bluuebunny/crossref_metadata_2025 huggingface dataset:
Subband emissions of InGaN multi-quantum-well laser diodes under room-temperature continuous wave operation
Authors: Nakamura Shuji , Senoh Masayuki , Nagahama Shin-ichi , Iwasa Naruhito , Yamada Takao , Matsushita Toshio , Sugimoto Yasunobu , Kiyoku Hiroyuki
Published: July 2002

The emission spectra of InGaN multi-quantum-well (MQW) laser diodes (LDs) under continuous-wave (CW) operation at room temperature (RT) showed periodic subband emissions with an energy separation of 2 meV. The peak wavelength of the laser emission was measured as a function of the operating current. The peak wavelength showed mode hopping toward higher energy with increasing operating current. Each single-mode laser emission was located at a peak of each periodic subband emission. These periodic subband emissions probably result from the transitions between the subband energy levels of the InGaN quantum dots formed from In-rich regions in the InGaN well layers. High-power InGaN MQW LDs with an output power of 40 mW were performed under RT CW operation.
Flux pinning by collective stacking faults in Y0.6Ho0.4Ba2Cu3Oy prepared by powder melting process
Authors: Feng Yong , Wen J. G. , Koshizuka N. , Zhou Lian
Published: July 2002

The correlation between microstructure and flux pinning of Y0.6Ho0.4Ba2Cu3Oy (123) sample prepared by the powder melting process method has been investigated. Transmission electron microscopy observations show that there exists a large number of novel stacking faults (double CuO chains) in this sample. The shape of the stacking faults looks like collective stairs. The stacking faults are different from those observed in the conventional melt textured 123 materials and not related to 123/Y2BaCuO5 interface. The sample is resintered at 900 °C purposefully in order to reduce the density of stacking faults. The magnetization measurements indicate that the critical current density and irreversibility lines in both field orientations (H∥c and H⊥c) are significantly reduced by the decrease in the density of stacking faults. This means that the collective stacking faults work as effective pinning centers in the 123 superconductors prepared by the powder melting process method in a wide range of temperatures and fields.
In situ controlled fabrication of stacks of high-Tc intrinsic Josephson junctions
Authors: Yurgens A. , Winkler D. , Claeson T. , Zavaritsky N. V.
Published: July 2002

Stacked series arrays of intrinsic Josephson (IJ) tunnel junctions have been fabricated on the surfaces of Bi2Sr2CaCu2O8+δ  single crystals using photolithography and Ar-ion milling together with in situ monitoring of the resulting current–voltage (I–V) characteristics. The number of unit-cell-sized junctions in the stack (along the c-axis) may be varied from 1–5 to ∼200 in a controlled way. The c-axis resistivity ρc, estimated from the resistance of an individual tunnel junction is ≈30 Ω cm at 90 K. The temperature dependence ρc(T)∝ exp(Λ/T) with Λ≈43 meV, suggesting thermally activated hopping mechanism of transport in the c-axis direction.
Modification of the density profile in a toroidal plasma source using a bias electric field
Authors: Zhang B. C. , Cross R. C.
Published: July 2002

As in other plasma devices with a curved magnetic field geometry, an asymmetric density profile is observed in the PLADEPUS, a toroidal plasma source, at the University of Sydney. In this letter, we demonstrate that the asymmetric density profile can be improved by means of a positive bias electric field at the edge of the plasma. With the bias field, the density profile becomes symmetric and broadened, and the plasma density is enhanced.
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damage of ferroelectric Pb(Zr,Ti)O3 thin-film capacitors—The role of catalytic and adsorptive activity of the top electrode
Authors: Shimamoto Y. , Kushida-Abdelghafar K. , Miki H. , Fujisaki Y.
Published: July 2002

Large-scale integrated fabrication in a H2 containing atmosphere, for example, during the passivation process, can cause serious damage in metal/Pb(Zr,Ti)O3/metal capacitors (i.e., Pt/PZT/Pt capacitors). To reveal the cause of the H2 damage, we investigated the behavior of hysteresis curves and the leakage current of capacitors with a top electrode of Pt, Pd, Au, or Ag. Capacitors with a top electrode of Au or Ag are more resistant to the H2 annealing damage than those of Pt or Pd. We found that the H2 damage was strongly affected by the catalytic activity and adsorptive properties of the top electrode when exposed to H2.
Determination of significant transport parameters of two-dimensional electron gas systems by microwave methods
Authors: Brensing A. , Mazloom-Tehrani M. , Bauhofer W.
Published: July 2002

The main transport parameters of a two-dimensional electron gas (2DEG) system, namely, the effective mass m*, electron sheet concentration ns, transport lifetime τc, and quantum lifetime τq, were determined exclusively by contactless microwave transmission methods in the frequency range 26.5–40 GHz. Shubnikov–de Haas oscillations were detected by measuring σxx with parallel waveguides while crossed waveguides were used for Hall measurements. The microwave results are in good agreement with values obtained from conventional direct current investigations. The 2DEG is realized in a modulation doped InGaAs/InP double heterostructure.
Normal incident long-wavelength quantum well infrared photodetectors using electron intersubband transitions
Authors: Wang S. Y. , Lee C. P.
Published: July 2002

Grating-free quantum well infrared photodetectors (QWIPs) for 8–10 μm applications have been fabricated. The QWIPs fabricated with InGaAs/GaAs quantum wells show excellent performance with normal-incident infrared radiation. A detectivity of 2×1010 cm Hz1/2/W and a responsivity of 0.23 A/W have been obtained for these devices. The devices were compared with QWIPs with 1D and 2D surface gratings. No significant improvement in responsivity is observed for devices with 1D gratings. Devices with 2D gratings have significantly higher peak responsivity but only in a very limited spectral range. The GaAs/AlGaAs QWIPs in the similar spectral range have also been fabricated and, however, shown much weaker TE absorption.
Depth dependent carrier density profile by scanning capacitance microscopy
Authors: Kang C. J. , Kim C. K. , Lera J. D. , Kuk Y. , Mang K. M. , Lee J. G. , Suh K. S. , Williams C. C.
Published: July 2002

The depth dependent carrier density was measured on an arsenic implanted silicon sample using scanning capacitance microscopy (SCM). The capacitance versus voltage scan was performed by applying dc biases with a dither ac signal. A strong dc bias dependence was observed at the interface of an abrupt junction between n+ and p. The bias dependent SCM images show good agreement with quasi-three dimensional simulations, suggesting that they can be used to map a device structure.
Pulsed laser deposition of liquid crystals
Authors: Gonzalo J. , Dyer P. E. , Hird M.
Published: July 2002

Thin films of 4-cyano-4’-pentylbiphenyl (5CB) liquid crystal have been fabricated by pulsed laser deposition. The suitability of different lasers (ArF, KrF and CO2) has been investigated over a range of fluence using visible-UV and infrared absorption and optical microscopy to characterise the films. High performance liquid chromatography (HPLC) and matrix assisted laser desorption ionization mass spectroscopy (MALDI-MS) were used to assess the extent of decomposition of the films. The results suggest that the CO2 laser acts as a quasi-steady heat source, while for ArF laser irradiation severe photodecomposition is observed. However, use of the KrF laser allows the production of excellent quality submicron films, showing properties similar to the 5CB target with only slight photodecomposition.
Improvement in gate oxide integrity on thin-film silicon-on-insulator substrates by lateral gettering
Authors: Hong S. Q. , Wetteroth T. , Shin H. , Wilson S. R. , Werho D. , Lee T.-C. , Schroder D. K.
Published: July 2002

Lateral gettering is implemented in thin-film silicon-on-insulator (TFSOI) substrates by introducing crystalline defects in the vicinity of metal-oxide-semiconductor device channel regions prior to gate oxidation. As a result of the gettering a significant improvement in gate oxide integrity is achieved, with increased oxide breakdown voltages and charge-to-breakdowns, as well as a reduction in localized oxide charge trapping. The same gettering effect on separation-by-implantation-of-oxygen and bonded silicon-on-insulator substrates suggests that the lack of effective gettering is mainly responsible for the oxide degradation regardless of the TFSOI type. This work also demonstrates the feasibility of achieving bulk-comparable gate oxides on TFSOI substrates.
Relaxed template for fabricating regularly distributed quantum dot arrays
Authors: Xie Y. H. , Samavedam S. B. , Bulsara M. , Langdo T. A. , Fitzgerald E. A.
Published: July 2002

Relaxed SiGe thin films are used as templates to control the nucleation of three-dimensional Ge islands on Si(100) substrates. Using the relaxed template, Ge islands form a rectangular array with all islands located exclusively above the intersections of dislocations. The registration is lost when the Ge growth temperature is lowered to 300 °C, and the Ge coverage is decreased to 0.4 nm.
Composition evaluation of InxGa1−xAs Stranski-Krastanow-island structures by strain state analysis
Authors: Rosenauer A. , Fischer U. , Gerthsen D. , Förster A.
Published: July 2002

The compositional analyses of InxGa1−x/GaAs (001) island structures grown by molecular beam epitaxy at a substrate temperature of 560 °C with nominal In contents of x=60% and 100% are presented on the basis of high resolution transmission electron microscopy micrographs. The linear dependence of the lattice parameter on the In content (Vegard’s law) is exploited to quantitatively derive composition profiles on an atomic scale by measuring local lattice parameters and displacements. The relaxation of the thin transmission electron microscopy specimen is taken into account by the accurate thickness determination using the quantitative analysis of the information from transmission electron micrographs procedure. The final evaluation step consists of finite element modeling with the appropriate sample geometry, where the In distribution is chosen to obtain the best fit between experimental and simulated displacements. The observed In content is significantly smaller than the nominal In concentration which is due to segregation of In and diffusion of Ga from the GaAs buffer into the island during the growth. The measured mean In concentration of the islands with a nominal In content of 60% (100%) is 24% (45%).
The reaction of carbon tetrachloride with gallium arsenide (001)
Authors: Li L. , Gan S. , Han B.-K. , Qi H. , Hicks R. F.
Published: July 2002

Carbon tetrachloride dissociatively adsorbs on the Ga-rich (4×2) reconstruction of GaAs (001) at 200 °C. Upon heating to 440 °C, the chlorine desorbs as GaCl, which etches the surface. Scanning tunneling micrographs reveal that this reaction transforms the (4×2) into a Ga-rich (3×2) structure that is interlaced with As-rich (2×4) phases. The (3×2) is well ordered, while the (2×4) phases exhibit a high degree of disorder. This work establishes the surface reaction pathway for carbon doping of GaAs with CCl4.
Experimental and theoretical density-dependent absorption spectra in (GaInSb/InAs)/AlGaSb superlattice multiple quantum wells
Authors: Olesberg J. T. , Anson S. A. , McCahon S. W. , Flatté Michael E. , Boggess Thomas F. , Chow D. H. , Hasenberg T. C.
Published: July 2002

A broadly tunable, ultrafast optical parametric oscillator is used to measure carrier-density-dependent absorption spectra in a 340-meV band gap (GaInSb/InAs)/AlGaSb superlattice multiple quantum well structure. Similar structures have been implemented recently as the active region in midinfrared diode lasers. The measured spectra are compared with calculated spectra computed using a semiempirical eight-band superlattice K⋅p model. The model provides good agreement with the experimentally observed spectral and density dependence of the absorption. These results provide confirmation that the model may be used for band structure engineering of optimized midinfrared laser active regions.
Effect of coupling structure of Eu on the photoluminescent characteristics for ZnO:EuCl3 phosphors
Authors: Park Y.-K. , Han J.-I. , Kwak M.-G. , Yang H. , Ju S.-H. , Cho W.-S.
Published: July 2002

In this study we have synthesized ZnO:EuCl3 phosphors under various sintering atmospheres and temperatures, and investigated the effect of coupling structure of Eu in ZnO upon the photoluminescent characteristics for the purpose of searching for optimum conditions towards pure red emission. The analysis of x-ray diffraction and photoluminescence spectra measurements indicate that, for ZnO:EuCl3 phosphors sintered in vacuum, Eu exists in the host lattice as EuOCl and effectively quenches the broad-band emission of the ZnO host, consequently isolating the red emission due to Eu3+ ion.
Local environment of erbium atoms in amorphous hydrogenated silicon
Authors: Masterov V. F. , Nasredinov F. S. , Seregin P. P. , Kudoyarova V. Kh. , Kuznetsov A. N. , Terukov E. I.
Published: July 2002

The Er169(169Tm)emission Mössbauer spectroscopy has evidenced that photoluminescence centers in Er-doped amorphous hydrogenated silicon are [Er–O] clusters. The local environment of the Er3+ ions in the clusters is similar to the Er3+ environment in Er2O3.
Influence of rapid thermal annealing on the optical properties of gallium nitride grown by gas-source molecular-beam epitaxy
Authors: Li X. B. , Sun D. Z. , Zhang J. P. , Kong M. Y. , Yoon S. F.
Published: July 2002

Raman scattering, photoluminescence (PL), and nuclear reaction analysis (NRA) have been employed to investigate the effects of rapid thermal annealing (RTA) on GaN films grown on sapphire (0001) substrates by gas-source molecular-beam epitaxy. The Raman spectra showed the presence of the E2 (high) mode of GaN and shift of this mode from 572 to 568 cm−1 caused by annealing. The results showed that RTA has a significant effect on the strain relaxation caused by the lattice and thermal expansion misfit between the GaN epilayer and the substrate. The PL peak exhibited a blueshift in its energy position and a decrease in the full width at half maximum after annealing, indicating an improvement in the optical quality of the film. Furthermore, a green luminescence appeared after annealing and increased in intensity with increasing annealing time. This effect was attributed to H concentration variation in the GaN film, which was measured by NRA. A high H concentration exists in as-grown GaN, which can neutralize the deep level, and the H-bonded complex dissociates during RTA. This leads to the appearance of a luminescent peak in the PL spectrum.
Composition dependence of room temperature 1.54 μm Er3+ luminescence from erbium-doped silicon:oxygen thin films deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition
Authors: Shin Jung H. , Kim Mun-Jun , Seo Se-young , Lee Choochon
Published: July 2002

The composition dependence of room temperature 1.54 μm Er3+ photoluminescence of erbium-doped silicon:oxygen thin films produced by electron cyclotron resonance plasma enhanced chemical vapor deposition of SiH4 and O2 with concurrent sputtering of erbium is investigated. The Si:O ratio was varied from 3:1 to 1:2 and the annealing temperature was varied from 500 to 900 °C. The most intense Er3+ luminescence is observed from the sample with a Si:O ratio of 1:1.2 after a 900 °C anneal and the formation of silicon nanoclusters embedded in the SiO2 matrix. The high active erbium fraction, efficient excitation via carriers, and high luminescence efficiency due to the high quality SiO2 matrix are identified as key factors in producing the intense Er3+ luminescence.
Paramagnetic and ferromagnetic resonance imaging with a tip-on-cantilever magnetic resonance force microscope
Authors: Wago K. , Botkin D. , Yannoni C. S. , Rugar D.
Published: July 2002

A magnetic resonance force microscope with a “tip-on-cantilever” configuration was used to compare imaging characteristics of paramagnetic and ferromagnetic samples. Three-dimensional electron paramagnetic resonance (EPR) imaging of diphenylpicrylhydrazil (DPPH) particles was accomplished by scanning the sample in two dimensions while stepping an external field. The EPR force map showed broad response reflecting the size and shape of the sample, allowing a three-dimensional real-space magnetization image to be successfully reconstructed. In contrast to the EPR case, ferromagnetic resonance imaging of a micron-scale yttrium iron garnet sample showed no significant line broadening despite the strong field gradient (∼10 G/μm). Two-dimensional force maps revealed spatial dependence of magnetostatic and magnetoelastic modes.
Formation of PIn defect in annealed liquid-encapsulated Czochralski InP
Authors: Zhao Y. W. , Xu X. L. , Gong M. , Fung S. , Beling C. D. , Chen X. D. , Sun N. F. , Sun T. N. , Liu S. L. , Yang G. Y. , Guo X. B. , Sun Y. Z. , Wang L. , Zheng Q. Y. , Zhou Z. H. , Chen J.
Published: July 2002

Fourier transform infrared spectroscopy measurements have been carried out on liquid-encapsulated Czochralski-grown undoped InP wafers, which reproducibly become semi-insulating upon annealing in an ambient of phosphorus at 800–900 °C. The measurements reveal a high concentration of hydrogen complexes in the form VInH4 existing in the material before annealing in agreement with recent experimental studies. It is argued that the dominant and essential process producing the semi-insulating behavior is the compensation produced by an EL2-like deep donor phosphorus antisite defect, which is formed by the dissociation of the hydrogen complexes during the process of annealing. The deep donor compensates acceptors, the majority of which are shallow residual acceptor impurities and deep hydrogen associated VIn and isolated VIn levels, produced at the first stage of the dissociation of the VInH4 complex. The high concentration of indium vacancies produced by the dissociation are the precursor of the EL2-like phosphorus antisite. These results show the importance of hydrogen on the electrical properties of InP and indicate that this largely results from low formation energy of the complex VInH4 in comparison with that of an isolated VIn.
Two-dimensional network of dislocations and nanocavities in hydrogen-implanted and two-step annealed silicon
Authors: Gao Min , Duan X. F. , Wang Fenglian , Li Jianming
Published: July 2002

Conventional transmission electron microscopy and energy-filtering were used to study the dislocations and nanocavities in proton-implanted (001) silicon. A two-dimensional network of dislocations and nanocavities was found after a two-step annealing, while only isolated cavities were present in single-step annealed Si. In addition, two-step annealing increased materially the size and density of the nanocavities. The Burgers vector of the dislocations was mainly the 1/2〈110〉 type. The gettering of oxygen at the nanocavities was demonstrated.
Near-field scanning solid immersion microscope
Authors: Ghislain L. P. , Elings V. B.
Published: July 2002

We report a near-field scanning optical microscope using a solid immersion lens having a sharp tip that is mounted to a cantilever. The sharp tip allows the sample to enter the near field of the illumination. The cantilever provides sensitive control of forces. We describe two types of near-field optical contrast, interference and reflection, that simultaneously measure surface topography and reflectivity. Using a super-hemispherical lens with index n=2.2 and 442 nm illumination, the microscope resolves optical features smaller than 150 nm, a factor of 2 improvement over a conventional optical microscope.
Low-temperature Si epitaxy with high deposition rate using ion-assisted deposition
Authors: Bergmann R. B. , Zaczek C. , Jensen N. , Oelting S. , Werner J. H.
Published: July 2002

Ion-assisted deposition is suitable for the formation of epitaxial Si films at high deposition rate and low substrate temperature. We demonstrate epitaxial deposition of Si films on (100)-oriented Si wafers using deposition rates up to 0.3 μm/min at deposition temperatures in the range of 500–650 °C. Hall-effect measurements show a majority carrier mobility of 200 cm2/V s at a hole concentration of 1.4×1017 cm−3 in our films. A minority carrier diffusion length of 4.5 μm is determined from quantum efficiency measurements in the epitaxially grown Si films.
Surface photovoltage spectroscopy of n-n+ and p-n+ AlGaAs/GaAs heterojunctions
Authors: Kumar Shailendra , Ganguli Tapas , Bhattacharya Pijush , Roy U. N. , Chandvankar S. S. , Arora B. M.
Published: July 2002

A comparative study of n-n+ and p-n+ semiconductor heterojunctions has been done using the surface photovoltage spectroscopy (SPS) in the chopped light geometry. Heterojunctions n-Al0.4Ga0.6As/n+ GaAs and p-Al0.37Ga0.67As/n+ GaAs and substrate n+ doped GaAs have been studied in the wavelength range 600–1000 nm. A sharp decrease in SPS at the band-gap energies of AlGaAs and GaAs with a broad peak in the subband-gap region of GaAs has been observed. The magnitude of surface photovoltage (SPV), for a constant photon flux for n-n+ samples, is less by more than two orders of magnitude than that for p-n+ samples in the wavelength range 645–870 nm. Changes in the dipole moments due to the redistribution of excess carriers in the space-charge regions are in opposite directions of the n-n+ heterojunctions giving less SPV, while for p-n+ heterojunction, the changes in the dipole moments are in the same direction giving more SPV in comparison to the n-n+ samples.
High-frequency electron beam modulation in a diode with an active plasma cathode
Authors: Krasik Ya. E. , Dunaevsky A. , Felsteiner J.
Published: July 2002

We have carried out experiments with an active plasma cathode showing the possibility to generate a modulated electron beam with a repetition rate of 2 Hz without the use of a high-frequency power supply. The modulation of the beam current amplitude reaches values ⩾30%. This modulation is found to have a frequency of 325±5 MHz for a discharge capacitor of 1 nF and a duration ⩾1 μs. In addition, the modulated electron beam is accompanied by electromagnetic radiation with the same frequency. We suggest that this high-frequency modulation is caused by electron oscillations within the potential well which is created inside the cathode structure by the positive potential of the plasma.
Application of a semiconductor tip to capacitance microscopy
Authors: Goto Kazuya , Hane Kazuhiro
Published: July 2002

A semiconductor tip has been applied to the scanning capacitance microscopy (SCM). Local electrostatic fields are measured through depletion of carriers at the tip end. A Si microcantilever with the sharp end is employed. This SCM technique has been used in a capacitance observation of a dielectric/electrode sample. Potentiometry using this technique is demonstrated in an experiment of charge injection recording on a polymer film.
Self-organization of (In,Ga)As/GaAs quantum dots on relaxed (In,Ga)As films
Authors: Pan Dong , Xu Jian , Towe Elias , Xu Qin , Hsu J. W.
Published: July 2002

We report the synthesis of (In,Ga)As/GaAs quantum dots on strain-relaxed (In,Ga)As epitaxial films. It is found that the incorporation of a relaxed prelayer provides a systematic and effective method for controlling the dot distribution and emission wavelength. The robustness of the optical properties of quantum dots to dislocations may provide a method for engineering the band structure of quantum dot devices. We demonstrate, for example, that longer band-to-band emission wavelengths can be obtained by simply decreasing the residual strain in the relaxed films.
Superradiant lasing from J-aggregated molecules adsorbed onto colloidal silver
Authors: Özçelik Serdar , Özçelik Isin , Akins Daniel L.
Published: July 2002

The picosecond time-resolved emission spectrum of the cyanine dye 1,1′-diethyl-3,3′bis-(3-sulfopropyl)-5,5′,6,6′-tetrachlorobenzimidazolocarbocyanine (also known as BIC) adsorbed onto colloidal silver was examined as a function of laser pulse energy at room temperature. BIC is found to aggregate on colloidal silver, and the number of coherently responding molecules involved in the one-exciton state (i.e., the coherence length) was estimated to involve 8–9 molecules. Lasing at a remarkably low incident pulse energy threshold was found for this system and explained in terms of a mechanism involving superradiant states created in coherently coupled adsorbed molecules that emit photons which stimulate emission from other spatially distributed superradiant states.
Magnetic homogeneity of colossal-magnetoresistance thin films determined by alternating current magnetic susceptibility
Authors: Araujo-Moreira F. M. , Rajeswari M. , Goyal A. , Ghosh K. , Smolyaninova V. , Venkatesan T. , Lobb C. J. , Greene R. L.
Published: July 2002

We report measurements of the alternating current (ac) magnetic susceptibility, χac=χ′+iχ″, performed on colossal-magnetoresistance (CMR) materials. We have studied thin film samples of La0.67Ca0.33MnO3 and Nd0.7Sr0.3MnO3. For homogeneous samples, the temperature of the peak observed in χ″(T) is in agreement with the temperature of peak resistivity (TP) obtained from transport measurements. This agreement is not found for inhomogeneous samples, where χ″(T) shows multiple peaks. The analysis of χ″(T) enables one to determine the quality of the CMR materials. The results obtained in thin films of La0.67Ca0.33MnO3 and Nd0.7Sr0.3MnO3, are consistent with those obtained from an homogeneous single crystal of La0.80Sr0.20MnO3. We show that the contactless ac magnetic susceptibility technique is a quick method to reveal inhomogeneities which are not directly evident in direct current transport measurements.
An optimal magnetic tip configuration for magnetic-resonance force microscopy of microscale buried features
Authors: Marohn John A. , Fainchtein Raúl , Smith Doran D.
Published: July 2002

To date, magnetic-resonance force microscopes employing a magnetic-field gradient source mounted to a microcantilever have suffered from a deleterious dependence of the effective cantilever spring constant on the external magnetic field. A “magnet-on-tip” configuration is introduced in which this dependence has been decreased by at least 200 fold, making it feasible to perform arbitrary-sample micron-scale magnetic resonance force microscopy at very high magnetic field. Alternating-gradient cantilever magnetometry is used to quantify the effect and to prove that the existing model of the tip-field interaction is only qualitatively correct. A model is proposed which quantitatively describes the tip-field interaction in the traditional tip configuration.
Visible light-emitting devices with Schottky contacts on an ultrathin amorphous silicon layer containing silicon nanocrystals
Authors: Fujita S. , Sugiyama N.
Published: July 2002

We have fabricated light-emitting diodes (LEDs) with Schottky contacts on a single ultrathin amorphous silicon (Si) layer containing Si nanocrystals formed by simple techniques as used for standard Si devices. Orange electroluminescence (EL) from these LEDs could be seen with the naked eye at room temperature when a reverse bias voltage was applied. The EL spectrum has a major peak with a photon energy of 1.9 eV and a minor peak with a photon energy of 2.2 eV. The operation voltage is reduced to 4.0−4.5 V, which is low enough to be applied to a standard Si transistor.
A refractive collimator for synchrotron radiation
Authors: Baron A. Q. R. , Kohmura Y. , Ohishi Y. , Ishikawa T.
Published: July 2002

We demonstrate that a simple and inexpensive plastic refractive lens may be used to collimate synchrotron radiation. The divergence of an 18.5 keV beam of radiation from an undulator at SPring-8 is reduced from 11 μrad, full width at half maximum, to less than 3.5 μrad, while preserving 75% of the incident intensity.
Investigation on Ag/Pb(Zr0.53Ti0.47)O3/YBa2Cu3O7−δ three-terminal system with small gate area
Authors: Liu B. T. , Hao Z. , Chen Y. F. , Xu B. , Chen H. , Wu F. , Zhao B. R. , Kislinskii Yu. , Stepantsov E.
Published: July 2002

The three-terminal devices Ag/Pb(ZrxTi1−x)O3/YBa2Cu3O7−δ(Ag/PZT/YBCO) have been fabricated onto (100) SrTiO3 by pulsed laser deposition technique and photolithography. For the purpose of application, we specially selected the PZT layer with morphotropic phase boundary composition as the gate to lower the coercive fields and decrease the operating voltage. We tried to minimize the electrode area to 6×10−6 cm2 for deeply investigating the leakage problem and getting sufficient polarization of the PZT gate, also for the high integration in future application. From the process, we obtained the following results at 64 K: the saturation polarization and the remanent polarization reach 60 and 41 μC/cm2, respectively. The coercive field is lower than 37 kV/cm, and the breakdown field is ⩾3×105 V/cm. The electric field effect measurement shows that the maximum modulation channel resistance ΔRDS/RDS is 3% under the gate voltage of ±9 V at 64 K (lower than the zero resistance temperature TC0, 70 K), at which the superconducting and normal state transition is driven by channel current IDS(IDS>Ic, Ic=15 mA).
Effect of poling procedure on the properties of lead zirconate titanate/vinylidene fluoride-trifluoroethylene composites
Authors: Chan H. L. W. , Ng P. K. L. , Choy C. L.
Published: July 2002

Lead zirconate titanate/vinylidene fluoride-trifluoroethylene [PZT/P(VDF-TrFE)] 0–3 composites for pyroelectric sensor and piezoelectric transducer applications have been fabricated by incorporating PZT powder into a P(VDF-TrFE) copolymer matrix. The properties of these composites can be tailored to suit designated applications by varying the ceramic volume fraction and by using different poling procedures. As both phases in the composite are ferroelectric, and the piezoelectric coefficients of the ceramic and copolymer phases have opposite signs while the pyroelectric coefficients have like signs, special ways can be used to produce three groups of samples with (1) only the ceramic phase poled, (2) two phases poled in the same direction to achieve reinforced pyroelectric activity and reduced piezoelectric activity, and (3) two phases poled in opposite directions to obtain reinforced piezoelectric activity and reduced pyroelectric activity. In this work, original experimental results on the properties of PZT/P(VDF-TrFE) composites poled under different conditions are presented and possible reasons behind the reinforcement and cancellation of piezoelectric and pyroelectric properties are discussed.
A role of illumination during etching to porous silicon oxidation
Authors: Salonen J. , Lehto V-P. , Björkqvist M. , Laine E.
Published: July 2002

The oxidation behavior of porous silicon (PS) has been found to be related to illumination during etching. The autocatalytic oxidation behavior at room temperature arises from the unrelaxed surface induced by the preparation under illumination and can be removed using thermal treatment in a nitrogen atmosphere. The effect is absent in the case of degenerate PS and smaller in p type than in n-type PS. The correlation between the oxidation behavior and the microstructural dimensions is also discussed.
Optical properties of three-dimensional photonic crystals based on III–V semiconductors at infrared to near-infrared wavelengths
Authors: Noda Susumu , Yamamoto Noritsugu , Kobayashi Hideaki , Okano Makoto , Tomoda Katsuhiro
Published: July 2002

The optical properties of three-dimensional photonic crystals based on III–V semiconductors are investigated. The crystals are constructed by stacking GaAs (or InP) stripes with a wafer-fusion technique to form an asymmetric face-centered-cubic structure. It is shown that a crystal with eight-stacked layers (two units), whose period is 4 μm, has a considerable band-gap effect (∼30 dB attenuation) in the transmission spectrum at infrared wavelengths (5–10 μm), and the band gap is observed independently of the incident angles. Then, a crystal with four-stacked layers with a submicron period is constructed, and a clear band gap (attenuation up to 10 dB) is successfully observed at near-infrared wavelengths (1–1.5 μm).
Electroreflectance bias-wavelength mapping of the modulation Si δ-doped pseudomorphic GaAs/InGaAs/AlGaAs structure
Authors: Tomaszewicz T. , Babiński A. , Suska D. , Baranowski J. M. , Tomaszewicz A.
Published: July 2002

The electroreflectance bias-wavelength mapping is proposed as a tool for characterization of low-dimensional structures. The results of room-temperature measurements on modulation Si δ-doped pseudomorphic GaAs/InGaAs/AlGaAs heterostructure with high mobility two-dimensional electron gas are presented. Franz–Keldysh oscillations (FKO) in GaAs layer are analyzed using fast Fourier transform (FFT) mapping in order to find an electric field in the GaAs layer. Two frequencies of FKO are identified in the FFT spectra, which are attributed to transitions involving heavy and light holes. Two transitions within the InGaAs quantum well are found at zero bias and an additional transition becomes apparent in reversely biased structure. Spectral features due to spin-orbit split holes in GaAs, back AlGaAs barrier, and AlGaAs/GaAs superlattice are also identified.
Observation of metal–oxide–semiconductor transistor operation using scanning capacitance microscopy
Authors: Nakakura C. Y. , Hetherington D. L. , Shaneyfelt M. R. , Shea P. J. , Erickson A. N.
Published: July 2002

We report scanning capacitance microscopy (SCM) images of a working p-channel metal–oxide–semiconductor field-effect transistor (P-MOSFET) during device operation. Independent bias voltages were applied to the source/gate/drain/well regions of the MOSFET during SCM imaging, and the effect of these voltages on the SCM images is discussed.
Selectivities among capillary bonds in mesoscale self-assembly
Authors: Wu Hongkai , Bowden Ned , Whitesides George M.
Published: July 2002

This letter describes the capillarity-driven self-assembly of mm-sized plates of poly(dimethylsiloxane) at the perfluorodecalin/H2O interface into complex arrays. The shape of the interacting menisci could be tailored by three strategies: (1) changing the shape of uniformly hydrophobic edges; (2) patterning the distribution of vertical hydrophobic strips on the edges and, in some cases, varying the density of the blocks; and (3) patterning the hydrophobic areas on a face to be chiral.
Integration and electrical properties of diffusion barrier for high density ferroelectric memory
Authors: Song Yoon J. , Kim H. H. , Lee Sung Y. , Jung D. J. , Koo B. J. , Lee J. K. , Park Y. S. , Cho H. J. , Park S. O. , Kim Kinam
Published: July 2002

A reliable Ir diffusion barrier was prepared on polysilicon plugged substrate with a contact size of 0.6 μm. Using a Ti adhesion layer and stress-relief process, it was possible to integrate the Ir barrier into a high density 4 Mb ferroelectric random access memory device. After heat treating sol-gel derived Pb(Zr1−xTix)O3 (PZT) films at 700 °C, the Ir barrier contact displayed an ohmic behavior and showed a low resistance of 130 Ω per contact in 1k serial contact array. The PZT films on Pt/IrO2/Ir poly-plugged substrate exhibited excellent ferroelectric properties such as remnant polarization and coercive voltage of 25 μC/cm2 and 1.15 V, respectively. Auger depth profile and transmission electron microscopy analyses confirmed that no appreciable oxidation was formed between the Ir barrier and the polysilicon plug.
Control of the band-gap shift in quantum-well intermixing using a germanium interlayer
Authors: Teng J. H. , Chua S. J. , Li G. , Helmy A. Saher , Marsh J. H.
Published: July 2002

A simple technique for controlling the shift in band gap in AlGaAs/GaAs and InGaAs/GaAs quantum-well (QW) structures is reported. It involves the evaporation of a thin Ge layer and then covering it with spin-on silica followed by rapid thermal annealing. The quantum-well intermixing was suppressed in the presence of this Ge layer between the sample surface and the spin-on silica. The interdiffusion rate was reduced by more than one order of magnitude compared to that without the Ge interlayer. The blueshift of the band gap can be controlled by varying the thickness of the Ge interlayer. A differential band-gap shift of more than 100 meV can be achieved with a 500 Å Ge interlayer for both the AlGaAs/GaAs and InGaAs/GaAs QW structures. The optical quality of the material was not deteriorated by the Ge cover compared to the SiO2 cover as seen from the photoluminescence intensity and spectral linewidth. Using an appropriate mask, this technique has the potential to tune the band gap in selected areas across a single wafer.
Charged defects in highly emissive organic wide-band-gap semiconductors
Authors: List E. J. W. , Kim C. H. , Shinar J. , Pogantsch A. , Leising G. , Graupner W.
Published: July 2002

A combined photoluminescence (PL) -detected magnetic-resonance (PLDMR) and thermally stimulated current (TSC) study of defects in wide-band-gap para-phenylene-type semiconductors is described. As TSC probes the density of mobile charge carriers after detrapping and PLDMR reveals the influence of trapped charges on the PL, their combination yields the concentration of traps, their energetic position, and their contribution to PL quenching. The reported trap densities, which are 2×1016 for the polymer and 1×1014 cm−3, for the oligomer, are the lowest reported for para-phenylene-type materials.
Structure and magnetic properties of nanocrystalline (Fe1−xCox)90Zr7B2Cu1 (0⩽x⩽0.6)
Authors: Kemény T. , Kaptás D. , Kiss L. F. , Balogh J. , Bujdosó L. , Gubicza J. , Ungár T. , Vincze I.
Published: July 2002

Nanocrystalline (Fe1−xCox)90Zr7B2Cu1 (0⩽x⩽0.6) alloys were investigated by x-ray diffraction, Fe57 Mössbauer spectroscopy, and magnetic measurements. The grain size did not change significantly with composition. Co was preferentially partitioned to the residual amorphous phase, and the bcc grains were accordingly enriched by Fe. The room-temperature coercive field increased with the Co addition, which is attributed to the increasing magnetostriction constant.
Second harmonic and ponderomotive forces acting on electrons in an inhomogeneous radio frequency field of an inductive discharge
Authors: Piejak R. B. , Godyak V. A.
Published: July 2002

The nonlinear second harmonic and ponderomotive forces acting on electrons in an inhomogeneous rf field have been derived from the electron equation of motion accounting for the energy dependence of electron–atom collisions. It is shown that in a collisionless plasma (ω≫ν) the second harmonic force F2ω and the ponderomotive Fdc force are similar in magnitude and frequency dependence (ω−2), where ω is the driving frequency and ν is the electron collision frequency. In a collisionally dominated plasma (ω<ν) both forces are diminished and have a different frequency dependence: F2ω∝(ων)−1 and Fdc∝ν−2. Therefore, in a collisional plasma, the second harmonic force is always greater than the ponderomotive force.
Magnetoresistive tunnel junctions deposited on laterally modulated substrates
Authors: Montaigne F. , Gogol P. , Briatico J. , Maurice J. L. , Nguyen Van Dau F. , Petroff F. , Fert A. , Schuhl A.
Published: July 2002

Co/Al 2 O 3 /NiFe tunnel junctions were deposited on misoriented silicon substrates. A thermal treatment activates a step bunching mechanism on the silicon surface leading to a modulated topology with a nanometric lateral period. The bottom magnetic electrode and the barrier follow this topology. Such junctions present good magnetotransport characteristics with a magnetoresistance about 14% at room temperature. Due to the uniaxial anisotropy induced by the topological modulation, the antiparallel configuration of the magnetization is well defined leading to perfect square magnetoresistance cycles at all temperatures. The magnetic behavior of patterned junctions has been investigated by transport measurements and Kerr microscopy. More than inducing a strong uniaxial anisotropy, the modulated topology is shown to strongly influence the switching mechanism of the magnetization.
Imaging of a silicon pn junction under applied bias with scanning capacitance microscopy and Kelvin probe force microscopy
Authors: Buh G. H. , Chung H. J. , Kim C. K. , Yi J. H. , Yoon I. T. , Kuk Y.
Published: July 2002

Scanning capacitance microscopy (SCM) and Kelvin probe force microscopy (KPFM) are used to image the electrical structure of a silicon pn junction under applied bias. With SCM, the carrier density inside a diode is imaged directly. With KPFM, the surface potential distribution of an operating diode is measured, revealing different behavior from that in bulk. The surface potential drop is extended deep into the lightly p-doped region at reverse bias, reflecting the existence of the surface space-charge region as confirmed by the numerical simulation.
Uniaxial anisotropy and switching behavior in epitaxial CrO2 films
Authors: Yang F. Y. , Chien C. L. , Ferrari E. F. , Li X. W. , Xiao Gang , Gupta A.
Published: July 2002

Epitaxial a-axis oriented CrO2 films with a strong in-plane uniaxial anisotropy exhibit easy-axis switching at small fields and coherent rotation of magnetization at larger fields. Unique angular dependence of |cos φ| and |sec φ| have been observed for remanence and switching field, respectively.
Metal–insulator–semiconductor tunneling microscope: two-dimensional dopant profiling of semiconductors with conducting atomic-force microscopy
Authors: Richter S. , Geva M. , Garno J. P. , Kleiman R. N.
Published: July 2002

A method for two-dimensional carrier profiling is presented, based on tunneling from a conducting atomic-force microscope (AFM) probe tip to a semiconductor sample. Current–voltage data are taken during the AFM scan on a cross-sectioned sample consisting of epitaxial InP multilayers. The results show a clear dependence of the current–voltage characteristics on the carrier concentration and different behavior for n-and p-type InP. Modeling of the data enables one to use this method as a quantitative tool for high-resolution two-dimensional dopant profiling.
Numerical simulation of hot electron interference in a solid state biprism: Conditions for interference observation
Authors: Machida Nobuya , Furuya Kazuhito
Published: July 2002

This article describes elucidations of conditions for electron interference observation, device designs, and numerical simulations for the solid-state biprism. The solid-state biprism is solid-state version of the already realized vacuum biprism, and is also proposed as a test ground for electron interference observation and a new conceptual device. Towards the realization of this device, the designed semiconductor device structures show that interference pattern with a pitch of 86 nm and a visibility of 0.6 can be realized with an electron energy of 20 meV, a transverse energy spread of 0.3 meV, and an operation temperature of 4 K.
Numerical study on the formation of cellular premixed flames at high Lewis numbers
Authors: Kadowaki Satoshi
Published: July 2002

Intrinsic instability and cell formation of premixed flames at high Lewis numbers (Le=1.0–3.0) are studied by two-dimensional, unsteady calculations of reactive flows. The relation between the growth rate and the wave number, i.e., the dispersion relation, is obtained to study intrinsic instability due to hydrodynamic and diffusive-thermal effects. The growth rate is positive at small wave numbers, and the marginal wave number separating stable and unstable ranges is found. The growth rate decreases and the unstable range narrows as the Lewis number becomes higher, since the diffusive-thermal effect has a stabilizing influence at Lewis numbers higher than unity. Positive growth rates caused by the hydrodynamic effect form a cellular flame. To study the formation of cellular flames, the disturbance with the linearly most unstable wave number is superimposed on a plane flame. The superimposed disturbance evolves, and eventually a cellular flame front is formed. The higher the Lewis number, the greater the cell size and cell depth. In addition, a stationary cellular flame is obtained when the inlet velocity of the unburned gas is set to the flame velocity, since cells on flame do not move laterally.
On the correspondence between forced magnetic reconnection and Alfvén resonances
Authors: Vekstein G.
Published: July 2002

This note aims to clarify the correspondence between forced magnetic reconnection and Alfvén resonances in a plasma with a sheared magnetic field subjected to continuous external driving. It is shown how a transition from one regime to another occurs, and what implications this has on the magnetic energy dissipation rate.
Dynamics of the vibrational predissociation of HCl dimer
Authors: Ni Hong , Serafin Joseph M. , Valentini James J.
Published: July 2002

A comprehensive study of the vibrational predissociation dynamics of the HCl dimer is reported. The predissociation lifetimes for three H–Cl stretch vibrationally excited states of (H35Cl)2 have been measured. Companion measurements for the H35Cl•H37Cl complex have also been made. These lifetimes range from 16(2) to 46(5) ns, lifetimes that are more than 106 times longer than the H–Cl stretch vibrational period. The correlated HCl(v′=0,j′)+HCl(v″=0,j″) fragment rotational state distributions have also been determined. These show a predominant dynamical bias that favors the production of j′,j″ pairs that maximize the rotational energy of the fragments and minimize their translational energy. The j′,j″ distribution is well described by a simple energy gap model of the dissociation. The results suggest a complex, for which there are substantial excursions from the equilibrium geometry, dissociation from a wide range of geometries, weak coupling of the H–Cl stretch vibrations to the dissociation coordinate, and a blurring of the distinction between hydrogen bonded and free HCl moieties. These results are consistent with theoretical studies of the HCl dimer potential energy surface.
Ultimate gate oxide thinness set by recombination-tunneling of electrons via Si–SiO2 interface traps
Authors: Kar S.
Published: July 2002

As the ever-decreasing gate oxide thickness approaches the threshold for direct tunneling of electrons across the gate oxide, i.e., about 3 nm, a defect-generation mechanism, which is not present in thicker gate oxides, becomes inevitable. The source of this mechanism is the recombination of channel electrons into the interface traps and their subsequent tunneling through the gate oxide to the gate metal. This carrier transport process generates additional interface traps, and the resultant regenerative feedback cycle culminates in a soft breakdown of the gate oxide, fatally compromising its reliability, and setting the ultimate gate oxide thinness to a value in the neighborhood of 3 nm.
In situ photodetection in strong radiation fields: Simultaneous irradiation of Si by photons and high-energy protons
Authors: Amekura H. , Kishimoto N. , Kono K.
Published: July 2002

Photoconductivity (PC) of crystalline Si induced by ∼1 eV photon irradiation has been studied under simultaneous 17 MeV proton irradiation. The PC during simultaneous irradiation is suppressed to 20%–50% of the value without the proton irradiation. The PC-suppression rate depends on the photon energy, the proton flux, and the defect concentration. These dependences are explained with a saturated variation of conductivity increment Δσ during the proton irradiation. The saturation is mainly ascribed to bimolecular-type recombination of excess carriers under high-density excitation. The understanding of the PC-suppression process contributes to the development of photodetectors for use in strong radiation fields. Guidelines to limit the effect of the PC suppression are also discussed.