GaN基大功率LED作为第四代电光源，具有体积小、低电压、寿命长、效率高、节能等优良特性，但目前还存在转换效率低、光通量小、可靠性差等缺点。这主要是由蓝宝石异质外延GaN晶格质量较差、GaN材料强烈的极化效应、p型GaN激活效率低等原因造成。本论文利用高分辨X光衍射（HRXRD）、光荧光（PL）与芯片测试等技术，设计并优化了底层GaN、有源区和p型层等关键结构的生长工艺，有效地改善大功率LED的光电性能，主要结论如下：1.PSS衬底外延GaN晶格质量的提升：研究了湿法制作图形化蓝宝石衬底，并在其上外延GaN和LED全结构。PL测量结果显示PSS衬底上外延GaN的本征峰发光强度要明显强于普通蓝宝...GaN-based power LEDs as the fourth generation of the electric light, have many advantages such as small size, low voltage, long life, high efficiency, energy saving and so on. However, there are still some shortcomings involving low conversion efficiency, luminous flux, and poor reliability, which are mainly caused by poor quality of GaN epifilm heteroepitaxial on sapphire, strong polarization eff...学位：博士后院系专业：物理与机电工程学院物理学系_凝聚态物理学号：201017000

张洁

Xiamen University Institutional Repository

学校编码：10384 学号：2010170001         博  士  后  学  位  论  文         高效率大功率LED的材料外延和器件研制         Growth and device development of highefficiency and high power LED         张洁         指导教师：黄美纯     吴志强            专业名称：凝聚态物理              答辩日期：2012年7月   厦门大学博硕士论文摘要库厦门大学学位论文原创性声明                  本人呈交的学位论文是本人在导师指导下,独立完成的研究成果。本人在论文写作中参考其他个人或集体已经发表的研究成果，均在文中以适当方式明确标明，并符合法律规范和《厦门大学研究生学术活动规范(试行)》。                  另外，该学位论文为(                  )课题(组)的研究成果，获得(                    )课题(组)经费或实验室的资助，在(          )实验室完成。(请在以上括号内填写课题或课题组负责人或实验室名称，未有此项声明内容的，可以不作特别声明。)                           声明人(签名)：                            年   月   日厦门大学博硕士论文摘要库厦门大学学位论文著作权使用声明                  本人同意厦门大学根据《中华人民共和国学位条例暂行实施办法》等规定保留和使用此学位论文，并向主管部门或其指定机构送交学位论文(包括纸质版和电子版)，允许学位论文进入厦门大学图书馆及其数据库被查阅、借阅。本人同意厦门大学将学位论文加入全国博士、硕士学位论文共建单位数据库进行检索，将学位论文的标题和摘要汇编出版，采用影印、缩印或者其它方式合理复制学位论文。                  本学位论文属于：                  (     )1.经厦门大学保密委员会审查核定的保密学位论文，于年 月 日解密，解密后适用上述授权。                  (     )2.不保密，适用上述授权。                  (请在以上相应括号内打“√”或填上相应内容。保密学位论文应是已经厦门大学保密委员会审定过的学位论文，未经厦门大学保密委员会审定的学位论文均为公开学位论文。此声明栏不填写的，默认为公开学位论文，均适用上述授权。)                           声明人(签名)：                            年   月   日厦门大学博硕士论文摘要库摘  要                  GaN基大功率LED作为第四代电光源，具有体积小、低电压、寿命长、效率高、节能等优良特性，但目前还存在转换效率低、光通量小、可靠性差等缺点。这主要是由蓝宝石异质外延GaN晶格质量较差、GaN材料强烈的极化效应、p型GaN激活效率低等原因造成。本论文利用高分辨X光衍射（HRXRD）、光荧光（PL）与芯片测试等技术，设计并优化了底层GaN、有源区和p型层等关键结构的生长工艺，有效地改善大功率LED的光电性能，主要结论如下： 1.PSS衬底外延GaN晶格质量的提升：研究了湿法制作图形化蓝宝石衬底，并在其上外延GaN和LED全结构。PL测量结果显示PSS衬底上外延GaN的本征峰发光强度要明显强于普通蓝宝石衬底上生长的GaN的本征峰的强度；XRD扫描结果表明，PSS衬底上GaN样品的晶体质量相对于普通蓝宝石衬底上的GaN得到明显提高。对PSS衬底上外延LED全结构的研究表明：相同规格的PSS衬底，无C面LED比有C面LED包灯光功率高，随着PSS图形深度增加，LED光功率增加，但深度增加到一定程度时，由于外延生长困难度的增加，晶体生长质量下降，反面会引起LED亮度的下降。另外，随着PSS衬底图案间距的减小及PSS衬底图案尺寸的增大，LED光功率也会增加。 2.有源区超晶格结构的生长与分析：研究了InGaN/GaN应力释放层的生长和规律，发现随着SL loop数的增加，亮度呈现先上升后下降的趋势，是因为SL厚度较薄时缓冲作用占主导，继续增加厚度时SL晶格质量变差占主导；研究了MQW的亮度和电压随QB厚度的变化规律，发现随着MQB的厚度增加，亮度也呈现先上升后下降的趋势，是因为MQB厚度较薄时，垒对晶格质量的改善占主导作用，厚度继续增加时，垒对空穴迁注入的抑制占主导作用；研究了采用p型AlGaN/InGaN超晶格对亮度和电压的影响规律，发现随着p-AlGaN/p-InGaNloop数增加，亮度呈先上升后下降的趋势，是因为p-Al SL结构阻挡了跃迁进入p-GaN的电子，减少非辐射复合的作用占主导，loop数继续增加时，p-Al SL结构对空穴的阻挡作用占主导。3.p型接触层的生长与分析：随着高掺p型GaN（p++）厚度的增加，LED电压先降低后升高，这是因为金半接触会产生很高的势垒，而高掺的p++层可以使势垒区宽度变薄，从而增强隧穿效果以降低电压。但是载流子隧穿几率随势垒变宽而明显下降厦门大学博硕士论文摘要库，导致电压升高；另一方面随着Mg掺杂的提高，空穴浓度增加，电阻率减小，电压降低。最后过高的Mg掺杂恶化了晶格质量，自补偿效应显著，空穴浓度变低，势垒厚度变大，载流子隧穿几率变小，导致电压升高；在p型InGaN接触层，当InGaN接触层由0.9 nm加厚至2.3 nm时，InGaN层提供的空穴浓度得到提升，有利于降低接触电阻从而降低电压，但是当InGaN层进一步加厚时，势垒高度和宽度进一步增加，隧穿效应变弱，导致电压逐渐升高。 4.高效率大功率LED的设计与性能：根据上述各关键层生长条件优化的结果，在优化后的PSS衬底上外延GaN层， 20周期的InGaN/GaN超晶格作为应力释放层和10周期的MQW有源区为发光层，6周期的p型AlGaN/InGaN超晶格作为电子阻挡层和200nm的p型GaN，接触层包括p++GaN和p型InGaN层。制作的50 mil*50 mil大功率LED芯粒全测LOP均值在430 mW左右，VF均值在3.1-3.3 V之间分布。包白灯亮度在140-150 lm，光效在130-135 lm/W，色温5000 K，显色指数70附近，色坐标数据正常，已经达到110lm/W的项目指标。结果得到700 mA电流驱动下室温老化96小时，光衰小于-10%，老化1008小时，老化光衰小于-15%，老化IR数据正常。         关键词：金属有机化合物气相沉积；X光衍射；光荧光；大功率LED；图形衬底；应力释放层；InGaN/GaN多量子阱；接触层厦门大学博硕士论文摘要库Abstract                  GaN-based power LEDs as the fourth generation of the electric light, have manyadvantages such as small size, low voltage, long life, high efficiency, energysaving and so on. However, there are still some shortcomings involving lowconversion efficiency, luminous flux, and poor reliability, which are mainly causedby poor quality of GaN epifilm heteroepitaxial on sapphire, strong polarizationeffect of GaN materials and low activation efficiency of p-type GaN. In this paper,we applied high resolution X-ray diffraction (HRXRD), photoluminescence (PL)and chip testing technology to design and optimize the growth process of the keystructure including the underlying GaN, the active region and the p-type layer.Finally, the optical and electrical properties of the high-power LED have beenimproved, and the main conclusions are as follows:1. PSS substrate epitaxial GaN lattice to enhance the quality: sapphire substratespatterned by wet chemical etching and epitaxial growth of GaN and LED on thepatterned sapphire substrates were mainly investigated. PL measurementsshowed the intrinsic luminescence intensity of GaN grown on the PSS was muchstronger than the one on the conventional sapphire substrate; XRD scan resultsshowed the crystal quality of GaN on PSS was obviously improved. Study of theLED structure with PSS substrate showed that for the same PPS depth, theenveloped LED on PPS substrate with c-plane had higher optical power than thewithout one. And following the increase of PPS’s depth, the optical power of LEDrise. However, increasing the depth to a certern extent, the crystal quality starts todeteriorate, which cause to the decline of the LED brightness. This is because thedifficulty of epitaxial growth is increased. In addition, with the space between thePSS patterns decreasing and the size of pattern rising, the optical power of LEDcontinues to rise.2. Growth and analysis of the active region with superlattice structure: the growth厦门大学博硕士论文摘要库and theory of InGaN / GaN strain release layer were studied, and the LEDbrightness firstly increased and then reduced with increasing superlattice loop.This is because the strain releasing effect plays a major role when thesuperlattice total thickness is thin, and then brightness starts to decrease with thesuperlattice growing thicker and becoming worseThen we researched the rule ofLED brightness and voltage with QB thickness variation. The brightness has afirst upword and then downward trend with the increasing QB the thickness. Thisis because the influence of crystal quality from thicker barrier plays a dominantrole at the first stage, and then thicker barrier inhibites the hole injection to MQWat the following stage. P-type AlGaN / InGaN superlattices as an electron blockinglayer show similar trend on the brightness and voltage. As the loop numberincreasing, the LED brightness first increase and then decrease, which isbecause thesuperlattices firstly block the electron injecting to pGaN to reduce non-radiativerecombination in p-GaN, and then also block the hole injecting to MQW withincreasing loops.3. Growth and analysis of p-type contact layer: With the high-doped p-GaN (p++)thickness increasing, the LED voltage shows first dropping and then rising.Because the high-doped p++ can reduce the high barrier caused by metal-semiconductor contact so that the tunneling effect becomes stronger and thevoltage declines. However, the carrier tunnelling probability through the barriersignificantly decreases with the widened barrier, which leads to the rise ofvoltage. On the other hand, the voltage firstly drops due to the hole concentrationincreasing and the resistivity decreasing. And obvious self-compensation with Mgoverdopping leads to hole concentration decreasing, carrier tunneling probabilitydroping and finally LED voltage rising. For the p-InGaN contact layer, the holeconcentration of InGaN layer increases when the InGaN contact layer varies from0.9 to 2.3nm, which favors to the reduction of the contact resistance and thereby厦门大学博硕士论文摘要库the voltage drops. But when the InGaN layer is further thickening, the height andwidth of barrier increase, which results in the weak tunneling effect and thevoltage gradually increasing.4. The design and performance of high-efficiency high-power LED: A LEDstructure was obtained based on the the previous design of the PSS substrate,with 20 loops InGaN / GaN superlattices as a stress release layer and 10 loopsMQW active region as light-emitting layer. P-type region consists of 6-loop p-typeAlGaN / InGaN superlattices, 200nm p-GaN, p++GaN and p-InGaN layer. 50mil *50mil power LED chips were fabricated with these wafers. The results indicate theaverage LOP is about 430mW, and VF distributes between 3.1-3.3V. Packagedwhite LED chips show luminous flux of 140-150lm, luminous efficiency of 130-135lm/W at the average correlated color temperature (CCT) of 5000K, the colorrendering index of 70, and the normal color coordinate data, all of which achieveto the subject targets. Under 700mA driving current at room temperature, theaging test results show the the lumens decay is less than -10% at 96 hours pointand less than -15% at 1008 hours point, and the IR data have been normal.         Keywords: Metal organic chemical vapor deposition(MOCVD); X-ray diffraction(XRD); photoluminescence (PL); high power LED; Patterned sapphire substrate(PSS); the stress release layer; InGaN / GaN multi-quantum well (MQW); contactlayer厦门大学博硕士论文摘要库参考资料         第一章[1] H. Amano, N. Sawaki, I. Akasaki, et al. Appl. Phys. Lett. 1986,48: 353.[2] H.Amano, M.Kito, K.Hiramatsu, et al. Jpn. J. Appl. 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Lett. 2001,79:2588厦门大学博硕士论文摘要库Degree papers are in the “Xiamen University Electronic Theses and Dissertations Database”. Fulltexts are available in the following ways: 1. If your library is a CALIS member libraries, please log on http://etd.calis.edu.cn/ and submitrequests online, or consult the interlibrary loan department in your library. 2. For users of non-CALIS member libraries, please mail to etd@xmu.edu.cn for delivery details.厦门大学博硕士论文摘要库

Growth and device development of high efficiency and high power LED

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Growth and device development of high efficiency and high power LED

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