Effects of SiO2 Deposition Methods on Leakage Currents of GaN Light - Emitting Diodes

• Main Authors: Sheng-Hui Lin, 林昇輝
• Other Authors: 武東星
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/13170666599394056670

碩士 === 國立中興大學 === 精密工程學系所 === 94 === Recently GaN-based materials have become mature in fabricating light-emitting diodes (LEDs) from green to ultraviolet wavelength region. Generally, the planar-electrode GaN LED structure was covered by a surface passivation layer to reduce the density of surface states and avoid the possible surface leakage current paths. The leakage current level will greatly influence the luminous intensity and reliability of the GaN LED sample. In this thesis, we investigate the effect of SiO2 passivation layer on the leakage current of the GaN LED chip, where the SiO2 layers were deposited by two different methods: electron-beam (EB) evaporation and plasma-enhanced chemical vapor deposition (PECVD). The characteristics of SiO2 layers deposited by EB evaporation and PECVD were compared in terms of refractive index, etch rate and leakage current. It was found that the deposition temperature and oxygen flow rate had large effects on the SiO2 passivation layer during the EB evaporation process. Under a constant oxygen flow rate (20 sccm), the higher deposition temperature (200~320°C) used for EB SiO2 deposition makes the lower leakage currents of GaN LEDs. The leakage current was found to increase when the oxygen flow rate increased under a fixed deposition temperature of 200°C. For the PECVD process, we can adjust the flow ratio of N2O/SiH4 and the deposition temperature to achieve a high-quality SiO2 thin film, i.e. the higher refractive index and lower etch rate. The leakage current deposited by PECVD can reduce to three order of magnitude lower than that deposited by EB evaporation. Therefore the PECVD passivation process was confirmed to improve the LED leakage current and production yield, avoiding the unwanted rework processes. Nevertheless, due to the lower production capability of PECVD as compared with the EB evaporation, the improvement of PECVD productivity will be the next step of this work.