Observation of Internal Light Intensity Distribution of Light Emitting Diodes Grown on Patterned Sapphire Substrate by Optical Microscopy

• Main Authors: CHUNG-HAO LEE, 李中皓
• Other Authors: Jung-Chieh Su
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/83264250963170104089

碩士 === 國立臺灣科技大學 === 電子工程系 === 102 === In general, the light emitting diodes (LEDs) are discussed its luminous quality by the variation of external light of LED. We use optical microscopy in combination of high magnification objective lens and mobile platform, We could focus on the surface and lateral regions of LED to investigate the epitaxy quality. Through the optical system we would investigate the light intensitiy distribution of pattern when the light emit in the patterned sapphire substrate, and we verify this phenomenon by lighttools optical simulation software. We could merger different luminous regions of LED by the different injection current. As the different injection current, we could investigate that current spreading in the internal regions of LED was not uniform. The light intensity would stronger concentrate in the nearby electrode regions. When the injection current increased, and the phenomenon was more obvious. Then we study of far-field light pattern variation between non-patterned sapphire substrate and patterned sapphire substrate. The results showed that far-field light pattern had same profile between non patterned sapphire substrate and patterned sapphire substrate LED. Finally, we design four different shapes of patterned sapphire substrates. We changed pattern’s spacing, height and radius to investigate the effects of light extraction efficiency. As the results showed that the light extraction efficiency higher when the pattern’s spacing was closer. We found that the pattern shape which aspect ratio = 1 has the best effect to enhance the extraction efficiency. The cone shape which has the highest light extraction efficiency 34%, and the enhancement of light extraction efficiency was 72 % compare with non-patterned sapphire substrate LED. Apply this system to measure in the internal regions of LED, the truly influence of the patterned sapphire substrate effect on LED would be performed. For designing greater efficiency light-emitting diode chip provides reference and assistance in the future.