bluuebunny/crossref_metadata_2025 huggingface dataset:
GaAs quantum well laser and heterojunction bipolar transistor integration using molecular beam epitaxial regrowth
Authors: Berger Paul R. , Dutta N. K. , Sivco D. L. , Cho A. Y.
Published: July 2002

To explore monolithically integrated phototransmitters, a graded-index quantum well laser was integrated with a selectivity regrown heterojunction bipolar transistor (HBT). The laser utilized a p-up configuration, and the HBT used collector down geometry. This scheme allowed the devices to be interconnected through the n+-GaAs substrate. The threshold current (Ith) for the ridge waveguide laser was ∼70 mA. The HBT exhibited a small signal gain of 26 at a collector current of 30 mA. The modulation index defined as the change in light output per unit change in base current is 1.2 mW/mA for our device.
Highly anisotropic electron mobilities of GaAs/In0.2Ga0.8As/Al0.3Ga0.7As inverted high electron mobility transistor structures
Authors: Schweizer T. , Köhler K. , Rothemund W. , Ganser P.
Published: July 2002

Anisotropic electron mobilities for GaAs/In0.2Ga0.8As/Al0.3Ga0.7As inverted high electron mobility transistor structures were observed using Hall effect measurements. If the In0.2Ga0.8As quantum-well thickness is below the critical layer thickness, a higher electron mobility in the 〈01–1〉 direction is observed in comparison to the 〈011〉 direction. Exceeding the critical layer thickness of the In0.2Ga0.8As quantum well results in a change in the behavior of the anisotropy, and a highly anisotropic electron mobility with a higher electron mobility in the 〈011〉 direction, in comparison to the 〈01–1〉 direction, is observed. With increasing In0.2Ga0.8As quantum-well width, the anisotropy increases. An increase of the anisotropy was also observed if the Hall-effect measurements were carried out at lower temperatures. The anisotropy in the electron mobility can be correlated to the occurrence of a highly asymmetric-dislocation density. The asymmetry in the dislocation density was observed using wavelength-selective catholuminescence measurements.
Effects of material processing in high temperature superconducting magnetic bearings
Authors: McMichael C. K. , Ma K. B. , Lin M. W. , Lamb M. A. , Meng R. L. , Xue Y. Y. , Hor P. H. , Chu W. K.
Published: July 2002

A study of the levitation forces related to superconducting bearing design was conducted on free-sintered and melt-textured Y1Ba2Cu3O7−δ(YBCO) materials. Comparisons were made between free sintered, variously oriented, and randomly oriented melt-textured materials. Magnetic force measurements were also conducted on oriented YBCO before and after neutron irradiation. A magnetic bearing of new design utilizing the phenomenon of flux pinning was then fabricated using melt-textured YBCO with permanent magnets and a speed of 135 000 rpm was achieved. Rotational dissipation and magnetic stiffness measurements were performed on the bearing prototype.
Y1Ba2Cu3O6+δ growth on thin Y-enhanced SiO2 buffer layers on silicon
Authors: Robin T. , Mesarwi A. , Wu N. J. , Fan W. C. , Espoir L. , Sega R. , Ignatiev A.
Published: July 2002

SiO2 buffer layers as thin as 2 nm have been developed for use in the growth of Y1Ba2Cu3O6+δ thin films on silicon substrates. The SiO2 layers are formed through Y enhancement of silicon oxidation, and are highly stoichiometric. Y1Ba2Cu3O6+δ film growth on silicon with thin buffer layers has shown c orientation and Tc0=78 K.
Oxide desorption from InP under stabilizing pressures of P2 or As4
Authors: Averbeck R. , Riechert H. , Schlötterer H. , Weimann G.
Published: July 2002

The oxide desorption processes of InP have been investigated under molecular-beam epitaxy conditions, determining thickness and composition of the surface layer by x-ray photoelectron spectroscopy and surface reconstructions by reflection high-energy electron diffraction (RHEED). Under P2 stabilization the oxide desorbs within 5 min at 490 °C and a (2×4) reconstruction is observed. On the other hand, heating in a flux of As4 molecules results in the formation of an InAs layer at the top of the oxide, which strongly reduces the oxide desorption rate. The complete removal of the oxygen requires at least 520 °C and typically leaves a 1-nm-thick overlayer of InAs. In this case RHEED gives no indication whether the surface is oxide free.
Anomalous etch rates of photoresist with argon dilution of CF4/O2 plasma afterglows
Authors: Koretsky Milo D. , Reimer Jeffrey A.
Published: July 2002

It is shown that the downstream etching of a photoresist with CF4/O2 mixtures can be enhanced by a factor of at least 2 with addition of argon to the gas mixture. Analysis of the oxygen and fluorine atom densities with gas-phase magnetic resonance downstream of the discharge suggests that argon metastables alter the homogeneous chemistry for fluorine atom production as well as the heterogeneous chemistry of photoresist chain scission.
High misfit epitaxial growth: Superconducting YBa2Cu3O7−x thin films on (100)BaF2 substrates
Authors: Wang S. Z. , Xiong G. C. , He Y. M. , Luo B. , Su W. , Yao S. D.
Published: July 2002

In situ epitaxial growth of YBa2Cu3O7−x superconducting thin films on (100)BaF2 substrates has been successful by an off-axis dc planar magnetron sputtering method. The zero-resistance temperatures of these thin films are about 81–84 K with transition width of 1.5 K. The characteristics of the films were examined by x-ray diffraction, reflection high energy electron diffraction, Rutherford backscattering spectroscopy ion channeling techniques, and scanning electron microscopy. The experimental results suggest that BaF2 is a promising material as substrates or buffer layers for the epitaxial growth of high Tc superconducting thin films, especially in high frequency applications. Discussions on the heteroepitaxy of the YBCO/BaF2 system are propounded.
Sum-frequency generation in segmented KTP waveguides
Authors: Laurell F. , Brown J. B. , Bierlein J. D.
Published: July 2002

Segmented KTP waveguides have been used to produce efficient type I sum-frequency generation. Two Ti-sapphire lasers, tunable between 730 and 1070 nm were used as pump sources and up-converted radiation near four wavelengths between 390 and 480 nm was obtained. More than 2 mW of blue light was generated with 100 mW at each of the two fundamental wavelengths, which is 2–3 orders of magnitude higher output power than previously reported for guided-wave sum-frequency generation. Tunability up to 3 nm was achieved for the up-converted light and an increased efficiency measured at the degeneracy point.
Room temperature blue lasing of ZnSxSe1−x alloys by photopumping
Authors: Yang X. H. , Hays J. , Shan W. , Song J. J. , Cantwell E. , Aldridge J.
Published: July 2002

Photopumped lasing of ZnS0.05Se0.95 alloys grown by seeded physical vapor-phase transport technique is observed at room temperature for the first time. This is achieved with the excitation photon energy tuned close to the band gap. The longitudinal lasing modes are well resolved. This work demonstrates that ZnSxSe1−x alloys can be used as an alternative to ZnSe in blue light-emitting device fabrications.
Phase transition of Al-Yb alloy films upon ion irradiation and thermal annealing
Authors: Ding J. R. , Che D. Z. , Zhang H. B. , Tao K. , Liu B. X.
Published: July 2002

Al80Yb20 multilayered alloy films were amorphized by ion beam mixing at room temperature. A new metastable phase of hexagonal structure was formed when the irradiation dose was greater than that required to amorphize the alloy films. The metastable phase turned amorphous when the film was annealed at 500 °C for 10 min. It was also found that Al-Yb multilayers could be amorphized by solid state reaction. Al1−xYbx multilayered alloy films, with 17<x<30 at. %, became amorphous through interdiffusion at 450 °C for 20 min.
Identifying the source of 1/f noise in SQUIDs made from high-temperature superconductors
Authors: Koch R. H. , Eidelloth W. , Oh B. , Robertazzi R. P. , Andrek S. A. , Gallagher W. J.
Published: July 2002

We compare model predictions for 1/f noise in dc SQUIDs with experimental data and show that the 1/f noise in the our devices results from fluctuations in the magnitude of the critical current of the Josephson junctions that form the SQUID. Operating the SQUID while the bias current direction was being alternated canceled the 1/f noise power from these fluctuations and reduced the output noise power by two orders of magnitude. Using this process, we have measured the 1/f noise in several SQUIDs to be 1×10−7 Φ02/Hz at 0.1 Hz and 77 K, the lowest value reported to date.
Epitaxial growth of MgO on (100)GaAs using ultrahigh vacuum electron-beam evaporation
Authors: Hung L. S. , Zheng L. R. , Blanton T. N.
Published: July 2002

Epitaxial layers of MgO grown on (NH4)xS-treated (100)GaAs substrates were prepared by electron-beam evaporation in an ultrahigh vacuum system without introducing additional oxygen. The films deposited at 500 °C were found to grow with stoichiometric composition and have (110) planar orientation. X-ray pole-figure analysis showed that the [11̄0] direction in the MgO(110) plane is parallel to the [011̄] direction in the GaAs(100) plane with a 4: 3 coincident site lattice. The film surface was smooth with no signs of structural defects or microcracks.
Growth and strain compensation effects in the ternary Si1−x−yGexCy alloy system
Authors: Eberl K. , Iyer S. S. , Zollner S. , Tsang J. C. , LeGoues F. K.
Published: July 2002

Strain compensation is an important aspect of heterostructure engineering. In this letter, we discuss the synthesis of pseudomorphic Si1−yCy and Si1−x−yGexCy alloy layers on a silicon (100) substrate by molecular beam epitaxy using solid sources and the controlled strain compensation that results from the introduction of the ternary system. The introduction of C into substitutional sites in the crystal lattice is kinetically stabilized by low-temperature growth conditions (400–550 °C) against thermodynamically favored silicon-carbide phases. The lattice constant in Ge is about 4% larger than in Si, whereas in diamond it is 52% smaller. Consequently, the compressive strain caused by 10.8% Ge in a pseudomorphic Si1−xGex alloy can be compensated by adding about 1% carbon into substitutional lattice sites of the film assuming Vegard’s law of linear change of the lattice constant in the alloy as a function of the composition. Using x-ray diffraction, we observe a partial strain compensation in Si0.75−yGe0.25Cy alloys on Si depending on the amount of carbon in the layer, with no observable misfit dislocation generation. The Raman spectra from Si1−yCy and Si1−x−yGexCy alloys show a substitutional carbon vibration mode at about 600 wavenumbers. No indication of silicon-carbide precipitation is observed in transmission electron microscopy and Raman spectroscopy.
Distributed feedback lasers with distributed phase-shift structure
Authors: Chen G. , Seshadri S. R. , Cerrina F.
Published: July 2002

Distributed feedback (DFB) lasers with distributed phase-shift (DPS) structures are suggested for reducing the spatial hole burning in conventional phase-shifted DFB lasers. Solving the coupled-mode equations subject to suitable boundary conditions, we have determined the threshold gain condition of a symmetric distributed phase-shift distributed feedback (DPSDFB) laser as well as the internal photon intensity distribution. The results show that by distributing the phase shift to a greater extent, the spatial hole burning can be reduced significantly and a large threshold gain difference between lowest gain oscillation modes can be maintained over a large phase-shift range. Moreover, a properly designed DPSDFB laser does not pose extra requirements on its fabrication.
Abnormal redistribution of Zn in InP/InGaAs heterojunction bipolar transistor structures
Authors: Kurishima K. , Kobayashi T. , Gösele U.
Published: July 2002

High n+ doping (≳1019 cm−3 of Si) in the subcollector of InP/InGaAs heterojunction bipolar transistor structures is observed to induce an anomalously high Zn diffusivity and an associated broadening of the base layers. It is proposed that due to Fermi level surface pinning and a long time constant for the recovery of point defect equilibrium the subcollector acts as a continuously operating source of group III interstitials which in turn diffuse into the subsequently grown base region and enhance Zn diffusion via the kick-out mechanism. In this sense, highly n+ doped grown-in subcollector layers may be considered as having the effect of a ‘‘time bomb’’ in terms of generating undesirable excess point defects during subsequent further crystal growth and device processing.
Influence of stress on the photoluminescence of porous silicon structures
Authors: Friedersdorf L. E. , Searson P. C. , Prokes S. M. , Glembocki O. J. , Macaulay J. M.
Published: July 2002

The blueshifting of photoluminescence spectra of porous silicon structures formed in p-type silicon is shown to be related to stresses in the porous material. A characteristic cellular structure, with varying length scale, is observed in the high porosity films due to high surface stresses. The cellular structure is not formed during the secondary open-circuit etching procedure itself but occurs during evaporation of the electrolyte after removal of the porous silicon from the etching solution.
Experiments on the interaction between long Josephson junctions and a coplanar strip resonator
Authors: Davidson A. , Pedersen N. F.
Published: July 2002

Experiments are reported on a new geometry designed to couple long Josephson junction fluxon oscillators to a resonant cavity. The junctions were made with a niobium-aluminum oxide-niobium trilayer process with a critical-current density of around 1000 A/cm2. Various numbers of such junctions were incorporated directly as part of a coplanar strip half-wave resonator, with fundamental mode of about 34 GHz. Both the current density and oscillation frequency are higher than in previous experiments. Evidence for phase locking of multiple junctions is presented.
Visible (657 nm) InGaP/InAlGaP strained quantum well vertical-cavity surface-emitting laser
Authors: Schneider R. P. , Bryan R. P. , Lott J. A. , Olbright G. R.
Published: July 2002

We report the first visible (657 nm) vertical-cavity surface-emitting laser. The photopumped undoped structure was grown using low-pressure metalorganic vapor-phase epitaxy in a single-growth sequence on misoriented GaAs substrates. The optical cavity consists of an In0.54Ga0.46P/In0.48(Al0.7Ga0.3)0.52 P strained quantum-well active region and a lattice-matched In0.48(AlyGa1−y)0.52 P (0.7≤y≤1.0) graded spacer region, while the distributed Bragg reflectors are composed of Al0.5Ga0.5As/AlAs quarter-wave stacks. Room-temperature optically pumped lasing was achieved with a very low-threshold power, clearly demonstrating the viability of this new technology. These results provide the foundation for visible semiconductor laser-diode arrays for a number of applications including laser projection displays, holographic memories, and plastic fiber communication.
Self-aligned native-oxide ridge-geometry AlxGa1−xAs-GaAs quantum well heterostructure laser arrays
Authors: Burton R. S. , Schlesinger T. E. , Holmgren D. J. , Smith S. C. , Burnham R. D.
Published: July 2002

Process conditions for fabricating ridge geometry AlxGa1−xAs-GaAs quantum well heterostructure laser arrays utilizing a high quality self-aligned native oxide of AlxGa1−xAs are presented. Wet oxidation is performed, after etching ridges, via H2O vapor in a N2 or N2/H2(10%) carrier gas at 435–445 °C for 15–20 min. The formation of a uniform smooth oxide was found to be critically dependent on the crystal environment prior to the oxidation process. Characteristics of devices fabricated by this process are presented.
Photonic memory switch consisting of multiple quantum well reflection modulator and heterojunction phototransistor
Authors: Matsuo Shinji , Amano Chikara , Kurokawa Takashi
Published: July 2002

We report a photonic memory operation of an exciton absorptive reflection switch, consisting of a multiple quantum well modulator, a distributed Bragg reflector (DBR), and a heterojunction phototransistor (HPT). For the memory function, some of the bias light incident on the modulator passes through the DBR to illuminate the HPT. The state of the device is maintained after removing the input light incident on the phototransistor and is reset by removing the bias light incident on the modulator. Waveform reshaping and retiming of the disordered input pulse is also demonstrated.
Temperature and intensity dependence of the saturated density of light-induced defects in hydrogenated amorphous silicon
Authors: Hata N. , Isomura M. , Wagner S.
Published: July 2002

We compare experimental data for the saturated light-induced defect density Nsat in hydrogenated amorphous silicon with results obtained by a quasi-equilibrium model. If the model draws on a limited pool of defects the results agree with the experimental data, but if the model relies on the conversion of valence-band-tail states they do not. The model reproduces all three regimes of Nsat: a constant, maximum value of Nsat at high carrier generation rate G and low-temperature T; the dependence of Nsat on both G and T at intermediate temperature; and independence of G coupled with dependence on T at high temperature.
Reaction and epitaxial regrowth at the Ni/GaAs(001) interface: A state-specific x-ray photoelectron diffraction investigation
Authors: Chambers S. A. , Loebs V. A.
Published: July 2002

We demonstrate, for the first time, that state-specific x-ray photoelectron diffraction can be used to determine the structural environment of reacted substrate atoms at a metal/semiconductor interface. Such measurements reveal that extensive reactivity at the Ni/GaAs(001) interface is followed by epitaxial regrowth of a CsCl phase in which Ni atoms occupy one sublattice and disrupted Ga and As atoms occupy the other sublattice.
Highly oriented YBa2Cu4O8 films fabricated at atmospheric pressure by the sol–gel method using metal alkoxides
Authors: Katayama Shingo , Sekine Masahiro , Fudouzi Hiroshi , Kuwabara Makoto
Published: July 2002

YBa2Cu4O8 films were fabricated at atmospheric pressure by the sol–gel method using metal alkoxides. Gel films on Ag substrates, prepared from a heterometallic alkoxide solution, were fired at 800 °C for 10 h to yield highly oriented YBa2Cu4O8 films. Simultaneously using both the sol–gel method and Ag as a substrate was found to be remarkably effective for promoting the formation of the YBa2Cu4O8 phase and producing highly oriented films.
Lattice-matched epitaxial growth of single crystalline 3C-SiC on 6H-SiC substrates by gas source molecular beam epitaxy
Authors: Yoshinobu Tatsuo , Mitsui Hideaki , Izumikawa Iwao , Fuyuki Takashi , Matsunami Hiroyuki
Published: July 2002

Lattice-matched epitaxial growth of 3C-SiC on 6H-SiC substrates using an alternate supply of disilane (Si2H6) and acetylene (C2H2) gas molecular beams in a high vacuum was carried out. On 6H-SiC(0001̄) substrates, epilayers of 3C-SiC(1̄1̄1̄) with a double-positioning twin structure were obtained. On the other hand, single crystalline 3C-SiC(001) epilayers without twin structure were obtained on 6H-SiC(01̄14̄) substrates even at low temperatures down to 850 °C.
Growth mode and dislocation distribution in the ZnSe/GaAs (100) system
Authors: Guha S. , Munekata H. , LeGoues F. K. , Chang L. L.
Published: July 2002

We have investigated the effect of the initial growth mode on the dislocation structure in ZnSe epilayers grown on GaAs(100) by molecular beam epitaxy. For the case where the initial growth occurred by the formation and coalescence of three-dimensional islands, the threading dislocation density was found to be an order of magnitude higher and misfit dislocation lengths much shorter than that for the case where the initial growth proceeded by a two-dimensional layer-by-layer mode. These differences are discussed in terms of dislocation formation at island coalescence boundaries for a three-dimensional growth mode.
Resonance and switching in a native-oxide-defined AlxGa1−xAs-GaAs quantum-well heterostructure laser array
Authors: El-Zein N. , Holonyak N. , Kish F. A. , Smith S. C. , Dallesasse J. M. , Burnham R. D.
Published: July 2002

A twin linear-array coupled-cavity AlxGa1−xAs-GaAs quantum-well heterostructure laser, a stripe-geometry coupled two-dimensional array, is described that, unlike the usual stripe laser, exhibits mode switching and multiple switching (ON–OFF twice) in the light power (L) versus current (I) characteristics (L-I) with increasing current.
Temperature-dependent mobility of a GaAs/AlGaAs heterostructure after deposition of MgO and superconducting YBa2Cu3O7−x
Authors: Tseng M. Z. , Nguyen C. , Tarsa E. , Chang L. D. , Hu E. L. , Kroemer H.
Published: July 2002

High quality YBa2Cu3O7−x films have been grown on MgO epitaxial buffer layers deposited onto a GaAs/AlGaAs heterostructure incorporating a two-dimensional electron gas (2DEG). The critical temperature of the YBa2Cu3O7−x, Tc(0) was ≳80 K, and Jc≳2×104 A/cm2 at 77 K. Electron mobilities and concentrations of 2DEG substrates were measured at different stages in the formation of YBa2Cu3O7−x/MgO/2DEG structure. Room-temperature mobilities and concentrations were unchanged after YBa2Cu3O7−x/MgO deposition, while low-temperature mobilities were slightly degraded. It is found that the degradation of electron mobility is correlated to the high growth temperature of YBa2Cu3O7−x. Since the 2DEG is only 1200 Å from the substrate surface, this constitutes a sensitive demonstration of the viability of the semiconductor substrate under these growth conditions.
Photoluminescence of ZnSe/CdSe short-period superlattices grown by self-limiting monolayer epitaxy
Authors: Juza P. , Zajicek H. , Sitter H. , Helm M. , Faschinger W. , Lischka K.
Published: July 2002

A series of symmetric ZnSen/CdSen superlattices (n=2–6, where n is the number of monolayers) was prepared by a novel growth method, the self-limiting monolayer epitaxy. For n≤3, the low temperature photoluminescence spectra of these superlattices are dominated by near-band-gap emission with full widths at half maximum (FWHM) of 17 meV. For longer periods the photoluminescence intensity drops drastically and the FWHM increases by a factor of 2 which is attributed to the formation of misfit dislocations. The energetic positions of the photoluminescence peaks are in good agreement with transition energy calculations based on a Kronig–Penney-type model.
Saturation of 1.064 μm absorption in Cr,Ca:Y3Al5O12 crystals
Authors: Eilers H. , Hoffman K. R. , Dennis W. M. , Jacobsen S. M. , Yen W. M.
Published: July 2002

Saturation absorption experiments are conducted on the title compound at 1.064 μm with laser light propagating along both the [001] and [111] crystallographic axes. Rotation of the crystals about these axes during the experiments reveals that the transmission of the polarized 1.064 μm radiation is highly anisotropic in the saturation regime. The details of the anisotropy and saturation curves are explained using a simple model of subsets of optical centers along with a relevant set of rate equations. The ground and excited-state absorption cross sections at 1.064 μm are calculated to be σgs=5.7(±2)×10−18 cm2 and σes=8(±2)×10−19 cm2, respectively, and the optimum crystallographic orientation for utilization in optical devices is discussed.
Comparison of triethylgallium and tri-isobutylgallium for growth of GaAs and AlGaAs by metalorganic molecular beam epitaxy
Authors: Abernathy C. R. , Wisk P. W. , Jones A. C. , Rushworth S. A.
Published: July 2002

We have investigated the use of tri-isobutylgallium (TIBG) as an alternative to the standard source, triethylgallium (TEG), for growth of GaAs and AlGaAs by metalorganic molecular beam epitaxy (MOMBE). With this source we have obtained specular morphologies and growth rates up to 83 Å/min and 92 Å/min for GaAs and AlGaAs, respectively. At low temperatures, <450 °C, both GaAs and AlGaAs show much less carbon when grown with TIBG rather than TEG. At 525 °C, carbon levels in GaAs are similar regardless of Ga source. However, by optimizing the V/III ratio, the carbon background in Al0.25Ga0.75As can be reduced to 3×1015 cm−3 with TIBG relative to the 2×1016 cm−3 normally obtained with TEG at this temperature. Furthermore, the use of TIBG reduces the oxygen background by roughly a factor of 2. Based on these results, we conclude that the oxygen background in MOMBE is no longer limited by oxygen contamination in the gaseous precursors.
Reliability characteristics of metal-oxide-semiconductor capacitors with chemical vapor deposited Ta2O5 gate dielectrics
Authors: Lo G. Q. , Kwong D. L. , Lee S.
Published: July 2002

This letter discusses the reliability characteristics of metal-oxide-semiconductor capacitors with chemical-vapor-deposited Ta2O5 gate dielectric films. To be compatible with the conventional polycrystalline Si-gate process, SiO2 or Si3N4 film was deposited on Ta2O5 as the top dielectric layer. It is found that under high-field stress, interface state generation is enhanced with the presence of the top dielectric layers, probably due to the anode-field increase caused by the positive-charge buildup in the stacked dielectrics capacitors. The significant positive-charge build-up in capacitors with top dielectrics is believed to be due to the hole-injection-barrier from Ta2O5 to SiO2 or Si3N4 and/or damage creation in the Ta2O5 films.
Passivation of the InP surface using polysulfide and silicon nitride overlayer
Authors: Kapila A. , Malhotra V.
Published: July 2002

For the first time, excellent passivation of the defect states at the SiNx/InP interface has been achieved using ammonium sulfide solution containing excess sulfur and phosphorous pentasulfide. Silicon nitride overlayers have been deposited at ∼200 °C using electron cyclotron resonance plasma-enhanced chemical vapor deposition technique. The room-temperature integrated photoluminescence (PL) intensity of the passivated InP approximately doubled following the nitride deposition. Under similar conditions, the PL intensity of the untreated sample decreased by a factor of five. The interface trap density, estimated using the high-low capacitance technique, is ∼1012 cm−2 eV−1. The devices are stable, with no noticeable change observed over a 30-day period.
Surface reconstructions of GaAs(111)A and (111)B: A static surface phase study by reflection high-energy electron diffraction
Authors: Woolf D. A. , Westwood D. I. , Williams R. H.
Published: July 2002

GaAs(111)A and (111)B static surface phase maps have been generated under a variety of substrate temperature and incident As4 flux conditions ranging from, respectively, 400–700 °C, and from 1×1014 to 1×1016 molecules cm−2 s−1. For the case of GaAs(111)A only a (2×2) reconstruction was observed. However, four GaAs(111)B surface reconstructions were identified below a critical As4 flux of JcAs4≂5×1015 molecules cm−2 s−1, viz.: (2×2); (1×1)LT; (√19×√19); and, (1×1)HT. Above JcAs4 the (√19×√19) surface phase was quenched, such that the (1×1)LT and (1×1)HT structures merged to form a single (1×1) phase. The transitions to and from each of these surface phases were found to be reversible, occurring at very specific substrate temperatures for a given incident As4 flux. The activation energies (εA) characterizing the reversible surface phase transitions were measured and compared with those on the GaAs(100) surface.
Fabrication of aluminum oxide thin films by a low-pressure metalorganic chemical vapor deposition technique
Authors: Kim J. S. , Marzouk H. A. , Reucroft P. J. , Robertson J. D. , Hamrin C. E.
Published: July 2002

Amorphous Al2O3 thin films were grown on Si(100) and glass substrates by low-pressure metalorganic chemical vapor deposition using aluminum acetylacetonate and water vapor as source materials. Water vapor played an important role in the oxidation process and produced carbon-free, pure Al2O3 films. The deposition temperature could be lowered to 230 °C. The films were characterized by means of x-ray diffraction, x-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, and ellipsometry.
Spiral growth in epitaxial YBa2Cu3O7−x thin films produced by high deposition rate chemical vapor deposition
Authors: Luo L. , Hawley M. E. , Maggiore C. J. , Dye R. C. , Muenchausen R. E. , Chen L. , Schmidt B. , Kaloyeros A. E.
Published: July 2002

A technologically useful chemical vapor deposition process with high growth rate (≳4 μm/h) was developed for the epitaxial growth of YBa2Cu3O7−x (YBCO) thin films. Even at the high growth rate used in this process, a spiral growth mechanism was observed and the films grown had electrical (Tc=92 K, Jc of 2×106A/cm2 at 77 K) and structural properties equal to films produced by physical vapor deposition.
Octadecyltrichlorosilane monolayers as ultrathin gate insulating films in metal-insulator-semiconductor devices
Authors: Fontaine P. , Goguenheim D. , Deresmes D. , Vuillaume D. , Garet M. , Rondelez F.
Published: July 2002

In order to fabricate metal-insulator-semiconductor (MIS) devices with gate insulating films thinner than 5.0 nm, organic monolayers have been grafted on the native oxide layer of silicon wafers. We demonstrate that a single monolayer of octadecyltrichlorosilane with a 2.8 nm thickness allows to fabricate a silicon based MIS device with gate current density as low as 10−8 A/cm2 at 5.8 MV/cm, insulator charge density lower than 1010 cm−2, fast interface state density of the order of 1011 cm−2 eV−1, and dielectric breakdown field as high as 12 MV/cm. Moreover, this insulating film is thermally stable up to 450 °C.
Simultaneous generation of UV and visible light in segmented KTP waveguides
Authors: Laurell F. , Brown J. B. , Bierlein J. D.
Published: July 2002

We report on simultaneous generation of ultraviolet, blue, and green radiation in segmented KTP waveguides using two infrared input frequencies and combinations of second-harmonic and sum-frequency generation.
Structural and electro-optic properties of pulsed laser deposited Bi4Ti3O12 thin films on MgO
Authors: Jo W. , Cho H-J. , Noh T. W. , Kim B. I. , Kim D-Y. , Khim Z. G. , Kwun S-I.
Published: July 2002

Ferroelectric Bi4Ti3O12 thin films have been grown on MgO (100) and MgO(110) substrates by the pulsed laser deposition. X-ray diffraction studies show that the films on both substrates have preferential crystallographic orientation such that most of their c axes are close to the substrate normal direction. The film on MgO(110) shows quadratic and hysteretic electro-optic characteristics with the effective coefficient of about 3.8×10−15 m2/V2.
Pulsed laser annealing of P-implanted diamond
Authors: Allen M. G. , Prawer S. , Jamieson D. N. , Kalish R.
Published: July 2002

Diamond deeply implanted with 4 MeV P ions to a dose of 1×1015/cm2 is annealed by a focused pulsed laser that is selectively absorbed by the implanted damaged layer. Laser treatment with multiple pulses at ever increasing power leads to excellent regrowth as measured by channeling Rutherford backscattering spectroscopy, surface profilometry, and by optical transmission. The importance of the deep implantation and the potential of this method for doping diamond is demonstrated.
High quality YBa2Cu3O7 Josephson junctions made by direct electron beam writing
Authors: Tolpygo S. K. , Shokhor S. , Nadgorny B. , Lin J.-Y. , Gurvitch M. , Bourdillon A. , Hou S. Y. , Phillips Julia M.
Published: July 2002

High-Tc Josephson junctions have been fabricated by direct electron beam writing over YBa2Cu3O7 thin-film microbridges, using scanning transmission electron microscope (STEM) with an accelerating voltage of 80–120 kV. Annealing at 330–380 K increases Tc and Ic of the junctions and makes them more stable. In the operating range of a few degrees below Tc, the junctions show 100% magnetic field modulation of the critical current, microwave-induced Shapiro steps oscillating according to the resistively shunted junction (RSJ) model, and RSJ current-voltage characteristics with IcRn product up to 0.5–0.6 mV at 75 K and 0.3 mV at 77 K.
Low pressure photodeposition of silicon nitride films using a xenon excimer lamp
Authors: Bergonzo P. , Boyd Ian W.
Published: July 2002

Excimer lamps have recently opened up the field of intense vacuum ultraviolet light generation. The power available from such lamps based on the dielectric barrier discharge generation method can be superior to those of typical low pressure mercury lamps. Additionally, a wide range of shorter and longer wavelengths can be generated as required. Following previous work on silicon dioxide deposition, here we present the use of these lamps for direct photodeposition of silicon nitride from mixtures of silane and ammonia. Optical and physical characterization reveal good film qualities, rendering this new technique promising for low temperature semiconductor and optoelectronic material processing.
SiGe gate oxide prepared at low-temperatures in an electron cyclotron resonance plasma
Authors: Li P. W. , Yang E. S.
Published: July 2002

SiGe gate oxide prepared at low temperatures (25–400 °C) by electron cyclotron resonance (ECR) plasma is reported. 100–200 Å oxides were grown on Si0.8Ge0.2 substrates by ECR oxidation under different bias conditions. The electrical properties of the ECR grown oxides are strong functions of processing conditions and post-processing treatments. High frequency (1 MHz) and quasistatic capacitance-voltage ECR grown oxides’ measurements indicate that device quality gate oxides can be produced by this process; specifically, the fixed charge and interface state densities are comparable to those of ECR grown metal-oxide-semiconductor capacitors on silicon with an aluminum gate.
Band-edge and deep level photoluminescence of pseudomorphic Si1−x−yGexCy alloys
Authors: Boucaud P. , Francis C. , Julien F. H. , Lourtioz J.-M. , Bouchier D. , Bodnar S. , Lambert B. , Regolini J. L.
Published: July 2002

Photoluminescence of strained Si1−x−yGexCy alloys grown by rapid thermal chemical vapor deposition on Si(100) is investigated. Two dominant features are reported: At low pump intensities, the photoluminescence is dominated by a deep level broad luminescence peak around 800 meV whereas at high pump intensities, a well-resolved band-edge luminescence (no phonon and transverse optic replica) is observed. At 77 K, we attribute this band-edge feature to an electron-hole plasma luminescence of the ternary alloy. The dependences of the deep level and band-edge peaks versus the excitation power density are, respectively square-root-like or superlinear. A blue shift of the energy gap of Si1−x−yGexCy alloys with respect to Si1−xGex alloy is observed. The blue shift increase with carbon content corresponds to what is expected for the bulk alloy. An eventual influence of the strain relaxation cannot be excluded.
c-axis preferred orientation of laser ablated epitaxial PbTiO3 films and their electrical properties
Authors: Tabata Hitoshi , Murata Osamu , Kawai Tomoji , Kawai Shichio , Okuyama Masanori
Published: July 2002

Ferroelectric PbTiO3 epitaxial thin films have been formed on a base electrode of Pt(100)/MgO(100) using ArF excimer laser ablation. The x-ray diffraction patterns of these films show c-axis orientation with a rocking angle of 0.5 when the film is cooled faster than 75 °C/min after the deposition. The films exhibit clear and large ferroelectric hysteresis loops. The dielectric constant of the films is 130 and remnant polarization is 80 μC/cm2. The values are almost the same as those theoretically predicted. The pyroelectric coefficient of these films is 1000–1500 V/W at 10 Hz, even without poling treatment.
Voltage oscillations in an array of tunnel junctions controlled by a scanning tunneling microscope gate at room temperature
Authors: Nejoh H. , Aono M.
Published: July 2002

We observe that a current through an array of tunnel junctions can be controlled by a gate at room temperature. Metal islands were formed on an insulating substrate and liquid crystal molecules were placed between these islands. Electrodes were placed 5 mm apart on the substrate and a bias was applied between them. A scanning tunneling microscope (STM) tip which acts as a gate was supported on molecules which act as the central electrodes. When this two-dimensional tunnel junction array was current biased, the tunnel current flow across this array could be controlled by the gate voltage at room temperature.
In situ acoustic temperature tomography of semiconductor wafers
Authors: Levent Degertekin F. , Pei Jun , Khuri-Yakub Butrus T. , Saraswat Krishna C.
Published: July 2002

Spatial temperature distribution in semiconductor wafers during rapid thermal processing is obtained by means of acoustic tomography. Ultrasonic Lamb waves are excited in the wafer by acoustic transducers bonded to spring-loaded quartz support pins located at the wafer periphery. The Lamb wave time of flight in the wafer is used to measure the average wafer temperature with ±0.5 °C accuracy for a S/N ratio exceeding 55 dB. Spatial temperature information is gathered by electronic switching of the transmitter and receiver transducers. Tomographic reconstruction techniques are then used to calculate the temperature distribution from the measurements with different pixel maps. Using eight transducers, the thermal image of a 10 cm, (100) silicon wafer is obtained with 2×2 cm2 pixel resolution. Thermal image rates of 2 images/s are achieved by the system enabling real-time control of wafer temperature distribution during rapid thermal processing.
Oxidation of polycrystalline-SiGe alloys
Authors: Tsutsu H. , Edwards W. J. , Ast D. G. , Kamins T. I.
Published: July 2002

Polycrystalline-SiGe (poly-SiGe) films with Ge concentrations ranging from 5% to 30% were wet oxidized with trichloroethane at temperatures ranging from 700 to 1000 °C. For oxidation temperatures ≥800 °C, the oxidation rate of poly-SiGe depends only weakly on the Ge concentration. At 700 °C, the oxidation rate increases with Ge concentration and can exceed that at 800 °C. Rutherford backscattering spectra show that, in samples oxidized at or above 800 °C, Ge is completely rejected from the oxide, resulting in a pileup at the interface and diffusion into the poly-SiGe. At 700 °C, however, Ge is partially incorporated into the growing oxide when layers with high Ge concentration (≥20%) are oxidized. Most of the Ge is still rejected from the oxide and diffuses into the poly-SiGe layer. This behavior differs from that observed during the oxidation of epitaxial SiGe. Our results can be explained by assuming that diffusion of oxidant through the oxide is the rate controlling step. The oxide composition in turn, depends on the degree with which Ge is rejected from the oxide. The Ge removal rate from the interface exceeds that of single crystal films because of the enhanced diffusion of Ge along grain boundaries.
Giant photoluminescence enhancement in deuterated highly strained InAs/GaAs quantum wells
Authors: Polimeni A. , Marangio D. , Capizzi M. , Frova A. , Martelli F.
Published: July 2002

The photoluminescence of InAs/GaAs pseudomorphic single quantum wells, of width 1, 1.2, and 1.6 monolayers, is studied before and after diffusion of monoatomic deuterium into the samples. The luminescence shows a red shift for increasing nominal well width, suggesting an interface roughness on a scale much smaller than the exciton size. The luminescence efficiency increases by several orders of magnitude after sample deuteration. A discussion about the origin of radiative recombination in these heterostructures, before and after deuteration, is also given.
Epitaxial KNbO3 thin films on KTaO3, MgAl2O4, and MgO substrates
Authors: Chow A. F. , Lichtenwalner D. J. , Woolcott R. R. , Graettinger T. M. , Auciello O. , Kingon A. I. , Boatner L. A. , Parikh N. R.
Published: July 2002

Epitaxial potassium niobate (KNbO3) thin films have been deposited on KTaO3 (100), MgAl2O4 (100), and MgO (100) substrates using ion-beam sputter deposition. X-ray-diffraction results show that KNbO3 films have orthorhombic (110) orientation on all three substrates. Rutherford backscattering channeling analysis of KNbO3 films on KTaO3, MgAl2O4, and MgO exhibits minimum scattering yields (χmin) of 7%, 9%, and 18% for the Nb peak, respectively. This illustrates how the quality of epitaxy improves as the lattice mismatch decreases. Prism-coupling measurements reveal near-bulk refractive indices of about 2.27 for TE modes and 2.22 for TM modes for films on each substrate.
Current induced drift mechanism in amorphous SiNx:H thin film diodes
Authors: Shannon J. M. , Deane S. C. , McGarvey B. , Sandoe J. N.
Published: July 2002

It is shown that the drift in the current–voltage characteristics of silicon-rich amorphous silicon nitride metal–semiconductor–metal diodes can be explained by a mechanism whereby electron trapping centers are created via hole–electron recombination. A first order model which includes excitation of holes by hot electrons moving into the anode and recombination of electrons with holes trapped in the valence band tail is in good quantitative agreement with the measured dependencies between drift, device thickness, current density, time, and charge passed through the device.
Topmost surface analysis of SrTiO3 (001) by coaxial impact-collision ion scattering spectroscopy
Authors: Yoshimoto M. , Maeda T. , Shimozono K. , Koinuma H. , Shinohara M. , Ishiyama O. , Ohtani F.
Published: July 2002

The terminating atomic plane of SrTiO3 (001) surface was investigated by means of coaxial impact-collision ion scattering spectroscopy (CAICISS). CAICISS spectra proved that SrTiO3 (001) surfaces of as-supplied substrates as well as of O2-annealed substrates were predominantly terminated with TiO2 atomic plane, while the SrO atomic plane came at the topmost surface of SrTiO3 (001) homoepitaxial film. This indicates the structural conversion of the topmost atomic layer from TiO2 to SrO occurred during the SrTiO3 homoepitaxial growth. The azimuth rotational CAICISS spectra exhibited a fourfold symmetry in the surface atom alignments, showing the square lattice structure of a terminating plane.
Native-oxide defined ring contact for low threshold vertical-cavity lasers
Authors: Huffaker D. L. , Deppe D. G. , Kumar K. , Rogers T. J.
Published: July 2002

Data are presented characterizing a new process for fabrication of vertical-cavity surface-emitting lasers based on the selective conversion of high Al composition epitaxial AlGaAs to a stable native oxide using ‘‘wet oxidation.’’ The native oxide is used to form a ring contact to the laser active region. The resulting laser active regions have dimensions of 8, 4, and 2 μm. The lowest threshold laser is achieved with the 8-μm active region, with a minimum threshold current of 225-μA continuous wave at room temperature.
Evidence for cathodoluminescence from SiOx in porous Si
Authors: Suzuki T. , Sakai T. , Zhang L. , Nishiyama Y.
Published: July 2002

The cathodoluminescence (CL) from porous silicon and thermal-oxidized porous silicon was examined by x-ray spectroscopy and photoluminescence (PL). Two dominant CL bands were observed at 460 nm (2.7 eV) and 650 nm (1.9 eV), respectively, which were not found in the PL spectrum. Electron beam irradiation caused degradation and/or increase in luminescence, and the two bands showed different variations. It has been concluded that electron beam excitation mainly occurs in amorphous SiO2, and the two bands are caused from different defects in amorphous SiO2 covering the porous silicon.
Leakage current behaviors of epitaxial and preferentially oriented Bi4Ti3O12 thin films grown on La0.5Sr0.5CoO3 bottom electrodes
Authors: Jo W. , Kim K. H. , Noh T. W.
Published: July 2002

Epitaxial and preferentially oriented Bi4Ti3O12 thin films were grown using pulsed laser deposition on LaAlO3(001) and Al2O3(0001) substrates, respectively, with La0.5Sr0.5CoO3 bottom electrode layers. X-ray diffraction analysis shows that the Bi4Ti3O12 films are grown (001) and (104) oriented on La0.5Sr0.5CoO3(001)/LaAlO3(001) and La0.5Sr0.5CoO3(111)/Al2O3(0001), respectively. These growth behaviors can be explained using arrangements of oxygen ions. Cross-sectional scanning electron microscopy shows that microstructures of the heterostructures depend on the substrates. It is found that the growth behaviors and the microstructure affect leakage current behaviors of the Bi4Ti3O12 layers. Ohmic and space-charge-limited conduction mechanisms are used to explain leakage current behaviors of the Bi4Ti3O12 film on La0.5Sr0.5CoO3/LaAlO3(001) and La0.5Sr0.5CoO3/Al2O3(0001), respectively.
Atomic force microscopy study of ordered GaInP
Authors: Stringfellow G. B. , Su L. C. , Strausser Y. E. , Thornton J. T.
Published: July 2002

This letter presents an experimental study, using high-resolution atomic force microscopy, of the nature of the steps on the surface of GaInP layers lattice matched to GaAs substrates. The substrates were intentionally misoriented from the (001) plane by angles of 3°, 6°, and 9° toward [1̄10] and the layers were grown by organometallic vapor phase epitaxy at temperatures of 570, 620, and 720 °C. The surfaces consist of a mixture of monatomic (2.9 Å) [110] steps and [110] oriented supersteps with a distribution of heights from 2 to approximately 17 monolayers. The height of the largest steps increases monotonically with increasing misorientation angle. The supersteps are apparently formed by bunching of monatomic steps producing high index (11n) surfaces (n=4 to 7). This leaves relatively large (several hundred Å) (001) facets adjacent to the supersteps. The superstep height increases and the density decreases with increasing growth temperature. An attempt is made to correlate the supersteps to the degree of order and the microstructure of the ordered domains.
Impact ionization coefficients in (100) GaInP
Authors: Fu S.-L. , Chin T. P. , Ho M. C. , Tu C. W. , Asbeck P. M.
Published: July 2002

Electron and hole impact ionization coefficients in (100)Ga0.5In0.5P have been measured by photomultiplication measurements. The ratio of hole to electron ionization coefficients, β/α, is shown to decrease from 2 to 1 when the electric field is increased from 3.5×105 to 6.5×105 V/cm. As confirmation, breakdown voltages were measured for several p+−n−−n+ diodes with various concentrations in the n− region. The values observed showed good agreement with those calculated from the ionization coefficients. Typical breakdown voltages are on the order of 1.6 times higher than those expected for GaAs.
Substitutionality of Ge atoms in ion implanted AlSb
Authors: Yu Kin Man , Moll A. J. , Chan Ning , Walukiewicz W. , Becla P.
Published: July 2002

The substitution of Ge atoms into ion implanted AlSb is investigated by extended x-ray absorption fine structure spectroscopy. Our results reveal that in the as-implanted material, the implanted Ge atoms are equally distributed between two specific sites, one surrounded by Al atoms and the other surrounded by Sb atoms. After annealing at 750 °C for 5 s, the coordination number of the Ge atoms increases from ∼3 to ∼4 indicating solid phase regrowth of the implantation induced amorphous surface layer. Moreover, in the annealed AlSb, the substitution of Ge atoms into the Al sublattice dominates with an estimated GeAl]:[GeSb]∼0.8:0.2. These results suggest that Ge atoms act preferentially as donor species in AlSb.
Atomic hydrogen density measurements in an ion source plasma using a VUV absorption spectrometer
Authors: Stutzin G. C. , Young A. T. , Schlachter A. S. , Stearns J. W. , Leung K. N. , Kunkel W. B. , Worth G. T. , Stevens R. R.
Published: July 2002

A system to determine the density and temperature of ground-state hydrogen atoms in a plasma by vacuum ultraviolet laser-absorption spectroscopy is described. The continuous tunability of the spectrometer allows for analysis at any of the Lyman transitions. The narrow bandwidth of the laser source allows for the accurate determination of the hydrogen absorption line shape and, hence, the translational temperature. The utility of the system is exemplified by data obtained on an ion source plasma. The measurements show the quality of the data as well as illustrating the behavior of these sources under varying discharge conditions.