bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of mechanism to control electrical properties of AlAs grown using amine-alane with metalorganic molecular-beam epitaxy
Authors: Miyakoshi Kaoru , Suemune Ikuo
Published: July 2002

A mechanism to control electrical properties of AlAs films grown by metalorganic molecular-beam epitaxy using trimethylamine-alane (TMAAl) and tris-dimethylamino-arsenic was studied. Electrical properties of AlAs showed a critical dependence on the V/III supply ratio of the precursors. Quadrupole mass spectrometric studies suggested that the main factor to control the electrical properties is the decomposition of trimethylamine in TMAAl on Al surfaces, which is normally stable and does not decompose on GaAs surfaces.
Exciton radiative lifetime in GaAs quantum wires grown by metalorganic chemical-vapor selective growth
Authors: Kono T. , Tsukamoto S. , Nagamune Y. , Sogawa F. , Nishioka M. , Arakawa Y.
Published: July 2002

We discuss measurement results of the exciton radiative lifetime in GaAs quantum wires grown by metalorganic chemical-vapor selective growth technique at 9 K. By changing the lateral width of the quantum wires in the range of 7–35 nm systematically, the lateral width dependence of the radiative exciton lifetime was measured. The results show that the measured lifetime increases from 260 to 422 ps with the decrease of the lateral width from 25 to 7 nm. This increase of the radiative lifetime can be explained by taking account of both reduced exciton coherence length and spreading of the wave function of electrons in the barrier region.
Optimum strain for the suppression of Auger recombination effects in compressively strained InGaAs/InGaAsP quantum well lasers
Authors: Lui Wayne W. , Yamanaka Takayuki , Yoshikuni Yuzo , Seki Shunji , Yokoyama Kiyoyuki
Published: July 2002

The primary mechanism that leads to the suppression of Auger recombination effects in compressively strained quantum wells is found due to the existence and the appropriate positioning of negative-curvature zones in the first valence subbands (zones in k space where the radial curvature of the first valence subband is negative). By studying previous Monte Carlo calculation results, strong correlations between the negative-curvature zones and its adverse effects on Auger recombinations are observed, thereby confirming this finding. Through this understanding, it is inferred that compressive strain is most effective for reduction of Auger recombination effects when the amount of strain is no more than 1.0%. Beyond 1.0%, the gain in device performance with respect to more compressive strain is expected to be greatly diminished.
Formation of cylindrical n/p junction diodes by arsenic enhanced diffusion along interfacial misfit dislocations in p-type epitaxial Si/Si(Ge)
Authors: Braga N. , Buczkowski A. , Kirk H. R. , Rozgonyi G. A.
Published: July 2002

Arsenic enhanced diffusion along individual misfit dislocations in Si/Si(Ge) heterostructures has been detected and imaged using scanning electron microscopy (SEM) and in the electron beam induced current (EBIC) mode. The formation of buried cylindrical, or conical, diodes surrounding misfit dislocations has been observed. The diffusion enhancement is not uniform for each dislocation. EBIC/SEM micrographs reveal a dark recombination contrast in the vicinity of the dislocation core and a white generation signal within the space-charge region of the surrounding n/p diode. Based on an experimental isoconcentration etching profile and a simple model for enhanced diffusion, the dislocation diffusion coefficient for arsenic is estimated to be up to six orders of magnitude higher than that in the host crystal.
Comparison of transport, recombination, and interfacial quality in molecular beam epitaxy and organometallic vapor-phase epitaxy GaAs/AlxGa1−xAs structures
Authors: Wolford D. J. , Gilliland G. D. , Kuech T. F. , Klem J. F. , Hjalmarson H. P. , Bradley J. A. , Tsang C. F. , Martinsen J.
Published: July 2002

We have studied free-carrier recombination and transport in GaAs structures prepared by different epitaxial growth techniques and with different ‘‘surface barriers’’ including molecular beam epitaxy (MBE) and organometallic vapor-phase epitaxy (OMVPE) prepared undoped, symmetric GaAs/Al0.3Ga0.7As double heterostructures and these same structures after etch removing the top Al0.3Ga0.7As layer and repassivating with Na2S. We find 300-K lifetimes of ≥2.5 μs (350 ns), and interface recombination velocities of 40 cm/s (250 cm/s) for our OMVPE (MBE) structures. Identical measurements for Na2S and bare surfaces yield interface recombination velocities of 5500 cm/s and 34 000 cm/s, respectively. Free-carrier transport in both types of structures is diffusive with hole mobilities of ∼350 cm2/V s.
Generation of dense, pulsed beams of refractory metal atoms using two-stage laser ablation
Authors: Kadar-Kallen Michael A. , Bonin Keith D.
Published: July 2002

We report a technique for generating a dense, pulsed beam of refractory metal atoms using two-stage laser ablation. An atomic beam of uranium was produced with a peak, ground-state number density of 1×1012 cm−3 at a distance of z=27 cm from the source. This density can be scaled as 1/z3 to estimate the density at other distances which are also far from the source.
Strained In0.40Al0.60As window layers for indium phosphide solar cells
Authors: Jain R. K. , Landis G. A. , Wilt D. M. , Flood D. J.
Published: July 2002

The efficiency of indium phosphide solar cells might be improved by a wide-band-gap window layer. In this work we calculate the performance of InP solar cells with a strained (pseudomorphic) In0.40Al0.60As window layer. Calculations show that the efficiencies of baseline and optimized p+n cells are increased to more than 22% and 24% (AM0, 25 °C), respectively, for In0.40Al0.60As window layer of 10 nm thickness. Comparatively little improvement is found for n+p cells.
Growth of β-FeSi2 on Si(111) by chemical beam epitaxy
Authors: Natoli J. Y. , Berbezier I. , Derrien J.
Published: July 2002

The growth of high quality semiconducting β-FeSi2 layers on silicon substrates is rather difficult due to a large lattice mismatch [up to ∼5.5% on Si(111)] and very different crystallographic structure (orthorhombic structure on top of the diamond one). We report on a new method using the chemical beam epitaxy (CBE) technique to stabilize at first the tetragonal α-FeSi2 phase (lattice mismatch ∼0.8% on Si(111)) at ∼550 °C. Then a post-annealing up to ∼650 °C induces a phase transition from the α to β phase via a tremendous coalescence of numerous small metallic α grains (∼200 Å width) into large semiconducting β-grains (≤1 μm width) of high quality, suitable for Si integrated optoelectronic technology.
Preparation of epitaxial TlBa2Ca2Cu3O9 high T
c thin films on LaAlO3 (100) substrates
Authors: Piehler A. , Reschauer N. , Spreitzer U. , Ströbel J. P. , Schönberger R. , Renk K. F. , Saemann-Ischenko G.
Published: July 2002

Epitaxial TlBa2Ca2Cu3O9 high Tc thin films were prepared on LaAlO3 (100) substrates by a combination of laser ablation and thermal evaporation of thallium oxide. X-ray diffraction patterns of θ-2θ scans showed that the films consisted of highly c axis oriented TlBa2Ca2Cu3O9. φ scan measurements revealed an epitaxial growth of the TlBa2Ca2Cu3O9 thin films on the LaAlO3 (100) substrates. Ac inductive measurements indicated the onset of superconductivity at 110 K. At 6 K, the critical current density was 4×106 A/cm2 in zero magnetic field and 6×105 A/cm2 at a magnetic field of 3 T parallel to the c axis.
Fast two-dimensional self-consistent kinetic modeling of low-pressure inductively coupled RF discharges
Authors: Kortshagen U. , Tsendin L. D.
Published: July 2002

In this letter a two-dimensional self-consistent model for an inductively coupled RF plasma is presented. The model is based on the spatially resolved determination of the electron distribution function (EDF) via solution of a kinetic equation in the nonlocal approach. The static space charge potential is computed from a 2D fluid model, the RF electric field profile is calculated from the wave equation. The model can easily be treated on usual personal computers with computation times of about one hour. The theoretical results are compared to measurements presented in a previous publication [U. Kortshagen, I. Pukropski, and M. Zethoff, J. Appl. Phys. 76, 2048 (1994)].
New lead-free, Sn-Ag-Zn-Cu solder alloy with improved mechanical properties
Authors: McCormack M. , Kammlott G. W. , Chen H. S. , Jin S.
Published: July 2002

A new, lead-free solder alloy based on Sn-3.5%Ag-1%Zn-0.5%Cu is described. The alloy exhibits mechanical properties superior to those in both the Sn-3.5%Ag binary and Sn-3.5%Ag-1%Zn ternary eutectic solder alloys. The addition of small amounts of Cu, at less than 1% levels, is found to refine the effective grain size while retaining the uniform distribution of Ag3Sn precipitates in the solidification microstructure, thus significantly improving the ductility. The addition of excess amounts of Cu or Zn beyond about 1% levels is not desirable as it causes precipitation of additional intermetallic phases that depletes the finely dispersed precipitates in the surrounding matrix and induces nonuniformities in the microstructure that consequently deteriorate the mechanical properties.
In situ microwave reflectivity measurements of the changes in surface recombination of crystalline silicon induced by the exposure to silane, silane/helium, and helium plasmas
Authors: Neitzert H. C. , Layadi N. , Cabarrocas P. Roca i , Vanderhaghen R.
Published: July 2002

Measurements of the transient photoconductivity detected via the change in microwave reflection after laser pulse illumination have been performed during the exposure of crystalline silicon substrates to a pure silane, silane/helium, and pure helium plasma. In all cases, a similar increase of the surface recombination rate is detected immediately after plasma start. While the surface recombination remains high in the case of the pure helium plasma, a decrease of the interface recombination is observed for the pure silane and silane/helium plasma, related to the deposition of hydrogenated amorphous silicon.
Magnesium doping of InGaAlP grown by low-pressure metalorganic chemical vapor deposition
Authors: Wu Chang-Cherng , Chang Chun-Yen , Chen Po-An , Chen Horng-Dar , Lin Kun-Chuan , Chan Shih-Hsiung
Published: July 2002

Bis(cyclopentadienyl) magnesium, CP2Mg, was used as a magnesium dopant in the InGaAlP layers by low-pressure metalorganic chemical vapor deposition. The hazy surface morphology of heavily doped InGaAlP layers is significantly improved by using magnesium dopant instead of the conventional zinc dopant. We demonstrate that the effective doping efficiency of magnesium is two orders of magnitude higher than that of zinc dopant in the heavily doped InGaAlP layer grown at 720 °C.
Elastic misfit stress relaxation in highly strained InGaAs/GaAs structures
Authors: Androussi Y. , Lefebvre A. , Courboulès B. , Grandjean N. , Massies J. , Bouhacina T. , Aimé J. P.
Published: July 2002

The strain contrasts associated with three-dimensional coherently strained islands formed during the epitaxial growth of highly strained In0.45Ga0.55As layers on GaAs (001) have been studied by transmission electron microscopy. It is demonstrated that the comparison of these experimental strain contrasts with simulated profiles makes it possible to assess the elastic relaxation of the islands.
Ion channeling studies on epitaxially grown a-axis YBa2Cu3O7−δ films
Authors: Ito W. , Yoshida Y. , Mahajan S. , Morishita T. , Kumagai M. , Yabuta K.
Published: July 2002

The crystal structure of a-axis oriented YBa2Cu3Ox (YBCO) films epitaxially grown on SrTiO3 (100) was investigated by ion channeling measurement. The lattice constant in the film plane was determined from the channeling angle through [110]/[103] angular scan measurements and a-axis lattice constant measured by the x-ray diffraction technique. The lattice constants of the a axis decreased with increasing film thickness, while the obtained lattice constants in the film plane revealed the close values to the lattice constant of the SrTiO3 substrate (3.905 Å). The relaxation of film strain was evaluated from the χ values estimated from [110]/[103] ion channeling. The χ values increased from 16.7% to 26.4% with increasing film thickness from 500 to 3500 Å. The effect of the strain relaxation on the superconductivity was confirmed for a-axis oriented YBCO films.
Stress relaxation in plasma deposited tungsten nitride/tungsten bilayer
Authors: Lee Chang Woo , Kim Yong Tae
Published: July 2002

The evolution of tensile to compressive stress has been found in plasma enhanced chemical vapor deposited W thin films incorporated with N atoms. The magnitude of stress varies from 6.25×109 to −7.79×109 dyne/cm2, corresponding to an increase of N atoms. In order to reduce the high tensile stress of a W film, W67N33 is interposed between W and Si. As a result, the stress of the W67N33/W bilayer relaxes from 7.98×109 to 3.41×109 dyne/cm2 after annealing at 900 °C for 30 min, which is ascribed to the interfacial pseudodiffusion layer formed at the interface of W and W67N33.
Aerosol-assisted chemical vapor deposition of copper: A liquid delivery approach to metal thin films
Authors: Roger Christophe , Corbitt Thomas S. , Hampden-Smith Mark J. , Kodas Toivo T.
Published: July 2002

Aerosol-assisted chemical vapor deposition has been used to attain high deposition rates (up to 800 Å min−1 at 140 °C) of crystalline, low-resistivity (1.7–3.5 μΩ cm) Cu films at low temperatures (120–200 °C) from toluene solutions of (hfac)Cu(1,5-COD), where 1,5-COD=1,5-cyclooctadiene, in a warm-wall reactor. Activation energies calculated from the deposition rate as a function of the preheating temperatures and the substrate temperature (varying also the nozzle-substrate distance) were 6.8, 8.9 (0.7 cm), and 9.1 (1.7 cm) kcal mol−1, respectively. The activation energy of 6.8 kcal mol−1 is similar to the enthalpy of vaporization of (hfac)Cu(1,5-COD).
Sweep-out times of electrons and holes in an InGaAs/GaAs multiple quantum well modulator
Authors: Yang Ching-Mei , Mahgerefteh Daniel , Garmire E. , Chen Li , Hu Kezhong , Madhukar A.
Published: July 2002

The switch-on and switch-off times of a p-i-n diode containing In0.13Ga0.87As/GaAs multiple quantum wells in the i region have been characterized by a time-resolved pump/probe technique. We observe bias-insensitive switch-on times and dramatically increasing switch-off times with decreasing bias. We use a simple model invoking the cross-well motion of holes as well as electrons to explain the experimental result. The effective drift velocities of both electrons and holes across the multiple quantum wells at different bias voltages are deduced from this model.
AlxGa1−xAs/GaAs quantum well structures grown by metalorganic molecular beam epitaxy using dimethylethylamine alane
Authors: Courboulès B. , Deparis C. , Massies J. , Leroux M. , Grattepain C.
Published: July 2002

Dimethylethylamine alane (DMEAA) has been used as an Al precursor for the growth of AlGaAs alloys and AlGaAs/GaAs quantum wells by metalorganic molecular beam epitaxy (MOMBE). It is shown that DMEAA is a very convenient source in terms of in situ calibration of growth rates and alloy composition by reflection high-energy electron diffraction. As indicated by secondary ion mass spectroscopy, low residual O and C impurity content is obtained by using this source. GaAs quantum well structures have been characterized by photoluminescence spectroscopy and compared to equivalent structures grown by standard solid-source molecular beam epitaxy. They are also compared with the results recently reported in the literature for analogous structures grown by MOMBE using alternate aluminum sources.
Atomic force microscope integrated with a scanning electron microscope for tip fabrication
Authors: Walters D. A. , Hampton D. , Drake B. , Hansma H. G. , Hansma P. K.
Published: July 2002

In a new combined atomic force microscope/scanning electron microscope, we have been able to fabricate and test electron-beam-deposited tips (e-beam tips). With this instrument it was possible to test newly grown e-beam tips within a few minutes of their formation, without ever breaking vacuum. Typical results on oxide-sharpened conventional tips showed that the radius of curvature could be reduced by a factor of 2.5 with the e-beam tips.
Electric field measurements in discharges by 2+1 photon laser Stark spectroscopy of atomic hydrogen
Authors: Booth J. P. , Fadlallah M. , Derouard J. , Sadeghi N.
Published: July 2002

We have developed a new method for measuring electric field magnitude using 2+1 photon laser-induced fluorescence of ground-state hydrogen atoms. The atoms are excited to the n=2 level by two 243-nm photons, then further excited to the n=6 level by one photon at 410 nm and detected by cascaded Hα fluorescence. The electric field magnitude is deduced from the Stark splitting of the n=6 level. The method was calibrated using H atoms from a distant source flowing through a region of known electric field. Results are presented for field profiles in dc discharges in 0.3 and 1 Torr pure H2.
Grain alignment in bulk YBa2Cu3Ox superconductor by a low temperature phase transformation method
Authors: Selvamanickam V. , Goyal A. , Kroeger D. M.
Published: July 2002

A quench and directional phase transformation process has been developed to achieve grain alignment in bulk YBa2Cu3Ox superconductors at temperatures about 100 °C below the peritectic temperature. Isothermal phase transformation of quenched precursors at 890 °C for 3 min is found to result in the formation of more than 75% of YBa2Cu3Ox phase without any formation of Y2BaCuO5. Phase transformation at higher temperatures leads to rapid formation of Y2BaCuO5 in addition to YBa2Cu3Ox. A well-aligned microstructure is achieved by directional phase transformation of the quenched compacts as a rate of 10 mm/h. The magnetic field dependence of the critical current density at 77 K of the directionally phase transformed material compares well with that of melt-textured YBCO and is superior to that of magnetically aligned and sintered YBCO.
Embrittlement of [001] twist grain boundaries induced by Bi segregation
Authors: Miura Hiromi , Nakata Hiroshi , Sakai Taku , Kato Masaharu , Mori T.
Published: July 2002

Cu bicrystals with various [001] twist boundaries doped with Bi were tensile tested at several temperatures. The fracture behavior depended strongly on misorientation angle and testing temperature. As the testing temperature increases, the difference in degree of embrittlement among different grain boundaries became more significant. Grain boundaries with higher energy are more brittle and fracture more easily with lower tensile stresses.
Lowering of the conduction threshold by carbon fiber formation in KrF excimer laser irradiated polyimide
Authors: Ball Z. , Sauerbrey R.
Published: July 2002

Lowering of the conduction threshold by carbon fiber growth on polyimide films is reported. The fiber growth takes place when samples are irradiated with KrF excimer laser pulses at fluences above the carbonization threshold of 20 mJ/cm2 when the sample is placed in a dc electric field of 600 V/cm.
Surface cleaning of GaAs by in situ chemical beam etching
Authors: Chiu T. H. , Tsang W. T. , Williams M. D. , Mendonça C. A. C. , Dreyer K. , Storz F. G.
Published: July 2002

Chemical beam etching using AsCl3 has been shown to provide accurate etch rate control at the atomic level, mask feature transfer at submicron scale, and a clean damage-free surface for regrowth. The etching process can be maintained in a two-dimensional fashion, if the etching conditions are designed to enable efficient cation diffusion that smooths the microroughness. In this work, we show from etching the heavily Be-doped GaAs surface that the in situ etching prior to growth is potentially a useful method for etch cleaning the surface. However, the effectiveness of this method depends on the ability to form volatile species with the contaminant in competition with the formation of group III chloride.
Coexistence of grains with differing orthorhombicity in high quality YBa2Cu3O7−δ thin films
Authors: de Obaldia E. I. , Ludwig K. F. , Berkowitz S. J. , Clark A. M. , Skocpol W. J. , Mankiewich P. M. , Rudman D. A. , Roshko A. , Moerman R. , Vale L. , Ono R. H.
Published: July 2002

High quality films of YBa2Cu3O7−δ on LaAlO3 have been grown by pulsed-laser deposition at oxygen pressures of 3.4–54 Pa (25–400 mTorr). X-ray diffraction reveals the coexistence of grains that align with the substrate axes (axial grains) and grains that are rotated by 0.4° from the substrate axes (diagonal grains). The axial grains are tetragonal while the diagonal grains achieve lattice parameters close to bulk YBa2Cu3O7. The relative proportion of axial grains accounts for the measured variations of normal-state conductance and superconducting critical current density from film to film, based on a simple two-dimensional model of randomly positioned, insulating axial grains.
Influence of heat treatment on the structure and magnetic properties of sputtered BaCoTiFe10O19 films
Authors: Gu B. X. , Zhang H. Y. , Zhai H. R. , Lu M. , Zhang S. Y. , Maio Y. Z.
Published: July 2002

BaCoTiFe10O19 films were prepared by sputtering. The as-sputtered films are amorphus and have a magnetization of 5 emu/cm3 and a coercivity of 700 Oe at room temperature. Compared with bulk BaCoTiFe10O19 hexaferrites, the magnetization is much smaller, but the coercivity is higher. After annealing at about 750 °C in an oxygen atmosphere, the films crystallize into an M-type hexagonal ferrite with a preferred orientation of the (110) plane being parallel to the film surface. The magnetization increases rapidly to 320 emu/cm3, but the coercivity decreases to 100 Oe. The amorphous samples with a large amount of Fe3+ ions show no ferromagnetic magnetic resonance spectra. After crystallization a well-defined ferromagnetic resonance spectrum occurs.
Dynamic Wannier–Stark effect in semiconductor superlattices
Authors: Khurgin J. B. , Lee S. J. , Lawandy N. M.
Published: July 2002

A novel effect, consisting of optically induced effective mass change due to the change in the degree of localization in the semiconductor superlattices is theoretically investigated. Possible application as a nonabsorbing differential light detector/switch is considered.
Ion-implantation induced interdiffusion in CdTe/CdMgTe quantum wells
Authors: Tönnies D. , Bacher G. , Eisert D. , Forchel A. , Waag A. , Litz Th. , Landwehr G.
Published: July 2002

The influence of ion implantation on the interdiffusion of Cd and Mg in CdTe/CdMgTe single quantum wells was studied. The samples were implanted with 150 keV Ar+ ions and subsequently annealed for 1 min by rapid thermal annealing at temperatures between 400 and 480 °C. Ion implantation and annealing lead to an intermixing of barrier and well material, causing a blue shift of the characteristic emission spectrum. The dependence of the energy shift on the ion dose and the annealing temperature was studied. For an ion dose of 1×1014 cm−2 and an annealing temperature of 400 °C a blueshift of 80 meV compared to a nonimplanted reference sample indicates a significant enhancement of the interdiffusion of Cd and Mg by the implantation.
Polarization dependence of the temporal response of metal-semiconductor-metal photodetectors
Authors: Kuta J. J. , van Driel H. M. , Landheer D. , Feng Y.
Published: July 2002

The effect of grating diffraction on metal-semiconductor-metal photodetector temporal response is shown to be significant, and largest for devices with electrode periods less than the optical wavelength. This is related to a polarization dependence of the initial photogenerated carrier densities and distributions. With subpicosecond illumination, the measured difference in peak temporal signal for orthogonal polarizations was up to three times larger than that of the time-integrated photocurrent, and risetimes differed by as much as 30%. Transmission efficiencies obtained from coupled-wave analysis of metal grating structures on GaAs show excellent agreement with the time-integrated photocurrent measurements.
Growth of c-axis in-plane YBa2Cu4O8 thin films through in situ annealing of precursors deposited by hybrid plasma sputtering
Authors: Yoshida Y. , Wen J. G. , Watanabe N. , Ito W. , Koshizuka N. , Morishita T.
Published: July 2002

Processing for the growth of YBa2Cu4O8 (Y124) thin films has been investigated by dc 94.92 MHz hybrid plasma sputtering with in situ annealing. The amorphous precursor is found to be the best candidate for growing pure Y124 phase through in situ annealing. The Raman spectrum confirms the Y124 phase by presenting the modes at 250 and 604 cm−1 related to the double Cu-O chains. X-ray diffraction as well as transmission electron microscopy further show that the films are composed of grain with orthogonal c axes in the film plane.
Magneto-optic Faraday effect in (La1−xCax)MnO3 films
Authors: Lawler J. F. , Lunney J. G. , Coey J. M. D.
Published: July 2002

Thin films of (La1−xCax)MnO3 prepared by laser ablation deposition are ferromagnetic when 0.2≤x≤0.5 with Tc≊250 K. These films show strong Faraday rotation both in the vicinity of the 2p(O)→3d(Mn) charge-transfer absorption at approximately 3.0 eV (θF≳40 000°/cm), and in the vicinity of the 3d(t2g)→3d(eg) excitation at approximately 1.5 eV (θF≳10 000°/cm just below Tc). The films are moderately transparent, having values of 2θF/α of approximately 0.1 at 1.5 eV and 0.5 at 3.0 eV.
Dynamics of a polymer shock optical microgauge studied by picosecond coherent Raman spectroscopy
Authors: Hare David E. , Franken Jens , Dlott Dana D. , Chronister Eric L. , Flores James J.
Published: July 2002

Picosecond coherent Raman scattering (ps CARS) is used to measure dynamic frequency shifts of a thin layer of polymer compressed by a laser driven shock wave. The shock response of this optical microgauge is calibrated by static measurements of frequency shift versus pressure and temperature. A peak shock pressure of 1.9 (±0.3) GPa is observed in a microgauge with a response time of about 2 ns. The use of ps CARS optical gauges to measure ultrafast shock-induced chemical reactivity of energetic materials is discussed briefly.
Nearly transform limited pulses from a gain-switched InGaAsP distributed-feedback laser using polarization dispersion effect
Authors: Thedrez B. , Takeshita H. , Kamiya T.
Published: July 2002

Due to the large change of carrier density during the pulse emission, gain-switched distributed feedback semiconductor lasers suffer from a large frequency chirp that can extend over several nanometers. As the chirp is generally nonlinear, it is difficult to achieve transform limited pulses after a linear compression stage. We demonstrate here that polarization dispersion can be used to filter the residual nonlinear chirp after linear compression. Pulses as short as 5.5 ps with a time bandwidth of 0.38 were obtained, a value less than half that observed without polarization dispersion filtering.
One-monolayer-terraced structure in ZnSe/ZnSSe superlattices as revealed by Brewster-angle reflection spectroscopy
Authors: Inoue Kuon , Kuroda Takashi , Yoshida Kouji , Suemune Ikuo
Published: July 2002

Electronic structure of ZnSe/ZnS0.18Se0.82 thin superlattices grown on the GaAs substrate at 515 °C by metalorganic vapor phase epitaxy was studied mainly by Brewster-angle reflection spectroscopy. The result has revealed that a heavy-hole-related excitonic spectral structure is composed of two or three well-split narrow lines each with 2 meV in the spectral width. This splitting can be interpreted as arising from the one monolayer difference of the well thickness, indicating the abrupt interfaces such that the interfaces are flat enough over a range wider than the relevant exciton Bohr diameter of 70 Å. The fact indicates that the epitaxial growth method at higher temperatures than those usually adopted, may be promising for fabricating high-quality II–VI superlattices.
New method for fabricating ultra-narrow metallic wires
Authors: Olson E. , Spalding G. C. , Goldman A. M. , Rooks M. J.
Published: July 2002

An improved, cryogenic shadowed evaporation technique has been developed to produce ultra-narrow metallic wires. It has been used to create wires of Pd with widths less than 15 nm and as long as 800 nm. Arrays of wires covering areas as large as 6400 μm2 have been made. This method, which can be extended to other materials and structures, is presently limited by the grain size of the ‘‘template’’ material, and therefore holds promise for even finer linewidths.
Tunneling current due to incident electrons derived from the valence bands in AlSb–InAs–AlSb double-barrier structures
Authors: Chiang Jih-Chen
Published: July 2002

This letter reports the theoretical study of the current–voltage characteristics of the AlSb–InAs–AlSb double-barrier structure with a thin InAs well at both 77 and 300 K, within a nearest-neighbor sp3 bond-orbital model in which the band-bending effects are also taken into account. We demonstrate that the tunneling current due to the incident electrons derived from the valence bands gives a significant contribution to the valley and background currents; in addition, it gives the dominant contribution to the valley current when the temperature is low enough.
Hard boron oxide thin-film deposition using electron cyclotron resonance microwave plasmas
Authors: Gorbatkin S. M. , Rhoades R. L. , Tsui T. Y. , Oliver W. C.
Published: July 2002

Hard boron suboxide thin films were deposited in an electron cyclotron resonance (ECR) microwave plasma system at substrate temperatures below 300 °C. A high-temperature effusion cell, operated at 2200°–2250 °C, was used for injection of boron downstream of an Ar/O2 ECR plasma. B ion bombardment is estimated to have been up to 6% of the total boron flux, and Ar ion bombardment is estimated to have contributed ∼100 eV/deposited atom. Boron suboxide films with oxygen concentrations of 11% exhibited hardnesses up to 30 GPa, equal to sapphire and near that of pure boron. The hardness/modulus ratio was 0.1, significantly better than that of sapphire (0.067) or solid boron (0.074), indicating these films may be of interest for a variety of tribological applications.
Stability of magnetic field-induced dipolar order in a ferroelectric side-chain liquid crystal polymer
Authors: Sprunt S. , Nounesis G. , Naciri J. , Ratna B. R. , Shashidhar R.
Published: July 2002

The stability of in-layer dipolar order in a side-chain ferroelectric liquid crystalline polymer has been investigated by probing the optical birefringence produced by aligning the mesogenic side groups with a high magnetic field. The temperature dependence of the decay time associated with the mesogen relaxation from a state of saturated alignment obeys an Arrhenius law, with an activation energy two to three times higher than the typical value for low molecular weight liquid crystals. The exponent characterizing the relaxation process is found to be temperature-dependent in the ferroelectric smectic-C* phase, and approaches unity near the polymer glass transition. The implications of these results for nonlinear-optics applications are discussed.
A planar method for patterning of high-temperature superconducting films and multilayers
Authors: Ma Q. Y. , Wong A. , Dosanjh P. , Carolan J. F. , Hardy W. N.
Published: July 2002

We present a novel technique for patterning high-temperature superconducting (HTS) film and multilayer device structures. In the process an impurity ion (e.g., Si) is implanted into HTS films through a photoresist mask. The impurity ions convert the irradiated portion of the film into an insulating form by chemical reaction between the ions and the oxygen in the film, without altering the overall crystalline structure of the film. Removal of the photoresist results in a flat surface, which allows the epitaxial growth and implantation patterning of subsequent films so that a complete multilayer device structure can be fabricated. We show in detail the patterning process, as well as the properties of patterned and regrown films. Some simple device structures, such as a vertical contact and a crossover, are demonstrated.
Spin selective x-ray absorption spectroscopy: Demonstration using high resolution Fe Kβ fluorescence
Authors: Peng G. , Wang X. , Randall C. R. , Moore J. A. , Cramer S. P.
Published: July 2002

In this letter it is shown that high resolution Fe Kβ excitation spectra can be used to separately probe empty spin-up and spin-down final states. Spin-selective x-ray absorption spectra were obtained by selectively monitoring different regions of the Kβ emission. The fluorescence was excited with monochromatized synchrotron radiation and analyzed using a spherically bent Ge(620) crystal. Spin–polarization was demonstrated by showing that the 1s→3d transition at the Fe K edge is seen with Kβ1,3 detection, but missing in the excitation spectrum using Kβ′ detection. The spin–polarization is also confirmed by ligand field atomic multiplet calculations that reproduce the Kβ spectra. Calculations are presented showing the applicability of spin–polarized Kβ detection to nearly all first transition metal ions.
Oxygen depletion of the crystalline (anatase) TiO2 initiated by ionization of the K shell
Authors: Uustare T. , Aarik J. , Elango M.
Published: July 2002

We have shown, using the Auger-spectroscopy technique, that irradiation of the crystalline (anatase) TiO2 by electrons leads to a considerable oxygen depletion and metallization of the irradiated surface. The threshold energy for this process has been found to be around 530 eV, which coincides with the ionization threshold of the K shell of oxygen.
High-speed InP/GaInAs metal-semiconductor-metal photodetectors grown by chemical beam epitaxy
Authors: Debbar Nacer , Rudra Alok , Carlin Jean-François , Ilegems Marc
Published: July 2002

We report the fabrication and characterization of lateral metal-semiconductor-metal (MSM) photodiodes on an InP substrate. The photoabsorbing layer is made of InGaAs covered by a thin InP Schottky barrier enhancement layer. Schottky contacts for the detectors were formed by the evaporation of Au and patterned using a lift-off technique. The MSM photodiodes exhibit a dark current lower than 200 nA at 15-V bias, an efficient photoresponse up to 1.6 μm, and a fast deconvoluted full width at half maximum response of about 25 ps at 12-V bias.
Effect of point defects on oxygen aggregation in Si at 450 °C
Authors: Tajima M. , Warashina M. , Takeno H. , Abe T.
Published: July 2002

The oxygen aggregation process at 450 °C has been investigated by comparing the distributions of the interstitial oxygen, the thermal donor (TD), and the defect responsible for the photoluminescence (PL) line at 0.767 eV in a rapidly cooled Czochralski-grown Si crystal in which point defects are frozen-in nonuniformly in the growth direction. The formations of the TD and the 0.767-eV PL defect are delayed in the vacancy-rich region, which is not explained by the oxygen variation. The present result leads us to suggest that the oxygen aggregation is retarded by excess vacancies, which is consistent with the reported models for the oxygen aggregation at 450 °C.
Effect of excess Zn around the active-stripe mesa on the lasing threshold current of a [01̄1] oriented InGaAsP/InP buried-heterostructure laser diode
Authors: Chu S. N. G. , Logan R. A. , Coblentz D. L. , Sergant A. M.
Published: July 2002

Buried-heterostructure lasers with current confinement by reverse biased junctions always demonstrate poor performance when oriented along the [01̄1] direction of a (100)InP substrate in comparison to the same structure oriented along the [011] direction. We have confirmed that the poor device performance is a result of the excess Zn incorporated in the vicinity of (111)In and (11̄1̄)In mesa sidewall interfaces. The localized enhancement of the Zn level in the first p-InP layer of a standard pnpn current blocking structure is due to the crystal orientation dependent dopant incorporation. The excess Zn precipitates out in the region adjacent to the mesa sidewall interface as observed by cross-sectional transmission electron microscopy. Electroluminescence imaging of active stripe further indicated that the excess Zn diffuses across the sidewall interfaces into the active stripe, generating massive nonradiative recombination centers along the active stripe and degrading the quantum efficiency of the lasers. By systematically reducing the Zn concentration in the mesa sidewall interfacial region, a correlation between an improvement in the lasing threshold current with reduced Zn concentration is demonstrated. A room-temperature threshold current of 10 mA has been achieved in [01̄1] oriented lasers.
Nanocrystal size modifications in porous silicon by preanodization ion implantation
Authors: Pavesi L. , Giebel G. , Ziglio F. , Mariotto G. , Priolo F. , Campisano S. U. , Spinella C.
Published: July 2002

A tuning of the nanocrystal sizes in porous silicon has been obtained by self-ion implantation in p-type silicon wafers before the anodization treatment. Sample porosity, luminescence spectra, Raman scattering, and transmission electron microscopy have been used to determine the structure of porous silicon samples. A porosity increase, a blue shift of the luminescence peak, a widening of the phonon resonance, and a decrease in the size features revealed by transmission electron microscopy (TEM) images are observed by increasing the ion implantation dose. It is suggested that this effect results from the increased resistivity of the Si wafer caused by the ion implantation damage.
Nondestructive mapping of carrier concentration and dislocation density in n+-type GaAs
Authors: Look D. C. , Walters D. C. , Mier M. G. , Sizelove J. R.
Published: July 2002

Transmission mappings (500 μm×500 μm resolution) at wavelengths of 0.9–1.5 μm on 3 in., n+-GaAs wafers (n≂1–2×1018 cm−3) correlate well with carrier concentration n, measured by the Hall effect, and dislocation density, as confirmed by KOH etch-pit patterns. The absorption for λ≳1.0 μm (below band edge) varies directly with n via free-carrier interconduction-band transitions, while the absorption for λ≲0.95 μm (near band edge) varies inversely with n because of band-filling effects. Both phenomena are highly useful for n+-GaAs wafer characterization.
Insulating boundary layer and magnetic scattering in YBa2Cu3O7−δ /Ag interfaces over a contact resistivity range of 10−8–10−3 Ω cm2
Authors: Sanders S. C. , Russek S. E. , Clickner C. C. , Ekin J. W.
Published: July 2002

We have measured interface transport in thin-film YBa2Cu3O7−δ /Ag interfaces having resistivities ranging from 10−8 to 10−3 Ω cm2. Analysis of the interface I-V data indicates that tunneling is the predominant transport mechanism even for the in situ interfaces having contact resistivities of 1–7×10−8 Ω cm2. Zero-bias conductance peaks are also observed for the entire range of interface resistivity. The similarity of the zero-bias conductance peaks among these widely varying interfaces suggests that the low-temperature interface transport is governed by the same mechanism in each case. These conductance peaks are analyzed in the framework of the Appelbaum–Anderson model for tunneling assisted by magnetic scattering from isolated magnetic spins in the interface.
Quantum wave bandstop filters
Authors: Wang Y. , Chou S. Y.
Published: July 2002

We propose and demonstrate, based on the concept of a microwave bandstop filter, two quantum wave bandstop filter structures. Both structures employ nanoscale gates in a heterojunction transistor to induce a quantum cavity connected by two one-dimensional wires. As the electron wavelength is changed by the gate voltage, we observed that, at certain gate voltages, the transmission of electron waves through the cavity is partially blocked and the drain current drops as large as 50%. This phenomenon is explained in terms of the destructive quantum interference between different electron wave modes in the cavity.
Selective ablation of a hydrogenated amorphous silicon thin layer by the second-harmonic radiation of a transversely excited atmospheric CO2 laser
Authors: Sumiyoshi Tetsumi , Ninomiya Yutaka , Shiratori Akira , Obara Minoru , Ishii Katsunori
Published: July 2002

The second-harmonic radiation of the transversely excited atmospheric CO2 laser generated by a AgGaSe2 nonlinear crystal is used for the selective ablation of a hydrogenated amorphous silicon (a-Si:H) thin layer on a quartz substrate. The vibrational energy of the Si—H bonds contained in a-Si:H at 10 at. % coincides with the photon energy of the 5 μm light and absorbed the laser photons to sufficiently ablate the layer without damage on the quartz substrate.
Temperature dependence of equilibrium electron density in AlGaAs governed by Sn-related DX centers
Authors: Ždánský K.
Published: July 2002

Capacitance and conductance of AlxGa1−xAs/GaAs heterostructures with an Sn-doped Al0.35Ga0.65As layer and with a p-n junction was measured as a function of frequency and temperature. The temperature dependence of the free-electron density n was determined from the measurement. A theoretical relation for n governed by two independent DX centers was derived. The experimental results were explained by the presence of two types of Sn-related DX centers. The binding energies of the two DX centers were determined and found to be in good accord with values, both experimental and theoretical, reported previously by other authors.
Structural and electrical properties of BaTiO3 grown on p-InP (100) by low-pressure metalorganic chemical vapor deposition at low temperature
Authors: Kim T. W. , Yom S. S.
Published: July 2002

Metalorganic chemical vapor deposition of BaTiO3 using Ba(tmhd)2, Ti(OC3H7)4, and N2O via pyrolysis at relatively low temperature (∼300 °C) was performed in order to produce high-quality BaTiO3/p-InP (100) interfaces and BaTiO3 insulator gates with dielectric constants of high magnitude. Scanning electron microscopy showed that the surfaces of the BaTiO3 films had very smooth morphologies. Auger electron spectroscopy measurements showed that the compositions of the as-grown films consisted of barium, titanium, and oxygen. Transmission electron microscopy showed that the BaTiO3 films had interdiffusion and local epitaxial formations near the BaTiO3/p-InP (100) interfaces. Room-temperature current-voltage and capacitance-voltage (C-V) measurements clearly revealed metal-insulator-semiconductor behavior for the BaTiO3 insulator gates, and the interface state densities at the BaTiO3/p-InP interfaces were approximately low 1011 eV−1 cm−2 at an energy about 0.6 eV below the conduction-band edge. The dielectric constant of the BaTiO3 thin film determined from C-V measurements was as large as 78.
Diffusion in nanolayers as measured by atom probing
Authors: Keilonat Christian , Camus Eric , Wanderka Nelja , Wollenberger Heinrich
Published: July 2002

Diffusion measurements by atom probing of Cu/Ni nanolayers are reported. Using the Matano analysis, we derive directly from the experimental data the concentration dependent interdiffusion coefficient in a temperature range from 653 to 703 K.
Gain characteristics of blue/green II-VI quantum well diode lasers
Authors: Kozlov V. , Salokatve A. , Nurmikko A. V. , Grillo D. C. , He Li , Han J. , Fan Y. , Ringle M. , Gunshor R. L.
Published: July 2002

Gain spectra of the room temperature ZnSe-based blue-green lasers have been measured in index guided, single quantum well (SQW) devices that show a peak gain coefficient at a laser threshold of approximately 1500 cm−1.
High quality Si/Si1−xGex layered structures grown using a mass-spectrometry controlled electron-beam evaporation system
Authors: Ni W.-X. , Henry A. , Larsson M. I. , Joelsson K. , Hansson G. V.
Published: July 2002

High quality, strained Si/Si1−xGex layered structures have been grown at temperatures in the range 400–625 °C, using a solid-source molecular-beam epitaxy (MBE) system with a mass-spectrometry-based loop-control to improve the accuracy and stability of the evaporation rates. Good control of the growth parameters has been achieved as verified by, e.g., high-resolution x-ray diffraction. Very high intensities and extremely small peak widths, down to 2.7 meV for the XNP transition at low excitation levels of photoluminescence spectra, indicate high crystalline quality of the layers. It is shown that some previously reported defect-related luminescence from MBE-grown SiGe layers is not intrinsic to the MBE process.
Interface roughness scattering in thin, undoped GaInP/GaAs quantum wells
Authors: Mitchel W. C. , Brown G. J. , Lo Ikai , Elhamri Said , Ahoujja Mohamed , Ravindran K. , Newrock R. S. , Razeghi Manijeh , He Xiaguang
Published: July 2002

Electronic transport properties of very thin undoped GaInP/GaAs quantum wells have been measured by temperature dependent low field Hall effect and by Shubnikov–de Haas effect. Strong Shubnikov–de Haas oscillations were observed after increasing the electron concentration via the persistent photocurrent effect. Low temperature mobilities of up to 70 000 cm2/V s at carrier concentrations of 6.5×1011 cm−2 were observed in a 20 Å quantum well. The results are compared with the theory of interface roughness scattering which indicates extremely smooth interfaces; however, discrepancies between experiment and theory are observed.
Wavelength dependence of the threshold in an InGaP-InAlGaP vertical cavity surface emitting laser
Authors: Chow W. W. , Schneider R. P. , Lott J. A. , Choquette K. D.
Published: July 2002

The wavelength dependence of the threshold in an InGaP-InAlGaP vertical cavity surface emitting laser is investigated using a microscopic theory of the semiconductor gain medium. Good agreement is found between experiment and theory for the minimum threshold lasing wavelength for a range of laser structures.
Photoemission studies with barium and LaB6 photocathodes and polarized laser light
Authors: Conde M. E. , Kwon S. I. , Young A. T. , Leung K.N. , Kim K.-J.
Published: July 2002

Photoemission measurements with barium and single crystal LaB6 photocathodes are reported. The barium cathode is prepared by depositing a barium thin film onto a copper substrate. The LaB6 cathode is a single crystal cut in the 〈100〉 plane. Radiation from a nitrogen laser (337 nm, 10 ns) is polarized and strikes the cathode surface at variable angles. An electron quantum yield as high as 2×10−3 is observed with barium. The dependence of the quantum yield on the beam polarization and angle of incidence is investigated. The results indicate that higher quantum yields are achieved when the angles of polarization and incidence are such as to minimize the reflection coefficient.
Preparation of crystallographically aligned layers of silicon carbide by pulsed laser deposition of carbon onto Si wafers
Authors: Rimai L. , Ager R. , Weber W. H. , Hangas J. , Poindexter B. D.
Published: July 2002

It is demonstrated that SiC films can be deposited epitaxially on [001] and [111] Si wafers by excimer laser ablation of just a carbon target, in vacuum, at deposition temperatures as low as 1100 °C. Diffraction studies show that the SiC films have the same crystalline orientation as the substrates. The film growth on the Si substrate to thicknesses as large as 4000 Å with no significant excess carbon indicates that in addition to reaction of the carbon in the plume with Si of the substrate, there is transport of Si within the SiC film. For continued deposition beyond this thickness a carbon layer will form.
Enhanced confinement of electrons at room temperature using a superlattice reflector
Authors: Campi D. , Rigo C. , Cacciatore C. , Neitzert H.-C.
Published: July 2002

We report the experimental study of the thermionic emission of electrons into overbarrier states of a superlattice, tailored to enhance electron confinement within a closely spaced quantum well. Partial suppression of the thermionic current is observed at room temperature. A critical evaluation of the practical applications of the effect is offered. Furthermore, the tunnel injection into partially delocalized Stark states of the superlattice is observed at low temperature.