| Summary: | 碩士 === 國立中興大學 === 精密工程學系所 === 98 === The brightness of a LED is determined by its radiant efficiency, i.e. the multiplication of the internal quantum efficiency and the external quantum efficiency. Even though the internal quantum efficiency of high quality LEDs with double hetero junction can reach as high as 99%, it is still very difficult to achieve an external quantum efficiency higher than 10%. This thesis studies the potential methods for increasing the external quantum efficiency of LEDs, including the roughening of the window layer and applying various patterns on the mirror layer; the patterns applied on the mirror layer are disordered roughening, ordered array, and regular flat surfaces, respectively. The experimental data show that the light emitting angle measured in full width half maximum (FWHM) of these specially-treated AlGaInP LEDs can vary from 12° reduction to 14° enhancement as compared to that of the traditional LEDs with flat window layer and flat mirror. The statistically averaged radiant efficiency of LEDs with rough window layer and flat mirror is 1.45 times that of traditional LEDs. However, the statistically-averaged radiant efficiency of LEDs with rough window layer and patterned mirror can only reach up to 1.38 times that of traditional LEDs. These results demonstrate that the patterned mirror can indeed change the radiant efficiency, but the patterns used in this study are not effective enough to increase the LED radiant efficiency. This might be due to the facts that an optimal mirror pattern has not been found or the itching process has reduced the mirror surface flatness, causing diffused scattering, trapping and absorption of the photons within the LEDs. If an optimal and higher quality patterned mirror can be designed and fabricated with the assistance of theoretical simulations, it should be possible to raise the radiant efficiency of LEDs.
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