bluuebunny/crossref_metadata_2025 huggingface dataset:
A silicon Coulomb blockade device with voltage gain
Authors: Smith R. A. , Ahmed H.
Published: July 2002

A silicon single electron tunneling transistor (SETT), which shows an inverting voltage gain greater than unity and as high as 3.7, has been fabricated. The blockade voltage as a function of gate voltage shows sawtooth oscillations when biased with a small current and measured at a temperature of 4.2 K. The SETT is fabricated in highly doped and oxidized silicon quantum wires of less than a 40 nm×50 nm cross section and 1.5 μm length.
Microscopic nature of Staebler-Wronski defect formation in amorphous silicon
Authors: Biswas R. , Pan B. C.
Published: July 2002

Light-induced metastable defects in a-Si:H are proposed to be silicon dangling bonds accompanied by pairs of hydrogen atoms breaking a silicon bond, forming a complex with two Si-H bonds. This supports the model of Branz. These defects are the analog of the H2* defect in c-Si and their energy correlates with the bond-angle strain. Several features of the annealing are well described by this defect complex.
Atomic step networks as selective epitaxial templates
Authors: Finnie P. , Homma Y.
Published: July 2002

A technique to control epitaxial growth laterally across a wafer is presented, which does not use a mask. A vicinal Si(111) substrate was patterned by optical lithography and heated to fabricate a regular pattern of bunches of atomic steps. Under appropriate growth conditions, it is seen that epitaxial material, here GaAs, sticks only to the step bunches, not to the terraces. It is possible to fabricate large-scale complex networks of GaAs with micron scale and submicron scale features. The conditions required to obtain selective growth are presented. It is shown that there are two regimes of selective growth—high temperature (>550 °C), or low temperature (<400 °C). Selectivity is obtained via two distinct mechanisms: desorption and diffusion, respectively.
Determination of carrier lifetimes using Hakki–Paoli gain data
Authors: Ongstad Andrew P. , Dente Gregory C. , Tilton Michael L. , Stohs Jonathan , Gallant David J.
Published: July 2002

This letter presents a technique for determining carrier lifetimes, which does not require a fast detector or rely on an experimentally complex implementation. The technique is based both on a measurement and a parallel calculation: (1) A Hakki–Paoli [J. Appl. Phys. 44, 4113 (1973)] measurement of modal gain versus current density, g(J), and (2) A theoretical determination of the modal gain versus carrier sheet density, g(N). Once the gain relationships have been determined, the carrier sheet density N can be functionally related to the current density J and the lifetime determined. We demonstrate this method on two InGaAs single quantum well lasers. This method may prove particularly useful for carrier lifetime estimations in long-wavelength semiconductor lasers.
Formation of visible light emitting porous GaAs micropatterns
Authors: Schmuki P. , Erickson L. E. , Lockwood D. J. , Fraser J. W. , Champion G. , Labbé H. J.
Published: July 2002

Pore growth on n-type GaAs (100) can be initiated in 1 M HCl solution by electrochemical polarization of the material anodic to a critical potential value—the pore formation potential (PFP). At surface defects, however, the PFP is significantly lower (shifted cathodically). Focused ion beam, implantation of Si++ was used to create defined patterns in the substrate. At these implant sites, the growth of porous GaAs was selectively achieved by polarization below the overall PFP. From the porous GaAs patterns visible photoluminescence at green-yellow wavelengths can be observed. This technique, thus, allows the production of light emitting porous GaAs micropatterns of arbitrary shape by a direct writing process.
High-order azimuthal spatial modes of concentric-circle-grating surface-emitting semiconductor lasers
Authors: Olson Craig , Greene Pamela L. , Wicks Gary W. , Hall Dennis G. , Rishton Steve
Published: July 2002

We report the emission properties of concentric-circle-grating, surface-emitting (CCGSE), distributed-feedback semiconductor lasers oscillating in single high-order azimuthal spatial modes. The evolution of the spatial profile of the beam emitted by such lasers with increasing excitation depends upon the spatial gain distribution and the depth of the circular waveguide grating. The polarization of the high-order spatial modes is predominantly radial.
Observation of chemical shifts of Si 2p level by an x-ray photoelectron spectroscopy system with a laser-plasma x-ray source
Authors: Kondo Hiroyuki , Tomie Toshihisa , Shimizu Hideaki
Published: July 2002

An x-ray photoelectron spectroscopy system with a laser-plasma x-ray source is shown to have energy resolution high enough to observe chemical shifts of Si 2p electrons in SiO2, Si3N4, and pure Si. A boron nitride (BN) plasma x-ray source is produced by irradiation of 100 mJ Q-switched YAG laser pulses. A single line emission at 4.86 nm is selected from the BN plasma by means of carbon foils. Fine spectra are acquired with only 96 laser shots. The results obtained confirm that a laboratory-sized x-ray photoelectron spectroscopy system with submicron spatial resolution and high spectral acquisition speed can be realized.
Silicon nanowires prepared by laser ablation at high temperature
Authors: Zhang Y. F. , Tang Y. H. , Wang N. , Yu D. P. , Lee C. S. , Bello I. , Lee S. T.
Published: July 2002

Silicon nanowires have been synthesized in high yield and high purity by using a high-temperature laser-ablation method with growth rates ranging from 10 to 80 μm/h. Transmission electron microscopic investigation shows that the nanowires are crystalline Si, and have diameters ranging from 3 to 43 nm and length up to a few hundreds microns. Twins and stacking faults have been observed in the Si core of the nanowires. The lattice structure and constant of the nanowires as determined from x-ray diffraction (XRD) are nearly identical to those of bulk Si, although the relative XRD peak intensities are different from those of randomly oriented Si crystallites. Raman scattering from the nanowires shows an asymmetric peak at the same position as that of bulk crystalline silicon.
Low noise multiwasher superconducting interferometer
Authors: Carelli P. , Castellano M. G. , Torrioli G. , Leoni R.
Published: July 2002

The dc-superconducting quantum interference device (SQUID) is a low-noise converter from magnetic flux to voltage which can have, in principle, an energy sensitivity near the quantum limit of ℏ/2. A critical parameter for the ideal performance is the device inductance, which must be kept as small as possible. Minimizing the SQUID inductance, however, is a major concern for a practical device; this requirement implies a small SQUID ring and hence magnetic coupling with an external signal is more difficult to achieve. Here we present an original scheme (called multiwasher) to circumvent this problem, and its implementation in an all-refractory thin-film device. Our scheme not only provides good magnetic coupling with a large input coil (0.5 μH) and very low SQUID inductance, but also shielding from outside uniform fields, such as those generated by ambient disturbances. The measured coupled spectral energy sensitivity in the white region at about 1 kHz is 28ℏ at 4.2 K and 5.5ℏ in a pumped helium bath at 0.9 K. The flux noise spectral density at 0.1 Hz and 0.9 K is Φn=1×10−6 Φ0/Hz.
In situ observation of electric field induced agglomeration of carbon black in epoxy resin
Authors: Prasse Torsten , Flandin Lionel , Schulte Karl , Bauhofer Wolfgang
Published: July 2002

This letter reports on the influence of a static electric field applied by metal electrodes on the agglomeration process of carbon black (CB) in epoxy resin. The growth of dendrites from the anode into the material is observed in situ by optical transmission microscopy. A percolating network is seen to form, combined with a drastic reduction in the sample resistivity. This behavior can be explained by taking into account the electrostatic interaction of the charged CB particles. The final resistance for composites with a given CB content can be controlled within a range of several decades by varying the applied voltage and the curing temperature of the mixture.
Pulsed laser deposition of superconducting Nb-doped strontium titanate thin films
Authors: Leitner Arnold , Rogers Charles T. , Price John C. , Rudman David A. , Herman David R.
Published: July 2002

We report on the growth of superconducting Nb-doped SrTiO3 thin films on LaAlO3 substrates by pulsed laser deposition. We find optimum Nb doping and high mobility for growth near 870 °C and chamber pressures below 3×10−4 Pa (2×10−6 Torr). The transport properties were measured from 300 K to 150 mK. The most highly doped samples display metallic behavior, and are superconducting below 350 mK, with transition temperatures similar to those of bulk single crystals.
Laser stimulated selective area growth of quantum dots
Authors: Wankerl A. , Schremer A. T. , Shealy J. R.
Published: July 2002

We report on the selective area growth of InAs quantum dots on GaAs by ultraviolet (UV) laser stimulated organometallic vapor phase epitaxy. At the low substrate temperature of 435 °C, exposure to a 248.2 nm continuous wave laser beam enhances the InAs growth rate by approximately 30%, causing the transition from two-dimensional (2D) to 3D growth mode to occur in the laser stimulated region only. Photoluminescence spectra from the UV laser stimulated growth region show both wetting layer and quantum dot luminescence, whereas only the wetting layer peak is present in the spectra from the dark grown regions. A photoluminescence map shows good spatial agreement between the region exhibiting quantum dot luminescence and the UV stimulated spot size. Since no quantum dot peak shifts are detected, but the luminescence intensity increases towards the center of the region stimulated with the Gaussian UV beam, we conclude that the island density rather than island size distribution is influenced by the UV intensity.
Optical gain in GaN epilayers
Authors: Hess S. , Taylor R. A. , Ryan J. F. , Beaumont B. , Gibart P.
Published: July 2002

We present optical gain and loss spectra measured over a range of carrier densities at low temperature in hexagonal GaN epilayers. We have determined the optical loss directly to be ∼80 cm−1. Photoluminescence spectra show that stimulated emission in our samples arises from electron–hole plasma recombination.
Complex admittance measurements of polymer light-emitting electrochemical cells: Ionic and electronic contributions
Authors: Yu Gang , Cao Yong , Zhang Chi , Li Yongfang , Gao Jun , Heeger Alan J.
Published: July 2002

Measurements of the frequency dependence of the complex admittance are used to separate the ionic and electronic contributions in polymer light-emitting electrochemical cells (LECs). At zero bias, a large polarizability, attributed to salt molecules in the electrolyte, is observed at low frequencies. Ions are generated when the LEC is biased at voltages above the threshold for electrochemical redox doping. Because of the slow ionic response, a novel pulsed drive scheme is proposed: the mean value stabilizes the induced p-i-n junction, while the peak value controls the carrier injection and the brightness of the electroluminescent emission. LECs operated in this way exhibit fast emissive response and improved operating life.
Precise control of atomic nitrogen production in an electron cyclotron resonance plasma using N2/noble gas mixtures
Authors: Fan Z. Y. , Newman N.
Published: July 2002

The atomic nitrogen flux and impacting ion kinetic energy are two important parameters which influence the quality of deposited nitride films using reactive growth. In this letter, a method is described to control the flux and kinetic energy of atomic and molecular nitrogen ions using an electron cyclotron resonance plasma with N2/Ar and N2/Ne gas mixtures. The results clearly show that the addition of neon to nitrogen plasma can remarkably enhance the production rate of atomic nitrogen due to Penning ionization involving the metastable state of Ne. In contrast, the addition of argon significantly decreases the rate.
Generation of intense excimer radiation from high-pressure hollow cathode discharges
Authors: El-Habachi Ahmed , Schoenbach Karl H.
Published: July 2002

By reducing the diameter of the cathode opening in a hollow cathode discharge geometry to values on the order of 100 μm, we were able to operate these discharges in noble gases in a direct current mode up to atmospheric pressure. High-pressure discharges in xenon were found to be strong sources of excimer radiation. Highest intensities at a wavelength of 172 nm were obtained at a pressure of 400 Torr. At this pressure, the vacuum ultraviolet (VUV) radiant power of a single discharge operating at a forward voltage of 220 V and currents exceeding 2 mA reaches values between 6% and 9% of the input electrical power. The possibility to form arrays of these discharges allows the generation of flat panel VUV lamps with radiant emittances exceeding 50 W/cm2.
Light emission spectra of AlGaAs/GaAs multiquantum wells induced by scanning tunneling microscope
Authors: Tsuruoka T. , Ohizumi Y. , Ushioda S. , Ohno Y. , Ohno H.
Published: July 2002

We have investigated the scanning-tunneling-microscope light emission (STM-LE) spectra of p-Al0.4Ga0.6As/p-GaAs multiquantum wells. The injection current level was kept as low as 0.1–0.5 nA to ensure that the sample is not damaged by the tunneling current. This is the current level ordinarily used for taking STM images. The peak energy of the emission shifts to the high energy side with decreasing well widths. A corresponding peak shift behavior was also observed in the photoluminescence (PL) spectra for the same samples. From comparisons of the STM-LE and the PL spectra, we find that although there is a difference in the excitation process, the final recombination process is identical in both cases.
Photoluminescence excitation spectroscopy of free-to-bound transitions in undoped GaN grown by hydride vapor phase epitaxy
Authors: Rhee S. J. , Kim S. , Reuter E. E. , Bishop S. G. , Molnar R. J.
Published: July 2002

Temperature-dependent photoluminescence excitation (PLE) spectroscopy has been carried out on the yellow band (YB) in GaN. The 5 K PLE spectra demonstrate that the exciting light must have photon energy large enough to generate free carriers or carriers localized on shallow impurities in order to excite the YB effectively. With increasing temperatures, progressively deeper energy levels can be thermally ionized, enabling extrinsic absorption by these deeper levels to generate the free holes required to excite the YB emission. The broad below-band gap PLE response then exhibits thermally activated onsets attributed to these free-to-bound transitions. One such onset corresponds to the well-known 205 meV acceptor, and a second onset provides conclusive evidence for the existence of a previously unconfirmed ∼120 meV impurity or defect level in GaN.
High critical current density in epitaxial HgBa2CaCu2OX thin films
Authors: Yan S. L. , Xie Y. Y. , Wu J. Z. , Aytug T. , Gapud A. A. , Kang B. W. , Fang L. , He M. , Tidrow S. C. , Kirchner K. W. , Liu J. R. , Chu W. K.
Published: July 2002

High quality superconducting HgBa2CaCu2Ox (Hg-1212) thin films have been reproducibly fabricated using cation-exchange method. The thin films have pure Hg-1212 phase and have smooth surface morphology. The superconducting transition temperatures of these films are in the range of 120–124 K. The critical current density Jc is up to 3.2×106 A/cm2 at 77 K and drops only by a factor of 2 at 100 K and self field. At 110 K, a Jc of 7.8×105 A/cm2 has been obtained. X-ray diffraction pole figures show that these films are epitaxially grown on LaAlO3(001) substrates, which is consistent with a χmin of 19% obtained using Rutherford backscattering/channeling analysis.
Mechanism of silicon exfoliation induced by hydrogen/helium co-implantation
Authors: Weldon M. K. , Collot M. , Chabal Y. J. , Venezia V. C. , Agarwal A. , Haynes T. E. , Eaglesham D. J. , Christman S. B. , Chaban E. E.
Published: July 2002

Infrared spectroscopy and secondary ion mass spectrometry are used to elucidate the mechanism by which co-implantation of He with H facilitates the shearing of crystalline Si. By studying different implant conditions, we can separate the relative contributions of damage, internal pressure generation, and chemical passivation to the enhanced exfoliation process. We find that the He acts physically as a source of internal pressure but also in an indirect chemical sense, leading to the reconversion of molecular H2 to bound Si–H in “VH2-like” defects. We postulate that it is the formation of these hydrogenated defects at the advancing front of the expanding microcavities that enhances the exfoliation process.
Neutron diffraction evidence for a new ferromagnetic phase in Cr doped Pr0.5Ca0.5MnO3
Authors: Damay F. , Martin C. , Maignan A. , Hervieu M. , Raveau B. , Bourée F. , André G.
Published: July 2002

Cr doping in Pr0.5Ca0.5MnO3 is known to destroy the low-temperature antiferromagnetic charge-ordered state and to induce a ferromagnetic component as well as colossal magnetoresistance properties. Effects of Cr doping on the magnetic and nuclear structures are studied here by neutron diffraction for Pr0.5Ca0.5Mn0.95Cr0.05O3. It is shown that, at low temperature, the strongly distorted charge ordered structure usually observed in Pr0.5Ca0.5MnO3 is replaced by a ferromagnetic phase in which the basal-plane distortion of the MnO6 octahedra has disappeared, in agreement with the restoration of the double–exchange interactions.
Tunnel diodes fabricated from CdSe nanocrystal monolayers
Authors: Kim S.-H. , Markovich G. , Rezvani S. , Choi S. H. , Wang K. L. , Heath J. R.
Published: July 2002

A parallel approach for fabricating nanocrystal-based semiconductor–insulator–metal tunnel diodes is presented. The devices consisted of a Au electrode, a monolayer of 38 Å CdSe nanocrystals, an insulating bilayer of eicosanoic acid (C19H39CO2H), and an Al electrode. Each device was approximately 100 μm2. Conductance measurements at 77 K reveal strong diode behavior and evidence of Coulomb blockade and staircase structure. A single barrier model was found to reproduce the electronic characteristics of these devices.
On the origin of tunneling barriers in silicon single electron and single hole transistors
Authors: Ishikuro Hiroki , Hiramoto Toshiro
Published: July 2002

To clarify the channel potential profiles, Coulomb blockades of single electron and single hole tunneling in Si nanosize narrow channel metal–oxide–semiconductor field-effect transistors are intensively studied. Devices with both n+ and p+ source/drain contacts were fabricated on silicon-on-insulator substrates. Transport properties of a hole system as well as an electron system induced in the same channel were investigated. It is found from the experimental results that potential fluctuations in the channel act as tunnel barriers for both electrons and holes. Lateral quantum confinement effects or silicon oxide (SiOx) are thought to be the cause of tunnel barriers.
Suppression of thermal interface degradation in (111) Si/SiO2 by noble gases
Authors: Stesmans A. , Afanas’ev V. V. , Revesz A. G.
Published: July 2002

Annealing-induced interface degradation of (111) Si/SiO2 has been studied in noble gas ambients. A remarkable impeding effect on degradation is found, inversely proportional to the gas atomic diameter. The noble gases physically obstruct SiO removal through their occupation of SiO accessible sites in the oxide, thus impeding degradation. The observed process represents blocking of a chemical reaction by physical action.
Light emission spectra of columnar-shaped self-assembled InGaAs/GaAs quantum-dot lasers: Effect of homogeneous broadening of the optical gain on lasing characteristics
Authors: Sugawara Mitsuru , Mukai Kohki , Nakata Yoshiaki
Published: July 2002

We examined the current–output power characteristics and light emission spectra for columnar-shaped self-assembled InGaAs quantum-dot lasers with a room temperature lasing threshold of 6 mA. Lasing threshold currents became obscure as temperature decreased below 180 K. While lasing occurred with one line including a series of longitudinal modes at room temperature, spectra at 80 K showed broad lasing emission over a range of 50–60 meV. We conclude that dots with different energies start lasing independently at low temperatures due to their spatial localization, while at room temperature the dots contribute to one-line lasing collectively via homogeneous broadening of optical gain.
Fabrication of silicon cones and pillars using rough metal films as plasma etching masks
Authors: Seeger K. , Palmer R. E.
Published: July 2002

We have developed a simple fabrication process which allows the production of nanoscale silicon structures. Rough silver films are used as an etching mask for reactive ion etching at 10 °C. Variation of the etching parameters, such as the rf power, allows control over the shape of the features; the production of both pillars and cones is possible. The density and diameter of these features are controlled by the etching time. Pillars with diameters as small as 5 nm are reported.
A device layout for tunneling spectroscopy of barrier-separated electron systems with tunable dimensionality
Authors: Ploner G. , Hirner H. , Maier T. , Strasser G. , Smoliner J. , Gornik E.
Published: July 2002

A selective depletion scheme relying on self-aligned side gates is used to establish independent Ohmic contacts to two low-dimensional electron gases separated by a tunneling barrier. The self-aligned side gate technique is also demonstrated to be suitable for inducing an electrically tunable lateral confinement on the active region of the tunneling device via a central gate. As the central gate voltage is increased, the measured tunneling differential conductance clearly reveals a transition from tunneling between two-dimensional electron gases to tunneling between one-dimensional quantum wire states. The one-dimensional subband spacing of the collector electron channel could be continuously varied up to 6 meV.
Extrinsic surface states traced by surface photovoltage in photoemission
Authors: Kipp L. , Adelung R. , Trares-Wrobel N. , Skibowski M.
Published: July 2002

Surface defect states are generally not directly accessable experimentally. In standard photoemission this is because of their low densities which are several orders of magnitude lower than intrinsic states. On semiconductor surfaces, however, they may induce band bending which is changing characteristically upon bias light intensity and temperature variation. We show that fitting surface photovoltage measured by photoemission to calculations considering high bias light levels and finite electric fields in the space charge layer explicitly allow for a quantitative determination of surface defect densities and the associated energy levels. The results obtained for the defect densities were corroborated by scanning tunneling microscopy investigations. For the covalent and layered semiconductor surfaces GaAs(110) and WSe2:Rb serving as model systems, we show the wide applicability and reliability of this technique.
Resonant hole localization and anomalous optical bowing in InGaN alloys
Authors: Bellaiche L. , Mattila T. , Wang L.-W. , Wei S.-H. , Zunger A.
Published: July 2002

Using large supercell empirical pseudopotential calculations, we show that alloying of GaN with In induces localization in the hole wave function, resonating within the valence band. This occurs even with perfectly homogeneous In distribution (i.e., no clustering). This unusual effect can explain simultaneously exciton localization and a large, composition-dependent band gap bowing coefficient in InGaN alloys. This is in contrast to conventional alloys such as InGaAs that show a small and nearly composition-independent bowing coefficient. We further predict that (i) the hole wave function localization dramatically affects the photoluminescence intensity in InGaN alloys and (ii) the optical properties of InGaN alloys depend strongly on the microscopic arrangement of In atoms.
Hot-electron energy relaxation, noise, and lattice strain in InGaAs quantum well channels
Authors: Matulionis A. , Aninkevičius V. , Liberis J. , Matulionienė I. , Berntgen J. , Heime K. , Hartnagel H. L.
Published: July 2002

Energy loss by hot electrons in lattice-matched and strained InGaAs layers is estimated from experimental data on microwave noise obtained for InP-based quantum well channels containing two-dimensional electron gas. A strong correlation of the energy relaxation time and the lattice strain is observed.
Three color coherent generation and control of current in low-temperature-grown GaAs
Authors: Fraser J. M. , Haché A. , Shkrebtii A. I. , Sipe J. E. , van Driel H. M.
Published: July 2002

We demonstrate coherent generation and control of electrical currents in low-temperature-grown GaAs at 300 K using three phase-related, 150 fs pulses derived from a parametric process. Interference between single photon (0.8 μm) and nondegenerate two photon (1.4 and 1.8 μm) absorption amplitudes generates ballistic electrical currents whose beam polarization dependence is in agreement with a simple Fermi’s golden rule calculation.
Distributed on-fiber thin film heaters for Bragg gratings with adjustable chirp
Authors: Rogers John A. , Eggleton Benjamin J. , Pedrazzani Janet R. , Strasser Thomas A.
Published: July 2002

This letter describes a fiber Bragg grating device that has tunable chirp. It relies on a distributed on-fiber resistive heater that consists of a thin metal film deposited onto the outer surface of a bare fiber; the thickness of this film varies continuously with position along the fiber. The physics of heat flow and diffusion in these structures leads to temperature gradients that follow, to a remarkably good approximation, the local resistance of the tapered metal film. This temperature distribution produces a chirp with a geometry that is defined by the thickness profile of the film and at a rate that can be adjusted by changing the current. Finite element modeling illuminates aspects of the flow of heat in these structures, and optical measurements demonstrate important characteristics of the devices.
Effect of annealing in two-center holographic recording
Authors: Adibi Ali , Buse Karsten , Psaltis Demetri
Published: July 2002

Persistent holograms are recorded with red light in lithium niobate crystals doped with manganese and iron. We find that the oxidation/reduction state of the crystal has a profound impact on the recording and readout performance. The underlying physical processes are investigated and the recording and readout responses are explained and optimized.
Raman spectroscopy for characterizing compositional intermixing in GaAs/AlGaAs heterostructures
Authors: Saher Helmy A. , Bryce A. C. , Ironside C. N. , Aitchison J. S. , Marsh J. H.
Published: July 2002

Compositional intermixing induced by the process of impurity-free vacancy (dielectric cap annealing induced) disordering in GaAs/AlGaAs is studied using Raman spectroscopy. The degree of intermixing in multiple-quantum-well structures was detected through the energy shift of certain Raman modes of the lattices. In addition, localized intermixing, with band-gap shifts as low as 6 nm realized in 1:1 band-gap grating patterns with different periods (⩾4 μm), was also detected through the energy shift and the full width at half maximum of the structures’s Raman modes.
In
x
Ga
1−x
N/GaN
band offsets as inferred from the deep, yellow-red emission band in InxGa1−xN
Authors: Manz Ch. , Kunzer M. , Obloh H. , Ramakrishnan A. , Kaufmann U.
Published: July 2002

The deep, yellow photoluminescence band well known in GaN has been studied in InxGa1−xN (x⩽0.14) grown pseudomorphically on GaN. The peak energy Ep of the band is found to shift gradually to the red with increasing x according to Ep=2.20−2.02x (eV). As in the case of GaN, the deep band in InxGa1−xN is assigned to shallow donor-deep acceptor pair recombination. The data show that the deep acceptor level does not follow the valence band edge. It is therefore assumed to be pinned to a reference level common to GaN and InxGa1−xN. The band offsets between GaN and strained InxGa1−xN evaluated under this assumption, are found to be given by ΔEc(x)≈2.02x (eV) and ΔEv(x)≈1.26x (eV) for x⩽0.14.
Buried single CdTe/CdMnTe quantum dots realized by focused ion beam lithography
Authors: Bacher G. , Kümmell T. , Eisert D. , Forchel A. , König B. , Ossau W. , Becker C. R. , Landwehr G.
Published: July 2002

Buried single CdTe/CdMnTe quantum dots are realized by implantation-induced intermixing using a focused 100 keV Ga+ ion beam. For an implantation dose of 5×1013 cm−2 and an annealing temperature of 390 °C, a lateral potential depth of about 65 meV is obtained. By means of photoluminescence spectroscopy, the formation of zero-dimensional multiexcitons in single quantum dots is investigated, yielding a biexciton binding energy of about 3.5 meV. In addition, the occurrence of an excited biexciton transition in the photoluminescence spectrum gives clear evidence of a suppressed exciton spin-flip process in quantum dots.
Si resonant interband tunnel diodes grown by low-temperature molecular-beam epitaxy
Authors: Thompson Phillip E. , Hobart Karl D. , Twigg Mark E. , Jernigan Glenn G. , Dillon Thomas E. , Rommel Sean L. , Berger Paul R. , Simons David S. , Chi Peter H. , Lake Roger , Seabaugh Alan C.
Published: July 2002

Si resonant interband tunnel diodes that demonstrate negative differential resistance at room temperature, with peak-to-valley current ratios greater than 2, are presented. The structures were grown using low-temperature (320 °C) molecular-beam epitaxy followed by a postgrowth anneal. After a 650 °C, 1 min rapid thermal anneal, the average peak-to-valley current ratio was 2.05 for a set of seven adjacent diodes. The atomic distribution profiles of the as-grown and annealed structures were obtained by secondary ion mass spectrometry. Based on these measurements, the band structure was modeled and current–voltage trends were predicted. These diodes are compatible with transistor integration.
Alkali metal coactivators in SrS: Cu,F thin-film electroluminescent devices
Authors: Keir P. D. , Wager J. F. , Clark B. L. , Li D. , Keszler D. A.
Published: July 2002

A unique approach for obtaining bright and efficient saturated green phosphors for alternating-current thin-film electroluminescent (ACTFEL) device applications is presented. The approach involves color-shifting blue SrS:Cu,F ACTFEL phosphors into the green region of the spectrum via the incorporation of alkali metal ions into the SrS lattice. Alkali metals are incorporated into SrS:Cu,F phosphors by using LiF, NaF, KF, RbF, or CsF coactivators. The best result to date is obtained by using a KF coactivator and results in a saturated green brightness and efficiency of 52.7 cd/m2 and 0.973 lm/W (at a frequency of 60 Hz and an overvoltage of 40 V). In addition to providing a color shift, the alkali-metal fluorides improve the overall performance of the ACTFEL device by increasing the magnitude of the electric field and its uniformity across the phosphor through suppression of positive space charge.
The niobium doping effects on resistance degradation of strontium titanate thin film capacitors
Authors: Lee Jian-Hung , Mohammedali Razak , Han Jeong H. , Balu Venkatasubramani , Gopalan Sundararaman , Wong Chun-Hui , Lee Jack C.
Published: July 2002

The rate of resistance degradation of thin (<450 Å) niobium-doped strontium titanate polycrystalline films with platinum top electrodes and iridium bottom electrodes was investigated as a function of direct current (dc) voltages, temperature, Nb atomic fractions [Sr(Ti1−xNbx)O3+y, x=0, 0.001, 0.01, and 0.05, respectively], and capacitor areas (from 2.50×10−5 to 2.91×10−3 cm2). It was found that by increasing the amount of niobium, the resistance degradation rates were greatly reduced, but the leakage currents increased. Also, the degradation rates seemed fairly independent of the areas of the devices.
Studies of metal–ferroelectric–GaN structures
Authors: Li W. P. , Zhang R. , Zhou Y. G. , Yin J. , Bu H. M. , Luo Z. Y. , Shen B. , Shi Y. , Jiang R. L. , Gu S. L. , Liu Z. G. , Zheng Y. D. , Huang Z. C.
Published: July 2002

A GaN-based metal–insulator–semiconductor (MIS) structure has been fabricated by using ferroelectric Pb(Zr0.53Ti0.47)O3 instead of conventional oxides as insulator gate. Because of the polarization field provided by ferroelectric and the high dielectric constant of ferroelectric insulator, the capacitance–voltage characteristics of GaN-based metal–ferroelectric–semiconductor (MFS) structures are markedly improved compared to those of other previously studied GaN MIS structures. The GaN active layer in MFS structures can reach inversion just under the bias of smaller than 5 V, which is the generally applied voltage used in semiconductor-based integrated circuits. The surface carrier concentration of the GaN layer in the MFS structure is decreased by one order compared with the background carrier concentration. The GaN MFS structures look promising for the practical application of GaN-based field effect transistors.
Investigation of the mechanism of titanium silicide reaction using ion-beam-assisted deposition
Authors: Chang Jaeho , Kim Gi Bum , Yoon Dong-Soo , Baik Hong Koo , Yoo Do-Joon , Lee Sung-Man
Published: July 2002

In order to promote the formation of C54 TiSi2, the suppression of C49 TiSi2 formation by ion-beam-assisted deposition of Ti film was investigated. When the Ti film was deposited without ion bombardment, C49 TiSi2 was formed at 600 °C. In contrast, in the case where the Ti film was deposited with concurrent ion bombardment, TiSi formation occurred at the same temperature. The formation of TiSi was attributed to the enhancement of both Si and Ti diffusion below 600 °C, due to grain refinement induced by Ar-ion-beam bombardment. By the adoption of ion-beam-assisted deposition to the conventional Ti silicide process, the gate line width dependence of C54 TiSi2 formation can be eliminated, since this formation is achieved via a direct interfacial reaction between TiSi and Si, and not a conversion of C49 TiSi2.
Epitaxial crystallization of amorphous SiO2 films deposited on single-crystalline α-quartz
Authors: Roccaforte F. , Dhar S. , Harbsmeier F. , Lieb K. P.
Published: July 2002

The epitaxial α-quartz thin film could be a promising material for fabricating optical devices because of its unique optical and mechanical properties and processing advantages compared to bulk materials. This letter reports on the solid-phase epitaxial growth of thin amorphous SiO2 films deposited by electron gun evaporation on single-crystalline α-quartz substrates. This was achieved by high-dose Cs+-ion implantation and subsequent thermal annealing in air. Also, a thin amorphous layer produced by Si+-ion implantation on α-quartz was epitaxially regrown, thus indicating that the epitaxy is independent of the preparation history of the amorphous layer. The results are explained on the basis of network modifications induced by alkali and oxygen in the SiO2 structure.
In enrichment in (In,Ga)As/GaAs quantum dots studied by high-resolution x-ray diffraction and pole figure analysis
Authors: Krost A. , Bläsing J. , Heinrichsdorff F. , Bimberg D.
Published: July 2002

We report on an x-ray study of a 15×(InAs/InGaAs/GaAs) multiquantum dot stack grown by metal organic chemical vapor deposition using high-resolution x-ray diffraction and pole figure analysis. No direct signal from the quantum dots is found by the high-resolution techniques. All rocking curves on different symmetric and asymmetric Bragg reflections can be simulated within the framework of dynamical theory assuming a perfect tetragonally distorted InAs/InGaAs/GaAs multiquantum well system. The analysis of the diffuse scattering intensity in the vicinity of the (113) reflection in the symmetric scattering geometry, however, reveals a signal from the quantum dots. The quantum dots consist of nearly pure InAs, whereas the mean In concentration in the wetting layer is only 43% indicating a strong In diffusion during the Stranski–Krastanow formation process.
Dynamics of ultrafast reversible phase transitions in GeSb films triggered by picosecond laser pulses
Authors: Siegel J. , Afonso C. N. , Solis J.
Published: July 2002

The dynamics and the reversibility conditions of crystalline↔amorphous transitions induced in thin Ge0.07Sb0.93 films upon picosecond laser pulse melting were studied by real-time reflectivity measurements with nanosecond and picosecond resolution. The full transformation time could be resolved in a single exposure experiment using a novel setup based on a streak camera. It is shown that under optimum conditions both crystallization and amorphization are completed within 400 ps. The fundamental requirement for the occurrence of such ultrafast phase transformations is to reduce the latent heat released upon solidification. Amorphization is then achieved via bulk solidification of the fully molten film at a very large supercooling.
Properties of Si-doped GaN films grown using multiple AlN interlayers
Authors: Koleske D. D. , Twigg M. E. , Wickenden A. E. , Henry R. L. , Gorman R. J. , Freitas J. A. , Fatemi M.
Published: July 2002

Electrical, optical, and structural properties of Si-doped GaN films grown on multiple AlN interlayers (IL) sandwiched between high-temperature (HT) GaN are presented. We show that as the number of AlN IL/HT GaN layers increases, the electron mobility increases in the top Si-doped GaN layer, showing a near doubling from 440 to 725 cm2 V−1 s−1. Cross-sectional transmission electron microscopy images reveal a significant reduction in the screw dislocation density for GaN films grown on the AlN IL/HT GaN layers. The symmetric and off-axis x-ray linewidths increase as the number of AlN IL/HT GaN layers increase, indicating a greater relative misalignment of the adjacent HT GaN layers. Photoluminescence spectra of undoped and Si-doped GaN films on the multiple AlN IL/HT GaN layers have small yellow-band intensity. Analysis based on a single-donor/single-acceptor model for the electrical conduction suggests that the improved electron mobility is the result of a reduced acceptor concentration in the top GaN film and that this acceptor may possibly be associated with threading screw dislocations in GaN.
Variation of field emission and photoelectric thresholds of diamond films with average grain size
Authors: Rouse A. A. , Bernhard J. B. , Sosa E. D. , Golden D. E.
Published: July 2002

We report a decrease in field emission threshold from 3.8 to 3.4 eV for room temperature electrophoresis grown polycrystalline diamond films on molybdenum tips as the diamond average grain size increases from 0.25 to 6 μm. The field emission thresholds agree with photoelectric work functions determined from photoelectron spectroscopy measurements of similarly grown flat samples. In addition, diamond surface states are observed at 0.4, 0.9, and 1.8 eV above the valence band. The results are consistent with an increasing negative electron affinity with grain size due to increased surface hydrogen bonding and with perhaps a contribution from surface defect states.
Wavelength dependence of the third-order nonlinear optical properties of a polythiophene/selenophene derivative film
Authors: Van Keuren Edward , Wakebe Takanori , Andreaus Reinhard , Möhwald Helmut , Schrof Wolfgang , Belov Vladimir , Matsuda Hiro , Rangel-Rojo Raul
Published: July 2002

The third-order nonlinear optical properties of a hybrid polymer film containing substituted thiophene rings copolymerized with unsubstituted selenophene were measured using the Z-scan technique. Large, resonantly enhanced third-order nonlinearities were found at wavelengths on the low-energy side of the absorption band. In contrast to the results on a similar copolymer film incorporating only thiophene, a strong two-photon absorption appeared in the near infrared. The imaginary part of the third-order susceptibility can be adequately explained as saturation of an exciton band, while the origin of the large negative real part is unknown.
Optical and structural properties of epitaxial MgxZn1−xO alloys
Authors: Sharma A. K. , Narayan J. , Muth J. F. , Teng C. W. , Jin C. , Kvit A. , Kolbas R. M. , Holland O. W.
Published: July 2002

The optical and structural properties of high-quality single-crystal epitaxial MgZnO films deposited by pulsed-laser deposition were studied. In films with up to ∼36 at. % Mg incorporation, we have observed intense ultraviolet band edge photoluminescence at room temperature and 77 K. The highly efficient photoluminescence is indicative of the excitonic nature of the material. Transmission spectroscopy was used to show that the excitonic structure of the alloys was clearly visible at room temperature. High-resolution transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectroscopy/ion channeling were used to verify the epitaxial single-crystal quality of the films and characterize the defect content. Post-deposition annealing in oxygen was found to reduce the number of defects and to improve the optical properties of the films. These results indicate that MgZnO alloys have potential applications in a variety of optoelectronic devices.
Ultrafast carrier trapping in Be-doped low-temperature-grown GaAs
Authors: Krotkus A. , Bertulis K. , Dapkus L. , Olin U. , Marcinkevičius S.
Published: July 2002

Time-resolved photoluminescence is used to study low-temperature-grown (LTG) GaAs with Be doping. It is observed that the carrier trapping time in the as-grown LTG GaAs increases with Be doping. Similar effect is observed also in the annealed samples doped with less than 3×1019 cm−3 of Be. At higher doping levels, the trapping time in these samples is abruptly reduced to below 100 fs. This behavior is attributed to changes in As antisite density and the compensation effect of Be.
Colossal magnetoresistance effect in perovskite-type La–Sn–Mn–O epitaxial films
Authors: Guo Xiangxin , Dai Shouyu , Zhou Yueliang , Yang Guozhen , Chen Zhenghao
Published: July 2002

La–Sn–Mn–O (LSnMO) thin films epitaxially grown on single-crystal substrates by pulsed-laser deposition are reported. The films have a perovskite structure and perform the colossal magnetoresistance effect with the maximum magnetoresistance (MR) ratio of 103% (at 233 K and 6 T). The dependence of electrical transport and magnetic properties on the film thickness has been studied. The analyses reveal that the electrical transport, in contrast with the magnetic phase transition, is more sensitive to the thickness of the films.
Plasma-assisted molecular-beam epitaxy of ZnO epilayers on atomically flat MgAl2O4(111) substrates
Authors: Chen Yefan , Hong Soon-ku , Ko Hang-ju , Nakajima Masa , Yao Takafumi , Segawa Yusaburo
Published: July 2002

Plasma-assisted molecular-beam epitaxy of ZnO epilayers on MgAl2O4(111) substrates is described. Acid mixed by H2SO4 and H3PO4 was used for the substrate etching, which provides atomically flat surfaces with a regular terrace array. The influence of the substrate on lateral growth and coalescence of ZnO islands during epitaxy is discussed with corresponding morphological and structural properties. The epitaxial relationship between the ZnO epilayer and MgAl2O4 substrate is determined as: ZnO[011̄0]∥MgAl2O4[1̄1̄2] and ZnO[21̄1̄0]∥MgAl2O4[1̄10]. X-ray diffraction, photoluminescence, and Hall-effect measurements are reported, which indicate that high-quality ZnO epilayers are obtained by using atomically flat MgAl2O4(111) substrates to suppress columnar growth.
Time-resolved photoresponse of a gallium-doped germanium photoconductor using a variable pulse-width terahertz source
Authors: Hegmann F. A. , Williams J. B. , Cole B. , Sherwin M. S. , Beeman J. W. , Haller E. E.
Published: July 2002

Picosecond to nanosecond-wide terahertz pulses are used to study the fast photoresponse of a gallium-doped germanium (Ge:Ga) photoconductor operating at 4.2 K. A recombination time of about 2 ns is observed in the time-resolved photoresponse. Laser-activated semiconductor reflection switches are used to “slice” the variable-width terahertz pulses from the quasicontinuous-wave output of a free-electron laser.
Doubling the frequency of depleted fundamental waves in periodically poled KTiOPO4
Authors: Eger D. , Oron M. B. , Bruner A. , Katz M. , Tzuk Y. , Englander A.
Published: July 2002

Frequency doubling of a diode-pumped Nd:YAG laser in 1 and 2 cm long periodically poled KTiOPO4 wafers has been investigated. Up to 60% doubling efficiency has been achieved. The good agreement obtained between measured results and those calculated by numerical integration of the coupled wave equations demonstrate that the efficiency is limited by the basic process of backconversion and dephasing rather than by thermal effects.
Atomically resolved scanning tunneling microscopy of hydrogen-terminated Si(001) surfaces after HF cleaning
Authors: Arima Kenta , Endo Katsuyoshi , Kataoka Toshihiko , Oshikane Yasushi , Inoue Haruyuki , Mori Yuzo
Published: July 2002

Atomic structures of hydrogen-terminated Si(001) surfaces after HF cleaning are investigated by scanning tunneling microscopy. It is revealed that the surface is macroscopically rough but is composed of terraces and steps. Inside a terrace, 1×1 structures are formed. This corresponds to the ideal 1×1 dihydride structure. The step edges run along the 〈110〉 direction. On the other hand, the 1×1 dihydride structure disappears when the surface is subsequently rinsed with ultrapure water, because every other dihydride row of the ideal 1×1 structure is preferentially etched in ultrapure water.
Multigate single-electron transistors and their application to an exclusive-OR gate
Authors: Takahashi Yasuo , Fujiwara Akira , Yamazaki Kenji , Namatsu Hideo , Kurihara Kenji , Murase Katsumi
Published: July 2002

The two-input exclusive-OR (XOR) function was implemented by a multigate single-electron transistor (SET). Two types of multigate SETs operating at 40 K were fabricated on a top silicon layer of an Si-on-insulator wafer by using a special technique called pattern-dependent oxidation. Two small gate electrodes which act as the input gates were formed over the small SET island. The output current of the devices took a high level when a high voltage was applied to either of the two gates with the other gate grounded, while it took a low level when both gates were grounded or fed with a high voltage. It is striking that such an XOR function can be implemented with just one device.
High electron mobility AlGaN/GaN heterostructures grown on sapphire substrates by molecular-beam epitaxy
Authors: Li L. K. , Turk B. , Wang W. I. , Syed S. , Simonian D. , Stormer H. L.
Published: July 2002

High-quality AlGaN/GaN heterostructures have been grown by ammonia gas-source molecular-beam epitaxy on sapphire substrates. Incorporation of a low-temperature-grown AlN interlayer during the growth of a thick GaN buffer is shown to substantially increase the mobility of the piezoelectrically induced two-dimensional electron gas (2DEG) in unintentionally doped AlGaN/GaN heterostructures. For an optimized AlN interlayer thickness of 30 nm, electron mobilities as high as 1500 cm2/V s at room temperature, 10 310 cm2/V s at 77 K, and 12 000 cm2/V s at 0.3 K were obtained with sheet densities of 9×1012 cm−2 and 6×1012 cm−2 at room temperature and 77 K, respectively. The 2DEG was confirmed by strong and well-resolved Shubnikov–de Haas oscillations starting at 3.0 T. Photoluminescence measurements and atomic force microscopy revealed that the densities of native donors and grain boundaries were effectively reduced in the AlGaN/GaN heterostructures incorporating low-temperature-grown AlN interlayers.