(In,Ga)N/GaN microcavities with double dielectric mirrors fabricated by selective removal of an (Al,In)N sacrificial layer

Comparable microcavities with 3/2 (~240 nm) active regions containing distributed (In,Ga)N quantum wells, grown on GaN substrates and bounded by two dielectric mirrors, have been fabricated by two different routes: one using laser lift-off to process structures grown on GaN-on-sapphire templates and the second using freestanding GaN substrates, which are initially processed by mechanical thinning. Both exploit the properties of an Al0.83In0.17N layer, lattice matched to the GaN substrate and spacer layers. In both cases cavity quality factors >400 are demonstrated by measurements of the cavity-filtered room-temperature excitonic emission near 410 nm

Magnetic Field Amplification in Galaxy Clusters and its Simulation

We review the present theoretical and numerical understanding of magnetic field amplification in cosmic large-scale structure, on length scales of galaxy clusters and beyond. Structure formation drives compression and turbulence, which amplify tiny magnetic seed fields to the microGauss values that are observed in the intracluster medium. This process is intimately connected to the properties of turbulence and the microphysics of the intra-cluster medium. Additional roles are played by merger induced shocks that sweep through the intra-cluster medium and motions induced by sloshing cool cores. The accurate simulation of magnetic field amplification in clusters still poses a serious challenge for simulations of cosmological structure formation. We review the current literature on cosmological simulations that include magnetic fields and outline theoretical as well as numerical challenges.Comment: 60 pages, 19 Figure

Thinning of N-face GaN (000-1) samples by inductively coupled plasma etching and chemomechanical polishing

The processing of N-polar GaN (000 (1) over bar) samples has been studied, motivated by applications in which extensive back side thinning of freestanding GaN (FS-GaN) substrates is required. Experiments were conducted on FS-GaN from two commercial sources, in addition to epitaxial GaN with the N-face exposed by a laser lift-off process. The different types of samples produced equivalent results. Surface morphologies were examined over relatively large areas, using scanning electron microscopy and stylus profiling. The main focus of this study was on inductively coupled plasma (ICP) etch processes, employing Cl-2/Ar or Cl-2/BCl3Ar gas mixtures. Application of a standard etch recipe, optimized for feature etching of Ga-polar GaN (0001) surfaces, caused severe roughening of N-polar samples and confirmed the necessity for specific optimization of etch conditions for N-face material. A series of recipes with a reduced physical (sputter-based) contribution to etching allowed average surface roughness values to be consistently reduced to below 3 nm. Maximum N-face etch rates of 370-390 nm/min have been obtained in recipes examined to date. These are typically faster than etch rates obtained on Ga-face samples under the same conditions and adequate for the process flows of interest. Mechanistic aspects of the ICP etch process and possible factors contributing to residual surface roughness are discussed. This study also included work on chemomechanical polishing (CMP). The optimized CMP process had stock removal rates of similar to 500 nm/h on the GaN N face. This was much slower than the ICP etching but showed the important capability of recovering smooth surfaces on samples roughened in previous processing. In one example, a surface roughened by nonoptimized ICP etching was smoothed to give an average surface roughness of similar to 2 nm

Dense low threshold PQR lasers can outdo LEDs (Blue Quest)

PQR lasers with ultra-low threshold current and sharp discrete multi-mode properties can outdo conventional LEDs. We have confirmed many advantages of low injection, high efficiency, high frequency PQR arrays over the conventional LEDs. We also present blue PQR laser arrays from GaN structures, which are promising for display applications as well as high efficiency solid state lighting. ? 2011 OSA.EI

Fabrication and performance of individually addressable gaN-based micro-stripe LED devices

This article covers Fabrication and performance of individually addressable gaN-based micro-stripe LED devices. It was presented at the 6th International Symposium on Blue Laser and Light Emitting Diodes in May 2006

Stripe rust resistance in wheat breeding lines developed for central Shaanxi, an overwintering region for <i>Puccinia striiformis</i> f. sp. <i>tritici</i> in China

<p>China is one of the largest stripe rust epidemic areas in the world. Central Shaanxi, an important overwintering region, serves as a ‘bridge’ between the western over-summering and eastern epidemic regions. Understanding of resistance levels and <i>Yr-</i>gene distribution in regional wheat breeding lines may provide valuable recommendations for releasing resistant cultivars for managing the disease. A total of 183 wheat breeding lines developed for central Shaanxi were tested for seedling resistance to nine Chinese races of <i>Puccinia striiformis</i> f. sp. <i>tritici</i> (<i>Pst</i>) in the greenhouse. In field tests, entries were evaluated for stripe rust resistance in Yangling, Shaanxi, an overwintering region for the pathogen and artificially inoculated with selected races. In Tianshui, Gansu Province, an over-summering region, entries were evaluated under natural infection of <i>Pst</i>. Molecular markers for <i>Yr5, Yr9, Yr10, Yr15, Yr17, Yr18, Yr26</i> and <i>Yr61</i> were used to determine the presence and absence of the genes. Among the 183 entries, 4 (2.2%) entries had effective all-stage resistance; 15 (8.2%) entries had adult-plant resistance; and 164 (89.6%) entries were susceptible to one or more races, especially to the potentially important races V26/CM42 and V26/Gui22. Over 95% of entries showed seedling stage susceptibility in Tianshui across years. Resistance genes <i>Yr9, Yr17</i> and <i>Yr24/Yr26</i> were postulated in some of the breeding lines based on the seedling responses and molecular markers. <i>Yr5, Yr10, Yr15, Yr18</i> and <i>Yr61</i> were not present in any of the breeding lines. These results suggest that, when multiple races of <i>Pst</i> disperse into Shaanxi from southern Gansu Province, over 90% of wheat breeding lines are susceptible. Based on the results, recommendations are made for releasing or not releasing the individual lines, and a strategy of combining genes for effective all-stage and adult-plant resistance is proposed for developing wheat cultivars with high-level durable resistance to stripe rust.</p