"Light Extraction Efficiency in GaN-Based Light-Emitting Diode Technology"
Department: Electrical and Computer Engineering Advisor: Professor Nelson Tansu
GaN-based light-emitting diodes (LEDs) have drawn much attention in recent years for solid state lighting and display applications. Low light extraction efficiency in LED technology exists mainly because of the Fresnel effect and total internal reflection (TIR), both of which relate to the difference between the indices of refraction at the interface between the LED and its surroundings. Recently, the use of a low-cost, large-scale practical method was implemented using various-sized silica/polystyrene microlens arrays to improve the light extraction efficiency of GaN-based LEDs. In this work, rapid convective deposition (RCD) is used to modify the surface properties of GaN-based LEDs to improve the light extraction efficiency by two to three times. The use of microlens array LEDs is extended from 1-µm SiO 2 microspheres down to 100-nm (500-nm, 400-nm, 250-nm, and 100-nm) SiO2 nanospheres to optimize the extraction efficiency of GaN-based LEDs. By varying the deposition speed, blade angle, suspension concentration, and suspension volume, it was possible to achieve optimized close-packed 2-D monolayer micro/nano lens structures. The analysis shows that the light extraction has a strong correlation with the size of the micro/nanospheres used to form the microlens array, and therefore the ability to fabricate a nanolens array is critical in the optimization process of the light extraction effic iency of GaN-based LEDs. In this study, the various-sized microlens array were deposited on the LED by the RCD method, and a comparison of the structures was carried out.
Peter Orlando Weigel is a senior Electrical Engineering major with minors in Business and Creative Writing. Starting in the fall of 2011, he conducted photonics research under Professor Nelson Tansu in the Center for Optical Technologies here at Lehigh University, where he worked on several projects related to novel simulated optical waveguides and more efficient light-emitting diode technology. Peter is also a member of the Martindale Student Associates Program, Tau Beta Pi national engineering honors society, Psi Upsilon fraternity, and Lehigh University Philharmonic Orchestra. Next fall, Peter will be attending graduate school to continue pursuing his research interests by working to obtain his Ph.D. in electrical engineering with a focus in applied physics.