Fully porous GaN p-n junction diodes fabricated by chemical vapor deposition

Producción CientíficaModern society is experiencing an ever-increasing demand for energy to power a vast array of electrical and mechanical devices. A significant amount of the energy consumed is used for lighting purposes. For instance, this demand is ~17% of the total energy consumed in the USA in 2011 [1]. Thus, any approach that can reduce energy consumption is important. In this context, the development of light emitting diodes (LEDs) incorporating at least one porous component, with improved light extraction efficiency, is being explored intensively [2]. However, up to now, only partially porous p-n junctions have been analyzed for this purpose.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA166A11-2 and VA293U1

Fabrication of p-type porous GaN on silicon and epitaxial GaN

Abstract : Porous GaN layers are grown on silicon from gold or platinum catalyst seed layers, and self-catalyzed on epitaxial GaN films on sapphire. Using a Mg-based precursor, we demonstrate p-type doping of the porous GaN. Electrical measurements for p-type GaN on Si show Ohmic and Schottky behavior from gold and platinum seeded GaN, respectively. Ohmicity is attributed to the formation of a Ga2Au intermetallic. Porous p-type GaN was also achieved on epitaxial n-GaN on sapphire, and transport measurements confirm a p-n junction commensurate with a doping density of 1018 cm 3. Photoluminescence and cathodoluminescence confirm emission from Mg-acceptors in porous p-type GaN

Fully porous GaN p-n junctions fabricated by Chemical Vapor Deposition: a green technology towards more efficient LEDs

Producción CientíficaPorous GaN based LEDs produced by corrosion etching techniques demonstrated enhanced light extraction efficiency in the past. However, these fabrication techniques require further postgrown processing steps, which increase the price of the final system. In this paper, we review the process followed towards the fabrication of fully porous GaN p-n junctions directly during the growth step, using a sequential chemical vapor deposition (CVD) process to produce the different layers that form the p-n junction.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13

Long Cycle Life, Highly Ordered SnO₂/GeO₂ Nanocomposite Inverse Opal Anode Materials for Li‐Ion Batteries

Nanocomposite SnO2/GeO2 inverse opals (IOs) provide long cycle life with excellent capacity retention when tested as anode materials for Li‐ion batteries. It is demonstrated that the electrochemical performance of SnO2 is significantly improved via the engineering of a nanocomposite of nanoparticles of tetragonal SnO2 and hexagonal GeO2 into a highly ordered, porous inverse opal architecture. By introducing a GeO2 component, the SnO2/GeO2 IOs demonstrate stepwise lithium storage processes to improve cycling stability by mitigating capacity fade from material volume variations in a material that already improves cycling repose by its architecture. This results in higher capacity and better capacity retention. SnO2/GeO2 IOs achieve a reversible capacity of ≈880 and 690 mAh g−1 after the 50th and 250th cycles, respectively, at a specific current of 150 mA g−1. SnO2/GeO2 IOs are capable of delivering high specific capacities (average value of ≈570 mAh g−1) with stable capacity retention over 750 cycles at a specific current of 450 mA g−1. Tailoring the composition of nanocomposite metal‐oxide anodes to exploit the combination of conversion and alloying mechanisms enables stable binder‐free Li‐ion anodes. Nanoscaling the walls of the ordered macroporous structure provides efficient reversible redox lithiation mechanisms involving the oxides of Sn and Ge, which are simpler to prepare

Novel solid-state route to nanostructured tin, zinc and cerium oxides as potential materials for sensors

© 2014 American Scientific Publishers.Solid-state sensor nanostructured materials (SnO2, ZnO and CeO2) have been prepared by pyrolysis of macromolecular complexes: PSP-co-4-PVP · (SnCl2)n, PSP-co-4-PVP · (ZnCl2)nand PSP-co-4-PVP · (Ce(NO3)3)nin several molar ratios under air at 800 °C. The as-prepared nanostructured SnO2 exhibits morphologies and particle sizes which are dependent upon the molar ratio of the SnCl2:PSP-co-4-PVP. When a larger weight fraction of the inorganic salt in the precursor mixture is used (1:10 > 1:5 > 1.1) larger crystalline crystals are found for each oxide. For ZnO and CeO2agglomerates of morphologies from the respective hexagonal and cubic structures were observed with typical sizes of 30-50 nm in both cases for a precursor mixture ratio of 1:1. Copyrigh

Influence of Binders and Solvents on Stability of Ru/RuOx Nanoparticles on ITO Nanocrystals as Li–O2 Battery Cathodes

Fundamental research on Li–O2batteries remains critical, and the nature of the reactions and stability are paramount for realising the promise of the Li–O2system. We report that indium tin oxide (ITO) nanocrystals with supported 1–2 nm oxygen evolution reaction (OER) catalyst Ru/RuOxnanoparticles (NPs) demonstrate efficient OER processes, reduce the recharge overpotential of the cell significantly and maintain catalytic activity to promote a consistent cycling discharge potential in Li–O2cells even when the ITO support nanocrystals deteriorate from the very first cycle. The Ru/RuOxnanoparticles lower the charge overpotential compared with those for ITO and carbon-only cathodes and have the greatest effect in DMSO electrolytes with a solution-processable F-free carboxymethyl cellulose (CMC) binder (<3.5 V) instead of polyvinylidene fluoride (PVDF). The Ru/RuOx/ITO nanocrystalline materials in DMSO provide efficient Li2O2decomposition from within the cathode during cycling. We demonstrate that the ITO is actually unstable from the first cycle and is modified by chemical etching, but the Ru/RuOxNPs remain effective OER catalysts for Li2O2during cycling. The CMC binders avoid PVDF-based side-reactions and improve the cyclability. The deterioration of the ITO nanocrystals is mitigated significantly in cathodes with a CMC binder, and the cells show good cycle life. In mixed DMSO–EMITFSI [EMITFSI=1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide] ionic liquid electrolytes, the Ru/RuOx/ITO materials in Li–O2cells cycle very well and maintain a consistently very low charge overpotential of 0.5–0.8 V