bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural and Optical Property Investigations on Mg-Alloying in Epitaxial Zinc Oxide Films on Sapphire
Authors: Sharma A.K. , Jin C. , Kvit A. , Narayan J. , Muth J.F. , Teng C.W. , Kolbas R.M. , Holland O.W. 
Published: September 2012

AbstractWe have synthesized single-crystal epitaxial MgZnO films by pulsed-laser deposition. High-resolution transmission electron microscopy, X-ray diffraction and Rutherford backscattering spectroscopy/ion channeling were used to characterize the microstructure, defect content, composition and epitaxial single-crystal quality of the films. In these films with up to ∼ 34 atomic percent Mg incorporation, an intense ultraviolet band edge photoluminescence at room temperature and 77 K was observed. The highly efficient photoluminescence is indicative of the excitonic nature of the material. Transmission spectroscopy revealed that the excitonic structure of the alloys was clearly visible at room temperature. Post-deposition annealing in oxygen reduced the number of defects and improved the optical properties of the films. The potential applications of MgZnO alloys in a variety of optoelectronic devices are discussed.
AlGaN/GaN High Electron Mobility Transistor Structure Design and Effects on Electrical Properties
Authors: Piner E.L. , Keogh D.M. , Flynn J.S. , Redwing J.M 
Published: September 2012

AbstractWe report on the effect of strain induced polarization fields in AlGaN/GaN heterostructures due to the incorporation of Si dopant ions in the lattice. By Si-doping (Al)GaN, a contraction of the wurtzite unit cell can occur leading to strain in doped AlGaN/GaN heterostructures such as high electron mobility transistors (HEMTs). In a typical modulation doped AlGaN/GaN HEMT structure, the Si-doped AlGaN supply layer is separated from the two-dimensional electron gas channel by an undoped AlGaN spacer layer. This dopant-induced strain, which is tensile, can create an additional source of charge at the AlGaN:Si/AlGaN interface. The magnitude of this strain increases as the Si doping concentration increases and the AlN mole fraction in the AlGaN decreases. Consideration of this strain should be given in AlGaN/GaN HEMT structure design.
Negative Differential Conductivity in AlGaN/GaN HEMTs: Real Space Charge Transfer from 2D to 3D GaN States?
Authors: Deng J. , Gaska R. , Shur M. S. , Khan M. A. , Yang J. W. 
Published: September 2012

AbstractWe report on non-thermal negative differential conductivity (NDC) in AlGaN/GaN HEMTs grown on sapphire substrates by low-pressure MOCVD. The sheet electron density was on the order of few times 1012cm−2 and the Hall mobility was 1,000 cm2/V.s. The HEMTs had threshold voltage close to zero and could operate at high positive gate bias up to 3 to 3.5 Volts, with a very low gate leakage current. NDC was observed at the gate bias larger than 1.5V and at the drain biases between approximately 0.5Vg and Vg. We excluded the possibility of self-heating as the cause, since the NDC occurs at relatively small power levels where self-heating effects are negligible.An explanation we provided for the NDC effect is the new mechanism of real space charge transfer from 2D to 3D GaN states, which leads to a decrease in the channel mobility at large 2D electron gas densities. The observed low leakage can be explained by an enhanced molar fraction of aluminum at the heterointerface that results in a larger conduction band discontinuity. Our model that accounts for the piezoelectric and pyroelectric effects is consistent with the observed NDC effect. The Hall mobility dependence on the gate bias and sheet carrier concentration [1] is consistent with the real space transfer mechanism.This NDC effect in GaN/AlGaN HEMTs may find applications in high-performance digital circuits at elevated temperatures.
High-Temperature Reliability of GaN Electronic Devices
Authors: Yoshida Seikoh , Suzuki Joe 
Published: September 2012

AbstractHigh-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 hightemperature 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 metalsemiconductor 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.
TEM Study of Bulk AlN Growth by Physical Vapor Transport
Authors: Sarney W.L. , Salamanca-Riba L. , Hossain T. , Zhou P. , Jayatirtha H.N. , Kang H.H. , Vispute R.D. , Spencer M. , Jones K.A. 
Published: September 2012

AbstractWe are attempting to grow bulk AlN that would be suitable as a substrate for nitride film growth. Bulk AlN films were grown by physical vapor transport on 3.5° offaxis and on-axis 6H SiC seed crystals and characterized by TEM, x-ray-diffraction, Auger electron microscopy, and SEM. TEM images show that the bulk AlN does not have the columnar structure typically seen in AlN films grown by MOCVD. Although further optimization is required before the bulk AlN is suitable as a substrate, we find that the structural characteristics achieved thus far indicate that quality bulk AlN substrates may be obtained in the future.
The Role of the Multi Buffer Layer Technique on the Structural Quality of GaN
Authors: Benamara M. , Liliental-Weber Z. , Mazur J.H. , Swider W. , Washburn J. , Iwaya M. , Akasaki I. , Amano H. 
Published: September 2012

AbstractSuccessive growth of thick GaN layers separated by either LT-GaN or LT-AlN interlayers have been investigated by transmission electron microscopy techniques. One of the objectives of this growth method was to improve the quality of GaN layers by reducing the dislocation density at the intermediate buffer layers that act as barriers to dislocation propagation. While the use of LT-AlN results in the multiplication of dislocations in the subsequent GaN layers, the LT-GaN reduces dislocation density. Based upon Burgers vector analysis, the efficiency of the buffer layers for the propagation of the different type of dislocations is presented. LT-AlN layer favor the generation of edge dislocations, leading to a highly defective GaN layer. On the other hand, the use of LT-GaN as intermediate buffer layers appears as a promising method to obtain high quality GaN layer.
MOVPE Growth of Quaternary (Al,Ga,In)N for UV Optoelectronics
Authors: Han Jung , Figiel Jeffrey J. , Petersen Gary A. , Myers Samuel M. , Crawford Mary H. , Banas Michael A. , Hearne Sean J. 
Published: September 2012

AbstractWe report the growth and characterization of quaternary AlGaInN. A combination of photoluminescence (PL), high-resolution x-ray diffraction (XRD), and Rutherford backscattering spectrometry (RBS) characterizations enables us to explore the contours of constant- PL peak energy and lattice parameter as functions of the quaternary compositions. The observation of room temperature PL emission at 351nm (with 20% Al and 5% In) renders initial evidence that the quaternary could be used to provide confinement for GaInN (and possibly GaN). AlGaInN/GaInN MQW heterostructures have been grown; both XRD and PL measurements suggest the possibility of incorporating this quaternary into optoelectronic devices.
Homo-Epitaxial Growth on Misoriented GaN Substrates by MOCVD
Authors: Zauner A.R.A. , Schermer J.J. , Enckevort W.J.P. van , Kirilyuk V. , Weyher J.L. , Grzegory I. , Hageman P.R. , Larsen P.K. 
Published: September 2012

AbstractThe N-side of GaN single crystals with off-angle orientations of 0°, 2°, and 4° towards the [1010] direction was used as a substrate for homo-epitaxial MOCVD growth. The highest misorientation resulted in a reduction of the density of grown hillocks by almost two orders of magnitude as compared with homo-epitaxial films grown on the exact (0001) surface. The features still found on the 4° misoriented sample after growth can be explained by a model involving the interaction of steps, introduced by the misorientation and the hexagonal hillocks during the growth process.
AlN Wafers Fabricated by Hydride Vapor Phase Epitaxy
Authors: Nikolaev Andrey , Nikitina Irina , Zubrilov Andrey , Mynbaeva Marina , Melnik Yuriy , Dmitriev Vladimir 
Published: September 2012

AbstractWe 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.
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: September 2012

AbstractIn 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 1mm using underlying Al0.05Ga0.95N layer. The underlying Al0.05Ga0.95N layer was grown directly on sapphire by using the lowtemperature-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.
High-Quality AlGaN/GaN Grown on Sapphire by Gas-Source Molecular Beam Epitaxy using a Thin Low-Temperature AlN Layer
Authors: Jurkovic M. J. , Li L.K. , Turk B. , Wang W. I. , Syed S. , Simonian D. , Stormer H. L. 
Published: September 2012

AbstractGrowth of high-quality AlGaN/GaN heterostructures on sapphire by ammonia gassource molecular beam epitaxy is reported. Incorporation of a thin AlN layer grown at low temperature within the GaN buffer is shown to result in enhanced electrical and structural characteristics for subsequently grown heterostructures. AlGaN/GaN structures exhibiting reduced background doping and enhanced Hall mobilities (2100, 10310 and 12200 cm2/Vs with carrier sheet densities of 6.1 × 1012 cm−2, 6.0 × 1012 cm−2, and 5.8 × 1012 cm−2 at 300 K, 77 K, and 0.3 K, respectively) correlate with dislocation filtering in the thin AlN layer. Magnetotransport measurements at 0.3 K reveal well-resolved Shubnikov-de Haas oscillations starting at 3 T.
High Quality AlN and GaN Grown on Si(111) by Gas Source Molecular Beam Epitaxy with Ammonia
Authors: Nikishin Sergey A. , Faleev Nikolai N. , Antipov Vladimir G. , Francoeur Sebastien , Peralta Luis Grave de , Seryogin George A. , Holtz Mark , Prokofyeva Tat'yana I. , Chu S. N. G. , Zubrilov Andrei S. , Elyukhin Vyacheslav A. , Nikitina Irina P. , Nikolaev Andrei , Melnik Yuriy , Dmitriev Vladimir , Temkin Henryk 
Published: September 2012

AbstractWe describe the growth of high quality AlN and GaN on Si(111) by gas source molecular beam epitaxy (GSMBE) with ammonia (NH3). The initial nucleation (at 1130-1190K) of an AlN monolayer with full substrate coverage resulted in a very rapid transition to two-dimensional (2D) growth mode of AlN. The rapid transition to the 2D growth mode of AlN is essential for the subsequent growth of high quality GaN, and complete elimination of cracking in thick ( > 2 μm) GaN layers. We show, using Raman scattering (RS) and photoluminescence (PL) measurements, that the tensile stress in the GaN is due to thermal expansion mismatch, is below the ultimate strength of breaking of GaN, and produces a sizable shift in the bandgap. We show that the GSMBE AlN and GaN layers grown on Si can be used as a substrate for subsequent deposition of thick AlN and GaN layers by hydride vapor phase epitaxy (HVPE).
Mg Segregation, Difficulties of P-Doping in GaN
Authors: Liliental-Weber Z. , Benamara M. , Swider W. , Washburn J. , Grzegory I. , Porowski S. , Dupuis R.D. , Eiting C.J. 
Published: September 2012

AbstractTransmission electron microscopy has been used to study defects formed in Mg-doped GaN crystals. Three types of crystals have been studied: bulk crystals grown by a high pressure and high temperature process with Mg added to the Ga solution and two types of crystals grown by metal-organic chemical vapor deposition (MOCVD) where Mg was either delta-doped or continuously doped. Spontaneous ordering was observed in bulk crystals. The ordering consists of Mg rich planar defects on basal planes separated by 10.4 nm and occurs only for growth in the N to Ga polar direction (000 1N polarity). These planar defects exhibit the characteristics of stacking faults with a shift vector of a 1/3 [1100] +c/2 but some other features identify these defects as inversion domains. Different type of defects were formed on the opposite site of the crystal (Ga to N polar direction), where the growth rate is also an order of magnitude faster compared to the growth with N-polarity. These defects are three-dimensional: pyramidal and rectangular, empty inside with Mg segregation on internal surfaces. The same types of defects seen for the two growth polarities in the bulk crystals were also observed in the MOCVD grown GaN samples with Mg delta doping, but were not observed in the crystals where Mg was added continuously.
The Sensitization of Nanoporous TiO2 Electrodes by Porphyrin Derivatives with Different Substituents
Authors: Pan Kai , Liu Zhaoyue , Xü Jinjie , Yu Miao , Wang Dejun , Bai Yubai , Li Tiejin 
Published: September 2012

AbstractNanoporous TiO2 electrodes were sensitized by different porphyrin derivatives, terahydroxyphenyl porphyrin (THPP) and tera-carboxylphenyl porphyrin (TCPP). Both kinds of sensitized electrodes were characterized by UV-vis, XRD and XPS. The results showed that the interaction between TiO2 and TCPP was stronger than that between TiO2 and THPP. Both kinds of the sensitized electrodes were assembled to photoelectrochemical cells. The photocurrent responses of the photoelectrochemical cell under different incident illumination directions were different significantly. The overall light-to-electric energy conversion yield (η) of TCPPsensitized cell was 0.11%, while the conversion efficiency of THPP-sensitized cell was 0.06%.
Nano Cuprous Oxides Film Prepared by Magnetron Sputtering
Authors: Lu Yang-Ming , Chen Jun-Yuan , Wey Tzuu-Shaang 
Published: September 2012

AbstractCuprous oxide (Cu2O) is a direct-gap semiconductor with band-gap energy of 2.0 eV and has been extensively investigated as a candidate for a photovoltaic material. However, practical applications have not been achieved to date due to the difficulty in controlling its physical properties. We have investigated the controllability of the formation of pure Cu2O thin films deposited by the reactive DC sputtering method and analysis by XPS and Raman spectrometer to identify the Cu+1 in the cuprous oxide. The formation of pure Cu2O films is not only dependent on the substrate temperature but also strongly effected by the oxygen and argon flow rate ratio. When the substrate temperature was kept constant at 100°C and varied the oxygen and argon flow rate ratio from 3ml/min to 10ml/min, it is found a mixture of Cu2O and CuO phases is formed. At the flow rate of oxygen to 5ml/min, the pure and single phase of Cu2O is formed. Further increasing the oxygen flow rate, the phase is changed to be the CuO phase. The crystallity is improved as increasing the substrate temperature. The electrical resistivity of Cu2O obtained in this study is about 316 ohm-cm at 100°C substrate temperature and 2.66Pa condition. The dependence of cupper oxides resistivity is not only on the substrate temperature and reactive gases but also on the sputter pressure. Because the characteristic resistivity values change with sputter pressure variation due to different phase compositions forming in the films. The lowest resistivity of Cu2O film is obtained when the Cu2O single phase exists in the films.
Electrical and Morphological Characterization of Electrochemically Deposited ZnO/dye Hybrid Films
Authors: Reemts J. , Parisi J. , Kittel A. 
Published: September 2012

AbstractDye sensitized solar cells of the Graetzel type are usually fabricated with TiO2 covered with dye after its synthesis as one electrode. ZnO is, aside from TiO2, a promising alternative semiconducting material for solar energy conversion due to its enhanced surface area and a strong attachment of non-aggregated sensitizer dyes. We investigate ZnO/dye electrodes where the dye is already added during the electro-deposition process of the ZnO. We examine the influence of the dye species and the dye concentration on the surface morphology by means of atomic force and scanning electron microscopy imaging. The electrical properties of the films are characterized by means of current-voltage measurements. In order to study the integral properties of the charge carrier transport in the lateral direction of the film we characterized ZnO thin films electro-deposited across an insulating gap between two microstructured electrodes made of gold.
Improved EDLC Characteristics of the CNTs Grown on the Nanoporous Alumina Templates
Authors: Wen Sun , Jung Mi , Joo Oh-Shim , Mho Sun-il 
Published: September 2012

AbstractThe specific capacitance of the carbon nanotube (CNT) electrode can be increased by using nanoporous alumina templates with the high pore density and the small and uniform pore diameter. The surface area of the CNTs was controlled and increased by preparing them with uniform diameters. The well-ordered nanoporous alumina templates were fabricated by a two-step anodization method. The cylindrical pore diameter, length, and density of the template utilized for the CNT growth was 53 ± 1 nm, 2 μm, and 3.1×1010 cm−2, respectively. The CNTs with uniform diameter of 44 ± 2 nm were grown on the porous alumina template as electrode materials for the electric double-layer capacitor (EDLC). The EDLC characteristic of the CNT electrodes was examined by measuring the capacitances from the cyclic voltammograms. The specific capacitance of the CNT electrodes can be increased to the value of 121 ± 5 F/g.
Optical Properties of Nanostructured Mesoporous Semiconductor Films
Authors: Nandhakumar Iris , Gabriel Timothy , Li Xiahong , Attard George S. , Markham Matthew , Smith David C. , Baumberg Jeremy J. 
Published: September 2012

AbstractDirect liquid crystal templating from non-ionic polyoxyethylene surfactants has been utilised to produce well-defined birefringent films of nanostructured cadmium telluride with mesoporous architectures of extended spatial periodicities. The template mixtures and films were characterised by X-ray diffraction, transmission electron microscopy and polarising optical microscopy to ascertain the presence of a regular nanostructure. UV-VIS reflectance spectroscopy was employed to investigate the films' optical properties.
Conductivity dependence on oxygen partial pressure and transport number measurements of La2Mo2O9
Authors: Tarancón A. , Dezanneau G. , Morata A. , Peiró F. , Morante J.R. , Norby T. 
Published: September 2012

AbstractTransport number measurements and impedance spectroscopy in controlled temperature and atmosphere were used to investigate the electrical properties of La2Mo2O9 sintered samples. These samples were prepared from nanocrystalline La2Mo2O9 powders as obtained from a new soft chemistry route involving the polymerisation of acrylamide. By means of the electromotive force method measurements, the sintered compound was found mainly oxygen conductor in the range of 400 °C-800 °C with oxide-ion transport number greater than 0.99. The effect of the oxygen partial pressure on the electrical conductivity of La2Mo2O9 was investigated by impedance spectroscopy from 1 to 10−22 atm, showing a highly stable conduction properties up to 10−17 atm at 800 °C.
Can a Semiochemical-Based Trapping Method Diminish Damage Levels Caused by Rhabdoscelus obscurus (Coleoptera: Curculionidae)?
Authors: Reddy GVP , Shi P , Mann C R , Mantanona DMH , Dong Z 
Published: September 2012

Abstract
The New Guinea sugarcane weevil, Rhabdoscelus obscurus (Boisduval) (Coleoptera: Curculionidae), is an important pest of palms, ornamental nurseries, and sugarcane in the Pacific Islands. Without effective control methods, R. obscurus populations can cause major or complete loss of palm production in Guam and other Micronesian Islands. Moreover, R. obscurus has inflicted severe attacks on coconut trees on Guam. The role of monitoring is important in judging the dynamics of R. obscurus and recording area wide population trends. There is no precise research information available on the trap catch threshold levels relative to the damage caused by R. obscurus. Here we investigated the assessment of trap catch threshold levels and the potential for predicting R. obscurus larval damage by using adult pheromone trap captures. Spatial patterns of capture were studied in relation to subsequent larval damaged betel nut plants at various locations in Guam, United States, during 2010–2012. The generalized additive model was used to describe the effects of the treatment level (traps/ha), ranging from 0 to 12, and time on reducing the damage of R. obscurus to palms. We find that these two predictors are statistically significant, and the treatment level is demonstrated to be the crucial predictor for reducing the damage. There is no significant difference in effectively controlling the damage between the treatment levels of 9 and 12 traps/ha. At least 9 traps/ha is suggested for effectively controlling the damage based on results from the current study.