bluuebunny/crossref_metadata_2025 huggingface dataset:
Layer Transfer and Simultaneous Crystallization Technique for Amorphous Si Films with Midair Structure Induced by Near-Infrared Semiconductor Diode Laser Irradiation and Its Application to Thin-Film Transistor Fabrication
Authors: Sakaike Kohei , Kobayashi Yoshitaka , Nakamura Shogo , Hayashi Shohei , Akazawa Muneki , Morisaki Seiji , Ikeda Mitsuhisa , Higashi Seiichiro
Published: May 2013

A novel layer transfer and simultaneous crystallization of amorphous silicon (a-Si) films induced by near-infrared semiconductor-diode-laser (SDL) irradiation has been investigated. The a-Si films supported by narrow quartz columns on a starting quartz substrate and a counter substrate [glass and poly(ethylene terephthalate)] were in face-to-face contact, and an SDL irradiated the a-Si films with midair structure. After SDL irradiation, the Si films were completely transferred and crystallized simultaneously on the counter substrates. In-situ monitoring revealed that the layer transfer took place either in the solid phase or the liquid phase followed by phase transformation in the cooling period. High performance polycrystalline Si thin-film transistors were successfully fabricated on the transferred Si films, which showed a high on/off ratio of more than 105and a field-effect mobility as high as 268 cm2V-1s-1.
Fabrication of Transparent CuCrO2:Mg/ZnO p–n Junctions Prepared by Magnetron Sputtering on an Indium Tin Oxide Glass Substrate
Authors: Chen Li-Fong , Wang Yung-Po , Chiu Te-Wei , Shih Wen-Ching , Wu Mu-Shiang
Published: May 2013

Transparent p–n junctions composed of zinc oxide and magnesium-doped copper–chromium oxide thin films were prepared using radio-frequency (RF) magnetron sputtering deposition on indium–tin oxide glass substrates. The temperature of the substrate during deposition was varied to examine differences in the diode characteristics of the current–voltage response effect. The crystalline structure of the diode films was verified using X-ray diffraction (XRD) analysis. The ratio of the forward current to the reverse current reached 85.9 in the range of +4 to -4 V at a deposition temperature of 450 °C. The p–n junction diode film had an optical transparency above 75% for wavelengths in the visible range.
Investigation of NOx Reduction by Low Temperature Oxidation Using Ozone Produced by Dielectric Barrier Discharge
Authors: Stamate Eugen , Irimiea Cornelia , Salewski Mirko
Published: May 2013

NO
x
reduction by low temperature oxidation using ozone produced by a dielectric barrier discharge generator is investigated for different process parameters in a 6 m long reactor in serpentine arrangement using synthetic dry flue gas with NO
x
levels below 500 ppm, flows up to 50 slm and temperatures up to 80 °C. The role of different mixing schemes and the impact of a steep temperature gradient are also taken into consideration. The process chemistry is monitored by Fourier transform infrared spectroscopy, chemiluminescence and absorption spectroscopy. The kinetic mechanism during the mixing in a cross flow configuration is investigated using three-dimensional simulations.
Performance of Integrated Cu Gap-Filling Process with Chemical Vapor Deposition Cobalt Liner
Authors: Kokaze Yutaka , Kodaira Shuji , Endo Youhei , Hamaguchi Junichi , Harada Masamichi , Kumamoto Shouichirou , Sakamoto Yuta , Higuchi Yasushi
Published: May 2013

Cu interconnects are used in semiconductor devices and their dimensions are downscaled markedly. Cu interconnects are fabricated by a damascene process, and it becomes difficult to fill Cu into trenches and vias structures by electroplating below the 20 nm feature size. We evaluated the process integration for Cu interconnects using a Co wetting layer by chemical vapor deposition (CVD), a Cu seed by magnetic-field-assisted ionized sputtering (MFIS) and a Cu reflow technique. The properties of a CVD-Co film, such as composition, resistivity, step coverage, and adhesion between Cu and Co, were investigated. By using CVD-Co as the wetting layer, the properties of Cu gap filling in a trench structure were improved, and the filling of Cu into a 14-nm-wide trench structure was achieved.
A New Copper Alloy Film for Barrierless Si Metallization and Solder Bump Flip-Chip Application
Authors: Lin Chon-Hsin
Published: May 2013

In this study, a copper alloy, Cu(MnN
x
), film is developed by cosputtering Cu and Mn on a barrierless Si substrate within an Ar/N2 gas atmosphere. The resulting alloy film exhibits good thermal stability and adhesion to the substrate with no noticeable interactions between the film and the substrate after annealing at 700 °C for 1 h, indicating that the film is thermally stable. The alloy film shall be able to replace both the wetting and diffusion layers for the flip-chip solder joints in conventional under bump metallurgy to reduce the manufacturing cost. We also observe that the Cu(MnN
x
) alloy exhibits a solder ability comparable to that of pure Cu and a dissolution rate lower than that of pure Cu by at least one order of magnitude. The alloy's consumption rate is comparable to that of Ni, rendering the alloy a candidate material in both barrierless Si metallization and solder bump flip-chip application.
Determination of Current Density Suppression Ability of Poly(ethylene glycol) during Copper Electrodeposition by an Electrochemical Analysis with a Microfluidic Device and an Electrochemical Quartz Crystal Microbalance
Authors: Saito Takeyasu , Tsujimoto Yuichi , Miyamoto Yutaka , Okamoto Naoki , Kondo Kazuo
Published: May 2013

The adsorption behaviour of poly(ethylene glycol) (PEG) as an additive during Cu electrodeposition was investigated using a microfluidic device. First, the current density (i) transition curves were measured by rapid exchange from the base electrolyte to electrolytes with different concentrations of additive PEG. Then, the effective surface coverage ratio (θEFF) of the electrodes by PEG was obtained. Equations relating θEFF and the PEG adsorption rate constant (k
a) as a function of c
PEG (or PEG flux, u·c
PEG) were determined from the PEG concentration (c
PEG) and average flow velocity of the electrolyte (u) dependency. Finally, the amount of increase the weight on the electrode (Δm) by PEG for different c
PEG was measured using a flow cell type electrochemical quartz crystal microbalance (EQCM), and then used to calculate θEFF, assuming the adsorbed PEG molecules are spherical. Results revealed a strong correlation between the Δm and a decrease in i.
Room-Temperature Formation of a ZnO-Based Adhesion Layer for Nanoprecision Cu/Glass Metallization
Authors: Teraoka Akira , Watanabe Mitsuhiro , Nabetani Yoichi , Kondoh Eiichi
Published: May 2013

This study demonstrated that a thin ZnO layer functions as a strong adhesion layer between Cu and glass, even when Cu films are formed near room temperature. The adhesion strength was studied with a scratch tester and the films and interfaces were characterized by scanning transmission electron microscopy. The origin of the high adhesion strength was discussed in terms of the presence of an extremely thin (approximately 10 nm) intermixing layer consisting of Cu, Pd, Zn, O, and Si.
Low-Resistance Metal Contacts for Nanocarbon/Cobalt Interconnects
Authors: Ueno Kazuyoshi , Takagi Masashi , Yano Hiroaki , Wakui Taichi , Yamazaki Yuichi , Sakuma Naoshi , Kajita Akihiro , Sakai Tadashi
Published: May 2013

Low-resistance metal contacts for CVD-nanocarbon (NC)/cobalt (Co) interconnects have been investigated among contact metals such as Ni, Ti, Au, and Cu. Contact resistivity was independent of contact area owing to low-resistance NC/Co interconnect structure. The lowest contact resistivity and superior adhesion were obtained from Ni. Although the factors for the low contact resistivity were not clear enough from the comparison of work-function difference and adhesion strength for the contact metals, Ni is a promising low-resistivity contact metal for CVD-NC interconnects in the future.
Superlattice Phase Change Memory Fabrication Process for Back End of Line Devices
Authors: Ohyanagi Takasumi , Takaura Norikatsu , Kitamura Masahito , Tai Mitsuharu , Kinoshita Masaharu , Akita Kenichi , Morikawa Takahiro , Tominaga Junji
Published: May 2013

The superlattice film with the periodical thin film layers of Sb2Te3/GeTe used as a phase change memory was studied for deposition in the crystal phase. We successfully fabricated the superlattice structure with the sputtering temperature of 200 °C. Moreover, the pillar structure with the size of 70 nm was dry-etched using a HBr/Ar gas mixture.
Low Threshold Current Density Operation of a GaInAsP/Si Hybrid Laser Prepared by Low-Temperature N2 Plasma Activated Bonding
Authors: Hayashi Yusuke , Osabe Ryo , Fukuda Keita , Atsumi Yuki , Kang JoonHyun , Nishiyama Nobuhiko , Arai Shigehisa
Published: May 2013

The integration of III–V active devices on a Si platform utilizing direct bonding is an attractive way to realize large-scale photonic integrated circuits. Because plasma activated bonding (PAB) is expected to have a higher bonding strength at a lower heating temperature as compared to conventional bonding methods, PAB is attractive for the reduction of non-radiative recombination centers in the III–V active region caused by thermal expansion during the bonding process. A GaInAsP/Si hybrid laser was fabricated with low-temperature (150 °C) N2 PAB, and a low threshold current density of 850 A/cm2 (170 A/cm2 per quantum well) was obtained.
Novel 0.50(Bi1-xLax)FeO3–0.35PbTiO3–0.15Bi(Zn1/2Ti1/2)O3Piezoelectric Ceramics for High Temperature High Frequency Filters
Authors: Hou Xianbo , Yu Jian
Published: May 2013

Perovskite-structured 0.50(Bi1-xLax)FeO3–0.35PbTiO3–0.15Bi(Zn1/2Ti1/2)O3ceramics withx= 0.0–0.2 were fabricated with traditional solid state reaction method. Their crystallographic structure, dielectric and piezoelectric properties were investigated with various La contents. It was observed that a structural phase transition undergoes from tetragonal to coexistent tetragonal and rhombohedral phase whenx≥0.05 and that the tetragonality ofc/aratio and Curie temperature decrease but piezoelectric properties increase with increasing La content. The enhanced piezoelectric performance with La substitution was attributed to the lattice structural changes from the tetragonal phase into the coexistent tetragonal and rhombohedral phase accompanying with tetragonality decreasing. For the Pb0.35Bi0.625La0.025(Ti0.425Zn0.075Fe0.5)O3ceramics closely at the structural phase boundary poled at 140 °C with 5 kV/mm DC electric field, a good piezoelectric property ofd33= 43 pC/N, ε33T/ε0= 367 andTC= 497 °C was obtained, which is comparable with the commercial Matsushita lead titanate (MLT) piezoelectric ceramics withd33= 51 pC/N, ε33T/ε0= 170 andTC= 495 °C and much promising for application in the fields of high temperature high frequency piezoelectric ceramic filters.
Electronic States of Trivalent Praseodymium Ion Doped in 20Al(PO3)3–80LiF Glass
Authors: Tsuboi Mizuki , Takeda Kohei , Nakazato Tomoharu , Kono Masahiro , Yamanoi Kohei , Cadatal-Raduban Marilou , Sakai Kohei , Nishi Ryosuke , Minami Yuki , Luong Mui Viet , Arikawa Yasunobu , Shimizu Toshihiko , Sarukurua Nobuhiko , Norimatsu Takayoshi , Nakai Mitsuo , Azechi Hiroshi , Murata Takahiro , Fujino Shigeru , Yoshida Hideki , Yoshikawa Akira , Sato Nakahiro , Kan Hirofumi , Kamata Kei
Published: May 2013

We investigate the photoluminescence (PL) and photoluminescence excitation (PLE) spectra of 20Al(PO3)3–80LiF+Pr glass (APLF+Pr) and Pr3+-doped LiCaAlF6 crystal (Pr:LiCAF) in order to determine the electronic states of Pr3+ in APLF glass host and to improve APLF+Pr scintillation properties. Ultraviolet (UV) emission bands at around 250 and 340 nm were observed from both materials and these can be ascribed to 4f5d→4f2 transitions in Pr3+. Emission at around 400 nm was also obtained and is principally attributed to 1S0→4f2 transition. Difference in the emission profiles of these two materials was found to be due to the extent of the 5d band and its position relative to the 1S0 state. Increasing the concentration of Pr3+ up to 2 mol % was found to improve UV emission ratio due to the faster cross-relaxation of 4f states. This could improve the quantum efficiency of APLF+Pr as a neutron scintillator for scattered-neutron diagnostics in laser fusion research.
Three-Terminal Hanle Signals in Schottky Tunnel Junctions with Co2FeAl0.5Si0.5 Full-Heusler Alloy Electrodes Deposited at Various Temperatures
Authors: Saito Tatsuya , Tezuka Nobuki , Matsuura Masashi , Sugimoto Satoshi
Published: May 2013

We investigated the crystal structures, electrical transport properties, and three-terminal (3T) Hanle signals of Co2FeAl0.5Si0.5 (CFAS)/n-GaAs Schottky tunnel junctions fabricated with different deposition temperature of the CFAS (T
CFAS). CFAS thin films were deposited on the n-GaAs at T
CFAS ranging from room temperature to 300 °C, and 3T-Hanle signals were observed for all CFAS/n-GaAs junctions. Although the degree of structural ordering in the CFAS electrodes decreased and the rectifying characteristic disappeared as T
CFAS decreased, the spin resistance area products (ΔRA) increased and the estimated spin relaxation time (τ) decreased monotonically with decreasing T
CFAS. Moreover, the bias voltage dependence of ΔRA and τ became larger and smaller with decreasing T
CFAS, respectively.
Instantaneous Generation of Many Flaked Particles by Impulsive Force of Electric Field Stress Acting on Inner Wall of Mass-Production Plasma Etching Equipment
Authors: Kasashima Yuji , Nabeoka Natsuko , Uesugi Fumihiko
Published: May 2013

To elucidate the mechanism of instantaneous generation of many flaked particles in plasma etching equipment, we investigate the relationship between the generation of flaked particles from deposited films (consisting of etching reaction products on the ground electrode) and the plasma stability under mass-production conditions. Many particles are observed with our particle monitoring system when plasma instability occurs. The generation of such flaked particles correlates well with the occurrence of a large, rapid change in floating potential on the chamber wall. Our results indicate that many flaked particles from films deposited on a ground electrode are generated by electric field stress acting instantaneously and working as an impulsive force.
Statistical Prediction of Micro-Arcing in Radio-Frequency Plasmas for Manufacture of Semiconductor Device
Authors: Jun Hyun-Su
Published: May 2013

A hard-arcing precursor that causes charging damage to semiconductor devices was found. The micro-arcing that occurs during the plasma etch process was statistically classified based on the optical intensity variation by using high-speed optical sensing. According to the level of effect on semiconductor device failure, the micro-arcing was categorized into soft-arcing I (8–11σ), soft-arcing II (11–15σ), and hard-arcing (over 15σ). Experimental results suggest that a sufficiently large increase in soft-arcing is directly associated with the occurrence of hard-arcing. By using this characteristic and based on a Gaussian distribution, hard-arcing was statistically predicted within 12 wafers. A mathematical model is also proposed to explain the same. This is the first control system capable of predicting and effectively restraining micro-arcing during the plasma process.
Calibration Technique Using Nonlinear Region in Cantilever Magnetometry Experiments and Presence of Universal Curve
Authors: Torizuka Kiyoshi , Tajima Hiroyuki , Yoshida Gosuke , Inoue Munenori
Published: May 2013

We have presented a calibration technique for commercially available atomic force microscopy (AFM) cantilevers used in torque magnetometry experiments. The absolute values (J/rad) of the torque can be derived against the output signal, which is the change in piezoresistivity due to the deflection of the cantilever beam. The calibration has been performed using the susceptibility of a graphite plane. The linearity between the output signal and the torque is confirmed up to ±1×10-8 J/rad of the torque. More importantly, since the nonlinear response of the cantilever is reproducible, we have also utilized the nonlinear region, so that the calibration range has been pushed up to ±4 ×10-8 J/rad. In the nonlinear range, an important finding is that any curve (torque vs output signal curve) that is cantilever-dependent reduces to a single universal curve, after multiplying an appropriate factor. This factor is cantilever-dependent, but can be derived by rotating the sample-mounted cantilever in a zero magnetic field. We have also proposed a simple model regarding the presence of this universal curve.
Effect of Biased Disc on Brightness of Highly Charged Uranium Ions from RIKEN 28 GHz Superconducting Electron Cyclotron Resonance Ion Source
Authors: Ozeki Kazutaka , Higurashi Yoshihide , Ohnishi Jun-ichi , Nakagawa Takahide
Published: May 2013

The emittance and beam intensity of highly charged heavy ions were measured as a function of the negative voltage of a biased disc. We observed that the brightness of the highly charged uranium ion beam generated by the RIKEN 28 GHz superconducting electron cyclotron resonance ion source was strongly influenced by the bias voltage.
High Quality, Low Cost Ammonothermal Bulk GaN Substrates
Authors: Ehrentraut Dirk , Pakalapati Rajeev T. , Kamber Derrick S. , Jiang Wenkan , Pocius Douglas W. , Downey Bradley C. , McLaurin Melvin , D'Evelyn Mark P.
Published: May 2013

Ammonothermal GaN growth using a novel apparatus has been performed on c-plane, m-plane, and semipolar seed crystals with diameters between 5 mm and 2 in. to thicknesses of 0.5–3 mm. The highest growth rates are greater than 40 µm/h and rates in the 10–30 µm/h range are routinely observed for all orientations. These values are 5–100× larger than those achieved by conventional ammonothermal GaN growth. The crystals have been characterized by X-ray diffraction rocking-curve (XRC) analysis, optical and scanning electron microscopy (SEM), cathodoluminescence (CL), optical spectroscopy, and capacitance–voltage measurements. The crystallinity of the grown crystals is similar to or better than that of the seed crystals, with FWHM values of about 20–100 arcsec and dislocation densities of 1 ×105–5 ×106 cm-2. Dislocation densities below 104 cm-2 are observed in laterally-grown crystals. Epitaxial InGaN quantum well structures have been successfully grown on ammonothermal wafers.
Development and Progress in Bulk c-Plane AlN Single-Crystalline Template Growth for Large-Area Native Seeds
Authors: Sumathi R. Radhakrishnan , Gille Peter
Published: May 2013

28-mm diameter free-standing AlN substrates were obtained from single crystalline templates grown hetero-epitaxially on (0001) SiC substrates by the sublimation method. The grown template crystals have fairly high structural quality with X-ray rocking curve FWHM values of 120 and 200 arcsec for symmetric and asymmetric reflections, respectively and an average etch pit density of about 5×105 cm-2. In Raman spectroscopy, the E2(high) phonon mode peak FWHM is 18 cm-1 and its position shift shows a very low tensile strain of ∼1.5×10-4 in the crystals. The presence of Si and C impurity-related local vibrational modes is observed. These impurities might be responsible for lowering the optical absorption band edge to 4.3 eV. Homo-epitaxial growth of 5-mm-thick bulk crystals, using 10 mm diameter seeds prepared from these templates demonstrates their suitability as native seeds for further growth.
Structural Analysis of Carbon-Added Na–Ga Melts in Na Flux GaN Growth by First-Principles Calculation
Authors: Kawamura Takahiro , Imabayashi Hiroki , Yamada Yuji , Maruyama Mihoko , Imade Mamoru , Yoshimura Masashi , Mori Yusuke , Morikawa Yoshitada
Published: May 2013

We investigated the fundamentals of the effect of C addition on Na flux GaN growth by first-principles calculation. We simulated C-added Na–Ga melts using molecular dynamics (MD) simulations to examine the local melt structure around a N atom. We also calculated C–N bond energy using constrained MD simulations. Results show that a N atom bonded to a C atom and there were no Ga atoms around the N atom because C–N bond energy was larger than Ga–N bond energy. This is the reason for the suppression of heterogeneous nucleation by C addition. It was also found that the C–N bond energy was affected by surrounding Ga atoms and that the C–N atomic distance increased with the Ga coordination number around the N atom.
Defect Reduction in Semi-Polar (112̄2) Gallium Nitride Grown Using Epitaxial Lateral Overgrowth
Authors: Zhu Tongtong , Sutherland Danny , Badcock Tom J. , Hao Rui , Moram Michelle A. , Dawson Philip , Kappers Menno J. , Oliver Rachel A.
Published: May 2013

We report on the characterization of semi-polar (112̄2) gallium nitride (GaN) films grown onm-plane (11̄00) sapphire by an asymmetric epitaxial lateral overgrowth (ELOG) process first reported by de Mierry et al. [Appl. Phys. Lett. 94 (2009) 191903]. The overgrowth conditions were engineered to greatly enhance the growth rate along the [0001] direction, which combined with the inclination of the [0001] axis from the film surface at ∼32°, allowing a low defect density wing to overgrow the highly defective window region and thus eliminating basal plane stacking faults (BSFs). By correlating cross-sectional transmission electron microscopy and cathodoluminescence data, we confirm that BSFs and dislocations are terminated by the coalescence boundary formed as a result of the overgrowth anisotropy. Low temperature photoluminescence spectra reveal a strong GaN emission at 3.485 eV associated with donor-bound exciton recombination and very small BSF-related emission at 3.425 eV. The intensity ratio between the GaN bound exciton and the BSF emission is ∼220, which is four orders of magnitude greater than that of the semi-polar seed layer. Scanning capacitance microscopy data showed that almost the entire film is unintentionally n-type. The impurity incorporation rate is strongly dependent on which crystallographic planes are present during different stages of the ELOG process.
GaN Lateral Overgrowth by Hydride Vapor Phase Epitaxy through Nanometer-Size Channels Fabricated with Nanoimprint Lithography
Authors: Usui Akira , Matsueda Toshiharu , Goto Hiroki , Sunakawa Haruo , Fujiyama Yasuharu , Ishihara Yujiro , Okada Akiko , Shoji Shuichi , Yamaguchi Atsushi A. , Nishihara Hiromi , Shinohara Hidetoshi , Goto Hiroshi , Mizuno Jun
Published: May 2013

Epitaxial lateral overgrowth (ELO) has been used for reducing the dislocation density to grow high-quality GaN crystals. In conventional ELO, micrometer-size channels formed on a mask material such as SiO2, where GaN growth starts, are generally used. In the present study, ELO through nanometer-size (50–80 nm) channels is investigated to improve the dislocation reduction ability. Channels are fabricated using nanoimprint lithography and dry etching. We demonstrate for the first time successful hydride vapor phase epitaxy (HVPE)-based GaN ELO growth through nanochannels. In the growth interface, distinct facet structures appear and coalescence between neighboring facets proceeds. The surface of a 20-µm-thick GaN layer becomes flat by the valleys between facet structures being buried. The dislocation density is shown to decrease to approximately 5×107 cm-2 for a 20-µm-thick GaN layer on sapphire. Photoluminescence measurements show a decay time of over 3 times longer than that of a conventional metalorganic chemical vapor deposition (MOCVD) template.
Modulation of Strain States in GaN Films by a Thin AlN/GaN Superlattice Interlayer Grown on Si(110) Substrates
Authors: Shen Xu-Qiang , Takahashi Tokio , Kawashima Hiroyuki , Ide Toshihide , Shimizu Mitsuaki , Okumura Hajime
Published: May 2013

The effect of a thin AlN/GaN superlattice structure (SLs) interlayer on the strain properties in GaN films grown on Si(110) substrates is investigated. By comparing the strain states in GaN films without the interlayer, it is found that the strain in GaN films can be modulated by the SLs interlayer, which can be converted from a tensile state to a compressive one. The realization of the compressive strain state in the GaN film results in the suppression of the crack generation in the thick GaN growth, which is a general problem in the GaN growth on Si substrates. Using this simple technique, we successfully grow a crack-free continuous GaN film exceeding 4 µm thick. Therefore, the SLs interlayer is a promising structure in growing crack-free thick GaN on the Si substrate for optic and electronic device applications.
Realization of Maskless Epitaxial Lateral Overgrowth of GaN on 3C-SiC/Si Substrates
Authors: Fang Hao , Takaya Yoshifumi , Miyake Hideto , Hiramatsu Kazumasa , Oku Hidehiko , Asamura Hidetoshi , Kawamura Keisuke
Published: May 2013

By virtue of the poor nucleation of GaN on 3C-SiC, a maskless epitaxial lateral overgrowth (ELO) of GaN was realized on 3C-SiC/Si substrates to improve crystalline quality. The mechanism of the maskless ELO process was investigated by observing surface morphologies at different growth steps. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) confirmed that the grain size of GaN crystallites was increased in the three-dimensional ELO. As a result, the stress in the GaN epilayer decreased with the smaller number of grain boundaries in the coalescence process. The luminescent property was also improved with a decrease in defect density.
A Simple Growth Method to Produce a-Plane GaN Thick Films by Hydride Vapor Phase Epitaxy
Authors: Wu Yin-Hao , Lee Chuo-Han , Chu Chung-Ming , Yeh Yen-Hsien , Chen Chan-Lin , Lee Wei-I
Published: May 2013

A-plane GaN was grown on r-plane sapphire using a two-step growth method by hydride vapor phase epitaxy (HVPE). In the first step, a-plane GaN formed triangular stripes along the m-direction ([1̄100] direction) at a low growth temperature. Then, increasing the growth temperature enhanced the lateral growth mode to coalesce a-plane GaN in the second step. There were triangular voids formed after growth. In this work, a new method was developed to produce the voids in the a-plane GaN film using the two-step growth method without optical lithography.
Effects of Nano- and Microscale SiO2 Masks on the Growth of a-Plane GaN Layers on r-Plane Sapphire
Authors: Son Ji-Su , Miao Cao , Honda Yoshio , Yamaguchi Masahito , Amano Hiroshi , Seo Yong Gon , Hwang Sung-Min , Baik Kwang Hyeon
Published: May 2013

We report on the combined effects of a-plane GaN layers on a nanoscale patterned insulator on an r-plane sapphire substrate and epitaxial lateral overgrowth (ELOG) techniques. The fully coalescent a-plane GaN layer using nano- and microscale SiO2 masks showed the formation of nano- and microscale voids on the masks, respectively. Atomic force microscopy (AFM) measurements revealed a surface roughness of 0.63 nm and a submicron pit density of ∼7.8 ×107 cm-2. Photoluminescence (PL) intensity was enhanced by a factor of 9.0 in comparison with that of a planar sample. Omega full-width at half-maximum (FWHM) values of the (112̄0) X-ray rocking curve along the c- and m-axes were 553 and 788 arcsec, respectively. A plan-view cathodoluminescence (CL) mapping image showed high luminescence intensity on the SiO2 masks.
Origins of Spectral Diffusion in the Micro-Photoluminescence of Single InGaN Quantum Dots
Authors: Reid Benjamin P. L. , Zhu Tongtong , Puchtler Timothy J. , Fletcher Luke J. , Chan Christopher C. S. , Oliver Rachel A. , Taylor Robert A.
Published: May 2013

We report on optical characterization of self-assembled InGaN quantum dots (QDs) grown on three GaN pseudo-substrates with differing threading dislocation densities. QD density is estimated via microphotoluminscence on a masked sample patterned with circular apertures, and appears to increase with dislocation density. A non-linear excitation technique is used to observe the sharp spectral lines characteristic of QD emission. Temporal variations of the wavelength of emission from single QDs are observed and attributed to spectral diffusion. The magnitude of these temporal variations is seen to increase with dislocation density, suggesting locally fluctuating electric fields due to charges captured by dislocations are responsible for the spectral diffusion in this system.
Crystalline-Structural Evaluations of Cubic AlN Thin Films Heteroepitaxially Grown on Sapphire (0001) by Pulsed Laser Deposition
Authors: Ueda Yūtaro , Daio Takeshi , Yoshida Tomohiro , Akamine Hiroshi , Tominaga Aki , Okajima Toshihiro , Yoshitake Tsuyoshi
Published: May 2013

Cubic β-AlN thin films with different thicknesses were grown on sapphire (0001) in nitrogen atmosphere by pulsed laser deposition with sintered AlN targets, and their film structures were evaluated by transmission electron microscopy (TEM) and X-ray diffraction (XRD). It was found that β-AlN layers with a lattice constant of 7.89 Å are epitaxially grown on sapphire (0001) with a relationship of βAlN(111)[111̄]∥Al2O3(0001)[11̄00] at film thicknesses of less than 20 nm, and at larger thicknesses, polycrystalline β-AlN grains are grown on the epitaxial β-AlN layers in the Stranski–Krastanov (SK) mode.
Stacking Faults and Luminescence Property of InGaN Nanowires
Authors: Tabata Takuya , Paek Jihyun , Honda Yoshio , Yamaguchi Masahito , Amano Hiroshi
Published: May 2013

InGaN nanowires (NWs) were grown on (111)Si substrate using radio-frequency plasma-assisted molecular beam epitaxy, and the density of the stacking faults (SFs) in the InGaN NWs was estimated. High-density SFs were observed in the scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) images of the InGaN NWs, and a few zincblende layers appeared in the wurtzite structure. When growth temperature increased, the density of the SFs in the InGaN NW, the photoluminescence (PL) peak wavelength, and the full width at half maximum (FWHM) of PL spectra decreased, whereas the integrated PL intensity increased. These results suggest that a high growth temperature is effective for decreasing the density of SFs in InGaN NWs, and InGaN NWs grown at high temperature have strong PL luminescence due to the low In composition and the corresponding low SFs density.
Effect of Silicon Doping on GaN Nanorods during Vapor–Liquid–Solid Growth
Authors: Ebaid Mohamed , Kang Jin-Ho , Lee June Key , Ryu Sang-Wan
Published: May 2013

High optical quality and reproducible Si-doped GaN nanorods (NRs) were grown by low pressure metal–organic chemical vapor deposition. Different fluxes of SiH4were introduced and at 2.7×10-9mol/min the optimized morphology was obtained. Clear improvement of GaN NRs morphology characterized by smooth side walls and straightness was achieved after Si-doping. Near-band edge (NBE) emission at 356.88 nm (3.474 eV) and small full width at half maximum (FWHM) of 27.3 meV, measured by room temperature photoluminescence, confirmed the high optical and crystalline qualities. For Si-doped GaN NRs, a small blue-shift of NBE emission peak was observed, which was attributed to the band-filling effects.
Growth of GaN Nanorods and Wires and Spectral Tuning of Whispering Gallery Modes in Tapered GaN Wires
Authors: Tessarek Christian , Dieker Christel , Spiecker Erdmann , Christiansen Silke
Published: May 2013

This paper reports on the growth of GaN nanorods and wires by metal–organic vapor phase epitaxy. Density, height and diameter are strongly influenced by the growth time. A deposition time of a few minutes leads to the formation of GaN nanorods. Increasing the deposition time up to 1 h yields wires with heights exceeding 47 µm. Transmission electron microscopy and convergent beam electron diffraction measurements are showing the presence of N- and Ga-polar GaN in a single nanorod. Cathodoluminescence measurements are performed showing the appearance of whispering gallery modes. Due to slight tapering of the wires the whispering gallery modes can be spectrally tuned by changing the position of the exposing electron beam at the sidewall facet of the rod.
Optical Properties of GaN Nanorods Containing a Single or Multiple InGaN Quantum Wells
Authors: Zhuang Yi D. , Lis Szymon , Bruckbauer Jochen , O'Kane Simon E. J. , Shields Philip A. , Edwards Paul R. , Sarma Jayanta , Martin Robert W. , Allsopp Duncan W. E.
Published: May 2013

Measurements of light emission from GaN nanorods of diameter between 80 and 350 nm, containing either a three-well multiple InGaN quantum well or a single quantum well, have been performed by photoluminescence (PL) and cathodoluminescence (CL) hyperspectral imaging. The PL underwent a Stark shift to the blue as the nanorod diameter was reduced, indicating substantial relaxation of the compressive strain in the quantum wells. The intensity of the nanorod emission per unit area can exceed that of the planar starting material. The CL measurements revealed that the wavelength of the quantum well emission varied with radial position in the nanorod. Simulations by a modal expansion method revealed that the light extraction efficiency varies with radial position and the variation is dependent on nanorod diameter. Finite difference time domain simulations showed that Bloch mode formation in the buffer layer below the nanorods impacts on the light extraction.
Influence of Carrier Lifetime, Transit Time, and Operation Voltages on the Photoresponse of Visible-Blind AlGaN Metal–Semiconductor–Metal Photodetectors
Authors: Schlegel Jessica , Brendel Moritz , Martens Martin , Knigge Andrea , Rass Jens , Einfeldt Sven , Brunner Frank , Weyers Markus , Kneissl Michael
Published: May 2013

We investigated the influence of lifetime and transit time of photogenerated carriers on the performance of visible-blind Al0.25Ga0.75N metal–semiconductor–metal photodetectors by a combination of experimental studies and numerical simulations. Good agreement between simulated and measured current–voltage (I–V) characteristics was achieved for several geometries of the interdigitated contact structure. Simulations of the external quantum efficiency (EQE) at low bias voltages showed that a long hole lifetime in the AlGaN absorption layer significantly influences the EQE due to the slow carrier transit in weak electric fields. At 1 V the EQE can be enhanced by a factor of 3 by increasing the hole lifetime from 10 ps to 1 ns. Reducing the electrode spacing from 10 to 1 µm as well as operating the device at higher voltages additionally increases the ratio between carrier lifetime and transit time, resulting in an enhancement of the EQE at a fixed carrier lifetime by one order of magnitude.
AlGaN-Based Light Emitting Diodes Using Self-Assembled GaN Quantum Dots for Ultraviolet Emission
Authors: Brault Julien , Damilano Benjamin , Vinter Borge , Vennéguès Philippe , Leroux Mathieu , Kahouli Abdelkarim , Massies Jean
Published: May 2013

Self-assembled GaN quantum dots (QDs) grown on Al0.5Ga0.5N have been used as the active region of light emitting diodes (LEDs). The LED emission wavelength exhibits a strong shift towards higher energies with increasing current density, which allows obtaining an emission in the UV range (down to 375 nm) above 100 A/cm2. Together with this shift, a reduction of the electroluminescence (EL) peak full width at half maximum (FWHM) is observed. These features are a consequence of the quantum confined Stark effect caused by the built-in electric field in the heterostructure. At larger current densities, an opposite behavior (i.e., an increase of the FWHM) is observed concomitant with the appearance of an additional peak on the EL high energy side. This characteristic has been confronted with calculations and attributed to a transition between the lowest electron state and the first excited hole state in the QDs.
Quasi-Whispering Gallery Mode Lasing Action in an Asymmetric Hexagonal GaN Microdisk
Authors: Kouno Tetsuya , Sakai Masaru , Kishino Katsumi , Hara Kazuhiko
Published: May 2013

The optical properties of an asymmetric hexagonal GaN microdisk, fabricated via crystal growth by radio-frequency plasma-assisted molecular beam epitaxy (rf-MBE), were investigated by experimental and theoretical methods to clarify the contribution of the light confinement modes of quasi-whispering gallery modes (QWGMs). Under the optically pumped condition, a lasing action was observed from the asymmetric GaN microdisk, indicating that there is a resonant scheme of QWGMs in such a microcavity of a GaN microdisk. In addition, the analysis of the light response of hexagonal GaN microdisk models by a three-dimensional finite difference time-domain method (3D-FDTD) indicates that the QWGMs preferentially contribute to a lasing action even in a microcavity with a regular hexagonal configuration with side lengths of 1 to 2 µm. The results of the experiment and the numerical analysis strongly indicate that it is important to take not only the WGM but also the QWGMs into account to clarify the optical responses of resonant modes in a hexagonal microdisk configuration.
Concentrating Properties of Nitride-Based Solar Cells Using Different Electrodes
Authors: Mori Mikiko , Kondo Shinichiro , Yamamoto Shota , Nakao Tatsuro , Iwaya Motoaki , Takeuchi Tetsuya , Kamiyama Satoshi , Akasaki Isamu , Amano Hiroshi
Published: May 2013

We investigated the concentration properties of GaInN-based solar cells using different window electrodes. A significant difference was observed between the concentrating properties of the window electrode structures. It was clearly found that indium tin oxide (ITO) is suitable as an electrode. The short-circuit current density, open-circuit voltage, fill factor, and energy conversion efficiency of nitride-based solar cells fabricated using an ITO electrode were 7.1×102 mA/cm2, 2.2 V, 79%, and 4.0%, respectively, under an air mass filter of 1.5G at 300 suns and at room temperature.
GaN-Based Vertical Cavities with All Dielectric Reflectors by Epitaxial Lateral Overgrowth
Authors: Okur Serdal , Shimada Ryoko , Zhang Fan , Hafiz Shopan Din Ahmad , Lee Jaesoong , Avrutin Vitaliy , Morkoç Hadis , Franke Alexander , Bertram Frank , Christen Juergen , Özgür Ümit
Published: May 2013

GaN-based vertical cavities with all dielectric top and bottom distributed Bragg reflectors (DBRs) on c-plane sapphire were investigated under optical injection and compared with those having AlN/GaN bottom and dielectric top DBRs on freestanding GaN. A novel fabrication method employing two epitaxial lateral overgrowth steps is introduced to produce a cavity on bottom dielectric DBRs without the need to remove the sapphire substrate. Under high optical excitation, the cavity with all dielectric DBRs exhibited quality factors up to 1400 and an order of magnitude lower stimulated emission threshold density (5 µJ/cm2) than those employing top dielectric DBRs but semiconductor AlN/GaN bottom DBRs on freestanding GaN. This novel approach is expected to lead to injection vertical cavity lasers with naturally formed nearly defect-free active regions and current confinement without any oxidation steps.
Highly Stable GaN Photocatalyst for Producing H2 Gas from Water
Authors: Ohkawa Kazuhiro , Ohara Wataru , Uchida Daisuke , Deura Momoko
Published: May 2013

Efficient production of H2 from water without the use of an extra bias or any sacrificial reagents is possible using a GaN photocatalyst with a NiO cocatalyst. The average energy conversion efficiency from light energy to H2 energy was approximately 1% for 500 h. The total amount of hydrogen was 184 mL/cm2 of the GaN surface. H2 production rate was as high as 0.37 mL/(cm2·h).
Photovoltaic Response of InGaN/GaN Multiple-Quantum Well Solar Cells
Authors: Valdueza-Felip Sirona , Mukhtarova Anna , Pan Qing , Altamura Giovanni , Grenet Louis , Durand Christophe , Bougerol Catherine , Peyrade David , González-Posada Fernando , Eymery Joel , Monroy Eva
Published: May 2013

We report on the fabrication and photovoltaic characterization of In0.12Ga0.88N/GaN multi-quantum-well (MQW) solar cells grown by metal–organic vapor phase epitaxy on (0001) sapphire substrates. Increasing the number of MQWs in the active region from 5 to 30 improves a factor of 10 the peak external quantum efficiency of the device at the price of a slight reduction and increase of the shunt and series resistance, respectively. Solar cells with 30 MQWs exhibit an external quantum efficiency of 38% at 380 nm, an open circuit voltage of 2.0 V, a short circuit current density of 0.23 mA/cm2 and a fill factor of 59% under 1 sun of AM1.5G-equivalent solar illumination. Solar cells with the grid spacing of the top p-contact varying from 100 to 200 µm present the same device performance in terms of spectral response and conversion efficiency.
Strain Rate Controlled Nanoindentation Examination and Incipient Plasticity in Bulk GaN Crystal
Authors: Fujikane Masaki , Yokogawa Toshiya , Nagao Shijo , Nowak Roman
Published: May 2013

Yield shear stress dependence on dislocation density and crystal orientation was studied in bulk GaN crystals by nanoindentation examination. The yield shear stress decreased with increasing dislocation density, and it decreased with decreasing nanoindentation strain-rate. It reached and coincided at 11.5 GPa for both quasi-static deformedc-plane (0001) andm-plane (101̄0) GaN. Taking into account theoretical Peierls–Nabarro stress and yield stress for each slip system, these phenomena were concluded to be an evidence of heterogeneous mechanism associated plastic deformation in GaN crystal. Transmission electron microscopy and molecular dynamics simulation also supported the mechanism with obtainedr-plane (1̄012) slip line right after plastic deformation, so called pop-in event. The agreement of the experimentally obtained atomic shuffle energy with the calculated twin boundary energy suggested that the nucleation of the local metastable twin boundary along ther-plane concentrated the indentation stress, leading to anr-plane slip.
Impact of Group-II Acceptors on the Electrical and Optical Properties of GaN
Authors: Lyons John L. , Janotti Anderson , Walle Chris G. Van de
Published: May 2013

We explore the properties of group-II acceptors in GaN by performing hybrid density functional calculations. We find that MgGagives rise to hole localization in zinc-blende GaN, similar to the behavior in the wurtzite phase. Alternative acceptor impurities, such as Zn and Be, also lead to localized holes in wurtzite GaN, and their ionization energies are larger than that of Mg. All these group-II acceptors also cause large lattice distortions in their neutral charge state, which in turn lead to deep and broad luminescence signals. We explore the consequences of these results for p-type doping.
Impact of AlN Spacer on Metal–Semiconductor–Metal Pt–InAlGaN/GaN Heterostructures for Ultraviolet Detection
Authors: Brazzini Tommaso , Pandey Saurabh , Romero Maria Fatima , Bokov Pavel Yu. , Feneberg Martin , Tabares Gema , Cavallini Anna , Goldhahn Rüdiger , Calle Fernando
Published: May 2013

We report on metal–semiconductor–metal (MSM) photodetectors (PDs) fabricated on InAlGaN/GaN two-dimensional electron gas (2DEG) heterostructures. Electrical and photodetection properties were compared in two structures with and without an AlN spacer between the barrier (InAlGaN) and the GaN. The presence of the spacer hugely reduces the leakage current, allowing biasing at higher voltages. In photodetection, gain is obtained in both structures at a high bias. The photocurrent transient behavior revealed a faster response for excitation energy close to the GaN band edge than for energy above the barrier band edge. The fabrication and improvement of this type of device can lead to integration with the already mature high-electron-mobility transistor (HEMT) technology.
Hole Injection and Electron Overflow Improvement in 365 nm Light-Emitting Diodes by Band-Engineering Electron Blocking Layer
Authors: Fu Yi-Keng , Lu Yu-Hsuan , Xuan Rong , Chen Jenn-Fang , Su Yan-Kuin
Published: May 2013

The work reports a theoretical and experimental study on the device performance of near ultraviolet light-emitting diodes (LEDs) with specific design on the electron blocking layer (EBL) by employing the band-engineering. The simulation results show the polarization-induced downward band bending is mitigated in the specific EBL design and, hence, the capability of hole transportation increases and the behavior of electron overflow decreases. The experimental results show the LEDs with specific EBL design exhibited a reduction of forward voltage from 4.40 to 4.07 V and a much enhancement of light output power from 30.6 to 51.9 mW, compared with conventional LED.
InN/GaN Superlattices: Band Structures and Their Pressure Dependence
Authors: Gorczyca Iza , Suski Tadek , Staszczak Grzegorz , Christensen Niels E. , Svane Axel , Wang Xinqiang , Dimakis Emmanouil , Moustakas Theodore
Published: May 2013

Creation of short-period InN/GaN superlattices is one of the possible ways of conducting band gap engineering in the green-blue range of the spectrum. The present paper reports results of photoluminescence experiments, including pressure effects, on a superlattice sample consisting of unit cells with one monolayer of InN and 40 monolayers of GaN. The results are compared with calculations performed for different types of superlattices: InN/GaN, InGaN/GaN, and InN/InGaN/GaN with single monolayers of InN and/or InGaN. The superlattices are simulated by band structure calculations based on the local density approximation (LDA) with a semi-empirical correction for the “LDA gap error”. A similarity is observed between the results of calculations for an InGaN/GaN superlattice (with one monolayer of InGaN) and the experimental results. This indicates that the fabricated InN quantum wells may contain some Ga atoms due to interdiffusion.
Observation of Negative Differential Resistance in a GaN/AlGaN/GaN: Possible Tunneling Junction Using Polarization
Authors: Watanabe Noriyuki , Yokoyama Haruki , Shigekawa Naoteru
Published: May 2013

We report an anomalous current–voltage behavior in an n-type GaN/undoped InGaN/undoped GaN/undoped AlGaN/n-type GaN diode grown by metalorganic chemical vapor deposition. The tunneling-junction-like band profile of the undoped GaN/undoped AlGaN/n-type GaN (GAG) structure is formed by a spontaneous and piezo polarization effect. We observe negative-differential resistance (NDR) behavior in the diode with the GAG structure. The NDR behavior suggests a possible tunneling junction consisting in the GAG structure.
Capacitance Voltage Characteristics and Electron Holography on Cubic AlGaN/GaN Heterojunctions
Authors: As Donat J. , Zado Alexander , Wei Qiyang Y. , Li Ti , Huang Jingyi Y. , Ponce Fernando A.
Published: May 2013

Cubic AlxGa1-xN/GaN heterostructures were grown by plasma-assisted molecular beam epitaxy on free-standing 3C-SiC(001). The samples consist of an unintentionally doped 600 nm thick c-GaN buffer and a 30 nm c-Al0.3Ga0.7N layer. Capacitance–voltage measurements were performed on metal–oxide–semiconductor heterojunction structure using SiO2as an insulator. A depth profile of the net donor concentrationNCVof the grown sample was measured, demonstrating a clear carrier accumulation at the heterojunction. By electron holography in a transmission electron microscope the potential profile was measured and a free electron concentration of 5.1×1011cm-2was estimated at the c-AlxGa1-xN/GaN interface. Using a one-dimensional (1D) Poisson simulator the results of both techniques are compared and a conduction-to-valence band offset ratio of about 4:1 for the cubic AlxGa1-xN/GaN interface is estimated, which promotes the electron accumulation. Our results demonstrate that the two-dimensional electron gas (2DEG) in cubic AlxGa1-xN/GaN heterostructures can be achieved without the need of polarization effects and is due to the residual background doping in the AlxGa1-xN and GaN.