bluuebunny/crossref_metadata_2025 huggingface dataset:
Chirp-controlled ultrafast optical nonlinearities in semiconductors
Authors: Kunde J. , Siegner U. , Arlt S. , Morier-Genoud F. , Keller U.
Published: July 2002

We experimentally demonstrate that the differential transmission (DT) response of bulk semiconductors excited well above the band edge can be manipulated by chirping of the broadband excitation and readout pulses. In particular, the maximum transmission change in spectrally integrated DT experiments can be modified on the 20 fs time scale. Spectrally resolved DT studies explain this chirp dependence. Depending on the sign of the chirp, positive or negative DT contributions at low or high photon energies are probed with varying efficiency around zero time delay. These results demonstrate that chirp can become an additional degree of freedom for the optimization of device performance in ultrafast all-optical switching.
High-resolution periodically poled structure in diazo-dye-substituted polymer film based on direct electron-beam writing technique
Authors: Sugihara Okihiro , Che Yanlong , Okamoto Naomichi , Fujimura Hisashi , Egami Chikara , Umegaki Shinsuke
Published: July 2002

A periodically poled pattern in diazo-dye-substituted nonlinear optical polymer film is fabricated by direct electron-beam (EB) writing. It is found that the second-order nonlinearity of corona-poled polymer thin film is erased after EB irradiation. Moreover, the exposed region can be easily removed by conventional wet development. A high-resolution periodically poled structure (i.e., χ(2) grating) with a period of 0.60 μm is demonstrated based on the direct EB writing technique.
Fullerene and nanotube formation in cool terrestrial “dusty plasmas”
Authors: Burden A. P. , Silva S. R. P.
Published: July 2002

The simultaneous generation of dust during the deposition of semiconducting thin films by radio frequency plasma enhanced chemical vapor deposition has so far been regarded as a troublesome by-product. However, we present results from recent microstructural investigations of carbonaceous dust particles from a methane precursor that demonstrate that the technique may be suited to generating fullerene molecules, nanotubes, and nanoparticles. Chemical analysis reveals that these particles contain few contaminant species, and we deduce that they nucleated in the plasma, with the carbon ions possibly self-arranging through the action of coulombic forces.
Self-consistent Green’s function approach to the analysis of dielectrically apertured vertical-cavity surface-emitting lasers
Authors: Klein B. , Register L. F. , Hess K. , Deppe D.G. , Deng Q.
Published: July 2002

Dielectrically apertured vertical-cavity surface-emitting lasers are modeled using a Green’s-function-based optical solver that allows calculation of the full-vector lasing modes and their threshold conditions. The laser is separated into subsystems consisting of a planar microcavity, a dielectric aperture, and an active gain medium. The exact Green’s function solution for a radiating point source in the planar microcavity is then used to construct an eigenvalue equation for the self-consistent lasing modes. The derived eigenvalue equation is numerically solved to evaluate threshold dependence on aperture and cavity design. Results show a low threshold for thin oxide apertures placed at field antinodes, as well as for tapered oxides with thin tapers placed at field nodes.
Fast, low insertion-loss optical switch using lithographically defined electromagnetic microactuators and polymeric passive alignment structures
Authors: Norwood R. A. , Holman J. , Shacklette L. W. , Emo S. , Tabatabaie N. , Guckel H.
Published: July 2002

A micro-optoelectromechanical switch that combines microactuator technology developed via the Lithographie Galvanformung Abformung process with lithographically defined polymeric alignment elements is described. The multimode optical switch achieves submillisecond switching times, low insertion loss (<1 dB), low cross talk (<70 dB), low voltage (3 V), and wavelength independence.
Hole-assisted Zener magnetotunneling in heterostructures
Authors: Cinelli Riccardo A. G. , Piazza Vincenzo , De Franceschi Silvano , Lazzarino Marco , Beltram Fabio , Sivco Deborah L. , Cho Alfred Y.
Published: July 2002

Electron transport at high electric fields is investigated in a periodic semiconductor heterostructure. We present the analysis of the magnetic-field dependence of resonant Zener tunneling from a valence-band subband to a conduction-band subband in a multiple-quantum-well heterostructure. It is shown that Zener tunneling can have a different physical origin in such structures with respect to bulk systems. The dominant role of holes trapped in the valence-band quantum wells in driving this process is demonstrated.
Application of linear elastic fracture mechanics on electric discharge breakdown in interconnects
Authors: Ouyang Hao , Lee Sanboh
Published: July 2002

Analog to the approach used in linear elastic fracture mechanics, the electric discharge breakdown in interconnects is analyzed. The electric field is solved using the conformal mapping technique. The direction of electric field at the upper slit surface is opposite to that at the lower surface. Similar to the Griffith fracture criterion, we propose that the critical power release rate for crack propagation is equal to the electric breakdown power required to create a unit area of microcrack. It is found that the power release rate increases with decreasing linewidth of interconnect.
Deformation of ferroelectric short-pitch helical liquid crystal by transverse electric field: Application for diffraction-based light modulator
Authors: Parfenov A.
Published: July 2002

The electro-optic effect in helical ferroelectric liquid crystal deformed by transverse electric field is exploited to realize a diffraction-based light modulator. Experiments show that a contrast ratio better than 100:1 is easily achievable for the short-pitch liquid crystal aligned homeotropically with oblique readout breaking the initial symmetrical geometry. The modulation obtains low polarization sensitivity for selected directions of the readout.
Time-resolved surface scattering imaging of organic liquids under femtosecond KrF laser pulse excitation
Authors: Hatanaka Koji , Itoh Tamitake , Asahi Tsuyoshi , Ichinose Nobuyuki , Kawanishi Shunichi , Sasuga Tsuneo , Fukumura Hiroshi , Masuhara Hiroshi
Published: July 2002

Time-resolved surface scattering imaging was performed for liquid benzyl chloride and liquid toluene under femtosecond KrF laser ablation conditions. No scattering image was obtained until 1 ns, while scattering started from 2 ns when the laser fluence exceeded 25 mJ/cm2, and its intensity increased with the passage of time. The higher the laser fluence was, the steeper the increasing slope was. The scattering is due to surface roughness, which is the initial stage of macroscopic morphological changes. Root-mean-square surface roughness was estimated from the scattering intensity by using frosted fused-silica plates as reference samples. The induced surface roughness increases to a few hundred nm in 10 ns.
Electron beam induced x-ray emission: An in situ probe for composition determination during molecular beam epitaxy growth
Authors: Pellegrino Joseph G. , Armstrong John , Lowney Jeremiah , DiCamillo Barbara , Woicik Joseph C.
Published: July 2002

An in situ, x-ray emission measurement technique is developed. This technique is demonstrated to measure composition at the monolayer level for the InGaAs/GaAs heterojunction system. This electron beam induced x-ray emission technique is a powerful method for in situ compositional analysis during molecular beam epitaxy (MBE) growth. Unlike the reflection high-energy electron diffraction (RHEED) method, this electron beam stimulated x-ray emission technique affords a new method for the real-time monitoring of the elemental composition while the sample is rotating during growth. The technique exhibits long term reproducibility, and in addition, compares reasonably well with RHEED. Well-characterized standards are required for quantitative analysis of the composition, and knowledge about the electron sampling trajectories is required for accurate elemental analysis at the monolayer level.
Stimulated emission characteristics of InGaN/GaN multiple quantum wells: Excitation length and excitation density dependence
Authors: Schmidt T. J. , Bidnyk S. , Cho Yong-Hoon , Fischer A. J. , Song J. J. , Keller S. , Mishra U. K. , DenBaars S. P.
Published: July 2002

Optically pumped stimulated emission (SE) from InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition has been systematically studied as a function of excitation length (Lexc). Two distinct SE peaks were observed from these structures: one that originates at 425 nm at 10 K (430 nm at 300 K) and another that originates at 434 nm at 10 K (438 nm at 300 K). The SE threshold for the high-energy peak was observed to always be lower than that of the low-energy peak, but the difference was found to decrease greatly with increasing Lexc. A detailed study of the emission intensity of these two SE peaks as a function of excitation density shows that the two peaks compete for gain in the MQW active region.
Si δ-layers embedded in GaAs
Authors: Holtz P. O. , Sernelius B. , Buyanov A. V. , Pozina G. , Radamson H. H. , Madsen L. D. , McCaffrey J. P. , Monemar B. , Thordson J. , Andersson T. G.
Published: July 2002

An ultrathin, 1–6 monolayers (MLs) thick, Si δ layer, is embedded in bulk GaAs. The normally observed self-assembling with resulting phase separation can be avoided until δ-layer thickness of 4 MLs, which opens the possibility to study two-dimensional (2D) properties of this III–V/IV heterostructure. Optical, electrical, transport, and structural characterization of the Si δ layer has been carried out. In luminescence, two novel emission bands are observed, which are blueshifted as the width of the Si δ layer is reduced, indicating pronounced 2D properties. The derived results on transition energies and electronic structure are compared with theoretical predictions obtained by a self-consistent approach.
Intensity-invariant subpicosecond absorption saturation in heavy-ion irradiated bulk GaAs
Authors: Stelmakh N. , Mangeney J. , Alexandrou A. , Portnoi E. L.
Published: July 2002

We demonstrate that bulk GaAs irradiated by heavy Au+ ions shows efficient saturable absorption with subpicosecond recovery time and without any relaxation rate saturation up to excitation densities as high as 1.6 mJ/cm2. A comparison with other types of ion irradiation shows that heavy-ion-irradiated GaAs is a very promising material for ultrafast optoelectronics and optical processing at high repetition rates.
Buried heterostructure InGaAsP/InP strain-compensated multiple quantum well laser with a native-oxidized InAlAs current blocking layer
Authors: Wang Zhi Jie , Chua Soo-Jin , Zhou Fan , Wang Wei , Wu Rong Han
Published: July 2002

An InAlAs native oxide is used to replace the p-n reverse-biased junction in a conventional buried heterostructure InP-based laser. This technique reduces the number of regrowth steps and eliminates leakage current under high-temperature operation. The InAlAs native oxide buried heterostructure (NOBH) laser with strain-compensated InGaAsP/InP multiple quantum well active layers has a threshold current of 5.6 mA, a slope efficiency of 0.23 mW/mA, and a linear power up to 22.5 mW with a HR-coated facet. It exhibits single transverse mode with lasing wavelength at 1.532 μm. A characteristic temperature (T0) of 50 K is obtained from the NOBH laser with a nonoptimized oxide layer width.
Structural characterization of thin GaN epilayers directly grown on on-axis 6H–SiC(0001) by plasma-assisted molecular beam epitaxy
Authors: Yang B. , Trampert A. , Jenichen B. , Brandt O. , Ploog K. H.
Published: July 2002

The structural properties of a series of thin (0.2–0.6 μm) GaN epilayers directly grown on 6H–SiC(0001) by plasma-assisted molecular beam epitaxy are studied. X-ray reciprocal space maps of the GaN(0002) reflection reveal negligible inhomogeneous strain within the layer but a comparatively large orientational spread of the GaN c axis. X-ray rocking curve measurements show, however, that this mosaicity steadily decreases with film thickness. In fact, the density of threading defects detected by transmission electron microscopy is found to decrease drastically with the distance away from the GaN/SiC interface, finally reaching a value of less than 5×109 cm−2 at a layer thickness of 0.5 μm. The formation mechanisms of the threading dislocations in the GaN films are discussed in consideration of the specific GaN/SiC interface structure.
Investigation of oval defects in InGaAs/GaAs strained-layer heterostructures using cathodoluminescence and wavelength dispersive spectroscopy
Authors: Russell-Harriott J. J. , Zou J. , Moon A. R. , Cockayne D. J. H. , Usher B. F.
Published: July 2002

Oval defects in In0.04Ga0.96As/GaAs strained-layer heterostructures have been investigated using cathodoluminescence (CL) and wavelength dispersive x-ray spectroscopy (WDS). WDS studies showed that the particulates seen at the center of oval defects are indium rich and gallium depleted. A luminescent halo was seen around the indium rich particulates in the CL mode. When the halo was studied further, it was shown that the peak obtained from CL spectroscopy due to the luminescent halo shifts to lower wavelengths as the beam is moved from the center of the oval defect to the edge of the halo region, indicating a decreasing gradient in indium concentration.
Magneto-optical Kerr effect and optical properties of amorphous Co1−xSix (0.59⩽×⩽0.77) alloy films
Authors: Cai J. H. , Yang W. , Zhou T. J. , Gu G. , Du Y. W.
Published: July 2002

The Kerr spectra and optical constants of amorphous Co1−xSix (0.59⩽×⩽0.77) alloy films were measured in the spectral range 1.6–3.5 eV. It was found that there is rather considerable Kerr rotation near the high-energy side of 3.5 eV for the films (0.67⩽×⩽0.75), and there is a maximum value of −0.35°, which is comparable with that of pure Co, at x=0.75. The considerable Kerr rotation was ascribed to the following two causes: (i) the finite, but nonzero, nondiagonal element of dielectric function; (ii) the large optical constant effect due to the appropriate diagonal element of dielectric function. These changes of dielectric function originated from the metal-to-semiconductor transition controlled by Si concentration. There may be potential magneto-optical application in blue light range for such kinds of material.
Possible control method for single-electron tunneling based on environmental-impedance modulation
Authors: Wakaya Fujio , Iwabuchi Shuichi , Higurashi Hitoshi , Nagaoka Yosuke , Gamo Kenji
Published: July 2002

A device that consists of a double tunnel junction and an environmental impedance is considered. The numerical results obtained show that the number of the island charge and the net current of the single-electron-tunneling (SET) device can be controlled by changing the resistive environmental impedance. This suggests a control method for SET devices.
Unipolar complementary circuits using double electron layer tunneling transistors
Authors: Moon J. S. , Simmons J. A. , Blount M. A. , Reno J. L. , Hafich M. J.
Published: July 2002

We demonstrate unipolar complementary circuits consisting of a pair of resonant tunneling transistors based on the gate control of two-dimensional–two-dimensional interlayer tunneling, where a single transistor—in addition to exhibiting a well-defined negative-differential resistance—can be operated with either positive or negative transconductance. Details of the device operation are analyzed in terms of the quantum capacitance effect and bandbending in a double quantum well structure, and show good agreement with experiment. Application of resonant tunneling complementary logic is discussed by demonstrating complementary static random access memory using two devices connected in series.
Implications of a model for instability during film growth for strained InGaAs and SiGe layers
Authors: Léonard François , Desai Rashmi C.
Published: July 2002

We analyze experiments on the morphology of strained InGaAs and SiGe layers using a nonequilibrium stability analysis. Stability diagrams for growing films as a function of the deposition rate, the temperature and the misfit are calculated and compared to experimental reports. We show that for InGaAs layers, the onset of surface roughening is due to an instability against simultaneous modulations of the surface profile and the composition. For SiGe, the onset of surface roughening cannot be described by an instability, but rather, is due to a nucleation mechanism.
Fabrication of nanomagnet arrays by shadow deposition on self-organized semiconductor substrates
Authors: Teichert C. , Barthel J. , Oepen H. P. , Kirschner J.
Published: July 2002

It is demonstrated how large-scale arrays of nanomagnets can be efficiently fabricated by shadow deposition onto faceted surfaces of self-organized Si1−xGex films. By pulsed laser deposition of Co in a grazing incidence geometry, we succeeded to cover just one selected type of facets resulting in isolated Co patches with an areal density of about 0.25×1012/in.2. These uniformly oriented nanomagnets have a parallelogram-shaped base with about 25 nm×35 nm edge lengths. Magneto-optic Kerr effect measurements reveal a clear in-plane anisotropy of the nanomagnets.
High-repetition-rate, high-average-power, mode-locked Ti:sapphire laser with an intracavity continuous-wave amplification scheme
Authors: Liu Zhenlin , Izumida Shinji , Ono Shingo , Ohtake Hideyuki , Sarukura Nobuhiko
Published: July 2002

We have demonstrated a high-average-power, mode-locked Ti:sapphire laser with an intracavity continuous-wave amplification scheme. The laser generated 150 fs pulses with 3.4 W average power at a repetition rate of 79 MHz. This simple amplification scheme can be applied for the power scaling of other lasers.
Electrical simulation of scanning capacitance microscopy imaging of the pn junction with semiconductor probe tips
Authors: O’Malley M. L. , Timp G. L. , Timp W. , Moccio S. V. , Garno J. P. , Kleiman R. N.
Published: July 2002

Scanning capacitance microscopy (SCM) enables the imaging of the two-dimensional carrier profiles of small transistors. Initial imaging utilized metal-coated probe tips but the limited resolution achievable with these tips due to their size led us to investigate micromachined silicon tips with a smaller tip diameter. Electrical simulations of a pn junction structure probed with semiconducting tips indicate that image improvements result from the semiconductor nature of the silicon tips as well as from the smaller tip size. The tip becomes active in the imaging process as the capacitance–voltage responses of the tip and sample interact to improve image contrast and decrease the Vbias dependence of the pn junction locations. SCM images of a 60 nm gate length n-metal–oxide–semiconductor device, obtained using a boron-doped silicon tip, demonstrate these effects.
Quantum constraints on technological superconductors
Authors: Thompson J. R. , Ossandon J. G. , Krusin-Elbaum L. , Song K. J. , Christen D. K. , Ullmann J. L.
Published: July 2002

Vortex pinning in textured Bi2Sr2CaCu2Ox/Ag superconducting tapes was enhanced by irradiation with 0.8 GeV protons, creating randomly oriented columnar defects. Measurements of the current density J versus time show that thermally-activated current decay was greatly decreased, compared with unirradiated tapes. However, temperature-independent quantum tunneling of vortices considerably limits J and its temporal stability, for a significant fraction of the finite-Jc region.
Graphite lattice synthesis catalyzed by chromium-containing crystallites
Authors: Okuyama Fumio , Hayashi Tatsuji , Fujimoto Yasutaka
Published: July 2002

The encapsulation of chromium-containing crystallites in carbon nanocages is shown to occur on glow-discharge anodes in the presence of an ac magnetic field. These encapsulants catalytically promote the synthesis of nanodimensional graphite lattices in their nearby free space as well as on their surface. The minimum unit of graphite crystals thus synthesized is “rail-like,” with a spacing somewhat larger than the (002) spacing of graphite.
Control of morphology changes in self-assembled Mn-based nanostructures overgrown with mismatched material
Authors: Bonanni A. , Seyringer H. , Sitter H. , Stifter D. , Hingerl K.
Published: July 2002

Reproducibility of size and shape for epitaxially grown self-assembling Mn-based nanostructures was achieved by tracing the formation process via reflectance difference spectroscopy. Pure Mn crystallites were at first fabricated on a CdTe(001) Te-terminated surface and, in a second stage, a variety of well-controlled strain-induced island morphologies was obtained with the deposition of semiconducting materials on the magnetic precursors.
Nonlinear optical response of Ge nanocrystals in a silica matrix
Authors: Dowd A. , Elliman R. G. , Samoc M. , Luther-Davies B.
Published: July 2002

Time-resolved degenerate-four-wave-mixing measurements were used to study the nonlinear optical response (intensity-dependent refractive index) of Ge nanocrystallites embedded in a silica matrix. Nanocrystals were fabricated by ion-implanting silica with 1.0 MeV Ge ions to fluences in the range from 0.6 to 3×1017 Ge cm−2, followed by annealing at 1100 °C for 60 min. For the highest fluence, this resulted in nanocrystals with a log-normal size distribution, having a geometric mean diameter of 3.0 nm and a dimensionless geometric standard deviation of 0.25. The intensity-dependent refractive index |n2| was measured at a wavelength of 800 nm and found to increase linearly with increasing Ge fluence. For the highest fluence, |n2| was determined to be in the range 2.7–6.9×10−13 cm−2 W−1, depending on the duration of the excitation pulse; values were consistently smaller for shorter pulse lengths. Relaxation of the nonlinear response was found to have two characteristic time constants, one <100 fs and the other ∼1 ps.
Intrinsic optical confinement and lasing in InAs–AlGaAs submonolayer superlattices
Authors: Ledentsov N. N. , Tsatsul’nikov A. F. , Egorov A. Yu. , Kop’ev P. S. , Kovsh A. R. , Maximov M. V. , Ustinov V. M. , Volovik B. V. , Zhukov A. E. , Alferov Zh. I. , Krestnikov I. L. , Bimberg D. , Hoffmann A.
Published: July 2002

We study the optical properties of structures composed of stacked InAs submonolayer insertions in an AlGaAs matrix grown on a GaAs(100) surface. The increased refractive index in the active region necessary for waveguiding is caused by the absorption peak due to excitons trapped by monolayer-height InAs islands. Despite a very low average InAs concentration, a thin AlGaAs buffer layer and an absorbing GaAs substrate photopumped lasing in the visible spectral range is already realized at low excitation density.
Threshold reduction in pierced microdisk lasers
Authors: Backes S. A. , Cleaver J. R. A. , Heberle A. P. , Baumberg J. J. , Köhler K.
Published: July 2002

GaAs microdisk lasers with holes pierced through the disk surface are investigated for their threshold characteristics. Disks are fabricated with either a single hole or two diametrically opposite holes at various distances from the disk outer edge. Even though the disk area is reduced by only 1%, we find that the lasing threshold for a disk with one hole is reduced by up to 50% compared to a disk with no hole. We attribute this reduction to the perturbation of nonlasing modes, which decreases the amplification of spontaneous emission in these modes and makes more carriers available to contribute to lasing.
Polarization self-modulated lasers with circular eigenstates
Authors: Vallet M. , Brunel M. , Bretenaker F. , Alouini M. , Le Floch A. , Agrawal G. P.
Published: July 2002

A polarization self-modulated laser made of a semiconductor laser with an external cavity containing a Faraday rotator is investigated theoretically and experimentally. It is shown that the Faraday rotator yields circularly polarized eigenstates for the laser. Stable optical pulses at a frequency equal to one half of the free spectral range are observed through a polarizer, independently of the Faraday rotator orientation. The pulses are generated through beating between the phase-locked lasing modes associated with the two circular eigenstates of the laser.
Disorder characterization by means of radiatively coupled quantum wells
Authors: Gurioli Massimo , Piantelli Silvia , Colocci Marcello , Franchi Secondo
Published: July 2002

We present an approach to the investigation of structural disorder in quantum wells (QWs) based on the reflectivity line shape analysis of radiatively coupled QWs. In the case of anti-Bragg structures, as a consequence of the condition of destructive interference, the reflectivity spectrum is indeed extremely sensitive to vertical disorder. We exploit the method in the case of GaAs/AlGaAs structures and we demonstrate the possibility of measuring differences in the excitonic transition energies of the two QWs as small as 10% of the inhomogeneous broadening.
Cell gap margin enlargement of in-plane switching mode liquid crystal displays using weak-anchoring effects
Authors: Yoneya Makoto , Iwasaki Kishirou , Tomioka Yasushi , Kondo Katsumi
Published: July 2002

A method to enlarge the allowable range of marginal variation of the cell gap to ensure uniform brightness of in-plane switching mode liquid crystal displays is proposed. The proposed method is based on enlargement of the effective cell gap using the extrapolation length that is generated with weak-anchoring effects at liquid crystal/alignment layer interfaces. The method is evaluated with simulations and experiments. The results support the effectiveness of the method.
Crystallographic and magnetic properties of intermetallic compound Nd3Co13B2
Authors: Chen Yi , Liu Q. L. , Liang J. K. , Chen X. L. , Shen B. G. , Huang F.
Published: July 2002

The crystal structure and magnetic properties of the intermediate compound Nd3Co13B2 have been investigated by x-ray diffraction and magnetic measurement. Nd3Co13B2 is a member of homologous series Rm+1Co5m+3B2 with m=2. It adopts the hexagonal La3Ni13B2-type structure with lattice parameters a=5.0722(4) Å and c=10.7840(5) Å. The Nd3Co13B2 compound is ferromagnetic with a Curie temperature of 420 K. Its saturation magnetic moment and anisotropy field are 20.8 μB/f.u. and 163 kOe at 1.5 K, respectively.
Development of a low-temperature GaN chemical vapor deposition process based on a single molecular source H2GaN3
Authors: McMurran Jeff , Kouvetakis J. , Smith David J.
Published: July 2002

We report the development of a simple and highly efficient chemical approach to growing GaN thin films between 150 and 700 °C using a single molecular source, H2GaN3. Uncommonly low-temperature growth of nanocrystalline GaN films with a wurtzite structure is readily achieved at 150–200 °C from the thermodynamically driven decomposition of the precursor via complete elimination of the stable and relatively benign H2 and N2 by-products. Highly oriented columnar growth of crystalline material is obtained on Si at 350–700 °C and heteroepitaxial growth on sapphire at 650 °C. Crucial advantages of this precursor include: significant vapor pressure which permits rapid mass transport at 22 °C; and the facile decomposition pathway of stoichiometric elimination of H2 and N2 over a wide temperature and pressure range which allows film growth at very low temperatures and pressures (10−4–10−8 Torr) with growth rates up to 80 nm per minute.
Domain wall mobility in ultrathin epitaxial Ag/Fe/Ag(001) films
Authors: Cowburn R. P. , Ferré J. , Gray S. J. , Bland J. A. C.
Published: July 2002

The dependence of domain wall velocity on applied field strength for an in-plane magnetized ultrathin epitaxial Ag/Fe/Ag(001) multilayer film has been measured using magneto-optics. Within the velocity range of 0–200 ms−1 we find a linear response, which is characteristic of viscous damping. We find a domain wall mobility value of 117±5 ms−1 Oe−1, which is comparable to that reported by other workers for high quality Fe whiskers. This shows that the Fe/Ag interfaces do not contribute substantially to the dynamic dissipation.
High efficient biexciton photoluminescence observed from single ZnCdSe quantum wells with continuous wave cold carrier generation
Authors: Wei Yanfeng , Huang Daming , Wang Xingjun , Yu Gencai , Zhu C. S. , Wang Xun
Published: July 2002

Biexciton photoluminescence was observed from single ZnCdSe quantum wells with excitation densities at least three orders of magnitudes lower than those reported in the literature. The very efficient biexciton photoluminescence is essentially due to the cold carrier generation under which the biexciton dissociation by hot carrier collision is greatly suppressed.
Silicon-based resonant-cavity-enchanced photodiode with a buried SiO2 reflector
Authors: Sinnis V. S. , Seto M. , ’t Hooft G. W. , Watabe Y. , Morrison A. P. , Hoekstra W. , de Boer W. B.
Published: July 2002

We report on a silicon-based resonant cavity photodiode with a buried silicon dioxide layer as the bottom reflector. The buried oxide is created by using a separation by implantation of oxygen technique. The device shows large Fabry–Pérot oscillations. Resonant peaks and antiresonant troughs are observed as a function of the wavelength, with a peak responsivity of about 50 mA/W at 650 and 709 nm. The leakage current density is 85 pA/mm2 at −5 V, and the average zero-bias capacitance is 12 pF/mm2. We also demonstrate that the buried oxide prevents carriers generated deep within the substrate from reaching the top contacts, thus removing any slow carrier diffusion tail from the impulse response.
Evolution of deep-level centers in p-type silicon following ion implantation at 85 K
Authors: Cho C. R. , Yarykin N. , Brown R. A. , Kononchuk O. , Rozgonyi G. A. , Zuhr R. A.
Published: July 2002

In situ deep-level transient spectroscopy measurements have been carried out on p-type silicon following MeV He, Si, and Ge ion implantation at 85 K. Deep levels corresponding to intrinsic and impurity-related point defects are only detected after annealing at temperatures above 200 K. In addition to divacancies, interstitial carbon, and a carbon–oxygen complex, the formation of another defect, denoted as K2, has been observed during annealing at 200–230 K in epitaxial wafers, and at 200–300 K in Czochralski grown material. The energy level of the K2 defect is located 0.36 eV above the valence band, which is very close to a previously observed level of the carbon–oxygen pair. The relative concentration of this defect is ∼10 times higher in samples implanted with Ge than in those implanted with He. Due to its formation temperature, equal concentration in epitaxial and Czochralski grown wafers, and absence in n-type samples, the K2 trap has been tentatively identified as a vacancy-related complex which probably contains boron.
Ballistic electron focusing by elliptic reflecting barriers
Authors: Heremans J. J. , von Molnár S. , Awschalom D. D. , Gossard A. C.
Published: July 2002

We investigate reflection of ballistic electrons off an elliptic barrier in a high quality AlGaAs/GaAs heterostructure. Electrons injected at one focal point of an ellipse are collected at the second focal point, or at the midpoint. Application of a magnetic field perpendicular to the plane of the ellipse modifies the focusing effects by distorting the electrons’ paths, resulting in a novel four-terminal negative magnetoresistance phenomenon. Several secondary features in the magnetoresistance are observed and are interpreted in the light of numerical path simulations.
Microscale lithography via channel stamping: Relationships between capillarity, channel filling, and debonding
Authors: Moran P. M. , Lange F. F.
Published: July 2002

A polymer or metallo-organic precursor solution may be transferred from the channels of a stamp to a substrate producing a micron or submicron scale pattern. The stamped polymer pattern is used as a mask for device fabrication. The stamped metallo-organic precursor solution is heat treated to produce a metal or ceramic pattern directly. Here we report conditions that optimize the filling of channels, the debonding of the solution from the channels during evaporation, and the transfer of the pattern to a substrate. We show that poor wetting can optimize these conditions.
Pump and probe measurement of intersubband relaxation time in short-wavelength intersubband transition
Authors: Asano Takashi , Noda Susumu , Tomoda Katsuhiro
Published: July 2002

Population relaxation dynamics of the short-wavelength (∼2.5 μm) intersubband transition (ISB-T) in narrow InGaAs/AlAs quantum wells is investigated. Femtosecond (∼100 fs) pump and probe measurement yields a relaxation time of ∼2.7 ps, which is as fast as those observed for 10–5 μm ISB-T (0.7–1.5 ps, respectively). The ISB relaxation time increases more rapidly than that predicted from the usual intersubband optical-phonon scattering model as the ISB-T energy increases. Our theoretical calculation, which takes into account the intrasubband energy relaxation process, agrees well with the experimental results. The intrasubband energy relaxation process is found to be important in the short-wavelength region.
Kinetic shape formation during Gd thin film and Si(100) solid phase reaction
Authors: Molnár G. L. , Petö G. , Vértesy Z. , Zsoldos E.
Published: July 2002

The initial stage of the solid phase reaction between gadolinium thin film and Si(100) substrate was investigated by x-ray diffraction and scanning electron microscopy. The interdiffusion was retarded by deliberate contamination of the Gd/Si interface to slow down the extremely rapid reaction. The surface of the reacted film showed pattern formation in separate spots. The fractal-like development of this rare-earth silicide indicates a kinetic-type process—modified by the structure of the Gd film and by the emerging stresses—rather than a previously proposed nucleation-controlled growth.
Multilayer thermionic cooler with a varying current density
Authors: Zhou R. , Dagel D. , Lo Y. H.
Published: July 2002

A multilayer structure for thermionic cooling is proposed. This structure uses semiconductor heterojunctions for barriers and a varying current density across the junctions. Compared with the conventional multijunction thermionic cooler with a uniform current density, the design can yield a significantly higher temperature gradient, thus cooling more effectively.
Controlled underdoping of cuprates using ultraviolet radiation
Authors: Schwaller P. , Berner S. , Greber T. , Osterwalder J. , Berger H.
Published: July 2002

A method for a controlled change of the doping level of high-temperature superconductors with ultraviolet radiation is presented. With photoemission it is shown that the exposure of Bi2Sr2CaCu2O8+δ samples to the light of a He gas-discharge lamp causes oxygen desorption. From measurements of the Fermi surface, it is found that the oxygen desorption causes a decrease of the doping level of the superconductors. From the desorption cross sections that strongly depend on the photon energy, two different oxygen desorption channels are inferred. This procedure for decreasing the doping level has the advantage that the crystallinity of the sample is not altered and that the doping level can be simultaneously measured by photoelectron spectroscopy.
SiGe/Si Mach–Zehnder interferometer modulator based on the plasma dispersion effect
Authors: Li Baojun , Jiang Zuimin , Zhang Xiangjiu , Wang Xun , Wan Jianjun , Li Guozheng , Liu Enke
Published: July 2002

A SiGe Mach–Zehnder interferometer modulator based on the plasma dispersion effect has been fabricated. A maximum modulation depth of 86% and a switching current of 40 mA with a π-phase-shift voltage of 0.9 V have been achieved at 1.3 μm wavelength. The device has a measured insertion loss of 2.5 dB and a response time of 238 ns.
Interfacet surface diffusion in selective area epitaxy of III–V semiconductors
Authors: Verschuren C. A. , Leys M. R. , Vonk H. , Wolter J. H.
Published: July 2002

In this letter, we discuss the interfacet diffusion of group-III species from {111} B facets to the (100) plane in planar selective area epitaxy. In general, this leads to enhanced vertical growth at the edges of the (100) surface. From such edge profiles, several groups have extracted adatom “diffusion lengths” of ∼1 μm. This is a factor of 100 larger than reported diffusion lengths obtained by reflective high energy electron diffraction, scanning tunneling microscopy, or growth-rate analysis. We show that these values are severely overestimated and that edge profiles only give information on the propagation velocity of macrosteps.
Lithium tantalate/lead zirconate titanate composite ultrasonic transducers
Authors: Chen Y. , Sayer M. , Zou L. , Jen C.-K.
Published: July 2002

Lithium tantalate (LiTaO3)/lead zirconate titanate (PZT) ceramic films of thickness about 50 μm have been deposited on stainless-steel substrates using a modified sol-gel process. LiTaO3 powders are dispersed in a PZT sol-gel matrix to form a 0–3 ceramic/ceramic composite. The dielectric, electric, and piezoelectric properties have been studied. Ultrasonic pulse-echo measurements using the composite films as piezoelectric ultrasonic transducers demonstrate a broadband frequency response and good signal-to-noise ratio up to a temperature of 368 °C.
Time-frequency spectroscopy of an InGaAs/InP quantum-well exciton Bragg reflector
Authors: Ogawa Kensuke , Matsui Yasuhiro
Published: July 2002

Ultrafast absorption saturation in an exciton Bragg reflector, consisting of InGaAs quantum wells embedded in InP/InGaAsP Bragg layers, is characterized by pump-induced transient reflectance spectroscopy at room temperature. Spectral modulation of the reflected probe pulses is caused by ultrafast absorption saturation of excitons in the quantum wells. The spectral modulation leads to an optical phase shift of 1.6 π. The exciton-induced phase shift is more than four times as large as that induced by free carriers in a Bragg reflector.
Epitaxial aluminum carbide formation in 6H–SiC by high-dose Al+ implantation
Authors: Stoemenos J. , Pécz B. , Heera V.
Published: July 2002

Aluminum carbide precipitates are formed after Al ion implantation with dose 3×1017 cm−2 at 500 °C into single crystalline 6H–SiC. The aluminum carbide (Al4C3) precipitates are in epitaxial relation with 6H–SiC matrix, having the following orientation relation, [0001]6H–SiC//[0001]Al4C3, and [112̄0]6H–SiC//[112̄0]Al4C3, as transmission electron microscopy reveals. The aluminum carbide appears around the maximum of the Al depth distribution. Silicon precipitates were also detected in the same zone.
Generation of pure, high-density metal-vapor plasma by capillary discharge
Authors: Kukhlevsky S. V. , Vér Cs. , Kaiser J. , Kozma L. , Palladino L. , Reale A. , Tomassetti G. , Flora F. , Giordano G.
Published: July 2002

Generation of pure, metal-vapor plasmas with peak densities above 1019 cm−3 is reported. The plasma production is based on the explosive ablation of electrode material in the capillary μs discharge. The plasma density is controlled by varying the discharge parameters. High purity and density were achieved by optimizing the electrode configuration, the capillary material, and dimensions.
Electronic structure of nickel silicide in subhalf-micron lines and blanket films: An x-ray absorption fine structures study at the Ni and Si L3,2 edge
Authors: Naftel S. J. , Coulthard I. , Sham T. K. , Xu D.-X. , Erickson L. , Das S. R.
Published: July 2002

We report a Ni and Si L3,2-edge x-ray absorption near edge structures (XANES) study of nickel–silicon interaction in submicron (0.15 and 0.2 μm) lines on a n-Si(100) wafer as well as a series of well characterized Ni–Si blanket films. XANES measurements recorded in both total electron yield and soft x-ray fluorescence yield indicate that under the selected silicidation conditions, the more desirable low resistivity phase, NiSi, is indeed the dominant phase in the subhalf-micron lines although the formation of this phase is less complete as the line becomes narrower and this is accompanied by a Ni rich surface.
Spatial modulation of the dielectric function using free carriers and/or coherent effects in quantum-well semiconductor microcavity
Authors: De Matos C. , Pugnet M. , L’Haridon H. , Le Corre A.
Published: July 2002

Results on picosecond degenerate four-wave mixing in semiconductor microcavity are presented. The device is made of GaInAs/GaInAsP multiple quantum wells enclosed in an asymmetric Fabry–Perot microcavity 80%–98%. For incident photon energies below the excitonic energy, the spatial modulation of the dielectric function can be generated by free carriers and/or coherent effects. We show that the last one can be significant; an input diffraction efficiency of 2% with only 1 μJ/cm2 pump fluence is achieved. This result demonstrates a new way to obtain ultrafast, sensitive, and low-dissipative devices.
In-plane alignment of noncentrosymmetric molecules by oblique-incidence molecular beam deposition
Authors: Müller Bert , Cai Chengzhi , Kündig Armin , Tao Ye , Bösch Martin , Jäger Matthias , Bosshard Christian , Günter Peter
Published: July 2002

The preferential orientation of noncentrosymmetric, organic molecules with intermolecular bonding is realized by means of oblique-incidence molecular beam deposition. The in-plane anisotropy in the optical properties of the thin films is shown by transmission spectra of ultraviolet light. Second-harmonic generation measurements demonstrate the preferential orientation of the molecules aligned in-plane. In addition, the dependence of the second-harmonic light intensity on the film thickness reveals the dominance of bulk effects with respect to surface contributions. Therefore, this molecular alignment technique is a promising method to produce stable thin films for applications in linear and nonlinear optics.
Plasma process-induced band-gap modifications of a strained SiGe heterostructure
Authors: Swain P. K. , Madapur S. , Misra D.
Published: July 2002

Exposure to plasma etching and subsequent annealing can relax the strain of coherently strained SiGe. This work investigates the change in valence-band discontinuity in plasma-exposed SiGe films due to strain relaxation by a capacitance–voltage (C–V) profiling technique using metal–oxide–semiconductor structures. Dry and wet etched samples annealed at 500, 600, 700, and 800 °C were investigated. Valence-band discontinuity ΔEV at the Si/SiGe interface reduced with annealing temperature and completely disappeared at higher temperature annealing. Dry etched samples demonstrated a faster relaxation mechanism as compared to their wet etched counterparts. The C–V method has turned out to be a simple, fast, and efficient approach to estimate any band-gap modifications in SiGe due to process-induced damage.
Raman characterization of SiNx deposition on undoped Al0.48In0.52As and n+ Ga0.47In0.53As layers for InP high electron mobility transistor applications
Authors: Boudart B. , Gaquière C. , Trassaert S. , Constant M. , Lorriaux A. , Lefebvre N.
Published: July 2002

Effects of SiNx deposition on undoped Al0.48In0.52As and n+ Ga0.47In0.53As bulk layers grown on InP substrate have been investigated using Raman spectroscopy. No significant effects induced from the dielectric deposition have been observed in the Al0.48In0.52As material, whatever the thickness and the temperature deposition used in the technological process. On the contrary, slight modifications of the Raman spectra have been noticed for n+ Ga0.47In0.53As samples passivated at 300 °C. The observed differences have been interpreted as a surface potential decrease of 0.15 V and correlated to electrical measurements made on InP-based high electron mobility transistors. In this case, an increase of the maximum drain current has been observed in agreement with the surface potential change deduced from Raman experiments.
Patterning of cubic and hexagonal GaN by Cl2/N2-based reactive ion etching
Authors: Fricke J. , Yang B. , Brandt O. , Ploog K.
Published: July 2002

Chlorine-based dry etching of hexagonal and cubic GaN epilayers grown by dc plasma-assisted molecular beam epitaxy is investigated using a conventional parallel electrode reactor. It is found that the addition of nitrogen results in a shallow maximum for etch rates at 37% N2 content in a low-pressure plasma and a monotonically decreasing etch rate in higher-pressure plasmas. Etching with a low-pressure plasma produces smooth surfaces and almost vertical sidewalls at sufficiently high etch rates.
Atomic ordering and temperature-dependent transient photoconductivity in Ga0.47In0.53As
Authors: Ahrenkiel S. P. , Johnston S. W. , Ahrenkiel R. K. , Arent D. J. , Hanna M. C. , Wanlass M. W.
Published: July 2002

Influences of CuPtB atomic ordering on transient photoconductivity in epitaxial Ga0.47In0.53As films grown by metal-organic chemical vapor deposition are examined. Low-injection lifetimes of several ms are measured in double-variant ordered samples at 77 K; these lifetimes decrease rapidly with temperatures above 180 K, giving a thermal activation energy for recombination of 0.19 eV. Single-variant ordered samples exhibit typical lifetimes of 30–60 μs, with no noticeable temperature dependence up to 300 K. Charge separation in double-variant samples may be driven by a type-II band alignment between ordered and disordered regions, or by an alternating internal electrical polarization between ordered variants. Recombination in both double- and single-variant samples may be influenced by inhibited transport across antiphase boundaries.
Direct observation of Marangoni convection-induced oscillation at silicon melt surface
Authors: Onuma Kazuo , Sumiji Masanobu , Nakamura Shin , Hibiya Taketoshi
Published: July 2002

Marangoni convection-induced oscillation at the molten silicon surface of a half-zone liquid column was directly observed using real-time moiré phase-shift interferometry. The oscillation frequency was analyzed by applying the Fourier transformation to the data of relative displacement versus time relationship of the melt surface. Several peaks of oscillation frequencies were observed at 0.5–5 Hz, being higher than the frequencies at 0.1–0.3 Hz observed in the previous studies by the temperature measurement using thermocouples and the x-ray flow visualization technique.
Role of surface defect states in visible luminescence from oxidized hydrogenated amorphous Si/hydrogenated amorphous Ge multilayers
Authors: Xu Jun , He ZhenHong , Chen Kunji , Huang Xinfan , Feng Duan , Han Hexiang , Wang Zhaoping , Li Guohua
Published: July 2002

Nanocrystalline Ge embedded in amorphous silicon dioxide matrix was fabricated by oxidizing hydrogenated amorphous Si/hydrogenated amorphous Ge (a-Si:H/a-Ge:H) multilayers. The structures before and after oxidation were systematically investigated. The orange-green light emission was observed at room temperature and the luminescence peak was located at 2.2 eV. The size dependence in the photoluminescence peak energy was not observed and the luminescence intensity was increased gradually with oxidation time. The origin for this visible light emission is discussed. In contrast to the simple quantum effect model, the surface defect states of nanocrystalline Ge are believed to play an important role in radiative recombination process.
Homeotropic liquid-crystal device with two metastable states
Authors: Chen Li-Yi , Chen Shu-Hsia
Published: July 2002

We report a homeotropic liquid-crystal device which has two metastable states when an electric field is applied. The behaviors of these two metastable states are similar to the bistable twist nematic device. We control this device electrically in the rising period to switch it from the homeotropic state toward either the twist or homogeneous state. It not only behaves as a conventional homeotropic cell but also provides another twist structure for further applications. The back-flow effect in the rising period plays an important role in the switching mechanism. The experimental results are described in this letter.