| Summary: | 碩士 === 國立交通大學 === 材料科學與工程學系所 === 102 === Patterned sapphire substrates was used to improve crystal quality and light extraction of LED. The study is focused on producing nano-scaled patterned sapphire substrates (NPSS) that possess nano- pits array by using anodic aluminum oxide (AAO). Then compare the effect of nano pattern on LED device with conventional sapphire substrates (CSS) and micro-patterned sapphire substrates (MPSS).
Adjust oxidation voltage between 100~160V in redox reaction to obtain AAOs with different morphology, and create pattern through RIE dry-etching. NPSS-S was fail to epitaxy due to few C-plane, while NPSS-G1 and G2 were success to fabricate 433nm blue light LED.
According to EPD and XRD results, NPSS with smaller pattern has better quality than MPSS and CSS. However, MPSS has larger light output power than NPSS. This indicates that the pits pattern of NPSS is ineffective in increasing LEE , although crystal quality was improved. Far-field radiation pattern shows that light was extracted from sidewalls of NPSS, which means the low LEE of NPSS.
Island liked pattern of MPSS has surface roughening effect to improve LEE, while pit pattern of NPSS cause no surface roughening on GaN. Smooth GaN surface could not redirect light direction, instead of restrict light extraction due to total internal reflection, and result in a low LEE.
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