Geometrical design and measurement of light-emitting diode for lighting

Abstract

Year 2014 is a milestone in the history of LEDs industry. Isamu Akasaki, Hiroshi Amano and Shuji Nakamura were awarded the Nobel Prize in Physics 2014 for their contribution in the application of “bright and energy-saving white light sources” with invention of efficient blue indium gallium nitrate (InGaN) light-emitting diodes (LED) [1]. This can be treated as an admission of the impotence of LED lighting in the modern human civilization.

Although the LED- related technologies had been well developed, there are still plenty room for improvement. Normally, size of an InGaN die is in dimensions of micrometers while the sizes of LED lamps are usually hundred times larger. Regardless of the purpose on better appearance, one of the main reasons behind this phenomenon is to change the property of the emitted light to fulfill the specific requirements for different usage. External components, including diffusers, silicone encapsulant, drivers, etc…., are common parts can be found in LED products. These components will, in facts, degrade the performance of the LEDs in aspects of optical and thermal performance. In another word, reduction of the dependencies on additional components will help in improving LED performance.

Performance of LEDs in different geometries had been compared by pioneers. Enhancements of light extraction efficiency by changing the geometry of LEDs had been justified [2]. Effects of geometrical design of LED chips on the characteristic of light emission are also worth to study as to eliminate the requirement of additional components.

In this dissertation, stripe-like LEDs with aspect ratio of 1:20 are fabricated from InGaN/GaN on sapphire wafer with standard fabrication process. A series of measurements are carried out to study their emission properties. Traditional cubic LEDs will be fabricated from the same material as reference. Comparison of emission properties among stripe-like LEDs and traditional cubic LEDs justified the enhancement of LED performance by increasing the aspect ratio, which also justified the possibility to reduce the dependency of additional components by modification of LED chips.