藍寶石基板上圖案的形貌與其對氮化鎵磊晶成長的影響

Abstract

本研究為利用二次溼式蝕刻技術，製備間距(Pitch)為3μm的類似金字塔狀之凸型陣列式圖案化藍寶石基板(Patterned Sapphire Substrate, PSS)，據研究此種形拓有利於側向磊晶成長(ELOG)時，讓貫穿性差排(Threading dislocations, TDs)被彎曲至側向，因此使得TDs而無法繼續往上延伸，並且因為其金字塔狀之多面體的特殊形拓，可有利於光子從發光二極體中被發射出去，故可以同時達到改善氮化鎵發光二極體的內部量子效率以及光的取出效率。

根據文獻記載，經過濕式蝕刻(0001)面的圖案化藍寶石，首先出現的面就是R{1-102}面族，但根據本實驗的結果和一般研究中所指出的R或R'{1-10K} 面族並不同，而是一個{1-437}的面族。

本研究還詳細觀察到金字塔狀之圖案化藍寶石基板，在一次蝕刻和二次蝕刻之各個時間點其形拓是如何形成，並且我們所製備出來的圖案形貌是一個上有三個面和下有六個面，分別屬於R'{1-105}面族和{1-437}面族，我們將針對它有所討論。

並且據文獻的記載，大部分的研究都希望減低藍寶石基板中的C-plane所佔的比例，以增加側向磊晶成長時的面積，在本研究中還從實驗過程中觀察到在減低C-plane所佔面積時，所發現到的問題，並歸納出在間距微縮下，濕式蝕刻製程所面臨的挑戰。

The purpose of this study is to investigate the effect of pattern morphology on the patterned sapphire substrate (PSS) for GaN epitaxial growth. Two-step wet etching technique was used to fabricate PSS. Pitch 3µm pyramidal-like patterns of convex array on C-plane sapphire were fabricated. PSS can provide a favorable condition to bend threading dislocations toward pyramid-like pattern. Besides, PSS can improve light extraction efficiency because it has multiple facets on one pattern. According to common paper, the first appears facet is R-plane when wet etching the C-plane sapphire. But we inspect the first appearing facet that is not belonged to R or R`-facet family. Because there are 6 facets on the first appears morphology, in a word that it is not fitting “3-fold symmetry” structure of sapphitre structure. And we define it a special facet family {1-437}. People were under the impression that PSS composed of R{1-102} and/or R'{1-10K} facets. However, in this study, we found that PSS composed of three top facets (R'{1-105}) and six bottom facets ({1-437}). The effects of these facets and percentage of C-plane area on the GaN crystal epitaxy quality were also investigated.