INVESTIGATION OF OPTICAL STRUCTURES FOR ENHANCING THE LIGHT EXTRACTION FICIENCY OF WHITE LED

Open Access
Author:
Chen, Wei-Liang
Graduate Program:
Electrical Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
August 27, 2009
Committee Members:
  • Shizhuo Yin, Thesis Advisor
Keywords:
  • Bragg reflector
  • Light-emitting diodes
  • Zemax
Abstract:
Recently, phosphor-conversion has been widely used in producing white light-emitting diodes (LEDs). In phosphor-converted (pc) LEDs, the blue LED chip is surrounded by the phosphor medium. When the blue light strikes the phosphor, some of the blue light is converted to yellow light, and the combination of two complementary lights produce the white light. In this method, the internal quantum efficiency could reach almost 100%; however, the light extraction efficiency of LED is still low. In this thesis, we add a Bragg reflector to the LED between the blue light chip and the yellow light phosphor layer. The reflector can reflect the backward yellow light and allow the forward blue light, and enhancement of the light extraction efficiency of LED is achieved. All of the optical models and simulations are made by ray-tracing software ZEMAX.