氮化鎵奈米柱發光二極體之光及頻率響應特性探討

隨著寬能隙氮化鎵發光二極體的蓬勃發展，在固態照明和光通訊相關領域受到了極大的關注。目前有許多研究團隊提出各式各樣的奈米結構技術來提升效率，而其中又以奈米柱發光二極體最受矚目。本篇論文中，我們發展一種嶄新且具實用價值之奈米小球微影術用以製作具有p-i-n結構之奈米柱陣列，並以電漿輔助化學氣相沉積法成長二氧化矽做為奈米柱側壁保護層，接著利用化學機械研磨方式去除包覆於奈米柱頂端之二氧化矽以利後續金屬接觸層之製作。此奈米柱發光二極體已被證實能有效地釋放發光層間的壓縮應力。目前常用來定義發光二極體內部量子效率的方法主要是透過低溫光致發光(photoluminescence)量測並假設當環境溫度非常低(接近0K)的時候，進行非輻射復合的載子數量會趨近於零，幾乎全部的載子都會進行輻射複合，因此定義此時的內部量子效率為100%。但是在我們低溫光致發光、低溫電致發光(electroluminescence)及低溫拉曼量測結果中發現，當溫度逐漸下降，每個元件缺陷逐漸被排除同時卻也伴隨著承受比室溫下更多的壓縮應力，因此我們提出了一個嶄新的方法來分析內部量子效率，此法不同於以往對於低溫的光致發光結果只歸因於缺陷的抑制，更將低溫下應力的因素一併考慮，故此法可幫助我們求出比以往更精確的內部量子效率。除了在固態照明的應用，發光二極體另一個潛在的應用領域就是可見光通訊(Visible Light Communication)，是目前尚在發展的研究技術。在這裡，我們藉由研製不同面積大小的奈米柱和平面結構發光二極體，探索電光(E-O)調製帶寬。在奈米等級的結構下，奈米柱發光二極體能有效的釋放應力並在空間上限制載子輸運，進而有機會降低載子壽命，使得二極體的電光響應速度得到改善。

關鍵字

氮化鎵；奈米柱；發光二極體；內部量子效率；光萃取效率；應力釋放；化學機械研磨；可見光通訊；電光調製帶寬；載子壽命

並列摘要

Recently, GaN-based wide bandgap light emitting diodes (LEDs) have been intensively developed and put applications in solid-state lighting and communication due to its superior optical and electrical characteristics. The InGaN/GaN nanorod light-emitting-diode array is one of the most popular structures. In this thesis, we demonstrated a novel and practical approach to fabricate InGaN/GaN nanorod LED arrays with p-i-n structure using nanosphere lithography for nanorod formation, PECVD (plasma-enhanced chemical vapor deposition) grown SiO2 layer for sidewall passivation, and chemical mechanical polishing (CMP) process for parallel metal contact. The nano-structure device has been proved to relax the compressive strain underneath the active layers effectively. Nowadays, a commonly employed method to find IQE of a LED is by assuming complete frozen of defects at very low temperature and thus the IQE to be 100%. Despite the simplicity, the method may have underestimates other factors for IQE. According to our temperature-dependent Raman measurement, there is a severer strain effect accompanying the eliminating defects with decreasing temperature. Thus, we proposed a method by taking both defects and strain into consider and figured out more accurate IQE. We further discussed the external quantum efficiency and the light extraction efficiency on planar and nanorod LEDs. Another potential application of LEDs is for visible light communications (VLC) system, which is a rapidly growing research technology. Together in this work, nanorod and planar devices with different mesa area were fabricated to explore frequency response on the E-O modulation bandwidth. With a diameter in nanoscale, the p-i-n diode arrays may have advantages in strain relaxation and confinement of carrier transport due to spatial separation of nanorod which may lead to a shorter carrier lifetime thus faster response speed in nanorod LEDs. These properties in nano-structure LEDs may be further used for application in VLC system both in free space and fiber-based embodiments.

並列關鍵字

GaN ； nanorod ； light emitting diode ； internal quantum efficiency ； light extraction efficiency ； strain relaxation ； chemical mechanical polishing ； visible light communication ； E-O modulation bandwidth ； carrier lifetime

參考文獻

[1] J. Ryou, P. Yoder, J. Liu, Z. Lochner, H. Kim, S. Choi, H. Kim and R. Dupuis, “Control of quantum-confined stark effect in InGaN-based quantum wells,” IEEE J. Sel. Topics Quantum Electron. 15(4), 1080-1091 (2009)

[2] Visible Light Communications Consortium, VLCC http://www.vlcc.net/

[3] IEEE 802.15 WPAN™ Task Group 7 (TG7) Visible Light Communication http://www.ieee802.org/15/pub/TG7.html

[5] R. Wirth, B. Mayer, S. Kugler, and K. Streubel, “Fast LEDs for polymer optical fiber communication at 650 nm,” Proceedings of the SPIE 60130F, 1-8 (2005)

[6] M.-Y. Hsieh, C.-Y. Wang, L.-Y. Chen, M.-Y. Ke and J. Huang, “InGaN–GaN Nanorod Light Emitting Arrays Fabricated by Silica Nanomasks,” IEEE J. Quantum Electron. 44, 468 (2008)

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氮化鎵奈米柱發光二極體之光及頻率響應特性探討

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