bluuebunny/crossref_metadata_2025 huggingface dataset:
Collapse and revival of exciton–polariton oscillation in a semiconductor microcavity
Authors: Cao H. , Jiang S. , Machida S. , Takiguchi Y. , Yamamoto Y.
Published: July 2002

We measured temporal evolution of the coherent emission from a semiconductor microcavity by a very sensitive ac balanced homodyne detection system. We observed collapse and revival of the exciton–polariton oscillation due to a three-mode beating.
A spatially resolved optical emission sensor for plasma etch monitoring
Authors: Shannon Steven , Holloway James Paul , Flippo Kirk , Brake M. L.
Published: July 2002

A spatially resolved optical emission spectroscopy sensor has been developed, and the resulting reconstructed radial emission profiles from an ArI and ArII line compare well with Ar sputter etch uniformity profiles. The new sensor collects light from a wedge shaped field of view, and is rotated around a single collection point in order to observe the entire plasma through a relatively small viewpoint.
Photoinduced metastable lattice dilation of CdF2:In crystals
Authors: Suchocki A. , Raułuszkiewicz J. , Langer J. M.
Published: July 2002

A novel technique for measuring differential lattice dilation by scanning tunneling microscope is proposed. The method was used to measure the metastable lattice dilation caused by a deep-shallow phototransformation of bistable In impurities in CdF2 crystals. A total linear crystal shrinkage of 1.8×10−6 results from a partial counterbalancing of the lattice contraction associated with the photoionized deep localized In state by a lattice expansion caused by weakly bound electrons at the shallower hydrogenlike state of the bistable In donors.
Discharge impedance variations in large area radio frequency excited CO2 lasers
Authors: Lapucci A. , Rossetti F. , Mascalchi S. , Ringressi R.
Published: July 2002

Some results from a systematic study on the impedance matching conditions and on the longitudinal power distributions in planar rf discharges for CO2 lasers, are given. They show that both plasma impedance and voltage distribution are different in cw and pulsed discharge modes revealing the importance of parameters such as the interelectrode temperature distribution and the local gas density and composition. These parameters have to be taken into account when designing matching networks and voltage smoothing schemes.
Ion mass effect in plasma-induced charging
Authors: Hwang Gyeong S. , Giapis Konstantinos P.
Published: July 2002

Simulations of charging and profile evolution during etching of high aspect ratio polysilicon gates in typical high-density plasmas containing heavy ions (e.g., BCl3+, Cl2+), predict a reduction in charging and notching when lighter ions (e.g., He+) are added. The reduction occurs because of the influence of the ion mass on the ratio R of the ion sheath transit time to the rf period, which determines the spread in the ion energy distribution at the wafer. The effect is most pronounced when R⩽0.1–0.2 for light ions and, simultaneously, R⩾0.6 for heavy ions; then, more light ions arrive at the patterned structure with low energies, where they help decrease localized charging. When the rf bias frequency is reduced so that R⩽0.3 for all ions, the effect disappears.
Pulse propagation of accumulated photon echoes in Nd3+ ion-doped silicate glass fiber
Authors: Yano Ryuzi , Uesugi Naoshi
Published: July 2002

Pulse-propagation phenomena of accumulated photon echo signals was investigated for the F3/24(1)–I9/24 transition of the Nd3+ ion doped with 20 ppm concentration in silicate glass fiber (core diameter of 6 μm) at 4.2 K using an 82 MHz mode-locked dye laser. The intensity of the transmitted probe pulses from the Nd3+ fiber was measured as a function of the Nd3+ fiber length. The fiber length for the maximum probe-pulse intensity induced by the pump pulses was determined to be 4 m when the pump pulses of 0.50 mW average power and the probe pulses of 0.25 mW average power were used. We derived the pulse area equations which take into account the coherent interaction between the pulses and the Nd3+ fiber. The fiber-length dependence of the signal intensity was explained well by the pulse area equations.
Scanning probe nanolithography of conducting metal oxides
Authors: Hung Chen-Jen , Gui Jianian , Switzer Jay A.
Published: July 2002

The scanning tunneling microscope (STM) was used to form nanometer-size holes in thin conducting films of thallium (III) oxide. Hole formation was only observed when the process was performed in humid ambient conditions. The hole formation was attributed to localized electrochemical etching reactions beneath the STM tip. Etching reactions consistent with the observed hole formation are a direct electrochemical reduction of thallium (III) oxide to soluble Tl (I) at negative sample bias, and local reduction of pH at positive sample bias. The fastest etching was observed at negative sample bias. Holes as small as 10 nm or as large as 1 μm in diameter could be etched in the films.
F induced layer disordering of GaAs/InGaP quantum wells
Authors: Das Utpal , Pathangey Balu , Osman Z. , Anderson Timothy J.
Published: July 2002

F implantation (80–175 keV) induced GaAs/InGaP quantum well disordering was performed in a conventional furnace at 600–750 °C and in lamp annealing at 850 °C. Group V intermixing is found to be substantially enhanced for certain implantation and anneal conditions. Either the group III intermixing leading to lower band gaps or group V intermixing leading to higher band gaps may be made to dominate by choosing the process conditions. Only 50% reduction in integrated luminescence intensities from the as-grown layer makes this quantum well disordering process suitable for device fabrication.
Internal oxidation of low dose separation by implanted oxygen wafers in different oxygen/nitrogen mixtures
Authors: Ericsson Per , Bengtsson Stefan
Published: July 2002

The electrical properties and the structure of the buried oxide in low dose SIMOX wafers were investigated after 1200 °C oxidation in different diluted oxygen ambients. The thickness of the silicon dioxide grown on top of the thin silicon films was the same for all samples. Correlating the breakdown field and the surface structure of the buried oxide with process conditions showed that the oxidation time was the key parameter for improving oxide performance while the oxygen partial pressure only played a minor role. We suggest that saturation of atomic oxygen in the thin silicon film during oxidation is responsible for this behavior.
Landau level formation in semiconductor quantum dots in a high magnetic field
Authors: Nomura S. , Samuelson L. , Pistol M.-E. , Uchida K. , Miura N. , Sugano T. , Aoyagi Y.
Published: July 2002

Landau level formations have been observed in the photoluminescence spectra of highly optically populated InP strained self-organized quantum dots in between barriers of In0.5Ga0.5P at a high magnetic field. The results clearly show the evolution of the discrete states caused by 3D confinement at 0 T into Landau level-like structures at 40.9 T.
Frequency locking of tunable Er:Yb microlasers to absorption lines of C132H2 in the 1540–1550 nm wavelength interval
Authors: Laporta P. , Taccheo S. , Longhi S. , Svelto C. , De Natale P.
Published: July 2002

We demonstrate frequency stabilization of widely tunable erbium–ytterbium microlasers in the wavelength interval between 1540 and 1550 nm by locking the oscillators to nine different absorption lines of C132H2, spaced by approximately 150 GHz. Frequency stability is evaluated by measuring the two-sample Allan variance of the heterodyne beat-note signal between two identical lasers. The square root of the Allan variance is 7×10−10 for integration times between 10−3 and 102 s.
Sensitivity of Bragg surface diffraction to analyze ion-implanted semiconductors
Authors: Hayashi M. A. , Morelhão S. L. , Avanci L. H. , Cardoso L. P. , Sasaki J. M. , Kretly L. C. , Chang S. L.
Published: July 2002

A special case of the x-ray multiple diffraction phenomenon, the Bragg surface diffraction (BSD), has been investigated under lattice damage due to ion implantation in GaAs (001) samples. The BSD profile is very sensitive to the diffraction regime (dynamical or kinematical) and provides information regarding crystalline perfection and lattice strains in both directions—parallel and perpendicular—to the sample surface. Results from grazing-incidence x-ray diffraction and reciprocal space mapping are also reported.
Low power submillimeter-wave mixing and responsivity properties of YBa2Cu3O7 hot-electron bolometers
Authors: Li C.-T. , Deaver B. S. , Lee Mark , Weikle R. M. , Rao R. A. , Eom C. B.
Published: July 2002

Low power characteristics of superconducting hot-electron bolometric mixers using YBa2Cu3O7 are reported. Near 77 K, these mixers have a responsivity of 780 V/W using 8 nW of local oscillator (LO) power at 585 GHz. The responsivity can be shown to be truly bolometric. Heterodyne mixing at 87 GHz shows an overall conversion gain of −47 dB at 1.8 GHz intermediate frequency, using 3.3 mW of incident LO power. The intrinsic conversion gain is estimated to be −16 dB with 1 μW of LO power, close to the calculated optimal values.
Due to an error in printing, the following article, originally published in the 4 August 1997 issue, is being republished in its entirety. Morphology definition by disclinations and dislocations in a mesostructured silicate crystal
Authors: Feng J. , Huo Q. , Petroff P. M. , Stucky G. D.
Published: July 2002

Curved surface morphologies resulting from disclinations are unusual in inorganic phases because the relatively large lattice energies generally permit only translational dislocations. In this letter, we show, however, that disclinations can be readily observed and identified in composite organic/inorganic phases. Disclinations and dislocations in MCM-41, a two-dimensional hexagonal (p6mm) mesophase crystal synthesized using silicate and surfactant precursors, were investigated by using transmission electron microscopy. We observed two types of dislocations and two types of disclinations. All dislocations observed are of the smallest Burgers vector a (the basis vector). Dislocation dipoles and disclination quadrupoles appear more frequently than isolated ones.
Spectroscopy of a ZnCdSe/ZnSSe quantum well diode laser in high magnetic fields
Authors: Song Y.-K. , Nurmikko A. V. , Schmiedel T. , Chu C.-C. , Han J. , Chen W.-L. , Gunshor R. L.
Published: July 2002

We have investigated the characteristics of green–blue II–VI semiconductor diode lasers at room temperature in high magnetic fields. Small spectral shifts, less than 2 meV during the sweep of a field up to 29 T, were measured in ZnCdSe/ZnSSe single quantum well index guided diode devices. This behavior is in contrast with expectations for a noninteracting electron-hole gas in a quantum well system at comparable pair densities (∼1012 cm−2), implying that the optical gain spectrum shifts diamagnetically. The measured diamagnetic shifts are in close agreement with the low injection electroluminescence and absorption spectra at the n=1 heavy-hole excitonic transition of the ZnCdSe QW.
The V3+ center in AlN
Authors: Thurian P. , Loa I. , Maxim P. , Hoffmann A. , Thomsen C. , Pressel K.
Published: July 2002

We investigated the magnetooptical properties of 0.9 eV luminescence in AlN. The zero-phonon lines at 0.943 eV in AlN are attributed to a transition within a d2 configuration because of a characteristic threefold ground-state splitting in magnetic fields. We determine a g value of 1.96±0.07 and a zero-field splitting of 120±30 μeV for the A32(F) ground state. On the basis of the temperature dependence in a magnetic field, we attribute the 0.943 eV zero-phonon line in AlN to the E1(D)−A32(F) transition of isolated V3+. The different fine structures of the excited state in AlN and GaN are explained in a Tanabe–Sugano diagram.
Substrate imposed stress-strain effect on photoluminescence in hydrogenated amorphous silicon alloys
Authors: Kim Keunjoo , Suh M. S. , Shim H. W. , Youn C. J. , Suh E-K. , Lee K. B. , Lee H. J. , Lee Hwack Joo , Ryu Hyun
Published: July 2002

Hydrogenated amorphous silicon films were deposited on the unstrained and strained Si substrates by an electron cyclotron resonance plasma source. The photoluminescence spectra show that emission energies are different from each other. The redshift of photoluminescence induced by the biaxial tensile stress is increased with decreasing the temperature in the range of 0.11–0.17 eV. The stress effect also enhances the quantum efficiency significantly. The pseudomorphic growth of Si on a relaxed Si0.75Ge0.25 (100) surface provides the strain energy of about 0.17 eV. These comparable results indicate that the shift of emission energy is attributed to the stress effect perturbing the polysilane structure.
Microstructure of Al contacts on GaAs
Authors: Karpov I. , Franciosi A. , Taylor C. , Roberts J. , Gladfelter W. L.
Published: July 2002

The microstructure of Al films deposited on GaAs(100) 2×4 surfaces through chemical vapor deposition from dimethylethylamine alane in the 100–160 °C temperature range exhibits a dominant (111) texture which is not encountered in evaporated films. Such a texture has been associated with enhanced electromigration resistance in related systems. Growth of (111)-oriented grains is observed when the deposition rate is limited by the surface reaction of the impinging precursor molecules, while at higher temperatures (160–400 °C) only the conventional texture is observed.
Breakdown measurement of a capacitive radio frequency discharge with insulated electrode
Authors: Shoji Masafumi , Sato Masumi
Published: July 2002

Breakdown voltages of a capacitively coupled radio frequency nitrogen discharge at 13.56 MHz are measured using an insulated electrode system made from glass-covered aluminum disk plates. The breakdown voltages measured against the gas pressure exhibit typical V-shaped characteristics without peculiar sharp bend in the left branch of the minimum of the curve appearing in a low pressure region when metal electrodes are employed. The observed results are compared with the theoretical calculation based on the electron diffusion and mobility-controlled model, and a satisfactory agreement is found except for the precise prediction of the location of the minimum point.
Sidewall gated double well quasi-one-dimensional resonant tunneling transistors
Authors: Kolagunta V. R. , Janes D. B. , Melloch M. R. , Youtsey C.
Published: July 2002

We present gating characteristics of submicron vertical resonant tunneling transistors in double quantum well heterostructures. Current–voltage characteristics at room temperature and 77 K for devices with minimum feature widths of 0.9 and 0.7 μm are presented and discussed. The evolution of the I–V characteristics with increasing negative gate biases is related to the change in the lateral confinement, with a transition from a large area 2D to a quasi-1D. Even gating of multiple wells and lateral confinement effects observable at 77 K make these devices ideally suited for applications in multi-valued logic systems and low-dimensional structures.
Monitoring of gravity drainage of water and light oil through a sand column by proton nuclear magnetic resonance
Authors: Choi C. , Bharatam J. , Frola I. , Dusseault M. B. , Geilikman M. B. , Chatzis I. , Pintar M. M.
Published: July 2002

Preliminary results of a proton nuclear magnetic resonance study of water and oil drainage under gravity through a sand column are reported. Evolution of the proton magnetization and its spin–spin relaxation time T2 are given as functions of drainage time. It was found that the bulklike fraction of the liquids drains out quickly, while the pendular and surface fractions drain slowly until an equilibrium is reached. The “undrainable,” residual liquid fraction was observed to be ∼6% and ∼48% of its initial value for water and light oil, respectively. The proton T2 of water and oil in different environments are analyzed by employing the fast exchange model. This method of monitoring the drainage of two liquids can be easily adapted to study the spacial and temporal evolution of the liquids in the presence of a gas phase.
Two types of spiral growth of C60 films on KBr(001)
Authors: Kim Y. , Jiang L. , Iyoda T. , Hashimoto K. , Fujishima A.
Published: July 2002

Two types of spiral growth, single and double spirals, of C60 epitaxial films on a KBr(001) substrate were observed by atomic force microscopy (AFM). These single and double spirals were found on films grown at different rates. All spiral islands show the threefold symmetry of the face-centered-cubic (fcc) structure. In the case of single spirals, many fringes were observed in three equivalent [11̄0] directions on the fcc (111) surface. From the AFM images, we concluded that the growth process of these spirals can be explained by the classical crystal growth theory of Burton, Cabrera, and Frank and that screw dislocations form without any direct influence of the substrate.
Bilayer growth period oscillation of the Sb2 reactivity during molecular beam epitaxy of AlSb (001)
Authors: Kaspi Ron , Loehr John P.
Published: July 2002

We report oscillations in Sb2 reactivity with the growth surface during layer-by-layer deposition of AlSb (001) by molecular beam epitaxy. Real-time measurements of the Sb desorption rate using line-of-sight mass spectrometry, in parallel with reflection high-energy electron diffraction specular beam intensity measurements, suggest that this behavior results from the periodic variation of the surface step density as these steps act as preferential adsorption sites for antimony. This is further supported by computer simulations that examine the surface step density as a function of bilayer coverage.
Electron diffraction due to a reflection grating in a conducting wire
Authors: Park KyoungWan , Lee Seongjae , Shin Mincheol , Yuk Jong Seol , Lee El-Hang , Kwon Hyuk Chan
Published: July 2002

We report on quantum transport in the presence of an electron reflection grating fabricated within a high electron mobility transistor structure. The grating was composed of a periodically corrugated potential wall by which the electron waves are diffracted. The low temperature conductance shows a number of peaks with respect to the gate voltage, which are consistent with the electron diffraction effect and are predicted by the Fraunhofer diffraction condition.
Smart pixel using a vertical cavity surface-emitting laser
Authors: Welker M. , Knüpfer B. , Malzer S. , Döhler G. H. , Gulden K. H. , Moser M. , Riel P.
Published: July 2002

We present a smart pixel with surface-normal optical input and output beams using a vertical cavity surface-emitting laser. In its present nonoptimized hybrid version, the smart pixel exhibits opto-optical switching with a contrast of 35 dB, an optical gain of 55 dB and a 3 dB bandwidth of 90 MHz. The optical switching energy is 715 fJ. NOR, and NAND logic operations at 4 Mbit/s with a fan-out of 5 are also demonstrated.
THz oscillations in the emission from a semiconductor microcavity
Authors: Tsuchiya M. , Koch M. , Shah J. , Damen T. C. , Jan W. Y. , Cunningham J. E.
Published: July 2002

We report the observation of ultrafast intensity oscillations in the time resolved optical emission from a semiconductor microcavity resonantly pumped with intense femtosecond pulses. The observed oscillations are pronounced, persist for several picoseconds, and have frequencies varying from 1.4 to 2.7 THz, depending upon the incidence angle of the pump beam. The angular dependence and spectra show that the oscillations result from interference between the pump and surface-normal modes of the microcavity.
Determination of irreversibility field variations in mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox tapes by transport current methods
Authors: Anderson J. W. , Parrell J. A. , Polak M. , Larbalestier D. C.
Published: July 2002

The irreversibility field, H*, has been measured for a variety of mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes using two different transport current techniques. It is common to characterize the quality of 2223 tapes by their zero-field, 77 K critical current density [Jc(0 T, 77 K)], even though this ignores the fact that significant self-fields depress Jc(0 T, 77 K) and the possibility that the in-field Jc(B) characteristics may be optimized independently of the Jc(0 T, 77 K) value. To provide more useful information, we propose a second characterization, that of the irreversibility field, H*. Having both H* and Jc(0 T, 77 K) information helps in separating the two independent contributions that better connectivity and stronger flux pinning can make to the Jc of a tape. We illustrate this point with results from a variety of mono- and multifilamentary Bi-2223/Ag tapes in damaged and undamaged conditions, which show that H* (77 K) can vary from ∼100 to ∼200 mT and not directly correlate with Jc(0 T, 77 K). The two proposed protocols for H* measurement are robust and compatible with common transport measurement procedures.
An efficient all-solid-state ultraviolet laser source
Authors: Kung A. H. , Jr-i Lee , Chen Poe-Jou
Published: July 2002

Stable high-power operation in the uv is achieved from a commercial multi-kHz diode-pumped multimode Q-switched Nd:YAG laser by fourth-harmonic generation in an external cavity. Over 640 mW at 266 nm in a TEM00 beam and an internal conversion efficiency of 30% were obtained. A lifetime of one-billion shots at several hundred mW and a long-term power stability of ±1% were recorded, demonstrating that this source has the potential of stable long-term operation using readily available components.
Room-temperature persistent spectral hole burning in Sm-doped KLaF4 crystals
Authors: Kodama Nobuhiro , Takahashi Tomoko , Hirao Kazuyuki
Published: July 2002

Persistent spectral hole burning is observed at room temperature in the excitation spectrum for the F07→D05 transition of Sm2+ in KLaF4 single crystals. The hole width and depth are about 10 cm−1 and 18% of the total intensity, respectively. It is concluded that the dominant burning mechanism in this crystal is a photoionization of electron trapping at a site other than Sm3+ ions because of the absence of an antihole around the burned hole.
Kinetic energy influence of hyperthermal dual ion beams on bonding and optical properties of carbon nitride films
Authors: Tsubouchi N. , Horino Y. , Enders B. , Chayahara A. , Kinomura A. , Fujii K.
Published: July 2002

Carbon nitride films were produced by simultaneous irradiation of well-defined hyperthermal (50–400 eV), isotopically mass-separated C2−12 and N+14 ions with various kinetic energy combinations. It was found that the intensity of CN-triple bonds normalized by the amount of nitrogen atoms in the films and the complex refraction index (n,k) are correlated with the energy combination of C2−12 and N+14 ions.
Role of arsenic clusters in carrier recombination in low-temperature grown AlGaAs/GaAs multiple quantum wells
Authors: Feng W. , Wang Y. , Wang J. , Ge W. K. , Huang Q. , Zhou J. M.
Published: July 2002

The low-temperature grown AlGaAs/GaAs multiple quantum well structures were characterized by photoluminescence (PL) spectroscopy. The samples were grown at 270–400 °C and annealed at 500–900 °C. After anneal, photoluminescence quenching was observed for the samples grown at temperatures below 350 °C, and found to show a strong dependence on the growth and anneal temperatures. The luminescence intensity for the PL-quenched sample exhibits a power law dependence on the excitation level with an exponent close to 2, indicating a bimolecular recombination process in parallel with strong nonradiative recombination. The photoluminescence quenching upon anneal is attributed to the formation of arsenic clusters that serve as new nonradiative recombination channels.
Radio frequency SQUIDs operating at 77 K with 1 GHz lumped-element tank circuits
Authors: He D. F. , Zeng X. H. , Krause H.-J. , Soltner H. , Rüders F. , Zhang Y.
Published: July 2002

We have developed a matching scheme for the operation of a rf superconducting quantum interference device (SQUID) with a lumped-element tank circuit at pumping frequencies up to 1 GHz. This conventional LC resonant circuit is inductively coupled to a matching coil, which is connected to the 50 Ω transmission line. We characterized the flux noise of high-temperature rf SQUIDs at resonant frequencies between 221 and 950 MHz. At about 900 MHz, we obtained the white flux noise of about 14.6 μφ0/Hz with a SQUID inductance LS=150 pH and 20 μφ0/Hz with LS=260 pH. Several of such tank circuits can be driven in parallel or in series with only one cable.
Internal oxidation of vacancy agglomerates in Czochralski silicon wafers during high-temperature anneals
Authors: Kissinger G. , Morgenstern G. , Vanhellemont J. , Gräf D. , Lambert U. , Richter H.
Published: July 2002

Fast pulled Czochralski silicon crystals usually contain large octahedral vacancy agglomerates. These voids are known as D defects, which degrade the integrity of thin gate oxides by causing time zero dielectric breakdown. After annealing the wafers at temperatures above 1100 °C, the gate oxide integrity is clearly improved. We show by theoretical estimation, light-scattering tomography and transmission electron microscopy studies that the vacancy agglomerates can be filled with silicon oxide by internal oxidation. This is brought about by diffusion of interstitial oxygen to the voids, which can be regarded as internal surfaces. In this way they become less detrimental for thin gate oxides, because now they consist of silicon oxide itself. However, they are still present in an octahedral-like geometry and can be observed by Brewster angle infrared light-scattering tomography.
Photochemical and thermal effects in laser irradiated fullerite: From periodic exfoliation to cone formation
Authors: Milani P. , Bottani C. E. , Parisini A. , Banfi G. P.
Published: July 2002

We report a characterization of fullerite surface modification by cumulative laser irradiation. We show that the nano- and mesostructure of the transformed material are related and that they depend on the laser wavelength and fluence. Irradiating the sample at 1064 nm we observe periodic exfoliation of the transformed surface which is composed, on a nanometer scale, of a network of graphitic elongated nanoparticles. Under UV irradiation, the nanostructure is characterized by tangled graphene layers and cone formation is observed on a mesoscopic scale. Our observations show that different destabilization mechanisms of C60 produce coalescence pathways towards different nanostructures and mesoscopic morphologies.
Modal and threshold analysis of dielectric-apertured vertical cavity surface emitting lasers
Authors: Chang K. Y. , Woodhead J. , Robson P. N.
Published: July 2002

The resonant wavelengths and mode radii of the dominant and certain higher order TEMmp modes supported by an oxide apertured vertical cavity surface emitting lasers are determined using a scalar variational formula. The reflectivity of the Bragg mirrors and the photon lifetime are calculated for each mode and both are found to decrease with decreasing oxide aperture diameter and increasing mode number. The aperture diameter, thickness, and axial position in the cavity, together with the refractive index contrast ratio used in the Bragg mirrors, are shown to be important in controlling the suppression of higher order modes.
Improvement of short pulse operation of AlGaAs quantum-well lasers by temperature increase
Authors: Khrushchev I. Y. , White I. H. , Penty R. V.
Published: July 2002

A theoretical model has been formulated using lumped rate equations to analyze the temperature dependence of the Q-switched (i.e., saturable absorber operated) and gain-switched operation of a quantum-well laser. The results are found to agree with experimental results obtained from AlGaAs quantum-well devices, and show that improvement in the pulse energy in Q-switched and gain-switched lasers can be achieved by optimizing the operating temperature above room temperature. With increasing temperature, the pulse energy increases due to the pulses broadening while the peak power remains approximately constant. The effect is mainly attributed to the decrease of the gain with temperature.
Long term stability of a poled side-chain nonlinear optical polymer
Authors: Man Hong-Tai , Yoon Hyun Nam
Published: July 2002

A side-chain nonlinear optical polymer consisting of copolymers of 4-methylamino-4′-nitrostilbene and methacrylate was poled and shown to be orientationally stable for almost 8 yrs. At approximately 110 °C below its glass transition, its electrooptic coefficient was reduced by less than 25% of its initial value. In addition, adding an annealing step during the poling process further improved its orientational stability. These behaviors are consistent with existing empirical models describing poling relaxation of nonlinear optical polymers, and demonstrate that with appropriate molecular design, they can become viable nonlinear optical materials for commercial devices.
Finite thickness and semi-infinite photothermal radiometric models for the characterization of semiconductors
Authors: Karmiotis Y. , Nestoros M. , Christofides C.
Published: July 2002

A comparative computational study of the finite thickness and semi-infinite photothermal radiometric model is carried out for silicon, germanium, and gallium arsenide. The sensitivity of the photothermal radiometric finite thickness model towards the existence of very thin amorphous layers on crystalline substrates is also explored. This study can be used as an important guide for experimentalists.
Acoustic waves generated by a line source in a viscoelastic anisotropic medium
Authors: Audoin B. , Guilbaud S.
Published: July 2002

The acoustic signature provided by laser-generated ultrasound in polymer matrix composites is difficult to interpret on account of the dispersive nature of these materials. In order to simulate such wave forms, a double numerical inverse transform is used to calculate the surface displacement generated by a line impact. This calculation method is preferred due to the frequency dependence connected with the viscoelastic rheology. The focusing effects that anisotropy gives rise to are represented. In addition, the spreading of the signals issued from absorption is correlated with the anisotropic changes of the slowness versus frequency. The predicted displacements are in good agreement with the result of experiments performed with a composite plate.
Improved N-layer materials for high-Tc superconductor/normal-metal/superconductor junctions and superconducting quantum interference device sensors
Authors: Zhou Ji Ping , McDevitt John T. , Jia Q. X.
Published: July 2002

In order to solve some of the formidable problems related to producing reliable and reproducible cuprate superconductor/normal-metal/superconductor (SNS) junctions, new N-layer compounds from the family of R1−xCaxBa2−yLayCu3−zMzO7−δ (R=Y, Gd and Pr; M=Co, Ni and Zn; 0⩽x⩽0.4; 0⩽y⩽0.4; 0⩽z⩽0.4) have been synthesized and their properties characterized. Thus, a crystal engineering approach has been adopted in an effort to generate reliable materials for use in high Tc superconducting devices. Careful analyses of the various prepared phases reveal optimum substitution levels for selected compositions where the N-layer compounds exhibit structures compatible with common superconductor electrode materials. The new compounds have been used for demonstration purposes as the N-layer material for the construction of ramp-edge-geometry SNS junctions and superconducting quantum interference device sensors.
Effect of many weak side modes on relative intensity noise of distributed feedback semiconductor lasers
Authors: Peral Eva , Marshall William K. , Provenzano Dan , Yariv Amnon
Published: July 2002

An increase of the relative intensity noise of nearly single-mode distributed feedback lasers with respect to that predicted by single-mode theory after propagation in dispersive fiber at frequencies up to 5 Ghz has been measured. A simplified multimode theory is presented which explains the increase in noise.
Comparison of morphology of CdTe/CdMnTe interfaces in heterostructures grown by molecular beam epitaxy in a standard and atomic layer modes
Authors: Godlewski M. , Wojtowicz T. , Karczewski G. , Kossut J. , Bergman J. P. , Monemar B.
Published: July 2002

Photoluminescence studies of CdTe/CdMnTe heterostructures grown either by the atomic layer epitaxy or by a standard molecular beam epitaxy are presented. Morphology of CdTe/CdMnTe interfaces is compared for heterostructures grown by these two methods. The inter-island exciton migration, reported until recently only for high quality GaAs/AlGaAs structures, is observed in our structures with the quantum well grown by the atomic layer epitaxy. This indicates that relatively large and flat quantum well islands with a width differing by one monolayer exist in these samples. The present study, thus, demonstrates an improved quality of interfaces in structures grown by the atomic layer epitaxy.
Effect of cross-type bias in a two-dimensional array of short Josephson junctions
Authors: Filatrella G. , Pedersen N. F. , Wiesenfeld K.
Published: July 2002

We investigate numerically the effect of cross-type bias on two-dimensional arrays of short Josephson junctions. We have demonstrated that, for the simplest circuit, this type of bias is able to phase lock the junctions yielding a substantial improvement over ordinary biasing schemes.
All-optical wavelength switching in a semiconductor laser using self-seeding and external injection-seeding
Authors: Yam S. P. , Shu C.
Published: July 2002

We developed an approach for efficient optical switching by employing the mechanism of gain competition between two different wavelengths. The lasing wavelengths are obtained by self-seeding and external injection-seeding of the same gain-switched Fabry–Pérot laser diode. A direct comparison shows that the latter yields a faster switching response owing to the injection of continuous oscillations. Optical switching has been demonstrated over a 20 nm tuning range with an injection power as small as 10 μW. An operating bandwidth in the tens of MHz frequency range can be expected using the switching scheme.
Formation of silicon nitride layers by nitrogen ion irradiation of silicon biased to a high voltage in an electron cyclotron resonance microwave plasma
Authors: Ensinger W. , Volz K. , Schrag G. , Stritzker B. , Rauschenbach B.
Published: July 2002

Silicon was pulse biased to −50 kV in a nitrogen plasma generated by microwave excitation in electron cyclotron resonance mode. Nitrogen ions from the plasma were accelerated in the electrical field and implanted into the silicon. Cross-section transmission electron microscopy showed that the resulting surface layer was amorphous. Tempering at 1500 K led to the formation of a 25 nm thick continuous crystalline film of α-Si3N4 buried under a 50 nm thick amorphous surface zone.
Microstructural difference between platinum and silver trapped in hydrogen induced cavities in silicon
Authors: Kinomura A. , Williams J. S. , Wong-Leung J. , Petravic M.
Published: July 2002

The gettering of implanted Pt and Ag to hydrogen-induced cavities in Si has been compared for doses from 1×1013 to 1×1015 cm−2. After annealing at 850 °C for 1 h, almost 100% of both implanted metals were relocated to the cavity band for doses less than 1×1014 cm−2. At higher doses, large differences were observed in the gettering behaviour of Pt and Ag, where the amount of Pt was saturated at close to a monolayer coverage of cavity walls, whereas the Ag accumulation at cavities continually increased with dose. Cross-sectional transmission electron microscopy revealed strong differences in the ability of Pt and Ag to form a bulk phase at the cavities. The results indicate that stable silicide formation at the near-surface and trapping of Ag to implantation damage are the main processes which limit gettering at the higher doses.
Magnetization curves and hysteretic losses in superconducting films with edge barrier
Authors: Maksimov I. L. , Elistratov A. A.
Published: July 2002

The influence of both bulk and edge pinning on the response of a thin-film superconductor to an oscillating magnetic field is considered. The magnetic-flux-defreezing field and the flux-exit field are defined. The hysteresis and magnetization curves of a sample are constructed for the entire cycle of the magnetic field. From this, we obtain the dependence of the hysteresis losses on the field amplitude.
Arsenic incorporation in HgCdTe grown by molecular beam epitaxy
Authors: Wijewarnasuriya P. S. , Sivananthan S.
Published: July 2002

We report the results of in situ arsenic doping in HgCdTe layers grown by molecular beam epitaxy (MBE). Arsenic incorporation was carried out by two mechanisms called conventional doping and planar doping. The obtained results indicate that for both mechanisms, after Hg anneal, arsenic was successfully incorporated as an acceptor during the MBE growth. Secondary ion mass spectrometry and Hall-effect measurements before and after Hg annealing were used to characterize arsenic activity in the grown layers. Close to 100% acceptor doping efficiency with arsenic has been obtained on these MBE grown layers up to total arsenic concentrations of approximately 2×1018 cm−3, which is more than sufficient for a wide range of infrared devices. At much higher total arsenic concentrations, electrical activity falls off drastically as the doping level saturates.
Preservation of atomic flatness at SiO2/Si(111) interfaces during thermal oxidation in a furnace
Authors: Miyata Noriyuki , Watanabe Heiji , Ichikawa Masakazu
Published: July 2002

SiO 2 / Si (111) interfaces formed by a furnace oxidation are studied by a scanning reflection electron microscopy (SREM). SREM observation indicates that the initial atomic steps on a Si(111) surface are preserved at the SiO2/Si interface and the interfacial steps do not move laterally even after 48-nm-thick oxidation. A profile analysis of reflection high-energy electron diffraction shows that the SiO2/Si interface consists of islands which have a diameter of about 5 nm and monolayer depth. Our results indicate that the layer-by-layer oxidation caused by two-dimensional island nucleation proceeds under furnace oxidation.
Spectral shifts associated with dark line defects in degraded II-VI laser diodes
Authors: Chao L.-L. , Cargill G. S. , Marshall T. , Snoeks E. , Petruzzello J. , Pashley M.
Published: July 2002

Spectral shifts associated with 〈100〉 dark line defects of degraded II-VI laser diodes based on ZnCdSe/ZnSSe/MgZnSSe separate confinement heterostructures have been studied by spatially resolved cathodoluminescence at room temperature. Dark line defects were induced by electron-beam bombardment. Peak shifts as large as 2 nm were observed towards the blue or the red depending on the local circumstances. Peak widths usually became narrower after degradation. Redshifts and blueshifts are explained in terms of strain relaxation and Cd out-diffusion associated locally with degradation, as well as the kinetic energy dependence of the degradation-related carrier capture cross section.
Hg
1−x
Cd
x
I
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/CdTe
heterostructures for nuclear radiation detectors: Effect of epitaxial growth on substrate properties
Authors: Sochinskii N. V. , Muñoz V. , Perez J. M. , Cárabe J. , Morales A.
Published: July 2002

We demonstrate the possibility to fabricate nuclear radiation detectors operating at room temperature from CdTe substrates affected by the vapor phase epitaxy (VPE) growth of Hg1−xCdxI2 layers. The VPE layers with the thickness 10–30 μm were grown using an α-HgI2 polycrystalline source at 220 °C and time in the range of 30–100 h. The as-grown heterostructures were chemically etched to remove the epilayers, and Au–CdTe–Au detectors were made. The substrates were characterized by synchrotron x-ray topography before and after the VPE growth, and the current–voltage (I–V) and spectroscopic measurements of the detectors were carried out. The effect of the VPE growth on the substrates and detectors has been studied and on the basis of this it has been possible to fabricate γ-ray detectors with Ohmic I–V characteristic and good spectral response.
Suppression of electron and hole leakage in 1.3 μm AlGaInAs/InP quantum well lasers using multiquantum barrier
Authors: Pan Jen-Wei , Chau Ken-Gi , Chyi Jen-Inn , Tu Yuan-Kuang , Liaw Jy-Wang
Published: July 2002

The slope efficiency and threshold current density of 1.3 μm AlGaInAs/InP lasers with AlInAs–AlGaInAs multiquantum barrier (MQB) are experimentally studied and compared with the conventional step-index separate confinement heterostructure (SCH) laser. With the MQBs at the guiding layers, the characteristic temperature can be improved as much as 10 K as compared with the conventional SCH laser. This is attributed to the suppression of electron and hole leakage currents.
Mid-infrared intersubband electroluminescence from a single-period GaAs/AlGaAs triple barrier structure
Authors: Li Y. B. , Cockburn J. W. , Skolnick M. S. , Duck J. P. , Birkett M. J. , Larkin I. A. , Grey R. , Hill G. , Hopkinson M.
Published: July 2002

This letter reports the observation of intersubband electroluminescence from a single-period resonant tunneling structure. Intersubband emission (λ≈8.4 μm), with a full width at half maximum of 7 meV, was observed from a GaAs/AlGaAs triple barrier structure with quantum well widths of 66 and 33 Å. The emission was coupled out of the sample by a metallic grating with a period of 5 μm deposited on the surface. The intensity of emission follows the resonance behavior in the I–V characteristics. As the temperature increases from 10 to 200 K, the emission intensity decreases monotonically by a factor of ∼2 and the emission energy shifts down slightly (ΔE≈2.7 meV). The temperature dependence of the emission energy is explained by a combination of thermal broadening of the electron distribution and the nonparabolicity of the conduction bands.
Field emission conduction mechanisms in chemical vapor deposited diamond and diamondlike carbon films
Authors: May Paul W. , Höhn Stefan , Wang Wang N. , Fox Neil A.
Published: July 2002

Field emission properties of undoped chemical vapor deposited diamond and diamondlike carbon films have been measured for a variety of different deposition conditions. The nature and appearance of the damage site after testing, together with the mathematical form of the observed current–voltage relations, are correlated with the conductivity of the film. This is consistent with a model for the overall current which is a combination of conduction mechanisms through the bulk of the film with Fowler–Nordheim tunneling.
Strongly enhanced soft x-ray emission at 8 nm from plasma on a neodymium-doped glass surface heated by femtosecond laser pulses
Authors: Nakano Hidetoshi , Nishikawa Tadashi , Uesugi Naoshi
Published: July 2002

We have demonstrated efficient soft x-ray generation from femtosecond laser plasma created on a neodymium-doped glass target. Nd ions doped in glass target enhanced soft x-ray emission near 8 nm without broadening the soft x-ray pulse duration when there is no prepulse. A weak prepulse caused strong enhancement in soft x-ray intensity at 8 nm. By introducing a prepulse at 50 ns before the main pulse, 1% energy conversion efficiency from laser pulse into soft x-ray at 8±0.5 nm was achieved by using a neodymium-doped glass target. This value is 1.2 times as high as that for Nd metal target case.
On the lack of influence of disorder in Cr3+-doped LiSr0.8Ca0.2AlF6
Authors: Holliday Keith , Russell D. L. , Nicholls J. F. H. , Henderson B. , Yamaga Mitsuo , Yosida Taturu
Published: July 2002

Optical and electron spin resonance spectroscopies have been used to investigate the thermal stability of lasers based on Cr3+:LiSr0.8Ca0.2AlF6, a material in which the onset of critically inhibiting nonradiative decay at temperatures below 300 K might be expected based on results from other Cr3+-activated disordered gain media. The influence of disorder on the Cr3+ environment is shown to be very small in LiSr0.8Ca0.2AlF6 so that the T24→A24 fluorescence transition is not broadened relative to that in LiSrAlF6 and the onset of significant nonradiative decay is also held above room temperature.
A piezoelectric pseudoshear multilayer actuator
Authors: Wang Qing-Ming , Cross L. E.
Published: July 2002

A type of high strain piezoelectric ceramic actuator, namely, pseudoshear multilayer actuator, is described. In this structure, a stack of prepoled rectangular piezoelectric transducer ceramic sheets are conductively bonded at alternate ends, while the bottom layer bonded on a fixed base. When driven, alternate layers elongate or shrink in the same direction through converse piezoelectric effect, which results in the actuator structure developing a strong shear motion about the face perpendicular to the bonding direction. Experimental results indicate that more than 50 μm displacement can be achieved from the top layer for an actuator consisting of 18 layers with dimensions of 25.57 mm×4.02 mm×0.51 mm (1×w×t). By reducing ceramic sheet thickness and using more layers, even large displacement can be obtained, and driving voltage can also be reduced while keeping the same field level. Nonlinear piezoelectric response under high driving field further enhances the displacement level.
Surface photovoltage analysis of copper in p-type silicon
Authors: Ramappa Deepak A. , Henley Worth B.
Published: July 2002

Surface photovoltage minority carrier lifetime/diffusion length analysis of copper-doped p-type silicon was performed. Minority carrier recombination behavior of the deep level induced by copper and its thermal stability in the temperature range of 25–300 °C was investigated. This defect is attributed to interstitial copper pairs in p-type silicon. Isochronal annealing to a temperature of 150 °C results in improvement in diffusion length. This change in recombination behavior is attributed to precipitation of copper. At temperatures higher than 150 °C, copper forms extended substitutional defects in silicon, which results in a decrease in diffusion length. Interstitial copper concentration is estimated using the change in recombination behavior with isochronal annealing. Since copper is known to precipitate rapidly during cooling from high temperatures, it is observed that less than 0.01% of the total copper dissolved in silicon occupies an interstitial position.
Self-stopping selective-oxidation process of AlAs
Authors: Yoshikawa Takashi , Saito Hideaki , Kosaka Hideo , Sugimoto Yoshimasa , Kasahara Kenichi
Published: July 2002

Self-stopping, selective oxidation of AlAs was demonstrated. Lateral oxidation was stopped where the thickness of AlAs was decreased from 30 to 15 nm because of the large stress arising from the layer boundary of the oxidized AlAs and the surrounding GaAs. The thickness could be varied without degrading the wafer quality by in situ selective growth using the masked molecular beam epitaxy method, which will be available to make oxidized vertical cavity surface emitting lasers uniformly and repeatedly.