bluuebunny/crossref_metadata_2025 huggingface dataset:
Femtosecond dephasing in porous silicon
Authors: Tomasiunas R. , Moniatte J. , Pelant I. , Gilliot P. , Hönerlage B.
Published: July 2002

We determine dephasing times T2 in free standing porous silicon samples using nondegenerate four-wave mixing. Within the framework of an idealized inhomogeneously broadened two-level system, values of 20 fs for different porosities are obtained. Fast energy relaxation times are found in the range of 1.5–3.5 ps for 64%–73% porosities, respectively. They are attributed to carrier thermalization within the band tails, originating from porous silicon nanocrystallites and their surface states.
Resonant absorption of terahertz electromagnetic waves by heated electrons in AlGaAs/GaAs heterostructures
Authors: Xu W. , Zhang C.
Published: July 2002

In this letter, we propose a mechanism which may cause a strong absorption of terahertz (THz) electromagnetic radiation in AlGaAs/GaAs-based two-dimensional semiconductor systems. In such systems, the rate of electronic transitions via hot electrons interacting with impurities and phonons is on the scale of 1012 s−1 so that the THz radiation will modify strongly the processes of electron momentum and energy relaxation and, consequently, a resonant absorption of the THz electromagnetic wave may occur. We find that in these sample systems, the absorption of the electromagnetic radiation at different frequencies can be tuned by heating the electrons to different temperatures. Our results can be used for understanding and interpreting the experimental results reported very recently.
Growth of optical superlattice LiNbO3 with different modulating periods and its applications in second-harmonic generation
Authors: Lu Ya-lin , Lu Yan-qing , Cheng Xiang-fei , Xue Cheng-cheng , Ming Nai-ben
Published: July 2002

Optical superlattice LiNbO3 crystals with a modulation period number over 200 and a modulation period from 2.0 to over 15.0 μm were grown by the Czochralski method in a carefully designed asymmetric temperature field system. Measurements of the frequency doubling efficiency for generating light from blue to green were performed. The largest efficiency obtained was 24.0% for frequency doubling of a picosecond 980 nm fundamental light. The angle tuning tolerance of a LiNbO3 optical superlattice was measured to be over 10° of the incidence angle.
Tensile-strained barrier GaAsP/GaAs single quantum-well lasers
Authors: Agahi Farid , Baliga Arvind , Lau Kei May , Anderson Neal G.
Published: July 2002

Device characteristics of tensile-strained barrier AlGaAs/GaAs1−yPy/GaAs separate-confinement heterostructure single-quantum well (SCH-SQW) broad area lasers are reported. Three phosphorous compositions of 9%, 15%, and 22% were used for the tensile-strained GaAs1−yPy barrier. For a 1000 μm long cavity device with a wellwidth of 113 Å and 15% P in the barrier, the threshold current density was as low as 233 A/cm2. The threshold current densities are slightly higher than those observed on similar device structures with tensile-strained GaAsP wells and unstrained GaAs wells with AlGaAs barriers.
Photon assisted field electron emission from SiO2/Si substrates
Authors: Jiménez I. , Sacedón J. L.
Published: July 2002

We report the observation of a field-emission effect in SiO2/Si samples assisted by the presence of photons. Electric fields in the oxide of the order of 10 MV/cm−1 are attained by photocharging during x-ray illumination and bring the vacuum level to a position below the equilibrium Fermi level. Hot electrons are injected from the Si substrate, traverse the SiO2 layer, and are emitted directly into vacuum. The large photocharging effect is related to the surface topography, consisting of multiple Si tips of about 1 μm high.
Early phenomena of capillary discharges for an electrothermal gun
Authors: Sueda T. , Katsuki S. , Akiyama H.
Published: July 2002

The 80 kJ electrothermal gun facility at Kumamoto University was assembled in order to investigate the phenomena of capillary discharges and to determine parameters of plasmas produced by a high power pulse discharge in the capillary. The behavior of capillary discharges is observed by using an image converter camera in order to make clear the early phenomena of the capillary discharge in different ambient pressures. The behavior of early capillary discharges varies from arc discharge to surface discharges with decreasing ambient pressure.
Characterization of shallow acceptors in GaAs by microsecond-scale time-resolved photoluminescence
Authors: Gilinsky A. M. , Zhuravlev K. S.
Published: July 2002

It is shown that examination of evolution of the low-temperature photoluminescence (PL) spectrum of GaAs with time after transient excitation in the microsecond range enables one to achieve enhanced separation of shallow-acceptor-related PL bands, and to clarify their nature. This provides a means for characterization of acceptors in GaAs, which can be applied to the study of material of both conductivity types in a wide range of material quality.
n-AlGaSb and GaSb/AlGaSb double-heterostructure lasers grown by organometallic vapor phase epitaxy
Authors: Wang C. A. , Jensen K. F. , Jones A. C. , Choi H. K.
Published: July 2002

n-type doping of AlxGa1−xSb epilayers (0≤x≤1) grown by organometallic vapor phase epitaxy has been achieved by using tritertiarybutylaluminum, triethylgallium, and trimethylantimony as the organometallic precursors and diethyltellurium as the doping source. Electron concentrations exceed 1017 cm−3 for layers with x<0.3, and decrease to ∼1016 cm−3 for x=1 as a result of higher residual acceptor concentration. Lattice-mismatched double-heterostructure diode lasers with AlGaSb cladding layers and GaSb active layer are demonstrated, and indicate the potential of OMVPE for growth of GaSb-based materials for electronic and optoelectronic devices.
Novel symmetry in the growth of gallium nitride on magnesium aluminate substrates
Authors: George T. , Jacobsohn E. , Pike W. T. , Chang-Chien P. , Khan M. A. , Yang J. W. , Mahajan S.
Published: July 2002

The growth of GaN by metalorganic chemical vapor deposition on (111) and (100) magnesium aluminate (MgAl2O4) substrates is examined using transmission electron microscopy. The results indicate that mainly wurtzite GaN is grown for both orientations. On the (111) substrate the following epitaxial relationship is observed: (0001)GaN ∥ (111)MgAl2O4, and [112̄0]GaN ∥ [11̄0]MgAl2O4. During the early stages of the (100) growth, four orientations of the wurtzite phase and a zinc-blende phase are formed. With increasing thickness, one of the wurtzite orientations dominates, with the epitaxial relationship being (11̄01)GaN ∥ (100)MgAl2O4 and the [112̄0]GaN nearly parallel to [011]MgAl2O4. This choice of growth orientation appears to be determined primarily by the nature of the interfacial bonding, with the basal plane of each of the four wurtzite GaN variants being nearly aligned along one of the four {111} planes intersecting the (100) surface of the MgAl2O4.
Photoluminescence excitation spectra in GaAs/AlAs trench-buried quantum wires with 20 nm wide rectangular cross-sectional shapes
Authors: Sogawa T. , Ando S. , Ando H. , Kanbe H.
Published: July 2002

Polarization-dependent photoluminescence excitation spectra (PLE) are measured in GaAs/AlAs rectangular trench-buried quantum wires (QWRs) with 20 nm width and various thicknesses. Experiments demonstrate that the polarization properties of the PLE spectra, which have several clear peaks corresponding to the optical transitions between quantized conduction and valence subbands, significantly depend on the cross-sectional ratios of the rectangular wires. Quantum indices of these transition levels are assigned by comparing the experiments with theory. The distinctive optical features of the QWRs with the rectangular cross sections are discussed in relation to the characteristics of one-dimensional valence subbands.
Oxygen precipitation in Czochralski-grown silicon wafers during hydrogen annealing
Authors: Izunome Koji , Shirai Hiroshi , Kashima Kazuhiko , Yoshikawa Jun , Hojo Akimichi
Published: July 2002

In studying the effect of the ramping process on oxygen precipitation in Czochralski-grown silicon wafers in hydrogen annealing, we have found that the oxygen precipitate density in the bulk region depends on the ramping-up rate at temperatures between 900 and 1200 °C. Few oxygen defects are observed when the ramping-up rate is 30 °C/min or more. Decreasing the ramping-up rate exponentially increases the oxygen precipitate density. The nucleation for oxygen precipitates can therefore be controlled by adjusting the ramping-up rate during hydrogen annealing.
Narrow linewidth, tunable distributed feedback photodetector
Authors: Sarathy J. , Anselm K. A. , Streetman B. G. , Campbell J. C.
Published: July 2002

We demonstrate a photodetector with a narrow spectral linewidth (approximately 2 Å) and a useful electrical-tuning range of 35 Å. The photodetector features a horizontal resonant cavity in which feedback is achieved using distributed feedback reflectors. The optical and electrical paths in this photodetector are orthogonal. Consequently, this normal incidence horizontal resonant cavity photodetector is completely integrable into wavelength division demultiplexing and other optoelectronic integrated circuits with a potential for high speed operation.
45 nm wavelength tuning range of an InP/InGaAsP photonic integrated tunable receiver
Authors: Jan Yu-Heng , Heimbuch Mark E. , Coldren Larry A. , DenBaars Steven P.
Published: July 2002

An integrated widely tunable photonic receiver including a semiconductor optical preamplifier, a two-section grating-assisted co-directional coupler optical filter, and a waveguide photodetector has been produced in the InP/InGaAsP materials system. Although sidelobes and bandwidth are still higher than desired, this integrated receiver can be continuously tuned for a record-wide 45 nm wavelength range.
Influence of carrier transport/capture and gain flattening in picosecond pulse generation of InGaAs microcavity lasers
Authors: Sogawa F. , Hangleiter A. , Watabe H. , Nagamune Y. , Nishioka M. , Arakawa Y.
Published: July 2002

We have fabricated and studied the dynamics of In0.16Ga0.84As λ-cavity lasers focusing on the influence of carrier transport/capture and gain flattening by using optical resonant pumping and off-resonant pumping. With the off-resonant pumping, shoulders in the lasing pulse shape were observed, while no shoulder appeared with the on-resonant pumping. From rate equation analysis and time-resolved photoluminescence measurement, it was concluded that the shoulders result from carrier transport/capture effects. Saturation of the inverse rise time was observed at high pump levels. This results from gain flattening due to the steplike density of states of 2D carriers. The pulse width obtained from the laser was as narrow as 7.7 ps.
Properties of InGaAs/InP thermoelectric and surface bulk micromachined infrared sensors
Authors: Dehé Alfons , Hartnagel Hans L. , Pavlidis Dimitris , Hong Kyushik , Kuphal E.
Published: July 2002

We present a concept for the realization of InGaAs/InP micromachined thermoelectric sensors. The advantages of InGaAs lattice matched to InP combine perfectly for this application. The high selectivity of wet chemical etching of InP against InGaAs is ideally suited for surface bulk micromachining. Thermoelectric InGaAs sensors profit from the high thermal resistivity combined with high electrical conductivity and Seebeck effect. Thanks to the material parameters a responsivity of 257 V/W and relative detectivity of 6.4×108 cm Hz−1/2/W are expected for infrared sensors.
Spectral-gate injection seeding in tunable lasers
Authors: Peshev Z. Y. , Deleva A. D. , Aneva Z. I.
Published: July 2002

A new concept, defined as spectral-gate injection seeding, is proposed for coupling the master oscillator (MO) and the forced oscillator (FO) in tunable injection-seeding laser systems. It is based on the use of a spectral selector as a tunable narrowband spectral gate between the partially coupled MO and FO cavities. The concept proposed enables one to implement compact and efficient injection-seeded tunable lasers. It is demonstrated experimentally on Nd:YAG-laser pumped dye lasers with a Fizeau interferometer as a spectral gate. Full suppression of the FO’s broadband spectral background is acheived even when the MO operates near the threshold.
Photorefractive grating formation in piezoelectric La3Ga5SiO14:Pr3+ crystals
Authors: Dam-Hansen C. , Johansen P. M. , Fridkin V. M.
Published: July 2002

Photorefractive grating formation and erasure in piezoelectric crystals of La3Ga5SiO14:Pr3+ are presented. The specific photoconductivity and the photorefractive sensitivity are determined. The polarization dependence of the grating formation due to the bulk photovoltaic effect is shown and compared favorably with the theoretical expression. This photorefractive material provides a possibility for separate investigations of the charge migration processes responsible for the photorefractive effect.
Annealing induced degradation of thermal SiO2: S center generation
Authors: Stesmans A. , Afanas’ev V. V.
Published: July 2002

Direct electron spin resonance evidence of profound intrinsic point defect generation in standard thermal SiO2 during postoxidation (PO) vacuum annealing is presented. The detected isotropic signal (peak-to-peak width 4.5–5.8 G; g=2.0028 at 4.3 K) is assigned to S centers, tentatively ascribed previously to E′-like defects (O3≡Si⋅ with one or two O replaced by Si). This process is advanced as atomic essence of the electrically well-known oxide degradation during PO annealing in inert ambient, likely effectuated by interface-initiated (volatile) SiO interaction. Coproduction of EX and Eδ′ defects is newly reported for thermal SiO2 as well.
Anomalous ion damage behavior in ZnSe
Authors: Yu Kin Man , Bourret-Courchesne E. D.
Published: July 2002

The structural properties of ZnSe damaged by 180 keV Zn ions are studied for a wide range of ion dose (1013–1016/cm2) using ion channeling techniques. We found that ZnSe cannot be rendered amorphous by implantation at either room temperature (RT) or liquid nitrogen temperature (LNT) in the range of doses investigated. For lower ion doses (1013–1014/cm2), ZnSe samples implanted at LNT result in less damage than those implanted at RT by as much as an order of magnitude. Moreover, no simple point defect or amorphous clusters are found in the implanted ZnSe. For high implant doses (≳1014/cm2), the samples are still monocrystalline but become highly defective with extended defects. Our results also suggests that point defects in the ZnSe created during implantation may be mobile at or below RT and that they may migrate rapidly under ion irradiation.
Electric field dependent intersubband optical transitions in a ZnCdSe–ZnSe superlattice
Authors: Guan Z. P. , Kobayashi T.
Published: July 2002

The polarization dependence of the excitonic transition in ZnSe-Zn0.8Cd0.2Se superlattices was studied by low-field electroreflection spectroscopy. A new peak observed in the lower energy side of the n=2 heavy-hole exciton E2hh at room temperature is attributed to the forbidden transition in zero field from the n=2 heavy-hole state to the n=1 electron state. This reflection change is found to be polarization dependent.
Polarization-insensitive field-induced refractive index change using a lattice-matched InGaAlAs/InAlAs multiple quantum well structure
Authors: Yoshimoto Naoto , Kondo Susumu , Noguchi Yoshio , Yamanaka Takayuki , Wakita Koichi
Published: July 2002

It is found that even a lattice-matched InGaAlAs/InAlAs multiple quantum well structure produces polarization-insensitive field-induced refractive index change (Δn). As the exciton absorption peak wavelength (λex) is set farther apart from the operation wavelength, the polarization of incident light by which larger Δn can be obtained changes from TE to TM mode. Moreover, as the thickness of the quantum well increases, enlargement of Δn induced on TM-polarized light is enhanced. These observations indicate that by selecting λex and the well thickness, the quaternary lattice-matched system has great flexibility in the device design for polarization-insensitive operation.
Electronic excitation of space charge waves in photorefractive materials
Authors: Kalinin V. A. , Solymar L.
Published: July 2002

The excitation of a space charge wave in a uniformly illuminated photorefractive crystal by an applied ac voltage is studied theoretically. A spatial differential equation for the ac component of the space charge field is derived and boundary conditions applicable both to Ohmic and rectifying junctions are obtained leading to an analytical solution for the space charge wave amplitude. It is shown that the low frequency space charge wave associated with the recharge of impurities can be efficiently excited with an amplitude approximately equal to the applied ac field. For the parameters of a BSO crystal, the space charge wave region declines within a few grating spacings near the cathode. The possibility of experimental observation of the effect is discussed.
Contact resistances of NiGeAu, PdGeTiPt, and TiPd ohmic contacts to GaAs and their temperature dependence from 4.2 to 350 K
Authors: Jones K. A. , Linfield E. H. , Frost J. E. F.
Published: July 2002

The specific contact resistance (rc) of NiGeAu and PdGeTiPt ohmic contacts to n-GaAs and TiPd and PdGeTiPt ohmic contacts to p+-GaAs were determined as a function of temperature between 4.2 and 350 K. The low rc obtained for some of the contacts at 4.2 K implies that much of the total contact resistance measured at 4.2 K in two-dimensional electron gas structures lies across the n–n heterojunction(s) in series with the metal semiconductor junction. Although NiGeAu contacts have a lower contact resistance to n-GaAs, PdGeTiPt contacts, which have much better edge definition, can be substituted for the NiGeAu when they are properly annealed. Also, contacts with low rc values at 4.2 K can be made to p+-GaAs using either TiPd or properly annealed PdGeTiPt contacts. The rc versus temperature curves for the TiPd and alloyed NiGeAu contacts fit the field emission model. The other contacts have a larger temperature dependence suggesting that tunneling occurs via thermionic field emission directly through the barrier or via defect states.
A novel sensitized photochromic organic glass for holographic optical storage
Authors: Wortmann R. , Lundquist P. M. , Twieg R. J. , Geletneky C. , Moylan C. R. , Jia Y. , DeVoe R. G. , Burland D. M. , Bernal M.-P. , Coufal H. , Grygier R. K. , Hoffnagle J. A. , Jefferson C. M. , Macfarlane R. M. , Shelby R. M. , Sincerbox G. T.
Published: July 2002

A new class of photochromic glasses for use in irreversible holographic optical storage applications is described. The recording mechanism involves a triplet-sensitized photoreaction of an organic chromophore. The materials are isotropic and red-sensitive, and exhibit high diffraction efficiencies and long hologram lifetimes. The wavelength sensitivity can be adjusted by the choice of sensitizer; C60, sensitive in the red, is described here. Single digital data page recording and error-free readout are demonstrated at a density of 0.5 Mb/cm2; multiplexing in a 150-μm-thick sample is also demonstrated.
Nonlinear distortion of a three-tone modulated laser diode followed by an interferometer
Authors: Yabre G.
Published: July 2002

The behavior of the light signal converted by means of a Mach-Zehnder interferometer is analyzed under the assumption of a three-tone modulation of the emitting laser source. The signal at the interferometer output is theoretically illustrated through the second-order harmonic as well as the second- and third-order intermodulation distortions. The corresponding direct intensity modulation (IM) distortions are also reported to facilitate a direct comparison with frequency modulation (FM). The results show that, as in the IM case, the FM-to-IM second- and third-order intermodulation products (IMPs) generated by a three-tone modulation result in a 6 dBc higher distortion level than the second-order harmonic and the two-tone third-order IMPs, respectively. The results show, moreover, that the FM-to-IM interferometric conversion technique would lead to lower distortion levels over the classical direct IM, thereby imposing less rigid requirements on the laser linearity.
Dynamics of photoexcited states and charge carriers in organic thin films: Alq3
Authors: Walser Ardie D. , Sokolik Igor , Priestley Richard , Dorsinville Roger
Published: July 2002

We demonstrate a method for observing and analyzing the dynamics of photoexcited molecular states and charge carriers in organic thin films, by measuring simultaneously the transient photoluminescence and photoconductivity. We show experimentally in tris-(8-hydroxyquinoline) aluminum (Alq3) that exciton–exciton annihilation dictates the behavior of the photoluminescence and photoconductivity at high excitation intensities. The experimental results are corroborated by calculations based on an exciton-exciton annihilation model.
An optical study of interdiffusion in ZnSe/ZnCdSe
Authors: Chai M. K. , Wee S. F. , Homewood K. P. , Gillin W. P. , Cloitre T. , Aulombard R. L.
Published: July 2002

This letter presents a study of intermixing in ZnSe/ZnCdSe quantum well structures, using repetitive thermal annealing with photoluminescence measurements. An improvement in the optical quality of the samples was found for anneals at temperatures (∼500 °C) for which macroscopic intermixing is not observed. The interdiffusion process of this system was found to be Fickian with no dependence on alloy composition or strain. An activation energy of 2.3±0.2 eV was obtained for the interdiffusion process over a 250 K temperature range and four decades of interdiffusion coefficient.
Structural modeling of the possible growth of oriented textured single-crystal diamond film on a silicon (111) surface
Authors: Zhang R. Q. , Wang W. L. , Esteve J. , Bertran E.
Published: July 2002

A model based on semi-empirical molecular orbital calculations and molecular mechanics is proposed for oriented textured diamond film growth on the Si(111) surface. The diamond <111≳ axis in our model is parallel to the silicon substrate <111≳ while the diamond <11̄0≳ is rotated 10.89° around the <111≳ axis referenced to the <11̄0≳ of the silicon substrate. The atomic density of the grown diamond in one dimension perpendicular to the <111≳ has a ratio 1.003:1 to that of a natural crystal, and thus is much better than the 1:1.015 of the heteroepitaxial diamond on the silicon (001) surface. We conjecture that this improvement in lattice match is important to achieve single-crystal growth. A model for heteroepitaxial growth with a diamond <111≳//Si<111≳ and diamond <11̄0≳//Si<11̄0≳ relationship is also studied but is found to have poorer bonding to the substrate and has a larger residual mismatch of 1:1.015.
Formation of semi-insulating 6H-SiC layers by vanadium ion implantations
Authors: Kimoto T. , Nakajima T. , Matsunami H. , Nakata T. , Inoue M.
Published: July 2002

Vanadium ion (V+) implantation has been successfully applied to the formation of semiinsulating 6H-SiC layers. The resistivity of V+-implanted layers strongly depended on the conduction type of initial 6H-SiC crystals. The resistivity at room temperature exceeded 1012 Ω cm and 106 Ω cm for p- and n-type samples, respectively. Compensation mechanism is discussed based on the temperature dependence of resistivity. This technique will be useful for device isolation, edge termination, and reduction of parasitic impedance of SiC devices.
X-ray reflectivity determination of interface roughness correlated with transport properties of (AlGa)As/GaAs high electron mobility transistor devices
Authors: Dura J. A. , Pellegrino J. G. , Richter C. A.
Published: July 2002

To explore the role of interface scattering in high electron mobility transistor (HEMT) device performance, a series of samples consisting of both a superlattice and a HEMT structure were grown by molecular beam epitaxy (MBE) at temperatures ranging from 500 to 630 °C. Hall measurements indicate a trend toward higher mobilities in samples grown at higher temperatures. Subsequent x-ray reflectivity measurements were made, and the data were fitted by least-squares refinement of a calculated reflectivity curve determined from a model of the sample structure to obtain the composition profile along the growth direction. These results indicate smoother interfaces for the samples with higher mobilities.
Transport properties and giant magnetoresistance behavior in La-Nd-Sr-Mn-O films
Authors: Zhang Wei , Boyd Ian W. , Elliott Martin , Herrenden-Harkerand William
Published: July 2002

The magnetoresistance of La-Nd-Sr-Mn-O films grown on Si(100) substrates using pulse laser deposition has been studied. Giant magnetoresistance behavior, with more than 70% (Δρ/ρ0) and 207% (Δρ/ρH) change in resistivity at 50 K under a magnetic field of 4.7 T has been obtained. The influence of the preparation conditions on the properties of the films grown is also described.
Morphological characterization and strain release of GaAs/InAs (001) heterostructures
Authors: Attolini G. , Chimenti E. , Franzosi P. , Gennari S. , Pelosi C. , Lottici P. P.
Published: July 2002

The surface morphology of GaAs layers on (001) InAs substrates, grown by MOVPE at temperatures in the range 500–650 °C and for times from a few seconds to minutes, has been observed by atomic force microscopy. Information on the strain release and on the surface quality has been obtained by Raman scattering and high resolution x-ray diffraction measurements. Large islands with different shapes and facets are generally formed and only at 550 °C is a quasi-2D growth observed. At the highest growth temperatures InxGa1−xAs is detected at the interface.
Splitting of the first generalized Rayleigh mode in thin layers deposited on anisotropic media
Authors: Mourad André , Desmet Carl , Thoen Jan
Published: July 2002

The dispersion curve for the first generalized Rayleigh mode on the surface on an anisotropic substrate covered with an anisotropic layer is calculated. We show that, for directions in which both the Rayleigh and leaky Rayleigh waves can propagate on the uncovered substrate, the dispersion curve of this generalized mode splits into two branches at a certain value of the product of the wave number and the thickness. This splitting has to be taken into consideration when deriving layer properties from dispersion curves. For the derivation, we considered the anisotropic layer as a perturbation of the anisotropic substrate. An efficient computer program based on the extended Tiersten approach was written to numerically calculate the phase velocity as a function of frequency.
Reduction in flux divergence at vias for improved electromigration in multilayered AlCu interconnects
Authors: Ting Larry , Hong Qi-Zhong , Hsu Wei-Yung
Published: July 2002

Using of W-plug vias in AlCu interconnects is known to significantly degrade electromigration (EM) performance because W is a diffusion barrier and prevents the depleting species by EM from being replenished at the via. In the present study, we demonstrate that this problem of limited source for EM migrating species can be dramatically alleviated in a multilayered metallization of TiN/AlCu/TiN using Al-plug vias. EM lifetime improvements as large as by an order of magnitude are accomplished by reducing the flux divergence at the Al-plug via. This flux divergence is critically determined by the effective thickness of some transition metal films at the via, which include a Ti/TiN stack for the via barrier and a TiN layer of antireflection coating for the bottom level metal lead. Scanning electron microscopy failure analysis also verifies that the samples with W-plug vias have the void damages consistently located at the via. For the samples with Al-plug vias and with the flux divergence at the via being largely reduced, the void failures locate on the metal lead and no visible damage at or within the via, indicating the reduced flux divergence at the via has become smaller than those generated on the metal lead due to microstructural variations.
Measurement of rapidly varying electric fields through parity oscillations in the Rydberg states of hydrogenic atoms
Authors: Shafer-Ray N. E. , Zare R. N.
Published: July 2002

Oscillations are shown to exist in the inversion symmetry of the electronic wave function of a hydrogenic atom coherently excited to a Rydberg state by a short pulse of laser radiation in a uniform electric field. The dependence of these oscillations on field strength is shown to scale as n2 where n is the principal quantum number. The possibility of using these oscillations to measure electric signals on picosecond timescales (terahertz frequencies) is suggested.
A combined Mössbauer and Rutherford backscattering spectroscopy analysis of the influence of nanosized cavities on CoSi2 formation
Authors: Deweerd W. , Moons R. , Verheyden J. , Milants K. , Langouche G. , Pattyn H.
Published: July 2002

For Co in Si, the competition between CoSi2 formation and cavity trapping is studied by Rutherford backscattering and Mössbauer spectroscopy. The presence of nanosized voids hampers the formation of a buried epitaxial silicide layer in its initial phase, preventing the small CoSi2 particles from forming a bulk layer. The Mössbauer spectra show that a pre-existing silicide phase can be partially dissolved in favor of cavity trapping. In addition, channeling measurements provide qualitative information about the voids, showing that the thermal stability of the voids is much higher than for defects resulting from self-implantation.
Study of the ground state splitting of N–O complexes in Cz–Si grown under nitrogen atmosphere
Authors: Shi X. H. , Liu P. L. , Shen S. C.
Published: July 2002

Far-infrared absorption spectra of Cz–Si grown under a reduced pressure of high pure nitrogen atmosphere have been investigated at different temperatures. Seven new series of lines resulting from the ground state splitting of N–O complexes [D(N–O)s] have been observed. The results indicate that the D(N–O)s have different structures. In addition, according to effective mass approximation, the binding energies of the split ground states have been obtained.
Observations of two separable photoquenching phenomena in lightly n-type bulk GaAs by optical absorption, Hall effect, and positron annihilation
Authors: Tüzemen S. , Le Berre C. , Corbel C. , Brozel M. R. , Yildirim M.
Published: July 2002

We show that two different types of photoquenching effect take place under low temperature illumination of lightly n-type bulk GaAs. Both phenomena result in an increase in positron trapping at vacancies. The first associated with a decrease in EL2 absorption, is produced with light of 1.1 μm wavelength and recovers near 100 K. While little photoquenching related to EL2 is observed after illumination close to the band edge (0.83 μm), persistent increases in Hall voltage and positron lifetime accompanied by a decrease in near band-edge absorption are observed. These latter phenomena recover at 50 K.
A three-well quantum well infrared photodetector
Authors: Tidrow M. Z. , Bacher K.
Published: July 2002

A simplified quantum well infrared photodetector (S-QWIP) has been designed and demonstrated which shows very high performance. The S-QWIP is designed to have only three quantum wells with detection peak wavelengths at 7.3, 8.3, and 10 μm, for the first, second, and third well, respectively. The two barriers between the three wells are graded to block the dark current effectively when reverse bias is applied. It also produces a built-in potential in the structure for a photovoltaic (PV) effect. The two end barriers are designed with different widths so that the electron transport can be compared when the bias directions are changed. The responsivity of the S-QWIP shows three photoreponse peaks at zero bias (PV effect) and migrates to one wide peak when the bias increases. The device is BLIP at 85 K within the operable reverse bias range. The responsivity is greatly enhanced at higher temperature and small bias. The conversion efficiency of photon absorption to photocurrent calculated conservatively at a bias voltage −0.8 V and peak wavelength 8.5 μm is 29%.
Visible luminescences from thermally grown silicon dioxide thin films
Authors: Choi Won Chel , Lee Min-Suk , Kim Eun Kyu , Kim Chun Keun , Min Suk-Ki , Park Chong-Yun , Lee Jeong Yong
Published: July 2002

We introduce visible photoluminescences (PL) of violet (432 nm) and yellow (561 nm) at room temperature from thermally treated silicon dioxide thin films. These luminescences were very strong with a near infinite degradation time. At an oxide layer thickness less than 200 nm, these luminescences were not seen, even with high temperature annealing at about 1000 °C. As a result of photoluminescence, x-ray photoelectron spectroscopy, Fourier transform infrared, and high-resolution transmission electron microscopy measurements, we conclude that the violet PL originates from the nanocrystalline silicon formed in the silicon oxide film by the thermal strain effect between the silicon substrate and the silicon dioxide film, while the yellow PL originates from the radiative decay of self-trapped excitons that are confined to oxygen sufficient structures.
Effect of multistep wafer-annealing on main traps in Czochralski-grown semi-insulating GaAs
Authors: Fang Z.-Q. , Look D. C. , Yamamoto H. , Shimakura H.
Published: July 2002

Both multistep wafer-annealed (MWA) and ingot-annealed semi-insulating (SI) GaAs wafers, grown by the Czochralski technique, are characterized by using normalized thermally stimulated current (NTSC) spectroscopy. Two main NTSC traps, T3 at 200 K and T5 at 140 K, which are thought to be related to arsenic vacancy defects, are found to be largely suppressed by MWA processes, especially by a new MWA process. Concomitant with a decrease of these traps, a significant increase of the threshold electrical field for both the thermal quenching of T5 and the low-temperature photocurrent saturation has been observed.
Electromagnetic excitation of ultrasound in electrolytes
Authors: Tankovsky N. S.
Published: July 2002

An electromagnetic explanation is given in earlier experimental evidence for the possibility of exciting acoustic signals by a transient electric field in an electrolyte. The theory is in agreement with experimental observations of acoustic signals excited by some elementary electric signals. The described mechanism can be applied to the construction of ultrasonic transducers operating in liquids or in living tissues.
Effect of a multiple-cusp magnetic field on electron confinement in a pulse-time-modulated plasma
Authors: Samukawa Seiji , Tsukada Tsutomu
Published: July 2002

Since ulrahigh frequency (UHF) plasma has a low electron temperature (less than 2 eV) and uniform density, the effects of electron confinement due to the sheath potential barrier or the plasma potential distributions are less prominent than with electron cyclotron resonance plasma or inductive coupled plasma. Consequently, with no magnetic fields, the pulsed UHF plasma discharge cannot be maintained. To confine electrons at the afterglow in the pulsed UHF plasma, multiple-cusp magnetic fields are required on the chamber wall. Under this condition, the pulsed UHF plasma can be maintained even at a pulse interval of 40 μs and can significantly improve the etching rate and etching selectivity. That is, electron confinement with magnetic fields plays a very important role for the generation of negative ions at the afterglow in a pulse-time-modulated plasma.
Interaction of high-power laser light with silver nanocluster composite glasses
Authors: Gonella F. , Mattei G. , Mazzoldi P. , Cattaruzza E. , Arnold G. W. , Battaglin G. , Calvelli P. , Polloni R. , Bertoncello R. , Haglund R. F.
Published: July 2002

The size and size distribution of silver nanoclusters embedded in soda-lime glasses (formed by ion irradiation of Ag+–Na+ ion-exchanged waveguides) has been modified by high-power laser irradiation. Optical transmittance in the visible range is found to increase above the energy threshold E*=0.3±0.1 J/cm2 for λ=532 nm and E*=5±1 J/cm2 for λ=1064 nm for pulse lengths of about 10 ns. Cluster size reduction has been observed. Small radii silver nanoclusters are also formed after laser irradiation of ion-exchanged waveguides. The optical response of the composites has been determined by optical absorption spectroscopy. Transmission electron microscopy, x-ray photoelectron and Auger electron spectroscopies, and Rutherford backscattering spectrometry have been used to characterize the composites.
Growth of YBa2Cu3O7−δ–Ag thin films (T
c(0)=89 K) by pulsed laser ablation on polycrystalline Ba2LaNbO6: A new perovskite ceramic substrate
Authors: Kurian J. , Varma H. K. , Koshy J. , Pai S. P. , Pinto R.
Published: July 2002

Synthesis and characterization of Ba2LaNbO6 which is a new substrate material for YBa2Cu3O7−δ superconductor are reported. Ba2LaNbO6 has a complex cubic perovskite structure (A2BB′O6) with a lattice constant a=8.60 Å. No detectable chemical reaction between YBa2Cu3O7−δ and Ba2LaNbO6 was observed even under severe heat treatment. The dielectric constant and loss factor of Ba2LaNbO6 are in a range suitable for its use as a substrate for microwave applications. Superconducting YBa2Cu3O7−δ–Ag thin films are grown in situ on polycrystalline Ba2LaNbO6 by pulsed laser ablation method. The film exhibited (00l) orientation of an orthorhombic YBa2Cu3O7−δ phase. The films gave a Tc onset of 91 K and Tc(0) of 89 K.
Chemical inhomogeneity and reactions of BiSrCaCuO surfaces detected by synchrotron imaging spectromicroscopy
Authors: Hwu Y. , Cheng N.-F. , Lee S.-D. , Tung C.-Y. , Alméras P. , Berger H.
Published: July 2002

A microscopic chemical analysis of BiSrCaCuO (BSCCO) 2212 single crystals was performed with an unprecedented combination of high (submicron) lateral resolution and high energy resolution (100 meV or better). These performances, achieved with imaging synchrotron spectromicroscopy, enabled us to detect in a very small fraction of the investigated specimens, morphological and chemical inhomogeneities. Specifically, we found deviations from stoichiometry in the surface Sr content which have a subtle effect on the chemical environment of at least one other element, Ca. The different chemical environment was found to influence surface chemical reactions.
Growth and field emission properties of multiply twinned diamond films with quintuplet wedges
Authors: Wang W. N. , Fox N. A. , Davis T. J. , Richardson D. , Lynch G. M. , Steeds J. W. , Lee J. S.
Published: July 2002

A unique microwave plasma chemical vapor deposition (MPCVD) technique was employed to produce multiply twinned diamond films with quintuplet wedges. Biased nucleation, nonbiased growth, and high methane/hydrogen ratio (≳5%) were used to prepare the multiply twinned diamond films. The growth parameter α was carefully controlled to be close but larger than 3/2 to allow the multiply twinned particles with quintuplets to outgrow the parent face to form the secondary crystals with uniformly distributed particle sizes and smooth surface. Since there is no need to suppress the natural growth of twins in vapor-grown diamond, higher growth rate was achieved. Excellent field emission properties of such films compared to the normal MPCVD diamond films were also obtained.
Lattice relaxation and pressure dependence of carbon and silicon impurity states in cubic boron nitride
Authors: Gubanov V. A. , Hemstreet L. A. , Fong C. Y. , Klein Barry M.
Published: July 2002

Impurity states in environments of relaxed crystal lattices around substitutional silicon and carbon impurities at both cation and anion sites in zinc-blende boron nitride (c-BN) have been investigated by the tight binding-linear combination of muffin tin orbitals-atomic sphere approximation (TB-LMTO-ASA) method. The pressure dependence of the impurity states of both silicon (Si)- and carbon (C)-doped c-BN is also investigated in the range of 0%–9% lattice compression. Shifts of the impurity bands, and the localization of the charge distributions under pressure are analyzed.
Enhancement of the magnetoresistance due to structural transition in Mg-doped perovskite Mn oxides
Authors: Anane A. , Dupas C. , Le Dang K. , Renard J. P. , Veillet P. , Pinsard L. , Revcolevschi A.
Published: July 2002

Substitution of magnesium for manganese in mixed perovskite La1−xSrxMnO3was found to reduce the electrical conductivity and the Curie temperature Tc. A remarkable jump in the resistivity ρ was observed in the 6% Mg-doped crystal with x=0.175. This sample remains semiconducting at low temperatures, contrary to the Mg-free crystal. The abrupt change of ρ reflects a first-order structural transition at a temperature Ts just below Tc. An applied magnetic field decreased Ts, leading to an enhancement of the magnetoresistance between Ts (0) and Ts (H). The microscopic properties of Mn3+ and Mn4+ ions due to Sr2+and Mg2+ substitutions were illustrated by 55Mn nuclear magnetic resonance study.
Modification of desorption phenomenon of Sb on Si surfaces by atomic hydrogen termination
Authors: Nakagawa Kiyokazu , Kimura Yoshinobu , Miyao Masanobu
Published: July 2002

Sb sticking and desorption on hydrogen terminated and clean Si surfaces are studied using molecular beam epitaxy. When Sb atoms impinge on Si surfaces, Sb atoms accumulate on a clean Si surface in proportion to Sb deposition time, independently of substrate temperature. For a hydrogen terminated surface, accumulation of Sb atoms is reduced by hydrogen treatment due to desorption with an energy of 0.14 eV, which correspond to the van der Waals bond energy, and the accumulated Sb atoms are thought to make clusters and the thermal activation energy of desorption changes from 0.14 to 1.35 eV of the Sb–Sb bond.
Epitaxial growth of cubic Laves phase intermetallic compounds (YCo2, TbCo2) and new epitaxial relationship between fcc (111) and bcc (110)
Authors: Robaut F. , Jaren S. , Cherief-Benbrahim N. , Meyer C.
Published: July 2002

YCo2 and TbCo2 Laves phase compounds were epitaxially grown on (110) W buffer layers by pulsed laser deposition at a base pressure of 5×10−10 Torr and a substrate temperature of 500 °C. The films were characterized in situ by reflection high-energy electron diffraction, and after deposition by grazing-incidence x-ray diffraction and scanning electron microscopy. The relative orientation of the RCo2(111), where R=Y or Tb, and the W(110) planes was found to be unlike any previously observed relationship between fcc and bcc materials. Two in-plane crystallographic domains of RCo2(111) have been pointed out and are discussed in terms of geometrical lattice matching.
High quality fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition at 120 °C
Authors: Song Juho , Ajmera P. K. , Lee G. S.
Published: July 2002

Electrical characteristics of the fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition at 120 °C using Si2H6 as silicon precursor and CF4 as fluorine precursor were studied. The addition of fluorine into Si–O network results in a decrease in the effective oxide charges as low as 1/6 of the value for the fluorine-free silicon oxide films. It also improves the film breakdown property by significantly reducing early failures, resulting in the measured average dielectric breakdown field strength of 8.91 MV/cm.
Influence of space charges on the resonant photoconductor employing a moving laser induced grating
Authors: Hundhausen M. , Ley L. , Witt C.
Published: July 2002

We discuss the performance of a recently proposed semiconductor device that converts the optical signal of frequency modulated laser beams into electrical signals of the same frequency in the GHz range. The device relies on a synchronous drift of photogenerated electrons with a moving intensity grating obtained from the interference of frequency shifted coherent lasers. The linearized rate equations for electrons and holes are solved in the limit of weak contrast of the intensity grating taking both drift and diffusion terms into account. One drift term due to the externally applied electric field is responsible for a resonantly enhanced amplitude of the photoelectron grating. A second drift term is related to internal fields set up by internal space charges and effectively reduces the electron grating amplitude in the lifetime regime.
Simple method for evaluating process-induced charging damage to the gate oxide of metal-oxide-semiconductor devices
Authors: Brożek Tomasz , Viswanathan Chand R.
Published: July 2002

This letter presents a simple approach to characterize process-induced charging damage in the gate oxide of metal-oxide-semiconductor (MOS) devices. The method uses the monitoring of voltage transients during constant-current stress performed on plasma-damaged and reference devices. The difference in transients allows direct extraction of the amount of electron traps created in the oxide by charging currents during processing. The method is verified by experimental simulation and applied to extract the density of electron traps introduced in the oxide by process-induced charging. This technique is a fast and efficient approach to assess device damage and extract physical parameters of generated traps which can be used later for lifetime prediction in reliability simulators.
Mechanism of nitrogen coimplant for suppressing boron penetration in p+-polycrystalline silicon gate of p metal–oxide semiconductor field effect transistor
Authors: Chao T. S. , Liaw M. C. , Chu C. H. , Chang C. Y. , Chien C. H. , Hao C. P. , Lei T. F.
Published: July 2002

The mechanism of the nitrogen co-implant to suppress the boron penetration in p+-polycrystalline silicon gate has been investigated. The nitrogen coimplant with the BF+2 combines with the boron to form a B–N complex which results in a retardation of boron diffusion. It is found that metal–oxide–silicon capacitors with nitrogen implantation show improved electrical properties.
Theory of effective response in dilute strongly nonlinear random composites
Authors: Hui P. M. , Wan W. M. V.
Published: July 2002

The effective response of random media consisting of two different kinds of materials, each of which with current density and electric field relation of the form J=χ|E|2E, is studied in the dilute concentration limit of one of the components. Based on linearizing the problem in standard mean field treatments and determining the mean fields self-consistently, a simple expression for the effective response is derived which is valid to the first order of the concentration of the dilute component. The result is then generalized to systems of arbitrary spatial dimensions and arbitrary nonlinearity. Our result represents a generalization of the low concentration expression widely used in linear random composites resulted from the Maxwell–Garnett approximation and the effective medium approximation to strongly nonlinear random composites of arbitrary dimensions and nonlinearity.
Oxygen ion beam-induced abnormal surface topographic development at Ta/Si interface
Authors: Kim Kyung Joong , Jung Kyung-Hoon , Moon Dae Won
Published: July 2002

We report on an abnormal surface topographic development at a Ta/Si interface, which is believed to be one of the major sources of the irregular interface artifacts in secondary ion mass spectrometry depth profiling by oxygen ion beam. Round crater type topographic development was observed at the interface by sputtering with a 7 keV O+2 ion beam and was found to have been formed by blister formation and gradual opening of its center. We suggest that the driving force for this abnormal topographic development is a buildup of compressive stress caused by a volume increase of the Ta layer near the interface, due to oxidation.