GaN Nanowire Schottky Barrier Diodes

A new concept of vertical gallium nitride (GaN) Schottky barrier diode based on nanowire (NW) structures and the principle of dielectric REduced SURface Field (RESURF) is proposed in this paper. High-threading dislocation density in GaN epitaxy grown on foreign substrates has hindered the development and commercialization of vertical GaN power devices. The proposed NW structure, previously explored for LEDs offers an opportunity to reduce defect density and fabricate low cost vertical GaN power devices on silicon (Si) substrates. In this paper, we investigate the static characteristics of high-voltage GaN NW Schottky diodes using 3-D TCAD device simulation. The NW architecture theoretically achieves blocking voltages upward of 700 V with very low specific on-resistance. Two different methods of device fabrication are discussed. Preliminary experimental results are reported on device samples fabricated using one of the proposed methods. The fabricated Schottky diodes exhibit a breakdown voltage of around 100 V and no signs of current collapse. Although more work is needed to further explore the nano-GaN concept, the preliminary results indicate that superior tradeoff between the breakdown voltage and specific on-resistance can be achieved, all on a vertical architecture and a foreign substrate. The proposed NW approach has the potential to deliver low cost reliable GaN power devices, circumventing the limitations of today's high electron mobility transistors (HEMTs) technology and vertical GaN on GaN devices

Nonequilibrium ferroelectric-ferroelastic 10-nm nanodomains : wrinkles, period-doubling, and power-law relaxation

Since the 1935 work of Landau and Lifshitz and of Kittel in 1946 all ferromagnetic, ferroelectric, and ferroelastic domains have been thought to be straight-sided with domain widths proportional to the square root of the sample thickness. We show in the present work that this is not true. We also discover period doubling domains predicted by Metaxas et al. (Phys. Rev. Lett. 2008, 217208) and modeled by Wang and Zhao Q. (Sci. Rpts. 2015, 5, 8887). We examine non-equilibrium ferroic domain structures in perovskite oxides with respect to folding, wrinkling, and relaxation and suggest that structures are kinetically limited and in the viscous flow regime predicted by Metaxas et al. in 2008 but never observed experimentally. Comparisons are made with liquid crystals and hydrodynamic instabilities, including chevrons, and fractional power-law relaxation. As Shin et al. [Soft Mat. 2016, 12, 3502] recently emphasized: “An understanding of how these folds initiate, propagate, and interact with each other is still lacking.” Inside each ferroelastic domain are ferroelectric 90-degree nano-domains with 10-nm widths and periodicity in agreement with the 10-nm theoretical minima predicted by Feigl et al. (Nat. Commun. 2014, 5, 4677). Evidence is presented for domain-width period doubling, which is common in polymer films but unknown in ferroic domains. A discussion of the folding-to-period doubling phase transition model of Wang and Zhao is included.PostprintPeer reviewe

Low temperature plasma-assisted double anodic dissolution : a new approach for the synthesis of GdFeO3 perovskite nanoparticles

Orthorhombic perovskite GdFeO3 nanostructures are promising materials with multiferroic properties. In this study, we developed a new low-temperature plasma-assisted approach via dual anodic dissolution of solid metallic precursors for the preparation of perovskite GdFeO3 nanoparticles which can be collected both as colloids as well as deposited as a thin film on a substrate. Two solid metallic foils of Gd and Fe were used as precursors, adding to the simplicity and sustainability of the method. The formation of the orthorhombic perovskite GdFeO3 phase was supported by high-resolution transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman measurements, while a uniform elemental distribution of Gd, Fe and O was confirmed by energy dispersive X-ray spectroscopy, proving the successful preparation of ternary compound NPs. The magnetic properties of the NPs showed zero remnant magnetization typical of antiferromagnetic materials, and saturation at high fields that can be caused by the spin interaction between Gd and Fe magnetic sublattices. The formation mechanism of ternary compound nanoparticles in this novel plasma-assisted method is also discussed. This method was also modified to demonstrate the direct one-step deposition of thin films, opening up opportunities for their future applications in the fabrication of magnetic memory devices and gas sensors

Metodología de elaboración de mapas acústicos como herramienta de gestión del ruido urbano - caso medellín

Dada la naturaleza de la variable ruido y su variabilidad espacio – temporal, se tomó como base fundamental la aplicación de la metodología Geoestadística para la predicción y valoración de la distribución del ruido en las zonas de estudio del proyecto “Elaboración del Mapa Acústico para el Municipio de Medellínâ€�, realizado en el año 2006, mediante Convenio 680 de 2005, entre el Área Metropolitana del Valle de Aburrá y el Politécnico Colombiano Jaime Isaza Cadavid, con la participación de la Universidad Nacional de Colombia, Sede Medellín. Con base en esta metodología se concluyó que Medellín presenta un nivel de ruido diurno global de 73dB(A), indicando que su zona urbana tiene niveles de ruido apropiados solo para sectores industriales. De igual manera en la noche, se presenta un nivel de ruido global de 68 dB(A), apropiado solo para el mismo tipo de sector