bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochromic Properties of Tungsten Oxide Films Prepared by Reactive Sputtering
Authors: Kim Min Hong , Kang Tai Young , Jung Yu Sup , Kim Kyung Hwan
Published: May 2013

WO3-x
thin films were deposited on induim tin oxide (ITO) glass substrates with various oxygen flow ratios from 0.55 to 0.7 by the reactive facing-target sputtering method, at a power density of 4 W/cm2 and room temperature. The structural properties of the WO3-x
thin films were measured by X-ray diffractometry and Raman spectral analysis. As-deposited WO3-x
thin films had an amorphous structure. In the Raman spectra, WO3-x
thin films exhibited two strong peaks at 770 and 950 cm-1 attributed to the vibrations of W6+–O and W6+=O bonds, respectively. The electrochemical and optical properties of WO3-x
thin films were measured by cyclic voltammetry and UV/vis spectrometry. The results showed the highest charge density at an oxygen flow ratio of 0.7 and the highest transmittance in the visible range. The maximum coloration efficiency was 30.82 cm2/C at an oxygen flow ratio of 0.7.
Comparison of Electrochemical Luminescence Characteristics of Titanium Dioxide Films Prepared by Sputtering and Sol–Gel Combustion Methods
Authors: Park Hee-Dae , Sung Youl-Moon , Park Min-Woo , Song Jae-Eun
Published: May 2013

Titanium dioxide (TiO2) films were deposited on fluorine-doped tin-oxide (FTO) glass by sputtering and sol–gel combustion (SGC) coating methods and investigated with respect to their electrochemical luminescence (ECL) performance. The sputtered TiO2 films were denser than the SGC-deposited films, while the SGC films were found to be superior in porosity to the sputtered films. The charge transfer resistance (R
2) of the SGC (450 °C) TiO2-based cell was found to be lower than those of the sputtered TiO2-based cells. The SGC (450 °C) cell emitted a more intense ECL than the sputter (450 °C) cells. The threshold voltage at which the emission starts was 3.0 V for the SGC (450 °C) cell, which was lower than that (3.5 V) for the sputter (450 °C) cell. The efficiencies were 0.04 lm/W for the sputter (450 °C) cell (R
2 = 22.3 Ω, porosity= 27.2%) and 0.085 lm/W for the SGC (450 °C) cell (R
2 = 12.8 Ω, porosity= 65.8%). The SGC-deposited TiO2 films were found to be superior in ECL efficiency to the sputtered TiO2 films.
Comparison between Damage Characteristics of p- and n-GaN Surfaces Etched by Capacitively Coupled Radio Frequency Argon Plasmas
Authors: Kawakami Retsuo , Niibe Masahito , Nakano Yoshitaka , Konishi Masashi , Mori Yuta , Takeichi Atsushi , Tominaga Kikuo , Mukai Takashi
Published: May 2013

Damage characteristics of p-GaN surfaces etched by capacitively coupled radio frequency Ar plasma at various gas pressures have been studied in terms of the ultraviolet (UV) light irradiation effect. The UV light corresponding to Ar II is emitted from the plasma at high gas pressures from 50 to 100 mTorr, whereas no UV light is emitted at a low gas pressure of 10 mTorr. The result of the etched p-GaN surface is compared with that of the etched n-GaN surface. The difference between the results of the p- and n-GaN surfaces depends strongly on the gas pressure. Both the experimental N/Ga ratios at the p- and n-GaN surfaces etched at the low gas pressure decrease with increasing etching time. The decreases in the experimental N/Ga ratios agree with the simulation results that N atoms at the p- and n-GaN surfaces are preferentially removed by Ar+ ions. The morphologies of the p- and n-GaN surfaces etched at the low gas pressure are similar to those of the as-grown surfaces. The damage characteristic of the p-GaN surface induced in the absence of the UV light irradiation also appears at the high gas pressures, although the p-GaN surfaces etched at the high gas pressures are irradiated with the emitted UV light. In contrast, both the experimental N/Ga ratios and morphologies of the n-GaN surfaces etched at the high gas pressures change with increasing etching time. The changes in the n-GaN surfaces probably result from the UV light irradiation.
Wavelength Dependence of Photon-Induced Interface Defects in Hydrogenated Silicon Nitride/Si Structure during Plasma Etching Processes
Authors: Fukasawa Masanaga , Matsugai Hiroyasu , Honda Takahiro , Miyawaki Yudai , Kondo Yusuke , Takeda Keigo , Kondo Hiroki , Ishikawa Kenji , Sekine Makoto , Nagahata Kazunori , Uesawa Fumikatsu , Hori Masaru , Tatsumi Tetsuya
Published: May 2013

The wavelength dependence of SiN
x
:H/Si interface defect generation caused by vacuum ultraviolet (VUV)/UV radiation from plasma etching processes was investigated. VUV radiation (λ< 200 nm) had almost no impact on the generation of defects at the SiN
x
:H/Si interface, since all the radiation in this wavelength range was absorbed in the upper SiN
x
:H film. However, UV radiation (200 < λ< 400 nm) was able to reach the underlying SiN
x
:H/Si interface and damage the interface. Direct UV radiation reaching the SiN
x
:H/Si interface dissociated the chemical bonds at the interface and generated interface-trapped charges. The estimated total energy of absorbed photons (E
total; 200 < λ< 400 nm) at the interface layer seems to be proportional to the interface-trapped charge density (D
it) measured by capacitance–voltage measurement. However, the mechanism underlying the relationship between E
total and D
it is not yet clear. Visible radiation (λ> 400 nm) had no influence on damage generation on the SiN
x
:H/Si structure, since the visible radiation was transmitted through upper SiN
x
:H film and underlying interface layer. The results revealed that UV radiation transmitted through the upper dielectrics can cause the electrical characteristics of underlying metal–oxide–semiconductor (MOS) devices to fluctuate.
Elongated Inductively Coupled Thermal Plasma Torch Operable at Atmospheric Pressure
Authors: Okumura Tomohiro , Kawaura Hiroshi
Published: May 2013

An elongated inductively coupled plasma (ICP) torch that enables instantaneous thermal processing over a large area has been newly developed. Its circular chamber configuration enabled the generation of elongated thermal plasma. A racetrack chamber with a groove showed improvement of plasma stability. The surface temperature distribution over a substrate was measured using a simplified perpendicular-racetrack-type torch with a length of 130 mm; the surface of a glass substrate was heated to 798 K at a scanning speed of 50 mm/s and the peak temperature variation over a substrate along the longitudinal line was within ±5.5 K in the best case. A sputtered amorphous silicon thin film was successfully crystallized.
Leading Wave Crystallization Induced by Micro-Thermal-Plasma-Jet Irradiation of Amorphous Silicon Films
Authors: Hayashi Shohei , Fujita Yuji , Kamikura Takahiro , Sakaike Kohei , Akazawa Muneki , Ikeda Mitsuhisa , Higashi Seiichiro
Published: May 2013

The crystalline grain growth of silicon induced by micro-thermal-plasma-jet irradiation has been directly observed using a high-speed camera. An oval-shaped molten region (MR) was formed after the solid phase crystallization (SPC), and it was clearly observed that laterally large grains grew perpendicular to the liquid–solid interface. Leading wave crystallization (LWC), which showed intermittent grain growth with a liquid–solid interface velocity as high as 4500 mm/s, was discovered in between the MR and SPC region. From numerical calculation, it has been clarified that the explosive lateral growth of LWC is triggered by the formation of a thin liquid layer and the explosive propagation of the layer is driven by released latent heat.
Simultaneous Formation of a Metallic Mn Layer and a MnOx/MnSixOy Barrier Layer by Chemical Vapor Deposition at 250 °C
Authors: Kurokawa Atsuko , Sutou Yuji , Koike Junichi , Hamada Tatsufumi , Matsumoto Kenji , Nagai Hiroyuki , Maekawa Kaoru , Kanato Hiroki
Published: May 2013

A metallic Mn layer was successfully formed on tetraethylorthosilicate (TEOS)–SiO2 substrate at the deposition temperature of 250 °C by chemical vapor deposition (CVD) using a newly developed Mn precursor, bis[1-(tert-butylamide)-2-dimethylaminoethane-N,N ']manganese. A thin and uniform Mn oxide layer was simultaneously formed at a CVD-Mn/TEOS–SiO2 interface, and was partially embedded in the TEOS–SiO2. This Mn oxide layer was composed of a bilayer of MnO
x
and MnSi
x
O
y
. After annealing at 400 °C in vacuum for 10 h, the interface Mn oxide layer showed a good barrier property and thermal stability.
Suppression of Stress-Induced Voiding by Controlling Microstructure of Cu Electroplated Films
Authors: Muranaka Seiji , Omori Kazuyuki , Mori Kenichi , Maekawa Kazuyoshi , Shibata Ryuji , Suzumura Naohito , Kudo Shuichi , Fujisawa Masahiko
Published: May 2013

In advanced LSI devices, the filling capability for the electroplating (ECP) process, impurities in Cu film, and grain growth after ECP are important properties of Cu interconnect reliability. It has been reported that the Cu grain growth depends on the ECP-Cu film characteristics and the annealing conditions. In this study, we focus on the deposition thickness of ECP-Cu films to control their microstructure. It is revealed that a thicker ECP-Cu film enlarges the Cu grain size and reduces the number of small grains. It is also revealed that Cu grains in a wide line with a thicker ECP-Cu film are larger, leading to reliability improvement. A film with larger grains has fewer grain boundaries and fewer diffusion paths of vacancies, and a film with fewer small grains has a decreased number of vacancies. As a result, stress-induced voiding phenomena are apparently suppressed by increasing the thickness of deposited ECP-Cu film.
Reduction of RuO2 Film to Metallic Ru Film Using Atomic Layer Deposition under Different Oxygen Partial Pressure
Authors: Park Taeyong , Lee Jaesang , Park Jingyu , Jeon Heeyoung , Jeon Hyeongtag
Published: May 2013

Thin ruthenium oxide film deposition on 100 nm SiO2 substrate by thermal atomic layer deposition (ALD) prior to ruthenium deposition. RuO2 was totally reduced to metallic Ru film when Ru deposition process with low oxygen partial pressure. Using this technique, we can improve overall deposition speed by reducing incubation time which is major problem of deposition Ru film. In addition, we compare properties of Ru film deposited by thermal ALD directly deposited on SiO2 substrate and Ru film obtained from reduction of RuO2 film. The Ru film from RuO2 has smoother surface RMS roughness than Ru film directly deposited on SiO2 substrate.
Novel On-Site Cupric Oxide Recovery Process from Waste Containing Copper
Authors: Kobayashi Takuya , Kano Kazunori , Suzuki Toshihiro , Kobayashi Atsushi
Published: May 2013

Although the copper-containing waste from semiconductor or printed circuit board (PCB) manufacturing contains a high concentration of copper, it is usually transported and treated outside of the factories. We studied a novel treatment technology for on-site recycling in the factories. In this technology, cupric oxide with a low-chloride-content was obtained from waste with a high copper concentration, such as cupric chloride etchant waste and cupric sulfate plating waste. In the proposed method, copper-containing waste mixed with H2O2 solution is added to NaOH solution by stepwise addition. In laboratory experiments, we optimized the reaction conditions and obtained low-chloride-content CuO from actual cupric chloride etchant waste and cupric sulfate plating waste. Based on the laboratory experiments, we constructed the first practical plant at a PCB factory and obtained low-chloride-content CuO.
Evaluation of In-Plane Microdeformation Distribution Characteristics of Polishing Pad Surface
Authors: Uneda Michio , Omote Tatsunori , Shibuya Kazutaka , Nakamura Yoshio , Ichikawa Daizo , Ishikawa Ken-ichi
Published: May 2013

In the chemical mechanical polishing (CMP) of a Si wafer, the physical properties of the polishing pad affect the processing characteristics. There have been several studies on the evaluation of pad surface asperity. In this study, we investigate the fundamental characteristics of polishing pads by the digital image correlation (DIC) method from two viewpoints. It was found that the pad surface deforms owing to shrinkage. Moreover, there is a strong relationship between the in-plane microdeformation characteristics and the amount of material removed from the pad in the conditioning process. Since the DIC method can measure changes in pad surface conditions, it can be used to evaluate future CMP monitoring systems.
Hybrid Cleaning Technology for Enhanced Post-Cu/Low-Dielectric Constant Chemical Mechanical Planarization Cleaning Performance
Authors: Ramachandran Manivannan , Cho Byoung-Jun , Kwon Tae-Young , Park Jin-Goo
Published: May 2013

During chemical mechanical planarization (CMP), a copper/low-ksurface is often contaminated by abrasive particles, organic materials and other additives. These contaminants need to be removed in the subsequent cleaning process with minimum material loss. In this study, a dilute amine-based alkaline cleaning solution is used along with physical force in the form of megasonic energy to remove particles and organic contaminants. Tetramethylammonium hydroxide (TMAH) and monoethanolamine (MEA) are used as an organic base and complexing agent, respectively, in the proposed solution. Ethanolamine acts as a corrosion inhibitor in the solution. Organic residue removal was confirmed through contact angle measurements and X-ray photoelectron spectroscopy analysis. Electrochemical studies showed that the proposed solution increases protection against corrosion, and that the hybrid cleaning technology resulted in higher particle removal efficiency from both the copper and low-ksurfaces.
Impact of Thermomechanical Stresses on Bumpless Chip in Stacked Wafer Structure
Authors: Mizushima Yoriko , Kitada Hideki , Uchibori Chihiro J. , Maeda Nobuhide , Kodama Shoichi , Kim Youngsuk , Fujimoto Koji , Yoshimi Seiichi , Nakamura Tomoji , Ohba Takayuki
Published: May 2013

Crack formation due to thermomechanical stresses generated by a dielectric polymer thicker than 20 µm and by that with high modulus during the bumpless chip-on-wafer (COW) process has been investigated. According to the stress simulation, thermal stresses increase with polymer thickness where the stress value ranges from 100 to 200 MPa for benzocyclobutene (BCB)-based resin. Thermal stresses in the hybrid structure using epoxy-based resin and BCB-based resin were calculated to be less than 100 MPa. Thus, the reduction of the thicknesses of the polymer as well as the Si chip was found to be effective in avoiding crack formation in the COW structure. Moreover, to investigate the crack driving force, the energy release rate (ERR) was calculated. The crack propagates toward the Si chip corner and the result is consistent with the experiment. On the COW structure, a thin Si chip and a low-modulus polymer expand the process window.
Plasma-Enhanced Atomic Layer Deposition Sealing Property on Extreme Low-k Film with k = 2.0 Quantified by Mass Metrology
Authors: Ishikawa Dai , Kobayashi Akiko , Nakano Akinori , Kimura Yosuke , Matsushita Kiyohiro , Kobayashi Nobuyoshi , Ditmer Gary , Kiermasz Adrian
Published: May 2013

We have investigated plasma-enhanced atomic layer deposition (PEALD) SiN pore-sealing film formation and diffusion behavior on highly porous SiOCH films. Mass measurement revealed the diffusion of the precursor used in PEALD into pores of SiOCH films, which was enhanced for higher-porosity SiOCH films. The diffusion of the precursor into the pores was reduced by applying UV-assisted restoration treatment before the pore-sealing process, which helped the formation of hermetic pore-sealing films. The results indicated that a 1-nm-thick SiN film was sufficient to seal the surface of the restored SiOCH film with k = 2.0. It was found that the decrease in k due to the pore-sealing deposition was as small as 0.02. The results indicated that the sequential application of UV-assisted restoration and PEALD-SiN pore sealing is a promising method of introducing the use of highly porous SiOCH films with k = 2.0 into interconnect integration.
High-Speed Coating Method for Photovoltaic Textiles with Closed-Type Die Coater
Authors: Imai Takahiko , Shibayama Norihisa , Takamatsu Seiichi , Shiraishi Kenji , Marumoto Kazuhiro , Itoh Toshihiro
Published: May 2013

We developed a closed-type die-coating method to fabricate thin films for electronic devices. We succeeded in the die-coating of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) water dispersions and regioregular poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) solution to fabricate thin films of these organic materials with extremely high speeds of 5 and 20 m/min, respectively. The film thicknesses were evaluated by cross-sectional scanning electron microscopy (SEM). The deviations of the film thicknesses from our target values were less than 5%. We fabricated Al/P3HT:PCBM/PEDOT:PSS/indium tin oxide (ITO)/poly(ethylene terephthalate) (PET) textiles as an example of an application of the method, and the photovoltaic characteristic of the devices was confirmed.
Characterization of Bar-Shaped Stacking Faults in 4H-SiC Epitaxial Layers by High-Resolution Transmission Electron Microscopy
Authors: Aoki Masahiko , Kawanowa Hitoshi , Feng Gan , Kimoto Tsunenobu
Published: May 2013

Stacking faults in 4H-SiC epitaxial layers were investigated by micro-photoluminescence (PL) mapping at room temperature and by transmission electron microscopy (TEM) observation. Stacking faults with a peak emission wavelength of 420 nm were identified by the PL measurements with a He–Cd laser of 325 nm excitation wavelength. The shape of the stacking faults was revealed to be bar-shape by the micro-PL intensity mapping at emission wavelength of 420 nm. The stacking sequences of the bar-shaped stacking faults were determined as (...2, 3, 2...), (...2, 3, 3, 3, 2...), and (...2, 3, 3, 3, 3, 3, 2...) in the Zhdanov's notation by high-resolution TEM.
Piezoelectric Properties of Fine-Grained Pb(Mg1/3Nb2/3)O3–Pb(Zr,Ti)O3–Bi(Zn1/2Ti1/2)O3Quaternary Solid Solution Ceramics
Authors: Yue Ruifang , Hou Xianbo , He Wenze , Yu Jian
Published: May 2013

On the basis of solid state reaction eutectic behavior between Pb(Mg1/3Nb2/3)O3–Pb(Zr,Ti)O3(PMN–PZT) and metastable perovskite-type Bi(Zn1/2Ti1/2)O3(BZT), perovskite-structured PMN–PZT–BZT quaternary solid solution piezoceramics with various compositions were experimentally demonstrated with an intrinsic low sintering temperature in the windows of 950–1050 °C. These fine-grained densified PMN–PZT–BZT ceramics were able to be poled sufficiently at room temperature through polarization–electric field hysteresis loop measurement, different from normal poling treatment with DC bias field at high temperature, which will simplify future device processing of monolithic multilayer piezoceramic transducers. A typical piezoelectric property of dielectric constant ε33T/ε0= 3471, piezoelectric constantd33= 480 pC/N, planar coupling coefficientkp= 0.41, thickness coupling coefficientkt= 0.50, mechanical quality factorQm= 68 and relaxor ferroelectric phase transition temperatureTm= 167 °C at 1 MHz was obtained for the fine-grained densified Pb0.96Sr0.04(Mg1/3Nb2/3)0.37Zr0.24Ti0.39O3+3%Bi(Zn0.5Ti0.5)O3+2%NiO ceramics sintered at 1020 °C, which is much promising to manufacture monolithic multilayer piezoelectric transducers with Ag95/Pd5 as inner electrode material.
Retrieval of Electronic Spectra of Charge Carriers in Organic Field-Effect Transistors from Charge Modulation Reflectance Spectra Distorted by Optical Interference
Authors: Miyata Kiyoshi , Ishino Yuta , Watanabe Kazuya , Miwa Kazumoto , Uemura Takafumi , Takeya Jun , Matsumoto Yoshiyasu
Published: May 2013

Charge modulation (CM) spectroscopy is useful for detecting and characterizing the electronic structure of charge carriers accumulated in organic field-effect transistors (OFETs). However, CM spectra are distorted by optical interference due to multiple reflections in OFETs particularly when reflection configurations are used. In this study, we demonstrated a method for retrieving the spectra of complex refractive indices of carriers from the distorted CM spectra by using a 4×4 matrix algorithm with general transition matrices. We tested this method by applying it to the CM spectra of a rubrene single-crystal FET measured at several incident angles of light. In spite of the strong distortion of the CM spectra, we could retrieve the spectrum of the imaginary part of refractive indices, which is similar to that observed in the transmission configuration. This method extends the applicability of CM spectroscopy to OFETs with opaque electrodes, where transmission configurations cannot possibly be applied.
Visual Cryptography Using Interference Color of High-Order Retarder Films
Authors: Harada Kenji , Yamaguchi Takenobu , Tsuchida Tomohiro , Sakai Daisuke
Published: May 2013

Visual cryptography is known as a method of sharing a secret image through several encrypted images. Conventional visual cryptography can display only monochrome images. We develop a multicolor visual encryption technique using the interference color of high-order retarder films. The encrypted films are composed of a polarizing film and retarder films. Retarder films exhibit an interference color upon sandwiching between two polarizing films. A prototype of a visual cryptography device using interference color is developed. Eight colors are represented by combining an encrypted image and a decoding mask composed of retarder films with various retardations.
Numerical Analysis on Birefringence of Photonic Crystal Fiber by Tuning Patterns and Infiltrating Materials of Innermost Air Holes
Authors: Sun Yuh-Sien , Chau Yuan-Fong Chou , Yang Wayne , Yeh Han-Hsuan , Wang Shinn-Fwu , Chu Yi , Jheng Ci-Yao , Sung Min-Jer
Published: May 2013

In this paper, we give a numerical analysis of a novel high-birefringence and low-confinement loss index-guiding photonic crystal fiber (PCF) using the finite element method by tuning patterns and filling the medium of innermost air holes. This PCF is composed of a solid silica core surrounded by six elliptical air holes and a cladding that consists of binary unit cells. The novelty of the proposed PCF structures is that the large elliptical air holes closest to the core have been rotated in different ways. Results show that the asymmetry in PCF cladding and the area of the PCF core are the key factors for determining the localization extent of the transverse mode. Modal birefringence values and confinement loss at the excitation wavelength of λ=1.55 µm can be easily achieved at a magnitude of the order of 10-2 and at less than 0.39 dB/km, respectively. From the viewpoint of numerical analysis, the effects of a material [with a refractive index <1 (i.e., a metamaterial)] on birefringence infiltrating into small (100–280 nm) innermost air holes, which are reported for the first time here, are also considered.
High-Frequency Capacitance–Voltage Characteristics of N-Type Metal–Oxide–Semiconductor Capacitor Based on Strained-Si/SiGe Architecture
Authors: Wang Bin , Zhang He-Ming , Hu Hui-Yong , Shu Bin , Zhang Yu-Ming , Song Jian-Jun
Published: May 2013

An accumulation metal–oxide–semiconductor (MOS) capacitor plays a key role in RF integrated circuits owing to its high linearity and independence of the operation frequency. The high-frequency capacitance–voltage (C–V) characteristics of a strained-Si/SiGe N-type MOS (NMOS) capacitor were studied to explain a measured behavior in which a “plateau” in the accumulation region was observed. By physically deriving the model of the NMOS capacitor, it was found that this plateau is substrate-doping-dependent and can also be strongly affected by the strained-Si layer thickness. The results from the model were compared with the experimental results and found to be in excellent agreement, indicating the validity of the model. The proposed model can provide valuable reference to the strained-Si device design and has been implemented in the software for extracting the parameter of a strained-Si MOSFET.
Effect of Channel Dopant Distribution on Effective Channel Length Extraction
Authors: Terada Kazuo , Sanai Kazuhiko , Matsuoka Shouhei , Tsuji Katsuhiro
Published: May 2013

The effect of the channel dopant distribution on the effective channel length (L
EFF) of metal–oxide–semiconductor field-effect transistors (MOSFETs) extracted by the channel resistance method (CRM) is studied using simple device models and experimental data. The simple device models explain how the channel dopant distribution affects extracted L
EFF. The measured data for various channel structures are qualitatively explained using those models. It is found that an accurate L
EFF can probably be extracted if plural samples having different dopant densities can be prepared.
Effect of Crystallinity on Residual Strain Distribution in Cast-Grown Si
Authors: Jiptner Karolin , Fukuzawa Masayuki , Miyamura Yoshiji , Harada Hirofumi , Sekiguchi Takashi
Published: May 2013

We report the correlation between the crystallinity of ingots grown by the directional solidification technique and the residual strain and dislocation distribution. It was found that mono-like ingots have a 20–25% higher averaged residual strain than multicrystalline Si ingots grown under the same conditions. However the existence of local high-strained areas, which were frequently found in multicrystalline Si ingots, is reduced in mono-like Si ingots. In addition, a reduction in dislocation density was observed. This effect and the decrease in local high strain could be attributed to the decrease in grain boundaries in the mono-like ingots.
Unstrained Epitaxial Zn-Substituted Fe3O4 Films for Ferromagnetic Field-Effect Transistors
Authors: Ichimura Takashi , Fujiwara Kohei , Kushizaki Takayoshi , Kanki Teruo , Tanaka Hidekazu
Published: May 2013

A field-effect transistor has been fabricated utilizing an epitaxial film of unstrained zinc-substituted magnetite (Fe3O4) as the active channel. A thin film of Fe2.5Zn0.5O4 was grown on a lattice-matched MgO(001) substrate by pulsed-laser deposition and covered by a parylene gate insulator to dope charge carriers by a field effect. The device showed a field-effect mobility of 1.2 ×10-2 cm2 V-1 s-1 at 300 K, which is higher by a factor of 15 than those of the devices with strained Fe2.5Zn0.5O4 channels on perovskite-type substrates. The enhanced response to the gate electric field is useful in exploring gate-tunable magnetism in magnetite.
Effects of Solution Stirring on the Growth of Bulk GaN Single Crystals by Na Flux Method
Authors: Murakami Kousuke , Matsuo Daisuke , Imabayashi Hiroki , Takazawa Hideo , Todoroki Yuma , Kitamoto Akira , Maruyama Mihoko , Imade Mamoru , Yoshimura Masashi , Mori Yusuke
Published: May 2013

Recently, we succeeded in fabricating centimeter-sized bulk gallium nitride (GaN) crystals with large dislocation-free areas on a GaN point seed. However, problems of polycrystal formation, skeletal growth, and low growth rate still remained. In this study, to suppress skeletal growth, polycrystals formation and increase the growth rate, we introduced two types of solution-stirring techniques – rotating stirring and swinging stirring – in the growth on point seeds by the Na flux method. We found that increasing the reversal frequency of the rotating stirring and increasing the rate of the swinging stirring increased the growth rate and suppressed the formation of polycrystals and skeletal growth. Moreover, the maximum c-direction growth rate of 46 µm/h was achieved without the formation of polycrystals and skeletal growth. We conclude that solution stirring may be an effective technique for fabricating high-quality large bulk GaN crystals.
Numerical Simulation of Heat and Fluid Flow in Ammonothermal GaN Bulk Crystal Growth Process
Authors: Masuda Yoshio , Suzuki Akira , Ishiguro Tohru , Yokoyama Chiaki
Published: May 2013

A numerical simulation of an ammonothermal process for growing GaN bulk single crystals has been performed. The autoclave and growing crystal are assumed to be axisymmetric and the raw material is assumed to be a porous medium. Heat transfer by natural convection is discussed in terms of the open-space ratio of the baffle and the height of the crystals. Simulation results show that a larger open-space ratio, at least 30%, is better for the crystal growth from the viewpoints of average surface temperature and flow direction.
GaN Overgrowth on Thermally Etched Nanoporous GaN Template
Authors: Miao Cao , Honda Yoshio , Yamaguchi Masahito , Amano Hiroshi
Published: May 2013

A thermal-etching process for fabricating nanoporous GaN templates in a metalorganic vapor phase epitaxy (MOVPE) reactor was proposed. Such nanoporous templates exhibited nearly complete strain relaxation and considerably increased photoluminescence (PL) intensity. The threading dislocation density (TDD) after overgrowth was reduced from 3 ×109 to 4 ×108 cm-2 for the template with poor quality, whereas little improvement was observed for the high-quality template (TDD, 4 ×108 cm-2). Multiple quantum wells (MQWs) grown on a nanoporous template fabricated from the high-quality GaN template were used to assess the effect on LED performance. The PL intensity of the sample with a nanoporous structure showed a twofold increase in PL intensity compared with the control sample.
Effects of Growth Temperature on Structural and Electrical Properties of InAlN/GaN Heterostructures Grown by Pulsed Metal Organic Chemical Vapor Deposition on c-Plane Sapphire
Authors: Xue JunShuai , Zhang JinCheng , Hao Yue
Published: May 2013

The authors report the effects of growth temperature on the structural and electrical properties of InAlN/GaN heterostructures, which were grown onc-plane sapphire substrates by pulsed metal organic chemical vapor deposition (PMOCVD). High resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) measurements indicate that the quality of InAlN barrier is strongly dependent on the growth temperature. It is observed that the indium composition and surface root-mean-square (rms) roughness value of InAlN barrier decrease with increasing the growth temperature, and a nearly lattice-matched InAlN/GaN heterostructure with a smooth surface is obtained at 710 °C. As a consequence, the variation of structural properties of InAlN barrier influences the electrical properties of InAlN/GaN heterostructures, and high electron mobility in excess of 1400 cm2V-1s-1is achieved at an optimized growth temperature window of InAlN barrier layer between 710 and 730 °C.
Control of Thickness and Composition Variation of AlGaN/GaN on 6- and 8-in. Substrates Using Multiwafer High-Growth-Rate Metal Organic Chemical Vapor Deposition Tool
Authors: Yano Yoshiki , Tokunaga Hiroki , Shimamura Hayato , Yamaoka Yuya , Ubukata Akinori , Tabuchi Toshiya , Matsumoto Koh
Published: May 2013

It is difficult to control the surface temperature gradient over a bowing GaN on a large-diameter silicon substrate by metal organic chemical vapor deposition (MOCVD) because the wafer bows convexly to store compressive strain during growth. In an attempt to grow uniform AlGaN/GaN on 6-in. (6'') silicon substrates using a 7×6'' reactor, we described in this paper the control of the surface temperature gradient over the wafer and the mass transport at the edge of the wafer. We attempted to grow Al0.23GaN/AlN/GaN/SLS/Al0.5GaN/AlN on six 8-in. (8'') silicon substrates using a 6×8'' reactor. The standard deviations of total thickness were less than 2.0% on wafer and 0.31% wafer to wafer. The growth rate of strained-layer superlattice (SLS) was as high as 2.8 µm/h. The typical electron mobility was 1670 cm2·V-1·s-1 at a sheet carrier density of 1.11×1013 cm-2.
Temperature-Dependence of Exciton Radiative Recombination in (Al,Ga)N/GaN Quantum Wells Grown on a-Plane GaN Substrates
Authors: Corfdir Pierre , Dussaigne Amélie , Teisseyre Henryk , Suski Tadeusz , Grzegory Izabella , Lefebvre Pierre , Giraud Etienne , Shahmohammadi Mehran , Phillips Richard T. , Ganiere Jean-Daniel , Grandjean Nicolas , Deveaud Benoît
Published: May 2013

This article presents the dynamics of excitons ina-plane (Al,Ga)N/GaN single quantum wells of various thicknesses grown on bulk GaN substrates. For all quantum well samples, recombination is observed to be predominantly radiative in the low-temperature range. At higher temperatures, the escape of charge carriers from the quantum well to the (Al,Ga)N barriers is accompanied by a reduction in internal quantum efficiency. Based on the temperature-dependence of time-resolved photoluminescence experiments, we also show how the local disorder affects the exciton radiative lifetime at low temperature and the exciton non-radiative lifetime at high temperature.
Theoretical Investigation of the Effect of Growth Orientation on Indium Incorporation Efficiency during InGaN Thin Film Growth by Metal–Organic Vapor Phase Epitaxy
Authors: Yayama Tomoe , Kangawa Yoshihiro , Kakimoto Koichi
Published: May 2013

The effect of growth orientation on In incorporation efficiency in InGaN films grown by metal–organic vapor phase epitaxy (MOVPE) is theoretically investigated. We propose a new theoretical model that explains the role of the surface N–H layer in In incorporation based on first-principles calculations. During III–nitride MOVPE, N-terminated reconstruction with N dangling bonds passivated by H is stable. A surface N–H layer that covers a group-III (In, Ga) atomic layer prevents In atoms from desorbing and being replaced by Ga atoms. In incorporation is therefore more efficient for higher N–H layer coverage and stability. To investigate this relationship, the enthalpy change for the decomposition of a N–H layer was calculated. This enthalpy change which depends on growth orientations is in good agreement with the experimental In content.
Improved Crystal Quality of (112̄2) Semi-Polar GaN Grown on A Nanorod Template
Authors: Xing Kun , Gong Yipin , Yu Xiang , Bai Jie , Wang Tao
Published: May 2013

(112̄2) semi-polar GaN with significantly improved crystal quality has been achieved by means of overgrowth on a (112̄2) semi-polar nanorod template. The nanorod template was fabricated on a standard (112̄2) semi-polar GaN layer on m-plane sapphire using a self-organized nickel nano-mask technique. In comparison with any conventional overgrowth technique, the nano-mask approach has demonstrated a very quick coalescence with a thickness of less than 1 µm. X-ray rocking curve measurements as a function of azimuth angle has shown a massive reduction in linewidth for our overgrown GaN. Transmission electron microscope measurements have confirmed a significant reduction in the dislocation density. Dramatic improvement in optical properties has been exhibited by photoluminescence (PL) measurements performed at room temperature, showing that the PL intensity from the band edge emission is 30 times higher than that of the standard semi-polar GaN on sapphire.
Investigation of the Effect of Oxygen on the Near-Surface Electron Accumulation in Nonpolar m-Plane (101̄0) InN Film by Hard X-ray Photoelectron Spectroscopy
Authors: Yang Anli , Yamashita Yoshiyuki , Yoshikawa Hideki , Yamaguchi Tomohiro , Imura Masataka , Kaneko Masamitsu , Ueda Shigenori , Sakata Osami , Nanishi Yasushi , Kobayashi Keisuke
Published: May 2013

A strong electron accumulation was observed in a near-surface region of an as-grown nonpolar m-plane (101̄0) InN film by analyzing the valence band hard X-ray photoelectron spectra as a function of the take-off angle. In addition, two oxygen chemical states correlated with electron carrier concentration were observed in the O 1s core-level spectra. By comparing with the oxygen concentration in a bulk-like region, the amount of oxygen drastically increased in a near-surface region, suggesting that the oxygen atoms in the near-surface region act as donors to contribute to the near-surface electron accumulation layer.
Injection-Activated Defect-Governed Recombination Rate in InN
Authors: Nargelas Saulius , Jarašiūnas Kęstutis , Vengris Mikas , Sakalauskas Egidijus , Yamaguchi Tomohiro , Nanishi Yasushi
Published: May 2013

Excess carrier dynamics was investigated by free-carrier absorption and light-induced transient grating techniques in InN layers with residual electron density varying from n
0=1.4×1018 to 4.7×1018 cm-3 in a wide excitation range (up to 1020 cm-3). Carrier lifetime τ decreased with injected carrier density ΔN≥n
0 and followed the same inverse relationship as on residual electron density τ∝[B(n
0+ΔN)]-1, thus confirming defect-related recombination mechanism. Its nonradiative origin was verified by τ(T) measurements and ascribed to injection-enhanced nonlinear recombination via defect-assisted Auger recombination with C
TAAR= B/N
T=(4.5±2)×10-28 cm6/s, assuming the defect density N
T being equal to electron density. Oxygen or hydrogen impurities are proposed as possible candidates for traps assisting in Auger process.
Role of Nonequivalent Atomic Step Edges in the Growth of InGaN by Plasma-Assisted Molecular Beam Epitaxy
Authors: Turski Henryk , Siekacz Marcin , Sawicka Marta , Wasilewski Zbig R. , Porowski Sylwester , Skierbiszewski Czeslaw
Published: May 2013

In this work, we study the growth mechanisms of InGaN in plasma-assisted molecular beam epitaxy (PAMBE). We demonstrate that for a metal-rich regime, in the range in which growth temperature limits the maximum In content, growth rate depends on gallium flux. This mechanism was investigated by the growth of InGaN/InGaN multi quantum wells (MQWs). We show that for constant growth temperature and nitrogen flux, the growth rate of MQWs decreases with decreasing gallium flux. We demonstrate also that at constant growth temperature and gallium flux, the In content in InGaN layers depends on nitrogen flux. We present an InGaN growth model that describes indium incorporation as a function of gallium and nitrogen fluxes, assuming that nonequivalent atomic step edges play an important role in indium incorporation mechanisms in PAMBE.
Effect of Supply Direction of Precursors on a-Plane GaN Low Angle Incidence Microchannel Epitaxy by Ammonia-Based Metal–Organic Molecular Beam Epitaxy
Authors: Uchiyama Shota , Lin Chia-Hung , Suzuki Yohei , Maruyama Takahiro , Naritsuka Shigeya
Published: May 2013

The effects of varying the supply direction of precursors on a-plane GaN low angle incidence microchannel epitaxy by ammonia-based metal–organic molecular beam epitaxy were studied. Lateral growth was found to be wider when precursors were supplied from the [0001] direction than from the [0001̄] direction. The (0001̄) face formed on the supply side suppressing lateral growth when the precursors were supplied from the [0001̄] direction, while lateral growth was enlarged by the intersurface diffusion of adatoms from the side to the top when supplied from the [0001] direction. A smaller cross-section of lateral growth was experimentally observed when the (0001̄) face appeared on the supply side, which suggests that the chemical character of the side also affects lateral growth. The offset angle of the opening is another important factor for determining the lateral growth, which largely affects the formation of facets on the sides and, consequently, the grown shape.
Effect of Stress Mitigating Layers on the Structural Properties of GaN Grown by Ammonia Molecular Beam Epitaxy on 100 mm Si(111)
Authors: Ravikiran Lingaparthi , Agrawal Manvi , Dharmarasu Nethaji , Radhakrishnan K.
Published: May 2013

The effect of AlGaN and AlN/GaN stress mitigating layers (SMLs) on the structural and morphological properties of GaN grown by ammonia molecular beam epitaxy (MBE) on 100 mm Si(111) has been studied. GaN grown on both AlGaN and AlN/GaN SMLs showed two-dimensional (2D) growth mode whereas the growth mode was three-dimensional (3D) for the GaN grown without the use of any SML. GaN on AlN/GaN SML showed lesser pit density on the surface, higher residual compressive strain and lower dislocation density compared to the GaN grown on AlGaN SML. Further enhancement in surface morphology with pit-free surface and reduced surface roughness was obtained by increasing the GaN growth rate from 0.22 to 0.70 µm/h in AlN/GaN SML structure.
GaN Nanowires Grown on a Graphite Substrate by Radio Frequency Molecular Beam Epitaxy
Authors: Nakagawa Shinta , Tabata Takuya , Honda Yoshio , Yamaguchi Masahito , Amano Hiroshi
Published: May 2013

Self-assembled GaN and InGaN nanowires (NWs) were directly grown on a highly oriented pyrolytic graphite (HOPG) substrate by radio frequency molecular beam epitaxy (RF-MBE). The GaN NWs grown on HOPG had a shorter length and larger diameter than those grown conventionally on a Si(111) substrate based on the analysis of scanning electron microscopy (SEM) images. They were also found to have good crystalline qualities with few stacking faults, as determined by scanning transmission electron microscopy (STEM) analysis. Photoluminescence (PL) measurements at room temperature indicated that the luminescence intensity of the GaN NWs on HOPG is stronger than that of NWs grown on a Si(111) substrate; however, the InGaN NWs on both substrates showed similar tendencies with respect to the shift of the luminescence wavelength as a function of the growth temperature. While In incorporation decreased as the growth temperature increased, the uniformity of the InGaN NW arrays improved rapidly.
Emission Wavelength Dependence of Internal Quantum Efficiency in InGaN Nanowires
Authors: Murotani Hideaki , Andoh Hiroya , Tsukamoto Takehiko , Sugiura Toko , Yamada Yoichi , Tabata Takuya , Honda Yoshio , Yamaguchi Masatoshi , Amano Hiroshi
Published: May 2013

The internal quantum efficiency (IQE) of InGaN nanowires with different emission wavelength of 485, 515, 555, and 580 nm has been studied by means of photoluminescence (PL) spectroscopy. It was found from the analysis of IQE as a function of excitation power density that the IQE was unchanged at about 100% under weak excitation conditions at low temperature. This indicated that the effects of nonradiative recombination processes were negligibly small at low temperature. Moreover, the IQE increased from 5 to 12% with increasing emission wavelength from 485 to 580 nm. Since the clear correlation between the IQE and the PL blue shift due to band filling effects of localized states was observed, the increase in the IQE reflected the increase in the effect of exciton localization with increasing indium composition.
Carrier Injections in Nitride-Based Light Emitting Diodes Including Two Active Regions with Mg-Doped Intermediate Layers
Authors: Matsui Kenjo , Yamashita Koji , Kaga Mitsuru , Morita Takatoshi , Suzuki Tomoyuki , Takeuch Tetsuya , Kamiyama Satoshi , Iwaya Motoaki , Akasaki Isamu
Published: May 2013

We achieved simultaneous two emissions from a single light emitting diode containing violet and blue GaInN/GaN quantum well active regions separated with an intermediate layer. By adjusting a thickness of a Mg-doped region in the intermediate layer, an intensity ratio between violet and blue emissions was changed, caused by different carrier distributions in the two active regions. The intensity ratio from two active regions was also changed by changing an amount of current injection. An unintentional Mg incorporation into the active region above the Mg-doped intermediate layer was observed, which is due to Mg memory effect.
Engineering the Lateral Optical Guiding in Gallium Nitride-Based Vertical-Cavity Surface-Emitting Laser Cavities to Reach the Lowest Threshold Gain
Authors: Hashemi Ehsan , Gustavsson Johan , Bengtsson Jörgen , Stattin Martin , Cosendey Gatien , Grandjean Nicolas , Haglund Åsa
Published: May 2013

In order to improve the current injection in GaN-based blue vertical-cavity surface-emitting lasers (VCSELs) a dielectric aperture is generally used in combination with an indium–tin-oxide (ITO) layer on the top intracavity p-contact layer. The most straightforward way to realize this introduces a depression of the structure near the optical axis and we show, by using a two-dimensional (2D) effective index method and a three-dimensional (3D) coupled-cavity beam propagation method, that this typically results in optically anti-guided structures with associated high optical losses and thus very high threshold gains. Remarkably, the threshold gain reduces with increased negative guiding, which is due to improved lateral confinement and reduction of lateral leakage. Still, moderately positively guided designs should be preferred to avoid the detrimental effect of lateral leakage and high diffraction loss. To ensure positive index guiding, we propose to planarize the structure or introduce an elevation near the optical axis by additional processing, with an associated reduction in threshold material gain from 6000 to 2000 cm-1 for the studied structures.
Metal-Free Graphene as Transparent Electrode for GaN-Based Light-Emitters
Authors: Stattin Martin , Rosa Cesar Lockhart de la , Sun Jie , Yurgens August , Haglund Åsa
Published: May 2013

Graphene contacts to p-GaN are considered as an alternative to indium–tin-oxide transparent electrodes in GaN based vertical-cavity surface-emitting lasers (VCSELs). Contact properties were investigated on light-emitting diode and p-GaN test structures, where dielectric apertures were used to eliminate the influence of the metal pads used to bias the contacts. Using single layer graphene we were able to operate light emitting diodes with current densities of 300 A/cm2. Addition of a second layer of graphene increased the maximum bias current to 1 kA/cm2. However, the contacts are non-linear and cannot withstand high current densities for a long time. The results are promising but further investigation and improvement is needed for graphene to be a viable alternative to indium–tin-oxide for blue VCSELs.
Red-Light-Emitting Diodes with Site-Selective Eu-Doped GaN Active Layer
Authors: Sekiguchi Hiroto , Takagi Yasufumi , Otani Tatsuki , Matsumura Ryota , Okada Hiroshi , Wakahara Akihiro
Published: May 2013

Mg codoping into Eu-doped GaN (GaN:Eu) changed the dominant optical site and increased the photoluminescence (PL) intensity at room temperature (RT). From the ratio of PL integrated intensity at 25 K to that at 300 K, PL efficiency of the GaN:Eu,Mg layer was evaluated to be as high as 77%. On the basis of this experiment, GaN:Eu-based LEDs grown by NH3 MBE were fabricated. Clear rectification characteristics with a turn-on voltage of 3.2 V were observed and a pure red emission was observed by the naked eye at RT. For the electroluminescence (EL) spectra, two predominant peaks of higher-efficiency optical sites A and C were selectively enhanced and the EL intensity was improved. This result suggests that GaN:Eu was very effective for realizing red-light-emitting devices using the nitride semiconductor.
Positron Annihilation Spectroscopy on Nitride-Based Semiconductors
Authors: Uedono Akira , Ishibashi Shoji , Oshima Nagayasu , Suzuki Ryoichi
Published: May 2013

Positron annihilation is a nondestructive tool for investigating vacancy-type defects in materials. Detectable defects are monovacancies to vacancy clusters, and there is no restriction of sample temperature or conductivity. Using this technique, we studied native defects in (AlInGa)N grown by metalorganic vapor phase epitaxy and plasma-assisted molecular beam epitaxy. For In
x
Ga1-x
N, the defect concentration increased with increasing In composition x and reached a maximum at x = 0.44–0.56. The major defect species was identified as cation vacancies coupled with multiple nitrogen vacancies. For Al
x
Ga1-x
N, the vacancy-type defects started to be introduced at above x = 0.54 and their concentration increased with increasing x. The observed behavior of point defects was discussed in terms of the transition of the growth mode.