bluuebunny/crossref_metadata_2025 huggingface dataset:
Remanent nonlinear magnetic response in superconducting Y-Ba-Cu-O
Authors: Shaulov A. , Dorman D. , Bhargava R. , Yeshurun Y.
Published: July 2002

We report a ‘‘memory’’ effect in the response of sintered Y-Ba-Cu-O to alternating magnetic fields. The application of a steady bias field, above a certain threshold, causes the generation of harmonic components in the response. These harmonics persist after the field is removed, exhibiting a logarithmic decay with time. We explain these phenomena in the framework of the Bean model, taking into account the granularity of the sample. The memory phenomenon offers a principle for a new recording mechanism which may allow extremely high storage capacity.
Effect of thin Ge layer on the surface depletion in GaAs
Authors: Mui D. S. L. , Salvador A. , Strite S. , Morkoç H.
Published: July 2002

We have investigated thin GaAs layers capped with 20 Å Ge pertaining to the extent of the well known surface depletion layer in this semiconductor. Using the transmission line method, the effective surface potential of 0.78 V measured in the GaAs surface was reduced to 0.45 V by the epitaxially grown Ge cap layer. About 0.26 of the 0.45 V is due to the conduction-band discontinuity at the Ge/GaAs heterointerface which leads to an actual surface potential of around 0.19 V. The same trend was also verified by photoreflectance and photoluminescence with variable excitation wavelengths. The results are encouraging for device applications despite the possibility that a considerable portion of the 20 Å Ge cap layer is oxidized.
Humidity-induced room-temperature decomposition of Au contacted indium phosphide
Authors: Fatemi Navid S. , Weizer Victor G.
Published: July 2002

We have found that Au-contacted InP is chemically unstable at room temperature in a humid ambient due to the leaching action of indium nitrate islands that continually remove In from the contact metallization and thus, in effect, from the InP substrate. While similar appearing islands form on Au-contacted GaAs, that system appears to be stable since leaching of the group III element does not take place.
Investigation of laser-surface interactions and optical damage mechanisms using excitation by pairs of picosecond laser pulses
Authors: Chase L. L. , Lee H. W. H. , Hughes Robert S.
Published: July 2002

It is demonstrated that laser-surface interactions that cause optical surface damage of nominally transparent materials can be investigated by observing the effects of excitation by pairs of picosecond pulses separated by a variable time delay. Laser-induced emission of neutrals is used as the detection mechanism in the present experiments.
Thermal stability of coevaporated Al-Pt thin films on GaAs substrates
Authors: Blanpain B. , Wilk G. D. , Olowolafe J. O. , Mayer J. W. , Zheng L. R.
Published: July 2002

We report on the stability of Al-Pt coevaporated thin films on GaAs substrates for aluminum concentrations ranging from 45 to 70 at. %. We show that for the region with compositions between AlPt and Al2Pt these alloy thin films fulfill the thermal stability requirements imposed by GaAs self-aligned gate technology.
Improved microwave performance in transistors based on real space electron transfer
Authors: Hueschen Mark R. , Moll Nick , Fischer-Colbrie Alice
Published: July 2002

Experimental results on an improved type of transistor based on real space electron transfer are presented. Microwave measurements through 25 GHz show an extrapolated fT of 60 GHz and a measured fMAX of 18 GHz. These gain-bandwidth products are approximately twice as high as any previously reported for this relatively new class of device. This improvement in performance results from a novel device design which incorporates a doped, pseudomorphic InGaAs channel, a GaAs collector drift region, and a collector-up structure.
Diffusion in GaAs of a native defect tagged with deuterium
Authors: Morrow Richard A.
Published: July 2002

We interpret published depth profiles of deuterium in n- and p-type GaAs, following long anneals at 500 °C in a gaseous deuterium atmosphere, as indicating the indiffusion of a native defect (probably VAs) and an impurity (possibly O), both tagged with deuterium. Model fits yield the 500 °C diffusivity of the tagged impurity as 4×10−14 cm2/s and the diffusivities of the tagged native defect as 3×10−15 cm2/s in n-GaAs and ∼8×10−15 cm2/s in p-GaAs.
Low-threshold disorder-defined buried-heterostructure AlxGa1−xAs-GaAs quantum well lasers by open-tube rapid thermal annealing
Authors: Richard T. A. , Major J. S. , Kish F. A. , Holonyak N. , Smith S. C. , Burnham R. D.
Published: July 2002

AlxGa1−xAs-GaAs single stripe quantum well heterostructure (QWH) lasers fabricated via Si impurity-induced layer disordering (IILD) in an As-free open tube rapid thermal annealing furnace are reported. The Si IILD, with good surface morphology, is obtained using a Si/Si3N4 source layer with the QWH wafer in face-to-face contact with a GaAs substrate during the anneal (13 min, 1000 °C). Continuous wave (cw) 300 K operation of the lasers with uncoated facets has produced output powers as high as 25 mW/facet with threshold currents as low as 7 mA. The devices operate single mode at a wavelength of 812 nm and have high differential quantum efficiencies of ∼44%, with some as high as 57%.
Electroreflectance and photoluminescence study of the effect of hydrogen on heavily doped GaAs/AlGaAs structures
Authors: Yang D. , Garland J. W. , Raccah P. M. , Coluzza C. , Frankl P. , Capizzi M. , Chambers F. , Devane G.
Published: July 2002

Highly doped semiconducting heteroepitaxial structures are commonly found in advanced devices. It is difficult to interpret quantitatively the results of optical measurements on such structures because the strong built-in electric fields present invalidate the low-field theories usually used to interpret those results. We have studied by electrolyte electroreflectance and photoluminescence a GaAs/AlGaAs resonant tunneling structure with a highly n-doped GaAs substrate and cap, before and after hydrogenation. We also have developed a new, improved microscopic theoretical treatment of the effects of strong fields on the local dielectric function and have used that treatment to evaluate quantitatively the effect of hydrogenation on the densities of shallow donor levels and of deep traps in the GaAs cap and to find the interface charges and band-pinning levels in the resonant tunneling junction.
Small-angle neutron scattering study of semiconductor microcrystallites in optical glasses
Authors: Degiorgio Vittorio , Banfi GianPiero , Righini Giancarlo , Rennie Adrian
Published: July 2002

The structure of semiconductor-doped glasses is studied by small-angle neutron scattering. We derive the average size of the microcrystals, and we give information on the spatial distribution of the microcrystals. A new aspect emerging from our data is the existence of a depletion region that during nucleation and growth each crystal creates around itself.
Cavity length dependence of the wavelength of strained-layer InGaAs/GaAs lasers
Authors: Chen T. R. , Zhuang Y. H. , Eng L. E. , Yariv A.
Published: July 2002

The lasing wavelength of a strained-layer InGaAs/GaAs single quantum well laser has been found to depend strongly on the cavity length. The relationship between the lasing wavelength and the cavity length was established experimentally and a cavity length tuning mechanism for a quantum well laser is thus made possible.
Low-temperature Si molecular beam epitaxy: Solution to the doping problem
Authors: Gossmann H.-J. , Schubert E. F. , Eaglesham D. J. , Cerullo M.
Published: July 2002

A major problem in group IV molecular beam epitaxy (MBE) is the difficulty to incorporate and control dopants due to the low incorporation probability and strong segregation in Si at typical growth temperatures. It is demonstrated here that growth at low temperatures yields a solution to this doping problem making thermal, coevaporative doping with excellent control possible in Si MBE without the need for any post-growth annealing. Unity incorporation and activation of Sb with concentrations reaching 5×1019 cm−3 are achieved for epitaxial growth of Si on Si(100) at temperatures of 325 °C. Hall electron mobilities in the films are close to bulk values indicating the high quality of the films. Capacitance-voltage measurements on Sb δ-doped films have full widths at half maximum of ≲50 Å, the narrowest Sb-doping profiles in Si determined with an electrical technique.
Comparative study of the substrate-film interfaces of GaAs grown by two molecular beam epitaxial methods
Authors: Tappura K. , Salokatve A. , Rakennus K. , Asonen H. , Pessa M.
Published: July 2002

Carrier concentration profiles in the region of a substrate-film homojunction for n- and p-type GaAs were studied using a capacitance-voltage carrier profiling technique. The GaAs films were grown on GaAs substrates by molecular beam epitaxy (MBE) and by gas-source molecular beam epitaxy (GSMBE). The GaAs homojunctions grown by MBE exhibited a much larger reduction in carrier concentration than those prepared by GSMBE. The highest quality interface, without an observable depletion region, was obtained when an additional hydrogen plasma was used during heat treatment prior to GSMBE growth.
Defects in preamorphized single-crystal silicon
Authors: Ayres J. R. , Brotherton S. D. , Shannon J. M. , Politiek J.
Published: July 2002

Direct electrical characterization of 1-μm-thick Si+ preamorphized and epitaxially regrown silicon layers has revealed a low concentration of residual deep-level defects within the regrown layer. A deep-level trap at Ec −0.40 eV has been found associated with the amorphous-crystalline boundary dislocation loops. In addition, a near mid-gap trap at Ev+0.54 eV, observed in p-type samples, is believed to be responsible for a spatially localized generation current of ∼2×10−6 A/cm2 associated with the dislocation loops.
Strain in porous Si formed on a Si (100) substrate
Authors: Bai Gang , Kim Kun Ho , Nicolet Marc-A.
Published: July 2002

The strain in a porous Si layer formed by anodization of a crystalline p+-Si(100) wafer in a HF electrolyte was measured by double-crystal x-ray diffractometry. The perpendicular strain in the as-formed porous Si layer is ∼10−3. The parallel strain is not measurable (<10−4). Upon annealing in vacuum from 200–800 °C, at elevated temperature, the perpendicular strain decreases while the parallel strain remains zero. Subsequently, the perpendicular strain of the annealed sample increases by amounts that depend on the ambient. The observed changes of strain in porous Si layers are explained as being mainly caused by modification of the stress in the native oxide layer due to desorption and absorption of gas. We propose that the strain in porous Si is the net result of stress induced by surface tension, oxide formation, and exchange of gas between the oxide and ambient.
Ion beam induced conductivity in chemically vapor deposited diamond films
Authors: Prawer S. , Hoffman A. , Kalish R.
Published: July 2002

Polycrystalline diamond films deposited by the microwave plasma chemical vapor deposition (CVD) technique onto quartz substrates have been irradiated with 100 keV C and 320 keV Xe ions at room temperature and at 200 °C. The dose dependence of the electrical conductivity measured in situ exhibited complicated, nonmonotonic behavior. High doses were found to induce an increase of up to ten orders of magnitude in the electrical conductivity of the film. The dose dependence of the conductivity for the CVD films was found to be very similar to that measured for natural, type IIa, single-crystal diamonds irradiated under identical conditions. This result suggests that the conduction mechanism in ion beam irradiated polycrystalline CVD diamond films is not dominated by grain boundaries and graphitic impurities as one might have expected, but rather is determined by the intrinsic properties of diamond itself.
GaAs/AlGaAs multiple quantum well field-induced optical waveguide
Authors: Huang T. C. , Chung Y. , Dagli N. , Coldren L. A.
Published: July 2002

Electrically controllable optical waveguides have been created by using only the increase in refractive index from linear and quadratic electro-optic effects in GaAs/AlGaAs multiple quantum well substrates for the first time. Unlike conventional fixed waveguides, lateral guiding of this field-induced guide (FIG) can be turned on and off, so that the confinement factor, propagation constant, and net loss can be adjusted over wide ranges electrically. This special property plus a very simple fabrication process suggest that the FIG could be an important base technology for photonic integrated circuits.
Effect of coherent strain on hydrogenic acceptor levels in InyGa1−yAs/AlxGa1−xAs quantum well structures
Authors: Loehr J. P. , Chen Y. C. , Biswas D. , Bhattacharya P. , Singh J.
Published: July 2002

The biaxial strain produced in lattice-mismatched epitaxy can have a substantial effect on the valence band structure. Theoretical results are presented for a hydrogenic acceptor in a quantum well under tensile and compressive strain. The acceptor level energy is a strong function of strain and could be used as a signature for the effect of strain on the valence band structure. Experimental studies are carried out on compressively strained InyGa1−yAs/ AlxGa1−xAs quantum well structures and the acceptor level energy is determined by photoluminescence measurements. Good agreement is found with the experiments.
Convergent beam electron diffraction study of lattice distortion in InGaAs/GaAs strained-layer superlattices grown by metalorganic chemical vapor deposition
Authors: Xie Q. H. , Fung K. K. , York P. K. , Fernandez G. E. , Eades J. A. , Coleman J. J.
Published: July 2002

The intensities of sidebands in convergent beam electron diffraction reflections from plan-view specimens of strain modulated InGaAs/GaAs superlattices are dependent on the natural lattice mismatch, the ratio of the thicknesses of the superlattice layers, the period (sum of layer thicknesses) of the superlattice, and the g vectors of the reflections. The intensities of kinematic higher-order Laue zone (HOLZ) reflections have been calculated from a simple model based on alternate contraction and expansion of lattice spacings of the superlattice layers. An accurate estimate of the In content of InGaAs can be deduced from the elastic strains in the superlattice layers so obtained.
Cathodoluminescence study of thin films of high T
c superconductors
Authors: Barkay Z. , Azoulay J. , Lereah Y. , Dai U. , Hess N. , Racah D. , Grünbaum E. , Deutscher G.
Published: July 2002

Cathodoluminescence (CL) of thin films of high Tc superconductors was studied in the scanning electron microscope. The depth and the lateral locations of the different phases can be revealed. In thin films, unlike the bulk superconductors, the CL information can be obtained either from the film itself or the substrate by varying the primary beam energy. At high beam energy, substrate defects and slight thickness variations of a single high Tc phase are observed. The resolution of the CL measurements improves at low temperatures.
Micro-Raman characterization of structural defects in patterned GaAs-on-Si
Authors: Duncan W. M. , Matyi R. J. , Shichijo H. , Kao Y.-C. , Liu H.-Y.
Published: July 2002

We have applied micro-Raman spectroscopy to the analysis of structural quality of GaAs-on-Si where the GaAs growth was performed through openings in an amorphous mask. The presence of the symmetry forbidden transverse optic (TO) phonon band and line shape of the longitudinal optic (LO) phonon band have been used to extract information concerning the structural quality of microscopic regions of GaAs from the Raman spectra. The utility of TO to LO phonon intensity ratios as a measure of crystal quality has been corroborated by correlation to x-ray rocking curve full width. The structural quality of selectively grown GaAs as determined from first-order Raman ratios is found to degrade in the vicinity of the transition between single crystal and polycrystalline regions. This work also shows that post-growth annealing significantly improves the quality of structures with minimum feature size as small as 2 μm.
Unpinning of GaAs surface Fermi level by 200 °C molecular beam epitaxial layer
Authors: Look D. C. , Stutz C. E. , Evans K. R.
Published: July 2002

Previous attempts to passivate the n-type (100)GaAs surface have significantly reduced only the surface recombination centers, but not the surface acceptors which pin the Fermi level. Here we show that a 100 Å molecular beam epitaxial layer grown at 200 °C reduces the effective surface potential energy − eφs from 0.70 to 0.17 eV, nearly eliminates light sensitivity, and permits nonalloyed ohmic contacts. After a 10 min, 450 °C anneal, − eφs increases only to 0.22 eV.
Anisotropy and intergrain current density in oriented grained bulk YBa2Cu3Ox superconductor
Authors: Selvamanickam V. , Salama K.
Published: July 2002

The intergrain transport current density and its anisotropy have been studied in oriented grained bulk YBa2Cu3Ox superconductors fabricated by the liquid phase processing method. Current density measurements were performed on oriented grained samples with the transport current aligned at different angles to the a-b plane. In these measurements, the transport current passed through several oriented grain boundaries. The results indicate that the critical current density drops rapidly when the transport current flows at small angles to the a-b plane and then decreases slowly at larger angles. At 77 K and zero magnetic field, an anisotropy ratio of about 25 is observed between Jc along a-b plane and that perpendicular to the plane. Further, the critical current density in these samples is found to depend weakly on magnetic field even though the current crosses grain boundaries. These results support the notion that grain boundaries of these superconductors are different in nature from those of solid-state sintered samples.
Observation of proposed flux pinning sites in neutron-irradiated YBa2Cu3O7−x
Authors: Lee J.-W. , Lessure H. S. , Laughlin D. E. , McHenry M. E. , Sankar S. G. , Willis J. O. , Cost J. R. , Maley M. P.
Published: July 2002

Microstructure and magnetic hysteresis have been compared for two samples of the YBa2Cu3O7−δ (δ∼0) high-temperature superconductor, one unirradiated, and one irradiated with fast neutrons (E≳0.1 MeV) to a fluence of 3×1018 n/cm2. Notable changes in the microstructure include strain-induced contrast from regions 2–7 nm in size. An intrinsic critical current density (Jc) of 4.6×106 A/cm2 in zero field at 4 K has been determined from magnetic hysteresis measurements for the irradiated sample while 1.2×106 A/cm2 is noted for the unirradiated sample. We propose that the observed defect structure in the irradiated material is responsible for increased pinning and consequently higher Jc’s.
Microscopic model for hot-electron trapping and detrapping in silicon dioxide
Authors: Porod W. , Kamocsai R. L.
Published: July 2002

We present a microscopic theory for high-field stressing and oxide degradation in SiO2. Hot electrons lead to a charge buildup in the oxide according to a dynamical trapping and detrapping model, where detrapping events are modeled as trap-to-band impact ionization processes. Electronic distributions obtained from Monte Carlo high-field transport simulations are used to determine ensemble averaged detrapping cross sections and experimentally observed flat-band voltage shifts. In comparing our microscopic theory to previously employed empirical rate equation models, we find significant differences in the predicted spatial distribution of oxide charge.
Superconducting YBa2Cu3O7−δ thin films on GaAs with conducting indium-tin-oxide buffer layers
Authors: Kellett B. J. , Gauzzi A. , James J. H. , Dwir B. , Pavuna D. , Reinhart F. K.
Published: July 2002

Superconducting YBa2Cu3O7−δ (YBCO) thin films have been grown in situ on GaAs with conducting indium-tin-oxide (ITO) buffer layers. Superconducting onset is about 92 K with zero resistance at 60 K. ITO buffer layers usually form Schottky-like barriers on GaAs. The YBCO film and ITO buffer layer, grown by ion beam sputter codeposition, are textured and polycrystalline with a combined room-temperature resistivity of about 1 mΩ cm.
Study of structural changes in YBa2Cu3O7−x by cathodoluminescence in the scanning electron microscope
Authors: Piqueras J. , Fernández P. , Vicent J. L.
Published: July 2002

Changes in the visible and infrared cathodoluminescence (CL) spectra of YBa2Cu3O7−x are detected during irradiation in the scanning electron microscope. Results indicate the influence of oxygen content on the appearance of a CL band at 450–600 nm. In irradiated samples an infrared band at 1600–1700 nm has been observed.
Unexpected effects of gold on the structure, superconductivity, and normal state of YBa2Cu3O7
Authors: Cieplak Marta Z. , Xiao Gang , Chien C. L. , Stalick J. K. , Rhyne J. J.
Published: July 2002

Using high-resolution x-ray and neutron diffraction measurements, we have shown that gold can be doped into YBa2Cu3O7 (1:2:3) up to 10% per formula unit, exclusively at the Cu(1) sites. Au doping causes a larger uniaxial expansion along the c axis, accompanying an increase in the Cu(1)—O(1) bond length and a decrease in the Cu(2)—O(1) bond length. The superconducting transition temperature (Tc) is enhanced upon Au doping and the normal-state transport properties are altered even for small levels of Au doping. The widely held belief in the inert nature of Au with regard to high Tc superconductors is therefore invalid. These findings also raise questions concerning results using single crystals grown from gold crucibles.
Millimeter-wave surface resistance of laser-ablated YBa2Cu3O7−δ superconducting films
Authors: Miranda F. A. , Gordon W. L. , Bhasin K. B. , Warner J. D.
Published: July 2002

We have measured the millimeter-wave surface resistance of YBa2Cu3O7−δ superconducting films in a gold-plated copper host cavity at 58.6 GHz between 25 and 300 K. High quality laser-ablated films of 1.2 μm thickness were deposited on SrTiO3 and LaGaO3 substrates. Their transition temperatures (Tc’s) were 90.0 and 88.9 K, with a surface resistance at 70 K of 82 and 116 mΩ, respectively. These values are better than the values for the gold-plated cavity at the same temperature and frequency.
Superconducting YBa2Cu3O7−x thin films on silver substrates by in situ plasma-enhanced metalorganic chemical vapor deposition
Authors: Zhao J. , Li Y. Q. , Chern C. S. , Norris P. , Gallois B. , Kear B. , Wessels B. W.
Published: July 2002

An in situ microwave plasma-enhanced metalorganic chemical vapor deposition process was used to fabricate highly c-axis oriented YBa2Cu3O7−x superconducting thin films on metallic Ag substrates. The films were deposited at a reduced substrate temperature of 740 °C in about 270 Pa of N2O ambient. Magnetic susceptibilities versus temperature of the as-deposited films show attainment of zero resistance of 85 K and composition of single (high Tc) phase. X-ray diffraction measurements reveal that the films deposited at 740 °C have highly preferential orientation of the crystallite c axes perpendicular to the substrate surface.
Formation of amorphous interlayers by solid-state diffusion in ultrahigh-vacuum-deposited polycrystalline Nb and Ta thin films on (111)Si
Authors: Cheng J. Y. , Chen L. J.
Published: July 2002

The formation of amorphous interlayers (a-interlayers) in ultrahigh-vacuum-deposited polycrystalline Nb and Ta thin films on (111)Si has been studied by cross-sectional transmission electron microscopy. The growth of a interlayers was found to follow a linear growth law initially in samples annealed at 450–500 °C and 550–625 °C for Nb/Si and Ta/Si, respectively. The growth then slows down and deviates from a linear growth behavior as a critical thickness of the a interlayer was reached. The a interlayer/crystalline Si interface was found to be rather smooth. The roughness of the interface between the Nb layer and a interlayer was observed to decrease with annealing temperature and time. The observation suggested that the growth of the a interlayer was interface reaction controlled initially.
Linear optical properties of quantum wells composed of all-binary InAs/GaAs short-period strained-layer superlattices
Authors: Hasenberg T. C. , McCallum D. S. , Huang X. R. , Dawson Martin D. , Boggess Thomas F. , Smirl Arthur L.
Published: July 2002

The linear optical properties of a variety of (InAs/GaAs)-GaAs multiple quantum well structures, where each well consists of a highly strained InAs/GaAs short-period superlattice, have been investigated in detail. The results attest to the improvement in material quality over previously reported structures of this type. Clearly resolved excitonic absorption peaks have been observed at room temperature in all samples. Photoluminescence and excitonic absorption linewidths at 15 K are less than 10 meV in each case, with the photoluminescence Stokes shifted by less than 1 meV. Temporally resolved photoluminescence measurements at 15 K indicate carrier lifetimes of 1.4–1.8 ns. Dramatic strain-related differences are observed when compared to random alloy InGaAs/GaAs quantum wells with an equivalent average indium mole fraction.
Dependence of crystalline orientation on film thickness in laser-ablated YBa2Cu3O7−δ on LaAlO3
Authors: Carim A. H. , Basu S. N. , Muenchausen R. E.
Published: July 2002

The microstructure of YBa2Cu3O7−δ thin films deposited on (001)LaAlO3 substrates by a laser ablation process has been investigated by scanning electron microscopy, x-ray diffraction, and cross-sectional transmission electron microscopy. Adjacent to the substrate, the film is entirely oriented with the c-axis perpendicular to the surface. At a thickness of about 0.4 μm, the occurrence of 90° boundaries brings about a transition to grains with their c-axes parallel to the surface (aligned along the [100] and [010] directions of the pseudocubic LaAlO3 substrate). This transition is discussed in terms of the crystal growth anisotropy and the retained strain that may precipitate the transition.
Application of photodeposited Cd to Schottky barrier diode and transistor fabrication on InP and In0.53Ga0.47As substrates
Authors: Licata Thomas J. , Schmidt Michael T. , Osgood Richard M. , Chan Winston K. , Bhat Rajaram
Published: July 2002

We report on using a thin (∼200 Å) layer of photodeposited Cd to form high Schottky barrier height contacts to InP and In0.53Ga0.47As. Current-voltage measurements of the Schottky diodes yield barrier heights of 0.70 and 0.55 eV to InP and In0.53Ga0.47As, respectively. The photodeposition process has been integrated with conventional clean room processing to fabricate Au/Cd/In0.53Ga0.47As transistors with high transconductances (∼200 mS/mm) and operating frequencies ( fmax∼30 GHz). X-ray photoelectron spectroscopy of thin Cd photodeposits on InP shows that the process produces an interfacial (∼10 Å thick) Cd-InP reaction zone covered by metallic Cd.
Enhancement of luminescence in GaAs by low levels of Cu
Authors: Third C. E. , Weinberg F. , Thewalt M. , Young L.
Published: July 2002

In a previous paper it was reported that GaAs, after rapid thermal annealing, exhibited bright regions adjacent to the sample surfaces in the cross-section cathodoluminescence image. In this report it is shown that these bright bands are associated with the presence of Cu, as indicated by photoluminescence measurements. It is proposed that the Cu diffuses into GaAs during annealing, from residual Cu on the sample surface. To test this hypothesis, samples were treated to alter the residual Cu prior to annealing. Removing the Cu markedly reduced the depth of the bright bands; adding Cu markedly increased the depth, in agreement with the proposed mechanism.
Properties of all YBa2Cu3O7 Josephson edge junctions prepared by in situ laser ablation deposition
Authors: Koren G. , Aharoni E. , Polturak E. , Cohen D.
Published: July 2002

Thin-film YBa2Cu3O7-YBa2Cu3O7 edge junctions of 0.4×10 μm2 cross section were prepared in situ by a multistep laser ablation deposition process. The fabrication time was about 3 h and the yield of good devices was 50%. Typical junctions reached zero resistance at 72 K and had a critical current density Jc of 300 A/cm2 at 70 K. Their Jc as a function of temperature increased slowly with decreasing temperature down to 65 K and much faster below it. In the region of low Jc we observed suppression of the critical current by a magnetic field. Under microwave radiation clear Shapiro steps were observed whose magnitude versus the microwave field agreed qualitatively with the resistively shunted junction model of a current biased junction.
Evidence for individual vortex pinning in ceramic YBa2Cu3O7−δ
Authors: Tessler Leandro R. , Provost Jackie , Maignan Antoine
Published: July 2002

We measured the pinning force density Fp in high quality YBa2Cu3 O7−δ ceramics as a function of the temperature and magnetic field up to 5 T. The results indicate that near 60 K the magnetic vortices are pinned individually. This implies that at this temperature the main pinning mechanism involves localized pinning centers separated by short distances rather than twin boundaries.
Mobility-lifetime products in hydrogenated amorphous silicon
Authors: Crandall Richard S. , Balberg I.
Published: July 2002

The most important parameters characterizing the photoelectronic quality of a semiconductor are its charge-carrier mobility lifetime, μτ, products. The two common experimental methods used to determine these parameters in hydrogenated amorphous silicon, a-Si:H, are the steady-state photoconductivity measurement and the life-of-flight charge-collection measurement. The two methods yield quite different results. We show that the difference can be resolved by an understanding of the physics involved in each of the measurements. We show that the steady-state μτ is expected to be up to three orders of magnitude larger than the time-of-flight μτ in undoped a-Si:H. This prediction is in excellent agreement with the corresponding experimental results.
Interstitial oxygen determination near epitaxial silicon and Czochralski silicon interface
Authors: Geddo M. , Pivac B. , Borghesi A. , Stella A. , Pedrotti M.
Published: July 2002

The oxygen content near epitaxial layer-substrate silicon interface was investigated using a micro Fourier transform infrared technique. Systematic measurements, performed in a transversal wafer cross-section configuration, clearly indicated the presence of interstitial oxygen in the epitaxial layer when it was grown on n-type substrates, while no evidence of oxygen in it was obtained (in concentration detectable by the infrared technique) when grown on p-type substrates. Interstitial oxygen profiles, near the epitaxial layer-substrate interface, obtained by analyzing the optical data, are reported and discussed considering different combinations of dopants in the substrate and in the epilayer.
Phonon study of strained InGaAs layers
Authors: Brafman O. , Fekete D. , Sarfaty R.
Published: July 2002

Relaxation of strain in InxGa1−xAs layers on GaAs is studied by Raman spectroscopy for layers below and above the critical thickness. We show that the enormous strain of the perfect epitaxial layer is released stepwise with the thickness. It is suggested that dislocations formed at the layer surface impose the growth of the next sublayer of partially released strain, preserving the former grown sublayer of higher strain.
New stacked capacitor structure using hemispherical-grain polycrystalline-silicon electrodes
Authors: Watanabe H. , Aoto N. , Adachi S. , Ishijima T. , Ikawa E. , Terada K.
Published: July 2002

A new technology which makes storage electrode surfaces uneven has been developed for realizing 64 Mbit dynamic random access memories (DRAMs). This technology utilizes a Si film which is deposited by low-pressure chemical vapor deposition at 550 °C and has hemispherical grains (HSG). The surface area of the HSG-Si film is about twice as large as Si films deposited at other temperatures. The specific temperature, 550 °C, corresponds to the transition temperature of the film structure from amorphous to polycrystalline. By applying the HSG-Si film as the storage electrode of a stacked capacitor, a capacitance of twice the value is obtained. The increase of the capacitance makes it possible to reduce the DRAM cell area, even by using a relatively thick dielectric film, thereby providing higher reliability.
Enhancement of field-induced optical absorption by potential modification of coupled quantum well structures
Authors: Chan Y. C. , Tada K.
Published: July 2002

A novel structure, in which the potential profile of the coupled quantum well system is slightly inclined, is proposed for lowering the electric field required to transform the coupled system to a set of uncoupled single quantum wells. Numerical calculations of absorption spectra of graded coupled quantum wells under an electric field and room-temperature photocurrent spectra of fabricated p-i-n diode samples confirm the above enhanced effect.
Schottky-limit barrier heights for CO-coated metal clusters on GaAs(110)
Authors: Komeda T. , Stepniak F. , Weaver J. H.
Published: July 2002

This letter discusses band bending induced by the deposition of metal clusters coated with onto GaAs(110). The layer of CO between the metallic clusters and the undisrupted semiconductor simulates a metal-insulator-semiconductor junction. The observed barrier height shows Schottky-limit-like dependence on the work function of the metal.
Superconducting characteristics of a planar-type HoBa2Cu3O7−x −La1.5Ba1.5Cu3O7−y−HoBa2Cu3O7−x junction
Authors: Tarutani Yoshinobu , Fukazawa Tokuumi , Kabasawa Uki , Tsukamoto Akira , Hiratani Masahiko , Takagi Kazumasa
Published: July 2002

A planar-type junction of HoBa2Cu3O7−x−La1.5Ba1.5Cu3O7−y −HoBa2Cu3O7−x having an electrode spacing as small as 0.1 μm is fabricated and its electrical characteristics are measured. Supercurrent through the La1.5Ba1.5Cu3O7−y layer is detected up to the temperature of 69 K. A superconducting region extends from the YBa2Cu3O7−x electrodes into a normal La1.5Ba1.5Cu3O7−y layer with a submicrometer scale. The superconducting decay length is 65 nm, which is two orders of magnitude larger than the value calculated from the conventional proximity theory.
High charge storage in amorphous BaTiO3 thin films
Authors: Li P. , Lu T.-M. , Bakhru H.
Published: July 2002

A high charge storage density was achieved in BaTiO3 thin films on Si substrates prepared by a reactive partially ionized beam deposition technique and rapid thermal annealing (RTA) treatment. The films, being deposited at a low substrate temperature, were amorphous. The films were then annealed by using RTA in N2 ambient at 500 °C for 1 min. After the annealing the relative dielectric constant of the films was 20 and the thickness of the films was 310 Å. The charge storage density of the films was calculated to be as high as 5.6 μC/cm2 at 10 V. The leakage current density was on the order of 10−7 A/cm2 at an applied electric field of l MV/cm. The potential application of this film in high density memory is discussed.
Submicron YBa2Cu3O7−δ grain boundary junction dc SQUIDs
Authors: Kawasaki M. , Chaudhari P. , Newman T. H. , Gupta A.
Published: July 2002

We have fabricated and measured the properties of micron-size single grain boundary junctions and dc superconducting quantum interference devices (SQUIDs). The width of the junctions was varied between 0.25 and 2 μm. The junctions were formed in c-axis oriented epitaxial films with a single 24° tilt boundary. They were fabricated using electron beam lithography and ion milling. All of the junctions operate at 77 K. The noise properties of SQUIDs made of these junctions have been characterized. They show a significant 1/f component which is comparable to published values. However, the white noise level, 3×10−31 J/Hz measured at 77 K, is the lowest ever reported.
Variations of resonant tunneling properties with temperature in strained Si1−xGex/Si double-barrier structures
Authors: Xu D. X. , Shen G. D. , Willander M. , Hansson G. V. , Luy J. F. , Schäffler F.
Published: July 2002

We have investigated the resonant tunneling feature variations with temperature in molecular beam epitaxy grown strained Si0.78Ge0.22/Si double-barrier structures with different well width w and spacer thickness LS. Both w and LS have strong effects on the temperature characteristics of the peak current JP, the valley current JV, and the current peak-to-valley ratio (PVR). When w is reduced, both JP and JV are greatly increased. The resonant tunneling devices (RTDs) also have better temperature stability and PVR decreases slower. The RTD with larger LS has higher peak current. Beside w and LS, the quasi-Fermi level position has a very important influence on the resonant tunneling feature variations, which is stressed in the present work.
Quantum capacitance of resonant tunneling diodes
Authors: Hu Yuming , Stapleton Shawn
Published: July 2002

We have developed a method for evaluating the capacitance created from charges stored in the quantum well. This capacitance is currently calculated by using the formula for a parallel-plate capacitor. We have shown that the simple formula for a parallel-plate capacitor is invalid for this estimation. Our method, which is based on the damped resonant tunneling model, predicts that the capacitance due to the charges stored in the well is about two to three orders of magnitude smaller than that previously estimated.
New test structure to identify step coverage mechanisms in chemical vapor deposition of silicon dioxide
Authors: Cheng Lie-Yea , McVittie James P. , Saraswat Krishna C.
Published: July 2002

A new test structure has been developed to identify unambiguously the main mechanism which determines the profiles of thin films deposited by low-pressure chemical vapor deposition (LPCVD) in structures such as steps, trenches, and via-holes. The two mechanisms considered are reemission due to a low surface reaction probability and surface diffusion. Experimental results using silane, diethylsilane (DES), tetraethoxysilane (TEOS), and tetramethylcyclotetrasiloxane (TMCTS) as the silicon sources for oxide deposition by LPCVD show that indirect deposition from reemission is the major contributing factor in determining the step coverage.
Watt-range, coherent, uniphase powers from phase-locked arrays of antiguided diode lasers
Authors: Botez D. , Jansen M. , Mawst L. J. , Peterson G. , Roth T. J.
Published: July 2002

Twenty-element near-resonant AlGaAs/GaAs arrays of antiguides have been optimized for maximum intermodal discrimination and large Strehl ratio. It is found that 1000-μm-long devices with two intracavity Talbot-type spatial filters, and a 3 to 1 ratio between element core and interelement spacing provide the best results. The intermodal discrimination is discussed for both Talbot and uniform devices. For devices with two Talbot-type spatial filters, diffraction-limited-beam operation is obtained to 1 W pulsed power, and operation in a beam with lobewidth 1.5× diffraction limit is obtained to 2 W and 19× threshold. cw diffraction-limited-beam operation is obtained to 0.5 W, limited by thermal considerations. Uniform devices operate in beams with lobewidth ≊3× diffraction limit to 5 W and 45× threshold. At 5 W total output the coherent uniphase power is 1.6 W, and the coherent power in the main lobe is 0.94 W.
Second-harmonic generation device with integrated periodically domain-inverted regions and distributed Bragg reflector in a LiNbO3 channel waveguide
Authors: Shinozaki K. , Miyamoto Y. , Okayama H. , Kamijoh T. , Nonaka T.
Published: July 2002

We propose a new structure of LiNbO3 guided wave second-harmonic generation device, in which the fundamental light beam is sufficiently confined by two distributed Bragg reflectors (DBRs) formed at input and output ports. The 40% increase in the conversion compared with a conventional device without DBR was achieved under a quasi-phase matching condition.
Formation of ultrashallow p+ layers in silicon by thermal diffusion of boron and by subsequent rapid thermal annealing
Authors: Inada T. , Kuranouchi A. , Hirano H. , Nakamura T. , Kiyota Y. , Onai T.
Published: July 2002

Boron atoms are incorporated into (100)Si wafers by heating the substrates at 800 °C for 30 min in a (B2H6+H2) atmosphere and by subsequent rapid thermal annealing above 900 °C. Atomic and carrier-concentration profiles of boron-doped layers have been examined by a secondary-ion mass spectrometry and by differential Hall measurements, respectively. Experimental results have clearly shown that ultrashallow p+ layers, 300 Å thick, with a surface carrier concentration of 7.26×1019/cm3 can be formed by diffusion of boron at 800 °C and by subsequent RTA at 100 °C.
Subband mixing effect in double-barrier diodes with a restricted lateral dimension
Authors: Tarucha Seigo , Hirayama Yoshiro , Tokura Yasuhiro
Published: July 2002

Tunneling characteristics of double-barrier diodes with a restricted lateral dimension are studied. When a large number of closely spaced emitter subbands contribute to the tunneling, the current versus voltage characteristics exhibit a series of peaks separated by the voltages that correspond to subband splittings in the double-barrier region. When the lowest emitter subband mainly contributes to the tunneling, they exhibit peaks separated by approximately twice the voltages that correspond to the subband splittings in the double-barrier region. These differences can be explained by the effects of mixing two-dimensional emitter subbands with one-dimensional subbands in the double-barrier region.
Recrystallization of silicon amorphized by carbon implantation
Authors: Chevacharoenkul Sopa , Ilzhoefer John R. , Feijóo Diego , Gösele Ulrich
Published: July 2002

Implanting (100) silicon substrates with 35 keV carbon ions at a dose of 1.5×1016 cm−2 causes Si to amorphize from the surface to a depth of 133±3 nm. Upon annealing at 800 °C the amorphized material recrystallizes to polycrystalline and highly defective single-crystal layers. An in situ annealing study of a cross-sectional transmission electron microscope specimen reveals that the minimum temperature needed to recrystallize the amorphous material is 725±25 °C. At this temperature grains that grow from the substrate surface dominate the recrystallization process leading to the formation of polycrystalline layer.
Direct evidence of oxygen precipitates in epitaxial silicon obtained by micro-Fourier transform infrared spectroscopy
Authors: Borghesi A. , Geddo M. , Pivac B. , Stella A. , Lupano P.
Published: July 2002

Oxygen redistribution near the interface between the epitaxial layer and substrate was monitored with micro-Fourier transform infrared measurements in a transversal wafer cross-section configuration. It has been shown that oxygen contamination of the epitaxial layer may induce the formation of SiO2 precipitates into the film, due to outdiffusion from the substrate. To our knowledge this is the first direct evidence of oxygen precipitation phenomena within the epitaxial layer.
Porous silicon membranes
Authors: Searson P. C.
Published: July 2002

Porous silicon membranes have been formed by electrochemical etching through wafers up to 500 μm in thickness. The results show that there is essentially no limit to the thickness of porous silicon layers and that self-supporting porous structures can be formed by this method. In addition, the membranes are structurally intact and can be removed from the wafer. The rate of porous layer formation, at an etching current of 50 mA cm−2, is in the range 20–50 nm s−1 and is dependent on the dopant type and concentration.
Brewster angle spectroscopy: A new method for characterization of defect levels in semiconductors
Authors: Lewerenz H. J. , Dietz N.
Published: July 2002

A new optical method which allows the identification of electronic defects in semiconductors is presented. Deep level characterization is done by detecting changes of the Brewster angle induced by optically excited transitions involving defects. An empirical model is developed which correlates the minima of the derivative of the Brewster angle as a function of photon energy with the energetic locations of defects in the semiconductor gap. Contactless room-temperature measurements on n-GaAs (100) and p-InP (111) clearly reveal defects with high accuracy, including the well known EL2 and EL12 centers in GaAs. The applicability of the method for semiconductor device technology processes is discussed.
Structural imperfections in silicon dioxide films identified with vacuum ultraviolet optical absorption measurements
Authors: Awazu Koichi , Kawazoe Hiroshi , Saito Yasutoshi , Watanabe Kikuo , Ando Toshio
Published: July 2002

The optical absorption of silicon dioxide films fabricated by dry oxidation at 1000 or 1100 °C was studied by measurements in the vacuum ultraviolet region. Two clear absorption bands at 7.6 and 6.7 eV were found for the films. Intensities of the bands decreased following heat treatment in a H2 ambient. The absorption band at 7.6 eV is considered to be caused by the defect having the structure of 3O≡SiSi≡O3. The concentration of the 3O≡SiSi≡O3 structure was estimated to be 6×1019 cm−3 and 5×1018 cm−3 for the films fabricated at 1000 and 1100 °C, respectively.
Effects of surface pretreatments on nucleation and growth of diamond films on a variety of substrates
Authors: Morrish A. A. , Pehrsson Pehr E.
Published: July 2002

The effects of surface pretreatments on nucleation and growth of chemical vapor deposited diamond films were studied. The pretreatments included scratching with diamond grit, coating with a low vapor pressure, high thermal stability hydrocarbon oil, and coating with a 100–200-Å-thick layer of evaporated carbon. The effects of the treatments on carbide and noncarbide forming materials are described.
Role of polysulfides in the passivation of the InP surface
Authors: Iyer R. , Lile D. L.
Published: July 2002

Motivated by the disagreement and irreproducibility observed by different groups, including ours, on the effects of passivating compound semiconductors with sulfur, we have attempted in this work to see if dissimilarities in the starting solution can account for variations in final electrical results. Specifically we have tried passivating InP with different ammonium sulfide solutions for metal-insulator–semiconductor (MIS) type applications. We have observed that InP treated with a polysulfide solution, prepared by bubbling O2 through ammonium sulfide with excess dissolved sulfur results in excellent interfaces, whereas polysulfide-free solutions have little effect. Interface state densities in the high 1010 cm−2 eV−1 as judged by quasistatic capacitance-voltage measurements were obtained on polysulfide treated MIS structures coated with indirect plasma-enhanced chemical vapor deposited SiO2. Low-temperature photoluminescence spectra show marked differences on polysulfide-treated InP when compared to InP that was treated with commercially available ammonium sulfide.
Second-harmonic generation in ion-implanted quartz planar waveguides
Authors: Babsail L. , Lifante G. , Townsend P. D.
Published: July 2002

We report the first example of second-harmonic generation in a quartz ion-implanted waveguide. The example operated with low-power pumping near 783 nm. The harmonic production near 392 nm follows a square law dependence. A detailed fit of the pumping efficiency with wavelength suggests there is a phase match throughout the length (z propagating) of the sample. The mode match used was between TE0 of the fundamental and TE2 of the harmonic (ordinary index).
Area scaling in slab rf-excited carbon monoxide lasers
Authors: Zhao H. , Baker H. J. , Hall D. R.
Published: July 2002

A large area (slab) waveguide carbon monoxide laser, excited by a transverse radio frequency discharge and cooled by diffusion, has been demonstrated at electrode temperatures down to −30 °C. A maximum laser power of 120 W has been achieved from a sealed 386×2 mm discharge at an extraction efficiency of 17%. Discharge area scaling factors of 15.5 kW m−2 have been observed and cw power extraction exceeding 50 W using tap water cooling has been achieved.