衬底切偏角和p型欧姆接触对Si衬底GaN基LED性能稳定性的影响

发布时间：2018-06-11 21:56

本文选题：Si衬底 + 偏角　；参考：《南昌大学》2015年硕士论文

【摘要】：Ga N基材料因其优异的性能在固态照明方面具有广泛的应用前景。与Ga N常用的异质外延衬底蓝宝石和Si C相比,Si衬底具有价格低、导电导热性能好、尺寸大、易于光电集成等优点,在Si衬底上制备Ga N基LED的技术路线非常有发展潜力,吸引了全球大量研究人员对其进行相关的研究。然而Ga N与Si衬底之间存在巨大的晶格失配和热失配,这会在Ga N薄膜的外延生长引入巨大的失配应力,进而会影响LED器件的性能。虽然近年来Si衬底Ga N基LED技术已取得了重大进展,其发光效率已逐步赶上蓝宝石衬底LED,产业规模也在逐渐扩大,但与其独特结构相关的一些问题仍需要进一步研究。本文从Ga N薄膜外延生长和器件可靠性两个方面着手进行了研究,一方面研究了Si衬底切偏角对Ga N基LED外延膜的影响,利用高分辨X射线衍射仪(HRXRD)、原子力显微镜(AFM)以及光致发光(PL)对外延薄膜的晶体质量、量子阱中In组分、表面形貌及光学特性进行了研究。另一方面研究了垂直结构芯片电老化过程中正向工作电压VF2下降的问题,首先,研究了单纯的热效应对器件老化过程中VF2变化的影响;然后,采用SIMS深度剖析技术分析了Si基LED芯片老化前后p-Ga N欧姆接触界面Mg、Ga、N、Ag等元素的纵向分布情况以及p-Ga N中H元素浓度的变化情况;最后,对比了纯Ag与Ni Ag Ni Ag两种结构器件的老化数据,研究了Ni在LED老化过程中的影响。基于以上两个方面研究,本文取得了以下研究成果:1.Si(111)衬底偏角对量子阱中的In组分、Ga N外延膜的表面形貌、晶体质量以及光学性能具有重大影响。为了获得高质量的Ga N外延薄膜,衬底偏角必须控制在小于0.5°范围。超出此范围,Ga N薄膜的晶体质量、表面形貌及光学性能都明显下降。2.开发出了一套满足二次离子质谱仪(SIMS)测试要求的Si基LED芯片试样制备工艺,该工艺也可应用于基于其它衬底制备的薄膜型LED芯片分析。3.老化过程所产生的热效应引起器件温度上升是有限的,还不足以激活Mg受主,不会引起器件VF2下降;老化过程中p-Ga N欧姆接触界面处的Mg、Ga、N、Ag元素均没有发生纵向扩散,且p-Ga N中H元素浓度基本上也没有发生变化,我们认为在老化过程中Mg-H络合物发生分解后,当有载流子正向注入时H+俘获电子变成H0,而H0是一种稳定状态不会钝化Mg。老化电压的下降是由于Mg受主在电注入的作用下被进一步激活,使受主浓度增加,引起p型层电导率上升,器件的VF2下降。4.纯Ag结构器件在老化过程中电压会下降0.2V左右,而N i Ag N i Ag结构的器件在老化过程中电压几乎不会下降。p型欧姆接触层采用Ni有利于提高Si基LED器件的稳定性。
[Abstract]:Gan-based materials have been widely used in solid-state lighting due to their excellent properties. Compared with gan heteroepitaxial sapphire and sic substrate, Si substrate has the advantages of low price, good thermal conductivity, large size and easy photoelectric integration. It has attracted a large number of researchers around the world to do related research. However, there is a huge lattice mismatch and thermal mismatch between gan and Si substrates, which will introduce a huge mismatch stress into the epitaxial growth of gan thin films, which will affect the performance of LED devices. In recent years, Ga N-based LED technology on Si substrate has made great progress, its luminescence efficiency has gradually caught up with the LED substrate of sapphire substrate, and the industrial scale is gradually expanding, but some problems related to its unique structure still need to be further studied. In this paper, the epitaxial growth and device reliability of gan thin films are studied. On the one hand, the influence of the cut angle of Si substrates on gan based LED epitaxial films is studied. The crystal quality, in composition, surface morphology and optical properties of epitaxial thin films were investigated by high resolution X-ray diffractometer (HRXRD), atomic force microscopy (AFM) and photoluminescence (PL). On the other hand, the problem of the decrease of the forward working voltage VF2 during the electric aging of the vertical chip is studied. Firstly, the effect of the pure thermal effect on the VF2 changes during the aging process of the device is studied. The longitudinal distribution of p-Ga N ohmic contact interface and the change of H concentration in p-Ga N were analyzed by Sims depth analysis technique before and after aging. The aging data of pure Ag and Ni Ag Ni Ag structures were compared, and the effect of Ni on the aging process of LED was studied. Based on the above two aspects, the following results have been obtained: 1. The substrate deflection angle has great influence on the surface morphology, crystal quality and optical properties of in composition gan epitaxial films in quantum wells. In order to obtain high quality gan epitaxial films, the substrate deflection angle must be controlled in the range of less than 0.5 掳. Beyond this range, the crystal quality, surface morphology and optical properties of gan thin films decreased significantly. A sample preparation process for Si-based LED chips which meets the requirements of secondary ion mass spectrometer (SIMS) testing has been developed. The process can also be applied to the analysis of thin film LED chips based on other substrates. The temperature rise caused by the thermal effect during aging is limited, which is not enough to activate mg acceptor and not cause VF2 decrease, and there is no longitudinal diffusion at the contact interface of p-Ga N ohmic contact. The concentration of H in p-Ga N has not changed. It is considered that after the decomposition of Mg-H complex during aging, the H trapping electron becomes H0 when there is positive carrier injection, and H0 is a stable state that does not passivate mg. The decrease of aging voltage is due to the further activation of mg acceptor under the action of electric injection, which leads to the increase of acceptor concentration and the increase of the conductivity of p-type layer, and the decrease of VF2 of the device by .4. The voltage of pure Ag structure device will decrease about 0.2 V during aging, while the voltage of Ni Ag structure device will hardly decrease during aging process. The use of Ni type ohmic contact layer can improve the stability of Si based LED device.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN312.8

【参考文献】