bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of metal–oxide–semiconductor capacitors, fabricated on (111) β-SiC epilayers grown on (111) TiC
Authors: Chen H-S. , Parsons J. D.
Published: July 2002

Metal–oxide–semiconductor (MOS) capacitors, fabricated on two n-type and one p-type (111) β-SiC epilayers, were characterized by C–V measurements. The β-SiC epilayers were grown on (111) bulk TiC substrates, by pyrolysis of disilylethane. Inversion, in the dark, was obtained in MOS capacitor structures on both n-type epilayers; demonstrating the feasibility of inversion mode MOS field effect transistors in β-SiC grown on TiC. The Terman method was used to estimate the interface trap density (Dit) at between 2×1011 cm−2 eV−1 and 1.4×1012 cm−2 eV−1; where Dit increased with carrier concentration.
dc SQUIDs based upon YBa2Cu3O7 nanobridges
Authors: Schneider J. , Mück M. , Wördenweber R.
Published: July 2002

Superconducting quantum interference devices (dc SQUIDs) were fabricated from high-temperature superconducting YBa2Cu3O7 thin films, using nanobridges as weak links. The weak link behavior in these devices caused by coherent motion of vortices was observed for bridges with dimensions smaller than the effective penetration depth, which was approximately 400–600 nm for the films. The dc SQUIDs consisted of two parallel nanobridges with widths of 100–500 nm. The size of the SQUID hole ranged from 2×2 to 2×10 μm2. The SQUIDs were operated in the temperature range from liquid helium up to 85 K and showed voltage modulations as a function of an applied magnetic field. At 75 K peak-to-peak values of 15 μV were observed. The flux noise at 4.2 K was determined to be smaller than 8×10−5 φ0 /√Hz.
One-dimensional parallel Josephson-junction arrays as a tool for diagnostics
Authors: van der Zant H. S. J. , Receveur R. A. M. , Orlando T. P. , Kleinsasser A. W.
Published: July 2002

We propose and demonstrate the use of underdamped, one-dimensional parallel arrays of Josephson junctions as a tool for circuit diagnostics. By measuring the Fiske modes and the critical current in a magnetic field, we determined the self- and nearest-neighbor inductances as well as the capacitances of single junctions. We have used this technique to find the capacitance of Nb-Al2Ox-Nb junctions for critical current densities of 0.3–20 kA/cm2. We find that the specific capacitance increases by about a factor of 2 over this range. This increase has important consequences for the design of single-flux-quantum circuits and SQUIDs. Measurement of the junction capacitance for critical current densities of 100 kA/cm2 is possible, but requires submicrometer junctions with dimensions of the order of 0.3 μm.
In situ pattern deposition of In2O3 and in situ pattern etching of GaAs
Authors: Ozasa Kazunari , Kim Eun Kyu , Aoyagi Yoshinobu
Published: July 2002

The selective deposition of In2O3 was studied on GaAs substrates having a carbon pattern prepared by electron beam (EB) irradiation, in order to fabricate an In2O3 mask for in situ processing. The carbon pattern less than 5 nm thick was formed on GaAs by the scanning irradiation of EB in trimethylindium (TMIn) ambient, and the subsequent deposition of In2O3 was carried out in situ with a simultaneous supply of TMIn and H2O2. By this two-step processing, the carbon pattern is transferred to an In2O3 film below 550 °C, which can be used as a mask for in situ selective epitaxy of semiconductors. We also found for the first time that the selective etching of GaAs takes place under H2O2 at temperatures above 600 °C. The mechanism of the etching process involves the oxidation of GaAs by H2O2 and the simultaneous desorption of GaAs oxide. The selectivity in the In2O3 deposition and the GaAs etching is derived from the suppression of TMIn decomposition or GaAs oxidation on the carbon pattern. Considering that the deep submicron carbon pattern can be formed by focused EB irradiation, the pattern transferring technique presented here is advantageous for in situ processing of nanostructures.
Study of Y1Ba2Cu3O7−δ film growth on (200) oriented yttria stabilized zirconia buffer layer on metallic substrates
Authors: Chatterjee R. , Fukutomi M. , Aoki S. , Togano K. , Maeda H.
Published: July 2002

This work presents the first report on the growth mechanism of 123 films on metallic substrates with (200) oriented and partially a-b plane oriented polycrystalline yttria stabilized zirconia (YSZ) buffer layer, with and without a metallic underlayer coating used between the substrate and the buffer layer. The microstructure and grain morphology of 9- and 160-nm-thick films of Y1Ba2Cu3O7−δ (YBCO) were studied by scanning electron microscopy, scanning tunneling microscopy, and x-ray diffraction. Our studies reveal that YBCO films on c-axis oriented and partial a-b plane oriented YSZ buffer layers on metallic substrates, initially grow two dimensionally, with the elongated grains of ∼100 nm length, mostly aligned along the 〈200〉 axis of the YSZ, owing to the strong atom-substrate bonding. The thicker films, however, show three-dimensional terraced island growth with several turns of the screws, with the screw edges still along the 〈200〉 axis of YSZ. These terraced islands seem to coalesce in the film with the highest Jc value, ∼1×105 A/cm2.
Experimental evidence of slow dynamics in amorphous metal using fiber-optic interferometry
Authors: Dagenais D. M. , Bucholtz F.
Published: July 2002

New results on the study of slow dynamics in ferromagnetic amorphous alloys are presented. Experimental evidence has been obtained of low-frequency relaxation phenomena in highly magnetostrictive amorphous alloys submitted to various anneal treatments. Dynamics of the amplitude and phase of intrinsic magnetic noise in the metallic glass Metglas 2605S-2 have been measured with a fiber-optic interferometer.
Simple microsecond YAlO3:Nd laser
Authors: Pokhsrarian K. M.
Published: July 2002

A simple technique for variable microsecond (1.5–5 μms) pulse generation with neodymium laser has been demonstrated using a laser cavity with a rotating mirror and amplifier configuration. Pulse energies up to 0.5 J have been achieved.
Highly nondegenerate four-wave mixing efficiency of an asymmetric coupled quantum well structure
Authors: Paiella Roberto , Vahala Kerry J.
Published: July 2002

An asymmetric coupled quantum well structure is theoretically investigated as a means of tailoring the conversion efficiency of the four-wave mixing process at terahertz detuning rates. In this structure, a coherent electronic oscillation between the two wells can be excited that introduces a resonance peak in the four-wave mixing frequency response. A calculation based on the density matrix formalism shows that an increase in the power conversion efficiency on the order of 10 dB can be attained at the selected resonance frequency for low temperature operation. Finally, we propose a novel technique for exciting the interwell oscillations that takes advantage of the polarization dependence of the interband optical transitions in alternating strain quantum wells.
Single-mode/multimode waveguide electro-optic grating coupler modulator
Authors: Wang Michael R. , Xu Guoda , Lin Freddie , Jannson Tomasz
Published: July 2002

A waveguide electro-optic grating coupler modulator based on a single straight channel waveguide and an interdigital modulation electrode structure on an electro-optic substrate, has been reported. Both single-mode and multimode operations are possible. Preliminary experiments have demonstrated the modulation on a proton exchanged LiNbO3 waveguide device. Modulation performed on other electro-optic waveguides, such as GaAs, LiTaO3, and EO polymers, are also possible.
Poled electro-optic photolime gel polymer doped with chlorophenol red and bromomethyl blue chromophores
Authors: Gerold Dave , Chen Ray T. , Farone William A. , Pelka David
Published: July 2002

An electro-optic polymer with chlorophenol red dye and type-A photolime gel was demonstrated. The electro-optic coefficient γ33 in the direction of the poling field was measured to be 28 pm/V. Chlorophenol red in polymer showed a 1/e relaxation time constant of 820 h, which is more stable than other dye demonstrated previously to be electro-optic in the same polymer.
Electrical characterization of AlxGa1−xAs grown by low-pressure organometallic vapor phase epitaxy using trimethylamine alane as the aluminum precursor
Authors: Paraskevopoulos Nicholas G. , McAfee Sigrid R. , Hobson William S.
Published: July 2002

The electrical properties of AlxGa1−xAs (0≤x≤0.44) grown by organometallic vapor phase epitaxy using trimethylamine alane as the Al precursor were investigated. High-quality AlGaAs Schottky barriers were fabricated and characterized by current–voltage, capacitance–voltage, and deep level transient spectroscopy measurements. The epilayers showed excellent electrical characteristics with low overall trap concentrations. In particular, the AlxGa1−xAs layers contained very low concentrations of EL2.
Band offset at p-ZnTe/p-ZnSe heterointerface
Authors: Ukita M. , Hiei F. , Nakano K. , Ishibashi A.
Published: July 2002

We have estimated the valence band discontinuity ΔEV at the p-ZnSe/p-ZnTe interface by means of electrical measurements. From capacitance-voltage measurement of a Schottky-like barrier at the heterojunction, ΔEV∼0.8 eV is found. The current-voltage characteristics of the junctions, however, suggest smaller values for ΔEV. The likely origin of this difference is leakage paths of the current in the barrier at the junction.
Near-band-edge absorption and positron trapping under illumination in semi-insulating GaAs: Role of As vacancies
Authors: Le Berre C. , Corbel C. , Mih R. , Brozel M. R. , Tüzemen S. , Kuisma S. , Saarinen K. , Hautojärvi P. , Fornari R.
Published: July 2002

We show that positron trapping at negative As vacancies revealed under illumination in bulk semi-insulating GaAs correlates with a form of near-band-edge absorption known as reverse contrast (RC). We conclude that it is the ionization of As vacancies to their negative charge state that gives rise to RC absorption.
Electroluminescence from porous silicon due to electron injection from solution
Authors: Kooij E. S. , Despo R. W. , Kelly J. J.
Published: July 2002

We report on the electroluminescence from p-type porous silicon due to minority carrier injection from an electrolyte solution. The MV+• radical cation formed in the reduction of divalent methylviologen is able to inject electrons into the conduction band of crystalline and porous silicon. The electrochemistry of this redox process at silicon electrodes is briefly described, and electroluminescence due to recombination of the injected electrons with holes from the substrate is described. The results are discussed in terms of a semiconductor model.
Shear piezoelectric properties of vinylidene fluoride trifluoroethylene copolymer, and its application to transverse ultrasonic transducers
Authors: Omote Kenji , Ohigashi Hiroji
Published: July 2002

Shear piezoelectric properties of a vinylidene fluoride trifluoroethylene copolymer [P(VDF/TrFE)] have been studied in a temperature range from 10 to 350 K. The shear electromechanical coupling factors k15 and k24 at 290 K are found to be 0.19 and 0.20, respectively, the values being largest among the piezoelectric polymers known at present. The factors k15 and k24 remain constant below 200 K, while k24 increases and k15 decreases above 200 K. The effectiveness of P(VDF/TrFE) as a transverse ultrasonic transducer material was demonstrated by measurements of transverse sound velocities and absorptions in aluminum and poly(methyl methacrylate) with P(VDF/TrFE) shear transducers.
Sequential tunneling in [100]- and [111]-oriented InGaAs/GaAs multi-quantum wells by photocapacitance
Authors: Sánchez-Rojas J. L. , Sacedón A. , Calleja E. , Muñoz E.
Published: July 2002

The features present in the capacitance– and conductance–voltage characteristics of [100]- and [111]-oriented InGaAs/GaAs multi-quantum well (MQW) p-i-n structures under illumination are described. Sequential tunneling of electrons and holes is proposed to explain the different peaks observed, as they occur at voltages corresponding to resonant alignment of energy levels of adjacent wells. Two kinds of piezoelectric [111] devices are analyzed, with positive or negative average electric fields in the MQW region. The voltage corresponding to zero average electric field in the MQW is detected by a feature in the dark device capacitance. For the sample with negative average electric field, the capacitance characteristics clearly reflect the presence and evolution with voltage of a long range screening of the piezoelectric fields by the photogenerated carriers.
Thin film relaxation in cross-sectional transmission electron microscopy specimens of GexSi1−x/Si strained-layer superlattices
Authors: Duan X. F.
Published: July 2002

A large-angle convergent-beam electron diffraction (LACBED) pattern with fine diffraction lines from a cross-sectional specimen of GexSi1−x/Si strained-layer superlattices (SLS) can give much information on local strain and misfit stress relaxation. The shift of the diffraction lines in the GeSi layers from those in the Si layers can be used to determine the strain relaxation. A profile of the thin film relaxation versus the specimen thickness is presented.
Controlled III–V semiconductor cluster nucleation and epitaxial growth via electron-beam lithography
Authors: Sleight J. W. , Welser R. E. , Guido L. J. , Amman M. , Reed M. A.
Published: July 2002

Controlled registration of InAs clusters and selective-area growth of InAs thin films on GaAs substrates is achieved via a combined high dose electron beam lithography/metalorganic chemical vapor deposition technique. Auger electron spectroscopy and secondary electron microscopy measurements show that growth inhibition is not a consequence of native oxide masking or processing related surface contamination, but instead is attributable to modification of the GaAs surface energy. This phenomenon is observed for a wide range of lithographic patterns and growth conditions on both (100) and (111)B oriented n-type and semi-insulating GaAs substrates.
Studying the insulator–conductor interface with a scanning tunneling microscope
Authors: Sumetskii Michael I. , Baranger Harold U.
Published: July 2002

We suggest that a scanning tunneling microscope (STM) may be used for investigating the insulator–conductor interface, in particular SiO2/Si, at nanometer scale. For an insulating film transparent to tunneling, we estimate, using a simple model, the roughness of the interface from the STM image. It is found that the interface roughness is less than the roughness of the image surface times the ratio of effective decay lengths in the film and in vacuum. For relatively wide films, of order 10 nm, STM measurement in the field emission regime can give the interface image with 1 nm precision.
Integrated high-T
c multiloop magnetometer
Authors: Ludwig F. , Dantsker E. , Kleiner R. , Koelle D. , Clarke John , Knappe S. , Drung D. , Koch H. , Alford Neil McN. , Button Tim W.
Published: July 2002

Two integrated, thin-film multiloop magnetometers (fractional turn SQUIDs) have been fabricated using a YBa2Cu3O7−x-SrTiO3-YBa2Cu3O7−x multilayer process. The magnetometers have 16 parallel loops, an outer diameter of 7 mm and effective areas of 1.84 and 1.89 mm2, respectively. The magnetic field noise of the better device, measured in a YBCO tube at 77 K with a bias reversal scheme, was 37 fT Hz−1/2 at 1 Hz and 18 fT Hz−1/2 at 1 kHz.
Coherent exciton lasing in ZnSe/ZnCdSe quantum wells?
Authors: Flatté M. E. , Runge E. , Ehrenreich H.
Published: July 2002

A new mechanism for exciton lasing in ZnSe/ZnCdSe quantum wells is proposed. Lasing, occurring below the lowest exciton line, may be associated with a BCS-like condensed (coherent) exciton state. This state is most stable at low temperatures for densities in the transition region separating the exciton Bose gas and the coherent exciton state. Calculations show the gain region to lie below the exciton line and to be separated from the absorption regime by a transparency region of width, for example, about 80 meV for a 90 Å ZnSe/Zn0.75Cd0.25Se quantum well. Experimental observation of the transparency region using differential spectroscopy would confirm this picture.
Prevention of oxide formation during liquid phase epitaxy of silicon
Authors: Weber K. J. , Blakers A. W.
Published: July 2002

Successful growth of silicon in a liquid phase epitaxial (LPE) system requires preventing the formation of a native oxide more than a few monolayers thick. It has been found that the desorption of oxygen and water vapor from the ends of the furnace tube can lead to oxidation of silicon wafers located in the tube center, thus inhibiting epitaxy. A simple method to avoid this problem and eliminate the need for long flush times is described. Evidence is presented that indium, a common solvent in LPE of silicon, plays a catalytic role in the oxidation of silicon.
Structure and magneto-optical properties of epitaxial PtMnSb(001) on W(001)/MgO(001)
Authors: Kautzky M. C. , Clemens B. M.
Published: July 2002

The growth of high-quality, sputter-deposited epitaxial PtMnSb(001) on W(001)/MgO(001) is described. X-ray diffraction results indicate that PtMnSb grows unrotated on the W seed layer with a modest in-plane tensile strain. Polar magneto-optic Kerr effect measurements show a peak rotation of 1.02° at 575 nm. In-plane magnetization is observed, indicating that the level of strain in the film is insufficient to induce perpendicular magnetization.
Area selective deposition of gold on silicon surface patterned by tip-induced anodization in scanning probe microcopy
Authors: Sugimura Hiroyuki , Nakagiri Nobuyuki
Published: July 2002

The difference in chemical reactivity between silicon (Si) and anodic oxide surfaces was used to fabricate gold (Au) nanostructures. By means of scanning tunneling microscope tip-induced anodization, a Si surface terminated with hydrogen (Si–H) was patterned with the anodic oxide. Subsequently, the patterned sample was treated in an electroless plating bath to deposit Au on it. Using a scanning electron microscope, an energy dispersion x-ray spectroscope, and an atomic force microscope, we confirmed that the Au deposition selectively occurred on the Si–H surface where it was not anodized. The anodic oxide surface served as a mask to prevent Au deposition. Au lines of less than 200 nm in width could be fabricated on the Si–H surface.
Microwave characteristics of coplanar waveguides on helium-implanted epitaxial p-InP
Authors: Rao H. G. , Liu Q. Z. , Kellner A. L. , Jiang X. S. , Lau S. S. , Yu P. K. L.
Published: July 2002

The electrodes of a microwave coplanar waveguide (CPW) on planar p-InP epitaxial layers are electrically isolated by helium implantation. Impedance, attenuation, and relative effective dielectric permittivity of implanted and unimplanted samples are compared over a frequency range of 0.13–20 GHz. The results show that coplanar waveguides on 4He+ implanted materials exhibit very low loss (<1.4 dB/cm) and low dispersion comparable to those fabricated directly on semi-insulating InP. CPWs made on uniformly implanted substrates show no significant change in dielectric permittivity after annealing at temperatures up to 310 °C.
Low regrowth–interface recombination rates in InGaAs–GaAs buried ridge lasers fabricated by in situ processing
Authors: Strand T. A. , Thibeault B. J. , Mui D. S. L. , Coldren L. A. , Petroff P. M. , Hu E. L.
Published: July 2002

We report the use of low damage dry etching and in situ molecular beam epitaxial (MBE) regrowth in creating high-quality regrown interfaces. By fabricating buried, etched ridge InGaAs/GaAs lasers, we are able to measure the interface recombination portion of the threshold current and extract the interface recombination velocity. We find that a two-part etching process composed of ion beam assisted etching and chlorine gas etching, followed by in situ MBE regrowth, results in a very low interface recombination velocity of 3×103 cm/s.
Use of a laser beam interference technique for the determination of the minority carrier diffusion length in layers of a p-n junction
Authors: Levy D. , Weiser K.
Published: July 2002

A new technique is reported for measuring the diffusion length of minority carriers in a layer of a p-n junction. The technique consists of illuminating a sample with a sinusoidally varying illumination pattern produced by two interfering laser beams and measuring the corresponding photovoltage along the plane of the sample. The diffusion length is obtained from the dependence of the voltage on the fringe distance.
Photoluminescence efficiency study of wet chemically etched CdTe/Cd1−xMgxTe wires
Authors: Illing M. , Bacher G. , Forchel A. , Litz T. , Waag A. , Landwehr G.
Published: July 2002

Optically active semiconductor wires with lateral extensions between 60 nm and 5 μm based on CdTe/Cd1−xMgxTe quantum well structures have been fabricated by electron beam lithography and subsequent pattern transfer using a wet chemical etching process. Changes of the relative photoluminescence efficiency have been studied by photoluminescence spectroscopy as a function of the wire widths. For narrow wires nonradiative recombination at the wire sidewalls becomes the major recombination mechanism, strongly decreasing the photoluminescence efficiency. We discuss the influence of the exciton diffusion on the photoluminescence efficiency by investigating the wire width dependence of the photoluminescence intensity as a function of temperature and quantum well thickness. High photoluminescence efficiencies are obtained in the case of small diffusion lengths as for example at low temperatures and narrow quantum wells.
Nonlinear theory of large-signal mode locking in a gyrotron oscillator
Authors: McCurdy A. H.
Published: July 2002

Nonlinear, time-dependent calculations have been carried out for closed-cavity gyrotron oscillations using a strongly modulated electron beam. It is found that radiation pulses of width 200 ps can be generated with carrier frequency of 18 GHz at over 10% efficiency. The gyrotron features a tapered wall radius to allow an equidistant spectrum of cavity modes. Evidence of a disruption in locking is found at electron beam currents several times the start oscillation value.
Gain properties of doped GaAs/AlGaAs multiple quantum well avalanche photodiode structures
Authors: Menkara H. M. , Wagner B. K. , Summers C. J.
Published: July 2002

A comprehensive characterization has been made of the static and dynamical response of conventional and multiple quantum well (MQW) avalanche photodiodes (APDs). Comparison of the gain characteristics at low voltages between the MQW and conventional APDs show a direct experimental confirmation of a structure-induced carrier multiplication due to interband impact ionization. Similar studies of the bias dependence of the excess noise characteristics show that the low-voltage gain is primarily due to electron ionization in the MQW-APDs, and to both electron and hole ionization in the conventional APDs. For the doped MQW APDs, the average gain per stage was calculated by comparing gain data with carrier profile measurements, and was found to vary from 1.03 at low bias to 1.09 near avalanche breakdown.
Enhanced real-space electron transfer in charge injection transistors with source-channel heterojunctions formed by graded AlxGa1−xAs layer and shallow Pd/Ge ohmic contacts
Authors: Lai Jiun-Tsuen , Ya-min Lee Joseph
Published: July 2002

Charge injection transistors (CHINTs) with source-channel heterojunctions are fabricated by using graded AlxGa1−xAs layers and shallow Pd/Ge ohmic contacts. Enhanced real-space electron transfer is observed in CHINTs with source-channel heterojunctions. The devices with graded AlxGa1−xAs launcher layers show lower threshold drain voltage for electron transfer, higher transconductance, and lower onset drain voltage for negative differential resistance than those without graded launchers. This is the first time that CHINT devices with source-channel heterojunctions are demonstrated experimentally to have enhanced electron transfer.
Determination of the time constant of fast photorefractive materials using the phase modulation technique
Authors: Sugg B. , Shcherbin K. V. , Frejlich J.
Published: July 2002

We present a method to determine the dielectric relaxation time using a phase-modulation technique. The predictions were checked using a GaAs crystal. The experimental results agree well with the theory.
Tunable, single frequency erbium fiber laser using an overlay bandpass filter
Authors: Gloag A. , Langford N. , McCallion K. , Johnstone W.
Published: July 2002

We describe a single frequency, unidirectional erbium fiber ring laser. Wavelength selection is performed by a ‘‘continuous fiber’’ filter of the fiber to planar waveguide coupler type. Varying the refractive index experienced by the exposed surface of the filter allowed the single longitudinal mode output from the laser to be tuned, discretely, from 1556–1561 nm with a resolution limited linewidth of 52 kHz.
Structural studies of tetrathiafulvalene–tetracyanoquinodimethane thin films by scanning tunneling microscopy
Authors: Ara Norihiko , Kawazu Akira , Shigekawa Hidemi , Yase Kiyoshi , Yoshimura Masamichi
Published: July 2002

Thin films of tetrathiafulvanene–tetracyanoquinodimethane (TTF-TCNQ) grown on mica substrates by vacuum deposition were studied by scanning tunneling microscopy (STM). STM images displayed the usual arrangement of alternative TTF and TCNQ columns aligned parallel to the crystal b axis. However, in addition to the same phase as that of a TTF-TCNQ bulk crystal, a new phase is observed. In this new phase the tilt angles the TCNQ and TTF molecular planes make with the a×b axis are different from those observed in the normal phase. This new phase can be explained by the introduction of a stacking fault on the surface.
Explanation for the temperature insensitivity of the Auger recombination rates in 1.55 μm InP-based strained-layer quantum-well lasers
Authors: Seki Shunji , Lui Wayne W. , Yokoyama Kiyoyuki
Published: July 2002

We study the temperature sensitivity of the Auger recombination rates in 1.55 μm InP-based strained-layer (SL) quantum-well (QW) lasers on the basis of the band structures obtained by the self-consistent numerical solution of the Poisson equation, the scalar effective-mass equation for the conduction band, and the multiband effective mass equation for the valence band. The results of the theoretical analysis are then compared with the recent experimental results to clarify the basic physical mechanism which determines the Auger recombination rates in SL-QW lasers. It is shown that the recent temperature sensitivity measurements of Auger recombination coefficients can be consistently explained in terms of the direct band-to-band Auger process in the quasi-two-dimensional system. We demonstrate that the Auger recombination process in 1.55 μm InP-based SL-QW lasers is mainly dominated by the direct band-to-band Auger process regardless of QW structures in the temperature range of 273–398 K.
Carrier and screening dynamics in strained [111]-oriented multiple quantum wells
Authors: Harken D. R. , Huang X. R. , McCallum D. S. , Smirl Arthur L. , Sánchez-Rojas J. L. , Sacedón A. , Calleja E. , Muñoz E.
Published: July 2002

We have time-resolved the piezoelectric optical nonlinearities of a strained, [111]-oriented InGaAs/GaAs multiple quantum well p-i-n structure. By monitoring the temporal evolution of the excitonic absorption spectrum, we follow the photogenerated carriers as they drift to form the space-charge field responsible for screening the piezoelectric field. From the carrier dynamics, we can separate the contribution of in-well screening from that of the long-range screening associated with carriers that have escaped the wells. We have determined that in narrow quantum wells, in-well screening is smaller than long-range screening and that in-well screening is obscured by the concurrent onset of strong bleaching.
Effect of Ti deposition temperature on T
i
S
i
x resistivity
Authors: Naeem M. D. , Orr-Arienzo W. A. , Rapp J. G.
Published: July 2002

The effects of Ti deposition temperature on the resistivity of as-deposited films are reported. The microstructure of as-deposited Ti films and its effect on electrical properties of TiSix formed during subsequent thermal annealing are investigated. Our work shows that the film deposition temperature not only affects the resistivity of as-deposited film but also influences the resistivity of TiSix formed during thermal anneals. The microstructure, specifically the grain size, of as-deposited Ti films appears to be the controlling factor in formation of TiSix phases.
One-dimensional transport of electrons in Si/Si0.7Ge0.3 heterostructures
Authors: Holzmann M. , Többen D. , Abstreiter G. , Wendel M. , Lorenz H. , Kotthaus J. P. , Schäffler F.
Published: July 2002

Magnetotransport of high-mobility electrons in quasi-one-dimensional quantum wires in Si/Si0.7Ge0.3 heterostructures is studied. Arrays of shallow and deep etched wires with a period of 480 nm are defined by laser holography and patterned by reactive ion etching. Typical features of transport in narrow electron channels, such as oscillations due to the depopulation of quasi-one-dimensional subbands and an anomalous resistance maximum at low magnetic fields are observed. The narrowest channels have an effective width of ≊70 nm and a sublevel spacing of 1 meV.
Polarization rotation modulator in a strained [110]-oriented multiple quantum well
Authors: McCallum D. S. , Huang X. R. , Smirl Arthur L. , Sun D. , Towe E.
Published: July 2002

The inherent optical anisotropy of a strained [110]-oriented multiple quantum well structure is used to make an optically addressed light modulator based on polarization rotation. The anisotropy of the multiple quantum well absorption coefficient for orthogonal polarizations causes rotation of the plane of polarization of light passing through the structure. By partially bleaching the quantum well exciton, the amount of polarization rotation is changed, and therefore modulation of the amplitude of the transmitted beam is achieved.
Post-growth tuning of inverted cavity InGaAs/AlGaAs spatial light modulators using phase compensating dielectric mirrors
Authors: Karim Z. , Kyriakakis C. , Tanguay A. R. , Cartland R. F. , Hu K. , Chen L. , Madhukar A.
Published: July 2002

A novel method is demonstrated for the correction of cavity thickness deviations imposed by technological limitations in the growth process of a resonant cavity spatial light modulator. This method is based on cavity phase compensation through the use of an externally-deposited dielectric Bragg mirror and provides an effective means of optimizing the device characteristics. In particular, such mirrors can significantly relax otherwise stringent epitaxial growth requirements in the fabrication of hybrid silicon/compound-semiconductor spatial light modulators incorporating Fabry–Perot cavities. We further demonstrate deposition of a conductive, index-tunable indium tin oxide (ITO) antireflection coating that is designed to maximize the contrast ratio and throughput of the inverted-cavity modulator configuration.
Beryllium diffusion in GaAs/AlGaAs single quantum well separate confinement heterostructure laser active regions
Authors: Kohnke G. E. , Koch M. W. , Wood C. E. C. , Wicks G. W.
Published: July 2002

Beryllium (Be) diffusion into the active layers of single quantum well separate confinement heterostructure lasers grown by molecular beam epitaxy is investigated using photoluminescence absorption spectroscopy, secondary ion mass spectroscopy, capacitance–voltage profiling, and laser threshold current measurements. A significant amount of Be diffusion occurs under normal growth conditions. Large concentrations of Be in the quantum well are correlated to the lack of an exciton feature in the absorption spectrum. The amount of Be in the active region is reduced through a combination of lower Be concentration and lower growth temperature in the upper cladding region of the laser.
Degradation mechanism of base current increase under forward current stress in AlGaAs/GaAs heterojunction bipolar transistors
Authors: Chang Y. H. , Li G. P.
Published: July 2002

Base current degradation mechanisms in carbon-doped AlGaAs/GaAs heterojunction bipolar transistors (HBTs) under forward current stress is investigated in transistors with a thin AlGaAs surface protection ledge. Although the base current in HBTs with ledge is relatively stable compared to that in HBTs without ledge, the base current increase in some of these passivated HBTs is still noticeable. An increase of surface recombination current in the region surrounding the AlGaAs ledge is identified as a primary degradation mechanism. To alleviate the base current instability, several passivated emitter-base junction fabrication processes are recommended.
Room temperature electron cyclotron resonance chemical vapor deposition of high quality TiN
Authors: Boumerzoug Mohamed , Pang Zhengda , Boudreau Marcel , Mascher Peter , Simmons John G.
Published: July 2002

High quality, gold-colored TiN was deposited at room temperature by decomposing TiCl4 in the downstream of an N2/H2 electron cyclotron resonance (ECR) plasma. The morphology of the as-deposited films was investigated by scanning electron microscopy, and the resistivity was measured using the four point probe technique. The films were uniform over 2 in. wafers, with resistivities of 100–150 μΩ cm. Auger electron spectroscopy was used for the determination of the Ti/N ratio and for the detection of contaminants, and shows that the as-deposited films were stoichiometric and chlorine free. The present results represent a major improvement in lowering the deposition temperature of TiN using ECR plasma-enhanced chemical vapor deposition with TiCl4 as reactant.
High temperature surface peaks and surface reconstruction of the (001) SrTiO3−δ substrate surfaces studied by channeling
Authors: Chin C. C. , Morishita T.
Published: July 2002

The temperature dependence of the surface peaks of the (001) SrTiO3 substrate surfaces was studied for the sample temperature up to 750 °C by channeling. The temperature dependence of the Sr surface peaks was found to be due to the thermal vibration of the Sr atoms. However, an anomalous temperature dependence of the Ti surface peak was observed which may be due to the displacement of Ti surface atoms. The Ti surface peaks are maximum at 400 °C. For the reduced SrTiO3−δ, surface reconstruction was observed on the Sr surface sublattice but the anomalous temperature dependence of the Ti surface peak disappeared.
Visible-wavelength surface-emitting devices with a 15-fold improvement in electrical-to-optical power conversion efficiency
Authors: Thomas K. J. , Guido L. J. , Beggy J. C. , Smith S. , Burnham R. D.
Published: July 2002

An AlxGa1−xAs p-n junction light emitting diode, with a thin In2O3 current spreading layer, on the top side, and an indirect band-gap AlAs-Al0.6Ga0.4As distributed Bragg reflector, on the bottom side, has been fabricated and characterized under continuous-wave, room-temperature operation. These relatively simple modifications yield a 15-fold increase in electrical-to-optical power conversion efficiency at λ∼675 nm, and a significant reduction in active region heating—in comparison with standard devices prepared and tested as controls.
Subpicosecond KrF laser-produced plasma as a possible reflective nonlinear medium
Authors: Kubodera Shoichi , Midorikawa Katsumi , Tashiro Hideo , Toyoda Koichi
Published: July 2002

We have observed the second harmonic radiation (124 nm) of a subpicosecond KrF laser using an ultrashort scale length plasma produced by the same laser. It is demonstrated that an ultrashort scale plasma with a steep density gradient acts as a reflective nonlinear medium. A model predicts that the second harmonic conversion efficiency of 10−4 would be obtainable at 124 nm.
Photothermal etching of C60 single crystal induced by laser irradiation
Authors: Manfredini M. , Milani P.
Published: July 2002

Modifications induced by laser heating of C60 single-crystal surface under different conditions are examined by scanning electron microscopy. The fullerite surface is etched in the presence of oxygen, whereas no substantial change is seen under inert atmosphere. The fragments, obtained after the oxygen-induced disintegration of fullerene, form a material with a nanostructure similar to amorphous carbon. Three-dimensional microstructures are produced depending on laser annealing conditions. Oxygen in the irradiated region substantially increases, according to energy dispersive x-ray spectroscopy of the surface.
Picovoltmeter based on a high transition temperature SQUID
Authors: Miklich A. H. , Koelle D. , Ludwig F. , Nemeth D. T. , Dantsker E. , Clarke John
Published: July 2002

We have fabricated and tested picovoltmeters in which the voltage source is connected in series with a calibrated resistor and a coil inductively coupled to a high-transition temperature superconducting quantum interference device operating at 77 K. The coil consists of either seven or ten turns of copper wire or of two turns patterned in a film of YBa2Cu3O7−x(YBCO). The lowest voltage noise achieved at 1 Hz was 30 pV Hz−1/2 and 2.3 pV Hz−1/2 for input coils made of copper and YBCO, respectively.
Image widening not only a question of tip sample convolution
Authors: Tegenfeldt Jonas O. , Montelius Lars
Published: July 2002

As the tip in the atomic force microscope is scanned over the sample surface an image results which contains information from the sample as well as from the tip. This mainly results in an increase of the apparent size of the sample. If the tip is reasonably sharp the contribution from the tip is small. In some cases the widening still persists in spite of a very sharp tip. In this letter, a model is presented which ascribes this to the lateral forces twisting the cantilever giving an offset between the apparent point of contact and the real point of contact. This results in a shift between forward and reverse scan of the sample position in the imaging window and, if the lateral forces due to the sample and substrate are different, a change in the apparent width of the sample.
Investigation of the epitaxial growth of InxGa1−xAs on GaAs(001) and extension of two-dimensional–three-dimensional growth mode transition
Authors: Li Wei , Wang Zhanguo , Liang Jiben , Liao Qiwei , Xu Bo , Zhu Zhanping , Yang Bin
Published: July 2002

The growth of highly strained InxGa1−xAs (x≳0.25) epilayer on GaAs (001) undergoes a two-dimensional–three-dimensional (2D-3D) growth mode transition beyond a critical thickness which depends on the strain. We show that the growth mode is controlled by the island-edge diffusion carrier which originates from elastic energy relaxation at the edge of 2D island. The 2D-3D growth mode transition depends upon whether or not a new layer nucleates on top of the island of 2 ML height before coalescence. The In atoms on the surface arising from surface segregation affect the island-edge diffusion barrier and nucleation, leading to a 3D growth mode at the critical thickness. The experimental investigation is explained satisfactorily.
Bond-structure changes of liquid phase deposited oxide (SiO2−xFx) on N2 annealing
Authors: Yeh Ching-Fa , Chen Chun-Lin , Lur Water , Yen Po-Wen
Published: July 2002

Fluorine can be naturally incorporated into the silicon oxide (SiO2−xFx) prepared by the liquid phase deposition (LPD) method at 35 °C. Fourier transform infrared and x-ray photoelectron spectroscopy spectra show that an annealing treatment can change its bond-structure. Changes in properties accompanying the restructuring are also observed. The annealing also densifies the LPD oxide and reduces its thickness because Si–F intensity decreases and the Si–O–Si intensity increases as annealing temperature increases.
Mechanical properties of submicron-grained TiAl alloys prepared by mechanical alloying
Authors: Oehring M. , Appel F. , Pfullmann Th. , Bormann R.
Published: July 2002

Ti-48 at. % Al powders of the metastable hexagonal-closed-packed solid solution with a grain size of 15 nm were prepared by mechanical alloying. The powders were consolidated to a density of greater than 99.5% by hot isostatic pressing (HIP) at 800 °C. After HIP the material exhibits a globular microstructure of the equilibrium phases α2 and γ with a mean grain size of 150 nm. Microhardness measurements show a Hall–Petch type [E. O. Hall, Proc. Phys. Soc. B 64, 747 (1951); N. J. Petch, J. Iron Steel Inst. 174, 25 (1953)] dependence on grain size. Room temperature compression tests reveal low ductility, but high fracture strengths ≥1800 MPa. On increasing the test temperature the yield strength drops sharply in the temperature range 600–800 °C to very low values. The results indicate that submicron-grained TiAl alloys can be deformed at much lower temperatures than coarse-grained material, making them suitable as precursors for net shaping, in particular if high deformation ratios are required.
Estimation of mean acoustic reflection coefficient of polycrystalline aggregate
Authors: Ihara I. , Koguchi H. , Aizawa T. , Kihara J.
Published: July 2002

Mean reflection coefficients of plane acoustic waves incident on a liquid-polycrystals interface are examined experimentally and numerically. The mean reflection coefficient is defined as the complex average value of the reflection coefficient for all the crystals existing in the measurement area. Experiments are performed for a texture controlled low-carbon steel which can be identified as the transversely isotropic polycrystalline material. The measured reflection coefficient agrees qualitatively with the mean reflection coefficient calculated by the integration of the reflection coefficients for each single crystal on the measurement area.
Growth morphology and characteristic structure in nanocrystalline Si film of high conductivity
Authors: Wang L. C. , Feng D. , Epicier T. , Esnouf C. , Xia H. , He Y. L. , Li Q. , Chu Y. M. , Ming N. B.
Published: July 2002

A new type of hydrogenated nanocrystalline Si film with high electronic conductivity is investigated by means of transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). Nearly parallel columnar structures with growth orientation along the [110] zone axis of Si are found from cross-sectional TEM images of the film. HRTEM observation reveals that these columns are composed of nanocrystallites (3–6 nm size) and dendritelike growth morphology, while in the region between columns the texture consists of smaller sized (<3 nm) grains embedded in a hydrogenated amorphous Si. The volume fraction of the crystalline component is about 58% measured by Raman spectroscopy. The conductivity of the film is very high, about 10−1 (Ω cm)−1. It is considered that this is directly related to the characteristic structure of the film.
Absorption in p-Si1−xGex quantum well detectors
Authors: Robbins D. J. , Stanaway M. B. , Leong W. Y. , Carline R. T. , Gordon N. T.
Published: July 2002

The normal incidence absorption between 2 and 14 μm in a pseudomorphic p-Si0.81Ge0.19/Si multiple quantum well sample with doping 5×1012 cm−2 per well is described by a Drude conductivity characteristic of free carriers, with an in-plane mobility of 32 cm2/V s and a relaxation time of 5.5 fs at 77 K. When the absorption is scaled with dopant concentration these parameters predict quantum efficiencies for quantum well infrared photodetectors in reasonable agreement with experiment.
Oxygen pressure dependence of the grain size and surface morphology in YBa2Cu3O7−x a-axis films
Authors: Trajanovic Z. , Takeuchi I. , Warburton P. A. , Lobb C. J. , Venkatesan T.
Published: July 2002

The granularity and surface roughness of a-axis YBa2Cu3O7−x films grown on (100) LaAlO3, (100) SrTiO3, and (100) LaSrGaO4 by pulsed laser deposition has been studied. For fixed deposition conditions, the size and the shape of the grains varied from substrate to substrate, while the mean roughness remained the same. We were able to systematically control the grain size and smoothness of films on LaSrGaO4 and LaAlO3. By gradually reducing the oxygen pressure during the deposition we obtained films with increased grain size and much reduced surface roughness (mean ∼40 Å over 5 ×5 μm2). Cracks observed in the films deposited on LaSrGaO4 at very low O2 pressures (∼20 mTorr) were successfully eliminated for deposition pressures above 40 mTorr.
Superconducting and microwave properties of spray pyrolized Tl2Ba2Ca2Cu3Ox films on 1 inch polycrystalline zirconia disks
Authors: Su L. Y. , Grovenor C. R. M. , Goringe M. J. , Jenkins A. P. , Dew-Hughes D.
Published: July 2002

The processing of spray pyrolyzed Tl2Ba2Ca2Cu3Ox films has been successfully scaled up to samples on 1 inch diameter, finely polished yttria-stabilized zirconia disks. Transport critical current density (JC) measurements on the films exhibited values of ≳3×104 A/cm2 at 77 K. The surface resistance (RS) of such films has been measured using a TE011 mode end-wall-replacement cavity at 20 GHz and 77 K. RS values of 5.3 mΩ and 1.3 mΩ at 20 GHz and 10 GHz respectively were obtained. These results are the best recorded RS values to date for thick films of any superconductor at the same frequencies and at 77 K.
New CdTe photoconductor array detector for x-ray applications
Authors: Yoo S. S. , Sivananthan S. , Faurie J. P. , Rodricks B. , Bai J. , Montano P. A.
Published: July 2002

A CdTe photoconductor array x-ray detector was grown using molecular beam epitaxy (MBE) on a Si(100) substrate. The temporal response of the photoconductor arrays is as fast as 21 ps rise time and 38 ps full width half-maximum (FWHM). The spatial resolution of the photoconductor was good enough to provide 75 μm FWHM using a 50 μm synchrotron x-ray beam. A substantial number of x-ray photons are absorbed effectively within the MBE CdTe layer as observed from the linear response up to 15 keV. These results demonstrate that MBE grown CdTe is a suitable choice of the detector materials to meet the requirements for x-ray detectors.
Microscopic structure of DX centers of column III and VII impurities in CdTe
Authors: Park C. H. , Chadi D. J.
Published: July 2002

The microscopic structures and binding energies of DX centers for column III and VII impurities in CdTe are determined through first-principles total energy calculations. The ionic displacements leading to DX formation for column VII impurities in II-VI semiconductors are found to be different than those for corresponding column VI impurities in III-V semiconductors. Three distinct types of structures with DX-like properties are found for column VII donors. The relative stability of these structures is impurity and pressure dependent.
Quantum interference effect and electric field domain formation in quantum well infrared photodetectors
Authors: Xu Yuanjian , Shakouri Ali , Yariv Amnon
Published: July 2002

An observation of quantum interference effect in photocurrent spectra of a weakly coupled bound-to-continuum multiple quantum well photodetector is reported. This effect persists even at high biases where the Kronig–Penney minibands of periodic superlattice potential in the continuum are destroyed. Our results show that electrons remain coherent over a distance of 40–50 nm. The observation was used to investigate electric field domain formation induced by sequential resonant tunneling in the superlattice. A large off-resonant energy level alignment between two neighboring wells in the high field domain was observed.
All in situ deposition and characterization of YBa2Cu3O7−x thin films by low-energy ion scattering spectroscopy
Authors: Nakamura T. , Tanaka S. , Iiyama M.
Published: July 2002

C-axis oriented YBa2Cu3O7−x (YBCO) thin films were deposited by an ozone-assisted reactive coevaporation method and characterized by in situ low-energy ion scattering spectroscopy (LEISS). We successfully evaluated compositional information in depth by an angle-resolved LEISS method and a depth profiling LEISS method. These LEISS analyses indicated that the second outermost layer of the YBCO surface consisted of Ba atoms. This result confirmed that YBCO surfaces were terminated by Cu(1)-O chains.