bluuebunny/crossref_metadata_2025 huggingface dataset:
Amplitude modulation mode locking of lasers by regenerative feedback
Authors: Turi L. , Krausz F.
Published: July 2002

We analyze the performance of regenerative feedback mode locking using intracavity amplitude modulation (AM). Regenerative feedback is predicted to improve the stability of AM mode locking especially at low and moderate repetition rates and short pulse durations. We report on AM regenerative-feedback mode locking of a continuous wave Nd:glass laser. The generated train of 8 ps pulses has an excellent long-term stability and is completely free of relaxation oscillation instabilities inherent in conventional AM mode locking.
Stable-mode operation of leaky-mode diode laser arrays at high pulsed and cw currents
Authors: Hohimer J. P. , Hadley G. R. , Craft D. C. , Shiau T. H. , Sun S. , Schaus C. F.
Published: July 2002

We report stable pulsed and cw fundamental mode operation for ten-stripe leaky-mode diode laser arrays which use the confinement factor effect for mode control. Lasing occurs in the fundamental mode for pulsed operation (≤1 μs) up to 10× threshold and for cw operation up to 3.4× threshold. For cw operation, a thermal decoupling of the outer array stripes broadens the far field slightly but does not affect the lasing mode order. Our two-dimensional model of these devices reproduces this decoupling of the outer array stripes when thermal effects are included.
Water protective surface layer on fluorozirconate glass produced by low-energy oxygen ion implantation
Authors: Dai Yisheng , Kawaguchi Toshiyasu , Suzuki Koichi , Suzuki Susumu , Yamamoto Kiyoshi , Masui Akio
Published: July 2002

Fluorozirconate glass with the composition of 53ZrF4-20BaF2-4LaF3-3AlF3-20NaF was implanted with 15 keV oxygen ions to the dose of 2×1017ions/cm2. The surface layer modified by the implantation exhibited excellent chemical durability against aqueous corrosion although it showed little influence on visible and infrared transmission of the glass. X-ray photoelectron spectroscopy measurement indicated that the zirconium on the implanted glass surface was oxidized and the fluorine was incorporated in an oxyfluoride structure. This chemically stable oxyfluoride layer prevented the glass from being corroded by water.
Analysis of cut-off frequency roll-off at high currents in SiGe double-heterojunction bipolar transistors
Authors: Gao Guang-bo , Fan Zhi-fang , Morkoç H.
Published: July 2002

Roll-off of the current gain cut-off frequency in NpN double-heterojunction bipolar transistors for large collector currents has been analyzed. The analysis includes such effects as the electron barrier formed at the collector base junction due to electron accumulation. Included in this investigation is also lateral electron diffusion before injection into the collector space-charge region at the base-collector heterointerface once the barrier is formed. The available data obtained in SiGe heterojunction bipolar transistors are in good agreement with this model.
Nanosecond scale optical pulse separations in double-exposure holographic interferometry for investigation of transient events
Authors: Ehrlich Michael J. , Wagner James W.
Published: July 2002

To investigate shock wave propagation in air, optical pulses with temporal separations ranging from 53 to 425 ns have been generated for use in double-exposure pulsed holography using a White cell [J. U. White, J. Opt. Soc. Am. 32, 285 (1942)] as an optical delay element. A single optical pulse from a Q-switched Nd:YAG laser was split using polarizing optics so that one pulse was guided directly to the experimental holographic recording setup; the other pulse was sent first into the White cell, emerging a set number of nanoseconds later. This delayed pulse then was used to record a second holographic exposure. Using the White cell construction, reproducible pulse separations between 53 and 425 ns could be generated. Shock wavefronts propagating at velocities greater than Mach 20 have been recorded using this method.
Role of bubbles in laser-assisted wet etching
Authors: Hussey B. W. , Haba B. , Gupta A.
Published: July 2002

Evidence is presented to explain laser-based aqueous salt etching in terms of vapor bubble growth conditions at the irradiated surface of a substrate. The effect of pulse and frequency modulation of a cw laser is investigated to determine growth behavior for adhering bubbles in pure water. The role of salt in solution (such as KOH, NaOH, or CaCl2) is discussed in terms of its function as a diffusion barrier for growing vapor bubbles. Etching data are presented for the case of a Cu-vapor laser applied to a Mn-Zn-ferrite substrate, comparing results with and without KOH in the etching solution.
Carbon doping in AlGaAs for AlGaAs/GaAs graded-base heterojunction bipolar transistor by flow-rate modulation epitaxy
Authors: Ito Hiroshi , Makimoto Toshiki
Published: July 2002

This letter investigates carbon doping in AlGaAs using flow-rate modulation epitaxy (FME). The tendency of hole concentration increasing with Al composition is explained by the thermal decomposition of trimethylaluminum molecules on the substrate surface. The highest hole concentration obtained is 3×1020 cm−3 in Al0.4Ga0.6As layers. An AlGaAs/GaAs heterojunction bipolar transistor with an FME-grown compositionally graded carbon-doped base layer was fabricated for the first time. It exhibits a current gain of 25 with 2×1019 cm−3 base doping.
Characteristics of Y-Ba-Cu-O superconductor films on GaAs with an Al2O3 or AlGaO3 buffer layer
Authors: Shewchun J. , Chen Yi , Hölder J. S. , Uher C.
Published: July 2002

By depositing a buffer layer of Al2O3 on GaAs, we have been able to laser ablate a superconducting film of Y1Ba2Cu3O7−x overtop. The onset of superconductivity is 92 K and zero resistance is observed at 80 K in a structure with a suitably annealed Al2O3 film which is converted to AlGaO3. Both the Al2O3-GaAs and the Al2O3-Y1Ba2Cu3O7−x interfaces are remarkably well preserved with virtually no interdiffusion or interaction. The Al2O3 or homolog AlGaO3 film also prevents decomposition of the GaAs at the deposition temperature of 730 °C.
Fast room-temperature growth of SiO2 films by molecular-layer dosing
Authors: Ehrlich D. J. , Melngailis J.
Published: July 2002

A molecular-layer dosing technique for room-temperature growth of α-SiO2 thin films has been developed. The process, based on the reaction of H2O and SiCl4 adsorbates, is catalyzed by the hydrated SiO2 growth surface and requires a specific surface phase of hydrogen-bonded water. Careful adjustment of the coverage of this last phase is used to moderate continuous or pulsed growth. Thicknesses can be controlled to molecular-layer precision; alternatively, fast conformal growth to rates exceeding 100 nm/min can be achieved by slight depression of the substrate temperature below room temperature. Potential applications are trench filling for integrated circuits and hermetic ultrathin layers, for multilayer photoresists. Excimer-laser-induced surface modification has been used to achieve projection-patterned selective-area growth on silicon. This last result relies on the conversion from hydrogen to hydroxyl termination of the initial growth surface.
Triisopropylantimony for organometallic vapor phase epitaxial growth of GaSb and InSb
Authors: Chen C. H. , Fang Z. M. , Stringfellow G. B. , Gedridge R. W.
Published: July 2002

In the past, trimethylantimony (TMSb) has been almost exclusively used as the Sb source in organometallic vapor phase epitaxy (OMVPE). However, TMSb decomposes at relatively high temperatures (above 500 °C). For growth at lower temperatures, TMSb is not an optimum choice. In addition, TMSb decomposition produces methyl radicals, a source for carbon contamination. Thus, it is important to investigate alternative Sb precursors. In this letter, we report the use of a newly developed Sb source, triisopropylantimony (TIPSb), for atmospheric pressure OMVPE. It is found that both GaSb and InSb can be grown with good surface morphologies at temperatures between 430 and 600 °C. The high growth efficiencies indicate that there are few parasitic reactions between TIPSb and trimethylgallium (TMGa) or trimethylindium (TMIn). The GaSb layers grown at 500 °C have background hole concentrations of 2×1016 cm−3. Low-temperature photoluminescence (PL) measurements indicate that the acceptor is due to Sb vacancies rather than carbon acceptors. The InSb epilayers have electron concentrations of about 5×1016 cm−3 at 77 K and low-temperature PL shows well-resolved exciton and acceptor-related peaks. These results indicate that TIPSb is a viable source for the OMVPE growth of Sb-containing III-V semiconductors.
Calculation of direct interband absorption in HgTe by a second-order k⋅p method
Authors: Man P. , Pan D. S.
Published: July 2002

An 8×8 second-order k⋅p approach is employed to treat direct interband absorption in HgTe. A detailed first-principle calculation of the absorption coefficient is performed with no adjustable parameter. Good agreement is found with experimental data up to at least ℏω≊500 meV which corresponds to k≊0.08(2π/a0). Even in the case of HgTe with a Γ6-Γ8 energy gap as narrow as −120 meV at T=300 K, our full second-order calculation still improves over the first-order k⋅p approach by about 17% around λ=10 μm (ℏω=124 meV) and more at shorter wavelengths. Substantial enhancement is expected for a wider energy-gap (‖Eg‖ ≳ 1 eV) zinc-blende bulk material. Comparable accuracy of k⋅p calculations for III-V and II-VI unstrained superlattices can also be projected under the envelope-function approximation.
Effect of melt-growth processing methods on Si-Ge-GaP homogeneity
Authors: Kilmer R. J. , Jesser W. A. , Rosi F. D.
Published: July 2002

Three processing methods were employed to homogenize a Si0.80Ge0.20 alloy hot pressed with additions of approximately 2 a/o GaP. The melt-growth methods investigated include single-pass zero melting, zone leveling, and splat cooling. Energy dispersive spectroscopy was performed in conjunction with scanning electron microscopy and transmission electron microscopy along with x-ray diffractometer analysis to characterize the resultant ingots. The single-pass zone-melted ingot exhibited a higher GaP content than the zone-leveled ingot probably as a consequence of a higher growth temperature during zone melting. Both ingots had large regions of uniform average composition whereas the splat cooled alloy exhibited a marked inhomogeneity.
Deposition of composition-controlled silicon oxynitride films by dual ion beam sputtering
Authors: Ray S. K. , Das S. , Maiti C. K. , Lahiri S. K. , Chakrabarti N. B.
Published: July 2002

Silicon oxynitride films of controlled composition have been deposited on silicon by dual ion beam sputtering (DIBS) making simultaneous use of an energetic argon ion beam to sputter silicon nitride from a target and a low-energy oxygen ion beam to react with the sputtered film on the substrate. The correspondence between film properties and oxygen beam parameters has been studied from measurements of refractive index, chemical etch rate, infrared absorption, and x-ray photoelectron spectroscopy spectra. In situ ion beam oxidation of silicon prior to oxynitride deposition results in a film with a low insulator charge density (3.5×1011 cm−2) and interface trap density (4×1011 cm−2 eV−1).
Defect reduction in GexSi1−x epitaxy by rapid thermal processing chemical vapor deposition using a low-temperature in situ preclean and a Si buffer layer
Authors: Jung K. H. , Hsieh T. Y. , Kwong D. L.
Published: July 2002

For chamber base pressure ≊5×10−4 mbar in a rapid thermal processing chemical vapor deposition system, a 900 °C H2 prebake for 60 s results in relatively high defect densities in the GexSi1−x epitaxial layer due to surface damage caused by the H2 prebake. We have demonstrated that a very low thermal budget in situ preclean (800 °C/15 s) can reduce the defect densities. In addition, the use of a Si buffer layer grown at 1000 °C for 60 s prior to the GexSi1−x growth is capable of significantly reducing defect densities.
Noise suppression by a novel probe beam polarization modulation in electro-optic sampling
Authors: Takahashi Ryo , Kamiya Takeshi
Published: July 2002

A new scheme of noise suppression in electro-optic sampling system by the probe beam polarization modulation is proposed, its operation principle is analyzed, and the performance is demonstrated experimentally. The method has the advantages that narrow-band detection can be used instead of modulating the device under test with doubled sensitivity compared with conventional methods.
Influence of crystal imperfection on high-resolution diffraction profiles of silicon single crystals measured by highly collimated x-ray beams
Authors: Kawado S. , Kojima S. , Maekawa I. , Ishikawa T.
Published: July 2002

We examined high-resolution diffraction profiles of as-grown and annealed magnetic-field-applied Czochralski (MCZ) silicon crystals which were about 300 μm thick and [001] oriented, and compared these profiles with the ultraplane wave x-ray topographs. Rocking curves for the symmetric 220 diffraction were measured in the Laue geometry using a (+m, −n, +n) separated three-crystal monochromator. Strain introduced in the sample preparation process gave a reduced oscillatory profile of a rocking curve although chemical etching recovered subsidiary peaks of the rocking curve. Strain frozen in as-grown crystals also gave a reduced oscillatory-profile, but a large number of oxygen precipitates produced by thermal annealing caused little reduction of subsidiary peaks.
New application for isothermal capacitance transient spectroscopy: Identification of tunneling in semiconductor-insulator interfaces
Authors: Paloura E. C. , Lagowski J. , Gatos H. C.
Published: July 2002

The GaAs-insulator interface is characterized by deep level transient spectroscopy (DLTS) and isothermal capacitance transient spectroscopy (ICTS). It is demonstrated that while DLTS can only detect transients with temperature-dependent emission rates, ICTS can detect temperature-independent phenomena as well. The GaAs-insulator interface is characterized by two electron traps, with activation energies 0.67 and 0.23 eV, respectively, and a tunneling component that is detected only by ICTS. This tunneling component, which dominates the ICTS spectrum at 80 K<T< 180 K and is characterized by a field-induced barrier reduction given by ΔEE=1.4×10−3q√E, is attributed to pure tunneling.
Heteroepitaxy of I-VII materials on III-V substrates
Authors: Tarnow Eugen , Zhang S. B.
Published: July 2002

We predict, on the basis of ab initio total energy calculations, that epitaxial growth of I-VII compounds on III-V substrates can be accomplished. We suggest specific combinations of I-VII materials and III-V substrates that minimize lattice mismatch and structural energy cost and show that the interface dipole can be minimal. This makes zinc-blende I-VII materials potential candidates for passivating layers, solid-state laser applications, III-V window material, and hole traps.
Valence-band-edge shift due to doping in p+ GaAs
Authors: Silberman J. A. , de Lyon T. J. , Woodall J. M.
Published: July 2002

Accurate knowledge of the shifts in valence- and conduction-band edges due to heavy doping effects is crucial in modeling GaAs device structures that utilize heavily doped layers. X-ray photoemission spectroscopy was used to deduce the shift in the valence-band-edge induced by carbon (p type) doping to a carrier density of 1×1020 cm−3 based on a determination of the bulk binding energy of the Ga and As core levels in this material. Analysis of the data indicates that the shift of the valence-band maximum into the gap and the penetration of the Fermi level into the valence bands exactly compensate at this degenerate carrier concentration, to give ΔEv =0.12±0.05 eV.
Observation of two in-plane epitaxial states in YBa2Cu3O7−δ films on yttria-stabilized ZrO2
Authors: Garrison S. M. , Newman N. , Cole B. F. , Char K. , Barton R. W.
Published: July 2002

We demonstrate that two distinctly different in-plane epitaxial states of c-axis oriented YBa2Cu3O7−δ (YBCO) films on (100) yttria-stabilized ZrO2 (YSZ) single-crystal substrates can be produced independently, namely, YBCO [100]//YSZ [100] or YBCO [100]//YSZ [110]. Both in-plane epitaxial relationships can be modeled by matching YBCO and YSZ oxygen sublattices at the film-substrate interface. High critical current densities (Jc), ∼5×105–1×106 A/cm2 at 77 K, are achieved when ≳90 vol % of either orientation is present. Jc can be degraded nearly four orders of magnitude in films with mixed orientation.
Index-guided operation in narrow stripe InGaAs-GaAs strained-layer quantum well heterostructure lasers by MeV oxygen implantation
Authors: Alwan J. J. , Honig J. , Favaro M. E. , Beernink K. J. , Klatt J. L. , Averback R. S. , Coleman J. J. , Bryan R. P.
Published: July 2002

Stable index-guided operation of variable stripe strained-layer InGaAs-GaAs-AlGaAs lasers achieved by MeV oxygen implantation-induced disorder of the active region is demonstrated. Well-behaved near- and far-field patterns for lasers implanted with 5×1016 cm−2 and 1×1017 cm−2 oxygen are observed to be stable with increasing drive current. Comparison with unimplanted, oxide-defined stripe lasers fabricated from the same wafer indicates a dramatic improvement in emission characteristics as a result of the presence of a lateral real-index waveguide in the oxygen-disordered regions which is stronger than the carrier-induced antiguide present in unimplanted InGaAs-GaAs strained-layer lasers.
Wavelength switching in narrow oxide stripe InGaAs-GaAs-AlGaAs strained-layer quantum well heterostructure lasers
Authors: Beernink K. J. , Alwan J. J. , Coleman J. J.
Published: July 2002

We have observed current-controlled wavelength switching in narrow oxide stripe In0.17Ga0.83As-GaAs-Al0.20Ga0.80As strained-layer single quantum well heterostructure lasers. Laser emission switches from the lowest (n=1) quantized state transition in the quantum well at low currents to the first excited state transition (n=2) at higher currents, with an energy difference of ≊50 meV. For currents near the switching point, we have also observed time-dependent lasing behavior, with a switch in the laser emission from the n=1 to the n=2 transition. The order of this temporal switching (from n=1 to n=2) is opposite that observed in narrow stripe gain-guided GaAs-AlGaAs quantum well lasers, due to strong antiguiding in InGaAs lasers, which negates the effect of a thermal guide.
Conductivity-type inversion following low-energy hydrogen implantation
Authors: Zhou Tian-Qun , Radzimski Zbigniew , Patnaik Bijoy , Rozgonyi George A. , Sopori Bhushan
Published: July 2002

A surface conductivity-type inversion has been observed following low-energy (400 eV), high-dose, hydrogen implantation of p-type silicon. Detailed structural, chemical, and electrical examination of the surface revealed that the inversion resulted from hydrogen forming n-type complexes with extended defects.
Fabrication of thin-film superconductors by bulk processing
Authors: Tiefel T. H. , Jin S. , Kammlott G. W. , Graebner J. E. , van Dover R. B. , Spencer N. D.
Published: July 2002

A simple processing technique for preparation of c-axis-oriented Bi-Pb-Sr-Ca-Cu-O thin films is reported. ∼3000-Å-thick superconductor films on silver substrate have been obtained by heavy cold rolling and partial melt processing of the superconductor-silver composite structure. The films are highly textured due to the interface-induced, layer-like growth of the superconducting phase, and are essentially free of weak links. They exhibited Tc∼80 K and Jc (4.2 K) ∼104–105 A/cm2. This technique, which does not require epitaxial growth from single-crystal substrates, may be suitable for high-speed, low-cost production of large-area thin films, and points to other novel thin-film processing possibilities.
Electronic structure of Sb substituted in BaBiO3
Authors: Eibschütz M. , Cava R. J. , Krajewski J. J. , Peck W. F. , Reiff W. M.
Published: July 2002

The Mössbauer effect of the 37.2 keV γ transition of 121Sb has been employed to study the electronic configuration of Sb ions in BaBi1−xSbxO3 with x=0.2, 0.4, and 0.5. A single resonance absorption line is observed. The isomer shift changes slightly with Sb content and falls in the region corresponding to an Sb(V) valence state. The isomer shift of 7.6 mm/s is significantly depressed (∼1 mm/s) relative to its value in a typical Sb(V)O6 chromophore and indicates a high degree of covalency, corresponding to significant 5sm5pn hybridization.
Enhanced photoemission from a bi-metallic LaB6/Au photocathode structure
Authors: Scott C. J. , Tang X. , Spencer M. G.
Published: July 2002

A bilayer LaB6/Au, laser driven, photoelectron source for high-speed pulsed electron applications has been investigated. Preliminary results show the cathode operating at a quantum efficiency of 1.4×10−5 when illuminated with a mode-locked, frequency quadrupled Nd:YAG, 266 nm laser source. The measured current output at a pressure of 1×10−5 Torr was found to be three times larger than a single-layer gold photocathode structure.   
Prediction of optical losses in SiO2- and GeO2-based glass hollow waveguides for the infrared
Authors: Nagano Nobuhiro , Saito Mitsunori , Miyagi Mitsunobu , Baba Nobuyoshi , Sawanobori Naruhito
Published: July 2002

Complex refractive indices of a series of SiO2- and GeO2-based glasses were measured to evaluate optical losses of hollow waveguides made of these glasses. Measured optical constants follow the well known dispersion formula and vary with the percentage of Si or Ge atoms to the whole cations. By using empirically defined relations between oscillation peaks and compositions, we can predict refractive indices and waveguide losses theoretically for the unknown SiO2- or GeO2-based glasses.
Reversible Eu2+↔Eu3+ transitions at Eu-Si interfaces
Authors: Henle W. A. , Ramsey M. G. , Netzer F. P. , Horn K.
Published: July 2002

Valence switching at Eu-Si interfaces is demonstrated by resonant photoemission during repeated oxidation-reduction cycles performed by room-temperature O2 exposure and mild heating. The Eu2+↔Eu3+ transitions are accompanied by Fermi level switching associated with changes in the stoichiometry of the surface heterostructure. The ability to cycle between two well-defined magnetic states at a surface may be attractive in technological applications.
Structure, properties, and thermal stability of in situ phosphorus-doped hydrogenated microcrystalline silicon prepared by plasma-enhanced chemical vapor deposition
Authors: Jeng S. J. , Kotecki D. E. , Kanicki J. , Parks C. C. , Tien J.
Published: July 2002

The correlations between structural, chemical, electrical, optical properties of in situ phosphorus-doped hydrogenated microcrystalline silicon prepared by plasma-enhanced chemical vapor deposition have been studied by high-resolution transmission electron microscopy, secondary-ion mass spectrometry, electrical conductivity, and optical measurements. Microcrystallinity has been observed at a substrate temperature as low as 100 °C with a 1% dilution of (1% PH3/SiH4) in H2. In situ phosphorous-doped hydrogenated microcrystalline silicon is best grown at 200–300 °C in terms of microstructure, H and P content, and dopant activation. The effects of thermal processing and the use of silicon nitride cap deposited prior to anneal on the structure and properties of phosphorous-doped hydrogenated microcrystalline silicon are also reported. The use of a silicon nitride capping layer is shown to inhibit recrystallization of hydrogenated microcrystalline silicon during rapid thermal anneal.
Use of methane in an electron cyclotron resonance plasma source for carbon delta-doping in GaAs molecular beam epitaxy
Authors: Mui D. S. L. , Evans K. R. , Fang S. F. , Biswas D. , Morkoç H.
Published: July 2002

An electron cyclotron resonance (ECR) plasma source has been used with methane gas to perform carbon delta-doping in GaAs grown by molecular beam epitaxy (MBE). The ECR plasma source is installed on a chemical vapor deposition chamber which is vacuum connected to a conventional MBE apparatus. Good surface morphologies, high sheet carrier densities (1–7×1012 cm−2), and reasonable hole mobilities (75–110 cm2/V s) are obtained.
Polarization-switchable microchip lasers
Authors: Zayhowski J. J.
Published: July 2002

Using a novel technique, we are able to controllably switch the polarization of microchip lasers in under 5 μs. The technique is applicable to a broad variety of lasers and theoretical modeling indicates that switching rates of several megahertz are possible.
Long switching delay mechanisms for optically triggered GaAs thyristors
Authors: Carson R. F. , Hughes R. C. , Weaver H. T. , Keshavarez A. A.
Published: July 2002

Long switching delays following optical triggering of GaAs thyristors are shown to result from near cancellation of carrier lifetime and current regeneration effects. Numerical simulations and analytical models account for the long delays, which are measured to be more than an order of magnitude larger than any lifetime or transit time in the device. Since the thyristor is in a low current state during the delay, this switching phenomena represents a form of dynamic information storage.
Intensity and temperature dependence of photodegradation of amorphous silicon solar cells under intense illumination
Authors: Yang L. , Chen L. , Catalano A.
Published: July 2002

The kinetics of the light-induced degradation of amorphous hydrogenated silicon (a-Si:H) based single junction solar cells was studied using an accelerated test with light intensity as high as 140 times that of the sun. A simple scaling law between the light intensity (I) and the exposure time (t), i.e., I1.8t=const, was found for the solar cell degradation. No apparent saturation was observed at 50 °C after an equivalent one sun exposure time of over 25 000 h. Saturation, however, did occur at higher temperatures and the level of saturation was found to depend on both temperature and light intensity. These results suggest that the long-term stability of a-Si:H solar cells is governed by the competition between light-induced degradation and thermal annealing, instead of the total number of possible sites for defect generation.
p-type doping of germanium grown by molecular beam epitaxy on Ge(100) substrates
Authors: Kesan V. P. , Iyer S. S. , Cotte J. M.
Published: July 2002

We have conducted studies of p-type doping using gallium and boron of germanium grown on germanium (100) substrates by molecular-beam epitaxy. Excellent germanium films have been grown on Ge substrates with little demarcation of the substrate-epi interface. Gallium doping of germanium takes place through an adlayer at the growth front, and between growth temperatures of 450 °C and 550 °C successful p doping of germanium by gallium with good activation has been accomplished. A first-order kinetic incorporation model has been used to describe the behavior of gallium in germanium as a function of surface coverage and growth temperature. Boron is an excellent p dopant in germanium with good activation at high concentrations and sharp transition profiles.
Magnetic ordering in TbxFe1−x amorphous films: An application of x-ray dichroism with linearly polarized light
Authors: Sacchi Maurizio , Kappert Ronald J. H. , Fuggle John C. , Marinero Ernesto E.
Published: July 2002

Magnetic x-ray dichroism (MXD) in the 3d→4f  absorption transitions of rare-earth ions is a new tool for the investigation of local magnetic properties. We have measured MXD in amorphous Tb-Fe magnetic thin films, showing its potentials and advantages with respect to other techniques, especially when surface magnetic properties are investigated.
Body current scanning: A novel technique for characterizing the floating body effects and parasitic bipolar action in silicon-on-insulator metal-oxide-semiconductor transistors
Authors: Liu Patrick S. , Li G. P.
Published: July 2002

Body current scanning (BCS) is a new concept that exploits body (substrate) current reversal in NPN bipolar transistors to characterize the floating body effects and parasitic bipolar action in n-channel silicon-on-insulator (SOI) metal-oxide-semiconductor (MOS) transistors. At sufficiently high drain biases, a parasitic bipolar transistor modeled in parallel with the SOI MOS transistor is activated by hole accumulation in the body. BCS directly measures the floating body potential corresponding to the parasitic bipolar base, and is capable of distinguishing between the respective current contributions from MOS and bipolar devices. Consequently, the evaluation of parasitic bipolar and the influence of floating body on SOI device characteristics are facilitated.
Surface-relaxation-controlled mechanism for occurrence of long range ordering in III-V semiconductor alloys grown by molecular beam epitaxy
Authors: Ogale S. B. , Madhukar A.
Published: July 2002

Influence of surface-atomic relaxations on adsorption processes and the dependence of the relaxations themselves on the chemical constitution of the already grown layers are shown to be the key factors in the occurrence of long range ordering in III-V semiconductor alloys grown by molecular beam epitaxy. The findings are based on the use of semiempirical potentials for energy minimization and involve surface-atomistic processes over a range of five monolayers.
Effects of substrate misorientation on anisotropic electron transport in InGaAs/GaAs heterostructures
Authors: Sun Q. , Lacelle C. , Morris D. , Buchanan M. , Marshall P. , Chow-Chong P. , Roth A. P.
Published: July 2002

The effects of substrate misorientation on anisotropic electrical properties of thick InGaAs layers grown on GaAs by low-pressure metalorganic vapor phase epitaxy are studied. Hall bar samples oriented along [110] and [1̄10] were cut from layers grown simultaneously on substrates oriented (a) exactly on (001) and (b) at 2° off (001) towards [011]. In layers grown on (001) oriented substrates a very large mobility anisotropy (μ[110]/μ[1̄10]≊ 1000) is observed and attributed mainly to a lattice mismatch induced anisotropy. For the misoriented substrates, the average electron mobility increases by an order of magnitude and shows only a small residual anisotropy in the opposite direction (μ[110]/μ[1̄10] ≊ 0.7).
Preparation of Tl2Ba2CaCu2O8 superconducting thin films on LaAlO3 substrates from metalorganic-chemical-vapor-deposition-prepared precursor films
Authors: Ladd J. A. , Collins B. T. , Matey J. R. , Zhao J. , Norris P.
Published: July 2002

Single phase Tl2Ba2CaCu2O8 thin films have been deposited on single-crystal LaAlO3 substrates, (100) orientation, via a two-step deposition process. First, Ba-Ca-Cu-O precursor films were deposited by metalorganic chemical vapor deposition (MOCVD) using barium, calcium, and copper-tetramethyl-heptanedionate, (tmhd)2, source materials under reduced pressure in an oxygen/argon atmosphere. Substrate temperatures were between 500 and 600 °C. Thallium was then incorporated by heating the films in a confined surface configuration with an unfired pellet of Tl2Ba2CaCu2Ox composition at 870 °C for 0.1 h. The resultant films (0.5–1 μm thick) showed a preferred orientation with the c axis normal to the substrate. The superconducting properties were characterized by resistance and mutual inductance versus temperature and by critical current measurements. Zero resistance temperatures as high as 98 K and Jc values close to 1×104 A/cm2 at 77 K were observed.
Étalon enhancement of nonlinear optical response in Bi1−xSbx
Authors: Youngdale E. R. , Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Partin D. L. , Thrush C. M. , Heremans J. P.
Published: July 2002

Measurements of the nondegenerate four-wave mixing of CO2 laser beams in a Bi1−xSbx film have yielded the largest high-power third-order nonlinear susceptibilities ever reported at that wavelength (χ(3)≳6×10−4 esu at P0≳2×105 W/cm2). Furthermore, an étalon effect resulting from the high reflectivity of the Bi1−xSbx films at both the air and substrate interfaces leads to an additional enhancement of the four-wave signal by as much as a factor of 30. A theoretical model based on optical modulation of the free-carrier susceptibility gives results which are in excellent agreement with the data.
Noncontacting alternating current surface probe measurements of transport critical currents in a slab geometry
Authors: Telschow K. L. , O’Brien T. K.
Published: July 2002

Determination of the critical state full penetration field of a slab of YBa2Cu3O7−x by induced screening currents is described. This geometry allows spatial measurements to be made by scanning with the probe coil even though nonuniform demagnetization effects are present. The onset of transport current dissipation was observed by the reduction of diamagnetism and appearance of dissipation in the probe coil induced current. The results are compared to contact four-point probe direct current measurements and to the critical state model.
Experimental studies of proton-exchanged lithium niobate waveguides using cinnamic acid
Authors: Pun E. Y. B. , Loi K. K. , Zhao S. A. , Chung P. S.
Published: July 2002

Proton-exchanged planar waveguides in z-cut LiNbO3 have been fabricated and characterized optically using cinnamic acid as the new proton source. Single-mode waveguides before and after annealing exhibit propagation losses of 0.81 and 0.33 dB/cm, respectively, measured at 0.633 μm wavelength. The diffusion rate is slower than that of the popular benzoic acid. Post-annealing changes the refractive index profile from a truncated-parabolic function to a step function and then a Gaussian-like profile. The effect of annealing on the surface index change and the waveguide depth increase could be accurately modeled by a power-law relationship.
Influence of the negative-U OAs defect in GaAs on the isolation behavior of oxygen-implanted AlGaAs/GaAs heterostructures
Authors: Schnell R. D. , Gisdakis S. , Alt H. Ch.
Published: July 2002

The isolation behavior of oxygen implants in AlGaAs/GaAs modulation-doped heterostructures has been studied in comparison to boron implants. After annealing between 400 and 550 °C a thermally activated compensation mechanism in addition to damage-induced deep levels is observed in the case of oxygen. Infrared absorption spectroscopy shows local vibrational modes of off-center substitutional oxygen in GaAs at wave numbers of 721 and 734 cm−1 in the implanted surface region after annealing. The substitutional oxygen acts as a deep electron trap and causes a chemical-induced compensation.
Comparison of the effects of surface passivation and base quasi-electric fields on the current gain of AlGaAs/GaAs heterojunction bipolar transistors grown on GaAs and Si substrates
Authors: Liu William , Costa Damian , Harris James
Published: July 2002

The effects of extrinsic base surface passivation and base quasi-electric field on the current gain of AlGaAs/GaAs heterojunction bipolar transistors (HBTs) grown upon GaAs and Si substrates are compared. The degree of improvement in the current gain realized by either the base field and/or passivation depends strongly on which substrate is used. It is also shown that base-emitter junction space-charge recombination current is a significant base current component for all devices, even at high current levels. The current gain for passivated devices with a base field of 1.25×104 V/cm achieves a maximum value of 1100 for a HBT-on-GaAs, and 100 for a HBT-on-Si.
Defect activated infrared multiphonon excitation in iron-doped semi-insulating indium phosphide
Authors: Peng Lung-Han , Broekaert Tom , Choi Woo-Young , Fonstad Clifton , Jones Victor
Published: July 2002

Multiphonon excitation induced by long-range order crystal-field and short-range order Jahn–Teller distortion effects is observed in Fe-doped semi-insulating InP in the spectral range from 400 to 1100 cm−1 for infrared light propagating in a slab waveguide geometry. Transmission measurement data are analyzed in terms of phonon energies at critical points in the Brillouin zone. The phonon energies obtained are in excellent agreement with recently reported second order Raman scattering spectra and two-phonon absorption measurements of crystalline InP. The energy differences between the nearly degenerate two phonon transverse optical+longitudinal optical transitions at the Γ, X, and L points are also resolved and shown to be 10 cm−1. No localized mode or vibronic level absorption is observed, consistent with the relatively low concentration of Fe impurities in the samples.
Formation of rotation-induced superlattices and their observation by tunneling spectroscopy
Authors: Seabaugh A. C. , Kao Y.-C. , Liu H.-Y. , Luscombe J. H. , Tsai H.-L. , Reed M. A. , Frensley W. R.
Published: July 2002

We show that superlattices can be formed in the ternary and quaternary In(GaAl)As alloys on InP by molecular beam epitaxy without mechanical shuttering. Periodic ordering is produced by rotation of the substrate through the naturally nonuniform distribution of beam fluxes at the rotating substrate. The growth rate and substrate rotation rate together determine the superlattice period which is measured by transmission electron microscopy and x-ray diffraction. Tunneling density-of-states measurements on resonant tunneling diodes, interpreted by a one-dimensional theoretical calculation of the miniband-structure, reveal the electrical properties of the superlattice.
Theoretical gain in compressive and tensile strained InGaAs/InGaAsP quantum wells
Authors: Corzine S. W. , Coldren L. A.
Published: July 2002

In this letter, we report theoretical predictions of gain in strained 40 Å InGaAs/InGaAsP quantum wells, using a finite barrier valence band mixing analysis to determine the complicated valence subband structure under compressive strain, no strain, and tensile strain. We first illustrate the dramatic effects that strain can have on the valence subband structure. We then show that these changes lead to dramatic alterations in the optical gain of the quantum well as a function of carrier density. Example gain curves are given for three different indium mole fractions. Finally, to observe the effects of strain in a more continuous fashion, we plot theoretical transparency values for carrier density and differential gain as a function of indium mole fraction in the well.
Interface resistance and reduction of I
cR product in YBa2Cu3O7-Ag-Pb proximity junctions
Authors: Lee Mark , Beasley M. R.
Published: July 2002

Studies of the proximity coupling of YBa2Cu3O7 through Ag to a Bardeen–Cooper–Schrieffer (BCS) superconductor have shown that the IcR product is systematically much smaller than the BCS limit of ∼5 mV. These IcR values range from 10 to 100 μV in the YBa2Cu3O7 a direction to apparently zero in the c direction. The reduced IcR in the a direction can be understood as arising from a large boundary resistance, consistent with the mismatch of carrier densities across the YBa2Cu3O7-Ag interface. The same analysis gives an IcR in the c-oriented junctions that is at least three orders of magnitude larger than observed.
Growth behavior of YBa2Cu3O7−δ and NdBa2Cu3O7−δ thin films observed by electron diffraction
Authors: Shimizu Takashi , Nonaka Hidehiko , Arai Kazuo
Published: July 2002

Growth behavior of thin films of YBa2Cu3O7−δ and NdBa2Cu3O7−δ has been observed in reflection high-energy electron diffraction (RHEED) during coevaporation of constituent metal atoms with a NO2 supersonic molecular beam. The intensity oscillations of RHEED specular beam have been observed during deposition. The nucleation behavior of NdBa2Cu3O7−δ is found to be different from that of YBa2Cu3O7−δ in RHEED observation.
Self-quasi-phase-matched second-harmonic generation in the proton-exchanged LiNbO3 optical waveguide with periodically domain-inverted regions
Authors: Shinozaki K. , Fukunaga T. , Watanabe K. , Kamijoh T.
Published: July 2002

A self-quasi-phase matching technique for second-harmonic generation (SHG) that uses a proton-exchanged LiNbO3 optical waveguide with periodically domain-inverted regions is proposed and demonstrated. The fundamental wave satisfying quasi-phase-matching (QPM) condition was generated by an InP/InGaAsP laser diode (LD) with antireflection coated facets which was optically connected to the LiNbO3 waveguide. As the domain-inverted regions in the optical waveguide act as the distributed Bragg reflector (DBR), the LD is lased by the feedback waves from the DBR. We designed the period of domain-inverted regions to satisfy the QPM conditions and the high-reflectance conditions of the fundamental wave. We confirmed that the LD was lased at the wavelength satisfying the QPM conditions and SHG was observed simultaneously.
Secondary electrons generated by fast neutral bombardment of the growing film during laser ablation deposition
Authors: Brongersma S. H. , Kools J. C. S. , Baller T. S. , Beijerinck H. C. W. , Dieleman J.
Published: July 2002

Using an ion-probe method, time-of-flight measurements have been performed on the particles produced during excimer ablation of TiN. It is found that the number of ions produced in these ablation processes is quite small. The positive current due to secondary electrons departing from the detector and generated by fast neutral bombardment of the growing film vastly exceeds the current of positive ions arriving at the detector. This renders the ion-probe method unsuited for the determination of ion concentrations and ion velocity distributions.
High temperature superconductivity in air quenched YBa2Cu3O7−δ doped with Sb2O3
Authors: Paulose K. V. , Koshy J. , Uma Devi P. , Damodaran A. D.
Published: July 2002

The superconducting properties of YBa2Cu3O7−δ compounds doped with Sb2O3 have been studied by x-ray diffraction and electrical and magnetic measurements. It is found that the widely accepted procedure of slow cooling or annealing at 600 °C for several hours for oxygenation is not essential to obtain superconductivity in these doped samples. Superconducting transition (92 K) was obtained by directly quenching the doped specimen from the sintering temperature of 950 °C. Tetragonal to orthorhombic transformation has taken place within this short period, indicating that the rate of oxygen absorption has been increased tremendously by Sb2O3 addition in the YBa2Cu3O7−δ compound. Undoped samples quenched in air were always tetragonal and nonsuperconducting.
High-field magneto-optical study of type-II GaAs/AlAs short-period superlattices
Authors: Sasaki Satoshi , Miura Noboru , Horikoshi Yoshiji
Published: July 2002

Magnetoabsorption and magnetophotoluminescence spectra of type-II (GaAs)m/(AlAs)n superlattices with (m,n)=(3,5) and (5,6) have been measured in pulsed high magnetic fields up to about 40 T. Large dependence of the diamagnetic shift of the excitons on the field direction was observed in magneto-photoluminescence spectra, strongly suggesting XZ character of the conduction band minima for these values of m and n. Oscillatory structures related to the higher lying Γ-like conduction band are also resolved.
Photoacoustic detection of nonlinear absorption in NaCl and MgF2
Authors: Petrocelli G. , Scudieri F. , Martellucci S.
Published: July 2002

Nonlinear absorption induced by an excimer XeCl-pumped dye laser in NaCl and MgF2 has been measured by photoacoustic detection. Four-photon absorption is the dominant mechanism of energy absorption in the spectral region of 540–560 nm in NaCl. No evidence of the impact ionization process and electron avalanche formation is found.
Crystal-field splittings of Er3+(4f11) in molecular beam epitaxially grown ErAs/GaAs
Authors: Schneider J. , Müller H. D. , Ralston J. D. , Fuchs F. , Dörnen A. , Thonke K.
Published: July 2002

A detailed infrared-spectroscopic study is presented of the intra 4f-shell transitions 4I15/2→4I13/2 of Er3+(4f11), at λ=1.54 μm, in single-crystal ErAs films deposited on GaAs substrates by molecular beam epitaxy. Using Fourier-transform infrared absorption spectroscopy crystal-field splittings of both the 4I15/2 ground state and the first electronically excited state 4I13/2 are observed. Good agreement is found between the measured transition energies and those calculated for 4f11 ions in a crystal field of cubic (Oh) symmetry, as expected for the Er lattice site in unstrained ErAs. From the infrared absorption data, the relevant cubic fourth and sixth-order crystal field parameters are determined spectroscopically for the first time.
Meyer–Neldel rule in the space-charge-limited conduction of hydrogenated amorphous silicon
Authors: Oversluizen G. , Nieuwesteeg K. J. B. M. , Boogaard J.
Published: July 2002

The conductivity of a hydrogenated amorphous silicon n+-intrinsic-n+ (n-i-n) structure is reported as a function of temperature. The space-charge-limited conductivity σ is shown to follow the Meyer–Neldel rule (MNR) [W. Meyer and H. Neldel, Z. Tech. Phys. 18, 588 (1937)]: σ =σ00 exp(Ea/kT0) exp(−Ea/kT), where Ea is the conductivity activation energy, k is Boltzmann’s constant, and T is the absolute temperature. The characteristic MNR parameters found are σ00=10−2.4±0.1(Ω cm)−1 and T0=590±10 K. These values are practically equal to those previously found for the MNR in the ohmic conductivity in a series of hydrogenated amorphous silicon n-i-n structures with varying i-layer thicknesses. It is argued that the MNR can be quantitatively explained by the statistical shift of the Fermi energy and that a single set of parameters corresponding to σ00 =10−3±1(Ω  cm)−1 and T0=550±100 K is applicable for both the space-charge limited and the ohmic conductivity of i-type hydrogenated amorphous silicon. The MNR parameters are rather insensitive to density of states details.
dc SQUID made of Ag-doped YBa2Cu3O7 a-b plane-edge junctions
Authors: Koren G. , Cohen D. , Polturak E. , Aharoni E.
Published: July 2002

Preparation and characterization of dc SQUIDs based on YBa2Cu3O7/Ag/YBa2Cu3O7 edge junctions is reported. The SQUIDs were prepared in situ by a multistep all laser ablation deposition process. Since the Ag on YBa2Cu3O7 was exposed to 730 °C in O2 ambient, the barrier resistance was quite high, ∼0.6 Ω. The SQUIDs showed voltage periodicity versus magnetic field H⊥ up to ∼80 K and had a maximum response of 30 μV/Φ0 at ∼70 K, where IcRN was 30 μV. The SQUID response versus H⊥ was superimposed on a diffractionlike pattern of its junctions, indicating an improved uniformity in the junction cross section. When the SQUID was exposed to microwave radiation, many pronounced Shapiro steps were observed in the I-V curve, which modulated with the microwave power.
Comparison of optical nonlinearities of type II and type I quantum wells
Authors: Meissner K. , Fluegel B. , Binder R. , Koch S. W. , Khitrova G. , Peygambarian N.
Published: July 2002

We have performed low-temperature femtosecond pump and probe experiments on GaAs/AlAs type II and GaAs/AlGaAs type I multiple quantum wells of similar well sizes. The measurements are analyzed using a many-body theory appropriate for both types of systems. It is found that the type I and type II nonlinearities are very similar at early times after excitation. However, the very fast (<1 ps) Γ to X electron scattering in the type II samples causes pronounced differences at later times, allowing the observation of hole relaxation in the type II samples.