bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous local laser etching of copper by chlorine
Authors: Tang Hua , Herman Irving P.
Published: July 2002

Etching of copper films by chlorine is induced by a scanning cw laser that locally heats the film. In experimental regimes with relatively high laser power, low chlorine pressure and fast scan speed, laser etching of copper is well characterized by a kinetic model based on the calculated temperature rise. In other regimes, a thick nondesorbed copper chloride layer forms on top of the etched copper region that significantly decreases the rate of copper chlorination. Notably, in certain regimes the copper etch depth is shown to increase with increasing scan rate, which is a very unusual dependence.
Nanostructure fabrication with the scanning tunneling microscope by tunneling medium manipulation
Authors: Tang S. L. , McGhie A. J. , Lewittes M. E.
Published: July 2002

A polymer coating inserted between the tunneling tip and the graphite substrate has been found to improve the writing of nanostructure by short voltage pulses with the scanning tunneling microscope. Structures ranging from 5 to 30 Å with up to 95% success rate were obtained. Unlike previous reports, this structure fabrication process can be carried out even in ultrahigh vacuum. Comparison of pulse heights and structure sizes between coatings of water-soluble polyvinyl alcohol and a less hygroscopic, water-insoluble fluorocarbon polymer suggests that the role played by moisture is physical as well as chemical in nature.
Ultralow threshold multiquantum well InGaAs lasers
Authors: Chen T. R. , Zhao B. , Zhuang Y. H. , Yariv A. , Ungar J. E. , Oh S.
Published: July 2002

Ultralow threshold currents have been obtained in multiquantum well strained-layer InGaAs lasers. A cw threshold current of 1 mA in an uncoated double quantum well laser and a 0.35 mA (pulsed threshold current 0.25 mA) in a coated laser are demonstrated.
Spin dependent photocurrents in ribbon solar cells
Authors: Seager C. H. , Venturini E. L. , Schubert W. K.
Published: July 2002

Microwave resonance induced variations in the short circuit photocurrent of edge-defined film-fed growth ribbon silicon solar cells have been observed. These signals have zero-crossing g values and linewidths which are similar to electron spin resonance and spin dependent transport (SDT) observations on silicon bicrystals, damaged silicon, and polycrystalline silicon. The SDT signals seen here depend on cell illumination levels in a way that suggests that the values of recombination velocity at electrically active linear boundaries decrease with illumination intensity. Hydrogen processed cells show markedly smaller SDT response, consistent with the passivation of Si dangling bond defects. While only dangling bond SDT response is apparent at 300 K, we suggest that similar experiments performed at low temperatures may have the resolution to identify the centers responsible for the majority of the electron-hole recombination events in these cells.
Vapor etching of GaAs and AlGaAs by CH3I
Authors: Krueger C. W. , Wang C. A. , Flytzani-Stephanopoulos M.
Published: July 2002

With the objective of developing an improved process for in situ etching of GaAs-based materials in organometallic vapor phase epitaxy reactors, GaAs wafers and AlxGa1−xAs epilayers have been etched with CH3I vapor in a horizontal reactor operated at atmospheric pressure with H2 or He carrier gas. For a H2 flow rate of 2.1 s lpm, etching temperatures from 400 to 625 °C, and CH3I mol fractions (yCH3I)from 0.0012 to 0.015, the measured GaAs etch rate r (in Å min−1) is given by r = k0 y0.83CH3I exp[ − 45(kcal mol−1)/RT] with k0=3.2×1016 Å min−1. The value of k0 depends on the type of carrier gas, flow rate, total pressure, and reactor geometry. The etch rate appears to be controlled mainly by the decomposition of CH3I to CH3 and I, for which the activation energy has been reported to be 43.5 kcal mol−1. The etch rate of AlxGa1−xAs epilayers with x up to 0.7, which was measured at 480 °C with yCH3I= 0.015, does not depend on Al content. The surface morphology of etched GaAs wafers improves with decreasing temperature. Specular surfaces are maintained at temperatures below 500 °C for etch depths up to 5000 Å.
Dislocation reduction in the annealed undercut GaAs on Si
Authors: Sakai Shiro , Shao Chun Lin , Wada Naoki , Yuasa Takayuki , Umeno Masayoshi
Published: July 2002

The dislocations in the undercut GaAs on Si (UCGAS) was investigated by the cross-sectional transmission electron microscope. The UCGAS structure was fabricated by first growing Al0.7Ga0.3As and GaAs on Si substrate and then partially etching the Al0.7Ga0.3As layer in the lateral direction. No dislocation was found in the annealed UCGAS at 800 °C for 10 min, while dislocations were observed in the region where the GaAs layer was connected to the Si substrate. The dislocation reduction mechanism in the UCGAS was also discussed in this letter.
Possible new structure for one-dimensional electron-gas systems by interface bending of n-AlGaAs/u-GaAs heterojunctions
Authors: Sawada Akemi , Usagawa Toshiyuki , Ho Shirun , Yamaguchi Ken
Published: July 2002

A new concept in one-dimensional electron-gas (1DEG) systems is proposed by introducing periodic bending of the heterointerface of an n-AlGaAs/u-GaAs modulation-doped structure. The carrier densities and the electrostatic potential of this system are numerically analyzed based on the classical drift-diffusion model where the doping concentration ND of n-AlzG1−zAs is 1.0×1018 cm−3, the aluminum molar fraction z of AlzGa1−zAs is 0.3, the carrier density of p-type GaAs is 1.0×1014 cm−3, and the bending angle of the heterointerface is 90°. We found that electrons are more accumulated in convex regions of the u-GaAs layer than in concave ones, and the electron density in a convex region is about twice that in the conventional two-dimensional electron-gas structure. We can treat this high density of electrons as a 1DEG channel for field-electron transistors (FETs) when the period of the bending interface is about 850 Å.
Fabrication and characterization of ZnSe/GaAs heterostructure bipolar transistors grown by molecular beam epitaxy
Authors: Glaeser Annette S. , Merz James L. , Nahory Robert E. , Tamargo Maria C.
Published: July 2002

Fabrication of the first molecular beam epitaxy grown ZnSe/GaAs heterostructure bipolar transistor (HBT) is described. The ZnSe/GaAs heterointerface is attractive for the design of an Npn HBT since it combines a large valence band offset with a small conduction band offset. These initial devices had common emitter dc current gains of 16 at current densities of 1.6×104 A/cm2. Issues identified to be addressed further include a relatively high (1 K Ω) emitter-base resistance and a large offset voltage (2.8 V) in the common emitter characteristic.
Significant improvement in depth resolution of Cr/Ni interfaces by secondary ion mass spectrometry profiling under normal O2+ ion bombardment
Authors: Kim Kyung Joong , Moon Dae Won
Published: July 2002

Depth resolution in secondary ion mass spectrometry profiling of Cr/Ni multilayered thin films was studied as a function of ion beam incidence angle. As the incidence angle from the surface normal increased from 30° to 80°, the depth resolution improved as generally observed. However, between incidence angles of 20° and 30°, the depth profiling resolution improved abruptly and significantly. The best depth resolution of about 6 nm was obtained for normal incident O2+ ion beams for all the Cr/Ni interfaces of depth down to 500 nm. It was found that the observed variation of depth resolution was very well related to the surface topographic development, which was very sensitive to the incidence angle of the ion beam.
Metalorganic vapor phase epitaxical growth and 1.5-μm laser fabrication using ethyldimethylindium, tertiarybutylphosphine, and tertiarybutylarsine
Authors: Ogasawara Matsuyuki , Sato Kenji , Kondo Yasuhiro
Published: July 2002

High-quality InGaAsP lattice matched to InP was grown by low-pressure metalorganic vapor phase epitaxy using ethyldimethylindium (EDMIn), tertiarybutylphosphine (TBP), and tertiarybutylarsine (TBA). The background carrier concentrations of undoped InP and InGaAs were as low as 1.5×1015 and 2.2×1015 cm−3, respectively. Good compositional control of In-GaAsP was also possible. The performance of the double heterostructure wafers employed as lasers as characterized by threshold current density, internal loss, and internal quantum efficiency. The threshold current density for a 300-μm cavity was as low as 2.0 kA/cm2. In addition, ridge-waveguide distributed feedback lasers were successfully fabricated. These results show that EDMIn, TBP, and TBA might be used to replace conventional sources for growing InGaAsP/InP lasers.
Atomic-scale morphology and interfaces of epitaxially embedded metal (CoAl)/semiconductor (GaAs/AlAs) heterostructures
Authors: Tanaka M. , Ikarashi N. , Sakakibara H. , Ishida K. , Nishinaga T.
Published: July 2002

We have grown GaAs/AlAs/CoAl/AlAs/GaAs epitaxially embedded metal/semiconductor heterostructures by molecular beam epitaxy. When the growth temperature of overgrown GaAs is relatively low (440 °C), the buried metallic CoAl film with the thickness of 50 Å is uniform and planar with extremely smooth and abrupt metal/semiconductor interfaces. The top (AlAs-on-CoAl) interface is atomically smooth with the roughness of at most 1 monolayer, while the bottom (CoAl-on-AlAs) interface has the roughness of 2–3 monolayers. This sample shows very low resistivity of 11–41 μ Ω cm at room temperature, indicating that the electrically continuous metallic film is grown. In contrast, when the GaAs overlayer is grown at 580 °C, CoAl dots with the size of 200–250 Å, which are covered with {001} and {111} facets, are fabricated, resulting from agglomeration.
Dissociation energies of acceptor-hydrogen complexes in InP
Authors: Pearton S. J. , Hobson W. S. , Abernathy C. R.
Published: July 2002

The dissociation energies of Zn-H, Cd-H, and Mg-H complexes in p-InP have been determined from the reactivation kinetics of these passivated dopants in reverse-biased Au Schottky diodes. The reactivation process is first order under these conditions, yielding thermal dissociation energies of 1.20±0.10 eV for Zn acceptors, 1.40±0.10 eV for Cd acceptors, and 1.35±0.10 eV for Mg acceptors. These results are consistent with the model in which the hydrogen passivates the acceptor by attaching to a neighboring P atom, leaving the acceptor essentially threefold coordinated. They also indicate that acceptor-hydrogen retrapping during cool down after epitaxial growth of p-InP layers is the primary cause of apparently stable acceptor passivation seen in such layers.
Study of diffusion of a fluorinated hydrocarbon in ion beam irradiated poly(styrene) by nuclear resonance analysis
Authors: Umezawa Kenji , Gibson Walter M. , Weltch John T. , Zhou Peiguang , Xu Qihua , Frisch Harry L.
Published: July 2002

The diffusion of a fluorinated hydrocarbon into 30 keV-H+ irradiated glassy poly(styrene) (PS) was studied by using nuclear resonance reaction analysis. The diffraction coefficient and front velocity for diffusing a particular fluorinated hydrocarbon, 3, 5-bis (trifluoromethyl) aniline (TFMA) in PS (MW=400 000) are dramatically decreased on irradiation with 5×1013–1×1014 atoms/cm2 at 22.5 °C. These ion beam irradiation effects are similar to temperature effects on diffusion. A possible application of the observed effect is the control of diffusion of a vapor into cross-linked polymer glasses by means of ion beam implantation techniques. It is our belief that this is the first report of this phenomena due to the effects of ion beam irradiation.
Observation of superstructures on the surfaces of sputtered YBa2Cu3O7−x thin films by low-energy electron diffraction
Authors: Behner H. , Rauch W. , Gornik E.
Published: July 2002

The surface structures of sputtered c-axis-oriented YBa2Cu3O7−x (YBCO) thin films were studied by means of low-energy diffraction (LEED). The in situ analysis, without exposing the films to air, showed the formation of superstructures of the YBCO (001) 2×2 and YBCO (001) 4×1 type. Air-exposed surfaces showed no LEED pattern but could be transformed into the YBCO (001) 2×2 structure by annealing at 500 °C. The observed superstructures are interpreted as being due to oxygen loss of the YBCO surface region, causing an oxygen vacancy ordering in the basal CuO planes.
High-resolution study of stimulated emission from blue-green laser diodes
Authors: Yu Z. , Ren J. , Sneed B. , Bowers K. A. , Gossett K. J. , Boney C. , Lansari Y. , Cook J. W. , Schetzina J. F. , Hua G. C. , Otsuka N.
Published: July 2002

The first high-resolution study of emission spectra from ZnSe-based blue-green laser diodes is reported.
Formation of zinc clusters in ionized cluster beam film deposition
Authors: Urban Frank K. , Feng Susan W. , Nainaparampil Josekutty J.
Published: July 2002

Ionized cluster beam deposition uses a beam of ionized, accelerated atom clusters to grow thin films. Earlier unsuccessful attempts at forming such cluster beams used 1×1 mm nozzles at crucible pressures around 2 Torr. Recently, Gspann [Proceedings of the Ger. Phys. Soc. 3, 387 (1992)] produced zinc clusters by increasing the crucible pressure to the 1000 Torr range and using a converging–diverging nozzle 18 mm long and 0.4 mm in diameter at the throat. The work reported here uses electron bombardment heating and deflected deposition cluster measurement. Results indicate significant numbers of zinc clusters, 1400 atoms in average size, in general agreement with Gspann.
Physical model for defect mediated boron diffusion during rapid thermal annealing of ion implanted BF2
Authors: Kinoshita H. , Kwong D. L.
Published: July 2002

A diffusion model for ion implanted BF2 has been developed based on the diffusion and reactions of point defects and B. The simulation of enhanced diffusion under rapid thermal annealing condition has been accomplished for 2×1013–1.5×1015 cm−2 dose BF2 implant. The effects of implant damage, surface amorphization, and fluorine atoms on B diffusion have been investigated by using the as-implant defect profiles obtained from Monte Carlo simulation as the initial condition. From excellent agreement between experimental and model results, we find that chemical effects of F on B diffusion in low dose BF2 implant is minimal, and for high dose BF2 implant, the surface amorphization can be modeled by modifying the point defect profile within the amorphized region.
Chemical characterization of (In,Ga)As/(Al,Ga)As strained interfaces grown by metalorganic chemical vapor deposition
Authors: Kim J. , Alwan J. J. , Forbes D. V. , Coleman J. J. , Robertson I. M. , Wayman C. M. , Baumann F. H. , Bode M. , Kim Y. , Ourmazd A.
Published: July 2002

We have used quantitative chemical mapping to determine the chemical abruptness of interfaces in In0.2Ga0.8As/Al0.2Ga0.8As strained multilayers grown by metalorganic chemical vapor deposition. We observe a large difference in the interfacial width, depending on the order in which successive layers are grown; the (Al0.2Ga0.8As on In0.2Ga0.8As) interface is twice as wide as the (In0.2Ga0.8As on Al0.2Ga0.8As).
Interdiffusion problems at CdTe/InSb heterointerfaces grown by temperature gradient vapor transport deposition
Authors: Kim T. W. , Jung M. , Park H. L. , Na H. K. , Kim J. S.
Published: July 2002

CdTe epitaxial films were grown by a simple method of temperature gradient vapor transport deposition on p-InSb (111) orientation substrates in the growth temperature range between 200 and 280 °C. Raman spectroscopy showed the optical phonon modes of the CdTe thin films and the formation of an indium telluride interfacial layer in the CdTe/InSb heterostructures. The stoichiometry of the CdTe/InSb heterostructures was observed by the Auger electron spectroscopy, and Auger depth profiles also demonstrated that the CdTe/InSb heterointerface was not abrupt. The results indicated that the films grown at about 265 °C posed a significant problem due to interdiffusion from the InSb substrates during the growth.
Growth of InAs on EuBa2Cu3O7−y superconducting thin films with SrF2 interlayers
Authors: Watanabe Y. , Maeda F. , Oshima M. , Michikami O.
Published: July 2002

In order to prevent reactions at the superconducting EuBa2Cu3O7−y (EBCO) and InAs interface, SrF2 interlayers have been grown on EBCO thin films. X-ray photoemission spectroscopy study demonstrates the effectiveness of SrF2 interlayers in suppressing both removal of oxygen from the EBCO surface and oxidation of the InAs overgrown at room temperature. To crystallize InAs, a two-step growth process was applied. X-ray diffraction results show the 1-μm-thick InAs to be mainly (111) oriented crystalline. The Tc (zero)’s for InAs-deposited EBCO and annealed EBCO (300 °C) are 73 and 82 K, respectively, implying that the use of an interlayer and two-step growth process is promising for depositing InAs layers without disruption of the underlying EBCO.
High purity synthesis of YBa2Cu4O8 at low oxygen pressure
Authors: Bonoldi L. , Sparpaglione M. , Zini L.
Published: July 2002

Two new simple procedures for the synthesis of the YBa2Cu4O8−δ compound are presented. The x-ray diffraction (XRD) spectra show the presence of the 124 just after 20 h of high-temperature treatment. The resistivity measurements show that the material produced is a superconductor. For one of the procedures the XRD analysis does not show the presence of impurities after 92 h of total treatment.
Anomalous liquid crystal undershoot effect resulting in a nematic liquid crystal-based spatial light modulator with one millisecond response time
Authors: Sayyah Keyvan , Wu Chiung-Sheng , Wu Shin-Tson , Efron Uzi
Published: July 2002

We report here, a single crystal silicon-based spatial light modulator demonstrating a millisecond response time using a nematic liquid crystal operated in the surface mode configuration. This unexpected fast response time can be explained by a combination of liquid crystal voltage undershoot and the transient nematic effect. The fast response time measured is concurrent with high spatial resolution and gray scale capability which make this device unique in its class.
Crystallinity, strain, and thermal stability of heteroepitaxial Si1−xGex/Si (100) layers created using pulsed laser induced epitaxy
Authors: Kramer K.-Josef , Talwar Somit , Sigmon Thomas W. , Weiner Kurt H.
Published: July 2002

Heteroepitaxy of Si1−xGex/Si alloy layers on Si (100) substrates has been achieved using pulsed laser induced epitaxy (PLIE). The energy of 1 to 20 pulses from a spatially homogenized XeCl excimer laser beam is used to melt a structure consisting of electron-beam evaporated Ge on Si (100) substrates. Alloy films with different Ge fractions are investigated and films with up to 21% Ge content are found to exhibit excellent crystallinity, as confirmed by MeV-ion channeling along the 〈100〉 direction. MeV-ion channeling is also used to determine the level of strain in the layers. This is done by comparing angular yield curves around the 〈110〉 direction for the substrate and alloy layer. The strain values obtained match with calculations for an ideally strained layer state. The strain is also measured for layers that have been subjected to different thermal cycles. A high level of strain is preserved in the alloy layer even after heating to 950 °C for 1 h. This unusual thermal stability is believed to be due to two process features, the ultrarapid nature of the process and the interfacial grading of the Ge fraction created during the melt-regrowth process.
Difference of the electrical properties of screw and 60° dislocations in silicon as detected with temperature-dependent electron beam induced current technique
Authors: Kusanagi Susumu , Sekiguchi Takashi , Sumino Koji
Published: July 2002

Well-defined hexagonal-shaped dislocation loops were introduced into an n-type silicon crystal grown by the floating-zone technique. The electron beam induced current (EBIC) contrasts of screw parts and 60° parts of the loops showed different dependencies on the temperature of observation. Such difference is interpreted with the idea that the physical parameters controlling carrier recombination at the dislocation core are different between screw and 60° dislocations.
Microwave growth from the beam breakup instability in long-pulse electron beam experiments
Authors: Menge P. R. , Gilgenbach R. M. , Bosch R. A.
Published: July 2002

The beam breakup (BBU) instability has been investigated in high-current, long-pulse electron beams propagating through microwave cavities. Experiments are performed using a relativistic electron-beam generator with diode parameters: 0.7–0.8 MV, 1–15 kA, and 0.5–1.5 μs. The magnitude of the solenoidal magnetic field places these experiments in an intermediate regime between strong focusing and weak focusing. The electron-beam transport system consists of ten identical pillbox cavities each containing a small microwave loop antenna designed to detect the TM110 beam breakup mode. The TM110 microwave mode is primed in the first cavity by a magnetron tuned to the resonance frequency of 2.5 GHz. The BBU instability growth is measured through the amplification of the 2.5 GHz microwaves between the second and tenth cavities. Strong growth (25–38 dB) of the TM110 microwave signal is observed when the initial cavity is primed exactly on resonance, with a rapid decrease of the growth rate off-resonance. The magnitude of microwave growth is consistent with the predictions of BBU theory.
Electrical and magnetic transport properties of laser-deposited Ba1−xKxBiO3 thin films
Authors: Schweinfurth R. A. , Platt C. E. , Teepe M. R. , Van Harlingen D. J.
Published: July 2002

We report measurements of the electrical and magnetic transport properties of high-quality superconducting Ba1−xKxBiO3 (BKBO) thin films grown by in situ pulsed laser deposition. The best films exhibit sharp resistance and magnetic transitions with zero resistance above 28 K and widths of 0.3 K, and nearly linear normal state resistance extending from the transition to above room temperature. Critical current densities obtained by transport in patterned BKBO lines are greater than 3×106 A/cm2 at 4 K. The transverse magnetoresistance exhibits predominantly BCS-like behavior with an upper critical field slope of −0.78 T/K near Tc, giving Hc2(0)=15.2 T and a BCS coherence length ξ=46 Å. We also observe substantial field broadening suggestive of flux flow dissipation.
Regenerative switching properties of a sawtooth-doping-superlattice-collector bipolar transistor
Authors: Liu Wen-Chau , Sun Chung-Yih , Guo Der-Feng
Published: July 2002

A molecular beam epitaxially grown GaAs three-terminal switching device with controllable S-shaped negative differential resistance (NDR) and switching voltages has been fabricated and demonstrated. The current-voltage and switching characteristics of this device are excellent and reproducible. The switching voltage VS=9.6 V and holding voltage VH=5.1 V are obtained under two-terminal operation. If a base current IB is applied, this device exhibits a controllable S-shaped NDR phenomena both at the forward and reverse IB conditions. A bipolar transistor behavior with a current gain of over 20 is further achieved when the forward IB is employed. The proposed device having good potential for high speed and switching circuit applications has been shown by the results.
Partial pressure gradients due to temperature gradients in a mixture of reactive gases
Authors: Porat O. , Riess I.
Published: July 2002

Partial pressure gradients due to temperature gradients in a mixture of reactive gases, limit the possible use of sensors. Problems arise when a partial pressure sensor is subjected to a temperature, different from that of the sample. A model is proposed that allows the calculation of the partial pressure distributions in a temperature gradient. Experiments conducted using O2, H2, and H2O in Ar confirm the predictions. It is shown how to relate the sensor’s reading to the parameter of interest. It is also concluded that in certain cases it is advisable to deliberately add a reactive gas, as this facilitates the interpretation of the measurements.
Compression of pulses from a mode locked GaAs laser diode in an extended cavity with a fiber grating reflector
Authors: Carter Gary M. , Zheng Liu , Huang Kao-Yang
Published: July 2002

A GaAs diode laser was actively mode locked with one end of its extended cavity formed by a fiber grating. The laser repetition rate, 4 GHz, was the 19th harmonic of the fundamental extended cavity resonance. The pulses from the extended cavity laser had a bandwidth of 2 Å and were frequency chirped. A pulse compressor was used to reduce the duration of the pulses from 30 to 19 ps. The average power output after the pulse compressor was 1.2 mW.
Ultraviolet-induced annealing of hydrogen bonds in silica films deposited at low temperatures
Authors: Debauche C. , Licoppe C. , Flicstein J. , Dulac O. , Devine R. A. B.
Published: July 2002

Exposure of photodeposited silica to ultraviolet irradiation with wavelengths comprised between 170 and 250 nm is shown to cause full removal of Si—H bonds. The photoreaction occurs at low temperatures (0–200 °C) in the bulk of the films, is independent of the film thickness, and does not lead to the creation of dangling bonds. An important reaction path involves water groups in the silica films, while direct photolysis of Si—H bonds is ruled out.
Control of GaAs Schottky barrier height by formation of a thin off-stoichiometric GaAs interlayer grown by low-temperature molecular beam epitaxy
Authors: Fujieda Shinji
Published: July 2002

Thin (10 to 20-Å-thick) nonstoichiometric GaAs layers were grown by molecular beam epitaxy at 200 °C under a wide range of As pressure and placed at the interface of metal-GaAs Schottky barriers. The influence of these interlayers on the Schottky barrier heights was explored. By changing the As pressure for the interface film growth, the Schottky barrier heights obtained using both Al and Au metals varied in the range of 0.5 to 1.0 eV on n-GaAs and of 0.4 to 0.9 eV on p-GaAs. The wide variation of barrier heights, essentially independent of metal work function, can be explained by a strong Fermi-level pinning controlled by the defect levels in the interface layer. These defects are directly related to the layer’s nonstoichiometry.
Interplay between oscillatory exchange coupling and coercivities in giant magnetoresistive [Ni80Fe20/Cu/Co/Cu] multilayers
Authors: Valet T. , Jacquet J. C. , Galtier P. , Coutellier J. M. , Pereira L. G. , Morel R. , Lottis D. , Fert A.
Published: July 2002

We have observed giant magnetoresistance in [Ni80Fe20/Cu/Co/Cu] multilayers with well-defined oscillations in magnitude as a function of the Cu layer thickness both at 300 and 4.2 K. The phase and period are found to be very similar to those previously measured in Co/Cu and, more recently, Ni81Fe19/Cu multilayers. However, the existence of a strong contrast in coercive fields between Ni80Fe20 and Co leads to a significant magnetoresistance for Cu layer thicknesses where coupling is zero or even moderately ferromagnetic. At room temperature, resistance changes as large as 7% are observed within a few tens of oersted of zero field.
Magnetic hysteresis in thin film dc SQUID magnetometers
Authors: Sun J. Z. , Gallagher W. J. , Koch R. H.
Published: July 2002

Measurements of the magnetic hysteresis of thin film dc SQUID magnetometers in applied magnetic fields up to 1 mT are reported herein. The hysteresis characteristic for the 77 K YBaCuO high Tc SQUIDS has a similar behavior to that of low Tc Nb thin film SQUIDs operating at 4.2 K. A quadratic dependence on the amplitude of the sweeping field was found in the high field limit.
Operation of the grating-coupled oscillator at submillimeter/far-infrared wavelengths
Authors: Price E. J. , Walsh J. E.
Published: July 2002

Grating-coupled oscillator experiments covering the 1 cm–400 μm wavelength range are reported. Two coexisting modes of operation have been identified; a relatively low frequency signal (LFM) that is widely tunable with voltage and a high frequency signal (HFM) that tunes over a more reduced wavelength and voltage range. Observed wavelength and start oscillation currents of the LFM correspond well with a simple model of the beam-electromagnetic wave interaction. Electronic tuning ranges of 50 GHz with start oscillation currents of 0.5–1.5 A at beam voltages of 50–100 kV are typical. Power levels approach a kW at longer millimeter wavelengths.
Single-crystal diamond plate liftoff achieved by ion implantation and subsequent annealing
Authors: Parikh N. R. , Hunn J. D. , McGucken E. , Swanson M. L. , White C. W. , Rudder R. A. , Malta D. P. , Posthill J. B. , Markunas R. J.
Published: July 2002

We describe a new method for removing thin, large area sheets of diamond from bulk or homoepitaxial diamond crystals. This method consists of an ion implantation step, followed by a selective etching procedure. High energy (4–5 MeV) implantation of carbon or oxygen ions creates a well-defined layer of damaged diamond that is buried at a controlled depth below the surface. For C implantations, this layer is graphitized by annealing in vacuum, and then etched in either an acid solution, or by heating at 550–600 °C in oxygen. This process successfully lifts off the diamond plate above the graphite layer. For O implantations of a suitable dose (3×1017 cm−2 or greater), the liftoff is achieved by annealing in vacuum or flowing oxygen. In this case, the O required for etching of the graphitic layer is also supplied internally by the implantation. This liftoff method, combined with well-established homoepitaxial growth processes, has considerable potential for the fabrication of large area single crystalline diamond sheets.
Passivation of (NH4)2S-treated GaAs surface with an As2S3 film
Authors: Mada Yoichi , Wada Kazumi , Wada Yoshinori
Published: July 2002

This letter describes the suppression of (NH4)2S-treated GaAs surface degradation by coating the treated surface with an evaporated As2S3 film. The photoluminescence intensity of the treated GaAs surface shows no decrease even after 100 days. The properties of the As2S3/GaAs interface were also evaluated by metal-insulator-semiconductor techniques. A small hysteresis capacitance-voltage curve with reduced frequency dispersion was obtained, which indicates low interface state density. The passivation of the (NH4)2S-treated surface by coating with an As2S3 film is very promising for GaAs surface electronic property improvements.
Compositional variation and ordering of GaxIn1−xP on GaAs structured substrates
Authors: Buchan N. , Jakubowicz A. , Broom R. F. , Heuberger W. , Roentgen P.
Published: July 2002

Nominally lattice-matched GaxIn1−xP grown on near-(001) GaAs substrates containing etched trenches oriented in the [1̄10] and [110] directions have been analyzed by scanning electron microscopy, energy dispersive x-ray spectrometry, transmission electron microscopy, and cathodoluminescence. The trench walls exhibit a high deposition rate and Ga content, accentuated on walls that are oriented toward {111}A planes. Walls oriented toward {111}B lead to selective atomic ordering on (1̄11) or (11̄1) planes, whereas walls oriented toward {111}A exhibit disorder. We discuss the combined effect of composition and ordering on the band gap.
Growth orientation dependence of normal incidence absorption in ellipsoidal-valley quantum wells
Authors: Xie H. , Katz J. , Wang W. I.
Published: July 2002

We have investigated theoretically the dependence of normal incidence absorption from interconduction subband transitions on the growth direction in ellipsoidal-valley quantum wells. Due to the effective-mass anisotropy of electrons in the ellipsoidal valleys, normal incidence absorption is allowed in these structures when the growth direction is not collinear with the principal axes of the ellipsoidal valley which is associated with the ground state. We found that in the AlAs X-valley system the absorption is near optimal for such low-index orientated structures as [210] and [113] quantum wells, while in the Ga0.7Al0.3Sb L-valley system the absorption reaches a maximum for the [110] growth direction.
A uniformity degradation mechanism in rapid thermal chemical vapor deposition
Authors: Öztürk Mehmet C. , Sanganeria Mahesh K. , Sorrell F. Yates
Published: July 2002

In this letter, a new physical mechanism that can significantly degrade the thickness uniformity in rapid thermal chemical vapor deposition (RTCVD) has been identified and experimentally verified using polycrystalline silicon (polysilicon) deposition on silicon dioxide. The mechanism is initiated by small temperature variations across the wafer typically caused by edge cooling or large area patterns. The amount of light absorbed in a silicon wafer is determined by the wafer absorptivity weighted by the emission spectrum of the heat lamp. The absorptivity is a strong function of the thickness and optical properties of the layers on the wafer surface. Consequently, during RTCVD, once a nonuniform deposition pattern is established, the absorptivity and hence, the temperature uniformity become strongly dependent upon the thickness uniformity. This causes the nonuniformity to increase with process time and the thickness of the deposited layer.
Visible to UV up-conversion in Er3+ doped cadmium chloride and zinc chloride glasses
Authors: Gharavi Ali , McPherson Gary L.
Published: July 2002

Up-conversion luminescence in the UV has been observed in Er3+ doped cadmium chloride and zinc chloride glasses (Cd0.5Ba0.3K0.2Cl1.8 and Zn0.5K0.5Cl1.5) when the 4S3/2(E) excited state is pumped by pulsed laser between 545 and 555 nm. The principal up-conversion emissions arise from the 4G9/2(T), 4G11/2(L), and 2H9/2(K) excited states at 36 200, 26 000, and 24 300 cm−1, respectively. The main up-conversion process is the sequential two-photon absorption at a single Er3+ ion to populate the 4G9/2(T) state. At excitation intensities of roughly 1018 photons/cm2 the UV emissions from the cadmium chloride glass are remarkably strong, approaching 5% of the intensity of the visible emission from the directly pumped state. The up-conversion luminescence from the zinc chloride glass is detectable but very weak. The emission from the 4G9/2(T) state decays nonexponentially over roughly 200 μs in the cadmium chloride glass. The 4G9/2(T) emission decays in less than 1 μs in the zinc chloride glass.
Scanning probe microscopy and scanning tunneling spectroscopy of porous silicon
Authors: Amisola G. B. , Behrensmeier R. , Galligan J. M. , Otter F. A. , Namavar F. , Kalkoran N. M.
Published: July 2002

Atomic force microscope and scanning tunneling microscope images of photoluminescent anodically etched porous silicon are presented and the development of the porous structure due to different etching stages is investigated. These measurements show that the vertical surface roughness increases with etching while the lateral dimensions remain almost constant, in agreement with known etching models. In addition, the results give strong evidence for an amorphous surface layer that partially covers the porous structure. Tunneling spectroscopy of porous silicon and unetched silicon are also presented. The surface density of states (DOS) measurements of porous silicon are compared with its photoluminescence spectrum. The DOS measurements do not show a peak corresponding to the 1.8 eV photoluminescent peak energy nor do they show an increase in the band gap energy of porous silicon compared with crystalline silicon. However, these measurements do show that while the unetched silicon surface remains p type, the porous silicon surface behaves like an n-type material.
Visible photoluminescence from porous Si formed by annealing and chemically etching amorphous Si
Authors: Jung K. H. , Shih S. , Kwong D. L. , Cho C. C. , Gnade B. E.
Published: July 2002

We have studied the visible photoluminescence (PL) and microstructure of amorphous Si (a-Si) after annealing and etching. The a-Si layers were grown on (100)Si substrates and partially crystallized by annealing between 550–1150 °C. Porous Si layers (PSLs) were then produced by etching in HF-HNO3. While no visible PL was observed from unannealed and etched a-Si, visible PL was detected after annealing and etching. The observation of visible PL after etching coincided with the observation of Si microcrystallites in the annealed layer. The results suggest that an initial crystalline structure is important for fabricating luminescent PSLs.
A high-power electron beam source based on the superemissive cathode
Authors: Hsu T.-Y. , Gundersen M. A.
Published: July 2002

A robust, high current electron beam, produced by emission from a refractory metal cathode operating in the superemissive mode, is reported. Electron beam current of ≳150 A is produced by a back-lighted thyratron during the conductive phase. Electron energies are several hundred eV and the electron beam has the duration of the discharge pulse. A simple differential pumping scheme has been used to demonstrate extraction of the electron beam into a low pressure (<7 mTorr) region.
Optically induced absorption and paramagnetism in lead lanthanum zirconate titanate ceramics
Authors: Warren W. L. , Seager C. H. , Dimos D. , Friebele E. J.
Published: July 2002

Electron paramagnetic resonance (EPR) and photothermal deflection spectroscopy measurements have been performed to identify the nature of the centers responsible for the subgap absorption in both unilluminated and ultraviolet (UV) illuminated lead lanthanum zirconate titanate (PLZT) ceramics. In the PLZT ceramics we find that the absorption near 2.6 eV is correlated with the presence of Ti+3 centers. UV exposure of these ceramics leads to the generation of two charged paramagnetic defects, Pb+3 and Ti+3, as well as an increased subgap absorption. These observations demonstrate strong correlations between the UV-induced EPR and optical responses, suggesting that both are due to the same trapping centers.
Enhanced surface cation mobility on Sn delta-doped (Ga,Al)As
Authors: Petrich G. S. , Dabiran A. M. , Cohen P. I.
Published: July 2002

During the growth of GaAs and AlAs on vicinal GaAs(100) by molecular-beam epitaxy, reflection high energy electron diffraction was used to measure the transition temperature between two-dimensional nucleation and pure step propagation when submonolayer amounts of Sn were present on the surface. On samples misoriented by 0.5° to either the [011] or the [011̄] direction, the transition temperature decreased by approximately 100 °C after the deposition of 0.6 monolayers of Sn, indicating that the Ga mobility increased. The presence of Sn also increased the surface mobility of the Al adatoms on AlAs(100) surfaces as indicated by the annealing behavior of the AlAs surface at 600 °C.
Oxygen based electron cyclotron resonance etching of semiconducting homoepitaxial diamond films
Authors: Grot S. A. , Ditizio R. A. , Gildenblat G. Sh. , Badzian A. R. , Fonash S. J.
Published: July 2002

Oxygen-based electron cyclotron resonance (ECR) plasma etching of boron doped homoepitaxial diamond films with no de bias has been achieved. The process was developed to the point where it can provide a uniform and reproducible etching procedure that yields smooth damage-free etched surfaces. Etch rates attained under these conditions of smooth damage-free etched surfaced were about 86 Å/min.
High activation efficiency in Mg+ implanted GaAs by P+ coimplantation
Authors: Shen Honglie , Zhou Zuyao , Xu Honglai , Xia Guanqun , Zou Shichang
Published: July 2002

Coimplantation of 125 keV Mg+ ions and 160 keV P+ ions with the same dose of 5×1014 cm−2 was investigated. Samples were annealed in a conventional furnace or a halogen tungsten lamp rapid thermal annealing system. It was found that the additional implant of P+ improves the electrical quality of the Mg+ implanted GaAs more effectively than additional implant of As+. By using rapid thermal annealing, a maximum activation efficiency of 92% with a sheet resistance of 145 Ω/⧠ was obtained for Mg+ and P+ coimplantation after an anneal at 1050 °C for 5 s, while the maximum activation efficiency for Mg+ single implant was 36% corresponding to a sheet resistance of 358 Ω/⧠ after an anneal at 800 °C for 5 s. Coimplantation of P+ evidently can also reduce the redistribution of the implanted Mg.
Molecular beam epitaxial growth of superconducting Ba2DyCu3O6.5 thin films at 420 °C using NO2 as an oxidant
Authors: Norimoto Kei-ichiro , Sekine Rika , Mori Masami , Hanada Takashi , Kudo Masahiro , Kawai Maki
Published: July 2002

A superconducting Ba2DyCu3O6.5 (orthorhombic II phase) thin film is formed on a MgO(100) substrate at 420 °C by molecular beam epitaxial growth using NO2 as an oxidant. Metal elements Ba, Dy, and Cu are sequentially supplied from K cells onto MgO(100) at 420 °C under a flow of 5×10−5 Pa of NO2. The film gradually cooled in situ under the identical pressure of NO2 shows metallic behavior in the normal state and a Tczero of 50 K. The lattice constant of the c axis is observed at 11.75 Å, which is known as an orthorhombic II phase of bulk Ba2DyCu3O6.5. Due to the slow deposition rate, the film thus formed is oriented with the c axis perpendicular to the surface in spite of the low-temperature growth condition.
Reactive ion etching end-point determination by plasma impedance monitoring
Authors: Patel V. , Singh B. , Thomas J. H.
Published: July 2002

Impedance monitoring of a rf glow discharge is successfully used to determine the end point of reactive ion etching. The feasibility of using this technique is demonstrated on diode, triode, and magnetic multipole enhanced triode reactors applied to etching polycrystalline silicon on SiO2 on Si and Si3N4 on Si in an SF6 plasma, and to stripping photoresist on Al on Si in an O2 plasma. The end point of etching is determined by monitoring changes in the induced dc bias, the rf voltage, the rf current, or the phase relationship between them on either of the powered electrodes (in the cases of the triode configurations). This method is easily applicable as in in-process end-point detector and eliminates the need of optical access to either the plasma or the substrate.
Saturation of the defect density in hydrogenated amorphous silicon by pulsed light soaking
Authors: Hata Nobuhiro , Ganguly Gautam , Wagner Sigurd , Matsuda Akihisa
Published: July 2002

We report the first observation of saturation of the defect density and of the photoconductivity in hydrogenated amorphous silicon after light soaking with laser pulses. The saturated defect density reaches approximately the same value as the density established by soaking with continuous light. Comparison of pulsed with cw light-soaking experiments, via an effective light-soaking time, shows the use of pulsed light to be equivalent to that of continuous wave light, in defect saturation.
Normal incidence infrared absorption in AlAs/AlGaAs x-valley multiquantum wells
Authors: Katz Jennifer , Zhang Y. , Wang W. I.
Published: July 2002

We report the first observation of normal incidence infrared absorption due to interconduction subband transitions in AlAs/AlGaAs x-valley multiquantum wells. Infrared absorption measurements were performed on samples grown on [111], [113], [115], and [001] substrates with normal incidence radiation at wavelengths of 5–20 μm. Two absorption peaks were observed in the [113] and [115] multiquantum wells with well widths of 40 Å and sheet doping concentrations of 1012 cm−2. One peak, due to transitions between the ground state and the continuum band occurred at 7.1 μm; a second peak originating from interconduction subband transitions between the ground state and the first excited state occurred at 17 μm. The experimental results indicate the potential of these novel structures for use as normal incidence infrared photodetectors.
Amorphous diamondlike carbon-silicon heterojunction devices formed by ion implantation
Authors: Konofaos N. , Thomas C. B.
Published: July 2002

Amorphous carbon films grown onto silicon substrates and characterized as diamondlike have been ion implanted with boron and nitrogen to achieve p-type and n-type conductivity, respectively. Energies of 120 keV were used for the ion implantation. After isothermal heat treatment, the films revealed diode characteristics for both p-carbon/n-carbon and n-carbon/p-silicon structures. Current-voltage characteristics and capacitance-voltage curves show that the devices performed as heterojunctions between the carbon and the silicon. The difference between the currents for reverse and forward bias were as high as six orders of magnitude.
Tertiarybutyldimethylantimony: A new Sb source for low-temperature organometallic vapor phase epitaxial growth of InSb
Authors: Chen C. H. , Stringfellow G. B. , Gordon D. C. , Brown D. W. , Vaartstra B. A.
Published: July 2002

III-V semiconductors such as InAsSb, InSbBi, and InAsSbBi are useful materials for far-infrared applications. Their growth usually requires low temperatures. The standard Sb source, trimethylantimony (TMSb), decomposes very slowly at low temperatures. In this work, a new Sb source, tertiarybutyldimethylantimony (TBDMSb), is investigated for OMVPE growth of InSb. Good surface morphology InSb layers were obtained for growth temperatures from 450 to as low as 325 °C. The growth temperature can be lowered by more than 100 °C when TBDMSb replaces TMSb. The growth efficiency of InSb using trimethylindium (TMIn) and TBDMSb is on the order of 1×104 μm/mole. The high values of growth efficiency indicate that there is neglectible parasitic reaction between TMIn and TBDMSb. The results indicate that TBDMSb is an excellent replacement for TMSb and TIPSb in the growth of Sb-containing alloys.
Molecular-beam-epitaxial growth of n-AlGaAs on clean Cl2-gas etched GaAs surfaces and the formation of high mobility two-dimensional electron gas at the etch-regrown interfaces
Authors: Kadoya Y. , Noge H. , Kano H. , Sakaki H. , Ikoma N. , Nishiyama N.
Published: July 2002

By using an ultrahigh vacuum multichamber process system, very clean GaAs surface is successfully prepared by chlorine-gas etching and AlGaAs is subsequently grown by molecular beam epitaxy to show that two-dimensional electron gas is successfully formed at etch-regrown AlGaAs/GaAs interface. Mobility as high as 114 000 cm2/V s at 9.8 K is achieved for the carrier concentration NS=4.5×1011 cm−2. From the secondary-ion-mass-spectroscopy measurement, the carbon concentration at the interface is estimated to be 2×1010 cm−2, and is found to be a dominant scatterer for the two-dimensional electrons. A transmission-electron-microscope image has evidenced a very flat feature of etch-regrown interface.
Strong photoluminescence from AlP/GaP disordered superlattice grown by atmospheric pressure organometallic vapor phase epitaxy using tertiarybutylphosphine
Authors: Wang Xue-Lun , Wakahara Akihiro , Sasaki Akio
Published: July 2002

AlP/GaP disordered superlattices (d-SLs) are grown for the first time by atmospheric pressure organometallic vapor phase epitaxy using tertiarybutylphosphine as the phosphorous source. Strong photoluminescence (PL) is observed from the d-SL, comparing with the ordered superlattice (o-SL) and the bulk alloy (b-AL). The PL intensity of the d-SL is 158 times stronger than that of the o-SL and 114 times than that of the b-AL. The strong PL from the d-SL is attributed to the localized states created by the artificial disordering.