bluuebunny/crossref_metadata_2025 huggingface dataset:
Caracterización de cristales no lineales y su uso en la caracterización de pulsos ultracortos
Authors:   ,   Pontificia Universidad Católica de Chile. Instituto de Física, Hidalgo Rojas Diego Mauricio
Published: March 2023

Los cristales no lineales se usan ampliamente en la óptica no lineal y en la caracterización de pulsos. Estos cristales no lineales suelen ser materiales birrefringentes, ya que su anisotropía óptica da mayor facilidad para obtener altas eficiencias en fenómenos como la conversión de armónicos, por ejemplo, generación del segundo armónico y del tercer armónico. Durante bastante tiempo se han estudiado y utilizado cristales inorgánicos u orgánicos, siendo los primeros los más comunes en el comercio. No obstante, existe un nuevo material que debido a su gran respuesta no lineal teórica es un buen candidato para ser un cristal no lineal ideal, capaz de ser ajustado en su composición para mejorar la eficiencia en ciertas longitudes de ondas, estos cristales son los “metal-organic framewroks” MOFs, los cuales son cristales híbridos que poseen en su estructura iones metálicos unidos con ligandos orgánicos. Los cristales no lineales se han utilizado en varios experimentos, uno de estos es la caracterización de pulsos ultracortos. Esto abrió un área que parecía estancada por la imposibilidad de obtener, desde la electrónica, la información completa de un pulso. Con los cristales no lineales se comienzan a utilizar fenómenos no lineales en diferentes métodos para obtener una señal y reconstruir el pulso en base a ésta, lo que se conoce como problema inverso. En esta tesis se muestran dos investigaciones relacionadas por el uso de cristales no lineales. Primero se estudia un MOF sintetizado en la Universidad de Santiago de Chile llamado Zn(3 − ptz)2. El tamaño de las muestras resultan ser mayores a 1 mm dando la posibilidad de estudiar tanto la birrefringencia como la generación del segundo armónico de manera precisa y sin métodos que utilicen polvos, esto es, estudiando muestra por muestra de manera individual. De esta forma fuimos capaces de caracterizar lineal y no linealmente el cristal, coincidiendo con varios resultados calculados teóricamente. Además, se muestra por primera vez en cinco años de estudios, la generación del tercer armónico en este cristal. La segunda investigación se basa en el uso de un cristal no lineal comercial en la caracterización de pulsos ultracortos con un método no interferométrico y usando un algoritmo directo, dando mayor rapidez en la obtención de los resultados, se reconstruyeron pulsos complejos generados con un “pulse shaper” obteniendo errores menores al 1 %. De esta forma, no solo hemos caracterizado un nuevo cristal no lineal de gran tamaño, si no que además hemos reconstruido pulsos utilizando un cristal no lineal comercial.
On accumulation points of volumes of stable surfaces with one cyclic quotient singularity
Authors:   ,   Pontificia Universidad Católica de Chile. Facultad de Matemáticas, Torres Valencia Diana Carolina
Published: March 2023

The set of volumes of stable surfaces does have accumulation points. In this paper, we study this phenomenon for surfaces with one cyclic quotient singularity, towards answering the question under which conditions we can still have boundedness. Effective bounds allow listing singularities that might appear on a stable surface after fixing its invariants. We find optimal inequalities for stable surfaces with one cyclic quotient singularity, which can be used to prove boundedness under certain conditions. We also introduce the notion of generalized T-singularity, which is a natural generalization of the well-known T-singularities. By using our inequalities, we show how the accumulation points of volumes of stable surfaces with one generalized T-singularity are formed.
Características de la atención de salud efectiva para la población que se identifica con el colectivo LGBTI
Authors:   ,   Pontificia Universidad Católica de Chile. Facultad de Medicina, Cabezas Oyarce Yasna Karina
Published: March 2023

El propósito de este proyecto de investigación es identificar las necesidades de los usuarios del colectivo LGBTI en el contexto de la atención primaria de salud en Chile. Para poder determinar las brechas existentes en las políticas públicas asociadas a los servicios de salud, se ha efectuado un grupo focal conformado por usuarios pertenecientes al colectivo, dirigentes de organizaciones involucradas y especialistas en la atención de salud. Se identifican las características con las que debiesen contar los equipos integrales de atención, revelando a través de las vivencias de los usuarios circunstancias y experiencias que permiten el acercamiento a una atención efectiva que dé respuesta a sus necesidades y al reconocimiento de sus derechos, deberes y acceso.
Milan System for Reporting Salivary Gland Cytopathology- An overview with Interobserver Variability and Clinicoradiological Concordance
Authors: Bajpai Divya , Agrawal Ranjan , Bisht Mithila , Arya Anjana , Mohan Nitesh
Published: March 2023

Introduction: Salivary gland lesions are one of the most heterogenous lesions with overlapping features between low grade malignancy and benign lesions thus making them one of the most difficult areas for diagnosing. Cytology of salivary gland lesions plays an extremely important part in diagnosing the lesions and categorising them into non neoplastic, benign and malignant neoplasms, thereby allowing the patients and clinicians to make an accurate decision regarding whether the lesion is followed, biopsied, excised or a radical operation might be needed. Aim: To classify salivary gland lesions according to MILAN System for Reporting Salivary Gland Cytopathology (MSRSGC). Materials and Methods: This observational study was conducted from June 2021 to May 2022 where Fine Neddle Aspiration Cytology (FNAC) of salivary gland lumps was done on patients presenting to the Department of Pathology Rohilkhand Medical College and Hospital, Bareilly. The clinical and radiological features were noted. The cases were diagnosed on conventional cytopathology. Additionally categorisation as per MILAN System was done by two pathologists independently. The results were compared with histopathology, where available. Data was collected, entered and compiled in Microsoft excel followed by analysis using the software Statistical Package for Social Sciences (SPSS) version 23.0. The data was represented in frequency and further analysed using Kappa statistics. Also the validity was calculated in terms of sensitivity, specificity, Positive Predictive Value and Negative Predictive Value (NPV). Results: Total of 60 cases were included with M:F ratio as 1.6:1. Most common age group was third decade with 17 (28.3%) cases, closely followed by fourth decade with 11 (18.3%) cases. Most common salivary gland to be affected was parotid gland with 30 (50%) cases. Most common MILAN category was II, non neoplastic with 26 (43.3%) cases, followed by IV A, benign neoplasm with 19 (31.67%) cases. The Cohen kappa coefficient was 0.952 which showed a near perfect agreement between the two pathologists. The sensitivity, specificity, PPV and NPV and accuracy was 75%, 92.8%, 75% and 92.8%, 89% respectively. The Risk of Malignancy (ROM) for category I,II,III,IVA,VI was 0%, 0%, 50%, 9%, 100% respectively. Conclusion: The MILAN System for Reporting Salivary Gland Cytopathology (MSRSGC) offers a structured reporting system. The terminologies are reproducible and convey clear meaning among all the medical professionals including different pathologists and treating physician or surgeon and guide in deciding the accurate treatment based on the ROM for different categories.
The Phosphorus Availability Due to Various Ameliorants in a New Rice Field of Barito Kuala Regency South Kalimantan
Authors: Yusran Fadly Hairannoor , Mariana Zuraida Titin , Juhrian
Published: March 2023

Aims: To optimize the dose of three ameliorants (biochar, lime, and compost) and their interactions on the availability of macronutrient P.

Study Design: This research was a laboratory incubation study using soil samples from the newly opened rice fields.

Place and Duration of Study: Paddy field of Ray 7, Balandean Village, Alalak District, Barito Kuala Regency, South Kalimantan Province from May to November 2021.

Methodology: The study used factorial design with the treatments of 1) Biochar, with levels of 0, 10, and 20 t ha-1, 2) Lime, with levels of 0, 2, and 4 t ha-1, 3) Compost with levels of 0, 5, and         10 t ha-1. All were arranged in Completely Randomized Design with three replications. The experimental units were 300 g of soil sample in 81 of 10 cm plastic pots. They immersed up to 2 cm water and incubated to imitated field conditions for three months and then analyzed for the parameters.

Results: Biochar and lime increased available-P quadratically and linearly following orthogonal polynomial analyses. Their interaction was highly significant in increasing available-P. The doses for both could be increased for the maximum availability of P.

Conclusion: Biochar increased P availability with the tendency of increasing beyond the dose of the treatment. The main treatment of compost was not as good as biochar. However, when applied together with biochar and lime, compost affected the solubility of P. However, to increase P availability, the combination of the ameliorants showed a good synergism.
Expression and characterization of the hepatitis G virus helicase
Authors: Laxton C. D. , McMillan D. , Ackrill V. Sullivan & A. M.
Published: July 2002

The hepatitis G virus (HGV) is a new member of the Flaviviridae family and has a genomic organization similar to that of hepatitis C virus (HCV). Protein sequence motifs are present suggesting that HGV encodes a serine proteinase, an RNA‐dependent RNA polymerase and a helicase. We have cloned and expressed the putative helicase of HGV and have shown that it contains a poly (U)‐stimulated NTPase activity and is able to function as a DNA helicase. Preliminary characterization of the HGV helicase activity reveals similarities with other members of the Flaviviridae, but especially with HCV, raising the possibility that HGV could be used as a surrogate virus for the development of therapies against HCV.
Influence of pulse width on ultraviolet laser ablation of poly(methyl methacrylate)
Authors: Srinivasan R. , Braren Bodil
Published: July 2002

The etching of poly(methyl methacrylate) using pulses of 248 nm laser radiation which had a full width at half maximum (FWHM) of 40–100 ns is reported. These pulses were created by combining two identical pulses, each of 40 ns FWHM, with a set time delay. The etch depth/pulse is sensitive to the pulse width and, therefore, the power density in this polymer. It can be explained by the changes in absorptivity during a pulse that have been reported by G. M. Davis and M. C. Gower [J. Appl. Phys. 61, 2090 (1987)]. The shape of the pulse was also found to influence the etch depth/pulse. The etching of polyimide by these extended pulses shows trends that are opposite to those observed in poly(methyl methacrylate). In this instance, the shielding of the latter portion of the incoming pulse by the products that are ablated by the front portion is probably a serious effect.
Deep level transient spectroscopy study of GaAs surface states treated with inorganic sulfides
Authors: Liu D. , Zhang T. , LaRue R. A. , Harris J. S. , Sigmon T. W.
Published: July 2002

Surface states of liquid-encapsulated Czochralski and molecular beam epitaxy grown n-type GaAs samples coated with Na2S and (NH4)2S films are studied with deep level transient spectroscopy measurements employing metal-insulator-semiconductor structures. Two deep levels at 0.58 and 1.15 eV below the conduction-band edge are found in the as-grown samples. The Ec−0.58 eV deep level is found to be greatly reduced after sulfide treatment, while the Ec−1.15 eV deep level remains with a very high density. The surface Fermi level is shifted deeper into the energy band gap toward the Ec−1.15 eV deep level after surface treatment. This new, deeper pinning position is believed to be the cause of the greatly enhanced photoluminescence intensity recently reported. This new pinning position is deeper than some of the recently reported sodium sulfide/GaAs results but consistent with the high Schottky barrier height, 1.15 eV measured for the gallium-rich GaAs surface.
Electron-electron interactions and resonant tunneling in heterostructures
Authors: Bandara K. M. S. V. , Coon D. D.
Published: July 2002

A Hartree–Fock approach [Z. Physik 61, 126 (1930)] is used to analyze electron-electron interactions in heterostructures. The analysis includes estimates of the effect of electron-electron interactions on localized states in quantum wells and resonant tunneling. Resonant tunneling is treated in a self-consistent narrow resonance approximation. The Hartree–Fock approach yields an explicit exchange interaction subband energy shift which is completely omitted in Poisson equation treatments. Exchange effects are found to be of the same order of magnitude but opposite in sign to direct interactions at typical electron densities.
Epitaxial Y-Ba-Cu-O films on Si with intermediate layer by rf magnetron sputtering
Authors: Miura S. , Yoshitake T. , Matsubara S. , Miyasaka Y. , Shohata N. , Satoh T.
Published: July 2002

Epitaxial films of Y-Ba-Cu-O were obtained on a Si substrate, using an epitaxial intermediate layer consisting of BaTiO3(or SrTiO3)/MgAl2O4. MgAl2O4 was epitaxially grown on the Si(100) substrate by chemical vapor deposition. Then, SrTiO3 or BaTiO3 was also epitaxially grown on the MgAl2O4 layer by means of rf magnetron sputtering. Epitaxial Y-Ba-Cu-O films were prepared on BaTiO3(SrTiO3)/MgAl2O4/Si substrates by rf magnetron sputtering. Preparation of an Y-Ba-Cu-O film directly on MgAl2O4/Si was also studied, but only a randomly oriented polycrystalline film has been obtained so far. Resistive superconducting transitions with zero resistance at 65 K on SrTiO3/MgAl2O4/Si and at 70 K on BaTiO3/MgAl2O4/Si were observed.
Nonaqueous chemical etch for YBa2Cu3O7−x
Authors: Vasquez R. P. , Hunt B. D. , Foote M. C.
Published: July 2002

A nonaqueous chemical etch, with Br as the active ingredient, is described which removes the insulating hydroxides and carbonates that form on high-temperature superconductor surfaces as a result of atmospheric exposure. X-ray photoemission spectra have been recorded before and after etching YBa2Cu3O7−x films. It is found that, after the etch, the high binding energy O 1s and Ba 3d peaks associated with surface contaminants are greatly reduced, the Y:Ba:Cu ratio is close to the expected 1:2:3, and the oxidation state of the Cu(2+) is not affected. The resistance of an etched film reaches zero at 78 K, compared to 81 K for a similar unetched film. The suitability of other nonaqueous halogen-based etches is discussed, as is the applicability of this etch to other high Tc superconductors.
Observation of ‘‘slow’’ states in conductance measurements on silicon metal-oxide-semiconductor capacitors
Authors: Uren M. J. , Collins S. , Kirton M. J.
Published: July 2002

We report the observation of a low-frequency plateau in conductance measurements on silicon metal-oxide-semiconductor capacitors. The signal is consistent with the ‘‘slow’’ states observed by other techniques, in particular those states responsible for 1/f noise in silicon metal-oxide-semiconductor field-effect transistors.
Low-threshold disorder-defined buried heterostructure strained-layer AlyGa1−yAs-GaAs-InxGa1−xAs quantum well lasers (λ∼910 nm)
Authors: Major J. S. , Guido L. J. , Hsieh K. C. , Holonyak N. , Stutius W. , Gavrilovic P. , Williams J. E.
Published: July 2002

The stability of strained-layer Aly Ga1−yAs-GaAs-InxGa1−x As single quantum well heterostructures against thermal processing is examined using transmission and scanning electron microscopy. A self-aligned impurity-induced layer disordering process employing Si-O diffusion is used to produce buried heterostructure stripe geometry lasers with a pseudomorphic InxGa1−x As quantum well active region. The 2-μm-wide stripe laser diodes exhibit high efficiency (η∼41%/facet), low threshold (Ith =7 mA), and high output power (Pout >20 mW/facet).
Diode laser pumped blue-light source based on intracavity sum frequency generation
Authors: Risk W. P. , Lenth W.
Published: July 2002

Sum frequency mixing in KTiOPO4 of the 809 nm light from a GaAlAs laser diode and the 1064 nm light from a diode-pumped Nd:YAG laser has been used to generate blue radiation at 459 nm. The specific problems associated with the use of high-power multimode GaAlAs diode lasers as the source of the 809 nm mixing radiation were investigated in detail. Rapid modulation of the blue output and generation of 5 ns pulses by direct modulation of the GaAlAs laser diode were demonstrated.
Influence of temperature on electron transport in bipolar devices
Authors: Bardyszewski Witold , Yevick David
Published: July 2002

We evaluate the inelastic electron lifetime in the p regions of III-V semiconductor devices with the aid of the exact temperature-dependent random phase approximation valence-band dielectric function. Our results demonstrate that at room temperature the low-energy electron lifetime decreases markedly while hot-electron lifetimes are reduced by several tens of percent. We subsequently repeat our calculations with the damped plasmon pole approximation for the dielectric function, obtaining acceptable values with a minimum of computational effort.
Effects of annealing on TlBaCaCuO thin films
Authors: Denhoff M. W. , Grant P. , Qiu C. X. , Shih I. , Robinson P. T. , Sproule I. , Mitchell D.
Published: July 2002

We have studied the effects of high-temperature anneals on sequentially deposited TlBaCaCu films in an environment containing O2 and TlOx . From Auger electron spectroscopy depth profiles, it was found that Tl was quite volatile and can be easily eliminated from the thin films after a short treatment at 830 °C. However, the Tl can be incorporated in the films after appropriate treatment.
Molecular beam epitaxy of GaAs/AlGaAs quantum wells on channeled substrates
Authors: Meier H. P. , Van Gieson E. , Walter W. , Harder C. , Krahl M. , Bimberg D.
Published: July 2002

GaAs/AlGaAs quantum wells (QWs) were grown by molecular beam epitaxy on GaAs (100) substrates patterned with ridges and grooves in the [011̄] direction. Low-temperature cathodoluminescence was used to measure the Al fraction and QW thickness on top of the ridges and grooves as a function of ridge and groove width. Surface diffusion during growth depletes Ga from the side facets while increasing the incorporation of Ga on the (100) sections of ridges and grooves. The QW thickness on top of a ridge grown at 710 °C increases from 72 to 95 Å, and the Al fraction x decreases from x=0.33 to x=0.29 as the ridge width is narrowed from 30 to 4 μm. Graded refractive index separate confinement heterostructure lasers with nominally 70 Å QWs and Al0.2Ga0.8As barriers were grown on patterned substrates at 695 and 725 °C. Lasers fabricated on the overgrown 4-μm-wide ridges have a 20 meV decrease in emission energy compared to laser diodes on 30 μm ridges.
X-ray photoelectron spectroscopy of ammonium sulfide treated GaAs (100) surfaces
Authors: Cowans B. A. , Dardas Z. , Delgass W. N. , Carpenter M. S. , Melloch M. R.
Published: July 2002

The effect of an ammonium sulfide treatment on the GaAs (100) surface has been investigated by x-ray photoelectron spectroscopy. The treatment produces a slight Ga enrichment on the surface and leaves roughly 0.6 of a monolayer of sulfide which inhibits initial oxidation of the surface. The sulfide is not lost as the surface becomes oxidized but appears to remain near the GaAs/oxide interface. Furthermore, in the oxidized layer, As oxide is preferentially drawn to the surface relative to Ga oxide.
Variation of lattice parameter with silicon concentration in n-doped, liquid-encapsulated Czochralski GaAs single crystals
Authors: Watson G. Patrick , Ast Dieter , Elliot A. Grant
Published: July 2002

The lattice parameters of several Si-doped and undoped GaAs wafers have been measured, using the Bond x-ray diffraction technique. The relative lattice parameters of wafers from the same boule were found to decrease monotonically from seed to tail by as much as 6×10−5(δa/a), following the same trend as the increase in Si content ranging from 1.3 to 9.4×1018 cm−3 (measured by secondary-ion mass spectroscopy). A plot of the change in lattice parameter versus the Si concentration shows a linear trend with a slope which is three times larger than that predicted by Vegard’s law. Possible explanations for this discrepancy are discussed.
Oriented high T
c superconductive layers on silver by devitrification of glasses formed in the Bi-Sr-Ca-Cu oxide system
Authors: Baker R. C. , Hurng W. M. , Steinfink H.
Published: July 2002

Highly oriented crystalline layers of Bi4(Sr,Ca)3Cu4O16+x high Tc superconductors were produced by the devitrification of aerosol suspensions of glasses prepared from the mixed oxides when the suspensions were brought into rapid contact with heated silver substrates. The best magnetic susceptibility signals, produced by superconductivity at 77 K, were obtained when the glass was rapidly heated to about 850 °C from room temperature. The deposited layers are composed of a nearly pure superconductive phase in the form of flat platelets up to several hundred microns in diameter that are oriented with the c axis normal to the substrate. The addition of a small amount of Pb to the glass lowers the optimum deposition temperature and improves the crystal morphology.
Soft magnetic Fe-Al-N/Si-N multilayered film with high thermal stability
Authors: Katori K. , Hayashi K. , Hayakawa M. , Aso K.
Published: July 2002

An attempt to obtain soft magnetic materials with high saturation magnetic flux density and thermal stability has been carried out with respect to a multilayered type of films containing Fe-N prepared by two-source magnetron rf sputtering. The addition of small amounts of elements such as Al is effective in improving soft magnetic properties of Fe-N films. Multilayered films of Fe-Al-N intervened by thin Si-N layers showed softer magnetic properties than the Fe-Al-N single layer films and also showed high thermal stability. Typically, Fe-Al-N (500 Å)/Si-N (12 Å) multilayered films exhibited a saturation magnetic flux density of 20 kG, a coercivity Hc of 0.3 Oe, and a permeability μ of 1900 at 5 MHz after annealing at 550 °C for 1 h.
Anisotropic thermionic emission of electrons contained in GaAs/AlAs floating gate device structures
Authors: Lott J. A. , Klem J. F. , Weaver H. T.
Published: July 2002

Thermionic emission rates are reported for electrons in GaAs epilayers, where electrostatic barriers within the layers and GaAs/AlAs heterojunctions form different sides of the potential well. Attempt times at the two barrier types were observed to differ by factors above 107 due to differing constraints on momentum conservation during emission. These emissions represent escape mechanisms for charge stored in a closed geometry, III-V compound floating gate transistor, with potential application as dynamic random access or nonvolatile memories.
Structural characterization of an Sb delta-doping layer in silicon
Authors: Slijkerman W. F. J. , Zagwijn P. M. , van der Veen J. F. , van Gorkum A. A. , van de Walle G. F. A.
Published: July 2002

Delta-function doped layers in Si have been prepared by deposition of Sb on Si(001) followed by solid phase epitaxy of Si. The morphology and the crystal quality of the grown structures are characterized in situ during all stages of preparation by high-resolution Rutherford backscattering spectrometry. The obtained doping profile is found to consist of a <0.8-nm-wide spike and a 4-nm-long tail in front of the spike. A large fraction of about 70% of the Sb atoms is confined to the spike while the remaining 30% is located in the tail. Ion channeling and blocking measurements demonstrate that at least 95% of the Sb atoms is located on substitutional lattice sites. At temperatures exceeding 1000 K, the Sb profile broadens and Sb atoms diffuse towards the surface where they desorb.
Electrical activation of B implants in Hg0.79Cd0.21Te by immersion annealing in a hot Hg bath
Authors: Uzan-Saguy C. , Kalish R.
Published: July 2002

Electrical activation of B implants in Hg0.79Cd0.21Te was achieved following annealing by immersion in a hot Hg bath at 320 °C for 8 min. Annealing of the implantation damage and partial electrical activation was obtained after such treatment as deduced from Rutherford backscattering combined with channeling and differential Hall measurements. The possibility that the observed behavior is not due to electrical activity of the B implants but is related to the implantation damage or to the immersion procedure was eliminated by control experiments on Ne-implanted and on nonimplanted samples.
Spatially selective modification of GaAs/AlGaAs quantum wells by SiO2 capping and rapid thermal annealing
Authors: Chi J. Y. , Wen X. , Koteles Emil S. , Elman B.
Published: July 2002

GaAs/AlGaAs quantum wells (QWs), selectively intermixed by SiO2 capping and rapid thermal annealing, have been characterized on a microscale using spatially resolved photoluminescence (PL) spectroscopy. From the evolution of the PL spectra across the boundary between the unmixed and intermixed regions, it was concluded that the transition region is narrower than the 1.5 μm excitation beam diameter. The magnitude of the intermixing was also found to increase with the thickness of the oxide. The present intermixed QWs were found to be stable against subsequent thermal treatment below the temperature limit imposed by the intrinsic interdiffusion. These results demonstrate that the effective band gap of QWs, and their physical properties, can be adjusted by controlling the oxide thickness profile.
Effects of stress on the electrical activation of implanted Si in GaAs
Authors: Vanasupa L. S. , Deal M. D. , Plummer J. D.
Published: July 2002

The effects of various plasma-enhanced chemical vapor deposition SiNx encapsulating films on the electrical activation of ion-implanted 29Si+ in GaAs were investigated. Films inducing the most tensile stress in the GaAs resulted in the lowest activation efficiency and films inducing the most compressive resulted in the highest. The results suggest that ratio of donors to acceptors, SiGa:SiAs, is a sensitive function of the stress state during the activation anneal.
Impedance matching for enhanced waveguide/photodetector integration
Authors: Deri R. J. , Wada O.
Published: July 2002

A novel impedance-matched structure is proposed for improved coupling in evanescently coupled, integrated waveguide/photodetectors. We show that insertion of an impedance-matching layer between waveguide and detector regions can improve the coupling by a factor of ≊7, resulting in shorter detectors with lower capacitance and higher frequency response. The impedance-matching mechanism is discussed in detail.
Stimulated emission at 2.8 μm from Hg-based quantum well structures grown by photoassisted molecular beam epitaxy
Authors: Giles N. C. , Han Jeong W. , Cook J. W. , Schetzina J. F.
Published: July 2002

We report on the first observation of stimulated emission from Hg-based quantum well structures in which the active region is a HgCdTe superlattice. The laser structures were grown on (100) CdZnTe substrates photoassisted molecular beam epitaxy. Cleaved laser cavities were optically pumped using the 1.06 μm output from a cw Nd:YAG laser. Stimulated emission cavity modes were seen at cw laser power densities as low as 3.4 kW/cm2 and at temperatures ≥ 60 K.
New hybrid physical vapor deposition/organometallic chemical vapor deposition route to high T
c superconducting Tl-Ba-Ca-Cu-O thin films
Authors: Richeson D. S. , Tonge L. M. , Wang X. K. , Marcy H. O. , Marks T. J. , Ketterson J. B. , Chang R. P. H. , Kannewurf C. R.
Published: July 2002

High Tc superconducting Tl-Ba-Ca-Cu-O thin films have been prepared by a novel hybrid technique that combines electron beam evaporation with organometallic chemical vapor deposition (OMCVD). Multilayer thin films of Ba-Ca-Cu-O are prepared by sequential evaporation of BaF2, CaF2, and Cu sources onto single-crystal MgO (100) or yttria-stabilized zirconia substrates followed by annealing in a water vapor-saturated oxygen atmosphere. Thallium is then incorporated in these films in either of two ways: (1) OMCVD using thallium(cyclopentadienide) as the source or (2) vapor diffusion using bulk Tl-Ba-Ca-Cu-O superconductor as the source. The resultant films are single phase, consisting predominantly of Tl1Ba2Ca2Cu3Ox with crystallite Cu-O planes preferentially oriented parallel to the substrate surface. Resistivity measurements indicate superconducting onset temperatures above 120 K with zero resistance by 104 K. By eliminating the water vapor in the initial anneal, fluoride (originating from the Ba and Ca sources) may be retained in the film. Upon T1 incorporation, this promotes formation of the Tl1Ba2Ca1Cu2Ox phase with preferential crystallite c-axis orientation perpendicular to the substrate surface.
Role of substrate threading dislocation density in relaxation of highly strained InGaAs/GaAs quantum well structures
Authors: Klem J. F. , Fu W. S. , Gourley P. L. , Jones E. D. , Brennan T. M. , Lott J. A.
Published: July 2002

Structures with highly strained InGaAs/GaAs single quantum wells have been grown on GaAs substrates with KOH etch pit densities from ∼1000 to ∼45 000 cm−2. These structures were characterized by photoluminescence microscopy and 77 K Hall measurements to determine the extent to which the substrate threading dislocation density affects the misfit dislocation density at the quantum well interfaces. For well thicknesses near or below the Matthews–Blakeslee critical thickness, similar results are obtained for substrates of different dislocation density. However, for metastable structures significantly above the critical thickness, the misfit dislocation density is a sensitive function of the substrate quality.
Electrical and structural properties of shallow p+ junctions formed by dual (Ga/B) ion implantation
Authors: Mei P. , Jalali B. , Yang E. S. , Stoffel N. G. , Hart D. L.
Published: July 2002

Ultrashallow p+ junctions formed by dual implanation of Ga and B with low-temperature rapid thermal anneal (RTA) are reported. The electrical and structural properties of the shallow junction were studied by sheet resistance and diode reverse recovery measurements, Rutherford backscattering channeling, and secondary-ion mass spectrometry. A junction of 400 Å depth (full width at half maximum) and an average carrier concentration of 3×1019 cm−3 were realized with RTA at 600 °C. It is shown that there is excess damage in the dual-implanted junctions which affects the minority-carrier lifetime.
Deep level photoluminescence spectroscopy of CdTe epitaxial layer surfaces
Authors: Shaw J. L. , Brillson L. J. , Sivananthan S. , Faurie J. P.
Published: July 2002

We have used deep level photoluminescence spectroscopy to investigate the surface electronic quality of molecular beam epitaxy (MBE) grown CdTe layers during ultrahigh vacuum cleaning. Spectra are highly sensitive to heat treatment, contamination, and electron beam exposure. The technique provides a guide to growth and cleaning of MBE films of optimal electronic quality, which exhibit intense near-band-edge and minimal deep level emission and which exceed substantially the electronic quality of bulk CdTe crystals.
p-channel negative resistance field-effect transistor
Authors: Favaro M. E. , Miller L. M. , Bryan R. P. , Alwan J. J. , Coleman J. J.
Published: July 2002

We experimentally demonstrate the first p-channel negative resistance field-effect transistor. Low-temperature current-voltage characteristics exhibit negative differential resistance in the drain circuit which is controlled by the substrate voltage. The negative differential resistance is attributed to the real-space transfer of holes.
Low-temperature laser deposition of tungsten by silane- and disilane-assisted reactions
Authors: Black J. G. , Doran S. P. , Rothschild M. , Ehrlich D. J.
Published: July 2002

A reaction, based on tungsten hexafluoride chemically reduced by silicon hydride vapors, has been developed for low-temperature laser deposition of high-purity tungsten. Compared to previous tungsten deposition methods, the new (pyrolytic) process requires very little thermal energy for initiation and propagation of the scanned reaction. WF6 and SiH4 (or Si2H6) mixtures have been optimized to yield tungsten interconnect lines with abrupt square cross section and conductivities of 12–25 μΩ cm. Impurity levels are below the detection limits of Auger spectroscopy. Lines 3–20 μm in width and 0.1–4 μm in thickness are written at scan speeds of ∼100 μm/s. Argon-ion laser powers (488 nm) are typically 30–60 mW, corresponding to reaction temperatures sufficiently low for direct writing on polyimide dielectrics.
Pt/Ti ohmic contacts to ultrahigh carbon-doped p-GaAs formed by rapid thermal processing
Authors: Katz A. , Abernathy C. R. , Pearton S. J.
Published: July 2002

Increasing the concentration of the carbon dopants in p-GaAs layers grown on semi-insulating substrates to levels of 1×1020 to 5×1020 cm−3 enables the formation of an ohmic contact with low resistance using the refractory Pt/Ti metallization. These contacts showed ohmic behavior prior to any heat treatment with specific contact resistance as low as 7×10−6 Ω cm2 (0.08 Ω mm) for the lower doping level and 8×10−7 Ω cm2 (0.04 Ω mm) for the higher level. Small improvements in the specific resistance of the former contact were achieved by rapid thermal processing at a temperature of 450 °C for 30 s, which yielded a value of 4.9×10−6 Ω cm2. The electrical nature of the contact to the heavily doped GaAs was not affected by heat treatments at temperatures up to 450 °C. Rapid thermal processing of these contacts at higher temperatures, however, caused an increase in the contact resistance which was correlated to the expanded Ti/GaAs and Pt/GaAs interfacial reactions. Current-voltage characteristics were found to be temperature independent. This suggested that the field emission quantum-mechanical tunneling was the dominant carrier transport mechanism in these contacts.
Linewidths of Cu i(511 nm) and Au i(628 nm) laser transitions at room temperature
Authors: Wen Chuan-Dong , Tobin R. C.
Published: July 2002

Sharp spectral lines are obtained for the Cu i 511 nm and the Au i 628 nm transitions from a sputtering-based laser operating at room temperature. The Au i line exhibits a single peak with a linewidth of 360 MHz and the Cu i line consists of three well-resolved peaks with linewidths of 800, 700, and 700 MHz in order of increasing frequency. The spectral lines result from saturated emission on the strongest hyperfine components.
High specific output energy operation of a vacuum ultraviolet molecular fluorine laser excited at 66 MW/cm3 by an electric discharge
Authors: Kakehata Masayuki , Hashimoto Etsu , Kannari Fumihiko , Obara Minoru
Published: July 2002

An output laser energy of 83 mJ, which corresponds to a specific output energy of 2.9 J/l, was obtained by exciting a 10 atm He/F2 gas mixture by an extremely intense electric discharge at a peak excitation rate of 66 MW/cm3. A fast rise of the voltage between the discharge electrodes prior to the discharge induction increases the breakdown voltage and, at the same time, improves the discharge stability resulting in an increase of the laser output and intrinsic efficiency.
Transverse modulators with a record reflection change of >20%/V using asymmetric Fabry–Perot structures
Authors: Yan R. H. , Simes R. J. , Coldren L. A. , Gossard A. C.
Published: July 2002

An asymmetric Fabry–Perot structure with a multiple quantum well active region is demonstrated to provide a reflection change of >45% for an operating voltage swing of only ∼2 V, with a contrast ratio of more than 15. Photocurrent measurements show that the same devices also work as voltage-tunable detectors. Such devices compete effectively with low-voltage waveguide modulators, with further advantages of easy coupling and compact sizes, i.e., small capacitances.
Sm-Fe-Ti magnets with room-temperature coercivities above 50 kOe
Authors: Schnitzke K. , Schultz L. , Wecker J. , Katter M.
Published: July 2002

Using mechanical alloying and an additional annealing, we prepared bulk material of a new Sm20 Fe70 Ti10 phase observed before only in sputtered films deposited in the amorphous state and then crystallized. Crystallization of rapidly quenched and partially amorphous ribbons leads to a two-phase material with a considerable amount of this phase but with the Fe2 Sm phase as a majority phase. This new phase (named 20:70:10 phase) has a Curie temperature of 380 °C and an estimated saturation magnetization of 6–7 kG. The magnetically isotropic, mechanically alloyed samples show room-temperature coercivities of up to 50.3 kOe.
Ultrahigh Au/p-GaAs Schottky barriers due to plasma hydrogenation
Authors: Ashok S. , Wang Y. G. , Nakagawa O. S.
Published: July 2002

GaAs surface modification caused by rf plasma hydrogenation has been studied by electrical characterization of subsequently fabricated Au/GaAs Schottky barriers. While the Schottky barrier height on n-GaAs is found to reduce slightly, exceptionally high barriers have been seen for p-GaAs. The effective barrier height of Au/p-GaAs diodes increases from 0.35 eV for unhydrogenated control to 0.84 eV with plasma hydrogenation.
As-grown superconducting thin films of Bi(Pb)-Sr-Ca-Cu-O by magnetron sputtering
Authors: Hakuraku Y. , Higo S. , Ogushi T.
Published: July 2002

As-grown superconducting thin films of Bi(Pb)-Sr-Ca-Cu-O have been prepared on MgO (100) at 620–740 °C by dc magnetron sputtering using a single target. The as-grown process followed by no special annealing yields c-axis oriented superconducting thin films with a smooth surface. Although the superconducting properties of the thin films are very sensitive to the substrate temperatures during film growth, reproducible results were obtained. The c-axis lattice constant of the films was also controlled to the values of about 24, 31, and 37 Å by changing the substrate temperature. The as-grown film deposited at 720 °C showed zero resistivity at 81 K and the critical current density increased from 8×104 A/cm2 at 77 K to 3×106 A/cm2 at 4.2 K.
Thermal bias annealing evidence for the defect pool in amorphous silicon thin-film transistors
Authors: Deane S. C. , Powell M. J. , Hughes J. R. , French I. D. , Milne W. I.
Published: July 2002

Thin-film transistors were thermally annealed while a bias voltage was applied to the gate electrode. The transfer characteristics were then measured, and the density of states distributions derived by field-effect analysis. The results indicate that the equilibrium distribution and number of defects in the transistor channel region depend on the position of the Fermi energy during annealing. Thus the density of states can be increased or decreased in parts of the band gap. A high Fermi energy during annealing results in few states high in the gap and more states low in the gap. The reverse is true for annealing while the Fermi energy is low. This is consistent with the defect pool model for silicon dangling bond states and suggests that most deep states are part of the defect pool.
Optical waveguide microscopy
Authors: Hickel Werner , Knoll Wolfgang
Published: July 2002

Optical waveguide microscopy is introduced as a novel imaging technique that allows for the microscopic characterization of thin-film samples by using guided optical waves as illumination light source. Excellent thickness (<1 nm) and good lateral resolution (<10 μm) is demonstrated. As a first application we image and analyze the two-dimensional thickness profile of a planar polymeric spun-on waveguide structure.
Characterization of D
X centers in selectively doped GaAs-AlAs superlattices
Authors: Ababou S. , Marchand J. J. , Mayet L. , Guillot G. , Mollot F.
Published: July 2002

Using deep level transient spectroscopy (DLTS), DX center has been characterized in GaAs-AlAs superlattices grown by molecular beam epitaxy and selectively Si-doped either in the AlAs layers or in the middle of the GaAs layers. The activation energy for thermal emission, which is the summation of the binding energy Et and the thermal capture energy Ec, is Ea=0.42 eV in both superlattices. The lowest DX concentration is obtained for the case where the only GaAs layers are doped. For the first time, a study of the capture reveals a capture activation energy Ec=0.36 eV, which locates the DX at Et≊60 meV below the conduction miniband. Taking into account the measured energies and trap concentrations, we show that the only observed DX on such structures is due to the silicon diffusion into AlAs layers.
Heterostructure p-n junction tunnel diodes
Authors: Day D. J. , Chung Y. , Webb C. , Eckstein J. N. , Xu J. M. , Sweeny M.
Published: July 2002

Heterostructure p-n junction tunnel diodes with high peak to valley ratios (12: 1) at room temperature are demonstrated. The variation of peak and valley currents in diodes with different tunnel barriers is described, and the mechanisms responsible for the valley current and its temperature dependence are proposed. Ways to improve the peak to valley ratio and reduce junction capacitance are discussed.
Modulation bandwidth of high-power single-mode semiconductor lasers: Effect of intraband gain saturation
Authors: Agrawal Govind P.
Published: July 2002

The effect of intraband gain saturation on the modulation bandwidth of single-mode semiconductor lasers is discussed by using a nonperturbative form of the optical gain that is valid at high-power levels. The small-signal analysis of the modified rate equations is used to predict the power dependence of the modulation bandwidth. The results are used to discuss the ultimate modulation bandwidth of InGaAsP distributed feedback semiconductor lasers and its dependence on various device parameters.
New hydrogenated amorphous silicon alloys
Authors: Lin G. H. , Kapur M. , Bockris J. O’M.
Published: July 2002

New alloys of hydogenated amorphous silicon with Al, Ga, S, and Se have been prepared by the rf glow discharge method. The energy gap of these materials can be varied in the 1–2 eV range, with the Al and Ga alloys being low band-gap semiconductors, and the S and Se alloys having higher energy gaps. The light to dark conductivity ratios of the various systems have been measured. The best photoresponse (102–103) was obtained with the Se and S alloys.
Instability of partially disordered carbon-doped AlGaAs/GaAs superlattices
Authors: Szafranek I. , Major J. S. , Cunningham B. T. , Guido L. J. , Holonyak N. , Stillman G. E.
Published: July 2002

Superlattices of Al0.3Ga0.7As/GaAs grown by metalorganic chemical vapor deposition and heavily doped with carbon using CCl4 were annealed for 24 h at 825 °C under a variety of ambient and surface encapsulation conditions. Pronounced changes in photoluminescence from the annealed superlattices with storage time at room temperature, as opposed to an excellent reproducibility of that from the as-grown, not annealed samples, are reported. These changes may be indicative of degraded thermal stability of the annealed superlattice crystals due to high-temperature-induced lattice defects. The systematic failure to fabricate buried-heterostructure quantum well lasers via impurity-induced layer disordering in similarly doped AlGaAs/GaAs crystals, which may be related to the same effect, is also discussed.
Low-density high-mobility electron gas in wide parabolic GaAs/AlxGa1−xAs wells
Authors: Hopkins P. F. , Rimberg A. J. , Gwinn E. G. , Westervelt R. M. , Sundaram M. , Gossard A. C.
Published: July 2002

Remotely doped wide parabolic GaAs/AlxGa1−xAs wells are used to create thick (≳ 1000 Å) layers of high-mobility (≳ 2×105 cm2/V s) electron gas with three-dimensional densities below (by a factor ∼3) the metal-insulator transition for doped GaAs. The temperature dependences of the Hall mobility and sheet density show no qualitative changes in a series of three samples spanning the metal-insulator transition. Shubnikov–de Haas oscillation measurements are used to determine the width of the electron gas layers.
Hydrogen neutralization of acceptors in highly doped GaInAs:Zn
Authors: Jalil A. , Theys B. , Chevallier J. , Huber A. M. , Grattepain C. , Hirtz P. , Pajot B.
Published: July 2002

We have investigated the behavior of atomic hydrogen (or deuterium) introduced by plasma in highly doped GaInAs:Zn epitaxial layers. Different experimental techniques have been used: secondary-ion mass spectrometry (SIMS) profiling, electronic transport measurements, and infrared absorption spectroscopy. After hydrogenation the concentration of free holes is drastically reduced. SIMS profiles follow erfc functions. This corresponds to weak hydrogen-dopant interactions. This weakness is confirmed by the annealing experiments from which a low dissociation energy can be estimated.
In situ deposition of superconducting Bi-Pb-Sr-Ca-Cu-O thin films on MgO(100) substrates by rf magnetron sputtering and laser ablation
Authors: Moodera J. S. , Rao A. M. , Kussmaul A. , Tedrow P. M.
Published: July 2002

Superconducting thin films of Bi-Pb-Sr-Ca-Cu-O (BPSCCO) have been prepared in situ by magnetron sputtering and laser ablation onto heated MgO (100) substrates. Post-deposition annealing at higher temperatures was not required to obtain superconducting BPSCCO films, and a narrow temperature window in a very similar temperature region was observed for the growth of oriented films for both the laser ablation and magnetron sputtering technique. The best films were smooth and shiny with their c axes oriented perpendicular to the substrate surface but scanning electron microscope analysis showed particulates on the film surface. Room-temperature resistivity values of the order of 2–3 mΩ cm were obtained for these films. At 70 K and 8 T, the resistivity ratio for the H⊥ and ∥ to the plane of the film was ∼25 for an applied current density J of 0.8 A/cm2. Rutherford backscattering analysis on the laser-ablated and sputtered films indicates that the BPSCCO films had 2223 composition while the x-ray diffraction studies indicated mixed 2212 and 2223 phases.  
Selective-area epitaxial growth of gallium arsenide on silicon substrates patterned using a scanning tunneling microscope operating in air
Authors: Dagata J. A. , Tseng W. , Bennett J. , Evans C. J. , Schneir J. , Harary H. H.
Published: July 2002

Selective-area epitaxial growth of gallium arsenide on n-Si(100) substrates is reported, where the oxide (SiOx) mask consists of 1–2 monolayer-thick features patterned onto a silicon substrate using a scanning tunneling microscope (STM) operating in air. The technique for generating the STM patterns on hydrogen-passivated silicon was reported recently [J. A. Dagata, J. Schneir, H. H. Harary, C. J. Evans, M. T. Postek, and J. Bennett, Appl. Phys. Lett. 56, 2001 (1990)]. The GaAs epilayer was grown by migration-enhanced epitaxy at 580 °C and its morphology was investigated by scanning electron microscopy. The chemical selectivity of the STM-patterned regions was verified by imaging time-of-flight secondary-ion mass spectrometry. The implications of these results for the development of a unique, STM-based nanostructure fabrication technology are discussed.
Electro-optical bistability in strained InxGa1−xAs/Al0.15Ga0.85As multiple quantum wells
Authors: Fujiwara Kenzo , Kawashima Kenji , Kobayashi Kikuo , Sano Naokatsu
Published: July 2002

Using photocurrent spectroscopy, we have studied optical absorption properties of strained InxGa1−xAs/Al0.15Ga0.85As multiple quantum wells grown by molecular beam epitaxy in the presence of electric fields perpendicular to the heterointerface. In the wavelength region where the bulk GaAs substrate is transparent, we observe the quantum confined Stark effect. Optical bistability of a self-electro-optic effect device is demonstrated at room temperature without removal of the GaAs substrate.