Investigation on Light-Output Enhancement of Light Emitting Diodes by the Nano-roughness structure and Pattern Substrate

• Main Authors: Chien-Chun Wang, 王建鈞
• Other Authors: Yeong-Her Wang
• Format: Others
• Language: en_US
• Online Access: http://ndltd.ncl.edu.tw/handle/99673202224965070354

博士 === 國立成功大學 === 光電科學與工程研究所 === 96 === In this article, the investigation is light-output enhancement of light emitting-diode by a technique of non-encroached epitaxial layer. First, a porous anodic alumina (PAA) film with nanoroughening is added on the top window layer of AlGaInP light-emitting diodes (LEDs) to improve the light extraction of the device. The PAA film has a natural porosity, allowing an increase of light emission intensity with no loss of damage to the semiconductor material. Because of more light to be effectively scattered into the air by the nano-pores of PAA film and a large critical angle to avoid a high level of internal light reflection by inserting PAA between air and the GaP window layer, these benefits favor the LED to have the light output improvement by 1.29 times than the conventional device. For the same sample followed by pore-widening at 40 min, the light output intensity is optimally achieved to 1.39 times. Therefore, without increasing any complexity or expense of the manufacturing processes, the PAA film and with a suitable pore-widening could substantially enhance the light extraction efficiency of a LED. One the other hand, we using a three-dimensional model with finite-difference and time-domain was established to investigate the enhancement of the light output intensity of AlGaInP light-emitting diodes (LEDs) for getting optimum parameter and realized this resolution in experiment. Second, GaN-based light-emitting diodes (LEDs) with bottom pillar (BP) structure were investigated. In this structure, a three-dimensional model with finite-difference and time-domain was established to investigate the enhancement of the light output intensity. Through comparing the normalized light extraction intensity of GaN LEDs with or without BP in different dimensions, the theoretical results show that the light output intensity in the LED with BP structure involved could be enhanced by about 30%. The influence of BP structure on the light output intensity of a LED could be explained by the physical model of light interaction. In addition, the experimental results also show the same trend to the theoretical calculations.