轉移至矽基板之薄膜氮化鎵發光二極體之研究

Abstract

使用矽做為基板，成長氮化鎵薄膜有很多好處，像是低成本，大面積使用率，不錯的電熱導率等。然而對於氮化鎵成長在矽基板上還是有很多問題。 第一，氮化鎵與矽基板因為有晶格常數(~17%)、熱膨脹係數(~54%)的不匹配而有破裂和高缺陷密度的產生，造成非輻射複合。第二，矽基板容易吸光，成長氮化鎵薄膜會降低光萃取效率，因此相較成長在藍寶石基板上，有較低的外部量子效率，為了解決這些問題，使用薄膜轉移技術可以減少因應力所引起的壓電極化場，使得內部量子效率有所提升。 論文的第一部份，成功製作出兩種不同類型的氮化鎵薄膜鍵合在矽基板上。使用光激發螢光量測，可以發現不論是氮化鎵薄膜成長在藍寶石基板或是矽基板，藉由薄膜轉移技術後，都會使內部量子效率提升，這個實驗結果也使用在室溫下共焦變深度拉曼量測得到證實，因為氮化鎵薄膜成長在藍寶石基板和矽基板經由薄膜轉移技術後都會使氮化銦鎵的壓縮應力獲得釋放。 論文第二部分，使用感應耦合電漿系統和化學機械研磨對氮化鎵薄膜鍵合在矽基板的厚度進行減薄，當氮化鎵薄膜厚度剩下1 m時，內部量子效率有62.9%，並且相較於原始結構有40.3%的提升率，原因是因為氮化銦鎵受到的壓縮應力得到釋放。

Using silicon as substrate for GaN film growth has various advantage, such as low cost, large scale availability, good thermal and electrical conductivity. However, there are still some problems in the development of GaN on silicon. First, the large mismatch in the lattice constant (~17%) and the thermal expansion coefficient (~54%) between the GaN and silicon substrate lead to nonradiative recombination with more cracks generation and high dislocation density. Second, silicon is easily absorptive substrate. LEDs grown on silicon will repress light extract efficiency. Therefore, it has lower external quantum efficiency compared with LEDs grown on sapphire. For solve these issues, use thin film GaN technology to decrease strain-induced polarized field at multiple quantum wells (MQW) can improve internal quantum efficiency. On the first part of this study, we have successfully fabricated two different kinds of thin film GaN bonded on silicon substrate. By photoluminescence measurement, no matter what GaN on sapphire or silicon with thin film technology can improve internal quantum efficiency compared with original structure. Axial resolution of confocal Raman measurement can also confirm this results at room temperature because GaN on sapphire and silicon with thin film technology compressive strain in MQWs are relaxed. On the second part of this study, we use Inductively-Coupled Plasma (ICP) and Chemical-Mechanical Planarization (CMP) equipment to reduce the n-GaN thickness of thin GaN LED bonded on silicon. The experiment shows that as GaN thickness is resuced to 1 m, the internal quantum efficiency is 62.9% and increase by 40.3% compared with original structure because compressive strain in MQWs is relaxed.