bluuebunny/crossref_metadata_2025 huggingface dataset:
Dependence of critical current density on filament diameter in round multifilament Ag-sheathed Bi2Sr2CaCu2Ox wires processed in O2
Authors: Motowidlo L. R. , Galinski G. , Ozeryansky G. , Zhang W. , Hellstrom E. E.
Published: July 2002

Ag-sheathed Bi2Sr2CaCu2Ox round wires having 37 and 259 filaments, with filament diameters ranging from 11 to 100 μm, were fabricated by the oxide-powder-in-tube method. They were heat treated using step-solidification melt processing in air and pure O2. The transport critical current density was highest in wires processed in pure O2. It increased with decreasing filament diameter and was highest [165 000 A/cm2 (4.2 K, O T)] in wires with 11 μm filaments processed in O2.
Two-band hopping conductivity in the nonmetallic barrier material PrBa2Cu2.8Ga0.2Oy (y∼7)
Authors: Fisher B. , Genossar J. , Patlagan L.
Published: July 2002

Using combined thermoelectric and resistivity measurements on fully oxygenated PrBa2Cu2.8Ga0.2Oy samples, we show that carriers from two energy bands probably participate in the hopping transport. We obtain estimates of the density of states and the localization length of carriers in one of these bands, and of the energy gap between them.
Influence of plasma on silicon surface during low-energy plasma deposition process: The comparative study on Si3N4/Si structures
Authors: Ivančo J. , Thurzo I. , Pinčík E.
Published: July 2002

The use of plasma-enhanced chemical vapor deposited silicon nitride (Si3N4) in the role of both passivation of semiconductor devices and electrically active layer is primarily determined by the Si3N4/Si interface quality. To enhance the control of the interface formation, we separated the deposition of the Si3N4 into two steps; At the beginning, we deposited a ‘‘shielding’’ Si3N4 layer in the remote mode, including minimal damage of the silicon surface. This layer would hamper the deterioration of the insulator/semiconductor interface properties by the energetic species bombardment during the following ‘‘quick’’ deposition of a thick bulk dielectric layer in the direct mode. On the base of small-signal charge deep-level transient spectroscopy of metal-nitride-silicon capacitors, we found the inserted remotely deposited Si3N4 layer with a thickness of about only 2–3 nm is able to effectively avert the energetic radiation-induced damage of the silicon surface.
Experimental observation of microwave envelope solitons of dipolar magnetostatic waves
Authors: Dragoman M. , Marcelli R. , De Gasperis P.
Published: July 2002

Experimental observation of microwave bright envelope solitons of dipolar magnetostatic surface waves is reported. Both time domain analysis and input-output microwave power measurements have been exploited to detect such magnetostatic surface wave solitons in the pure dipolar regime. Possible applications of the observed nonlinear effect in microwave signal processing are outlined.
Superconducting epitaxial (Tl,Bi)Sr1.6Ba0.4Ca2Cu3O9−δ film with high critical current in magnetic field
Authors: Ren Z. F. , Wang C. A. , Wang J. H.
Published: July 2002

High-quality 1-μm-thick (Tl,Bi)Sr1.6Ba0.4Ca2Cu3O9−δ films were synthesized by a simple two-step procedure. A prefilm of TlxBiySr1.6Ba0.4Ca2Cu3Oy was first deposited on the (100) surface of LaAlO3 by laser ablation at 300–500 °C. This prefilm was placed on a gold plate sitting between two similarly placed unfired Tl0.95Bi0.22Sr1.6Ba0.4Ca2Cu3O8.76 pellets, wrapped in silver foil, and subsequently heated in air at 840–870 °C for 25–60 min. The resulting glossy film exhibited at 77 K a transport Jc of 2×106 A/cm2 at 0 T and 1.5×106 A/cm2 at 0.5 T with magnetic field parallel to the film. These observed values show the absence of weak links effect. X-ray diffraction (XRD) reflections reveal the existence of only 1223 phase with nearly perfect c-axis alignment. The half-width of rocking angle monitored at (006) reflection is only 0.365°. XRD φ scan also shows no trace of intergranular misalignment along the a and b axes.
On nonuniform pumping for multiple-quantum well semiconductor lasers
Authors: Lin C. H. , Chua C. L. , Zhu Z. H. , Lo Y. H.
Published: July 2002

Optical gain distribution among quantum wells for (strained) multiple-quantum well (MQW) lasers was analyzed to understand the effect of nonuniform pumping. The nonuniform gain distribution is mainly caused by stagnant hole transport across the quantum wells. Contrary to what people expected, neither uniformly p-doped MQWs nor selectively p-doped MQWs can alleviate the nonuniform pumping problem. The most effective solution is employing an exponential p-doping profile which can counterbalance the nonuniform injection effect. Our simulation results showed that such an exponential p-doping profile has a characteristic length around one-half of the ambipolar diffusion length.
Eye-diagram and scattering parameter characterization of superconducting and gold coplanar transmission lines
Authors: Kruse J. , Chang W. H. , Scherrer D. , Feng M. , Scharen M. , Cardona A. , Forse R.
Published: July 2002

We report the gigahertz experimental results of time and frequency performance on YBCO high-temperature superconductor and gold coplanar transmission lines. An on-wafer direct probing measurement system was used to collect data at cryogenic temperatures on both YBCO and gold coplanar lines. The insertion loss of the 6 cm lines at a frequency of 2.5 GHz was measured to be −0.03 dB for the superconducting line compared to −10.4 dB for the gold line at 80 K. Eye-diagram measurements were performed on the packaged lines and show the correlation between the insertion loss of the line and the attenuation of a pseudorandom bit sequence. The measured eye height was 170 mV for the YBCO compared to 90 mV for a gold line at 1 Gbit/s and a temperature of 77 K for the packaged 6 cm lines.
GaxIn1−xAs/AlAs resonant tunneling diodes grown by atmospheric pressure metalorganic chemical vapor deposition
Authors: Keller B. P. , Yen J. C. , DenBaars S. P. , Mishra U. K.
Published: July 2002

We report on the growth of GaxIn1−xAs/AlAs double-barrier heterostructures on InP and the fabrication of GaxIn1−xAs/AlAs resonant tunneling diodes (RTDs) by metalorganic chemical vapor deposition (MOCVD). High resolution x-ray diffraction measurements were used to evaluate the heterostructure interface quality. The RTDs achieved a room-temperature peak to valley ratio of 7.7:1 with peak current density of 9.6×104 A/cm2. These are the best reported room-temperature results for any reported RTDs grown by MOCVD.
Hydrogenation of multiple-quantum-well optical-modulator structures
Authors: Woodward T. K. , Cunningham J. E. , Jan W. Y. , Kastalsky A.
Published: July 2002

We report studies of hydrogenated multiple-quantum-well (MQW) optical-modulator structures via electron-cyclotron-resonance-derived plasmas. Responsivity, optical transmission, current-voltage, and capacitance-voltage characterizations of Schottky- as well as pin-diode modulator structures were performed. We find photocurrent-collection efficiency and photoluminescence intensity to be enhanced by hydrogenation, with measurable improvement in electrically biased exciton-absorption linewidth also seen. We interpret our results as arising from increased carrier lifetime in the MQW region, because of passivation of deep levels/defects. The improvements were stable after 550 °C heat treatment. These effects may be useful for improving the yield of usable MQW devices grown in a given system.
Spectroscopy of hydrogen-related complexes in GaP:Zn
Authors: McCluskey M. D. , Haller E. E. , Walker J. , Johnson N. M.
Published: July 2002

Using infrared spectroscopy, local vibrational modes in GaP:Zn exposed to a remote hydrogen or deuterium plasma were observed. The modes at 2379.0 and 1729.4 cm−1 are assigned to hydrogen—phosphorus and deuterium—phosphorus bond-stretching modes of complexes adjacent to the zinc acceptors. The isotopic ratio r=νH/νD=1.3756 is very close to that of the zinc-hydrogen complex in InP (r=1.3744), which suggests that they have the same structure.
Pb-doping effect on irreversibility fields of HgBa2Ca2Cu3O8+δ superconductors
Authors: Isawa Kazuyuki , Tokiwa-Yamamoto Ayako , Itoh Makoto , Adachi Seiji , Yamauchi H.
Published: July 2002

We prepared nearly single-phase polycrystalline samples of HgBa2Ca2Cu3O8+δ(Hg-1223) without and with Pb doping, i.e., Pb-free Hg-1223 and (Hg0.8Pb0.2)-1223, by means of a sample encapsulation technique. According to quantitative energy dispersive x-ray spectroscopy analyses and iodometric oxygen titration, the Pb-free Hg-1223 and the (Hg0.8Pb0.2)-1223 sample were identified to be Hg0.97Ba2.00Ca2.04Cu3.00O8.33 and (Hg0.79Pb0.29)Ba2.00Ca1.98Cu2.94O8.42, respectively. The highest Meissner-signal onset temperatures for the Pb-free Hg-1223 (after post-annealing in O2 gas) and the (Hg,Pb)-1223 (as-sintered) sample were observed at 135.4 and 132.0 K, respectively. The difference in the irreversibility fields (Hirr) for both samples was very small at temperatures above 80 K, while, at temperatures below 70 K, the Hirr versus T curve for the (Hg,Pb)-1223 sample shifted toward the higher field side. Thus, Pb doping was effective for the improvement of magnetic property of Hg-1223 superconductors, at least, at temperatures below 70 K.
All-YBa2Cu3O7 trilayer tunnel junctions with Sr2AlTaO6 barrier
Authors: Ying Q. Y. , Hilbert Claude
Published: July 2002

A new barrier material, Sr2AlTaO6, was employed in fabricating all-YBa2Cu3O7 trilayer tunnel junctions using in situ coevaporation and sputtering deposition. It was found that the superior material properties of Sr2AlTaO6 allow the use of a very thin barrier layer. A dramatic increase in the quasiparticle density of states at the YBa2Cu3O7 superconductive gap was observed for the first time from thin-film all-YBa2Cu3O7 devices. Well-defined gap structures were observed at temperatures up to 47 K. The tunneling characteristics are consistent with the typical superconductor-insulator-superconductor behavior. The temperature dependence of the superconductive gap is compared with the BCS theory.
Accurate multiple-quantum-well growth using real-time optical flux monitoring
Authors: Chalmers S. A. , Killeen K. P. , Jones E. D.
Published: July 2002

We report a real-time molecular beam epitaxy control system based on optical flux monitoring (OFM) that is capable of producing thin AlAs/GaAs layers of accurate thickness. We demonstrate the system’s ability to detect and compensate for growth rate variations by growing AlAs/GaAs multi-quantum-well structures while deliberately ramping the GaAs growth rate to simulate a severe effusion cell instability. Results show that a sample grown under these conditions without OFM control (i.e., while using conventional timed shutter control) exhibited multiple photoluminescence peaks, indicating that its quantum wells differed in thickness, while a sample grown using OFM shutter control exhibited a single narrow peak, indicating that its quantum wells were nearly identical in width. Analysis of the OFM shutter control sample’s photoluminescence linewidth shows that the resulting quantum-well thickness variation were less than 1%.
Reactions of divalent Ge in hydrogen loaded germanosilicate optical fibers: Identification of a new monohydride defect
Authors: Zhang Bulin , Raghavachari Krishnan
Published: July 2002

Microscopic mechanisms for the reactions of H2 with divalent Ge defects in hydrogen loaded germanosilicate optical fibers have been studied by ab initio quantum chemical techniques. The reaction with the lowest energy barrier corresponds to H2 breaking a Ge–O bond at the divalent Ge site forming a –Ge–H bond. Alternatively, H2 addition yielding a dihydride followed by hydrogen migration from Ge to an adjacent O also leads to this –Ge–H defect. We have assigned the vibrational frequency corresponding to this –Ge–H defect to a previously observed, but unassigned, Raman mode at 1875 cm−1. The reverse reaction barrier is very small, indicating that this –Ge–H defect is likely to be easily bleached at higher temperatures.
Optical property of GaAsP/AlGaAs strained-layer quantum well grown on GaAs-(111)B substrate
Authors: Zhang Xiong , Karaki Koichi , Yaguchi Hiroyuki , Onabe Kentaro , Ito Ryoichi , Shiraki Yasuhiro
Published: July 2002

GaAs1−xPx/AlyGa1−yAs (x=0.07–0.15, y=0.3) strained-layer quantum wells have been grown on GaAs-(111)B substrates by low-pressure metalorganic vapor phase epitaxy and characterized by photoluminescence (PL) spectroscopy. Evident energy blue shifts of the excitonic transition peaks (some of them as large as 33 meV) were achieved by increasing the excitation power during the PL measurement. The large optical nonlinearity mainly due to the strain-induced piezoelectric field screened by the photoexcited carriers, is comparable to, or larger than, the reported values for a self-electro-optical effect device or other (111)-oriented strained-layer quantum well structures which are composed of InGaAs/GaAs or GaAs/GaAsP. This fact indicates that our (111)-GaAsP/AlGaAs strained-layer quantum well is a good candidate for making optoelectronic devices like optical switches and modulators.
Observation of enhanced lateral confinement of excitons in GaAs quantum wires with various sizes (7–30 nm) by magnetophotoluminescence measurements
Authors: Nagamune Y. , Tanaka T. , Kono T. , Tsukamoto S. , Nishioka M. , Arakawa Y. , Uchida K. , Miura N.
Published: July 2002

We investigated magnetophotoluminescence spectra up to 40 T of GaAs quantum wires with various lateral widths (7–30 nm) grown by the selective metalorganic chemical vapor deposition. The photoluminescence peak shift due to the magnetic fields is more suppressed with decreasing the wire width. The observed energy shift was in good agreement with the calculation based on a variation method. These results clearly demonstrate existence of the two-dimensional confinement effect and enhanced binding energy of excitons. In the narrowest wire (7 nm), however, comparison of the experimental results with the calculation indicates penetration of exciton wavefunction from the two-dimensional potential to the barrier region.
Structure characteristics and Curie temperature of magnesium diffused lithium niobate single-crystal substrates
Authors: Que Wenxiu , Zhang Liangying , Yao Xi
Published: July 2002

A Mg-ion indiffusion process was applied to the lithium niobate single-crystal substrates deposited with magnesium oxide thin film. By means of x-ray diffraction analysis and differential thermal analysis, we find that the magnesium diffused layer exhibits the crystal structure of an unknown compound of the Mg-Li-Nb-O ternary system. It is proposed, that this unknown compound and MgNb2O6 are the real sources for the Mg-ion indiffusion. The changes in Curie temperature with diffusion parameters such as diffusion temperature, diffusion times, and the thickness of magnesium oxide film are noted.
Photomodulated reflectance spectra of In0.2Ga0.8As/GaAs single quantum wells
Authors: Jiang S. , Shen S. C. , Wang S. M. , Andersson T. G.
Published: July 2002

The photomodulated reflectance spectra of In0.2Ga0.8As/GaAs single quantum wells with the same well width and different cap layer thickness have been measured at 77 K. Several optical structures which are caused by excitonic transition are observed, and, taking into account both the strain and the quantum well effects, the subband structures of the samples have been calculated. A strong influence of the cap layer thickness on the lattice relaxation and optical quality has been found. By fitting the experimental results to calculations, we find that in lattice mismatched semiconductor quantum well systems both the well width and the barrier thickness determine the lattice relaxation and the optical quality. This is a new result and different from the point that the lattice relaxation is determined by well width in InGaAs/GaAs system.
Spatial confinement effects on type II quantum well intersubband transitions
Authors: Peng Lung-Han , Fonstad Clifton G.
Published: July 2002

A study is made of the polarization dependence of intersubband transitions in n+ InP/InAlAs type II quantum wells (QWs), and it is shown that the type II nature of the valence bands and heavy electron band in these QWs is reflected in the spectra. Specifically it is found that the lack of spatial confinement to the QW in the Γ15v valence bands and higher conduction band in InP/InAlAs quantum wells (i) eliminates the coupling between Γc1 conduction subbands and heavy holes and electrons, and (ii) diminishes the normal-incidence intersubband activity in type II QWs, in accordance with the predictions of a recently published 14-band k⋅p analysis of quantum well subband levels.
Fabrication of all in-plane oriented a-axis YBa2Cu3O7−x/ insulator/ YBa2Cu3O7−x heterostructures
Authors: Takeuchi I. , Trajanovic Z. , Peng J. L. , Li Z. Y. , Warburton P. A. , Lobb C. J. , Venkatesan T.
Published: July 2002

In-plane oriented a-axis heteroepitaxial multilayers consisting of YBa2Cu3O7−x/PrBa2Cu3O7−y bilayers and insulating LaSrGaO4 and Nd2CuO4 on (100) LaSrGaO4 substrates have been fabricated. φ-scan measurements of reflections from (101) Nd2CuO4 and (102) YBa2Cu3O7−x planes display twofold symmetry, indicating in-plane oriented growth of the top and middle layers in superconductor-insulator-superconductor structures for an insulating barrier thickness of 3000 Å. For structures with a Nd2CuO4 barrier, both top and bottom layers had Tc(R=0)≥85 K.
Direct high-resolution electron microscopy observation of nonunit-cell nucleation in the initial stage of high-T
c superconducting film growth
Authors: Wen J. G. , Morishita T. , Koshizuka N. , Traeholt C. , Zandbergen H. W.
Published: July 2002

The relationship between the starting and ending atomic layers of YBa2Cu3O7−x and Bi2Sr2CaCu2O8 thin films is studied by high-resolution electron microscopy. Experimental results show that the starting atomic layer of the thin film is determined by surface chemistry and the interaction between the thin film and the substrate, while the ending layer of the thin film is thermodynamically determined by the high-Tc cuprate itself. Therefore, nonunit cell nucleation is often observed in certain cases. The surface atomic layers of YBa2Cu3O7−x and Bi2Sr2CaCu2O8 were found to be the CuO layer and single BiO layer, respectively.
Interface between low-temperature grown GaAs and undoped GaAs as a conduction barrier for back gates
Authors: Maranowski K. D. , Ibbetson J. P. , Campman K. L. , Gossard A. C.
Published: July 2002

We present a back gated 2DEG (two-dimensional electron gas) structure using low-temperature grown (LTG) GaAs as a barrier layer between the back gate and the undoped GaAs channel. The sheet concentration of the 2DEG can be linearly varied from full depletion up to 3×1011 cm−2 at 12 K. When this charge modulation is modeled by a simple parallel plate capacitor, we find that the distance between the plates is approximately equal to the channel thickness rather than the actual spacing between the 2DEG and the back gate (which is the channel thickness plus the LTG GaAs thickness). We explain this behavior by observing that the leakage path is limited by the triangular barrier to conduction formed at the interface between the LTG GaAs defect band and the undoped GaAs channel conduction band.
Vertical silicon metal–semiconductor–metal photodetectors with buried CoSi2 contact
Authors: Hermanns J. P. , Rüders F. , Stein von Kamienski E. , Roskos H. G. , Kurz H. , Hollricher O. , Buchal C. , Mantl S.
Published: July 2002

We report on design, fabrication, and characterization of an ultrafast vertical metal–semiconductor–metal photodetector. A CoSi2 layer in silicon acts both as a bottom Schottky contact and a buried light reflector. A semi-transparent metallization on top of a photosensitive silicon mesa serves as top Schottky contact. Time-domain studies of the pulse response are performed by electro-optic sampling measurements on photodetectors integrated monolithically into microstrip transmission lines. At room temperature, carrier sweep-out is dominated by hopping transport involving shallow traps. At low temperatures, hopping transport is strongly suppressed. As a consequence, the speed of the diode is considerably enhanced, reaching a pulse response with a full width at half maximum of 6.5 ps.
Scanning tunneling microscopy study of GaAs(001) surface prepared by deoxygenated and de-ionized water treatment
Authors: Hirota Y. , Fukuda T.
Published: July 2002

This letter presents the scanning tunneling microscopy (STM) images of GaAs(001) surfaces prepared by deoxygenated and de-ionized water (DODIW) treatment. The STM images reveal that the missing-dimer rows and unit cells of the 2×4 structure and atomic-layer steps of Ga–As clearly appear after heating the samples above 500 °C in an ultrahigh vacuum. These experimental results suggest the DODIW treatment can attain atomically flat GaAs(001) surface.
Probing the interfacial and sub-surface structure of Si/Si1−xGex multilayers
Authors: Sugden S. , Sofield C. J. , Noakes T. C. Q. , Kubiak R. A. A. , McConville C. F.
Published: July 2002

The ability to determine structural and compositional information from the sub-surface region of a semiconductor material has been demonstrated using a new time-of-flight medium energy ion scattering spectroscopy (ToF-MEISS) system. A series of silicon–silicon/germanium (Si/Si1−xGex) heterostructure and multilayer samples, grown using both solid source molecular beam epitaxy (MBE) and gas source chemical vapor deposition (CVD) on Si(100) substrates, have been investigated. These data indicate that each individual layer of Si1−xGex (x∼0.22) in both two- and three-period samples, can be uniquely identified with a resolution of approximately 3 nm. A comparison of MBE and CVD grown samples has also been made using layers with similar structures and composition. The total Ge content of each sample was confirmed using conventional Rutherford backscattering spectrometry.
Characteristics of a δ -doped GaAs/InGaAs p-channel heterostructure field-effect transistor
Authors: Hsu R. T. , Hsu W. C. , Kao M. J. , Wang J. S.
Published: July 2002

A δ-doped GaAs/In0.2Ga0.8As p-channel heterostructure field-effect transistor grown by low-pressure metalorganic chemical vapor deposition is demonstrated. The mobilities and two-dimensional hole gas concentrations at 300 (77) K are 260 (2600) cm2/v s and 1012 (5.5×1011) cm−2, respectively. For a gate length of 1.5 μm, the maximum extrinsic transconductances are 15 mS/mm at 300 K and 24 mS/mm at 77 K. The high transconductances extend a wide range versus gate voltage.
Kinetics of slow buildup of photoconductance in n-type 6H–SiC
Authors: Evwaraye A. O. , Smith S. R. , Mitchel W. C.
Published: July 2002

The slow buildup of photoconductance due to a peak centered at 1.13 eV below the conduction band in n-type 6H–SiC samples has been studied using optical admittance spectroscopy. The background doping of the samples ranges from 3.2×1015 cm−3 to 2×1018 cm−3. The results indicate that the carriers responsible for the observed conductance are excited from defect levels that are energetically close. The photoconductance transients are completely described by a sum of two exponential expressions. The relevant parameters, α1,α2,Gmax(1), and Gmax(2), are determined as functions of temperatures. The background doping ND-NA has no effect on the conductance buildup process, this indicates that the nitrogen donors play no role either in the formation of the defect or in the buildup process of the photoconductance.
High yield, low cost Fabry–Pérot modulators utilizing correctable partial antireflection coatings
Authors: Goossen K. W. , Cunningham J. E. , Jan W. Y. , Centanni J.
Published: July 2002

Reduced-finesse asymmetric Fabry–Pérot modulators are presented utilizing partial antireflection coatings (PAR-ASFP). Nonuniformity in semiconductor layer thicknesses may be corrected for by adjusting the thickness of the partial antireflection layer. Reduced thickness of the semiconductor layers is corrected for by reducing the thickness of the PAR layer, leading to natural extensions to manufacturing. By correcting the PAR, we obtain greater than 6.7:1 contrast over an entire 2 in. wafer at a single wavelength and drive voltage of 9 V.
Fading and self-irradiation of potassium halide thermoluminescence dosimeters
Authors: Pashchenko L. P. , Pérez Salas R. , Aceves R. , Barboza-Flores M.
Published: July 2002

The fading characteristics of KCl:Eu2+ (150 ppm) thermoluminescent crystals is determined. It is shown that the fading cannot be correctly measured without taking into account the phenomenon of self-irradiation of the crystals, due to natural radioactive nuclide 40K which is presented in potassium halide dosimeters. The results obtained can be useful in those applications of KCl: Eu2+ crystals dealing with long-time exposures, or low-dose levels of radiation.
Performance enhancement in a metal-insulator-semiconductor–like pseudomorphic transistor by utilizing an n−-GaAs/n+-In0.2Ga0.8As two-layer structure
Authors: Liu Wen-Chau , Hsu Wei-Chou , Laih Lih-Wen , Tsai Jung-Hui , Lour Wen-Shiung
Published: July 2002

A high performance metal-insulator-semiconductor–like pseudomorphic field-effect transistor utilizing an n−-GaAs/n+-In0.2Ga0.8As two-layer structure was fabricated and demonstrated. The n−-GaAs layer is used as the Schottky contact layer whereas the n+-In0.2Ga0.8As quantum well is employed as the active channel. Due to the excellent properties of the InGaAs layer and carrier confinement effect at the In0.2Ga0.8As–GaAs heterointerface, the device under study shows the advantages of high breakdown voltage, high current capability, very large gate voltage swing for high transconductance operation, and ease of fabrication. For a 2×100 μm2 gate device, a breakdown voltage of 17.4 V, a maximum drain saturation current of 930 mA/mm, a maximum extrinsic transconductance of 230 mS/mm, and a very wide gate voltage range larger than 3 V with the extrinsic transconductance higher than 200 mS/mm are obtained. Therefore, the device has great potential for use in high speed, high power, and large input signal circuit applications.
Improved structures for evanescent wave sensors
Authors: Rehouma F. , Elflein W. , Persegol D. , Kevorkian A. , Clauss G. , Benech P. , Rimet R.
Published: July 2002

Integrated optics evanescent wave sensors suffer from attenuation losses and reduced contrast ratio when the sensing layer index is too close to the waveguide index. This is attributed to an increase in mode mismatch at inner interfaces of the devices. By properly balancing the losses on each arm of an integrated Mach–Zehnder the contrast ratio is increased to nearly 100% on the entire index range, furthermore, a new technique used to make a smooth transition between sensing and nonsensing waveguides reduced the losses by 5 dB.
Observation of the Wohlleben effect in HoBa2Cu3O7−δ films
Authors: Guan Weiyan
Published: July 2002

A paramagnetic moment (Wohlleben effect) is observed in superconducting HoBa2Cu3O7−y films both in field cooling and zero field cooling measurements. This effect is explained by a model of a negative critical Josephson current in the weak-link loops in the films.
Diamond growth in premixed propylene-oxygen flames
Authors: Shin Ho Seon , Goodwin David G.
Published: July 2002

Diamond film growth in low-pressure premixed propylene/oxygen flames is demonstrated. Well-faceted films are grown at a pressure of 180 Torr and a fuel/oxygen ratio of 0.47. Using propylene as the fuel may greatly improve the economics of flame synthesis of diamond, since propylene is an order of magnitude cheaper than acetylene.
Improvement of the electrical properties of metal-ferroelectric BaMgF4-silicon capacitor by rapid thermal annealing
Authors: Kim Kwang-Ho , Kim Je-Deok , Ishiwara Hiroshi
Published: July 2002

Use of a rapid thermal annealing technique is shown to improve the electrical properties of metal-ferroelectric BaMgF4-silicon capacitors. The fluoride film was deposited in an ultrahigh vacuum system at a substrate temperature of 300 °C. A postdeposition annealing was conducted for 10 s at 600 °C followed by subsequent annealing for 5 s at 750 °C. The results were found out to increase the resistivity of the ferroelectric BaMgF4 film from a typical value of 1–2×1011 Ω cm before the annealing to about 5×1013 Ω cm at 1 MV/cm and reduce the interface state density of the BaMgF4/Si interface to about 8×1010/cm2 eV. Ferroelectric hysteresis measurements using a Sawyer–Tower circuit yielded remanent polarization and coercive field values of about 0.26 μC/cm2 and 315 kV/cm, respectively.
Switching of superradiance in semiconductor superlattices
Authors: Lee S. J. , Khurgin J. B. , Li S.
Published: July 2002

Radiative recombination of the excitonic states in semiconductor superlattices with an applied electric field is studied theoretically. It is shown that when the electron-hole Coulomb interaction energy exceeds the miniband width, a coherent excitonic state is created whose oscillator strength surpasses the oscillator strength of a single quantum well by orders of magnitude. It is also demonstrated that a small external field can split the coherent state into isolated well states and thus severely deplete the oscillator strength of the exciton. This opens the possibility of modulating and switching of superradiance in semiconductor devices.
Rate equation model of high-temperature performance of InGaAsP quantum well lasers
Authors: Bernussi A. A. , Pikal J. , Temkin H. , Coblentz D. L. , Logan R. A.
Published: July 2002

We present a steady-state phenomenological rate equation model describing the temperature dependence of the threshold current and slope efficiency of compressively strained InGaAsP multiquantum well lasers. The model is supported by measurements of differential carrier lifetime and gain carried out as a function of temperature. Differential gain, carrier density at transparency, and internal losses are shown to be the key parameters controlling the temperature sensitivity of our devices.
Back bias depending polarization sensitivity of PtSi/p-Si Schottky barrier detectors
Authors: Kapser K. , Deimel P. P.
Published: July 2002

The optical response of PtSi/p-Si Schottky barrier detectors structured with a lamellar grating was investigated. The quantum efficiency Y for TE and TM polarized light for different samples with grating constants Λ=3 μm, 4 μm, 5 μm, and with a grating amplitude h=1100 nm was measured. The ratio YTM/YTE strongly depends on the back bias of the diode. Theoretical calculations are presented which explain the results taking into account the locally varying Schottky barrier height and optical absorption induced by the grating.
Infrared fluorescence ‘‘decay-time’’ temperature sensor
Authors: Grattan K. T. V. , Palmer A. W.
Published: July 2002

The principle of the change in the ‘‘decay time’’ of the fluorescence of a small sample of neodymium in a glass matrix, excited by infrared radiation from a high-power light emitting diode has been used in the construction of a fiber-optic temperature sensor. Such a device is an inexpensive transducer and has demonstrated a fiber-optic sensor not requiring referencing to the intensity of the exciting radiation.
Hybrid dielectric/AlGaAs mirror spatially filtered vertical cavity top-surface emitting laser
Authors: Morgan R. A. , Hibbs-Brenner M. K. , Lehman J. A. , Kalweit E. L. , Walterson R. A. , Marta T. M. , Akinwande T.
Published: July 2002

A novel AlGaAs/AlAs–TiO2/SiO2 hybrid distributed Bragg reflector is implemented in a planar vertical cavity (top)-surface emitting laser (VCSEL) to control emission (near 850 nm) to a single TEM00-like mode. This structure exhibits ≳30 dB side-mode suppression ratio and constant divergence (or modal profile) throughout its operating range (i.e., the detrimental effects of thermal lensing inherent in implanted VCSELs are eliminated); moreover, a record low threshold voltage ≂1.6 V, (0.16 V above photon energy) is obtained, without sacrificing the producibility of the standard all-epitaxial structure.
Upconverting Tm-doped BaYYbF8 optical waveguides epitaxially grown on GaAs
Authors: Hung L. S. , Paz-Pujalt G. R. , Blanton T. N. , Tuschel D. D.
Published: July 2002

TM-doped BaYYbF8 films were epitaxially grown on both (100) and (111) GaAs substrates using CaF2 or LiF as intermediate layers. The BaYYbF8 phase was found to be a previously unreported cubic phase with a lattice constant of 0.5711 nm, which is different from a monoclinic phase reported for bulk crystals. The films produced UV and visible radiation with wavelengths at 360 nm (UV), 450–480 nm (blue), and 500–550 nm (green) when pumped by laser radiation at 647 nm.
Demonstration of a two stage backward-wave oscillator and free-electron laser
Authors: Liang Zheng , Yang Ziqiang , Den Tianquan , Liu Shengang
Published: July 2002

The experimental study of a two-stage scheme in which the same intense relativistic electron beam (0.6 MV, 3 kA, 70 ns) first produces powerful radiation (100 MW) at 3.0 cm and then the radiation is used as a pump wave for a free-electron laser interaction at 3.0 mm is described. The results of the experiment and nonlinear theory are discussed.
Quantitative measurement of the composition of AlxGa1−xAs heterostructures using a simple backscattered electron detector
Authors: Sercel Peter C. , Lebens John A. , Vahala Kerry J.
Published: July 2002

We describe a technique for the quantitative measurement of composition in AlxGa1−xAs heterostructures using a simple solid-state backscattered electron detector in a scanning electron microscope. Calibration data are presented and are shown to be consistent with the Castaing [Adv. Electron. Electron Phys. 13, 317 (1960)] theory. The technique is applied to image representative AlxGa1−xAs heterostructures including a graded index separate confinement heterostructure (GRINSCH) laser structure.
Scientific instrumentation for hot microhardness measurements on amorphous solids
Authors: Yannacopoulos S. , Kasap S. O.
Published: July 2002

A technique and a simple and convenient apparatus are described to carry out hot microhardness measurements on amorphous solids to enable the Vickers hardness number to be monitored as a function of temperature and heating rate. The apparatus consisted of modifying a commercially available microhardness test instrument so that the specimens could be mounted on a temperature-controlled aluminum platform, and the temperature of the indenting tip maintained equal to the that of the sample. A microcomputer and a data-acquisition system, with an appropriate algorithm and software, were used to ramp the temperature of the sample at any selected heating rate. A thermocouple and a heater arrangement attached to the indenter, with the same microcomputer and data-acquisition system, assured that the indenter tip temperature did not differ from that of the sample more than a fraction of a degree. The technique was applied to studying the influence of temperature on the Vickers hardness number (HV) of vacuum-deposited amorphous selenium-arsenic (a-Se0.997As0.003) alloy layers as used in x-ray medical imaging. It was found that the microhardness of such a typical chalcogenide glass decreases with the temperature, and in the glass transition region it undergoes a sharp fall, similar to the drop observed in the real part of the elastic constants of many glassy polymers. It is shown that an empirical glass transformation temperature Tg defined at the ‘‘break point’’ of the log HV-vs-log T plot depends on the heating rate r and that the Tg-r data can be adequately described by a Vogel–Tammann–Fulcher type of temperature dependence of the form exp[−333.4/(T−284 K)] similar to the general behavior of the viscosity of many chalcogenide glasses. It is expected that the variable heating rate technique with the modified microhardness apparatus described in this paper will be applied to study phase and glass transformations in many other amorphous solids. The technique is therefore aptly named ‘‘thermomicrohardness analysis’’ (TμHA).
Lattice relaxation in InxAl1−xAs/GaAs heterostructure grown on exact oriented and misoriented GaAs substrates
Authors: Baek Jong-Hyeob , Lee Bun , Yoon Meeyoung , Lee El-Hang , Kim Chang Soo
Published: July 2002

We have examined lattice relaxation properties of 2 μm thick InxAl1−xAs epitaxial layers grown simultaneously on a (100) exact oriented GaAs substrate and on a 2° misoriented GaAs substrate by low pressure metalorganic chemical vapor deposition method. Double crystal x-ray diffractometry has been used to determine the alloy compositions at various azimuthal angles. As a result of (400) x-ray rocking curve analysis, it was found that the full width at half-maximum (FWHM) of x-ray rocking curves for both samples were strongly dependent on the azimuthal angle, indicating that the lattice relaxation depended greatly on the substrate orientation. From the data of {511} asymmetric measurements for four different directions, the In contents of the epitaxial layers found were 24%. The In0.24Al0.76As epitaxial layers grown on an exact oriented substrate and on a misoriented substrate both showed 82% relaxation, which was a larger value in comparison with the similarly mismatched InGaAs/GaAs heterostructure. The periodic FWHM of the x-ray rocking curves shows that the anisotropy of residual strain was independent of the nominal substrate misoriented direction. For both types of substrate, it is most likely that the variation of the FWHM originates from asymmetric densities of misfit dislocation.
Ultrafast photodetector materials based on oxygen-doped metalorganic vapor phase epitaxy GaAs
Authors: Frankel Michael Y. , Huang J.-W. , Kuech T. F.
Published: July 2002

Controlled incorporation of deep level states into III/V materials tailor their electrical and optical characteristics for ultrafast optoelectronics. We investigate the photoinjected carrier dynamics in GaAs grown by metalorganic vapor phase epitaxy (MOVPE) with (C2H5)2AlOC2H5 as an oxygen precursor providing the deep level state control. Photoconductor switching was used to determine the free-carrier trapping times, and femtosecond photoreflectance at 2 eV was used to measure the trapped charge recombination time as a function of oxygen concentration. We also use electro-optic sampling to demonstrate a photodetector with 650-fs measured response time and to show the material applicability to ultrafast optoelectronics.
Effect of barrier recombination on the high temperature performance of quaternary multiquantum well lasers
Authors: Bernussi A. A. , Temkin H. , Coblentz D. L. , Logan R. A.
Published: July 2002

We use spectrally resolved measurements of spontaneous emission to investigate the temperature characteristics of strained and lattice matched InGaAsP multiquantum well lasers. Carrier overflow into the barriers and separate confinement layers and the resulting recombination are demonstrated to be an important factor limiting high temperature performances in these devices. The barrier recombination does not saturate above threshold, instead it increases with the drive current. This effect is further enhanced with increased temperature. We show that the reduction in the barrier recombination correlates quantitatively with increased high temperature slope efficiency.
Possibility of off-resonance lasing in vertical cavity surface emitting lasers
Authors: Register Leonard F. , Baca Rich , Kosinovsky Gregory A. , Grupen Matt , Hess Karl
Published: July 2002

Light emission from vertical cavity surface emitting lasers (VCSELs) is modeled as directed radiation away from a localized source within the VCSEL optical cavity into an open system as a continuous function of frequency, analogous to antenna radiation, but with field sources provided by spontaneous emission and gain. To allow near-analytical solution, a quasi-one-dimensional system is analyzed. This approach reproduces the familiar threshold condition, mode gain times lifetime equals unity, at the cavity quasimode frequency; however, it also predicts that lasing is not restricted to the quasimode frequency.
Traverse electric mode characteristics in a cylinder waveguide with a periodic dielectric cladding
Authors: Ping Er-Xuan
Published: July 2002

The transverse electric mode characteristics in a cylinder waveguide with a periodic dielectric cladding have been analytically studied. The periodic dielectric cladding induces band structures in the characteristics and enhances the confinement of the electromagnetic energy in the core compared to a cylinder waveguide with a uniform cladding. Potential applications based on the characteristics are discussed in optical communications and photonics.
Self-aligned hybrid integration of semiconductor lasers with micromachined micro-optics for optoelectronic packaging
Authors: Lin L. Y. , Lee S. S. , Pister K. S. J. , Wu M. C.
Published: July 2002

Novel self-aligned hybrid integration of semiconductor lasers with three-dimensional micro-optical components has been demonstrated. The self-alignment structures are fabricated integrally with other three-dimensional micro-optical elements such as micro-Fresnel lenses, mirrors, and gratings on a single Si chip by surface micromachining technology. The Si substrate serves as a free-space micro-optical bench for active and passive optoelectronic components. A divergent beam emitted from an edge-emitting semiconductor laser has been successfully collimated by the integrated micro-Fresnel lens. The integration scheme offers a new approach for optoelectronic packaging and a new technology platform for integrating complete free-space micro-optical system on a single chip.
Novel power switch using oblique incidence to a nonlinear slab
Authors: Liu Hwei-Yuan , Wang Way-Seen
Published: July 2002

The waveguiding characteristics of a novel power switch with one input and n outputs (1×n) using oblique incidence to a nonlinear slab is proposed. With a proper incident optical power, the emitted soliton in the nonlinear slab can be efficiently directed to any waveguide in a array of n waveguides. For digital signal switching application, the number n can be increased simply by increasing the slab thickness. Moreover, it is found that the soliton offsets calculated by Snell’s law with an index obtained by averaging over the index distribution are in good agreement with those calculated by the beam propagation method.
Room-temperature photoluminescence of GemSinGem structures
Authors: Gail M. , Abstreiter G. , Olajos J. , Engvall J. , Grimmeiss H. , Kibbel H. , Presting H.
Published: July 2002

Photoluminescence of pseudomorphic Ge wells grown by conventional molecular beam epitaxy on Si substrate is studied. The samples consist of p-type doped Gem–Sin–Gem structures embedded in a Si1−xGex alloy. The luminescence lines shift to lower energy with increasing m, the observed band gap agrees with subband calculation based on an effective mass approximation. The temperature stability of the luminescence depends on m. In the case of m=4 the luminescence persists up to room temperature with only small reduction in intensity. The activation energies determined from the exponential drop of luminescence intensity agree with band discontinuities in the sample structures.
Electron traps in β-SiC grown by chemical vapor deposition on silicon (100) substrates
Authors: Zekentes K. , Kayiambaki M. , Constantinidis G.
Published: July 2002

Deep electron traps in heteroepitaxial β-SiC films grown on Si(100) substrates by chemical vapor deposition were investigated. Capacitance deep level transient spectroscopy revealed the presence of several traps, the majority of which are rather process-induced as expected for a highly defective material such as β-SiC grown heteroepitaxially on Si. Samples of different origin as well as various surface treatments have been used to determine traps intrinsic to β-SiC heteroepitaxial material. Three main traps were detected, independently of the surface treatment, at 0.32, 0.52, and 0.56 eV below the conduction-band minimum. Comparison with theoretically predicted activation energies for the single native defects did not permit the assignment of the observed traps to any of these defects.
Technique for measuring absolute intensity of weak magnetic fields by a SQUID pick-up coil system
Authors: Geng Q. , Minami H. , Chihara K. , Yuyama J. , Goto E.
Published: July 2002

A method to measure the absolute intensity of a weak magnetic field is described. This method uses patterned superconducting strip lines as a spatial modulator of the field and detects the magnetic field distribution over them as a function of applied magnetic fields. The field distribution change measured by an rf SQUID system is proportional to the component of the absolute intensity of the magnetic field at the specimen that is parallel with the pick-up coil axis. The magnetic field intensity can be determined absolutely from about 1 μG by this method. A spatial resolution of the field as good as a few millimeters is obtained. Some practical limitations of this method and possible ways for improving are also discussed.
Photothermal microscope for high-T
c superconductors and charge density waves
Authors: Wu X. D. , Kino G. S. , Fanton J. T. , Kapitulnik A.
Published: July 2002

We have developed a new photothermal technique to investigate electronic phase transitions associated with high temperature superconductivity and charge density waves (CDW). The phase shift of the thermal wave yields the anisotropic thermal diffusivity coefficient of the sample. The amplitude of the photothermal signal is sensitive to electronic phase transitions of the second kind and measures directly the effect of thermodynamic fluctuations near the transitions. This noncontacting high-definition technique is well suited to measurements of small and fragile samples. Good comparisons between our experimental results and second-order phase transition theory are obtained on a high-Tc superconductor and a CDW sample.
A procedure for temperature-dependent, differential van der Pauw measurements
Authors: Bartels A. , Peiner E. , Schlachetzki A.
Published: July 2002

A two-step procedure is presented for temperature-dependent carrier-concentration and mobility profiling of InP and GaAs epitaxially grown on Si. Carrier concentrations and mobilities are determined by the van der Pauw technique between 14 and 300 K using a refrigerator-cooled cryostat. Anodic oxidation and oxide stripping by chemical etching were selected for the subsequent removal of controlled thin sublayers. By the combination of differential and temperature-dependent van der Pauw measurements, mobilities and carrier concentrations in dependence on depth and temperature have been extracted whereby the carrier-concentration profile at room temperature agrees very well with the results obtained by the electrochemical C/V technique. For InP/Si at a distance of more than 0.7 μm away from the heterointerface, the dependence of the carrier mobility on the concentration at room temperature is essentially the same as for InP/InP layers. At low temperatures, e.g., 77 K, scattering by dislocations results in a mobility reduction in InP/Si and GaAs/Si with respect to homoepitaxy. Due to the nonuniform distribution of impurities and dislocations the temperature dependences of carrier concentration and mobility vary considerably with depth, thus strongly recommending the use of the differential technique.