30% external quantum efficiency from surface textured, thin-film light-emitting diodes

There is a significant gap between the internal efficiency of light-emitting diodes (LEDs) and their external efficiency. The reason for this shortfall is the narrow escape cone for light in high refractive index semiconductors. We have found that by separating thin-film LEDs from their substrates (by epitaxial lift-off, for example), it is much easier for light to escape from the LED structure and thereby avoid absorption. Moreover, by nanotexturing the thin-film surface using "natural lithography," the light ray dynamics becomes chaotic, and the optical phase-space distribution becomes "ergodic," allowing even more of the light to find the escape cone. We have demonstrated 30% external efficiency in GaAs LEDs employing these principles

One-instanton predictions for non-hyperelliptic curves derived from M-theory

One-instanton predictions are obtained from certain non-hyperelliptic Seiberg-Witten curves derived from M-theory for N=2 supersymmetric gauge theories. We consider SU(N_1)\times SU(N_2) gauge theory with a hypermultiplet in the bifundamental representation together with hypermultiplets in the defining representations of SU(N_1) and SU(N_2). We also consider SU(N) gauge theory with a hypermultiplet in the symmetric or antisymmetric representation, together with hypermultiplets in the defining representation. The systematic perturbation expansion about a hyperelliptic curve together with the judicious use of an involution map for the curve of the product groups provide the principal tools of the calculations

A Superstring Theory in Four Curved Space-Time Dimensions

Neveu-Schwarz-Ramond type heterotic and type-II superstrings in four dimensional curved space-time are constructed as exact $N=1$ superconformal theories. The tachyon is eliminated with a GSO projection. The theory is based on the N=1 superconformal gauged WZW model for the anti-de Sitter coset $SO(3,2)/SO(3,1)$ with integer central extension $k=5$. The model has dynamical duality properties in its space-time metric that are similar to the large-small ($R\rightarrow 1/R$) duality of tori. To first order in a $1/k$ expansion we give expressions for the metric, the dilaton, the Ricci tensor and their dual generalizations. The curvature scalar has several singularities at various locations in the 4-dimensional manifold. This provides a new singular solution to Einstein's equations in the presence of matter in four dimensions. A non-trivial path integral measure which we conjectured in previous work for gauged WZW models is verified.Comment: 12 page

Ultra-high External Efficiency From Surface Textured Thin-film LEDs

Dire need for high external quantum efficiency (η_(ext)) visible light-emitting-diodes (LED's) is clearly seen as the flat panel display technology is rapidly evolves. However, there is an enormous gap between the theoretical efficiency of LED's and their actual efficiency. It has been known that good quality III-V double heterostructures can have over 90% internal quantum yields (η) for direct band-gap compounds and over 99% for AlGaAs/GaAs/AlGaAs, as we have demonstrated recently. On the other hand, run-of-the-mill commercial LED's are usually only a few percent efficient (externally)

Implications of multi-Regge limits for the Bern-Dixon-Smirnov conjecture

Planar ${\cal N} =4$ super Yang-Mills SU(N) theory is expected to exhibit stringy behavior, anticipated by the 't Hooft genus expansion and the $AdS/CFT$ correspondence. We examine the Bern-Dixon-Smirnov (BDS) conjecture for $n$-gluon amplitudes in the context of single-Regge and multi-Regge limits and show that these amplitudes have the expected Regge form in the Euclidean region.Comment: 48 pages, 8 figures; Noted added commenting on related work which appeared after the initial posting. References and clarifications added, as well as typos correcte