标题: 雷射剥离对发光二极体中图形化蓝宝石基板的影响
Effect of laser lift-off process on the pattern sapphire substrates of LED device
作者: 方星凯
Fang, Hsin-Kai
吴耀铨
材料科学与工程学系所
关键字: 雷射剥离;图形化蓝宝石基板;laser lift-off;pattern sapphire substrates
公开日期: 2013
摘要: 目前在改良发光二极体(Light-emitting diode, LED)元件效能及应用的技术包括了图形化蓝宝石基板(Patterned sapphire substrate, PSS)、雷射剥离(Laser lift-off)等。结合上述两种技术不但可以增加LED的光取出率、提升LED的内部量子效率,也能降低热效应对元件所造成的影响。然而当结合PSS及LLO两种技术时,LED的漏电流往往会有些许的提升;另外,我们发现PSS的表面形貌在经过LLO之后与原PSS的形貌有明显的不同,且此现象原因尚未被讨论。本论文系对于LLO后的PSS做研究并且讨论其产生变化的原因。
本实验利用盐酸(HCl)、磷酸(H3PO4)以及氢氧化钾(KOH)在不同的温度下,依步骤清洗雷射玻璃后的图形化蓝宝石基板用以区别其表面的残留物,并且利用SEM观察其表面,藉此评估图形化蓝宝石基板重复使用的可行性。在经过雷射剥离的制程后,从剥离能量E1以及Eb可观察到,图形化蓝宝石基板的高度有明显的下降,从原本的1.5μm分别降至1.43以及1.29μm,将试片进一步的利用盐酸及磷酸清洗过后更降至1.16μm及1.04μm。
此外,由TEM、EDX分析可以得知,图形化蓝宝石基板顶部部分的单晶氧化铝因为在短时间内快速的升、降温,在过程中转变成为非晶质的结构。此现象可由简单的司乃尔定律解释:顶部能量密度原本就较大,再加上部分光线在到达氮化镓层之前就在图形化蓝宝石基板内发生全反射,导致PSS顶部温度急遽上升,使得不但氮化镓分解,氧化铝也达到软化甚至融化的温度。显示雷射剥离后蓝宝石基板若要回收再利用,必须在图形化方式进一步作改良。
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.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT070051546
http://hdl.handle.net/11536/72677
显示于类别:Thesis


文件中的档案:

  1. 154601.pdf

If it is a zip file, please download the file and unzip it, then open index.html in a browser to view the full text content.