bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of undoped polycrystalline Si by an ultrahigh vacuum chemical vapor deposition system
Authors: Lin Horng-Chih , Lin Hsiao-Yi , Chang Chun-Yen , Lei Tan-Fu , Wang P. J. , Chao Chih-Yeh
Published: July 2002

Deposition of undoped polycrystalline-silicon (poly-Si) films on SiO2 using an ultrahigh vacuum chemical vapor deposition system was investigated. Poly-Si films with high crystallinity were obtained at a temperature as low as 525 °C. The layer growth process was found to proceed with an activation energy of 44±2 kcal/mol, and is dominated by the desorption rate of surface-bonded hydrogen atoms. An incubation time was observed prior to the film deposition. This incubation period increased with decreasing growth temperature, resulting from slower nucleation and growth rates at lower temperatures.
Carrier velocity-field characteristics and alloy scattering potential in Si1−xGex/Si
Authors: Li S. H. , Hinckley J. M. , Singh J. , Bhattacharya P. K.
Published: July 2002

The alloy scattering potential is an important parameter in SiGe alloys since it not only affects the velocity-field characteristics for carrier transport, but also allows increased optical transitions by relaxing k-selection rules. In this letter, we report on the velocity-field measurements for relaxed and coherently strained SiGe alloys. The alloy scattering potential is obtained from a careful fit to the data. The hole velocity at any field is found to have a bowing behavior as a function of alloy composition. This reflects a strong alloy scattering potential which is calculated to be 0.6 eV for the valence band.
Stability of beryllium-doped compositionally graded and abrupt AlInAs/GaInAs heterojunction bipolar transistors
Authors: Hafizi Madjid , Metzger Robert A. , Stanchina William E.
Published: July 2002

Stability of base-emitter (BE) junction characteristics and dc current gain is analyzed for high-performance AlInAs/GaInAs heterojunction bipolar transistors (HBTs). HBT devices with heavily beryllium-doped base layers were stressed with a constant collector current at elevated temperatures (180 and 208 °C). Devices with compositionally abrupt and graded BE junctions were compared. The compositionally abrupt devices showed signs of significant Be diffusion under bias stress (i.e., drift in turn-on voltage and drop in dc current gain). The graded junction devices, however, remained extremely stable under bias stress. The compositional grading at the BE junction was accomplished by a nine-period AlInAs/GaInAs superlattice and is believed to be responsible for the stability of the graded devices.
Boron-implanted 6H-SiC diodes
Authors: Ghezzo Mario , Brown Dale M. , Downey Evan , Kretchmer James , Kopanski Joseph J.
Published: July 2002

Ion implanted planar p-n junctions are important for silicon carbide discrete devices and integrated circuits. Conversion to p-type of n-type 6H-SiC was observed for the first time using boron implantation. Diodes were fabricated with boron implants at 25 and 1000 °C, followed by 1300 °C post-implant annealing in a furnace. The best diodes measured at 21 °C exhibited an ideality factor of 1.77, reverse bias leakage of 10−10 A/cm2 at −10 V, and a record high (for a SiC-implanted diode) breakdown voltage of −650 V.
Dispersion of second-order optical properties of new high thermal stability guest chromophores
Authors: Shi R. F. , Wu M. H. , Yamada S. , Cai Y. M. , Garito A. F.
Published: July 2002

A new class of high thermal stability fused-ring guest chromophores intended for incorporation into highly stable host polyimides has been successfully developed. Thermal stabilities far in excess of 300 °C have been achieved for both the pure guest and the parent guest-host systems. dc-induced second harmonic generation measurements of the microscopic second order β of the guest chromophores in solution have been performed using an optical parametric generation technique. In the near-infrared region, values of the standard product μβ of order 103×10−48 esu have been observed. These values are in good agreement with quantum many-electron calculations.
Paramagnetic center in porous silicon: A dangling bond with C3v symmetry
Authors: Uchida Yoshishige , Koshida Nobuyoshi , Koyama Hideki , Yamamoto Yuko
Published: July 2002

Paramagnetic centers in self-supporting porous Si films formed by anodization of Si(100) and (111) wafers have been studied by X-band electron paramagnetic resonance (EPR) at room temperature. The EPR spectra indicate that this center has C3v symmetry, and the angular dependence of the line position is described by a g tensor axially symmetric about a 〈111〉 axis; g∥=2.0024, g⊥=2.0080 for the (100) film and g∥=2.0020, g⊥=2.0088 for the (111) film. The small g shift along the 〈111〉 axis indicates that the center is assigned to be a dangling bond localized on a single silicon atom. The results indicate that the surface of as-anodized porous Si maintains a crystallinity of silicon.
Effect of an eigenstrain on slow viscous flow of compressible fluid films
Authors: Murray Paul E.
Published: July 2002

We present a general formulation of the mechanics of slow viscous flow of slightly compressible fluid films in the presence of an eigenstrain. An eigenstrain represents a constrained volume change due to temperature, concentration of a dissolved species, or a chemical transformation. A silicon dioxide film grown on a silicon surface is an example of a viscous fluid film that is affected by a constrained volume change. We obtain a general expression for pressure in a fluid film produced by a surface chemical reaction accompanied by a volume change. This result is used to study the effect of an eigenstrain on viscous stress relaxation in fluid films.
Band-edge refractive optical nonlinearities in molecular beam-grown ZnSe epilayers
Authors: Bolger J. A. , Galbraith I. , Kar A. K. , Simpson J. , Wang S. Y. , Prior K. A. , Cavenett B. C. , Wherrett B. S.
Published: July 2002

We report novel measurements of the room temperature refractive optical nonlinearities in a molecular beam epitaxy-grown ZnSe epilayer at frequencies near to the band edge. Time-resolved changes in the transmission spectrum due to a two-photon generated plasma of free carriers are monitored with a broad-band white-light continuum probe. The refractive index changes, measured for photon energies between 0.8 and 0.05 eV below the free-exciton line at 2.68 eV, with photoexcited carrier densities of (2–5)×1018 cm−3, are found to be in good agreement with a many-body plasma calculation.
Low-energy oxygen ion bombardment effect on BaTiO3 thin films grown by multi-ion-beam reactive sputtering technique
Authors: Peng C.-J. , Hu H. , Krupanidhi S. B.
Published: July 2002

Low-energy oxygen ion bombardment was employed to modify the physical properties of BaTiO3 thin films grown by the multi-ion-beam reactive sputtering technique. The bombardment effect was shown in terms of film morphology, dielectric properties, dc resistivity degradation, and current-voltage characteristics. The results showed that oxygen ion bombardment can lead to denser morphology, a higher dielectric constant, a lower dissipation factor, slower dc resistivity degradation rate, and lower leakage current. The possible reasons for these improvements include the changes in void network structure, grain boundary structure, and defect structure of the films.
Pulse shaping using spectral filtering in gain-switched quantum well laser diodes
Authors: Yamada N. , Nakagawa Y.
Published: July 2002

This letter describes how to eliminate the long trailing edges from the gain-switched optical pulses in GaAs multiple quantum well lasers simultaneously operating at both the first and second quantized states. By filtering out the emission of the first quantized transition, nearly symmetrical pulses were obtained along with pulse-width reductions, while peak power was at least 50% that of the original pulse. The experimental results are qualitatively explained by the theoretical calculations.
Near-infrared electrochromism in LixC60 films
Authors: Klein J. D. , Yen A. , Rauh R. D. , Clauson S. L.
Published: July 2002

Fullerene thin films deposited on transparent substrates were found to exhibit electrochromic switching in the near infrared. The as-deposited films were optically transparent between 0.9 and 2.0 μm. The oxidation state of the fullerene films was altered by electrochemical insertion of Li ions from a liquid electrolyte. Upon Li insertion the transmittance of the films decreased markedly in the near infrared. Subsequent Li extraction restored most of the original transparency. The observed electrochromism occurs due to switching between the C60 and C601− oxidation states. Electrochemically, the insertion process is highly reversible. The lack of complete optical reversibility is attributed to solubility of C601− in the electrolyte employed.
Small-signal admittance and switching measurements of the resonant-tunneling diode
Authors: Mattia J. P. , Brown E. R. , Calawa A. R. , Manfra M. J.
Published: July 2002

Measurements of the small-signal admittance and the large-signal switching time of In0.53Ga0.47As/AlAs resonant-tunneling diodes are presented. The small-signal admittance in the positive differential-resistance region is found to be only a weak function of frequency. In contrast, the admittance in the negative differential-resistance region is a strong function of frequency, and the associated time constant is a strong function of bias voltage. It is found that the large-signal switching time is approximately a factor of 10 greater than the small-signal time constant.
7Ni-O chemical interaction and the transition temperature of Ni-doped Bi2Sr2Ca1Cu2O8
Authors: Alméras P. , Keszei B. , Berger H. , Forro L. , Margaritondo G. , Bussy F.
Published: July 2002

We find that even very low Ni doping levels of high-quality Bi2Sr2Ca1Cu2O8 single crystals strongly affect the transition temperature Tc. We also observed that Tc is not related to the total Ni concentration, but only to that of Ni engaged in NiO-type bonds. By controlling the temperature during crystal growth, one can modify the relative weight of Ni in NiO-type bonds with respect to other configurations—and therefore Tc.
In situ growth of epitaxial Bi2Sr2CaCu2O8−x and Bi2Sr2CuO6−x films by pulsed laser ablation
Authors: Zhu S. , Lowndes D. H. , Chakoumakos B. C. , Budai J. D. , Christen D. K. , Zheng X.-Y. , Jones E. , Warmack B.
Published: July 2002

Pulsed-laser ablation has been used to grow epitaxial films of Bi2Sr2CaCu2O8−x (Bi-2212) and Bi2Sr2CuO6−x (Bi-2201) on (001) MgO with entirely in situ processing. The films’ layer-stacking sequence, microstructure, and superconducting Tc are highly sensitive to the growth temperature and deposition rate. Pure Bi-2212 films exist over only a narrow temperature range. Pure Bi-2201 films appear at higher growth temperature, while lower growth temperature enhances the Bi-2223 phase, though it is mixed with Bi-2212. The phase homogeneity, in-plane connections among grains, and superconducting Tc of Bi-2212 grown at a given temperature are greatly improved by reducing the deposition rate. Epitaxial Bi-2212 films grown at 740 °C and 0.5 Hz (∼0.05 nm/s) have Tc0 (R=0)=71 K, with Jc∼8×105 A/cm2 at 50 K and Jc∼5×106 A/cm2 at 4.2 K.
Comparison of electroabsorption in tensile-strained and lattice-matched GaAs(P)/AlGaAs quantum wells
Authors: Gomatam Badri N. , Anderson Neal G. , Agahi Farid , Musante Charles F. , Lau Kei May
Published: July 2002

The performance of tensile-strained GaAsP/AlGaAs multiple-quantum well (MQW) reflection modulators is compared to that of similar lattice-matched GaAs/AlGaAs devices operating in the same wavelength range. The tensile-strained modulators utilize ∼95 Å GaAs0.92P0.08 quantum wells, which are designed to make use of the field-induced merging of electron-to-light-hole (e-lh) and electron-to-heavy-hole (e-hh) excitonic absorption edges achievable in tensile strained wells. Unstrained ∼46 Å GaAs quantum wells yielding similar excitonic gaps are utilized in the lattice-matched devices, but the strained and unstrained modulators are otherwise virtually identical. Room-temperature differential reflection spectra reveal increased modulation depths at low drive voltages in the tensile-strained devices, consistent with electroabsorption enhancements expected in these structures from merging of the elh and ehh transitions.
InSb p-channel metal-oxide-semiconductor field-effect transistor prepared by photoenhanced chemical vapor deposition
Authors: Liu Biing-Der , Lee Si-Chen , Liu Kou-Chen , Sun Tai-Ping , Yang Sheng-Jehn
Published: July 2002

The InSb metal-oxide-semiconductor field-effect transistor (MOSFET) was fabricated successfully. The SiO2 prepared by photoenhanced chemical vapor deposition was used both as the gate insulator and the source/drain passivation layer to reduce the source/drain pn junction surface leakage current. The common-source current-voltage (I-V) characteristics show a breakdown voltage exceeding 2 V indicating excellent pn junction reverse characteristics. The achieved field-effect mobility for a hole in the linear region is 230 cm2/V s. An anomalous kink effect is observed in the common-source I-V characteristics when the substrate is floating.
Suitability of metalorganic chemical vapor deposition-derived PrGaO3 films as buffer layers for YBa2Cu3O7−x pulsed laser deposition
Authors: Han Bin , Neumayer Deborah A. , Marks Tobin J. , Rudman David A. , Zhang Hong , Dravid Vinayak P.
Published: July 2002

Phase-pure thin films of the YBa2Cu3O7−x (YBCO) lattice matched and low loss tangent perovskite insulator PrGaO3 have been grown in situ on single-crystal (110) LaAlO3 substrates by metalorganic chemical vapor deposition (MOCVD). Films were grown at temperatures of 750–800 °C using β-diketonate precursors M(dpm)3 (M=Pr,Ga; dpm =dipivaloylmethanate). YBCO films were then grown on the MOCVD-derived PrGaO3 by pulsed laser deposition (PLD). Scanning electron microscopy reveals that the PrGaO3 films have smooth, featureless surfaces. As assessed by x-ray diffraction, the PrGaO3 films grow epitaxially on LaAlO3 with a high degree of (001) and/or (110) plane orientation parallel to the substrate surface, and the subsequent YBCO films grow with a (00l) orientation. Rocking curve and φ-scan analyses reveal that the PrGaO3 and YBCO films grow epitaxially. Cross-sectional high resolution electron microscopy and transmission electron microscopic selected area diffraction confirm that the PrGaO3 and YBCO layers grow epitaxially. YBCO films grown by PLD on the MOCVD-derived PrGaO3 exhibit Tc=91 K and Jc=6×106 A/cm2 at 77 K in zero field.
In situ metalorganic vapor phase epitaxy control of GaAs/AlAs Bragg reflectors by laser reflectometry at 514 nm
Authors: Raffle Y. , Kuszelewicz R. , Azoulay R. , Le Roux G. , Michel J. C. , Dugrand L. , Toussaere E.
Published: July 2002

In situ reflectometry with a 514-nm laser beam was used to monitor AlAs and GaAs layer thicknesses grown by metalorganic vapor phase epitaxy. The effective optical indices of these materials have been calibrated at the growth temperature by using an original method based on ex situ double crystal x-ray diffraction measurement. According to these measured indices, the in situ laser reflectometry at 514 nm appears to be well suited for a real-time thickness control of the GaAs/AlAs based Bragg reflectors. Finally, Bragg reflectors centered at 980 nm have been grown using the reflectometry at 514 nm. X-ray diffraction and reflectivity measurements performed on these reflectors confirm a 1% reproducibility and accuracy of the wavelength stop band center.
Proton irradiation effects on strained Si1−xGex/Si heterostructures
Authors: Park J. S. , Lin T. L. , Jones E. W. , Gunapala S. D. , Soli G. A. , Wilson B. A.
Published: July 2002

Proton irradiation effects on strained Si1−xGex/Si heterostructures have been studied. For the experiment, p+-Si1−xGex/p−-Si heterojunction diodes were fabricated by molecular beam epitaxy (MBE) growth of strained p+-boron doped SiGe layers on p−-Si(100) substrates. Due to the valence band discontinuity between SiGe and Si layers, and degenerate doping in the SiGe layer, the characteristics of these heterojunction diodes are similar to those of metal-semiconductor Schottky barrier diodes. The SiGe/Si heterojunction diodes are irradiated by 1 Mrad of protons at 1 and 8.5 MeV energies. The current-voltage (I-V) characteristics are measured as a function of temperature before and after irradiation. I-V characteristics show a decrease of the reverse bias leakage current after irradiation. The effective heterojunction barrier heights (Φb) and Richardson constants (A**) are measured before and after irradiation using activation energy measurements. The measurements show an increase of Φb and A** after irradiation. The increase of the effective barrier height is attributed to reduction of free-holes in the SiGe layers due to proton induced displacement defects. The increase of effective barrier height suggests that the strain in the SiGe layers is conserved after 1 Mrad of proton irradiation.
Liquid crystal alignment on polyimide Langmuir–Blodgett films prepared on a newly designed Langmuir trough using a flowing subphase
Authors: Zhu Yang-Ming , Lu Zh-Hong , Qian Feng , Yang Xiao-Min , Wei Yu
Published: July 2002

Nematic and smectic liquid crystals are homogeneously aligned on polyimide Langmuir–Blodgett films prepared by horizontal lifting on a novel Langmuir trough using a flowing subphase. Atomic force microscopy observation of the polymer monolayer deposited on graphite reveals that the polymer chains are elongated and aligned in the flow direction. Thus the alignment may act through the orientation of polyimide molecules.
Transient elastic wave generation by an array of thermoelastic sources
Authors: Noroy M.-H. , Royer D. , Fink M.
Published: July 2002

A set of 16 thermoelastic strip sources, equivalent to a phased array of ultrasonic transducers has been implemented on a solid by irradiating its surface with a multiple beam pulsed YAG laser. Longitudinal elastic waves were focused in the sample by time delaying each laser pulse. Results of experiments performed on duraluminum in the thermoelastic regime are presented and compared with simulations based on the surface center of the expansion model. It is shown that with this technique, a high energy focusing, together with an ultrasonic beam scanning can be achieved in a wide angular range leading to a significant improvement in the signal-to-noise ratio of a laser based ultrasonic system.
Detection of particle traps by spatially resolved optical emission spectroscopy over grooved electrodes in radio frequency discharges
Authors: Dalvie M. , Selwyn G. S. , Surendra M. , Guarnieri C. R. , McGill J. J.
Published: July 2002

Isophotal maps of spatially resolved optical emission signal from neutral, excited argon are used to detect regions of enhanced electron induced excitation over topographically contoured, rf-coupled electrodes in argon discharges. By aligning a lengthwise groove in one such electrode with the optical axis, it is possible to monitor the plasma homogeneity inside, along and above the groove. The use of a grooved electrode, previously shown to ‘‘trap’’ particles, is also shown to produce enhanced excitation in localized, well defined regions, depending on the discharge pressure and sheath thickness. At low and intermediate pressures (<100 mTorr) a single ‘‘bright’’ spot is noted above the center of the groove. Higher pressure operation causes two bright spots to form, symmetrically placed, close to the groove sidewalls. Laser light scattering is used to simultaneously detect the coordinates of suspended particles during the discharge. A correlation is noted between these bright spots and the location of trapped particles. These results suggest that trap formation is related to changes in the local ionization rate which alter the local potential profile.
Overlayer strain: A key to directly tune the topography of high-index semiconductor surfaces
Authors: Tournié Eric , Nötzel Richard , Ploog Klaus H.
Published: July 2002

The surface topography of GaxIn1−xAs and InAs layers grown by solid-source molecular-beam epitaxy on (311)-InP and (311)-GaAs substrates, respectively, is investigated in situ by reflection high-energy electron diffraction. In a wide temperature range, the (311)-GaxIn1−xAs surfaces are corrugated on a nanometer scale in a way similar to that previously reported for (311)-GaAs surfaces [R. Nötzel, N. N. Ledentsov, L. Däweritz, M. Hohenstein, and K. Ploog, Phys. Rev. Lett. 67, 3812 (1991)]. Moreover, the period of the corrugations varies with the overlayer strain which we demonstrate to be the key parameter to control the surface topography.
Organometallic chemical vapor deposition and characterization of indium phosphide nanocrystals in Vycor porous glass
Authors: Hendershot D. Greg , Gaskill D. Kurt , Justus Brian L. , Fatemi Mohammad , Berry Alan D.
Published: July 2002

Indium phosphide has been deposited in 40 and 150 Å Vycor porous glass by the reaction of trimethylindium with excess PH3. X-ray diffraction (XRD) of the red, transparent samples confirms the presence of crystalline indium phosphide. The amount of III-V material deposited within the glass matrix (loading) and annealing conditions influence the crystallinity and particle size of the nanocrystallites. The absorption spectra of vacuum-annealed samples is blue shifted with respect to bulk InP, with maxima ranging from 500 to 700 nm for both the 40 and 150 Å samples and is consistent with size quantization. The nonlinear optical properties of these nanocrystallite composites have been evaluated by Z-scan measurements and are characterized by a defocusing refractive nonlinearity influenced by a substantial nonlinear loss presumed to be caused by two-photon absorption.
X-ray characterization of strain relaxation in InGaAs/GaAs strained-layer superlattices
Authors: Li Jianhua , Mai Zhenhong , Cui Shufan , Zhou Junming , Feng Wei
Published: July 2002

Strain relaxed InGaAs/GaAs superlattices grown on GaAs(001) substrate by molecular beam epitaxy have been studied by means of double-crystal x-ray diffractometry. Theoretical simulations of the rocking curves were successfully performed by taking into account the relaxation mechanism, the tilt between the multilayer and the substrate, and the peak broadening effects. It was found that in our sample the misfit strain is relaxed on the multilayer/substrate interface. This leads to the formation of misfit dislocations on the interface with a mean linear density about 9×104 cm−1 and a tilt of 325 s. toward the [010] direction between the multilayer and the substrate.
Atomic structure of Ge-related point defects in Ge-incorporated oxide films
Authors: Zvanut M. E. , Carlos W. E. , Paine D. C. , Caragianis C.
Published: July 2002

Germanium-incorported oxides formed by high pressure wet oxidation of Si90Ge10 substrates are examined using electron paramagnetic resonance spectroscopy. Simulations based on the g tensor for the Ge E′ center suggest that the dominant defect observed in annealed 10 Mrad irradiated samples is an oxygen vacancy at a site of a substitutional Ge atom. Comparison of thin film and bulk samples suggests that the centers found in the films are associated with hydrogen. The results presented here should be directly applicable to optical components fabricated on semiconductor substrates for photon integrated circuits.
Enhanced phosphorus diffusion during the glow discharge deposition of n-type amorphous silicon hydrogen alloy
Authors: Chou Jenq-Shiuh , Wei Jeng-Hua , Lee Si-Chen
Published: July 2002

Phosphorus outdiffusion during glow discharge deposition of amorphous silicon hydrogen alloy (a-Si:H) is investigated. From the measurement of phosphorus profile using secondary ion mass spectroscopy on a double layer structure (n+/i/quartz and i/n+/quartz), it is found that the thermally assisted phosphorus diffusion is negligibly small at 300 °C. However, the phosphorus diffusion is enhanced significantly after passivation with hydrogen plasma at the same temperature. It is proposed that the release of phosphorus by atomic hydrogen to form PHx radicals is the rate limiting step for enhanced diffusion.
Spatial confinement of misfit dislocations at the interface of CdSe/GaAs(111)
Authors: Grün M. , Klingshirn C. , Rosenauer A. , Zweck J. , Gebhardt W.
Published: July 2002

High-resolution electron microscopy of wurtzite type CdSe epilayers grown on (111) GaAs revealed that interfacial misfit dislocations are perfect 60° dislocations with Burgers vectors parallel to the interface. Glide is therefore limited to the (0001) interface plane and the extension of dislocations into the epilayer is suppressed. Single-beam bright field imaging shows that the 7% mismatched epilayer is free of a dislocation network in its volume.
Transport properties of YBa2Cu3O7−δ/Y0.3Pr0.7Ba2Cu3O7−δ/YBa2Cu3 O7−δ Josephson junctions
Authors: Stölzel C , Siegel M. , Adrian G. , Krimmer C. , Söllner J. , Wilkens W. , Schulz G. , Adrian H.
Published: July 2002

YBa2Cu3O7−δ/Y0.3Pr0.7Ba2Cu3O7−δ /YBa2Cu3O7−δ Josephson junctions have been prepared by a multistep laser ablation process using an improved shadow mask technique. Junctions with barrier layer thicknesses larger than 12 nm exhibit current-voltage characteristics which are close to those predicted by the resistively shunted junction (RSJ) model. Under microwave irradiation, clear Shapiro steps, which could be well described by the RSJ model, occur in the current-voltage curves. From the exponential decrease of the critical current density with increasing barrier layer thickness, an order parameter decay length ξn of 21±4 nm at T=4.2 K has been determined for Y0.3Pr0.7Ba2Cu3O7−δ. The increase of the junction resistance with decreasing temperature indicates that the barrier layer dominates the junction properties.
Anomalous conductivity phenomenon and quantum size effects in a new microstructure-modulated superlattice
Authors: Liu Jun , Feng Lianghuan
Published: July 2002

Quantum size effects such as the modulation of activation energy have been observed and investigated in hydrogenated microcrystalline silicon (μc-Si:H)/hydrogenated amorphous silicon (a-Si:H) microstructure-modulated superlattices. The longitudinal dark conductivity changes anomalously around a temperature in the temperature dependence of the longitudinal dark conductivity for these superlattices. Studies indicate that these superlattices exhibit negative resistance above room temperature. We owe the anomalous conductivity phenomenon to the multibarrier resonant tunneling through the μc-Si:H/a-Si:H multiple-quantum-well structure. By considering the resonant tunneling effects, the anomalous conductivity behavior can be successfully explained.
Realization of crescent-shaped SiGe quantum wire structures on a V-groove patterned Si substrate by gas-source Si molecular beam epitaxy
Authors: Usami N. , Mine T. , Fukatsu S. , Shiraki Y.
Published: July 2002

SiGe/Si quantum wire structures were successfully fabricated on a V-groove patterned Si substrate by using gas-source Si molecular beam epitaxy (GS-SiMBE). A cross sectional image of transmission electron microscope clarified a crescent-shaped SiGe layer at the bottom of the V-groove owing to anisotropy of the growth rate on the different crystal orientations in GS-SiMBE.
Hot electron luminescence in ZnS alternating-current thin-film electroluminescent devices
Authors: Douglas A. A. , Wager J. F. , Morton D. C. , Koh J. B. , Hogh C. P.
Published: July 2002

Hot electron luminescence experiments are performed on ZnS alternating-current thin-film electroluminescent (ACTFEL) devices in order to determine the extent to which the electron distribution is heated. The luminescence spectrum is found to be broad and essentially featureless up to a high energy cutoff of approximately 3.7 eV, which is determined by optical absorption within the ZnS. This result indicates that under normal operating conditions in a ZnS ACTFEL device, a significant fraction of the electrons transported across the phosphor possess energies equal to or in excess of the ZnS band gap.
Optical properties of modulation-doped quantum wires fabricated by electron cyclotron resonance reactive ion etching
Authors: Weiner J. S. , Calleja J. M. , Pinczuk A. , Schmeller A. , Dennis B. S. , Goñi A. R. , Pfeiffer L. N. , West K. W.
Published: July 2002

Modulation-doped GaAs/AlGaAs quantum wires have been fabricated using electron-beam lithography followed by electron-cyclotron resonance reactive ion etching to selectively deplete the electron gas. This technique has the advantages of low damage to the quantum well, strongly anisotropic etching, and reproducible control over the etch depth. The quantum wires exhibit high photoluminescence efficiencies when etched as close as 200 Å to the electron gas. The fundamental gaps show the large optical red shifts associated with strongly spatially indirect transitions. The spacings between one-dimensional subbands determined from inelastic light scattering measurements are larger than 2 meV.
Anomalous carrier level dependence of normal resistivity of La2−xSrxCuO4
Authors: Sugahara Masanori , Jiang Jian-Fei
Published: July 2002

An experimental study is made concerning the dependence of normal resistivity ρ on hole-carrier level x′ using carefully made La2−xSrxCuO4 sintered specimens. Sharp dips are observed in the ρ vs x′ relation at the carrier levels x′=1/4N (N=1,2,3,...).
Study of photogenerated charge carrier dispersion in chlorinated a-Se:0.3%As by the interrupted field time-of-flight technique
Authors: Polischuk B. , Kasap S. O. , Baillie A.
Published: July 2002

Dispersion of photogenerated charge carriers due to their mutual Coulombic repulsion hitherto has been neglected in considering the spread of the photocurrent in a typical drift mobility experiment such as the time-of-flight transient photoconductivity measurement. Interrupted field time-of-flight experiments carried out on a high-resistivity semiconductor material (a-Se) with a well-defined mobility clearly show that the overwhelming mechanism for the dispersion of the charge packet in the absence of an applied field is due to Coulombic repulsion. Dispersion is directly proportional to time and the amount of photogenerated charge and puts a lower limit to the resolution of photodetector devices operating in the constant mobility regime.
Generation of ultrashort pulses from a superluminescent diode with a monolithically integrated absorber in a coupled-cavity configuration
Authors: Lin C. F. , Tang C. L.
Published: July 2002

We report the generation of extremely short pulses using a superluminescent diode with a monolithically integrated absorber in an external cavity coupled to an additional empty cavity. The pulses obtained have an autocorrelation width of 1.8–2.6 ps without pulse compression. After pulse compression external to the coupled cavity, the pulse width is further reduced to as short as approximately 190 fs. The short pulses are obtained by careful adjustment of the length of the auxiliary cavity to match that of the main cavity.
Difference in light-induced annealing behavior of deposition- and light-induced defects in hydrogenated amorphous silicon
Authors: Hata N. , Matsuda A.
Published: July 2002

First experimental results on light-induced annealing (LIA) of deposition-induced defects (DID) in hydrogenated amorphous silicon (a-Si:H) are reported. LIA of DID and of light-induced defects (LID) showed a big difference: the reduction in density of DID by LIA is as low as one third or less of LID reduced by LIA, while thermal annealing reduced DID and LID very similarly. Those results indicate a structural difference between DID and LID, and are discussed in connection with a structural model of a-Si:H.
Low energy (100 eV) C+ ion doping into GaAs using combined ion beam and molecular beam epitaxial technology
Authors: Iida Tsutomu , Makita Yunosuke , Kimura Shinji , Winter Stefan , Yamada Akimasa , Shibata Hajime , Obara Akira , Niki Shigeru , Fons Paul , Tsai Yushin , Uekusa Shin-ichiro
Published: July 2002

Low-energy (100 eV) carbon ion (C+) irradiation during molecular beam epitaxy of GaAs was carried out using combined ion beam and molecular beam epitaxy (CIBMBE) technology for the growth temperature (Tg) range between 500 and 590 °C. Carbon incorporation was identified by both low-temperature (2 K) photoluminescence and Hall effect measurements. In the PL spectra, two well-established specific emissions, ‘‘g’’ and [g-g], which are closely related to acceptor impurities, were observed for the above Tg range. The results indicate that carbon was both optically and electrically well activated as an acceptor even at Tg as low as 500 °C. Maximum net hole concentration, ‖NA-ND‖, as high as 3×1018 cm−3 was obtained with no appreciable radiation damages and undesired impurity contamination.
1-to-12 surface normal three-dimensional optical interconnects
Authors: Chen Ray T. , Tang Suning , Li Maggie M. , Gerald David , Natarajan Srikanth
Published: July 2002

We present a surface normal optical interconnect with a 1-to-12 collinear fan-out. Two types of polymer-based holograms were fabricated to provide a collinear 1-to-12 fan-out from guided mode to substrate modes and twelve 1-to-1 surface normal interconnects. Fluctuation of up to 7.2 dB for the 1-to-12 fan-out hologram was observed due to the oscillating and the film saturation effects of the transmission hologram. Diffraction efficiency better than 70% was observed for all the total internal reflection holograms. The result reported herein greatly enhanced optical signal processing capability of guided wave optical interconnects. The advantages of free space optical interconnect, such as global interconnect, three dimension, massive fan-out/fan-in capabilities, and surface normal optical interconnect, can be realized using the demonstrated architecture. The coupling from waveguide to fiber can be realized from the surface rather than the edge of a photonic integrated circuit.
Planar single-facet teardrop-shaped AlxGa1−xAs-GaAs quantum well heterostructure laser
Authors: Caracci S. J. , Krames M. R. , Ries M. J. , Holonyak N.
Published: July 2002

Data are presented demonstrating the laser operation of an AlxGa1−xAs-GaAs quantum well heterostructure (QWH) crystal patterned into a smoothly curved folded resonator, a ‘‘teardrop’’-shaped resonator, with a single output facet. A deep AlxGa1−xAs native oxide formed entirely through the top confining layer is utilized to produce a large effective index step for lateral optical confinement. The teardrop-shaped laser operates primarily in a TM (transverse magnetic) longitudinal mode polarized with a TM/TE (transverse electric) power ratio of 7:1. Continuous wave 300 K threshold currents as low as ∼127 mA, external differential quantum efficiencies of η∼15%, and total output power in excess of 75 mW (uncoated facet) are achieved.
Defect and strain redistribution in InxGa1−xAs/GaAs multiple quantum wells studied by resonant Raman scattering
Authors: Wagner J. , Larkins E. C. , Herres N. , Ralston J. D. , Koidl P.
Published: July 2002

Resonant Raman scattering by longitudinal optical (LO) phonons in the GaAs barriers of InxGa1−xAs/GaAs multiple quantum well structures has been used to study the onset of strain relaxation as the number of quantum wells is increased. The intensity of scattering from one and two GaAs LO phonons for excitation in resonance with the GaAs E0+Δ0 band gap is found to be highly sensitive to the formation and/or redistribution of defects and the buildup of strain in the barriers, and thus to strain relaxation in the InxGa1−xAs quantum wells. This behavior allows us to detect the onset of strain redistribution, even in samples where the frequencies of both the GaAs LO phonon in the barrier layers and the GaAs-like LO phonon in the InxGa1−xAs quantum wells show no measurable shift. Here, the GaAs LO phonon frequency observed in structures with fully strained InxGa1−xAs wells and unstrained GaAs barriers is used as a reference.
One-step-metalorganic-vapor-phase-epitaxy-grown AlGaInP visible laser using simultaneous impurity doping
Authors: Anayama C. , Sekiguchi H. , Kondo M. , Sudo H. , Fukushima T. , Furuya A. , Tanahashi T.
Published: July 2002

We fabricated a GaInP/AlGaInP visible laser with a real-index guide structure by one-step metalorganic vapor phase epitaxy using simultaneous impurity doping. We achieved an effective self-aligned current-confinement structure in the AlGaInP cladding layer and a threshold current of only 18 mA. The laser had stable transverse-mode oscillation with a beam astigmatism less than 1 μm.
Granular giant magnetoresistance at low fields in bilayer thin films
Authors: Coffey K. R. , Hylton T. L. , Parker M. A. , Howard J. K.
Published: July 2002

Granular giant magnetoresistance is observed at saturation fields of 350–1100 Oe in thin-film structures consisting of a discontinuous layer of Co or NiFe deposited on an insulating substrate and overcoated with Cu. The phenomena are similar to that recently observed in codeposited immiscible alloys such as Co-Cu, although at lower fields. The bilayer structure does not require immiscibility and thus allows a greater materials choice. Magnetoresistance values up to 3% are observed and the reduced saturation fields are attributed to the controlled size and shape of the ferromagnetic islands.
Spatial resolution of selectively deposited diamond stripes on ion implanted Si(100)
Authors: Huang J. T. , Lin S. J. , Hwang J. , Lin T. S.
Published: July 2002

Diamond stripes were successfully grown on the P+ ion implanted Si(100) substrate without the diamond abrasives pretreatment. The pattern of a transmission line model (TLM) was used to define the shape of the diamond stripes on Si(100). Lateral resolution of diamond stripes depended on the thickness of SiO2 on the patterned Si(100) substrate. The width of each diamond stripe was about the same as that of the corresponding SiO2 open window for the SiO2 layer of 18 000 and 9000 Å. A critical SiO2 thickness existed for diamond stripe deposition on the implanted Si(100), below which good spatial resolution of diamond stripes could not be achieved.
Thermal currents in proton isolated gallium arsenide structures at elevated temperatures
Authors: Sadwick L. P.
Published: July 2002

Using a new and simple technique, thermal currents between proton isolated devices fabricated on semi-insulating gallium arsenide (GaAs) substrates have been observed for the first time at temperatures from 25 °C up to 300 °C. The thermal currents show definite Ohmic behavior with respect to the applied voltage at a fixed temperature. An Arrenhius plot of the thermal current at a fixed bias voltage level for a given test structure yields a straight line with an activation energy that can be ascribed to known deep levels in GaAs. The implications that this thermal leakage current have on the functionality of GaAs metal-semiconductor field-effect transistors at high temperatures are also addressed in this work.
Multi-pulse operation of three-wavelength pulsed Q-switched Nd:Y3Al5O12 laser
Authors: Milev I. Y. , Ivanova B. A. , Danailov M. B. , Saltiel S. M.
Published: July 2002

By using a spatially dispersive resonator, three wavelength operation of Nd:Y3Al5O12 laser in pulsed Q-switched regime at 1064, 1061, and 1052 nm was achieved. The laser output consisted of three pulses corresponding to the three generated wavelengths. The number of simultaneously emitted lines was increased by frequency doubling the laser output pulses in a potassium dihydrogen phosphate crystal.
Lateral resonant tunneling through constrictions in a δ -doped GaAs layer
Authors: Blaikie R. J. , Nakazato K. , Oakeshott R. B. S. , Cleaver J. R. A. , Ahmed H.
Published: July 2002

We have fabricated constrictions in δ-doped GaAs using implanted gates to provide the lateral confinement. Large conductance oscillations are observed when the gate voltage is varied. The drain-source current-voltage characteristics are highly nonlinear; as many as 30 peaks are present, and peak-to-valley ratios greater than 100 have been measured. These results are explained in terms of resonant tunneling through the random potential distribution in the point contact. Using a simple model for the potential distribution we are able to simulate qualitatively the structure in the conductance.
Radiation and focusing of SH0 elastic waves in anisotropic sheets
Authors: Chen Han-Yang , Man Chi-Sing
Published: July 2002

The excitation and propagation of SH0 elastic waves in anisotropic sheets are studied. The wave equations are solved by the method of Fourier transforms. It is shown that the velocities determined in the far-field region are the group velocities in the directions of measurement. Analytical and numerical simulation results are presented. These results are in good agreement with our own measurements made on an anisotropic aluminum sheet, and they correctly explain the experimental data of other investigators, a satisfactory interpretation of which has been wanting. Our analysis shows that the energy of radiated SH0 waves in anisotropic sheets tends to focus in some directions, which can be shown to be the directions of maximum phase velocities for weakly orthotropic sheets. Quantitative comparison is made between this theoretical prediction and our experimental measurements.
New interfacial shear wave in piezoelectrics
Authors: Danicki E.
Published: July 2002

The propagation of a shear wave in piezoelectric media by an embedded conducting plane inside it is described. The plane affects the electric field only, so that the medium remains mechanically continuous across it. Several applications of the discussed wave are expected in surface acoustic wave devices.
Irradiation effect on electron transport through GaAlAs barriers
Authors: Chaabane H. , Bourgoin J. C.
Published: July 2002

The effect of electron irradiation on the electronic transport through GaAlAs barriers has been studied. A drastic change in the current voltage characteristics has been observed. At low-temperature scattering by the introduced defects induces tunneling via X band states. At high temperature the transport is dominated by electric field enhanced electron emission from defect levels.
Zero-loss multiple-quantum-well electroabsorption modulator with very low chirp
Authors: Devaux Fabrice , Muller Sandrine , Ougazzaden Abdallah , Mircéa Andréi , Ramdane Abderrahim , Krauz Philippe , Semo Jacques , Huet Fredéric , Carré Madeleine , Carenco Alain
Published: July 2002

We report on the integration on InP of an electroabsorption modulator and an amplifier using the same active layer. The amplifier compensates for the various losses and provides net fiber-to-fiber gain at 1.55 μm. The extinction ratio is 10.5 dB for a modulator drive voltage of 2 V. The small-signal bandwidth is 18 GHz. In addition, the effective chirp parameter is as low as 0.16.
Metal/semiconductor compound ultrathin films for laminated optical polarizers
Authors: Shiraishi K. , Hatakeyama H. , Ishibashi N. , Matsumura K.
Published: July 2002

Metal included semiconductor ultrathin films for laminated polarizers are proposed. Compound films consisting of germanium and stainless steel are fabricated by use of a rf magnetron sputtering system. Generally speaking, imaginary parts of the specific dielectric constants of the films increase in proportion to the metal concentration. Laminated polarizers utilizing the compound films as absorptive layers are found to have high performances, extinction ratios more than 50 dB with insertion losses less than 0.2 dB over the wavelength range from visible to infrared.
Noise study of a high-T
c Josephson junction under near-millimeter-wave irradiation
Authors: Gupta R. , Hu Qing , Terpstra D. , Gerritsma G. J. , Rogalla H.
Published: July 2002

Noise studies of both the dc and ac Josephson effects have been performed on a high-Tc ramp-type Josephson junction irradiated at 176 GHz. Well-established analytical results for noise in overdamped RSJs are used to model the measured I-V characteristics, and their agreement is excellent. Noise-rounded I-V curves at the critical current and the first and second Shapiro steps under coherent 176 GHz radiation have been studied in detail at several temperatures and rf power levels. The noise temperatures inferred from these simulations are close to the physical temperatures. An increase of noise temperatures at high radiation power levels is a result of radiation heating, which could be due to a bolometric effect.
Comparative study of J
c-H characteristics for silver-sheathed superconducting Bi(2:2:1:2) and Bi(2:2:2:3) tapes
Authors: Shibutani K. , Wiesmann H. J. , Sabatini R. L. , Suenaga M. , Hayashi S. , Ogawa R. , Kawate Y. , Motowidlo L. , Haldar P.
Published: July 2002

Critical current densities Jc of silver sheathed Bi2Sr2CaCu2O8 and Bi2Sr2Ca2Cu3O10 composite tapes fabricated by a partial melt and a powder-in-tube process, respectively, were measured at 4.2, 27, and 64 K as a function of applied magnetic field and the angle between the tape face and the direction of applied magnetic field. These measurements indicate that (1) the fraction of the grain boundaries, which are strongly coupled, are greater in the Bi(2:2:1:2)/Ag tapes than in the Bi(2:2:2:3)/Ag tapes; (2) the alignment of the Bi cuprate platelets with the c-axis perpendicular to the tape face is significantly greater for the Bi(2:2:1:2) than for the Bi(2:2:2:3)/Ag tapes; and (3) the E-J curves for both kinds of the tapes are described well by an expression, E∼exp[−(J0/J)μ], where μ and J0 are constants below their transition magnetic fields H*g.
On the propagation of pure plane waves in anisotropic media
Authors: Ditri John J.
Published: July 2002

In this letter it is shown that, for plane longitudinal waves propagating in generally anisotropic media, any direction in which the polarization vector is collinear with the propagation direction is also a direction in which the energy flux vector is collinear with the propagation direction. For transverse waves, the condition that the polarization vector is perpendicular to the propagation direction is shown to imply that the energy flux vector is collinear with the propagation direction only if the anisotropic media satisfies certain implicit symmetry conditions. Possible applications of these results to the determination of the elastic moduli of anisotropic media are discussed.
Langmuir–Blodgett technique without solvent
Authors: Hasegawa K. , Hosoi K. , Tomioka A. , Miyano K.
Published: July 2002

A new Langmuir–Blodgett (LB) technique has been developed in which molecules are dispersed on the water surface by evaporation. Films of materials hard to dissolve in conventional volatile solvents can thus be formed and be transferred onto solid substrates. As a demonstration, unsubstituted quinacridone LB films have been formed.
Monolayer thickness fluctuations in infrared photoluminescence for [211]-oriented HgTe-CdTe superlattices
Authors: Meyer J. R. , Reisinger A. R. , Harris K. A. , Yanka R. W. , Mohnkern L. M.
Published: July 2002

We report the observation of multiple photoluminescence peaks due to monolayer thickness fluctuations in HgTe-CdTe superlattices. The spectra for seven different [211]-oriented superlattices with band gaps varying from 133 to 495 meV exhibit double peaks, and in nearly all cases the energy splitting corresponds to a difference of ≊1.5 ML in the quantum well thickness.
Epitaxial growth of cadmium sulfide layers on indium phosphide from aqueous ammonia solutions
Authors: Lincot Daniel , Ortega-Borges Raúl , Froment Michel
Published: July 2002

Epitaxial growth of cadmium sulfide on indium phosphide monocrystals has been achieved by using chemical deposition from cadmium ammonia-thiourea aqueous solutions. The epitaxial growth takes place on InP (1̄1̄1̄) substrates with the c axis of hexagonal CdS perpendicular to the surface. The epitaxy relations are determined by means of electron diffraction techniques. The deposition conditions appear to be flexible with reaction temperatures ranging from 60 to 90 °C, and growth rates about 0.1–0.5 μm h−1.