bluuebunny/crossref_metadata_2025 huggingface dataset:
Secondary ion mass spectrometry study for Josephson junction with Nb/AlOx-Al/Nb structure
Authors: Morohashi Shin’ichi , Kataoka Yuji , Imamura Takeshi , Hasuo Shinya
Published: July 2002

We studied the interface changes of niobium (Nb) Josephson junction structures (Nb/Al/Nb and Nb/AlOx-Al/Nb) using secondary ion mass spectrometry (SIMS). Using a cesium (Cs+) primary beam, CsM+ ions (M=H, O, OH, Nb, and Al) were monitored for cesium bombardment. In the SIMS depth profile, the CsH+ and CsO+ intensity indicated accumulation at junction interfaces, where these intensities were larger for the Al/Nb base electrode interface than for the Nb counterelectrode/Al interface. We think a layer of absorbed water vapor with a thickness a few nm, is formed on the junction interface, and is attributed to chamber outgassing. In the Nb/Al/Nb structure, the annealing changes for the Al/Nb base electrode interface were smaller than those for the Nb counterelectrode/Al interface. We confirmed that the absorbed water vapor layer plays an important role in the junction structure, that is, it acts as a barrier for grain boundary diffusion between Nb and Al.
Free-running XeF(C-A) lasing at 2.2 atm in a commercial discharge excimer laser
Authors: Cheng Yong-Kang , Yang Shao-Peng , Wang Min-Xiao , Ma Zu-Guang
Published: July 2002

Efficient free-running lasing on the XeF(C-A) electronic transition has been demonstrated in an unmodified commercial discharge excited excimer laser at a reduced buffer gas pressure of 2.2 atm and a moderate low pump rate of 2.76 MW/cm3, using a four-component gas mixture of Xe, NF3, Kr, and He with a net peak gain of 1.24%/cm. The laser spectrum showed a peak wavelength at 477 nm and a bandwidth of 32 nm (FWHM). The laser output energy was 1.17 mJ, representing peak power, energy density, and intrinsic efficiency values of 0.062 MW, 9 mJ/ℓ, and 0.016%, respectively.
In situ growth of superconducting YBa2Cu3O7−x thin films by a hot-wall sputtering process
Authors: Lin R. J. , Chen L. J.
Published: July 2002

YBa2Cu3O7−x (YBCO) superconducting thin films with Tc of 89 K and Jc of 2.7×106 A/cm2 at 77 K, zero field were prepared by a modified high pressure (1.5 Torr) dc planar diode sputtering process. The design and construction of the simple, economic hot-wall sputtering system which has been achieved in growing high-quality YBCO films on (001)MgO, (001)LaAlO3, and (001)YSZ substrates are reported.
Time-resolved luminescence study of ultrafast carrier transport in GaAs metal-semiconductor-metal devices
Authors: Kersting R. , Plettner J. , Leo K. , Averin S. , Kurz H.
Published: July 2002

Femtosecond time-resolved luminescence spectroscopy is used as a novel tool to study the ultrafast transport in interdigitated metal-semiconductor-metal Schottky diodes. The time-resolved luminescence signals of GaAs-MSM diodes depend strongly on bias voltage and carrier density. In these experiments, field-induced transfer to indirect valleys is directly observed in the time domain for the first time.
Homoepitaxial growth of diamond thin films by electron cyclotron-resonance microwave plasma chemical-vapor-deposition apparatus with CO/H2 gaseous source
Authors: Komori Masaaki , Maki Tetsuro , Kim Taigen , Hou Gen Liang , Sakaguchi Yoshiyuki , Sakuta Ken , Kobayashi Takeshi
Published: July 2002

Homoepitaxy of the diamond thin films has been carried out by employing the ECR microwave plasma CVD apparatus with a CO/H2 gaseous source. From RHEED observation, it appeared that the surface morphology of (100) oriented film was much better than that of the (110) oriented. The (2×1) surface reconstruction remained unchanged even when the film was cooled down in H2 ambient after the epitaxy was completed. Although the synthetic diamond substrates had nonuniformity in their cathodoluminescence patterns, epitaxial films grown onto them offered uniform ones.
Investigation of charge trapping centers in silicon nitride films with a laser-microwave photoconductive method
Authors: Zhong Lei , Shimura Fumio
Published: July 2002

A new method using a laser microwave photoconductance (LMPC) technology for the investigation of charge trapping centers in silicon nitride films was demonstrated by studying the ultraviolet (UV) irradiation effect upon minority-carrier recombination lifetime of silicon with the film. The lifetime is found dependent on the film thickness. UV irradiation dramatically decreases the lifetime for the samples with the thick film. The decreased lifetime is transient and recovers to the initial value after long time storage at room temperature. The recovery accelerates with increasing temperature. The lifetime behavior is correlated with the charge states of K centers in the nitride film. It is then shown that the electronic structure of the charge trapping centers can be studied by an investigation of the lifetime recovery process after UV irradiation with temperature controlled LMPC measurements.
Continuous wave operation on extremely low-temperature (375 °C)-grown AlGaAs quantum-well lasers
Authors: Miyazawa Sei-ichi , Sekiguchi Yoshinobu , Okuda Masahiro , Hasegawa Mitsutoshi , Nojiri Hidetoshi
Published: July 2002

We report on the continuous wave (cw) operation of AlGaAs single-quantum-well (SQW) lasers grown at a low temperature (375 °C) by molecular-beam epitaxy (MBE). The threshold current and the differential quantum efficiency of the ridge-waveguide laser were 10 mA and 82%, respectively. During the life test, no obvious degradation was observed beyond 2300 h under 8 mW cw operation at 50 °C. The cw operation of SQW lasers grown at low temperatures was achieved by the long baking of the MBE system and the reduction of the V/III flux ratio.
Compositional effects in YxBayCuzO7−δ thin films prepared by metalorganic chemical vapor deposition
Authors: Schulte B. , Maul M. , Häussler P. , Adrian H.
Published: July 2002

We report on effects of composition onto superconducting and structural properties of Y-Ba-Cu-O thin films, prepared by a carrier-gas free metalorganic chemical vapor deposition technique. Thin films with critical temperatures Tc≥90 K, transition widths ΔTc≤1 K, and critical current densities jc (T=77 K, B=0 T)≥106 A/cm2 can be prepared by this method. Here we report on a strong dependence of the Tc on the ratio of Ba/Cu. For Ba/Cu<2 the surfaces show CuO precipitates, increasing in quantity and size with increasing concentration of Cu. An excess of Y leads to oriented inclusions of cubic Y2O3. A deficit of Y and Cu causes an expansion of the c-lattice parameter. To investigate the influence of Y2O3 and CuO precipitates on the pinning potential, resistive transitions in magnetic fields up to 12 T were measured and interpreted by a thermal activated flux-creep model. These measurements indicate the inefficiency of both, inclusions and precipitates, on the enhancement of the pinning potential.
Longitudinal expansion of space-charge dominated drifting beam bunches with a parabolic line charge density distribution
Authors: Wang J. G. , Wang D. X. , Reiser M.
Published: July 2002

An experiment was performed for the first time to demonstrate linear longitudinal space-charge forces on drifting electron beam bunches with a parabolic line charge density distribution. The parabolic electron beam bunch was produced by a gridded electron gun and guided into a short transport channel consisting of an induction acceleration module and three matching lenses. The time-resolved beam energy was measured at the end of the channel by both a retarding field energy analyzer and a deflecting field energy analyzer. The experimental results were compared with theory and good agreement was found.
Polarization dependent refractive index of an interdiffusion induced AlGaAs/GaAs quantum well
Authors: Li E. Herbert , Weiss Bernard L. , Chan K. S. , Micallef Joseph
Published: July 2002

The polarization dependent refractive index, nR, at room temperature is calculated for interdiffusion-induced Al0.3Ga0.7As/GaAs single quantum well (QW) structures for the wavelength range 0.75–2 μm. The confinement profile is modeled by an error function and nR is determined using the real and imaginary parts of the dielectric function, including contributions from the Γ, X, and L Brillouin zones. Results show that at longer wavelengths nR decreases with increasing interdiffusion, which normally provides a positive index step with respect to a less interdiffused QW. For shorter wavelengths (around the QW band edge), the wavelength range for a positive refractive index step increases as the extent of disordering between two interdiffused QWs is increasing.
Effect of self-implantation on structure and oxidation behavior of single crystal β-SiC
Authors: Du Honghua , Libera Matthew , Yang Zunde , Lai Po-Jen , Jacobson Dale C. , Wang Yu. C. , Davis Robert F.
Published: July 2002

Single crystal β-SiC was self-implanted with high-dose Si and C at 773 K. In situ lattice recovery occurred and SiC remained single crystalline during implantation. Notable structural damage resulted in the implanted region. The residual damage significantly accelerated the oxidation rate of SiC at 1373 K but caused no appreciable rate increase at 1573 K. The diminishing of the effect of the damages on oxidation can be attributed to enhanced damage annealing with temperature.
Generation of 13-fs pulses from a mode-locked Ti:Al2O3 laser with reduced third-order dispersion
Authors: Proctor Bob , Wise Frank
Published: July 2002

The third-order dispersion of a mode-locked Ti:Al2O3 laser has been reduced by replacing a pair of flint glass prisms with a sequence of four quartz prisms. This allows transform-limited 13-fs pulses to be generated with a gain crystal 20 mm long. To date, these are the shortest pulses generated directly from a laser.
Shallow donor in separation by implantation of oxygen structures revealed by electric-field modulated electron spin resonance
Authors: Vanheusden K. , Stesmans A.
Published: July 2002

Electric-field modulated K-band electron spin resonance measurements on Si/SiO2/Si structures, formed by implantation of oxygen (SIMOX), were carried out at 4.3–30 K. Large area metal-oxide-silicon capacitors were fabricated on these structures and optimized for cavity loading. Sweeping of the Si band gap through the Fermi level near the buried oxide interfaces resulted in the observation of a shallow donor in Si of fairly high local density (≊1018 cm−3), residing in this area; its electron spin resonance signal is turned on and off by positive and negative gate biasing, respectively. The same donor signal has previously been observed in γ-irradiated SIMOX, revealing that γ irradiation has the same effect as positive biasing.
Fused silica masks for printing uniform and phase adjusted gratings for distributed feedback lasers
Authors: Pakulski G. , Moore R. , Maritan C. , Shepherd F. , Fallahi M. , Templeton I. , Champion G.
Published: July 2002

A method for producing durable fused silica self-interference grating photomasks is described. These masks allow repeated printing of both uniform and phase adjusted gratings. Periods as fine as 200 nm have been demonstrated. The fabrication of these masks via holographic and focused ion beam lithography and their use as a lithography tool are explained. Distributed feedback lasers, with gratings made by this technique, were produced. These lasers operated in a single longitudinal mode at a wavelength of either 1.55 or 1.3 μm.
Effect of germanium implantation on metal-oxide-semiconductor avalanche injection
Authors: Lin Ta-Cheng , Young Donald R.
Published: July 2002

The effect of germanium on the hot electron current of a metal-oxide-semiconductor device has been studied by avalanche electron injection from the silicon to the silicon dioxide. Different doses of germanium ranging from 1012 to 1015 atoms/cm2 are implanted into the Si-SiO2 interface. The ‘‘lucky’’ hot electron population is suppressed by the germanium implantation. We have used the charge-voltage technique to measure the interface state density. The interface state density increase caused by the Ge implantation is negligible if the dose is lower than 1014 Ge/cm2. Our results show that the Ge implantation is a promising method to solve the hot carrier problem that has become important in submicrometer devices.
Synthesis of Nd(FeTi)12 films by sputtering
Authors: Panagiotopoulos I. , Wang D. , Niarchos D. , Sellmyer D. J.
Published: July 2002

Nd(FeTi)12 films have been synthesized by dc magnetron sputtering. The films have tetragonal ThMn12 crystal structure as confirmed by XRD and magnetic measurements. The lattice parameters are a=8.57 and c=4.801 Å. The degree of the ThMn12 phase formation and the texture of the films are found to be dependent on deposition parameters. The films can be aligned with the (001) basal plane in the film plane by suitable deposition conditions. Thus the films are textured so that the easy axis, which is the c-axis, is perpendicular to the film plane. After nitrogenation, the tetragonal ThMn12 crystal structure is retained and the lattice parameters increase to a=8.67 and c=4.862 Å, corresponding to a volume expansion of 3.6%. The coercivity also increases upon nitrogenation.
Effect of Ag2O additive on microstructure and superconductivity of the Tl2Ba2Ca2Cu3Oy compound
Authors: Koo H. S. , Hurng W.-M. , Lee W. H. , Tseng T. Y. , Chen M. , Lo J. R.
Published: July 2002

A series of Ag-doped Tl2Ba2Ca2Cu3Oy superconducting oxides were prepared by a solid-state reaction and the influence of Ag2O content, with a varying molar ratio which ranged from 0 to 1.0, was also investigated. The normal-state resistance of the samples decreased with an increase in the content of Ag2O additive, while the critical superconducting temperatures of the Ag-doped samples increased once the Ag2O content was increased. The doping of the silver oxide was indicated from the results of the x-ray diffraction pattern to be favorable to the formation of the three CuO layers with a high-Tc phase Tl2Ba2Ca2Cu3Oy. The diamagnetic property of the samples was also confirmed by the magnetic measurements to become enhanced by doping with silver oxide. The platelike grains of Tl2 Ba2CaCu2Oy phase were observed from scanning electron micrographs to be primarily present in the undoped sample, while the amount of the needlelike Tl2Ba2Ca2Cu3Oy grain increased with an increase in the doping amount of Ag2O.
Determination of oxygen and carbon contaminations in InGaAs molecular beam epitaxy using growth interruptions
Authors: Harmand Jean-Christophe , Juhel Marc
Published: July 2002

InGaAs layers were grown by molecular beam epitaxy with growth interruptions. Oxygen contamination was clearly detected by secondary ion mass spectroscopy at growth interruption interfaces. Carbon was not observed. After quantification, these measurements were extrapolated to estimate the contamination in bulk material with a very low detection limit (typically 1014 cm−2), depending on the growth interruption time. The oxygen contamination was unambiguously shown to be strongly related to the As source. A correlation was observed with the electrical properties.
Quenching of electron-acoustic phonon scattering in quantum wires by a magnetic field
Authors: Telang N. , Bandyopadhyay S.
Published: July 2002

We demonstrate the possibility of a dramatic quenching of acoustic phonon scattering in semiconductor quantum wires due to an external magnetic field. This quenching is important in understanding the suppression of inelastic backscattering at high magnetic fields which leads to the quantum Hall effect (in the Büttiker picture). Additionally, such quenching can give rise to strong negative magnetoresistance in narrow quantum wires which may have important applications in electronic devices and magnetic field sensors.
Effects of interdiffusion on the polarization dependent refractive index of a strained InGaAs/GaAs quantum well
Authors: Micallef Joseph , Li E. Herbert , Weiss Bernard L.
Published: July 2002

The polarization dependent refractive index of disordered, strained InGaAs/GaAs single quantum wells is calculated using the complex dielectric function, taking into consideration the contributions from the Γ, X, and L Brillouin zones. At longer wavelengths the refractive index decreases as the extent of disordering increases, resulting in a positive refractive index step when the lateral confining regions are more extensively disordered. The structure also exhibits birefringence in the quantum well band edge to barrier band-edge wavelength range which decreases with interdiffusion. The refractive index is polarization independent outside this wavelength range. Interdiffusion extends this zero birefringence to shorter wavelengths.
Electrical resistance of electron beam induced deposits from tungsten hexacarbonyl
Authors: Hoyle P. C. , Ogasawara M. , Cleaver J. R. A. , Ahmed H.
Published: July 2002

We studied the change in electrical conductivity of deposits from focused electron beam induced dissociation of W(CO)6 for different exposure conditions. Lines were deposited by scanning repeatedly to build up the same total electron dose; with different electron doses per scan, resistance differences of more than one order of magnitude resulted. The lines with lower deposited thicknesses also have lower resistances, and so cannot be explained in terms of constant resistivity and different cross-sectional areas. A theoretical description involving an intermediate and a final product is proposed and compared to the experimental results.
Multilevel registered polymeric Mach–Zehnder intensity modulator array
Authors: Tumolillo Thomas A. , Ashley Paul R.
Published: July 2002

Described here is the first known demonstration of a registered two level guided wave polymeric electro-optic Mach–Zehnder intensity modulator array. The device consists of two complete vertically stacked levels. Both levels were independently poled and operated. There was no measurable optical or electrical cross talk due to a high resistivity thermoset polymer buffers layer employed. Fabrication and performance of the device is discussed.
Phase development of Tl2Ba2CaCu2O8 thin films on LaAlO3 substrates
Authors: Lanham M. , James T. W. , Eddy M. , Lange F. F. , Clarke D. R.
Published: July 2002

The evolution of phases leading to the formation of epitaxial films of nominal composition Tl2Ba2CaCu2O8 on (100) LaAlO3 by post-deposition annealing of amorphous precursor films has been investigated by examining interrupted heat-treatment samples using analytical microscopy and x-ray diffraction. The superconductor, with a composition of Tl1.8Ba2Ca0.94Cu2.6Ox, forms from a melt, which itself formed from intermediary crystalline phases during the continual loss of Tl2O. It is concluded that Tl1.8Ba2Ca0.94Cu2.6Ox, Cu2O, and Tl3Ca5Ox are in subsolidus equilibrium and that a melt phase exists between at least 780 and 860 °C under reducing conditions controlled by the Tl2O vapor.
Direct observation of ordered crystalline organic quantum-well structures using reflection high-energy electron diffraction
Authors: Burrows P. E. , Forrest S. R.
Published: July 2002

We directly observe by reflection high-energy electron diffraction, the quasiepitaxial growth of crystalline organic quantum-well structures grown by the ultrahigh vacuum process of organic molecular beam deposition. We show that each of four alternating layers of two organic molecules grows in a crystalline form without sufficient strain to induce amorphous growth, regardless of significant lattice mismatch which might exist between the alternating films. Our results clearly demonstrate the ability to engineer a completely new class of van der Waals-bonded thin film materials and structures based on crystalline organic semiconductors, with applications to optoelectronics.
Energy levels of the SbGa heteroantisite defect in GaAs:Sb
Authors: Lagowski J. , Morawski A. , Sen S. , Edelman P.
Published: July 2002

A transient capacitance study of antimony-doped bulk GaAs has led to the identification of two energy levels related to the SbGa heteroantisite defect. The levels with electron emission activation energies of 0.54 and 0.70 eV are typically overshadowed by omnipresent EL3 and EL2 traps related to oxygen defect and the arsenic antisite, respectively. Positive identification of the levels, and determination of their emission rate signatures, was made possible employing GaAs crystals with a defect structure especially engineered to achieve very low concentrations of background traps. Relationship of the levels to the SbGa defect is deduced from excellent agreement with previous electron paramagnetic resonance results.
Epitaxial growth of (Hg,Mn)Te by the interdiffused multilayer process
Authors: Funaki M. , Brinkman A. W. , Hallam T. D. , Tanner B. K.
Published: July 2002

Epitaxial films of (Hg,Mn)Te have been grown by metalorganic vapor phase epitaxy using the interdiffused multilayer process (IMP), on GaAs (100) substrates with a ∼1 μm buffer layer of CdTe. In order to grow the MnTe component, it was found necessary to grow at 380 °C with a precursor partial pressure ratio (Mn:Te) of 5–8. The IMP layers were found to be more uniform in composition and thickness than comparable layers of (Hg,Mn)Te grown by the more conventional direct alloy growth method. X-ray rocking curve widths for IMP layers were typically ∼200″ with a variation across the layer of ∼10%. Variations in composition were <10%.
Light-induced annealing of metastable defects in hydrogenated amorphous silicon
Authors: Graeff C. F. O. , Buhleier R. , Stutzmann M.
Published: July 2002

Measurements of light-induced creation and annealing of metastable dangling bond defects in undoped hydrogenated amorphous silicon thin films are reported. A decrease of the defect density by 50% induced by continuous illumination is observed after fast defect creation by pulsed light. The kinetics of creation and recovery are discussed, as well as the implications for present models treating metastable defects in hydrogenated amorphous silicon.
Pulsed-laser induced desorption and subsequent readsorption in ambient gas
Authors: Holler Gregor , Albrecht Uwe , Herminghaus Stephan , Leiderer Paul
Published: July 2002

We have investigated the phenomenon of readsorption after pulsed-laser induced thermal desorption during the presence of ambient gas. The temporal evolution of the readsorption of water has been measured as a function of the ambient gas pressure for helium and carbon-dioxide atmospheres. CO2 pressures above 10 mbar lead to a virtually complete readsorption of the desorbed material. A model based on a nearly one-dimensional diffusion scheme explains this remarkable result.
In situ detection of relaxation in InGaAs/GaAs strained layer superlattices using laser light scattering
Authors: Celii F. G. , Beam E. A. , Files-Sesler L. A. , Liu H.-Y. , Kao Y. C.
Published: July 2002

We report the use of laser light scattering (LLS) for the in situ detection of strained epitaxial layer relaxation. Strained layer superlattices (SLSs) of InGaAs/GaAs were prepared by molecular beam epitaxy. The rapid increase in the LLS signal was interpreted as increased surface roughness due to surface steps generated during InGaAs relaxation. The LLS signal was sharply peaked with respect to the azimuthal angle (the rotation angle between crystal axes and the detection axis), indicating the scattering comes primarily from α misfit dislocations which run parallel to the (011̄) direction. The growth time at which the LLS signal onset occurred, together with the InGaAs growth rate, yielded the critical layer thickness, hc. The hc value for SLSs of In0.17Ga0.83As/GaAs with thicknesses of 4.6/17 and 4.6/7.8 nm were 25 and 23 nm, respectively, and almost identical to values obtained for single InGaAs layers. The observed values of hc are greater than those calculated using the standard force-balance model. Dynamic effects of dislocation propagation and surface smoothing were also observed in real-time.
Observation of quantum confinement effects in strained Si0.84Ge0.16/Si quantum wells at room temperature
Authors: Chen Y. F. , Dai Y. T. , Chou H. P. , Chang D. C. , Chang C. Y. , Wang P. J.
Published: July 2002

We report the first study of quantum confinement shifts of energy gap in strained Si0.84Ge0.16/Si quantum wells at room temperature by photothermal deflection spectroscopy (PDS) technique. The experimental results obtained from the amplitude and phase of the PDS signal are in good agreement with quantum well subband calculation.
Controlling of Schottky barrier heights for Au/n-GaAs and Ti/n-GaAs with hydrogen introduced after metal deposition by bias annealing
Authors: Jin S. X. , Wang H. P. , Yuan M. H. , Song H. Z. , Wang H. , Mao W. L. , Qin G. G. , Ren Ze-Ying , Li Bing-Chen , Hu Xiong-Wei , Sun Guo-Sheng
Published: July 2002

Up to now, in most of the research work done on the effect of hydrogen on a Schottky barrier, the hydrogen was introduced into the semiconductor before metal deposition. This letter reports that hydrogen can be effectively introduced into the Schottky barriers (SBs) of Au/n-GaAs and Ti/n-GaAs by plasma hydrogen treatment (PHT) after metal deposition on 〈100〉 oriented n-GaAs substrates. The Schottky barrier height (SBH) of a SB containing hydrogen shows the zero/reverse bias annealing (ZBA/RBA) effect. ZBA makes the SBH decrease and RBA makes it increase. The variations in the SBHs are reversible. In order to obtain obvious ZBA/RBA effects, selection of the temperature for plasma hydrogen treatment is important, and it is indicated that 100 °C for Au/n-GaAs and 150 °C for Ti/n-GaAs are suitable temperatures. It is concluded from the analysis of experimental results that only the hydrogen located at or near the metal-semiconductor interface, rather than the hydrogen in the bulk of either the semiconductor or the metal, is responsible for the ZBA/RBA effect on SBH.
Effects of annealing conditions on heavily carbon-doped InGaAs
Authors: Han W. Y. , Calderon L. , Lu Y. , Schauer S. N. , Moerkirk R. P. , Lee H. S. , Flemish J. R. , Jones K. A. , Yang L. W.
Published: July 2002

Two heavily carbon doped InGaAs samples (2.20×1019 and 1.92×1019 cm−3) with low In mol fractions (1% and 8%) were annealed with or without silicon nitride caps in H2 containing 0.3% AsH3 over the temperature range 5000–800 °C. Hall effect, secondary ion mass spectroscopy, double crystal x-ray diffraction, and integrated photoluminescence measurements showed that H outdiffuses over the annealing temperature range when the films were capped with silicon nitride. However, there was almost no net H outdiffusion for uncapped samples annealed in the same ambient and temperature range. Recombination centers formed during high temperature anneals in samples with less In (1%), but did not appear to form as readily in the one with more In (8%).
Fine magnetic domain structure of stressed amorphous metal
Authors: Koike K. , Matsuyama H. , Tseng W. J. , Li J. C. M.
Published: July 2002

The fine magnetic domain structure which appears on a stressed amorphous ribbon is studied using a spin-polarized scanning electron microscope. The detected domain structure differs from any so far reported. The magnetization direction inside the wavy stripelike closure domain fluctuates along the stripes. We propose two possible models to explain this domain structure.
Wave function deformation and mobility of a two-dimensional electron gas in a backgated GaAs-AlGaAs heterostructure
Authors: Kurobe A. , Frost J. E. F. , Grimshaw M. P. , Ritchie D. A. , Jones G. A. C. , Pepper M.
Published: July 2002

The transport properties of a two-dimensional electron gas in a GaAs-AlGaAs heterostructure were studied at low temperatures as a function of both back- and frontgate voltages. The mobility increased by a ratio as high as 5 as the backgate voltage was changed from 0 to +1.4 V, and also showed a carrier density dependence steeper than that expected from remote ionized impurity scattering when the carrier density was lower than 2×1011 cm−2. The experimental results were compared to theoretical calculations based on the shape of the wave function.
Guided modes with ordinary refractive index in proton exchanged LiNbO3 waveguides
Authors: Olivares J. , Cabrera J. M.
Published: July 2002

A method is proposed and demonstrated to fabricate guiding layers on ordinary refractive index in proton exchanged LiNbO3 waveguides. The process consists of performing a reverse exchange in a melt very rich in lithium on a substrate previously exchanged in normal benzoic acid. Layers supporting several modes with ordinary polarization are easily obtained. Losses for these modes have been found to be below 0.7 dB/cm. Together with the increase of ordinary index, a decrease of the extraordinary one is obtained so that buried modes can be guided with this polarization. The influence on the reverse process of the exchange temperature, the substrate cut, and the melt composition is studied.
Optical bistability at 980 nm in a strained InGaAs/GaAs multiple quantum well microcavity with resonant periodic nonlinearity
Authors: Pellat D. , Azoulay R. , Leroux G. , Dugrand L. , Rafflé Y. , Kuszelewicz R. , Oudar J. L.
Published: July 2002

We report on a novel monolithic all-optical bistable device operating at 980 nm, based on the dispersive optical nonlinearity of strained InGaAs/GaAs quantum wells located at the antinodes of the microcavity optical field. This design maximizes the interaction with the intracavity field and allowed to use only twelve quantum wells of 10 nm thickness. The first observation of all-optical bistability with strained InGaAs/GaAs quantum wells is reported, with a contrast ratio of 7:1 and a threshold intensity of 1 kW/cm2. The operating wavelength offers key advantages such as the substrate transparency and compatibility with vertical cavity surface emitting lasers.
Admittance spectroscopy of boron doped diamond
Authors: Glesener J. W. , Snail K. A. , Morrish A. A.
Published: July 2002

The boron acceptor level in diamond was investigated using admittance spectroscopy. The conductance of a flame grown sample was measured between 125 and 200 K at five frequencies between 0.1 and 5.0 kHz using a 16.0 mV ac signal applied across a Schottky diode at zero dc bias. The admittance spectroscopy technique yielded a deep impurity level of 0.33 eV. From the same set of data, a hole capture cross section of 2×10−12 cm2 was also measured. The cross section reported here is assumed to be caused by ionized boron acceptors.
Enhancement of photosensitivity by ultraviolet irradiation and photoconductivity spectra of diamond thin films
Authors: Vaitkus R. , Inushima T. , Yamazaki S.
Published: July 2002

The evolution of photocurrent in time under ultraviolet (UV) irradiation of free-standing diamond thin films, prepared by chemical vapor deposition method, have been observed. A significant enhancement of the photosensitivity in visible-near-infrared region of UV illuminated samples have been obtained. The linear dependence of relative change of photocurrent on UV radiant intensity have been found. The photoconductivity spectra have been investigated in the energy range 1–6.2 eV. The results of investigation have shown that diamond thin films possess similar properties as radiation damaged crystalline diamond.
In situ, rf plasma deposition of Bi2Sr2Ca2Cu3Ox thin films at atmospheric pressure
Authors: Shah A. , Patel S. , Narumi E. , Shaw D. T.
Published: July 2002

Superconducting Bi2Sr2Ca2Cu3Ox thin films have been prepared in situ at atmospheric pressure by an inductively coupled, argon-oxygen rf plasma. This high Tc phase has been achieved by exposing the grown film, in situ, to the same argon-oxygen plasma used for the deposition of the film. No post-annealing steps are required. Bi2Sr2Ca2Cu3Ox films with critical temperatures of 100 K and critical current densities of 1×105 A/cm2 at 77 K and zero field have been obtained at a deposition rate of 100–200 Å/min. The films are mirror smooth with very few particulates and pinholes. Control of the substrate heater temperature is critical as high-quality films grow only in a narrow temperature range. The effect of plasma treatment and substrate heater temperature is discussed.
Carbon doping in GaAs layers grown with trimethylgallium and solid arsenic in a mixture of hydrogen and nitrogen
Authors: Peña-Sierra R. , Escobosa A. , Sanchez-R. V. M.
Published: July 2002

Carbon doped GaAs epitaxial layers have been grown using solid arsenic and trimethylgallium. Carbon incorporation, proceeding from the organic radicals, was found to be dependent on the hydrogen partial pressure. The latter was fixed by the introduction of nitrogen in the carrier gas. Controlled p-doping between 1016 and 1221 cm−3 has been obtained by adjusting the composition of the carrier gas. The growth rate of the layers was found to be reduced by the introduction of nitrogen. Mirrorlike surfaces were obtained if at least 2% hydrogen was mixed in the carrier gas, but only polycrystalline films could be grown in a pure nitrogen atmosphere.
Photoemission spectroscopy of Al0.27Ga0.73As:As photodiodes
Authors: McInturff D. T. , Woodall J. M. , Warren A. C. , Braslau N. , Pettit G. D. , Kirchner P. D. , Melloch M. R.
Published: July 2002

We report on photoemission measurements of MBE-grown Al0.27Ga0.73As p-i-n structures in which the optically active insulating layers contain arsenic precipitates (Al0.27Ga0.73As:As). Al0.27Ga0.73As:As layers were formed by low temperature growth of Al0.27Ga0.73As followed by a high temperature anneal. GaAs layers grown in this way have been reported to be sensitive to subband-gap light. A Fowler plot constructed from an internal photoemission measurement gave a barrier height of 0.93 eV. We compare this result with the barrier height of arsenic in GaAs that was found to be 0.7 eV using the same structure and measurement scheme. This result demonstrates that the barrier height of embedded metallic arsenic clusters in AlxGa1−xAs is consistent with the heterostructure conduction band offset and can be selected by changing the composition of the host material.
Anomalous As desorption from InAs(100) 2×4
Authors: Sasaoka C. , Kato Y. , Usui A.
Published: July 2002

Arsenic desorption from the InAs(100) 2×4 surface is investigated through temperature programmed desorption (TPD), isothermal desorption, and reflection high-energy electron diffraction. TPD area analysis indicates that the As coverage, θAs, of the InAs 2×4 structure is 0.7 monolayers. The As TPD spectrum shows two desorption features; a broad tail from 300 to 400 °C and a distinct peak at 430 °C. The 430 °C peak is well described in terms of a first-order-desorption kinetics with a preexponential factor ν of 1.5×1019 s−1. This extremely high ν value explains well the narrow window of optimal molecular beam epitaxy growth conditions for InAs.
C54-TiSi2 formed by direct high current Ti-ion implantation
Authors: Zhu D. H. , Tao K. , Pan F. , Liu B. X.
Published: July 2002

We report, in this letter, the formation of TiSi2 by direct Ti-ion implantation into silicon wafers using a metal vapor vacuum arc ion source. Implantation was conducted by 80 KeV Ti ions to a dose of 5×1017/cm2 with various ion current densities. When the ion current density exceeded 100 μA/cm2, the equilibrium TiSi2 of the C54 structure was uniquely formed. Additional evidence of the formation of C54-TiSi2 was given by the resistivity measurements, i.e., the sheet resistivity was below 3.0 Ω/⧠. The formation mechanism is also discussed in terms of the beam heating effect during implantation.
Zinc doping of Ga0.51In0.49P grown on GaAs(100) substrates by chemical beam epitaxy
Authors: Kapre R. M. , Tsang W. T. , Ha N. T. , Wu M. C. , Chen Y. K.
Published: July 2002

We report on the p-type doping of Ga0.51In0.49P lattice matched to GaAs(100) using gaseous diethylzinc by chemical beam epitaxy. The doping concentration was found to decrease with substrate temperature with an apparent activation energy of 5.3 eV. It was found necessary to keep the substrate temperature below about 500 °C to obtain doping in the 1018/cm3 range. The doping concentration shows a 0.8th power law with increasing dopant flow rate and saturates at approximately 5×1018/cm3. The p-doped GaInP layers were used as cladding layers for 0.98 μm strained InGaAs/GaAs lasers which show state-of-the-art performance.
Local silicon molecular beam epitaxy with microshadow masks
Authors: Hammerl E. , Eisele I.
Published: July 2002

A novel method for the in situ patterning of silicon layers grown by molecular beam epitaxy is investigated. Using microshadow masks deposited directly onto silicon substrate epitaxial mesa patterns can be fabricated. The local growth and the resulting geometrical shape of the mesa structures is studied as a function of the substrate temperature during the MBE process.
Enhancement of zone-folding effects in the second order response of the [(Si)5/(Ge)5]/(Si0.4Ge0.6)(001) superlattice
Authors: Ghahramani Ed , Sipe J. E.
Published: July 2002

We have carried out a full band structure calculation of the second harmonic generation (SHG) coefficient and the linear response function of a [(Si)5/(Ge)5] superlattice (SLS) on a Si0.4Ge0.6 alloy substrate. Our calculation gives the first indication of the magnitude, frequency dependence, and anisotropy of the second order response in this SLS. The ratio of the features due to zone-folded transitions to those due to bulk-like transitions is an order of magnitude larger than the same ratio in the linear response. Yet these zone-folded effects are still very small. Nonetheless, the overall size of the SHG coefficient for this SLS is slightly larger than that of the corresponding SLS on a Si(001) substrate.
Buried modes in combined Ti diffused and Li outdiffused LiNbO3 slab waveguides
Authors: Arad Eli , Ruschin Shlomo , Nir David
Published: July 2002

Buried waveguiding planar modes of well-defined profiles were observed in samples undergoing simultaneous Ti indiffusion and Li outdiffusion in a water vapor atmosphere. Each of these modes was distinctly excited by end-fire fiber coupling and suffered no loss by metal loading. An index profile which fits the mode shapes measured, and a mechanism is suggested based on the influence of a Ti-rich layer compound on the Li outdiffusion process.
Green/yellow light emitting diodes from isoelectronically doped ZnSe quantum well structures
Authors: Hagerott M. , Ding J. , Jeon H. , Nurmikko A. V. , Fan Y. , He L. , Han J. , Saraie J. , Gunshor R. L. , Hua C. G. , Otsuka N.
Published: July 2002

Green/yellow emission has been obtained from ZnSe-based pn junction heterostructures where Te is introduced as an isoelectronic center by planar doping of (Zn,Cd)Se quantum wells with ZnTe. The spectra show details which are directly related to the strong coupling of excitons to the lattice at the Te-rich sites.
Graphoepitaxy of YBa2Cu3O7 thin films
Authors: Dozier William D. , Platt Christine E.
Published: July 2002

We report on the graphoepitaxial growth of YBa2Cu3O7 (YBCO) thin films on LaAlO3 (LAO) substrates textured with submicron features. This is the first use of a substrate microstructure to template and control the morphology of a thin film. Two-dimensional close-packed crystalline monolayers of polystyrene spheres 482 nm in diameter are used as lithographic masks for the ion milling of arrays of conical posts in the substrates. This regular pattern is reflected in the growth of the YBCO film which is at once epitaxial to the substrate and disrupted on the same length scale as the substrate texture. The YBCO thin films are structurally and electrically of the same quality as films deposited on untreated substrates.
Temperature characteristics of (InAs)1/(GaAs)4 short-period superlattices quantum well laser
Authors: Dutta N. K. , Chand Naresh , Lopata J. , Wetzel R.
Published: July 2002

The temperature characteristics of (InAs)1/(GaAs)4 superlattice quantum well lasers are analyzed both experimentally and theoretically. The measured threshold current density as a function of temperature is characterized by a T0=135 K for 115 K<T<380 K and by T0=47 K for 420 K<T<480 K. The radiative and nonradiative recombination rates and the gain versus carrier density relationship in monolayer superlattice structures are calculated. Inclusion of the nonradiative recombination process is necessary to explain the observed high-temperature characteristics of these lasers.
980 nm ridge waveguide laser reliability at 100 mW
Authors: Heath L. S. , Meehan K. , Chin A. K. , Gavrilovic P. , Zarrabi J. H. , Wober M. , Bisberg J. E.
Published: July 2002

Reliable, single-mode, 100 mW operation of strained-layer InGaAs single quantum well ridge waveguide lasers is demonstrated. The mean time to failure of coated, 5 μm wide lasers aged at constant current is over 100 000 h at 25 °C. Peak output power is 300 mW per facet, limited by thermal effects. The lasing wavelength is 980 nm. Preliminary results of pumping an erbium-doped fiber laser are reported.
Observation of thin film of one-dimensional organic conductor tetrathiofulvalene tetracyanoquinodimethane by means of atomic force microscopy
Authors: Nakajima Ken , Kageshima Masami , Ara Norihiko , Yoshimura Masamichi , Kawazu Akira
Published: July 2002

Thin films of the charge transfer complex of tetrathiofulvalene tetracyanoquinodimethane (TTF-TCNQ) deposited on KC1 and KBr were studied by atomic force microscopy (AFM). Structures corresponding to the molecular arrangement of the crystallographic ab-plane were observed in the molecular-scale AFM images. Large-scale imaging (15×15 μm) revealed that the films consist of rectangular islands whose longer sides (corresponding to the highly conductive b-axis) orient in the [110] or [1̄10] direction of the KC1 and KBr(001) surfaces. A small number of islands rotated 32° from the [110] direction were also observed on the KBr substrate. The arrangement of these islands can be explained by considering the adsorption of a TCNQ molecule to the metastable state.
Observation of phonon-plasmon coupled modes at the interface between ZnSe and semi-insulating GaAs by micro-Raman spectroscopy
Authors: Ichimura M. , Usami A. , Wada T. , Fujita Sz. , Fujita Sg.
Published: July 2002

We demonstrate that the nature of the interface between ZnSe and semi-insulating GaAs can be studied by observing the phonon-plasmon coupled mode by micro-Raman spectroscopy. When the GaAs substrate is sulfur-treated before the growth of ZnSe, the phonon-plasmon coupled mode is clearly observed in micro-Raman spectra. The plasmon is believed to be composed of electrons excited by the focused laser beam used in the micro-Raman measurement. The coupled mode is weak when the substrate is not sulfur-treated. The reduction in the coupled-mode intensity will be due to interface states which widen the depletion layer and shorten the lifetime of excess carriers.
High performance strained InGaAs/AlGaAs buried-heterostructure quantum-well lasers fabricated by in situ etching and regrowth
Authors: Chand Naresh , Dutta N. K. , Chu S. N. G. , Syrbu A. V. , Mereutza A. Z. , Yakovlev V. P.
Published: July 2002

We report a novel method for growth and fabrication of high performance strained InGaAs/AlGaAs quantum-well buried-heterostructure (BH) lasers. The method involves growth of the laser structure by molecular beam epitaxy, mesa formation by in situ melt etching using SiO2 stripes as a mask, and regrowth of p−-p-n AlGaAs isolating layers by liquid phase epitaxy. The method allows etching, preservation of high quality sidewalls, regrowth, and planarization in one step with negligible thermal disordering. Compared to ridge waveguide lasers, the BH lasers so fabricated have significantly lower threshold current, higher power output, higher temperature operation, lower cavity losses, and kink-free light-current (L-I) characteristics, as expected. A cw power of 150 mW/facet at 986 nm was measured from a 400-μm-long BH laser with 11 μm active stripe width. A minimum threshold current of 2.5 mA was measured for lasers with 3.0 μm active width and 300–400 μm cavity length. The L-I characteristics of 500-, 800-, and 1300-μm-long lasers with 3.0 μm active width were linear up to the currents corresponding to a current density of 10 kA cm−2. At higher current densities, a sublinear increase of power with current was observed. Stable fundamental transverse mode operation was obtained up to 100 mW emitted power.
Direct observation of gold valence change as a function of oxygen stoichiometry in YBa2Cu3−yAuyO7−δ
Authors: Eibschütz M. , Lines M. E. , Reiff W. M. , van Dover B. , Waszczak J. V. , Zahurak S. , Felder R. J.
Published: July 2002

A study of the Au197 Mössbauer resonance is reported as a function of oxygen stoichiometry for gold-doped YBa2Cu3O7−δ. Three separate Mössbauer features are identified and correspond respectively to gold metal particles, Au3+ in a square-planar Cu(1) site, and Au+ in a two-ligand c-axis coordinated Cu(1) site. All the gold successfully incorporated into the 123-structure is trivalent at full oxygenation (O7.02) but is reduced as a function of decreasing oxygen content until only monovalent gold remains at the orthorhombic to tetragonal transition (≊O6.4). A significant fraction of the Au3+ in the oxygenated sample resides near grain boundaries and is precipitated as gold particles upon reduction. The observation of monovalent gold in the reduced sample is the first report of the existence of Au+ with uniquely oxygen coordination for any material.
New technique to produce Au/Mox (M=Ti or Al) glass composite containing Au microcrystals at high concentration
Authors: Noguchi Toru , Hayashi Shigehiko , Kawahara Masahito , Gotoh Kazuo , Yamaguchi Yoshio , Deki Shigehito
Published: July 2002

A new technique for the preparation of metal oxide glass composite uniformly containing a very large amount of nanometer-size microcrystals up to 80 mol % is reported. Due to the strong interactions between Au and metal oxides, Au microcrystals were surrounded and held in Ti or Al oxides, and, therefore, did not aggregate. The interactions also affected the plasmon bands of Au particles.
Low-voltage hetero-nipi waveguide modulators with GaAs/AlAs quantum wells
Authors: Yoffe G. W. , Brübach J. , Karouta F. , van der Vleuten W. C. , Kaufmann L. M. F. , Wolter J. H.
Published: July 2002

We present a waveguide modulator with a GaAs/AlAs multiple-quantum-well hetero-nipi core. Selective lateral ohmic contacts connect all the p-type layers together and likewise all the n-type layers. A small applied voltage creates a large change in the field across each thin undoped quantum well region, causing large changes in the absorption coefficient and refractive index. A 300-μm-long device gave a 10:1 modulation ratio at 1-V reverse bias with 4-dB zero-bias absorption loss. 400- and 900-μm-long devices gave a 180° phase shift with negligible absorption loss at 1.5 and 0.9 V, respectively.
Effects of nonuniform current injection on the spectral dynamics of multisection distributed feedback lasers
Authors: Iannelli J. M. , Schrans T. , Chen T. R. , Zhuang Y. H. , Yariv A.
Published: July 2002

The effects of nonuniform current injection on the linewidth enhancement factor (α) and the adiabatic chirp in a multielectrode distributed feedback laser are measured through a FM/AM modulation technique. This technique measures the adiabatic chirp due solely to carrier density effects and excludes the contributions of current induced temperature changes. The effects are shown to be a function of the pumping ratio between two active sections in the laser. The adiabatic chirp is enhanced by as much as a factor of 3 and the α parameter is reduced from a value of approximately 4 to 2.