| Summary: | 碩士 === 國立成功大學 === 光電科學與工程研究所 === 97 === In the mid-1990s, nitride-based material was first successfully grown on sapphire by Shuji Nakamura of Nichia co. using Metal Organic Chemical vapor deposition (MOCVD) technology. Up to now, lots efforts have been made in the promotion of light extraction and efficiency of blue GaN-based LEDs. Owing to its advantageous of small volume, long life, fast responding time, low power consumption, lasting, better quality of reliability, smaller flexible lighting fixtures, intrinsically safety, and no mercury added, a novel solid-state white lighting source, so called " new generation lighting source " has been proposed using blue GaN-based LEDs and yellow phosphor powder or direct combination of lights emitting from RGB color LEDs.
However, challenging issues of GaN-based LEDs including poor light conversion efficiency and poor thermal conducting caused by the sapphire substrate, and non-scalable light output with respect to the chip size, etc., are still open questions.
This thesis aims to tackle the challenging issues of present GaN-based LEDs. Various methods including replacing the sapphire substrate with an electroplating substrate by laser lift-off technology, designing three kinds of bottom reflectors for vertical LED, the fabricating of 40 mil-high power vertical-structured metallic GaN-based LEDs were proposed. According to the material analysis and optoelectronic characterizations, the measured optoelectronic performances of vertical LED reveal a great improvement as compared to that of conventional lateral-structured LEDs.
As compared to regular-LEDs under an injection current of 350 mA, the working Voltage is similar to conventional LED, and the increase in light EL intensity is about 97% have been obtained. It is expected that the use of LLO in conjunction with Cu/Ni substrate and the improvement of bottom reflector would make possible the fabrication of vertical LED with even larger area, higher power and better efficiency.
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