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New Linewidth Measurement System Using Environmental ScanningElectron Microscope Technology
Authors: Yamaguchi Takeshi , Kawata Shintaro , Suzuki Shohei , Tatsuo Sato Tatsuo Sato , Yu Sato Yu Sato
Published: February 2005

A new linewidth measurement system is developed using the environmental scanning electron microscope (ESEM) technology. The system shows good performance for a deep submicron device metrology tool. Here we will describe outlines of the system and some results of linewidth measurement and hole observation.
Simulation of Scanning Electron Microscope Image for Trench Structures
Authors: Kotera Masatoshi , Yamaguchi Satoru , Sachio Umegaki Sachio Umegaki , Hiroshi Suga Hiroshi Suga
Published: February 2005

Scanning electron microscope images for trench structures are simulated by calculating electron trajectories with a Monte Carlo method. Electron trajectories both inside and outside the trench are fully simulated. Using this simulation, the natures of the secondary electron image and the backscattered electron image are quantified. The signal variations are shown as functions of the size of the trench, the primary electron energy, and the beam diameter.
Wedge-Shaped Silicon Emitter Fabricated by New Method
Authors: Hashiguchi Gen , Sakamoto Hikaru , Satoshi Kanazawa Satoshi Kanazawa , Hidenori Mimura Hidenori Mimura
Published: February 2005

We have fabricated a wedge-shaped silicon emitter using a new fabrication method. The method is based on anisotropic etching and local oxidation of silicon (LOCOS), and makes the fabrication of wedge-shaped silicon emitters easy and reproducible without high-resolution lithography.
Spin Wave Stiffness Constants of the Amorphous Fe90-xNixZr10 (x=5, 10) Alloys
Authors: Yu Seong-Cho , Lynn Jeffrey W. , Fish Gordon E.
Published: February 2005

We report here the spin wave stiffness constants of the amorphous Fe90-x
Ni
x
Zr10 (x=5, 10) alloys obtained from the low temperature magnetization curves and the spectroscopic splitting g values. The temperature dependence of the magnetization was measured with a vibrating sample magnetometer and the g values were estimated from the ferromagnetic resonance (FMR) experiments. The magnetization is found to obey the usual law M
s(T)=M
s(0) (1-B
T
3/2-C
T
5/2···) and the softening of the spin wave stiffness constant confirms that these alloys are in the Invar class of materials.
Experimental and Computer Simulated Makyoh Images of Semiconductor Wafers
Authors: Korytár Dus̆san , Hrivnák Milan
Published: February 2005

Makyoh or magic mirror method, used recently as a new rapid non-destructive tool to evaluate surface flatness irregularities, has been studied by means of Monte Carlo simulation. Results on the influence of geometrical parameters of the method upon makyoh image parameters have been obtained. Experimental examples of the method are introduced as well, and in some cases they are compared with the corresponding interferometric images. Thorough analysis has shown the makyoh contrast of growth striations in Sb-doped silicon to be caused by surface unevenness, what could not be stated for the case of circular dark and bright features in a semiinsulating GaAs wafer.
Damage to the Silicon Substrate by Reactive Ion Etching Detected by a Slow Positron Beam
Authors: Wei Long , Yasushi Tabuki Yasushi Tabuki , Shoichiro Tanigawa Shoichiro Tanigawa
Published: February 2005

Defects in reactive ion-etched Si have been investigated by means of a slow positron beam. A thin carbon-containing film (<30 Å) was formed on the Si surface after reactive ion etching (RIE). Vacancy-type defects, which were estimated to distribute over 1200 Å in depth by numerical fitting using the positron trapping model, were observed in the damaged subsurface region of Si. Aside from ion bombardment, ultraviolet radiation is also presumed to affect the formation of vacancies, interstitials in oxide and the formation of vacancies in Si substrate. The ionization-enhanced diffusion (IED) mechanism is expected to promote the diffusion of vacancies and interstitials into Si substrate.
High-Speed Dynamics in InP Based Multiple Quantum Well Lasers
Authors: Fukushima Toru , Nagarajan Radhakrishnan , Masayuki Ishikawa Masayuki Ishikawa , John E. Bowers John E. Bowers
Published: February 2005

In this paper, the problem of low frequency rolloff and limited bandwidth in long wavelength InP based multiple quantum well (MQW) lasers is discussed by investigating the dependence of resonance frequency and the damping factor on the strain, and structural design of the wells and barriers. To explain the small bandwidth, we use a model of the carrier transport effect with two parts of the carrier density, inside and outside of the quantum wells. The dependence of the K factor on the operating temperature is investigated, and the results of this measurement are found to fully support the proposed carrier transport model. The solutions to this carrier transport problem are discussed. Finally, we propose a measurement method of the intrinsic modulation response free from the carrier transport effect.
Liquid Phase Epitaxial Growth of High-Quality GaInAsSb/InAs
Authors: Xiuying Gong , Kan Hirofumi , Yamaguchi Tomuo , Yamada Takahiro , Suzuki Isao , Aoyama Mitsuru , Saito Nobuo , Hayakawa Yasuhiro , Kumagawa Masashi
Published: February 2005

High-quality Ga1-x
In
x
As1-y
Sb
y
/InAs with mirror-smooth surfaces were grown at 650-595°C by means of Liquid Phase Epitaxy (LPE). The compositional and growth temperature dependences of the cutoff wavelength for epilayers were investigated. Van der Pauw measurements, optical microscopy, Fourie Transform IR (FTIR) spectroscopy, Electron Probe Microanalysis (EPMA), Secondary Ion Mass Spectroscopy (SIMS) and Photoluminescence (PL) spectroscopy were used to characterize the quality of epilayers. The results show that the purity of epilayers is considerably improved by doping Gd in the melt. Room-temperature electron mobility up to 30000 cm2/(V·s) with carrier density of 5.7×1015 cm-3 and full width at halfmaximum (FWHM) of the PL spectra as narrow as 12.45 meV, which are the best results so far for this material to our knowledge, have been achieved. The cutoff wavelengths of epilayers are between 3.4 and 5.0 mm at room temperature.
Internal Stress Distribution Estimation in Liquid-Encapsulated Czochralski Grown GaAs Single Crystals Using Measured Temperature on Dummy Crystals
Authors: Nishio Johji , Toshio Yasunaga Toshio Yasunaga , Yuhji Nakata Yuhji Nakata
Published: February 2005

The surface temperature on BN dummy crystals was measured under the same conditions as those for the actual liquid-encapsulated Czochralski (LEC) growth of GaAs single crystal. The solid-liquid interface shapes in the computation models were determined by the striations in the GaAs single crystal. Temperature and stress distributions inside the crystals were analyzed by the finite element method (FEM) using these data as the boundary conditions. By comparing the temperature distribution and the stress distribution, we have concluded that the reason for the high dislocation density in the crystal periphery is different from that in the center region, i.e., a kink in the axial temperature gradient versus the nature of the radial temperature gradient (solid-liquid interface shape is not flat), respectively.
Investigation of Persistent Photoconductivity from Compensated Amorphous Hydrogenated Silicon
Authors: Dao Hua Zhang Dao Hua Zhang
Published: February 2005

The decay of persistent photoconductivity from compensated amorphous hydrogenated silicon obeys a power law time dependence in the first five hours and an exponential dependence thereafter. Photoconductivity and persistent photoconductivity both increase with illumination time and follow a power law dependence on light intensity, σαF
γ, although the values of γ are different. Interesting phenomena were observed from prolonged exposure of 200 mW cm-2. All the results mentioned above can be qualitatively explained by our model previously proposed for n
i
p
i··· multilayers, which involves P-B deep-trap and P-B-H shallow-trap complexes. It is also predicted that the new states introduced by compensation are possibly associated with complexes involving phosphorus, boron and hydrogen.
Study of Point Defects in Bulk ZnSe Grown by Nonstoichiometric Annealing
Authors: Terashima Kazutaka , Tokizaki Eiji , Uedono Akira , Tanigawa Shoichiro
Published: February 2005

Point defects in bulk ZnSe crystals were investigated by using positron annihilation to identify the defect structures that are closely related to anomalous grain growth. It was found that the self-interstitial-type defects were clearly observed in crystals grown by annealing under a selenium atmosphere. This result suggests that the interstitial-type defects strongly enhance atomic migration due to their instability in the crystal and assist in recrystallization by dislocation climb during annealing.
Reactive Ion Etching of Al Alloy Films in a Rotating Magnetic Field
Authors: Tanabe Masafumi , Matsuda Akio , Sunada Takeshi , Hideki Fujimoto Hideki Fujimoto , Toshio Hayashi Toshio Hayashi
Published: February 2005

Excellent etching characteristics of Al-1%Si-0.5%Cu/TiN film were obtained at low pressure of 0.9 Pa using a magnetically enhanced reactive ion etching system with a rotational permanent magnet. A 2-step resist stripping process was also developed in order to avoid after-corrosion and resist residue. Negative and positive flatband voltage (V
fb) shifts of Al/Si3N4/SiO2/Si capacitor were observed using a static magnetic field, and the V
fb distribution is uniformalized using the rotational magnetic field. We simulated the drift motion of secondary electrons in the cathode sheath in order to clarify the origin of the V
fb distribution. The simulation results showed that the E×B drift motion of the electrons caused the nonuniform distribution of electron density on the wafer, and that this nonuniform distribution of the electrons corresponded to the V
fb distribution.
Oxygen Partial Pressure Dependence of the In Situ Growth of Ba1-xKxBiO3 Films by Laser Ablation
Authors: Lin Wen-Tai , Chen Shyi-Ming Pan
Published: February 2005

The in-situ growth of the superconducting Ba1-x
K
x
BiO3 (BKBO) films as a function of oxygen partial pressure and substrate temperature by laser ablation has been studied. The superconducting BKBO films can be grown at a temperature of 410-500°C within two pressure ranges of 15-60 mTorr and 200-400 mTorr, respectively. Oxygen partial pressure was found to be important to control the growth of the superconducting BKBO films. The optimum pressure for growing the superconducting BKBO films is 40 mTorr, under which potassium is readily doped into the BKBO phase by oxygen. In the present study the best film with T
c(onset) of 28 K and T
c(zero) of 25 K is grown at 450°C in 40 mTorr of O2.
Structural Characteristics of 2212-Phase Single Crystal in the Bi-Sr-Ca-Cu-O Superconductor
Authors: Guien Zhou , Lei Shi , Yunlan Huang , Yunbo Jia , Jiang Lu , Genda Gu , Weili Cai , Yaozhong Ruan , Zhang Yuheng Zhang Yuheng
Published: February 2005

A single crystal of Bi-Sr-Ca-Cu-O 2212 superconducting phase has been studied by combining the Laue method with the method of X-ray diffractometry. It is suggested that the single-crystal structure of a superconductor is a modulated structure of a three-dimensional period coexisting with a two-dimensional lattice. In the structure, the Bi-concentrated bands, which form a three-dimensional modulated structure that corresponds to the results observed in high-resolution electron microscopy, do not entirely enter the parent structure lattice, but divide the parent structure into oxygen-deficient pervoskitelike layers. The pervoskitelike layer has a quasi-two-dimensional structure. The element modulation of Sr and Ca appears in the two-dimensional lattice, which is caused by the effect of Bi-concentrated bands. Meanwhile, the superlattice is formed on the ab plane. The three-dimensional structure of periodic modulation is formed by the pervoskitelike layer and Bi-concentrated band as a unit.
Optical Emission during Layered Growth of PrBa2Cu3O7-x/YBa2Cu3O7-x High Tc Superconducting Thin Film by Pulsed Laser Evaporation
Authors: Pramanick Shekhar , Ashok Kumar Ashok Kumar , Jagdish Narayan Jagdish Narayan
Published: February 2005

Emission spectra from PrBa2Cu3O7-x
and YBa2Cu3O7-x
plasma during layered growth of PrBa2Cu3O7-x
/YBa2Cu3O7-x
high T
c superconducting thin films by pulsed laser evaporation are presented here. Intense molecular fluorescence from the PrBCO plasma plume show the marked departure from YBCO spectra, whereas emission from neutral and ionic species such as Cu I, Ba I, Ba II show strong similarities in YBCO and PrBCO plasma, which is evident by similar intensities and linewidths. Plasma transport mechanism and its role in deposition in PLE has been discussed in terms of similarities and differences in PrBCO and YBCO pulsed laser evaporated plasma.
Stable and Large Second Harmonic Generation in Sol-Gel-Processed Poled Silica Waveguides Doped with Organic Azo Dye
Authors: Izawa Kazuyuki , Naomichi Okamoto Naomichi Okamoto , Okihiro Sugihara Okihiro Sugihara
Published: February 2005

Sol-gel-processed silica films doped with organic azo dye, Disperse Red 1 (DR1) in a higher concentration of 21.7 wt%, were prepared at a higher baking temperature with corona poling of higher voltage than in other reports to obtain stable and large second harmonic generation (SHG) and film strength. A large effective SHG coefficient of 75 pm/V was measured for the film of 0.2-µm thickness at a fundamental wavelength of 1064 nm, and the value was unvaried for 700 h with no relaxation. Moreover, a waveguide SHG device of four-layer structure with DR1-doped sol-gel film as a top layer was fabricated for the first time, and Cherenkov-type phase-matched SHG was observed successfully.
Coupling Efficiencies between Laser Diodes and Photo Diodes of InGaAsP/InP LD-PD Devices with Inclined PD Facets Considering PD Absorption
Authors: Hideho Saito Hideho Saito , Yoshio Noguchi Yoshio Noguchi
Published: February 2005

Coupling effiniencies between LDs (laser diodes) and PDs (photo diodes) of InGaAsP/InP LD-PD (laser diode with photo diode) devices with 30-35° inclined PD facets are calculated and compared with experimental results. The calculations are carried out by developing an electric field with the phase difference caused by the inclined PD facet to the sum of the higher order Hermite-Gaussian beams, considering up to the 15-th order mode, and taking into account PD active layer absorption by calculating confinement factors and intensities of Hermite-Gaussian beams spreading and decreasing in PD crystal. The experimental coupling efficiencies of the LD-PD devices with 30-35° inclined PD facets agree with the calculated results, using the PD active layer absorption coefficient for band edge emitting light of 850 cm-1. This absorption coefficient value corresponds to the experiment value derived from the PD length dependence of the PD photocurrent. The calculations can be used for the design of the LD-PD devices with the inclined PD facets.
Erasing Characteristics and Crystallization Process of GeSbTe Phase-Change Optical Disk Media at Very Fast Linear Velocities
Authors: Chiba Reiichi , Yamazaki Hiroki , Yagi Shougo , Fujimori Susumu
Published: February 2005

The erasing characteristics of phase-change optical disk media with a recording layer made of either Ge2Sb2Te5 or Ge19Sb25Te56 alloys were investigated at very high linear velocities ranging from 10 m/s to 60 m/s. We used transmission electron microscope to observe incompletely erased marks, and used computer simulation to treat laser beam heating process in terms of time and temperature. Following results were obtained. (1) The crystallization times, in which the amorphous marks can be erased completely, for Ge19Sb25Te56 and Ge2Sb2Te5 recording films are 55 ns and less than 33 ns respectively. (2) The erasing ratio of Ge19Sb25Te56 disk degrades at high linear velocity (higher than 40 m/s). (3) The erasing ratio degradation is caused by decreasing the number of crystals formed in the marks. (4) When the annealing time τ50 is less than 55 ns, nucleation process becomes bottleneck for crystallization of Ge19Sb25Te56 recording films, and the nucleation time for each grain in the marks is different from one another.
A Simple Method for Measurement of Wavelength Chirping of a High-Peak-Power Laser Diode Array during Pulsed Operation
Authors: Naito Kenta , Nishida Yoshio , Nosaka Taizo , Ishikawa Koji , Ohmi Masato , Sato Tsuyoshi , Yamanaka Masanobu , Masahiro Nakatsuka Masahiro Nakatsuka , Sadao Nakai Sadao Nakai
Published: February 2005

The wavelength chirping of a two-dimensional high-power laser diode array was measured by a newly developed method utilizing an absorption band of Nd:Y3Al5O12 (Nd:YAG). The validity of this method was verified by the time-resolved spectroscopic measurement. It was shown that this method is useful for the quantitative evaluation of the wavelength chirping and other emitting properties of a two-dimensional laser diode array.
Bistable Spatial Light Modulator Using Guest-Host Liquid Crystal and Bi12GeO20 Photoconductive Crystal
Authors: Fujikake Hideo , Kuniharu Takizawa Kuniharu Takizawa , Hiroshi Kikuchi Hiroshi Kikuchi
Published: February 2005

This paper describes a new bistable spatial light modulator consisting of a guest-host type of 90°-twisted nematic liquid crystal layer and a Bi12GeO20 photoconductor. The optical bistability is generated by an internal electro-optic feedback effect based on the nonlinear transmittance property of the guest-host liquid crystal layer and the photoconductive property of the Bi12GeO20 crystal. This device has various optical threshold functions, where the optical threshold level is easily controlled by varying the drive voltage of the device or its frequency. Optical image binarization and optical parallel logic operations based on optical bistability are realized by illuminating the liquid crystal layer with blue light. It has a limiting resolution of 25 lp/mm, and the rise and decay times of the device are approximately 30 ms and 90 ms, respectively.
Two-Mode Frequency Stabilization of an Internal-Mirror 1.523-µm He-Ne Laser
Authors: Huang Tong-Long , Lin Tyson , Shy Jow-Tsong
Published: February 2005

Under a small transverse magnetic field, the output of an internal-mirror 1.523-µm He-Ne laser has two orthogonal linearly polarized modes over a wide range, and it can be easily stabilized within 1 MHz using simple two-mode method.
Photoinduced Surface Potential in Polyimide Langmuir-Blodgett Films
Authors: Mitsumasa Iwamoto Mitsumasa Iwamoto , Atsushi Fukuda Atsushi Fukuda
Published: February 2005

We examined the photoresponse of the surface potential across polyimide (PI) Langmuir-Blodgett (LB) films deposited on base-Au electrodes, and then analyzed the surface potential change initiated with photoirradiation by assuming a model based on the three-step process of photoconductivity in polymers. In the model, photogeneration of carriers is of the Onsager type, where a space charge field formed at the PI/base-Au electrode interface makes a significant contribution to the photogeneration, and the succeeding carrier transport does not suffer from bimolecular recombination.
Polarization Analysis of a Black and White Supertwisted Nematic Liquid Crystal Display with Two Laminated Birefringent Films of Different Optical Axes
Authors: Hirakata Jun-ichi , Kando Yosiharu Nagae
Published: February 2005

Film supertwisted nematic liquid crystal displays (F-STN-LCDs) with a single birefringent plastic film can be used for monochromatic black-and-white (B/W) LCDs, but their contrast ratio is inferior to that of Double layered (D-)STN-LCDs. By measuring the wavelength dependence of the ellipticity and azimuth in STN-LCDs, the F-STN cell conditions which increase the contrast ratio are obtained. The incident linearly polarized light needs to pass through the STN-LCDs without changing the state of its polarized light in all wavelength regions. Accordingly an optical compensating layer which has the same wavelength dependence for the ellipticity and azimuth as the driving STN cell, must be positioned between the polarizer and the driving STN cell. By laminating two birefringent films with different optical axes, the optical activity caused by the liquid crystal's twist structure is canceled, and the contrast ratio of the F-STN-LCDs increases from 10:1 to 20:1.
Physical Vapor Transport Process in Closed Tubes
Authors: Yumoto Hisami , Watanabe Tsuneo , Kaneko Tsutomu , Ariyama Takashi
Published: February 2005

In some closed-tube systems, the growth rates (R) depend on the temperature of the growth site (T
c), but rarely on the temperature of the vapor source site (T
v). While this observation cannot be explained by a diffusion model, we give our interpretation in a heat transport theory. In general, R is proportional to both supersaturation σ and equilibrium vapor pressure P
0(T
c) at the growth site. Both experimental and theoretical results show that σ in the closed tubes is proportional to the temperature gradient, but not to the differenee of the vapor pressure: P
0(T
v)-P
0(T
c). This shows that σ is controlled by the flux of transported heat. However, as the variation of σ is smaller than that of P
0(T
c), the growth rate is highly dependent on T
c or P
0 (T
c).
Internal Photoemission and X-Ray Photoelectron Spectroscopic Studies of Sulfur-Passivated GaAs
Authors: Kenji Sato Kenji Sato , Hideaki Ikoma Hideaki Ikoma
Published: February 2005

Internal photoemission and X-ray photoelectron spectroscopic (XPS) measurements were performed to investigate the effect of sulfur passivation on the GaAs surface and the degradation of the GaAs surface exposed to air ambient after the passivation. The reverse bias dependence of the Schottky barrier height was very small in the as-sulfur-treated sample and was mainly explained by the image force lowering effect. However, it increased as this sample was exposed to air, indicating an increase in the interface state density. The XPS studies showed that both the Ga and As oxides were hardly observed in the sulfur-passivated samples. This indicates that sulfur passivation strongly suppresses oxidation of GaAs. However, a small amount of elemental arsenic was observed with a trace of the As suboxides (such as AsO) after exposure to air and it increased as the exposure time was increased. These results were probably correlated with the increase in the bias dependence of the Schottky barrier height in samples exposed to air after the passivation. Thermal oxidation of GaAs was found to be retarded by sulfur passivation until oxidation time was about 10 min at 300°C. A possible model of suppression of oxidation by sulfur passivation was also discussed.
Aluminum Film Deposition Using an Ultrahigh-Vacuum Sputtering System
Authors: Kiyota Tetsuji , Toyoda Satoru , Kouichi Tamagawa Kouichi Tamagawa , Hiroyuki Yamakawa Hiroyuki Yamakawa
Published: February 2005

Deposition of pure aluminum films on (100)Si and analysis of impurities during the sputtering process were carried out using an ultrahigh-vacuum sputtering system. A large amount of impurities desorbed from the surfaces of vacuum components in the process chamber which were exposed to discharge by rf-excited plasma was measured just after rf discharge, although the process chamber was evacuated to ultimate pressure after bake-out. This discharge desorption occurring concurrently with bake-out was found to be very effective as a means of chamber cleaning. As a result, high-quality aluminum films with impurity levels as low as that of the sputtering target were obtained. Furthermore, the aluminum films grown by rf-dc sputtering showed higher crystallinity than those grown by conventional dc sputtering.
Optical Properties and Growth Process of Thin Copper Films on Glass Substrate Studied by In-Situ Ellipsometry
Authors: Takeshi Kawagoe Takeshi Kawagoe , Tadashi Mizoguchi Tadashi Mizoguchi
Published: February 2005

The complex reflectance ratio, R
p/R
s, and the optical thickness, d
o, of thin films of Cu deposited on Pyrex glass were measured at various substrate temperatures (T
sub) by means of in-situ ellipsometry. It is revealed, from the observed growth curves, that the films are continuous and homogeneous only when the thickness d is larger than a critical thickness d
c, which is about 40 Å at T
sub=20°C, and larger for higher substrate temperatures. The dependence of the optical constant of thick copper films on the substrate temperature was interpreted by the model of surface oxidation and surface roughness.
Theoretical Analysis of Electron Velocity Distribution Functions and Transport Coefficients in HCl in a DC Electric Field
Authors: Naohiko Shimura Naohiko Shimura , Toshiaki Makabe Toshiaki Makabe
Published: February 2005

The electron transport parameters in HCl in a DC electric field have been calculated over a wide range of reduced field strength E/N, 1≤E/N≤2000 Td using the direct numerical method of the Boltzmann equation. The velocity distributions related to each swarm parameter have also been obtained and the structure is discussed.
Low-Frequency Waves in SF6 Positive Columns Diluted with N2 Gas
Authors: Ishikawa Itsuo , Kondo Kenji , Nakatani Yasuo , Suganomata Shinji , Michio MATSUMOTO Michio MATSUMOTO
Published: February 2005

Backward waves with frequencies around 1 kHz were observed in SF6 positive columns which contain N2 gas in concentrations of 10% or more at the total pressures of 0.7 and 1.0 Torr. The wave amplitude decreases as the mixing ratio of N2 gas increases. This decrease results in the depression of the generation of negative ions due to N2 gas.
Mass Spectrometric Observation of Decomposition Products SFx (x=1, 2) in SF6 Discharge at 13.56 MHz
Authors: Nagaseki Kazuya , Ishikawa Itsuo , Nishimura Eiichi , Yukinori Saito Yukinori Saito , Shinji Suganomata Shinji Suganomata
Published: February 2005

The presence of a smaller mass fragment SF2 was indicated from the output signal of a quadrupole mass spectrometer by means of direct sampling from an SF6 discharge space at a pressure of 50 or 100 mTorr. Its intensity was observed to increase with the discharge power according to the degree of fragmentation of SF6.
Spectroscopic System for Measurements of Turbulent Electric Fields Originating from Intense Relativistic Electron Beam-Plasma Interactions
Authors: Yoshikawa Masayuki , Ritoku Ando Ritoku Ando , Masaru Masuzaki Masaru Masuzaki
Published: February 2005

A multichannel spectroscopic system has been developed in order to measure strong Langmuir turbulent electric fields originating from interactions of an intense relativistic electron beam with plasma.
Magnetooptical Kerr Spectrometer for 1.2-5.9 eV Region and its Application to FePt/Pt Multilayers
Authors: Sato Katsuaki , Hongu Hidetoshi , Ikekame Hiroshi , Tosaka Yasuhiro , Watanabe Masato , Takanashi Koki , Fujimori Hiroyasu
Published: February 2005

The apparatus for measurement of magnetooptical spectra using a polarization modulation technique has been improved to extend the short-wavelength limit to about 200 nm in the ultraviolet range. Short-wavelength characteristics of the light source, the focusing system including mirrors and lenses, the monochromator, the polarizer and the analyzer were improved. The techniques of calibration for Kerr rotation and ellipticity were also refined. With the use of the newly designed system, the magnetooptical Kerr rotation and Kerr ellipticity of FePt/Pt multilayers, as well as of FePt alloys of different compositions were evaluated for photon energies between 1.2 and 5.9 eV.
Growth of Single Crystal AlxGa1-xN Films on Si Substrates by Metalorganic Vapor Phase Epitaxy
Authors: Hirosawa Koji , Hiramatsu Kazumasa , Akasaki Nobuhiko Sawaki
Published: February 2005

Al
x
Ga1-x
N(0001) films with flat surfaces in the composition range of x=0.1-0.4 are successfully grown directly on Si(111) using two-flow-channel metalorganic vapor phase epitaxy (MOVPE). Reflection high-energy electron diffraction (RHEED) patterns are spotty for growth temperatures between 1000°C and 1150°C, indicating that the Al
x
Ga1-x
N film is a single crystal. In addition, good control of the AlN mole fraction (0.1 to 0.4) is achieved by changing the gas ratio of the group III gas sources.
Silicon Precipitation Induced by Argon Excimer Laser in Surface Layers of Si3N4
Authors: Ohmukai Masato , Naito Hiroyoshi , Okuda Masahiro , Kurosawa Kou , Sasaki Wataru , Matsushita Tatsuhiko , Tsunawaki Yoshiaki , Nozawa Shigenori , Igarashi Tatsushi
Published: February 2005

The effects of argon excimer laser irradiation on silicon nitride films deposited on GaAs substrates have been investigated. The precipitation of crystalline silicon induced by the irradiation is detected in the surface layer of silicon nitride with X-ray photoelectron and Raman spectroscopy. The silicon precipitation mechanism is basically a photochemical breaking of Si-N bonds. From the dependence of the silicon precipitation on the film thickness, it is shown that temperature above 1300°C is an additional factor necessary for precipitation.
Preparation of Carbon Nanotubes by Arc-Discharge Evaporation
Authors: Iijima Yoshinori Ando
Published: February 2005

Extremely thin graphite filaments with a tubular structure were grown in carbon deposits formed on the negative electrode during generation of fullerenes by dc carbon-arc-discharge evaporation. The filaments and small graphite particles coexist in the central portion of the deposits. Three kinds of morphologies of carbon, namely nanotubes, polyhedra and sheets were observed in transmission electron micrographs. The filaments were formed in He, Ar or CH4 gas environment at a pressure between 20-200 Torr.
Dynamic Method for Measuring the Velocity Variation of Ultrasound in Piezoelectric Ceramics with Stress
Authors: Yasuo Cho Yasuo Cho , Fumihiko Matsuno Fumihiko Matsuno
Published: February 2005

The development and application of a new dynamic method for measuring velocity variation of piezoelectric materials, especially of lead zirconate titanate (PZT) ceramics, with step and alternating stress are presented. This method enable us to separate the velocity variation due to the nonlinear effect from that due to temperature change, to obtain the adiabatic nonlinear coefficients, to fix the sign of the nonlinear coefficient, and to determine the coefficient of each order of velocity variation as a function of the applied stress.
Deep Level Transient Spectroscopy Characterization of Defects Introduced in n-GaAs after Alpha Irradiation at 15 K
Authors: S. A. Goodman S. A. Goodman , F. D. Auret F. D. Auret
Published: February 2005

Using conventional deep level transient spectroscopy (DLTS), we have characterised the defects introduced in OMVPE n-GaAs at 15 K by 5.4 MeV alpha particle irradiation from an americium 241 radio-nuclide. After this low temperature irradiation two new defects not yet reported for alpha irradiated GaAs before, Eα7 and Eα9, were detected 0.07 eV and 0.19 eV below the conduction band, respectively. The introduction rates of Eα7 and Eα9 are calculated to be 41 cm-1 and 187 cm-1 respectively. It was observed that both defects obeyed first order annealing kinetics, with Eα9 being removed at 225 K and Eα7 at 245 K corresponding to the well known stage I annealing region. The annealing rate of Eα7 corresponds to an activation energy of 0.86 eV, with a pre-exponential factor of 1.0×1015 s-1; and the removal of Eα9 has an activation energy of 0.88 eV and a pre-exponential factor of 1.7×1017 s-1.
Carbon δ-Doping in GaAs by Metal-Organic Molecular Beam Epitaxy
Authors: Yamada Takumi , Shirahama Masanori , Tokumitsu Eisuke , Makoto Konagai Makoto Konagai , Kiyoshi Takahashi Kiyoshi Takahashi
Published: February 2005

δ-Doping of carbon into GaAs by metal-organic molecular beam epitaxy (MOMBE) has been studied in detail using trimethylgallium (TMG), Ga and As4. TMG was adsorbed in the wide range of temperatures from 20°C to 550°C during growth interruption. It is shown that Ga deposition after TMG adsorption is effective for obtaining a high peak hole concentration. This is in contrast to the case with As evaporation, which drastically reduces the peak carrier concentration. The dependence of peak hole concentration on the TMG adsorption temperature shows a specific feature. The highest peak hole concentration is 4×1019 cm-3 for a TMG adsorption temperature of 20°C.
Initial Growth of Epitaxial (001)SrTiO3 Film Deposited In Situ on (001)YBaCuO/(100)MgO
Authors: Ohara Tomoyuki , Ken Sakuta Ken Sakuta , Takeshi Kobayashi Takeshi Kobayashi
Published: February 2005

The surface morphology of both YBa2Cu3O
y
(YBCO) thin film on a MgO substrate and SrTiO3 (STO) thin film on a YBCO film was observed using scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) methods. These films were deposited by the ArF excimer laser deposition method. The c-axis-oriented YBCO film of 100 nm thickness grew spirally on a (100)MgO substrate in an island growth mode. The heteroepitaxial STO thin film deposited in situ on the YBCO film grew as if they had filled in the steps of the spiral structure of the YBCO thin film at the stage of initial growth, i.e., STO grew in a kink growth mode. The LEED pattern indicates that the film surface coverd with STO was stable against ordinary air, although the thickness of STO thin film was about 1 nm.
Conversion from GaAs to GaAsP by Annealing a GaAs Layer on GaP in Ga-As-P Solution
Authors: Sukegawa Tokuzo , Udono Haruhiko , Kimura Masakazu , Hironobu Katsuno Hironobu Katsuno , Akira Tanaka Akira Tanaka
Published: February 2005

A new liquid phase epitaxial (LPE) technique of preparing alloy layers of a desired composition lattice-mismatched with a substrate has been developed. A GaAs layer was grown on a GaP substrate through step cooling from 800°C to 795°C, followed by contact with Ga-As-P solution at a constant temperature of 795°C. This treatment led to a transformation in the composition of the grown GaAs to GaAsP. Thus a GaAsP layer with the composition of 0.65 GaAs mole fraction, which was not grown directly on GaP, could be prepared on GaP substrates.
Determination of Molecular Inclination in Rubbed Polymer for Liquid Crystal Alignment by Measuring Retardation
Authors: Han Kwan-Young , Peter Vetter Peter Vetter , Tatsuo Uchida Tatsuo Uchida
Published: February 2005

Liquid crystal molecules on a rubbed polymer alignment layer are aligned at some polar angle away from the surface, but the physical reason for this pretilt is not yet clearly understood. In our research, we have developed a new method to determine the tilted direction of the polymer by a precise measurement of the optical retardation using Senarmont ellipsometry. Using this method, we also studied the tilt angle of the polymer molecules near the surface of a side-chain polymer layer as a function of the rubbing strength and compared the pretilt angle of the liquid crystal to the tilted direction of the polymer.
Modification of Silicon Dioxide by Hydrogen and Deuterium Plasmas at Room Temperature
Authors: Iwakuro Tsukasa Kuroda
Published: February 2005

Silicon dioxides exposed to H2 and D2 plasmas have been investigated using X-ray photoelectron spectroscopy and secondary ion mass spectrometry. D2 plasma exposure at the self-bias voltage of 230 V results in reduction of Si on the SiO2 surface, but not in the H2 plasma exposure at the same self-bias voltage. This difference between the D2 and H2 plasma exposures is attributable to the larger momentum transfer effect of the deuterium ions. The hydrogen or deuterium atoms incorporated diffuse through the SiO2 film during the plasma exposure and pile up at the Si-SiO2 interface.
Change in Scanning Tunneling Microscope (STM) Tip Shape during Nanofabrication
Authors: Yokoi Naoki , Ueda Satoshi , Susumu Namba Susumu Namba , Mikio Takai Mikio Takai
Published: February 2005

The influence of voltage pulses upon scanning tunneling microscope (STM) tips during nanofabrication has been studied. The tips were observed by scanning electron microscopy (SEM) before and after application of voltage pulses with various pulse amplitudes, pulse widths and tunneling gap widths, and were found to be damaged by highly concentrated current flowing through the tunneling gap, which resulted in melt and/or evaporation of tips.
Band Offsets in CdZnS/ZnS Strained-Layer Quantum Well and Its Application to UV Laser Diode
Authors: Taguchi Tsunemasa , Onodera Chikara , Yamada Yoichi , Masumoto Yasuaki
Published: February 2005

Conduction- and valence-band offsets have been estimated as a function of well layer thickness in Cd
x
Zn1-x
S/ZnS strained-layer superlattices with various compositions using the model-solid theory. Relatively large values of approximately 180-260 meV in the conduction-band offset can be obtained for x=0.2-0.3. The valence-band offset depends strongly on the well layer thickness, while the conduction-band offset is nearly independent of the well layer thickness up to 200 Å. This strained-layer structure was applied to fabricate ultraviolet (UV) laser diodes with multiple quantum wells. Stimulated emission can be observed either under optical pumping at RT or under pulsed injection at 30 K in the spectral range of 357-390 nm. A spectral narrowing in the emission spectrum with increasing current in the UV injection diode was clearly observed in the vicinity of 375 nm at 30 K.
Novel Phenomenon of the Al-1 wt%Si Contacts on the NF3/Ar Post-Etching-Treated n-Si Substrates
Authors: Cheng Huang Chung , Chen Yeong E , Juang Miin Horng , Yen Po Wen , Lin Larry
Published: February 2005

Post-etching treatment (PET) using an in situ NF3/Ar low-energy plasma was reported to be efficient in removing the residual layer and defects caused by reactive ion etching (RIE) as well as producing a clean surface conventionally believed suitable for electrical contacts. However, the PET process was found to increase the contact resistance between Al-1 wt%Si and n+-Si substrate for the first time. It is attributed to the formation of p-type-like Si epitaxy on the n+-Si substrate and the lower effective surface donor concentration.
Fabrication of YBCO/PBCO/SrTiO3/PBCO/YBCO Layered Structure for Superconductor-Insulator-Superconductor Tunnel-Type Josephson Junction
Authors: Matsubara Gensoh , Eikyu Katsumi , Miyazaki Masayuki , Hiroshi Kimura Hiroshi Kimura , Yoichi Okabe Yoichi Okabe
Published: February 2005

The fabrication process of all-oxide layered structures of YBCO/PBCO/SrTiO3/PBCO/YBCO on MgO(100) substrates for superconductor-insulator-superconductor (SIS) tunnel junctions was investigated by in situ rf magnetron sputtering. Fully c-axis-oriented structure was obtained by varying the sputtering conditions. The optimized structure had a well-defined interface at each boundary between layers. A planar junction was fabricated by the atomic milling technique, and Josephson supercurrent and microwave response were observed. Moreover, a structure resembling an energy gap was found by differential resistance measurement.
Measurement of Magnetostriction Constants in (111)-Oriented Polycrystalline PdCo Alloy and Multilayered Films
Authors: Takahashi Hiroshi , Tsunashima Shigeru , Satoshi Iwata Satoshi Iwata , Susumu Uchiyama Susumu Uchiyama
Published: February 2005

A method for measuring magnetostriction constants λ100 and λ111 was developed for (111)-oriented polycrystalline films. Magnetostriction constants were estimated from the magnetic anisotropy induced by the application of in-plane uniaxial strain. In sputtered Pd100-x
Co
x
alloy films, the estimated magnetostriction constants agree with those of PdCo single-crystal alloys. The magnetostriction constants of Pd/Co multilayered films (MLs), with decreasing bilayer period D, approach those of alloy with the same constitution, while with increasing D, they approach the values for fcc-Co obtained from the extrapolation of the data for the alloy films. These results are explained by the effect of electron hybridization and/or alloy formation at the interface of Pd and Co.
Orientation of Polymer Molecules in Rubbed Alignment Layer and Surface Anchoring of Liquid Crystals
Authors: Lee Eung Sang , Vetter Peter , Tetsuya Miyashita Tetsuya Miyashita , Tatsuo Uchida Tatsuo Uchida
Published: February 2005

In order to better understand liquid crystal alignment on a rubbed polymer surface, the authors investigated the relationship between the orientation of polymer molecules and the surface anchoring strength of liquid crystals on a rubbed surface. Measuring the IR-absorption and the optical retardation, it was found that the polymer molecules were oriented parallel to the rubbing direction. The order of molecular orientation in the polymer and the surface anchoring strength of liquid crystal both increased with the rubbing strength.
Transverse Effects on Antiphase Laser Dynamics
Authors: Kenju Otsuka Kenju Otsuka
Published: February 2005

Transverse effects on antiphase dynamics in a multi-longitudinal-mode solid-state laser are investigated experimentally. We show a three-dimensional self-organization resulting from the cross saturation dynamics in the longitudinal and transverse directions, in which the intensity noise spectrum of partial output within the beam cross-section possesses the antiphase relaxation oscillation components inherent in multi-longitudinal-mode lasers and the noise spectrum changes along transverse direction, while these antiphase components vanish completely for the entire beam. Modulation dynamics in a multi-transverse-mode laser featuring transverse synchronization and clustering is also demonstrated.
Three-Color Whispering-Gallery-Mode Dye Lasers Using Dye-Doped Liquid Spheres
Authors: Hiroshi Taniguchi Hiroshi Taniguchi , Shinji Tanosaki Shinji Tanosaki
Published: February 2005

A multiple laser operation in blue, green and orange spectral regions (3-colors) due to whispering-gallery mode (WGM) using dye-doped liquid spheres, by UV N2 laser pumping, was achieved. A technique of forming liquid spheres with stable droplet-size and fundamental characteristics concerning the energy-transfer effects in dye mixtures are also presented.
Improvement of the Transmission Spectra of Tunable Wavelength-Selective Liquid Crystal Fabry-Perot Interferometer Filters
Authors: Kurokawa Katsuhiko Hirabayashi
Published: February 2005

A reflection-type tunable liquid-crystal Fabry-Perot filter, in which the input light beam passes through a cell twice after reflection by a mirror, is shown to have improved transmission characteristics. Simulation and experimental results show that this is an effective way to decrease the cross talk between neighboring channels, even though there is a slight increase in loss due to the double pass and the mirror. When these filters are applied to wavelength division multiplexing systems with analog-amplitude modulation, they increase the channel capacity to three times the original value.
DC-Bias-Field-Induced Dielectric Relaxation in Antiferroelectric Phase of TFMHPOBC
Authors: Moritake Hiroshi , Masanori Ozaki Masanori Ozaki , Katsumi Yoshino Katsumi Yoshino
Published: February 2005

Dielectric properties in TFMHPOBC (4-(1,1,1-trifluoromethyl-heptyloxycarbonyl) phenyl 4'-octyloxybiphenyl-4-carboxylate) have been investigated as functions of temperature and dc bias field. In the antiferroelectric phase under no bias field, relaxation due to the soft mode and molecular rotation around the short axis are observed. Under dc bias field, a new relaxation is observed in chiral smectic CA (Sm CA
*). The dielectric strength of this relaxation depends on the bias field, while the relaxation frequency is not affected by the dc bias field.
Heteroepitaxial Growth of Layered GaSe Films on GaAs(001) Surfaces
Authors: Abe Hideki , Ueno Keiji , Koichiro Saiki Koichiro Saiki , Atsushi Koma Atsushi Koma
Published: February 2005

Epitaxial films of layered GaSe with (0001) surfaces have been grown on GaAs(001) substrates in spite of the large difference in their crystal symmetry. In situ observation of reflection high-energy electron diffraction has revealed that a number of facets grow on the surface of GaAs(001) under Se irradiation. The existence of those facets is essential to the single-domain growth of a layered GaSe film on a GaAs(001) surface.
Investigations on the Formation of SiO2in Si+-Implanted Al2O3
Authors: Shimizu-Iwayama Tsutomu , Niimi Tetsuji , Nakao Setsuo , Saitoh Kazuo
Published: February 2005

We measured Raman spectra of Si+-implanted Al2O3at room temperature before and after annealing in vacuum. It is found that SiO2is formed even before annealing and the Raman band attributed to the network Si-O-Si symmetric-stretching vibration mode grows with annealing between 300°C and 500°C. It is also found that Al atoms are emitted from the surface of Al2O3with annealing above 900°C. In forming SiO2in the surface layer of Al2O3, implanted Si atoms obtain oxygen atoms from Al2O3by breaking Al-O-Al bonds. We discuss the chemical reactions of implanted Si atoms with Al2O3induced by ion implantation and subsequent thermal annealing.
Etching of InAs in HCl Gas and Selective Removal of InAs Layer on GaAs in Ultrahigh-Vacuum Processing System
Authors: Kadoya Yutaka , Yoshida Takashi , Someya Takao , Akiyama Hidefumi , Noge Hiroshi , Sakaki Hiroyuki
Published: February 2005

The etch rate of InAs in HCl gas is studied for the first time and is found to be far greater than that of GaAs. The complete removal of an InAs layer grown on GaAs was achieved by this etching, resulting in a very flat surface. This is confirmed by the photoluminescence study on a novel GaAs/AlGaAs quantum well (QW), which was prepared by depositing a 50 nm InAs film at the center of the well, and subsequently etching it off before the remainder of the QW was formed. This unique selectivity can be employed to remove an InAs film which is used in the in situ patterning technique of GaAs.
Extrinsic Base Surface Recombination Current in Surface-Passivated InGaP/GaAs Heterojunction Bipolar Transistors
Authors: Ito Hiroshi , Nakajima Osaake , Nagata Koichi , Takashi Makimura Takashi Makimura , Tadao Ishibashi Tadao Ishibashi
Published: February 2005

Recombination currents at the emitter mesa periphery of InGaP/GaAs heterojunction bipolar transistors (HBTs) with and without extrinsic base surface passivation layers are evaluated and compared. The obtained ideality factor for the extrinsic base surface recombination curtent in InGaP/GaAs HBTs with the surface passivation layer is 1.6, which is considerably larger than the near-unity value for the HBTs without the surface passivation layer. This indicates a difference in the surface recombination mechanism between passivated and unpassivated InGaP/GaAs HBTs.
Low-Temperature Preparation and Properties of Spinel-Type Iron Oxide Films by ECR Plasma-Enhanced Metalorganic Chemical Vapor Deposition
Authors: Torii Eiji Fujii
Published: February 2005

Spinel-type iron oxide films (Fe3O4) have been prepared on soda-lime glass substrates by ECR plasma-enhanced Metalorganic Chemical Vapor Deposition (MOCVD) using Iron (III) acetylacetonato complex [Fe(C5H7O2)3] or ferrocene [Fe(C5H5)2] as the source material. The X-ray diffraction pattern, Auger spectrum and conversion electron Mössbauer spectrum indicated that high-crystallinity and carbon-free Fe3O4film was obtained at a low temperature of 150°C using ferrocene as the soruce material. SEM images showed that the film had a smooth surface and a columnar structure. Magnetization curves measured by VSM indicated that the film had no definite magnetic anisotropy.
Piezoelectric Sensing of Particles Produced by Pulsed-Laser Ablation of YBa2Cu3O7-δ
Authors: Okada Tatsuo , Kumuduni Wanniarachchi K. A. , Yoshiki Nakata Yoshiki Nakata , Mitsuo Maeda Mitsuo Maeda
Published: February 2005

A piezoelectric probe was used to monitor particle transport through an ambient gas in pulsed-laser ablation of YBa2Cu3O7-δ. The piezoelectric signals were compared with the results of one-dimensional laser-induced fluorescence observation on the propagation of YO molecules produced in the ablation. It was shown that the piezoelectric probe is a simple and useful means of monitoring particle transport in a pulsed-laser deposition environment.