Measurement of minority carrier lifetimes in nanocrystalline silicon devices using reverse-recovery transient method

A new technique for measuring minority carrier lifetimes in p-i-n device configurations, and is used to measure the effective hole lifetimes in nanocrystalline silicon materials. The technique is the reverse-recovery transient method. A forward current in a p-n junction is suddenly switched, and a high constant reverse current flows for a certain period of time. This time is related to the time the injected minority carriers take to recombine in the base. The technique allows for analysis of hole lifetimes in typical thin film nanocrystalline silicon device with very common testing equipment.;The samples used for testing were fabricated using VHF-PECVD reactors using silane and hydrogen as source gases. Both hydrogen profiled nanocrystalline silicon and superlattice nanocrystalline silicon devices were fabricated. The shallow and deep donor states were measured using a junction capacitance technique. The minority carrier diffusion length was determined using a combination of capacitance and quantum efficiency techniques.;The measured hole lifetimes was seen to range from 200-600 ns. Lifetimes were plotted versus inverse defect density, and a linear correlation was seen. This showed the lifetimes followed the Shockley-Read-Hall recombination model. It was also seen for devices deposited at high temperature that a final hydrogen plasma treatment or hydrogen anneal step, the lifetimes and diffusion lengths improved, possibly due to grain boundary passivation. Finally, it was shown that lifetimes in superlattice devices correlated with defect density and diffusion lengths indicating transport in these samples is the same as hydrogen profiled samples.;This technique has been demonstrated for the first time in nanocrystalline silicon devices. An advantage to measuring lifetimes with this technique is that the actual device was not modified in any way to accommodate the measurement. Also, the method only required equipment that can be found in any common electronics lab

Product carbon footprints as tool for a low-carbon economy

Stabilizing greenhouse gas emissions at a level that prevents a global warming beyond plus two degree celsius is a formidable challenge. The required emission reductions can only be achieved by a series of technological, organizational and social innovations

Alles Große steht im Sturm - alles Kleine aber auch: differentielle Vulnerabilität und gesellschaftliche Reaktionsmuster auf Klimaextreme in der weiten Karibik

"Die weitere Karibik, einschließlich der Küstenstaaten im Süden der USA, stellt eine soziologisch sehr interessante Weltregion dar: Vom Naturraum her ähnlich, findet sich hier auf relativ kleinem Gebiet ein Flickenteppich aus kleineren und größeren Staaten und Territorien, die hinsichtlich ihrer Wirtschaftskraft, ihrer politischen Verfassung, der zivilgesellschaftlichen Organisation sowie der Kultur deutliche Unterschiede aufweisen. Eine Paraderegion des Vergleichs also, und in mancher Hinsicht die große Welt im Kleinen. Die Natur - oder, wie viele Klimawissenschaftler behaupten, in wachendem Maße 'der Mensch' - unterzieht diese Region alljährlich einem entsetzlichen Prozess: der Hurrikansaison. Die Hurrikansaison 2005 war eine besonders intensive und folgenschwere: 28 tropische Stürme wurden registriert, davon 15 Hurrikans. 7 davon wiederum waren der besonders zerstörerischen Kategorie 3-5 zuzurechnen. Die Schäden in der weiteren Karibikregion belaufen sich auf rd. 166 Mrd. US Dollar, über 2.500 Menschen kamen um, die Zahl der Obdachlosen beträgt mehrere Zehntausende." (Autorenreferat

Designing a Broadband Pump for High-Quality Micro-Lasers via Modified Net Radiation Method

High-quality micro-lasers are key ingredients in non-linear optics, communication, sensing and low-threshold solar-pumped lasers. However, such micro-lasers exhibit negligible absorption of free-space broadband pump light. Recently, this limitation was lifted by cascade energy transfer, in which the absorption and quality factor are modulated with wavelength, enabling non-resonant pumping of high-quality micro-lasers and solar-pumped laser to operate at record low solar concentration. Here, we present a generic theoretical framework for modeling the absorption, emission and energy transfer of incoherent radiation between cascade sensitizer and laser gain media. Our model is based on linear equations of the modified net radiation method and is therefore robust, fast converging and has low complexity. We apply this formalism to compute the optimal parameters of low-threshold solar-pumped lasers. It is revealed that the interplay between the absorption and self-absorption of such lasers defines the optimal pump absorption below the maximal value, which is in contrast to conventional lasers for which full pump absorption is desired. Numerical results are compared to experimental data on a sensitized Nd[superscript 3+]:YAG cavity, and quantitative agreement with theoretical models is found. Our work modularizes the gain and sensitizing components and paves the way for the optimal design of broadband-pumped high-quality micro-lasers and efficient solar-pumped lasers.Russell Berrie Nanotechnology InstituteTechnion, Israel Institute of Technology. Grand Technion Energy ProgramIsrael Strategic Alternative Energy Foundatio

Robust Replication Control Is Generated by Temporal Gaps between Licensing and Firing Phases and Depends on Degradation of Firing Factor Sld2

Temporal separation of DNA replication initiation into licensing and firing phases ensures the precise duplication of the genome during each cell cycle. Cyclin-dependent kinase (CDK) is known to generate this separation by activating firing factors and at the same time inhibiting licensing factors but may not be sufficient to ensure robust separation at transitions between both phases. Here, we show that a temporal gap separates the inactivation of firing factors from the re-activation of licensing factors during mitosis in budding yeast. We find that gap size critically depends on phosphorylation-dependent degradation of the firing factor Sld2 mediated by CDK, DDK, Mck1, and Cdc5 kinases and the ubiquitin-ligases Dma1/2. Stable mutants of Sld2 minimize the gap and cause increased genome instability in an origin-dependent manner when combined with deregulation of other replication regulators or checkpoint mechanisms. Robust separation of licensing and firing phases therefore appears indispensable to safeguard genome stability

A CDK-regulated chromatin segregase promoting chromosome replication

The replication of chromosomes during S phase is critical for cellular and organismal function. Replicative stress can result in genome instability, which is a major driver of cancer. Yet how chromatin is made accessible during eukaryotic DNA synthesis is poorly understood. Here, we report the characterization of a chromatin remodeling enzyme-Yta7-entirely distinct from classical SNF2-ATPase family remodelers. Yta7 is a AAA+ -ATPase that assembles into \~1 MDa hexameric complexes capable of segregating histones from DNA. The Yta7 chromatin segregase promotes chromosome replication both in vivo and in vitro. Biochemical reconstitution experiments using purified proteins revealed that the enzymatic activity of Yta7 is regulated by S phase-forms of Cyclin-Dependent Kinase (S-CDK). S-CDK phosphorylation stimulates ATP hydrolysis by Yta7, promoting nucleosome disassembly and chromatin replication. Our results present a mechanism for how cells orchestrate chromatin dynamics in co-ordination with the cell cycle machinery to promote genome duplication during S phase