bluuebunny/crossref_metadata_2025 huggingface dataset:
New nonthermal mechanism for negative differential resistance in heterojunction bipolar transistors
Authors: Lee T.-W. , Houston P. A.
Published: July 2002

A new mechanism for the explanation of negative differential resistance (NDR) in the output characteristics of heterojunction bipolar transistors is proposed. The traditional recourse to thermal effects is not required and modeled characteristics successfully reproduce the correct experimentally observed shape. The effective conduction band spike height variation with bias at the emitter-base junction, together with the base narrowing effects, can account for NDR.
Approach for magnetically estimating temperature dependence of the critical current density
Authors: Xu Ming
Published: July 2002

A method has been proposed to determine the critical current density (Jc) from remanent magnetization measurements for type II superconductors. The method provides a consistent measurement of Jc to Bean’s original assumption in the critical state model. The temperature dependence of Jc can be easily obtained from this method. As an example, the temperature dependence of Jc in a single crystal of Bi2Sr2CaCu2Oy has been determined and discussed.
Silicon epitaxial growth at 300 °C by plasma enhanced chemical vapor deposition from SiH4/H2
Authors: Chen Cheng-Hsien , Wan Chi-Meen , Yew Tri-Rung , Shieh Ming-Deng , Kung Chung-Yuan
Published: July 2002

This letter presents structural properties of silicon epitaxy grown at 300 °C by plasma enhanced chemical vapor deposition from SiH4/H2. The ratio of H2 to SiH4 flow rate and rf power of plasma was found to play an important role for epitaxial growth. The base pressure of the chamber was greater than 3×10−6 Torr. The substrates were ex situ cleaned by the spin-etch method prior to wafer loading. A H2 baking step was carried out prior to epitaxial deposition. Cross-section transmission electron microscopy and secondary ion mass spectroscopy were used to inspect the quality of Si films. The thickness of the silicon epitaxy is about 0.3 μm, which is grown at a rate of 5.6 nm/min.
Effect of thermionic-field emission on effective barrier height lowering in In0.52Al0.48As Schottky diodes
Authors: Umemoto Yasunari , Schaff William J. , Park Hyunchang , Eastman Lester F.
Published: July 2002

The effective lowering of the Schottky barrier height in In0.52Al0.48As diodes under reverse bias conditions is investigated by fitting experimental reverse-bias I-T relationships to the thermionic-field emission theory. This lowering can be explained by thermionic-field emission without assuming a lack of Fermi level pinning. The electron effective mass deduced experimentally from the fitting procedure ranges from 0.072m0 to 0.087m0, which is comparable to the published data. The effective barrier height is largely dependent on the temperature range of the current. The amount of the lowering is dependent on the electron effective mass, but not on the zero-field Schottky barrier height.
Aluminum-arsenide precipitation in an arsenic-implanted aluminum thin film
Authors: Kikkawa Takamaro , Kitajima Hiroshi , Sato Tatsuo , Shiotani Keiji
Published: July 2002

Arsenic (As) ion-implanted Al thin films were investigated by transmission electron microscopy (TEM). The TEM analysis revealed that fcc aluminum-arsenide precipitates were formed both in the grains and along the grain boundaries of the arsenic-implanted Al layer after annealing at 450 °C. Large precipitates were formed at the grain boundaries while no intragranular precipitates were formed in the vicinity of grain boundaries, due to vacancy accumulation at the grain boundaries and to vacancy depletion in the vicinity of grain boundaries, respectively.
Laser-driven synthesis of nanocrystalline alumina powders from gas-phase precursors
Authors: Borsella E. , Botti S. , Giorgi R. , Martelli S. , Turtù S. , Zappa G.
Published: July 2002

Carbon dioxide laser synthesis from gaseous precursors has been successfully applied to produce nanosized Al2O3 particles. Trimethylaluminum [Al(CH3)3] and nitrous-oxide (N2O) were used as gas phase reactants. Ethylene (C2H4) was added as sensitizer gas. The as-synthesized powder particles showed considerable carbon contamination and an amorphouslike structure. After thermal treatment at 1200–1400 °C, the powder transformed to hexagonal α-Al2O3 with very low carbon contamination, confirmed by x-ray diffraction, x-ray photoelectron spectroscopy, and chemical analysis. The thermally treated powder was composed of spherical single-crystal nanoparticles with a mean size 〈D〉 of 15–20 nm, as determined by x-ray diffraction, electron microscopy, and Brunauer–Emmett–Teller specific surface measurements. The laser synthesized Al2O3 particles are suitable dispersoids for intermetallic alloy technology.
Confinement of high Be doping levels in AlInAs/GaInAs npn heterojunction bipolar transistors by low temperature molecular-beam epitaxial growth
Authors: Metzger R. A. , Hafizi M. , Stanchina W. E. , Liu T. , Wilson R. G. , McCray L. G.
Published: July 2002

AlInAs/GaInAs npn heterojunction bipolar transistors (HBTs) have been grown over a substrate temperature range of 280–450 °C with Be base doping levels ranging from 2.0×1019 to 1.6×1020 cm−3. We have determined that for a desired base doping level there exists an optimum growth temperature at which the Be is confined in the base and at the same time the dc current gain of the HBT is maximized.
Self-stabilization of the multiplication factor in blocked impurity band photodetectors
Authors: Shadrin V. D. , Coon V. T. , Blokhin I. K.
Published: July 2002

Dependence of the electron multiplication factor on the bias voltage was considered for the blocked impurity band (BIB) detector. It was found that in high gain BIB detectors multiplication factor self-stabilization can be achieved. When bias voltage VB increases, the multiplication factor curve flattens, starting at a certain value VB. This can be explained by the presence of an electric field and electron current in the neutral region of the BIB detector IR-active layer.
Formation of shallow p+ layer in silicon by plasma doping
Authors: Hara Tohru , Nakagawa Shin , Shinada Kiyotaka , Nakamura Shigeaki
Published: July 2002

Boron doping of silicon is achieved by employing a diode parallel-plate-type dc plasma reactor, where diborane (B2H6) gas diluted with Ar (0.5 mol %) is used as doping gas. Total boron concentration changes from 1.17×1015 to 1.82×1015 atoms with varying applied dc bias voltage, Vdc, from 1600 to 3000 V. Shallow and low sheet resistance highly doped p(p+) layer is formed with annealing of the layer doped above total doping concentration of 1.20×1015 atoms. Peak carrier concentration of 2.20×1020/cm3 and a sheet resistance of 86 Ω/⧠ are attained in 140 nm depth p+ layer.
Ferroelectricity in a Langmuir–Blodgett multilayer film of a liquid crystalline side-chain polymer
Authors: Pfeiffer S. , Shashidhar R. , Fare T. L. , Naciri J. , Adams J. , Duran R. S.
Published: July 2002

The observation of ferroelectric behavior in a Langmuir–Blodgett (LB) film of a liquid crystalline polymer is reported. It is established that a 30-layer film exhibits spontaneous polarization and electro-optic switching. The magnitude of the polarization of the LB film is found to be similar to that of the bulk material. The polarization current in the LB film follows the applied triangular wave field to higher frequencies as compared to the same material in a surface stabilized (sandwich) cell.
Refractive index fluctuations in deformed Ti:LiNbO3 waveguides due to SiO2 overlayer deposition
Authors: Nagata Hirotoshi , Kiuchi Kazumasa , Sugamata Tohru
Published: July 2002

During the fabrication process of Ti:LiNbO3 optical modulators, the deformation into a convex configuration of the LiNbO3 wafer occurs after the deposition of the micrometer-thick SiO2 buffer layer. This deformation remains in the modulator chip and possibly generates the strain in the waveguides. The strain induced change of refractive index (Δn) in the waveguide is estimated from consideration of the piezo-optic effect. This Δn is on the order of 10−5 and is close to that due to the electro-optic effect. The corresponding optical phase retardation is in agreement with measured values.
Wavelength conversions ∼1.5 μm by difference frequency generation in periodically domain-inverted LiNbO3 channel waveguides
Authors: Xu C. Q. , Okayama H. , Shinozaki K. , Watanabe K. , Kawahara M.
Published: July 2002

Wavelength conversions ∼1.5 μm are realized by difference frequency generation in periodically domain-inverted LiNbO3 channel waveguides for the first time. A wide wavelength conversion bandwidth, which is very important for future wavelength division multiplexing optical communication system, is demonstrated in this kind of devices.
Diamondlike carbon films as protective coatings for superconducting YBa2Cu3O7 films
Authors: Ganapathi L. , Giles S. , Rao Rama
Published: July 2002

We have investigated the use of diamondlike carbon (DLC) films for protecting superconducting YBa2Cu3O7 (YBCO) films against degradation from exposure to moisture and acid. YBCO thin films on single crystal LaAlO3 and MgO substrates were deposited by laser ablation followed by DLC encapsulation. DLC films were deposited at pressures ranging from high vacuum to 0.1 Torr He. Substrate temperature was varied from 20 to 100 °C during the deposition of DLC. The process compatibility of laser ablation was found convenient to sequentially deposit YBCO and DLC films from high purity stoichiometric targets. Epitaxial YBCO films on (100)LaAlO3 (Tc−zero=89 K) and (100)MgO( Tc−zero=85 K) substrates showed identical superconducting transitions before and after encapsulation by a DLC layer. The encapsulated films showed no degradation due to acid treatment or aging over a period of 45 days.
Shallow angle lapping of III-V semiconductor thin layer structures by an ion beam/chemical etching technique
Authors: Eckart D. W. , Casas L. M.
Published: July 2002

Layer thicknesses of <2 nm have been resolved in GaAs-AlGaAs superlattice structures using a novel method involving the chemical etching of the shallow lapped area surrounding an ion beam sputter crater formed after Auger electron spectroscopy depth profiling. This method can be used to measure layer thickness variations across a wafer of a nominal 15 nm InGaAs layer in a pseudomorphic high electron mobility transistor. It can also be used to probe interlayer lattice mixing at selected areas on the wafer, for example, near an ohmic contact.
Low-temperature deposition of ferroelectric Bi4Ti3O12 films by the reactive ionized cluster beam method
Authors: Kaneko Norio , Yamamoto Keisuke , Tsukamoto Takeo
Published: July 2002

Using the reactive ionized cluster beam method, ferroelectric Bi4Ti3O12 is deposited at a low temperature. This method utilizes ionized and accelerated Bi and Ti clusters. Under optimum conditions, c-axis oriented films can be formed on quartz and on Si(100) substrates at 200 and 250 °C, respectively. The crystal orientation can be controlled without changing the substrate material and temperature. Furthermore, it is found that the ionization and acceleration conditions of the Bi and Ti elements are responsible, respectively, for the BIT formation and its orientation. The dielectric constant of the films is 135 at 100 kHz and the spontaneous polarization is 4.2 μC/cm2. These ferroelectric properties are almost identical to the bulk material.
Observation of the valence-subband level crossing in GaAs/GaAsP strained-barrier quantum well structures using circularly polarized photoluminescence excitation spectroscopy
Authors: Ota Kazunobu , Yaguchi Hiroyuki , Onabe Kentaro , Ito Ryoichi , Takahashi Yutaka , Muraki Koji , Shiraki Yasuhiro
Published: July 2002

We have investigated the valence-subband level configuration in GaAs/GaAsP strained-barrier quantum wells as a function of the well width. As we systematically varied the well width, we observed the crossover behavior between the n=1 heavy- and light-hole states around the well width of 4 nm. Circularly polarized photoluminescence excitation (CPPLE) spectroscopy was used to identify the heavy- or light-hole character of the observed transitions. Distinct polarization properties were observed in the strain-split heavy- and light-hole states in the GaAsP barriers, which indicated that the photoexcited electrons in the barriers retained spin memory well even after the capture into the well through the relaxation process of energy and momentum. Taking advantage of this method we were able to identify unequivocally the heavy- and light-hole characters of the transitions in the quantum well. The well-width dependence of the intersubband transition energies obtained by the CPPLE measurement is in good agreement with the calculation based on the effective mass approximation.
Secondary-neutral microprobe with electron-gas post-ionization
Authors: Bieck W. , Gnaser H. , Oechsner H.
Published: July 2002

The essential features and the performance data of a recently developed secondary-neutral microprobe are described which interfaces the well-established technique of electron gas (plasma) post-ionization with a high-transmission magnetic sector mass spectrometer. Small-area analysis is accomplished by means of a separate high-brightness liquid-metal (Ga+) ion source. For 20 keV Ga+ ions and 1 nA beam current the intensities of post-ionized sputtered neutrals amount to some 103 counts/s for pure elements, and secondary neutral micrographs can be acquired with an image resolution in the μm range. Due to the high transmission of the mass spectrometer secondary-neutral intensities up to 109 counts/s per 1 mA primary current can be obtained in the direct bombardment mode (i.e., by extracting the sputtering beam out of the plasma), thus extending the detection limit down to the 10 ppb regime. Furthermore, the instrument can be operated at high mass resolution (M/ΔM=9500) providing the option of isotope analysis by means of secondary-neutral mass spectrometry.
Electronic beam induced poling of BaTiO3 thin films
Authors: Lu H. A. , Wills L. A. , Wessels B. W. , Lin W. P. , Wong G. K.
Published: July 2002

The effect of electron beam irradiation on second harmonic generation of BaTiO3 thin films was studied. Enhanced second harmonic intensity was measured from BaTiO3 thin films irradiated by electron beams of 10, 15, and 25 keV using a scanning electron microscope. The enhancement of the second harmonic generations is attributed to the electron beam-induced poling of the film. The effectiveness of the electron beam irradiation on second harmonic generation enhancement is comparable to that of the corona poling of the film at room temperature. This electron beam induced poling technique offers a promising method for nonlinear optical device fabrication.
Ultraviolet dosimetric properties of α-Al2O3 crystals
Authors: Pérez Salas R. , Aceves R. , Meléndrez R. , Barboza-Flores M. , Pashchenko L. P.
Published: July 2002

Thermoluminescence (TL) measurements were performed in crystal samples of α-Al2O3 (TLD 500 K) subjected to UV irradiation in the range of 200–320 nm. The material is very sensitive to UV light and can be considered potentially useful for actinic region dosimetry. The TL glow curve is composed of two glow peaks centered at 58 and 184 °C, respectively. The TL excitation spectrum shows a maximum for 220 nm light.
Dopant migration and lateral p-n junctions in metalorganic vapor phase epitaxy of AlGaAs on nonplanar GaAs substrates
Authors: Wang T. Y. , Heath L. S. , Stutius W.
Published: July 2002

Lateral p-n junctions have been demonstrated in the low pressure metalorganic vapor phase epitaxial growth of AlGaAs structures on nonplanar GaAs substrates. It is shown that the final distribution of dopant atoms is governed by the dopant migration over the structured surface evolving during the growth. This result has allowed the single-step growth of index-guided lasers with a built-in lateral current confinement scheme.
Systematics of electron mobility in Si/SiGe heterostructures
Authors: Nelson S. F. , Ismail K. , Jackson T. N. , Nocera J. J. , Chu J. O. , Meyerson B. S.
Published: July 2002

We have investigated limits to the low temperature electron mobility in modulation-doped Si/SiGe heterostructures grown by ultrahigh vacuum chemical vapor deposition. The temperature dependence and peak value of the mobility suggest that interface roughness is the chief scattering mechanism in samples with a thin buffer layer below the channel. Up to about 2 μm, increasing the thickness of the buffer layer raises the mobility. We have also observed a systematic increase of electron mobility with spacer (or setback) thickness, which is characteristic of remote ion scattering. The influence of background impurities is seen in the decrease of mobility with decreasing two-dimensional gas density.
1.3 μm electroabsorption reflection modulators on GaAs
Authors: Lord S. M. , Trezza J. A. , Larson M. C. , Pezeshki B. , Harris J. S.
Published: July 2002

We demonstrate a reflection electroabsorption modulator grown on a GaAs substrate operating near 1.3 μm, the dispersion minimum for silica fibers. The device was grown by molecular beam epitaxy and uses a novel technique of integrating the bottom quarter-wave mirror into a buffer with linearly graded In composition. The active area consisted of thirty InGaAs quantum wells with GaAs barriers. The mirror was formed by layers of InGaAs and InAlAs where the In concentration was graded from 0% to 35%. A maximum relative change in reflectivity, ΔR/R, of 73% at 1.33 μm was achieved. Experimental results agree with simulations performed using the transfer matrix technique.
Optimization of the growth parameters for the molecular-beam epitaxial growth of strained In0.16Ga0.84As/Al0.33Ga0.67As single quantum-well structures
Authors: Emeny M. T. , Skolnick M. S. , Whitehouse C. R. , Hayes D. G. , Calcott P. D. J. , Higgs A. W.
Published: July 2002

A systematic study of the optical properties of strained InxGa1−xAs/AlyGa1−yAs (x=0.16, y=0.33) single quantum-well structures grown by molecular-beam epitaxy is presented. An optimized growth procedure is shown to produce quantum-well structures exhibiting 2 K photoluminescence linewidths as low as 2.6 meV, very close to those observed for corresponding InxGa1−xAs/GaAs control structures.
Low-temperature YBa2Cu4O8-to-YBa2Cu3O7 decomposition process for enhanced intra- and intergrain critical current densities in Y-Ba-Cu-O/Ag composites
Authors: Wu Nae-Lih , Yu Hon-Da , Yao Yeong Der , Ruckenstein Eli
Published: July 2002

When bulk YBa2Cu4O8 (the 124 compound)/Ag composites were subjected to the high-temperature (900–920 °C) 124-to-123 (YBa2Cu3O7−δ) decomposition process, the intergrain Jc of the composite was found to decrease dramatically in spite of significant enhancement in the intragrain one. The decrease in the intergrain Jc was attributed primarily to the incongruent melting of the resulted 123 phase at grain boundaries via interactions with the Cu-O precipitates and Ag. On the other hand, by conducting the decomposition process at lower temperatures in subatmospheric oxygen pressures where melting of 123 is avoided, enhancement in both intra- and intergrain Jc s can be achieved. Decomposition carried out at 700 °C in 2.5 Torr of oxygen, for example, has produced a 30-fold increase in the intragrain Jc (1.5×106 A/cm2 at 40 K and H=0.5 T) and a nearly twofold increase in the intergrain one. A phase diagram showing other viable conditions, including temperature and oxygen pressure for such a low-temperature approach, is proposed.
Ultrashort pulse reshaping using a semiconductor laser amplifier in a ring cavity
Authors: Langlois Patrick , Piché Michel
Published: July 2002

We describe an interferometric method for the reshaping and amplification of a mode-locked train of short laser pulses, based on a ring cavity containing a semiconductor laser amplifier. The amplifying medium provides both the gain and the phase nonlinearity needed for pulse reshaping. Numerical simulations have shown that the best reshaping occurs with the use of a low finesse cavity operated at laser threshold. Upon these conditions, calculations have shown that both pulse compression and amplification are obtained over a broad range of values of the linear phase shift between the cavity and pulse train. Pulse amplification and compression factors exceeding 50 and 100, respectively, resulting in peak power amplification factors up to 1000, are predicted for a 25 dB amplifier. These factors can be increased by decreasing the ratio of the input pulse energy over the saturation energy of the amplifier.
Vertical and lateral hole aluminum filling characteristics employing electron cyclotron resonance plasma sputtering with high magnetic field
Authors: Shingubara S. , Morimoto N. , Takehiro S. , Matsui Y. , Utsunomiya I. , Horiike Y. , Shindo H.
Published: July 2002

Filling of submicrometer vertical and lateral holes was investigated by employing ECR (electron cyclotron resonance) aluminum sputtering with two times higher magnetic field than the usual condition of 875 G. Deep submicron contact holes with no adhesive metal layer were satisfactorily filled at 350 °C, which was a much lower temperature than conventional methods. Buried lateral trenches with 1-μm depth were also completely filled at 300 °C. The filling mechanism is considered to be a cooperative effect of an enhanced diffusion by an ion bombardment effect, and the formation of dense aluminum islands at the inner wall which act as an adhesive layer.
Femtosecond carrier dynamics in the presence of a cold plasma in GaAs and AlGaAs
Authors: Acioli L. H. , Ulman M. , Vallée F. , Fujimoto J. G.
Published: July 2002

The femtosecond dynamics of hot carriers interacting with a cold high density electron-hole plasma are investigated in GaAs and Al0.2Ga0.8As. Studies are performed using a three pulse pump-probe technique where a cold plasma is first generated by a femtosecond pulse, then pump-probe transmission measurements are performed after a few hundred picoseconds delay. The results indicate only a small increase of the hot carrier thermalization rate even for plasma densities as high as 1018 cm−3.
Insulating nanoparticles on YBa2Cu3O7−δ thin films revealed by comparison of atomic force and scanning tunneling microscopy
Authors: Thomson R. E. , Moreland J. , Missert N. , Rudman D. A. , Sanders S. C. , Cole B. F.
Published: July 2002

The surface topography of YBa2Cu3O7−δ thin films has been studied with both atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The AFM images reveal a high density of small distinct nanoparticles, 10–50 nm across and 5–20 nm high, which do not appear in STM images of the same samples. In addition, we have shown that scanning the STM tip across the surface breaks off these particles and moves them to the edge of the scanned area, where they can later be imaged with the AFM.
Optical beam deflection imaging of the electron beam interaction volume in semiconductors
Authors: Chang G. Y. , Givens R. B. , Spicer J. W. M. , Osiander R. , Murphy J. C.
Published: July 2002

The distribution of electrons injected into CdS in a scanning electron microscope is imaged using an optical beam deflection technique. The contributions to the deflection due to carrier density, electron recombination, thermalization, and diffusion are identified for both pulsed and periodically modulated electron beams. The electron interaction volumes are analyzed to determine the energy dependence of the primary electron range and the lateral spread, presumably due to scattering of fast secondary electrons. The electron distributions are compared with Monte Carlo simulations.
Surface outgrowths on sputtered YBa2Cu3O7−x films: A combined atomic force microscopy and transmission electron microscopy study
Authors: Catana A. , Bednorz J. G. , Gerber Ch. , Mannhart J. , Schlom D. G.
Published: July 2002

We have structurally and morphologically characterized the surface of sputtered YBa2Cu3O7−x films on (001) SrTiO3 using atomic force microscopy and transmission electron microscopy. Atomic force microscopy reveals three types of outgrowths with different shapes and heights between 2 and 200 nm: type I exhibits cubic habit, type II tabular habit, and type III is an agglomerate of no particular shape. Some of the type-III outgrowths are located at the center of growth spirals where the screw dislocation intersects the film surface, suggesting that in YBa2Cu3O7−x films these defects promote the occurrence of one another. Using high-resolution electron microscopy and electron diffraction the surface outgrowths have been identified as follows: type I is Y2O3, type II Y2O3 and CuYO2, and type III YBa2Cu3O7−x, CuO, and Y2O3. In contrast to types-I and -II outgrowths which are both epitaxially related to the surrounding YBa2Cu3O7−x, the large type-III agglomerates consist of epitaxial and nonepitaxial grains. As it is found that the outgrowing nonepitaxial phases emanate from screw dislocations and from a,b-axis domain boundaries, it is suggested that both internal stresses and high interfacial energies promote such outgrowths on YBa2Cu3O7−x films.
Use of fullerene films as surfaces of uniform electric potential
Authors: Camp J. B. , Schwarz R. B.
Published: July 2002

Continuous fullerene films (85% C60, 15% C70) of thickness ∼10 nm have been sublimed on a metallic substrate previously coated with a 1-nm-thick Ge sublayer. The films show no surface potential variations when scanned with a Kelvin probe of 1 mV and 1 mm potential and spatial resolutions. Transmission electron microscopy reveals the fullerene films to be amorphous.
Laser-plasma deposition of diamond phase at low temperatures
Authors: Seth Jayshree , Padiyath R. , Rasmussen D. H. , Babu S. V.
Published: July 2002

Diamond crystallites were deposited on single-crystal (100) silicon substrates by the KrF (248 nm) excimer laser ablation of pyrolytic graphite in an argon rf plasma ambient. No external heating or seeding of the rf biased substrates was used. The rf plasma ambient caused surface restructuring of the silicon substrate, presumably via sputtering, which facilitated the nucleation of 0.01–0.15 μm diamond crystallites. The diamond cubic structure was confirmed by transmission electron diffraction analysis. However, the Raman 1332 cm−1 mode, characteristic of diamond, was not detected. The rf bias accelerates the ions in the laser-induced plume and rf plasma discharge towards the substrate likely facilitate nucleation of the diamond phase on the restructured and roughened silicon substrate.
Measuring the junction temperature of AlGaAs/GaAs heterojunction bipolar transistors using electroluminescence
Authors: Fukai Yoshino K. , Matsuoka Yutaka , Furuta Tomofumi
Published: July 2002

Rises in the junction temperatures of heterojunction bipolar transistors (HBTs) due to self-heating effects during transistor operation are measured using the electroluminescence of the band-to-band recombination. This method is useful for the direct junction temperature monitoring of small geometry devices. Junction temperatures measured in AlGaAs/GaAs HBTs with five 2×20 μm2 emitter fingers are raised 115 °C when the product of the collector current and the emitter-collector voltage is 0.25 W. The thermal resistance is determined to be 260 °C/W at 300 K.
Deposition of TiN using tetrakis(dimethylamido)-titanium in an electron-cyclotron-resonance plasma process
Authors: Weber A. , Nikulski R. , Klages C.-P.
Published: July 2002

High-quality TiN layers were deposited in an electron-cyclotron-resonance (ECR) plasma process at substrate temperatures between 350 and 600 °C. Tetrakis(dimethylamido)-titanium [Ti(NMe2)4] was used as precursor and introduced into the downstream region of an ECR nitrogen plasma. The electrical properties of the gold-colored TiN layers (45–100 μΩ cm) depend on the deposition rate, the substrate temperature, the microwave (MW) power, and the plasma gas composition. TiN with a resistivity of 45 μΩ cm could be obtained at a substrate temperature of 600 °C and a MW power of 400 W. The measured resistivities are so far the best reported values obtained by using a metalorganic precursor for TiN deposition. The deposits were characterized by resistivity measurements and electron probe microanalysis for chemical analysis. The morphology and step coverage was checked by atomic force and scanning electron microscopy.
114 Gbit/s soliton train generation through Raman self-scattering of a dual frequency beat signal in dispersion decreasing optical fiber
Authors: Chernikov S. V. , Dianov E. M. , Richardson D. J. , Laming R. I. , Payne D. N.
Published: July 2002

We report the generation of 114 Gbit/s trains of 250 fs fundamental solitons. The pulses are generated due to the conversion of an intense optical beat signal (generated from two DFB laser diodes and an erbium doped fiber amplifier combination) into a soliton train due to nonlinear propagation in a 1.6 km fiber of steadily decreasing dispersion. The train repetition rate corresponds to the beat frequency of the input signal and was readily tunable between 80 and 120 GHz. The results of a computer simulation of the system are found to be in good qualitative agreement with the experimental observations.
Formation of a metastable superlattice by x-ray interaction with standing surface acoustic waves
Authors: Roshchupkin D. V. , Brunel M.
Published: July 2002

X-ray diffraction on the surface of the YZ cut of a LiNbO3 ferroelectric crystal modulated by standing surface acoustic waves (SAW) was investigated under the total external reflection conditions. It is shown that a metastable superlattice is formed in the near-surface region in the process of the interaction between the incident x-ray radiation and the ferroelectric crystal surface modulated by standing SAW. The metastable superlattice may be stored for a long time period and may be read out by x-ray and laser radiation.
Nonlinear analysis of complexities in striations of Czochralski silicon crystals
Authors: Miyano Takaya , Shintani Akira
Published: July 2002

Complexities in striations of Czochralski silicon crystals are explored on the basis of time-series analysis by neural networks and by nonlinear regression of a simplex projection method. Two categories of the time series of striations along the crystal growth axis, observed using x-ray topograph, are forecasted by the simplex projection method and characterized in terms of the dependence of prediction accuracy on embedding dimension and prediction-time interval. The time series have short-term predictability, independent of embedding dimension. The back-propagation network that has learned the dynamics in one time series can make predictions about the other striation. These results suggest that there exist underlying nonlinear dynamics common to both the striations.
Band-edge photoluminescence of SiGe/strained-Si/SiGe type-II quantum wells on Si(100)
Authors: Nayak Deepak K. , Usami Noritaka , Fukatsu Susumu , Shiraki Yasuhiro
Published: July 2002

A high-quality completely relaxed SiGe buffer layer is grown on Si(100) by gas-source molecular-beam epitaxy. A pseudomorphic Si layer is grown on this relaxed SiGe buffer to form SiGe/strained-Si/SiGe type-II (staggered) quantum wells. Intense band-edge photoluminescence is observed from these quantum wells for the first time. The quantum confinement effect in SiGe/strained-Si/SiGe type-II quantum wells is demonstrated from the systematic shift of photoluminescence energy peaks with the width of the quantum well. Transitions from the strained-Si quantum well are identified as radiative recombination of excitons, which are confined into the quantum well.
Carrier transport in GaAs/AlGaAs heterostructures by microwave time-of-flight technique
Authors: Khorram S. , Wang K. L. , Block T. , Streit D.
Published: July 2002

An improved experimental method has been developed to study perpendicular carrier transport in heterostructures by a microwave time-of-flight technique. Transport properties of three samples, one with bulk GaAs, one with a AlGaAs barrier, and one with a AlGaAs/GaAs superlattice have been measured and analyzed in a comparative manner. A direct measurement of miniband conduction in superlattices is presented. The carrier velocity-field characteristic of GaAs/AlGaAs superlattice is measured in the field range of 10–40 kV/cm at 77 K.
Nitrogen-bound excitons in gallium phosphide, a new acoustic-phonon spectrometer
Authors: Bouma T. , Dijkhuis J. I.
Published: July 2002

Excitons bound to isoelectronic nitrogen in dilute GaP:N are shown to be applicable as phonon spectrometers with extreme sensitivity and broad spectral range (100 GHz–1 THz). Exploratory heat-pulse experiments indicate that the acoustic-phonon dynamics in GaP around 200 GHz is dominated by frequency conversion of phonons at the crystal surfaces.
In situ mechanical relaxation of Cu films growing on a Si substrate
Authors: Su C. M. , Wuttig Manfred
Published: July 2002

A novel technique has been applied to study the mechanical relaxation during thin film growth. The stress as a function of time and thickness was investigated by measuring the resonance frequency of the vibrating membrane substrate. The stress relaxation and intrinsic damping of the film/substrate composite were monitored simultaneously in situ during film growth. A pronounced stress increase was found in films deposited on Si substrate with thicknesses ranging from 1 to 20 nm. The characteristic time of the stress generation and damping kinetics was found to be the sum of a thickness independent term and a term proportional to the film’s total thickness.
Photorefractive and domain gratings in barium titanate
Authors: Cudney R. S. , Fousek J. , Zgonik M. , Günter P. , Garrett M. H. , Rytz D.
Published: July 2002

We present concrete evidence for the formation of ferroelectric domain gratings induced by photorefractive space-charge electric fields in top-seeded solution-grown barium titanate crystals. These domain gratings are not destroyed by light and, by applying a field, can be reconverted into photorefractive gratings that diffract much more light than the photorefractive gratings that create them, as much as 67% of an incident beam.
Radiation from an annular grating on a planar optical waveguide
Authors: Jordan Rebecca H. , Hall Dennis G.
Published: July 2002

This letter discusses the radiation scattering properties of a concentric-circle grating on the surface of an optical waveguide. A boundary perturbation method is used to obtain an analytical expression for the field radiated by a set of concentric rings located at the film–cover interface of the waveguide. The analytical expression for the radiation field consists of a scattering integral which is integrated to predict the field’s intensity at points in the far field.
Significant effect of lateral resistivity on optical nonlinear responses of a quantum well p-i-n photodiode
Authors: Abe Yuji , Tokuda Yasunori
Published: July 2002

A p-i-n photodiode with GaAs/AlAs asymmetric coupled quantum well absorption layers at room temperature exhibited an optical bistable response for a focused optical beam with no external electrical element. From dependence of the bistable responses on a position of the light beam, it is concluded that lateral resistance of the p-AlGaAs layer plays an important role, and thus the result is interpreted in terms of a response of a nonbiased self-electro-optic effect device with an internal feedback element.
635 nm GaInP/GaAlInP surface-emitting laser diodes
Authors: Ou S. S. , Yang J. J. , Jansen M.
Published: July 2002

Monolithic, in-plane visible surface-emitting laser diodes operating at 635 nm have been demonstrated. Both the deflecting 45° and 90° micromirrors were fabricated by ion beam etching. An interesting self-optical-annealing phenomenon was observed from these facet-etched GaInP/GaAlInP devices. By employing this unique characteristic, pulsed output powers of 170 mW, and 70 mW at room temperature were achieved from etched-cleaved and etched-etched uncoated devices, respectively. Output powers will increase to 725 mW with facet coatings.
Magnetic and magneto-optical properties of the Co-γFe2O3 perpendicular magnetic films
Authors: Tamari K. , Doi T. , Horiishi N.
Published: July 2002

Co-γFe2O3 films have been prepared by annealing Fe3O4/CoO multilayers. The crystalline orientation of multilayers change with bilayer thickness Λ; the [100] axis of Fe3O4 and CoO orients perpendicular to the film plane for Λ<80 Å and the [111] axis orients for Λ≳100 Å. The Co-γFe2O3 films obtained from multilayers of Λ<80 Å have positive perpendicular anisotropy. The magnetic coercivity and the squareness of perpendicular hysteresis curves are about 5.0 kOe and 0.8, respectively. The films show high magneto-optical effects and the figure of merit is 5.5 deg, which is about three times larger than that of CoFe2O4.
High speed optoelectronic response from the edges of lead zirconate titanate thin film capacitors
Authors: Thakoor Sarita
Published: July 2002

This letter reports on a high speed (∼10 ns), nondestructive, polarization-dependent photoresponse from lead zirconate titanate (PZT) thin films, when illuminated with λ=532 nm, at ∼mW/μm2 of incident optical power. This photoresponse emerges primarily from the edges of the sandwich ferroelectric capacitors, consisting of PZT films with predominant c-axis orientation. This response, in contrast with the thermally triggered effect, is unipolar in nature and occurs at an order of magnitude lower power level, and therefore offers a greater application potential. Its dependence on the crystal orientation and remanent polarization in the PZT film, and therefore its ability to track the built-in E fields within the film, may offer such photoresponse as a high speed nondestructive evaluation tool.
Extended temperature and wavelength performance of vertical cavity top surface emitting lasers
Authors: Catchmark J. M. , Morgan R. A. , Kojima K. , Leibenguth R. E. , Asom M. T. , Guth G. D. , Focht M. W. , Luther L. C. , Przybylek G. P. , Mullally T. , Christodoulides D. N.
Published: July 2002

We report over 130 °C continuous wave operation of unbonded vertical cavity top-surface emitting lasers emitting more than 1.0 mW at 110 °C. Furthermore, we control threshold currents to within only ±1.35 mA (±12%) over a 150 °C temperature range. We are also able to control the threshold current to within a factor of 2 over a 50 nm wavelength range using the same epidesign.
Surface study of a,b-axis oriented YBa2Cu3O7−δ epitaxial thin films by in situ angle resolved x-ray photoemission spectroscopy
Authors: Terada N. , Ishibashi S. , Jo M. , Hirabayashi M. , Ihara H. , Yamamoto S.
Published: July 2002

In situ angle resolved x-ray photoemission spectroscopy has been performed on superconducting a,b-axis oriented YBa2Cu3O7−δ epitaxial films. The relative intensities of the Cu 2p Ba 3d, and Y 3d core emissions have shown the diffraction-like dependence on the electron escape angle due to the spatial distribution of elements in the surface layer. The calculated results by the single scattering cluster model on the surface with the Cu-O outermost layer show a better agreement with the experiment than the (Y, Ba)-O in the outermost layer.
High quality In0.52Al0.48As grown by modulated arsenic molecular beam epitaxy
Authors: Chou S. T. , Cheng K. Y.
Published: July 2002

A modulated arsenic molecular beam epitaxy method has been developed for growing high quality In0.52Al0.48As under a condition compatible to the optimal growth condition of In0.53Ga0.47As without using a buffer layer or growth interruption. In this method, the As shutter is periodically opened and closed while the Al and In shutters are held constantly open. By adjusting the As shutter modulation rate, a layer-by-layer growth mode can be maintained throughout the growth as evident from the persistent strong reflection high-energy electron diffraction intensity oscillations. Without an In0.53Ga0.47As buffer layer, the unintentionally doped In0.52Al0.48As samples grown at 500 °C show very strong photoluminescence intensity and n-type conductivity with a background carrier concentration of ∼5×1015 cm−3 and electron mobilities of 1900 and 3900 cm2/V s at 300 and 77 K, respectively. Very narrow 77 K photoluminescence spectra have been observed from In0.53Ga0.47As/In0.52Al0.48As quantum well stack structures grown by this new method.
Enhancement of Josephson photoresponse of granular high-T
c superconductor thin films by deoxygenation
Authors: Schneider Gi. , Blau W. , Stangl E. , Bäuerle D. , Huggard P. G. , Prettl W.
Published: July 2002

The dependence of the far infrared Josephson photoresponse of current biased granular high-Tc superconductor thin films on deoxygenation is presented. Bi2Sr2CaCu2O8 and TlBa2Ca2Cu3O9 thin films were heated in vacuum to temperatures of between 200 and 500 °C. The resulting deoxygenation weakens the intergrain coupling, thereby reducing the critical current and enhancing the photoresponse. In this way the optimum temperature for the fast Josephson response may be tuned to lie outside the temperature region of the slow bolometric signal.
Temporally stable hybrid dye-Ti:sapphire laser by self-induced gain switching
Authors: Peshev Z. Y. , Deleva A. D.
Published: July 2002

A novel simple Nd:YAG-laser-pumped pulsed hybrid dye-Ti:sapphire laser is described. A spectral linewidth of 0.28 nm is selected near threshold and tuned from 705 to 770 nm in a compact (15-cm long) cavity. When the threshold is exceeded by a factor of 1–3, the jitter in the onset of the Ti:sapphire laser pulse is reduced to 10 ns. This is about 7% of the 140-ns jitter for a pure Ti:sapphire laser under equivalent conditions. The result is achieved via accelerated gain switching in the Ti:sapphire induced by intracavity injection of radiation from the dye.
Diffusion and doping of Si into GaAs from undoped SiOx/SiN film
Authors: Matsushita S. , Terada S. , Fujii E. , Harada Y.
Published: July 2002

The diffusion and n-type doping of Si into GaAs from a novel diffusion source consisting of an undoped SiOx/SiN double-layered film were achieved by rapid thermal annealing at 860–940 °C. The film properties of the double-layered films employed as Si diffusion sources are experimentally presented. The characteristics of the Si diffused layers were investigated by secondary ion mass spectrometry, capacitance-voltage measurement, and the Hall method. The carrier profiles exceeded 2×1018 cm−3 and featured an abrupt diffusion front, while a maximum electron concentration of 6×1018 cm−3 was obtained at 940 °C. The diffused Si profiles were consistent with the SiGa+−VGa− pair diffusion model.
Observation of birefringence induced by intersubband transitions in quantum wells
Authors: Almogy Gilad , Shakouri Ali , Yariv Amnon
Published: July 2002

We present a direct measurement of the birefringence induced by the intersubband transitions in quantum wells. Phase delays of up to 40° were observed in our samples, corresponding to a 0.07 difference in the index of refraction between the polarizations parallel and perpendicular to the plane of the wells in a GaAs/AlGaAs silicon-doped structure. The measurement was conducted at several wavelengths—enabling us to deduce the total linear birefringence near the absorption resonance. The observed birefringence is in close agreement with the Kramers–Kronig transform of the absorption spectra.
Lifetime measurements on silicon-on-insulator wafers
Authors: Freeouf J. L. , Braslau N. , Wittmer M.
Published: July 2002

We report noncontact measurements of the effective minority carrier lifetime in the superficial silicon layer of silicon-on-insulator wafers. The carriers are excited by a pulse of short-wavelength photons (λ≤350 nm), all of which are absorbed in the first 500 Å of the silicon layer. The carriers are detected by the change in microwave reflectance in a resonant circuit to which the wafer is coupled. The results obtained vary from ∼3 μs for a three year old separation by implanted oxygen (SIMOX) wafer to ∼25 μs for current vendor SIMOX and bond-etchback samples. The variation in free surface recombination velocity is eliminated by HF passivating the samples prior to measurement.
Ultrathin film deposition of Ba1−xRbxBiO3 by molecular beam epitaxy using distilled ozone
Authors: Ogihara M. , Makita T. , Abe H.
Published: July 2002

A Ba1−xRbxBiO3 (BRBO) ultrathin film (120 Å) with a zero-resistance transition temperature of 14 K was deposited on a SrTiO3(110) substrate by molecular beam epitaxy using distilled ozone. The critical current density of 2×105 A/cm2 was achieved in 200-Å-thick BRBO thin film, and this observed critical current density is much larger than the previously reported data. The dependence of BRBO film properties on film thickness is studied for the first time.
Enhancement of optical nonlinearity of heavy-metal oxide glasses by replacing lead and bismuth with thallium
Authors: Yumoto J. , Lee S. G. , Kippelen B. , Peyghambarian N. , Aitken B. G. , Borrelli N. F.
Published: July 2002

We report on the results of degenerate four-wave mixing experiments at a wavelength of 1.06 μm on a number of heavy-metal gallate glasses. The replacement of lead (Pb) and/or bismuth (Bi) by thallium (Tl) leads to an enhancement of the optical nonlinearity, resulting in the largest nonresonant electronic nonlinearity yet reported for an oxide glass. χ(3) is proportional to the concentration of Tl; samples with more than 25 cation % Tl have χ(3) larger than that of carbon disulfide (CS2). The optical nonlinearity has an off-resonant electronic origin, which is confirmed by measurements of the diagonal and off-diagonal components of the χ(3) tensor.
Optically reversible switching between binary states using multistable loops
Authors: Tokuda Yasunori , Abe Yuji , Tsukada Noriaki , Nara Shigetoshi
Published: July 2002

We present a novel method of optically reversible switching between binary transmission states by taking advantage of the optical multistability which can be obtained from two bistable devices optically connected in series. The basic set and reset functions were experimentally demonstrated by use of an n-i-p-i-n device in which two quantum well self-electro-optic effect devices are vertically integrated.
Midinfrared amplitude and phase modulation by intersubband transitions in biased GaAs/GaAlAs double quantum wells
Authors: Dupont E. , Delacourt D. , Papuchon M.
Published: July 2002

Efficient midinfrared electro-optical effects based on intersubband transitions in doped double quantum wells are demonstrated. The system is based on field-induced perturbations of the wave functions associated with the excited and interacting sublevels of an asymmetric coupled quantum well structure. Like for interband modulation, the absorption and the refractive index changes are reported to be very sensitive to a dc bias voltage applied on the structure.
Nitrogen radical doping during metalorganic vapor phase epitaxy of ZnSe
Authors: Morimoto Keizo , Fujino Takahiro
Published: July 2002

The availability of nitrogen radical doping in low-pressure metalorganic vapor phase epitaxy of N-doped ZnSe layers is reported. Active nitrogen generated by low-frequency dielectric discharge was supplied alternately with source materials. The narrow and distinct peak for the acceptor-bound exciton, together with donor-acceptor pair peaks, is predominant in the low-temperature cathodoluminescence spectra for the layers prepared with alternate growth and doping.
Optimization of InGaAsP/InP quantum well heterostructures for enhanced excitonic electroabsorption effects at 1.55 μm
Authors: Shim Sugie , Lee El-Hang
Published: July 2002

We report an optimization method on the basis of theoretical calculation to enhance the excitonic electroabsorption effect in the quaternary InGaAsP/InP quantum well structures for use in the bistable switching devices operating at 1.55 μm wavelength. We searched for the maximum value of a parameter γ, defined as [α(0)−α(F)]/α(F), by adjusting x, y, and quantum well width in the In1−xGaxAsyP1−y/InP heterostructure assuming that the heavy-hole excitonic absorption peaks at zero electric field occur at 1.55 μm wavelength. We obtained 30.2 as the maximum value of γ for y=1.0, x=0.477, and quantum well width 90 Å, and found that this value is about three times as high as that of the conventional ternary quantum well structure.