bluuebunny/crossref_metadata_2025 huggingface dataset:
Positron Annihilation in Germanium in Thermal Equilibrium at High Temperature
Authors: Uedono Akira , Moriya Tsuyoshi , Komuro Naoyuki , Kawano Takao , Ikari Shoichiro Tanigawa
Published: October 2002

Annihilation characteristics of positrons in Ge in thermal equilibrium at high temperature were studied using a monoenergetic positron beam. Precise measurements of Doppler broadening profiles of annihilation radiation were performed in the temperature range between 300 K and 1211 K. The line shape parameters of Doppler broadening profiles were found to be almost constant at 300–600 K. The changes in these parameters were observed to start above 600 K. This was attributed to both the decrease in the fraction of positrons annihilating with core electrons and the lowering of the crystal symmetry around the region detected by positron-electron pairs. This suggests that behaviors of positrons are dominated by some form of positron-lattice coupling in Ge at high temperatures. The temperature dependence of the diffusion length of positrons was also discussed.
A Comparative Examination of Ion Implanted n+p Junctions Annealed at 1000°C and 450°C
Authors: Herzl Aharoni Herzl Aharoni , Tadahiro Ohmi Tadahiro Ohmi , Tadashi Shibata Tadashi Shibata , Mauricio Massazumi Oka Mauricio Massazumi Oka , Akira Nakada Akira Nakada , Yukio Tamai Yukio Tamai
Published: October 2002

A comparative examination is presented between two series of As+ implanted junctions into (100) Si substrates with varying Boron concentration N
s. The post-implantation annealing temperatures were 1000°C for one series and 450°C for the other. This is done in order to identify the specific cause for the inferior performance of the 450°C junctions which was shown to progressively degrade as N
s increases. It is found that the increase in N
t, the trapping centers concentration in the 450°C junctions is not the only reason for the above behavior and that the trend of E
t, the trapping centers energy level with respect to E
i, the intrinsic energy level is dominant. The data show that in contrast to the 1000°C junctions, ∣E
t - E
i ∣ decreases with increasing N
s in the 450°C junctions, increasing the generation rate, resulting the inferior performance. Junctions in 1.6×1014 cm-3 substrates, outstandingly exhibit comparable performance in both annealing temperatures.
Easily Manufacturable Shallow Trench Isolation for Gigabit Dynamic Random Access Memory
Authors: Roh Byung Hyug , Cho Yun Hee , Shin Yu Gyun , Hong Chang Gi , Gwun Sang Dong , Lee Kang Yun , Kang Ho Gyu , Ki Nam Kim Ki Nam Kim , Jong Woo Park Jong Woo Park
Published: October 2002

A simple and easily manufacturable shallow trench isolation (STI) process is developed for 1 Gbit dynamic random access memory (DRAM) and possibly DRAMs with ever greater capacity. The main features of this STI scheme are dual slope trench formation and selective dry-etching-assisted chemical mechanical polishing (CMP) planarization. The dual slope trench is formed by utilizing polymer generation during trench etching to improve the sub-threshold conduction characteristics (hump-free sub-threshold) and reduce the threshold voltage variation. The basic elements of dry-etching-assisted planarization are to locally form oxide mesas using a highly selective dry etching, and to minimize the amount of CMP simply by removing the locally formed oxide mesas. This new dry-etching-assisted CMP planarization significantly reduces dishing in the large field area and improves the flatness between the high and low pattern density areas such as the cell array and periphery region in a high-density DRAM.
Effect of Grain Alignment on the Coercivity for Sintered NdFeB Magnets
Authors: Ru-Wei Gao Ru-Wei Gao , De-Heng Zhang De-Heng Zhang
Published: October 2002

Taking account of the effect of the degree of grain alignment on the coercivity, the angular dependence of the coercivity for sintered NdFeB magnets is discussed in terms of various coercivity mechanisms. The comparison between various theoretical results and experiments indicates that the misalignment of the grains makes coercivity of the magnets increase rather than decrease and the starting field theory of coercivity is in better agreement with experiments than either the nucleation or pinning mechanisms.
Observation of Double Stable Clouds of Cold Atoms in Magneto-Optical Traps
Authors: Bagnato V. S. , Bigelow N. P. , L. G. Marcassa L. G. Marcassa , S. C. Zilio S. C. Zilio
Published: October 2002

We present the observation of double stable clouds of cold trapped atoms in a magneto-optical trap and its explanation with a simple model based on radiative forces. This structure occurs for a specific misalignment of the trapping laser beams whose Gaussian profiles introduce an extra term in the equation of motion for the trapped atom. We were able to obtain simple analytical expressions for the trap potential and for the separation of the clouds, and carried out a numerical calculation which agrees well with the experimental observations.
High Performance Holographic Frequency Domain Optical Storage
Authors: Ruan Yu , Zhai Jinhui
Published: October 2002

A novel holographic frequency-domain optical storage technique is investigated. The mathematics relations of the system characteristics versus material properties and read/write conditions are developed. The system performances: recording density, signal-noise-ratio, parallel access, are analyzed in detail. The results show that this technique can realize high performance storage.
Electrical Conduction near Percolation Threshold in Polymer Composite Containing Conducting Polypyrrole-Coated Insulating Polymer Fiber
Authors: Yin Xiao Hong , Yoshino Katsumi , Yamamoto Hideo , Watanuki Toshiro , Isa Isao , Nakagawa Shinichi , Adachi Mikio
Published: October 2002

New types of conductor-insulator composites are prepared, in which conducting polymer-coated insulating polymers (polyethylene in spheres, nylon66 in fibers), whose size and shape are well controlled, are used as the conductor, and noncoated polyethylene spheres are used as the insulator. The dependence of electrical conductivity on the concentration of coated insulating polymers near the percolation threshold is studied in detail. The percolation threshold decreased with increasing length of coated nylon66 fibers. In the composite made of polypyrrole-coated polyethylene spheres and noncoated polyethylene spheres, the critical exponent t is evaluated to be 2.0±0.2. In the composite made of polypyrrole-coated nylon fibers (400 µ m, 800 µ m) and noncoated polyethylene spheres, a larger value t (3.0±0.4) is obtained. The dependence of t on applied voltage is also studied. In the composites made of polypyrrole-coated nylon66 fibers, t increases with increasing applied voltage. This can be explained by taking interparticle tunneling conduction into consideration in the percolation model.
New Low Temperature Processing of Sol-Gel SrBi2Ta2O9 Thin Films
Authors: Ito Yasuyuki , Ushikubo Maho , Yokoyama Seiichi , Matsunaga Hironori , Atsuki Tsutomu , Yonezawa Tadashi , Ogi Katsumi
Published: October 2002

A new low temperature processing method for preparation of SrBi2Ta2O9
thin films is proposed. These thin films were prepared on Pt/Ta/ SiO2/Si
substrates by a sol-gel method, and their structural and electrical
properties were investigated. Films were annealed before and after the top
Pt electrode deposition. The 1st annealing was performed in a 760 Torr
oxygen atmosphere at 600° C for 30 min, and the 2nd annealing was performed
in a 5 Torr oxygen atmosphere at 600° C for 30 min. The films were well crystallized
and fine grained after the 2nd annealing. The electrical
properties of the 200-nm-thick film obtained using this new processing
method, i.e., the remanent polarization (P
r), coercive field (E
c), and
leakage current density (I
L), were as follows: P
r=8.5 µ C/cm2, E
c=30 kV/cm,
and I
L=1×10-7 A/cm2 (at 150 kV/cm). This new processing method is very
attractive for highly integrated ferroelectric nonvolatile memory
applications.
Ferroelectric Properties of Sol-Gel-Derived PbTiO3 Type Thin Films
Authors: Takashi Iijima Takashi Iijima , Norio Sanada Norio Sanada
Published: October 2002

The degradation of ferroelectric properties with decreasing film thickness is a
common problem of PbTiO3 type ferroelectric thin films. We suspected that this
degradation was caused mainly by oxygen vacancies that diffused from the film
surface through the grain boundaries during firing. Thus we have been attempting
Al3+ substitution for Ti4+ in PbTiO3 using a sol-gel method. In this study, the
relationship between the ferroelectric properties of Pb(Ti0.85Al0.15)O3-
x

thin films and
the firing conditions in the thin film preparation process was investigated. The
0.14-µ m- thick Pb(Ti0.85Al0.15)O3-
x

films fired at 700° C for 15 min in air exhibited
good ferroelectric properties. For these firing conditions, the dielectric constant,
remanent polarization and coercive field were ε=356, Pr=9 µ C/cm2 and Ec=84 kV/cm, respectively.
Electrical Properties of (Bi, La)4Ti3O12 Based Thin Films Prepared by RF Sputtering
Authors: Noboru Ichinose Noboru Ichinose , Masanobu Nomura Masanobu Nomura
Published: October 2002

We describe the preparation of (Bi, La)4Ti3O12 thin films on various substrates such as MgO, glass Pt(100)/ MgO(100)
and Pt(111)/glass by rf magnetron sputtering. Perovskite-type thin films were prepared on these substrates. The chemical
composition of the thin films was found to be (Bi3.56La0.57)Ti3O12 by ICP analysis. Thin film on Pt(100)/MgO(100)
substrate showed fairly good fatigue properties: initial state, P
r=7.5 µ C/cm2, E
c=174 kV/cm
and after 109 pulses, P
r=5.7 µ C/cm2, E
c=117 kV/cm.
Preparation and Characterization of Ferroelectric Bi 4Ti 3O 12 Thin Films Grown on (100)-Oriented Silicon Wafers
Authors: Masaki Yamaguchi Masaki Yamaguchi , Takao Nagatomo Takao Nagatomo , Osamu Omoto Osamu Omoto
Published: October 2002

Ferroelectric bismuth titanate (Bi4Ti3O12) thin films were prepared directly on (100) silicon substrate by rf planar magnetron sputtering using a Bi2TiO5 ceramic target. Highly c-axis-oriented films were obtained at a high deposition rate of about 17 nm/min. The deposited thin films, consisting of plate-like grains about 2 µm in diameter, were grown uniformly parallel to the substrate surface. The remanent polarization (P
r) and the coercive field (E
c) of this film at 50 Hz were estimated to be 0.8 µC/cm2 and 20 kV/cm, respectively.
Preparation and Characterization of PZT Thin Films on CeO 2(111)/Si(111) Structures
Authors: Ikuo Sakai Ikuo Sakai , Eisuke Tokumitu Eisuke Tokumitu , Hiroshi Ishiwara Hiroshi Ishiwara
Published: October 2002

We report the crystalline quality and electrical properties of
PbZr1-x
TixO3 (PZT) films on Si substrates with epitaxially
grown CeO2 buffer layers.
CeO2 buffer layers were deposited by the electron-beam-assisted
evaporation technique, and PZT films were formed by the sol-gel technique.
It is shown that CeO2 buffer layers, which were epitaxially grown
on Si(111) substrates at 500°C, effectively suppressed Si and Pb
interdiffusion between PZT films and Si
substrates. Furthermore, the capacitance-voltage
and current-voltage properties of PZT/CeO2/Si indicated
a ferroelectric nature and excellent breakdown strength.
Optical Activity in Antiferroelectric Liquid Crystals
Authors: Hirokazu Furue Hirokazu Furue , Hiroyuki Uehara Hiroyuki Uehara , Jun Hatano Jun Hatano , Hideo Saito Hideo Saito , Shin'ichi Saito Shin'ichi Saito , Eiji Okabe Eiji Okabe
Published: October 2002

Molecular orientational structures in chiral smectic phases of a family of antiferroelectric liquid crystals (AFLCs) with different alkyl chain lengths were investigated by means of optical rotatory power and circular dichroism measurements. In the ferroelectric chiral smectic C phase, SmC*, molecules of rectus configuration are arranged in a left-handed helix, and the pitch of the helix becomes longer and saturates to a constant value with decreasing temperature.
In the antiferroelectric chiral smectic C A phase, SmC A
*, the helical handedness is opposite to that of SmC*, and the helical pitch is shorter than that of SmC* and independent of temperature. In some AFLCs with shorter alkyl chain, however, a divergence of the pitch and a simultaneous change in the handedness were observed in SmC A
*. Alkyl chains in AFLCs play an important role in stabilizing the helical structures, and the molecules with long alkyl chains tend to form a tight helix. The experimental results for subphases between SmC* and SmC A
* were discussed on the basis of the competition between helical twisting powers of the phases.
Microstructure and Dielectric Properties of SrTiO3–PbTiO3–CaTiO3 Ceramics
Authors: Inomata Yasuyuki , Hirokazu Chazono Hirokazu Chazono , Hiroshi Kishi Hiroshi Kishi
Published: October 2002

The electrical properties and microstructures of SrTiO3–PbTiO3–CaTiO3–Bi2O3–TiO2 systems were investigated. It was found that the materials had two
inhomogeneous regions, called “grain core-grain shell”, by field-emission scanning
electron microscopy (FE-SEM) and transmission electron microscopy (TEM)
observations. The dielectric constant showed two peaks. The dielectric constant at
temperatures below 0° C decreased, whereas that at temperatures above 100° C
increased slightly under DC bias field. D-E loops revealed that the ferroelectric state
existed at temperatures below 0° C, and the paraelectric-like state existed at
temperatures above 100° C. The observed frequency dependence and aging
phenomena showed that this material was a relaxor. A relationship between the
electrical properties and microstructure has been proposed.
Effects of Adding Various Metal Oxides on Low-Temperature Sintered Pb(Zr, Ti)O3 Ceramics
Authors: Murakami Kenji , Mabuchi Daisuke , Kurita Takahiro , Kaneko Yosuke Niwa
Published: October 2002

In order to investigate the effects of additives on the electrical
properties, 0.5 wt% Mn O2-added Pb(Zr0.52Ti0.48)O3 ceramics has been
sintered with the various oxide forms of BiFeO3- and Ba(Cu0.5W0.5)O3-related
additives at 935° C for 90 min. The addition of any combination
of the various metal oxides did not change the phase relations observed
in the XRD pattern. It is indicated again from the density measurement
that a Cu component is effective for the promotion of densification at
low temperature. The SEM observations reveal that a W component
is effective for grain growth at low temperature. It is also found that
the BF-related additives are useful in improving the mechanical quality
factor, and the BCW-related additives are useful for improving the
dielectric constant.
Low-Voltage Switching Characteristics of SrBi2Ta2O9 Capacitors
Authors: Kazushi Amanuma Kazushi Amanuma , Takemitsu Kunio Takemitsu Kunio
Published: October 2002

Ferroelectric capacitor arrays were fabricated using SrBi2Ta2O9 (SBT) thin films. Hysteresis and pulse responses were measured as functions of capacitor size and applied voltage. The remanent polarization (P
r) at 5 V does not depend on capacitor size, though P
r at low applied voltage decreases considerably as capacitor size decreases below 10 µ m. High-voltage pulse application enhances
low-voltage polarization switching. Retention characteristics strongly depend on operating voltage. Switching charge at 2 V or above is stable up to 104 s retention, while that at 1 V operation decreases with increasing retention time.
Effect of Free Carriers on ac-Driven Electroluminescent Devices with Hydrogenated Amorphous Silicon Carbide Thin Films
Authors: Claus-Dieter Abel Claus-Dieter Abel , Toshihiko Toyama Toshihiko Toyama , Tetsuyuki Matsui Tetsuyuki Matsui , Hiroaki Okamoto Hiroaki Okamoto , Yoshihiro Hamakawa Yoshihiro Hamakawa
Published: October 2002

The benefit of free carriers on ac-driven electroluminescence (EL) in hydrogenated amorphous silicon carbide (a-SiC:H) thin films has been investigated by observing the photoenhanced EL and analyzing of EL in multilayers. The EL intensity was found to be increased with the intensity of the illuminating laser with a sub-band gap energy. This has been correlated with photoluminescence quenching. The EL quenching at higher electric fields observed only with irradiation has been attributed to the effect of a combination of an increased number of free carriers and interaction of impact-generated electron-hole pairs. Moreover, the reduction in the threshold voltage of a-SiC:H/hydrogenated amorphous carbon (a-C:H) multilayers has been found to be related to the a-SiC:H thickness. The slope of the linear increase in EL intensity with ac voltage depends on the multilayer sequence. Both observations can be explained using a microscopic model based on impact excitation by free carriers.
Features of Nanocrystallization of Metallic Glass Fe 78B 13Si 9 Induced by High-Current-Density Electropulsing
Authors: Teng Gongqing , Chao Yuesheng , Dong Lin , Yan Geng Yan Geng , Zuhan Lai Zuhan Lai
Published: October 2002

The microstructure of the nanocrystalline \Fe78B13Si9 alloy, prepared by means of high-current-density electropulsing from the parent amorphous alloy (2605S-2), has been investigated by Mössbauer spectroscopy along with X-ray diffraction and transmission electron microscopy. The experimental results show that nanocrystalline \Fe78B13Si9 alloy is uniformly composed of the grains about 23 nm in diameter, with an interfacial component. Two crystalline phases are a disordered α-Fe(Si) solid solution with an Si concentration of 11.3 at.% and t -Fe2B. The interface phase is ferromagnetic Fe6.7B4.1Si2.2 with large number of voids, and is estimated to be about 1.3 nm thick with four to five atomic layers. The examination of a comparable isothermally annealed amorphous \Fe78B13Si9 sample reveals that the crystalline of the amorphous \Fe78B13Si9 alloy and its ultrafine grain structure should be attributed mainly to the electromagnetic effect from high-current-density electropulsing. The mechanism involved is discussed.
The Influence of Metal Film Thickness on Wave Properties of Surface Plasma Waves
Authors: Lee Cheng-Min , Liao Chin-Hsiung , Liann-Be Chang Liann-Be Chang , Ting-Liang Chiao Ting-Liang Chiao
Published: October 2002

In this study, the characteristics of surface plasma waves (SPWs) propagating in multilayer thin film are determined by the refractive indices of materials and the thickness of metal film sandwiched between these materials. A prism coupler is used to create the SPWs. The intensities of SPWs generated on different interfaces are discussed and the damping rates of SPWs on those interfaces are calculated. This study leads to a conclusion that the damping rate of SPW is much more sensitive to thinner metal film.
Selective Generation of Defects in Polydiacetylene Langmuir-Blodgett Films on Si Substrates as Studied by X-Ray Photoelectron Spectroscopy
Authors: Yamamoto Seiji , Ogawa Taro , Tomioka Kozo Mochiji
Published: October 2002

The defects in Langmuir-Blodgett films formed on Silicon substrates at the early stages of the accumulation process were studied by X-ray photoelectron spectroscopy for the first time. It was found that the defects are generated even in the first monolayer, especially on the thickly oxidized area and that the defects due to molecular elimination are generated selectively on the thickly oxidized area when the second layer is accumulated on the first layer. From this study, inelstic mean free paths of low-energy electrons in polymer material were also obtained, which are valuable for the analyses of their trajectories.
Emittance Diagram of Electron Beams Generated by a Field-emitter Array
Authors: Ishizuka Hiroshi , Kawasaki Sunao , Kubo Haruya , Watanabe Akihiko , Shiho Makoto
Published: October 2002

The emittance diagram of electron beams generated with a field-emitter array (FEA) was obtained by a new method of diagnostics. The beams were accelerated to several keV, propagated over a distance of 1 m through a focusing lens, and projected on a fluorescent screen. A magnified image of the FEA was formed on the screen, and images of the emitting tips were observed separately. An electrostatic quadrupole lens, inserted halfway between the focusing lens and the fluorescent screen, was used to modify the electron trajectories. The width of the fluorescent pattern in the defocusing direction showed a minimum, when the strength of the quadrupole lens was increased. This provided a simple way of determining a parallelogram enclosing the electron distribution in trace space.
Shock-Wave-Driven Instability at Material Interface in Laser Driven Implosion
Authors: Sunahara Atsushi , Takeuchi Hajime , Hideaki Takabe Hideaki Takabe , Kunioki Mima Kunioki Mima
Published: October 2002

Material mixing induced by hydrodynamic instability in the implosion process is the most important issue in studying implosion processes in inertial confinement fusion (ICF). We have studied the elementary process of the Richtmyer-Meshkov instability driven at an uneven material interface, when a shock wave passes through it. The second-order Godunov scheme is adopted to study the generation of vortices, mushroom formation and triple point generation on the surface of the transmitted shock wave. Results of detailed studies on why the interface is unstable regardless of the density ratio across the material interface are described. In addition, the rippling of the transmitted shock wave is explained relative to the up-and-down motion of the triple point.
Shape of a Co–Nd Liquid Alloy Ion Source
Authors: Hesse E. , Driesel W. , Dietzsch Ch. , Bischoff L. , Teichert J.
Published: October 2002

Co–Nd-liquid alloy ion sources (LAIS) were operated of a special specimen holder in situ in a 1 MeV transmission electron microscope. The dynamics of the tip shape in dependence of the ion emission current, spatial shifts of the liquid cone and the process of double cone formation have been observed. This results in a better understanding of the ion emission processes from Co–Nd LAISs in a large range of ion current. A linear dependence of the decrease of the cone half-angle α and of the increase of the jet length l and of the diameter d on the increased ion emission current was found. No emission of microdroplets at the shanks of the Taylor cone and behind the cone has been detected.
Electronic Structure of GaP 1-xNx Alloys Determined Using Pseudopotentials and Gaussian Orbitals
Authors: Sadanojo Nakajima Sadanojo Nakajima , Hidenori Ohshiba Hidenori Ohshiba , Tao Yang Tao Yang , Shiro Sakai Shiro Sakai
Published: October 2002

A simple model based on empirical pseudopotentials, Gaussian orbitals, and the virtual-crystal approximation is employed to study the electronic structure of GaP1-x
N
x
alloys. First, the pseudopotential form factors and the scaling parameters of the Gaussian orbitals are determined for the zinc-blende GaN constituent, and then the pseudopotential form factors are adjusted for GaP, by fitting to experimental data and the results of more accurate calculations. The band structure of the alloys is then calculated using the parameters obtained. Large nonlinear dependences of the direct Γ–Γ and indirect Γ–X gaps on nitrogen concentration are predicted. We found that the bowing parameters of these energy gaps are large, but not large enough to yield a negative band-gap energy.
Effect of the i-Layer Optical Gap on the Light-Induced Degradation of a-SiGe Solar Cells
Authors: Terakawa Akira , Masao Isomura Masao Isomura , Shinya Tsuda Shinya Tsuda
Published: October 2002

The light-induced degradation and thermal recovery behaviors of a-SiGe single-junction solar cells with i-layers having various optical gaps (E
opt) have been investigated. The cells with narrower E
opt show slower degradation under light-soaking than the cells with wider E
opt. However, they recover upon thermal annealing at 150° C as fast as the cells with wider E
opt. The results indicate that the light-induced processes are suppressed in the materials with narrower E
opt, but that the thermally induced process does not depend on E
opt. The slower light-induced processes of the cells with narrower E
opt are attributable to the lower recombination energy, which is a driving force of light-induced defect creation. Differences in the hydrogen content, the hydrogen bonding configuration and the germanium content are less likely to cause variation in the degradation time constant.
Properties of High-Mobility Cu2O Films Prepared by Thermal Oxidation of Cu at Low Temperatures
Authors: Matsumura Hideki , Asako Fujii Asako Fujii , Tomohiro Kitatani Tomohiro Kitatani
Published: October 2002

Cuprous oxide ( Cu2O) films are prepared by simple thermal dry oxidation of sputtered Cu films at temperatures lower than 350° C. The relationship between growth rate of Cu2O film and oxidation temperature is formulated from both optical and Rutherford backscattering measurements, along with a similar relationship for the growth of cupric oxide (CuO). Electrical and structural properties of Cu2O films are measured by the van der Pauw and the X-ray diffraction methods respectively. It is found that stable Cu2O films can be obtained under suppression of CuO growth when Cu films are oxidized at about 300° C, and that the Hall mobility of such Cu2O films is relatively high and reaches to several tens cm2/Vs.
Analysis of Thermal Effect on the Interfacial Oxide between Polysilicon and Silicon for Polysilicon Bipolar Transistors by Capacitance and Contact Resistance Measurements
Authors: Nakano Noboru , Tada Yoshihide , Rafael Reif Rafael Reif
Published: October 2002

Thermal effect on the interfacial oxide between polysilicon and silicon doped with arsenic was analyzed by capacitance and contact resistance measurements. The annealing temperature was varied from 850° C to 1000° C and, with the increase of annealing temperature, the oxide breakup was enhanced and the contact resistance decreased. It is shown for the first time that the capacitance also decreased with the increase of annealing temperature. This suggests that the interfacial area of the oxide layer decreases and the oxide layer thickness increases due to the oxide breakup. Capacitance characteristics are also compared with bipolar transistor characteristics.
A Negative Experimental Result for the Structural Change of Benzene Crystal in the Premelting Process
Authors: So Kitagawa So Kitagawa , Yohko Fujiwara Yohko Fujiwara , Takao Iijima Takao Iijima
Published: October 2002

The X-ray diffraction pattern of a polycrystalline sample of benzene was observed using an energy-dispersive method over a range of temperature from -20°C to 5.5°C (m.p.). A series of measurement was repeated seven times and the diffraction pattern showed no change in four of the seven series. Thus we concluded that the structural change of benzene crystal in the premelting process reported by Tohji and Murata [Jpn. J. Appl. Phys. 21 (1982) 1199] did not occur.
A Study of Sheath Electric Fields in Planar Magnetron Discharges using Laser Induced Fluorescence Spectroscopy
Authors: Choi Young Wook , Mark Bowden Mark Bowden , Katsunori Muraoka Katsunori Muraoka
Published: October 2002

Measurement of electric field distributions in magnetron sputtering discharges is a necessary step in understanding the dynamics of the sputtering process. Electric field measurements were made in BCl3 and helium DC magnetron discharges using two different laser induced fluorescence spectroscopic techniques. Direct measurement of the electric field distribution was possible for the helium plasma measurements.
Photodissociation of Adsorbed Dimethylcadmium at 193 nm
Authors: Ohashi Masafumi , Wada Ryuichi , Yutaka Matsumi Yutaka Matsumi , Masahiro Kawasaki Masahiro Kawasaki
Published: October 2002

The 193 nm photodissociation mechanism of Cd(CH3)2 adsorbed on a quartz substrate at 170 K has been studied by means of laser-induced fluorescence time-of-flight spectroscopy. The translational energy distribution of the ejected neutral Cd atoms is characterized by two different distributions; one is a modified Boltzmann distribution with a temperature of 230±30 K and the other is that with a temperature of 1000±200 K.
Grating External Cavity Diode Lasers with Broad Tunable Range and Narrow Spectral Linewidth for High-Resolution Spectroscopy
Authors: Tomohiro Kiguchi Tomohiro Kiguchi , Akira Uematsu Akira Uematsu , Masao Kitano Masao Kitano , Hisanao Ogura Hisanao Ogura
Published: October 2002

A grating external cavity technique is used to improve the poor spectral qualities of commercially available semiconductor lasers in order to realize high-resolution spectroscopy. We describe a method of coating an anti-reflector onto the front facet of semiconductor lasers to suppress the intrinsic laser oscillation. The coated laser operates in an external cavity with a Littrow-mounted diffraction grating. The spectral linewidth of the resultant laser system is confirmed to be less than 250 kHz, and the system can be scanned over 25 nm. In order to demonstrate its improved tunability, we observed three resonance lines of two alkali-metal atoms, Rb-D2 (780.0 nm), K-D1 (769.9 nm) and K-D2 (766.5 nm), without replacing the laser chip.
Spectro-ellipsometric Studies of Amorphization and Thermal Annealing in Ion-implanted Silicon
Authors: Lee Soonil , Sang Youl Kim Sang Youl Kim , Soo-ghee Oh Soo-ghee Oh
Published: October 2002

The damage profiles in the P+, BF2
+, As+ and B+ ion-implanted silicon specimens are investigated using the nondestructive spectroscopic ellipsometry (SE) technique. The effective dielectric functions of the damaged layers are calculated using the Bruggeman's effective medium approximation, assuming that the damaged layer can be optically represented by the mixture of crystalline and amorphous silicon. By selectively using either the dielectric function of implanted amorphous silicon, or that of the relaxed amorphous silicon as the reference data for the amorphous silicon, we have improved the accuracy in modeling. The model parameters regarding the damaged layer thickness and the degree of amorphization are found to depend on implanting ion species, implantation energies, and total doses. Also, the implantation induced damage profiles are computer simulated and compared with the SE results. When annealed at lower temperatures, implanted amorphous silicon turns into the relaxed amorphous silicon and starts to recrystallize from the interface of the c-Si side due to solid-phase epitaxial growth. At annealing temperatures higher than 600°C, relaxed amorphous layers become crystalline silicon.
Reflection High-Energy Electron Diffraction Image Analysis during Molecular Beam Epitaxial Growth of InAs/AlGaAsSb Deep Quantum Well Structures
Authors: Goto Hiromasa , Kuze Naohiro , Masahiro Matsui Masahiro Matsui , Ichiro Shibasaki Ichiro Shibasaki
Published: October 2002

We have investigated the lattice strain relaxation during the initial stage of Al

x

Ga1-
x

AsSb (0<x<0.5) growth on GaAs (100) substrates by molecular beam epitaxy (MBE). Using time-resolved reflection high-energy electron diffraction (RHEED) image analysis, we have found that AlGaAsSb on a GaAs surface quickly relaxes within 3 to 7 monolayers (MLs). We have also observed that two-dimensional (2D) growth occurs after deposition of 20MLs of GaAsSb on GaAs surfaces. Furthermore, we have confirmed the InAs grows on AlGaAsSb two-dimensionally because AlGaAsSb is lattice matched to InAs. With a total thickness of less of than 700 nm in the InAs/AlGaAsSb deep quantum wells (DQWs), we have achieved very high electron mobilities of more than 32,000 cm2/(V·s) at room temperature.
Analysis of Ellipsometric and Thermoreflectance Spectra for P-Based III–V Compounds GaP and InP
Authors: Hisashi Yoshikawa Hisashi Yoshikawa , Sadao Adachi Sadao Adachi
Published: October 2002

Spectroscopic-ellipsometry (SE) and thermoreflectance (TR) spectra of GaP and InP are presented. Both measurements are carried out on the same samples in the 1.4–5.6-eV photon-energy range at room temperature. The measured SE and TR spectra reveal distinct structures at energies of the E
0, E
0+Δ0, E
1, E
0', E
2 and E
2+δ critical points. The Γ
8

v
→X6

c
indirect-gap peak at 2.25 eV can also be clearly seen in the TR spectrum of GaP. These spectra are analyzed based on a simplified model of the interband transitions. The results agree well with the experimental SE and TR data over the entire range of photon energies.
Growth and Characterization of Bulk Si–Ge Single Crystals
Authors: Honda Tatsuya , Masashi Suezawa Masashi Suezawa , Koji Sumino Koji Sumino
Published: October 2002

Si–Ge single crystals, 7 mm in diameter and about 20 mm long with compositions ranging from 0 to 50 at.% Si were grown by the traveling solvent method. The compositions of the crystals were shown to be uniform parallel and perpendicular to the growth axis using EPMA measurement. Raman spectra indicated that the ratio of the numbers of Si–Ge and Ge–Ge bonds agreed with that expected for a random distribution of Si and Ge atoms. The band gap energy of the alloy increased linearly up to 15 at.% Si and increased gradually above 15 at.% Si. From photoluminescence measurements done under uniaxial stress along the <111> direction, it was shown that the dependence of excitonic no-phonon spectrum on the stress changed at about 15 at.% Si. These results indicated that the position of the conduction band minimum of Si–Ge alloy in the k-space changed at about 15 at.% Si.
High-Voltage Emitter Short Diode (ESD)
Authors: Kitagawa Mitsuhiko , Ken-ichi Matsushita Ken-ichi Matsushita , Akio Nakagawa Akio Nakagawa
Published: October 2002

We report the effects of emitter short structures, ESD(a) and ESD(b), as well as the effect of a very shallow emitter, on the reverse recovery characteristics for 4 kV high-voltage diodes. It was found that a diode with a shallow p-emitter and emitter short structures attains half the reverse recovery current I
rr, compared to conventional punch-through p-i-n diodes. ESD has a further advantage in that the leakage current is as low as that of conventional p-n junction diodes, even at 125° C. ESD structures with a fine n+ and p+ short structure attain no parasitic effect, even at a current density of 100 A/cm2 and di/ dt of -1000 A/µs.
Agglomeration and Diffusion of Ag Associated with Electrical Contacts on Single Crystal Bi2Sr2CaCu2Oy
Authors: Rajaram Guruswamy , Murata Keizo , Yamaguchi Yuji , Yuko Yokoyama Yuko Yokoyama , Yoshikazu Nishihara Yoshikazu Nishihara
Published: October 2002

For the purpose of obtaining good small-area electrical contacts on single crystals of Bi2Sr2CaCu2O

y

(Bi-2212) for transport study, the nature of the Ag film on a Bi-2212 single crystal was examined. Ag films of ∼100 nm thickness deposited on cleaved surfaces of Bi-2212 crystals and annealed at 500° C have been studied for microstructural changes and diffusive behavior by scanning electron microscopy (SEM) and electron probe micro-analysis (EPMA). It is found that the Ag films undergo a thermally activated softening/roughening on annealing. On prolonged annealing, film break-up and segregation takes place, accompanied by a small diffusion of Ag into and along the surface of Bi-2212. Based on these results, a method for electrical contact formation on a Bi-2212 crystal cleaved surface is presented.
Millimeter Wave Mixing Properties of EuBa 2Cu 3O 7-δ Bicrystal Grain Boundary Junction Arrays
Authors: Koji Tsuru Koji Tsuru , Kazunori Miyahara Kazunori Miyahara , Minoru Suzuki Minoru Suzuki
Published: October 2002

We report the millimeter wave mixing properties of high-T
c superconductor Josephson junction arrays using a waveguide-to-microstrip converter in the 100 GHz frequency range. The junction arrays consist of 3 weak links fabricated from EuBa2Cu3O7-δ thin films grown on an MgO bicrystal substrate. In these junction arrays, Shapiro steps are observed in the presence of 100 GHz irradiation at intervals of 3 times the fundamental step voltage. Millimeter wave mixing with an input local oscillator frequency of 99.142 GHz and an input signal frequency of 99.880 GHz is detected as the IF output at 738 MHz. The IF output power peaks at voltages corresponding to those of the dynamic resistance dV/ dI. A mixing conversion efficiency of -24.1 dB is obtained for a 3-junction array.
Accurate Frequency Control of External-Cavity Laser Diode by Sideband Locking Technique
Authors: Fujii Takashi , Nayuki Takuya , Nemoto Koshichi , Kozuma Mikio , Kourogi Motonobu , Ohtsu Motoichi
Published: October 2002

We developed a new, simple laser diode (LD) system in which the laser frequency can be tuned continuously and stabilized at a desired value. The frequency of the 780 nm LD which had no additional antireflection coating on the output facet was varied continuously over a range of 22 GHz by scanning the grating angle and the drive current simultaneously. The LD frequency was offset locked by locking of the frequency of one of the sidebands to a Fabry-Perot interferometer which was locked to a frequency-stabilized He–Ne laser. The sidebands were generated by passing the laser beam through a traveling-wave EO-modulator. By varying the modulation frequency of the EO-modulator, the laser frequency was varied smoothly in a range of 200 MHz, and was stabilized at a frequency which differed by 500 MHz from the resonance frequency of the Fabry-Perot interferometer.
Theory behind and Experimentation on the Spectral Control of a Laser Diode with a Michelson External Cavity
Authors: Zhang Tiejun , Yoshiaki Hashimoto Yoshiaki Hashimoto , Motoki Yonemura Motoki Yonemura
Published: October 2002

We present the theory behind and discuss experimentation on the spectral control of a laser diode with a Michelson external cavity. This structure is advantageous in terms of variable resonance mode spacing and the wavelength tuning range achieved by adjusting the path-length difference of the external cavity. This laser diode is easy to construct and uses mainly inexpensive components. In theory, we replace the end facet of the laser medium and the mirrors of the external cavity with an equivalent mirror, and therefore, resonance conditions of the laser diode with the external cavity can be analyzed. Through experiment, we investigated dependences of the bandwidth and wavelength tuning range of the laser diode on the path-length difference of the external cavity and the injection current. We achieved a 0.75 nm extension of the wavelength tuning range and a 1/6 reduction in the bandwidth.
Heavily Carbon Doped Base InP/InGaAs Heterojunction Bipolar Transistors Grown by Two-Step Metalorganic Chemical Vapor Deposition
Authors: Ito Hiroshi , Yamahata Shoji , Naoteru Shigekawa Naoteru Shigekawa , Kenji Kurishima Kenji Kurishima
Published: October 2002

A novel growth procedure for realizing high hole concentrations in the C-doped base layers of InP/InGaAs heterojunction bipolar transistors (HBTs) is presented. The H out-diffusion behavior from the epi-layer in relation to the cap layer thickness is investigated in detail. A relatively thin n-InP cap layer is found to be nearly transparent to out-diffusion of H at a relatively high annealing temperature of 550° C and to act as a barrier to re-hydrogenation during re-growth at 450° C. Using this non-reciprocal feature of thin n-InP cap layers with respect to hydrogen permeability, hydrogen was annealed out from the base layer outside the growth chamber, and then the rest of emitter and cap layers were re-grown without significant re-hydrogenation. The fabricated HBT has a base current ideality factor close to unity, indicating that the re-growth procedure has no serious influence on the device characteristics. A small device with a base layer hole concentration of 2.5×1019 /cm3 has a maximum oscillation frequency (f
max) of 170 GHz at J
C=1.7×105 A/cm2.
Time-Dependent Global-Model Simulation for a Pseudospark Discharge with a Cylindrical Hollow Cathode
Authors: Hae June Lee Hae June Lee , Jae Koo Lee Jae Koo Lee
Published: October 2002

Some properties of pseudospark discharge in a hollow cathode are analyzed using a global model. The time-dependent volume-averaged densities of electrons and ions, and electron temperature are calculated, taking into account secondary electron emission and recombination effects. The electron current from a hollow cathode is also estimated and compared with the beam current measured in experiments. With an appropriate power factor, defined as the ratio of the energy delivered to the system to the total energy stored in the external capacitor, the simulated beam currents agree with the experimental results. The calculated beam current density is about 1 kA/cm2 and the maximum average electron density in the cylindrical hollow cathode is estimated to be in the range of 1014 cm-3 under the breakdown conditions of 10–40 mTorr pressure of argon gas and 5–24 kV breakdown voltage.
Performance of a Torque Magnetometer in High Magnetic Fields using a Hybrid Magnet
Authors: Masashi Kosaka Masashi Kosaka , Hideya Onodera Hideya Onodera , Takurou Nakamichi Takurou Nakamichi , Yasuo Yamaguchi Yasuo Yamaguchi
Published: October 2002

Measurements using a torque magnetometer are performed under high magnetic fields generated by a hybrid magnet. It is clarified that rotation angle determination by a double-coil method is advantageous compared with that by a single-coil method. Interference by ripple fields induced by vibration of a water-cooled magnet is eliminated to a sufficient degree through the use of a Cu shield. In the measurement, a sudden jump of the rotation angle occurs in the case of unsaturated magnetization. After the reason is discussed based on simulation of the jump behavior, supplementary measurement by the reverse rotation method is recommended for more favorable data accumulation. Examples of torque measurement for a Co single crystal and a sintered Nd2Fe14B sample are provided.
Tracking Simulation of the Ions Trapped in the Nonlinear Field of Electron Beams in Storage Rings
Authors: Yoshikazu Miyahara Yoshikazu Miyahara
Published: October 2002

Tracking simulation was performed on the ions trapped in linear and nonlinear fields of an electron beam in storage rings. The stability of the ions was investigated with regard to the homogeneous partial-fill mode and the equidistant-bunch and -burst modes of the electron beam. It was found that the oscillation amplitude of the ions trapped in the beam grows very rapidly to 100–1000 times larger than the electron beam size, even in the nonlinear field, under some ion-beam conditions. The results are expressed as a stability diagram of the ions, and the diagrams for the linear and nonlinear fields are basically similar to each other, both representing a periodic structure of the parametric resonance. The critical mass in the equidistant bunched beam is the same for the linear and nonlinear fields. The present results are consistent with the experimental results in the storage rings of European Synchrotron Radiation Facility (ESRF) and Photon Factory of National Laboratory for High Energy Physics (KEK-PF).
Fluoride Glasses for 193 nm Optics
Authors: Toratani Hisayoshi , Xuelu Zou Xuelu Zou , Yasutaka Matsumoto Yasutaka Matsumoto
Published: October 2002

Aluminum fluoride based fluoride glasses were evaluated in comparison with silica glass for their potential for use in 193 nm lithography optics. A pure fluoride glass and fluoride glasses containing a small amout of phosphate exhibit UV absorption edges shorter than that of silica glass. Their reflection spectra in the vacuum UV region also indicate that they have wider band gaps than silica glass, suggesting that they are promising materials for 193 nm optics. However, strong induced absorption in the UV region was observed under ArF excimer laser exposure, of which the absorption bands were attributed to photo-induced oxidation of Fe2+ to Fe3+ and formation of electron trapped centers on [ PO4] groups. It is important to keep the contents of both transition metal impurities and phosphate as low as possible in fluoride glasses intended for use in 193 nm lithography optics.
Fabrication Process of Character Projection Mask for EB Lithography
Authors: Jun Takamatsu Jun Takamatsu , Toru Koike Toru Koike , Yoshiyuki Kato Yoshiyuki Kato , Hitoshi Sunaoshi Hitoshi Sunaoshi , Kiyoshi Hattori Kiyoshi Hattori , Kazuyoshi Sugihara Kazuyoshi Sugihara , Tadahiro Takigawa Tadahiro Takigawa
Published: October 2002

A new structure for a character projection (CP) mask has been developed for the electron-beam (EB) lithography system, EX-8D. The mask comprises an electroplated Au membrane on which apertures are formed and a (110) oriented Si substrate. The Au membrane is 4 µm thick, which is thick enough to stop 50 keV electrons. The aspect ratio of the Au aperture is much less than that of the conventional Si aperture, so that the size of the apertures can be well controlled. By a repair process using a focused ion beam (FIB), the edge roughness and the curvature radius at the corner of the aperture are reduced to less than 0.2 µm. Since the demagnification ratio of EX-8D is 1/36, these errors are 0.006 µm on the wafer and sufficiently small for 0.15 µm lithography. On the CP mask, we arranged a 7×7 array of apertures in a 1650×1650 µm2 area with a small amount of dead space. This arrangement can be realized by the use of a Si (110) substrate on which back-etched holes with ve rtical sidewalls were formed. In addition, this CP mask has sufficient mechanical rigidity and heat conductivity, because the aperture membrane is supported by Si struts.
A Beam Drift Reduction Device for the X-Ray Mask E-Beam Writer, EB-X2
Authors: Kato Junichi , Saito Kenichi , Hirofumi Morita Hirofumi Morita , Nobuo Shimazu Nobuo Shimazu
Published: October 2002

A new drift reduction device for the X-ray mask e-beam writer, EB-X2, has been designed to keep reflected electrons (REs) and secondary electrons (SEs), which can charge the inner surface of the column, from re-entering the column. First, two electrodes, which have a circular opening in the center through which the incident beam passes, are placed between the column and the specimen. They keep REs re-entering the column. Second, a voltage of -50 V is applied between the two electrodes to prevent SEs from re-entering the column. Electron trajectory calculations revealed that the device keeps 84% of REs and 100% of SEs from re-entering the column. The effects of this device on the EB-X2's electron optical characteristics–that is, beam shape distortion, deflection distortion, and beam shift caused by electric-field leakage from the electrodes–were also estimated numerically. The calculated results show that the device can reduce beam drift without degrading the patterning accuracy.
Evaluation of Replicated Dynamic Random Access Memory Cell Patterns using X-Ray Lithography
Authors: Kikuchi Yukiko , Murooka Ken-ichi , Sugihara Shinji , Mitsui Soichiro , Nomura Hiroshi , Kondo Kenzo , Shino Tomoaki , Kawaguchiya Hitomi , Sunouchi Kazumasa , Deguchi Kimiyoshi , Miyoshi Kazunori , Fukuda Makoto
Published: October 2002

We have evaluated the exposure latitude and the mask linearity of the lines and spaces (L/S), the isolated lines and the cell patterns used for DRAMs for various sizes down to 0.12 µ m. The exposure latitude was larger than 10% for all types of patterns with sizes larger than 0.12 µ m, using a mask of contrast of 3.7 in a mask-to-wafer gap of 20 µ m. We found that the mask linearity is insufficient and that mask pattern bias is required. The image shortening effect in the cell pattern was also evaluated. The results showed that the value of the shortening is higher when the design rule is smaller, the pattern density is sparser and the mask-to-wafer gap is larger. The value of the shortening in a 0.12-µ m- design- rule cell pattern was 13 nm, which is small enough to be corrected by simply giving a bias in the mask pattern.