Recent Developments in LEDs

Here is some more information about the inverted Pyramid LED.
It was described quite recently (M.R. Krames et. al., "High-Power truncated-inverted-pyramid (AlxGa1-x)0.5In0.5P/GaP light-emitting diodes exhibiting >50% external quantum efficiency," Applied Physics Letters, 75[16], pp. 2365, (1999)) and has a large optical efficiency leading to a "external quantum efficiency" which is simply the what we called total external efficiency of 55% (as compared to about 30 % of the former champion).
The cross section below shows why: There are few reflection losses. Otherwise the device is not quite as simple as looks like. It is based on an epitaxially-grown aluminum gallium indium phosphide/gallium phosphide (AlGaInP/GaP) multiwell active region sandwiched between an n-type gallium phosphide (GaP) layer and a p-type GaP layer.
CrOss section Ofinverted pyramid LED
More information can be found in a recent article from the internet or in the Scientific American from February 2001.

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© H. Föll (Semiconductor - Script)