bluuebunny/crossref_metadata_2025 huggingface dataset:
Luminescence properties of nitrogen ion implanted ZnSe after thermal annealing
Authors: Kamata A. , Moriyama T.
Published: July 2002

Nitrogen atoms were implanted into ZnSe layers which were grown by metalorganic chemical vapor deposition. The implanted crystals were thermally annealed in a nitrogen atmosphere. Photoluminescence spectra show an acceptor-bound excitonic emission line (I1) and donor-to-acceptor pair (DAP) recombination emission, which reveal the activation of nitrogen atoms as shallow acceptors. An additional DAP emission was observed at 462 nm, which is often seen for ZnSe:N grown by molecular beam epitaxy. The selenium vacancy generation accelerates the occupation of nitrogen atoms at the selenium sites and the excess vacancy generation brings about the formation of deep donor complexes.
Thulium-doped fiber optic decay-time temperature sensors: Characterization of high temperature performance
Authors: Zhang Z. Y. , Grattan K. T. V. , Meggitt B. T.
Published: July 2002

The main objectives of this study were to investigate the thermometric potential of Tm-doped optical fiber and yttrium aluminum garnet (YAG) crystals for applications up to temperatures as high as 1300 °C, and to realize a prototype high temperature fluorescence fiber probe based on earlier Nd-doped fiber work for temperature measurement up to 750 °C. The research showed that the fluorescence characteristics of the Tm-doped YAG crystal were very stable at high temperatures and capable of providing a temperature measurement reproducibility better than ±6 °C over the region from room temperature up to 1350 °C.
Reflection high-energy electron diffraction study of the molecular beam epitaxial growth of CaF2 on Si(110)
Authors: Liu W. K. , Fang X. M. , McCann P. J.
Published: July 2002

Molecular beam epitaxial growth of CaF2 on Si(110) was studied using reflection high-energy electron diffraction (RHEED) and scanning electron microscopy (SEM). An optimum substrate temperature range exists between 800 and 900 °C within which (110)-oriented epitaxy can be sustained. At the initial growth stage, long strips of CaF2 parallel to the [1̄10] direction are formed due to the growth anisotropy on the (110) surface. This is followed by the development of low-energy {111} facets, producing a ridged and grooved surface morphology. Growth then proceeds via the stacking of {111} planes on the sidewalls of the ridges. This surface morphology is believed to result from the combination of favorable energetics in exposing the low-energy {111} facets and the presence of twinned crystallographic domains.
Ag-induced multistep formation on Si(001)
Authors: Fölsch S. , Winau D. , Meyer G. , Rieder K. H. , Horn-von Hoegen M. , Schmidt T. , Henzler M.
Published: July 2002

The step topography of 4°-misoriented Si(001) surfaces was examined by scanning tunneling microscopy and spot profile analyzing–low-energy electron diffraction. The clean Si(001)-(2×1) surface proves to be a single domain substrate, which is characterized by a regular array of double steps. This step structure is changed dramatically upon adsorption of submonolayer quantities of Ag at ∼700 K. In this case, the formation of multisteps with fourfold, sixfold, and eightfold step heights occurs. The single domain character of the substrate is preserved, now showing a Ag-induced (3×2) reconstruction.
New observation of trapped charge transportation on circularly bound polymethylmethacrylate surface
Authors: Gong H. , Ong C. K. , Le Gressus C.
Published: July 2002

Bright rings are observed in the scanning electron microscope (SEM) image when charge flashover in vacuum occurs on circularly bound polymethylmethacrylate surfaces using a SEM. The number and diameters of these rings vary with the applied observation voltage. These bright rings in the SEM correspond to the charge accumulation in the sample. The trapped charge transport in the insulator is either in the form of a large polaron or in the highly excited state.
Equilibrium contact angle and intrinsic wetting hysteresis
Authors: Yang X. F.
Published: July 2002

Wetting and adhesion should be treated as inherently irreversible processes, because, in the process of joining and separating two surfaces, available energy is dissipated. In a system that undergoes inherently irreversible processes, the second law of thermodynamics is always satisfied and can offer no information regarding the system’s equilibrium state. Therefore, to determine the equilibrium wetting angle, the law of energy conservation should be used. As a result, the advancing contact angle is found to be intrinsically higher than the receding one, regardless of the surface heterogeneity, and the extent of hysteresis is dependent on the amount of energy dissipated in the process of wetting and dewetting.
High second-harmonic conversion efficiency of quasi-phase-matched LiTaO3 waveguides pumped by single-mode pulsed AlGaAs laser diodes
Authors: Azouz A. , Stelmakh N. , Lourtioz J.-M. , Delacourt D. , Papillon D. , Lehoux J.
Published: July 2002

We show that the averaged second-harmonic conversion efficiency of quasi-phase-matched LiTaO3 waveguides can be increased by a factor larger than 15 with the use of single-mode pulsed AlGaAs laser diodes as the optical sources. The proton exchange followed by thermal annealing is used both to periodically change the sign in d33 nonlinear coefficient and to fabricate the waveguides. Laser pulses are produced by strong rf modulation of the diode current while single-mode operation is achieved with a grating-tuned external cavity. The averaged conversion efficiency is found to linearly increase with peak power of pulses even in the case of pulses whose spectral width is larger than the spectral acceptance of LiTaO3 waveguides. Experimental results are in agreement with calculated ones. The conversion efficiency of 450 %/W presently reached at optimum (i.e., 1% for 2.2 mW pump and 1 cm interaction length) is among the highest performances reported to date for frequency doubling of laser diodes.
The phase transition and transport properties of Sr0.56C60O1.5
Authors: Zhang Q. M. , Huang Y. N. , Shen H. M. , Yan F. , Gu G. , Du Y. W. , Wang Y. N.
Published: July 2002

X-ray diffraction and dielectric measurement have been applied to investigate the phase transition and transport properties of Sr0.56C60O1.5 which is obtained by the reaction of SrCl2 with C60 anion aquatic solution. The new compound has a similar structure, but different transport properties as compared with metallic Sr-doped C60. X-ray diffraction shows that a first-order phase transition around 100 °C is related to the rearrangement of Sr2+ in the interstitial sites of the C60 lattice. The step change of ac conductivity near 100 °C is also attributed to the hopping of Sr2+ between interstitial sites. The ionic conductivity indicates the possibility of synthesizing superionic conductors based on C60 and its derivatives.
Visible photoluminescence from He-implanted silicon
Authors: Bisero D. , Corni F. , Nobili C. , Tonini R. , Ottaviani G. , Mazzoleni C. , Pavesi L.
Published: July 2002

Visible photoluminescence has been observed at cryogenic temperatures from crystalline Si bombarded with He and exposed to H either as plasma or gas in the 250–450 °C temperature range. The experimental results are consistent with the formation of Si nanoparticles produced by He segregation, which is responsible for exciton localization, and H passivation of the nonradiative recombination centers.
Three-terminal laser structure for high-speed modulation using dynamic carrier heating
Authors: Tolstikhin Valery I. , Mastrapasqua Marco
Published: July 2002

A three-terminal laser structure is proposed as a means to achieve laser modulation using dynamic carrier heating. The injection of hot electrons, with energy tuned by variable joule heating over a high electric field region, is used to govern the carrier temperature in the active layer of a laser, while a separate heterojunction controls the injection rate. Simulations show the possibility of generating good-shaped picosecond optical pulses by modulating the voltage that controls the heating electric field.
Total reflection x-ray excited photoelectron spectra of copper phthalocyanine thin layer on Si wafer
Authors: Kawai Jun , Kawato Shin’ichi , Hayashi Kouichi , Horiuchi Toshihisa , Matsushige Kazumi , Kitajima Yoshinori
Published: July 2002

Photoelectron spectra of a Si wafer, on which copper phthalocyanine was evaporated with a thickness of 50 Å, were measured using grazing incidence x rays under a total reflection condition. It was observed that the backgrounds owing to inelastic electron scattering in solids were reduced. It was also observed that the substrate Si signal was removed and that surface signal was enhanced due to the total x-ray reflection. Oxygen depth was determined using the angle dependence of the x-ray photoelectron spectral intensity.
Determination of the X conduction-subband energies in type II GaAs/AlAs/GaAs quantum well by deep level transient spectroscopy
Authors: Zhu Qin-Sheng , Gu Zong-Quan , Zhong Zhan-Tian , Zhou Zeng-Qi , Lu Li-Wu
Published: July 2002

Using deep level transient spectroscopy (DLTS) the X conduction-subband energy levels in an AlAs well sandwiched by double GaAs layers were determined. Calculation gives eight subbands in the well with well width of 50 Å. Among them, five levels and the other three remainders are determined by using the large longitudinal electron effective mass m1(1.1m0) and transverse electron effective mass mt(0.19m0) at X valley, respectively. Two subbands with the height energies were hardly detectable and the other six ones with lower energies are active in the present DLTS study. Because these six subbands are close to each other, we divided them into three groups. Experimentally, we observed three signals induced from the three groups. A good agreement between the calculation and experiment was obtained.
High intensity femtosecond laser pump-probing measurements of a Cu surface
Authors: Liu Ding , Alexander D. R.
Published: July 2002

Both the time and pumping power dependences of the reflectivity of a Cu surface were measured. The role of free electrons and the d-band electrons in the time dependent reflectivity changes are analyzed. Theoretical calculations based on a d-band transition model have been performed to describe the power dependence of the reflectivity changes. Results suggest that d-band electron transitions play an important role especially at early times and low pumping intensities.
Physical modeling of pyrometric interferometry during molecular beam epitaxial growth of III–V layered structures
Authors: Lee H. P. , Ranalli E. , Liu X.
Published: July 2002

A detailed physical model of pyrometric interferometry during molecular beam epitaxy growth of III–V layers is presented. The pyrometric radiation intensity is expressed as spatial convolution of the spontaneous emission rates and the propagation response of the sample. The new formalism, together with empirical modeling of background signal provide a generic framework for implementing a model-reference closed-loop control system for epitaxial growth of multilayer structures.
Effects of hydrogen addition and growth-etch cycling on the oxy-acetylene torch deposition of homoepitaxial diamond
Authors: Weimer R. A. , Thorpe T. P. , Snail K. A. , Merzbacher C. E.
Published: July 2002

Homoepitaxial diamond films were deposited onto (110) single crystal substrates using oxy-acetylene torch deposition at a constant substrate temperature of 1150 °C. Growth-etch cycling of the deposition increased the linear growth rates of the (100) and (111) faces by a factor of 2. The growth-etch films were shown to be less transparent in the infrared than the reference depositions as determined by microfocus Fourier transform infrared spectroscopy. Using the growth-etch technique, the growth rates of the (100), (111), and (110) faces decreased with increasing hydrogen addition to the combustion flame for hydrogen flow rates up to 50% of the acetylene flow rate. The additional hydrogen did not improve the growth-etch films’ transparency.
Increase in the infrared response of silicide Schottky barrier diodes by grain boundary scattering
Authors: Roca E. , Larsen K. Kyllesbech , Kolodinski S. , Mertens R.
Published: July 2002

The infrared response of polycrystalline and epitaxial CoSi2/Si Schottky diodes with similar silicide thickness has been measured. For the polycrystalline diodes the quantum efficiency is found to be two times higher than for the epitaxial diodes, although both types of diodes present very similar barrier height. The observed improvement is attributed to grain boundary scattering of the excited carriers.
Outdiffusion of impurity atoms from silicon crystals and its dependence upon the annealing atmosphere
Authors: Zhong Lei , Kirino Yoshio , Matsushita Yoshiaki , Aiba Yoshiro , Hayashi Kenro , Takeda Ryuji , Shirai Hiroshi , Saito Hiroyoki , Matsushita Junichi , Yoshikawa Jun
Published: July 2002

The outdiffusion of boron, antimony, and phosphorus from the bare silicon wafer at 1200 °C, especially its dependence upon the annealing atmosphere, has been studied with spreading resistance and secondary ion mass spectroscopy (SIMS). It is found that the boron outdiffusion proceeds when the crystal is annealed in hydrogen, but is completely suppressed in argon even if the doping concentration is as high as 3×1018 cm−3 and the annealing time is as long as 2 h. The dramatic dependence upon the atmosphere has not been observed for the other impurities and is temporarily related with the desorption process of boron atoms from the surface.
Dynamic vapor pressure measurements of the dimethyl zinc.triethylamine adduct using an ultrasonic monitor
Authors: Griffiths C. L. , Stafford A. , Irvine S. J. C. , Maung N. , Jones A. C. , Smith L. M. , Rushworth S. A.
Published: July 2002

The 1:1 adduct of dimethyl zinc with triethylamine is an attractive precursor for the growth, using metal organic vapor phase epitaxy (MOVPE), of zinc based II-VI compounds due to its high purity and suppression of unwanted pre-reactions. A key parameter in MOVPE is the vapor pressure of the precursors which needs to be known in order to control the correct concentrations of organometallics entering the reactor. The literature on the vapor pressure of this precursor has been based on static measurements and has been inconsistent with the observed growth rates for ZnTe and ZnSe. An Epison ultrasonic monitor has been used to measure the concentrations under dynamic conditions and predict saturated vapor pressure (log10p=9.80–2596/T) which agree closely with the growth rate measurements but are up to a factor of 10 smaller than the static measurements. The reasons for these discrepancies are discussed.
Near-field optical data storage
Authors: Terris B. D. , Mamin H. J. , Rugar D.
Published: July 2002

A recently developed near-field optical technique, the solid immersion lens (SIL), is utilized in a realistic demonstration of near-field optical data storage. Using 830 nm light, a 360 nm optical spot size is obtained at the exit surface of the SIL and is transferred across a small air gap to the surface of a spinning magneto-optical disk. Reading and writing of data are achieved at a density of 3.8× 108 bits/cm2 with a data rate of 3.3×106 bits/s. The subwavelength gap between the lens and the disk is maintained at a media velocity of 1.25 m/s by incorporating the lens into an air-bearing slider.
Diffraction of surface acoustic waves on the zigzag domain wall in a Gd2(MoO4)3 crystal
Authors: Alexeyev A. N. , Roshchupkin D. V.
Published: July 2002

This letter reports a scanning electron microscopy investigation of surface acoustic wave diffraction on the zigzag domain wall in a Gd2(MoO4)3 crystal. The zigzag domain wall with ∼80 μm period was formed in a Gd2(MoO4)3 crystal by applying the external mechanical stress. It is shown that the surface acoustic wave diffracts on the zigzag domain wall in a ferroelastic Gd2(MoO4)3 crystal.
Reduction of hot electron degradation in metal oxide semiconductor transistors by deuterium processing
Authors: Lyding J. W. , Hess K. , Kizilyalli I. C.
Published: July 2002

We report experimental results that replacing hydrogen with deuterium during the final wafer sintering process greatly reduces hot electron degradation effects in metal oxide semiconductor transistors due to a new giant isotope effect. Transistor lifetime improvements by factors of 10–50 are observed. A plausible physical theory suggests that the benefits of deuterium use may be general and also applicable to other areas of semiconductor device processing and fabrication.
Preparation of CuCl microcrystals-doped SiO2 glass by co-sputtering method
Authors: Takami Seiichi , Egashira Yasuyuki , Honma Itaru , Komiyama Hiroshi
Published: July 2002

CuCl microcrystals-doped SiO2 glass is prepared by the co-sputtering method using extremely pure CuCl source materials as well as a pure SiO2 target. Low temperature optical absorption spectra (2 K) show the shift of the Z1,2 as well as the Z3 exciton peaks, indicating that the mean radius of the microcrystals is about 5.8 nm.
Polarization-insensitive wavelength filters by birefringence compensation of vertical couplers
Authors: Deri R. J. , Emanuel M. A. , Patterson F. G. , Dijaili S. P. , Nguyen L. T.
Published: July 2002

We demonstrate a novel birefringence compensation technique to reduce the polarization dependence of AlGaAs directional coupler wavelength filters operating in the 770 to 970 nm wavelength range. By using a multiple quantum well structure to compensate intrinsic waveguide birefringence, we fabricated vertical coupler filters with polarization-dependent wavelength shifts from 0.1 to 2 nm, significantly less than those achieved for conventional devices. Experimental results show that both the filter wavelength and insertion loss can be rendered polarization insensitive by this technique.
Unconnected junction contrast in ion beam induced charge microscopy
Authors: Kolachina S. , Ong V. K. S. , Chan D. S. H. , Phang J. C. H. , Osipowicz T. , Watt F.
Published: July 2002

A new contrast mechanism in ion beam induced charge imaging in semiconductors is reported. Junctions not directly connected to the charge collection preamplifier were found to give rise to significant charge collection signals. Imaging with these signals is carried out, thus enabling the mapping of junctions not directly connected to the charge collection amplifier.
Si/Ge films on laterally structured surfaces: An x-ray study of conformal roughness
Authors: Tolan M. , Vacca G. , Sinha S. K. , Li Z. , Rafailovich M. H. , Sokolov J. , Lorenz H. , Kotthaus J. P.
Published: July 2002

X-ray diffraction measurements in the region of small incidence and exit angles on thin amorphous silicon/germanium films on laterally structured surfaces are performed. From fits of the data we obtain directly how the Fourier components of the substrates propagate through the evaporated films without being influenced by the intrinsic statistical roughness of the interfaces. The results show that a replication factor extracted from a given model can be quantitatively tested with our measurements.
Precipitation behaviors of Cu and Fe on Frank-type partial dislocations in Czochralski-grown silicon
Authors: Shen B. , Zhang R. , Shi Y. , Zheng Y. D. , Sekiguchi T. , Sumino K.
Published: July 2002

Precipitation behaviors of Cu and Fe on Frank-type partial dislocations bounding bulk stacking faults in Czochralski-grown silicon are investigated by means of the electron beam-induced-current (EBIC) technique and transmission electron microscopy (TEM). Frank partials in a Cu-contaminated specimen do not exhibit an EBIC contrast at room temperature when the specimen is cooled slowly; however, in the Fe-contaminated specimen, they exhibit EBIC contrast at room temperature due to their Fe contamination. The TEM micrograph shows that Cu develops precipitate colonies in the region away from stacking faults and does not precipitate on Frank partials in the specimen. The results indicate that Fe impurity decorates Frank partials more easily than Cu impurity in Si.
Dependence of Al0.48In0.52As Schottky diode properties on molecular beam epitaxial growth temperature
Authors: Brown A. S. , Bhattacharya P. , Singh J. , Zaman P. , Sen S. , Turco F.
Published: July 2002

We have observed a degradation in the epitaxial layer quality of AlInAs when it is grown by molecular beam epitaxy at a substrate temperature of about 400 °C compared to that for alloys grown at 300 and 500 °C. The barrier height and ideality factor of Ti– and Au–AlInAs Schottky diodes also exhibit large spatial variations and dependence on growth temperatures. The observed phenomena can be explained by invoking a kinetic growth model or thermodynamic phase equilibria in the growing surface layer.
Effect of thermal annealing on electrical conductivities in arsenic-ion-implanted GaAs
Authors: Chen Wen-Chung , Chang C.-S.
Published: July 2002

The effect of thermal annealing on the electrical conductivities of arsenic-ion-implanted GaAs has been investigated by deep level transient spectroscopy and temperature-dependent conductance measurements. For the annealed films of arsenic-ion-implanted GaAs a band of deep-level defects with the activation energy of around 0.55 eV below the conduction band is found. The dense concentration of traps is able to reduce the carrier concentration from 3×1018 to 2×1017 cm−3. The cross section of the deep level is calculated to be 1.5×10−14 cm2. The carrier-transport mechanisms of both as-implanted GaAs and postannealed GaAs are dominantly shown to be a separate hopping and active-type conduction.
Use of photocurrent difference spectroscopy to determine higher confined states in wide multiquantum well structures
Authors: Tanaka K. , Kotera N. , Nakamura H.
Published: July 2002

Using a novel photocurrent difference spectroscopy, six conduction subbands have become observable in 20-nm-wide In0.53Ga0.47As/In0.52Al0.48As multiquantum wells. The observed wavelength range was 0.8–1.8 μm. A proper choice of electric fields in the well on the order of 90-170 kV/cm made it possible to magnify the photocurrent difference spectrum by 1×104, owing to the Stark shift of about 20–100 meV. The interband optical transitions were limited to the field-sensitive ones of mostly forbidden type. As a result, conduction-subband eigen energies in the wells were determined at room temperature.
High energy particle irradiation effects on the low-frequency noise of Czochralski silicon junction diodes
Authors: Simoen E. , Vanhellemont J. , Dubuc J. P. , Claeys C. , Ohyama H.
Published: July 2002

The effect of high energy particle irradiation on the low-frequency (LF) noise behavior of forward biased Czochralski (Cz) silicon p-n junction diodes is reported. It is shown that in the near-ideal diode region, the LF noise is hardly affected by up to 2×1011 cm−2 MeV proton (H+) and by up to 1015cm−2 MeV electron (e−) irradiations, respectively, and is therefore resistent to both bulk and ionization radiation damage. At higher injection levels, where the forward current and LF noise are series resistance dominated, a clear increase of the noise can be observed due to the high energy particle irradiation, which mainly creates displacement damage in the bulk of the wafer. The same noise observations hold for 60Co γ-irradiated Cz n+p diodes, which were performed for comparison purposes. In the latter case, the main degradation source is ionization damage in the peripheral lateral oxide isolation regions, as shown by reverse current and gated diode measurements.
Effect of electric current on duration of cleavage luminescence
Authors: Busch E. , Haneman D. , McAlpine N. S.
Published: July 2002

The dependence on time t of the room temperature luminescence S(t) emitted by Si crystals cleaved in vacuum, is strongly affected by relatively low electric current densities passed through the specimen at the initiation of cleavage, even though the luminescence continues long after the cracking is complete and the current has stopped. Above approximately 30 mA cm−2, there is no further effect. An empirical expression has been obtained for S(t), having one adjustable parameter that varies with the current density. The effects do not appear to be possible unless cleaved surfaces attain temporary high temperatures, and point to the complexity of bond rupture phenomena.
Longitudinal size effect on conductivity in double quantum wells
Authors: Vasko F. T.
Published: July 2002

Dependence of the longitudinal conductivity on the length of double quantum wells (DQWs) with different conductivities is studied under the linear response regime. The conditions for the observation of the size effect due to near-edge redistribution of longitudinal current across DQWs is found in the case of nonresonant tunnel coupling. Due to such redistribution, the effective conductivity of DQWs with common contacts increases under increasing structure length.
Wavelength-selective waveguide photodetectors in silicon-on-insulator
Authors: Pezeshki B. , Agahi F. , Kash J. A. , Welser J. J. , Wang W.-K.
Published: July 2002

We show that silicon-on-insulator substrates, combined with a low index waveguide, can yield intrinsically wavelength-selective devices for multiwavelength applications. We demonstrate a simple wavelength-selective photodetector that resembles an asymmetric directional coupler with a polymer waveguide coupled to a silicon waveguide. Only certain wavelengths are phase-matched between the two guides and transfer from the polymer to the silicon. Operating the device at the band edge of silicon, the coupled radiation is absorbed and generates photocurrent. The 400 μm long detector exhibits a linewidth of a few nm, limited by the uniformity of the silicon-on-insulator material.
A nanoscale self-organization induced by removing Ga atoms on the Si(111)–∛×∛–Ga surface
Authors: Fujita Ken , Kusumi Yukihiro , Ichikawa Masakazu
Published: July 2002

A novel self-organization has been found to modify the Si(111)–∛×∛–Ga surface on the nanometer scale with atomic accuracy. The self-organization is induced by removing Ga atoms from a certain area on the entire ∛×∛–Ga surface with a tip of scanning tunneling microscopy. Using this phenomenon, a stripe 7.0 nm in width and more than 140 nm in length of the Si(111)–7×7 structure has been successfully formed on the ∛×∛–Ga surface.
White-beam synchrotron topographic characterization of flux-grown KTiOAsO4
Authors: Liu W. J. , Jiang S. S. , Huang X. R. , Hu X. B. , Ge C. Z. , Wang J. Y. , Jiang J. H. , Wang Z. G.
Published: July 2002

KTiOAsO4 crystals grown from tungstate fluxes have been studied by white-beam synchrotron radiation topography. It is shown that growth striations are primary planar defects. By anomalous scattering, ferroelectric domains in KTA are investigated and the ratio of ‖F(004)‖2 to ‖F(004̄)‖2 is calculated. The mechanisms of domain inversion via 2-fold axis or n-glide plane are also discussed in terms of the structural characteristics of KTA.
Growth mode, strain relief, and segregation of (Ga,In)Sb on GaSb(001) grown by molecular beam epitaxy
Authors: Bertru N. , Brandt O. , Wassermeier M. , Ploog K.
Published: July 2002

We investigate the molecular beam epitaxy of InSb on (001) GaSb by reflection high energy electron diffraction and atomic force microscopy. The growth process is found to follow the Stransky–Krastanov growth scheme with the onset to three-dimensional growth occurring between 1.7 and 2.8 InSb monolayers depending on substrate temperature. The critical thickness is enhanced at low temperature because of a kinetically limited adatom diffusion length and, apparently, at high temperature because of the thermally activated desorption of In. On the basis of these results, the segregation of In during the growth of (Ga,In)Sb is analyzed in situ, yielding a segregation energy of 0.11 eV.
Preparation of three-dimensionally oriented polycrystalline Si film
Authors: Di G. Q. , Lin H. , Uchida N. , Kurata Y. , Koumoto K. , Hasegawa S.
Published: July 2002

The crystal structure and morphology of polycrystalline Si films deposited using a plasma-enhanced chemical vapor deposition method, have been investigated by x-ray diffraction and atomic force microscopy. When the 〈110〉-oriented films were prepared at 690 °C with a hydrogen dilution ratio H2/SiH4=3 and rf power of 20 W, it was found that the grains with almost the same size are uniformly distributed within the film, and their shapes in a top view become rectangular. The longer sides of rectangles stand in line in the direction of gas flow (the plasma also spreads in this direction), indicating that the gas-flow direction and the plasma assist the growths of essentially three-dimensionally oriented grains.
Reduced lateral straggling of implantation induced defects in III/V heterostructures by ion implantation along channeling directions
Authors: Kieslich A. , Doleschel H. , Kieseling F. , Reithmaier J. P. , Forchel A.
Published: July 2002

Argon ions at an energy of 50 keV were implanted in patterned GaInAs/GaAs quantum well structures to investigate the lateral broadening of the implantation induced defect profile. In order to study the influence of ion channeling on the lateral spread of the damage distribution, implantations were carried out along channeling axes and along random directions. The degradation of the photoluminescence emission intensity of the laterally damaged quantum well layers was measured as a function of the implantation mask width. The experimental results were modeled by using a simple diffusion calculation, which considers the diffusivity of the electron-hole pairs beneath the implantation mask. This model allows the evaluation of an effective lateral straggling length for channeling as well as for random implantations. In comparison to randomly implanted samples, a clearly reduced lateral spread of the damage profile could be determined for implantations along the [100]- or the [110]-axis of the crystal.
Realization of optically pumped second-order GaInN-distributed-feedback lasers
Authors: Hofmann R. , Gauggel H.-P. , Griesinger U. A. , Gräbeldinger H. , Adler F. , Ernst P. , Bolay H. , Härle V. , Scholz F. , Schweizer H. , Pilkuhn M. H.
Published: July 2002

Room temperature distributed-feedback (DFB) laser operation is demonstrated with emission wavelengths ranging from 389 to 399 nm. Second-order DFB gratings were defined by electron beam lithography and reactive ion etching in the top GaN barrier layer of a GaInN/GaN double heterostructure grown by metalorganic vapor phase epitaxy. Our data allow a precise determination of the effective refractive index neff(λ) over the whole emission range. neff(λ) is compared with previously published values for GaN and GaInN.
Quenching of the spontaneous current oscillations in GaAs/AlAs superlattices under domain formation
Authors: Zhang Yaohui , Klann Robert , Ploog Klaus H. , Grahn Holger T.
Published: July 2002

Self-sustained current oscillations in a dc biased GaAs/AlAs superlattice exhibiting domain formation can be quenched by applying an external ac driving voltage with a large amplitude. The frequency of the driving voltage has to be much larger than the oscillation frequency and the well-to-well hopping frequency of the domain boundary. Under this condition, the oscillations of the domain boundary cannot follow anymore the ac driving signal. Consequently, for a fixed dc bias voltage the accumulated charge forming the domain boundary is confined within a single quantum well resulting in stationary domains.
Ramp-type YBa2Cu3O7−δ Josephson junctions with high characteristic voltage, fabricated by a new, completely in situ, growth technique
Authors: Strikovskiy M. D. , Engelhardt A.
Published: July 2002

We have fabricated YBa2Cu3O7−δ/PrBa2Cu3O7−δ/YBa2Cu3O7−δ ramp-type Josephson junctions with high characteristic voltage Vc=IcRn at a temperature of 77 K. A microshadow mask technique was used to grow completely in situ a ramp-type multilayer structure. Junctions with barrier thicknesses of about 13 and 45 nm were characterized. Junctions with a thicker barrier exhibited supercurrent up to 80 K and showed a resistively shunted-junction-like current voltage characteristics with a Vc as high as ∼1.5 mV at 77 K and 16 mV at 15 K. Junctions with a thinner barrier worked up to 90 K and exhibited the ac Josephson effect at 77 K under 8.9 GHz microwave radiation.
Analysis of In0.07Ga0.93As layers on GaAs compliant substrates by double crystal x-ray diffraction
Authors: Carter-Coman Carrie , Bicknell-Tassius Robert , Brown April S. , Jokerst Nan Marie
Published: July 2002

Double crystal x-ray diffraction data is presented from the most extensive compliant substrate experiment to date. Five consecutive InGaAs–GaAs growths were performed simultaneously on GaAs-based thin film compliant substrates and thick reference substrates. The In0.07Ga0.93As layers were grown to thicknesses below and above the conventional critical thickness. It was found that InGaAs films grown on the compliant substrates have a larger critical thickness and slower strain relief than InGaAs grown on conventional GaAs substrates.
Quasiphase matched surface emitting second harmonic generation in periodically reversed asymmetric GaAs/AlGaAs quantum well waveguide
Authors: Fiore A. , Beaulieu Y. , Janz S. , McCaffrey J. P. , Wasilewski Z. R. , Xu D. X.
Published: July 2002

We experimentally demonstrate surface-emitting second harmonic generation in a waveguide containing asymmetric coupled GaAs/AlGaAs quantum wells. The nonlinear conversion efficiency is enhanced by reversing the asymmetric well orientation every coherence length, in order to quasiphase match the vertical second harmonic generation process. The measured spectrum of the asymmetric quantum well susceptibility is dominated by an excitonic peak at a pump frequency corresponding to half of the first electron-heavy hole transition energy.
Modification of the second-order optical nonlinearities in AlGaAs asymmetric multiple quantum well waveguides by quantum well intermixing
Authors: Street M. W. , Whitbread N. D. , Hamilton C. J. , Vögele B. , Stanley C. R. , Hutchings D. C. , Marsh J. H. , Aitchison J. S. , Kennedy G. T. , Sibbett W.
Published: July 2002

We demonstrate that a quantum well intermixing technique can be used to control the second-order nonlinearity χzzz(2) in an AlGaAs asymmetric coupled quantum well waveguide structure at 1.52 μm. Photoluminescence measurements also indicate that the spatial resolution of the impurity-free vacancy disordering process used for quantum well intermixing is better than 1.5 μm which should be sufficient for first-order quasiphase-matched second harmonic generation.
Spontaneous emission factor in oxide confined vertical-cavity lasers
Authors: Kuksenkov D. V. , Temkin H. , Lear K. L. , Hou H. Q.
Published: July 2002

We report on measurements of the spontaneous emission factor for oxide-confined InGaAs vertical cavity surface emitting lasers. The spontaneous emission factor is determined as a function of the active layer volume from the measurement of small-signal harmonic distortion at threshold. For a 3×3 μm oxide aperture device we obtain spontaneous emission factor of 4.2⋅10−2 at room temperature.
Three-dimensional image reconstruction using strontium barium niobate
Authors: Ketchel Brian P. , Wood Gary L. , Anderson Richard J. , Salamo Gregory J.
Published: July 2002

A definitive demonstration of the use of a photorefractive crystal to project a three-dimensional image in space is reported on. The image is bright and different perspective views of the object appear as the viewing direction is changed.
Reorientational magnetic transition in mesoscopic cobalt dots
Authors: Hehn M. , Ounadjela K. , Ferré R. , Grange W. , Rousseaux F.
Published: July 2002

We have measured magnetic anisotropy constants and domain structures in arrays of magnetic dots 0.5 μm wide fabricated out of an epitaxial (0001) hcp cobalt film. Occurrence of a concentric stripe domain pattern for which the magnetization is mostly in-plane with small alternately up and down perpendicular components is found for a 25-nm-thick cobalt dot array. Interestingly, this sample produces a spin reorientation from a quasi in-plane to a fully perpendicularly oriented magnetization when the temperature is lowered, due to an increase of the perpendicular anisotropy at low temperature.
Increased radiative lifetime of rare earth-doped zinc oxyhalide tellurite glasses
Authors: Sidebottom D. L. , Hruschka M. A. , Potter B. G. , Brow R. K.
Published: July 2002

We have investigated the structural and optical properties of rare earth-doped zinc tellurite glasses modified by the substitution of ZnF2. Raman and phonon sideband spectroscopies were employed to characterize changes in the glass structure as well as to probe vibrational behavior in the immediate vicinity of the rare earth ion. These measurements are combined with photoluminescence and optical absorption to monitor the effect of halide substitution upon the optical behavior of the rare earth dopant. A substantial increase in the intrinsic radiative lifetime of Nd3+ is observed with increasing halide concentration.
Electron emission from boron nitride coated Si field emitters
Authors: Sugino Takashi , Kawasaki Seiji , Tanioka Kazuhiko , Shirafuji Junji
Published: July 2002

Electron emission characteristics of sulfur (S)-doped boron nitride (BN) films synthesized by plasma-assisted chemical vapor deposition (PACVD) are investigated. The BN film consists of hexagonal grains of 3 nm in size. The energy gap is estimated to be as wide as 6.0 eV from ultraviolet-visible optical transmission measurement. The electrical resistivity is reduced to 4.9×102 Ω cm. Si tip field emitters coated with the BN film are fabricated. The electron emission occurs at an electric field as low as 6 V/μm, while a high electric field of 20 V/μm is needed to emit electrons from the Si tip array without BN coating. It is deduced that the tunneling barrier height of 0.1 eV exists at the surface of the BN film.
Transparent nanocrystalline diamond ceramics fabricated from C60 fullerene by shock compression
Authors: Hirai H. , Kondo K. , Kim M. , Koinuma H. , Kurashima K. , Bando Y.
Published: July 2002

Transparent nanocrystalline diamond ceramics, consisting of a few nanometer-sized diamond crystallites that are unstable in themselves because of higher surface energy, were fabricated successfully from C60 fullerene using a shock compression and rapid quenching technique. The platelets were transparent and very hard, nearly comparable to type IIa diamond. Transmission electron microscopy and electron energy loss spectroscopy revealed that individual crystallites had combined directly or through a very thin and modified sp3 carbon layer, which possibly stabilized the nanometer-sized crystallites. The size order and sp3 configuration of the nanotexture caused the transparency and hardness of the present material.
Thermally stable high-gain photorefractive polymer composites based on a tri-functional chromophore
Authors: Hendrickx E. , Herlocker J. , Maldonado J. L. , Marder S. R. , Kippelen B. , Persoons A. , Peyghambarian N.
Published: July 2002

We report on the photorefractive properties of thermally stable polymer composites based on the dye 2, N, N-dihexylamino-7-dicyanomethylidenyl-3,4,5,6,10-pentahydronaphthalene. At an applied field of 50 V/μm, we have achieved a dynamic range of Δn=8.5×10−3 and a net two-beam coupling gain of 202 cm−1. The diffraction efficiency peaks at an applied field of 28 V/μm, giving an external diffraction efficiency of 71%.
A method for the formation of polymer walls in liquid crystal/polymer mixtures
Authors: Kim Yoan , Francl Jim , Taheri Bahman , West John L.
Published: July 2002

We have investigated the formation of polymer walls for high polymer content liquid crystal (LC) formulations, using a patterned electric field to induce phase separation. The effect of this field on the phase separation temperature of a LC/monomer mixture is studied as a function of the photopolymerizable monomer concentration. The phase separation temperature increases with the patterned field strength. The application of a patterned field results in segregation of the LC molecules in the high electric field regions, i.e., pixels, whereas the monomers segregate in the low-field regions, i.e., interpixels. Subsequent photopolymerization results in the formation of polymer walls around the pixels. The structure of the polymer walls was investigated using scanning electron microscopy.
Metamorphic InGaAs/InAlAs quantum well structures grown on GaAs substrates for high electron mobility transistor applications
Authors: Behet M. , van der Zanden K. , Borghs G. , Behres A.
Published: July 2002

Modulation-doped In0.5Ga0.5As/In0.5Al0.5As quantum well structures grown by molecular beam epitaxy on GaAs substrates using a relaxed AlGaAsSb buffer showed carrier mobilities of 8500 cm2/V s for a sheet concentration of 3.5×1012 cm−2 at room temperature. The crystallinity of the quaternary buffer layer was verified by x-ray diffractometry. Transistors with 0.25×100 μm2 gates demonstrated transconductance values as high as 800 mS/mm. S-parameter measurements revealed a cutoff frequency fT of 87 GHz and a maximum oscillation frequency fMAX of 140 GHz (both extrinsic values).
Reduction of threading dislocations by InGaAs interlayer in GaAs layers grown on Si substrates
Authors: Takano Y. , Hisaka M. , Fujii N. , Suzuki K. , Kuwahara K. , Fuke S.
Published: July 2002

High-quality GaAs epilayers with dislocation densities of 1.2×106 cm−2 on (100)Si substrates have been obtained by insertion of an InGaAs strained interlayer combined with thermal cycle annealing instead of strained layer superlattices. All the layers were grown by low-pressure metalorganic vapor phase epitaxy. The threading dislocation density near the surface of 4 μm thick GaAs was measured by plan-view transmission electron microscopy. The threading dislocation density was found to be very sensitive to the In composition of the interlayer and the specifics of thermal cycle annealing.
Luminescence behavior of pulsed laser deposited Eu:Y2O3 thin film phosphors on sapphire substrates
Authors: Cho K. G. , Kumar D. , Holloway P. H. , Singh Rajiv K.
Published: July 2002

Europium-doped yttrium oxide (Eu:Y2O3) luminescent thin films have been grown in situ on single crystal (0001) sapphire substrates using a pulsed laser deposition technique. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. The photoluminescence (PL) and cathodoluminescence (CL) brightness data obtained from the Eu:Y2O3 films grown under optimized conditions have indicated that sapphire is a promising substrate for the growth of high quality Eu:Y2O3 thin film red phosphor. The success in the fabrication of Eu:Y2O3 films with high PL and CL brightness is attributed to favorable optical properties (low absorption of and low refractive index for red light) of the substrate material and improved growth of grains with unidirectional orientation on (0001) sapphire substrates.
Influence of the implantation parameters on the microstructure of carbon onions produced by carbon ion implantation
Authors: Cabioc’h T. , Jaouen M. , Denanot M. F. , Bechet P.
Published: July 2002

We study the influence of implantation parameters (temperature, implanted dose, and current density) on the microstructure of carbon onions produced by carbon ion implantation into silver substrates held at elevated temperature. Carbon onions are synthesized only for temperatures higher than 400 °C. An increase of the average diameter of the onions as well as a structure presenting less defects are observed when the temperature increases from 500 to 800 °C. For implantation doses varying from 5×1016 cm−2 to 5×1017 cm−2, we observe an increase of the average diameter, spherical onions with a very sharp distribution in size being obtained for doses ⩽1017 cm−2. We also vary the current density of the carbon ion beam from 2 to 45 μA cm−2, but this parameter does not induce any visible microstructural evolution of the onions. From the results presented here, one can now carry out studies related to the evolution of the physical properties of well defined size carbon onions having a controlled amount of defects.
Growth and characterization of 10-nm-thick c-axis oriented epitaxial PbZr0.25Ti0.75O3 thin films on (100)Si substrate
Authors: Maruyama T. , Saitoh M. , Sakai I. , Hidaka T. , Yano Y. , Noguchi T.
Published: July 2002

A 10-nm-thick PbZr0.25Ti0.75O3 thin film is epitaxially grown on a SrRuO3/BaTiO3/ZrO2/Si heterostructure substrate by reactive evaporation. Structural and electrical properties of the film are investigated. It is concluded that the film is ferroelectric and retains a native uniform upward polarization. Artificial downward polarization domains, whose average diameter is 24 nm, can be formed in the film.
Epitaxially-stacked multiple-active-region 1.55μm lasers for increased differential efficiency
Authors: Kim J. K. , Hall E. , Sjölund O. , Coldren L. A.
Published: July 2002

Semiconductor lasers emitting at 1.55 μm with external differential efficiencies >1 have been created by monolithically connecting several active regions in series within a single optical waveguide. This is accomplished by epitaxially stacking a number of p–i–n multiquantum well active regions with intermediate n++–p++ back diodes, which enable the entire terminal current to flow through each active region stages in series. Such lasers should also improve the impedance match as well as provide for low-noise, high-efficiency microwave links.
Pulsed excitation of low-mobility light-emitting diodes: Implication for organic lasers
Authors: Tessler N. , Pinner D. J. , Cleave V. , Thomas D. S. , Yahioglu G. , Le Barny P. , Friend R. H.
Published: July 2002

We present a theoretical and experimental study of electrical pulsed excitation in polymer light-emitting diodes (LEDs). We find that the low mobility results in a relatively high charge density within an electrically pumped structure. The broad spectrum of the charge-induced absorption and its overlap with the ground-state absorption pose a significant barrier for achieving net gain and lasing. We suggest an approach that might circumvent this problem using suitable emitters and an appropriate driving scheme. We also suggest methods for ultrafast modulation of LEDs as well as direct determination of the space charge within the recombination zone.
Stable hexagonal-wurtzite silicon phase by laser ablation
Authors: Zhang Yan , Iqbal Zafar , Vijayalakshmi Sankaran , Grebel Haim
Published: July 2002

A stable phase of relatively large hexagonal-wurtzite silicon crystals (up to 20 μm) was directly deposited at low pressure using ultraviolet laser ablation. The films were grown on a variety of substrates at room temperature from a single crystal, cubic silicon target. Crystallites of the hexagonal-wurtzite phase of silicon were clearly identified using selected area electron diffraction. Further support for this identification was provided by confocal scanning micro-Raman spectroscopy. The deposition of hexagonal silicon films may lead to novel two-dimensional optoelectronic devices, and pave the way to studies of the electronic properties of this lower symmetry, uncommon silicon phase.
Terabit-per-square-inch data storage with the atomic force microscope
Authors: Cooper E. B. , Manalis S. R. , Fang H. , Dai H. , Matsumoto K. , Minne S. C. , Hunt T. , Quate C. F.
Published: July 2002

An areal density of 1.6 Tbits/in.2 has been achieved by anodically oxidizing titanium with the atomic force microscope (AFM). This density was made possible by (1) single-wall carbon nanotubes selectively grown on an AFM cantilever, (2) atomically flat titanium surfaces on α-Al2O3 (1012), and (3) atomic scale force and position control with the tapping-mode AFM. By combining these elements, 8 nm bits on 20 nm pitch are written at a rate of 5 kbit/s at room temperature in air.