Optically functional structures on GaN-based light-emitting diodes for light-extraction efficiency enhancement and emission pattern control
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Authors
Ma, Ming
Issue Date
2013-05
Type
Electronic thesis
Thesis
Thesis
Language
ENG
Keywords
Materials engineering
Alternative Title
Abstract
In this dissertation, we present a technique that provides full control of refractive index and surface structure at the LED surface: LEDs having patterned graded-refractive-index (GRIN) coatings (GRIN LEDs). Micro-patterned GRIN coatings that enhance light extraction and enable control of the emission pattern in GaN-based LEDs are designed and demonstrated. The coatings are patterned into arrays of GRIN micro-pillars, which are composed of five dielectric layers made of (TiO_2)_x(SiO_2)_1-x with the bottom coating (adjacent to semiconductor) having the highest refractive index and the top coating (adjacent to air) having the lowest refractive index. The GRIN micro-pillars, including their planar geometric shape and size, are structured for maximum LEE and emission-pattern control. LEDs patterned with an array of four-pointed-star-shaped GRIN micro-pillars show a 155% enhancement in light-output power over an uncoated planar reference LED. In addition, the peak emission intensity of the GRIN LEDs is shown to be controllable from ±20° to ±50° off the surface-normal, demonstrating GRIN LEDs with high LEE and emission-pattern control. These two characteristics can be tuned to match specific target applications of the LEDs.
Description
May 2013
School of Engineering
School of Engineering
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY