利用圖案化基板所成長的紫外光LED磊晶品質及其材料特性之拉曼量測分析

Abstract

隨著紫外光LED需求增加，製備高品質紫外光LED也成了首要目標，然而氮化鎵的異質磊晶使的氮化鎵薄膜產生大量穿隧差排，產生非輻射電子電洞複合中心，大幅度降低磊晶品質以及發光效率。 在本篇論文中，我們使用圖案化藍寶石基板技術，並透過有機金屬化學氣相沉積磊晶出高品質的氮化鎵，我們使用拉曼頻譜分析與濕蝕刻蝕刻孔洞密度的方法，來證實圖案化藍寶石基板技術確實提高了氮化鎵的磊晶品質。實驗結果顯示，利用圖案化藍寶石基板技術，我們成功將拉曼頻譜半高寬由平片2.64 (cm-1) 降到2.31 (cm-1)，縮減了12.6%，蝕刻孔洞法亦指出缺陷密度減少了20.5%，大幅度提升了氮化鎵薄膜磊晶品質。 研究亦透過設計不同週期、比例、深度的微結構，獲得不同磊晶品質的氮化鎵薄膜，以半高寬及殘存應力建構一套完整的物理模型，我們的物理模型成功預測不同週期、比例與深度的品質變化，並可透過此預測LED磊晶之結果。

With the increasing demand for ultraviolet LEDs, the fabrication of high-quality UV LEDs has also become the primary work. However, the heteroepitaxial of GaN on sapphire substrate induces a large number of threading dislocation. These dislocations become electron-hole pair non-radiative recombination centers, which dramatically decline the quality of GaN and reduce luminous efficiency. In this paper, we grow GaN through Metal-Organic Chemical Vapor Deposition (MOCVD) and introduce its crystal quality by introduce the patterned-sapphire substrate technology. We use Raman spectrum analysis and etch pit density method to investigate and calculate the defect density. The Raman spectrum shows a decrease of FWHM from 2.64 (cm-1) to 2.31 (cm-1), which is about 12.6% improvement, and the EPD method indicates around 20.5% reduction of defect density. The results successfully confirmed that the epitaxial quality of GaN is improved with the patterned-sapphire substrate technology. Different periods, ratio, and depths of pattern structures have been designed to verify the trend of crystal quality, and we conclude a complete physics model for the quality prediction of GaN epitaxy.