本文關(guān)鍵詞： MOCVD SiC襯底 GaN LED 發(fā)光均勻性　出處：《吉林大學》2015年碩士論文　論文類型：學位論文

【摘要】：GaN基半導(dǎo)體材料光學和電學性質(zhì)優(yōu)良，非常適合發(fā)光器件的制備。早在1993年，GaN基藍光LED就已被成功研制，并得到推廣應(yīng)用。然而圍繞著高性能GaN基LED研究的熱度絲毫不減，原因是商用的藍光LED基于藍寶石襯底，存在著一些固有的缺陷，如散熱問題以及在大電流下效率衰退效應(yīng)。如果采用GaN作為襯底進行同質(zhì)外延，上述問題雖可解決，但是國內(nèi)仍然無法生產(chǎn)高質(zhì)量、大尺寸、適合作為GaN基器件襯底的GaN體單晶。 為了克服上述困難，我們決定采用和GaN晶格匹配較好的SiC單晶作為襯底研制GaN基藍光LED。SiC襯底具有良好的導(dǎo)熱性能能有效地解決散熱問題，更適合制備大功率發(fā)光器件。同時，其所具備的易解理的特點降低了器件工藝的難度。最重要的是，SiC與GaN間的晶格失配為3%，與通常作為緩沖層材料的AlN間的晶格失配僅為1%，可極大地降低失配位錯密度，是制備高質(zhì)量GaN外延層的理想襯底材料。 實驗的前半部分圍繞著優(yōu)化外延層生長參數(shù)，目的是獲得滿足LED生長的工藝條件；后半部分則基于之前的研究結(jié)果生長LED結(jié)構(gòu)，，并優(yōu)化外延片的發(fā)光波長均勻性，以提高外延片的利用率。研究工作包括如下內(nèi)容： (1) AlN作為緩沖層與SiC具有良好的浸潤性，生長初期即進入二維平面生長。在1100℃下生長200nmAlN緩沖層可獲得結(jié)晶質(zhì)量較高的GaN外延層，同時引入足量的壓應(yīng)力，避免薄膜在降溫過程中開裂。在AlN與GaN層之間插入Al組分漸變AlGaN緩沖層，克服了相鄰界面間晶格失配過大而出現(xiàn)的重新成核現(xiàn)象，減少了失配位錯的產(chǎn)生，并使由不同組分間晶格失配引入的壓應(yīng)力得到保存。 (2)有源區(qū)中，量子阱采用了壘層/蓋層/阱層的結(jié)構(gòu)，防止了壘層的高溫生長對阱層的破壞。并對阱層InGaN材料的生長條件進行優(yōu)化，分別研究了In/Ga輸入比和生長溫度對阱層InGaN中In組分的影響。認為當Ga輸入量一定時，提高In/Ga輸入比有助于InGaN材料中In組分的提高；低溫更有利于In的并入，而在高溫下InGaN材料的結(jié)晶質(zhì)量更高；對于量子阱發(fā)光波長的調(diào)控，可以通過改變阱層生長溫度來實現(xiàn)，阱層生長溫度每升高1℃，量子阱發(fā)光波長藍移2nm。 (3)如果外延片在量子阱結(jié)構(gòu)生長過程中存在翹曲，勢必導(dǎo)致外延片與托盤熱接觸不良，因此單純調(diào)整溫區(qū)參數(shù)對外延片發(fā)光均勻性的作用并不明顯。實驗中采用了初始翹曲為290km-1的SiC襯底，有效地補償了量子阱生長過程中的凸翹曲，外延片的發(fā)光波長均勻性因此得到了極大的改善。
[Abstract]:GaN based semiconductor materials have excellent optical and electrical properties and are very suitable for the fabrication of luminescent devices. As early as 1993, GaN-based blue light LED has been successfully developed. However, the research on high performance GaN based LED does not decrease, because the commercial sapphire LED has some inherent defects based on sapphire substrate. If GaN is used as substrate for homoepitaxy, these problems can be solved, but it is still unable to produce high quality and large size in China. It is suitable for GaN bulk single crystal on GaN substrate. In order to overcome these difficulties. We have decided to use SiC single crystal which matches well with GaN lattice as substrate to develop GaN based blue LED.SiC substrate with good thermal conductivity which can effectively solve the problem of heat dissipation. It is more suitable to fabricate high power luminescent devices. At the same time, it has the characteristics of easy cleavage to reduce the process difficulty. The most important thing is that the lattice mismatch between sic and GaN is 3%. The lattice mismatch between AlN and AlN, which is usually used as buffer layer, is only 1, which can greatly reduce the mismatch dislocation density. It is an ideal substrate material for the preparation of high quality GaN epitaxial layer. The first half of the experiment is focused on the optimization of the growth parameters of the epitaxial layer. The purpose of the experiment is to obtain the technological conditions that satisfy the growth of LED. In the latter part, the LED structure is grown based on the previous results, and the luminescent wavelength uniformity of the epitaxial wafer is optimized to improve the utilization ratio of the epitaxial wafer. The research work includes the following contents: 1) AlN has good wettability as buffer layer and SiC. The GaN epitaxial layer with high crystallization quality can be obtained by the growth of 200nmAlN buffer layer at 1100 鈩

本文編號：1481468