bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient Phase Conjugation Wave Generation from a GaAs Single Quantum Well in a Microcavity
Authors: Shimano Ryo , Inouye Shin , Kuwata-Gonokami Makoto , Nakamura Takeshi , Yamanishi Masamichi , Ogura Ichirou
Published: October 2002

We propose a scheme of efficient phase conjugation wave generation with a semiconductor microcavity. We show experimental results for a GaAs single quantum well (SQW) in a planar AlGaAs microcavity at 13 K. A single pump beam directed normally to the planar cavity produces counterpropagating pump fields in the QW region. Using the quantum confined Stark effect, we tune the exciton resonance energy around the fixed cavity resonance. Large enhancement of the signal occurs when the exciton resonance coincides with the cavity resonance.
Doping of Phosphorus and Boron into Silicon by Solid-Phase Diffusion at Low Temperatures ( <650° C)
Authors: Ishikawa Yutaka , Sugioka Katsutoshi
Published: October 2002

The diffusion of phosphorus and boron into silicon at lower than 650° C was achieved. Spin-coated glass was used for the diffusion source and samples were heated with a tungsten halogen lamp. The key to diffusing these impurities into silicon at such low temperatures is to decrease the temperature of silicon without reducing some of the light radiated from the halogen lamp. Impurity concentrations at the silicon surface were 1-2×1020 cm-3 at 620-720° C. These impurities diffused into silicon typically at least 0.1 µ m from the silicon surface after 40 min of 620° C annealing.
Synchrotron-Radiation-Excited Growth of ZnTe by Alternating Gas Supply Using Metalorganic Sources
Authors: Ogata Toshihiro , Gheyas Syed Irfan , Ogawa Hiroshi , Nishio Mitsuhiro
Published: October 2002

Crystal growth of ZnTe has been studied using synchrotron radiation as a light source, by the atomic layer epitaxial technique, i.e., by supplying diethylzinc and diethyltelluride alternately. ZnTe film with excellent thickness uniformity is grown epitaxially on the (100) GaAs substrate at room temperature. It has been confirmed by X-ray photoelectron spectroscopy that no carbon is included in the ZnTe film. The growth rate becomes almost saturated at one monolayer per cycle.
Temperature Dependence of Power Reflectivity of the First-Wall Materials in the Synchrotron Radiation Range
Authors: Noriharu Takada Noriharu Takada , Masaaki Nagatsu Masaaki Nagatsu , Michiya Shimada Michiya Shimada
Published: October 2002

The temperature dependence of power reflectivity in the synchrotron radiation range was measured for candidate first-wall materials of the fusion reactor, such as B4C-coated isotropic graphite, C/C composite material, silicon carbide (SiC), tungsten (W), molybdenum (Mo) and SUS-316. The measurements were carried out using a vacuum vessel with a pressure of about 3 mTorr to avoid oxidation. Distinct temperature dependence of reflectivity was observed only for B4C-coated isotropic graphite. For the other materials, power reflectivities were insensitive to temperature in the range from 300 K to ∼900 K. Theoretical analysis of the results is also presented.
Epitaxy of Si1-xGex by Ultrahigh-Vacuum Chemical Vapor Deposition Using Si2H6 and GeH4
Authors: Chen Liang-Po , Chou Tsung-Chih , Tsai Wen-Chung , Huang Guo-Wei , Tseng Hua-Chou , Lin Horng-Chih , Chang Chun-Yen
Published: October 2002

Disilane and germane were used to grow Si1-
x

Ge

x

epilayers at 550° C by ultrahigh-vacuum chemical vapor deposition (UHVCVD). The solid composition x and growth rate of Si1-
x

Ge

x

were evaluated from double-crystal X-ray rocking curves and show very strong dependence on the total source gas flow rate ( [ GeH4]+[Si2H6]) and the gas ratio ( [GeH4]/[GeH4]+[Si2H6]). The solid composition increases with increase of the gas ratio and also with increasing the total source flux by keeping gas ratio constant. The growth rate increases with the solid composition at lower values and then becomes saturated in the higher composition range (x>0.22). The results can be explained by the relationships of the source fluxes, relative incorporation efficiency at activated surface sites and hydrogen desorption under different growth conditions.
Distributed-Feedback Color Center Lasers Using N2Centers in KCl
Authors: Kurobori Toshio , Hibino Hirotoshi , Chen Yao Qiang , Inabe Katsuyuki
Published: October 2002

We report on a distributed-feedback (DFB) color center laser based on N2centers in KCl. A periodic grating with fringe spacings as fine as 440 nm was produced by means of a two-photon coloration process using two interfering beams. Coloration and photoaggregation processes and the DFB laser action can be availed by the fourth- and second-harmonic and the fundamental lines of a Q-switched Nd:YAG laser, respectively. The linewidth of the DFB output is less than 0.3 nm in the spectrally important 1300 nm region.
Alignment of Liquid Crystals by Copying an Aligning Function of Polymer Films into a UV Cured Polymer Surface
Authors: Yamaguchi Rumiko , Susumu Sato Susumu Sato
Published: October 2002

We have successfully fabricated liquid crystal (LC) alignment layers of UV cured polymer without using linearly polarized light or direct rubbing treatment. The LC aligning function of polymer films in the direction of their slow axis or rubbing can be copied onto the UV cured polymer surface in the curing process and the polymer films can be used repeatedly. Twisted nematic cells are prepared using substrates coated with the UV cured polymer and a rubbed polyvinylalcohol (PVA) film, and their electro-optical properties are measured.
Quantitative Analysis of Tunneling Current through Ultrathin Gate Oxides
Authors: Yoshida Takeshi , Imafuku Daisuke , Alay Josep Lluis , Miyazaki Seiichi , Masataka Hirose Masataka Hirose
Published: October 2002

The tunneling current through ultrathin (3.0-6.0 nm) gate oxides has been measured as a function of the voltage across SiO2, V
OX, and compared with results of existing theories utilizing the WKB approximation. The electron effective mass in the Fowler-Nordheim tunneling region (V
OX≥3.25 V) is obtained to be (0.34±0.04)m
0 and that in the direct tunneling region (V
OX<3.25 V) is (0.29±0.02)m
0. It is also shown that the charge-to-breakdown for electron injection from n+poly-Si gates is not significantly degraded by decreasing the oxide thickness and is even dramatically improved for the case of a 3.0 nm-thick gate oxide.
Spatial Distribution Measurement of Microwave Electric Field Using Thermal Sensitive Paper in a Microwave Etching System
Authors: Watanabe Seiichi , Furuse Muneo , Watanabe Katsuya , Kawasaki Sunao
Published: October 2002

A method for 2-D measurement of microwave electric field distribution using thermal sensitive paper has been developed. This measurement method has little influence on the microwave propagation and the plasma generation. In a cavity-resonator microwave plasma generation system, the relationship between the plasma uniformity and the microwave electric field distribution was investigated using this method. The cavity-resonator microwave plasma source was found to generate high-density plasma stably and uniformly over a large area through the excitation of a ring-shaped microwave electric field in the cavity resonator.
Debris Formation from an Aluminum Nitride Ceramic Plate by Microprojectile Impact
Authors: Tamura Hideki , Fukushima Seiji , Akira B. Sawaoka Akira B. Sawaoka
Published: October 2002

In order to study the feasibility of using a spacecraft bumper composed of ceramics and metal, double-layer plate targets were prepared with an aluminum nitride sheet and an aluminum sheet. They were impacted by glass microprojectiles in the velocity range of 2-3 km/s. It was found that debris from the metal-ceramics target show a markedly wide dispersion depending on the position of the aluminum nitride sheet in the target.
In Situ GaAs Patterning and Subsequent Molecular-Beam Epitaxial Regrowth of AlGaAs/GaAs Wire Structures
Authors: López Máximo , Tanaka Nobuyuki , Matsuyama Isamu , Tomonori Ishikawa Tomonori Ishikawa
Published: October 2002

We report on the use ofin situelectron-beam (EB) lithography, a processing technique which is conducted entirely in an ultrahigh vacuum, to pattern GaAs substrates with mesa stripes on which AlGaAs/GaAs wire structures are subsequently regrown by molecular-beam epitaxy. First, a thin GaAs oxide layer is selectively formed by EB-stimulated oxidation in a controlled oxygen atmosphere, and then used as a mask material to define mesa stripes by Cl2gas etching. Subsequently, ridge structures are formed on the mesa stripes by the regrowth of a GaAs layer. Wire structures are fabricated on the top of the ridges by the growth of an AlGaAs/GaAs quantum well. The high quality of the resulting structures has been confirmed by cathodoluminescence measurements at 77 K.
Magnetically Excited Plasma Oxidation of InP
Authors: Akihiro Funyu Akihiro Funyu , Shingo Sato Shingo Sato , Hideaki Ikoma Hideaki Ikoma
Published: October 2002

High-quality oxide of InP having an excellent interface with InP was successfully grown with magnetically excited plasma oxidation of InP and annealing at 260°C for 15 min in \morO ambient. Outstanding capacitance-voltage (C-V) characteristics were obtained, which clearly showed both inversion and accumulation behaviors. The C-V curves at 300 K and 80 K coincided well with each other, indicating the absence of frequency dispersion. X-ray photoelectron spectroscopic measurements showed that InPO4, the perfect oxide of InP, was the dominant component species in the oxide with a small amount of In2O3.
Superconducting Fault-Current Limiter for 200-Vrms-Class Circuits Using YBa2Cu3Ox Thin Film by Chemical Vapor Deposition
Authors: Matsuno Shigeru , Umemura Toshio , Uchikawa Fusaoki , Hayashi Tatsuya , Mori Teijiro , Ikeda Bunko
Published: October 2002

A superconducting fault-current limiter (FCL) for 200-Vrms-class circuits using YBa2Cu3O

x

(YBCO) thin film fabricated by chemical vapor deposition (CVD) was investigated. The FCL consisted of a 400-nm-thick YBCO film with meander pattern of 1 mm wide×115 mm long. The film was coated with a protective silver film having a thickness varying between 110 and 130 nm from place to place. Half-cycle alternating voltage (50 Hz) was applied to the FCL device which was immersed in liquid nitrogen (77 K), and a typical current-limiting waveform was measured. When a voltage of 200 Vrms was applied, the fault current with a peak of 400 A was limited to the peak let-through current of 11 A.
The beginning time of the current limiting was about 0.1 ms.
Rise and Fall of Surface Level of Water Solutions under High Magnetic Field
Authors: Noriyuki Hirota Noriyuki Hirota , Takuro Homma Takuro Homma , Hiroharu Sugawara Hiroharu Sugawara , Koichi Kitazawa Koichi Kitazawa , Masakazu Iwasaka Masakazu Iwasaka , Shoogo Ueno Shoogo Ueno , Hiroyuki Yokoi Hiroyuki Yokoi , Yozo Kakudate Yozo Kakudate , Shuzo Fujiwara Shuzo Fujiwara , Mitsutaka Kawamura Mitsutaka Kawamura
Published: October 2002

Magnetic field effects on the surface profile have been investigated for water and copper sulfate aqueous solutions that have very small magnetic susceptibility. When a field of 10 T is applied in a horizontal superconducting magnet, the surface of distilled water was lowered by 39 mm at the field center, relative to the level at the zero field region (Moses effect). In contrast, the surface of a nearly saturated copper sulfate aqueous solution was raised by roughly the same height at the center (reversed Moses effect). The profiles were systematically explained based on the dia- and paramagnetic volume susceptibility values of distilled water and copper sulfate aqueous solution, respectively.
Fabrication of Si/Al2O3/Si Silicon on Insulator Structures Grown by Ultrahigh-Vacuum CVD Method
Authors: Takayuki Kimura Takayuki Kimura , Atsuhiro Sengoku Atsuhiro Sengoku , Makoto Ishida Makoto Ishida
Published: October 2002

A double-heteroepitaxial Si/γ-Al2O3/Si structure was fabricated for the first time by ultrahigh-vacuum chemical vapor deposition (UHV-CVD). An epitaxial γ-Al2O3(100) layer was grown on a Si(100) substrate with Al(CH3)3 and N2O gases at substrate temperatures of 850–1000°C. Subsequently, an epitaxial Si(100) layer was also grown on a γ-Al2O3(100)/Si(100) substrate by UHV-CVD with Si2H6 gas at substrate temperatures of 750–950°C. These epitaxial layers were characterized by reflection high-energy electron diffraction (RHEED), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), cross-sectional transmission electron microscopy (TEM), Hall effect measurement and ellipsometry. The reflection high-energy electron diffraction of the 5000-Å-thick silicon epitaxial layer indicated streaked 2×1 patterns. From these results, the UHV-CVD method is proven to be an effective method for Al2O3 and silicon growth at low growth temperatures, yielding uniform film thickness and good crystalline quality.
Effect of Pulse Duration on Ablation Characteristics of Tetrafluoroethylene-hexafluoropropylene Copolymer Film Using Ti:sapphire Laser
Authors: Nakamura Shinki , Midorikawa Katsumi , Kumagai Hiroshi , Minoru Obara Minoru Obara , Koichi Toyoda Koichi Toyoda
Published: October 2002

Pulse duration dependence of ablation characteristics of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) film has been investigated with femtosecond and picosecond Ti:sapphire laser pulses at 798 nm. Laser fluence dependence of ablation rates was examined for the laser pulse duration from 170 fs to 12 ps. Surface morphology of ablated holes was investigated using a scanning electron microscope. A great difference has been found in the ablation characteristics for laser pulse durations around 170-fs and longer than 500 fs. From the analysis of the fluence dependence of ablation rates and observation of the ablated surface, we have found that five-photon absorption predominated over other processes only for 170-fs pulses. It has also been found that the ablation threshold intensity was inversely proportional to the square root of the pulse duration in the region from 170 fs to 200 ps.
Aluminum-Selective Chemical Vapor Deposition Induced by Hydrogen Desorption on Silicon
Authors: Sakaue Hiroyuki , Katsuda Yoshihiko , Konagata Shinobu , Shoso Shingubara Shoso Shingubara , Takayuki Takahagi Takayuki Takahagi
Published: October 2002

We studied the influence of the chemical structure of silicon-hydride species on Al deposition rate in Al-chemical vapor deposition (CVD) employing dimethylaluminum hydride (DMAlH) on a hydrogen-terminated Si surface. It was revealed that the peak temperature of hydrogen desorption from Si–H2 and Si–H3 in TDS spectra coincides well with the peak temperature of the Al deposition rate. We found that thermal hydrogen desorption from dihydride and/or trihydride species induced the Al-selective deposition reaction. Monohydride is not useful for the deposition at 240–290°C because of its higher desorption temperature of 350°C. In the early stage of Al deposition, a lower density of Al nuclei on the NH4F-treated surface compared with that on the HF-treated surface suggests that Al nucleation occurred at step edges on which di- and trihydride species exit.
Double Graded-Gap Hydrogenated Amorphous Silicon Carbide Thin-Film Light-Emitting Diode with Composition-Graded N Layer and Carbon-Increasing P Layer
Authors: Chen Yen-Ann , Chen Jyh-Kuan , Tsay Wen-Chin , Laih Li-Hong , Chang Jyh-Wong Hong
Published: October 2002

An hydrogenated amorphous silicon carbide (a-SiC:H) p-i-n thin-film light-emitting diode (TFLED), in which a composition-graded n layer and carbon-increasing p layer respectively replace the constant optical-gap p-a-SiC:H layer and n-a-SiC:H layer employed in the previously reported double graded-gap (DG) TFLED and which contains dopant-graded p-i and i-n junctions, was successfully fabricated to improve the electroluminescence (EL) of TFLED. This device had a brightness of 400 cd/m2 at an injection current density of 600 mA/cm2 and its EL threshold voltage (V
th) was only 9.9 V. The device EL spectrum showed a peak at 586 nm wavelength and emitted yellowish-orange light. The proposed TFLED had good stability of EL intensity and the EL spectrum during normal operation. The optimum conditions of rapid thermal annealing (RTA), which improved the ohmic contact between the amorphous layer and external electrode of the device, were 5 min at 300°C in a 250 Torr H2 ambient.
Initial Oxidation Processes of H-Terminated Si(100) Surfaces Studied by High-Resolution Electron Energy Loss Spectroscopy
Authors: Hiroya Ikeda Hiroya Ikeda , Koji Hotta Koji Hotta , Shinya Furuta Shinya Furuta , Shigeaki Zaima Shigeaki Zaima , Yukio Yasuda Yukio Yasuda
Published: October 2002

The initial oxidation processes of H-terminated Si(100)-1×1 surfaces have been investigated using high-resolution electron energy loss spectroscopy at room temperature and 300°C. It has been found that oxygen atoms adsorb on one of the two back-bond sites of a surface Si atom until the oxygen coverage is 0.4 and in the sequential oxidation process, other adsorption sites such as the other back-bond sites and/or Si–Si dimer-bond sites, become occupied by oxygen atoms. The structural relaxation in Si–O–Si bonds is observed when a surface Si atom has two Si–O bonds, and is considered to originate from the change in the force constant of Si–O bonds.
Ferroelectric Microdomains in Ti-diffused LiNbO3 Optical Devices
Authors: Toshinori Nozawa Toshinori Nozawa , Shintaro Miyazawa Shintaro Miyazawa
Published: October 2002

Etched hillock density on the -Z plane of a titanium-diffused LiNbO3 optical device was studied as a function of water vapor content in a diffusion atmosphere of oxygen and argon. It was found that the hillock formation depended greatly upon the water vapor content and the type of carrier gas. Furthermore, the shapes of the hillocks in the devices were observed on a microscopic scale. Scanning electron micrographs (SEM) clearly showed the crystallographic shape of steeple-crowned pyramidal hillocks. The shape of the steeple (i.e., the core) was compared with a cross-sectional view of an etched LiNbO3 single-crystal c-axis fiber, and it was revealed that the core was a microdomain whose polarization was opposite that of the outer matrix. The mechanisms which cause the microdomains to form during the Ti-diffusion process are also discussed.
Characterization of Surface Potential and Strain at Ultrathin Oxide/Silicon Interface by Photoreflectance Spectroscopy
Authors: Takaaki Imai Takaaki Imai , Akira Fujimoto Akira Fujimoto , Masanori Okuyama Masanori Okuyama , Yoshihiro Hamakawa Yoshihiro Hamakawa
Published: October 2002

Si surface potential and strain at the Si–SiO2 structure with a thermally grown or a native SiO2 ultrathin film have been characterized by photoreflectance (PR) spectroscopy. The surface potentials of Si–SiO2 structures are determined from the modulation light intensity dependence of the PR signal intensity. Although the signal intensity decreases drastically with increasing SiO2 film thickness, it can be increased by applying dc bias voltage and increasing the surface potential of Si. The strains at the Si surface have been obtained by an analysis of the transition energy shift in the SiO2/Si structure with a thermally oxidized ultrathin film.
Depth-Resolved In - Situ TEM Observation of Electromigration in a Submicron-Wide Layered Al–0.5%Cu Line
Authors: Okabayashi Hidekazu , Komatsu Masao , Mori Hirotaro
Published: October 2002

We studied electromigration (probably at ∼350°C) in a submicron-wide Al–0.5 wt%Cu-on-TiN line with a drift-velocity measurement structure by using depth-resolved (side-view) in-situ transmission electron microscopy. Voiding at the cathode was characterized by uniform thinning of a grain and by mass transport from no-current flow ledges with a (111) faceted plane. The adjacent grain began to void when the grain upstream in the electron flow was almost depleted. The voiding proceeded in a manner similar to that in the upstream grain. Voiding between the cathode and the anode began mostly at the intersection of the Al top surface with grain boundaries. It proceeded mainly downward along the anode side of the grain boundary until it reached the Al bottom surface causing a gap in the Al. Then it grew laterally toward the anode. The cathode side surface of the void remained stationary during the void evolution.
Double-Level Cu Inlaid Interconnects with Simultaneously Filled Via Plugs
Authors: Minamihaba Gaku , Iijima Tadashi , Shimooka Yoshiaki , Tamura Hitoshi , Kawanoue Takashi , Hirabayashi Hideaki , Sakurai Naoaki , Ohkawa Hideki , Obara Takashi , Egawa Hidemitu , Idaka Toshiaki , Kubota Takeshi , Shimizu Toshio , Koyama Mitsutoshi , Ooshima Jiro , Suguro Kyoichi
Published: October 2002

A double-level Cu interconnection process for lower submicron generation ULSIs was developed. Cu interconnects were successfully formed by Cu/WSiN sputtering, XeCl excimer laser annealing and Cu/WSiN chemical mechanical polishing. The composition of the WSiN barrier metal was optimized to WSi0.6N and the diffusion barrier capability was confirmed by physical analyses and electrical measurements. The electrical resistivity of the inlaid Cu was 1.9±0.1 µ Ω·cm and contact resistivity between the first-level Cu and the second-level Cu was (1.54–5.78)×10-9 Ω·cm2. The electromigration lifetime of laser-annealed Cu/WSiN wiring was found to be one order of magnitude longer than that of previously reported Cu interconnects. The activation energy for electromigration was determined to be 1.1 eV.
Suppression of Resistance Increase in Annealed Al/W Interconnects by Capacitively Coupled Plasma Nitridation on W Surface
Authors: Sekiguchi Mitsuru , Fujii Toyokazu , Michinari Yamanaka Michinari Yamanaka
Published: October 2002

The suppression of the resistance increase in annealed Al/chemical vapor deposition (CVD)-W interconnects has been achieved by exposing the W surface to N2 plasma before Al deposition. The N2 plasma was generated in a capacitively coupled parallel-plate reactor. This process forms a thin WN
x
layer at the interface between the Al and the W layer. The WN
x
layer prevents Al-W alloy formation during annealing at 450°C. With this N2 plasma treatment, the resistance increase after annealing at 450°C is suppressed to only 10% compared to 140–180% in samples without the N2 plasma treatment. The N/W ratio and the thickness of the WN
x
layer are about 1.1 and 4 nm, respectively. The WN
x
layer formed in our experiment is found to be thicker and have a higher N concentration than the WN
x
layer formed by electron cyclotron resonance (ECR) plasma nitridation. This is probably due to the large self-bias voltage of the N2 plasma generated in a capacitively coupled parallel-plate reactor.
Optimization of Contact Process with Monte Carlo Study for Advanced CMOS Devices
Authors: Sumi Hirofumi , Yanagida Toshiharu , Sugano Yukiyasu , Ikeda Yuji , Kishida Satoru , Tokutaka Heizo , Sasserath Jay N.
Published: October 2002

A new pretreatment method for metallization was developed using on inductive coupled plasma (ICP) soft etch with Ar. The ICP soft etch, which is used instead of conventional HF pretreatment, is anisotropic etching with high-density plasma and low incident energy, and can uniformly remove native oxide at the bottom of fine contact holes. As a result, excellent ohmic characteristics, low junction leakage current and superior reliability of thin gate oxide can be achieved using the ICP soft etch with optimized low bias voltage. Furthermore, the mechanism for the formation of stable ohmic contacts was theoretically analyzed using a Monte Carlo topological simulation. This simulation was especially useful in that it helped to yield an understanding of the mechanism controlling removal of the native oxide in anisotropic etching. Using an ICP soft etch with low sputtering yield, it is possible to prevent resputter deposition on the bottom of holes with 0.1 µm diameter.
Effect of Alkoxy Substitution on Photophysical Properties of Poly(p-phenylenevinylene)
Authors: Lee Geon Joon , Kim Dongho , Lee Jeong Ik , Shim Hong Ku , Kim Yong Wan , Jo Jae Cheol
Published: October 2002

The effect of alkoxy substitution on the photophysical properties of poly(p-phenylenevinylene) [PPV] was investigated using steady-state and time-resolved photoluminescence, visible and infrared absorption spectroscopies. By substituting the alkoxy group (methoxy or butoxy) into the phenylene ring of PPV, the prolongation of effective conjugation length accompanied by the disappearance of the well-resolved vibronic structure was detected in the absorption spectra. These experimental results were attributable to the electron donating effect and the steric hindrance of the alkoxy substituent. These conjectures were compared with the effect of the alkoxy substitution on the photoluminescence and the Fourier-transform infrared spectra. Also, it was found that, alkoxy substitution slowed down the exciton relaxation process from the lower exciton state to the ground state, and lowered the height of the potential barrier in an excitonic potential well.
Complementary Digital Logic Using Resistively Coupled Single-Electron Transistor
Authors: Yoshikawa Nobuyuki , Jinguu Yasuyuki , Hiroshi Ishibashi Hiroshi Ishibashi , Masanori Sugahara Masanori Sugahara
Published: October 2002

A new complementary digital logic based on resistively coupled single-electron transistors (R-SET) was proposed and its basic characteristics were numerically analyzed using the Monte Carlo method. The proposed logic has a logic threshold independent of background polarization charges which induce crucial problems in logic operation in the case of a capacitively coupled logic. In addition, the proposed complementary R-SET logic has larger output voltage swing and better logic level stability than those of a conventional resistance-load R-SET logic. The stability of the logic level of the complementary R-SET logic was investigated by calculating the data retention time of flip-flop circuits, and its dependence on temperature and shot noise was examined. For stable operation of the flip-flop circuit, estimated optimal operation temperature and switching delay time are e
2/80C
t
k
B and 1500 R
t
C
t, respectively, where C
t and R
t are capacitance and resistance of the tunnel junction.
Estimation of Cotunneling in Single-Electron Logic and Its Suppression
Authors: Shuhei Amakawa Shuhei Amakawa , Hironobu Fukui Hironobu Fukui , Minoru Fujishima Minoru Fujishima , Koichiro Hoh Koichiro Hoh
Published: October 2002

It is known that cotunneling causes a serious decline in the reliability of single-electron logic circuits. We report the effects of cotunneling on single-electron logic circuits studied using computer simulation in which both two-electron cotunneling and normal single-electron tunneling are taken into account. It is proved that the cotunneling reduces the operation accuracy of single-electron logic circuits considerably even at absolute zero. At finite temperatures both normal tunneling and cotunneling are enhanced by thermal fluctuation. Temperature dependence of tunneling rates of both processes is also discussed. In order to suppress cotunneling, we consider the tunnel resistance of junctions as one of the design parameters and show that the cotunneling rate can be reduced by optimizing the resistance. In addition, we present an inverter circuit that exhibits a better tolerance of the cotunneling effect.
Deep Level and Conduction Mechanism in Low-Temperature GaAs Grown by Molecular Beam Epitaxy
Authors: Shiobara Syunsuke , Tamotsu Hashizume Tamotsu Hashizume , Hideki Hasegawa Hideki Hasegawa
Published: October 2002

Deep levels in low-temperature (LT) GaAs layers grown by molecular beam epitaxy were investigated by deep level transient spectroscopy (DLTS), photocapacitance and photoluminescence (PL) techniques. Five electron traps were detected, for the first time, in Si-doped conductive LT-GaAs layers grown at 300–400°C. The dominant trap was found to be the S1 level with an activation energy of 0.64 eV and an electron capture cross section of σ n=2–4×10-14 cm2. The S1 level showed remarkable photoquenching behavior. No PL was observed from LT-layers. The mechanism responsible for the semi-insulating property of LT-GaAs layers is probably due to compensation by the S1 trap, which is not EL2 but a new electron trap peculiar to LT-GaAs layers.
Electrical Properties of High-Quality Stacked CdTe/Photo-Enhanced Native Oxide for HgCdTe Passivation
Authors: Su Yan-Kuin , Lin Chung-Te , Huang Hsin-Tien , Chang Shoou-Jinn , Sun Tai-Ping , Chen Gin-Shiang , Luo Jiunn-Jye
Published: October 2002

A novel surface treatment method for obtaining a high-quality CdTe/HgCdTe interface is proposed. By stacking photoenhanced native oxide and CdTe films, we successfully passivated HgCdTe. This technique is advantageous because photoenhanced native oxides can form an excellent interface and adhere to HgCdTe substrate well. Using this novel technique, we have fabricated metal/CdTe/photoenhanced native oxide/HgCdTe structured metal-insulator-semiconductor (MIS) capacitors. From capacitance-voltage (C-V) measurement, we found that the flat-band voltage of such a MIS capacitor is about -0.2 V with a fixed oxide charge of 1×1010 cm-2. For comparison, conventional metal/CdTe/HgCdTe structured MIS capacitors were also fabricated. We found that capacitors with the photoenhanced native oxide layer have a much lower leakage current. Such a marked leakage current reduction is due to the good interfacial properties between the photoenhanced native oxide and the HgCdTe substrate.
Numerical Study of Collector-Base Junction Design for Ultra-High-Speed InP/InGaAs Heterojunction Bipolar Transistors
Authors: Gregory Khrenov Gregory Khrenov , Elena Kulkova Elena Kulkova
Published: October 2002

High-frequency operation of nonplanar and planar InP/InGaAs heterojunction bipolar transistors (HBTs) with various collector doping profiles has been investigated using a Monte Carlo particle simulation. It is shown that vertical scaling of the collector does not provide a substantial improvement in HBT overall speed performance due to the dramatic increase in the collector capacitance charging time with decreasing collector layer thickness. A considerable improvement in HBT high-frequency performance has been obtained in HBTs with buried subcollector and nonuniform collector doping profile.
New Fabrication Technology for Integrating Field Effect Transistors and Diodes
Authors: Jung Jong-Wan , Song-Cheol Hong Song-Cheol Hong , Young-Se Kwon Young-Se Kwon
Published: October 2002

We demonstrated a new integration technology for field effect transistors (FETs) and diodes. This technology uses selective-area metalorganic chemical vapor deposition (MOCVD) for FET and diode layers. FETs (called FECFET) fabricated by this technology have very short distances between the drain and source, so that the characteristics such as knee voltage and transconductance are superior to those of conventional FETs with the same gate length. Because this structure has an n+-doped contact layer under an n-doped active layer, it is easy to integrate with a high-quality diode having low series resistance. By this approach, diodes with low series resistance and low junction capacitance have been fabricated. To demonstrate the integration of the diode and FECFET, a 36 GHz single balanced diode mixer and an intermediate frequency (IF) amplifier have been fabricated on a GaAs wafer.
Growth of (411)A Faceted GaAs/AlGaAs Ridges by Growth-interrupted Chemical Beam Epitaxy
Authors: Ro Jeong-Rae , Park Seong-Ju , Sung-Bock Kim Sung-Bock Kim , El-Hang Lee El-Hang Lee
Published: October 2002

Faceted (411) and (100) ridges of GaAs/AlGaAs have been successfully grown on mesa-etched GaAs(100) substrates by chemical beam epitaxy employing growth-interruption technique. The growth-interruption method was found to be very efficient in evolving and forming (411) faceted ridge structures. The formation of (411) ridge structures were attributed to the Ga migration enhanced by growth-interruption and also to the increased desorption of Ga on the (411) face compared to (100) face. We also observed the growth of triangular-shaped GaAs structure with (411)-(100) planes which are surrounded by AlGaAs barrier layer. This results shows that the formation of quantum wires could be possible using this method.
Anomalous Effect in La2-xSrxCuO4 of Doping Level x= 1/4n
Authors: Sugahara Masanori , Han Xiao-Yi , Lu Hong-Fei , Ito Akihiro , Maejima Shinroku , Wu Song-Bin , Gao Hua , Uno Kazushi , Haneji Nobuo , Hisayoshi Kaneda Hisayoshi Kaneda , Nobuyuhi Yoshikawa Nobuyuhi Yoshikawa
Published: October 2002

Anomalous electric response of La2-x
Sr
x
CuO4 thin film at Sr doping levels of x≈1/4 and 1/16 is observed when charge moves along the c axis. The capacitance C
t of the Pd/La2-x
Sr
x
CuO4/SrTiO3/Pd structure increases sharply, exceeding the capacitance C
STO of the Pd/SrTiO3/Pd structure. Oscillatory negative voltage is observed in 4-terminal resistivity measurements of La2-x
Sr
x
CuO4 thin film using Pd electrodes at small current. These phenomena are explained by a model of the spatial ordered state in which CuO2 layers of La2-x
Sr
x
CuO4 is replete with O hole pairs.
Nitrogen Ion Implantation and Thermal Annealing in 6H–SiC Single Crystal
Authors: Miyajima Takeshi , Tokura Norihito , Fukumoto Atsuo , Hayashi Hidemitsu , Kunihiko Hara Kunihiko Hara
Published: October 2002

The interrelationships among implantation-induced defect density, carrier activation rate, substrate temperature during nitrogen implantation and annealing in 6H–SiC have been clarified. Several defects, whose energy required for recovery of lattice damage depends on the substrate temperature during implantation, were examined. Although defect density was sufficiently low that it was undetectable by Rutherford backscattering spectrometry, the carrier activation rate was 3.3% under the condition that the implanted nitrogen density was 1.8×1019 cm-3. According to the first principles local-density functional calculation using the cubic SiC crystal model, the complex defect composed of interstitial carbon and substituted nitrogen, which produces a localized electronic state and a half-occupied level in the band gap, is considered to be one cause of the low carrier activation rate in nitrogen-implanted SiC.
Simple Kinetic Model of ECR Reactive Ion Beam Etching Reactor for the Optimization of GaAs Etching Process
Authors: Sugiyama Masakazu , Yamaizumi Takayuki , Nezuka Masahiro , Shimogaki Yukihiro , Nakano Yoshiaki , Tada Kunio , Hiroshi Komiyama Hiroshi Komiyama
Published: October 2002

In order to efficiently optimize electron cyclotron resonance/reactive ion beam etching (ECR-RIBE) process for GaAs, we studied the kinetic mechanism of the process. First we examined the relationship between etching performances and process parameters. We paid particular attention to the effect of the Cl2 flow rate. To explain this effect, we examined the effect of Cl2 flow rate on Cl radical concentration by optical emission spectroscopy (OES). The Cl emission intensity depended on Cl2 flow rate and the substrate area. We introduced a simple model of our ECR-RIBE reactor and explained the observed dependence of emission intensity of Cl and Ga. We also explained the flow rate dependence of etching rate in terms of the effect of etching products. We obtained some rate constants of etching reactions according to our model. Our study revealed that the macroscopic phenomena in the reactor, such as the change in gas residence time, should affect the etching performances at a micron level.
Oxidation Using AFM and Subsequent Etching in Water of Inverted-Type Delta-Doped HEMT
Authors: Masami Ishii Masami Ishii , Kazuhiko Matsumoto Kazuhiko Matsumoto
Published: October 2002

Using an atomic force microscope, we have formed an oxide wire on a channel region of the inverted-type delta-doped high-electron-mobility transistor. We discovered that the oxide wire is etched in water, and that consequently a trench is formed. Using this property, we have controlled the height of the potential barrier in the two-dimensional electron gas channel.
Electrical Properties of Ferroelectric Gate HEMT Structures
Authors: Ohmi Shun-ichiro , Yoshihara Makoto , Okamoto Takeo , Eisuke Tokumitsu Eisuke Tokumitsu , Hiroshi Ishiwara Hiroshi Ishiwara
Published: October 2002

Electrical properties of ferroelectric BaMgF4 films grown on AlGaAs/GaAs(100) high-electron-mobility transistor (HEMT) structures are investigated. It is shown that a spontaneous polarization of 1.3 µC/cm2 and a coercive field of 200 kV/cm are obtained from polarization vs electric field (P-E) hysteresis measurements for mainly (140)-oriented BaMgF4 films. In addition, a threshold shift (memory window) as large as 1.2 V is demonstrated in capacitance-voltage (C-V) hysteresis measurements for a BaMgF4(140)/HEMT structure in which the growth temperature of the BaMgF4 film is about 550°C. This work indicates that the suitable growth temperature of BaMgF4 films on the HEMT structure is 550°C.
Near-infrared Intersubband Transitions in InGaAs/AlAs Quantum Wells on GaAs Substrate
Authors: Takashi Asano Takashi Asano , Susumu Noda Susumu Noda , Tomoki Abe Tomoki Abe , Akio Sasaki Akio Sasaki
Published: October 2002

We report intersubband transitions in InGaAs/AlAs quantum wells on GaAs substrate. The intersubband-transition wavelength and absorption coefficient are investigated as functions of sample structure and growth conditions. It is shown that a decrease in well width leads to a shorter transition wavelength but a reduction in the absorption coefficient. The reduction in the absorption coefficient can be recovered by increasing the In composition of the well and by suppressing the segregation of In during growth. With these optimizations, a very short intersubband-transition wavelength of 1.9 µm is achieved.
Carrier Dynamics in Piezoelectric Quantum Wells Grown on GaAs (111)A, (211)A and (311)A Studied by Time-Resolved Photoluminescence Spectroscopy
Authors: Vaccaro Pablo O. , Hosoda Makoto , Kazuhisa Fujita Kazuhisa Fujita , Toshihide Watanabe Toshihide Watanabe
Published: October 2002

In0.2Ga0.8As/GaAs strained quantum wells (SQWs) grown on As (111)A, (211)A and (311)A-oriented substrates have a built-in electric field due to the piezoelectric effect that shifts the photoluminescence (PL) peaks to longer wavelengths. This electric field was screened by photocarriers generated with an optical pulse and a blueshift of the PL peaks was observed. The PL peaks returned to longer wavelength as the carrier density and the field screening in the wells decreased with time. The PL decay time dependence on wavelength reflected the evolution of the photocarrier distribution in the well. We calculated the dependence of optical transition energies and degree of electron-hole wave function overlap on photocarrier density for (111)A-oriented SQWs. A model of the carrier dynamics in the well that successfully explains the experimental results is also presented.
Extremely Sharp Photoluminescence Lines from Nitrogen Atomic-Layer-Doped AlGaAs/GaAs Single Quantum Wells
Authors: Toshiki Makimoto Toshiki Makimoto , Naoki Kobayashi Naoki Kobayashi
Published: October 2002

We have applied nitrogen atomic-layer-doping to AlGaAs/GaAs single quantum wells. The atomic-layer-doping was performed at the center of the GaAs quantum well. The resulting structures show sharp photoluminescence lines with a full width at half maximum of 0.3 meV at 8 K. These lines are observed at longer wavelength than those obtained for undoped single quantum wells, indicating that they correspond to the excitons bound to nitrogen atoms in the quantum wells. The full width at half maximum of these nitrogen-related lines depends on the quantum well width. The lines remain sharp above a well width of 10 nm, while they become broad at 5 nm. This suggests that the diameter of the exciton bound to N atoms is about 10 nm. Furthermore, the binding energy of the excitons increases with increasing substrate temperature during the atomic-layer-doping.
Influence of Type-I to Type-II Transition by an Applied Electric Field on Photoluminescence and Carrier Transport in GaAs/AlAs Type-I Short-Period Superlattices
Authors: Naoki Ohtani Naoki Ohtani , Hidenori Mimura Hidenori Mimura , Makoto Hosoda Makoto Hosoda , Koji Tominaga Koji Tominaga , Toshihide Watanabe Toshihide Watanabe , Kenzo Fujiwara Kenzo Fujiwara
Published: October 2002

We have investigated the influence of type-I to type-II transition by an applied electric field on photoluminescence and carrier transport by time-of-flight experiments in GaAs/AlAs short-period superlattices. Type-I to type-II transition was confirmed by observing degenerated photoluminescence spectra caused by Γ-X mixing. The rise time of the time-resolved photocurrent was found to increase by the type-I to type-II transition. This result clearly shows that the tunneling time through type-II alignment is longer than that through type-I alignment. The delayed carrier transport is most likely caused by Γ-X-Γ transfer. The results suggest that in type-II superlattices, carriers prefer Γ-X-Γ transfer to Γ-Γ sequential tunneling.
Preferential Nucleation of Nanocrystalline Silicon along Microsteps
Authors: Otobe Masanori , Kawahara Jun , Oda Shunri
Published: October 2002

We propose digital plasma processing for the fabrication of silicon quantum dots on SiO2 substrates patterned with microtrenches. It has been found that nucleation of nanocrystalline Si (nc-Si) takes place preferentially along the trench structure with post hydrogen plasma annealing of the hydrogenated amorphous Si (a-Si:H) layer at a substrate temperature of 250°C. The preferential nucleation of nc-Si can be explained in terms of a “hydrogen diffusion model”, in which hydrogen radicals which diffuse through the a-Si:H layer to the interface of a-Si:H and SiO2 trigger the crystallization.
Confinement Potential in an Asymmetrically Biased Quantum Point Contact
Authors: Fujio Wakaya Fujio Wakaya , Junichi Takahara Junichi Takahara , Sadao Takaoka Sadao Takaoka , Kazuo Murase Kazuo Murase , Kenji Gamo Kenji Gamo
Published: October 2002

Two-dimensional Schrödinger and Poisson equations are solved numerically to determine the position of the electron channel and the lateral confinement potential of an asymmetrically biased split-gate quantum point contact (QPC). The conductance of an asymmetrically biased QPC was measured at low temperature, and a change in the widths of conductance plateaus was observed, suggesting that the lateral confinement potential became broad under the asymmetric bias conditions. It is concluded that asymmetric bias affects not only the position of the electron path but also the confinement potential.
New Method of the Determination of HgCdTe/CdZnTe Composition by Infrared Transmission
Authors: Yongtaek Jeoung Yongtaek Jeoung , Taeseok Lee Taeseok Lee , Hongkuk Kim Hongkuk Kim , Jaemook Kim Jaemook Kim , Myungsu Han Myungsu Han , Taewon Kang Taewon Kang
Published: October 2002

A new method for compositional determination in Hg1-
x

Cd

x

Te/CdZnTe has been studied. In case of Hg1-
x

Cd

x

Te (MCT) epilayer grown onto Cd(Zn)Te substrates by liquid phase epitaxy (LPE), compositional graded region exists between the substrate and epilayer. This compositional graded region affects the infrared (IR) transmission curve. In this study, the IR transmission curves as a function of compositional profile and epilayer thickness were simulated based on the theoretical IR transmission model. From these results, a new and simple equation for calculating the composition of an epilayer MCT was obtained. This equation is related to the wavenumber (Z
1/2) of the 50% T
max transmission point, where T
max is the maximum transmission, the wavenumber (Z
500) of the 500 cm-1 absorption coefficient point, and the wavenumber (Z
1000) of the 1000 cm-1 absorption coefficient point. This equation is as follows: x=a+b×Z+(c+d×Z)×ln
(10/T), where Z is the specific wavenumber in cm-1, T is the epilayer thickness in µ m, and a, b, c, and d are fitting parameters depending on the specific wavenumber. The compositions can be calculated easily using the new equation with an accuracy of ±0.002 in the range of 0.17≤x≤0.30. The new method can be also applied successfully to the samples with nonuniformity into depth and radial directions.
Fabrication of Quantum Wire and Minute Buried Heterostructure by In Situ Etching and Selective MOCVD Growth
Authors: Ogura Mutsuo , Wang Xue-Lun , Matsuhata Hirofumi , Tada Tetsuya , Hamoudi Ali , Ikawa Seiji , Takehiko Miyagawa Takehiko Miyagawa , Kazuhisa Takeyama Kazuhisa Takeyama
Published: October 2002

Among the various methods used for the fabrication of III–V semiconductor quantum nanostructures, the flow rate modulation epitaxy (FME) on a patterned substrate, in-situ dry-etching and regrowth process, and in-situ gas-phase etching and regrowth process are presently investigated from the viewpoints of interface quality, uniformity, and freedom in the structural and material design.
Optical Properties of Silicon Nanocrystallites Prepared by Excimer Laser Ablation in Inert Gas
Authors: Yamada Yuka , Orii Takaaki , Umezu Ikurou , Shigeru Takeyama Shigeru Takeyama , Takehito Yoshida Takehito Yoshida
Published: October 2002

Optical properties of silicon (Si) nanocrystallites prepared by excimer laser ablation in constant-pressure inert gas have been studied in relation to the particle size. Visible photoluminescence (PL) bands in the red and green spectral regions appear at room temperature after an oxidation process. The red PL band is independent of the particle size and is stable without degradation by excitation light irradiation. It is concluded that the red PL is emitted from the surface states of the oxidized Si nanocrystallites. In contrast, the green PL band depends on the particle size. The green PL intensity decreases during excitation light irradiation in air, and then recovers in the subsequent vacuum evacuation. These results suggest that the origin of the green PL is associated with a quantum confinement effect of Si nanocrystallites.
Capacitance of Nanostructures
Authors: Teruhiro Ohba Teruhiro Ohba , Kenji Natori Kenji Natori
Published: October 2002

The nanostructure capacitance is analyzed and is shown to consist of three serially connected components; the first one is an extension of the classical capacitance in electrostatics, the second is due to the electronic density of states of the conductor, and the third comes from the electronic charge distribution inside the conductor. The latter two are due to the electronic states inside the conductor, and have only the self-capacitance contribution. A diagrammatic expression of the capacitance is given. As an example, the capacitance-voltage curve for the dual gate silicon on insulator (SOI) metal-oxide-semiconductor (MOS) junction is discussed.
Temperature-Dependent Current-Voltage Characteristics of Fully Processed Ba0.7Sr0.3TiO3 Capacitors Integrated in a Silicon Device
Authors: Shimada Yasuhiro , Inoue Atsuo , Nasu Toru , Arita Koji , Nagano Yoshihisa , Matsuda Akihiro , Uemoto Yasuhiro , Fujii Eiji , Azuma Masamichi , Oishi Yoshiro , Shin-ichiro Hayashi Shin-ichiro Hayashi , Tatsuo Otsuki Tatsuo Otsuki
Published: October 2002

Temperature-dependent current-voltage characteristics of fully processed Ba0.7Sr0.3TiO3 thin film capacitors integrated in a charge-coupled device delay-line processor as bypass capacitors were studied. The thin film capacitors with a film thickness of 185 nm were formed by metal-organic decomposition processing. The leakage current measured after completion of the integration process was 1 to 2 orders of magnitude higher than that measured after capacitor patterning. The leakage current at low voltages (<1 V, 50 kV/cm) indicated ohmic conduction within a measured temperature range of 300–423 K. At high voltages (>10 V, 500 kV/cm), the Schottky mechanism plays a dominant role in leakage current, while the Frenkel-Poole emission begins to contribute to the leakage current as the temperature is elevated.