bluuebunny/crossref_metadata_2025 huggingface dataset:
A capacitive two-phase flow slug detection system
Authors: Teyssedou A. , Tye P.
Published: July 2002

A capacitive-type two-phase slug detection and characterization system has been developed. The main goal of this work consisted of developing a measurement technique that satisfies the following requirements: to be able to detect a wide range of liquid film thickness from a few millimeters up to the case when the channel is completely filled with water, to have a fast time response, to be nonintrusive and movable, to have a linear response for void fraction of up to 70%, and to be insensitive to the structure of the test section and to proximity effects. In order to detect very small changes in capacity required to fulfill these requirements, a nonlinear twin-T type bridge is used as the front end stage of the instrument. Furthermore, the linearity and stability response criteria are achieved by the appropriate selection of the geometry and topology of the electrodes; the calibration of the system shows an almost linear response for void fractions of up to 70%. The instrument is presently used to determine the slug propagation velocity and frequency in counter-current two-phase flow experiments.
Determination of Al mole fraction for null conduction band offset in In0.5Ga0.5P/AlxGa1−xAs heterojunction by photoluminescence measurement
Authors: Kim Kwan-Shik , Cho Yong-Hoon , Choe Byung-Doo , Jeong Weon Guk , Lim H.
Published: July 2002

Photoluminescence properties of In0.5Ga0.5P/AlxGa1−xAs heterojunctions in both staggered and straddling band alignment regimes have been investigated. From the relation between the energies of below-band gap luminescence and Al compositions in the staggered band alignment regime, we determined the Al composition for null conduction band offset of the heterojunction as well as the conduction band offset value of In0.5Ga0.5P/GaAs heterojunction. Assuming the transitivity between the conduction band offset values, we also obtained the fraction of the band gap energy difference that is associated with the conduction band offset of an AlGaAs/GaAs heterojunction.
Comparison of electron cyclotron resonance plasma characteristics discharged by 7.0, 8.0, and 9.4 GHz
Authors: Kawai Y. , Saburi T. , Kim S-H. , Fujii Y. , Suzuki T.
Published: July 2002

Argon electron cyclotron resonance plasma characteristics discharged by 7.0, 8.0, and 9.4 GHz microwaves are measured at 0.013 and 0.080 Pa in a cylindrical chamber. The plasma densities and electron temperatures were found to be almost independent of the microwave frequency at 0.013 Pa, whereas clear differences were seen at 0.080 Pa. At 0.080 Pa, the plasma densities were observed to increase with the increase in the discharge frequency. Electron temperatures at 0.080 Pa also appeared to become higher with the increase in discharge frequency.
Increasing the space-charge limit and other effects of cesium seeding in hydrogen negative ion sources
Authors: Whealton J. H. , Bacal M. , Bruneteau J. , Raridon R. J.
Published: July 2002

The role of cesium seeding in increasing the negative ion current in volume sources is described. By a reduction in the local plasma potential the current of extracted electrons is vastly reduced. As a result, cesium increases the fraction of the transverse space-charge limit available to the ions by as much as a factor of 3. In addition, cesium can increase the total space-charge limit by injection of Cs+ into the presheath—a newly recognized phenomenon consistent with experimental measurements and determined from application of a Double–Vlasov model for negative ion extraction.
Heavy-ion sources: The Star, or the Cinderella, of the ion-implantation firmament? (invited)
Authors: Freeman Harry
Published: July 2002

The Star, because of the invaluable contribution which the heavy-ion source has already made to the successful development of semiconductor implantation. And the Star, too, because it is evident that the key characteristics of such sources, which are now used on a quite routine industrial basis—their reliability, their ease of operation and, above all, their extraordinary versatility—have still not been fully exploited. This ensures that there is still scope, at least in the short term, for further optimization, which will go some way to meet the increasingly stringent industrial doping requirements. The Cinderella, because of my belief that these heavy-ion sources have now contributed to the successful operation of ion implanters so well, and for so long, that their present level of performance is mistakenly taken for granted. The result has been a paucity of meaningful research and development. Despite this, in this article I aim to show that, like Cinderella, who was so neglected that her true merit was long overlooked, there is the prospect too of achieving the significantly larger improvements in beam quality which the semiconductor industry will eventually be seeking.
The contribution of the INFN-LNS to the development of electron cyclotron resonance ion sources (invited)
Authors: Gammino S. , Ciavola G.
Published: July 2002

The study of the axial injector for the superconducting cyclotron of the Laboratori Nazionali del Sud (LNS) began in 1989, with the aim of replacing the radial injection from a 15 MV Tandem with the injection by a modern electron cyclotron resonance ion source (ECRIS) which could be able to produce beams of highly charged ions to the same extent. The design of a superconducting ECRIS, named SERSE, was established in the two following years and funded since 1993, 2 yr before the extraction of the first beam from the cyclotron; the construction took more than 4 yr and in August 1997 SERSE, was ready in the test bench of CEA/DRFMC in Grenoble. The source was moved to LNS in May 1998 and since then it is operating with excellent results. During 1993–95, the concept of High B mode, on which SERSE was based, was tested at MSU-NSCL and the results have been applied to other sources, including the room temperature CAESAR that will share with SERSE the duty of the production of ions for the cyclotron. Even though the performances of this source are not comparable to the ones of SERSE, CAESAR is able to perfectly fulfill the ordinary request of our accelerator complex. The last project of LNS concerns the design of a scaled version of SERSE with higher field, to be operated at the gyrotron frequency (28 GHz or higher). The results of the existing sources will be reviewed, along with the main features of the new project.
Feasibility study of a new negative ion source using a transformer coupled plasma source
Authors: Hwang Y. S. , Lee G. H.
Published: July 2002

Multicusp volume ion sources with radio frequency (rf) antenna are well accepted negative ion sources except for the contamination problem from the rf antenna immersed in the plasma. The transformer coupled plasma (TCP) developed as high-density plasma sources for processing of microelectronics is newly recognized as a good candidate for negative ion sources without this contamination problem. High-density plasmas can be generated with the rf antenna outside of the plasma chamber separated by a dielectric window. Also, this high-density, high-temperature, heating region can be well separated from the negative ion extraction region where low electron temperatures are required. Moreover, TCP does not require a magnetic field for plasma generations; electron filtering with transverse magnetic field is compatible. Feasibility of the TCP negative ion source has been confirmed with plasma characteristics. Conceptual design of a new novel ion source based on the TCP source is performed.
Intense pulsed ion beam sources for industrial applications
Authors: Zhao W. J. , Remnev G. E. , Yan S. , Opekounov M. S. , Le X. Y. , Matvienko V. M. , Han B. X. , Xue J. M. , Wang Y. G.
Published: July 2002

The different kinds of intense pulsed ion beam (IPIB) sources and their applications to surface modification of materials, e.g., IPIB technology, are reviewed. Intense pulsed energy effects on the surface microstructure as well as properties of 45# steel have been experimentally investigated in this work with different pulse parameters of the IPIB, such as current density and pulse duration. It is shown that ion beams with power density (106–108 W/cm2) are very promising ones, but the modification result is affected significantly by the pulsed ion beam parameters. New requirements to the IPIB sources for the industrial applications are discussed.
Fast and accurate current-voltage curves of metallic quantum point contacts
Authors: Hansen K. , Nielsen S. K. , Lægsgaard E. , Stensgaard I. , Besenbacher F.
Published: July 2002

We present an experimental setup for measuring the electrical conductance through metallic quantum point contacts (QPCs) under constant or time-dependent bias voltage conditions. The response time of the setup is as short as 25 ns and typical bias voltages range from 10 mV to 2 V. A function generator is used as bias voltage supply. With this, voltage bursts with a frequency of up to 100 kHz can be applied to the QPCs, whereby current-to-voltage (I–V) curves can be acquired using a homebuilt, 30 MHz bandwidth I–V converter, and a 100 Msamples/s digital storage oscilloscope. Test experiments on resistors show that nonlinear contributions to the I–V curves are always less than 1% of the current for all applied voltages. From the slope of the I–V curves, the conductance can be determined with an accuracy better than 1%. The QPCs are formed between a single-crystal metal sample and the tip of a scanning tunneling microscope under clean ultrahigh vacuum conditions. We demonstrate how the setup can be used to capture the I–V curves of several metastable states in a Au QPC, as it breaks during a period of 200 μs at room temperature.
Operation of high-temperature rf SQUID magnetometers using dielectric SrTiO3 resonators
Authors: Zhang Y. , Gottschlich M. , Soltner H. , Sodtke E. , Schubert J. , Zander W. , Braginski A. I.
Published: July 2002

The operation of YBa2Cu3O7 rf superconducting quantum interference devices (SQUIDs) using a dielectric SrTiO3 resonator as tank circuit was tested. At 77 K, we attained for such resonators unloaded quality factors Q0 up to 7000 at resonant frequencies near 1 GHz, when measuring without electromagnetic shielding. For a washer SQUID with an area of 4×4 mm2 and an inductance of ≂100 pH, which was properly coupled to the resonator, we measured an approximately 60 μV peak-to-peak SQUID signal and a white flux noise spectral density of SΦ1/2=1×10−5Φ0/√Hz, corresponding to a field sensitivity of BN=105 fT/√Hz. With an additional single-layer flux transformer with a diameter of the pickup loop of 22 mm in flip-chip arrangement, the field sensitivity was improved to 30 fT/√Hz.
Dependence of the density and type of stacking faults on the surface treatment of the substrate and growth mode in ZnSxSe1−x/ZnSe buffer layer/GaAs heterostructures
Authors: Kuo L. H. , Salamanca-Riba L. , Wu B. J. , Hofler G. , DePuydt J. M. , Cheng H.
Published: July 2002

A systematic dependence of the density and type of stacking fault defects with substrate surface chemistry and film growth mode was observed in ZnSe-based films grown on GaAs substrates. Namely, the density of Frank-type stacking faults is very large for films grown on Ga-rich surfaces, but is very low for films grown on As-stabilized surfaces exposed to Zn prior to the growth of the film. In contrast, the density of Shockley-type stacking faults increases for films grown by 3D growth mode at the initial stages of growth, but decreases greatly if the films are grown by the layer-by-layer growth mode. Films with stacking fault densities as low as 104/cm2 were obtained by growing the films by the layer-by-layer growth on GaAs epilayers with As-stabilized surfaces that were exposed to Zn for 1–2 min prior to the growth of the films.
Work function and desorption energy of H− from heated CaH2
Authors: Kawano Hiroyuki , Serizawa Naoshi , Takeda Makiko
Published: July 2002

A powdery sample of CaH2 heated to ∼730–790 K in a readily attainable high vacuum (∼1 ×10−7 Torr) was found to emit thermal electrons (∼ 10−7–10−5 A) and H− ions (∼ 10−15–10−12 A, mass analyzed) from its surface (∼ 0.1 cm2). The work function of the sample and the desorption energy of H− were 4.8 ± 0.1 and 7.4 ± 0.2 eV, respectively. The latter fairly agreed with the value (7.1 ± 0.1 eV) derived theoretically by our simple model for the thermal negative ion emission.
Ultrasonic thin-walled tube wave devices for sensor applications
Authors: Li X. , Cheeke J. D. N. , Wang Z. , Jen C. K. , Viens M. , Yi G. , Sayer M.
Published: July 2002

Integrated gravimetric sensor configurations have been demonstrated by employing a sol–gel processed thin piezoelectric lead zirconate titanate (PZT) film coated coaxially on stainless-steel tubes and interdigital transducers (IDT) fabricated as the transmitter and receiver on the curved tube surfaces. We have observed tube waves along both the axial and circumferential directions between 1 and 8 MHz. Theoretical analysis indicates that high mass sensitivity can be achieved by keeping the tube wall thin.
Ferromagnetism above room temperature in Mn–Si–C alloy films
Authors: Gajdzik M. , Sürgers C. , Kelemen M. , Hillebrands B. , Löhneysen H. v.
Published: July 2002

Mn–Si–C alloy films are prepared by e-beam coevaporation onto a Si substrate held at 600 °C. Ferromagnetism is observed below Tc=(360±5) K with SQUID magnetometry and magneto-optical Kerr effect. This is the highest Curie temperature Tc yet observed for a Mn-based alloy. Although the composition determined by Auger depth profiling varies appreciably for different films, their Tc is the same indicating that ferromagnetism is caused by an alloy of well-defined composition independent of precipitations.
Effect of electrode microstructure on leakage current in lead–lanthanum–zirconate–titanate multilayer capacitors
Authors: Kumar P. S. Asoka , Panda B. , Ray S. K. , Mathur B. K. , Bhattacharya D. , Chopra K. L.
Published: July 2002

Lead–lanthanum–zirconate–titanate (PLZT) multilayer capacitors involving platinum bottom electrodes have been fabricated on a silicon nitride/silicon (SiN/Si) substrate system. Leakage current characteristics show strong dependence on the processing temperature of the bottom electrode. A drop in leakage current by five orders of magnitude has been observed for capacitor with platinum electrode deposited at room temperature. Scanning tunneling microscopy (STM) studies reveal significant differences in the microstructure of platinum films deposited at different substrate temperatures. Based on STM results, a correlation between the microstructure of the bottom electrode, space layer at PLZT/Pt interface, and the nucleation of PLZT has been suggested to explain this new observation.
Anisotropic surface morphology of GaAs (001) surfaces passivated with nitrogen radicals
Authors: Kasu M. , Makimoto T. , Kobayashi N.
Published: July 2002

We have studied GaAs (001) surfaces passivated with nitrogen (N) radicals at submonolayer N coverage mainly using scanning tunneling microscopy and transmission electron microscopy. We determined that GaN-rich regions are elongated in the [1̄10] direction, suggesting that N passivation proceeds in the [1̄10] direction. This can be explained in terms of minimization of the tensile strains in the [110] direction induced when the supplied N atoms replace first-layer As atoms on the (2×4) surface.
Cathodoluminescence and writing of optical patterns on porous silicon by scanning electron microscopy
Authors: Bruska A. , Chernook A. , Schulze St. , Hietschold M.
Published: July 2002

Cathodoluminescence (CL) imaging has been used to characterize thin layers of porous silicon. A system for cathodoluminescence (CL) mapping is built in a scanning electron microscopy and able to detect radiation from 350 to about 550 nm. The whole system is operated under a computer control giving the possibility to perform imaging in both secondary electron detection usual for scanning electron microscopy (SEM) and the cathodoluminescence mode. We have mapped inhomogeneous CL from the sample surface and modified the CL intensity by irradiation of the sample with the electron beam. A sample of porous silicon can be easily irreversibly patterned on a micrometer scale using such a focused controlled irradiation. Possible applications in optoelectronics will be discussed.
Separation of partition noise from generation-recombination noise in a three-terminal quantum well infrared photodetector
Authors: Chen C. J. , Kurdak Ç. , Tsui D. C. , Choi K. K.
Published: July 2002

In this letter, we present results from our systematic study of the low frequency noise in an infrared hot-electron transistor. By measuring the correlation between emitter and collector noise currents, we are able to separate the partition noise and the generation-recombination (g-r) noise present in this three terminal device. Through the whole current range of more than two decades, the collector current noise SIc is always much larger than the cross-spectrum density between emitter and collector currents SIeIc. We thus conclude that SIc comes mostly from the filtering process.
Optoelectronic properties of hydrogenated amorphous silicon films grown using a modified pulsed plasma discharge
Authors: Mukherjee C. , Anandan C. , Seth Tanay , Dixit P. N. , Bhattacharyya R.
Published: July 2002

Hydrogenated amorphous silicon (a-Si:H) films were deposited by a modified pulsed plasma decomposition of silane and disilane in which a nonzero low power level was maintained throughout the discharge. Deposition rate (rd), optical band gap (Eg), dark and photoconductivity (σD and σph), and photosensitivity (σph/σD) were investigated as a function of pulse parameters. By combining dwell time (τ) and the high power level (HPL) it has been shown that Eg can be tailored over a fairly wide range. Similarly, σD and σph/σD have been shown to depend, in addition to HPL, on τ as well, thereby proving the possibility of using τ as an additional process parameter. High band-gap a-Si:H material of quality (σph=4.4×10−6 Ω−1 cm−1, σph/σD≊105) comparable to that of device quality a-Si:C:H has been deposited by this technique.
Electronic properties of defects introduced during low-energy He-ion bombardment of epitaxially grown n-GaAs
Authors: Auret F. D. , Goodman S. A.
Published: July 2002

We have employed deep level transient spectroscopy to investigate the defects introduced by low-energy (5 keV) He-ion bombardment of epitaxially grown n-GaAs. This introduced four electron traps, EHe1–EHe4, with discrete energy levels identical to those of the Eα1–Eα4 defects introduced during high-energy (5.4 MeV) α-particle irradiation of the same n-GaAs, but in different relative concentrations. EHe3 with a level at Ec−0.35 eV exhibits the same metastability as Eα3. In addition, low-energy ion bombardment introduced a band of defects close to the GaAs surface with a continuous energy distribution.
Electrical and structural properties of PtSi films in deep submicron lines
Authors: Xu D.-X. , McCaffrey J. P. , Das S. R. , Aers G. C. , Erickson L. E.
Published: July 2002

Electrical and structural properties of platinum monosilicide (PtSi) in deep submicron lines are reported. The sheet resistance of the silicide films was found to be rather independent of the linewidth down to dimensions as small as 0.15 μm. Plan-view and cross-sectional transmission electron microscopy was performed to study the structural properties of these films, including their gain structures and lateral growth. The insensitive nature of the electrical properties of the silicide films to the linewidths is correlated with their structural properties.
Stark effect in individual luminescent centers observed by tunneling luminescence
Authors: Lindahl J. , Pistol M.-E. , Montelius L. , Samuelson L.
Published: July 2002

We have measured photon emission from individual luminescent states in GaInP/InP heterostructures, containing InP dots, using local injection from a scanning tunneling microscope tip. By changing the tip-sample bias we are able to see the Stark shift of the emission peaks, as well as the onset of impact ionization. We find that the exciton diffusion length is about 1 μm, while the minority carrier diffusion length is much less in our samples. Below the threshold for impact ionization the excitation is extremely local, limiting the excitation to one or a few quantum dots.
Axial extraction of high-power microwaves from relativistic traveling wave amplifiers
Authors: Naqvi S. A. , Kerslick G. S. , Nation J. A. , Schächter L.
Published: July 2002

We report theoretical and experimental results from research into coaxial extraction of high-power microwaves from X-band traveling wave tube amplifiers. Power levels exceeding 60 MW have been measured at 9.1 GHz. The output level is relatively constant for the full 70 ns duration of the 700 kV, 500 A electron beam pulse. Results indicate that this coaxial geometry is broadband when compared to traditional, highly tuned radial extraction and may thus have applications in a range of high-power microwave devices.
LiNbO3 phase gratings prepared by a single excimer pulse through a silica phase mask
Authors: Luo G. P. , Lu Y. L. , Lu Y. Q. , Guo X. L. , Xiong S. B. , Ge C. Z. , Zhu Y. Y. , Liu Z. G. , Ming N. B. , Wu J. W. , Ding D. S. , Lu Z. H.
Published: July 2002

A transmission silica phase mask grating was used to fabricate LiNbO3 wafer phase gratings by a single excimer pulse at 248 nm. The morphologies of the LiNbO3 wafer gratings were studied with an atomic force microscope as well as an optical microscope. The crystal structures of the gratings were characterized by x-ray diffraction and three new crystal phases were found at the gratings’ surface besides the substrate phase of LN (110).
Time-resolved cathodoluminescence study of carrier relaxation in GaAs/AlGaAs layers grown on a patterned GaAs(001) substrate
Authors: Rich D. H. , Lin H. T. , Konkar A. , Chen P. , Madhukar A.
Published: July 2002

We have examined the kinetics of carrier relaxation in three-dimensionally confined GaAs/AlGaAs layers obtained by growth on prepatterned GaAs(001) with time-resolved cathodoluminescence (CL). Time-delayed CL spectra at 87 K reveal that (i) relaxation of hot carriers into the largest 3D confined regions occurs on a time scale of a few hundred ps during the onset of luminescence, and (ii) the luminescence decay time also increases for these larger confined regions, owing to thermal reemission from QWs, diffusion across AlxGa1−xAs barriers, and carrier feeding from surrounding thinner QWs.
Optical properties of defects in ion implanted silicon carbide probed at λ=633 nm
Authors: Musumeci P. , Calcagno L. , Grimaldi M. G. , Foti G.
Published: July 2002

The damage produced in silicon carbide single crystal by ion implantation was investigated by in situ optical transmittance and reflectance at 633 nm and by Rutherford backscattering channeling spectroscopy. Implantations were performed at room temperature with different ions (He, N, Ar, Kr, and Xe) in the fluence range 1011–2.5×1016 ions/cm 2. During irradiation a reduction of transmittance and a contemporary increase of reflectance occurred. RBS indicated a continuous accumulation of damage within a depth comparable with the ion range until the formation of an amorphous layer. A combination of optical and RBS data allowed to correlate the optical constant (n,k) to the damage produced during irradiation. Such a correlation was identical for every ion pointing out that the optical properties of the damaged material are independent of the energy density inside the single cascade.
Grain interaction effect in electronic properties of silicon nanosize films
Authors: Filonov A. B. , Kholod A. N. , Novikov V. A. , Borisenko V. E. , Vervoort L. , Bassani F. , Saul A. , d’Avitaya F. Arnaud
Published: July 2002

Electronic properties of both nanometer thickness (111) monocrystalline and nanocrystalline free standing silicon films were calculated within a self-consistent linear combination of atomic orbitals method. Grained nature of the nanocrystalline films is found to induce both a direct band gap and its reduction (down to about 2 eV) with respect to an isolated grain of same size.
Si nanowire growth with ultrahigh vacuum scanning tunneling microscopy
Authors: Ono Takahito , Saitoh Hiroaki , Esashi Masayoshi
Published: July 2002

Using a scanning tunneling microscope (STM), Si nanowires were grown by applying a voltage at a constant current between a Si substrate and a gold STM tip. Silicon atoms were deposited onto a gold tip by field evaporation. The field evaporation rate of silicon atoms was activated by heating the substrate. Silicon nanowire was grown on the gold tip at a substrate temperature of 700 °C. Nanowires could not be grown on a clean tungsten tip when using a gold-free Si substrate. The presence of gold atoms is important for the growth of silicon. Apparently, gold atoms deposited on the silicon substrate by field evaporation reduce the activation energy of field evaporation by attacking Si–Si bonds.
Quantum shift of band-edge stimulated emission in InGaN–GaN multiple quantum well light-emitting diodes
Authors: Sun C. J. , Zubair Anwar M. , Chen Q. , Yang J. W. , Asif Khan M. , Shur M. S. , Bykhovski A. D. , Liliental-Weber Z. , Kisielowski C. , Smith M. , Lin J. Y. , Jiang H. X.
Published: July 2002

We report on the band-edge stimulated emission in InGaN–GaN multiple quantum well light-emitting diodes with varying widths and barrier thicknesses of the quantum wells. In these devices, we observe that the stimulated emission peak wavelength shifts to shorter values with decreasing well thickness. From the comparison of the results of the quantum mechanical calculations of the subbands energies with the measured data, we estimate the effective conduction- and valence-band discontinuities at the GaN–In0.13Ga0.87N heterointerface to be approximately 130–155 and 245–220 meV, respectively. We also discuss the effect of stress on the estimated values of band discontinuities.
Spatio-temporal imaging of voltage pulses with an ultrafast scanning tunneling microscope
Authors: Jensen Jacob R. , Keil Ulrich D. , Hvam Jo/rn M.
Published: July 2002

Measurements on an ultrafast scanning tunneling microscope with simultaneous spatial and temporal resolution are presented. We show images of picosecond pulses propagating on a coplanar waveguide and resolve their mode structures. The influence of transmission line discontinuities on the mode structure is investigated. It is also demonstrated how common and differential modes of electrical pulses are generated. The capacitive coupling between the tip and the transmission line is explained in terms of two contributions: a long range and a local coupling. We also show how these contributions affect the imaging of the propagating pulses.
Investigation of the compensation mechanism in semi-insulating GaAs from alpha-spectra studies at low temperature
Authors: Chen J. W. , Ebling D. G. , Geppert R. , Irsigler R. , Schmid Th. , Rogalla M. , Ludwig J. , Runge K.
Published: July 2002

We present the results of charge collection measurements on liquid encapsulated Czochralski grown semi-insulating GaAs devices for alpha particles. Experimental evidence is given which demonstrates a drastic enhancement of charge collection efficiency after prolonged illumination with 1.086 μm below-gap light. The recovery of EL2 from metastable state to normal state can also be achieved by electric field at high bias voltage. The experimental result shows that the EL2 defect is practically the dominant trap for free charge carriers and together with other shallow defects responsible for the electric compensation in semi-insulating GaAs. The metastable transition of the EL2 defect is always simultaneously accompanied by the neutralization of a shallow acceptor. No change in the type of conductivity was found.
In situ selective etching of GaAs for improving (Al)GaAs interfaces using tris-dimethylaminoarsenic
Authors: Li N. Y. , Hsin Y. M. , Bi W. G. , Asbeck P. M. , Tu C. W.
Published: July 2002

We have investigated the in situ chemical beam etching (CBET) process of (Al)GaAs using tris-dimethylaminoarsenic (TDMAAs) within a chemical beam epitaxy chamber. The optimal CBET condition of (Al)GaAs is established, according to the analysis of atomic force microscopy, capacitance–voltage carrier profiles, and current–voltage (I–V) measurements. This CBET process using TDMAAs is shown to provide a good etching selectivity (>20) of GaAs over AlxGa1−xAs (x⩾0.35) with a very smooth etched surface at the nanometer scale and a clean etched/regrown interface for regrowth applications. Improved I–V characteristics of etched/regrown p-n AlxGa1−xAs (x⩽0.35) junctions is also successfully demonstrated when the GaAs cap layer is preferentially etched first by TDMAAs before regrowth of AlxGa1−xAs.
Depletion of charge around mesoscopic voids in semiconductors
Authors: Nolte D. D.
Published: July 2002

Self-consistent Hartree–Fock energy levels of mesoscopic voids in tetrahedrally bonded semiconductors are calculated within the Haldane–Anderson model revealing a high-multiplicity Coulomb ladder of discrete charge-state energies distributed across the semiconductor band gap. These discrete states can compensate shallow dopants. In GaAs, voids with radii of only 5 nm can compensate as many as 25 charges of either sign, producing depletion spheres around the voids in doped n-type or p-type material. The compensation and depletion behavior of the voids is similar to the behavior of metallic precipitates in nonstoichiometric GaAs.
Full band Monte Carlo investigation of electron transport in strained Si grown on Si1−xGex substrates
Authors: Bufler F. M. , Graf P. , Keith S. , Meinerzhagen B.
Published: July 2002

In-plane drift velocities determined by full band Monte Carlo simulations and drift mobility calculations are reported for electrons in strained Si grown on Si1−xGex substrates up to x=0.4 at 77 and 300 K. Drift mobilities of 28200 cm2/(V s) at 77 K and 2230 cm2/(V s) at 300 K are found for x=0.3. Strain enhances the drift velocity significantly only below electric fields of about 50 kV/cm. At 77 K the Gunn effect is predicted to occur above 15 kV/cm.
Using microcontact printing to generate amplitude photomasks on the surfaces of optical fibers: A method for producing in-fiber gratings
Authors: Rogers John A. , Jackman Rebecca J. , Whitesides George M. , Wagener Jefferson L. , Vengsarkar Ashish M.
Published: July 2002

This letter describes a method for producing in-fiber gratings that reduces the effects of mechanical and optical instabilities limiting other methods. In this technique, opaque lines formed on the outside of the fiber using a procedure known as microcontact printing, serve as an amplitude photomask for exposure to ultraviolet light. Long-period fiber optic attenuators formed by ths technique demonstrate its advantages.
An x-ray spectromicroscopic study of the local structure of patterned titanium silicide
Authors: Singh S. , Solak H. , Krasnoperov N. , Cerrina F. , Cossy A. , Diaz J. , Stöhr J. , Samant M.
Published: July 2002

Results from a spectromicroscopic study of the formation of TiSi2 in patterned structures are reported. An x-ray spectromicroscope was used to acquire spectra and images with photoabsorption signals using synchrotron radiation. A patterned TiSi2 sample with feature sizes ranging from 100 μm to 0.1 μm was studied. The silicidation reactions were carried out in ultrahigh vacuum using rapid thermal processing. Lateral variations in the local chemistry of the titanium silicide could be directly imaged and are attributed to the formation of the C54 phase in large areas and the C49 phase at feature edges and in narrow features.
Fabrication of amorphous-carbon-nitride field emitters
Authors: Chi Eung Joon , Shim Jae Yeob , Baik Hong Koo , Lee Sung Man
Published: July 2002

To improve silicon field emitters, an amorphous-carbon-nitride (a-CN) coating was applied by helical resonator plasma-enhanced chemical vapor deposition. By this process, a-CN was very uniformly coated on silicon tips without any damage. Microstructural and electrical investigation of the silicon and a-CN coated field emitters were performed. a-CN coating lowered turn-on voltage and increased emission current. Negative electron affinity of carbon nitride is suggested for enhancing emission current.
Optically detected cyclotron resonance properties of high purity ZnSe epitaxial layers grown on GaAs
Authors: Drechsler M. , Meyer B. K. , Hofmann D. M. , Ruppert P. , Hommel D.
Published: July 2002

The conduction band electron properties in ZnSe epitaxial layers on GaAs grown by molecular beam epitaxy are determined by far-infrared optically detected cyclotron resonance experiments. The high ωτ-value (in excess of 800) allows the observation of the spin splitting of the cyclotron resonance. The splitting is 8 mT in agreement with theoretical predictions.
Noise performances in polycrystalline silicon thin-film transistors fabricated by excimer laser crystallization
Authors: Carluccio R. , Corradetti A. , Fortunato G. , Reita C. , Legagneux P. , Plais F. , Pribat D.
Published: July 2002

A systematic study of the noise performances of polycrystalline silicon (polysilicon) thin-film transistors (TFTs) made by excimer laser crystallization is presented. The drain current spectral density of these devices shows an evident 1/f behavior and the origin of the noise was attributed to carrier number fluctuations. The flat-band voltage spectral density was found to be strongly correlated with the field-effect mobility, suggesting that the microscopic mechanism causing the carrier number fluctuations involves the localized states present at the grain boundaries. The noise level in the devices with the best electrical characteristics is comparable with that observed in c-Si metal–oxide–semiconductor field effect transistors, a major improvement if compared to polysilicon TFTs made by solid-phase crystallization.
Temperature effects on charge retention characteristics of integrated SrBi2(Ta,Nb)2O9 capacitors
Authors: Shimada Y. , Nakao K. , Inoue A. , Azuma M. , Uemoto Y. , Fujii E. , Otsuki T.
Published: July 2002

Temperature effects on charge retention characteristics of integrated SrBi2(Ta,Nb)2O9 thin film capacitors were examined in the temperature range of 27–150°C. The decay in remanent polarization at 27°C was linear in logarithmic time from 10−3 to 105 s with a decay rate of 0.24 μC/cm2 per decade. The elevation of storage temperature resulted in an instantaneous decrease in remanent polarization, while the decay rate at elevated temperatures after the instantaneous decrease was as small as that at 27°C. The instantaneous decrease in remanent polarization caused by elevating the temperature was explained by the temperature dependence of spontaneous polarization in the vicinity of the second order transition temperature. The development of asymmetry in the hysteresis loop during high temperature storing indicates that the logarithmic time dependence of the decay in remanent polarization is due to redistribution of space charges rather than polarization reversal.
Doped rare-earth perovskite Mn films with colossal magnetoresistance
Authors: Wang J.-Q. , Barker R. C. , Cui G.-J. , Tamagawa T. , Halpern B. L.
Published: July 2002

We have fabricated, using Jet Vapor Deposition, films of Pb doped rare-earth perovskite Mn oxides which show colossal magnetoresistance (CMR) effect. We have achieved epitaxial CMR films at a high deposition rate of typically 0.3 nm/s, uniformly over a large area. Films grown on LaAlO3 with a wide range of thickness (0.2–1.1 μm) show epitaxial characteristics. Scanning electron microscope analysis indicates that the surface is smooth. The measured magnetization and magnetoresistance show comparable performance compared to similar CMR films made by other methods.
Band alignments of the platinum/SrBi2Ta2O9 interface
Authors: Gutleben C. D.
Published: July 2002

In situ x-ray photoelectron spectroscopy was used to determine the band alignments of the platinum to SrBi2Ta2O9 contact. The interfaces were prepared by incremental evaporation of Pt onto a vacuum/O2 annealed polycrystalline surface grown by the sol-gel method. The results track the development of the band alignments from the submonolayer to the thick metal-film regimes. The Fermi level to ferroelectric valence-band offset of the asymptotic full metal contact was found to be 2.9 eV. The contact was also clearly shown to be highly disrupted with a bismuth-platinum alloy forming at the interface.
Internal laser cooling of Yb3+-doped glass measured between 100 and 300 K
Authors: Mungan C. E. , Buchwald M. I. , Edwards B. C. , Epstein R. I. , Gosnell T. R.
Published: July 2002

Laser cooling of a solid can occur when it emits photons of higher mean energy than those it absorbs. Photothermal deflection spectra of a fluorozirconate glass (ZBLANP) doped with 1 wt% Yb3+ show cooling in an internal volume of the sample at temperatures between 100 and 300 K. A cooling efficiency of ∼1% relative to the absorbed laser power at 1015 nm is maintained at all temperatures. The results show promise for solid-state cooling of bulk materials at temperatures below 150 K.
Complex magnetic and electronic transport properties of (La,Gd)1−xSrxMnO3+δ perovskites
Authors: Sun J. R. , Rao G. H. , Liang J. K. , Shen B. G. , Wong H. K.
Published: July 2002

The magnetic and transport properties of (La,Gd)1−xSrxMnO3+δ (x=0.15, 0.2, 0.25, and 0.3) with a fixed tolerance factor t=0.913 are studied. Special attention is paid to the postannealing effects of the compounds. Two magnetic transitions are observed in samples x=0.2 and 0.25 which are single phase in structure according to powder x-ray diffraction. Different effects on the two resulting states are produced by the postannealing. Accompanying the weakening of the state at lower temperature, the magnetic ordering of high-temperature state is enhanced substantially by the introduction of excess oxygen due to annealing the samples in O2. One typical paramagnetic–ferromagnetic transition occurs in samples x=0.15 and 0.3. There is a strong indication that the magnetic states in x=0.15 and 0.3 are, respectively, the developments of the high- and low-temperature states in x=0.2 (or x=0.25). The occurrence of two metal–semiconductor transitions in x=0.15–0.25 and their responses to postannealing suggest magnetic heterogeneity in the compound. By assuming the coexistence of vacancy-rich and vacancy-deficient domains in the compounds, these observations can be understood qualitatively.
Measurement of perpendicular giant magnetoresistance of Fe/Si superlattices
Authors: Endo Yasushi , Kitakami Osamu , Shimada Yutaka
Published: July 2002

The superlattices Fe/Si exhibit an antiferromagnetic coupling for very thin Si layers and giant magnetoresistance (GMR) is observed accompanying this coupling. The GMR for these superlattices measured with a current in the plane of the sample (CIP-GMR) is usually less than 0.2%. Considering a shunt effect due to large resistivity of Si layers, we measured the GMR with a current perpendicular to the sample plane (CPP-GMR). The thickness and width of the electrodes for the CPP measurement were carefully designed so that the current is always homogeneous in the sample. As a result, CPP-GMR for these superlattices is found to be about 3–6 times larger than CIP-GMR. Although a careful design of the electrodes is needed for homogeneity of the current, the technique is much easier than the CPP measurement for metal/metal superlattices and expected to provide valuable information on the spin-dependent electron transport phenomena in the Fe/Si superlattices.
Effects of buried oxide stress on thin-film silicon-on-insulator metal–oxide–semiconductor field-effect transistor
Authors: Lee Jong-Wook , Nam Myung-Hee , Oh Jeong-Hee , Yang Ji-Woon , Lee Won-Chang , Kim Hyung-Ki , Oh Min-Rok , Koh Yo-Hwan
Published: July 2002

Thin-film silicon-on-insulator (SOI) device characteristics have been investigated in terms of stress in the buried oxide interface by both simulation and experiment. Bonded SOI wafer with a 400 nm buried oxide and SOI wafer with a 100 nm buried oxide which is made by implanted oxygen are used as a substrate for device fabrication. From the simulation, it is demonstrated that the 100 nm buried oxide has higher compressive stress than the 400 nm counterpart after the local oxidation of silicon process. With the highly compressive-stressed buried oxide, boron atoms may accumulate at the silicon side, especially at the silicon edge, under tensile stress so that these accumulated boron atoms increase threshold voltage of the edge channel. Therefore, it is found that there is no hump of the drain current in the subthreshold drain current–gate-voltage characteristics of thin-film SOI n-channel metal–oxide–semiconductor field-effect transistors (MOSFET) with the highly compressed buried oxide.
Brominated plastic equation of state measurements using laser driven shocks
Authors: Koenig M. , Benuzzi A. , Faral B. , Krishnan J. , Boudenne J. M. , Jalinaud T. , Rémond C. , Decoster A. , Batani D. , Beretta D. , Hall T. A.
Published: July 2002

In order for brominated plastic (CHBr) to be used in future large lasers, such as the National Ignition Facility, capsule design, and equation of state (EOS) data are needed to address uncertainties in modeling. We have performed CHBr EOS measurements using the impedance matching technique. Laser beams spatially smoothed, and giving a spot size of 400 μm and intensities ⩽5×1013 W/cm2, produced high-quality shock waves allowing the simultaneous measurements of the shock velocities in two materials, one used as reference. Results are compared to other experiments and to EOS calculations. We obtained very good agreement with the theoretical curve for pressures ranging from 1 to 3 Mbar.
Secondary electron emission patterning of diamond with hydrogen and oxygen plasmas
Authors: Park Minseo , Choi W. B. , Streiffer S. K. , Hren John J. , Cuomo Jerome J.
Published: July 2002

Secondary electron emission patterning of single crystal diamond surfaces with hydrogen and oxygen plasma treatments was demonstrated. Hydrogen plasma treated regions were much brighter than the oxygen terminated regions. Results of atomic force microscopy confirmed that the observed contrast is not topographical. Several other possible negative electron affinity (or low positive electron affinity) materials such as chemical vapor deposited (CVD) diamond, aluminum nitride, and tetrahedrally bonded amorphous carbon (txa−C1−x) were also investigated. Faint image contrast (patterning) was also observed from polycrystalline CVD diamond and polycrystalline aluminum nitride films; however, no contrast at all was obtained from tetrahedrally bonded amorphous carbon (txa−C1−x) films.
Low noise operation of integrated YBa2Cu3O7 magnetometers in static magnetic fields
Authors: Krey S. , David B. , Eckart R. , Dössel O.
Published: July 2002

The noise of two integrated YBa2Cu3O7-SrTiO3-YBa2Cu3O7 multilayer magnetometers in static magnetic fields up to 110 μT is investigated: An inductively coupled magnetometer with integrated flux transformer and a multiloop magnetometer. In both samples, only a moderate increase of the low frequency flux noise is found in high fields, due to the high epitaxial quality of the involved multilayer films. So for moderately shielded or unshielded applications in the earth’s magnetic field, high-quality integrated YBa2Cu3O7 magnetometers can be operated with low excess noise.
Room-temperature formation of erbium-related luminescent centers in anodic alumina
Authors: Lazarouk S. K. , Mudryi A. V. , Borisenko V. E.
Published: July 2002

Luminescent Er-doped Al2O3 films have been fabricated at room temperature by a technique including magnetron deposition of Er-doped Al film on a silicon substrate and its subsequent electrochemical anodization. The films demonstrate strong Er-related photoluminescence at about 1.53 μm as recorded in the temperature range of 4.2–300 K. The effect is not influenced by annealing of the samples up to 200 °C. Upon annealing at 300–500 °C the luminescence intensity decreases, while above 600 °C it starts to recover. Annealing at 1000 °C restores the photoluminescence spectra to the initial level. The annealing peculiarities observed have been explained by dominant hydrogen outdiffusion at 300–500 °C, rearrangement of point defects at 600–800 °C, and recrystallization processes above 850 °C in the alumina film. Activation energies of these processes have been estimated to be 0.76 eV (for parabolic rate), 0.58 eV (for linear rate), and 0.46 eV (for linear rate), respectively.
Thermo-optical nonlinearity of GaN grown by metalorganic chemical- vapor deposition
Authors: Zhao G. Y. , Ishikawa H. , Yu G. , Egawa T. , Watanabe J. , Soga T. , Jimbo T. , Umeno M.
Published: July 2002

A study of thermo-optical coefficient (dn/dT) of GaN using spectroscopic ellipsometry is made, and a large thermo-optical nonlinearity near band edge, which increases with increasing temperature, has been observed. Kramers–Kronig transformation has been used to verify our results and a qualitative consistency has been obtained.
In situ determination of the terminating layer of La0.7Sr0.3MnO3 thin films using coaxial impact-collision ion scattering spectroscopy
Authors: Yoshimoto M. , Maruta H. , Ohnishi T. , Sasaki K. , Koinuma H.
Published: July 2002

In situ analysis of the terminating atomic plane of c-axis oriented La0.7Sr0.3MnO3 thin films grown epitaxially on SrTiO3(100) substrate by laser molecular beam epitaxy has been carried out employing coaxial impact-collision ion scattering spectroscopy (CAICISS). The CAICISS time-of-flight spectroscopic studies reveal that the (001) surface of c-axis oriented La0.7Sr0.3MnO3 thin films is predominantly terminated with MnO2 plane. The azimuth rotational CAICISS measurements show a fourfold symmetry in the surface atom alignments establishing the square lattice structure of the terminating plane.
Sample stage induced dose and energy nonuniformity in plasma immersion ion implantation of silicon
Authors: Fan Zhineng , Chu Paul K. , Chan Chung , Cheung Nathan W.
Published: July 2002

Plasma immersion ion implantation has been demonstrated to be a viable technique for microelectronics processing such as fabrication of shallow junction and silicon on insulator. However, a wider acceptance of this fledgling technology by the semiconductor industry is not possible unless the stringent dose and energy uniformity requirements can be met. We have recently discovered that the lateral dose and energy nonuniformity that is unacceptable to the silicon industry stems from the insulating shroud commonly used around the sample stage to reduce the current demand on the power supply. We have developed a theoretical model to explain the experimental results. The model can also be used to optimize the operating conditions and equipment design to achieve the desired dose and energy uniformity across a planar silicon wafer to satisfy the semiconductor industry.
Magnetoresistance of ferromagnetic tunnel junctions with Al2O3 barriers formed by rf sputter etching in Ar/O2 plasma
Authors: Nassar J. , Hehn M. , Vaurès A. , Petroff F. , Fert A.
Published: July 2002

Co/Al 2 O 3 /Ni 80 Fe 20 tunnel junctions were grown by sputtering at room temperature on glass and Si substrates, the barrier being formed by rf sputter etching of aluminum in a Ar/O2 plasma. The resistance is controlled for a given junction area by adjusting the oxide barrier thickness. Magnetoresistance ratios of 16% at 4.2 K and 6% at room temperature are obtained with good reproducibility over three orders of magnitude of resistance. Effects related to substrate shunting and oxidation of the bottom Co electrode are discussed.