bluuebunny/crossref_metadata_2025 huggingface dataset:
MOCVD Growth of Bi1.5Zn1.0Nb1.5O7 (BZN) Epitaxial Thin Films and Their Electrical Properties
Authors: Okaura Shingo , Suzuki Muneyasu , Okamoto Shoji , Uchida Hiroshi , Koda Seiichiro , Funakubo Hiroshi
Published: October 2005

Bi1.5Zn1.0Nb1.5O7 (BZN) epitaxial thin films were prepared on (111)Pt∥(001)Al2O3 substrates at 500°C by metal organic chemical vapor deposition (MOCVD). The electrical properties of the as-deposited films were investigated by comparing them with those of the (111)-one-axis-oriented films prepared on (111)Pt/TiO2/SiO2/(100)Si substrates for making a Pt/BZN/Pt capacitor structure. The relative dielectric constant of the epitaxial film was almost the same as that of the one-axis-oriented one, but its changes with frequency dependence and tan
δ were smaller than those of the one-axis-oriented one.
Preparation and Characterization of Ti-Doped LiNbO3 Films Grown by the Sol-Gel Method
Authors: Takahashi Makoto , Yoshiga Tsuyoshi , Kajitani Naofumi , Sato Shoji , Nishiwaki Akira , Wakita Koichi , Yagi Touru , Sahashi Ietaka
Published: October 2005

Crack-free and very smooth Ti-doped LiNbO3 (LN) films were obtained on z-cut LN substrates by the sol-gel method using solutions containing the LN precursor and a large amount of polyvinyl alcohol (PVA). Titanium (Ti) ions were added to the precursor solutions to prepare optical waveguide films on LN wafers using our sol-gel method. The characteristics of the films containing various Ti concentrations were investigated. The refractive indexes of the films prepared from the sol containing 1.5 mol % Ti ions were n
o=2.307 and n
e=2.257. The average transmission loss for the films was about 0.5 dB/cm in the TM mode at a wavelength of 632.8 nm.
Microscopic Stress Analysis of BaTiO3 Using Optical Activity of Its Point Defects
Authors: Yamashita Yasuhisa , Yamamoto Hiroshi , Sakabe Yukio , Pezzotti Giuseppe
Published: October 2005

Microscopic stress analysis of BaTiO3 thin films was performed on the basis of the optical activity of their point defects by means of piezo-spectroscopic (PS) method applied to cathodoluminescence (CL) measurements. Accordingly, the interfacial residual stress that accumulates during manufacturing between a BaTiO3 film and its sapphire substrate could be estimated. Taking advantage of the dependence of the penetration depth of the electron beam in CL measurement on accelerating voltage, CL spectra collected as a function of accelerating voltage could be considered to represent an in-depth profile. In this context, an approximately 2 nm CL spectral shift between the film surface and interface was observed. The accelerating voltage that corresponded to the CL spectrum in the vicinity of the interface was chosen on the basis of the appearance of the sapphire F-band at approximately 330 nm. A PS coefficient was measured using CL spectra from a BaTiO3 single crystal, and a three-dimensional PS coefficient, Π=21.8 nm/GPa, could be retrieved. Because of the biaxial nature of interfacial stress, an averaged biaxial PS coefficient (2/3Π=14.5 nm/GPa) was employed for calculating interfacial stress from the observed spectral shift. This procedure allowed us to measure a maximum tensile stress of 140 MPa near the film/substrate interface in the BaTiO3 film. FEM simulation was also performed, and the results were compared with those of CL measurements.
Mechanism of Capacitance Aging under DC Electric Fields in Multilayer Ceramic Capacitors with X7R Characteristics
Authors: Tsurumi Takaaki , Shono Motohiro , Kakemoto Hirofumi , Wada Satoshi , Saito Kenji , Chazono Hirokazu
Published: October 2005

Capacitance aging under DC electric fields has been studied on multilayer ceramic capacitors (MLCCs) with X7R characteristics. The capacitance change with time was divided into two consecutive stages. The first stage was due to the nonlinear permittivity of dielectrics and it should not be involved in the aging phenomenon. The second stage depended on the MnO content, grain size and firing conditions of the dielectrics. The aging was markedly depressed above the Curie temperature. From the behavior of the second stage, it was concluded that the capacitance aging is caused by the 90° domain switching in BaTiO3 in the core. An equation that represents the aging behavior in the second stage was presented and the mechanism that explains the capacitance aging was proposed. The first stage was due to the nonlinear permittivity and the second stage was due to the domain switching, but the domain switching was also included in the first stage if the domain walls were moved by the first application of a DC field. The change in the aging behavior with the intensity of the DC field could be explained by separating capacitance change into that due to the nonlinear permittivity and that due to the domain switching according to the mechanism proposed in this study. Finally, a methodology for handling the capacitance aging under DC fields was proposed.
Ferroelectric Studies on Sr0.61Ba0.39Nb2O6 Single Crystal Grown by Double-Crucible Stepanov Technique
Authors: Ganesamoorthy S. , Kumaragurubaran S. , Takekawa S. , Nakamura M. , Mohankumar R. , Kitamura K.
Published: October 2005

Sr0.61Ba0.39Nb2O6 crystals grown by a modified double-crucible Stepanov technique have coercive fields independent of thickness. The coercive field is about 250 V/mm as measured from the ferroelectric hysteresis loop. However, the coercive field is found to depend strongly on the ramp rate. Dielectric measurements revealed a diffused phase transition at about 352 K and a Curie constant of about 4.5 ×105 K.
Elasticity Control of Piezoelectric Lead Zirconate Titanate (PZT) Materials Using Negative-Capacitance Circuits
Authors: Imoto Kenji , Nishiura Mitsuhiro , Yamamoto Ken , Date Munehiro , Fukada Eiichi , Tajitsu Yoshiro
Published: October 2005

A piezoelectric material was inserted in an elastic wave vibration transmission system to improve sound insulation. The apparent elasticity of the inserted piezoelectric material was controlled using an electric circuit called a negative-capacitance circuit. We prepared two identical brass bars with a length of 1.5 m and a diameter of 10 mm. The two brass bars were joined with a lead zirconate titanate (PZT) material, and two additional PZT materials were attached to the end of the brass bars. An elastic wave in the ultrasonic frequency range was applied to one end of the bar system and propagated through the bar, the PZT material and the other brass bar. A negative-capacitance circuit was attached to the PZT material. The increase in transmission loss excluding the normally existing loss in the PZT material was measured before and after connecting the negative-capacitance circuit that softens the PZT material. A maximum increase in transmission loss of more than 60% was obtained.
Nonlinear Piezoelectric Coefficients in Compositions near Morphotropic Phase Boundary of PbZrO3-PbTiO3-Pb(Mg1/3Nb2/3)O3 Piezoelectric Ceramics
Authors: Tashiro Shinjiro , Tokunaga Wataru , Ishii Keisuke , Nagata Kunihiro
Published: October 2005

Linear and nonlinear piezoelectric coefficients of second- and third-higher terms in length-extensional vibration were experimentally investigated in the compositions near the morphotropic phase boundary (MPB) of PbZrO3-PbTiO3-Pb(Mg1/3Nb2/3)O3 ternary piezoelectric ceramics. The Zr/Ti ratio showing the maximum value of the piezoelectric constant d
31 disagreed with that showing the maximum value of the electromechanical coefficient k
31 in the transverse vibration. The disagreement increased with Pb(Mg1/3Nb2/3)O3 (PMN) content. The nonlinear piezoelectric coefficients of the second- and third-higher terms showed their minimum values at the Zr/Ti ratios showing the maximum values of d
31. Hence, the Zr/Ti ratio showing the maximum value of d
31 was regarded as the MPB composition. The nonlinear coefficients of the second- and third-higher terms on the MPB compositions showed different dependences on PMN content. The nonlinear coefficient of the second-higher term showed a grain size dependence in its change, and that of the third-higher term showed a mechanical quality factor dependence in its change. The difference in the dependences was discussed from the viewpoint of the difference in the occurrence mechanism of nonlinear phenomena dominating the two nonlinear coefficients.
Dielectric and Piezoelectric Properties of Pb[(In1/2Nb1/2)0.24(Mg1/3Nb2/3)0.42Ti0.34]O3 Single Crystals
Authors: Hosono Yasuharu , Yamashita Yohachi , Hirayama Kentaro , Ichinose Noboru
Published: October 2005

The dielectric and piezoelectric properties of the 0.24Pb(In1/2Nb1/2)O3-0.42Pb(Mg1/3Nb2/3)-0.34PbTiO3 (PIMNT 24/42/34) ternary system was investigated in order to improve thermal stability and voltage-proof nature of electrical properties. A PIMNT 24/42/34 single crystal 25 mm in diameter and 30 mm in length was successfully grown by the solution Bridgman method using PbO-B2O3 flux; the highest temperature was 1250°C and the growth rate was 0.4 mm/h. The Curie temperature, T
c, and the phase transition temperature between rhombohedral and tetragonal phases, T
rt, were 184°C and 89°C, respectively. The dielectric constant after poling, ε
33

T
/ε
0 = 4,900, electromechanical coupling factors for the sliver mode, k
33'=80.3%, piezoelectric constant, d
33=2,200 pC/N, and coercive field, E
c=6.8 kV/cm, were confirmed. Moreover, k
33' was very stable until about 80°C because of the high T
rt.
Dielectric and Piezoelectric Properties of Low-Temperature-Sintering Pb(Mg1/2W1/2)O3-Pb(Ni1/3Nb2/3)O3-Pb(Zr,Ti)O3 Ceramics for Multilayer Piezoelectric Actuator
Authors: Yoo Juhyun , Yoo Kyungjin , Lee Hyunseok , Lee Sangho , Chung Kwanghyun , Lee Hyeunggyu , Kang Hyungwon
Published: October 2005

In this study, in order to develop low-temperature-sintering ceramics for a multilayer piezoelectric actuator, Pb(Mg1/2W1/2)O3-Pb(Ni1/3Nb2/3)O3-Pb(Zr,Ti)O3 (PMW-PNN-PZT) ceramics were fabricated using Li2CO3 and CaCO3 as sintering aids and their dielectric and piezoelectric properties were investigated in relation to the amount of Bi substitution. Piezoelectric actuators require both a high piezoelectric constant (d
33) and a high electromechanical coupling factor (kp). Accordingly, in this study, Bi was substituted at the Pb site of basic composition PMW-PNN-PZT ceramics for the enhancement of kp and d
33.
With increasing Bi substitution, density gradually increased. At the sintering temperature of 900°C, the electromechanical coupling factor (kp) and piezoelectric constant (d
33) of PMW-PNN-PZT composition ceramics with 1.0 mol % Bi substitution as well as 0.2 wt % Li2CO3 and 0.25 wt % CaCO3 showed the optimal value of 0.618 and 473 pC/N, respectively, for multilayer piezoelectric actuator application.
Piezoelectric Properties of SrBi2Nb2O9 Textured Ceramics
Authors: Ogawa Hirozumi , Sawada Takuya , Kimura Masahiko , Shiratsuyu Kosuke , Wada Nobuyuki , Ando Akira , Tamura Hiroshi , Sakabe Yukio
Published: October 2005

The textured ceramics of the bismuth layer structured ferroelectrics SrBi2Nb2O9 (SBN)-type compound were fabricated by the templated grain growth (TGG) method, and their characteristics and piezoelectric properties were studied. Platelike particles with a large shape anisotropy, which were needed as template particles in the TGG process, were obtained for the composition with 10% Nd substitution on the Sr site of SBN. Highly (00ℓ) textured Sr0.9Nd0.1Bi2Nb2O9 (SNBN) ceramics were successfully obtained using the TGG process with platelike particles, and the orientation degree of the textured ceramics was 96%. The electromechanical coupling factor of the 96% orientation degree textured ceramics in the thickness shear vibration mode was three times as large as that for the randomly oriented ceramics. The temperature coefficient of the resonant frequency (TCF) of the textured ceramics was +20.9 ppm/°C, whose absolute value was two-thirds of that of the randomly oriented ceramics. The resonant frequency of the textured ceramics increased with temperature, while the resonant frequency of the randomly oriented ceramics decreased with increasing temperature. This result indicated the possibility of obtaining an excellent TCF by the optimization of grain orientation. Therefore, textured ceramics with orientation degrees from 54% to 96% were prepared using template particles of different average diameters, and an excellent TCF of -0.4 ppm/°C was obtained for the specimen with an orientation degree of 76%.
Raman Scattering Study of Piezoelectric (Na0.5K0.5)NbO3-LiNbO3 Ceramics
Authors: Kakimoto Ken-ichi , Akao Koichiro , Guo Yiping , Ohsato Hitoshi
Published: October 2005

A Raman scattering study of (Na0.5K0.5)NbO3 (NKN)-LiNbO3 (LN) lead-free piezoceramics has been carried out on nominal compositions of (1-x)NKN-xLN (0 ≤x ≤0.70). The Raman spectra demonstrated a variety of changes with x, mainly classified as lattice translations involving motions of the alkaline cations and internal modes of NbO6 octahedra. At 0.05 ≤x ≤0.07, the broadening of the scattering peaks corresponding to the internal modes of the NbO6 octahedra occurred preferably, which is consistent with the evidence for a morphotropic phase boundary (MPB). Furthermore, an abrupt shift was observed in the peak position of the symmetric stretching mode v
1 to a higher frequency, resulting from the distortion of O-Nb-O angles caused by incorporating small Li ions into the perovskite units. This is considered to be a prologue for the structural transformation in the NKN-LN solid solution from orthorhombic to tetragonal symmetry. At compositions in which x increases above the MPB, the translational mode of the Li+ cation emerged clearly, and the overall scattering pattern gradually changed to complex patterns caused by the formation of a tungsten-bronze K3Li2Nb5O15 (KLN) secondary phase and an increase in the number of distorted LiNbO3-type crystal units.
Fabrication of Microdevices Using Bulk Ceramics of Lead Zirconate Titanate
Authors: Tanaka Katsuhiko , Konishi Takahiro , Ide Masato , Meng Zhicong , Sugiyama Susumu
Published: October 2005

Piezoelectric microdevices using lead zirconate titanate (PZT) bulk ceramics are desired for use in actuators requiring a large driving force. We have designed a fabrication process for microdevices using PZT bulk ceramics together with Si single crystals. The key techniques of the process are the bonding of PZT bulk ceramics to Si single crystals, the thinning of bulk ceramics, and the micromachining of bulk ceramics. PZT ceramics were bonded to Si using a gold thin film as an intermediate layer. The tensile strength of the PZT-Si bonded wafers depended on the PZT poling process. A dicer or a KrF excimer laser was used to cut the PZT ceramics along the designed pattern. A PZT-Si diaphragm was fabricated as an example of a basic structure that can be used in a device such as a piezoelectric micropump.
Fabrication of Optical Micro Scanner Driven by PZT Actuators
Authors: Kobayashi Takeshi , Tsaur Jiunnjye , Maeda Ryutaro
Published: October 2005

We have designed, simulated, fabricated and tested microelectromechanical system (MEMS) based one-dimensional (1D) optical micro scanners driven by piezoelectric actuators. The designed micro scanners have a micro mirror (1 mm ×1 mm) supported by rotation bars connected to hinges and piezoelectric cantilevers. Pt/Ti/PZT/Pt/Ti/SiO2/SOI multi-layered structure was subjected to MEMS fabrication to form the micro scanners. Through the fabrication, we have obtained 3 types of scanners with 5, 10 and 20 µm-wide hinges. The resonant frequency corresponding to a torsional mode was measured to be 4100, 5563 and 6025 Hz, respectively. We also compared the optical scanning angle of the micro scanners actuated at the resonant frequency. The micro scanner with 10 µm-wide hinge actuated at 5563 Hz showed the widest scanning angle. The scanning angle reaches 25 deg at the actuation voltage of 20 V.
Crystal Structure and Microwave Dielectric Properties of Aeschynite-Type R(W0.5Ti1.5)O6 (R = Nd, Sm, Eu, Gd and Dy) Ceramics
Authors: Kan Akinori , Ogawa Hirotaka , Oishi Takeshi , Yokoi Atsushi , Ohsato Hitoshi
Published: October 2005

The microwave dielectric properties and crystal structure of aeschynite-type structured R(W0.5Ti1.5)O6 (R=Nd, Sm, Eu, Gd and Dy) ceramics were characterized to investigate a microwave dielectric ceramic that is suitable for use in the base station. A single phase of R(W0.5Ti1.5)O6 ceramics was obtained; it was recognized that the lattice parameters of the ceramics vary linearly, depending on the ionic radii of the R ions. The dielectric constants of R(W0.5Ti1.5)O6 ceramics were also related to the ionic radii of the R ions and changed linearly with the ionic radii. From the result of crystal structure analysis, a decrease in the covalency of the (W,Ti)-O bond was observed with increasing the ionic radii of the R ions; these variations in covalency corresponded to the linear increases in the dielectric constants of the R(W0.5Ti1.5)O6 ceramics. The Q·f and τ
f
values significantly depended on the R ions; the highest Q·f value with a near zero τ
f
value was obtained for the Sm(W0.5Ti1.5)O6 ceramic (Q·f =35000 GHz and τ
f
=-0.7 ppm/°C).
Dielectric Properties of Spherical Dielectric Oxide Powder and Its Ceramic-Polymer Composite
Authors: Che Shenglei , Kanada Isao , Sakamoto Norimasa
Published: October 2005

A spherical filler of Ca0.65Sr0.35TiO3 dielectric oxide was prepared by flame fusion to improve the fluidity of ceramic-polymer compounds. The dielectric permittivity of the powder decreased by about 20% after melting-spheroidization but recovered after being heat-treated above 1150°C for 4 h. Composite dielectrics made from the spherical powder and a thermosetting polymer exhibited lower viscosity before hardening, thus making it possible to increase the filler concentration by over 5 vol %. A dielectric permittivity between 12 and 19 was achieved by adjusting the filler concentration of the spherical powder in the range of 40–70 vol %.
Piezoelectric Characteristics of Chiral Polymer Composite Films Obtained under Strong Magnetic Field
Authors: Nakiri Takuo , Okuno Masaki , Maki Nobuyuki , Kanasaki Masayoshi , Morimoto Yu , Okamoto Satoshi , Ishizuka Masayuki , Fukuda Kazuyuki , Takaki Toshihiko , Tajitsu Yoshiro
Published: October 2005

It is difficult to obtain a drawn chiral polymer/inorganic material composite membrane with shear piezoelectricity by the conventional method because the chiral polymer/inorganic material composite membrane breaks during the drawing process by which shear piezoelectricity is realized. Using a strong magnetic field, we propose to manufacture a drawn composite membrane of poly-l-lactic acid (PLLA), a chiral polymer, and hydroxyapatite (Hap), an inoroganic material (PLLA/Hap composite membrane). The manufacturing method used here is effective for obtaining a drawn PLLA/Hap composite membrane with a large uniform area. Also, the shear piezoelectric constant of the drawn PLLA/Hap composite membrane is about 20 pC/N. This value is large for piezoelectric polymers.
Molecular Orientation Dynamics of Polymer-Stabilized Ferroelectric Liquid Crystals
Authors: Furue Hirokazu , Gonda Mizuho , Hatano Jun
Published: October 2005

The dynamic behavior of ferroelectric liquid crystal molecules can be studied in terms of the phase difference angle and the angle of the relative amplitude ratio of elliptically polarized light, measured by time-resolved transmission ellipsometry. It has been known that the phase difference angle and the angle of the relative amplitude ratio indicate qualitatively the out-of-plane and in-plane molecular rotations of the cell substrate, respectively, but not quantitatively. In this study, first we formulate an idea of quantatively determining the in-plane and the out-of-plane angles from the angle of the relative amplitude ratio and the phase difference angle, respectively, and then, this analysis method is applied to the measurement results of polymer-stabilized ferroelectric liquid crystals (PSFLCs).
Measurement of Electrically Induced Vibration Profile in Freely Suspended Film of Ferroelectric Liquid Crystal
Authors: Moritake Hiroshi , Ozaki Masanori , Yoshino Katsumi , Toda Kohji
Published: October 2005

A mechanical vibration profile of a freely suspended film of a ferroelectric liquid crystal induced by applying a sinusoidal electric field is observed using a laser Doppler vibrometer. Mechanical resonance profiles of the freely suspended diaphragm are represented in the form of mechanical vibration distributions. The number of modes in the mechanical vibration increases with frequency. The peak displacement decreases with frequency and the magnitude is of the order of 0.8 µm under the application of 100 V/mm. The vibration displacement is proportional to the electric field applied to the liquid crystal diaphragm existing between two parallel electrodes. The observed mechanical displacements are due to the resonance of the freely suspended diaphragm, which is essential for the construction of a membrane device in relation to light beam reflection.
Apparent Colossal Dielectric Relaxation in SrTiO3 at High Temperature
Authors: Fukunaga Mamoru , Uesu Yoshiaki , Kobayashi Wataru , Terasaki Ichiro
Published: October 2005

Complex dielectric constants of SrTiO3 ceramics and single crystals were measured in the temperature range of 303 K to 673 K and the frequency range of 100 mHz to 100 kHz. It was found that the ceramic sample exhibits a steplike colossal dielectric relaxation similar to the distorted perovskite CaCu3Ti4O12, while the single crystal exhibits a relaxor-like relaxation. Both features can be explained with a heterogeneous structure model.
Synthesis and Physical Properties of Single Crystals and Ceramics of New Ferroelectric BaTi2O5
Authors: Akishige Yukikuni
Published: October 2005

Single crystals of ferroelectric BaTi2O5 were grown by a floating zone method, and the dielectric constant and specific heat were measured in a temperature range of 300–800 K. The dielectric constant and dielectric loss along the b-axis show a large dielectric dispersion at T
C=730 K, similar to the ferroelectric phase transition of the order-disorder type. Transition enthalpy and transition entropy were estimated to be ΔH=98.6 J/mol and ΔS=0.136 J/molK, respectively. The optical absorption edge of the crystals exists near 365 nm. Single-phase BaTi2O5 powder was successfully synthesized through a sol-gel route, using barium diethoxide and titanium tetraisopropoxide, and the porous ceramics sintered at 1375 K show a broad maximum in the electrical capacitance vs T curve at approximately 600 K.
Effects of Grain Boundary and Segregated-Phases on Reliability of Ba(Ti,Zr)O3-Based Ni Electrode MLCs
Authors: Okamatsu Toshihiro , Sano Harunobu , Takagi Hiroshi
Published: October 2005

The reliability in the highly accelerated life test (HALT) for multilayer ceramic capacitors (MLCs) composed of the Ba(Ti,Zr)O3-Gd-Mg-Mn-Si system was markedly improved by controlling the amount of SiO2 and the ratio of Ba/(Ti+Zr). We observed the following characteristics in the microstructures when the reliability was improved. 1) The segregated-phases, which consisted of Mg oxides and Si oxides, were dispersed well in the dielectric layers and their size was considerably small. 2) The corrosion resistance of grain boundaries was improved. 3) The electric potential as a contrast in the focused ion beam scanning ion microscopy was homogeneous in both the grains and the grain boundaries. We can design these microstructures by controlling the additives to generate BaMg2Si2O7 and BaSi2O5, which have low melting points.
III–Nitride UV Devices
Authors: Khan M. Asif , Shatalov M. , Maruska H. P. , Wang H. M. , Kuokstis E.
Published: October 2005

The need for efficient, compact and robust solid-state UV optical sources and sensors had stimulated the development of optical devices based on III–nitride material system. Rapid progress in material growth, device fabrication and packaging enabled demonstration of high efficiency visible-blind and solar-blind photodetectors, deep-UV light-emitting diodes with emission from 400 to 250 nm, and UV laser diodes with operation wavelengths ranging from 340 to 350 nm. Applications of these UV optical devices include flame sensing; fluorescence-based biochemical sensing; covert communications; air, water and food purification and disinfection; and biomedical instrumentation. This paper provides a review of recent advances in the development of UV optical devices. Performance of state-of-the-art devices as well as future prospects and challenges are discussed.
Digital Alloys of AlN/AlGaN for Deep UV Light Emitting Diodes
Authors: Nikishin Sergey A. , Holtz Mark , Temkin Henryk
Published: October 2005

We report a systematic study of the optical and electrical properties of deep ultraviolet light emitting diodes based on digital alloy structures of AlN/Al0.08Ga0.92N grown by gas source molecular beam epitaxy with ammonia. Digital alloys are formed by short period superlattices consisting of Al0.08Ga0.92N wells, 0.50 or 0.75 nm thick, and AlN barriers, 0.75 to 1.5 nm thick. For digital alloys with effective bandgap of 5.1 eV, average AlN composition 72%, we obtain room temperature electron concentrations up to 1×1019 cm-3 and resistivity of 0.005 Ω·cm and hole concentrations of 1×1018 cm-3 with resistivity of 6 Ω·cm. Light emitting diodes based on digital alloys are demonstrated operating in the range of 250 to 290 nm.
Metalorganic Chemical Vapor Deposition Conditions for Efficient Silicon Doping in High Al-Composition AlGaN Films
Authors: Keller Stacia , Cantu Pablo , Moe Craig , Wu Yuan , Keller Salka , Mishra Umesh K. , Speck James S. , DenBaars Steven P.
Published: October 2005

The influence of the metalorganic chemical vapor deposition conditions on the electrical and optical properties was investigated for silicon-doped Al
x
Ga1-x
N films with x>0.5 grown on sapphire and 6H–SiC substrates. At a constant silicon concentration in the layers, the electron carrier concentration was the highest in films deposited at reduced temperatures and high V/III ratios, despite the higher residual carbon and oxygen concentrations in the layers grown at lower temperatures. The electrical properties of the films were correlated with the intensity of the emission bands in the 410 to 440 nm and the 510 to 550 nm ranges observed in the 300 K photoluminescence spectra of the samples. The influence of impurities, native defects and threading dislocations on the film properties is discussed.
Role of Ion Energy and Flux on Inductively Coupled Plasma Etch Damage in InGaN/GaN Multi Quantum Well Light Emitting Diodes
Authors: Han Sang Youn , Yang Hyuck Soo , Baik K. H. , Pearton S. J. , Ren F.
Published: October 2005

The effect of inductive coupled plasma (ICP) etching of GaN light-emitting diodes (LEDs) on the device performance was investigated. InGaN/GaN multi-quantum well LEDs with emission wavelengths 420 nm were fabricated using Cl2/Ar ICP etching to form the mesa for the n-contact. Different rf chuck powers (controlling incident ion energy) and source powers (controlling ion flux) were used to examine their effect on junction leakage current. At high ion fluxes (source powers > 500 W), the junctions were very heavily damaged. The forward turn-on voltage was increased by using higher ion energies from 4.55 V for 120 eV ion energy to 5.1 V for 300 eV. The reverse bias current was much less sensitive to the ion energy during plasma etching and increased only above an average ion energy of ∼300 eV. The current transport in the LEDs is dominated by generation-recombination and surface leakage components (ideality factor ≥2) in all cases.
Optical Control of Transmittance by Photo-Induced Absorption Effect in InGaN/GaN Structures
Authors: Nomura Masahiro , Arakawa Yasuhiko , Shimura Tsutomu , Kuroda Kazuo
Published: October 2005

We have investigated the optical modulation properties of transmittance using the photo-induced absorption effect in 10 periods of In0.10Ga0.90N/GaN (60 nm/60 nm) structures grown by metal-organic chemical vapor deposition. Transmittance was modulated by 22% at 398 nm under a continuous-wave laser pumping at 405 nm with an intensity of 1 W/cm2. We have also investigated the influences of He+ ion irradiation on optical modulation properties, such as magnitude, time response, and spatial resolution. The modulation of transmittance reduces at a high pump on/off frequency mainly due to the relatively slow recovery process. The ion-irradiated samples showed a faster recovery and this resulted in the enhancement of the cutoff frequency from 30 to 130 kHz at 1 W/cm2. The irradiation process also improved the spatial resolution at the expense of the magnitude of transmittance modulation. However, the spatial resolution of the device is of the order of 100 µm; thus, substantial improvement is essential for two-dimensional optical device applications.
Localization Effects in InGaN/GaN Double Heterostructure Laser Diode Structures Grown on Bulk GaN Crystals
Authors: Czernecki R. , Franssen G. , Suski T. , Świetlik T. , Borysiuk J. , Grzanka S. , Lefebvre P. , Leszczyński M. , Perlin P. , Grzegory I. , Porowski S.
Published: October 2005

We demonstrate a double heterostructure (DH) nitride laser diode (LD) with an untypically wide 9.5 nm InGaN active region instead of the commonly used narrow InGaN quantum wells. Structures were grown on bulk GaN, which ensures low dislocation densities and therefore low concentrations of nonradiative recombination centers. The efficient screening of polarization induced electric fields in the structures under investigation, which contained heavily (1×1019 cm-3) Si doped barriers, was demonstrated by means of hydrostatic pressure dependent photoluminescence measurements on a simplified sample with identical active region. Since the detrimental separation of carriers by electric fields becomes more pronounced for wider InGaN active regions, efficient screening of polarization induced electric fields is essential for the investigated heterostructures. Optical and electrical parameters of this LD were comparable to those of comparable devices with typical QWs of ∼4 nm as active region. We observed a high thermal stability of the photoluminescence intensity and, via time-resolved photoluminescence, a relatively temperature-independent radiative decay time. These observations support the significance of carrier localization phenomena for the radiative recombination processes of the investigated structure. The implications of these results for DH LD structures are discussed.
AlGaN Deep-Ultraviolet Light-Emitting Diodes
Authors: Zhang Jianping , Hu Xuhong , Lunev Alex , Deng Jianyu , Bilenko Yuriy , Katona Thomas M. , Shur Michael S. , Gaska Remis , Khan M. Asif
Published: October 2005

We report on the development of AlGaN based deep ultraviolet (DUV) light-emitting diodes (LEDs) grown by migration-enhanced metalorganic chemical vapor deposition (MEMOCVD). Improved quality of AlGaN has allowed us to achieve milliwatt-power at wavelengths ranging from 365 to 265 nm. For 295 and 280 nm LEDs, record CW powers with wall-plug-efficiency approaching 1.0% were realized. The CW power reached 1.2 and 1.0 mW at 20 mA for 280 and 295 nm LEDs, respectively. A multiple-chip package (UV lamp) emitted CW power of 11 mW at the wavelength of 280 nm. Under pulse operation, the 280 nm UV lamp produced power as high as 56 mW. The CW power levels at 20 mA were 0.5, 0.25 and 0.15 mW for a single-chip 275, 270 and 265 nm LEDs, respectively. A 265 nm UV lamp exhibited a record high CW power exceeding 1.5 mW. The applications of these DUV LEDs in bio-agents detection have been demonstrated and the preliminary results will be presented.
Effect of Carrier Blocking Layers on the Emission Characteristics of AlGaN-based Ultraviolet Light Emitting Diodes
Authors: Park Ji-Soo , Fothergill Daryl W. , Zhang Xiyao , Reitmeier Zachary J. , Muth John F. , Davis Robert F.
Published: October 2005

AlGaN-based thin film heterostructures suitable for ultraviolet light emitting diodes have been grown and fabricated into working devices with and without p-type and n-type AlGaN carrier-blocking layers at the top and the bottom of the quantum wells, respectively. The principal emission from each device occurred at 353 nm. The highest intensities of this peak were measured at all values of the injection current in the device with a p-type carrier-blocking layer at the top of the quantum well; this device also exhibited the highest values of light output power. Growth of an n-type carrier-blocking layer at the bottom of the quantum wells had an adverse effect on the light emitting diode characteristics. A broad peak centered at ∼540 nm exhibited yellow luminescence and was present in the spectra acquired from all the devices. This peak is attributed to absorption of the UV emission by and re-emission from the p-GaN and/or to the luminescence from the AlGaN within quantum wells by current injection. The intensity of this peak increased and saturated by the same order of magnitude as the intensity of the UV emission at 353 nm.
Characterization of MgxZn1-xO Films Grown by Remote-Plasma-Enhanced Metalorganic Chemical Vapor-Deposition using bis-Ethylcyclopentadienyl Magnesium
Authors: Nakamura Atsushi , Yamamoto Kenji , Ishihara Junji , Aoki Toru , Temmyo Jiro
Published: October 2005

Mg
x
Zn1-x
O films were successfully grown on a-plane sapphire (112̄0) substrates by remote-plasma-enhanced metalorganic chemical vapor-deposition (RPE-MOCVD) using diethyl zinc (DEZn) and bis-ethylcyclopentadienyl magnesium (EtCp2Mg). By increasing magnesium content in the films, the crystal structure was shifted through a mixed state from wurtzite to rock salt. The optical band-gap of the films at nearly 3.28 eV was shifted to 3.69 eV by alloying with magnesium depending on the alloy composition. Both optical absorption edges and emission peaks of Mg
x
Zn1-x
O films shifted to higher energy when the magnesium content at room temperature was increased, showing alloy broadening. The Stokes' shift of wurtzite Mg
x
Zn1-x
O alloy films was quantitatively evaluated. The results are relevant to exciton localization.
Free-Carrier Effects on Zero- and One-Phonon Absorption Onsets of n-Type ZnO
Authors: Makino Takayuki , Segawa Yusaburo , Yoshida Shin , Tsukazaki Atsushi , Ohtomo Akira , Kawasaki Masashi , Koinuma Hideomi
Published: October 2005

Epitaxial, n-type ZnO:Ga layers grown by laser molecular-beam epitaxy were investigated by Hall-effect and spectroscopic techniques. We have studied the effects of free carriers on their optical properties in the spectral range close to the fundamental energy gap. To precisely determine the absorption onset energies, line-shape analysis of the absorption spectrum was performed using a model taking the many-body effect due to the presence of high-density electron gas into account. As a result, donor doping gives rise to a systematic blueshift of the fundamental absorption edge, consistent with the Burstein–Moss effect. The Burstein–Moss shifting behavior of ZnO:Ga is compared with that in the case of ZnO:Al. The experimental data for ZnO:Ga agree very well with the theory developed by Sernelius et al. [Phys. Rev. B 37 (1988) 10244], while the data for ZnO:Al do not. The temperature-dependent spectroscopy allowed us to investigate the effect of free carrier also on an exciton-phonon complex. It was found that, at low temperatures, the spectrum had an abrupt onset followed by two asymmetric peaks, including the anti-Stokes phonon sideband, which is explained in terms of optical singularities.
Electrical and Optical Properties of n-ZnO/p-SiC Heterojunctions
Authors: Alivov Ya. I. , Johnstone D. , Özgür Ü. , Avrutin V. , Fan Q. , Akarca-Biyikli S. S. , Morkoç H.
Published: October 2005

A series of n-ZnO/p-6H–SiC heterostructures have been grown by molecular-beam epitaxy, and electrical and optical properties of the mesa diodes have been studied. Current versus voltage (I–V) characteristics of the samples revealed a good rectifying behavior of all samples with a typical leakage current less than 10-7 A at -8, and with forward currents changing from sample to sample and at 8 V lying in the range 0.8–10 mA. Capacitance–voltage (C–V) profiles and double pulse deep level transient spectroscopy (DDLTS) indicate interface states in the 1012–1013/cm2 eV range, sharply peaked below 0.5 eV. Under forward bias electroluminescence (EL) emission was observed from most of the samples in yellow and violet regions with maxima at ∼2.1 and ∼2.92 eV, which attributed to the SiC side of the n-ZnO/p-6H–SiC heterojunction, from the comparison with the photoluminescence spectra of n-ZnO and p-SiC.
Heating Layer of Diamond-Like Carbon Films Used for Crystallization of Silicon Films
Authors: Sameshima Toshiyuki , Andoh Nobuyuki
Published: October 2005

Rapid thermal crystallization of silicon films with a heating layer of diamond-like carbon (DLC) films is reported. DLC films 200 nm thick have an optical absorbance higher that 0.7 for wavelengths shorter than 1000 nm. They are also heat resistant to about 5000 K. A crystalline volume ratio of 0.85 is achieved for silicon films through heat diffusion from DLC heated by 30-ns-pulsed XeCl excimer laser irradiation at 200 mJ/cm2 for 100 nm DLC/5 nm SiO2/25 nm Si/quartz, while it is only 0.4 for 25 nm Si/quartz because of high reflection loss. Crystallization of silicon films is also achieved by 1064 nm YAG laser heating of the 200 nm DLC layer overlying the silicon films.
High-Efficiency Crystallization of Amorphous Silicon Films on Glass Substrate by New Metal-Mediated Mechanism
Authors: Lin Chiung-Wei , Lee Seng-Chi , Lee Yeong-Shyang
Published: October 2005

A new crystallization technique for crystallizing amorphous silicon (a-Si) film with a low thermal budget is proposed. A highly crystalline polycrystalline silicon (poly-Si) film can be rapidly obtained on a low-cost glass substrate by this technique. A material with a large IR absorption coefficient provides energy for crystallizing a-Si film into poly-Si film. By this new technique, we can make highly crystalline poly-Si film efficiently. Atomic force microscopy (AFM), Raman scattering, X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) with energy dispersive spectrometer (EDS) measurements demonstrated that a-Si film can be fully crystallized by annealing with five 5 s pulses at 870°C. The roughness of film processed by this new technique is only 0.59 nm which is superior to the 7.8 nm obtained by the conventional excimer laser crystallization (ELC) technique. The average grain size and grain growth rate obtained in this technique are 0.82 µm and 120 µm/min, respectively.
Back-Surface-Field Effects at the Heterojunctions between Boron-Doped p-Type Hydrogenated Amorphous Silicon and Crystalline Silicon in Thin-Film Crystalline Silicon Solar Cells
Authors: Sakata Isao , Yamanaka Mitsuyuki , Shimokawa Ryuichi
Published: October 2005

We have found that the back-surface recombination velocity, S
b, of minority carriers in crystalline silicon (c-Si) thin film solar cells can be reduced to less than 103 cm/s when a boron (B)-doped p-type hydrogenated amorphous silicon (a-Si:H) layer is deposited on the back surface of a p-type c-Si substrate at 200°C, while the value of S
b is 106 cm/s when a B-doped p-type layer is epitaxially grown on the c-Si substrate. We have clarified, from internal photoemission (IPE) and attenuated-total-reflection Fourier transform infrared (ATR-FTIR) spectroscopy measurements, that the band lineup of the heterojunction between B-doped p-type a-Si:H and c-Si and the hydrogen passivation of defects in B-doped a-Si:H are possible reasons for the observed low value of S
b.
Epitaxial Growth of Cubic SiC Film on Si Crystal with Curved Surface
Authors: Sun Yong , Miyasato Tatsuro
Published: October 2005

3C–SiC films were epitaxially grown on a Si(100) substrate with a curved surface at 1000–1100°C by the hydrogen plasma cosputtering of the Si and C targets. The entire surface of a Si(100) crystal was pyramided by KOH solution etching. The surface of pyramids on the crystal was curved by selecting the etching conditions. SiC films were grown on a curved surface of the Si substrate above 950°C, and an (200)-oriented epitaxial growth of 3C–SiC was observed above 1000°C. No hollow voids were formed at the SiC/Si interface at growth temperatures below 1075°C. The formation of Si–C bonds was a thermally active reaction with an activation energy of 5.5 eV below 1000°C, which becomes 0 eV in the epitaxial growth above 1000°C. This small activation energy for the formation of Si–C bonds at a curved surface plays an important role in the prevention of hollow void formation at the SiC/Si interface.
Electric and Crystallographic Characterizations on Hydrogen Passivated Spherical Silicon Solar Cells
Authors: Okamoto Chikao , Minemoto Takashi , Murozono Mikio , Takakura Hideyuki , Hamakawa Yoshihiro
Published: October 2005

Hydrogen passivation (H-passivation) was performed to inactivate the electrically active defects in spherical Si solar cells fabricated by the dropping method. The atomic hydrogen activated by RF plasma passivated the dangling bonds in the crystal grains, and solar cell performance was improved. The distribution of defects and the crystal quality before and after H-passivation were observed by electron-beam-induced current (EBIC) and transmission electron microscopy (TEM). The recombination sinks were observed by EBIC as dark lines of grain boundaries, wide dark areas and local dark spots in the grains. The effect of H-passivation was observed at parts of the grain boundaries and the wide dark areas, but not at the local dark spots in the grains. TEM observation showed that the crystal grains of the areas with dark spots included many dislocations and that the crystal quality at the wide dark areas is microcrystalline (<100 nm). These results indicate that the bulk region of microcrystal grains and portions of grain boundaries are inactivated effectively by H-passivation.
New Triple Self-Aligned (SA3) Split-Gate Flash Cell with T-Shaped Source Coupling
Authors: Sung Hung-Cheng , Lei Tan Fu , Huang Chen-Ming , Kao Ya-Chen , Lin Yung-Tao , Wang Chung S.
Published: October 2005

A new triple self-aligned (SA3) split-gate flash cell with a T-shaped source coupling approach is described in this paper. This novel structure can significantly enhance coupling capacitance between the source and floating gate without increasing cell size. The enhancement can be simply modulated by an oxide-etching step. This new structure can be applied to program voltage reduction and cell size scaling. For program voltage reduction, the maximum program voltage of the new cell can be reduced from 7.4 to 6.4 V, which is characterized by a newly developed methodology for program vs disturb window characterization. For cell size scaling, comparable sort-1 and sort-2 yields are demonstrated using the new cell with a shorter floating length and a shallower source junction. To understand the relationship between source coupling ratio (SCR) and the program/erase mechanism, an insightful discussion on the program and erase mechanisms for our split-gate flash cell is also shown in this paper.
Electronic Structure of Ordered Ga0.5In0.5P/GaAs Heterointerface Studied by Raman-Scattering and Photoluminescence-Excitation Measurements
Authors: Yamashita Kenichi , Oe Kunishige , Kita Takashi , Wada Osamu , Wang Yong , Geng Christian , Scholz Ferdinand , Schweizer Heinz
Published: October 2005

We have investigated the electronic band structure of a long-range-ordered Ga0.5In0.5P/GaAs heterointerface by optical measurements and a semi-empirical calculation. Raman-scattering spectra of the ordered Ga0.5In0.5P/GaAs samples show plasmon–phonon coupled modes induced by dense electron accumulation at the heterointerface, in contrast to that of the unordered sample which shows the spectrum of bulk GaAs. Furthermore, the Franz–Keldysh oscillation observed in the photoluminescence-excitation spectrum indicates a strong interface electric field. According to the results of a comparison between the experiment and a semi-empirical calculation based on Poisson's law, it is found that the spatial distribution of the accumulated electron density is modified strongly by the conduction-band discontinuity and the interface field, depending on the order parameter.
A Stochastic Photoresist-Polymer Dissolution Model Combining the Percolation and Critical Ionization Models
Authors: Sarris V. , Patsis G. P. , Constantoudis V. , Boudouvis A. G. , Gogolides E.
Published: October 2005

A new model for photoresist-polymer dissolution in aqueous base is presented combining the critical ionization model [P. C. Tsiartas et al.: Macromolecules 30 (1992) 4656] and the percolation model [A. Reiser et al.: Angew. Chem., Int. Ed. 35 (1996) 2428]. The dependence of dissolution rate on molecular weight and hydrophilic fraction of the polymer has been studied using the new model, as well as the “gel” layer thickness formed during dissolution. The new model predicts available experimental data, and can be a basis for line-edge roughness predictions.
The Effect of Backside Particles on Substrate Topography
Authors: Bearda Twan , Mertens Paul W. , Holsteyns Frank , Bisschop Peter De , Compen René , Meer Aschwin van , Heyns Marc M.
Published: October 2005

The presence of a particle on the backside of a wafer is commonly acknowledged to produce a deflection of the wafer when it is held on a flat surface by means of a pressure difference. We simulated this wafer topography, taking into account both elastic and plastic deformations. The simulations are backed up by experimental evidence. The results show that height variations of 100 nm can extend over several mm. At the same time, indentation and plastic deformation reduce the surface height variations to values that are orders of magnitude below those predicted in the ITRS roadmap.
High-Efficiency Nitride-Based Light-Emitting Diodes with Moth-Eye Structure
Authors: Kasugai Hideki , Miyake Yasuto , Honshio Akira , Mishima Shunsuke , Kawashima Takeshi , Iida Kazuyoshi , Iwaya Motoaki , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu , Kinoshita Hiroyuki , Shiomi Hiromu
Published: October 2005

Nitride-based blue light-emitting diodes (LEDs) with a moth-eye structure on the back of a 6H–SiC substrate have been developed. The moth-eye LED has a roughness less than the optical wavelength at the back surface of the SiC substrate fabricated by reactive ion etching (RIE) with CF4 gas. The light extraction efficiency and corresponding output power have been increased to 3.8 times those of a LED with a conventional structure. The experimental findings agree with the results of a theoretical analysis of the effect of the moth-eye structure.
Thermal Annealing Effect of Indium Tin Oxide Contact to GaN Light-Emitting Diodes
Authors: Hsu Chin-Yuan , Lan Wen-How , Wu YewChung Sermon
Published: October 2005

We have fabricated GaN-based light-emitting diodes (LEDs) using transparent indium tin oxide (ITO) for p-type contacts. The current–voltage (I–V) characteristics of the devices have been studied. When annealed at 700°C, the p–n junction of the diodes became very leaky, and even electrical short circuits have been observed. According to scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometer analyses (EDS), it was found that indium (In) diffused into the LED structure with defects such as threading dislocations (TDs) or V-pits. The defects provide leakage paths to cause short circuits in p–n junctions at high annealing temperatures.
Magnetization and High-Frequency EMR Measurements on the Lithium-Ion Battery Substance LiMn2O4
Authors: Kimura Shojiro , Kaji Tomoyuki , Okubo Susumu , Yoshida Makoto , Inagaki Yuji , Asano Takayuki , Ohta Hitoshi , Kunimoto Takashi , Dziembaj Roman , Molenda Marcin , Rudowicz Czeslaw
Published: October 2005

We report on the magnetization and high-frequency EMR studies of lithium manganese spinel LiMn2O4 powder samples obtained by the sol–gel method with calcinations at several temperature ranges. The results indicate that the low temperature magnetization and EMR spectra vary strongly between samples. Analysis of the experimental data enables a deeper characterization of the samples. It appears that a small amount of the impurity phase Li2MnO3 exists in the samples obtained by calcinations at 900°C.