bluuebunny/crossref_metadata_2025 huggingface dataset:
THz electromagnetic wave radiation from coherent oscillation of exciton population in high-Q semiconductor microcavities
Authors: Hokomoto Y. , Kadoya Y. , Yamanishi M.
Published: July 2002

The radiation of THz electromagnetic waves (EMWs) induced by impulse excitation from dc-biased high-Q semiconductor microcavities was observed. The oscillation period corresponding to the polariton (normal) mode splitting and the dependence of the EMW intensity on the dc bias and the excitation wavelength indicate that the EMWs are radiated from the polarized excitons in the quantum well. Hence, the results manifest the oscillation of the exciton population, and in turn, the coherent energy exchange between the excitons and the cavity-mode photons, the heart of the polariton concept.
Surface-mode lasing from stacked InGaN insertions in a GaN matrix
Authors: Sakharov A. V. , Lundin W. V. , Krestnikov I. L. , Semenov V. A. , Usikov A. S. , Tsatsul’nikov A. F. , Musikhin Yu. G. , Baidakova M. V. , Alferov Zh. I. , Ledentsov N. N. , Hoffmann A. , Bimberg D.
Published: July 2002

We report surface-mode lasing in a structure with 12-fold stacked InGaN insertions in a GaN matrix without using of Bragg mirrors. At high excitation densities, one of the modes of the Fabry–Perot cavity formed by the GaN sapphire and the GaN air interfaces, shows a strong superlinear increase in intensity with excitation density rise. The possibility to reach surface lasing in a very low finesse microcavity is due to the ultrahigh material gain of the InGaN insertions. The strong modulation of the absorption-gain spectrum with increase in the excitation density results in a pronounced energy shift of the cavity modes. We found that the threshold excitation density is weakly affected by temperature up to 110 K, while increases at higher temperatures. This behavior is attributed to thermal evaporation of carriers from InN-rich nanodomains and is typical for quantum dot lasers.
Dose calibration for through-oxide doping distributions from time-dependent secondary-ion-mass-spectrometry depth profiles with only one sensitivity factor
Authors: Wittmaack K. , Lee J. J. , Patel S. B.
Published: July 2002

A simple method is described for calibrating the dose of impurity depth profiles in Si, SiO2, and SiO2 on Si by secondary ion mass spectrometry (SIMS). Use is made of the fact that, with normally incident O2+ beams, the ionization probabilities of impurity and matrix secondary ions as well as the partial Si sputtering yields are the same for Si and SiO2. This allows dose calibration against a reference sample to be achieved for any sequence of layers of the two materials and without depth calibration. SIMS profiles of 5 keV 11B equal-dose implants in Si, SiO2, and a thin layer of SiO2 on Si show that the concept is valid to ±1% or better. Differences in the reflection coefficient of 11B from the different targets could be identified clearly.
Effect of dangling-bond density on luminescence in tritiated amorphous silicon
Authors: Sidhu Lakhbeer S. , Kosteski Tome , Zukotynski Stefan , Kherani Nazir P. , Shmayda Walter T.
Published: July 2002

Self-luminescence in tritiated amorphous silicon is observed. The substitution of tritium for hydrogen in a hydrogenated semiconductor provides a powerful tool for the study of dangling bonds. The radioactive decay of tritium leads to an increase in the dangling-bond concentration in the material of several orders of magnitude over a period of a few weeks with little other modification in the structure of the material. We report here results of a study of photoluminescence as a function of time in tritiated amorphous silicon. An analysis of the data in terms of a simple theoretical model in which dangling bonds are treated as nonradiative recombination centers yields a capture radius of 32 Å for the D0 defect.
Thermo-optically tuned cascaded polymer waveguide taps
Authors: Taboada John M. , Maki Jeffery J. , Tang Suning , Sun Lin , An Dechang , Lu Xuejun , Chen Ray T.
Published: July 2002

Polymer thermo-optic-waveguide taps have a potential application as light routers for guided-wave optical interconnects involving cascaded fanouts. The taps can guide light from an optical bus bar and direct it into other devices in a switching/modulation network. Thermo-optic waveguide taps are designed and fabricated on silicon wafers using standard very large-scale integrated fabrication techniques. Coupling of light into an adjacent waveguide tap is observed to increase by 12.3% from 38.7% to 51.0% with the application of 34 mW of power.
Ballistic-electron-emission-spectroscopy detection of monolayer thickness fluctuations in a semiconductor heterostructure
Authors: Guthrie D. K. , First P. N. , Gaylord T. K. , Glytsis E. N. , Leibenguth R. E.
Published: July 2002

Ballistic-electron-emission spectroscopy (BEES) is used to measure fluctuations in the thickness of buried Ga0.8Al0.2As layers. The device under measurement is a half-electron-wavelength Fabry–Perot filter that has been designed to have two quasibound states. By performing BEES at several different spatial locations and by utilizing the relationship between the thicknesses of the device layers and the location (in energy) of the quasibound states, single-monolayer variations are detected in the thicknesses of both the GaAs quantum well and the surrounding Ga0.8Al0.2As barriers. The lateral resolution is shown to be better than 20 nm.
Demonstration of the high-frequency optical heterodyne technology using near-field fiber-optic probes
Authors: Han S. K. , Kang K. Y. , Ali M. E. , Fetterman H. R.
Published: July 2002

We demonstrate the use of near-field fiber-optic probes in optical heterodyne characterization of high-speed devices. The submicron-size optical beam obtained from the fiber-optic probe was employed to selectively excite a small local portion of the active region of the device. Optical heterodyne measurements on heterojunction bipolar transistors were conducted at 1550 nm with a difference frequency of 100 GHz. The significant response of the device with a signal-to-noise ratio of 30 dB was observed. The dc and the ac photoresponses were also measured as a function of the distance between the fiber-optic probe and the device under test. The data showed clearly distinguishable regimes of near- and far-field operation. The high-frequency near-field optical heterodyne technique as explored in this letter provides us with capabilities that can be effectively utilized in the field of optical millimeter-wave interaction in ultrafast devices.
Infrared monitoring system for the detection of organic contamination on a 300 mm Si wafer
Authors: Endo Michiaki , Yoshida Haruo , Maeda Yasuhiro , Miyamoto Nobuo , Niwano Michio
Published: July 2002

An infrared (IR) monitoring system has been developed for the detection and characterization of hydrocarbon contamination on 300 mm (12 in.) Si wafer surfaces. IR propagates through the Si wafer, internally reflecting about 600 times, which enables us to detect a trace of organic contamination on the wafer surface. The present system allows for the detection of hydrocarbon contamination on 300 mm Si wafer surfaces with a contamination level of below 1011 carbon atoms/cm2.
Local microstructures of Si in GaN studied by x-ray absorption spectroscopy
Authors: Lu Z. H. , Tyliszczak T. , Broderson P. , Hitchcock A. P. , Webb J. B. , Tang H. , Bardwell J.
Published: July 2002

Si K-edge x-ray absorption spectroscopy (XAFS) has been used to study the local structure of Si dopant in GaN crystalline material. Doping concentrations NSi from 8.0×1016 to 4.4×1019 cm−3 were investigated. It is observed that the near-edge spectra vary significantly as a function of NSi. At low concentrations the Si K-edge spectra exhibit features similar to that obtained from N K-edge measurement, while at high concentrations the near-edge spectra shape is similar to that recorded from Si3N4. We interpret the results as an indication that Si is not randomly distributed. The changes of the near-edge spectra as a function of doping level is explained as due to changes in the magnitude of Si local lattice contraction caused by the formation of various types of Si clusters. The interpretation is further supported by extended XAFS spectra analysis. A Si-induced strain-field near the surface is proposed as the main force for the cluster formation during epitaxial growth.
Enhancement of Coulomb blockade and tunability by multidot coupling in a silicon-on-insulator-based single-electron transistor
Authors: Park J. W. , Park K. S. , Lee B. T. , Lee C. H. , Lee S. D. , Choi Jung B. , Yoo K.-H. , Kim J. , Oh S. C. , Park S. I. , Kim K. T. , Kim J. J.
Published: July 2002

A dual-gate-controlled single-electron transistor with coupled dot geometry has been fabricated on a silicon-on-insulator structure. Coupled dots are defined by tunable gates which are designed to separately control the tunneling potential barriers to compensate for disorder due to size fluctuation in quantum dots. The Coulomb-blockade phenomena observed in linear and nonlinear transport regimes were found to be enhanced by the multidot coupling. The Coulomb staircase (nonlinear effect) appears more clearly with the increasing number of coupled dots, indicating definite suppression of the inevitable cotunneling process. In the linear regime, the frequency of Coulomb oscillation was able to be tuned by changing the interdot coupling strength. These results indicate that enhancement of the Coulomb blockade and tunability can be achieved through replacing the traditional single dot by gate-controlled multidots in future single-electron devices.
Exposure of self-assembled monolayers to highly charged ions and metastable atoms
Authors: Ratliff L. P. , Minniti R. , Bard A. , Bell E. W. , Gillaspy J. D. , Parks D. , Black A. J. , Whitesides G. M.
Published: July 2002

The doses of neutral metastable argon atoms (Ar*) and highly charged xenon ions (HCIs) required to damage self-assembled monolayers (SAMs) of alkanethiolates on gold are compared in a set of experiments carried out concurrently. The extent of damage to the SAM is determined by developing the samples in a gold etching solution, then measuring the decrease in reflectivity of the gold; ≈105 Ar* are required to cause the same amount of damage as 1 HCI, as measured by this assay. We have also demonstrated HCI micropatterning of a surface using a physical mask, suggesting the application of this system in lithography.
Multiple distributed feedback operation at 1.55 μm with uniform output powers in a single laser diode
Authors: Talneau A. , Charil J. , Ougazzaden A.
Published: July 2002

We demonstrate in a single laser diode the simultaneous operation on different wavelengths around 1.55 μm while preserving the spectral distributed feedback selection mechanism for each wavelength. The grating that exists all along the cavity is a multiwavelength grating obtained by the linear transfer of superimposed multiple holographic exposures. Such a grating acts as a reflectivity comb, the action of each reflector being uniformly distributed all along the cavity. Thanks to a clever incorporation of a phase shift, the lasing wavelengths are deterministically placed on the Bragg modes. The equal strengths of the different spatial frequencies of the grating translate into uniform optical output powers on the simultaneous lasing modes.
Photoconductive detection of millimeter waves using proton implanted GaAs
Authors: Wong C. S. , Dai J. M. , Tsang H. K.
Published: July 2002

We show that ion-damaged GaAs may be used to detect millimeter electromagnetic waves in photoconductive sampling gates. The semi-insulating GaAs material which was implanted with a dose of 1014 cm−2 protons at an energy of 200 keV gave a signal to noise improvement of about 11.4 dB when compared with as-grown semi-insulating GaAs. The improvement is in spite of a reduced carrier mobility in the ion-implanted material and is due to the shorter carrier lifetime and formation of ohmic contacts with the ion-damaged semi-insulating GaAs.
Compensated dispersion tuning in harmonically mode-locked fiber laser
Authors: Chan K. , Shu C.
Published: July 2002

Electrical tuning of wavelength has been demonstrated in a harmonically mode-locked fiber laser using a compensated dispersion-tuning approach. The cavity consists of a standard single-mode fiber (SMF) and a dispersion-compensated fiber (DCF), providing equal and opposite group velocity dispersion to wavelength components around 1.55 μm. Tuning is achieved by controlling the delay time between electrical pulse signals applied to two modulators connecting the SMF and the DCF. The tuning relation exhibits a linear characteristic and matches with the calculated result. A 21.5 nm tuning range is obtained with an extinction ratio as high as 47 dB at a constant operating frequency of 1 GHz.
Experimental investigation of wavelength conversion based on four-wave mixing in a three-electrode distributed feedback laser
Authors: Tomkos Ioannis , Zacharopoulos Ioannis , Roditi Eugenia , Syvridis Dimitris
Published: July 2002

A wavelength converter based on four-wave mixing in a three-electrode distributed feedback laser is experimentally investigated. The output power and the signal to background noise ratio characteristics of the converted waves were measured for highly nondegenerate conditions, up to 2 THz detuning frequency. The dependence of the converted wave power on the pump and probe input power has been also investigated. Moreover, a comparison with a highly performing converter based on four-wave mixing in a 1.5-mm-long semiconductor optical amplifier has been carried out.
Wavelength shifting of optical pulses through cascaded second-order processes in a lithium–niobate channel waveguide
Authors: Cristiani I. , Banfi G. P. , Degiorgio V. , Tartara L.
Published: July 2002

We investigate the efficiency of wavelength shifting (generation of a pulse at the wavelength λp−Δλ from a signal at λp+Δλ under the action of a pump at λp) through a cascaded second-order process in a lithium–niobate channel waveguide. With a 58-mm-long Ti-diffused channel waveguide, λp=1.1 μm (the wavelength of phase matching for the first step of the second-harmonic generation), Δλ of several nanometers and 20 ps pulse duration, wavelength conversion with unit efficiency is obtained with a pump pulse energy of the order of 102 pJ.
Kelvin probe and scanning tunneling microscope characterization of Langmuir–Blodgett sapphyrin films
Authors: Goletti C. , Sgarlata A. , Motta N. , Chiaradia P. , Paolesse R. , Angelaccio A. , Drago M. , Di Natale C. , D’Amico A. , Cocco M. , Troitsky V. I.
Published: July 2002

The work function of solid layers of increasing thicknesses of E2M8− sapphyrin, deposited on a gold substrate by the Langmuir–Blodgett method, has been measured by the Kelvin-probe technique. The results show that the contact-potential-difference values depend upon the layer thickness, reaching saturation after a certain amount of deposited sapphyrin. Scanning tunneling microscope images taken at the same coverages show that corresponding with this threshold, sapphyrin forms a true continuous layer on gold, completely covering the substrate. Evolution of the layer towards its completion is accompanied by a continuous variation of the work-function value, consistent with an increasing dipole term due to the interaction of sapphyrin with the metal substrate.
Accommodation of excess Ti in a (Ba, Sr)TiO3 thin film with 53.4% Ti grown on Pt/SiO2/Si by metalorganic chemical-vapor deposition
Authors: Levin I. , Leapman R. D. , Kaiser D. L. , van Buskirk P. C. , Bilodeau S. , Carl R.
Published: July 2002

The microstructure and chemistry of a Ti-rich (Ba, Sr)TiO3 film with 53.4% Ti deposited on a Pt/SiO2/Si substrate by metallorganic chemical-vapor deposition was studied using high-resolution transmission electron microscopy and elemental mapping in electron energy-loss spectroscopy. We established that the Ti/Ba ratio at all the grain boundaries in this film is significantly higher than that in the grain interiors. Structural images revealed the presence of disordered amorphous-like regions at some of the grain boundaries and triple junctions; these regions were tentatively identified as those having the highest Ti/Ba ratio in the chemical maps. Analysis of the electron energy-loss near-edge structure for the O–K edge indicated an increased titanium-to-oxygen coordination at the grain boundaries. No second phase was detected at the (Ba, Sr)TiO3/Pt interface.
The reduction of base dopant outdiffusion in SiGe heterojunction bipolar transistors by carbon doping
Authors: Gruhle A. , Kibbel H. , König U.
Published: July 2002

In SiGe heterojunction bipolar transistors (HBTs) the outdiffusion of the base dopant out of the SiGe region into emitter or collector strongly degrades device performance. This letter describes an extremely sensitive method to quantitatively determine the amount of this diffusion by electrical characterization of fabricated HBTs. The method was used to investigate the reduction of boron diffusion by carbon doping as a function of carbon concentration and position within the base. It was found that carbon is only effective when it is placed within the doped base region. At a carbon level of 2×1019 cm−3 the allowable anneal time may be increased by a factor of 3.
Ejection of ferrofluid grains using nonlinear acoustic impulses— A particle dynamical study
Authors: Sen Surajit , Manciu Marian , Manciu Felicia S.
Published: July 2002

We consider a model dilute ferrofluid with the grains suspended in water (e.g.,γ-Fe2O3) and subject the system to a strong, homogeneous magnetic field directed perpendicular to the surface such that there is chain formation along the field direction. We show that an appropriate impulse initiated at the base of the container might travel as a nondispersive soliton pulse with sufficient energy to overcome surface tension and eject the ferrofluid grain nearest to the liquid–air interface. The proposed mechanism, if successfully realized in the laboratory, could help design a nozzle-free, ink-jet printer of unparalleled resolution.
Boron retarded self-interstitial diffusion in Czochralski growth of silicon crystals and its role in oxidation-induced stacking-fault ring dynamics
Authors: Sinno Talid , Susanto Hendi , Brown Robert A. , von Ammon Wilfried , Dornberger Erich
Published: July 2002

The effect of boron doping on the position of the oxidation-induced stacking-fault ring (OSF ring) during Czochralski (CZ) crystal growth is described using a comprehensive model for point defect dynamics including the role of boron. The important interactions between boron atoms and intrinsic point defects are selected on the basis of tight-binding estimates for the energies of formation for boron-point defect structures. Intrinsic point defect properties used are taken from a parameterized model of point defect dynamics for predicting OSF-ring dynamics. Entropies of formation for boron-point defect species are obtained by fitting the predictions of the model to experimental data for OSF-ring dynamics. The model successfully predicts OSF-ring dynamics for a variety of doping and growth conditions. The effect of boron on the OSF ring is caused by the retardation of point defect recombination at temperatures near the melting point caused by dynamic storage of self-interstitials in complexes with boron.
Substitution sites of Pb and Y in Bi2Sr2Ca1Cu2O8+δ: X-ray photoelectron diffraction as fingerprinting tool
Authors: Pillo Th. , Hayoz J. , Schwaller P. , Berger H. , Aebi P. , Schlapbach L.
Published: July 2002

The substitution site of Y and Pb in the cuprate-type high temperature superconductor Bi2Sr2Ca1Cu2O8+δ is determined in a very direct and unambiguous way by means of angle-scanned x-ray photoelectron diffraction (XPD). Using XPD as a fingerprinting tool, we conclude that Y occupies the Ca sites and Pb the Bi sites, respectively. Furthermore, low-energy electron diffraction data unequivocally show the presence of the incommensurate lattice modulation which is known for pure Bi2212, but not for sufficiently Pb doped Bi2212. We can, therefore, attribute the reappearance of the modulation directly to the Y doping.
Reversible gas doping of bulk α-hexathiophene
Authors: Schön J. H. , Kloc Ch. , Batlogg B.
Published: July 2002

The sensitivity of the electrical properties of α-hexathiophene single crystals to exposure to air, oxygen, helium, and nitrogen is investigated by space charge limited current spectroscopy. Whereas no changes are seen in helium and nitrogen atmosphere, the acceptor concentration and trap density increase in air or oxygen. Nevertheless, stable equilibrium concentrations, much lower than in thin films, are reached after a few days of exposure and remain unchanged for many months. Therefore, the observed thin film device instabilities and their degradation have to be ascribed to grain boundary-enhanced or interface effects. The present results indicate that air-stable electronic devices can be prepared from oligothiophenes.
Ferromagnetic cluster behaviors and magnetoresistance in Ni-doped LaSrMnO3 systems
Authors: Feng Ji-Wen , Hwang Lian-Pin
Published: July 2002

We have studied the magnetic and magnetotransport properties of the perovskites La8Sr0.2Mn8Ni0.2O3 and La0.7Sr0.3Mn0.8Ni0.2O3. Ferromagnetic cluster behaviors have been observed. The most interesting feature is that the cluster-glass state exhibits both macroscopic insulator-like transport behavior and largely enhanced magnetoresistance (MR) at low temperature. Such a low-temperature MR is weakly temperature dependent. In particular, a low-temperature magnetoresistance ratio (Δρ/ρ0) as high as 60% has been found in La0.7Sr0.3Mn0.8Ni0.2O3. We attribute the low-temperature magnetotransport to the spin-dependent scattering inside the grains.
Switching dynamics of near-infrared vertical-cavity surface-emitting lasers by injection of near-infrared and midinfrared femtosecond pulses
Authors: Fortusini D. , Burr K. C. , Robert F. , Tang C. L.
Published: July 2002

We report the switch-off and recovery dynamics of a vertical-cavity surface-emitting semiconductor laser induced by injection of near-infrared or midinfrared femtosecond optical pulses. The laser is switched off by carrier-density depletion or carrier-heating effects, depending on the spectral range of the injected pulses. In both cases, the recovery of the laser output can be described by standard rate equations.
Upconversion luminescence of Er-implanted GaN films by focused-ion-beam direct write
Authors: Chao L. C. , Lee B. K. , Chi C. J. , Cheng J. , Chyr I. , Steckl A. J.
Published: July 2002

Upconversion luminescence has been obtained from Er-implanted GaN films by focused-ion-beam (FIB) direct write. FIB implantation was performed on GaN films grown by molecular beam epitaxy, hydride vapor phase epitaxy, and metalorganic chemical vapor deposition. After implantation, the GaN samples were annealed at 1100 °C for 1 h in various ambients (Ar, N2, and O2). Strong green upconversion was observed at 523 and 546 nm under red (840 nm) and infrared (1.0 μm) excitation. Upconversion intensity was measured for Er doses ranging from 4.3×1012 to 2.4×1016 atoms/cm2. Maximum upconversion intensity at 546 nm was observed at a dose of 1–2×1015 atoms/cm2, which corresponds to an atomic percentage of 0.3%–0.6%.
Anisotropic propagation of light in planar waveguides containing InGaAs–InP quantum wells
Authors: Guettler T. , Krebs O. , Voisin P. , Faini G. , Rondi D. , Alibert C.
Published: July 2002

We report on the observation of anisotropy of the propagation index with respect to propagation direction in planar waveguides containing InGaAs–InP quantum wells. We discuss the relation between this effect and the recently discovered in-plane polarization anisotropy of the absorption observed for light propagating along the growth axis.
Persistent photoconductivity in Ga1−xInxNyAs1−y
Authors: Li J. Z. , Lin J. Y. , Jiang H. X. , Geisz J. F. , Kurtz Sarah R.
Published: July 2002

Electrical properties of unintentionally doped p-type Ga0.95In0.05N0.013As0.987 quaternary alloys grown by metal–organic vapor-phase epitaxy have been investigated by Hall-effect and photoconductivity measurements. Persistent photoconductivity (PPC) has been observed in this material at temperatures T<320 K. The PPC buildup and decay kinetics have been systematically measured at different temperatures and photoexcitation energies and formulated in the context of lattice-relaxed deep levels (or AX-like centers). The parameters which characterize the AX centers in GaInNAs, namely, the thermal and optical ionization energies, hole capture barrier, and the Stokes shift, have been determined. Our results indicate that AX-like deep levels strongly influence the electronic properties of the GaInNAs quaternary system.
High temperature c-axis resistivity of Bi2Sr2CaCu2O8+x single crystals and dependence on oxygen stoichiometry
Authors: Yang G. , Abell J. S. , Gough C. E.
Published: July 2002

The c-axis resistivity of Bi2Sr2CaCu2O8+x crystals has been measured as a function of thermal cycling in the range between 70 and 856 K in flowing oxygen and nitrogen. Hysteresis in the temperature-dependent c-axis resistivity provides evidence of thermally activated oxygen diffusion in and out of the crystal varying as D(T)=6×107 exp(−Δ1/kT) and D(T)=55 exp(−Δ2/kT), where Δ1=2.2 eV and Δ2=1.2 eV, respectively. Oxygen diffusion into the crystals becomes significant above T0∼595 K and out of the crystal above T1∼750 K. The implications for the stoichiometric control, superconductivity, and intrinsic high temperature dependence of the resistivity of Bi2Sr2CaCu2O8+x crystals are considered.
Ballistic transport in p-type GaAs
Authors: Xie Zhijian , Lyon S. A.
Published: July 2002

The ballistic transport of electrons in the lightly p-type GaAs base of ballistic transistors has been measured at temperatures from 4.2 to 80 K and base lengths of 0.2, 1.7, and 5.7 μm. The transistors have n-type emitters, p-type base and collector with an undoped superlattice as the energy analyzer, and the electron energy is below that of the longitudinal optical phonon. Ballistic transport through the 5.7 μm base device is seen at up to 25 K while in the 0.2 μm transistor ballistic effects persist to liquid nitrogen temperature. A mean free path about 3 μm at 5 K is deduced from the experiments with little change up to 15 K. Calculation shows that neutral impurities dominate the scattering in this temperature range, and the calculated ballistic range of 3.2 μm is in excellent agreement with the experimental results.
Electrical and photoelectrical properties of Si/In–Te heterojunctions
Authors: Jansen R. , Moodera J. S.
Published: July 2002

Heterojunctions between the chalcogenide In–Te and crystalline Si have been fabricated in ultrahigh vacuum, and are characterized for their electrical and photoelectrical properties. The junctions are formed by evaporation of In–Te thin films onto p-type Si(100) substrates at elevated temperature or at room temperature, yielding In–Te in either a crystalline or an amorphous phase. For either of the two phases, diodes display rectifying transport with low reverse-bias leakage current, especially for crystalline In–Te. Only for heterojunctions with crystalline In–Te do we find significant photosensitivity, increasing for thicker In–Te films. The results suggest that at least part of the collected photocarriers originate from the In–Te side of the heterostructure.
Heterointerface quality of InGaP–GaAs superlattices determined by photopumping, x-ray analysis, and transmission electron microscopy
Authors: Yang Q. , Kellogg D. A. , Lin C. , Stillman G. E. , Holonyak N.
Published: July 2002

Data are presented on the room-temperature, photopumped, continuous laser operation of multiple-well InGaP–GaAs quantum-well heterostructures and superlattices grown by low-pressure metalorganic chemical vapor deposition. Continuous laser operation at room temperature indicates high material quality and minimal nonradiative recombination at the heterointerfaces. The lasing wavelength near the GaAs band gap is consistent with weak bandfilling, and small quantum confinement of electrons and large confinement of holes (mh>me, ΔEv>ΔEc). Double-crystal x-ray diffraction and transmission electron microscopy data confirm the high material quality and heterointerface abruptness.
Stress-dependent growth kinetics of ultraviolet-induced refractive index change and defect centers in highly Ge-doped SiO2 core fibers
Authors: Tsai Tsung-Ein , Taunay Thierry , Friebele E. Joseph
Published: July 2002

The evolution of the index change of type-IIa gratings observed in 28 mol % Ge–SiO2 core fibers with 1.8 μm core diameter under various strains was measured from the optical spectra, and the induced defects at high and low strains were studied with electron spin resonance. Data will be presented to show that the index modulation (Δnmod) of type-IIa gratings is likely associated with Ge E′ centers.
Photoinduced luminescence quenching and insolubilization of star-like branched organosilicon compounds
Authors: Sonoda Tooru , Rahmat Hidayat , Ozaki Masanori , Yoshino Katsumi , Schneider Wolfgang , Lee Kyung Koo , Naka Akinobu , Ishikawa Mitsuo
Published: July 2002

Soluble star-like branched organosilicon compounds having silanylene and oligothienylene in their arms are stable in vacuum upon light irradiation, and remain highly light emissive, but degrade upon light irradiation in air. Though the change of absorption spectrum upon light irradiation is not so large, photoluminescence (PL) intensity is strongly suppressed without notable change in spectrum shape. Remarkable shortening of PL decay time due to degradation upon light irradiation in air has been confirmed by time-resolved PL measurement. These results are discussed in terms of scission of Si–Si bonds and oxidation. Optical recording utilizing photoinduced insolubilization of these materials has also been demonstrated.
Oxygen arrangement on Hg0.5Tl0.5Ba2CuOx (100) surface studied by high-resolution electron microscopy
Authors: Oku Takeo , Nakajima Satoru
Published: July 2002

Oxygen arrangement on Hg0.5Tl0.5Ba2CuOx (100) surface was studied by high-resolution electron microscopy. The {100} planes were found to be stable and to have preferred atomic surface. A surface structure model of Hg0.5Tl0.5Ba2CuOx was proposed and compared to the image calculations, which indicated the surface consists of Ba layers and oxygen atoms on the (Hg, Tl) layers. The present work indicates that the stable {100} planes of Hg-1201-type superconducting oxides would be suitable for the future device application.
Polar-optical-phonon induced nonlinearity at semiconductor interfaces
Authors: Gelmont B. L. , Woolard D. L.
Published: July 2002

The dynamical behavior of GaAs-based Schottky-diode interfaces near the polar-optical-phonon (POP) resonance frequency is addressed. The manifestation of a tetrahertz-regime coupling mechanism between the temporal evolution of the diode barrier and POPs is revealed. Specifically, POPs are shown to perturb the spatial dependence of the displacement field within the depletion region and strongly enhance the nonlinearity associated with diode current. This resonance coupling emerges in the unscreened barrier region and leads to dramatic nonlinear effects on both the resistive (i.e., emission particle transport) and the reactive (displacement transport) physics. This strong and highly localized frequency-space phenomenon has broad implications to all polarsemiconductor-based heterostructure devices that utilize nonlinear electron transport effects.
Sub-Poisson current noise in ballistic space-charge-limited diodes with linear I–V characteristics
Authors: Bulashenko O. M. , Rubı́ J. M. , Kochelap V. A.
Published: July 2002

It is generally believed that the I–V characteristics for a ballistic space-charge-limited (SCL) diode exhibits the Child law I∝V3/2. In this letter, we present the exact formulas which describe the I–V characteristics and the current noise (noise temperature) in a semiconductor ballistic SCL diode from which follows the linear or sublinear I–V dependencies, while the noise is strongly suppressed by Coulomb correlations below the Poissonian level.
Simple and convenient nonoptical shear force sensor for shear force and near-field optical microscopes
Authors: Bai Y. , White J. D. , Zhang G. , Chen G. , Hou X.
Published: July 2002

A simple, compact, and inexpensive method for shear force distance regulation is presented. A single piezoelectric cantilever is employed to both dither a fiber probe and to detect the decrease in piezotension-induced voltage as it approaches the sample surface. On resonance, the large piezotension-induced voltage (∼0.2 mV/nm) allows for simple electronics to be used. It is expected to find application both in shear force microscopy and for shear force distance regulation in near-field optical microscopy.
On-chip spectroscopic detection of terahertz radiation emitted from a quasiparticle-injected nonequilibrium superconductor using a high-Tc Josephson junction
Authors: Kume E. , Iguchi I. , Takahashi H.
Published: July 2002

We report a novel sensitive terahertz spectroscopy in which both the electromagnetic generator and the detector are fabricated on the same chip. The radiation emitted from a tunnel-injected nonequilibrium high temperature (high-Tc) YBa2Cu3O7−y superconductor is detected by a high-Tc bicrystal Josephson junction. The observed data are converted to the spectral data by means of inverse Hilbert transformation. The resultant emitted spectra exhibit a broad peak around 1 THz, extending up to 2.5 THz. The relation to the Josephson plasma emission is discussed.
Fabrication and transport properties of clean long one-dimensional quantum wires formed in modulation-doped GaAs/AlGaAs heterostructures
Authors: Liang C.-T. , Simmons M. Y. , Smith C. G. , Ritchie D. A. , Pepper M.
Published: July 2002

We describe the fabrication and transport properties of clean long one-dimensional quantum wires formed in high-quality modulation-doped GaAs/AlGaAs heterostructures. In a 3 μm wire, we observe 25 conductance steps with no superimposed resonant features. With increasing split-gate length, we observe a crossover from ballistic towards diffusive transport, and in 5 and 6 μm wires, a reduction of conductance plateau values as large as 8% and 25% is observed, respectively.
Coupled resonator vertical-cavity laser diode
Authors: Fischer A. J. , Choquette K. D. , Chow W. W. , Hou H. Q. , Geib K. M.
Published: July 2002

We report the operation of an electrically injected monolithic coupled resonator vertical-cavity laser which consists of an active cavity containing InxGa1−xAs quantum wells optically coupled to a passive GaAs cavity. This device demonstrates modulation characteristics arising from dynamic changes in the coupling between the active and passive cavities. A composite mode theory is used to model the output modulation of the coupled resonator vertical-cavity laser. It is shown that the laser intensity can be modulated by either forward or reverse biasing the passive cavity. Under forward biasing, the modulation is due to carrier induced changes in the refractive index, while for reverse bias operation the modulation is caused by field dependent cavity enhanced absorption.
High-pressure, high-efficiency operation of a chemical oxygen-iodine laser
Authors: Wani Fumio , Endo Masamori , Fujioka Tomoo
Published: July 2002

High-pressure subsonic mode operation of a chemical oxygen-iodine laser (COIL) was demonstrated. Singlet delta oxygen generated by a liquid-jet type singlet oxygen generator (SOG) was directly utilized in the laser cavity, without supersonic expansion. The operating pressure in the laser cavity was 0.80 kPa (6.0 Torr). Cooled nitrogen gas was added to the singlet oxygen flow to enhance the output power. An output power of 448 W was obtained for a chlorine input rate of 19.7 mmol/s. This is equivalent to a chemical efficiency of 25.0%, and it is comparable to the highest reported chemical efficiency of COIL using nitrogen as the buffer gas. The obtained value of specific energy of 3.5 J/liter, is more than fivefold higher than that for our supersonic COIL device.
Quantum point contact in a magnetic field: Far-infrared resonant heating observed in photoconductivity
Authors: Heron R. J. , Lewis R. A. , Kane B. E. , Facer G. R. , Clark R. G. , Dzurak A. S. , Lumpkin N. E. , Starrett R. P. , Rickel D. G. , Pfeiffer L. N. , West K. W.
Published: July 2002

We report on the far-infrared photoresponse of a quantum point contact device fabricated on a top-gated GaAs/AlGaAs heterostructure. The top-gated architecture avoids the disorder built into conventional modulation-doped structures. We observe a distinctive far-infrared magnetophotoresponse. This depends on the wavelength of the radiation and on the carrier density, which is controlled by the gate voltage. We conclude by comparison with transport data that the oscillations observed in photoconductivity and which are centred around the cyclotron energy arise from the resonant heating of electrons by the far-infrared radiation.
Quantum-dot vertical-cavity surface-emitting laser based on the Purcell effect
Authors: Deppe D. G. , Huang H.
Published: July 2002

A quantum-dot vertical-cavity surface-emitting laser based on a modified Purcell effect is described. It is shown that the quantum-field confinement can greatly improve the modulation response, while arrays of such elements can generate power levels useful for high-speed data communication. The high-speed pulse response allows bias-free operation and makes the microcavity array an attractive replacement for single-aperture vertical-cavity surface-emitting lasers.
Effects of interference in quasiphase-matched periodically segmented potassium titanyl phosphate waveguides
Authors: Benaich Zachary S. , Pradhan Ranjit D. , Mian Shabbir M. , Melikechi Noureddine
Published: July 2002

We show that optical interference of two input beams coupled into a periodically segmented KTiOPO4 waveguide can increase the efficiency of the generated second harmonic by a factor of three over coupling a single beam with the same total power. A simple model based on two interfering Gaussian beams indicates that the second harmonic output increases by enhancing the coupling of the fundamental energy into the waveguide. A Mach–Zehnder interferometer scheme is used to demonstrate this effect. The variation of the second harmonic power with the fundamental input power of the interfering beams shows excellent qualitative agreement between experimental results and the model presented.
Influence of a local magnetic field on the movement of a single vortex pinned in a niobium thin-film direct current superconducting quantum interference device
Authors: Gail J. , Mück M. , Heiden C.
Published: July 2002

To avoid pinning of many vortices, we prepared superconducting quantum interference devices (SQUIDs) with a square loop of only 1 μm linewidth. At one side of the SQUID, the loop widens to an area of 4 μm×5 μm, which offers enough space for a few vortices. If a vortex is trapped in this pinning area, it begins to migrate by thermally activated hopping between the pinning sites. It was possible to influence the hopping process via a Lorentz force on the vortex produced by a local magnetic field. We were able to show that the vortex was located in the extra area of the SQUID loop and not in any other part of the SQUID.
a-axis tilt grain boundaries for YBa2Cu3O7−x superconducting quantum interference devices
Authors: Testa G. , Sarnelli E. , Carillo F. , Tafuri F.
Published: July 2002

Superconducting quantum interference devices (SQUIDs) have been fabricated using YBa2Cu3O7−x [100] 45°-tilt grain-boundary Josephson junctions based on a controllable biepitaxial technique. These devices are characterized by large characteristic voltages, desirable magnetic-flux-to-voltage transfer parameters and low flux noise. An energy resolution of 1.6×10−30 J/Hz at liquid helium has been measured, which is the lowest value reported for biepitaxial SQUIDs. These junctions exhibit a phenomenology different from traditional [001] 45°-tilt biepitaxials probably due to the absence of π junctions. The performance of the presented SQUIDs demonstrates that significant improvements in the biepitaxial technique are possible, and the resulting devices have potential for applications.
Optical coupling between monocrystalline colloidal crystals and a planar waveguide
Authors: Zhao Y. , Avrutsky I. , Li B.
Published: July 2002

We have experimentally demonstrated an optical material structure consisting of monocrystalline colloidal crystals and a planar waveguide. We have performed experimental studies of light coupling into the waveguide structure via colloidal gratings, as well as the multiplexing capability of the structure. Effective index obtained from measured parameters agrees well with theoretical calculations. Effect of crystal nonuniformity on diffraction line shape and width, as well as possible applications are discussed.
Evolution of residual stress in plasma-enhanced chemical-vapor-deposited silicon dioxide film exposed to room air
Authors: Park Youngsoo , Lee June Key , Jung Ilsub , Heo Soo-Bong , Lee Jai-Young
Published: July 2002

Considerable increase in compressive stress was observed in silicon dioxide films upon prolonged exposure to atmospheric moisture. The compressive stress change upon exposure to atmosphere consisted of a reversible change and an irreversible change. The irreversible component was found to be due to structural changes in the Si–O–Si network. The reversible change in stress is due to water molecules absorbed on walls of the pores.
Single step process for epitaxial lateral overgrowth of GaN on SiC and sapphire substrates
Authors: Smart J. A. , Chumbes E. M. , Schremer A. T. , Shealy J. R.
Published: July 2002

Using flow modulation organometallic vapor phase epitaxy, a process has been developed which produces epitaxial lateral overgrowth of GaN-base materials directly on SiC and sapphire substrates patterned with silicon nitride. The key feature of this single step process is the use of a high temperature AlGaN nucleation layer which wets the exposed substrate surface, without significant nucleation on the mask. This eliminates the need for regrowth while producing smooth growth surfaces in the window opening as well as over the mask. Subsequent GaN deposition results in relatively defect free materials grown laterally over the mask. Using arrays of stripe windows aligned parallel to the 〈11_00〉 crystal direction, the epitaxial films completely planarize after roughly 5 microns of growth. Defect densities estimated from atomic force micrographs indicate a reduction from mid 108 to 105 cm−2 in regions over the window and over the mask, respectively. This process represents a significant simplification over currently used regrowth methods for obtaining low defect density laterally overgrown GaN materials.
High-quality GaAs on Si substrate by the epitaxial lift-off technique using SeS2
Authors: Arokiaraj J. , Soga T. , Jimbo T. , Umeno M.
Published: July 2002

In this letter, we demonstrate the realization of strong bonding between GaAs epilayers on Si substrates by using selenium sulphide (SeS2) compound. After bonding, the sample has been transplanted to Si substrate using the epitaxial lift-off process. Such a transplanted film was found to be very smooth and adhered well to Si. The resulting chemical bond was covalent in nature, robust, and withstood clean room processing steps. The film bonded in this manner exhibited very good photoluminescence and high crystal quality by double crystal x-ray diffraction. The double crystal x-ray diffraction had a low full width at half maximum of 44 arcsec, and the strain was absent in these types of heterostructures. The interfacial chemical reaction and bonding were studied by depth profile x-ray photoelectron spectroscopy. It was concluded that Ga–Se and Si–S phases such as Ga2Se3 and SiS2 were responsible for the strong bonding between GaAs and Si.
Direct far-field observation of surface-plasmon propagation by photoinduced scattering
Authors: Velinov T. , Somekh M. G. , Liu S.
Published: July 2002

A tightly focused laser beam is shown to act as a scatterer of surface plasmons. The energy released into free space due to the scattering is collected by far-field optics. Scanning the laser beam over the plasmon field gives a map of their propagation. Evidence is given which shows that the surface-plasmon map gives much more detail of plasmon propagation and film structure than the photothermal image, which monitors the heat deposited during plasmon propagation.
Polarization-independent four-wave mixing in a bidirectional traveling-wave semiconductor optical amplifier
Authors: Contestabile G. , D’Ottavi A. , Martelli F. , Mecozzi A. , Spano P. , Tersigni A.
Published: July 2002

In this work, we demonstrate polarization-independent four-wave mixing using a single semiconductor optical amplifier. The result is obtained using a polarization-diversity scheme, in which all the injected fields are split by a polarization beam splitter and the two resulting patterns are injected counterpropagating in the amplifier. The use of two orthogonally polarized pumps allows a conjugate generation with efficiency also independent of the signal-conjugate detuning. A comparison of the amplifier performance with mono- and bidirectional propagation is given.
Dielectric constant and light emission in Si/SiO2 superlattices
Authors: Tran Muoi , Tit Nacir , Dharma-wardana M. W. C.
Published: July 2002

The real part of the frequency-dependent dielectric function ε1(ω) and the light-absorption coefficient α(ω), of Si slabs confined within SiO2 barriers have been calculated as a function of Si-slab thickness dsi. The calculation uses the imaginary part ε2(ω) of the dielectric function obtained from tight-binding calculations. The resulting static dielectric constants are found to increase with the decreasing Si-slab width, contrary to some reported theoretical results for H-terminated Si or pure-Si clusters. The calculated integrated light absorption in the range 1.0–2.6 eV is a maximum for for slabs with dsi∼20 Å, in agreement with experimental work on light emission from Si/SiO2 superlattices and other oxidized Si nanostructures.
Enhancement of hot-carrier injection resistance for deep submicron transistor gate dielectric with a powered solenoid
Authors: Cha Cher-Liang , Tee Kheng-Chok , Chor Eng-Fong , Gong Hao , Prasad Krishnamachar , Bourdillon Anthony J. , See Alex , Chan Lap , Lee Mike Myung-Ok
Published: July 2002

The operational reliability of ultrathin gate dielectrics in forthcoming metal–oxide–semiconductor field-effect transistors (MOSFETs) will be impaired if there is the occurrence of hot-carrier injection (HCI) into the gate across the gate dielectric. In this work, a method is proposed to mellow the undesired effects incurred by HCI in a n-type MOSFET (NMOSFET) via a reduction in its frequency. The method involves the powering of a polycrystalline silicon (polysilicon) solenoid at the same time when the gate and drain of transistors are powered. The localized magnetic field generated from the solenoid can impose a downward force (Hall effect) to counteract or compensate the upward driving force exerted on the energetic electrons reaching the drain by the applied gate voltage. Fewer electrons will be trapped and the quality, reliability, and lifetime of the device will improve as a consequence.