bluuebunny/crossref_metadata_2025 huggingface dataset:
Current transport in free-standing porous silicon
Authors: Diligenti A. , Nannini A. , Pennelli G. , Pieri F.
Published: July 2002

The electrical conduction of free-standing porous silicon layers, obtained from n+ silicon with various anodization currents and illumination conditions, has been investigated in vacuum as a function of the temperature in the interval 300-210 K. The two-contact I-V characteristic is determined by the metal/porous silicon rectifying interface, whereas, by using the four-contact technique, a linear dependence of the current vs voltage was found. The resistance of free-standing samples showed a thermally activated behavior, with activation energies ranging from 0.1 to 0.44 eV. It was found that the activation energy decreased if the light intensity during the anodization was reduced. Variations of activation energy were also observed if the anodization current was changed but, in this case, it was not possible to find any correlation over the parameter range investigated.
Growth and characterization of AlInGaN quaternary alloys
Authors: McIntosh F. G. , Boutros K. S. , Roberts J. C. , Bedair S. M. , Piner E. L. , El-Masry N. A.
Published: July 2002

We report on the deposition of AlyInxGa1−x−yN in the (0<y<0.15) and (0<x<0.14) composition range by metalorganic chemical vapor deposition. AlInGaN quaternary alloys offer a lattice-matched platform for InGaN-based light emitting heterostructure devices. Epitaxial growth of AlInGaN on (0001) sapphire substrates has been achieved at 750 °C. Alloy composition, lattice constants, and band gaps were obtained by energy dispersive spectroscopy, x-ray diffraction, and room temperature PL. Band edge emissions dominate the PL spectra of these quaternary films. Preliminary data suggest that the lattice constant of AlInGaN can be deduced from chemical composition using Vegard’s law, indicating solid solution in the grown quaternary films.
Trimethylarsenic as an alternative to arsine in the metalorganic vapor phase epitaxy of device quality In0.53Ga0.47As/InP
Authors: Pautet C. , Abraham P. , Dazord J. , Favre R. , Cauwet F. , Monteil Y. , Bouix J. , Ougazzaden A. , Rao E. V. K. , Mircea A.
Published: July 2002

We have investigated the use of trimethylarsenic (TMAs) as an alternative to arsine in the metalorganic vapor phase epitaxy (MOVPE) of device quality InGaAs lattice matched to InP. Films were deposited with arsine or trimethylarsenic over a wide range of growth conditions in a horizontal low pressure (LP)-MOVPE reactor. In order to minimize carbon incorporation, triethylgallium has been chosen instead of trimethylgallium as the gallium precursor. A minimal growth pressure of 250 mbar and a minimal growth temperature of 550 °C are found to be necessary to ensure specular morphology with TMAs. Electrical and optical properties of InGaAs layers grown using TMAs in the temperature range 600 to 650 °C are comparable to those of layers grown using AsH3.
Anisotropic magnetoresistance in tetragonal La1−xCaxMnOδ thin films
Authors: Eckstein J. N. , Bozovic I. , O’Donnell J. , Onellion M. , Rzchowski M. S.
Published: July 2002

We have fabricated thin films of La1−xCaxMnOδ with tetragonal symmetry. For low temperatures and magnetic fields the measured magnetoresistance is anisotropic: initially positive for applied magnetic field perpendicular to the film plane and negative for field applied parallel to the film plane. At high temperatures the magnetoresistance is negative for all fields and field orientations. We also observe an in-plane magnetoresistance anisotropy with an angular dependence corresponding to that observed in transition metal ferromagnets. We suggest an interpretation requiring a substantial spin-orbit interaction in the material.
Current transport through single grain boundaries: A scanning tunneling potentiometry study
Authors: Schneider M. A. , Wenderoth M. , Heinrich A. J. , Rosentreter M. A. , Ulbrich R. G.
Published: July 2002

Spatial variations of the local electric fields in current-carrying thin gold films were studied with a scanning tunneling microscope on a nanometer scale. With a refined potentiometry technique we resolved potential steps at grain boundaries and investigated the potential gradients within each grain. These gradients are caused by nonlocal background scattering of the conduction electrons and are used to measure the local current density. We determine the reflectivity of an individual grain boundary without invoking an averaging procedure over the whole film. We find that the reflectivity of grain boundaries varies between R=0.7 and 0.9 and depends on their orientation.
Pyroelectricity in gallium nitride thin films
Authors: Bykhovski A. D. , Kaminski V. V. , Shur M. S. , Chen Q. C. , Khan M. A.
Published: July 2002

We report on the measurements of the pyroeffect in wurtzite n-type GaN films deposited over basal plane sapphire substrates. We measured the voltage drop between the contacts while the sample was subjected to the uniform heating or cooling. The pyroelectric voltage coefficient extracted from our data is comparable to that of the pyroelectric ceramics (∼104 V/m K). Our results show that the pyroelectric effect in GaN is a combination of a fast response to an initial heat flow and a slower response related to a change in the sample temperature.
Atomic force microscopy study of self-organized Ge islands grown on Si(100) by low pressure chemical vapor deposition
Authors: Capellini G. , Di Gaspare L. , Evangelisti F. , Palange E.
Published: July 2002

In this letter, we present an atomic-force-microscopy investigation of the Stranski–Krastanov growth of Ge on Si(100). Upon increasing the base width of the islands, two morphology transitions are found. The first transition occurs at a base width of ∼50–60 nm and marks the evolution from few-monolayer-thick terraces to square-base pyramidal islands. In the second transition, which takes place when the base width exceeds ∼300 nm, the island shape changes from square base pyramids to tetragonal truncated pyramids. Both transitions are brought about by the need for the system to minimize the elastic energy.
A study on specific optic impedance of materials
Authors: Mohanan S. , Vaidyan V. K. , Kurian K. V.
Published: July 2002

The optic impedance Z of a medium for the propagation of electromagnetic waves is deduced from the definition of wave impedance. A new optical parameter Zo called “specific optic impedance” is defined. The temperature dependence of Zo is examined and an exponential relationship between specific optic impedances at two different temperatures has been derived. The validity of the new relationship is established using the published data on ethyl acetate, cyclohexane, benzene, and a binary mixture of polyvinyl pyrrolidone in N,N-dimethyl formamide solutions from the literature.
High-speed resonant-cavity separate absorption and multiplication avalanche photodiodes with 130 GHz gain-bandwidth product
Authors: Nie Hui , Anselm K. A. , Hu C. , Murtaza S. S. , Streetman B. G. , Campbell J. C.
Published: July 2002

Previously it has been shown that resonant-cavity, separate absorption and multiplication (SAM) avalanche photodiodes (APDs) exhibit high peak external quantum efficiency (∼75%), low dark current, low bias voltage (<15 V), and low multiplication noise (0.2<k<0.3). We describe the frequency response of resonant-cavity AlGaAs/GaAs/InGaAs SAM APDs. A unity-gain bandwidth of 23 GHz and a high gain-bandwidth product of 130 GHz have been achieved.
Arsenic mediated reconstructions on cubic (001) GaN
Authors: Feuillet G. , Hamaguchi H. , Ohta K. , Hacke P. , Okumura H. , Yoshida S.
Published: July 2002

The 4×1 (respectively 1×1) (001) GaN surfaces obtained when molecular-beam-epitaxy (MBE) growth is carried out on (001) cubic SiC were exposed to an As background pressure in the MBE chamber: The reconstructions rapidly and irreversibly changed to 2×2 [respectively c(2×2)] as usually observed for GaN growth on (001) GaAs. The usual reversible 2×2/c(2×2) transitions were consequently observed when bringing the Ga flux up or down. The respective positions for the 4×1/1×1 and 2×2/c(2×2) transitions were worked out as a function of the growth parameters. These observations indicate that the 2×2 and c(2×2) GaN surface reconstructions are mediated by As atoms which we tentatively assign to a surfactant effect. A simple structural model involving As dimers is proposed that accounts for Ga coverages of 0.5 and 1 monolayer for the 2×2 and c(2×2) growth regimes, respectively.
Photo-pumped ZnCdSe/ZnCdMgSe blue-green quantum well lasers grown on InP substrates
Authors: Guo Yongming , Aizin Gregory , Chen Y. C. , Zeng Linfei , Cavus Abdullah , Tamargo Maria C.
Published: July 2002

We report the operation of new photo-pumped blue-green ZnCdSe/ZnCdMgSe graded-index separate confinement heterostructure single quantum well lasers grown lattice matched on InP substrates. Laser emission at 512 nm was observed. The T0 value is 150 K at room temperature. These materials are proposed as alternative materials for the fabrication of visible semiconductor lasers.
As/P exchange on InP(001) studied by reflectance anisotropy spectroscopy
Authors: Sobiesierski Z. , Westwood D. I. , Parbrook P. J. , Ozanyan K. B. , Hopkinson M. , Whitehouse C. R.
Published: July 2002

Reflectance anisotropy spectroscopy (RAS) has been used to investigate the As/P exchange reaction for group V stabilized InP(001) surfaces exposed to As2 and/or P2, under molecular beam epitaxy conditions. By comparing RAS spectra taken before, during, and after As2 exposure it is possible to confirm that the As/P exchange reaction is exactly reversible over a range of temperatures from 420 to 560 °C. Time-resolved RAS measurements of the reaction rate, monitored at an energy of 2.65 eV, indicate that the activation energy for the exchange is 1.23±0.05 eV.
Enhancement of optical nonlinearity in strained (InGa)As sidewall quantum wires on patterned GaAs (311)A substrates
Authors: Nötzel Richard , Ramsteiner Manfred , Niu Zhichuan , Schönherr Hans-Peter , Däweritz Lutz , Ploog Klaus H.
Published: July 2002

Strong enhancement of the optical nonlinearity occurs in strained (InGa)As sidewall quantum wires grown on patterned GaAs (311)A substrates by molecular beam epitaxy. The wires are formed on the fast growing sidewall of mesa stripes along [01-1] and have a smooth, convex-curved surface profile. The blue shift of the photoluminescence peak energy of the wire in dependence on the excitation power is one order of magnitude larger compared to that of the surrounding well. This enhanced optical nonlinearity is assigned to additional lateral optical band gap modulation due to internal piezoelectric fields effective in the present quantum-wire structure.
Strain relaxation and defect formation in heteroepitaxial Si1−xGex films via surface roughening induced by controlled annealing experiments
Authors: Ozkan Cengiz S. , Nix William D. , Gao Huajian
Published: July 2002

Mechanisms of strain relaxation and defect formation during surface roughening in Si1−xGex films grown epitaxially on (100)Si substrates have been investigated by controlled annealing experiments. Epitaxial films 10 nm in thickness and containing 18% Ge, which are subcritical with respect to the formation of misfit dislocations, show strain relaxation through surface roughening on annealing at 850 °C, where surface grooves are aligned along 〈100〉 directions. Other films with 22% Ge and supercritical thicknesses have also been studied, where surface grooves are aligned along 〈110〉 directions.
The enhancement of InGaAs Schottky barrier height by the addition of Pr2O3 and In2O3 in the liquid phase epitaxy
Authors: Wang H. T. , Chou S. T. , Chang L. B. , Wang T. W. , Tang H. C.
Published: July 2002

In this work, a barrier height of ∼0.7 eV is constantly observed from the In0.53Ga0.47As Schottky diodes, regardless of the utilization of different metals as Schottky contacts. By the addition of Pr2O3 and In2O3 in the liquid phase epitaxy, a very low background impurity concentration is also obtained. The low background concentration is credited to the gettering effect from the addition of Pr and oxygen in the growth melt. The high Schottky barrier is attributed to the formation of a stable oxide layer on the surface of the epilayer, which in turn forms a metal-insulator-semiconductor structure in our Schottky diodes. The high Schottky barrier is very stable even at a high measuring temperature and was repeatedly obtained after four months of exposure to the environment.
Polymeric anodes for improved polymer light-emitting diode performance
Authors: Carter S. A. , Angelopoulos M. , Karg S. , Brock P. J. , Scott J. C.
Published: July 2002

We have studied polyaniline and polyethylenedioxythiophene transparent electrodes for use as hole-injecting anodes in polymer light emitting diodes. The anodes were doped with a variety of polymer and monomer-based acids and cast from either water or organic solvents to determine the effect of the dopant and solvent on the hole-injection properties. We find that the anodes with polymeric dopants have improved device quantum efficiency and brightness relative to those with small molecule dopants, independent of conductivity, solvent, or type of conducting polymer. For the most conducting polymer anodes [σ>2(Ωcm)−1], diodes could be made without an indium tin oxide underlayer. These diodes show substantially slower degradation.
Reverse current transient behavior in amorphous silicon Schottky diodes at low biases
Authors: Hornsey R. I. , Aflatooni K. , Nathan A.
Published: July 2002

The application of hydrogenated amorphous silicon Schottky diodes to large-area imaging requires knowledge of the variation in reverse-bias current over long timescales. When the diode is subject to electrical stress, a power-law dependence of reverse current with time is observed. This is followed by a stretched-exponential behavior during the subsequent zero-bias recovery period. Both of these results are attributed to dispersive electron transport in the Schottky diode.
High resolution visualization of acoustic wave fields within surface acoustic wave devices
Authors: Hesjedal T. , Chilla E. , Fröhlich H.-J.
Published: July 2002

We present the submicron visualization of surface acoustic wave (SAW) fields within interdigital transducers (IDTs) obtained by a scanning acoustic force microscope. Utilizing the nonlinear force curve of the tip-to-surface interaction, a periodic deflection of the cantilever appears when the SAWs are excited intermittently. This deflection depends on the amplitude of the surface oscillation and was measured by lock-in technique. SAWs with operating frequencies above 600 MHz were detected. The influence of the mass loading on the local oscillation amplitude was studied for various layer thicknesses of the IDT electrodes.
Gas-source molecular beam epitaxy growth of an 8.5 μm quantum cascade laser
Authors: Slivken S. , Jelen C. , Rybaltowski A. , Diaz J. , Razeghi M.
Published: July 2002

We demonstrate preliminary results for an 8.5 μm laser emission from quantum cascade lasers grown in a single step by gas-source molecular beam epitaxy. 70 mW peak power per two facets is recorded for all devices tested at 79 K with 1 μs pulses at 200 Hz. For a 3 mm cavity length, lasing persists up to 270 K with a T0 of 180 K.
Theory of menisci and its applications
Authors: Gao Chao
Published: July 2002

A theory for liquid menisci formed at an arbitrary interface is developed including surface interactions and liquid evaporation. Its applications to scanning probe techniques and laser textured magnetic disks are also given. The meniscus force is shown to be proportional to meniscus size for none-spherical contacts, but nearly independent for spherical contacts. Stronger surface interactions on the liquid film result in the formation of smaller menisci, whereas a thicker liquid film causes larger menisci. The theory predicts that the meniscus (adhesion) force can be effectively reduced when using the same surface material for the interface that can be wetted by the liquid film. Analytical formulae for meniscus forces are derived for widely encountered spherical/conical tips. Comparisons with existing experiments and macroscopic theories are also discussed.
Ellipsometric studies of Cd1−xMgxTe (0⩽x⩽0.5) alloys
Authors: Choi S. G. , Kim Y. D. , Yoo S. D. , Aspnes D. E. , Miotkowski I. , Ramdas A. K.
Published: July 2002

The determination of the above band gap optical properties of zincblende Cd1−xMgxTe (0⩽x⩽0.5) ternary alloys are reported on. Using the parabolic-band critical point model, room-temperature critical point energies of the E0, E0+Δ0, E1, E1+Δ1, E2, and E0′ interband transitions from numerically calculated second energy derivatives of ellipsometric spectra were obtained. The presence of two distinct structures in the E2 feature for x>0 was also observed.
Metalorganic vapor phase epitaxy of coherent self-assembled InAs nanometer-sized islands in InP(001)
Authors: Marchand H. , Desjardins P. , Guillon S. , Paultre J.-E. , Bougrioua Z. , Yip R. Y.-F. , Masut R. A.
Published: July 2002

The metalorganic vapor phase epitaxy of coherent self-assembled InAs islands on InP(001) is demonstrated. Samples are characterized using transmission electron microscopy and photoluminescence (PL) spectroscopy at 77 K. The deposition of ∼2.4–4.8 monolayers (ML) of InAs at 500°C followed by a 30 s growth interruption results in the formation of coherent islands whose average diameter is 30–35 nm with a standard deviation of 8 nm and whose areal density is (3–4)×1010 cm−2. The PL emission is centered at 0.79 eV and has a full width at half maximum (FWHM) of 90 meV. When the nominal deposited thickness is increased to ∼9.6 ML, the average island diameter increases to ∼120 nm while the areal density decreases to ∼109 cm−2. The resulting PL is then centered at 0.83 eV with a FWHM of 130 meV and also displays a peak at 1.23 eV which is attributed to an InAs wetting layer ∼2 ML in thickness.
Photoluminescence and time-resolved photoluminescence characteristics of InxGa(1−x)As/GaAs self-organized single- and multiple-layer quantum dot laser structures
Authors: Kamath K. , Chervela N. , Linder K. K. , Sosnowski T. , Jiang H-T. , Norris T. , Singh J. , Bhattacharya P.
Published: July 2002

The characteristics of ground and excited state luminescent transitions in In0.4Ga0.6As/GaAs and In0.35Ga0.65As/GaAs self-organized single- and multiple-layer quantum dots forming the active regions of lasers have been studied as a function of incident excitation intensity, temperature and number of dot layers. The results have been correlated with molecular beam epitaxial growth conditions. The threshold excitation density for the saturation of the ground state increases with the number of dot layers and no saturation is observed in samples with more than six dot layers up to an excitation power density of 2 kW/cm2. The luminescent decay times for the ground and excited states are around 700 and 250 ps, respectively, almost independent of the number of dot layers.
Fast ambipolar carrier transport in smectic phases of phenylnaphthalene liquid crystal
Authors: Funahashi Masahiro , Hanna Jun-ichi
Published: July 2002

The carrier transport of a new calamitic liquid crystal, i.e., 2-(4′-octylphenyl)6-dodecyloxynaphthalene (8-PNP-O12) was investigated by the time-of-flight technique. The fast ambipolar electronic conduction was observed in two smectic phases of 8-PNP-O12. The carrier mobilities were determined to be 1.6×10−3 cm2/V⋅s in the lower temperature smectic phase (Sm1) between 79 and 100 °C and to be 2.5×10−4 cm2/V⋅s in the higher temperature phase (Sm2) between 100 and 121 °C, regardless of carrier signs, i.e., electron and hole. The slower ambipolar transport was observed in isotropic phase as well, whose mobility was 8×10−5 cm2/V⋅s. These mobilities were independent of applied electric fields and temperature.
Germanium dots with highly uniform size distribution grown on Si(100) substrate by molecular beam epitaxy
Authors: Wang Xun , Jiang Zui-min , Zhu Hai-jun , Lu Fang , Huang Daming , Liu Xiaohan , Hu Chang-wu , Chen Yifan , Zhu Ziqiang , Yao Takafumi
Published: July 2002

The growth of very uniform Ge dots on Si(100) is achieved by using molecular beam epitaxy. The atomic force microscopy and the transmission electron microscopic observations illustrate that the size uniformity of the dots is not worse than ±3%, i.e., the base dimension is 100±3 nm. The Raman spectrum reveals a peak downward shift of Ge-Ge mode caused by the phonon confinement in the Ge dots. A very narrow photoluminescence peak with the width of 1.6 meV at the energy of 0.767 eV is observed at the temperature of 16 K. We attribute this peak to the free exciton longitudinal acoustic phonon replica originated from the Ge dots.
High spatial resolution quantitative microwave impedance microscopy by a scanning tip microwave near-field microscope
Authors: Gao Chen , Wei Tao , Duewer Fred , Lu Yalin , Xiang X.-D.
Published: July 2002

A recently developed scanning tip microwave near-field microscope has been improved to achieve a spatial resolution of 100 nm (∼λ/106). Furthermore, explicit calculations of the field distribution using a simplified model allow quantitative microscopy of dielectric properties for dielectric materials. A detection sensitivity of δε/ε∼6×10−4 has been achieved.
Hot hole induced breakdown of thin silicon dioxide films
Authors: Tomita Takayuki , Utsunomiya Hiroto , Kamakura Yoshinari , Taniguchi Kenji
Published: July 2002

Hole induced dielectric breakdown of thin gate oxide films is investigated using substrate hot hole (SHH) injection technique. The breakdown characteristics due to SHH stress differ from the case of Fowler-Nordheim (FN) tunneling current stress; the gate current increases gradually just before the breakdown. Measured hole-fluences-to-breakdown, 2–30 C/cm2, which are much larger than that observed in FN stress, 0.1 C/cm2, depend on hole current density. Moreover, the oxide breakdown due to FN stress is accelerated for the oxides subjected to prior hole injection.
Modulating electron beams for an X band relativistic klystron amplifier
Authors: Friedman M. , Pasour J. , Smithe D.
Published: July 2002

A large diameter thin annular intense relativistic electron beam was modulated at a frequency of 10 GHz. The electron beam propagated inside a narrow annular drift tube in which gaps feeding radial cavities were inserted. An external source injected microwave power of 180 kW into a single input cavity followed by a simple idler structure. A stable 10 kA rf current modulation was induced on the 400 keV electron beam.
The effect of growth interruption on the properties of InGaAs/InAlAs quantum well structures
Authors: Choy W. C. H. , Hughes P. J. , Weiss B. L. , Li E. H. , Hong K. , Pavlidis D.
Published: July 2002

The effect of the growth interruption time during the growth of InGaAs/InAlAs quantum well structures is shown to have a significant effect on both the interband transitions, as determined by photoreflectance, and the electrical properties of the as-grown structure. The results show that, for increasing growth interruption time, the quantum well heterointerfaces become more abrupt and the carrier mobility increases, thereby demonstrating that long interruption times are preferable for the growth of high quality rectangular quantum well structures.
Observation of the size-dependent blueshifted electroluminescence from nanocrystalline Si fabricated by KrF excimer laser annealing of hydrogenated amorphous silicon/amorphous-SiNx:H superlattices
Authors: Wang Mingxiang , Huang Xinfan , Xu Jun , Li Wei , Liu Zhiguo , Chen Kunji
Published: July 2002

Nanocrystalline silicon (nc-Si) was fabricated by KrF excimer laser annealing of hydrogenated amorphous silicon/amorphous-SiNx:H superlattices. A stable and reproducible electroluminescence (EL) based on these structures was observed at room temperature. It was found that the EL peak was significantly blueshifted from 780 to 600 nm with decreasing the a-Si:H sublayer thickness from 4.0 to 1.0 nm, while the intensity was also notably enhanced. The results suggest that the quantum confinement effect may play an essential role in visible light emissions from our present samples.
Electrical characterization of GaN/SiC n-p heterojunction diodes
Authors: Torvik John T. , Leksono Moeljanto , Pankove Jacques I. , Van Zeghbroeck Bart , Ng Hock M. , Moustakas Theodore D.
Published: July 2002

GaN/SiC heterojunction diodes have been fabricated and characterized. Epitaxial n-type GaN films were grown using metalorganic chemical vapor deposition (MOCVD) and electron cyclotron resonance assisted molecular beam epitaxy (ECR-MBE) on p-type Si-face 6H-SiC wafers. The I–V characteristics have diode ideality factors and saturation currents as low as 1.2 and 10−32 A/cm2, respectively. The built-in potential in the MOCVD- and ECR-MBE-grown n-p heterojunctions was determined from capacitance–voltage measurements at 2.90±0.08 eV and 2.82±0.08 eV, respectively. From the built-in potential the energy band offsets for GaN/SiC heterostructures are determined at ΔEC=0.11±0.10 eV and ΔEV=0.48±0.10 eV.
Band discontinuity in strained In(As,P)/InP heterostructures
Authors: Monier C. , Vilela M. F. , Serdiukova I. , Freundlich A.
Published: July 2002

Photocurrent and photoluminescence measurements have been performed on strained InAsxP1−x/InP multiquantum wells grown by chemical beam epitaxy, for arsenic content 0.25<x<0.65 and various well widths. The energies deduced from photocurrent spectra of well-resolved electron–heavy-hole and electron–light-hole fundamental excitonic transitions are compared with calculations within the envelope function formalism including strain effects. A conduction-band offset ratio QC of 0.70±0.02 is determined and is found to be independent of the arsenic composition in wells.
Photoreflectance study of Si-doped GaN grown by metal–organic chemical vapor deposition
Authors: Zhang Xiong , Chua Soo-Jin , Liu Wei , Chong Kok-Boon
Published: July 2002

Si-doped n-GaN films grown by metal–organic chemical vapor deposition were studied by photoreflectance (PR) spectroscopy. Based on the intense optical transitions observed in the room-temperature PR spectra, the energy positions of the near-band-edge transition for n-GaN samples with different Si-doping levels were determined through theoretical curve fitting under the weak-field approximation. Furthermore, based on the observed dependence of the redshift in the near-band-edge transition energy with the carrier concentration and the approach using the many-body theory, the band-gap renormalization coefficient for GaN was derived to be (2.4±0.5)×10−8 eV cm. This value was found to be nearly 35% larger than that for GaAs.
Single-electron charging effects in Nb/Nb oxide-based single-electron transistors at room temperature
Authors: Shirakashi Jun-ichi , Matsumoto Kazuhiko , Miura Naruhisa , Konagai Makoto
Published: July 2002

We have reported the single-electron charging effects in Nb/Nb oxide-based single-electron transistors (SETs) at room temperature (T=298 K). The SETs were first fabricated by a scanning probe microscope based anodic oxidation. Then, the miniaturization of tunnel junctions was performed by thermal oxidation. Ultra-low-capacitance tunnel junctions were easily obtained by utilizing both kinds of oxidation processes, which realizes room-temperature Nb-based SETs.
Advantages of ultraviolet Raman scattering for high temperature investigations
Authors: Zouboulis E. , Renusch D. , Grimsditch M.
Published: July 2002

We show that UV Raman spectroscopy is eminently well suited for the in situ investigation of samples at high temperatures. Using sapphire as a test material, we have recorded Raman spectra from ambient temperature to 1700 K using different excitation wavelengths, both in the visible and near UV region of the spectrum. These spectra show that, because of the very rapid decrease of blackbody radiation in the short wavelength region, Raman spectra recorded in the near UV region of the spectrum are free from the blackbody radiation background, which typically hampers experiments in the visible. With 266 nm exciting radiation, we observe no thermal background even at 1700 K. We foresee that the method will become a powerful tool for in situ investigations of high-temperature materials.
Radio-frequency amplifier based on a niobium dc superconducting quantum interference device with microstrip input coupling
Authors: Mück Michael , André Marc-Olivier , Clarke John , Gail Jost , Heiden Christoph
Published: July 2002

A dc superconducting quantum interference device (SQUID) was used to amplify radio-frequency signals that were coupled to one end of the microstrip formed by the input coil and the SQUID washer. For one device, the resonant frequency of the microstrip was increased from about 200 to 620 MHz by progressively shortening the length of the coil. At an operating temperature of 4.2 K, the gain was typically 18 dB, and the system noise temperature ranged from 0.5±0.3 K at 80 MHz to 3.0±0.7 K at 500 MHz.
Role of defects in producing negative temperature dependence of breakdown voltage in SiC
Authors: Raghunathan R. , Baliga B. J.
Published: July 2002

Electron beam induced current (EBIC) techniques were employed in order to understand the role of defects on the breakdown characteristics of SiC. EBIC images revealed that certain defects caused enhanced multiplication leading to the catastrophic failures in SiC diodes. The impact ionization coefficients for holes measured at the defective site (αp,eff) were found to be higher than those measured at a nondefective site. Also, αp,eff measured at the defective site was found to increase with increasing temperature in contrast with a defect free diode where αp decreases with increasing temperature, clearly indicating that the defects produce the observed negative temperature coefficient of breakdown voltage in SiC.
Effects of thermal annealing on the indium tin oxide Schottky contacts of n-GaN
Authors: Sheu J. K. , Su Y. K. , Chi G. C. , Jou M. J. , Chang C. M.
Published: July 2002

In this work indium tin oxide (ITO) films were prepared using electron beam evaporation to form Schottky contacts on n-type GaN films. The thermal stability of ITO on n-type GaN was also investigated by annealing the samples at various temperatures. In addition, current–voltage (I–V) measurements were taken to deduce the Schottky barrier heights. Owing to the large series resistance, the Norde method was used to plot the F(V)–V curves and the effective Schottky barrier heights were determined as well. The effective Schottky barrier heights were 0.68, 0.88, 0.94, and 0.95 eV for nonannealed, 400, 500, and 600 °C annealed samples, respectively. Results presented herein indicate that an increase of the barrier heights may be attributed to the formation of an interfacial layer at the ITO/GaN interface after annealing.
Effects of Si-doping in the barriers of InGaN multiquantum well purplish-blue laser diodes
Authors: Chichibu S. , Cohen D. A. , Mack M. P. , Abare A. C. , Kozodoy P. , Minsky M. , Fleischer S. , Keller S. , Bowers J. E. , Mishra U. K. , Coldren L. A. , Clarke D. R. , DenBaars S. P.
Published: July 2002

Optical gain spectra of InGaN multiquantum well laser diode wafers having Si-doped or undoped InGaN barriers were compared. Although evidence for effective band-gap inhomogeneity was found in both structures, the wells with the Si-doped barriers exhibited a smaller Stokes-like shift. Si doping suppressed emergence of a secondary amplified spontaneous emission peak at 3.05 eV, which was uncoupled with the primary one at 2.93 eV. Furthermore Si doping reduced the threshold power density required to obtain the stimulated emission.
Design and simulation of low-threshold antimonide intersubband lasers
Authors: Vurgaftman I. , Meyer J. R. , Julien F. H. , Ram-Mohan L. R.
Published: July 2002

Optically and electrically pumped infrared lasers based on intersubband transitions in InAs/GaSb/AlAsSb quantum wells are modeled in detail. The large conduction-band offset of the AlAsSb barriers with respect to the InAs wells allows the lasing wavelength to be shortened to at least 1.9 μm. Furthermore, the small InAs electron mass results in longer phonon-limited lifetimes in the upper lasing subband as well as larger dipole matrix elements. This leads to the prediction of lower threshold currents, and hence, higher cw operating temperatures than for quantum cascade lasers based on the InGaAs/InAlAs/InP system.
Hydrogen passivation of silicon carbide by low-energy ion implantation
Authors: Achtziger N. , Grillenberger J. , Witthuhn W. , Linnarsson M. K. , Janson M. , Svensson B. G.
Published: July 2002

Ion implantation of deuterium is performed to investigate the mobility and passivating effect of hydrogen in epitaxial α-SiC (polytypes 4H and 6H). To avoid excessive damage and the resulting trapping of hydrogen, the implantation is performed with low energy (600 eV 2H2+). The H2 depth profile is analyzed by secondary ion mass spectrometry. Electrical properties are measured by capacitance–voltage profiling and admittance spectroscopy. In p-type SiC, hydrogen diffuses on a μm scale even at room temperature and effectively passivates acceptors. In n-type SiC, the incorporation of H is suppressed and no passivation is detected.
An optoelectronic thyristor-based analog-to-digital converter for parallel processing
Authors: Cai J. , Taylor G. W.
Published: July 2002

A single pixel optoelectronic analog-to-digital converter is described which is suitable for two-dimensional (2D) arrays as would be required for a digital optical signal processor. The conversion is based upon the use of an optoelectronic thyristor in the form of the double heterostructure optoelectronic switch as a comparator. Using the switch configured as a VCSEL and one field-effect transistor load device, the comparator delivers the binary output optically and, at the same time, provides an electrical output to combine with the input signal to determine the next lower order bit. The function is similar to the algorithmic electrical converter with several optoelectronic advantages. Resolution of 10 bits is expected at speeds of 100 MHz with scaled transistor technology. The compact size of the circuit and the algorithm suggest a viable approach for conversion of 2D data arrays in real time.
Transport properties of two-dimensional electron gases containing InAs self-assembled dots
Authors: Kim G. H. , Ritchie D. A. , Pepper M. , Lian G. D. , Yuan J. , Brown L. M.
Published: July 2002

We present a study of the transport properties of two-dimensional electron gases formed in GaAs/AlGaAs heterostructures in which InAs self-assembled quantum dots have been inserted in the center of a GaAs quantum well. We observed that, while maintaining a constant carrier density, the mobility increased as the InAs dot density was reduced. The ratio of the transport to the quantum lifetime was measured to be approximately five with the dominant scattering mechanism attributed to short-range scattering from the inserted InAs dots.
Auger coefficients in type-II InAs/Ga1−xInxSb quantum wells
Authors: Meyer J. R. , Felix C. L. , Bewley W. W. , Vurgaftman I. , Aifer E. H. , Olafsen L. J. , Lindle J. R. , Hoffman C. A. , Yang M.-J. , Bennett B. R. , Shanabrook B. V. , Lee H. , Lin C.-H. , Pei S. S. , Miles R. H.
Published: July 2002

Two different approaches, a photoconductive response technique and a correlation of lasing thresholds with theoretical threshold carrier concentrations have been used to determine Auger lifetimes in InAs/GaInSb quantum wells. For energy gaps corresponding to 3.1–4.8 μm, the room-temperature Auger coefficients for seven different samples are found to be nearly an order-of-magnitude lower than typical type-I results for the same wavelength. The data imply that at this temperature, the Auger rate is relatively insensitive to details of the band structure.
Interfacial electronic structures in an organic light-emitting diode
Authors: Lee S. T. , Wang Y. M. , Hou X. Y. , Tang C. W.
Published: July 2002

Direct measurements of electronic properties have been made for the metal/organic and organic/organic interfaces in a multilayer organic light-emitting diode (LED) using ultraviolet photoemission spectroscopy. The device configuration considered is indium–tin oxide (ITO)/copper phthalocyanine (CuPc)/N,N′-bis-(1-naphyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamne (NPB)/8-hydroxyquinoline aluminum (Alq)/Mg. For the material interfaces considered here, our result indicates that the traditional concept of vacuum-level alignment, though not valid for metal/organic interfaces, still holds at organic/organic interfaces. This implies that little charge transfer occurs at the interfaces due to the small interaction between organic molecules. The largest band offsets are observed between the lowest unoccupied state levels of the organic molecules. Based on the directly measured energy-level alignments, a model is proposed to explain the improved efficiency of multilayer organic LEDs, as compared to those with a single organic layer structure.
Strong normal-incidence infrared absorption in self-organized InAs/InAlAs quantum dots grown on InP(001)
Authors: Weber A. , Gauthier-Lafaye O. , Julien F. H. , Brault J. , Gendry M. , Désieres Y. , Benyattou T.
Published: July 2002

InAs self-assembled quantum dots in InAlAs matrix grown on InP(001) substrates have been fabricated using Stranski–Krastanov growth mode. A strong in-plane polarized intraband absorption in the 10.6–20 μm wavelength region has been observed and ascribed to a transition from the ground electron state to an excited state confined in the layer plane along the [110] direction. The absorption at normal-incidence reaches 7.8% for ten layers of n-doped quantum dots. The oscillator strength of the intraband transition is comparable to that achieved in quantum wells for a conduction band intersubband transition. The dependence of the intraband absorption on carrier concentration and temperature suggests a quantum-wire type confinement potential.
An embedded quantum wire model of dielectric breakdown
Authors: Ting D. Z.-Y.
Published: July 2002

The reverse gate bias current–voltage characteristics of n+ polycrystalline-Si/SiO2/p-Si tunnel structures containing nanoscale quantum wires embedded in ultrathin oxide layers are analyzed using a three-dimensional quantum mechanical scattering calculation. By varying wire geometry, our model can qualitatively reproduce experimental current–voltage characteristics for ultrathin oxides having undergone soft breakdown or breakdown. We find that low-bias current densities can be greatly enhanced by resonant tunneling, and that this mechanism is highly temperature dependent. We demonstrate that funneling of wave functions into quantum wires results in highly efficient localized conduction paths which contributes to dramatic current increases in the direct tunneling regime. We also explain how quantum wires which extend partially into the oxide layer from the SiO2/p-Si interface can be used to model soft breakdown current–voltage characteristics.
Erbium (III) tris(8-hydroxyquinoline) (ErQ): A potential material for silicon compatible 1.5 μm emitters
Authors: Gillin W. P. , Curry R. J.
Published: July 2002

Samples of erbium (III) tris(8-hydroxyquinoline) (ErQ) have been prepared and their photoluminescence measured. Clearly resolved peaks due to intra-atomic transitions between the I413/2 and I415/2 levels can be observed at room temperature. The possibility of depositing ErQ on to silicon to produce organic electroluminescent diodes offers the possibility of a cheap 1.5 μm emitter based on silicon technology.
Ultrathin and highly insulating amorphous-Ta2O5 films formed on Ru/TiN/Ti/n+-Si substrates
Authors: Moon B. K. , Aoyama J. , Katori K.
Published: July 2002

This letter reports on highly insulating amorphous-Ta2O5 (a-Ta2O5) films with ultrathin SiO2 effective thickness [teff(SiO2)]. Insulating properties were improved using dry-O3 annealing at 450 °C, in which the typical leakage current density and resistivity at 1.5 MV/cm were 3×10−8 A/cm2 and 5×1013 Ω cm, respectively. Typical teff(SiO2) of 1.2 nm was obtained for the a-Ta2O5 film formed on a Ru/TiN/Ti/n+-Si substrate, where a Ru layer can act as an effective barrier against oxidation as well as interdiffusion during annealing. In contrast, the teff(SiO2) of the Ta2O5 film prepared on a conventional TiN/Ti/n+-Si substrate was increased by interfacial degradation. Technology employing Ru bottom electrodes and dry-O3 annealing will open a new era of logic embedded memory for 1 Gbit generation.
Effect of the elastic modulus of the matrix on magnetostrictive strain in composites
Authors: Chen Y. , Snyder J. E. , Schwichtenberg C. R. , Dennis K. W. , Falzgraf D. K. , McCallum R. W. , Jiles D. C.
Published: July 2002

The effect of the matrix material on the magnetostriction of composites containing highly magnetostrictive particles has been studied. Experimental results showed that the elastic modulus of the matrix is an important factor determining the bulk magnetostriction of the composite. For a series of composites with the same volume fraction of magnetostrictive particles but different matrix materials, the bulk magnetostriction was found to increase systematically with decreasing elastic modulus of the matrix. A model theory for the magnetostriction of such composites has been developed, based on two limiting assumptions: uniform strain or uniform stress inside the composite. The theory was then used to predict the magnetostriction of the entire material from the volume fractions of the components, their elastic moduli and magnetostrictions. These predictions were in agreement with the experimental results. It is concluded that to obtain a high magnetostriction and adequate mechanical properties of a composite, the elastic moduli of the magnetostrictive phase and the matrix should be as close as possible in value.
High-density three-dimensional optical data storage in a stacked compact disk format with two-photon writing and single photon readout
Authors: Pudavar Haridas E. , Joshi Mukesh P. , Prasad Paras N. , Reinhardt Bruce A.
Published: July 2002

Using a polymer block doped with a highly efficient two-photon dye, we have achieved a high density data storage with gray-scale control in multiple planes as stacked compact disks at a separation of 10 μm. The absorption and fluorescence of the dye at the written spot shift to a longer wavelength, permitting an easy fluorescence mode readout with a linear excitation using an inexpensive laser source. The storage capacity in this case is estimated to be 1012 bits/cm3.
Trapping of minority carriers in multicrystalline silicon
Authors: Macdonald D. , Cuevas A.
Published: July 2002

Abnormally high effective carrier lifetimes have been observed in multicrystalline silicon wafers using both transient and steady-state photoconductance techniques. A simple model based on the presence of trapping centers explains this phenomenon both qualitatively and quantitatively. By fitting this model to experimental data acquired with a quasi-steady-state photoconductance technique, it is possible to determine the trap density, trap energy, and the ratio between the mean-trapping time and mean-escape time. A correlation between trap density and dislocation density in the material has been found.
Optical gain and stimulated emission of cleaved cubic gallium nitrite
Authors: Holst J. , Hoffmann A. , Broser I. , Schöttker B. , As D. J. , Schikora D. , Lischka K.
Published: July 2002

In this letter, we report on the observation of optically excited stimulated emission of c-GaN layers grown by molecular-beam epitaxy (MBE). Stimulated emission was observed at 1.8 K and room temperature. The threshold intensity for excitation of stimulated emission from our MBE-grown c-GaN layers is significantly lower than that reported for c-GaN grown by metalorganic chemical vapor deposition (MOCVD). The experimental data of optical gain and stimulated emission presented in this letter demonstrate that this material has a good potential for the future realization of cleaved cavity blue light-emitting laser diodes.
Bonding constraints and defect formation at interfaces between crystalline silicon and advanced single layer and composite gate dielectrics
Authors: Lucovsky G. , Wu Y. , Niimi H. , Misra V. , Phillips J. C.
Published: July 2002

An increasingly important issue in semiconductor device physics is understanding of how departures from ideal bonding at silicon–dielectric interfaces generate electrically active defects that limit performance and reliability. Building on previously established criteria for formation of low defect density glasses, constraint theory is extended to crystalline silicon–dielectric interfaces that go beyond Si–SiO2 through development of a model that quantifies average bonding coordination at these interfaces. This extension is validated by application to interfaces between Si and stacked silicon oxide/nitride dielectrics demonstrating that as in bulk glasses and thin films, an average coordination, Nav, greater than three yields increasing defective interfaces.
Contact resistance of carbon nanotubes
Authors: Tersoff J.
Published: July 2002

Electrical contacts to carbon nanotubes typically exhibit high resistance, posing a serious obstacle to their application in electronic devices. One important factor may be their unique electronic structure, which gives weak electronic coupling at the Fermi surface. This suggests some possible ways to reduce contact resistance.
Red light emission by photoluminescence and electroluminescence from Pr-doped GaN on Si substrates
Authors: Birkhahn R. , Garter M. , Steckl A. J.
Published: July 2002

Visible light emission has been obtained at room temperature by photoluminescence (PL) and electroluminescence (EL) from Pr-doped GaN thin films grown on Si(111). The GaN was grown by molecular beam epitaxy using solid sources (for Ga and Pr) and a plasma gas source for N2. Photoexcitation with a He–Cd laser results in strong red emission at 648 and 650 nm, corresponding to the transition between P03 and F23 states in Pr3+. The full width at half maximum (FWHM) of the PL lines is ∼1.2 nm, which corresponds to ∼3.6 meV. Emission is also measured at near-infrared wavelengths, corresponding to lower energy transitions. Ar laser pumping at 488 nm also resulted in red emission, but with much lower intensity. Indium-tin-oxide Schottky contacts were used to demonstrate visible red EL from the GaN:Pr. The FWHM of the EL emission line is ∼7 nm.
Amplified spontaneous emission and lasing in conducting polymers and fluorescent dyes in opals as photonic crystals
Authors: Yoshino K. , Tatsuhara S. , Kawagishi Y. , Ozaki M. , Zakhidov A. A. , Vardeny Z. V.
Published: July 2002

Spectral narrowing of photoluminescence (PL) and evolution of sharp emission lines upon optical excitation have been observed in opals made of SiO2 spheres infiltrated with conducting polymers such as OOPPV and MDDOPPV and also fluorescent dyes such as rhodamine 6G, NK-3483, and coumarin 120. Their emission properties are dependent on the sort of the opal and the solvents used for infiltration. With increasing optical excitation intensity, spectral narrowing and evolution of sharp lines have been observed in the green opal infiltrated with OOPPV, MDDOPPV, or rhodamine 6G but not in the infiltrated red and purple opals. With a solvent having a refractive index similar to that of SiO2, the evolution of the sharp emission lines is greatly suppressed and the lines exhibit a blueshift with decreasing refractive index. In NK-3483 and coumarin 120 which show red and purple PL, respectively, evolution of sharp lines is observed when they were infiltrated in red and purple opals, respectively, but not in other opals. These results are discussed in terms of amplified spontaneous emission and multimode lasing due to optical feedback in the opal matrix with a periodic structure.