【作者】 蒋超；

【导师】 陆海；

【作者基本信息】 南京大学 ， 微电子学与固体电子学， 2014， 硕士

【摘要】 GaN材料具有禁带宽度大、击穿电场强、电子饱和漂移速度高以及同其他Ⅲ族氮化物易形成异质结等优越特性,是制备大功率电子器件的优选材料。目前,在Si衬底上外延生长GaN正受到人们的广泛关注。同传统的蓝宝石衬底相比,Si衬底的热导率较高,在功率器件领域具有明显的优势。另外,Si衬底的晶体质量高、尺寸大,并且价格低廉。然而,Si衬底同GaN材料之间具有大的晶格失配和热膨胀失配,这极大地增加了生长高质量GaN外延层的难度。在这篇论文中,我们研究了Si衬底AlGaN/GaN异质结肖特基二极管的反向击穿特性,并且对器件结构进行了优化。1、首先,我们在AlGaN/GaN异质结上制备了不同肖特基电极同欧姆接触间距的肖特基二极管,测量了器件的反向击穿电压(BV)。实验结果显示,随着电极间距的增大,器件的击穿电压先是迅速增大,在大间距时趋于饱和。我们认为出现饱和的原因是大间距器件经由GaN buffer层发生了垂直击穿。接下来我们研究了Si02钝化层对器件击穿特性的影响。结果显示,Si02钝化能在小电极间距下提高器件的击穿电压并且抑制器件的反向漏电流。2、我们接着采用微光显微镜(EMMI)对器件的击穿机制进行了分析。我们对比击穿后器件的光学显微照片和EMMI强片,发现小间距器件和大间距器件的热斑分布明显不同。我们分析后认为,产生热斑分布的差异正是由于大间距器件是垂直击穿而小间距器件是表面的水平击穿所致。3、最后,我们采用场板结构对己钝化器件的肖特基电极进行了优化。采用场板结构之后,器件的击穿电压超过了600V。我们通过计算得到电极间距10μm器件的导通电阻RON为3.15mΩ·cm2。再结合其击穿电压,最终得到器件的功率优值系数(BV2/RON)为114MV·cm-2。更多还原

【Abstract】 GaN is one of the most promising candidate materials for power electronics applications due to its superior material characteristics such as large bandgap, high breakdown electrical field, high electron saturation velocity, and the ability to form hetero-junctions with other Ⅲ-nitride materials. Recently, GaN grown on silicon substrate has drawn much attention. Compared with conventional sapphire substrate, the high thermal conductivity of silicon is highly desirable for power device applications. Meanwhile, high-quality Si substrate with large diameter can be easily obtained at low cost. However, growth of GaN on Si is difficult due to the large lattice and thermal mismatch between the two materials. In this work, we investigated the breakdown characteristics of AlGaN/GaN planar Schottky barrier diodes (SBDs) fabricated on silicon substrate.1. Firstly, AlGaN/GaN-based SBDs with various spacings between ohmic and Schottky contacts were fabricated on silicon substrate. The breakdown voltage (BV) of the SBDs first increases as a function of contact spacing and then tends to saturate at larger spacing. The saturation behavior of BV is likely caused by vertical breakdown through the intrinsic GaN buffer layer on silicon. Then, we studied the effect of SiO2 passivation on the breakdown characteristics of the SBDs. It is found that SiO2 passivations could enhance the BV of the SBDs and suppress the reverse leakage current at lower reverse bias.2. Then, we used EMMI measurement to verify the physical analysis of the breakdown modes. The devices under test were post-breakdown SBDs. Based on the conventional optical images and their corresponding EMMI images, we found that the hot spots of the SBDs with various contact spacings revealed different primary leakage path after the hard breakdown. Thus, the EMMI result agrees with the physical picture of horizontal breakdown at small electrode spacing and vertical breakdown at large electrode spacing.3. For comparative study, some passivated devices were further terminated by field plates. Field plate termination was found effective to enhance BV of the SBDs. A high BV of 600 V is obtained with a low on-resistance (RON) of 3.15 mΩ·cm2, yielding a power figure-of-merit (BV2/RON) of 114 MW/cm2.更多还原