bluuebunny/crossref_metadata_2025 huggingface dataset:
Optically detected magnetic resonance of deep centers in molecular beam epitaxy ZnSe:N
Authors: Murdin B. N. , Cavenett B. C. , Pidgeon C. R. , Simpson J. , Hauksson I. , Prior K. A.
Published: July 2002

Optically detected magnetic resonance has been used to investigate the deep level recombination processes in p-type ZnSe grown by molecular beam epitaxy and doped with nitrogen. In addition to the well-known shallow donor resonance at g=1.11, an anisotropic deep donor resonance is observed with g=1.38 and a deep acceptor resonance is detected at g=2. These results are consistent with the pair recombination processes proposed by us previously where the compensating deep donor was assigned to the VSe-Zn-NSe complex.
Di- and Tricarboxylic-acid-based etches for processing high temperature superconducting thin films
Authors: Ginley D. S. , Ashby C. I. H. , Plut T. A. , Urea D. , Siegal M. P. , Martens J. S.
Published: July 2002

The development of passive and active electronics from high temperature superconducting thin films depends on the development of process technology capable of producing appropriate feature sizes without degrading the key superconducting properties. We present a new class of chelating etches based on di- and tricarboxylic acids that are compatible with positive photoresists and can produce submicrometer feature sizes while typically producing increases the microwave surface resistance at 94 GHz by less than 10%. This simple etching process works well for both the Y-Ba-Cu-O and Tl-Ba-Ca-Cu-O systems.
X-ray photoemission characterization of thin epitaxial Fe silicide phases on Si(111)
Authors: Kafader U. , Wetzel P. , Pirri C. , Gewinner G.
Published: July 2002

Depending on preparation conditions, Fe silicides grown on Si(111) by means of solid phase epitaxy and molecular beam epitaxy show the formation of the bulk ε-FeSi and β-FeSi2 phases as well as epitaxially grown metastable CsCl- and CaF2-type Fe silicides. The valence-band of these Fe silicides are measured with monochromatized Al Kα x-ray photoemission and angle resolved ultraviolet photoemission and are found to be in remarkable agreement with calculated densities of states.
Single-wavelength all-optical phase modulation in a GaAs/AlAs hetero-nipi waveguide: Towards an optical transistor
Authors: Yoffe G. W. , Brübach J. , Karouta F. , Wolter J. H.
Published: July 2002

We propose and demonstrate a single-wavelength all-optical transistor-like device, exploiting the polarization-dependent absorption coefficient in quantum wells. The device is a GaAs/AlAs multiple-quantum-well hetero-nipi waveguide structure. A transverse-electric (TE)-polarized control beam is absorbed, changing the refractive index through carrier-induced effects. A transverse-magnetic-polarized probe beam at the same wavelength, to which the material is transparent, undergoes a phase shift, which can be converted to amplitude modulation if required. The probe can be more powerful than the control beam, so the device can exhibit gain. We obtained a 180° phase shift in the probe beam with 4.2 mW of absorbed control light. The effect was greater with an applied dc bias. A 180° phase shift was obtained at 831 nm with 2.8 mW absorbed TE light and 0.5 V bias.
High power continuous wave blue light generation in KNbO3 using semiconductor amplifier seeded by a laser diode
Authors: Goldberg L. , Busse L. E. , Mehuys D.
Published: July 2002

Diffraction limited emission of a GaAlAs tapered amplifier seeded by a laser diode is frequency doubled in a 12.4-mm-long KNbO3 crystal to generate 62 mW of 429 nm continuous wave emission, corresponding to a conversion efficiency of 1.1%/W cm. Reductions in the conversion efficiency due to nonuniform temperature distribution caused by blue-enhanced infrared absorption were characterized.
Microwave surface impedance at 10 GHz and quasiparticle scattering in YBa2Cu3O7 films
Authors: Gao F. , Kruse J. W. , Platt C. E. , Feng M. , Klein M. V.
Published: July 2002

The surface impedance of superconducting YBa2Cu3O7 films as a function of temperature at 10 GHz has been measured in a parallel plate resonator geometry. The penetration depth λ(T), complex microwave conductivity σ(T), and quasiparticle scattering rate 1/τ(T) were also determined. After a rapid fall as T is lowered below Tc, the surface resistance Rs exhibits a linear dependence from 65 K down to 6 K. As T drops below Tc, the real part of the conductivity σ1 has a rapid rise, which is attributed to the observed dramatic increase in τ. The normal-fluid density shows a linear behavior at low temperatures, which is inconsistent with s-wave BCS superconductivity.
Nucleation and growth of hydrogenated amorphous silicon-carbon alloys: Effect of hydrogen dilution in plasma-enhanced chemical vapor deposition
Authors: Lu Yiwei , An Ilsin , Gunes M. , Wakagi M. , Wronski C. R. , Collins R. W.
Published: July 2002

The microstructural evolution of hydrogenated amorphous silicon-carbon (a-Si1−xCx:H) alloy thin films with optical gaps of ∼1.95 eV has been characterized by real time spectroscopic ellipsometry versus hydrogen dilution of the reactive gases (CH4+SiH4) used in plasma-enhanced chemical vapor deposition. As the H2/(CH4+SiH4) flow ratio is increased to 24, the monolayer-scale features of nucleation and growth suggest an enhancement in the diffusion length of the film precursors on the substrate and film surfaces, leading to an increase in the surface structural stability and bond-packing density of the final material. We suggest a causal connection between the monolayer-scale processes and the ultimate photoelectronic properties of the a-Si1−xCx:H, which also improve with H2 dilution over the same range.
Influence of the oxygen stoichiometry on the structural and optical properties of reactively evaporated ZrOx films
Authors: Bellotto M. , Caridi A. , Cereda E. , Gabetta G. , Scagliotti M. , Braga Marcazzan G. M.
Published: July 2002

Thin ZrOx films are deposited by reactive electron beam evaporation of pure zirconium metal at different oxygen partial pressures. Stoichiometry, structural composition and optical properties of these films are studied. Results from x-ray diffraction and ellipsometry show that the crystallographic phase composition and the optical properties of the films can be controlled by a proper choice of the oxygen partial pressure. In comparison with direct evaporation of ZrO2, the reactive evaporation of zirconium metal improves the homogeneity of the refractive index along the film thickness thanks to an increased homogeneity in the crystallographic phase composition.
Effective carrier mean-free path in confined geometries
Authors: Richardson R. A. , Nori Franco
Published: July 2002

The concept of exchange length is used to determine the effects of boundary scattering on transport in samples of circular and rectangular cross section. Analytical expressions are presented for an effective mean free path for transport in the axial direction. The relationship to the phonon thermal conductivity is discussed.
Hot-electron distribution in multiple quantum well infrared photodetectors
Authors: Kuan C. H. , Tsui D. C. , Choi K. K. , Newman P. G. , Chang W. H.
Published: July 2002

The hot-electron distribution in the GaAs/AlxGa1−xAs multiple quantum well structure of 10-μm infrared photodetectors is measured with a built-in energy analyzer at different temperatures. The distribution width is found to depend strongly on T in the T≊40 to 90 K range. It increases with T, reaches a maximum at around 70 K, and then decreases at higher T’s. The experiment makes it possible to unambiguously identify thermally assisted tunneling as the dominant source of the dark current at 77 K.
Si/SiGe modulation-doped structures with thin buffer layers: Effect of substrate orientation
Authors: Zhou G. L. , Ma Z. , Lin M. E. , Reed J. , Allen L. H. , Morkoç H.
Published: July 2002

High quality Si (strained)/Si0.7Ge0.3 (relaxed) modulation-doped structures incorporating unusually thin (700 nm) buffer layers were grown with molecular beam epitaxy at 700 °C. By utilizing (100) substrates misoriented toward (011) by 4°, the density of threading dislocations was reduced by over an order of magnitude as compared with conventional techniques. These layers produced exceptionally high Hall mobilities of 1790 cm2/V s at 300 K and 19 000 cm2/V s at 77 K on n-type modulation-doped heterostructures. The effect of substrate misorientation on threading dislocation density was investigated using transmission electron microscopy and Nomarski microscopy.
Thin film Bi2Sr2CaCu2O8+x Josephson junctions and direct current superconducting quantum interference devices on (001) SrTiO3 bicrystals
Authors: Amrein T. , Seitz M. , Uhl D. , Schultz L. , Urban K.
Published: July 2002

Single-layer Josephson junctions and dc superconducting quantum interference devices (SQUIDs) have been prepared from epitaxial, laser-deposited thin films of Bi2Sr2CaCu2O8+x on (001) SrTiO3 bicrystals with a misorientation angle of 36.8°. The current-voltage characteristics of the Josephson junctions are of resistively shunted junction type. The Ic(B) patterns look rather periodical and symmetrical but show clear irregularities in comparison to an ideal Fraunhofer-like pattern. However, the supercurrent can be suppressed almost completely by applying an external magnetic field. The best dc-SQUID—with a SQUID hole of 5 μm×20 μm and an estimated inductance of about 36 pH—works up to 77 K. At 76 K the flux to voltage conversion ∂V/∂Φ at the appropriate flux bias is 20 μV/Φ0. The best equivalent flux noise which was measured in the flux locked loop mode at 62 K is 25 μΦ0/√Hz at 1 Hz and 4 μΦ0/√Hz in the white noise region for f≥350 Hz, corresponding to an energy resolution of 4×10−29 J/Hz at 1 Hz and 9×10−31 J/Hz in the white noise region.
High temperature superconductor-normal metal-superconductor Josephson junctions with high characteristic voltages
Authors: Rosenthal P. A. , Grossman E. N. , Ono R. H. , Vale L. R.
Published: July 2002

We have fabricated step edge superconductor-normal metal-superconductor microbridges using YBa2Cu3O7−x(YBCO) and noble metals with critical current-normal resistance (IcRN) products as high as 10 mV and normal resistances up to 38 Ω. Our fabrication process achieves high values of the IcRN product by exploiting the anisotropy in the properties of epitaxial YBCO films, allowing contact only between normal metal and superconductor through the crystalline axes which support the largest Josephson coupling. This results in a dramatic increase in the normal resistance of a junction without decreasing its critical current. We discuss the role of the superconductor-normal metal boundary resistance on the junction electrical properties. We have coupled submillimeter wave rf currents quasioptically into junctions integrated at the feeds of noble metal planar log periodic antennas and have induced up to 7 Shapiro steps in the current-voltage characteristics with a 760 GHz beam from a far infrared laser.
Generation of a violet phase-matched second-harmonic wave with a new organic single crystal, 8-(4′-acetylphenyl)-1,4-dioxa-8-azaspiro[4.5] decane
Authors: Sagawa M. , Kagawa H. , Kakuta A. , Kaji M.
Published: July 2002

A new organic nonlinear optical material, 8-(4′-acetylphenyl)-1, 4-dioxa-8-azaspiro[4.5]decane (APDA) was synthesized. Under collinear type I phase-matching conditions, second-harmonic beams in a 380–450 nm wavelength region were obtained from a Ti-sapphire laser pumping with the single crystal. Nonlinear optical properties and sample preparation of the single crystal are reported.
Effects of electron beam during ion implantation and ion beam assisted deposition
Authors: Liu Xianghong , Ma Tengcai
Published: July 2002

This letter investigates the effects of a continuous electron beam with certain area and low energy density during ion implantation and ion beam assisted deposition (IAD). It is found that electron beams with certain energy can make the implantation range deeper and the combination of the deposition thin film and the substrate stronger. However, it is also found that they make the surface microhardness decrease.
High power AlGaAs quantum well laser diodes prepared by molecular beam epitaxy
Authors: Hayakawa T. , Matsumoto K. , Morishima M. , Nagai M. , Horie H. , Ishigame Y. , Isoyama A. , Niwata Y.
Published: July 2002

Stable and reliable AlGaAs high power single quantum well lasers prepared by molecular beam epitaxy have been realized. We have prepared both 50-μm devices operating in multiple modes and ridge-waveguide single transverse-mode devices. Good reliability has been confirmed under the operating condition of 500 mW at 50 °C for the former type of devices and under the condition of 50 mW at 50 °C for the latter type of devices over 1000 h. These results indicate that molecular beam epitaxy is capable of making reliable high power laser diodes.
Formation of boron nitride and boron carbide composite by nitrogen implantation at elevated temperature
Authors: Yu N. , Romero-Borja F. , Zhang Z. H. , Cui X. T. , Liu J. R. , Wood L. T. , Chu W. K. , Marton D. , Rabalais J. W. , Forster K. M. , Reeber R. R.
Published: July 2002

Boron carbide (B4C) is a wear resistant material with hardness slightly less than that of diamond. It has an excellent strength to weight ratio and relatively high toughness under controlled processing. These essential mechanical properties make B4C an ideal candidate for cutting tool and bearing applications. We will demonstrate that hexagonal boron nitride (h-BN), a good solid lubricant, can be formed on B4C surfaces through high temperature (850 °C) nitrogen ion implantation. The formation of composite B4C and h-BN on the B4C surface can potentially reduce surface friction coefficients, making the material more attractive for tribological applications.
Measurement of parametric interactions in YBa2Cu3O7−x step edge junctions
Authors: Kain Aron Z. , Fetterman H. R.
Published: July 2002

We have fabricated and tested series arrays of YBa2Cu3O7−x (YBCO) step edge junctions for four photon parametric effects at 10 GHz. The series array of 25 junctions shows a 10 dB increase in reflected signal power as the pump power is increased at 10 K. At 50 K the reflected signal power shows a 3 dB increase. The reflected power at the characteristic idler frequency of 2ωp−ωs suggests four photon parametric interaction. In addition, an anomalous gain saturation effect is experimentally observed whereby the reflected signal power maintains a constant increased value even as the reflected idler power decreases.
Oxygen poisoning of diamond film growth
Authors: Howard William N. , Spear Karl E. , Frenklach Michael
Published: July 2002

Diamond films were deposited by a cyclic growth-etch process for up to 72 h. Initial growth rates are typical for the deposition of quality diamond films by continuous process chemical vapor deposition, however, they show a distinct decline as growth progresses. The films show a crystalline faceting characteristic of good quality diamond, but the intensity of the 1332 cm−1 diamond Raman band decreases after 10 h of growth, with a loss of all characteristic carbon Raman bands at 72 h of growth. The present cycling experiments differ from typical continuous diamond deposition processes in that the gas phase composition during the etching cycle is significantly richer in OH, O, and H. Oxygen is proposed to poison the growing surface by forming strongly chemisorbed sites which are trapped in the growing film. Defective carbon deposited above the trapped oxygen etches rapidly in subsequent cycles, and the buildup of such trapped oxygen defects may account for the observed decline in growth rate and quality.
Optical control of microwaves with semiconductor n-i-p-i structures
Authors: Kost Alan , West Linda , Hasenberg T. C. , White Jeffrey O. , Matloubian Mehran , Valley George C.
Published: July 2002

We control the microwave transmission of a GaAs n-i-p-i structure by illuminating it with a cw argon ion laser. Tests in a broadband microwave modulator wave spectrometer show that an optical intensity of 800 mW/cm2 produces a 50% change in transmission for microwaves between 10 and 50 GHz.
Realization of nearly two-dimensional growth mode for AlP on Si(100) substrate by a low temperature migration enhanced epitaxy
Authors: Maruyama H. , Pak K. , Sakakibara K. , Yonezu H.
Published: July 2002

AlP layers were successfully grown on Si(100) substrates with a nearly two-dimensional growth mode using a low temperature migration enhanced epitaxy. The reflection high-energy electron diffraction intensity oscillations were observed at the initial growth stage although a three-dimensional mode occurred at all times in the molecular beam epitaxy growth. The Auger electron spectroscopy measurement also showed that the nearly two-dimensional growth mode proceeded from the start of the AlP growth.
Electron intersubband absorption in Ge/Si1−xGex quantum-well structures grown on Si (001) substrate
Authors: Lee Chanho , Wang K. L.
Published: July 2002

Strong electron intersubband infrared absorption is observed for Sb δ-doped Ge/Si1−xGex multiple-quantum-well structures grown on Si (001) substrates. The intersubband absorption occurs in the Ge wells and is shown to be allowed for the optical field components both perpendicular and parallel to the quantum wells. The latter is due to the tilted ellipsoids of constant energy surfaces. An absorption coefficient of 15 000 cm−1 is measured by a Fourier transform infrared spectrometer using a waveguide structure with ten internal reflections and absorption peaks ranging from 5 to 10 μm are observed. The peak transition energy is shown to be tunable by changing the Ge composition in Si1−xGex barriers and/or the doping concentration in the Ge quantum wells.
Optical second-harmonic reflection from polycrystalline silicon and its relation to grain boundaries
Authors: Hua Y. M. , Hu C. , Li G. P.
Published: July 2002

Grain boundary contributions to optical second-harmonic generation give rise to an unusually high reflected second-harmonic intensity from polycrystalline silicon. At the grain boundaries, the dangling bonds affect the second order nonlinear susceptibility via the electric dipole contribution. The second-harmonic signal dependence on dangling bonds passivation by hydrogen is experimentally observed to support the grain boundary model.
Single-electron Coulomb exclusion on the atomic level
Authors: Averin D. V. , Register L. F. , Likharev K. K. , Hess K.
Published: July 2002

The possibility of processing digital information coded by single electrons on the atomic scale is discussed by analyzing the dynamics of one and two electrons within a simple model structure. Specifically, the probability of passage of an electron within a chain of atomic sites through a potential well, either empty or already occupied by another electron, is investigated both analytically and numerically. It is demonstrated that quantum effects can significantly decrease the reliability of the control that one electron has over the propagation of another. For the structure considered, a few tens of atomic sites and a specific choice of the potential well depth are necessary for reliable control.
Mode-mixing in an x-ray thin-film waveguide
Authors: Feng Y. P. , Deckman H. W. , Sinha S. K.
Published: July 2002

Mode-mixing in a thin-film x-ray waveguide with 4–6 Å interfacial roughness was analyzed using a formalism based on the coupled power theory for optical waveguides. The mode mixing was found to occur between nearest-neighbor modes with a uniform probability of ∼1.1% per bounce. The small mixing probability and the nearest-neighbor selection rule are consistent with a mixing mechanism arising from diffuse scattering, which at subcritical angles of incidence displays dramatically different behavior in x-ray waveguides than in optical counterparts.
Large normal resistance and THz electromagnetic-wave response in YBaCuO step-edge microbridge Josephson junction
Authors: Fukumoto Yoshito , Hayashi Seiji , Ogawa Rikuo , Kawate Yoshio
Published: July 2002

A YBaCuO Josephson junction with a large normal resistance (R) was fabricated and characterized. The junction exhibited an extremely sharp transition on the current-voltage curve with R=10.8 Ω and IcR=1.8 mV at 15 K. The temperature dependence of critical current (Ic) of the junction was Ic∝(1−T/Tc), while another junction with a smaller R (0.57 Ω) showed a dependence of Ic∝(1−T/Tc)2. The difference can be explained by a picture of a grain boundary junction as a parallel array of superconductor-normal-superconductor and superconductor-insulator-superconductor elements. From the results of 110 GHz mixing experiments, it was shown that the present junction could be operative for electromagnetic waves over 2 THz.
Effect of zinc impurity-induced disordering on the refractive index of GaAs/AlGaAs multiquantum wells
Authors: Han Sang-Kook , Sinha Sanjai , Ramaswamy Ramu V.
Published: July 2002

We report on the variation of the refractive index of a GaAs/AlGaAs multiquantum well of well width 6.5 nm and barrier width 19 nm, introduced by zinc impurity-induced disordering. We employ a structure consisting of several uncoupled, multiquantum well ridge waveguides with tapered disordering across the transverse direction. The refractive index changes have been deduced as a function of the interdiffusion length of Ga/Al by the use of an interference technique. We measured a maximum index change of 0.083 and 0.062 for significant disordering (Ld=6.6 nm) at 35 and 100 meV below the band edge of the undisordered multiquantum well, respectively.
A novel surface emitting GaAs/AlGaAs laser diode beam steering device based on surface mode emission
Authors: Köck A. , Gmachl C. , Gornik E. , Rosenberger M. , Thanner C. , Korte L.
Published: July 2002

We present a novel surface-emitting GaAs/AlGaAs laser diode beam steering device, which is based on a surface mode emission process. The coupling of the laser mode to a surface mode results in surface emission with a beam divergence of 0.4°, which is steerable at a rate of dα/dλ=−0.245°/nm by a tuning of the laser emission wavelength. The continuous control of the surface mode dispersion by external parameters allows a definite adjustment of the emission angle. In addition, the feedback of the surface mode to the laser mode provides a kind of single mode operation.
Experimental and theoretical study of the facet phase influence on the wavelength shift in InGaAs/InAlGaAs quantum well distributed feedback lasers
Authors: Hillmer H. , Hansmann S. , Walter H. , Burkhard H.
Published: July 2002

Physical laser parameters such as differential gain and differential refractive index are determined for InGaAs/InAlGaAs quantum well structures by comparing experimental results of different lasers with theoretical data from transfer matrix model calculations. By using the determined parameter set, the wavelength shift with current λ(I) is found to depend strongly in shape and magnitude on the end facet phases. Within one order of magnitude we found weak and strong variations related to the variation of the axial nonuniformity of the carrier and photon densities with current.
Electrical and optical properties of selectively doped Al0.25Ga0.75As/InyGa1−yAs (0.25≤y≤0.45) pseudomorphic heterostructures grown by molecular-beam epitaxy
Authors: Kudo Makoto , Mishima Tomoyoshi , Washima Mineo
Published: July 2002

Electrical and optical properties of highly strained selectively doped Al0.25Ga0.75As/InyGa1−yAs (0.25≤y≤0.45) pseudomorphic heterostructures grown by molecular-beam epitaxy are investigated. At a low growth temperature of 400 °C, the In mole fraction exceeds than 0.30 without degrading crystalline quality. The maximum mobility and sheet electron concentration at room temperature reach 6560 cm2/(V s) (y=0.34) and 2.94×1012 cm−2 (y=0.425), respectively. Photoluminescence measurements confirm the In mole fraction. This work suggests that InyGa1−yAs channels (y≳0.3) grown at 400 °C improve the performance of high-electron-mobility transistors.
Fluctuating deep-level trap occupancy model for Hooge’s 1/f noise parameter for semiconductor resistors
Authors: Folkes Patrick A.
Published: July 2002

A theoretical expression for Hooge’s 1/f noise parameter α, for a Schottky barrier field-effect transistor, which has been biased at a small drain-source voltage (a gate-controlled semiconductor resistor), has been derived. The theory is based on the fluctuating occupancy of deep level traps in the depletion region. The theory explains the large variations in the observed values of Hooge’s parameter since the derived expression shows that α varies approximately as n−7/2, where n is the electron density, and that α is sensitive to the trap concentration, the gate (or semiconductor surface) potential, the thickness of the semiconductor conducting layer, and the low-field electron mobility-depletion depth profile. Detailed experimental characterization of a semiconductor resistor has been carried out resulting in the accurate determination of α over a range of the applied gate voltage, Vg. We obtain excellent agreement between the theoretical and experimental dependence of α on Vg.
Oxygen control of dc-sputtered Bi2Sr2Ca1Cu2O8+δ films
Authors: Auge Jürgen , Rüdiger Ulrich , Frank Hartmut , Roskos Hartmut G. , Güntherodt Gernot , Kurz Heinrich
Published: July 2002

We report the preparation of Tc-optimized Bi2Sr2Ca1Cu2O8+δ thin films on SrTiO3 substrates using a planar dc-sputtering method. The oxygen content of these films is adjusted in situ by controlling the oxygen flow during sputtering. The oxygen content can be varied continuously from the overdoped state (Tc=72 K) to the condition with optimum oxygen content (Tc=88 K), and further, to the underdoped state (Tc=76 K). The oxygen content is determined by x-ray measurements of the c-axis lattice parameter.
Anomalous photoresponse of thick bismuth films to pulsed laser excitation
Authors: de Sande J. C. G. , Sánchez Balmaseda M. , Guerra Pérez J. M.
Published: July 2002

Current-biased 4.3-μm Bi films give an anomalous photoresponse when they are illuminated with 20-ns 1.064-μm laser pulses. The films resistivity decreases during irradiation. This observation excludes a simple bolometric process as a cause for the induced transients and supports the prediction of a previously reported model which required the optical pumping of carriers into a metastable band.
Observation of bias-induced resonant tunneling peak splitting in a quantum dot
Authors: Wang Y. , Chou S. Y.
Published: July 2002

We have observed that, in zero magnetic field, a dc bias across a lateral confined quantum dot (QD) splits each resonant peak in the differential conductance versus the gate voltage measurement into two. The splitting is nearly linear with the applied bias VD. Temperature-dependence study indicates that the corresponding energy separation between the two splitting peaks is close to eVD. A model is proposed that explains this splitting in terms of the bias-induced shifting of energy levels in the QD and the splitting of the Fermi level. Using our model, the bias-induced energy level shift in the QD can be calculated.
Photoluminescence spectrum redshifting of porous silicon by a polymeric carbon layer
Authors: Teschke O. , Galembeck F. , Gonçalves M. C. , Davanzo C. U.
Published: July 2002

Photoluminescence of porous silicon at room temperature shifts to a larger wavelength in low-resistivity Si samples (0.006 Ω cm) when compared to the one emitted by high resistivity samples (0.4 Ω cm). This shift is associated with a coating of hydrocarbon over the porous silicon structure. The hydrocarbon coating was identified by electron energy loss spectroscopy imaging together with infrared spectroscopy.
Pressure dependence of the band gaps in Si quantum wires
Authors: Yeh Chin-Yu , Zhang S. B. , Zunger Alex
Published: July 2002

The pressure coefficients a of interband transitions in (001) silicon wires are calculated using a plane-wave basis and carefully fitted empirical pseudopotentials. We find purely red shifts (a<0). Their magnitudes, as well as changes with wire sizes can be interpreted in terms of the ‘‘truncated crystal model’’ which describes the wire conduction bands as linear combination of the lowest bulk conduction bands along the Γ-X line.
Importance of collector doping in the design of AlInAs/GaInAs/InP double heterojunction bipolar transistors
Authors: Hafizi M. , Liu T. , Stanchina W. E. , Rensch D. B. , Lui M. , Brown Y. K.
Published: July 2002

AlInAs/GaInAs/InP double heterojunction bipolar transistors (DHBTs) have been made with an InP collector thickness of 0.75 μm and collector dopings of 1.4, 2.4, and 3×1016 cm−3. It is shown that because of the conduction band potential barrier between the GaInAs base and the InP collector in DHBTs and particular velocity-field characteristics of InP, the dc and rf performance of the DHBT is very sensitive to the collector doping level. With a collector doping of 3×1016 cm−3 devices conducted a collector current density of 1×105 A/cm2 without gain compression and had a IC-VCE saturation voltage of about 2 V. Base-collector and collector-emitter breakdown voltages were 22 and 14.5 V, respectively, and fT and fmax were in the range of 65–70 GHz.
Millisecond time-resolved reflectance difference measurements of GaAs grown by short-pulse supersonic nozzle beam epitaxy
Authors: Cui Jie , Zhang Suian , Tanaka Akihiko , Aoyagi Yoshinobu
Published: July 2002

We report the millisecond time-resolved reflectance difference (RD) measurements during short-pulse supersonic nozzle beam epitaxy of GaAs using trimethylgallium (TMG) and arsine (AsH3). A rapid rise of RD signal upon the injection of TMG short pulse was observed, and was assigned due to the density change of As dimers on the growing surface. With changes of the TMG pulse width and the substrate temperature, the corresponding changes of the rise time of the RD signal were observed. It is concluded that the rise in the RD signal is related to the As dimer annihilation caused by TMG decomposition, and As dimer formation. Our results also show that the growth amount under monolayer is proportional to the TMG molecular population in the TMG pulse.
Optimization of the surface morphology of magnetron-sputtered Y1Ba2Cu3O7−x films
Authors: Auge Jürgen , Jansen Margit , Roskos Hartmut G. , Kurz Heinrich
Published: July 2002

We demonstrate that the surface morphology of 20–200-nm-thick magnetron-sputtered Y1Ba2Cu3O7 films can be optimized by careful control of the plasma current. The optimization can be performed at different substrate temperatures allowing us to maximize the transition temperature Tc and the homogeneity of the films independently from the optimization of the surface morphology. This sequence allows us to retain the characteristic high Tc values (Tc≳90 K, Jc≳106 A/cm2 at 77 K). To obtain very thin films (<40 nm) with similar superconducting properties, the deposition temperature has to be ramped during the sputter process.
Green and violet light generation in LiNbO3 optical superlattice through quasiphase matching
Authors: Lu Ya-lin , Mao Lun , Ming Nai-ben
Published: July 2002

Picosecond 531 nm green and 385 nm violet light generation through first-order and third-order quasiphase matching (QPM) has been performed in a LiNbO3 optical superlattice. The conversion efficiency is 11.4% and 1.6%, respectively. A comparison between theoretical analyses and experimental results of frequency doubling peak value and full width at half-maximum for both the first- and third-order QPM are given. Possible simultaneous generation of green and violet light in the crystal are predicted for constructing a compact two outputting wavelengths light source.
Role of hot electron base transport in abrupt emitter InP/Ga0.43In0.53As heterojunction bipolar transistors
Authors: Ritter Dan , Hamm R. A. , Feygenson A. , Smith P. R.
Published: July 2002

The high frequency performance of InP/Ga0.47In0.53As heterojunction bipolar transistors (HBTs) with a varying base thickness was measured. The diffusion constant of minority carrier electrons in the heavily doped base was found to be 105 cm2/s. It is demonstrated that the short base transit times in fast InP/Ga0.47In0.53As HBTs is mainly due to the high value of the diffusion constant of thermalized electrons. The contribution of hot electron ballistic transport is relatively small.
Band discontinuity of strained-layer GaInAs/GaInAsP heterostructures
Authors: Queisser I. , Härle V. , Dörnen A. , Scholz F.
Published: July 2002

We performed low temperature photoluminescence excitation and photocurrent measurements on tensile and compressively strained GaxIn1−xAs quantum-well layers grown on GaInAsP, which was lattice matched to the InP substrate. From these measurements the excitonic transitions in the unstrained and strained samples can be identified. We determine the effective masses in growth direction GaxIn1−xAs (0.3<xGa<0.6) and the band offsets of the GaxIn1−xAs/GaInAsP heterojunction (0.4<xGa<0.6).
Harmonic generation in ferroelectric liquid crystals: Phase matching loci
Authors: Arnett Kenneth E. , Velsko Stephan P. , Walba David M.
Published: July 2002

Ferroelectric liquid crystals (FLCs), a new class of organic nonlinear materials have a variety of interesting properties and potential applications. Using commercial FLCs and an FLC mixture specifically formulated for enhanced nonlinear optical properties, we studied the room-temperature global phase-matching properties for type I and type II frequency doubling of 1.06-μm radiation. Although the second-harmonic coefficients of the different FLC mixtures differ by as much as two orders of magnitude, the phase-matching loci are remarkably similar.
Wave propagation in periodic nonlinear dielectric superlattices
Authors: Hennig D. , Gabriel H. , Tsironis G. P. , Molina M.
Published: July 2002

We investigate wave propagation in a superlattice consistent of dielectric material with a nonlinear Kerr coefficient. We find gaps in the propagating properties of the medium that depend critically on the injected wave power. This property can be used for transmission of information.
Laser elemental mass analysis at large distances
Authors: De Young Russell J. , Situ Wen
Published: July 2002

A Nd:YAG laser is used to produce a plasma on targets of Al, Cu, Ge, Ag, and a lunar simulant. Ion energies for 1×109 W/cm2 were found to be between 550 and 900 eV. Some of these ions travel down a 11.1-m evacuated tube to an ion trap 1-m time-of-flight spectrometer producing a mass spectrum of a lunar simulant, demonstrating the ability to analyze targets at significant remote distances.
Mixing of Fe2O3 markers into amorphous and crystalline alumina
Authors: Cooper Elizabeth A. , Nastasi Michael
Published: July 2002

Thin markers of iron oxide embedded between sapphire and amorphous alumina were ion irradiated with Ar in a temperature range of −166 °C to 700 °C. The marker mixing was examined by Rutherford backscattering spectroscopy and found to have both a ballistic and a temperature dependent mixing regime with different levels of ballistic mixing and different temperature dependencies for the amorphous and crystalline matrices.
Measurement of composition in Hg1−xCdxTe epilayers
Authors: Liu Kun , Chu J. H. , Li Biao , Tang Dingyuan
Published: July 2002

A new model has been presented for evaluating the composition distribution in both the transverse (perpendicular to the direction along the depth) and longitudinal (along the depth) directions in HgCdTe epitaxy materials by fitting room temperature transmission spectroscopy data.
Strip-loaded semiconductor ring lasers employing multimode interference output couplers
Authors: Krauss T. , DeLaRue R. M. , Gontijo I. , Laybourn P. J. R. , Roberts J. S.
Published: July 2002

Strip-loaded semiconductor ring lasers were successfully fabricated in the GaAs/AlGaAs material system. The radius was 400 μm and a 2×2 3 dB multimode interference coupler 320 μm long was used to extract the output signal. Devices operated continuous wave at 140 mA threshold current with a differential quantum efficiency of 7% per output, which we believe is the highest value reported to date for lasers of this type.
Nonlinear optical characterization of new thermoset hydrosilation polymers
Authors: Gibbons W. M. , Grasso R. P. , O’Brien M. K. , Shannon P. J. , Sun S. T.
Published: July 2002

The second harmonic generation thermal stability of a new class of thermoset matrix for nonlinear optical (NLO) polymers based on the hydrosilation reaction of tetramethylcyclotetrasiloxane with chromophores possessing reactive carbon-carbon double bonds is presented. One such chromophore with double bonds of different reactivity toward hydrosilation that were covalently attached to two different sites on the NLO π system generated a nonlinear optical polymer with thermal stability in excess of 190 °C and a nonlinear optical coefficient of d31=3±1 pm/V.
717-mV open-circuit voltage silicon solar cells using hole-constrained surface passivation
Authors: Zhao J. , Wang A. , Aberle A. , Wenham S. R. , Green M. A.
Published: July 2002

A virtual saturation of the supply of holes leading to an injection level dependent reduction in surface recombination velocity has been shown to be responsible for the improved performance of recent high efficiency silicon solar cells. By fabricating test cells taking advantage of this and other recombination reduction mechanisms, improved open-circuit voltages of 717 mV have been independently confirmed for experimental silicon cells. These voltages correspond to saturation current densities of 25 fA/cm2 at 25 °C, also the lowest demonstrated for a silicon junction device. Further improvement in both voltage and cell efficiency is expected to result from this work.
Thermal velocity limits to diffusive electron transport in thin-base np+n GaAs bipolar transistors
Authors: Harmon E. S. , Melloch M. R. , Lundstrom M. S. , Cardone F.
Published: July 2002

We present experimental evidence that minority electron transport across a thin, quasineutral p+ GaAs region is limited by the thermal velocity of the electrons rather than by conventional diffusive transport. A set of GaAs homojunction np+n transistors with base widths of 4000, 2000, 1000, and 500 Å was fabricated and characterized. The diffusive model predicts that the dc collector current of the 500-Å base width transistors should be eight times larger than the collector current of transistors with a 4000-Å-wide base. The experimental results, however, show only a factor of ∼3.5 increase in collector current. The measured collector current versus base width characteristic agrees well with theoretical treatments of thin-base transport. These new results present evidence of quasiballistic electron transport in p+ GaAs and have important implications for GaAs transistor design.
Hall effect of metallic Langmuir–Blodgett films based on bisethylenedioxytetrathiafulvalene complex of decyltetracyanoquinodimethane
Authors: Takenaga Mitsuru , Abdulla Aniwar , Kasai Akinari , Nakamura Akira , Nakamura Takayoshi , Matsumoto Mutsuyoshi , Horiuchi Sachio , Yamochi Hideki , Saito Gunzi
Published: July 2002

The Hall effect of a metallic Langmuir–Blodgett film based on bisethylenedioxytetrathiafulvalene complex of decyltetracyanoquinodimethane has been investigated using a double ac Hall method. The polarity of the Hall coefficient is positive over the measuring temperature range. The carrier density is of the order of 1021 cm−3, almost independent of temperature, and the Hall mobility, of around 0.05 cm2 (V s)−1 at room temperature, is in a single activated process. The Hall results have been interpreted with an inhomogeneous structure model, and support that metallic domains are developed throughout the whole sample.
Nonlinear electron dynamics in a resonant tunneling diode: Langevin-quantum-dynamics simulations on a massively parallel computer
Authors: Nakano Aiichiro , Kalia Rajiv K. , Vashishta Priya
Published: July 2002

A quantum-dynamics (QD) simulation scheme is developed to study highly nonlinear electron dynamics far from equilibrium. The time-dependent density functional theory is combined with the Langevin equation to incorporate quantum effects, electron-electron interaction, and dissipation. We perform QD simulations on a massively parallel computer to study the many-electron dynamics in a resonant tunneling diode. The dynamic response of electrons in n+-doped layers on the femtosecond scale is found to have a profound influence on the current-voltage (I-V) characteristic. The resulting time-averaged I-V characteristics are in excellent agreement with experiments.
Analysis of strain and mosaicity in a short-period Si9Ge6 superlattice by x-ray diffraction
Authors: Koppensteiner E. , Hamberger P. , Bauer G. , Holy V. , Kasper E.
Published: July 2002

Triple axis x-ray diffractometry was employed for the structural characterization of a 100 period Si9Ge6 superlattice grown by molecular beam epitaxy on a thick step-graded SiGe alloy buffer. From the distribution of diffusely scattered intensity around reciprocal lattice points the correlation function of the deformation field due to structural defects has been calculated using kinematical theory of x-ray diffraction. From the extension of the correlation function it turns out that on the average the entire superlattice (0.2 μm thick) scatters coherently along growth direction, whereas laterally the coherently scattering regions are extended only over about 40 nm.
Red photoluminescence and optical absorption in hydrogen-treated GeO2-SiO2 sol-gel-derived planar waveguides
Authors: Simmons K. D. , Potter B. G. , Stegeman G. I.
Published: July 2002

We report the effects of post-deposition, reducing atmosphere heat treatment on the optical absorption, and photoluminescence response of 45 GeO2-55 SiO2 thin films produced using the sol-gel process. With increasing heat treatment, a linear increase in the 242 nm absorption peak (associated with oxygen-deficient germania centers) is found to contrast a reduction in the intensity of red photoluminescence (attributed to hydrogen centers in the glass structure). These results are discussed in terms of the photosensitive response of these materials.
Large differences in Ti thermal diffusion caused domain inversion between undoped and MgO-doped LiNbO3
Authors: Xu C. Q. , Okayama H. , Kawahara M.
Published: July 2002

The periodic modulation of domain polarizations by Ti thermal diffusion on the +c face of LiNbO3 with and without MgO doping was studied systematically. It was shown that the depth of the inverted domain is quite different for these two substrates. Under the same fabrication conditions, the depth of domain inversion in the MgO-doped substrate is less than one-tenth that of the undoped substrate. This large difference can be explained by the presence of MgO in LiNbO3, which decreases the Ti diffusion constant and increases the minimum Ti concentration required for domain inversion.
Asymmetric dark current in quantum well infrared photodetectors
Authors: Tsai K. L. , Lee C. P. , Chang K. H. , Liu D. C. , Chen H. R. , Tsang J. S.
Published: July 2002

Asymmetric dark current versus voltage characteristics in quantum well infrared photodetectors have been studied. A model based on asymmetrical potential barriers was proposed. The asymmetrical potential barriers, which are most likely due to the accumulation of oxygen impurities at one of the interfaces, cause the asymmetrical I-V characteristics. The height of the potential spike is found to increase with the Al content in the AlGaAs barriers. Calculations based on our model agree well with experimental results.
Excitonic properties of ZnSe/ZnSeS superlattices
Authors: Cingolani R. , Lomascolo M. , Lovergine N. , Dabbicco M. , Ferrara M. , Suemune I.
Published: July 2002

We report an optical investigation of the excitons in ZnSe/ZnSeS superlattices of well widths ranging between 2 and 15 nm. An almost constant exciton binding energy is found. The exciton confinement is found to be dominated by the hole quantization, consistent with the expectation of negligible conduction-band discontinuity in these heterostructures. The effect of strain has been included to properly reproduce the well width dependence of the light-hole energies. Finally strong evidence of hot exciton photogeneration is obtained from the oscillatory behavior of the photoluminescence excitation spectra. This is consistent with the strong exciton-phonon coupling deduced from the temperature dependence of the excitonic linewidth measured by transmission experiments.
Laser-induced sputtered neutral mass spectrometry study of arsenic concentration profiles in a polycrystalline silicon/single-crystal silicon system
Authors: Higashi Yasuhiro , Maruo Tetsuya , Homma Yoshikazu , Kodate Jun’ichi , Miyake Masayasu
Published: July 2002

Arsenic concentration profiles in a polycrystalline silicon/single-crystal silicon system were investigated by sputtered neutral mass spectrometry using a high-repetition-rate excimer laser. Beforehand, the arsenic profile in a SiO2/Si sample was measured to verify that this method can provide accurate profiles, unlike secondary ion mass spectrometry. The 300-nm polycrystalline silicon film was implanted with 5×1016 As ions cm−2 at 100 keV and then annealed at 850 °C for 30 min. The arsenic segregation at the polycrystalline silicon/single-crystal silicon interface was indisputably confirmed and the amount was accurately determined to be 2.2×1015 cm−2.
Resistance switching in indium phosphide using hydrogen passivation of acceptors
Authors: Balasubramanian Sathya , Kumar Vikram , Balasubramanian N. , Premachandran V.
Published: July 2002

This letter demonstrates the use of dopant passivation by hydrogen in a highly doped semiconductor, for resistance switching applications. The acceptor passivation by hydrogen was utilized to form a rectifying contact on InP which otherwise showed nonrectifying behavior due to high dopant concentration. A reverse bias annealing of the diodes converted the rectifying contact into a nonrectifying one whereas an anneal without bias left it unchanged. The attainment of selective conversion is explained in terms of the reactivation processes involved.
Competition between negative and positive photoconductivity in silicon planar-doped GaAs
Authors: de Oliveira A. G. , Ribeiro G. M. , Soares D. A. W. , Chacham H.
Published: July 2002

Photo-Hall free electron concentrations were measured on molecular beam epitaxy grown silicon planar-doped GaAs samples, with silicon nominal concentration ranging from 1.4×1012 to 8.8×1013 cm−2, as function of temperature. We found conclusive results showing competition between positive photoconductivity and negative persistent photoconductivity effects. At temperatures below a critical Tc, the negative photoconductivity effect is dominant, while above Tc the positive effect dominates. We also found some evidence that the positive effect is related to spatial charge separation and that the negative effect is related to the DX center.
Liquid crystal dyes with high solubility and large dielectric anisotropy
Authors: Wu Shin-Tson , Margerum J. David , Ho Mei-Sing , Fung Bing M.
Published: July 2002

Several new liquid crystal dyes were synthesized and their physical properties characterized. These dyes exhibit an excellent solubility in nematic liquid crystals, high birefringence, and huge dielectric anisotropy. High solubility results from their small enthalpy of fusion and relatively low melting point, high birefringence from their long molecular conjugation, and huge dielectric anisotropy from their large dipole moment. Potential use of these dyes in infrared and millimeter wave liquid crystal modulators are emphasized.