bluuebunny/crossref_metadata_2025 huggingface dataset:
Electromigration in p-type ZnSe:Li
Authors: Haase M. A. , DePuydt J. M. , Cheng H. , Potts J. E.
Published: July 2002

Electromigration has been observed in certain Li-doped p-type ZnSe epitaxial layers. A correlation is observed between the magnitude of the electromigration and the degree of compensation in the layers, which is consistent with electromigration of Li interstitials. Significantly, uncompensated layers show no electromigration, illustrating that Li atoms on Zn lattice sites (acceptors) are stable at room temperature. The effects of electromigration on the behavior of ZnSe blue light-emitting diodes is considered, and shown to be beneficial in devices with compensated p-type layers.
Deep level transient spectroscopy based on conductance transients
Authors: Fourches N.
Published: July 2002

A new technique derived from the original deep level transient spectroscopy (DLTS) analysis is presented here. We show that for materials, which have a too low free-carrier concentration and are therefore unsuitable for the capacitance transient method, it is nevertheless possible to construct a DLTS signal which enables the observation of deep traps in the space-charge region of the sample studied. This method is based on the analysis of conductance transients. We demonstrate the usefulness of this technique when applied to the study of neutron-induced traps in thick (1.5 cm) high-purity germanium samples.
Raman analysis of Si/Ge strained-layer superlattices under hydrostatic pressure
Authors: Sui Zhifeng , Herman Irving P. , Bevk Joze
Published: July 2002

Raman scattering was used to study optical phonons in a Si12Ge4 strained-layer superlattice on c-Si(001) that was subjected to hydrostatic pressure at room temperature. The change of phonon frequency with pressure, dω/dP, for the principal quasi-confined LO mode in the Ge layers, is found to be significantly smaller than that for bulk crystalline Ge. This difference is shown to be due to the tuning of biaxial strain in the Ge layers and the pressure response of the confined mode as hydrostatic pressure is varied. Both strain and confinement make comparable contributions to dω/dP for the Ge layers in the superlattice examined here.
Generation of 27 fs pulses of 70 kW peak power at 80 MHz repetition rate using a cw self-pulsing Ti:sapphire laser
Authors: Likforman J. P. , Grillon G. , Joffre M. , Le Blanc C. , Migus A. , Antonetti A.
Published: July 2002

We have built a self-mode-locked Ti:sapphire cw oscillator delivering up to 2 W of average output power. This oscillator provides 100 fs pulses tunable in the 770–807 nm range. Using a fiber-prism compressor at the cavity output, the pulses have been compressed down to 27 fs at 785 nm, while keeping 200 mW average power.
Observation of photoluminescence from InAs surface quantum wells grown on InP(100) by molecular beam epitaxy
Authors: Sobiesierski Z. , Clark S. A. , Williams R. H. , Tabata A. , Benyattou T. , Guillot G. , Gendry M. , Hollinger G. , Viktorovitch P.
Published: July 2002

Photoluminescence (PL) measurements are presented for thin epitaxial layers of InAs, 2.5 Å<d <36 Å, grown on InP(100) by molecular beam epitaxy. The combination of efficient carrier capture and PL redshift with increasing InAs thickness clearly indicate the formation of InAs quantum wells on the InP surface. Data are also presented for InAs/InP structures capped with strained layers of either GaAs or In0.5 Al0.5 As. Since radiative recombination within the InAs layers can be distinguished from PL arising from both bulk and surface defects, this system allows us to monitor the quality of both the InAs/InP and InAs/air interfaces via their influence on the InAs quantum well luminescence.
Na2 violet band excimer emission by electron beam excitation
Authors: Xing Da , Ueda Ken-ichi , Takuma Hiroshi
Published: July 2002

We have observed an amplified spontaneous emission of the Na2 violet diffuse band in electron beam excited mixtures of sodium vapor with either argon or helium buffer gas. The strong continuum emission centered at 436 nm was attributed to the 23Π+g → a3Σ+u bound-free triplet band of Na2, which was already observed in the optical pumping.
Proton radiation effects in microwave cavities and ring resonators fabricated from YBa2Cu3O7−δ
Authors: Weaver B. D. , Pond J. M. , Chrisey D. B. , Horwitz J. S. , Newman H. S. , Summers G. P.
Published: July 2002

We report the first radiation effects study on a superconducting ring resonator made from thin-film YBa2Cu3O7−δ. Exposure to 2 MeV protons causes the superconducting transition temperature Tc to decrease predictably with fluence. For temperatures below about 0.9Tc , there is no significant change in the transmission coefficient, the center frequency, or the quality factor Q of the resonator, even for doses in excess of 4×1016 protons/cm2 (∼0.04 displacements per film atom). Similarly, the low-temperature surface resistance Rs of an unpatterned film does not change with irradiation. We show that this insensitivity to radiation is not predicted by standard theory, and that the dominant part of Rs at low temperature is the residual resistance R0. Thus any viable theory describing the origin of R0 must, as a criterion, explain the origin of its insensitivity to large irradiation doses. This criterion is used to evaluate theories ascribing R0 to weak links, flux pinning, impurities, and lattice imperfections.
Ion-implanted extrinsic Ge photodetectors with extended cutoff wavelength
Authors: Wu I. C. , Beeman J. W. , Luke P. N. , Hansen W. L. , Haller E. E.
Published: July 2002

Far-infrared properties of a two-layer structure consisting of an ion-implantation doped layer on a thin ultrapure slice of germanium have been studied. Photoresponse extends beyond the shallow impurity absorption edge at 120 μm to about 192 μm. Photoconductivity studies have been performed between 4.2 and 1.3 K. Detectors with an area of 1×1 mm2 have dark currents of less than 100 electrons/s at temperatures ≤1.3 K at a bias of 70 mV. A responsivity of 0.9 A/W and a noise equivalent power of 5×10−16 W/Hz1/2 have been measured using photons in a narrow band 99±0.5 μm.
Crystal structure and superconductivity of (La,Sr)2CuO4/Sm2CuO4 superlattices prepared by excimer laser deposition
Authors: Tabata Hitoshi , Kawai Tomoji , Kawai Shichio
Published: July 2002

We have grown superlattices of (La,Sr)2CuO4/Sm2CuO4 [1/1 to 120/120] onto SrTiO3 substrates by an excimer laser deposition technique. These superlattices can be classified into three regions. For the short periodicity of the stacking up to 4/4, new structures are constructed having a large unit cell made of a CuO5 pyramid, CuO6 octahedral, and CuO4 sheet. For the large periodicity more than 60/60, the superlattices exhibit the same superconducting behavior as the standard (La,Sr)2CuO4. The superlattices of the intermediate periodicity, from 60/60 to 15/15 on the other hand, show changes in the critical temperature as the variation of the stacking periodicity. This phenomenon is explained to be derived from a pressure effect caused by a lattice mismatch between (La,Sr)2CuO4 and Sm2CuO4 layers.
Subpicosecond characterization of carrier transport in GaAs-metal-semiconductor-metal photodiodes
Authors: Lambsdorff M. , Klingenstein M. , Kuhl J. , Moglestue C. , Rosenzweig J. , Axmann A. , Schneider Jo. , Hülsmann A. , Leier H. , Forchel A.
Published: July 2002

The temporal evolution of the photocurrent in interdigitated GaAs metal-semiconductor- metal Schottky photodiodes is directly measured in the time domain by photoconductive and electro-optic sampling with subpicosecond resolution. Excellent agreement is found between experiment and theoretical data obtained by two-dimensional self-consistent Monte Carlo calculations.
X-ray scattering studies of the SiO2/Si(001) interfacial structure
Authors: Rabedeau T. A. , Tidswell I. M. , Pershan P. S. , Bevk J. , Freer B. S.
Published: July 2002

X-ray scattering has been utilized in a study of the SiO2/Si(001) interfacial structure. Scattering data provide evidence for a low coverage 2×1 epitaxial structure at the SiO2/Si interface for dry oxides grown on highly ordered Si surfaces at room temperature. The observed scattering is consistent with distorted dimer models of the interfacial structure. Thermal annealing substantially reduces the order of the 2×1 structure while prolonged exposure to humid air almost eliminates the 2×1 symmetry scattering. These findings suggest that the observed 2×1 order is associated with a metastable, intermediate state of the dry oxidation process.
Thermally stimulated current in neutron-transmutation-doped semi-insulating GaAs
Authors: Kuriyama K. , Yokoyama K. , Satoh Akemi
Published: July 2002

The evaluation of the defects in neutron-transmutation-doped semi-insulating GaAs was studied using a thermally stimulated current (TSC) method. Some native defects were decomposed by the neutron irradiation and one TSC peak was observed in an as-irradiated sample. This peak is associated with a complex defect, which is identified as a AsGa-VAs complex according to the analysis of the activation energy.
Dynamic optical reflectivity to monitor the real-time metalorganic molecular beam epitaxial growth of AlGaAs layers
Authors: Farrell Trevor , Armstrong John V. , Kightley Philip
Published: July 2002

Oscillations in the reflectivity of AlxGa1−xAs, grown on GaAs at 870 K have been measured at 632.8 nm over the range 0≤x≤1. The oscillations are fitted to the standard theory of reflection from a bilayer with the complex refractive index (n+ik) of substrate and film as fitting parameters. For GaAs the values of n and k are measured as 3.9+i0.23 at 870 K. Assuming n varies linearly with x for AlxGa1−xAs between 3.1(A1As) and 3.9(GaAs) then the period of the oscillations gives an accurate measurement of growth rate, while the amplitude allows the film composition to be monitored simultaneously. All layers were grown by metalorganic molecular beam epitaxy (MOMBE).
High quantum efficiency strained InGaAs/AlGaAs quantum-well resonant-cavity inversion channel bipolar field-effect phototransistor
Authors: Daryanani S. , Taylor G. W. , Cooke P. , Evaldsson P. , Vang T.
Published: July 2002

A high-efficiency, resonant-cavity, bipolar inversion channel field-effect transistor detector is demonstrated with a triple-strained InGaAs quantum-well absorbing region. A quantum efficiency of 80% is obtained at a resonant wavelength of 0.94 μm, and a bandwidth of 20 Å, giving a 26-fold enhancement in absorption due to resonance. The transistor detector operates in the FET mode with an independent gate electrode to control its sensitivity, and in a bipolar mode with a photogain of 25. The structure is identical to that used in other inversion channel laser structures, and hence provides an optimum configuration for optoelectronic integration. This is the first demonstration of a three-terminal quantum-well resonant-cavity photodetector.
Symmetric Si/Si1−xGex two-dimensional hole gases grown by rapid thermal chemical vapor deposition
Authors: Venkataraman V. , Schwartz P. V. , Sturm J. C.
Published: July 2002

Single and symmetric double p-type modulation-doped structures have been fabricated in Si/SiGe for the first time by rapid-thermal chemical-vapor deposition. Temperature-dependent electrical measurements and high-field magnetotransport measurements demonstrate the presence of a well-confined two-dimensional hole gas in these samples. Nominally-symmetric normal and inverted structures differ in carrier density and mobility at most by 20%, indicating that there is little asymmetry due to surface segregation or autodoping effects. Measurements on double heterostructures confirm that the interfaces are symmetric to within 10 Å. Peak mobilities reached 2500 cm2/V s at 10 K, comparable to those obtained in similar samples grown by ultrahigh vacuum techniques.
Electron-cyclotron-resonance plasma-enhanced chemical vapor deposition of epitaxial Si without substrate heating by ultraclean processing
Authors: Fukuda Koichi , Murota Junichi , Ono Shoichi , Matsuura Takashi , Uetake Hiroaki , Ohmi Tadahiro
Published: July 2002

By Ar plasma-enhanced decomposition of SiH4 using ultraclean electron-cyclotron-resonance plasma processing, low-temperature Si epitaxy has been achieved even without external substrate heating for the first time. Ar plasma pre-exposure experiments have revealed that Ar ion energies lower than a few eV are favorable for Si epitaxy at low temperatures, in order to suppress plasma damage on the surface crystallinity. Furthermore, it has been found that addition of H2 to the Ar plasma is extremely effective to remove the native oxide layer on the Si surface.
Optical parametric amplification in a lithium triborate crystal tunable from 0.65 to 2.5 μm
Authors: Lin Shujie , Huang J. Y. , Ling Jiwu , Chen Chaungtian , Shen Y. R.
Published: July 2002

We investigate the phase-matching properties and the performances of lithium triborate (LBO) crystals, angle- and temperature-tuned to achieve type-I phase matching for ps, high-power, tunable optical parametric amplification (OPA). A novel retracing behavior was observed in the tuning curves of the LBO OPA.
Redistribution of epitaxial Si on (001) GaAs during overgrowth by GaAs
Authors: Brandt O. , Crook G. E. , Ploog K. , Wagner J. , Maier M.
Published: July 2002

We examine the stability of pseudomorphic submonolayer Si films embedded in (001) GaAs by molecular-beam epitaxy. Secondary ion-mass spectrometry depth profiling reveals the presence of 1019 Si-atoms/cm3 in the first 40 nm of the GaAs cap layer. The systematic investigation of samples having different cap thickness by Hall effect measurements and local vibrational mode Raman spectroscopy allows us to identify the site distribution of Si atoms in the cap layer and yields insight into the migration mechanism.
Critical-current enhancement in particle-irradiated cuprate semiconductors
Authors: Weaver B. D. , Reeves M. E. , Summers G. P. , Soulen R. J. , Olson W. L. , Eddy M. M. , James T. W. , Smith E. J.
Published: July 2002

Detailed measurements have been made of the magnetic field (0<H<6 T) and temperature (10 K<T<100 K) dependencies of the critical current density jc in Tl2CaBa2Cu2O8 films before and after irradiation with incremental fluences (0<Φ<3×1016 cm−2) of 2 MeV protons. The results are interpreted quantitatively in terms of radiation-induced changes in (1) the critical temperature, (2) the rate of thermal flux creep, and (3) local scale superconductivity. Radiation-induced enhancements in jc are described by an expression which allows the fluence that maximizes jc to be predicted as a function of H, T, pinning energy, and particle type.
High power laser-amplifier photonic integrated circuit for 1.48 μm wavelength operation
Authors: Koren U. , Jopson R. M. , Miller B. I. , Chien M. , Young M. G. , Burrus C. A. , Giles C. R. , Presby H. M. , Raybon G. , Evankow J. D. , Tell B. , Brown-Goebeler K.
Published: July 2002

We demonstrate a laser amplifier photonic integrated circuit having 370-mW cw output power emitted in a single transverse mode a 1.48 μm wavelength, suitable for pumping erbium-doped fiber amplifiers.
X-ray reflectivity measurements of the expansion of carbon films upon annealing
Authors: Lucas C. A. , Nguyen T. D. , Kortright J. B.
Published: July 2002

Measurements have been made of the x-ray reflectivity from ultrathin, amorphous carbon films both before and after annealing. Analysis of the x-ray results indicates that annealing causes an increase in film thickness with a corresponding decrease in density. Such behavior is uncharacteristic of amorphous thin films and is interpreted as being due to changes in the interatomic bonding associated with transition to a more graphitic microstructure.
Thermochemistry on a fluorinated diamond (111) surface
Authors: Harris Stephen J. , Belton David N.
Published: July 2002

We have performed calculations to evaluate mechanisms for growth of diamond on fluorinated diamond surfaces. These surfaces are very hard and have excellent tribological properties. Our calculations show that steric repulsion between neighboring F atoms on the fully fluorinated surface studied is small, which−given the strength of C—F bonds−implies that this surface should be chemically very stable. Our analysis also shows that in the absence of hydrogen, growth of diamond on a fluorinated surface is thermodynamically so unfavorable that it will not occur. Finally, diamond growth on fluorinated surfaces could be quite favorable in the presence of hydrogen and hydrocarbons.
Nonlinear transport phenomena in a triangular quantum well
Authors: Kastalsky A. , Peeters F. , Chan W. K. , Florez L. T. , Harbison J. P.
Published: July 2002

We have measured transport properties in an AlGaAs/AlxGa1−xAs, triangular quantum well whose energy spectrum has been varied by means of gate bias. We have observed several nonlinear effects in the lateral conductance arising at positive gate voltages as the increasing Fermi level is moved toward the lowering energy positions of the excited subbands in the quantum well. We interpret our results in terms of electron population of the excited subbands in which electrons possess low mobility. Finally, we find new features at high lateral voltages which are considered to be an evidence of previous predicted electrophonon resonance.
Observation of the InP surface thermally cleaned in an arsenic flux using a scanning tunneling microscope
Authors: Ohkouchi Shunsuke , Tanaka Ichiro
Published: July 2002

An InP surface thermally cleaned in an arsenic flux was observed using an ultrahigh-vacuum scanning tunneling microscope (UHV-STM). In the STM image, about 1.6 nm period lines of 0.8 nm width with two rows were observed along the [110] direction. This result suggests that the surface comprises two In-In dimers and two missing dimers per (4×2) cells.
Linewidth dependence of critical current density in Y1Ba2Cu3O7 thin-film microbridges
Authors: Zhao Y. J. , Chu W. K. , Christen D. K. , Jones E. C. , Davis M. F. , Wolfe J. C. , Deshmukh S. C. , Economou D. J.
Published: July 2002

A study of the dependence of the transport critical current density (Jc) on the width of Y1Ba2Cu3O7 thin-film microbridges with widths down to 2 μm has been made. No evidence of edge pinning, which leads to larger Jc’s in narrower microbridges, was found. Due to the limitation in resolution of photolithography encountered in common usage, a tapered or radiation damaged edge was always present, which may have introduced a significant error in the cross section and hence in the estimation of Jc. By normalizing the critical current (Ic) to the room-temperature resistance of the microbridge, we can eliminate this mask-defined cross-sectional error.
Hexagonal barium titanate films
Authors: Kumar C. V. R. Vasant , Dhar Ajay , Mansingh Abhai
Published: July 2002

The fabrication of hexagonal barium titanate films by sputtering technique is reported. Compressed powders of hexagonal barium titanate were sputtered in argon/oxygen gas mixtures. The as-grown films were amorphous and a post-deposition annealing above 700 °C resulted in the crystallization of the films with hexagonal crystal structure. Transmission electron microscopy was used to study the crystallization of the amorphous films.
Deep levels associated with oxidation induced stacking faults in n-type silicon
Authors: Kaniewski J. , Kaniewska M. , Peaker A. R.
Published: July 2002

Deep level transient spectroscopy (DLTS) has been used to measure the electrical activity of oxidation induced stacking faults in silicon. It is found that if the entire stacking fault is examined, a broad, almost featureless DLTS spectrum is observed. If, however, the fault is spatially profiled, the spectrum deconvolutes into the form of DLTS peaks usually associated with point defects. We link one of the states specifically with the Frank partial dislocation bounding the stacking fault. This state has an activation energy which depends on its position along the partial dislocation.
Broadly tunable InGaAsP/InP laser based on a vertical coupler filter with 57-nm tuning range
Authors: Alferness R. C. , Koren U. , Buhl L. L. , Miller B. I. , Young M. G. , Koch T. L. , Raybon G. , Burrus C. A.
Published: July 2002

We have integrated a broadly tunable grating-assisted vertical coupler as an intracavity filter to demonstrate a novel monolithic multiple-quantum-well InGaAsP/InP laser. The narrow, bandpass intracavity filter results in an extended cavity laser with a measured electrical tuning range of 57 nm with single-frequency operation over most of that range.
Formation of TiN-encapsulated copper structures in a NH3 ambient
Authors: Li Jian , Mayer J. W. , Shacham-Diamand Y. , Colgan E. G.
Published: July 2002

A TiN-encapsulated copper structure was made by annealing a Cu-10 at. %Ti alloy film evaporated on a SiO2/Si(100) substrate at 550 °C in a NH3 ambient. A fast heating rate (70 °C/min) to 550 °C can effectively suppress the formation of Cu3Ti and enhance the TiNx formation near the surface of the copper film. Oxygen incorporation in the TiNx layer was found by Auger depth profiling measurement. This self-encapsulated Cu structure exhibits good adhesion to SiO2 and oxidation resistance.
Radiation-induced E′ centers in H2-annealed oxide films
Authors: Zvanut M. E. , Stahlbush R. E. , Carlos W. E.
Published: July 2002

In oxides fabricated by thermal oxidation or ion implantation, an order-of-magnitude increase is observed in the concentration of radiation-induced E′ centers when the oxide is first exposed to H2 at temperatures greater than 600 °C. To the authors’ knowledge, we report the first data indicating that preirradiation hydrogen annealing of thermal oxides causes a large increase in the concentration of radiation-induced E′ centers. We discuss evidence suggesting that the hydrogen anneal creates a new E′ precursor, Si—H, from Si—Si bonds.
Absorption spectra of ZnSe-ZnS strained-layer superlattices grown on (001) GaAs by molecular beam epitaxy
Authors: Shen Aidong , Wang Hailong , Wang Zhijiang , Lü Shaozhe
Published: July 2002

The absorption spectra of ZnSe-ZnS strained-layer superlattices were measured at temperatures ranging from 16 K to room temperature. Three excitonic absorption peaks corresponding to 1E-1HH, 1E-1LH, and 1E-3HH transitions were observed for the first time.
Processing of a uniaxial ferroelectric Pb5Ge3O11 thin film at 450 °C with c-axis orientation
Authors: Lee J. J. , Dey S. K.
Published: July 2002

Uniaxial Pb5Ge3O11 thin films were successfully fabricated by the sol-gel processing route. Crack-free and c-axis oriented thin films (1600 Å) were observed on (111) Pt-coated Si substrates when heat treated at 450 °C for 15 min. The thin films exhibited well saturated P-E hysteresis loops with Pr=3.3 μC/cm2, Ps=3.7 μC/cm2, and Ec=135 kV/cm. Specifically, a 1600 Å film switched at 2.2 V. The possible applications such as nonvolatile ferroelectric memories and CCD IR image sensors without fatigue or retention problems, are discussed.
Use of tertiarybutylarsine in atomic layer epitaxy and laser-assisted atomic layer epitaxy of device quality GaAs
Authors: Chen Q. , Beyler C. A. , Dapkus P. D. , Alwan J. J. , Coleman J. J.
Published: July 2002

The use of trimethylgallium (TMGa) and tertiarybutylarsine (TBAs) in atomic layer epitaxy (ALE) and laser-assisted atomic layer epitaxy (LALE) of GaAs is studied for the first time. TBAs is found to be a direct and suitable replacement for arsine (AsH3) in achieving monolayer self-limiting growth. Carbon contamination in the GaAs films grown by LALE using TMGa and TBAs is greatly reduced relative to those using TMGa and AsH3. Laser structures single GaAs quantum wells grown by ALE and LALE using TBAs exhibit threshold current density as low as 300 and 520 A/cm2, respectively.
Ferroelectric lead niobate films by pulsed thermal processing
Authors: Vasant Kumar C. V. R. , Sayer M. , Pascual R.
Published: July 2002

Ferroelectric lead niobate (PbNb2O6) exists in an orthorhombic phase at room temperature. The fabrication of lead niobate in this ferroelectric form has often been reported to be difficult due to the stabilization of nonferroelectric phases during processing. In this letter, the stabilization of the orthorhombic phase in magnetron sputtered lead niobate films using ‘‘pulsed thermal processing’’ is reported, and various processing factors which influence the destabilization of this phase are discussed. The room-temperature dielectric constant and loss tangent of the resulting films at 1 kHz were 320 and 0.4, respectively. Polarization versus electric-field hysteresis loops showed no saturation, with a remanent polarization of 15 μC/cm2 and a coercive field of 500 kV/cm. The films were highly resistive with a dc conductivity of 1−10 Ω−1 cm−1 at 300 K.
Low threshold, 633 nm, single tensile-strained quantum well Ga0.6In0.4P/(AlxGa1−x)0.5In0.5P laser
Authors: Bour D. P. , Treat D. W. , Thornton R. L. , Paoli T. L. , Bringans R. D. , Krusor B. S. , Geels R. S. , Welch D. F. , Wang T. Y.
Published: July 2002

Low threshold, 633 nm diode lasers are demonstrated. These devices contain a single, 80 Å, tensile-strained Ga0.6In0.4P quantum well (QW) active region, and Al0.5In0.5P cladding layers, grown by low-pressure organometallic vapor phase epitaxy on misoriented substrates. Operating characteristics are compared with low-threshold, 680 nm compressively strained Ga0.4In0.6P QW lasers. Although performance is not as good as for the 680 nm devices, the 633 nm lasers have characteristic temperature T0∼60 K and low pulsed threshold current density (400 A/cm2). These improved characteristics are believed due to the incorporation of a single, tensile-strained QW, along with (Al0.6Ga0.4)0.5In0.5P confining layers, which offer increased electron confinement.
Evidence for heavy ion channeling in AlGaAs at low energies
Authors: Stoffel N. G. , Schwarz S. A. , Pudensi M. A. A. , Kash K. , Florez L. T. , Harbison J. P. , Wilkens B. J.
Published: July 2002

We used a new molecular dynamics simulation program to model the scattering of low-energy ions into the relatively open 〈011〉 axial channels of zinc-blende crystals. We also implanted 1–5 keV Si ions into GaAs/AlGaAs multiple-quantum well samples and used secondary ion mass spectrometry and photoluminescence to search for the deep ion penetration and optical damage which are characteristic of this ion channeling. Both the simulated and measured Si depth distributions have exponential tails extending at least 20 times further than the mean ion range. The photoluminescence efficiencies are severely degraded in the quantum wells which are overlapped by the observed Si profile tails. These results suggest that unintentional ion channeling is a major factor in the extensive degradation of optical and electrical properties of semiconductor surfaces which are exposed to low-energy ion bombardment during device fabrication.
Observation of light emission from real-space transfer devices
Authors: Higman T. K. , Hagedorn M. S. , Chen Jihong , Cheng K. Y.
Published: July 2002

Light emitters based on real-space transfer devices can be brought about by several mechanisms. The most efficient of these is the injection of minority electrons across a semiconductor heterojunction into a p-type collecting layer. So far, problems associated with the growth of p-type collecting layers have hindered efforts in this area. In this letter we report on light emission caused by the real-space transfer of majority electrons into an n-type collecting layer. We propose a mechanism to account for this light which consists of hole creation by impact ionization of real-space transferred electrons.
Novel strained InP/InAsxP1−x quantum-well modulation-doped heterostructures
Authors: Hong W.-P. , Bhat R. , Hayes J. , DeRosa F. , Leadbeater M. , Koza M.
Published: July 2002

We report the first investigation of transport properties of two-dimensional electron systems in strained InAsxP1−x quantum-well channels. The InP/InAsxP1−x modulation-doped heterostructures were grown by the low-pressure OMCVD technique. The dependence of the transport parameters on the arsenic composition (x) has been studied using Hall, Shubnikov de Haas, and cyclotron resonance measurements. Hall mobilities of 6100 and 52 700 cm2/V s, with carrier concentrations of 2.3×1012 and 1.5×1012 cm−2 at 300 and 77 K, respectively, were measured for x=0.6.
On the debris phenomenon with laser-sputtered polymers
Authors: Kelly Roger , Miotello Antonio , Braren Bodil , Otis Charles E.
Published: July 2002

The sputtering of polymer films with 248 or 308 nm laser pulses causes two groups of particles to be emitted. Light particles are emitted more rapidly and escape to form a shock wave. Heavy particles are emitted more slowly and under some conditions are impeded by the light ones, expand sideways, and leave debris on the target surface. Debris formation can be understood from ordinary gas dynamics where it is equivalent to recondensation beyond the bombarded spot. This is shown by numerical solution of the flow equations.
Ultraviolet defined selective in-diffusion of organic dyes in polyimide for applications in optical interconnection technology
Authors: Chakravorty K. K.
Published: July 2002

We report here, for the first time, a novel ultraviolet (UV) defined selective in-diffusion technique for refractive index alterations in a BTDA-alkylated diamine type of preimidized polyimide film. This has been achieved by in-diffusing disperse red 1 (DR1) dye into the polyimide film from an organic solvent-based solution. UV photocrosslinking of the polyimide chains was observed to significantly suppress the in-diffusion of DR1 and provided the means for selective doping of this dye in the polyimide film. This technique is amenable to a laser direct write maskless approach for applications in integrated optics. We have demonstrated this technique by fabricating a low-loss (<0.5 dB/cm) embedded polyimide channel waveguide.
Heat propagation in high T
c films investigated by optical response measurements
Authors: Zeuner S. , Lengfellner H. , Betz J. , Renk K. F. , Prettl W.
Published: July 2002

The optical response of granular Tl-Ba-Ca-Cu-O films has been used to investigate thermal properties of the films. An analysis of the response using a heat transfer model yields a thermal diffusivity D=10−3 cm2/s at 150 K which rises to 6×10−3 cm2/s at a temperature of 30 K and allows for an estimation of the boundary resistance Rbd≊10−3 K cm2/W between film and substrate. The dependence of the response time on film thickness obtained from the heat transfer model is compared with published data indicating that in many experiments the observed response is mainly bolometric in origin.
Very high efficiency GaInAsP/GaAs strained-layer quantum well lasers (λ=980 nm) with GaInAsP optical confinement layers
Authors: Groves S. H. , Walpole J. N. , Missaggia L. J.
Published: July 2002

A large increase in differential quantum efficiency from 35% to ≳45% per facet is obtained using a GaInAsP alloy (Eg≊1.65 eV), instead of GaAs, for the optical confinement layers in GaInAsP/GaAs strained-layer single quantum well separate confinement heterostructure diode lasers (λ=980 nm). The maximum value measured corresponds to a double-ended differential quantum efficiency of 93.4% and a slope efficiency of 1.18 mW/mA. The effective internal cavity loss in these structures is only ∼1 cm−1.
Single-electron effects in a point contact using side-gating in delta-doped layers
Authors: Nakazato Kazuo , Thornton Trevor J. , White Julian , Ahmed Haroon
Published: July 2002

Side-gated point-contact structures in delta (δ)-doped layers have been used to form single-electron tunnel junctions with variable resistance. Clear Coulomb-blockade effects have been observed in the current-voltage characteristics. The measured characteristics are described in terms of a series of single-electron transistors formed by microsegments within the point contact. The effective tunnel capacitance and side-gate capacitance are estimated to be 10 and 1 aF, respectively, which are both one order of magnitude smaller than the reported capacitance of tunnel junctions made from Al or GaAs/AlGaAs heterostructures.
Hydrogenation of wide-band-gap II-VI semiconductors
Authors: Pong C. , Johnson N. M. , Street R. A. , Walker J. , Feigelson R. S. , De Mattei R. C.
Published: July 2002

The incorporation of plasma-generated monatomic hydrogen into a wide-band-gap II-VI zincblende semiconductor (e.g. ZnSe) has been achieved by using a deposited layer of silicon dioxide as a hydrogen-permeable encapsulation to prevent decomposition (etching) of the semiconductor during hydrogenation. Depth profiles from secondary-ion mass spectrometry demonstrate deuterium penetration into ZnSe layers epitaxially grown on GaAs. Low-temperature photoluminescence reveals that the commonly observed donor-acceptor pair transitions are selectively removed by hydrogenation.
Magneto-optical observation of flux pinning at the grain boundary in a Bi2Sr2CaCu2Ox superconductor
Authors: Nakamura N. , Gu G. D. , Takamuku K. , Muarkami M. , Koshizuka N.
Published: July 2002

Magnetic flux density distributions in a Bi2Sr2CaCu2Ox superconducting crystal for fields perpendicular to the bc plane are observed by a magneto-optical technique. It is recognized that flux is pinned at the low angle grain boundary while barely pinned at the high angle boundary or in the intragranular regions. The contributions of the low angle boundary to the critical current density and the magnetization are estimated from the magneto-optical results by using a flux pinning model, and then compared with the results of magnetization measurements.
Differential gain in InP-based strained layer multiple quantum well lasers
Authors: Nichols D. , Bhattacharya P.
Published: July 2002

Compressive biaxial strain has been predicted to enhance the small-signal modulation bandwidth of quantum well lasers, owing to increased differential gain in these devices. However, the effect of tensile strain on these devices is less clear. We have investigated the effects of both compressive and tensile strain on the differential gain for multiple quantum well lasers with InxGa1−xAs quantum wells for 0.33≤x≤0.73. We observe markedly increased differential gain for both compressive and tensile strain, indicating that large modulation bandwidths can be obtained in both cases.
Photorefractive effect in a new organic system of doped nonlinear polymer
Authors: Cui Yiping , Zhang Yue , Prasad Paras N. , Schildkraut Jay S. , Williams David J.
Published: July 2002

We report an experimental observation of the photorefractive effect in a new polymeric system in which a nonlinear organic polymer was doped with a photosensitizer, borondiketonate (BDK), and a hole transport agent, tri-p-tolylamine (TTA). The photoconductivity and the electro-optic effect have been studied. The process of grating formation with the applied field is presented. A strong electric field dependence of the diffraction coefficient has been observed.
Photostructural defect states and residual potential in chlorine and arsenic doped amorphous selenium films
Authors: Chand Suresh , Sharma G. D. , Batheja R. C. , Chandra Subhas
Published: July 2002

The mechanism of photostructural defect states and buildup of residual potential in pure, chlorine doped, and combinationally doped, i.e., chlorine and arsenic doped amorphous selenium films (∼100 μm) has been studied using the thermally stimulated discharge current technique. Combinationally doped films show minimum buildup of residual potential even though the photostructural defect states in them lie between the pure and the chlorine doped amorphous selenium films. These results have been explained in terms of the conductivity enhancement role of chlorine and the complimentary role of arsenic in sustaining the acceptance potential in the doped films.
Improved ultrathin oxynitride formed by thermal nitridation and low pressure chemical vapor deposition process
Authors: Maiti Bikas , Hao Ming Yin , Lee Insup , Lee Jack C.
Published: July 2002

In this letter, we will present the electrical and reliability characteristics of ultrathin oxynitrides (65–73 Å) formed by thermal nitridation of silicon substrate followed by deposition of silicon dioxide by low pressure chemical vapor deposition (LPCVD) technique. The dielectric integrity has been compared to those of the conventional thermal oxide and reoxidized nitrided oxides. It has been found that the new oxynitrides have lower electron trapping, higher charge-to-breakdown, and lower interface state generation under electrical stress even in comparison to reoxidized nitrided oxides with the same thermal budget. The improved characteristics are believed to be due to the combination of the nitrogen-rich layer at the Si/SiO2 interface, the higher quality of LPCVD oxides over thermally grown oxides, and the reduced hydrogen concentration in the dielectrics in comparison to conventional nitrided oxides. The results indicate that these new oxynitride films may be promising for ultra large scale integrated metal-oxide-semiconductor device applications, especially in cases where low thermal budget processes are desirable.
Visible light emission from a porous silicon/solution diode
Authors: Bressers P. M. M. C. , Knapen J. W. J. , Meulenkamp E. A. , Kelly J. J.
Published: July 2002

Reduction of S2O82− ions at the interface between an n-type porous Si electrode and an aqueous solution gives rise to electroluminescence showing evidence of quantization effects. A broad emission band with a maximum at 670 nm is observed similar to the photoluminescence spectrum of the same layers. The results suggest that holes are ‘‘injected’’ into the valence band of the porous semiconductor from an intermediate of the reduction reaction, the SO4−⋅ radical ion. The resulting electron-hole recombination is responsible for the visible light emission.
In situ oxidation of a thin layer of Ge on Si(001): Observation of GeO to SiO2 transition
Authors: Prabhakaran K. , Nishioka T. , Sumitomo K. , Kobayashi Y. , Ogino T.
Published: July 2002

A thin layer of Ge grown on Si(001) surface is oxidized in situ and investigated using XPS, AES, RHEED, and MEIS. The samples used are, Ge layer formed by deposition at room temperature and SiGe mixed layer formed by deposition at 550 °C. Oxidation at 250 °C of the RT grown layer leads to the formation of GeO and on heating the surface to 360 °C, oxygen bonds with Si forming SiO2, thereby reducing GeO to elemental Ge. In the epitaxially grown layer (grown at 550 °C), after oxidation, SiO2 and a small amount of GeO are formed. Similar reaction takes place on this surface also, forming SiO2 as the final product on the surface. In the RT grown layer, after oxidation, MEIS shows evidence for the diffusion of Si through the Ge layer towards the surface.
Photon-assisted quantum transport in quantum point contacts
Authors: Hu Qing
Published: July 2002

We have studied the feasibility of photon-assisted quantum transport in semiconductor quantum point contacts or electron waveguides. Due to photon-induced intersubband transitions, it is expected that the drain/source conductance of the quantum point contacts can be modulated by far-infrared (f≥300 GHz) radiation, which is similar to the photon-assisted tunneling in superconducting tunnel junctions. An antenna/gate electrodes structure will be used to couple far-infrared photons into quantum point contacts of submicron dimensions. A calculation of the photon-induced drain/source current as a function of the far-infrared radiation power is also presented.
Aspheric waveguide lenses for photonic integrated circuits
Authors: Verdiell J.-M. , Newkirk M. A. , Koch T. L. , Gnall R. P. , Koren U. , Miller B. I. , Buhl L. L.
Published: July 2002

We report the fabrication of aspheric waveguide lenses on the InP/InGaAsP material system. A wide aperture (f/5) lens working at 1.5 times the diffraction limit is reported. Insertion loss below 1 dB is also measured. The lens is fabricated by a selective chemical etch of a planar waveguide and has potential applications in InP-based photonic integrated circuits.
Nanometer scale patterning of a monolayer Langmuir–Blodgett film with a scanning tunneling microscope in air
Authors: Day H. C. , Allee D. R. , George R. , Burrows V. A.
Published: July 2002

Nanometer scale patterns have been fabricated on a Langmuir–Blodgett deposited monolayer film of stearic acid using a scanning tunneling microscope in air. Carbon deposits build up underneath the tip for tip voltages with absolute value greater than 4 V. Using an atomic force microscope for image, lines 25 nm wide on a 60 nm period have been written. As confirmed with Auger electron spectroscopy, the unexposed film can be removed with a chloroform soak without affecting the existing carbon patterns, and no additional patterns could then be written because of the removal of the monolayer film.
All-optical modulation with ultrafast recovery at low pump energies in passive InGaAs/InGaAsP multiquantum well waveguides
Authors: Tsang H. K. , Snow P. A. , Day I. E. , White I. H. , Penty R. V. , Grant R. S. , Su Z. , Kennedy G. T. , Sibbett W.
Published: July 2002

We report on the observation of ultrafast (<1 ps) recovery of all-optical modulation based on below band gap, optically induced excess absorption using pump pulse energies of less than 4 pJ. At higher pump pulse energies, the hot carriers produced by two-photon absorption significantly reduce the recovery rate. The increase in absorption recovery times at the higher densities of hot carriers is consistent with a contribution to the nonlinear absorption change from hot electron assisted absorption. The measured hot electron assisted absorption cross section of 2×10−20 m2 is in good agreement with the theoretical value.
Native oxide-embedded AlyGa1−yAs-GaAs-InxGa1−xAs quantum well heterostructure lasers
Authors: Sugg A. R. , Chen E. I. , Richard T. A. , Holonyak N. , Hsieh K. C.
Published: July 2002

Data are presented on the photopumped laser operation of an AlAs-AlyGa1−yAs-GaAs-InxGa1−xAs quantum well heterostructure in which the GaAs-InxGa1−xAs active region is embedded, top and bottom, in native oxide. The upper and lower wider gap confining regions of the laser are selectively converted to oxide, leaving the active region intact. The oxidation (H2O+N2, 425 °C) proceeds laterally (perpendicular to the crystal growth direction) from a chemically etched mesa edge. The photopumped oxide-embedded heterostructure operates as a laser continuously at 77 K and pulsed at 300 K. In comparison with the as-grown crystal, the oxidized sample shows no significant laser threshold degradation.
Comparison between different schemes for passivation of multicrystalline silicon solar cells by means of hydrogen plasma and front side oxidation
Authors: Ghannam M. , Palmers G. , Elgamel H. E. , Nijs J. , Mertens R. , Peruzzi R. , Margadonna D.
Published: July 2002

Different schemes for passivation of solar cells fabricated using casted multicrystalline silicon from Eurosolare are investigated. The efficiency of solar cells with front side oxide surface passivation, front side and/or back side hydrogen plasma passivation are compared. It is shown that oxide passivation of the front surface combined with hydrogen passivation from the back side is the optimum passivation scheme. A 16.2% top efficiency is obtained on 4 cm2 cells implementing this passivation scheme and a 16.8% top efficiency is estimated with an optimized ARC combination.
Method for accurate growth of vertical-cavity surface-emitting lasers
Authors: Chalmers S. A. , Killeen K. P.
Published: July 2002

We report a method for accurate growth of vertical-cavity surface-emitting lasers (VCSELs). The method uses a single reflectivity spectrum measurement to determine the structure of the partially completed VCSEL at a critical point of growth. This information, along with the extracted growth rates, allows imprecisions in growth parameters to be compensated for during growth of the remaining structure, which can then be completed with very accurate critical dimensions. Using this method, we can now routinely grow lasing VCSELs with Fabry–Perot cavity resonance wavelengths controlled to within 0.5%.
Unidirectional operation in a semiconductor ring diode laser
Authors: Hohimer J. P. , Vawter G. A. , Craft D. C.
Published: July 2002

We report the first demonstration of a unidirectional ring diode laser based on the use of an active crossover waveguide. The crossover waveguide introduces both a nonreciprocal loss and gain into the ring cavity to promote unidirectional lasing in the clockwise ring direction. Up to 95% of the continuous-wave lasing output of 3.5 mW (at 150 mA ring current) is emitted from this preferred lasing direction. Unidirectional operation of the ring diode laser is also shown to increase the linearity of the light-vs-current curves, eliminating kinks otherwise occurring from gain competition in the ring cavity.
Large blue shift of light emitting porous silicon by boiling water treatment
Authors: Hou X. Y. , Shi G. , Wang W. , Zhang F. L. , Hao P. H. , Huang D. M. , Wang X.
Published: July 2002

A boiling water treatment of light emitting porous silicon can give rise to a large blue shift of its photoluminescence spectrum and meanwhile strengthen the skeleton of porous Si by filling up many pores with aqueous oxide. A stable blue-green light emission at the peak wavelength down to 500 nm is achieved. FTIR measurements show that the formation of Si dihydride on the sidewall surfaces of the Si rods is not responsible to the visible luminescence for the very thin Si wires.
Growth of analog AlxGa1−xAs/GaAs parabolic quantum wells by molecular beam epitaxy
Authors: Wang S. M. , Treideris G. , Chen W. Q. , Andersson T. G.
Published: July 2002

Parabolic AlxGa1−xAs/GaAs quantum wells have been grown by molecular beam epitaxy with linear ramping of the Al effusion cell temperature, where the ramping rate was carefully analyzed to avoid a flux lag. The calculated potential profile from the temperature variation was very close to the parabolic one. Low-temperature photoluminescence showed clear interband transitions up to the n=3 sublevels. The equal energy spacing between adjacent transitions involving heavy-hole states confirmed the parabolic shape of the quantum well.
Giant magnetoresistance and its evolution in the granular FexAg100−x system (0≤x≤100)
Authors: Xiao Gang , Wang Jian Qing , Xiong Peng
Published: July 2002

We have studied the magnetotransport and magnetic properties of a metallic granular FexAg100−x system, fabricated by using a magnetron cosputtering technique. Giant magnetoresistance was observed in a narrow range between x=10 and 25 vol %. Both the Fe volume fraction and the sample orientation significantly influence the magnetoresistance. This granular system also demonstrates some unique features as compared to multilayer systems.
Elimination of secondary defects in preamorphized Si by C+ implantation
Authors: Nishikawa Satoshi , Yamaji Tetsuo
Published: July 2002

In preamorphization of Si, secondary defects formed at the original amorphous/crystal (a/c) interface were studied as a function of the dose of carbon ion implantation. The preamorphized depth was 230 nm. The carbon was implanted at 78 or 90 keV at 2×1012–2×1015/cm2. The size and density of dislocation loops near the a/c interface decreased with increasing C+ dose. The C+ implantation at a dose of 1×1015/cm2 reduced the density of atoms bound by dislocation loops from 5.9×1014/cm2 to 2.6×1013/cm2. At C+ doses higher than about 1×1015/cm2, additional defects with a diameter of less than about 5 nm were observed. These defects are SiC agglomerates that act as a sink for excess self-interstitials, which results in a reduction in the density of secondary defects.