Influence of Patterned Substrate on the Reliability of InGaN Light Emitting Diode Chips

• Main Authors: Chia-Hong Sun, 孫嘉鴻
• Other Authors: Man-Fang Huang
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/60284071297579575291

碩士 === 國立彰化師範大學 === 光電科技研究所 === 103 === In this thesis, the influence of patterned substrate on the reliability of InGaN light emitting diode chips was investigated. First of all, a historical review on the development of light-emitting diodes (LEDs), including basic structures, III-nitride material properties, electro-optical characteristics, and failure mechanisms were introduced in chapter one. In chapter two, some reliability-related literautres were reviewed. From studying the change in electro-optical characteristics of LEDs after burn-in stress, the failure mechanisms of LEDs can be understood, which might include defect generation, increase of leakage current shunt paths, wavelength shift and current crowding. When LEDs were operated under a high current sress, defects, originated from lattice mismatch or gallium and nitrogen vacancies, might be further generated owing to heat generation caused by non-radiative recombination. Furthermore, defect-related leakage current shunt paths could also cause nonuniform current spreading which leads to electrode degradation and decrease output power. In chapter three, threading dislocation densities and indium compositions of two LED samples, with conventional or patterned sapphire substrates, were analyzed by XRD first. From experimental results, we found that InGaN LEDs grown on patterned substrates had a higher turn-on voltage due to low indium composition in active region, and small threading dislocation density compared with conventional LEDs. Under a high current stress, the output power of conventional LED degrade due to defect generation, which leads to a low-resistance current path, and causes current crowding effect and electrode degradation. However, under a high temperature stress, the output power of conventional LED was improved slightly due to better current spreading caused by thermal annealing. On the contrary, the output power of LED with patterned substrate was increased owing to better crystal quality and improved current spreading casued by annealing effect. Although after a longer stress duration, we found that output power of LED with patterned substrate started to degrade due to defect generation and electrode degradation. Finally, chapter four is the summary of this thesis. We concluded that LED with patterned sapphire substrate has a better reliability and performace. The cause of output power improvement due to anneaing cant be further studied in the future.