bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantum confinement in amorphous silicon layers
Authors: Allan G. , Delerue C. , Lannoo M.
Published: July 2002

The electronic structure of hydrogenated amorphous silicon layers is calculated within the empirical tight binding approximation. We predict an important blueshift due to the confinement for layer thickness below 3 nm, and we compare with crystalline silicon layers. The radiative recombination rate is enhanced by the disorder and the confinement but remains much weaker than that in direct band gap semiconductors. The comparison of our results with experimental data shows that the density of defects and localized states in the studied samples is quite small.
Five-wavelength surface emitting laser diode array based on postgrowth adjustment of emission wavelength
Authors: Golshani A. , Kellermann P. O. , Köck A. , Gornik E. , Korte L.
Published: July 2002

A five-wavelength surface emitting laser diode array based on surface mode emission is reported. The wavelength control is achieved by postgrowth adjustment of the surface structure. Wavelength spacing between laser groups is 1.1 nm in average and the wavelength reproducibility is ±0.13 nm. The total change in the emission wavelength over the array is 4.78 nm. The single array elements show single mode emission with a full width at half-maximum of 0.08 nm in average and a side mode suppression ratio up to 20 dB. This type of laser diode is of high interest for wavelength division multiplexing applications.
Optical studies of very high-purity GaAs grown by metal–organic chemical-vapor deposition using a point-of-use arsine (AsH3) generator
Authors: van der Ziel Jan P. , Tang Xuefei , Johnson Ralph
Published: July 2002

We describe low-temperature photoluminescence studies of high-purity epitaxial GaAs and GaAs/AlGaAs quantum wells grown in a low-pressure metal–organic chemical–vapor deposition (MOCVD) reactor using electrolytically generated AsH3 as the group V source material and trimethylgallium and trimethylaluminum as the group III sources. The use of on-site point-of-use generated AsH3, made using the electrolytic conversion of solid As source material, greatly improves the safety of the MOCVD growth process, since AsH3 is generated only as needed, and at any time only a small volume of AsH3 is present. The photoluminescence studies indicate that very high-purity GaAs and GaAs/AlGaAs quantum wells layers are obtained using this source of AsH3. The GaAs/AlGaAs material has been used for a variety of devices including photodetectors and low threshold vertical cavity surface emitting lasers.
Low energy proton-induced displacement damage in shielded GaAs solar cells in space
Authors: Summers G. P. , Messenger S. R. , Burke E. A. , Xapsos M. A. , Walters R. J.
Published: July 2002

The energy dependence of the cumulative fraction of the damage produced by protons in shielded GaAs solar cells in space is presented. The results show that typically <20% of the damage is produced by protons emerging into the cell with energies <0.1 MeV, including those protons that stop in the active regions of the cell.
Fully oriented decagonal quasicrystalline thin films on crystalline substrates
Authors: Li Guohong , Zhang Dianlin , Jiang Hongwei , Lai Wuyan , Liu Wei , Wang Yunping
Published: July 2002

Fully oriented AlCuCo decagonal quasicrystalline films on crystalline substrates were successfully prepared by multitarget magnetron sputtering followed by postannealing. The width of the rocking curve competes with that of a single crystal. To explain the result, we suggest that the full orientation of the films originates from the fact that only one atomic flat plane of the structure is available to match the flat surface of the substrate, which gives a minimum interface free energy.
Selection of substrate orientation and phosphorus flux to achieve p-type carbon doping of Ga0.5In0.5P by molecular beam epitaxy
Authors: Friedman D. J. , Kibbler A. E. , Reedy R.
Published: July 2002

We show that the p-type doping of Ga0.5In0.5P grown by solid-source molecular beam epitaxy using CBr4 as a carbon source is very strongly dependent upon the phosphorus flux and upon the substrate misorientation from (100). High densities of A-type steps and low phosphorus flux favor the incorporated carbon acting as a p-type dopant. We demonstrate that with the substrate orientation and phosphorus flux chosen to satisfy these two criteria, doping of C:Ga0.5In0.5P into the mid-1018 holes/cm3 range can be achieved for the as-grown material.
Nondestructive assessment of the grain size distribution of SnO2 nanoparticles by low-frequency Raman spectroscopy
Authors: Diéguez Angel , Romano-Rodrı́guez Albert , Ramón Morante Juan , Bârsan Nicolae , Weimar Udo , Göpel Wolfgang
Published: July 2002

A nondestructive methodology is reported to obtain the grain size distribution of SnO2 nanoparticles, with grain sizes below 10 nm, using low-frequency Raman scattering measurements. The position of the main low-frequency Raman bands depends on the grain size and can be correlated with the spheroidal vibration modes of a spherical elastic body with “rigid” boundaries. The grain size distributions deduced from Raman scattering are in agreement with the direct measurements from transmission electron microscopy, especially for the smaller grains.
Optical measurement of effective recombination lifetime in silicon epitaxial layers
Authors: Cutolo A. , Irace A. , Spirito P. , Zeni L.
Published: July 2002

In this letter we present a novel all-optical pump-probe technique for the measurement of effective recombination lifetime in silicon epitaxial layers. The procedure is based on the measurement of the variation of the attenuation coefficient due to optically injected free carriers of a planar dielectric waveguide defined by the epitaxial layer cladded between the substrate and the air. Perturbation theory is used to take into account nonuniform refractive index distribution due to nonzero surface recombination. The measurement technique is validated by both numerical simulation and experimental results.
Ambipolar diffusion coefficient and carrier lifetime in a compressively strained InGaAsP multiple quantum well device
Authors: Zhu Daniel X. , Dubovitsky Serge , Steier William H. , Burger Johan , Tishinin Denis , Uppal Kushant , Dapkus P. Daniel
Published: July 2002

By using the technique of noncollinear nearly-degenerate four-wave mixing, ambipolar diffusion coefficients and carrier lifetimes were directly determined for a compressively-strained InGaAsP multiple quantum well semiconductor optical amplifier operating at 1.3 μm. A diffusion coefficient of 8.0 cm2/s and a carrier lifetime of 1.33 ns, were obtained at the amplifier current density of 1.88 kA/cm2. The current-density dependent measurements show that the diffusion coefficient will drop with increasing amplifier pumping current, which is consistent with the prediction of the conventional semiconductor theory.
Bias-enhanced nucleation of diamond on silicon dioxide
Authors: Irwin M. D. , Pantano C. G. , Gluche P. , Kohn E.
Published: July 2002

Characterization of amorphous SiO2 surfaces after biasing pretreatments, which induce nucleation of diamond, has been carried out using x-ray photoelectron spectroscopy and Raman spectroscopy. A mixture of silicon carbide, silicon oxycarbide, and diamond are formed upon exposure of biased SiO2 surfaces to a CH4+H2 plasma used for diamond deposition. It is concluded that nucleation of diamond on amorphous SiO2 surfaces is promoted by formation of a SiC surface layer. Textured diamond films have been fabricated on bulk SiO2 substrates using biasing pretreatments to induce diamond nucleation.
Spectroscopic applications and frequency locking of THz photomixing with distributed-Bragg-reflector diode lasers in low-temperature-grown GaAs
Authors: Chen Pin , Blake Geoffrey A. , Gaidis M. C. , Brown E. R. , McIntosh K. A. , Chou S. Y. , Nathan M. I. , Williamson F.
Published: July 2002

A compact, narrow-linewidth, tunable source of THz radiation has been developed for spectroscopy and other high-resolution applications. Distributed-Bragg-reflector (DBR) diode lasers at 850 nm are used to pump a low-temperature-grown GaAs photomixer. Resonant optical feedback is employed to stabilize the center frequencies and narrow the linewidths of the DBR lasers. The heterodyne linewidth full-width at half-maximum of two optically locked DBR lasers is 50 kHz on the 20 ms time scale and 2 MHz over 10 s; free-running DBR lasers have linewidths of 40 and 90 MHz on such time scales. This instrument has been used to obtain rotational spectra of acetonitrile (CH3CN) at 313 GHz. Detection limits of 1×10−4Hz1/2 (noise/total power) have been achieved, with the noise floor dominated by the detector’s noise equivalent power.
Preservation of rectangular-patterned InP gratings overgrown by gas source molecular beam epitaxy
Authors: Koontz E. M. , Lim M. H. , Wong V. V. , Petrich G. S. , Kolodziejski L. A. , Smith Henry I. , Matney K. M. , U’Ren G. D. , Goorsky M. S.
Published: July 2002

The ability to preserve a grating profile during epitaxial overgrowth is vital to the design and operation of devices such as planar waveguide-coupled Bragg-resonant filters. Intentional preservation of rectangular-patterned InP gratings during gas source molecular beam epitaxial overgrowth has been accomplished. The use of a low temperature atomic hydrogen-assisted oxide removal technique alleviates the dependence on elevated temperatures for desorption of the native oxide, and is crucial to the preservation of the patterned profile. Confirmation of the overgrown grating fidelity is demonstrated via scanning electron microscopy and triple axis x-ray diffractometry.
GaAs/AlGaAs ridge lasers with etched mirrors formed by an inductively coupled plasma reactor
Authors: Horst S. C. , Agarwala S. , King O. , Fitz J. L. , Smith S. D.
Published: July 2002

Etched mirrors for semiconductor lasers are necessary for optoelectronic integrated circuit applications. This letter reports on the use of an inductively coupled plasma (ICP) reactor to create etched mirrors on GaAs/AlGaAs ridge lasers. Etch chemistries consisting of boron trichloride and chlorine were used to achieve both smooth and vertical mirror surfaces. Optical measurements indicate that devices fabricated with ICP etched mirrors are comparable to devices formed by cleaved mirrors.
Observation of multiple electrically induced phase transitions and a decoupling of the induced strain and polarization in Sn-modified lead zirconate titanate
Authors: Forst Donald , Li Jie-Fang , Viehland Dwight
Published: July 2002

Studies of Pb0.98Nb0.02[(Zr1−xSnx)0.97Ti3]1−zO3 (PZST x/3/2) were performed for 0<x<0.20 by electrically induced polarization and strain methods. Maximum electrically induced strains (ε) and polarizations (P) were found in the compositional range around x=0.15, where ferroelectric and antiferroelectric regions coexisted. In addition, these studies demonstrated evidence for two electrically induced phase transitions: (i) an antiferroelectric–ferroelectric near 40 kV/cm, and (ii) a secondary ferroelectric–ferroelectric near 60–80 kV/cm. The dominate contribution to ε was associated with the secondary transition, whereas the dominate contribution to P was associated with the first.
Influence of separate confinement heterostructures on the effective carrier recombination coefficient in quantum well laser structures
Authors: Yamamoto Tsuyoshi , Odagawa Tetsufumi , Tanaka Kazuhiro , Ogita Shouichi
Published: July 2002

We analyzed the carrier recombination coefficient of quantum well laser structures by combining two-level ambipolar rate equations and a carrier diffusion equation for the separate confinement heterostructure (SCH) layer. We derived a new analytical expression for the effective carrier recombination coefficient (Beff) in quantum well laser structures. From our analysis, we found out that the dominant factor that determines Beff is not the diffusion across the SCH layer but the ratio of confined carriers in the well to the total carriers in both the well and the SCH layers. Our new expression well explained the measured results of 1.3 μm strained-layer quantum well lasers with SCH layers of different thicknesses.
Performance of superconducting microwave devices passivated with dielectric materials
Authors: Henderson Michelle L. , Kohl Paul A. , Eddy Michael M. , Zuck Betty F.
Published: July 2002

We present a set of experiments which show that three dielectric processing variables in particular affect the performance of superconducting microwave devices: processing time and temperature, moisture content of the dielectric material, and surface interactions with the high temperature superconductor (HTS). The changes in microwave performance of a straight-line microstrip resonator before and after passivation were quantified by measurements of the loaded and unloaded quality factors for each resonator. Dielectric materials of varying moisture content were used. The dielectrics were processed at different times and temperatures. This study shows that the degradation of the microwave devices can be minimized by choosing dielectrics which (i) have a low moisture content, (ii) interact as little as possible with the HTS surface, and (iii) can be rapidly processed at relatively low temperatures.
Novel main-chain poly-carbazoles as hole and electron transport materials in polymer light-emitting diodes
Authors: Tao X. T. , Zhang Y. D. , Wada T. , Sasabe H. , Suzuki H. , Watanabe T. , Miyata S.
Published: July 2002

We report the use of substituted main-chain poly-carbazoles as hole and electron transporting polymers for electroluminescence (EL) applications. The polymers are soluble in common organic solvents and high quality thin films are obtained by spin coating method. A single layer of hole or electron transfer devices with indium tin oxide anode and aluminum cathode shows current densities up to 40–50 mA/cm2, respectively, but no visible emission from either layer. Double-layer structures combining the hole and electron transfer polymers show strong emission originated from the electron transfer layer. The peak of double-layer EL spectrum is about 30 nm redshifted to the peak of corresponding photoluminescence spectrum, which may be due to the formation of an exciplex between the two layers.
Conversion efficiency and damage threshold measurements of CsLiB6O10 with a train of laser pulses
Authors: Srinivasan-Rao T. , Babzien M. , Sakai F. , Mori Y. , Sasaki T.
Published: July 2002

The energy conversion efficiency and the damage threshold of a CsLiB6O10 crystal have been measured for a pulse train with 80 pulses at 532 nm, each with energy up to 200 μJ, 14 ps duration and 25 ns pulse to pulse spacing. Maximum energy conversion efficiency of 38% has been measured when the crystal was used to convert 532 nm to 266 nm. The damage threshold of the crystal for this pulse train was measured to be >130 and <520 GW/cm2. Both the high intensity of the micropulse and the fluence of the macropulse appear to affect the damage threshold.
High-speed all-semiconductor optically addressed spatial light modulator
Authors: Tayebati Parviz , Canoglu Ergun , Hantzis Christos , Sacks Robert N.
Published: July 2002

We report a monolithically grown optically addressed multiple-quantum-well spatial light modulator with high-frame rate operation (>44 kHz) and large sensitivity (<1 μJ/cm2). The separated-detector-modulator device operates in the reflection mode and can provide a modulation gain of 35 with 60% modulation depth. We also show that higher modulation gains (>50) can be achieved at the expense of modulation depth. In addition, by using a voltage pulse, we reduce the recovery time of the device from 90 ms to 1 μs such that high-frame rate operation can be achieved. We demonstrate 60% modulation of the reflected readout beam at 44 kHz by only using 43 mW/cm2 cw writing illumination.
Stability of dc superconducting quantum interference devices fabricated using ramp-edge superconductor/normal-metal/superconductor technology
Authors: Jia Q. X. , Reagor D. , Mombourquette C. , Fan Y. , Decker J. , D’Alessandris P.
Published: July 2002

The degradation with time was determined for high-temperature superconducting quantum interference devices (SQUIDs) with ramp-edge geometry Josephson junctions (Ag:YBa2Cu3O7−x/PrBa2Cu3O7−x/Ag:YBa2Cu3O7−x). The critical current of the devices tended to decrease with a mean percentage of less than 7% over a period of more than 500 days. The junction resistance, on the other hand, increased with a mean percentage of 5%. The voltage modulation of the SQUIDs was unchanged within experimental reproducibility, presumably due to the cancellation of the changes in critical current and resistance.
Evidence of a blue shift in near surface ultra thin InAs/InP island like quantum wells
Authors: Sallese J. M. , Carlin J. F. , Gailhanou M. , Ilegems M.
Published: July 2002

We report evidence of a large blue shift (up to 70 meV) in the photoluminescence spectra of InAs/InP island like quantum wells following the reduction of the InP top barrier layer thickness from 6 nm to near zero. The photoluminescence intensity only starts to decrease when the top barrier thickness falls below 1.5 nm, indicating that radiative recombinations in the islands are very efficient. These results are well understood by a model assuming a vacuum confinement energy close to 5 eV.
Atomic configuration of segregated B on Si(001) surface
Authors: Komeda T. , Nishioka Y.
Published: July 2002

The atomic configurations of segregated B atoms on a highly B-doped Si(001) surface is investigated with scanning tunneling microscopy (STM) observation and first-principle cluster calculation, on which characteristic comb-shape step structures are observed. The characteristic features in the STM image are (1) dark regions in the occupied state, and (2) paired protrusions in the unoccupied state. The calculation shows that models of a B dimer on the top surface and B atoms bonded to two neighboring Si atoms in a dimer row can reproduce STM images well for (1) and (2), respectively.
Surface roughening by electron beam heating
Authors: Grozea D. , Landree E. , Marks L. D.
Published: July 2002

The effect of electron beam heating during the preparation of clean silicon surfaces suitable for epitaxial studies in ultrahigh vacuum conditions was investigated using surface chemical characterization techniques and transmission electron microscopy. The electron beam irradiation produced a disordered surface on the incident side of the sample and well-ordered monoatomic steps on the other surface, even at electron energies as low as 3 keV. These results have significant implications for epitaxial thin film growth.
A novel waveguide structure to reduce beam divergence and threshold current in GaInP/AlGaInP visible quantum-well lasers
Authors: Li Wen-Liang , Su Yan-Kuin , Chang Shoou-Jinn , Tsai Chin-Yao
Published: July 2002

A novel waveguide structure for AlGaInP visible separate confinement heterostructure quantum well laser with inserting low-refractive-index AlAs layers is theoretically investigated using the transfer matrix method. By using this structure, we can significantly improve the transverse beam divergence and reduce the threshold current. Otherwise, the inserting AlAs can also be used as a wet etching automatic stopped layer. Because the thermal resistance of AlAs is smaller than that of AlGaInP, the thermal characteristics of this novel structure are also better than the conventional AlGaInP visible lasers. With the inserting AlAs layers, the transverse beam divergence and the threshold current density can be reduced from 38° to 8.84° and 787 to 666.8 A/cm2, respectively.
Multivariable dependence of modulation spectroscopy in semiconductor superlattices
Authors: Pearsall T. P. , DiVergilio A.
Published: July 2002

The modulation spectrum of semiconductor superlattices is shown to be a sensitive function of photon wavelength and local energy band-bending in the superlattice structure. The added dependence leads directly to the concept of a modulation spectroscopy surface for heterostructures as opposed to a simple plot in two dimensions of amplitude as a function of photon energy. The implications of these results for the use of modulation spectroscopy methods such as contactless photoreflectance spectroscopy, where the band bending cannot be controlled, are discussed.
Magnetic materials-based electrorheological fluids
Authors: Wen Weijia , Wang Ning , Tam Wing Yim , Sheng Ping
Published: July 2002

A type of electrorheological (ER) system, denoted the magnetic materials-based electrorheological fluids, is introduced. The solid particles of this system are 40–50 μ-microspheres obtained by the sol–gel processing of a ferroelectric material containing a ferromagnetic component. Since the solid material is magnetic, the presence of a small magnetic field, such as that from a small permanent magnet, can suspend the microspheres in liquid. The incorporation of a small amount of magnetic materials thereby solves the long standing problem of particle sedimentation in ER fluids. It is found that this type of ER fluid is very stable and exhibits a strong ER effect at low electric field.
Solution to the bistability problem in shear force distance regulation encountered in scanning force and near-field optical microscopes
Authors: Zvyagin A. V. , White J. D. , Kourogi M. , Kozuma M. , Ohtsu M.
Published: July 2002

The bistability problem, common to scanning microscopes employing lateral dithering of the probe for image formation (i.e., shear force microscope) or probe-sample distance control (i.e., near-field optical microscope) is shown to stem from the two nearly degenerate vibration degrees of freedom possessed by a laterally dithered fiber. Controlling the fiber vibration direction by means of a four-sectioned piezo was found to be a simple and effective solution of the problem. An image of a microtubule is presented to demonstrate the improved imaging ability.
Ultrafast (370 GHz bandwidth) p-i-n traveling wave photodetector using low-temperature-grown GaAs
Authors: Chiu Yi-Jen , Fleischer Siegfried B. , Lasaosa Daniel , Bowers John E.
Published: July 2002

The authors demonstrate p-i-n traveling wave photodetectors utilizing low-temperature-grown GaAs as the absorption layer. The electro-optically measured impulse response was found to exhibit a pulsewidth of 1.1 ps full width at half maximum, corresponding to a −3 dB bandwidth of 370 GHz with an external quantum efficiency of 8% at 800 nm.
Charge–carrier diffusion length in photorefractive crystals computed from the initial hologram phase shift
Authors: Freschi A. A. , Garcia P. M. , Frejlich J.
Published: July 2002

The phase shift between the pattern of light onto a photorefractive crystal and the resulting hologram at the very beginning of the recording process in two-wave mixing is analyzed and measured as a function of the applied electric field. These data allow one to compute the diffusion length of photoexcited charge carriers and to evaluate the actual electric field inside the crystal. A diffusion length of 0.14 μm is measured in a nominally undoped photorefractive Bi12TiO20 crystal using a 532 nm wavelength laser illumination, in agreement with results obtained from other methods.
A new mechanism for spontaneous nanostructure formation on bottom-patterned compliant substrates
Authors: Carter-Coman Carrie , Brown April S. , Metzger Robert A. , Jokerst Nan Marie , Pickering Jason , Bottomley Lawrence A.
Published: July 2002

Bottom-patterned compliant substrates can be used to laterally modulate the properties of a mismatched epilayer. At temperatures where strain-dependent growth kinetics are significant, the GaAs bottom pattern compliant substrates affected the growth of strained InGaAs epilayers by causing lateral modulation in material height. Spatially aligned mounds and quantum dots were observed on the samples grown at high temperatures. A new mounding mechanism was observed on InGaAs layers grown on the compliant substrates. Strain-dependent growth kinetics and the bottom patterned compliant substrate are used to explain these effects.
Cu crystallographic texture control in Cu/refractory-metal layered structure as interconnects
Authors: Abe Kazuhide , Harada Yusuke , Onoda Hiroshi
Published: July 2002

The effect of underlayer texture on Cu film orientation has been studied. The crystallographic orientation of sputter-deposited Cu film depends strongly on the underlayer refractory-materials. Cu (111) orientation can be controlled by changing the preferred orientation of the TiN underlayer that has the same cubic structure as Cu. TEM observation of the Cu/RTN–TiN interface has revealed that the Cu (111) plane grows epitaxially on the TiN (111) plane. It has been also clarified that the atomic arrangement between the Cu (111) and TiN (111) planes has a rotational angle within ±10° around the 〈111〉 axis.
Critical temperature of 1.3 μm InP-based strained-layer multiple-quantum-well lasers
Authors: Seki Shunji , Yokoyama Kiyoyuki
Published: July 2002

We study the critical behavior of 1.3 μm InP-based strained-layer (SL) multiple-quantum-well (MQW) lasers at elevated temperatures. We show that, under the critical injection condition where the carrier density in the quantum wells reaches the maximum possible without causing any extra pile-up of carriers in the separate heterostructure confinement regions, an InP-based SL-MQW system exhibits an absorption-to-gain phase transition at some critical temperature (Tc). The characteristic feature of this phase transition shows excellent agreement with Landau theory of second-order phase transitions. It is demonstrated that Tc is a significant and meaningful quantity not only for laser design but also for characterizing the nature of an InP-based SL-MQW system in terms of condensed matter physics.
Growth and doping of Si layers by molecular-jet chemical vapor deposition: Device fabrication
Authors: Lubben D. , Eres G. , Jellison G. E. , Westbrook R. D. , Wood R. F.
Published: July 2002

Homoepitaxial Si films doped both n- and p-type were deposited by molecular-jet chemical vapor deposition (CVD) from 10% Si2H6 in H2. Doping was accomplished from the background using PH3 for n-type and B2H6 for p-type. The dopant concentration was controlled over four orders of magnitude (1015–1019 cm−2) for films deposited between 650 and 800 °C, and n-type films had significantly higher growth rates and doping levels compared to films deposited by very-low pressure CVD at equal Si2H6 throughput in the same reactor. Even without optimization, solar cells constructed from these films had open-circuit voltages and short-circuit currents as high as 490 mV and 21 mA cm−2, respectively, with fill factors as high as 70%.
Due to an error in printing, the following article, originally published in the 4 August 1997 issue, is being republished in its entirety. Demonstration of an imide coupling reaction on a Si(100)-2×1 surface by molecular layer deposition
Authors: Bitzer T. , Richardson N. V.
Published: July 2002

In this letter, we report the successful growth of an ultrathin organic film on Si(100)-2×1 by reactive coupling of polyimide precursors. Using the molecular layer deposition technique, 1,4-phenylene diamine and pyromellitic dianhydride were sequentially dosed on clean Si(100)-2×1 under ultrahigh vacuum conditions. The interfacial imidization was initiated by thermal curing at 200 °C. High resolution electron energy loss spectroscopy was employed to identify surface species. The spectra show clearly, that an oligimide chain has been formed which stands upright on the substrate. The chain bonds to the silicon substrate via a Si–(NH)–C linkage.
Large signal dynamics of distributed feedback lasers with spatial modulation of their coupling coefficient and grating pitch
Authors: Fessant Thierry
Published: July 2002

A multimode time domain model is used to study the large signal dynamics of complex distributed feedback lasers with nonuniform grating pitch and coupling coefficient. Lasers with longitudinal variation of their grating pitch Λ (corrugation-pitch-modulated lasers) can exhibit poor steady-state side mode suppression ratios. Numerical simulations show that an adequate profile of the coupling coefficient κ (stronger coupling at the center of the cavity) can help to achieve improved steady-state single mode operation with respect to conventional Bragg-detuned cavities (uniform coupling coefficient). However, it is found that in such lasers (z-dependent κ), side modes are liable to be excited during the turn-on transient interval. A careful study of the turn-on transient is needed to determine the maximum (keeping dynamic single mode regime) bias current.
The crucial role of doping for high repetition rate monolithic mode locking of multiple quantum well GaAs/AlGaAs lasers
Authors: McDougall S. D. , Vögele B. , Stanley C. R. , Ironside C. N.
Published: July 2002

Monolithic colliding pulse mode locking of a molecular beam epitaxy (MBE) grown GaAs/AlGaAs quantum well laser has been achieved through back doping of the active region to simulate the residual doping present in metal organic vapor phase epitaxy grown mode-locked laser wafers. Frequency domain measurements are presented which show multiple colliding pulse mode-locked operation of an MBE grown device at 186 and 372 GHz. Devices with no intentional doping in the active layer showed no evidence of mode-locked operation. Band-edge absorption spectra are also presented which indicate the effect doping has in broadening the excitonic linewidth in the saturable absorber.
Formation of a crystalline phase in amorphous hydrogenated carbon-germanium films by electron beam irradiation
Authors: Tyczkowski J. , Pietrzyk B. , Mazurczyk R. , Polański K. , Balcerski J. , Delamar M.
Published: July 2002

The influence of electron beam irradiation on morphology of plasma deposited amorphous hydrogenated carbon-germanium films produced from tetramethylgermanium in a three-electrode af reactor has been studied. It has been found that the insulating films are insensitive to this treatment, whereas a crystalline phase occurs in the semiconducting films. Although the molar content of germanium in these films amounts only to about 0.2, the crystalline phase is composed of pure germanium nanocrystals which contain about 70% of the whole amount of germanium existing in the films. The nanocrystals are agglomerated in globules of 50–500 nm in diameter.
Surface step bunching and crystal defects in InAlAs films grown by molecular beam epitaxy on (111)B InP substrates
Authors: Bécourt N. , Peiró F. , Cornet A. , Morante J. R. , Gorostiza P. , Halkias G. , Michelakis K. , Georgakilas A.
Published: July 2002

The surface morphology and crystal structure of InAlAs films grown by molecular beam epitaxy on (111)B InP substrates misoriented 1° toward [2̄11] have been investigated. Combined plane view transmission electron microscopy and atomic force microscopy observations have revealed spectacular terracelike topographies, induced by surface step bunching during the growth. Furthermore, cross section transmission electron microscopy analysis has shown the presence of threading dislocations, related to the giant steps, as well as strain inhomogeneities attributed to composition modulation. We have also demonstrated the potential use of the giant steps for local deposition of InAs.
Cathodoluminescence study of laser recrystallized CdTe layers
Authors: Fernández P. , Piqueras J. , Sochinskii N. V. , Muñoz V. , Bernardi S.
Published: July 2002

CdTe(100)/GaAs(100) and CdTe(111)/CdTe(111) layers grown by metalorganic vapor phase epitaxy (MOVPE) were investigated. The layers were recrystallized to improve their morphology by scanning the surface with a 100 μm diameter spot from an Ar ion laser beam (λ=514.4 nm). Cathodoluminescence spectra from both as-grown and recrystallized CdTe MOVPE layers are used to monitor the effect of the recrystallization procedure. The laser recrystallization results in important changes on the spectral distribution of luminescence. Deep-level bands associated to different defects are shown to be very sensitive to the laser recrystallization procedure. The effect of the different substrates on the defect structure of the layers is also related to the changes observed in the cathodoluminescence spectra.
Influence of germanium content on the photoluminescence of erbium- and oxygen-doped SiGe grown by molecular beam epitaxy
Authors: Neufeld E. , Sticht A. , Brunner K. , Abstreiter G. , Holzbrecher H. , Bay H. , Buchal Ch.
Published: July 2002

The photoluminescence at 1.54 μm of erbium- and oxygen-doped Si/Si1−xGex samples grown completely by molecular beam epitaxy has been investigated for germanium concentrations ranging from x=0 to x=0.165. The dopants were either placed into the Si1−xGex or into the Si layers of an alternating Si/Si1−xGex layer structure. Because of the good crystal quality after growth, it was possible to obtain all luminescence data from as-grown samples without annealing. We observed a decrease in photoluminescence (PL) intensity and a stronger temperature dependence with increasing Ge content. For samples with the same Si/Si1−xGex layer structure, an enhancement of PL intensity at low temperature was seen when erbium and oxygen were placed into the Si1−xGex layers rather than into the Si layers. We attribute this effect to a capture of photogenerated carriers in the Si1−xGex layers.
Control of nematic director orientation by exposing rubbed polyimide films to linearly polarized ultraviolet light
Authors: Kim Jae-Hoon , Shi Yushan , Kumar Satyendra , Lee Sin-Doo
Published: July 2002

The delicate interplay between the effects of mechanical rubbing and subsequent photo-induced chemical reactions on polyimide films has been studied for aligning liquid crystals. Exposure to linearly polarized ultraviolet (LPUV) light was found to profoundly alter the direction and the degree of molecular orientations obtained by rubbing. A simple model is presented to describe the observed changes in the director orientation. The results show that LPUV exposure can be very effectively used to control and fine-tune liquid crystal alignment.
Observing lateral temperature and refractive index profiles in an optically pumped midinfrared laser through temporally and spatially resolved spectra
Authors: Yan Chi , McDaniel Donald L. , Moeller Charles E. , Falcon Michael D. , Gianardi Donald M.
Published: July 2002

We show how temporally and spatially resolved lasing spectra may be interpreted to obtain quantitative information on the lattice temperature and refractive index distribution in an optically pumped GaInAsSb/AlGaAsSb quantum well 1.8 μm midwave-infrared laser. We present this technique as a method for evaluating and comparing high power laser structures in terms of optical and thermal efficiency. We also suggest how this method might provide insight into the particulars of filamentation and heat transport in both electrically and optically pumped structures.
An improved analysis for the determination of trap levels in silicon from laser microwave photoconductive decay measurements
Authors: Ling C. H. , Cheng Z. Y.
Published: July 2002

Dominant trap energy levels in silicon are extracted from the temperature dependence of minority carrier recombination lifetime, observed through laser microwave photoconductive decay. A small correction is made to the Arrhenius plot by incorporating the weakly temperature-dependent term in the recombination lifetime expression, hitherto ignored. The new extraction technique is simple to implement and the results are in good agreement with published data.
Mutual phase locking on resonant flux-flow steps in stacked long Josephson junctions
Authors: Carapella G. , Costabile G.
Published: July 2002

We demonstrate that, independently biasing the junctions in a two stack in the resonant flux-flow regime, we can obtain mutual locking in four different states. Two of them possibly consist of out-of-phase Josephson oscillations and two consist of in-phase oscillations. They are found experimentally to be very stable for a quite large range of applied magnetic field.
Layer-dependent magnetization in ultrathin Eu films on Gd(0001)
Authors: Arenholz Elke , Starke Kai , Kaindl Günter
Published: July 2002

The magnetic order of ultrathin Eu films on Gd(0001) was studied in a layer-resolved way by magnetic circular dichroism in 4f photoemission in combination with layer-dependent 4f core-level shifts. It was found that Eu films up to 2 monolayers thick show a high net magnetization parallel to that of the Gd substrate, exhibiting a 6×6 reconstruction, while for thicker Eu layers both the superstructure and the ferromagnetic alignment break down.
Chemical vapor deposition growth and characterization of undoped and doped Ge and Ge1−xCx quantum dots on Si
Authors: Seal Chayan Kumar , Samara Dean , Banerjee Sanjay K.
Published: July 2002

Germanium quantum dots have been grown on Si substrates at various temperatures for different durations and studied with atomic force microscopy to determine the growth conditions for the smallest and most uniform size quantum dots. Ge1−xCx quantum dots grown at varying Ge:C ratios have been characterized to study the effects of strain compensation by C. The effects of P and B doping on both Ge and Ge1−xCx dots have also been investigated. The results show fewer quantum dots in Ge1−xCx due to strain compensation of Ge by C, and suggest the formation of larger dots with P doping and smaller and more uniform dots with B doping. X-ray diffraction measurements on the samples show the strain in the films, with the rocking curves changing with the ratio of C in the quantum dots.
Second-harmonic generation from (Si5Ge5)100 superlattices with an applied external electric field
Authors: Zhang Xinhui , Chen Zhenghao , Xuan Linzhen , Peng Changsi , Pan Shaohua , Yang Guozhen
Published: July 2002

The electric field controlled bulk-like optical second-order susceptibility χ(2) in thicker (Si5Ge5)100 superlattices is reported. The relation between χ(2) and the broken structural symmetry by applied external field was observed. The measured large value of χ(2) for (Si5Ge5)100 superlattices is evaluated to be ∼5×10−6 esu with the external field of 100 kV/cm, which indicates that (Si5Ge5)100 superlattices have potential applications in optoelectronic devices.
Determination of optical constants of strained Si1−xGex epitaxial layers in the spectral range 0.75–2.75 eV
Authors: Chen Weize , Westhoff Richard , Reif Rafael
Published: July 2002

Optical characterization of strained Si1−xGex (0<x⩽0.30) heteroepitaxial layers has been performed using a spectroscopic phase modulated ellipsometer in the near infrared to the visible range (0.75–2.75 eV). The dielectric function of the Si1−xGex layers in this spectral range was fitted to an empirical formula with five parameters which were determined using a series of samples with known compositions. Accurate ellipsometry measurement of thickness and composition has been successfully demonstrated using this formula. This study provides a numerical expression for the optical constants of strained Si1−xGex in the spectral range of interest for most optoelectronic applications.
Self-consistent multicomponent envelope function calculation of normal incidence second-harmonic generation in p-type doped symmetric quantum wells
Authors: Liu Ansheng
Published: July 2002

In a self-consistent multicomponent envelope function approach, we showed that χxxx(2) component of the second-harmonic susceptibility tensor of a symmetric p-type quantum well (QW) exists, because of the valence-band mixing at nonzero values of the in-plane wave vector. For a highly doped narrow GaAs/Al0.3Ga0.7As QW, our calculation indicates that at low temperatures a large value (∼10−7 m/V) of χxxx(2) can be achieved in the far-infrared frequency range without satisfying double resonance conditions. This value is comparable to the experimentally observed value of χzzz(2) in n-type asymmetric QW structures.
Use of solid electrolytic erosion for generating nano-aperture near-field collectors
Authors: Mulin David , Courjon Daniel , Malugani Jean-Pierre , Gauthier-Manuel Bernard
Published: July 2002

A new way in the fabrication of metallized nano-apertures for near-field optical microscopy is proposed. The method is based on the electrolysis between a silver metallized probe and an electrolytic glass. By dry electrolytic erosion, the metal on the tip apex is removed and lead to a very small metal free aperture. This method applied here to tapered fibers, can be extended to any other metallized tip in a rather reproducible way.
Temperature dependence of Fermi level obtained by electroreflectance spectroscopy of undoped n+-type doped GaAs
Authors: Huang K. M. , Wang K. L. , Wang D. P. , Huang K. F. , Huang T. C. , Chu A. K.
Published: July 2002

The electroreflectance (ER) spectra of an undoped n+-type doped GaAs have been measured over a range of temperature from 25 to 400 K. Many Franz–Keldysh oscillations were observed above the band-gap energy, which enabled the electric field strength and, hence, also the Fermi level to be determined. The photovoltaic effect is shown to be negligible, even at the low temperature. The experiment shows that the Fermi level decreases with increasing temperature and has almost the same temperature dependence as the energy gap. It is pinned at about 0.63 of energy gap below the conduction band.
Room-temperature oxidation of a GaAs(001) surface induced by the interaction of hyperthermal atomic oxygen and studied by x-ray photoelectron spectroscopy and ion scattering spectroscopy
Authors: Wolan John T. , Mount Charles K. , Hoflund Gar B.
Published: July 2002

In this study a hyperthermal oxygen atom source has been used to form an oxide layer on an Ar+-sputtered GaAs(001) surface at room temperature, and this layer has been examined using x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). XPS data indicate that the Ga in the near-surface region is oxidized predominantly to Ga2O3 with a significant contribution from GaAsO4 while the As is oxidized predominantly to an AsOx species with significant contributions from As2O3 and GaAsO4 and/or As2O5. The oxide layer thickness is estimated to be about 25 Å, and the XPS Ga:As atom ratio increases from 1.1 to 1.6 during the oxidation. The ISS data indicate that the resulting oxide layer formed is more electrically insulating than a native oxide layer on this surface.
Mesoscopic caverns and nucleation twins formed in the growth of Co on Cu
Authors: Zhou G. L. , Flynn C. P.
Published: July 2002

Mesoscopic caverns in the form of facetted voids are observed to form when Cu pumps through pinholes to the outer surface during the epitaxial growth of fcc Co(111) on Cu(111) near 500 °C. We prove that the pinholes are located mainly at boundaries between fcc twin domains that occur with ABC and ACB stacking.
Failure of phase-matching concept in large-signal parametric frequency conversion
Authors: Trillo S. , Millot G. , Seve E. , Wabnitz S.
Published: July 2002

Four-wave mixing experiments in a low-birefringence optical fiber reveal an unexpected sudden increase of the conversion efficiency as the signal power crosses a threshold value. In this regime, peak frequency conversion is achieved outside the small-signal parametric gain spectrum. A nonlinear model of wave mixing fits the measured data well.
Six-fold coordinated silicon at grain boundaries in sintered α-Al2O3
Authors: Kaneko Kenji , Tanaka Isao , Yoshiya Masato
Published: July 2002

High-resolution transmission electron microscopy (HRTEM) and analytical electron microscopy (AEM) have been carried out on Si-doped sintered α-Al2O3. HRTEM shows that there is no amorphous phase at grain boundaries. The Si-segregated boundary is found to be much more sensitive to irradiation damage than undoped Al2O3 grain boundaries. AEM with energy dispersive x-ray spectroscopy (EDS) shows the significant segregation of Si at grain boundaries, and AEM with electron energy-loss spectroscopy (EELS) reveals the existence of six-fold coordinated Si at the grain boundaries. The theoretical calculations obtained by the molecular orbital method support the data obtained by EELS.
Defect annealing in a II–VI laser diode structure under intense optical excitation
Authors: Jordan C. , Fewer D. T. , Donegan J. F. , McCabe E. M. , Huynh A. , Logue F. P. , Taniguchi S. , Hino T. , Nakano K. , Ishibashi A.
Published: July 2002

Defect annealing under intense pulsed optical excitation has been observed in a II–VI laser diode structure at room temperature. More than one order of magnitude increase in photoluminescence intensity has been obtained when the annealed area is probed at low excitation intensity. High-resolution confocal photoluminescence images of the annealed region do not show any sign of degradation. Together, these results suggest that an initial density of intrinsic point defects present within the active region can be removed by the optical annealing. Recombination-enhanced defect reactions in the vicinity of the point defects are responsible for this nonthermal annealing effect.
Monte Carlo estimation of avalanche noise in thin p+-i-n+ GaAs diodes
Authors: Ong D. S. , Li K. F. , Rees G. J. , David J. P. R. , Robson P. N. , Dunn G. M.
Published: July 2002

We use a Monte Carlo model to investigate the improvement of avalanche noise performance in thin p+-i-n+ GaAs diodes. The model predicts a decrease in avalanche noise as the multiplication length decreases from 1.0 to 0.05 μm, in good agreement with recent experimental measurements. Our simulations suggest that electron initiated multiplication in short devices has inherently reduced noise despite higher feedback from hole ionization, as compared to long devices. This low noise behavior results from the narrower ionization probability distribution and larger dead space effect as a higher operating electric field needed in short devices.
Generation of programmable multi-wavelength picosecond pulses using an optical-loop-mirror multiplexer
Authors: Lee K. S. , Shu C.
Published: July 2002

An all fiberoptic configuration to generate multi-wavelength picosecond optical pulses by self-seeding of a gain-switched 1.53 μm semiconductor laser has been proposed and experimentally demonstrated. The configuration consists of a 600 m highly dispersive fiber and an optical loop mirror multiplexer. Four-wavelength optical pulses with a spectral separation of 2.6 nm, a side-mode-suppression ratio of 16 to 20 dB, and a pulse width of 75 ps have been generated. The repetition rate of these pulses has been multiplied to 3.4 GHz, and totally 13.6 Gb/s (4×3.4 Gb/s) pulse signals have been produced. With the optical bit patterns generated from the multiplexer, output pulses with one, two, or four wavelengths at different combinations can be obtained.
High bias transport and magnetometer design in open quantum dots
Authors: Switkes M. , Huibers A. G. , Marcus C. M. , Campman K. , Gossard A. C.
Published: July 2002

We report transport measurements as a function of bias in open semiconductor quantum dots. These measurements are well described by an effective electron temperature derived from Joule heating at the point contacts and cooling by Wiedemann-Franz out-diffusion of thermal electrons. Using this model, we propose and analyze a quantum dot based sensor capable of measuring absolute magnetic field at micron scales with a noise floor of ∼110 nT/Hz at 300 mK. Non optimized measurements reported here are ∼2 orders of magnitude above this floor.