bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of Influence of Alkyl Sources on Deep Levels in GaN by Transient Capacitance Method
Authors: Chen Jenn-Fang , Chen Nie-Chuan , Huang Wen-Yen , Feng Wei-I Lee
Published: October 2002

The transient capacitance method was used to analyze GaN samples grown by low-pressure organometallic vapor phase epitaxy (OMVPE) with triethylgallium (TEGa) or trimethylgallium (TMGa) as the alkyl source. Two deep levels at 1.10 and 1.27 eV were observed in the TMGa sample, while a deep level at 0.60 eV was observed in the TEGa sample. Using light illumination, levels deeper than those above were investigated in TEGa and TMGa samples.
Utilization of GaAs Masking Layers for Formation of Patterned Porous Silicon
Authors: Lee Ming-Kwei , Cheng-Chung Hu Cheng-Chung Hu , Yu-Hsiung Wang Yu-Hsiung Wang
Published: October 2002

GaAs on a Si heteroepitaxial layer grown by metalorganic chemical vapor deposition (MOCVD) is used as the masking layer for the fabrication of porous silicon (PS) on silicon substrates. The photoluminescence (PL) of PS shows red light centered at a wavelength of around 630 nm. Of particular interest in the utilization of the GaAs masking layer is the anisotropic growth of PS (lateral/vertical growth ratio <1), the much higher resistance to anodization in HF solution than other kinds of masking layers (nitride, oxide, SiC, etc.) and lack of destruction in non-PS regions (implantation or irradiation). The nitride masking layer used to define the growth of PS is also studied. Surface and cross-sectional scanning electron microscopy (SEM) are carried out to determine which mask is better. The GaAs masking layer studied in this paper will lead to the realization of PS optoelectronic integrated circuits (OEIC).
Photoinduced Degradation of Photoluminescence in Polysilane Films
Authors: Kurando Yoshikazu Nakayama , Oka Kunio , Dohmaru Takaaki , West Robert
Published: October 2002

The photoinduced degradation of photoluminescence (PL) from the σ*-σ transition in polysilane films with thickness greater than the penetration depth of excitation light has been investigated. The PL intensity decays by the power law, the exponent of which changes when the transmittance of the films begins to increase significantly. We explain the first decay in terms of an interaction of excitons with trapped carriers. The trapped carriers result from free charged carriers which are photogenerated and diffuse into the bulk with decreasing their number by the Auger process. The second decay corresponds to a decrease in the absorption of the excitation light.
Differential Body Effect Analysis and Optimization of the LArge Tilt Implanted Sloped Shallow Trench Isolation Process (LATI-STI)
Authors: Deleonibus Simon , Heitzmann Michel , Gobil Yveline , Martin François , Demolliens Olivier , Jean-Charles Guibert Jean-Charles Guibert , Alain Toffoli Alain Toffoli
Published: October 2002

The optimization of a LArge Tilt Implanted Sloped shallow Trench Isolation (LATI-STI) process for Non Volatile Memories is presented. The process uses 70° sloped and large tilt angle (up to 55°) implanted trench sidewalls, combined with a single step Chemical-Mechanical Polishing (CMP) planarization. A new method, so-called differential body effect method, enables very accurate and statistical electrical analysis of the subthreshold humped transistors characteristics under strong body bias (V
B) values: compared to a 90° sloped trenches case larger process margins are obtained with the LATI-STI scheme. 15 V holding isolation is demonstrated for 0.45 µ m finished spacings between diffusions.
Fluoridation of GaAs Surface in a Remote SF 6 Plasma
Authors: Kwang-Ho Kim Kwang-Ho Kim , Kyung-Soo Suh Kyung-Soo Suh
Published: October 2002

Gallium fluoride films were directly grown on gallium arsenide (GaAs) at temperatures below 300°C using a radio frequency (RF) remote SF6 plasma.The growth kinetics are exhibited a rapid initial increase for 60 minutes, with no significant increase thereafter. Rutherford backscattering spectrometry (RBS) and secondary ion mass spectrometry (SIMS) showed that the GaF3 films had almost stoichiometric composition. The as-grown films exhibit a current density of less than 1 µA/cm2 at a breakdown field of 1 MV/cm and a refractive index of 2.0–2.3 at a wavelength of 632.8 nm. A typical value of the dielectric constant is about 5.5 as derived from 1 MHz capacitance-voltage ( C-V) measurements. The minimum interface state density is estimated to be around 1 × 1012 cm-2·eV.
Impact of Hydrogenating Plasma Induced Oxide Charging Effects on the Characteristics of Polysilicon Thin Film Transistors
Authors: Lee Kan Yuan , Fang Yean Kuen , Cheng Chii Wen , Huang Kou Chin , Liang Mong Song , Wuu Sou Gow
Published: October 2002

The impact of electrostatic charging damage on the characteristics and gate oxide integrity of polysilicon thin film transistors (TFTs) during plasma hydrogenation were investigated. Hydrogen atoms passivate trap states in the polysilicon channel; however, plasma processing induced electrostatic charging effects damage the gate oxide and the oxide/channel interface. The passivation effect of hydrogen atoms is antagonized by the generation of interface states. TFTs with different areas of antennas were used to study the damage caused by electrostatic fields. Oxide charging damage during plasma hydrogenation also seriously degrades the integrity of the gate oxide and the channel/oxide interface.
Dislocation-Free Oxidation of Porous Silicon Formed Using Highly Phosphorus-Diffused Silicon and Its Application
Authors: Yoshinobu Arita Yoshinobu Arita , Kunihiro Kuranari Kunihiro Kuranari
Published: October 2002

Porous silicon was formed using highly phosphorous-diffused n-type silicon. Dislocation generation mechanisms due to the force caused by marked volume expansion at the early stage of porous silicon oxidation and strain generation caused by oxidation are investigated. The height of the step produced by oxidation and the relationship between the rate of increase in step height and stress are discussed. The experimental results concerning the step height versus the direct oxidation time are qualitatively explained based on the oxidation time dependence of the amount of SiO2 in oxidized porous silicon calculated using a simple model. Two dislocation-free oxidation methods are proposed. One is oxidation in wet oxygen through a SiO2 film deposited on the porous silicon by low-temperature chemical vapor deposition. The other is oxidation in dry and wet oxygen after annealing in nitrogen atmosphere. The porous silicon oxidized by the former dislocation-free oxidation method was applied to reduce the parasitic capacitance between the base electrode and the collector region in a high-speed bipolar transistor. This reduction resulted in an increase of the cut-off frequency and maximum frequency.
Novel Optical Compensators of Negative Birefringence for Wide-Viewing-Angle Twisted-Nematic Liquid-Crystal Displays
Authors: Hiroyuki Mori Hiroyuki Mori
Published: October 2002

A novel optical compensator with a negative birefringence structure is proposed to widen the viewing angle of twisted-nematic liquid-crystal displays (TN-LCDs). We describes the design concept and the simulation results to give a theoretical basis for the development of this new class of material. Computer simulation of viewing-angle characteristics using the Jones matrix indicates (a) that the optical compensator can effectively minimize the amount of light leakage of the black on-state of TN-LCD, (b) that the compensator with a fixed director structure, which is the same as that of the on-state of TN-LCD, gave the best results, and (c) that the optical compensator is effective in several optical configurations.
A Simple Optical Properties Modeling of Microcrystalline Silicon for the Energy Conversion Application by the Effective Medium Approximation Method
Authors: Woo Yeong Cho Woo Yeong Cho , Koeng Su Lim Koeng Su Lim
Published: October 2002

The optical properties of microcrystalline silicon ( µc-Si) were estimated using the effective medium approximation (EMA) method. This modeling was based on two-phase mixture, amorphous silicon (a-Si) and crystalline silicon (c-Si) with volume fractions of f
a and f
c respectively. It could be possible to understand that µc-Si has lower light absorption characteristics than a-Si over all solar spectrum by considering hydrogen involvement in embedded a-Si part of µc-Si and crystalline volume fraction. It is proposed that p-type µc-Si is superior to n-type µc-Si because of its high optical gap of E
04 and its low absorption coefficient spectrum shape.
Structure and Magnetic Properties of Co/Mn Multilayers Composed of Ultrathin Films
Authors: Uchiyama Kiyoshi , Ishida Iwao , Hirota Eiichi , Hamada Kouichi , Okada Akira
Published: October 2002

In multilayers of [Co(10 Å)/Mn( t
Mn Å)]20 deposited onto glass substrates under an ultra-high-vacuum (UHV), the saturation magnetic moment per Co, Ms Co, is observed to increase with increasing Mn thickness and eventually the magnetic moment to exceed that of bulk Co. The saturation magnetic moment also varies depending upon the deposition conditions of Mn-buffer layers, and magnetic moments are observed to be 1.5 to 2 times as large as that of bulk Co. This suggests that atomic layers of Mn adjacent to Co layers contribute ferromagnetically to the magnetic moment by forming ferromagnetic coupling between Mn and Co atoms at their interfaces.
Hydrothermal, Hydrothermal-Electrochemical and Electrochemical Synthesis of Highly Crystallized Barium Tungstate Films
Authors: Woo-Seok Cho Woo-Seok Cho , Masahiro Yoshimura Masahiro Yoshimura
Published: October 2002

Highly crystallized polycrystalline films of BaWO4have been synthesized on tungsten metal substrates by hydrothermal-electrochemical and electrochemical methods from room temperature to 200 °C. The hydrothermal method did not produce a film because only discrete BaWO4particles appeared on the tungsten substrate. The crystallization of BaWO4was characterized by three-dimensional nucleation and growth behaviors. In the case of the electrochemical method, an amorphous tungsten oxide film formed after the BaWO4film formation, while the hydrothermal-electrochemical method did not produce an amorphous film.
Multiply Charged Ions by Constant Voltage Arc Ion Plating and Its Applications
Authors: Akira Suzuki Akira Suzuki
Published: October 2002

Applications of multiply charged ions are few. In the reactions between multiply charged ions and gases, different thin films are expected to be obtained. Among various methods to make thin films, arc ion plating is suitable for investigating the effect of ions because of its high ionization rate. For arc discharge, an ordinary constant voltage power source cannot be used, so a constant current power source is used. In order to control the discharge voltage, the author has devised a pulse power source, where the peak voltage of this pulse power source is controlled. By employing this new power source, TiN films of good quality are produced and are successfully applied to cutting tools.
Pressure Dependences of Electron Energy Distribution and Power Dissipation in Symmetrical RF Discharges of Inert Gases
Authors: Takashi Kimura Takashi Kimura , Kazuyuki Ohe Kazuyuki Ohe
Published: October 2002

The plasma parameters, including the electron energy distribution function (EEDF), are measured with a Langmuir probe in symmetrically capacitively coupled RF (13.56 MHz) discharges of Ne, Ar and Xe over a range of gas pressures from 0.1 to 0.8 Torr, while keeping the RF current constant at 150 mA. The EEDFs are Druyvesteyn-like for these discharges. The average electron energy decreases with the gas pressure and the electron density increases. In bulk plasmas of respective gases, joule heating is more dominant than stochastic heating and heating due to ion acceleration, except for low-pressure Ne discharges.
Experimental Studies on Longitudinal Mode Characteristics of a Hollow Cathode He–Cd+ White Light Laser
Authors: Guang Xu Guang Xu , Kan-ichi Fujii Kan-ichi Fujii , Shigeru Nakayama Shigeru Nakayama , Akira Honma Akira Honma , Yoshihiro Uchiyama Yoshihiro Uchiyama , Yasuhiro Tokita Yasuhiro Tokita , Yoshihiro Hanazawa Yoshihiro Hanazawa
Published: October 2002

A hollow cathode CW He–Cd+ white light laser can oscillate simultaneously at three primary colors (five transitions) in a single tube. The frequency characteristics are important parameters in many applications. Therefore, we have investigated the longitudinal mode of our white light laser. In our experiment, we have found that the red and green transitions oscillate in a single longitudinal mode in spite of a wide gain profile and that the blue transition oscillates in a few longitudinal modes. We consider that this single-mode operation can be caused by hole burning due to mode competition between the longitudinal modes and the saturation coupling. Furthermore, we measured the pressure broadenings and the natural linewidths of the five transitions upon changing of the He gas pressure in the He–Cd+ white light laser.
Novel Porous Films Having Low Dielectric Constants Synthesized by Liquid Phase Silylation of Spin-On Glass Sol for Intermetal Dielectrics
Authors: Nobuo Aoi Nobuo Aoi
Published: October 2002

A novel technique for synthesis of highly porous inorganic SOG films such as aerogels using conventional spin-on processing has been developed. The porous films exhibit dielectric constants as low as 2.3 and the average pore diameter was about 80 nm. The relative dielectric constants of the films compare favorably with those of organic polymers, and the films were demonstrated to exhibit relatively low hygroscopic characteristics. This novel technique for synthesis of porous film is the first step in the development of nanofoam materials for future low k dielectrics.
Suppression of Boron Penetration in P+-Poly-Si Gate Metal-Oxide-Semiconductor Transistor Using Nitrogen Implantation
Authors: Chao T. S. , Chien C. H. , Hao C. P. , Liaw M. C. , Chu C. H. , Chang C. Y. , Lei T. F. , Sun W. T. , Hsu C. H.
Published: October 2002

The mechanism and the optimization of nitrogen implantation for suppression the boron penetration in p+-poly-Si gate metal-oxide-semiconductor capacitor is reported. This nitrogen co-implantation process exhibits a good suppression of boron penetration and a better electrical characteristic than that of control sample. It was found that nitrogen combines with the boron to form a B-N complex, retarding the penetration of boron itself, was identified by XPS measurements. The optimum nitrogen dosage is also found in this study.
Identification of Grain-Boundary Trap Properties Using Three-Level Charge-Pumping Technique in Polysilicon Thin-Film Transistors
Authors: Kee-Jong Kim Kee-Jong Kim , Ohyun Kim Ohyun Kim
Published: October 2002

The grain-boundary trap properties in polysilicon thin film transistors (poly-Si TFTs) are evaluated using the three-level charge-pumping (3CP) technique. By measuring the 3CP current with various fall times, we can obtain the grain-boundary trap distribution for each time constant window. The 3CP current versus step voltage characteristics indicate that the total change of 3CP currents drastically increase as the fall time decreases and as the step time increases. The large change of 3CP current indicates that a large number of grain-boundary traps (D
gb ≥4 ×1011 eV-1·cm-2) exist in the upper half of the band gap in the n-channel TFTs. The grain-boundary trap density is derived from the step voltage dependence of the 3CP current. The influence of process temperature on trap properties is examined using the 3CP technique.
Study of 4.5 kV MOS-Power Device with Injection-Enhanced Trench Gate Structure
Authors: Mitsuhiko Kitagawa Mitsuhiko Kitagawa , Akio Nakagawa Akio Nakagawa
Published: October 2002

We propose two new MOS-power device structures, which realize lower on-state voltage than previously proposed injection-enhanced gate transistors (IEGTs). One is an improved IEGT (or IEGN), and the other is a MOS-controlled diode (or IEGD). Using 2-D numerical simulations, it has been confirmed that the IEGN and the IEGD realize a lower on-state voltage drop than the conventional IEGT, retaining MOS gate drivability. This means that the injection-enhanced gate structure improves the effective electron injection efficiency not only for transistor structures, but also for devices with a low-injection efficiency emitter. It has also been confirmed that the 4.5 kV IEGN and IEGD can operate under the same circuit conditions as a 4.5 kV GTO-thyristor.
A Study on the Fabrication of a Multigate/Multichannel Polysilicon Thin Film Transistor
Authors: Kim Jae-Hong Park
Published: October 2002

In this study, the new polysilicon thin film transistors (TFTs) incorporating a multigate and a multichannel were fabricated and their electrical characteristics were estimated. An average field-effect mobility as high as 30 cm2/Vs was achieved for multigate/multichannel polysilicon TFTs. A subthreshold slope of 3 V/dec and a threshold voltage of 3 V were obtained. The switching ratio was about 105. Through the experimental results, it was found that multigate/multichannel TFTs can overcome the limitation of the multigate TFT whose on-current is smaller than that of a single-gate TFT with the same aspect ratio. Moreover, the bias-dependence of their off-current was not apparent even when the multichannel structure was employed. This is thought to be caused by the increase of the total channel resistance by the division of the channel. Compared with that of the conventional TFT employing the large gate width, the off-current flow in the new multigate/multichannel polysilicon TFT was greatly reduced without much loss of the on-current, in spite of the small total gate width.
Analysis of Si–H, Si–O–H and Si–O–O–H Defects in SiO 2 Thin Film by Molecular Orbital Method
Authors: Takeshi Kanashima Takeshi Kanashima , Masanori Okuyama Masanori Okuyama , Yoshihiro Hamakawa Yoshihiro Hamakawa
Published: October 2002

Energy states of hydrogen-related defects in SiO2 such as Si–H, Si–O–H and Si–O–O–H have been studied by theoretical analysis using molecular orbital (MO) calculation. The theoretical analyses have been carried out using both the semiempirical and ab-initio MO methods, and the ab-initio MO calculation results shows that the transition energy from the excited-singlet state to the ground state is 3.89 eV in a Si–O–O–H cluster. This value is close to that of the photoluminescence peak energy measured in the SiO2 film grown by photo-induced chemical vapor deposition. The strengths of the hydrogen bonds with Si and Si–O have been investigated, and it was found that Si–OH is more stable than Si–H.
Low Dielectric Constant Insulator Formed by Downstream Plasma CVD at Room Temperature Using TMS/O2
Authors: Akiko Nara Akiko Nara , Hitoshi Itoh Hitoshi Itoh
Published: October 2002

We present an insulator with a dielectric constant lower than 3.0, thermal stability up to 500° C and good gap-filling characteristics. This insulator was formed by downstream plasma chemical vapor deposition (CVD) at room temperature using tetra-methylsilane (TMS)/O2 gases. It contained a large amount of water in the as-deposited state. Annealing at 350° C resulted in a decrease in the water content of the insulator, and the insulator did not absorb water after the annealing. The film is constructed from Si–O and S
i–C
H
3 bonds, which produce a low dielectric constant and high thermal stability.
Reduction of Charge Build-Up during Reactive Ion Etching by Using Silicon-On-Insulator Structures
Authors: Kiyoshi Arita Kiyoshi Arita , Masashi Akamatsu Masashi Akamatsu , Tanemasa Asano Tanemasa Asano
Published: October 2002

The charge build-up of silicon-on-insulator (SOI) structures during reactive ion etching has been investigated. The charge build-up was evaluated by using metal/nitride/oxide/silicon (MNOS) capacitors fabricated on SOI. It has been found that the charge build-up can be drastically reduced by using SOI, while the reduction in etching rate is only 3% less than that attained using bulk Si wafers at a relatively high RF power condition. The amount of charge build-up has been found to decrease the thickness of the buried oxide layer increases. A model to explain these phenomena is discussed.
0.8 µm CMOS Process Compatible 60 V–100 m Ω·mm 2 Power MOSFET on Bonded SOI
Authors: Kawaguchi Yusuke , Yamaguchi Yoshihiro , Funaki Hideyuki , Yoshinori Terazaki Yoshinori Terazaki , Akio Nakagawa Akio Nakagawa
Published: October 2002

In the present paper, we propose high voltage lateral power metal-oxide-semiconductor field effect transistor (MOSFET) on silicon on insulator (SOI), using the pure 0.8 µm complementary metal-oxide-semiconductor (CMOS) processes without diffusion self-alignment. The measured specific on-resistance of the developed lateral power n-channel MOSFET (NMOSFET) was 100 m Ω·mm2 and breakdown voltage was 60 V. The fabricated device attains its on-resistance comparable to that of diffusion self-align MOSFET (DMOSFET). It also achieves high side switch operation by a reasonable cost, and can be integrated with Bipolar CMOS (BiCMOS) circuits and micro processing unit (MPU). Compatibility of the developed MOSFET to these low voltage circuits are demonstrated. Furthermore, we show that the MPUs and BiCMOS analog circuit on SOI is suitable for high temperature operation.
Experimental Analysis of Velocity Overshoot Degradation in Sub-0.1 µm Fully-Depleted SOI-MOSFETs
Authors: Ryuji Ohba Ryuji Ohba , Tomohisa Mizuno Tomohisa Mizuno
Published: October 2002

We have experimentally investigated the carrier velocity overshoot and the physical mechanism for the carrier velocity degradation in fully-depleted silicon-on-insulator (SOI) n-channel metal-oxide-semiconductor field-effect-transistors (nMOSFETs). In sub-0.1 µm region, the velocity overshoot greater than 1×107 cm/s is realized at room temperature when the gate drive is low. However, in the higher gate drive region, the carrier velocity is degraded remarkably. The velocity degradation due to the self-heating effects is found to be smaller than the degradation caused by the increase of the vertical field. Moreover, in addition to the above velocity degradation mechanism, the velocity is also degraded by some anomalous scattering at higher gate drive. However, in sub-0.1 µm SOI-nMOSFETs, a high performance can be achieved by using the velocity overshoot effect at a low supply voltage.
Visible and Ultraviolet Photoluminescence from Cu–III–VI2 Chalcopyrite Semiconductors Grown by Metalorganic Vapor Phase Epitaxy
Authors: Chichibu Shigefusa , Shirakata Sho , Isomura Shigehiro , Hisayuki Nakanishi Hisayuki Nakanishi
Published: October 2002

We optimized the overall process of heteroepitaxial growth of wide-gap Cu–III–VI2 chalcopyrite semiconductors by using the low-pressure metalorganic vapor phase epitaxy technique, and obtained very high quality epilayers of them. All end-point compounds, namely CuGaSe2, CuGaS2, CuAlSe2 and CuAlS2, exhibited predominant free and bound excitonic photoluminescence (PL) peaks at low temperature. The color of the emission varied from red to ultraviolet. The room temperature (RT) PL spectra exhibited predominant near-band-edge emission except for that for CuAlSe2. A noticeable excitonic feature was found in the PL spectra for CuAlS2 and CuGaS2 even at RT. Time-resolved and excitation intensity-dependent PL measurements revealed the existence of free-to-bound (FB) and donor-acceptor pair recombination emission centers in some undoped and impurity-doped compounds and alloys. The ionization energy of the recombination centers increased with increasing band gap energy of the matrix, reflecting an increase in the hole effective mass. The potential of heteroepitaxial layers of chalcopyrite semiconductors as new light-emitting materials was demonstrated.
Proposal of a New Self-Limited Growth and Its Application to the Fabrication of Atomically Uniform Quantum Nanostructures
Authors: Wang Xue-Lun , Mutsuo Ogura Mutsuo Ogura , Hirofumi Matsuhata Hirofumi Matsuhata
Published: October 2002

A new self-limited growth technique based on control of surface migration in flow rate modulation epitaxial growth on nonplanar substrates is proposed. The proposed self-limited growth is experimentally confirmed by growing AlGaAs/GaAs quantum wires on V-grooved substrates. Using this new self-limited growth technique, atomically uniform semiconductor quantum nanostructures are expected to be fabricated easily.
High-Power-Density and High-Efficiency Atomic-Planar-Doped AlGaAs/InGaAs Quantum-Well Power High-Electron-Mobility Transistors for 2.4 V Medium-Power Wireless Communication Applications
Authors: Lai Yeong-Lin , Chang Edward Y. , Chang Chun-Yen , Liu T. H. , Wang S. P.
Published: October 2002

A high-power-density and high-efficiency molecular-beam-epitaxy-grown atomic-planar-doped AlGaAs/InGaAs quantum-well power high-electron-mobility transistor (HEMT) was developed for low-voltage medium-power wireless communication applications. The HEMT exhibited a maximum drain current of 420 mA/mm and a maximum transconductance of 275 mS/mm. A two-dimensional electron gas with a high sheet charge density and a high electron mobility in the InGaAs quantum well contributed to the high current density and high transconductance of the HEMT and enhanced the device power performance at low operating voltage. An output power density of 177 mW/mm and a power-added efficiency of 61% were achieved by the 2 mm HEMT at a drain voltage of 2.4 V and a frequency of 900 MHz. At 2.1 V drain voltage and 2.4 GHz frequency, the device demonstrated an output power of 24.4 dBm and a power-added efficiency of 57.4%. An adjacent channel leakage power of -55 dBc was attained for the 1.9-GHz π/4-shifted quadrature phase shift keying modulation when the output power was 22.2 dBm and the drain voltage was 2.4 V.
Improvement of Coupling Efficiency for Passive Alignment of Stacked Multifiber Tapes to a Vertical-Cavity Surface-Emitting Laser Array
Authors: Kobayashi Yasuhiro , Matsuda Kenichi , Chino Toyoji , Takayuki Yoshida Takayuki Yoshida , Kenzo Hatada Kenzo Hatada
Published: October 2002

High-efficiency coupling of stacked multifiber tapes to a vertical-cavity surface-emitting laser (VCSEL) array is demonstrated. Three fiber tapes, each of which includes four multimode fibers, are coupled to a 4 ×3 VCSEL array simply by inserting fibers into guiding holes fabricated on the back side of the substrate. Mirrorlike smooth floors of the holes are formed by electron cyclotron resonance reactive ion beam etching, which results in great improvement of coupling efficiency. The average measured coupling efficiency is 81.3%.
Ultrafast Photoconductive Switches with a 43 nm Gap Fabricated Using an Atomic Force Microscope
Authors: Itatani Taro , Kotaki Yuichi , Nakagawa Tadashi , Matsumoto Kazuhiko , Uchiki Yoshinobu Sugiyama
Published: October 2002

The process of oxidation of titanium using an atomic force microscope was applied for ultrafast metal-semicon- ductor-metal photoconductive switches. The photoconductive gap was formed by oxidation of a 4-nm-thick titanium layer. The photoconductive gap was 43 nm wide and covered with the oxidized titanium. The oxidized titanium is not only a good insulator but also transparent to the excitation beam. A full-width at half maximum(FWHM) response of 770 fs for the transverse component of the electric field was obtained at a bias voltage of 6 V.
Tunneling Spectroscopy of InAs Wetting Layers and Self-Assembled Quantum Dots: Resonant Tunneling through Two- and Zero-Dimensional Electronic States
Authors: Toshi-kazu Suzuki Toshi-kazu Suzuki , Kazumasa Nomoto Kazumasa Nomoto , Kenichi Taira Kenichi Taira , Ichiro Hase Ichiro Hase
Published: October 2002

Using GaAs/AlGaAs/InAs/AlGaAs/GaAs tunneling diodes, we have investigated the resonant tunneling current through InAs wetting layers and self-assembled quantum dots obtained from the Stranski-Krastanow growth mode. For InAs layers both with and without the quantum dots, resonant tunneling current through two-dimensional (2D) electronic states in the wetting layers is observed. From this observation, we can determine the 2D ground state energy. On the other hand, current peaks due to resonant tunneling from three-dimensional (3D) electronic states in the emitter to zero-dimensional (0D) states in the quantum dots are observed only for the case of an InAs layer with the quantum dots.
Scanning Capacitance Microscopy as a Characterization Tool for Semiconductor Devices
Authors: Yamamoto Takuma , Suzuki Yoshihiko , Miyashita Masayuki , Hiroyuki Sugimura Hiroyuki Sugimura , Nobuyuki Nakagiri Nobuyuki Nakagiri
Published: October 2002

Differences in dopant types and dopant concentrations in silicon were non-destructively imaged using a scanning capacitance microscope (SCM). Contrasts between regions with different dopant types, which could not be observed by atomic force microscope (AFM), were clearly observed. The contrasts visible in the SCM images taken at various dc bias voltages changed according to the dc bias applied to the sample with the ac modulation voltage. The dc bias dependence of the dC/dV signal (dC/dV-V) was also measured at three different locations selected on the SCM image.
Reversal of Zeeman Splitting in InGaAs/InP Quantum Wires in High Magnetic Field
Authors: Hammersberg Johan , Notomi Masaya , Weman Helge , Potemski Marek , Tamamura Toshiaki , Okamoto Minoru , Sugiura Hideo
Published: October 2002

We report interband circularly polarized magneto-photoluminescence results for In0.53Ga0.47As quantum wires of various widths in magnetic fields up to 28 T. The experimental results reveal a highly wire width dependent Zeeman splitting compared to the quantum well reference and even a reversal of the Zeeman split transitions arising from the lowest conduction and valence states in the quantum wires. The total g-factor, g=g
e+g
v, is therefore highly wire width dependent.
A Novel Electron Wave Interference Device Using Multiatomic Steps on Vicinal GaAs Surfaces Grown by Metalorganic Vapor Phase Epitaxy: Investigation of Transport Properties
Authors: Akabori Masashi , Motohisa Junichi , Irisawa Tomoki , Hara Shinjiroh , Jun-ya Ishizaki Jun-ya Ishizaki , Takashi Fukui Takashi Fukui
Published: October 2002

We have studied the transport properties of novel lateral surface superlattice electron wave interference devices in which multiatomic steps are utilized to introduce periodic potentials into two dimensional electron systems. The device structure was fabricated by metalorganic vapor phase epitaxy (MOVPE) on vicinal GaAs surfaces, and spontaneously formed multiatomic steps were periodically embedded at the heterojunction of n-AlGaAs/GaAs. Oscillations of the transconductance as a function of gate voltage were found in three different devices. Our simple analysis suggests that the oscillations found in two devices result from the periodic potentials induced by the multiatomic steps and coherent electron wave interference, whereas those in the other one arise from random interference. Our results imply the effect of height and randomness in the periodic potential on the characteristics of electron wave interference devices.
Influence of Depth Position of End-of-Range Defects on Current-Voltage and Noise Characteristics of Shallow (p+/n) Junctions
Authors: Alquier Daniel , Van Haaren Bart , Bergaud Christian , Plana Robert , Graffeuil Jacques , Martinez Augustin
Published: October 2002

The goal of this work is to study the relationship that exists between a population of end of range (EOR) defects, measured by TEM, and electrical properties of the Ge preamorphized ( p+/n) junctions. In this paper, we report current-voltage (I-V) and low frequency (L-F) noise measurements, performed on crystalline and Ge preamorphized diodes, as a function of temperature. The I-V measurements reveal the conduction process which is dominant in the shallow ( p+/n) junctions, while L-F noise characteristics confirm the presence of generation-recombination centers in direct relation to the presence of EOR defects in the n region. Moreover, temperature-L-F noise measurements have shown a drawback of this shallow ( p+/n) junction formation procedure, independent of the preamorphization step. Nevertheless, high-quality ( p+/n) junctions can be obtained by low-energy boron implantation into germanium preamorphized Si substrates using rapid thermal annealing for dopant activation through the judicious choice of Ge implantation energy.
Fast Electromigration-lifetime Prediction of Al-based Layered Metallization using the Similarity of Resistance Increase Curve
Authors: Kondo Seiichi , Deguchi Osamu , Kenji Hinode Kenji Hinode
Published: October 2002

Electromigration characteristics are analyzed using the resistance increase curves of ten kinds of Al-based layered metallizations. It was found that the shape of the resistance curve is basically determined by the layered structure and its material, and that the resistance curve of each layered metallization tends to show a similar shape independent of current density. In particular the step, which appears at the specified amount of the resistance curve due to the difference in electromigration resistance of each layer, is a good index to understanding the degree of void growth in the metallization regardless of current density. We show application of the similarity of the resistance curve to a new method of fast electromigration-lifetime prediction. It can reduce the test time to less than one hundredth that of the conventional method which predicts the lifetime based on the Black's equation.
Theoretical Study of Surface Acoustic Wave Propagation on KNbO3/MgO/GaAs Layered Structures
Authors: Wen-Ching Shih Wen-Ching Shih , Mu-Shiang Wu Mu-Shiang Wu
Published: October 2002

The propagation characteristics of surface acoustic waves (SAW) in KNbO3/MgO/GaAs structures were investigated theoretically. Phase velocities (v
p) increase for all the different layered structures when the h
K value of the MgO buffer layer increases from 0 to 0.25 for a specified thickness of the KNbO3 film. The value of the coupling coefficient (K
2) can be as high as 13%. The KNbO3(110)[001]/MgO/GaAs layered structure with the interdigital transducer (IDT) located on top of the KNbO3 film is a better choice for device fabrication if we select a coupling coefficient of 1% as a reference for comparison. The results could be beneficial for combining optical devices, semiconductor devices and SAW devices on the same GaAs substrate.
Characterization and Removal of Trace Heavy Metal Contamination on Si-Surface Resulted from CHF3/C2F6 Reactive Ion Etching
Authors: Lee Chun Su , Kang Seung Youl , Woo Seong Ihl , Jong Tae Baek Jong Tae Baek , Hyung Joun Yoo Hyung Joun Yoo
Published: October 2002

The characteristics of removal of trace heavy metal contamination on the silicon surface resulted from CHF3/ C2F6 reactive ion etching (RIE) was studied using total reflection X-ray fluorescence spectroscopy (TRXRF). In order to investigate the depth profile of metallic contaminants near the surface, TRXRF measurements containing glancing angle scans were performed after slightly etching of silicon surface by repeating the cleaning procedures that diluted HF (DHF) removed the oxide grown by the mixture of H2SO4 and H2O2 (SPM) or O2 plasma ashing treatment. RIE and O2 plasma ashing processes resulted in metal contamination such as Fe, Ni, Zn, etc. They were present as both of plate-type and bulk-type, and the large part of plate-type contamination was removed easily. Especially, Fe resulted from RIE was the most abundant contaminant and its concentration was ∼1011 atoms/ cm2. Fe was mainly distributed within ∼2 nm from silicon surface and could be effectively reduced below ∼2×1010 atoms/ cm2 by etching of ∼2.5 nm depth of the silicon substrate.
Light Behavior Analysis of Twisted Nematic Liquid Crystal Display
Authors: Yoshida Hidefumi , Kelly Jack R.
Published: October 2002

We investigated the light behavior in a twisted nematic (TN) cell by plotting the polarization and liquid crystal director on a Poincaré sphere. We calculated the polarization using Berreman's 4×4 matrix method. We have clarified (1) the polarization of light propagating in a liquid crystal layer for oblique viewing in upper, lower, right, and left azimuth, (2) the reason for each oscillation and peak of transmittance–voltage characteristics at oblique viewing angles, (3) the reason for the difference between the viewing angle characteristics of e-mode and o-mode TN-LCDs, and the reason why e-mode and o-mode TN-LCDs have the same characteristic in some azimuth, (4) the reason why normally black mode does not have symmetrical viewing angle characteristic.
DC Conductivity in Barium Hexaferrites Doped with Bismuth Oxide
Authors: Pal M. , Brahma P. , Chakraborty B. R. , D. Chakravorty D. Chakravorty
Published: October 2002

Barium hexaferrites of compositions BaO·(6- x)Fe2O3· xBi2O3 with 0 \leqslantx \leqslant0.4 have been synthesized by the ceramic calcination route. The bismuth substituted hexaferrites exhibit dc electrical conductivities more than two orders of magnitude higher than the pure ones. This is believed to arise due to an increase in the concentration of Fe2+ ions as a result of the presence of Bi5+ ions in these compounds. The dc conductivity at temperatures higher than 250 K can be explained on the basis of a non-adiabatic hopping model of small polarons, the variable valence iron ions forming the polaronic sites. At temperatures lower than 220 K a variable range hopping mechanism appears to control the conductivity.
A High-Resolution X-ray Photoelectron Spectroscopy Study of Carbon-Nitrogen Impurity in Chemical Bath Deposited CdS Thin Films
Authors: Wirde Angela Kylner
Published: October 2002

By means of X-ray Photoelectron Spectroscopy (XPS) we show the existence of a carbon-nitrogen (CN) impurity in chemical bath deposited (CBD) CdS thin films grown on Cu(In,Ga)Se2. The very broad nitrogen N(1s) feature ( ca. 3 eV) indicated a high degree of disorder around the carbon-nitrogen bond in as-deposited films. By vacuum-annealing the disorder decreased. This interpretation was supported by Infrared Spectroscopy (FTIR). At the same time as the CdS growth started the CN incorporation began and it continued throughout the deposition. The CN impurity is fairly water-soluble and effectively reduced by water treatments at 60° C. Cadmium cyanamide (CdNCN) has been proposed as a possible impurity, but our XPS analysis (N/C-ratio etc.) could not confirm this compound. Other decomposition products of thiourea ( e.g. Cd(SCN)2) were considered. The CBD-CdS film investigated here results in high-efficiency Cu(In,Ga)Se2/CdS thin film solar cells. However, if the presence of the CN impurity is responsible for the enhanced cell efficiency remains to be investigated.
Simulation of Switching Properties of Ferroelectrics on the Basis of Dipole Lattice Model
Authors: Tura Vasile , Ricinschi Dan , Mitoseriu Liliana , Harnagea Catalin , Ando Shizutoshi , Tsukamoto Takeyo , Okuyama Masanori
Published: October 2002

A discrete lattice model developed by Ishibashi is used to explain the field, temperature and grain size dependence of the switching responses of ferroelectrics. Partial switching processes have been simulated using both pulse frequency modulation (PFM) and pulse width modulation (PWM). A new interpretation of the differences between the switching and non-switching responses of the ferroelectric has been obtained on the basis of analyzing the temporal dependence of dipoles' orientation, as described by the proposed model.
Weak Antilocalization in Si δ-Doped InxGa1-xAs Systems
Authors: Takagaki Yukihiko , Hey Rudolf , Däweritz Lutz , Ploog Klaus , Seigo Tarucha Seigo Tarucha
Published: October 2002

We have investigated the transport properties of a quasi-two-dimensional electron gas in Si δ-doped In

x

Ga1-
x

As/GaAs (001) systems with x=0.2 and 0.3 at T=0.3–3 K. A large electron density of 8.4×1016 m-2 is obtained for the doping density 1017 m-2. We have evaluated the phase breaking time and the spin-orbit scattering time by means of the weak antilocalization effect. The two-dimensional electron-electron interaction in disordered systems is found to be responsible for the dephasing.
Fabrication and Characterization of IrO2-Based Microsensors for Fast Detection of Carbon Dioxide
Authors: Jaw-Chyng Lue Jaw-Chyng Lue , Shuchi Chao Shuchi Chao
Published: October 2002

A pair of closely spaced IrO2 electrodes covered by a polymer film is employed as a new solid-state microsensor for CO2 gas at 1 atm and room temperature. Its function is based on IrO2 sensitivity to the pH-lowering effect produced by CO2 equilibration in the polymer film. This sensitivity is made “asymmetric” by leaving one IrO2/polymer “masked” to CO2 gas exposure. The potential difference is measured and found to be reversible and reproducible for the concentration determination of CO2 between ∼0.1–100% CO2 in N2. Since the microsensor shows fast response, it can also be employed in transient flow-injection experiments for the volumetric analysis of CO2. When calibrated carefully and used with care, the new microsensor based on IrO2 is capable of measuring either the concentration or volume of CO2 with high precision and negligible baseline drift.
Characterization of Oxygen and Carbon in Undoped AlGaAs Grown by Organometallic Vapor-Phase Epitaxy
Authors: Kakinuma Hiroaki , Mikio Mohri Mikio Mohri , Masahiro Akiyama Masahiro Akiyama
Published: October 2002

We have systematically characterized oxygen (O) and carbon (C) impurities in undoped gallium aluminum arsenide ( Al

x

Ga1-
x

As) epitaxial layers grown by organometallic vapor-phase epitaxy (OMVPE). The concentrations of O and C impurities are evaluated by secondary-ion mass spectroscopy. For x≤0.63 the increase rate of O concentration, [O], with x is nearly proportional to the flow rate of trimethylaluminum (TMA), indicating that the oxygen is contained in the TMA molecules. In contrast, [O] and [C] increase superlinearly with x for x≥0.83, and particularly, [O] exceeds 1018 cm-3. The vibration mode of Al–O bonds is observed at 900–1050 cm-1 for the x=0.83 sample using Fourier-transformation infrared measurements. The superlinear increase of [O] with x is attributed to the increased adsorption of residual O2 or H2O molecules. The mechanism of the superlinear increase is discussed in terms of statistic consideration of the –Al– arrangement on the Al

x

Ga1-
x

As surface. Hall measurements show that the hole concentration markedly decreases for x>0.63 and the Al

x

Ga1-
x

As layer becomes semi-insulating, which was attributed to hole compensation by the O-related deep hole traps. The hole mobility also decreases in the same x range.
Mechanical Properties of (Ti1-xAlx)N0.3 Films Prepared by the Dynamic Ion Mixing Method
Authors: Nakamura Isao , Kamiya Makoto , Ichiro Takano Ichiro Takano , Yoshio Sawada Yoshio Sawada
Published: October 2002

Ti1-
x

Al

x

N films were prepared using a dynamic ion mixing apparatus with two electron beam evaporation sources. The Ti and Al contents of the films were changed by independent control of the evaporation rates of the two sources at a constant N concentration of 30 at%. The chemical shifts of the films determined by X-ray photoelectron spectroscopy (XPS) were smaller than those of the standard TiN and AlN, because one N atom combined with a Ti and an Al atom. The hardness and wear resistance of the Ti1-
x

Al

x

N films were determined, and it was found that an increase in the Al content of the films resulted in a decrease in the hardness and the wear resistance. The hardness and wear resistance changed drastically with change in x from 0.5 to 0.64 despite no such changes of XPS and X-ray diffraction (XRD). It was obvious from SEM images that the film with x=0.5 had a results of denser cross-sectional structure and a smoother surface than the film with x=0.64. From the results of mechanical tests, the optimum composition for a film having excellent mechanical properties was concluded to be (Ti0.5Al0.5)N0.3.
Fabrication of LiNbO3 Microfiber Core/Clad Structure by Liquid Phase Epitaxy
Authors: Kawaguchi Tatsuo , Kitayama Hiroshi , Fukuda Minoru Imaeda
Published: October 2002

Fabrication of a LiNbO3 microfiber core/clad structure consisting of a Nd-doped core fiber grown using the micro-pulling-down method and a Mg-doped cladding layer formed using liquid phase epitaxy is discussed. Etching experiments revealed an inverted ferroelectric domain structure of the cladding layer grown on the core fiber surface oriented toward the +z direction.
Spatial Effects of Laser Beam Propagation and Photoionization in a Multilevel Photoionization System
Authors: Keiji Nomaru Keiji Nomaru , Yasukazu Izawa Yasukazu Izawa
Published: October 2002

Spatial near-resonant effects on laser beam propagation in an atomic laser isotope separation system have been studied by 2D simulation. It was found that the initial amplitude of nonuniformity grows up during the propagation, which degrades the photoionization rate of the target atom. The spatial effects become large for the longer incident laser pulse.
Precise Evaluation of Pattern Distortion with Variation of the Impurity Concentration and Conductivity of Silicon Films
Authors: Ogino Satoshi , Fujiwara Nobuo , Takahiro Maruyama Takahiro Maruyama , Masahiro Yoneda Masahiro Yoneda
Published: October 2002

Many types of silicon film are used as materials for the gate electrodes of ultra large scale integration (ULSI) devices. The influence of varying the type of silicon film on local side etch depth and etch rate is investigated using an ECR plasma etching system. Resistivity of silicon films is varied using various impurity concentrations and annealing temperatures. The etch rate of silicon film is confirmed to increase as resistivity decreases in the case of phosphorus doped film. However, the etch rate is constant or decreases to a small extent in the case of boron doped silicon film. In contrast, it is found that the dependence of local side etch depth on resistivity is different to the dependence of etch rate on resistivity. The local side etch depth decreases in the case of phosphorus doped silicon and is almost constant in the case of boron doped silicon as the resistivity decreases. Thus it is found that local side etch depth does not always increase as resistivity of silicon film decreases. The depth of local side etch is influenced by the vertical etch rate, because the ratio of the just etching time to the overetching time is fixed. It is found that the local side etch rate is almost constant in this experiment. Therefore, it is concluded that the difference in local side etch depth is mostly caused by the difference in vertical etch rate.
Ab initio Molecular Orbital Study of Water Absorption and Hydrolysis of Chemical Vapor Deposited SiOF Films II
Authors: Nakasaki Yasushi , Miyajima Hideshi , Hayasaka Ryota Katsumata
Published: October 2002

In part 1, we reported the mechanism of water absorption and hydrolysis of SiOF films theoretically using the ab initio molecular orbital (MO) method with small SiF

n

(OH)4-
n

(n=0–3) tetrahedral model clusters. It was revealed that the multiple F-substituted Si atoms had a higher reactivity against both OH- and H2O than Si atoms with one or no Si–F bonding. Also, defect sites such as non bridging oxygens (NBOs) and free spaces around Si–F bonding were proved to promote the hydrolysis and successive water adsorption. The structure required to initiate the hydrolysis reaction was the multiple F-substituted Si, in particular, =SiF2. In part 2, we attempt to show the possibility of suppressing the formation of =SiF2. The results of a Monte Carlo investigation corresponding to such as an F-ion implantation into SiO2 suggested the possibility of achieving higher doping of F with suppression of the formation of SiF

x

by modulating the probability of F substitution into SiO2.