bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical switching in a superconductor–semiconductor–superconductor Josephson junction
Authors: Bastian G. , Göbel E. O. , Schmitz J. , Walther M. , Wagner J.
Published: July 2002

We have fabricated Josephson junctions with a two-dimensional electron gas based on InAs/AlSb/GaSb as the barrier. The behavior of the junction during and after illumination with different wavelengths was studied. Due to a persistent positive and negative photoeffect, depending on the excitation wavelength, the carrier density and hence the critical current as well as the normal resistance could be switched between two different stable states.
Photoluminescence and photoluminescence excitation spectroscopy of Er-doped Si prepared by laser ablation
Authors: Ng Wai Lek , Temple M. P. , Childs P. A. , Wellhofer F. , Homewood K. P.
Published: July 2002

Strong room-temperature photoluminescence (PL) peaks of Er3+ (4I13/2→4I15/2) ions at ∼1.535 μm are obtained from Er-doped thin-film Si layers prepared by laser ablation. The Si sample was found to produce optimum photoluminescence peaks at an annealing temperature of about 450 °C. Experimental results also shows that the thermal quenching of the luminescence intensity from 80 K to room temperature is a factor of 2.5 only. PL excitation measurements reveal that the Er luminescence is significantly excited via the silicon band edge. The lifetime of the luminescence from the Si:Er samples is 90±10 μs.
Role of low-energy electrons in Ar emission from low-pressure radio frequency discharge plasma
Authors: Moshkalyov S. A. , Steen P. G. , Gomez S. , Graham W. G.
Published: July 2002

Optical emission spectra from a low-pressure Ar plasma were studied with high spatial resolution. It has been shown that the intensity ratios of Ar lines excited through metastable levels to those excited directly from the ground state are sensitive to the shape of electron energy distribution function. From these measurements, important information on the spatial variation of plasma parameters can be obtained.
Stability of proximity gettering of platinum in silicon implanted with alpha particles at low doses
Authors: Schmidt D. C. , Svensson B. G. , Barbot J. F. , Blanchard C.
Published: July 2002

Platinum has been diffused into epitaxial n-type silicon at 700 °C from 10 to 50 min in steps of 10 min following implantation with 3.3 MeV alpha particles at a dose of 1×1013 cm−2. Thereafter, the samples were characterized using deep level transient spectroscopy (DLTS). All samples show only one deep level at 0.23 eV below the conduction band that is attributed to substitutional platinum. DLTS profiling reveals a decoration of the region of maximal damage by the platinum for diffusion times of 30 min or shorter with a platinum concentration peak in the region of the maximal vacancy concentration. However, for longer diffusion times, the peak of the platinum concentration decreases. An explanation is proposed where silicon self-interstitial clusters behind the projected range dissociate, and where the liberated self-interstitials will drive the platinum away from the region of maximal damage. In order to achieve an equilibrium distribution, the platinum then diffuses further into the bulk.
Adjustment of the critical current in a Nb–InxGa1−xAs/InP Josephson contact by light exposure
Authors: Schäpers Th. , Müller R. P. , Kaluza A. , Hardtdegen H. , Lüth H.
Published: July 2002

The critical current of a Nb–InGaAs/InP Josephson junction is increased stepwise by light exposure. Shubnikov–de Haas effect measurements under illumination show that the increase of the critical current originates from photogenerated electrons in the quantum well. A further enhancement of the critical current is gained under continuous illumination.
Improvement of amorphous-carbon active-layer thin-film light-emitting diodes using room-temperature ultrasound treatment
Authors: Cho Woo Yeong , Lim Koeng Su , Ostapenko S.
Published: July 2002

Ultrasound treatment (UST) applied at room temperature enhances electroluminescent intensity (maximum at 600 nm) and optical output in thin-film light-emitting diodes with hydrogenated amorphous-carbon as an active layer. This positive UST effect is attributed to a reduction of the diode series resistance caused by a change of the interface and contact resistances. The UST effect is saturated with increase of the ultrasound amplitude.
Step decoration during deposition of Co on Ag(001) by ultralow energy ion beams
Authors: Dekoster J. , Degroote B. , Pattyn H. , Langouche G. , Vantomme A. , Degroote S.
Published: July 2002

A possibility for decorating atomic steps on single-crystal surfaces by using ultralow energy ion beams is reported. Isotopically pure ion beams are produced by a mass separator and subsequently decelerated by an electrostatic lens. The lens was designed to allow sweeping of the ion beam in order to obtain a uniform deposition over a large area. The preferred sites of single Co atoms on Ag are investigated with in situ scanning tunneling microscopy measurements. A clear indication is found that by increasing the energy of the deposited Co to several electron volts, an enhanced Co decoration of the Ag steps is induced. This technology opens perspectives for an increasing number of elements which can form self-organized nanostructures such as atomic wires on vicinal crystal surfaces.
Atomic force microscopy phase imaging of conductive polymer blends with ultralow percolation threshold
Authors: Planès Jérôme , Samson Yves , Cheguettine Yasmina
Published: July 2002

Tapping-mode atomic force microscopy is used to image the conducting network of polyaniline inside organic blends. The greater stiffness of the conducting polymer phase with respect to the matrix leads to good resolution phase contrast imaging. Cross-section images provide a unique insight in the distribution of the conductive phase within the matrix.
Self-aligned current confinement structure using AlAs/InP tunnel junction in GaInAsP/InP semiconductor lasers
Authors: Sekiguchi Shigeaki , Miyamoto Tomoyuki , Kimura Tadayoshi , Koyama Fumio , Iga Kenichi
Published: July 2002

We propose a current confinement structure which can be self-formed by thermal annealing of a electrode metal with a self-aligning process. The migrated metal selectively destroys an AlAs/InP tunnel junction to form a high resistance isolation layer. The hole current can be injected through a preserved tunnel junction window. We confirmed its lateral confinement effect from the near-field pattern of fabricated GaInAsP/InP stripe lasers. The proposed current confinement structure is very simple and useful for the lateral injection in semiconductor optical devices including long-wavelength vertical-cavity surface-emitting lasers.
High-performance resin-bonded magnets produced from zinc metal-coated Sm2(Fe0.9Co0.1)17Nx fine powders
Authors: Noguchi K. , Machida K. , Yamamoto K. , Nishimura M. , Adachi G.
Published: July 2002

Fine powders of Sm2(Fe0.9Co0.1)17Nx (x=∼3) with particle sizes (d) around 1 μm as coated with zinc metal produced via the photodecomposition of diethylzinc [Zn(C2H5)2], which still provided high remanence (Br) and coercivity (Hcj) values of ∼1.43 T and ∼0.85 MAm−1, were molded to compression-type resin bonded Zn/Sm2(Fe0.9Co0.1)17Nx magnets with density values of ∼6.33 g cm−3. By optimizing the preparation conditions such as grinding, surface coating, and molding for them, the highest maximum energy product of (BH)max=186 kJm−3 for Hcj=0.73 MAm−1 was recorded among all kinds of the Sm–Fe–N based magnets reported to date. Furthermore, the excellent aging behavior of the bonded Zn/Sm2(Fe0.9Co0.1)17Nx magnets was observed after standing in air at ∼393 K and the thermal coefficient for permanent magnet was evaluated to be α(Br)=−0.04% K−1.
Thermal stability and doping efficiency of intrinsic modulation doping in InP-based structures
Authors: Buyanova I. A. , Chen W. M. , Bi W. G. , Zeng Y. P. , Tu C. W.
Published: July 2002

Doping efficiency and thermal stability of intrinsic modulation doping in InP/InGaAs heterostructures, where intrinsic defects (PIn antisites) are used as an electron source, are investigated. A high efficiency of the intrinsic doping is demonstrated from a comparison between the intrinsically doped and conventional extrinsically doped structures. The thermal stability of the intrinsically doped heterostructures is shown to be largely affected by the thermal stability of the InP surface.
Magnetic-field-modulated microwave reflectivity of high- Tc superconductors studied by near-field mm-wave microscopy
Authors: Lann A. F. , Abu-Teir M. , Golosovsky M. , Davidov D. , Goldgirsch A. , Beilin V.
Published: July 2002

We report local studies of magnetic-field-modulated microwave reflectivity (MFMMR) of high-Tc superconductors using a near-field scanning aperture probe operating at 96 GHz. The MFMMR signal appears as a sharp peak at transition temperature and is very useful in identifying superconducting phases in multiphase samples. We show that MFMMR is qualitatively different from such a routine characterization tool as inductive technique. Simultaneous MFMMR and inductive measurements allow us to distinguish between the surface and bulk superconducting properties. The MFMMR technique may be easily extended for the study of giant magnetoresistance materials.
A continuous-wave tunable solid-state blue laser based on intracavity sum-frequency mixing and pump-wavelength tuning
Authors: Wang C. Q. , Chow Y. T. , Gambling W. A. , Yuan D. R. , Xu D. , Zhang G. H. , Jiang M. H.
Published: July 2002

We report on continuous-wave tunable blue-light generation from a Nd:Y3Al15O12 laser by intracavity sum-frequency mixing of its fundamental laser line at 946 nm with the pump light from a tunable Ti:sapphire laser by use of cadmium–mercury–thiocyanate nonlinear crystal. The tunable range of the blue light was 434.4–437.5 nm, and the maximum output power at 436 nm was measured to be 310 μW.
Metal/fluorinated-dielectric interactions in microelectronic interconnections: Rapid diffusion of fluorine through aluminum
Authors: Kim S. E. , Steinbrüchel Ch.
Published: July 2002

Rather surprising behavior has been observed when aluminum (Al) is in contact with fluorine-doped silicon dioxide (FSG). With Al deposited onto FSG, x-ray photoelectron spectroscopy shows that there is only a very minor reaction at the interface, producing a small amount of AlF3. No fluorine is observed in the bulk of the Al film, but fluorine diffuses readily through the Al even at room temperature and reacts at the free metal surface. On the other hand, with FSG deposited onto Al, the native aluminum oxide provides quite good protection against fluorine diffusion. By contrast, when pure Cu is in contact with FSG, there is almost no interaction or fluorine diffusion. Various approaches to reducing fluorine diffusion into a metal are also discussed, including using a diffusion barrier (TiN, Ta, TaN) or a suitable plasma treatment of the FSG before metal deposition.
Interpretation of electrical and galvanomagnetic properties of diamond monocrystals
Authors: Somogyi K.
Published: July 2002

An exponential type description of the temperature dependence of hole mobility and the experimentally observed mobility maxima reveal that activation energies obtained from the temperature dependence of the resistivity and that of the hole concentration differ from each other in a range from 0.03 to 0.08 eV for diamond monocrystals. This difference is too high to be simply neglected. On the other hand, the existence of a mobility maximum and of a steep high temperature slope on the temperature dependence of mobility is explained here solely by the dominance of the ionized impurity scattering.
Implantation-induced amorphization of InP characterized with perturbed angular correlation
Authors: Bezakova E. , Byrne A. P. , Glover C. J. , Ridgway M. C. , Vianden R.
Published: July 2002

The perturbed angular correlation (PAC) technique has been used to characterize the implantation-induced crystalline-to-amorphous transformation in InP. Radioactive In111 probes were first introduced in InP substrates which were then irradiated with Ge ions over an ion-dose range extending 2 orders of magnitude beyond that required for amorphization. Crystalline, disordered and amorphous probe environments were subsequently identified with PAC. The dose dependence of the relative fractions of the individual probe environments were determined, a direct amorphization process consistent with the overlap model was quantified and evidence for a second amorphization process via the overlap of disordered regions was observed. Given the ability to differentiate disordered and amorphous probe environments, a greater effective resolution was achieved with the PAC technique compared with other common analytical methodologies.
Coherence based contrast enhancement in x-ray radiography with a photoelectron microscope
Authors: Hwu Y. , Lai B. , Mancini D. C. , Je J. H. , Noh D. Y. , Bertolo M. , Tromba G. , Margaritondo G.
Published: July 2002

We show that a photoelectron spectromicroscope of the photoelectron emission microscope type can be used as an x-ray imaging detector for radiology. Using high penetration hard-x-ray photons (wavelength <0.1 nm), samples as thick as a few millimeters can be imaged with submicron resolution. The high imaging resolution enables us to substantially decrease the object-detector distance needed to observe coherent based contrast enhancement with respect to the standard film-based detection technique. Our result implies several advantages, the most important being a marked reduction of the required source emittance for contrast enhanced radiology.
Room-temperature lasing oscillation in an InGaN self-assembled quantum dot laser
Authors: Tachibana Koichi , Someya Takao , Arakawa Yasuhiko , Werner Ralph , Forchel Alfred
Published: July 2002

We have demonstrated laser action of an InGaN self-assembled quantum dot (QD) laser by optical pumping. We have grown the laser structure with the In0.2Ga0.8N QDs embedded in the active layer, using atmospheric-pressure metalorganic chemical vapor deposition. A clear threshold was observed in the relation between the excitation and emission intensity at room temperature. Above the threshold, the width of the emission peak was below 0.1 nm (resolution limit), and the emission was strongly polarized in the transverse electric mode. These results indicate that lasing oscillation in the InGaN self-assembled QD laser has been achieved at room temperature.
All-solid-state 12 ps actively passively mode-locked pulsed Nd:YAG laser using a nonlinear mirror
Authors: Mani A. A. , Hollander Ph. , Thiry P. A. , Peremans A.
Published: July 2002

Efficient mode locking of a flash-lamp-pumped Nd:YAG laser at 1.064 μm is achieved by combining the passive–positive feedback of a frequency doubling nonlinear mirror (FDNLM) and the passive–negative feedback of a GaAs platelet. the FDNLM consists of a BBO crystal and of a dichroïc mirror. Pulse durations as short as 12 ps are obtained. Temporal evolution of pulse duration in the pulse train is presented and discussed.
Noninvasive simultaneous determination of conductivity and permeability
Authors: Schnyders H. S. , Saboungi Marie-Louise , Enderby J. E.
Published: July 2002

Simultaneous measurements of both the conductivity and permeability are presented using noninvasive methods based on inductive coupling. Explicit expressions for cylindrical and spherical geometries are derived. The technique, especially relevant to liquids and solids in extreme environments, will also be valuable for nanomaterials and other systems where external contacts are difficult to establish.
Current transients in almost-ideal Czochralski silicon p–n junction diodes
Authors: Poyai A. , Simoen E. , Claeys C.
Published: July 2002

The nature of the reverse current transients in large-area nearly ideal p–n junction diodes fabricated on Czochralski silicon substrates is investigated. It is shown that they can be generated by an electrical or optical excitation pulse. A typical nonexponential behavior with time is observed. The best fit is found for a power-law function. The impact of the reverse bias and the temperature on the prefactor and on the exponent will be presented. From the observations, it is concluded that the capture of electrons is a necessary step for the generation of the transients. A discussion of the possible nature of the underlying defects is given, and the implications for practical current–voltage characterization will be discussed.
Effect of initial surface reconstruction on the GaS/GaAs(001) interface
Authors: Pelzel R. I. , Nosho B. Z. , Shoenfeld W. V. , Lundstrom T. , Petroff P. M. , Weinberg W. H.
Published: July 2002

We have used photoluminescence of a GaAs/Al0.3Ga0.7As near-surface quantum well structure to study the quality of the interface between GaAs and GaS deposited in ultrahigh vacuum (UHV) using [(tBu)GaS]4. In addition to the luminescence of the near-surface and the deep/reference quantum wells, luminescence was observed for the GaAs cap following the deposition of 100 Å of GaS. This additional feature demonstrates the high quality GaS/GaAs interface achievable through the UHV deposition of this precursor. The ratios of the integrated luminescence intensity of both the GaAs cap and the near-surface GaAs quantum well to the deep/reference quantum well indicate that there are fewer GaS/GaAs interface states for deposition on the Ga-rich GaAs(001)-(4×2)/(2×6) surface compared to deposition on the As-rich GaAs(001)-(2×4) surface. Furthermore, GaS passivated samples exposed to ambient conditions for eight months exhibit no luminescence degradation for the near-surface quantum well confirming that these films provide adequate passivation longevity.
Two-color picosecond experiments on anti-Stokes photoluminescence in GaAs/AlGaAs asymmetric double quantum wells
Authors: Hohng S. C. , Kim D. S.
Published: July 2002

Two-color photoluminescence experiments are performed on the anti-Stokes photoluminescence in GaAs/AlGaAs asymmetric double quantum wells. Direct evidence for forbidden absorption is shown, and its many intriguing aspects, particularly the role of long-lived defects, are revealed. Our experiments shed light on the ongoing controversies between many different models.
Wavelength-adjustable surface-emitting single-mode laser diodes with contradirectional surface-mode coupling
Authors: Kellermann P. O. , Finger N. , Schrenk W. , Gornik E. , Winterhoff R. , Schweizer H. , Scholz F.
Published: July 2002

Single-mode surface emission has been achieved from visible red GaInP/AlGaInP laser diodes by applying the contradirectional surface-mode coupling technique. The emission wavelength (679.4 nm) of the laser structures was adjusted (decreased) in steps of 0.2 nm in an interval of 1.2 nm by reducing the thickness of the waveguide on top of the laser diode. The laser diodes emitted via the surface with a beam divergence of 0.12° and showed single-mode emission both in ac as well as in dc operation with a minimum spectral linewidth of 0.09 nm. The highest side-mode suppression achieved in dc operation was 26 dB.
On-chip frequency-domain submillimeter-wave transceiver
Authors: Zamdmer N. , Hu Qing , McIntosh K. A. , Verghese S. , Förster A.
Published: July 2002

We demonstrate and model an on-chip frequency-domain transceiver which uses low-temperature-grown GaAs photoconductors to emit and detect continuous waves in the frequency range from 20 to 700 GHz propagating in a coplanar waveguide circuit. Our device has a possible frequency resolution (∼1 MHz) that is about 103 times better than similar devices used for time-domain spectroscopy, and is therefore appropriate for high-resolution spectroscopy with a “lab-on-a-chip”-type integrated circuit.
Optical signal inversion phenomenon for 1.53 μm laser in an erbium-doped lithium niobate
Authors: Maeda Yoshinobu , Nagata Hirotoshi , Nakashima Taizou , Ichikawa Junichiro , Higuma Kaoru
Published: July 2002

Modulation characteristics of a negative nonlinear absorption effect were investigated in 3 wt % erbium-doped lithium niobate using a 1530 nm laser diode. With a decreasing incident modulation degree, a reversed-phase waveform was obtained in the transmitted laser at modulation degrees smaller than 85% for a sample length of 14 mm. The reversed-phase transmitted waveforms were observed at modulation frequencies from 1 kHz to 10 GHz. The negative nonlinear absorption effect for 1.5 μm can be explained by considering an enhanced absorption model for a four-level system of the Er3+ ion.
Suppression of growth-induced perpendicular magnetic anisotropy in Co–Pt alloys by trace amounts of Si
Authors: Shapiro A. L. , Vajk O. , Hellman F. , Ring K. M. , Kavanagh K. L.
Published: July 2002

( Co x Pt 1−x ) 1−y Si y alloys with Si content from 1 to 20 at. % have been grown over a range of growth conditions. Co-deposition of even trace amounts of Si with Co–Pt alloys causes the growth-induced magnetic anisotropy and chemical clustering found in these vapor-deposited alloy films to decrease or vanish. It also causes significant reduction in grain size. Addition of 5 at. % Si eliminates anisotropy completely. Addition of 1 at. % Si produces a film with magnetic properties identical to pure Co–Pt alloys grown at lower deposition temperatures. We suggest this suppression of anisotropy and related effects are due to a decrease in surface mobility during growth in the presence of even trace amounts of Si.
Optimizing growth conditions for GaN/AlxGa1−xN multiple quantum well structures
Authors: Zeng K. C. , Li J. , Lin J. Y. , Jiang H. X.
Published: July 2002

We have investigated the optimal growth conditions for GaN/AlxGa1−xN multiple quantum well (MQW) structures by metal organic chemical vapor deposition. Optical properties of a set of GaN/AlxGa1−xN MQW samples grown under systematically varied growth conditions have been studied by employing picosecond time-resolved photoluminescence (PL) spectroscopy. The PL emission efficiency, the linewidth of the PL emission spectra, the ratio of the barrier emission intensity to the well emission intensity, and the temperature dependence of the PL decay lifetime of these GaN/AlxGa1−xN MQW structures have been measured and compared with each other carefully. Based on our studies, we concluded that the optimal growth conditions for GaN/AlxGa1−xN MQW structures are GaN-like rather than AlxGa1−xN-like or other conditions. The GaN/AlxGa1−xN MQW structures grown under the GaN-like growth conditions exhibited higher quantum efficiencies and narrower PL emission linewidths than those grown under other conditions. PL emission from barrier regions was not observed in the MQW structures grown under the GaN-like growth conditions, which is highly preferred for ultraviolet light emitter applications.
Photoenhanced wet oxidation of gallium nitride
Authors: Peng L.-H. , Liao C.-H. , Hsu Y.-C. , Jong C.-S. , Huang C.-N. , Ho J.-K. , Chiu C.-C. , Chen C.-Y.
Published: July 2002

We investigate the photo-oxidation process and the corresponding passivation effects on the optical properties of unintentionally doped n-type gallium nitride (GaN). When illuminated with a 253.7 nm mercury line source, oxidation of GaN is found to take place in aqueous phosphorus acid solutions with pH values ranging from 3 to 4. At room temperature, the photo-oxidation process is found reaction-rate limited and has a peak value of 224 nm/h at pH=3.5. Compared with the as-grown GaN layers, threefold enhancement in the photocurrent and photoluminescence response are observed on the oxidized GaN surfaces. These results are attributed to the surface passivation effects due to the deep ultraviolet-enhanced wet oxidation on GaN.
Microscopic magnetization reversal in perpendicular anisotropy CoCr thin films
Authors: Wastlbauer Gottfried , Skidmore George D. , Merton Chris , Schmidt Jake , Dahlberg E. Dan , Skorjanec Joseph
Published: July 2002

Magnetic force microscopy was used to observe the magnetization reversal in a CoCr thin film on a grain/subgrain scale. The combination of high resolution topographic and magnetic images were used to relate microscopic magnetization changes to the microstructure of the sample. Both uniformly and partially magnetized grains and both uniform and partial magnetization reversal were observed. Statistically, the uniform magnetic state was more prevalent. In addition, there was a visualization of the flux closure between grains.
Relaxor behavior in BaTiO3
Authors: Mahesh Kumar M. , Srinivas K. , Suryanarayana S. V.
Published: July 2002

BaTiO 3 shows relaxation effects when minute concentrations of Bi+3 and Fe+3 are added in varying molar ratios. Addition of Bi+3 at the A site reduces the transition maximum (Tm), whereas Fe+3 addition at the B site reduces the value of dielectric constant. Doping of Bi+3 and Fe+3 in equimolar ratios shows a positive shift in relaxation, while excess addition of either of the dopants produces a negative shift in the transition maximum with increasing frequency. Relaxation effects follow the Vogel–Fulcher law for spin glasses. The dielectric loss also shows relaxation effects.
High-contrast topography-free sample for near-field optical microscopy
Authors: Kalkbrenner T. , Graf M. , Durkan C. , Mlynek J. , Sandoghdar V.
Published: July 2002

The issue of topography artifacts has proven to play a very important role in interpreting images recorded in scanning near-field optical microscopy. We report on the fabrication and characterization of samples with essentially no topographic features while possessing very high optical contrast on the nanometric lateral scale. These samples open the door to routine and uncontroversial examinations of the resolution obtained in a scanning near-field optical microscope.
Coiled structure of eccentric coaxial nanocable made of amorphous boron and silicon oxide
Authors: Suenaga K. , Zhang Y. , Iijima S.
Published: July 2002

Exotic nanocable with coiled structure has been found in soot obtained by a reactive laser ablation as a byproduct of the formerly reported coaxial nanocables [Y. Zhang, K. Suenaga, C. Colliex, and S. Iijima, Science 281, 973 (1998)]. Electron energy-loss spectroscopic imaging has revealed the coaxial structure made of amorphous boron and silicon dioxide with amorphous carbon sheath. We infer that the coiled structure is attributed to a difference in the growth rate between amorphous boron and silicon dioxide that are found to comprise eccentric coaxial nanocable.
Mesoscopic electronic devices made by local oxidation of a titanium film covering gold islands
Authors: Vullers R. J. M. , Ahlskog M. , Cannaerts M. , Van Haesendonck C.
Published: July 2002

The local oxidation produced by the tip of an atomic force microscope scanning on a thin metallic film allows to define narrow oxide lines, thus providing a method to fabricate lateral tunnel junctions. In such devices, with rather thick tunnel junction barriers, the electrical transport is governed by thermally activated hopping rather than by direct electron tunneling. In this letter we show that tunneling barriers can also be produced with Ti films covering small gold islands. The gold islands significantly shorten the effective tunneling distance, allowing to observe temperature-independent electron tunneling across the lateral barriers. The mixed Ti/Au tunnel barriers reveal Coulomb blockade effects which may be used for single-electron devices consisting of a single oxide line.
Enhanced coherent terahertz emission from indium arsenide in the presence of a magnetic field
Authors: McLaughlin R. , Corchia A. , Johnston M. B. , Chen Q. , Ciesla C. M. , Arnone D. D. , Jones G. A. C. , Linfield E. H. , Davies A. G. , Pepper M.
Published: July 2002

We demonstrate enhancement of terahertz (THz) emission from indium arsenide at 170 K in magnetic fields (B) up to 8 T. An order of magnitude increase in visible to terahertz conversion efficiency was observed, with no suggestion of saturation of the TE polarization at higher magnetic fields. Free-space electro-optic sampling measurements confirmed the coherent nature of this radiation over the field range investigated, and gave an insight into the carrier motion subsequent to photoexcitation, which may be responsible for the observed THz power enhancement.
Composition effect on the growth mode, strain relaxation, and critical thickness of tensile Ga1−xInxP layers
Authors: Wallart X. , Schuler O. , Deresmes D. , Mollot F.
Published: July 2002

In this work, we compare the growth and relaxation behavior of tensile Ga0.7In0.3P/GaAs and Ga0.2In0.8P/InP layers using reflection high-energy electron diffraction, double-crystal x-ray diffraction, and atomic-force microscopy. Although the lattice mismatch is similar in both cases, we show that the relaxation process and the related critical thickness are very different and, hence, drastically dependent on the alloy composition. We interpret this result considering the predicted composition range for which alloy decomposition should occur.
Polarization-insensitive thermo-optic switch based on multimode polymeric waveguides with an ultralarge optical bandwidth
Authors: Lu Xuejun , An Dechang , Sun Lin , Zhou Qingjun , Chen Ray T.
Published: July 2002

A promising polarization-insensitive thermo-optic switch based on multimode polymeric waveguides is reported. This device has a packing density of 40 channels/cm. Simulation result shows that an extinction ratio of greater than 20 dB can be achieved with the device–electrode interaction length of 30 mm. The thermo-optic switch operating at wavelengths of 632.8 nm and 1.3 μm has been demonstrated experimentally with extinction ratios of 21 and 22 dB, respectively. Such a device has an intrinsic wide optical bandwidth due to the large dynamic range of the phase-matching condition implied by the multimode waveguides. The material employed provides us with a switching speed of 100 μs.
Modification of the hole injection barrier in organic light-emitting devices studied by ultraviolet photoelectron spectroscopy
Authors: Ding X. M. , Hung L. M. , Cheng L. F. , Deng Z. B. , Hou X. Y. , Lee C. S. , Lee S. T.
Published: July 2002

Ultraviolet photoelectron spectroscopy has been applied to the investigation of modified hole injection barriers in organic light-emitting devices (OLEDs). Different from those reported previously, the indium tin oxide (ITO) surface treated in situ by oxygen plasma possesses a work function of 5.2 eV, and the organic ITO interface thereafter formed shows a 0.5 eV smaller hole injection barrier compared to that on untreated ITO. Insertion of an ultrathin SiO2 layer between the organic and ITO results in a similar reduction of the barrier. This indicates that improved hole injection favors efficient operation of OLEDs, as manifested by enhanced efficiency by the SiO2 insertion.
Dynamics of carriers in resonantly excited quantum-well lasers studied by intersubband absorption
Authors: Shtrichman I. , Mizrahi U. , Gershoni D. , Ehrenfreund E. , Maranowski K. D. , Gossard A. C.
Published: July 2002

Using infrared picosecond pulses to probe the intersubband absorption of GaAs/AlGaAs quantum-well lasers following their optical excitation, we directly measure the dynamics of carriers in these devices. We find no evidence for excitonic gain even at cryogenic temperatures and resonant excitonic excitation.
High duty cycle and continuous terahertz emission from germanium
Authors: Bründermann Erik , Chamberlin Danielle R. , Haller Eugene E.
Published: July 2002

We measured laser emission from Be-doped Ge crystals with intercontact distances as small as 0.5 mm. An improved heat sink allowed a twofold increase of the laser duty cycle to 5%. We also report the measurements of THz emission from small Be-doped Ge crystals under continuous excitation with volumes as small as 0.5 mm3.
Organic probe for inhomogeneous band bending
Authors: Park S. , Kampen T. U. , Zahn D. R. T. , Braun W.
Published: July 2002

The initial stage of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) adsorption on Se-passivated n-type GaAs(100)-(2×1) surface was investigated using high-resolution soft x-ray photoemission spectroscopy. A very small amount of PTCDA (≪1 ML) is sufficient to induce a reduction of inhomogeneous band bending at the surface as judged from the sharpening of the core level spectra. This is interpreted in terms of preferential sticking of the organic molecules to surface defects. The results presented in this letter indicate that organic molecules may also serve as very suitable probes for inorganic semiconductor surface evaluation through the photoemission studies.
Tuning of conduction intersublevel absorption wavelengths in (In, Ga)As/GaAs quantum-dot nanostructures
Authors: Pan Dong , Towe Elias , Kennerly Steve , Kong Mei-Ying
Published: July 2002

We demonstrate that by increasing the amount of (In, Ga)As deposit in a quantum dot layer, the intersublevel absorption wavelength for (In, Ga)As/GaAs quantum-dot infrared photodetectors can be blue-shifted from 15 to 10 μm while the photoluminescence peak is red-shifted. We directly compare the measured energy spacing between intersublevels obtained from infrared absorption spectroscopy with those obtained from photoluminescence spectroscopy. We find that the intersublevel energy spacing determined from absorption measurements is much larger than that obtained from the photoluminescence measurements.
Comparison of excited nitrogen sources for molecular-beam-epitaxy GaN growth: Radio frequency and electron cyclotron resonance plasma sources
Authors: Cho Sung-Hwan , Okumura Hajime , Akimoto Katsuhiro
Published: July 2002

A comparative study of electron cyclotron resonance (ECR) and radio frequency (rf) plasma as a nitrogen source for molecular-beam epitaxy GaN was carried out. The effects of differences in the excited nitrogen species on the optical signals during GaN growth were investigated by 77 K photoluminescence (PL). For epitaxial layers grown at optimum V/III ratio using ECR and rf plasma, the PL spectra were dominated by near band-edge emission at 3.47 eV. However, when the V/III ratio was less than the optimum V/III ratio, a broad emission band at about 3.2–3.3 eV was observed in the PL spectrum for the GaN epilayer grown using rf plasma, while in the case of growth using ECR plasma, a deep level emission at about 2.2 eV appeared. These characteristics in PL spectra can used to identify differences in the chemical species in the nitrogen plasma.
Electrically assisted self-confinement and waveguiding in planar nematic liquid crystal cells
Authors: Peccianti M. , De Rossi A. , Assanto G. , De Luca A. , Umeton C. , Khoo I. C.
Published: July 2002

We report on spatial soliton formation and self/cross waveguiding in planar cells containing a nematic liquid crystal in the presence of an externally applied voltage. Self-confinement and cross-induced guidance are demonstrated with an Argon ion laser (514 nm) and a helium–neon probe (633 nm), respectively, over millimeter lengths and with milliwatt pump powers.
A quantum cascade laser fabricated using planar native-oxide layers
Authors: Farmer C. D. , Keightley P. T. , Ironside C. N. , Stanley C. R. , Wilson L. R. , Cockburn J. W.
Published: July 2002

We present work on the application of a thermal wet oxidation process to the fabrication of quantum cascade lasers. The native oxide of the Al0.48In0.52As upper cladding layer was formed and used to provide electrical and optical confinement for lasers operating at λ≈5 μm. Initial results include 1.4 W peak output power and 0.69 W/A slope efficiency at 10 K, and a reduced temperature dependence of the threshold current density (T0=142) K.
High-repetition-rate, all-solid-state, Ti:sapphire-pumped optical parametric oscillator for the mid-infrared
Authors: Phillips P. J. , Das S. , Ebrahimzadeh M.
Published: July 2002

We report a low-pump-threshold, all-solid-state subpicosecond optical parametric oscillator (OPO) for the mid-infrared based on periodically poled LiNbO3 and synchronously pumped by a mode-locked Ti:sapphire laser. Using a semimonolithic cavity design and hemispherical focusing, pump power thresholds of 17 mW and mid-infrared idler powers of 64 mW have been obtained in the 3.9–6 μm spectral range in a simple, practical, and compact configuration at pulse repetition rates of up to 322 MHz. The OPO delivers a signal output power of up to 280 mW at ∼35% extraction efficiency and can provide transform-limited signal pulses with durations of 0.4 ps over the spectral range of 1.00–1.14 μm.
Discharge efficiency in plasma displays
Authors: Oversluizen G. , Klein M. , de Zwart S. , van Heusden S. , Dekker T.
Published: July 2002

The dependence of the panel efficacy of an alternating current-surface-discharge plasma display on the input power is investigated. Test panels with a design resembling the one used in main stream commercial products are used. The input power is varied in two ways: namely by changing the dielectric layer capacitance (thickness) and by changing the sustain voltage. An interesting different behavior is found: for increasing capacitance the efficacy decreases markedly, whereas for increasing sustain voltage the efficacy increases slightly. The different behavior is attributed to changes in the ion heating losses. It is found that plasma saturation, which implies a fundamental trade-off between luminance and efficacy, is not significant at practical input power values. A high luminance and a high efficacy are concurrent for a plasma panel design with a low dielectric layer capacitance and a high sustain voltage.
Topographic effects in low-energy radiation damage
Authors: Rahman M. , Mathieson K.
Published: July 2002

We have studied the effect of low-index channeling on sidewall dry-etch damage. A quantum electron beam in the two-dimensional electron gas of a GaAs/AlGaAs heterostructure was used to probe electrical damage at a specific depth down an etched sidewall. In analyzing the measured behavior as a function of etch time we have developed a model for the sidewall damage distribution that takes into account the geometry of the 〈110〉 channels in detail. The analysis shows that more damage is possible beneath regions of high topography than is usually assumed.
Electronic structures of polycrystalline ZnO thin films probed by electron energy loss spectroscopy
Authors: Ong H. C. , Dai J. Y. , Hung K. C. , Chan Y. C. , Chang R. P. H. , Ho S. T.
Published: July 2002

The microstructure of polycrystalline ZnO thin films grown on amorphous fused quartz has been studied by transmission electron microscopy and electron energy loss spectroscopy (EELS). The optical functions of the grain and grain boundary of ZnO acquired from EELS are compared to elucidate the mechanism of the formation of self-assemble laser cavities within this material. It is found that the refractive index of the grain boundary is significantly lower than that of the grain due to the lack of excitonic resonance. This large refractive index difference between the grain and grain boundary substantiates the scenario that the formation of laser cavities is caused by the strong optical scattering facilitated in a highly disordered crystalline structure. In addition, our results also imply that the optical characteristics of ZnO have very high tolerance on defects.
Edge-pinned states in patterned submicron NiFeCo structures
Authors: Shi Jing , Tehrani S.
Published: July 2002

Magnetization reversal in patterned submicron NiFeCo structures has been studied. Application of a transverse field lowers the easy axis switching threshold of the center of the structures but the edge magnetization remains pinned along the initial direction until a higher reversal field is applied. Complete switching between the two stable magnetization states occurs only after depinning and reversal of the edge magnetization. The edge depinning field is found to be very insensitive to the transverse field strength. Micromagnetic simulations are used to characterize the magnetization reversal process.
Temperature dependence of the transition from two-dimensional to three-dimensional growth of Ge on (001)Si studied by reflection high-energy electron diffraction
Authors: Cimalla V. , Zekentes K.
Published: July 2002

Germanium islands have been grown on Si(001) by solid-source molecular-beam epitaxy at temperatures between 325 and 900 °C. The formation of metastable {105} faceted clusters and macroislands was investigated by real-time reflection high-energy electron diffraction. Up to 600 °C, the two-dimensional (2D)-three-dimensional (3D) growth transition through the formation of hut clusters appears at a temperature-independent critical thickness, while the coalescence to macroislands is thermally activated. An activation barrier was also found for the 2D–3D growth transition directly to macroislands at growth temperatures above 600 °C. The crossing of the two competing transitions at 600 °C determines the two growth regimes.
Radiative and nonradiative recombination processes in lattice-matched (Cd,Zn)O/(Mg,Zn)O multiquantum wells
Authors: Makino T. , Chia C. H. , Tuan Nguen T. , Segawa Y. , Kawasaki M. , Ohtomo A. , Tamura K. , Koinuma H.
Published: July 2002

Time-resolved photoluminescence studies have been performed on (Cd,Zn)O/(Mg,Zn)O multiquantum wells, which are almost perfectly lattice matched (0.034%), grown by laser molecular-beam epitaxy on a ScAlMgO4 substrate. Radiative recombination of excitons in the wells exhibits a significant spectral distribution of times. This distribution was interpreted in terms of localization of excitons by potential fluctuations due to alloy disorder and to well width and depth variations. The temperature dependence of the radiative lifetime of excitons was deduced from the measurement of both the photoluminescence decay time and intensity. We found that the radiative lifetime increases linearly with temperature, showing a two-dimensional feature of excitons in the quantum wells.
Structural and chemical characterization of free-standing GaN films separated from sapphire substrates by laser lift-off
Authors: Stach E. A. , Kelsch M. , Nelson E. C. , Wong W. S. , Sands T. , Cheung N. W.
Published: July 2002

Laser lift-off of GaN heteroepitaxial layers from sapphire substrates is a promising method for electronic device integration and GaN substrate creation. Of critical importance is the structural and chemical quality of the GaN layers following laser processing. In this letter, transmission electron microscopy techniques are used to characterize the modifications that occur at the resulting GaN surfaces. Structural alteration and chemical intermixing following lift-off are confined to approximately the first 50 nm. These results indicate that laser lift-off is a viable route for GaN substrate creation, as well as for electronic device integration.
Optical properties of spontaneous lateral composition modulation in AlAs/InAs short-period superlattices
Authors: Francoeur S. , Zhang Yong , Norman A. G. , Alsina F. , Mascarenhas A. , Reno J. L. , Jones E. D. , Lee S. R. , Follstaedt D. M.
Published: July 2002

The effect of lateral composition modulation, spontaneously generated during the epitaxial growth of an AlAs/InAs short-period superlattice, on the electronic band structure is investigated using phototransmission and photoluminescence spectroscopy. Compared with uniform layers of identical average composition, the presence of the composition modulation considerably reduces the band-gap energy and produces strongly polarized emission and absorption spectra. We demonstrate that the dominant polarization direction can selectively be aligned along the [1̄10] or [010] crystallographic directions. In compressively strained samples, the use of (001) InP substrates slightly miscut toward (111)A or (101) resulted in modulation directions along [110] or [100], respectively, and dominant polarization directions along a direction orthogonal to the respective composition modulation. Band-gap reductions as high as 350 and 310 meV are obtained for samples with composition modulation along [110] and [100], respectively. Ratios of polarized intensities up to 26 are observed in transmission spectra.
Semiclassical modeling of state-specific dissociation rates in diatomic gases
Authors: Macheret Sergey O. , Adamovich Igor V.
Published: July 2002

A nonempirical, containing no adjustable parameters, theoretical model is suggested for calculations of state-specific dissociation rates in diatomic gases. Effects of molecular rotation and three dimensionality of collisions are consistently accounted for. The model is based upon a modified forced harmonic oscillator (FHO) scaling, with anharmonic frequency correction and energy symmetrization. The FHO scaling allows close-coupled calculations of multiquantum transitions between vibrational states, and it requires evaluation of collisional energy transfer to classical oscillator. Three-dimensional classical energy transfer models in both free-rotation and impulsive (sudden) approximations were used in conjunction with the FHO quantum scaling. The new theory describes the role of various degrees of freedom in dissociation both qualitatively and quantitatively. One of the predictions is that at low and moderate temperatures, dissociation is strongly preferential, with state-specific rates sharply increasing with vibrational energy; however, at high temperatures, the rate dependence on vibrational energy becomes less steep, turning into a virtually nonpreferential. Calculated thermal (equilibrium) and nonequilibrium dissociation rates of oxygen and nitrogen show a very good agreement with shock-tube experimental data taken from the literature.
Refractive index dispersion functions of solid-phase polymers by multicolor optical diffraction
Authors: Ford J. V. , Sumpter B. G. , Noid D. W. , Barnes M. D. , Otaigbe J. U.
Published: July 2002

We show that fourth-order dispersion functions of solid-phase polymers can be determined by multicolor optical diffraction. Electrodynamically trapped microparticles of polyethylene glycol with different molecular weights were probed by two-dimensional optical diffraction with four different laser wavelengths (632.8, 514.5, 488.0, and 457.9 nm); subsequent Mie analysis of one-dimensional scattering patterns yielded size and refractive index (both real and imaginary parts). Using a single wavelength as a size reference, the nonlinear dependence of the refractive index of solid (nonevaporating) polymer microparticles was determined by finding the refractive index for a given wavelength that best matched a Mie calculation subject to the reference size constraint. The experimentally determined refractive index values were fit to a standard fourth-order Cauchy function to obtain values for n0, n1, and n2.
Microfabrication and characterization of an array of diode electron source using amorphous diamond thin films
Authors: Xu N. S. , She J. C. , Chen Jian , Deng S. Z. , Chen Jun
Published: July 2002

Details are given of an experimental study of microfabrication and characterization of a diode electron source using amorphous diamond (a-D) thin films. 〈100〉 n-type etched Si wafers with microscale-rough surface were used as cathode substrates. Filtered cathodic vacuum arc deposition technique was employed to coat a thin layer of a-D film on the Si substrate. Using the conventional photolithography, an array of well-defined diode structures with 20 μm gate diameter were formed. In addition, x-ray energy dispersive spectroscopy and atomic force microscopy were used to characterize the diode structure. Furthermore, the total emission current versus applied gate voltage of the diode electron source was measured. The physics of the emission process from the a-D diode was discussed.