recent white LED article in Nature--
Saw this on the Fool board--basically the authors seem to say, and demonstrate, that there is a better substrate than SiC or sapphire upon which to grow GaN for optoelectronic devices--LiAlO2.
Nitride semiconductors free of electrostatic fields for efficient white light-emitting diodes
Authors:
P. Waltereit, O. Brandt, A. Trampert, H. T. Grahn, J. Menniger,
M. Ramsteiner, M. Reiche & K. H. Ploog
Paul-Drude-Institut fur Festkorperelektronik, Hausvogteiplatz 5-7,
D-10117 Berlin, Germany
Abstract:
Compact solid-state lamps based on light-emitting diodes (LEDs)
are of current technological interest as an alternative
to conventional light bulbs. The brightest LEDs available so far
emit red light and exhibit higher luminous efficiency than
fluorescent lamps. If this luminous efficiency could be transferred
to white LEDs, power consumption would be dramatically
reduced, with great economic and ecological consequences. But
the luminous efficiency of existing white LEDs is still very low,
owing to the presence of electrostatic fields within the active
layers. These fields are generated by the spontaneous and piezo-electric
polarization along the [0001] axis of hexagonal group-III
nitrides—the commonly used materials for light generation.
Unfortunately, as this crystallographic orientation corresponds to
the natural growth direction of these materials deposited on
currently available substrates. Here we demonstrate that the
epitaxial growth of GaN/(Al,Ga)N on tetragonal LiAlO2 in a
non-polar direction allows the fabrication of structures free of
electrostatic fields, resulting in an improved quantum efficiency.
We expect that this approach will pave the way towards highly
efficient white LEDs.
sunshine42 on the Fool board has actually posted a pdf file of the article:
boards.fool.com |
