Micro-hemisphere array fabrication : improving efficiency and color tunability of GaN LED

• Main Author: Lai, Xinyi
• Other Authors: Sun Handong
• Format: Theses and Dissertations
• Language: English
• Published: 2016
• Subjects: DRNTU::Science
• Online Access: http://hdl.handle.net/10356/69018
• Institution: Nanyang Technological University

Light emitting diodes (LED), is used prevalently in many current lighting applications. Creating high powered and efficient LEDs decreases energy wastage, bringing forth environmental and financial benefits. We propose an original method of increasing the efficiency of LEDs by fabricating epoxy-based micro-hemisphere of different spacing on the surface of the LED using a micro-plotter, through a simple and inexpensive fabrication process. This new methodology will improve the power output, external quantum efficiency and tune the emission color of Gallium Nitride (GaN) LED, with a cheaper and less complex procedure as compared to current methods used in the industry. From the results, a 10 mA injection current and 50!!m separation of the micro- hemisphere is able to achieve 23 % increase in the power output, with an enhancement factor of 1.23 in the external quantum efficiency as compared to one without the micro- hemisphere arrays. Internal heating within the LED is also reduced significantly as observations show a 0.79 nm decrease in red shift from the photoluminescence spectrum of the LED with fabricated micro-hemisphere array. Reduced internal heating will improve the lifetime of the LED devices. The color of the LED is tuned by doping the fabricated micro-hemisphere with suitable dye material. It is shown that by doping with Rhodamine 6G (R6G) and Coumarin 540A (C540A) dye, GaN LED is able to emit red and green light through the area fabricated with the micro-hemisphere array. When color emission can be properly controlled via doping, white color LED light with more practical uses can be achieved.