| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 97 === Recently, for the advance high brightness light emitting diodes (LEDs) has been obtained of epitaxy technology. The internal quantum efficiency of AlGaInP LED is up to 99% for a good quality crystalline, the external quantum efficiency is still very poor. Therefore, the output power of LED is still low compared to conventional light sources for high-flux lighting systems, requiring further improvements on LED light-output efficiency. The purpose of this thesis is by using various chip shapes of LEDs to improve the external quantum efficiency and light extraction.
In this thesis, we design some methods of fabrication-process to improve light-output. At first, remove partial of the GaAs sidewall substrate by wet etching technique. By etching GaAs sidewall substrate, the non-radiative center caused by defects around the optical devices would be reduced. Besides, the reflected photons comes from Distributed Bragg reflector (DBR) would be improved. The light out of the reflection angle of DBRs could pass through by the sidewall etching region, and enhanced the Luminous intensity. Longer etching time led to higher luminous intensity. However, the improvement was limited to the proportion of sidewall etching to chip size is being 13.4%, confined by numerical calculation. Efficiency was raised by 10.9% and 18.7% at an operation current of 20mA for chip size 9mil and 12mil sizes, respectively.
Followed, the fabrication process was dry etching on GaP window layer, which is implemented by inductively coupled plasma (ICP) employing the mixture of CH4 and BCl3 gases. The slanted sidewall angle was about 67°. The oblique sidewall could reduce total internal reflection and enhance the light extraction. It was found that the longer etching time led to higher luminous intensity at the cost of poor the electrical property, i.e., the forward voltage was slightly increased. Under the operation current of 20mA, the brightness of the shaped 9 mil AlGaInP LEDs was increased to 1.104 times as compared with the conventional LED.
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