SiC衬底上GaN基蓝光LED的MOCVD外延生长研究

发布时间：2018-02-01 08:57

  本文关键词： MOCVD SiC衬底 GaN LED 发光均匀性　出处：《吉林大学》2015年硕士论文　论文类型：学位论文

【摘要】：GaN基半导体材料光学和电学性质优良，非常适合发光器件的制备。早在1993年，GaN基蓝光LED就已被成功研制，并得到推广应用。然而围绕着高性能GaN基LED研究的热度丝毫不减，原因是商用的蓝光LED基于蓝宝石衬底，存在着一些固有的缺陷，如散热问题以及在大电流下效率衰退效应。如果采用GaN作为衬底进行同质外延，上述问题虽可解决，但是国内仍然无法生产高质量、大尺寸、适合作为GaN基器件衬底的GaN体单晶。 为了克服上述困难，我们决定采用和GaN晶格匹配较好的SiC单晶作为衬底研制GaN基蓝光LED。SiC衬底具有良好的导热性能能有效地解决散热问题，更适合制备大功率发光器件。同时，其所具备的易解理的特点降低了器件工艺的难度。最重要的是，SiC与GaN间的晶格失配为3%，与通常作为缓冲层材料的AlN间的晶格失配仅为1%，可极大地降低失配位错密度，是制备高质量GaN外延层的理想衬底材料。 实验的前半部分围绕着优化外延层生长参数，目的是获得满足LED生长的工艺条件；后半部分则基于之前的研究结果生长LED结构，，并优化外延片的发光波长均匀性，以提高外延片的利用率。研究工作包括如下内容： (1) AlN作为缓冲层与SiC具有良好的浸润性，生长初期即进入二维平面生长。在1100℃下生长200nmAlN缓冲层可获得结晶质量较高的GaN外延层，同时引入足量的压应力，避免薄膜在降温过程中开裂。在AlN与GaN层之间插入Al组分渐变AlGaN缓冲层，克服了相邻界面间晶格失配过大而出现的重新成核现象，减少了失配位错的产生，并使由不同组分间晶格失配引入的压应力得到保存。 (2)有源区中，量子阱采用了垒层/盖层/阱层的结构，防止了垒层的高温生长对阱层的破坏。并对阱层InGaN材料的生长条件进行优化，分别研究了In/Ga输入比和生长温度对阱层InGaN中In组分的影响。认为当Ga输入量一定时，提高In/Ga输入比有助于InGaN材料中In组分的提高；低温更有利于In的并入，而在高温下InGaN材料的结晶质量更高；对于量子阱发光波长的调控，可以通过改变阱层生长温度来实现，阱层生长温度每升高1℃，量子阱发光波长蓝移2nm。 (3)如果外延片在量子阱结构生长过程中存在翘曲，势必导致外延片与托盘热接触不良，因此单纯调整温区参数对外延片发光均匀性的作用并不明显。实验中采用了初始翘曲为290km-1的SiC衬底，有效地补偿了量子阱生长过程中的凸翘曲，外延片的发光波长均匀性因此得到了极大的改善。
[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

本文编号：1481468