bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-linear Frequency Response and Stability Analysis of Piezoelectric Nanoresonator Subjected to Electrostatic Excitation
Authors: Hashemi Kachapi Sayyid H. , Dardel Morteza , Mohamadi daniali Hamidreza , Fathi Alireza
Published: April 2019

The effects of surface energy on the non-linear frequency response and stability analysis of piezoelectric cylindrical nano-shell as piezoelectric nanoresonator are investigated in the current paper using Gurtin–Murdoch surface elasticity and von Karman–Donnell’s theory. The nanoresonator is embedded in visco-Pasternak medium and electrostatic excitation. The governing equations and boundary conditions are derived using Hamilton’s principle and also the assumed mode method is used for changing the partial differential equations into ordinary differential equations. Complex averaging method combined with arc-length continuation is used to achieve an approximate solution for the steady-state vibrations of the system. The validation of the mentioned system is achieved with excellent agreements by comparison with numerical results. The parametric studies such as the effects of geometrical and material properties, different boundary conditions, the ratio of length to radius

L

/

R

$L/R$

for different values of the voltages

V

D
C

${V_{{\rm{DC}}}}$

and

V

A
C

${V_{{\rm{AC}}}}$

, the gap width of the nanoresonator

b

/

L

$b/L$

, the effect of the voltages

V

D
C

${V_{{\rm{DC}}}}$

and

V

A
C

${V_{{\rm{AC}}}}$

and also the effect of piezoelectric voltage

V
p

${V_p}$

are conducted on the non-linear frequency response and stability analysis of the piezoelectric nanoresonator.
Die Effekte deutscher Direktinvestitionen im Empfängerland vor dem Hintergrund des Leistungsbilanzüberschusses
Authors: Görg Holger , Marchal Léa
Published: April 2019

Deutschland hat seit Jahren einen Leistungsbilanzüberschuss, der international kritisiert wird. Die Bedeutung der deutschen Direktinvestitionen im Ausland ist dabei in den letzten Jahren stark gestiegen. Vor diesem Hintergrund untersuchen Holger Görg und Léa Marchal die Effekte von Direktinvestitionen auf Unternehmen im Gastland. Dazu werden Unternehmensdaten für Frankreich verwendet. Insgesamt liefert die Studie zwei wirtschaftspolitisch relevante Ergebnisse. Zum einen haben deutsche Übernahmen von französischen Unternehmen im Durchschnitt keine negativen Auswirkungen auf Produktivität, Qualifikationsstruktur und Handelsaktivität der übernommenen Unternehmen. Zum anderen zeigt sich, dass sich die Präsenz deutscher Unternehmen positiv auf französische Unternehmen, die in derselben Industrie angesiedelt sind, auswirkt. Dies gilt sowohl hinsichtlich der Produktivität und Qualifikationsstruktur als auch der Export- und Importaktivität der Unternehmen. Der Effekt auf Exporte erscheint dabei stärker als der auf Importe. Dies hat Implikationen für die Leistungsbilanz. Zwar erhöhen, saldenmechanisch, deutsche Direktinvestitionen im Ausland den bestehenden Leistungsbilanzüberschuss der Bundesrepublik. Sie haben jedoch auch Implikationen für Unternehmen im Empfängerland, die ihre Produktivität und Handelsaktivität steigern.
Klassenlage und Interessenorientierung
Authors: Hack Lothar , Krause Wulf , Schmidt Ute , Wachutka Werner
Published: April 2019

Die Konstitution von Bewußtseinsstrukturen und Verhaltensmustern ist zu begreifen im Kontext der doppelten Konstitution sozialer Realität. Die Analyse des Einflusses von Kultur und Subkultur auf Verhalten und Bewußtsein verweist zurück auf die objektiven Bedingungen, auf deren Grundlage die als Problemlösungsstrategien faßbaren kulturellen Muster entstehen bzw. entstanden sind. Diese objektiven Bedingungen resultieren aus dem objektiven Konstitutionsprozeß, dessen ideeller Ausdruck vor allem in drei Bestimmungen geschehen kann: (1.) Arbeitskraft als Ware, (2.) Produktionsprozeß als widersprüchliche Einheit von Arbeitsprozeß und dominierendem Verwertungsprozeß, (3.) doppelt gebrochene Kooperation als spezifische Form des gesellschaftlichen Charakters der Arbeit. In diesen Konstitutionsbestimmungen begreifbar geschieht die ständige Produktion und Reproduktion der sozialen Realität, deren Verselbständigung und Fremdwerden aber bedeuten, daß das bereits Produzierte je subjektiv noch einmal eingeholt werden muß in einem zweiten, subjektiven Konstitutionsprozeß. Die Vermittlung zwischen den beiden Konstitutionsprozessen wird (a) in spezifischer Form in den kulturellen Mustern tradiert und geschieht (b) immer neu im Handeln in sozialen Situationen, aus dem auch die kulturellen Muster einmal hervorgegangen sind. Es wird versucht, den spezifischen Gegenstand aus diesem Kontext heraus zu entfalten.
Statistische Signifikanz und sozialwissenschaftliche Relevanz
Authors: Kriz Jürgen
Published: April 2019

Grundlage statistischer Entscheidungsmodelle ist eine unrealistische HO - dies führt zu einer Gefahr der Fehlinterpretation, wenn Signifikanztests nicht mehr nur ein Glied in einer von der sozialwissenschaftlichen Fragestellung her relevanten Forschung darstellen, sondern heute oftmals zum Ritual werden, indem sie als Rechtfertigung für die Forschung dienen und so den Anspruch eines Relevanzkriteriums erheben. Ein solcher - an ihrer ursprünglichen Konzeption gemessener - Mißbrauch der Signifikanztests kann möglicherweise verringert werden, wenn man Entscheidungsmodelle so umformuliert, daß der Forscher gezwungen wird, bestimmte Gesichtspunkte der Relevanz - die, wie gezeigt wird, auf jeden Fall implizit in die Signifikanztests eingehen - explizit zu formulieren. Dies wird exemplarisch am Beispiel des t-Test-Modells diskutiert, und daraus wird ein solches Alternativmodell ansatzweise entwickelt.
Ultrasonically Facilitated Electrochemical Degradation of Acetaminophen Using Nanocomposite Porous Cathode and Pt Anode
Authors: Darvishi Cheshmeh Soltani Reza , Mashayekhi M.
Published: April 2019

In the present research study, an electrochemical process (EC) equipped with a porous

cathode was combined with ultrasound (US) to efficiently degrade acetaminophen (ACE) as the target pollutant. The carbonaceous porous cathode was used for in situ generation of hydrogen peroxide. The generation of hydrogen through the cathodic reduction was current-dependent. As a result, the combination of US with EC resulted in the highest degradation efficiency (%) of 74.6 %. Increasing the concentration of Na2SO4 (as supporting electrolyte) from 0.01 to 0.1 M led to enhanced ACE degradation efficiency (%) from 50.6 to 75.7 %, respectively, while a significant drop in ACE removal efficiency from 93.0 to 22.0 % occurred when the initial concentration of ACE increased from 1 to 10 mg L–1, respectively. The operation of US/EC with pulse mode of US irradiation led to a slight increase in ACE degradation efficiency (%) (79.0 %). The presence of halide compounds (chloride ions) significantly enhanced the removal of ACE (96.1 %), while alcoholic compounds, especially methanol, produced a substantial suppressive effect on the treatment of ACE.
Treatment of Bisphenol-A Using Sonication-assisted Photo-Fenton Hybrid Process
Authors: Dükkancı Meral
Published: April 2019

Sonication-assisted photo-Fenton oxidation of an endocrine disrupting compound, bisphenol-A (BPA), was studied under visible-light irradiation in the presence of a LaFeO3 perovskite catalyst. The effects of the parameters: initial BPA concentration ([BPA]0), H2O2 concentration ([H2O2]0), catalyst loading, initial pH of the BPA solution, and reaction temperature were studied on the sonication-assisted photo-Fenton oxidation of an aqueous BPA solution. The optimum conditions for the oxidation were determined to be: [BPA]0 = 10 ppm, [H2O2]0 = 4.8 mM, catalyst loading = 0.75 g L–1, pH = 2.6, temperature = 313 K. During all runs, sonication power of 40 W, visible lights power of 150 W+150 W, BPA solution volume (0.5 L), and stirring speed of 500 rpm were kept constant. Under these conditions, degradation of 56.3 %, COD removal of 50.9 %, and TOC removal of 15.6 % were achieved after 6 h of reaction. The small amount of iron that leached into the solution indicated high stability of the catalyst. The sonication-assisted photo-Fenton oxidation of BPA was described by the second order kinetics with an activation energy of 15.34 kJ mol–1. Toxicity tests were also performed and the results revealed that the intermediates formed in the sonication-assisted photo-Fenton oxidation of BPA were less toxic compared to the parent BPA molecule at a neutral pH value. However, the same interpretation was not valid at the acidic pH of 2.6.
El comportamiento del consumidor de las plazas de mercado de Villavicencio, Meta
Authors: Prieto Delgadillo Mario Fernando , Chinchilla Mora Maria Cristina
Published: April 2019

Las plazas de mercado son uno de los sectores más beneficiosos para el país, dado que satisface una necesidad de primera categoría y aporta a la economía de la región, por lo que su conservación y análisis se hace importante para dicho sector. El presente artículo es el análisis del comportamiento de los consumidores de las plazas de mercado en la ciudad de Villavicencio, donde existe un comercio bastante notorio en cuanto a frutas y legumbres en el país, que desde allí se suministran los pueblos. Por ende, se hizo una investigación exploratoria descriptiva, donde se recopiló información sobre las estadísticas de compra del consumidor, en los diferentes mercados y bajo diferentes conceptos y circunstancias.
¿Por qué acudir a la literatura para recrear la configuración del perdón en el conflicto armado interno colombiano?
Authors: Vásquez Santamaría Jorge Eduardo , Merino Martínez Catalina , López Salazar Estefanía
Published: April 2019

Hablar de posacuerdo implica comprender que la paz no surge de la convención formal entre actores en conflicto, sino de la reconstrucción lenta de una sociedad fragmentada por el dolor a partir de la interacción y el perdón entre víctimas y victimarios. Por ello, el perdón emerge como elemento imprescindible para la reestructuración de la civilidad, y una de las maneras posibles de alcanzarlo se encuentra en la literatura, testimonio ético-político que deja huella del acontecimiento en la memoria colectiva y constituye el escenario propicio para el encuentro y la afirmación de la otredad y de la memoria. Con la literatura como escenario se propuso la pregunta: ¿cómo se ha configurado el perdón a partir de los géneros literarios dentro del conflicto armado interno en Colombia (1948-2016)? Interrogante desde el cual se analizaron las distintas configuraciones que ha asumido el perdón a partir de los géneros literarios en el desarrollo del conflicto armado interno. Con el perdón, el conflicto, las narrativas y los géneros literarios como categorías predefinidas de investigación se ejecutó una metodología soportada en el modelo cualitativo, con enfoque histórico-hermenéutico y aplicación del método hermenéutico. Dando lugar así a un constructo teórico y reflexivo de la literatura como herramienta potencial para la configuración del perdón en la sociedad en posacuerdo. Este texto se propone entonces responder la pregunta ¿por qué acudir a la literatura para recrear la configuración del perdón en el conflicto armado interno colombiano?
Segregación socioespacial bajo el nuevo modelo de ciudad en América Latina. Características, perspectivas e implicaciones
Authors: López Martínez Alexandra
Published: April 2019

El fenómeno de segregación socioespacial ha cambiado su patrón tradicional, principalmente desde finales del siglo xx de acuerdo a las transformaciones económicas que trajo consigo la globalización en su etapa más desarrollada que es el neoliberalismo. En este artículo se persiguen dos objetivos, por un lado,caracterizar el patrón de segregación socioespacial contemporáneo desde la perspectiva de escala como grado y como valor; y por el otro, avanzar sobre las transformaciones que han producido los agentes y actores sociales a partir de la territorialización de sus acciones en la construcción del espacio urbano. Para el desarrollo de estos objetivos la autora analiza teórica y cualitativamente las características del fenómeno segregativo a escala periubana. Concluye que, a pesar de no darse un proceso de metropolización como en las ciudades globales, la ciudad difusa se va a encontrar mayoritariamente en las ciudades independiente de su preponderancia —si son grandes o no—, y demuestra así que la segregación a pesar de haber cambiado su patrón —geográficamente los grupos sociales se encuentran menos alejados— no ha dejado de ser un fenómeno que está en aumento no por suseparación física sino social.
La emergencia emotiva del pensamiento objetivo
Authors: Suárez Acevedo Camila , Pérez  Jiménez Miguel Ángel
Published: April 2019

El auge del externismo sobre los contenidos mentales ha motivado enfoques interpretativos sobre la atribución de pensamientos. La teoría de la triangulación destaca en ese contexto, pues hace compatibles el externismo físico y el social al señalar que la atribución de pensamientos responde a los estándares de racionalidad del intérprete aplicados a una base de evidencia constituida por la interacción causal y social del interpretado con su entorno. Esta dependencia externa causal y social del pensamiento es lo que lo hace objetivo. Sin embargo, la triangulación tiene problemas para explicar la atribución de pensamiento objetivo cuando la base evidencial es insuficiente, tal como ocurre en los primeros estadios del desarrollo psicológico. Este caso pone en evidencia un cúmulo de suposiciones no explicadas del externismo sobre las relaciones mente-mundo e interpretado-intérprete. El problema se debe a un error fundamental en la definición de los escenarios triangulares de interpretación, que puede subsanarse introduciendo algunas tesis sobre las emociones básicas que a su vez conllevan una redefinicióndel concepto mismo de triangulación.
Pueblos indígenas y minorías nacionales: similitudes y diferencias en la protección internacional de sus derechos
Authors: Andrade Martínez María José
Published: April 2019

Pueblos indígenas y minorías nacionales son grupos étnicos con características comunes, pero también con diferencias relevantes. Este artículo examina los instrumentos que protegen sus derechos en la comunidad internacional y compara el contenido de los mismos, planteando que la diferencia más significativa es el reconocimiento del derecho de autodeterminación a los pueblos indígenas –no así a las minorías nacionales-, del cual derivan otros relevantes. Por otro lado, a pesar de los avances en la codificación internacional de sus derechos, ambos comparten falencias en su aplicación debido a la reticencia de los Estados a dar atribuciones a estos colectivos. La comparación entre ambos grupos puede aportar en buena medida en las contribuciones mutuas que puedan hacerse en el ámbito de la protección de sus derechos
Analysis of Nitrogen Oxides Emission by Modern Vehicles when Used Hydrogen or Other Natural and Synthetic Fuels in Combustion Chamber
Authors: Shcheklein S. E. , Dubinin A. M.
Published: April 2019

This paper presents calculated analysis of the equilibrium emission of nitrogen oxides at the exhaust of carburetor and diesel internal combustion engines. The temperature of the fuel oxidation process is assumed to be 1,400 °C, the pressure for carburetor and diesel engines to be 60 and 80 at, respectively. We have conducted studies for natural and artificial fuels: hydrogen, ethanol, methanol, gasoline, diesel fuel and methane with an excess air ratio corresponding to the oxidation temperature of fuels 1,400 °C. The method of calculating the equilibrium composition based on the equilibrium constant and the equations of mass conservation is applied. It is shown that with an increase in pressure from 1 to 60 bar for the carburetor engines and up to 80 bar for the diesel engines the reaction of nitrogen dioxide formation shifts towards an increase in NO2. Increasing the pressure has no effect on the formation of NO, since the reaction proceeds without changes in the volume. It is established that the main polluting atmospheric component is NO. However, it is advisable to make greater use of fuel with the lowest yield nitrogen dioxide (methane and methanol) because nitrogen dioxide (NO2) pertaining to the chemicals 2ndclass of danger is the most dangerous to humans. It is established that the reducing temperature of oxidation using hydrogen as fuel for electrochemical power generators allows us to reduce the emission of nitrogen oxides over an order of magnitude in comparison with the best results for internal combustion engines.
Unconditional basic income as an instrument for reducing income inequalities. The case of Poland
Authors: Misztal Piotr
Published: April 2019

Unconditional basic income (UBI) is the income allotted to all members of society individually, without the need to work. The right to this income and its level are unconditional and independent of the size and structure of households. In addition, the unconditional income is paid regardless of the income of citizens from other sources. The aim of this paper is to provide a theoretical and an empirical analysis of the UBI, with particular emphasis on the genesis and the effects of introducing this mechanism. The research was based on the analysis of economics literature and empirical results. In the empirical part, the effects of the UBI pilot program implemented in various high and low economically developed countries have been taken into account. In particular, the effects of the Family 500+ program introduced in Poland have been presented, which is widely identified with the UBI program.
Principal component analysis in negative interest rate environment
Authors: Lazarević Milan
Published: April 2019

Principal Component Analysis (PCA) is a risk management technique which is, due to the consequences of multicollinearity, particularly suitable to describe the yield curve. Its final results in this segment are presented through three main factors: shift, slope and curvature. They express predictive trajectories and explain over 95% of variability under normal market conditions. The main goal of this paper is to assess whether the established behavioural patterns are observable in the presence of negative interest rates. The EU bond market was used as an empirical basis with respect to the reactions of the European Central Bank and the establishment of negative reference interest rates in the assessed period. The algebraic properties of the principal components in the presence of negative interest rates correspond to the determined directions of movement, except that the slope and curvature have different signs given their diametrically opposite trends. The percentage of variability explained with the help of PCA is lower compared to the normal market conditions and if an equivalent level of approximation is required, it is necessary to include a fourth factor in PCA. This factor is, due to its properties, aptly named oscillatority. An implicit conclusion of our research is that the duration in the conditions of negative interest rates has less useful power in managing the interest rate risk of individual instruments.
Fabrication of GaN with Buried Tungsten (W) Structures Using Epitaxial Lateral Overgrowth (ELO) via LP-MOVPE
Authors: Miyake Hideto , Yamaguchi Motoo , Haino Masahiro , Motogaito Atsushi , Hiramatsu Kazumasa , Nambu Shingo , Kawaguchi Yasutoshi , Sawaki Nobuhiko , Iyechika Yasushi , Maeda Takayoshi , Akasaki Isamu
Published: April 2019

A buried tungsten (W) mask structure with GaN is successfully obtained by epitaxial lateral overgrowth (ELO) technique via low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). The selectivity of GaN growth on the window region vs. the mask region is good. An underlying GaN with a striped W metal mask is easily decomposed above 500 °C by the W catalytic effect, by which radical hydrogen is reacted with GaN. It is difficult to bury the W mask because severe damage occurs in the GaN epilayer under the mask. It is found that an underlying AlGaN/GaN layer with a narrow W stripe mask width (mask/window = 2/2 μm) leads the ELO GaN layer to be free from damage, resulting in an excellent W-buried structure.
Structural Properties of Laterally Overgrown GaN
Authors: Zhang R. , Shi Y , Zhou Y.G. , Shen B. , Zheng Y.D. , Kuan T.S. , Gu S.L. , Zhang L. , Hansen D.M. , Kuech T.F.
Published: April 2019

Structural properties of epitaxially laterally overgrown (ELO) GaN on patterned GaN ‘substrates’ by hydride vapor phase epitaxy (HVPE) have been investigated. The epitaxially lateral overgrowth of GaN on SiO2 areas is realized and a planar ELO GaN film is obtained. Scanning electron microscope, transmission electron microscope (TEM) and atomic force microscope (AFM) are used to study the structure and surface morphology of the ELO GaN materials. AFM images indicate that no observable step termination is detected over a 4 μm2 area in the ELO region. TEM observations indicate that the dislocation density is very low in the ELO region. No void at the coalescence interface is observed. Lattice bending as high as 3.3° is observed and attributed to pileup of threading dislocations coming from the underlying GaN “seeding layer” and tilting horizontally and quenching at the coalescence interface.
HVPE and MOVPE GaN growth on slightly misoriented sapphire substrates
Authors: Parillaud Olivier , Wagner Volker , Bühlmann Hans-Jörg , Lelarge François , Ilegems Marc
Published: April 2019

We present preliminary results on gallium nitride growth by HVPE on C-plane sapphire with 2, 4 and 6 degrees misorientation towards M and A directions. A nucleation GaN buffer layer is deposited prior the growth by MOVPE. Surface morphology and growth rates are compared with those obtained on exact C-plane oriented sapphire, for various growth conditions. As expected, the steps already present on the substrate surface help to initiate a directed step-flow growth mode. The large hillocks, which are typical for HVPE GaN layers on (0001) sapphire planes, are replaced by more or less parallel macro-steps. The width and height of these steps, due to step bunching effect, depend directly on the angle of misorientation and on the growth conditions, and are clearly visible by optical or scanning electron microscopy. Atomic force microscopy and X-ray diffraction measurements have been carried out to quantify the surface roughness and crystal quality.
Growth of InN By MBE
Authors: Chen W.-L. , Gunshor R. L. , Han Jung , Higashimine K. , Otsuka N.
Published: April 2019

A series of experiments were performed to explore the growth of InN by Molecular Beam Epitaxy (MBE). The growth conditions were optimized based on the study of RHEED during growth and InN dissociation experiments. Characterization of the InN thin films were performed by various techniques such as TEM and XRD.
Evidence From EELS of Oxygen in the Nucleation Layer of a MBE Grown III-N HEMT
Authors: Eustis Tyler J. , Silcox John , Murphy Michael J. , Schaff William J.
Published: April 2019

The presence of oxygen throughout the nominally AlN nucleation layer of a RF assisted MBE grown III-N HEMT was revealed upon examination by Electron Energy Loss Spectroscopy (EELS) in a Scanning Transmission Electron Microscope (STEM). The nucleation layer generates the correct polarity (gallium face) required for producing a piezoelectric induced high mobility two dimensional electron gas at the AlGaN/GaN heterojunction. Only AlN or AlGaN nucleation layers have provided gallium face polarity in RF assisted MBE grown III-N’s on sapphire. The sample was grown at Cornell University in a Varian GenII MBE using an EPI Uni-Bulb nitrogen plasma source. The nucleation layer was examined in the Cornell University STEM using Annular Dark Field (ADF) imaging and Parallel Electron Energy Loss Spectroscopy (PEELS). Bright Field TEM reveals a relatively crystallographically sharp interface, while the PEELS reveal a chemically diffuse interface. PEELS of the nitrogen and oxygen K-edges at approximately 5-Angstrom steps across the GaN/AlN/sapphire interfaces reveals the presence of oxygen in the AlN nucleation layer. The gradient suggests that the oxygen has diffused into the nucleation region from the sapphire substrate forming this oxygen containing AlN layer. Based on energy loss near edge structure (ELNES), oxygen is in octahedral interstitial sites in the AlN and Al is both tetrahedrally and octahedrally coordinated in the oxygen rich region of the AlN.
Formation of BN and AlBN During Nitridation of Sapphire Using RF Plasma Sources
Authors: Ptak A.J. , Ziemer K.S. , Holbert L.J. , Stinespring C.D. , Myers T.H.
Published: April 2019

Evidence is presented that nitrogen plasma sources utilizing a pyrolytic boron nitride liner may be a significant source of B contamination during growth and processing. Auger electron spectroscopy analysis performed during nitridation of sapphire indicate the resulting layers contain a significant amount of BN. The formation of Al1-xBxN would explain the observation of a lattice constant several percent smaller than AlN as measured by reflection high-energy electron diffraction. The presence of cubic inclusions in layers grown on such a surface may be related to the segregation of BN during the nitridation into its cubic phase.
Role of Arsenic Hexagonal growth-suppression on a Cubic GaNAs Growth using Metalorganic Chemical Vapor Deposition
Authors: Yoshida S. , Kimura T. , Wu J. , Kikawa J. , Onabe K. , Shiraki Y.
Published: April 2019

The hexagonal domain suppression-effects in cubic-GaNAs grown by metalorganic chemical-vapor deposition (MOCVD) is reported. A thin buffer layer (20 nm) was first grown on a substrate at 853 K using trimethylgallium and dimethylhydrazine (DMHy), and GaNAs samples were grown at different AsH3 flow rates (0 ∼ 450 μmol/min) at 1193 K. As a result, three types of surface morphologies were obtained: the first was a smooth surface (AsH3 = 0 μmol/min); the second was a mirrorlike surface having small and isotropic grains (AsH3 : 45 ∼ 225 μmol/min ); and the third involved three-dimensional surface morphologies (above 450 μmol/min of AsH3 flow rate). Furthermore, it was confirmed using X-ray diffraction that the mixing ratio of hexagonal GaNAs in cubic GaNAs decreased with an increase of the AsH3 flow rate. We could obtain GaNAs having a cubic component of above 85% at AsH3 flow rates above 20 μmol/min. Therefore, the MOCVD growth method using AsH3 and DMHy was mostly effective for suppressing hexagonal GaNAs. It was observed that the photoluminescence intensity of GaNAs was decreased with increase of arsine flow rate.
Metal organic vapor phase epitaxy of GaAsN/GaAs Quantum wells using Tertiarybutylhydrazine
Authors: Schmidtling T. , Klein M. , Pohl U.W. , Richter W.
Published: April 2019

GaAsN epilayers and quantum wells with a good structural quality and surface morphology were grown by low pressure metal organic vapor phase epitaxy using tertiarybutylhydrazine as a novel nitrogen source. The dependence of nitrogen incorporation on growth temperature was studied for epitaxy with arsine and tertiarybutylarsine precursors. A nitrogen content of 6.7 % was achieved using tertiarybutylhydrazine and tertiarybutylarsine at a low growth temperature of 530 °C. The observed room temperature luminescence shows an increasing redshift with increasing nitrogen contents of the wells.
Microstructure and Physical Properties of GaN Films on Sapphire Substrates
Authors: Chen Zhizhong , Zhang Rong , Zhu Jianming , Shen Bo , Zhou Yugang , Chen Peng , Li Weiping , Shi Yi , Gu Shulin , Zheng Youdou
Published: April 2019

Transmission electron microscopy (TEM), x-ray diffraction (XRD), photoluminescence (PL) and Raman scattering measurements were applied to study the correlation between the microstructure and physical properties of the GaN films grown by light radiation heating metalorganic chemical vapor deposition (LRH-MOCVD), using GaN buffer layer on sapphire substrates. When the density of the threading dislocation (TD) increases about one order of magnitude, the yellow luminescence (YL) intensity is strengthened from negligible to two orders of magnitude higher than the band edge emission intensity. The full width of half maximum (FWHM) of the GaN (0002) peak of the XRD rocking curve was widened from 11 min to 15 min, and in Raman spectra, the width of E2 mode is broadened from 5 cm−1 to 7 cm−1. A “zippers” structure at the interface of GaN/sapphire was observed by high-resolution electron microscope (HREM). Furthermore the origins of TD and relationship between physical properties and microstructures combining the growth conditions are discussed.
Formation and stability of the prismatic stacking faultin wurtzite (Al,Ga,In) nitrides
Authors: Ruterana P. , Béré A. , Nouet G.
Published: April 2019

The formation of the {1 10} stacking fault, which has two atomic configurations in wurtzite (Ga,Al,In)N, has been investigated by high resolution electron microscopy and energetic calculations. It originates from steps at the SiC surface and it can form on a flat (0001) sapphire surface. A modified Stillinger-Weber potential was used in order to investigate the relative stability of the two atomic configurations. They have comparable energy in AlN, whereas the 1/2<10 1>{1 10} configuration is more stable in GaN and InN. In GaN layers, only the 1/2<10 1>{1 10} configuration was observed. The 1/6<20 3> configuration was found in small areas inside the AlN buffer layer where it folded rapidly to the basal plane, and when back into the prismatic plane, it took the 1/2<10 1>{1 10} atomic configuration.
Co-doping Characteristics of Si and Zn with Mg in P-type GaN
Authors: Kim K.S. , Oh C.S. , Han M.S. , Kim C.S. , Yang G.M. , Yang J.W. , Hong C.-H. , Youn C.J. , Lim K.Y. , Lee H.J.
Published: April 2019

We investigated the doping characteristics of Mg doped, Mg-Si co-doped, and Mg-Zn co-doped GaN films grown by metalorganic chemical vapor deposition. We have grown p-GaN film with a resistivity of 1.26 Ωcm and a hole density of 4.3 × 1017 cm−3 by means of Mg-Si co-doping technique. The Mg-Si co-doping characteristic was also explained effectively by taking advantage of the concept of competitive adsorption between Mg and Si during the growth. For Mg-Zn co-doping, p-GaN showing a low electrical resistivity (0.7 Ωcm) and a high hole concentration (8.5 × 1017 cm−3) was successfully grown without the degradation of structural quality of the film. Besides, the measured specific contact resistance for Mg-Zn co-doped GaN film is 5.0 × 10−4 cm2, which is lower value by one order of magnitude than that for only Mg doped GaN film (1.9 × 10−3Ωcm2).
High-Temperature Reliability of GaN Electronic Devices
Authors: Yoshida Seikoh , Suzuki Joe
Published: April 2019

High-quality GaN was grown using gas-source molecular-beam epitaxy (GSMBE). The mobility of undoped GaN was 350 cm2/Vsec and the carrier concentration was 6×1016 cm−3 at room temperature. A GaN metal semiconductor field-effect transistor (MESFET) and an n-p-n GaN bipolar junction transistor (BJT) were fabricated for high-temperature operation. The high-temperature reliability of the GaN MESFET was also investigated. That is, the lifetime of the FET at 673 K was examined by continuous current injection at 673 K. We confirmed that the FET performance did not change at 673 K for over 1010 h. The aging performance of the BJT at 573 K was examined during continuous current injection at 573 K for over 850 h. The BJT performance did not change at 573 K. The current gain was about 10. No degradation of the metal-semiconductor interface was observed by secondary ion-mass spectrometry (SIMS) and transmission electron microscopy (TEM). It was also confirmed by using Si-ion implantation that the contact resistivity of the GaN surface and electrode materials could be lowered to 7×10−6 ohmcm2.
Fabrication and Characterization of GaN Junctionfield Effect Transistors
Authors: Zhang L. , Lester L. F. , Baca A. G. , Shul R. J. , Chang P. C. , Willison C. G. , Mishra U. K. , Denbaars S. P. , Zolper J. C.
Published: April 2019

Junction field effect transistors (JFET) were fabricated on a GaN epitaxial structure grown by metal organic chemical vapor deposition. The DC and microwave characteristics, as well as the high temperature performance of the devices were studied. These devices exhibited excellent pinch-off and a breakdown voltage that agreed with theoretical predictions. An extrinsic transconductance (gm) of 48 mS/mm was obtained with a maximum drain current (ID) of 270 mA/mm. The microwave measurement showed an fT of 6 GHz and an fmax of 12 GHz. Both the ID and the gm were found to decrease with increasing temperature, possibly due to lower electron mobility at elevated temperatures. These JFETs exhibited a significant current reduction after a high drain bias was applied, which was attributed to a partially depleted channel caused by trapped electrons in the semi-insulating GaN buffer layer.
Thermal expansion of GaN at low temperatures - a comparison of bulk and homo- and heteroepitaxial layers
Authors: Kirchner Verena , Heinke Heidrun , Einfeldt Sven , Hommel Detlef , Domagala Jaroslaw Z. , Leszczynski Michal
Published: April 2019

The thermal expansion of different GaN samples is studied by high-resolution X-ray diffraction within the temperature range of 10 to 600 K. GaN bulk crystals, a homoepitaxial layer and different heteroepitaxial layers grown by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) were investigated. Below 100 K the thermal expansion coefficients (TEC) were found to be nearly zero which has to be taken into account when estimating the thermal strain of GaN layers in optical experiments commonly performed at low temperatures. The homoepitaxial layer and the underlying GaN substrate with a lattice mismatch of −6·10−4 showed identical thermal expansion. The comparison between the temperature behavior of lattice parameters of heteroepitaxial layers and bulk GaN points to a superposition of thermally induced biaxial strain and compressive hydrostatic strain.
AlN Wafers Fabricated by Hydride Vapor Phase Epitaxy
Authors: Nikolaev Andrey , Nikitina Irina , Zubrilov Andrey , Mynbaeva Marina , Melnik Yuriy , Dmitriev Vladimir
Published: April 2019

We report on AlN wafers fabricated by hydride vapor phase epitaxy (HVPE). AlN thick layers were grown on Si substrates by HVPE. Growth rate was up to 60 microns per hour. After the growth of AlN layers, initial substrates were removed resulting in free-standing AlN wafers. The maximum thickness of AlN layer was about 1 mm. AlN free-standing single crystal wafers with a thickness ranging from 0.05 to 0.8 mm were studied by x-ray diffraction, transmission electron microscopy, optical absorption, and cathodoluminescence.
GaN 20-mm Diameter Ingots Grown from Melt-Solution by Seeded Technique
Authors: Sukhoveyev V.A. , Ivantsov V.A. , Nikitina I.P. , Babanin A.I. , Polyakov A.Y. , Govorkov A.V. , Smirnov N.B. , Mil’vidskii M.G. , Dmitriev V.A.
Published: April 2019

In this paper, we describe the seeded growth of ∼20 mm diameter 15 mm long GaN ingots from the melt-solution. This is the first successful attempt to conduct growth of GaN boule-crystals. GaN ingots were grown from Ga-based melt in the temperature range of 800-1000°C at less than 2 atm ambient pressure. Growth was performed at ∼2 mm/hr growth rate. X-ray diffraction revealed polycrystalline structure of the ingots. Homoepitaxial GaN layers were deposited by HVPE technique on the substrates, which were fabricated from the grown GaN ingots.
Preparation and Characterization of Single-crystal Aluminum Nitride Substrates
Authors: Schowalter Leo J. , Carlos Rojo J. , Yakolev Nikolai , Shusterman Yuriy , Dovidenko Katherine , Wang Rungjun , Bhat Ishwara , Slack Glen A.
Published: April 2019

Large (up to 10mm diameter) aluminum nitride (AlN) boules have been grown by the sublimation-recondensation method to study the preparation of high-quality single crystal substrates. The growth mechanism of the boules has been studied using AFM. It has been determined that large single crystal grains in those boules grow with a density of screw dislocations below 5×104 cm−3 while edge dislocations are at lower density (none were observed). High-quality AlN single crystal substrates for epitaxial growth have been prepared and characterized using Chemical Mechanical Polishing (CMP) and AFM imaging, respectively. Also, the differential etching effect of KOH solutions on the N and Al-terminated faces of AlN on vicinal c-faces has been investigated. In order to identify the N or Al-terminated face, convergent beam electron diffraction has been used.
Growth of Crack-Free thick AlGaN Layer and its Application to GaN-Based Laser Diode
Authors: Akasaki I. , Kamiyama S. , Detchprohm T. , Takeuchi T. , Amano H.
Published: April 2019

In the field of group-III nitrides, hetero-epitaxial growth has been one of the most important key technologies. A thick layer of AlGaN alloy with higher AlN molar fraction is difficult to grow on sapphire substrate, because the alloy layer is easily cracked. It is thought that one cause of generating cracks is a large lattice mismatch between an AlGaN and a GaN, when AlGaN is grown on the underlying GaN layer. We have achieved crack-free Al0.07Ga0.93N layer with the thickness of more than 1μm using underlying Al0.05Ga0.95N layer. The underlying Al0.05Ga0.95N layer was grown directly on sapphire by using the low-temperature-deposited buffer layer (LT-buffer layer). Since a lattice mismatch between the underlying Al0.05Ga0.95N layer and upper Al0.07Ga0.93N layer is relatively small, the generation of cracks is thought to be suppressed. This technology is applied to a GaN-based laser diode structure, in which thick n-Al0.07Ga0.93N cladding layer grown on the Al0.05Ga0.95N layer, improves optical confinement and single-robe far field pattern in vertical direction.
Zirconium Mediated Hydrogen Outdiffusion From p-GaN
Authors: Kaminska E. , Piotrowska A. , Barcz A. , Jasinski J. , Zielinski M. , Golaszewska K. , Davis R.F. , Goldys E. , Tomsia K.
Published: April 2019

We have shown that Zr-based metallization can effectively remove hydrogen from the p-type GaN subsurface, which eventually leads to the formation of an ohmic contact. As the release of hydrogen starts at ∼900°C, the thermal stability of the contact system is of particular importance. The remarkable thermal behavior of the ZrN/ZrB2 metallization is associated to the microstructure of each individual Zr-based compound, as well as to the interfacial crystalline accommodation.
A Comparative Study Of GaN Diodes Grown by MBE on Sapphire and HVPE-GaN /Sapphire Substrates
Authors: Sampath Anand V. , Misra Mira , Seth Kshitij , Fedyunin Yuri. , Ng Hock M. , Iliopoulos Eleftherios , Feit Zeev , Moustakas Theodore .D.
Published: April 2019

In this paper we report on the fabrication and characterization of GaN diodes (Schottky and p-n junctions) grown by plasma assisted MBE. We observed that Schottky diodes improve both in reverse as well as forward bias when deposited on 5 μm thick HVPE n+-GaN/sapphire instead of bare sapphire substrates. These improvements are attributed to the reduction of disloctions in the MBE homoepitaxially grown GaN. Similar benefits are observed in the reverse bias of the p-n junctions which according to EBIC measurements are attributed to the reduction of etch pits in the MBE grown p-GaN.
Fabrication and Characterization of Metalferroelectric-GAN Structures
Authors: Li W.P. , Zhang R. , Yin J. , Liu X.H. , Zhou Y.G. , Shen B. , Chen P. , Chen Z.Z. , Shi Y. , Jiang R.L. , Liu Z.G. , Zheng Y.D. , Huang Z.C.
Published: April 2019

GaN-based metal-ferroelectric-semiconductor (MFS) structure has been fabricated by using ferroelectric Pb(Zr0.53Ti0.47)O3 (PZT) instead of conventional oxides as gate insulators. The GaN and PZT films in the MFS structures have been characterized by various methods such as photoluminescence (PL), wide-angle X-ray diffraction (XRD) and high-resolution X-ray diffraction (HRXRD). The Electric properties of GaN MFS structure with different oxide thickness have been characterized by high-frequency C-V measurement. When the PZT films are as thick as 1 μm, the GaN active layers can approach inversion under the bias of 15V, which can not be observed in the traditional GaN MOS structures. When the PZT films are about 100 nm, the MFS structures can approach inversion just under 5V. All the marked improvements of C-V behaviors in GaN MFS structures are mainly attributed to the high dielectric constant and large polarization of the ferroelectric gate oxide.
Temperature Distribution in InGaN-MQW LEDs under Operation
Authors: Schwegler Veit , Seyboth Matthias , Schad Sven , Scherer Marcus , Kirchner Cristoph , Kamp Markus , Stempfle Ulrich , Limmer Wolfgang , Sauer Rolf
Published: April 2019

The temperature distribution in InGaN-MQW light emitting diodes was examined during operation with spatially resolved micro-Raman and micro-Electroluminescence measurements. The experimental results were compared to finite element simulations. A good agreement between the different experimental and calculated data is found. Maximum operation temperatures up to 140 °C at a moderate forward currents of 30 mA are revealed by all three independent methods. Influences of substrate thickness, different substrates, and even bond-wires are shown.
Microstructure-based lasing in GaN/AlGaN separate confinement heterostructures
Authors: Bidnyk S. , Lam J. B. , Little B. D. , Gainer G. H. , Kwon Y. H. , Song J. J. , Bulman G. E. , Kong H. S.
Published: April 2019

We report on an experimental study of microstructure-based lasing in an optically pumped GaN/AlGaN separate confinement heterostructure (SCH). We achieved low-threshold ultra-violet lasing in optically pumped GaN/AlGaN separate confinement heterostructures over a wide temperature range. The spacing, directionality, and far-field patterns of the lasing modes are shown to be the result of microcavities that were naturally formed in the structures due to strain relaxation. The temperature sensitivity of the lasing wavelength was found to be twice as low as that of bulk-like GaN films. Based on these results, we discuss possibilities for the development of ultra-violet laser diodes with increased temperature stability of the emission wavelength.
Comparative study of structural properties and photoluminescence in InGaN layers with a high In content
Authors: Vantomme A. , Wu M.F. , Hogg S. , Langouche G. , Jacobs K. , Moerman I. , White M.E. , O’Donnell K.P. , Nistor L. , Van Landuyt J. , Bender H.
Published: April 2019

Rutherford backscattering and channeling spectrometry (RBS), photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM) have been used to investigate macroscopic and microscopic segregation in MOCVD grown InGaN layers. The PL peak energy and In content (measured by RBS) were mapped at a large number of distinct points on the samples. An indium concentration of 40%, the highest measured in this work, corresponds to a PL peak of 710 nm, strongly suggesting that the light-emitting regions of the sample are very indium-rich compared to the average measured by RBS. Cross-sectional TEM observations show distinctive layering of the InGaN films. The TEM study further reveals that these layers consist of amorphous pyramidal contrast features with sizes of order 10 nm. The composition of these specific contrast features is shown to be In-rich compared to the nitride matrix.
An Investigation of Long and Short Time-Constant Persistent Photoconductivity in Undoped GaN Grown By RF-Plasma Assisted Molecular Beam Epitaxy
Authors: Ptak A.J. , Stoica V.A. , Holbert L.J. , Moldovan M. , Myers T.H.
Published: April 2019

Photoconductance decay and spectral photoconductance measurements were made on a set of ten undoped layers of GaN grown by rf-plasma MBE. The layers, also characterized by Hall, photoluminescence and reflectance measurements, represented a wide variety in electrical and optical properties, and several were grown under atomic hydrogen. Spectral photoconductance indicated transitions at 1.0-1.1, 1.92, 2.15, 3.08 and 3.2-3.4 eV. All layers exhibited persistent photoconductivity to some degree. In contrast with previous reports, a clear correlation was not observed between persistent photoconductivity and yellow luminescence or, indeed, with any measurement made. Analysis of photoconductance decay indicates that more than one type of persistent photoconductivity may be present.
Prism coupling as a non destructive tool for optical characterization of (Al,Ga) nitride compounds
Authors: Dogheche E. , Belgacem B. , Remiens D. , Ruterana P. , Omnes F.
Published: April 2019

An optical characterization technique is proposed for GaN based compounds deposited on sapphire. In AlGaN films grown by MOCVD, the film optical behavior and the substrate to layer interface are qualified from the measured optical data. The experimental and theoretical approach used for this purpose is described in detail. The results clearly show bending effects at the interface which may be related to structural defects; a good agreement with transmission electronic microscopy analysis is obtained.
Deep level related yellow luminescence in p-type GaN grown by MBE on (0001) sapphire
Authors: Salviati Giancarlo , Armani Nicola , Zanotti-Fregonara Carlo , Gombia Enos , Albrecht Martin , Strunk Horst P. , Mayer Markus , Kamp Markus , Gasparotto Andrea
Published: April 2019

Yellow luminescence (YL) has been studied in GaN:Mg doped with Mg concentrations ranging from 1019 to 1021 cm-3 by spectral CL (T=K) and TEM and explained by suggesting that a different mechanism could be responsible for the YL in p-type GaN with respect to that acting in n-type GaN.

Transitions at 2.2, 2.8, 3.27, 3.21, and 3.44 eV were found. In addition to the wurtzite phase, TEM showed a different amount of the cubic phase in the samples. Nano tubes with a density of 3×109 cm−2 were also observed by approaching the layer/substrate interface. Besides this, coherent inclusions were found with a diameter in the nm range and a volume fraction of about 1%.

The 2.8 eV transition was correlated to a deep level at 600 meV below the conduction band (CB) due to MgGa-VN complexes. The 3.27 eV emission was ascribed to a shallow acceptor at about 170-190 meV above the valence band (VB) due to MgGa.

The 2.2 eV yellow band, not present in low doped samples, increased by increasing the Mg concentration. It was ascribed to a transition between a deep donor level at 0.8-1.1 eV below the CB edge due to NGa and the shallow acceptor due to MgGa. This assumption was checked by studying the role of C in Mg compensation. CL spectra from a sample with high C content showed transitions between a C-related 200 meV shallow donor and a deep donor level at about 0.9-1.1 eV below the CB due to a NGa-VN complex. In our hypothesis this should induce a decrease of the integrated intensity in both the 2.2 and 2.8 eV bands, as actually shown by CL investigations.