bluuebunny/crossref_metadata_2025 huggingface dataset:
Bolometric detection in a precipitation free Y1Ba2Cu3O7−δ film at 77 K
Authors: Chou Hsiung , Chen H. Z. , Hong M. T. , Chen Y. C. , Chow T. C.
Published: July 2002

A photodetector with high responsivity has been fabricated with a high quality Y1Ba2Cu3O7−δ film on a regular SrTiO3 (100) substrate that has no thinning or etching. The film exhibits a precipitation-free morphology and has an extremely smooth surface having a rms roughness smaller than 5 nm. The film was patterned into a 25×650 μm2 long microbridge by a conventional photolithography technique. The Tco of the microbridge can be tuned by applying different bias currents, which results in a tunable operation temperature of the photodetector at 77.35±1 K. This makes it operationally more practical and economical. The noise voltage at 10 mA bias current is less than the resolution of our setup, 15 nV  Hz−0.5. A high responsivity of 2.3×103 V/W was obtained when a bias current of 8 mA and a low power density He–Ne laser of 0.08 J/cm2 s chopped at 2 Hz were applied on the microbridge at 77.35 K. Under the same condition, the noise equivalent power (NEP) and detectivity (D*) have been measured to be 4.34×10−12 W Hz−0.5 and 3×109 cm Hz0.5 W−1, respectively.
Nonuniform oxide charge and paramagnetic interface traps in high-temperature annealed Si/SiO2/Si structures
Authors: Vanheusden K. , Warren W. L. , Schwank J. R. , Fleetwood D. M. , Shaneyfelt M. R. , Winokur P. S. , Devine R. A. B.
Published: July 2002

Trivalent silicon Pb0 and Pb1 defects were identified at both the top Si(100)/buried-SiO2 and buried-SiO2/bottom-Si(100) interfaces in high-temperature (1320 °C) annealed Si/SiO2/Si struc- tures. The paramagnetic defects are generated by annealing in a flow of pure nitrogen (N2) or forming gas [N2H2; 95:5 (by volume)] at 550 °C. In addition, the forming-gas anneal also generated positive charge in the buried oxides; significant lateral nonuniformities in the buried oxide charge density were observed following this anneal. These macroscopic inhomogeneities may be linked to previous reports of homogeneity related problems involving the SIMOX buried oxide, such as early breakdown and etch pits, suggesting that these types of measurements may be useful as nondestructive screens of SIMOX wafer quality.
Thermal stability of undoped strained Si channel SiGe heterostructures
Authors: Klauk H. , Jackson T. N. , Nelson S. F. , Chu J. O.
Published: July 2002

We have investigated the thermal stability of Si/SiGe n-channel heterostructures. To eliminate the complication of dopant diffusion, we have fabricated undoped Si/SiGe heterostructure Hall effect devices. With no modulation doping used in our structures, the electron concentration in the strained Si channel is controlled from a back gate. Our devices show high electron mobility of up to 19 500 cm2/V s at 77 K and are stable with negligible 77 K mobility reduction after anneals at 800 °C for 30 min and at 950 °C for 3 min. These results conform well with a simulation of the diffusion of Ge into the Si channel.
Direct measurement of the refractive index change of silicon with optically injected carriers
Authors: Yu L. S. , Liu Q. Z. , Guan Z. F. , Lau S. S.
Published: July 2002

Silicon phase modulators are important silicon optoelectronic devices. The relationship of the refractive index change with injected carrier concentration is the basis for the operation of silicon phase modulators. No direct experimental data of this relationship have been reported. We have developed a new method for the direct measurement of this relationship using a Fabry–Perot interference and optical injection of carriers. The experimental results of the refractive index change are reported for the first time in the range of injected carrier concentration between 1013 and 1015 cm−3. It should be noted that our experiment results are about 5 to 10 times larger than those predicted by theory. The reliability of our experiments is also discussed.
Low frequency noise in two-dimensional metal-semiconductor field effect transistor
Authors: Levinshtein M. E. , Rumyantsev S.-L. , Simin G. S. , Park H. , Peatman W. C. B. , Shur M. S.
Published: July 2002

Low frequency noise in the two-dimensional metal-semiconductor field effect transistor (2D-MESFET) is reported. It is shown that the noise level S is rather small. At room temperature the value of Hooge constant α was about 2×10−5 for frequency f=20 Hz. The frequency dependence of the relative spectral density of current fluctuations SI/I2 at 300 K was close to S∼1/f0.6 in the frequency range 20 Hz–20 kHz. Two local maxima were observed in the temperature dependence of S in the ranges 100–180 K and 200–300 K.
Single-crystal Si islands on SiO2 obtained via excimer-laser irradiation of a patterned Si film
Authors: Song H. Jin , Im James S.
Published: July 2002

We have developed a single-pulse based excimer-laser crystallization technique that transforms photolithographically patterned and SiO2-encapsulated a-Si regions into single-crystal islands on SiO2. The method utilizes the substantial superlateral growth distances that are attainable at high substrate temperatures in combination with precise manipulation of the evolution of the solidification front in order to allow only one of the several grains that originate from the intentionally incompletely melted (i.e., the seed) portion of an island to pass through a constriction and propagate into the rest of the island. This converts the main portion of the island, which extends tens of microns in the lateral dimensions, into a high-angle-grain boundary free crystalline material, in so far as the size of the island is commensurate with achievable superlateral growth distances.
Tantalum deposition on and reaction with the hydrogen terminated diamond (100) surface studied by Auger electron and electron energy loss spectroscopy
Authors: Pitter M. , Hugenschmidt M. B. , Behm R. J.
Published: July 2002

The evolution of the tantalum/diamond interface upon room-temperature Ta deposition on the (100) surface of a boron doped, synthetically grown diamond single crystal was monitored by Auger electron spectroscopy (AES), ionization loss spectroscopy (ILS), and electron energy loss spectroscopy (ELS). Characteristic loss peaks indicate carbide formation at the interface from very low coverages on, reflecting the strong interaction between tantalum and carbon. Thicker layers of TaC are formed during subsequent thermal annealing by diffusion of carbon into the tantalum film, at the same time the topmost diamond region is transformed into poorly ordered graphitic carbon.
Bond-length disorder and metastability in hydrogenated amorphous silicon
Authors: Li Qiming , Biswas R.
Published: July 2002

A model of metastable defect formation via H-rebonding in hydrogenated amorphous silicon is developed where the defect density and defect formation energy are controlled by the bond-length disorder of the material. The relaxation of thermal equilibrium defects is stretched exponential, with stretch parameters varying approximately linearly with temperature and relaxation times that are thermally activated.
Carbon implantation in AlxGa1−xAs
Authors: Pearton S. J. , Abernathy C. R.
Published: July 2002

Maximum hole densities of 4×1018 cm−3 were produced in Al0.3Ga0.7As by C+Ga implantation and subsequent annealing at ∼800 °C. The activation efficiency decreases with increasing AlAs mole fraction and the use of higher temperatures for the Ga coimplantation, due to a reduced vacancy concentration under these conditions. The C diffusivity is ≤1.3×10−13 cm2 s−1 at 950 °C in implanted Al0.3Ga0.7As, demonstrating that C is a much more thermally stable acceptor than Be, Mg, or Zn.
Low-temperature epitaxial growth of CoGe2(001)/GaAs(100) films using the partially ionized beam deposition technique
Authors: Mello K. E. , Soss S. R. , Murarka S. P. , Lu T.-M. , Lee S. L.
Published: July 2002

The partially ionized beam (PIB) deposition technique was used to deposit CoGe2(001) thin films heteroepitaxially on GaAs(100) substrates. The epitaxial arrangement is CoGe2(001)/GaAs(100). It is found that the best epitaxy was obtained with an ion energy around 1100 eV and with a substrate temperature of 280 °C. The wafers were treated only by immersion in HF:H2O 1:10 immediately prior to deposition. Contacts grown at the optimal epitaxial formation conditions displayed Ohmic behavior, while contacts grown at higher or lower substrate temperatures had rectifying behavior. Epitaxial formation of CoGe2, a high melting point, low resistivity cobalt germanide phase, offers the possibility of forming a stable contact to n-GaAs.
Compressibility studies of double electron and double hole gas systems
Authors: Millard I. S. , Patel N. K. , Simmons M. Y. , Linfield E. H. , Ritchie D. A. , Jones G. A. C. , Pepper M.
Published: July 2002

Double layer structures have been used to measure the compressibility of both two-dimensional electron (2DEG) and two-dimensional hole gases (2DHG). This has been achieved by making independent contacts to the lower layer and using it to detect the compressibility of the upper layer. Both positive and negative compressibilities are observed, with the negative compressibility enhanced for hole gases, where the changes of the interaction energy are larger than those of the kinetic energy. The negative compressibility of the top layer leads to a charge transfer between the layers; this has been modelled and gives good agreement with the experiments when exchange and correlation is included. Due to disorder in the layers, however, the model deviates from the experimental results close to depletion. The dependence of the charge transfer upon distance between the electron gases has also been studied, with the charge transfer decreasing linearly with increasing spacing between the 2DEGs. This suggests that inter-layer interactions are insignificant.
Ultrafast carrier dynamics and saturable absorption in HgCdTe
Authors: Pelouch Wayne S. , Schlie L. A.
Published: July 2002

The ultrafast carrier dynamics in Hg0.6Cd0.4Te and Hg0.33Cd0.67Te are studied using a femtosecond optical parametric oscillator and the optical transmission-correlation spectroscopy method. The band gaps of these materials are 2.85 μm (0.435 eV) and 1.47 μm (0.844 eV) at room temperature, respectively. The collective relaxation occurs within the 0.5 to 2 ps range and a fast scattering process is observed in the 150 to 200 fs range. Saturation effects are detected in the 0.844 eV band gap sample resulting in a transmission maxima near 2 ps in addition to the standard transmission peak at zero time delay. The magnitude of the saturable absorption is also measured as a function of carrier density and initial kinetic energy of the photoexcited carriers.
Polarization effect in light emitting diodes with ordered GaInP active layers
Authors: Greger E. , Gulden K. H. , Riel P. , Schweizer H. P. , Moser M. , Schmiedel G. , Kiesel P. , Döhler G. H.
Published: July 2002

We report on polarization effects in surface emitting light emitting diodes based on p-i-n AlGaInP/GaInP double heterostructures grown by metal organic vapor phase epitaxy. Devices with an ordered GaInP active layer show polarized light output with a ratio of 4:3 for polarization along the [011] and [011̄] crystal direction, respectively. This polarization is nearly independent of diode current and mesa geometry, but is not observed if disordered GaInP active layers are used. The effect is considered to be an important means for polarization control in vertical cavity surface emitting lasers.
Strain relaxation mechanism of 250 °C grown Si0.33Ge0.67/Si(001) heterostructure
Authors: Lee Seung-Chang
Published: July 2002

The strain relaxation mechanism of a 500-nm-thick Si0.33Ge0.67 layer grown on Si(001) at 250 °C by molecular beam epitaxy has been investigated. During growth, the strain relaxation occurs without misfit dislocations. Moreover, a strained region coexists with a relaxed one in a single Si0.33Ge0.67 layer. In the relaxed region of Si0.33Ge0.67 layer, stacking faults, instead of misfit dislocations, are the major relief source of strain energy. These anomalous behaviors which are different from conventional relaxation mechanism have been interpreted by the characteristics of the stacking fault.
Conductive thin films of bis(ethylenedithio)tetrathiafulvalene salt fabricated by a successive dry-wet process
Authors: Miura Yasuhiro F. , Ohnishi Satomi , Hara Masahiko , Sasabe Hiroyuki , Knoll Wolfgang
Published: July 2002

Conductive molecular thin films of a BEDT-TTF [bis(ethylenedithio)tetrathiafulvalene] salt have been fabricated by a successive dry-wet process. Neutral BEDT-TTF molecules were evaporated onto an electrode-coated substrate under ultrahigh-vacuum conditions. Then an electrochemical doping process was carried out: the as-deposited film was immersed in an aqueous solution of LiClO4 and was doped with ClO4− anions. The lateral conductivity of the film was in the range 10−3–10−4 S/cm at room temperature. We have demonstrated that the successive dry-wet process has the potential to be a versatile technique to fabricate conductive thin films based on BEDT-TTF salts.
Compositional mapping of semiconductor structures by friction force microscopy
Authors: Tamayo J. , González L. , González Y. , García R.
Published: July 2002

Topographic and chemical mapping of materials at high resolution define the goals of a microscope. Force microscopy can provide methods for simultaneous topography and chemical characterization of materials. Here we describe the use of the atomic force microscope to map chemical variations of semiconductor samples. Chemical maps of semiconductor InP/InGaAs alloys have been determined with 3 nm spatial resolution while 10% changes in indium composition are resolved in InxGa1−xAs structures. The present resolution is limited by the tip’s curvature radius, cantilever lateral force constant, and the total applied force. Theoretical calculations predict lateral compositional resolutions of about 1 nm.
Magnetically tunable YBaCuO microstrip resonators and bandpass filters
Authors: Trotel A. , Pyée M. , Lavigne B. , Chambonnet D. , Lederer P.
Published: July 2002

We report experimental results on frequency tuning in superconductive resonators and bandpass filters with controlling magnetic fields. The frequency shifts are attributed to the presence of vortices modifying the microwave penetration depth and therefore the kinetic inductance of the circuit. 7-pole microstrip filters with a center frequency of 14 GHz and a bandwidth of 4% were fabricated using YBaCuO films deposited on MgO substrate with Au ground plane. A negative frequency shift of −12 MHz for fields lower than 0.1 mT was observed at 40 K.
Two-bandpass fiber-optic radiometry for monitoring the temperature of photoresist during dry processing
Authors: Dankner Yair , Eyal O. , Katzir A.
Published: July 2002

The temperature of a thin photoresist layer on a silicon wafer was measured in situ during dry etching by using a silver halide optical fiber noncontact thermometer. A two-bandpass radiometer was constructed to reduce errors arising from geometrical factors and emissivity changes. Such a system may be used to monitor surface temperatures during dry processing of semiconductors and to prevent overheating that may cause damage, such as cross linking of photoresists.
Pulsed laser deposition of SrCuO2/CaCuO2 superlattices
Authors: Aruta C. , Balestrino G. , Desfeux R. , Martellucci S. , Paoletti A. , Petrocelli G.
Published: July 2002

We have shown that the pulsed laser deposition (PLD) technique, with no in situ diagnostic, can be used to grow good quality superlattices based on the infinite layer compounds SrCuO2 and CaCuO2. We demonstrated that the major source of disorder in these superlattices, grown at temperatures lower than 600 °C, comes from random discrete thickness fluctuations. However the random discrete thickness fluctuations affect essentially only one unit cell. This makes the PLD technique very attractive for the growth of new artificial high-Tc structures based on the infinite layers compounds.
Effect of channeling of halo ion implantation on threshold voltage shift of metal oxide semiconductor field-effect transistor
Authors: Hwang Hyunsang , Lee Dong Hoon , Ahn Jae-Gyung , Byun Jeong Soo , Yang Dooyoung
Published: July 2002

In this letter, we report threshold voltage shift of metal oxide semiconductor field effect transistor (MOSFET) after the halo ion implantation process. Although halo implantation can significantly reduce the short channel effect, it causes a threshold voltage shift of a long channel device due to dopant channeling through polycrystalline silicon grain boundary. Although the chemical vapor deposited (CVD) cap oxide on polycrystalline silicon gate was used as a blocking layer of dopant, threshold voltages shift clearly indicate dopant channeling through polycrystalline silicon. To avoid a channeling problem, a thicker cap oxide layer or lower halo implantation energy is necessary.
Growth and in situ x-ray characterization of YBa2Cu3Ox/LaAlO3 superlattices
Authors: Williams S. M. , Maglic S. , Thomas C. , Lin C. T. , Wagoner M. J. , Chang R. P. H. , Ketterson J. B.
Published: July 2002

We utilized a miniature sputtering cell with mylar windows and multitarget sputtering guns in order to study the growth of YBCO/LaAlO3 superlattices on SrTiO3 substrates. Computer modeling of the diffraction spectra enabled us to determine the interface width between the layers. After deposition of the superlattices, the substrate temperature was increased to study any interdiffusion.
Metal-insulator-semiconductor solar cells with silicon oxynitride tunnel insulator by using rapid thermal processing
Authors: Beyer A. , Ebest G. , Reich R.
Published: July 2002

Metal-insulator-semiconductor (MIS) solar cells were prepared with silicon oxynitride as tunnel insulator by using rapid thermal processing (RTP). During the reaction of NH3 at the silicon surface the growing of the oxynitride layer was investigated at temperatures up to 950 °C and layer thicknesses up to 2 nm. The elemental composition of the layer was characterized by using Auger electron spectroscopy (AES). Extensive electrical characterizations on MIS tunnel diodes and MIS cells were carried out and an improved thermal stability (up to 350 °C) of the Al-oxynitride-silicon system was found in comparison to the conventional silicon oxide as a tunnel insulator up to 270 °C.
Faraday rotation of Hoya FR5 glass at cryogenic temperature
Authors: Lee Hyeon Gon , Won Y. H. , Lee G. S.
Published: July 2002

Faraday rotation and magnetization in Hoya FR5 glass is investigated in a magnetic field up to 80 kG under cryogenic temperature between 4.2 K and 10 K at the wavelength of 514.5 nm. For H/T≳10 kG K−1, the saturation is observed both in magnetization and in Faraday rotation and is interpreted by using the quantum theory of paramagnetism about the doped Tb3+ active ion. It is found that the temperature dependence of the Verdet constant is correlated with the magnetic susceptibility and the dispersion of the Verdet constant is due to the effective electric dipole transition of 4f8→4f75d1 with the resonance wavelength of 213 nm.
Double acceptor doped Ge: A new medium for inter-valence-band lasers
Authors: Bründermann E. , Linhart A. M. , Reichertz L. , Röser H. P. , Dubon O. D. , Hansen W. L. , Sirmain G. , Haller E. E.
Published: July 2002

We report on intervalence-band laser emission from Be- and Zn-doped germanium crystals. The duty cycle of 10−3 at a repetition rate of 1 kHz is one order of magnitude larger than the highest duty cycle reported for p-Ge lasers doped by group II acceptors. This improvement is due to the much larger hole binding energy of double acceptors Be and Zn which results in a strong reduction of the internal absorption of the generated far-infrared radiation. Laser action has been achieved with crystal volumes as small as 0.04 cm−3, and a laser pulse length of 25 μs has been reached. Germanium crystals doped with these acceptors may offer an opportunity for achieving the ultimate goal of continuous wave operation.
Time-resolved photoluminescence study on AlxGa1−xAs spontaneous vertical quantum well structures
Authors: Usami Noritaka , Pan Wugen , Yaguchi Hiroyuki , Ito Ryoichi , Onabe Kentaro , Akiyama Hidefumi , Shiraki Yasuhiro
Published: July 2002

We report on time-resolved photoluminescence study of AlxGa1−xAs spontaneous vertical quantum well (SVQW) structures on GaAs V-grooved substrates. Four distinct photoluminescence peaks are observed originating from the spatial nonuniformity of the alloy compositions spontaneously formed during metalorganic vapor phase epitaxial growth. The decay time of the (111)A sidewall AlGaAs decreased with increasing temperature, while that of the SVQW increased. The rise time of the SVQW was found to be longer than the typical value of the exciton formation and increases with increasing temperature, indicating that the exciton formation is not limiting factor of the rise time. These results are explained in terms of the exciton diffusion toward the SVQW from the outer AlGaAs layers with less Ga compositions. In addition, two dimensionality of the SVQW was evidenced by temperature dependence of the radiative lifetime.
Broadband Bragg filter in microfabricated AlGaAs waveguides
Authors: Espindola R. P. , Udo M. K. , Chu D. Y. , Wu S. L. , Ho S. T. , Tiberio R. C. , Chapman P. F. , Hou H. Q. , Chang T. Y.
Published: July 2002

We report on the fabrication and characterization of broadband Bragg filters in microfabricated AlGaAs waveguides. Electron-beam lithography and chemically assisted ion-beam etching were used to fabricate first-order gratings with 250 nm period. Bragg filters with rejection bandwidth ∼15 nm and centered at ∼1.6 μm are demonstrated.
CaF2:Er3+ molecular beam epitaxial layers as optical waveguides
Authors: Bausá L. E. , Lifante G. , Daran E. , Pernas P. L.
Published: July 2002

CaF2:Er thin films grown by molecular beam epitaxy on CaF2 substrates have been characterized as optical waveguides. The characterization has been carried out by measuring the synchronous angles in attenuated total reflection experiments. It has been found that the incorporation of Er3+ ions to the CaF2 crystal produces an increase of the refractive index of the material giving rise to the formation of a steplike planar optical waveguide. The refractive index increase shows a linear dependence with Er3+ concentration up to 35 mol %, at which point saturation is observed. The obtained results compared well with previously reported data on the lattice parameter of CaF2:Er3+ bulk crystals and fluorescence quenching from Er3+ ions in these layers. The results of this work show that the preparation of CaF2:Er3+ layers on CaF2 substrates by molecular beam epitaxy is an ideal method to produce monomode active optical waveguides useful for optoelectronic devices.
Epitaxial quality of thin Ag films on GaAs(100) surfaces cleaned with various wet etching techniques
Authors: Mello K. E. , Soss S. R. , Murarka S. P. , Lu T.-M. , Lee S. L.
Published: July 2002

2θ and pole figure x-ray analysis have been used to examine the crystal structure and orientation of Ag films deposited on GaAs(100) substrates cleaned by a variety of wet etches. Where epitaxy was observed, it was of the type Ag(110)/GaAs(100). The H3PO4/HCl sequential etch yielded the film with the highest degree of preferred orientation, with the H2SO4/HCl, NH4OH, and HF etches producing films of decreasing quality in the order named. The epitaxial quality is thought to scale with elemental As concentration on the GaAs(100) surface, and have an inverse relationship to the amount of surface oxides present before deposition.
Equivalence of voltage bias and geometric waveguide design in directional couplers
Authors: Feuerstein R. J. , Feng Wei , Powelson Judith C. , Lin Sihan , Bintz Lou , Mickelson A. R.
Published: July 2002

Using Poincaré coordinates we show that any relative amplitude and phase between the two modes of a directional coupler can be obtained through varying a single electrode voltage and by selecting the correct length for the coupling region. Alternatively, curved waveguide sections can be employed to accomplish the same feat without applied voltage, which we demonstrate using beam propagation simulations.
High quality epitaxial Si films onto γ-Al2O3 (111)/Si (111) substrates using Al predeposition layers
Authors: Jung Young-Chul , Wado Hiroyuki , Ohtani Kentaro , Ishida Makoto
Published: July 2002

Very flat epitaxial Si(111) films with high crystalline quality were grown using thin Al layers deposited onto γ-Al2O3 (111)/Si (111) substrates at room temperature, prior to the growth of Si films by Si2H6 gas source molecular beam epitaxy. Epitaxial Si layers grown with a 10-Å-thick Al predeposition layers showed 7×7 streaked reflection high-energy electron diffraction patterns and a mirrorlike surface. The epitaxial Si layer had a significantly improved crystalline quality and surface morphology comparable to that grown without the Al predeposition layer. The optimum Al thickness for a high quality Si film was 5–10 Å, even though the thickness was varied from 0 to 25 Å. The Al deposited surface was changed to an Al–O surface (rather than a metallic Al layer) just before Si growth at 800 °C, and a decrease in the incubation time was observed for an Al thickness of 5–10 Å. It is believed that a modification of the Al2O3 surface occurs, which results in improved crystalline quality of Si films grown on the Al2O3.
Valence-band offset at the Si/GaP (110) interface
Authors: Lazzouni M. E. , Peressi M. , Baldereschi A.
Published: July 2002

We present the results of self-consistent ab initio pseudopotential calculations of the valence-band offset at the Si/GaP (110) interface. For the abrupt interface we find an offset of 0.55 eV including spin-orbit splittings, self-energy corrections, and the effects of atomic relaxation. We also study how much the atomic interdiffusion across the interface can modify the offset and attribute to Si–Ga swaps the discrepancy between the commonly accepted experimental value of 0.80 eV and our results for the abrupt interface.
Photoluminescence studies of InAs/InGaAs/AlAs strained single quantum well structures
Authors: Shen W. Z. , Shen S. C. , Chang Y. , Tang W. G. , Lu Y. , Li A. Z.
Published: July 2002

We report on steady-state photoluminescence spectra from a strained InAs/In0.53Ga0.47As/AlAs single quantum well (SQW) structure grown by molecular beam epitaxy. Strong luminescence in the wavelength of ∼1.9 μm for the well width of 7 ML was obtained. The radiative process in the InAs quantum well is dominated by the excitonic luminescence. Based on a steadystate of the lumines- cence intensity allow us to conclude that the photogenerated carriers in the well come from tunneling from the InGaAs layer via the AlAs barrier.
Electrical transport properties of [001] tilt bicrystal grain boundaries in YBa2Cu3O7
Authors: Steel D. G. , Hettinger J. D. , Yuan F. , Miller D. J. , Gray K. E. , Kang J. H. , Talvacchio J.
Published: July 2002

The zero-field electrical transport properties of 24° [001] tilt bicrystal grain boundaries in YBa2Cu3O7 were found to be in excellent agreement with the Ambegaokar–Halperin model over an extended range of currents and voltages. This model gives a firm basis for characterizing and comparing boundaries, and provides two independent measures of the critical current, which were proportional to (1−T/Tc)2 close to the transition temperature Tc.
Linearly polarized, single-frequency, widely tunable Er:Yb bulk laser at around 1550 nm wavelength
Authors: Taccheo S. , Laporta P. , Svelto O.
Published: July 2002

We report on a 36 nm tunable, single-frequency, linearly polarized Er:Yb:glass laser. A tuning range from 1528 to 1564 nm, with output power ranging from 1 to 8 mW, is achieved. Wavelength tuning and linearly polarized output are simultaneously obtained by using a special polarizing etalon with anisotropic absorption losses.
Color-variable electroluminescence from multilayer polymer films
Authors: Hamaguchi Maki , Yoshino Katsumi
Published: July 2002

Color-variable emission has been observed from a multilayer polymer electroluminescent device composed of three polymer layers: perfluoropropylated poly(p-phenylene) (F-PPP) sandwiched between two emissive polymers, poly (3-dodecylthiophene) (PDT) and poly (p-phenylenevinylene) (PPV). Green and red emissions were observed when a negative bias was applied to the PPV and PDT side electrodes, respectively. F-PPP was supposed to act as an electron-blocking layer due to its small electron affinity (2.2 eV) compared with those of PPV (2.7) and PDT (3.5), and to facilitate the confinement of the excitons in the negatively biased polymer layer, where the radiative recombination of the charge carriers takes place.
Exciton diffusion length in microcrystalline chlorophyll a
Authors: Nasr Chouhaid , Taleb Toufik , Leblanc Roger M. , Hotchandani Surat
Published: July 2002

The measurements of photocurrent as a function of depletion layer or Schottky barrier width have been performed to determine the exciton diffusion length (L) in microcrystalline chlorophyll a (Chl a). This method of determining L is particularly advantageous in that it does not require a prior knowledge of the absorption coefficient of the material as is usually the case with other, e.g., constant surface photovoltage or constant photocurrent techniques. A value of 180 Å has been obtained for L in Chl a. While this value is comparable to those for many organic semiconductors, it is much inferior to that for the minority carriers in inorganic photoconductors. The smaller diffusion length may, in part, explain the feeble power conversion efficiency of Chl a and other organic photovoltaic cells.
Ultrasonic wave propagation in reticulated foams saturated by different gases: High frequency limit of the classical models
Authors: Leclaire Ph. , Kelders L. , Lauriks W. , Allard J. F. , Glorieux C.
Published: July 2002

Transmission experiments are performed on high porosity reticulated polyurethane foams saturated by different gases at ultrasonic frequencies up to 800 kHz. An excess attenuation is observed at high frequencies, when the wavelength is not sufficiently large compared to the lateral dimensions of the fibers. At lower frequencies, these experiments lead by using classical models of equivalent fluids, to a fast and reliable method for determining the characteristic length Λ.
Self-assembled quantum dots of InSb grown on InP by atomic layer molecular beam epitaxy: Morphology and strain relaxation
Authors: Ferrer J. C. , Peiró F. , Cornet A. , Morante J. R. , Uztmeier T. , Armelles G. , Briones F.
Published: July 2002

Self-organized InSb dots grown by atomic layer molecular beam epitaxy on InP substrates have been characterized by atomic force and transmission electron microscopy. Measurement of high-energy electron diffraction during the growth indicates a Stransky–Krastanov growth mode beyond the onset of 1.4 InSb monolayer (ML) deposition. The dots obtained after a total deposition of 5 and 7 ML of InSb present a truncated pyramidal morphology with rectangular base oriented along the 〈110〉 directions, elongated towards the [110] direction with {111}B lateral facets, with {113}/{114}/{111}A lateral facets in [11̄0] views, and (001) flat top surfaces. The mismatch between the dot and the substrate has been accommodated by a network of 90° misfit dislocation at the interface. A corrugation of the InP substrate surrounding the dot has been also observed.
An optical correlator using a low-temperature-grown GaAs photoconductor
Authors: Verghese S. , Zamdmer N. , Hu Qing , Brown E. R. , Förster A.
Published: July 2002

A sampling correlator is described which is useful for characterizing optical pulses with subpicosecond resolution. The correlator exploits the ultrafast nonlinear response of a photoconductor made of low-temperature-grown (LTG) gallium arsenide, which is connected to a coplanar-waveguide line. Instead of using a nonlinear crystal, the LTG-GaAs correlator uses a nonlinearity associated with the transmission line and photoconductor functioning as a voltage divider. The resulting nonlinearity is used to measure the intensity autocorrelation function.
Theory and properties of quasiwaveguide modes
Authors: Wang Huitian , Aruga Tadashi , Ye Peixian
Published: July 2002

A theory is developed to explain the origin of physical phenomena in quasiwaveguide, based on the forward scattering and multiple-wave interference effects. The properties of quasiwaveguide modes, such as positions, linewidths, the reflectivity of the reflected light spot, and the reflectivity distribution of scattered light are described. The shape of the m-lines is derived theoretically. Applications of the theory are also discussed.
Kohlrausch exponent of amorphous Zr65Al7.5Cu27.5 determined by anelastic relaxation measurements
Authors: Weiss M. , Moske M. , Samwer K.
Published: July 2002

Anelastic relaxations of amorphous Zr65Al7.5Cu27.5 have been studied in the range of the glass transition and in the supercooled liquid. Applying a force step function, an anelastic aftereffect of the form exp(t/τ)β (Kohlrausch–Williams–Watts function) is expected with an exponent β<1. From the measurement a value of β=0.67±0.03 is determined at Tg which confirms the empirical correlation between the fragility index m (36.4 for Zr65Al7.5Cu27.5) and β, established by Böhmer et al. This result is another indication for the metallic glass Zr65Al7.5Cu27.5 being a rather strong glass former. Furthermore, a strong increase in β just above Tg is found and is interpreted in the framework of a cluster model.
Band-gap blue shift by impurity-free vacancy diffusion in 1.5-μm-strained InGaAsP/InP multiple quantum-well laser structure
Authors: Cao N. , Elenkrig B. B. , Simmons J. G. , Thompson D. A. , Puetz N.
Published: July 2002

The effects of defect-enhanced, impurity-free, quantum-well (QW)-barrier compositional intermixing caused by the SiO2 cap annealing at 750 °C of a 1.5-μm InGaAsP/InP multiple quantum-well (MQW) laser structure have been studied by photoluminescence (PL). A substantial band-gap blue shift, as much as 112 nm (∼66 meV), was found in the structure and the value of the shift can be controlled by the anneal time. The amount of the shift does not depend on the thickness of the SiO2 cap layer. Ridge-waveguide lasers were fabricated on the different areas of the wafer, with and without a SiO2 cap during a 60 s anneal. The lasing wavelength of the laser produced with the SiO2 cap has a 78 nm blue shift over that of the laser without the SiO2 cap.
Demonstration of quantized conductance in deeply reactive ion etched In0.53Ga0.47As/InP electron waveguides with in-plane gates
Authors: Wesström Jan-Olof J. , Hieke Katharina , Stålnacke Björn , Palm Thomas , Stoltz Björn
Published: July 2002

Clear conductance quantization at T=4.2 K has been demonstrated in a 140 nm wide and 200 nm long trench-isolated In0.53Ga0.47As/InP electron waveguide with in-plane gates, using the surrounding two-dimensional electron gas as the gate. It was fabricated using metalorganic vapor phase epitaxy, electron beam lithography, and CH4/H2 reactive ion etching. In a T=20 K measurement on a 60 nm wide and 100 nm long device, only the first conductance plateau of 2e2/h was reached.
High exchange anisotropy and high blocking temperature in strongly textured NiFe(111)/FeMn(111) films
Authors: Choe G. , Gupta S.
Published: July 2002

Strongly textured NiFe(111) underlayers, deposited by dc magnetron sputtering with applied substrate bias, are utilized to grow large, epitaxial grains of FeMn(111). These perfectly oriented (111) NiFe/FeMn bilayers exhibit the highest interfacial exchange anisotropy energy (0.17 erg/cm2), lowest coercivity (∼2 Oe) of the pinned layer, and highest blocking temperature (205 °C) ever reported, to the best of our knowledge. The relationship between the blocking temperature and the x-ray diffraction intensity of FeMn(111) indicates that the exchange interaction across the NiFe and FeMn interface is enhanced by the well-oriented, large, defect-free FeMn(111) crystals.
Influence of Zr/Ti ratios on the deformation in the hysteresis loop of Pb(Zr,Ti)O3 thin film capacitors
Authors: Lee Eun Gu , Wouters Dirk J. , Willems Geert , Maes Herman E.
Published: July 2002

Electric field shift and deformation in the polarization-electric field characteristics of Pb(Zr,Ti)O3 (PZT) thin film capacitors with various Zr/Ti ratios have been studied as a function of the annealing temperature after patterning the top sputter-deposited Pt electrode using reactive ion etch with Ar gas. A large field shift and a constriction in the hysteresis loops are observed, particularly in low Zr/Ti PZT films annealed below 400 °C. A strong blocking layer effect in unannealed capacitor is found to be related to the internal field caused by trapped charges near electrodes. As the Zr/Ti ratio decreases, the field shift increases and the annealing temperature at which the internal field disappears also increases.
Temperature dependent tunnelling current at metal/polymer interfaces—potential barrier height determination
Authors: Koehler M. , Hümmelgen I. A.
Published: July 2002

It has been demonstrated that the expression for the temperature dependent tunneling current through a triangular potential barrier at metal/polymer interfaces fits experimental data including the deviation from a straight line observed in Fowler–Nordheim plots. The fitting parameters can be used to calculate the potential barrier height at the metal/polymer interface, which is of crucial importance for the control of charge injection in organic light emitting diodes. The tunneling current density expression reproduces the observed dependence of the current with temperature.
Determination of the interfacial magneto-optical effects in Co/Pt multilayer structures
Authors: Gao Xiang , Thompson Daniel W. , Woollam John A.
Published: July 2002

In this letter, we present results of a study of the magneto-optical Kerr response in Co/Pt superlattices by solving for optical constants and Voigt parameters of constituent layers in the structure. The absolute values of the Voigt parameters of Co/Pt interfaces were found to be about twice as large as for the Co layer in the superlattice. Furthermore, using the determined optical constants and Voigt parameters, we can generate the Kerr rotations and ellipticities for Co/Pt superlattices or sandwich structures with continuously changed layer thicknesses and different repeat numbers. Comparison of these theoretical results to the experimental magneto-optical responses for selected structures exhibits strong consistency.
Efficient doping of nitrogen with high activation ratio into ZnSe using a high-power plasma source
Authors: Kimura K. , Miwa S. , Yasuda T. , Kuo L. H. , Jin C. G. , Tanaka K. , Yao T.
Published: July 2002

We have developed a high-power (5 kW) rf plasma source for nitrogen doping in ZnSe molecular beam epitaxy. Optical emission spectroscopy shows dominant atomiclike emissions around 800 nm due to excited neutral nitrogen atoms in the high power region and their intensities rapidly increase with increasing the rf power from 1 to 3 kW. The high net acceptor concentration (NA–ND) of 1.2×1018 cm−3 was achieved at the growth temperature of 220 °C and the activation ratio [(NA–ND)/N] as high as 60%, which is the highest value so far obtained for NA–ND∼1018 cm−3. Consequently, the PL spectrum showed well-resolved deep donor-acceptor pair emissions even with high NA–ND.
Photoluminescence and far-infrared absorption in Si-doped self-organized InAs quantum dots
Authors: Phillips J. , Kamath K. , Zhou X. , Chervela N. , Bhattacharya P.
Published: July 2002

We report far-infrared absorption in directly doped self-organized InAs quantum dots. Photoluminescence spectra demonstrate a blue shift in peak intensity for increasing doping in the quantum dots. Far-infrared absorption measurements using a Fourier transform infrared spectrometer show absorption in the range of 13–18 μm for quantum dots with Al0.15Ga0.85As and GaAs as the barrier material.
Optical data storage read out at 256 Gbits/in.2
Authors: Martin Y. , Rishton S. , Wickramasinghe H. K.
Published: July 2002

A new form of read out for high density read-only memory is presented whereby a data density of 400 bits/μm2, corresponding to 256 Gbits/in.2, can be accessed at data rates in the tens of MHz range. The technique is based on detecting the modulation in light scattering from a sharp scattering object due to the dipole-dipole coupling between the probe and surface being scanned using a sensitive homodyne interferometer. Theoretical considerations indicate that data densities in the 100 Tbits/in.2 range could be accessed at data rates of 100 MHz using this technology.
Tailoring of trap-related carrier dynamics in low-temperature-grown GaAs
Authors: Smith P. W. E , Benjamin S. D. , Loka H. S.
Published: July 2002

In this letter, we present the results of an experimental study of low-temperature-grown GaAs, which clearly resolves separately both carrier trapping and recombination processes. We extend our previous model to account for the observed carrier dynamics, and show how the material growth and annealing conditions can be adjusted to optimize the material properties for all-optical device applications.
Electrical transport properties of artificially layered films of [BaCuO2]2/[(Sr,Ca)CuO2]n
Authors: Arciprete F. , Balestrino G. , Martellucci S. , Medaglia P. G. , Paoletti A. , Petrocelli G.
Published: July 2002

In this letter we show that SrCuO2/BaCuO2 and CaCuO2/BaCuO2 based artificial structures of very good crystallographic quality can be grown by pulsed laser deposition. We demonstrate that the most important parameters which determine the superconductive properties are the chemical composition, the oxygen growth pressure, and the CO2 contamination. A major difference is found in the behavior of resistivity between films containing Sr and Ca, respectively. Namely [BaCuO2]2/[SrCuO2]n films never show any trace of superconductivity, while [BaCuO2]2/[CaCuO2]n films result in having, for growth oxygen pressures PO2⩾0.2 mbar, a full transition with Tc (zero resistance) up to 46 K. Furthermore we demonstrate that even a tiny amount of CO2 in the oxygen growth atmosphere can suppress completely the superconducting properties of these artificial structures.
Cooperative effects in blue light emission of poly-(para-phenylene)-type ladderpolymer
Authors: Kranzelbinder G. , Nisoli M. , Stagira S. , De Silvestri S. , Lanzani G. , Müllen K. , Scherf U. , Graupner W. , Leising G.
Published: July 2002

A hyperlinear increase of radiative quantum efficiencies of poly(para-phenylene)-type ladderpolymer in the blue–green region as a function of subpicosecond excitation intensity is reported. The light emission in the range from 485 to 495 nm undergoes a change from linear behavior to a second order response; the two regimes are separated by a distinct threshold of 3.1 mJ/cm2. Above this threshold, investigation by femtosecond excitation–correlation measurements indicate that the hyperlinear blue emission is associated with a characteristic excitonic depopulation of 2 ps.
Faraday rotation in magnetic γ-Fe2O3/SiO2 nanocomposites
Authors: Guerrero H. , Rosa G. , Morales M. P. , del Monte F. , Moreno E. M. , Levy D. , Pérez del Real R. , Belenguer T. , Serna C. J.
Published: July 2002

Faraday rotation spectrum has been measured at room temperature in a magnetic nanocomposite of γ-Fe2O3/SiO2. The material consists of isolated γ-Fe2O3 nanoparticles dispersed in a silica matrix, and it was prepared through a sol-gel method. The composite contains 18% of γ-Fe2O3 in weight with an average particle size of 20 nm. It has a coercitivity of 30 Oe and an MS of 6 emu/g. The specific Faraday rotation spectrum exhibits a narrow peak centered around 765 nm, reaching a value of 110°/cm and an absorption coefficient of 64 cm−1. Faraday rotation versus applied field has also been measured, and a cycle similar to the one described by the magnetization has been found.
Memory window of Pt/SrBi2Ta2O9/CeO2/SiO2/Si structure for metal ferroelectric insulator semiconductor field effect transistor
Authors: Kim Yong Tae , Shin Dong Suk
Published: July 2002

We have proposed a Pt/SrBi2Ta2O9/CeO2/SiO2/Si structure for a ferroelectric gate of metal ferroelectric insulator field effect transistor. A memory window of the proposed ferroelectric gate increases as electric field applied to the SrBi2Ta2O9 layer increases, and the memory window of Pt/SrBi2Ta2O9/CeO2/SiO2/Si is relatively greater than that of Pt/SrBi2Ta2O9/SiO2/Si. As a result, the Pt/SrBi2Ta2O9(140 nm)/CeO2(25 nm)/SiO2/Si structure has sufficiently programmable memory windows from 0.9 to 2.5 V in the low gate voltage range of 4–7 V.
Decay kinetics and thermoluminescence of PbWO4: La3+
Authors: Nikl M. , Bohäc̆ek P. , Nitsch K. , Mihoková E. , Martini M. , Vedda A. , Croci S. , Pazzi G. P. , Fabeni P. , Baccaro S. , Borgia B. , Dafinei I. , Diemoz M. , Organtini G. , Auffray E. , Lecoq P. , Kobayashi M. , Ishii M. , Usuki Y.
Published: July 2002

Correlated measurements of emission spectra, photoluminescence and scintillation decays, thermoluminescence, and light yield were performed on a selected set of undoped and La-doped PbWO4 single crystals. The samples were grown from 5N purity raw powders and show the blue emission component only. Distinct influence of La doping was found in the decays, thermoluminescence and light yield characteristics. It is discussed in the light of the direct influence of La doping on suppressing the creation of point defect centers in the PbWO4 lattice, which are involved in the energy transfer and storage processes in this material.
Metallic conductivity of amorphous carbon films under high pressure
Authors: Bhattacharyya Somnath , Subramanyam S. V.
Published: July 2002

Amorphous carbon films are prepared by plasma-assisted chemical vapor deposition. Resistivity of the films is measured from 300 down to 8 K showing a negative temperature coefficient of resistivity. An increase of room temperature conductivity from 102 S cm−1 to a value of about 104 S cm−1 is found at a pressure of 2 GPa. At a fixed pressure of 0.5 GPa, the films show a positive temperature coefficient of conductivity in the range from 300 to 200 K, followed by a very weak dependence of temperature down to 15 K. At a pressure of 2 GPa a positive temperature coefficient of resistivity is observed in the range between 300 and 15 K. The metallic behavior of the carbon films under high pressure is explained using electronic structure.
The effects of oxidation temperature on the capacitance–voltage characteristics of oxidized AlN films on Si
Authors: Kolodzey J. , Chowdhury E. A. , Qui G. , Olowolafe J. , Swann C. P. , Unruh K. M. , Suehle J. , Wilson R. G. , Zavada J. M.
Published: July 2002

The thermal oxidation of AlN thin films produces a high quality insulator which exhibits the gate voltage-controlled charge regimes of accumulation, depletion, and inversion on Si surfaces. The temperature dependence of oxidation is important for device processing. We report on the composition, structure, and electrical properties of the AlN versus the oxidization temperature. AlN layers 500 nm thick were deposited by rf sputtering on p-type Si (100) substrates, followed by oxidation in a furnace at temperatures from 800 to 1100 °C with O2 flow. An oxidation time of 1 h produced layers of Al2O3 with small amounts of N having a thickness of 33 nm at 800 °C, and 524 nm at 1000 °C. Electrical measurements of metal-oxide-semiconductor capacitors indicated that the dielectric constant of the oxidized AlN was near 12. The best layer had a flatband voltage near zero with a net oxide trapped charge density less than 1011 cm−2. These results show that oxidized AlN has device-grade characteristics for the gate regions of field effect transistors, and for optoelectronic applications.