed advantages over previous simulation methods and allows for realistic three-dimensional studies of the kinetics of both pseudomorphic and misfit growth modes and of the transformation between them. Elements of the method are of general utility and can also be used to substantially improve the efficiency of continuous-space Monte Carlo and molecular dynamics simulations of growth and other atomic transformations.
Fractional states in few-electron systems
Authors: Hansen W. , Smith T. P. , Lee K. Y. , Hong J. M. , Knoedler C. M.
Published: July 2002

We have observed fractional quantization of very few electrons confined in a semiconductor quantum dot using capacitance spectroscopy. The number of electrons per dot varies from 0 to about 40 as a function of bias on the quantum capacitors. The capacitance spectra have clear minima at gate voltages and magnetic fields, where the filling factors are 1/3 and 2/3. These measurements may allow direct comparison with few-particle calculations.
On-demand atmospheric pressure storage system for AsH3 and PH3
Authors: Sillmon R. S. , Freitas J. A.
Published: July 2002

An on-demand atmospheric pressure storage system for AsH3 and PH3, which eliminates the sudden release hazard associated with compressed gases, has been developed and tested with AsH3. The storage system is based on the adsorption of these gases into the microcavities of synthetic zeolites at 23 °C and subsequent desorption at higher temperatures. The adsorption isotherm and isobar of AsH3 on NaA and CaA zeolites were measured. At 23 °C and 760 Torr AsH3 pressure, an adsorption capacity of 25 wt. % (AsH3/zeolite) was measured for CaA zeolite. About 100% of the adsorbed AsH3 was recovered at desorption temperatures below 190 °C. Preliminary results of operating a 500 cc prototype AsH3-zeolite storage system connected to an organometallic vapor phase epitaxy reactor for the growth of GaAs and AlGaAs show that the purity of the AsH3 is retained during the adsorption/desorption process.
Coherent coupling of independent grating-surface-emitting diode laser arrays using an external prism
Authors: Carlson N. W. , Evans G. A. , Lurie M. , Hammer J. M. , Kaiser C. J. , Liew S. K.
Published: July 2002

Pairs of grating surface-emitting arrays, on a single wafer but free-running, were externally coupled with a prism. The prism acted as an optical coupler between one distributed Bragg reflector in each array. Injection locking was demonstrated by observing a dramatic increase in the lateral coherence of the far field of the prism-coupled arrays.
Wavelength switching in InGaAs/InP quantum well lasers
Authors: Berthold K. , Levi A. F. J. , Tanbun-Ek T. , Logan R. A.
Published: July 2002

The threshold current density of multiple and single quantum well lasers as a function of cavity length has been investigated. A dramatic change of the lasing wavelength and a strong increase of the threshold current density is observed for a single quantum well laser when the cavity length is reduced to ∼400 μm. In addition, discrete widely separated wavelength switching with changes up to 50 nm is achieved using an intracavity electroabsorption region.
Anomalous oxygen precipitation in Czochralski silicon
Authors: Lin Wen , Oates A. S.
Published: July 2002

The effect of curvature of the liquid-solid interface of the Czochralski silicon crystal on microdefect occurrence is examined via the crystal’s oxygen precipitation behavior. Curved interface regions were found to contain more microdefects than the flat interfaced regions. Annealing results at high and low-high temperatures show that oxygen precipitation is dominated by heterogeneous nucleation at a high temperature (1050 °C) without a prior low-temperature nucleation treatment. Therefore, oxygen precipitation in crystals lacking grown-in microdefects would be retarded. When a low-high cycle containing a low temperature near 700 °C is used, the homogeneous nucleation mechanism dominates, and the impact of grown-in microdefects on oxygen precipitation is diminished.
Submilliampere continuous-wave room-temperature lasing operation of a GaAs mushroom structure surface-emitting laser
Authors: Yang Ying Jay , Dziura Thaddeus G. , Wang S. C. , Hsin Wei , Wang Shyh
Published: July 2002

We report a GaAs mushroom structure surface-emitting laser at 900 nm with submilliampere (0.2–0.5 mA) threshold under room-temperature cw operation for the first time. The very low threshold current was achieved on devices which consisted of a 2–4 μm diameter active region formed by chemical selective etching, and sandwiched between two Al0.05Ga0.95 As/ Al0.53Ga0.47 As distributed Bragg reflectors of very high reflectivity (98–99%) grown by metalorganic chemical vapor deposition.
Design of superlattice termination layers
Authors: Coon D. D. , Sorar E.
Published: July 2002

Problems associated with quantum mechanical reflection of miniband carriers at the ends of superlattices are examined. Möbius transformations which map miniband Bloch wave reflectivity into plane wave reflectivity and vice versa are derived. These transformations facilitate the design of blocking and antiblocking layers which are analogous to reflective and antireflective coatings on optical elements. An example of termination layer design which is easy to implement is given. Applications include superlattice infrared detector design.
Influences of trace metal impurities on the thermal quenching of photoluminescence in hydrogenated amorphous silicon by homogeneous chemical vapor deposition
Authors: Qian Z. M. , Nijs J. , Michiel H. , Leclair J. , Vandervorst W. , Ammel A. Van , Mertens R.
Published: July 2002

The influence of trace metal impurities of low-temperature undoped amorphous silicon by homogeneous chemical vapor deposited a-Si:H has been explored for the first time. The metal impurities Ni, Cr, and Fe cause a shift of the transition temperature for the double-activated regime to a relatively low value. However, Ga and B impurities quench the photoluminescence intensity at a low temperature. Both of them cause weak photoemission of the films at room temperature. The shift of the transition temperature can be explained by the presence of non-radiative deep recombination centers. The quenching of the photoluminescence intensity is caused by the presence of nonradiative recombination centers.
Influence of the impurity concentration on charge carrier dynamics in GaAs films
Authors: Werner A. , Kunst M. , Moustakas T. D.
Published: July 2002

The influence of the silicon concentration on excess charge carrier kinetics in molecular beam epitaxy grown GaAs films has been studied by transient photoconductivity measurements with a contactless microwave conductivity technique. Several decay channels can be distinguished: an initial, fast second-order decay more active in low impurity films and at high excitation intensities, and a slower decay component characterized by effective decay times ranging from 6 μs for low impurity samples and increasing decay times with increasing Si concentration. The initial, fast second-order decay is attributed to electron-hole recombination and is quenched by hole traps present at higher Si concentrations. In low impurity samples, the slower decay channel is ascribed to a deep electron trapping channel which can be saturated at higher excitation intensities. In high impurity samples, the decay time exceeds 100 μs and may be due to electron-trapped hole transitions.
Novel spectral response of a coupled quantum well photodiode
Authors: Tokuda Yasunori , Kanamoto Kyozo , Tsukada Noriaki
Published: July 2002

Novel hysteretic spectral response of a coupled quantum well p-i-n photodiode was demonstrated by combining a self-electro-optic effect with interwell coupling effects on the optical absorption. The phenomena may be sueful for new optical detection, in which high sensitivity is obtained for a monochromatic optical signal within a restricted wavelength range which is controllable by the bias voltage.
Threshold current reduction in patterned quantum well semiconductor lasers grown by molecular beam epitaxy
Authors: Kapon E. , Simhony S. , Harbison J. P. , Florez L. T. , Worland P.
Published: July 2002

Reduction of threshold current in GaAs/AlGaAs patterned quantum well (PQW) lasers grown by molecular beam epitaxy is studied. Application of high reflection coating results in threshold currents as low as 0.35 mA. Dependence of the measured threshold currents on the optical cavity losses agrees well with a simple model accounting for gain saturation in the quantum well active region. It is shown that gain saturation and finite optical confinement in the lateral direction lead to a minimum in the threshold current for an optimal width of the optical waveguide. Threshold currents as low as ∼100 μA are predicted for PQW lasers with ∼0.2-μm-wide active regions.
Influence of off-oriented substrates on the crystallinity of (Ca,Sr)F2 layers grown on Si (100)
Authors: Minemura Tetsuroh , Asano Junko , Tsutsui Kazuo , Furukawa Seijiro
Published: July 2002

Off-oriented Si (100) substrates had considerable influence on the crystallinity of a (Ca,Sr)F2 layer, which is lattice matched with GaAs and grown on the substrates by molecular beam epitaxy. The (Ca,Sr)F2 layer grown on the Si (100) substrate, off oriented toward 〈011〉, was not a single crystal but had a columnar structure. The (Ca,Sr)F2 layer grown on the exact Si (100) susbstrate, however, was a single crystal in which the crystallinity was quite good with a minimum channeling yield (χmin ) of the mixed fluoride layer in the Rutherford backscattering spectra of about 0.1. To obtain such good crystallinity, the temperature range was limited to around 500 °C. The influence of off-oriented substrates was opposite that found in GaAs/Si (100) structures.
Superconducting thin-film multiturn coils of YBa2Cu3O7−x
Authors: Wellstood Frederick C. , Kingston John J. , Clarke John
Published: July 2002

We describe a technique for fabricating superconducting thin-film multiturn coils from the high-temperature superconductor YBa2Cu3O7−x. We have built 10-turn and 19-turn square spiral coils, 1 mm on a side, that are suitable for coupling to a thin-film dc superconducting quantum interference device. The coils are constructed with a three-layer crossover technology using SrTiO3 as an insulator. Each layer is deposited in situ with a pulsed excimer laser, and is patterned with shadow masks or photoresist and an Ar ion mill. The best coil had a transition temperature of approximately 82 K, and a critical current at 77 K of 1.4 mA, corresponding to a critical current density of 2×104 A cm−2.
Electronic structure of Sb in BaPb1−xSbxO3 superconducting compounds
Authors: Eibschütz M. , Reiff W. M. , Cava R. J. , Krajewski J. J. , Peck W. F.
Published: July 2002

The Mössbauer effect of the 37.2 keV γ transition of 121Sb has been employed to study the electronic configuration of Sb ions in BaPb1−xSbxO3 superconducting materials. The isomer shift is constant as a function of Sb content and falls in the region correspoding to the Sb(V) valence state. The isomer shift of 7 mm/s is the lowest value yet observed for an Sb(V)O6 chromophore and indicates a high degree of covalency, corresponding to significant 5sm 5pn hybridization. The mixed valence state of an equal amount of Sb(III) and Sb(V) has not been observed.
Scanning tunneling microscopy imaging of transition-metal dichalcogenides
Authors: van Bakel G. P. E. M. , De Hosson J. Th. M. , Hibma T.
Published: July 2002

Structural features of TiS2 were studied by scanning tunneling microscopy (STM) and single-crystal x-ray diffraction was applied as a complementary technique. STM images in air and at room temperature revealed, besides the trigonal symmetry of the lattice, several new features having this symmetry as well. We conclude that these features are not only to be described by structural defect phenomena which affect sites in the 1T-CdI2 structure but tetrahedral sites as well. Sample orientation determination by x-ray diffraction provides a unique relation between feature types and sites. A model is proposed in which displaced Ti atoms account for the observed features.
In situ preparation of the Gd-Ba-Cu-O superconducting thin films on (100) LaAlO3 by sputtering
Authors: Li H. C. , Yi H. R. , Wang R. L. , Chen Y. , Yin B. , Ron X. S. , Li L.
Published: July 2002

High-temperature superconductor GdBa2Cu3O7 thin films were grown in situ on LaAlO3 single-crystal substrates by dc magnetron sputtering using a single planar target. 93% samples had a zero resistance transition temperature Tc0 more than 90 K and a transition width less than 1 K. The best films had a Tc0 of 92.5 K, a transition width of 0.57 K, and a critical current density of 3.6×106 A/cm2 at 77 K. The reproducibility is very good. X-ray diffraction analysis showed c axis normal to the film’s surface.
I
n s
i
t
u epitaxial growth of Bi2(Sr,Ca)3Cu2Ox films by ion beam sputtering with an atomic oxygen source
Authors: Fujita J. , Yoshitake T. , Igarashi H. , Satoh T.
Published: July 2002

I n situ epitaxial growth of Bi2(Sr,Ca)3Cu2Ox films was performed by ion beam sputtering in atomic oxygen ambience at the substrate temperature of 640 °C. The films showed an epitaxial growth in which the a and b axes were parallel to 〈100〉 MgO, and the superstructure according to the incommensurate modulation along the b axis was also observed. The superconducting properties of the as-grown films seemed to sensitively depend on the oxidation treatment during the cooling down process. The zero resistivity temperature Tc(R=0) of a 600-Å-thick film cooled down in the same atomic oxygen density as the film growth ambience was 60 K, but it increased up to 80 K after a post-deposition annealing at 500 °C for 1 h in air. In contrast, as-grown films cooled down in insufficient oxidation ambience showed the Tc(R=0) of 76 K without post-deposition annealing. The control of the oxygen concentration is critical for the superconductivity of as-grown films.
Creation of strong pinning sites by x-ray irradiation for Gd1Ba2Cu3O7−x superconducting thin films
Authors: Kohiki Shigemi , Hatta Shin-ichiro , Setsune Kentaro , Wasa Kiyotaka , Higashi Yasuhiro , Fukushima Sei , Gohshi Yohichi
Published: July 2002

A large enhancement of critical current density with the small rate of flux creep was realized by x-ray irradiation before the oxygen annealing for Gd1Ba2Cu3O7−x superconducting thin films. The significantly increased magnetization showed both the temperature independence and the small magnetic relaxation. The activation energy estimated by the flux creep model increased from 0.1 to 0.25 eV with the x-ray irradiation treatment.
Occurrence of maximum T
c at an optimal carrier concentration in superconducting bismuth and thallium cuprates
Authors: Somasundaram P. , Vijayaraghavan R. , Nagarajan R. , Seshadri Ram , Umarji A. M. , Rao C. N. R.
Published: July 2002

The superconducting transition temperatures in Bi2Ca1−xLnxSr2Cu2O8+δ, TlCa1−xLnxSr2Cu2O6+δ, and Tl0.8Ca1−xLnxBa2Cu23O6+δ (Ln=Y or rare earth) vary with composition and show a maximum at a specific value of x or δ. This observation suggests that an optimal carrier concentration is required to attain maximum Tc in such cuprates which seem to be two-band systems.
Molecular beam epitaxial growth of InAs on a TlBaCaCuO superconducting film
Authors: Rao M. R. , Tarsa E. J. , Kroemer H. , Gossard A. C. , Hu E. L. , Petroff P. M. , Olson W. L. , Eddy M. M.
Published: July 2002

Results of growth of InAs on a superconducting TlCaBaCuO (2-1-2-2) thin film are reported. The InAs was grown by molecular beam migration-enhanced epitaxy at a substrate temperature of 250 °C. The Tc(zero) of the Tl film before and after InAs deposition was 106 and 100 K, respectively. X-ray diffraction and reflection electron microscopy studies showed the InAs to be polycrystalline, having grains in the 300 Å size range. This is the first report of deposition of a III-V semiconductor on superconductor, without significant degradation of Tc.
Effect of oxygen plasma annealing on superconducting properties of Bi2(Sr,Ca)3Cu2Ox and YBa2Cu3O7−δ thin films
Authors: Yoshitake T. , Miura S. , Fujita J. , Shohata N. , Igarashi H. , Satoh T. , Sekiguchi A. , Katoh K.
Published: July 2002

Thin films of the Bi2(Sr,Ca)3Cu2Ox and YBa2Cu3O7−δ system were annealed at 400 °C in a high-density oxygen plasma and its effect on superconducting properties was investigated. After being annealed in the oxygen plasma, their superconducting transition temperatures decreased by about 10 K and 2 K, respectively, and the c-axis lattice constants of these films were also found to decrease as a result of the annealing in the oxygen plasma. These results suggest that excessive oxygen incorporated into the films by the annealing in the oxygen plasma caused the excessive hole carriers, which deteriorated the superconducting transition temperatures of these films.
Simultaneous three primary color laser emissions from dye mixtures
Authors: Saito Y. , Kato M. , Nomura A. , Kano T.
Published: July 2002

Simultaneous two- and three-band laser emissions were obtained in a process of mixing two and three kinds of dyes excited by a nitrogen laser. They were blue, green, and yellow in a coumarin 460 (C460)/disodium fluorescein (DF)/rhodamine 610 (R610) dye mixture, and blue, green, and red in a C460/DF/rhodamin 640 (R640) dye mixture. Strong energy transfers from DF to R610 and to R640 were shown. R610 and R640 laser emissions on mixing with DF were obtained at very low concentrations. They were 4×10−6 mol/ℓ  for R610 and 1×10−5 mol/ℓ  for R640, compared to the lasing threshold concentration of 1×10−4 and 2×10−4 mol/ℓ  of each dye alone. Also, the R610 radiation moved about 35 nm to a shorter wavelength at the reduced concentration.
Manufacture and performances of rhodium/carbon multilayer x-ray mirrors
Authors: Boher Pierre , Houdy Philippe , Kaïkati Pierre , Ouahabi Mustapha , Barchewitz Robert
Published: July 2002

A diode rf-sputtering technique was used to produce Rh/C multilayers for application in the soft-x-ray domain. In situ kinetic ellipsometry is used to calibrate the deposition rates and to analyze precisely the interface structure formation. Grazing x-ray reflectivity at the Cu-Kα line (1.54 Å), and absolute soft-x-ray reflectivity at the Cu-Lα line (13.33 Å) and at the C-Kα line (44.7 Å) are also measured on the same multilayers. A model which assumes a quasi-sharp C-Rh interface (4 Å thick) and a diffused Rh-C interface (22 Å) in the stack is used to fit the reflectivity curves at the three experimental wavelengths. Reflectivities as high as 22% at 13.3 Å and 24% at 44.7 Å were measured on a 17-period multilayer structure having a period of ≂69 Å.
Comment on ‘‘New class of unstable orbits of the equilibrium electrons in free-electron lasers’’ [Appl. Phys. Lett. 5
5, 1380 (1989)]
Authors: Wang Changbiao
Published: July 2002

A recent claim of a new class of unstable orbits in free electron lasers when the radial self-electric field and azimuthal self-magnetic field are considered is disputed. The choice of the self-fields of the electron beam is questioned. (AIP)
Response to ‘‘Comment on ‘New class of unstable orbits of the equilibrium electrons in a free-electron laser’ ’’ [Appl. Phys. Lett. 5
7, 837 (1990)]
Authors: Zhang Shi-Chang , Zhang Zhong
Published: July 2002

The authors defined their calculation against the comments of the preceding letter. (AIP)
Characterization of a GaAs current-controlled bipolar-unipolar transition negative differential resistance transistor
Authors: Yarn K. F. , Wang Y. H. , Chang C. Y.
Published: July 2002

GaAs current-controlled bipolar-unipolar transition negative differential resistance (NDR) transistors using an n+-i-p+-i-n+ homojunction structure prepared by molecular beam epitaxy are demonstrated. For a base thickness of 200 Å and using a highly doped sheet concentration of 1013 cm−2, a NDR region is revealed for IB<100 μA. The peak-to-valley current ratios are about 8 at room temperature. This is proposed to be due to the bipolar–unipolar transition reaction. When IB>=100 μA, the proposed device operates as a conventional bipolar transistor. Additionally, the effects of base thickness on current-voltage characteristics are also investigated.
Proximity coupling effect in NbTi fine-multifilamentary superconducting composites
Authors: Matsumoto Kaname , Akita Shirabe , Tanaka Yasuzo , Tsukamoto Osami
Published: July 2002

In order to shed light on the proximity effect in fine multifilamentary wires with NbTi filaments, measurements of magnetic susceptibility were conducted at 4.2 K for various values of electrical resistivity of the matrix between filaments, of the distances between filaments, and of the applied magnetic field strength. It was confirmed experimentally that in weak fields (10 mT or less), the critical distance for the occurrence of proximity coupling was several multiples of the characteristic leak distance of Cooper pairs in normally conductive metal, and that when the distances between filaments were large, the breakdown field decreased exponentially, irrespective of the electrical resistivity of the matrix.
InGaAs/InP distributed feedback quantum well laser
Authors: Temkin H. , Tanbun-Ek T. , Logan R. A. , Olsson N. A. , Sergent M. A. , Wecht K. W. , Cebula D. A.
Published: July 2002

We describe InGaAs/InP multiquantum well distributed feedback (DFB) lasers with novel properties atrributable to the quantum well based active layer. The low internal loss waveguide and shallow gratings have allowed the fabrication of lasers with a cavity length varying from 0.5 to 2 mm, and corresponding threshold currents of 22 and 100 mA, respectively. A mode rejection ratio as high as 50 dB has been obtained in lasers with one antireflection-coated facet. The long cavity devices exhibit linewidths as low as 600 kHz at a power output of 35 mW. Transmission experiments through 70 km of fiber, at 1.7 Gb/s, showed a dynamic chirp penalty of only 0.25 dB, a factor of 8–10 smaller than in conventional lasers.
Observation of domain boundaries on the Si (111) 7×7 surface by scanning tunneling microscope
Authors: Sumita I. , Yokotsuka T. , Tanaka H. , Udagawa M. , Watanabe Y. , Takao M. , Yokoyama K.
Published: July 2002

A highly reliable scanning tunneling microscope system equipped with a field ion microscope yielded successful observation of a domain boundary on the Si(111) 7×7 reconstructed surface. For the first time, we revealed its detailed structure at the atomic level. The boundary consists of holes far larger than the corner holes of the dimer-adatom-stacking fault (DAS) model and bridge-like structures with three 2×2 subunits. The ditch structure of this boundary is running to the [1̄10] direction, i.e., to the direction of the shorter diagonal of the 7×7 unit cell. We discussed that a misfit of the 7×7 periodicity between the neighboring domains caused this ditch structure.
Occupation of quantum states determined by energy storage in superlattice quantum state transfer devices
Authors: Kirchoefer S. W.
Published: July 2002

Quantum state occupation is observed in admittance measurements of two well type (bilevel) superlattice channel conduction devices known as quantum state transfer devices. A small-signal measurement is used to identify the energy storage in applied electric fields between adjacent dissimilar quantum wells. The spatially dependent nature of the miniband structure of bilevel superlattices is thereby confirmed. This energy storage is found in the same regime of device voltage bias as the previously investigated negative differential resistance, supporting the proposition of a common quantum origin between these two phenomena.
Ultraviolet reflectance of AlN, diamond-like carbon, and SiC thin films
Authors: David M. , Babu S. V. , Chaudhry I. , Flint B. K.
Published: July 2002

The vacuum ultraviolet (VUV) (120–200 nm) and extreme ultraviolet (EUV) (80–120 nm) reflectance characteristics of as-deposited films of amorphous aluminum nitride (AlN) and diamond-like carbon (DLC), and of single-crystal β-silicon carbide (SiC) have been measured. AlN and DLC films have been grown by plasma-enhanced chemical vapor deposition (PECVD) and the SiC film by chemical vapor deposition (CVD). The VUV reflectivities of AlN and SiC exceed 50% while the reflectance of DLC film is low (∼10%). Furthermore, DLC and SiC films display EUV reflectance characteristics that are very desirable. The reflectivity of as-deposited SiC is 40% and that of DLC is about 20%.
Columnar epitaxy of PtSi on Si (111)
Authors: Fathauer R. W. , Xiao Q. F. , Hashimoto Shin , Nieh C. W.
Published: July 2002

Columnar grains of PtSi surrounded by high quality epitaxial silicon are obtained by ultrahigh vacuum codeposition of Si and Pt in an 8:1 ratio on Si(111) substrates heated to 610–810 °C. The areal density of columns varies from 120 to 3.8 μm−2, and layers with thicknesses from 100 nm to 1 μm have been demonstrated. This result is similar to that found previously for CoSi2 (a nearly lattice-matched cubic-fluorite crystal) on Si(111), in spite of the orthorhombic structure of PtSi. The PtSi grains are also epitaxial and have one of three variants of the relation defined by PtSi(010)//Si(111), with PtSi[001]//Si〈110〉.
Use of tertiarybutylarsine in the fabrication of GaAs/AlGaAs quantum wells and quantum well lasers
Authors: Hummel S. G. , Beyler C. A. , Zou Y. , Grodzinski P. , Dapkus P. D.
Published: July 2002

Tertiarybutylarsine was used in the growth of GaAs and AlGaAs by metalorganic chemical vapor deposition over a range of compositions and V/III ratios. GaAs layers were obtained with both n- and p-type background carrier concentrations in the low 1014 cm−3 range. AlGaAs was grown at 20, 30, and 50% compositions, and photoluminescence of the Al0.2Ga0.8As indicates high quality material with full width half maximum (FWHM) values of the peaks being comparable to arsine-grown AlGaAs. High quality multiple Al0.3Ga0.7As/GaAs quantum wells of various widths produced photoluminescence spectra with FWHM values comparable to arsine-grown samples. Minority-carrier lifetimes as long as 400 ns were measured for a heterostructure of 0.5 μm GaAs with Al0.3Ga0.7As barrier layers. Graded index separate confinement heterostructure lasers were fabricated, and broad- area test results of these devices produced threshold current densities as low as 186 A/cm2.
Monitoring the performance of a semiconductor optical amplifier
Authors: Dutta N. K. , Piccirilli A. B. , Lin M. S. , Halemane T. R.
Published: July 2002

Measurements of optical gain and spontaneous emission of optical amplifiers show that the latter is a good measure of the former. A device structure is fabricated where a photodetector is integrated next to the amplifier. A fraction of the spontaneous emission from the amplifier impinges on the photodetector in this device producing a photocurrent. The photodetector current is found to be a monotonic function of the amplifier gain. Hence, the photodetector output can be used to monitor the performance of the amplifier.
Indirect stimulated emission at room temperature
Authors: Rinker M. , Kalt H. , Köhler K.
Published: July 2002

Stimulated emission in indirect band-gap AlxGa1−xAs is observed at room temperature. This indirect stimulated emission is based on alloy disorder induced no-phonon band-to-band transitions. Picosecond luminescence spectroscopy as a function of alloy composition reveals a quadratic dependence of the threshold pump intensity on the energy separation of the renormalized direct and indirect conduction bands. These threshold intensities increase exponentially with lattice temperature. The temperature dependence of the threshold intensity is much weaker than in direct band-gap AlxGa1−xAs.
Eye-safe Nd:YAG laser
Authors: Wong S. K. , Mathieu P. , Pace P.
Published: July 2002

We have demonstrated that a significant amount of laser energy can be extracted at 1.4444 μm from Nd:YAG at room temperature. The stimulated emission cross section at 1.4444 μm is not unduly small. More than 1 J of laser energy in the non-Q-switched mode and over 130 mJ with a pulse width of 85 ns full width at half maximum in the Q-switched mode have been obtained. The 1.4444 μm laser has also been operated successfully at repetition rates up to 10 Hz at the 100 mJ/pulse level. Other lasing transitions at 1.064, 1.3187, 1.3381, 1.3572, and 1.4150 μm have also been observed.
Valley current density activation energy and effective longitudinal optical phonon energy in triple well asymmetric resonant tunneling diode
Authors: Bolognesi C. R. , Mand R. S. , Boothroyd A. R.
Published: July 2002

In this letter we report the Arrhenius-type dependence of the valley current density on inverse temperature in a triple-well asymmetric resonant tunneling diode. The activation energy is found to be equal to the effective phonon energy representing the AlAs and GaAs-like mode of AlAs in the AlxGa1−xAs barrier layers of a triple well asymmetric resonant tunneling (RT) diode operating at temperatures as high as 350 K. The data presented here correlate the longitudinal optical phonons to the excess valley current found in AlxGa1−xAs/GaAs RT devices between 200 and 350 K and raise the possibility of phonon spectroscopy of high quality barrier layers via resonant tunneling transport experiments.
Measurement of plasma-neutralized super-vacuum currents in a gyrotron configuration
Authors: Kirkpatrick D. A. , Gold S. H. , Manheimer W. M. , Black W. M. , Kinkead A. K. , Hardesty D. L. , Killian K. W. , Sucy M.
Published: July 2002

Experimental results are reported on the transport of an electron beam with current in excess of the vacuum space-charge-limited value, in a configuration directly applicable to gyrotron oscillators. The vacuum space-charge limit is circumvented by the introduction of a neutralizing background plasma which is produced by an array of four plasma guns placed immediately downstream of the electron gun anode.
High contrast multiple quantum well optical bistable device with integrated Bragg reflectors
Authors: Sfez B. G. , Oudar J. L. , Michel J. C. , Kuszelewicz R. , Azoulay R.
Published: July 2002

Monolithic bistable étalons with a GaAs/Al0.3Ga0.7As multiple quantum well active layer and AlAs/Al0.1Ga0.9As Bragg reflectors have been fabricated by metalorganic vapor phase epitaxy. The design of the whole structure is such that a good cavity finesse and a high contrast in the reflective mode are simultaneously obtained. This results in a bistability power threshold of <3 mW at 838 nm and a contrast ratio as high as 30:1. The nonlinear refractive index is shown to saturate at higher power, which evidences the need of a good cavity finesse for such bistable devices.
Defect-free, conformally grown (100) GaAs films
Authors: Pribat D. , Dupuy M. , Legagneux P. , Collet C.
Published: July 2002

By using selective epitaxy, submicron-thick (100) GaAs films can be conformally grown between two sandwiching dielectric layers. The defect structure of such GaAs films is investigated using chemical etching and transmission electron microscopy. The conformally grown films exhibit specular surfaces and appear virtually free from defects. A qualitative model for defect trapping is presented which suggests that the dislocations are blocked on the capping dielectric layer when they should thread laterally.
Effect of patterning on defect structure in GaAs grown on Si
Authors: Tsai H. L. , Kao Y. C.
Published: July 2002

In this letter, we address the effectiveness of patterned growth in reducing defect density in GaAs on Si. Defect reduction is considered to be subject to the effect of edge profile and the density of defects in initial GaAs islands. Pattern edges (mask edges or large steps) are often the sites for generating microtwins/stacking faults. Mutual interaction of dislocations inhibits the gliding of dislocations to pattern edges, thus affecting the effectiveness of patterned growth in improving the epilayer quality. The study also shows that surface orientation influences the formation of misfit dislocations with a preferred Burgers vector. This observation is interpreted by considering the variation of misfit with different lattice planes across the interface between Si and ‘‘tilted’’ GaAs lattices.
Simple method for creating pulse shortening in x-ray lasers
Authors: Rose S. J. , Rogoyski A. M. , Tragin N.
Published: July 2002

A simple method for creating pulse shortening in recombination x-ray lasers is proposed in which the motion of the gain medium is utilized in a novel target geometry.
InGaAs-GaAs-AlGaAs gain-guided arrays operating in the in-phase fundamental array mode
Authors: Beernink K. J. , Alwan J. J. , Coleman J. J.
Published: July 2002

We compare the operation of single-stripe gain-guided InGaAs-GaAs-AlGaAs strained-layer quantum well heterostructure lasers emitting at wavelengths ≳1.0 μm to five-element gain-guided arrays with 8 μm stripe width and center-to-center spacings S from 14 to 30 μm. Arrays with large interelement spacings exhibit a twin-lobed far-field pattern corresponding to the highest order supermode with 180° phase shift between adjacent elements. Devices with smaller interelement spacing exhibit a single lobe in the far field suggestive of in-phase operation. Pulsed L-I characteristics show kink-free operation of arrays with S=15 μm to 730 mW per uncoated facet at 1.8 A.