bluuebunny/crossref_metadata_2025 huggingface dataset:
AlxGa1−xAs-AlAs quantum well surface-normal electroabsorption modulators operating at visible wavelengths
Authors: Goossen K. W. , Yan R. H. , Cunningham J. E. , Jan W. Y.
Published: July 2002

We have produced AlxGa1−xAs-AlAs quantum well p-i-n diode electroabsorption modulators with x as high as 0.56. Even though the material is indirect in momentum space, strong excitonic absorption exists at the direct band gap which can be modulated with an applied field. For x=0.33, 0.43 and 0.56, we measure relative transmission changes (ΔT/T0, in a surface-normal configuration) of 62%, 51%, and 23%, respectively, at wavelengths of 677, 622, and 575 nm for 15 V bias with the intrinsic layer being 0.6 μm thick.
Annealing effect on the carrier concentration in heavily C-doped p+-AlGaAs
Authors: Watanabe Kazuo , Yamazaki Hajime
Published: July 2002

Carrier concentration in heavily carbon-doped p+-AlGaAs epilayers grown by metalorganic chemical vapor deposition is increased by annealing at temperatures from 500 to 800 °C under a SiN capped condition in nitrogen gas ambient and is decreased by annealing at 850 °C. The carrier concentration reaches a maximum value corresponding to nearly 100% activation at about 600 °C. These thermal behaviors can be well explained by the overlapping of two components. One is the carrier increase which occurs even at as low as 500 °C and is related to the decrease of hydrogen atoms in the epilayers. The hydrogen atoms probably deactivate the carbon acceptors in a nearly one-to-one correspondence. The other is the carrier decrease at temperatures higher than 600 °C, which may be due to a change in the occupation site preference of carbon atoms from arsenic sites.
Role of substrate temperature in molecular-beam epitaxial growth of high-power GaAs/AlGaAs lasers
Authors: Iyer S. V. , Meier H. P. , Ovadia Shlomo , Parks C. , Arent D. J. , Walter W.
Published: July 2002

The growth of high-quality GaAs/AlGaAs graded-index separate-confinement heterostructure single-quantum-well diode lasers is shown to be critically dependent on growth temperature. The temperature-dependent nature of oxygen incorporation in the cladding and active regions and its effect on laser performance is investigated in detail. A model is presented that takes the incorporation, desorption, and accumulation of impurities in different regimes into account.
Stress relaxation in Mo/Si multilayer structures
Authors: Kola R. R. , Windt D. L. , Waskiewicz W. K. , Weir B. E. , Hull R. , Celler G. K. , Volkert C. A.
Published: July 2002

The as-deposited stress in sputtered, 75-Å-period Mo/Si multilayers was measured to be approximately −350 MPa (compressive), and relaxed to approximately −150 MPa after thermal cycling to 200 °C. The multilayer period was found to decrease by 0.25 Å as a result of thermal cycling, with only a slight decrease in peak soft-x-ray reflectance. The stress-temperature behavior of individual Mo and Si films was also measured, and correlated with the multilayer behavior: stress relaxation in the multilayer is attributed to viscous flow associated with defect annihilation, occurring predominantly in the amorphous Si layers.
Tunable coupled-quantum-well laser controlled by an electric field
Authors: Liu L. Y. , Mendez E. E. , Meier H.
Published: July 2002

We propose a novel field-effect semiconductor laser whose wavelength can be tuned by an electric field parallel to the growth direction of two tightly coupled quantum wells in the active region. We have demonstrated the concept by optically pumping a laser heterostructure whose active region consisted of two 50 Å GaAs wells separated by a 20 Å Ga0.77Al0.23As potential barrier, in which, at 5 K, we have achieved tuning of the stimulated emission by more than 7 nm.
Direct measurement of piezoelectric field in a [111]B grown InGaAs/GaAs heterostructure by Franz–Keldysh oscillations
Authors: Shen H. , Dutta M. , Chang W. , Moerkirk R. , Kim D. M. , Chung K. W. , Ruden P. P. , Nathan M. I. , Stroscio M. A.
Published: July 2002

We report the first photoreflectance measurement of strain-induced piezoelectric field in a (111)B InGaAs/GaAs structure. The InGaAs quantum well was pseudomorphically grown in the undoped regions of a GaAs undoped–heavily doped structure. Four structures, two each with the same layer structures but different orientation, (111)B and (100), were used in this study. The electric fields in the undoped GaAs region were measured by Franz-Keldysh oscillations in photoreflectance. All the samples have a surface barrier height of about 0.7 eV. However, the measured electric field is 30% stronger in the (111)B sample compared to the (100) sample. We attribute this difference to the strain-induced electric field in the (111)B sample. The piezoelectric field in (111)B strained In0.15Ga0.85As obtained in this measurement is 2.2±0.5×105 V/cm, which agrees very well with theory.
Photoconductive gain mechanism of quantum-well intersubband infrared detectors
Authors: Liu H. C.
Published: July 2002

Taking into account the discrete nature of the quantum-well intersubband infrared detectors, we construct a model to calculate the photoconductive gain. It is shown that the photoconductive gain is inversely proportional to the number of quantum wells and that the detector-current responsivity is independent of the number of wells.
Photoluminescence on high-quality AlxGa1−xAs grown by metalorganic vapor-phase epitaxy using alane bis(dimethylethylamine)
Authors: Olsthoorn S. M. , Driessen F. A. J. M. , Giling L. J. , Frigo D. M. , Smit C. J.
Published: July 2002

Photoluminescence (PL) spectra are reported of initial results of AlxGa1−xAs grown by metalorganic vapor-phase epitaxy (MOVPE), using a new precursor, alane bis(dimethylethylamine), as the aluminum source. The advantage of this new precursor over other alane precursors used previously is that it is liquid at room temperature. Using this new precursor instead of trimethylaluminum (TMAl), we found a reduction by a factor 6 in carbon incorporation when it was used together with trimethylgallium (TMGa), whereas a reduction by a factor 50 was found when it was used in combination with triethylgallium (TEGa). At low excitation density the linewidth of the separate donor bound exciton (D0,X) was 2.6 meV at an Al fraction of 0.31. This is comparable with the smallest values ever reported in literature for MOVPE-grown AlxGa1−xAs with an Al fraction higher than 20%. This narrow linewidth indicates a very uniform aluminum composition.
Gallium desorption during growth of (Al,Ga)As by molecular beam epitaxy
Authors: Reithmaier J.-P. , Broom R. F. , Meier H. P.
Published: July 2002

A new two-phase model for gallium desorption can quantitatively explain the change of the desorption energy as a function of the III/V ratio. In this model, the gallium loss rate is described as a phenomenon of simultaneous desorption from a Ga fluid state and a GaAs solid state. This behavior was experimentally verified by accurate thickness measurements of epitaxial AlxGa1−xAs layers by transmission electron microscopy. The results show the Ga loss rate is directly dependent only on the Ga coverage on the surface, while the desorption energy is independent of the aluminum concentration. By varying the III/V ratio, we found that the Ga desorption energy increases from 3.1 eV at low arsenic flux to 4.7 eV at high arsenic flux.
Blue-light stimulated emission from a localized state formed by well-barrier fluctuation in a II-VI semiconductor superlattice
Authors: Kuroda Yasuhide , Suemune Ikuo , Fujii Yoshihisa , Fujimoto Masahiro
Published: July 2002

A well-defined exciton absorption peak from a localized state was observed for the first time. The localized state was formed by fluctuation of well-barrier interfaces in a ZnSe/ZnSSe superlattice structure. Stimulated emission was observed from the localized state up to 100 K, and the physical origin is discussed from the temperature dependence of the stimulated emission peak. This opens the possibility to form a natural quantum box structure by controlling the well-barrier fluctuation.
Integrated optic mode-size tapers by selective organometallic chemical vapor deposition of InGaAsP/InP
Authors: Deri R. J. , Caneau C. , Colas E. , Schiavone L. M. , Andreadakis N. C. , Song G. H. , Pennings E. C. M.
Published: July 2002

We demonstrate low-loss optical mode-size tapers in InGaAsP/InP optical waveguides fabricated by selective organometallic chemical vapor deposition. The tapers increase the vertical mode size by ≊300%. Taper losses as low as 0.4 dB (on-chip, excluding coupling) were achieved, with 2.6 dB coupling loss to a flat-end, single-mode fiber at 1540 nm wavelength.
Theoretical comparison of sensitivities of acoustic shear wave modes for (bio)chemical sensing in liquids
Authors: Kovacs Günter , Venema Adrian
Published: July 2002

A theoretical comparison of the sensitivities of various acoustic shear wave modes applied in (bio)chemical sensing in a liquid environment is presented. The sensitivity which is defined as the relative change of oscillation frequency due to mass adsorption in a (bio)chemical interface is obtained from perturbation theory. It is shown that the application of a Love wave mode for chemical compound sensing in liquids is very promising because of its high sensitivity.
Fabrication of ultrathin metal oxide films using Langmuir–Blodgett deposition
Authors: Amm D. T. , Johnson D. J. , Laursen T. , Gupta S. K.
Published: July 2002

Thin Y2O3 films have been fabricated using a Langmuir–Blodgett (LB) process. Uniform LB films of yttrium arachidate have been successfully deposited up to 200 layers. These films were found to decompose uniformly above 300 °C leaving a thin oxide layer. X-ray diffraction, laser reflection, and Rutherford backscattering have been used to determine crystal structure and stoichiometry of the film before, during, and after thermal decomposition. This test system demonstrates the potential application of Langmuir–Blodgett deposition for inorganic oxide film fabrication of thicknesses ranging from 0.1 to 40 nm.
Oxynitiride gate dielectrics prepared by rapid thermal processing using mixtures of nitrous oxide and oxygen
Authors: Okada Yoshio , Tobin Philip J. , Hegde Rama I. , Liao Jimmy , Rushbrook Peter
Published: July 2002

A rapid thermal oxynitridation process using mixtures of nitrous oxide and oxygen for the fabrication of metal-oxide-semiconductor (MOS) capacitors is presented herein. This approach provides excellent control of Si/SiO2 interfacial nitrogen concentration from 0–1 at. % by varying growth temperature and N2O mol %. The dielectric quality of oxynitrides with interfacial nitrogen concentrations of 0.10, 0.22, 0.39 at. % was studied. As-processed oxynitride capacitors have Dit and fixed charge density as low as oxide capacitors. However, a small nitrogen incorporation at the interface improves Qbd and suppresses interface state generation caused by Fowler–Nordheim (FN) injection.
Improved ohmic contacts for p-type ZnSe and related p-on-n diode structures
Authors: Lansari Y. , Ren J. , Sneed B. , Bowers K. A. , Cook J. W. , Schetzina J. F.
Published: July 2002

The problem of obtaining ohmic contacts for p-type ZnSe is related to the deep valence band of ZnSe. We have addressed this problem by employing an epitaxial layer of the semimetal HgSe to decrease the interfacial energy barrier, or valence band offset, to about 0.6 eV. This has resulted in improved ohmic contacts for p-type ZnSe films and related diode structures.
Local structure of 1.54-μm-luminescence Er3+ implanted in Si
Authors: Adler D. L. , Jacobson D. C. , Eaglesham D. J. , Marcus M. A. , Benton J. L. , Poate J. M. , Citrin P. H.
Published: July 2002

Extended x-ray absorption fine structure measurements from Er-implanted Czochralski-grown Si samples, which exhibit strong luminescence at 1.54 μm, reveal a local sixfold coordination around Er−not of Si−but of oxygen atoms at an average distance of 2.25 Å. By contrast, similar concentrations of Er implanted in high purity float-zone Si samples, which are essentially optically inactive, show that Er is coordinated to 12 Si atoms at a mean distance of 3.00 Å.
In situ probing at the growth temperature of the surface composition of (InGa)As and (InAl)As
Authors: Gerard Jean-Michel
Published: July 2002

A sudden shift from a bidimensional to a three-dimensional growth mode is observed when InAs is deposited by molecular-beam epitaxy on a pseudomorphic buffer layer grown on GaAs. The critical thickness for this shift is merely sensitive to the indium composition of the surface monolayer prior to growth. This property allows a direct in situ probing of the surface composition at the temperature of the growth. A detailed quantitative study of the surface segregation of indium atoms is performed for (InGa)As and (InAl)As alloys.
N- and P-type dopant profiles in distributed Bragg reflector structures and their effect on resistance
Authors: Kopf R. F. , Schubert E. F. , Downey S. W. , Emerson A. B.
Published: July 2002

We report the n- and p-type dopant profiles obtained in AlAs/GaAs structures. When structures were doped with Si or C, targeted dopant profiles were achieved. However, when Be was used, significant redistribution of the dopant occurred, which resulted in an accumulation of Be on the GaAs side of the heterointerfaces, and a maximum incorporation of Be of ∼5×10−17 cm−3 in the AlAs layers. Similar results were obtained for Be dopant profiles in AlGaAs/AlAs quarter-wave distributed Bragg reflectors (DBR). Be segregation and diffusion during growth resulted in a high electrical resistance in these DBR structures. The resistance was significantly reduced when the structure was doped with C.
Thermomechanical writing with an atomic force microscope tip
Authors: Mamin H. J. , Rugar D.
Published: July 2002

We have developed a new technique to perform fast, reliable nanoindentation of polymer surfaces for possible applications to high density data storage. In this technique, an infrared laser is focused on an atomic force microscope (AFM) tip, which is in contact with a transparent polymethyl methacrylate (PMMA) substrate. The heat from the tip softens the PMMA in the contact region, at which point the local tip pressure creates a pit. The pits range in size from several hundred angstroms to 1 μm, depending on the size of the laser pulse and the loading force on the tip. Pits have been made with pulses as short as 0.3 μs at loads of 10−7 N. By operating the AFM on a rotating disk, we have shown that the features can be written and read at frequencies up to at least 100 kHz.
Epitaxial growth of ferromagnetic ultrathin MnGa films with perpendicular magnetization on GaAs
Authors: Tanaka M. , Harbison J. P. , DeBoeck J. , Sands T. , Philips B. , Cheeks T. L. , Keramidas V. G.
Published: July 2002

We have successfully grown ferromagnetic MnGa ultrathin films on GaAs substrates by molecular beam epitaxy. Reflection high energy electron diffraction and cross-sectional transmission electron microscopy show that monocrystalline MnGa films are grown with the c axis of the tetragonal unit cell normal to the (001) GaAs substrates. Both magnetization measurements by vibrating sample magnetometer and extraordinary Hall effect (EHE) measurements indicate perpendicular magnetization, with the remnant magnetization of 225 emu/cm3 and EHE resistivity in the range of 0.5–4 μΩ cm at room temperature. The material possesses properties ideal for certain nonvolatile magnetic memory coupled with underlying III-V circuitry.
Electron mobility enhancement from coupled wells in delta-doped GaAs
Authors: Zheng X. , Carns T. K. , Wang K. L. , Wu B.
Published: July 2002

It is found that when two Si delta (δ) doped wells in GaAs are placed in close proximity to one another, the electron Hall mobility is enhanced two to five times over that of the single well case. The temperature dependence of the mobility is also reported. Samples with a variety of spacer widths have been studied. Our theoretical and experimental data show that the excited subbands in the double well structure have significant carrier densities located in the undoped region where Coulombic scattering is reduced, and are thus found to play an important role in the observed mobility behavior.
Novel technique for p-type nitrogen doped ZnSe epitaxial layers
Authors: Taskar N. R. , Khan B. A. , Dorman D. R. , Shahzad K.
Published: July 2002

We report a novel technique to obtain p-type ZnSe layers doped with nitrogen. The layers were grown in a low-pressure metalorganic vapor phase epitaxy system using ammonia as the dopant source. A rapid thermal anneal was used to enhance the activation of the nitrogen acceptors. Net acceptor concentration values as high as 3×1016/cm3 were obtained from capacitance-voltage measurements and the profile was uniform over the thickness of the epitaxial layers. The 7 K photoluminescence spectrum was dominated by the acceptor bound exciton peak; the donor-acceptor pair spectra were also observed.
Self-consistent fluid modeling of radio frequency discharges in two dimensions
Authors: Dalvie M. , Surendra M. , Selwyn G. S.
Published: July 2002

Results from a two-dimensional (2D) fluid simulation of a parallel plate, capacitively coupled radio frequency discharge bounded by a cylindrical insulator with a grounded exterior surface are presented. We find that the radial sheath at the insulator focuses current into the plasma region adjacent to the sheath. This 2D effect has important ramifications for the ionization rate, which peaks sharply in the metal-insulator corners. We have experimentally observed the enhancement of the emission rate in a corner using spatially resolved optical emission spectroscopy. A ‘‘thick’’ insulator yields radial profiles for the time-averaged plasma density and potential that are essentially uniform. A ‘‘thin’’ insulator, however, results in an off-axis maximum in the plasma density and potential due to the corner ionization.
Biaxial Young’s modulus of silicon carbide thin films
Authors: Jean A. , El Khakani M. A. , Chaker M. , Boily S. , Gat E. , Kieffer J. C. , Pépin H. , Ravet M. F. , Rousseaux F.
Published: July 2002

We have investigated the biaxial Young’s modulus of amorphous SiC thin films which have been produced by using laser ablation, triode sputtering, and plasma enhanced chemical vapor deposition techniques. It is observed that the biaxial Young’s modulus increases with the Si—C bond density in the films.
Optical properties of fractal quantum wells
Authors: Gourley P. L. , Tigges C. P. , Schneider R. P. , Brennan T. M. , Hammons B. E. , McDonald A. E.
Published: July 2002

We report the growth of new fractal quantum-well structures and the first studies of their optical properties. In these (Al,Ga)As structures the composition is varied in a fractal sequence between layers to create a highly branched, self-similar distribution of quantum wells. Experimentally, we studied optical absorption, luminescence and excitation spectra, and electron-hole recombination dynamics. We computed the electron and hole wave functions and transition energies and found good agreement with experiment. The optical and transport properties are strikingly different from those in single or periodic quantum wells. First, the band-edge absorption slope (change in optical density per unit energy) can be controlled over wide limits simply by modifying the sequence. Second, the transport of carriers across the quantum-well layers can be adjusted to control the carrier relaxation rate and energy distribution within the quantum wells. These results suggest possible applications of these new materials for several new devices including broadband emitters, solar cells, electro-optical, and nonlinear optical devices.
Acoustic waves in a piezoelectric plate loaded by a dielectric fluid
Authors: Yang C.-H. , Chimenti D. E.
Published: July 2002

Measurements and calculations of reflection spectra of an X-cut LiNbO3 plate immersed in a dielectric fluid have been performed, with the numerical results presented in an innovative image data format. The influence of dielectric fluid loading on all branches of the reflection coefficient function has been investigated. Strong piezoelectric coupling leads to unexpected plate wave dispersion in the fundamental symmetric mode, where the group velocity exceeds the phase velocity at low frequency. The experimental data are in excellent agreement with the results of an exact partial wave analysis. These phenomena and their effect on plate wave behavior can play an important role in the performance of chemical or physical liquid sensing devices.
Room-temperature electron mobility in strained Si/SiGe heterostructures
Authors: Nelson S. F. , Ismail K. , Chu J. O. , Meyerson B. S.
Published: July 2002

We report on room-temperature electron transport measurements in modulation-doped strained Si/SiGe heterostructures, grown by ultrahigh-vacuum chemical vapor deposition. A high room-temperature mobility is expected in such samples because of the strain-induced splitting of the conduction band in the silicon channel. Record values of over 2600 cm2/V s have been measured, almost twice the theoretical maximum for relaxed silicon.
Photoconductive gain and generation-recombination noise in multiple-quantum-well infrared detectors
Authors: Beck W. A.
Published: July 2002

The photoconductive gain, g, and generation-recombination (GR) noise of multiple-quantum-well infrared detectors are calculated for structures in which the well capture probability, pc, and the fraction of current derived from tunneling are allowed to vary through the structure. For uniform pc and no tunneling current, g=1/(Npc), where N is the number of wells. The GR noise power under the same conditions is 4eĪgB(1−pc/2), where e is electronic charge, Ī is the mean current, and B is the measurement bandwidth. When pc≪1, the noise contributions from carrier generation and decay (recombination) are equal as in a homogeneous photoconductor. However, when pc→1, the recombination noise decreases to zero, and the noise is equal to the shot noise of N series-connected, independent junctions.
Epitaxial LiTaO3 thin films by pulsed laser deposition
Authors: Agostinelli John A. , Braunstein Gabriel H. , Blanton Thomas N.
Published: July 2002

Epitaxial LiTaO3 thin films having excellent crystalline properties have been achieved on (0001)-sapphire substrates using the technique of pulsed laser deposition. X-ray diffraction analysis revealed that completely single-phase c-oriented LiTaO3 films were produced. X-ray rocking curve analysis showed that the range of misalignment of the c-axis direction was about 0.2°. Ion channeling studies indicated a minimum backscattering yield of only 4.9%. Channeling also revealed an improvement in crystalline perfection as a function of distance above the interface with the sapphire substrate. Optical waveguiding with losses on the order of 1 dB/cm was demonstrated.
Investigation of the growth kinetics of low pressure diamond films by in situ elastic scattering of light and reflectivity
Authors: Bonnot A. M. , Mathis B. S. , Moulin S.
Published: July 2002

A detailed analysis of in situ optical measurements of elastic scattering of light and reflectivity during diamond film synthesis is presented. From the results we propose a growth kinetic model for the very first stages when isolated tiny particles are formed and until they coalesce to form a continuous diamond film.
Control of anomalous boron diffusion in the base of Si/SiGe/Si heterojunction bipolar transistors using PtSi
Authors: Xu D.-X. , Peters C. J. , Noël J.-P. , Rolfe S. J. , Tarr N. G.
Published: July 2002

In Si/SiGe/Si heterojunction bipolar transistor structures, very shallow arsenic implant on the emitter has been found to cause anomalous boron diffusion in the base. This phenomenon imposes stringent constraints on the device fabrication processes. We discovered that by using platinum silicide, which also served as a self-aligned low resistance contact material to the emitter and base, the anomalous diffusion in the base was significantly reduced. In this letter, we report the experiment results, and propose possible explanations.
High hole mobility in SiGe alloys for device applications
Authors: Ismail K. , Chu J. O. , Meyerson B. S.
Published: July 2002

We report high hole mobility in modulation-doped SiGe alloys with Ge content up to 80%. The layers which are grown using ultrahigh-vacuum chemical vapor deposition are of high crystalline quality, have smooth surfaces, and have a low density of misfit dislocations. As a result of strain and high Ge content, we have measured hole mobilities in the range of 800–1050 cm2/V s at room temperature, and 3300–3500 cm2/V s at 77 K. The corresponding two-dimensional sheet hole density is about 3×1012 cm−2. Those numbers are, to our knowledge, the highest numbers ever reported for a SiGe alloy. The resistivity of this two-dimensional hole channel at room temperature is, to our knowledge, the lowest for any p-type semiconductor quantum well.
Molecular beam epitaxy of CdF2 layers on CaF2(111) and Si(111)
Authors: Sokolov N. S. , Gastev S. V. , Novikov S. V. , Yakovlev N. L. , Izumi A. , Furukawa S.
Published: July 2002

Cadmium fluoride single crystal layers have been grown on CaF2/Si(111) or Si(111) substrates by molecular beam epitaxy. The structures are expected to have attractive electronic properties. The growth was monitored by reflections high energy electron diffraction (RHEED) techniques. A distinct (√3×√3) R30° superstructure has been observed on the CdF2(111) surface at growth temperatures below 150 °C. RHEED intensity oscillations indicate a two-dimensional growth mode of CdF2.
Reflection high-energy electron diffraction intensity oscillations during the growth by molecular beam epitaxy of GaAs (111)A
Authors: Fahy M. R. , Sato K. , Joyce B. A.
Published: July 2002

We have made a study of reflection high-energy electron diffraction intensity oscillations during the growth of GaAs on singular GaAs (111)A substrates by molecular beam epitaxy. The behavior is quite different from growth of GaAs on (001) orientated substrates in that the oscillation period is growth temperature and As4:Ga flux ratio dependent. We speculate that this is due to the (110)-like configuration of the (111)A 2×2 reconstructed surface, which requires direct interaction of a Ga and an As atom for growth to occur.
GaAs quantum dots with lateral dimension of 25 nm fabricated by selective metalorganic chemical vapor deposition growth
Authors: Nagamune Y. , Nishioka M. , Tsukamoto S. , Arakawa Y.
Published: July 2002

We report on in situ fabrication and the photoluminescence spectra of pyramid-shaped GaAs dot structures grown on (100) GaAs substrates using selective epitaxial growth by metalorganic chemical vapor deposition. The dot structures have lateral size of 25 nm and the period of 140 nm, showing a clear photoluminescence peak with strong intensity. In addition, energy change of magnetophotoluminescence spectra demonstrates the enhancement of exciton binding energy due to lateral confinement.
Design of ohmic contacts to p-ZnSe
Authors: Dandrea R. G. , Duke C. B.
Published: July 2002

First-principle density functional calculations are used to design improved ohmic contacts to p-ZnSe. Two design strategies are applied: the use of a graded semiconductor epilayer with a large valence band offset, and the imposition of an interlayer to reduce the metal/p-ZnSe Schottky barrier. In the former strategy we study BeTe because it is lattice matched to ZnSe. We find the BeTe/ZnSe valence band offset is nearly the same as the ZnTe/ZnSe offset, so that if BeTe can be sufficiently p doped, its grading with ZnSe should lead to an ohmic contact comparable to a ZnTe-grading contact, but without the deleterious presence of misfit dislocations. For the latter strategy we consider the use of a thin As-Si interlayer between the II-VI material and metal. The As effects an extra microscopic dipole at the interface that lowers the Fermi level 1 eV in the II-VI band gap, leading to greatly decreased rectification at p-type contacts. Applying both strategies simultaneously suggests that a metal/Si-As/BeTe/ZnSe multilayer structure would afford a nearly ideal ohmic contact to p-ZnSe.
Doping of a quantum dot
Authors: Tsu Raphael , Babić Davorin
Published: July 2002

The doping of a quantum dot is an important issue particularly because the luminescence of porous silicon has been attributed to quantum confinement. Since electrochemical etching and possible electroluminescence devices are intimately connected with extrinsic conduction, the quantum size effect on doping, including interactions with induced charges at the dielectric discontinuity, requires investigation.
Electrical characterization of an ultrahigh concentration boron delta-doping layer
Authors: Weir B. E. , Feldman L. C. , Monroe D. , Grossmann H.-J. , Headrick R. L. , Hart T. R.
Published: July 2002

We report a boron δ-doping layer in crystalline silicon with an electrically active concentration of 1×1022 cm−3 and a mobility of ∼20 cm2/V s. This structure was fabricated by low-temperature molecular-beam epitaxy with boron confined to 3 monolayers in the silicon growth direction. Complete electrical activation is observed, showing metallic conduction down to 4 K. This two-dimensional doped layer, incorporated into the crystal lattice, represents a volume concentration exceeding the solid solubility of boron in silicon by two orders of magnitude. These high-concentration structures fill an unexplored region of the mobility versus concentration curve.
Atomic force microscopy study of strained InGaAs quantum disks self-organizing on GaAs (n11)B substrates
Authors: Nötzel Richard , Fukui Takashi , Hasegawa Hideki , Temmyo Jiro , Tamamura Toshiaki
Published: July 2002

Strained quantum-box structures are naturally formed during the interrupted growth of AlGaAs and InGaAs films on GaAs (n11)B substrates. InGaAs films organize spontaneously into orderly rows of nanoscale disks buried beneath AlGaAs microcrystals. A comparative study by atomic force microscopy shows the alignment and uniformity to be optimum on (311)B surfaces. Both the uniformity and the shape of the microcrystals are not changed for base widths between 220 and 70 nm. Moreover the size and distance can be controlled independently by the In composition and the InGaAs layer thickness, respectively. In contrast, step bunching occurs on GaAs (n11)A substrates to form wirelike microstructures on GaAs (311)A substrates.
Color variation with electroluminescent organic semiconductors in multimode resonant cavities
Authors: Dodabalapur A. , Rothberg L. J. , Miller T. M.
Published: July 2002

The range of possibilities in controlling the color of an organic semiconductor based light emitter diode (LED) by incorporating the active layers in a multimode Fabry–Pérot cavity is demonstrated. The combination of carefully designed multimode microcavities and electroluminescent organic semiconductors makes possible the realization of mixed colors such as white, purple, etc. with a single LED. The parameters affecting the color include the total optical thickness of the device and the position of the electromagnetic-field antinodes with respect to the location of the emitting dipoles. The electrical characteristics and quantum efficiency of such devices are also reported.
Strong photoluminescence emission at room temperature of strained InGaAs quantum disks (200–30 nm diameter) self-organized on GaAs (311)B substrates
Authors: Nötzel Richard , Temmyo Jiro , Kamada Hidehiko , Furuta Tomofumi , Tamamura Toshiaki
Published: July 2002

We have recently found that quantum-box-like structures are formed during spontaneous reorganization of a sequence of AlGaAs and strained InGaAs epitaxial films grown on GaAs (311)B substrates by metalorganic vapor-phase epitaxy into InGaAs islands (disks) buried beneath AlGaAs. The size of the disks is directly controlled by the In content in the range 200–30 nm. Strong photoluminescence (PL) efficiency at room temperature is observed in these strained quantum disks. Even for the 30 nm disk the radiative efficiency is not reduced compared to the reference (100) quantum well. The PL spectra are characterized by narrow linewidth and well resolved exciton resonances in excitation spectroscopy.
Hillock formation during electromigration in Cu and Al thin films: Three-dimensional grain growth
Authors: Gladkikh A. , Lereah Y. , Glickman E. , Karpovski M. , Palevski A. , Schubert J.
Published: July 2002

The evolution of microstructure in Al and Cu thin film lines during electromigration has been studied using a transmission electron microscopy. Grain boundary migration was found to be critically involved in the electromigration induced hillock formation that can be described as a three-dimensional growth of a single grain.
Resistance bi-stability in resonant tunneling diode pillar arrays
Authors: Alphenaar B. W. , Durrani Z. A. K. , Heberle A. P. , Wagner M.
Published: July 2002

We have fabricated and characterized resonant tunneling diode pillar arrays. The array resistance switches between two stable states with a maximum room temperature current peak to valley ratio of 500:1. Both the high and the low resistance states are stable at zero bias suggesting that the device may be used for non-volatile memory storage.
Electroluminescence coupling in multiple quantum well diodes and solar cells
Authors: Araújo Gerardo L. , Martí Antonio
Published: July 2002

Electroluminescence coupling between the wells in multiple quantum well (MQW) structures is taken into account to show how, if the emissivity of one well equals its absorptivity, then, the emissivity of the whole structure also equals its absorptivity. This result is used to critically analyze previously reported results in which the limiting efficiency of MQW solar cells were supposed to exceed the limiting efficiency of single bandgap solar cells.
Transport study of self-supporting porous silicon
Authors: Fejfar A. , Pelant I. , Šípek E. , Kočka J. , Juška G. , Matsumoto T. , Kanemitsu Y.
Published: July 2002

We have measured dark DC conductivity and time-of-flight (TOF) of carriers in self-supporting porous silicon films in the temperature range 298–480 K. The dark I-V curves show superlinear behavior with activation energies of 0.38–0.67 eV. The TOF measurements allowed us to evaluate the drift-length of non-equilibrium carriers and revealed a significant decrease of the collected charge with increasing delay (tdel≥1 ms) of the exciting 3 ns laser pulse after the voltage application, probably due to field redistribution in the Si crystallites.
Spectroscopic measurements on the Joint European Torus using optical fibers to relay visible radiation
Authors: Morgan P. D. , Behringer K. H. , Carolan P. G. , Forrest M. J. , Peacock N. J. , Stamp M. F.
Published: July 2002

Light from the Joint European Torus (JET) tokamak is relayed by optical fibers to detectors outside the biological shield, where personnel access is unrestricted. This arrangement, which is described in detail, will permit routine recording during the intense neutron emission associated with the production of D–T plasmas—scheduled for 1989. The diagnostic has been in routine use since JET began operation in mid-1983. A selection of results obtained is presented. The likely degradation in fiber performance, due to irradiation, during the D–T phase of the program is assessed. Methods of overcoming the problems due to induced absorption are presented.
Automatic, digital system for profiling rough surfaces
Authors: Keller Kirk , Bonner Brian P.
Published: July 2002

Four pneumatically actuated reciprocating probes and a translating table are computer controlled to map surfaces with asperity heights of up to 25 mm. The height of a calibration surface can be determined to 0.002 mm. Individual traces may be sampled as often as every 0.025 mm with a neighboring trace as near as 0.031 mm. Surfaces with dimensions of up to 355×150 mm can be scanned with the system.
Thomson parabola time-of-flight ion spectrometer
Authors: Weber R. , Balmer J. E. , Lädrach P.
Published: July 2002

A novel type of ion spectrometer for laser-produced plasma diagnostics is described. The Thomson parabola configuration is used to separate the expanding plasma ions according to their different charge-to-mass ratios. One particular ion species is subsequently collected by a parabola-shaped charge collector. In this way ion velocity distributions of a single charge-to-mass ratio are obtained through simple time-of-flight analysis. Measured ion energies can be as low as 1 keV per nucleon.
Method of precision temperature control using flowing water
Authors: Ogasawara Hiromitsu
Published: July 2002

A high-precision temperature control method using flowing water near room temperature is described in this paper. The temperature of a thermostatic cell immersed in a water flow within a water jacket is regulated by controlling the temperature of the water circulating through the jacket. This control is accomplished by three-step controlled heating and constant cooling. The method provides control with a short response time. Temperature stabilization-process control within a fluctuation of ±25 μK over a period of 12 h and temperature variation-process control at a rate of 320 μK/h with a fluctuation of less than ±50 μK are achieved. All of the electric devices for controlling and measuring, as well as the thermostatic cell, are placed in thermostatic containers the temperature of which is controlled within a fluctuation of ±0.05 K. The total error in these temperature measurements is estimated to be approximately ±11 μK.
High transmission polarization analyzer for Lyman-α radiation
Authors: Winter H. , Ortjohann H. W.
Published: July 2002

We report on an analyzer for elliptically polarized Lyman-α radiation (λ=121.6 nm) which has a high transmission (14%) and can be used in ultrahigh vacuum. The analyzer consists of a pile of four MgF2 plates and a MgF2 quarter-wave plate for Lyman-α light. We discuss examples for the application of this device by measurements of polarized Lyman-α light emitted after ion-atom and ion-surface collisions.
Miniature cryogenic diamond-anvil high-pressure cell
Authors: Dunstan D. J. , Scherrer W.
Published: July 2002

A novel diamond-anvil cell is described which measures 19-mm diameter by 28 mm long to fit the Oxford Instruments CF 1204 flow cryostat, while providing full axial and tilt adjustment of the diamonds. The drive mechanism provides for pressure changes while the cell is in the cryostat. The small dimensions are achieved because the drive force is not transmitted through the tilt mechanism, and by the Bowden cable technique used for the drive mechanism. This cell makes high pressure a readily portable technique that can be brought to many already existing experimental apparatuses.
Investigation of a radial transmission line transformer for high-gradient particle accelerators
Authors: Petr R. A. , Nunnally W. C. , Smith C. V. , Clark M. H.
Published: July 2002

This paper discusses the use of a photoconductively switched radial transmission line transformer as a high-gradient particle accelerator power system. In particular, a 1.8-m-radius radial line with a one-way transit time of 10 ns was fabricated and the voltage attenuation/amplification of a radially traveling wave measured. These results are compared with numerical solutions to the radial-wave equations using the method of characteristics. The line was operated as a step-down transformer by driving the inner radius with a pulse generator and measuring open circuit voltage at its outer radius. The voltage attenuation of the transformer agrees fairly well with an approximate theory for short-pulse propagation along the line (where pulse lengths are roughly one-tenth the one-way transit time of the line), and a more accurate computer solution using the method of characteristics has correctly predicted the voltage response of the line. These results imply that moderate voltage, short duration pulses (approximately 1 ns) can be amplified to very high voltages by uniformly driving the outside radius of this type of transmission line. The use of photoconductive switches to generate a radially converging, high-power wave transient required for high-gradient particle accelerators is suggested as an alternative to other methods because the switches can be synchronized to within several tens of picoseconds, and control of subsequent sections can be accomplished for relativistic systems.
Ion temperature measurements on JT-60 using He beam scattering (invited)
Authors: Takeuchi H. , Tobita K. , Kusama Y. , Nemoto M. , Itoh T. , Tsukahara Y. ,   JT-60 Team
Published: July 2002

In order to measure the ion temperature of the JT-60 tokamak, we have developed a Rutherford scattering system using a helium atom beam. A positive-ion beam generated by an ion source which has a capability of beam energy 200 keV and drain current 3.5 A is converted to a helium atom beam by collision with cold helium gas. The He atom beam, equivalent to 0.6 A, reaches the center of the vacuum chamber of the JT-60 tokamak. The scattering angle is 7.0°. Scattered helium atoms are analyzed by an E∥B-type neutral particle energy analyzer with a gas stripping cell. This scattering system has been applied to investigate additionally heated plasmas by the method of neutral beam injection (NBI), ion cyclotron wave (ICRH), lower hybrid wave (LHRH), and combined heating of NBI+LHRH or ICRH in a parameter range of Bt=4.0 to 4.5 T, Ip=1.0 to 3.2 MA, and n̄e≲1×1020 m−3. The ion temperatures obtained by the system are consistent with those measured by Doppler broadenings of Ti xxi and Ti xxii resonance lines. To investigate the influence of ion temperature and density profiles and the beam component of NBI heating on the determination of ion temperature, we have evaluated an energy spectrum of scattered atoms by using a simulation code. The result shows that in JT-60 plasmas the beam component hardly exerts an important influence on the determination of ion temperature by this diagnostic system.
A far infrared laser sideband spectrometer in the frequency region 550–2700 GHz
Authors: Verhoeve P. , Zwart E. , Versluis M. , Drabbels M. , ter Meulen J. J. , Meerts W. Leo , Dymanus A. , McLay D. B.
Published: July 2002

This paper describes a tunable far-infrared (FIR) spectrometer. Tunable radiation is obtained by frequency mixing, fixed frequency FIR laser radiation and tunable microwave radiation in Schottky barrier diodes. An optically pumped laser and an HCN discharge laser are used as FIR sources and klystrons in the frequency range of 22–114 GHz as microwave sources. This yields an 85% coverage of the frequency region between 550 and 2700 GHz. Up to sixth order sidebands have been generated and used for spectroscopy. The ultimate sensitivity corresponds to a minimum detectable fractional absorption of 10−5 at 1-s RC time. The applicability of the spectrometer in high-resolution spectroscopy of transient species has been demonstrated by the observation of spectra of OD and N2H+. New laser emissions of optically pumped CH2F2 have been found and accurate frequencies have been determined for some of them.
Stability studies on Kiev cryogenic germanium resistance thermometers
Authors: Besley L. M. , Szmyrka-Grzebyk A.
Published: July 2002

The stability of 19 germanium resistance thermometers manufactured in Kiev, USSR, has been studied by cycling them 30 times between temperatures of 20 and 300 K. Resistance measurements were made on each thermometer at 20 K on each cycle and also at 15 K on each cycle of the first 20 cycles. All but one of nine four-lead, standard-size thermometers were stable within the ±0.2 mK precision of the measurements at 20 K, while the observed changes in resistance at 20 K of 10 miniature thermometers correspond to temperature variations that ranged between 20 and 49 mK.
Tightly confined one-dimensional states in T-shaped GaAs edge quantum wires with AlAs barriers
Authors: Someya T. , Akiyama H. , Sakaki H.
Published: July 2002

We have designed and prepared a T-shaped GaAs edge quantum wire (T-QWR) structure with AlAs barriers by cleaved edge overgrowth method. Three photoluminescence (PL) peaks have been observed and their origins are identified using the spatially resolved PL technique. The effective binding energy of carriers in this T-QWR is precisely determined as the energy spacing between T-QWRs and the adjacent QWs. When the well width of constituent QWs was 5 nm, the effective binding energy is found to be as large as 35 meV, which is far beyond the thermal energy kT at room temperature.
A high-throughput Raman notch filter set
Authors: Puppels G. J. , Huizinga A. , Krabbe H. W. , de Boer H. A. , Gijsbers G. , de Mul F. F. M.
Published: July 2002

A chevron-type Raman notch filter (RNF) set is described. lt combines a high signal throughput (up to 90% around 1600 cm−1 and ≳80% between and 700 and 2700 cm−1) with a laser line suppression of 108–109. The filter set can be used to replace the first two dispersion stages in triple-stage Raman monochromators commonly employed in multichannel detection systems. This yields a gain in intensity of the detected Raman signal of a factor of 4. It is shown that in Raman spectrometers with a backscatter geometry, the filter set can also be used to optically couple the microscope and the spectrometer. This leads to a further increase in signal intensity of a factor of 3–4 as compared to the situation where a beam splitter is used. Additional advantages of the RNF set are the fact that signal throughput is almost polarization independent over a large spectral interval and that it offers the possibility to simultaneously record Stokes and anti-Stokes spectra.
On-line tangential soft x-ray/VUV tomography on COMPASS-C
Authors: Durst R. D. ,   The COMPASS Group
Published: July 2002

A tangentially viewing pinhole camera has been used to image the COMPASS-C plasma in the vacuum ultraviolet and soft x-ray spectral regions with framing rates up to 330 Hz. The PC-based system acquires up to 256 128×128 pixel images per shot and incorporates an array processor to allow on-line tomographic reconstructions. Data compression is used to reduce the data load by a factor of 4.
The 50 MeV H− linear accelerator for HERA:LINAC3 collaboration
Authors: Criegee L. , Dederichs H. , Ebel H. , Franke G. , Kong D. M. , Krause H. , Lewendel B. , Luo Z. H. , Nagl M. , Papakonstantinou A. , Pape K. H. , Peters J. , Qiao J. M. , Qiu H. , Schempp A. , Schirm N. , Schneemann H. , Schröder V. , Sha H. , Tessmann I. , Timm U. , Wagner R. , Wang S. H. , Winter G. G. , Wu M. , Zhang H. S. , Zimmermann W.
Published: July 2002

The components of the first 50 MeV accelerator in the chain of injectors to the 820 GeV HERA proton ring are described including the high energy transport line. An H− beam originates in the cesium loaded magnetron source, is preaccelerated by a radio frequency quadrupole to 750 keV, raised to 50 MeV energy in three rf resonators, and is analyzed in the transport line. The H− ions are converted to protons by stripping, when the beam is injected over several turns into the synchrotron DESY3.
Diffusion of implanted Be in AlxGa1−xAs as a function of Al concentration and anneal temperature
Authors: Lee Cynthia C. , Deal Michael D. , Bravman John C.
Published: July 2002

Diffusion of ion implanted Be in AlxGa1−xAs was studied as a function of Al concentration and annealing temperature and was compared to diffusion in GaAs. The behavior of Be in AlxGa1−xAs is similar to that in GaAs, even showing the anomalous behavior of increasing redistribution with decreasing temperature. The diffusivity of Be appears to increase with Al content which may be due to increasing bonding strength of matrix atoms with the addition of Al, preventing the easy transferral of Be from interstitial to substitutional sites. The oversaturation of Be interstitials may also explain the persistence of anomalous diffusion behavior in AlxGa1−xAs with respect to anneal temperature. This is discussed in terms of the substitutional-interstitial diffusion mechanism, the relative amount of interstitial and substitutional Be, and the relative difficulty of moving from an interstitial to a substitutional site.