Effects of Passivation Layers on Characteristics of GaN-Based Light-Emitting Diodes

• Main Authors: Chung-Yi Lin, 林中一
• Other Authors: 武東星
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/70023580408584659087

碩士 === 國立中興大學 === 精密工程學系所 === 95 === Dielectric thin-film materials such as SiNx and SiO2 are widely used in the semiconductor industry. In this thesis, the dielectric passivation layers deposited by plasma-enhanced chemical vapor deposition were attempted to protect the GaN light-emitting diodes (LEDs) and to enhance the light extraction efficiency. The effects of refractive index and thickness of the passivation layers on the performance of GaN LEDs (λp=460 nm) are investigated and discussed. The refractive index of the SiNx film used in this study was measured to be 1.81, 1.86, 1.99, and 2.03 while 1.46 for the SiO2 film. Based on these data and Trace Pro simulation, the LED bare chip with an optimum SiO2 thickness can achieve 40% light extraction efficiency. Furthermore, the LED bare chip with an optimum SiNx thickness (n=1.81) after epoxy package can achieve the light extraction efficiency of 61.4%. Under a 20-mA current injection, the output power of the LED chip with a 2000-Å thick SiO2 can reach 10.29 mW. For the lamp package sample, the output power can reach 18.7 mW using a 1500-Å-thick SiNX passivation layer. In contrast, the output powers of the GaN LED bare chip and lamp samples without any passivation showed only 8.05 and 14.66 mW, respectively. A prime concern of the passivation layer on GaN LED is their reliability issues. It was found that the passivated GaN LED samples can maintain the forward voltage (Vf) and leakage current (Ir) performance with the degradation below 20% and 1 μA, respectively (after 504 hours). These results indicate that the reliability and the light extraction efficiency of the GaN LED can be improved using the chip passivation technique.