bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced saturation magnetization, electronic structure, and compositional segregation in epitaxially grown Co–Cr thin films
Authors: Krishnan Kannan M.
Published: July 2002

We have used the recently established linear correlation between the total intensities of the L3,2 ‘‘white lines’’ in electron energy-loss spectroscopy and the number of unoccupied 3d states to probe the local electronic structure in epitaxially grown Co–Cr thin films. The significant enhancement of saturation magnetization measured for these epitaxial films, when compared to homogenized bulk alloys, has been correlated directly to the unoccupied 3d states to the Co atoms in these materials. These measurements are the first direct electronic structure evidence that may support models associating the enhancement of saturation magnetization with intragranular segregation in Co–Cr thin films.
Cross-sectional transmission electron microscopy study of isolated diamond particles grown on a mirror-polished Si substrate
Authors: Tarutani M. , Shimato Y. , Takai Y. , Shimizu R.
Published: July 2002

Isolated diamond particles grown by chemical vapor deposition on a mirror-polished Si substrate have been studied by cross-sectional transmission electron microscopy. Focused ion beam micromachining enabled the cross-sectional specimen to be carved out precisely at the center of the particle. Atomic scale observation of the diamond/Si interface revealed the presence of an ∼3 nm thick amorphous intermediate layer including a few pits around the nucleation site of the particle. Growth mechanism and relationship between growth orientation and internal defect structure of the diamond particle are discussed.
An investigation of energy-band offsets in the ZnSe/Zn1−xMgxSySe1−y multiquantum wells system
Authors: Shahzad K. , Petruzzello J. , Gaines J. M. , Ponzoni C.
Published: July 2002

We present an analysis of optical data from ZnSe strained-layer quantum wells surrounded by Zn1−xMgxSySe1−y barrier layers to extract the band offsets. If we use only the ground state transitions from our experimental data, no unique value of the offset can be obtained: a direct consequence of the fact that there are no uniquely agreed upon values of the effective masses for ZnSe available. However, if we include the excited states, only one out of six considered sets of effective masses gives a reasonable fit to the experimental data, giving the conduction band offset of only 10% of the band gap difference.
Metal-insulator-semiconductor inversion layer solar cells by using rapid thermal processing
Authors: Beyer A. , Ebest G. , Reich R.
Published: July 2002

The possibility of producing solar cells using rapid thermal processing (RTP) was reported in recent years. This process was applied with good results to pn-solar cells. In this work we used the RTP technique for the metal-insulator-semiconductor (MIS) inversion layer cells. Simultaneously with the growth of the tunneling oxide at the front side a p+/p ‘‘high-low’’ junction forms by alloying the Al into Si at the back contact. The efficiencies reached with this process are about 15%.
Significant reduction in the soft error susceptibility of GaAs field-effect transistors with a low-temperature grown GaAs buffer layer
Authors: Weatherford Todd R. , McMorrow Dale , Campbell Arthur B. , Curtice Walter R.
Published: July 2002

The use of a low temperature grown GaAs buffer layer beneath the channel of a metal-semicon- ductor field-effect transistor is shown via computer simulation to reduce ion-induced charge collection by two or more orders of magnitude. This reduction in collected charge is expected to reduce the heavy ion soft error rate by four to seven orders of magnitude in GaAs integrated circuits, and could have significant implications for the applicability of GaAs technology in space-based systems.
Wide bandwidth AlAs/AlGaAs tandem Bragg reflectors grown by organometallic vapor phase epitaxy
Authors: Lee W. I.
Published: July 2002

Wide bandwidth AlAs/Al0.6Ga0.4As tandem Bragg reflectors were grown by organometallic vapor phase epitaxy. Quarter-wave reflector stacks designed for different wavelengths were placed in cascade in epitaxially grown structures to expand the high reflectance bands. Intermediate low-index layers were put in between every two stacks to suppress the transmission peaks in the centers of the combined high reflectance bands. While a single-stack structure showed a full width half-maximum bandwidth of 500 Å, the two-stack and the three-stack structures effectively doubled and tripled this bandwidth to approximately 1000 and 1500 Å, respectively.
Electrical properties of surface phases on silicon capped by amorphous Si layers
Authors: Zotov A. V. , Wittmann F. , Lechner J. , Eisele I. , Ryzhkov S. V. , Lifshits V. G.
Published: July 2002

A set of the different Si:Al and Si:B surface phases capped by amorphous Si layers were grown by molecular beam epitaxy (MBE). The formation of the buried interfaces was studied by low-energy electron diffraction and Auger electron spectroscopy. The conductivity and Hall effect measurements of the grown samples revealed that only the buried Si(111)√3×√3−B surface phase manifests itself as a highly doped degenerated layer, while all the buried Si:Al surface phases covered by amorphous Si show negligible activation of dopants. The difference in electrical properties of the buried surface phases are discussed in terms of the characteristics of their atomic structure.
Light emission of C60 embedded in porous silicon
Authors: Wang Shen-Yi , Shen Wen-Zhong , Shen Xue-Chu , Zhu Lei , Ren Zhong-Min , Li Yu-Fen , Liu Kai-Feng
Published: July 2002

We have fabricated samples with C60 implanted into porous silicon with the ionized cluster beam deposition approach for improving the light emission of C60. We have obtained intense and well-resolved photoluminescence spectra under excitation of Ar+ laser (514.5 nm) at room temperature. The depth analysis of secondary ion mass spectroscopy showed that C60 had been incorporated into porous silicon. A large number of fine-structure peaks in the photoluminescence spectrum indicated the strong coupling of vibrational progressions with electronic states of C60 induced by the interaction between C60 molecule and nanometer-sized silicon particles.
Strain relaxation of Ge1−xSix buffer systems grown on Ge (001)
Authors: Li J. H. , Holy V. , Bauer G. , Nützel J. F. , Abstreiter G.
Published: July 2002

We have investigated the strain relaxation behavior of biaxial tensile strained Ge1−xSix buffer systems grown on Ge (001) by a high-resolution x-ray reciprocal space mapping technique. The molecular beam epitaxy grown structures contain a linearly graded buffer, followed by a uniform buffer and a modulation-doped heterostructure with a high mobility two-dimensional hole gas in a Ge channel. Our quantitative measurements of the in-plane strain show that the lower part of the graded buffer is completely strain relaxed, while the top part of this region and the uniform alloy buffer are partly strain relaxed showing a linear increase of strain towards to surface.
Effect of anion vacancy on the chromacity of luminescence for Sr(S,Se):Ce,Cl thin film electroluminescent devices
Authors: Yang H. , Park Y. K. , Ju S. H. , Chang B. H.
Published: July 2002

We report the luminescence characteristics of Sr(S,Se):Ce,Cl thin film electroluminescent devices, fabricated by co-evaporation of SrS:Ce,Cl pellet and elemental Se. From the electroluminescence spectra measurements for varied S:Se mole ratio and temperature, it is found that the relative intensity of green emission band to blue emission band decreases with increasing lattice constant of the host lattice. This can be qualitatively accounted for as being caused by a nonradiative energy transfer from the emission band of Ce3+ to the absorption band due to defects associated with anion vacancies in the host lattice.
Deep-oxide curved resonator for low-threshold AlGaAs–GaAs quantum well heterostructure ring lasers
Authors: Krames M. R. , Minervini A. D. , Holonyak N.
Published: July 2002

Data are presented on curved-resonator AlGaAs–GaAs quantum well heterostructure laser diodes employing a deep-oxide guiding structure formed by a combination of impurity-induced layer disordering and native oxidation. Room-temperature, continuous wave (cw) threshold currents as low as ∼13 mA are measured for a ∼5 μm wide, 100 μm radius half-ring laser employing a deep-oxide structure. For similar 150 μm radius devices, cw threshold currents as low as ∼19 mA are observed (∼7 μm width), with total output powers exceeding 30 mW. Spectral data indicate single-mode operation over a large current range (25–100 mA). The low-threshold characteristics are attributed to the excellent current and optical confinement of the deep-oxide structure, combined with low edge scattering loss.
Instability mechanisms for the hydrogenated amorphous silicon thin-film transistors with negative and positive bias stresses on the gate electrodes
Authors: Tai Ya-Hsiang , Tsai Jun-Wei , Cheng Huang-Chung , Su Feng-Cheng
Published: July 2002

The hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) with silicon nitride as a gate insulator have been stressed with negative and positive bias to realize the instability mechanisms. It is found that the threshold voltages of the a-Si:H TFTs are positively shifted under low negative bias stress and then negatively shifted for large negative gate bias. The positive threshold voltage shift is ascribed to the increased states in the band gap near the conduction band by the negative gate bias. As the negative bias continuously increases, the hole trapping in the silicon nitride or at the a-Si:H/silicon nitride interface will become dominant, resulting in the negative threshold voltage shift. A similar turnaround phenomenon is also observed with respect to the stress time. On the other hand, for the TFTs stressed with positive gate bias, the monotonic increase of the threshold voltage shift with stress time is attributed to the state creation. Nevertheless, the distributions of the created states in the energy band gap for the a-SiH TFTs after the stress will be affected by the bias polarity based on the defect pool model, reflecting the asymmetrical subthreshold swing change against the positive and negative stress bias.
Diode-laser-based atomic absorption monitor using frequency-modulation spectroscopy for physical vapor deposition process control
Authors: Wang Weizhi , Hammond R. H. , Fejer M. M. , Ahn C. H. , Beasley M. R. , Levenson M. D. , Bortz M. L.
Published: July 2002

We have developed an atomic monitoring system for physical vapor deposition process control based on a frequency-modulation (FM) spectroscopy scheme using a 670 nm external cavity diode laser. FM detection made it possible to measure absorption as low as 10−6. For electron-beam evaporated yttrium, deposition rate control with a relative accuracy better than 1% at a rate of 3.5 Å/s has been realized, corresponding to a deposition rate resolution of 0.03 Å/s. Variations in Doppler shifts due to the velocity distribution of the atomic vapor within the deposition chamber have been measured, demonstrating the possibility of velocity mapping of evaporated atoms in the deposition process.
Secondary ion mass spectroscopy study of Au trapping and migration in the Au-irradiated YBa2Cu3O7−δ film
Authors: Li Yupu , Kilner J. A. , Liu J. R. , Chu W. K. , Wagner G. A. , Somekh R. E.
Published: July 2002

The range data and migration of Au in YBa2Cu3O7−δ film were studied with implanted 197Au (1.5 MeV 5×1015 Au+/cm2) as a tracer. The film was a c-axis oriented film, ∼750 nm thick, deposited by high-pressure planar dc sputtering on 〈100〉 LaAlO3. Analysis by secondary ion mass spectroscopy shows that the as-implanted Au concentration distribution is essentially Gaussian-like and the depth (R̂p) of maximum Au concentration (∼1.2 wt %) is 201 nm. The projected range (R̄p) and (R̂p) are found to be in very good agreement with the simulated data by TRIM−95, whereas the measured ‘‘straggle’’ (ΔRp*) is about 20% larger than that by TRIM−95 simulation. It has also been found that the implanted 197Au starts to migrate within the film at a temperature between 650 and 700 °C, which is much higher than that for the implanted 2H (∼175 °C) and the implanted 18O (between 250 and 300 °C) in c-oriented YBa2Cu3O7−δ films.
Tunable phase locking of stacked Josephson flux-flow oscillators
Authors: Goldobin E. , Kohlstedt H. , Ustinov A. V.
Published: July 2002

A tuning technique for mutual phase locking of two vertically stacked long Josephson junctions is suggested and successfully tested. The technique is based on passing a current through the middle electrode between two tunnel barriers. Mutually synchronized oscillation modes in the Nb/Al–AlOx/Nb stack are found to be tunable in the frequency range from 180 to 420 GHz. Presented results extend the possibility of using stacked long Josephson junctions as coherently operating oscillators for millimeter and submillimeter wave bands.
Overcoming weak links at grain boundaries in Bi2Sr2CaCu2Ox thick films by incorporation of superconducting whiskers
Authors: Funahashi Ryoji , Matsubara Ichiro , Dimesso Lucangelo , Ogura Toru , Ueno Kazuo , Ishikawa Hiroshi , Konishi Masayoshi , Ohno Nobuhito
Published: July 2002

Bi2Sr2CaCu2Ox (Bi-2212) superconducting thick films incorporating Bi-2212 superconducting whiskers have been prepared using a partial melting method. Hysteresis behavior of critical current density (Jc) for magnetic field is observed in a film without whiskers (monolithic film), but not noticeably in composite film (whisker content: 20 wt %). It is found from ac susceptibility measurement that a peak in χ″, resulting from weak links, appears at a higher temperature for the composite film than for the monolithic film. Jc decreases with increasing magnetic field more rapidly for the monolithic film than for the composite film less than 1 T. These results indicate that the incorporation of the whiskers is effective for overcoming weak links. In consequence Jc for the composite film is about three times higher than for the monolithic film. It is clear from SEM observation that a microstructural improvement leads to an increase in Jc.
Surface migration of ZnSe regrowth using compound source molecular beam epitaxy
Authors: Nishikawa Takashi , Kubo Minoru , Sasai Yoichi
Published: July 2002

We studied ZnSe epitaxial growth on ZnSe and ZnSSe patterned layers with two methods. One was conventional-type molecular beam epitaxy (MBE) which uses elemental materials as its sources. The other one was compound source molecular beam epitaxy (CSMBE) which uses compound polycrystals. We found that the epilayer is regrown on undercut mesa sidewall by CSMBE, while nothing is grown on the sidewall by conventional MBE. The surface migration length on ZnSSe (221)B plane was estimated from the surface edge profile of the regrown layer by CSMBE.
Nonradiative defects in Si and SiGe/Si heterostructures grown by molecular beam epitaxy
Authors: Chen W. M. , Buyanova I. A. , Henry A. , Ni W.-X. , Hansson G. V. , Monemar B.
Published: July 2002

Important grown-in nonradiative defects in Si epilayers and SiGe/Si heterostructures prepared by molecular beam epitaxy are studied by the optically detected magnetic resonance technique. Several nonradiative defects are observed that have been introduced by ion bombardment during growth or by the low surface adatom mobility during low-temperature growth. These defects are shown to provide efficient nonradiative channels for carrier recombination and, to a large extent, control the carrier lifetime.
A quantum structure for high-temperature operation of AlGaAs lasers: Multiple-quantum barrier and multiple-quantum well in active region
Authors: Kumar Rajesh , Onda Shouichi , Hara Kunihiko , Kuno Hironari , Matsui Takeshi , Kachi Tetsu
Published: July 2002

We propose a quantum structure of AlGaAs lasers designed for high-temperature operation. In this design, the superlattice structure multiple-quantum barrier (MQB) is located in the middle of active region which improves the injection efficiency of holes from the cladding into the active region, compared to MQB in cladding structure. Simulation results showed that low energy electrons can tunnel through the MQB barriers, while high energy electrons were reflected back by effective potential barrier to suppress the electron overflow from active to the cladding region. Multiple-quantum wells (MQWs) are integrated at each side of MQB to minimize the overflow of tunneled electrons. A differential quantum efficiency change as small as 5% was achieved in the temperature range of 20–100 °C from MQB+MQW in active lasers.
Improved materials characterization by pressure-dependent ultrasonic attenuation in air-filled permeable solids
Authors: Nagy Peter B. , Johnson David Linton
Published: July 2002

Recently developed airborne ultrasonic inspection techniques can supplement other methods routinely used for materials characterization of permeable solids. In particular, the velocity and attenuation of the slow compressional wave transmitted through thin plates of a few millimeter thickness can be used to assess the tortuosity and dynamic permeability of the specimen. The main advantage of the ultrasonic method over conventional flow resistivity, electrical conductivity, and other measurements is that it can be used to study the heterogeneity of the pore structure at scales comparable to the grain size. In the 100–500 kHz frequency range slow wave images can be obtained with resolution on the order of 1 mm or better. However, due to substantial viscous and scattering losses, the sensitivity of the method is relatively low therefore, the technique is limited to materials of at least 10% connected porosity and permeability higher than 200 mD. It is demonstrated in this letter that varying the air pressure significantly enhances the capabilities of slow wave inspection. Using high-pressure air saturation significantly reduces the absorption losses so that better resolution can be achieved by increasing the frequency. Alternatively, materials of lower permeability or specimens of higher thickness can be inspected at the same frequency. In addition, scattering losses can be eliminated by subtracting images taken at the same frequency but at different pressures.
X-ray standing wave study of a Si-adsorbed GaAs(001) surface
Authors: Sugiyama Munehiro , Maeyama Satoshi , Oshima Masaharu
Published: July 2002

The adsorption site of Si atoms deposited on a GaAs(001)-(2×4) surface at 400 °C was investigated by back-reflection x-ray standing wave analysis using asymmetric (111) and (11̄1) reflections. It was concluded that Si atoms occupy both As and Ga sites. The occupancy of Si atoms in the Ga site and the As site was estimated to be about 75% and 25%, respectively. The As coverage on a GaAs(001)-(2×4) clean surface of 0.75 may be related to the occupancy of Si atoms in the Ga site.
Noncritical phase-matched second-harmonic generation with an organic crystal, 4-(isopropylcarbamoyl)nitrobenzene
Authors: Endoh Hiroyuki , Kawaharada Miho , Hasegawa Etsuo
Published: July 2002

This letter reports an organic crystal that can generate a second-harmonic beam under type II noncritical phase-matching conditions. The cleavage plane of a 4-(isopropylcarbamoyl)nitrobenzene (PCNB) crystal was found by theoretical calculation to have a type II noncritical phase-matched incident surface. This enables the PCNB crystal to convert Ti:sapphire laser light (930 nm) into 465 nm blue light with high conversion efficiency (1%/W at 5.5 mm path length).
Growth of n- and p-type Al(As)Sb by metalorganic chemical vapor deposition
Authors: Biefeld R. M. , Allerman A. A. , Pelczynski M. W.
Published: July 2002

AlSb and AlAsxSb1−x epitaxial films grown by metalorganic chemical vapor deposition were successfully doped p- or n-type using diethylzinc or tetraethyltin, respectively. AlSb films were grown at 500 ° C and 76 Torr using trimethylamine alane and triethylantimony. AlAs0.16Sb0.84 films lattice matched to InAs were grown at 600 ° C and 76 Torr by adding arsine. Secondary ion mass spectroscopy showed C and O levels below 2×1018 and 6×1018 cm−3, respectively, for undoped AlSb. Similar levels of O were found in AlAs0.16Sb0.84 films but C levels were an order of magnitude less in undoped and Sn-doped AlAs0.16Sb0.84 films. Hall measurements of AlAs0.16Sb0.84 showed hole concentrations between 1×1017 to 5×1018 cm−3 for Zn-doped material and electron concentrations in the low to mid- 1018 cm−3 for Sn-doped material.
Determination of the off-diagonal element of the dielectric tensor without measuring the ellipticity
Authors: You Chun-Yeol , Shin Sung-Chul
Published: July 2002

In addition to the measurement of the Kerr rotation angle, the measurement of the ellipticity is generally known to be necessary for determining the off-diagonal element of the dielectric tensor. We have found a new method for determining the off-diagonal element of the dielectric tensor, without measuring the ellipticity, for a sample deposited on a transparent substrate.
Photothermal measurements on amorphous thin films deposited on crystalline silicon
Authors: Seas Antonios , Christofides Constantinos , Munidasa Mahendra
Published: July 2002

Nondestructive photothermal reflectance and radiometric measurements have been performed on amorphous silicon thin films of various thicknesses deposited on crystalline silicon substrate. The influence of the film thickness on the photothermal reflectance and radiometric signals (amplitude and phase) is shown.
Band-edge photoluminescence from pseudomorphic Si0.96Sn0.04 alloy
Authors: Khan Al-Sameen T. , Berger Paul R. , Guarin Fernando J. , Iyer Subramanian S.
Published: July 2002

Band-edge related photoluminescence from a strained Si0.96Sn0.04 alloy grown by molecular beam epitaxy on Si(100) substrate has been seen for the first time. We report band-edge related photoluminescence from a compressively strained pseudomorphic Si0.96Sn0.04 alloy. The luminescence observed consisted of two dominant features, a well-resolved band-edge luminescence consisting of a no-phonon and a transverse optical phonon replica, and a deep-level broad luminescence peak around 770 meV. The band-edge feature is attributed to a no-phonon free excitonic recombination in the binary alloy and exhibits a near linear power dependence. We also observe a red shift of the energy gap of Si0.96Sn0.04 alloy with respect to Si, which corresponds to the bulk alloy effect.
A four channel polarization and wavelength separation element using substrate-mode stacked holograms
Authors: Chang Jen-Tsorng , Su Der-Chin , Huang Yang-Tung
Published: July 2002

A four channel polarization and wavelength separation element using substrate-mode stacked holograms is proposed based on the diffraction efficiency characteristics for polarization and the wavelength selectivity of a transmission-type phase volume grating. We fabricated a sample device and measured its polarization selectivity, output spectrum, and insertion loss of each channel to demonstrate its performance.
Equilibrium tunneling between two-dimensional and quasi-one-dimensional electron gases in devices fabricated by in situ focused ion beam lithography
Authors: Kardynal/ B. , Linfield E. H. , Ritchie D. A. , Brown K. M. , Barnes C. H. W. , Jones G. A. C. , Pepper M.
Published: July 2002

Equilibrium resonant tunneling between an array of quasi-one-dimensional wires and two-dimensional electron gas has been studied as a function of the Fermi energy of the tunneling electrons, which was varied by the bias voltage applied to an in-built back gate. The equilibrium resonant tunneling differential conductance, measured in the double quantum well system, reflects both the electron density and wave functions of the one-dimensional electron gas.
Epitaxial growth of zinc-blende ZnSe/MgS superlattices on (001) GaAs
Authors: Uesugi Katsuhiro , Obinata Toshio , Suemune Ikuo , Kumano Hidekazu , Nakahara Jun’ichiro
Published: July 2002

We report the growth of zinc-blende ZnSe/MgS superlattices (SLs) on GaAs (001) substrates. The SLs were grown with metalorganic vapor phase epitaxy by selecting appropriate precursors for Mg and S. MgS naturally forms rocksalt structures, but zinc-blende MgS layers were grown. The lattice constant of MgS was estimated to be 5.59 Å. X-ray diffraction measurements show that the ZnSe/MgS SLs are grown coherently to the GaAs substrates up to the total thicknesses of ∼3000 Å.
High quality Nb/Al–AlOx/Nb superconducting tunnel junctions for radiation detection
Authors: Joosse K. , Nakagawa H. , Akoh H. , Takada S. , Maehata K. , Ishibashi K.
Published: July 2002

Nb/Al–AlOx/Nb tunnel junctions designed for x-ray detection have been manufactured and characterized at temperatures down to 0.35 K. At a bias voltage of 0.5 mV, a leakage current of the order of 0.1 pA/μm2, and a dynamic resistance exceeding 106 times the normal state resistance, were achieved in junctions with dimensions up to 200×200 μm2 and critical current densities of order 200 A/cm2. The combination of high critical current density, low leakage current, and large area represents an important step towards the development of superconducting tunnel junction detectors with improved spectroscopic performance.
Atomic layer epitaxial predeposition for GaAs growth on Si
Authors: Das Utpal , Dhar S. , Mazumdar Mousumi
Published: July 2002

We report a two-step growth process, using an atomic layer epitaxially grown GaAs predeposition layer for the growth of GaAs/Si layers by metalorganic vapor phase epitaxy technique. Photoluminescence and deep-level transient spectroscopy techniques are used to show that the quality of the grown material is comparable to that grown by a much complicated procedure involving strained layer superlattice buffers introduced between the active GaAs layer and the Si substrate.
Electron energy relaxation in infrared hot-electron transistors
Authors: Choi K. K. , Tidrow M. Z. , Chang W. H.
Published: July 2002

In hot-electron transistors and infrared hot-electron transistors, the energy distribution ρ(E) of the injected electrons after passing through the base can be directly measured at the collector. In this letter, a theoretical calculation on ρ(E) is presented, taking optical phonon emission and plasmon emission into account. We found that the relative contributions of these two mechanisms depend on the base doping density Nd. When Nd is less than 3.3×1017 cm −3, phonon emission dominates. For a larger Nd, plasmon emission becomes more important. We applied the calculation to devices with different Nd, and obtained quantitative agreement with the experiment.
Irreversible light-enhanced degradation in amorphous silicon solar cells at elevated temperatures
Authors: Carlson D. E. , Rajan K.
Published: July 2002

An irreversible light-enhanced degradation has been observed in amorphous silicon solar cells exposed to intense illumination (50 suns) at elevated temperature (≳130 °C). Unlike the light-induced degradation observed at lower temperatures, the light-enhanced degradation observed at elevated temperatures is not reversed by annealing and it not suppressed by a strong reverse bias. An analysis of the time decay of the short-wavelength spectral response at various temperatures indicates that the degradation mechanism is associated with the diffusion of hydrogen at elevated temperatures both in the dark and under intense illumination.
Room-temperature negative differential resistance in AlAs/ErAs/AlAs heterostructures grown on (001)GaAs
Authors: Tanaka M. , Tsuda M. , Nishinaga T. , Palmstro/m C. J.
Published: July 2002

We have fabricated resonant tunneling structures having a buried ErAs semimetallic quantum well and AlAs double barriers, on (001)GaAs substrates. In order to suppress the three-dimensional island growth of GaAs and AlAs on ErAs and to obtain flat interfaces, we adopted a template approach, in which one monolayer of Mn was deposited on ErAs prior to the growth of AlAs, in molecular beam epitaxy. In the current–voltage characteristics at room temperature, negative differential resistance was clearly observed in a significant number of diodes with the ErAs thickness ranging from 2.6 to 5.0 nm. This room-temperature device operation on (001) substrates is, we believe, an important step towards the realization of semimetal/semiconductor hybrid quantum devices.
Observation of a large dc Kerr effect in the intervalence subband of Si1−xGex/Si multiple quantum wells
Authors: Zhang Xinhui , Chen Zhenghao , Cui Dafu , Yang Guozhen , Wang Ruizhong
Published: July 2002

The observation of intervalence subband transitions induced third-order nonlinear effect in Si1−xGex/Si multiple quantum wells was reported. The dc Kerr in a symmetric quantum well, in which the linear-electro-optic effect is absent, was measured. The spectra of the absorption coefficient changes Δα under external field was obtained using experimental Fourier transform infrared absorption data. The resulting changes of refractive index due to quantum-confined Stark effect was obtained by Kramers–Kronig relations based on measured absorption data. Moreover, under both 45° incident angle and normal incidence, TE-active transition was excited and corresponding changes of refractive index under dc field was observed. The measured large changes of refractive index make Si1−xGex/Si multiple quantum wells quite attractive for potential application in electro-optic devices such as modulators and switches.
Carrier lifetime and x-ray imaging correlations of an oxide-induced stacking fault ring and its gettering behavior in Czochralski silicon
Authors: Raebiger Jan , Romanowski Andrzej , Zhang Qiung , Rozgonyi George
Published: July 2002

The characterization of a unique crystal originated and thermally activated defect zone in Si wafers called an oxide-induced stacking fault (OSF) ring has been carried out using two noncontacting techniques. The minority-carrier lifetime has been mapped using the laser microwave photoconductance decay (LM-PCD) method and correlated with a transmission x-ray topographic image of the wafer. Additional details of the lateral and depth dependent stacking fault density were revealed by preferential etching. The minority-carrier lifetime within the annular OSF ring itself was about one order of magnitude lower than that outside the ring, while intermediate lifetime values were observed inside the ring. Temperature-dependent LM-PCD measurements revealed that a redistribution of the metallic impurity Fe occurred via gettering by the stacking faults. These findings were confirmed and quantified by deep-level transient spectroscopy. Implications for radial variations in device yield are discussed in the context of the depth distribution of the extended defects, their impurity gettering action, and wafer-to-wafer variations in the nature of the OSF ring.
Highly active BaTi4O9/RuO2 photocatalyst by polymerized complex method
Authors: Kakihana Matsato , Arima Momoko , Sato Tsugio , Yoshida Kiyohide , Yamashita Yohichi , Yashima Matsatomo , Yoshimura Masahiro
Published: July 2002

A polymerized complex (PC) technique was utilized to prepare high-purity barium tetratitanate (BaTi4O9) fine powders at a low temperature (700 °C). BaTi4O9 via the PC route, combined with RuO2, exhibited 2.4 times larger photocatalytic activities for the decomposition of water compared to those for a sample prepared by a solid-state reaction method. A considerably large surface area (∼30 m2/g) of the BaTi4O9/RuO2 powder via the PC route, when compared with ∼5 m2/g for the solid-state reaction powder, was supposed to be one of the key factors responsible for the high photocatalytic activity observed.
High resolution x-ray diffraction study of the Bragg peak width in highly mismatched III–V heterostructures
Authors: Ferrari C. , Francesio L. , Franzosi P. , Gennari S.
Published: July 2002

Recently, a method has been proposed in order to measure the threading dislocation density in epitaxial layers, based on x-ray diffraction and the analysis of the Bragg peak width β. According to this model, β is broadened by a strain effect (a modification of the lattice parameter near the dislocation line) and by a tilt effect (a bending of lattice planes caused by the dislocation), independent of each other. In the present work, this method is applied on GaAs/InAs and InAs/GaAs heterostructures. Different geometrical conditions and reflections, including (004), (115), (335), (444), and (117), have been investigated, showing a strong difference in β when, the reflection fixed, the grazing incidence or grazing emergence geometry is chosen. We demonstrate that this effect can be explained in terms of a lateral nonuniformity of the eplilayer induced by the misfit dislocations.
Incoherent collisions between one-dimensional steady-state photorefractive screening solitons
Authors: Shih Ming-feng , Chen Zhigang , Segev Mordechai , Coskun Tamer H. , Christodoulides Demetrios N.
Published: July 2002

We report the observation of collisions between mutually incoherent, one-dimensional, bright, steady-state photorefractive screening solitons. Using the theory of planar dielectric waveguides together with the theory of photorefractive screening solitons, we explain how the collisions depend on the peak intensity of the solitons and the externally applied biased field. Finally, we compare the experimental results with direct numerical simulations.
Observation of quantum carrier confinement near Zn0.61Cd0.39Se/InP heterointerface
Authors: Shum Kai , Zeng L. , Dai N. , Tamargo M. C.
Published: July 2002

We report on the experimental observation of quantum carrier confinement near the ZnCdSe/InP interface using the capacitance voltage profiling technique. Three subband states are identified at different spatial position-expectation value. Type II band alignment between ZnCdSe and InP is determined. The conduction band discontinuity at the Zn0.61Cd0.39Se/InP heterointerface is estimated to be −102 meV.
Intensity profile in a distributed feedback fiber laser characterized by a green fluorescence scanning technique
Authors: Loh W. H. , Samson B. N. , de Sandro J. P.
Published: July 2002

We report on an experimental technique for investigating the intensity profile in distributed feedback fiber lasers. By scanning along the laser length and monitoring the side green fluorescence, the intensity distribution in the laser can be inferred. With this approach, we experimentally verify the sharply peaked intensity distribution predicted for λ/4 phase-shifted distributed feedback lasers.
High quality epitaxial Si grown by a simple low pressure chemical vapor deposition at 550 °C
Authors: Chin Albert , Lin B. C. , Chen W. J.
Published: July 2002

We have designed a simple-hot wall low pressure chemical vapor deposition (LPCVD) system to grow high quality epitaxial Si films from 550 to 900 °C. The epitaxial film has been examined by scan electron microscopy for surface morphology, and by x-ray diffraction and cross-sectional transmission electron microscopy for crystallinity. Its quality has been found comparable to that of the substrate. Reduction of moisture and oxygen in the ambient is critical to the success of the growth at low temperatures. A combination of a leak-tight LPCVD reactor, a high flow rate of 61/min of H2 purge, and a pre-bake at high temperature of 950 °C has been used to achieve the reduction of moisture and oxygen. Degraded films form with increasing full width at half maximum of x-ray diffraction peak when a pre-bake at lower temperature is used.
Self-induced persistent photoconductivity in resonant tunneling devices
Authors: Neves B. R. A. , Alves E. S. , Sampaio J. F. , de Oliveira A. G. , Moreira M. V. B.
Published: July 2002

We report on the observation of a novel effect in resonant tunneling devices (RTD): a self-induced persistent photoconductivity (SIPPC). The SIPPC manifests itself as a permanent shift of the resonant peak position to lower voltages, which is induced by the RTD itself and not by external sources. The SIPPC is due to the presence of DX centers in the device, which are ionized by light generated in the device itself through the recombination of electron-hole pairs created by impact ionization of hot electrons in the depletion layer of the device.
Quantum-well intermixing in Si1−xGex/Si strained-layer heterostructures using ion implantation
Authors: Labrie D. , Lafontaine H. , Rowell N. , Charbonneau S. , Houghton D. , Goldberg R. D. , Mitchell I. V.
Published: July 2002

A demonstration of quantum well intermixing using ion implantation in Si1−xGex/Si strained-layer heterostructures is presented. The quantum-well related photoluminescence lines of implanted and annealed samples are blue shifted by up to 40 meV relative to those measured in annealed-only samples. Optical and structural qualities of the heterostructure remain high after implantation and annealing treatments.
Effect of cyclic process on the {100}-oriented texture growth of diamond film
Authors: Kim S. H. , Park Y. S. , Han I. T. , Lee J.-W. , Yun W. S.
Published: July 2002

The {100}-oriented texture growth of diamond film on (100) Si substrates (1×1 cm2) has been achieved by a three-step procedure (carburization→nucleation→growth) in a microwave- plasma-enhanced chemical vapor deposition (MPECVD) system. The surface morphology is found to be strongly affected by the cyclic process applied during the nucleation step. Furthermore, the density of {100}-oriented grains as well as the coverage area are enhanced by the application of the cyclic process merely during the nucleation step. We also observed the increase in the nucleation density by the cyclic process. This increase may be the origin for the increase in the density of the {100}-oriented grains.
Infrared absorption in silicon at elevated temperatures
Authors: Rogne H. , Timans P. J. , Ahmed H.
Published: July 2002

Isothermal electron beam heating combined with in situ optical measurements has been used to measure the temperature dependence of the spectral emissivity of lightly doped silicon in the range 345–723 °C for wavelengths between 1 and 9 μm. The absorption coefficient was deduced from the spectral emissivity and compared with the predictions of a model including phonon-assisted processes involved in interband transitions, free-carrier absorption, and lattice absorption. The experimental data agree well with the model’s results.
Faraday–Stark optoelectronic effect
Authors: Lee Z. K. , Heiman D. , Wang H. , Fonstad C. G. , Sundaram M. , Gossard A. C.
Published: July 2002

An optoelectronic effect based on Faraday or Kerr rotation and the quantum-confined Stark shift is demonstrated. It is novel in that the degree of rotation is controlled by an electric field as opposed to a magnetic field. By applying an electric field to a quantum well structure, the Faraday rotation can be tuned into resonance, thereby varying the rotation angle of plane polarized light. We have observed a resonant rotation of 10° in GaAs at a magnetic field of 1 T. By applying a gate voltage of 2 V to a GaAs/AlGaAs superlattice structure, we observed a change in rotation of 1.3° at 2 K. The Faraday–Stark effect could be useful in electrically controlled light switches and high-speed optical modulators.
Ohmic contacts to n-type silicon-germanium
Authors: Nelson S. F. , Jackson T. N.
Published: July 2002

We have studied both alloyed metal and ion-implanted Ohmic contacts to n-type silicon/silicon germanium heterostructures. We found that gold/antimony contacts can distort low temperature mobility measurements, and seriously degrade a sample after a short time. A more reliable alternative alloy is silver/antimony. We also found phosphorous ion-implanted contacts, annealed to 600 °C for 30 min, to be reliably Ohmic and of low resistivity at low temperatures.
Quartz micromachining by lithographic control of ion track etching
Authors: Hjort Klas , Thornell Greger , Schweitz Jan-Åke , Spohr Reimar
Published: July 2002

A micromachining process, using ion track etching in combination with lithographic patterning, is presented. The technique employs a substrate pre-irradiated with swift heavy ions and uses a conventional lithographic technique to control the access of a track-selective etching medium to the ion tracks. Experimental results show the possibility of generating high aspect ratio structures in virtually any direction in single crystalline quartz, which otherwise exhibits a strong ‘‘natural’’ anisotropy to conventional wet etching. In this way complex, three-dimensional quartz structures of 80 μm height with vertical or pre-defined inclination angles of the walls were produced. The process can be applied to other, even highly radiation resistant, dielectric materials such as mica and organic polymers.
Diffusion of hydrogen in K1−xLiyTa1−yNbxO3 doped crystals
Authors: Tong Xiaolin , Zhang Min , Yariv Amnon , Agranat Aharon
Published: July 2002

Based on infrared spectra and protonic conductivity measurements, we propose a model of hydrogen ion migration in K1−yLiyTa1−xNbxO3 doped crystals and use it to obtain a theoretical estimate of the diffusion constant pre-exponential factor D0 that is in reasonable agreement with the experimental result. This model shows that the transition energy of the second, and higher, overtone(s) of the [OH] vibration can be higher than the activation energy of hydrogen ion migration.
Stress reduction and interface quality of buried Sb δ doping layers on Si(001)
Authors: Falta J. , Bahr D. , Hille A. , Materlik G. , Kammler M. , Horn-von Hoegen M.
Published: July 2002

We have investigated the width dependence of Sb delta (δ) doping layers grown by Si solid phase epitaxy (SPE) on the Sb surface reconstruction prior to Si deposition. Depending on the Sb adsorption conditions a 2×1 and a 2×n surface reconstruction is observed. Measurements of crystal truncation rods and x-ray standing waves show a drastically reduced interface roughness and a better crystal quality for δ layers grown on Sb:Si(001)−2×n substrates in comparison to Sb:Si(001)-2×1, which we attribute to reduced surface stress of the Sb:Si(001)-2×n reconstruction.
Nonlinear space-charge waves in a relativistic electron beam drifting along a Kerr-like medium
Authors: Ueda T. , Shiozawa T.
Published: July 2002

We investigate the nonlinear characteristics of space-charge waves, which propagate along a relativistic electron beam drifting near the surface of a semi-infinite Kerr-like medium, under the condition that the drift velocity of the electron beam does not exceed the Cherenkov threshold. On the basis of the linear fluid model for the electron beam and the stationary wave analysis, we obtain some interesting features for the nonlinear space-charge waves such as power dependence of wave numbers and hysteresis characteristics.
Integrated YBa2Cu3O7 magnetometer with flux transformer and multiloop pick-up coil
Authors: Scharnweber R. , Schilling M.
Published: July 2002

We report on a novel integrated magnetometer concept that combines inductance matching by a flux transformer with the low inductance of a multiloop pick-up coil. A 90 pH dc superconducting quantum interference device together with a five turn flux transformer is coupled to a multiloop pick-up coil resulting in an effective magnetometer area of 1.4 mm2 on a 10×10 mm2 substrate. Using ramp-type Josephson junctions with PrBa2Cu3O7 barriers, a white noise level of √SB(1 kHz) = 44 fT/√Hz is measured. The 1/f-flux noise of the integrated magnetometer is suppressed successfully by operation in a flux-locked loop mode with bias current modulation. At 77 K we find a flux density noise of √SB(1 Hz) = 100 fT/√Hz.
Rapid thermal annealing using the combustion of H2 with N2O
Authors: Sameshima T. , Sunaga Y. , Takashima N. , Tajima A.
Published: July 2002

The combustion of H2 gas with N2O gas was investigated in order to rapidly heat substrate to a high temperature. A transient thermometry with a 100-nm-thick Cr film as a temperature sensor formed on quartz substrate was used to measure temperature change at the surface. The gas combustion was induced by heating a W filament. It propagated with a velocity higher than 100 m/s throughout a chamber for an initial total gas pressure of 500 Torr ([H2]/[N2O]=1). The sample surface is heated to 800 °C for an initial substrate temperature at 300 °C. The full heating time width at half maximum was 4.5 ms. This letter shows a possibility of millisecond-order rapid thermal treatment.
Double-crystal x-ray diffraction from silicon film on insulator
Authors: Zhong Lei , Hayashi Kenro , Takeda Ryuji
Published: July 2002

This letter describes a simple and straightforward approach to the thickness measurement of silicon film on insulator, whose double-crystal x-ray diffraction curve is found of a sinusoidal slit function, as predicted by the dynamical scattering theory.
A measurement of the electron-hole lifetimes in CdZnTe at 300 and 79 K using a pulsed x-ray microwave technique
Authors: Tepper Gary , Losee Jon
Published: July 2002

Electron-hole lifetimes in CdZnTe at 300 and 79 K have been measured using a pulsed x-ray microwave technique. The technique does not require charge extraction or electrical contacts to the sample and is sensitive enough to detect single x rays absorbed in a semiconductor. The carrier lifetimes at 79 K are observed to be over 100 times longer than at 300 K.
Mechanism of self-organized light-induced scattering in periodically poled lithium niobate
Authors: Sturman B. , Aguilar María , Agulló-López F. , Pruneri V. , Kazansky P. G. , Hanna D. C.
Published: July 2002

It is shown that the photorefractive grating produced by a pair of plane waves in periodically poled lithium niobate includes an additional set of spatial harmonics related to the periodic domain structure. This results in new schemes for photorefractive wave coupling. Using the modified phase matching conditions and the concept of optical oscillation we accurately describe the position of the diffraction peaks and explain the main characteristics of self-organized photoinduced scattering reported recently.
Effects of grain boundary scattering on the electron drift velocity behavior in diamond films: A Monte Carlo analysis
Authors: Joshi R. P. , Srivastava A.
Published: July 2002

Monte Carlo calculations of the electron drift velocity in polycrystalline diamond are presented based on a formulation that includes grain boundary scattering. Our results indicate field dependent reductions of the drift velocity in polycrystalline diamond. The grain boundaries are predicted to have negligible effect on the drift velocity at high fields exceeding 70 kV/cm. However, significant drift velocity decreases are predicted at fields below 1 kV/cm, and at low temperatures. This trend is in keeping with experimental mobility data that is becoming available from pulsed excitation measurements.
Improvement of the superconducting transition and demagnetization factor in YBa2Cu3O7−δ single crystals by laser cutting
Authors: Bhattacharya Anand , Grupp Daniel E. , Goldman Allen M. , Welp Ulrich
Published: July 2002

Single crystals of YBa2Cu3O7−δ have been cut into disc shapes using an excimer laser. The bulk superconducting transition was found to be sharpened in all cases measured. This is associated with the removal of material at the edges which may be depleted of oxygen or otherwise damaged. The magneto-optical images for one crystal have been correlated with the optical image. The angular dependence of the demagnetizing factor for field applied in the plane was drastically reduced in disc-shaped crystals relative to rectangular ones. The field of first flux entry was also increased.
Resonance fluorescence of a single molecule under near field excitation
Authors: Chang Railing , Fann Wunshain , Lin S. H.
Published: July 2002

We report here theoretical investigations on the resonance fluorescence of a two-level molecule, probed by the near field optical microscopy technique in illumination mode. The proposed model considers the influence of a coated tapered fiber probe on the radiative properties of the molecule. It is observed that both the radiative decay rate as well as the fluorescence power depend sensitively on the position and direction of the transition dipole of the molecule.