| Summary: | 碩士 === 國立臺灣海洋大學 === 光電科學研究所 === 96 === In this thesis, we used the temperature dependent photoluminescence (PL) and X-ray diffraction (XRD) measurements to study the luminescent properties of ultraviolet InGaN/(Al)GaN multiple quantum wells (MQWs) light-emitting diode (LED) structures. The compositions of the InGaN/(Al)GaN layers studied here were In0.03Ga0.97N/Al0.07Ga0.93N (sample 365), In0.04Ga0.96N/Al0.002Ga0.998N (sample 385) and In0.06Ga0.94N/GaN (sample 405), respectively.
Experimental results indicated that sample 365 has the largest internal quantum efficiency, the fast quenching rate in PL intensity with increasing temperature and the smallest light extraction efficiency. The largest Al compositions in AlGaN barrier layers of sample 365 leads to the highest quantum confined energy of carriers. The possible diffusion of Al atoms into quantum well layers may result in the largest carrier localization energy and exciton binding energy. On the other hand, the XRD patterns showed the existence of the most deteriorated interfaces of MQWs of sample 365. This may possibly led to the fast quenching rate in PL intensity with increasing temperature. Besides, the extraction efficiency of sample 365 is also the smallest due to the smallest critical angle of light internal reflection for the InGaN/p-AlGaN interface. Considering all these results, the smaller PL intensity of sample 365 than that of sample 405 can be understood.
Accordingly, though increasing Al composition in the AlGaN barrier layers can help to increase internal quantum efficiency, it may cause the lower interface quality and the lower external quantum efficiency. Thus, to prevent the interface quality from becoming poor as increasing the Al content in AlGaN barrier layers is an important issue for the fabrication of high efficient ultraviolet LEDs.
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