bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarized electroabsorption spectra and light soaking of solar cells based on hydrogenated amorphous silicon
Authors: Jiang Lin , Wang Qi , Schiff E. A. , Guha S. , Yang J.
Published: July 2002

We present grazing-incidence measurements of polarized electroabsorption spectra in p–i–n solar cells based on hydrogenated amorphous silicon (a-Si:H). We find a significantly stronger polarization dependence in the present measurements compared with earlier work based on electroabsorption detected using coplanar electrodes on a-Si:H thin films. We do not find any significant dependence of the polarized electroabsorption upon light soaking, although this effect was found in previous work with coplanar electrodes.
Fiber image guide with subwavelength resolution
Authors: Ghaemi H. F. , Li Yao , Thio Tineke , Wang T.
Published: July 2002

A coherent fiber image guide comprised of individual fibers with a core diameter as small as 250 nm is reported. By using optical fibers with a very large difference between the indices of refraction of the core and cladding materials, efficient containment of light inside the core is achieved even for submicron core diameters, without the need for metallization. Images with subwavelength resolution are obtained with such an image guide.
Anomalous temperature dependence of erbium-related electroluminescence in reverse biased silicon p–n junction
Authors: Emel’yanov A. M. , Sobolev N. A. , Yakimenko A. N.
Published: July 2002

Electroluminescence (EL) and electrophysical characteristics of erbium and oxygen coimplanted and annealed p–n junctions, characterized by higher values of the Er3+-related EL intensity at ∼1.54 μm in the breakdown regime at 300 K as compared with that at 85 K, have been studied in the temperature range from 85 to 300 K. Hole traps in the Er–O codoped n layer were found to be responsible for the anomalous EL behavior. Er-related EL was observed in the same samples in avalanche breakdown at high temperatures and in tunnel breakdown at low temperatures.
Light emission from nanocrystalline Si thin-film light emitting diodes due to tunneling carrier injection
Authors: Toyama Toshihiko , Kotani Yoshihiro , Okamoto Hiroaki , Kida Hirotsugu
Published: July 2002

Electroluminescence (EL) from nanocrystalline Si (nc-Si) has been studied by using thin-film light emitting diodes with a structure of glass/SnO2/p-type nc-Si/Al. When positive bias voltages are applied on the SnO2 electrode, light emission from the nc-Si occurs with a peak energy of 1.57 eV at room temperature. When the temperatures is increased from 100–350 K, both the EL and photoluminescence (PL) peak energies shift to red. In addition, both the integrated EL and PL intensity rapidly decrease when the temperatures is increased over 200 K. Considering the similar temperature dependence found on the EL and the PL properties, the EL is attributed to the radiative recombination of electrons injected from the Al electrode and holes in the p-type nc-Si layer. From the analysis of the current–voltage characteristics, electron tunneling at the interface of nc-Si/Al appears to be the most probable mechanism for the electron injection.
InGaAsP grown by He-plasma-assisted molecular beam epitaxy for 1.55 μm high speed photodetectors
Authors: Kang Jin U. , Frankel Michael Y. , Esman Ronald D. , Thompson D. A. , Robinson B. J.
Published: July 2002

Simple photoconductive optical detectors for 1.55 μm wavelength have been fabricated on InGaAsP grown by He-plasma assisted molecular beam epitaxy. Characterization of the photodetectors shows that their speed is determined by the free carrier trapping time, with a full width at half-maximum impulse response of approximately 6 ps.
GaSb–PbSe–GaSb double heterostructure midinfrared lasers
Authors: Shi Z.
Published: July 2002

A GaSb/PbSe/GaSb double heterojunction laser structure is proposed. The advantages and feasibility of fabricating such lasers are discussed. Theoretical calculations show that the threshold gain for GaSb/PbSe lasers is much smaller than for traditional PbEuSe/PbSe lasers. Electrical confinement and heat dissipation is also significantly improved. The resulting much lower threshold currents and temperature difference between the active layer and heat sink should allow GaSb/PbSe lasers to operate in continuous wave mode above room temperature.
Liquid crystal display with wide viewing angle
Authors: Liang Bau-Jy , Chen Shu-Hsia , Wang Y. F.
Published: July 2002

A conic-cylindrical-cavities liquid crystal (conic CCLC) cell is developed for wide-viewing-angle displays. This conic-CCLC cell has been successfully manufactured and inquired. This display has a superwide viewing angle of over ±70° in both the horizontal and vertical directions under the condition of no gray-scale inversion. The enhancement of viewing angle is believed to result from the director symmetric alignment in the conic-CCLC.
On the feasibility of using ultraviolet/ozone grown oxide as an atomic interdiffusion barrier in Ge/GaAs heterojunctions
Authors: Lui K. M. , Chik K. P. , Kwok R. W. M. , Choy W. H. , Wilson I. H.
Published: July 2002

A 10 Å ultraviolet/ozone grown oxide was used as an atomic diffusion barrier in a Ge/GaAs heterostructure. Good thermal stability of the oxide layer has been demonstrated by the appearance of dendritic crystallization [K. M. Lui, K. P. Chik, and J. B. Xu, J. Appl. Phys. 81, 7757 (1997)], induced by in situ thermal pulse annealing, of the Ge overlayer. In this work, an abrupt heterointerface was revealed by aligned Rutherford backscattering spectroscopy after annealing and compared with a control with no barrier at the interface where considerable diffusion had taken place. Current–voltage measurement indicated good rectifying properties of the oxide barrier heterojunction.
Ballistic-electron-emission microscopy and spectroscopy of metal/GaN interfaces
Authors: Bell L. D. , Smith R. P. , McDermott B. T. , Gertner E. R. , Pittman R. , Pierson R. L. , Sullivan G. J.
Published: July 2002

Ballistic-electron-emission microscopy (BEEM) spectroscopy and imaging have been applied to the Au/GaN interface. In contrast to previous BEEM measurements, spectra yield a Schottky barrier height of 1.04 eV that agrees well with the highest values measured by conventional methods. A second threshold is observed in the spectra at about 0.2 V above the first threshold. Imaging of the Au/GaN interface reveals transmission in nearly all areas, although the magnitude is small and varies by an order of magnitude. BEEM of other GaN material shows no transmission in any areas.
Effect of external electric field on the growth of nanotubules
Authors: Srivastava Anchal , Srivastava A. K. , Srivastava O. N.
Published: July 2002

In the present investigation, we have studied the effect of electric field on the growth of carbon nanotubules. Different electric fields corresponding to 3, 6, 9, 15, and 21 V have been applied during the growth of the tubules. The estimate of the electric field corresponding to these voltages cannot be precisely evaluated in view of only approximately defined electrode dimensions. It has been observed that the application of electric field leads to the agglomerates (bundles) of nanotubules. The size, length, and alignment of these bundles varies with the strength of the applied electric field. The best results have been obtained with electric field corresponding to 6 V where the as-formed tubules are in parallel alignment and exist as bundles. As the electric field is increased, the alignment of tubules in the bundle becomes randomly oriented. The degree of randomness increases with increase of electric field after its optimum value corresponding to 6 V. The parallel alignment of the graphitic tubules is thought to result due to orientation of the tubule axis along the direction of the applied electric field corresponding to an optimum value (which for the present case is 6 V) of the impressed voltage.
Pump intensity profiling of vertical-cavity surface-emitting lasers using near-field scanning optical microscopy
Authors: Vander Rhodes G. H. , Pomeroy J. M. , Ünlü M. S. , Goldberg B. B. , Knopp K. J. , Christensen D. H.
Published: July 2002

We have mapped the internal pump intensity distribution of an optically pumped vertical-cavity surface-emitting laser. Spontaneous emission from quantum wells placed throughout the distributed Bragg reflectors is correlated to the pump intensity. The emission is monitored along the cleaved edge using the high spatial resolution and shallow depth of field provided by near-field scanning optical microscopy. Our results show a distinct buildup of optical intensity between the mirror stacks. Simulations performed using the transfer matrix method match well with the experimental data.
Creation of nanometer-scale patterns with selected metal films
Authors: Moore Jon T. , Beale Paul D. , Winningham Thomas A. , Douglas Kenneth
Published: July 2002

We demonstrate the utilization of various transition metals in a biologically derived, nanometer-scale patterning process. This process created large arrays of nanometer-scale dots (nanodot arrays) with several of these metals. The correlation between nanodot array formation and the interaction energies between metal atoms, other metals atoms, and the surface of the sample was explored. The behavior of the metal films was then investigated with the aid of a Monte Carlo solid-on-solid simulation.
Effective passivation of the low resistivity silicon surface by a rapid thermal oxide/plasma silicon nitride stack
Authors: Narasimha S. , Rohatgi A.
Published: July 2002

A passivation scheme involving plasma silicon nitride (PECVD SiN) deposition on top of SiO2 grown by rapid thermal oxidation is developed to attain a low surface recombination velocity (S) of nearly 10 cm/s on the 1.25 Ω cm p-type (100) silicon surface. Such low S values are achieved by the stack structure even when the rapid thermal oxide (RTO) or PECVD SiN films individually yield poorer surface passivation. Critical to achieving low S by the RTO/PECVD SiN stack is the use of a short, moderate temperature anneal (in this study 730 °C for 30 seconds) after the stack formation. This thermal treatment is believed to enhance the release and delivery of atomic hydrogen from the SiN film to the Si–SiO2 interface, thereby reducing the density of interface traps at the silicon surface. Compatibility with this post-deposition anneal makes the stack passivation scheme attractive for cost-effective solar cell production where a similar anneal is required to form screen-printed contacts.
Electromagnetic wave propagation in and scattering from random media
Authors: Wang L. , Lee P. H. Y. , Barter J. D. , Caponi M.
Published: July 2002

We have developed a model for electromagnetic wave propagation in and scattering from random media. Scattering potentials are introduced to account for the reflections and refractions from boundaries. The differential cross sections for backscatter are calculated in the Kirchhoff approximation. We find that, in single scattering processes, the polarizations of differential cross sections are conserved and the differential cross sections are independent of the polarizations. The cross-polarized differential cross sections are symmetric and solely attributed to multi-scattering processes. Our results are in good agreement with experimental measurements.
Truly ohmic contacts in engineered Al/Si/InGaAs(001) diodes
Authors: De Franceschi Silvano , Beltram Fabio , Marinelli Claudio , Sorba Lucia , Lazzarino Marco , Müller Bernhard H. , Franciosi Alfonso
Published: July 2002

We report the fabrication of nonalloyed ohmic contacts on n-InxGa1−xAs (0.25⩽x⩽0.38) grown by molecular beam epitaxy (MBE) on GaAs(001). This result is obtained by suppression of the native Al/InGaAs Schottky barrier by means of the MBE growth of Si bilayers at the metal-semiconductor interface. Truly ohmic contacts are demonstrated by x-ray photoemission spectroscopy and current-voltage techniques.
Emission of silicon cluster ions by molecular ion bombardment
Authors: Yamamoto Hiroyuki , Baba Yuji
Published: July 2002

Silicon cluster ions (Sin+) with n⩽8 emitted from a Si(100) surface under bombardment with 4 keV SF5+, SF+, F+, and Xe+ ions have been observed. It was shown that, in all cases, the relative cluster yields (Y) roughly exhibited a power-law dependence, Y(n)∝n−δ, where n is the number of atoms in the cluster ion. The exponents δ of the power law were in the order of δ(SF5+)<δ(SF+)<δ(Xe+)<δ(F+), which was the same order as that of the size of these ions. The results indicate that the size of the bombarded ions greatly affects the cluster-ion emission. For the SF5+ bombardments, the intensity of even-n clusters (Si2+, Si4+, Si6+) was greater than that of the adjacent cluster ions with odd-n, which is in good agreement with the calculated stability of silicon cluster ions in the gas phase. It is concluded that the silicon cluster ions are effectively produced by the polyatomic SF5+ bombardment through the formation of high-density collision cascades at the irradiated local area.
Stable polarization self-modulation in vertical-cavity surface-emitting lasers
Authors: Li Hua , Hohl Angela , Gavrielides Athanasios , Hou Hong , Choquette Kent D.
Published: July 2002

The characteristics of polarization self-modulation in a vertical-cavity surface-emitting laser (VCSEL) were studied for frequencies up to ≈9 GHz both experimentally and theoretically. Polarization self-modulation was obtained by rotating the linearly polarized output of the VCSEL by 90° and reinjecting it into the laser. Experimentally we simultaneously recorded time traces, optical and radio-frequency spectra. We found for increasing modulation frequencies that the output characteristics changed from square-wave to sinusoidal and the VCSEL system assumed new polarization eigenstates that are different from the free-running VCSEL eigenstates. We modeled polarization self-modulation as an interband process and found a good qualitative agreement between our experimental and numerical results.
Influence of W via on the mechanism of electromigration failure in Al–0.5 Cu interconnects
Authors: Le H. A. , Tso N. C. , Rost T. A. , Kim C.-U.
Published: July 2002

This letter reports the effects of via current density on electromigration (EM) failure in Al–0.5 Cu conductors. Two-level metallization structures, differing in the number of feeding vias (1, 6, and 15), were made with the same pattern of Al lines at two levels to allow simultaneous EM testing of upper- and lower-level lines. It was established that the lower-level lines were more susceptible to the impact of the via, resulting in a failure by the formation of a local void beneath a via and a strong dependence of EM lifetime on the via current density. The results led to a phenomenological equation that incorporates via structure into failure kinetics.
High resolution electron microscopy and x-ray photoelectron spectroscopy studies of heteroepitaxial SixGe(1−x) alloys produced through laser induced processing
Authors: Frangis N. , Van Landuyt J. , Larciprete R. , Martelli S. , Borsella E. , Chiussi S. , Castro J. , León B.
Published: July 2002

Pulsed laser induced epitaxy has been used to produce graded heteroepitaxial SixGe(1−x) alloy layers on Si(100) wafers by melting an a-Ge film, previously grown by laser induced chemical vapor deposition, together with part of the wafer itself. High resolution electron microscopy and x-ray photoelectron spectroscopy analyses of SixGe(1−x) alloys suggest the formation of two sublayers; a strained one starting from the substrate up to Ge concentration of about 10–15 at. % and a partially relaxed one on top. The complete crystallization of the alloy without the formation of precipitates and with low threading dislocation density, proves that the combination of these laser-induced techniques represents a new and alternative process for the attainment of high quality SixGe(1−x) heterostructures.
Domain inversion by pulse poling in polymer films
Authors: Taggi V. , Michelotti F. , Bertolotti M. , Petrocco G. , Foglietti V. , Donval A. , Toussaere E. , Zyss J.
Published: July 2002

We report on an original technique for poling polymeric thin films, which allowed us to obtain a second-order nonlinear inverted domain structure, which could be used for frequency-doubling waveguides under quasi-phase-matching condition. Measurements of the local value and orientation of the electro-optic r33 tensor component were performed by a reflection microscopic electro-optic ellipsometer. The measured parameters for the nonlinear structure induced in the polymeric film result to be consistent with the expected values.
Directly coupled direct current superconducting quantum interference device magnetometers based on ramp-edge Ag:YBa2Cu3O7−x/PrBa2Cu3O7−x/Ag:YBa2Cu3O7−x junctions
Authors: Jia Q. X. , Yan F. , Mombourquette C. , Reagor D.
Published: July 2002

Directly coupled dc superconducting quantum interference device (SQUID) magnetometers on LaAlO3 substrates were fabricated using ramp-edge superconductor/normal-metal/superconductor junctions, where Ag-doped YBa2Cu3O7−x was used for the electrode and PrBa2Cu3O7−x for the normal-metal barrier. A flux noise of 8×10−6 Φ0 Hz−1/2 at 10 kHz measured with a dc bias current was achieved at 75 K, which corresponded to a field sensitivity of 400 fTHz−1/2 for a magnetometer with a pick-up loop area of 8.5 mm×7.5 mm. Most significantly, the noise floor increased at lower frequencies with a frequency dependence slightly less than 1/f. The field noise of the SQUID magnetometers increased by only 25% after cycling the devices from zero field to 500 mG. In a static earth’s magnetic field background, the field noise of the SQUID magnetometers increased by less than a factor of 2.
A single-mode high-power vertical cavity surface emitting laser
Authors: Milster T. , Jiang W. , Walker E. , Burak D. , Claisse P. , Kelly P. , Binder R.
Published: July 2002

We show how a structural element introduced into a vertical cavity surface emitting laser (VCSEL) results in the device operating in single stable high-order mode. The results from a 55 μm diameter device, λ=772 nm, are presented. The stability of the mode structure is investigated as a function of injection current. A simple theory, based on a modal loss discrimination mechanism in VCSELs with slightly perturbed mirrors, is used to explain the preferred lasing mode in VCSEL structures using a central etched well.
The dielectric properties of polycrystalline C60
Authors: Yan Feng , Wang Ye-Ning
Published: July 2002

The dielectric properties (1–50 kHz) of polycrystalline C60 have been carefully studied from 70 to 300 K. Below 170 K, the ac conductance σ(T) is proportional to the temperature, which is thought to be due to the phonon-assisted jump of electrons between localized states around the Fermi level. A significant change of the slope of the capacitance versus temperature curve occurs at 85 K, which can be attributed to the glass transition. It is confirmed that electric dipoles may be induced by orientational defects in C60 crystal. The capacitance drop around 256 K is found to originate from the disappearance of the orientational defects above the order–disorder phase-transition temperature.
Uniform component of index structure induced in Ge-SiO2 fibers by spatially modulated ultraviolet light
Authors: Tsai Tsung-Ein , Williams Glen M. , Friebele E. J.
Published: July 2002

Experimental data are presented to show that Ge(1) and Ge(2) centers are induced by trapping photoinduced electrons from the conduction band, in agreement with our previous proposal that both are trapped electron centers. The spacing (Λ) dependence of ultraviolet (UV) light bleaching of the pre-existing Ge E′ centers illustrates that the electron diffusion length is greater than Λ of the spatially modulated UV light used in the fabrication of fiber Bragg gratings (FBGs) with Bragg wavelengths ⩽1.5 μm (short period grating) for laser powers as low as 25 mJ/cm2. The Ge(1) and Ge(2) centers are uniformly induced by the spatially modulated UV light and therefore contribute to the uniform component of the index structure of FBGs.
Photoluminescence from gas-suspended SiOx nanoparticles synthesized by laser ablation
Authors: Geohegan David B. , Puretzky Alex A. , Duscher Gerd , Pennycook Stephen J.
Published: July 2002

Time-resolved photoluminescence (PL) spectra are reported for gas-suspended 1–10 nm diameter SiOx particles formed by laser ablation of Si into 1–10 Torr He and Ar. Three spectral bands (1.8, 2.5 and 3.2 eV) similar to PL from oxidized porous silicon were measured, but with a pronounced vibronic structure. Particle size and composition were determined with Z-contrast transmission electron microscopy imaging and high resolution electron energy loss spectroscopy linescans of individual nanoparticles. Maximized violet (3.2 eV) PL from the gas-suspended nanoparticles was correlated with an ex situ SiO1.4 overall particle stoichiometry. Cryogenically-collected gas-suspended nanoparticles produced web-like-aggregate films exhibiting very weak PL. Standard anneals restored strong PL bands without vibronic structure, but otherwise in agreement with the PL measured from the gas-suspended nanoparticles.
Stress-induced lateral confinement of light in epitaxial BaTiO3 films grown by radio-frequency magnetron sputtering
Authors: Barrios Pedro , Kim Hong Koo
Published: July 2002

We report channel waveguides formed in epitaxial BaTiO3 films that were grown on MgO single-crystal substrates using rf magnetron sputtering. In the channel waveguides developed, the lateral confinement of light is achieved via the photoelastic and piezoelectric/electro-optic effects in BaTiO3 induced by thin-film stress. Numerical analyses were also carried out on the stress and piezoelectric field distributions in the channel structure, assuming bulk materials properties. The refractive index changes were then calculated taking into account both the photoelastic and electro-optic effects of BaTiO3. The simulation result suggests that the electro-optic effect (caused by the stress-induced piezoelectric field) accounts for a significant portion (∼10%) of the refractive index change in the channel region.
On the nitridation of silicon by low energy nitrogen bombardment
Authors: Petravić M. , Williams J. S. , Conway M. , Deenapanray P. N. K.
Published: July 2002

High-resolution Rutherford backscattering and channeling has been used to study the formation of surface nitrides during room temperature bombardment of silicon with nitrogen in a secondary ion mass spectrometry system. Slightly N-rich silicon nitride is formed at angles of incidence (to the surface normal) <27°. Nitrogen buildup profile exhibits several intense oscillations before reaching a constant level. Implanted metals were found to show little tendency for segregation under nitrogen bombardment even when a silicon nitride layer forms at the surface.
Modulation-doped Cd1−xMnxTe/Cd1−yMgyTe quantum well structures with spatial in-plane profiling of the well width and the doping intensity
Authors: Wojtowicz T. , Kutrowski M. , Karczewski G. , Kossut J.
Published: July 2002

We report on the design and growth by molecular beam epitaxy of two types of graded Cd1−xMnxTe/Cd1−yMgyTe quantum well structures having a precisely controlled spatial profile of either the quantum well width and/or of the number of donors in one of the directions perpendicular to the growth axis. The existence of a spatially varying quantum well width was demonstrated by different wavelengths of the photoluminesce emitted from different regions of the sample. The presence of two-dimensional electron gas with a spatially varying concentration produced by graded modulation doping was evidenced by magneto-optical studies which revealed signatures of either excitons, or negatively charged exciton–electron complexes (X−), or Fermi-edge singularity, all in a single sample grown in one molecular beam epitaxy process. Such structures may be very useful for tunable wavelength radiation sources as well as in detailed studies of various physical characteristics of the quantum wells.
Dynamics of recombination-enhanced defect reaction in a ZnCdSe single quantum well
Authors: Tang Minxue , Shum Kai , Zeng Linfei , Tamargo Maria C.
Published: July 2002

Room temperature photoluminescence spectra from a ZnCdSe single quantum well have been measured as a function of time in a minute time scale under several photoexcitation levels (4–40 W/cm2). Spectrally integrated photoluminescence intensity increases as the measurement time increases and reaches a maximum level that is 37 times higher than the initial intensity. We attribute this dynamical behavior to recombination-enhanced defect reactions in the vicinities of point defects. These reactions reduce the density of point defects and enhance radiation quantum efficiency. A new point defect reduction rate was discovered to fit our experimental data.
Nanostructure of ordering variants in (AlxGa1−x)0.52In0.48P grown on different vicinal GaAs substrates
Authors: Dörr U. , Kalt H. , Send W. , Gerthsen D. , Mowbray D. J. , Button C. C.
Published: July 2002

We have investigated the nanostructure of ordered (Al0.5Ga0.5)0.52In0.48P using conventional and high-resolution transmission electron microscopy. As in the case of ternary Ga0.52In0.48P, the morphology of the ordered material depends strongly on the substrate orientation. For a substrate orientation with equal densities of [1̄10] and [11̄0] steps (and, hence, no preference for one particular ordering variant) a nanostructure is found which exhibits similarities to those observed in ternary Ga0.52In0.48P with equivalent substrate orientations. For a substrate orientation which preferentially selects one ordering variant without completely suppressing the formation of the other, we have identified a new type of nanostructure. In this structure, antiphase boundaries between domains containing the preferred variant are frequently formed by thin slices of the suppressed variant. This structural form is directly deduced from high-resolution images.
Improved Mg-doped GaN films grown over a multilayered buffer
Authors: Zhang Xiong , Chua Soo-Jin , Li Peng , Chong Kok-Boon , Wang Wen
Published: July 2002

Mg-doped p-GaN films have been grown on sapphire substrate with a multilayered buffer (MLB) by metalorganic chemical vapor deposition and characterized by photoluminescence spectroscopy. The MLB consists of GaN/AlxGa1−xN (0<x⩽1) superlattice-like layer structures although the material combination as well as the periodicity and uniformity in layer thickness and composition are not essential issues for constituting a MLB. It was found that the p-GaN films grown on MLBs gave much stronger optical emission than those grown on conventional GaN or AlxGa1−xN (0<x⩽1) single-layer buffer or GaN/AlxGa1−xN double-layer buffer under identical reactor configuration. This fact indicates that, by using the newly-developed MLB, the crystalline quality of group-III nitride-based-semiconductor epitaxial layers can be significantly improved.
Demonstration of an InGaN/GaN-based optically pumped multiquantum well distributed feedback laser using holographically defined third-order gratings
Authors: Hofstetter Daniel , Thornton Robert L. , Kneissl Michael , Bour David P. , Dunnrowicz Clarence
Published: July 2002

We demonstrate an optically pumped InGaN/GaN-based multiquantum well distributed feedback laser in the blue spectral region. The third-order grating providing feedback was defined holographically and dry etched into the upper waveguiding layer by chemically assisted ion-beam etching. When aligning the stripe-shaped pump beam either parallel or perpendicular to the grating grooves, we found a considerably lower pumping threshold, higher slope efficiency, a slightly longer emission wavelength, and a much narrower linewidth for the geometry with the pump beam orthogonal to the grating lines. A nearly constant emission wavelength of 400.85 nm and a linewidth of 0.7 Å were observed under various pump intensities. To the best of our knowledge, this is the narrowest linewidth ever reported for an optically pumped device in this material system.
Transmission electron microscopy and photoluminescence studies of Er implanted low-temperature grown GaAs:Be
Authors: Maltez R. L. , Liliental-Weber Z. , Washburn J. , Behar M. , Klein P. B. , Specht P. , Weber E. R.
Published: July 2002

Characteristic 1.54 μm 4f-4f emission has been observed from Er3+ centers in Er-implanted and annealed, low-temperature grown GaAs:Be samples, while cross-sectional transmission electron microscopy (TEM) studies reveal very little structural damage for elevated temperature implants. No Er emission was observed from any of the as-implanted samples, while the Er emission intensity was significantly more intense after 650 °C anneals than after 750 °C anneals. Significant enhancement of the optically active Er incorporation was achieved when the implantation was carried out at 300 °C. For the two total Er fluences employed (5.5×1013 and 13.6×1013 Er/cm2) the Er emission intensity exhibited a linear dependence upon implantation fluence, while TEM indicated no significant increase in the damage level at the higher fluence 300 °C implant.
Probing interfacial and bulk magnetic hysteresis in roughened CoFe thin films
Authors: Freeland J. W. , Bussmann K. , Lubitz P. , Idzerda Y. U. , Kao C.-C.
Published: July 2002

The hysteretic behavior of interfacial magnetic moments for CoFe thin films with varying roughness is determined in an element specific manner by monitoring the applied magnetic field dependence of the specular and off-specular (diffuse) contributions to the x-ray resonant magnetic scattering signal. Increasing the interfacial roughness generates a larger variation of the relative coercive field associated with the interfacial moment in comparison to the bulk.
Operation of a single column focused ion/electron beam system based on a dual ion/electron source
Authors: Chen L. W. , Wang Y. L.
Published: July 2002

A focused ion/electron beam system has been constructed by introducing a dual ion/electron point source into an optical column of electrostatic lenses. Ions are extracted from a W needle covered by liquid In while electrons are from the same source after the In has been in situ solidified. The switching between ion and electron beam is achieved by exchanging the polarity of the potentials applied to the electrodes. In comparison to the ion emission, the electron emission appears to exhibit narrower angular distribution but larger intensity fluctuation and emission point migration. Despite the undesirable features in the electron source, the first operation of the focused ion/electron beam system has demonstrated the potential of a dual-beam single-column system.
Phonon signatures of spontaneous CuPt ordering in Ga0.47In0.53As/InP
Authors: Cheong Hyeonsik M. , Ahrenkiel S. Phillip , Hanna Mark C. , Mascarenhas Angelo
Published: July 2002

Polarized Raman scattering spectra of spontaneously ordered Ga0.47In0.53As alloys, combined with low-temperature photoluminescence and transmission electron microscopy, are used to find a unique phonon signature of CuPtB-type ordering. In the Raman spectra of ordered alloys, a new phonon peak that is absent in the spectrum of the random alloy appears at 181 cm−1. The intensity of this peak correlates with the degree of ordering inferred from electron diffraction measurements. We propose that Raman scattering measurements can be used as a nondestructive probe to detect spontaneous ordering in this alloy.
Scanning second harmonic microscopy techniques with monomode and near field optical fibers
Authors: Adameck M. , Blum R. , Eich M.
Published: July 2002

Extending our scanning second harmonic microscopy (SSHM) technique for the detection of lateral orientational inhomogeneities in high field poled polymer films, we present results with considerably improved lateral resolution by using optical fiber technology. Two experimental setups for measuring the χ(2) susceptibility of thin films are introduced. The first setup uses a standard monomode infrared-fiber with 10 μm core that carries the coherent fundamental infrared wave to the surface of a poled polymer film (illumination mode). The generated doubled frequency wave behind the nonlinear optical sample is detected by a photomultiplier tube. In the second setup a lens focuses the fundamental wave into the poled film. The resulting second harmonic wave is coupled into a 2.5 μm single mode fiber. SSHM micrographs of high field poled nonlinear optical polymer films were obtained with lateral resolutions of <3.5 μm. SSHM was also realized with a scanning near field optical microscopy fiber in pick up mode.
Patterned birefringence by photoinduced depoling in electro-optic polymers and its application to a waveguide polarization splitter
Authors: Lee Sang-Shin , Garner Sean , Chen Antao , Chuyanov Vadim , Steier William H. , Guo Lan , Dalton Larry R. , Shin Sang-Yung
Published: July 2002

Photobleaching by ultraviolet light at 410 nm wavelength of selected electro-optic poled polymers leads to birefringence which can be patterned on a submicron scale. Measurements at 1310 nm of the effect in a azo dye attached to poly(methylmethacrylate) is presented along with data showing the effect is not present is hardened cross linked polymer hosts. An integrated optic polarization splitter using the patterned birefringence has crosstalk at the transverse electric and transverse magnetic outputs of −23 and −27 dB, respectively, and excess loss 0.2 and 0.3 dB at 1310 nm.
Improved optical response of superlattice graded InAlAs/InGaAs p-i-n photodetectors
Authors: Lenox C. , Nie H. , Kinsey G. , Yuan P. , Holmes A. L. , Streetman B. G. , Campbell J. C.
Published: July 2002

A number of important optoelectronic device utilize the InAlGaAs/InP material system. The reduction of carrier trapping at the In0.53Ga0.47As/In0.52Al0.48As heterointerface is advantageous towards improving both the quantum efficiency and frequency response of devices utilizing InGaAs active regions. Direct current and transient optical response characteristics were measured for p-i-n double-heterojunction photodiodes utilizing either abrupt or superlattice (SL) graded heterointerfaces. SL graded devices showed improved collection efficiency at electric fields <3 kV/cm and faster temporal response at electric field <70 kV/cm as compared to identical devices having abrupt interfaces.
Tunneling transport and diffusion in weakly coupled quantum dot ensembles
Authors: Deppe D. G. , Deng Q.
Published: July 2002

The lateral tunneling rate and carrier diffusion in weakly coupled quantum dots are analyzed. In the weak coupling limit, localization of charge within a single dot is obtained through superposition of the lowest-energy eigenstates of coupled dots. The free evolution of the wave function leads to tunneling, but with a time dependence that includes dephasing. Idealized quantum dot boundary conditions are used to estimate tunneling times, and these are compared with recent experiments.
Nonlinear magneto-optical Kerr effect and second harmonic generation interferometry in Co–Cu granular films
Authors: Murzina T. V. , Ganshina E. A. , Guschin S. V. , Misuryaev T. V. , Aktsipetrov O. A.
Published: July 2002

Magnetoinduced effects in second harmonic (SH) generation are experimentally studied in the CoxCu1−x granular films. Significant nonlinear magneto-optical Kerr effect (NOMOKE) is observed both in longitudinal and transverse configurations. The interference of the SH fields generated by the interface and bulk, nonmagnetic and magnetoinduced nonlinear polarizations is discussed as a mechanism of NOMOKE enhancement. The bulk nonmagnetic dipole quadratic susceptibility of Co nanocrystals stems from the lack of inversion symmetry in the Co granules.
Resonant enhancement of the photocurrent in multiple-quantum-well photovoltaic devices
Authors: Raisky O. Y. , Wang W. B. , Alfano R. R. , Reynolds C. L. , Stampone D. V. , Focht M. W.
Published: July 2002

Sequential resonant tunneling is proposed to enhance the photocurrent and reduce recombination losses in photovoltaic devices based on multiple-quantum-well (MQW) heterostructures. An InGaAsP/InP MQW p–i–n diode with built-in sequential resonant tunneling has been fabricated, and demonstrates an increase in the photocurrent and reduction in photoluminescence intensity. These effects are attributed to the resonance tunneling effect.
Defect densities in tetrahedrally bonded amorphous carbon deduced by junction capacitance techniques
Authors: Palinginis Kimon C. , Lubianiker Yoram , Cohen J. David , Ilie Adelina , Kleinsorge Britta , Milne William I.
Published: July 2002

Junction capacitance measurements performed on tetrahedrally bonded amorphous carbon (ta-C)/crystalline-Si (c-Si) heterostructures are used to deduce the defect density in thin ta-C films. Using the drive level capacitance profiling technique, we determine a homogeneous defect density of 6±1.5×1017 cm−3 in the undoped (p-type) ta-C films and one order of magnitude larger in the nitrogen-doped (n-type) films. Admittance measurements reveal defect states at the ta-C/c-Si interface with a density exceeding 2×1012 cm−2.
An x-ray spectromicroscopic study of electromigration in patterned Al(Cu) lines
Authors: Solak H. H. , Lorusso G. F. , Singh-Gasson S. , Cerrina F.
Published: July 2002

We studied the surface properties of patterned Al(Cu) lines related to the electromigration phenomena using photoemission spectromicroscopy techniques. We stressed the lines for electromigration in situ in the ultrahigh vacuum microscope chamber and observed the changes on the line surface. Our results show surface precipitation of Cu beneath the Al2O3 layer on the line surface as well as on side walls. Enrichment of grain boundaries in Cu due to electromigration flux was observed in areas downstream of voids with respect to the electron flow.
Wavelength shifting of optical pulses in a polydiacetylene waveguide
Authors: Grando Daniela , Sottini Stefano , Banfi Gian Piero , Fortusini Davide , LoPapa Monica
Published: July 2002

We characterize the process of wavelength shifting (generation of a pulse at the wavelength λp−Δ from a signal at λp+Δ under the action of a pump at λp) in a planar waveguide of poly (3BCMU) for short. With a propagation length of 4.5 mm, pulses of 20 ps time duration, and λ′ s around 1.3 μm, we observe wavelength conversion with 1% efficiency when the energy of the pump pulse per unit width is about 10−5 J/m.
Formation of double-monolayer-height islands on a Si(001) surface by alternating current heating in molecular beam epitaxy
Authors: Doi Takahisa , Ichikawa Masakazu , Hosoki Shigeyuki , Kakibayashi Hiroshi
Published: July 2002

Molecular beam epitaxy (MBE) of Si atoms onto a Si(001) 1×2 surface is investigated using reflection electron microscopy. A 1×2 surface with wide 1×2 and narrow 2×1 terraces is prepared by passing a direct current from the down side to the up side at the surface steps. After sample heating to 900 °C using an alternating current without deposited Si atoms, the 1×2 surface changes to a double-domain surface, where the width of the 2×1 terraces is approximately equal to that of the 1×2 terraces. With MBE, however, the 1×2 surface remains the 1×2 surface, and the double-monolayer-height islands with an approximately circular shape are stably formed on it.
Analysis of contamination, hydrogen emission, and surface temperature variations using real time spectroscopic ellipsometry during p/i interface formation in amorphous silicon p-i-n solar cells
Authors: Fujiwara H. , Koh Joohyun , Wronski C. R. , Collins R. W.
Published: July 2002

The formation of p/i interfaces in hydrogenated amorphous silicon p-i-n solar cells prepared by plasma-enhanced chemical vapor deposition has been studied in detail using real time spectroscopic ellipsometry. With this technique, three effects have been successfully separated and quantified: (i) contaminant layer deposition at the p-layer surface with a sensitivity of ±0.1 Å, (ii) thermal emission of bonded hydrogen from the p layer with a sensitivity of ±0.1 at. % (±2 meV in optical gap), and (iii) surface temperature variations with a sensitivity of ±1 °C. The separation of these competing effects has yielded a better understanding of p/i interface formation and device optimization.
Resolution of polymethyl methacrylate: Molecular weights of 950 000 vs 50 000
Authors: Dobisz Elizabeth A. , Brandow Susan L. , Bass Robert , Shirey Loretta M.
Published: July 2002

The work examines the resolution and line-to-line resolution of two molecular weights of polymethyl methacrylate (PMMA), developed in 25%–50% solutions of methylisobutyl ketone in isopropanol. Both PMMA’s exhibited similar minimum linewidths of 15–18 nm. Measured linespread functions showed primary Gaussian standard deviations of 11.7 and 28 nm for the 950 and 50 K molecular weight PMMAs, respectively. Developer strength produced ⩽1 nm difference in the width of the linespread function. Atomic force microscope images of latent grating patterns show the same line-to-line resolution for the two undeveloped resists. Developed gratings show the 950 K PMMA to have superior line-to-line resolution. The results are analyzed through integration of the measured linespread functions.
Evidence for coupling of Si–Si lattice vibration and Si–D wagging vibration in deuterated amorphous silicon
Authors: Shih An , Lee Si-Chen , Chia Chih-ta
Published: July 2002

The Raman spectra of hydrogenated and deuterated amorphous silicon films (a-Si:H, a-Si:D) have been investigated. It is suggested that the asymmetrical broadening of the transverse-optical (TO) Raman peak of a-Si:D compared to the TO Raman peak of a-Si:H results from the coupling between the Si–D wagging mode and the Si–Si TO phonon mode rather than the structural difference.
Strong influence of SiO2 thin film on properties of GaN epilayers
Authors: Wang X. C. , Xu S. J. , Chua S. J. , Li K. , Zhang X. H. , Zhang Z. H. , Chong K. B. , Zhang X.
Published: July 2002

In this letter, we report strong degradation of photoluminescence (PL) performance of GaN epilayers due to SiO2 layers that were deposited on GaN surfaces by electron-beam evaporation. Secondary ion mass spectrometry measurements show that the oxygen concentration of GaN with SiO2 layers is one order of magnitude more than that of as-grown GaN. This fact indicates that oxygen can very easily replace nitrogen in GaN. It was also found that rapid thermal processing can recover and improve the optical quality of GaN with SiO2 layer. As a reference, SixNy was found to have little effect on PL performance of GaN.
The nature of encapsulated silicon nanoclusters in zeolite Y
Authors: He J. , Ba Y. , Ratcliffe C. I. , Ripmeester J. A. , Klug D. D. , Tse J. S.
Published: July 2002

Luminescent silicon clusters have been synthesized by chemical vapor deposition of Si2H6 into the supercages of H32Na24Y zeolite. The encapsulated Si clusters are air stable and exhibit a room-temperature photoluminescence in the green-yellow region. The electronic band gap of the cluster is determined to be about 2.4 eV from photoelectron and photoabsorption spectroscopies. A saturation loading of seven disilane molecules per supercage was determined directly from multiple quantum H1 nuclear magnetic resonance spin counting of the precursor material. Intrazeolitic Sin clusters are formed after heating with loss of SiH4 and H2. The new quantitative spin counting result is consistent with an average value of 12±2 Si/cluster obtained from previous indirect measurements using x-ray photoelectron spectroscopy and Si K-edge x-ray absorption near-edge spectroscopy [J. He, D. D. Klug, J. S. Tse, C. I. Ratcliffe, and K. F. Preston, Appl. Phys. Lett. 71, 3194 (1997)]. This observation reveals a mechanism for the conversion of gaseous Si2H6 into silicon nanoclusters.
Resistless patterning of Si for processing
Authors: Shiralagi Kumar , Tsui Raymond
Published: July 2002

Results are presented on our efforts in the patterning of Si wafers without using photoresist. The process is similar to the recently reported surface modification of GaAs with ultraviolet (UV) light to produce a stable mask surface. However, in the absence of an easily modifiable surface oxide on Si, a hydrogen-passivated and oxide-free Si surface is exposed to UV light in the presence of oxygen to form an oxide in the irradiated regions. Selective Si growth and etching were demonstrated on wafers so patterned, and preliminary results showing the promise of this technique are reported in this letter.
Metalorganic vapor phase epitaxy of high-quality GaAs0.5Sb0.5 and its application to heterostructure bipolar transistors
Authors: Xu X. G. , Hu J. , Watkins S. P. , Matine N. , Dvorak M. W. , Bolognesi C. R.
Published: July 2002

We report the growth and characterization of high-quality InP/GaAs0.5Sb0.5/InP heterostructures and their application to double-heterojunction bipolar transistors (DHBT). The GaAs0.5Sb0.5 layer quality was evaluated by high-resolution x-ray diffraction (XRD), low-temperature photoluminescence (PL), and atomic force microscopy (AFM). The observed 4.2 K PL linewidth was 7.7 meV and XRD rocking curves matched those of dynamical scattering simulations. In contrast to previously reported InP/GaAs0.5Sb0.5/InP DHBTs, the present devices show nearly ideal base and collector currents, low turn-on and collector offset voltages, and a high current gain. Self-aligned DHBTs exhibit a cutoff frequency over 75 GHz and common-emitter current gain greater than 100 at 300 K.
Photorefractive properties of potassium lithium niobate crystals
Authors: Yang Changxi , Song Youting , Zhang Daofan , Wang Xiaomin , Zhou Tang , Fan Feidi , Wu Xing
Published: July 2002

We report the photorefractive properties of K3Li2−xNb5+xO15+2x crystals grown by the edge-defined, film-fed technique. The crystals with lithium/niobate ratio from 18.5/51.5 to 26/44 are grown and investigated by two-beam coupling technique. The crystal of composition K3Li1.783Nb5.687O16.61 exhibits an intensity coupling constant of 8 cm−1 and an effective trap density of 1.8×1022 m−3. The photorefractive majority carriers are electrons in as-grown crystals. The grating recording time and erasure time are 530 and 260 ms, respectively, at an intensity of 2 W/cm2.
Electronic structure of nanometer-scale quantum dots created by a conductive atomic force microscope tip in resonant tunneling structures
Authors: Yamauchi Miyuki , Inoshita Takeshi , Sakaki Hiroyuki
Published: July 2002

We report on a self-consistent electronic structure calculation for an AlAs/InGaAs/AlAs near-surface quantum well with a conductive atomic force microscope tip placed immediately above and biased at a positive voltage. The result indicates that the application of a modest voltage (∼V) to the tip creates zero-dimensional electron states (quantum dot) in the well with lateral confinement size <10 nm. These discrete states can be directly probed by resonant tunneling using the tip as an electrode. We also propose that p doping in the cap layer is very useful for the achievement of tighter lateral confinement.
90° magneto-optical polar Kerr effect in layered magnetic semiconductor/metal structures
Authors: Uspenskii Yu. A. , Harmon B. N.
Published: July 2002

Using analytical and numerical methods, we show that the polar Kerr rotation θK of 90° may be attained in a large class of (magnetic-semiconductor)/metal layered structures just below the absorption edge. The corresponding reflectivity varies over wide limits. For example, in a EuS/Ag multilayer with a small period it is of several percent, while in a thick layer of EuS deposited on Ag it achieves 95%.