| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 94 === 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 patterned laser lift-off (patterned LLO) technology, depositing a sputtered-Indium-Zinc Oxide film as a current spreading layer atop n-GaN layer for the fabricating of 40 mil-high power vertical-structured metallic GaN-based LEDs (VM-LEDs) were proposed. Using a KrF excimer laser (248 nm) and nickel electroplating, it takes about 10 min for the transfer of GaN epi-layer from 2” sapphire substrate to Ni substrate with an acceptable yield(>50%). According to the material analysis and optoelectronic characterizations, the measured optoelectronic performances of VM-LEDs reveal a great improvement as compared to that of conventional lateral-structured LEDs.
In experiments, the use of inductive coupling plasma (ICP) dry-etching to increase the carrier concentration of n-GaN layer and sputtered-IZO as a transparent conducting layer to enhance current spreading was demonstrated and discussed. As compared to regular-LEDs under an injection current of 350 mA, the series resistance of VM-LEDs was lowered by about 60% and forward voltage drop was also decreased by 0.3 ~ 0.5 V, and the increase in light output power (LOP) is about 97% have been obtained. It is expected that the use of LLO in conjunction with Ni substrate and optimum-thickness IZO TCL would make possible the fabrication of VM-LEDs with even larger area, higher power and better efficiency.
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