| Summary: | 碩士 === 正修科技大學 === 電子工程研究所 === 93 === In this thesis, InGaN based white LEDs were successfully fabricated by using metal organic chemical vapour deposition (MOCVD). In the process, p-GaN without and with surface roughness were epitaxial grown under normal temperature (10000C) and low temperature (8000C), respectively. It was found that we could achieve a high output extraction and reduce the probability of total reflection between GaN and air. Hence, the external efficiency and color stability of white LED with p-GaN surface roughness were much better than that without surface roughness. In contrast, the performance of current-voltage characteristics of white LED with p-GaN surface roughness was a little poor.
Then, the two different current conditions were used as the testing current to complete acceleration tests. First, the various current increased with time will be adopted to decide the better reliability between white LEDs without and with p-GaN surface roughness. It can be found that, under high injection current, the output light related to YAG phosphor from InGaN white LED was decreased due to the degradation of YAG phosphor. It was also found that the red shift of peak wavelength for InGaN blue LEDs can be discovered with increasing temperature. The other testing current is constant current. There are four conditions of 50mA, 60mA, 70mA, 80mA to realize acceleration test. Under high injection current, we could predict white LEDs life-time at 20mA by first order exponential decay mathematics model. The estimated life-time of white LED without and with p-GaN surface roughness are 19498 and 44668 hours, respectively.
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