bluuebunny/crossref_metadata_2025 huggingface dataset:
Near-surface electronic structure on InAs(100) modified with self-assembled monolayers of alkanethiols
Authors: Tanzer T. A. , Bohn P. W. , Roshchin I. V. , Greene L. H. , Klem J. F.
Published: July 2002

Surface chemical modification is used to eliminate the problem of high surface recombination velocity and control surface band bending on InAs(100). Alkanethiols, RSH; R=CH3(CH2)n, both neat and in ethanolic solutions, are used to passivate this surface against oxidation, as characterized by Raman scattering and x-ray photoelectron spectroscopy of the adsorbate-covered and bare surfaces. The magnitude of the interfacial band bending is obtained by analysis of Raman scattering from the unscreened longitudinal optical phonon, which arises from the near-surface charge accumulation region. Removing the native oxide with a Br2:CH3OH chemomechanical etch reduces the surface band bending, but atmospheric oxidation increases band bending to its original level over several hours. In contrast, alkanethiol passivation of InAs(100) prevents band bending for periods of up to several weeks.
Structural relationship of polycrystalline cobalt silicide lines to (001) silicon substrate
Authors: Alberti A. , La Via F. , Spinella C. , Rimini E.
Published: July 2002

A local investigation of the structural properties of polycrystalline CoSi2 strips onto (001) Si wafers has been performed by transmission electron microscopy. CoSi2 crystal grains exhibit different behavior depending upon their position within the line. Grains close to the center of the strip are randomly oriented, while most of the grains at the edge of the strip grow epitaxially, obeying three different epitaxial relationships. Some of these grains maintain the substrate orientation with the presence of twin defects. High-resolution analysis demonstrates the presence of misfit dislocations at the CoSi2/Si interface, which accommodates the lattice mismatch.
Properties of two-dimensional electron gas containing self-organized quantum antidots
Authors: Vasilyev Yu. , Suchalkin S. , Zundel M. , Heisenberg D. , Eberl K. , von Klitzing K.
Published: July 2002

A nonuniform two-dimensional electron gas in a heterojunction with inserted self-organized electrically inactive dots (acting as antidots) has been fabricated by molecular-beam epitaxy of AlGaAs/AlInAs/GaAs layer sequences. Transport measurements give the ratio of the transport mobility to the quantum mobility less than four, which suggests that the dominant scattering at low magnetic fields is the short-range scattering from the lateral potential of the antidots. Far-infrared cyclotron resonance (CR) spectra show an absorption mode as narrow as 0.5 cm−1 at high magnetic fields associated with the high-mobility electron gas formed between the antidot islands and confined in the lateral directions. The confinement energy of 14 cm−1 is derived from the CR spectra.
Low-temperature homoepitaxial growth on high-miscut Si(111) mediated by thin overlayers of Pb
Authors: Wei Li-Chung , Su Ching-shen
Published: July 2002

Homoepitaxial growth of Si on high-angle miscut (3.0°) Si(111) substrates through an overlayer of Pb is shown to occur at 280 °C. In this work, films can be deposited up to 2000 Å in thickness with no indication that this is an upper limit for high-quality epitaxy. Samples were analyzed using Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy. It is shown that a distinct range of Pb coverage (0.8–1.0 monolayer) results in the best quality growth, with no measurable amount of Pb trapped at either the interface or within the grown films.
Limits of residual stress in Cr films sputter deposited on biased substrates
Authors: Misra A. , Nastasi M.
Published: July 2002

Stress evolution in thin Cr films on Si substrates is studied as a function of substrate bias. With increasing bias voltage, the tensile stress is observed to increase to a maximum, transition to compressive stress that also reaches a maximum. We relate the tensile stress maximum to the maximum in attractive interatomic forces between the coalescing islands, and the compressive stress maximum to the saturation in Frenkel defect concentration, with smaller contribution from entrapped Ar. We show that the maxima in both tensile and compressive residual stress correspond to the film yield strength. Compressive yield strength is higher as compared to tensile due to hardening from point defects.
Observation of harmonic current oscillations on partially oxidized Si(111) surfaces by scanning tunneling microscopy
Authors: Xie Fangqing , von Blanckenhagen Peter
Published: July 2002

Harmonic oscillations of the tunneling current on partially oxidized Si(111) and on Au clusters deposited on these surfaces were observed by scanning tunneling spectroscopy (STS). The frequencies of the current oscillations are independent of the bias voltage. They are the product of a basic frequency (29.99±0.01 Hz) times an integer N. It is assumed that the basic frequency is the reciprocal of the capture time of an electron in an individual trap, that N is related to the number of traps taking part in the charge-discharge processes during STS, and that the electron traps in the small area participating in the local STS are functionally correlated by some unknown mechanism which reduces the electron capture time proportional to 1/N.
Morphology and microstructure of BaTiO3/SrTiO3 superlattices grown on SrTiO3 by laser molecular-beam epitaxy
Authors: Wang N. , Lu H. B. , Chen W. Z. , Zhao T. , Chen F. , Peng H. Y. , Lee S. T. , Yang G. Z.
Published: July 2002

The morphology and microstructure of BaTiO3/SrTiO3 (BTO/STO) superlattices grown epitaxially on STO (001) substrates by a computer-controlled laser molecular-beam epitaxy deposition system have been characterized by means of atomic force microscopy and high-resolution transmission electron microscopy (HRTEM). It is found that the HRTEM images taken along the [120] direction of BTO and STO show the maximal contrast difference. It is, therefore, observed that the superlattices consist of a highly oriented and single-crystalline multilayered structure. As identified by HRTEM, the number of unit cells in each BTO or STO layer matches very well with that obtained from reflection high-energy electron diffraction oscillations. The surfaces and interfaces of the superlattices are atomically smooth. In the superlattices, the ratio between the c axis of BTO and STO is about 4% larger than that measured from BTO or STO bulk crystals.
Ohmic contacts to p-type ZnSe using a ZnSe/BeTe superlattice
Authors: Vigué F. , Brunet P. , Lorenzini P. , Tournié E. , Faurie J. P.
Published: July 2002

Various configurations of pseudograded BeTe/ZnSe superlattices have been investigated to form a nonalloyed contact onto nitrogen-doped p-type ZnSe layers. Best results were obtained by using a fully N-doped superlattice with a 20-ML-thick pseudoperiod and with the thickness of individual layers in the pseudoperiod varying by 1 ML steps. A specific contact resistance of 6×10−2 Ω cm2 has been measured for a ZnSe p-type doping level of 2×1017 cm−3. Truly perfect ohmic contact is obtained.
X-ray reflectivity of ultrathin twist-bonded silicon wafers
Authors: Eymery J. , Fournel F. , Rieutord F. , Buttard D. , Moriceau H. , Aspar B.
Published: July 2002

Ultrathin Si (001) layers (<15 nm) are hydrophobic bonded to a full 4 in. Si (001) wafer. The interface quality and surface roughness, checked by specular x-ray reflectivity, are very good. This technique, well suited to measure the homogeneity thickness, shows that the samples have very small thickness fluctuations, and no extended defects. Quantitative analysis proves that the interfacial layer resulting from the bonding is very thin (about 8 Å). Its atomic density is significantly different from bulk Si only for large bonding twist angles (>5°).
Dithered-edge sampling of terahertz pulses
Authors: Bromage Jake , Walmsley Ian A. , Stroud C. R.
Published: July 2002

We introduce a technique for ultrawideband measurement of terahertz pulses called dithered-edge sampling (DES). The technique makes use of a photoconductive receiver, but the detection bandwidth is much wider than that of the receiver alone. The key to increasing the bandwidth is the addition of an ultrafast optically triggered attenuator that chops the terahertz pulse before its detection. The bandwidth is limited only by the duration of the optical pulse used to trigger the attenuator. We use a combination of derivative dither and an integrating receiver to recover the terahertz field directly from the measured signal. When used alone, the slow receiver blurs the measured terahertz pulse width to 1.3 ps. However, the increased time resolution of the DES system (triggered attenuator plus receiver) allows one to measure source-limited terahertz pulse widths (400 fs in this case).
High-quality fully relaxed In0.65Ga0.35As layers grown on InP using the paramorphic approach
Authors: Damlencourt J. F. , Leclercq J. L. , Gendry M. , Regreny P. , Hollinger G.
Published: July 2002

Thin and thick fully relaxed In0.65Ga0.35As layers have been grown on InP substrates (0.81% misfit), with high structural and high optoelectronic quality at an operating wavelength of ∼2.0 μm. Full relaxation is achieved, using the paramorphic approach, by growing the In0.65Ga0.35As layers lattice matched to an InAs0.25P0.75 seed membrane of predetermined lattice parameter. The InAs0.25P0.75 layer was originally grown pseudomorphically strained on the InP substrate before being separated and elastically relaxed using surface micromachining.
Activation energy for fluorine transport in amorphous silicon
Authors: Nash G. R. , Schiz J. F. W. , Marsh C. D. , Ashburn P. , Booker G. R.
Published: July 2002

The transport of ion-implanted F in amorphous Si is studied using secondary ion mass spectroscopy and transmission electron microscopy. Significant redistribution of F is observed at temperatures in the range 600–700 °C. The measured F depth profiles are modeled using a simple Gaussian solution to the diffusion equation, and the diffusion coefficient is deduced at each temperature. An activation energy of 2.2 eV±0.4 eV for F transport is extracted from an Arrhenius plot of the diffusion coefficients. It is shown that the F transport is influenced by implantation-induced defects.
Correlation of end-of-range damage evolution and transient enhanced diffusion of boron in regrown silicon
Authors: Robertson L. S. , Law M. E. , Jones K. S. , Rubin L. M. , Jackson J. , Chi P. , Simons D. S.
Published: July 2002

Amorphization of a n-type Czochralski wafer was achieved using a series of Si+ implants of 30 and 120 keV, each at a dose of 1×1015 cm2. The Si+ implants produced a 2400 Å deep amorphous layer, which was then implanted with 4 keV 1×1014/cm2 B+. Postimplantation anneals were performed in a tube furnace at 750 °C, for times ranging from 15 min to 6 h. Secondary ion mass spectrometry was used to monitor the dopant diffusion after annealing. Transmission electron microscopy (TEM) was used to study the EOR defect evolution. Upon annealing, the boron peak showed no clustering, and TED was observed in the entire boron profile. TEM results show that both {311} defects and dislocation loops were present in the EOR damage region. The majority of the {311} defects dissolved in the interval between 15 min and 2 h. Results indicate that {311} defects release interstitials during the time that boron exhibits TED. These results show that there is a strong correlation between {311} dissolution in the EOR and TED in the regrown silicon layer. Quantitative TEM of dislocation loop growth and {311} dissolution indicates that in addition to {311} defects, submicroscopic sources of interstitials may also exist in the EOR which may contribute to TED.
Absolute measurement of penetration depth in a superconducting film by the two-coil technique
Authors: Wang R. F. , Zhao S. P. , Chen G. H. , Yang Q. S.
Published: July 2002

A two-coil mutual-inductance apparatus that is optimized to allow for the measurement of the absolute value of penetration depth λ in superconducting films is described. Nb films with thickness d ranging from 20 to 90 nm are used to illustrate the measurement. For a 70-nm-thick Nb film at 4.2 K, with d/λ∼0.6, the uncertainty in the measured λ is about ±2.3%. From the results on the Nb film series, we show that a satisfactory determination of the absolute value of λ is possible for these films with d/λ<0.95.
Microdischarges with plane cathodes
Authors: Biborosch Leopold D. , Bilwatsch Oliver , Ish-Shalom Shlomo , Dewald Eduard , Ernst Uwe , Frank Klaus
Published: July 2002

By reducing the dimensions of the electrodes to the submillimeter range, it is possible to operate dc gas discharges at pressures up to 760 Torr (argon). A plane geometry for the cathode, different from the well-known microhollow cathode discharge, was used in these experiments. For anode hole diameters smaller than 0.6 mm and pD (D diameter of the anode hole) larger than 9 Torr cm, the differential resistivity in the I–V characteristics is similar to the hollow cathode one. The emission in the visible range is distributed more homogeneously over the entire cathode surface. By using a end-on coupled configuration of hollow and plane cathode geometries, the discharge can be stabilized over the entire (pD) range between 1 and 23 Torr cm. The discharge is stable, for both the hollow–plane and hollow–hollow cathode configurations in aligned geometries.
Phase separation in InGaN multiple quantum wells annealed at high nitrogen pressures
Authors: Romano L. T. , McCluskey M. D. , Van de Walle C. G. , Northrup J. E. , Bour D. P. , Kneissl M. , Suski T. , Jun J.
Published: July 2002

Phase separation was found to occur in In0.33Ga0.67N/GaN multiple-quantum-well structures after annealing at 975 °C in a hydrostatic pressure of 5 kbar N2 for 4 h. X-ray diffraction (XRD) spectra of the as-grown samples showed superlattice peaks that were replaced by a broad, single-phase peak after annealing. Transmission electron microscopy (TEM) images of the annealed samples show In-rich precipitates and voids that are found only within the quantum-well region. Both TEM and XRD measurements indicated that the formation of voids and second phases were suppressed after annealing in a hydrostatic pressure of 15 kbar. In addition, optical absorption measurements on these samples showed no indication of a peak at 2.65 eV that was observed in previous annealing studies.
Mode switching in shear-strained and modulated photonic lattices by vertical-cavity surface-emitting laser arrays by means of injection locking
Authors: Fishman T. , Hardy A. , Kapon E.
Published: July 2002

Mode switching in shear-strained (i.e., laterally shifted) lattices of vertical cavity surface emitting laser arrays by means of injection locking is theoretically demonstrated. Switching between four- and six-lobed far-fields modes is examined near the critical value of lattice strain. Switching between localized modes of modulated lattices is also considered, and, as an example, mode switching of randomly disordered lattice is demonstrated. Both the shear-strained and the random disordered lattices are shown to be ideal candidates for all-optical switching devices.
Nongeometric field enhancement in semiconducting cold cathodes and in metal–insulator–semiconductor structures
Authors: Bilbro Griff L. , Nemanich Robert J.
Published: July 2002

We extend the usual one-dimensional equilibrium theory of the surface space charge region that screens a semiconductor from an external electric field in order to admit perturbations in three dimensions and time. We identify a class of perturbations of the one-dimensional equilibrium that grow exponentially in time at least until our first-order perturbation theory fails. The resulting spontaneous field enhancement may explain enhancement factors observed in electron emission from semiconducting cathodes and may similarly contribute to gate leakage in metal–oxide–semiconductor field effect transistors.
Quantum confinement of E1 and E2 transitions in Ge quantum dots embedded in an Al2O3 or an AlN matrix
Authors: Teng C. W. , Muth J. F. , Kolbas R. M. , Hassan K. M. , Sharma A. K. , Kvit A. , Narayan J.
Published: July 2002

Alternating layers of Ge quantum dots embedded in either Al2O3 or AlN matrices were deposited on sapphire substrates by pulsed-laser deposition. The characteristics of the dots are shown to be independent of the surrounding matrix. The dots size (73, 130, 160, and 260 Å±5%) was controlled by the laser energy density and deposition time, and was characterized by high-resolution transmission electron microscopy. The dots were single crystalline with no apparent GeOx interfacial layers. Transmission spectroscopy at room temperature and 77 K was used to probe the above-band-edge absorption of the Ge nanodots. The spectral positions of both E1/E1+Δ1 and E2 transitions were found to shift to higher energy in the absorption spectra with decreasing nanodot sizes. This indicates that strong quantum-confinement effect permits the optical properties of Ge dots to be modified in a controlled manner.
Unidirectional ring TI3+:Al2O3 laser generation at the wavelength of an atomic absorption line by bidirectional passive self-injection locking
Authors: Deneva M. A. , Nenchev M. N. , Barbé R. , Keller J.-C.
Published: July 2002

A simple, purely optical approach to produce, in a ring Ti:Al2O3 laser, a pulsed unidirectional generation, spectrally fixed at a reference atomic absorption line is described. The control relies on the unbalance between two opposite, passive, wavelength-scanned self-injections that is produced by the absorption at the reference line. It is shown both experimentally and theoretically that: (i) the emitted spectrum is centered at the absorption maximum and (ii) due to the nonlinear character of the process the spectrum is narrowed several times compared with an absorption linewidth.
Relative electrical resistivities and poling of nonlinear optical polymeric waveguides
Authors: Pliška Tomáš , Meier Joachim , Eckau Arne , Ricci Vincent , Le Duff Anne-Claire , Canva Michael , Stegeman George I. , Raymond Paul , Kajzar François , Chan Kwok Pong
Published: July 2002

A method based on Maker fringe measurements of nonlinear optical coefficients has been used to determine the relative dc electrical resistivities of a series of linear and nonlinear optical polymers. The method can be used to identify low resistivity linear cladding materials for optimized electric field poling of nonlinear optical polymeric waveguides. As an example of the application of the technique we have studied the resistivity of poly(methyl methacrylate)-polystyrene (PMMA-PS) copolymers with varying content of the two components. The resistivity of PMMA was found to be one order of magnitude lower than that of PS.
Two-photon absorption study of GaN
Authors: Sun Chi-Kuang , Liang Jian-Chin , Wang Jiun-Cheng , Kao Fu-Jen , Keller Stacia , Mack Michael P. , Mishra Umesh , DenBaars Steven P.
Published: July 2002

Two-photon absorption coefficients of GaN for below band gap ultraviolet wavelength and midgap infrared wavelength were measured by using femtosecond pulsewidth autocorrelation and Z-scan techniques. Large two-photon absorption coefficients were obtained. Taking advantage of the large two-photon absorption, we have demonstrated two-photon confocal imaging of a GaN thin film. Direct correlation was found between the yellow luminescence and suppression of bandedge luminescence.
Drift mobility of semiconductive La0.5Sr0.5CoO3 films measured using the traveling wave method
Authors: Yin J. , Wang L. , Liu J. M. , Chen K. J. , Liu Z. G. , Huang Q.
Published: July 2002

The conductivity and the drift mobility of La0.5Sr0.5CoO3 films deposited on fused silica substrates at 650 °C by pulsed-laser deposition have been measured by using the traveling-wave method. At room temperature, La0.5Sr0.5CoO3 films with semiconductivity have a hole density of 1×1021 cm−3, and drift mobility of 0.01 cm2/V s. The films underwent a paraferromagnetic transition around 240 K. The hopping process and tunneling effect of small polarons may be responsible for the conductive behavior above the Curie temperature.
Defined crystallization of amorphous-silicon films using contact printing
Authors: Bae Sanghoon , Fonash Stephen J.
Published: July 2002

Patterned Ni layers are printed on amorphous-silicon (a-Si) films and, during this printing, the metal patterns induce lateral crystallization of the precursor a-Si layer. The printing process consists of simultaneously pressing the Ni printing plate to an a-Si layer and annealing at 550 °C. Printing times of 1 and 3 h are explored. The growth rate of the Ni-induced lateral crystallization is about 8 μm/h in this process. After this printing, Raman spectra show that the resulting polycrystalline-silicon (poly-Si) regions have the characteristic transverse-optical 519 cm−1 phonon peak typical of crystalline silicon. The nonprinted, noncrystallized a-Si areas have the Raman signature of a-Si; i.e., they do not have any peak. The resulting laterally crystallized Si area shows a morphological texture (i.e., a strip-like morphology) originating from the printed Ni area and growing in one direction in transmission electron microscope imaging. In terms of the selective area diffraction pattern (i.e., diffraction spot position and crystal structure), the signature of the area directly contacted by the Ni cannot be distinguished from that of the surrounding laterally crystallized silicon film. This printing approach can be used for channel crystallization/device isolation resulting in a saving of device fabrication steps.
Analyzing the polarization distribution in poled polymer films by scanning Kelvin microscopy
Authors: Blum Robert , Ivankov Andrei , Schwantes Stefan , Eich Manfred
Published: July 2002

We present a method for analyzing the homogeneity of the χ(2) distribution in poled nonlinear optical polymer films. The second-order nonlinear coefficient in these polymers is commonly induced by electric-field poling methods which can lead to a χ(2) distribution with poor spatial homogeneity. In this letter, we analyze the χ(2) distribution using scanning Kelvin microscopy. This allows us to detect the height and the direction of the induced polarization through the probing of the countercharges that are present on the polymer surface. We compare the response to that obtained from the scanning second-harmonic microscopy method, in which the direction of the orientation, and thus the phase of χ(2), cannot be seen.
Blue light generation in an external ring cavity using both cavity and grating feedback
Authors: Sun X. G. , Switzer G. W. , Carlsten J. L.
Published: July 2002

A simple scheme for the efficient frequency doubling of a Fabry–Perot diode laser in a bow tie ring cavity is described. By feeding back the ring cavity transmission into the laser after reflection off a grating, the diode laser operates in single mode and the frequency locks to the cavity resonance. Using a simple analytic form of the beam parameters for the ring cavity, the optimum cavity configuration is found for a high degree of mode matching between the diode output beam and the ring cavity.
Room-temperature observation of the Coulomb blockade effects in Al two-terminal diodes fabricated using a focused ion-beam nanoparticle process
Authors: Kim T. W. , Kang S. O. , Choo D. C. , Shim J. H.
Published: July 2002

Al two-terminal diodes were fabricated on a basis of an artificial pattern formation method using focused ion-beam (FIB) techniques. The results of current–voltage and conductance–voltage measurements at room temperature showed the Coulomb staircase and the Coulomb blockade effects, respectively. The Coulomb blockade effects originate from the many nanoparticles created by the defects due to the Ga+ ion beam. These results indicate that Al two-terminal diodes fabricated by using the FIB system hold promise for potential applications in single-electron transistors operating at room temperature.
Rectangular nanovoids in helium-implanted and thermally annealed MgO(100)
Authors: Kooi B. J. , van Veen A. , De Hosson J. Th. M. , Schut H. , Fedorov A. V. , Labohm F.
Published: July 2002

Cleaved MgO(100) single crystals were implanted with 30 keV He3 ions with doses varying from 1×1019 to 1×1020 m−2 and subsequently thermally annealed from 100 to 1100 °C. Transmission electron microscopy observations revealed the existence of sharply rectangular nanosize voids at a depth slightly shallower than the helium-implantation range. Monitoring of the defect depth profile and the retained amount of helium was performed by positron-beam analysis and neutron depth profiling, respectively.
Photoluminescence of high-quality AlGaAs layers grown by molecular-beam epitaxy
Authors: Zhuravlev K. S. , Toropov A. I. , Shamirzaev T. S. , Bakarov A. K.
Published: July 2002

We report a photoluminescence study of high-purity AlxGa1−xAs layers grown by molecular-beam epitaxy over the 0⩽x⩽0.295 composition range. The intense excitonic line dominates in the photoluminescence spectra of the layers. The full width at half maximum of the excitonic line is in excellent agreement with values calculated by Lee and Bajaj [J. Appl. Phys. 73, 1788 (1993)] for perfectly random alloys, and in the spectra of the layers with AlAs fractions of x=0.15 and x=0.209 it equals to 1.24 and 1.48 meV, respectively. A linear dependence of the exciton line intensity on excitation power evidences negligible concentration of nonradiative recombination centers in the layers.
High-power wavelength-tunable circular-grating surface-emitting distributed Bragg deflector lasers
Authors: Penner R. S. , Bedford R. , Luo H. , Mendes S. , Fallahi M.
Published: July 2002

We present a promising approach to achieve wavelength tuning in high-power circular-grating surface-emitting lasers. A transparent electrode of indium tin oxide (ITO) was used to inject carriers into the second-order grating section of the device. Powers in excess of 225 mW and slope efficiencies of better than 0.40 mW/mA are reported. A continuous tuning range of 0.5 nm was achieved, while an overall wavelength shift of 1 nm was obtained for an ITO injection current of 30 mA.
Observation of in-plane optical anisotropy of spin-cast rigid-rod electroluminescent polymer films
Authors: Law Carrie W. Y. , Wong K. S. , Yang Z. , Horsburgh L. E. , Monkman A. P.
Published: July 2002

Transmittance difference spectroscopy has been applied to study the optical properties of spin-cast rigid-rod polymer films. Significant in-plane optical anisotropy is observed for both the real and the imaginary parts of the transmittance of the poly(2,5-pyridine diyl) films. This in-plane optical anisotropy is a result of the partial alignment of the polymer chains, oriented radially outward from the center of the film, during the spin casting process. This observation has important implications for emissive polymer devices, particularly for devices sensitive to polarization direction and those using waveguide confinement where relatively long propagation distance within the films are required.
Self-aligned current aperture in native oxidized AlInAs buried heterostructure InGaAsP/InP distributed feedback laser
Authors: Wang Zhi-jie , Chua Soo-jin , Zhang Zi-ying , Zhou Fan , Zhang Jing-yuan , Wang Xiao-jie , Wang Wei , Zhu Hong-liang
Published: July 2002

A InGaAsP/InP self-aligned, native oxidized buried heterostructure (BH) distributed feedback (DFB) laser is proposed. It is as easy to process as the ridge waveguide DFB laser and has superior performance. The current aperture can be easily controlled without selective regrowth. The laser exhibits a low threshold of 5.0 mA with 36 dB side mode suppression ratio at the emission wavelength of 1.562 μm. It emits in a single lobe with full width at half maximum angles of 33.6° and 42.6° for the lateral and vertical fields, respectively. Its beam is more circular than that of the as-grown BH laser because the lower refractive index of oxide compared to the as-grown layer and results in a larger lateral optical confinement. Its characteristic temperature (T0) is 50 K at room temperature but increases in value at the higher temperature range.
Two-photon photocurrent imaging of vertical cavity surface emitting lasers
Authors: Xu Chris , Chirovsky Leo M. F. , Hobson W. S. , Lopata J. , Knox Wayne H. , Cunningham John E. , Jan William Y. , D’Asaro L. A.
Published: July 2002

We show that two-photon photocurrent imaging can be used to nondestructively study vertical cavity surface emitting lasers on a microscopic level. In particular, we study the aperture isolation created by shallow ion implantation. The combination of two-photon backside imaging and a probe station is ideal for internal and full wafer characterization. The required peak and average power levels for testing can be easily satisfied by available compact ultrafast laser sources, making the technique practical and user friendly.
Thermal imaging through ordered bundles of infrared-transmitting silver-halide fibers
Authors: Rave E. , Shemesh D. , Katzir A.
Published: July 2002

Ordered bundles of infrared-transmitting silver-halide (AgClxBr1−x) fibers were fabricated by extrusion. Bundles of total area 5–20 mm2 and lengths 5–50 cm included 100–2500 individual fibers and the packing fraction was 0.2–0.3. Each of the individual fibers was transparent in the spectral range 3–30 μm, and therefore, the whole bundle was suitable for thermal imaging. The modulation transfer function was studied using the “bar chart” and the “knife-edge” methods. The resolution was found to be 4–5 lines/mm for a 900 fiber bundle. Thermal images of objects at room temperature were transmitted from the entrance ends to the exit ends of the bundles.
Photoluminescence dynamics of amorphous Si/SiO2 quantum wells
Authors: Kanemitsu Yoshihiko , Iiboshi Makoto , Kushida Takashi
Published: July 2002

We have studied photoluminescence (PL) spectrum and dynamics of amorphous silicon (a-Si) based quantum wells at low temperatures. In a-Si/SiO2 quantum-well samples with thin a-Si layers, the PL spectra appear in the visible spectral region. With a decrease of the a-Si well thickness, the PL peak energy shifts to higher energy and the PL lifetime becomes shorter. The well-thickness and temperature dependence of the PL lifetime show that the nonradiative recombination of carriers occurs at the a-Si/SiO2 interface and the lifetime is determined by the energy relaxation process in the a-Si well and the carrier diffusion to the interface. The quantum confinement and localization of carriers in a-Si/SiO2 quantum-well structures will be discussed.
Elimination of carrier-density nonuniformities by surface acoustic waves
Authors: Takagaki Y. , Wiebicke E. , Friedland K.-J. , Kostial H. , Ploog K. H.
Published: July 2002

The action on a two-dimensional electron gas (2DEG) by electric fields that accompany surface acoustics waves (SAWs) propagating in GaAs-AlxGa1−xAs heterostructures is typically negligible because of screening. In the quantum Hall regime, the longitudinal conductivity of the 2DEG is nearly zero when the Fermi level lies in the Landau gap. Consequently, the SAWs can build up electric fields that are strong enough to rake off mobile electrons. We demonstrate that inhomogeneous carrier distributions produced in the course of photoionization of DX centers can be flattened out by applying the SAWs in high magnetic fields.
Self-sustained secondary discharge in inductively coupled plasma reactor
Authors: Walewski Joachim , Larjo Jussi , Hernberg Rolf
Published: July 2002

This work reports on observations of intense atomic line radiation near a substrate during diamond film growth in an inductively coupled thermal plasma. Evidence is given, indicating that the radiation is caused by electron collisions which are driven by the radio-frequency field.
Parallel molecular stacks of organic thin film with electrical bistability
Authors: Li J. C. , Xue Z. Q. , Li X. L. , Liu W. M. , Hou S. M. , Song Y. L. , Jiang L. , Zhu D. B. , Bao X. X. , Liu Z. F.
Published: July 2002

A thin film of 1,1-dicyano-2,2-(4-dimethylaminophenyl) ethylene (DDME) has been grown by a modified vacuum deposition. The films were characterized by Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning tunneling microscopy (STM). Highly ordered parallel molecular stacks were repeatedly observed with STM under ambient conditions. The dc current–voltage (I–V) characteristics of device Au/DDME/Au were measured, and the film was found to possess good electrical bistability and electrochromic properties. Nanometer-scale recording was realized on the film by applying pulse voltage between the STM tip and substrate. The possible switching mechanism is discussed.
High-quality strain-relaxed SiGe alloy grown on implanted silicon–on–insulator substrate
Authors: Huang F. Y. , Chu M. A. , Tanner M. O. , Wang K. L. , U’Ren G. D. , Goorsky M. S.
Published: July 2002

We report on the growth and characterization of high-quality strain-relaxed SiGe alloys on a compliant silicon–on–insulator (SOI) substrate. The annealing temperature required for strain transfer has been reduced through boron implantation to the buried oxide, leading to a high quality SiGe alloy free from dislocations as evident from the near-band gap photoluminescence. Nearly complete strain relaxation (∼95%) for SiGe alloy of a thickness beyond the conventional critical thickness has been obtained.
Frequency-selective incoherent detection of terahertz radiation by high-Tc Josephson junctions
Authors: Divin Y. Y. , Poppe U. , Volkov O. Y. , Pavlovskii V. V.
Published: July 2002

The detector response of YBa2Cu3O7−x Josephson grain-boundary junctions to monochromatic radiation with the frequency f in the range from 60 GHz to 4 THz has been studied. Frequency-selective odd-symmetric resonances in the responses ΔI(V) of these junctions to radiation with different frequencies f have been observed near the voltages V=hf/2e in almost a decade of spectral range for any operating temperature in the range from 30 to 85 K. The spectral range of the selective detection has scaled with the IcRn product of the Josephson junction, reaching the range of 0.16–3.1 THz for a IcRn product of 1.5 mV. A resolving power δf/f of around 10−3 has been demonstrated in the selective detection by Josephson junctions. The high-frequency falldown of the amplitude of the selective response has been found to be proportional to exp[−P/P0], where P=(hf/2e)2/Rn is the power dissipated in the junction at the resonance and P0 is a characteristic power level. The values of P0 for our junctions were around 20 μW at 34 K and 2 μW at 78 K.
Doping dependence of the Josephson coupling in Bi2Sr2Ca1−xGdxCu2O8+δ single crystals
Authors: Li X.-G. , Zhao X. , Fan X. J. , Sun X. F. , Wu W. B. , Zhang H.
Published: July 2002

The Gd and oxygen doping effects on the Josephson coupling in Bi2Sr2Ca1−xGdxCu2O8+δ single crystals have been studied systematically. It was found that a pseudo-transition at temperature TcJ, attributed to the Josephson coupling between CuO2 layers, shifts dramatically to lower temperature with increasing magnetic field, and the temperature dependence of the pseudo-upper-critical-field HcJ associated with the coupling shows a clear upward curvature. For the Gd-doped as compared with the oxygen-doped crystal, the value of TcJ is smaller at the same carrier density, which implies that the substitution of Gd for Ca reduces the Josephson coupling more severely. The characteristics of the pseudo-transition associated with the Josephson coupling between CuO2 layers are different from those of the superconducting transition occurring in the CuO2 layers.
In
0.34
Al
0.66
As
0.85
Sb
0.15
/δ(n
+
)-
InP
heterostructure field-effect transistors
Authors: Lin Y. S. , Hsu W. C. , Yeh C. Y. , Shieh H. M.
Published: July 2002

A lattice-matched δ-doped In0.34Al0.66As0.85Sb0.15/InP heterostructure field-effect transistor (HFET) which provides large band gap (∼1.8 eV), high Schottky barrier height (φB>0.73 eV), and large conduction-band discontinuity (ΔEc>0.7 eV) has been proposed. In0.34Al0.66As0.85Sb0.15/InP heterostructures are shown to be type II heterojunctions with the staggered band lineup. This HFET demonstrates a output conductance of less than 1 mS/mm. Two-terminal gate-source breakdown voltage is more than 20 V with a leakage current as low as 170 μA at room temperature. High three-terminal off-state breakdown voltage as high as 36 V, and three-terminal on-state breakdown voltage as high as 18.6 V are achieved. The gate voltage swing is also significantly improved.
Control of phase modulation in InGaAs epilayers
Authors: González D. , Aragón G. , Araújo D. , Garcı́a R.
Published: July 2002

A theoretical description of the phase modulation state of epitaxial InGaAs layers has been recently published [D. González et al. Appl. Phys. Lett. 74, 2649 (1999)]. To verify experimentally the deduced phase diagram, InGaAs structures with In compositional steps were grown using different growth conditions. Transmission electron microscopy studies have revealed the modulation state in each layer and have allowed us to define the experimental In composition and temperature dependence of the phase transition. The results show that InGaAs layers with and without composition modulation can be obtained by changing the growth temperature. An excellent agreement with the model predictions is observed.
High-Tc superconductor Bi2Sr2CaCu2O8+δ tunnel junction with Zn counterelectrode
Authors: Li Shao-Xiong , Tao Hong-Jie , Xuan Yi , Zhao Bo-Ru , Zhao Zhong-Xian
Published: July 2002

Using Zn thin film as counterelectrode, Bi2Sr2CaCu2O8+δ tunnel junctions were prepared. Temperature-dependent tunneling spectra of these planar junctions provided measurements of energy gap, 2Δ, and transition temperature, Tc. The spectra also allowed the observation of pseudogap in normal state and showed strong evidence of d-wave symmetry of the superconducting order parameter. The present junction may find its way in the electronics applications.
All-optical nonlinear feedback devices derived from the negative nonlinear absorption effect in erbium–yttrium aluminum garnet crystals
Authors: Maeda Yoshinobu , Matsuoka Yoichi
Published: July 2002

All-optical nonlinear feedback devices derived from the negative nonlinear absorption effect in erbium–yttrium aluminum garnet crystals were demonstrated using a feedback ring resonator and an erbium-doped fiber amplifier. The output modulation degree depends on the dosage of erbium and the amplifier gain. The maximum value was 83% when the input modulation degree was 55%. The inverted output signal was amplified by approximately ten times as large as the input signal. The output modulation degree increased abruptly at an amplifier gain of more than 25 dB when it has feedback. The device was characterized by the property that optical signals for 1.53 μm light can be inverted and amplified.
Tetravalent tin complex with high electron affinity for electroluminescent applications
Authors: Tao X. T. , Shimomura M. , Suzuki H. , Miyata S. , Sasabe H.
Published: July 2002

We report the synthesis and electroluminescent properties of the organometallic complex diphenyltin bis-hydroxyquinoline (Sph2q2). The complex was prepared by the reaction of diphenyltin dichloride with 8-hydroxyquinoline and shows an absorption cutoff wavelength of 460 nm and bright photoluminescence with a peak wavelength at 508 nm. The ionization potential of Sph2q2 was determined to be ∼6.0 eV by photoemission apparatus, and the electron affinity is estimated to be 3.3 eV. Sph2q2 was used as an emitting and electron injection layer in bilayer devices. The electroluminescence (EL) properties and charge injection properties of Sph2q2 are characterized. Sph2q2 is easily soluble in common organic solvents and further modification of its properties is possible. The results indicate that tetravalent tin complexes are potential emitting and charge injection materials for EL applications.
Alternating current Josephson effect in intrinsic Josephson bridges in Tl2Ba2CaCu2O8 thin films
Authors: Chana O. S. , Kuzhakhmetov A. R. , Warburton P. A. , Hyland D. M. C. , Dew-Hughes D. , Grovenor C. R. M. , Kinsey R. J. , Burnell G. , Booij W. E. , Blamire M. G. , Kleiner R. , Müller P.
Published: July 2002

We have performed transport measurements on bridges patterned in misaligned thin films of the superconductor Tl2Ba2CaCu2O8. There is a c-axis component of current flow along the bridge, giving rise to hysteretic Josephson-like current–voltage curves. The temperature dependence of the critical current follows the Ambegaokar–Baratoff theory with IcRN up to 26 mV at 4.2 K. Microwave emission from the Josephson junctions near Tc (≈103 K) has been detected using an X-band detector. We show that 700±15 junctions in the bridge are actively oscillating, confirming that the junctions are “intrinsic” junctions formed by adjacent copper oxide planes in the Tl2Ba2CaCu2O8 crystal structure.
Simulation of the superconducting multiturn flux transformer integrated with a coplanar resonator
Authors: Yi H. R. , Zhang Y. , Klein N.
Published: July 2002

The analysis of the structure of a superconducting multiturn flux transformer integrated with a coplanar resonator for radio-frequency superconducting quantum interference devices is described. Electromagnetic simulations indicate that the loss is dominated by the high loss tangent of the dielectric film used for the separation of the upper and lower superconducting films. The simulated current distribution at its resonant frequency shows that the highest current density is distributed on the multiturn input coil. This current distribution leads to a very high loss when the loss tangent of the dielectric film is high. However, for the same loss tangent of the dielectric film, it is possible to get a reasonably high unloaded quality factor by providing a normal shunt for the multiturn input coil.
Generation of wavelength-tunable single-mode picosecond pulses from a self-seeded gain-switched Fabry–Perot laser diode with a high-birefringence fiber loop mirror
Authors: Li Shenping , Chiang K. S. , Gambling W. A.
Published: July 2002

We demonstrate a simple self-seeding scheme for generating wavelength-tunable single-mode picosecond pulses at a fixed repetition rate with a Fabry–Perot (FP) laser diode. In this scheme, the FP laser diode is self-seeded from a high-birefringence (HiBi) fiber loop mirror that acts as a periodic multichannel wavelength filter. By setting the channel spacing of the filter properly, stepwise wavelength tuning over a wide range can be achieved by either changing the FP cavity roundtrip phase shift or tuning the fiber loop mirror filter. With this scheme, fast electrical tuning is also possible by incorporating a phase-control section into the FP cavity. Using a HiBi fiber loop mirror with a channel spacing of 1.56 nm and a FP laser diode with a mode spacing of 1.45 nm, we were able to generate picosecond pulses at a repetition rate of approximately 2 GHz, whose wavelength could be tuned stepwise over ten successive laser cavity modes by either changing the temperature of the laser diode or tensioning/pressing a section of the HiBi fiber in the loop mirror. A side-mode suppression ratio over 15 dB over the entire tuning range was achieved.
Oxygen migration during epitaxial regrowth in Cs+-irradiated α-quartz investigated by means of nuclear reaction analysis
Authors: Roccaforte F. , Harbsmeier F. , Dhar S. , Lieb K. P.
Published: July 2002

The migration of oxygen in ion-beam-amorphized c-SiO2 (α-quartz) was investigated by means of nuclear reaction analysis using the resonant reaction O18(p,α)15N for oxygen depth profiling. Only very small amounts of oxygen were observed to diffuse in crystalline or in Xe+-ion beam-amorphized α-quartz after high-temperature annealing. However, a dramatic migration of oxygen occurs in Cs+-implanted α-quartz in the same temperature range (600–900 °C), where Cs diffuses out of the amorphized layer and epitaxial recrystallization occurs. These results point out to a strong correlation of all these processes. A mechanism to explain the observed indiffusion of O18 is proposed and is related to the Cs migration and the topological modification to achieve epitaxial regrowth of the SiO2 matrix.
70+ μm deep domain inversion in X-cut LiNbO3 and its use in a high-speed bandpass integrated-optic modulator
Authors: Kishino Tetsuya , Tavlykaev Robert F. , Ramaswamy Ramu V.
Published: July 2002

A deep domain inversion (DI) technique for X-cut LiNbO3 is reported. DI regions as deep as 70 μm, i.e., deep enough for virtually any guided-wave application, were obtained by electric-field poling, with even deeper DI regions possible. As an application of the DI technique, a bandpass traveling-wave Mach–Zehnder modulator is demonstrated with a 15 GHz bandwidth centered at 21 GHz.
Vapor-phase epitaxial growth on porous 6H–SiC analyzed by Raman scattering
Authors: Spanier Jonathan E. , Dunne Greg T. , Rowland Larry B. , Herman Irving P.
Published: July 2002

SiC vapor-phase epitaxy on porous silicon carbide (PSC) substrates formed by electrochemical anodization is reported. Raman scattering indicates that the polytype of the optically smooth SiC grown on PSC formed in both p-type and n-type 6H substrates is 6H. The Raman scattering selection rules in these films are the same as those observed in the bulk substrate and epilayers grown on bulk, indicating high crystalline quality. The formation of epitaxial 6H–SiC on porous 6H–SiC may open up new possibilities for dielectric device isolation, fabrication, and epitaxial lift-off.
Theory of ballistic electron emission microscopy with constant current feedback
Authors: Pearson D. A. , Sham L. J.
Published: July 2002

A theory of ballistic electron emission microscopy is presented that incorporates constant tunnel current feedback and models the band structure and space charge effects on the electron transmission. The computation is beyond the effective mass approximation but short of being from first principles. We compare theory and experimental Au/GaAs(001) dI/dV data and find that the L point does not contribute to an observable threshold and that the corresponding experimental feature is due to band structure effects.
On the possibility of diamond wafer bonding in ultrahigh vacuum
Authors: Conrad D. , Scheerschmidt K. , Gösele U.
Published: July 2002

The possibility of bonding clean diamond surfaces covalently in ultrahigh vacuum is investigated by molecular dynamics simulations based on a tight binding model. Our simulations predict that strong covalent bonding is possible for C(001)-2×1 surfaces. C(111)-2×1 surfaces will bond very weakly and debond already at moderate temperatures.
n-
Si/SiO
2
/Si
heterostructure barrier varactor diode design
Authors: Fu Y. , Mamor M. , Willander M. , Bengtsson S. , Dillner L.
Published: July 2002

Symmetric C–V and antisymmetric I–V characteristics are essential for a heterostructure barrier varactor (HBV) to generate odd harmonics in a frequency multiplier. Practically high multiplier efficiency is obtained when the shape of the C–V characteristic is sharp near zero bias and the conduction current is low. Here we present the design of an n-type Si/SiO2/Si-based HBV and its state-of-the-art device performance. Self-consistent solutions of the Schrödinger and Poisson equations show a drastic decrease of the conduction current due to the large electron effective mass and the SiO2 barrier height. The shape of the C–V curve can be easily tuned by modifying the thickness of the SiO2 layer. By the techniques compatible with the conventional Si technology, a Si/SiO2/Si varactor junction (having a SiO2 layer of 20 nm) has been processed and the device characteristics are very promising.