bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of high-peak pulse beam of hydrogen plasma for use in short-pulsed chemical beam epitaxy
Authors: Ozasa Kazunari , Aoyagi Yoshinobu
Published: July 2002

We present and discuss the generation of high-peak pulse beam of hydrogen plasma, which has a high potential for use in semiconductor crystal growth. The scheme proposed in the present work is the pulse injection of hydrogen gas to a compact electron cyclotron resonance plasma gun, in order to achieve a relatively high concentration of hydrogen in a small microwave discharge cavity and the increase of plasma intensity for a short time after stopping the hydrogen injection. By this scheme, plasma pulses having 170-ms width and peak intensity 50–600 times higher than the case of continuous hydrogen flow can be generated. The total ion current obtained was higher as well, since plasma intensity was found to increase superlinearly with hydrogen supply. The application of the high-peak hydrogen plasma pulses to crystal growth was briefly examined in short-pulsed chemical beam epitaxy of AlAs.
Internal photoemission studies of artificial band discontinuities at buried GaAs(100)/GaAs(100) homojunctions
Authors: dell’Orto Tiziana , Almeida J. , Coluzza C. , Baldereschi A. , Margaritondo G. , Cantile M. , Yildirim S. , Sorba L. , Franciosi A.
Published: July 2002

Internal photoemission phototransport measurements revealed 0.27±0.04 eV conduction- and valence-band discontinuities induced by a Si intralayer at p-GaAs(100)/n-GaAs(100) homojunctions. The interface dipole originating from the heterovalent character of the Si—GaAs bonds raises the bands of the GaAs overlayer above that of the GaAs substrate.
Photolithographic patterning of protective arsenic capping on molecular beam epitaxy grown AlxGa1−xAs(001)
Authors: Husby H. , Grepstad J. K. , Bernstein R. W.
Published: July 2002

Patterning of an arsenic capping layer deposited in situ on AlxGa1−xAs(100) epilayer surfaces is demonstrated, using standard photolithography and subsequent etching in a hydrogen radical (H*) beam. These data suggest that the protection offered by such capping during ambient storage, may be exploited for molecular beam epitaxy overgrowth and device processing purposes. The technique needs further refinement, however, as trace amounts of surface oxide and carbon impurities were found on the H* etched surfaces by core-level photoelectron spectroscopy. Moreover, the scanning electron micrographs unveil residues of the As cap along the photomask edges, after completed etching.
Low temperature molecular beam epitaxial growth of DyBaCuO superconducting thin films
Authors: Mamutin V. V. , Kartenko N. F. , Goloschapov S. I. , Tretjakov V. V. , Kop’ev P. S.
Published: July 2002

Superconducting DyBa2Cu3O6.7 (orthorhombic I phase) thin films were grown in situ on NdGaO3 (001) and (100) substrates at 400–440 °C by molecular beam epitaxy method. The c-axis lattice constant and the critical temperature were c=11.72 Å and Tc∼70 K, respectively, and they became c=11.70 Å and Tc=88 K after annealing in O2 at 400 °C. Due to the slow deposition rates in the range of 0.01–0.10 Å/s, only films with the c-axis perpendicular to the substrate surface were grown in situ in spite of the low temperature growth conditions. The full width at half-maximum of the (005) x-ray diffraction peak rocking curve was ∼0.35°, indicating together with the reflection high-energy electron diffraction that the in situ grown films were high quality epitaxial single crystals.
Photoluminescence properties of Si1−xGexSi disordered superlattices
Authors: Wakahara Akihiro , Hasegawa Toshimichi , Kuramoto Kyosuke , Vong Kam Koc , Sasaki Akio
Published: July 2002

Si1−xGex/Si disordered superlattices (d-SLs) are fabricated by solid source molecular beam epitaxy. Photoluminescence properties of Si1−xGex/Si d-SL are studied at low temperature by comparing with a conventional ordered superlattice (o-SL) where the macroscopic chemical composition is same as that of the d-SL. Strong intensity of the PL peak compared with the o-SL is observed in the d-SL. Carrier confinement rather than localization effects by artificially introduced disordering enhances the luminescence process in SiGe strained layers.
Photon-stimulated desorption of H− from a BaO surface
Authors: Baker D. H. , Champion R. L. , Doverspike L. D. , Wang Yicheng
Published: July 2002

Photon-stimulated desorption of H− ions has been observed from a BaO surface for photon energies in the range of 3–5 eV, with a yield that increases sharply for energies above the threshold at 3 eV. A possible explanation is that a chemisorbed H atom captures a photoemitted electron and desorbs as H− via the Menzel–Gomer–Redhead mechanism.
Scaling laws for gain-guided vertical cavity lasers with distributed Bragg reflectors
Authors: Babić Dubravko I. , Ram Rajeev J. , Bowers John E. , Tan Michael , Yang Long
Published: July 2002

General scaling laws for gain-guided vertical cavity lasers with distributed Bragg reflectors are introduced. The validity of these laws is verified using a self-consistent calculation of transverse modes and propagation constants for two-dimensional laser cavities. The definition of Fresnel number is generalized to cavities with distributed mirrors. We show that all of the resonator parameters—the threshold gain, the frequency spectrum, and the transverse mode patterns scale with the ratio between the Fresnel number and the cold cavity finesse.
Integrated micromachined magnetic field sensor with on-chip support circuitry
Authors: Paranjape M. , Filanovsky I. , Ristic Lj.
Published: July 2002

This letter presents an integrated magnetic field sensor that has been fabricated in a standard complementary metal-oxide semiconductor process. Along with the sensor, on-chip circuitry has been realized to amplify the resulting Hall voltage signal. Furthermore, to increase device sensitivity, the sensor has been subjected to a post-process etching step. The integrated sensor exhibits a ten times higher output signal compared with the output signal of the sensor alone.
Electron acceleration resonant with sheath motion in a low-pressure radio frequency discharge
Authors: Okuno Yoshihiro , Ohtsu Yasunori , Fujita Hiroharu
Published: July 2002

A new electron acceleration method in low-pressure radio-frequency (rf) discharges, leading to high density plasmas, is proposed. Electrons are resonantly accelerated by multiple interactions with a moving rf sheath under a specific magnetic flux density which satisfies the condition that twice the electron cyclotron frequency is equal to the rf driving frequency. Experimental evidence is presented. This technique might be useful for the generation of low-pressure high density rf plasmas.
Anomalous diffusion of isoelectronic antimony implant induced defects in GaAs-AlGaAs multiquantum well structures
Authors: Rao E. V. K. , Krauz Ph. , Thibierge H. , Azoulay R. , Vieu C.
Published: July 2002

We present here evidence on the deep diffusion of isoelectronic Sb implant induced defects in thick GaAs-AlGaAs multiquantum well structures (MQW) to depths as far as ∼30 times the implant projected range (Rp). This observation has been confirmed by performing low temperature photoluminescence depth scanning measurements and cross-sectional transmission electron microscopy (XTEM) analysis on room temperature Sb implanted thick MQW samples. An explanation based on the isoelectronic nature of Sb and its substitution on As site (SbAs) has been proposed to understand the anomalous diffusion of defects during implant and their contribution to Al/Ga disordering during post-implant annealing.
Radiatively controlled lifetimes in AlxGa1−xAs grown by metalorganic vapor phase epitaxy
Authors: Thomeer R. A. J. , Hageman P. R. , Giling L. J.
Published: July 2002

We report long minority charge carrier lifetimes in AlxGa1−xAs/AlyGa1−yAs x<y) double heterostructures grown by metalorganic vapor phase epitaxy. The lifetime (τbulk=8.8 μs) is found to be controlled by radiative processes in samples with aluminum concentrations of x=0.10 for the active regime and y=0.20 for the cladding layers; an extremely low interface recombination velocity of S≂6.5 cm/s is found. At higher aluminum concentrations both the bulk and interface recombination rate increase rapidly.
Experimental study of p layers in ‘‘tunnel’’ junctions for high efficiency amorphous silicon alloy multijunction solar cells and modules
Authors: Banerjee A. , Yang J. , Glatfelter T. , Hoffman K. , Guha S.
Published: July 2002

The role of the p layer in the formation of good quality ‘‘tunnel’’ junctions and its dependence on the attainment of high efficiency hydrogenated amorphous silicon alloy (a-Si:H) multijunction cells has been investigated. A new technique, namely, the evaluation of the current-voltage characteristics of the NIPN structure consisting of a single-junction n-i-p cell with an overlying doped n layer, has been developed for the determination of losses at the ‘‘tunnel’’ junction. Using an optimized p layer, an initial conversion efficiency of 11.4% has been obtained on a double junction a-Si:H module of aperture area ∼900 cm2.
Monolayer thickness control of InxGa1−xAs/GaAs quantum wells grown by metalorganic molecular beam epitaxy
Authors: Courboulès B. , Massies J. , Deparis C. , Grandjean N. , Leymarie J. , Monier C. , Vasson A. M. , Vasson A.
Published: July 2002

High strained InxGa1−xAs/GaAs quantum well (QW) structures have been grown by metalorganic molecular beam epitaxy (MOMBE) with the aim of investigating the capability of this epitaxial growth method in terms of thickness control. Emission lines from QWs with thicknesses differing by 1 monolayer (ML) are well resolved by low temperature photoluminescence. It is thus demonstrated that MOMBE allows a thickness control with 1 ML precision.
Uniaxial stress dependence of exciton emission from seeded physical vapor transport ZnSe
Authors: Cotal H. L. , Maxson J. B. , McKeever S. W. S. , Cantwell E.
Published: July 2002

Uniaxial stress dependence of photoluminescence has been employed to study the exciton emission in seeded physical vapor transport ZnSe. By examining the stress behavior of the photoluminescence line Ix , it is suggested that this line is due to recombination of a deep donor-bound exciton. From measurements of the π- and σ-polarized luminescence spectra the heavy-hole and light-hole components of the exciton emissions were followed as a function of applied stress. From these data the linear hydrostatic and shear deformation potential constants were calculated to be a=−5.1 and b=−0.74 eV, respectively.
Quantum confinement and strain effects on the lateral mode stability of an unstable resonator semiconductor laser
Authors: Ru P. , Chow W. W. , Moloney J. V. , Koch S. W.
Published: July 2002

The gain medium effects on the lateral mode stability of an unstable resonator semiconductor laser are investigated. A physical optics laser model based on a many-body semiclassical laser theory of the gain medium is used. The consistent treatment of bulk, quantum well, and strained quantum well structures shows that quantum confinement or strain can result in single lateral mode operation over significantly wider ranges of unstable resonator configurations and gain medium excitation.
All-fiber source of 100-nJ subpicosecond pulses
Authors: Fermann M. E. , Galvanauskas A. , Harter D.
Published: July 2002

Chirped pulse amplification of a stretched pulse passively mode-locked erbium fiber laser is demonstrated. The two-stage all-fiber amplifier system delivers 800-fs pulses with pulse energies up to 100 nJ at a repetition rate of 200 kHz.
Modified KTiOPO4 crystals for noncritical phase matching applications
Authors: Loiacono G. M. , Stolzenberger R. A. , Loiacono D. N.
Published: July 2002

Crystals of K1−xNaxTiOPO4 were grown by the high temperature solution method and their optical and electrical properties evaluated. In the composition range 18<x<47 mol %, noncritical phase matching of 1064 nm light should be achievable along the crystallographic [100]. Substitution of Na for K also shifts the short wavelength cutoff from 994 to 981 nm. This is the shortest wavelength to be type II frequency doubled by a member of the KTiOPO4 family of materials.
Luminescent characteristics of a novel porous silicon structure formed in a nonaqueous electrolyte
Authors: Propst Eric K. , Rieger Melissa M. , Vogt Kirkland W. , Kohl Paul A.
Published: July 2002

Novel porous silicon layers which photoluminesce and electroluminesce in an aqueous solution have been formed by oxidation of (100) silicon in anhydrous acetonitrile-HF solutions. The novel porous structures consisted of large, noninterconnected pores, 1–2 μm diam, which grew normal to the surface. The pores were spaced 2–3 μm apart, and the length, which could be over 150 μm, was dependent on etch time and current density. Microporous structures (i.e., <100 nm), often associated with luminescence from porous silicon, were not detected by TEM, SEM, or infrared examination. The porous surface was hydride terminated, which was critical to the luminescence process. Since water and oxygen were not present during the formation of the porous structure and the pores were relatively large, neither silicon-oxygen species (e.g., siloxenes) nor quantum size structures, appeared necessary for the generation visible luminescence from porous silicon.
Dense random packing formation of gold cluster-based film characterized by scanning tunneling microscope
Authors: Ma J. X. , Han M. , Zhang H. Q. , Gong Y. C. , Wang G. H.
Published: July 2002

Gold films prepared by neutral gold cluster deposition on the HF-treated Si(111) surface in a static argon atmosphere of 50 Pa have been characterized by scanning tunneling microscope in air at room temperature. Our studies demonstrate that the gold film is just the stacking up of clusters formed in the static argon atmosphere and shows dense random packing formation of clusters. The structure of the gold cluster-based nanophase film is very compact and stable.
Growth of high quality Ge films on Si(111) using Sb as surfactant
Authors: Larsson Mats I. , Ni Wei-Xin , Joelsson Kenneth , Hansson Göran V.
Published: July 2002

High quality, completely relaxed Ge films have been grown on Si(111) using Sb as surfactant at the initial stage of growth. After desorbing the surface Sb layer, cusplike reflection high-energy electron diffraction intensity oscillations indicated excellent Ge layer-by-layer epitaxy. High resolution x-ray diffraction analysis showed a very high crystalline quality and well resolved thickness fringes consistent with a flat relaxed Ge layer. Chemical preferential etching experiments revealed a defect density of down to ∼3×104 cm−2.
Application of limited reaction processing to atomic layer epitaxy: Growth of cadmium telluride using diisopropyl telluride and dimethyl cadmium
Authors: Emerson Robert M. , Hoyt Judy L. , Gibbons James F.
Published: July 2002

A new thin film growth technique is introduced which combines the advantages of atomic layer epitaxy and limited reaction processing. Using this technique, the temperature of each portion of the atomic layer growth cycle may be individually optimized. In this work, thin films of cadmium telluride are grown using diisopropyl telluride and dimethyl cadmium. Experimental results show that isothermal atomic layer epitaxy is not possible using these two reactants, as the self-limited temperature regimes for the cadmium and tellurium deposition cycles differ by approximately 150 °C. Layer-by-layer, self-limited growth is demonstrated using the new growth technique, using temperature ranges of 150 to 175 °C and 300 to 320 °C for the cadmium and tellurium deposition cycles, respectively.
Synthesis of dislocation free Siy(SnxC1−x)1−y alloys by molecular beam deposition and solid phase epitaxy
Authors: He Gang , Savellano Mark D. , Atwater Harry A.
Published: July 2002

Synthesis of strain-compensated single-crystal Siy(SnxC1−x)1−y alloy films on Si (100) substrates has been achieved with compositions of Sn and C greatly exceeding their normal equilibrium solubility in Si. Amorphous SiSnC alloys were deposited by molecular beam deposition from solid sources followed by thermal annealing. In situ monitoring of crystallization was done using time-resolved reflectivity. Solid phase epitaxy for Si0.98Sn0.01C0.01 occurs at a rate about 20 times slower than that of pure Si. Compositional and structural analysis done using Rutherford backscattering, electron microprobe, ion channeling, x-ray diffraction, and transmission electron microscopy are consistent with substitutional C and Sn, and with defect-free single crystal films.
Granularity and superconductor-insulator transition in electrochemically anodized Al films
Authors: Wu Wenhao , Adams P. W. , McCarley R. L. , Dunaway D. J.
Published: July 2002

We report the use of an electrochemical anodization process to fabricate ultrathin granular Al films at room temperature. These films display a superconductor-insulator transition of the same character as those found in quench-condensed granular films. The granularity of the films and the unusually narrow distribution of the grain sizes are shown by scanning force microscopy.
Effect of free carriers on the luminescence efficiency of InP:Er
Authors: Wang X. Z. , Wessels B. W.
Published: July 2002

A systematic study of the effect of free carriers on the luminescence efficiency of Er-doped InP is reported. As free carrier concentration increases from 1013 to 1017 cm−3, an increase in the Er3+-related emission intensity is observed. This increase is attributed to the enhanced probability of formation of bound excitons at the rare earth centers. For carrier concentrations of greater than 3×1017 up to 1020 cm−3, the luminescence intensity is only weakly quenched. Free carrier Auger processes play a limited role in determining the Er3+ luminescence efficiency.
Chemical beam epitaxy growth of 1.3 μm InGaAsP/InP double heterostructure lasers using all gas source doping
Authors: Rao T. Sudersena , Lacelle C. , Rolfe S. J. , Dion M. , Thompson J. , Marshall P. , Chow-Chong P. , Ross D. , Davies M. , Roth A. P.
Published: July 2002

Low threshold 1.3 μm InGaAsP/InP double heterostructure lasers were fabricated using all gas source chemical beam epitaxy (CBE). Gas source doping of n- and p-type InP and InGaAs was successfully achieved using tetraethyltin and diethylzinc. The minimum threshold current density (Jth) for a 1800 μm cavity length laser was 680 A/cm−2. This is lowest Jth value reported for CBE grown double heterostructure lasers at 1.3 μm. These lasers exhibited an internal quantum efficiency (ηi) and internal loss (αi) of 51% and 16 cm−1, respectively. The temperature dependence of the threshold current is described by a single exponential T0 of 51 K.
Selenium-treated GaAs(001)-2×3 surface studied by scanning tunneling microscopy
Authors: Shigekawa Hidemi , Oigawa Haruhiro , Miyake Koji , Aiso Yoshiaki , Nannichi Yasuo , Hashizume Tomihiro , Sakurai Toshio
Published: July 2002

An Se-passivated GaAs(001) surface was found to be stabilized by 2×3 reconstruction, previously reported as an intermediate structure, under the condition of a low Se chemical potential. Ordered elliptical protrusions with ∼0.6-nm periodicity in the [110] direction were observed by scanning tunneling microscopy, the structure of which was in good agreement with a double-layered dimer model. A comprehensive model to explain the 2×3 structure together with the formation of a Ga2Se3-like structure with ordered 1/3 ML Ga vacancies was proposed.
High-speed characterization of p-i-n photodetectors by nonlinear photocurrent spectroscopy
Authors: Bender G. , Schneider H.
Published: July 2002

By analyzing the photocurrent nonlinearity, observed under excitation with two successive picosecond optical pulses, we investigate the carrier transport and electric field recovery in high-speed p-i-n photodetectors containing In0.2Ga0.8As/GaAs quantum wells in the intrinsic region. The nonlinearity originates from the distortion of the electric field by the free carriers generated by the leading pulse, which changes the absorption of the subsequent pulse. The nonlinear signal is resonantly enhanced by orders of magnitude at suitable excitation wavelengths due to excitonic resonances. For the recovery time of the electric field we find values less than 15 ps.
Nonlinear transient photovoltaic response in Al/C60/Au devices: Control of polarity with optical bias
Authors: Lee C. H. , Yu G. , Moses D. , Heeger A. J. , Srdanov V. I.
Published: July 2002

We report fast (nanosecond) transient photovoltaic response and steady-state photovoltage of rectifying Al/C60/Au sandwich devices. The transient photovoltage changes polarity at a critical light intensity, which can be varied and controlled by applying steady-state light as bias. This ability to change the polarity of the transient photovoltaic response and to control the intensity at which the polarity changes sign offers potential for use in applications in the area of fast nonlinear optoelectronic detectors.
Frequency modulation–continuous wave method to generate and detect sound beams at 35 GHz
Authors: Scheffold B. , Weis O.
Published: July 2002

We report on successful application of frequency modulation–continuous wave (FM-CW) technique in sound-echo experiments at microwave frequencies. As an electromagnetic source, a reflex klystron with only 100 mW CW power or even less is sufficient to produce outstanding spectral echo signals in the kHz frequency range using homodyne detection. In contrast to the common pulse-echo technique in the GHz range, there is no need of a high power source like a magnetron and no need of a separate local oscillator that is essential in heterodyne detection. The FM-CW technique seems to be a very promising method for sound experiments at still higher frequencies.
Multiple deep levels in metalorganic vapor phase epitaxy GaAs grown by controlled oxygen incorporation
Authors: Huang J. W. , Kuech T. F.
Published: July 2002

Oxygen intentionally introduced into GaAs, grown through the metalorganic vapor phase epitaxy process, is shown to introduce a controlled series of deep levels. A novel, commercially available, oxygen precursor, (C2H5)2AlOC2H5, was used as the oxygen source. Capacitance measurements have revealed compensation of both donors and acceptors in these materials when using this source. The determination of the deep level structure of these films has been carried out through the use of deep level transient spectroscopy (DLTS). The DLTS investigation, carried out on GaAs p+-n homojunctions, indicates that unlike the case of bulk oxygen-doped GaAs (GaAs:O), several deep levels are introduced and directly associated with the intentional oxygen introduction. Two principal traps are found to be located at 0.95 and 0.75 eV below the conduction-band edge, with several other minor traps being observed. These intentionally introduced deep levels have been used to form highly resistive GaAs, providing an analog to the currently employed low-temperature semi-insulating nonstoichiometric GaAs grown by molecular beam epitaxy.
Ultrahigh speed performance of a quantum well laser at cryogenic temperatures
Authors: Yu Rangchen , Nagarajan Radhakrishnan , Reynolds T. , Holmes A. , Bowers J. E. , DenBaars S. P. , Zah Chung-En
Published: July 2002

We have systematically studied the high speed performance of a 1.55 μm InGaAsP multiple quantum well laser diode at cryogenic temperatures from 10 to 300 K. We show that the maximum modulation bandwidth of the laser diode increases from 10 GHz at room temperature to over 27 GHz at the vicinity of 100 K. Our analysis indicates that this bandwidth is mainly limited by the device parasitics above 100 K and carrier transport below it.
Laser-ablation-assisted-plasma discharges of aluminum in a transverse-magnetic field
Authors: Lash J. S. , Gilgenbach R. M. , Ching C. H.
Published: July 2002

Laser-ablation-assisted-plasma discharges (LAAPD) have been used to enhance the ionization of laser ablated aluminum metal. Ablation is accomplished by focusing a KrF excimer laser (248 nm, 40 ns, ≤0.4 J) on a solid aluminum target with a fluence of 4 J/cm2. Peak plasma discharge voltage is 1–4 kV and peak plasma current is 0.2–1 kA, while peak power is 0.1–1 MW. Gated emission spectroscopy is used to determine the charge states and the electronic temperatures within the plasma discharge. With unmagnetized discharge parameters of 3 kV and 760 A, the observed light emission is dominated by transitions from Al2+ ions indicating nearly complete ionization of the plume. From the emission spectra intensities, an Al2+ electronic temperature of 3.3 eV is determined. Emission spectra from unmagnetized LAAPD of 1.2 kV and 280 A show no visible Al2+ ion transitions indicating cooler plasma and a lower ionization state. Introducing a 620 G transverse magnetic field (at 1.2 kV, 280 A) enhances the ionization due to the increased electron confinement and leads to the observance of the Al2+ lines as seen with discharges of 3 kV and 760 A.
Domain inversion in LiNbO3 by proton exchange and quick heat treatment
Authors: Zhu Yong−yuan , Zhu Shi−ning , Hong Jing−fen , Ming Nai−ben
Published: July 2002

Experimental studies on the domain inversion in LiNbO3 by proton exchange followed by quick heat treatment was performed. The relationship between the inverted depth and the quick heat treatment conditions was investigated. Using this method, a periodically domain−inverted structure was fabricated. The inverted domains are arc shaped.
Superconducting and epitaxial (Tl,Pb)Sr2Ca1−xYxCu2O7 thin films by in situ deposition
Authors: Myers K. E. , Face D. W. , Kountz D. J. , Nestlerode J. P.
Published: July 2002

We report the growth of thin films of (Tl,Pb)Sr2Ca1−xYxCu2O7 with x=0–0.2 by off-axis magnetron sputtering in the presence of thallium oxide vapor. The (Tl,Pb)Sr2Ca1−xYxCu2O7 films are highly c-axis oriented on the pseudocubic (100) surface of LaAlO3 or on (001)NdGaO3. The 〈100〉 axes of the films grown on LaAlO3 align to the pseudocubic 〈100〉 axes of the substrate while for films on NdGaO3 they are rotated 45° relative to orthorhombic 〈100〉 substrate axes. After an in situ heat treatment, undoped (Tl,Pb)Sr2CaCu2O7 films are superconducting at temperatures up to 82 K, compared with 85 K for the bulk material. Yttrium doping on the calcium site increased the transition temperature as expected. The highest transition temperature observed was 86 K for x=0.1 and 93 K for x=0.2.
Band-edge emission from strained SiGe alloy layers on Ge(100) substrates
Authors: Terashima Koichi , Ikarashi Taeko , Tweet Douglas , Miyanaga Keiko , Tatsumi Toru , Tajima Michio
Published: July 2002

We have fabricated strained SixGe1−x/SiyGe1−y multiple quantum wells on Ge(100) substrates and measured the photoluminescence (PL) spectra, observing band-edge emission from the SiGe alloy layers. The emission is due to the recombination of both bound excitons and free excitons in the quantum wells. From the positions of the observed PL lines, we have evaluated the band-gap energies of the strained SiGe alloy layers, and found them to be smaller than those of bulk SiGe alloys. The band-gap energy increases with the Si content of the alloy, reaching a maximum at about 15% Si, and subsequently decreases. These results agree well with the theoretical calculations for strained layers, and suggest a type II band alignment in some cases for SixGe1−x/SiyGe1−y heterostructures on Ge(100).
Characteristics of hydrogenated amorphous silicon alloy solar cells on a Lambertian back reflector
Authors: Banerjee A. , Yang J. , Hoffman K. , Guha S.
Published: July 2002

Hydrogenated amorphous silicon (a-Si) alloy n i p solar cells have been prepared on back reflectors exhibiting Lambertian light scattering characteristics. The Lambertian back reflector consists of highly textured Ag/ZnO films deposited on stainless-steel substrates. Contrary to expectation, the current voltage (I-V) characteristics under illumination are marginally poorer than the corresponding characteristics of cells grown on conventional back reflectors. The stabilized efficiency is similar for both cases. The dependence of the cell performance on the texture of the back reflector is discussed.
1/f noise and electromigration in aluminum films: The role of film microstructure and texture
Authors: Smith R. G. , Biery G. A. , Rodbell K. P.
Published: July 2002

The role of crystallographic texture on excess noise and the ability of excess noise to predict the electromigration behavior of pure aluminum films is examined. We report the excess noise and electromigration behavior of pure Al films which were deposited under a variety of conditions to obtain significantly different crystallographic textures. The noise magnitude and the logarithmic slope (α) were measured on three distinct sets of aluminum films as a function of linewidth (∼0.5–2 μm). Previously the electromigration lifetimes of these films were directly related to the (111) volume fraction. This study shows that excess noise is inversely proportional to the (111) volume fraction, suggesting that excess noise may not be measuring the same rate limiting atomic process as electromigration. The effect of film texture combined with a lower noise magnitude with decreasing linewidth implies that grain boundaries are a major source of noise in Al films.
Diffusion of ion implanted Sn in Si, Si1−xGex, and Ge
Authors: Kringho/j Per , Elliman Robert G.
Published: July 2002

The chemical distribution of Sn ion implanted into Si, Si0.79Ge0.21, Si0.47Ge0.53, and Ge was measured with secondary ion mass spectrometry. By comparing the chemical distribution of Sn before and after high temperature annealing, the diffusion coefficient of Sn was extracted as a function of temperature. The diffusion coefficients exhibited Arrhenius behavior in all four cases, yielding activation energies for diffusion of 4.91, 4.61, 3.88, and 3.05 eV, respectively, for each of the four samples. At a given temperature the diffusion coefficient for Sn was found to increase almost exponentially with increasing Ge content. Although the diffusion coefficient for Sn in Si and Ge is higher, relative to the corresponding value for self-diffusion, the activation energies are similar to that for Si and Ge self-diffusion. This suggests that the diffusion mechanism for Sn is similar to that for self-diffusion in Si and Ge and for SiGe alloys.
Modulation-doped GaInAs/GaInAsP strained multiple-quantum-well lasers grown by chemical beam epitaxy
Authors: Mawatari Hiroyasu , Iga Ryuzu , Sugiura Hideo , Tohmori Yuichi , Yoshikuni Yuzo
Published: July 2002

We report the characteristics of Be-modulation-doped strained multiple-quantum-well (MQW) buried heterostructure lasers grown by chemical-beam epitaxy. Secondary ion mass spectroscopy revealed that the Be-modulation-doping profile was fabricated and maintained even after annealing at 620 °C for 30 min, which is the same condition used to fabricate the buried heterostructure. A linewidth enhancement factor (α parameter) of only 0.8 was obtained in 3×1018 cm−3 Be-modulation-doped strained MQW Fabry–Perot lasers at a wavelength of 35 nm shorter than the gain peak.
Preparation of PbTiO3 thin films by plasma-enhanced metalorganic chemical vapor deposition
Authors: Fujii Eiji , Tomozawa Atsushi , Fujii Satoru , Torii Hideo , Takayama Ryoichi
Published: July 2002

Thin films of PbTiO3 have been prepared on glass substrate by plasma-enhanced metalorganic chemical vapor deposition. Lead dipivaloylmethane, and titanium tetraisopropoxide were used as the source materials. High crystalline and tetragonal a-axis oriented PbTiO3 film was obtained at rf power of 200 W and substrate temperature of 570 °C. The deposition rate of the film was as high as 0.18 μm/min. The film had a smooth surface and a columnar structure. The average columnar diameter was about 80 nm. Dielectric constant and tan δ of the deposited film was 250 and 0.04, respectively. The influence of deposition conditions on deposition rate and film properties has been investigated.
High-purity vapor phase purification of C60
Authors: Averitt R. D. , Alford J. M. , Halas N. J.
Published: July 2002

A method is described which utilizes the difference in vapor pressure between C60 and heavier fullerenes to produce ultrahigh purity C60. Fullerene extract is introduced into one end of a distillation column with a series of evenly spaced perforated baffles inside. The extract is heated to 970 K under high vacuum, and a linear temperature gradient is established along the column. As the mixed fullerene vapor effuses down the column, it becomes enriched in the more volatile species. C60 with a purity of 99.97% has been obtained. This method shows promise in the purification of more exotic fullerene compounds.
Hole effective mass in remote doped Si/Si1−xGex quantum wells with 0.05≤x≤0.3
Authors: Whall T. E. , Plews A. D. , Mattey N. L. , Parker E. H. C.
Published: July 2002

The effective masses in remote doped Si/Si1−xGex hole quantum wells with 0.05≤x≤0.3, have been determined from the temperature dependence of the Shubnikov–de Haas oscillations. The values are lower than previously observed by other workers, but still somewhat higher than the theoretical Γ-point values for the ground-state heavy hole subband. The differences are attributed to finite carrier sheet densities and can be satisfactorily accounted for by nonparabolicity corrections.
Infrared absorption frequencies and oscillator strengths of acceptors confined in GaAs/AlGaAs quantum wells
Authors: Zhao Q. X. , Monemar B. , Holtz P. O. , Willander M. , Pasquarello Alfredo
Published: July 2002

Infrared absorption of acceptors confined in a GaAs/AlGaAs quantum well (QW) has been calculated with and without magnetic field perturbation. The absorption frequency and oscillator strength of the dominating infrared transitions of acceptors in the QW are examined. The results show that the frequency of the acceptor transition is blueshifted with decreasing well width up to 50 Å. The normal incident absorption oscillator strength of the dominating acceptor transition first increases with decreasing well width, reaches the maximum of about 90 Å wide QW, and then decreases with further decreasing well width.
Relation between porous silicon photoluminescence and its voltage-tunable electroluminescence
Authors: Bsiesy A. , Muller F. , Ligeon M. , Gaspard F. , Hérino R. , Romestain R. , Vial J. C.
Published: July 2002

The voltage-tunable electroluminescence (VTEL) observed on porous silicon-electrolyte system is investigated in relation with the material photoluminescence (PL). It is shown that the PL line is the envelope of all the emitted EL spectra obtained upon the bias variation. Consequently, a blueshift of the (PL) line leads to a similar shift of all the corresponding EL lines. This strongly suggests a common origin of these two phenomenon. Moreover, this study seems to indicate that the VTEL of porous silicon is related to the size and efficiency distributions of the silicon nanocrystallites associated with an electrically induced selective carrier injection.
Coupling between one-dimensional states in a quantum point contact and an electron waveguide
Authors: Saito M. , Usuki T. , Okada M. , Futatsugi T. , Kiehl R. A. , Yokoyama N.
Published: July 2002

A study of electron-wave interference effects in a structure which is comprised of a split-gate point contact with a parallel reflector gate is reported. The structure constricts the injected electrons to a waveguide. The variation of point contact conductance with reflector voltage has novel oscillations directly related to the one-dimensional (1D) states in the waveguide. The oscillations are caused by the change in matching between a mode for the 1D waveguide state and an electron wave injected into the states. The oscillations are also found to be quenched with weak magnetic fields due to electron wave deflection.
Modes in optical waveguides formed by diffusion revisited
Authors: Ye Zhen
Published: July 2002

For an optical waveguide with index of refractive having a small exponential variation superimposed on a constant background value, the wave equation can be solved exactly. It is shown that the characteristic equation determining the optical modes can be solved in an uncomplicated form. The number of normal modes depends on the waveguide properties through a simple equation.
Dislocation nucleation barrier in SiGe/Si structures graded to pure Ge
Authors: Mooney P. M. , LeGoues F. K. , Jordan-Sweet J. L.
Published: July 2002

High-resolution triple-axis x-ray diffraction measurements were used to study strain relaxation in the individual layers of a SiGe/Si structure step-graded to pure Ge. The tilt of each layer is explained by extending the model previously proposed for obtaining the nucleation activation energy of dislocations to account for the reduced miscut of the growth surface as the sample relaxes and the variation in the materials properties with alloy composition.
Nitrogen in the isotopically enriched 12C diamond
Authors: Zhang Shigang , Zvanut M. E. , Vohra Y. K. , Vagarali Suresh S.
Published: July 2002

An electron paramagnetic resonance (EPR) characterization study of isotopically enriched 12C diamond grown by General Electric has been carried out. While other commonly used techniques detect no nitrogen in this diamond, the clear EPR spectrum consistently measured a nitrogen concentration of about 0.05 ppm by calibration against a few standards. The concentration is about 2 orders of magnitude lower than that of a few natural IIa diamonds and over 4 orders of magnitude smaller than that of a typical yellow Ib diamond. The 12C diamond is evaluated to be ideal for research of diamonds under high pressure as well as irradiated diamonds. Both the experimental line shape and second moment do not support a random nitrogen distribution in this diamond. Instead, we found that nitrogen atoms tend to stay apart from one another. This uniformly dispersed nitrogen distribution is a new state of nitrogen found in diamond.
Optical properties of lithium-intercalated V2O5-based films treated in CF4 gas
Authors: Talledo A. , Stjerna B. , Granqvist C. G.
Published: July 2002

Fluorocarbon-doped vanadium pentoxide films were produced by dc magnetron sputtering in Ar+O2+CF4 followed by annealing in the same gas. The films served as excellent hosts for galvanostatic and potentiodynamic lithiation. The luminous transmittance was improved by the doping. Lithium intercalation changed the optical band gap and the electrochemical performance in a manner that could be understood from a simple band structure model.
Effect of the barrier thickness on interface defect density in amorphous-Si:H/amorphous-Si1−xCx:H multilayers
Authors: Wang F. , Fischer T. , Schwarz R.
Published: July 2002

The constant photocurrent spectra (CPM) have been measured in a series of undoped a-Si:H/a-Si1−xCx:H multilayers with different thickness (db) of the a-Si1−xCx:H barrier layers from 5 to 100 Å. It is found that the apparent defect absorption and the apparent Urbach energy in the CPM spectra increase monotonically with db. These results show that the interface properties are strongly affected by the barrier layer thickness. The interface defect density, as evaluated from the CPM spectra, increases from 5×109 to 9×1011 cm−2 with db.
Novel method for deposition of in situ arsenic-doped polycrystalline silicon using conventional low pressure chemical vapor deposition systems
Authors: Thakur R. P. S. , Turner C.
Published: July 2002

We studied low pressure chemical vapor deposition of in situ arsenic-doped silicon films using a standard vertical thermal reactor. The films were deposited as a stack of doped and undoped layers for a targeted thickness. The redistribution of the dopant was achieved with postanneals in a rapid thermal processor. We fabricated stacked capacitors to study depletion capacitance effects. This deposition method is easily integrated for high volume production of thicker polycrystalline silicon films used for dynamic random access memory cell capacitor plates in complementary metal oxide semiconductor technology. Using this method, we achieved thickness and sheet resistance nonuniformities of less than 3% for deposited and subsequently annealed films.
Photopyroelectric study of nonlinear heat transport phenomena at a liquid crystal phase transition
Authors: Marinelli M. , Mercuri F. , Zammit U. , Gusev V.
Published: July 2002

A front detection photopyroelectric configuration has been used to study the nonlinear heat transport processes that take place in the vicinity of the smectic A–nematic phase transition of the 9 CB liquid crystal. An increase in the sensitivity of this technique with respect to other photothermal techniques as far as the phase transition detection is concerned has been obtained.
Photoenhanced chemical-vapor deposition of BaTiO3
Authors: Zhang Jiming , Beetz Charles P. , Krupanidhi S. B.
Published: July 2002

High quality BaTiO3 films have been deposited on MgO (100) and Pt coated Si (Pt/Ta/ONO/Si) substrates at 600 °C by photoenhanced chemical-vapor deposition (photo-CVD). X-ray-diffraction measurements show that highly a-axis oriented BaTiO3 was formed on MgO (100) substrates at 600 °C by photo-CVD. BaTiO3 films deposited on Pt coated Si substrates by photo-CVD were randomly oriented. In contrast, the x-ray-diffraction peaks of the BaTiO3 films deposited at the same temperature without UV light irradiation were much weaker than those with UV light irradiation. Raman-scattering measurements showed a pronounced peak at 522 cm−1, which is characteristic peak of perovskite BaTiO3, for photo-CVD deposited films. The dielectric constant of photo-CVD deposited BaTiO3 films (ε=580) was more than double than that of thermal CVD deposited films, while the dissipation factor (loss) of photo-CVD deposited BaTiO3 films was reduced by a factor of 2. These results unambiguously demonstrated that photo-CVD is a promising technique for low-temperature deposition of high quality ferroelectric films.
Direct growth of heteroepitaxial CuInSe2 layers on Si substrates
Authors: Tiwari A. N. , Blunier S. , Kessler K. , Zelezny V. , Zogg H.
Published: July 2002

Heteroepitaxial CuInSe2 (CIS) layers have been directly grown on Si substrates by molecular beam epitaxy. Epitaxial growth is achieved by using a proper thermal treatment of the substrate prior to the growth and also during the initial stage of CIS growth. (100)-oriented and (112)-oriented CIS layers with chalcopyrite crystal structure, and free from impurity phases have been obtained on Si(100) and Si(111), respectively. Different methods have been used to study the growth kinetics and structural quality of the epitaxial layers. Twinning in (112)-oriented CIS layers depends on the deposition recipe. A Rutherford backscattered ion channeling minimum yield of about 13%, and an x-ray rocking-curve width of about 900 arcsec have been measured for a 0.4 μm thick heteroepitaxial CIS(112) layer on Si(111) substrate.
Novel surface gate structure to induce sharp potential barriers in two-dimensional electron systems
Authors: Lu J. P. , Ying X. , Shayegan M.
Published: July 2002

A novel surface gate structure, consisting of a central gate and two side gates, is proposed to generate an effectively sharp potential barrier for two-dimensional electrons confined to a semiconductor heterojunction deep below the sample surface. The side gates are biased at a higher potential than the central gate to enhance the large-wave-vector Fourier components of the potential and therefore to compensate partially for the strong decay, due to fringing fields, of these components as a function of the distance below the surface. The reflection coefficient calculated for the proposed potential barrier exhibits strong oscillations as a function of barrier height, much stronger than a conventional single gate. The results suggest that the proposed gate structure should find use in realization of an electron interferometer which can serve as a building block for novel electron interference devices.
Correlation between distribution of outgrowths and microwave surface resistance for YBa2Cu3O7 thin films
Authors: Tian Y. J. , Li L. , Guo L. P. , Liu J. Z. , Zhao Z. X. , Xu S. F. , Lu H. B. , Zhou Y. L. , Chen Z. H. , Cui D. F. , Yang G. Z.
Published: July 2002

A model was proposed to describe the effects of surface outgrowths on the microwave surface resistance of high Tc superconducting thin films. Calculated with experimental data the microwave surface resistance at 10 GHz for c-axis oriented YBa2Cu3O7 thin films with no outgrowths could be as low as 70 and 4 μΩ at 77 and 4.2 K, respectively. The effect of the orientation of the surface outgrowths on the microwave loss has been discussed.
Direct growing of lightly doped epitaxial silicon without misfit dislocation on heavily boron-doped silicon layer
Authors: Lee Ho-Jun , Kim Chang-Soo , Han Chul-Hi , Kim Choong-Ki
Published: July 2002

Without buffer layers, a lightly boron-doped epitaxial layer of good crystalline quality has been directly grown on a heavily boron-doped silicon layer by eliminating misfit dislocations in the heavily boron-doped layer. X-ray diffraction analysis revealed that the epitaxial silicon has good crystallinity, similar to that grown on lightly doped silicon substrate. The leakage current of an n+/p diode fabricated in the epitaxial silicon has been measured to be 0.6 nA/cm2 at 5 V.
Infrared absorption of holes in a parabolic quantum well
Authors: Sundaram M. , Allen S. J. , Geller M. R. , Hopkins P. F. , Campman K. L. , Gossard A. C.
Published: July 2002

We observe the infrared absorption of holes in a wide graded AlxGa1−xAs parabolic quantum well to be at a single frequency, independent of the number of holes in the well. The resonant absorption frequency appears to be determined by the light hole mass, not the heavy hole mass.
Interface characterization of InAs/AlSb heterostructures by far infrared optical spectroscopy
Authors: Fuchs F. , Schmitz J. , Schwarz K. , Wagner J. , Ralston J. D. , Koidl P. , Gadaleta C. , Scamarcio G.
Published: July 2002

We present high resolution measurements of the far infrared reflectance and absorbance of InAs/AlSb type II heterostructures, grown on GaAs substrates by molecular beam epitaxy. Quantum wells grown with AlAs-like interfaces show broadening and blue shifting of the InAs transverse optical (TO) phonon compared to samples with InSb-like interfaces. This is explained by incorporation of arsenic in the AlSb barriers. The InSb-interface mode, recently reported from Raman investigations, could be observed in the multiple quantum well. Two lines are observed, which are attributed to the normal (AlSb on InAs) and the inverted (InAs on AlSb) interfaces.
Stochastic resonance in a semiconductor distributed feedback laser
Authors: Iannelli J. M. , Yariv A. , Chen T. R. , Zhuang Y. H.
Published: July 2002

The observation of stochastic resonance in a semiconductor distributed feedback laser is reported. Bistable modal and intensity operation is obtained using the degenerate modes of the grating. Through an observation of longitudinal-mode switching under current modulation, an enhancement in the signal-to-noise ratio of the laser’s output wavelength switching of 22 dB is measured.
Color changes in photoluminescence by doped, unconverted and partially converted poly(p-phenylene vinylene)
Authors: Esteghamatian M. , Xu G.
Published: July 2002

Although green-light-emitting devices based on poly(p-phenylene vinylene) ppv, have been made and reported by several researchers, it is also of interest to design light emitting devices which emit light in various parts of the visible spectrum, particularly in the blue region. In this letter the effect of doping and conversion time on the photoluminescence (PL) of pvv are investigated. It is observed that treating ppv films with sulfuric acid shifts the PL peaks to the blue region, and Li doping red-shifts the spectra. Unconverted and partially converted ppv films, on the other hand, show PL peaks at about 470 to 480 nm in the dark blue range. The shift in PL peak from green to blue is expected to be due to the decrease in conjugation length which determines the size of the band gap.