bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure isolation testing using a scanning electron microscope
Authors: Mahant-Shetti S. S. , Aton T. J. , Gale R. J. , Bennett-Lilley M. H.
Published: July 2002

A new form of testing is described that is suitable for verifying isolation in many forms of microstructures. Excess charge is deposited on the microstructures by a scanning electron microscope (SEM) beam. On elements of the microstructures that are isolated, this excess charge induces a voltage contrast that is detected at the same time by the same beam. Isolation to approximately 2×1011 Ω can be verified. The method is simple and fast, requiring only a standard SEM and simple test structures.
Patterned tungsten chemical vapor deposition on amorphous silicon by excimer laser modification of the native oxide
Authors: Howe A. T. , Reddy K. V. , Wuensch D. L. , Niccum J. T. , Zajac G. W.
Published: July 2002

We report a method of patterning tungsten on hydrogenated amorphous silicon by excimer laser modification of the native oxide, thereby inhibiting the deposition of tungsten on the exposed regions in a subsequent tungsten chemical vapor deposition step. The method demonstrates how intermediate fluence radiation (∼100 mJ/cm2), which does not damage masks, can be utilized for patterning.
Permeable base transistor fabrication by selective epitaxial growth of silicon on a submicrometer WSi2 grid
Authors: Badoz P. A. , Bensahel D. , Guérin L. , Puissant C. , Regolini J. L.
Published: July 2002

We report the epitaxial growth of silicon on a tungsten disilicide grating using a rapid thermal processing, low-pressure chemical vapor deposition reactor. Results indicate that silicon grows selectively on the patterned Si/WSi2 structure, irrespective of the grating periodicity (from 0.6 μm up to several tens of microns). The epitaxial growth of silicon is shown to proceed two dimensionally on the Si surface and laterally over the WSi2 lines without any reaction with the underlying WSi2 grid. Preliminary electrical measurements of the Si/WSi2/Si overgrown permeable base transistor thus fabricated are presented, showing current densities Jmax of up to 6000 A/cm2 and transconductances gm of 5 mS/mm.
Self-electro-optic effect based on anticrossing of excitonic transitions in a coupled quantum well structure
Authors: Tokuda Yasunori , Kanamoto Kyozo , Tsukada Noriaki
Published: July 2002

We demonstrate electrically controlled photocurrent (absorption) tristability in an asymmetric coupled quantum well p-i-n diode connected to a series resistive load. The phenomenon, which is explained in terms of a self-electro-optic effect, is brought about by making use of an anticrossing behavior of excitonic optical transitions instead of the usual quantum-confined Stark effect.
Fabrication and characterization of quantum well wires grown on corrugated GaAs substrates by molecular beam epitaxy
Authors: Kojima Keisuke , Mitsunaga Kazumasa , Kyuma Kazuo
Published: July 2002

Single quantum wells were grown on GaAs triangular gratings by molecular beam epitaxy. Cross-sectional transmission electron microscopy revealed that the quantum wells had a triangular shape above the ridge of the grating. The photoluminescence spectra at 77 K showed strong anisotropy, indicating that the electrons are confined two dimensionally. The calculation confirmed that the electrons tend to be localized at the corner of the bent quantum well wires, and the effective width of the quantum well wire was estimated to be 30 nm.
Far-infrared absorption spectra measured in InAs/Al0.36Ga0.64Sb quantum wells
Authors: Kim J.-H. , Bhattacharya P. K. , Singh J. , Gulari E.
Published: July 2002

Far-infrared absorption spectra have been measured for molecular beam epitaxial InAs/Al0.36Ga0.64Sb multiquantum wells by Fourier transform infrared spectroscopy using light incident normal to the layers. The special band lineup for this heterostructure system causes an overlap of the electron and hole states. The measured absorption peak varies in the wavelength range of 5–10 μm in the temperature range of 100–300 K.
Femtosecond dynamics of the nonlinear index near the band edge in AlGaAs waveguides
Authors: Anderson K. K. , LaGasse M. J. , Wang C. A. , Fujimoto J. G. , Haus H. A.
Published: July 2002

The transient behavior of the nonresonant nonlinear index is investigated in AlGaAs waveguides with femtosecond time resolution. Both the refractive index and the absorption changes are measured by time division interferometry and pump probe techniques. Different mechanisms which contribute to the nonlinear index are distinguished by examining their dynamics, including the optical Stark effect, resonantly excited carriers, and two-photon absorption processes. The relative contribution from each mechanism is a strong function of wavelength near the band edge.
Topographic study on an InAs lattice-mismatched heteroepitaxial layer grown on GaAs by means of x-ray scattering radiography
Authors: Suzuki Yoshifumi , Chikaura Yoshinori , Akazaki Tatsushi
Published: July 2002

X-ray scattering radiography has been successfully applied to an InAs lattice-mismatched heteroepitaxial layer grown on GaAs (001) by molecular beam epitaxy. It was found that the lattice of the epitaxial layer varied the orientation over 18 min in arc around a [100] direction, whereas the substrate has a small lattice bend around [110] by less than 2 min in arc. The bending forms the layer into a concave with a valley along [100]. The independent lattice deformation in two layers comes from a complicated effect of the lattice mismatches and thermal expansion. Also local various structures were observed in the scattering radiographs.
Photothermal imaging of copper-decorated grain boundary in silicon
Authors: Inglehart L. J. , Broniatowski A. , Fournier D. , Boccara A. C. , Lepoutre F.
Published: July 2002

Using a scanning photothermal reflectance microscope we have observed a large enhancement of the modulated reflectance signal accompanied by a phase change of π in the region of a copper-decorated grain boundary in silicon. A preliminary analysis of the data is given in terms of the thermal and plasma waves generated in the specimen. Orders of magnitude of recombination velocities of the surface and the boundary are determined in reasonable agreement with electrical measurements.
Heteroepitaxial growth of InxGa1−xAs on graphoepitaxially grown germanium
Authors: Kanata T. , Takakura H. , Matsunaga M. , Hamakawa Y.
Published: July 2002

InxGa1−xAs films have been grown by molecular beam epitaxy on graphoepitaxially grown germanium films on nickel replica sheets fabricated from an anisotropic etched silicon (001) surface. The crystallographic and optical properties of the InxGa1−xAs films have been characterized. The crystallographic orientation of the heteroepitaxial InxGa1−xAs has a small deviation from the orientation of synthesized surface relief in the graphoepitaxial substrate. This deviation in the heteroepitaxial film is caused by misorientation of the crystallographic orientation during the graphoepitaxial growth of germanium. The energy gap of the InxGa1−xAs has also a slight deviation from the expected one. The mechanism and its evidence have been studied.
Absence of 13C incorporation in 13CCl4-doped InP grown by metalorganic chemical vapor deposition
Authors: Cunningham B. T. , Baker J. E. , Stockman S. A. , Stillman G. E.
Published: July 2002

Intentional carbon doping of low-pressure metalorganic chemical vapor deposition (MOCVD) grown InP has been attempted with a 500 ppm mixture of 13CCl4 in high-purity H2, which has been used to obtain carbon-acceptor concentrations as high as 1×1019 cm−3 in GaAs. Under growth conditions similar to those used for heavy carbon incorporation in GaAs, injection of 13CCl4 into the growth reactor during growth of InP did not produce any measurable change in the carrier concentration of the InP epitaxial layers or any change in the 13C concentration above the 13C background in secondary-ion mass spectroscopy analysis. These results support previous low-temperature photoluminescence measurements of high-purity InP in which no residual carbon acceptor is observed under many growth techniques and growth conditions, and hence support the hypothesis that carbon is not incorporated in InP grown by MOCVD.
Observation of multiple precipitate layers in MeV Au++-implanted silicon
Authors: Alford T. L. , Theodore N. D. , Fleischer E. L. , Mayer J. W. , Carter C. B. , Bo/rgesen P. , Ullrich B. M. , Cheung N. W. , Wong H.
Published: July 2002

Room-temperature MeV Au++ implantation into silicon with energies above 1.8 MeV shows a splitting of the Au concentration profile in the Rutherford backscattering spectrometry (RBS) spectra. Cross-section transmission electron microscopy micrographs show two distinct regions of Au precipitates corresponding to the peaks in the RBS spectra. The double peaks can be explained by the segregation of Au into the highly damaged region near the end of the implant range and Au segregation along a dislocation network. These dislocations arise from dynamic beam annealing during the implant and act as paths for rapid diffusion. Precipitation occurs when the Au concentration exceeds the solubility limit. Lower energy implants resulted in the expected Gaussian distributions.
High-power operation of heterobarrier blocking structure InGaAlP visible light laser diodes
Authors: Itaya K. , Watanabe Y. , Ishikawa M. , Hatakoshi G. , Uematsu Y.
Published: July 2002

Heterobarrier blocking structure InGaAlP visible light laser diodes employing a thin active layer (0.04 μm) and asymmetry coatings have been fabricated. The high light-output power operation with this heterobarrier blocking structure was investigated. The light-output power versus cw current curve was linear up to 43 mW and a maximum light output power of 51 mW was obtained. A high-power operation such as 20 mW was maintained at 40 °C. Stable oscillation in the fundamental transverse mode was obtained up to 30 mW. These results show that this heterobarrier blocking structure supplies a sufficient current confinement effect even under a high-light output power operation.
Light scattering determination of subband structure and population of modulation-doped multiple quantum wells
Authors: Richards D. , Fasol G. , Ploog K.
Published: July 2002

We show that electronic Raman scattering measurements of the plasmon dispersion in combination with calculations of the random phase approximation dielectric response and self-consistent electronic subband calculations can determine the subband structure and populations of modulation-doped GaAs/AlxGa1−xAs multiple quantum wells with multiple subband occupancy. Thus we present a contactless optical alternative to measurements of Shubnikov–de Haas oscillations for the determination of carrier concentrations. The same technique can also be applied for the characterization of parallel conduction from doped AlGaAs layers in modulation-doped heterostructures.
Bulk BiPbSrCaCuO rf SQUIDs operating up to 101 K
Authors: Zhang Yi , Xu Yunhui , Heiden C.
Published: July 2002

rf superconducting quantum interference devices (SQUIDs) of bulk Bi1.4Pb0.6Sr2Ca2Cu3Ox samples have been fabricated using an adjustable break junction and operated from 4.2 to 101 K. An adjustable break junction is used as weak link whose critical current can be varied to obtain the optimum signal at each given temperature. These SQUIDs can be reproducibly operated after many thermal cycles and moisture-drying processes. Flux noise spectra as function of both of frequency and temperature have been measured. The typical values of flux noise and energy resolution at a frequency of 200 Hz and 77 K are ∼2×10−4 φ0/(Hz)1/2 and ∼8.6×10−28 J/Hz, respectively, which are comparable to that of bulk YBa2Cu3O7−y rf SQUIDs.
Doubly resonant optical parametric oscillator synchronously pumped by a frequency-doubled, mode-locked, and Q-switched diode laser pumped neodymium yttrium lithium fluoride laser
Authors: Maker G. T. , Ferguson A. I.
Published: July 2002

We report on the synchronous pumping of an optical parametric oscillator (OPO) using a frequency-doubled, mode-locked, and Q-switched diode laser pumped yttrium lithium fluoride laser. Using a 1 W pump diode, frequency modulation mode locking, and acousto-optic Q switching, a pulse envelope of 75 ns duration and 45 μJ of energy in 21 ps pulses at 360 MHz repetition rate was obtained. This was frequency doubled in 90° phase-matched MgO:LiNbO3 with 47% energy conversion efficiency. The doubly resonant OPO based upon temperature-tuned MgO:LiNbO3 had an energy conversion efficiency of 20% at degeneracy. The tuning range of 983–1119 nm was limited by the mirror reflectivities.
Contribution of second-harmonic generation to the creation of free carriers in CdTe single crystals
Authors: Petrovic Mark S. , Suchocki Andrzej , Powell Richard C. , Cantwell Gene , Aldridge Jeff
Published: July 2002

It is shown that cadmium telluride exhibits second-harmonic generation under 1064 nm ps pulse excitation despite strong absorption of the green light which is generated. The process of second-harmonic generation contributes to the creation of an electron-hole plasma in CdTe which affects the measured value of the two-photon absorption coefficient and other nonlinear properties of the material.
Optical bistability in hydrogenated amorphous silicon
Authors: Tann J. , Gal M. , Meaney K. , Taylor P. C.
Published: July 2002

Room-temperature optical bistability has been demonstrated in hydrogenated amorphous silicon at wavelengths greater than about 700 nm. Switching powers as low as 0.8 mW (switching intensities 1.7 kW/cm2) are observed. The measured switching times are found to be compound, with time constants from 50 μs to 1 ms.
Cyclotron resonance measurements of the high electron mobility transistor
Authors: Chang Chian-Sern , Fetterman Harold R. , Green Arold
Published: July 2002

The photoconductivity cyclotron resonance measurement is used to determine the effective masses of the high electron mobility transistor. The experimental data show that the effective mass is a function of the gate voltage.
Possible contribution of SiH2 and SiH3 in the plasma-induced deposition of amorphous silicon from silane
Authors: Vepřek Stan , Vepřek-Heijman Maritza G. J.
Published: July 2002

A self-consistent quantitative analysis of recent kinetic data on the role of di- and trisilane in the plasma-induced deposition of amorphous silicon from monosilane confirms the conclusion that the dominant reactive intermediate responsible for the formation of di- and trisilane and, consequently, for the deposition of a high quality amorphous silicon is SiH2. The data show that the SiH3 radical may play only a negligible, if any, role in this process.
High T
c Y-Ba-Cu-O thin films prepared by i
n s
i
t
u low-temperature codeposition of Y, BaF2, and Cu on α-Al2O3 substrates
Authors: Chromik Š. , Hanic F. , Adam R. , Jergel M. , Liday J. , Beňačka Š.
Published: July 2002

Thin Y-Ba-CU-O films were prepared in-situ by low-temperature codeposition on Al2O3 substrates. The temperatures during preparation did not exceed 600 °C. As a source of Ba the BaF2 was used. The zero resistance Tc values were higher than 84 K, Jc =4×104 A/cm2 at 4.2 K/OT. The Auger electron spectroscopy analysis has shown almost a homogeneous distribution of the film components throughout the film thickness. X-ray diffraction revealed the presence of unoriented 1-2-3 phase besides BaF2 and CuO and, one undefined phase, which might be oxyfluoride compound.
Type II broken-gap quantum wires and quantum dot arrays: A novel concept for self-doping semiconductor nanostructures
Authors: Sercel Peter C. , Vahala Kerry J.
Published: July 2002

A novel concept for creating self-doping quantum wires and quantum dot arrays based upon the InAs-GaSb material system is proposed. The unusual type II, broken-gap band line-up in this system allows charge transfer across the InAs-GaSb interfaces. We employ a recently developed coupled band formalism to examine analytically the band structure of InAs-GaSb quantum dots and wires. The analysis shows that appropriately engineered nanostructures which contain high free-carrier densities are possible without intentional impurity doping. Quantum dots in this system behave as artificial quasiatoms, with ionization energy and valence determined by fabricationally determined parameters. Synthetic p-(n-)type semiconductors may therefore be formed from arrays of InAs(GaSb) quantum dots embedded in GaSb(InAs). InAs-GaSb quantum wires are also investigated and found to exhibit self-doping behavior. Possible fabrication schemes utilizing recently developed technologies are discussed.
S-bend loss in disorder-delineated GaAs heterostructure laser waveguides with native and blue shifted active regions
Authors: Tang T. , Swanson P. , Herzinger C. , Miller L. M. , Cockerill T. M. , Bryan R. P. , DeTemple T. A. , Coleman J. J.
Published: July 2002

The routing ability of waveguide S-bend structures patterned by SiO2 impurity induced layer disordering of a single GaAs quantum well graded barrier laser structure is investigated. For a raised-cosine bend with 100 μm offset guides, the measured transition length for 3 dB loss was less than 300 μm for near single mode guides of 1 μm width. In addition, vacancy-induced disordering of the native quantum well region is investigated and is shown to increase the band gap to a point where the material is low loss for radiation generated by the laser. The 3 dB length for these blue shifted cores actually decreased to about 230 μm, a fact attributed to reduced mode conversion.
GaAs-AlAs low-voltage refractive modulator operating at 1.06 μm
Authors: Goossen K. W. , Cunningham J. E. , Jan W. Y.
Published: July 2002

We have produced a nonabsorbing surface-normal optical modulator operating at 1.06 μm (e.g., for a high-power Nd-YAG pump laser) which has a relative transmission change of 16% for −1 to 1 voltage swing. The structure is a GaAs-AlAs dielectric mirror with alternating n- and p-type δ doping at each interface. Doping selective contacts are made to the sample so that an applied voltage appears equally across each period of the device, yielding a strong field which changes the index of the GaAs and hence shifts the mirror.
Net gain in photorefractive InP:Fe at λ=1.32 μm without an applied field
Authors: Strait J. , Reed J. D. , Saunders A. , Valley G. C. , Klein M. B.
Published: July 2002

We have observed two-beam coupling gain (0.273 cm−1) that exceeds absorption (0.145 cm−1) in InP:Fe without applying an external field at λ=1.32 μm. Measurements of the gain coefficient as a function of grating spacing fit the photorefractive theory for simultaneous electron-hole transport, with the effective density of traps NE = (3.86 ± 1.1)NE=(3.86±1.1)× 1015 cm−3 and ξ, the factor that accounts for competition between electrons and holes, equaling −0.729±0.026. Absorption measurements, combined with the photoionization cross sections of electrons and holes, confirm these results. The agreement between theory and experiment suggests how to choose impurity concentrations that optimize net gain.
Magneto optics of two-dimensional holes in a strained-layer InAs0.15Sb0.85/InSb superlattice
Authors: Lin S. Y. , Tsui D. C. , Dawson L. R. , Tigges C. P. , Schirber J. E.
Published: July 2002

Cyclotron resonance (CR) of two-dimensional holes is observed in the magneto transmission of circularly polarized far-infrared radiation through two InAs0.15Sb0.85/InSb strained-layer superlattice samples at 4.2 K. Effective masses are (0.034±0.004)me and (0.054±0.006)me at a hole density of 9.4×1010/cm2 per quantum well. This observation is direct evidence that the energy-band line-up of the InAs0.15Sb0.85/InSb strained-layer superlattice is type II. In addition, a spin resonance is observed in the hole CR-inactive polarization from which an effective g factor of 140 is deduced.
Inequivalent impurity and trap incorporation at normal and inverted interfaces of AlGaAs/GaAs quantum wells grown by molecular beam epitaxy
Authors: Köhrbrück R. , Munnix S. , Bimberg D. , Mars D. E. , Miller J. N.
Published: July 2002

The influence of growth interruption time on the incorporation of shallow impurities and traps in molecular beam epitaxy grown GaAs/AlGaAs quantum wells is studied by means of steady-state and time-resolved photoluminescence. With increasing interruption time, the GaAs surface becomes appreciably smoother, and increasing incorporation of shallow impurities, but not incorporation of traps is observed. At the AlGaAs surface the concentration of traps strongly increases with growth interruption time, but the surface does not become smoother. Additionally, strong accumulation of shallow impurities at the AlGaAs surface (inverted interface) is directly visualized.
Optical properties of quantum steps
Authors: Shen H. , Pollak Fred H. , Tsu Raphael
Published: July 2002

We have developed a method to calculate the density of states of quantum steps which allows us to sum the optical transitions for the determination of optical properties. We have demonstrated that quantum steps introduce quasistationary states. The calculated peaks agree well with the photoreflectance result.
Three-center Auger excitation mechanism of ytterbium intrashell emission in ZnS
Authors: Świa̧tek K. , Suchocki A. , Godlewski M.
Published: July 2002

A new, very efficient excitation mechanism of Yb intrashell 4f-4f emission in ZnS is reported. We show that the energy transfer from donor-acceptor pairs to Yb sites leads to Yb ionization (Yb3+⇒Yb2+), followed by capture of ionized carriers via the Yb3+ external excited state (bound exciton state), an energy transfer to the Yb3+ 4f shell, and Yb3+ 4f-4f radiative recombination. Since three centers (donor, acceptor, and Yb) participate in the energy transfer process in which Yb is first ionized, the above excitation mechanism is of three-center Auger transition nature. A similar excitation mechanism is expected for Eu, Sm, and Tm in ZnS, i.e., for these rare earth (RE) ions which can change their charge state from 3+ to 2+ in this lattice. For wider band-gap sulfides, such as CaS or SrS, this mechanism can be of importance also for other REs, such as, for example, Pr, Dy, and Er.
Surface kinetics of chemical beam epitaxy of GaAs
Authors: Liang B. W. , Tu C. W.
Published: July 2002

A new kinetic model for chemical beam epitaxy of GaAs using triethylgallium and arsine is proposed. Both group III and group V species are equally important in the surface reactions. This model can fit experimental data very well. Various aspects of the growth rate as a function of substrate temperature, triethylgallium and arsine flow rates are examined.
Picosecond photoluminescence excitation spectroscopy of GaAs/AlGaAs quantum wells
Authors: Freeman M. R. , Awschalom D. D. , Hong J. M.
Published: July 2002

A synchronous pair of pulsed dye lasers is used to obtain continuous photoexcitation energy spectra of quantum well luminescence at fixed time delays following carrier generation, with picosecond time resolution. A measurement of the energy-dependent initial luminescence polarization of photoexcited carriers in GaAs/AlGaAs quantum wells, from a pulsed optical pumping experiment, is presented as an illustration of the technique.
Time and injection rate dependence of minority-carrier diffusion length in solar cells irradiated with x rays
Authors: Edmonds Ian
Published: July 2002

The minority-electron diffusion length in commercial n+p silicon solar cells was determined from measurements of transient photocurrent generated by low-energy x rays. The results show an order of magnitude increase in diffusion length over a time interval inversely proportional to the square of the injection rate. This accounts for the occurrence of dose rate sensitivity of silicon detectors of x rays at very low injection rates. The strong rate dependence observed suggests a space-charge trapping mechanism.
Equilibrium oxygen potential for the decomposition of YBa2Cu4O8
Authors: Mathews Tom , Jacob K. T.
Published: July 2002

On lowering the chemical potential of diatomic oxygen, the compound YBa2Cu4O8 was found to decompose into a mixture of YBa2Cu3O6+x and CuO. The equilibrium oxygen potential corresponding to this decomposition has been measured from 870 to 1150 K using a solid-state cell incorporating yttria-stabilized zirconia as the solid electrolyte and pure oxygen at a pressure of 1.01×105 Pa as the reference electrode: Pt, O′2‖YBa2Cu4O8+YBa2Cu3O6+x+CuO∥(Y2O3) ZrO2∥O2(1.01×105 Pa), Pt. The low oxygen potential boundary for the stability of YBa2Cu4O8 can be represented by ΔμO2=−238 900+207.7 T(±800) J mol−1. At the standard pressure of oxygen (1.01×105 Pa) the decomposition occurs at 1150 K.
Observation of optical bistability by charge-induced self-feedback in biased AlGaAs multiple quantum well structures
Authors: Obata K. , Yamanishi M. , Yamaoka Y. , Kan Y. , Hayashi J. , Suemune I.
Published: July 2002

A new type of optical bistable device is demonstrated. We report the first observation of optical bistable switching caused by charge-induced self-feedback due to field screening in GaAs/AlGaAs multiple quantum well structures, both at room temperature and at low temperature (110 K). A bias voltage supply is directly connected to the p-i-n diode with the multiple quantum well structure to attain optical bistability. Since no external series resistance is required, the device is attractive from the standpoint of a practical application. The mechanism for the self-feedback underlying the operation of the device is elaborated. The theoretical consideration about the resolvable spot size on the device operation is shown.
High-gain photorefractive two-beam coupling in semi-insulating GaAs with pump-controlled suppression of the Schottky barrier
Authors: Chomsky Doron , Sternklar Shmuel , Zigler Arie , Jackel Steven
Published: July 2002

Suppression of the Schottky barrier effect in semi-insulating GaAs is demonstrated by centering the pump irradiation on the reverse bias crystal-electrode interface. A photorefractive gain coefficient Γ of 2.7 cm−1 is achieved. The irradiation suppression overcomes the need for externally applied ohmic contacts.
Determination of the density of states effective mass and the energy minimum of the X7 satellite conduction band in GaAs from the X6→X7 absorption spectrum
Authors: Wang W. B. , Ockman N. , Cavicchia M. A. , Alfano R. R.
Published: July 2002

A time-resolved picosecond pump-infrared-probe technique was used to measure the X6→X7 absorption spectrum in an intrinsic GaAs crystal. From the long-wavelength onset of the induced X6→X7 absorption spectrum, the energy gap between the minima of the X6 and X7 bands was directly determined to be 0.345±0.017 eV. By fitting the experimental data, the density of states effective mass for the X7 band was found to be 0.48±0.06m0.
Er/Si (111) interface intermixing investigation using core level photoemission
Authors: Haderbache L. , Wetzel P. , Pirri C. , Peruchetti J. C. , Bolmont D. , Gewinner G.
Published: July 2002

We present in this letter Si 2p core level photoemission measurements on the Er/Si (111) interface formed at room temperature. These spectroscopic data are compared with those measured on amorphous silicide films for various Er concentrations grown by coevaporation of Er and Si species at room temperature under ultrahigh vacuum conditions. This study reveals a strong interaction between Er and the Si (111) substrate even at very low coverage. A mixed interface is observed with silicide formation up to 6 monolayers of deposited metal which corresponds to the onset of erbium metal overgrowth. The Er concentration in the interfacial silicide is found to increase as a function of the deposited Er thickness. A model for the interface is proposed and discussed.
Thermally induced hole-electron competition in photorefractive InP:Fe due to the Fe2+ excited state
Authors: Delaye P. , Halter P. U. , Roosen G.
Published: July 2002

The photorefractive coupling gain is limited in InP:Fe even if there is no direct hole-electron competition. One has to take into account the excited state of Fe2+ (5T2) with its strong thermal emission(1/βth≂100 ns). This leads to an indirect hole-electron competition mechanism and helps to explain experimental results. This coupling gain reduction is inherent to the nature of the Fe dopant in InP for wavelengths below 1.2 μm and temperature above 170 K.
High intensity electron channeling and perspectives for a bright tunable x-ray source
Authors: Genz H. , Gräf H.-D. , Hoffmann P. , Lotz W. , Nething U. , Richter A. , Kohl H. , Weickenmeier A. , Knüpfer W. , Sellschop J. P. F.
Published: July 2002

Using the continuous wave electron beam of the new Darmstadt superconducting electron accelerator and high intensity axial channeling in a diamond crystal, the possibility for the production of an intense tunable photon source in the x-ray region is investigated. Due to low emittance of the machine and its high current it has become possible, for the first time, to produce channeling radiation in the energy region of a few keV with an intensity of up to 2×1010 photons/s in an x-ray energy window of 10%. This is six orders of magnitude more than what has been observed previously.
High-power operation of buried-heterostructure strained-layer InGaAs/GaAs single quantum well lasers
Authors: Chen T. R. , Eng L. E. , Zhuang Y. H. , Xu Y. J. , Zaren H. , Yariv A.
Published: July 2002

Very high power levels (330 mW) were obtained from single waveguide, single quantum well InGaAs/GaAs lasers. The lasers are shown to possess superior current threshold, temperature and optical damage characteristics.
Application of organometallic chemical vapor deposition mechanisms to lateral band-gap patterning on stepped surfaces
Authors: Colas E. , Clausen E. M. , Kapon E. , Hwang D. M. , Simhony S.
Published: July 2002

We report the study of organometallic chemical vapor deposition (OMCVD) on the stepped surfaces obtained by crystal growth on nonplanar vicinal (100) GaAs substrates. Scanning and transmission electron microscopy investigations were combined to identify two distinct diffusion mechanisms in OMCVD: one mechanism involves the gas phase and allows us to selectively distribute the incoming flux of volatile reactants between two adjacent facets; the other one involves surface diffusion of nonvolatile species over distances in the hundred nm range. Spectrally and spatially resolved cathodoluminescence imaging of the light emissions from a single quantum well structure gives direct evidence that the quantum well thickness variations, which can be controlled over a wide range (up to 1:5) by growth parameters, produce effective band-gap variations.
Superconducting thin-film flux transformers of YBa2Cu3O7−x
Authors: Wellstood F. C. , Kingston J. J. , Ferrari M. J. , Clarke J.
Published: July 2002

Using a three-layer YBa2Cu3O7−x-SrTiO3-YBa2Cu3O7−x in situ laser deposition process, we have constructed thin-film flux transformers which have pickup loops 10 mm on a side and input coils with ten turns. Each layer was patterned with a shadow mask or photolithography. The flux transformers were inductively coupled to a dc superconducting quantum interference device (SQUID) at 4.2 K to determine their transition temperature, and the temperature dependence of their critical current and coupling efficiency. The best flux transformer had a transition temperature of 77 K, and enhanced the magnetic field response of the SQUID by a factor of 9.5.
5 W GaAs/GaAlAs laser diodes with a reactive ion etched facet
Authors: Ou S. S. , Yang J. J. , Jansen M.
Published: July 2002

GaAs/GaAlAs laser diodes with reactive ion etched facets have been demonstrated for the first time with high output powers (5 W from 100-μm-wide apertures), high output power density (15 MW/cm2), and high slope efficiencies (66%) in junction-up configuration under quasi-cw operation. Mirror etching was performed in a pure SiCl4 gas environment by maintaining a low background pressure and gas pressure. High quality etched facets have been achieved with almost no scattering loss.
Fluorination of diamond (100) by atomic and molecular beams
Authors: Freedman Andrew , Stinespring Charter D.
Published: July 2002

Diamond (100) substrates have been fluorinated under ultrahigh vacuum conditions with both atomic and molecular fluorine. X-ray photoelectron spectra of the resulting samples indicate that atomic fluorine, F, reacts efficiently at 300 K producing a saturation coverage of about three quarters of a monolayer (one monolayer ≂1.6×1015 cm−2) after 40 monolayers exposure. The carbon fluoride adlayer is thermally stable to 700 K but slowly desorbs at temperatures above this. In contrast, molecular fluorine, F2, reacts quite slowly; a saturation coverage of less than one fifth of a monolayer is achieved after several hundred monolayer exposure to F2 at temperatures from 300 to 700 K. Diamond surfaces saturated with fluorine atoms showed no loss of fluorine after sequential exposure to beams of H2 and O2 at temperatures between 300 and 700 K.
Phase decomposition and structural defects in a Y-Ba-Cu-O superconductor
Authors: Ramesh R. , Jin S. , Nakahara S. , Tiefel T. H.
Published: July 2002

Phase decomposition of a bulk Y2Ba4Cu8O16 superconductor has been studied. The microstructure of the sample is heavily faulted and contains many stacking defects, including a new ‘‘125’’ structure. It is likely that these fine-scale (10–30 Å thick) stacking defects are responsible for the significantly improved flux pinning in the phase-decomposed sample. It is proposed that the decomposition process begins with the reaction ‘‘248’’ 0><fv/0 ‘‘123’’+‘‘125’’, which could possibly occur by a spontaneous, short-range diffusion reaction. Further decomposition involves gradual removal of the extra CuO chains by long-range diffusion to produce a mixture of ‘‘123’’+CuO.
New substrate PrGaO3 for a high T
c superconducting YBa2Cu3Ox epitaxial film
Authors: Sasaura Masahiro , Mukaida Masashi , Miyazawa Shintaro
Published: July 2002

The potential of a new substrate, PrGaO3, for high Tc oxide superconducting films is investigated and results indicate it is the most suitable material studied so far. Single crystals were grown by the Czochralski method. The lattice mismatch between PrGaO3 and YBa2Cu3Ox superconductor was estimated to be only 0.02% at the elevated deposition temperature. The dielectric constant value was 24 at 10 kHz. The c-axis oriented YBa2Cu3Ox films were deposited onto PrGaO3 substrates by the laser ablation technique. Their superconducting transition temperature was as high as 90 K, even for a film thickness of only 500 Å.
Evaluation of LiB3O5 for second-harmonic generation of femtosecond optical pulses
Authors: Pelouch W. S. , Ukachi T. , Wachman E. S. , Tang C. L.
Published: July 2002

The optical characteristics of the new nonlinear crystal lithium triborate (LiB3O5) are evaluated for second-harmonic generation (SHG) in the femtosecond regime. Using crystals grown in our laboratory, we demonstrate the use of LiB3O5 for autocorrelation measurements of ultrashort optical pulses. We find that pulse widths down to 40 fs can be measured accurately with crystal thicknesses varying from 0.195 to 4.165 mm. The effect of crystal length on the autocorrelation shape is also investigated.
Formation of low dislocation density silicon-on-insulator by a single implantation and annealing
Authors: EL-Ghor M. K. , Pennycook S. J. , Namavar F. , Karam N. H.
Published: July 2002

High quality silicon-on-insulator structures have been formed with dislocation densities in the top silicon layer below 104 cm−2 by oxygen implantation and one-step annealing at 1300 °C for 6 h. Careful control of the implantation conditions is required in order to produce a high density of cavities in the top silicon layer. These cavities provide a stress-free sink for silicon and oxygen interstitials, reducing the point-defect supersaturations and, therefore, the nucleation and growth of oxide precipitates and dislocation loops. They also provide an internal surface which blocks free propagation of dislocation loops to the surface avoiding the formation of threading dislocations. With continued annealing, both the cavities and the oxide precipitates eventually dissolve, leaving a high quality silicon surface layer with a very low dislocation density.
Anisotropic transport and cation disorder in superconducting Tl2Ca2Ba2Cu3Ox single crystals
Authors: Tigges C. P. , Venturini E. L. , Kwak J. F. , Morosin B. , Baughman R. J. , Ginley D. S.
Published: July 2002

We have measured for the first time the temperature-dependent anisotropic resistivity of several Tl2Ca2Ba2Cu3Ox single crystals. The resistivity ratio between the c axis and the a-b plane orientations in the best crystals is approximately 60 at room temperature. Resistivity data indicate substantial differences in both Tc and the transition width of nominal Tl2Ca2Ba2Cu3Ox plates grown from two different melt compositions. A Tl-O and CuO-rich flux yielded approximately stoichiometric plates with sharp transitions beginning near 113 K, while a Tl-O-rich flux produced plates containing more Tl and less Ba with broad transitions starting near 103 K. These data demonstrate the extreme sensitivity of the superconductivity to cation site disorder in the Tl-Ca-Ba-Cu-O system.
Optical technique for the measurement of turbulent spectra using the photorefractive properties of BaTiO3
Authors: Albrecht G. F. , Robey H. F. , Moore T. R.
Published: July 2002

An optical technique for obtaining two-dimensional spectra of turbulent flows is presented. A coherent beam is passed through a turbulent flow and acquires phase perturbations which are related to the density field of the flow. This phase-modulated beam is focused to obtain the Fourier transform of the incoherent, fluctuating portion of the field. The coherent portion of the field is removed by exploiting the photorefractive properties of BaTiO3 as a temporal filter. The technique is an improvement over existing methods in that it is nonintrusive, has a wide dynamic range, and requires no assumption of isotropy of the turbulence.
Ge on Bi2Sr2−xCa1+xCu2O8+y: Reduced reactivity through cluster assembly
Authors: Ohno T. R. , Yang Y.-N. , Weaver J. H. , Kimachi Y. , Hidaka Y.
Published: July 2002

Photoemission studies of low-temperature deposition of ∼30-Å-diam Ge clusters on single-crystal Bi2 Sr2−x Ca1+x Cu2 O8+y (100) show that an interface is produced with no evidence of substrate disruption. Analysis of the superconductor core level emission as a function of coverage indicates uniform overlayer growth and complete surface coverage. These cluster-assembled interfaces were stable when warmed to 300 K, with only a slight reduction of Cu 2p3/2 satellite emission characteristic of the superconductor. In contrast, conventional atom-by-atom Ge deposition produces a Ge oxide layer and surface disruption.
Laser surface seeding for via plug filling
Authors: Zhu N. , Cacouris T. , Scarmozzino R. , Osgood R. M.
Published: July 2002

In this letter we report on a novel technique for metallizing contact holes and via plugs which is based on laser-surface-seeded selective chemical vapor deposition (LSS/CVD) of aluminum from dimethylaluminum-hydride (DMAlH). In this metallization process, a laser is used to photolytically deposit a thin layer of metal, which provides a seed layer for subsequent selective CVD. In this work we apply the LSS/CVD technique to via hole filling, and demonstrate that small-diameter (0.7 μm), high-aspect-ratio (3:1) aluminum plugs can be formed without the incorporation of voids. The morphology of the plug metal is very good, and the resistivity of aluminum deposited with this technique can be as low as twice that of the bulk metal.
Poling of polymeric thin films at ambient temperatures for second-harmonic generation
Authors: Barry Stephen E. , Soane David S.
Published: July 2002

Carbon dioxide is used in induce glass transition in amorphous polymer films, allowing efficient alignment of chromophores with an applied electric field. The noncentrosymmetric films thus produced are capable of second-harmonic generation. This method has advantages over previously investigated poling schemes, including poling at ambient temperatures and use of high glass transition temperature polymers.
High powers and subpicosecond pulses from an external-cavity surface-emitting InGaAs/InP multiple quantum well laser
Authors: Jiang W. B. , Friberg S. R. , Iwamura H. , Yamamoto Y.
Published: July 2002

We demonstrate that surface-emitting lasers operating in an external cavity can produce high average powers, high peak powers, and ultrashort pulses. By optical pumping of InGaAs/InP multiple quantum well samples in an external cavity, we generated 190 mW both in continuous and mode-locked operation at 1.5 μm. Synchronous pumping at 100 MHz yielded 7.7 ps pulses with 15 mW average power. These were shortened to 1. 1 ps pulses with 64 W peak power by chirp compensation using diffraction gratings, and to 710 fs by negative group-velocity dispersion in an optical fiber.
Wavelength-agile operation of an injection-controlled XeF(C→A) laser system
Authors: Hofmann Th. , Yamaguchi S. , Dane C. B. , Wilson W. L. , Sauerbrey R. , Tittel F. K. , Rubino R. A. , Nighan W. L.
Published: July 2002

The performance of a pulsed laser system consisting of an electron beam pumped XeF(C→A) amplifier injection-controlled by a wavelength-agile dye laser is reported. Random sequence tuning over a 27 nm spectral region, centered at 478.5 nm, was demonstrated at a 1 Hz pulse repetition frequency. Laser output energies of 0.8 J with pulse durations of 10 ns were measured.
Secondary electron emission spectroscopy: A sensitive and novel method for the characterization of the near-surface region of diamond and diamond films
Authors: Hoffman Alon , Prawer Steven , Folman Mordechai
Published: July 2002

Secondary electron emission (SEE) spectroscopy has been employed in the characterization of different carbon allotropes and distinctive signatures were observed for diamond, graphite, and amorphous carbon. Via an examination of the SEE spectrum of Ar+ (1 keV) irradiated diamond surfaces, this spectroscopy is shown to be very sensitive to crystalline perfection. It is also shown that SEE spectroscopy can be used as a very effective and sensitive tool for the characterization of the near-surface region of diamond thin films.
Enhanced flux creep in Nb-Ti superconductors after an increase in temperature
Authors: Cross R. W. , Goldfarb R. B.
Published: July 2002

The magnetic fields of Superconducting Super Collider (SSC) dipole magnets change with time when the magnets are operated at constant current. The decay of the field is thought to be a consequence of flux creep in the Nb-Ti filaments in the superconducting cables. However, measured magnetic relaxation of small samples of SSC cable as a function of time is unlike the large decays that are observed in the fields of the actual magnets. We have made relaxation measurements on sample SSC conductors at 3.5 and 4.0 K after field cycling. The decay at both temperatures was 2.8% in 50 min. However, the relaxation measured after a temperature increase from 3.5 to 4.0 K was 4.8% in 50 min. A likely reason for the greater magnetization decay is that, after an increase in temperature, the Nb-Ti is in a supercritical state, with shielding currents flowing at a density greater than the new critical current density. This causes enhanced flux creep. We suggest that a small temperature rise during the operation of SSC magnets may contribute to the unexpectedly large magnetic field decay.
Noninteracting beams of ballistic two-dimensional electrons
Authors: Spector J. , Stormer H. L. , Baldwin K. W. , Pfeiffer L. N. , West K. W.
Published: July 2002

We demonstrate that two beams of two-dimensional ballistic electrons in a GaAs-AlGaAs heterostructure can penetrate each other with negligible mutual interaction analogous to the penetration of two optical beams. This allows electrical signal channels to intersect in the same plane with negligible crosstalk between the channels.
Microwave properties of EuBa2Cu3O7−x thin films on MgO
Authors: Asano Hidefumi , Satoh Makoto , Konaka Tsuneo
Published: July 2002

We have measured the microwave surface resistance of sputtered EuBa2Cu3O7−x superconducting films on MgO in a gold-plated Invar host cavity at 50 GHz. Low surface resistance of 2 mΩ was achieved even at 77 K and 50 GHz for highly c-axis oriented films with good in-plane epitaxy together with a Tc of 93 K and a Jc of 1.4×106 A/cm2 at 90 K. This surface resistance value is slightly lower than that for a classical superconductor of Nb at the same frequency at the same reduced temperature (T/Tc) of 7.7 K.
Fabrication and characterization of deep mesa etched ‘‘anti’’-dot superlattices in GaAs-AlGaAs heterostructures
Authors: Weiss D. , Grambow P. , von Klitzing K. , Menschig A. , Weimann G.
Published: July 2002

By etching a periodic array of holes through a ;mobility two-dimensional electron gas we define high-a lateral, ‘‘anti’’-dot-type superlattice with periods a=200 and a=300 nm, much smaller than the electron mean free path in the unpatterned material. The devices are fabricated using electron beam lithography and reactive ion etching techniques, and characterized by magnetotransport experiments. Commensurability effects and the observed quenching of the Hall effect indicate that the electron gas between the etched holes essentially maintains its initial high electron mobility.
Room-temperature exciton luminescence in II-VI quantum wells
Authors: Stanley R. P. , Hawdon B. J. , Hegarty J. , Feldman R. D. , Austin R. F.
Published: July 2002

We observe free excitons in absorption and emission at room temperature in Cd0.25Zn0.75Te/ZnTe multiple quantum wells. A large overlap between luminescence and absorption peaks observed at 10 K is maintained up to room temperature showing that the luminescence is predominantly excitonic. From a rate equation analysis we calculate the branching ratio for free carriers relaxing into excitons to free-carrier radiative recombination.
Evolution of spectrally discriminated spatial uniformity of line-shaped plasmas
Authors: Wang Xiao-fang , Xu Zhi-zhan , Chen Shi-sheng , Qian Ai-di , Fan Pin-zhong , Zhang Zheng-quan , Lin Li-huang , Feng Xian-ping , Gong Mei-xia , Shan Bing , Gao Sheng-chen
Published: July 2002

A space-resolved soft x-ray (SXR) transmission grating spectrometer and a SXR streak camera are used to investigate the evolution of spectrally discriminated spatial uniformity of line-shaped plasmas produced by uniform laser illumination in line focus. It is found that the spatial nonuniformity of SXR emissions and ion turbulence occur during optical laser’s heating. Various instabilities can be excited due to the long scale length in line-shaped plasmas to produce the phenomenon.
Low-power, all-optical nonlinear absorption in asymmetric double quantum wells
Authors: Dawson P. , Galbraith I. , Kucharska A. I. , Foxon C. T.
Published: July 2002

We demonstrate all-optical nonlinearities at low cw pump powers (50 W/cm2) using a novel heterostructure design which spatially separates photoexcited electron-hole pairs. Theoretical calculations based on many-body interactions are in good agreement with the measured spectra.
Dependence of the magnetization in YBa2Cu3O7−x thin films on the applied magnetic field direction
Authors: Teshima H. , Oishi A. , Izumi H. , Ohata K. , Morishita T. , Tanaka S.
Published: July 2002

The dependence of the magnetization on the applied magnetic field direction was investigated at 5 K on superconducting thin films of YBa2Cu3O7−x prepared by ArF laser ablation with the c axis perpendicular to the film plane. The difference of the magnetic moment between the increasing and decreasing branches of the hysteresis curves at zero field depends on the angle θ between the film normal and the magnetic field as ‖cos θ‖. This result can be attributed to the magnetic moment perpendicular to the film plane.