氮化鎵發光二極體受應力影響之研究

Study of stress effect on GaN-based LED

張家綸(Chang Chia-Lun)

指導教授 ： 劉正毓

國立中央大學/工學院/化學工程與材料工程學系/博士(2010年)

摘要

由Ⅲ–Ⅴ族GaN直接能隙(direct bandgap)化合物半導體所發展出的GaN-based發光二極體，已成熟且廣泛地被運用在各類型商業化光電產品。發光二極體具備發光效率高、環保、節能的優勢。目前，不論在背光源、照明等應用，LED的使用都有相當顯著的成長，未來的發展空間無可限量。本論文開發晶圓級(wafer-level, thin-GaN)晶片製程及封裝技術，來提升GaN-based發光二極體的發光效率。本研究利用晶圓鍵合及雷射剝離(Laser Lift-Off) 技術將GaN LED磊晶薄膜從sapphire上轉移至高散熱與低電阻值基材上，如Si或Mo基材，在GaN磊晶薄膜轉移至Si基材上的過程中，發現GaN磊晶薄膜內的壓縮應力可以獲得舒解，而降低GaN磊晶薄膜內因壓縮應力所產生的壓電極化效應。當GaN磊晶薄膜內的壓電極化效應降低，可提升GaN LED發光層內的"有效"電子-電洞對數目，而使得因電子-電洞對復合所產生的光子數量增加，進而達成GaN-based LED發光效率提升的目的。在論文研究的過程可以了解，當壓電材料(GaN)受到應力(stress)產生形變(strain)，使得壓電材料內部產生一壓電場。當操作GaN-based LED時所注入的電子與電洞於空間上的分佈行為將受到此壓電場大小所影響，進而影響GaN-based LED的光電特性。藉由此論文的研究成果可探討出GaN磊晶薄膜內壓縮應力大小對GaN-based LED的光電特性的影響模式。

關鍵字

應力 ； 發光二極體 ； 晶圓鍵合

並列摘要

This study shows that the optical characteristics of the GaN-based LED is affected by the LED package and vertical thin-GaN LED process. Chapter 2 demonstrates that the wavelength of the planar-GaN based LED with being die-attached on the Si substrate blue-shifts and the internal quantum efficiency of GaN-based LED is enhanced. It is because that the thermal stress from the Si substrate acting on the sapphire substrate relaxes the stress-level of the GaN LED epi-layer after the die-attachment process. Chapter 3 shows the fabrication process of the high-power vertical thin-GaN LED. The GaN LED epi-layer is transferred onto the high thermal conductivity substrate (Si) by the wafer bonding and the laser-lift off (LLO) processes. With the GaN epi-layers transferring process, the compressive stress of the GaN epi-layer suffered the MOCVD growth process can be relaxed. Chapter 4 shows the mechanism of the compressive stress relief in the transferred GaN epi-layer, and the degree of compressive stress relief in the GaN epi-layer can be controlled by the wafer bonding system. The compressive stress in the GaN epi-layer results in a piezoelectric field cross the quantum wells. Chapter 5 discusses the effective of the piezoelectric field on the distortion of the energy-levels in the quantum wells. The distortion in the energy-levels changes the density distribution of the effective electron-hole pairs in the quantum wells. Then, the optical characteristics of the GaN-based LED, like emitting wavelength shifts and the internal quantum efficiency degrades. By studying this work, a new mechanism of the recombination behaviors of the electron-hole pairs in the quantum wells can be proposed, which can be used to calculate the efficiency of the GaN-based LED. Finally, the goal of this work is working on the relation among the stress in the GaN epi-layer, the piezoelectric field in the quantum wells, and the internal quantum efficiency of the GaN-based LED.

並列關鍵字

wafer bonding ； LED ； stress

參考文獻

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