bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation of pyrite films by plasma-assisted sulfurization of thin iron films
Authors: Bausch S. , Sailer B. , Keppner H. , Willeke G. , Bucher E. , Frommeyer G.
Published: July 2002

Pyrite films were prepared using the pure elements as source materials: thin iron films were evaporated on quartz substrates and exposed to a sulfur plasma. The process was controlled by a transmission measurement. X-ray spectroscopy was used to characterize the films and preliminary optical and electrical measurements were carried out.
CaNdAlO4 perovskite substrate for microwave and far-infrared applications of epitaxial high T
c superconducting thin films
Authors: Berkowski M. , Pajaczkowska A. , Gierl/owski P. , Lewandowski S. J. , Sobolewski R. , Gorshunov B. P. , Kozlov G. V. , Lyudmirsky D. B. , Sirotinsky O. I. , Saltykov P. A. , Soltner H. , Poppe U. , Buchal Ch. , Lubig A.
Published: July 2002

Single-crystal perovskite calcium-neodymium aluminate CaNdAlO4 has been grown and tested as a substrate material for high Tc superconducting thin films. The material is chemically stable, can be fabricated into the form of large, twin-free wafers, permits deposition of epitaxial Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O films, and exhibits low dielectric permittivity (ε≂20) and very low losses (tan δ≂10−3 at 100 K) at sub-THz frequencies. Its high potential in microwave applications of thin-film high Tc superconductors is clearly demonstrated.
Excimer laser direct writing of titanium lines on lithium niobate
Authors: Izquierdo R. , Lavoie C. , Meunier M.
Published: July 2002

We have investigated the deposition of titanium lines from titanium tetrachloride (TiCl4) onto lithium niobate (LiNbO3). The deposition is induced using a KrF excimer laser (λ=248 nm). Our objective is the formation of titanium indiffused LiNbO3 optical waveguides. The titanium lines contain little chlorine ([Cl] <2 at. %) and are typically 20–100 nm thick, and 3–20 μm wide. We find that the process is controlled by photochemistry of TiCl4. However it is difficult, at this point, to detemine whether the gas or the adsorbed layer is the primary source of thin-film growth.
Magneto-optical investigation of flux penetration in Y1Ba2Cu3O7 thin films
Authors: Forkl A. , Dragon T. , Kronmüller H. , Habermeier H.-U. , Mertens G.
Published: July 2002

Using the magneto-optical Faraday effect the magnetic flux penetration into high Tc superconducting Y1Ba2Cu3O7 thin films is investigated. Epitaxially grown high quality films (Tc≳88 K, jc≳106 A/cm2 at 77 K) show a flux penetration in three steps, the formation of a flux front if the acting magnetic field reaches Hc1 at the edge of the specimen, the movement of the flux front towards the center of the sample, and the increase of the flux density after the flux front reaches the center. The remanent state shows trapped magnetic flux in the film, indicating inhomogeneously distributed pinning centers.
Redistribution of Sb in an atomic-layer-doped Si
Authors: Fukatsu S. , Kubo S. , Shiraki Y. , Ito R.
Published: July 2002

We investigated the redistribution of an atomic-layer-doped (ALD) Sb in Si upon post-growth annealing using secondary-ion mass spectrometry (SIMS). Shoulder development in the SIMS profile was observed after annealing over 710 °C, suggesting the presence of two different diffusion mechanisms. Diffusivities were found to be in excess of the bulk diffusivity and were concentration dependent above n(Sb)≊5×1017 cm−3. Asymmetric diffusion of ALD Sb in the epitaxial layers and Sb segregation at the oxide interface were also observed.
Designing resonant tunneling structures for increased peak current density
Authors: Wie C. R. , Choi Y. W.
Published: July 2002

We report a simple method to increase the peak current density in a double-barrier resonant tunneling structure by using a small band-gap emitter spacer layer. We have fabricated AlAs/GaAs/AlAs resonant tunneling structures using a Ga1−xInxAs spacer layer in the emitter. The peak current density was increased systematically with the increasing indium content by a factor ranging from 2.5 at x=0.05 to 5 at x=0.2 from the value at x=0. The increased peak current density was accompanied by increases in the peak voltage and peak-to-valley ratio. The lowering of the bottom of electron energy distribution in the GaInAs emitter spacer layer is shown to explain both the peak current and voltage increases. In the sequential tunneling picture, the peak current increases because of the increase in the number of resonant electrons which occurs if the bottom of energy distribution is lowered. We also report for the first time a strong bistability in the current-voltage characteristics at T≤240 K in the asymmetric spacer layer structure (GaInAs emitter, GaAs collector) in an otherwise symmetric structure.
InGaAs-GaAs quantum well vertical-cavity surface-emitting laser using molecular beam epitaxial regrowth
Authors: Lei C. , Rogers T. J. , Deppe D. G. , Streetman B. G.
Published: July 2002

Data are presented demonstrating a design and fabrication process for the realization of high-efficiency, low-threshold vertical-cavity InGaAs-GaAs quantum well lasers with light emission through the top (epitaxial) surface. Crystal growth is performed using a two-step molecular beam epitaxial growth process to utilize lateral current injection into the device active region. The device structure allows the top surface (emission side) reflector to be optimized (for either high efficiency or low threshold) after crystal growth through the deposition of electron beam evaporated dielectric layers. Maximum continuous-wave output power in excess of 1.2 mW at 300 K, and differential quantum efficiency greater than 25% (3.9 mA threshold) are demonstrated. Low-threshold values of 2.3 mA are measured on devices with increased mirror reflectivity (through the addition of dielectric layers).
Negative charge state of hydrogen species in n-type GaAs
Authors: Yuan M. H. , Wang L. P. , Jin S. X. , Chen J. J. , Qin G. G.
Published: July 2002

Having been exposed to hydrogen plasma, the Te-doped GaAs wafers were deposited with metal Ti, to form the Ti/n-GaAs Schottky barrier diodes (SBDs). The profiles of donor concentration after successive annealing of the hydrogenated SBD at several reverse biases at 100 °C, indicated that the donor concentration in the strong electrical field region of the depletion layer increase monotonically and the donor concentration in the weak electrical field region of the depletion layer decrease monotonically with time. It is confirmed that hydrogen can be present as a negatively charged species in n-type GaAs and thus one can conclude that besides the deep donor level determined previously, hydrogen in GaAs has an acceptor level in the lower half of the energy gap or near the mid gap. There is evidence that the stronger the electrical field in strong field region of depletion layer, the faster the TeH complexes decompose in that region during a reverse bias annealing.
Photoluminescence study of critical thickness of pseudomorphic quantum wells grown on small area mesa stripes
Authors: Zou Yao , Grodzinski Piotr , Osinski Julian S. , Dapkus P. Daniel
Published: July 2002

Pseudomorphic In0.18Ga0.82As single quantum wells (QWs) have been grown by metalorganic chemical vapor deposition (MOCVD) on patterned substrates with mesa sizes of 3.5 μm oriented along [110] and [11̄0] directions. Using a post-growth masking technique, photoluminescence (PL) has been used to characterize the optical properties of the as-grown QWs. Our results show the increase of the critical thickness by about 50% for growth on [110] undercut mesa as compared with that on the planar substrate due to the discontinuous growth behavior and no increase of critical thickness of [11̄0] oriented mesas due to the continuous growth behavior and outdiffusion of In from the facet wall of the groove to the mesa top.
Atomically precise superlattice potential imposed on a two-dimensional electron gas
Authors: Stormer H. L. , Pfeiffer L. N. , Baldwin K. W. , West K. W. , Spector J.
Published: July 2002

We have been able to fabricate a two-dimensional electron gas containing an atomically precise, lateral Kronig–Penney potential of 102 Å periodicity. The structure was formed by modulation-doped molecular beam epitaxy overgrowth on the cleaved edge of a 71 Å GaAs/31 Å AlGaAs compositional superlattice. Low-temperature magnetotransport reveals clear quantum Hall characteristics. From the onset of the Shubnikov–de Haas oscillations at 0.25 T we deduce a lower limit of the mobility of μ≳40 000 cm2/V s at an electron density of 3.0×1011 cm−2 and infer that the carriers are crossing more than 200 GaAs/AlGaAs interfaces without losing phase coherence.
Compositional disordering by solid phase regrowth
Authors: Xia W. , Han C. C. , Pappert S. A. , Hsu S. N. , Guan Z. F. , Yu P. K. L. , Lau S. S.
Published: July 2002

The principle of solid phase regrowth (SPR)has been used to induce compositional disordering in AlGaAs/GaAs superlattice structures in the temperature range of 400 °C (30 min)–650 °C (30 s) as compared to the conventional diffusion method in the temperature range of 600–850 °C for hours. The SPR process is simple to implement, requiring only thin-film deposition and annealing. The crystal quality as well as the photoluminescence signals emerging from the disordered region generally improve with increasing processing temperature. The simplicity, the low process temperature, and the short process duration of the SPR technique are distinct advantages for optoelectronic applications, especially for self-aligned devices.
Biaxially aligned high T
c superconductors
Authors: Chen F. , Zhang B. , Markiewicz R. S. , Giessen B. C.
Published: July 2002

A new technique is described for preparing polycrystalline samples of high Tc superconductors, which should have superior properties for many applications, including potentially much higher critical currents.
Realization of low facet density and the growth mechanism of GaAs on GaAs(110) by migration-enhanced epitaxy
Authors: López M. , Takano Y. , Pak K. , Yonezu H.
Published: July 2002

Smooth GaAs layers were successfully grown by migration-enhanced epitaxy on exactly (110) oriented substrates. The surface of layers grown by conventional molecular beam epitaxy was completely covered with facets, whose density was higher than 106 cm−2. The facet density was reduced remarkably by three orders of magnitude using the migration-enhanced epitaxy method. Observing the intensity oscillations of the specular spot of reflection high-energy electron diffraction patterns, the growth mode and the migration characteristics of surface adatoms have been investigated.
Mass and geometry effects on the anisotropic transport in ion mixing
Authors: Auner Gregory W. , Cheng Yang-Tse , Alkaisi M. H. , Padmanabhan K. R.
Published: July 2002

Experimental investigations of the effect of target species atomic mass and system geometry on the anisotropic transport in the ion mixing of metallic systems are reported. Bilayer samples with zero heats of mixing and similar cohesive energies, but different atomic mass and geometry, such as Ta on top of Nb(Ta/Nb), Nb on top of Ta(Nb/Ta), Hf on top of Zr (Hf/Zr), and Zr on top of Hf(Zr/Hf) were irradiated by 300 keV Kr2+ at a dose of 2 × 1016 Kr2+/cm2 at 77 K. The samples were investigated using embedded markers and Rutherford backscattering spectrometry. The experimental results indicate that the anisotropic transport is dominated by a preferential displacement of the top layer species into the bottom layer. This is probably due to an anisotropy in the momentum distribution within the collision cascade. In addition, there is an enhancement of the inward displacement when the lighter species is on top indicating a small preferential recoil displacement of the lighter species over the heavier one.
Characterization of dry etch-induced damage in semiconductor materials using a noncontact photothermal radiometric probe
Authors: Crean G. M. , Little I. , Herbert P. A. F.
Published: July 2002

Defects induced in n-type silicon (Si) and gallium arsenide (GaAs) substrates by argon ion bombardment in reactive ion etch and reactive ion beam etch reactors, respectively, have been studied for the first time using photothermal radiometry (PTR). A significant shift in measured PTR signal amplitude has been observed as a function of isochronal bias voltage variation (0–600 V) etching studies. The experimental results have been interpreted using a model for the photothermal radiometric response from a layered semiconductor material. The detection of a threshold effect for dry etch induced process defects in GaAs has been correlated with Raman spectroscopy measurements. Both theory and experimental results indicate that PTR has the requisite surface sensitivity to variations in lattice quality to be a suitable technique for rapid and noncontact process control monitoring of dry-etch-induced damage.
Densities of states below midgap determined from the space-charge-limited currents of holes in intrinsic hydrogenated amorphous silicon
Authors: Dawson R. M. , Wronski C. R. , Bennett M.
Published: July 2002

Space-charge-limited currents of holes have been obtained in intrinsic hydrogenated amorphous silicon layers using p-i-p structures and have been used to derive the densities of states distribution between 1.0 and 0.7 eV from the hole mobility edge. The densities obtained near midgap are consistent with the measured densities of dangling bond defects located over an energy range of about 0.3 eV. At 0.7 eV from the valence-band mobility edge, the densities are consistent with the densities expected from the Urbach edge tail states. Such space-charge-limited currents offer a powerful tool for the direct measurement of the densities of states below the Fermi level in a-Si:H and its alloys.
Photoconducting electro-optic polymer films
Authors: Schildkraut Jay S.
Published: July 2002

We describe electro-optic polymer films that also exhibit photoconductivity. An acrylic polymer containing (as a side chain) a stilbene chromophore with a high second-order nonlinear susceptibility was doped with a perylene sensitizer for photocharge generation and a triarylamine hole transporting molecule. A polymer film was fabricated that had an electro-optic coefficient of 2.5 pm/V. Absorption of light by the sensitizer, that occurs in a region in which the polymer is otherwise transparent, results in a photocurrent and charge trapping. The quantum efficiency of photocharge generation and photorefractive figures of merit were calculated.
Demonstration of InGaAs/AlGaAs strained-layer distributed-feedback grating-surface-emitting lasers with a buried second-order grating structure
Authors: Liew S. K. , Carlson N. W. , Bour D. P. , Evans G. A. , Gieson E. Van
Published: July 2002

We have fabricated InGaAs/AlGaAs strained-layer distributed-feedback grating-surface-emitting lasers with a buried grating structure. The device consists of a pumped distributed-feedback section terminated on both sides by unpumped distributed Bragg reflector sections. cw operation in a stable single longitudinal mode is achieved up to six times threshold. The threshold current density is ∼600 A/cm2. The far-field beam divergence is predominantly single lobed and diffraction limited. The spectral linewidth is 1.0 MHz at an output power of 8 mW.
Determination of V/III ratios on phosphide surfaces during gas source molecular beam epitaxy
Authors: Chin T. P. , Liang B. W. , Hou H. Q. , Ho M. C. , Chang C. E. , Tu C. W.
Published: July 2002

Phosphorus-controlled growth rate of homoepitaxial (100) InP, GaP, and AlP on GaP substrates by gas source molecular beam epitaxy was investigated. Elemental group-III sources and thermally cracked phosphine were used. The growth rate was monitored by the specular beam intensity oscillations of reflection high-energy electron diffraction. This technique gives exact values of V/III ratio on the surface by measuring the amount of phosphorus which is actually incorporated into the film. Here the V/III ratio is defined as P-controlled growth rate divided by group-III-controlled growth rate instead of the beam flux V/III ratio. Also the phosphorus surface desorption activation energies were measured to be 0.61 eV and in the range between 0.89 and 0.97 eV for InP and GaP, respectively.
Processing of a TlBa2Ca2Cu3Oy superconducting film by liquid-gas solidification
Authors: Chou H. , Chen H. S. , Kortan A. R. , Kimerling L. C. , Thiel F. A. , Wu M. K.
Published: July 2002

We succeed for the first time in growing a superconducting TlBa2Ca2Cu3Oy film on MgO〈100〉 substrate using a liquid-gas solidification process (LGS). The films are grown in situ; they are deposited by LGS. There is no post-anneal or compensation of Tl applied after the initial deposition. The as-grown film shows a flat and uniform morphology with the c axis perpendicular to the MgO〈100〉. It exhibits a resistant transition onset of 117 K and zero resistance at 103 K.
Modulated electric conductivity in Fe3O4/NiO superlattices
Authors: Chern G. , Berry S. D. , Lind D. M. , Mathias H. , Testardi L. R.
Published: July 2002

High quality Fe3O4/NiO multilayered structures with nominal artificial periodicity 17 Å/ 17 Å and 34 Å/34 Å have been made by molecular beam epitaxy. The conductivity of the modulated structures is orders of magnitude higher for current parallel to the layers than for the transverse direction, reaching a ratio of 106−a value which is comparable with the largest known anisotropy for any material. This strong anisotropy shows that a like modulation of electrical conductivity has been achieved over distances as small as tens of Å and also suggests the possibility of voltage controlled superlattice phenomena.
Effect of rapid thermal annealing on planar-doped pseudomorphic InGaAs high electron mobility transistor structures
Authors: Streit D. C. , Jones W. L. , Sadwick L. P. , Kim C. W. , Hwu R. J.
Published: July 2002

We have investigated the effects of rapid thermal annealing on the electrical and optical properties of planar-doped AlGaAs/InGaAs/GaAs high electron mobility transistor structures grown by molecular beam epitaxy. Hall effect and photoluminescence measurements on samples with In0.22Ga0.78As and In0.28Ga0.72As channels reveal a temperature-dependent degradation in sheet charge density, Hall mobility, and photoluminescence response. The structures were essentially stable through the temperature range used in normal device processing. However, annealing temperatures greater than 700 °C resulted in strain relaxation and layer intermixing, especially for the In0.28Ga0.72As sample.
Oscillatory interlayer magnetic coupling of sputtered Fe/Mo superlattices
Authors: Brubaker Mary E. , Mattson J. E. , Sowers C. H. , Bader S. D.
Published: July 2002

Sputtered Fe/Mo superlattices grown on sapphire exhibit an oscillatory magnetic coupling as a function of Mo thickness. Ferromagnetic Fe layers 25 Å thick couple across the nonmagnetic Mo layers ferro- or antiferromagnetically with a period of ∼11 Å Mo. Ferromagnetically aligned films show the anticipated trend in longitudinal Kerr-rotation values based on calculation, while the antiferromagnetically coupled films in zero field yield only weak Kerr signals due to their characteristically ‘‘pinched’’ hysteresis loops. The films are well ordered and exhibit up to seven low-angle, x-ray diffraction peaks, but have negative magnetoresistive anomalies that are only ≲2% at 4.2 K.
Dielectric enhancement layers for a Pt/Co multilayer magneto-optical recording medium
Authors: Carcia P. F. , Reilly M. , Zeper W. B. , van Kesteren H. W.
Published: July 2002

Transparent ZnO with an optical index of refraction n∼2 is a suitable candidate for a dielectric enhancement layer in a magneto-optical disk. Surprisingly, sputtering a Pt/Co multilayer on a ZnO layer not only increased the optical Kerr rotation but also increased the magnetic coercivity and improved the rectangular magnetic loop shape. Sputter etching the dielectric surface prior to the metal deposition also improved magnetic properties.
Selective growth of GaAs by organometallic vapor phase epitaxy at atmospheric pressure
Authors: Azoulay R. , Dugrand L.
Published: July 2002

Complete selective epitaxy of GaAs by organometallic vapor phase epitaxy at atmospheric pressure was achieved by using TMG, AsH3, and AsCl3 as starting gases. Selectivity was observed at growth temperatures ranging from 650 to 750 °C. The blocking of polycrystal deposition on the mask, Si3N4, or W, is attributed to the adsorption of HCl on the mask, thus preventing the nucleation of GaAs. On the openings, the growth rate may be adjusted by controlling the TMG/AsCl3 ratio. When TMG/AsCl3<1, no growth occurs, but etching is observed.
Effect of spatial localization of dopant atoms on the spacing of electron subbands in δ-doped GaAs:Si
Authors: Wagner J. , Ramsteiner M. , Richards D. , Fasol G. , Ploog K.
Published: July 2002

Using Raman spectroscopy we have investigated the spacing of the electron subbands in nominally δ-doped GaAs structures which show a considerable spread of the silicon dopant atoms along the growth direction. For optical excitation in resonance with the E0+Δ0band gap, spin-density intersubband excitations are observed. For excitation in resonance with the E1 band gap we find a strong enhancement of scattering by collective intersubband plasmon-phonon modes. The measured energy spacings between the electron subbands deviate significantly from what is expected for ideal δ doping. Self-consistent electronic subband calculations taking into account the spread of the dopant atoms along the growth direction, in contrast, yield a good quantitative agreement between calculated and measured subband spacings. This demonstrates the potential of intersubband Raman spectroscopy for the analysis of the spatial localization of dopant atoms in δ-doped structures.
Mixed-state behavior in large magnetic fields of high-temperature superconducting films prepared by metalorganic deposition
Authors: McIntyre Paul C. , Cima Michael J. , Liebenberg Donald H. , Francavilla Thomas L.
Published: July 2002

Films of Ba2YCu3O7−x prepared by metalorganic deposition (MOD) are demonstrated to have large critical current densities in high magnetic fields. The current-voltage (I-V) characteristics are reported for an MOD film in applied fields from 0 to 6 T at 77 K. The zero field critical current density was 600 000 A/cm2 and fell to 60 000 A/cm2 at 1 T. The critical current is approximately proportional to 1/H1/2. The variation in I-V curves above the critical current indicates the voltage has a power law behavior with values for the current exponent varying from 5.2 to 1.7 for magnetic fields from 0 to 6 T.
Recombination-enhanced impurity diffusion in Be-doped GaAs
Authors: Uematsu Masashi , Wada Kazumi
Published: July 2002

Recombination-enhanced impurity diffusion (REID) in Be-doped GaAs has been observed for the first time. Current-induced degradation of tunnel diodes has been investigated. The Be diffusion under forward bias is enhanced by a factor of about 1015 at room temperature, and the activation energy for the diffusion is reduced from 1.8 eV for thermal diffusion to 0.6 eV for REID. The RElD of Be, in which the energy released on minority-carrier injection at the recombination center could enhance the diffusion, is thought to be the origin of the degradation.
Electro-optic characterization of ion beam sputter-deposited KNbO3 thin films
Authors: Graettinger T. M. , Rou S. H. , Ameen M. S. , Auciello O. , Kingon A. I.
Published: July 2002

The Electro-optic properties of potassium niobate thin films deposited using a computer-controlled ion beam sputtering technique have been studied for the first time. Epitaxial and polycrystalline films were deposited on single crystal magnesium oxide and highly (111) oriented films were deposited on sapphire for the study. All films exhibited a quadratic-like dependence of birefringence shift on the applied electric field. The microstructure of the films and its relation to the observed electro-optic properties is discussed.
High phosphorus doping of epitaxial silicon at low temperature and atmospheric pressure
Authors: Sedgwick T. O. , Agnello P. D. , Ngoc D. Nguyen , Kuan T. S. , Scilla G.
Published: July 2002

High concentrations of electrically active phosphorus have been grown in Si epitaxial layers at 750 °C and below in an atmospheric pressure deposition system using PH3 and SiCl2H2 in H2. PH3 remarkably enhances the silicon deposition rate in the range 550–750 °C in contrast to previously reported doping studies using SiH4. Chemical concentrations as high as 2.5×1020 cm−3 with an electrical activity of 1×1020 cm−3 were obtained in layers that were free of defects by transmission electron microscopy. The doping level can be modulated between 1×1019 and 5×1016 cm−3 indicating that there are no complications due to dopant retention on sample or reactor wall surfaces. Emitter-base diodes formed in the epitaxial layers exhibited ideal forward and low-leakage reverse characteristics.
Amorphous phase formation in an as-deposited platinum-GaAs interface
Authors: Ko Dae-Hong , Sinclair Robert
Published: July 2002

The presence of a thin amorphous intermixed layer at the platinum-GaAs interface in as-deposited Pt/GaAs and Si/Pt/GaAs samples has been investigated via high-resolution electron microscopy, microdiffraction, and energy dispersive spectroscopy. The intermixed layer forms below the native oxide of the GaAs substrate and consists of three elements, platinum, gallium, and arsenic. We suggest that this layer forms during the deposition process of the platinum.
Si ultrashallow p+n junctions using low-energy boron implantation
Authors: Bousetta A. , van den Berg J. A. , Armour D. G. , Zalm P. C.
Published: July 2002

Ultrashallow boron-doped junctions in silicon have been investigated using secondary-ion mass spectroscopy and four-point probe technique. The junctions were obtained by implanting B+ ions into n-type Si(100) at 200 eV to doses of 1.5×1014 and 6×1014 cm−2 and at substrate temperatures in the range 30–900 °C during B implantation. Both post-implantation in situ annealing by electron bombardment heating and rapid thermal annealing in a separate system were employed. The results show that sub 20 nm p+n junctions are obtained without the need for further processes such as preamorphization and high-temperature annealing.
Growth of heavily Be-doped AlInP by gas source molecular beam epitaxy
Authors: Yokotsuka T. , Takamori A. , Nakajima M.
Published: July 2002

Heavily Be-doped p-type AlInP layers have successfully grown on (001)GaAs by gas source molecular beam epitaxy (GSMBE) using phosphine (PH3). Net hole concentration (Nh) as high as about 3.5×1018 cm−3 is achieved for the first time. The surface morphology is found to be smooth up to a Be concentration of 3×1019 cm−3. The resistivity for Nh=3.5×1018 cm−3 is as low as 0.3 Ω cm. The improvement of the electrical activity and surface morphology may be ascribed to subhidrides of phosphorus decomposed from PH3 during GSMBE growth.
Quantum Hall effect in InAs/AlSb quantum wells
Authors: Hopkins P. F. , Rimberg A. J. , Westervelt R. M. , Tuttle G. , Kroemer H.
Published: July 2002

We demonstrate via low-temperature electron transport measurements the realization of a high-mobility (≳300 000 cm2/V s) two-dimensional electron gas in unintentionally doped InAs/AlSb single 120 Å quantum wells grown on GaAs substrates by molecular beam epitaxy. Magnetoresistance and Hall measurements at T∼0.4 K show a well-formed quantum Hall effect, with effects due to spin splitting observed at filling factors as high as ν=17. The electron densities of these wells could be reduced by a factor ∼5 by using the negative persistent photoconductivity of these samples.
Native oxide stabilization of AlAs-GaAs heterostructures
Authors: Sugg A. R. , Holonyak N. , Baker J. E. , Kish F. A. , Dallesasse J. M.
Published: July 2002

Data are presented on the stabilization of AlAs-GaAs heterostructures against atmospheric (destructive) hydrolysis using the native oxide that can be formed (N2+H2O, 400 °C, 3 h) on the AlAs layer. The ∼0.1-μm-thick native oxide formed from the AlAs layer is shown to be stable with aging (∼100 days), while unoxidized samples degrade through the AlAs (0.1 μm) down into the GaAs as deep as ∼1 μm. Relative to oxides formed (∼25 °C) on AlAs (or AlxGa1−xAs, x ≳ 0.7) under atmospheric conditions (hydrolysis), oxides formed (via N2 +H2O) at higher temperatures (≳400 °C) are much more stable and seal the underlying crystal (e.g., GaAs).
Electroabsorptive modulators in InGaAs/AlGaAs
Authors: Pezeshki B. , Lord S. M. , Harris J. S.
Published: July 2002

Theoretical and experimental work shows that electroabsorption improves and the quantum-confined Stark effect becomes stronger in In0.2Ga0.8As/AlxGa1−xAs quantum wells as the aluminum concentration (x) is increased in the barriers. This improved electroabsorption was used in a reflection modulator that exhibited the largest reported reflectivity change of 77%.
Lateral solid phase crystallization of amorphous Si induced by patterned indium tin oxide on a glass substrate
Authors: Guendouz M. , Richard J. , Joubert P. , Haji L.
Published: July 2002

Undoped amorphous silicon films were deposited by plasma-enhanced chemical vapor deposition on patterned indium tin oxide (ITO) onto glass substrate. The solid-phase crystallization of these films, after successive annealing at 500 and 600 °C, was studied by optical and transmission electron microscopy. It was found that nucleation occurs very quickly on ITO and slowly on glass. The ITO patterns act as nucleation centers for grains which laterally grow and the crystalline phase spread over the glass. Results are compared with those obtained from silicon films deposited by low pressure chemical vapor deposition.
Disorder-induced transition from Gaussian to dispersive carrier transport in molecularly doped polymers
Authors: Kanemitsu Yoshihiko , Funada Hiroshi , Masumoto Yasuaki
Published: July 2002

Dynamics of hopping charge transport in a polymer matrix doped with two different charge-transport molecules was studied by means of time-of-flight (TOF) photoconductivity measurements. In polymers doped with two molecules of little different ionization potential, the Gaussian (near-rectangular) TOF signal was observed over all compositions and the tail of the Gaussian TOF signal is broadened by a wide distribution of hopping time among molecules due to off-diagonal disorder. On the other hand, in polymers doped with two molecules of different ionization potential, the transition from the Gaussian to the dispersive TOF signal was observed and this is mainly caused by diagonal disorder. It is found that the energetic and spatial distribution of hopping sites play a key role in carrier transport in molecularly doped polymers.
Strained multiple quantum well lasers emitting at 1.3 μm grown by low-pressure metalorganic vapor phase epitaxy
Authors: Coblentz D. , Tanbun-Ek T. , Logan R. A. , Sergent A. M. , Chu S. N. G. , Davisson P. S.
Published: July 2002

Low-threshold and high-output power of the first InGaAsP/InP graded index strained multiple quantum well lasers emitting near 1.3 μm wavelength is reported. A continuous wave threshold current of 10 mA and a quantum efficiency of 60% with maximum output power of 100 mW/facet is observed in uncoated lasers having compressively strained InGaAsP quantum wells. With high reflectivity on both facets, a reduced threshold current as low as 3.5 mA is observed. Highest output power of 250 mW was observed in lasers with antireflection-high reflection coating configuration operating at 10 °C. The improved performance of the lasers is attributed to both the reduced internal absorption loss (6 cm−1) and the suppressed nonradiative recombination in the structure.
Effect of applied mechanical stress on the electromigration failure times of aluminum interconnects
Authors: Kahn H. , Thompson C. V.
Published: July 2002

Accelerated lifetime electromigration tests were performed on pure aluminum interconnect lines which were subjected to an applied mechanical bending stress. The median time to open failure (MTTF) was found to decrease with increasing applied tensile stress. The diminished failure times suggest a decrease in the activation energy for aluminum grain boundary self-diffusion on the order of 0.003 eV per 100 MPa of applied stress, resulting in a MTTF reduction of 10% at 210 °C for an increase in tensile stress of 100 MPa.
Phosphorus diffusion in Si0.7Ge0.3
Authors: Mathiot D. , Dupuy J. C.
Published: July 2002

We report on the results of an experimental study of the diffusion of phosphorus in Si0.7Ge0.3 alloys for temperatures between 800 and 1050 °C. When the phosphorus concentration is lower than the intrinsic carrier concentration at the diffusion temperature, the diffusion has a simple Fickian behavior. The corresponding intrinsic diffusivity has an activation energy of 1.62 eV. On the other hand, at high concentration, the diffusion behavior of P in SiGe is similar to what is observed in pure Si, with concentration profiles exhibiting ‘‘kink and tail’’ shapes. This suggests that the diffusion mechanisms are similar in both materials.
Interference phenomena due to a double bend in a quantum wire
Authors: Wu J. C. , Wybourne M. N. , Yindeepol W. , Weisshaar A. , Goodnick S. M.
Published: July 2002

Narrow channel devices were fabricated using a split-gate high electron mobility transistor structure in which electrons are forced through a double-bend discontinuity. The low-temperature conductance shows a number of peaks in the lowest quantized conductance plateau which correspond qualitatively to resonance effects that are predicted for the geometrical discontinuities of the double bend.
Cumulative laser irradiation effects on ions in the plume of YBa2Cu3O7−δ and particulates at the film surface
Authors: Izumi H. , Ohata K. , Sawada T. , Morishita T. , Tanaka S.
Published: July 2002

Direct observations of ions in the laser plume of YBa2Cu3O7−δ impinging onto a substrate surface revealed the increase of heavy species in the plume after multiple laser pulses on the YBa2Cu3O7−δ target. The beginning of heavy species emission from the target was observed at around 100 laser beam pulses (1 J/cm2) in our experiments. Particulate formation at the film surface was observed in the film deposited under this condition.
Effects of substrate misorientation on incorporation of ambient oxygen and interfacial roughness in AlGaAs/GaAs heterostructures grown by molecular-beam epitaxy
Authors: Chand Naresh , Chu S. N. G. , Geva M.
Published: July 2002

By secondary ion-mass spectrometry (SIMS) and transmission-electron microscopy (TEM), we have studied the effects of substrate misorientation and GaAs monolayers on the incorporation of ambient oxygen and interfacial roughness in AlxGa1−xAs/GaAs heterostructures grown by molecular-beam epitaxy. Consistent with earlier works, O is found in AlGaAs only, and not in GaAs. Incorporation of O, and surface and interfacial roughness are reduced if the substrate is misoriented towards 〈111〉A. The O atoms in AlGaAs are mobile enough to segregate on the surface and remain trapped at the GaAs/AlGaAs inverted interfaces, even when the GaAs layer is as thin as one monolayer.
Carrier heating in AlGaAs single quantum well laser diodes
Authors: Kesler Morris P. , Harder Christoph S. , Latta Eberhard E.
Published: July 2002

The nonamplified spontaneous emission of AlGaAs single quantum well graded index separate confinement heterostructure laser diodes has been measured for photon energies between 1.35 and 2.05 eV and at pump currents up to 19 kA cm−2 and optical flux densities up to 35 MW cm−2. The spectra are very complex and we observe the following three features. First, the spontaneous emission intensity increases slowly with current, even above threshold. Second, the carrier temperature increases slightly above the lattice temperature, 28 K at a pump rate of 1.5×1029 cm−3 s−1. Third, at high power densities the high-energy spontaneous emission at a photon energy of 1.9 eV increases dramatically.
High-temperature operation of periodic index separate confinement heterostructure quantum well laser
Authors: Chen Y. K. , Wu M. C. , Hobson W. S. , Chin M. A. , Choquette K. D. , Freund R. S. , Sergent A. M.
Published: July 2002

High-temperature operation of the InGaAs/GaAs/AlGaAs quantum well lasers with an expanded vertical optical mode is demonstrated for the first time using a periodic index separate confinement heterostructure (PINSCH) laser. Continuous wave (cw) operation up to 145 °C is achieved with a coated 3 μm×508 μm PINSCH laser. The measured characteristic temperature (170 K) and external differential quantum efficiency (0.75 mW/mA) are comparable to those obtained in a graded index separate confinement heterostructure laser fabricated at the same time. These results illustrate the excellent capability of the PINSCH laser to compress the transverse beam divergence without sacrificing the electrical carrier confinement.
In situ growth and properties of single-crystalline-like La2−xSrxCuO4 epitaxial films by off-axis sputtering
Authors: Kao H. L. , Kwo J. , Fleming R. M. , Hong M. , Mannaerts J. P.
Published: July 2002

Excellent quality La2−xSrxCuO4 epitaxial films of 0.07≤x≤0.34 in (001) and (103) orientations have been successfully grown in situ on SrTiO3, LaAlO3, and Y-stabilized ZrO2 substrates using 90° off-axis sputtering. A record low ion channeling minimal yield χmin of 1.9% is observed for the first time, and a χmin of 3% is routinely attained. The surface exhibits a featureless morphology under high-resolution scanning electron microscope, suggesting a roughness ≤30–40 Å. Superconductivity is maximized at Sr=0.15 with a typical Tc (R=0) of 35 K, a Jc (4.2 K) of 1–3×106 A/cm2, and a normal state resistivity two to three times lower than single crystals. Tc shows a marked reduction with thickness, and the results are interpreted on the basis of partially relieved strained-layer growth coupled with a sensitive dependence of Tc on uniaxial stress.
Largely enhanced bound-to-miniband absorption in an InGaAs multiple quantum well with short-period superlattice InAlAs/InGaAs barrier
Authors: Yu Larry S. , Li Sheng S. , Ho Pin
Published: July 2002

We report for the first time, the intersubband absorption at 10.7 μm between the localized ground state and the global miniband state in an n-type InAlAs/InGaAs multiple quantum well and short-period superlattice barrier heterostructure. The use of enlarged quantum well width and the superlattice reinforced miniband structure has shown a significant enhancement in the net intersubband absorption. An integrated optical absorption strength of IA=19.5 Abs cm−1 was obtained under the Brewster’s incident angle at T=300 K, which is about five times larger than that of the conventional single bound-to-bound transition in the InAlAs/InGaAs quantum well structure.
Multi-gigahertz-bandwidth intensity modulators using tunable-electron-density multiple quantum well waveguides
Authors: Zucker J. E. , Jones K. L. , Wegener M. , Chang T. Y. , Sauer N. J. , Divino M. D. , Chemla D. S.
Published: July 2002

We report the first measurement of modulation bandwidth in electron transfer quantum well modulators. A device with 1 pF capacitance provides ≳10 dB optical modulation depth at 1.537 μm wavelength with a 3 dB electrical bandwidth of 5.7 GHz. Optical pump-probe measurements indicate that the fundamental response time is determined by the voltage-dependent speed of carrier escape from the well.
Nanolithography of chemically prepared Si with a scanning tunneling microscope
Authors: Yau S.-T. , Zheng X. , Nayfeh M. H.
Published: July 2002

Permanent nanometer structures were fabricated on chemically prepared Si by chemical activation of loosely bound hydrocarbon clusters triggered by voltage pulses across the tunneling gap of a scanning tunneling microscope. Current-voltage measurements show that the fabrication process results in a local transition from a Schottky junction behavior to a MIS junction behavior, indicating the formation of topographic structures. Our experimental results indicate that the size and density of the clusters and the shape of the tunneling tip are important factors of the process. An example of parallel fabrication is presented.
High-temperature operation of high-power InGaAlP visible light laser diodes with an In0.5+δGa0.5−δP active layer
Authors: Nitta K. , Itaya K. , Nishikawa Y. , Ishikawa M. , Okajima M. , Hatakoshi G.
Published: July 2002

High-power and high-reliable operation of transverse-mode stabilized InGaAlP laser diodes has been achieved by a selectively buried ridge waveguide structure with a thin (0.02 μm) active layer. A composition-shifted In0.5+δGa0.5−δP active layer was employed in order to improve the temperature characteristic. A maximum cw light output power of 54 mW was obtained for the laser with antireflection and high-reflection coatings. A high-power cw operation above 30 mW output power was maintained even at a 60 °C heat-sink temperature. Stable cw operation exceeding 1000 h has been achieved for 20 mW output power at 50 °C.
Anisotropic Nd-Fe-M-B flakes by single-roller melt spinning
Authors: Chin Tsung-Shune , Huang S. H. , Yau J. M.
Published: July 2002

Anisotropic Nd13Fe81−xMxB6 flakes (M=0.5–3 at. % one of Ti/Zr/V/Ta/Mo/Zn) are reproducibly obtainable using single-roller melt spinning at lower substrate velocities (Vs, 8–15 m/s). The degree of preferred orientation (DPO) of spun flakes calculated from x-ray diffraction patterns is 70%–97% on the free surface, 50%–80% on the wheel surface, at Vs=8, 10 m/s. In the case of adding 1 at. % of Ti/V/Mo/Zr/Ta, Vs=8 m/s, the resultant DPO value can be higher than 50% across the whole thickness. Magnetic measurements on spun flakes show highly anisotropic behavior. Maximum energy product of Nd13Fe80ZrB6 flakes spun at 12 m/s, pulse magnetized to 5.5 T, and measured normal or parallel to the flake surface is 144 kJ/m3 (18 MGOe) or 124 kJ/m3 (15.5 MGOe), respectively.
Size-dependent homogeneous linewidth of Z3 exciton absorption spectra in CuCl microcrystals
Authors: Wamura Tetsuro , Masumoto Yasuaki , Kawamura Tomohiro
Published: July 2002

Size-dependent homogeneous linewidth of Z3 exciton absorption spectra in CuCl microcrystals was measured at 2 K by the pump-and-probe spectroscopy. Observation of the hole burning gave us the homogeneous linewidth. The size-dependent part of the homogeneous linewidth is inversely proportional to the square of the radius of microcrystals. This dependence is explained by a simple model that a generated exciton dephases through the scattering at the irregular surface of microcrystals.
Third-order nonlinear optical properties of poly(diphenyl amine) and poly(4-amino biphenyl), novel processible conducting polymers
Authors: Chandrasekhar P. , Thorne Jonathan R. G. , Hochstrasser Robin M.
Published: July 2002

Off-resonant third-order nonlinear optical susceptibilities using degenerate four-wave mixing measurements in solution at 1.064 μm are reported for partially doped states of the soluble, stable, reprocessible conducting polymers poly(4-amino biphenyl) [P(4ABP)] and poly(diphenyl amine) [P(DPA)] whose synthesis and properties were reported earlier. The polymers show appreciable nonlinearities, χ(3)xxxx being (1.4±0.3)×10−10 esu for P(4ABP) and (1.3±0.3)×10−10 esu for P(DPA), with a time response faster than 40 ps.
Fabrication of first-order periodically domain-inverted structure in LiTaO3
Authors: Mizuuchi Kiminori , Yamamoto Kazuhisa , Taniuchi Tetsuo
Published: July 2002

We report on fabrication of first-order periodically domain-inverted structure in LiTaO3 by using selective proton exchange and heat treatment. Observation of the formation process of domain inversion makes it clear that the shape of the inverted region depends on time and temperature of heat treatment. As a result, enlargement of inversion width in heat treatment is suppressed by shortening the heat treatment time. First-order periodically domain-inverted structure, which has 3.5 μm period and 1.5 μm depth, is realized.
Observation of enhanced infrared photoresponse in forward-biased amorphous silicon p-i-n diodes
Authors: Wind J. , Müller G.
Published: July 2002

The photoconductive response of hydrogenated amorphous silicon (a-Si:H) p-i-n diodes has been investigated under conditions of low-temperature operation. We show that cooled p-i-n diodes exhibit an enhanced infrared response when operated under forward bias conditions. The induced IR response is of the order of 10−3A/W, extending out to wavelengths of about 2–3 μm with the long wavelength cutoff being determined by the properties of the glass/indium–tin–oxide entrance window. We propose that the IR photoeffect is due to the re-excitation of band-tail trapped excess carriers injected into the localized conduction and valence band tail states in the vicinity of the n+- and p+-contact regions.
Photoinduced intersubband absorption in lattice-matched InGaAs/InP multiquantum well
Authors: Oiknine-Schlesinger J. , Ehrenfreund E. , Gershoni D. , Ritter D. , Panish M. B. , Hamm R. A.
Published: July 2002

We report the observation of strong photoinduced intersubband absorption in a lattice-matched In0.53Ga0.47As/InP multiquantum well structure. The absorption, which is induced by optical pumping with an above gap light is polarized along the growth direction and is assigned to the transition from the first to the second subband in the conduction-band quantum well. The measured intersubband transition energy is in very good agreement with an effective-mass-approximation model including nonparabolicity effects. Assuming a linear dependence of the electron effective mass on the energy, we find a nonparabolicity parameter of 1.35±0.25 eV−1 for the In0.53Ga0.47As well.
All high T
c edge-geometry weak links utilizing Y-Ba-Cu-O barrier layers
Authors: Hunt B. D. , Foote M. C. , Bajuk L. J.
Published: July 2002

High quality YBa2Cu3O7−x/normal-metal/YBa2Cu3O7−x edge-geometry weak links have been fabricated using nonsuperconducting Y-Ba-Cu-O barrier layers deposited by laser ablation at reduced growth temperatures. Devices incorporating 25–100 Å thick barrier layers exhibit current-voltage characteristics consistent with the resistively shunted junction model, with strong microwave and magnetic field response at temperatures up to 85 K. The critical currents vary exponentially with barrier thickness, and the resistances scale linearly with Y-Ba-Cu-O interlayer thickness and device area, indicating good barrier uniformity, with an effective normal metal coherence length of 20 Å.
Sensitive YBa2Cu3O7−x thin-film magnetometer
Authors: Miklich A. H. , Kingston J. J. , Wellstood F. C. , Clarke John , Colclough M. S. , Char K. , Zaharchuk G.
Published: July 2002

Our YBa2Cu3O7−x thin-film magnetometer consists of a dc superconducting quantum interference device with bi-epitaxial Josephson junctions, fabricated on one chip, and a flux transformer with a multiturn input coil, fabricated on a second chip. Photolithographic processing is used to pattern all layers. The magnetometer operates in a flux-locked loop at temperatures up to 81 K, with the flux transformer improving the magnetic field sensitivity by a factor of 83±3. The low-frequency rms magnetic field noise scales approximately as 1/f1/2, where f is the frequency, with a magnitude of 0.6 pT Hz−1/2 at 10 Hz and 0.09 pT Hz−1/2 at 1 kHz with the magnetometer immersed in liquid N2.