bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning tunneling spectroscopy under pulsed spin injection
Authors: Ngai J. , Tseng Y. C. , Morales P. , Pribiag V. , Wei J. Y. T. , Chen F. , Perovic D. D.
Published: March 2004

An experimental technique combining cryogenic scanning tunneling spectroscopy (STS) and pulsed quasiparticle spin injection has been developed. The spin injection is intended to perturb a superconducting thin film from spin equilibrium, while the STS monitors its steady-state quasiparticle spectrum. A pulsed injection circuit was designed to minimize Joule heating while being both synchronized with and decoupled from the STS circuitry. A detailed description of the technique is presented, along with its application to spin-injection heterostructures comprising the half-metallic ferromagnet La0.7Ca0.3MnO3 and the high-Tc superconductor YBa2Cu3O7−δ.
Microfluidic tunable photonic band-gap device
Authors: Domachuk P. , Nguyen H. C. , Eggleton B. J. , Straub M. , Gu M.
Published: March 2004

We introduce a method for tuning a photonic band-gap material by means of displacing microfluidic plugs. The fluid is introduced into air voids that constitute the structure of the photonic crystal and is displaced using a capillary heater. The photonic crystal geometry is obtained using a microstructured optical fiber, comprising a periodically spaced array of air holes that is interrogated in the transverse direction, creating a “tall microchip.” Optical spectra are compared to band structure calculations of an idealized band-gap material.
Rapid photon flux switching in two-dimensional photonic crystals
Authors: Wang X. , Kempa K. , Ren Z. F. , Kimball B.
Published: March 2004

We have investigated the out-of-plane propagation of light in two-dimensional photonic band-gap crystals consisting of long dielectric nanorods. Defects, which sufficiently break the crystal symmetry, can produce photonic states localized at the defect sites. We show that this localization can result in a sharp transition between the state of the out-of-plane light propagation through the entire photonic crystal, and the state in which light propagates only along the defect channels. This switching can be induced by slight changes of the dielectric constant at the defect sites. We propose a practical way of achieving this, and suggest applications.
Multilevel memory based on molecular devices
Authors: Li Chao , Fan Wendy , Lei Bo , Zhang Daihua , Han Song , Tang Tao , Liu Xiaolei , Liu Zuqin , Asano Sylvia , Meyyappan Meyya , Han Jie , Zhou Chongwu
Published: March 2004

Multilevel molecular memory devices were proposed and demonstrated for nonvolatile data storage up to three bits (eight levels) per cell, in contrast to the standard one-bit-per-cell (two levels) technology. In the demonstration, charges were precisely placed at up to eight discrete levels in redox active molecules self-assembled on single-crystal semiconducting nanowire field-effect transistors. Gate voltage pulses and current sensing were used for writing and reading operations, respectively. Charge storage stability was tested up to retention of 600 h, as compared to the longest retention of a few hours previously reported for one-bit-per-cell molecular memories.
Densification and improved electrical properties of pulse-deposited films via in situ modulated temperature annealing
Authors: Conley J. F. , Ono Y. , Tweet D. J.
Published: March 2004

We find that the modulated temperature annealing of pulse-deposited high dielectric constant films, in which brief in situ elevated temperature anneals are performed after every deposition cycle, results in film densification, a reduction in interfacial layer thickness, and a strong improvement in electrical properties. The densification and improvement of electrical properties could not be achieved solely by postdeposition annealing at temperatures up to 850 °C.
Large scale inhomogeneity of inertial particles in turbulent flows
Authors: Boffetta G. , De Lillo F. , Gamba A.
Published: March 2004

Preferential concentration of inertial particles in turbulent flow is studied by high resolution direct numerical simulations of two-dimensional turbulence. The formation of network-like regions of high particle density, characterized by a length scale which depends on the Stokes number of inertial particles, is observed. At smaller scales, the size of empty regions appears to be distributed according to a universal scaling law.
Inertia-induced electrophoretic interactions
Authors: Yariv Ehud
Published: March 2004

Electrophoretic interactions occurring between two colloidal particles of identical zeta potential are investigated using a perturbation expansion in the small Reynolds number. Particle interactions appear in the form of buoyancy-type forces, similar to the pressure forces encountered in bubbly flows. The dynamical system governing the evolution of the pair configuration is derived for the case of spherical particles, and closed-form solutions describing remote particle trajectories are obtained therefrom.
Rewritable nanopattern on a Ge(001) surface utilizing p(2×2)-to-c(4×2) transition of surface reconstruction induced by a scanning tunneling microscope
Authors: Takagi Yasumasa , Yamada Masamichi , Nakatsuji Kan , Komori Fumio
Published: March 2004

We present rewritable, nanometer-scale patterns formed on Ge(001) at 80 K, which are based on the transition between c(4×2) and p(2×2) surface reconstructions induced by a scanning tunneling microscope (STM). We have found that a negative (−0.8 V and 0.5 s) sample bias voltage pulse creates a c(4×2)-reconstructed domain of ∼1.6×2.0 nm2 in a p(2×2)-reconstructed region. Applying the negative pulses at approriate positions, we form an intended pattern of the c(4×2) reconstruction. The course of patterning can be monitored by STM with a small bias voltage (−0.2 V) without affecting the written pattern. The whole region can be initialized to the p(2×2) by a scan with the bias voltage of +0.8 V.
Single-charge-carrier-type sensing with an insulated Frisch ring CdZnTe semiconductor radiation detector
Authors: McNeil W. J. , McGregor D. S. , Bolotnikov A. E. , Wright G. W. , James R. B.
Published: March 2004

Performance optimization of an insulated Frisch ring design was investigated for a 3×3×6 mm CdZnTe planar semiconductor detector. The Frisch ring was composed of copper and was insulated from the detector surface with Teflon. Optimization variables included the Frisch ring length and the bias voltage. Optimized overall device performance was found using a 5 mm long Frisch ring extending from the cathode toward the anode, leaving a 1 mm separation between the Frisch ring and the anode. The best energy resolution observed was 1.7% full width at half maximum at 662 keV with the ring extending 4 mm from the cathode toward the anode.
Coherent grazing exit x-ray scattering geometry for probing the structure of thin films
Authors: Pfeiffer Franz , Zhang Wei , Robinson Ian K.
Published: March 2004

We demonstrate a diffraction geometry which provides strong sensitivity to the microstructure of thin films. While a coherent beam of x rays is being reflected from the surface of the sample, measurements were made of the scattering of the exit beam below the critical angle for total external reflection. This results in a strong signal with speckle modulations that are characteristic of the internal arrangement of grains at different depths within the film.
Coupled displacive and order–disorder dynamics in LiNbO3 by molecular-dynamics simulation
Authors: Phillpot S. R. , Gopalan V.
Published: March 2004

We demonstrate that molecular-dynamics simulations can reproduce the ferroelectric behavior of LiNbO3 and the ferroelectric–paraelectric phase transition. We find that this phase transition is a two-stage process involving a displacive transition in the Nb–O cages at a temperature below the Curie temperature and an order–disorder transition in the Li–O planes at the Curie temperature itself.
Fabrication of (In,Ga)As quantum-dot chains on GaAs(100)
Authors: Wang Z. M. , Holmes K. , Mazur Yu. I. , Salamo G. J.
Published: March 2004

Nanostructure evolution during the growth of multilayers of In0.5Ga0.5As/GaAs (100) by molecular-beam epitaxy is investigated to control the formation of lines of quantum dots called quantum-dot chains. It is found that the dot chains can be substantially increased in length by the introduction of growth interruptions during the initial stages of growth of the GaAs spacer layer. Quantum-dot chains that are longer than 5 μm are obtained by adjusting the In0.5Ga0.5As coverage and growth interruptions. The growth procedure is also used to create a template to form InAs dots into chains with a predictable dot density. The resulting dot chains offer the possibility to engineer carrier interaction among dots for novel physical phenomena and potential devices.
Development of a dual-channel scanning microwave/optical microprobe
Authors: Aga Roberto S. , Brookman Jason , Dizon Jonathan , Wu Judy Z.
Published: March 2004

A dual-channel scanning microprobe (dual probe) has been developed for simultaneous mapping of microwave and optical properties of a sample. It employs a tunable open-ended coaxial resonator with a tapered and metal-coated fiber optic tip, from which microwave and light can be emitted/collected simultaneously. The microwave channel of this probe, operating at 1.5 GHz, can detect changes in sheet resistance (Rx) above 293 mΩ with a spatial resolution ranging from 5 to 10 μm. The optical channel, on the other hand, has a spatial resolution ∼1 μm. The poorer spatial resolution in the microwave channel was attributed to its lower sensitivity. Imaging of dielectric grid and high-Tc superconducting microwave resonators was carried out at ambient temperature.
“Umbrella”-like precipitates in nitrogen-doped Czochralski silicon wafers
Authors: Kvit A. , Karoui A. , Duscher G. , Rozgonyi G. A.
Published: March 2004

Nitrogen effect on nucleation of oxygen precipitates in Czochralski Si has been investigated by transmission electron microscopy, Z-contrast imaging, and electron energy loss spectrometry (EELS). We have examined unusual “umbrella” shape oxygen precipitates in bulk of ingot in depths of more than 40 μm. Two predominant orientations of “umbrella” have been found along [110] and [−1−10] directions. We have investigated the distribution of nitrogen, oxygen, and interstitial Si by EELS profile taken simultaneously with HR Z-contrast image. The mechanism of nitrogen-enriched oxygen precipitates nucleation has been discussed.
Nonradiative recombination centers in Ga(As,N) and their annealing behavior studied by Raman spectroscopy
Authors: Ramsteiner M. , Jiang D. S. , Harris J. S. , Ploog K. H.
Published: March 2004

Nitrogen-related defects in diluted Ga(As,N) have been detected by Raman scattering in resonance with the localized E+ transition. These defects are attributed to local vibrational modes of nitrogen dimers on Ga- and As-lattice sites. Rapid thermal annealing under appropriate conditions is found to be able to remove the nitrogen dimers. The required minimum annealing temperature coincides with the threshold-like onset of strong, near-band-gap photoluminescence. This finding suggests that the nitrogen dimers are connected with nonradiative recombination centers.
Quantum-well-base heterojunction bipolar light-emitting transistor
Authors: Feng M. , Holonyak N. , Chan R.
Published: March 2004

This letter reports the enhanced radiative recombination realized by incorporating InGaAs quantum wells in the base layer of light-emitting InGaP/GaAs heterojunction bipolar transistors (LETs) operating in the common-emitter configuration. Two 50 Å In1−xGaxAs (x=85%) quantum wells (QWs) acting, in effect, as electron capture centers (“traps”) are imbedded in the 300 Å GaAs base layer, thus improving (as a “collector” and recombination center) the light emission intensity compared to a similar LET structure without QWs in the base. Gigahertz operation of the QW LET with simultaneously amplified electrical output and an optical output with signal modulation is demonstrated.
Local self-organization of islands in embedded nanodot systems
Authors: Zhang Jianjun , Zhang Kaiwang , Zhong Jianxin
Published: March 2004

We show that strain distribution on the surface of an isotropic spacer layer induced by an embedded island of large base-to-height aspect ratio deviates significantly from the description of the point force dipole model in the regime of small spacer layer thickness. In this regime, the strain profile displays several local maxima above the embedded island. The regions with local strain maxima serve as nucleation centers for growth of surface islands under appropriate growth conditions, resulting in locally well-organized surface islands above the embedded island. Our theoretical results are in excellent agreement with recent experiments for Ge islands embedded in Si.
Long-range Babinet’s effect in complementary left-handed material with gold nanoparticles
Authors: Wu S.-C.
Published: March 2004

Babinet’s effect occurs at a long wavelength span of incident light during Fourier transform infrared spectroscopy scanning in complementary left-handed material (LHM) samples. The occurring wavelength region ranges from 4 to 20 μm. The LHM sample is composed of split ring resonator and wire array. Complementary samples were prepared using standard integrated-circuit processes on a Si wafer. Gold nanoparticles were deposited on the conducting parts of the patterns. Transmittance-enhanced behavior was also identified from those consequent data. The surface plasmon resonated on Au nanoparticle appears to contribute to this enhancement.
Contacts to p-type ZnMgO
Authors: Kim Suku , Kang B. S. , Ren F. , Heo Y. W. , Ip K. , Norton D. P. , Pearton S. J.
Published: March 2004

Ohmic and Schottky contacts to p-type Zn0.9Mg0.1O are reported. The lowest specific contact resistivity of 3×10−3 Ω cm2 was obtained for Ti/Au annealed at 600 °C for 30 s. Ni/Au was less thermally stable and showed severe degradation of contact morphology at this annealing temperature. Both Pt and Ti with Au overlayers showed rectifying characteristics on p-ZnMgO, with barrier heights of ∼0.55–0.56 eV and ideality factors of ∼1.9. Comparison of these results with the same metals on n-type ZnO indicates that high surface state densities play a significant role in determining the effective barrier height.
Delay of vortex ring pinchoff by an imposed bulk counterflow
Authors: Dabiri John O. , Gharib Morteza
Published: March 2004

The Kelvin–Benjamin variational principle has been previously used to predict that vortex ring pinchoff can be delayed if the energy of the leading vortex ring is decreased during formation and/or the energy delivered by the vortex generator is increased. We present experimental results in which the former and latter energy effects were simultaneously accomplished by imposing a bulk axisymmetric counterflow during vortex ring formation. Measurements indicate that the formation number is retarded sufficiently to allow increased ingestion of fluid circulation by the leading vortex ring. This serves as a first demonstration of artificial manipulation of vortex ring formation for potential propulsive benefits in starting jets.
Control of optical polarization anisotropy in edge emitting luminescence of InAs/GaAs self-assembled quantum dots
Authors: Jayavel P. , Tanaka H. , Kita T. , Wada O. , Ebe H. , Sugawara M. , Tatebayashi J. , Arakawa Y. , Nakata Y. , Akiyama T.
Published: March 2004

We have studied the polarization properties of cleaved-edge photoluminescence (PL) from InAs/GaAs self-assembled quantum dots. Transverse-electric (TE) and transverse-magnetic (TM) mode PL intensities have been analyzed for the dots having 8 nm InxGa1−xAs capping layer with indium (In) composition of x=0 and 0.13. Polarization results show a dramatic change with the capping layer In compositions; TE-mode dominant PL is observed for dots with x=0, on the other hand, TM-mode dominant PL for dots with x=0.13. This polarization change has been attributed to the dot shape change using transmission electron microscopy images. These results suggest that the optical polarization anisotropy of the quantum dots can be controlled by manipulating the capping layer In composition.
Effect of surface hydrophilicity and water vapor pressure on the interfacial shear strength of adsorbed water layer
Authors: Kim Doo-In , Ahn Hyo-Sok , Choi Dong-Hoon
Published: March 2004

We investigated the effect of water vapor pressure and surface hydrophilicity on the tribological behavior in wearless sliding condition. Friction and interfacial shear strength of silicon surfaces with different water affinity (contact angles of <5°, 30°, and 85°) against a glass sphere (contact angle 40°) were examined under various water vapor pressure conditions. The friction of hydrophilic surface decreased as vapor pressure increased and the least hydrophilic surface showed stable and low friction force regardless of relative vapor pressure. However, it showed that the hydrophilic surface with high relative vapor pressure exhibited lower shear strength than a less hydrophilic surface independent of capillary effect. It was explained in terms of capillary wetting and the role of adsorbed water in contact area.
High-power characteristics of GaN/InGaN double heterojunction bipolar transistors
Authors: Makimoto Toshiki , Yamauchi Yoshiharu , Kumakura Kazuhide
Published: March 2004

High-power characteristics have been investigated for GaN/InGaN double heterojunction bipolar transistors (HBTs) on SiC substrates. A base-collector diode showed a high breakdown voltage exceeding 50 V, which is ascribed to a wide band gap of a GaN collector. The maximum collector current is proportional to the emitter size in the emitter-size ranging from 1.5×10−5 to 1.4×10−4 cm2. The corresponding maximum collector current density is as high as 6.7 kA/cm2, indicating the high current density characteristics of bipolar transistors. A 50 μm×30 μm device operated up to a collector–emitter voltage of 50 V and a collector current of 80 mA in its common-emitter current–voltage characteristics at room temperature. The corresponding power density is as high as 270 kW/cm2, showing that nitride HBTs are promising for high-power electronic devices in terms of both the material and the device structure.
Role of fluorine in suppressing boron transient enhanced diffusion in preamorphized Si
Authors: Impellizzeri G. , dos Santos J. H. R. , Mirabella S. , Priolo F. , Napolitani E. , Carnera A.
Published: March 2004

We have explained the role of fluorine in the reduction of the self-interstitial population in a preamorphized Si layer under thermal treatment. For this purpose, we have employed a B spike layer grown by molecular-beam epitaxy as a marker for the self-interstitial local concentration. The amorphized samples were implanted with 7×1012, 7×1013, or 4×1014 F/cm2 at 100 keV, and afterwards recrystallized by solid phase epitaxy. Thermal anneals at 750 or 850 °C were performed in order to induce the release of self-interstitials from the end-of-range (EOR) defects and thus provoke the transient enhanced diffusion of B atoms. We have shown that the incorporation of F reduces the B enhanced diffusion in a controlled way, up to its complete suppression. It is seen that no direct interaction between B and F occurs, whereas the suppression of B enhanced diffusion is related to the F ability in reducing the excess of silicon self-interstitials emitted by the EOR source. These results are reported and discussed.
Near-field optical study of AlGaN/GaN quantum-well waveguide
Authors: Shakya J. , Lin J. Y. , Jiang H. X.
Published: March 2004

Ultraviolet near-field scanning microscopy and near-field spectroscopy have been employed to study the optical properties of AlGaN/GaN quantum-well waveguides. The divergence of the spontaneous emission emerging from the waveguide exit port was measured. The near-field optical image revealed a half-angle in-plane divergence of 6° and vertical divergence of 40°. Optical loss of the spontaneous emission inside the waveguide at λ=350 nm was found to be 106 cm−1. These parameters are important for the achievement of future III-nitride photonic integrated circuits for various applications.
Pressure effect of glass transition temperature in Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk metallic glass
Authors: Jiang J. Z. , Roseker W. , Sikorski M. , Cao Q. P. , Xu F.
Published: March 2004

Pressure effects on glass transition temperature and supercooled liquid region of a Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass have been investigated by performing in situ high-temperature and high-pressure x-ray powder diffraction measurements using synchrotron radiation. The glass transition was detected from the change of the slope of peak position as a function of temperature. It is found that the glass transition temperature increases with pressure by 4.4 K/GPa for the Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass, and the supercooled liquid range decreases with pressure by 2.9 K/GPa in a pressure range of 0–2.2 GPa. This method opens a possibility to study the pressure effect of glass transition process in glassy systems under high pressures (>1 GPa).
Measurement of orientation dependent stress-optic coefficient of GaAs single crystals
Authors: Peng H. J. , Wong S. P. , Ho H. P. , Zhao Shounan
Published: March 2004

The stress-optic coefficient C for (001) and (111) GaAs single crystal wafers at various observation directions was measured precisely using a simple four-point bending technique. Our experimental values of C for (001) GaAs wafers vary from 0.65×10−12 cm2/dyn (at 〈100〉 directions) to 1.43×10−12 cm2/dyn (at 〈110〉 directions). For (111) GaAs wafers, the experimental values of C show much smaller dependence on the observation direction and vary from 1.97×10−12 cm2/dyn (at 〈112〉 directions) to 2.11×10−12 cm2/dyn (at 〈110〉 directions). The combinations of piezo-optic coefficients π11–π12 and π44 were also derived from C for GaAs.
Formation of spinel from olivine
Authors: Liu Zongwen , Kelly Patrick M. , Drennan John , Mora Peter , Kanda Hisao
Published: March 2004

High-resolution transmission electron microscopy (HRTEM) was used to study the olivine to spinel transformation. HRTEM structure images of Mg2GeO4 olivine deformed under a pressure of 6 GPa at 600 °C clearly show that a shear mechanism dominates the transformation. The transformation is not a nucleation and growth mechanism. It also differs in certain crucial aspects from the type of martensitic transformation proposed before. During the transformation, it is a shear movement that brings the oxygen anions to their positions in the spinel structure. An edge dislocation following each shear then puts the cations in their spinel sites. The Burgers’ vector of each dislocation is perpendicular to the anion shear direction.
Surface plasmon polariton propagation around bends at a metal–dielectric interface
Authors: Hasegawa K. , Nöckel J. U. , Deutsch M.
Published: March 2004

We analyze theoretically the propagation of surface plasmon polaritons about a metallic corner with a finite bend radius, using a one-dimensional model analogous to the scattering from a finite-depth potential well. We obtain expressions for the energy reflection and transmission coefficients in the short wavelength limit, as well as an upper bound for the transmittance. In certain cases we find that propagation on nonplanar interfaces may result in lower losses than on flat surfaces, contrary to expectation. In addition, we also find that the maximum transmittance depends nonmonotonously on the bend radius, allowing increased transmission with decreasing radius.
High uniformity of site-controlled pyramidal quantum dots grown on prepatterned substrates
Authors: Baier M. H. , Watanabe S. , Pelucchi E. , Kapon E.
Published: March 2004

We studied the uniformity of site-controlled, pyramidal InGaAs/AlGaAs semiconductor quantum dots (QDs) grown by organometallic chemical vapor deposition on prepatterned substrates. The inhomogeneous broadening of the QD ground state emission has been determined to be 7.6 meV by statistical single QD photoluminescence spectroscopy on a set of 120 individual QD structures. Taking into account the ground-to-excited state separation of 55 meV, such a small value has not yet been observed in QD systems where other growth mechanisms are employed. Moreover, a high reproducibility of the sharp QD emission features in the single exciton regime has been observed.
Thermal conductivity of nanoporous bismuth thin films
Authors: Song D. W. , Shen W.-N. , Dunn B. , Moore C. D. , Goorsky M. S. , Radetic T. , Gronsky R. , Chen G.
Published: March 2004

The thermal conductivity of nanoporous Bi thin films has been experimentally determined. Samples are fabricated by a liquid phase deposition, and their thermal conductivities are measured by a differential 3ω method. Nanoporous Bi thin films exhibit an order-of-magnitude reduction in thermal conductivity compared to that of solid films, most likely the result of a reduction in phonon mean free path. When porous Bi films are exposed to a hydrogen plasma, thermal conductivity measurements reveal no variation with extent of porosity, while electrical conductivity is much more sensitive to porosity, suggesting the possibility of independent control of these two intrinsic properties.
Oligothiophene-S,S-dioxides as a class of electron-acceptor materials for organic photovoltaics
Authors: Camaioni N. , Ridolfi G. , Fattori V. , Favaretto L. , Barbarella G.
Published: March 2004

Oligothiophene-S,S-dioxides are proposed as electron acceptors materials in organic blended photovoltaic devices. Photoinduced charge transfer is demonstrated in blends between a regioregular poly(3-hexylthiophene) and the oligomers, via photoluminescence spectroscopy. The enhanced photovoltaic performance exhibited by the blended cells, with respect to that of pristine devices in which the polymer is the active layer, represents further evidence for exciton dissociation. An increase of the power conversion efficiency up to sixty-fold is achieved by blending the polymer with the oligothiophene-S,S-dioxides.
Experimental verification on the origin of plateau-like current–voltage characteristics of resonant tunneling diodes
Authors: Qiu Z. J. , Gui Y. S. , Guo S. L. , Dai N. , Chu J. H. , Zhang X. X. , Zeng Y. P.
Published: March 2004

Current-voltage (I–V) characteristics of GaAs-based resonant tunneling diodes have been investigated in the presence of a perpendicular magnetic field. Electron resonant tunneling is strongly suppressed by the applied magnetic field, leading to peak current decreasing with increasing magnetic field. The observed plateau-like structures appear in negative differential resistance region on the I–V curves and are magnetic-field dependent. The plateau-like structures are due to the coupling between the energy levels in the emitter well and in the main quantum well.
High-performance carbon nanotube transistors on SrTiO3/Si substrates
Authors: Kim B. M. , Brintlinger T. , Cobas E. , Fuhrer M. S. , Zheng Haimei , Yu Z. , Droopad R. , Ramdani J. , Eisenbeiser K.
Published: March 2004

Single-walled carbon nanotubes (SWNTs) have been grown via chemical vapor deposition on high-κ dielectric SrTiO3/Si substrates, and high-performance semiconducting SWNT field-effect transistors have been fabricated using the thin SrTiO3 as gate dielectric and Si as gate electrode. The transconductance per channel width is 8900 μS/μm. The high transconductance cannot be explained by the increased gate capacitance; it is proposed that the increased electric field at the nanotube–electrode interface due to the high-κ SrTiO3 decreases or eliminates the nanotube-electrode Schottky barrier.
High-power AlGaInP light-emitting diodes with metal substrates fabricated by wafer bonding
Authors: Peng Wei Chih , Wu YewChung Sermon
Published: March 2004

High-power light-emitting diodes (LEDs) fabricated on Cu substrates were investigated in this study. The AlGaInP LED structure was bonded to a Cu substrate by using indium-tin-oxide as the diffusion barrier layer. It was found that Cu-substrate-bonded LED devices could be operated in a much higher injection forward current, 800 mA, which was eight times higher than that used in traditional GaAs-substrate LEDs. The luminous intensity of the Cu-substrate LEDs could reach as high as 1230 mcd, which was three times higher than that of the GaAs-substrate LEDs.
Are surfaces elastically softer or stiffer?
Authors: Zhou L. G. , Huang Hanchen
Published: March 2004

This letter addresses the issue of surface softening versus stiffening during elastic deformation. Using a combination of molecular statics and ab initio calculations, we show that a solid surface can be either softer or stiffer elastically than the corresponding bulk. Whether a particular surface is softer or stiffer depends on the competition between atomic coordination and electron redistribution (which sometimes is referred as bond saturation) on the surface. Taking Cu as an example, we demonstrate that the Young’s modulus along 〈110〉 direction on {100} surface is larger than its bulk counterpart; meanwhile, it is smaller along 〈100〉 direction on {100} surface.
Enhanced electro-optic effect in GaInAsP–InP three-step quantum wells
Authors: Mohseni H. , An H. , Shellenbarger Z. A. , Kwakernaak M. H. , Abeles J. H.
Published: March 2004

We report on the enhanced electro-optic coefficient of GaInAsP three-step quantum wells (3SQW) for high power electrorefraction modulator applications. Measured electro-optic coefficient of the 3SQW is nearly three times higher than the conventional rectangular quantum well (RQW) at λ=1.55 μm. The enhanced electro-optic effect, combined with a low optical absorption coefficient α<1 cm−1 in the 3SQW increases a modulator figure of merit by nearly 36 times, and decreases the power consumption by nearly one order of magnitude compared with a conventional RQW design.
Carrier trapping and current collapse mechanism in GaN metal–semiconductor field-effect transistors
Authors: Anwar A. F. M. , Islam Syed S. , Webster Richard T.
Published: March 2004

A mechanism for current collapse in GaN metal–semiconductor field-effect transistors is proposed, which assumes the existence of acceptor traps with multiple states in the band gap. Current collapse has been experimentally observed in the current–voltage characteristic after the drain voltage sweep had exceeded the threshold for impact ionization in a previous measurement. In the proposed model, electrons generated by impact ionization are captured by neutral acceptor trap states in the substrate located above the valence band. The charged trap states move to an energy level located near midgap, creating a positively charged depletion region in the channel, and causing current collapse. With increasing drain bias, the quasi-Fermi level approaches the charged trap states at the drain end of the gate, initiating detrapping of the electrons and restoring the current. The calculated results show good agreement with published experimental data.
Electron emission through a multilayer planar nanostructured solid-state field-controlled emitter
Authors: Semet V. , Binh Vu Thien , Zhang J. P. , Yang J. , Khan M. Asif , Tsu R.
Published: March 2004

We have measured the field electron emission (FE) from a surface covered with two ultrathin layers of semiconductor, 4 nm GaN on 2 nm Al0.5Ga0.5N. The threshold field was 50 V/μm, with stable FE current densities up to 3×10−2 A/cm2. We have also measured the FE dependence with field and temperature and determine then an effective surface tunneling barrier ⩽0.5 eV, coexisting with an effective thermal activation energy of ∼0.85 eV. To interpret these experimental results, we propose a dual-barrier model, related to the nanostructured layers, with a serial two-step mechanism for the electron emission, taking into account the space charge formation in the quantum well structure at the surface.
High quality InN/GaN heterostructures grown by migration enhanced metalorganic chemical vapor deposition
Authors: Fareed R. S. Qhalid , Jain R. , Gaska R. , Shur M. S. , Wu J. , Walukiewicz W. , Khan M. Asif
Published: March 2004

We report on the structural properties and optical and electrical characteristics of InN epitaxial layers grown on highly resistive GaN templates using migration enhanced metalorganic chemical vapor deposition (MEMOCVD). The material quality of InN improved significantly for the layer thickness larger than 150 nm. The highest extracted value of the room temperature electron mobility was close to 850 cm2/V s for samples with electron carrier concentration of ∼4×1018 cm−3. The measured dependence of the electron mobility on electron concentration is interpreted using the model accounting for ionized impurity scattering, polar optical scattering, and compensation. The MEMOCVD-grown material exhibited stronger photoluminescence (PL) compared to InN deposited using conventional metalorganic chemical vapor deposition. Room temperature PL spectra were similar to InN grown using molecular beam epitaxy (MBE) with peak emission at 0.8 eV. The obtained results demonstrate the potential of the MEMOCVD technique for deposition of high quality InN epitaxial layers at reduced temperatures comparable to those used in MBE growth.