bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and properties of epitaxial Ba0.5Sr0.5TiO3/SrRuO3/ZrO2 heterostructure on Si grown by off-axis sputtering
Authors: Hou S. Y. , Kwo J. , Watts R. K. , Cheng J.-Y. , Fork D. K.
Published: July 2002

We report the growth and characterization of epitaxial Ba0.5Sr0.5TiO3/SrRuO3/ZrO2 on Si for potential charge storage applications. Both Ba0.5Sr0.5TiO3 (BST) and SrRuO3 (SRO) are grown (110)-oriented on yttrium-stabilized ZrO2 (YSZ) (100)-buffered Si. These films show a high degree of crystallinity with minimal interdiffusion at the interfaces as evidenced from x-ray diffraction, Rutherford backscattering, and transmission electron microscopy. Studies on the in-plane crystallographic relations between the layers revealed an interesting rectangle-on-cube epitaxy between BST/SRO and YSZ. The dielectric constant and loss tangent of the BST dielectric layer are 360 and 0.01 at 10 kHz, respectively. The leakage current density is lower than 4×10−7 A/cm2 at 1 V. A strong frequency dependence on both dielectric constant and loss tangent is observed in 1–10 MHz frequency range. This is attributed to the effect of a series resistance in the measurement loop, which is likely related to the bottom SrRuO3 electrode.
Deposition of high quality wurtzite GaN films over cubic (111) MgAl2O4 substrates using low pressure metalorganic chemical vapor deposition
Authors: Sun C. J. , Yang J. W. , Chen Q. , Asif Khan M. , George T. , Chang-Chien P. , Mahajan S.
Published: July 2002

We report the deposition of high quality single-crystal wurtzite GaN films on cubic (111) spinel (MgAl2O4) substrates. The room-temperature electron mobility and the optically pumped stimulated emission threshold for these films are nearly identical to those of films deposited on basal plane sapphire. Using cross sectional high resolution TEM we have determined the following orientation relationship between the film and the substrate: [0001]GaN//[111]MgAl2O4 and [112̄0]GaN//[110]MgAl2O4. This should provide a common cleavage plane for (111) spinel and the wurtzite GaN films over it.
The temperature dependence of the ion beam induced interfacial amorphization in silicon
Authors: Henkel T. , Heera V. , Kögler R. , Skorupa W. , Seibt M.
Published: July 2002

The temperature dependence of the ion beam induced interfacial amorphization process (IBIIA) in silicon has been investigated at temperatures above 80 K using Rutherford backscattering spectrometry/channeling (RBS/C) and cross-sectional transmission electron microscopy (XTEM). Three regimes are observed. Above temperatures of about 320 K there is a strong temperature dependence of the IBIIA rate (thermal regime). At lower temperatures the rate moves towards a saturation value (transition regime). Below ∼150 K, IBIIA is nearly temperature independent (ballistic regime). This low-temperature regime can be explained by an athermal transport of point defects like in ballistic mixing processes.
Size classification of silicon nanocrystals
Authors: Camata Renato P. , Atwater Harry A. , Vahala Kerry J. , Flagan Richard C.
Published: July 2002

We report on the synthesis of size-classified silicon nanocrystals by differential mobility classification of a polydisperse ultrafine silicon aerosol. Using the described technique, the average nanocrystal size can be tuned by simply adjusting an electric field. Samples of nonagglomerated silicon nanocrystals have been obtained and size control has been achieved within 15%–20% in the 2–10 nm size regime.
Ordering along 〈111〉 and 〈100〉 directions in GaInP demonstrated by photoluminescence under hydrostatic pressure
Authors: Dong Jianrong , Wang Zhanguo , Lu Dacheng , Liu Xianglin , Li Xiaobing , Sun Dianzhao , Wang Zhijie , Kong Meiying , Li Guohua
Published: July 2002

Photoluminescence of GaInP epilayers under hydrostatic pressure is investigated. The Γ valley of disordered GaInP shifts sublinearly upwards with respect to the top of the valence band with increasing pressure and this sublinearity is caused by the nonlinear dependence of lattice constant on the hydrostatic pressure. The Γ valleys of ordered GaInP epilayers rise slower than that of the disordered one. Considering the interactions between the Γ valley and folded L and X valleys, the pressure dependence of the band gap of ordered GaInP is calculated and fitted. The results demonstrate that not only ordering along 〈111〉 directions but also sometimes simultaneous ordering along 〈111〉 and 〈100〉 directions can occur in ordered GaInP.
Optical gain in GaInN/GaN heterostructures
Authors: Frankowsky G. , Steuber F. , Härle V. , Scholz F. , Hangleiter A.
Published: July 2002

By optical gain spectroscopy we have studied the fundamental laser properties of GaInN/GaN heterostructures grown on sapphire. Utilizing the stripe excitation method we have measured optical gain spectra at room temperature. Due to the low symmetry of the wurtzite structure and the resulting splitting of the uppermost valence bands, we find optical gain only for the TE mode. Our analysis shows that the optical gain is due to direct band-to-band transitions in an electron-hole plasma. For gain amplitudes typically found in lasers, we find carrier densities up to 3×1019 cm−3, which are likely to lead to rather large threshold current densities.
High-quality GaInN/GaN multiple quantum wells
Authors: Koike M. , Yamasaki S. , Nagai S. , Koide N. , Asami S. , Amano H. , Akasaki I.
Published: July 2002

High-quality Ga0.92In0.08N–GaN multiple quantum wells structures (MQW) were grown successfully by metalorganic vapor phase epitaxy. Fine multilayer structures with a thickness period of 7–9 nm were detected by secondary ion mass spectroscopy. The dislocation density in the MQW was found to be in the range of 0.5–2×109 cm−2 by transmission electron microscopy. The MQW extremely enhanced by two orders of magnitude, the cathodoluminescence intensity compared with bulk Ga0.91In0.09N.
Influence of precursor gases on the structure of plasma deposited amorphous hydrogenated carbon–nitrogen films
Authors: Franceschini D. F. , Freire F. L. , Silva S. R. P.
Published: July 2002

The atomic structure of amorphous hydrogenated carbon–nitrogen films was studied by electron energy loss spectroscopy (EELS). The films were deposited onto Si(100) substrates by rf plasma decomposition of CH4–NH3 and CH4–N2 mixtures, with substrates placed on the powered electrode of a diode glow-discharge system. The sp2 fraction of C and N atoms as a function of the nitrogen content in the films was obtained by EELS analysis. An increase of the carbon sp2 fraction with increasing fraction of NH3 and N2 feed gases was observed. The variation in the atomic structure of the a-C(N):H thin films is correlated to the internal compressive stress.
Continuous-wave operation of a blue vertical-cavity surface-emitting laser based on second-harmonic generation
Authors: Yamada Norihide , Kaneko Yasuhisa , Nakagawa Shigeru , Mars Dan E. , Takeuchi Tetsuya , Mikoshiba Nobuo
Published: July 2002

An InGaAs/GaAs vertical-cavity surface-emitting laser has been fabricated on a (311)B GaAs substrate. Pulsed lasing operation is obtained at room temperature, and continuous-wave lasing operation is obtained at less than 270 K. From the device, blue laser emission based on second-harmonic generation is observed. The wavelength of the blue laser emission is 482 nm. At 135 K, its output power is 1 nW under continuous-wave operation and more than 10 nW under pulsed operation.
Temperature sensitivity and thermal expansion coefficient of benzocyclobutene thin films studied with ellipsometry
Authors: Guo S. , Lundström I. , Arwin H.
Published: July 2002

Temperature induced changes in thickness and refractive index of thin films of benzocyclobutene (BCB) have been studied with ellipsometry in the temperature range 22–190 °C. The ellipsometric parameters Ψ and Δ, which depend on both the thickness and the optical constants of the BCB films, change significantly with temperature with short response times. The temperature sensitivity, resolution, and dynamic range depend on film thickness and wavelength. For a film with thickness 4.73 μm, a sensitivity of 0.2°/°C with a resolution of 0.25 °C is achieved within a range of 170 °C. Thermal expansion coefficients (TEC) of BCB films with different thicknesses evaluated from spectroscopic ellipsometric measurements are in the range 6.1–6.5×10−5/°C. Based on the findings here, a real-time detection system for remote optical monitoring of surface temperature variation can be developed. A technique for the determination of TEC of some organic films is also feasible.
Study of anomalous peak in the dielectric spectra of CdTe thin films using photoellipsometry
Authors: Paulson P. D. , Dutta V.
Published: July 2002

Dielectric constants of CdTe thin films in the presence of a weak pump beam have been measured at room temperature using photoellipsometric technique in the energy range 1.5–5 eV. An anomalous peak is observed in the dielectric spectra of CdTe thin films deposited in oxygen ambient. The peak height depends on the oxygen content in the film and intensity of the pump beam. No peak was observed when the films were deposited under high vacuum (2×10−6 Torr) or if the pump beam power was <25 μW.
Direct comparison of GaAs surface morphology between migration enhanced epitaxy and molecular beam epitaxy using in situ scanning electron microscopy
Authors: Homma Yoshikazu , Yamaguchi Hiroshi , Horikoshi Yoshiji
Published: July 2002

We have used scanning electron microscopy (SEM) for real-time-observation to compare the surface evolution during the early stage growth of GaAs with molecular beam epitaxy (MBE) and migration enhanced epitaxy (MEE), at the substrate temperature of 500 °C. Surface roughness during MEE growth is about 1 ML and much smaller than during MBE growth. Immediately after growth termination, monolayer steps can be seen and the surface recovers to initial smoothness in MEE, while islands do not disappear without higher temperature annealing in MBE. Present results confirm high surface atom mobility in MEE growth.
Hydrostatic pressure dependence of the photoluminescence of Si nanocrystals in SiO2
Authors: Cheong Hyeonsik M. , Paul W. , Withrow S. P. , Zhu J. G. , Budai J. D. , White C. W. , Hembree D. M.
Published: July 2002

We have measured the hydrostatic pressure dependence of the photoluminescence (PL) of Si nanocrystals in SiO2 layers at room temperature and at pressures up to 50 kbar. The samples were fabricated by ion implantation and subsequent annealing. For the two samples measured, negative pressure coefficients of −0.4 and −0.6 meV/kbar were obtained. These values are not in good quantitative agreement with an estimate based on the quantum confinement model. Possible implications of this disagreement are discussed.
Magnetoconductivity and Hall effects in La0.67Ca0.33MnO3
Authors: Snyder G. Jeffrey , Beasley M. R. , Geballe T. H. , Hiskes Ron , DiCarolis Steve
Published: July 2002

The observed H2 and |H| dependence of the magnetoresistance above and below TC, respectively, may be explained by general time-reversal symmetry considerations. We further find empirically that the saturation observed in the magnetoresistance is best fit by a simple resistor in series with a magnetoconductor: ρ(H)=ρ∞+1/(σ0+γ|H|) for TTC. This provides a functional form to analyze and predict the magnetoresistance over a wide range of fields. This suggests that the underlying mechanism of ‘‘colossal magnetoresistance ’’ may be magnetoconductive, not magnetoresistive. The magnetoresistance and Hall effects on an annealed epitaxial thin films of La0.67Ca0.33MnO3 were measured at 0.9 TC and 1.1 TC. At low fields, anisotropic magnetoresistance plays a dominant role. The high field Hall effect shows holelike carriers above and below TC. The apparent change in sign at low fields is likely due to the anomalous Hall effect.
Role of silicon surface in the removal of point defects in ultrashallow junctions
Authors: Sultan A. , Banerjee S. , List S. , Rodder M.
Published: July 2002

The role of the Si surface in the annihilation of point defects has been studied for ultrashallow p+/n junctions. The dopant and defect distributions for low-energy implants lie within a few hundred angstroms of the surface. The proximity of the Si surface has been shown to help in the efficient removal of point defects for the shallower junctions. A 5 keV, 1×1015 cm−2 BF2 implant and a 30 keV, 3.3×1014 cm−2 BF2 implant were estimated to create comparable damage at different depths. After identical anneals, the higher-energy implant sample showed end-of-range dislocation loops in cross-sectional transmission electron microscopy analysis, while the low-energy sample, for which the point defect distribution was closer to the surface, was defect free. This is attributed to the role of the Si surface as an efficient sink for the removal of point defects.
Determination of the oxide-precipitate–silicon-matrix interface energy by considering the change of precipitate morphology
Authors: Senkader S. , Hobler G. , Schmeiser C.
Published: July 2002

A model of strain relief via interactions with point defects during oxygen precipitation is presented. Assuming that precipitation of oxygen is diffusion limited and that it evolves in such a way that the total system free energy is minimized the governing relations describing strain relief are obtained. The impact of strain and of point defects on the precipitate morphology is adressed. The model is used to calculate the precipitate–matrix interface energy using published data on precipitate morphology changes. The results suggest that the interface energy should be much larger than the presently well-accepted values.
Preparation of epitaxial metallic LaNiO3 films on SrTiO3 by metalorganic decomposition for the oriented growth of PbTiO3
Authors: Li Aidong , Ge Chuanzhen , Lü Peng , Ming Naiben
Published: July 2002

Epitaxial metallic LaNiO3 (LNO) films on SrTiO3 (STO) were prepared by metalorganic decomposition. X-ray θ–2θ scans, x-ray φ scans, and the Rutherford backscattering channeling technique were used to determine the degree of crystallinity of the films. The trend of resistance as a function of annealing temperature of LNO films on STO and Si substrates indicated that LNO films on STO have lower crystalline temperature and higher transition temperature from conductor to insulator than on Si. (001)-oriented PbTiO3 (PT) films were grown on LNO-coated STO by the sol-gel method. Scanning electron microscopy of a cross section of PT/LNO/STO showed sharp boundaries. The ferroelectric capacitor fabricated from these films displayed promising P-E hysteresis characteristics.
Fabrication and microscopic photoluminescence imaging of ridge-type InGaAs quantum wires grown on a (110) cleaved plane of AlGaAs/GaAs superlattice
Authors: Arakawa T. , Watabe H. , Nagamune Y. , Arakawa Y.
Published: July 2002

We have fabricated ridge-type InGaAs quantum wire structures on a (110) cleaved plane of AlGaAs/GaAs superlattice using selective metalorganic chemical vapor deposition growth. The lateral width of the quantum wires was about 25 nm. Spatially resolved photoluminescence (PL) of the quantum wires was observed by using microscopic photoluminescence measurement at low temperature, showing PL from the quantum wire region and its polarization dependence.
Synthesis of SiGe and SiGeC alloys formed by Ge and C implantation
Authors: Lu Xiang , Cheung Nathan W.
Published: July 2002

In this study, near surface SiGe and SiGeC alloys with germanium peak composition up to 16 at.% were formed using high-dose ion implantation and subsequent solid phase epitaxial growth. Rutherford backscattering spectroscopy (RBS) channeling spectra and cross-sectional transmission electron microscopy (XTEM) studies showed that high quality Si0.92Ge0.08 and Si0.91Ge0.08C0.01 crystals were formed at the Si surface, while Si0.84Ge0.16 and Si0.82Ge0.16C0.02 layers had extended defects. X-ray diffraction experiments demonstrated that carbon could reduce the lattice strain in SiGe alloys but without significant crystal quality improvement as detected by RBS channeling spectra or XTEM observations.
Strain effects on valence band structure in würtzite GaN quantum wells
Authors: Sirenko Yu. M. , Jeon J.-B. , Kim K. W. , Littlejohn M. A. , Stroscio M. A.
Published: July 2002

The effect of strain on valence band spectra in both bulk and in pseudomorphic GaN quantum wells is studied theoretically using recent experimental results for deformation potential constants. Wave functions and dispersion curves for A-, B- and C-hole subbands are obtained from linear combination of bulk analytical solutions for the 3×3 würtzite block-Hamiltonian. A detailed analysis is presented for the dependence of hole spectrum on quantum well width, depth, and strain due to lattice mismatch.
Theoretical study of thresholdless Auger recombination in compressively strained InAlAsSb/GaSb quantum wells
Authors: Andreev Aleksey D. , Zegrya Georgy G.
Published: July 2002

The effect of strain on thresholdless Auger recombination in quantum wells has been studied theoretically. A detailed analysis of overlap integrals between the initial and final states of carriers has been carried out. It is shown that the strain affects both qualitatively and quantitatively the overlap integral between the electron and hole states. The Auger recombination coefficient is calculated for InAlAsSb quantum well and its dependence on quantum well parameters, strain, and temperature is analyzed.
Tuning of the single-particle relaxation time of a high mobility electron gas in a Ga0.25In0.75As/InP quantum well
Authors: Ramvall P. , Carlsson N. , Omling P. , Samuelson L. , Seifert W. , Wang Q.
Published: July 2002

Two different scattering mechanisms determine the momentum relaxation time, τ, and the single particle relaxation time, τs, of the electrons in a modulation doped Ga0.25In0.75As/InP quantum well. We show that τ is mainly limited by alloy disorder scattering, while τs is determined by the remote ionized impurity scattering rate. This means that the Ga0.25In0.75As/InP material system offers the unique possibility of tuning τs by varying the distance between the modulation doped layer and the two-dimensional electron gas, while τ is kept constant. The variation of τs can thus be monitored, for example, by observing the appearance of spin-split Landau levels, at different magnetic fields, as a function of spacer layer width.
Using microcontact printing to fabricate microcoils on capillaries for high resolution proton nuclear magnetic resonance on nanoliter volumes
Authors: Rogers John A. , Jackman Rebecca J. , Whitesides George M. , Olson Dean L. , Sweedler Jonathan V.
Published: July 2002

This letter describes a method for producing conducting microcoils for high resolution proton nuclear magnetic resonance (1H-NMR) spectroscopy on nanoliter volumes. This technique uses microcontact printing and electroplating to form coils on microcapillaries. Nuclear magnetic resonance spectra collected using these microcoils, have linewidths less than 1 Hz for model compounds and a limit of detection (signal-to-noise ratio=3) for ethylbenzene of 2.6 nmol in 13 min.
Nanometer-scale Si selective epitaxial growth on Si(001) surfaces using the thermal decomposition of ultrathin oxide films
Authors: Fujita Ken , Watanabe Heiji , Ichikawa Masakazu
Published: July 2002

Nanometer-scale Si crystals were produced by selective epitaxial growth on Si(001) surfaces passivated with 0.3-nm-thick oxide films. Window areas for the growth were provided by void formation during the thermal decomposition of the oxide films. Dynamical processes of the void formation and epitaxial growth were observed at 630–730 °C by scanning tunneling microscopy. The crystal shape was a quadrangular pyramid and the typical size was 20 nm in length and 0.8 nm in height. The thin oxide films were found to act as masks for the selective epitaxial growth of nanoscale structures.
The dissolution behavior of the void defects by hydrogen annealing in Czochralski grown silicon crystals
Authors: Nakamura K. , Saishoji T. , Tomioka J.
Published: July 2002

The annihilation of grown-in defects by hydrogen annealing have been explained as the dissolution of oxygen precipitates, because it has been generally thought that grown-in defects in Czochralski silicon crystals are gigantic oxygen precipitates. However, it is necessary to re-examine the mechanism of the annihilation of the defects by hydrogen annealing, because recently it has been shown that the grown-in defects were voids of octahedral shape. In this letter, a simulation model is presented which describes the annihilation process of void defects by hydrogen annealing.
Characterization of SrBi2Ta2O9 ferroelectric thin films deposited at low temperatures by plasma-enhanced metalorganic chemical vapor deposition
Authors: Seong Nak-Jin , Yoon Soon-Gil , Lee Seaung-Suk
Published: July 2002

Ferroelectric bismuth-layer SrBi2Ta2O9(SBT) thin films were prepared on Pt/Ti/SiO2/Si substrate by plasma-enhanced metalorganic chemical vapor deposition. The films were crystallized at temperatures between 500 and 600 °C. The dielectric constant and dissipation factor of SBT films were 320 and 0.04 at an applied frequency of 1 MHz, respectively. The remanent polarization (Pr) and the coercive field (Ec) obtained for a 200 nm thick Sr0.9Bi2.3Ta2.0O9 films deposited at 550 °C were 15 μC/cm2 and 50 kV/cm at an applied voltage of 3 V, respectively. The leakage current density was about 5.0×10−8 A/cm2 at 300 kV/cm. The films showed fatigue-free characteristics up to 1.0×1011 switching cycles under 6 V bipolar pulse.
Wavelength switching in multicavity lasers
Authors: Kanjamala A. P. , Levi A. F. J.
Published: July 2002

By controlling optical loss in a multiple cavity laser, it is possible to sequentially switch the lasing wavelength with a mode suppression ratio greater than −35 dB. Our experiments use an antireflection coated semiconductor laser diode with optical feedback from Bragg gratings embedded in a single mode fiber. Residual reflectivity from the antireflection coating plays a critical role in determining device operation.
Deposition-induced photoluminescence quenching of tris-(8-hydroxyquinoline) aluminum
Authors: Choong V.-E. , Park Y. , Shivaparan N. , Tang C. W. , Gao Y.
Published: July 2002

Ca, Ag, and Ge atoms quench the photoluminescence (PL) of an organic thin film, tris-(8-hydroxyquinoline) aluminum (Alq3), a model organic material for organic light emitting diodes. The observed PL quenching behavior was similar for all three elements, independent of their metallic nature. Due to strong interactions at the Ca/Alq3 interface, the quenching was much less effective at submonolayer coverages. We have also observed that proper oxidation of Ca at the Ca/Alq3 interface can significantly recover the quenched luminescence of Alq3.
Effects of the auxiliary electrode radius during plasma immersion ion implantation of a small cylindrical bore
Authors: Zeng X. C. , Kwok T. K. , Liu A. G. , Chu P. K. , Tang B. Y. , Sheridan T. E.
Published: July 2002

The temporal evolution of the plasma sheath in a small cylindrical bore in the presence of an auxiliary electrode is determined for different electrode radii. The ion density, velocity, flux, dose, ion energy distribution, and average impact energy are calculated by solving Poisson’s Equation and the equations of ion motion and continuity using finite difference methods. The particle-in-cell method is also used to confirm the validity of the data. Our results indicate that more ions will attain high impact energy when the auxiliary electrode radius is increased, but the dose will decrease. Our results suggest that the normalized auxiliary electrode radius should range from 0.10 to 0.30 in order to maximize the dose and produce a larger number of ions with higher impact energy.
Tuning self-assembled InAs quantum dots by rapid thermal annealing
Authors: Malik Surama , Roberts Christine , Murray Ray , Pate Malcolm
Published: July 2002

Blueshifts in the photoluminescence emission energies from an ensemble of self-assembled InAs quantum dots are observed as a result of postgrowth thermal annealing. Enhancement of the integrated photoluminescence emission and narrowing of the full width half-maxima (from 55 to 12 meV) occur together with blueshifts up to 300 meV at annealing temperatures up to 950 °C. Evidence that the structures remain as dots comes form the observation of level filling and photoluminescence excitation studies which reveal LO phonon peaks occurring at multiples of ∼30 meV from the detection energies.
Competitive adsorption effects in the metalorganic vapor phase epitaxy of GaN
Authors: Briot O. , Clur S. , Aulombard R. L.
Published: July 2002

The growth mechanisms of GaN grown on a GaN buffer deposited onto sapphire substrates are studied here. The growth rate was measured at different temperatures versus ammonia flow and was found to decrease with increasing NH3 flow. This surprising behavior is modeled in terms of competitive adsorption of species on the growing surface. Very good agreement is obtained between the model and the experimental data.
Suppression of ferroelectric polarization by an adjustable depolarization field
Authors: Black C. T. , Farrell Curtis , Licata Thomas J.
Published: July 2002

We have measured the effect of a depolarizing field on the properties of a ferroelectric capacitor. By systematically adjusting the amount of charge available to compensate the polarization, we can control the strength of the field inside the ferroelectric. We find that even a few percent of uncompensated polarization charge results in a significant suppression of measured ferroelectric properties, and a complete lack of compensating charge leaves a greatly reduced, although nonzero, polarization. The effect of a depolarizing field is briefly discussed in terms of proposed ferroelectric device applications.
Wavelength shifting in GaAs quantum well lasers by proton irradiation
Authors: Tan H. H. , Jagadish C.
Published: July 2002

Proton irradiation followed by rapid thermal annealing was used to selectively induce layer intermixing and thus shift the emission wavelengths of GaAs–AlGaAs graded-index separate-confinement-heterostructure quantum well lasers. Up to 40 nm shifts were observed in 4 μm ridge waveguide devices irradiated to a dose of 1.5×1016 cm−2. Although the wavelength shifts were accompanied by some degradation in the lasing threshold current and differential quantum efficiency, they were still quite acceptable at moderate wavelength shifts. This technique provides a simple and promising postgrowth process of integrating lasers of different wavelengths for wavelength-division-multiplexing applications.
Improved spatial resolution in magnetic force microscopy
Authors: Skidmore George D. , Dahlberg E. Dan
Published: July 2002

Electron beam deposited spikes for use in magnetic force microscopy have been grown onto atomic force microscope tips and coated with magnetic thin films using thermal evaporation. The resulting magnetically active regions are a close approximation to monopoles or dipoles located on the very end of the spikes. We show that these tips image with increased spatial resolution and less sample perturbation than the standard, commercially available tips.
Structural and electrical properties of low-temperature-grown Al(As,Sb)
Authors: Blank H.-R. , Kroemer H. , Mathis S. , Speck J. S.
Published: July 2002

We have investigated structural and electrical properties of Al(As,Sb) dual-anion compounds grown by molecular beam epitaxy at low substrate temperature. We find single-crystal growth down to substrate temperatures as low as 275 °C. Additional donor-type defects form when Al(As,Sb) is grown at 450 °C or less, with the defect density increasing with decreasing substrate temperature. We find no evidence for the formation of precipitates upon annealing low-temperature-grown (LTG) Al(As,Sb) in contrast to LTG arsenides.
Optical properties of low band gap GaAs(1−x)Nx layers: Influence of post-growth treatments
Authors: Rao E. V. K. , Ougazzaden A. , Le Bellego Y. , Juhel M.
Published: July 2002

A detailed study on the optical quality of atmospheric pressure metalorganic vapor phase epitaxy grown GaAs(1−x)Nx epilayers (on GaAs substrates) in which the N incorporation is accomplished using dimethylhydrazine precursor is reported. We show here that the poor optical quality of these as-grown layers can be significantly improved by carefully planned post-growth heat treatments. Optical data are presented to demonstrate unambiguously that such treatments affect in no way the physical properties of these metastable layers (no phase separation) and that the improvement of their optical quality is closely connected to the incorporation behavior of N in this growth method.
Enhanced thermodynamic stability of tetragonal-phase field in epitaxial Pb(Zr,Ti)O3 thin films under a two-dimensional compressive stress
Authors: Oh S. Hoon , Jang Hyun M.
Published: July 2002

A two-dimensional thermodynamic model was developed to account for the observed difficulty in the fabrication of epitaxial Pb(Zr,Ti)O3 (PZT) thin films in which tetragonal and rhombohedral phases coexist. The thermodynamic formalism based on the Landau–Devonshire’s phenomenological theory predicts the enhanced thermodynamic stability of the tetragonal-phase field under a two-dimensional compressive stress. We have experimentally proved this prediction by fabricating an epitaxially oriented tetragonal PZT thin film on MgO substrate with the target composition corresponding to the bulk morphotropic phase boundary (MPB).
Observation of voltage-locked states in strongly coupled stacked Josephson junctions
Authors: Carapella G. , Costabile G.
Published: July 2002

We have fabricated and tested two stacks of strongly coupled long Josephson junctions with access to the intermediate electrode so that they can be independently biased. In these samples, we find four families of voltage-locked states in zero external magnetic field. One of these families is identified with the zero field steps already observed and interpreted in the case of weaker coupling; the others appear to be new phenomena. The voltage spacing of one of them suggests the necessity of a refinement of the current model to obtain a full description of the dynamical states in stacked junctions.
Mechanical parametric amplification in piezoresistive gallium arsenide microcantilevers
Authors: Dâna A. , Ho F. , Yamamoto Y.
Published: July 2002

Preamplification of mechanical signals in external force detection systems can improve overall sensitivity in a case where sensitivity is limited by secondary detection noise. We report experimental data on degenerate and nondegenerate mechanical parametric amplification in GaAs piezoresistive atomic force microscopy cantilevers due to an inherent mechanical nonlinearity. The mechanical nonlinearity is estimated to be a result of curvature at the cantilever base. Characteristics of parametric amplification such as phase sensitive gain, small signal gain, gain saturation, and self-oscillation have been studied. A small signal phase sensitive gain of 19.5 dB was observed for the degenerate parametric amplifier.
Acoustic time reversal with mode conversion at a solid-fluid interface
Authors: Draeger Carsten , Cassereau Didier , Fink Mathias
Published: July 2002

Acoustic time-reversal experiments are mostly carried out in fluid media. This letter presents experiments proving the capability of a time-reversal mirror to obtain simultaneous focusing of both propagation modes inside a solid. The mirror is located in a surrounding fluid and records the longitudinal and transverse wavefronts (created by a laser impact on the solid) after conversion into pressure waves at the solid-fluid interface. We show that the time-reversed pressure wavefronts are reconverted mostly to their original propagation mode and focus simultaneously at the location of the laser impact.
Evidence for misfit dislocation-related carrier accumulation at the InAs/GaP heterointerface
Authors: Gopal V. , Kvam E. P. , Chin T. P. , Woodall J. M.
Published: July 2002

The electrical properties of the mismatched interface between InAs and GaP have been investigated. High-resolution transmission electron microscopy images show the presence of strain relieving, 90° misfit dislocations at this interface. Hall measurements and electrochemical capacitance–voltage profiling indicate the presence of a high-density sheet of carriers (electrons and holes) at the interface. A linkage is drawn between interfacial carriers and misfit dislocations. A model based on Fermi-level pinning in InAs at the interface by misfit dislocations is proposed to account for the observed electrical behavior.
Magnetotransport of delta-doped In0.57Ga0.43As on InP(001) grown between 390 and 575° C by molecular beam epitaxy
Authors: Zervos Matthew , Bryant Adam , Elliott Martin , Beck Mathias , Ilegems Marc
Published: July 2002

Silicon (Si) delta- (δ-) doped In0.53Ga0.47As layers were grown by molecular beam epitaxy on InP(001) substrates between 390 °C and 575 °C. Subbands formed at the δ layer were examined with Hall and Shubnikov-de Haas effect measurements in conjunction with self-consistent Poisson-Schrödinger modeling. Below a growth temperature of 525 °C we find good agreement with modeling, but above 525 °C a decrease in active doping level suggests possible surface aggregation, or reaction with impurities in the growth chamber. Significant surface segregation spread of the Si is only found for growth above 450 °C. There is some evidence that DX-like centers may be present, since their incorporation improves slightly the quality of the fits to subband occupancies. Samples grown at 390 °C show strong persistent photoconductivity at low temperatures, attributed to defect states in the InGaAs.
Enhancement of x-ray lasing due to wavefront correction of line-focusing optics with a large-aperture deformable mirror
Authors: Yoon Geun-Young , Imani Takeomi , Daido Hiroyuki , Jitsuno Takahisa , Kato Yoshiaki , Nakatsuka Masahiro , Wang Shiji , Lin Zunqi , Gu Yuan , Huang Guanlong , Tang Huajing , Zhang Guoping
Published: July 2002

Intense x-ray laser radiation at 7.92 nm in nickel-like neodymium has been achieved by improving the line-focusing pattern using a large-aperture deformable mirror. A deformable mirror of 40 cm diameter with hexagonally arranged 37 mechanical actuators has been developed. The wavefront aberration due to a cylindrical lens used for line focusing has been corrected with the deformable mirror to produce a line-focusing pattern of uniform narrow width and uniform intensity distribution. The intensity of the x-ray laser beam has increased six times due to the improvement of the line-focusing pattern.
Band offsets at GaInP/AlGaInP(001) heterostructures lattice matched to GaAs
Authors: Zhang X. H. , Chua S. J. , Fan W. J.
Published: July 2002

In this work, the band offsets at the Ga0.5In0.5P/AlxGa0.5−xIn0.5P heterojunction lattice matched to (001) GaAs was calculated over the whole range of aluminum composition from x=0.0 to 0.5 using the first-principles pseudopotential method with virtual crystal approximation. The valence band offset, VBO, varies with x as VBO=0.433x eV, while the inferred conduction band offset CBO at Γ minimum (band-gap difference minus the valence band offset) varies in x as CBOΓ=0.787x eV. Our results are in good agreement with the experimental data.
Quantitative nonlinear dielectric microscopy of periodically polarized ferroelectric domains
Authors: Gao Chen , Duewer Fred , Lu Yalin , Xiang X.-D.
Published: July 2002

A nonlinear dielectric scanning tip microwave near-field microscope capable of submicron quantitative imaging of nonlinear dielectric constant was developed. This nondestructive technique was used to image the nonlinear dielectric constant profiles of an yttrium-doped LiNbO3 single crystal with periodically polarized ferroelectric domains.
Effect of fluorine on the diffusion of boron in ion implanted Si
Authors: Downey Daniel F. , Chow Judy W. , Ishida Emi , Jones Kevin S.
Published: July 2002

Ion implants of 1 keV B+11 and 5 keV BF2+, to a dose of 1×1015/cm2 at a tilt angle of 0°, were implanted into preamorphized (Si+,70 keV, 1×1015/cm2) wafers. These samples were rapid thermal annealed in an ambient of 33 ppm of oxygen in N2 at very short times (<0.1 s spike anneals) at 1000 and 1050 °C to investigate the effects of the fluorine in BF2 implants on transient enhanced diffusion (TED). By using a relatively deep preamorphization of 1450 Å, any difference in damage between the typically amorphizing BF2 implants and the nonamorphizing B implants is eliminated because the entire profile (<800 Å after annealing) is well contained within the amorphous layer. Upon annealing, the backflow of interstitials from the end-of-range damage from the preamorphization implant produces TED of the B in the regrown layer. This allows the chemical effect of the fluorine on the TED of the B in the regrown Si to be studied independent of the damage. The secondary ion mass spectroscopy results show that upon annealing, the presence of fluorine reduces the amount of B diffusion by 30% for the 1000 °C spike anneal, and by 44% for the 1050 °C spike anneal. This clearly illustrates there is a dramatic effect of F on TED of B independent of the effects of implant damage. Analysis of the temperature dependence of the enhancement factors point to transient enhanced diffusion not boridation as the source of the interstitials.
High-temperature phase transformation in Ti-diffused waveguide layers of LiNbO3
Authors: Zolotoyabko E. , Avrahami Y. , Sauer W. , Metzger T. H. , Peisl J.
Published: July 2002

Phase formation processes accompanying high-temperature Ti diffusion in thin waveguide layers of LiNbO3 were studied by grazing-incidence x-ray diffraction and complementary techniques. The development and decay of a rutilelike phase (Li0.25Nb0.75O2)1−x (TiO2)x was directly observed as a function of annealing time. A solid-state reaction is proposed, which clarifies the mechanism of phase transformation, relating it to cation replacements.
Octahedral boron nitride fullerenes formed by electron beam irradiation
Authors: Golberg D. , Bando Y. , Stéphan O. , Kurashima K.
Published: July 2002

Here we report on the formation of fullerenes with a reduced number of layers (typically ⩽3) in boron nitride (BN) which was subjected to in situ electron irradiation at 20 and 490 °C in a high resolution 300 kV transmission electron microscope (HRTEM). The BN fullerenes exhibited B/N stoichiometry of ∼1 as confirmed by electron energy loss spectroscopy using a 1 nm electron probe. The fullerene HRTEM images revealed rectangle-like shapes when viewed in specific projections, unlike the quasispherical carbon fullerene morphology. The octahedral BN fullerene model [O. Stéphan, Y. Bando, A. Loiseau, F. Willaime, N. Shramchenko, T. Tamiya, and T. Sato, Appl. Phys. A 67, 107 (1998)] is verified by the BN fullerene observations at different viewing angles.
Pressure and temperature dependence of the absorption edge of a thick Ga0.92In0.08As0.985N0.015 layer
Authors: Perlin Piotr , Subramanya Sudhir G. , Mars Dan E. , Kruger Joachim , Shapiro Noad A. , Siegle Henrik , Weber Eicke R.
Published: July 2002

We have studied the pressure and temperature dependence of the absorption edge of a 4-μm-thick layer of the alloy Ga0.92In0.08As0.985N0.015. We have measured the hydrostatic pressure coefficient of the energy gap of this alloy to be 51 meV/GPa, which is more than a factor two lower than that of GaAs (116 meV/GPa). This surprisingly large lowering of the pressure coefficient is attributed to the addition of only ∼1.5% nitrogen. In addition, the temperature-induced shift of the edge is reduced by the presence of nitrogen. We can explain this reduction by the substantial decrease of the dilatation term in the temperature dependence of the energy gap.
Determination of the valence-band offset for GaInAsSb/InP heterostructure
Authors: Chang J. R. , Su Y. K. , Lu Y. T. , Jaw D. H. , Shiao H. P. , Lin W.
Published: July 2002

Unstrained Ga0.64In0.36As0.84Sb0.16/InP single quantum-well structures were grown on InP substrates by metalorganic vapor phase epitaxy. Transmission electron microscopy and temperature-dependent photoluminescence (PL) measurements were performed. The valence-band offset of the GaInAsSb/InP heterojunction was estimated by the dependence of PL peak energy on the well width at 8 K. We estimated the valence-band offset to be 70±5% of the band-gap difference for the Ga0.64In0.36As0.84Sb0.16/InP heterostructure.
Characterization of the low-frequency noise in high-temperature radio frequency superconducting quantum interference devices cooled in static magnetic fields
Authors: Borgmann J. , David P. , Otto R. , Schubert J. , Braginski A. I.
Published: July 2002

We have performed a study of the low-frequency noise in high-temperature radio frequency (rf) superconducting quantum interference devices (SQUIDs) cooled in static magnetic fields. At 77 K, the noise of different thin-film YB2C3O7−x washer rf SQUIDs was measured in static magnetic fields up to 55 μT. The SQUID inductances ranged from 150 to 300 pH. The measured low-frequency flux noise of the SQUIDs SΦ1/2 at 1 Hz was between 70 and 350 μΦ0/√Hz, and in terms of magnetic field noise SB1/2 between 120 and 1100 fT/√Hz. The low-frequency noise of all devices at 1 Hz showed no significant increase for all applied static fields.
A monoclinic ferroelectric phase in the Pb(Zr1−xTix)O3 solid solution
Authors: Noheda B. , Cox D. E. , Shirane G. , Gonzalo J. A. , Cross L. E. , Park S-E.
Published: July 2002

A previously unreported ferroelectric phase has been discovered in a highly homogeneous sample of PbZr0.52Ti0.48O3 by high-resolution synchrotron x-ray powder diffraction measurements. At ambient temperature the sample has tetragonal symmetry (at=4.037 Å, ct=4.138 Å), and transforms below ∼250 K into a phase which, unexpectedly, has monoclinic symmetry (am=5.717 Å, bm=5.703 Å, cm=4.143 Å, β=90.53°, at 20 K). The intensity data strongly indicate that the polar axis lies in the monoclinic ac plane close to the pseudocubic [111] direction, which would be an example of the species m3m(12)A2Fm predicted on symmetry grounds by Shuvalov.
Electrodeposited spin valves on n-type GaAs
Authors: Attenborough K. , Boeve H. , De Boeck J. , Borghs G. , Celis J.-P.
Published: July 2002

Soft switching, spin-valve Co/Cu heterostructures have been electrodeposited onto n-type (100) GaAs. A symmetric spin-valve configuration is used which incorporates an artificially hard substructure. A magnetoresistance change of up to 5.4% is observed with sensitivities up to 0.55% per Oersted and a saturation field of 100 Oe, the highest sensitivity so far observed in electrodeposited structures. The magnetoresistance measurements show a double switching step which we conclude is due to the free layers having differing coercivities. The Co/GaAs interface induces an in-plane anisotropy in the films which is responsible for these remarkable spin-valve properties.
High conduction-band offset of AlInAsSb/InGaAs multiple quantum wells grown by metalorganic vapor phase epitaxy
Authors: Chang J. R. , Su Y. K. , Lin C. L. , Wu K. M. , Lu Y. T. , Jaw D. H. , Shiao H. P. , Lin W.
Published: July 2002

Unstrained Al0.66In0.34As0.85Sb0.15/In0.53Ga0.47As multiple-quantum-well (MQW) structures have been grown by metalorganic vapor phase epitaxy. Low-temperature photoluminescence was performed for these MQW structures. We compared the experimental data with the theoretical calculations. The conduction-band offset ratio of AlInAsSb/InGaAs heterojunction was set as an adjustable parameter in the theoretical model. We estimated the conduction-band offset ratio to be 0.90±0.05 for the Al0.66In0.34As0.85Sb0.15/In0.53Ga0.47As heterojunction.
AlGaN/GaN heterostructures on insulating AlGaN nucleation layers
Authors: Smart J. A. , Schremer A. T. , Weimann N. G. , Ambacher O. , Eastman L. F. , Shealy J. R.
Published: July 2002

A single temperature process using AlGaN nucleation layers has been developed that produces device-quality, GaN-based materials with bilayer step surfaces. The AlGaN nucleation layer is deposited by flow modulation organometallic vapor phase epitaxy at temperatures in excess of 1000 °C, where GaN and AlGaN films can be subsequently grown. We have optimized this process on both sapphire and SiC substrates, where the conditions for nucleation are found to be quite different. For growth on SiC, aluminum mole fractions ranging from 6% to 35% result in featureless surfaces. Optimizing the alloy composition and thickness of the nucleation layer on SiC allows the deposition of GaN buffer layers exceeding 5 μm without the formation of cracks. A minimum of 15% aluminum in the nucleation layer is required for smooth growth on sapphire substrates. High room temperature two-dimensional electron gas mobilities of 1575 and 1505 cm2/Vs with sheet charge densities of 1.0×1013 and 1.4×1013 cm−2 are observed in undoped AlGaN/GaN structures placed on insulating AlGaN nucleation layers on sapphire and SiC, respectively.
Hydrogen blister depth in boron and hydrogen coimplanted n-type silicon
Authors: Höchbauer T. , Nastasi M. , Mayer J. W.
Published: July 2002

We have studied the depths of hydrogen surface blisters in 〈100〉 n-type silicon, which formed after B+H coimplantation and heat treatment. The silicon substrates had three different dopant levels, ranging from 1014 to 1019 cm−3. The Si substrates were first implanted with B+ ions at 147 keV to a dose of 1015 cm−2. Some of the B-implanted samples were left in their as-implanted state; others were electrically activated by a rapid thermal anneal. The samples were then implanted with 40 keV H+ to a dose of 5×1016 cm−2. At the chosen implantation energies, the hydrogen- and boron-implantation distributions overlap. Following H+ implantation, all the samples were vacuum annealed and examined by ion-beam analysis and scanning electron microscopy. In all cases, the blister depth was consistently found to be strongly correlated with the H damage profile rather than the H or B concentration profiles.
Near-field photoluminescence imaging of single defects in a ZnSe quantum-well structure at low temperatures
Authors: von Freymann G. , Lüerßen D. , Rabenstein C. , Mikolaiczyk M. , Richter H. , Kalt H. , Schimmel Th. , Wegener M. , Okhawa K. , Hommel D.
Published: July 2002

Single bright-spot, bow-tie-shaped defects in a ZnSe heterostructure are spectroscopically imaged with 200 nm spatial resolution at a sample temperature of 20 K. The local thickness variations in the single ZnSe quantum-well lead to a lateral double-well potential resulting in a shift and enhancement of the quantum-well photoluminescence. The luminescence images of the ZnMgSSe barrier material are governed by nonradiative recombination at the four associated Frank partial dislocations.
Formation dynamics of silicon nanoparticles after laser ablation studied using plasma emission caused by second-laser decomposition
Authors: Makimura Tetsuya , Mizuta Taiji , Murakami Kouichi
Published: July 2002

We have investigated the dynamic formation of silicon nanoparticles after pulsed-laser ablation of a silicon target into argon gas, in order to fabricate the nanoparticles that exhibit visible photoluminescence with higher efficiency. The nanoparticles growing in argon gas were detected by measuring plasma emission resulting from decomposition of the nanoparticles by a second pulsed-laser beam. It was directly observed that the nanoparticles grow on the time scale of 1 ms.
A relation between surface oxide and oxygen-defect complexes in solid-phase epitaxial Si regrown from ion-beam-amorphized Si layers
Authors: Petkov Mihail P. , Chen Claudine M. , Atwater Harry A. , Rassiga Stefano , Lynn Kelvin G.
Published: July 2002

We present a direct evidence that ion implantation through thin (⩽5 nm) surface oxide layers is a source of O impurities, which form O-defect complexes during thermal treatment. The impurity-defect complexes are identified by correlating the results from positron annihilation spectroscopy, secondary-ion mass spectroscopy, and Monte Carlo simulations. The O atoms are introduced in the bulk by multiple recoil implantation by the primary ions. The signatures of large VmOn formations are observed at 800 °C, which implies the existence of smaller species at lower temperatures.