电流拥挤效应与LED器件可靠性分析

对小功率GaN基白光LED的电流拥挤效应进行了研究,发现串联灯组(8只为一组)在经过22 V电压冲击后出现漏电失效现象。通过Pspice软件对串联LED灯组进行模拟,发现与其他样品相比,受损样品承受了更大的电压和功率;对器件加-2 V偏压,利用光发射(EMMI)显微镜对芯片表面不同量级漏电流进行定位分析比较,结果表明漏电流集中在p型扩展电极端点附近。分析认为,电压冲击的破坏路径穿过了LED的量子阱结构,而电流的不均匀分布造成了 p型扩展电极附近的电流拥挤,加剧了pn结的损伤程度,提高电流扩展的均匀性可以有效提高LED的可靠性。最后还对在正向电流-电压区域出现微分负阻特性的器件进行了失效分析。

Study of Current Crowding Effect and Reliability of LED Devices

The current crowding effect of low-power GaN base LEDs was investigated. It is found that LED module (eight LEDs in series as a set of group) suffered voltage surge sometimes presented current leakage failure. Pspice was applied to simulate LED module. It showed the damaged samples bore more voltage and power compared with the normal results. The orientation of leakage current of LED chip was studied via Emission Microscope (EMMI), the result indicated the leakage current intensively spreaded on the end of the p-type extended electrode. We assumed that the damaged route of voltage surged through the quantum well of LED, and the un-distribution current led to the effect of current crowding near the p-type extended electrode, which aggravated the injury severity of pn junction. Well-distributed current could improve the reliability of LED. Finally, the failure analysis of LED with differential negative resistance effect in the current-voltage characteristics was given.