bluuebunny/crossref_metadata_2025 huggingface dataset:
In situ native oxide removal from AlGaInAs surfaces by hydrogen radical treatment for molecular beam epitaxy regrowth
Authors: Hase A. , Gibis R. , Künzel H. , Griebenow U.
Published: July 2002

Removal of native oxide from Al0.24Ga0.24In0.52As layers grown lattice-matched onto InP substrates is successfully achieved by an in situ hydrogen radical treatment prior to molecular beam epitaxy (MBE) overgrowth. Cleaning conditions using moderate substrate temperatures not necessitating a surface stabilizing arsenic flux were elaborated, which ensured complete oxide removal without deterioration of the underlying AlGaInAs material. The surface quality as assessed by high energy electron diffraction, and the quality of epitaxial layers deposited onto this surface were found to be at least equivalent to that achieved with epitaxial growth directly on InP substrates, indicating the achievement of thorough oxide removal, low residual contamination levels, and a surface smoothness adequate for MBE regrowth.
Anisotropic structural, electronic, and optical properties of InGaAs grown by molecular beam epitaxy on misoriented substrates
Authors: Goldman R. S. , Wieder H. H. , Kavanagh K. L. , Rammohan K. , Rich D. H.
Published: July 2002

We have investigated the structural, electronic, and optical properties of partially strain-relaxed InxGa1−xAs layers, grown by molecular beam epitaxy on both misoriented and nominally flat (001) GaAs substrates. We find large anisotropies in bulk strain relaxation, interfacial misfit dislocation density, dark-line defect density, and electron mobility, as well as a polarization anisotropy in cathodoluminescence for epilayers grown on misoriented substrates, in comparison with those grown on flat substrates.
Significantly improved mechanical properties in Pb-free, Sn-Zn-In solder alloy by Ag doping
Authors: McCormack M. , Kammlott G. W. , Chen H. S. , Jin S.
Published: July 2002

The 87%Sn-8%Zn-5%In alloy is a new Pb-free solder designed for possible drop-in replacement of Pb-Sn solders. This Sn-Zn-In solder has a melting point of ∼188 °C, which is comparable to that of the widely used eutectic Pb-Sn solder. However, because of the rather coarse and nonuniform distribution of platelike, dendritic features throughout the microstructure, the alloy exhibits a limited ductility (tensile elongation of ∼20%). In this letter, we show that the addition of small amounts of Ag (as small as 0.1%) dramatically improves the tensile ductility to ∼40%. The observed improvement in ductility is attributed to the elimination of the coarse planar features and nonuniformities within the microstructure. The addition of Cu has a similar beneficial effect, although it is less preferable to the Ag addition from the stand point of melting temperature.
Interferometric detection of cross-phase modulation in CdS
Authors: Hirlimann C. , Wassmuth E. , Kling E. , Petit S. , Pereira dos Santos M.
Published: July 2002

Using short 130 fs light pulses in a pump-probe experiment we measured the transmission change under a strong irradiation (≊5 GW/cm2) of a Fabry–Perot-like CdS sample, at room temperature, Using a simple model we deduced a nonlinear index n2=5×10−13 cm2/W. This index is only due to the electric field effect of the pulse for it is measured in a time shorter than the electronic relaxation time. We show that this experimental method could be used for measuring the duration of ultrashort light pulses at their fundamental frequency with intensities less than a few GW/cm2.
Electrically detected transient photocarrier grating method
Authors: Wang F. , Schwarz R.
Published: July 2002

We present the measurement and analysis of the transient behavior of the photocurrent in amorphous semiconductor thin films in the presence of a photocarrier grating. The photocurrent transients are governed essentially by two processes, recombination and interdiffusion. The general features of the experimental findings can be reproduced analytically under small-signal conditions. In a new method, which we call the electrically detected photocarrier grating method, the response time of photogenerated carriers and the ambipolar diffusion coefficient can be measured simultaneously.
Monosteps on extremely flat YBa2Cu3O7−x surfaces grown by liquid-phase epitaxy
Authors: Scheel H. J. , Klemenz C. , Reinhart F.-K. , Lang H. P. , Güntherodt H.-J.
Published: July 2002

We report the growth of extremely flat YBa2Cu3O7−x (YBCO) films onto NdGaO3 substrates by liquid-phase epitaxy (LPE). Macroscopic growth spirals with large interstep distances (several μm) and with hollow cores are observed by optical (Nomarski) microscopy and by atomic force microscopy, in contrast to the microscopic spiral islands formed in epitaxy from the vapor phase. Typical step heights of LPE-grown YBCO vary between monosteps (1.2 nm) and 7.2 nm. Extremely flat epitaxial YBCO surfaces with continuous step flow have been achieved. They are of interest for fundamental physical studies (gap, photoemission) and for a reliable high-temperature superconductivity tunnel-device technology.
Unusually large shielding fields in single-grain YBa2Cu3O7−δ
Authors: Gao L. , Xue Y. Y. , Meng R. L. , Chu C. W. , Hannahs S. , Thang V. , Rubin L.
Published: July 2002

Magnetic field trapping and shielding by several unirradiated single-grain YBa2Cu3O7−δ disks have been investigated between 4.2 and 71 K up to 20 T. Flux avalanches due to thermal instabilities limited the trapping field to ∼5 T below 45 K and often caused microcracks in the disks. However, a shielding field greater than 19 T was detected at 4.2 K in the same sample assembly even after it was damaged by flux avalanches. This violates the expected symmetry between shielding and trapping fields. The shielding field of ≳19 T exceeds the total quench field of 10 T predicted by the Swartz–Bean model. The observations suggest that thermomechanical properties play an important role in field shielding and trapping and mechanical stress may be effectively used to enhance the field trapped by disks of high temperature superconductors.
Asymmetric dual GeSi/Si Bragg mirror and photodetector operating at 632 and 780 nm
Authors: Murtaza S. S. , Campbell J. C. , Bean J. C. , Peticolas L. J.
Published: July 2002

We report the successful combination of asymmetric and dual mirror designs to fabricate a strained-layer GeSi/Si Bragg mirror with twin peaks at 632 and 780 nm. The absorption in the GeSi/Si mirror is found to be small and is compensated by the increased refractive index step available at shorter wavelengths. We also propose a dual photodetector that will exhibit high efficiencies at both the resonant wavelengths. The small absorption thickness of this photodetector as compared to conventional silicon photodiodes is expected to result in higher speeds.
High temperature operation of GaInAsSb/AlGaAsSb double-heterostructure lasers emitting near 2.1 μm
Authors: Baranov A. N. , Fouillant C. , Grunberg P. , Lazzari J. L. , Gaillard S. , Joullié A.
Published: July 2002

Mesa-stripe injection lasers have been prepared from liquid phase epitaxial Ga0.88In0.12As0.10Sb0.90/Al0.47Ga0.53 As0.04Sb0.96 double heterostructures having an active zone of n-type conductivity. These laser diodes could operate pulsed at heatsink temperatures up to 120 °C, and showed high characteristic temperature near ambient (T0≊110 K), comparable with theoretical value.
Ultrafast graded-gap electron transfer optical modulator structure
Authors: Agrawal Niraj , Wegener Martin
Published: July 2002

We demonstrate an ultrafast graded-gap electron transfer optical modulator structure with electron escape times on the order of 1 ps. All other aspects important for high-speed applications, for example, electroabsorption and electrical behavior remain essentially unaffected.
Control of electron population by intersubband optical excitation in potential-inserted double quantum well structures
Authors: Akiyama H. , Sugawara H. , Kadoya Y. , Lorke A. , Tsujino S. , Sakaki H.
Published: July 2002

A remarkable change in photoluminescence spectra was observed when CO2 laser light was incident to induce an intersubband transition in a novel asymmetric double quantum well structure where the second subbands of both wells are resonantly coupled, while the ground subbands are not. It is found that the observed change originates from the CO2-laser-induced transfer of electrons from one well to the other, demonstrating the controllability of electron population by means of infrared light.
Visible luminescence from silicon by hydrogen implantation and annealing treatments
Authors: Pavesi L. , Giebel G. , Tonini R. , Corni F. , Nobili C. , Ottaviani G.
Published: July 2002

Luminescence at an energy higher than the Si band-gap energy has been observed following H implantation and annealing treatments of Si samples. This phenomenon is discussed considering the damage caused by the H implantation and its evolution with thermal treatments. No definitive answer on the origin of the luminescence is given but various possible models are proposed.
Third-order optical nonlinearity of conjugated poly(4,4-disubstituted-1,6-heptadiyne)s
Authors: Park Soo Young , Cho Hyun-Nam , Kim Nakjoong , Park Jong-Wook , Jin Sung-Ho , Choi Sam-Kwon , Wada Tatsuo , Sasabe Hiroyuki
Published: July 2002

Large third-order optical nonlinearity was found with the soluble conjugated polymers (substituted polyacetylenes) synthesized by the ring-forming metathesis polymerization of 4,4-disubstituted-1,6-heptadiynes. These polymers were of quite high molecular weight (∼105) and were highly soluble in common organic solvents. The linear optical property and the third-order optical nonlinearity of these polymers were investigated in terms of the chemical structure of the 4,4-disubstituents using the polymer films of around 100-nm thickness fabricated by the spin coating of tetrahydrofuran solutions. The π-π* transition of the conjugated π-electron main chain was characterized as the strong absorption peak at around 540 nm of the electronic spectra, where the optical density of the transition was found to be largely dependent on the molar volume of the substituents. The near-resonant values of the third-order nonlinear optical coefficient, χ(3)(−3ω;ω,ω,ω) were found to be 2.6 to 6.5×10−11 esu, which also were controlled by the molar volume of the substituent group.
Semi-insulating InP grown at low temperature by metalorganic chemical vapor deposition
Authors: Gardner Nathan F. , Hartmann Quesnell J. , Stockman Stephen A. , Stillman Gregory E. , Baker Judith E. , Malin Jay I. , Hsieh K. C.
Published: July 2002

The growth of semi-insulating epitaxial InP layers at low substrate temperature (460 °C) by low-pressure metalorganic chemical vapor deposition has been demonstrated using CCl4 as a dopant source. The resistivity of the material is a function of diluted CCl4 flow rate used during growth. For flow rates less than 5 sccm the material is n type, but for higher flows the resistivity of the material is approximately 5×109 Ω cm. The semi-insulating behavior of the material is maintained after annealing at 600 °C. Transmission electron microscopy does not reveal the presence of phosphorus precipitates in as-grown samples or in samples annealed at 400 and 600 °C. There is significant carbon, hydrogen, and chlorine incorporation in the layers, as measured by secondary ion mass spectrometry. Room-temperature photoluminescence measurements suggest that nonradiative recombination is significant in the material and increases in samples grown with higher CCl4 flows.
Subnanosecond photovoltaic response in 6H–SiC
Authors: Saddow Stephen E. , Cho Pak S. , Goldhar Julius , Lee Chi H. , Neudeck Phillip G.
Published: July 2002

We report observation of a subnanosecond photovoltaic response in 6H–SiC illuminated with an ultraviolet laser. Using different incident laser energies, the transient photovoltaic response in 6H–SiC was investigated and photovoltaic electrical pulses with various durations and amplitudes observed. Subnanosecond electrical pulses, with amplitudes of hundreds of millivolts, were generated from 6H–SiC lateral photoconductive switches excited by a nanosecond laser pulse without external bias. Modeling of this fast photovoltaic response has been performed and good qualitative agreement obtained.
Electric field effects on the photoluminescence in modulation-doped pseudomorphic AlGaAs/InGaAs/GaAs single quantum wells
Authors: Yang G. M. , Seo K. S. , Choe Byung-Doo
Published: July 2002

Electric field effects on the photoluminescence spectra of modulation-doped AlGaAs/InGaAs/GaAs single quantum wells grown by metalorganic chemical vapor deposition are studied. The electron density is continuously varied by the use of a Schottky gate. Parity forbidden transition is observed in the samples with a high electron density of more than 1×1012 cm−2. The luminescence line shape has strong dependence on the external bias. External field-induced blue and red shifts of the optical transition at the n=1 conduction subband are found. The mechanism for this can be related to the quantum-confined Stark shift, due to the competition between the built-in field and the external field. No photoluminescence intensity enhancement is observed at the Fermi edge.
InAlGaAs impact ionization rates in bulk, superlattice, and sawtooth band structures
Authors: Tsuji Masayoshi , Makita Kikuo , Watanabe Isao , Taguchi Kenko
Published: July 2002

Electron and hole impact ionization rates in bulk, superlattice, and sawtooth band structures consisting of an InAlGaAs system are determined from their photomultiplication characteristics. The impact ionization rate ratios are derived as 2.2, 3.0, and 3.6 for the bulk, superlattice and sawtooth structures, respectively, at an electric field of 470 kV/cm. The hole impact ionization rate in the InAlGaAs sawtooth structure is nearly equal to that of the InAlAs/InAlGaAs rectangular-well superlattice. In contrast, the electron impact ionization rate in the sawtooth structure is larger than that in the superlattice. This difference is attributed to a lack of energy loss for electrons at the staircase band condition in the sawtooth structure.
Paramagnetic centers at and near the Si/SiOx interface in porous silicon
Authors: Pivac B. , Rakvin B. , Pavesi L.
Published: July 2002

Formation of paramagnetic centers in aged porous silicon samples is studied by electron paramagnetic resonance. Samples oxidized by aging in air at room temperature exhibit the Pb centers as dominant defects. These are formed at the interfaces between the Si nanocrystallites and the amorphous SiOx layer into which the nanocrystallites are embedded and which is formed during the aging. No other paramagnetic centers, such as the E′ center that is characteristic of thin SiO2 layers on Si, are observed. This finding is explained by the hydrogen passivation of E′ centers in oxygen-rich porous structures and by the instability of the E′ center near the interface. The Pb center is stable after γ irradiation.
Ultraviolet laser fabrication of strong, nearly polarization-independent Bragg reflectors in germanium-doped silica waveguides on silica substrates
Authors: Strasser Thomas A. , Erdogan Turan , White Alice E. , Mizrahi Victor , Lemaire Paul J.
Published: July 2002

Strong Bragg reflectors (≳4 nm width) have been fabricated in Ge-doped silica waveguides on silica substrates by ultraviolet (UV)-induced refractive index change. Index changes in excess of 3×10−3 were obtained by deuterium sensitization. The passband quality, polarization dependence, and loss of the reflectors are reported.
Dispersion of thermo-optic coefficients in a potassium niobate nonlinear crystal
Authors: Ghosh Gorachand
Published: July 2002

The thermo-optic coefficients, i.e., the variation of refractive index with temperature (dn/dT) for potassium niobate crystal, KNbO3, are analyzed critically by use of a physically meaningful model. This model is based on the thermal expansion coefficient, and the optical band gaps, such as excitonic and isentropic instead of the consideration of the spontaneous polarization as suggested earlier. The computed optical constants have been used to calculate refractive indices for any wavelength from 0.4 to 3.4 μm at any operating temperature within orthorhombic phase accurately.
Generalized breakdown voltage characteristic of the pseudospark
Authors: Rhee M. J. , Liu C. J.
Published: July 2002

A simple empirical scaling law is determined for the pseudospark breakdown voltage characteristic that includes the effect of the cavity dimension. It is found that the breakdown voltage characteristic has two distinctive regimes: the breakdown voltage is a function of the product of the gas pressure and the anode–cathode distance pd and a function of the product p2d for the gap distance greater than and less than approximately three times the cavity diameter, respectively.
Optical photodetector for near-field optics
Authors: Kolb G. , Karraï K. , Abstreiter G.
Published: July 2002

A p-n homojunction GaAs-based photodetector is developed in order to operate in the near field of a subwavelength sized light source. It has a spatial resolution of about 270 nm, limited by diffusion of minority carriers. A detector with a built-in AlGaAs diffusion barrier is also studied, demonstrating an improved resolution of better than 100 nm.
Pressure dependence of optical transitions in ordered GaP/InP superlattices
Authors: Franceschetti Alberto , Zunger Alex
Published: July 2002

We have calculated the pressure coefficients α of a few optical transitions in (001), (111), (110), and (201) GaP/InP ordered superlattices using ab initio methods. The equilibrium atomic geometries under hydrostatic pressure are obtained by direct minimization of the elastic enthalpy. We find that (i) the pressure coefficient of the lowest energy transition is uniformly high, due to the Γ1c character of the conduction-band minimum; (ii) the pressure coefficient of the transition to the second lowest conduction state at Γ̄ distinguishes the (111)-oriented (CuPt) superlattice (α=4.0 meV/kbar) from the remaining structures (α≂−2 meV/kbar). This is so because in CuPt we have L folding, while in the other structures we have X folding; (iii) the calculated pressures for the Γ→X crossover are 45, 43, 12, and 16 kbar for the (001), (111), (110), and (201) superlattices, respectively. These trends reflect the zero-pressure Γ1c–X1c energy separation and the Γ1c pressure coefficient of these structures.
Postgrowth annealing of YBa2Cu3O7−x thin films in an electron cyclotron resonance oxygen plasma
Authors: François I. , Borghs G.
Published: July 2002

As-deposited epitaxial YBa2Cu3O7−x films have been prepared by laser ablation in molecular oxygen followed by a cooling procedure in an electron cyclotron resonance (ECR) plasma. We demonstrate that cooling in a plasma provides a more homogeneous oxygenation than cooling in a neutral oxygen environment. Alternating-current susceptibility, resistivity, and x-ray diffraction measurements have been used to compare the influence of the cooling in an ECR oxygen plasma and a neutral oxygen environment on the properties of YBa2Cu3O7−x thin films. The role of the atomic oxygen content of the plasma is discussed starting from an optical and electrical diagnosis of the plasma.
Optical transmission systems employing vertical cavity surface emitting lasers and monolithically integrated photoreceivers
Authors: Nichols D. T. , Hobson W. S. , Vakhshoori D. , Wynn J. D. , Zydzik G. J. , Morgan R. A. , Dutta N. K. , Sivco D. L. , Cho A. Y. , Leibenguth R. E.
Published: July 2002

We report on an optical fiber transmission system employing a vertical cavity surface emitting laser and an integrated p-i-n/metal–semiconductor field effect transistor (MESFET) photoreceiver. The surface emitting laser utilizes proton implantation for current confinement and has a small signal bandwidth of 10 GHz. The p-i-n/MESFET photoreceiver has a bandwidth of 4.5 GHz. A transmission experiment using the vertical cavity surface emitting lasers source and the p-i-n/MESFET photoreceiver was carried out and error-free operation was demonstrated.
Reflection high-energy electron diffraction intensity oscillations of germanium growth on Si(100) using gas source molecular beam epitaxy
Authors: Xie M. H. , Zhang J. , Mokler S. M. , Fernández J. M. , Joyce B. A.
Published: July 2002

Reflection high-energy electron diffraction intensity oscillations during Ge heteroepitaxy on Si(100) have been observed using a gas source molecular beam epitaxy system. Intensity oscillations can be observed over 6 ML (monolayers) of growth in the temperature range 400–650 °C. The oscillation frequency, however, varies from the first to subsequent layers and this variation is interpreted primarily as a change in the limiting growth kinetics as the surface composition changes from Si to Ge. Growth temperature and GeH4 flux dependence data indicate that the surface Ge concentration increases gradually, not abruptly, over the first several layers of deposition. Surface roughening effects which are attributed to Stranski–Krastanov type growth, are also found to contribute to the nonuniform oscillation frequency.
Residual stresses and microstructure of Ag-Ni multilayers
Authors: Badawi K.-F. , Durand N. , Goudeau Ph. , Pelosin V.
Published: July 2002

A direct determination of residual stresses in very-low-period Ag-Ni multilayers has been performed by x-ray diffraction using the sin2ψ method. Stresses in silver layers as thin as three atomic planes and in nickel layers as thin as four atomic planes could be determined. They range from −3.07 to 0.522 GPa, and their genesis excludes any interfacial coherency relationship. The variation of the multilayer microstructure with respect to the period has been studied by measurement of the stress free lattice parameter and microdistortions. Important deviations with respect to the bulk microstructure have been observed and discussed.
Deep levels in GaAs grown by atomic layer molecular beam epitaxy
Authors: Gombia E. , Mosca R. , Bosacchi A. , Madellaf M. , Franchi S.
Published: July 2002

We present a study on deep levels in GaAs:Si grown by atomic layer molecular beam epitaxy (ALMBE). We show that in ALMBE GaAs grown at temperatures TS in the range 370–530 °C, the deep level concentrations: (i) are up to 3 orders of magnitude smaller than those of material grown by molecular beam epitaxy (MBE) at similar temperature ranges, and (ii) can be compared to those of GaAs grown by MBE at 600 °C. These features are independent whether Si is supplied during: (a) both the Ga and As subcycles, (b) the As subcycles, or (c) the Ga subcycles. Therefore, as for deep levels, ALMBE GaAs grown at 370≤TS≤530 °C can be related to GaAs prepared by MBE at conventional temperatures.
Compact high-efficiency carbon monoxide laser at 1 kW
Authors: Yu G. , Baker H. J. , Rodrigues N. A. S. , Hall D. R.
Published: July 2002

A fast-axial-flow, cryogenically cooled, carbon monoxide laser has been operated at 28% efficiency producing a continuous wave output power of 1.08 kW. The laser uses two cylindrical discharge sections, each 225 mm in length, which are excited by transverse radio-frequency fields at 27 MHz in a linear stable optical resonator. A specific power output of 2.41 kW m−1 and an extraction power density of 9.41 W cm−3 have been attained by optimization of the transverse and longitudinal electrode configuration.
Small mesa structure in split-gate wires fabricated by scanning tunneling microscope for observing Coulomb blockade effects
Authors: Yamada Syoji , Yamamoto Masafumi
Published: July 2002

Fabrication and transport properties of small mesa/split-gate hybrid structures are described. In order to make small semiconductor mesas acting as an ‘‘impurity’’ at a desired wire surface position, we used a scanning tunneling microscope/scanning electron microscope combined system operated in vacuum. The fabrication method is simple electrical evaporation with a tungsten tip. In a split-gate quantum wire having a small mesa (70 nm diameter and 15 nm tall) in the center, clear Coulomb blockades and staircases corresponding to the size of the mesa were observed at 0.3 K.
Periodic cladding surface structures induced when recording fiber Bragg reflectors with a single pulse from a KrF excimer laser
Authors: Mihailov S. J. , Gower M. C.
Published: July 2002

Observations are presented of ∼1 μm deep periodic structures on the cladding surface of optical fibers which are simultaneously induced when recording first-order fiber Bragg reflectors by single pulse KrF excimer laser holographic exposure.
Optically generated liquid crystal gratings
Authors: Gibbons Wayne M. , Sun Shao-Tang
Published: July 2002

Optically controlled planar orientation of liquid crystal molecules with polarized light is used to make phase gratings in liquid crystal media. The electro-optical properties of liquid crystal linear and chirped gratings are discussed.
Metal-organic chemical vapor deposition/open flow thallium annealing route to epitaxial Tl2Ba2Ca2Cu3O10 thin films
Authors: Hinds B. J. , Schulz D. L. , Neumayer D. A. , Han B. , Marks T. J. , Wang Y. Y. , Dravid V. P. , Schindler J. L. , Hogan T. P. , Kannewurf C. R.
Published: July 2002

Phase-pure epitaxial Tl2Ba2Ca2Cu3O10 thin films have been grown on single crystal (110) LaAlO3 substrates using an improved metal-organic chemical vapor deposition process. First, Ba-Ca-Cu-Ox precursor films are grown on LaAlO3 (110) substrates using Ba(hfa)2⋅tet, Ca(hfa)2⋅tet, and Cu(hfa)2 (hfa=hexafluoroacetylacetonate; tet=tetraglyme) as volatile metalorganic precursors. Thallium is then incorporated into the films during a post-anneal in the presence of a Tl2O3, BaO, CaO, CuO powder mixture at 820 °C for 12 h in a flowing 10% O2/Ar atmosphere. The films have a transport-measured Tc=115 K and Jc=1.5×105 A/cm2 (80 K), while magnetic hysteresis measurements yield Jc=6×105 A/cm2 (77 K). Preliminary surface resistance measurements give Rs=0.35 mΩ at 5 K, 10 GHz.
Low-temperature conductivity of epitaxial ZnSe in the impurity band regime
Authors: Vaziri M.
Published: July 2002

Low-temperature conductivity of several samples of ZnSe grown by molecular-beam epitaxy has been measured. The data indicate that for samples with carrier concentration below or near Nc, metal insulator transition, the conductivity obeys σ=σ0 exp[−(T0/T)s] at low temperatures with s=1/2. This behavior is a characteristic of variable-range hopping conduction in the presence of a Coulomb gap.
Multiple wavelength light source using an asymmetric waveguide coupler
Authors: Pezeshki B. , Kash J. A. , Kisker D. W. , Tong F.
Published: July 2002

We obtained multiple wavelength light emission from a coupled waveguide structure formed from a conventional waveguide and a vertical cavity resonator. The cavity and quarter-wave mirrors are optimized to act as another waveguide, thus forming an asymmetric directional coupler. This asymmetry between the waveguide and the vertical cavity causes wavelength selectivity in the cavity light emission. By tapering the cavity, the phase-matched wavelength becomes a function of position, and pumping different regions along the length of the waveguides causes different wavelengths to be emitted from the device. We obtained narrow-band luminescence with a minimum width of 1 nm using a 75-Å quantum well in a GaAs/AlGaAs vertical cavity structure coupled to a low index polymer waveguide.
Uniform GaAs quantum dots in a polymer matrix
Authors: Salata O. V. , Dobson P. J. , Hull P. J. , Hutchison J. L.
Published: July 2002

A novel technique suitable for the preparation of uniformly sized nano- and microparticles of a wide range of compound semiconductors embedded in different polymers is described. Optical absorption spectra and high resolution electron micrographs of a new composite material—GaAs quantum dots in a polymer matrix—are presented and are discussed.
Annihilation of grown-in defects in Czochralski-grown silicon probed with variable-energy positron beam
Authors: Kitano T. , Saito S. , Tanigawa S.
Published: July 2002

The annihilation of grown-in defects in Czochralski-grown silicon was investigated during the process of oxygen out-diffusion, by the positron measurements with a variable-energy beam. The diffusion length of positrons L becomes larger as the annealing time increases, although the line shape parameter S is constant. The information on L, based on the ‘‘semitrapping’’ phenomenon including the formation of positron Rydberg states between positrons and defects, is more sensitive for detecting minute defects. The increase in L values indicates that the grown-in defects are annihilated. The concentration of annihilated defects, related to oxygen clusters, was decreasing down to one-tenth, compared with that for an as-grown crystal. Also, the grown-in defects were annihilated at high temperature, e.g., 1150 °C.
Tunneling hot electron transistor as a high power source at terahertz frequencies
Authors: Dellow M. W. , Cronin N. J. , Bending S. J.
Published: July 2002

A novel device is proposed, based upon a tunneling hot electron transfer amplifier, which exhibits the characteristics of negative differential resistance (NDR) coupled with high current gain. The mechanism which produces the NDR is known to be extremely fast. The combination of these features suggests that such a device could be used as a high power source of terahertz radiation.
Carbon doping of AlAs using CCl4 and CBr4 during growth by metalorganic molecular-beam epitaxy
Authors: Abernathy C. R. , MacKenzie J. D. , Hobson W. S. , Wisk P. W.
Published: July 2002

CBr4 and CCl4 have been investigated as carbon doing sources for deposition of AlAs:C by metalorganic molecular-beam epitaxy. Through the use of CBr4, hole concentrations up to 4.5×1019 cm−3 were achieved in as-deposited AlAs layers. Attempts to increase the hole concentration in as-grown material beyond this level resulted in a decrease in the hole concentration even though (SIMS) and (XRD) analysis show the carbon concentration to increase with increasing dopant flow. By annealing the AlAs after growth, the maximum achievable hole concentration could be increased to 1.1×1020 cm−3, which is the highest yet reported for AlAs:C. This increase in p after annealing is believed due to removal of hydrogen from the lattice which passivates the carbon acceptor. Neither carbon source increased the oxygen background beyond the level of ∼5×1017 cm−3 normally observed in AlAs grown under similar conditions. These compounds do introduce Cl and Br, and reduce the Al incorporation rate due to parasitic etching reactions with the adsorbed halogen.
Synchrotron radiation photoelectron spectroscopy study for GaAs (001) surface prepared by deoxygenated and de-ionized water treatment
Authors: Hirota Y. , Ogino T. , Watanabe Y. , Oshima M.
Published: July 2002

The thermal effects on an n-type GaAs (001) surface prepared by deoxygenated and de-ionized water (DODIW) treatment are investigated by synchrotron-radiation photoelectron spectroscopy (SRPES) in the temperature range from room temperature (RT) to 500 °C. SRPES confirms there are no oxides. There is, however, excess elemental arsenic and/or hydrogenated arsenic on the surface before heating, which evaporates when heated in a high vacuum. SRPES also shows that the surface Fermi level lies almost 0.9 eV above the maximum of valence band before heating, and moves toward the midgap during heating. After cooling to RT, it returns to the near-flat band position (1.0 eV). These experimental results suggest that DODIW-treated GaAs (001) surface can attain a low-density surface state.
Phonon-assisted carrier capture into a quantum well in an electric field
Authors: Thibaudeau L. , Vinter B.
Published: July 2002

We have theoretically investigated the capture of electrons into a quantum well by LO phonon scattering. The calculation was performed for a single, undoped GaAs/AlxGa1−xAs quantum well under applied electric bias. We have derived an expression for the time constant associated with the exchange of electrons between the fundamental ground state and the continuum states. The results are found to be in fairly good agreement with impedance spectroscopy measurements.
Defect passivation in multicrystalline-Si materials by plasma-enhanced chemical vapor deposition of SiO2/SiN coatings
Authors: Chen Z. , Rohatgi A. , Bell R. O. , Kalejs J. P.
Published: July 2002

It is shown for the first time that plasma-enhanced chemical vapor deposition (PECVD) passivation which involves low temperature PECVD of ∼100 Å SiO2 and ∼600 Å SiN followed by photoassisted anneal is very effective for both surface and bulk defect passivation in multicrystalline-Si materials. It is found that the effective recombination lifetime increased by a factor of 2–10 depending upon the multicrystalline material. Some solar cells were fabricated using a three-layer PECVD coating (100 Å SiO2/600 Å SiN/950 Å SiO2), the bottom two for passivation and the top two for antireflection coating. The bulk and surface passivation effects were quantified and decoupled by a combination of internal quantum efficiency measurements and computer modeling. It was found that the PECVD passivated solar cells increased bulk lifetime from 10 to 20 μs, and decreased the surface recombination velocity from 2×105 to 5×104 cm/s.
Photoassisted doping of nitrogen into ZnSe using ethyl azide
Authors: Hayashi Keiji
Published: July 2002

Use of ethyl azide as a dopant for nitrogen doping into ZnSe was proposed. Also attempted was photoexciting ethyl azide during metalorganic vapor phase epitaxial growth of nitrogen-doped ZnSe. Low temperature photoluminescence spectra of moderately doped samples were dominated by donor–acceptor pair emissions. Moreover, a substantial photoenhancement of an acceptor incorporation was indicated by the photoluminescence measurements. Supportive evidence of the photoenhancement of chemical reactivity of the ethyl azide molecules was obtained by an in situ optical reflection measurement. A possible mechanism of nitrogen incorporation into ZnSe is discussed.
Observation of localized above-barrier excitons in (CdTe)1(ZnTe)2/ZnTe short-period-superlattice multiple quantum wells by photoluminescence spectroscopy
Authors: Lao Pudong , Guo Yile , Zheng Weimin , Siu G. G. , Li Jie , Yuan Shixin
Published: July 2002

The calculation of energy levels and wave functions of (CdTe)1(ZnTe)2/ZnTe short-period- superlattice multiple quantum wells is performed. It indicates that there may be above-barrier excitons localized in the ZnTe barrier layer. The photoluminescence arising from recombination of the above-barrier excitons has been observed.
Study of interwell carrier transport by terahertz four-wave mixing in an optical amplifier with tensile and compressively strained quantum wells
Authors: Zhou Jianhui , Park Namkyoo , Vahala Kerry J. , Newkirk Michael A. , Miller Barry I.
Published: July 2002

Interwell carrier transport in a semiconductor optical amplifier having a structure of alternating tensile and compressively strained quantum wells was studied by four-wave mixing at detuning frequencies up to 1 THz. A calculation of transbarrier transport efficiency is also presented to qualitatively explain the measured signal spectra.
Electrochromism in tungsten oxyfluoride films made by chemically enhanced dc sputtering
Authors: Azens A. , Stjerna B. , Granqvist C. G. , Gabrusenoks J. , Lusis A.
Published: July 2002

Tungsten oxyfluoride films were prepared by reactive dc sputtering in plasmas containing O2+CF4.. The deposition rate was large, particularly when chemical sputtering was promoted by heating the target. The films could show large charge insertion/extraction and high coloration efficiency.
Sub-100 μA current operation of strained InGaAs quantum well lasers at low temperatures
Authors: Zhao B. , Chen T. R. , Eng L. E. , Zhuang Y. H. , Shakouri A. , Yariv A.
Published: July 2002

Very low threshold currents (<100 μA) have been achieved in InGaAs strained single quantum well lasers at cryogenic temperatures. Threshold currents of 38 and 56 μA and external quantum efficiency ∼1 mW/mA have been demonstrated under cw operation condition at temperatures of 6 and 77 K, respectively. The external quantum efficiency increased by about a factor of 2 at low temperatures (<100 K) in comparison to that at room temperature. These results are relevant to the prospect of integration of semiconductor lasers with low temperature electronics for high performance
Deep donor state of vanadium in cubic silicon carbide (3C-SiC)
Authors: Dombrowski K. F. , Kaufmann U. , Kunzer M. , Maier K. , Schneider J. , Shields V. B. , Spencer M. G.
Published: July 2002

Electron spin resonance (ESR) of silicon-substitutional vanadium in its neutral V4+Si (3d1) state has been observed in cubic bulk 3C-SiC single crystals. By photo-ESR the position of the (0/+) deep donor level of vanadium could be located at EV+1.7 eV. Using this level as common reference in 3C-SiC and 6H-SiC, the valence-band discontinuity in the 3C-SiC/6H-SiC interface is predicted as ΔEV=0.1 eV, with the valence band of 3C-SiC lying lower in energy. We also offer an explanation for the absence of intra-3d-shell infrared luminescence of V4+ (3d1) in 3C-SiC.
Equilibrium defect density in hydrogenated amorphous germanium
Authors: Ebersberger B. , Krühler W. , Fuhs W. , Mell H.
Published: July 2002

The defect density ND of hydrogenated amorphous germanium (a-Ge:H) has been studied as a function of the Fermi level position EF using photothermal deflection spectroscopy. A strong increase of ND is observed as EF is shifted towards either one of the band edges by doping with boron or phosphorus, respectively. This behavior is similar to that of amorphous silicon (a-Si:H) and can be explained by a hydrogen-mediated equilibrium between weak bonds and dangling bonds. From a fit of this model to our data the lowest limit of the defect density in a-Ge:H is estimated to be 2×1016 cm−3, which is larger by about two orders of magnitude than in a-Si:H. The reason for this difference is the smaller band gap of a-Ge:H which entails smaller formation energies of dangling-bond defects than in a-Ge:H.
Morphology and size distribution of oxide precipitates in as-grown Czochralski silicon crystals
Authors: Sueoka K. , Ikeda N. , Yamamoto T.
Published: July 2002

The morphology and size distribution of oxide precipitates in as-grown Czochralski (CZ) silicon crystals, with growth rates of about 1.1 mm/min, have been studied using infrared light scattering tomography (LST). The following results were obtained. (1) The morphology of oxide precipitates in as-grown CZ silicon is polyhedral. (2) The length of the side of the polyhedral precipitates is about 80 nm. According to their morphology and size distribution, it was concluded that they were formed in the high temperature range (≥1000 °C) during crystal growth.
Implementation of superconducting synapses into a neuron-based analog-to-digital converter
Authors: Mizugaki Yoshinao , Nakajima Koji , Sawada Yasuji , Yamashita Tsutomu
Published: July 2002

A superconducting synapse circuit, which allows digitally variable synaptic weights, is presented. Each bit of the synapse circuit consists of 2m (m=0, 1, 2,...) double-junction SQUIDs (superconducting quantum interference devices). Numerical simulation shows that the output current of the circuit can be changed digitally by switching the bias currents. To demonstrate this ability of the synapse experimentally, a superconducting neural network which functions as a 3-bit A/D (analog-to-digital) converter has been fabricated using a niobium integration technology. The network contains three neurons composed of coupled SQUIDs and three synapses composed of double-junction SQUIDs. This is the first successful implementation of such an active synapse into a superconducting neural network.
InGaAs/GaAs quantum well lasers with dry-etched mirror passivated by vacuum atomic layer epitaxy
Authors: Frateschi N. C. , Jow M. Y. , Dapkus P. D. , Levi A. F. J.
Published: July 2002

We report measurements of strained InGaAs/GaAs quantum well laser diodes with electron cyclotron resonance (ECR) plasma etched mirrors that are passivated and smoothed with a novel technique involving the selective area growth of GaAs by vacuum atomic layer epitaxy. The threshold current of as-cleaved, etched, and passivated devices has been studied and a significant improvement in mirror feedback is shown with the passivation and smoothing of etched mirrors oriented along the [001] planes.
Increased transition temperature in in situ coevaporated YBa2Cu3O7−δ thin films by low temperature post-annealing
Authors: Berkowitz S. J. , De Obaldia E. , Ludwig K. F. , Skocpol W. J. , Mankiewich P. M. , Ono R. H. , Beall J. A. , Vale L. R. , Rudman D. A. , O’Malley M. L. , Drabeck L. M. , Polakos P. A.
Published: July 2002

In situ coevaporated YBa2Cu3O7−δ thin films have a slightly depressed transition temperature Tc, though they have excellent radio-frequency surface resistance characteristics. These films consistently have less orthorhombic strain than laser ablated or post-annealed films. Low temperature (320–420 °C) post-annealing of in situ coevaporated films in 100 kPa of O2 raised Tc to values as high as 91.5 K with some increase in the orthorhombic strain. All measured thin films show less variation of Tc with orthorhombic strain than does bulk material.
Novel approach for synthesizing Ge fine particles embedded in glass by ion implantation: Formation of Ge nanocrystal in SiO2-GeO2 glasses by proton implantation
Authors: Hosono Hideo , Matsunami Noriaki , Kudo Atsushi , Ohtsuka Tosiaki
Published: July 2002

Nanometer-sized crystalline Ge colloid particles have been formed by implantation of protons into substrate glasses having a composition of 1 GeO2-9SiO2 to a fluence of 1×1018 cm−2 at an energy of 1.5 MeV at room temperature without post-thermal annealing. Intensities of the absorption band due to Ge particles reach a maximum at ∼30 μm from the surface and their depth profile is close to that of the electronic energy loss. No formation of Si particles was observed in SiO2 or SiO2:GeO2 glasses implanted with protons at the same conditions and fluence.
Consequences of the silicon donor distribution tail in δ-doped, pseudomorphic AlxGa1−xAs/In1−yGa1−yAs modulation-doped heterostructures
Authors: Young A. P. , Chen Jianhui , Wieder H. H.
Published: July 2002

We have investigated the properties of modulation-doped, pseudomorphic AlxGa1−xAs/ InyGa1−yAs heterostructures containing embedded, Si δ-doped GaAs wells. From resistivity and Hall effect measurements, and from Shubnikov–de Haas measurements at 1.6 K, we have determined the charge transport parameters before and after optically induced ionization of the DX centers in the structures. We find a DX center diffusion tail associated with the δ-doped donors extending into the undoped AlxGa1−xAs barrier and spacer layers and conclude that for efficient modulation doping of a quantum well, δ-doping and embedding of the donors within a GaAs well can reduce but not entirely eliminate the effects of DX centers on the charge transport parameters.
Self-mode-locking suppression with intracavity fullerenes
Authors: Zeng Heping , Luo Ting , Zhao Jiran , Jiang Minghua , Mao Sen , Meng Zhicong , Lin Fucheng
Published: July 2002

We present the experimental results on how to suppress self-mode-locking in a free-run or Q-switched Nd:YAG laser with intracavity fullerenes. It was demonstrated that the self-mode-locking was partly or completely suppressed when a certain sample containing fullerenes, such as C60 toluene solution, C60 in polystyrene host, or optical glass doped with fullerenes, was placed within the laser resonator, and that the degree of suppression was dependent upon the length and fullerenes concentration of the sample. Qualitative analysis showed that the nonlinear absorption of the intracavity fullerenes resulted in this effect.
Violet luminescence from anodized microcrystalline silicon
Authors: Zhao Xinwei , Schoenfeld Olaf , Aoyagi Yoshinobu , Sugano Takuo
Published: July 2002

Microcrystalline silicon (μ-Si) thin films were anodized in dilute HF solutions in the same manner as forming porous materials. It is demonstrated for the first time that the anodized μ-Si thin films show strong violet luminescence (415 nm) at room temperature. Visible green and red emissions were also observed accompanying the violet luminescence. Structural investigations with scanning electron microscopy indicate that any formation of micrometer-sized pores which is typical for porous silicon does not exist in the anodized μ-Si thin films as reported here. This fact is useful for device applications of silicon-based materials.
Second-harmonic generation in a waveguide with domain-inverted regions like periodic lens sequence on z-face KTiOPO4 crystal
Authors: Yamamoto Yukihiro , Yamaguchi Satoshi , Suzuki Kazuo , Yamada Noriko
Published: July 2002

A domain-inverted waveguide with refractive-index distribution of a periodic lens sequence instead of a conventional square shape was fabricated in a z-cut KTiOPO4 (KTP) crystal. In the periodic lens sequence waveguide, the propagated laser beam through the waveguide was collimated and focused into a spot with a minimum amount of dispersion. The reason for the phenomenon of this periodic lens sequence waveguide structure can be explained from the viewpoint of ray matrix approximation.
Effect of electron-hole correlation on acoustic phonon broadening of bound exciton spectra
Authors: Chou C. J. , Neumark G. F.
Published: July 2002

It is well-known, experimentally, that bound exciton lines are extremely sharp, particularly in comparison to other related spectra. This has not been theoretically explained. We show here that this is due to the electron-hole correlation, which effectively suppresses the electron-phonon interaction and thus the associated spectral broadening. Using appropriate correlated exciton wave functions together with the deformation potentials and the piezoelectric coupling for the acoustic phonons, we obtain exciton line widths in good agreement with experiment. Our results have direct application to the recently demonstrated blue-green injection laser.
Low resistance ohmic contact on n-CdTe
Authors: Brun D. , Daudin B. , Ligeon E.
Published: July 2002

Metallic europium has been epitaxially grown by molecular beam epitaxy on (001) n-CdTe, with formation of an interfacial layer resulting from a rare-earth–CdTe reaction. One basic result is that the interfacial layer can be formed not only with Eu but also with other rare earths, namely Sm or Nd. It has been demonstrated that the specific contact resistance of such heterostructures is dependent on the rare earth involved in the interfacial layer formation. In the case of a Nd-based layer, the lowest specific contact resistance of the Eu/interfacial-layer/n-CdTe heterostructure is found to be ρc≂2⋅10−3 Ω cm2.
Diamagnetic shifts of excitons associated with symmetric and antisymmetric wave functions in coupled InxGa1−xAs-GaAs quantum wells
Authors: Reynolds D. C. , Look D. C. , Jogai B. , Stutz C. E.
Published: July 2002

Magneto-optical data obtained from photoluminescence and photoluminescence excitation measurements performed in the presence of applied magnetic fields were used to determine the diamagnetic shifts of free excitons. The samples studied were coupled InxGa1−xAs–GaAs quantum wells. In all cases the excitons associated with antisymmetric wave functions were found to have larger diamagnetic shifts than the excitons associated with symmetric wave functions. This suggests that the excitons associated with antisymmetric wave functions have a smaller binding energy than excitons associated with symmetric wave functions. These properties are consistent with the fact that excitons associated with antisymmetric wave functions are less confined than excitons associated with the symmetric wave functions.