氟化石墨烯/高k介质复合体系的钝化特性及其应用研究

GaN HEMT, which has demonstrated its excellent potential in high frequency, high power, and new energy applications, is the research hotspot around the world nowadays. Conventional passivation for GaN introduces Oxygen to the surface to form the Ga-O defect states, which increase the device leakage current and lead to current collapse. While fluorinated graphene has advantages, it can suppress the formation of Ga-O, its excellent insulativity can improve the device gate voltage swing, and the negative charges introduced during fluorination favor the enhanced device. Hence, we propose a novel passivation method by using fluorinated graphene/high-k dielectric stack. We intend to investigate the key preparation technology of the fluorinated graphene/high-k dielectric stack and the effect of fluorinated graphene on the GaN interface. The passivation mechanism by fluorinated graphene/high-k dielectric stack and its impact on the device leakage current, flat-band voltage, and current collapse will be analyzed. This project is expected to present theoretical basis and technical support for the application of fluorinated graphene/high-k dielectric stack, and to provide a new approach for GaN HEMT passivation.

宽禁带半导体GaN HEMT器件在高频、大功率电子器件与新能源领域有着广泛的应用前景，是当前国际上研究与开发的热点。常规的钝化层方案易在GaN表面引入氧元素，形成Ga-O键缺陷态，增加了泄漏电流甚至引起电流崩塌效应。而氟化石墨烯具有抑制Ga-O缺陷的形成；极好的绝缘性有利于提高器件栅摆幅；氟化过程引入负电荷有利于形成增强型器件等优点。为此本项目提出一种基于氟化石墨烯/高k介质复合体系的新型钝化技术。重点研究氟化石墨烯/高k介质复合结构的关键制备技术；氟化石墨烯对GaN界面微观结构的影响；探索氟化石墨烯/高k介质复合层对GaN器件泄漏电流、平带电压、电流崩塌等的影响及其钝化作用机理。项目的预期研究成果将为氟化石墨烯/高k介质复合结构体系的应用提供理论基础和技术支撑，为HEMT器件界面钝化提供新的思路。

氟化石墨烯的选择透过性和高击穿特性决定了它作为宽禁带半导体电子器件中扩散阻挡层的应用潜力。在高k介质与半导体衬底之间引入氟化石墨烯层，有望对改善介质/半导体界面问题提供一种新的途径。为此，本项目我们聚焦于氟化石墨烯/高k介质这一复合体系的钝化特性以及在宽禁带半导体器件上的应用。我们研究了GaN表面复合高k介质钝化，以及等离子体钝化的方法，发现原位Ar与NH3等离子体作用可以有效消除GaN表面的Ga-O缺陷；HfO2/Al2O3复合介质介电常数达~30.2，临界击穿场强~7.6 MV/cm，泄漏电流~0.68 µA/cm2@Vg=10V，是GaN器件适合的栅介质。氟化石墨烯钝化有效抑制了GaN表面N的分离和O的结合，减少了界面电荷密度，因此减小了表面漏电，减弱了表面正电中心对2DEG的捕获以及对迁移率的影响。与普通MIS-HEMT相比，氟化石墨烯/高k介质复合体系钝化的MIS-HEMT饱和输出电流提高了34.3%，峰值跨导提高了14.4%，动态导通电阻降低了21.6%，关态栅漏电流降低了2个数量级，电流崩塌效应得到了有效抑制。本研究的成果可为氟化石墨烯/高k介质复合体系的应用提供技术支撑，为HEMT器件界面钝化提供新的思路。

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