Outreach Programs

Education Programs Technology Outreach Program International Programs Distinguished Lecturer Series International Center for Materials Research MRL Diversity Fellowship MRL Travel Fellowship

Intern: Karun Vijayraghavan, Electrical Engineering, UC Santa Barbara Mentor: Natalie Fellows Faculty Supervisor: Steven Denbaars Department: Materials

PACKAGING OF BLUE PUMPED-YELLOW PHOSPHOR LIGHT EMITTING DIODES

Surface roughening methods applied to encapsulated blue-pumped yellow phosphor white light emitting diodes (LEDs) for the enhancement in light extraction was studied. Extraction loss due to total internal reflection is present because of the large reduction step change in the refractive index of the encapsulation material (n~1.4 - 1.6) relative to air (n=1). The theory put at test is a higher probability of light transmission if the boundary between the two media is diffuse as opposed to specular. Total internal reflection is less likely to occur for diffuse profiles because of an increase in surface texture and is conducive to a greater amount of phonon flux leading to higher light extraction efficiencies. LED packaging consists of a die encapsulated in a silicone resin having a spatial geometry of cylindrical sidewalls topped with a hemispherical dome. Surface profile analysis via scanning electron microscopy reveals a desirable uniform roughened topography and radiometric measurements of packaged InGaN blue LEDs show a maximum of 7 percent increase in power when compared to unroughened packages.

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