Effect of laser lift-off process on the pattern sapphire substrates of LED device

• Main Authors: Fang, Hsin-Kai, 方星凱
• Other Authors: 吳耀銓
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/53063388692646590554

碩士 === 國立交通大學 === 材料科學與工程學系所 === 102 === Current LED manufacture technology including pattern sapphire substrate (PSS) and laser lift-off (LLO). When we combine this two technology not only can increase light extraction efficiency and internal quantum efficiency, but also can decrease the effect of joule heat effect. However when we come by PSS and LLO two technology the leakage current might increase several times. We also found that the PSS morphology after LLO is different from the original PSS, and this phenomenon hasn't been discussed yet. In this experiment we use hydrochloric acid , phosphoric acid and potassium hydroxide to clean PSS at different temperature step by step. We use SEM analysis to evaluate PSS is reusable or not. After the laser lift off ,the height of PSS on E1 and Eb was decrease to 1.43 µm and 1.29 µm from 1.5 µm, and further decrease to 1.16 µm and 1.04 µm after hydrochloric acid and phosphoric acid cleaning. By TEM and EDX analysis we know that the sapphire on the top of PSS change to amorphus aluminum oxide from crystal structure because of the temperature increase in a very short time. We can explain this via Snall's law. The origenal energy density on top of PSS is larger than the energy density on buttom of PSS. Too much energy may cause large density of defect and increase the leakage current. Moreover, because of the nitrigen gap between PSS and GaN layer, the internal reflection will happen inside the PSS ,and cause more energy density on top of PSS. As a result, the sapphire on top of PSS may melt and turn to liquid phase, and finally formed amorphous aluminum oxide. The experiment shows that if we want to reuse the PSS after LLO, we must change the shape of PSS.