利用陽極氧化鋁製作奈米尺寸圖形化藍寶石基板用以成長氮化鎵發光二極體

Abstract

圖形化藍寶石基板常（PSS）被用以進行氮化鎵異質磊晶，以提升磊晶品質及光取出效率。本研究為利用陽極氧化鋁(Anodic aluminum oxide, AAO)製作具有凹洞陣列的奈米尺寸圖形化藍寶石基板(Nano Patterned Sapphire Substrate, NPSS)，並與傳統平面基板(conventional sapphire substrate, CSS)和微米圖形藍寶石基板(Micro Patterned Sapphire Substrate, MPSS)比較奈米尺寸圖形對LED元件的影響。

調整100-160V的氧化電壓進行氧化還原反應得出不同形貌之AAO，並經過RIE乾蝕刻在基板形成三角錐形孔洞後,在C面進行氮化鎵磊晶，製作成波長為433nm之藍光發光二極體。C面太小的NPSS-S難以磊晶出平整的氮化鎵，預先沉積一層薄氮化鎵的NPSS-G1和G2則磊晶成功。

根據EPD和XRD的結果分析，圖形尺寸縮小的NPSS擁有比MPSS和CSS好的磊晶品質。然而MPSS卻有最大的發光強度，說明孔洞型NPSS雖然能夠提升磊晶品質，加強內部量子效率，但是對光取出率沒有太大幫助。從遠場發散角圖形也看出NPSS基板由側面出光，光取出效率低落。

MPSS基板圖形為島狀圖形，能對氮化鎵磊晶層形成表面粗化，有效提升光取出率。而NPSS基板的孔洞圖形沒有表面粗化的效果，平整的磊晶層界面難以改變光子方向，甚至會形成全反射，限制光取出率。

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.