bluuebunny/crossref_metadata_2025 huggingface dataset:
Hydrogen passivation effect in Si molecular beam epitaxy
Authors: Hirayama Hiroyuki , Tatsumi Toru
Published: July 2002

Hydrogen passivation of the clean Si(100) surface to prevent growth of native oxides after air exposure was studied by supplying atomic hydrogen at several temperatures between room temperature and 650 °C. Atomic hydrogen was generated with high efficiency by the electron cyclotron resonance plasma cell of the gas source Si molecular beam epitaxy apparatus. The passivation effect was examined by observing the oxygen KLL Auger peak height of the passivated wafer after 12 h air exposure. The wafer supplied with atomic hydrogen at temperatures below 400 °C showed an obvious passivation effect, while the wafer supplied with hydrogen at temperatures above 400 °C showed no passivation effects. The solid source Si MBE growth was done on these hydrogen-passivated and 12 h air-exposed wafers at the growth temperature of 600 °C without any initial surface cleaning process. A good crystal quality film which showed a sharp 2×1 reflection high-energy electron diffraction pattern was obtained on the wafer supplied with hydrogen at temperature below 400 °C.
Indirect trench sidewall doping by implantation of reflected ions
Authors: Fuse Genshu , Ogawa Hisashi , Tamura Kayoko , Naito Yasushi , Iwasaki Hiroshi
Published: July 2002

Ion implantation (i/i) technology is employed for silicon trench sidewall doping. The aspect ratio of trenches for high Mbit DRAM is very large (depth/width≥10), so that very small glancing-angle i/i to sidewalls is necessary. In this case, reflected ions are large in number and are implanted to the opposite sidewall. It is very important to know the elemental depth profile in the opposite sidewall to understand the implantation mechanism. For the first time, we measured the depth profiles at several positions of the opposite trench sidewall by secondary-ion mass spectroscopy for arsenic and boron ion implantations. It is found that reflected ions are distributed near the facing region of the directly implanted region with smaller energies than the primary energy. These findings are compared with the simulations based on the marlowe program.
Observation of envelope soliton propagation in a new nonlinear transmission line
Authors: Dragoman M. , Căţoiu M.
Published: July 2002

This letter reports narrowing and splitting of microwave pulses in a new nonlinear transmission line whose elements are yttrium iron garnet resonators. At certain power levels, the observed behavior can be interpreted as envelope solitons.
As-grown crystallized thin film of Bi-Sr-Ca-Cu-O and its low-temperature annealing effect
Authors: Miura S. , Nakai A. , Shimakawa Y. , Yoshitake T. , Miyasaka Y. , Shohata N. , Satoh T.
Published: July 2002

The as-grown crystallized films of low Tc phase (Tc∼80 K) in a Bi-Sr-Ca-Cu-O system were prepared by rf magnetron sputtering and were annealed in argon or oxygen atmosphere below 500 °C. Superconducting properties and the c-axis lattice constant varied according to the annealing temperature and atmosphere. These results suggest that the oxygen content in the film is varied by low-temperature annealing and that the variation of oxygen content affects the superconducting and structural properties. By cooling the sample in the chamber in 760 Torr oxygen, the as-grown film with Tc end at 74 K was obtained.
Crystal structure of DyBa2Cu4O8: A new 77 K bulk superconductor
Authors: Hazen Robert M. , Finger Larry W. , Morris Donald E.
Published: July 2002

Single-crystal x-ray diffraction data from DyBa2Cu4O8 are used to confirm the structure of RBa2Cu4O8 (R=Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, and Tm), all of which have been synthesized in bulk and display substantial Meissner diamagnetism. The structure is orthorhombic, space group Ammm, with a=3.846 3(3), b=3.872 6(3), and c=27.237(2) Å. Copper-oxygen layers parallel to (001) are dimpled as in the 1-2-3 structure. Unique copper-oxygen strips parallel to (100) have copper in distorted square-planar coordination. Magnitudes of oxygen anisotropic thermal vibrations are significantly less than in the 1-2-3 structure; thus the oxygen content of 1-2-4 is expected to be significantly more stable.
Shallow, silicided p+/n junction formation and dopant diffusion in SiO2/TiSi2/Si structure
Authors: Ku Y. H. , Lee S. K. , Kwong D. L. , Chu P.
Published: July 2002

Shallow silicided p+/n junctions have been formed by implanting boron ions into titanium disilicide layers and the subsequent drive-in of the implanted boron into the Si substrate by rapid thermal annealing (RTA). Results of boron diffusion in titanium disilicide layer, its segregation at both silicide/Si and oxide/silicide interfaces, and the junction quality are presented. The precipitation of boron at the SiO2/TiSi2 interface is identified for the first time in the form of B2O3. p+/n diodes and short-channel metal-oxide-semiconductor field-effect transistors with good electrical characteristics have been fabricated using doped silicide technology.
Narrow tracks in YBa2Cu3O7 thin films defined by laser ablation
Authors: Humphreys R. G. , Satchell J. S. , Chew N. G. , Edwards J. A.
Published: July 2002

The use of cw laser ablation for defining narrow tracks in YBa2Cu3O7 thin films on (001) SrTiO3 substrates is described. Critical current densities have been observed up to 5×105 A/cm2 in 4-μm-wide tracks at 77 K. For these films, it is found that the value of critical current density calculated is insensitive to the length of track and the voltage criterion used.
Fabrication of stable superconductive wires with YBa2Cu3Ox/Ag2O composite core
Authors: Sen S. , Chen In-Gann , Chen C. H. , Stefanescu D. M.
Published: July 2002

The problem of maintaining the oxygen stoichiometry of the Y1Ba2Cu3Ox (the so-called 123) compound at the desired level of x=6.0±0.1 when fabricating superconducting wires using the powder-in-tube method is addressed. A solution to this problem appears to be incorporating an unstable oxide like Ag2O in the core material, such that it acts as an in situ oxygen donor during the final sintering or annealing stage. Moreover, the segregation of Ag at the grain boundaries of the 123 grains and at the porosities seems to be a possible reason for the considerable improvement of the critical current density Jc of these wires. The effect of processing parameters, like different sintering temperatures and addition of various percentages of either Ag or Ag2O, is presented. Finally, in order to test conservation of superconductive properties during handling, the wires were subjected to different degrees of bending, and the subsequent effect on superconducting transition temperature, Tc and Jc, is reported.
Laser-assisted etching of YBa2Cu3O7−δ
Authors: Hussey B. W. , Gupta A.
Published: July 2002

Superconducting YBa2Cu3O7−δ has been etched using a focused cw Ar+ laser beam in KOH solution. The results indicate clean and rapid removal of reaction products leaving high aspect ratio grooves. Etch rates are investigated under several conditions; etch geometry is discussed as a function of laser power density and scan speed. The surface reaction with KOH is thermally activated, and the residual material is identified by energy dispersive x-ray spectroscopy, x-ray powder diffraction, and chemical analysis.
Superconducting films grown i
n s
i
t
u by the activated reactive evaporation process
Authors: Prakash S. , Umarjee D. M. , Doerr H. J. , Deshpandey C. V. , Bunshah R. F.
Published: July 2002

The low-pressure activated reactive evaporation process was used successfully to grow superconducting thin films that were uniform in thickness, free of cracks, voids, spits, and other source-related defects, and with mirror-like surface smoothness. These are important considerations for the practical use of these materials in thin-film form. No post-deposition annealing was carried out. Tc (0) for films on yttria-stabilized zirconia (YSZ) substrates is close to 80 K, and the (001) preferred orientation was observed with higher deposition temperatures in the range 550–650 °C. Films on silicon and sapphire substrates were adversely affected by interdiffusion, showing a Tc (0) of 56 and 72 K, respectively.
Combined effect of strained-layer superlattice and annealing in defects reduction in GaAs grown on Si substrates
Authors: El-Masry N. A. , Tarn J. C. L. , Bedair S. M.
Published: July 2002

The high defect density in GaAs grown on Si can be reduced by the combined use of the strained superlattices (InGaAs-GaAsP) and annealing. The strained-layer superlattice (SLS) bends the dislocations and acts as a medium for dislocations interactions, and annihilations. Highly strained SLS (∼2%) is required to bend the dislocations and keep them bent at the SLS interfaces. The SLS coupled with annealing permits a remarkable reduction of threading dislocation density. Annealing provides the energy for threading dislocations to interact with the SLSs and improves their efficiency significantly.
Observation of ultrashort (<4 ps) gain-switched optical pulses from long-wavelength multiple quantum well lasers
Authors: Nagarajan Radhakrishnan , Kamiya Takeshi , Kasukawa Akihiko , Okamoto Hiroshi
Published: July 2002

Optical pulses of less than 4 ps full width at half maximum have been generated by electrical gain switching of long-wavelength multiple quantum well lasers, and were observed directly on a streak camera. This is the first ever generation of optical pulses of such short duration using direct electrical gain switching. We have identified the higher differential gain due to the second quantized state transition in the multiple quantum well laser to be responsible for the generation of these ultrashort optical pulses. We also discuss the possible resolution limits of the streak camera measurement system.
Influence of the crystallinity of the alignment layer on the bistability of the surface-stabilized ferroelectric liquid-crystal effect
Authors: Hartmann W. J. A. M. , Luyckx-Smolders A. M. M. , Kessel R. P. v.
Published: July 2002

The influence of the crystallinity of the alignment layers on the electro-optical behavior of ferroelectric liquid crystals has been quantitatively demonstrated. The degree of crystallization of thin nylon 6.6 alignment layers was varied using thermal anneal methods and determined by Fourier transform infrared spectroscopy. The reaction of an obtained memory state of surface-stabilized ferroelectric liquid-crystal samples to small disturbing electric fields decreased when the degree of crystallization of the incorporated nylon 6.6 alignment layers was higher.
Void formation and inhibition of layer intermixing in ion-impIanted GaAs/AlGaAs superlattices
Authors: Chen Samuel , Lee S.-Tong , Braunstein G. , Tan T. Y.
Published: July 2002

Voids have been found in the near-surface region of GaAs/AlGaAs superlattices in a transmission electron microscopy study. The superlattices were Si- or Al-implanted and subsequently either furnace or rapid thermally annealed. Concurrent with the presence of voids is an inhibition of superlattice layer intermixing enhancement in the near-surface region. This inhibition does not occur in the deeper region of the samples where voids are not found. The voids can form via condensation of the Ga and As vacancies produced by the implantation process. We suggest that voids can depress dopant activation, suppress dopant diffusion, and inhibit the superlattice layer intermixing enhancement.
Electrical characterization of p-type ZnSe
Authors: DePuydt J. M. , Haase M. A. , Cheng H. , Potts J. E.
Published: July 2002

ZnSe epitaxial layers doped with lithium have been found to be p type with resistivities as low as 2.9 Ω cm. The majority-carrier types of these films were determined using both capacitance-voltage and potential profiling techniques. The sample resistivities were obtained using ac resistivity measurements and potential profiling. Uncompensated acceptor densities have been measured to be as high as 8×1016 cm−3 using capacitance-voltage profiling. Current-voltage traces taken with evaporated and sputtered gold contacts typically show reverse breakdown which is consistent with avalanche breakdown in these materials.
Effect of As4 overpressure on initial growth of gallium arsenide on silicon by molecular beam epitaxy
Authors: Palmer J. E. , Burns G. , Fonstad C. G. , Thompson C. V.
Published: July 2002

We have demonstrated great improvement in the smoothness and defect density of GaAs films on Si by lowering the arsenic overpressure during growth of the initial layer (the first 500 Å) of GaAs. We have studied the morphology and defect density of GaAs on Si films in which the initial layers were grown under either low As4 overpressure (7As4:1Ga, beam equivalent pressure) or high As4 overpressure (15As4:1Ga) conditions, with a constant gallium flux. In the early stages of growth there is a significant change in island morphology depending on the As4 overpressure. There is dramatic improvement of surface smoothness and crystal quality with reduced arsenic overpressure for 500-Å-thick layers both immediately after growth at 350 °C and after heating to 580 °C. Diodes fabricated in 3.5-μm-thick films grown on initial layers that were grown under low arsenic overpressure have a very sharp reverse breakdown at voltages as high as 45 V, whereas diodes fabricated in films grown on initial layers that were grown under high arsenic overpressure have a soft reverse breakdown at about 5 V. This demonstrates a significant reduction in the density of electrically active defects in the thick GaAs films with decreasing arsenic overpressure conditions during growth of the initial 500 Å of GaAs on Si. The improvement in film quality for low As4 overpressures is discussed in terms of the observed changes in island morphology.
Diffusion of implanted beryllium in gallium arsenide as a function of anneal temperature and dose
Authors: Deal Michael D. , Robinson Heyward G.
Published: July 2002

The diffusion of implanted Be in GaAs was studied by annealing samples of GaAs implanted with low and high doses of Be. The high-dose (1×1014 cm−2) samples show an increase in diffusion with increasing anneal temperature from 700 to 900 °C. However, the low-dose (2×1013 cm−2) samples show a decrease in diffusion as the temperature is increased. The temperature dependence of the low-dose case can be reversed by coimplantation of 1×1014 cm−2 boron. This behavior is explained in terms of the substitutional-interstitial diffusion mechanism and the relative concentrations of Be interstitials and Be substitutionals for the different cases.
Identification of a nickel double-acceptor state in indium phosphide
Authors: Korona K. P. , Hennel A. M.
Published: July 2002

We present the first successful attempt to identify the Ni impurity level in indium phosphide. Ni-doped n-type InP crystals were investigated using deep level transient spectroscopy and optical absorption. A new electron trap with energy of 0.27±0.02 eV below the InP conduction band and an electron capture cross section of 10−13 cm2 was found. In the absorption spectrum a new zero-phonon line with energy of 0.57 eV was observed. We interpret these results as an observation of a Ni2+/Ni+ double acceptor level and an optical intracenter transition 2T2→2E within the Ni+(3d9) configuration. A vacuum-referred binding energy of the nickel double acceptor state in InP determined in our experiment is in good agreement with the vacuum-referred binding energies of the nickel impurity in GaAs and GaP.
Reaction of trimethylgallium in the atomic layer epitaxy of GaAs (100)
Authors: Yu Ming L. , Memmert Ulrich , Kuech Thomas F.
Published: July 2002

The initial reaction of the As-rich c(2×8) GaAs(100) surface with trimethylgallium (TMGa) has been studied by x-ray and ultraviolet photoemission. TMGa was found to chemisorb dissociatively at temperatures below 300 °C with many of the methyl radicals remaining on the surface. Bonding requirements and steric effects limit the saturation coverage to about 0.1 monolayer. At temperatures above 300 °C, TMGa was observed to dissociate on the surface, release all the methyl groups, and deposit Ga up to a self-limiting coverage. This process is most effective at high temperatures. We propose a model for the temperature dependence of the chemisorption which explains and unites many reported observations in the atomic layer epitaxy of GaAs using TMGa and arsine.
Electron transport coefficients in dusty argon plasmas
Authors: McCaughey Michael J. , Kushner Mark J.
Published: July 2002

Low-temperature partially ionized plasmas, as used in plasma processing reactors and gas lasers, are often contaminated by gas phase particulates (1–10’s μm radius) resulting from electrode sputtering or gas phase chemical reactions. Particles having sizes comparable to or greater than the Debye length will negatively charge in the plasma and form a sheath at their surfaces. These particles thereby become a Coulomb-like scatterer of electrons. A hybrid Monte Carlo/molecular dynamics computer simulation has been developed to study the effect of such particulate contamination on electron transport in glow discharges and this letter presents results for argon. The dominant effect of particulate contamination is to shift the electron energy distribution to lower energies, thereby reducing electron impact rate coefficients for processes which have high threshold energies, particularly ionization. The self-sustaining E/N of discharges having dusty plasmas is therefore increased. The effect, proportional to particle density, begins to become important at a density of 103–105 cm−3 for gas pressures of 0.1–3 Torr.
High-power, in-phase-mode operation from resonant phase-locked arrays of antiguided diode lasers
Authors: Mawst L. J. , Botez D. , Roth T. J. , Peterson G.
Published: July 2002

A resonant phase-locked array of antiguides is demonstrated for the first time. A 10/11 element AlGaAs/GaAs antiguided array is grown by two-step metalorganic chemical vapor deposition. Longitudinally, the structure consists of two noncollinear sets of antiguides separated by a half-Talbot distance, an ensemble that acts as a spatial filter. Out-of-phase-mode operation is suppressed both by this diffractive-type spatial filter and by large interelement loss. Resonant in-phase-mode operation is a result of the interelement spacing corresponding to one leaky-wave half wavelength in the lateral direction. Near the in-phase-mode resonance, array modes adjacent to the in-phase-mode are discriminated against because they have large radiation losses in the antiguided structure and significant edge diffraction losses in the spatial filter. Stable, diffraction-limited in-phase-mode beam patterns are achieved to 10 times threshold and 450 mW output power.
Hole tunneling times in GaAs/AlAs double-barrier structures
Authors: Yu E. T. , Jackson M. K. , McGill T. C.
Published: July 2002

We have calculated hole tunneling times in GaAs/AlAs double-barrier structures taking quantum well band-mixing effects into account. Our results indicate that for sufficiently high hole temperatures and concentrations, band-mixing effects reduce average hole tunneling times from the pure heavy hole value to values comparable to electron tunneling times in the same structure. For very low hole temperatures and concentrations, band mixing is less important and average hole tunneling times should approach the pure heavy hole value. These results provide an explanation for previously reported experimental results in which electrons and holes were found to be characterized by very similar tunneling times.
Resonant tunneling of holes in AlSb/GaSb/AlSb double-barrier heterostructures
Authors: Beresford R. , Luo L. F. , Wang W. I.
Published: July 2002

We have made the first observations of resonant tunneling in the AlSb/GaSb material system. Double-barrier p-type heterostructures exhibit two distinct features in their current-voltage characteristics, indicating resonant tunneling via confined valence-band states. The measured energy level positions are consistent with a substantial valence-band offset of approximately 0.4 eV.
Investigation of dislocation jump distance during creep of NaCl single crystals using nuclear magnetic resonance pulse techniques
Authors: Murty K. Linga , Begert D. , Munter R. , Kanert O.
Published: July 2002

Nuclear magnetic resonance pulse techniques are applied in situ to investigate the dynamics of mobile dislocations during creep deformation of NaCl single crystals. 23Na spin-lattice relaxation rates were measured in the rotating frame (T1ρ) during compression creep of single crystals of NaCl along the [110] direction at 478 K and 20 MPa. The relaxation rates are evaluated from the spin-echo height following a π/2 locking and 64° pulse sequence. The mean jump distance of the mobile dislocations, evaluated from the ratio of the signal heights without deformation and during creep, decreased with time/strain reaching a constant value at the onset of the steady-state creep regime. The results are compared with the dislocation-dislocation spacing, the subgrain size, and the jump distance predicted from creep models.
Novel method to fabricate corrugation for a λ/4-shifted distributed feedback laser using a grating photomask
Authors: Okai M. , Tsuji S. , Chinone N. , Harada T.
Published: July 2002

A novel method was developed to fabricate corrugation for a λ/4-shifted distributed feedback (DFB) laser. Mechanically ruled grating patterns were transferred photolithographically to the surface of an InP substrate. The resultant λ/4-shifted DFB laser operated in a single longitudinal mode at the Bragg wavelength.
Metalorganic chemical vapor deposition of Tl2CaBa2Cu2Oy superconducting thin films on sapphire
Authors: Zhang K. , Boyd E. P. , Kwak B. S. , Wright A. C. , Erbil A.
Published: July 2002

Superconducting Tl2CaBa2Cu2Oy thin films have been successfully grown on the single-crystal sapphire (11̄02) substrate by using the metalorganic chemical vapor deposition technique. The growth rate of the films was about 5 μm/h. The as-deposited film was post-annealed in a partially sealed ceramic crucible in the presence of a Tl2Ca2Ba2Cu3Oy pellet to achieve the superconducting phase. The x-ray data show strong diffraction from the Tl2CaBa2Cu2Oy superconducting phase in addition to the trace amounts of Ca2CuO3 and BaCO3. Superconducting transition temperatures with onset above 100 K and zero resistance at 94 K can be obtained by further heat treatment at 500 °C in oxygen.
Optical study of residual strains in CdTe and ZnTe layers grown by molecular beam epitaxy on GaAs
Authors: Dang Le Si , Cibert J. , Gobil Y. , Saminadayar K. , Tatarenko S.
Published: July 2002

Residual strains in (001) and (111) thick layers of CdTe and ZnTe grown by molecular beam epitaxy on nominal or slightly tilted (001) GaAs have been investigated by reflectance, photoluminescence, and optical pumping experiments at low temperature. Strains are found to be independent of both layer orientations and thicknesses in the range 2–6 μm. They are compressive ≊−0.5×10−3 in CdTe and tensile ≊10−3 in ZnTe. Estimates of thermal expansion effects show that they are the dominant cause of residual strains in these heterostructures.
New field-effect resonant tunneling transistor: Observation of oscillatory transconductance
Authors: Yang C. H. , Kao Y. C. , Shih H. D.
Published: July 2002

We present device characteristics of a field-effect, unipolar, resonant tunneling transistor. An oscillatory tunneling current in the transfer characteristics is observed for the first time. Our observation confirms a recent hypothesis that a mere three-to-two dimensional resonant tunneling can occur when scattering rate is less than the attempt frequency of tunneling electrons in the quantum well.
Second-harmonic generation of interface waves
Authors: Mao Y. W. , Shui Y. , Jiang W. , Lu Z. , Wu W.
Published: July 2002

The second-harmonic generation of leaky waves at the interface between glass and iron has been investigated. Fundamental frequency interface waves are excited by bulk shear waves, incident at the critical angle, and the generated second-harmonic surface waves are detected by reradiated bulk shear waves. The amplitudes of the generated second harmonic obey the square law. The second-harmonic generation decreases sharply as the incident and detection drive deviate from the critical angle.
Pseudomorphic GaInP Schottky diode and high electron mobility transistor on InP
Authors: Loualiche S. , Ginudi A. , Le Corre A. , Lecrosnier D. , Vaudry C. , Henry L. , Guillemot C.
Published: July 2002

GaInP material has been used as a high-gap semiconductor on InP to fabricate Schottky diodes. The experimental results show that the devices exhibit good electrical properties when the ternary strained layer is below the critical thickness. The best device is obtained with a gallium composition of 100% and a GaP thickness of 11 Å, and exhibits a barrier height of 0.8 eV, an ideality factor of 1.1, and a reverse current of 0.1 nA at −1 V. A high electron mobility transistor has been fabricated on an InP substrate by molecular beam epitaxy using a high-gap GaInP material, and a transconductance of 300 mS/mm has been measured on a device of 1.3 μm gate length.
Characterization of InGaAs-GaAs strained-layer lasers with quantum wells near the critical thickness
Authors: Beernink K. J. , York P. K. , Coleman J. J. , Waters R. G. , Kim J. , Wayman C. M.
Published: July 2002

Data are presented on the efficiency, reliability, and temperature dependence of wavelength and threshold for strained-layer InxGa1−xAs-GaAs (x∼0.25, λ>1.06 μm) separate confinement heterostructure lasers for several thicknesses near the critical thickness. Devices with well thicknesses of 100 Å exhibit excellent time-zero characteristics and reliability, while those with 143 Å wells have higher initial thresholds and degrade rapidly.
Low-frequency noise measurements on AlGaAs/GaAs resonant tunnel diodes
Authors: Weichold M. H. , Villareal S. S. , Lux R. A.
Published: July 2002

An experimental apparatus and procedure using noise measurement techniques in order to identify conduction mechanisms in resonant tunnel diodes (RTDs) due to defect-assisted tunneling is developed. The theory of noise measurements is discussed as the basis for the appropriate modeling of RTD noise data. Nonlinear and linear algorithms are developed to model these data and simulation test results are presented. Equipment target specifications are outlined and a functional equipment setup and procedure are also discussed. Sample results of a RTD noise measurement and of a determination of activation energy and capture cross section are presented.
Inductive current measurements in an oriented grained YBa2Cu3Ox superconductor
Authors: Küpfer H. , Keller C. , Salama K. , Selvamanickam V.
Published: July 2002

The critical current of grain aligned YBa2 Cu3Ox bulk material was investigated by inductive flux profile and ac susceptibility measurements. The induced current was directed perpendicular to the a-b plane oriented grains where high values of the transport current, have been previously reported. In spite of the unfavorable geometry of the investigated shielding current, no features of granularity were observed. The results yield a uniform bulk critical current density jc of 3×104 A/cm2 at zero field and 77 K. Field and temperature dependences of this jc are discussed and compared with those in a granular Y-Ba-Cu-O material.
Ion beam thinning and polishing of YBa2Cu3O7 films
Authors: Hebard A. F. , Fleming R. M. , Short K. T. , White A. E. , Rice C. E. , Levi A. F. J. , Eick R. H.
Published: July 2002

Successive ion beam milling at grazing angles of a 2400-Å-thick, c-axis-oriented YBa2Cu3O7 film is shown to give smooth films which superconduct at thicknesses on the order of tens of angstroms. The thinning and polishing process is characterized at successive milling stages using resistance transitions, x-ray analysis, scanning electron microscopy, and Rutherford backscattering and channeling analysis of composition and surface quality. As thinning proceeds, scanning electron microscopy and diffraction features associated with a-axis texture are removed and crystalline quality, as measured by x rays and channeling, markedly improves.
Thermal fluctuation and 1/f noise in oriented and unoriented Y1Ba2Cu3O7−x films
Authors: Black R. D. , Turner L. G. , Mogro-Campero A. , McGee T. C. , Robinson A. L.
Published: July 2002

We report on electrical noise measurements made on YBCO (Y1 Ba2 Cu3 O7−x ) films on SrTiO3, on bulk silicon with a ZrO2 buffer layer, and on thin dielectric membranes. We have found that 1/f noise predominates in the unoriented films and that thermal fluctuation noise is the chief source of noise in good films on SrTiO3 .
Growth of single-crystal columns of CoSi2 embedded in epitaxial Si on Si(111) by molecular beam epitaxy
Authors: Fathauer R. W. , Nieh C. W. , Xiao Q. F. , Hashimoto Shin
Published: July 2002

The codeposition of Si and Co on a heated Si(111) substrate is found to result in epitaxial columns of CoSi2 if the Si:Co ratio is greater than approximately 3:1. These columns are surrounded by a Si matrix which shows bulk-like crystalline quality based on transmission electron microscopy and ion channeling. This phenomenon has been studied as functions of substrate temperature and Si:Co ratio. Samples with columns ranging in average diameter from approximately 25 to 130 nm have been produced.
Critical current enhancement in field-oriented YBa2Cu3O7−δ
Authors: Chen K. , Maheswaran B. , Liu Y. P. , Giessen B. C. , Chan C. , Markiewicz R. S.
Published: July 2002

The crystalline anisotropy of YBa2 Cu3 O7−δ is found to have a significant effect in degrading critical current Jc . Pressed polycrystalline pellets of field-oriented grains have significantly higher Jc values (>5 times larger) than unoriented samples of the same material. Effects of annealing and metal doping are also discussed.
Evidence for enhancement of critical current by intergrain Ag in YBaCuO-Ag ceramics
Authors: Dwir B. , Affronte M. , Pavuna D.
Published: July 2002

We report the evidence for enhancement of critical current density Jc by ∼50%, which occurs when ∼10 wt. % Ag is added to Y1Ba2Cu3O7−δ ceramics. The maximal Jc (∼700 A/cm2 at T=77 K) appears simultaneously with maximum YBaCuO compactness in the samples. The silver fills the intergranular space (holes) without Cu substitution, and the critical temperature Tc is not reduced from the bulk value (∼91 K). Normal-state resistivity of Ag-YBaCuO samples is decreased by an order of magnitude, and samples exhibit improved contact resistance and resistance to water. While the critical density is improved by adding ∼10 wt. % Ag, it decreases at higher Ag concentrations.
Mode selection and spatial hole burning suppression of a chirped grating distributed feedback laser
Authors: Zhou Ping , Lee G. S.
Published: July 2002

A new kind of distributed feedback (DFB) laser with a linearly chirped grating is proposed and investigated theoretically for the first time. The eigenmodes of the chirped grating DFB (CG-DFB) and the field intensity distribution are calculated. With a suitable cavity length and chirp factor, the threshold gain difference to the next competence mode can be very large and will keep the single longitudinal mode stable. The chirp factor can be chosen to make the field intensity distribution quite uniform and at the same time keep the threshold gain difference large. This behavior effectively suppresses spatial hole burning and hence makes CG-DFB lasers that are stable single mode at high power, and with a narrow linewidth.
Transmission electron microscope characterization of AlGaInP grown by organometallic vapor phase epitaxy
Authors: Chen G. S. , Wang T. Y. , Stringfellow G. B.
Published: July 2002

AlGaInP epitaxial layers grown at 690 °C by atmospheric pressure organometallic vapor phase epitaxy are investigated by transmission electron microscopy. For the first time, compositionally modulated and ordered structures are simultaneously observed in AlGaInP alloys. The ordering is of the CuPt type with ordering along the {111} directions. The ordered regions appear as plate-like microdomains, while the composition modulation takes the form of a fine columnar constrast oriented along the growth direction. In addition, from the results of (001) plan-view diffraction contrast examination, the principal strain direction associated with the modulation structures is found to be perpendicular to the growth direction and lies in the surface plane. Thus, it is concluded that the spinodal decomposition is initiated and developed on the surface during the growth of the AlGaInP epitaxial layers and, finally, forms the columnar structure.
Formation of oriented high T
c superconducting Bi-Sr-Ca-Cu-O thin films on silver substrates by organometallic chemical vapor deposition
Authors: Zhang J. M. , Wessels B. W. , Tonge L. M. , Marks T. J.
Published: July 2002

Highly oriented thin films of the high Tc Bi-Sr-Ca-Cu-O superconductor have been deposited on silver substrates by low-pressure organometallic chemical vapor deposition. The volatile metalorganic complexes Cu(acetylacetonate)2, Sr(dipivaloylmethanate)2, Ca(dipivaloylmethanate)2, and triphenyl bismuth are used as precursors with N2O as a reactant gas. X-ray diffraction measurements reveal that the films deposited at 625 °C contain a mixture of the Bi2(Sr,Ca)2CuOx and Bi2(Sr,Ca)3Cu2Ox phases. The post-annealed films are predominantly composed of the Bi2(Sr,Ca)3Cu2Ox phase with preferential orientation of the crystallite c axes perpendicular to the substrate surface. Magnetic susceptibility measurements indicate the superconducting onset temperature of the annealed films to be at 80 K. The zero-field critical current density, estimated from magnetization measurements, is ∼3.9×105 A/cm2 at 5.5 K.
Experimental determination of transparency current density and estimation of the threshold current of semiconductor quantum well lasers
Authors: Chen T. R. , Eng L. E. , Zhuang Y. H. , Yariv A.
Published: July 2002

An experimental method for determining the transparency current density of semiconductor quantum well lasers is demonstrated in a strained-layer InGaAs/GaAs single quantum well laser system. The experimental results are then used as a practical guide to the study of ultralow threshold lasers. A threshold current as low as 0.75 mA is observed.
Resonant Raman studies of structural ordering in Hg1−xCdxTe: Dependence on growth conditions
Authors: Compaan A. , Bowman R. C. , Cooper D. E.
Published: July 2002

Resonant Raman scattering with photon energies between 2.35 and 2.7 eV has been used to study both the alloy composition and local structural order in Hg1−xCdxTe for x values near 0.25 and for samples prepared by bulk growth, liquid phase epitaxy, molecular beam epitaxy, and metalorganic chemical vapor deposition. The resonance behavior of the HgTe-like transverse optical and longitudinal optical (LO) modes, the CdTe-like LO mode, and that of an additional mode probably due to preferential clustering of three Hg and one Cd about the Te sites, all indicate strong enhancement at the E1 edge. However, surfaces annealed with a Nd:yttrium-aluminum-garnet-pumped dye laser show strong suppression of the cluster mode (but not the LO mode) in all samples, which suggests that extremely rapid epitaxial regrowth may inhibit the 3:1 cluster formation.
Observation of AlGaAs/GaAs multiquantum well structure by scanning tunneling microscopy
Authors: Gómez-Rodríguez J. M. , Baró A. M. , Silveira J. P. , Vázquez M. , González Y. , Briones F.
Published: July 2002

We have imaged an AlGaAs/GaAs multiquantum well structure by scanning tunneling microscopy (STM). In order to localize the structure the STM is integrated in a conventional scanning electron microscope. The observed surface structure has a periodicity of ≊180 Å and shows an apparent corrugation of ≊10 Å in the constant current mode. We discuss the possible mechanisms of the observed contrast, which we tentatively attribute to the different electrical properties of the two different layers.
Velocity electric field relationship for minority electrons in highly doped p-GaAs
Authors: Furuta T. , Tomizawa M.
Published: July 2002

Using the time-of-flight method, the drift velocity for minority electrons in highly doped p-GaAs was successfully measured at room temperature. The obtained velocity electric field relationships indicate that the velocity does not decrease but slightly increases and then saturates with increasing hole concentration above 1×1019 cm−3. Such behavior is well explained by the effects of degeneracy, which reduces the electron-hole interaction, and the hole distribution function dependence on electric field from the Monte Carlo calculation.
Electro-optical multistability in GaAs/AlAs superlattices at room temperature
Authors: Schneider H. , Fujiwara K. , Grahn H. T. , Klitzing K. v. , Ploog K.
Published: July 2002

We have studied the optical absorption properties of a GaAs/AlAs short-period superlattice at room temperature in an electric field perpendicular to the layers. Several pronounced optical transitions related to Wannier–Stark localization are observed indicating a coherence length of at least five superlattice periods. These transitions produce multiple regions of negative differential photoconductivity which are used to realize a multistable self-electro-optic effect device.
Hydrogen passivation of Zn acceptors in InGaAs during reactive ion etching
Authors: Moehrle Martin
Published: July 2002

It is shown that the use of hydrogen-containing gases such as CHF3/H2, CHF3, CH4 /H2, and CH4 /He in reactive ion etching processes leads to a drastic reduction of the concentration of electrically active acceptors in a thin layer at the surface of highly Zn-doped InGaAs. This passivation effect leads to strongly nonlinear current/voltage characteristics of nonalloyed Ti/Pt/Au contacts when applied directly on as-treated p++ -InGaAs layers. The observed deactivation of acceptors is inferred to be caused by hydrogen since no such an effect was found with the use of hydrogen-free etching gases.
Ellipsometric study of GaAs/GaP superlattices
Authors: Armelles G. , Rodríguez J. M. , Briones F.
Published: July 2002

Ellipsometric measurements were performed to study the E1 and E1+Δ1 transitions on a set of GaAs/GaP strained-layer superlattices. The experimental results show the existence of small quantum confinement effects.
Enhancement of the guided-wave second-harmonic generation in the form of Cerenkov radiation
Authors: Hayata K. , Yanagawa K. , Koshiba M.
Published: July 2002

A method for enhancing guided-wave second-harmonic generation (SHG) phase matched by a Cerenkov radiation scheme by means of tailoring the transverse (y direction) nonlinear susceptibility profile in the waveguide channel is proposed. Specifically, linear and domain-inverted (poled) channels embedded in a nonlinear substrate are considered, and the SHG efficiency for each structure is compared with that for the conventional nonlinear channel without domain inversion. Through electromagnetic field analysis, a significant enhancement of SHG is demonstrated, particularly with the domain inverted channel.
Exponential thermal emission transients from D
X centers in heavily Si-doped GaAs
Authors: Calleja E. , Mooney P. M. , Theis T. N. , Wright S. L.
Published: July 2002

The kinetics for the thermal emission of electrons from DX levels are shown to be exponential in heavily Si-doped GaAs. Isothermal voltage transients, obtained at constant capacitance, show a perfect exponential behavior. In contrast, a clear deviation from a single exponential function is observed when the transients are recorded at constant voltage, due to the nonuniform doping profile in these structures. The exponential emission kinetics seen in GaAs support the proposal that nonexponential emission kinetics observed at constant capacitance in AlxGa1−xAs are due to different emission rates for DX levels having different local atomic configurations in the alloy.
New measurements of the elastic properties of composition modulated Cu-Ni thin films
Authors: Moreau A. , Ketterson J. B. , Mattson J.
Published: July 2002

Using a new ultrasonic method which relies on the measurement of the in-phase and quadrature components of a continuous ultrasonic excitation as a function of position, we have measured the flexural modulus of composition modulated Cu-Ni self-supporting thin films. For some of the films, we have also observed the shear (Sz) modulus (allowing the calculation of the biaxial and Young’s moduli). No enhancement of these moduli was observed for composition wavelengths in the range of 17–40 Å.
Normally-off high-contrast asymmetric Fabry–Perot reflection modulator using Wannier–Stark localization in a superlattice
Authors: Law K-K. , Yan R. H. , Merz J. L. , Coldren L. A.
Published: July 2002

A normally-off surface normal Fabry–Perot reflection modulator with a contrast ratio of more than 60:1 with an operating voltage swing of 8 V has been demonstrated. The asymmetric Fabry–Perot structure consists of 100 periods of a 30 Å GaAs/30 Å Al0.3Ga0.7As superlattice sandwiched between a highly reflecting quarter-wavelength stack on the substrate side, and a less reflecting front mirror (air-semiconductor interface) on the top. The net Fabry–Perot reflection is turned on by reducing the cavity loss at resonance through the blue-shifted electroabsorption effect of Wannier–Stark localization in the superlattice.
Anisotropic Josephson junctions of Y-Ba-Cu-O/Au/Nb film sandwiches
Authors: Akoh H. , Camerlingo C. , Takada S.
Published: July 2002

Superconductor-normal metal-superconductor (SNS) Josephson junctions consisting of Y-Ba-Cu-O/Au/Nb film-layered structure have been fabricated using epitaxial Y-Ba-Cu-O films. SNS junctions with a-b plane orientated Y-Ba-Cu-O films exhibit the Josephson effect, while the junctions with c-axis orientated Y-Ba-Cu-O films have no Josephson current. Moreover, a-b plane orientated junctions show anisotropic Fraunhofer patterns in the magnetic field dependence of the critical current according to the direction of film orientations. These anisotropic behaviors reveal that the proximity effect is strongly affected by the anisotropic coherence length and the magnetic penetration depth of Y-Ba-Cu-O films.
Noise and dc characteristics of thin-film Bi-Sr-Ca-Cu-oxide dc SQUIDs
Authors: Face D. W. , Graybeal J. M. , Orlando T. P. , Rudman D. A.
Published: July 2002

Highly oriented Bi-Sr-Ca-Cu-oxide thin films with Tc≥100 K and large (10–20 μm) grains were used to produce thin-film dc superconducting quantum interference devices (SQUIDs). The best SQUID, which operated up to 75 K, had an inside loop diameter of ∼18 μm and an estimated loop inductance of 30 pH. The device was patterned by standard photolithography and had weak links that were likely due to existing grain boundaries around the loop. The effective loop area, calculated from the period of the SQUID modulation, is roughly consistent with the geometrical area of the SQUID loop. Significant hysteresis was observed in the flux-voltage characteristic which depended on the amplitude of the magnetic field sweep. The 1/f noise levels measured at 100 Hz in this device gave a flux noise Sφ of 1.0×10−8 Φ20/Hz at 4.8 K and 2.3×10−7 Φ20/Hz at 60 K. The detailed noise measurements which we report for this SQUID are the first for any Bi-Sr-Ca-Cu-oxide based SQUID.
Rapid thermal anneal of hydrogen-implanted metal-silicon nitride-silicon dioxide-silicon structure
Authors: Panwar B. S. , Bhattacharyya A. B.
Published: July 2002

A post-implant rapid thermal annealing technique is proposed to achieve very low interface trap density (<1010/eV cm2) at the SiO2-Si interface in a metal-Si3N4-SiO2-Si structure. The constitution of a donor layer induced by implanted hydrogen is explained with the aid of a model that predicts the formation of SiH groups. The proposed model is substantiated by comparing the IR data for furnace and rapid thermal annealed samples.
Preparation of the Tl-Ba-Ca-Cu-O thick film by processing the screen-printed Ba-Ca-Cu-O film in Tl2O3 vapor
Authors: Zeng Lingwen , Zhao Zijiang , Zhang Li , Chen Hongqi , Qian Zhengnan , Wu Daiming
Published: July 2002

Superconducting Tl-Ba-Ca-Cu-O thick films on yttria-stablized zirconia (YSZ) substrates have been obtained by processing the screen-printed Ba-Ca-Cu-O films in Tl2O3 vapor. The properties of the films are found to be dependent sensitively on the Tl2O3 vapor processing conditions. The best film with a zero resistance Tc at 115 K was heated in Tl2O3 vapor at 890 °C for 4 min followed by cooling to 300 °C at a rate of 2–3 °C/min. X-ray diffraction and energy dispersive x-ray studies indicated that the films are polyphase, but the high Tc phase Tl2Ba2Ca2Cu3Ox is predominant.
Formation of superconducting (Tl,Bi)Sr2CaCu2Oy thin films by rf sputtering and thallium diffusion
Authors: Liu R. S. , Edwards P. P. , Hunneyball P. D. , Bennett M. J. , Jedamzik D. , Harrison M. R. , Horley R. J.
Published: July 2002

We have prepared new high Tc superconducting thin films of (Tl,Bi)-Sr-Ca-Cu-O by combining low temperature (500 °C) rf sputtering of Bi-Sr-Ca-Cu-O precursor films and thallium diffusion. A typical film has Tc(onset) =80 K, Tc(midpoint) =79 K, and Tc(zero) =50 K. X-ray diffraction and energy dispersive spectroscopic studies were carried out to determine the composition and crystal structure of the superconducting phase within the film. We identified a material with the chemical composition of (Tl0.7 Bi0.3 )Sr2CaCu2Oy and tetragonal symmetry (a=3.795 Å and c=12.095 Å), and propose that this phase is responsible for superconductivity around 80 K. The film also has a highly preferred orientation with the c axis perpendicular to the surface of the (100)MgO substrate.
Epitaxial growth of InSb on GaAs by metalorganic chemical vapor deposition {au}R. M. ,Biefeld and
Authors: Hebner G. A.
Published: July 2002

InSb epitaxial layers have been grown on GaAs substrates by metalorganic chemical vapor deposition using trimethylindium and triethyl- or trimethylantimony as sources of In and Sb. Transmission electron microscopy revealed the existence of a large number of misfit dislocations at the substrate-epitaxial layer interface and, in some samples, misoriented grains. The quality of the layers improved with thickness as indicated by transmission electron microscopy, x-ray rocking curve widths, and Hall mobilities. The mobility was correlated with surface roughness, x-ray rocking curve width, and the Sb/In ratio. Hall mobilities up to 60 900 and 27 000 cm2/V s were obtained at 300 and 77 K, respectively, on a 2.9-μm-thick epitaxial InSb layer grown using a two-step growth procedure.
MeV oxygen ion implantation induced compositional intermixing in AlAs/GaAs superlattices
Authors: Xiong Fulin , Tombrello T. A. , Schwartz C. L. , Schwarz S. A.
Published: July 2002

We present in this letter an investigation of compositional intermixing in AlAs/GaAs superlattices induced by 2 MeV oxygen ion implantation. The results are compared with implantation at 500 keV. In addition to Al intermixing in the direct lattice damage region by nuclear collision spikes, as is normally present in low-energy ion implantation, Al interdiffusion has also been found to take place in the subsurface region where MeV ion induced electronic spike damage dominates and a uniform strain field builds up due to defect generation and diffusion. Uniform compositional intermixing of the superlattices results after subsequent thermal annealing when Al interdiffusion is stimulated through recovery of the implantation-induced lattice strain field, the reconstruction and the redistribution of lattice defects, and annealing of lattice damage.
InAs-AlSb heterostructure field-effect transistors fabricated using argon implantation for device isolation
Authors: Werking James , Tuttle Gary , Nguyen Chanh , Hu Evelyn L. , Kroemer Herbert
Published: July 2002

We have fabricated planar heterostructure field-effect transistors with InAs quantum well channels and AlSb barrier layers. Argon implantation was used to form a damaged layer, which resulted in partial device to device isolation. A 1.5 μm gate device had a room-temperature extrinsic transconductance of 208 mS/mm.