bluuebunny/crossref_metadata_2025 huggingface dataset:
Metal-grating-outcoupled, surface-emitting distributed-feedback diode lasers
Authors: Kasraian Masoud , Botez Dan
Published: July 2002

The theoretical analysis of antiphase, surface-emitting, complex-coupled, distributed feedback (SE-CC-DFB) lasers is presented. The specific configuration chosen for analysis is relatively simple: a metallic second order grating placed atop a diode-laser structure. This type of SE-CC-DFB structure can be fabricated by a lift-off and evaporation process; can operate in a single-lobed, orthonormal beam with a rather uniform near-field intensity pattern, and external differential quantum efficiency, ηd, values in excess of 30%. The dependence of the gain threshold on grating duty cycle for both the symmetric and antisymmetric (longitudinal) modes is presented and discussed. The external differential quantum efficiency for the symmetric mode is found to steadily increase with grating length at the expense of the degree of near-field-pattern uniformity.
A gratingless wavelength stabilized semiconductor laser
Authors: Pezeshki Bardia , Agahi Farid , Kash Jeffrey A.
Published: July 2002

A single frequency laser structure is obtained by coupling a high order mode of a semiconductor waveguide to a low index polymer waveguide. The device does not require a grating or regrowth, emits in a mode compatible with optical fibers, and may be immune to catastrophic mirror damage. The epilayers of the semiconductor waveguide use quarterwave reflectors to support a mode with a low enough effective index to phase match to the polymer waveguide. The coupling between the two waveguides is highly frequency selective and therefore stabilizes the wavelength. Preliminary structures emit in a single longitudinal and spatial mode, have 30 dB of sidemode suppression, and emit about 6 mW into a fiber compatible mode.
Caterpillar-type piezoelectric d33 bimorph transducer
Authors: Kugel V. D. , Chandran Sanjay , Cross L. E.
Published: July 2002

A piezoelectric bimorph transducer utilizing piezoelectric d33 coefficient was developed. This bimorph consists of piezoelectric segments bonded by a polymeric agent and was fabricated by a dicing and layering technique. The transducer has superior piezoelectric characteristics compared to standard piezoelectric d31 bimorphs. Piezoelectric coefficients, electrical admittance, mechanical compliance, and losses of the actuator were found to increase with increasing driving electric field.
Epitaxial Pb(Zr0.53Ti0.47)O3/LaNiO3 heterostructures on single crystal substrates
Authors: Yu Tao , Chen Yan-Feng , Liu Zhi-Guo , Xiong Si-Bei , Sun Li , Chen Xiao-Yuan , Shi Lian-Je , Ming Nai-Ben
Published: July 2002

Epitaxial near-stoichiometric ferroelectric Pb(Zr0.53Ti0.47)O3 thin films were fabricated on epitaxial metallic LaNiO3 electrodes deposited on (001) SrTiO3 and (001) LaAlO3 single crystal substrates by pulsed laser ablation. The P–E hysteresis loop of PZT in the trilayer of Ag/PZT/LNO/STO was measured using the Sawyer–Tower circuit. The remnant polarization Pr and coercive field Ec at room temperature were 30 μC/cm2 and 69.3 kV/cm (peak-to-peak voltage=30 V, 50 Hz), respectively.
Light emission from a silicon quantum well
Authors: Steigmeier E. F. , Morf R. , Grützmacher D. , Auderset H. , Delley B. , Wessicken R.
Published: July 2002

We compare the photoluminescence (PL) properties of silicon (Si) single quantum well structures, consisting of an either amorphous or crystalline Si layer of 3 nm thickness, embedded between silicon–nitride layers. These structures are grown by plasma-enhanced chemical vapor deposition on Si substrates. After crystallization of the originally amorphous Si layers and passivation by hydrogen, strongly polarized PL is observed in the entire visible spectrum. In contrast, a reference structure without the 3 nm silicon layer, but otherwise identical, shows PL in the red and infrared only, but also strongly polarized. Thus, the PL in the blue and green part of the spectrum comes from recombination via Si quantum well states, while the red and infrared PL is due to states at the interface between crystalline Si and silicon–nitride.
Monolayer epitaxy of GaAs at 650 °C by metal–organic chemical-vapor deposition with surface photoabsorption monitoring
Authors: Kim Y. D. , Nakamura F. , Yoon E. , Forbes D. V. , Coleman J. J.
Published: July 2002

We report monolayer-by-monolayer epitaxy of GaAs at 650 °C using surface photoabsorption (SPA) to monitor growth. Our results show, as confirmed by photoluminescence measurements, the possibility of growing highly accurate quantum well heterostructures by metal–organic chemical-vapor deposition at conventional growth temperatures. In addition, we observe a continuous increase of the SPA signal during trimethylgallium exposure that cannot be explained by present growth models.
Determination of crystallite propagation in laser annealed amorphous silicon by normal incidence spectral reflectance
Authors: Williams G. , Sands D. , Geatches R. M. , Reeson K. J.
Published: July 2002

Analysis of normal incidence spectral reflectivity of excimer laser annealed α-Si:H shows that the annealed material can be modeled as a stratified system comprising a large-grained polycrystalline layer, a fine grained polycrystalline layer, and residual amorphous silicon in agreement with transmission electron microscopy. Optically, the large-grained poly-Si behaves as single-crystal silicon and the fine-grained material is modeled, using effective medium theory, as a mixture of single-crystal silicon and amorphous silicon.
Four-wave mixing in bulk GaAs microcavities at room temperature
Authors: Buhleier R. , Bardinal V. , Collet J. H. , Fontaine C. , Hübner M. , Kuhl J.
Published: July 2002

We studied pico- and femtosecond degenerate four-wave mixing in bulk GaAs Fabry–Pérot microcavities at room temperature. For wavelengths below the GaAs band edge, a cavity with a finesse of approximately 20 yields an enhancement of the diffracted signal by more than two orders of magnitude as compared to a cavityless GaAs layer of the same thickness (685 nm). The cavity-enhanced nonlinearity of the interband transition results in a diffraction efficiency η≊0.5% for 150 pJ pulses with a duration of 900 fs at 878 nm, being 400 times larger than that for the bare GaAs reference sample.
A field-sensitive photoconductive probe for sampling through passivation layers
Authors: Hwang Jiunn-Ren , Lai Richard K. , Nees John , Norris Ted , Whitaker John F.
Published: July 2002

A field-sensitive photoconductive sampling technique has been demonstrated in measurements performed through an insulating layer without the need for conductive contact. Sampled signals are sensed by a virtual-ground, floating-gate amplifier without draining charge from the device under test or the photoconductive switch. The minimum detectable signal is 2.5 μV/Hz1/2 with a spatial resolution of 7 μm, while the sampling bandwidth is essentially that observed using photoconductive sampling with a conductive contact to the device under test. The photovoltaic and shot current noise are negligible in comparison with the lock-in amplifier noise since the current flowing in this high-impedance, floating-gate probe is negligible.
Wide bandwidth (100) GaAs/fluorides quarter-wavelength Bragg reflectors grown by molecular beam epitaxy
Authors: Shi Z. , Zogg H. , Müller P. , Jung I. D. , Keller U.
Published: July 2002

Broadband quarter-wavelength Bragg reflectors that consist of periodic stacks of fluorides (CaF2–BaF2–CaF2) and GaAs, centered at 1.4 μm, were grown by molecular beam epitaxy. Despite a total fluoride thickness as high as 720 nm, crack-free surface morphology was obtained. In this letter, we report a crack-free standard quarter-wavelength III–V semiconductor-fluoride Bragg reflector. With only three stacks, the bandwidth with reflectance above 95% is about 650 nm (1.15–1.80 μm), while, near the center wavelength, the reflectivity is as high as 99%. Both important wavelengths of 1.3 and 1.55 μm for optical communication are included in the very wide high reflectance plateau. These mirrors are expected to have wide applications for optical and optoelectronic devices.
Ring and stripe oxide-confined vertical-cavity surface-emitting lasers
Authors: Huffaker D. L. , Deng H. , Deng Q. , Deppe D. G.
Published: July 2002

Ring and stripe oxide-confined vertical-cavity surface-emitting lasers are studied. Interesting coupling effects are observed due to the nonzero propagation velocity of the optical mode in the plane of the cavity. The stripe geometries appear interesting due to the very low threshold and provide a convenient means for increasing the aperture size while maintaining uniform current pumping. The ring laser provides a means of obtaining well defined multiple spots in the far field.
Fundamental operation of single-flux-quantum circuits using coplanar-type high-T
c SQUIDs
Authors: Fuke Hiroyuki , Saitoh Kazuo , Utagawa Tadashi , Enomoto Youichi
Published: July 2002

We have fabricated coplanar type dc SQUIDs using NdBa2Cu3Oy superconducting thin films and operated fundamental single-flux-quantum (SFQ) circuits. The Josephson junctions were made by the narrow-focused ion beam irradiation technique. For a 145 μm wide and 10 μm long logic SQUID having a critical current of 105 μA and an inductive parameter (βL) of 28, a store and a restore of the flux quantum have been demonstrated at temperatures of 4.2–30 K. These operations were performed with an input pulsewidth of 5 ns (5 ns was the shortest input pulse width available from our function generating equipment). These results show experimentally the possibility of high speed operation in all high-Tc superconducting digital circuits.
The molecular beam epitaxial growth of InSb on (111)B GaAs
Authors: Michel E. , Kim J. D. , Javadpour S. , Xu J. , Ferguson I. , Razeghi M.
Published: July 2002

The molecular beam epitaxial growth of InSb on (111)B GaAs has been investigated. It was found that for a given Sb/In ratio, a higher growth temperature was required for the growth of InSb on (111)B GaAs compared to that on (001) GaAs. This difference has been attributed to the bonding characteristics of the (111)B and (001) surface. Once growth had been optimized, it was found that the material characteristics of (111)B InSb were almost identical to that of (001) InSb, i.e., independent of orientation. For example, the x-ray full width at half-maximum and 300 K mobility had the same absolute values for (111) InSb and (001)InSb and followed the same dependence with the sample thickness. Te was found to be a well-behaved n-type dopant for (111)B InSb.
Visible photo- and electroluminescence from electrochemically formed nanocrystalline Si thin film
Authors: Toyama Toshihiko , Matsui Tetsuyuki , Kurokawa Yasuhito , Okamoto Hiroaki , Hamakawa Yoshihiro
Published: July 2002

Visible photo- (PL) and electroluminescence (EL) were observed at room temperature from nanocrystalline Si (nc-Si) thin film; nc-Si was electrochemically formed in HF aqueous solution from boron doped microcrystalline Si (μc-Si) deposited by a rf plasma chemical vapor deposition method on a glass substrate with a SnO2 transparent conductive layer. From the scanning electron microscope images, the ‘‘pore’’ structure is not found on the surface of the nc-Si thin film. PL occurs with a broadband spectrum peaking at an energy around 1.7 eV and its spectral shape resembles that of conventional porous Si made from a crystalline Si substrate. The dependence of PL intensity on crystalline volume fraction in μc-Si implies that the quantum size effects operate in the emission process in nc-Si. Visible EL emission was observed in a p-i-n heterostructured diode consisting of the nc-Si and amorphous layers with the spectral peak energy of 1.8 eV.
Mechanisms of upconverted fluorescence in an Er3+ doped LiNbO3 single crystal
Authors: Ju J. J. , Kwon T. Y. , Yun S. I. , Cha M. , Seo H. J.
Published: July 2002

Two different upconversion mechanisms leading to green fluorescence in an Er3+ doped LiNbO3 crystal have been investigated with pulse laser excitations at the wavelengths of 1064 and 980 nm. In the case of the 1064 nm pump, the Er3+ ions become excited by the phase-matched second harmonic wave generated in the LiNbO3 crystal, whereas sequential two-photon absorption is mainly responsible for the excitation with the 980 nm pump. The second harmonic excitation is of an order of magnitude more efficient than the sequential two photon excitation in the upconversion of the near-infrared pump photons to the green fluorescence.
Secondary defect dissolution by voids in silicon
Authors: Raineri V. , Campisano S. U.
Published: July 2002

Clustering of point defects into dislocations as a consequence of ion implantation and annealing in silicon has been inhibited through the presence of cavities produced by helium ion implantation and located at depths up to 1 μm. We will show that annealing at 1200 °C will result in the complete absence of extended defects for the case of either partial damage produced by boron ion implantation or continuous amorphous layers produced by germanium implantation. The suppression of dislocation formation does not depend on the depth at which cavities are located, on their density and on the purity of the adopted silicon wafer. The results are interpreted on the basis of the measured efficiency of voids in the capture of interstitial silicon atoms.
A direct current piezoelectric effect in fluorinated ethylene-propylene copolymer due to space charge
Authors: Faria Roberto M.
Published: July 2002

A dc piezoelectric effect was observed in corona charged fluorinated ethylene-propylene membranes. After an appropriate thermal treatment the charge deposited on the sample surface penetrated the bulk material, with the charge centroid remaining at the center of the sample was indicated by heat pulse measurements. The charged sample responded to an applied pressure with a constant voltage signal or, if in short circuit, with a transient external electric current. This phenomenon was interpreted as being caused by a relative movement of the stored charges with respect to the material structure. A semiquantitative analysis based on this relative movement was carried out that allowed physical parameters such as the volumetric charge density and the longitudinal piezoelectric coefficient to be obtained.
Characterization of carbon nitride thin films prepared by dual ion beam sputtering
Authors: Fernández A. , Prieto P. , Quirós C. , Sanz J. M. , Martin J.-M. , Vacher B.
Published: July 2002

Carbon nitride thin films obtained by dual ion beam sputtering have been investigated by electron energy-loss spectroscopy (EELS), transmission electron microscopy, and Fourier transform infrared spectroscopy. The nitrogen content in the films depends on deposition conditions. A maximum value of N/C=0.8 has been achieved. A new peak at 286.7 eV energy loss in the C K-edge EELS spectra has been assigned to C=N bonds with C in the sp2 hybridization state. In addition, experimental evidences are presented of the formation of β-C3N4 crystallites embedded in a layer of a polymer like CNx amorphous phase. An evaluation of the experimental parameters that lead to the highest N content in the films is also included.
Surface morphology of laser deposited diamondlike films by atomic force microscopy imaging
Authors: Park Hwantae , Hong Young-Kyu , Kim Jin Seung , Park Chan , Kim Jae Ki
Published: July 2002

The surface morphologies of diamondlike carbon (DLC) films with atomic force microscopy (AFM) are reported. The films were prepared by laser ablation with tuning power densities range from 3×108 to 1×1010 W/cm2. For power densities above 2×109 W/cm2, the films reveal smooth surfaces with uniform shapes of nanometer sized carbon clusters (sp3 bonding) and retain the surface roughness of the silicon substrate. For power densities below that, graphitic films are formed, and the surface roughness increases with decreasing laser intensity. The present AFM studies confirm that there exists a clear correlation between surface morphologies and the degree of diamondlike qualities.
Strain-modulated epitaxy: A flexible approach to 3-D band structure engineering without surface patterning
Authors: Carter-Coman Carrie , Brown April S. , Bicknell-Tassius Robert , Jokerst Nan Marie , Allen Mark
Published: July 2002

Thin compliant growth substrates have been used to reduce the strain in lattice-mismatched overlayers during epitaxial growth. This letter reports a new thin compliant substrate technology which allows these thin substrates to be patterned on the bottom, bonded surface. This lateral strain variation (inverted stressor) in the growing film can be combined with the additional effects of strain-dependent growth kinetics to realize the lateral control of composition and thickness without any surface topography on the substrate. Initial demonstrations of the growth of InGaAs on GaAs bottom-patterned thin substrates are presented herein.
Improvement in low energy ion-induced damage with a low temperature GaAs capping layer
Authors: Chen Ching-Hui , Hu Evelyn L. , Mishra Umesh K. , Ibbetson James P. , Wu Xuehua , Speck Jim S.
Published: July 2002

A thin capping layer of annealed GaAs (∼210 Å) grown at low temperature (LT-GaAs) can effectively block incident ions from penetrating into the growth substrate. Ion-bombarded, multiple quantum well structures capped by an annealed LT-GaAs layer show a dramatic improvement in the photoluminescence, compared to samples capped with ‘‘normal’’ GaAs. The improvement appears to be correlated with the microstructures of the LT-GaAs, since the improvement is particularly notable for samples annealed at 600 °C. This improvement in low energy ion-induced damage is primarily the result of the reduced channeling of ions through the LT-GaAs layer. These results suggest a potential application of LT-GaAs in reducing ion damage and underscore the importance of the microstructure of arsenic precipitates in LT-GaAs layers.
High linear density written transitions in exchange isolated Pt/CoCrTa multilayer thin films
Authors: Liu Wen H. , Schouterden Kris , Mei Lin , Ho Kuoksan , Lairson Bruce M. , Payne Alexander P.
Published: July 2002

Multilayer Pt/CoCrTa thin-film structures have been prepared which display little intergranular exchange coupling and nearly 100% remanence in the perpendicular direction. Magnetic recordings of continuous square wave patterns have been made and characterized using an inductive contact recording transducer and by magnetic force microscopy. Written transitions appear to retain good fidelity at more than 300 000 transitions per inch. With exchange isolation of the grains, media noise becomes negligible relative to thermal noise from the recording system electronics. Analysis of magnetic force microscopy images yields a signal to integrated noise ratio of 17 dB at 309 000 transitions per inch written in a 4 μm wide track, which is comparable to a measured signal to total noise ratio of 8 dB at 350 000 reversals per inch measured using an inductive transducer at 100 in./s. These results are contrasted with observations on exchange coupled Pt/Co multilayers.
Scanned-probe lateral-force determination of fluid-dynamic effects near a solid surface in air
Authors: Drummond Roby M. A. , Wetsel G. C. , Wang C.-Y.
Published: July 2002

A calibrated method for the experimental determination of dynamic lateral force using a scanned probe in air has been applied to the measurement of force vs distance as the probe tip approaches a solid surface. The probe is a fused silica fiber vibrated with its axis perpendicular to the surface in a configuration commonly used for distance regulation in near-field scanned optical microscopes. Quantitative agreement of a fluid-dynamic model with the approach data demonstrates that the effects of fluids between the probe and the surface dominate the force on the probe in the optical far field. A two-layer fluid model indicates that fluid-dynamic effects must also be considered in lateral-force determination in the optical near field.
Tunable electron-hole gases in gated InAs/GaSb/AlSb systems
Authors: Drndic M. , Grimshaw M. P. , Cooper L. J. , Ritchie D. A. , Patel N. K.
Published: July 2002

Gated structures have been fabricated on the InAs/AlSb/GaSb system enabling the control of the relative electron and hole carrier densities in these type II crossed band gap structures. By using insulated gates, a wide gate voltage range, with very low leakage levels, is obtained, allowing the study of these systems from electron dominated transport through to hole dominated. Associated with this transition, a change from positive to negative transconductance is observed. Studies of the quantum Hall effect show features related to both electron and hole Landau level formation with the crossover from electron to hole dominated transport found to be a function of the perpendicular magnetic field.
Accelerated hole transfer by double-layered metallophthalocyanine thin film for effective electroluminescence
Authors: Tominaga Tsuyoshi , Hayashi Kohei , Toshima Naoki
Published: July 2002

An electroluminescent device was constructed using tris(8-hydroxyquinoline)aluminum as an emitting layer and metallophthalocyanine as a hole-transfer layer. When the metallophthalocyanine layer is sufficiently thin, the device shows a brightness of more than 1000 cd m−2. The device using double hole-transfer layers of two kinds of metallophthalocyanine exhibits a higher brightness than that using a single hole-transfer layer of the corresponding metallophthalocyanine. This phenomenon is well explained by the accelerated hole transfer in the double layer due to the construction of a “sequential potential field.”
Spreading of a void along a singular surface during electromigration: A failure mode
Authors: Chu X. , Bauer C. L. , Mullins W. W.
Published: July 2002

Previous treatments of void shape evolution during electromigration have been restricted to nonsingular void surfaces. We consider the lateral spreading of a void when its leading surface is a singular facet. The facet may nucleate at the leading surface of a void migrating within one grain or may develop when a singular surface is exposed by impingement of the void at a (transverse) grain boundary. Advance of the facet requires a source of steps that we assume to be absent; void spreading results. A stationary void shape is possible when a dimensionless parameter is less than a critical value (estimated), whereas above this value the void spreads indefinitely.
A thin film diamond p-channel field-effect transistor
Authors: Pang Lisa Y. S. , Chan Simon S. M. , Jackman Richard B. , Johnston Colin , Chalker Paul R.
Published: July 2002

A depletion-mode metal-insulator-semiconductor field-effect transistor has been fabricated from thin film polycrystalline diamond with a p-type (boron doped) channel and an insulating diamond gate. This device has been successfully operated at 300 °C displaying pinch off when in depletion and high levels of channel current modulation in enhancement. A transconductance value of 174 μS/mm has been measured, the highest reported value to date for this type of device.
Photocurrent self-oscillations in a direct-gap GaAs-AlAs superlattice
Authors: Ohtani Naoki , Hosoda Makoto , Grahn Holger T.
Published: July 2002

Undamped photocurrent self-oscillations have been observed in a direct-gap GaAs-AlAs superlattices. The oscillations in the MHz regime appear over a wide voltage range, where the time-averaged I-V characteristic exhibits a strong negative differential conductivity. The frequency distribution is strongly dependent on the applied voltage and the laser intensity.
Thermal and ion irradiation stability of direct current sputtered TiN/B–C–N multilayers
Authors: Fayeulle S. , Nastasi M. , Lu Y. C. , Kung H. , Tesmer J. R.
Published: July 2002

The response of TiN/B–C–N multilayers to vacuum annealing at 900 °C and to 300 keV argon irradiation is studied. Changes in composition, stress field, bilayer repeat length, and layered structure are reported. The modifications observed during thermal annealing are mainly related to the departure of nitrogen because of the initial high state of compressive stress. During irradiation, the viscous flow of atoms perpendicular to the stress field causes an increase of the bilayer repeat length and interdiffusion between each layer. This mechanism leads to relaxation of stress and to the disappearance of the layered structure for higher dose.
Surface topology of GaAs(100) after focused ion beam implantation of Si++
Authors: Schmuki P. , Erickson L. E. , Champion G. , Mason B. F. , Fraser J. , Moessner C.
Published: July 2002

GaAs(100) was implanted with Si++ doses ranging from 3×1013 to 3×1016 cm−2 using a focused ion beam. The surface topology and roughness of implanted lines and squares was studied by atomic force microscopy. Above a threshold dose, protrusions of the ion beam treated areas in the range of 1–15 nm in heights and an increase in surface roughness were found. The height of the protrusions and surface roughness increase with increasing implantation dose up to a saturation level. Both the onset of substrate bulging and saturation of the effect are both dependent on the linewidth of the implant. Different causes for the protrusions are discussed. From Monte Carlo simulations, it is deduced that the volume expansion is most likely due to the creation of vacancies during implantation.
Photoluminescence study of hydrogenated aluminum oxide–semiconductor interface
Authors: Shi Song S. , Hu Evelyn L. , Zhang Jing-Ping , Chang Ying-lan , Parikh Primit , Mishra Umesh
Published: July 2002

We present a study of oxide–semiconductor interfaces formed by wet thermal oxidation of a thin epitaxial AlAs layer. Photoluminescence (PL) from a quantum well in close proximity to the interface is monitored before and after oxidation. The normalized PL intensity was found to decrease roughly in proportion to the degree of completeness of the oxidation. The diminishing luminescence is attributed to the presence of trap states formed at the oxide–semiconductor interface formed during the oxidation process; hydrogen ion treatment is effective in the partial restoration of the luminescence. In addition to the traps, the oxidation process also “disorders” the material within ∼15 nm from the semiconductor–oxide interface, as revealed by transmission electron micrographs.
Grating formation in orientational optomechanical media at microwave frequencies
Authors: Tsap Boris , Pister Kristofer J. , Fetterman Harold R.
Published: July 2002

Orientational optomechanical media, consisting of three dimensional arrays of elongated metal coated dielectric beams suspended by torsional springs, was fabricated using microelectromechanical system (MEMS) technology. Response of a single rotating element to a polarized electromagnetic radiation was found to be in a good agreement with theory. Spatial grating formation in fabricated orientational optomechanical media was detected and measured under the influence of two orthogonally polarized electromagnetic fields at 15 GHz. This process demonstrates the feasibility of using optomechanical media for phase conjugation, via degenerate four-wave mixing, and for other nonlinear processes at microwave and millimeter wave frequencies.
Prediction of multiple-feature effects in plasma etching
Authors: Hwang Gyeong S. , Giapis Konstantinos P.
Published: July 2002

Charging and topography evolution simulations during plasma etching of dense line-and-space patterns reveal that multiple-feature effects influence critically the etch profile characteristics of the various lines. By including neighboring lines, the simulation predicts a peculiar notching behavior, where the extent of notching varies with the location of the line. Feature-scale modeling can no longer be focused on individual features alone; “adjacency” effects are crucial for understanding and predicting the outcome of etching experiments at reduced device dimensions.
Effect of substrate miscut on low-temperature homoepitaxial growth on Si(111) mediated by overlayers of Au: Evidence of step flow
Authors: Wilk G. D. , Chervinsky John F. , Spaepen Frans , Golovchenko J. A.
Published: July 2002

Observations of homoepitaxial growth on low-angle miscut (∼0.1°) Si(111) substrates through an overlayer of Au, together with earlier results on highly miscut Si(111) surfaces, indicate that growth in this system occurs by step flow. The growth temperatures were between 375 and 500 °C. In the optimum range of Au coverage (0.6–1.0 ML), ion channeling measurements yield at best χmin=5.0%, and cross-sectional transmission electron microscopy reveals stacking faults on (111) planes. Films produced under similar conditions on bare Si(111) substrates are much more defective. On the other hand, the defect density in the present films is higher than that in films grown on substrates with a higher miscut angle. The improvement in film quality resulting from the Au overlayers is attributed to an increase in the diffusion length of the Si adatoms, caused by Au passivation of the Si terraces. It is suggested that Au is more efficient than other overlayers in promoting step flow because Au passivates the Si(111) terraces without passivating the step edges.
Application of real time spectroscopic ellipsometry for high resolution depth profiling of compositionally graded amorphous silicon alloy thin films
Authors: Fujiwara H. , Koh Joohyun , Wronski C. R. , Collins R. W.
Published: July 2002

Real time spectroscopic ellipsometry (RTSE) has been applied to characterize compositionally graded amorphous silicon-carbon alloy (a-Si1−xCx:H) thin films, prepared using continuous variations in the flow ratio z=[CH4]/{[SiH4]+[CH4]} during rf plasma-enhanced chemical vapor deposition. Triangular variations in z versus time, yielding 50–130-Å-thick a-Si1−xCx:H graded layers with 0.02⩽x⩽0.24, were applied in order to assess the performance of the RTSE data analysis procedure. This procedure employs a four-medium virtual interface approximation, and returns the time evolution of (i) the near-surface C content, (ii) the instantaneous growth rate, and (iii) the surface roughness layer thickness. In the depth profiles of the graded structures, an apparent resolution of ∼10 Å is obtained with a composition uncertainty of ±0.004.
A step-free InAs quantum well selectively grown on a GaAs (111)B substrate
Authors: Nishida Toshio , Kobayashi Naoki
Published: July 2002

By combining finite-area selective growth and surface stoichiometry control, a step-free InAs quantum well was successfully obtained. An InAs/GaAs quantum-well structure was selectively grown by metalorganic vapor phase epitaxy on a GaAs (111)B substrate masked by a SiO2 pattern. A 100 nm thick and 8 μm diameter step-free GaAs buffer layer was grown at 800 °C and a step-free monolayer of InAs was grown on this surface at 650 °C. To eliminate indium segregation during the capping procedure, the InAs layer was buried by GaAs under a stable As-rich condition. The formation of a step-free InAs monolayer quantum well was confirmed by ex situ atomic force microscopy, and this observation was also supported by spatially resolved photoluminescence measurement.
Distributed microwave damping filters for superconducting quantum interference devices
Authors: Jin I. , Amar A. , Wellstood F. C.
Published: July 2002

We describe a distributed thin-film filter for the broad-band damping of microwave resonances in thin-film superconducting strip lines and coils used in Nb–Al/AlOx–Nb superconducting quantum interference devices (SQUIDs). The filter consists of an array of 14 μm diameter thin-film Au–Cu dots which are insulated from the strip lines or coils by an SiO2 layer. Damping occurs via eddy current induced in the dots. Our measurements show that the filter removes resonance steps from the current–voltage curves of SQUIDs which are coupled to the coils and reduces white noise associated with the resonances.
Electrical properties of oxides grown on strained Si using microwave N2O plasma
Authors: Bera L. K. , Ray S. K. , Nayak D. K. , Usami N. , Shiraki Y. , Maiti C. K.
Published: July 2002

Microwave plasma oxidation (below 200 °C) of strained Si on relaxed Si1−xGex buffer layers in N2O ambient is reported. The electrical properties of grown oxide have been characterized using a metal-oxide-semiconductor structure. Fixed oxide charge density and mid-gap interface state density are found to be 6×1010 cm−2 and 1.2×1011 cm−2 eV−1, respectively. The oxide on strained-Si samples has exhibited hole trapping behavior and moderately low interface state generation on constant current stressing.
Δn=0.22
birefringence measurement by surface emitting second harmonic generation in selectively oxidized GaAs/AlAs optical waveguides
Authors: Fiore A. , Berger V. , Rosencher E. , Crouzy S. , Laurent N. , Nagle J.
Published: July 2002

We have measured the birefringence enhancement due to lateral selective oxidation of AlAs in GaAs/AlAs optical waveguides. The birefringence was measured by imaging the surface-emitted second harmonic generated by the nonlinear interaction of counterpropagating TE and TM modes. In a waveguide containing a single AlAs layer the birefringence is enhanced from Δn=0.017 (before oxidation) to Δn=0.038 (after oxidation). In an oxidized multilayer GaAs/AlAs waveguide, a birefringence as high as Δn=0.22 is measured. This birefringence is sufficient to phase-match the difference frequency generation of 3–5 μm infrared radiation from two near-infrared pumps.
Double-crystal x-ray rocking curve study of (Al,Ga)As:As grown by low temperature molecular beam epitaxy
Authors: Sacks R. N. , Carlin J. A. , Melloch M. R. , Chang J. C. P. , Yap K. S.
Published: July 2002

A substantial difference has been found in the initial incorporation mechanism of excess As into low temperature grown (LTG) (Al,Ga)As compared to LTG GaAs. In as-grown LTG GaAs the excess As initially incorporates as point defects (interstitials and/or antisite defects) resulting in an expansion of the lattice parameter. Only upon subsequent annealing does the excess As coalesce into precipitates, allowing the lattice parameter to relax back to its normal value. In contrast, as-grown LTG (Al,Ga)As shows no expansion of the lattice parameter until close to the maximum achievable excess As concentration has been reached, and most of the excess As is incorporated immediately as small precipitates.
Third-order nonlinear optical properties of trans-dihydroxy-1,6,11,16-tetra(tert.butyl)porphyrazine germanium thin films
Authors: Nalwa Hari Singh , Engel Michael Klaus , Hanack Michael , Pawlowski Georg
Published: July 2002

Third-order nonlinear optical susceptibilities χ(3) of trans-dihydroxy-1,6,11,16-tetra-(tert.butyl) porphyrazine germanium [t-Bu4PazGe(OH)2] thin films measured by the third-harmonic generation technique are reported for the first time. The χ(3)(−3ω;ω,ω,ω) value as high as 1.3×10−11 esu was observed from a dominant three-photon resonance. The χ(3) values of porphyrazine germanium derivative are analogous to metallophthalocyanines and these results imply that axial substitution is beneficial for enhancing third-order optical nonlinearity.
Underdamped long Josephson junction coupled to overdamped single-flux-quantum circuits
Authors: Zhang Y. M. , Borzenets V. , Kaplunenko V. K. , Dubash N. B.
Published: July 2002

We report a circuit that integrates an underdamped long Josephson junction with overdamped single-flux-quantum (SFQ) circuits. We confirm that the resonant soliton modes in the long junction are not affected by SFQ cells coupled to the junction, and demonstrate that the radiation frequency and linewidth of the soliton resonances can be measured with SFQ T-flip-flops. Our experimental results also show that a 4π quantum mechanical phase leap at the end of the long junction, which is due to the reflection of a soliton, creates two single flux quanta propagating in the overdamped Josephson transmission line.
Optical investigation of strain and defects in (100) CdTe/Ge/Si and ZnTe/Ge/Si grown by molecular beam epitaxy
Authors: Hutchins J. W. , Skromme B. J. , Chen Y. P. , Sivananthan S. , Posthill J. B.
Published: July 2002

Low temperature (1.7 K) reflectance and photoluminescence (PL) have been used to assess residual strain and impurities in molecular beam epitaxial (100) CdTe/Ge/Si and (100) ZnTe/Ge/Si. Both types of samples exhibit residual biaxial tensile thermal strain as expected from differences in previous thermal expansion data, but the measured magnitudes (0.72×10−3 for CdTe/Ge/Si and 1.5×10−3 for ZnTe/Ge/Si) are smaller than predicted. The results are consistent with either residual lattice mismatch stress or partial relaxation of the thermal strain during cooling. Residual acceptors in the CdTe include Cu and a frequently observed 49 meV level, whose PL peaks lack the previously reported linear polarization. However, a new series of linearly polarized bound exciton lines is reported in CdTe.
Ex situ ellipsometry characterization of excimer laser annealed amorphous silicon thin films grown by low pressure chemical vapor deposition
Authors: Kuo Chau-Hong , Hsieh In-Cha , Schroder Dieter K. , Maracas George N. , Chen Sheau , Sigmon Thomas W.
Published: July 2002

Spectroscopic ellipsometry was used to monitor excimer laser annealed thin (∼100 nm) amorphous silicon (a-Si) films grown on quartz substrates by low pressure chemical vapor deposition (LPCVD). The peak position of the imaginary part of the complex dielectric function ε2 was used to determine the degree of crystallization of the a-Si. The amplitude of ε2 at the Si E1 transition energy is found to be a good indicator of the polycrystalline silicon (poly-Si) grain size after laser annealing with good correlation between ex situ ellipsometric data and poly-Si grain sizes being observed. Spectroscopic ellipsometry provides a contactless, nondestructive, and simple technique for monitoring laser annealing both in situ during the annealing process or ex situ after annealing.
Current-density enhancements of the highest-Tc superconductors with GeV protons
Authors: Thompson J. R. , Krusin-Elbaum L. , Christen D. K. , Song K. J. , Paranthaman M. , Ullmann J. L. , Wu J. Z. , Ren Z. F. , Wang J. H. , Tkaczyk J. E. , DeLuca J. A.
Published: July 2002

In several Tl- and Hg-based high-Tc superconducting materials, vortex-pinning defects were formed by irradiation with 0.8 GeV protons. The protons cause heavy constituent nuclei (Tl, Hg, Bi, …) to fission, which generates randomly oriented tracks. These columnar defects lead to significant enhancements in the current-conducting properties. We investigated bulk materials and thin films, irradiated with or without Pb or Au “amplifier foil” overlayers, which increase the number of column-creating fission fragments.
Reverse bias tuned multiple quantum well ridge guide laser with uniform frequency modulation response
Authors: Huang X. , Seeds A. J. , Roberts J. S.
Published: July 2002

We report a multiple quantum well ridge guide laser tuned by the quantum confined Stark effect. In contrast to carrier-induced effect tuned lasers, the frequency modulation response of our laser is highly uniform (±0.7 dB) over the frequency range from 10 kHz to 100 MHz, and within ±2.5 dB from 5 kHz to 500 MHz, with the upper frequency parasitic capacitance limited. We predict that the response could be extended to over 20 GHz by using a low parasitic contacting structure.
Hole intersubband relaxation in CdTe/CdMnTe quantum wells
Authors: Likforman J.-P. , Alexandrou A. , Vanelle E. , Cibert J.
Published: July 2002

We report a direct measurement of the hole relaxation time in undoped CdTe/CdMnTe quantum wells. The internal piezoelectric field in a (111)-grown structure is screened by e1h1 and e1h2 excitons with different efficiency. Thus, the temporal evolution of the screened field, as monitored by the e1h1 exciton energy in a pump-probe transmission experiment, allows the determination of the e1h2−e1h1 relaxation time. We obtained a relaxation time of 15±5 ps for a splitting of 15 meV, smaller than the longitudinal-optical (LO) phonon energy. Deformation-potential scattering is too slow to explain this relaxation time which we attribute to hole-hole scattering and LO-phonon emission by e1h2 excitons acquiring enough kinetic energy.
Free electron laser annealing of N-ion-implanted 3C-SiC films
Authors: Ohyama Hideaki , Suzuki Toshiji , Nishi Kazuhisa , Mitsuyu Tsuneo , Tomimasu Takio
Published: July 2002

Infrared laser annealing at a variety of wavelengths (10.0–13.0 μm) was performed under room temperature for cubic silicon carbide (3C-SiC) films after N-ion implantation by using a free electron laser with features of wide-range tunability, ultrashort pulse operation (∼10 ps), and intense peak power (∼MW). Infrared absorption spectroscopy indicated that the annealing at 12.6 μm, which corresponds to the absorption peak of Si–C stretch mode, was effective for removing the crystalline damage induced by the ion implantation. On the other hand, Hall effect measurements showed an increase of carrier density for samples annealed at around 10.4 μm, whereas the absorption was weak at this wavelength. This important result is most likely attributed to the activation of N donors caused by the direct excitation of a local vibration mode associated with N atoms in the SiC matrix.
Integral coupler/resonator for silicon-based switching and modulation
Authors: Bieber Amy E. , Brown T. G.
Published: July 2002

An optically resonant periodic electrode structure designed as a combined waveguide coupler/Bragg reflector can function as an optical or optoelectronic switch. We present experimental results showing self-modulation of the reflectivity from such a structure using Nd:YAG laser pulses, and show self-modulation at lower intensities using an optically resonant periodic electrode structure equipped with a central phase shift.
Stimulated transparency of a superconducting plate caused by nonlinear interaction of electromagnetic waves
Authors: Derev’anko S. A. , Lyubimova I. O. , Yampol’skii V. A. , Pérez-Rodrı́guez F.
Published: July 2002

A nonlinear effect in the electrodynamics of hard superconductors is predicted and theoretically studied. It is shown, that a low-frequency (LF) electromagnetic wave can pass through a superconducting plate, due to its interaction with another wave propagating in the opposite direction, even at small amplitudes of the LF wave when it cannot reach the opposite boundary of the sample without assistance. The dependence of the LF surface impedance on the amplitude of the high-frequency (hf) wave is studied within the framework of the critical state model. The LF surface impedance is found to be drastically increased by the overlapping of the regions of wave penetration.
Effect of the miniband width on the characteristics of a surface-normal reflective optical modulator at 1.3 μm using the Wannier–Stark effect
Authors: Tadanaga Osamu , Kagawa Toshiaki , Matsuoka Yutaka
Published: July 2002

A surface-normal reflective optical modulator for 1.3 μm wavelength was investigated using the Wannier–Stark effect of an InP/InGaAsP superlattice. Electroabsorption properties of two devices with different miniband widths were compared. A larger extinction ratio was obtained from the modulator with the larger miniband width. The extinction ratio of 3.3 dB was achieved at 28 V.
Low-dimensional structures generated by misfit dislocations in the bulk of Si1−xGex/Si heteroepitaxial systems
Authors: Shiryaev S. Yu. , Jensen F. , Wulff Petersen J. , Lundsgaard Hansen J. , Nylandsted Larsen A.
Published: July 2002

The capability of misfit dislocations to generate nanostructures in the bulk of Si1−xGex/Si heteroepitaxial systems is demonstrated. It is shown that dislocation slip originating from compositionally graded Si1−xGex layers can produce a range of low-dimensional structures including nanowires, nanodots, and mosaic superlattices. Formation of the nanostructures is achieved in parallel processing, through a simple two-step cycle which includes growth of layered planar structures and postgrowth annealing.
Electroluminescence from a soluble poly(p-phenylenevinylene) derivative generated using a scanning tunneling microscope
Authors: Lidzey D. G. , Alvarado S. F. , Seidler P. F. , Bleyer A. , Bradley D. D. C.
Published: July 2002

A scanning tunneling microscope was used to generate electroluminescence (EL) from thin films of the conjugated polymer poly(1,3-phenylenevinylene-co-2,5-dioctyloxy-1,4-phenylenevinylene). This allowed the spatial distribution of EL to be mapped across the film, and also measurements of local EL emission spectra to be recorded. It was observed that both the emission spectra and their intensity are highly nonuniform on length scales ≳2 nm. This is important in the context of light emitting diodes since it indicates that control of nanostructure can greatly improve device performance.
Electrical characterization of defects in SiCl4 plasma-etched n-GaAs and Pd Schottky diodes fabricated on it
Authors: Auret F. D. , Myburg G. , Meyer W. E. , Deenapanray P. N. K. , Nordhoff H. , Goodman S. A. , Murtagh M. , Ye Shu-Ren , Crean G. M.
Published: July 2002

We employed deep-level transient spectroscopy to determine the electrical properties of defects introduced in epitaxially grown n-GaAs during dry etching in a SiCl4 plasma at different rf powers and plasma pressures. We found that SiCl4 etching introduced two prominent defects, one of which is metastable. Current–voltage measurements demonstrated that high barrier Schottky barrier diodes can be fabricated on SiCl4-etched n-GaAs surfaces for all power and plasma pressure conditions investigated. The defect concentration decreased and the diode quality improved when etching at lower rf power and higher plasma pressure.
Nanostructure fabrication in silicon using cesium to pattern a self-assembled monolayer
Authors: Younkin R. , Berggren K. K. , Johnson K. S. , Prentiss M. , Ralph D. C. , Whitesides G. M.
Published: July 2002

This letter describes the formation of nanometer-scale features in a silicon substrate using a self-assembled monolayer (SAM) of octylsiloxane on silicon dioxide as a resist sensitive to a patterned beam of neutral cesium atoms. The mask that patterned the atomic beam was a silicon nitride membrane perforated with nm and μm scale holes, in contact with the substrate surface. In a two-step wet-chemical etching process, the pattern formed in the SAM was transferred first into the SiO2 layer and then into an underlying silicon substrate. This process demonstrated the formation of silicon features with diameter ∼60 nm.
Controlled morphology of biologically derived metal nanopatterns
Authors: Moore Jon T. , Beale Paul D. , Winningham Thomas A. , Douglas Kenneth
Published: July 2002

We report the ability to control the morphology of nanometer thick Ti oxide films that were created via a parallel nanofabrication process using a two-dimensional protein crystal as a template. Atomic force microscopy was used to examine the evolution of these structures from a periodic array of nanometer-scale dots (nanodots) to a screen containing a periodic array of nanometer-scale holes (nanoscreen) as the film thickness was increased. A Monte Carlo solid-on-solid simulation was then developed to explain the thickness dependence of the morphology as the metal film self-organizes into these nanopatterns.
Photoluminescence of InGaAs/GaAs single quantum well adjacent to a selectively oxidized AlAs layer
Authors: Pratt A. R. , Takamori T. , Kamijoh T.
Published: July 2002

Photoluminescence (PL) has been used to characterize an InGaAs/GaAs single quantum well (SQW) adjacent to a selectively oxidized AlAs layer. For a direct interface between the SQW and AlAs, the room temperature PL intensity is drastically reduced after oxidation indicating the presence of an efficient non-radiative pathway. However, a 20 nm AlGaAs layer grown between the SQW and the AlAs effectively isolates the SQW and yields a luminescence efficiency after oxidation identical to that of the as grown material.