bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetostatically induced giant magnetoresistance in patterned NiFe/Ag multilayer thin films
Authors: Hylton T. L. , Parker M. A. , Coffey K. R. , Howard J. K. , Fontana R. , Tsang C.
Published: July 2002

Thin film multilayer structures consisting of two permalloy layers separated by Ag spacers show little or no giant magnetoresistance in their as-deposited state, due to a predominantly ferromagnetic interlayer exchange coupling that does not oscillate in sign with variations in the Ag spacer thickness. Upon patterning these films into arrays of dots and other geometries with micron scale features, however, antiferromagnetic coupling and giant magnetoresistance are observed due to magnetostatic interactions between layers that are induced at the edges of the patterns. In this letter we present our experimental results and discuss their relevance as magnetoresistive sensors for magnetic recording heads and other applications.
Electron–phonon interactions in the wide band-gap semiconductor GaN
Authors: Sheih S. J. , Tsen K. T. , Ferry D. K. , Botchkarev A. , Sverdlov B. , Salvador A. , Morkoç H.
Published: July 2002

Picosecond Raman spectroscopy has been employed to study electron–phonon interactions in the wide band-gap semiconductor GaN. By using very intense picosecond laser pulses in the visible spectral range, electron-hole pairs were generated through the two-photon absorption in GaN. The relaxation of these high energy electrons and holes were used to interrogate electron–phonon interactions. We have found that electrons thermalize toward the bottom of the conduction band by emitting primarily longitudinal optical phonons. Our work demonstrates that the Fröhlich interaction is much stronger than the deformation potential interaction in wurtzite GaN.
Capacitance based scanner for thickness mapping of thin dielectric films
Authors: Graham John , Kryzeminski Marek , Popovic Zoran
Published: July 2002

We have recently developed a technique capable of mapping variations in the thickness of thin dielectric films. This technique is based on accurately recording the capacitance between a spherical probe and the conductive substrate of a dielectric film. Once the capacitance has been recorded, and assuming the dielectric constant is known, the thickness of the film can be readily extracted, with better than 0.2 μm accuracy. In the current experimental configuration, the probe can be raster scanned with respect to the surface of the dielectric film, enabling one to record three-dimensional images and observe any spatial variations in sample thickness. The spatial resolution (i.e., the imaging resolution) of the technique is primarily dictated by the size of the probe and currently rests at ∼200 μm. This technique is applicable to any dielectric film on a conductive substrate, assuming the dielectric constant is known.
Lithographic point contacts for transverse electron focusing in bismuth
Authors: Jaeger M. D. , Tsoi V. , Golding B.
Published: July 2002

An electron-beam lithography technique for fabricating submicron point contacts to planar surfaces of bulk samples is described. We have demonstrated the technique by creating a linear array of point contacts, oriented along the bisectrix axis of a bismuth single crystal, which act as emitters and collectors in multiprobe transport measurements. In a transverse electron focusing geometry, we find the expected series of periodic voltage peaks as a function of applied magnetic field at low temperatures. The lithographically fabricated contacts offer advantages over conducting-needle probes in electrical integrity, thermal robustness, lack of damage to the contact site, ability to make multiple submicron contacts with ≤10 μm separations and ability to align the contacts precisely along crystallographic axes.
Pulse-time-modulated electron cyclotron resonance plasma etching with low radio-frequency substrate bias
Authors: Samukawa Seiji
Published: July 2002

The etching characteristics of polycrystalline silicon (poly-Si) by short-time modulated electron cyclotron resonance (ECR) determined by using a Cl2 etchant were investigated. It was found that the poly-Si etching rate was improved by increasing the pulse interval of the microwaves to more than 50 μs for a 50% duty ratio and applying a 600 kHz rf bias to the substrate. A large amount of negative chlorine ions are generated in the afterglow which occurs for more than 50 μs in high-density, low-pressure plasmas. The low rf bias alternately accelerates both the negative and positive ions to the substrate surface. As a result, the pulse-time modulated ECR plasma can produce high rate and charge-free etching with a 600 kHz rf bias.
Alternating-current light-emitting devices based on conjugated polymers
Authors: Wang Y. Z. , Gebler D. D. , Lin L. B. , Blatchford J. W. , Jessen S. W. , Wang H. L. , Epstein A. J.
Published: July 2002

Most polymer electroluminescent devices to date are represented as tunnel diodes and operate under direct-current (dc) driving field. Here we report the fabrication of symmetrically configured alternating-current (ac) light-emitting (SCALE) devices based on conjugated polymers. The new devices consist of an emissive polymer layer sandwiched between two redox polymer layers. This configuration enables the SCALE devices to work under both forward and reverse dc bias as well as in ac modes. The nearly ohmic electrode/redox polymer contacts improve the charge injection efficiency significantly and make the SCALE device operation insensitive to electrode work functions. Symmetric operation supports the key role of redox polymer/emissive polymer interface states.
Polarization fields and band offsets in GaInP/GaAs and ordered/disordered GaInP superlattices
Authors: Froyen Sverre , Zunger Alex , Mascarenhas A.
Published: July 2002

Using the first-principles pseudopotential method we have calculated band offsets between ordered and disordered Ga0.5In0.5P and between ordered GaInP2 and GaAs. We find valence band offsets of 0.10 and 0.27 eV for the two interfaces with the valence band maximum on ordered GaInP2 and GaAs, respectively. Using experimental band gaps these offsets indicate that the ordered/disordered Ga0.5In0.5P interface has type I band alignment and that the ordered GaInP2/GaAs interface has type II alignment. Assuming transitivity of the band offsets, these results suggest a type I alignment between disordered Ga0.5In0.5P and GaAs and a transition from type I to type II as the GaInP side becomes more ordered. Our calculations also show that ordered GaInP2 has a strong macroscopic electric polarization. This polarization will generate electric fields in inhomogeneous samples, strongly affecting the electronic properties of the material.
Luminescence quenching in erbium-doped hydrogenated amorphous silicon
Authors: Shin Jung H. , Serna R. , van den Hoven G. N. , Polman A. , van Sark W. G. J. H. M. , Vredenberg A. M.
Published: July 2002

Hydrogenated amorphous silicon thin films are doped with erbium by ion implantation. Room-temperature photoluminescence at 1.54 μm, due to an intra-4f transition in Er4+, is observed after thermal annealing at 300–400 °C. Excitation of Er3+ is shown to be mediated by photocarriers. The Er3+ luminescence intensity is quenched by a factor of 15 as the temperature is raised from 10 K to room temperature. Codoping with oxygen (1 at. %) reduces the luminescence quenching to a factor of 7. The quenching is well correlated with a decrease in luminescence lifetime, indicating that nonradiative decay of excited Er3+ is the dominant quenching mechanism as the temperature is increased.
The investigation of defect formation in chemical vapor deposited diamond using photoluminescence by ultraviolet synchrotron radiation
Authors: Won Jaihyung , Hatta Akimitsu , Ito Toshimichi , Sasaki Takatomo , Hiraki Akio
Published: July 2002

Photoluminescence (PL) of microwave assisted chemical vapor deposited (CVD) diamond was obtained using ultraviolet synchrotron radiation. The PL spectrum of the 5RL band (intrinsic defect), which cannot be detected in cathodoluminesence, was observed for both undoped (as grown) and boron doped (200 ppm) CVD diamond. The defect formation was characterized in the thin near-surface layer. The peak of boron related origin (2.3 eV) was detected in the boron doped CVD while band A (2.9 eV) was not observed. After remote hydrogen plasma treatment (RHPT), the near-surface defect related peak in the PL spectra disappeared. During RHPT the diamond was rehybridized by hydrogen radicals without etching.
Characterization of interface charge at Ga0.52In0.48P/GaAs junctions using current–voltage and capacitance–voltage measurements
Authors: Lim T. H. , Miller T. J. , Williamson F. , Nathan M. I.
Published: July 2002

Al/i:GaInP/n:GaAs Schottky structures of varying undoped layer thicknesses (100–1000 Å) were grown in situ by gas source molecular beam epitaxy (GSMBE). Effective Schottky barrier heights (φbIV)of 0.87±0.02 eV were determined from the current–voltage (I–V) method with ideality factor of <1.05 which is characteristic of thermionic emission but a decrease in barrier height (φbCV) with increasing GaInP thickness as measured by the capacitance–voltage (C–V) method was observed. We found that the plot of φbIV minus φbCV versus GaInP thickness is a straight line. This can be explained by modeling a positive delta sheet charge at the GaInP/GaAs interface which will result in a constant electric field (slope of the above line) with sheet charge estimated to be 5×1011 cm−2. This sheet charge is proposed to be the result of ionized donor states at such interface.
Influence of the size dispersion on the emission spectra of the Si nanostructures
Authors: Khurgin J. B. , Forsythe E. W. , Tompa G. S. , Khan B. A.
Published: July 2002

A systematic study of the size dependence of the photoluminescence spectra of Si quantum nanocrystals in the SiO2 matrix has been performed. The results have been fitted to a quantum-confinement model that includes the nanocrystal size dispersion rather than a specific size of the nanocrystal. This, in conjunction with the results [Z. H. Lu, D. J. Lockwood, and J.-M. Baribeau, Nature 378, 258 (1995)] for amorphous Si layers serves as a strong confirmation of the confinement-induced nature of the photoluminescence.
A fiber-mounted, micromachined photoconductive probe with 15 nV/Hz1/2 sensitivity
Authors: Lai Richard K. , Hwang Jiunn-Ren , Nees John , Norris Theodore B. , Whitaker John F.
Published: July 2002

We report the performance of a micromachined, photoconductive-sampling probe that is fabricated on low-temperature-grown GaAs and mounted on a single-mode optical fiber. The epitaxial probe has a temporal resolution of 3.5 ps, a spatial resolution of 7 μm, and a sensitivity of 15 nV/(Hz)1/2 when integrated with a high impedance, junction field-effect transistor source follower. The fiber, which couples short laser pulses to the interdigitated detector pattern on the probe, also provides flexible support and mobility. The probe’s compact cross section makes it ideal for applications as an internal-node, picosecond-response, photoconductive sampling probe or wave form launcher for test and characterization of integrated circuits.
Light distribution measurements in absorbing materials by optical detection of laser-induced stress waves
Authors: Paltauf G. , Schmidt-Kloiber H. , Guss H.
Published: July 2002

A method for optimized generation and detection of thermoelastic stress waves for the measurement of tissue optical properties and structure is investigated. The stress waves are formed by short pulsed irradiation of an absorbing dye solution with a Q-switched Nd:YAG laser at 532 nm. An optical transducer based on pressure-induced reflectivity changes of a continuous laser beam at a glass-water interface detects the stress wave in front of the irradiated sample surface. It is shown theoretically and experimentally that this kind of detector, where the active area is a small spot close to the irradiated surface, minimizes signal distortion due to acoustic diffraction. Comparisons of absorption coefficients measured acoustically and from optical transmission show a good agreement between the two methods. The high sensitivity of the detector (1.5 mV/bar) makes it possible to keep the temperature and pressure rise in the investigated target low, which enables in vivo applications of the optical transducer.
In situ growth of optically active erbium doped Al2O3 thin films by pulsed laser deposition
Authors: Serna R. , Afonso C. N.
Published: July 2002

Thin Al2O3 films are grown and in situ doped with erbium by pulsed laser deposition in a single step process, by alternate ablation from Al2O3 and Er targets. The as-deposited films have an Er step dopant profile throughout the film thickness, whose concentration depends on the number of pulses at the Er target. The as-grown films are optically active, as evidenced by the photoluminescence spectrum centered at 1.533 μm, corresponding to intra-4f transitions in Er3+. The photoluminescence intensity increases upon annealing due to an increase of the luminescence lifetime. This is most likely a result of a decrease in the nonradiative decay channels, related to annealing of defects in the Al2O3 film.
Visible light emission from Si nanocrystals grown by ion implantation and subsequent annealing
Authors: Guha S. , Pace M. D. , Dunn D. N. , Singer I. L.
Published: July 2002

Photoluminescence (PL), electron spin resonance (ESR), and high resolution transmission electron microscopy (HRTEM) were used to investigate the luminescence mechanism in Si nanocrystals. Si ions were implanted in SiO2 films at 190 keV to a dose of 3×1017/cm2.An intense photoluminescence (PL) band at 755 nm (1.65 eV) was observed when the implanted films were annealed above 800 °C in air or in nitrogen. HRTEM images showed Si nanocrystals of sizes between 1 and 6 nm from these annealed samples. ESR indicated Si dangling bonds. Upon annealing at 900 °C in air a few times, the particle sizes were reduced to less than 2 nm due to oxidation. The red PL band is attributed to emission from Si nanocrystals.
Temperature determination in shocked condensed materials using Raman scattering
Authors: Pangilinan G. I. , Gupta Y. M.
Published: July 2002

The use of time-resolved Raman scattering measurements to determine temperature in shocked materials is demonstrated. Experimental data were obtained by monitoring the stokes and antistokes intensities of the 460 cm−1 vibrational mode, at 50 ns intervals, in liquid carbon tetrachloride shocked to 12 GPa using step wise loading. The ratio of antistokes to stokes intensities changes in a pronounced manner with increasing pressure. Procedures to obtain precise temperatures are outlined, and improvements for future work are indicated.
High performance photorefractive polymer with improved stability
Authors: Grunnet-Jepsen A. , Thompson C. L. , Twieg R. J. , Moerner W. E.
Published: July 2002

A novel photorefractive polymer composite is reported which exhibits a high two-beam coupling gain coefficient (Γ=200 cm−1 at 120 V/μm, fast response time (τg=50 ms at 1 W/cm2), overmodulation of diffraction efficiency, and high sensitivity. The composition and processing have been altered to yield greatly improved material stability.
High bond energy and thermomechanical stress in silicon on sapphire wafer bonding
Authors: Kopperschmidt P. , Kästner G. , Hesse D. , Zakharov N. D. , Gösele U.
Published: July 2002

Silicon on sapphire wafer pairs are formed by direct wafer bonding of 3-in. silicon and sapphire wafers. Subsequent annealing commonly used to increase the bond energy imposes serious thermomechanical strain. The corresponding bending, recorded in situ as a function of temperature, reveals relaxations by de- and rebonding until the silicon wafer cracks into small fragments that mostly remain bonded. After further annealing up to 800 °C and cooling to room temperature, a strong curvature of the fragments indicates a frozen-in high temperature bond state with elastic energies around 100 J/m2. Cross-sectional transmission electron microscopy of the interface reveals an amorphous intermediate layer the thickness of which considerably increases with increasing the oxygen partial pressure during annealing.
Enhancement of secondary electron emission from heavily Si-implanted and Si-doped GaAs
Authors: Iwase F. , Nakamura Y.
Published: July 2002

The enhancement of secondary electron emission was observed for both heavily Si-implanted and heavily Si-doped GaAs after annealing at 950 °C. The enhancement was found to be related to the generation of Ga vacancy during annealing. The assessment of electrical properties of the enhanced area revealed that the enhancement arises from the secondary electron production process in the bulk region, not from the surface effect including band bending at the wafer surface. We suggested that the excitons produced by primary electrons would ionize the lattice defects introduced in ion implantation and/or annealing processes.
Determination of transport parameters in fullerene films
Authors: Priebe G. , Pietzak B. , Könenkamp R.
Published: July 2002

We report the electron and hole drift mobilities and the recombination lifetime in thin polycrystalline C60 films. The data are obtained from photocurrent measurements involving an optical interference grating moving at variable velocity across the sample surface. Considerable degradation of the transport parameters is observed as the samples are exposed to air. The initial values for the electron and hole drift mobilities are 1.3±0.2 cm2/V s and (2±1)×10−4 cm2/V s, respectively, and for the recombination lifetime (1.7±0.2)×10−6 s.
Preparation and characterization of sol-gel derived Er3+: Al2O3-SiO2 planar waveguides
Authors: Benatsou M. , Capoen B. , Bouazaoui M. , Tchana W. , Vilcot J. P.
Published: July 2002

Er 3+ doped aluminosilicate thin films were prepared on silica and silica Si substrates by the sol-gel method. The Er ion concentration was varied from 0.25% to 1%. Fluorescences of Er ions in the visible and infrared regions were characterized. Green and red up-conversion fluorescences centered at 548 and 655 nm for, respectively, the (2H11/2+4S3/2)→4I15/2 and 2F9/2→4I15/2 were observed. A broadband peak was observed at 1531 nm corresponding to the 4I13/2 → 4I15/2 transition, with the full width at half-maximum of 47 nm comparable to those prepared by other methods. The fluorescence lifetime of the 4I13/2 excited state was found to be constant and equal to 3.5 ms until a high Er doping of 0.5 at. %.
Effects of well thickness and Si doping on the optical properties of GaN/AlGaN multiple quantum wells
Authors: Zeng K. C. , Lin J. Y. , Jiang H. X. , Salvador A. , Popovici G. , Tang H. , Kim W. , Morkoç H.
Published: July 2002

Effects of well thickness and Si doping on the optical properties of GaN/AlGaN (MQWs) have been investigated by picosecond time-resolved photoluminescence (PL) measurements. Our results have yielded that (i) the optical transitions in nominally undoped MQWs with narrow well thicknesses (Lw<40 Å) were blue shifted with respect to the GaN epilayer due to quantum confinement, however, no such blue shift was evident for the MQWs with well thicknesses larger than 40 Å, (ii) the band-to-impurity transitions were the dominant emission lines in nominally undoped MQWs of large well thicknesses (Lw>40 Å) at low temperatures, and (iii) Si doping improved significantly the crystalline quality of MQWs of large well thicknesses (Lw>40 Å). The implications of these results on the device applications based on III-nitride MQWs have been discussed.
High-efficiency and high-resolution fiber-optic probes for near field imaging and spectroscopy
Authors: Islam M. N. , Zhao X. K. , Said A. A. , Mickel S. S. , Vail C. F.
Published: July 2002

We demonstrate that fiber-optic probes with an intermediate section followed by a rapidly tapering tip lead to transmission efficiency enhancement of better than four orders-of-magnitude at 60 nm tip diameter and more than five orders-of-magnitude at smaller than 40 nm tip diameter over typical taffy-pulled fiber probes. Our highest resolution probes have a tip diameter of 30 nm with a transmission efficiency of 0.02%, and as an example we image tobacco mosaic virus with a resolution better than 35 nm. The probes are made in a two-step process involving pulling and then etching that permits both high efficiency and control of the mechanical resonance properties. The efficiency is enhanced by reducing the distance that the electromagnetic mode travels in the cut-off mode of the fiber probe. The higher resolution is achieved because sharper tips can be made through the etching process.
Growth conditions for complete substitutional carbon incorporation into Si1−yCy layers grown by molecular beam epitaxy
Authors: Zerlauth S. , Seyringer H. , Penn C. , Schäffler F.
Published: July 2002

To study the conditions for substitutional incorporation of carbon into Si layers, we grew pseudomorphic Si1−yCy/Si superlattices with absolute carbon concentrations between 0.3% and 2% and growth temperatures varying between 400 and 650 °C. We employed a novel technique to derive the amount of substitutional carbon, which is based on comparative x-ray rocking analyses of Si1−yCy/Si superlattices grown with constant and step-graded temperature profiles. At growth rates around 1 Å/s, we find complete substitutional incorporation of carbon up to growth temperatures of 550 °C and carbon concentrations of about 1%. At higher growth temperatures and/or higher carbon concentrations, the percentage of substitutional carbon drops significantly, concomitant with a thus far unnoticed morphological transition to island growth.
Microwave intermodulation in thin film high-Tc superconducting microstrip hairpin resonators: Experiment and theory
Authors: Willemsen Balam A. , Dahm T. , Scalapino D. J.
Published: July 2002

We present experimental results for microwave intermodulation in a series of superconducting hairpin resonators. We find that geometry plays a dominant role in determining both the losses and intermodulation in these resonators. The experimental data can be reproduced using recent theoretical calculations with a single parameter, JIMD (77 K). We compare the response of the fundamental and the first harmonic modes of these resonators to find that the use of the first harmonic mode gives less intermodulation, but we also find higher losses due to the more extended fields of this mode.
The influence of the deformation on the two-dimensional electron gas density in GaN–AlGaN heterostructures
Authors: Gaska R. , Yang J. W. , Bykhovski A. D. , Shur M. S. , Kaminski V. V. , Soloviov S. M.
Published: July 2002

We report on the effect of external strain on the two-dimensional electron gas density in AlGaN/GaN heterostructures grown on sapphire by low pressure metalorganic chemical vapor deposition. The electron sheet concentration in the studied samples was 4×1012–2×1013 cm−2 and decreased with compressive strain. Lower doped heterostructures had a higher sensitivity to applied strain. The comparison between the experimental data and our model shows that the GaN layers are primarily nitrogen terminated at the heterointerface.
Effect of matrix on InAs self-organized quantum dots on InP substrate
Authors: Ustinov V. M. , Weber E. R. , Ruvimov S. , Liliental-Weber Z. , Zhukov A. E. , Egorov A. Yu. , Kovsh A. R. , Tsatsul’nikov A. F. , Kop’ev P. S.
Published: July 2002

InAs self-organized quantum dots in In0.53Ga0.47As and In0.52Al0.48As matrices have been grown on InP substrates by molecular beam epitaxy. The dot size in InGaAs has been found to be 3–4 times larger, but the areal density about an order of magnitude smaller than that in InAlAs. Low-temperature photoluminescence (PL) of the InAs/InGaAs quantum dots is characterized by a narrow (35 meV) PL line as compared to that of InAs/InAlAs quantum dots (170 meV). Quantum dot formation increases the carrier localization energy as compared to quantum well structures with the same InAs thickness in a similar manner for both InAs/InGaAs and InAs/InAlAs structures. The effect of the barrier band gap on the optical transition energy is qualitatively the same for quantum well and quantum dot structures. The results demonstrate a possibility of controlling the quantum dot emission wavelength by varying the matrix composition.
New phosphor (Gd2−xZnx)O3−δ:Eu3+ with high luminescent efficiency and superior chromaticity
Authors: Sun Xiao-Dong , Xiang X.-D.
Published: July 2002

A new phosphor, (Gd1.54Zn0.46)O3−δ:Eu0.063+, with a photoluminescent quantum efficiency of ≈86% and a superior color chromaticity (x=0.656, y=0.344) compared to the state of art red phosphor Y2O3:Eu3+ was identified using the combinatorial thin film synthesis method. This phosphor may replace Y2O3:Eu3+ in display applications where a more saturated red phosphor is preferred.
Regular step arrays on silicon
Authors: Viernow J. , Lin J.-L. , Petrovykh D. Y. , Leibsle F. M. , Men F. K. , Himpsel F. J.
Published: July 2002

Highly regular arrays of steps are produced on vicinal Si(111)7×7. The step edges are atomically straight for up to 2×104 lattice sites. The terraces are single domain, which produces a minimum kink width of 2.3 nm (half a 7×7 unit cell) and thus a high barrier for creating kinks. Criteria for obtaining optimum step arrays are established, such as the miscut [≈1° towards (1̄1̄2)] and an annealing sequence which passes through step bunching regions quickly.
Carbon incorporation in Si1−yCy alloys grown by molecular beam epitaxy using a single silicon–graphite source
Authors: Dashiell M. W. , Kulik L. V. , Hits D. , Kolodzey J. , Watson G.
Published: July 2002

Pseudomorphic Si1−yCy alloys on silicon (100) were grown by molecular beam epitaxy using a single effusion source of silicon contained in a graphite crucible, producing carbon concentrations of y=0.008. The behavior of carbon incorporation using this source was studied as a function of growth temperature using x-ray diffraction and infrared spectroscopy, and was compared to previous studies, where Si1−yCy was grown from separate silicon and graphite sources. An increased energy barrier for the surface diffusion of carbon was observed using the single silicon–graphite source. An infrared absorption mode near 725 cm−1, observed for growth temperatures up to 700 °C, was attributed to a transitional phase between the loss of substitutional carbon and the formation of silicon carbide precipitates.
Unconventional hysteresis behavior in compositionally graded Pb(Zr,Ti)O3 thin films
Authors: Brazier Mark , McElfresh M. , Mansour Said
Published: July 2002

Thin-film lead–zirconate–titanate (PZT) capacitors with composition gradients normal to the substrate were fabricated via a novel technique using pulsed laser deposition. These capacitors exhibited large polarization offsets when driven by an alternating electric field. The direction of the offsets depended on the direction of the gradient with respect to the substrate. The largest offset, greater than 400 μC/cm2 when driven with a 50 V/μm field, was nearly an order of magnitude greater than any reported for other graded ferroelectric films. This difference is attributed to both the high spontaneous polarization of PZT and the high-quality films obtained by pulsed laser deposition.
The fraction of substitutional boron in silicon during ion implantation and thermal annealing
Authors: Caturla Maria Jose , Johnson Mark D. , Diaz de la Rubia T.
Published: July 2002

We present results from a kinetic Monte Carlo simulation of boron transient enhanced diffusion (TED) in silicon. Our approach avoids the use of phenomenological fits to experimental data by using a complete and self-consistent set of values for defect and dopant energetics derived mostly from ab initio calculations. The results predict that, during annealing of 40 keV B-implanted Si at 800 °C, there exists a time window during which all the implanted boron atoms are substitutional. At earlier or later times, the interactions between free silicon self-interstitials and boron atoms drive the growth of boron clusters and result in an inactive boron fraction. The results show that the majority of boron TED takes place during the growth period of interstitial clusters and not during their dissolution.
Measurement and calculation of gain spectra for (GaIn)As/(AlGa)As single quantum well lasers
Authors: Ellmers C. , Girndt A. , Hofmann M. , Knorr A. , Rühle W. W. , Jahnke F. , Koch S. W. , Hanke C. , Korte L. , Hoyler C.
Published: July 2002

The gain spectrum of a (GaIn)As/(AlGa)As single-quantum-well laser diode is precisely measured at various currents in order to quantitatively check the predictions of a microscopic model. The theory includes carrier—carrier and carrier—LO-phonon collisions which lead to optical dephasing and screening of the Coulomb interaction. The measurements are based on a transmission technique using the broad spectrum of a 10 fs Ti:sapphire laser to obtain sufficient signal to noise ratio over a wide spectral range. We obtain excellent agreement between theoretical and experimental gain spectra and thus can clearly demonstrate the predictive capability of our microscopic model.
Influence of potential fluctuation on optical and electrical properties in GaN
Authors: Oh Eunsoon , Park Hyeongsoo , Park Yongjo
Published: July 2002

We observed strong correlation between optical properties and transport properties in GaN. Both the intensity and the energy of near-band edge photoluminescence (PL) peak in GaN:Si vary with its mobility. Such behavior has been explained by the potential fluctuation associated with the inhomogeneous impurities or local defects, leading to the space-charge scattering of carriers and the redshift of the PL line. We also discuss the strain relaxation in GaN:Si.
Equilibrium phase diagrams for dislocation free self-assembled quantum dots
Authors: Daruka István , Barabási Albert-László
Published: July 2002

The equilibrium theory of self-assembled quantum dot (SAQD) formation can account for many of the experimentally observed growth modes. Here, we show that despite the large number of material constants entering the free energy of strained islands, there are only four topologically different phase diagrams describing the SAQD formation process. We derive each of these phase diagrams and discuss the physical properties of the predicted growth modes.
Behavior of Al–Al2O3–Al single-electron transistors from 85 mK to 5 K
Authors: Kenyon M. , Amar A. , Song D. , Lobb C. J. , Wellstood F. C.
Published: July 2002

Using e-beam lithography and conventional double-angle evaporation, we have fabricated Al–Al2O3–Al single-electron transistors and studied their behavior from 85 mK to about 5 K. The total island capacitance CΣ of the devices ranges from 120 to 200 aF, with typical estimated junction overlaps of about 30 nm×30 nm. At 4.2 K, our devices display well-behaved periodic I–Vg characteristics with the maximum charge-transfer function ∂I/∂Q0 ranging from 4 to 130 pA/e. The electrical characteristics of these devices agree well with the predictions of the Orthodox Theory, with current modulation being observed up to a temperature T≃e2/(2CΣkB). Below 1 K small deviations occur, which are partly due to island self-heating effects.
Comparison of the annealing behavior of high-dose nitrogen-, aluminum-, and boron-implanted 4H–SiC
Authors: Seshadri S. , Eldridge G. W. , Agarwal A. K.
Published: July 2002

Room temperature free carrier concentrations exceeding 1×1018 cm−1 have been achieved with 1000 °C implants into 4H–SiC using N and Al (1×1017 cm−3 using B). A decrease in resistivity is observed for annealing temperatures above ∼1300, ∼1500, and ∼1750 °C for N, Al, and B, respectively. Rutherford backscattering spectroscopy measurements indicate almost complete recrystallization for N-implanted samples and partial recrystallization on the silicon, but not the carbon, sublattice for B- and Al-implanted samples. An implant and species related step formation is also observed. Only boron is observed to diffuse appreciably. A crystal stoichiometry and Fermi level dependent model is proposed to explain the activation results.
Imaging of vortices in superconductors by electron beam scanning
Authors: Martin J. , Huebener R. P. , le Grand J. B. , Mears C. A. , Labov S. E. , Barfknecht A. T.
Published: July 2002

Abrikosov vortices trapped in a superconducting tunnel junction and oriented perpendicular to the barrier plane were imaged by electron beam scanning at 1.6 K. We have used NbAlOxNb junctions. As an important feature, the top Nb electrode was covered with a SiO2 film of 300 nm thickness, absorbing most of the 5 keV beam energy. The signal generating the image is explained by a model, assuming that the beam-induced electronic excitations in the SiO2 overlay film are trapped in the local magnetic field protruding from a vortex, resulting in an increased recombination rate. In addition to providing a novel approach to the imaging of the vortices in superconductors, our results are important for understanding quasiparticle losses in tunnel junction detectors.
Nonalloyed ohmic contact to n-GaAs with GaS/GaAs quasi-metal-insulator-semiconductor structure
Authors: Okamoto Naoya , Takahashi Tsuyoshi , Tanaka Hitoshi
Published: July 2002

We report on nonalloyed ohmic contact to n+-GaAs (≈2×1018 cm−3) with a Ti-based metal/ultrathin GaS (≈15 nm)/GaAs quasi-metal-insulator-semiconductor (QMIS) structure. The GaS film was grown by molecular beam epitaxy employing the precursor, tertiarybutyl-galliumsulfide-cubane ([(t-Bu)GaS]4). For Au/Pt/Ti/GaS/n+-GaAs QMIS structure, the as-deposited contact resistivity of low 10−2 Ω cm2 was improved to 4.1×10−6 Ω cm2 by low-temperature annealing at 300 °C for 10 min. With annealing, we observed the formation of TiGaS on GaAs, but did not see any alloying reaction between GaAs and metals and sulfur diffusion into GaAs.
Selectable dual-wavelength pulses generated from a laser diode using external feedback from a two-chromatic fiber grating
Authors: Zhao Y. , Shu C.
Published: July 2002

A simple, robust, and easily integrable external cavity is demonstrated for the generation of self-seeded dual-wavelength pulses at about 1550 nm. The key component for wavelength selection is a two-chromatic fiber grating. Dual-wavelength pulses with equal intensities at the wavelengths and side-mode-suppression ratio of about 18 dB are obtained. By controlling the bias current and the polarization state, the laser can also be switched into single wavelength oscillation. Discrete tuning of the dual-wavelength pulses has also been demonstrated over a total range of 12.1 nm while maintaining a constant spacing of 6.3 nm.
Possible intermediate in H2S dissociation on GaAs(100)
Authors: Wei X. M. , Liu Q. P. , Zou Z. , Xu G. Q.
Published: July 2002

The adsorption and dissociation of H2S on GaAs(100) has been studied using high-resolution electron energy loss spectroscopy, thermal desorption spectroscopy, and isotope exchange techniques. The dissociative adsorption of H2S at 100 K produces only H–As species with a vibrational frequency of 2072 cm−1. Upon warming to 200 K, the vibration of H–As clearly shifts to 2105 cm−1, corresponding to a free H–As species. In addition, the formation of H–Ga (1887 cm−1) is also observed upon thermal annealing. In coadsorption studies of H2S and D atoms, three main desorption features of H2S were observed at 135, 200, and 375 K, respectively. The peaks at 135 and 375 K can be attributed to the desorption of molecularly adsorbed H2S and the recombinative desorption of adsorbed H and HS, respectively. In addition to the 375 K peak, the desorption feature at 200 K also undergoes isotope exchange between coadsorbed D atoms and H2S. These observations strongly suggest that the dissociative adsorption of H2S on GaAs(100) involves an intermediate of Ga–HS—H–As.
In situ monitoring of ion sputtering and thermal annealing of crystalline surfaces using an oblique-incidence optical reflectance difference method
Authors: Zhu X. D. , Nabighian E.
Published: July 2002

We demonstrate that the morphology of crystalline surfaces during ion sputtering and thermal annealing can be monitored in situ with an oblique-incidence polarization-modulated optical reflectance difference technique. Such a technique is effective under high ambient pressures as well as ultrahigh vacuum. We studied the Ne ion sputtering and thermal annealing of Ni(111) from 623 to 823 K. We found that the rate-limiting step (with an activation energy of 1.1 eV/atom) during annealing is most likely to be direct evaporation of Ni atoms from step edges.
Lateral etching and filling of high aspect ratio nanometer-size cavities for silicon device structures
Authors: King C. A. , Kim Y. O. , Ng K. K.
Published: July 2002

We study a process technique involving SiO2 lateral etching coupled with amorphous Si (α-Si) refilling as a possible alternative to improve performance and lower costs for bipolar complementary metal–oxide semiconductor technologies. We investigated the lateral etching of oxide layers with thicknesses between 50 and 2.5 nm confined between a Si substrate and a multilayer stack composed of polycrystalline Si, WSix, and Si3N4. We found that the lateral etching of SiO2 proceeds even with the smallest thickness (2.5 nm) to create extremely small cavities. The etch extent (fixed time) dependence with SiO2 thickness suggests that capillary action may be an important mechanism. Using standard amorphous Si deposition techniques, we refilled all the small cavities without void formation as witnessed from transmission electron micrographs.
Analytical descriptions of the tapping-mode atomic force microscopy response
Authors: Wang Lugen
Published: July 2002

The tapping-mode atomic force microscopy response has been analyzed by the Krylov–Bogolubov–Mitropolsky asymptotic method. Due to the presence of repulsive force, attractive force and damping in the tip-sample interaction, the response exhibits complicate nonlinear phenomena. The numerical and experimental results shows that the phenomena can be well described by this approximation solution when the driving frequency is close to the free resonance frequency and the setpoint amplitude ratio is larger than 0.4.
High-quality ultrathin gate oxide prepared by oxidation in D2O
Authors: Kim Hyojune , Hwang Hyunsang
Published: July 2002

In this letter, we present a process to incorporate deuterium at the Si/SiO2 interface using deuterium oxide (D2O) as an oxidizing gas. We have investigated the electrical and reliability characteristics of ultrathin gate oxide grown in D2O ambient. Compared with a control oxide grown in H2O, an oxide grown in D2O exhibits a significant reduction of charge trapping and interface state generation. Based on secondary ion mass spectroscopy analysis, we found a deuterium-rich layer at the Si/SiO2 interface. The improvement of electrical and reliability characteristics can be explained by the deuterium incorporation at the Si/SiO2 interface.
A metal-free, full-color stacked organic light-emitting device
Authors: Gu G. , Parthasarathy G. , Forrest S. R.
Published: July 2002

We report the demonstration of a transparent, completely metal-free, full-color stacked organic light-emitting device (SOLED). The SOLED emits light from both top and bottom (substrate) surfaces with total external quantum efficiencies of 0.65%, 1.3%, and 2.2% for the green, blue, and red stacked subpixels, respectively. The respective top emission quantum efficiencies for the three subpixels are 0.23%, 0.63%, and 1.6%. The angular dependence of emission colors due to microcavity effects is weak when viewed from the top device surface. This metal-free SOLED is from 21% to 50% transparent over the entire visible spectral range. Capability for top emission makes this device suitable for integration with electronic components in active matrix display backplanes.
Visible and infrared rare-earth-activated electroluminescence from indium tin oxide Schottky diodes to GaN:Er on Si
Authors: Garter M. , Scofield J. , Birkhahn R. , Steckl A. J.
Published: July 2002

Visible and infrared rare-earth-activated electroluminescence (EL) has been obtained from Schottky barrier diodes consisting of indium tin oxide (ITO) contacts on an Er-doped GaN layer grown on Si. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources for Ga, Mg, and Er and a plasma source for N2. RF-sputtered ITO was used for both diode electrodes. The EL spectrum shows two peaks at 537 and 558 nm along with several peaks clustered around 1550 nm. These emission lines correspond to atomic Er transitions to the I15/24 ground level and have narrow linewidths. The optical power varies linearly with reverse bias current. The external quantum and power efficiencies of GaN:Er visible light-emitting diodes have been measured, with values of 0.026% and 0.001%, respectively. Significantly higher performance is expected from improvements in the growth process, device design, and packaging.
Piezoelectric effects in the optical properties of strained InGaN quantum wells
Authors: Peng L.-H. , Chuang C.-W. , Lou L.-H.
Published: July 2002

We investigated the carrier-injection effects in the emission spectrum of strained GaN/InGaN/AlGaN quantum well (QW) blue emitters using a pulsed current excitation technique. Spectral blueshift as large as 80 meV in the emission peak energy was observed as the injection current increases from 1 mA to 1 A. Based on a self-consistent calculation that couples the Poisson equation with a wurtzite-type Rashba–Sheka–Pikus Hamiltonian, four important interactions are evaluated in order to determine the optical properties of InGaN QW. It is shown that the spectral redshifting caused by a piezoelectricity induced quantum confined Stark effect and carrier-induced band gap renormalization is counteracted by a blueshift due to the band filling and charge screening effects. The increase of InGaN QW emission peak energy and intensity with injected carriers suggests a dominant contribution from the latter in a band-to-band recombination process.
High-efficiency diode lasers at high output power
Authors: Wang Jun , Smith Barry , Xie Xiaomin , Wang Xinqiao , Burnham Geoffrey T.
Published: July 2002

808 nm lasers grown by molecular beam epitaxy show extremely high internal quantum efficiency and low internal loss, which results in very high slope efficiency at a long cavity length, and consequently, extremely high total power conversion efficiency at high continuous-wave power output.
Infrared and self-frequency doubled laser action in Yb3+-doped LiNbO3:MgO
Authors: Montoya E. , Capmany J. , Bausá L. E. , Kellner T. , Diening A. , Huber G.
Published: July 2002

Stable continuous-wave laser action in the near-infrared and in the green spectral region has been obtained in a self-frequency doubling solid-state laser, the Yb3+:MgO:LiNbO3 nonlinear crystal. By pumping with a Ti:sapphire laser and using a nearly concentric cavity, laser action at 1.06 μm was achieved with an absorbed power threshold of 101 mW and efficiency around 47%. As much as 60 mW of self-frequency-doubled radiation at 530 nm was also obtained with absorbed pump powers of 800 mW in critical cavity alignment. Efficient laser action was also obtained in the near-infrared region under pumping with diode laser.
Far-infrared laser oscillation from a very small p-Ge crystal under uniaxial stress
Authors: Hiromoto N. , Hosako I. , Fujiwara M.
Published: July 2002

We report on pulse laser oscillation from a p-Ge intervalence band (IVB) laser composed of a Ga-doped Ge crystal measuring about 1×1×5 mm3 which is a very small volume compared with those reported so far for shallow-acceptor-doped Ge. Laser oscillation is only achieved under uniaxial stresses greater than 1300 kg/cm2. We find that the optimum stress for lasing is around 3500–4100 kg/cm2 when the p-Ge IVB lasers are operated at liquid helium temperature. The minimum electric power needed for lasing is only 280 W at a peak period of pulse emission.
Biased switching of small magnetic particles
Authors: Stamps R. L. , Hillebrands B.
Published: July 2002

High-frequency switching of single domain, uniaxial magnetic particles is discussed in terms of transition rates controlled by a small transverse bias field. It is shown that fast switching times can be achieved using bias fields an order of magnitude smaller than the effective anisotropy field. Analytical expressions for the switching time are derived in special cases, and general configurations of practical interest are examined using numerical simulations.
Interstitial-type defects away from the projected ion range in high energy ion implanted and annealed silicon
Authors: Kögler R. , Peeva A. , Anwand W. , Brauer G. , Skorupa W. , Werner P. , Gösele U.
Published: July 2002

Defects in high energy ion implanted silicon have been investigated, especially in the depth range around half of the projected ion range RP/2 after annealing at temperatures between 700 and 1000 °C. Preferable trapping of metals just in this depth range proves the existence of defects there. No vacancy-like defects could be detected by variable energy positron annihilation spectroscopy after annealing at temperatures T>800 °C. Instead, interstitial-type defects were observed in the RP/2 region using cross section transmission electron microscopy of a specimen prepared under special conditions. The results indicate the presence of small interstitial agglomerates at RP/2 which remain after high temperature annealing.
Crystallization kinetics and glass transition of Zr41Ti14Cu12.5Ni10−xFexBe22.5 bulk metallic glasses
Authors: Zhuang Yan Xin , Wang Wei Hua , Zhang Yong , Pan Ming Xiang , Zhao De Qian
Published: July 2002

The crystallization kinetics and glass transition behavior of Zr41Ti14Cu12.5Ni10−xFexBe22.5 (x=0, 2, and 5) bulk metallic glasses (BMGs) have been investigated by means of differential scanning calorimeter under nonisothermal conditions. The glass transition temperature Tg, the onset crystallization temperature Tx, and the crystallization peak temperature Tpi of the BMGs are found to depend on the heating rate during the continuous heating. The effective activation energy and the frequency factor of the glass transition and crystallization of the BMGs are determined by the Kissinger method. The glass forming ability of the glass forming alloys has been discussed in view of the crystallization kinetics.
Nuclear magnetic resonance quantum computing using liquid crystal solvents
Authors: Yannoni Costantino S. , Sherwood Mark H. , Miller Dolores C. , Chuang Isaac L. , Vandersypen Lieven M. K. , Kubinec Mark G.
Published: July 2002

Liquid crystals offer several advantages as solvents for molecules used for nuclear magnetic resonance quantum computing (NMRQC). The dipolar coupling between nuclear spins manifest in the NMR spectra of molecules oriented by a liquid crystal permits a significant increase in clock frequency, while short spin-lattice relaxation times permit fast recycling of algorithms, and save time in calibration and signal-enhancement experiments. Furthermore, the use of liquid crystal solvents offers scalability in the form of an expanded library of spin-bearing molecules suitable for NMRQC. These ideas are demonstrated with the successful execution of a two-qubit Grover search using a molecule (13C 1HCl3) oriented in a liquid crystal and a clock speed eight times greater than in an isotropic solvent. Perhaps more importantly, five times as many logic operations can be executed within the coherence time using the liquid crystal solvent.
High-frequency-induced phase-dependent dc current by Bloch oscillator non-ohmicity
Authors: Seeger K.
Published: July 2002

A calculation is presented for the phase-dependent dc current induced in a semiconductor superlattice by the simultaneous application of an ac field and its phase-shifted second harmonic. The dc current is a result of the Esaki–Tsu non-ohmicity of the superlattice for the case where it Bloch oscillates. The effect provides a tool for a determination of the relaxation time of the electrons.