Nanopatterned Sapphire Boosts Green Emission

Corresponding author Christian Wetzel from Rensselaer Polytechnic Institute (RPI), NY, believes that his team's work can help the development of high efficacy LEDs covering the entire visible spectrum. This could culminate in efficient lighting with a very high colour quality. Switching from a planar substrate to one patterned with 250 nmwide circular holes increased light output and reduced the threading dislocation density.

By analysing interference fringes associated with green electroluminescence from the LED, the researchers determined that nanopatterning increased light extraction by 58 percent.Although the team recorded the output from many dies, they only considered a few patterning parameter values, and Wetzel believes that a more systematic study of the influence of patterning on LED light output is warranted. Transmission electron microscopy images of the nitride films revealed that nanopatterning of sapphire cuts threading dislocation densities from 6.4 x 108 cm-2 to 3.6 x 108 cm-2.Improvement in crystal quality stems from the absence of threading dislocations from the bottom of etched holes, which are mostly stopped by open voids; and the strong suppression of threading dislocations originating from the inclined facets that change direction, and propagate within the growth plane.

After loading the patterned substrate into an MOCVD tool, an epitaxial structure was deposited that included an active region with eight 3 nm-thick InGaN quantum wells separated with GaN barriers.A doped, 10 nm-thick AlGaN electronblocking layer also formed part of the high power laser diodes.Devices with no encapsulation and dimensions of 350

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