氮化銦鎵綠光發光二極體之研製; Investigation of InGaN Green Light-Emitting Diodes

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題名:	氮化銦鎵綠光發光二極體之研製;Investigation of InGaN Green Light-Emitting Diodes
作者:	林宏誠;Hung-Cheng Lin
貢獻者:	電機工程研究所
關鍵詞:	氮化鎵;氮化銦鎵;發光二極體;GaN;InGaN;LED
日期:	2009-06-24
上傳時間:	2009-09-22 12:05:31 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	本論文主旨為開發525 nm 氮化銦鎵多重量子井綠光發光二極體磊晶及製程關鍵技術。首先我們提出兩種有效提升綠光發光二極體效率的磊晶技術，其一是『三甲基銦處理量子井磊晶技術』，其二是『氮化銦鎵/氮化鎵超晶格結構與調變摻雜鎂磊晶技術』，分別研究其材料特性及探討發光效率提升之原理。隨後將氮化鎵及綠光發光二極體結構成長於不同幾何外型之微透鏡陣列圖案化藍寶石基板上方，研究其成長模式與材料特性，並分析其對於提升綠光發光二極體發光效率之影響。最後，我們提出兩種有效提升光萃取效率的製程技術，分別為『自然形成遮罩法濕式蝕刻藍寶石基板技術』與『利用切割道圖案化提升光萃取效率技術』，並探討不同蝕刻深度對於元件光電特性及萃取效率之影響。在探討三甲基銦處理量子井提升綠光發光二極體發光效率的研究上，藉由原子力顯微鏡與穿遂式電子顯微鏡觀察分析，我們發現三甲基銦處理量子井技術，可以有效降低量子井內部的V型缺陷密度，並改善量子井介面間的平坦度。藉由此技術，綠光發光二極體操作於20 mA下，其發光效率有43%的提升。在『氮化銦鎵/氮化鎵超晶格結構與調變摻雜鎂磊晶技術』方面，我們利用氮化銦鎵/氮化鎵超晶格結構的極化場效應，與調變摻雜技術，可以有效提升鎂的活化率，並可降低材料串連阻值，藉由此技術應用於綠光發光二極體，可以有效提升約兩倍之發光效率。在電性方面，使用此成長技術之綠光發光二極體具有很低的逆向漏電流之優點。在成長氮化鎵與綠光發光二極體結構於不同幾何外型之微透鏡陣列圖案化藍寶石基板上方之研究，藉由掃瞄式電子顯微鏡、穿遂式電子顯微鏡、電子束激發光譜法觀察分析氮化鎵成長模式與材料特性，我們發現抑制氮化鎵之晶核層成長於微透鏡幾何外型之凸部，可以提供較多側向成長氮化鎵區域，減少缺陷密度，進而提升氮化鎵之材料品質。接著我們將525 nm 綠光發光二極體結構成長於不同幾何外型之微透鏡圖案藍寶石基板，我們發現其有不同之發光強度。經由拉慢光譜及X光繞射研究殘餘應力顯示，底層氮化鎵殘餘應力越小，綠光發光二極體之發光效率越高。在『自然形成遮罩法應用於濕蝕刻藍寶石基板技術』的研究上，藉由高溫硫酸蝕刻藍寶石基板表面，形成Al(SO4)及Al(SO4)3•17H2O之多晶硫酸鹽鋁化合物做為自然遮罩，並同時蝕刻藍寶石基板，再配合高溫磷酸兩段式蝕刻法，去除自然遮罩，形成微角錐幾何外型之圖案化藍寶石基板。此技術應用於氮化銦鎵發光二極體上，約有20%效率提升，此種技術由於不需要額外黃光微影製程技術，具有簡單且低成本之優點。在『利用切割道圖案化提升發光效率之製程技術』的研究上，我們提出一種提高光萃取效率之方法，此技術對於操作電壓的影響相當少（約0.04V），這是因為將電流路徑與高光萃取率區域分離，可將表面態或缺陷對於操作電壓之影響降到最低。在蝕刻深度的研究上，我們發現蝕刻深度對於光萃取效率有很大影響，當在蝕刻深度為1.5微米時，具有最高之光萃取效率，這是因為當蝕刻至藍寶石基板時，破壞了光波導區域，主動層所發出光無法順利傳導致高光萃取效率區域時，對於光萃取效率反而減少之效果。 This dissertation describes the growth and characterization of InGaN/GaN multiple-quantum-well (MQW) green light-emitting diode structures grown by low-pressure metal-organic vapor phase epitaxy (MOVPE). The content of this thesis is divided into the following three parts. First, we propose two methods for enhancing the luminescence efficiency of MQW. They are trimethylindium (TMIn) treatment process and Mg modulation-doped InGaN/GaN superlattices (MD-SLS) structure. Green light-emitting diodes prepared by the TMIn treatment method exhibit higher output power than the control device. The external quantum efficiency of the LEDs is increased by 43%. Both atomic force microscopy and transmission electron microscopy images indicate that TMIn treatment process produces InGaN/GaN MQW with smooth interface and low V-shape defect density, which are essential for high efficiency InGaN/GaN LEDs in the green and longer wavelength region. In addition, we demonstrate that low-temperature grown Mg modulation-doped InGaN/GaN superlattices structure is well suited for the p-contact layer of InGaN-based green LEDs. The light output of LEDs with this p-contact layer is increased approximately twofold as compared with that of conventional LEDs. The observed increase in quantum efficiency is attributed to the enhanced activation of Mg through the piezoelectric field in MD-SLS. Second, we prepare a series of patterned sapphire substrates with micro-lens of different shapes. Their effects on growth mode, material quality, residual strain, as well as the optical properties of the GaN epilayers and 525 nm green LEDs are systematically investigated. Growth mode analysis shows that micro-lens with a sharp tip prohibits the nucleation and growth of GaN on its top and leads to a wider lateral growth region with low dislocation density. Green light-emitting diodes grown on these PSSs also exhibit different external quantum efficiency. Experimental results show that the output power of 525 nm green LEDs is higher when grown on GaN with lower residual strain. The spectral blue shift with injection current is also less. This phenomenon might be attributed to the lower internal field in the quantum wells grown on GaN buffer layer with lower residual strain. Finally, we present two novel patterning techniques to improve the external quantum efficiency of InGaN/GaN quantum well light-emitting diodes. They are naturally etched sapphire substrates (NESSs) and dicing streets technology. Simply leaving a sapphire substrate in hot sulfuric acid, faceted islands are formed on the substrate due the spontaneous formation of an insoluble mixture of polycrystalline aluminum sulfates as a natural mask. It is shown that the light output power of InGaN LEDs grown on the substrate is enhanced by nearly 20% despite the fact that the LEDs already have an indium-tin oxide transparent contact layer and a roughened surface. The uniformity of luminescence intensity and wavelength of the LEDs grown on two inch NESSs is also better than that of the LEDs grown on flat sapphire substrates. Furthermore, patterning dicing streets is also found effective in enhancing the light extraction efficiency of InGaN/GaN multiple-quantum-well light-emitting diodes. The external quantum efficiency is increased by 9.4% for the LEDs with a partially etched pattern while its forward voltage is increased only 0.04 V. This result demonstrates that the proposed approach, which separates the current flow from the light extraction region, gives less adverse effect often encountered in conventional patterning and roughening processes.
顯示於類別:	[電機工程研究所] 博碩士論文

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