AlGaN/GaN 高电子迁移率晶体管漏电流退化机理研究

本文首先制备了与AlGaN/GaN高电子迁移率晶体管 (HEMT) 结构与特性等效的AlGaN/GaN异质结肖特基二极管, 采用步进应力测试比较了不同栅压下器件漏电流的变化情况, 然后基于电流-电压和电容-电压测试验证了退化前后漏电流的传输机理, 并使用失效分析技术光发射显微镜 (EMMI) 观测器件表面的光发射, 研究了漏电流的时间依赖退化机理. 实验结果表明: 在栅压高于某临界值后, 器件漏电流随时间开始增加, 同时伴有较大的噪声. 将极化电场引入电流与电场的依赖关系后, 器件退化前后的 log(I_FT/E)与√E 都遵循良好的线性关系, 表明漏电流均由电子Frenkel-Poole (FP) 发射主导. 退化后 log(I_FT/E)与√E 曲线斜率的减小, 以及利用EMMI在栅边缘直接观察到了与缺陷存在对应关系的“热点”, 证明了漏电流退化的机理是: 高电场在AlGaN层中诱发了新的缺陷, 而缺陷密度的增加导致了FP发射电流I_FT的增加. 关键词： AlGaN/GaN 高电子迁移率晶体管 漏电流 退化机理

Degradation mechanism of leakage current in AlGaN/GaN high electron mobility transistors

In order to study the degradation mechanism of leakage current in AlGaN/GaN high electron mobility transistors (HEMTs), we have fabricated AlGaN/GaN heterojunction Schottky diodes having equivalent structure and characteristics to AlGaN/GaN HEMTs. Step stress tests were then performed to compare the leakage current changes at different gate voltages. The transport mechanism of leakage current before and after degradation was validated based on the current-voltage and capacitance-voltage measurements. The light emission from the device surface was examined by emission microscopy (EMMI) to investigate the time-dependent degradation of leakage current. Experimental results show that the leakage current increases with increasing time and is accompanied by a large noise when the applied gate voltage exceeds a critical value. After introducing the polarization field into the current-field dependence, log(I_FT/E) exhibits a good linear relationship with √E both before and after degradation, indicating that the leakage current is dominated by the Frenkel-Poole (FP) emission. The slope of log(I_FT/E)-√E curve decreases after degradation, and the ‘hot spots’ corresponding to defects are directly observed by EMMI at the gate edge of the degraded device, suggesting that the degradation mechanism is: New defects are induced by high electric field in the AlGaN layer, and the increase of defect density leads to the increase of FP emission current.
Keywords： AlGaN/GaN high electron mobility transistor leakage current degradation mechanism