二次退火对Au/Ni/Au/Ni/p-AlGaN欧姆接触组织结构的影响

Effect of secondary annealing on the microstructure of Au/Ni/Au/Ni/p-AlGaN ohmic contact

在蓝宝石衬底上,利用金属-有机物化学气相沉积(MOCVD)方法制备p-i-n结构AlGaN基体,采用常规工艺制作台面型紫外探测器。电子束蒸发蒸镀Ni/Au/Ni/Au(20nm/20nm/20nm/20nm)结构制备p电极。经空气中550℃/3 min一次退火和N2气氛中750℃/30s二次退火后得到欧姆接触。利用高分辨透射电镜(HRTEM)和能谱(EDS)研究不同退火条件下p电极接触的组织结构演变。结果表明:一次退火p电极金属层出现明显扩散,但仍维持初始的分层状态,金属/半导体接触界面产生厚约4nm的非晶层;二次退火后,金属电极分层现象和界面非晶层消失。金/半界面结构表现为半共格关系,界面结构有序性提高。Ni向外扩散,Au向内扩散,Ga扩散至金属电极,造成界面附近金属层富集Au、Ga元素,导致p电极欧姆接触的形成。

AlGaN semiconductor with p-i-n structure was grown on sapphire substrate using metal-organic chemical vapor deposition（MOCVD）system.Mesa-structure ultraviolet detectors were fabricated by conventional technology.Ni/Au/Ni/Au（20nm/20nm/20nm/20nm）metal schemes were deposited by electron beam evaporation as p-type contact.After first annealing in air ambient at 550℃for 3min and secondary annealing in N2 ambient at 750℃for 30 s,an ohmic contact formed.Analysis on the microstructure evolution of the annealed p-electrode is carried out by high-resolution transmission electron microscopy（HRTEM）and energy dispersive spectrometer（EDS）.The results reveal that after first annealing,elements diffusion occurrs in p-electrode,but metal schemes maintain the initial layers of the asdeposited sample.And a 4nm-thick amorphous layer appears on the interface of metal and semiconductor.While after secondary annealing,the metal schemes change sharply and the amorphous layer disappears.Microstructure analysis on the metal-semiconductor interface shows a semi-coherent relationship and enhanced orderliness.Ni outdiffused to the surface of p-electrode,Au indiffused to the surface of GaN,and Ga diffused to metal electrode,which results in the enrichment of Au and Ga near the interface.These phenomena contribute to the formation of p-AlGaN ohmic contact.