bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiply charged cluster ion crossed-beam apparatus: Multi-ionization of clusters by ion impact
Authors: Bergen T. , Biquard X. , Brenac A. , Chandezon F. , Huber B. A. , Jalabert D. , Lebius H. , Maurel M. , Monnand E. , Opitz J. , Pesnelle A. , Pras B. , Ristori C. , Rocco J. C.
Published: July 2002

An experimental setup is described, which is used to multi-ionize neutral clusters and to study their stability and the importance of different decay processes. Clusters are ionized in collisions with slow multiply charged ions (projectile charge z ranging from 1 to 30, kinetic energies ranging from 1 to 20 keV/charge). Both ion and cluster beamlines, as well as the characteristics of the analysis and detection systems, are described. Collisions with highly charged ions such as Ar8+ or Xe30+ turn out to be efficient tools in preparing clusters in high charge states without increasing significantly their internal temperature. Measurements performed in coincidence with the number of electrons stabilized by the projectile ion after the collision allowed us to control the charge and the excitation energy of the ionized system. The efficiency of the method is demonstrated for sodium clusters and C60 molecules.
A crossed molecular beam apparatus using high-resolution ion imaging
Authors: Yonekura Nobuaki , Gebauer Christian , Kohguchi Hiroshi , Suzuki Toshinori
Published: July 2002

A new crossed molecular beam apparatus with a high-resolution ion imaging detector is described. Two pulsed supersonic molecular beams are crossed at right angles in a vacuum of 10−7 Torr. The collision region is irradiated with a tunable laser pulse that ionizes the scattered particles state selectively. The generated ions are accelerated by stacked electrodes in a two-dimensional (2D) space focusing mode that increases the velocity resolution of the apparatus. A cylindrical hexapole deflector is placed in the middle of the time-of-flight mass spectrometer to compensate the center-of-mass velocity of the ions and to direct them to the center of the 2D imaging detector. Real-time image processing of the charge coupled device camera signal eliminates blurring of the image detector. The performance of the apparatus was examined by observing the inelastic scattering of NO+Ar at a collision energy of 66 meV. The observed multiple rainbow peaks clearly demonstrate the high performance of the apparatus.
Quantum well states in Ni/Cu/Ni spin valve structures
Authors: Himpsel F. J. , Rader O.
Published: July 2002

Quantized states are mapped in Ni/Cu/Ni(100) trilayer structures, which are taken as a more accurate rendering of spin valve devices than the bilayers studied previously. We find that an extra Ni overlayer affects the energy of quantized states in the Cu layer, explaining why the magnetic coupling is affected by the thickness of the magnetic layer, and how a phase difference may occur between magnetic coupling oscillations in trilayers and density of states oscillations in bilayers. The potential step that confines electrons to the Cu spacer is determined to be 0.9 eV.
Laser produced Ag ions for direct implantation
Authors: Woryna E. , Wolowski J. , Králiková B. , Krása J. , Láska L. , Pfeifer M. , Rohlena K. , Skála J. , Peřina V. , Boody F. P. , Höpfl R. , Hora H.
Published: July 2002

The amount and properties of ions produced by laser ablation of Ag targets have been analyzed. The maximum ion current density jmax=21.0 mA and maximum charge state Ar37+ of the ions produced by a laser power density of about 1×1014 W cm−2 at 1.315 and 0.657 μm on an Ag target have been determined. Direct implantation of the Ag ions from the laser-produced plasma has also been studied. An implanted ion density of 3.5×1016 cm−2 at a depth of 500 nm in Al samples was determined by RBS.
Some consequences to ion source behavior of high plasma drift velocity
Authors: Brown I. G. , Monteiro O. R. , Bilek M. M. M. , Keidar M. , Oks E. M. , Vizir A.
Published: July 2002

We consider the case of energetic ion beam formation when the ion streaming velocity within the source plasma is substantial, i.e., when the ions have a drift speed (in the positive downstream direction) that is on the order of or greater than the ion acoustic speed in the plasma. Some interesting consequences can follow, including the capability of a negatively biased substrate located in the plasma stream to maintain high bias voltage, and of an ion source with no extractor or “conventionally poor” extractor providing a kind of plasma immersion ion implantation mode of operation. Here we summarize the kind of plasma geometry in which this situation can occur, and describe some experimental observations we’ve made of these effects, with reference to a simple theoretical basis for the mechanism.
Origins and effects of thermal processes on near-field optical probes
Authors: La Rosa A. H. , Yakobson B. I. , Hallen H. D.
Published: July 2002

An aluminum-coated tapered fiber probe, as used in near-field scanning optical microscopy (NSOM), is heated by the light coupled into it. This can destroy the probe or may modify the sample, which can be problematic or used as a tool. To study these thermal effects, we couple modulated visible light of various power through probes. Simultaneously coupled infrared light senses the thermal effects. We report their magnitude, their spatial and temporal scales, and real-time probe damage observations. A model describes the experimental data, the mechanisms for induced IR variation, and their relative importance.
Reversible hydrogen annealing of metal-oxide-silicon carbide devices at high temperatures
Authors: Baranzahi Amir , Spetz Anita Lloyd , Lundström Ingemar
Published: July 2002

We report on a reversible hydrogen annealing effect observed in platinum–silicon dioxide–silicon carbide structures at temperatures above about 650 °C. It appears as a decrease of the inversion capacitance in the presence of hydrogen. This phenomenon is shown to depend on hydrogen atoms, created on the catalytic metal, that pass through the oxide and interact with charge generation sites at the oxide–silicon carbide interface. The consequence of the observation for chemical sensors based on silicon carbide is discussed. The results are phenomenological, since no details of the annealing chemistry could be developed from the present experiments. We find, however, that the annealing process and its reversal have activation energies of about 0.9 eV and 2.9 eV/site, respectively.
‘‘Turn-around’’ effects of stress-induced leakage current of ultrathin N2O-annealed oxides
Authors: Lai Kafai , Chen Wei-Ming , Hao Ming-Yin , Lee Jack , Gardner Mark , Fulford Jim
Published: July 2002

Studies of the thickness dependence on stress-induced leakage current (SILC) have been performed in the thickness range of 41 to 87 Å for N2O-annealed and O2-grown oxides. N2O-annealed oxide shows significantly reduced SILC leakage currents. Furthermore, SILC currents were found to increase with decreasing oxide thickness, as reported earlier. However, a ‘‘turn-around’’ effect at ∼50 Å has been observed in these films. SILC currents begin to decrease when oxide thickness is scaled below 50 Å. This turn-around effect can be explained using the trap-assisted tunneling model. For thicknesses equal or less than 41 Å, defect-related current and direct tunneling current become dominant over SILC current. Our results indicated that for N2O-based oxides in the ultrathin thickness regime, stress-induced leakage currents become less significant.
Photodegradation of poly(p - phenylenevinylene) by laser light at the peak wavelength of electroluminescence
Authors: Zyung Taehyoung , Kim Jang-Joo
Published: July 2002

We report the photodegradation of poly(p-phenylenevinylene) polymer when the film was irradiated with laser light at a wavelength corresponding to the peak wavelength of electroluminescence. Degradation in photoluminescent properties was significant in an air environment but not under vacuum. This indicates that the oxygen in air aids photodegradation and this hypothesis was confirmed by optical spectroscopy. This degradation may be associated with long-term stability of the electroluminescence device.
Carrier lifetimes in dielectric cap disordered GaAs/AlGaAs multiple quantum well with SiN capping layers
Authors: Choi W. J. , Lee S. , Kim Y. , Woo D. , Kim S. K. , Kim S. H. , Lee J. I. , Kang K. N. , Chu J. H. , Yu S. K. , Seo J. C. , Kim D. , Cho K.
Published: July 2002

Time resolved photoluminescence (PL) characteristics of a SiN cap disordered GaAs/AlGaAs multiple quantum well (MQW) structure exhibit a decrease in carrier lifetime in conjunction with an increase in quantum well disordering (QWD) as the SiN capping layer thickness is increased. The decrease in carrier lifetime is attributed to enhanced carrier trapping due to the defects introduced during dielectric cap quantum well disordering and the relaxation of the momentum conservation during radiative recombination by QWD. Potential applications of these effects on high speed optical devices such as laser diodes (LD’s) and optical modulators are discussed.
Self-organized InP islands on (100) GaAs by metalorganic vapor phase epitaxy
Authors: Sopanen M. , Lipsanen H. , Ahopelto J.
Published: July 2002

The effect of growth temperature, deposition rate, and substrate misorientation angle on size, density, and uniformity of InP islands grown on (100) GaAs by metalorganic vapor phase epitaxy is investigated. The density of InP islands is observed to remain constant as a function of growth temperature in the temperature range of 620–680 °C. Below 620 °C the island density increases with decreasing temperature. Above 605 °C a subset of islands having a uniform size is observed. The degree of uniformity depends largely on the deposition rate and the size of the uniform islands on the growth temperature.
Compensation of the temperature coefficient of the dielectric constant of barium strontium titanate
Authors: Cava R. J. , Peck W. F. , Krajewski J. J. , Fleming D. A.
Published: July 2002

We report a significant decrease in the temperature coefficient of the dielectric constant (TCK) for polycrystalline ceramics of barium–strontium–titanate through admixture with tetragonal bronze-type barium strontium niobate. For Ba0.5Sr0.5TiO3 ceramics, a 10% admixture of the niobate decreases TCK by a factor of 2.5 at 10 MHz, with negligible degradation of the dielectric loss; a 37.5% admixture decreases TCK by a factor of more than 100. Dielectric constants for the mixtures are in the range of 200–500.
Digital transmission link using surface emitting lasers and photoreceivers
Authors: Dutta N. K. , Nichols D. T. , Vakhshoori D. , Sivco D. L. , Cho A. Y.
Published: July 2002

Transmission system experiments using surface emitting lasers (SEL) and integrated photoreceivers have been carried out. The surface emitting laser utilizes proton implantation for current confinement and has a small signal bandwidth of 10 GHz. The p-i-n/modulation doped field effect transistor photoreceiver has a bandwidth of 11 GHz. Bit error rates of less than 10−9 were demonstrated using the SEL source and the photoreceiver. The receiver sensitivity is −16.5 dBm at 10 Gb/s.
AlGaN pn junctions
Authors: Dmitriev V. A. , Irvine K. , Carter C. H. , Zubrilov A. S. , Tsvetkov D. V.
Published: July 2002

AlGaN pn homo- and heterojunctions were fabricated on silicon carbide substrates by metalorganic chemical vapor deposition. AlN concentration in AlGaN layers ranged from 2 to 8 mol %. Mesa structures were made by reactive ion etching. Electroluminescence (EL) from AlGaN pn junctions was studied. EL peaks associated with near band-to-band transition in AlGaN were detected. The minimum wavelength of EL peak of ∼348 nm (hν∼3.56 eV, 300 K) was measured for a p-Al0.08GaN0.92/n-Al0.06Ga0.94N heterojunction. The dependence of the photon energy of the edge EL peak on AlN concentration in AlGaN was measured.
Cleaved GaN facets by wafer fusion of GaN to InP
Authors: Sink R. K. , Keller S. , Keller B. P. , Babić D. I. , Holmes A. L. , Kapolnek D. , DenBaars S. P. , Bowers J. E. , Wu X. H. , Speck J. S.
Published: July 2002

Basal plane sapphire is a common substrate for the heteroepitaxy of GaN. This presents a challenge for fabrication of cleaved-facet GaN lasers because the natural cleavage planes in (0001) α-Al2O3 are not perpendicular to the wafer surface. This letter describes a method for achieving perpendicular cleaved facets through wafer fusion that can potentially be used to fabricate GaN based in-plane lasers. We demonstrate successful fusion of GaN to InP without voids or oxide at the interface and fabricate optically flat cleaved GaN facets that are parallel to the crystallographic planes of the host InP. I–V measurements have been performed across the n-N fused interface. These results show that the fused junction exhibits a barrier of several electron volts for electrons passing from the InP to the GaN and ohmic conduction of electrons moving in the opposite direction.
Ion-implanted GaN junction field effect transistor
Authors: Zolper J. C. , Shul R. J. , Baca A. G. , Wilson R. G. , Pearton S. J. , Stall R. A.
Published: July 2002

Selective area ion implantation doping has been used to fabricate GaN junction field effect transistors (JFETs). p-type and n-type doping was achieved with Ca and Si implantation, respectively, followed by a 1150 °C rapid thermal anneal. A refractory W gate contact was employed that allows the p-gate region to be self-aligned to the gate contact. A gate turn-on voltage of 1.84 V at 1 mA/mm of gate current was achieved. For a ∼1.7 μm×50 μm JFET with a −6 V threshold voltage, a maximum transconductance of 7 mS/mm at VGS=− 2V and saturation current of 33 mA/mm at VGS=0 V were measured. These results were limited by excess access resistance and can be expected to be improved with optimized n+ implants in the source and drain regions.
Carbon-doped boron nitride cold cathodes
Authors: Pryor R. W.
Published: July 2002

These results reflect what is believed to be the first observation of electron emission from carbon-doped boron nitride (BN). The n-type BN films were synthesized on n-type polycrystalline diamond on (100)Si using reactive laser ablation. The electron emission current density measured at room temperature shows a power law dependence. Emission currents as high as 60 mA  cm−2 have been measured from 150 nm thick n-type BN films on a 24 μm n-type polycrystalline diamond film on a (100)Si substrate. These films show a current density/applied field behavior indicative of negative electron affinity.
Direct observation of oxygen-induced luminescent states in porous silicon by tunable excitation time-resolved spectroscopy
Authors: Komuro Shuji , Kato Takashi , Morikawa Takitaro , O’Keeffe Patrick , Aoyagi Yoshinobu
Published: July 2002

Time-resolved photoluminescence (TRPL) using a dye laser pumped by a N2 laser has been employed to clarify the recombination processes of carriers selectively excited to energy levels ranging from 3.68 to 1.94 eV in oxidized porous silicon (PS). Selective excitation of carriers to energy levels around 2.7±0.4 eV significantly enhances the radiative recombination probability. The decay time of this enhanced PL is estimated to be about 4 ns. This PL enhancement is considered to be due to the creation of oxygen-induced defect states which are located at the oxidized surface layer and/or the interface between the Si bulk and the SiOx layer.
A 10 μm GaAs/AlxGa1−xAs intersubband photodetector operating at zero bias voltage
Authors: Schönbein C. , Schneider H. , Bihlmann G. , Schwarz K. , Koidl P.
Published: July 2002

We report on a GaAs/AlxGa1−xAs quantum well intersubband photodetector for the long wavelength infrared region, which operates at zero bias voltage. Detection without bias is achieved by using an asymmetrical barrier structure as well as modulation doping, giving rise to a built-in field across the barrier layers. The maximum of the spectral response is centered at 10 μm with a spectral bandwidth of 1.6 μm and a 77 K peak detectivity of 2.5×109 cm√Hz/W at 0 V.
Scaling laws for particle growth in plasma reactors
Authors: Lemons D. S. , Keinigs R. K. , Winske D. , Jones Michael E.
Published: July 2002

We quantify a model which incorporates observed features of contaminant particle growth in plasma processing reactors. According to the model, large ‘‘predator’’ particles grow by adsorbing smaller, typically neutral, ‘‘prey’’ protoparticles. The latter are supplied by an assumed constant mass injection of contaminant material. Scaling laws and quantitative predictions compare favorably with published experimental results.
Metastable γ phase in ion beam synthesized FeSi2
Authors: Yang Z. , Shao G. , Homewood K. P.
Published: July 2002

Ion beam synthesized iron silicide (FeSi2) (200 keV, 350 °C, 4×1017 Fe+/cm2) was studied by transmission electron microscopy. Face-centered cubic FeSi2 (γ phase) was observed in the as-implanted sample and the samples annealed at temperatures up to 600 °C. It is suggested that the formation of the equilibrium semiconducting FeSi2 (β phase) is preceded via a transition γ phase due to its better lattice match with the silicon matrix. The absence of metallic FeSi2 (α phase) can be attributed to the high iron dose implantation.
Growth of dark spots by interdiffusion across organic layers in organic electroluminescent devices
Authors: Fujihira Masamichi , Do Lee-Mi , Koike Amane , Han Eun-Mi
Published: July 2002

In order to clarify the propagation mechanism of dark spots in an organic multilayered electroluminescent device, in situ electroluminescence microscopy as well as photoluminescence (PL) microscopy and Auger electron spectroscopy of the degraded device was carried out. The difference in local PL spectra between the dark spots and the normal surface area was also observed by using scanning near-field optical/atomic force microscopy. The growing mechanism of the dark spots was proposed from these observations.
Cavity–dislocation interactions in Si–Ge and implications for heterostructure relaxation
Authors: Follstaedt D. M. , Myers S. M. , Lee S. R.
Published: July 2002

Cavities formed in Si and Ge and their alloys by He implantation and annealing are demonstrated to have a strong short-range, attractive interaction with dislocations, with a binding energy calculated to be ≳100 eV when they overlap. Cavities can alter the relaxation of strained Si86Ge14 layers on Si in several ways: cavities placed at the interface enhance relaxation rates by increased nucleation of misfit dislocations, reduce the number of dislocations protruding into the substrate, and may increase relaxation at thermodynamic equilibrium.
Formation of Schottky barriers at interfaces between metals and molecular semiconductors of p- and n-type conductances
Authors: Harima Y. , Okazaki H. , Kunugi Y. , Yamashita K. , Ishii H. , Seki K.
Published: July 2002

In order to clarify electronic structures of molecular semiconductor/metal interfaces, a Schottky–Mott rule is examined for vacuum-sublimed films of two kinds of porphyrins, which have similar chemical structures, but opposite conductance types. The result shows that Schottky barrier heights are simply determined by the difference in work function between the porphyrin solids and metals irrespective of the conductance types of the porphyrin semiconductors, indicative of negligible influence of surface states on the Schottky barrier formation. Measurements of photocurrent generation efficiencies at these Schottky junctions indicate that a surface recombination process is not a major deactivation route for electron-hole pairs generated in the molecular semiconductors by light.
Ultraviolet prepulse for enhanced x-ray emission and brightness from droplet-target laser plasmas
Authors: Berglund M. , Rymell L. , Hertz H. M.
Published: July 2002

We show that an ultraviolet prepulse significantly enhances the water-window x-ray emission and brightness for a droplet-target laser plasma. By combining a 65 mJ, 120 ps, λ=532 nm main pulse with an up to 3 mJ prepulse, the emitted x-ray photon flux may be increased more than eight times. The resulting C VI λ=3.37 nm line emission is more than 3×1012 photons/sr⋅pulse, corresponding to a conversion efficiency above 3%/line. The integrated spectral brightness is increased two times and is found to reach its maximum for different prepulse parameters than those resulting in maximum photon flux.
Effects of the oxidation process on the electrical characteristics of oxidized nitride films
Authors: Mazumder M. K. , Katayama T. , Kobayashi K. , Mashiko Y. , Koyama H. , Yasuoka A.
Published: July 2002

The effects of the oxidation process on the electrical characteristics of metal–oxide–semiconductor (MOS) capacitors were studied. It was found that electrical and time dependent dielectric breakdown (TDDB) characteristics are improved for the MOS capacitor with a wet oxidized nitride film over the N2O oxidized nitride film. The depth profile of the oxidized nitride film is also studied by Auger electron spectroscopy. It is observed that from the top surface of an oxidized nitride film of about 2 nm (nitride film oxidized in the wet oxidation process or in N2O ambient by rapid thermal processing), the level of oxygen is the same but, compared to a N2O oxidized nitride film, the level of nitrogen is greater in a wet oxidized nitride film. The improvement of the electrical and TDDB characteristics of the wet oxidized nitride film over the N2O oxidized nitride can be thought due to the increased amount of nitrogen from the top surface to a depth of nearly 2 nm of the oxidize nitride films.
Tunable polarization converter based on ordered AlGaInP waveguide structures
Authors: Wirth R. , Moritz A. , Geng C. , Scholz F. , Hangleiter A.
Published: July 2002

An electrically tunable transverse electric/transverse magnetic polarization converter using ordered AlGaInP waveguide structures is presented. The structures are grown on (001) GaAs substrates with the surface tilted 6° towards {111}B. This selects one of the two possible {111}B variants for the ordering planes. Thus, also on a macroscopic scale, the symmetry of the planar waveguide is broken. The properties of the guided modes are very sensitive to the size and orientation of the axes of the dielectric tensor. So a slight modification of their magnitudes due to electrorefraction leads to a remarkable change in the propagation constants. This change is used to accomplish tunable rotation of polarization by 90°.
Properties of Schottky contacts of aluminum on strained Si1−x−yGexCy layers
Authors: Mi Jian , Gupta Ashawant , Yang Cary Y. , Zhu Jintian , Yu Paul K. L. , Warren Patricia , Dutoit Michel
Published: July 2002

Schottky contacts of Al/Si1−x−yGexCy were fabricated using conventional Si technology. Effects of thermal processing of the alloys on the electrical properties of the Al/Si1−x−yGexCy Schottky diodes were investigated. Current–voltage (I–V), capacitance–voltage (C–V), and x-ray diffraction measurements were performed. These thick alloy films (100–150 nm) experienced strain relaxation upon annealing at 700 °C. Nearly ideal I–V and C–V behaviors were obtained for strain-compensated samples. I–V and C–Vcharacteristics show evidence of dislocation-related traps for strain-relaxed samples. Carbon incorporation improves the I–V and C–V characteristics by lessening the extent of lattice relaxation due to thermal processing.
Kinetic roughening and smoothing of the crystalline–amorphous interface during solid phase epitaxial crystallization of GeSi alloy layers
Authors: Elliman R. G. , Wong W. C.
Published: July 2002

The morphology of the crystalline–amorphous interface is studied during solid-phase epitaxial crystallization of amorphous GeSi alloy layers with depth-dependent Ge distributions. The interface is shown to undergo an initial strain-induced roughening transition when the Ge concentration exceeds 6.6 at. %. As crystallization continues in strain-relaxed material the interface is shown to further roughen or smooth in response to changes in the Ge distribution. This evolution of the interface morphology is shown to be a consequence of kinetic effects whereby the differential velocity between the leading and trailing edges of the rough interface increases in regions of increasing Ge concentration and decreases in regions of decreasing Ge concentration.
Near ultraviolet luminescence of Be doped GaN grown by reactive molecular beam epitaxy using ammonia
Authors: Salvador A. , Kim W. , Aktas Ö. , Botchkarev A. , Fan Z. , Morkoç H.
Published: July 2002

Be doped GaN films grown by reactive molecular beam epitaxy (MBE) are investigated. The room temperature photoluminescence spectrum of the films that were studied shows features in the 390–420 nm range, similar to those observed in Mg doped GaN films, and indicates that Be can form acceptor states about 250 meV above the valence band of GaN. This is in contrast to previous works on GaN:Be films where the only luminescence feature seen was a broad peak centered at 2.16 eV (560 nm). Hot probe measurement indicates p-type conduction for GaN:Be doped films without any postgrowth annealing. Current–voltage measurements of fabricated mesas of MBE grown layers, consisting of a GaN:Be doped film grown over a Si doped GaN layer, show p–n diodelike rectification. A weak electroluminescence at 380–390 nm is observed when the device is driven with a pulsed current of 600 mA.
Optical studies of GaN and GaN/AlGaN heterostructures on SiC substrates
Authors: Shan W. , Fischer A. J. , Song J. J. , Bulman G. E. , Kong H. S. , Leonard M. T. , Perry W. G. , Bremser M. D. , Davis R. F.
Published: July 2002

We present the results of spectroscopic studies on GaN based epitaxial materials on SiC substrates by metalorganic chemical vapor deposition. A variety of techniques has been used to study the optical properties of GaN epilayers and GaN/AlGaN heterostructures. Sharp spectral structures associated with the intrinsic free excitons were observed by photoluminescence and reflectance measurements from GaN based materials grown on SiC substrates. The residual strain was found to have a strong influence in determining the energies of exciton transitions. Picosecond relaxation studies of exciton decay dynamics suggest that an AlGaN cladding layer with a small mole fraction of AlN can be relatively effective in enhancing the radiative recombination rate for excitons by reducing the density of dislocations and suppressing surface recombination velocity in the GaN active layer for the GaN/AlGaN heterostructure samples.
Novel surface emitting laser diode using photonic band-gap crystal cavity
Authors: Hirayama Hideki , Hamano Tetsuko , Aoyagi Yoshinobu
Published: July 2002

A novel surface emitting laser diode consisting of a three-dimensional (3D) photonic band-gap crystal cavity is proposed. Spontaneous emission is controlled so as to radiate in the lasing direction with a narrow radiation angle by introducing a plane phase shift region into the cavity. The radiation pattern of the localized phase shift mode in the photonic band gap is analyzed with a plane-wave method by using a two-dimensional (2D) model. We show that the radiation angle of spontaneous emission in the photonic crystal cavity is as narrow as that of the stimulated emission of conventional surface emitting laser. Therefore, the photonic band-gap crystal cavity laser operates as a light source without threshold and spatial-emission-noise, and therefore is very attractive for use as the light source in spatially integrated optical circuits.
Microcavity devices based on a ladder-type poly(p-phenylene) emitting blue, green, and red light
Authors: Cimrová Vera , Scherf Ulrich , Neher Dieter
Published: July 2002

Light emitting devices with emission either in the blue, green, and red spectral region have been fabricated based on ladder-type poly(p-phenylene) (LPPP). Color tuning has been achieved simply by adjusting the LPPP layer thickness. Microcavity effects could be proven to control the shape of the electroluminescence and photoluminescence spectra of the single layer devices between aluminum and gold electrodes. The full width at half-maximum was strongly reduced from ∼150 to 200 nm for the ‘‘free space’’ photoluminescence or for the electroluminescence spectra of devices with indium–tin oxide hole injecting electrodes to values between 60 and 70 nm for the three individual single color devices.
Implantation and growth of large β-FeSi2 precipitates and α-FeSi2 network structures in silicon
Authors: Reuther H. , Dobler M.
Published: July 2002

Iron implanted and subsequently annealed n-type Si(111) was studied by conversion electron Mössbauer spectroscopy and Auger electron spectroscopy. Results of Mössbauer spectroscopy indicate the formation of a mixture of β- and α-FeSi2 due to the implantation and a complete transition of the mixture to the β and the α phase after annealing at 900 °C for 18 h and 1150 °C for 1 h, respectively. The iron concentration profiles determined with Auger electron sputter depth profiling are Gaussian shaped for the as-implanted and broadened with depth depending fluctuations for the annealed samples. Investigations of the annealed samples with scanning Auger electron spectroscopy show the formation of large precipitates with, depending on the annealing procedure, different structures.
Longitudinal mode spectra and ultrashort pulse generation of InGaN multiquantum well structure laser diodes
Authors: Nakamura Shuji , Senoh Masayuki , Nagahama Shin-ichi , Iwasa Naruhito , Yamada Takao , Matsushita Toshio , Sugimoto Yasunobu , Kiyoku Hiroyuki
Published: July 2002

Longitudinal modes with a mode separation of 0.04 nm were observed on InGaN multiquantum well structure laser diodes (LDs). Other peaks different from the longitudinal modes, appeared with increasing current above the threshold current. Lasing was observed up to a pulsed current duty ratio of 40%. The operating voltage of the LDs at the threshold was around 11 V. Ultrashort pulsed light from the LDs with a pulse width of 50 ps, an output power of 300 mW, and a peak wavelength of 404.2 nm was obtained. The damping constant and the frequency of the relaxation oscillation were 0.8 ns and 3 GHz, respectively.
Aluminum free GaInP/GaAs quantum well infrared photodetectors for long wavelength detection
Authors: Jelen C. , Slivken S. , Hoff J. , Razeghi M. , Brown G. J.
Published: July 2002

We demonstrate quantum well infrared photodetectors based on a GaAs/Ga0.51In0.49P superlattice structure grown by gas-source molecular beam epitaxy. Wafers were grown with varying well widths. Wells of 40, 65, and 75 Å resulted in peak detection wavelengths of 10.4, 12.8, and 13.3 μm with a cutoff wavelength of 13.5, 15, and 15.5 μm, respectively. The measured peak and cutoff wavelengths match those predicted by eight band theoretical analysis. Measured dark currents were lower than equivalent GaAs/AlGaAs samples.
Substrate effect on CdTe layers grown by metalorganic vapor phase epitaxy
Authors: Sochinskii N. V. , Muñoz V. , Bellani V. , Viña L. , Diéguez E. , Alves E. , da Silva M. F. , Soares J. C. , Bernardi S.
Published: July 2002

CdTe layers were grown by metalorganic vapor phase epitaxy (MOVPE) on different substrates like sapphire, GaAs, and CdTe wafers. The growth was carried out at the temperature 340 °C and time in the range of 2–4 h using dimethyl-cadmium and diisopropil-tellurium as precursors. The layers were studied by scanning electron microscopy, Rutherford backscattering spectroscopy, and high resolution low-temperature photoluminescence spectroscopy. The surface morphology and RBS and PL spectra of CdTe MOVPE layers are reported and the substrate effect on the layer properties is demonstrated.
Large Jc enhancement by ion irradiation for thick YBa2Cu3O7−δ films prepared by photoassisted metalorganic chemical vapor deposition
Authors: Ignatiev A. , Zhong Q. , Chou P. C. , Zhang X. , Liu J. R. , Chu W. K.
Published: July 2002

Thick superconducting films of YBa2Cu3O7−δ grown by photoassisted metalorganic chemical vapor deposition that have shown a decrease of Jc with increasing thickness (>1 μm) have been exposed to ion irradiation in an attempt to enhance Jc. A 4.5 μm thick film irradiated with 1 MeV protons at a dose of 3×1014/cm2 has shown an increase of Jc by a factor of nearly 20–1.7×106 A/cm2 corroborating the proposal that a lack of pinning centers in the grown thick films, due to their high crystalline quality, contributed to the observed decrease of Jc with increasing film thickness.
Structure control of Pb(Zr,Ti)O3 films using PbTiO3 buffer layers produced by magnetron sputtering
Authors: Cattan E. , Velu G. , Jaber B. , Remiens D. , Thierry B.
Published: July 2002

The orientation of Pb(Zr,Ti)O3 (PZT) thin films grown by sputtering on a Si/SiO2/Ti/Pt substrate using a PbTiO3 (PT) buffer layer was controlled by changing the thickness of the buffer layer. The x-ray diffraction of PT as a function of the thickness, in the range of 20–400 Å, showed modification of the PT orientation. That suggests a gradual evolution of the lattice parameters in the nucleation stage of PT films. The main growth mechanism was certainly due to the passing from an island growth to a continuous layer. The (111) oriented and (100) oriented PZT films were grown on 50 and 200 Å PT buffer layers, respectively.
Complex photothermal refractive index change in host-guest liquid crystals determined with a novel interferometric method
Authors: Ono Hiroshi , Kawatsuki Nobuhiro
Published: July 2002

A complex photothermal refractive index change in host-guest liquid crystals was determined with a novel interferometric method. The complex refractive index change was proportional to the pump beam intensity. The absolute value of the real part was about ten times as large as that of the imaginary one. The absolute value of the extraordinary refractive index change was about nine times as large as that of the ordinary one. The real part of the extraordinary refractive index change was negative, while that of the ordinary one was positive, and the imaginary part of both the extraordinary and ordinary refractive index change was negative. These results can be explained by the photothermal effects in the host-guest liquid crystals and dyes.
Effect of nitrogen incorporation on electrical properties of boron-doped diamond films
Authors: Sonoda S. , Won J. H. , Yagi H. , Hatta A. , Ito T. , Hiraki A.
Published: July 2002

The effect of a small amount of nitrogen incorporated in chemical vapor deposited diamond films on their electrical properties was studied. Upgrading the purity of CH4 gas from the conventional ultra-high purity to the grade with no detection of nitrogen resulted in improvement of electrical properties of the boron-doped homoepitaxial diamond films; the Hall mobility was increased by 4.3 times at the room temperature. Decrease in nitrogen concentration in the diamond films was confirmed by investigating the 2.16 eV center of cathodoluminescence induced by ion beam irradiation and subsequent annealing.
Blocking effect of charge transfer at the porous silicon/silicon interface
Authors: Dittrich Th. , Rappich J. , Timoshenko V. Yu.
Published: July 2002

The photoluminescence (PL) of a thin porous silicon (por-Si) layer and of bulk c-Si is investigated in situ after the formation in 0.2 M NH4F (pH 3.2) and in water, ethanol, and their vapors. The excitation light of the used pulsed N2 laser is absorbed in the por-Si surface layer. This allows the contactless study of changes of the diffusion of excess carriers from the por-Si layer into the c-Si by using the PL of c-Si as a probe. The radiative recombination of c-Si decreases after exchanging the electrolyte by the other media while the PL intensity of the por-Si increases strongly. The strongest increase of the PL of por-Si is observed in ethanol atmosphere. The results are discussed on the basis of blocking of the out diffusion of excess carriers from the por-Si layer into the bulk c-Si due to electrical charging of interface states.
Anisotropy of the nitrogen conduction states in the group III nitrides studied by polarized x-ray absorption
Authors: Lawniczak-Jablonska K. , Suski T. , Liliental-Weber Z. , Gullikson E. M. , Underwood J. H. , Perera R. C. C. , Drummond T. J.
Published: July 2002

The energy distribution of the nitrogen antibonding electron states in the hexagonal epitaxial layers of AlN, GaN, and InN and cubic epitaxial layers of GaN and InN along pxy plane and pz direction is reported. The study was performed by the polarized x-ray absorption at the K edge of N. A strong polarization dependence of the absorption spectra indicating the significant anisotropy of the conduction band was found in the case of hexagonal samples. Very weak polarization dependencies observed in cubic samples correspond well with the defect distribution anisotropy. Qualitatively different and cation dependent antibonding states distribution point out the role played by a contribution of hybridized cation-nitrogen electronic states to the individual conduction band structures of AlN, GaN, and InN.
Thermodynamic considerations in epitaxial growth of GaAs1−xNx solid solutions
Authors: Qiu Y. , Nikishin S. A. , Temkin H. , Elyukhin V. A. , Kudriavtsev Yu. A.
Published: July 2002

We describe epitaxial growth of solid solutions of GaAs1−xNx with high nitrogen concentrations. The equilibrium constants of reactions needed for the formation of single phase alloys are calculated and compared with experimental pressure and growth temperature data. We show good agreement between the experiment and the calculated thermodynamic growth conditions. In addition, our calculations indicate that at room temperature the alloys of GaAs1−xNx are either unstable or metastable with respect to decomposition, for the entire range of compositions.
Improvement of the dielectric properties of Ta2O5 through substitution with Al2O3
Authors: Cava R. J. , Peck W. F. , Krajewski J. J. , Roberts G. L. , Barber B. P. , O’Bryan H. M. , Gammel P. L.
Published: July 2002

For bulk ceramic materials, small substitutions of Al2O3 in Ta2O5 are shown to cause a moderate enhancement of the dielectric constant. For compositions near 0.95Ta2O5–0.05Al2O3, the temperature coefficient of the dielectric constant at 20 °C dramatically decreases, from more than 200 ppm/°C for pure Ta2O5 to less than 20 ppm/°C. The quality factors (Q) at 1 MHz, are 2000–5000. Measurements to 14 GHz at 20 °C show that the dielectric constant is maintained to microwave frequencies, with a Q of ∼600 at 5 GHz.
Theoretical performance of mid-infrared broken-gap multilayer superlattice lasers
Authors: Flatté Michael E. , Olesberg J. T. , Anson S. A. , Boggess Thomas F. , Hasenberg T. C. , Miles R. H. , Grein C. H.
Published: July 2002

We present calculations of the differential gain and threshold current densities for a 3.7 μm multiple quantum well structure consisting of a “well” composed of several periods of an InAs/InGaSb superlattice alternating with a quinternary alloy “barrier.” We find serious limitations to the optical properties of active regions composed of these multiple quantum wells, and propose a four-layer superlattice structure which corrects these problems.
Characterization of InGaN multiquantum well structures for blue semiconductor laser diodes
Authors: Nishio Johji , Sugiura Lisa , Fujimoto Hidetoshi , Kokubun Yoshihiro , Itaya Kazuhiko
Published: July 2002

In 0.15 Ga 0.85 N/GaN and In0.15Ga0.85N/In0.05Ga0.95N multi quantum well (MQW) structures grown on (0001) sapphire substrates were investigated by high-resolution x-ray diffraction and cross-sectional transmission electron microscopy. The results show that ultrathin MQWs with fairly good crystallinity and precisely controlled clear parallel interfaces were grown. Laser diode structures with MQWs were also studied, and the results suggest that these superlattice structures retain their high quality even after being subjected to high temperatures during the subsequent growth of p-type GaN as the optical guiding layer, p-type GaAlN as the cladding layer, and p-type GaN as the contact layer.
Manipulation of liquid crystal textures with a focused near infrared laser beam
Authors: Hotta Jun-ichi , Sasaki Keiji , Masuhara Hiroshi
Published: July 2002

Optical manipulation of disclinations and defects in liquid crystal films was demonstrated and discussed in terms of mass transfer induced by radiation pressure and of molecular rotation under the optical electric field. Orientation of liquid crystal molecules was controlled by changing the polarization direction of a focused cw laser beam. A disclination line could be deformed by moving the focal spot, just like drawing a bow. A point defect followed the laser beam so that it could be freely transported in the film. When two disclination points were optically manipulated to become fused, the defects disappeared immediately and did not return after switching off the laser.
Optical gain and high quantum efficiency of matrix-free, closely packed CdSe quantum dots
Authors: Gindele F. , Westphäling R. , Woggon U. , Spanhel L. , Ptatschek V.
Published: July 2002

Solid films of matrix-free, closely packed CdSe nanocrystals have been prepared and surface stabilized. An efficient suppression of nonradiative recombination channels is achieved. The absolute quantum efficiency has been determined spectrally resolved using an integrating sphere, and values between 1% and 10% are obtained in dependence on temperature. Spectrally broad optical gain has been found with the maximum around 510 nm.
The effect of reactive plasma etching on the transient enhanced diffusion of boron in silicon
Authors: Privitera Vittorio , Priolo Francesco , Mannino Giovanni , Campisano Salvatore Ugo , Carnera Alberto , Arena Giuseppe , Spinella Corrado
Published: July 2002

Silicon wafers oxidized and stripped by reactive plasma etching were implanted with 5 keV B, 1×1013/cm2. The transient enhanced diffusion of B, usually observed in samples which receive such implants over characteristic time scales, is strongly retarded in these plasma etched samples upon annealing at 800, 900, or 1000 °C, as measured by secondary ions mass spectrometry. These results suggest that the defects generated by the plasma etching procedure in the near surface region, represent an efficient sink against the flow of interstitials which cause the transient enhanced diffusion. A slow release of interstitials from this trapping immobile background occurs with characteristic time scales which are, however, a factor of 30–60 times higher than the usual lifetimes of transient diffusion. This release is characterized by an activation energy of 2.4 eV. These data are reported and their implication on shallow junction formation are discussed.
Long-term reliability of Al-free InGaAsP/GaAs (λ=808 nm) lasers at high-power high-temperature operation
Authors: Diaz J. , Yi H. J. , Razeghi M. , Burnham G. T.
Published: July 2002

We report the long-term reliability measurement on uncoated Al-free InGaAsP/GaAs (λ=808 nm) lasers at high-power and high-temperature operation. No degradation in laser performance has been observed for over 30 000 h of lifetime testing in any of randomly selected several 100-μm-wide uncoated lasers operated at 60 °C with 1 W continuous wave output power. This is the first and the most conclusive evidence ever reported that directly shows the high long-term reliability of uncoated Al-free lasers.
Submicron GaMn quasicrystals in ferromagnetic GaAs
Authors: Zhang J. P. , Cheetham A. K. , Sun K. , Wu J. S. , Kuo K. H. , Shi J. , Awschalom D. D.
Published: July 2002

GaMn icosahedral particles with quasicrystalline order have been found in Mn implanted and rapidly annealed GaAs by means of selected-area electron diffraction, high-resolution, and dark-field electron microscopy. The orientation relationship between the submicron quasicrystals with the icosahedral (2/m 3̄5̄) symmetry and the face-centered cubic (fcc) GaAs matrix is determined to be: i5̄ (the fivefold inversion axis in (2/m 3̄5̄))//[110]GaAs, i3̄ (the threefold inversion axis)//[111̄]GaAs, and i2 (the twofold axis)//[121̄]GaAs. The statistics of these structural studies, combined with magnetic force microscopy, indicate that the submicron quasicrystals are ferromagnetic.
Determination of the surface recombination velocity of semiconductor by surface photovoltaic measurement
Authors: Yan Yongmei
Published: July 2002

A method based on the surface photovoltaic measurement at various temperatures is proposed for determining the surface recombination velocity (SRV) Sn of a semiconductor and the excess minority carrier concentration Δn(w) at the boundary of surface barrier in an atmospheric environment. The experiment was carried out on a (111) p-type Si single crystal. The SRV is determined to be 9.6×103 cm s−1, which agrees well with the result of the contactless measurement method reported by Otaredian. Δn(w)=1.5×109 cm−3 is obtained under an incident light of intensity I0=4.12×1013 cm−2 s−1 and wavelength λ=0.80 μm.
Preparation of piezoelectric-coefficient modulated multilayer film ZnO/Al2O3 and its ultrahigh frequency resonance
Authors: Hu W. S. , Liu Z. G. , Wu R. X. , Chen Y.-F. , Ji W. , Yu T. , Feng D.
Published: July 2002

Multilayer films composed of piezoelectrically active ZnO and inactive Al2O3 layers were prepared on silicon by a pulsed laser deposition technique. The ZnO layers were completely (001) textured to generate a single piezoelectric coefficient d33 perpendicular to the substrate surface and the Al2O3 layers were amorphous at 375 °C. The interfacial sharpness and the film orientation were analyzed by low and high angle x-ray diffraction θ–2θ scanning. High frequency resonance of 10.6 GHz was measured and higher values up to 100 GHz are expected in the multilayer films with periods 320 nm or smaller.
A diode-pumped, high gain, planar waveguide, Nd:Y3Al5O12 amplifier
Authors: Shepherd D. P. , Brown C. T. A. , Warburton T. J. , Hanna D. C. , Tropper A. C. , Ferrand B.
Published: July 2002

We report the use of a 5-mm-long planar Nd:yttrium aluminum garnet waveguide grown by liquid-phase epitaxy as an amplifier at 1.064 μm. In a double-pass configuration pumped by a 1.2 W diode laser, small signal gains of 686 (28 dB) have been observed and efficient power extraction demonstrated with output powers of up to 290 mW being obtained.
Using soft lithography to fabricate GaAs/AlGaAs heterostructure field effect transistors
Authors: Hu Junmin , Beck R. G. , Deng Tao , Westervelt R. M. , Maranowski K. D. , Gossard A. C. , Whitesides George M.
Published: July 2002

This letter describes the fabrication of functional GaAs/AlGaAs field effect transistors using micromolding in capillaries—a representative soft lithographic technique. The fabrication process involved three soft lithographic steps and two registration steps. Room temperature characteristics of these transistors resemble those of field effect transistors fabricated by photolithography. The fabrication of functional microelectronic devices using multilayer soft lithography establishes the compatibility of these techniques with the processing methods used in device fabrication, and opens the door for their development as a technique in this area.
Changes in the growth mode of low temperature GaN buffer layers with nitrogen plasma nitridation of sapphire substrates
Authors: Kim Min Hong , Sone Cheolsoo , Yi Jae Hyung , Yoon Euijoon
Published: July 2002

Low temperature GaN buffer layers were grown by remote plasma enhanced metalorganic chemical vapor deposition on various pretreated sapphire substrates. The effects of the initial nitridation of sapphire substrates by rf nitrogen plasma on the subsequent growth mode and the crystallinity of the GaN buffer layers were studied. GaN buffer layers on non-nitridated sapphire substrates showed a three-dimensional island growth mode with rough surfaces and misoriented islands. On the other hand, those grown on nitridated sapphire substrates showed an enhanced two-dimensional growth mode with near-equilibrium truncated hexagonal pyramids. The structural quality of the low temperature GaN buffer layer improved significantly with nitrogen plasma nitridation.