bluuebunny/crossref_metadata_2025 huggingface dataset:
The optical and electrical studies of hydrogen passivation in GaInP/GaAs heterostructures
Authors: Fan J. C. , Wang J. C. , Chen Y. F.
Published: July 2002

It is shown that hydrogen passivation by the photochemical vapor deposition method can have a significant influence on GaInP/GaAs heterostructures. The effect has been investigated by low-temperature photoluminescence and current–voltage and capacitance–voltage experiments. The photoluminescence measurement shows a strong increase in the luminescence intensity after hydrogenation. It is interpreted in terms of the passivation of nonradiative recombination defect centers by atomic hydrogen. The effect is also accompanied by a simultaneous decrease in the carrier concentration as shown from the capacitance–voltage measurements. In addition, the effect of hydrogenation is confirmed by the improvement of the Schottky-diode properties. These results provide concrete evidence to support the passivation of impurities and defects by atomic hydrogen in GaInP/GaAs heterostructures.
Heterodyne detection of alternating magnetic fields with a resonating xylophone bar magnetometer
Authors: Givens R. B. , Wickenden D. K. , Oursler D. A. , Osiander R. , Champion J. L. , Kistenmacher T. J.
Published: July 2002

A resonating xylophone bar magnetometer has been utilized as the mixer in a heterodyne detector for variable-frequency alternating magnetic fields. To illustrate the range of this detection scheme, examples offered include the response to low frequency, sinusoidal magnetic fields at 2, 10, and 20 Hz and to high frequency sinusoidal magnetic fields in the MHz regime. In a final example, the response of the magnetometer to the field generated by a 20 Hz square wave has been compared to the Fourier components of an idealized square wave, with no apparent loss in sensitivity and a mean deviation from expected values of less than 0.5%.
Integration of wavelength signal divider and infrared photodetectors based on the plasma dispersion effect in SiGe/Si
Authors: Li Baojun , Jiang Zuimin , Pei Chengwen , Qin Jie , Wang Xun , Li Guozheng , Wan Jianjun , Liu Enke
Published: July 2002

Based on the plasma dispersion effect, a single-mode SiGe wavelength signal divider (WSD) integrated with infrared photodetectors for optical communication at the wavelengths of 1.3 and 1.55 μm is proposed and fabricated by molecular beam epitaxy. The device performances are measured. The crosstalks of the WSD at a forward modulation bias of 1.2 V are −25 and −18 dB at 1.3 and 1.55 μm, respectively. The insertion losses are 2.01 and 2.64 dB for 1.3 and 1.55 μm, respectively. At −5 V reverse bias, the dark currents of the detectors at the 1.3 and 1.55 μm output branches are 45 and 64 nA, respectively. Photocurrent responsivities of 0.08 and 0.07 A/W for the two detectors at the 1.3 and 1.55 μm output branches have been achieved. The quantum efficiencies of the whole WSD and detector integration system are estimated to be about 19% and 18.2% for the 1.3 and 1.55 μm output branches, respectively.
Structural characterization of amorphized InP: Evidence for chemical disorder
Authors: Glover C. J. , Ridgway M. C. , Yu K. M. , Foran G. J. , Lee T. W. , Moon Y. , Yoon E.
Published: July 2002

Extended x-ray absorption fine-structure measurements at the In K edge of amorphous InP are presented. The presence of chemical disorder in the form of like-atom bonding has been unambiguously demonstrated in stoichiometric InP amorphized by ion implantation. In–In bonding comprised 14%±4% of the In–atom constituent bonds. Also, relative to the crystalline value of four P atoms, an increase in the total In coordination number to 4.16±0.32 atoms was observed for the amorphous phase, as composed of 3.56±0.19 P and 0.60±0.13 In atoms. Experimental results were consistent with recent ab initio structural calculations and, furthermore, demonstrated that amorphous InP is best described by a Polk-like continuous random network, containing both even- and odd-membered rings.
Characterization of carrier-trapping phenomena in ultrathin chemical oxides using x-ray photoelectron spectroscopy time-dependent measurements
Authors: Hagimoto Y. , Fujita T. , Ono K. , Fujioka H. , Oshima M. , Hirose K. , Tajima M.
Published: July 2002

We report a technique to characterize carrier-trapping phenomena in SiO2 by measuring the Si 2p core-level energy of Si substrates covered with thin SiO2 layers as a function of x-ray irradiation time. It is found that the Si 2p peak energy, which corresponds to the band bending at the SiO2/Si interface, changes as the x-ray irradiation time increases. We attribute this to carrier-trapping phenomena in SiO2. By using this technique, it is found that the carrier-trapping phenomena differ remarkably among several chemical oxides. We also discuss the atomic structure of the traps that cause the trapping phenomena.
Evidence of N-related compensating donors in lightly doped ZnSe:N
Authors: Tournié E. , Brunet P. , Faurie J.-P.
Published: July 2002

We have used a nitrogen/argon mixed plasma to dope p-type ZnSe during molecular beam epitaxy. We show that this technique allows control of the net acceptor concentration in the whole range from 1015 to 1018 cm−3. The unique ability to fine tune the doping at very low levels provides new insight into the compensation mechanisms. We provide a direct demonstration that not only the deep but also the shallow compensating donor detected by photoluminescence spectroscopy is a N-related defect. Further, our results show that both these compensating donors are generated from the very onset of N incorporation.
Transfer function and thermal noise of YBa2Cu3O7−δ direct current superconducting quantum interference devices operated under large thermal fluctuations
Authors: Barthel K. , Koelle D. , Chesca B. , Braginski A. I. , Marx A. , Gross R. , Kleiner R.
Published: July 2002

Direct current superconducting quantum interference devices (SQUIDs) made from high transition temperature superconductors typically exhibit a still unexplained higher white noise and smaller transfer function than numerical simulations based on the coupled Langevin equations predict. We present a systematic study that compares experimental results with both numerical simulations and a recently developed analytical approach based on a Fokker–Planck equation. To cover a wide range of SQUID parameters, two samples of different inductances were measured at variable temperature. While several predictions of the analytical theory could be verified and a good qualitative agreement with both theories is observed, only one sample showed good quantitative agreement. Furthermore, our simulations performed in the limit of large thermal fluctuations show excellent agreement with the analytic theory.
Dislocation-induced changes in quantum dots: Step alignment and radiative emission
Authors: Leon R. , Okuno J. O. , Lawton R. A. , Stevens-Kalceff M. , Phillips M. R. , Zou J. , Cockayne D. J. H. , Lobo C.
Published: July 2002

A transition between two types of step alignment was observed in a multilayered InGaAs/GaAs quantum-dot (QD) structure. A change to larger QD sizes in smaller concentrations occurred after formation of a dislocation array. Cathodoluminescence (CL) spectra show a bimodal peak with lower energy peak enhancement when probing at lower e-beam energies. The two peaks separate as a result of QD interdiffusion. CL imaging and cross-sectional transmission electron microscopy showed contrast from a dislocation array formed at the interface between GaAs and the first InGaAs QD layer. Strong QD emission in the near infrared (800–1100 nm) was obtained despite the presence of dislocations.
Optical and electrical tuning of the frequency in self-oscillating multiple shallow quantum-well diodes
Authors: Kwon O-Kyun , Lee Kyu-Seok , Chu Hye Yong , Lee El-Hang , Ahn Byung-Tae
Published: July 2002

We have studied photoinduced self-oscillation characteristics in GaAs/AlGaAs multiple shallow quantum-well diodes as a function of bias voltage and laser power. Under the illumination of a laser of wavelength corresponding to the exciton absorption energy, the I–V curve of the diode revealed a large negative differential conductance region where the electrical and optical oscillations were observed in the same phase. The oscillation frequency was widely tuned by either bias voltage or laser power, and this demonstrates a large potential of the device scheme for the electrical and optical signal generators with wide frequency tunability.
A 2.0 μm cutoff wavelength separate absorption, charge, and multiplication layer avalanche photodiode using strain-compensated InGaAs quantum wells
Authors: Dries J. Christopher , Gokhale Milind R. , Forrest Stephen R.
Published: July 2002

We report an avalanche photodiode structure for use at wavelengths as long as 2.1 μm. Light is absorbed in a 100 period structure consisting of In0.83Ga0.17As quantum wells strain compensated by In0.83Ga0.17P barrier layers. Photogenerated electrons are injected into a high field In0.52Al0.48As (ionization rate ratio=0.2) gain region initiating low noise avalanche multiplication. Primary dark currents of ∼5 nA and responsivities of 45 A/W at a wavelength of 1.9 μm are observed.
Simulation and characterization of the selective area growth process
Authors: Alam M. A. , People R. , Isaacs E. , Kim C. Y. , Evans-Lutterodt K. , Siegrist T. , Pernell T. L. , Vandenberg J. , Sputz S. K. , Chu S. N. G. , Lang D. V. , Smith L. , Hybertsen M. S.
Published: July 2002

A simple three-dimensional vapor phase model is used to interpret and clarify the selective area growth process. The model predicts both normal and anomalous profiles of thickness and composition, including long range effects. These are verified by an extensive set of experiments.
Interfacial defects in thin refractory metal films imaged by low-energy electron microscopy
Authors: Świȩch W. , Mundschau M. , Flynn C. P.
Published: July 2002

Low-energy electron microscopy is employed to image defects at buried interfaces through the strains they cause at the front surface. The interfacial defects studied here occur in high quality films of Mo(110) grown by molecular beam epitaxy on Al2O3(112̄0). The defects include steps and inclusions on the original sapphire surface and interfacial dislocations created where epitaxial strain causes slip.
Low-onset organic blue light emitting devices obtained by better interface control
Authors: Koch N. , Pogantsch A. , List E. J. W. , Leising G. , Blyth R. I. R. , Ramsey M. G. , Netzer F. P.
Published: July 2002

We demonstrate that highly efficient single-layer light emitting devices (LED) can be realized by better control in the device production process, especially regarding the interface between the active material and the metal cathode. The device cross-section was investigated using Auger depth profiling and spectroscopy. Following this approach, LEDs with para-sexiphenyl (optical gap: 3.1 eV) as active medium and aluminum as cathode were realized, which emit blue light at a bias of only 3.5 V, when the aluminum deposition rate is drastically reduced, namely from 10 to below 1 Å/s. We find that the lower deposition rate of Al results in a decreased width of the interfacial region, where carbon, aluminum, and oxygen are intermixed. At the same time the relative oxygen concentration at the cathode interface is increased. However, the presence of oxygen does not lead to the formation of oxidized aluminum species, as verified by the Al local mixing model (LMM) Auger signal.
Nonlinear quantum capacitance
Authors: Wang Baigeng , Zhao Xuean , Wang Jian , Guo Hong
Published: July 2002

We analyze the nonlinear voltage dependence of electrochemical capacitance for nanoscale conductors. This voltage dependence is due to the finite density of states of the conductors. Within Hartree theory we derive an exact expression for the electrochemical capacitance–voltage curve for a parallel plate system. The result suggests a quantum scanning capacitance microscopy at the nanoscale: by inverting the capacitance–voltage expression one is able to deduce the local spectral function of the nanoscale conductor.
A simple method for optically enhancing the small electro-optical effects of fast switching electroclinic liquid crystals
Authors: Xu H. , Davey A. B. , Wilkinson T. D. , Crossland W. A.
Published: July 2002

We report a method for optically enhancing the small electro-optic effect of fast switching liquid crystals in order to allow the liquid-crystal electro-optical devices to operate at very high speed. In comparison with the method using grating-excited guided modes, this method makes device fabrication and operation much easier as the cell structure is similar to a conventional cell but with a metallic mirror coated on the bottom glass substrate. Using this method, a contrast ratio of >5 has been obtained for optical switches with an electro-optical response time of 700 ns and a field of 12 V/μm.
Degenerate four-wave mixing in (Pb, La) (Zr, Ti)O3 polycrystalline film fabricated by metalorganic chemical-liquid deposition
Authors: Jin G. H. , Nemet B. , Lu Y. L. , Hsu C. , Cronin-Golomb M. , Wang F. L. , Jiang H. , Zhao J.
Published: July 2002

We have demonstrated a large photorefractive effect in thin-film polycrystalline (Pb, La) (Zr, Ti)O3 (8.5/65/35) fabricated by metalorganic chemical-liquid deposition. With an applied external electric field, this film exhibited a high photorefractive diffraction efficiency measured by degenerate four-wave mixing. Poling phenomena and depolarization processes in the film were also investigated.
Flow dynamics of sheared liquids explored by inelastic neutron scattering
Authors: Magerl A. , Zabel H. , Frick B. , Lindner P.
Published: July 2002

We have applied high resolution neutron spectroscopy to elucidate the dynamics of sheared liquids. At room temperature, the macroscopic flow of the lubricant yields a peak of the scattered intensity at roughly half the velocity of the driving disk demonstrating a nonclassical flow, whereas at higher temperature the expected linear velocity profile establishes. The data also give information on a modification of local diffusion modes for a liquid in a shear field.
The electrical behavior of Pt3In7 and NiIn contacts to p-GaN
Authors: Ingerly D. B. , Chang Y. A. , Chen Y.
Published: July 2002

Based on the criteria for the solid-state exchange reaction with p-GaN, we have investigated the intermetallic compounds, Pt3In7 and NiIn, as possible ohmic contacts. The as-deposited contacts were found to be rectifying and using current–voltage characterization rapid thermal annealing of the contacts was shown to significantly decrease their resistance, with contacts annealed at 800 °C for 1 min yielding the lowest resistance. Pt3In7 contacts to p-GaN when annealed at 800 °C for 1 min exhibited a specific contact resistance (ρc) of 9.5×10−2Ω cm2 while NiIn was more than an order of magnitude lower at 8.0×10−3Ω cm2. The NiIn contacts also show a lower specific contact resistance than the more traditionally used Ni/Au contacts (ρc=1.3×10−2Ω cm2) processed under the same conditions. Atomic force microscopy was used to examine the morphology of the reacted contacts. While the Ni/Au contacts showed the formation of deep spikes (<200 nm) after annealing the NiIn contact showed a much smoother reaction region with no evidence of spiking.
Controllable bistabilities and bifurcations in a photoexcited GaAs/AlAs superlattice
Authors: Luo K. J. , Teitsworth S. W. , Kostial H. , Grahn H. T. , Ohtani N.
Published: July 2002

Self-sustained photocurrent oscillations and bifurcation processes have been experimentally investigated in an undoped, photoexcited GaAs/AlAs superlattice by varying the laser intensity. Within a certain range of laser intensities, a bistability of the photocurrent can be observed in the photocurrent versus voltage characteristics. The width of the bistability region can be controlled by varying the laser intensity. In the bistable regime, the photocurrent oscillations disappear via a subcritical Hopf bifurcation with increasing applied voltage. Outside this regime, the transition from oscillations to a static state is a supercritical Hopf bifurcation for lower laser intensities, while at higher laser intensities a homoclinic connection is observed.
Bifunctional molecular glass for efficient photorefractive material
Authors: Ogino Kenji , Park Sang-Hun , Sato Hisaya
Published: July 2002

Two bifunctional succinates have been prepared as molecular photorefractive materials, which contain a hole-transporting triphenylamine moiety and an electro-optically active chromophore. The synthesized succinates formed stable amorphous glasses at room temperature. Succinate with 4-dicyanovinylaniline moiety as an electro-optic chromophore showed excellent photorefractive properties, i.e., 65% of diffraction efficiency, and 188 cm−1 of two-beam coupling gain at 60 V/μm, which are comparable to that observed in one of the most efficient photorefractive polymers.
Metal/ferroelectric/insulator/semiconductor structure of Pt/SrBi2Ta2O9/YMnO3/Si using YMnO3 as the buffer layer
Authors: Choi Kyu-Jeong , Shin Woong-Chul , Yang Jung-Hwan , Yoon Soon-Gil
Published: July 2002

The ferroelectric SrBi2Ta2O9 (SBT) and YMnO3 buffer layers for the metal/ferroelectric/ insulator/semiconductor (MFIS) structure were deposited using pulsed-laser ablation and metalorganic chemical vapor deposition, respectively. Memory windows of the MFIS structure were in the range of 0.3–1.5 V when the gate voltage varied from 2 to 6 V. There were no reactions between ferroelectric SBT and Si in the MFIS structure annealed at 900 °C. The YMnO3 buffer layer plays an important role in alleviating the interdiffusion between elements of SBT and Si. The proposed MFIS structure of Pt/200 nm–SBT/25 nm–YMnO3/Si is attractive for nondestructive read-out ferroelectric random access memory applications.
Nonresonant femtosecond second hyperpolarizabilities of intramolecular charge-transfer molecules with great excited- and ground-state dipole-moment differences
Authors: Yamashita Mikio , Kikuma Shinji , Yamaoka Yoshihisa , Murakami Hidetoshi , Morita Ryuji , Shigekawa Hidemi
Published: July 2002

The femtosecond second hyperpolarizability due to the nonresonant electronic polarization for two intramolecular charge-transfer molecules, 6-propionyl-2-dimethylamino naphthalene and 2-anilinonaphthalene-6-sulfonic acid which possess the great permanent dipole-moment difference between the excited state and the ground state, is obtained from the measurement of the ultrafast change in refractive index using a time-resolved interferometer. It is found that the second hyperpolarizability increases parabolically from 5×10−34 to 4.3×10−32 esu with increasing the dipole-moment difference from 7.7 to 40 D, and this quantitative relationship is well explained by a quantum-mechanical equation describing the electronic second hyperpolarizability of one molecule with the permanent dipole-moment difference.
Selective distribution of arsenic precipitates in low-temperature-grown III–V heterostructures
Authors: Chang M. N. , Yeh N. T. , Lu C. M. , Hsieh K. C. , Chyi J.-I.
Published: July 2002

We have investigated arsenic precipitation in arsenide heterostructures grown at low temperature by molecular beam epitaxy. In these heterostructures, both doping and bond strength are found to affect arsenic precipitation during thermal annealing. For GaAs/Al0.3Ga0.7As multiple quantum wells, where GaAs is Be doped and Al0.3Ga0.7As is Si doped, arsenic precipitates preferentially appear in the GaAs region after annealing. For In0.1Ga0.9As/GaAs/In0.1Al0.9As heterostructures, whether they are doped or not, arsenic precipitates always tend to condense in the In0.1Ga0.9As region, indicating that the bond strength effect dominates the process of arsenic precipitation over the doping effect.
Exchange-biasing asymmetric spin valves using a pulsed current
Authors: Sankar S. , Beach R. S. , Berkowitz A. E.
Published: July 2002

The asymmetric spin valve features a quiescent state in which the two ferromagnetic layers are antiparallel for any spacer thickness. It consists of AFM/FM/spacer/FM/AFM, where AFM is an antiferromagnet and FM is a ferromagnet. By cooling through the Néel temperature (TN) with a large current flowing, the FM layers are exchange biased in antiparallel directions. Current along is found to be sufficient to heat the device above TN. Devices with a 45 Å spacer layer were exchanged biased using a steady dc current which is turned down after T>TN; devices with thinner spacer layers (20 and 30 Å) were destroyed by a steady dc current due to excessive heating.
A deep semiconductor defect with continuously variable activation energy and capture cross section
Authors: Lourenço M. A. , Ng Wai Lek , Homewood K. P. , Durose K.
Published: July 2002

A deep level with a continuously varying activation energy and capture cross section has been observed in CdS/CdTe thin-film solar cells. Given that the activation energy and capture cross section of a level are usually considered to be a unique identifier or signature for a particular deep level, this has important implications for the application of deep-level transient spectroscopy and related techniques for the characterization of deep levels in this and similar systems. We believe this phenomenon explains the well-known but poorly understood efficacy of CdCl2 treatment for CdS/CdTe thin solar cells.
Azimuthal anchoring energy of a chiral nematic in cylindrical cavities
Authors: Aloe R. , Nicotera I. , Golemme A.
Published: July 2002

We report on the determination of the azimuthal anchoring energy for a chiral nematic in elongated droplets obtained by phase separation in a polyvinylidene fluoride matrix. H-NMR2 techniques were used to establish the director configuration in samples with different chirality and different sizes of the quasicylindrical cavities. Minimization of the free energy, including surface, elastic, and field terms, allowed us to measure for the anchoring energy a value of Wφ≈10−4 J/m2.
Recrystallization of carbon–aluminum ion coimplanted epitaxial silicon carbide—evidenced by room temperature optical measurements
Authors: Feng Z. C. , Chua S. J. , Tone K. , Zhao J. H.
Published: July 2002

Effects of carbon (C)-aluminum (Al) coimplantation and annealing of epitaxial n-type 6H polytype silicon carbide (6H–SiC) have been studied by Raman scattering, photoluminescence (PL), and optical transmission (OT), measured at room temperature. The amorphization and damage of 6H–SiC due to ion implantation are observed. The recovery of the 6H–SiC crystallinity by a high temperature annealing at 1550 °C for 30 min after C–Al implantation has been confirmed from the Raman, PL, and OT measurements. Evidences of the recrystallization of C–Al coimplanted epitaxial 6H–SiC are obtained nondestructively by these three optical techniques.
Fiber-like lanthanum tungstate crystal for efficient stimulated Raman scattering
Authors: Urata Yoshiharu , Wada Satoshi , Tashiro Hideo , Fukuda Tsuguo
Published: July 2002

A solid-state Raman material, fiber-shaped single crystal lanthanum tungstate (LWO) has been successfully grown by the micro-pulling-down method. The fiber-shaped LWO crystals yielded intense Stokes pulses with an energy shift of 940 cm−1. In stimulated Raman conversion, a conversion efficiency of 6.8% (internal efficiency of 37%) to the first Stokes wave was achieved.
A photoconductive model for superior GaAs THz photomixers
Authors: Brown E. R.
Published: July 2002

Theoretical methods are used to evaluate the THz output from photomixer structures consisting of interdigitated electrodes and planar antennas on top of a low-temperature-grown GaAs layer. Consistent with experiment, the THz power from a standard photomixer is found to be limited by low external quantum efficiency (∼1%). This arises primarily from low photoconductive gain, which is attributed to a long transit time (between electrodes) for the majority of photocarriers generated in the structure. The modeling is then applied to an improved structure containing a thinner absorbing layer (≈0.34 μm for λ=0.85 μm pump) with a dielectric mirror below it to induce resonant-cavity absorption near the surface where the gain is higher. Through increased gain and absorptivity, the model predicts ≈7× greater THz output for the same optical pump power.
An isolated silicon single chain end-grafted onto a substrate surface
Authors: Furukawa K. , Ebata K. , Matsumoto N.
Published: July 2002

We report atomic force microscopy images of one-dimensional silicon chains (polysilanes) individually bonded to a substrate surface [quartz glass (SiO2), sapphire (Al2O3), and Si(111)]. The sample was prepared by a one-to-one chemical reaction between a reactive anchor of alkylbromide on the surface and a polysilanyl lithium. We observed dot images with variable densities which depended on the reactive anchor density. Each dot, with a diameter of about 20 nm and a height of about 5 nm, corresponded to an isolated single polysilane molecule with a collapsed structure typical of usual end-grafted polymers under poor solvent conditions.
A 3×3 millimeter-wave micromachined imaging array with superconductor–insulator–superconductor mixers
Authors: de Lange Gert , Konistis Konstantinos , Hu Qing
Published: July 2002

Results from a 3×3 micromachined millimeter-wave focal-plane imaging array with superconducting tunnel junctions as mixing elements are presented. The array operates in a frequency range of 170–210 GHz. The imaging array chip uses relatively large-area 9 μm2 and low-impedance (4–5 Ω) junctions. Integrated tuning structures are implemented to match the devices to the antenna impedance. Noise measurements yielded the lowest double-sideband noise temperature of 52 K (at 190 GHz) from the central element. The lowest noise temperatures from the off-axis elements are in the range of 60–100 K, with a uniform bandwidth of 30 GHz. Antenna beam patterns with an essentially Gaussian profile have been measured for on- and off-axis elements.
Electrical method of monitoring percolation and abrasion of conducting spheres due to shear flow of a dense suspension in a narrow gap
Authors: Mannan S. H. , Hutt D. A. , Whalley D. C.
Published: July 2002

This letter describes a method for studying the behavior of rigid particles in a dense suspension when they are forced into contact during flow within a narrow gap. The particles form transient percolating networks spanning the boundary walls, and will be crushed together. The method involves measuring the dc electrical resistance across the gap. The suspension (e.g., solder paste) consists of electrically conducting particles suspended in an insulating fluid. The electrical resistance drops when the particles are in contact with each other and the walls, and the insulating films on the surface of the conductors have been broken through. The results show a dramatic change in behavior as the ratio of gap to particle diameter is varied.
Thermal conveyers
Authors: Borromeo M. , Marchesoni F.
Published: July 2002

A tunable noise rectifier is construed in which the net output current results from the interplay of equilibrium thermal noise and a pulsated amplitude modulation propagating along a periodic potential (thermal conveyer). The transport efficiency of such a device attains its maximum for an optimal value of the temperature and the pulse speed. A thermal conveyer whose modulation parameters depend on the output current, may operate as an active noise rectifier for an appropriate setting of the control parameters.
Noise in slow saturable absorber mode-locked semiconductor lasers
Authors: Dubbeldam J. L. A. , Lenstra D.
Published: July 2002

A theoretical investigation of the influence of noise in a passively mode-locked semiconductor laser with a slow saturable absorber is presented. Difference equations for the pulse energy and jitter are derived. We find that noise leads to increased pulse durations and considerable jitter. The influence of noise, for systems with and without self-phase modulation and group velocity dispersion, on the pulse energy and stability regions is discussed.
Ultra-high-finesse IV–VI microcavities for the midinfrared
Authors: Schwarzl T. , Heiß W. , Springholz G.
Published: July 2002

IV–VI semiconductor-based midinfrared microcavities with very high-quality factors were grown by molecular-beam epitaxy. The structures consist of PbTe/EuTe Bragg mirrors with three to five layer pairs rendering reflectivities in excess of 99.7%. The PbTe resonator layer between the reflectors has an optical length of λ/2, which yields a first-order cavity. The transmission spectra of the microcavities show a very narrow Lorentzian-shaped Fabry–Perot resonance at 1877 cm−1 (λ=5.32 μm) with a full width at half maximum of 0.63 cm−1 78 μeV. This corresponds to an ultrahigh effective cavity finesse of 1700.
Observation of critical gate oxide thickness for substrate-defect related oxide failure
Authors: Bearda Twan , Houssa Michel , Mertens Paul W. , Vanhellemont Jan , Heyns Marc
Published: July 2002

The presence of crystal originated particles in silicon substrates leads to gate oxide failures in metal–oxide–semiconductor devices. A nonlinear relationship is known to exist between the oxide defect density and the oxide thickness, but the mechanism behind this remains unclear. In this work, we evaluate the gate oxide integrity for oxide thicknesses ranging from 2.5 to 26.5 nm. The results show no appreciable oxide degradation below an oxide thickness of approximately 5 nm; above this threshold value, the defect density depends strongly on the presence of crystal originated particles. Oxide thinning is unlikely to be responsible for this behavior.
A method of highly efficient hydrolyzation oxidation of III–V semiconductor lattice matched to indium phosphide
Authors: Koley B. , Johnson F. G. , King O. , Saini S. S. , Dagenais M.
Published: July 2002

We have demonstrated a method of efficient wet oxidation process for devices grown on indium phosphide. It was found that oxidation of a strain compensated InAs/AlAs short-period superlattice grown on InP proceeds at a rate of 0.28 μm/min. An edge-emitting laser using current confinement provided by the oxide has been fabricated. This method might be also well suited for long wavelength vertical cavity surface emitting laser application.
Electroabsorption and retardation due to intersubband transitions in coupled quantum wells
Authors: Kapon R. , Cohen N. , Sa’ar A. , Thierry-Mieg V. , Planel R.
Published: July 2002

Electro-optical modulation due to intersubband transitions in a coupled quantum well structure is experimentally studied. By using an appropriate set of cross/parallel polarizer-analyzer measurements, we were able to resolve the contribution of electroabsorption and electroretardation to the overall modulation of the infrared light. Fitting the experimental results to a simple model that allows the quantum properties of the structure to vary with the applied electric field revealed that the most significant contribution to the modulation comes from linewidth broadening of the optical transition. We attribute this effect to a larger degree of localization of the envelope states near the interfaces that give rise to a faster dephasing time due to elastic scattering.
Influence of target–substrate angle on the elemental concentration of c-axis YBa2Cu3O7−x thin films
Authors: Pugel D. E. , Greene L. H.
Published: July 2002

The thermalization processes in sputtering suggest a spatial dependence of elemental concentration in the sputter plume. A variety of analysis techniques demonstrate that c-axis films grown at angles which deviate from the standard off-axis geometry produce nominally YBa2Cu3O7−x in the bulk with dramatic changes in the surface morphology and deposition rate. In addition to the common materials characterization techniques of scanning electron microscopy, x-ray diffraction, transport measurements, and conventional Rutherford backscattering spectrometry (RBS), angle-dependent RBS is employed to probe surface inhomogeneities of films grown at target–substrate angles away from the standard off-axis position.
High breakdown voltage symmetric double δ-doped In0.49Ga0.51P/In0.25Ga0.75As/GaAs high electron mobility transistor
Authors: Lin Y. S. , Hsu W. C. , Wu C. H. , Lin W. , Hsu R. T.
Published: July 2002

A double δ-doped In0.49Ga0.51P/In0.25Ga0.75As/GaAs high electron mobility transistor has been successfully fabricated by metalorganic chemical-vapor deposition. Improved electron mobility as high as 5410 (19 200) cm2/V s at 300 (77) K along with turn-on voltage as high as 2.3 V and reverse gate-to-drain voltage up to 75 V are achieved. These characteristics are attributed to the use of the δ-doped, undoped InGaP Schottky layer, and undoped GaAs setback layer. Moreover, the parasitic parallel conduction can be eliminated. The activation energy is also deduced.
Blue-green variable light-emitting diode based on organic–molecule-doped polymer
Authors: Xu Chunxiang , Cui Yiping , Shen Yingzhong , Gu Hongwei , Pan Yi , Li Yinkui
Published: July 2002

Monolayer organic light-emitting diodes based on the organic molecule [(3,4-dimethoxybenzyldehycle-2′-hydroxy naphthylimine)dimethyl gallium]-doped [poly(2-mehtyoxy-5-ethyloxy)-4-di-(2-methyoxy-5′-octaoxy)phenylene vinylene] have been fabricated by a spin-coating method. Color variation from green to blue has been observed. The results have been attributed to the variation of the recombination zone and the charge transfer between the materials.
Grain growth in thin-film strontium sulfide electroluminescent phosphors
Authors: Xin Y. B. , Summers C. J.
Published: July 2002

A comprehensive study of grain growth in strontium sulfide (SrS) thin-film electroluminescent (TFEL) phosphors is reported. It is suggested that the grain growth during annealing is influenced by the migration of the dopant ion from the grain boundary into a lattice position. The difference in the free energy of formation between SrS and the sulfur compounds of the dopants changes the activation energy for the grain boundary movement and promotes the grain growth. This understanding has successfully been used to explain the grain growth phenomena observed in SrS TFEL phosphors with different dopants, such as Cu, Ag, Mn, and Ga.
Amplified stain-rate dependence of deformation in polymer-dispersed liquid-crystal materials
Authors: Cairns Darran R. , Genin Guy M. , Wagoner Amy J. , Briant Clyde L. , Crawford Gregory P.
Published: July 2002

The mechanical properties of polymer-dispersed liquid crystals (PDLCs) are investigated to elucidate their fundamental microstructural and mechanistic underpinnings, and overall structural integrity under deformation. High strain-rate loading experiments and quasistatic compression tests on PDLC materials reveal an amplified strain-rate dependence relative to the matrix material. A finite-element micromechanical model of PDLC materials explains this behavior in terms of strain-rate concentrations at the equators of the spherical liquid-crystal droplets. The model also predicts a weak dependence of the aspect ratio of deforming liquid-crystal droplets on their volume fraction.
Macroscopic residual stress in chemical-vapor-deposition free-standing diamond films by x-ray diffraction analyses
Authors: Durand O. , Olivier J. , Bisaro R. , Galtier P. , Krüger J. K. , Brierley C. J. , Kennedy G. R.
Published: July 2002

We present a structural analysis of plasma-assisted chemical-vapor-deposition self-supporting diamond films with different qualities, black, gray and white. Experimental results show a weak fiber texture and a large average grain size at the growth side, consistent with the model usually used to described chemical-vapor-deposition growth with a preferred orientation of the grains. Macroscopic residual stresses have been determined by means of x-ray measurements, through the “sin2 ψ” method. Compressive and tensile stresses are reported at both faces of the samples. We show that stresses present at both growth face and nucleation face cannot be explained by the usual models involving the average grain size. For some samples, a closer analysis of the sin2 ψ curves reveals a shift from the linear behavior. This effect comes from various stress states and/or lattice parameters between the grains belonging to the texture and the randomly oriented grains.
The ferroelectricity of perovskite-type oxides with alkylamine interlayer
Authors: Zhong Zhaohui , Ding Weiping , Chen Yi , Chen Xiaoyuan , Zhu Yongyuan , Min Naiben
Published: July 2002

The ferroelectricity of layer perovskite-type oxides intermittent with alkylamine, synthesized by hydrothermal method, has been reported. Ferroelectric hysteresis loops were observed in these newly synthesized powder crystals, which were pressed into wafers with platinum electrodes deposited by a pulsed laser. Element analysis shows 69% cations between two layers were exchanged into alkyl ammonium. X-ray powder diffraction pattern, infrared spectra, Raman spectra, and electron microscopy were used to characterize the samples. The results show that perovskite layer contributes to the ferroelectric property. So-synthesized samples may make up a new group of materials with potential use especially in the field of fatigue-free ferroelectricity.
Comparison of the quantum efficiencies of interwell and intrawell radiative transitions in quantum cascade lasers
Authors: Donovan K. , Harrison P. , Kelsall R. W.
Published: July 2002

A theoretical study has been made to compare the quantum efficiencies of interwell and intrawell radiative transitions in quantum cascade lasers based on AlxGa1−xAs/GaAs technology. Radiative and nonradiative intersubband transition rates were calculated for a range of temperatures between 4 and 300 K at an applied electric field of 4 kV cm−1 for structures designed to emit in both mid-infrared and far-infrared frequency ranges. It is found that the internal quantum efficiency of mid-infrared devices is a maximum for diagonal, or interwell, transitions. Conversely, for the far-infrared devices, the quantum efficiency is a maximum for vertical, or intrawell, transitions.
Soft x-ray emissions from laser plasma of cryogenic mixture targets
Authors: Shimoura Atsushi , Mochizuki Takayasu , Miyamoto Shuji , Amano Sho , Uyama Tadao
Published: July 2002

Soft x-ray spectral radiation from Xe–CO2 mixture cryogenic targets with a Xe mole fraction of 0% (pure CO2) to 100% (pure Xe) irradiated by a 1 μm pulse laser at a laser intensity IL of 0.3–1.0×1012 W/cm2 has been observed. The x-ray conversion efficiency per Xe mole fraction was found to have maximum values at the Xe fractions of 10% for IL=6.0×1011 W/cm2 and 5% for IL=1.2×1012 W/cm2, which were about five and ten times as large as that in a pure Xe target, respectively. The x-ray conversion efficiencies in the cryogenic mixture targets at Xe fractions of 10%–40% were about 1.3 %/sr/nm for λ=10.8 nm and IL=1012 W/cm2, which was as high as that in a pure Xe cryogenic target. The physical mechanism behind this enhanced emission is discussed.
Strong reduction of interchain interaction by bridged chain substitution in luminescent phenylenevinylene thin films
Authors: Chiavarone Luca , Di Terlizzi Marco , Scamarcio Gaetano , Babudri Francesco , Farinola Gianluca M. , Naso Francesco
Published: July 2002

The strong reduction of interchain interaction in poly-(2,5-dialkoxy-1,4-phenylenevinylene) films with a 2,5 O–(CH2)12–O closed chain substitution (bridged PPV), engineered to reduce the molecular packing in the solid state, is reported. Evidence of this effect unambiguously stems from the systematic comparison between the optical properties of a series of dialkoxy-PPV derivatives with bridged and open chain side groups. Reduction of interchain energy relaxation channels explains the close similarity between the optical spectra of bridged-PPV films and solutions, the higher photoluminescence efficiency and the lower threshold for the observation of spectral line narrowing in the solid state.
Two-phonon absorption spectra in wurtzite GaN
Authors: Azuhata Takashi , Shimada Kazuhiro , Deguchi Takahiro , Sota Takayuki , Suzuki Katsuo , Chichibu Shigefusa , Nakamura Shuji
Published: July 2002

Two-phonon absorption spectrum was measured for wurtzite GaN and was compared with two-phonon density of states of zinc-blende GaN obtained by lattice-dynamical calculations with an adiabatic bond-charge model. All structures in the spectrum were well explained by phonon structures of zinc-blende GaN. As a method to analyze two-phonon absorption spectra of wurtzite materials, proposed was the utilization of phonon dispersion curves of corresponding zinc-blende modifications, and the method was found to be useful.
Growth of high quality, large grain size, highly oriented diamond on Si (100)
Authors: Janischowsky K. , Stammler M. , Stöckel R. , Ley L.
Published: July 2002

Microwave and hot filament chemical vapor deposition processes were combined to deposit highly oriented and textured diamond films on Si (100). The sequential growth process yields closely packed crystallites with (100) surfaces that show no grain boundaries over areas of up to 60 000 μm2 by scanning electron microscopy. The diamond crystallites have the same orientation as the Si (100) substrate and their orientational order and surface quality as measured by low energy electron diffraction is comparable to that of single crystal diamond. Micro-Raman spectroscopy confirms the exceptional quality of the film surface by the complete absence of a luminescence background as well as the absence of spectral features attributed to nondiamond carbon phases.
Thermal relaxation processes probed by intersubband and inter-valence-band transitions in Si/Si1−xGex multiple quantum wells
Authors: Adoram B. , Krapf D. , Shappir J. , Sa’ar A. , Levy M. , Beserman R. , Thomas S. G. , Wang K. L.
Published: July 2002

Thermal relaxation processes due to strain relaxation and Si/Ge interdiffusion were investigated in pseudomorphic p-type SiGe/Si quantum wells using infrared-polarization-resolved absorption spectroscopy. The samples were annealed from room temperature up to 1060 °C and intersubband transitions between the lowest heavy-hole states and inter-valence-band transitions between heavy-hole and spin-split-off hole states were utilized to probe thermal activation processes. The strain relaxation process is activated at temperatures above 750 °C and causes a decrease of the intersubband absorption and an increase of the inter-valence-band absorption. At temperatures above 940 °C, we found that a second process of Si/Ge interdiffusion causes a reduction of all absorption lines in the spectrum. We proposed a simple model that provides a qualitative explanation to the above results.
Dielectric properties of metal-organic chemical vapor deposited highly textured Pb(ScTa)1−xTixO3 (x=0–0.3) relaxor ferroelectric thin films on LaNiO3 electrode buffered Si
Authors: Lin C. H. , Lee S. W. , Chen Haydn , Wu T. B.
Published: July 2002

Highly (100) textured Pb(ScTa)1−xTixO3 (x=0–0.3) thin films were grown on LaNiO3/Pt/Ti electrode-coated Si substrate using metal-organic chemical vapor deposition at 685 °C. Ti addition was introduced to modify the dielectric properties. Diffuse phase transition, typical of relaxor ferroelectrics was noticed. As Ti content increased from 0% to 30%, the phase transition temperature (Tmax) gradually shifted from −10 to 120 °C with the dielectric constant at Tmax increased from 1397 to 1992 (1 kHz). Loss tangent values are generally below 0.025.
Demonstration of a three-dimensional simple-cubic infrared photonic crystal
Authors: Zavieh Lisa , Mayer Theresa S.
Published: July 2002

This letter reports on the use of nonselective dry and selective wet etching to fabricate a gallium arsenide (GaAs) based three-dimensional infrared photonic crystal with a simple-cubic lattice structure. A two-and-one-half-period photonic crystal fabricated using this procedure demonstrated a drop in transmission of approximately 10 dB at a center wavelength of 12 μm for normally incident angles. A shift in the long-wavelength shoulder from 16 to 15 μm was observed as the incident infrared beam was varied from normal to oblique incidence. The measured drop in transmission agrees well with the band gap predicted theoretically for this simple-cubic structure.
High-speed operation of gain-switched midinfrared quantum cascade lasers
Authors: Paiella Roberto , Capasso Federico , Gmachl Claire , Bethea Clyde G. , Sivco Deborah L. , Baillargeon James N. , Hutchinson Albert L. , Cho Alfred Y.
Published: July 2002

We report on a simple technique for the generation of short pulses of midinfrared (5 and 8 μm) radiation, based on gain-switched quantum cascade lasers. In particular, an integrated step-recovery diode source (comb generator) is used to drive the lasers, properly packaged for high-speed operation. Using a fast HgCdTe detector, we measure optical pulses with duration as short as 200 ps, broadened by the detector response time, and peak power of a few tens of mW. The maximum operating temperature of these gain-switched sources is approximately 120 K.
Heavy Si doping in AlGaAs near modulation-doped heterointerfaces
Authors: Sasajima Yuichi , Hata Masahiko
Published: July 2002

We propose that the local Fermi-level modulation that occurs at heterojunctions enables the achievement of a higher carrier concentration in a limited thin layer than that can be achieved in a thick layer. We studied heterojunctions consisting of Si-doped AlGaAs (Al=20%) (AlGaAs:Si)/InGaAs (In=20%) grown by metalorganic chemical vapor deposition to demonstrate effectiveness of our doping method. The thickness and doping concentration of the AlGaAs:Si were designed carefully not to form a neutral region in the structure. We obtained a maximum electron concentration Nd=2.4×1019 cm−3 at 300 K in AlGaAs:Si; this value is about seven times higher than that reported for AlGaAs:Si so far. We believe that the AlGaAs/InGaAs heterojunction positions the Fermi level in the AlGaAs:Si (near the heterojunction) far from the conduction-band minimum, and that this effectively suppresses creation of compensation centers in AlGaAs:Si, then all the Si donors in AlGaAs:Si are activated.
The effect of implantation, energy, and dose on extended defect formation for MeV phosphorus implanted silicon
Authors: Jasper Craig , Hoover Allen , Jones Kevin S.
Published: July 2002

The effect of dose and energy on postannealing defect formation, for high energy (MeV) phosphorus implanted into epitaxially grown silicon, has been studied by etch pits and transmission electron microscopy (TEM). The phosphorus dose was varied from 1×1013 to 5×1014 cm−2 and the energy was varied from 180 to 5000 keV. After implantation, the wafers were processed through subsequent annealing cycles which simulates a typical advanced complementary metal–oxide–semiconductor process to understand the formation of the defects in the near surface and projected range. For phosphorus energies above 500 keV, the threading dislocation density (TDD), increases dramatically with increasing dose from below the minimum detection limit (5×103 cm−2) at a dose of 1×1013 cm−2 to a maximum above 1×106 cm−2 for a dose of 1×1014 cm−2. However, with further increases in dose, the TDD decreases back close to the minimum detection limit. Plan-view TEM suggests that with increasing dose, the formation of extended defects at the projected range reduces the TDD. For a fixed dose of 1×1014 cm−2, the TDD exhibits a superlinear increase of nearly 3 orders of magnitude as the implant energy is increased from 180 to 2000 keV. With further increases in implant energy, the TDD saturates at a value around 2×106 cm−2. The marked effect of dose and energy on the TDD can be partially understood from homogeneous nucleation theory.