Room temperature midinfrared electroluminescence from GaInAsSbP light emitting diodes. .

Room temperature electroluminescence in the midinfrared near 4 µm is reported from GaInAsSbP light emitting diodes grown on GaSb by liquid phase epitaxy. Comparison of the electro- and photoluminescence revealed that light is generated on the p side of the diode. The energy shift (24 meV) is consistent with band gap narrowing and recombination via band tail states due to the Zn doping (1×1018 cm−3) in the p layer of the structure. The temperature dependent behavior of the luminescence and the improved emission intensity was attributed to recombination from localized states arising from electrostatic potential fluctuations due to compositional inhomogeneities in these alloys

Evaluation of the two-photon absorption characteristics of GaSb/GaAs quantum rings

The optical parameters describing the sub-bandgap response of GaSb/GaAs quantum rings solar cells have been obtained from photocurrent measurements using a modulated pseudomonochromatic light source in combination with a second, continuous photo-filling source. By controlling the charge state of the quantum rings, the photoemission cross-sections describing the two-photon sub-bandgap transitions could be determined independently. Temperature dependent photo-response measurements also revealed that the barrier for thermal hole emission from the quantum rings is significantly below the quantum ring localisation energy. The temperature dependence of the sub-bandgap photo-response of the solar cell is also described in terms of the photo-and thermal-emission characteristics of the quantum rings. (C) 2014 AIP Publishing LLC

Simulation of the enhanced infrared photoresponse of type-II GaSb/GaAs quantum ring solar cells

The extended photo-response of solar cells containing ten periods of GaSb/GaAs quantum rings imbedded in the p-i-n junction has been described using a single-band representation of the type-II quantum ring structure. By fitting the experimental data, the authors were able to deduce that the quantum rings are well represented by a Gaussian height distribution and a large valence band discontinuity. The simulated band of states is shown to be well matched to the photoluminescence analysis of the structure, with the inhomogeneous size distribution resulting in a band of hole states roughly 390 meV above the valence band

Photoluminescence studies of individual and few GaSb/GaAs quantum rings

We present optical studies of individual and few GaSb quantum rings embedded in a GaAs matrix. Contrary to expectation for type-II confinement, we measure rich spectra containing sharp lines. These lines originate from excitonic recombination and are observed to have resolution-limited full-width at half maximum of 200 µeV. The detail provided by these measurements allows the characteristic type-II blueshift, observed with increasing excitation power, to be studied at the level of individual nanostructures. These findings are in agreement with hole-charging being the origin of the observed blueshif

Geospatial analysis and living urban geometry

This essay outlines how to incorporate morphological rules within the exigencies of our technological age. We propose using the current evolution of GIS (Geographical Information Systems) technologies beyond their original representational domain, towards predictive and dynamic spatial models that help in constructing the new discipline of "urban seeding". We condemn the high-rise tower block as an unsuitable typology for a living city, and propose to re-establish human-scale urban fabric that resembles the traditional city. Pedestrian presence, density, and movement all reveal that open space between modernist buildings is not urban at all, but neither is the open space found in today's sprawling suburbs. True urban space contains and encourages pedestrian interactions, and has to be designed and built according to specific rules. The opposition between traditional self-organized versus modernist planned cities challenges the very core of the urban planning discipline. Planning has to be re-framed from being a tool creating a fixed future to become a visionary adaptive tool of dynamic states in evolution